From Bulk Copper Samples to Functional DCB Test Boards: Process Transfer and Joint Characterization of Pressure-Less Nano-Silver Sintering

Abstract Increasing operating temperatures in power electronic applications require joining technologies with improved thermal and mechanical stability compared with conventional Sn-based soldering. Silver sintering is a promising alternative, but many sintering processes still require elevated temperatures and external pressure. Pressure-less sintering using in-situ nano-silver precursor pastes offers a potential route for low-temperature joining without applied joining pressure. In this study, a pressure-less nano-Ag sintering process previously investigated on bulk copper samples was transferred to application-oriented direct copper bonding (DCB) test boards. A Cu-cube/DCB test structure was developed to enable four-terminal resistance measurement, die shear testing, metallographic analysis, and SEM characterization of the sintered joint region. The as-joined Cu-cube/DCB joints showed low electrical resistance and shear strength values mainly in the range of 70–80 MPa. Metallographic analysis revealed a continuous Ag-based bonding layer between the Cu-cube and the DCB substrate. SEM observations showed a porous sintered Ag microstructure with local non-uniformities, especially near the edge regions. Fracture surface analysis indicated predominantly cohesive fracture within the sintered Ag layer, with local interfacial contributions. Overall, the results demonstrate that precursor-based pressure-less nano-Ag sintering can be transferred from simplified bulk copper samples to functional DCB test boards. The Cu-cube/DCB configuration provides a suitable platform for electrical, microstructural, and mechanical assessment of pressure-less sintered Ag joints.