Effects of temperature and strain rate on the mechanical properties of lead-free solders

Recently studies of mechanical properties of lead-free solders show that large reductions in stiffness, yield stress, ultimate strength, and strain to failure (up to 35%) were found after 2 months of aging at room temperature. It also shows that the tensile properties of both lead-free solders and Sn–Pb solders tend to become relatively stable after 10 days of aging at room temperature. In this study, in order to minimize any room temperature aging contribution in the investigation of the dependence of temperature and strain rates, all specimens tested were preconditioned after 10 days of aging at room temperature. All tests were conducted under the same conditions. Testing has been performed at three strain rates, 10−3, 10−4, and 10−5 s−1, in temperature range from −40 to 150 °C. A linear relationship was found between the temperature and the tensile properties (elastic modulus, yield stress, and ultimate stress), while a power law relationship was found between strain rate and tensile properties. Constitutive models have also been developed based on the experimental data with multiple variables of strain rate and temperature for both lead-free and lead content solders. With the obtained constitutive models, tensile properties of lead-free solders can be predicted at any testing strain rate and temperature.