Effect of Al content on microstructure and solder joint reliability of SAC305-2.0Sb-3.0Bi-0.1Ni solder alloys

Currently, most studies on solder alloy reliability focus on six-element systems, while research on seven-element solder alloy alloys, particularly concerning the influence of Al is limited. To address this gap, this study investigates the effect of Al microalloying on the mechanical and interfacial properties of a newly developed seven-element solder alloy. SAC305-2.0Sb-3.0Bi-0.1Ni was used as the base composition, and varying amounts of Al were added to form the SACSBN- x Al alloy system. Microstructural analysis and mechanical testing were conducted, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-temperature aging, to evaluate hardness, tensile strength, and intermetallic compound (IMC) growth behavior. The results show that the addition of Al significantly refines the microstructure and promotes a more uniform phase distribution. Notably, at 0.2 wt% Al addition, the solder exhibited the highest hardness (22.133 HV) and tensile strength (67.575 MPa), indicating substantial performance enhancement. Furthermore, high-temperature aging tests revealed that the IMC growth coefficient at the solder/substrate interface reached a minimum of 0.0128, suggesting improved interfacial stability. These findings demonstrate that Al microalloying, particularly at 0.2 wt%, effectively enhances the reliability and mechanical performance of the solder joint. • Al microalloying significantly refines microstructure in SACSBN solder alloy. • Optimal Al content (0.2 wt%) enhances hardness to 22.133 HV and strength to 67.575 MPa. • XRD and SEM confirm improved phase distribution and interfacial stability. • IMC growth rate after aging is minimized at 0.2 wt% Al (growth coefficient 0.0128). • Solder joint reliability is maximized with 0.2 wt% Al addition.