Post-molding interfacial design of sintered silver and copper joints for enhanced fracture resistance and polymer adhesion: Experimental and numerical investigations

The mechanical integrity of sintered die-attach joints in power electronic modules is strongly affected by subsequent polymer-based packaging processes, yet the underlying interfacial mechanisms remain poorly understood. In this study, we systematically investigate the interfacial evolution and bonding mechanisms of copper (Cu) and silver (Ag) sintered joints subjected to transfer molding and post-curing thermal histories. Using nanoporous Ag sheets and Cu pastes as die-attach materials, we track microstructural, mechanical, and chemical changes at the bonding interfaces before and after molding and curing. Both Cu and Ag sintered joints exhibit increases in bonding strength and fracture energy following thermo-mechanical exposure, indicating process-induced interfacial strengthening. In contrast, markedly different adhesion behaviors are observed at the epoxy–metal interfaces, with the epoxy/Cu interface showing substantially higher adhesion strength than the epoxy/Ag interface. First-principles calculations reveal that this contrast originates from the formation of Cu–O–C bonding and enhanced Si diffusion at the Cu surface, whereas limited interfacial chemical interaction is present at the Ag surface. These results elucidate the coupled chemical and mechanical origins of interfacial strengthening in sintered joints and provide fundamental insights into the design of reliable Cu and Ag interconnects under complex processing conditions.