Hi Paul,
The explanation you got for your BGA via failures does not sound right. Vias
fail because of the tension on the via barrel during high temperature
excursions, and the barrel copper not being good (thickness, strength, ductility) to
successfully resist this thermal expansion mismatch.
If forcing out too much resin during the lamination process, you get
delaminations, not voids; but reduced resin content actually reduces the thermal
expansion mismatch.

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com

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