An automatic inspection of SMT rectangular chips based on PCA algorithm

In this paper, we present a practical approach to automatic visual inspection of SMT PCBs. There are thousands of chip components mounted on the notebook SMT PCB. The images of those chip components could not be exactly same due to the variance of shift, orientation, scale, and illumination condition. Even so, we could not memorize all kinds of inspection reference values for the different conditions. Most of inspection algorithms with fixed window template such as template matching, Fourier analysis, OCR, etc., do not show good performance for images with shifted, oriented, scaled, and variable illumination conditions. We propose a practical automatic inspection method of SMT rectangular chips; correcting the image variance of shift, orientation, and scale with practical speed, and updating the decision reference values in the inspection process. The performance of the proposed method is tested on numerous samples of rectangular chips on SMT PCB.