Kinetics of Au-containing ternary intermetallic redeposition at solder/UBM interface

In this study, the effects of the under bump metallurgy (UBM) structure and Cu content in solders on the redeposition rate of Au-containing ternary intermetallics at the solder/UBM interface were investigated. A UBM structure with a Ni diffusion barrier, Au/Ni/Cu, appeared to promote the redeposition of ternary Au-containing intermetallics at the solder/UBM interface of the ternary during the solid-state aging treatment and the Au-embrittlement of the solder interconnections. Copper added to the eutectic Sn-Pb and Sn-Ag solders was observed to be very effective in retarding the redeposition by forming the ternary intermetallics in solder matrices and preventing the Au-embrittlement. These phenomena were discussed with the microstructures observed.