Measurement of the mechanical properties of brightness enhancement films (BEFs) for LCDs by optical interferometry

The brightness enhancement film (BEF) is one of the important components in the liquid crystal displays (LCDs). Since the thicknesses of BEFs are very less, it increases the difficulty to measure their mechanical properties. In this paper, we successfully propose a methodology by combining the micro tensile test and optical interferometry to characterize Young’s moduli and Poisson’s ratios of BEFs. In addition, the thermal and hygrothermal effects on the mechanical properties of BEFs were also investigated. The finite element analysis (FEA) was utilized to verify the precision of our proposed methodology. The results show that Young’s moduli of BEFs are influenced by temperature and humidity whereas Poisson’s ratios of BEFs are less influenced by temperature and humidity.