Properties of Cu-Al intermetallic compounds in copper wire bonding

Because of its high thermal conductivity, great electrical property and low cost, copper wire is considered to replace the conventional gold wire and is becoming widely used in IC assembly processes recent years. Compared to gold wire, copper wires has higher thermal conductivity, lower electrical resistivity, and higher pull strength allowing for a reduced wire diameter. Besides, copper wire is much cheaper than gold wire, which reduces the overall cost of IC assembly. However, copper wire bonding also has its own limitations and only few results are reported on the research of Cu-Al intermetallic compounds (IMC) in bonding process. In the paper, the study is focused on Cu-Al IMC´s properties and its behaviors in copper wire bonding, combining theories with many analysis means such as SEM, TEM and EDS. The paper gives a systematic study on Cu-Al IMC micro-structure and micro-compositions. Moreover, as the application of copper wire coated with Palladium is a solution to prevent copper oxidation during the bonding process, we also give a discussion on the differences in IMC growing between copper wire and copper wire with Pd coated. We study the IMC structure in copper wire bonding process with Palladium coated using TEM and analyze the impact that Palladium has on IMC growing and reliability.