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 (EM) performance. The two treatment groups consist of aluminum wire bonds autocatalytically (electrolessly) nickel plated or aluminum oxide coated (utilizing atomic layer deposition (ALD)). 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 EM 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 due to the increased conductive cross-sectional area. Compared to the control group, EM lifetime performance of aluminum oxide coated bonds was similar if not slightly improved and significantly reduced for nickel plated bonds. Based on energy-dispersive X-ray (EDX) scans of the nickel plated bonds after testing, it was determined that the elevated ambient temperature and joule heating driven by the elevated current density during EM testing caused an aluminum-nickel intermetallic system to form, which had elevated electrical resistance. This development caused more of a fuse failure of the nickel plated bonds under the same conditions that EM failure was seen in the control group and the aluminum oxide coated group. 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 density and high temperature environments.