Influence of IMC morphology on fatigue stress, strain and life of solder layer between SiC chip and DBC substrate in IGBT under thermal cycling

The influence of IMC morphology between solder layer and DBC substrate on fatigue stress, strain, and life of the solder in IGBT module was studied by ANSYS workbench. The IGBT model (SiC chip-SAC305-DBC (Cu/Al
2
O
3
/Cu)) for FEM was built. Under thermal cycling, both the equivalent stress and plastic strain of the solder are concentrated near the corner of the interface of solder/substrate. Then the sub-models with scallop-like IMCs (Cu
6
Sn
5
) built with sine function as profile were located at the corner. In the sub-model, the stress and plastic strain concentration of solder occur in the recessed solder/IMC interface caused by scallop-like IMCs. The model based on plastic strain energy for the prediction of fatigue life was used to analyze the influence of different IMC roughness and thickness on the fatigue life of the solder layer. It is found that both the decrease in IMC roughness and the increase in IMC thickness will lead to the shortening of the fatigue life of the solder layer.