Fabrication, Characterization, and Electromechanical Reliability of Stretchable Circuitry for Health Monitoring Systems

In this study, commercially available stretchable hybrid conductors including silver flakes in an elastomeric matrix were screen printed on thermoplastic polyurethane (TPU) followed by encapsulation via the stretchable dielectric. Test vehicles include straight and serpentine lines with various thicknesses and wavelengths, respectively. Metrology was also performed to assess line thickness, width, and variability. The modular force stage (MFS) was used to characterize the initiation and propagation of microcracks. The results of the uniaxial tensile test showed that increasing the strain amplitude resulted in an increase in the electrical resistance and the rate of damage accumulation in the serpentine traces was lower than that of the straight traces. Additionally, the serpentine trace with the highest ratio of meander arm length to curvature remained conductive up to a strain amplitude of 150%. A systematic increase in electrical resistance from cycle to cycle was observed when the conductor was subjected to a strain amplitude of 10% for 1000 stretching cycles. The effect of processing conditions as well as test conditions will be discussed in detail.