Hi Ross,
Solder, as you have found, will creep=plastically deform, until all stresses
are reduced to near zero. Since your loading is in compression, the loading
itself has no impact on SJ reliability, but the creep will reduce one of the
most important physical parameters of SJs, their height. Since cyclic life of
SJs is dependent to roughly the square power of ths heigth, it does not take
much to produce a significant reduction in fatigue life.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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