The Performance and Reliability of Screen-printed Flexible Multilayer Leads for Wearable Vital Sign Monitoring Devices

Wearable vital sign monitoring (VSM) devices are becoming an integral part of healthcare delivery systems to ensure continuous patient monitoring and improve care efficiency. Flexible hybrid electronics (FHE) technology offers great potential to develop low-cost, reliable, and user-friendly VSM devices with clinical accuracy. Flexible multilayer leads are vital components that affect the overall system reliability of a VSM device. Inferior leads cannot overcome the effects of triboelectric noise and mechanical stresses on signal quality and may fail under electrical impulses during defibrillation treatments. Nevertheless, proper lead design and structure, and the correct choice of materials and processes could significantly improve the performance and reliability of the leads. Hence, presented here are the development of flexible multilayer leads and the evaluation of their performance and reliability under triboelectric noise, electrical impulses, and mechanical stresses. Multilayer leads with conductor, shield, insulation, and encapsulation layers were fabricated by screen printing and heat lamination techniques on a 2-mil polyethylene terephthalate (PET) substrate. Leads of three different shield configurations (in-plane shielded, single-side shielded, and double-side shielded), and three different shield/conductor (S/C) width ratios (2, 4, and 6) were considered. The results revealed that the double-side shielded leads with a higher shield/conductor width ratio are more effective in minimizing triboelectric noise. Also, leads with a sufficiently thick, uniform, screen-printed insulation layer could withstand at least four electrical impulses of 5 kV. Finally, the multilayer leads achieved the required ECG signal quality under mechanical stresses caused by bending at a 1.5 mm radius and creasing with a 2 kg weight.