Effect of Crack Evolution on the Resistance and Current Density of the Al Metallization in the IGBT Module During Power Cycling

This study quantifies the correlations between crack evolution and electrical performance degradation of the Al metallization in insulated gate bipolar transistor (IGBT) modules. The resistance of the Al metallization under different power cycling times was measured by the four-point probe method. The cracks that occur in the Al metallization were investigated by measuring crack geometric parameters, e.g., shape, geometric size and density. Simplified analytical models containing different crack geometric parameters were established by the finite element method (FEM). The influences of crack evolution on the resistance and current density of the Al metallization were quantitatively analyzed. The results indicate that the crack depth has the largest effect on the Al metallization resistance compared with the crack length and width. At the later stage of power cycling, increasing the crack depth plays a critical role in metallization resistance degradation. In addition, cracks affect the current flow direction and the maximum current density in the Al metallization. With increasing crack depth and length, the maximum current density in the crack vicinity increases continuously. However, increasing the crack width reduces the maximum current density.