A solder bump on a semiconductor substrate is provided. The solder bump comprises a semiconductor substrate having a top copper pad thereon, a protective layer on the semiconductor substrate and at least one inorganic passivation layer overlying the protective layer with a first opening exposing the top copper pad, wherein the inorganic passivation layer has a thinner portion adjacent a top portion of the first opening. The solder bump further comprises a soft passivation layer on the inorganic passivation layer with a second opening larger than the first opening, an under bump metal layer conformally formed along the first opening and the second opening and a solder bump formed on the under bump metal layer.