, Volume 20, Issue 11, pp 1083-1089
Date: 04 Dec 2008

Rate-dependent deformation of Sn–3.5Ag lead-free solder

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Abstract

Compression experiments on bulk Sn-3.5Ag lead-free solder specimens have been carried out to help formulate the material constitutive behaviour of this alloy using the concept of an evolving internal stress. Tests covered the temperature range 0–125 °C and fixed strain rates between 3 × 10−7–3 × 10−3 s−1. Flow behaviour was found to be compatible with that for a deforming a tin-rich matrix (stress exponent n = 7, activation energy Q = 46.7 kJ/mol) in which the external applied stress is reduced by an internal back stress due to the presence of precipitate phase particles. Stress–strain curves have been satisfactorily modelled using rate equations incorporating linear hardening and diffusion-controlled recovery. Comparison with supplementary tension and creep experiments, and with data from other researchers, indicates that inconsistencies in reported flow behaviour is most likely to be due to variations in initial microstructure rather than the nature of the applied loading.