SME Initiative
Critical processes related to electronic materials
ESA SME Initiative
Course D:Materials
Dr. Ton de Rooij
Head of Materials Mechanics and Processes Section
Materials and Processes Division
Product Assurance and Safety Department
Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 1
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
Sheet 2
SME Initiative
Specifications
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ECSS-Q-70-08A
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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)
ECSS-Q-70-18A
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Space product assurance - manual soldering of
high-reliability electrical connections
ECSS-Q-70-10A
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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
Space product assurance - wire-wrapping of highreliability electrical connections
ESA PSS-01-738
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the preparation, assembly and mounting of RF
coaxial cables
ECSS-Q-70-26A
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ECSS-Q-70-28A
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
Sheet 3
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
Sheet 4
SME Initiative
Soldering processes
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Soldering processes
Solder flux
solder alloys
cleaning
accept/reject criteria
conformal coatings
thermal cycling
operator training and certification
Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 5
SME Initiative
Soldering processes, cont..
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Hand soldering
qualification
machine soldering
verification and approval
surface mounting
verification and approval
Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 6
SME Initiative
Soldering processes, cont..
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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
Sheet 7
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
Sheet 8
SME Initiative
Soldering processes, cont..
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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
Sheet 9
SME Initiative
Principles of reliable soldered connections
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Reliable soldered connections result from proper design, control
of tools, materials and work environments, and careful
workmanship
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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
Sheet 10
SME Initiative
Acceptance criteria
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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
Sheet 11
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
Sheet 12
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
7
6
3
5
1
4
2
2
1
3
6
5
4
7
1
2
5
3
6
4
7
5
6
1
7
1
1
1
1
3
6
3
7
2
5
outgass manned
ing
spacecraft
surface leaded microwire
mount component bonds
1=good
1=good
s
7=poor
1
4
1
5
7
6
1
1=best
1
1
1
1
1
6
7
Materials and Processes Division
ESA/ESTEC/TOS-QM
1
1
4
1
5
7
6
7=poor
total
1=good 4=fail
7=fail
1
2
4
3
5
6
7
1
6
4
7
1
1
4
1
1
4
1
4
4
4
22
33
36
42
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45
51
Sheet 13
SME Initiative
Thermal fatigue
Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 14
SME Initiative
Verification of solder-joints not in ECSS spec.
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No cracked solderjoints or part damage after 200 thermal cycles and
vibration testing
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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
Sheet 15
SME Initiative
Operator and inspector training and certification
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Trained and competent personnel shall be employed for all soldering
operations and inspections
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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
Sheet 16
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-std-8739.5
Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 17
SME Initiative
Soldering of surface mount devices to pcb’s
ESA PSS-01-738
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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
Sheet 18
SME Initiative
Soldering of surface mount devices to pcb’s, cont..
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Request for verification
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Technology sample
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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.
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
Sheet 19
SME Initiative
Soldering of surface mount devices to pcb’s, cont..
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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
Sheet 20
SME Initiative
Automatic machine wave soldering
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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
Sheet 21
SME Initiative
high-reliability electrical connections
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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
Sheet 22
SME Initiative
Crimping of high-reliability electrical connections, cont..
Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 23
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
Sheet 24
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
Sheet 25
SME Initiative
Wire-wrapping of high-rel. electrical connections
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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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Recommended wire insulations
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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)
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
Sheet 26
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
Sheet 27
SME Initiative
Repair and modification of PCB assemblies
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ECSS_Q-70-28
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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
Sheet 28
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
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whisker growth on Tin-plated brass
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Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 29
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
Sheet 30
SME Initiative
SMT solderjoints
Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 31
SME Initiative
Good quality joints
Cross section of smd devices
flatpack
J-lead
Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 32
SME Initiative
Failures: soldering to gold
Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 33
SME Initiative
Failures: No pretinning
Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 34
SME Initiative
Failures: After thermal cycling
Top view
Cross section
Materials and Processes Division
ESA/ESTEC/TOS-QM
Sheet 35
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
Sheet 36