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56 The PCB Magazine • July 2014 In a recent an article by Julian Coates of Mentor Graphics, Smart Data Formats Automate CAD/CAM (The PCB Magazine, February 2014), in which Coates promotes more widespread adoption of the ODB++ format, the arguments he uses indeed make it seem like OBD++ is the great panacea for our industry, one that promises to eliminate all problems for CAD-to- CAM data transfer without any downsides. In order to promote ODB++, Coates unfor- tunately reverts to Gerber-bashing rather than explaining the strengths of ODB++. And his arguments are highly misleading, as they are based on some tired old fallacies that I would like to address here. Before starting, though, it's important to clarify that when referring to Gerber, I mean RS-274X Extended Gerber, the current Gerber format. This supersedes the ear- lier RS-274-D Standard Gerber format, which is obsolete. Bashing RS-274-D Standard Gerber is like railing against Windows because MS-DOS only allowed eight-character file names. If Coa- tes wants to bash RS-274-D, I'll gladly join him. Having said this, less than 2% of all jobs are transferred using the old format, so it's practi- cally a non-issue. Extended Gerber is the PCB industry's de facto image data transmission format. New formats have come and gone; some, like the ODB++ format, have been around for decades, but still today, more than 90% of the world's PCBs, from the simplest to the most complex, are still manufactured using Gerber, which tells me that this is an image format that the industry trusts. And the industry is right to trust it—it's the best there is. Used properly, it delivers on its promises, without fail, every time. So let's have a look at some of Coates' arguments. He quotes Viasystems as stating that, "about 25% of the data packages they receive have issues relating to: • Missing layers, fabrication drawings, drill files, etc… • Netlist format violations • Netlist exception violations." If true, this is indeed a sorry state of affairs, and needs rectifying. But if this is the extent of the problems, then there is nothing wrong with the format. Viasystems' issues are in fact due to some rather trivial bugs in the CAD ven- dors' implementations, so the solution is to fix the implementations rather than to adopt com- pletely new software by switching to a new for- mat. The article is not clear about whether the- se omissions and violations relate to ODB++ or Gerber files, or a mix of the two. However they arise, I can only recommend that Viasystems report these issues to their customers with a re- quest to contact their CAD software suppliers. If the CAD software vendors fix these simple bugs, the issues will be resolved once and for all. If they are unable or unwilling to do so, there is no solution: neither in Gerber, nor in ODB++, nor anywhere else for that matter. Coates also mentions that Gerber files sometimes contain syntax errors, low numerical accuracy and other errors. This is no doubt true, but again these are simply bugs in the Gerber output. Do we need a new format to fix syntax errors in the current one? Surely the solution is to fix the bugs in the Gerber output. And ODB++ itself is not immune to syntax errors; if anyone would like some invalid ODB++ files, I can provide a few. The reality is that Gerber files very rarely generate the wrong image. This is because while l e t t e r S editor's note: This response refers to an article by Mentor Graphics' Julian Coates, which ran in the February issue of The PCB Magazine, and was received in early June. Mr. Coates was given the courtesy of a rebuttal so they could be published side-by-side in the same issue. The rebuttal follows. Gerber—the Smartest Way Forward reader resPoNse

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