This paper proposes novel geometric methods for reducing the maximum electric field of direct bonded copper (DBC) substrates, which can contribute to higher partial discharge inception voltage of medium-voltage power modules. The technologies include adding the guard rings with a specific voltage between the high-voltage and grounded islands on the top layer, and removing the bottom-layer copper opposite the top-layer trench. In addition, a low-cost geometric solution is proposed to obtain the optimal guard ring voltage even under varying potential using an integrated voltage divider. The proposed methods are verified using finite element simulations and partial discharge (PD) experiments. The results show that by using these methods, maximum electric field can be decreased by up to 43%, and the partial discharge inception voltage (PDIV) can be increased by up to 44.8%.
