Influence of Au Substrate Crystal Structure on Ag–Au Interdiffusion for WBG Packaging

The rapid diffusion of Ag–Au usually results in weak interface joints, which significantly impacts the stability of wide bandgap (WBG) devices. Therefore, the interdiffusion mechanism at the atomic scale is essential to effectively inhibit excessive interdiffusion and ultimately achieve robust joints. Herein, die-attach samples were prepared by Au substrate with different crystal structures, in which the shear strength reached 43.5 and 34.4 MPa for Sample I and Sample II, respectively. The following crystal structures analysis confirms the sintered Sample I exhibited a higher interface connection rate (ICR) of 47% and lower Ag–Au interdiffusion thickness of $0.2~\mu $ m, both of which benefit the high-quality bonding. Compared to Sample II (~82.3%), the relatively low proportion of high-angle grain boundaries in Sample I (~81%) may inhibit interdiffusion and favor higher shear strength. Finally, molecular dynamics simulations (MDSs) were employed to better understand the performance difference between Sample I and Sample II. The simulation results reveal that the interdiffusion process tends to occur on Au substrates with small grain size, high-angle grain boundaries, high proportion of Au (111) plane, and elevated sintering temperatures. The proposed interdiffusion mechanism facilitates the development of die-attach through sintered Ag paste and Au metallization substrate, enhancing the reliable packaging of WBG devices.