Influence of Interfacial Interaction Between Various Metal Substrates and Epoxies on Bonding Reliability Under High Temperture

Abstract

The shift from gel encapsulation to epoxy encapsulation has been driven by the need to reduce the size of power modules. However, the dissimilar bond between the encapsulation epoxy and substrate is seen as a potential weak point. Previous studies have largely focused on the impact of epoxy materials on package reliability. Our prior research has highlighted the crucial role played by interfacial interactions between copper substrates and epoxy. In this study, we investigate the influence of interfacial interactions between three metal substrates (copper, Ag-plated copper, nickel-plated copper) and epoxy on the reliability of epoxy encapsulation under high temperature. Two types of epoxy (bisphenol A and cycloaliphatic) were used to encapsulate metal substrates. Encapsulated packages were subjected to a high-temperature storage test (HST) at 200°C for 1000 hours, and changes in bonding strength were measured. We then analyzed the fracture surface and bonding interface at the nanoscale. Our results indicate that substrate material has a significant impact on the reliability of epoxy encapsulation. Both epoxies exhibited the highest initial bonding strength with copper, followed by Ag-plated copper and nickel-plated copper. After HST, we found that the catalytic effect of metals caused the epoxy in contact with the metal substrate to decompose. The decomposition was most significant in epoxy in contact with Ag, followed by copper, which resulted in a significant drop in bonding strength. In contrast, epoxy in contact with nickel showed little decomposition and only little change in bonding strength. These findings will greatly benefit power module design.