Electromigration in Eutectic Gold-Tin (80Au20Sn-wt%) Solder Joints

Abstract Eutectic gold-tin solder joints (80Au20Snwt%) with a diameter of 300 μ m diameter were subjected to electromigration (EM) conditions of 10,000–20,000 A/cm 2 in the ambient temperature range of 125–215 °C. The present work examines a set of 36 experimental test runs using two different test coupons (18 runs with each coupon type and a total of 90 joints tested). Seven of the 36 coupons survived the maximum test duration period of 500 h. One coupon type created a linear electric current pathway through two lengths of 254- μ m-diameter copper wire connected by a single gold–tin joint. The other coupon type daisy-chained four gold–tin joints together in series in a flip-chip configuration using two Rogers 4003C printed circuit boards with electroless nickel immersion gold (ENIG)-finished 2-oz (c.56.6-g) copper traces and a 240- μ m solder mask defined (SMD) pads. The time to EM failure (TTEF) was recorded for each experimental run, demonstrating reduced lifetime with increasing current density and/or ambient temperature. To account for the Joule heating associated with the high current densities used in this study, temperature coefficient of resistance measurements (TCR) were carried out for both sample groups. To describe the TTEF data, a lifetime model for 80Au20Sn-wt% joints combining the experimental testing conditions with TCR data has been developed. Post-failure analysis (PFA) on the tested solder joints shows several morphological phenomena occurring in the gold–tin joints under EM conditions, including solder migration into the trace, spinodal decomposition, phase coarsening, and phase separation.