Lifetime prediction of Cu-Al wire bonded contacts for different mould compounds

Large scale conversion of gold to copper wiring in microelectronics can only become successful when all the failure mechanisms that can be encountered during reliability testing, or during product application life are understood. One of these mechanisms is corrosion of the contact between the copper (Cu) ball and the aluminum (Al) bond-pad, consisting of various intermetallic compounds (IMCs), which are more sensitive to corrosion compared to gold (Au) Al IMC. This study elaborates on three corrosion mechanisms present in the Cu-Al system: interfacial Cu-Al IMC corrosion, bulk Cu-Al IMC corrosion and Al bond pad corrosion. For the first mechanism, which is dominant, an empirical corrosion model is introduced. To gather data for this model, a recently developed method for analyzing the IMC contact area to study the dynamics of the dominant mechanism is used. Data was collected from various devices, which were exposed to accelerated aging conditions. The focus of this paper is on unbiased conditions using a wide temperature and humidity range. In total four epoxy molding compound types have been investigated and are compared to each other, using the empirical model proposed in this paper. Finally, it is shown that the model allows the prediction of the life time of Cu-Al ball contacts for different application conditions and also allows the selection of an appropriate mould compound type.