Preparation of Conductive Silver Paste Using Bimodal Particles

Networking and density of silver particles is a great importance to obtain low electrical resistivity of silver paste. In order to improve packing density, interconnectivity and conductivity at low sintering temperature, silver paste was prepared from bimodal silver particles, i.e., consisting of micro- and nano-sized particles. In order to fit nano-Ag particle into the interstices of the micro-Ag particles of 1.6 μm in size, the interstices need to be approximate below 360 nm in size. Therefore, we prepared nano-Ag particles of 100–300 nm in size by chemical reduction method. The silver paste prepared by mixing the bimodal powders, Pb-free frit and vehicle were printed on an alumina substrate by screen printing and sintered at temperature of 400–500 °C. As increasing the amount of nano-Ag particles and sintering temperature, packing density and electrical conductivity were increased. The nano-Ag particles placed between the micro-Ag particles contributed to improve interconnectivity and densification of the printed films. Accordingly, as the amount of nano-Ag particles was increased, the electrical resistivity were decreased. The thick film at sintered 500 °C showed the lowest electrical resistivity of 3.9 μΩ cm which can be compatible for application in microelectronics devices.