Recently IoT and 4th industrial revolutions, research on human body -attached wearable devices has been increasing. These attached wearable devices also require stable electrical characteristics for bending and tensioning in electronic devices. To attach to the human body, it must also be used in joints such as the human elbow, knee, etc. To develop wearable devices, substrates and wiring must be wearable. Thermoplastic polyurethane and PDMS are typical of wearable substrates. However, reliability issues arise due to the crack in the joint with the electronic components when repeated tensioning and bending are used on wearable substrates. To slove this reliability problem, studies are focused on wearable wiring, which also has flexibility. Examples include wavy electrode, nanowires or graphene. which pre-strain wearable wiring to form a pleated metal thin film, porous electrode method that prevents loss of electrical properties even when tensile, and electrophoretic properties of metal and polymers. The wavy selection has the advantage of having excellent electrical properties because it uses metal, but the disadvantage is that the tensile and bending are limited and that the adhesion between the metal and the polymer is weak. Noowires, CNT, and graphene have stable electrical properties and excellent adhesion in the early days of use, but have disadvantages that are prone to detachment during repeated tensile and bending tests. In the case of porosity, the porous electrode has the advantage of not weakening its electrical properties even in repetitive tensile force due to its large volume, but the disadvantage is that the porous position is formed irregularly.
Istudy, we intended to manufacture wearable substrates and wiring using metal-polymer electrode, which has stable electrical characteristics and adhesion. Metals can be used to possess good electrical properties, and the same polymer as the substrate was mixed with the metal to improve adhesion. Ag powder, which does not corrode easily with metal and has excellent electrical properties, was selected and the polymer manufactured ag-PDMS composite paste by selecting PDMS with similar elasticity to the human body. In addition, PDMS substrates with protrusions were developed to address reliability problems at joints. The purpose was to adjust the content of Ag-PDMS to measure and optimize its electrical characteristics and viscosity, and to adjust the curing time to achieve the most stable electrical characteristics. In addition, an ag-PDMS was applied to the LEGO-Study substrate with protrusions to measure electrical resistance during the tensile process, and the wiring was formed in the same way as the substrate without the protrusion, and the repeated tensile and FEM simulations were conducted to perform a comparative analysis. In Ag-PDMS, cross-sectional analysis was performed to check whether the ag powder was distributed and electrical resistance was measured according to void and dispersion.
Based on the above research details, wiring was formed to the LEGO-Study Substrate using 80 wt.% Ag-PDMS and LED chips were mounted. LED was attached on the Ag-PDMS and repetitive tensile tests were carried out in this study.