Hi Robert,
You did not give a lot of pertinent info: what is the PCB thickness, drilled
hole diameter, minimum Cu plating thickness,  Cu plating thickness
uniformity, Cu tensile strength and ductility as measured from concurrently
plted mandrel-samples?
PTH/PTV copper barrels--if they crack--always crack at the prepreg layers
closest to the PCB center. The reason is that the prepreg layer always have a
higher resin content than the laminate layers and the resin is less
completely cured in addition. That translates into significantly higher
thermal expansion of these layers in the z-direction--ergo, the barrel cracks
occur there.
If you need more info on this, come to my workshop at IPCWorks in Miami on
September 10, 2000.

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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