Desired Properties of a Nonlinear Resistive Coating for Shielding Triple Point in a Medium-Voltage Power Module

This work explores a nonlinear resistive field-grading material to shield the triple points prior to silicone encapsulation, thus, increasing the power module's partial discharge inception voltage. The material is aimed at coating the metal edges of a trench on a direct-bond-copper substrate for over 10 kV applications. To find the desired coating properties that would significantly reduce the field intensity at the triple point, an application-specific guideline is first prescribed for determining the baseline properties of the coating. Then, electric field simulations show that with only 10% coverage of coating at each triple-point edge, the field stress across the trench could be reduced by as much as 40%, i.e., over 67% improvement in the partial discharge inception voltage. A parametric study is done to evaluate the effect of each of the material properties, as well as the coating width, and shows that the improvement in field-stress reduction could be further increased. The material properties prescribed in this study can serve as targets for materials designers and engineers to develop insulation materials for packaging medium-voltage power modules.