Development of a full roll-to-roll manufacturing process of through-substrate vias with stretchable substrates enabling double-sided wearable electronics

In the recent years, there has been a growing interest towards printed stretchable electronics used in diagnostics, health-monitoring, and wearable applications. Double-sided electronic circuits with through-substrate vias offer a solution where the amount of printed circuitry and assembled SMDs (surface-mount devices) in direct contact with the human skin can be minimized. This improves not only the wearability and cost-effectiveness of the printed electronic devices but also the product safety and comfort to wear. Another factor decreasing the unit costs in printed electronics is the use of high volume, high speed, and continuous roll-to-roll (R2R) manufacturing processes. In this current paper, a full R2R process for the manufacturing of through-substrate vias on stretchable thermoplastic polyurethane (TPU) substrate was developed and verified. The through-substrate via-holes were manufactured in R2R using either laser-cutting or die-cutting. Rotary screen printing was used to print conductive tracks onto both sides of the stretchable substrate and to fill the via-holes. Eventually, conductive and stretchable through-substrate vias with low sheet resistance and low resistance deviation were reliably achieved with the developed process.