Effect of SAC105 Solder Alloys High Strain Rate Property Evolution on Plastic Work at Low Operating Temperatures

Abstract

Electronic devices in extreme harsh environment may endure the high thermal loads as well as high strain loads during their life span. Some of harsh environment applications include automotive and defense. Electronic devices may be exposed to high strain loads (1-100 per sec) such as drop & shock, vibration events. Thermal loads can be in range of -40°C to 125°C in these harsh conditions during their service, handling, or storage. Electronic industry migrated to leadfree solder alloy due to growing environmental concern in use of leaded solder alloys. The most used are SAC solder alloys including SAC105, SAC305. Leadfree solder behave differently due to drop-shock, and vibration loads. Therefore, knowing the mechanical performance of solder joint is essential to design and improve reliability of electronic products. Leadfree solder alloy constantly evolve due to thermal loads for prolonged duration which cause degradation in their mechanical properties. A better understanding of SAC solders is needed to improve design and for optimizing electronic package reliability, at low and high temperatures and strain rates. In addition, there is lack of constitutive model in published literature which capture the mechanical deformation under transient dynamic loads at low- and high-test temperature for aged conditions. In this paper, the evolution of Anand parameters for SAC105 lead free solder alloys at high strain rates has been investigated induced under sustained periods of thermal aging up to 1-year at 50°C. The thermal aged leadfree SAC105 solder specimen has been tested at high strain rates (10-75 per sec) at low operating temperatures of (-65 to 0°C) using tensile testing. Anand constitutive model has been used to describe nonlinear behavior of SAC105 solder. A good correlation was found between experimental data and Anand data. FE based model has been used to simulate the drop event for ball grid array package using Anand constitutive model to determine the plastic work and hysteresis loop over wide range of thermal aging and operating temperatures.