Development of SiC power module structure by micron-sized Ag-paste sinter joining on both die and heatsink to low-thermal-resistance and superior power cycling reliability

In this study, the thermal characteristics and structure reliability during power cycling for the four types of SiC power module fabricated using a SiC-heater chip, direct bonded aluminum (DBA) substrate, and aluminum (Al) heatsink were evaluated. Two die-attach materials, including a Sn-Ag-Cu (SAC 305) solder and an Ag paste sinter, were used to bond the SiC to DBA substrate. Furthermore, three types of substrates bonding layer, including SAC solder and Ag paste sinter, and Si grease, were used to bond the DBA substrate to Al heatsink. The large area bonding between the DBA substrate (30 x 30 mm2) and Al heatsink was achieved. In addition, comparing with the tradition SAC solder-Si grease joint structure, the SiC chip temperature decreased from 265.5 ℃ to 180.4 ℃ and the total thermal resistance of the joint structure decreased from 1.58 K/W to 0.85 K/W for the Ag-Ag sinter joint at the same input power. The heat dissipation improved by 1.86 times. The results were validated and fit well using 3D finite element analysis. The failure time was improved 14.5 times from 2340 cycles to 33926 cycles for the AgAg sinter joint during the power cycling test. This study will help us to create a SiC power device structure that is smaller, thinner, and possesses ultra-low thermal resistance, and high reliability.