Development of Corrosion-Resistant Aluminum Alloy Wire

A study was undertaken to find a corrosion-resistant aluminum alloy wire for improving the reliability of resin-molded devices using aluminum ball bonding. Palladium (Pd) was selected to be alloyed to aluminum matrix in order to improve corrosion resistance on the basis of the passivation theory that some metals are passivated when certain noble elements are dispersed uniformly in the matrix. AI-Pd alloy wires were made containing magnesium (Mg) which was added to improve bondability between aluminum balls and aluminum electrodes. It was found that AI-Pd-Mg alloy wires exhibit outstanding corrosion resistance compared with AI-Si and AI-Mg wires in both the pressure cooker test (PCT) and another test in which the wires were dipped into a bath of boiling water together with resin powder. Intergranular corrosion was recognized in AI-Si and AI-Mg wires in PCT. AI-Pd-Mg wire hardly corroded even after 500 h of PCT. Dissolution of the wires was observed in the dipping test. However, dissolution of the AI-Pd-Mg wire is much less than that of the other wires. A good quality aluminum ball, highstrength bonding, and good looping characteristics can be realized using AI-Pd-Mg wire. It is concluded that AI-Pd-Mg wire satisfies all the major requirements of bonding wires. The corrosion protection mechanism of AI-Pd alloy was explained as the strengthening of surface protection film on the aluminum matrix by the addition of Pd.