Strengthening Copper Nano-Solder Pastes with Group IV 2D Materials: A Molecular Dynamics Insight

This study investigates the effects of three group IV two-dimensional (2D) materials (graphene, silicene, and germanene) on the sintering process and tensile properties of copper nanoparticle pastes for electronic packaging. Using atomic-scale simulations, we constructed models of pure copper and composite pastes, tracking particle rearrangement, neck formation, and pore closure under identical sintering conditions, followed by uniaxial tensile testing. All composites formed continuous copper networks, with densification rates increasing in the order: graphene < silicene < germanene. The yield strength of the pure copper paste was 2.41 GPa and increased to 2.96, 4.39, and 5.46 GPa with graphene, silicene, and germanene, respectively, corresponding to gains of about 23%, 82%, and 127% relative to pure copper. Increasing the sintering temperature led to a monotonic increase in the tensile strength of the germanene composite, with the highest value being obtained at 650 K. Dislocation and stress field analyses revealed that silicene and germanene strengthen the material by promoting pronounced plastic accommodation in neck regions, whereas graphene mainly redistributes strain along the interfaces and produces a more moderate increase in strength. These findings demonstrate that the strength and deformation mode of copper nano-solder joints can be effectively tuned by selecting the type of 2D filler and optimizing the sintering temperature.