Effect of electromigration on mechanical shock behavior in solder joints of surface mounted chip components

The mechanical shock behavior of Sn-Ag-Bi-In (SABI) solder has been investigated by micro-Charpy impact test after subjecting the solder to high electric current stress. A trace amount of Co added (0.1 wt %) is used as a refiner in the SABI solder, and the joint soldered by conventional reflow exhibits a refined grain microstructure. The SABI+Co joint exhibits higher toughness, i.e., 70% more energy is absorbed during impact than a typical SABI joint. After 80 h of 20 A electric current applied at 160 °C, electromigration (EM) is observed in both the SABI and SABI+Co joints. However, the SABI+Co joint exhibits a constant mechanical strength, while the typical SABI joint exhibits a strength decreased by 16% at the Charpy absorption energy. The mechanical strength improved by Co addition implies that microstructure refinement is useful for enhancing the EM resistance of a solder joint structure for surface mount packaging.