Rate-dependent mechanical behavior of dual-phase structure of Sn interconnect materials

This study systematically investigates the effects of strain rate (from 1.67 × 10⁻5 to 10⁻1 s⁻1) on the tensile deformation and fracture behavior of β-Sn-based dual-phase alloys including Sn5Sb, Sn25Sb, Sn37Pb, and Sn58Bi. Both pure Sn and Sn5Sb exhibit an increased elongation with rising the strain rate, while Sn25Sb, Sn37Pb, and Sn58Bi display inversely a reduced ductility. At low strain rates, Sn37Pb and Sn58Bi demonstrate a superplastic behavior characterized by the stress index n values of 3.4 and 4.3, respectively, indicating a dominant deformation mechanism involving grain boundary migration/slip and dislocation climb. At high strain rates, their stress indices abruptly increase to 12.6 and 15.3, suggesting a transition to dislocation slip-controlled deformation. Pure Sn, Sn5Sb, and Sn37Pb maintain ductile fracture throughout the tested strain range, whereas Sn25Sb exhibits a brittle fracture under all loading rates. Notably, Sn58Bi shows a strain rate-dependent fracture mode transition: brittle fracture predominates at low strain rates but shifts to quasi-brittle fracture at elevated rates, revealing its unique strain rate-sensitive fracture mechanism.