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SMT-July2016

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86 SMT Magazine • July 2016 More often than not, if a board has been de- signed in a CAD system, using the exported data will result in the easiest and most reliable meth- od of importing the data. This data is known as a Gerber file, a 2D vector file that describes everything about the board for manufacturing, as well as populating and assembling them. It defines multiple layers of images that make up the board, including the size of pads, centroids, through-hole locations, etc. Once the board has been acquired, the methods for programming the board vary widely, so evaluating the available methods against your particular processing needs will help guide the selection process. It's easy to add expensive bells and whistles, but for a low volume application or shop, they may not be necessary. On the other hand, some medium to high volume applications will benefit sig - nificantly from the time-saving options that improve productivity . Importing Board Data Software for selective soldering machines is nearly always hosted on an offline PC. The idea is to import the board data, whether it's a visual representation from a scan or photo, or from a digital Gerber file, then scale its length and width on the computer screen to match the physical dimensions of the board itself. So, now that the board image has been imported into the software, it appears as an overlay of the co- ordinates of the points behind the board image. With a simpler software interface, addition- al PCB data may need to be entered (in addition to the border and size of the board)—such as all the solder process data (temperature, preheat speed, preheat dwell), as well as the up/down Z-axis speed. And this is where it gets tricky. Selective solder is not just a pattern of dip points on a board. It also represents opportuni- ties to drag solder across multiple points with- out changing the elevation, or height (Z), from the board. Furthermore, if nozzle changes will be necessary to accomplish some solder opera- tions, they should be minimized to reduce dead time. On some boards, using a single nozzle to perform less efficient operations than would otherwise make sense for a different nozzle may still be faster than a time-consuming nozzle change. SELECTING A SELECTIVE SOLDERING SYSTEM, PART 4 Figure 2: Programming from image file.

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