A stress model for multiobjective design optimization of a power electronic module

One of the most common failure mechanisms in power electronic modules is fa tigue of the die attach due to shear stresses created by a mismatch in the thermal expansion of the die and the substrate. This paper presents a shear stress model in the die attach that incorporates viscoplastic stress compo nents that become more important at the elevated temperatures in power elec tronic modules. The paper also describes;a multiobjective design optimizati on approach utilizing a genetic algorithm for minimizing the chance of modu le failure, not only by die attach fatigue, but also by other competing fai lure mechanisms such as overheating of the chip, die fatigue, and substrate fatigue. It is shown that a successful power electronic module (PEM) desig n must balance the tendencies to fail by these competing failure mechanisms . Several tradeoff solutions in PEM design are presented for different size and material choices for a PEM design.