We have studied the wetting behaviors and interfacial reactions of Pb‐containing (63Sn‐37Pb, 95Pb‐5Sn) and Pb‐free solders (pure Sn, 96Sn‐4Ag, 57Bi‐43Sn, 77.2Sn‐20In‐2.8Ag) on Au foils in order to understand the role of Pb in Pb‐based solders. Surface morphology, wetting angle, and interfacial reaction of the solders were studied by Scanning Electron Microscopy (SEM) and Energy Dispersive X‐ray Analysis (EDX). Pb‐containing and Pb‐free solders (pure Sn, 96Sn‐4Ag, 77.2Sn‐20In‐2.8Ag) showed rough surfaces due to the precipitation of intermetallic compounds on the surface of the solder caps. The eutectic SnBi (57Bi‐43Sn) solder, however, showed a smoother surface. The wetting angle of the eutectic SnPb (63Sn‐37Pb), pure Sn, 96Sn‐4Ag, and 77.2Sn‐20In‐2.8Ag solders decreased significantly with reflow time, while the eutectic SnBi and 95Pb‐5Sn solders showed a much smaller decrease. A large amount of intermetallic compounds was formed throughout the entire region of the solder cap for the eutectic SnPb, 96Sn‐4Ag, 95Pb‐5Sn, and 77.2Sn‐20In‐2.8Ag, mainly due to the high solubility of Au in these solders. Slow intermetallic compound growth was observed for the eutectic SnBi solder.
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