Large-scale bare Cu bonding by 10 μm-sized Cu–Ag composite paste in low temperature low pressure air conditions

In this study, three kinds of Cu-Ag composite paste were fabricated. We used 10 μm Cu particles as the main component of the paste as they are significantly cheaper than Ag and Cu nanoparticles. To understand the bonding performance and mechanism, the flake-shape Cu-Ag paste with a different solvent and a Cu spherical particle with a diameter of 10 μm were separately implemented for the bare Cu bonding. A detailed and systematic analysis of Cu-Ag paste sintering was performed. In addition, for the flake-shape Cu-Ag paste, the bonding strength and thermal conductivity were evaluated at different sintering temperatures between 180–350 °C. A robust bonding strength of 56.7 MPa was achieved for the SiC chip on bare Cu bonding under low-temperature and low-pressure (300 °C, 2 MPa) air conditions. In addition, a large area of the direct bonded copper substrate (30 mm × 30 mm) was bonded to the Cu baseplate using Cu-Ag paste. The thermal conductivity of 243.7 W/m·K was better than that of almost all the Pb-free solders and comparable with the Ag sinter paste. The results revealed that the reducing agent plays a significant role in anti-oxidation and necking growth. This study offers a deeply understand of Cu-Ag composite paste on bare Cu bonding in air for SiC power devices for its high-temperature applications.