US Patent 7915741 Solder bump UBM structure

Disclosed is an under bump metallization structure including a plurality of metal or metal alloy layers formed on chip bond pads. The disclosed UBM structure has a stress improvement on the semiconductor device because the thickness of the copper-base layer is reduced to between about 0.3 and 10 microns, preferably between about 0.3 and 2 micron. The presence of the pure tin layer prevents oxidation and contamination of the nickel-base layer. It also forms a good solderable surface for the subsequent processes. Also disclosed are semiconductor devices having the disclosed UBM structure and the methods of making the semiconductor devices.