Comparison of sintered silver micro and nano particles: From microstructure to property

In this paper, two types of silver pastes with distinguishing particle size are incorporated to investigate the correlation of microstructure and physical properties of sintered materials. The one consists of the silver nanoparticles with an average size of 25 nm, while the other consists of the silver particles of 0.43 μm and the flakes of 16.5 μm in the micrometer scale. The morphology is observed with a field emission scanning electron microscope. The prepared disc-like samples own the diameter of 13.0 mm and the thickness of 3.0 mm, which satisfy the measurement requirement of thermal and electrical conductivities. Thermal conductivity is the multiplication of thermal diffusivity, specific heat and density. The laser flash method is used to measure the thermal diffusivity of at least three positions on this thin disc in the thickness direction bases on the temperature rise at the rear face of the thin-disc specimen resulting from an energy pulse on the front face. For electrical conductivity, both of the sintered samples were measured at the room temperature of about 23°C by a four-probe method. In addition, nanoindentation experiments were conducted on the prepared disc-like samples. The substrate effect can be negligible, as the penetration is less than the 0.1% of the thickness. By controlling the penetrating velocity of the Berkovich indenter, constant strain rates can be achieved. Upon the maximum penetration depth of 2000 nm, the indenter is held for 50 s to release the creep deformation. The corresponding creep strain rate are compared from the strain rate sensitivity point of view. In order to compare the plastic behaviour, the residual indentation are examined.