Evaluation of reliability of (mu)BGA solder joints through twisting and bending

Dislocation generation and multiplication in heterojunction bipolar transistors (HBTs) under electrical bias was studied using a finite element model. This model was developed to solve a physical viscoplastic solid mechanics problem using a time-dependent constitutive equation relating the dislocation dynamics to plastic deformation. The dislocations in HBTs are generated by the excessive stresses including thermal stress generated by the temperature change in the device during operation. It was found that the dislocation generation rate at the early stage and the stationary dislocation densities depend strongly on the current density. © 1999 Elsevier Science Ltd. All rights reserved.