Degradation behaviors of micro ball grid array (μBGA) solder joints under the coupled effects of electromigration and thermal stress

Abstract

Due to the complicated configuration of real micro ball grid array (μBGA) package, kinds of physical failure mechanisms occurs and mixed together in high current density applications. By considering electromigration and thermal stress-related effects, the degradation behaviors of actual μBGA solder joints were studied under the current density of 1 × 104 A cm−2 at 120 °C. Experimental results indicated that severe current crowding and open failure occurred at the narrow on-chip metal trace. At the current crowding region, the Ni under bump metallization was dissolved under the electromigration coupled with the thermal stress-induced stress migration, while the narrow Cu trace were consumed by the dominated electromigration. Meanwhile, the Sn and Pb atoms backfilled the vacancies formed by the migration of Cu and Ni. With the joule heat-induced temperature increasing, the backstress released, and those backfilled Sn and Pb atoms were migrated away, resulting in the final open failure. Additionally, due to polarity effect, the excessive growth of dendritic (Cu, Ni)6Sn5 compounds at anode side was also a potential source of failure in microelectronic devices.