Hi George,
I do not know whether to "evaluate the plated cracks as wicking, or
evaluate the plated cracks as laminate voids" either, and I do not know what
difference it makes how you evaluate a potential problem in a 'paper' sense.
You need to be more concerned about, whether your observed condition
represents a problem to your product.
First, as you recognized correctly, this "raises concerns with possible
shorting." Your problem could lead to shorts in the presence of high moisture
absorption—a distict possiblility with polyimide—and high potential
differences with closely spaced PTHs. These shorts have been observed in
accelerated testing along the glass fiber/dielectric interfaces as condcutive
anodic filaments (CAF).
Second, copper plating into the dielectric matrix, can reduce the PTH copper
barrel plating thickness in the areas of these 'wicked copper'. This creates
stress risers in the PTH barrel wall which can lead to premature PTH barrel
failure.

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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