Effect of Temperature on the High Strain Rate Properties of SAC Leadfree Alloys at Temperatures up to 200°C

Electronics in downhole drilling, automotive and aerospace applications is expected to sustain prolonged periods of operation at high temperature while being subjected to shock and vibration. High temperature shock and vibration loads may be generally in the strain rate range of 1-100 per sec. Material data on properties at elevated temperatures and high strain rates is scarce. There is lack of material models that capture the mechanical deformation under transient dynamic loads at elevated temperatures. Anand Viscoplasticity models which have been widely used for modeling of material behavior of solder alloys require nine-constants to describe material constitutive behavior. Prior published data on Anand Constants for SAC leadfree solder alloys is limited to either low strain rates or lower temperatures in the neighborhood of 125 degrees C. In this paper, mechanical properties and the non-linear constitutive behavior has been reported for two of the commonly used lead free alloys including Sn1Ag0.5Cu (SAC105) and Sn3Ag0.5Cu (SAC305) for strain rates 1-100 per sec at elevated temperatures up to 200 degrees C. The stress-strain behavior has been measured using uniaxial tension specimen fabricated using reflow profile representative of production assemblies. Data has been reported at discrete constant strain rates including 10, 35, 50 and 75 per sec at various operating temperatures of 50 degrees C, 75 degrees C, 100 degrees C, 125 degrees C, 150 degrees C, 175 degrees C, and 200 degrees C. The measured experimental data has been fit to the Anand Viscoplasticity model for both the alloys and the model constants verified by predicting the measured stress-strain behavior for the complete range of temperatures and strain rates and comparing the predictions with the prior experimentally measured values.