Bump structure of the semiconductor package

A bump structure of a semiconductor package having a metal layer, a first dielectric layer formed on the metal layer and an opening formed through the first dielectric layer to expose a first part of the metal layer, wherein the first electric layer has a first length and the bump structure comprises:

• an under bump metallurgy (hereinafter UBM) formed on the first part of the metal layer, a sidewall of the opening and a top surface of the first dielectric layer, wherein the UBM has a second part corresponding to the top surface of the first dielectric layer and the second part has a second length;
• a first buffer layer formed between the second part of the UBM and the top surface of the first dielectric layer, wherein the first buffer layer has a third length that is longer than the second length and shorter than the first length;
• and
• a metal bump formed on the UBM.