Enhanced microstructure and mechanical property of large-area nano-Ag joints by porous Cu foam at low temperature

This study presented a novel approach for reinforcing nano Ag sintered joints with Ag-coated Cu foam, aimed at achieving reliable and large-area bonding for power electronics. Two joint sizes, 3×3 mm² and 10×10 mm², were successfully fabricated at low temperatures to evaluate the impact of Ag-coated Cu foam on the microstructure, mechanical properties and fracture mechanism of sintered joints, in comparison to pure nano-Ag and uncoated Cu foam/nano-Ag joints. Results demonstrated that porous Cu foam significantly improves joint uniformity and minimizes defects, particularly in the central area of large-area sintered joints by facilitating evaporation paths for organic solvents during sintering. The addition of Ag coating on Cu foam further enhances shear strength, reaching up to 33.14 MPa, over 2.5 times greater than that of pure nano-Ag joints. Molecular dynamics (MD) simulations revealed that the Ag coating promotes stable interfacial bonding by increasing dislocation density and stacking faults at the Ag/Ag interface. These findings support the potential of Ag-coated Cu foam composite joints as a robust solution for high-performance power electronic packaging.