Creep resistance of tin-based lead-free solder alloys

This paper reports on the microstructure-creep property relationship of three precipitation-strengthened tin (Sn)-based lead (Pb)-free solder alloys (Sn-0.7Cu, Sn-3.5Ag, and Sn-3.8Ag-0.7Cu) in bulk samples, together with Sn-37Pb as the alloy for comparison at temperatures of 303 K, 348 K, and 393 K. The creep resistance of these three Sn-based Pb-free solders increases, i.e., the steady-state creep rates decrease, with increasing volume fraction of precipitate phases for the Pb-free solder alloys. Their apparent stress exponents (n_a ∼ 7.3-17), which are all higher than that of pure Sn, attain higher values with increasing volume fraction of precipitate phases at constant temperature, and with decreasing temperature for the same solder alloy.