Lowest sinterable temperature Ag nanoporous sheet bonding at 145–175 °C on Ag-plated Cu and interfacial microstructural degradation under 250 °C aging: Correlation with strength and fracture energy

Abstract

This study investigates the microstructural evolution and mechanical reliability of silver (Ag) nano-porous sintered joints bonded at low temperatures (145–175 °C) onto Ag-plated copper (Cu) substrates. We focus on their interfacial degradation behavior during thermal aging at 250 °C. Despite the exceptionally low bonding temperature, strong initial bonding was achieved, and thermal exposure for up to 250 h enhanced sinter neck growth and interfacial connectivity, resulting in increased shear strength and fracture energy absorption. However, extended aging beyond 500 h led to the formation of interfacial Cu_xO layers and Kirkendall voids at the Cu/Cu_xO interface, causing bond line thickness transition with delamination and a critical decline in mechanical performance. Microstructural and crystallographic analyses using SEM, EBSD, and XRD revealed stagnation of grain coarsening, texture development, and recrystallization behavior in both the sintered Ag and Ag plating layers. The failure mode transitioned from cohesive fracture within the Ag layer to interfacial separation at the oxidized Cu interface. These findings demonstrate that low-temperature Ag nanoporous sheet bonding can initially deliver robust interfacial strength, but long-term reliability at elevated temperatures is limited by diffusion-driven oxidation and void formation at the Cu interface.