Damage and viscoplastic behavior of sintered nano-silver joints under shear loading

Compared with most of the traditional solder materials, sintered nano-silver shows better high-temperature service performance and is expected to replace the traditional packaging materials in the next-generation of electronic devices. However, there exist substantial voids inside the sintered nano-silver layer after sintering, and the conventional continuum damage mechanics has certain limitation to describe the shear stress-strain relationship of sintered nano-silver materials. To analyze the void evolution and microstructure of sintered nano-silver, gold-plated sintered nano-silver specimens were tested under shear loading at different temperatures. A unified viscoplastic constitutive model is proposed to describe the properties of sintered nano-silver specimen under shear loading, in which the viscous overstress is replaced by the potential function of Gurson-Tvergaard-Needleman model and the effects of void on the yield surface of viscoplastic material is considered. To describe the influence of void evolution to the deterioration of mechanics properties at high temperatures, a damage variable is incorporated into the drag strength to indicate the damage mechanism with respect to the softening of sintered nano-silver material. The numerical predictions are compared with the experimental data, which shows that the developed model can describe the shear constitutive behavior of sintered nano-silver specimen with reasonable accuracy.