Strain rate sensitivity of sintered silver nanoparticles using rate-jump indentation

Nanoindentation experiments were performed at room temperature on pressure-less sintered silver nanoparticles (AgNP) samples. Two representative die attach solder materials: sintered electrically conductive silver adhesive and conventional Sn-3.0Ag-0.5Cu solder were investigated. A novel technique of multiple strain-rate jumps is adopted accompanied by the continuous stiffness measurement, which can effectively determine the strain rate sensitivity (SRS) with good accuracy. Different strain rates and indentation depths are considered to obtain the nanomechanical properties such as hardness and Young's modulus. Compared with Young's modulus of sintered AgNP, the effect of applied strain rate is more influential to the hardness. In the loading stage, the SRS exponent decreases due to a smaller variation of hardness at a greater indentation depth. In the holding stage prior to the unloading of the applied indentation force, the creep displacement is relatively insensitive to the applied strain rate, however, the creep strain rate decays exponentially and the corresponding stress exponents are determined.