Capillary-assisted automated silver direct bond of chip-on-chip through a novel sponge-dipping approach

Silver direct bonding is an organic-free joining technique for chip-on-chip power electronic assemblies that eliminates the need for sinter paste, but also removes the temporary chip-tacking function that the paste normally provides. This paper presents a simple and cost-effective sponge-dipping approach, in which a water-soaked sponge module is integrated into a conventional pick-and-place process. The resulting capillary forces retain the chips in position during multi-chip stacking without requiring a dedicated dispensing unit or hydrophobic surface patterning. Experiments on five-chip stack assemblies with three chip footprints (4 × 4, 8 × 8, and 10 × 10 mm²) show that capillary assistance increases the yield to 100% for the two larger footprints, eliminates complete placement failures across all chip sizes, and reduces misalignment. SAM and cross-sectional SEM/EDX analyses reveal no significant mineral contamination at the Ag-Ag bonding interface, indicating that the applied DI water does not measurably affect bond quality under the tested conditions.