Copper diffusion into epoxy under high temperature

High reliability is critical for semiconductors, especially power semiconductors, which usually work in high temperature conditions. One important reliability issue for power semiconductors is the copper diffusion into polymers. Copper diffusion accelerated polymer decomposition. Also, severe copper diffusion even causes short circuits. Although copper diffusion has been identified, the reason for the initiation of copper diffusion is still not well understood. Here, we encapsulated copper substrate with five different epoxies to investigate the reason for the initiation of copper diffusion. The influence of epoxy impurity elements and epoxy cross-link density was investigated. The results show that the initiation of copper diffusion into epoxy is highly related to the impurity elements, sulfur (S) and chlorine (Cl). In contrast, the low cross-link density of the epoxy cannot initiate copper diffusion. It implies that using S-free and Cl-free epoxy is necessary for semiconductors requiring high reliability.