Improve the high-temperature reliability of epoxy encapsulation with copper substrates through a copper thiolate complex layer

The need to reduce the size of power modules has driven the shift from gel encapsulation to epoxy encapsulation. To ensure reliability, epoxy encapsulation must bond well with inside substrates, dies, and wires. Previous studies have shown that epoxy encapsulation failure is mainly due to the epoxy materials' low glass-transition temperature (Tg) and mismatch of the coefficient of thermal expansion (CTE) with the metal substrate. Therefore, optimizing epoxy materials has been the focus of many previous studies. However, our study found that even high-end epoxy materials failed during high-temperature storage tests (HST) due to copper-catalyzed thermal oxidation degradation. As a result, preventing copper-catalyzed thermal oxidation degradation is critical for epoxy encapsulation. In this study, we proposed a solution for improving reliability by coating the copper substrate with a copper thiolate complex layer. It shows that this layer can improve the initial bonding strength with epoxy and also keeps the bonding strength after HST.