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November 2014 • SMT Magazine 31 Figure 4 (left to right): pin detection algorithm identifies terminals of QFp, bGa, plCC and bTC QFNs components. The computer is used to find changes of brightness in an image and interpret them as edges. Along with the information about the type of component being analyzed, the mathe- matics will identify, for example, regions in the images that represent the rectangular-shaped pins of a QFP component. Some similar procedures have to be imple- mented to identify the pins of individual SMD components, such as BGAs, QFPs, BTC QFNs, and PLCC components. The benefit for the us- ers is that they do not have to deal with any component-related data sets; they simply place the component onto a region above the camera and the software will find the pins of the com- ponent by itself. When the component terminals are com- pletely identified, the next objective is to find the pin pattern in the image of the PCB. A num- ber of other mathematical calculations lead to a virtual overlay of the detected pin structure and the initially detected target area. The best result of this matching procedure can be presented to the operator for final approval or manual cor- rection. The calculated offset between the cur- rent component location and the desired target position is used to place the part. In the auto- matic mode, the machine processes the entire sequence by itself. In order to optimize the alignment accuracy for QFP components another algorithm is used to ideally match the pads and the pins. The pad row analysis compares the signals of the pad pattern and the pin pattern and readjusts the images until the best result has been detected. additional benefits of the gantry system The matching result is usually calculated within some seconds and if the PCB to rework is only one out of a batch, the placement and following soldering procedure can be fully auto- mated. In this case the gantry system will move the BGA to the target position, the heating head will move there in the next step and the prese- lected thermal process of soldering is begun. As the rework machine is equipped with a precise gantry system, other beneficial aspects figure 5: Target image with virtual pin overlay of the Bga component. new PLacement tecHnoLogy For rework systems continues feaTure