Synergistic role of Bi, Ni, and Pd alloying in SAC305 for enhanced IMC suppression and superior thermo-mechanical performance

In this study, the effect of dopants on solder joint reliability was investigated by examining the mechanical behavior of solder joints with respect to solder composition; standard Sn-3.0Ag-0.5Cu (SAC305) solder and SAC alloy with bismuth (Bi), nickel (Ni), and palladium (Pd) (SAC-BNP). To analyze the creep behavior, bulk type solders specimens are fabricated, and creep tests are conducted under three temperatures (25, 75, 125 °C) and three stress levels (5, 10, 15 MPa). The intermetallic compounds (IMCs) growth and shear strength on the PCB of both solder types are studied during thermal aging. Also, the thermo-mechanical fatigue reliability is tested and compared by thermal shock tests ranging from 0°C to 125°C with ball grid array (BGA) assemblies. The results show that SAC-BNP exhibit superior creep resistance, suppression of IMC growth, and about 40% higher shear strength compared to SAC305. In thermal cycling, SAC-BNP demonstrate approximately 65.8% longer fatigue life, withstanding 2306 cycles before failure, compared to 1390 cycles for SAC305. These findings suggest that incorporating Bi, Ni, and Pd into SAC alloys significantly improves the reliability of solder joints under thermal and mechanical stress conditions.