Dynamic growth mechanism of tin whisker driven by compressive stress under thermal-mechanic-electric-diffusion coupling

The dynamic growth mechanism of tin whiskers was studied by combining the phase field method, molecular dynamics simulation, and experiments. The growth driving forces of tin whiskers were defined considering the interaction effects of intrinsic stress, temperature, concentration and current, under the effect of thermal-mechanical-electrical-diffusion coupling. Tin whisker growth is a dynamic stress accumulation and relaxation process.When the stress and stress gradient accumulate to the critical value, tin whiskers start to grow and then decrease until they stop growing. Thereafter, tin whisker growth is triggered again when the stress and stress gradient accumulate to a critical value. The electromigration effect increases the stress caused by the accumulation of anode intermetallics and promotes tin whisker growth. Three-point bending results show that the length and density of tin whiskers in high-pressure stress area are noticeably larger than other areas owing to the superposition and counteraction of stress.