Reliability of screen-printed conductors and resistors during fatigue cycling on flexible substrate

Abstract

Abstract Scalable printing of conductor and resistor components has revolutionized the field of flexible electronics by enabling a myriad of low cost highly conformable devices. Flexible electronic devices need to exhibit reliable performance under strenuous mechanical deformations to be adopted in applications such as human and asset monitoring. The reliability of the devices is in turn affected by the microstructure of the materials, manufacturing processes, and conditions of use. In this research, the mechanical behavior and microstructural properties of stretchable silver conductor and stretchable carbon conductor inks on flexible substrate are studied. The test vehicles (such as 4- point probe structures are screen printed on thermoplastic polyurethane (TPU) and cured in a convection oven. The quality of the printed traces including the resolution and thickness profile are measured by Confocal Laser Scanning microscope. The microstructure of the sample including particle/nanoparticles morphology is studied by Scanning Electron Microscopy (SEM). The electrical resistance is measured by 4-point probes method and the sheet resistance of the printed samples is calculated. The mechanical and electrical reliability of the samples are investigated by fatigue-cycling and in-situ measuring of the electrical resistance. In terms of electrical conductivity, the silver printed traces show different behavior compared to the carbon printed samples when exposed to fatigue cycling. The electrical resistance of the printed silver trace increases during the fatigue cycling. Higher extension rate along with higher strain magnitude accelerate the rate of increase in the electrical resistance. The relative electrical resistance of the carbon trace initially drops to 0.7 after 40 cycles and remains constant for the rest of the cycles. The extension rate does not considerably change the electrical resistance of carbon trace. The stability in electrical resistance is crucial in applications where electrical shielding is concerned.