Hi Mike,
While I most often use pi/4 * [(tpwb + dptv)^2 - (dptv)^2] as the area of
influence of the epoxy on the PWB, where tpwb is the PWB thickness and dptv is
the drilled PTV diameter, I have found that a diameter of influence defined as
(tpwb + dptv) is not always adequate. My model in IPC-TR-579 has been improved
since than (see IPC-D-279, APPENDIX B) and you find a discussion about the
diameter of influence.
But why do you want to generate a 3-D Electro-Thermal FEA model for PTVs? That
has been done during at least on two prior efforts by Ray Iannuzzelli at DEC
and at the U. of Maryland (Bhandarkar, S. M., A. Dasgupta, D. Barker, M.
Pecht, and W. Engelmaier, "Thermo-Mechanical Stress Analysis of Plated Through
Hole Structures," ASME J. Electronic Packaging, Vol. 114, No. 1, March 1992,
pp. 8-13). What has not been modelled is the actual MLB structure which
consists of alternating layers that are more resin-rich (pre-preg) and less
resin-rich (laminate). Failures in the PTV barrel cracking failure mode always
occur in the resin-rich layer regions near the MLB center.

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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