Processing and Characterization of Die-attach on Uncoated Copper by Pressure-less Silver Sintering and Low-pressure-assisted Copper Sintering

Die-attach by metal-powder sintering is being widely adopted in the power electronics industry for manufacturing power semiconductor discrete devices and modules. Thus far, the most widely practiced process involves pressure-assisted silver sintering on direct-bond copper (DBC) substrates that are surface-finished with a coating of silver or gold. In this paper, sintering die-attach processes were done on native DBC substrates by pressure- less sintering of a silver paste and pressure-assisted sintering of a copper paste. To prevent copper oxidation, the silver die-attach process was done in a mixture of formic- acid gas and air, while the copper process in forming-gas (4%H2/N2). The effects of sintering atmosphere, temperature, and pressure on die shear strength were investigated. We achieved strong die-shear strength and oxidation-free sintered bond-line with either bonding process under less stringent demands on materials and processing conditions for low-cost implementation of the die-attach technology in manufacturing.