Novel interface material used in high power electronic die-attaching on bare Cu substrates

Abstract

Silver paste sintering on bare Cu substrates can be of significant interest in power semiconductor manufacturing. However, the bare Cu substrates easily oxidized and the die attachment using the silver paste commonly applied pressure. In this study, these problems are solved by using a prepared novel silver paste, which could be pressure-less low temperature sintered completely under inert gas (99.99 wt% N2). The silver paste consists of wide size distribution particles as Ag nanoparticles, Ag sub-micro-sized particles and micro-sized Ag flakes. High content of organic system mixture in the silver paste need more evaporating time to avoid cracks in the sintered Ag film. During sintering, the Ag flakes in situ formation of highly reactive silver nanoparticles is crucial for the sintering to occur between the silver flake and particles, unlike the sintering between the silver particles. A dense silver film contributed to the sintered silver flakes, which has the nature of good densification, well sintering with the silver nanoparticle. The possible joining mechanisms of metallic bond and hydrogen bonds between bare Cu and sintered Ag were proved. Accordingly, the sandwich joints (chip/silver paste/bare Cu) include high bonding strength and low thermal impedance.