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8/7/2019 Lead-Free Wave Solder Processing Sept 17
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Lead-Free Wave Solder
ProcessingCPS Study Phase I
Initial Lessons Learned from Cookson
Performance Solutions L-F Wave Solder Study
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Wetting Balance TestingTo Determine Lead-Free Solder Pot Temperature
Laboratory test designed to determine the best
temperature to wave solder an alloy with.
Data not relevant to SMT processing
Test Conditions
Preheat after flux immersion: Test coupon held 0.1 above solderpot for 5 seconds
Dwell time in solder: 5 seconds
15 test coupons per test
Cleaned as follows:
- degreased in boiling IPA
- Cleaned in Alpha 922 copper cleaner for 15 seconds
- Two DI water rinses: 5 & 10 seconds
- Two IPA rinses: 5 seconds each
Test using cleaned coupons as well as clean coupons oxidized for 1 hour
@ 100C (212F)
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Wetting time vs. Solder temperature (RF 800, oxidized Cu)
0.5
1.3
2.1
2.9
3.7
4.5
450 460 470 480 490 500 510 520 530
Solder Temperature (F)
Wetting
Time(sec.)
Sn63/Pb37 Sn96.5/Ag3.5 Sn99.3/Cu0.7
Sn95.5/Ag4/Cu0.5 Sn96/Ag2.5/Bi1/Cu0.5 Sn96.2/Ag2.5/Sb0.5/Cu0.8
232 238 243 249 254 260 265 271 277
Solder Temperature (C)
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Wetting force vs. Solder temperature (RF 800, oxidized Cu)
0
70
140
210
280
350
450 460 470 480 490 500 510 520 530
Solder Temperature (F)
WettingFo
rce(uN/mm
)
Sn63/Pb37 Sn96.5/Ag3.5 Sn99.3/Cu0.7
Sn95.5/Ag4/Cu0.5 Sn96/Ag2.5/Bi1/Cu0.5 Sn96.2/Ag2.5/Sb0.5/Cu0.8
232 238 243 249 254 260 265 271 277Solder Temperature (C)
CPS Lead-Free StudyCPS Lead-Free Study
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Wetting Balance Observations & Discussions
The Binary & Ternary Tin, Silver & Copper alloys
generally produced the fastest wetting times and
maximum wetting forces.
520F (271C) appears to be an appropriate solder
pot temperature for these alloys when the flux used
is a low solids, no-clean type. 500F (260C) appears to be an appropriate solder
pot temperature for these alloys with high solids
content, non-activated rosin flux (Control Flux). DATA NOT SHOWN
CPS Lead-Free StudyCPS Lead-Free Study
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Alloy Run Order Pot Temp.
Sn63-Pb37 (Sn-Pb) 500 F / 260 C Sn99.3-Cu0.7 (Sn-Cu) 530 F / 276 C
Sn96.5-Ag3.0-Cu0.5 (SAC305) 520 F / 270 C
Sn95.5-Ag4.0-Cu0.5 (SAC405) 530 F / 276 C
Sn96.5-Ag3.5 (Sn-Ag) 530 F / 276 C
CPS Lead-Free StudyCPS Lead-Free Study
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CPS L-F Study Bottom of Test Vehicle
Designed
forDefects
Note that TH
Components are
for positionreference only
and board is
prior to solder.
CPS Lead-Free StudyCPS Lead-Free Study
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Wave Machine Configuration
Air Environment
Spray Fluxer (Accuspray)
Three bottom forced convection heaters (for water-based fluxes)
Two bottom forced convection heaters (for alcohol-based fluxes)
Dual wave with Air Knife Rotary Chip Wave
Lambda Wave
Hot air knife (Accuknife) Finger conveyor
Electrovert Vectra Oven
CPS Lead-Free StudyCPS Lead-Free Study
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Processing ParametersParameter NR330 RF800 SLS65C 5280E 615-25
Solvent Water Alc. (Rosin) Alcohol Water Alc. (RMA)
Solids content % 4.0% 4.1% 2.2% 11.0% 25.0%
Top preheat (rec.) 0F 210 - 235 190 - 230 210 - 250 220 - 240 180-200T (B-T) (rec.) 0F 0 to +40 0 to +65 0 to +65 0 to +65 not spec.
Speed (rec) ft/min 3.5 - 6.5 4.0 - 6.0 3.5 - 6.5 4.5 - 6.0 not spec.
Top preheat (actual) 0F 218 - 230 216 - 235 207 - 229 230 - 256 241 - 258
T (B-T) (actual) 0F 7 - 19 9 - 27 9 - 25 7 - 16 9 - 24Speed (actual) ft/min 5.0 - 6.0 5.0 - 6.5 5.0 - 6.5 5.0 - 6.0 3.0 - 6.0
For statistical data: Once a set of processing parameters was set
for a given flux/alloy, all the boards in the experiment were run
without further changes. This gives a first-level of optimization only.
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ThermalProfilesAlloy: SAC405
Flux: 615-25
Size: 0.062"
Environment: Air
0
100
200
300
400
500
50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
Time (seconds)
Tem
perature(F)
top-side TC #3
top-side TC #2
top-side TC #1
bottom-side TC
Ttop-side (ave) = 251 C
Tbottom-side = 266 C
T = 15 F
CPS Lead-Free StudyCPS Lead-Free Study
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Thermal Impact on Chemistry
Lead-Free processing will require higher preheats to
thermally pre-condition the boards prior to their contact
with the higher pot temperatures.
Higher pre-heats, ambient temp over the pot and pot
temperatures, volatize off more of the flux material prior to the
wave. Fluxes need to be engineered to handle these higher
temperatures.
CPS Lead-Free StudyCPS Lead-Free Study
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Flux Solids Comparison Sn/Ag with OSP
25% solids
RMA(615-25 Alcohol
Based)
4% solids
( NR330 Water
Based)
2.2% solids
(SLS65C-
Alcohol Based)
4.1% solids
Rosin(RF800 -Alcohol Based)
11% solids
(5280E Water
Based)
CPS Lead-Free StudyCPS Lead-Free Study
Indicates High Solids not absolutely necessary for Lead-Free.
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Sn-Cu Alloy
Alloy Comparison OSP Finish/RF800 Flux
SAC405 Alloy
SAC305 Alloy
Sn-Ag Alloy
530 F
(276 C)
530 F
(276 C)
530 F
(276 C)
520 F
(270 C)
CPS Lead-Free StudyCPS Lead-Free Study
Indications arethat Lower Temp
yielded higher
defects for SAC.
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Environment Comparison with Sn Cu AlloyNR330 VOC Free Flux
Air Environment Inert (N2) Environment
530 F (276 C)
CPS Lead-Free StudyCPS Lead-Free Study
For certain Sn/Cu applications N2 may be required!
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Loss of Solder Yield - Dross Removal
Loss of Solder Mass due to Dross RemovalLead-Free Wave Study
0
510
15
20
25
30
0 1 2 3 4 5Sn/Cu SAC
305
SAC
405
Sn/Ag Sn/Ag/Bi/Cu
Mass
Lost
(g/min1)
1. Grams/minute of mass removed during typical dross removal per minute of wave run time.
Data based on min of 4 separate 2 to 4 hour run experiments.
EstimatedSn/Pb
mass loss
rate
CPS Lead-Free StudyCPS Lead-Free Study
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Initial Conclusions - Drossing Rates
Lead-Free alloys produce a continuous, thinlayer of dross across the surface of the lambda
wave under an air environment
Dross rates were lowest for Sn-Cu followed by
the SAC alloys
CPS Lead-Free StudyCPS Lead-Free Study
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0.062 in /1.6 mm boards flexed significantly as
they passed through the waves. Warpage of
boards was significant. The Delta T between top and bottom side of the
board never exceeded 30 F
OSP finish was the most difficult to solder and allof the metalized finishes performed better and
approximately the same
Initial Qualitative ConclusionsLF Wave Study
CPS Lead-Free StudyCPS Lead-Free Study
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Overall the 615-25 & NR330 showed the best
performance with 5280E a close third
High-solids fluxes: 615-25 was the best Low-solids fluxes: the water-based VOC Free NR330
was the best
Qualitative inspection indicated SAC405 alloyperformed the best in our study
It should be stressed that the SAC305 was run at 10C lower Solder Pot Temperature and that may explainthe increase in defects over the SAC405
Initial Qualitative Conclusions - contLF Wave Study
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Lead-Free Wave Processing Observations
Pot temperatures of 270 -277 C (520 -530 F)needed.
Nitrogen inerted wave may be needed for certain applications
using Sn-Cu system.
Contamination Issues during the transition to Lead-Free Solder baths prone to lead contamination if substrates and
components are Sn/Pb coated
CPS Lead-Free StudyCPS Lead-Free Study
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Whats Next for the Wave Solder Project?
Visual inspection of solder joints to J-standard-001B
Extensive stress-testing program utilizing Thermal Cycling
& Thermal Shock (-55 C - 125 C) Scanning Acoustic Microscopy and X-ray imaging for
solder defects for cycled/shocked and control boards
(voids, etc.) Lead-pull testing for each device type on the test vehicle
Cross sectioning (fillet/joint quality, Intermetallic layer
growth)
CPS Lead-Free StudyCPS Lead-Free Study