Enabling high volume fine pitch copper wire bonding: Enhancements to process and equipment capability

Copper wire bonding has matured quickly in recent years, motivated mostly by the significant increase in the cost of gold, which has nearly doubled in the last three years. In response, manufacturers of wire bonding assembly equipment and consumable materials have become committed to support copper wire bonding packaging roadmaps and continue to invest heavily in research and development to create new copper bonding capabilities and advanced processes. Recently, the focus of developing new capabilities has shifted towards developing the more advanced processes that are needed to enable bonding higher pin count, finer pitch, and high performance applications. This paper discusses many of the recent studies performed to improve our fundamental understanding of copper wire bonding. Advanced computational fluid dynamics (CFD) models were created to characterize the inert gas environment requirements for oxide-free copper ball formation and guide development of new gas delivery hardware. 1^st and 2^nd bond process enhancements have been made, resulting in improved reliability, throughput, and MTBA. Wire loop shaping guidelines for Cu wire are being created with particular attention to ultra-low loop heights. Lastly, bonding with Pd-coated Cu as an alternative to bare Cu wire is discussed.