An explanation for the effect of Au surface finish on the quality of sintered Ag-Au joints

Abstract

As an environmentally friendly interconnection material in power electronics, silver paste is widely used in gold surface finish. To explain the delamination at the Ag-Au interface and clarify the mechanism of Ag-Au interconnection, the bonding properties of sintered silver joints on different gold-plated substrates are studied. It was concluded that the effect of grain size on Ag-Au diffusion is greater than that of grain boundary type. The gold-plating layer with larger grains provides fewer grain boundaries, which inhibits the rapid diffusion of Ag atoms due to high angle grain boundaries. In addition, to investigate the effects of Au grain boundary misorientation on Ag-Au interdiffusion, molecular dynamics simulation is carried out on the sintering process. It is not found that high angle grain boundary of Au layer promotes the diffusion of Ag atoms during pre-drying. However, in the sintering stage, the MSD (mean square displacement) of Ag atoms in the substitute-model with high angle grain boundaries is about 4 times that of with low angle grain boundaries. It is proved that owing to lots of high angle grain boundaries in the gold-plated substrate, the diffusion of Ag atoms is faster in the sintering stage.