High-strength Sn–Bi-based low-temperature solders with high toughness designed via high-throughput thermodynamic modelling 1

Abstract

Low-temperature Pb-free solders are in demand in the electronic industry for reducing processing emissions and enhancing product reliability. Sn–Bi-based alloys have drawn great interests. We performed high-throughput CALculation of PHAse Diagram modelling and systematically screened 35,343 alloy compositions among the Sn–Bi–Ag–In and Sn–Bi–Ag–Zn quaternary systems. An optimal alloy of each system was proposed, experimentally characterised based on microstructural, thermal, and mechanical analyses, and their phase equilibria and solidification reactions are elaborated. The designed Sn–Bi–Ag–In alloy with solidus and liquidus temperatures of 137.6 and 157.1°C, respectively, shows superior mechanical properties, e.g. the ultimate tensile strength of 57 MPa, elongation of 50%, and toughness of 20.6 × 10⁶ J m⁻³, which is a promising material for low-temperature interconnection.