Screen-printed Water-soluble Resistors for Wearable Electronics: An Analysis of the Fabrication Process

Screen-printing of functional materials is a well-established process in the printed electronics industry. Recent advancements of flexible electronics demand screen-printing of a wide range of functional materials on flexible and stretchable polymeric substrates. The printability, quality of the printed structures, and their reliability during storage and usage are determined by the key fabrication process parameters such as the material properties, printing parameters, curing conditions, and environmental factors. Therefore, proper analysis of distinctive fabrication processes is crucial for problem-solving and process improvements in order to ensure optimum outcomes. In the present study, a low-cost, disposable, multilayer Sweat Rate Electrode (SRE) was fabricated on a flexible and highly stretchable Thermoplastic Polyurethane (TPU) substrate by screen-printing, using a Silver-filled conductive ink and a water-based Carbon-filled conductive ink. Exposure to low humidity and high temperature adversely affected the fabrication process and the robustness of the SRE. These challenges were overcome by better control of environmental conditions in the printing atmosphere and proper selection of the materials, printing parameters, curing conditions, and fabrication process flow. We demonstrate the fabrication of a defect-free, robust SRE on TPU substrate.