Growth mechanism of intermetallic compound in SnAg/Cu interface of micro-bumps under extremely low-temperature by phase field method

Abstract

Scientific investigation will increasingly focus on deep space exploration. Spacecraft will be subjected to extremely low-temperature, changing internal microstructure and micro-bumps mechanics, reducing reliability. Thus, micro-bumps must be tested in extremely low temperatures. This research examines the impact of low-temperature storage on IMC (Intermetallic Compound) growth and micro-bumps crystallography at −196 °C. Secondly, a diffusion-weak coupled phase field theory is summarized, and the COMSOL multi-physics simulation platform simulates the growth of IMC layer in micro-bumps developing during extremely low-temperature storage. Finally, microhardness and elastic modulus of various phases were studied. Experimental data indicate that holding Sn at −196 °C for 1000 h produces recrystallization, resulting in tiny grains with diverse orientations. Micro-bumps with Sn/IMC interfaces have highest von Mises equivalent stress. Strain gradient thickens IMC layer at low temperatures with storage time, and edge IMC layer is thinner than axis IMC layer. The diffusion-force weak coupling phase field model's driving force curve indicates that stress gradient, not phase separation, drives IMC growth at extremely low temperatures. Low-temperature storage enhances Sn microhardness and elastic modulus through compressive stress and grain refining. IMC microhardness and elasticity decrease with tensile stress.