Patent ID: 6875683

Claim:
A method of forming a bump on a wafer, wherein the wafer has an active surface, and the active surface is provided with a passivation layer and a bonding pad exposed by the passivation layer, the method comprising: forming an adhesive layer on the active surface of the wafer to cover the bonding pad and the passivation layer; forming a barrier layer on the adhesive layer; forming a wettable layer on the burner layer; forming a photomask on the wettable layer by a photolithography process, wherein the photomask exposes a portion of the wettable layer; removing the exposed wettable and sequentially the barrier layer and the adhesive layer thereunder by etching, until the active surface of the wafer is exposed; removing the photomask; bonding a plurality of conductive studs onto the wettable layer by wire bonding, wherein the conductive stud is made of a material selected from tin/lead alloy, leadless alloy and pure tin, and each conductive stud has a top surface and a bottom surface opposite to the top surface, the bottom surface being in contact with the wettable layer and the top surface being flattened by polishing, so that the top surfaces of the conductive studs are coplanar; and performing a reflow process to form a plurality of ball-shaped bumps.