Effects of alloying elements on microstructure and thermal aging properties of Au bonding wire

We studied the effects of alloying elements Cu and Ni on the microstructure and the thermal aging properties of Au bonding wire. The thermal aging properties of samples bonded with an Al pad, and annealed at 200 °C for durations ranging from 0 to 300 h was investigated using mechanical tests. Both of the alloyed specimens showed higher thermal aging properties than the 4 N Au-bonded specimen, as investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), an electron probe micro analyzer (EPMA) and transmission electron microscopy (TEM). The Cu-alloyed Au bonding wire formed, at the Au–Al interface, a discontinuous Cu-rich layer that was considered to have delayed the growth of the Au–Al intermetallic compound (IMC). Meanwhile, at the Au–Al interface, the Ni-alloyed Au bonding wire formed secondary phase particles that were believed to have improved the bonding strength by interrupting micro-crack propagation.