Bare Cu Bonding by Cu-Ag Composite Paste in Low Temperature Low Pressure Air Sintering

Recently, Ag and Cu sinter paste joining is a proven bonding technology for SiC power modules application with a good thermal conductivity and which can be performed in low-temperature low-pressure. However, Ag material is expensive, and Cu are easily oxidized in air storage and sintering. This paper proposes a novel Cu particle-Ag composite paste (Cu-Ag paste) to address the high material cost of Ag and the oxide problems of Cu in air sintering. We used <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10-μ m</tex> Cu particles, adding in Ag paste for a SiC chip to a bare Cu bonding in air. The cross section proved that there are not Cu oxide layer generation, with a robust shear strength achieved to 57.8 MPa in a low pressure (5 MPa) and low temperature (250°C) with sintering time of 1 hour. In addition, a rapid sintering process was also discussed, where the sintering time only was 1 min, 3 min and 5 min, at 250°C. The shear strength was larger than 20 MPa when the sintering time is only 3 min without generating any Cu oxide layer, meaning that the Cu-Ag paste can become a strong candidate bonding material in SiC power devices.