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74 The PCB Design Magazine • December 2015 CAM operator can use to set the layer structure manually in his CAM system. Naturally, you're hoping that neither of you make mistakes. The best option is to express the file fun- ction in the file name. The Gerber .Filefunction attribute actually allows defining a file naming convention. The Gerber Standard File Naming (GSFN) convention reflects file function in the file name—it encodes the .FileFunction attribu- te in the file name. This is the closest you will get to a standard without X2 support. The GFSN standard file name consists of three parts: 1. A free-to-choose prefix identifying the job. This prefix is common to all files for any one job. 2. A postfix identifying file function. The postfix starts with an underscore ('_') followed by the FileFunction value string where the comma (','), which can create confusion in file names, is replaced by '$'. 3. The standard extension .gbr. Example: GJ01911Rev2.1_Legend$Top.gbr GJ01911Rev2.1_Soldermask$Top.gbr GJ01911Rev2.1_Copper$L1$Top.gbr GJ01911Rev2.1_Copper$L2$Inr$Plane.gbr … GJ01911Rev2.1_Copper$L10$Inr$Plane.gbr … By following the GSFN you clearly identify file function. It is your best option if you cannot use Gerber X2. Express the layer structure in a standardized way by using Gerber X2. If the standard is not available use clear file names. PCBDESIGN This column has been excerpted from the Guide to PCB Fabrication Data: Design to Fabri- cation Data Transfer. article THE GERBER GUIDE, CHAPTER 5 Figure 1: The layer structure. So what should you do if your PCB layout software is not capable of outputting the current Gerber version with attributes? This is a pro- blem, and indeed the temptation is to suggest that you consider switching to layout software that supports up-to-date Gerber output. X2 is the Gerber standard to transfer the layer structure. If you cannot output X2, you will need to use an informal method to defi- ne the layer structure in a legible form that the karel Tavernier is managing director of ucamco.

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