Electrohydrodynamic Jet Printing of Silver Seeds: Micro Scale Patterning by Electroless Copper Deposition

Abstract

The paper describes a new method for micro scale patterning of highly conductive features on flexible and flat surfaces. The method uses electrohydrodynamic jet printing to deposit silver seeds on-demand that serve as catalysts for subsequent electroless deposition of copper. The electroless deposition of copper on substrates occurred only where silver seeds exist. In the study, ethylenediaminetetraacetic acid (EDTA) and triethanolamine (TEA) were used as chelating agents, and formaldehyde as reducing agent. Copper growth rate and resistivity were investigated using microscopic and profilometer to determine optimal concentration of each agents in reaction solution. The results indicated that EDTA significantly affects copper growth rate, playing an important role in complexing, while TEA in the dual-complexing system will balance deposition rate and stability of solution. Optimal temperature and time for copper deposition on silver nanoparticles were also discussed in the study. The techniques of activating substrates by selective printing and electroless metallization was successfully used to pattern on glass, and flexible polymer films, and both flat and curved substrates were used. The proposed technique was also capable of fabricating metal structures on flexible substrates with excellent conductivity. Metal filaments with resistivity four times bulk copper and thickness up to 15μm were demonstrated in the research.