Comparison of pressure-less Ag sinter-bonding properties with varying substrate surface finishes and Ag particle shapes and sizes: Influence of necking region and fracture behavior

This study was carried out to investigate the bonding characteristics of Ag surface-finished chips bonded using Ag paste with different particle shapes and sizes to Cu, ENIG, and immersion Ag surface-finished substrates. The bonding process was performed without applied pressure at 250 °C for 90 min, and the bonded joints were analyzed in terms of cross-sections, void fraction, necking region, and shear strength. The necking region length exhibited the same trend as shear strength, suggesting that it plays a more critical role in shear strength than the void fraction. While bonding was generally successful, interfacial separation and microvoids were observed in Cu and ENIG substrates, whereas the Ag substrate formed a long necking region without defects and exhibited the highest shear strength. In Cu and ENIG substrates, only interfacial fracture occurred, whereas the Ag substrate showed a mixed fracture, typically found in well-bonded joints. This fracture behavior was identified as a key factor explaining the superior shear strength of the Ag substrate.