Development of SnAgCu solders with Bi and In additions and microstructural characterization of joint interface

Properties of lead-free solder alloys and microstructural characterization of solder joints made from Sn1.0Ag0.5Cu1.0Bi and Sn0.9Ag0.5Cu0.9Bi1.0In (composition given in weight %) with Cu plate were widely studied in this work. The influence of Bi and In additions in these solder alloys was studied as well. The melting temperatures, diffluence and wetting properties, microstructures and costs were observed and evaluated. Thermo-Calc software was used for phase composition prediction. Altogether, 1500 cycles were carried out for the thermal cycling test in the range from +150 to -40 C-omicron where the solder joints' reliability was assessed due to practice requirement. Optical microscopy, scanning electron microscopy (EDX microanalysis) and shear strength test were used for the evolution of microstructure, structural integrity and mechanical strength of thermal-cycled solder joints. The reliability test results after temperature cycling indicate two lead-free solder alloys as the most convenient for soldering in the microelectronics industry.