Behavior of Au and Pd and the effects of these metals on IMCs in Pd-Au-coated copper wire

A comparative study of the differences in the interfacial behaviors of thermally aged bare Cu wire, Pd-coated Cu wire and Pd-Au-coated Cu wire with Al pad was conducted using scanning electron microscopy and transmission electron microscopy. During high-temperature lifetime testing of these wires bonded with Al pads at 150 °C for up to 1500 h, different growth rates and growth characteristics were investigated in CuAl intermetallic compounds (IMCs), in this case Cu9Al4, CuAl and CuAl2. Because continuously uniform distributions of Pd and PdAu in the Cu wire formed in the upper IMC area, the bonding reliability and the IMC growth rate were improved. The formation of a completely solid solution was considered to have improved the bonding reliability by protecting the IMC from the propagation of micro-cracks.