Printing of conducting inks on paper

Paper has many attractions as a substrate for the manufacture of flexible electronics, particularly the comparative ease of recycling and recovering the constituents of the inks. However, it is not as smooth as the polymer substrates and also does not normally have sufficient barrier properties for sensitive reactive inks. By careful attention to the coating process a paper has been created that has sufficient smoothness for printing of electronics. As a first stage of the evaluation of this coated stock, a series of trials have been undertaken where appropriate images have been offset printed using a silver conducting ink. This paper presents an analysis of the images in terms appropriate for the manufacture of electronics. It looks at traditional concepts, such as tone gain, as this affects the minimum printable line. The surface roughness, both of the printed image and the paper, edge straightness, defects (including shorts), the resistance of the lines and the impedance of fine line gaps were measured. These are evaluated through two print runs to provide consistency data as required for the manufacture of electronics. In the second print run, an overprint was used to increase the film thickness and hence reduce the resistance of the conductors. This highlighted the problems associated with wet on wet printing and the difficulties of obtaining continuity between the two layers. The results are encouraging and show the potential of paper as a substrate for volume manufacture of disposable electronics.