A false alarm reduction method for PWB pattern inspection system

Among optical pattern inspection methods for PWBs (printed wiring boards), a feature-extraction method achieves higher throughput than a design-data-comparison method, but it cannot avoid false alarms completely. The authors propose an error-code-chain method to reduce these false alarms. A hierarchical defect analysis technique is employed, combining the feature-extraction method and the error-code-chain method. It discriminates between fatal defects and false alarms, taking global features into account. This method has been applied to the pattern inspection system described by G. Odawara et al. (1986), and it has achieved both false alarm reduction and video-rate processing