Synthesis of Antioxidative Conductive Copper Inks with Superior Adhesion.

Conductive films have attracted much attention in the printed electronics industry. To date, expensive conductive silver inks have been utilized widely in these conductive films, which ultimately increase the cost. Hence the alternative low-cost copper inks will be of great interest in the future. This paper will present how to synthesize antioxidative conductive copper inks with superior adhesion to FR4 substrates. The antioxidative conductive copper inks were prepared by dispersing the antioxidative copper nanoparticles in diethylene glycol with the bisphenol-F type BEF170 epoxy resin as a binder and the Methyl-5-norbornene-2,3-dicarboxylic anhydride (NMA) as a curing agent, then were coated on FR4 substrates to form the copper films, followed by sintering at 250 °C in nitrogen atmosphere for 20 minutes. We found that the formation of three-dimensional structure between BFE170 binder and curing agent NMA don't affect the conductivities of copper films, and meanwhile can enhance the adhesion strength on FR4 substrates. The lowest resistivity of 158 μΩ · cm determined by using the four-point probe method and the highest adhesion of no peeling after the 10 times peel-off test with 3 M Scotch 600 tape were achieved with the copper ink composed of 1 wt% of BEF170 epoxy resin binder mixed with curing agent NMA in an equivalent ratio of 1:1.