Flexible Printed Circuitry on Fabric for Wearable Electronics Applications

Health awareness has increased worldwide since the COVID 2019 pandemic, creating a strong demand for wearable electronics. Wearable sensors for monitoring a patient's health are prevalent to reduce medical costs and decrease in-person clinic visits. Integrating electronics into clothes is challenging because most fabrics are porous and incompatible with the existing manufacturing methods, such as screen printing. The indirect printing method was employed to fabricate electrical circuitry on a textile substrate by printing it on a heat transfer polymer (HTP) and attaching it to the target cloths by stitching or glueing. Such a fabrication process has the potential to lead the way in developing new intelligent clothes. However, the durability of the printed circuitry in this manufacturing process on a cloth is still unknown and requires investigation. Therefore, this paper's objective is to study the durability of printed circuitries on fabric by applying constant cyclic loading. The test vehicle is a printed conductive silver interdigitating circuitry on fabric. Another test vehicle on a polyethylene terephthalate (PET) substrate was fabricated for a benchmark. A constant cyclic loading at 1Hz at a 50% duty cycle was applied to the test vehicles 100,000 times. The printed circuitry was monitored by logging the voltage in an electrical voltage divider configuration while the sensor was pressed and released. The result indicates that the fabric test vehicle can still function after the 100,000 cycles of the cyclic loading test and is comparable to that on the PET substrate. The recorded voltage-to-force values of the printed sensor on the fabric drifted upward and downward up to 3% over the loading cycles. The optical microscope observation on the cyclic loading samples showed signs of shear stresses on the printed silver and electrically conductive films, which could cause the tips of the silver interdigitating fingers to shatter. The study indicates that the properly manufactured circuits on fabric can be reliable and utilized for wearable applications.