Enhancement of Copper Nanoparticle Paste by Pressure-less Sintering on Different Substrates in Pt-catalyzed Formic Acid Atmosphere

With the rapid development of wide bandgap semiconductor materials, next generation power devices are attracting increasing attention in electronic application. Due to the high conductivity and electromigration resistance, the bonding technology by copper paste sintering is a promising method to meet the demands for reliability of power devices. However, the oxidation of copper nanoparticle in paste is still the bottleneck in pressure-less sintering process at low temperature. In this paper, a pressure-less sintering process was developed in Pt-catalyzed formic acid atmosphere to improve the sintering property of copper paste at 220°C. The H radicals generated from Pt-catalyzed formic acid atmosphere effectively protected the copper nanoparticles from oxidation through the whole of evaporation of solvent and decomposition of organics, thus facilitated the grains growth. By this process, we achieved denser sintered layers and obtained a 22.5 MPa shear strength with NiPdAu finished substrates. This pressure-less sintering process is of great significance to the high temperature packaging technology.