Screen Printing Fine Pitch Stretchable Silver Inks onto a Flexible Substrate for Wearable Applications

This article presents the development and optimization of the screen printing process for printing stretchable silver ink onto a stretchable thermoplastic polyurethane substrate. A test vehicle was designed including 50 μm/5 mm (line width/line length) to 350 μm/35 mm lines (at four biases). A two-level factorial design with three replicates was selected to investigate the effect of process parameters on the quality of prints. We proposed calculated sheet resistance based on the measured resistance value, trace width, and trace length, which can replace trace height measurements on rough profile substrates. We found that squeegee pressure and emulsion thickness have statistically significant effects on calculated sheet resistance of print traces, whereas print speed does not have statistically significant effects. In our experiment setting levels, the lower the squeegee pressure, the lower the calculated sheet resistance that is achieved. The emulsion with higher emulsion over mesh (EOM) is better than the emulsion with lower EOM because it can achieve lower sheet resistance. After optimizing the screen printing process, we were able to print 100 μm (4 mils) trace width and spacing with high consistency.