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80 The PCB Design Magazine • August 2016 Karel Tavernier UCAMCO It is possible to fabricate PCBs from the fa- brication data sets currently being used; it's being done innumerable times every day, all over the globe. But is it being done in an ef- ficient, reliable, automated and standardized manner? At this moment in time, the honest answer is no, because there is plenty of room for improvement in the way in which PCB fabrica- tion data is currently transferred from design to fabrication. This is not about the Gerber format, which is used for more than 90% of the world's PCB production.There are very rarely problems with Gerber files themselves; they allow images to be transferred without a hitch. In fact, the Gerber format is part of the solution, given that it is the most reliable option in this field. The pro- blems actually lie in which images are transfer- red, how the format is used and, more often, in how it is not used. Each month, we look at a different aspect of the design to fabrication data transfer pro- cess. In this monthly column, Karel Tavernier explains in detail how to use the newly revised Gerber data format to communicate with your fabrication partners clearly and simply, using an unequivocal yet versatile language that enables you and them to get the very best out of your design data. Chapter 17: Pads on Copper Layers The main function of copper is to conduct, but pads also have other functions: SMD, com- ponent, connector and test pads on outer layers provide electrical access to the circuit via the solder, paste and platings that they carry; ther- mal relief pads confine heat; and via pads, as well as providing electrical connections betwe- en the track and the barrel, also provide mecha- nical support for the barrel, and create room for drill positioning tolerances. It is essential that pads be identified indivi- dually during the design and CAM stages so that they can be treated appropriately during the production processes: Via pads on soldermasks need a different treatment from SMD pads, and connector pads that are to be gold plated need a special gold mask for the plating process. And for electrical test, the test probes will only do their work properly if the location, size and shape of all pads is known. It is also important to reali - se that copper pads must be differentiated from other copper features when compensating for The Gerber Guide Chapters 17 & 18 ARTICLE

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