2017 Volume 58 Issue 11 Pages 1593-1600
Minor Zn was alloyed into Cu substrate to improve the electromigration reliability of Sn-58Bi/Cu solder joints in this paper. Electromigration behavior of Sn-58Bi/Cu and Sn-58Bi/Cu-4.89Zn was studied with the current density of 1.0 × 104 A/cm2 from the microstructural evolution on the surface morphologies and the interior interfacial structure. In case of the surface morphologies in Sn-58Bi joints, the existence of Zn in Cu substrate effectively postponed the formation of Sn hillocks of whiskers at the anode side and the depletions/voids at the cathode side. From the observation of interior interfacial structure, Cu-Zn substrate obviously depressed Bi segregation and the growth of Bi-rich layer at the anode interface. Because Zn atoms were migrated from the anode to the cathode while Bi atoms were migrated from the cathode to the anode during electromigration, Zn atoms would fill the vacancies left behind by the migration of Bi atoms. The electromigration resistance of Sn-58Bi solder joints was correspondingly improved by Zn alloyed into Cu substrate. the calculated DZ* of Bi atoms in the Cu and Cu-4.89Zn substrate is 3.69 × 10−11 cm2/s and 1.76 × 10−11 cm2/s, which also illustrates there exists a slower diffusion rate for Bi atoms in Sn-58Bi solder joint with Cu-Zn substrate.