Study on preparation and rapid laser sintering process of nano silver pastes

Nano silver pastes have emerged as the most promising electronic packaging materials, with excellent electrical conductivity, thermal conductivity and high temperature mechanical properties. In this paper, nano silver particles (Ag NPs) with diameters of 62nm are prepared by chemical reduction method and adopts rapid laser sintering to get the sintered joints with shear strength of 12-38MPa in 5-15s. Sorts of influencing factors in both morphology and performance of joints, such as laser power, sintering time, applied pressure and defocusing amount, are discussed. The results show that the density and shear strength of sintered joints increase with the increase of laser power, sintering time and pressure. The back sintering can avoid the damage caused by laser direct exposure to the chip, and the shear strength increases slightly. The increase in the defocus distance can make the distribution of power density more uniform, but it will reduce the shear strength. The sintering mechanism is proposed by analyzing the evolution of microstructure morphology of the sintered joints.