i have seen some SnAgCu (SAC) solder joint embrittlement and solder
joint failure on parts larger than .2 inches
during reheating of  SnAg solder on a Cu PCB. (This is not really SAC
solder but SnAg soldering to Cu PCB).

Larger parts exhibit "Hot Tearing" as described in these 1998 NIST
reports:
See NIST report about "Hot Tearing" at Project Title: SOLDERABILITY
MEASUREMENTS FOR MICROELECTRONICS at
http://www.metallurgy.nist.gov/techactv1998/AnnualReport1998.html#electronics
These non-eutectic alloys have a mushy freezing range, and TCE
differences can rip the IMC apart fracturing the solder joints.

See this analysis of Fillet Lifting by NIST.
http://www.seas.ucla.edu/ethinfilm/Pb-freeWorkshop/pdf/handwerker.pdf


Has anyone seen "Hot Tearing" with SnAg on OSP Copper PCB's ?





Paul Signorelli
Reliability Engineer
Sanmina-SCI Corporation, Plant 432
702 Bandley Dr.
Fountain, CO 80817

eMail address: [log in to unmask]
Phone: 719-382-2352,   Fax: 719-382-2520

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