Effect of surface potential distribution on corrosion behavior of Cu/Al interface in Cu wire bonding applications

As Cu is appearing to be a promising alternative for Au in wire bonding applications the corrosion behavior of the Cu/Al intermetallic compounds (IMCs) is becoming a concern. In this study, the corrosion behavior of Cu/Al IMC layers in NaCl solution is investigated. Among Cu9Al4, CuAl and CuAl2 IMCs only CuAl IMC appears to be corroded. The surface potential difference between Cu, Al, and Cu/Al IMCs are measured using scanning Kelvin probe force microscopy and the largest surface potential difference appears to be between Cu9Al4 and CuAl suggesting the formation of a galvanic cell at the interface between Cu9Al4 and CuAl causing CuAl to act as the anode.