Effect of EMCs on the high current reliability of Cu wirebonds operating in harsh environments

Copper (Cu) wire bonding, which is a newer alternative to Gold (Au) wire bonding, gets affected greatly by the variety of operating conditions. Selection of different materials, such as epoxy molding compound (EMC) used in the molding process plays key role in defining lifetime for wirebond system. Higher ionic contamination adversely affects the reliability of Cu wirebonds. Interaction of the EMCs with different properties with the Cu wirebond under harsh environment in presence of bias has not been fully understood. Quantification of the acceleration of the wirebond degradation under bias conditions is yet to be established. Previous research mainly investigates failure mechanisms upon failure, however does not report progression of damage which is leading to the failure. This information and understanding of the progression mechanism can yield into development of prognostics based life prediction models. In this paper, Cu wire bonded parts were subjected to high temperature aging conditions. One set of packages was subjected to unbiased test, and another set was subjected to biased condition. Change in electric response of both sets was monitored and was correlated with degradation of Cu-Al interface using ball shear test. Effect of EMC properties as well as voltage bias on the wirebond was then established and discussed in details.