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PCBD-Mar2016

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72 The PCB Design Magazine • March 2016 drawing is often absolutely essential. A technical drawing is intended not for digital processing, but for humans to look at, and it is made according to time-hallowed rules as shown in Figure 1, and includes a frame, title block, notes and legends. As drawings are images, they too are best transferred in Gerber (more in Chapter 10). Alas, sometimes digital data and drawings are confused and a drawing frame is added to digital data, resulting in a copper layer (Figure 2). While the frame is essential in a drawing that is made for people, it becomes junk when added to a digital data file such as a copper layer that is to be digitally processed by CAM software—and this junk must be removed manually by the CAM operator before the data can be used. Digital data does not automatically become a drawing because it represents graphic information. And expressing both drawings and graphical digital data in Gerber does not automatically make them drawings—or purely digital files. Use only pure data files, without junk or embellishments. You may object that the title block contains useful information. This may well be—if so, the solution is to put that information in a separate text file or a true drawing. The data is then pure and can be used without manual cleanup and the information intended for the human operator is conveniently available in a separate file. Remember, put only data in data files. Chapter 8: Always Include the Netlist Basically, a netlist is a set of nets, where each net has a name and a set of nodes identified by their XY coordinates. Nodes on the same net must be electrically connected. Nodes on different nets must be isolated. the gerBer guide, chapter 7 & 8 Figure 1: A typical frame for a technical drawing.

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