ISRO-PAX-300
Issue 5, November 2012
Workmanship Standards
for the Fabrication of
Electronic Packages
ISRO Reliability Standards
Directorate of Systems Reliability and Quality, ISRO Headquarters, Bangalore
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Indian Space Research Organisation
Department of Space
Government of India
Antariksh Bhavan
New BEL Road, Bangalore - 560 231, India
Telephone : +91-80-2341 5241/2217 2333
Fax : +91-80-23415328
e-mail : chairman@isro.gov.in
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Dr. K. Radhakrishnan
Chairman
MESSAGE
ISRO Reliability Standards, addressing the various disciplines of Engineering, have been in vogue for
almost three decades now. These standards are followed across ISRO centres as well as external work
centers for design, fabrication, testing, analysis and other processes involved in the realization of Launch
Vehicles, Spacecraft, Space Applications, Ground support systems and other launch infrastructure. The
need for standardization of processes towards achieving high reliability systems can never be over
emphasized, and ISRO Reliability Standards are just an attempt towards explicitly stating this.
With the advent of newer techniques and with the evolution of technology itself, over the last 30 years,
it has become essential to revisit the existing ISRO Reliability Standards and revise and update the
standards wherever essential. Towards this, the Directorate of Systems Reliability and Quality (DSRQ) at ISRO Headquarters
has taken an initiative to re-invigorate the reach and visibility of ISRO Reliability standards across all the Centres of ISRO. Specific
Inter-centre teams were formed to revise each of these documents and I would like to place on record their commendable
efforts in bringing out these documents.
There is a pressing need for ensuring uniformity of practices, across various functions of design, fabrication, testing, review
mechanisms etc., across the centres and units of ISRO. Towards this goal, the mandatory adoption of ISRO Reliability Standards
will ensure standardization in quality processes and products. I am certain that this will go a long way towards ensuring overall
system level Quality and Reliability and in achieving the goal of zero defects in the delivery of space systems of ISRO.
K Radhakrishnan
Chairman, ISRO
Directorate of Systems Reliability & Quality
ISRO Headquarters
Antariksh Bhavan
New BEL Road, Bangalore -560231
Ph :080 - 2341 5414
Fax :080 – 2341 2826
Cell:09448397704
Email: sselvaraju@isro.gov.in
S Selvaraju
Senior Advisor, Systems Reliability and Quality
PREFACE
ISRO Reliability standards are a result of the need for standardization of processes towards achieving high reliability systems.
The transfer of knowledge and techniques from the seniors to their successors is best done with proper documentation and
checklists translating the entire know-how into black and white.
This document on ‘Workmanship standards for the fabrication of electronic packages’ addresses the complete
assembly of launch vehicle, spacecraft, and critical check-out systems for all projects of ISRO, from the point of view of quality
and workmanship requirements to be met during fabrication of electronic and electromechanical packages. This document has
undergone a large scale revision, compared to its previous issue, considering the advancement of technology.The details regarding
facility, tools, materials, soldering and cleaning of Printed Circuit Board assemblies are discussed at length. Particulars related
to crimping, interconnecting cables, harnesses and wiring are also given specific attention. The role of Quality professionals and
aspects of Quality assurance are also elucidated. Additional details regarding polymeric applications, conformal coating, electro
static discharge, repair and rework and bonded stores are also made clear.
It is deemed essential that these standards be strictly adhered to, in order to ensure uniformity of practices across ISRO centers
and achieve zero defects in the delivery of space systems.
I am grateful to Chairman ISRO, for being the source of inspiration in the release of these documents.Thanks are also due to the
centre Directors for their encouragement. I am also thankful to the Heads of SR Entities/Groups of various ISRO centres for
their relentless support and guidance. I am also indebted to the members of the Integrated Product Assurance Board (IPAB) for
the meticulous review of these documents. I also owe gratitude to the task team members and other experts for putting efforts
in the realization of these documents. I am glad to carry forward this rich lineage of ISRO reliability standards, championed by
Shri R Aravamudan, a revered pioneer in the area of Quality & Reliability in ISRO.
S Selvaraju
Sr. Advisor (SRQ)
LIST OF CONTENTS
1
SCOPE
01
2
APPLICABLE DOCUMENTS
02
2.1 Other Related Documents
02
2.2 Definitions
02
FACILITY
03
3.1 Environmental Conditions for Work Area
03
3.2 Lighting Requirements
03
3.3 ESD Requirements
03
3.4 Wiring & Assembly Area
03
3.5 Cleaning Area
03
3.6 Tinning Area
03
3.7 Conformal Coating & Potting Area
04
3.8 Mechanical Assembly Area
04
3.9 Special Processes Area
04
TOOLS
05
4.1 Tools and Equipments
4.1.1
Brushes
4.1.2
Cutters and pliers
4.1.3
Bending tools
4.1.4
Clinching tools
4.1.5
Antiwicking Tools
4.1.6
Holding Devices
4.1.7
Insulation strippers
4.1.8
Thermal Shunts
05
05
05
05
06
06
06
06
07
4.2 In-Process Storage and Handling
07
4.3 Soldering, cleaning and Inspection Equipments
4.3.1
Contact Type (Soldering irons)
4.3.2
Non-contact Type Soldering machines
4.3.3
Solder Baths
4.3.4
Cleaning equipment and systems
4.3.5
Inspection Optics (Magnification Aids)
07
07
08
09
09
09
MATERIALS
11
3
4
5
5.1 General
11
5.2 Solder
5.2.1
5.2.2
11
Solder Preform
Solder Composition
11
11
5.2.3
6
Maintenance of paste purity
12
5.3 Flux
5.3.1
Rosin-based fluxes
12
12
5.4 Cleaning Solvents
5.4.1
Approved Cleaning Solvents
13
13
5.5 Flexible insulation materials
13
5.6 Terminals
5.6.1
Terminal Material
5.6.2
Type of terminal
5.6.3
Shape of terminals
13
13
14
14
5.7 Wires
14
5.8 PCBs
5.8.1
Boards
5.8.2
Gold finish on conductors
5.8.3
Classification of boards
14
14
14
14
5.9 Adhesives (potting compounds & heat sinking), Encapsulants & conformal coatings
15
COMPONENT MOUNTING
16
6.1 Principles of reliable soldered connections
16
6.2 Preparatory conditions
6.2.1
Facility cleanliness
6.2.2
Preparation of Components leads, conductors, terminals and solder cups
16
16
16
6.3 Surfaces to be soldered
6.3.1
Cleaning
6.3.2
De-golding of gold-plated leads and terminals
6.3.3
Methods for degolding
6.3.4
Pretinning of stranded wires
6.3.5
Pre-tinning of Component leads and solid-wire conductors
6.3.6
Preparation of the soldering bit
17
17
17
18
18
18
19
6.4 Storage
6.4.1
Components
6.4.2
PCBs
6.4.3
Storage of wired PCBs
19
19
19
19
6.5 Preparation of PCBs for soldering
19
6.6 Parts Mounting
6.6.1
General requirements
6.6.2
Stress Relief
6.6.3
Stress relief of components with bendable leads
6.6.4
Dual in-line package
6.6.5
Part Positioning
6.6.6
Visibility of Markings
6.6.7
Heavy components
6.6.8
Metal-case components
6.6.9
Glass Encased Parts
20
20
20
20
21
23
23
23
23
24
6.6.10
6.6.11
6.6.12
6.6.13
6.6.14
7
Hookup /Jumper Wire
Lead Bending and Cutting
Coated Parts
Splices
Location
24
24
25
25
25
6.7 Parts Mounted To PWB’s
6.7.1
Axial Lead Mounting
6.7.2
Boards Lead Terminations, Printed Wiring
6.7.3
Lead bending requirements
6.7.4
Mounting of terminals to PCBs
25
26
28
32
32
6.8 Mounting requirement for SMD
6.8.1
General
6.8.2
Registration of devices and pads
6.8.3
Lead forming
6.8.4
Mounting devices in solder paste
6.8.5
Leadless devices
6.8.6
Area array devices
6.8.7
Potting of heavy devices
35
35
35
35
35
36
36
36
SOLDERING
37
7.1 Securing conductors
7.1.1
Thermal shunts
37
37
7.2 Solder application to terminals
7.2.1
Soldering of swaged terminals onto PCBs
7.2.2
Soldering of conductors onto terminals (except cup terminals)
7.2.3
Soldering of conductors onto cup terminals
37
37
37
37
7.3 Solder application to PCBs
7.3.1
Application of flux
7.3.2
Solder application
7.3.3
Solder coverage
7.3.4
Solder fillets
7.3.5
Wicking
7.3.6
Solder rework
37
37
38
38
38
39
39
7.4 Soldering of SMDs
7.4.1
General requirements
7.4.2
End-capped and end-metallized devices
7.4.3
Hand soldering of chip capacitors and resistors
7.4.4
Bottom terminated chip devices
7.4.5
Cylindrical end-capped devices
7.4.6
Castellated chip carrier devices
7.4.7
Devices with round, flattened, ribbon, “L” and gull-wing leads
7.4.8
Devices with “J” leads
7.4.9
Tall profile devices
39
39
40
40
41
41
41
42
43
44
8
9
7.5 Ceramic Column Grid Array Devices
7.5.1
Handling Precautions for CCGA Devices
7.5.2
Bare CCGA Device Inspection
7.5.3
Bare PCB Inspection (For CCGA assembly point of View)
7.5.4
Post soldering CCGA Assembly Inspection
7.5.5
Visual Inspection
7.5.6
Radiographic Inspection (X-ray)
44
45
45
47
47
47
50
7.6 High-voltage connections
52
7.7 BGA devices
52
7.7.1 Handling Precautions for BGA Devices
52
7.7.2 Bare BGA Device Inspection
53
7.7.3 Bare PCB Inspection (For CCGA assembly point of View)
53
7.7.4 Post soldering BGA Assembly Inspection
54
Cleaning of PCB assemblies
56
8.1 Acceptable cleaning systems
8.1.1
Manual Cleaning
8.1.2
Vapour Degreasing – General Requirements
56
56
56
8.2 Monitoring for cleanliness
8.2.1
Cleanliness testing
8.2.2
Test limits
8.2.3
Test method
57
57
57
57
Quality assurance
58
9.1 Data
58
9.2 Nonconformance
58
9.3 Calibration/ Validation
58
9.4 Inspection 58
9.5 Acceptance criteria
58
9.6 Rejection criteria
59
9.7 Operator and inspector training and certification
59
9.8 Quality records
60
9.9 Typical accept / reject illustrations
9.9.1
Workmanship illustrations for SMDs
10 CRIMPING, INTERCONNECTING CABLES, HARNESSES, AND WIRING
60
60
73
10.1 Principles of Reliable Cabling and Wiring
73
10.2 General requirements
73
10.3 Tool and Equipment Control
74
10.4 Solvents and Cleaners
74
10.5 Mounting of Terminals
74
10.6 Attachment of conductors to terminals, solder cups and cables
10.6.1 General
10.6.2 Conductors
10.6.3 Breakouts from cables
10.6.4 Insulation clearance
10.6.5 Solid hook-up wire
10.6.6 Stress relief
10.6.7 Insulation clearance
75
75
75
75
76
76
76
76
10.7 Stripping insulation from conductors and cable
10.7.1 Stripping Round Conductors
10.7.2 Stripping Jackets over Shields
77
77
78
10.8 Turret, Bifurcated, hook and cup terminals
10.8.1 Turret and Straight Pin Terminals
10.8.2 Bifurcated terminals
10.8.3 Hook terminals
10.8.4 Pierced terminals
10.8.5 Solder cups (connector type)
10.8.6 Insulation sleeving
78
78
78
81
82
82
82
10.9 Wire and cable interconnections
10.9.1 General
10.9.2 Preparation of shielded wires and cables
10.9.3 Pre-assembly
10.9.4 Soldering procedures
10.9.5 Cleaning
10.9.6 Workmanship
10.9.7 Connection of stranded wires to PCBs
83
83
83
83
84
85
85
85
10.10 Interconnecting cable/harness fixturing
10.10.1 General
10.10.2 Mockup and Wiring Board Design Parameter
10.10.3 Temporary Identification
10.10.4 Interconnecting Cable and Harness Protection
86
86
86
86
86
10.11 Forming wires and cables into harnesses
10.11.1 General
10.11.2 Fabric Braid Sleeving (Pre-woven)
10.11.3 Lacing
10.11.4 Continuous Lacing
10.11.5 Straps
10.11.6 Insulation Sleeving/Tubing
86
86
90
91
92
93
93
10.12 Cable shielding and shield termination
10.12.1 General RFI/EMI Practices
10.12.2 Shield Termination
10.12.3 Individual Shield Termination Using Heat Shrinkable Solder Sleeves
10.12.4 Long Lengths of Shrinkable Sleeving
10.12.5 Floating Shield Terminations
10.12.6 Unshielded Wire Exposure and Total Length of Grounding Wires
94
94
95
95
95
96
97
10.13 Wire crimping
10.13.1 Crimping Requirements:
10.13.2 Crimping Operations
10.13.3 Crimping Tools
10.13.4 Calibration of Crimping Tools
10.13.5 Insulation Clearance
10.13.6 Insulation Support
10.13.7 Integrity of Crimped Connections
10.13.8 Examination of Test Samples
10.13.9 Inspection
10.13.10 Inspection Prior to Crimping
10.13.11 Microsectioning of Crimped Pin:
97
98
98
99
103
104
104
104
105
105
105
106
10.14 Connector assembly
10.14.1 Assembly of Crimp-Type Connectors (Including Terminal Junctions)
107
107
10.15 Interconnecting harness and cable cleaning
10.15.1 General
10.15.2 Cleaning the Harness Assembly
10.15.3 Cleaning Harness Connectors
10.15.4 Cleaning Coaxial Connectors (Assembled)
10.15.5 Harness handling and protection
10.15.6 Interconnecting Harness and Cable Storage Protection
10.15.7 Connector mating
108
108
108
108
109
109
109
109
10.16 Testing and inspection
10.16.1 General
10.16.2 Wet Probe Testing
110
110
111
10.17 Quality assurance provisions
10.17.1 Method of Inspection.
10.17.2 Magnification Aids
10.17.3 Documentation Verification
111
111
112
112
10.18 Wire visual aids and illustrations
10.18.1 Wiring: connectors, cabling, and harnessing - wire dress to connectors
10.18.2 Wiring: connectors, cabling, and harnessing stress relief shrinkable sleeving on solder cups
10.18.3 Wiring: connectors, cabling, and harnessing,
wire preparation, thermal stripping
10.18.4 Wire preparation: mechanical stripping
10.18.5 Wiring: connectors, cabling, and harnessing,
wire preparation, thermal stripping
10.18.6 Wiring: connectors, cabling, and harnessing,
wire preparation, tinning stranded conductors
10.18.7 Wiring: connectors, cabling, and harnessing - installation of straps
10.18.8 Crimps: insulation clearance
10.18.9 Crimps: Acceptable and Unacceptable
116
116
119
120
121
121
10.19 Critical problems in coaxial cable assembly
122
116
117
118
119
11 SEMI-RIGID CABLE ASSEMBLY
125
11.1 Introduction
125
11.2 Principles of Reliable Soldered or Crimped Semi-Rigid Cable Connections
125
11.3 Material 125
11.4 Tools
11.4.1 Fabrication tool kits from following manufacturer’s are available.
11.4.2 Cutting Tools
11.4.3 Cable Forming Tools
11.4.3 Cable Forming Tools
11.4.4 Cable Stripping and Dressing Tools
11.4.5 Heat Treatment Chamber
11.4.6 Soldering Equipment
11.4.7 Crimping Equipment
126
126
126
126
126
127
127
127
127
11.5 Semi Rigid Cable Assembly Process
11.5.1 General
11.5.2 Cable Straightening
127
127
128
11.6 Cable Assembly Drawing
128
11.7 Cable Cutting
128
11.8 Preconditioning Heat Treatment
129
11.9 Cable Templates
129
11.10 Cable Bending
129
11.11 Cable Bending General Requirements
11.11.1 Cable Bending Tools & Aids
11.11.2 Cable Bending Procedure
130
130
131
11.12 Cable Assembly Support Requirements
132
11.13 Cable Outer Jacket Stripping
11.13.1 Inspection of Stripped Cable Ends
132
132
11.14 Stripping the Dielectric
11.14.1 Stripping the Dielectric Alone After Outer Jacket Stripping
11.14.2 Stripping of Dielectric & Outer Jacket Simultaneously
133
133
133
11.15 Centre Conductor End Forming
133
11.16 Preparation for soldering of Cable Outer Jacket and Centre Conductor Tinning
134
11.17 Degolding of Gold Plated Connector Parts and Pre-tinning
11.17.1 De-golding By Three Solder Pot Method
11.17.2 Solder Preforms
11.17.3 Assembly Plan
11.17.4 General Requirements for Connector Assembly
134
134
135
137
137
11.18 Specific Requirements
11.18.1 SMA Right Angle Connector
11.18.2 SMA female connector
137
137
138
11.19 Solder Assembly of Semi­Rigid Cables
11.19.1 Straight cable­end connector
138
138
11.20 Right Angle Cable End Connector
139
11.21 Teflon Bush Insertion In Connector
11.21.1 In Case of Straight SMA Connector
11.21.2 In case of TNC connector
140
140
140
11.22 Semi Rigid Cable Preconditioning
11.22.1 Necessity
11.22.2 Phase-I Preconditioning
11.22.3 Phase-II Preconditioning
11.22.4 Phase-III Preconditioning
141
141
142
142
143
11.23 Inspection & Acceptance/Rejection Criteria
11.23.1 Inspection of Cable After Cutting To Required Length
11.23.2 Inspection after Cable Bending
11.23.3 Inspection After Cable Jacket Cutting,
Dielectric Stripping Pin Forming and Tinning
11.23.4 Inspection of De-Golded Connector Parts
11.23.5 Inspection of Pin Soldering
11.23.6 Inspection After Soldering of Connector Parts
To Sem-irigid Cable Before Phase III Preconditioning
11.23.7 Inspection of Finished Cable Assembly after Phase –III reconditioning
143
143
144
146
147
11.24 Specific
11.24.1 Right angle connector cable assembly
11.24.2 Straight connector cable assembly
11.24.3 TNC connector cable assembly
147
147
148
148
11.25 Semi-rigid cable fabrication flow charts
149
11.26 Sample diagram of cable assembly
160
11.27 Typical stress relieving bends used in Semi rigid cable assembly
161
12 POLYMERIC APPLICATIONS
12.1 Preparation for polymeric applications
12.1.1 Surface Preparation
12.1.2 Masking
12.1.3 Priming
12.1.4 Local Potting
12.1.5 Requirements
13 CONFORMAL COATING
144
146
146
163
163
163
163
163
163
164
171
13.1 Purpose
171
13.2 Safety Precautions
171
13.3 Poly Urethane Type Coating Applications
13.3.1 Spraying
13.3.2 Brush Method
13.3.3 Dipping Method
13.3.4 Pouring Method
171
172
172
172
172
13.4 Curing
172
13.5 Parylene Conformal Coating
13.5.1 Preparation for Coating (For Polyurethane and Parylene)
172
172
13.6 Application Procedure
13.6.1 Procedure for coating with Parylene:
173
173
13.7 Deposition Process
13.7.1 Sublimation
13.7.2 Precautions for Local Potting & Conformal Coating
173
173
178
13.8 Bonding
13.8.1 General
178
178
14 REPAIR & REWORK
179
14.1 Repair/Rework
179
14.2 Repair criteria
179
14.3 Number of repairs
179
14.4 Modifications
14.4.1 Modification criteria
179
179
14.5 Number of modifications
179
14.6 Rework
14.6.1 Rework criteria
14.6.2 Number of reworks
14.6.3 Other requirements
179
179
179
179
14.7 Removal of conformal coating
14.7.1 Requirements
14.7.2 Procedure
14.7.3 Acceptance criteria
179
179
180
180
14.8 Solder joint removal and unclinching
14.8.1 Procedure
14.8.2 Acceptance criteria
180
180
180
14.9 Repair of damaged conductor tracks
14.9.1 Requirements
14.9.2 Procedure
14.9.3 Acceptance criteria
180
180
180
180
14.10 Repair of lifted conductors
14.10.1 Requirements
14.10.2 Procedure
14.10.3 Acceptance criteria
181
181
181
181
14.11 Wire­to­wire joints
14.11.1 Requirements
14.11.2 Procedure
14.11.3 Acceptance criteria
181
181
181
181
14.12 Removal and replacement of axial and multi­lead components
14.12.1 Requirements
14.12.2 Procedure
182
182
182
14.12.3 Acceptance criteria
182
14.13 Removal and replacement of flat­pack components
14.13.1 Procedure
14.13.2 Acceptance criteria
182
183
183
14.14 Modification of component connections
14.14.1 Requirements
14.14.2 Procedure
14.14.3 Acceptance criteria
183
183
183
184
14.15 Quality assurance
184
14.16 Removal of conformal coating
14.16.1 Introduction
14.16.2 Tools and materials
184
184
184
14.17 Methods for the removal of conformal coating
14.17.1 Method for the removal of polyurethane and silicone type coating
185
185
14.18 Solder joint removal and unclinching
14.18.1 Introduction
14.18.2 Tools and materials
14.18.3 Methods for solder joint removal and unclinching
186
186
186
187
14.19 Repair of damaged conductor tracks
14.19.1 Introduction
14.19.2 Tools and materials
14.19.3 Method for the repair of damaged conductor tracks
189
189
189
189
14.20 Repair of lifted conductors
190
14.21 Methods for repair of lifted conductors
14.21.1 Method for the use of epoxy under conductor
14.21.2 Method for the use of epoxy over conductor
190
190
191
14.22 Wire to wire joints
14.22.1 Introduction
14.22.2 Method for wire­to­wire joining
191
191
191
14.23 Addition of Components
14.23.1 Method for additional component mounting
on reverse (non component side) of board
14.23.2 Method for additional components mounting
on component side of board
191
192
14.24 Method for the addition of a wire link onto metallized cap
of chips directly glued on PCB
192
14.25 Method for the addition of a wire link onto terminal pad of soldered chips
193
15 SPECIAL PROCESSES
15.1 SPLICING
15.1.1 General
15.1.2 General Information
15.1.3 Design Considerations
15.1.4 Splicing Methods
191
194
194
194
194
194
194
15.1.5
Soldered Splices
195
15.2 Lap Splice
15.2.1 Preparation.
15.2.2 Soldering.
15.3
Lash Splice
15.3.1 Preparation
15.3.2 Soldering
195
195
195
195
196
196
15.4 Solder Sleeve
15.4.1 Preparation
15.4.2 Soldering.
196
196
197
15.5 Crimped Splices
197
15.6 Modified Crimp Contact
197
15.7 Butt Splice
15.7.1 Preparation.
15.7.2 Contact Sizing
15.7.3 Assembly
15.7.4 Inspection
198
198
198
199
199
16 ELECTRO STATIC DISCHARGE (ESD)
200
16.1 General
200
16.2 ESD Modeling
200
16.3 Triboelectrification
16.3.1 Induction charging
200
200
16.4 Need of ESD Control
202
16.5 Classifications of ESD Devices
202
16.6 Type of ESD Failure
16.6.1 Catastrophic failure
16.6.2 Parametric failure
16.6.3 Latent failure
202
202
202
203
16.7 ESD Control Program
16.7.1 ESD Sensitivity Levels
16.7.2 Methods of ESD Control
16.7.3 Personnel safety
16.7.4 ESD protected areas (EPA)
203
203
204
206
206
16.8 ESD Control Requirements For Facilities
16.8.1 General
16.8.2 Identification and access - ESD areas
16.8.3 Prohibited Materials And Activities
16.8.4 ESD Protective Work Surfaces
16.8.5 ESD-Protective floor surfaces
16.8.6 Personal grounding devices
16.8.7 Integrity testing of personal grounding devices
16.8.8 Equipment and facilities
16.8.9 ESD safe protective packaging
206
206
206
208
208
209
210
210
211
215
16.8.10 Clothing requirements
16.19 ESDS Item Handling
16.9.1 General
16.9.2 Special Requirements for Highly Sensitive Items
16.9.3 Equipment
16.9.4 Identification and marking
17 BONDED STORES
215
216
216
216
217
218
220
17.1 Introduction
220
17.2 Environment of the bonded stores
220
17.3 Operation of the bonded stores
17.3.1 Contents of the bonded stores
220
220
17.4 Storage
17.4.1 General
17.4.2 Electronic Component Storage Area
17.4.3 Storage of Materials and Chemicals
17.4.4 Operation
17.4.5 Operator
17.4.6 Documentation
220
220
221
221
221
222
222
18 TERMS AND DEFINITIONS
223
19 TECHNICAL STANDARD IMPROVEMENT PROPOSAL
236
19.1 Instructions
236
LIST OF FIGURES
Figure 4.1
: Profiles of correct and incorrect cutters for trimming leads
05
Figure 4.2
: Typical lead forming/bending tool
06
Figure 4.3
: Typical mechanical wire stripper
06
Figure 6.1
: Methods for incorporating stress relief with components having bendable leads
21
Figure 6.2
: Assembly of under filled TO-39 and TO-59, and adhesively staked CKR06
22
Figure 6.3
: Not acceptable body and seal conditions23
Figure 6.4
: Minimum lead bend
25
Figure 6.5
: Horizontal Mount
26
Figure 6.6
: Radial Leaded Parts
26
Figure 6.7
: Obstruction of solder flow (Not acceptable)
27
Figure 6.8
: Stress Relief Part Termination
27
Figure 6.9
: Bend Angle
27
Figure 6.10 : Lapped Lead Height above Board
28
Figure 6.11 : Lapped Round Termination
29
Figure 6.12 : Lapped Ribbon Leads
30
Figure 6.13 : Clinched Termination
30
Figure 6.14 : Lead Bend
31
Figure 6.15 : Straight-Through Termination
31
Figure 6.16 : Straight-Through Lead Retention
31
Figure 6.17 : Leads with solder termination on both sides
32
Figure 6.18 : Types of terminal swaging
33
Figure 6.19 : Terminal swaging sequence
33
Figure 6.20 : Method of stress relieving parts attached to terminals
34
Figure 6.21 : Fuse mounted on bifurcated, where post is cut
35
Figure 6.22 : Exposed element
36
Figure 7.1
: Solder fillet for plated through holes
39
Figure 7.2
: Solder fillet for non through holes where leads are clinched
39
Figure 7.3
: Mounting of rectangular and square end-capped and end-metallized devices
40
Figure 7.4
: Mounting of bottom terminated chip devices
41
Figure 7.5
: Mounting of cylindrical end-capped devices
42
Figure 7.6
: Mounting of castellated chip carrier devices
42
Figure 7.7
: Mounting of devices with round, flattened, ribbon, “L” and gull-wing leads
43
Figure 7.8
: Mounting of devices with “J” leads
43
Figure 7.9
: Dimensions of tall profile components.
44
Figure 7.10 : Typical CCGA device build -up
44
Figure 7.11 : Typical assembled CCGA device
45
Figure 7.12 : Underside view showing missing column
46
Figure 7.13 : Solder fillet 360° coverage around the column circumference: Accept
46
Figure 7.14 : Side view showing column; column by more than 5°: Reject
46
Figure 7.15 : X-ray view showing voids in column solder joint more than 25%: Reject
47
Figure 7.16 : Example of acceptable solder fillet coverage around column,
more than 50%: Accept
48
Figure 7.17 : Example of acceptable column tilt up to 10º
48
Figure 7.18 : CGA mounted on PCB showing columns tilted < 5°: Accept
49
Figure 7.19 : Micrograph of CGA mounted on PCB
49
Figure 7.20 : Micrograph of CGA mounted on PCB
49
Figure 7.21 : Radiograph of CGA mounted on PCB
50
Figure 7.22 : Radiograph of CGA mounted on PCB showing missing column: Reject
50
Figure 7.23 : Radiograph of CGA mounted on PCB showing insufficient solder: Reject
51
Figure 7.24 : Radiograph of CGA mounted on PCB showing solder bridge: Reject
51
Figure 7.25 : Radiograph of CGA showing excessive voiding in
solder fillets at base of columns: Reject
51
Figure 7.26 : High voltage connection
52
Figure 7.27 : Missing of balls
53
Figure 7.28 : Sum of voids in some BGA balls exceeds 25 % of
ball’s cross section diameter: Reject
53
Figure 7.29 : Non wetted ball in X-Ray (Absence of tear drop shape)
54
Figure 7.30 : Ball shall be centered on land
54
Figure 7.31 : Ball bridging is not accepted
55
Figure 7.32 : Insufficient wetting of left most ball
55
Figure 7.33 : Crack on the ball to PCB solder joint
55
Figure 9.1
: Preferred solder for chip devices
62
Figure 9.2
: Maximum acceptable solder
62
Figure 9.3
: Un acceptable solder due to poor wetting
62
Figure 9.4
: Acceptable, minimum solder: Terminal wetted along end, face and sides
64
Figure 9.5
: Preferred solder
64
Figure 9.6
: Unacceptable Excessive solder
64
Figure 9.7
: Unacceptable insufficient solder
65
Figure 9.8
: Ribbon/Gull wing leaded devices
67
Figure 9.9
: Unacceptable : Excessive solder (middle joint)
67
Figure 10.1 : Terminal Damage
74
Figure 10.2 : Roll Flange Terminal
74
Figure 10.3 : V-Funnel Type Swage Roll
75
Figure 10.4 : Flare and extension of funnel flanges
75
Figure 10.5 : Elliptical funnel swage
75
Figure 10.6 : Wrap Orientation
77
Figure 10.7 : Side- and bottom-route connections to turret terminals
79
Figure 10.8 : Bottom-route connections to bifurcated terminal
79
Figure 10.9 : Side-route connection to bifurcated terminal
80
Figure 10.10 : Top-route connection to bifurcated terminal
81
Figure 10.11 : Connections to hook terminals
81
Figure 10.12 : Connections to pierced terminals
82
Figure 10.13 : Connections to solder cups (connector type)
83
Figure 10.14 : Methods for securing shielded wires
84
Figure 10.15 : Connection of stranded wires to PCBs
85
Figure 10.16 : Line Drawing of Typical Harness Layout
87
Figure 10.17 : Starting Stitch
88
Figure 10.18 : Spot Tie (Typical)
88
Figure 10.19 : Closing Stitch and Single Thread—Illustration
89
Figure 10.20 : Alternate Closing Stitch and Single Thread—Illustration
89
Figure 10.21 : Running Lockstitch
89
Figure 10.22 : Flat Lacing Stitches
90
Figure 10.23 : Securing Fabric Braid Sleeving
90
Figure 10.24 : Spot Tie Principle
91
Figure 10.25 : Spot Tie
91
Figure 10.26 : Serve Method of Tying
92
Figure 10.27 : Serve at the Point of Origin
92
Figure 10.28 : Running Stitch
92
Figure 10.29 : Single Lock Stitch
93
Figure 10.30 : Double Lock Stitch
93
Figure 10.31 : Plastic Strap Orientation
93
Figure 10.32 : Individual Shield Termination Using a Heat shrinkable Solder sleeving
95
Figure 10.33 : Installation of Long Lengths of Sleeving to Achieve Controlled Dimensions
96
Figure 10.34 : Floating Shield Termination
96
Figure 10.35 : Conductor Exposure for Individual Shield Termination Types
97
Figure 10.36 : Folded back shield with splice termination to multi strand wire
97
Figure 10.37 : Specific Interconnection
98
Figure 10.38 : Crimp Joint Tensile Failure Categories
105
Figure 10.39 : Example of a typical connector barrel and single wire crimping
106
Figure 10.40 : Example of a typical connector barrel and multi-wire crimping
106
Figure 10.41 : Visual Examination Inside the Socket Contact for Flux Residue
109
Figure 10.42 : Illustration of Proper trim back of Jacket to Isolate it from the Clamping Sy stem123
Figure 10.43 : Broken Solder Joint Caused by Insufficient Solder Fill
124
Figure 10.44 : Problem Point for Kynar Stress Relief Sleeving
124
Figure 11.1 : Typical cable cut­off fixture
129
Figure 11.2 : Typical cable forming tool
131
Figure 11.3 : Dimensional inspection requirements
133
Figure 11.4 : Method of producing solder preforms
136
Figure 11.5 : Approved and non­approved straight solder­type cable­end connectors
136
Figure 11.6 : Centre contact assembly
138
Figure 11.7 : Right angle cable-end connector assembly
141
Figure 12.1 : Default Potting for Horizontally-Mounted Sleeveless Cylindrical Part
165
Figure 12.2 : Single Wire Potting
165
Figure 12.3 : Potting for Radial Lead Components
166
Figure 12.4 : Potting for Radial Multi-lead Rectangular Components
166
Figure 12.5 : Default Potting of a Single Vertically-Mounted Rectangular Part
167
Figure 12.6 : Default Potting for an Array of Vertically-Mounted Rectangular Parts
167
Figure 12.7 : Wire Bundle Potting
168
Figure 12.8 : Typical Toroid Potting
168
Figure 12.9 : Vibration Dampening Potting
169
Figure 12.10 : Typical Vibration Isolation Potting
170
Figure 13.1 : Conformal Coating – Bubbles
175
Figure 13.2 : Conformal Coating – Scratches
176
Figure 13.3 : Conformal Coating - Lifting and Peeling
177
Figure 13.4 : Conformal Coating – Coverage Defects
178
Figure 14.1 : Removal of multi-lead components, clipping of component leads
182
Figure 14.2 : Removal of flat pack components
183
Figure 14.3 : Removal of coating by thermal parting device
186
Figure 14.4 : Continuous vacuum solder extraction on stud lead
187
Figure 14.5 : Pulse­type solder sucker in use
188
Figure 14.6 : Hot Jet Blower Method
188
Figure 14.7 : Cross-sectional view of wicking method
198
Figure 14.8 : Hot unclinching with thermal parting device
189
Figure 14.9 : Lifted conductors
190
Figure 14.10 : Repair using epoxy under conductor
190
Figure 14.11 : Repair using epoxy over conductor
191
Figure 14.12 : Additional components mounted on reverse (no component) side of board
192
Figure 14.13 : Addition of a wire link onto metallized cap of chips directly glued on PCB
193
Figure 14.14 : Addition of a wire link onto terminal pad of soldered chips
193
Figure 15.1 : Pre-Tinned Conductors
195
Figure 15.2 : Soldered Conductors
195
Figure 15.3 : Sleeving over Soldered Connection
195
Figure 15.4 : Double Sleeving over Soldered Connection
195
Figure 15.5 : Pre-Tinned
196
Figure 15.6 : Lashing of Pre-Tinned Conductors
196
Figure 15.7 : Soldered Connection
196
Figure 15.8 : Pre-Lash End Type Splice
196
Figure 15.9 : Lash End Type Splice
196
Figure 15.10 : Soldered Lash Splice
196
Figure 15.11 : Sleeved Lash Splice
196
Figure 15.12 : Solder Sleeve Prior to Flow
197
Figure 15.13 : Fully Melted Solder Sleeve
197
Figure 15.14 : Stripped Wires Prior to Insertion
197
Figure 15.15 : Stripped Wire Bundle Prior
198
Figure 15.16 : Wires Crimped Within
198
Figure 15.17 : Contact Trimmed and Deburred
198
Figure 15.18 : Contact Covered With Shrink Sleeving
198
Figure 15.19 : Butt Splice
198
Figure 15.20 : Butt Splice Prior to Wire Insertion
198
Figure 15.21 : Butt Splice Prior to Crimp
199
Figure 15.22 : Properly Crimped Butt Splice
199
Figure 15.23 : Butt Splice with Shrink Sleeving.
199
Figure 16.1 : ESD Symbols
205
Figure 16.2 : Typical ESD Grounded Workstation
208
Figure 16.3 : Workstation Common Point Ground
209
Figure 16.4 : Main Service Box
212
Figure 16.5 : Sensitive Electronic Device Caution Symbol
(With & without sensitivity class level)
218
Figure 16.6 : ESD Protective Item Symbol
218
Figure 16.7 : ESD Common Point Ground Symbol
219
Figure 17.1 : Segregation of electronic components
221
Figure 17.2 : Segregation of material
221
Figure 17.3 : Segregation of chemicals
221
LIST OF TABLES
Table 4‑1
: Solder baths for degolding and pretinning
09
Table 5‑1
: Guide to choice of solder types
11
Table 5‑2
: Chemical composition of solders
12
Table 5‑3
: Classification of printed circuit boards and substrates
14
Table 6‑1
: Clearances for insulation
17
Table 6‑2
: Baking conditions
20
Table 6‑3
: List of material used for isolation
24
Table 7‑1
: Dimensional and solder fillet requirements for rectangular
and square end capped devices
40
Table 7‑2
: Dimensional and solder fillet requirements for bottom terminated chip devices
41
Table 7‑3
: Dimensional and solder fillet requirements for cylindrical end-capped devices
42
Table 7‑4
: Dimensional and solder fillet requirements for castellated chip carrier devices
42
Table 7‑5
: Dimensional and solder fillet requirements for
devices with round, flattened, ribbon, “L” and gull-wing leads
43
Table 7‑6
: Dimensional and solder fillet requirements for devices with “J” leads
43
Table 10‑1
: Clearances for insulation.
76
Table 10‑2
: Dimensions for Figure 10‑16
86
Table 10‑3
: Bend Radii for Completed Interconnecting Cable or Harness
87
Table 10‑4
: Spot Tie, and Stitch Spacing Dimensions
88
Table 10‑5 : Distances From Connectors or Connector Accessories to
Beginning of Harness Ties
90
Table 10‑6
: Selection Guide for Use of Polyolefin / Kynar sleeves
94
Table 10‑7
: Shield Termination Control
97
Table 10‑8
: Required ultimate axial strength for compactive and dispersive crimped joints
107
Table 11‑1
: Cable diameter and bend radius
130
Table 11‑2
: Cable pre-conditioning : Phase1
142
Table 11‑3
: Cable pre-conditioning : Phase2
143
Table 11‑4
: Cable pre-conditioning : Phase3
143
Table 13‑1
: Conformal coating materials
171
Table 14‑1
: Wire diameters for given conductor widths
181
Table 16‑1
: Triboelectric Series
201
Table 16‑2
: ESDS Component Sensitivity Classifications – HBM
203
Table 16‑3
: ESDS Component Sensitivity Classifications – MM
204
Table 16‑4
: ESDS Component Sensitivity Classifications – CDM
204
Table 16‑5
: ESD Protective materials
205
Table 16‑6
: ESD Control Program Verification Schedule and Measurements
207
Table 16‑7
: ESD Sensitivity for Selection and Performance of Air Ionizers
214
Table 16‑8
: Summary of Recommendations Applicable to HBM Class 0 and MM Class M1
217
Table 16‑9
: Susceptibility of Devices to ESD
219
Table 16‑10 : Typical Electrostatic Voltages
219
Table 16‑11 : Effects of Electrical Current on Humans
219
1
SCOPE
This specification states the quality and workmanship requirements to be met during fabrication of electronic and
electromechanical packages for complete assembly of spacecraft, launch vehicle systems and critical check out
systems of all projects of ISRO so as to maintain an acceptable uniform quality level. The fabrication requirements
specified herein are applicable for all onboard avionics elements and addtional requirements wherever necessary
are specified in relevant sections.
Adherence to the procedures specified herein shall be mandatory for all work centres of ISRO and their subcontractors
in order to realize reliable operation of the systems. The procedures are thus drawn to ensure that all modules
fabricated meet the performance and reliability requirements criteria. In general, greater importance shall be given
for preventive measures leading to defect free systems rather than allowing for possible rework at later stage,
although rework or repair cannot be totally dispensed with. ISRO reserves the right to undertake inspection at any
stage of fabrication at work centres including sub contractors.
1
2
APPLICABLE DOCUMENTS
Doc Number
Title
ISRO-PAX-301
Design Requirements for Printed Circuit Board Layout Artwork
ISRO-PAX-304
Test specification for Printed Circuit Boards.
ISRO-PAS-207
Storage, Handling & Transportation Requirements for Electronic Hardware
ISRO-PAS-100
Non Conformance Control Requirements for ISRO Projects
2.1 Other Related Documents
ECSS-Q-ST-70-38C
High-reliability soldering for surface-mount and mixed technology
ECSS-Q-ST-70-08C
Manual soldering of high-reliability electrical connections
ECSS-Q-ST-70-28
Space product assurance - Repair and modification of printed circuit board assemblies
for space use
ECSS-Q-ST-70-26C
The Crimping of High Reliability Electrical Connections.
ANSI-J-STD-004
Flux Soldering Liquid (Rosin Base)
ANSI- J-STD-006
Tin Alloy, Tin Lead Alloy and lead Alloy Solder.
MIL-STD-1686
Electrostatic discharge control program for protection of electrical and electronic parts,
assemblies and equipment (excluding electrically initiated explosive devices)
MIL-HDBK-263
Electrostatic discharge control handbook for protection of electrical and electronic
parts, assemblies and equipment (excluding electrically initiated explosive devices)
(metric)
In the event of any conflict, this specification along with the production details shall supersede the applicable
documents.
2.2 Definitions
Terms and definitions used in this document are given in Chapter 18.
2
3
FACILITY
3.1 Environmental Conditions for Work Area
Clean surroundings must be maintained in the area where electronic fabrication is carried out.
The soldering area shall have a controlled environment to limit the entry of contaminants.
• Clean room area shall be class 100,000 or better.
• The clean room temperature shall be maintained at 22 °C ± 3 °C.
• The relative humidity (RH) at room temperature of the facility shall be maintained at 55 % ± 5 %.
• Clean room should have positive pressure difference to the outside area.
• Areas used for assembly or cleaning of parts and areas where toxic or volatile vapours are generated or
released shall include a local air extraction system.
• Dirt, dust, solder particles, clipped wires etc., shall be removed at frequent intervals.
• The work area shall have good ventilation.
• The filter shall be changed every six months or earlier depending upon the use.
3.2 Lighting Requirements
• Lighting intensity shall be a minimum of 1100 lumens/sq. m on the work surface.
• The additional lighting near the operator coming from the sides with suitable shading on the eyes of the
operator shall be provided, to be switched on by the operator whenever necessary.
3.3 ESD Requirements
A full fledged ESD proof work station shall be employed for fabrication of charge sensitive devices as listed in
Chapter 16
3.4 Wiring & Assembly Area
Clean surroundings shall be maintained in the wiring and assembly area as listed in 3.1. Care shall be taken to remove
cut leads of parts, wires and wire braids. Care shall be taken to ensure cleanliness during pre-cleaning for flux
removal. Tissue papers and other materials used for pre-cleaning shall be disposed off away from the work table.
3.5 Cleaning Area
Cleaning area shall have proper ventilation to avoid toxic fumes affecting personnel involved in cleaning operations.
Approved cleaning solvents shall be used for cleaning of PCBs, packages and subsystems. Precaution shall be taken
while handling these chemicals as they are susceptible to flammability.
3.6 Tinning Area
Tinning area shall have proper ventilation to carry fumes away from the work area. Cleaning of part’s leads and wires
during pre tinning shall be done in a manner so that the loose particles removed shall not lie in the work area. They
shall be collected in cleaning solvent and shall be disposed off regularly. Tinning Pots shall be kept at locations with
fume hood to avoid contamination.
3
3.7 Conformal Coating & Potting Area
Conformal coating and potting area shall have proper ventilation to conduct away the toxic fumes from
materials used.
3.8 Mechanical Assembly Area
Mechanical assembly area shall have clean surroundings with good ventilation and have provision for mechanical
operations such as minor fitting, cutting and filling operations for Semi-rigid Cables and correcting the hardware.
This area shall be isolated from the fabrication area to avoid contamination due to mechanical operations.
3.9 Special Processes Area
Special Processes such as subsystems assembly, optical assembly such as VHRR assembly of packages having Microwave
Integrated Circuits (MIC), sensor elements like PRTs etc., shall be carried out in an area approved by the QA team
of the ISRO Centre. Integration of packages, subsystems on the panels etc., shall also be carried out in the special
process area. Preferably in class 100 laminar tables.
4
4
TOOLS
4.1 Tools and Equipments
All equipments and tools shall be inspected to ensure that they are not defective prior to use.
4.1.1 Brushes
• Medium-stiff natural or synthetic bristle, ESD-safe, brushes shall be used for cleaning provided that they do
not damage any surface to be cleaned or adjacent materials.
• Brushes shall be cleaned properly in a solvent.
• Brushes shall not be damaged by the solvents used for PCB cleaning.
• Wire brushes shall not be used.
4.1.2 Cutters and pliers
• Cutting edge profiles and cutter usage shall be in accordance with Figure 4‑1.
• The cutter used for trimming conductor wire and component leads shall shear sharply, producing a clean, flat,
smooth-cut surface along the entire cutting edge.
• No twisting action shall occur during the cutting operation.
• Cutting edges shall be checked for damage and maintained in a sharp condition.
• Smooth, round long-nose pliers or tweezers can be used for attaching or removing conductor wires and
component leads.
• Smooth round nose pliers are also used for making wire loops.
Cutter
Lead cut correctly
Lead cut incorrectly
Using correctly profiled cutters
Incorrect lead cutting using incorrectly profiled cutters
Figure 4.1: Profiles of correct and incorrect cutters for trimming leads
4.1.3 Bending tools
• Bare component leads shall be bent or shaped using bending tools, including automatic bending tools, which
do not cut, nick or damage the leads or insulation.
• Components shall not be damaged by the bending process. It is good practice to use bending tools with
polished finish. The preferred surface finish for shaping tools is hard chromium plating.
• Bending tools shall have no sharp edges in contact with the component leads. Typical lead bending tool is
shown in Figure 4.2.
5
Figure 4.2:Typical lead forming/bending tool
4.1.4 Clinching tools
Clinching tools shall not damage the surfaces of printed-circuit conductors, components or component leads.
4.1.5 Antiwicking Tools
Antiwicking tools shall be of a design that fits only a specific conductor gauge size and shall be marked with that
conductor gauge size.
4.1.6 Holding Devices
Tools, fixtures, and materials used to hold or restrain conductors and parts shall be of a design that will not damage
or deform the conductors, conductor insulation, or parts.
4.1.7 Insulation strippers
4.1.7.1 Mechanical Strippers
Mechanical strippers shall be of the following types:
Mechanical strippers used to remove insulation from stranded or solid conductor wires may be of the hand
operated or automatic high volume machine type.
Automatic power-driven strippers shall be with precision, factory-set, cutting and stripping dies and wire guards, or
Precision-type hand strippers with accurately machined and factory-preset cutting heads.
The conductor shall not be twisted, ringed, nicked, cut or scored by the process.
Figure 4.3:Typical mechanical wire stripper
4.1.7.2 Thermal Strippers
• Thermal insulation strippers can be used for wire insulation types susceptible to damage by mechanical
strippers.
• The temperature of the stripper shall not burn, blister or cause excessive melting of the insulation.
6
• Temperature controls shall be sufficient to prevent damage to the wire or unstripped insulation.
• It is a good practice to apply thermal strippers for use with AWG 22 and thinner wire sizes where there is a
possibility of the wire stretching if a mechanical stripper is used.
4.1.7.3 Chemical Stripper
• Chemical solutions, pastes, and creams used to strip wires shall be suitable for removal of the insulation to be
stripped and shall not cause degradation to the wire.
• The enamel shall be removed by chemical means.
• The enamel may be removed by mechanical means provided that visual inspection using a minimum magnification
of 40x is carried out to ensure that the conductor is undamaged.
4.1.8 Thermal Shunts
Thermal shunts shall be used to absorb heat from part leads as necessary to protect parts, insulating materials, and/
or previously completed connections from damage during soldering operations.
4.2 In-Process Storage and Handling
Each operator performing soldering operations shall develop and implement requirements and procedures that
control conditions to prevent damage to and degradation of, parts and deliverable items.
In particular, means shall be provided to prevent damage or contamination to printed wiring terminating areas,
terminals, connectors, wire ends, or part leads during handling and storage.
Contact with bare hands shall be avoided. When handling metal surfaces that are to be soldered is unavoidable,
clean, lint-free gloves or finger cots shall be used.
Gloves and finger cots used shall not generate electrostatic charges.
Electrostatic discharge sensitive (ESDS) parts or assemblies shall be stored, handled, or otherwise processed in
accordance with Para 16.
Controlled Environmental cabinets, Desiccators, dry nitrogen purged bags or Conductive bags shall be used for such
storage.
4.3 Soldering, Cleaning and Inspection Equipments
4.3.1 Contact Type (Soldering irons)
• The size and shape of the soldering iron and bit shall not damage adjacent areas or connections during
soldering operations.
• Temperature-controlled soldering irons shall be used.The idling temperature shall be controlled within ±5.5°C.
It is good practice to verify periodically the soldering iron tip temperature.
• Files shall not be used for dressing plated copper soldering-iron tips.
• A selection of bit sizes, shapes & power appropriate to each soldering operation envisaged shall be available.
• The soldering iron shall maintain the set temperature at the joint throughout the soldering operation.
• Thermal shunts shall be used to protect thermally-sensitive components.
7
• For soldering conventional electronic components on PCBs (double sided and PTH), the soldering iron bit
temperature shall be between 260 °C and 280 °C. For MLBs higher bit temperatures may be used if required,
but limited to 320°C maximum.
• The bit temperature up to 320°C may be used for polyimide PCBs with heat sinks, wide tracks or ground
planes.
4.3.2 Non-contact Type Soldering machines
4.3.2.1 General
• The soldering machine shall be grounded in order to avoid electrostatic discharge.
• Shall ensure that the soldering conditions do not exceed the values given by the individual component
data sheets (e.g. maximum temperature to avoid internal melting, removal of marking ink, degradation of
encapsulating plastic).
• Temperature and time profiles for assembly shall be identified and approved.
• When supplemental heat is applied by hot gases, radiant energy, or any other source for aiding the hand and
wave soldering process, the equipment shall be set up, operated, and maintained by personnel using established
and documented procedures.
4.3.2.2 Hot gas reflow machines
Hot gas reflow machines shall conform to the following requirements;
• There shall be no relative motion between the conductors, part leads, terminals and the printed wiring
board termination areas during solidification.
• Preheats an assembly with solder paste to the temperature recommended by the solder paste manufacturer
prior to soldering.
• Heats the area of the assembly to be soldered to a preselected temperature between 220 °C and 250 °C as
measured on the substrate surface.
• Prevents the reflow of adjacent components.
• Maintains the preselected reflow temperature within 5 °C as measured at the substrate surface.
4.3.2.3 Radiation (LASER & IR) reflow systems
Radiation reflow machines shall be of design such that the system meets the following requirements;
• Provides a controlled temperature profile and does not transmit movement or vibration into the assembly
being soldered.
• Preheats an assembly with solder paste to the temperature recommended by the solder paste manufacturer
prior to soldering.
• Heats the area of the assembly to be soldered using focused or unfocussed energy, to a preselected temperature
that is a minimum of 12 °C above the melting point of the solder being used as measured at laminate or
substrate surface.
• Maintains the preselected temperature to within 6 °C in the reflow zone during soldering.
4.3.2.4 Solder Deposition equipment
• Equipment used to deposit solder pastes shall be of a screening, stenciling, dispensing, dotting type.
• Equipment shall apply pastes of a viscosity and quantity such that the positioned device is retained on the
board before and during soldering operations, ensuring self-centering and solder fillet formation.
• Equipment used to apply solder preforms shall ensure alignment of the preform with the land or device lead
and termination.
8
4.3.2.5 Automatic device placement equipment
• Automatic or computer controlled equipment used for device placement shall be of the coordinate-driven
pick-and-place type or of the robotic type.
• Equipment shall not generate, induce or transmit electrostatic charges to devices being placed
• The placement equipment used shall be of a type that;
o
Prevents device or board damages.
o
Aligns the device leads or castellation with the board terminal areas.
o
Indexes devices with respect to the circuit.
4.3.3 Solder Baths
Solder baths used for degolding and pretinning shall be in accordance with Table 4‑1
• Surface impurities shall be removed from the bath surface before use.
• A controlled method shall be established and implemented for the replacement of solder baths, based on
either:
o
Contamination: Replace the solder bath alloy when the contamination limits exceeds as given in
Table 4‑1.
o
Time: Establish a schedule of solder-bath replacement with justification of the replacement frequency.
• Solder pots shall be capable of maintaining the solder temperature at ±5°C of the preselected temperature.
Solder pots shall be grounded.
Table 4‑1 : Solder baths for degolding and pretinning
Solder bath 1
Solder bath 2
Use
Gold dissolution
Pretinning
Temperature range (°C)
240 to 260
240 to 260
Contamination limits
(weight %)
Au < 1
Cu < 0.25; Au < 0.2; (Cu + Au) < 0.3;
Zn, Al and Fe: Trace.
4.3.4 Cleaning equipment and systems
Cleaning tools shall be selected based on their ability to minimize the generation of static charge. Typical cleaning
tools include natural bristle brushes, lint-free tissue, cotton swabs, etc. Steel-wire brushes, knives, erasers, emery
cloth, sandpaper and other devices that produce an abrasive action or cause contamination shall not be used.
Vapour degreaser or manual cleaning (Three-tray method) shall be used for cleaning assembled PCBs. Refer
para 8.1.2 for vapour degreasing method.
4.3.4.1 Cleanliness testing equipment
Cleaning of the printed wiring assemblies shall be carried out using solvents listed in para 5.4.1. Cleaning method
followed shall be as per para 8.1. Also assemblies shall be tested for the cleaning as per para 8.2.
4.3.5 Inspection Optics (Magnification Aids)
Visual inspection shall be performed using magnification aids conforming to the following:
• Magnification aids shall be capable of rendering true colors, proportional dimensions, and adequate resolution
at the chosen magnification to perform the specified inspection.
9
• The light source shall provide shadow-less illumination on the area being viewed.
• Shall have anti-glare light source (preferably white light)
• Each soldered connection shall be visually inspected in accordance with the criteria specified in the clauses
below.
• Inspection shall be aided by magnification appropriate to the size of the connections between 10X to 40X
with stereo zoom microscopes or similar devices like AOI.
10
5
MATERIALS
5.1 General
• Material selection shall be performed in accordance with approved material list of ISRO centres or ISRO
Declared Material List
5.2 Solder
5.2.1 Solder Preform
• For soldering, ribbon, wire, solder bar or preforms shall be used provided that the alloy meets the requirements
as given in Table 5‑2.
• For degolding and pretinning, solder alloys shall be supplied without flux.
5.2.2 Solder Composition
The solder alloy with their composition and application are given in Table 5‑1
Table 5‑1 : Guide to choose solder types
Solder type
Melting range (°C)
Solidus
Liquidous
Uses
63 tin solder (eutectic)
183
183
Soldering printed circuit boards where temperature
limitations are critical and in applications with an
extremely short melting range. Preferred solder for
surface mount devices.
62 tin silver loaded
179
190
Soldering of terminations having silver and or silver
palladium metallization. This solder composition
decreases the scavenging of silver surfaces.
60 tin solder
183
188
Soldering electrical wire/cable harnesses or terminal
connections and for coating or pretinning metals.
96 tin silver (eutectic)
221
221
Can be used for special applications, such as soldering
terminal posts.
75 indium lead
145
162
Special solder used for low temperature soldering
process when soldering gold and gold-plated finishes. Can
be used for cryogenic applications.
70 indium lead
165
175
For use when soldering gold and gold-plated finishes
when impractical to degold.
10 tin lead
268
290
For use in step-soldering operations, to avoid reflow
of initial solder on making the second joint (limited to
connections internal to devices).
11
Table 5‑2 : Chemical composition of solders
Designation
Sn
Pb
In
Sb
min% max %
max %
min % –
max %
63 tin
solder
62.5-63.5
remain
-
0.05
62 tin silver
loaded
61.5-62.5
remain
-
60 tin
solder
59.5-61.5
remain
96 tin
solder
remain
0,10
75 indium
lead
max 0.25
70 indium
lead
10 tin lead
Ag
max % min %–
max %
Bi
Cu
Fe
Zn
Al
As
Cd
Others
max % max % max %
max %
max % max % max %
-
0.10
0.05
0.001
0.001
0.05
1.8-2.2
0.10
0.05
0.02
0.001
0.001
0.03
0.002
0.08
-
0.05
-
0.10
0.05
0.02
0.001
0.001
0.03
0.002
0.08
-
0.05
3.5-4.0
0.10
0.05
0.02
0.001
0.001
0.03
0.002
0.08
remain
74.0-76.0
0.05
-
0.10
0.05
0.02
0.001
0.001
0.03
0.002
0.08
0.00-0.10
remain
69.3-70.7
0.05
-
0.10
0.05
0.02
0.001
0.001
0.03
0.002
0.08
9.0-10.5
remain
-
0.05
-
0.10
0.05
0.02
0.001
0.001
0.03
0.002
0.08
0.02
0.03 0.002
max %
0.08
5.2.3 Maintenance of paste purity
• When purchased premixed or mixed in house, the purity of solder paste shall be maintained.
• Manufacturers’ instructions shall be applied for the handling and storage of containers of solder paste purchased
premixed.
• Refrigerated solder paste shall reach room temperature before opening the container.
• Neither paste purchased premixed nor paste mixed in-house shall be used if the use-by date or shelf life
recommended by the manufacturer of the paste or paste constituents has expired.
• When the solder paste’s shelf life has expired, it shall not be used unless, relifing is performed.
• Tests that include visual inspection and viscosity measurements (according to the manufacturer’s
recommendations) shall pass successfully.
• When relifing is performed, and the material passes the specified tests, the new shelf life shall be half the initial
shelf life.
• Tools used for removing solder paste from the container shall not contaminate the paste dispensed or that
remaining within.
5.3 Flux
5.3.1 Rosin-based fluxes
The use of liquid rosin, mildly activated (RMA) flux is recommended for the soldering, wicking-off procedures, for
rework of soldered connections, tinning operations and reflow soldering. Liquid flux used with flux cored solder
shall be chemically compatible with the solder core flux and with the materials with which it will come into contact.
Flux shall conform to requirements of ANSI-J-STD-004.
Note: Flux residue shall be cleaned at the earliest as the residues may lead to performance deterioration of
the assembly.
12
5.3.1.1 Application of flux
• The quantity of flux used shall be such that the solder joint is in accordance with acceptable criteria as
pera. 9.5
• When flux-cored solder is used, it shall be positioned such that the flux flows and covers the components to
be joined as the solder melts.
• When an external liquid flux is used in conjunction with flux-cored solders, the fluxes shall be compatible.
• When external flux is used, liquid flux shall be applied to the surfaces to be joined prior to the application of
heat.
5.4 Cleaning Solvents
• Shall be electrically non-conductive and non-corrosive.
• Shall not dissolve or degrade the quality of parts or materials.
• Solvents shall not remove component identification markings.
• Solvents showing visual evidence of contamination or decomposition shall not be used.
• Solvents shall not be used such that dissolved flux residue contaminates electrical contact surfaces.
5.4.1 Approved Cleaning Solvents
The following solvents are acceptable for cleaning electronic assemblies during soldering operations.
• Isopropyl alcohol, electronic grade, 99.5% pure by volume.
• Trichloro-trifluoro-ethane, clear 99.8% pure. This shall not be used when assembly contains silicone rubber
elastomer.
• Aziotropic mixture of the above two solvents as below shall be used.
o
50% weight of Isopropyl alcohol and 50% by weight of trichloro-trifluoro-ethane.
• De-ionised water with resistivity greater than 1.0 M ohms.
• Water-based solvents containing saponifiers shall not be used.
5.5 Flexible insulation materials
• Materials shall have low outgassing properties and shall meet the requirements of Declared Material List of
respective centre.
• The following flexible insulation materials may be used in a space environment:
o
ETFE, FEP and PTFE.
o
Polyolefin and Kynar® sleeving for heat-shrinkable wire terminations.
o
Irradiated polyethylene, fluorinated resin and polyimide.
• PTFE materials shall not be heated above 250 °C.
5.6 Terminals
5.6.1 Terminal Material
• Terminals shall be made from one of the following materials:
o
Bronze (copper/tin) alloys. It is good practice to use bronze terminals.
o
Brass (copper/zinc) alloys.
• When a brass terminal is used it shall be plated with a barrier layer of copper or nickel of 3 µm to 10 µm.
Note-1: A barrier layer is necessary on brass items to prevent the diffusion, and subsequent surface oxidation,
of zinc.
13
Note-2: It is good practice to use a copper barrier layer on brass terminals because nickel is magnetic and
has poor solderability.
• Terminals with coatings on the mounting surface shall be rejected if the coatings loosen in subsequent soldering
operations.
5.6.2 Type of terminal
• Terminals on PCBs shall not be tin, silver or gold plated.
• Tin, silver or gold-plated finishes shall be replaced using pretinning.
5.6.3 Shape of terminals
Bifurcated and turret terminals shall have ledges or grooves to allow both the accurate location of connecting wires
and the flow of solder.
5.7 Wires
• Wire shall be selected from Declared Material List of respective centre.
• Chemical stripping materials shall be completely neutralized and be cleaned such that there are no residues
from the stripping, neutralizing, or cleaning steps.
• The enamel shall not be visually contaminated by the stripping process.
5.8 PCBs
5.8.1 Boards
Boards shall be made of materials, and manufactured, according to the requirements of ISRO-PAX-300.
5.8.2 Gold finish on conductors
• De-golding of conductors shall be in accordance with para 6.3.2
5.8.3 Classification of boards
• Printed circuit boards and substrates shall be selected from the classes given in Table 5‑3
• The class of board selected shall have a coefficient of thermal expansion (CTE) characteristic compatible with
the CTE of the devices.
• The warp and twist of the printed circuit multilayer board shall be in accordance with ISRO-PAX-304.
Table 5‑3 : Classification of printed circuit boards and substrates
Class
Description
CTE
(10-6/ 0C)
1
Non-compensated printed
board
14 – 17
Epoxy-woven glass and
polyimide-woven glass
2
Ceramic
5 –7
Alumina and Aluminium
Nitride
3
Compensated printed
board
11 – 13
14
Remarks
Epoxy / Polyimide resin
with low CTE fibers such as
aramid, quartz or carbon
4
5
Compensated printed
board
Compensated printed
board
9 – 11
CTE compensated boards
use standard construction
and are compensated with
materials such as distributed
plane consisting of low CTE
material
5–9
CTE compensated boards use
standard construction and are
compensated with materials
such as low CTE substrate
or cores. Typical cores are
copper plated invar and
copper plated molybdenum
5.9 Adhesives (potting compounds & heat sinking), Encapsulants & Conformal
coatings
• Limited shelf life items shall be stored and controlled in accordance with the material manufacturer’s
recommendations or in accordance with the manufacturer’s documented procedures for controlling shelf life
and shelf life extensions where permitted.
• Adhesives shall be dispensable, non-stringing, and have a reproducible dot profile after application.
• The uncured (tack) strength shall be capable of holding devices in place during handling prior to cure.
• Adhesives, encapsulants and conformal coatings shall be non-corrosive to devices and substrates.
• No materials that emit acetic acid, ammonia, amines, hydrochloric acid and other acids shall be used. Such
compounds can cause stress corrosion cracking of part leads.
• Adhesives, encapsulants and conformal coatings shall conform with the outgassing requirements ISRO DML
requirements.
• Shrinkage of resin during cure and repair shall not degrade the coated articles.
• Materials covered by this clause shall be individually assessed in accordance with DML, when flammability
requirements are applicable.
• Stress relief of device leads shall not be reduced by the encapsulant or conformal coating.
15
6
COMPONENT MOUNTING
6.1 Principles of reliable soldered connections
The following are the general principles to ensure reliable soldered connections:
• Reliable soldered connections are achieved by using proper design, having control of tools, selecting the right
materials, trained & qualified personnel, applying processes with precaution in a controlled work environment
and taking into account inspection requirements.
• The basic design concepts to ensure reliable connections and to avoid solder joint failure are as follows:
o
Stress relief is an inherent part of the design, which reduces detrimental thermal and mechanical stresses
on the solder connections.
o
Where adequate stress relief is not possible, a method of solder-joint reinforcement is incorporated.
o
Materials are selected such that the mismatch of thermal expansion coefficients is a minimum at the
constraint points in the component-mounting configuration.
o
Materials and processes which result in the formation of brittle intermetallics, such as soldering to gold
using tin-lead alloy, are avoided.
o
The assembled substrates are designed to allow inspection.
6.2 Preparatory conditions
6.2.1 Facility cleanliness
• Personnel facilities shall be separated from the soldering areas.
• Furniture shall be arranged to allow thorough cleaning of the floor.
• Areas used for soldering shall be kept free from contaminants.
• Working areas shall be kept free from any tools or equipment not used for the current task.
• Working surfaces shall be covered with an easily-cleaned hard top or have a replaceable surface of clean, noncorrosive, silicone-free paper.
• Tools used during soldering operations shall be free of visible contaminant.
• However overall clean room requirement shall be as per para 3.
6.2.2 Preparation of Components leads, conductors, terminals and solder cups
6.2.2.1 Stripping tools
Stripping tools or machines shall be in accordance with section (tools).
6.2.2.2 Damage to insulation
• The remaining conductor insulation shall not be damaged by the insulation removal process.
• Conductors with damaged insulation shall not be used.
• Insulation damage includes nicks, cuts, crushing and charring.
• The operation of mechanical stripping tools can leave slight pressure markings in the remaining conductor
insulation. This effect is considered to be normal.
• The insulation material shall not be charred by thermal stripping.
• However Discoloration of the insulation material after thermal stripping is normal.
16
6.2.2.3 Damage to conductors
• The conductor shall not be damaged by the insulation removal process.
• Conductor damage includes twisting, ringing, nicks, cuts or scores.
• Part leads and other conductors that are reduced in cross-sectional area by the insulation removal process
shall not be used.
• Copper visibility shall not be accepted.
6.2.2.4 Maximum insulation clearance
The maximum insulation clearance, measured from the solder joint, shall be as stated in Table 6‑1
In the case of the assembly of coil winding wires, maximum insulation clearances may be exceeded provided that
electrical clearances are maintained.
6.2.2.5 Minimum insulation clearance
For PTFE-insulated wire, the minimum distance between the insulation and the solder fillet shall be 1 mm.
The minimum clearance distance for PTFE insulation accommodates cold flow.
The minimum insulation clearance shall not result in insulation imbedded in the solder joint.
The minimum insulation clearance shall not obscure the contour of the conductor at the termination end of the
insulation.
This table is not applicable for high voltage cables.
Table 6‑1: Clearances for insulation
Wire diameter
(AWG)
Conductor
diameter without
insulation, d (mm)
Insulation
clearance
(minimum)
Insulation
clearance
(max.)
32 to 24
0.200 to 0.510
d
4×d
22 to 12
0.636 to 2.030
d
3×d
≥ 10
≥ 2.565
d
2×d
6.3 Surfaces to be soldered
6.3.1 Cleaning
Before assembly, devices, wire, terminal and connector contacts shall be visually examined for cleanliness, absence of
oil films and freedom from tarnish or corrosion.
Conducting surfaces to be soldered shall be cleaned using approved solvents specified in 5.4.1
Abrasives shall not be used for surface preparation except in the case of gold-plating on substrates and devices.
Abrasives can include pumice-impregnated erasers.
6.3.2 De-golding of gold-plated leads and terminals
63/37 Tin-lead solders shall not be used for soldering to gold finish. Recommended solders for gold plated surfaces
are listed in para 5.2.2. Also use anti wicking tweezers wherever possible to avoid thermal damage.
17
6.3.3 Methods for degolding
6.3.3.1 Solder bath method
• Solder bath for de-golding process is described in para 4.3.3.
• Gold-plated component leads and terminals shall be dipped into solder bath 1 for 2 to 3 seconds.
• Unless otherwise specified, solder bath contamination shall be monitored periodically (Once in 6 months)
6.3.3.2 Soldering iron method
• Solder shall be melted onto the conductor using a heated soldering iron.
• Solder shall be wicked-out using stranded wire/ wicking tape.
6.3.3.3 Solder cup method: to dissolve the gold plating
• Solder shall be melted within the gold-plated solder cup. The liquid solder dissolves the gold plating.
• The liquid solder shall be wicked-out using stranded wire/ wicking tape.
6.3.3.4 Constraints on degolding and pretinning methods
• The maximum temperature rating of the component, stated by the manufacturer, shall not be exceeded.
• Thermal shunts, in accordance with para 4.1.8 may be used.
• Components having glass-to-metal lead seals shall be preformed with tools as per para 4.
• Liquid solder shall not come into contact with the component body or its glass meniscus.
• The limit of the pretinned coating shall not be less than 0.75mm from any lead-to-glass seal of the component
package.
6.3.4 Pretinning of stranded wires
• Solder shall penetrate to the inner strands of stranded wire.
• Solder shall not obscure the wire contour at the termination end of the insulation.
• Anti-wicking tools in accordance with para 4.1.5 may be used.
• Pretinning shall not degrade the characteristics of the wire.
• Flow of solder (wicking) beyond the insulation can reduce the flexibility of the wire hence not acceptable
• The insulation shall not be damaged by the pretinning.
• Flux shall be removed by means of a cleaning solvent (Refer para 5.4.1).
6.3.4.1 Solder bath method
• Solder baths for pretinning shall be in accordance with para 4.3.3
• The insulation shall be removed in accordance with para 10.7
• Rosin Mildly Activated (RMA) flux shall be applied to the end of the strands.
• The fluxed end of the wire shall be dipped into solder bath 2 for a time between 2 and 3 seconds.
• Pretinning promotes Solderability and prevents untwisting or separation of stranded wires.
6.3.4.2 Soldering iron method
• Stranded wires may also be pre-tinned by applying solder to the wire using a heated soldering-iron tip.
• Solder shall be melted onto the conductor using a heated soldering iron.
6.3.5 Pre-tinning of Component leads and solid-wire conductors
6.3.5.1 Solder bath method
Solder baths for pretinning shall be in accordance with para 4.3.3. Component leads with unacceptable Solderability
18
in accordance with the component procurement specification and solid wires shall be pre-tinned by dipping into
solder bath 2 for a period between 2 and 5 seconds. Also use anti wicking tweezers wherever possible to avoid
thermal damage.
• It is good practice to observe an immersion period between 3 and 4 seconds.
• A slow, vertical and smooth withdrawal of the component lead from the bath promotes an even coating.
• The cross-sectional area of conductors shall not be reduced by dissolution into the solder bath.
The component shall cool before cleaning. Rapid cooling by contact with cleaning solvents can crack packages or
glass-to-metal seals.
6.3.5.1 Soldering-iron method
Solder shall be melted onto the conductor using a heated soldering iron.
6.3.6 Preparation of the soldering bit
6.3.6.1 Bit
• The bit shall be fitted in accordance with the equipment manufacturer’s specification.
• Oxidation products shall be removed from the bit. Build up of oxidation products can reduce the ability of the
tip to transfer heat.
• Plated tips shall be examined for cracking. Cracked platings allow the liquid solder to alloy with and erode the
underlying copper, forming intermetallics which reduce heat transfer and lead to unacceptable joints.
• Prior to soldering, solder present on the surface shall be removed when the iron is hot by wiping the bit with
moist, lint-free, sponge material.
• Bits with cracked platings shall be removed from the soldering area.
6.4 Storage
6.4.1 Components
• Storage facilities shall protect components from contamination and damage.
• Storage boxes and bags shall be made of materials which do not degrade the solderability of the
components.
• Storage materials shall not contain amines, amides, silicones, sulphur or polysulphides.
6.4.2 PCBs
PCBs shall be stored in controlled environment or desiccators.
6.4.3 Storage of wired PCBs
• The baking process shall be carried out again according to Table 6‑2 when assembled PCBs are stored in
ambient conditions for more than 24 hours prior to soldering.
• Dry nitrogen, dry air, vacuum or desiccants may be used to extend the storage period.
• Additional baking if required may be done as and when required
6.5 Preparation of PCBs for soldering
• PCBs shall be cleaned using Approved cleaning solvent
• PCBs shall be demoisturized in accordance with Table 6‑2
19
Table 6‑2 : Baking conditions
Sr. No.
Description
1.
Double sided /
Multilayer PTH PCB
2.
Polyimide / Flex-Rigid
MLB PCB
Baking Condition
Bare PCB (PWB)
Assembled PCB (PWA)
93°C, 4Hrs.
65°C, 4 Hrs.
120°C, 4 Hrs.
65°C, 4 Hrs.
PWA : Printed Wiring Assembly
3.
PWB : Printed Wiring Board
Vacuum baking at 3mm of Hg / 3 torr may be used for PWAs at 650C, 2.5 Hours
6.6 Parts Mounting
6.6.1 General requirements
Parts, terminals, and conductors shall be mounted and supported as prescribed herein. Dimensions provided in this
chapter are for acceptance and/or rejection criteria only. Unusual environmental applications require special design
measures to provide necessary environmental survival capability. Such measures shall be detailed on the appropriate
engineering documentation. Engineering documentation shall prescribe which alternative approach is selected, as well
as potting compounds and conformal coating requirements.They shall also detail any special mounting arrangements
or design requirements not fully covered herein.
6.6.2 Stress Relief Stress relief shall be incorporated into all leads and conductors terminating in solder connections to provide freedom
of movement of part leads or conductors between points of constraint. Leads shall not be temporarily constrained
against spring-back force during solder solidification so that the joint is subject to residual stress.
6.6.3 Stress relief of components with bendable leads
• Stress relief shall be incorporated into:
o Soldered leads and conductors,
o Interfacial connections.
o Stress relief provides freedom of movement for component leads or conductors between points of
constraint.
o Stresses can arise between points of constraint due to mechanical loading or temperature variations.
o Stress relief methods, shown in Figure 6.1
o The assembly of TO-39,TO-59 and CKR-06 packages shall be performed in accordance with Figure 6‑2
when assembled without stress relief.
o Stress relief designs shall not damage the assembly.
o Long lead lengths or large loops between constraint points can vibrate and damage the assembly.
o Leads shall not be temporarily constrained against spring-back force during soldering so that residual
stresses are not produced in the lead material or solder joint.
20
o Solder fillets shall not cover the stress relief bends.
o CKR-06 and similar packages shall be adhesively potted in accordance with Figure 6‑2.
o TO 39 and TO 59 packages may have an underfill as shown in Figure 6‑2
SR
C
SR
C
C
C
(a) Clinched lead
(b) Stud-mounted lead
C
Pad
SR
C
(c) Offset lap joint
C
Transistor mounting pad
SR
C
Plated-through hole
(d) Stud-mounted leads
SR
C
SR
C
(e) Alternative methods
Figure 6.1 : Methods for incorporating stress relief with components having bendable leads
6.6.4 Dual in-line package
A Dual in line package (DIP) used in conjunction with printed wiring assemblies shall be mounted in accordance
with the following requirements.
21
Figure 6.2 : Assembly of under filled TO-39 and TO-59, and adhesively staked CKR06
Figure 6.2 : Assembly of under filled TO-39 and TO-59, and adhesively staked
CKR06
DIP devices up to DIP 24 may be assembled without additional stress relief, provided that the tapered portions of
the leads are clear of the component-side lands of the plated-through holes.
• The base of the device shall be spaced from the surface of the printed wiring board a minimum of 0.25 mm
and a maximum of 2.0 mm.
• The base of the device shall be parallel to the surface of the printed wiring board within one percent of the
length of the DIP and shall not be greater than 0.2 mm.
• DIP devices shall not be mounted in sockets or other plug in devices, which rely upon contact pressure for
part retention. Leads of the DIP device shall be soldered in place.
• The lead-to-body seals of mounted devices shall not be damaged. Body chip outs that extends to or into the
glass seal and chip outs that expose a normally encased area of lead are unacceptable. Hairline cracks in either
the seal or the body are not acceptable as in Figure 6‑3.
• In order to achieve acceptable stand-off, a shim can be used.
22
Figure 6.3 : Not acceptable body and seal conditions
Figure 6.3 : Not acceptable body and seal conditions
6.6.5 Part Positioning Parts shall be positioned in compliance with the engineering documentation and mounted in accordance with the
requirements specified herein.
Parts shall be mounted so that terminations of other parts are not obscured. When this is not possible, interim
assembly inspection shall be carried out to verify that the obscured solder joints meet the requirements herein.
Parts having conductive cases mounted over printed conductors or which are in close proximity with other
conductive materials shall be separated by insulation of suitable thickness. Insulation shall be accomplished so that
part identification markings remain visible and legible.
6.6.6 Visibility of Markings
Where possible, parts shall be mounted in such a manner that markings pertaining to value, part type, etc., are visible
and has same orientation of left to right / bottom to top). For parts marked in such a way that some of the marking
will be hidden regardless of the orientation of the part, the following shall be the order of precedence for which
markings shall be visible.
• Polarity
• Traceability code (if applicable).
• Piece part value and type.
6.6.7 Heavy components
• Components weighing more than 7g per lead shall be supported by either of the following methods:
o
Adhesive compounds in accordance with Chapter 5 and12.
o
Mechanical methods such as Lacing.
• The support method shall not impose stresses that result in functional degradation or damage to the part or
assembly.
• The support method shall not damage stress relief designs.
• Component which requires fastening shall be fastened first then soldered and not vice versa.
6.6.8 Metal-case components
• Metal-case components shall be electrically insulated using space-approved material under the following
conditions:
23
o
o
Mounted over printed conductors.
In contact with a conductive material which in turn provide electrical connection to other elements.
Metal-cased components shall not be mounted over soldered connections.
Component identification marks shall not be obscured by the insulation.
6.6.9 Glass Encased Parts
Glass encased parts such as diodes, thermistors, or resistors shall be covered with transparent resilient sleeving
or other approved material when epoxy material is used for potting, conformal coating, or encapsulating or where
damage from other sources is likely. The epoxy material shall not be applied directly to glass. When using heat
shrinkable sleeving, extreme care should be taken to prevent part damage due to excessive heat or shrinkage of the
sleeving.
Table 6‑3 : List of material used for isolation
Device
Material for sleeving / isolation
Glass diodes / Glass bodied components
Polyolefin sleeves /Kynar sleeves / RTV
Glass-encased parts shall be enclosed with sleeving when epoxy material is used for potting, conformal coating or
encapsulating. Polyurethene Epoxy material shall not be applied directly to the glass.
Glass-encased components may be enclosed in resilient transparent sleeving or in heat-shrinkable sleeving. Heating
and shrinkage of sleeving can damage glass-encased components. Hence end of the sleeve may be shrunk with
soldering iron tip to arrest the slippage of sleeve.
When silicon based conformal coating is used, glass bodied components need not be sleeved.
6.6.10 Hookup /Jumper Wire
Hookup wire (single strand) / multi strand jumper wire shall be supported by a means other than the solder
connections or conformal coating if wire length exceeds 2.54cm (1 inch). Attachment to a surface by potting is
considered adequate support.
• Hook-up wire shall be supported at intervals not exceeding 25 mm.
• The support shall be provided by Potting.
• The wire shall be covered with shrinkable sleeve if wire cross over the conductor pattern.
• Use PTFE insulated jumper wires
6.6.11 Lead Bending and Cutting
During bending or cutting, part leads shall be supported on the body side to minimize axial stress and avoid damage
to seals or internal bonds. The distance from the bend to the end seal shall be approximately equal at each end
of the part. The minimum distance from the part body or seal to the start of the bend in a part lead shall be 2
lead diameters for round leads and 0.5mm (0.020 inch) for ribbon leads Ref. Figure 6.4. The stress relief bend
radius shall not be less than the lead diameter or ribbon thickness. The direction of the bend should not cause the
24
identification markings on the mounted part to be obscured. Where the lead is welded (as on a tantalum capacitor)
the minimum distance is measured from the weld.
• Part leads shall be formed so that they may be installed into the holes in the PWB without excessive
deformation that can stress the part body or end seals.
• Soldered terminations shall not be cut after the soldering operation
• All leads shall be tinned and formed before mounting the part. Where possible, part leads that is subject to
stress corrosion cracking (e.g. kovar leads), shall be preformed and trimmed prior to tinning.
• Whether formed manually or by machine, part leads shall not be mounted if they show evidence of nicks or
deformation. Smooth impression marks (base metal not exposed) resulting from tool holding forces shall not
be a cause for rejection.
• Tempered leads (sometimes referred to as pins) shall not be bent nor formed for mounting purposes since
body seals and connections internal to the part may be damaged. Tempered leads or leads with a diameter
of 1.27mm (0.05 inch) or more shall not be cut with diagonal cutters or other tools that impart shock to
connections internal to the part.
Figure 6.4: Minimum lead bend
6.6.12 Coated Parts
• Parts shall be mounted so that the insulating coating meniscus applied by the manufacturer on the leads does
not enter the mounting hole or soldered connection.
6.6.13 Splices
• Broken or damaged conductors, part leads, or printed wiring conductors shall not be spliced.
6.6.14 Location
• Part bodies shall not be in contact with soldered terminations.
6.7 Parts Mounted to PWB’s
Solder terminations shall be visible for inspection after soldering. In the cases where visual inspection cannot be
accomplished, a non destructive method of inspection shall be performed (e.g., X-ray, endoscope or fiberscope or
suitable apparatus).The non destructive method of inspection to be used shall be documented and approved by QA,
ISRO Center prior to use.
25
6.7.1 Axial Lead Mounting
Axial leaded parts shall be mounted as follows:
6.7.1.1 Horizontal Mount
Parts intended for horizontal mounting shall be parallel to, and in contact with, the mounting surface
(see Figure 6.6), or as specified in the assembly documentation. Slight angularity is permissible. When assemblies
are to be conformal coated with silicon, a small gap, say 0.3 to 0.5mm is acceptable.
Figure 6.5 : Horizontal Mount
6.7.1.2 Radial Lead Mounting
Plated through-hole: The part body shall be mounted with at least 0.5mm (0.020 inch) to a maximum of 1.27mm
(0.050 inch) above the PCB and shall allow inspection of the solder joint. The part body includes any extension such
as coating meniscus, solder seal or weld bead (see Figure 6.6A).
Non-plated-through-hole: The part body may be mounted flush with the PCB surface and terminated with an
off-the-pad lap solder joint (See Figure 6.6B).
Figure 6.6 : Radial Leaded Parts
6.7.1.3 Hole Obstruction
Parts shall not be mounted such that they obstruct solder flow or prevent cleaning of the topside termination
areas.
26
Figure 6.7 : Obstruction of solder flow (Not acceptable)
Figure 6.7 : Obstruction of solder flow (Not acceptable)
Figure
6.7 Leads
: Obstruction
of on
solder
flow Sides
(Not acceptable)
6.7.1.4
Parts with
Terminating
Opposite
Stress relief shall be provided in the part lead between the part body and solder terminations (Figure 6.8).The lead
may be terminated by clinch, straight-through, or lap configuration.
Figure 6.8 : Stress Relief Part Termination
Figure 6.8 : Stress Relief Part Termination
6.7.1.5 Parts with Leads Terminating on the Same Side
Stress relief shall be provided by forming the part leads at a bend angle to the PWB of not more than 95°nor less
Figure
6.8(Figure
: Stress
Relief Part Termination
than 45°
6.9).
2d min.
45° to 95°
Figure 6.9 : Bend Angle
Figure 6.9 : Bend Angle
27
6.7.2 Parts Lead Terminations, Printed Wiring
6.7.2.1 Part Lead Terminations
Part leads shall be of the lap, clinched, or straight-through configuration as defined by the engineering documentation
and shall be terminated in accordance with paragraphs 6.7.2.1 through 6.7.2.2 No more than one item, whether
conductor or part lead, shall be inserted in any one hole.
6.7.2.1.1 Lapped Terminations
Lapped terminations consist of both round and flat ribbon leads. It is preferred that leads be seated in contact with
the termination area for the full length of the foot. Separation between the foot of the lead and the surface of the
termination area shall not exceed 0.25mm (0.010 inches) (see Figure 6.10).
Figure 6.10 : Lapped Lead Height above Board
6.7.2.1.2 Lapped RoundFigure
Leads 6.10 : Lapped Lead Height above Board
The round lead shall overlap the solder pad a minimum of 3.5 times the lead diameter to a maximum of 5.5 times
the lead diameter, but in no case shall the length be less than 1.27mm (0.050 inch). The cut-off end of the lead
shall be no closer than ½ the lead diameter to the edge of the solder pad. Only that portion of the lead extending
to the part body or to another soldered connection shall be beyond the solder pad (Figure 6.11A). For lapped
terminations where the part body is on the same side of the PWB as the termination area, a heel fillet is mandatory
(Figure 6.11B).
28
Figure 6.11 : Lapped Round Termination
Figure 6.11 : Lapped Round Termination
6.7.2.1.3 Lapped Ribbon Leads
The ribbon lead shall overlap the solder pad a minimum of 3 lead widths to a maximum of 5.5 lead widths. Only
that portion of the lead extending to the part body or to another soldered connection shall be beyond the pad. The
cut-off end of the lead shall be a minimum of 0.25mm (0.010 inch) from the end of the pad. One edge of the lead
may be flush with the edge of the solder pad. There shall be sufficient area around two of the three lead edges to
accommodate solder filleting (see Figure 6.12).In instances where ribbon leads are less than 0.5mm (0.020 inch) in
width, ribbon overlap shall be no less than 1.27mm (0.050 inch). For lapped terminations where the part body is on
the same side of the PWB as the termination area, a heel fillet is mandatory (Figure 6.12).
6.7.2.1.4 Clinched Lead Terminations
The length of the clinched portion of conductors and part leads shall be at least ½ the largest dimension of
the solder pad or 0.78mm (0.031 inch), whichever is greater. Lead overhang shall not violate minimum electrical
spacing requirements. The lead shall be bent in the direction of the longest dimension of the solder pad. If the
pad dimensions are not sufficient, the lead shall be bent in the direction of the printed wire path (Figure 6.13).
There shall be sufficient solder pad area extending beyond the sides of the lead to accommodate solder filleting.
Fully clinched leads are defined as leads bent between 20°and 40° from a horizontal line parallel to the PWB
(Figure 6.14). Non bendable leads shall not be clinched.
29
FigureRibbon
6.12 :Leads
Lapped
Figure 6.12 : Lapped
Ribbon Leads
Figure 6.13 : Clinched Termination
Figure 6.13 : Clinched Termination
30
Figure 6.13 : Clinched Termination
Figure 6.14 : Lead Bend
6.7.2.2 Straight-Through Lead Terminations Figure 6.14 : Lead Bend
Part leads terminated straight through the PWB shall extend a minimum of 0.5mm (0.020 inch) and a maximum
of 2.29mm (0.090 inch) (Figure 6.15) .The minimum lead length shall be determined prior to soldering (actual
measurement is not required except for referee purposes). Straight-through leads may be bent up to 30° from a
vertical plane to retain parts during the soldering operation (Figure 6.16). Non-bendable leads shall not be bent.
Figure 6.15: Straight-Through Termination
Figure
Figure 6.15:
6.15: Straight-Through
Straight-Through Termination
Termination
Figure 6.16:
Straight-Through Lead Retention
Figure
Figure 6.16:
6.16: Straight-Through
Straight-Through Lead
Lead Retention
Retention
31
6.7.2.3 Consideration for Conformal coating and encapsulation
Coatings compounds shall not bridge stress relief loops or bends at terminations in component leads or
connecting wires.
Stress relief of device leads shall not be impaired by encapsulants or conformal coatings.
6.7.3 Lead bending requirements
6.7.3.1 Conductors terminating on both sides of a non-plated-through hole
Stress relief shall be provided in the component lead on both sides of the PCB in accordance with Figure 6.17(a)
When a solid hook-up wire is used to interconnect solder terminations on opposite sides of a PCB, stress relief shall
be provided in the wire between the two terminations in accordance with Figure 6.17(b)
SR
C
C
C
SR
SR
C
C
(a)
(b)
Figure 6.17: Leads with solder termination on both sides
Figure 6.17: Leads with solder termination on both sides
6.7.4 Mounting of terminals to PCBs
Swage-type terminals, designed to have the terminal shoulder soldered to printed conductors, shall be secured to
single-sided PCBs by a roll swage in accordance with Figure 6.18(a).
Swage-type terminals that are mounted in a plated-through hole shall be secured to the PCB by an elliptical funnel
swage in accordance with Figure 6‑18 (b).
An elliptical funnel swage enables complete filling of the plated-through hole with solder.
The PCB shall not be damaged by the swaging process.
After swaging, the terminal shall be free from circumferential splits or cracks.
After swaging, the terminal may have a maximum of three radial splits or cracks, provided that the splits or cracks
do not extend beyond the swaged area of the terminal and are a minimum of 90° apart.
32
Solder
Conductor
Board
Roll swage
(a) Single sided
Slight reflowed
solder fillet
Conductor
Board
Plated-through
hole
Solder
Elliptical swage
(b) Double sided
Figure 6.18:Types of terminal swaging
6.7.4.1 Terminal swaging procedure
6.7.4.1 Terminal swaging procedure
Figure 6.18: Types of terminal swaging
Top view of the bifurcated
Bottom view of the
Typical swaging tool
Top view terminal
of the bifurcated Bottom
viewterminal
of
the Typical swaging tool
bifurcated
terminal
bifurcated terminal
Figure 6.19:Terminal swaging sequence
Figure
Terminal
swaging
sequence
• Adjust
the6.19:
distance
between
punch &
anvil equal to PCB thickness approximately
• Clean bifurcated turrets and PCB by ultrasonic cleaner
• Bifurcated turrets shall enter freely into the mounting holes
• Orientation of bifurcated turrets shall be as per wiring requirement
• Operate the punch gently to just open out the terminal in the form of the funnel
• Ensure that the bifurcated turrets are fixed firmly without rotational movement
• Don'ts :
o Neither modify terminal to accept over size conductor nor modify the conductor to accommodate in
under size terminal.
33
• Checks :
o Check for selection of proper size of bifurcated turrets
o Check for swaging side -`C’ side or `P’ side
o Check for under swaging free rotation or play of bifurcated turrets
o Check for over swaging which may lead to pad lifting, measling or crazing.
o Check for cracks in the terminal shank
o Check for deformation of bifurcated turret posts
o Check for pad lifting
o Check for copper visibility at bifurcated turret & pad end
o Check for damage to pad / pattern
o Check bifurcated turret swaging for power diodes / resistors / fuses. Such cases require turret post
cutting (refer Figure 6.21).
6.7.4.2 Mounting of components to terminals
The lead length between the component and the terminals shall be similar at both ends, except where component
package shapes dictate staggering.
Example: Top hat diodes with flanges.
Stress relief shall be provided in accordance as in the stud leads.
CC
2d
min.
2dm
in.
SR
SR
CC
(a)
Offset
mounting
(a) O
ffset mounting
CC
SR
SR
2d
2dmmin.
in.
d
(b)(b)In-line
mounting
In-linemounting
SR =SStress
relief
R = Stre
ssreliebend
f bend
C =C
Constraint
point
= Constraint
point
Figure 6.20: Method of stress relieving parts attached to terminals
Figure 6.20: Method of stress relieving parts attached to terminals
6.7.4.3 Mounting of connectors to PCBs
• Connectors shall be mounted in accordance with para 6.7.2.
• PCB connectors shall be supplied with either pre-formed leads supporting stress relief bends, or straight,
epoxy-bonded leads.
• De-golding and pre-tinning of leads, in accordance with para 6.3.3, shall be performed before mechanical
fixing of connectors to the PCB.
• Before soldering, the operator shall ensure that there is no contact between the solder fillet to be formed
and the gold plating.
• Connector leads shall protrude through the board in accordance with (straight thru lead termination
34
para 6.7.2.2)
Figure 6.21: Fuse mounted on bifurcated turret where post is cut
6.8 Mounting requirement
for SMD
Figure 6.21: Fuse mounted on bifurcated, where post is cut
6.8.1 General
Devices to be mounted shall be designed for and be capable of withstanding the soldering temperatures of the
particular process being used for fabrication of the Board.
Surface mounted devices may be mounted on either one side or both sides of a printed circuit board.
Devices incapable of withstanding machine soldering temperatures shall be hand soldered in a subsequent
operation.
6.8.2 Registration of devices and pads
Devices shall be mounted on their associated terminal pads (lands).
The spacing between conductive elements shall not be reduced below the minimum electrical spacing.
Some surface mounted components that are not bonded to the PCB can self-align during the soldering process. It
is the registration after soldering that is important.
6.8.3 Lead forming
The leads of leaded surface mount devices shall be formed to their final configuration prior to mounting.
• Forming shall not degrade the solderability or cause loss of plating adhesion to the leads.
• Forming shall not cause mechanical damage to the leads or attachment seals.
• Leads of dual-in-line and gull-wing packages, flat-packs and other multileaded devices shall be dressed
(mechanically re-aligned) to ensure co-planarity.
6.8.4 Mounting devices in solder paste
Both leaded and leadless surface mounted devices shall be mounted in solder paste prior to reflow soldering.
It is good practice to optimize the pick and place mounting force on the device lead, ball or column.
35
The solder paste deposited on each solder land shall be visually inspected for registration and coverage by the
operator prior to mounting the devices.
After device mounting, the solder paste can extend beyond the edge of the pad by up to 40 % of the conductor
separation.
6.8.5 Leadless devices
• Devices shall not be stacked.
• Devices shall not bridge the spacing between other parts or components such as terminals or other properly
mounted devices.
Except for RF applications, devices with electrical elements deposited on an external surface (such as resistors)
shall be mounted with that surface facing away from the printed circuit board or substrate. See Figure 6.22 for
details.
Devices that are bonded to the PCB prior to soldering/reflow-soldering shall be placed such that the adhesive shall
not extend onto the solder pads.
Figure 6.22: Exposed element
Surface mounting of leaded (round or flattened cross section) devices shall be parallel to the board surface.
6.8.6 Area array devices
There shall be no more than three reflow operations on a single device.
6.8.7 Potting of heavy devices
• Potting compounds shall be selected in conformance with material chapter 5.
• All devices except area arrays weighing more than 7 g /lead shall be potted.
• Contamination shall be removed prior to potting.
• Potting compounds shall be mixed and cured in accordance with the manufacturer’s procedures.
• The process of applying the potting compound shall be controlled by a written procedure which defines
the location of the potting compound, the volume and the spread area (between device bottom surface and
substrate upper surface).
The potting compound shall not negate the stress relief of the device, nor come into contact with surrounding
devices.
36
7
SOLDERING
7.1 Securing conductors
There shall be no relative movement between conductors and terminals during soldering or solder solidification.
Conductors shall not be temporarily constrained against spring-back force during solder solidification as they will
produce residual stresses in the lead material or solder joint.
7.1.1 Thermal shunts
Thermal shunts shall be used to protect thermally-sensitive components.
Example: Conductors, insulation, components and previously soldered connections.
7.2 Solder application to terminals
7.2.1 Soldering of swaged terminals onto PCBs
Terminals swaged to a solid flat conductor shall be soldered to one surface of the conductor.
7.2.2 Soldering of conductors onto terminals (except cup terminals)
A concave fillet of solder shall be present between the terminal and the sides of the conductor.
The contour of the conductor shall be visible after soldering.
Terminals with more than one wire shall have each wire in contact with, and soldered to, the terminal.
7.2.3 Soldering of conductors onto cup terminals
The workmanship shall be in accordance with para 10.6.
The solder shall form a fillet between the conductor and the cup entry slot.
The fillet shall follow the contour of the cup opening.
Solder spillage may be present on the outside surface of the solder cup provided that it does not interfere with the
function or the assembly of the connector.
7.3 Solder application to PCBs
7.3.1 Application of flux
• The quantity of flux used shall be such that the solder joint is in accordance with acceptable criteria as per
para 9.5
• When flux-cored solder is used, it shall be positioned such that the flux flows and covers the components to
be joined as the solder melts.
• When an external liquid flux is used in conjunction with flux-cored solders, the fluxes shall be compatible.
• Type R or RMA (Rosin Mildly Activated) flux shall be used for soldering.
• When external flux is used, liquid flux shall be applied to the surfaces to be joined prior to the application of
heat.
37
7.3.2 Solder application
Solder shall be applied only to the solder side of a plated-through hole.The soldering iron bit shall be pretinned.The
heated soldering iron bit shall be applied at the junction of pad & lead.
Solder shall be introduced initially at the junction of the soldering iron bit and the joint. The molten solder makes a
heat bridge thus promoting heat transfer between the tip and the connection. Once heat transfer has been achieved
the solder shall be applied only to the joint.
Where the rate of heat loss from the joint is too high to allow an acceptable solder joint on the component side,
additional heating shall be used.
• Example: High thermal masses or adjacent heat sinks.
• Heat can be applied to both sides of the plated-through hole simultaneously.
• PCB with metal cores/thermal planes shall be pre heated during soldering operations. Preheating can be done
by hot plate/ IR hot plate.
• Additional heating shall not damage components or materials.
• The process of additional heating shall be documented.
• In any case board temperature during pre-heating shall not be more than 1200C.
7.3.3 Solder coverage
The molten solder shall flow around the conductor and over the termination area.
For high-voltage connections refer para 7.6.
In case of insulated wires, solder shall not obscure the contour of the conductor at the end of the insulation.
Contour of the lead shall be clearly visible.
Copper visibility shall not be present at the end of the cropped leads.
Leads shall be cropped before soldering operation.
7.3.4 Solder fillets
Preferred Solder fillets at component side & solder side shall be as shown below. Detailed accept / Reject criteria
shall be in accordance with para 9.5 and para 9.6.
A conductor mounted as a lap termination shall have a heel fillet where it bends away from the pad.
On lap terminations where one side of a conductor is flush with the edge of the termination pad, a fillet of solder
shall be present along at least three of the four sides of the lead.
The fillet of solder along the lead shall extend up the side of the lead to a minimum distance of half the lead thickness
or diameter.
38
Component side
Solder side
Figure 7.1 : Solder fillet for plated through holes
Figure 7.1 : Solder fillet for plated through holes
Solder side
Figure 7.2 : Solder fillet for non through holes where leads are clinched
7.3.5 Wicking
Soldering aids shall be used to restrict the wicking of flux or solder under insulation.
7.3.6 Solder rework
Rework of soldered PCB assemblies shall be done when the solder joint does not meet the acceptance criteria.
For reworking, the solder has to be completely removed from the termination.
7.4 Soldering of SMDs
7.4.1 General requirements
• As far as possible all SMD components shall be reflow soldered.
• Additional preheating techniques/precautions shall be used when manual soldering multilayer ceramic chip
capacitors
• Devices shall not be mounted on flexible substrates
• Soldering to gold with tin/lead alloys shall not be performed
• Devices shall not be stacked nor bridge the space between other parts or components (e.g. as terminals or
other properly mounted devices).
• Mispositioning of devices shall not reduce the specified minimum electrical clearance to adjacent tracks or
other metallized elements.
• Non-axial-leaded devices (e.g. small outline, flat-packs and similar devices) shall be mounted with all leads
seated on a terminal area to ensure mechanical strength.
• Solder shall cover and wet the solderable surfaces. Accept/Reject criteria is listed in para 9.10.
39
7.4.2 End-capped and end-metallized devices
• There shall be no discernible discontinuities in the solder coverage of the terminal areas of devices.
• Solder shall not encase any non-metallized portion of the body of the device following reflow.
• The solder joints to these devices shall meet the dimensional and solder fillet requirements of Table 7‑1 and
Figure 7.3
• End-capped and end-metallized devices having terminations of a square or rectangular configuration (such as
chip resistors, chip capacitors, MELFs and similar leadless discrete components) can have three or five face
terminations, shown as “A” and “B” in Figure 7.3
Table 7‑1 : Dimensional and solder fillet requirements for rectangular and square end capped devices
Parameter
Dimension
Dimension limits
Maximum side overhang
A
0.1 × W
End overhang
B
Not permitted
Minimum lap contact
L
0.13 mm
Minimum fillet height
M
X + 0,3 × H or
X + 0,5 mm
whichever is less
Stand-off (elevation)
X
Present up to
0.4 mm
Maximum tilt limit
C
10°
Minimum solder coverage of
edges on terminal pad
-
-
Figure 7.3: Mounting of rectangular / square end-capped and end-metallized devices
Figure 7.3: Mounting of rectangular and square end-capped and end7.4.3 Hand
soldering
of chip capacitors and resistors
metallized devices
Make sure that devices are having excellent solderability
• Set the temperature of soldering iron bit to below 250°C
• Use a soldering iron with tip size smaller than the width of soldering pad
• Preheat the component at 140 to 150°C for two minutes on a temperature controlled heating plate
40
• Apply the optimum quantity of flux required
• Place the soldering iron tip on the pad without touching the component terminal
• When the solder begins to flow, slowly move the tip towards the chip and quickly remove the iron.
• Remove the soldering iron bit as quickly as possible. Maximum time allowed is restricted to
five seconds.
• If the pad size differs from each other the pad with smaller area shall be soldered first.
• Thoroughly clean the solder joint immediately after soldering.
7.4.4 Bottom terminated chip devices
Use of such devices shall be limited. In case of non availability of end caped components these devices may be
used.
Devices having metallized terminations on the bottom side only (e.g. discrete chip components, ceramic leadless
chip carriers) shall meet the dimensional and solder fillet requirements of Table 7‑2 and Figure 7.4
Table 7‑2 : Dimensional and solder fillet requirements for bottom terminated chip devices
Parameter
Dimension
Dimension limits
Maximum side overhang
A
0.1 x W
End overhang
B
Not permitted
Minimum lap contact
L
0.75 x W
Stand-off (elevation)
X
0.1 mm to 0,4 mm
Figureof
7.4:
Mounting
of bottom terminated
chip devices
Figure 7.4: Mounting
bottom
terminated
chip devices
7.4.5 Cylindrical end-capped devices
Solder joints to components having cylindrical terminations (such as MELF and SOD components) shall meet the
dimensional and solder fillet requirements of Table 7‑3 and Figure 7.5.
7.4.6 Castellated chip carrier devices
Joints to castellated device terminations shall meet the dimensional and solder fillet requirements of Table 7‑4 and
Figure 7.6.
• The stand-off enables adequate cleaning beneath the assembled LCCC and also to enhance solder fatigue life
(Refer para 6.8.5)
• LCCC devices with greater than 16 pin count to be used (On Class 1 substrate) with QA approval of
respective centres.
41
Table 7‑3: Dimensional and solder fillet requirements for cylindrical end-capped devices
Parameter
Dimension
Dimension limits
Maximum side overhang
A
0.25 x D
End overhang
B
Not permitted
Minimum fillet width
E
0.5 x D
Minimum fillet height
M
X + 0.3 x D or
X + 1.0 mm
whichever is less
Minimum side fillet length
L
0.5 x T
Stand-off (elevation)
X
~ 0.75 mm
Figure 7.5:
Mounting of cylindrical
end-capped
devices
Figure 7.5: Mounting
of cylindrical
end-capped
devices
Table 7‑4 : Dimensional and solder fillet requirements for castellated chip carrier devices
Parameter
Dimension
Dimension limits
Maximum side overhang
A
Zero
Maximum fillet length
E
P
Minimum fillet height
M
0.25 x H
Stand-off (elevation)
X
0.1 mm to 0.4 mm
Figure 7.6: Mounting of castellated chip carrier devices
Figure 7.6: Mounting of castellated chip carrier devices
7.4.7 Devices with round, flattened, ribbon, “L” and gull-wing leads
Solder joints formed to round, flattened, ribbon,“L” and gull-wing shaped leads shall meet the dimensional and solder
fillet requirements of Table 7‑5 and Figure 7.7.
42
Figure 7.6: Mounting of castellated chip carrier devices
Table 7‑5 : Dimensional and solder fillet requirements for devices with round, flattened, ribbon,
“L” and gull-wing leads
Parameter
Dimension
Dimension limits
Maximum side overhang
A
0.1 x W
Minimum distance to pad edge
at toe
B
0.20 mm
Minimum distance to pad edge
at heel
L
0.5 x W
Minimum side joint length
D
1.5 x W
Minimum heel fillet height
E
X +T
Figure7.7:
7.7: Mounting
Mounting of of
devices
with round,
ribbon, “L” and
gull-wing
Figure
devices
with flattened,
round, flattened,
ribbon,
“L”leads
and gull-wing
7.4.8 Devices with “J” leads
Solder joints formed to “J” and “V” shaped leads shall meet the dimensional and solder fillet requirements of
Table 7‑6 and Figure 7.8.
Table 7‑6 : Dimensional and solder fillet requirements for devices with “J” leads
Parameter
Dimension
Dimension limits
Maximum side overhang
A
0.1 x W
Minimum side joint length
L
1.5 x W
Minimum heel fillet height
M
X +T
Maximum stand-off
X
0.75 mm
Figure 7.8: Mounting of devices with “J” leads
43
7.4.9 Tall profile devices
Tall profile components having bottom only terminations, as illustrated in Figure 7‑7, shall not be used if the height
(V) is greater than the width or breadth (T).
Devices taller than 12 mm in height shall be potted or secured to the board. This is to minimize shock and vibration
loading on the part leads
Figure 7.9: Dimensions of tall profile components.
Figure 7.9: Dimensions of tall profile components.
7.9: Dimensions
of tallArray
profileDevices
components.
7.5Figure
Ceramic
Column Grid
The outer row of solder joints shall be visually inspected by looking from the side in accordance with the requirements
given in subsequent paragraphs.
Inner rows of solder joints shall be inspected using X-ray techniques in accordance with para 7.5.6.
As it is impossible to visually inspect solder joints to area array devices, reliability of these devices cannot be assured
by inspection and rework. Even using X-ray techniques, some types of defect are difficult to detect. Therefore,
reliability of these solder joints can only be assured by robust process control. Quality assurance guidance for these
types of devices is given below and sub paragraphs.
Figure 7.10:Typical CCGA device build -up
44
Figure 7.11:Typical assembled CCGA device
Figure 7.11: Typical assembled CCGA device
7.5.1 Handling Precautions for CCGA Devices
The CCGA packages are very fragile & ESD sensitive. Following precautions shall be taken while handling these
devices,
• All the ESD related precautions shall be taken care.
• Solder columns are very delicate & fragile. So care shall be taken such that no mechanical damage to the
device & solder columns shall occur while handing.
• Storage shall be in ‘moisture free & ESD’ safe tray carrier with a column protection feature.
• Device shall not be handled by bare hands, use ESD tweezers for handling.
7.5.2 Bare CCGA Device Inspection
All CCGA devices and columns shall be inspected prior to installation & shall be used to establish that the parts
comply with the following criteria:
• All column locations and dimensions shall comply with the device manufacturer’s drawing
• Package to column solder joint shall meet the requirement as shown in Figure 7.13
• There shall not be any missing column. Refer Figure 7.12
• Solder fillet shall be present 100% around the circumference of the column.
• Columns shall appear uniform with no indication of bending or tilting by more than 5°. Refer Figure 7.14
• Radiographic inspection of CCGA column solder joint shall be carried out & the void area shall be less than
25% of the device side solder joint cross section area. Refer figure 7.15
45
Good consistency of column alignment: Accept
Good consistency of column alignment: Accept
Missing column: Reject.
Missing column: Reject.
Figure 7.12 : Underside
showing
missing
column
Figure 7.12view
: Underside
view showing
missing
column
Figure 7.12 : Underside view showing missing column
Figure 7.13 : Solder fillet 360° coverage around the column circumference:
Figure 7.13 : Solder fillet 360° coverage around the column circumference: Accept
Accept
Figure 7.14 : Side view showing column; column by more than 5°: Reject
46
Figure 7.14 : Side view showing column; column by more than 5°: Reject
Figure 7.15 : X-ray view showing voids in column bent solder joint more than 25%: Reject
7.5.3 Bare PCB Inspection (For CCGA assembly point of View)
• CCGA mounting area shall be inspected at 10x magnification & column solder pad shall be 100% free from
solder mask material & the minimum clearance of 50µm shall be maintained between solder mask & solder
pad.
• PCB warpage shall be less than 0.75% of diagonal distance.
• Co-planarity in CCGA mounting zone shall be less than 100μm.
• PCB thickness shall be greater than 2.2mm
• CCGA mounting area shall be free from dirt, dust, contamination & corrosion.
• PCB baking (100°C 4Hrs) shall be done prior to CCGA assembly. Post baking inspection shall be carried
out.
7.5.4 Post soldering CCGA Assembly Inspection
Visual inspection of outer row to the extent possible & radiographic inspection shall be carried out to evaluate the
quality of solder joints.
7.5.5 Visual Inspection
Visual inspection of all the outer row CCGA solder joints (top and bottom) shall be carried out at 10x magnification
or higher using the following criteria:
• Column to PCB & Column to package solder joint shall meet the quality requirement as given in this para
below.
• Solder fillet shall present 50% (minimum) around the circumference of the column. Refer Figure 7.16
• The final solder joint to a solder column often has an asymmetrical fillet with the columns aligned to the edge
of the solder pads. This also causes the columns to be tilted sometimes in different directions. This is normal
and acceptable.
47
Figure 7.16 : Example of acceptable solder fillet coverage around column, more
than 50%: Accept
Figure 7.16 : Example of acceptable solder fillet coverage around column, more than 50%: Accept
Figure 7.16 : Example of acceptable solder fillet coverage around column, more
• All of the
columns
be tilted uniformly up to 10º is acceptable as in Figure 7‑17. Tilt is only acceptable if
than
50%:may
Accept
all columns are tilted uniformly.
Figure 7.17 : Example of acceptable column tilt up to 10º
Individual columns shall not be bent more than 5º relative to other columns.
48
R25
T25
P25
Pre-testing
Figure 7.18: CGA mounted on PCB showing columns tilted < 5°: Accept
Note: Asymmetry of solder fillets at PCB is consequence of teardrop pads and is acceptable
Figure 7.19: Micrograph of CGA mounted on PCB
Bent column: Reject
Figure 7.19: Bent column: Reject
Figure 7.19: Micrograph of CGA mounted on PCB
Bent column: Reject
Figure 7.20: Soldered ball: Reject
Figure 7.20: Micrograph of CGA mounted on PCB
Unsoldered column: Reject.
Unsoldered
column:
Reject.
• Solder fillet
shall have concave
shape
& solder material shall not flow outside the solder pad.
• Inner pins
shall also
be Micrograph
inspected for of
these
criteria,
to the on
greatest
Figure
7.20:
CGA
mounted
PCBextent possible
Unsoldered column: Reject.
49
7.5.6 Radiographic Inspection (X-ray)
All columns shall be inspected using radiographic methods to detect the workmanship defects. X-ray equipment
shall allow the operator to view the assembled PWA at a tilt, such that each individual column can be inspected,
including the solder joints at the component and PCB sides.
• Solder joints, with voids which appear to reduce the solder joint area by greater than 25% is rejected.
• Solder bridging which results in shorting or reducing the spacing between electrically isolated conductors
more than 75% of specified spacing is not acceptable.
• Metallic or conductive contamination in the CCGA area shall be a cause for rejection. Any solder ball having
a diameter greater than 0.1 mm shall be rejected. The total number of solder balls having a diameter greater
than 0.03 mm shall not exceed 10 per device.
Figure 7.21 : Radiograph of CGA mounted on PCB
Figure 7.21 : X-radiograph of CGA mounted on PCB
Figure 7.22: Radiograph of CGA mounted on PCB showing missing column: Reject
Figure 7.22: X-radiograph of CGA mounted on PCB showing
missing column: Reject
50
Figure 7.22: X-radiograph of CGA mounted on PCB showing
missing column: Reject
Figure 7.23: Radiograph of CGA mounted on PCB showing insufficient solder: Reject
Figure 7.23: X-radiograph of CGA mounted on PCB showing
insufficient solder: Reject
Figure
7.24:
Radiograph
of CGA
mounted
on PCB
showing
soldersolder
bridge:
Reject
Figure
7.24:
X-radiograph
of CGA
mounted
on PCB
showing
bridge:
Figure 7.24:
RejectX-radiograph of CGA mounted on PCB showing solder bridge:
Reject
Figure 7.25: Radiograph
of CGA showing excessive voiding in solder fillets at base of columns: Reject
Figure 7.25: X-radiograph of CGA showing excessive voiding in solder fillets at
base of columns: Reject
51
7.6 High-voltage connections
High-voltage connections where corona suppression is necessary shall be as defined on the engineering documentation
Where soldering of high voltage connections is required, all elements of the connection shall be covered by a smooth
fillet and free of discontinuity or severe change in contour (see Figure 7‑26).
Soldered joints for corona suppression shall be performed in two stages with an intermediate inspection:
The first soldering stage produces a standard soldered connection.
The joint then has additional solder alloy added. This second soldering stage produces a final joint, see Figure 7.26,
having:
• Smooth convex fillets,
• No discontinuities,
• No severe changes in contour,
• No sharp edges or points.
Figure 7.26: High voltage connection
Figure 7.26: High voltage connection
7.7 BGA devices
7.7.1 Handling Precautions for BGA Devices
BGA packages are ESD sensitive. Following precautions shall be taken while handling these devices,
• All the ESD related precautions shall be taken care.
• Solder balls are very delicate & fragile. So care shall be taken such that no mechanical damage to the device &
solder balls shall occur while handing.
• Storage shall be in ‘moisture free & ESD’ safe tray carrier with a ball protection feature.
• Device shall not be handled by bare hands, use ESD tweezers for handling.
52
7.7.2 Bare BGA Device Inspection
BGA device balls shall be inspected prior to installation & shall be used to establish that the parts comply with the
following criteria:
• All ball locations and dimensions shall comply with the device manufacturer’s drawing
• There shall not be any ball missing as shown in following figure.
Figure7.27:
7.27: Missing
of of
ballsballs
Figure
Missing
• Balls shall not have voids as shown below. Sum of voids in some BGA balls shall not exceed 25 % of ball’s cross
section diameter.
•
Figure 7.28 : Sum of voids in BGA balls exceeds 25 % of ball’s cross section diameter: Reject
Figure 7.28 : Sum of voids in BGA balls exceeds 25 % of ball’s cross section
diameter: Reject
7.7.3 Bare PCB Inspection (For BGA assembly point of view)
• BGA mounting area shall be inspected at 10x magnification & column solder pad shall be 100% free from
solder mask material & the minimum clearance of 50µm shall be maintained between solder mask & solder
pad.
53
• PCB warpage shall be less than 0.75% of diagonal distance.
• Co-planarity in BGA mounting zone shall be less than 100μm.
• PCB thickness shall be greater than 2.2mm
• BGA mounting area shall be free from dirt, dust, contamination & corrosion.
• PCB baking (100°C 4Hrs) shall be done prior to BGA assembly. Post baking inspection shall be carried out.
7.7.4 Post soldering BGA Assembly Inspection
Visual inspection of outer row to the extent possible & radiographic inspection shall be carried out to evaluate the
quality of solder joints.
• Balls shall be completely wetted and solder fillet is present 100% around the circumference of the ball.
Figure 7.29 : Non wetted ball in X-Ray (Absence of tear drop shape)
Figure 7.29 : Non wetted ball in X-Ray (Absence of tear drop shape)
• BGA shall
be centered
on thewetted
land. ball in X-Ray (Absence of tear drop shape)
Figure
7.29 : Non
Figure 7.30 : Ball shall be centered on land
Figure 7.30 : Ball shall be centered on land
• BGA balls shall not be bridged.
Figure 7.30 : Ball shall be centered on land
54
Figure 7.31 : Ball bridging is not accepted
Figure 7.31 : Ball bridging is not accepted
Figure 7.31 : Ball bridging is not accepted
• BGA balls shall be completely wetted.
Figure 7.32 : Insufficient wetting of left most ball
Figure 7.32 : Insufficient wetting of left most ball
• BGA solder joint shall not have crack.
Figure 7.32 : Insufficient wetting of left most ball
Figure 7.33 : Crack on the ball to PCB solder joint
Figure 7.33 : Crack on the ball to PCB solder joint
55
8
Cleaning of PCB assemblies
When the solder has solidified and cooled, flux and residue shall be removed from soldered connections using a
approved solvents as per para 5.4.1
Solvent shall be applied in such a manner that avoids its penetration under wire insulation and prevents its entry
into the interior of parts.
Flux and residue shall be removed within a maximum period of 8 hours after soldering operations.
It is good practice to remove flux as soon as possible because even rosin fluxes are difficult to remove after longer
ageing.
• Note: PCB assemblies shall not be immersed in cleaning solvents for more than 30 minutes for each cleaning
operation.
• Long immersion times can promote galvanic corrosion between adjacent metallic surfaces.
Cleaning system and equipment used to clean solder connections of surface mounted parts and PCB assemblies
integrating surface mounted parts may be manual or automated multiple zone types.
8.1 Acceptable cleaning systems
• Manual (Brush)
• Vapor degreasing equipment
• Three tray method.
CAUTION: ULTRASONIC CLEANING SHALL NOT USED FOR CLEANING ASSEMBLIES THAT CONTAIN
ELECTRONIC PARTS.
8.1.1 Manual Cleaning
Manual cleaning shall as a minimum be the three-tray method. The manual cleaning process shall contain the
following: PCB assemblies shall be immersed in an approved solvent bath and scrubbed with a natural bristle
brush until all visible contaminants have been removed. The PCB assemblies shall then be rinsed by immersion
in a second clean approved solvent bath. The PCB assemblies shall finally be rinsed by immersion in the third
clean approved solvent bath or by spraying / pouring the f re s h solvent on the inclined card. This process shall be
repeated until there is no visible evidence of the flux residue or other contaminants. Spray should only be used if
the nozzle is properly grounded or if it has been tested to show that the solvent is static free.
Note: Solvent baths shall be replaced when it becomes visibly contaminated.
8.1.2 Vapour Degreasing – General Requirements
Following precautions / requirements shall be adhered to.
Vapour degreaser cleaning document shall contain the following information as a minimum:
• Use of solvents other than those mentioned in the approved material list, (Chapter 5) require approval
from QA.
56
• Do not use to clean Conformal Coated PCB assemblies.
• Maintain vapour degreaser temperature and other parameters as per manufacturer’s recommendations.
• Parts or PCB assemblies shall not have contact with the boiling sump. A handling rack shall be used which will
prevent part damage and assures vapour circulation around all parts / PCB assembly surface and provide for
condensed drainage
• Cleaning solvent and its purity requirement.
• The rate of speed for lowering and raising the PCB assemblies in and out of the vapour zone shall be such
that parts dry as they exit the vapour.
• Length of time the PCB assemblies are exposed to the vapour or condense sump after spraying.
• If a spray nozzle is used the distance from the end of the nozzle to the PCB assemblies and pressure
of the nozzle.
8.2
Monitoring for cleanliness
8.2.1 Cleanliness testing
The effectiveness of the cleaning process employed for PCB assemblies (post-soldering) shall be tested using a
sodium chloride (NaCl) equivalent ionic contamination test in accordance with para 8.2.3.
The fabrication facility shall implement and maintain records of test results.
• The records can aid early detection of a trend towards non-conformance.
• When a test result is unacceptable, all PCB assemblies cleaned since the last successful test shall be subject to
review by the Approval authority (QA).
8.2.2 Test limits
The sodium chloride (NaCl) ionic contamination equivalence value shall be less than 1.56 µg/cm2 of PCB surface
area.
8.2.3 Test method
Sodium chloride (NaCl) equivalent ionic contamination shall be measured as follows:
• Use a solution of 75 % isopropyl alcohol and 25 % deionized water for the sodium chloride (NaCl) equivalent
ionic contamination test.
• Calibrate the equipment using a sodium chloride solution of known quantity and composition.
• Testing shall be performed according to the equipment manufacturer’s instructions.
• The cleanliness test values shall be as follows:
• Starting resistivity: greater than 20 × 106 Ω cm.
• Ending value shall be greater than 7.7 × 106 Ω cm OR less than 1.56 µg/cm2 equivalent NaCl.
57
9
Quality assurance
9.1 Data
Quality records shall be retained for at least ten years, or in accordance with the project requirements.
9.2 Nonconformance
Non-conformance in the soldering process shall be disposed in accordance with ISRO-PAS-100.
9.3
Calibration/ Validation
Insulation strippers, soldering irons, measuring equipment and reference standards shall be calibrated or validated.
Defective or out of calibration equipment or tools shall be labeled or removed from work areas.
The Approval authority shall be notified of the non conformance.
9.4 Inspection
During all stages of the process, the inspection check lists shall be implemented.
Each component mounting and soldered connection shall be visually inspected for compliance with quality
requirements
Inspection shall be aided by magnification appropriate to the size of the connections between 10x to 40x
Additional magnification shall be used to resolve suspected anomalies or defects.
Parts and conductors shall not be physically moved to aid inspection.
9.5 Acceptance criteria
Acceptable solder connections shall be characterized by:
• A clean, smooth & bright undisturbed surface as shown
below
• Contour of the lead shall be clearly visible
• Complete wetting as evidenced by a low contact angle
between the solder and the joined surfaces
• Acceptable amount and distribution of solder
• Absence of any of the defects
• Solder fillets between conductor and termination shall
be concave with dihedral angle of 5 to 20 degrees as
shown below
• High-voltage connections in accordance with para 7.6
58
9.6 Rejection criteria
The following are some characteristics of unsatisfactory conditions, any of which shall be cause for rejection:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Charred, burned or melted insulation of parts.
Conductor pattern separation from circuit board.
Burns on base materials.
Continuous discoloration between two conductor patterns.
o For example measling, delamination, haloing effect.
Excessive solder (including peaks, icicles and bridging),
Contaminated solder joints (including flux, lint and extraneous material).
Flux residue, solder splatter, solder balls, or other foreign matter on circuitry, beneath components or on
adjacent areas.
Dewetting, insufficient solder, pits, holes or voids, or exposed base metal (excluding the ends of cut leads) in
the soldered connection.
Granular or disturbed solder joints.
Fractured or cracked solder connection.
Cut, nicked, gouged or scraped conductors or conductor pattern.
Incorrect conductor length.
Incorrect direction of clinch or lap termination on a PCB.
Damaged conductor pattern.
Bare copper or base metal, excluding the ends of cut wire or leads or sides of tracks and soldering pads on
substrate.
Soldered joints made directly to gold-plated terminals or gold-plated conductors using tin-lead solders.
Cold solder joints.
Component body embedded within solder fillet.
Open solder joints.
o For example tombstoning.
Probe marks present on the metallization of chip devices caused by electrical testing after assembly.
Crack or chipping in glass seal.
• Impaired stress relief.
9.7 Operator and inspector training and certification
Trained and certified personnel shall be employed for soldering operations and inspections.
A training programme shall be developed, maintained and implemented by the respective centre QA to provide
excellence of workmanship and personnel skill in soldering.
The training programme shall include procedures for the training, certification, maintenance of certified status,
recertification and revocation of certified status for soldering and inspection personnel.
Trained personnel performing soldering operations and inspections shall be certified.
Certification is based on objective evidence of soldering quality, resulting from test and inspection of soldered
joints.
59
Personnel shall be retrained or re-assessed in the following circumstances:
• Repeated quality non-conformance.
• Change in soldering techniques.
• Change in soldering parameters.
• Additional process skills
• Out of work for more than 180 days
Operators performing hand soldering and inspectors shall be trained and certified by the Approval authority.
9.8 Quality records
The quality records shall be made of, as a minimum, the following:
• PID (including the summary tables and workmanship standards).
• Audit report established by the approval authority.
• Verification report, as output of the verification test programme.
9.9 Typical accept / reject illustrations
9.9.1 Workmanship illustrations for SMDs
9.9.1.1 Chip components
9.9.1.1 Chip components
Chip Part Registration to Land
PREFERRED
• The preferred registration of a chip part is
with the part centered on each land pattern
area
Chip Part Registration to Land
MAXIMUM ACCEPTABLE
• Lateral overhang of chip to land pattern area
is not more than 25 percent of the part width
(W).
• Inside overhang of chip to land pattern area
is not more than 50 percent of the end
termination width (t).
60
Chip Part Tilting
PREFERRED
• The preferred attachment is placement of
the part on its respective land areas with no
tilting relative to the surface of the PWB.
Chip Part Tilting
MAXIMUM ACCEPTABLE
• The maximum tilt is not more than 25
percent the part thickness.
• Solder fills the entire space between the part
and the land area.
• The tilt does not prevent the proper
placement and mounting of neighboring
parts.
Chip Part Solder
MINIMUM ACCEPTABLE
• The minimum fillet reaches 50 percent of the
part thickness up the termination
Chip Part Solder
MAXIMUM ACCEPTABLE
• The maximum fillet extends over the top of
the metalized termination of the part.
• This maximum fillet extends the entire width
of the part that is in contact with the land
area.
• The maximum fillet exhibits a positive angle
of wetting at the top of the termination and
the edge of the land area
61
Figure 9.1 : Preferred solder for chip devices
Figure 9.2 : Maximum acceptable
solder
Figure 9.2
: Maximum acceptable solder
Figure 9.2 : Maximum acceptable solder
Figure 9.3 : Un acceptable solder due to poor wetting
Figure 9.3 : Un acceptable solder due to poor wetting
Figure9.9.1.2
9.3 : Un
acceptable
solder due to poor wetting
MELF
Devices
9.9.1.2 MELF Devices
62
Figure 9.3 : Un acceptable solder due to poor wetting
9.9.1.2 MELF Devices
9.9.1.2 MELF Devices
MELF Registration to Land
PREFERRED
• The preferred registration of a MELF part is
with the part centered on each land pattern
area.
MELF Registration to Land
MAXIMUM ACCEPTABLE
• Lateral overhang of MELF to land pattern
area is not more than 25 percent of the
termination thickness (T).
• Inside overhang of MELF to land pattern
area is not more than 25 percent of the
termination width (W).
MELF Solder
MINIMUM ACCEPTABLE
• The minimum fillet reaches 50 percent of the
thickness up the termination.
• This minimum fillet extends the entire width
of the part that is in contact with the land
area.
MELF Solder
MAXIMUM ACCEPTABLE
• The maximum fillet reaches the full thickness
of the MELF end termination.
• This maximum fillet extends the entire width
of the part that is in contact with the land
area.
• The maximum fillet exhibits a positive angle
of wetting at the top of the termination and
the edge of the land area.
• The termination remains visible through the
solder fillet.
63
Figure 9.4 : Acceptable, minimum solder: Terminal wetted along end, face and
sides
Figure 9.4 : Acceptable, minimum solder:Terminal wetted along end, face and sides
Figure 9.4 : Acceptable, minimum solder: Terminal wetted along end, face and
sides
Figure 9.5 : Preferred solder
Figure 9.5 : Preferred solder
Figure 9.5 : Preferred solder
Figure 9.6 : Unacceptable Excessive solder
Figure 9.6 : Unacceptable Excessive solder
64
Figure 9.6 : Unacceptable Excessive solder
Figure 9.6 : Unacceptable Excessive solder
Figure 9.7 : Unacceptable insufficient solder
Figure 9.7 : Unacceptable insufficient solder
9.9.1.3
Ribbon,
and Gull-wing
leadedsolder
devices
Figure
9.7 : “L”
Unacceptable
insufficient
9.9.1.3 Ribbon, “L” and Gull-wing leaded devices
9.9.1.3 Ribbon, “L” and Gull-wing leaded devices
Gull Wing Lead Registration to Land
PREFERRED
• The preferred registration of a gull wing lead
is with the lead centered across the width of
the land pattern area.
Gull Wing Lead Registration to Land
MAXIMUM ACCEPTABLE – Lateral
Overhang
• The part lead is misaligned but lateral
overhang does not exceed 25 percent of
the lead width (W), and does not violate the
minimum spacing requirements as defined
by the engineering documentation.
Gull Wing Lead Registration to Land
MAXIMUM ACCEPTABLE – Toe
Overhang
• The part lead is misaligned but toe overhang
does not exceed 25 percent of the lead width
(W), and does not violate the minimum
spacing requirements as defined by the
engineering documentation.
65
Gull Wing Lead Planarity to Pad
PREFERRED
• The preferred planarity of the lead to the
land pattern area is with the foot soldered
parallel to the pad by the engineering
documentation.
Gull Wing Lead Planarity to Pad
MAXIMUM ACCEPTABLE
• The maximum acceptable non-planarity is
when any portion of the foot is soldered not
more than .26 mm (0.010”) above the pad.
Gull Wing Lead Solder
MINIMUM ACCEPTABLE
• Solder is minimum, but the connection is
well wetted and bonded with a concave fillet
between the lead and the land pattern area.
• A heel fillet is mandatory.
Gull Wing Lead Solder
MAXIMUM ACCEPTABLE
• Solder is maximum, but the connection is
well wetted and bonded with a concave fillet
between the lead and the land pattern area.
• The contour of the lead remains visible
through the solder fillet.
• A heel fillet is mandatory.
66
Figure 9.8 : Ribbon/Gull wing leaded devices
Figure 9.8 : Ribbon/GullFigure
wing9.8
leaded
devices
: Ribbon/Gull
wing leaded devices
Figure 9.8 : Ribbon/Gull wing leaded devices
Figure 9.9 : Unacceptable
: Excessive
solder solder
(middle
joint)
Figure 9.9 : Unacceptable
: Excessive
(middle
joint)
Figure 9.9 : Unacceptable : Excessive solder (middle joint)
9.9.1.4 J-Leaded devices
Figure
9.9 : Unacceptable : Excessive solder (middle joint)
9.9.1.4 J-Leaded
devices
9.9.1.4 J-Leaded devices
9.9.1.4 J-Leaded devices
J-Lead Registration to Land
PREFERRED
• The preferred registration of a J-Lead is with
the lead centered across the width of the
land pattern area.
\
\
\
67
J-Lead Registration to Land
MAXIMUM ACCEPTABLE – Lateral
Overhang
• The part lead is misaligned but lateral
overhang does not exceed 25 percent of
the lead width (W), and does not violate the
minimum spacing requirements as defined by
the engineering documentation.
J-Lead Registration to Land
MAXIMUM ACCEPTABLE – Toe
Overhang
• The part lead is misaligned but toe overhang
does not exceed 25 percent of the lead
width (W), and does not violate the minimum
spacing requirements as defined by the
engineering documentation.
J-Lead Solder
MINIMUM ACCEPTABLE
• The minimum fillet reaches the start of the
lead bend.
• A heel fillet is mandatory.
J-Lead Solder
MAXIMUM ACCEPTABLE
• The maximum fillet reaches 50 percent of
the lead height.
• The solder fillet can be convex, but shows no
evidence of a negative wetting angle.
• The contour of the lead remains visible
through the solder fillet.
• A heel fillet is mandatory.
L-Lead Registration to Land
PREFERRED
• The preferred registration of an L lead is
with the lead or termination centered across
the width of the land pattern area.
68
L-Lead Registration to Land
MAXIMUM ACCEPTABLE –
Lateral Overhang
• Part is misaligned but lateral overhang
does not exceed 25 percent of the lead or
termination width (W) and does not violate
minimum spacing requirements as defined by
the engineering documentation.
L-Lead Solder
PREFERRED
• Complete heel fillet across the contact area.
L-Lead Solder
MAXIMUM ACCEPTABLE
• The maximum fillet reaches 75 percent of
the lead height and across the full width of
the lead contact area.
• The lead remains visible through the solder
fillet.
9.9.1.5
9.9.1.5 LLCC
devicesLLCC devices
9.9.1.5 LLCC devices
LLCC Castellation Registration
to Land
9.9.1.5 LLCC devices
PREFERRED
• The preferred registration of an LLCC is with
the castellation centered across the width of
the land pattern area.
69
LLCC Castellation Registration
to Land
MAXIMUM ACCEPTABLE
• Castellation is NOT centered on the land
and there is no overhang.
LLCC Castellation Solder
MINIMUM ACCEPTABLE
• The connection is well wetted and bonded
with a concave fillet between the castellation
and the land pattern area.
• The minimum fillet extends up at least 75
percent of the thickness of the metallized
portion of the castellation.
• The standoff height above the PWB substrate
shall not be less than 0.127mm (.005 in)
LLCC Castellation Solder
MAXIMUM ACCEPTABLE
• The maximum solder fillet may have a
bulbous appearance, but the connections are
well wetted and bonded with a positive angle
of wetting between the solder fillet and the
castellation and/or land pattern area.
9.9.1.6 Supported Holes
Supported Hole microsection
ACCEPTABLE
• 100% fill
70
Supported Hole component side
ACCEPTABLE
• 360° wetting present on lead and barrel
Supported Hole component side
NOT ACCEPTABLE
• Non wetting on lead or barrel.
Supported Hole component side
NOT ACCEPTABLE
• Solder on lead bent area.
Supported Hole component side
ACCEPTABLE
• Solder shall not reach the coating meniscus.
71
Supported Hole component side
NOT ACCEPTABLE
• Coating meniscus touches PTH hole.
Supported Hole component side
NOT ACCEPTABLE
• Copper visibility at lead edge and evidence of
fracture between lead and solder fillet.
Supported Hole component side
ACCEPTABLE
• Sufficient insulation clearance.
Supported Hole component side
NOT ACCEPTABLE
• Enamel coating touches the PTH. Insufficient
insulation clearance.
Supported Hole
ACCEPTABLE
• Holes are completely filled with solder.
• The tops of lands show good wetting.
72
10 CRIMPING, INTERCONNECTING CABLES, HARNESSES,
AND WIRING
This section describes the requirements for interconnecting cable and harness assemblies that connect electrical/
electronic and electromechanical components.
10.1 Principles of Reliable Cabling and Wiring
Reliable interconnecting cable and wire harnesses result from proper design, control of tools, materials, work
environments, and careful workmanship by trained and certified personnel.
Design Considerations. The basic design considerations to assure reliable interconnecting cable and wire assemblies
are as follows:
• The associated materials, parts, and hardware used shall be selected (ISRO Centre Approved Material List) to
provide proper fit, function, and support of wiring and cabling.
• Tools used shall be those that properly process wires and cables during preparation and assembly without
damaging them.
• Wires shall not be too tight (in tension); provision shall be made for appropriate stress relief.
• Wiring installation and connectors shall be assembled, tested, and inspected to verify conformance to
requirements.
• Support of wiring, wire bundles, and harnesses shall be designed to control and minimize the transfer of
shock and vibration induced while loading into the connector and/or wire terminations. Excessive flexing or
pressure over sharp or rough edges shall be precluded.
• Harness and cable protection shall be added in areas where sharp or rough edges are present and abrasion
could occur.
10.2 General requirements
Harness design shall make provision for special performance requirements of any specific harness section (e.g., ease
of bending, flexibility in twisting, electrical isolation, and ability to fit into confined spaces). Design considerations
should include protective devices such as heat- shrinkable sleeving for protection, stress relief, electrical insulation,
and identification purposes.
Precautions shall be taken to prevent the mismatching of connectors, caused by interchanging or by reversing,
through one of the following techniques:
Use of constraints that locate similar connectors built into interconnecting cables and harnesses so they cannot be
interchanged.
Ensure clarity in marking and coding of connectors.
Use of confidence loop circuits (Connector mating status loops) if necessary to check out proper mated positions
73
10.3 Tool and Equipment Control Tool and Equipment shall meet the requirements listed in 4.1 with following additional requirements
• Clean and properly maintain all tools and equipment
• Examine all elements of tools, used in cabling, for physical damage
• Prohibit unauthorized, defective, or uncalibrated tools in the work area/facility
10.4 Solvents and Cleaners
• Solvents shall be nonconductive and noncorrosive and shall not dissolve or degrade the quality of parts or
materials and shall be selected from para 5.4.
10.5 Mounting of Terminals
Use of terminals shall generally be restricted to situations where parts are expected to be removed and replaced,
or where there are other compelling design requirements for their use.
• Terminals shall not be used as the interface connections in non-plated through holes (NPTH’s). Swaging of
terminals shall be performed in a way that does not damage the PWB.
• After swaging or flaring, the rolled area or flange shall be free of circumferential splits or cracks, but may have
a maximum of three radial splits or cracks provided that the splits or cracks are separated by at least 90° and
do not extend beyond the coiled or flared area of the terminal as shown in Figure 10‑1.
Figure 10.1 : Terminal Damage
• Swage type terminals in non-PTH’s, designed to have the terminal shoulder soldered to the printed wiring
conductor, shall be secured to the PWB by a roll swage (Figure 10.2).
Figure 10.2 : Roll Flange Terminal
• PWB designs calling for soldering of the swaged end of the terminal to the printed wiring conductor on a
single-sided PWB shall have the terminal secured with a V-funnel swage (Refer Figure 10‑3).
74
Figure 10.3 :V-Funnel Type Swage Roll
Funnel flanges shall be formed to an included angle between 120 and 150 degrees and shall extend between 0.4
mm and 0.8 mm beyond the surface of the terminal area as shown in Figure 10‑4.
Figure 10.4 : Flare and extension of funnel flanges
Swage type terminals that are mounted in a PTH shall be secured to the PWB by a V- funnel swage (Figure 10‑4)
or an elliptical funnel (Figure 10‑12) swage.
The elliptical funnel swage is the preferred method for attachment. Terminals shall be swaged such that they can be
rotated under finger force.
Figure 10.5 : Elliptical funnel swage
10.6 Attachment of conductors to terminals, solder cups and cables
10.6.1
General
10.6.2
Conductors
A conductor shall be wrapped on to a terminal in the same sense (direction/orientation) as the final curvature of
the wire.
10.6.3
Breakouts from cables
The length of individual wires routed from a common cable to equally-spaced terminals shall be uniform (including
wire ends and stress-relief bends).
Uniform lengths prevent stress concentration in any one wire.
75
10.6.4 Insulation clearance
Where characteristic impedance or circuit parameters are not affected, the insulation clearance values shall be as
Table 10-1
Where characteristic impedance or circuit parameters are affected, the insulation clearance requirements may be
modified and the modification shall be documented in the process procedures. Example : High-voltage circuits or RF
coaxial line terminations.
10.6.5 Solid hook-up wire
• Solid hook-up wire shall be supported at intervals not exceeding 25 mm.
• Support shall be provided by staking or potting.
10.6.6 Stress relief
Conductors terminating at solder connections shall incorporate stress relief.
Wicking shall not be allowed in the insulation clearance area
Anti-wicking tools shall be used for pre-tinning the stranded wires.
10.6.7 Insulation clearance
Minimum and Maximum Insulation Clearance. The insulation shall not be imbedded in the solder joint. The contour of
the conductor shall not be obscured at the termination end of the insulation. Clearance shall meet the requirements
listed in Table 10‑1. Also excess Insulation Clearance shall not permit shorting between adjacent conductors.
Insulation clearance shall be referenced from the first point of contact of the conductor to the terminal.
Table 10‑1 : Clearances for insulation.
Wire diameter (AWG)
Conductor diameter without
insulation, d (mm)
Insulation clearance
(minimum)
Insulation
clearance (max.)
32 to 24
0.200 to 0.510
d
4×d
22 to 12
0.636 to 2.030
d
3×d
≥ 10
≥ 2.565
d
2×d
• Multiple Parallel Entry. For multiple parallel entry of conductors to a terminal, insulation clearances need not
be equal.
• Variations. When characteristic impedance or other circuit parameters are affected, as in high-voltage circuits
or coaxial line terminations, the insulation clearance requirements may be modified. All variations shall be
documented.
• Breakouts from Wire Bundles. For multiple conductors routed from a common wire bundle to equally spaced
soldered terminals, the length of the conductor ends, including bend allowance, shall be uniform to prevent
stress concentration on any one conductor .
• Mechanical Support. Wire bundles shall be supported so that the solder connections are not subjected to
mechanical loads.The methods, means, and location of this support shall be specified on the design engineering
documentation.
76
• Stress Relief. Conductors shall be provided with sufficient slack to preclude tension on the solder termination
or conductor.
• Wrap Orientation. Conductors may be wrapped clockwise or counterclockwise on the terminal and shall
continue the curvature of the dress. The conductor shall not interfere with the wrapping of other conductors
on the terminal. The curvature of the dress shall not exceed 20° from a perpendicular line from the last point
of contact between the conductor and terminal (Figure 10‑6).
Figure 10.6 :Wrap Orientation
Figure 10.6 : Wrap Orientation
10.7 Stripping insulation from conductors and cable
10.7.1 Stripping Round Conductors
Insulated wires shall be prepared in accordance with the following requirements:
• Insulation Removal. Stripping tools, used to remove conductor insulation shall be of the correct size and in
correct adjustment and/or calibration. The stripping tools shall be in compliance with para. 4
• Damage to Insulation. After removal of the insulation segment, the remaining conductor insulation shall not
exhibit any damage such as nicks, cuts, crushing, or charring. Conductors with damaged insulation shall not be
used. Scuffing from mechanical stripping or slight discoloration from thermal stripping is acceptable
• Damage to Conductors. After removal of the conductor insulation, the conductor shall not be nicked, cut, or
scraped to the point that base metal is exposed. Conductors that were reduced in the cross-sectional area
shall not be used
• Wire Lay. The lay of wire strands shall be restored as nearly as possible to the original lay if disturbed. The
conductor shall be cleaned following restoration to the original lay
• Tinning of Conductors for Solder Cups. The portion of stranded wires that will eventually become a part
of the finished solder connection shall be coated with tin-lead solder and cleaned prior to attachment.
Additional flux may be used. The flux shall be applied so that it does not flow under the insulation except for
traces carried by solder wicking. Flux shall be removed with cleaning solvent applied so that its flow under the
conductor insulation is minimal (by avoiding use of excessive solvent and positioning the conductor so that
the gravity keeps the solvent from flowing under the insulation). Flow (wicking) of solder along the conductor
is permitted but shall not mask the conductor strands at the termination end of the insulation
• Minimum Insulation Clearance. The insulation shall not be imbedded in the solder joint. The contour of the
conductor shall not be obscured at the termination end of the insulation
• Maximum Insulation Clearance. The insulation clearance shall be less than two wire diameters, including
insulation, but in no case shall permit shorting between the conductors connected to adjacent terminal
• Electrically common conductors. Insulation clearance shall be referenced from the first point of contact of the
conductor to the terminal
77
10.7.2 Stripping Jackets over Shields
• Jackets over shields may be stripped by either thermal or mechanical means. Nicked cut shield strands shall
not exceed 10 percent of the total number of strands. There shall be no severed strands.
• Terminal Fill. Conductors and part leads shall be in full contact with the terminal. They shall not be wrapped
onto each other or extend beyond the top of the terminal
• Part Leads. Part leads shall not be used as terminals unless the part is designed for the lead to function as a
terminal.
10.8 Turret, Bifurcated, hook and cup terminals
10.8.1 Turret and straight pin terminals
10.8.1.1 Side route
• Side route connections shall be made in such a way that, conductors shall be wrapped around the post
o
a minimum of 1/2 turn see Figure 10‑7(c).
o
a maximum of 3/4 turn Figure 10‑7(c).
• For turret terminals, all conductors shall be confined to the guide slots.
• Conductors shall not project beyond the base of the terminal.
• Wires shall not be wrapped over other wires.
• More than one wire may be installed in a single slot of a terminal post provided that the combined diameters
of the wires are less than the width of the slot.
• Wires terminating at terminals that do not have a mechanical shoulder or turret shall not be attached closer
than one conductor diameter to the top of the terminal.
10.8.1.2
Bottom route
The conductor shall enter the terminal from the bottom, pass through the side slot at the top, and be wrapped as
for the side route, see Figure 10‑7(b).
10.8.2
Bifurcated terminals
• Top, side or bottom routes, or combinations thereof, shall be used.
• Top route and side route shall not be used together on the same terminal.
10.8.2.1
Bottom route
• Bottom route connections shall be as shown in Figure 10‑8
• Conductors may project beyond the diameter of the base; see Figure 10‑8(c), provided that clearances,
environmental and electrical characteristics are not compromised.
78
Figure 10.7 : Side- and bottom-route connections to turret terminals
Figure 10.7 : Side- and bottom-route connections to turret terminals
Figure 10.8 : Bottom-route connections to bifurcated terminal
79
10.8.2.2 Side route
• Side route connections shall be as shown in Figure 10‑9
• The conductor shall enter the mounting slot perpendicular to the posts.
• When more than one conductor is connected to a terminal, the direction of bend of each additional conductor
shall alternate, see Figure 10‑9 (b) and (d).
• Side-route connections shall not project above the top of the terminal.
• Conductors may project beyond the diameter of the base, see Figure 10‑9(c), provided that clearances,
environmental and electrical characteristics are not compromised.
• Conductors shall be wrapped a minimum of ¼ turn (Figure 10‑9 (a)) to a maximum of ½ turn
(Figure 10.9 (c)) around the post.
Figure 10.9: Side-route connection to bifurcated terminal
Figure 10.9: Side-route connection to bifurcated terminal
10.8.2.3 Top route
• The top route shall not be used where side entry is possible.
• Top route connections shall be as shown in Figure 10.10
• Conductors shall be inserted between the vertical posts to the depth of the shoulder, except for combined
top and bottom routes
• Conductors which do not fill the gap, see Figure 10.10, shall be either accompanied by a tinned filler wire
(solid or stranded), such that the combined diameters fill the gap, or bent double, provided that the combined
diameters fill the gap.
80
Figure 10.10:Top-route connection to bifurcated terminal
Figure 10.10: Top-route connection to bifurcated terminal
10.8.2.4 Combination of top and bottom routes
• The bottom route conductor shall be installed before the top route conductor.
• The top-route conductor shall be inserted to contact the bottom-route conductor.
10.8.2.5 Combination of side and bottom routes
The bottom route conductor shall be installed before the side route conductor.
10.8.3 Hook terminals
• Connections to hook terminals shall be as shown in Figure 10‑11
• The bend to attach conductors to hook terminals shall be
o
a minimum of 1/2 turn
o
a maximum of 3/4 turn
• Protrusion of conductor ends shall not damage insulation sleeving
• Where more than one conductor is attached to a terminal, the direction of bend of each conductor shall
alternate (see Figure 10‑11(b))
Figure 10.11: Connections to hook terminals
Figure 10.11: Connections to hook terminals
81
Figure 10.11: Connections to hook terminals
10.8.4 Pierced terminals
• Connections to pierced terminals shall be as shown in Figure 10‑12
• The bend to attach conductors to pierced terminals shall be:
o
a minimum of 1/2 turn,
o
a maximum of 3/4 turn.
• Protrusion of conductor ends shall not damage insulation sleeving.
Figure 10.12: Connections to pierced terminals
Figure 10.12: Connections to pierced terminals
10.8.5 Solder cups (connector type)
• Conductors shall enter the solder cup as shown in Figure 10.13
• Conductors shall be bottomed in the cup
• Conductors shall be in contact with the inner wall of the cup
• Multiple conductors may be inserted provided that each is in contact with the full height of the inner wall of
the cup
• Flux shall not be trapped within the solder cup
• Conductors shall not misalign floating contacts
Example: Solid, rigid conductor wire into connectors.
10.8.6 Insulation sleeving
• Connections that are not protected by insulation grommets, potting, or conformal coating shall be protected
by insulating sleeving. For example: Hook terminals, solder cups and bus wires.
• Insulation sleeving shall be transparent and heat-shrinkable.
• A component shall not move within the sleeving when the sleeving is mechanically supported.
• Heat shrinking of the sleeve shall not damage the assembly.
82
Figure 10.13: Connections to solder cups (connector type)
Figure 10.13: Connections to solder cups (connector type)
10.9 Wire and cable interconnections
10.9.1 General
• Interconnection methods shall not use fluxed solder preforms within heat-shrinkable sleeves.
• Soldered wire interconnection methods shall enable the removal of flux and flux residue.
• Soldered wire interconnection methods shall enable visual inspection of the interconnection and
surrounding materials.
• After soldering, conductors shall be covered with heat-shrinkable sleeving.
• Fluorocarbon sleeves shall not be used because these sleeves have high shrinkage temperatures that can
damage or reflow soldered connections.
10.9.2 Preparation of shielded wires and cables
• The area of exposed shield shall be either:
o
at the end of the wire or cable (end termination),or
o
at any position along the length of a wire or cable (centre splice).
• The insulation jacket shall be removed for:
o
a minimum length of 5 mm,
o
a maximum length of 12 mm.
• The insulation jacket shall be scored and removed using a sharp cutting tool like scalpel.
• The preparation process shall not damage the exposed shield material
• The shield material shall be cleaned using a solvent in accordance with para 5.4.1.
10.9.3 Pre-assembly
10.9.3.1 Heat-shrinkable sleeving
• Heat-shrinkable sleeving shall provide electrical insulation and mechanical support to the finished
interconnection.
83
• The sleeving shall be cut to a length that covers the finished soldered joint and extends over the remaining
insulation of each conductor for a distance of 5 mm ± 2 mm.
• The cut sleeving shall be threaded over one of the wires to be joined.
• The heat-shrinkable insulation sleeving shall be centred over the cleaned and inspected interconnection.
• The sleeving shall be shrunk using heated gas or radiant energy.
• Heat shall not be applied for more than 8 seconds.
• The heat-shrinking temperature shall not exceed 140 °C or shall be as per manufactures recommendation.
10.9.3.2 Conductors
• Conductors shall be secured to prevent disturbance during soldering and solidification using one, or a
combination of, the following methods:
o A holding fixture that clamps the wires ensuring correct alignment.
• A strand of binding wire, wrapped a minimum of 3 turns, as shown in Figure 10‑14 (a). Example: Bare,
tinned-copper wire.
• Rings of heat-shrinkable sleeving positioned over the ends of the wire insulations, Figure 10‑14(b) and (c).
• A twist-splice around the braid, see Figure 10‑14 (c).
• The conductors to be joined shall lie parallel and in contact.
• Conductors may be preformed when the cable insulation prevents a parallel lay.
• Bending tools for the preforming of conductors shall be in accordance with para 4.1.3
• Wires shall be spliced using lap joints.
• For shield terminations, the conductor of the grounding wire shall be positioned on the exposed shield.
• Insulation overlap shall not be greater than the diameter of the largest conductor of the interconnection.
10.9.4 Soldering procedures
The soldering iron shall be selected in accordance with para 4.3
The solder alloy shall be in accordance with para 5.2.
The flux shall be in accordance with para 5.3.
Soldering aids shall be used to restrict wicking of flux or solder under the insulation in accordance
with chapter 4.
• After solder solidification, the contour of each wire conductor shall be visible.
•
•
•
•
• After solder solidification, adjacent conductors shall be connected by concave solder fillets.
Figure 10.14: Methods for securing shielded wires
Figure 10.14: Methods for securing shielded wires
84
10.9.5 Cleaning
The removal of flux and residues shall be in accordance with para section 8
10.9.6 Workmanship
• Joints shall have a smooth, bright appearance.
• The workmanship of solder joints shall be in accordance with para 9.5 and 9.6.
10.9.7 Connection of stranded wires to PCBs
• Stranded wires shall be soldered to PCB terminations using lap joints or plated-through holes in accordance
with Figure 10.15 (a), (b) and (c).
• The dimensions shown in Figure 10‑15 shall be in accordance with Table 10‑2
• Stress relief shall be provided.
• For any type of wire, the minimum distance between the insulation and the solder fillet shall be 1 mm.
Figure 10.15: Connection of stranded wires to PCBs
Figure 10.15: Connection of stranded wires to PCBs
85
Table 10‑2 : Dimensions for Figure 10‑16
r≥2d
d
r1 ≥ 2 D
D = outer wire diameter
1 mm ≤ H ≤ 2 mm
H = insulation clearance
1.5 mm ± 0.8 mm
LP = lead protrusion through board
= conductor diameter
10.10 Interconnecting cable/harness fixturing
10.10.1 General
Layout and fixturing shall be provided for all complex interconnecting cables and harnesses . Permanent bends and
offsets shall be built into harnesses so that the final wire dress will not be under continuous stress and tension
after installation. Connector back shells shall accommodate bends and offsets in wire harnesses, as appropriate, to
avoid continuous stress. Additionally, the layout shall be designed to limit the amount of bending, pulling, and other
handling stresses a harness will receive during installation.
10.10.2 Mockup and Wiring Board Design Parameter
Wiring boards and other mockups shall be constructed full size, 3-dimensional, and shall account for all the
physical restraints the interconnecting harness or cable will encounter. Typical harness board layout is shown in
Figure 10.16.
10.10.3 Temporary Identification
Temporary identification markers may be used for in-process identification requirements. All temporary markers
shall be removed from completed cabling and harnessing. The markers shall not leave a contaminating residue.
10.10.4 Interconnecting Cable and Harness Protection
The facility shall establish and implement procedures to protect interconnecting cables and harnesses from damage
and degradation. Connectors not being actively assembled shall be individually protected by wrapping them in
bubble pack or other physical covering. All harnesses not in active fabrication (those in temporary storage) shall be
covered by protective covering to prevent ESD failures.
10.11 Forming wires and cables into harnesses
10.11.1 General
Wiring shall be assembled in interconnecting cables or harnesses as described herein. Fabrication methods and
assembly techniques that assure the production of high quality interconnecting cables and harnesses shall be used
86
Figure 10.16 : Line Drawing of Typical Harness Layout
Lacing for Trunk, Branches and Breakouts
Figure 10.16 : Line Drawing of Typical Harness Layout
• Starting Stitch. Harnesses laced with single thread shall initially be tied with a starting stitch . Single-thread
starting stitches shall be the same as a spot tie with a running end (see item 2 of this paragraph), or as shown
in Figure 10.17 View A. Starting stitches for double lacing shall be as shown in Figure 10‑17 View B.
Starting stitches shall not place stress on wire terminations
• Spot Ties. Spot ties shall consist of a clove hitch followed by a square knot as shown in Figure 10.18 or other
non-slip knots. See Figure 10.18 for spot tie spacing.
• Closing Stitch. Single or double lacing thread shall be terminated with a closing stitch as shown in
Figure 10.19. Lacing shall be terminated at every major breakout or branch and at the extremity of the
harness. (Major breakouts normally contain a large percentage of the wire volume, such as 25 to 30 percent
or more.) The stitching shall terminate close to the extremity of the harness but shall not stress the wire
terminations. Closing and starting stitches at branches and breakouts shall be next to the breakout. An
alternate closing stitch method is shown in Figure 10.20. Single or small multiple breakouts of two or
three wires need not have closing and starting stitches, but may have running lockstitches on each side
(Figure 10.21).
Table 10‑3 : Bend Radii for Completed Interconnecting Cable or Harness
Wire Type
Optimum Bend Radius
Minimum Bend Radius
10 x OD *
6 x OD
Polyimide (Kapton) insulated
15 x OD
10 x OD
Overall harness (with coaxial cable or AWGsize 8
or larger).
10 x OD
6 x OD
Overall harness (with AWG size 10 or smaller
without coaxial cable).
10 x OD
3 x OD
Overall harness (with polyimide insulated wires
included).
15 x OD
10 x OD
Individual coaxial cable.
87
*
Outside Diameter
Figure 10.17 : Starting Stitch
Figure 10.17 : Starting Stitch
Figure 10.17 : Starting Stitch
Figure 10.18 : Spot Tie (Typical)
Figure 10.18 : Spot Tie (Typical)
Table 10‑4 : Spot Tie, and Stitch Spacing Dimensions
Harness Diameter mm
Maximum Distance Between Harness Ties mm
6 or
less : Spot Tie (Typical)
Figure
10.18
12
25
Larger than 25
88
20
40
50
70
Figure 10.19 : Closing Stitch and Single Thread—Illustration
Figure
10.19
: Closing
Stitch
andand
Single
Thread—Illustration
Figure
10.19
: Closing
Stitch
Single
Thread—Illustration
Figure 10.20 : Alternate Closing Stitch and Single Thread—Illustration
Figure 10.21 : Running Lockstitch
Figure 10.21 : Running Lockstitch
89
Table 10‑5 : Distances From Connectors or Connector Accessories to Beginning of Harness Ties
Harness-Bundle Diameter mm
Distance From Connector or Connector
Accessory to Start of First Tie mm
Less than 12
25 - 50
12 to 25
50-76
25 or larger
76-101
Flat stitching shall utilize either of the stitches pictured in Figure 10.22.
Figure 10.22 : Flat Lacing Stitches
10.11.2 Fabric Braid Sleeving (Pre-woven)
Prewoven fabric (unvarnished) braid sleeving to be installed over the wire harness shall be slightly oversized so that
it can be slid over the bundle. Braided sleeving shall be snugly dressed down over the wire bundle. Continuous braid
sleeving shall be secured at the ends by cable straps, spot ties, clamps, heat shrinkable sleeving, or a potting material
. When secured, the covering shall not slide freely. Sleeving shall be trimmed and terminated at a breakout but shall
not be punctured or slit to provide openings for breakout . After installation, braided sleeving shall be secured or
treated in one of the following ways to eliminate fraying or unraveling .
Figure 10.23 : Securing Fabric Braid Sleeving
• Braided sleeving may be secured by a spot tie or nylon cable strap. The end of the braid shall be tucked under
and secured with a spot tie or plastic strap (Figure 10.23).
• The end of the braid may be secured by connector clamps, other hardware, or potting.
Figure 10.23 : Securing Fabric Braid Sleeving
90
• The ends of glass braids may be bonded using an adhesive. Excessively frayed material shall be trimmed away
prior to application of the adhesive . When the adhesive is dry, the braid shall be secured by spot tying or
other means so that it does not slip on the wire bundle.
10.11.3 Lacing
Wires shall be tied together in bundles to prevent damage to insulation and the joints due to vibration and shock.
Lacing shall not be tight to avoid cold flow.Waxed nylon lacing thread or nylon cable ties or Dacron shall be used
for tying of wire harness. Following are some of the recommended methods of lacing.
• Spot ties are individual ties made with lacing thread using a square knot. The procedure for making the
square knot and spot ties is shown in Figure 10.24. It is used at the service loops, access doors etc., where
flexibility of harness is required. Typical example of a spot tie is shown in Figure 10.25
Figure 10.24 : Spot Tie Principle
Figure 10.24 : Spot Tie Principle
Figure 10.24 : Spot Tie Principle
Figure 10.25 : Spot Tie
Figure 10.25 : Spot Tie
• Serve Knot (also known as endless tie) shall be used at the bundle branches or breakouts and at all terminations
of large sizes (more than 25mm diameter) to prevent the lacing from loosening.
Figure 10.25 : Spot Tie
91
Procedure for making a serve knot is as follows:
• Form a loop along the bundles with lacing thread, keeping the ends of the thread towards the bundle
end. Wrap the lacing end of the thread around the bundle and over the loop, till the required length of the
serve is made. Pass the lacing end through the loop and pull the ends away from each other. Adjust by pulling
until the cross is under the serve.
• A typical example of serve knot is shown in Figure 10.26 & Figure 10.27
Figure 10.26 : Serve Method of Tying
Figure 10.26 : Serve Method of Tying
Figure 10.26 : Serve Method of Tying
Figure 10.27 : Serve at the Point of Origin
Figure Continuous
10.27 : ServeLacing
at the Point of Origin
10.11.4
• Running stitches are made by passing the free end of the lacing thread around the bundle and through the
loop as shown in. This type of lacing shall be used for harness diameter of less than 5 mm or upto 15 mm for
supported harness.
Figure 10.27 : Serve at the Point of Origin
Figure 10.28 : Running Stitch
• Single lock stitches are the most commonly used lacing methods. Single lock stitch is made by passing the
Figure
10.28
: Running
Stitchand through a loop as in Figure 10.30 This type of lacing shall be used for
lacing
between
two stitches
harness of diameter 5 mm to 15 mm where harness is not supported.
92
Figure 10.29 : Single Lock Stitch
• Double lock stitches are used primarily to prevent lacing from loosening and is preferred for the harness
bundle with diameter more than 15mm which undergo more frequent handling. It is made by forming two
single
stitches
around
the bundle
then securing both with lock stitch as shown in the following figure.
Figure
10.29
: Single
Lock and
Stitch
Figure 10.30 : Double Lock Stitch
10.11.5 Straps
• Installed straps shall be locked to prevent them from loosening or opening. Straps shall be placed on both
sides of a breakout; otherwise, spacing between straps shall be as required by Table 10‑4. The “ribbed” side
of a strap shall always be placed against the wires. Straps shall be tightened so that they do not slide back and
forth on the assembly; however, they shall not be so tight as to cause noticeable indentation or distortion of
the wires in the harness . Proper strap orientation is shown in Figure 10.31.
• Plastic straps are usually installed by tooling. Tooling shall be tension-controlled to meet the strap-tightening
requirements previously stated . Surplus strap ends shall be trimmed flush at the back end of the strap head
(this is done automatically by most tooling).
Figure 10.31 : Plastic Strap Orientation
10.11.6 Insulation Sleeving/Tubing
• Insulation sleeving shall be installed on all terminations that are not otherwise insulated or potted, except
those at ground potential (e.g., overall shield and coaxial cable terminations). Sleeving shall be installed to
meet the dimensional requirements of the applicable drawing or specification.
93
• Heat-Shrinkable Sleeving. The heat-shrinkable sleeving selected shall be larger than the maximum diameter of
the object being covered, and after shrinking it shall provide a tight fit over the object in the area of maximum
diameter.This will cause the sleeving to have a tight mechanical grip on the item it covers. A guide for selecting
sleeving sizes is given in Table 10‑6. There shall be no partially or incompletely shrunken areas. Sleeving may
have a slight surface crazing, but it shall be free of cracks, punctures, and charred or burned areas .
• Tubing. Tubing shall be secured by spot ties or otherwise restrained to prevent them from sliding back and
forth over the wire bundle.
Table 10‑6 : Selection Guide for Use of Polyolefin / Kynar sleeves
I.D. As
Supplied
I.D. Recovered
(After Heating)
Cable Diameter
Sleeving Size
1.2
(0.046)
0.6
(0.023)
0.30 to 0.70 (0.01 to 0.026)
1.2
(3/64)
1.6
(0.063)
0.8
(0.031)
0.71 to 1 (0.028 to 0.038)
1.6
(1/16)
2.4
(0.093)
1.2
(0.046)
1.01 to 1.40 (0.039 to 0.54)
2.4
(3/32)
3.2
(0.125)
1.5
(0.061)
1.41 to 2.00 (0.055 to 0.077)
3.2
(1/8)
4.7
(0.187)
2.4
(0.093)
2.01 to 2.80 (0.078 to 1.109)
4.8
(3/16)
6.4
(0.250)
3.2
(0.125)
2.81 to 4.00 (0.110 to 0.156)
6.4
(1/4)
9.5
(0.375)
4.7
(0.187)
4.01 to 5.50 (0.157 to 0.218)
9.5
(3/8)
12.7
(0.500)
6.4
(0.250)
5.51 to 7.90 (0.219 to 0.312)
12.7
(1/2)
19.1
(0.750)
9.5
(0.275)
7.91 to 11.10 (0.313 to 0.437)
19.1
(3/4)
25.4
(1.000)
12.7
(0.500)
11.11 to 15.90 (0.438 to 0.625)
25.4
(1)
38.1
(1.500)
19.1
(0.750)
15.91 to 22.2 (0.626 to 0.875)
38.1
(1-1/2)
50.8
(2.000)
25.4
(1.000)
22.21 to 31.80 (0.876 to 1.250)
50.8
(2)
76.2
(3.000)
38.1
(1.500)
31.81 to 44.50 (1.251 to 1.750)
76.2
(3)
101.6 (4.000)
50.8
(2.000)
44.51 to 63.5 (1.751 to 2.500)
101.6 (4)
The 2 to 1 shrink ratios shown apply to commonly used polyolefin sleeving
10.12 Cable shielding and shield termination
10.12.1 General RFI/EMI Practices
Interconnecting cables and harnesses shall be designed and constructed to minimize electromagnetic couplings
between wires within the assembly that are sensitive to induced interference. On RF signal cables, both the inner
conductor and outer conductor braid shall be electrically continuous . Methods by which program isolation
requirements can be achieved are listed in the following text.
• Isolation of Signals. Signals can be isolated by using separate connectors and wire harnesses. When a
combination of signals passes through a single connector, wires carrying similar signals can be grouped together
and laced separately in the harness.
• Wire and Cable Types. RFI/EMI caused by coupling of external fields can be reduced in harnesses by careful
selection of wire types that provide control of radiated fields. Listed in order of increasing control are:
94
o
Twisted pairs
o
Shielded wires with single core or twisted pair.
o
Single-braid coaxial cable.
o
Double-braid coaxial cable.
10.12.2 Shield Termination
Shields shall be terminated using one or more of the following methods :
• Individual shields using solder sleeves.
• Individual shields using two-piece crimp rings.
• Large compression ring grounding or bands and Floating shield.
10.12.3 Individual Shield Termination Using Heat Shrinkable Solder Sleeves
An individual shield that is terminated using heat shrinkable solder sleeves to attach grounding wires to the shield
braid is shown in Figure 10.32. Heat shrinkable solder sleeves should be installed in accordance with manufacturers’
instructions.
Figure 10.32 : Individual Shield Termination Using a Heat shrinkable Solder sleeving
10.12.4 Long Lengths of Shrinkable Sleeving
Figure 10.32 : Individual Shield Termination Using a Heat shrinkable Solder
Long lengths of shrinkable sleeving installed over interconnecting harnesses and cables shall provide protective
sleeving
coverage of the designated area without leaving residual stress in the material (Requirement). The sleeving shall be
in contact with the interconnecting harness or cable along its length (Requirement). One method of controlling
endwise shrinkage (reduction in length) of the sleeving during installation is shown in Figure 10‑33.
NOTE: Medium to long lengths of harnesses/cables with shrink sleeving are extremely difficult to bend and coil without
damage
95
Figure 10-33
Figure 10.33 : Installation of Long Lengths of Sleeving to Achieve Controlled Dimensions
Figure 10.33 : Installation of Long Lengths of Sleeving to Achieve Controlled
Dimensions
10.12.5 Floating
Shield Terminations
The outer jacket shall be trimmed to expose the shielding braid.The braid shall be folded back over the outer jacket
as illustrated in Figure 10‑34. Combing the braid is optional. Heat-shrinkable sleeving shall be installed over the
trim point.
Figure 10.34 : Floating Shield Termination
Figure 10.34 : Floating Shield Termination
96
10.12.6 Unshielded Wire Exposure and Total Length of Grounding Wires
Exposed wire beyond a shield termination is subject to induced RFI/EMI interference. Any excessive length of
grounding wire may act as an antenna in picking up interference. Distances to terminations and maximum
lengths of grounding wires attached directly to an individual shield are given in Table 10‑7 and illustrated in
Figure 10.35. Shield terminations shall be staggered behind the connector/accessory 13mm (0.5 inch) minimum and
100mm (4 inches) maximum to assure minimum buildup of the wire bundle diameter in the shield termination area
(see Figure 10.35).
Table 10‑7: Shield Termination Control
Nature of Circuit
X-Distance Recommended
Max Length mm (Inches)
Y-Distance mm
(Inches)
Interference sensitive1/
20 (0.75)
40 (1.5)
Ordinary interference
protection
100 (4.0)
150 (6.0)
Figure 10.35 : Conductor Exposure for Individual Shield Termination Types
Figure 10.35 : Conductor Exposure for Individual Shield Termination Types
Figure 10.35 : Conductor Exposure for Individual Shield Termination Types
Figure 10.36 : Folded back shield with splice termination to multi strand wire
Figure
10.36 : Folded back shield with splice termination to multi strand wire
10.13 Wire
crimping
Crimping is a method of joining an electric conductor (multi strand wire) and another current carrying member
Figure 10.36 : Folded back shield with splice termination to multi strand wire
(contact terminal) wherein the terminal is compressed on to the conductor wire using a specially designed and
calibrated tool and the compressed joint thus formed is known as a crimp joint.
97
Crimping is preferred to soldering being cleaner and more reliable technique. Crimping is often preferred when
weight and space are major constraints. It is also used when high temperature soldering iron could cause some
hazards. Soldering may be used if terminals are not accessible for crimping.
10.13.1 Crimping Requirements:
Crimping requirements for the following crimping wire terminations intended for high reliability electrical connections
for SPACE use (Refer Figure 10.37).
• Removable contacts, single wires
• Removable contacts, multiple wires
• Co-axial connectors, ferrules
• Lugs and splices
Removable
Removable contacts,
contacts, single
single wires
wires
Removable
contacts,
single
wires
Removable
contacts,
single
wires
Removable
contacts,
single
wires
Removable
Removable contacts,
contacts, multiple
multiple wires
wires
Removable
contacts,
multiple
wires
Removable
contacts,
multiple
wires
Removable
contacts,
multiple
wires
Lugs
and
splices
Lugs
splices
Lugsand
and
splices
Lugs
andand
splices
Lugs
splices
Co-axial
connectors,
ferrules
Co-axial
connectors,
ferrules
Co-axial
connectors,
ferrules
Co-axial
connectors,
ferrules
Co-axial
connectors,
ferrules
Figure 10.37 : Specific Interconnection
10.13.2 Crimping Operations
The factors governing a good crimped joint are controlled to a large extent by the tools and materials used, but
workmanship is a factor in the careful application of these. Workmanship includes carefully butting the wire
against the stop in the stripping operation to ensure correct insulation gap, loading of connector pin in the
position to the full distance, inserting the stripped wire into the connector pin barrel until it shows the inspection
hole and re-twisting the strands where the lay has been disturbed during the stripping operation. Clean lint free
gloves or finger cots are preferred for this operation.
98
Strands of wires shall not be doubled back to increase the conductor diameter nor shall extra strands be inserted
to compensate for an over-sized barrel.
All conductor strands shall be inserted cleanly into the barrel without any buckling. Strands shall not be left outside
or cut to reduce the conductor diameter to fit an under-sized barrel. The use of tin plated wire in crimp
type connector is not recommended because it can present severe electrical problems (poor corrosion
resistance when coupled to gold and formation of inter-metallic). Nickel plate gives increased resistance at elevated
temperatures and is not suitable for low voltages.
Silver plated copper wire is recommended for most applications when crimped inter connections are envisaged.
Some provision may be necessary to avoid tarnish during storage and in instances where the same wire will also be
joined by soldering.
10.13.3 Crimping Tools
10.13.3.1 Crimping Tool No
Following types of crimping tools shall be used for crimping the wires.
Sr. No.
Crimping Tool Detail
Locator/ Positioner Detail
1
Daniels/DMC M22520/2-01
K-42, MIL-M22520/2-06
2
9507 - AFM8 M22520/2-01
K41, 9502-3, MIL-M22520/2-06
3
DMC - AFM8 M22520/2-01
K13, L3198-20
4
Astro-615717, M22520/2-01
SS-0060000001 MIL-M22520/2-01
5
DMC - AFM8 M22520/2-01
DMC, L3198-20HD
6
DMC - AFM8 M22520/2-01
DMC, K-13, 2026 pin & soc,L3198-20HD
7
DMC - AFM8 M22520/2-01
DMC, K-13, 2026 pin & soc, L3198-20HD
8
DMC, M22520/2-01
DMC, K41, 9502-3, MIL-M22520/2-06
9
DMC, M22520/1-01
DMC, TH 29 CAGE 11851
10
DMC, AFM8 M22520/2-01
DMC, K-13, 2026
11
DMC,AFM8, M22520/2-01
DMC, K-13, 2026
12
DMC, AFM8, M22520/2-01
DMC, K-41
99
10.13.3.2 Typical Crimp Tool Selector Positioner Setting
Following are the typical crimping tool No., crimp pin detail & Positioner setting.
Locator/
Positioner
Detail
Sr.
No.
Wire/Cable Details
Crimp Pin Detail
1.
26AWG
Kapton Poly.
206071-1-RFP
(H D pin/connector)
Daniels/DMC
M22520/2-01
K-42, MILM22520/2-06
3
2.
24 AWG
Kapton Poly.
206071-1-RFP
(H D pin/connector)
Daniels /DMC
M22520/2-01
K-42,
MIL-M22520/2-06
4
3.
22AWG
Spec55
(RAYCHEM)
FC8022D-50-1202-0
(H D pin/connector)
(Positronics make)
9507 - AFM8
M22520/2-01
K41, 9502-3
MIL-M22520/2-06
4
4.
26AWG
Kapton poly.
FC8022D-50-1202-0
(HD pin/connector)
(Positronics make)
9507 - AFM8
M22520/2-01
K41, 9502-3
MIL-M22520/2-06
3
5.
20 AWG
Spec55
5000-007-0020-0
Plug
(Amphenol make)
DMC - AFM8
M22520/2-01
K13, L3198-20
7
6.
28 AWG
26 AWG
Suitable for 26 & 28
AWG wires
DMC,
M22520/2
-
6
7.
26 AWG
Kapton poly.
FC8022D-50-1202-0
(H D pin/connector)
(Positronics make)
9507 - AFM8
M22520/2-01
K41, 9502-3
MIL-M22520/2-06
5
8.
26 AWG
Spec55
0060421-20ROG
(HYPERTAC)
Astro-615717
M22520/2-01
SS-0060000001
MIL-M22520/2-01
3
9.
22 AWG
Spec55
0060421-20ROG
(HYPERT AC)
Astro-615717
M22520/2-01
SS-0060000001
MIL-M22520/2-01
4
10.
26 AWG
Kepton Poly.
20607-1-RFP, 26
AWG, Socket, HD
(Pamir electronics)
DMC - AFM8
M22520/2-01
DMC,
M24308 /12-1
3
26 AWG
Kepton Poly.
5100-054-0020
26 AWG, Socket
(Matrix make)
DMC - AFM8
M22520/2-01
DMC,
L3198-20HD
6
11.
100
Crimping Tool
Detail
Setting of
Positioner
Sr.
No.
Wire/Cable Details
12.
20 AWG
Spec55
13.
Crimp Pin Detail
Crimping Tool
Detail
Locator/
Positioner
Detail
Setting of
Positioner
5100-014-0020-0
20 AWG, Socket
(Matrix make)
DMC - AFM8
M22520/2-01
DMC,
L3198-20HD
6
26 AWG
Kepton poly.
3401 005 03B
26 AWG, Plug
(ITT Cannon make)
DMC - AFM8
M22520/2-01
DMC, K-13,
2026 pin & soc,
L3198-20HD
5
14.
20 AWG
Spec55
3401 005 01B
20 AWG, Plug
(ITT Cannon make)
DMC - AFM8
M22520/2-01
DMC, K-13,
2026 pin & soc,
L3198-20HD
7
15.
22 AWG
Spec55
3401 005 01B
22 AWG, Plug
(ITT Cannon make)
DMC - AFM8
M22520/2-01
DMC, K-13,
2026 pin & soc,
L3198-20HD
6
16.
24 AWG
Kepton poly.
3401 005 01B
24 AWG, Plug
(Matrix make)
DMC - AFM8
M22520/2-01
DMC, K-13,
2026 pin & soc,
L3198-20HD
5
17.
24 AWG
Kepton poly.
5100-014-0020-0
24 AWG, Socket
(Matrix make)
DMC - AFM8
M22520/2-01
DMC, K-13,
2026 pin & soc,
L3198-20HD
6
18.
22 AWG
Spec55
5100-014-0020-0
22 AWG, Socket
(Matrix make)
DMC - AFM8
M22520/2-01
DMC, K-13,
2026 pin & soc,
L3198-20HD
6
19.
26+26 AWG
Kepton polyimide
5100-014-002-0
20 AWG, Socket
(Matrix make)
DMC,
M22520/2-01
DMC, K-13,
2026 pin & soc,
L3198-20HD
7
20.
26+24 AWG
Kepton poly.
5100-014-002-0
20 AWG, Socket
(Matrix Make)
DMC,
M22520/2-01
DMC, K-13,
2026 pin & soc,
L3198-20HD
7
21.
26+26 AWG
Kepton poly.
3401-005-01 B
20 AWG Plug
(ITT Cannon make)
DMC,
M22520/2-01
DMC, K-13,
2026 pin & soc,
L3198-20HD
7
26+24 AWG
Kapton poly.
3401-005-01 B
20 AWG, Plug
(Matrix Make)
DMC,
M22520/2-01
DMC, K-13,
2026 pin & soc,
L3198-20HD
6
22.
101
Sr.
No.
23.
Setting of
Positioner
DMC,
M22520/2-01
DMC, K41,
9502-3
MIL-M22520/2-06
3
16 AWG Male – TB
A30
16 AWG Female –
A30 B05
(Allied make)
DMC,
M22520/1-01
DMC,
TH 29 CAGE
11851
14
8525-16R14B19
SNH, Socket
(Souriau Make)
Code-11851
DMC - AF8
M22520/1-01
Red
Crimp Pin Detail
24 AWG
Kepton poly.
FC8022D-05-1202-0
Catalog :
SDD44F 1000G
24 AWG, (Socket
HD) (Positronics
Make)
26+26
AWG
24.
Locator/
Positioner
Detail
Wire/Cable Details
22+22
AWG
18
AWG
Teflon wire
(Crimping &
subsequent
soldering)
Crimping Tool
Detail
25.
RG 316
7 strand, 26 AWG
Centre conductor
26.
26 AWG
Kepton poly
3401-005-04 B
26 AWG, Socket
(ITT Cannon make)
DMC,
M22520/2-01
DMC, K-13,
2026 pin & Socket
L3198-20HD
7
27.
22 AWG
Spec 55
3401-005-02 B
20 AWG, Socket
(ITT Cannon make)
DMC, AFM8
M22520/2-01
DMC,
K-13, 2026
7
28.
20 AWG
Spec 55
3401-005-02 B
20 AWG, Socket
(ITT Cannon make)
DMC,AFM8
M22520/2-01
DMC,
K-13, 2026
7
29.
26 AWG
Kepton Poly.
3401-005-08B-ESA-B
22/26 AWG,
Socket (HD) (Souriau
make)
DMC, AFM8
M22520/2-01
DMC, K-41
3
DMC, AFM8
M22520/2-01
DMC, K-41
3401-005-08B-ESA-B
30.
24 AWG
1553 wire
22-26 AWG,
Socket (HD)
(Souriau make)
102
26-1
4
Sr.
No.
Wire/Cable Details
Crimp Pin Detail
Crimping Tool
Detail
Locator/
Positioner
Detail
Setting of
Positioner
206071-1-RFP
31.
24 AWG
1553 wire
24 AWG, Socket
(H D pin/connector)
DMC, AFM8
M22520/2-01
DMC, K-41
4
DMC, AFM8
M22520/2-01
DMC, K-13
6
DMC, AFM8
M22520/2-01
DMC, K-13
5
(Pamir Electronics)
5100-014-0020-0
32.
24 AWG
1553 wire
33.
24 AWG
1553 wire
34.
26 AWG
Kapton Poly.
3401-005-07B-ESA-B
22/26 AWG, Plug
(H D pin/connector)
(Souriau make)
DMC, AFM8
M22520/2-01
M22520/2-06
3
35.
24 AWG
|1553 wire
3401-005-07B-ESA-B
22/26 AWG, Plug,
(H D pin/connector)
(Souriau make)
DMC, AFM8
M22520/2-01
M22520/2-06
4
20 AWG, Socket
(Matrix make)
5000-007-0020-0
20 AWG, Plug
(Matrix make)
10.13.4 Calibration of Crimping Tools
10.13.4.1 Initial Calibration
Crimping tools, both manual and power driven, shall be calibrated when initially set- up for each specific wire size,
connector size and type prior to first use.The setting by the tool manufacturer shall not be relied upon, but the tool
shall be set up using the go : no-go gauge specified for the terminal size, and the wire type and size.
10.13.4.2 Verification
Tool calibration shall be verified and approved by the QA division of the concerned ISRO Centre as per audit
requirements. This shall be accomplished with the go-nogo gauges approved for the terminal size and type, number
of strands and plating of the wire etc, or by tensile strength measurement on minimum 5 specimens samples.
10.13.4.3 Return and Reissue
Upon completion of crimping operations on a given size terminal and type of wire the manual crimping tool shall
be returned to the tool facility for calibration. If the calibrated seals are broken for any reason the tool must be
returned immediately for calibration.
10.13.4.4 Sealing
Calibrated crimping tools shall be sealed to insure against unauthorized alteration or adjustment of settings.The tool
103
shall be sealed by a non-reusable decal seal, which will be visibly, damaged if the calibrated setting is altered. Seals
shall be placed on all external adjustment points on the tool.
Tools with a sealed setting and sealed locator or position. If the tool is broken or damaged, or if the seal is broken,
the tool shall be removed from fabrication.
10.13.4.5 Ratcheting
Tools used shall employ some internal mechanism which controls the crimping operation to the extent that,
once the “operation” is started, they cannot be opened until the crimping cycle is complete.
10.13.5 Insulation Clearance
Maximum: For AWG 30 up to 22 AWG sizes the maximum insulation gap shall be equal to the outside diameter
(over the insulation) of the wire being used. For larger wire sizes the gap shall not exceed 1.5 mm.
Minimum: There is no minimum gap required except that the conductor wire shall be visible to enable inspection.
10.13.6 Insulation Support
Where the terminal or contact is supplied with insulation supports, the wire insulation shall enter into the support
to the extent that no bare wire is exposed.
10.13.7 Integrity of Crimped Connections
10.13.7.1 Test Interval
The crimp tools and each contact-conductor combination to be used in a production run shall be tested at the
start and at the end of each work shift or production run, whichever is shorter (Requirement). Test results shall be
recorded and maintained for each crimp tool and contact-conductor combination.
10.13.7.2 Number of Test Samples
A minimum of five test samples shall be prepared for each crimp tool and crimp-contact-conductor combination, at
the intervals specified in test intervals
10.13.7.3 Test Method
The crimp contacts shall be placed in a tensile-testing device with appropriate fixtures, and sufficient force shall be
applied to pull the wire out of the assembly or to break the wire or crimped item. The head travel speed of the
tensile device shall be 25.4 +/- 6.3 mm (1.0 +/- .25 in) per minute. The holding surfaces of the tensile device clamp
may be serrated to provide sufficient gripping and holding ability.
10.13.7.4 Required Crimp Strength
The tensile strength of the crimp test sample connections shall be in accordance with Table 10‑8. For those
contact-conductor crimp connections not contained in Table 10‑8, the tensile strength of the crimp connection
shall be no less than 60 percent of the tensile strength of the wire.
104
ISRO SPECIFICATION
ISRO PAX - 300
Issue-5, October 2012
10.13.7.5 Failure Categories
After pulling, the test specimens shall be examined under a microscope to determine the method of conductor
failure. Crimp joint tensile failures will fall into one of the categories shown in Figure 10.38. The crimp tool setting
which produces the maximum number of fray breaks and breaks outside the contact
shall be used for assembly (see Note in Figure 10.38). If multiple settings provide identical tensile strengths for a
crimp joint, the setting selected shall be the one that provides more wire breaks than wire pull- outs.
Figure 10.38 : Crimp Joint Tensile Failure Categories
NOTE:
All categories are acceptable if separation occurs above minimum
tensile strength
NOTE:
Breaks at the entrance of the contact wire barrel, caused by conductor
cutting because the contact is not held squarely in the tester jaws,
shall not be preferred breaks.
10.13.8
NOTE:
Figure 10.38 : Crimp Joint Tensile Failure Categories
Examination of Test Samples
All categories are acceptable if separation occurs above minimum tensile strength.
Each individual test sample shall be inspected to the requirements of this
the observations
recorded
and maintained
(Requirement).
Breaks at the document
entrance of and
the contact
wire barrel, caused
by conductor
cutting because
the contact is not held
Inspection
squarely 10.13.9
in the tester jaws,
shall not be preferred breaks.
10.13.8 Examination of Test Samples
10.13.10
Inspection Prior to Crimping
Each individual test sample shall be inspected to the requirements of this document and the observations recorded
The connectors and the conductor shall be examined prior to insertion of
and maintained (Requirement).
wire under magnification and following defects form rejection criteria:
10.13.9 Inspection
• Any evidence of spotting or film formation (e.g. dark spots, blotches,
10.13.10 Inspection lines)
Prior to Crimping
improperly
processed
dents,
The connectors and •theDamaged
conductor or
shall
be examined
prior to (e.g.
insertion
of bends)
wire under magnification and
•
Cracking
or
clipping
Plating
defects
(e.g.
peeling,
chipping and voids)
following defects form rejection criteria:
• Any evidence of spotting or film formation (e.g. dark spots, blotches, lines)
• Damaged or improperly processed (e.g. dents, bends)
Indian Space Research Organisation, Bangalore
• Cracking
or ISRO
clipping
Plating defects
(e.g. peeling,
and voids)
Issued by
Reliability
Office (ISREL),
ISROchipping
Headquarters
• Improper or damaged marking
105
P a g e | 169
• Unclean able Contamination
• Tarnishing or discoloration of the plating.
• Plating removal or flaking.
• Out-of-roundness of the wire well entrance
• Exposed base metal.
10.13.10.1 Inspection after Crimping
Each crimped contact shall be examined under magnification and shall be rejected if any of the following defects
are observed.
• Nick, cut or damage of the wire strands.
• Reduction in cross section of the wire
• Embedding of insulation into the contact barrel
• Damage (e.g. cracking, bending) to the contact showing improper or over crimping.
• Excess deformation of wire strands
• Voids in wire strands bundle showing under crimping
• Non-visibility of wire strands through the inspection hole in the crimp contact barrel.
10.13.11 Microsectioning of Crimped Pin:
Allowable Contact-Conductor Combinations: The contact-conductor combinations shall be in accordance
with manufacturer’s recommendations. Contacts or conductors shall not be modified .
Figure 10.39 : Example of a typical connector barrel and single wire crimping
Figure 10.39 : Example of a typical connector barrel and single wire crimping
Figure 10.40 : Example of a typical connector barrel and multi-wire crimping
106
The wire contact joint shall have uniform deformation and in case of defects occurring in the joints, the tool setting
shall be checked and if the setting is found to be correct, the tool shall be tested using go-no go gauges.
10.14
Connector assembly
• Connector back shells shall be potted and molded, or use stress relief boots as required,
• The mating surfaces of all unmated connectors shall be protected by covers during storage, handling, and
installation of interconnecting cables and harnesses (Requirement).
10.14.1 Assembly of Crimp-Type Connectors (Including Terminal Junctions)
Crimp contacts are assembled to conductors outside of the connector and are subsequently installed into the
connector body. When a connector is properly assembled, contacts are captured inside the connector. Retaining
clips are one means of securing contacts in place inside connector cavities. When retaining clips are present,
contacts shall be fully seated and locked into place by the clip (Requirement). Improperly seated contacts can “push
back” causing intermittent and open circuits. In all instances, non-metal contact insertion and removal tools shall be
used to prevent damage to connectors, contacts, or conductors.
The installation of unwired contacts into an environmental connector is mandatory for high humidity and moisture
environments and is optional for other applications. Terminal junctions shall not have unwired contacts installed in
unused cavities. Plastic sealing plugs shall be used in all unwired contact cavities of environmental connectors.
Table 10‑8 : Required ultimate axial strength for compactive and dispersive crimped joints
Axial strength (Newton)
Wire barrel
Wire size(AWG)
Silver plated
copper wire
Nickel-plated
copper wire
0
0
2
3210
2450
2800
2200
-
2
2
4
2450
1780
2200
1600
-
4
4
6
1780
1330
1600
1200
-
6
6
8
1330
980
1200
890
-
8
8
1250
1150
-
10
10
12
710
500
-
-
12
12
14
500
320
-
-
107
Silver plated
copper-alloy
wire
16
16
18
20
230
155
90
-
-
20
20
22
24
90
60
-
185
115
60
22
22
24
26
60
-
-
115
60
45
24
24
26
28
-
-
60
45
30
26
26
28
-
-
45
30
28
28
-
-
30
NOTE 1 Wire barrel size < 6 AWG Tools are without adjustable setting.
NOTE 2 Wire barrel sizes >8 AWG Tools are generally with adjustable settings which permit
optimized crimped joints having higher axial strengths.
10.15
Interconnecting harness and cable cleaning
10.15.1 General
Interconnecting cable and harness assemblies shall be clean and free of contamination prior to installation in the
mission hardware system.
10.15.2 Cleaning the Harness Assembly
Particles and debris shall be cleaned from the harness or cable assembly by vacuum-removal methods. Brushing with
solvent shall be used as required to remove other contamination. Only solvents as per para 5.4.1 shall be used .
10.15.3 Cleaning Harness Connectors
The following cleaning procedures shall be used with connectors:
For solder-type connectors, flux rundown into the mating part of socket contacts shall be removed . Solvent
cleaning by brushing may be used. Contact surfaces of pins, sockets, and connector bodies shall be free of flux
residue (see Figure 10.40), solder splash, metal flakes, moisture, and other contaminants that may jeopardize the
integrity of the connector system .
Crimp-type multipin and coaxial electrical connectors shall be solvent-cleaned by brushing before assembly to the
harness or unit cable. Contact surfaces of pins and sockets and the interior surfaces of the connector shall be free
of contaminants .
The internal surfaces of dust covers and connector covers shall be cleaned by solvent brushing before the covers
are fitted onto cleaned connectors.
108
If necessary, connectors that were subjected to frequent mating and demating operations during fabrication and test
shall receive additional cleaning prior to the final mating. Visual examination of the contact surfaces of connectors
shall not reveal the presence of contaminants such as metal flakes or large dust particles .
10.15.4 Cleaning Coaxial Connectors (Assembled)
Coaxial connectors shall not have accumulated contaminants such as metal flakes, dirt, moisture, and other foreign
materials . The connector interface shall be cleaned by brushing with solvent, vacuum procedures, or a combination
thereof until the contaminants have been removed .
Figure 10.41 :Visual Examination Inside the Socket Contact for Flux Residue
Figure 10.41
: Visual
10.15.5 Harness
handling
andExamination
protection Inside the Socket Contact for Flux Residue
10.15.5.1 General
Interconnecting harnesses and cables often receive their maximum stresses when they are moved, handled, or
installed in their permanent locations. Harnesses shall be handled with considerable care and attention .
10.15.6 Interconnecting Harness and Cable Storage Protection
Harnesses and cables shall be protected during fabrication as follows:
• Keep a large harness mounted on its own wiring board until final inspection .
• Protect all connectors, cables, and harnesses not on a wiring board or fixture by wrapping individually in bubble
wrap or an approved clean cushioning material and placing them in a sealed antistatic bag or equivalent
• Harnesses that are not being worked on shall have appropriate protection.
• Protect all unmated connectors with clean dust covers (connector caps).
• Wiring harnesses may either be stored on the wiring board or otherwise protected .
• All unmated connectors (including test equipment) shall be protected with clean dust covers (connector
caps) when not in use . After the cleanliness of the connector has been verified visually, it shall be protected
with a clean dust cover until it is ready for final mating
10.15.7 Connector mating
10.15.7.1 General
Although most electrical connectors are considered to be durable, each of them has a finite life. During testing and
system checkout, certain connectors may be subject to frequent mating and demating. When this situation exists,
wear and potential damage can be reduced by the use of ”connector-savers”. Connector-savers transfer the wear
109
from the flight connector to nonflight jumper harness connectors. It also prevents uncontrolled (and possibly
damaged) test equipment connectors from mating directly with the cable or harness assembly connectors. Any
connector, including connector savers, mating with flight hardware shall be in accordance with Approved Fabrication
sequence.
10.15.7.2 Connector Mating and Demating
The following practices and precautions shall be exercised in mating and demating connectors:
Prior to connector mate/demate operations, verify that the circuit has been de-energized
Examine connectors for contamination, pin, and shell damage prior to mating .
All flight qualified, ac/dc power interface and test equipment connectors that mate with flight and support equipment
connectors shall be protected against damage and contamination during mating and demating operations, and when
they are in a demated condition.
• Blind mating shall be avoided.
• Caution shall be applied to mating and demating operations to preclude damage to connectors. In some cases
a demating tool may be utilized
• Harness connectors mated to test tees or breakout boxes shall be provided with stress relief to restrict
flexing of connectors and cables
• Mate/demate operations between the flight hardware, support equipment connectors, system test equipment,
and also in final assembly shall be performed by authorized personnel only.
• The use of connector savers is recommended. A connector saver can be a short harness jumper that has a
mating interface connector to engage the unit. The other end of the harness has the same interface as the
unit. Connector savers shall be clearly marked. Connector savers shall meet the same requirements as a flight
connector .
• Interfacial seals, which are not bonded to the connector shall be examined and, if necessary, replaced with new,
clean seals prior to final mating.
• When required, a log of mate and demate operations and a bent pin log shall be kept for flight connectors .
• Flight connectors shall be torqued as specified .
• Electrostatic discharge (ESD) protective caps shall be installed on exposed connectors of harnesses that are
attached to ESDS hardware.
10.15.7.3 Coaxial Connector Mating
The final mating of coaxial connectors shall be done using the specified torque values. When mating coaxial
connectors, the cable assemblies shall be held such that only the connector coupling is rotated.
10.16
Testing and inspection
10.16.1 General
Completed interconnecting harnesses and cables shall be verified as meeting all applicable functional, electrical, and
design requirements. Visual examination and electrical testing shall be performed as required . Interconnecting cable
and harness assemblies shall be tested for point-to-point electrical continuity .
110
10.16.2
Wet Probe Testing
ISRO
SPECIFICATION
ISRO PAX - 300
Issue-5, October 2012
All the space craft harness shall be subjected to the wet probe test as per the procedure given below,
1.
Wet probe test shall be carried out on the harness after completion of one-end wiring and shield formation
electrical
connection
Megger
as shown
in the following sketch. One
to locate
any damage
or peeling ofwith
insulation
material
due to handling.
2.
3.
of theconnector,
test probe
of Megger
shall
be kept
immersed
alcohol.
One shorting
compatible
with the
harness
multipin
connectorin
shall
be prepared and connected
• harness
Apply connector.
100V from Megger across two probes for 1minutes and measure
to the
9
It placed
shall inbe
in the alcohol
order and
of connect
10 _ or
If connection
any damage
or
Harnessresistance.
bundle shall be
isopropyl
themore.
electrical
with Megger
as
peeling
of insulation
material
willprobe of Megger shall be kept immersed in alcohol.
shown in
the following
sketch. One
of the test
5
shows
a loweracross
resistance
in the
order
of 10
as offered
by alcohol.
• Apply •100V
from Megger
two probes
for one
minute
and _,
measure
resistance.
It shall be in the order
9
of 10 ohm or more. If any damage or peeling of insulation, material will show a lower resistance, in the order
of 105 ohm, as offered by alcohol.
10.17
Quality assurance provisions
Workmanship
shall
be of a levelprovisions
of quality adequate to assure that the processed products meet the performance
10.17
Quality
assurance
requirements of the subsystems/systems and criteria described herein .
Workmanship shall be of a level of quality adequate to assure that the processed
Inspection
for acceptability
be performed.
Conductors
be physically disturbed
to criteria
aid inspection.
products
meet the shall
performance
requirements
ofshall
the not
subsystems/systems
and
described
Inspections
shall be herein
made at. appropriate points during assembly, at the completion of assembly, and after installation
to establish that the appropriate requirements have been met. Inspection may include visual inspection, mechanical
Inspection for acceptability shall be performed. Conductors shall not be
physically disturbed to aid inspection. Inspections shall be made at appropriate
specified
on theduring
applicable
planning documents.
points
assembly,
at the completion of assembly, and after installation to
establish that the appropriate requirements have been met. Inspection may include
10.17.1 Method of Inspection.
visual inspection, mechanical measurements, electrical testing, and other methods
100% Visual
inspectionnecessary.
of all connections
shall be performed
in-process
and shall
after final
as appropriate.
as deemed
Inspection
and testing
points
be assembly,
specified
on the
applicable planning documents.
measurements, electrical testing, and other methods as deemed necessary. Inspection and testing points shall be
Quality Assurance. Quality Assurance has the responsibility to verify compliance with all requirements of this
document. Specific functions are as follows:
10.17.1
Method of Inspection.
• Verify that all practices, inspections, and measurements specified by this document have been performed.
P a g e | 180
• Verify that all personnel who assemble or inspect hardware in accordance with this document have been
Indian
Space
trained
andResearch
certified . Organisation, Bangalore
Issued by ISRO Reliability Office (ISREL), ISRO Headquarters
111
• In-process surveillance of all assembly operations to verify that all processes and procedures implementing
the requirements of this document are current, approved, adequate, and being properly implemented.
• Verify that contacts, connectors, and conductors have been inspected prior to being assembled.
• Verify and monitor that the facility cleanliness, environmental conditions, and lighting requirements of para 3
this standard are being met.
• Verify and monitor that procedures defining cleaning, drying, handling, and packaging are followed.
• Verify that all torque requirements are met.
• Inspect that crimp terminations are in accordance with para 10.17.3.3.3 of this Standard.
• Verify installation processes and acceptance/rejection criteria for solder sleeve termination devices were
implemented.
• Verify that other processes such as potting and molding, necessary to fabricate a cable or harness, are defined
by the fabrication document and approved.
10.17.2 Magnification Aids
Visual inspection shall be aided by magnification between 10X and 40X. Additional magnification shall be used, as
necessary, to resolve suspected anomalies or defects.
10.17.3 Documentation Verification
Quality Audit Representatives shall verify that all required documentation is current and approved.The documentation
shall include:
10.17.3.1 Records
•
•
•
•
•
•
•
•
•
•
•
•
Results of the visual examination.
Evidence of operator and inspector certification
Production and inspection tool calibration.
Connector mate/de-mate log and bent pin log
Cabling and harnessing program
Training and certification program
Tooling and equipment operation
Calibration system
Electrostatic Discharge Control Program
In-process storage and handling
Compounds and special design requirements used for potting of lacing knots
Acceptance testing for cable and harness assemblies.
• Traceability
10.17.3.2 Acceptance Criteria
10.17.3.2.1 Stripped Conductor
• The insulation shall be uniform and shall exhibit no damage except slight discoloration when thermal strippers
have been used.
• The conductor shall be clean and free from damage. Strands shall be twisted together in the original lay, or as
nearly as possible to the original lay .
• Shield strands shall be clean. The number of nicked shield strands shall not exceed 10 percent of the total
number of strands.
• Flat conductors shall be clean and free of damage.
112
10.17.3.2.2 Shield Terminations
• Shield terminations shall be free of projecting strands
• The wire insulation and shrink sleeving shall be free of punctures, cuts, and nicks
• Metal ferrules are tightly and symmetrically crimped.
• The solder inside the solder sleeve shall show evidence of proper flow and fillet to the ground wire and shield
braid
• The solder sleeve may exhibit discoloration.
• The insulation sleeving shall be uniformly shrunk and provide proper covering of the termination
• Solder sleeves are as specified in fabrication documentation.
• The solder fillets along the interfaces shall have a smooth, concave appearance
10.17.3.2.3 Crimped Connections
• Contact deformed only by tool indentations.
• Crimp indents properly located in the correct area of the contact.
• Wire strands visible in inspection hole of barrel.
• Metal ferrules tightly and symmetrically crimped.
• The clearance between the wire insulation termination and the crimp contact barrel is between 0.25mm (0.01
in) to 0.75mm (0.03 in) for wire sizes AWG 20 and smaller, and 0.25mm (0.01 in) to 1.25mm (0.05 in) for wire
sizes AWG 18 and larger.
10.17.3.2.4 Cable and Harness Ties
• Properly tied clove hitch and square or other non-slip knot.
• Correct and uniform spacing of ties for bundle size.
• Correct material as specified on the engineering documentation.
• Lacing terminated with a closing stitch and ends trimmed.
• No damage to or contaminants on the tie or adjacent wiring.
• Strap or tie properly secures wire bundle.
10.17.3.2.5 Cable and Harness Assemblies
• Connectors are not damaged.
• Pin/sockets meet retention force requirements and are not damaged.
• Even distribution of tension throughout cable and harness.
• Length of wire twist is between 8 and 16 times the outer diameter of the harness.
• Cable and harness ties are properly spaced.
• Clamps are properly placed.
• Cable and harness are not distorted by ties or clamps.
• Minimum crossover.
• Proper bend radius of breakouts.
• Proper identification.
• All exposed metal is covered as defined on the applicable drawing.
• Heat shrinkable sleeving or nonconductive thread extends at least 5.1 mm (0.2 inch) beyond exposed metal.
• Sleeving is uniformly shrunk.
• Sleeving is free of cracks, punctures, and charred or burned areas.
• Location of shield terminations on wire as per engineering documentation.
113
•
•
•
•
•
•
•
•
•
Braid is terminated properly.
Cable or harness dimensions and configurations are in accordance with engineering documentation.
Cable or harness is clean.
Unused wires properly terminated.
Routing does not expose cables and harnesses to abrasion, cold flow, or cut-through.
Spiral sleeving with plastic straps are installed correctly.
Protective separator applied over wire bundle beneath metal braid shielding, if required.
Connector back shells and strain relief clamps are tightened as specified by engineering documentation.
High strength copper alloy is used for AWG 24 and smaller conductors.
• Proper handling and protection.
10.17.3.2.6 Coaxial Cables
•
•
•
•
Proper strip length and assembly of center conductor into contact.
Proper securing of outer conductor.
Center contact location meets requirements for proper mating.
Mating surfaces and coupling means are undamaged.
• Connector back shells and strain relief clamps are tightened as specified by the engineering documentation.
10.17.3.2.7 Solder Sleeves
• The solder shall be visible through the insulation sleeving
.
• The solder fillets along the interfaces shall have a smooth, concave appearance
• Solder sleeves shall not be damaged . Slight discoloration resulting from the heating process is permissible.
• Solder sleeves shall cover all exposed metal in the spliced area
• There shall be no protruding wire strands from under or through solder sleeves
10.17.3.3 Rejection Criteria
The following are unsatisfactory conditions and shall be cause for rejection:
10.17.3.3.1 Stripped Conductor
• Damaged, crushed, cut, or charred insulation.
• Nicked, gouged, damaged, or severed conductors.
• Frayed conductor strands.
• Severed shield braid strands.
10.17.3.3.2 Shield Terminations
• Loose or projecting strands.
• Nicked shield strands exceeding 10% of the total number of strands.
• Wire insulation with cuts, punctures, or crushing.
• Metal ferrules crimped with improper alignment.
• Cracked, charred, or split insulation sleeving.
• Cracked or fractured solder.
• Insufficient solder or poor wetting.
• Improper sleeving coverage.
114
10.17.3.3.3 Crimped Connections
• Metal ferrules crimped with improper alignment.
• Cracks in crimp barrel.
• Bird caging of conductor.
• Wire strands not visible in inspection hole.
• Peeling or flaking of plating on contact.
• Damaged or deformed crimp contact.
• Crimp indents not located in the correct area on the contact.
• Tarnished, corroded, or contaminated crimp contact.
• Improper insulation clearance.
• Insulation whiskers that extend into the crimp barrel.
10.17.3.3.4 Cable and Harness Ties
• Improperly laced ties.
• Incorrect material.
• Wire bundle damaged or deformed by tie.
• Loose ties.
• Ends not trimmed.
• Damaged or contaminated ties or wiring.
• Incorrect spacing of ties for bundle size.
• Improper handling or protection.
10.17.3.3.5 Cable and Harness Assemblies
• Projecting strands on shield terminations.
• Wire insulation with cuts, punctures, or crushing.
• Metal ferrules crimped with improper alignment.
• Cracked, charred, or split insulation sleeving.
• Improper sleeving coverage.
• Bird caging of conductor.
• Peeling or flaking of plating on connectors or pins/sockets.
• Damaged or deformed contacts.
• Damaged insulation in excess of slight discoloration.
• Tarnished, corroded, or contaminated contact.
10.17.3.3.6 Coaxial Cables
• Improper strip length and incorrect assembly of center conductor into contact.
• Improper securing of outer conductor.
• Center contact location does not meet requirements for proper mating.
• Damaged mating surfaces and coupling means.
• Connector back shells and strain relief clamps are not tightened as specified by the engineering
documentation.
115
10.17.3.3.7 Solder Sleeves
• The solder connection is not visible through the insulation sleeving.
• Solder fillet(s) having an uneven and broken flow and/or a convex appearance.
• Solder fillet not visible at the interfaces of the stranded wire to shield braid, or stranded wire to stranded
wire.
• Solder fillet is along only one side of the stranded wire to shield braid, or stranded wire to stranded wire
interface.
• Solder sleeves do not cover all the metal exposed by the splice installation.
• Solder sleeves are split, burned, or damaged.
• Wire strands protrude from under or through solder sleeves.
10.18
Wire visual aids and illustrations
10.18.1 Wiring: connectors, cabling, and harnessing - wire dress to connectors
PREFERRED
• All wires dressed with even bends to terminate
in solder cups.
NONCONFORMING
• End wire on the right is taut with no stress
relief.
10.18.2 Wiring: connectors, cabling, and harnessing - stress relief shrinkable sleeving on
solder cups
PREFERRED
• Sleeving on wire covers solder cup and
provides support over wire insulation Sleeving
is fully shrunk over the insulation, wire, and
solder cup.
• Sleeving is sufficiently rigid to provide stress
relief and prevent wire bending at the solder
joint.
116
NONCONFORMING
• The sleeving is not fully shrunk and permits
wire bending and flexing at the joint
NONCONFORMING
• The sleeving is not fully shrunk
NONCONFORMING
• Sleeving does not grip at least half of the cup
barrel below the opening
10.18.3 Wiring: connectors, cabling, and harnessing, wire preparation, thermal stripping
PREFERRED
• Insulation has been removed from the
conductor with no visible damage to the wire
strands.
• Normal lay of wire, if disturbed, shall be retwisted to the original wire lay.
117
ACCEPTABLE
• Minor burnishing and indentation; base metal
not exposed
NONCONFORMING
• Wire strands are gouged and scraped exposing
base metal.
• Original lay of stranding has been straightened
and distorted
NONCONFORMING
• Wire strands show evidence of a nicked
condition caused by stripper blades
10.18.4 Wire preparation: mechanical stripping
ACCEPTABLE
• Wire lay undisturbed; no visible damage to
wire strands.
UNACCEPTABLE
• Wire strands combed straight. If retwisted to
original lay, may be acceptable
UNACCEPTABLE
• Excessive retwist
118
UNACCEPTABLE
• Wire strands re-twisted in excess of normal
lay and overlapped
10.18.5 Wiring: connectors, cabling, and harnessing, wire preparation, thermal stripping
PREFERRED
• Insulation stripped by thermal stripping shall
have minimum edge flash with no damage to
the wire strands
ACCEPTABLE
• Mechanical or thermal stripped insulation
irregularity is acceptable if it does not exceed
1/4 of the outside diameter of the wire with
insulation
ACCEPTABLE MINIMUM
• Edge flash, due to improper stripping, should
not exceed 1/4 of the outside diameter of the
wire with insulation
NON CONFORMING
• Burned or charred insulation, as shown, is the
result of improper application of heat
10.18.6 Wiring: connectors, cabling, and harnessing, wire preparation, tinning stranded
conductors
PREFERRED
• Complete wetting of the tinned area has
resulted in a bright, thin, and even tinning of
the strands
• Tinning has reached insulation, but wicking is
minimal
119
ACCEPTABLE
• Traces of solder wicking under insulation,
but the contour of the stranding is easily
discernible
ACCEPTABLE
• Length of tinning is determined by type of
termination; however, it should be sufficient
to prevent separation of strands when wire is
wrapped around a terminal
10.18.7 Wiring: connectors, cabling, and harnessing - installation of straps
ACCEPTABLE.
• Conductors secured with a plastic strap.
• When tightened correctly, strap will not
move laterally along the bundle under normal
handling but can be rotated in place
UNACCEPTABLE
• Strap is too tight and is deforming the
insulation on the wire.
UNACCEPTABLE
• Strap is too loose and will slip easily along the
bundle with normal handling
120
10.18.8 Crimps: insulation clearance
MINIMUM CONDUCTOR
EXPOSURE
• Insulation terminates 0.010 in. minimum from
contact crimp barrel
MAXIMUM CONDUCTOR
EXPOSURE
• Amount of exposed bare wire between
the insulation and the contact crimp barrel
does not exceed 0.03 inch maximum for
No. 20 AWG wire and smaller, and 0.05 inch
maximum for No. 18 AWG wire and larger
10.18.9 Crimps: Acceptable and Unacceptable
ACCEPTABLE
• Care should be taken when seating contacts
in the crimping tool. The tool indentors
should crimp the contact midway between
the shoulder of the insulation support and
the inspection hole. The wire is visible in the
inspection hole
UNACCEPTABLE
• If the wire is not stripped back far enough
or incorrectly seated in the contact, the wire
will not be visible in the inspection hole, as
shown
121
UNACCEPTABLE
• Failure to properly seat contact in crimping
die, or use of incorrect crimping tool will
result in improperly crimped contacts.
Crimping over the radius of the shoulder as
shown
UNACCEPTABLE
• Failure to properly seat contact in crimping
die, or use of incorrect crimping tool will
result in improperly crimped contacts.
Crimping over the inspection hole as shown
10.19
Critical problems in coaxial cable assembly
Because of poor connector design, faulty assembly instructions, or wrong choice of materials, certain types of coaxial
cable assembly failures occur frequently. Problem areas are as follows:
Plastic Jacket Layer in the Compression System. Certain manufacturers’ RF-connector designs or assembly
instructions allow the jacket to be in the clamping system. For example, the metal clamp nut presses against the teflon
cable jacket, which presses against the metal braid, which presses against the metal cable barrel of the connector.
The problem encountered with this arrangement is that after torquing, the teflon jacket cold-flows, and the connection
becomes loose. Intermittent circuits and system failure can result. Either this type of connector should not be used,
or the plastic jacket should be trimmed back so that only metal-to-metal compression exists (see Figure 10.42). If
the connector design is such that satisfactory metal-to- metal compression cannot be achieved after torquing, the
connector should not be used.
Inadequate Center Conductor to Center Contact Solder Joint. Certain manufacturers recommend that the center
conductor be tinned, and that this tinned conductor be placed in the center contact. Then, the solder joint between
the center conductor and center contact is made by reflowing the tinning in the center contact. Invariably, this
makes an insufficient solder joint (see Figure 10.43). A sufficient solder joint is made by placing a small length of
rosin core solder in the contact wire well, e.g., 3.17mm (0.125 inch) length, 0.38 mm (0.015 inch) diameter. The
122
center conductor is inserted into the wire well and the contact is heated to melt the solder and position the contact
on the center conductor.
Breakage of Stress-Relief Sleeving. In assemblies where shrinkable sleeving is used to provide stress relief from a
connector ferrule to the cable, there is often a major transition in diameter as shown in Figure 10.74. If MIL-I23053/8 sleeving is used for stress relief, it often cracks at the large diameter of the transition. The use of MIL-I23053/8 sleeving for these applications should be avoided.
Figure 10.42 : Illustration of Proper trim back of Jacket to Isolate it from the Clamping Sy stem
123
Figure 10.43 : Broken Solder Joint Caused by Insufficient Solder Fill
Figure 10.43 : Broken Solder Joint Caused by Insufficient Solder Fill
Figure 10.44 : Problem Point for Kynar Stress Relief Sleeving
Figure 10.44 : Figure B-3. Problem Point for Kynar Stress Relief Sleeving
124
11 SEMI-RIGID CABLE ASSEMBLY
11.1
Introduction
This Chapter describes the general guidelines to be followed during the assembly of semi rigid cable with solderable
& crimpable connectors. The inspection requirements at various stages of assembly are also covered.
Also this section defines the technical requirements and quality assurance provisions for the assembly and mounting
of high reliability, radio­frequency (RF) coaxial cable interconnections for use as transmission lines in spacecraft and
associated subsystems.
These cable assemblies give greater shielding effectiveness; lower VSWR, reduced phase length variation over
temperature variations & smaller insertion loss for given size when compared with flexible braided cable assemblies.
In general, these assemblies are designed for low­loss, stable operation from the relatively low frequencies through
the higher frequencies in the microwave regions.
However, in order to ensure the reliability required for space hardware, it is essential to take extreme care in
design, fabrication and integration of semi rigid cable assemblies in the spacecraft systems.
11.2
Principles of Reliable Soldered or Crimped Semi-Rigid Cable Connections
Reliable soldered or crimped connections result from proper design, control of tools, materials and work environments
and careful workmanship.
The basic design concept, adherence to which ensures reliable connections and prevents joint failure, are:
1.
Avoidance of dimensional mismatch between the coaxial cable assembly and the units being connected;
i.e. not forcing the semi­rigid cable assembly into position and thereby cracking or pre­stressing one of the
joints.
2.
Use of cable end connectors with retractable (non­captive) coupling nuts; after completion of mounting,
the coaxial cable assembly is not in a state of tension resulting from axial movement when the connectors
are threaded together.
3.
Minimizing the internal stresses on the soldered or crimped connections resulting from exposure to
thermal cycling. The thermal coefficient of expansion of the dielectric is about ten (10) times that of
copper and in service this can introduce a tensile stress on the joint.
4.
The various assembly and mounting processes are covered by quality control inspection steps.
Material & Tools
11.3
Materials
All the materials like solder, liquid flux, cleaning solvents, tissue paper, semi rigid cable, connectors etc. shall be from
approved material list & shall be used only after approval/certification by QA for use after incoming inspection.
Preferably only one type solder shall be used for soldering, de-golding & tinning
125
Material traceability records like lot or batch code Nos. of each material or issue Nos. of Bonded Store, cable spool
Nos. etc. shall be maintained in the history records of each cable assembly.
1.
The fabricator shall use solder ribbon, wire and preforms, flux and cleaning solvents provided that the
alloy and flux conform to the requirements of para 5.
2.
The facility shall procure semi­rigid cables in conformance with the detailed requirements of MIL-C17G(3) SUP1. The selection of a particular coaxial cable involves consideration of the specific electrical,
mechanical and environmental requirements of the project.
3.
The facility / user shall procure semi­rigid cable with outer conductor diameter standardized as either
0.085 inches or 0.141 inches (±0,001 inches) & 0.25 inches and fabricated from copper.
4. Facility shall use only approved connectors for assembling solder or crimp type semi­rigid cables.
11.4
Tools
The fabrication facility shall only use the equipment, tools, and processes for the assembly of the cables and connectors
that are designed to avoid damage or degradation of the cables and connectors.
11.4.1
1.
2.
3.
4.
5.
Fabrication tool kits from following manufacturer’s are available.
SEALECTRO
RADIAL
OMNI SPECTRA
SEVEN ASSOCIATE.
OTHERS
The preferred combination of tools, application wise, may be selected by fabrication facility and shall be approved by
QA. The part No. of the tool shall be checked from recommended tool list before actual use. In case of special tool
requirement from other manufacturer for any operation compatibility of the same with above tool kit being used
shall be established/verified. The tools shall be checked for finishes, damages if any prior to use. Periodic inspection
shall be done for every tool kit by QC.
11.4.2
1.
Cutting Tools
The fabricator shall use at least the following cutting tools for the preparation of the semi­rigid cable:
a. Jeweller’s saws having fine teeth, preferably 0.28 mm – 0.33 mm blade.
b. Single edged razor blades
c. Wire cutters.
2.
The fabricator shall use the jeweller’s saw together with a cable clamping device. An example of such a
cable clamping device is shown in Figure 11‑1
3.
The fabricator shall cut the dielectric and inner conductor with a tool that produces a clean, smooth cut
surface along the entire cutting edge.
4.
The fabricator shall not perform any twisting action during this cutting operation.
11.4.3
Cable Forming Tools
1.
The fabricator shall use bending jigs to form the cable to predetermined shapes as identified by the
engineering drawing. An example of such a bending jig is shown in Figure 11‑2.
2.
The fabricator shall use roller sizes consistent with each cable diameter.
126
3
The fabricator shall use this equipment in such a way that it does not introduce dents, nicks, wrinkles or
cracks in the cable outer conductor.
11.4.4
Cable Stripping and Dressing Tools
1. The fabricator shall use cable stripping and dressing tools in such a way that they do not twist, ring, nick, or
score the underlying material surface.
2. The fabrication facility shall perform either periodic calibration or sample evaluation during a production
run.
11.4.5
Heat Treatment Chamber
1.
The facility shall use thermal cycling chamber capable of maintaining temperatures between -40 °C and
+100 °C
2.
The operator/inspector shall calibrate the working zone to within ±5 °C.
11.4.6
1.
2.
11.4.7
Soldering Equipment
The fabrication facility shall accomplish one of the following soldering methods
a.
Hand Soldering
b.
Using a resistance heating unit
c.
Other contact heat source.
When non­contact heat sources are utilized, the fabrication facility shall set up, operate and demonstrate
to the satisfaction of QA that the particular method and schedule produces joints of an acceptable
standard.
Crimping Equipment
The fabricator shall use the settings recommended by the tool manufacturer as a guide. This is necessary since
manual crimping tools are available; they are custom designed and applicable only for particular connector shells.
11.5
Semi Rigid Cable Assembly Process
11.5.1
General
Fabricator shall ensure that the delivered coaxial cables are in the form of straight lengths. The initial preparation is
similar for each cable diameter and each connector type and whether joining is by soldering or crimping.
Semi rigid cable assembly process consists of following in general:
1.
Cable preparation like straightening, cutting, bending, dielectric stripping, centre conductor end forming,
tinning etc.
2.
Cable preconditioning to relive stresses induced in due to shipping, storage & in above processes.
3.
Preliminary compatibility check after cable bending.
4.
Connector soldering.
5.
Preconditioning to relive stresses introduced in soldering process.
6.
Inspection and rework at each process steps.
7.
Compatibility check with actual packages.
The detailed process flow charts for all cases of connector assembly in-general are given in 11.26
127
11.5.2
Cable Straightening
Usually the cables are available in coil forms for storage & shipment. While uncoiling, handling & straightening of
cable great care must be taken to avoid introducing stresses in the cable.
Straightening of the cable in case of coiled cable rolls may be carried out in steps of Unit lengths required by
following methods.
1. Use of conventional roller machine having at least 3 sets of rollers. Manually with the help of rollers with
grooves of appropriate size & guide blocks.
2. Manually using cable-bending tools carefully.
3. Manually by hand with slight finger pressure, whenever required. The flat surface plate may be used for visual
judgment for the straightness.
4. If cables available in the straight length then handle carefully during process to avoid dents nicks etc
CAUTIONS:
1. Hammer or similar type tool shall not be used for straightening.
2. The cable shall not be twisted while straightening or bending.
11.6
Cable Assembly Drawing
The cable routing drawing shall be made with reference to the template fabricated as described earlier and with
other package design details PDR minutes etc.
The dimensions in the drawing will be approximate estimates & shall be finalized only after the cable assembly
compatibility approvals, electrical testing & final acceptance. The sample cable assembly drawings are illustrated in
listed in para 11.27
11.7
Cable Cutting
1. Cable cutting may be carried out by one of following tools/aids recommended by the Cable fabrication
facility
a.
Power driven carborundum wheel.
b.
Silica impregnated disc (elastic wheel) at high speed with controlled feed.
c.
A jeweller’s saw with assembly jig. & vice.
d.
Carbide saw.
2. A small excess length of 10 mm than that required for actual job shall be kept for final trimming for length
adjustments, rework, allow for bending, preconditioning and end dressing etc.
3. The fabricator shall hold the cable in a special fixture and cut it to the initial oversize length using the jeweller’s
saw. Such as fixture is illustrated in following Figure.
4. The fabricator shall not over tighten the special fixture. This is to avoid damage to the cable.
5. The fabricator shall debur and examine the cut end.
128
Clamp screws
Cable
Cable size designators
Saw blade in slot
Figure 11.1 :Typical cable cut­off fixture
Figure 11.1 : Typical cable cut-off fixture
CAUTION:
1. Cable cutting using fluid cooling or lubrication is prohibited to prevent possible wicking of fluid/lubricant into
the cable through ends ports.
2. The cable shall not be bent or moved or twisted from its axial direction while cutting.
11.8
Preconditioning Heat Treatment
1. The fabricator shall achieve core stress relief by preconditioning each cable before it becomes a cable
assembly.
2. The fabricator shall place the entire cable in the thermal cycling arrangement.
3. The rate of change of temperature shall not exceed 2 °C per minute. Recommendations for dealing with special
requirements (e.g. higher operating temperature extremes) can be obtained from cable manufacturers.
11.9
Cable Templates
Cable template is simulation of cable bending on a aluminium solid conductor of diameter equivalent to actual
cable diameter. The template is useful for better visualization & approximation for cable drawing preparation.
This may be used as a reference while actual cable bending. The cable template shall be fabricated with actual package
or dummy packages equivalent to actual package mounted in the final assembly configuration / condition. The
equivalence of dummy package with actual package must be assured prior to cable bending.
11.10
Cable Bending
Each bend of semi rigid cable shall be as per approved drawing or as per approved template.The cable bending shall
be carried out with manufacturer’s recommended bending tools only. For multiple/complex bending requirements
combination of tools may be used.
129
11.11
Cable Bending General Requirements
1. The total number of bends shall be kept minimum and preferably in two planes wherever possible
to minimize overall length & to avoid stresses while mating / de-mating. Over all integration aspects,
accessibility for assembly & disassembly shall be kept in mind.
2. While designing cable bend radius and the type of bend following points shall be considered
a.
PDR recommendations
b.
Minimum bend radius recommended by manufacturer for a particular type of cable shall be assured.
c.
Bend radius dimension selected shall be available in the bending tool/rollers.
d.
Distance at which support shall be available in the package design.
Minimum bend radius recommended by cable manufacturers for commonly used cables are as given for design
purpose.
Table 11‑1: Cable diameter and bend radius
CABLE DIAMETER
MIN. INSIDE BEND RADIUS
0.085”(2.16mm)
0.125”(3.175mm)
0.141”(3.58mm)
0.25”(6.36mm)
0.251”(6.38mm)
0.375”(9.525mm)
0.325”(8.26mm)
0.75”(9.08mm)
3. A minimum 3 mm straight length of cable shall be maintained from connector & cable interface outside the
connector body before any cable bend starts.
4. Stress relief bends shall be provided for all cable assemblies especially near connector termination ports.
This shall take care of slight mismatch possibility because of cumulative tolerances involved in subsystem
integration & also avoid stress on connector solder joint while mating. This stress relief helps in preventing
cable or solder joint failure during vibration and thermal expansion.
5. Slight adjustment of bend may be done to take care of slight mismatch error (2 to 5 mm) at termination
alignment purpose after phase – III preconditioning. Care shall be taken that the cable shall be held
in binding fixture during bend adjustment stress shall not come on solder joint while adjustment.
6. While giving dimension of the cable assembly in the drawing the length shall be specified from the respective
connector’s Interface Reference Plane (IRP) in case of straight connectors & from end of centre of solder
post in case of right angle connectors.
7. The types of bend s and routings shall be as per approved cable assembly drawings & shall be fabricated
on actual package or equivalent dummy package.
NOTE: Para 11.27 illustrates some of the typical stress relief bends in semi rigid cable assemblies.
11.11.1 Cable Bending Tools & Aids
The cable bending shall be done by manufacturers recommended set of tools only. The tools type may be one or
combination of the following types.
1. Hand held mandrel & clamp set with set of rollers machine for the particular cable diameter.
2. Temporary tool set up using standard rollers, blocks, clamps etc. Mounted on magnetic block. This suited for
smaller diameter cables.
130
3. Dedicated tooling or jigs specially designed for precision and/or for complex cable forms with compound
angles. The cable is formed by hand or mandrel.
CAUTION:
The surface finishing of the tools in the cable captivation area shall be smooth, free of crack, chips, projections
sharp edges etc. Periodic checks shall be done on the tools for the same.
11.11.2 Cable Bending Procedure
The bending procedure using tools identified in Figure 11.2 is illustrated for example.
1. Select the mandrel such that the groove used for guiding the cable shall be slightly larger than outside
diameter of the cable.
2. Check that the groove has smooth surface throughout the circumferential length of the roller.
3. Ensure that cable is completely captivated in the guide at the tangent point of the bend.
4. The mandrel shall of slightly smaller radius than the specified bend radius. So that the cable shall have slight
amount of ‘spring back’. Usually larger the bend radius greater is the spring back.
5. Apply appropriate & controlled pressure while bending the cable along the groove. If wrinkles starts developing
at the inside radius of cable conductor material increase the pressure & if blister starts developing
on the outer conductor decrease the pressure. To get proper judgment of pressure application trial
fabrication may done on dummy cables.
6. Bend slowly, event & continuously until the required angle of bend is achieved.
7. All cables shall be formed to the required shape dimensions before cable preconditioning using a bending jig.
Roller for bend radii
Cable stop
Figure 11.2 :Typical cable forming tool
Figure
11.2 : Typical
forming
tool
1. The fabricator
shall perform
only onecable
bending
operation
to form each shape.
2. The fabricator shall not make attempts to reshape a bent cable.
3. The fabricator shall establish design rules with minimum bend radii as given in Error! Reference source
not found..
4. Each finished cable end shall have a minimum straight length of cable to allow for clearance during the
assembly and mounting operations.
5. The straight length shall be greater than 10 mm for 0.085 diameter cable.
6. The straight length shall be greater than 20 mm for 0.141 diameter cable.
7. The fabricator shall prevent wrinkling or cracking when forming the cable.
8. Fabricator shall apply a slow, even and continuous pressure when bending of the cable.
131
11.12
Cable Assembly Support Requirements
The support requirements of the semi rigid cable bending design in initial stage itself considering the integration
aspects with other subsystems. However additional support may be added during actual fabrication if required.
In general the cable assembly shall be supported.
1. In the plane of running length at every 100-150mm straight length.
2. Before the stress relief bend provided near terminations but on straight portion of the cable & min 5 mm away
from the stress relief bend end.
3. Near to the connecter terminator or before turning point of cable assembly in case where as per assembly
sequence it is necessary to connect connecter on one end & then the cable has to run in different planes
before mating at other end. This is to take care of stresses involved on cable termination while handing.
Saddles types and cable ties shall be used as per the approved material list only.The tieing location on the saddle
shall also be specified in drawings, as a note.
11.13
Cable Outer Jacket Stripping
This may be carried out by one of the following methods.
1. With a jewellers saw & a universal block jig-specially designed for guiding the cable through holes of different
diameters. The slot in the block is provided to guide the saw & controls the depth of cut. The cable shall be
rotated while cutting because the depth of cut is already being controlling by universal blocks.
2. Select combination of tools or tool specifically designed for stripping the jacket & dielectric together.
3. With automatic machines having predetermined set pressure & adjustable depth, and position of cuts. In all
above methods circumferential score or Scribe mark of depth approximately ½ to ¾ of copper thickness
is made. The scribe line shall be singular & ends shall meet together to prevent step on the broken edge.
The conductor shall be broken at this scribe line by gently flexing outer jackets in the opposite direction to
fracture at the score line & pull off the stripped length by using pair of pliers with forked ends. The outer
conductor cut edge shall be smoothened to remove all burrs and ragged edges.
11.13.1 Inspection of Stripped Cable Ends
1. For each of the stripped ends, the inspector shall perform a quality control inspection checking the following
criteria:
a.
No metal or foreign particles are on the face of the dielectric.
b.
The outer conductor contains no burrs or major surface defects and is flush with the dielectric.
c.
Unremoved dielectric near the centre conductor does not exceed 0.2 mm.
2. The inspector shall report measurements of the external length of the centre conductor as shown in
Figure 11‑3 and shall entre in the logbook for cable prior to assembly with SMA connectors having separate
pin contacts.
CAUTION:
• Maximum length of copper jackets shall be removed at time shall not exceed 12.5 mm.
• Care shall be taken while cutting the jackets that the cable dielectric is not be penetrated as this would
cause outer conductor edge being rolled into the dielectric resulting in a electric discontinuity at that
point.
• The dielectric shall not be deformed by applying too much pressure while flexing outer conductor or while
pulling it off.
• The cutting blade shall be replaced if any defect/damage observed.
132
Remove burrs
Dielectric
Centre conductor
Outer conductor
0,2 mm max. unremoved dielectric is acceptable
Figure 11.3 : Dimensional inspection requirements
11.14
Stripping the Dielectric
11.14.1 Stripping the Dielectric Alone After Outer Jacket Stripping
Some specific tools are developed by some of standard manufacturer for stripping the dielectric. The manufacturer
recommended procedure using the right tools shall be followed. These tools may be used provided they have
guide to limit the penetration depth precisely so as to avoid damaged to the centre conductor.
Any damaged to centre conductor not only affect the electrical performance but also lead to breakage during
subsequent cable assembly or during usage. The flakes or burrs of dielectric shall be carefully removed.
The dielectric cutting depth shall have minimum 0.254mm (0.01 inch) clearance from the outer edge of centre
conductor. Centre conductor shall be cleaned & tinned immediately after the stripping the dielectric.
Once the dielectric has been stripped and subsequently thermal cycled, the small protruding dielectric cannot be
gripped with pliers and hence extremely difficult to trim without damaging the centre conductor by any of the
method described earlier.
For stripping of this small length of protruding dielectric following method shall be adapted. Using sharp knife
or blade, make circumferential cut the in the dielectric upto approximately 80 to 90% of the depth. Then the
dielectric shall be removed by giving slight axial pressure on the cut dielectric towards the cable end by using
twizer. Slight dielectric burr remaining around the centre conductor due to above stripping method shall be
acceptable.
11.14.2 Stripping of Dielectric & Outer Jacket Simultaneously
Stripping of dielectric can be done along with the outer jacket simultaneously by some specially designed
tools like clamping part & pointer manufactured by M/S RADIAL. These tools shall be used after ensuring that
the finished job satisfy all the requirements specified for dielectric stripping & cable outer jacket cutting & the
length of centre conductor. Trial assemblies may be fabricated to ensure this.
11.15
Centre Conductor End Forming
The prepared cable held in the vice & the cable end is pushed into the aperture in front of forming/pointing
tool & the body of the tool is rotated while applying slight axial pressure to the cable. This is repeated till
133
final stripped length of centre conductor,. as per specification of connector assembly procedure is achieved
with 60 to 90 deg. end point.
Alternatively this can be done carefully by manually filling it with microfile. Care shall be taken that axial alignment
of centre conductor shall be maintained. The formed surface & the edge shall be smooth. This step is not
applicable for the right angle connector.
11.16
Preparation for soldering of Cable Outer Jacket and
Centre Conductor Tinning
The cable outer jacket in the soldering area shall be tinned by solder in solder pot prior to the outer jacket
stripping.The rate of dipping and withdrawal from solder pot shall be such that no extra material is built up on the
cable & the dielectric material shall not be charred/ damaged during this procedure. In the above procedure the
liquid flux penetrates inside the cable to some extent but the same shall be minimized by adjusting the
rate of dipping, withdrawal & duration of dipping subsequent to above tinning process, the cable ends shall be dipped
in isopropyl alcohol or other cleaning solvent to remove the flux. If solvent is maintained at higher temperature
(boiling) the flux extraction shall be very effective. The cable centre conductor tinning shall be done in pot by
controlling depth of dipping in the bath just sufficient for soldering and avoid solder or flux penetration in
and around the dielectric. The solder bath temperature and solder material contamination shall be properly
monitored.
11.17
Degolding of Gold Plated Connector Parts and Pre-tinning
The presence of gold Intermetallic in the solder joint can cause solder joint failure at the interface of semi rigid
cable to connector so degolding at the complete area involved in soldering of gold plated connector parts shall
be meticulously done prior to connector soldering. Following methods are recommended.
1. Using three solder pot method for the portion “A” & “B” followed by using normal soldering iron for the
portion “C”.
2. Using normal soldering iron carefully complete gold removal without any discoloration or corrosion
product shall be assured. First methods shall be preferred & is described in details in following paragraph.
11.17.1 De-golding By Three Solder Pot Method
The solder pots shall be identified as Bath-1, Bath-2 & Bath-3. The solder bath material shall be the same as
used for soldering actual joint i.e. Sn60 only. The solder bath temperature shall be solder melting temperature
+ 500 C (maximum). The dipping time in the solder bath shall be 2-3 Sec. (typical) but max. 5 Sec. After tinning of
the parts in bath-1 & bath-2 sequentially. Final tinning of the parts shall be done in bath-3.
During this process regular analysis of Bath-1 & Bath-2 shall be made for gold content & other impurities to
keep them within specified limits or alternatively the solder material in these baths may be regularly replaced
after tinning of certain number of connectors. The record of connector degolded & bath analysis shall be done
for this purpose.
134
The bath solder material impurity specifications are as follows:
1.
The gold content in Bath1 shall not exceed 0.4% by weight.
2.
Bath 2 shall not be contaminated with copper in excess of 0.25% by weight & gold in excess of 0.2% by
weight. The total gold plus copper shall not excess 0.3% by weight. Also whenever the tinning process
produces a dull, frosty or granular appearance on the part the bath shall be removed from use.
3.
On no account final tinning be carried out in Bath 1 or Bath 2.
4.
Suitable part holding tool shall be used to provide firm grip on part.
5.
The depth of dipping of part in the bath shall be precisely controlled by suitable means.
6.
The fabricator shall remove gold from all surface areas to be joined by soldering. The central contact pin
can be degolded and pretinned with a soldering iron by melting a short length of 63 Sn or 60 Sn solder
wire within the cup to dissolve gold plating; the liquid solder can then be wicked­out with stranded wire.
7.
Fabricator shall degold and pre-tin the jointing surface of the connector body by fitting the connector to
a suitable sized PTFE plug held vertically in a vice.
8.
The fabricator may melt solder wire onto the jointing area and remove it with the aid of a solder wick at
least twice until the solidified pre-tinned surface has a shiny appearance indicating a gold free condition.
9.
With the right angle type of connector, the fabricator shall de-gold and pre-tin the solder mounting surfaces
of the inspection and assembly cover and the corresponding surfaces of the body before assembly.
10.
The fabricator shall pre-tin the cable’s outer and inner conductors.
11.
The fabricator shall check for possible dielectric protrusion after the cable has cooled down to room
temperature.
12.
The fabricator shall trim any protrusion with a scalpel blade.
13.
The fabricator shall check the fit of the pre-tinned cable in the connector.
14.
The fabricator may use activated fluxes for de-golding and pre-tinning operations.
15.
There shall be no dewetting of the solder on the cable conductor or on the connector.
16.
The fabricator shall clean all surfaces with an approved solvent until they are free from all residual flux
and other visible contamination. For solvents refer para 5.4.1
17.
The recommended de-golding and pre-tinning temperatures are 250 °C to 280 °C, and 210 °C to 260 °C,
respectively, when using solder immersion.
18.
The fabricator should perform pre-tinning just before proceeding with the assembly of the connector on
the cable.
11.17.2 Solder Preforms
1.
The fabricator shall either
a.
Use solder preforms with an internal diameter matching the outer diameter of the coaxial cable
which are available as pre-fluxed continuous rings as shown in Figure 11.4
b.
Prepare solder preforms by winding solder wire around mandrels having the same outer diameter
as the coaxial cable (0.085 or 0.141 inches).
2.
The fabricator shall predetermine the diameter of the wire and the number of turns by trials. This is
necessary since they depend on the type of connector.
3.
The fabricator shall make as many preforms as the number of connectors to be soldered.
4.
The fabricator shall use a scalpel blade to cut solder turns in a direction perpendicular to the wire
wrap.
135
Figure 11.4 : Method of producing solder preforms
NOTE BeforeFigure
use, the11.4
fabricator
shall clean
the preforms
withpreforms
one of the solvent cleaners as in para 5.4.1
: Method
of producing
solder
Centre contact
Body
Coupling nut
Shoulders on the body and the coupling nut enable
both rotation and retraction of the coupling nut with
respect to the body.
a. Approved connector with non-captive coupling nut
Teflon plug
Copper sheath
PTFE dielectric
Solder joint
Circlip permits rotation of the coupling nut with
respect to the body only. Retraction of the
coupling nut along the cable is not possible
b. Non-approved connector with captive coupling nut
Figure 11.5 : Approved and non­approved straight solder­type cable­end connectors
Assembly of Connectors to RF Coaxial Cables
136
11.17.3
Assembly Plan
Connector assembly plan shall be generated by designer referring to the manufacturer’s assembly instruction/
recommendations for each connector type. This plan shall be reviewed by QA before actual assembly. The plan
shall include following.
• Connector identification No. & part details.
• List & descriptions of tools like clamping tools, soldering tools, special jigs, torque wrench etc.
• List of material like solder, flux, cleaning solvents etc.
• Cable preparation steps described earlier with stripping dimensions etc.
• Various connector parts assembly procedure/sequence.
• Cable clamp/nut tightening torque values.
• Specific notes/instructions if any.
11.17.4 General Requirements for Connector Assembly
1.
The connector assembly shall be carried out in accordance with approved connector assembly plan.
2.
All gold plated connector parts shall be properly degolded in the soldering areas as per method as
para 6.3.2
3.
All the connector parts & cable shall be thoroughly cleaned prior to assembly to avoid entrapment of
contamination like flux residue etc. which can lead to corrosion.
4.
After phase-II preconditioning the earlier tinned portion of the cable jacket shall be re-tinned by
soldering iron after slight cleaning. This is to avoid dewetting problems. However, tinning time shall
be kept a minimum. Cleaning for the flux entrapment shall be immediately done after tinning.
5.
It is recommended to solder in the shortest possible time with minimum possible temperature (280ºC)
to avoid problem of dielectric core protrusion due to excess heat applied during soldering.
6.
Resistance soldering with suitable tongs (giving circumferential grip) is preferred than the conventional
temperature controlled soldering iron. Induction soldering method may also be followed.
7.
During soldering heat sink as recommended by manufacturer shall be used.
8.
There shall not be any movement of parts while soldering. Necessary clamp, jigs/ vice as recommended
by the manufacturer shall be used to hold the parts.
9.
Suitable jigs/vice shall be used to hold the bent cable at one or more points to avoid cable slipping
towards the pin side while soldering cable jacket to connector body.
0.
Care must be taken to preserve the plated finish & axial alignment of the centre conductor as this
forms an important basis in subsequent connector mating.
11.
Do not use external agents or cleaning solvents to cool soldered area fast. Let the solder joint cool
naturally.
11.18
Specific Requirements
11.18.1 SMA Right Angle Connector
The connector body should be assembled and soldered in position prior to centre pin soldering. The cable jacket
cutting edge shall be aligned with the connector barrel edge inside the connector such that jacket edge should
not be projected beyond the connector barrel edge.
137
11.18.2 SMA female connector
In the assembly of semi-rigid cable to connector female pin proper gauge recommended by manufacturer shall
be used to ensure proper insulation clearance.
11.19 Solder Assembly of Semi­Rigid Cables
11.19.1 Straight cable­end connector
11.19.1.1 Centre Contact Assembly
Use correct size of solder wire gauge. (Ref. Manufacturer assembly procedure)
1.
Tin cable centre conductor and inner diameter of contact pin. For this drop a small piece of solder into
contact pin and heat it.Then insert multi strand 26 AWG stripped wire inside, while heating the contact
pin & remove the wire quickly so that the excess solder quantity inside the pin shall be wicked out by
the wire strands.
2.
Use center contact holder to align contact pin and maintain pressure of contact pin to compensation
gauge during soldering operation.
3.
Remove excess solder, if any on the pin’s outer surface by soldering iron to avoid difficulty while mating
& cleaning thoroughly.
4.
The centre contact shall be slid onto the prepared centre conductor of the cable with an easy sliding fit.
5.
The centre conductor shall be visible across the full diameter of the inspection hole.
6.
The gap between the rear/end of the centre contact and the face of the dielectric/outer conductor shall
be as specified in the assembly instructions for the type of cable­end connector being used. An example is
given in below figure.
Inspection hole
Gap to be as specified in the
connector assembly instructions
Figure 11.6 : Centre contact assembly
7.
The fabricator shall solder the centre contact to the centre conductor with the solder specified in
Table 5‑1 and the tools specified in para 4.1
8.
After the solder has solidified and cooled, the fabricator shall clean the joint with one of the solvent
cleaners as per para 5.4.1
9.
After soldering, the fabricator shall recheck the gap between the centre contact and the face of the
dielectric/outer conductor.
10.
The inspector shall inspect the solder connection against the following criteria:
a.
The inspection hole is filled with solder.
b.
The appearance of the solder joint satisfies the “Acceptance criteria” given in para 9.5
c.
There is no flux or other residues on the cable or the contact.
d.
There is no solder spillage or flow onto the mating surfaces of the contact.
138
Where any solder flow or spillage has occurred on the non­mating outer surfaces of the contact, it does not cause
the effective contact dimensions to exceed those specified for successful connector assembly.
11.19.1.2 Connector­Body/Cable Assembly
1.
The fabricator shall assemble the remaining connector parts to the cable in the following sequence:
e.
Slide any cable identification and other sleeves onto the cable in the sequence defined by the cable
assembly or layout drawings or specifications.
f.
In the case of a straight cable­end connector, slide the coupling nut onto the cable with the internal
thread facing the end of the cable to which the connector is being assembled.
g.
Slide the solder pre­form (if used) onto the cable.
h.
Assemble the body of the connector to the centre contact and the end of the cable.
2.
The assembly of the body of the connector to the centre contact and the end of the cable should be with
an easy sliding fit in both cases (centre contact and pre-tinned outer conductor fitting).
3.
At this stage, the fabricator/inspector shall check the dimensional relationships of the connector body
to the centre conductor and the correct full insertion of the cable outer conductor into the connector
body.
4.
The fabricator shall solder the outer conductor of the cable to the body of the connector with the
solder
After the solder has solidified and cooled, the fabricator shall clean the joint with one of the solvent cleaners
specified in para 5.4.1
11.19.1.3 Inspection of Assembly
After soldering and cleaning, the inspector shall inspect the assembly of the connector to the cable against the
following criteria:
1.
The dimensional relationship of the centre contact and body of the connector is correct.
2.
The appearance of the outer conductor to connector body solder joint satisfies the visual “Acceptance
criteria” given in para 9.5
3.
There is no solder flow or other residues on the cable or connector.
4.
There is no solder flow or spillage onto the mating surfaces of the connector or onto the shoulder of the
connector body where it interfaces with the coupling nut.
5.
Any other solder flow or spillage onto the body of the connector does not affect the operation of the
coupling nut.
6.
There is no solder spillage or other contamination on the coupling nut.
11.20
Right Angle Cable End Connector:
• The fabricator shall assemble the connector to the cable­end in conformance with the QA requirements.
• After preconditioning, the fabricator shall cut the cable end to the dimensions necessary for correct fitting to
the connector
• The fabricator shall then degold and pretin the cable-end as defined in para 6.3
• The fabricator shall prepare the connector by degolding the bifurcated pin, the seating for the cover and the
cover.
139
• The fabricator shall insert the cable into the connector and the assembly (cable and connector) and shall
ensure that the angular relationship between preformed cable and connector is correct.
• The inspector shall inspect the insertion of the cable into the connector via the inspection/assembly hole to
ensure that it is in conformance with Figure 11.6
• The fabricator shall make first the solder joint between the inner conductor of the cable and the bifurcated
pin of the connector with the aid of a fine soldering iron.
• After the solder has solidified and cooled, the fabricator shall clean the centre conductor solder joint and the
cavity in the connector body with one of the solvent cleaners as in para 5.4.1
• The inspector shall inspect the solder joint to ensure that full insertion of the inner conductor of the cable
into the bifurcated pin of the centre conductor of the connector has taken place.
• The inspector shall inspect the solder joint to ensure that the “Final inspection” requirements of para 9.5
are satisfied.
• The fabricator shall now solder the outer conductor of the cable to the body of the connector with the aid
of the solder.
• After the solder has solidified and cooled, the fabricator shall clean the joint with one of the solvent cleaners
as in para 5.4.1
• The inspector shall inspect the solder joints between the cable and the connector to ensure that the dimensions
of the cable connector interface.
• The inspector shall inspect the solder joints between the cable and the connector to ensure that the solder
joints conform to the “Final inspection” requirements of para 9.5
• The fabricator shall now assemble the cover to the inspection/assembly hole and the solder joint formed with
a soldering iron using the solder as in para 5.2
• The fabricator shall not add extra solder during this operation. This is to prevent the flow of excess solder
into the cavity in the connector body.
• After the solder has solidified and cooled, the fabricator shall clean the joint with one of the solvent
cleaners.
• The inspector shall inspect the cover solder joint with respect to the following criteria:
o
The solder joint extends around the complete periphery of the cover.
o
The cover is fully inserted into the shoulder of the hole.
o
The solder joint conforms to the “Final inspection” as in para 9.5
11.21
Teflon Bush Insertion In Connector
11.21.1 In Case of Straight SMA Connector
Teflon bush shall be inserted only by using tool recommended by manufacturer after verifying the dimension of
bush as per the connector specifications.
11.21.2 In case of TNC connector
Immerse Teflon bush/insulator in liquid Nitrogen for approximately 5 minutes just before insertion into the connector
assembly, so that the bush shrinks to the required size & have press fit insertion.
140
see Note 1
see Note 3
see detail
below and
Note 2
Teflon plug
Copper sheath
PTFE dielectric
see Note 4
Solder joint
Note 1
The cable is inserted into the connector
body so that the outer conductor and
PTFE dielectric are flush with the inner
wall of the connector cavity.
Note 2
With the cable inserted as described in
Note 1, the inner conductor is fully inserted
into the bifurcated end of the inner contact
of the connector.
Note 3
Cover fully inserted and soldered into
shoulder of connector cavity.
Note 4
Captive-type coupling nut (see Figure B-3).
Taking care to avoid stress during cable
mounting.
Detail of cable inner conductor inserted into
bifurcated end of inner contact of connector
Figure 11.7 : Right angle cable-end connector assembly
11.22
Semi Rigid Cable Preconditioning
11.22.1 Necessity
The electrical & mechanical performance specified for semi rigid cable is achieved by compression fit between the
outer conductor & the dielectric core. No matter how careful manufacture may be when making the semi
rigid cable two inherent problems do occur,
• Unavoidable work hardening of copper tube.
• Deformation of dielectric core by compression & elongation
141
This may cause complex randomly distributed stresses. Bending of cables for coiling, storing & shipment also tend
to introduce additional stresses. The thermal coefficient of expansion of the core dielectric insulation is about
ten times greater than that of metal conductors. Since core dielectric is viscoelastic nature, the above- mentioned
stresses try to equalize with time & temperature. This causes recession of core dielectric from the cable ends &
the resultant air void at the cable/connector interface causes VSWR of the cable assembly to increase.
On the other hand protrusion of core from the end of its coaxial tube because of excess dielectric expansion
causes the forces to be transmitted on the coaxial tube when connector is threaded to its matting connector &
results into a tensile stress on the solder joints.
Hence it is essential that these stresses are relieved during cable assembly processing & no residual stress
remains in the cable assembly so that it is also observed that preconditioning also helps in screening out
the cable for major deviation like, teared or cracked outer jacket, occasionally the outer jacket of the cable
gets cracked during the preconditioning. Cable preconditioning in three phases is recommended for this purpose.
11.22.2 Phase-I Preconditioning
The semi rigid / flexible cable shall be subjected to following thermal cycle conditions on straight sections
of selected lengths of the cable assemblies before any bending/stripping operations. This shall be identified in the
connector assembly flow chart.
Table 11‑2 : Cable pre-conditioning : Phase1
TEMPERATURE
DURATION (MINIMUM)
100º C
1 hour
Ambient
1 hour
- 40º C
1 hour
Ambient
1 hour
11.22.2.1 Temperature transition rate: 3º C /minute
The cable shall be subjected to 5 such cycles subsequently. The cable shall then be maintained at room temperature
for 24 hours minimum. In case dielectric core protrudes from outer conductor press the dielectric core
with standard dielectric recess tool to reset it into cable outer jacket to the extent possible. The cable shall be
thoroughly inspected before further processing.
11.22.3 Phase-II Preconditioning
The semi rigid cable assembly shall be subjected to following thermal cycling conditions, after the bending
of the cable, tinning the outer jacket at both ends for sufficient length and compatibility with actual package is
checked tentatively. This shall be identified in the connector assembly flow chart.
11.22.3.1 Temperature transition rate: 3ºC/minute
The cable shall be subjected to 5 such cycles subsequently. The cable shall then be maintained at room temperature
for 24 hours minimum, before inspection & proceeding with further processing.
142
Table 11‑3 : Cable pre-conditioning : Phase2
TEMPERATURE
DURATION (MINIMUM)
100º C
1 hour
Ambient
1 hour
- 40º C
1 hour
Ambient
1 hour
11.22.4 Phase-III Preconditioning
The semi rigid cable assembly shall be subjected to following thermal cycling conditions after completing
soldering of the connector on both side of the cable. This shall be identified in the connector assembly flow chart.
Table 11‑4 : Cable pre-conditioning : Phase3
TEMPERATURE
DURATION (MINIMUM)
100º C
1 hour
Ambient
1 hour
- 40º C
1 hour
Ambient
1 hour
11.22.4.1 Temperature transition rate: 3 deg.C /minute
The cable shall be subjected to 5 such cycles subsequently. The cable shall then be maintained at room temperature
for 24 hours minimum before any rework & inspection. In case of straight connector assembly press on
protruded dielectric core if any from outer conductor with standard dielectric recess tool to reset it into copper
tube to the extent possible.
11.23
Inspection & Acceptance/Rejection Criteria
Each semi rigid cable /cable assembly shall be thoroughly cleaned & then inspected at stages mentioned in flow chart
for minimum of following points given in each section with suitable magnification (10X). Higher magnification
may be used to resolve suspected anomalies or defects and/or for measurement purpose.
11.23.1 Inspection of Cable After Cutting To Required Length
The entire cable shall be visually inspected for minimum of the following:
• Cracks in outer jacket or plating.
• Tear
• Twists.
• Discoloration
143
• Plating peel off
• Deep plating scratch extending in the base material
1.
Inspection After Phase-I & II Preconditioning
2.
Required number of thermal cycles and recovery period shall have been completed and recorded in
history sheet.
3.
The dielectric core shall be tight fit with outer conductor jacket and centre conductor.Any circumferential
air gap or void shall cause for rejection.
4.
The cable shall be free from discoloration, contamination and plating damage.
5.
There shall not be any crack in outer conductor.
6.
The rework for the protrusion of dielectric shall have been completed or rework stage at a later
stage of processing before soldering shall have been identified.
7.
Recession of dielectric in the cable shall be < 1mm.
11.23.2 Inspection after Cable Bending
1.
The specified cable identification marking, tag of the cable and Traceability record in history sheet shall
be matching.
2.
The cable bending shall be as per approved drawings and template.
3.
The entire cable length shall be free from:
a.
Kink
b.
Twist
c.
Bend or rebend within bend radius
d.
Deep scratch on the outer jacket to the extent of copper visibility
e.
Blisters
f.
Crack in outer conductor extending in the base jacket material
g.
Wrinkles
h.
Discoloration not cleaned with normal cleaning methods
i.
Circumferential scratch
j.
Plating damage with copper visibility
11.23.3
1.
Inspection After Cable Jacket Cutting, Dielectric Stripping Pin Forming and Tinning
The edge of cable shall be free from,
a.
Insulation burr
b.
Outer conductor smear on / in dielectric
c.
Cracked edge of outer jacket
d.
Sharp protrusion of outer jacket
e.
Dielectric burr remained very near to center conductor while dielectric stripping shall be
acceptable.
2.
The cable shall be free from contaminations entrapped in the dielectric and in space between the outer
jacket & the dielectric as well as between center conductor & dielectric.
3.
The cable jacket shall be free from discoloration, plating damage.
144
4.
The cutting plane shall be perpendicular to cable axial plane within + 3 degrees.
5.
The stripped length shall be as per specified dimension in the assembly drawings for the particular
connector.
6.
The center conductor alignment shall be within + 3 deg.
7.
The center conductor alignment shall be free from
a.
Score line with copper visibility
b.
Nicks or cuts.
c.
Contaminations
d.
Evidence of bend or twist or bend & rebend which may cause axial misalignment while mating /
pin soldering.
e.
Copper visibility.
f.
Corrosion.
8.
The center conductor end point forming shall be approx. 60 to 90 deg. & smooth surface without any
sharp edge.
9.
The tinned area shall be have smooth & shinning surface with uniform solder thickness.
10.
Tinned surface shall be free from flux, solder flakes, dewetted
11.
The edge of cable shall be free from,
a.
Insulation burr
b.
Outer conductor smear on/in dielectric
c.
Cracked edge of outer jacket
d.
Sharp protrusion of outer jacket
areas frosty & granular structure.
e.
Dielectric burr remained very near to center conductor while dielectric stripping shall be
acceptable.
12.
The cable shall be free from contaminations entrapped in the dielectric and in space between the outer
jacket & the dielectric as well as between center conductor & dielectric.
13.
The cable jacket shall be free from discoloration, plating damage.
14.
The cutting plane shall be perpendicular to cable axial plane within + 3 degrees.
15.
The stripped length shall be 2.16mm + 0.13mm.
16.
The center conductor of cable shall be straight axially within + 3 deg.
17.
The center conductor shall be free from
a.
Score line with copper visibility
b.
Nicks or cuts
c.
Contaminations
d.
Evidence of bend or twist or bend & rebend which may cause axial misalignment while mating /
pin soldering.
e.
Copper visibility.
f.
Corrosion
145
18.
The center conductor end point forming shall be approx. 60 to 90 deg. & smooth surface without any
sharp edge.
19.
The cable end corners shall be smooth.
11.23.4 Inspection of De-Golded Connector Parts
The parts (the connector body under solder coverage & centre pin – refer connector assembly plan) shall be free
from,
• Gold platting in soldering area.
• Discoloration
• Frosty or granular appearance of the tinned surface.
• Flux residues & any other contamination
• Corrosion
• Extra solder material build up in the soldering area obstructing the proper mating for soldering
11.23.5 Inspection of Pin Soldering
1.
Adequate gap between centre pin and Teflon of cable shall be available without any solder build
up. This gap shall be as per manufacture’s recommendation or specified in the assembly drawing
of the particular connector.
2.
Solder shall be visible at inspection hole
3.
There shall not be solder build up on centre pin.
4.
Centre pin & dielectric shall be free from contamination and flux residue.
5.
Solder fillet shall be visible around the periphery of the centre pin or atleast 80% of circumference.
6.
Pin inclination shall less then 20
11.23.6 Inspection After Soldering of Connector Parts To Sem-irigid Cable Before
Phase III Preconditioning
1.
The type no. of connector shall be as per approved drawings.
2.
The cable traceability / identification marking / tag on the cable.
3.
There shall be complete wetting of solder with smooth, shining concave fillet in the soldered areas.
4.
There shall not be any discoloration or burning mark on dielectric or dielectric to cable interface & inside
/ outside portion of connector body.
5.
The dielectric and soldered area shall be free from solder flakes.
6.
The entire cable shall be free from flux residues & any other type of contaminations.
7. In case of straight connector assembly the semi rigid cable outer jacket edge shall be in flux with flanged
edge of connector sleeve, when looked from open end of the connector. Solder build up & cable dielectric
protrusion beyond the cable stop and (i.e. At connector barrel), shall be within 0.05 mm.
8.
In case of right angle connector assemble there shall be evidence of semi rigid cable completely inserted
upto cable sitting plane of connector & also the center conductor properly resting on post either in
flux with edge of post or projection to a maximum distance of 0.5mm from post, or within the
acceptance tolerance of pin length, as recommended by manufacturer / connector assembly plan.
146
11.23.7 Inspection of Finished Cable Assembly after Phase–III reconditioning
11.23.7.1 General
1.
The cable assembly identification marking/tag cable and corresponding Traceability records shall be
matching with that of specified.
2.
Overall assembly of different parts with respect to positions shall be as per approved connector
assembly drawings/manufacturer’s recommendations.
3.
The finished cable assembly shall be as per approved drawings & shall be compatible with actual
integrated package assembly after Teflon bush insertion.
4.
The protective cap at connector end or polyethylene bag packaging separate for each cable assembly shall
be available.
5.
The connector soldering inspection shall have been completed & shall be acceptable as specified in
para 9.5
6.
There shall be no discoloration, which is not cleanable with normal solvents & methods, on any part.
7.
The center pin shall not have evidence of any damage.
8.
Axial alignment of center pin shall be within + 1 degree.
9.
The connector mating length shall be free from any dielectric material burr, excess dielectric protrusion,
contaminations & metal particles or any other foreign material.
10.
Entire cable assembly including solder joints shall be free from crack, pits & copper visibility.
11.
The cable assembly identification marking / tag on cable and corresponding Traceability records shall be
matching with that of specified.
12.
The finished cable assembly shall be as per approved drawing & shall be compatible with actual integrated
package assembly.
13.
The protective cap at connector end or polyethylene bag packaging separate for each cable assembly shall
be available.
14.
All external surfaces shall be free of foreign particles & contaminations.
15.
There shall be no evidence of corrosion, peeling of plating / finishes, pinholes, blisters on the surface of
connector body & cables.
16.
The entire cable length & connector body shall be free from cracks of materials involved.
17.
The Teflon projection shall be <=0.05 mm.
18.
The crimping shall not show under-crimp evidenced by the crimping sleeve not touching to the shoulder
of connector body.
19.
The crimping shall not show over-crimp evidence by deformation of crimping sleeve, plating damage or
Teflon deformation or deformation of connector body in mating length.
20.
The crimp sleeve shall not be inclined.
21.
The cable surface & connector surface shall not have any discoloration due to oxidation.
22.
The connector center pin shall not be bent or inclined (>50) or deformed.
11.24
Specific
11.24.1 Right angle connector cable assembly
1.
When inspected before cap is soldered, there shall be no evidence of dielectric protrusion greater
than 50% of gap between center conductor soldered post of connector and cable jacket edge.
147
2.
Void or circumferential gap in the interface of cable dielectric & outer jacket/pin shall not be
present.
3.
Recession of dielectric core into cable jacket shall be less than approx.1 mm.
11.24.2 Straight connector cable assembly
1.
Dielectric protrusion shall be less approx. 0.1 mm.
2.
Cable jacket protrusion from its correct position shall be less than
3.
Recession of dielectric in to the cable jacket shall be less than approx. 1 mm.
4.
Void or circumferential gap in the interface of cable dielectric / bush & outer jacket / pin shall not be
present.
approx. 0.05 mm.
11.24.3 TNC connector cable assembly
1
All the parts of TNC connector shall be assembled in proper sequence.
2.
Lock washer or ‘C’ washer or ‘O’ ring shall be fully inserted, remain in position and shall not have any
damage. This may be verified ensured only by disassembling one sample connector.
3.
The connector shall be tightened with the recommended torque specified by the manufacturer or
connector assembly drawing.
148
11.25
Semi-rigid cable fabrication flow charts
APPENDIX-1
FLOW CHART NO -1
SEMI RIGID FABRICATION WITH SMA SOLDERABLE CONNECTOR
RECEIVED CABLE IN COIL FORM &
CONNECTOR
CHECK
FOR QA
CLEARANCE
NO
CORRECTIVE
ACTION
REJECT
CORRECTIVE
ACTION
REJECT
CORRECTIVE
ACTION
REJECT
CORRECTIVE
ACTION
CABLE STRAIGHTENING &
CUTTING TO REQUIRED LENGTH
CABLE PRECONDITIONING
PHASE-1
INSPECTION
ACCEPT
APPROVED DRAWING
AND/OR TEMPLATE
CABLE BENDING AS PER
TEMPLATE/DRAWING
INSPECTION
ACCEPT
CABLE PRECONDITIONING
PHASE – 11
INSPECTION
ACCEPT
A
149
A
IN CASE OF RIGHT ANGLE
CONNECTOR
IN CASE OF ST CONNECTOR
& FEMALE ADAPTOR
B
C
CONTD.ON
PAGE No.154
CONTD.ON
PAGE No 156
150
MALE SMA CONNECTOR WITH CENTER PIN
B
CABLE OUTER JACKET
RETINNING & CONNECTOR
CENTER PIN TINNING
DEGOLDING OF
SOLDERING AREA
ON THE CONNECTOR
CONNECTOR CENTER PIN
SOLDERING
INSPECTION
REJECT
CORRECTIVE
ACTION
ACCEPT
INSPECTION
ACCEPT
CONNECTOR SOLDERING AT
BOTH ENDS OF CABLE
INSPECTION
REJECT
CORRECTIVE
ACTION
ACCEPT
CABLE PRECONDITIONING
PHASE-111
FINAL CLEANING
INSPECTION
REJECT
CORRECTIVE
ACTION
ACCEPT
B-1
151
REJECT
CORRECTIVE
ACTION
B-1
FINAL CABLE ASSEMBLY
COMPATIBILITY CHECK WITH
ACTUAL UNIT
REJECT
CORRECTIVE
ACTION
REJECT
CORRECTIVE
ACTION
ACCEPT
FINAL CABLE ASSEMBLY
ACCEPTABLE INSPECTION
ACCEPT
CABLE ASSEMBLY READY FOR
INTEGRATION
152
RIGHT ANGLE CONNECTOR
DEGOLDING OF
SOLDERING AREA
ON THE CONNECTOR
C
CABLE OUTER JACKET
RETINNING
SOLDERING OF
1. CONNECTOR BODY
TO CABLE OUTER
JACKET
2. CABLE CENTER
CONDUCTOR
TO CONNECTOR
CENTRE POST
INSPECTION
ACCEPT
REJECT
INSPECTION
CORRECTIVE
ACTION
ACCEPT
CABLE
PRECONDITIONING
PHASE-111
REJECT
INSPECTION
CORRECTIVE
ACTION
ACCEPT
FINAL
COMPATIBILITY CHECK
OF CABLE ASSEMBLY WITH
ACTUAL UNIT
REJECT
CORRECTIVE
ACTION
ACCEPT
C-1
153
REJECT
CORRECTIVE
ACTION
C-1
FINAL CABLE ASSEMBLY
INSPECTION
REJECT
ACCEPT
CABLE ASSEMBLY READY
FOR INTEGRATION
154
CORRECTIVE
ACTION
FLOW CHART NO-2
SEMI RIGID CABLE ASSEMBLY WITH TNC CONNECTOR
RECEIVED CABLE IN COIL
FORM & CONNECTOR
CHECK
FOR QA
CLEARANCE
REJECT
CORRECTIVE
ACTION
ACCEPT
CABLE STRAIGHTENING &
CUTTING TO REQUIRED LENGTH
CABLE PRECONDITIONING
PHASE-1
INSPECTION
REJECT
CORRECTIVE
ACTION
ACCEPT
APPROVED
DRAWING AND/OR
TEMPLATE
CABLE BENDING AS PER
TEMPLATE/DRAWING
INSPECTION
ACCEPT
CABLE PRECONDITIONING
PHASE – 11
CABLE OUTER JACKET CUTTING
& DIELECTRIC STRIPPING AND
PIN FORMING
E
155
REJECT
CORRECTIVE
ACTION
E
DEGOLDING OF CONNECTOR
SOLDERING AREA
INSPECTION
REJECT
CORRECTIVE
ACTION
ACCEPT
INSPECTION
ACCEPT
SOLDERING OF CENTER PIN TO
CABLE CENTER CONDUCTOR
INSPECTION
REJECT
CORRECTIVE
ACTION
ACCEPT
ASSEMBLY OF ALL THE PARTS
OF CONNECTORS AS PER
MANUFACTURER’S INSTRUCTION
& SEQUENCE
ON LINE
INSPECTION & CORRECTION
ACCEPT
FINAL CABLE
ASSEMBLY COMPATIBILITY
CHECK WITH ACTUAL UNIT
REJECT
CORRECTIVE
ACTION
REJECT
CORRECTIVE
ACTION
ACCEPT
FINAL CABLE
ASSEMBLY ACCEPTABLE
INSPECTION
CABLE ASSEMBLY READY FOR
INTEGRATION
156
REJECT CORRECTIVE
ACTION
FLOW CHART NO-3
SEMI RIGID CABLE FABRICATION INCASE OF EQUI PHASE CABLE ASSEMBLY
CABLE STRAIGHTENING &
CUTTING TO REQUIRED LENGTH
CABLE PRECONDITIONING
PHASE-1
INSPECTION
REJECT
CORRECTIVE
ACTION
REJECT
CORRECTIVE
ACTION
REJECT
CORRECTIVE
ACTION
ACCEPT
APPROVED
DRAWING AND/OR
TEMPLATE
CABLE BENDING AS PER
TEMPLATE/DRAWING
INSPECTION
ACCEPT
CABLE PRECONDITIONING
PHASE – 11
INSPECTION
ACCEPT
DEGOLDING OF
CONNECTOR
SOLDERING AREA
CABLE OUTER JACKET CUTTING,
TINNING, DIELECTRIC CUTTING
AND PIN FORMING AT ONE END
REJECT
INSPECTION
CORRECTIVE
ACTION
ACCEPT
INSPECTION
CONNECTOR PIN &
CONNECTOR SOLDERING
AT ONE END
F
157
ACCEPT
REJECT
CORRECTIVE
ACTION
F
REJECT
INSPECTION
CORRECTIVE
ACTION
ACCEPT
PHASE MEASUREMENT & LENGTH
ADJUSTMENT BY DESIGNER
ACCEPT
JACKET STRIPPING DIELECTRIC
CUTTING PIN FORMING AT
OTHER END OF CABLE
REJECT
INSPECTION
CORRECTIVE
ACTION
ACCEPT
CONNECTOR SOLDERING
OTHER END
REJECT
INSPECTION
CORRECTIVE
ACTION
ACCEPT
CABLE PRECONDITIONING
PHASE – 11
REJECT
INSPECTION
CORRECTIVE
ACTION
ACCEPT
FINAL
COMPATIBILITY
CHEACK OF CABLE
ASSEMBLY WITH ACTUAL
UNIT
REJECT
ACCEPT
F-1
158
CORRECTIVE
ACTION
F-1
ELECTRICAL
PERFORMANCE CHECK
REJECT
CORRECTIVE
ACTION
REJECT
CORRECTIVE
ACTION
ACCEPT
FINAL CABLE
ASSEMBLY ACCEPTABLE
INSPECTION
ACCEPT
CABLE ASSEMBLY READY FOR
INTEGRATION
159
11.26
Sample diagram of cable assembly
Semi Rigid Cable Assembly
160
11.27
Typical stress relieving bends used in Semi rigid cable assembly
161
SEALECTRO
TOOL KIT
OMNISPECTRA
TOO KIT
ALL DIMENSIONS ARE IN MM.
AVAILABLE BEND RAD11 AND MINIMUM STRAIGHT DIST ANC
REQUIRED FOR 0.141”(3.58MM) SEMIRIGD CABLE WITH
SEALECTRO MAKE AND OMNISPECTRA MAKE TOOL KITS.
162
12 POLYMERIC APPLICATIONS
12.1 Preparation for polymeric applications
12.1.1
Surface Preparation
• The PWAs shall be cleaned and demoisturized within 10 hours before any polymeric application .
• Demoisturizing may be accomplished by an oven bake at 65°C ± 5 °C for a minimum of 4 hours.
12.1.2
Masking
• Material. Shall be as per approved material list
• Areas to be kept free of polymeric material shall be masked with approved tape, covers, or other suitable
masking material or devices.
• Masking material shall be compatible with the PWA being processed.
• ESD protective tapes containing conductive adhesive shall not be applied over PWB Conductor patterns.
• Precautions shall be taken to assure that no residues are left when the masking material is removed.
• It must adhere well to surfaces involved
• Easy to apply and reworkable if needed
• Cures at temperature having no effect on components
o
electrically insulated
o
Meeting specification of cleanliness for space use
o
Transparent/opaque
o
Total mass loss (TML) of 1% and Collectible Volatile Condensable Mass (CVCM) of 0.1% within limits.
• Masking for vapor phase Conformal Coating.
• Unsealed parts and areas not to be coated shall be properly masked to prevent C C vapors from penetrating
minute openings .
• Masking materials shall be compatible with the primer and the vacuum deposition system.
12.1.3
Priming
• Materials shall be as per manufacturer’s recommendations.
• When a primer is used, it shall be of a material recommended by the same manufacturer that produced the
conformal coating material and be applied and cured in accordance with the manufacturer’s instruction.
• Any excess buildup of primer shall be removed.
• Re-Priming Requirements. Most primers are effective only for a specified period of time with well-protected
storage. If, after priming, subsequent conformal coating has not been applied within the manufacturer’s
recommended elapsed time, re-priming is mandatory
12.1.4
Local Potting
Local potting is filleting or moulding of part with a suitable adhesive compound in order to protect them
from mechanical shock or vibration. Room Temperature Vulcanize materials (RTV) are used as local potting
materials. It is applied for mechanical support and electrical insulation, main purpose is to protect components
from vibration.
163
12.1.5
Requirements
12.1.5.1
Application Sequence.
Potting shall be performed prior to conformal coating unless it is specifically stated otherwise on the Fabrication
documentation.
Potting shall be performed after conformal coating when polyurethane conformal coating is used.
Figures shown in this chapter is only for illustrative purpose and not to the scale.
12.1.5.2
Application
Potting material shall be applied to the parts and areas specified by the approved Fabrication documentation. Spatulas
and syringes, with or without pressure- control pneumatic dispensers, may be used to apply the material.
12.1.5.3
Materials
Both Dow Corning RTV 3145 and Anabond 666 materials are space qualified. However, Anabond 666 is
indigenous and is therefore preferred.
Potting material shall adhere to all surfaces to be joined.
• Potting Concerns. When Potting, the following shall be assured:
o The potting compound does not negate stress relief of parts and enclose joints, part leads, or mechanically
compromise the reliability of the hardware
o Potting material is free from contamination
o Glass-bodied parts are covered with resilient material prior to potting with rigid material, such as
epoxy
o Potting material does not enter the inside of mounting holes or cover vent holes .
o
Potting material shall not be allowed to bridge between the bottom of ceramic-bodied DIPs or surface
mounted parts and the PWB
Jumper wires in excess of 2.54 cm (1 inch) and axial leaded tantalum capacitors of all case sizes shall be staked.
• For Axial leaded component, sleeveless (See Figure 12‑1)
• Fillet location: between the board and the length of the body
• Fillet length ≥ 75% of the body length
• Fillet height ≥ 25% and ≤ 50% of the body diameter
• The top of the component is visible for its entire length .
12.1.5.4
Jumper wires
• Fillet location: at intervals of 2.54 cm (1 inch) maximum and at every change of direction beyond the radius
of curvature for a radius bend that is shorter than 2.54 cm (1 inch) Ref. Figure 12.2.
• Be in contact around the full circumference of the wire and in contact with the board
164
Fillet Length: ≥75%L to 100%L
Fillet Height: ≥25%d to 50%d
Top of component is visible for its entire length.
Figure 12.1 : Default Potting for Horizontally-Mounted Sleeveless Cylindrical Part
Figure 12.2 : Single Wire Potting
TO-type packages
Stacking of TO transistores is to be done whenever necessary
• At least three fillets, spaced approximately evenly around the periphery of the component
• Fillet height: ≥25%, extension over the top of the part is controlled by clearance requirements at the next
higher level of assembly .
• Slight flow under the part is allowed however potting shall not contact lead, enclose the lead, or negate stress
relief .
• At least three fillets spaced approximately evenly around periphery of the component. Fillet Height: ≥25% to
100% of the component body height
• Slight flow underneath component, but fillets do not contact lead seals, enclose the lead, or negate stress
relief.
165
Figure 12.3 : Potting for Radial Lead Components
Radial-leaded square or rectangular packages
• Potting shall be used at each corner .
• Fillet height: ≥ 25%, extension over the top of the part is controlled by clearance requirements at the next
higher level of assembly .
• Slight flow under the part is allowed however potting shall not contact lead, enclose the lead, or negate stress
relief .
• Surface mount area array packages require engineering analysis and design instructions to address all necessary
polymeric applications and acceptance criteria.
Figure 12.4 : Potting for Radial Multi-lead Rectangular Components
Fillets on all four corners. Fillet Height: ≥25% to 100% of the component body height Slight flow underneath
component, but fillets do not contact lead seals enclose the lead, or negate stress relief.
• Radial-leaded component whose height is larger than one of its base dimensions (see Fig. 12.5).
• Fillet required on both sides, fillet height: ≥ 50% to 100%, fillet width: ≥ 50%
• Slight flow under the part is allowed however potting shall not contact lead, enclose the lead, or negate stress
relief.
• When in an array of between two and four devices, potting material shall connect the tops of the parts in the
array for the entire width of each part and connect the end faces of the two parts at each end of the array to
166
the substrate for ≥ 50% to 100% of the height of the parts and ≥ 50% of the width of the parts.
Figure 12.5 : Default Potting of a Single Vertically-Mounted Rectangular Part
Fillet Height: ≥50% H to 100% H Fillet Width: ≥50% W
Slight flow underneath component, but fillets do not contact lead seals or enclose the lead, or negate stress relief.
• When in an array of greater than four devices, both outer side surfaces of every other part shall contain a fillet
to the board ≥25% to 100% of the height of the part. (See Fig. 12.6).
Figure 12.6 : Default Potting for an Array of Vertically-Mounted Rectangular Parts
Two outside ends – Fillet Height: ≥50% H to 100% H End Fillet : ≥50% W
Inner surfaces: Fillet is in contact with both surfaces for 100% of component width
Wire bundles
Width of potting stripe shall be a minimum of 1x the diameter of the bundle.
Minimum 1X diameter of wire bundle
167
:Wire
BundlePotting
Potting
Figure Figure
12.7 :12.7
Wire
Bundle
Figure 12.8 :Typical Toroid Potting
Curing
Figure 12.8 : Typical Toroid Potting
• Potting material shall be cured in accordance with the manufacturer’s recommended cure schedule or as
specified in the engineering documentation
• Potting material shall be tack-free when cured For RTV 3145 and Anabond 666 at Room temperature for
2 hours. (however after 24 hours of curing sub systems can be inspected and cleared for electrical testing).
Environmental testing can be carried out after 72 hours only.
168
Figure 12.9 :Vibration Dampening Potting
Figure
12.9 : Vibration Dampening Potting
169
Figure 12.10 :Typical Vibration Isolation Potting
170
13 CONFORMAL COATING
13.1 Purpose
Conformal coatings are intended to provide electrical insulation and environmental protection thus minimizing the
performance degradation to electronic PWAs by humidity, handling, debris, and contamination. Conformal coating
materials may include solvents (diluents), fillers, and catalysts and/or accelerators, in addition to the basic resin.
Conformal coating is applied by spraying, brushing, dipping, or vacuum deposition methods and then allowed to cure
to provide a uniform, continuous coating over the surface of the PWA or electronic assembly. Vacuum deposition
methods involve processes, equipment, and materials that are departures from those applicable to the other
application methods. Potting shall be performed prior to conformal coating unless it is specifically stated otherwise
on the engineering documentation
It is an thin uniform layer of electrically non conductive coating to a printed wire assembly packages to provide
protection against degradation of electronic assembly by environment influences and to provide electrical insulation.
The most suitable material for coating is polyurethane and para xylylene. However silicon based conformal
coating materials are widely used for launch vehicle applications. Conformal coating should have following
properties:
Good adhering and wetting to most of the surfaces
Less shrinkage and easily curable
High mechanical strength after curing
Table 13‑1 : Conformal coating materials
Type of material
Application method
Thickness
Poly Urethane
Conap CE1155
Brush
Dipping
Spraying
50 to 100 µm
Parylene
Vapor phase deposition
15 to 25 µm
Silicon DC-2577
Brushing, dipping or pouring or
flow coating
60 to 120 µm
Manufacturers curing schedule shall be filled for conformal coated assembly.
13.2 Safety Precautions
Conformal Coating material may affect the skin so that the Protective care shall be taken during processing, in
case chemical contact with the body part wash it immediately with cold water and take the medical advice if
required. Solvents and compounds shall be stored as per manufacturer’s recommendations. Inhaling of chemical
fumes shall be avoided.
13.3 Poly Urethane Type Coating Applications
Conformal coating can be done by spraying, brushing, dipping and pouring, depending upon the requirements.
171
13.3.1
Spraying
Spray coating is applied using a jet. Spraying shall be done from all four directions to cover all areas.
Due to line of sight spraying and the shadowing effect, it may not be possible to get a uniform coating on
the PCB. It is not used since it requires 100% exhaust along with clean air and not easy to implement.
(Thickness 10 – 20 µm.)
13.3.2
Brush Method
The material using a brush without forming fillets and thickness particular attention shall be paid under side of
components and lead wires. The brush selected shall provide adequate coverage. Brush method is adequate for
rework and for coating. Minimum three coats shall be applied to achieve the proper coating thickness.
Recommended coating thickness for polyurethane is 20 to 50 micron.
13.3.3
Dipping Method
The entire assembly shall be dipped. The extraction rate shall be such as to allow the coating material to stop
running and minimum composition filleting is achieved. The wired assembly board shall be immersed withdrawn
vertically at the rate of 5 mm to 30 mm per minute. Slow immersion allows air escape. If the card is immersed rapidly
it causes foaming and air gets entrapped.
13.3.4
Pouring Method
Sufficient material shall be poured or flowed on to the assembly so that optimum coverage can be achieved by
spreading outward and downward without air entrapment.
13.4
Curing
Manufacturer’s instructions shall be followed for curing the conformally coated assembly. For Conap; CE 1155; 60
degrees temperature for 3 hours or at Room temperature for 7 days.
13.5
Parylene Conformal Coating
Parylene is the generic name for the members of the unique polymer series. The basic member of the series is poly
paraxylylene, a completely linear highly crystalline material. Parylene conformal coating provides
corrosion
resistance and dielectric protection for electronic components and assemblies. Conformality means that all surfaces,
even corners and sharp edges like cutting wire ends are coated to a constant thickness. The applicant should take
care of the true conformability of surface and deep penetration into small spaces, coupled with excellent electrical
and atmospheric properties.
13.5.1
Preparation for Coating
13.5.1.1
Cleaning
The surface to be coated shall be cleaned by suitable methods, which will assure that the assemblies are free
from solder flux and other ionic, oily and other particulate contaminants as per applicable standards for space
use. Assemblies shall undergo ionic contamination test prior to conformal coating.
172
13.5.1.2
Masking
Masking is required in those areas, requiring no conformal coating. It shall be done by suitable materials like 3M
adhesive tapes, shrinkable sleeves, RTV, epoxies, spot on etc. In the areas where coating is not required such as
tuning screws of variable resistors and capacitors, masking shall be done prior to coating. The areas, which have to
be soldered later, shall be protected using approved masking materials, which do not leave a residue.
13.6
Application Procedure
Procedure for conformal coating “CONAP CE 1155” application with Brush method:
Clean the PCB, beaker and glass rod with alcohol and dry it with blower. Mix part A and part B of the above
conformal coating material in the ratio of 10:7 and thinner 15 to 20 % of the above mixture by volume, and apply it
with soft brush on the required surfaces.
13.6.1
Procedure for coating with Parylene:
The PCB assemblies which require Parylene conformal coating shall be cleaned as per para 13.5.1.1 and dried in an
oven at 60 °C for a minimum of two hrs. For enhanced adhesion property a simple treatment with dilute solution of
an organic Silane can be carried out. For details of preparation and treatment with Silane, manufacturer’s instruction
can be followed.The quantity of Dimer to be taken is determined by taking into consideration the surface area and the
required coating thickness. If required,Anthracene equivalent to 0.25% by weight may be added with the Dimer and mix
them properly. Pour the mixture into a Dimer boat and place the boat in the vaporizer section of the Parylene coater.
13.7
Deposition Process
The Parylene polymers are deposited from the vapor phase by a process, which resembles vacuum metalizing. The
process consists of 3 major steps.
13.7.1
Sublimation
The parylene powder goes from solid state to vapor state directly by heating at temperature around 200oC.
Vaporization of parylene, a dimer takes place in the vapor generator. Under vacuum at approximately 200oC the
stable crystalline dimer, di-para+xylylene produces vapors of the material. This part of the system is called vaporizer
zone.
13.7.1.1
Pyrolysis
The vapor undergoes pyrolysis when it passes through a hot temperature zone of 610oC to deposition chamber,
where the vapor turns into gaseous paraxylelene, the reactive monomer. This part of the system is called pyrolysis
zone.
13.7.1.2
Deposition and polymerization
Deposition and simultaneous polymerization of the paraxylylene to poly paraxylelene takes place in the deposition
chamber. When the monomer enters into the chamber at the room temperature it simultaneously deposits and
polymerizes on the surface of the component or assembly being coated.
173
13.7.1.3
Advantages
The process assures precise control of thickness and inherent uniformity, no bridging or sag, superior barrier
properties for environmental protection as compared to other coating materials. Tough, pin-hole free coating as
thin as 1 µm can also be achieved. This physically stable and chemically inert material which is extremely resistant to
chemical attack, is also insoluble in most known solvents. It provides excellent corrosion protection from moisture,
salt-spray, corrosive vapors and other hostile environments. Parylene coating increases the pull strength of wire,
lead bonds, face bonded chips and conductor bridges along with high dielectric characteristics, thermal stability and
stress freeness.
13.7.1.4
Precautions
The assembly to be conformably coated shall be cleaned with approved cleaning solvents. It shall be confirmed prior
to coating that the shelf life prescribed by the manufacturer is not crossed. Manufacturer’s instruction shall be
followed in preparing the component used for coating.
The parylene is thin, uniform and inert, so visual inspection of parylene coating is difficult. Ultra Violet light (UV)
inspection is a convenient and widely accepted method for visual assessment of continuity and uniformity of the
coating. Parylene when deposited according to recommended techniques is virtually non-fluorescent. Adding 0.25%
by weight anthracene material to the parylene dimer would help in visual inspection. Anthracene being a neutral
material, doesn’t affect the parylene properties.
13.7.1.5
Inspection uniformity
• Coating shall be uniform in colour and texture.
• Coating shall be continuous and present a smooth and ripple free
• It shall adhere to all coated surface.
• Coating shall be uniform in thickness with no excessive build up around components. The acceptable limit of
thickness is 15 to 50 microns for different type of coatings preferably 25 µm for electronic assemblies.
Pre-Cure Examination
Immediately after material application, the uncured conformal coating shall be examined for:
• Bubbles and Air Entrapments: Prior to cure, bubbles and air entrapments shall be broken using locally qualified
methods such as piercing with a sharp probe or by vacuum methods
• Bridging: Conformal coating material shall not be allowed to bridge between the bottom of a leaded surface
mount device and the PCB, or between the part lead and the PCB, thereby negating stress relief
Post Cure Inspection
After the cure cycle, the conformally coated PWA shall be examined to assure that the following conditions are met.
See Figure 13‑1 through Figure 13‑4 for additional requirements.
• Conformal coating is uniform in color, thickness, texture, tack-free, and shows proper adhesion to all coated
surfaces.
• Conformal coating covers all areas as specified in the engineering documentation, has a smooth continuous
surface, and follows the contours of the PWA. Minor pull back from sharp points and edges is permissible
174
• Conformal coating is free from contamination
• Terminals are encapsulated with conformal coating, including the insulation gap of the wire, unless there is a
solder ball type connection (as in high voltage connection.This is normally applied with a brush after the initial
conformal coating application).
• Conformal coating does not exhibit discoloration (due to such things as excessive curing oven temperature
or contamination). Change of color due to temperature aging during normal exposures to test temperatures
or standard rework is allowed.This allowance is not intended to apply to color changes resulting from the use
of incorrect or defective material.
When fluorescent conformal coating materials are used, coverage and location shall be verified by Ultraviolet (UV)
light illumination.
PREFERRED
Completed uniform coverage with no visual
bubbles.
ACCEPTABLE
Small bubbles, but they do not bridge between noncommon conductors, expose a bare conductor
surface, or exceed 0.76mm (0.03 inch) in any
dimension.
UNACCEPTABLE
Excessive bubbling
Figure 13.1 : Conformal Coating – Bubbles
175
PREFERRED
Smooth, continuous, and without bubbles,
scratches or imperfections.
UNACCEPTABLE
Scratch exposes conductive areas.
Figure 13.2 : Conformal Coating – Scratches
PREFERRED
Uniform color, texture, and thickness with
apparent good adhesion on parts and
board surface. The coating should show
uniform fluorescence under a UV light.
ACCEPTABLE
No variation in coating thickness.
176
UNACCEPTABLE
Lifting and peeling indicating improper
surface cleaning or excessive thickness.
Any
lifting
on
conductive
areas
is
nonconforming.
Figure 13.3 : Conformal Coating - Lifting and Peeling
ACCEPTABLE
Not to exceed 5 percent of PWB surface
area.
Conformal
Coating
Conformal Coating
– Runs– Runs
Conformal Coating – Runs
ACCEPTABLE
Not to exceed 5 percent of PWB surface
area.
Fish Eyes
Conformal Coating – Fish Eyes
Conformal Coating
– Fish–Eyes
Conformal
Coating
Fish Eyes
177
Conformal Coating – Dewetting
Conformal Coating – Dewetting
Conformal Coating – Fish Eyes
UNACCEPTABLE Loss of adhesion.
Conformal Coating – Dewetting
Conformal Coating – Dewetting
Figure 13.4
: Conformal
Coating – Defects
Coverage Defects
Figure 13.4 : Conformal
Coating
– Coverage
13.7.2
Precautions for Local Potting & Conformal Coating
Presence of any of the contaminants or bubbles larger than 0.76mm (0.03 inch) or bubbles bridging more than
50% of the distance between electrically, uncommon conductors, for normal electrical voltages be rejected.
There should not be any contaminants, otherwise it will lead to rejection. Coating shall exhibit no charred
spots, no excessive runs or build up. Coating can be measured on a separate test samples and it is peeled off and
its thickness can be determined using micrometer.
13.8
Bonding
13.8.1
General
Bonding provides a method for joining surfaces of parts or materials using a polymer rather than fasteners.
13.8.1.1
Surface Preparation.
Surfaces being bonded shall be cleaned and prepared in such a manner as to achieve an acceptable bond between
the surface and the adhesive. When cleaning and priming surfaces, as required, masking may be needed to prevent
contamination of adjacent surfaces.
13.8.1.2
Requirements
• Markings shall be clearly visible after completion of bonding processes unless otherwise allowed by the
assembly documentation
• The bonding material shall adhere to all surfaces to be joined.
• The leads of these types of components shall be staked
• For thermal joints, bond line control and coverage shall be as per the assembly documentation and verified
by QA.
• Bonding shall be performed before conformal coating
178
14 REPAIR & REWORK
14.1
Repair/Rework
• Repair involves part change whereas rework does not require part change.
14.2
Repair criteria
• The facility shall carry out repairs only when it is necessary to restore the functional or performance capability
of a printed circuit assembly that has been damaged during assembly or during testing.
14.3
Number of repairs
• The total number of repairs (involving soldering or epoxy adhesives) to any one printed circuit board assembly
shall be made minimal preferably less than 2% of total component count.
• When a printed circuit board assembly supports more than 120 passive chip components, the total number
of repairs shall not exceed 5 % of the passive chip components.
14.4
Modifications
14.4.1
Modification criteria
• The modification of a printed circuit assembly shall be the revision of interconnecting features by interrupting
conductors or adding components as well as wire connections.
• The revision of connections to one component or connector shall count as one modification.
• The addition of one component shall count as one modification.
14.5
Number of modifications
The total number of such modifications on any one printed circuit board shall not exceed three for any area of 25 cm2.
14.6
Rework
14.6.1
Rework criteria
• All aspects of the reworked solder joint shall conform to para 9.5 and 9.6.
14.6.2
Number of reworks
• The total number of such reworks on any one joint shall not exceed two times.
14.6.3
Other requirements
• Do not reuse the removed components.
• It shall be ensured that any rework doesn’t affect other components in its vicinity.
14.7
Removal of conformal coating
14.7.1
Requirements
• The facility shall not use soldering irons for coating removal.
o
The high operating temperatures cause charring of the coatings and possible de-lamination in the
base laminate.
• It shall be verified that no damage occurs to the printed wiring assembly by cutting around the area to be
repaired.
179
• While using the thermal parting tip, it shall be ensured that no damage occurs on any adjacent solder joints
and circuitry.
14.7.2
Procedure
• Use method 14.17.1 for polyurethane and silicone type coatings.
• Use method 14.17.1.1 for epoxy type coatings.
14.7.3
Acceptance criteria
• The solder on the area to be repaired shall be accessible.
• None of the following shall occur:
o
Melting of adjacent solder joints or circuitry;
o
Blistering, delamination, measling or charring of coating or laminated base material;
o
Cuts, scratches or other damage to printed wiring.
14.8
Solder joint removal and unclinching
14.8.1
Procedure
• Depending on the kind of solder joint, the facility should use one or more of the methods described in
14.18.3
o
To select the appropriate method refer to the method descriptions.
o
Prior to commencing, the facility should remove any conformal coating that has been applied to the
circuit in conformance with the procedure set out in 14.16.
14.8.2
Acceptance criteria
• There shall be no solder splatters present on the PCB.
• None of the following shall occur:
o
Melting of adjacent solder joints or circuitry;
o
Lifting of the solder joint or pad track;
o
Delamination of the base laminate;
o
Damage to printed wiring or solder joint or pad.
o
Damages such as cuts, scratches.
14.9
Repair of damaged conductor tracks
14.9.1
Requirements
• The damage shall not involve a length of track in excess of five times the conductor width.
14.9.2
Procedure
• For conductor tracks having a thickness > 30 um, the selection of tinned copper or silver wire shall be in
conformance with Table 14‑1.
• The maximum wire diameter shall not be greater than two thirds of the width of the conductor.
• The facility should use method 14.19.3
14.9.3
Acceptance criteria
• After repair, the facility shall inspect the soldered joints in conformance with the accept/reject criteria of
para 9.5 & 9.6
180
Table 14‑1: Wire diameters for given conductor widths
14.10
Conductor width (mm)
Wire size AWG
Wire diameter (mm)
minimum
0.30
34
0.16
0.40
32
0.20
0.50
30
0.25
0.80
28
0.32
1.60
26
0.40
3.20
24
0.51
Repair of lifted conductors
14.10.1 Requirements
• The length of the lifted conductor to be repaired shall not exceed one-half of the length of conductor
between two terminal areas and 2 cm, whichever is smaller.
• The number of repairs per printed circuit board assembly shall conform with the requirements detailed in
para 14.3
14.10.2
Procedure
• Depending on their applicability, the facility should use either method 14.21.1 or 14.21.2
• Before applying method 14.21.1 or 14.21.2 the facility shall remove any components or solder that can
interfere with the repair of the damaged conductor as described in clauses 14.9 before proceeding.
14.10.3
Acceptance criteria
• The lifted conductor track shall be secured to the base laminate by the epoxy
• The epoxy shall be fully cured.
• The epoxy shall not cover areas that require subsequent soldering.
• Where components have been removed and subsequently replaced, the facility shall inspect the soldered
joints in conformance with the accept/reject criteria of para 9.5
14.11
Wire to wire joints
14.11.1 Requirements
• The facility shall undertake repairs only after necessary approval.
• If the wire is shaped to by­pass a component, the wire shall have additional fixing at each bend.
• During the process, the facility shall avoid the ingress of flux between conductor and insulating sleeve.
14.11.2
Procedure
• The facility shall use method 14.22.
14.11.3
Acceptance criteria
• The facility shall inspect the joint as per agreed method.
• No damage allowed to adjacent conductor tracks, base laminate or components.
181
14.12
Removal and replacement of axial and multi­leaded components
14.12.1
Requirements
• If the portion of lead on the solder side of the board is removed, any clinched portion of the lead shall also
be removed
• Exercise extreme caution when dealing with circuit boards having plated through holes as the connecting
surfaces rupture easily. Very small lands are also hazardous as they loosen if the temperature of the base
material is too high or excessive force is exerted during removal of the leads.
14.12.2 Procedure
14.12.2.1 Axial leaded devices
• Cut the vertical section of the component leads just above the solder fillet and parallel to the surface of the
board. Ensure that burrs are not formed.
• Remove the remaining portion of the lead on the other side of \the board using either a soldering iron with
wick or vacuum extractor, then gently pull the lead with long-nose pliers when the solder is molten.
• Remove excess solder with a vacuum extractor or solder remover.
• Clean up the area of the joint with an approved solvent.
• Mount a new component and solder in place
14.12.2.2 Multi leaded devices
• Cut component leads using diamond saw or side-cutting pliers
• older and remove the remaining portion of the leads on the other side of the board, while gently pulling with
long-nose pliers when the solder is molten. Ref. figure 14.1.
• Remove excess solder with a vacuum extractor or by the wicking method.
• Clean the area of the joint with an approved solvent.
• Mount a new component and solder in place
Figure 14.1 : Removal of multi-lead components, clipping of component leads
14.12.3 Acceptance criteria
• After repair, the facility shall inspect the soldered joints in conformance with the accept/reject criteria of
para 9.
14.13
Removal and replacement of flat­pack components
182
14.13.1 Procedure
• Apply heat to the soldered joint,simultaneously lifting the leads by sliding a piece of thin Kapton® orTeflon® sheet progressi
vely from the non-soldered section of the lead towards the soldered section
• Remove adhesive bonding, if applicable, by suitable means.
• Clean solder area using an approved cleaning solvent.
• Inspect surface of joint for raised areas of track and overheated solder.
• Remove overheated solder by wicking and re-tin the solder area.
• Position new component, tack it to the board for stability if required and solder in place using a heatcontrolled soldering iron. If package density allows, a reflow machine with a single lead tip (pegtip) may be used. Ref. figure 14.2.
• Apply new adhesive if required
Figure 14.2 : Removal of flat pack components
14.13.2 Acceptance criteria
• After repair, the facility shall inspect the soldered joints in conformance with the accept/reject criteria of
para 9
14.14
Modification of component connections
14.14.1
Requirements
• For modification of DIL package connections, the facility shall not crop or insulate more than one third of the
leads per side.
• No more than two leads shall be cropped or insulated on each side of a 14­lead DIL package
14.14.2
Procedure
• Using lint free paper, mask as much as possible of the circuitry surrounding the area to be re-worked.
• Remove the existing DIL package
• As required, crop the leads of a replacement component in line with the bottom of the component body. (The
component may be of either a “J” lead or a “side-brazed” lead configuration).
• De-gold and pre-tin the leads in two operations. If connection of cropped leads to the board is required, then
de-gold and pre-tin the cropped leads by hand. For cropped side-brazed leads de-gold and pre-tin the entire
lead shoulder (but this does not necessarily include the gold-plating on the braze fillet).
• Solder the replacement component into position.
183
• Strip, pre-tin (with use of a heat sink to prevent wicking) and form approved insulated wire for connection of
cropped leads to board.
• Solder, wire to cropped leads to form a lap joint. Wires may be led down onto the board or may pass away
from the board. Use the lap joint with a length of three times the stripped wire diameter. For cropped “J”leads, solder for not more than 3 seconds at a tip temperature of (250 ± 5) °C. For cropped “side-brazed”
leads, solder for not more than 3 seconds at a tip temperature of (250 ± 5) °C.
• Clean soldered area with approved solvent.
• Position wire connections on board and bond to the board.
• Re-apply conformal coating and cure in conformance with the manufacturer data sheet.
14.14.3
Acceptance criteria
• After modification and where components have been removed and subsequently replaced, the facility shall
inspect the soldered joints in conformance with the accept/reject criteria as per para 9
14.15
Quality assurance
14.15.1.1 Data
• The facility shall retain the quality records (e.g. logbooks) for at least ten years
• Quality records shall contain, as a minimum, the following:
o
Copy of final inspection documentation
o
Index of limited life articles and their use times
o
Non-conformance reports and corrective actions
o
Copy of the inspection and test results with reference to the relevant procedure.
14.15.1.2 Non-conformance
• Any non-conformance shall be handled as per ISRO-PAS-100.
• The facility shall record repair, modification or rework in the documentation of the printed circuit board
assembly.
14.16
Removal of conformal coating
14.16.1 Introduction
The operator removes any conformal coating before the disassembly of components from printed circuit assemblies
to ensure that:
• the solder on the area to be repaired is freely accessible
• The re­soldered joint is not contaminated.
14.16.2 Tools and materials
• Suitable cutting instrument,
• Thermal parting device complete with tips,
• Brushes,
• approved solvent and
• Pencil type vacuum cleaner.
184
14.17
Methods for the removal of conformal coating
14.17.1 Method for the removal of polyurethane and silicone type coating
• Carefully cut through the conformal coating that envelopes the component to be replaced, using a suitable
cutting instrument.
• Peel away the cut area and, while doing so, apply the vacuum cleaner to the area to remove any small loose
particles of conformal coating.
• Thoroughly clean the exposed area with an approved solvent, as specified in para 5.4.1 before removal of
solder joints and apply minimum quantity of solvent and prevent solvent ingress beneath the exposed edges
of the conformal coating.
14.17.1.1 Method for the removal of epoxy type coating
• Select an appropriate thermal parting tip to suit the work piece configuration. Set the nominal tip temperature,
using the manufacturer’s recommended procedure. Ref. figure 14.3.
• Apply the thermal parting tip to the coating, using a light pressure. Regulate the tip temperature to a point
where it will effectively “break down” the coating without scorching or charring. Gradually reduce the coating
thickness around the component body without contacting the board surface. Remove as much coating as
possible from around component leads to allow easy removal of the leads. Preclip the leads of the component
to be removed. This makes it possible later to remove the component body separately from leads and
solder joints. Use the pencil type vacuum cleaner and a bristle brush to remove waste material during the
parting process to allow good visual access and prevent inadvertent damage to the board and particulate
contamination.
• When sufficient coating has been removed, leaving only a small bonded joint between component and board,
heat the component body with the thermal parting unit or small soldering iron to weaken the bond at the
component or epoxy interface and lift the component free of the circuit board.
• Remove now,
• The remaining coating material by additional thermal parting. Then remove the remaining leads and solder
joints by an appropriate solder extraction means as described in 14.18.
185
Pencil type vacuum
cleaner
Thermal parting device
Figure 14.3 : Removal of coating by thermal parting device
Figure 14.3 : Removal of coating by thermal parting device
14.18
Solder joint removal and unclinching
14.18.1 Introduction
A basic step for the repair of an electronic circuit is the removal of the solder joint retaining the component in
position.There are various methods of achieving this and avoiding thermal and mechanical damage during component
replacement. The following clauses describe a number of removal methods which can be used according to the
facilities and the specific conditions.
14.18.2 Tools and materials
• Soldering iron or hot jet blower (as applicable)
• Solder sucker: continuous vacuum device, solder wicking wire (as applicable)
• Thermal parting device, tweezers, pliers (as applicable)
• Side cutters
• soldering iron, solder and flux
• heating means (infrared or hot air)
• approved solvent
• wire stripper
• heat shunt
• heat shrink sleeving (transparent, approved type)
186
• approved insulated wire
• wire clamping device
• Cotton gloves or finger cots
• Approved solvent
• space approved epoxy adhesive (compatible with base epoxy)
• plastic or wooden toothpicks
• strip of thin PTFE sheet and small weights.
14.18.3 Methods for solder joint removal and unclinching
14.18.3.1 Method for solder extraction with continuous vacuum
To obtain the continuous vacuum, the operator either uses a vacuum pump or a separate vacuum device attached to
the soldering iron. The solder can then be withdrawn from the joint either directly through the tip of the soldering
iron or through a separate vacuum device attached to the soldering iron. The heated tip of the iron is applied to the
soldered joint and, when a melt is noted, the vacuum is activated,
With appropriate handling, this method will minimise the overheating problem. The correct positioning of the
vacuum device tip is shown below
Vacuum device tip
Vacuum device tip
Air flow
Air flow
Figure 14.4 : Continuous vacuum solder extraction on stud lead
14.4
: Continuous
vacuum solder extraction on stud lead
14.18.3.2 Method Figure
for solder
extraction
using sucker
This is a method in which the molten solder is removed by means of a sucker tip. There are several variations
of this technique, but all of them have the disadvantage that the vacuum is applied only in short pulses and the
procedure may have to be repeated several times. In addition, since the work is performed with two different devices
simultaneously, i.e. soldering iron and sucker tip (refer to 0), this method finds only limited use.
14.18.3.3 Method for hot jet extraction
This method relies on a thin jet of heated air (200 oC to 300 oC) to melt the defective solder joint. It is well suited
Hand sucker
to circuits in flat packages. Owing
to the controlled dimensions of the jet, one can unsolder connecting wires
individually without affecting the other joints. The molten solder is then wicked off or vacuumed away. This method
finds only limited use.
Figure 14.5 : Pulse-type solder sucker in use
187
Figure 14.4 : Continuous vacuum solder extraction on stud lead
Hand sucker
Figure 14.5 : Pulse­type solder sucker in use
Figure 14.5 : Pulse-type solder sucker in use
Hot jet blower
Protective sleeving
Hot jet blower
Figure 14.6 : Hot Jet Blower Method
Figure 14.6 : Hot Jet Blower Method
14.18.3.4 Wicking Method
Protective sleeving
This method incorporates braiding, saturated with flux or stranded wire heated in contact with the solder joint.
Capillary action causes the molten solder to be drawn into the wick. This method works well on large surface
joints and can be applied to through hole solder joints or, with more difficulty, to the solder between a clinched
Figure 14.6 : Hot Jet Blower Method
lead and a terminal area. As the amount of wicked out solder increases, the capillary action becomes less effective.
Thus, joints containing a large amount of solder often require the repeated application of heat, creating a danger of
overheating.
Wicking braid
Wicking
braid
Component
Figure 14.7 : Cross-sectional view of wicking method
Component
Figure 14.7 : Cross-sectional view of wicking method
Figure 14.7 : Cross-sectional view of wicking method
188
14.18.3.5 Method for unclinching of leads
• Initial solder removal: first use method 14.18.3.1 (Vacuum) or Wicking method to remove at least the surface
solder from around the clinched lead and terminal area. This permits observation of the true circumstances
of the clinched lead contact to the terminal area and the extent of the remaining solder joint between them.
• After solder removal from the clinched area, the joint is allowed to cool down for a few seconds and the wire
is carefully lifted with a thin plastic rod or similar device. This method is designed to prevent damage to the
terminal area. In lieu of the thermal parting device, tweezers or pliers may be used, provided that no contact
is made with the terminal area.
• Final solder removal: once the clinched leads are straightened, one may proceed to remove the solder joints
by method 14.18.3.1, treating them as if they were originally unclinched leads.
Thermal parting device
Figure 14.8 : Hot unclinching with thermal parting device
Figure 14.8 : Hot unclinching with thermal parting device
14.19
Repair of damaged conductor tracks
14.19.1 Introduction
The damage to the conductor can be in one of the following forms:
• complete break;
• Scratches or nicks that reduce the current carrying capacity of the conductor to levels below standard
requirement.
14.19.2 Tools and materials
• Soldering iron and solder,
• Tweezers,
• Epoxy resin,
• Approved solvent,
• Fibre eraser,
• Cleaning tissue.
14.19.3 Method for the repair of damaged conductor tracks
• Clean both sides of break in conductor, to at least three times the track width on each side, with a fibre eraser
and then with an approved solvent.
• Cut a piece of applicable gauge tinned copper or silver wire to at least six times the track width.
• Hold the wire with a pair of tweezers on centre line of conductor and solder in place.
• Clean the area with approved solvent.
189
• Flow a small amount of epoxy resin over the entire repair and cure.
• Alternative coatings after approval may be used.
14.20
Repair of lifted conductors
This procedure is applicable where a porti on of the conductor has lifted from the substrate but not broken.
2 cm max.
Lifted conductor
Base laminate
Figure 14.9 : Lifted conductors
Figure 14.9 : Lifted conductors
14.21
Methods for repair of lifted conductors
14.21.1 Method for the use of epoxy under conductor
• Clean underside of lifted conductor and surrounding area with an approved solvent.
• Remove all particles that prevent the lifted conductor from making intimate contact with the surface of the
substrate.
• Using a hot air lance, gently blow the adhesive under the entire length of lifted conductor. Ensure the epoxy
does not come into contact with surfaces required subsequently for soldering.
• Press conductor into contact with substrate by the application of small weights; cover the interface between
the weights and track with a thin piece of PTFE. Cure in conformance with the manufacturer data sheet
• Do not handle repaired units until the epoxy has cured.
Epoxy
Figure 14.10 : Repair using epoxy under conductor
Figure 14.10 : Repair using epoxy under conductor
190
Figure 14.10 : Repair using epoxy under conductor
14.21.2 Method for the use of epoxy over conductor
• Clean the upper face of the lifted conductor and surrounding area with an approved solvent
• Apply epoxy to the surface of the lifted conductor and to its surroundings to a distance of at least 3 mm in
all directions from the damaged area.
• Cure in conformance with the manufacturer data sheet.
• Do not handle repaired units until the epoxy has cured.
Epoxy
Figure 14.11 : Repair using epoxy over conductor
Figure 14.11 : Repair using epoxy over conductor
14.22
Wire to wire joints
14.22.1 Introduction
Wire­to­wire joints are used for wires that are broken or require lengthening for modification purposes.
14.22.2 Method for wire to wire joining
• Cut wires to the correct length.
• Remove wire insulation as detailed in para 10.6.4 and ensure proper insulation clearance. If disturbed,
restore the lay of a stranded conductor. Do not use bare fingers to achieve this.
• Pre­tin the wires in conformance with para 10.18.6 Place heat shrink sleeving over the wire insulation in
readiness for sliding over the joined wire.
• If necessary, position the wires into joined configuration and maintain position with clamping device
• Solder the wires together (using heat shunt on each lead) to form a lap type joint. Ensure a low contact angle
between the solder and wires and ensure that the contour of the individual conductor wires is visible.
• Clean the area with approved solvent to remove flux.
• Position shrink sleeve over joint and shrink to size in conformance with manufacturer’s instructions. Ensure
that the shrink temperature is always below the melting point of the solder.
• Position the extended wire on the board and bond to the board using a suitable approved adhesive. Bond
the lead along its length at intervals of not more than 2.5 cm. Make the first spot bond of the extension wire
within 1.5 cm from the component­to­wire soldered joint.
14.23
Addition of Components
Methods for addition of components
14.23.1
Method for additional component mounting on reverse (non component side)
of board
• Using lint free paper, mask as much as possible of the circuitry surrounding the area to be worked.
• Carefully remove any conformal coating from the area to be worked. Use the method described in 14.16.
• If the new component lead traverses conductors, assemble insulating sleeve to the section of the lead that will
not be soldered
• Form the component lead. Form the section of lead to be soldered so that it follows the centre­line of the
conductor track.
191
• Use component lead diameter (or width) less than or equal to two thirds of track width.
• Solder into position.
• Remove protective paper.
• Clean soldered area with approved solvent.
• Apply conformal coating and cure in conformance with the manufacturer data sheet
PCB track
4 mm min.
Insulating sleeving
New component
Base laminate
Figure 14.12 : Additional components mounted on reverse (no component) side of board
Figure 14.12 : Additional components mounted on reverse (no component) side of
14.23.2board
Method for additional components mounting on component side of board
• Using lint free paper, mask as much as possible of the circuitry surrounding the area to be worked.
• Carefully remove any conformal coating from the area to be worked. Use the method described in 14.16.
• Drill holes in the printed circuit assembly adjacent to the conductor tracks to which the component is to
be joined. Use the vacuum cleaner during this operation to remove any fine dust particles. Drill holes with
diameters equal to component lead diameter, plus 0.25 mm to 0.50 mm. Position the hole such that the edge
of the hole is a minimum of 0,2 mm from the edge of the conductor.
• Form the component leads and assemble the component to the board. Components may also be mounted
parallel with existing tracks to avoid additional bending of leads. Consider the stress relief and bend radius
requirements.
• Place the section of the component lead to be soldered along the centre line of the conductor and solder into
this position.
• Use component lead diameter (or width) less or equal to two thirds of track width.
• Clean soldered area with approved solvent.
• Inspect in conformance with clause para 9
• Apply conformal coating and cure according to the manufacturer data
14.24
Method for the addition of a wire link onto metallized cap of
chips directly glued on PCB
• Precautions given by part manufacturer should be strictly adhered to.
• This operation shall be carried out after obtaining necessary approvals.
• Put an epoxy spot at the centre of the component, suited with the size of package.
• Bond the chip on PCB and cure.
192
• Check that the epoxy spot does not extend onto metallized cap.
• Solder the silver wires or insulated wire (refer to Figure 14.13)
• Clean the soldered area with approved solvent.
• Inspect in conformance with para 9
• Position the extended wire on the board and bond to the board by using a suitable space approved adhesive
(epoxy spot). Bond the lead along its length at intervals of not more than 3 cm. if it is longer than 3 cm, make
the first spot bond of the extension wire just after the wire stress relief.
• Re­apply conformal coating and cure in conformance with the manufacturer data sheet.
Figure 14.13 : Addition of a wire link onto metallized cap of chips directly glued on PCB
Figure 14.13 : Addition of a wire link onto metallized cap of chips directly glued on
PCB
14.25
Method for the addition of a wire link onto terminal pad of soldered chips
• Precautions given by part manufacturer should be strictly adhered to.
• This operation shall be carried out after obtaining necessary approvals.
• Flux the chip solder joint with brush.
• Solder the silver wires or insulated wires (refer to Figure 14.14) over a length greater than 1.2 mm.
• Clean soldered area with approved solvent.
• Inspect joint in conformance with section 9.5
• Position the extended wire on the board and bond to the board by using an approved adhesive (epoxy spot).
Bond the lead along its length at intervals of not more than 3 cm. If it is longer than 3 cm, make the first spot
bond of the extension wire just after the wire stress relief.
• Re­apply conformal coating and cure in conformance with the manufacturer data sheet.
Figure 14.14 : Addition of a wire link onto terminal pad of soldered chips
Figure 14.14 : Addition of a wire link onto terminal pad of soldered chips
193
15 SPECIAL PROCESSES
15.1 SPLICING
15.1.1
General
Splices may be configured as a simple splice, having one conductor joined to another conductor, or as a complex
splice with one or more conductors joined to one or more other conductors. Splices may be completed using
crimping or soldering processes.
15.1.2
General Information
The use of splices in a harness design should be minimized as much as possible. Unless identified as part of the design
in the fabrication documentation, splices shall be considered as repairs.
Solder connections shall be inspected prior to and after shrink tube heat application . All areas that will be under
insulation sleeving shall be cleaned with an approved solvent in para 5.4.1. Cleaning solution application shall be
controlled to minimize propagation to other areas of the harness or cable being spliced.
15.1.3
Design Considerations
The simplest and most reliable wiring design is one that results in the routing of a dedicated, continuous, and
unbroken conductor from point to point. The following shall be incorporated into any splice design:
• Shrink sleeve over the splice area shall be protected from cold flow and abrasion
• Splices shall be covered with a single layer of heat-shrinkable tubing. The tubing/insulation shall completely
encapsulate the splice body and extend over the wires’ insulation a minimum of two times (2X) the diameter
of the largest wire in the splice. Additional layers of tubing/insulation may be added to increase electrical
isolation or to provide additional environmental or mechanical protection. Each additional layer shall overlap
the underlying layer by at least two (2) diameters of the largest wire in the splice at each end.
• Splices shall be staggered to minimize buildup of the wire bundle diameter.
• Splices shall not be located in areas of the cable where flexing may occur or in bend radii where the primary
insulation may be compromised.
• There shall be no splices within two harness diameters of a breakout.
• Splices, including location and type, shall be identified and fully defined on the associated drawings.
• Heat shrinkable tubing shall not be used in the vicinity of sensors, optics, or other devices whose performance
can be degraded by surface contamination.
• The solder alloy and the flux type in heat shrinkable soldering devices shall be selected for the type of wire
being spliced.
• Multiple splices along the same conductor should be avoided.
• Splices shall not be installed where adjacent components, wires, solder joints, structures, etc. cannot be
adequately shielded or otherwise protected from a heat source during the splice installation.
15.1.4
Splicing Methods
Splices shall be terminated using one or more of the following methods:
• Lap Splice
• Lash Splice
194
• Solder Sleeve
• Western Union
• Solder Ferrule
• Crimped Contact
• Crimp Ferrule
• Wire In-Line Junction Devices (Jiffy Junctions)
15.1.5
Soldered Splices
Solder-style splices are primarily designed for the termination of a single conductor to a single conductor, but may
be used for the termination of multiple conductors (i.e., a branch or fan-out circuit), providing the splice design
is appropriately configured/sized to accommodate all the conductors without modifications. Solder-style splices
produce a smaller, more compact splice termination, with significant weight reductions over crimp-style splices.
15.2 Lap Splice
A lap splice is where the conductor ends are laid parallel to, and overlap each other, and are terminated with a
solder joint (see Figure 15‑1 and Figure 15‑2). Lapped end type splices shall be accomplished in accordance with
paragraph 15.3.2
Figure 15.1 : Pre-Tinned Conductors
15.2.1
Figure 15.2 : Soldered Conductors
Preparation.
Figure15.1
15.1: :Pre-Tinned
Pre-TinnedConductors
Conductors
Figure
Figure15.2
15.2: :Soldered
SolderedConductors
Conductors
Figure
The conductors shall be pre-tinned, parallel to, and in contact with each other at least three wire diameters, but not
more than six wire diameters. The conductors to be spliced shall not be twisted together. Conductors shall not
overlap the insulation of the other wire. There shall be no protruding wire strands
.
15.2.2
Soldering.
Figure
15.1
Pre-TinnedConductors
Conductors
Figure15.2
15.2: :Soldered
SolderedConductors
Conductors
: :Pre-Tinned
Figure
Apply solderFigure
so that15.1
a fillet
forms on both
sides of the conductors
for the
entire length
of the area where they
overlap. After soldering, the conductors’ contours shall be discernible
Figure
15‑3 and
Figureover
15‑4).
Figure(see
15.4
: Double
Sleeving
Figure 15.4 : Double Sleeving over
Soldered Connection
Connection
Soldered
Figure15.3
15.3: :Sleeving
Sleevingover
over
Figure
Soldered
Connection
Soldered Connection
Figure 15.3 : Sleeving over Soldered Connection
Figure 15.4 : Double Sleeving over Soldered Connection
Figure15.4
15.4: :Double
DoubleSleeving
Sleevingover
over
Figure
Soldered Connection
Connection
Soldered
Figure 15.3 : Sleeving over
Connection
Soldered Connection
15.3 : Sleeving over
15.3 Lash Figure
Splice
Soldered
A lash splice (see Figure 15.6) is a soldered splice identical to the lap splice (see Figure 15.7) except for the
addition of a single strand wire winding (over lash) that binds the conductors together.
195
15.3.1
Preparation
The conductors to be spliced shall be pre-tinned (see Figure 15.5), parallel to, and in contact with each other at
least three wire diameters, but not more than six wire diameters. The conductors to be spliced shall not be twisted
together. Conductors shall not overlap the insulation of the other wire. There shall be no protruding wire strands.
Figure
15.5: Pre-Tinned
: Pre-Tinned
Figure
15.5
Figure
15.6 :: Lashing
of
15.715.7
: Soldered
Connection
Figure
15.6
Lashing
of Figure
Figure
: Soldered
Pre-Tinned
Conductors
Connection
Pre-Tinned
Conductors
The wire used to lash the conductors together shall be a solid wire. It shall be wrapped a minimum of 6 turns and
the wraps shall not extend past the end of either conductor (see Figure 15.6). The lash may be either open spiral
(no more than 2 lashing wire diameters between turns) or closed (each wrap is in contact with its adjacent wrap).
The wraps shall not overlap and the ends of the wrap shall be trimmed flush prior to soldering to prevent the ends
Figure
Figure
15.515.5
: Pre-Tinned
: Pre-Tinned Figure
Figure
15.615.6
: Lashing
: Lashing
of of
Figure
Figure
15.715.7
: Soldered
: Soldered
Pre-Tinned
Pre-Tinned
Conductors
Conductors Connection
Connection
from protruding through insulation. An alternative configuration for the lash splice is the Lash End Type Splice (see
Figure 15.8 and Figure 15.9).
Figure 15.8 : Pre-Lash End Type
Splice
Figure 15.8 : Pre-Lash End Type Splice
Figure
Figure
15.815.8
: Pre-Lash
: Pre-Lash
EndEnd
Type
Type
Splice
Splice
15.3.2 Soldering.
Figure 15.9 : Lash End Type Splice
Figure 15.9 : Lash End Type Splice
Figure
Figure
15.915.9
: Lash
: Lash
EndEnd
Type
Type
Splice
Splice
Apply solder so that a fillet forms on both sides of the conductors for the entire length of the area where they
overlap and all turns of the wire used to lash the conductors together. After soldering, the conductors’ contour need
not be discernible, however the ends of the conductors and the contour of the wire used to lash the conductors
together shall be discernable.
Figure
: Soldered
Lash Splice
Splice
Figure
Figure15.10
15.1015.10
: :Soldered
Soldered
Lash
Lash
Splice
15.4
Solder Sleeve
15.4.1
Preparation
Figure
15.11
: Sleeved Lash
Splice
Figure
Figure
15.11
15.11
: :Sleeved
Sleeved
Lash
Lash
Splice
Splice
Ensure that the solder ring is centered over the stripped conductors to be spliced and the sealing rings are over the
wires’ insulation (see Figure 15‑12).
Figure
Figure15.12
15.12: :Solder
SolderSleeve
SleevePrior
PriortotoFlow
Flow Figure
Figure15.13
15.13: :Fully
FullyMelted
MeltedSolder
SolderSleeve
Sleeve
196
15.4.2
Soldering.
Equipment (e.g., heat gun) used shall be capable of providing uniform heat of the type (e.g., IR, convection) and
temperature range recommended by the manufacturer of the solder sleeve. Apply heat until the solder ring is
fully wetted to the conductors and the outline of the ring is no longer discernible (see Figure 15‑13): the insulation
sleeve conforms to the profile of the wires being spliced: and the sealing rings are in intimate contact with the outer
circumference of the insulation of the wires being spliced. After soldering, the connection shall comply with the
Figure 15.10 : Soldered Lash Splice
inspection
Figurerequirements.
15.10 : Soldered Lash Splice
Figure 15.11 : Sleeved Lash Splice
Figure 15.11 : Sleeved Lash Splice
Figure 15.12 : Solder Sleeve Prior to Flow
Figure 15.13 : Fully Melted Solder Sleeve
Figure 15.12 : Solder Sleeve Prior to Flow Figure 15.13 : Fully Melted Solder Sleeve
Figure 15.12 : Solder Sleeve Prior to Flow Figure 15.13 : Fully Melted Solder Sleeve
15.5 Crimped Splices
Crimping wires into contacts is a method for splicing wires together without soldering. The tooling verification process
and the completed termination shall comply with all the requirements of this document for a crimp termination
except as specified herein for jiffy junction devices. The contact/wires size and crimp tool setting combination shall
be verified using the same requirements as for any machined contact .Create 3 test specimens and pull each wire in
the specimen. The wire pulled shall meet the tensile requirement for a single wire of the same gage being tested in
its “properly sized” contact
When crimping multiple wires into a contact, the total circular-mil-area (CMA) of all the wires must be calculated
into an Equivalent Wire Size (EWS) in order to select the properly sized contact. If the calculated EWS does
not exactly match a single wire size, use the wire size that is next largest to the calculated CMA to select the
contact size.
Figure 15.14 : Stripped Wires Prior to Insertion
Figure 15.14 : Stripped Wires Prior to Insertion
15.6 Modified Crimp Contact
Use the appropriate crimping tool and positioner. Determine the crimp tool selector setting based on the contact
and “equivalent” wire size. Strip the wires to be spliced. The wires being spliced shall not be twisted and shall be
inserted into the barrel parallel to each other (see Figure 15‑15 and Figure 15‑16). All wires shall be seated
against the bottom of the barrel (see Figure 14‑16). Crimp and inspect per the requirements of this document.
The pin section of the contact shall be trimmed at its base and deburred (see Figure 14‑17). Cuts extending into
the crimp barrel body or distortions of the crimp barrel body shall be cause for rejection. Shrink sleeving shall be
197
installed over the termination so that it extends at least 2 crimp barrel diameters beyond the end of the contact and
beyond the insulation of the wire that has the greatest insulation gap (see Figure 14‑18).
Figure 15.15 : Stripped Wire Bundle Prior
Figure 15.16 : Wires Crimped Within
to Insertion
Contact
Figure15.15
15.15: :Stripped
StrippedWire
WireBundle
BundlePrior
Prior
Figure15.16
15.16: :Wires
WiresCrimped
CrimpedWithin
Within
Figure
Figure
toInsertion
Insertion
Contact
to
Contact
Figure 15.15 : Stripped Wire Bundle Prior to Insertion
Figure 15.16 :Wires Crimped Within Contact
Figure
15.15
: Stripped
Wire
Bundle
Prior
15.16
: Wires
Crimped
Within
Figure
15.15
: Stripped
Wire
Bundle
Prior Figure
Figure
15.16
: Wires
Crimped
Within
to Insertion
Contact
to Insertion
Contact
Figure 15.17
Figure 15.18
Contact Trimmed
and15.17
Deburred:
Figure
15.17
Figure
Contact Covered With
Shrink
Sleeving
Figure
15.18
Figure
15.18
Figure 15.17 : Contact Trimmed and Deburred
Figure 15.18 Contact Covered With Shrink Sleeving
ContactTrimmed
Trimmedand
andDeburred:
Deburred:
Contact
ContactCovered
CoveredWith
WithShrink
ShrinkSleeving
Sleeving
Contact
Figure
15.18
Figure 15.18
15.7 ButtFigure
Splice
15.17
Figure
15.17
The butt splice (see Figure 15‑19) is one of the simplest and most often used crimp splices, and obtains its name
Contact
Trimmed
andand
Deburred:
Contact
Trimmed
Deburred:
Contact
Covered
With
Shrink
Sleeving
Contact
Covered
With
Shrink
Sleeving
from the alignment of the conductors in the crimp barrel. The crimp is available in both insulated and uninsulated
versions. The splice provides a very small diameter profile when installed in a harness.
15.7.1
Preparation.
Figure 15.19 : Butt Splice
Figure
15.19 : Butt Splice
Figure
15.19
Butt
Spliceinto the crimp barrel, such that the
Figure
Splice
The conductor(s) shall be stripped) and trimmed to
length15.19
to
allow: :Butt
full
insertion
conductor ends are visible in the wire inspection hole
15.7.2
Contact Sizing
.
Figure
15.19
: Butt
Splice
Figure
15.19
: Butt
Splice
• Single Conductor Configurations. The butt splice contact shall be sized and selected according to the
conductor-crimp combinations listed in MIL-DTL-22520G [Table III], or as specified by the crimp contact
manufacturer.
• Multiple Conductor Configurations. For designs involving the crimping of multiple conductors in one or
both ends of the contact (see Figure 15.20), the equivalent wire size (EWS) must be determined in order
to select the appropriate contact size. To calculate EWS, the sum of the circular mill area (CMA) of the
wires to be spliced, multiplied by 1.25, shall determine the equivalent wire size and the corresponding initial
contact size.
Figure 15.20 : Butt Splice Prior to Wire Insertion
Figure 15.20 : Butt Splice Prior to Wire Insertion
198
Figure
15.20
: Butt
Splice
Prior
Wire
Insertion
Figure
15.20
: Butt
Splice
Prior
to to
Wire
Insertion
Figure
15.21
::Butt
Splice
Prior
to Crimp
Figure
15.22
: Properly
Crimped Butt
Butt
Splice
Figure
15.21
Butt
Splice
Prior
CrimpFigure
Figure
15.22
: Properly
Crimped
Butt
Splice
Figure
15.21
: Butt
Splice
Prior
to to
Crimp
15.22
: Properly
Crimped
Splice
15.7.3
Assembly
• The conductor(s) shall be fully inserted in the crimp barrel, parallel to each other, and without modification
to the conductor(s) or crimp barrel (see Figure 15.21).
• Conductor insulation gap(s) should be approximately equal, but shall comply with the insulation gap
requirements specified in (par 10.6.7) for each conductor size.
• The contact shall be crimped to the conductor per the contact manufacturer’s recommendations or engineering
documentation. Indentions shall be symmetrical and centered along the longitudinal axis of the crimp barrel.
Single crimp indents shall be located opposite of the barrel weld (see Figure 15.22).
• Pre-insulated contacts shall be assembled and crimped as per the contact manufacturer’s recommendations
or engineering documentation. Crimp indentions shall be symmetrical and centered on each crimp zone. The
insulation crimp shall be properly set to provide strain relief (Figure 15.23).
Figure 15.23 : Butt Splice with Shrink Sleeving
15.7.4
Inspection
Figure 15.23 : Butt Splice with Shrink Sleeving.
Crimped connections shall be visually inspected in order to verify compliance with this document including the
following additional requirements:
• Crimp indentions shall be symmetrical and properly located within each crimp zone (as specified in the crimp
manufacturer’s data sheet or engineering documentation).
• Single crimp indents shall be located opposite of the barrel seam/weld.
• Insulated crimps with integral strain relief shall exhibit proper crimping of the strain relief feature.
199
16 ELECTRO STATIC DISCHARGE (ESD)
16.1
General
ESD is the sudden transfer of electrical charge between two objects at different potentials. Almost everyone has
experienced ESD. One example occurs when you, wearing shoes, walk across a carpet and touch a conductive object,
such as a metal doorknob.The ““zap”” that you feel and hear is a form of ESD.A problem associated with ESD usually
involves triboelectrification and induction charging and corona charging as prime generation sources.
16.2
ESD Modeling
The human body or other conductive objects can become;
1.
Electrostatically charged if not properly grounded. If this charge comes in contact with or passes near an
ESD sensitive (ESDS) device, ESD damage can occur. Charge is not localized on the surface of a conductor,
but is spread out uniformly over the conductor’s surface. Thus, very low voltages are capable of damaging
ESDS devices.
2.
Cathode ray tubes and other high voltage electric devices can create high electrical field potentials.
Moving an ESDS device through such a field can induce current to flow through the device, thus causing
damage even if the device does not come into contact with the charged surface. In addition, grounding a
device that has become charged in an external electrostatic field can cause damage.
3.
The physical structures on modern devices are extremely small and continue to shrink in size as technology
advances.Very small charges accumulated on conductive elements of a device can exceed the breakdown
potential of the insulating layers or the air gaps between them, causing the device to destroy itself. The
presence of mechanical damage, such as fine scratches or contaminants within and on the surface of the
device, tends to increase its ESD sensitivity.
4.
Conductive, static dissipative and insulative materials in the work place can become charged due to the
triboelectric effect. These must be controlled to below damaging potentials through the use of grounding
in the case of conductive and dissipative materials, or through the use of air ionization for insulative
materials.
5.
The smallest ESD event most people can detect is about 2,000 volts. This same voltage, when applied to
an ESDS device, can result in catastrophic failure. Some parts are severely damaged by ESD events of tens
of volts. Thus, many damaging ESD events are not noticeable by human detection alone.
16.3
Triboelectrification
Two dissimilar materials can become charged with equal and opposite polarities due to contact and separation
between the materials. The material with the higher work function will become charged negatively, after contact
and separation with a material of lower work function. The amount of charge remaining is a function not only of the
materials in contact but also several other variables including the areas of contact, relative movement of surfaces,
contact pressure, the ambient conditions and surface contaminants. The magnitude and polarity of charge depends
on the type of the materials involved. Table 16 ‑1gives a turboelectric series listing materials according to work
function.
Example: The human body can be modeled as a conductor covered with an insulating skin of finite resistance. The
surface charge reading on the shoe sole will be the flow of induced charges on the body so that the neutral body
becomes polarized.
200
Table 16‑1:Triboelectric Series
POSITIVE ( + )
AIR
HUMAN HANDS
ASBESTOS
RABBIT FUR
GLASS
MICA
HUMAN HAIR
NYLON
WOOL
FUR
LEAD
SILK
ALUMINUM
PAPER
COTTON
STEEL
WOOD
AMBER
SEALING WAX
HARD RUBBER
NICKEL,COPPER
BRASS,SILVER
GOLD,PLATINUM
SULFUR
ACETATE NYLON
POLYESTER
CELLULOID
ORLON
SARAN
POLYURETHANE
POLYETHYLENE
POLYPROPYLEN
PVC(VINYL)
KEL F
SILICON
TEFLON
NEGATIVE ( - )
201
16.3.1
Induction charging
A source of electro-static energy induces a current in a previously uncharged device (polarization and conductive
charges). An electrostatic field or lines of force exist between a charged body and a body at a different electrostatic
potential, such as a body with more or less electron charges. In a conductive body, electrons close to the more
negative part of the field are repelled, leaving that area relatively positive part of the field creating negative and
positively charged areas although the net charge on the body remains zero.
16.4
Need of ESD Control
Electrical and electronic parts assemblies and equipment that are sensitive to ESD voltages of 15000 volts or
less include microelectronic devices, dielectric, semiconductors, film resistors, thick and thin film devices and
piezo electric crystals are susceptible to ESD.
16.5
Classifications of ESD Devices
ESD Devices are classified as:
−
Class 1
:
0 to 100 volts
−
Class 2
:
100 To 4000 volts
−
Class 3
:
4000 to 15000 volts
An integrated Circuit (IC) consists of several circuits. The speed of an IC is increased and the power consumption
reduced by decreasing the thickness of gate oxide layer and inter connecting lines. Then static electricity can burn
these fine lines easily and damage the IC. Hence the need to control ESD comes to picture. IC is considered
equivalent to multiple paths to ground if one pin is grounded, the potential developed is sufficient to cause
breakdown or crack between isolation regions and may discharge though the device.
One person can generate up to 30000 volts. The control of ESD is not only required for devices’ safety but also for
operator’s safety. An electric over stress is the result of the improper application of a device and a failure is generally
seen as a hot spot development at the semiconductor junction resulting in a cumulative process making the device
fail.
16.6
Type of ESD Failure
Three general ESD damage failure modes can be defined:
16.6.1
Catastrophic failure
In a catastrophic failure, the device does not function at all. The fact that the failure could be detected during
testing, reduces the risks of carrying a latent failure and of more costly consequences from failures found at
higher levels of assembly and schedule points closer to the launch date.
16.6.2
Parametric failure
A parametric performance failure occurs when the device has been slightly damaged so that it still performs, but
202
not to specification. For example, the device may not oscillate at the correct frequency, may exhibit intermittent
performance, or may be unstable.The device still works when tested, but some performance parameters may be out
of the acceptable tolerance limits. Again, this type of failure results in increased cost and schedule delay, but the fact
that the failure could be detected during testing is positive.
16.6.3
Latent failure
A latent failure occurs when a device has been damaged so slightly that it does not fail but performs within its parametric
tolerance limits. The damage remains hidden for a period of time until the device fails or the performance degrades
earlier than its designed life. Parts with latent damage are sometimes referred to as the “walking wounded.”
Both catastrophic and parametric failures are usually found during product testing, where isolation and replacement
are possible. Correcting these failures often results in increased costs and schedule delays.
Latent failures remain undetected during routine system testing and product development. However, after time and
use, the damage leads to early failure. Depending upon the type and location of the products, the repair of a latent
failed part may be impossible. A latent failure on a launched spacecraft could reduce mission effectiveness or lead to
possible loss of a mission.Thus, the need to control ESD to prevent catastrophic, parametric, and latent ESD failures
is crucial to the success of all space projects.
16.7
ESD Control Program
16.7.1
ESD Sensitivity Levels
The ESD sensitivity of devices is determined using three different electrical models: the Human Body Model, the
Machine Model, and the Charged Device Model. Device classification using any of the electrical model Classes in
Table 16‑2,Table 16‑3, & Table 16‑4 indicates that the device will not be damaged by that type of discharge, with
an energy level that relates to the voltage level shown for that Class level.
16.7.1.1
Human Body Model (HBM)
This simulates the discharge from the fingertip of an operator to an electronic component. In the HBM, a 100-pF
capacitor is discharged through a 1500-ohm resistor to ground.
Table 16‑2: ESDS Component Sensitivity Classifications – HBM
Class
Voltage Range
0
<250 V
1A
250 to <500 V
1B
500 to <1000 V
1C
1000 to < 2000 V
2
2000 to <4000 V
3A
4000 to <8000 V
3B
>8000 V
203
16.7.1.2
Machine Model (MM)
It is a faster discharge model, designed to simulate ESD events in automatic handling and testing equipment. In this
model, a 200-pF capacitor is discharged directly to ground.
Table 16‑3: ESDS Component Sensitivity Classifications – MM
16.7.1.3
Class
Voltage Range
M1
<100 V
M2
100 to <200 V
M3
200 to <400 V
M4
>400 V
Charged Device Model (CDM)
This model considers the situation where a device is charged and then discharged to ground through one pin or
connector. The CDM sensitivity of a given device may be package dependent.
Table 16‑4: ESDS Component Sensitivity Classifications – CDM
16.7.2
Class
Voltage Range
C1
<125 V
C2
125 to <250 V
C3
250 to <500 V
C4
500 to <1000 V
C5
1000 to <1500 V
C6
1500 to <2000 V
C7
>2000 V
Methods of ESD Control
Though ESD protections are used at both device and system levels, semiconductor device is susceptible to ESD at
all stages of its life, including; fabrication, test, system integration and manufacture, system use, repair/rework, storage
and handling. Hence we have to implement the static control at all stages from beginning till last stage. One of the
easiest methods to prevent it is to stop from generation.
16.7.2.1
Protective Materials
These may be separated into four distinct categories based upon range of surface resistivity.
204
Table 16‑5 : ESD Protective materials
Material
Resistivity
Conductive
100 kilo ohms/sq. or less
Static Dissipative
Between 105 to 109 ohms/sq
Antistatic
9
14
Between 10 to 10 ohms/sq
Insulative
Greater than 10
14
ohms/sq
For static control, we have to take precautions at different areas of concern.
16.7.2.2
Personnel Training
Persons should be trained to use ESD preventive materials so that everyone involved in manufacturing,
inspection, packing, shipping, storage, installation and maintenance use them and strictly adheres to ESD preventive
programs and well aware of ESD documents also. It should be made mandatory to wear proper wristbands for
all device handling.
16.7.2.3
Material Handling
The areas of concern are at handling, storage, and shipping. (Refer Figure 16.1 for different ESD symbols).
Figure 16.1 : ESD Symbols
Figure 16.1 : ESD Symbols
1.
Antistatic bags generally consist of a conductive carbon or metal layer sandwiched between static
dissipative or anti-static material, laminated by polyurethane. As the bag is sealed the conductive layer
provides a Faraday Cage effect means preventing any charge, reaching inside. The Antistatic layer
prevents sparking between the components inside and the conductive layer.
2.
Antistatic materials shield devices from triboelectric charge because the material itself is unable to
generate static charge. Devices can be protected from discharge with non-conductive insulation. For the
protection against electric field conductive container will drain the charge to ground before it can reach
the device.
• Different protective bags should have the following properties
o
Degree of transparency
o
Abrasion resistance
o
Puncture resistance
o
Permeability to water vapor
o
Heat seal strength
Carbon has disadvantages that it generally tends to slough off when exposed, endangers the device and
making unsuitable for clean room. It can be too conductive and must be shielded from sensitive part to prevent
damage from spark. Pink poly bags provide protection against triboelectric charging but no protection against
external electrostatic fields.
205
Antistatic and conductive foams are widely used for protecting static sensitive devices during shipment. Foam
prevents bending or misalignment of device leads absorbs vibration and physical shocks and short device leads
provide equal potential bonding. DIP stickers/tubes are used for dual in line package IC’s for shipping.
Benstat stickers, new Antistatic coated PVC stickers, carbon loaded stickers, and clear PVC stickers are used.
Antistatic-coated PVC stickers are available.
16.7.3
Personnel safety
The procedures and equipment described in this document may expose personnel to hazardous electrical
conditions. Users of this document are responsible for complying with applicable laws, regulatory codes, and
both external and internal safety policy. Users are cautioned that this document cannot replace or supersede
any requirements for personnel safety.
Ground fault circuit interrupters (GFCI) and other safety protection should be considered whenever personnel
might come into contact with electrical sources.
Electrical hazard reduction practices should be exercised and proper grounding must be followed.
16.7.4
ESD protected areas (EPA)
An EPA may be a single workstation, laboratory, room, or building, or any area with pre- defined boundaries, that
is designed to limit damage to electrical hardware by electrostatic discharge events. EPAs may be permanent or
temporary.
16.8 ESD Control Requirements For Facilities
16.8.1
General
This section pertains to EPAs, including facilities, equipment, tools and materials.
The instructions and
recommendations in this section include specific facility inspection methods used by ESD program monitors
and ESD program managers in periodic verifications and certification audits.
Where an ESD protection level applies that is more restrictive than HBM Class 1A (i.e., protects more highly
sensitive items), signage is used to clearly mark and communicate to personnel the boundaries and class level
of the ESD protected area (EPA).
The measurements of Table 16‑6 are performed operators at the EPA perform tests numbers 5, 7, 8 (continuous),
11, and 13 as they apply to their area.
16.8.2
Identification and access - ESD areas
Clear demarcation of the presence and boundaries of EPAs, where ESDS items are to be processed, is achieved
using prominently placed signs and a partition, rope guards, or similar barrier. The boundary defining method
is intended to prevent unauthorized and untrained personnel from entering the EPA. Personnel who are not
ESD-certified that must enter the EPA can do so with an ESD-certified escort (e.g., visitors or maintenance
personnel).
206
Table 16‑6 : ESD Control Program Verification Schedule and Measurements
207
16.8.3
Prohibited Materials and Activities
• The following housekeeping practices are critical for continuous EPA compliance:
o
Smoking, eating and drinking in EPAs is not allowed.
o
Materials not related to the work being done in the EPA are not allowed.
o
Clipboards, books, notebooks, loose sheets of paper, etc., used to read or record data or follow instructions
(this manual included), are kept at least 1 meter (3.3 ft.) from ESDS items or placed in ESD-safe bags.
Materials specifically made and verified to be safe in an ESD area are exempt from this requirement.
o
Floors or mats are kept free of dust, dirt and other contaminants.
• 1-meter minimum separation is recommended between the location where ESDS items are handled and
““tacky mats”” which are used at the entrance to Clean rooms, CRT displays, and other equipment, and which
generate a static charge.
• The risk of damaging an item by an ESD event is heightened when the item is left exposed and/or unattended
at a workstation or elsewhere. This risk is mitigated by placing ESDS items on an ESD protective surface and
wrapping or covering them with static shielding material when they must be left unattended for short periods
of time, such as a lunch break.
16.8.4
ESD Protective Work Surfaces
• The recommended default for the conductivity level for all work surfaces in an ESD-protected area is static
dissipative (>105 to <109 Ω for surface resistance). Some work in EPAs requires conductive surfaces (<105 Ω)
(e.g., optical benches).
• ESD-safe surfaces shall be electrically connected to the Common Point Ground. The common point ground
may be a terminal strip, bus bar, or any other convenient configuration that is, within itself, electrically
continuous to no greater than 1 ohm measured from point to point with an ohm-meter.
Figure 16.2 :Typical ESD Grounded Workstation
Figure 16.2 : Typical ESD Grounded Workstation
• When conductive surfaces are used, a 1 M Ω optional resistor may be needed to provide a soft ground
between the work surface and the common point ground, see the Figure 16.3.
Figure 16.3.
208
Figure 16.2 : Typical ESD Grounded Workstation
Figure 16.3.
Figure 16.3:Workstation Common Point Ground
Extreme care is required when using conductive work surfaces.
To eliminate the safety hazard associated with a high current event that results from touching a high voltage
circuit with one hand and a hard ground with the other hand, work surfaces must either be soft grounded by
installing a resistor in series with the ground (> 800 kΩ) or a Ground Fault Circuit Interrupter (GFCI) must be
used (GFCI, disconnects the circuit when an unsafe current event is detected, usually a p p r o x . 5 mA). The use
of 1 MΩ (±20%) optional resistors is acceptable in lieu of the GFCI. Conductive work surfaces also generate a
Charged Device Model [for electrostatic discharge] CDM hazard for very sensitive devices.
Selection of the protective work surface will ensure that;
• It does not release particle contaminants.
• It will resist attack by common solvents or cleaners.
• It is sufficiently large to accommodate the resting of common hand tools on the protective surface rather than
on adjacent non-protected surfaces.
Soft grounding of dissipative work surfaces shall measure < 109 ohms. When highly conductive work surfaces
(e.g., stainless steel or copper) are used, and they need to be connected directly to the equipment or auxiliary
ground without the optional resistor, GFCIs shall be used in the ESD-protected workstation. Type ““A”” GFCIs
are preferred. GFCIs shall be tested at least once a month using their self-test feature.
16.8.5
ESD-Protective floor surfaces
Conductive or dissipative floors and/or grounded conductive/dissipative floor mats are used in EPAs where
personnel are not wearing wrist straps. To provide the intended ESD protection under these conditions, the
use of leg straps, heel straps or conductive shoes is required. Conductive/dissipative flooring combined with
ESD chairs are strongly recommended in HBM - EPAs to provide equi-potential ground.
209
ESD protective flooring is not affective if it is not grounded. It may be connected directly to equipment or auxiliary
ground without the optional resistor. For testing purposes, the dissipative floor-to-system ground resistance target
is < 109 ohms.
Measure the floor resistance between the equipment ground and a point on the floor at least 12
inches away from the floor-to- ground connection.
After certain numbers of cleaning, floor resistance is verified and the results are recorded. Vacuuming or dry
sweeping the floor does not require a subsequent check.
Proper use of conductive waxes requires compliance with manufacturer recommendations. Floor resistance is always
verified after application and the results are recorded. Some conductive waxes may be a source of contaminating
volatiles. Make sure the type used has been approved for use around flight hardware.
A conductive wax on non-conductive floors is not considered an effective method of ESD control.
16.8.6
Personal grounding devices
Wrist Strap: The wrist strap is the preferred means for ESD protection. It is the ““first line of defense.” The
wrist strap system consists of four major components:
Lead: Only the lead supplied with the wrist strap should be used, as it may contain the safety resistor.
Cuff: The design of the wrist strap cuff ensures conductive contact with the wearer’s skin. Metallic cuffs are
preferred over plastic or fabric cuffs. Bead type chains are not effective and are normally prohibited.
Safety Resistor: All wrist strap systems are expected to contain an integral current-limiting safety resistor (1 MΩ
± 20%). This resistor may be an integral part of the lead.
Ground Termination: The wrist strap ground termination must ensure a positive and durable connection between
the lead and the Common Point Ground (CPG). The resistance between CPG and the equipment ground, for testing
purposes, shall be <1.0 ohm. For wrist straps ground, protected through a Continuous Monitoring Systems (CMS),
the value shall be <3.5x107 ohms.
Foot Grounding: Foot grounding devices such as leg, toe or heel straps, or conductive shoes worn in conjunction
with a conductive floor and/or conductive floor mats, are acceptable alternatives to a wrist strap in those situations
where the operator needs to be mobile and the use of a wrist strap is impractical or unsafe. When used, foot
grounding devices are worn on both feet and are not to be worn outside the ESD protected area. The total
resistance of these devices shall be < 3.5x107 Ω. When employing foot grounding devices, it is the responsibility
of the ESD program monitor to set up a footwear checker and log to monitor the continued performance of the
personal grounding device system.
NOTE: Foot grounding devices which are not kept clean will have reduced effectiveness from
contaminants inhibiting their conductive interface with the floor.
16.8.7
Integrity testing of personal grounding devices
The integrity of the connection between the operator, the personal grounding device, and the ground connection
210
is critical to proper ESD protection. Periodic, scheduled verification of personal grounding device performance
will identify non-compliant units. Typically, damaged or worn units are not repairable and must be replaced.
Wrist straps are expected to be either continuously monitored or checked each time the wearer enters the
ESD protected area using an approved wrist strap tester. The first daily check should be logged. Logging wrist
strap checks is not needed for EPAs that use CMS. If a CMS is used at a workstation, it is recommended that all
wrist strap connection points be enabled through the CMS. Exceptions should be made for instances where
the voltage-sensing from the CMS may damage very sensitive components.
Foot grounding devices are checked and logged each time the wearer enters the ESD protected area. Foot
grounding devices are worn on both feet and are checked one foot at a time.
Workstation Real Time Continuous Monitoring Devices are checked to ensure functionality just before handling
ESDS items. (The monitor’s alarm should sound and the appropriate red light should light when the lead is temporarily
removed from the cuff)
If one of the checks in ‘a’ through‘ d ’ fails, corrective action is taken before work is performed and a subsequent
re-check is used before work resumes.
Appropriate corrective actions include:
• Replace cord.
• Replace complete system.
• Use a conductive lotion designed for use with ESD wrist straps (if acceptable in the area of use).
• Wrist band cleaning.
If it is found that an ESDS item was handled in an EPA with faulty ESD protection (e.g., wrist straps, grounding,
etc.), that item will carry a risk lien that must be retired by the affected Project. The failure of the ESD protection
is recorded by the ESD program monitor.
16.8.8
Equipment and facilities
Facilities Grounding: The preferred practice is to use the third wire AC line ground for grounding all items at
the ESD protected area (EPA). When a separate grounding line is present or used in addition to the equipment
ground, it should be electrically bonded to the equipment ground at each ESD protected work station to
minimize the difference in potential. The resistance of the conductor from the Common Point Ground to
the equipment ground (AC ground) should be less than1 ohm. The impedance from the area Common Point
Ground to the neutral bond at the main service box should be less than 2 ohms. See Figure 16‑4. Daisy
chaining is not permitted.
211
Power Mains
Main service box
ESD work station
Hot wire
Neutral bond
Equipment ground conductor
Hard ground
Common
point
ground
Auxiliary ground
Figure 16.4 : Main Service Box
Figure 16.4 : Main Service Box
16.8.8.1
Stool, Chairs and Carts
Stools, chairs and carts in EPAs: Marking certified chairs, stools, and carts with identifying stickers facilitates
their proper use and certification maintenance.
Local ESD Safety procedures will address EPA-specific uses of
chairs, stools and carts relative to the employed grounding scheme.
Certification: The recommended verification levels and verification intervals for chairs and stools are shown in
Table 16‑6. The resistance shown in Table 16‑6 applies to measurements between any part of the chair and a
groundable point. The resistance for any part of the chair to a groundable point shall be <109 ohms.
Grounding: For handling Class 0 sensitive items a positive electrical contact between the Common Point Ground
and the chair or stool is recommended. This contact may be achieved through an ESD protective floor or ESD
protective floor mat.
16.8.8.2
Mobile Equipment Carts
Where carts, wagons, trams, or other mobile equipment are used, they are required to be grounded while in use
in the EPA. When conductive floors are being utilized, it is recommended that positive electrical contact be made
between the floor and conductive structure of the mobile equipment. The required resistance used for verification
from the equipment to the Common Point Ground is shown in Table 16‑6. If the floor is non-conductive, the
vehicle will have to be grounded before ESDS items are loaded or removed from the vehicle. The use of protective
packaging applies (ESD approved wrap material, totes, etc.) when moving ESDS items for transport away from the
EPA, even if a certified-safe cart is employed.
212
Other Mobile Equipment: When other tabletop equipment such as microscopes or lead bending equipment is
used within an EPA, it should be ESD grounded. Note that such equipment may have a large capacitance and present
a hazard to components susceptible CDM type pulses.To avoid damage, the equipment and the component must be
at the same potential before they contact each other. This can be done by using dissipative materials to make first
contact to both the component and the equipment.
16.8.8.3
Humidity
The relative humidity (RH) target range for ESD-protected areas (EPAs) is 50% to 60% when monitored near the
ESDS item. At levels below 50%, ESD risk increases, requiring the use of additional precautions, such as turning
on a humidifier to achieve the required humidity or using an air ionizer. If additional precautionary methods are
not available (e.g., the use of an ionizer), it is recommended that work is halted until the required humidity level is
obtained.
A check of the RH level in each EPA is performed at the start of the workday and the result is logged. Continuous
compliance is verified with periodic observations and recording of the results. If the RH level is close to 50% or is
seen to be dropping rapidly, extra vigilance is recommended. Data loggers with an integral alarm system are suitable
substitutes for the daily check.
Maximum RH depends on the equipment and device under test (DUT) to be protected as condensation due to
temperature variations can cause corrosion, short circuits or moisture contamination.
Sealed ESD bags which have been stored in ““dry boxes”” or may have desiccant gel bags to prevent high humidity
problems are easily charged when rubbed against the ESD protective bag. Care should be taken when removing
ESDS items from them to prevent ESD events from Triboelectric charging.
NOTE: Surface resistivity changes exponentially with humidity changes.
16.8.8.4
Air Ionizers
Air ionization is a technique used to neutralize charges on insulators and ungrounded conductors. Air Ionizers
are considered necessary when handling Class 0 sensitive parts or when the relative humidity falls below 30%
in the work area.
Air ionizers are designed to work where unrestricted airflow exists between the ionizer and the ESDS item.
Their design also requires sufficient distance between the ionizer and the ESDS items to ensure proper
ion balance in that airflow. Consult the ionizer manufacturer’s documentation for detailed ionizer operating
instructions.
Careful selection of the ionizer is needed in order to realize the benefits of ionizers in the EPA and may be
application dependent. Ionizers require routine maintenance and testing in accordance with manufacturer’
recommendations to ensure acceptable continued performance.
The presence of ionized air creates an increased risk for corona discharge in the presence of ““powered-up”” highvoltage or RF-sensitive equipment, therefore, the use of ionizers is not recommended in those environments.
To avoid fire hazards from corona discharge, keep flammable materials away from air ionizers.
213
Electrostatic survey meters in conjunction with a charging plate may be used to verify the effectiveness of
ionizers in extremely sensitive work areas (e.g., Class 0, Class M1) before work is started. It is important that
the meter used has sufficient resolution and time response to detect values beyond the minimum performance
limits required. To avoid meter saturation or generating false data, the meter should be slowly moved into the
area being measured while watching for readings close to the limits of the meter.
Though the use of ionizers is recommended for Class 0 EPAs, it is important that the ESD program monitor
ensure that the ionizer is not the source of unacceptable charge deposition into the ESDS items. In these cases,
the ESD program monitor will ensure in advance that the ionizer peak balance potential is less than one half
the susceptibility of the most sensitive part (”50% of item sensitivity level)
CAUTION:
An improperly adjusted air ionizer can actually charge ESDS devices and lead to possible damage to
the device. Only use calibrated air ionization systems.
Table 16‑7:ESD Sensitivity for Selection and Performance of Air Ionizers
1
2
Class
ESD Sensitivity
Air
Ionization
Discharge time
Float
Potential
1A
>250 volts
Optional
± 1000 to < ± 100 V in < 45
sec.
< ± 100 V
01
>100 V to < 250
V
Required
± 1000 to < ± 50 V in < 20
sec.
< ± 50 V
02
”100 V
Required
± 1000 to < ± 20 V in < 20
sec.
Note 2
M13
<100 volts
Required
± 1000 to < ± 20 V in < 20
sec.
< ± 20 V
Class 0 covers all HBM <250 V but it is not sensitive enough to protect some newer parts.
Class 0 with sensitivities at or below 100 V the ionizer peak balance potential shall be less than one half the
susceptibility of the most sensitive part in the assembly.
3
This level is intended for use with automatic equipment therefore it uses MM vs. HBM
16.8.8.5
Hand tools, equipment and fixtures
The ESD program monitor is responsible for approving the use of all tools in the EPA.
Tools designed for ESD areas, such as static dissipative cushioned tools or un-insulated metal hand tools such as
pliers, cutters, tweezers and wire strippers, are preferred in ESD-protected areas.
Hand tools should be kept on the grounded work surface when not in use.
It is recommended that only antistatic solder extractors made of metal, or having a metalized plastic barrel and
tip, be used in an ESD-protected area (EPA).
The following criteria are recommended for electrical tools used in EPAs:
214
• They employ a three-wire grounded power cord.
• They have static dissipative handle grips.
• That the tool’s contact point (e.g., soldering iron tip) which touches the work piece has a resistance of less
than 20 ohms (< 1 Ω when new) and the potential difference does not exceed 2 mill volts.
• Motor driven tools are not recommended for use near ESDS items due to inductive charging in the ESDS
devices.
Caution: GFCI systems can indicate a faulty soldering station but do not prevent damage to hardware from
damaged soldering tips. Soldering stations are easily moved to the workbench however their records are not usually
kept by lab monitors and the tips cannot be easily identified as verified ESD-safe.
• Digital Millimeters (DMMs) may introduce voltage spikes when changing scales and/or have high voltages
when measuring resistance. Make sure that the measuring equipment is compatible with the hardware being
measured.
• Fixtures used while working at an ESD protected area must be ESD safe and ground bonded to the
Common Ground Point.
• Measuring equipment, breakout boxes, harnesses, etc. must be properly discharged (grounded) before
making connection to flight hardware. Consult with the designer to ensure that work instructions clearly
document hardware limitations and procedural considerations relative to the equipment normally used
in the laboratory.
16.8.9
ESD safe protective packaging
• Electrostatic protective packaging must prevent charge generation (e.g., triboelectric contact and separation)
and protect from external electrostatic fields. Static dissipative materials used in packaging are considered
to provide both properties. Static dissipative materials in intimate contact with devices shall have a surface
resistance of ≥105 & < 109 ohms.
• Protective bags and packaging are considered ESD protective based on the following application methods:
• Materials used in protective bags and pouches shall satisfy the resistance requirements to avoid triboelectric
charge buildup.
• Acceptable bags and pouches used for electrostatic shielding are constructed from a single folded piece of
material. Two-piece construction is not considered ESD-safe. If bags or pouches are not transparent, allowing
identification of contents without removal, a label stating contents shall be placed on the outside of the bag
or pouch.
• Materials in contact with the protected hardware shall have a dissipative surface.
• Neither static dissipative impregnated nor topically treated plastics provide electrostatic shielding. Both types
need to be enclosed in an outer container which will provide shielding to the contents during shipping. For
acceptable electric field shielding, the package must be electrically conductive with a surface resistance of <
104 ohms.
• ESD-safe tote boxes shall be made of conductive or static dissipative material. Compliant tote boxes shall
be fitted with covers of the same conductivity as the bottom sections that fit tightly enough to ensure
conductivity across this interface.
16.8.10 Clothing requirements
• Static dissipative outer garments (smocks) must be worn at all times when in EPAs. A compliant smock will
cover all personal garments above the wrist except at the neck area and make intimate contact with the skin.
Smocks must be fully zipped / buttoned all the time they are worn.
• The garments must be properly checked after laundering. This requirement may be met by using an approved
cleaning facility for ESD garments which provide this service.
215
• When handling ESD Class 0 sensitive parts, the ESD smock must be connected to the common point ground
or wrist strap lead. Otherwise, it becomes an isolated ungrounded conductor. Some garments have the
provision for attachment to the wrist strap coil cord snap. Some configurations also allow for continuous
monitoring.
• When cuff-to-cuff resistance of the garment is < 3.5x107Ω, the garment can be grounded using a single wire
wrist strap cord. This arrangement, when used with the corresponding continuous monitor device meets the
requirements and can be used in lieu of the wrist strap or foot grounding systems. This setup does not work
with the dual wire Continuous Monitoring Systems.
• For less sensitive areas (Class 1A and above), smocks may be used over cotton shirts or short-sleeved
shirts without the extra ground connection. This configuration permits slow static dissipation of the charge
acquired by the garment (wrist straps shall be worn).
• ESD program monitors are responsible for ensuring that finger cots and gloves, when worn in an ESDprotected area, are made of static dissipative materials.
• All connectors of partial or complete Assemblies shall use conductive Or dissipative caps during store.
•
All harness cables shall be grounded by connectivity through shield with ground temporarily prior to
connection with partial or complete assemblies prior to test / integration.
16.9
ESDS Item Handling
16.9.1
General
ESDS items must be handled only in ESD protected areas (EPAs). When outside of EPAs, ESDS items must be
completely enclosed inside ESD-protective packaging in ESD protective container.
Paperwork accompanying an ESDS item (e.g., QA records, routings, and instructions) must be contained in static
dissipative bags or envelopes. This paperwork must never come in physical contact with an ESDS item. Materials
specifically made and verified to be safe in an EPA are exempt from this requirement.
Shunts, such as bars, clips, or conductive coverings, are used to protect an ESDS item when it is not being
tested or worked on. However an ESD event may occur if extreme care is not exercised to ensure that both
items are at the same potential when attaching any conductive material to an ESDS device. Process-essential
insulators (e.g., Kapton tape) must be neutralized with an ionizer before they are moved within 12 inches of
ESDS items.
All containers, tools, test equipment, and fixtures used in ESD protected areas must be grounded before and
during use. Before connecting or disconnecting test cables, a common soft ground between an ESDS item and
any test equipment is to be established.
While in the vicinity of ESDS items, personnel handling ESDS items must avoid physical activities that produce
static charges (e.g., wiping feet, or adding or removing items of clothing).
16.9.2
Special Requirements for Highly Sensitive Items
Table 16‑8 summarizes the recommendations made throughout this document which are particular to HBM
Class 0 and MM Class M1 only. For higher sensitivity levels, for devices sensitive to CDM events, or for other
special cases, the Project engineers should partner with the ESD Program Manager to determine suitable ESD
Control Program requirements.
216
When assembling parts sensitive to low voltage and low energy pulses, the measures prescribed for HBM
and MM models do not provide sufficient component protection. This section provides guidance for handling
components sensitive to breakdown voltages as low as 2 volts and energies as low as 0.3 J. Electromagnetic
interference (EMI) signals can inductively charge components with these low level sensitivities and put them
at risk from an ESD event that is so rapid that it evades HBM and MM safety methods. Parts in this category
include detectors, some high-frequency low-voltage differential signal (LVDS) transceivers, low noise amplifiers
(LNAs), Noise diodes, and integrated circuit radio frequency (IC RF) switches.
16.9.3
Equipment
All ports in the flight hardware should use shorting plugs/ESD caps when not in use, including when inside their
ESD bags. RF ports may use a metal dust cap to form a Faraday cage.
Operators should use ESD finger cots instead of ESD gloves.
Table 16‑8 : Summary of Recommendations Applicable to HBM Class 0 and MM Class M1
Topic
Chairs & stools
Conductive or
dissipative floors or
floor mats
Relative Humidity
Recommendation
Ground and periodically verify as ESD protective. See Table 7-1 for
intervals
Use them in the area in front of the protected area or in the
designated EPA
floor space
Kept over 40%, monitor and record just before work is started.
Additional precautions must be used to operate below 40% RH.
Keep them in place and working properly. See Table 7-2. It is
Ionizers
recommended that an ESD survey meter be used to check the area
before work is begun.
Must be grounded to the Common Point Ground or through the wrist
Smocks
strap. However, the CMS, if used, must not interfere with grounding of
the smock or vice versa.
Mating and De-mating
Must be discharged to ground through an approved method prior to
cables and harnesses
mating and de-mating to ESD sensitive assemblies
Soldering irons
Check for proper ESD operation before start of operation.
Signage
Display them, describing the Class sensitivity level for the area
• The DUT should be placed on metal which in turn is placed on a certified ESD workbench. This plate should
be permanently grounded to the power supply in the test setup using a separate ground braid and connected
in the same fashion as the chassis connection called out in the test procedure setup.
o
Caution: This step may compromise components with low voltage CDM sensitivity. For CDM protection
below 100V one should avoid metal-to-metal contact.
217
• ESD garments should have conductive elastic cuffs or have means by which they can be grounded.
• Avoid highly triboelectric materials under the ESD garment (e.g., silk, wool). Cotton or cotton blends are
recommended.
• Continue to use wrist straps per the current requirements.
• If a Continuous Monitoring System (CMS) is used, the sensing voltage of the system is to be lower than the
most sensitive component to be handled. If CMS cannot be used, the operator/garment combination needs
to be checked and recorded at least once a day. The operator should check himself every time he/she enters
the area.
• A voltmeter check of all powered equipment grounding (including soldering irons, power supplies, spectrum
analyzers, etc.) is to be performed before removing the shorting plugs and making contact with the DUT.
• Cleaning procedures around sensitive parts should be performed using isopropyl alcohol and a small horsehair
brush (not Q-tips). Hot air guns are not to be used.
16.9.4
Identification and marking
ESDS items, equipment, and assemblies must be identified in order to warn personnel before any potentially
ESD-damaging procedure can be performed. For this purpose, packing lists, inspection reports, travelers, and
other paperwork accompanying the hardware must contain ESDS labels and cautionary notes.
The standard ESD Protective Item Symbol is to be used to identify items which are specifically designed to
provide ESD protection for ESDS assemblies & devices. This symbol is illustrated in Figure 16.5.
Figure 16.5 : Sensitive Electronic Device Caution Symbol
Figure
16.5
: Sensitive Electronic
Device
CautionCaution
Symbol Symbol
Figure
16.5
: Sensitive
Electronic
Device
Note: If the Class sensitivity level is not specified within the symbol, or is other
Note: If than
the Class
sensitivity
levelorisC1,
not it
specified
within the
symbol,
or is other than Classes 0, M1, or C1, it will
Classes
0, M1,
will default
Class
1A.
Note:
If the
Class
sensitivity
level istonot
specified
within the symbol, or is other
default tothan
ClassClasses
1A.
0, M1, or C1, it will default to Class 1A.
0
0
Figure 16.6 : ESD Protective Item Symbol
Figure 16.6 : ESD Protective Item Symbol
The standard ESD common point ground symbol is used to indicate the location of an acceptable Common
Point Ground.
Figure 16.6 : ESD Protective Item Symbol
218
Figure 16.6 : ESD Protective Item Symbol
Figure 16.7 : ESD Common Point Ground Symbol
Figure 16.7 : ESD Common Point Ground Symbol
ESD Protected Area Certification Shall be done in line with this section. Typical values of the ESD susceptibility is
given in the following tables
Table 16‑9 : Susceptibility of Devices to ESD
Device
Susceptibility (Volts)
VMOS
MOSFET EPROM
JFET SAW
Op-amp CMOS
Thick film resistor Bipolar
transistor SCR
Schottky TTL
30 to 1800
100 to 200
100
140 to 7000
150 to 300
190 to 2500
250 to 3000
300 to 3000
380 to 7000
680 to 1000
1000 to 2500
Table 16‑10 :Typical Electrostatic Voltages
Relative Humidity
Means of static generation
10-20%
Walking Across Carpet Walking over vinyl floor
Worker at bench
Vinyl envelopes for work instructions Common poly
bag picked up from bench Work chair padded with
poly urethane foam
35000
12000
6000
7000
20000
18000
65 – 90%
1500
250
100
600
1200
1500
Table 16‑11 : Effects of Electrical Current on Humans
CURRENT VALUES
(MILLIAMPERS)
EFFECTS
AC (60 Hz)
DC
0-1
1-4
4-21
21-40
40-100 Over 100
0-4
4-15
15-80
80-160
160-300 Over
300
Perception Surprise Reflex Action
Muscular Inhibition Respiratory
Block Usually Fatal
219
17 BONDED STORES
17.1
General
The R & QA plan and recommendations for the Bonded Stores are given below giving details on ‘Environment
of the Bonded Stores’, ‘The operation of the Bonded Stores’, and ‘QA Audit check list’.
‘Operation of the Bonded Stores’, describes the requirements for contents of the bonded stores, storage,
documentation and general operation procedures. A QA audit checklist is enclosed as a ready reference and one to
one verification of the R & QA requirements and the audit points.
17.2
Environment of the bonded stores
• Temperature
:
22 + 3oC
• Humidity
:
40 to 60 % RH.
• Light intensity
:
100 ft candle minimum
• Cleanliness
:
class 1,00,000
• Antistatic measures
:
Conductive floor mats, Conductive table mats, Conductive chair covers,
Conductive covers to waste paper bins.
All antistatic mats should have surface resistivity of 105 to 109 Ohms per square, and should be grounded through
1MΩ resistor.
Cleanliness level is applicable for only electronic components and materials storage area. It is not applicable for
the chemicals storage area.
17.3
Operation of the bonded stores
17.3.1
Contents of the bonded stores
The Bonded stores shall store the following:
• Electric components for ETM (Engineering Thermal Model) and FM (Flight Model).
• Materials for ETM and FM.
• Chemicals for ETM and FM.
• Reference Documents received along with the components and materials, (Test data, reports, etc).
• Requisition and issue records
17.4
Storage
17.4.1
General
Storage area for ‘materials’, ‘chemicals’, ‘electronic components’, ‘rejected components and materials’ and
the ‘Issue and Receipt area’ should be separate and isolated from each other. The documents and records should be
stored in the Issue and Receipt area. The Air conditioning system for the Electronic components and materials
shall not be used to cover the chemical storage area. Separate Air conditioning systems should be used for the
Chemical storage area.The chemicals storage area shall be provided with adequate exhaust paths and systems.
The materials used for storage shall be free from corrosive compositions and halides.All clean room procedures shall
be implemented for control of the contaminations and Electrostatic charge generation
220
17.4.2
Electronic Component Storage Area
The electronic component storage area should have the following:
• Vaccuumised / Dry nitrogen purged storage for semiconductor chips
• Dry nitrogen purged storage for components / parts / finished products.
• Antistatic storage for static sensitive components.
• Segregation of electronic components: as shown Figure 17‑1.
Components
Screened Accepted
Unscreened
Active
passive
Active
passive
Static
sensitive
Non
sensitive
Static
sensitive
Non
sensitive
Rejected & Life expired
Figure 17.1 : Segregation of electronic components
Each and every element completing 5 years of storage life from the year marked on it shall be marked as “Rescreening
required”.
The rejected and life expired components shall be quarantined.
17.4.3
Storage of Materials and Chemicals
The material and chemicals shall be segregated as shown in Figure 17.2 & Figure 17.3.
Material
Rejected and life expired
Material Accepted
Figure 17.2 : Segregation of material
The accepted material shall be marked as “re-testing required” after specified years of storage.
Chemical
Hazardous not
accepted
Non hazardous
accepted
Rejected and
life expired
Figure 17.3 : Segregation of chemicals
17.4.4
Operation
All the enquiries and requisitions by the project, QA and the fabrication facilities shall be given to the bonded
stores through LAN. This will minimize the entries to the Bonded Stores.
221
To maintain the cleanliness level of the main storage area entry of non Bonded Storage (B.S) personnel shall be
allowed to the issue and receipt area only except during Audit. During audit, the non B.S. personnel shall be allowed
to the main storage area also. The counting of the components shall be done on a separate table near the issue
counter. The counting table shall be isolated from the issue and receipt counter and shall have adequate light and
antistatic aids, like table mats, hand gloves, wrist strap, trays, bags, etc. Tweezers shall be used for delicate items. The
antistatic trays, bins, foam, etc shall be used for handling the static sensitive parts.
17.4.5
Operator
• Clean room garments shall be used for the routine activities.
• Anti static aids shall be used for handling static sensitive items.
17.4.6
Documentation
17.4.6.1
General
All the documents shall be stored in the issue and receipt area. This will help to maintain the cleanliness level and
will reduce the static charge built up in the main storage area.
Documents to be maintained:
• The documents received from the component suppliers.
• Component / material Inspection reports.
• Issue and Requisition records
17.4.6.1.1 Log Book and Records
The log book of the following records should be maintained.
Item
Frequency
Daily once, at alternate
a. Temperature & Humidity reading
mornings and evenings.
b. Light intensity
Once in a 2 weeks
c. Cleanliness (Particle Count)
Weekly once
d. Antistatic aids:
wrist strap physical & Electrical verification
Daily once
The table and floor mats physical and electrical verification
Antistatic trays, bins and inner surface of the storage bags:
Once in alternate weeks
physical and electrical verification
Once in a month.
e. Random Component Segregation internal audit
Once in a month
f. Random Physical component balance Internal Audit
Once in a 2 month
g. Random QA audit
Once in 3 months
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18 TERMS AND DEFINITIONS
Accelerator – A compounding material used in small amounts with a curing agent to increase the cure rate.
Adhesive – Materials used to hold parts in place during wave or reflow soldering, which may become a permanent
part of the PWA, or be subsequently removed.
Adjustable indenter tool – Crimping tool which has an adjustable part (setting variable) that indents or compresses
the conductor barrel or ferrule
Area Array Package – A package with an X-Y grid interconnect pattern on the under-surface (Ex:- Ball grid array,
column grid array, land grid array, pin grid array).
Bifurcated (split) terminal - Terminal containing a slot or split in which wires or leads are placed before
Birdcage – A defect in stranded wire where the strands in the stripped portion between the covering of an insulated
conductor and a soldered connection (or an end-tinned lead) have separated from the normal lay of the strands.
Blister – Raised areas on the surface of the laminate causes by the pressure of volatile substances entrapped within
the laminate.
Blow Hole - A cavity in the solder surface whose opening has an irregular and jagged form, without a smooth
surface.
Bonding - Bonding refers to fastening parts or materials to a substrate or assembly using a polymer sandwich
construction
Bridging - A buildup of solder between components, conductors, and/or base substrate forming an undesired
conductive path.
Castellation – Metalized features that are recessed on the edges of a chip carrier, which are used to interconnect
conducting surfaces or planes within the chip carrier or on the chip carrier.
Certification – The act of verifying and documenting that personnel have completed required training and have
demonstrated specified proficiency and have met other specified requirement
Chip Carrier – A low - profile four sided (rectangular) part package, whose semiconductor ship cavity or mounting
is a large fraction of the package size.
Circumferential Separation – A crack or void in the plating extending around the entire circumference of a
PTH, or in the solder fillet around the conductor, in the solder fillet around an eyelet, or at the interface between a
solder fillet and a land.
Clean Room – A clean room is an enclosed area employing control over the particulate matter in the air with
temperature, humidity, and pressure controls, as required.
223
Class 100,000 - A Clean room in which the particulate count does not exceed a total of 3500 particles per litre
(100,000 particles per cubic foot) of a size 0.5 micron and larger, or 25 particles per litre (700 particles per cubic
foot) off a size 5.0 microns and larger.
clinched-lead termination - conductor or component lead which passes through a printed circuit board and is
then bent to make contact with the printed circuit board pad .
Coefficient of Thermal Expansion (CTE): The measure of the fractional change in dimension per unit change
in temperature.
Cold Flow – Movement of insulation (e.g. Teflon) caused by pressure.
Cold Solder Connection – A solder connection exhibiting poor wetting and a grayish, porous appearance due to
insufficient heat, inadequate cleaning before to soldering, or excessive impurities in the solder.
It can appear either shiny or dull, but not granular. The joint normally has abrupt lines of demarcation rather than
a smooth, continuing fillet between the solder and the surfaces being joined. These lines are caused by either
insufficient application of heat or the failure of an area of the surfaces being joined to reach soldering temperature.
Charged Device Model - A specified circuit characterizing an electrostatic discharge, which results when a
device isolated from ground is first charged and then subsequently grounded.
Component – Device which performs an electronic, electrical or electromechanical function and consists of one
or more elements joined together and which cannot normally be disassembled without destruction.
Conduction Soldering – Method of soldering which employs a soldering iron for transfer of heat to the soldering
area.
Conductive Material resistivity <104 ohms-cm.
A material that has a surface resistivity of <105 ohms per square or a volume
Conductor – A lead, solid or stranded, or printed wiring path serving as an electrical connection.
Conformal Coating - A thin electrically nonconductive protective coating that conforms to the configuration of
the covered assembly.
Conformal Coating Specimen - A representative sample of the conformal coating process that is created
simultaneously with the same materials, at the same time, and with the same processes as used to coat the finished
item.
Construction Analysis - The process of destructively disassembling, testing, and inspecting a device for the purpose
of determining conformance with applicable design, process, and workmanship requirements. This process is also
known as Destructive Physical Analysis (DPA).
Contact angle – Angle enclosed between half-planes, tangent to a liquid surface and a solid-liquid interface at their
intersection In particular, the contact angle of liquid solder in contact with a solid metal surface. An approximate
224
value for this can be determined by shadow projection or other means, by measuring after the solder has solidified.
The contact angle is always the angle inside the liquid.
Contaminant – An impurity or foreign substance present in a material that affects one or more properties of the
material.
Contamination, Ionic or polar - Forms free ions when dissolved in water, making the water a more conductive
path.
Contamination, Non-ionic - Does not form free ions, nor increase the water’s conductivity.Ionic contaminants
are usually processing residue such as flux activators, finger prints, and etching or plating salts.
Cracked solder joint - Soldered connection which has fractured or broken within the solder.
Crazing – An internal condition occurring in the laminate base material in which the glass fibers are separated from
the resin.
Crimping tool – Mechanical tool used for permanently attaching a wire termination device to a conductor by
pressure deformation or by reshaping the barrel around the conductor to establish good electrical and mechanical
contact.
Cup Terminal - A hollow, cylindrical terminal to accommodate one or more conductors.
Cure - A chemical reaction that hardens and changes the physical properties of a material(s).
Delamination - A separation between plies within a base material or any planar separation within a multilayer
PWB.
Deterioration – (As in the context of the condition of stored polymer materials) A change in the material that
can be observed prior to its use, or during use, that indicates it no longer meets its performance requirements.
Deteriorated in this context includes degraded or separated.
Dewetting – The condition in a soldered area in which the liquid solder has not adhered intimately, but has receded,
characterized by an abrupt boundary between solder and conductor, or solder and terminal/termination area leaving
irregularly shaped mounds of solder separated by areas covered with a thin solder film.
Dielectric – A material with a high resistance to the flow of electrical current, and which is capable of being
polarized by an electrical field.
Dielectric Strength – The maximum voltage that a dielectric can withstand under specified conditions without
resulting in a voltage breakdown, usually expressed as volts per unit dimension.
Diluent – Any material that reduces the concentration of the fundamental resin; usually a liquid added to the resin
to afford lower viscosity.
225
Disturbed
solder joint – The condition in a soldered area in which the liquid solder has not adhered intimately,
but has receded, characterized by an abrupt boundary between solder and conductor, or solder and terminal/
termination area leaving irregularly shaped mounds of solder separated by areas covered with a thin solder film.
Dross – Unsatisfactory connection resulting from relative motion between the conductor and termination during
solidification of the solder.
Electrode Down – Oxide and other contaminants that form on the surface of molten solder.
Force – The force that the electrodes exert on the materials being joined.
Embedment – The complete encasement of a component or module in a resin. Equivalent to “encapsulation.”
Emulsion – A material that is built up on a printing screen to block portions of the screen. The open portions
define the pattern for depositing solder paste on a PWB.
Encapsulating Compound –An electrically nonconductive compound used to completely enclose and fill in voids
between electrical components or parts.
Equipotential Bonding - Connection between two points with a maximum resistance between them of
< 109 ohms [with no current flow].
Electrostatic Discharge ( ESD) - A transfer of electrostatic charge between bodies at different electrostatic
potentials caused by direct contact or induced by an electrostatic field.
ESD Program Monitor - An individual who is trained and certified who are responsible for the day-to- day
maintenance of the certification status of an ESD protected area.
ESD Protected Area - An area that is constructed and equipped with the necessary ESD-protective materials
and equipment to limit ESD voltage below the sensitivity level of ESDS items handled therein. This may include
benches, rooms or buildings.
ESD-Protective Material - Material capable of one or more of the following functions: limiting the generation
of static electricity; safely dissipating electrostatic charges over its surface or volume; or providing shielding from
ESD spark discharge or electrostatic fields.
ESD-Protective Packaging - Packaging with ESD-protective materials to prevent damage to ESDS items
during storage or transport.
ESD Protected Workstation - See ESD Protected Area.
ESD Sensitive (ESDS) Items - Electrical and electronic parts, assemblies and equipment which are sensitive
to ESD voltages or electrostatic fields.
Electrostatic Field - A voltage gradient between an Electrostatically charged surface and another surface of a
different electrostatic potential.
226
Encapsulation - The complete encasement of a component or module in a resin. Encapsulation is equivalent to
“potting,” “embedment,” and “molding.”
Engineering Documentation – Drawings and specifications which provide instructions, design features,
requirements, acceptance criteria, and other documentation to invoke and/or modify requirements.
Eutectic alloy – Alloy of two or more metals that has one distinct melting point
One eutectic solder is a tin-lead alloy containing 63 % Sn and 37 % Pb which melts at 183 oC.
Examination – A verification of a set of requirements during the manufacturing process that may or may not
be consider mandatory by the procuring installation. If an examinations considered mandatory by the procuring
installation, then the examination will resulting a sign-off of a certain operation by quality assurance personnel.
Excessive Solder Joint – Unsatisfactory solder connection wherein the solder obscures the configuration of the
connection.
Eyelet - A hollow tube inserted in a terminal or PWB to provide mechanical support for component leads or for
electrical connection.
Ferrule – short metal tube used to make crimp connections to the outer conductor of shielded or coaxial cables.
Filler - A material added to polymers in order to reduce cost or modify physical properties.
Fillet – A smooth, generally concave, buildup of material between two surfaces (e.g., a buildup of conformal coating
material between a part and the printed wiring board (PWB)).
Flat pack – A part with two straight rows of leads (normally on 1.27mm (0.050 inch) centers) that are parallel to
the part body.
Flux – A chemically-active compound which, when heated, removes minor surface oxidation, minimizes oxidation of
the basis metal, and promotes the formation of an intermetallic layer between solder and basis metal.
Fractured Solder Joint – A joint showing evidence of cracking, resulting from movement between the conductor
and termination, after solidification of the solder.
Gelling - Formation of a semi-solid system consisting of a network of solid aggregates in which liquid is held; the
initial gel-like solid phase that develops during the formation of a resin from a liquid.
Glass meniscus –glass fillet of a lead seal which occurs where an external lead leaves the package body.
Glass Transition Temperature (Tg) – The approximate midpoint of the temperature range over which the glass
transition takes place. The glass transition is a reversible change in an amorphous polymer or in amorphous regions
of a partially crystalline polymer from (or to) a viscous or rubbery condition to (or from) a hard and relatively
brittle one. Not only do hardness and brittleness undergo rapid changes in this temperature region, but other
properties, such as dissipation factor, thermal expansibility, and specific heat, also change rapidly. The glass transition
227
has its origin in short scale segmental motion involving intramolecular rotation of the main chain, and, if present, side
chains or pendant groups. Moreover, the observed transition temperature can vary significantly depending on the
specific property chosen for observation and on details of the experimental technique (for example, rate of heating,
frequency). Therefore, the observed Tg should be considered only an estimate.
Ground - A mass such as earth, a ship, or a vehicle hull, capable of supplying or accepting a large electrical
charge.
Groundable Point - Any point with low impedance to ground where grounding may be attached. Usually it
is the common point ground.
Haloing – Mechanically-induced fracturing or delaminating on or below the surface of the base PWB material; it is
usually exhibited by a light area around holes, other machined areas, or both.
Hook Terminal – A terminal formed in a hook shape.
Hard Ground - A connection to earth ground either directly or through low impedance.
Human Body Model -An electrostatic discharge circuit that meets the set model
values by conforming to
waveform criteria specified in ESD-STM 5.1, characterizing the discharge from the fingertip of a typical human
being.
I or Butt Lead (Package) – A SMD lead, which is formed such that the end of the lead contacts the PWB land
pattern.
Impregnation – An encapsulation process that results in complete saturation of the unit with the insulating
material to include penetration and filling of every void replacing all air and gasses.
Insufficient Solder Connection – A solder connection characterized by incomplete coverage of one or more of
the metal surfaces being joined or by incomplete solder fillets.
Interfacial Connection – A conductor that connects conductive patterns between opposite sides of a PWB.
Insulative Material
• RTT < 1012
• RTG < 1011
A material having a surface resistivity <1012
ohms/square or a volume resistivity <1011
J - Lead (Packages) – A SMD lead, which is formed into a J pattern folding under the part body.
Land Pattern – A combination of lands intended for the mounting, interconnection, and testing of a particular
part.
Lap joint – Joining or fusing of two overlapping metal surfaces with solder without use of any other mechanical
attachment or support.
Lateral Edge - The two longest sides of a rectangular shaped conductive area or land.
228
Leaching – The dissolution of a metal coating, such as silver and gold into liquid solder, Nickel barrier under plating
is used to prevent leaching.
Lead less Chip Carrier (LLCC) – A chip carrier whose external connections consist of metallized
terminations.
Lifted Land - A land that has lifted or separated from the base material, whether or not any resin is lifted with the
land.
Lug – Metallic tube with drilled flange projection for fixing to threaded terminal.
Measling – Discrete white spots below the surface of the base material usually caused by moisture, pressure, and/
or thermally induced stress.
Mix Record – A record of the procedure followed for mixing the polymeric compounds.
Module – A separable unit in a packaging scheme.
Molding -The complete encasement of a component or module in a resin. Equivalent to “encapsulation.”
Machine Model - An electrostatic discharge simulation test based on a discharge network consisting of a
charged 200 Pico farad capacitor at (nominally) zero ohms of series resistance. Actual series resistance and
inductance are specified in terms of the current waveform through a shorting wire. The simulation test
approximates the electrostatic discharge from a machine. (See ESD STM 5.2)
Multi-layer circuit board – Product consisting of alternate laminates of printed circuit substrates
and
insulators, bonded together by simultaneous application of heat and pressure prior to drilling and plating holes for
interconnections.
Nick - A cut or notch on a conductor.
Non-wetting – A condition whereby a surface has contacted molten solder, but the solder has
not adhered to
all of the surface, basis metal remains exposed.
Off contact - Printing with a snap off. Squeegee deflects screen to PWB.
On contact - Printing with the stencil directly in contact to the PWB throughout the printing process.
Outgassing – Gaseous emission from a liquid or solid material when exposed to vacuum pressure, heat, or both.
Operator - An individual who is trained and certified to perform tasks in an ESD Protected area.
Overheated Joint – An unsatisfactory solder joint, characterized by rough solder surface; dull, chalky, grainy, porous
or pitted.
Pad – A portion of a conductive pattern used as a soldering area. Also called a land.
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Peeling – The separation of conformal coating from the PWA, usually due to improper preparation or abrasion.
Peeling is distinguished from lifting in that the layer of conformal coating is not continuous.
Pin hole – A solder connection with a small hole penetrating from the surface of the solder to a void of indeterminate
size within the solder connection.
Pit – A relatively small recess in the solder surface, the bottom of which is visible from all angles of vision.
Planarity – The relationship between part plane and substrate plane.
Plastic Leaded Chip Carrier (PLCC) – A chip carrier whose external connections consist of metalized around
and down the sides of the package.
Plated-Through Hole – Plated-through hole is one formed by a deposition of metal on the inside surface of a
through-hole. Also known as a supported hole. The configuration is used to provide additional mechanical strength
to the soldered termination or to provide an electrical interconnection on a multilayer PWB.
Polymer – A compound of high molecular weight that is derived from either the joining together of many small
similar or dissimilar organic molecules or by the condensation of many small molecules by the elimination of water,
alcohol, or a solvent.
Porous Solder Joint – A joint having a grainy or gritty surface.
Potting – The complete encasement of a component or module in a resin. Equivalent to “encapsulation.”
Potting compound - An electrically nonconductive compound used to partially encapsulate or for a filler between
parts, conductors, or assemblies.
Printed Wiring Assembly (PWA)
Printed circuit board (PCB) – Product resulting from the process of selectively etching unwanted copper from
one or both surfaces of a copper-clad insulating substrate to form a desired circuitry pattern which is subsequently
solder - or gold -plated.
Printed Wiring Assembly – The PWA consists of the PWB, components, and associated hardware and
materials.
Radial Lead – Lead wire extending from a component or module body along its latitudinal axis
Radial Split – A crack or other separation in the flange of an eyelet or other circular connector, which extends
outward from the center. Such cracking is usually the result of swaging or other setting process as the item is
embraced in a printed wiring board.
Repair – Operations performed on a nonconforming article to place it in usable condition. Repair is distinguished
from rework in that alternate processes rather than reprocessing are employed.
Resin - Any synthetic organic material produced by polymerization
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Resistance Soldering – Method of soldering by passing a current between two electrodes through the area to
be soldered.
Rework – The act of reprocessing noncomplying articles, through the use of original or alternate equivalent
processing, in a manner that assures compliance of the article with applicable drawings or specifications.
Rosin –A synthetic resin.
Rosin Solder Joint – Unsatisfactory connection that has entrapped rosin flux. This entrapment is usually due to
insufficient heat or insufficient time at soldering temperature, or both, not enabling the rosin to rise to the surface
of the solder. This results in insufficient bonding and/or high electrical resistance.
Saponifiers - Chemicals, added to water, which convert rosin/resin flux residues into water-soluble soaps.
Screen Mesh – A Structure of woven fibers, which supports the emulsion, but does not block the solder paste
when used to selectively screen print solder paste into a PWB.
Shield – Metallic sheath surrounding one or more wires, cables, cable assemblies, or a combination of wires and
cables that is used to prevent or reduce the transmission of electromagnetic energy to or from the enclosed
conductors.
Soft Ground - A connection to ground through impedance sufficiently high to limit current flow to safe levels
for personnel (normally 5 milli amperes). Impedance needed for a soft ground is dependent upon the voltage
levels which could be contacted by personnel near the ground. By this definition a hard ground protected by
a functional GFCI is considered a soft ground.
Static Dissipative
• RTT 106 - 109 ohm
• RTG 105 - 108 ohm
• Property of a material having surface resistivity
105 but <1012 ohms per square or a volume resistivity
104 but <1011 ohms-cm.
Slump Test Snap Off - A test performed on solder paste to measure the distance the solder metal in the solder
paste spreads after printing, during the drying, and before the reflow process.
Solder – Non-ferrous fusible metallic alloy of two or more metals (usually tin and lead) used when melted to join
or fuse metallic surfaces together and to provide a low resistance electrical path.
Solder Balls - Very small balls of solder that separate from the main body of solder, which forms the joint, and
remain adhered to the base laminates. Primarily caused by oxides in the solder paste that inhibits solder fusion
during reflow.
Solder Connection – An electrical/mechanical connection that employs solder for the joining of two or more
metal surfaces.
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Solder Fillet – A blended or meniscold (rounded) configuration of solder around a part or wire lead and land.
Surface Resistivity. - The surface resistivity is an inverse measure of the conductivity of a
material.Surface
resistivity of a material is numerically equal to the surface resistance between two electrodes forming opposite
sides of a square. The size of the square is immaterial. Surface resistivity applies to both surfaces and materials
with constant volume conductivity and has the value of ohms per square.
Solder icicle – conical peak or sharp point of solder usually formed by the premature cooling and solidification of
solder upon removal of the heat sources.
Solder Mask – Coating material used to mask or protect selected areas of a pattern from the action of an etchant,
solder, or plating.
Solder Pad – Termination area on a printed wiring conductor.
Solder Paste – A homogeneous combination of minute spherical solder particles, flux, solvent and a gelling
suspension agent, which is used in the surface mount reflow soldering process, solder paste can be deposited onto
a PWB via screen or stencil or via manual or automated dispensing systems.
Solder Silvers – Portions of tin-lead (solder) plating overhang on conductor edges partially or completely
detached.
Solder Spatter – Extraneous irregular-shape solder fragments.
Solder Spike/Peak - A cone shaped peak or sharp point of solder usually formed by the premature cooling and
solidification of solder on removal of the heat source.
Solder Wave – A method of soldering complete PWAs where the PWB with parts mounted is passed through one
or more waves of molten solder, which is continuously moving to maintain fresh solder in contact with the PWB.
Solder Webbing – A continuous film or curtain of solder parallel to, but not necessarily adhering to, a surface or
between separate sections or circuit that should be free of solder.
Solder, Dispensing Grade – Solder paste contained in a syringe type applicator.
Solder, Insufficient – Unsatisfactory connection where the solder fillet it short or otherwise incomplete.
Solder, Overheated – An unsatisfactory solder joint, characterized by a rough solder surface.
Solder, Porous – Solder having a grainy or gritty surface.
Solderability – The property of a surface that allows it to be wetted by molten solder.
Solder-cup terminal – Hollow, cylindrical terminal closed at one end to accommodate one or more conductors.
Soldering – The process of joining clean metallic surfaces through the use of solder without direct fusion of the
base metals.
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Soldering Infrared Reflow – A reflow soldering furnace using infrared heating as the primary source of heat
transfer in a oven environment.
Soldering, Reflow – A process of joining metallic surfaces (without the melting of basis metals) through the mass
heating of the entire PWA.This mass heating process causes pre-placed solder paste to melt in predefined metalized
areas. Soldering is accomplished in an upright position.
Splice – Device for joining two or more conductors to each other.
Squeegee – A blade used in screen printing to wipe across the screen to force the solder paste through the screen
mesh or stencil onto the foot print.
Squeeze-out – The resin and/or reinforcement that is visible at the edges of a bond.
Potting – The process of bonding and securing components or parts to PWB’s and electronic assemblies by means
of an adhesive material.
Potting Compound – An electrically nonconductive adhesive material used for additional support.
Stencil - A metal mask used in place of a screen. These are normally used for thicker paste deposits or paste with
different characteristics as there is no Snap Off. The do not deflect or seal.
Straight Pin Terminal – A round post-type smooth terminal, with no grooves.
Straight-Through Termination – A conductor termination extending through a PWB without subsequent
forming of the lead.
Stress lines – Three forms of stress lines can appear on a finished solder fillet:
1.
Lines or folds running parallel to the mounting surface usually denote excessive soldering times or
temperatures and also rework. They are probably caused during soldering by differential expansions,
i.e. between the printed circuit board substrate which expands a far greater distance than the metallic
material of the joint.
2.
Lines running perpendicular to the mounting surface are commonly caused when the soldering iron bit is
removed too slowly from a liquid solder joint
3.
Lines running circumferentially around the mid section of the solder fillet caused by shrinkage during the
last stage of solidification
Stress relief – Method or means to minimize stresses to the soldered termination or component
Stud Termination – An unbendable conductor termination extending through a PWB.
Substrate – That surface upon which an adhesive is spread for any purpose, such as coating; a broader term than
“adherent.”
Tack Test Tilt – A test performed on solder paste to determine the surface tension holding force.
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Surface Mounting – The electrical connection of components to the surface of a conductive pattern that does
not utilize part holes.
Terminal – A tie point device used for making electrical connection.
Triboelectric - Pertaining to electricity generated by friction.
Test Specimen - A sample of the same material processed using the same method, at the same time, and under
the same conditions as the original end item product. It used as a quality record of the hardness and cure achieved
with the particular material batch and the operations performed.
Thermal Shunt – A device with good heat dissipation characteristics used to conduct heat away from an article
being soldered.
Tinning - The coating of a surface with a uniform layer of solder.
Traceability Code – The code uniquely identifying the production lot by the manufacturer, equivalent to batch
code, lot code, or date code.
Transmissivity – The fractional quantity of incident radiation transmitted by matter.
Turret Terminal – A round post-type grooved stud around which conductors are fastened before soldering.
Unsupported Hole – A hole containing no plating or other type of conductive reinforcement.
Via – A PTH used as an interlayer connection, but in which there is no intention to insert a component or other
reinforcing material.
Viscosity – A measure of the resistance of a material to flow under stress.
Visual Examination – The property of a fluid that enables it to develop and maintain an amount of shearing stress
dependent upon the velocity of the flow, and then to offer continued resistance to flow.
Void - A space enclosed on all sides by the solder.
Void Wetting – The qualitative observation of physical characteristics, utilizing the unaided eye or within stipulated
levels of magnification.
Wave Soldering – A process wherein PWAs are brought in contact with the surface of continuously flowing and
circulating solder.
Wetting – Flow and adhesion of a liquid to a solid surface, characterized by smooth, even edges and low contact angle.
Wetting, Negative – A total absence of material.
Wetting, Positive – Flow and adhesion of a liquid to a solid surface, characterized by smooth, even edges and a
low dihedral angle. When measured from the vertical plane, the solder fillet forms a negative angle. When measured
from the vertical plane, the solder fillet forms a positive angle.
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White Room – An environment that is equal to or better than a class 100,000 clean room, which however, does
not require certification records or additional record keeping.
Wicking – A flow of molten solder, flux, or cleaning solution by capillary action.
Working Life – The period of time during which a material, such as solder paste, remains.
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19 TECHNICAL STANDARD IMPROVEMENT PROPOSAL
1. DOCUMENT NUMBER
2. DOCUMENT TITLE
3. NAME OF SUBMITTING ORGANIZATION
4. ADDRESS
5. PROBLEM AREAS
a. Paragraph Number and Wording
b. Recommended Wording:
c. Rational for Recommendation:
6. REMARKS
7. NAME OF SUBMITTER
8. TELEPHONE NO / E-MAIL ID
9. DATE
19.1 Instructions
In a continuing effort to improve our ISRO Technical Standards, we invite all centres to use this form for submitting
comments and suggestions for improvements in the above format. Be as specific as possible about particular
problem areas. Supporting data should accompany any recommendations for changes.
236
Contributors
Task team:
Shri MM Vachhani, SAC
Shri MP James, ISAC
Shri G Jayaprasad, IISU
Shir V V Janardanan,VSSC
Shri G Shanmugam,VSSC
Co-opted members:
Shri Thomas John, VSSC
Shri Vasudevan Potti,VSSC
Shri R Saravanan,VSSC
Shri Mukesh. C. Gajjar, SAC
Shri Ishwarlal Prajapati, SAC
Shri Mukesh Patel, SAC
Shri Sreejith,VSSC