Room-temperture-sintered conductive ink made of silver nanoparticles

Conductive ink made of silver nanoparticles was developed for stamp printing, screen printing, drop-on-demand printing, and conductive line via a conductive pen. The conductive silver ink was synthesized by chemical reduction of silver salt solution with sodium borohydride. The obtained colloid of silver nanoparticles were highly concentrated and highly stabilized. When concentration of conductive silver ink was dilute to 1 ppm, the topographic image from atomic force microscope (AFM) showed silver particles size in the range of 5-30 nm. However, after a high concentration conductive ink (100,000 ppm) was deposited and dried on substrate under the ambient condition, the average size of silver particles 100 nm. Silver nanoparticles could sinter to be the larger particles at room temperature. After conductive silver ink was deposited and dried on substrate, the high silver load and sintering phenomenon enable electrical conductivity. The silver ink could be applied on thermal-sensitive substrate such as thin polymer film and paper without deforming or destroying the substrate. The conductivity of silver film could be improved by thermal treatment or by mechanical rubbing.