Study on microstructure and mechanical properties of silver-indium films for solid-state bonding in electronic packaging

Silver (Ag)-based solid solutions are regarded as significant candidates in solid-state bonding for electronic packaging. However, their widespread application is often limited by the inherent trade-off between strength and plastic deformation ability. In this work, silver-indium solid solutions (Ag–xIn, where x is the atomic percentage of the In element) with different microstructures and mechanical properties were fabricated at various magnetron sputtering powers. Furthermore, the formation mechanism of nanotwins and their influence on strength and plastic deformation ability for Ag–xIn were explored through in situ compression tests and first-principles calculations. In addition to nanotwins observed in Ag grains, the 9R structures were also identified within the Ag–7In and Ag–14In grains. Notably, stacking faults (SFs) distributed in four directions were observed at the kinks of the coherent twin boundaries (CTBs) in the compressed Ag–xIn micropillars, which is primarily attributable to the decrease in the stacking fault energy caused by the addition of In solute. Remarkably, Ag–14In exhibits high hardness (3.59 GPa), while Ag–7In exhibits high plastic deformation ability. The thickness and fraction of nanotwins, coupled with the introduction of SFs, are key factors governing the hardness, yield strength, and strain hardening of Ag–xIn. This work provides a strategy for designing Ag–xIn solid solution alloys with tunable mechanical properties via nanotwins and 9R structures, and offers guidance for material selection in solid-state bonding applications.