Space convertor base plate, its forming method and contact pad structure

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/mm . The second conductive material layer is over the first conductive material layer and has a second hardness over about 80 kg/mm . 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.