Preparation of Pb-free silver paste containing nanoparticles

Pb-free silver paste containing nanoparticles was prepared for low temperature sintering. The silver nanoparticles with size of 20–50 nm were synthesized by a chemical reduction method using surfactant. To prepare lead-free silver paste, 10 wt% and 20 wt% of the silver nanoparticles were added into conventional silver powder with an average particle size of 1.6 μm. Then, 3 wt% or 6 wt% of lead-free frit was added into the mixed powders. Using the lead-free silver paste, thick films were fabricated by a screen-printing on an alumina substrate and the films were sintered at temperatures of 400–550 °C. As increasing the sintering temperatures and glass contents, microstructure of the fired thick films appeared denser and sheet resistivity decreased corresponding to dense microstructure. However, as increasing the silver nanoparticles contents, sheet resistivity increased due to aggregation of silver nanoparticles with high surface energy. The films had thickness of 4–8 μm and sheet resistivity of about 4–11 μΩcm.