Effect of cooling rate on microstructure and mechanical properties of eutectic Sn-Ag solder joints with and without intentionally incorporated Cu6Sn5reinforcements

Solidification of eutectic Sn-Ag solder, with and without Cu6Sn5 composite reinforcements, on copper substrates, was investigated at two different coo ling rates. The size, orientation, randomness, and overall morphology of th e dendritic microstructure were examined as a function of cooling rate. Cu6 Sn5 particle reinforcements were found to act as nucleation sites for dendr ites, in addition to sites on the substrate/solder interface. The mechanica l properties of these solders were also examined as a function of cooling r ate. Solder joints with a lower load-carrying area were found to exhibit hi gher shear strength, but reduced ductility when compared to solder joints w ith more load carrying area.