Gerber File
From Free net encyclopedia
A Gerber File is a standard file used by Printed Circuit Board fabrication houses that contains information necessary for computer controlled machines to draw wires, drill holes, mill, and cut the PCB. It is named after the Gerber Scientific Instruments Company, a pioneer in photoplotter manufacturing, and a former division of Gerber Scientific, Inc. These files are produced by PCB designers using specialized Electronic Design Automation or EDA software, such as Orcad Layout, Altium Designer, Mentor Expedition, Cadence Allegro or TARGET 3001!.
Since a PCB may have many layers, the older Gerber format EIA RS274D always assumed a set of command files (one for each PCB layer) and one "tool" description file. The command files (consisting of short commands and X, Y coordinates) were called "Gerber files" and the tool files were called "aperture files". Unfortunately a standard for the aperture files never was established. So every EDA software had an own file format for the aperture information. This caused many problems for PCB manufacturers. Often the aperture information had to be reentered manually.
The newer Gerber format RS274X, also known as X-Gerber, now includes the aperture information into the Gerber file headers. So normally every X-Gerber file is a complete information on what a PCB layer should look like. But still there are some problems with the interpretation of these files, e.g. regarding polygons or the question which file to use for which layer. The Gerber file extensions are often "*.GBR" or "*.GBX"; sometimes extensions like "*.TOP" or "*.BOT" are used instead.
Up to now the world is still waiting for a good format to describe PCBs for simulation, production and test.