Patent ID: 6967153

Claim:
A bump fabrication process for forming a bump on a wafer having an active surface with a passivation layer and at least one bonding pad thereon such that the passivation layer exposes the bonding pad, the process comprising the steps of: forming a patterned solder mask layer with a pattern over the active surface of the wafer, wherein the solder mask layer has at least one opening that exposes the bonding pad, and a cross-sectional area through a bottom-section of the opening is smaller than a cross-sectional area through a mid-section of the opening, while a cross-sectional area through a top-section of the opening is smaller than the cross-sectional area through the mid-section of the opening; depositing a solder material into the opening; conducting a reflow process so that the solder material inside the opening fuses together to form a bump; and removing the solder mask layer.