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.
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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
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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).
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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.
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