Mechanical reliability of Au and Cu wire bonds to Al, Ni/Au and Ni/Pd/Au capped Cu bond pads

Abstract

This work is an assessment of the mechanical reliability of Au and Cu ball bonds to Al, Ni/Au and Ni/Pd/Au surfaces in terms of high temperature storage. All systems show very good shear strength after thermal storage for up to 120 days at 150 °C. The Au ball bonds on Al surface show Kirkendall voiding starting from 60 days. This did not decrease their mechanical strength but it is expected to become a reliability issue in the long run. The Cu wire bonds on Al caps show a higher initial strength, much slower intermetallics formation and no Kirkendall voiding. This makes them a potentially better industrial solution. Excellent bond strength was found for Cu- and Au-bonds on Ni/Au and Ni/Pd/Au caps. No intermetallics formation or other microstructural change have been found on these interfaces up to 120 days at 150 °C, which was related to the full solubility of the materials along these interfaces. This result suggests that they can be a successful industrial solution for the next generation of packages.