Microstructural evaluation of interfacial intermetallic compounds in Cu wire bonding with Al and Au pads

A comparative study on the difference in interfacial behavior of thermally aged Cu wire bonding with Al and Au pads was conducted using transmission electron microscopy. During high-temperature lifetime testing of Cu wire bonding with Al and Au pads at 175 °C for up to 2000 h, different growth rates and growth characteristics were investigated in the Cu-Al intermetallic compounds (IMCs), including CuAl2, CuAl and Cu9Al4, and in the Cu-Au IMCs, including (Au,Cu), Cu3Au and (Cu,Au). Because of the lower growth rates and greater ductility of Cu-Au IMCs compared to those of Cu-Al IMCs, the Cu wire bonding with the Au pad showed relatively better thermal aging properties of bond pull strength and ball shear strength than those with the Al pad counterpart. In this study, the coherent interfaces were found to retard the growth of IMCs, and a variety of orientation relationships between wire, pad and interfacial IMCs were identified.