lead-free wave solder processing sept 17

8/7/2019 Lead-Free Wave Solder Processing Sept 17

1/20

Lead-Free Wave Solder

ProcessingCPS Study Phase I

Initial Lessons Learned from Cookson

Performance Solutions L-F Wave Solder Study


2/20

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)

CPS Lead-Free StudyCPS Lead-Free Study


3/20

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)



4/20

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)



5/20

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



6/20

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



7/20

CPS L-F Study Bottom of Test Vehicle

Designed

forDefects

Note that TH

Components are

for positionreference only

and board is

prior to solder.



8/20

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



9/20

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.



10/20

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



11/20

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.



12/20

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)


Indicates High Solids not absolutely necessary for Lead-Free.


13/20

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)


Indications arethat Lower Temp

yielded higher

defects for SAC.


14/20

Environment Comparison with Sn Cu AlloyNR330 VOC Free Flux

Air Environment Inert (N2) Environment

530 F (276 C)


For certain Sn/Cu applications N2 may be required!


15/20

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



16/20

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



17/20

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



18/20

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



19/20

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



20/20

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)


lead-free wave solder processing sept 17

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