Die Attach Adhesion and Void Formation at the Gaas Substrate Interface

Abstract

A model is constructed to consider the stresses (analytically and with Finite Element Analysis (MiA)) which result from the thermal mismatch between the die and the substrate. FHA is used to simulate thermal stresses induced from temperature cycling with voids and without voids in the die-attach at the die-substrate interface. Local stress concentration caused by voids is found to be dependent on the location of the voids. The presence of an edge void at the die-attach interface changes the local stress and creates a longitudinal stress field. It is also observed that for die-attachment without voids or some center voids there will be no cracking whereas specimens with voids near the edge of the die are likely to have vertical die cracks. Using the void growth, stress relaxation equations, the void growth is simulated yielding an exponential relationship to void grow th and a saturation of void volume w ith time. Stress relaxation and void growth during cool down are simulated, once the material parameters and cooling rates are known. It yields a time dependence of the relative void volume (exponential decay).