SME
Initiative
Critical processes related to electronic materials
ESA SME Initiative
Course D:Materials
Ton de Rooij
Principal Metallurgist
Materials and Processes Division
Product Assurance and Safety Department
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet1
SME
Initiative
Content of presentation
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specifications
pcb’s manufacturing
soldering processes
crimping
wire wrapping
Repair and modification of PCB assemblies
cleaning
quality evaluations
good solderjoints
failure modes
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet2
SME
Initiative
Specifications
• ECSS-Q-70-08A
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• ECSS-Q-70-28
Space product assurance - manual soldering of
high-reliability electrical connections
• ECSS-Q-70-10
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Space product assurance - qualification and
procurement of multilayer printed circuit boards
(gold plated or tin-lead finish) - to be published (
now ESA PSS-01-710)
• ESA PSS-01-718
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Space product assurance - repair and modification
of printed circuit board assemblies - to be
published (now ESA PSS-01-728)
• ECSS-Q-70-30A
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Space product assurance - wire-wrapping of highreliability electrical connections
• ECSS-Q-70-38
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the preparation, assembly and mounting of RF
coaxial cables
• ECSS-Q-70-26
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Space product assurance - high-reliability soldering
for surface mount and mixed technology printed
circuit boards - to be published (now ESA PSS-01738)
Space product assurance - the crimping of highreliability electrical connections -to be published
(now ESA PSS-01-726)
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet3
SME
Initiative
PCB manufacturing
• Schematic representation of
major steps in multilayer
board fabrication
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laminate
• epoxy-impregnated fibreglas-laminated
weave
• polyimide-quartz laminate
• ceramic laminate
hole drilling
cleaning and electroless and electrolytic copper
plating
photoresist laminating exposure and development
tin-lead alloy electroplating
photoresist removal
etching
reflow
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet4
SME
Initiative
Approved PCB manufcaturers
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BOSCH Telecom GmbH, Germany
CIT (ALCATEL), France
LABTECH Ltd, England
PRINTCA AS, Denmark
SEXTANT Avionique, France
SPEMCO Group Ltd, England
STRASCHU Leiterplatten GmbH, Germany
SYSTRONIC S.A.L, France
VIASYSTEMS, div. CSI, Italy
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet5
SME
Initiative
Soldering processes
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Soldering processes
Solder flux
solder alloys
phase diagrams
cleaning
accept/reject criteria
conformal coatings
thermal cycling
operator training and certification
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet6
SME
Initiative
Soldering processes, cont..
• Hand soldering
• qualification
• machine soldering
• verification and approval
• surface mounting
• verification and approval
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet7
SME
Initiative
Soldering processes, cont..
• solder flux
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rosin-based
• pretinning: mildly activated (fully activated in cases of poor solderability)
• assembly: pure rosin flux
water-soluble acid flux
• only for pretinning when rosin-based fluxes are inadequate. (immediate cleaning after use is
required)
• solder alloy
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63 tin solder (63 Sn, 37 Pb)
62 tin silver-loaded solder (62 Sn, 2 Ag, 36 Pb)
60 tin solder (60 Sn, 40 Pb)
96 tin silver solder (96 Sn, 4 Ag)
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet8
SME
Initiative
Soldering processes, cont..
63 tin solder
(eutectic)
183
183
62 tin silver
loaded
175
189
60 tin solder
183
188
96 tin silver
(eutectic)
221
221
Soldering PCBs where temperature limitations are critical
and in applications where an extremely short melting
range is required
Soldering of components have silver-plated or ‘paint’ (i.e.
ceramic capacitor) finish. This solder composition is saturated with silver and prevents the scavenging of silver surfaces.
Soldering electrical wire/cable harnesses or terminal connections and for coating or pre-tinning metals
May be used for special applications such as soldering
terminal posts
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet9
SME
Initiative
Soldering processes, cont..
• Cleaning
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solvents shall be non-corrosive and non-conductive and shall not degrade parts or materials.
• Acceptable solvents are:
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ethyl alcohol (99.5% or 95% pure by volume)
isopropyl alcohol (best commercial grade, 99% pure)
deionized water at 40 oC maximum for certain fluxes (dry after use)
any mixture of the above
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet10
SME
Initiative
Principles of reliable soldered connections
• Reliable soldered connections result from proper
design, control of tools, materials and work
environments, and careful workmanship
• basic deign concepts:
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stress relief shall be inherent in the design
where adequate stress relief is not possible, solder-joint reinforcement is necessary
materials shall be so selected that the mismatch of thermal expansion coefficient is minimal
materials and processes which the formation of brittle intermetallic shall be avoided
the design shall permit inspection of the soldered joints
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet11
SME
Initiative
Phase diagram of Ag-Sn
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Liquid
Sn
 phase = Ag3Sn ordered structure
eutectic at 96.5 w% Sn ( 95 m% Sn with
5m%  phase according to lever rule)
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet12
SME
Initiative
Phase diagram of Sn-Pb
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Liquid
Pb
Sn
Liquid + Pb =
crystals of solid Pb
dispersed in the
liquid
Liquid + Sn =
crystals of solid Sn
dispersed in the
liquid
solid = fraction of
Pb and Sn
according to lever
rule
eutectic = overall
composition 62% Sn
rem Pb. Melting point
183 oC (45m% Pb
and 55m% Sn)
liquid
Pb
Liquid+solid (Pb)
Liquid+solid
(Sn)
Eutectic
Pb + Sn
solid
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet13
SME
Initiative
Phase diagram of Au-Sn
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Layers found in
solder joints when
soldering with a SnPb alloy to gold:
– gold
– AuSn
– AuSn2
– AuSn4
high volume of AuSn4
needles
– gold dissolution
into liquid
solder followed
by precipitation
during cooling
to RT
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet14
SME
Initiative
Acceptance criteria
• Clean, smooth, bright undisturbed surface
• solder fillets between conductor and termination
areas as illustrated
• contour of wire sufficiently visible to determine
presence of wire
• complete wetting as evidenced by a low contact
angle
• proper amount and distribution of solder
• absence of defects as mentioned in the next sheet
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet15
SME
Initiative
Rejection criteria
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Charred, burned, or melted insulation of
parts
conductor pattern separation for board
burns on base material
discoloration which is continuous between
two conductors
excessive solder (peaks, bridging)
flux residue, solder spatter, or other
foreign matter
dewetting
insufficient solder
pits, holes or voids, or exposed base metal
in the solder connection
granular or disturbed solder joints
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fractured or cracked solder connections
cut, nicked, gouged, or scraped
conductors or conductor pattern
improper conductor length or direction of
clinch and lap termination
repaired or damaged conductor
pattern(rework if applicable)
bare copper or base metal (except end of
cut wire or leads)
soldered joints made directly to goldplated terminals and conductors
cold solder joints
component moulding with solder fillet
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet16
SME
Initiative
Conformal coating
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Order of merit of conformal coating tested evaluated by:
Cost, Process, Repair, Solvent resistance, humidity, life test, resistance to thermal cycling,
outgassing, micro-vcm, flammability, offgassing, toxicity
coating type
CV 1144-0
Mapsil 213
Uralane 5750 LV
Sylgard 184
Conathane en11
Solithane 113
Scothcast 280
nature
silicone
silicone
polyurethane
silicone
polyurethane
polyurethane
epoxy
cost
process
repair
solvent humidity life test resistance to thermal cycling
resistance
7=dear
1=cheap
7=complicated
1=easy
7=difficult
1=easy
1=good
7=poor
1=good
7=poor
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6
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7
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5
outgass manned
ing
spacecraft
surface leaded microwire
mount component bonds
1=good
1=good
s
7=poor
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1=best
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7
Materials and Processes Division
ESA/ESTEC/TOS-QM
1
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7=poor
total
1=good 4=fail
7=fail
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33
36
42
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sheet17
SME
Initiative
Thermal fatigue
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet18
SME
Initiative
Verification of solder-joints not in ECSS spec.
• No cracked solderjoints or part damage after 200
thermal cycles and vibration testing
• Thermal cycling
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temperature cycling in air from RT to -55 oC to +100 oC and back to RT at a rate not to exceed 10 oC
per minute. Dwell time at each temperature extreme should be 15 minutes.
• Vibration testing
Sine vibration
Random vibration
Vibration amplitude
Frequency range
Sweep
Duration
Frequency range
Power spectral density
Duration
(Peak to peak) 10-70 Hz at 1.5 mm
70-2000 Hz at 15 g
1 octave per minute
1 cycle from 10-2000-10 Hz
20-2000 Hz at 15 g-rms
0.1 g2 Hz-1
10 minutes per axis
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet19
SME
Initiative
Operator and inspector training and certification
• Trained and competent personnel shall be employed for all
soldering operations and inspections
• Trained personnel performing soldering operations and
inspection shall be certified at a soldering school
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ZVE, Oberpfaffenhofen, Germany
Highbury College, Portsmouth, England
Italian Institute of welding (IIS), Genova, Italy
IFE, Oberpfaffenhofen, Germany
Hytek, Aalborg, Denmark
Institute de soudure, Paris, France
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet20
SME
Initiative
Training programmes
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Hand soldering to ESA PSS-01-708
inspection of solder joints
repair and modification of pcb’s to ESA PSS-01-728
RF cable assembly to ESA PSS-01-718
crimping and wire wrapping to ESA PSS-01-726/730
surface mounting techn. Ass. To ESA PSS-01-738
Instructor cat 1 to ESA PSS-01-748
fiber optic terminations to ESA-draft/NASA-std8739.5
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet21
SME
Initiative
Soldering of surface mount devices to pcb’s
ESA PSS-01-738
• Request for verification
• technology sample
• process identification document and process control
sheet
• audit of assembly line
• verification programme
• smd assembly approval
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet22
SME
Initiative
Soldering of surface mount devices to pcb’s, cont..
• Request for verification
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The verification of any SMD assembly line will be restricted to those companies which have been
selected for the fabrication of ESA sponsored projects.
• Technology sample
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the contractor will supply one sample from his SMD assembly process to ESTEC. This sample will be
examined at ESTEC or a recognised test house
• no conformal coating
• workmanship
• cleanliness
• metallography of soldered interconnections
• Audit of assembly process line
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following acceptance of the technology sample the manufacturing facility will be audited by ESA
findings of the audit remain as confidential to ESA
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet23
SME
Initiative
Soldering of surface mount devices to pcb’s, cont..
• Verification programme
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Details of verification programme will be discussed at the time of the audit
• acc. To ESA PSS-01-738
• thermal cycling (500: -55 to +100 oC)
• vibration
• visual, electrical test, cleanliness test, microsection control
the verification programme shall be established and approved by ESA
the verification programme shall be funded and performed by the contractor or one or more
independent test houses (test house require approval by ESA)
summary table for SMD verified to ESA PSS-01-738 shall be compiled
• SMD assembly approval
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following the successful completion of the verification programme a letter of approval will be issued by
ESA. ESA project approval by means of Project Declared Process List
The summary table for SMD’s will be attached to this letter
The validation period is indefinite until change to PID
history of supply, manufacturing defects and unauthorised change of materials and or manufacturing
methods will require new verification
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet24
SME
Initiative
Automatic machine wave soldering
• ECSS-Q-70-07A
• verification tests to establish confidence in all
automatic machine soldering lines
• technology samples
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technology samples, cleanliness, documentation
examination by recognised test house
• line audit
• verification testing
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testing according to ECSS-Q-70-70A: visual inspection, electrical tests, thermal cycling, vibration
when design deviates from ECSS-Q-70-08
microsectioning
pull testing of leads on board surface
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet25
SME
Initiative
high-reliability electrical connections
• CRIMPING
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Forms of crimps
Crimping optimisation
Workmanship examples
• WIRE WRAPPING
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wire types
recommended insulations
terminal posts
examples
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet26
SME
Initiative
Crimping of high-reliability electrical connections, cont..
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet27
SME
Initiative
Crimping of high-reliability electrical connections, cont..
Typical plots showing variation in crimp termination characteristics with increasing indentation depth
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet28
SME
Initiative
Crimping of high-reliability electrical connections, cont..
Unacceptable - undercrimp
(tool setting-2 positions
under optimum
Voids greater than 10%,
wire not deformed
Acceptable
All wire strands deformed
Voiding less than 10%
Preferred
Workmanship examples
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet29
SME
Initiative
Wire-wrapping of high-rel. electrical connections
• Wire used for wrapped connections shall conform to
ESA/SCC No. 3903 or other approved national wire
specification intended for wire wrapping
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the wire shall be a single solid round conductor. Stranded conductors shall not be used
Conductor size shall be between AWG 24 and AWG 30
• soft annealed high-conductivity copper for AWG 28 and AWG 30
• high strength high-conductivity copper for wire gauges AWG 28 and AWG 30
copper shall be silver plated (>2 micron)
• Recommended wire insulations
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outgassing according to ECSS-Q-70-02
ETFE (Tefzel), PFA (Perfluoroalkoxy), PVDF (Kynar), and Kapton poluimide over extruded PTFE
• Terminal post
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suitable grades of copper or nickel alloys (Copper-Zinc, Phosphor-bronze, copper-nickel-zinc,
beryllium-copper,nickel-copper(Monel) and nickel-cclad copper(Kulgrid)
1 to 3 microns of Gold over min. 1 micron of copper or nickel (barrier plating). No Silver undeplating
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet30
SME
Initiative
Wire-wrapping of high-rel. electrical connections, cont..
Satisfactory wire wrap cross-section of copper
alloy wire wrapped onto a 0.64 mm square
terminal post
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet31
SME
Initiative
Repair and modification of PCB assemblies
• ESA PSS-01-728
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example of method 11-1, wire-towire bonding
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cut wire to correct length
remove wire insulation per ESA PSS-01-708
if distrubed, the lay of stranded conductor
shall be restored. Do not use bare fingers
pre-tin wires per ESA PSS-01-708
place heat-shrink over wire insulation in
readiness for slicing over the joined wire
position wire into joined configuration and
maintain position
solder wire together (using heat shunt on
each lead) to form a lap-type joint
clean area with approved solvent to remove
flux
inspect joint per ESA PSS-01-708
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position shrink sleeve over joint and shrink to size in
accordance with manufacture’s instructions. At no
time shall the shrink temperature be allowed to
exceed to melting point of the solder
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position the extended wire on the board and bond to
board using a suitable space-approved adhesive,
with interval not more than 2.5 cm. The first spot not
more than 1.5 cm from soldered joint
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet32
SME
Initiative
Examples of solderjoints
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Good quality solderjoints
Good quality SMT solderjoints
Cross section of smd devices
soldering to gold
No pretinning
After thermal cycling
• whisker growth on Tin-plated brass
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet33
SME
Initiative
Good quality joints
Good designed stress relief loop
Few fatigue lines, but no failure
after thermal cycling
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet34
SME
Initiative
SMT solderjoints
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet35
SME
Initiative
Good quality joints
Cross section of smd devices
flatpack
J-lead
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet36
SME
Initiative
Failures: soldering to gold
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet37
SME
Initiative
Failures: No pretinning
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet38
SME
Initiative
Failures: After thermal cycling
Top view
Cross section
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet39
SME
Initiative
Whisker growth
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Occasionally, manufactures use pure tin
finishes on their pcb’s, as may be standard
practice for their commercial products. It is
the thermal cycling environment of the
spacecraft that makes this option extremely
dangerous, as it can promote the growth of tin
whiskers from sites within pure tin plated
through holes.
Terminal posts for pcb’s, grounding points,
and wire terminals and lugs for crimping
operations are frequently machined from
either copper or brass and simply tin-plated to
achieve a reasonable solderability and
protection from surface corrosion. This occurs
mainly with standard off-the-self items.
Tin-plated brass shows a short nucleation
period and produces whiskers with growth
rates of 8m per day.
Materials and Processes Division
ESA/ESTEC/TOS-QM
sheet40