The ductile-to-brittle-transition (DBT) of Sn occurring when the temperature decreases to a critical temperature poses a restriction on the Sn-based solders in the cryogenic electronics interconnection. Previous investigations about the DBT mainly adopt the Charpy impact test, however, the transient property of Charpy impact test makes it difficult to capture the deformation features accompanying DBT and clearly elucidate the DBT mechanism. In this paper, we studied the plastic deformation of Sn before cryogenic brittle fracture through in-situ cryogenic uniaxial tensile experiments under optical microscopy. It is found that {301} deformation twins were activated and thickened before the brittle fracture. Due to the occurrence of deformation twins, multiple twin-grain boundary intersections and twin-twin intersections formed within Sn grains, which could strongly prevent dislocation slip and thus lead to stress concentration. As a result, the brittle cracks initiate and propagate along these intersections. According to the suggested specific mechanism, we designed a green pre-treatment method of pre-twining-RT tempering to increase the cryogenic ductility of Sn-based solder alloys without any energy consumption. Eventually, the fracture elongation of Sn at LNT was significantly improved from ~6% to ~14%.

The applicability of wide bandage semiconductors at high temperatures promotes the development of high-temperature die-attach materials, such as silver nanoparticles (Ag NPs) paste. To enhance the bonding between Ag NPs and Cu substrate through an interdiffusion process, the Cu substrate was modified by electroplating a novel upright shell-like nanostructure. The optimized Cu substrate was then sintered with Ag NPs paste, in which the diffusion distance could achieve about 1.5 μm at 300 °C for 20 min. This sufficient interfacial diffusion is attributed to the numerous reactive positions and compatible sintering driving force between Ag NPs and modified Cu substrate caused by the upright shell-like Cu nanostructure.