Thermo-mechanical analysis on 10 kV SiC-MOSFETs to improve the reliability of solder layers

The study clarifies the thermo-mechanical characteristics of 10 kV SiC-MOSFET power modules to optimize die structures to improve their solder layer reliability The 10 kV SiC-MOSFET die is 8.1 mm square in size with 500 $\mu m$ thickness. As a reliability evaluation, a power cycle test (PCT) at a temperature swing 100 ${}^o$C was performed on 10 kV and 3.3 kV SiC-MOSFETs, which differ in die size, thickness, and die edge width. Both samples failed in the solder layer under the die. A number of cycles to failure $N_f$ of 3.3 kV, which has a shorter edge, was 30% compared to 10 kV. This $N_f$ difference matched the calculated $N_f$ based on plastic strain changes per cycle $\Delta {\varepsilon }_{pl}$ from 3D simulations. 3D simulations with various models indicate that the larger edge of SiC-MOSFETs, such as 10 kV, have higher solder lifetimes because the large temperature distribution of the die makes smaller solder temperature swings $\Delta T_{sol}$. As an investigation of the influence of 10 kV SiC-MOSFET die structures, reducing the die thickness with the rectangular die shape was improved $N_f$ by up to 3.5 times by halving $\Delta {\varepsilon }_{pl}$. These results contribute to achieving an efficient digital design through thermo-mechanical simulations.