Nanoindentation Tests and Constitutive Study of Sintered Nano-Silver

Sintered nano-silver, owing to the superior thermal and electrical conductivity, is considered as a highly promising lead-free solder material for electronic packaging applications. With the continuous advancement of microelectronic devices toward higher integration and miniaturization, the reduction in packaging structure size has imposed increasingly stringent requirements on the mechanical performance of materials at the microscale. However, the mechanical behavior of sintered nano-silver at such scales remains insufficiently and systematically studied. In this work, the mechanical response of sintered nano-silver was characterized using nanoindentation techniques, with a particular focus on the influence of loading rate on the hardness and Young's modulus of sintered nano-silver. A Unified Creep-Plasticity (UCP) constitutive model was developed to simulate the inelastic deformation behavior. Experimental results show that the hardness is insensitive to loading rate, maintaining a stable average value of approximately 0.55 GPa. In contrast, the Young's modulus exhibits a non-monotonic trend with respect to loading rate, initially decreasing and then increasing, with a minimum around 3 mN/s. Furthermore, to reproduce the nanoindentation process, the UCP constitutive model was incorporated into the finite element framework through a user-defined material subroutine (UMAT). The simulated load-displacement curves demonstrated good agreement with experimental data, confirming that the model can accurately capture the viscoplastic deformation behavior of sintered nano-silver under various loading conditions. These findings provide a basis for understanding of the microscale mechanical properties of sintered nano-silver. The proposed constitutive model can be applied to predict the mechanical response and reliability in electronic packaging, offering theoretical support for engineering applications.