Characterization of intermetallic compounds in Cu-Al ball bonds: Thermo-mechanical properties, interface delamination and corrosion

In high power automotive electronics copper wire bonding is regarded as the most promising alternative for gold wire bonding in 1^st level interconnects. In the Cu-Al ball bond interface the growth of intermetallic compounds can deteriorate the electrical and mechanical properties of the interconnection. A summary of the thermo-mechanical properties of Cu-Al intermetallic compounds is given. Delamination experiments were performed to study interfacial cracking in the Cu-Al system. Interfacial delamination initiates in the Al-rich intermetallics (CuAl, CuAl2) and propagates easily into other intermetallic layers. The Cu9Al4 — Cu s.s. is also found to be susceptible for delamination fracture. To quantify the corrosion and oxidation sensitivity of Cu-Al intermetallics 8 different aging experiments under various conditions (Δt, AT, air or halogen-rich solution or combined) were performed. In all cases the oxidation/corrosion attack at the non-equilibrium Cu s.s. — interface with the Cu-Al intermetallics is more severe than of a homogeneous bulk solid solution of aluminum in copper (with more than 5 wt% Al). The oxidation/corrosion attack is even more severe than for pure copper.