lead-free wave solder processing - the solder connection - no 1
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Lead-Free Wave SolderProcessingCPS Study Phase I
Initial Lessons Learned from CooksonPerformance Solutions L-F Wave Solder Study
Wetting Balance TestingTo Determine Lead-Free Solder Pot Temperature
• Laboratory test designed to determine the besttemperature to wave solder an alloy with.– Data not relevant to SMT processing
• Test Conditions– Preheat after flux immersion: Test coupon held 0.1” above solder
pot 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@ 100°C (212°F)
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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 530Solder Temperature (°F)
Wet
ting
Tim
e (s
ec.)
Sn63/Pb37 Sn96.5/Ag3.5 Sn99.3/Cu0.7Sn95.5/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)
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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 530Solder Temperature (°F)
Wet
ting
Forc
e (u
N/m
m)
Sn63/Pb37 Sn96.5/Ag3.5 Sn99.3/Cu0.7Sn95.5/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)
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Wetting Balance Observations & Discussions
• The Binary & Ternary Tin, Silver & Copper alloysgenerally produced the fastest wetting times andmaximum wetting forces.
• 520°F (271°C) appears to be an appropriate solderpot temperature for these alloys when the flux usedis a low solids, no-clean type.
• 500°F (260°C) appears to be an appropriate solderpot temperature for these alloys with high solidscontent, non-activated rosin flux (Control Flux).– DATA NOT SHOWN
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Alloy Run Order – Pot Temp.
• Sn63-Pb37 (Sn-Pb) 500º F / 260º C• Sn99.3-Cu0.7 (Sn-Cu) 530º F / 276º C• Sn96.5-Ag3.0-Cu0.5 (SAC305) 520º F / 270º C• Sn95.5-Ag4.0-Cu0.5 (SAC405) 530º F / 276º C• Sn96.5-Ag3.5 (Sn-Ag) 530º F / 276º C
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CPS L-F Study Bottom of Test Vehicle
“Designedfor
Defects”
Note that THComponents are
for positionreference onlyand board is
prior to solder.
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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 conveyorElectrovert Vectra Oven
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Processing ParametersParameter NR330 RF800 SLS65C 5280E 615-25Solvent 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 - 240 180-200∆T (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 setfor a given flux/alloy, all the boards in the experiment were runwithout further changes.
• This gives a “first-level” of optimization only.
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Thermal ProfilesAlloy: 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 200Time (seconds)
Tem
pera
ture
(°F)
top-side TC #3
top-side TC #2
top-side TC #1
bottom-side TC
Ttop-side (ave) = 251 °CTbottom-side = 266 °C∆T = 15 F
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Thermal Impact on Chemistry• Lead-Free processing will require higher preheats to
thermally pre-condition the boards prior to their contactwith the higher pot temperatures.– Higher pre-heats, ambient temp over the pot and pot
temperatures, volatize off more of the flux material prior to thewave.
– Fluxes need to be engineered to handle these highertemperatures.
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Flux Solids Comparison – Sn/Ag with OSP
25% solidsRMA
(615-25 AlcoholBased)
4% solids
( NR330 WaterBased)
2.2% solids
(SLS65C-Alcohol Based)
4.1% solidsRosin(RF800 -
Alcohol Based)
11% solids
(5280E WaterBased)
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Indicates High Solids not absolutely necessary for Lead-Free.
Sn-Cu Alloy
Alloy Comparison – OSP Finish/RF800 Flux
SAC405 Alloy
SAC305 Alloy
Sn-Ag Alloy
530 ºF(276 ºC)
530 ºF(276 ºC)
530 ºF(276 ºC)
520 ºF(270 ºC)
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Indications arethat Lower Tempyielded higherdefects for SAC.
Environment Comparison with Sn Cu AlloyNR330 VOC Free Flux
Air Environment Inert (N2) Environment
530 ºF (276 ºC)
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For certain Sn/Cu applications N2 may be required!
Loss of Solder Yield - Dross RemovalLoss of Solder Mass due to Dross Removal
Lead-Free Wave Study
05
1015202530
0 1 2 3 4 5Sn/Cu SAC305
SAC405
Sn/Ag Sn/Ag/Bi/Cu
MassLost
(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 lossrate
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Initial Conclusions - Drossing Rates• Lead-Free alloys produce a continuous, thin
layer of dross across the surface of the lambdawave under an air environment
• Dross rates were lowest for Sn-Cu followed bythe SAC alloys
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• 0.062 in /1.6 mm boards flexed significantly asthey passed through the waves. Warpage ofboards 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 all
of the metalized finishes performed better andapproximately the same
Initial Qualitative ConclusionsLF Wave Study
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• Overall the 615-25 & NR330 showed the bestperformance 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 alloy
performed the best in our study– It should be stressed that the SAC305 was run at 10
C 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 270º -277º C (520º -530º 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 andcomponents are Sn/Pb coated
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What’s 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)
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