Koichi Karasaki

Automatic Inspection System for Printed Circuit Boards

The purpose of this correspondence is to present problems and methods in automating visual inspection of printed circuit boards (PCBs). Vertical and diagonal illumination are useful in detecting PCB patterns correctly. An algorithm comparing local features of the patterns to be inspected with those of the pattern to be referenced is proposed. An inspection system using developed technologies is also described.

A system for PCB automated inspection using fluorescent light

Research was performed on the detection of faults such as shorts, cuts, and nicks in a printed circuit board pattern. The possibility was investigated of detecting a pattern by illuminating a printed circuit board with violet or ultraviolet rays and detecting the pattern using the (yellow or other) fluorescent light emitted by the base material consisting of glass-epoxy or glass-polyimide, etc. It was found that the pattern could be detected clearly by selecting an optical fiber that would separate the emitted fluorescent light from the illumination and using a detector consisting of a high-sensitivity TV camera that produces a silhouette image in which the base material is bright and the pattern is dark. A printed-circuit-board pattern inspector using this approach was developed. Test operation of the inspector in a plant demonstrated that it performs consistently good pattern inspections. >

Real-time X-ray inspection of 3-D defects in circuit board patterns

The paper reports defect detection techniques using X-rays in order to find three dimensional defects such as funnels in printed circuit board (PCB) patterns. X-ray images of fine PCB patterns, however, show patterns on more than one layer, having degrees of distortion that vary over an image, are subject to intensity variation due to fluctuations in the intensity of the X-ray source, and so on. To overcome these problems, we examined distortion caused by perspective transforms on the sphere surface of an X-ray detector and developed a defect detection algorithm based on feature extraction. Fluctuation of X-ray strength and heavy shading of the acquired image are compensated by signal processing. Evaluation of the system confirmed that the system could detect defects deeper than 20 /spl mu/m and with surface areas greater than 70/spl times/35 /spl mu/m/sup 2/ in fine PCB patterns and that the inspection time for a 600/spl times/800 mm/sup 2/ PCB was only 20 minutes.<<ETX>>

Modulation Compensation of Detected Circuit Pattern Signals.

When a circuit pattern is detected by an image sensor, degradation of the modulation of the detected image is inevitable. For automatic detection of defects in a pattern by image processing, a less degraded image is desirable. This paper presents a simple method to restore degraded modulation of a detected image. The method is intended for a practical image processing system. Its feature is that modulation compensation can be performed in real-time by a hard-wired logic circuit, so it can be implemented as a relatively simple circuit.