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The purpose of this study is to analyze the performance of the flexible conductive substrate by interfacial shear stress. This study performed automatic liquid-crystal modulating common-path interferometry (LMCI) optical inspections on 125-µm polyethylene terephthalate (PET) substrates having indium tin oxide (ITO) coating thicknesses of 80 nm, 160 nm, and 230 nm. The nonlinear characteristic of the stress-optical coefficient of the ITO material is obtained using LMCI. To validate the performance of the flexible conductive substrate, this study has utilized an automatic sliding-folding testing platform (ASTP) for a whole-folding test. Eventually, this study successfully has utilized interface shear stresses to validate the performance of the flexible conductive substrate depended on the different thicknesses of the conductive layers for whole-folding test by using LMCI and ASTP. According to the measurement results, as the folding radii decrease and the ITO thicknesses of ITO-coated PET substrates increase, the changes of interfacial shear stresses increase in compressive direction and the change-rates of electrical resistance of ITO-coated PET substrate also increase. Therefore, the interfacial shear stress measurement and analysis results depicted on flexible conductive substrates provide a validation for improving the manufacturing process and for reducing process residual stresses. [ABSTRACT FROM AUTHOR]

To improve folding electrical properties of flexible electronics, this study presents a new adhesive stress analysis of depositing an adhesion layer between the conductive film electrode and the flexible substrate during folding test by a folding test platform. The folding test platform controls folding curvature of the flexible conductive substrates, folding times, and velocities in this study. Moreover, the electrical properties of flexible conductive substrates are measured during folding testing by the folding test platform. Eventually, this study successfully analyzes residual strain, adhesive stress, and electrical properties of flexible gold coated on polydimethylsiloxane substrates with chromium, nickel, and titanium adhesion layers up to 0.5/cm folding curvature during folding testing. The chromium adhesion layer had the best performance based on the largest adhesive stress, only 3.74 Ω resistance increase and 4.53 Ω maximum resistance up to 0.5/cm folding curvature during folding test by a folding test platform. The experimental result with chromium adhesion layer is consistent with adhesive stress analysis and provides a better adhesive strength between gold and polydimethylsiloxane than nickel and titanium materials for folding test. Therefore, adhesive stress analysis is adapted to evaluate the foldable electronics performance for improving folding characteristics easier. [ABSTRACT FROM AUTHOR]