Examining Wire Bond Coatings for Application in High Power Density Systems

In this study, a control group of aluminum wire bonds is compared against two test groups of coated wire bonds in terms of fuse current and electromigration performance. The two treatment groups consist of aluminum wire bonds autocatalytically nickel plated or aluminum oxide coated. Fuse current testing results demonstrated a negative relationship between wire length and fuse current density for all three groups of bonds. The same behavior was seen with electromigration lifetime. Increasing ambient temperature was also shown to reduce fuse current density for each group. Compared to the control group, fuse current density was nearly the same or marginally higher for aluminum oxide coated bonds and was lower for nickel plated wires. Compared to the control group, electromigration lifetime performance of aluminum oxide coated bonds was similar and significantly reduced for nickel plated bonds. Based on EDX scans of the nickel plated bonds after testing, it was determined that the elevated ambient temperature and joule-heating during electromigration testing caused an aluminum-nickel intermetallic system to form, causing elevated electrical resistance. This development caused more of a fuse failure of the nickel plated bonds under the same conditions that electromigration failure was seen in the other two groups. An analytical examination of the effects of nickel plating on sample electrical performance has been provided to discuss this result. The present work emphasizes the need for continued efforts examining the impacts of interconnect alloy and surface modifications to qualify/disqualify them for use in high current, high temperature environments.