Binuclear Copper Complex Ink as a Seed for Electroless Copper Plating Yielding >70% Bulk Conductivity on 3D Printed Polymers

3D printed electronics is an emerging field of high importance in both academic research and industrial manufacturing. It enables fabrication of 3D devices with embedded or conformal electronic circuits, which are relevant to a variety of applications, such as Internet of things, soft robotics, and medical devices. Patterning of electrical conductors with conductivity higher than 50% bulk copper is challenging and usually involves electroless or electrolytic deposition processes that require the use of very costly catalyst, mainly palladium, as a seed material. Here, the use of a binuclear copper complex as a very efficient replacement for the conventional catalysts, which can be directly inkjet printed onto 3D plastic objects, is described. After printing, the copper complex is converted into pure copper upon short exposure to low-temperature plasma. By combining the binuclear complex with electroless plating, resistivity as low as 2.38 µΩ cm, which corresponds to a 72% conductivity of bulk copper, is obtained. The applicability of the complex ink and the process is demonstrated in the fabrication of a near-field communication antenna on a 3D printed plastic object.