Research On Automatic Optical Inspection System Of SMT Stencil

With the rapid development of microelectronics and semiconductor technology,electronic products are increasingly moving toward miniaturization and complexity.Therefore,the existing automatic optical inspection equipment needs to be greatly improved in performance stability and accuracy.In this paper,an automatic optical inspection system is designed by using the stencil template widely used on SMT(Surface Mount Technology).The present situation and development trend of related detection equipment at home and abroad are studied and analyzed.The system of defect detection is determined by studying the technical principle.According to the feature and accuracy requirements of the test target,the selection of hardware such as light source,illumination mode,camera and lens was completed,and the optical platform system was successfully built.The process of testing is described in the software section.Bilinear interpolation sub-pixel threshold segmentation algorithm,the fitting of edge contour,the calculation of gravity center coordinates based on image geometric moment,affine transformation and other image processing algorithms are introduced.And the defect detection algorithm is explained,accuracy is 20?m,in which it is found that the intensity of the light source has a great influence on the detection accuracy,and it needs to be optimized.The reason why the intensity of the light source affects the imaging quality is theoretically analyzed.The sharpness function based on different evaluation methods is used to evaluate the sharpness of the image,and the evaluation results are analyzed to obtain the evaluation function suitable for the lighting system,also provide theoretical basis for the choice of light intensity.Then,the image information of SMT stencil under different illumination intensities is collected through experiments.After extracting relevant feature information for data processing,it is analyzed from three aspects: the error of mesh area,the offset of position and the number of detection of burrs.For the influence of system detection error,the appropriate evaluation function is compared and analyzed,and the best evaluation method is obtained.Finally,the error correction and improvement method of SMT stencil defects detection system was carried out.Through the influence of the cumulative error of the machine on the physical splicing,a correction method for automatically calculating the error value feedback to the system for parameter adjustment is proposed,and an improved method for the real-time detection based on the spatial coordinate system without stitching.In this thesis,the theoretical analysis and experimental research of the system on the high precision and high stability of industrial detection are discussed.Through the research on the influence of light source intensity,the correction of motion cumulative error,and the improvement of real-time detection without stitching,In different environments,it can quickly find the best light intensity corresponding to it,while maximizing the performance of the machine,improving the detection accuracy and excellent stability of the machine.