Abstract:

In order to acquire high- contrast images in the defect inspection of the PCTP (Projected Capacitive Tou- ch Panel) ITO pattern by using the line- scan CCD,a coaxial illumination and imaging system based on the maxi- mum difference value between superposed reflection coefficients is designed and established according to the bright- field reflection illumination principle.Then,the illumination and imaging patterns are analyzed by taking into ac- count the optical properties of the glass substrate,the PCTP ITO material as well as the geometrical structure of the ITO pattern,and the influence factors of the imaging contrast between the ITO film and the glass substrate are ana- lyzed by considering the multi- layered composite structure of the ITO pattern.Finally,at a higher scan rate which can cause a higher productivity,the imaging parameters of the high- contrast images of the ITO pattern and the glass substrate are determined by comparing a series of images taken at different illumination intensities.Experiment re- sults indicate that,when the ITO substrate scans at a rate of 130mm/s with an inspection precision of 10μm and a light intensity of 190,image gray histograms have two apparent peaks,which helps to inspect the defects of ITO patterns.

Key words: image acquisition, line- scan CCD, ITO pattern, glass substrate, image contrast