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 μ 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 Δ ɛ p l 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 Δ T s o l . 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 Δ ɛ p l . These results contribute to achieving an efficient digital design through thermo-mechanical simulations. • The solder layer reliability on the power cycle test (PCT) was investigated with SiC-MOSFET power modules. • The 3.3 kV SiC-MOSFET had just 30% of the lifetime in the 10 kV SiC-MOSFET. • 3D thermo-mechanical simulations clarify that the larger edge in 10 kV SiC-MOSFETs increases solder reliability due to smaller solder temperature swings. • Further solder lifetime calculations showed structural optimization of the 10 kV SiC-MOSFET, which improved the Nf by up to 3.5 times by reducing the die thickness and making the die rectangular.