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 degrees C for up to 1500 h, different growth rates and growth characteristics were investigated in Cu-Al intermetallic compounds (IMCs), in this case Cu9Al4, CuAl and CuAl2. Because continuously uniform distributions of Pd and Pd-Au 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.