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  • PCB appearance inspection method
     
    Date :2017-8-7

     

    Printed circuit board appearance inspection system (AVI) research and application with the same online inspection system AOI, involving a number of cutting-edge disciplines, such as signal inspection technology, image processing, pattern recognition, artificial intelligence, neural networks, wavelet analysis and computer real- Control technology and so on. Their working principle is mostly consistent, are through the first object to check the parameters of access or acquisition, and then according to the corresponding processing method (algorithm) to get the results. Finally, the resulting results are embodied in the control object in a certain way.

     

    Existing printed circuit board defect inspection methods are many, can be divided into two categories: First, non-reference method. It is to check whether the PCB to meet the design rules, mainly for size inspection, that is, check the conductor and pad size to meet the design standards required for the coordinates, width and clearance, any design rules are inconsistent with the requirements are considered potential defects The Its advantage is that there is no need to refer to the PCB, so it does not need to be aligned, the disadvantage is that it can not be checked to meet the design size of the defect. Such as PCB on the hole or less holes, loss of a wire and so on. Second, reference to comparative law. It is the PCB to be measured with the standard PCB point by point or to be tested on the PCB to extract the characteristics (color characteristics) and standard PCB extracted from the characteristics of any difference are considered to be potential defects. Reference to the advantages of comparison method is conceptually intuitive, the circuit is relatively simple, the shortcomings of PCB and standard PCB is required to check the location of the precise alignment of the location, or check the virtual alarm more.

     

    This article says that this visual inspection machine uses a comparison method. In foreign countries based on the comparative method of visual inspection equipment can be roughly divided into two algorithms, one pixel processing, it is the standard PCB board for each pixel to establish the model, and then with the test board for point by point comparison. The advantage of this algorithm is that the transition between different colors (transition zone, refers to the convergence between the different colors) Obviously, the transition zone defect check effect is good, the drawback is the point by pixel comparison calculation, memory Processing large, the computer configuration requirements are high. Second, the regional processing method, which is the standard PCB board with different colors for the characteristics of information partitioning, each partition includes a feature color information, do not need to model each pixel, but the same Feature color for regional modeling. The advantage of this algorithm is to get more information on the characteristics of a more comprehensive description of the standard board, compared to more accurate, the disadvantage is that the transition zone is not obvious, the transition zone at the inspection effect is poor.

     

    From the advantages and disadvantages of the above two algorithms can be seen, the best way is to combine them together, the transition zone using pixel processing, other areas using regional processing, but to achieve this algorithm more difficult. At present, the most representative of the foreign pixel processing method is the production of the Japanese company's FP series of appearance machine, the use of regional processing is the most representative of another Japanese SHIRAL company's appearance machine. The company developed the appearance of the machine using the method of comparison method, this method is through the image acquisition system for the standard board for image acquisition and analysis, the establishment of standard information (standard library), the standard board information to be measured board information Comparison of the defect information to be measured.

     

    In the application of the appearance of the machine, mainly to study the type of PCB board, check the board defects, and how to establish a good standard library to check the different types and requirements of the appearance of defects. At present the industry is the development of the WG21 appearance of the function of the PCB board by metal materials are divided into: copper, gold plate, silver plate, OSP board. WG21 can check the appearance of defects include foreign body, exposed copper, fill the oil, scratches, poor gold, character error, uneven green, uneven pad, residual copper, missing and so on. The following main examples of the appearance of the machine in the trial to check some of the defects. as the picture shows.


    This article is mainly based on the machine vision of the printed circuit appearance inspection machine design and research for the majority of PCB manufacturers to solve the PCB appearance quality inspection of a major problem, to improve product quality, improve FQC efficiency, reduce customer returns, claims, Enhance the reputation of enterprises and so has important value.

     

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