Low Temperature High Strain Rate Material Properties for SAC-Q Leadfree Alloys

Abstract

Electronic devices in automotive and defense applications may exposed to high temperatures (> 150°C) as well as to low temperatures (-55 °C) and high strain rates (1-100 per sec) during storage, operation and handling which can contribute to the failures of electronics devices. Temperatures in these applications can varies between -55 to 200°C. Evolution in microstructure due to change in temperatures for lead free solder alloys can cause degradation in mechanical properties of solder alloys. Recently, SAC-Q are proposed with Sn-Ag-Cu with addition of Bi (SAC+Bi). Cai et.al. (2010) found that adding dopant (Bi, Ni, In, Mg, Mn, La, Ti) to SAC solder alloys can improve wettability, melting temperature, shock and drop reliability and microstructure. Prior microstructure studies have found that adding Bismuth (Bi) to SAC alloy can play an important role to make the alloy relatively insensitive to aging- induced degradations. Previously, evolution in mechanical properties and Anand model parameters for SAC (SAC105, SAC305 and SAC-Q) solder materials have been studied at different high strain rates (10, 35, 50, 75 /sec) and elevated temperature (25°C-200°C) for pristine samples and aged samples up to 1 year have been studied [Lall 2014–2019]. We observed that adding dopants to SAC alloys can help to improve the mechanical properties and to reduce aging-induced degradations. However, there are no data available in published literature for SAC-Q solder alloy at high strain rate at low operating temperature. In this paper, effect of low operating temperatures (-65°C-0°C) on high strain rates (10-75 per sec) mechanical behavior for unaged and aged SAC-Q solder alloys has been studied. Stress-Strain curves have been obtained at low operating temperatures using tensile tests. The SAC-Q leadfree solder samples were subjected to isothermal aging at 50°C before testing. To describe the material constitutive behavior, Anand Viscoplastic model and Ramberg Osgood Model has been used. Evolution of Anand Model parameters and Ramberg Osgood model parameters for SAC-Q solder has been investigated. To verify the accuracy of the model, the computed parameters from experimental data have been used to simulate the uniaxial tensile test. A good correlation was found between experimental data and Anand predicted data.