The demand for the display device with larger screen and higher resolution has been increased as the development of multimedia and information technology, which also make the defect inspection on the larger area with more patterns more rapidly to maintain the productivity. Display device consists of one or two-dimensional array of fine patterns and for manufacturing quality assurance of the patterns, a suitable inspection method is needed to detect abnormal patterns whose size or shape is not within allowable tolerance limits
An inspection method of machine vision for rapid detection of defects on shadow masks has been investigated. This method incorporates Fourier optics to effectively block off the regular pattern of fine holes using a hole-type spatial filter so that only defects can be extracted with minimum software image processing. Experimental results prove that this method is useful with a detection capability of 500$\mu^2$least defect size, which is sufficiently more than the industrial requirement of 1,000$m^2$ least defect size.
The Electrode plate of Plasma Display Panel (PDP) is made up of a thin glass substrate on which one-dimensional array of electrode pattern is deposited. For in-line quality assurance of such display devices, a collimated white light source is specially used to yield high spatial coherence with low temporal coherence to improve defect detection capabilities by avoiding undesirable coherent noise. Also, we investigated the effect of the spatial coherence of illumination on the system and spatial coherence is released to use efficient power of the light source. Also LCD is used as a spatial filter for easy filter-formation and alignment, the experimental results show that the contrast ratio of the LCD is not enough to block the periodic signal.
