Hi Paul, and others,
I have never worked with Sn96, let alone in connection with Au-plated Ni.
I was involved however in the IEEE CLTF (Compliant Lead Task Force) when
Ag-plated leads caused components to pop off PCBs (solder was near-eutectic
SnPb). We never did determine whether there is a critical Ag concentration,
similar to the 4% Au number that is bandied about. The culprit, as with Au,
were AgSn IMCs. All IMCs are brittle, most of them are strong except AuxSny
and AgxSny, which seem to be weak to boot. Further, some of these (Au, Ag)
IMCs come in geometries (platelets) that also result in weak intergranular
bonds.
It stands to reason, that these IMCs would behave similarly in Sn96. I do not
know what, if any, interactions would come from having both AuxSny and AgxSny
IMCs present, particularly in concentrations above the oft quoted 4%.
I do share your concern.
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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