Approaching a uniform bump height of the electroplated solder bumps on a silicon wafer

The investigation of the manipulation of the physical structure of an electrolytic cell to achieve uniform solder bumps on a silicon wafer is discussed. The variables investigated include: the applied current density, the distance and the area ratio of the electrode, and the width ratio between the cathode and the bath. The width ratio of one between the cathode and the bath was found to lead to a uniform bump height throughout the wafer. The reflow of the as-plated solder bumps raised bump height and produced uniform ball-shaped bumps. The deviations of the bump height on a wafer are within 5% after reflow of the uniform as-plated bumps.