The development of Cu bonding wire with oxidation-resistant metal coating

Although Cu bonding wire excels over Au bonding wire in some respects such as production costs, it has not been widely used because of its poor bondability at second bonds due to surface oxidation. We conceived an idea of electroplating oxidation-resistant metal on the Cu bonding wire to prevent the surface oxidation. The electroplating of Au, Ag, Pd, and Ni over Cu bonding wire all increased bond strengths as expected, but it caused problematic ball shapes except Pd-plated Cu bonding wire. The wire could produce the same ball shape as that of Au bonding wire. It was also proved to have excellent bondability sufficient to replace Au bonding wire. That is, it excelled in bond strengths, defective bonding ratio, and wideness of "Parameter Windows". It also showed the same stability as Au bonding wire in reliability tests, while bonds of Cu bonding wire were deteriorated in a few of the tests. In short, the Pd-plated Cu bonding wire can realize excellent bonding similar to Au bonding wire, while having much lower production costs.