Hi Paul,
You ask whether cracks could be found by interpolating the known good
tolerances
program against the tested resistivity variances. I doubt that you would have
sufficient sensitivity or actual differences. Some 15 years back, there was a
study by IBM-Minneapolis, that showed that you needed about a physical
separation of 80% of the fracture surfaces to have a 10% increase in
resistance for a single solder joint instrumented with a 4-point probe. On the
other hand, high-speed signals should show signal reflections and
deterioration of rise times, that should be detectable.

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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