THERMAL-STRESS AND FATIGUE ANALYSIS OF PLATED-THROUGH HOLES USING AN INTERNAL STATE-VARIABLE CONSTITUTIVE MODEL

Previous related research on plated-through hole (PTH) fatigue investi gations has been based on the so-called effective stress/strain method s, which did not account for the fact that fatigue crack nucleation an d growth is observed to occur on planes of specific orientation. Moreo ver, previous related thermal stress/strain analyses were at most base d on bilinear constitutive relations for modeling copper plating along with a linear kinematic hardening assumption, and this cannot capture many aspects of cyclic stress/strain behavior during thermal excursio ns. In this paper, thermal stress analyses using internal state variab le (ISV) models of metallic constituents of PTHs are conducted using t he finite element code ABAQUS (1996). Two thermal history profiles hav ing two repeated cycles were applied for the PTHs of a double layered printed wiring board (PWB) uniformly: (1) MIL-T-CYC (between - 65 degr ees C and 125 degrees C), and (2) IEC OIL-T-SHOCK (between 25 degrees C and 260 degrees C). A critical plane theory was used for purposes of multiaxial fatigue life prediction. The stress/strain results were re ported and compared at the PTH corner and barrel. For both cases, the thermomechanical mismatch between the FR4 and copper constituents of t he PWB generates nonproportional stress/strain responses. This complic ates PTH thermal fatigue investigation. (C) 1998 Elsevier Science B.V. All rights reserved.