Space transformer having multi-layer pad structures

摘要

Pad structures and methods for forming such pad structures are provided. For the pad structure, the first conductive material layer has a first hardness over about 200 kg/mm2. The second conductive material layer is over the first conductive material layer and has a second hardness over about 80 kg/mm2. For the method of forming the pad structure, a plurality of first conductive material layers is formed within each of a plurality of openings of a substrate. The substrate has a plurality of openings therein. The first conductive material layers are formed within each of the openings of the substrate. The first conductive material layers substantially have a round top surface. The second conductive material layers are formed and substantially conformal over the first conductive material layers. The second conductive material layers cover a major portion of the round top surface of the first conductive material layers.