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74 The PCB Design Magazine • July 2016 by 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 15: The Use of Gerber Viewers Before sending your Gerber files off to your fabricator, you are often advised to check them using a reputable Gerber viewer such as GC- Prevue. This is excellent advice. Note that this involves more than just verifying that the viewer displays your intended image: It is important that you check too that the file is valid. Even when handling invalid data, viewers typically try to reverse engineer the intended image by 'reading between the lines'. This is perfectly OK, but the file is still invalid and, according to Gerber specification: An invalid Gerber file is meaningless and does not represent an image. A file with errors must not be sent to the fabricator as if all is well, even if the intended image is shown. This is because even if your reader has reverse engineered the intended im- age from the invalid data, another reader may not be so successful. And that reader may be your fabricator's CAM, which will result in scrap. Should this happen, the fault lies squarely with The Gerber Guide Chapters 15 & 16 ARTICLE