Patent ID: 7261828

Claim:
A method of forming a plurality of bumps on a wafer having an active surface, wherein the wafer further comprises a plurality of bonding pads formed on the active surface and a passivation layer formed on the active surface to expose the bonding pads, the method comprising the steps of: forming an under bump metallurgy layer over the active surface of the wafer, wherein the under bump metallurgy layer comprises an adhesive layer and an electrically conductive layer disposed on the adhesive layer and covering the bonding pads and the passivation layer; removing portions of the electrically conductive layer not disposed above the bonding pads to leave un-removed portions of the electrically conductive layer on the bonding pads; forming a plurality of bumps on the un-removed portions of the electrically conductive layer; and removing portions of the adhesive layer not covered by the bumps by an etchant, wherein the etchant is an sulfuric acid solution and the concentration of the sulfuric acid solution ranges from about 50% to about 96%.