Key Theories Research On Cone-Beam CT Image Reconstruction For SMT And BGA Solder Detection Algorithm

The consumer electronics products (such as laptop, Smartphone, PDA, MP4, GPS and soon), industrial control electronics and defense high-end electronic information devices whichchanged with each passing day, all need PCB assembly products of all sizes electronicintegration. The PCB assembly products are the core of the various intelligent device andterminal equipments. As the Moore law of semiconductor technology took effect, integratedlevel of the integrated circuit has become increasingly higher. Surface Mounted Technology, anew technology of electronic assemblies has completely changed the traditional holeinstrumentation technology and made the electronics products become more miniaturizationand lightweight. However, Micro confocal X-ray precision testing equipment for SMT is thecritical equipment to detect the defects of PCB assembly structure. In order to improve thelevel of automation for the X-ray inspection systems, This paper deeply studied the intelligentdetection algorithm and reconstruction algorithm. The main contents are as follows:(1)Based on the detection of X rays, due to the Compton effect and X ray energyinstability occurs scattering phenomena etc. the image quality can degradate. On foundationof the summary and analysis of current image enhancement method, we propose the Retineximage enhancement method based on robust estimation. The method calls some date which isnot consistent with the hypothetical image data set "very little", according to the robustestimation that can be obtained to estimate the result that is not affected by the special effects,and process a special point by subarea domain with a robust estimation of the boundary pixelsas. Enhancement algorithms proposed in this paper utilize that Malik and Perona proposedanisotropic diffusion termination function with two kinds of boundary convex combination asa new form of boundary termination function, so as to increase the image contrast, overcomethe seriously blurred boundary and the artifact problem.(2) To separate the BGA solder joint image accurately and quickly from the X-rayimages, the project is about the BGA image segmentation algorithm based on patternrecognition theory, to have a quantitative judgment to the degree of separation between thetarget and background by the evaluation criteria of Fisher,and to classify image into twosorts--target and background in different gray value. When Fisher criterion function takes themaximum value, it comes out the best resolution of the target and background, and the grayvalue achieves the best threshold. Experiments show that this division is not only able to getthe image edge detail, but to overcome a defect of the edge breakpoints, a good method for the segmentation of BGA solder joints X-ray image.(3) According to the analysis and extract of the characteristics of solder joints, includingshort circuit,offset,less tin,cavity,warping,open circuit and so on, horizontal fault algorithmand vertical fault algorithm were proposed.Based on graphics characteristics, we candetermine continuity, offset, the area ratio, voidage and so on. Finally, we can judgewhether there are some defects with the decision rules. Furthermore, we distinguish the goodand the defect according to the Fisher Criterion Function,and put forward the BGA SolderJoints Detection Algorithm which is on the basis of Fisher Criterion,and verified it by meansof experiment.(4) This article propose one improved FDK-type algorithm of the ultra-short scan toresolve the limited-views problems which happen frenquently because of some mechanicaland physical limitations. It try to process the BGA reconstruction as a ROI reconstruction problem with an offset approach, and then modify the Parker’s weight function to let it adopt to3D situation. Through introduction of the algorithm, the time of scan and image reconstructionis reduced, the image quality of3D reconstruction can be guarantied while improving the detection efficiency, which will make CT more suitable in industrial applications.(5) This article has explored the synchronization type reconstruction algorithm andTV algorithm for BGA circuit board examination, which based on less angle projections. It proposed to use the information of projection value to control the back-projection speed whichcalled punishment-based algorithm: WP algorithm. At the same time, presented one S-TV algorithm which is quite suitable for flat-type objects as it give up a weak thickness direction of the object but can accurately reconstruct object with less angle projections.Finally, the main results of the dissertation are concluded, this article has also discussedthe future of the research focus and research directions based on X-ray test.