Further Visualization of Mechanical Stress on FHE During Folding

Knowledge of mechanical stresses on flexible hybrid electronics is important to develop FHE devices, such as flexible sensors and wearable devices. At the same time, in order to develop materials, such as substrate and adhesive for FHE, it is necessary to study the mechanical stress of FHE to provide proper materials. For conventional materials (in most cases those are not flexible, but rigid) mechanical stresses could be measured by strain gauges. However flexible things for FHE are so soft that it is difficult to measure stresses on those things by using a strain gauge, because strain gauges, themselves, are usually harder than those flexible things. That means when we put those strain gauges onto flexible things, those gauges will affect the flexibilities of those flexible things. In order to solve this situation, we apply several methods to visualize mechanical stresses. Previously, we, Yuasa System Co. Ltd., introduced 'Mechano-Luminescence (ML)' materials that emit intense light under mechanical stress. In order to study mechanical stresses of folding FHE, furthermore, we apply other technologies, such as 'Bending Film Edge profiler (BFEP)' and 'Defect Analysis System (DAS)'. BFEP uses a light and a video camera seeing from the side of folding area. This shows a side view of flexible things behavior under mechanical deformation. By evaluating that shape continuously, we could see how flexible things would change that behavior as the number of folding increases. For example, for adhesive film, we could see when starts delamination. DAS counts a number of defects that shows strange phenomena, such as small crack, during folding. By using this, we could see how flexible things change their characteristics under mechanical deformation. Now, we, Yuasa System, could provide those evaluation systems to evaluate FHE more precisely.