Study on moisture-induced corrosion mechanism of copper wire bonding by thermodynamic calculation

Understanding the moisture-induced corrosion mechanism of copper wire bonding is crucial for achieving longer life reliability of copper bonding. While the formation of Al-Cu intermetallic compound (IMC) is found to dominate the bond reliability, the mechanism remains unclear despite considerable efforts by experiments. Pourbaix (Eh-pH) diagrams have long been used to evaluate the theoretical activity of a given metal or alloy in a corrosion situation. However, the Eh-pH diagram of Cu-Al alloy in bonding condition is lack. In this work, by assessing various thermodynamic data of Cu-Al-Cl-H₂O, we construct the Pourbaix diagrams associated with Cu bonding involving IMCs and study the corrosion behaviors under various environmental parameters such as temperatures and chloride concentrations. The results yield greater insight into the corrosion mechanism which may lead to improving reliability of Cu bonding.