Low-Temperature Sintering of Nanoscale Silver Pastes for High-Performance and Highly-Reliable Device Interconnection

Abstract

In this paper, we report our development on making of nanoscale silver pastes and their low-temperature sintering for semiconductor device interconnections. The nanoscale silver pastes were prepared by dispersing 30-nm silver powder under ultrasonic vibration and mechanical agitation in an organic vehicle. Sintering of the silver paste prints at 280°C for 10 minutes resulted in a density of ~80% in the air ambient. Some important properties of the low-temperature sintered silver include ~2.4 W/K-cm for thermal conductivity, ~3.8 × 10−6 Ω-cm for electrical resistivity, and ~9 GPa for the effective elastic modulus. SiC Schottky rectifiers attached to either silver- or gold-coated direct bond copper (DBC) substrates show low forward voltage drops. The silver joints do not contain large voids but rather uniformly distributed microscale pores. Die-shear tests showed that bonding strengths of the silver joints were around 21 MPa on the gold-coated DBC substrates and 38 MPa on the silver-coated DBC substrates, respectively. The latter is comparable to that of reflowed eutectic lead-tin solder joints. Based on the findings in this work, the low-temperature sintering of nanoscale silver pastes is promising to be a high performance and highly-reliable semiconductor device bonding solution for high power packages.