Solid state growth kinetics of complex intermetallics in the Pb-free ball grid array (BGA) solder joint for MEMS packaging

Interfacial reaction and reliability related problems of the solder joint for both advanced electronic packaging applications and MEMS packaging applications are becoming crucial with the downscaling of the device size. In this study, the solid state interfacial reaction between the BGA Sn-3.5%Ag-0.5%Cu solder and the Au/Ni/Cu bond pad for MEMS applications was investigated at 150-200degC, for different time period ranging from 0 hrs to 400 hrs and compared with that of the Sn-3.5%Ag solder. It was found that 0.5 wt% Cu addition plays a strong role on the interfacial reaction products and the reaction kinetics - especially, at a high temperature near the melting point of the solder alloy. While the Sn-3.5%Ag solder reacts with the Au/Ni/Cu metallization simply by forming only one binary intermetallic compound (BIMC), the Sn-3.5%Ag-0.5%Cu solder reacts in a completely different manner