Microstructural evolution and degradation mechanism of SiC–Cu chip attachment using sintered nano-Ag paste during high-temperature ageing

Abstract

The high-temperature reliability of nano-Ag pastes on bare Cu substrates is of great significance in power electronics. Although Cu metallization in sintered joints is susceptible to oxidation in air, methods to inhibit the oxidation under high temperatures are rarely studied. In this paper, a SiC–Cu interconnection with an average shear strength of 161.7 MPa was fabricated using nano-Ag paste by a two-step sintering process. The microstructure of the sintered silver was investigated by the transmitted Kikuchi diffraction (TKD) technique, and the formation of robust joints was attributed to the low porosity, fine gain size and high density of twins. Pores in the sintered silver were isolated, which effectively impeded the penetration of oxygen and growth of Cu oxide during high-temperature thermal storage. Two kinds of failure mechanisms were determined: the growth of a Cu2O band and the evolution of a dense sintered layer. Overall, we propose a sintering method for SiC–Cu interconnections that could guarantee long-term service at 200 °C and short-term service at 300 °C in air.