Prediction of High Strain Rate Properties of SAC-Bi Solders Under Sustained High-Temperature Operation

Electronic components commonly face elevated high strain-rate loads in industries such as automotive and aerospace applications due to shocks, vibrations, and impact during storage and normal operation. Electronic components are routinely exposed to a wide range of surrounding temperatures, fluctuating between -65°C and 200°C in addition to high strain rates, varying from 1 to 100 per second. The industry has experimented with dopant addition to SAC solders in an effort to mitigate the harmful effects of prolonged exposure to high temperatures. Various doped solder alloys like SAC-Q, SAC-R, and M758 have been introduced, incorporating elements such as Bismuth, Nickel, and Antimony as dopants. The current literature does not adequately establish the mechanical characteristics of solder alloys at both very low and high working temperatures, especially for long aging times with high-temperature storage. Tensile specimens from different SAC Solders were subjected to testing at operational temperatures spanning from -65 to 200°C. The tests are conducted at strain rates of up to 75 per second, and the specimens undergo isothermal aging for up to 1 year at a storage temperature of 100°C. The obtained experimental data is then fitted to the Anand viscoplasticity model. Based on trends of properties vs. Bi-percent and thermal degradation rates vs. Bi-percent, prediction of mechanical properties of doped SAC solder containing higher Bismuth% (e.g., SAC + 4% Bismuth) was carried out. Anand constants are derived for tested and predicted solders, varying aging durations. Additionally, FE analyses for drop/shock events at 1500g are conducted for various conditions involving the assembly of CABGA208 packages with the PCB (77x77x1 mm) - dimensions according to the latest JEDEC standard JESD22-B111A (2016).