A fast modular RLE-based inspection scheme for PCBs

On-line inspection of PCBs requires acquisition and processing of gigabytes of image data in a matter of few seconds, especially when multi-layer and very high-resolution boards are used. To meet the demands for speed and accuracy, our inspection system uses run-length encoding (RLE) for storage and operations and an inspection scheme which exploits the availability of an artwork for comparison purposes. The system which is suitable for parallel processing consists of four parts: (i) segmentation of artwork and feature extraction, (ii) image acquisition, (iii) inspection of blank areas, and (iv) inspection of trace areas. First, the artwork which is available as a CAD file in Gerber Format, is segmented offline into primitive patterns and information related to the location and identification of each segment is stored in a large image database to be used later for real-time inspection. A time-and space-efficient technique based on RLE is used for storage of essential features and image operations.