Atomistic insights into silver-indium solid solution softening mechanism for microelectronics packaging

Silver-indium solid solution is the key material in advancing low-temperature/pressure solid-state technology for electronics packaging, due to its rare solid solution softening (SSS) phenomenon. In this work, the critical resolved shear stress (CRSS) for slip, ideal shear strength and critical twinning stress of silver-indium disordered solid solutions were systematically evaluated by the generalized planar fault energy (GPFE) analysis, using first-principles modelling. Compared with others, Ag-based metals have much lower ideal shear strength and critical twinning stress, whereas the CRSS for slip of silver-indium solid solutions decreases with the increases of indium content, therefore exhibiting a general trend of softening behaviors. For the first time, the electronic origin of silver-indium SSS mechanism has been unveiled, where the modification of its GPFE structure was the fundamental cause for the reduction of CRSS for slip, critical twinning stress and the corresponding SSS phenomenon. As confirmed by transmission electron microscopy, this work presents a new design criterion for the next-generation solid-state bonding materials development.