Pb‐free solder bumping for flip chip package by electroplating

Sn‐Pb and Sn‐Ag bumps (130 μm diameter, 250 μm pitch) made using an electroplating process were studied. As a preliminary experiment, the effects of current density and plating time on the Sn‐Pb and Sn‐Ag deposits were investigated. The morphology and composition of the plated surface were examined using scanning electron microscopy. The shape and thickness of the solder bumps were also compared. Bump shear testing was performed to measure the adhesion strength between the solder bumps and the under bump metallurgy. In electroplating, the Sn‐Ag plating thickness was proportional to the current density, while plated Sn‐Pb thickness saturated above the limiting current density. The optimal conditions for solder bump fabrication were found at 6 A/dm² for 3 h in the case of Sn‐Pb bump plating and 6 A/dm² for 1 h for the Sn‐Ag bump plating. The bump shear strength for Sn‐Ag was found to be higher than that of Sn‐Pb.