Sintering mechanism of micron/submicron-size silver particles

Low temperature sintering mechanism of two bimodal Ag micron/submicron pastes was analyzed. One paste (named as “P paste”) is prepared with polyol-synthesized Ag particles and the other (”A paste”) is prepared by mixing micron Ag flakes and submicron Ag particles. These two Ag pastes were printed to make Ag wirings. The electrical resistivity of wirings prepared with P paste decreased much faster than that of A paste when sintered at 200 °C. Microstructures of the printed pastes were observed during sintering. A lot of nanoparticles were observed in P paste even after sintering for only 5 min, which is considered as the main reason for the fast sintering process of the polyol-synthesized Ag paste. Rather, at the initial state Ag flakes was flat and Ag flake become bumpy with Ag hemisphere of 5 nm-900 nm diameter during sintering process. This bumpy area is mainly observed on Ag flakes but not in Ag particles. Based on the microstructure observation, after forming necking, high curvature gradient, as a local driving force, between Ag flake and Ag particle is important for diffusion to specific direction with curvature gradient for mass transportation of Ag.