Hi Russ,
Well, your problem comes down to two possible causes:
1) no solderability; your tests seem to exclude that.
2) inadequate soldering process; it certainly is possible that the solder
balls were never properly attached to the component. Your problem is not
likely related to shear strength of (or crack propagation in) nickel-tin
intermetalics, but the absenceof any IMCs which are the by-product of a good
intermetallic bond resulting from good wetting. Solder attachment strength to
nickel is about half that to copper.

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]

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