Hi George,
You leave an awful lot of important information out.
Some combination of materials clearly causes an overstress condition at your
failure location.
At what stage in your assembly process do the cracks occur (The vibration is
likely inly the means of finding already existing cracks)?
What are the thermal excursions prior to the appearance of the cracks/
What kind of copper foil is spec'ed for the layer?
Is your quad flat pack (32 pins) ceramic or plastic?
What is the transition geometry where the pad thins to the trace (stress
concentration)?
Is your 'standard via hole' only a via or does it have a component lead?
In which direction does the 300-mil-ling trace run from the pad?
Are there any jogs in the trace?
Where is the copper restraining core relative to the cracking surface layer?
What does a copper constraining core constrain?

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 973-543-2747
E-mail: [log in to unmask]

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