Effect of lead-free frit on conductivity of nanoparticles-aided silver paste.

Silver thick films were prepared from lead-free silver paste adding silver nanoparticles for low sintering temperature, and the effect of glass frit content on conductivity in the films was investigated. Silver pastes with different glass contents were prepared by mixing micron-scale silver powder of 1.6 microm and nanoparticles of 30-50 nm in size. To prepare lead-free silver paste, 5 wt% of the silver nanoparticles as a sintering aid were added to the micron-scale silver powder. Then, 3 wt%, 6 wt%, and 9 wt% of lead-free frits were added to the mixed powders. Using the paste, thick films were prepared by a screen printing on an alumina substrate and then the films were sintered at temperatures from 300 degrees C to 550 degrees C. As increasing the sintering temperature and content of lead-free frit, the thick films showed dense microstructure. The glass frit enhanced to develop denser microstructure by liquid phase sintering. However, excess of glass content increased sheet resistivity due to the formation of glass pool separated from particle network. Furthermore, the nanoparticles can assist to develop a conductive network in the film. The films with 6 wt% of glass frit had the best conductive network and the lowest sheet resistivity of 3.2 microomega cm.