Porosity effect on fatigue life of sintered silver during thermal cycling

In this study, porosity effect on fatigue life of sintered silver layer in SiC power devices was predicted by nonlinear finite element analysis (FEA). A microstructure model of sintered silver with sphere and Primitive (P) structure as the pore shape was established in which a viscoplastic constitutive relation is adopt for sintered silver. The evolution of the maximum equivalent stress and maximum equivalent viscoplastic strain in the sintered silver layer under thermal cyclic loading (–40 °C to 150 °C) was simulated by ABAQUS based on the sub-model technique. Near the corners of the sintered silver/copper substrate interface, the equivalent stress and viscoplastic strain of the sintered silver layer are concentrated. The empirical life model based on the Coffin-Manson rule was used to predict the fatigue life of the sintered silver layer, and the impact of various porosities was examined. It was found that the increase of porosity for sphere and Primitive (P) structure pores leads to a decrease of sintered silver fatigue life.