The addition of Sb element improves the reliability of SAC305/Cu solder joints and inhibits the growth of IMC layer

Abstract

Traditional SAC305 lead-free solder suffers from inferior wettability, excessive interfacial intermetallic compound (IMC) growth under high-temperature aging, and unsatisfactory mechanical performance and long-term reliability. To address these issues, trace Sb alloying modification was employed in this work, and SAC305-xSb composite solders (x = 1.5, 2.0, 2.5, 3.0 wt.%) were prepared. The influences of Sb doping content on the phase constitution, microstructural evolution, wettability, Vickers hardness, tensile strength and interfacial IMC growth kinetics of the solders were systematically explored. The results reveal that Sb can form solid solution in the β-Sn lattice and induce lattice distortion, whereas superfluous Sb precipitates as SnSb secondary phase. Moderate Sb addition evidently refines primary β-Sn grains, homogenizes the distribution of eutectic microstructure, and maintains the original interfacial IMC structure. The wettability, mechanical performance and IMC growth suppression capability are improved first and then deteriorated with increasing Sb content. Under isothermal aging at 150 ℃, IMC growth follows a diffusion-dominated parabolic law. The IMC growth coefficient k of SAC305-2.0Sb is only 0.05174, which is 34.6% lower than that of pristine SAC305, demonstrating a remarkable suppression effect on interfacial IMC proliferation. Considering wettability, interfacial thermal stability and mechanical performance comprehensively, 2.0 wt.% Sb exhibits the optimal comprehensive performance. Such an optimal doping level simultaneously optimizes wettability, strengthens mechanical properties and enhances interfacial stability, offering experimental support for the compositional design and practical engineering application of lead-free solders.