Investigation of Sn–Bi–In ternary solders with compositions varying from Sn–Bi eutectic point to 76 °C ternary eutectic

The solder properties of Sn–Bi–In ternary solders of seven different compositions are examined. The compositions are systematically chosen from the liquidus line extending from the Sn–Bi eutectic point to the ternary eutectic point at 76 °C. Using CALPHAD, we acquire information on the vertical-section of the phase diagram and other thermodynamic information such as pasty zone [liquidus temperature (Tliquidus) − solidus temperature (Tsolidus)] for each composition. DSC data obtained from the solder powders show the evolution of several endothermic peaks roughly consistent with the prediction of the phase diagrams. Solder balling testing indicates that the sample of the Sn–Bi eutectic composition forms a single ball whereas other samples, with a wide pasty zone, show the presence of small satellite balls. Microstructure analysis on the reflowed solder balls using scanning electron microscopy discloses that the ternary solder balls are composed of β-Sn, Bi, and BiIn phases. Shear test results indicate that the shear strength of the solders ranges between 41 and 63 MPa.