Abstract
This paper describes an automated pattern inspection system for circuit patterns of multilayer thin-film on a ceramic substrate. Thin-film layers, usually made of resin and metal circuit patterns, are alternately formed on a ceramic substrate. To inspect all those thin-film layers inline visual inspection is used. This inspection involves detecting defects existing in a surface layer just after the layer is formed. Surface circuit patterns must be optically differentiated from patterns on inner layers. For this purpose, bright and dark-field combined illumination is used and the wavelengh of reflected light to be detected is selected in a specific range. Illumination is achieved by a 4-fold ring-light-guide structure and bright-field illumination. The “Local Pattern Comparison Method” is used for defect detection in which a detected binary image is locally compared with a reference image. This method can be implemented by means of an image processing hardware system using a pipelined architecture for real-time operation. An automated pattern inspection system was constructed with the above mentioned pattern detection and defect detection method. According to the evaluation results, the inspection system can reliably detect defects as small as 10 μm.
