A method for forming a metal pillar bump structure is provided. In one embodiment, a passivation layer is formed over a semiconductor substrate and a conductive layer is formed over the passivation layer. A patterned and etched photoresist layer is provided above the conductive layer, the photoresist layer defining at least one opening therein. A metal layer is deposited in the at least one opening. Portions of the photoresist layer are etched along one or more interfaces between the photoresist layer and the metal layer to form cavities. A solder material is deposited in the at least one opening, the solder material filling the cavities and a portion of the opening above the metal layer. The remaining photoresist layer and the conductive layer not formed under the copper layer are removed. The solder material is then reflown to encapsulate the metal layer.