lead-free wave solder processing - the solder connection - no 1

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)

CPS Lead-Free StudyCPS Lead-Free Study

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)


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)


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


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


CPS L-F Study Bottom of Test Vehicle

“Designedfor

Defects”

Note that THComponents are

for positionreference onlyand board is

prior to solder.


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


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.


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


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.


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)


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)


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)


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


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


• 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


• 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


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


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)


lead-free wave solder processing - the solder connection - no 1

Documents