In a message dated 99-01-13 19:42:26 EST, you write:
<< Typically, we tend to fail at the interface between the substrate
(sometimes the PWB, sometimes the interposer) and the pad rather than in the
solder joint.   >>

James,
Guidelines for the dye penetrant procedure are available in a Motorola ".pdf"
file on BGA reliability . Last reference I had for this document was:
http://www.mot-sps.com/solutions/wired/pbga/pbga.html
(or do a search for "BGA reliability" at: http://mot2.indirect.com/cgi-
bin/search)

Failures at the interface between the BGA substrate and pads may and do occur
under your test conditions. They are an indication of not enough adhesion /
robustness in the pad area (even after a couple of joints have failed
elsewhere). One possible solution (if you are still in the design phase) is to
redesign with a larger copper area under the solder mask.
As mentionned by Per, you can also test at higher temperature which will help
shift the failures from the pad/substrate to the solder joint. It all depends
on what your goal is for that test and what your strength requirements are.

Jean-Paul
_____________________________________________________
Jean-Paul Clech
EPSI Inc., P. O. Box 1522, Montclair, NJ 07042, USA
tel: +1 (973)746-3796, fax: +1 (973)655-0815
SMT / BGA / CSP Reliability Specialists
home page: http://members.aol.com/Epsiinc1/index.html

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