High temperature performance study of gold wire bonding on a palladium bonding pad

Translating technology from aluminum based to copper based semiconductor has unique issues especially in wire bonding reliability. Copper is very easy to be oxidized when exposed to the air. Palladium was added to cover copper in order to resolve this problem. Finally, the gold wire is bonded with palladium instead of copper. The performance (mechanical and strength) of this interconnection between gold wire and palladium pad prior to high temperature storage was investigated. Failure and micro analysis were carried out through a series of applications of analytical tools including SEM, EDX, FIB, and BIT. Result of the observation showed that the interconnection of Au/Pd was very good. Intermetallic compound was not found and impurities in molding compound also did not have significant impact on the reliability. Migration profile of elements in bond pad was analyzed using X-ray photoelectron spectroscopy. Diffusion of gold into palladium and migration of copper over the palladium were observed. On the other hand, nickel and palladium were deduced as stable elements. There was no significant migration of these two elements. Overall, migration phenomena of these elements did not affect significantly to the reliability of gold wire/Pd pads.