Low-Pressure Silver Sintering of Automobile Power Modules with a Silicon-Carbide Device and an Active-Metal-Brazed Substrate

To improve the efficiency of power modules in environmentally friendly vehicles, silicon-carbide (SiC) chips and silicon-nitride (Si3N4) active metal-brazed (AMB) substrates were bonded by low-pressure silver (Ag) sintering at 220°C and 1 MPa using Ag paste. The initial bond strength of the sintered joint was 35.7 MPa, and the void content and bonding-layer thickness of the sintered joint were 4–7% and 94–99 μm, respectively. To verify the reliability of the silver-sintered joints, we conducted thermal cycling tests (TCTs) and high-temperature storage tests (HTSTs). The bond strength of the SiC chip/Si3N4 AMB substrate after the TCT decreased to 16.9 MPa, but increased to 43.6 MPa after the HTST. Thermomechanical fatigue cracks from the difference in the thermal-expansion coefficient occurred at the sintered joint interface during the TCT, which decreased the sintered joint strength. As the sintering process progressed continuously during the long test time at a high temperature, the densification of the sintered joint increased to 98.4%, which lead to an increase in bonding strength. In this study, a SiC device was sinterbonded to a Si3N4 AMB substrate using silver paste at a low pressure, and optimization at a commercialized level was achieved.