Solderability Analysis of Inkjet-printed Silver Pads with SAC Solder Joints

Inkjet printing has been studied as one of the potential complements to conventional photolithography for low-cost and rapid prototyping. Different functional inks are directly patterned on the substrate to achieve the desired purpose. In this work, we investigated direct printing of the under-bump metallization (UBM) with a thermally curable particle-free silver ink and the solderability of such printed pads with SAC solder. As silver dissolves in the molten solder and forms intermetallic compounds (IMCs), the thickness of the printed metallization layer is critical for reliable solder joints. Both metallographic cross-sectional analysis and ball shear tests were conducted on samples after the reflow.