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28 SMT Magazine • November 2014 fiducial marks in high precision, the component placement will always be satisfactory. Some of the units providing this technology come with a high price tag and may not meet the cost ex- pectations of many customers. a new Placement technology To combine and implement a new place- ment technology into a rework system with an acceptable market price is a challenging task. Digital cameras for image generation, image processing software and a precise gantry sys- tem are the baseline in order to establish this placement technology in the world of repair. USB cameras supply image information; image processing algorithms evaluate the data and do the necessary calculations to identify the cor- rect position for a component. The stepper mo- tor axis system is used to handle the device and locate it to the target position. Movements in x-, y- and z-directions are carried out with tol- erances in the micrometer range and also the rotation of the component can precisely be ex- ecuted. Digital cameras and image Processing Crucial for a successful solution is the cor- rect combination of the above-mentioned ele- ments. The cameras need to generate images in acceptable resolution. Numerous algorithms must restructure the data, and the calculated pixel offset needs to be perfectly converted into steps and micrometers to match the com- ponent to its target position. For the cameras new PLacement tecHnoLogy For rework systems continues feaTure an active operator. This is a disadvantage for at least two reasons: repeatability of component placement and the pure necessity to let an op- erator do the alignment. Placement with optical beam splitter Beam splitters allow operators to use one camera to visualize the PCB surface and compo- nent terminals in one image. This technology is commonly used, but reaches its limits in resolu- tion and illumination as the pitch gets smaller and smaller. Aligning the component to its tar- get position is a tiresome process for the opera- tor if, for example, the color of component pins (bottom) and PCB pads (top) is the same. Placement with alignment tool Another method involves use of a special tool that is aligned to the PCB pattern and later moves the desired electronic component onto the previously identified position. Due to a lack of magnification and possibly poor visibility, this technology is restricted to a certain num- ber of package types. The quality of the align- ment strongly depends on the user's abilities and skills. vision Placement Finally, the most promising method for component handling uses camera images and corner positions of the device and the target region. A computer-aided system calculates the offset and aligns virtual rectangular structures to each other. If the operator is identifying the Figure 2: a distorted image (left) and corrected image (right). (Source: MVTeC [1] )