Characterization of process and reliability of copper wire bonding on aluminum bond pads

Copper (Cu) wire bonding technology is both feasible and challenging. The main driver to pursue copper as a bonding wire is the package assembly cost savings that can be achieved by replacing the Gold (Au) wire. Other advantages of using a copper wire are its physical and electrical characteristics that are better than Au. However, the challenges such as high hardness of copper and its greater propensity to oxidize than gold not only influence the wire bonding process but also affects the wire bonded package reliability.;The first objective in this research was to check the compatibility of five different bond pad configurations by characterizing the copper wire bonding process and the analyzing the failure modes. One of the main findings is that not all bond pad structures would be compatible with Cu wire bonding. Further, not only the top metal thickness but also the entire bond pad structure is significant with respect to the copper wire bonding compatibility. Furthermore, other factors such as the wire bonding parameters, the wire bonders, and type of wire (bare Cu and Palladium coated Cu which is also referred as PdCu used also influenced significantly towards the compatibility of the bond pad structures.;Another objective in this study was to evaluate the impact of using Cu and PdCu wire on the package reliability under the industry standard temperature and humidity stress conditions. The Cu and the PdCu wire bonds passed the standard tests performed in this research. The main findings from these studies confirmed that the Cu-Al IMC growth is much slower and is stable than the Au-Al. Further, the Cu-Al bond can withstand accelerated stress conditions as Au wire bonds. Furthermore, the PdCu wire has an advantage over the bare Cu wire in humid environments.;This research effort highlighted that the copper wire bonding can be done with a compatible bond pad structure. Further, copper wire bonds are more reliable than the gold wire bonds with proper package configurations. Thus, copper wire bonding has the potential to replace gold as a wire bonding interconnect material and meet the necessary cost savings in electronic packages.