a1 Department of Electronic Engineering, City University of Hong Kong, Kowloon Tong, Hong Kong
a2 Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California 90095-1595
Systematic experimental work was carried out to understand the mechanism of Au diffusion to the solder interface, and a novel method was proposed to eliminate Au embrittlement by circumventing the continuous layer of (Au,Ni)Sn4 at the solder interface. Contrary to the usual expectation, it was determined that utilization of a very thin Ni metallization in the Au/Ni/Cu under bump metallization (UBM) was an effective means of maintaining mechanical integrity of the solder joint. It was found that the out-diffusion of Cu during the aging period changes the chemistry and morphology of the intermetallic compounds at the interface.
(Received July 14 2003)
(Accepted September 08 2003)