Electromigration-induced diffusion behavior of Zn and abnormal intermetallic growth in Cu/Sn-9Zn/Cu(Ni) interconnects

Purpose This study aims to investigate the interfacial reactions and electromigration (EM) behavior in Cu/Sn-9Zn/Cu and Cu/Sn-9Zn/Ni interconnects under high current density, focusing on the growth kinetics of intermetallic compounds (IMCs) and their impact on electromigration (EM) reliability. Design/methodology/approach The experiments were conducted under a current density of 5.0 × 10³ A/cm² at 150 °C. The interfacial reactions and IMC growth were analyzed in both Cu/Sn-9Zn/Cu and Cu/Sn-9Zn/Ni interconnects. The effects of EM flux (Jem), back stress gradient (Js) and chemical potential gradient (Jchem) on Zn atom migration and IMC formation were systematically studied. Findings A reverse polarity effect was observed in Cu/Sn-9Zn/Cu interconnects, where the Cu5Zn8 IMC at the cathode grew continuously and was significantly thicker than at the anode, driven by the combined effects of Jem and Js. In Cu/Sn-9Zn/Ni solder joints, the IMC layer at the Cu side was consistently thicker than at the Ni interface, regardless of electron current direction, primarily due to Jchem. The growth kinetics of interfacial IMCs in both interconnects followed the t¹/² law during EM. Abnormal Zn atom migration toward the Cu side in Cu/Sn-9Zn/Ni interconnects prevented substrate dissolution, enhancing EM reliability in micro-bump solder interconnects. Originality/value This study provides new insights into the EM-induced interfacial reactions and IMC growth mechanisms in Sn-9Zn-based interconnects. The findings highlight the role of chemical potential gradients (Jchem) and abnormal Zn migration in improving EM reliability, offering valuable guidance for the design of robust micro-bump solder interconnects in advanced electronic packaging.