Hi Guenter,
Your observations agree perfectly with mine. I do not think in terms of
grainboundary sliding (GBS) vs. dislocation climb (DC), since for most
applications the deformations take place exclusively in GBS. Accelerated
testing is a different matter, not just for the reasons you mentioned. Some
accelerated tests include thermal shock which not only puts you into DC, but
causes transient warpages of component and substrate inducing peeling
(tensile) stresses in the solder joints. Further, since fatigue in solder
causes the formation of microcracks relatively early in the life of a solder
joint, these microcracks act as stress risers during the high-stress inducing
excursions to the lower temperatures.
By the way, at 100C only about 90% of the stresses have relaxed as
experimental work of Les Fox at DEC has shown.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-mail: [log in to unmask]

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