The reliability performance of low cost bumping on aluminum and copper wafer

Abstract

A low cost bumping technology for semiconductor chips is described here using electroless Ni/Au plating for under bump metallurgy (UBM) formation, instead of traditional processes involving sputtering, photolithography, and etching which require a great deal of expensive equipment. Higher throughput and lower cost can be achieved if we combine electroless Ni/Au technology and stencil solder printing technology. Low cost bumping technology has been successfully developed on Al wafers. The results of reliability tests, such as high temperature storage, temperature cycling and temperature-humidity storage, show that solder bumps with electroless Ni/Au as UBM exhibit good reliability and are suitable for flip-chip applications. In addition to electroless Ni/Au plating on Al pads, the development of low cost bumping on Cu wafers is also presented in this paper. The performance of Ni/Au bumps on copper, such as morphology and shear strength, is superior to that on Al pads. The reliability tests of low cost solder bumps were also performed on dummy copper wafers that consist of sputtered Cu and PI passivation. Comparisons were also made of the reliability performance of low cost solder bumps on aluminum and copper pads in this paper.