Patent ID: 6989326

Claim:
A method of forming bumps over a silicon wafer having an active surface thereon, the method comprising the steps of: forming a first under-bump metallic layer over the active surface of the wafer; forming a second under-bump metallic layer over the first under-bump metallic layer; conducting a first photolithographic process to form a plurality of photoresist blocks over the second under-bump metallic layer; conducting a first etching operation to remove the second under-bump metallic layer outside the photoresist blocks so that only the second under-bump metallic layer underneath the photoresist blocks remains; removing the photoresist blocks; conducting a second photolithographic process to form a photoresist layer over the second under-bump metallic layer, wherein the photoresist layer has a plurality of openings that exposes the remaining second under-bump metallic layer and the opening is substantially the same or smaller in size than that of the second under-bump metallic layer in order to only expose the remaining second under-bump metallic and not expose the first under-bump metallic layer; filling a solder material into each of the openings in the photoresist layer by a plating method to form a solder bumps only disposed on the remaining second under-bump metallic layer and not disposed on the first under-bump metallic layer; removing the photoresist layer to expose the first under-bump metallic layer; conducting a second etching operation to remove the exposed first under-bump metallic layer so that only the first under-bump metallic layer underneath the remaining second under-bump metallic layer remains; and performing a reflow operation to form the solder bumps into ball-like shape bumps after the second etching operation.