Visualization of Delamination in Encapsulated Flexible Electronics Fabricated using Slot Die Coating

A major challenge in the flexible electronics industry is the inability to quickly and accurately assess the mechanical properties of barrier materials used to encapsulate various devices. The feasibility of using a low-cost approach, digital photoelasticity (DP), to determine stress formation in barrier film is analyzed so that inherent weak areas cannot only be identified, but also reinforced. In this experimental study, ethylene vinyl acetate (EVA) is slot die coated onto untreated polyethylene terephthalate (PET) or onto PET treated with indium tin oxide (ITO) or poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). An axial stress is imposed on each sample using a universal test machine, and DP was used to obtain the stress and grab profiles. It has been shown that highly concentrated and multilayer EVA coatings withstand higher stress. Also, it has been shown that the locations of delamination happen at the side edge of the encapsulation when EVA was coated on a homogenous surface, but for heterogeneous surfaces, the delamination occurred at the boundary between the PEDOT:PSS and ITO. All these data were depicted using DP in very quick fashion. Therefore, DP is a viable method for quickly and accurately determining stress in barrier films.