Gerber File

A Gerber File is a standard file format used by printed circuit board (PCB) fabrication houses that contains data necessary for computer controlled machines to draw exact patterns for circuit boards. These patterns are typically used to electrically connect components in electronics assemblies. The patterns usually contain features such as land patterns, signal traces, drilled holes, milling and cutting information. The "Gerber Format" was originally a subset of EIA RS-274-D. Later the format was then extended by the so called "Mass Parameters" and was then also called RS-274-X.

History

* On 1980-08-27 the first edition of the GERBER FORMAT, Plot Data Format Reference Book was published by Gerber Systems Corporation as a specification to drive the photoplotter of this company. At this time the photoplotter had a limited set of fixed apertures of different shapes (typically round and rectangular and a few others) in different sizes. An aperture could be exposed at a specific coordinate (flash) or the head was moved with open shutter from one coordinate to another to generate line or circular arc segments.
* Mechanical Gerber plotters used apertures made of photographic film, where the transparent portion could be any shape. Flash apertures in custom shapes were used for surface mount pads or edge connector pads or targets to align the layers. If a circle was used to draw a line, the middle of the line would be exposed to more light than the edges, so a Draw aperture was typically a doughnut shape with the center dark for uniform coverage. This is no longer necessary with raster plotters.
* There was no uniform position for the film apertures, so an aperture list (plain text) was used to inform the operator where to install the apertures before running the plot. The machine had a certain number of available aperture position numbers that were not consecutive 1..max, and usually not all were used for any given board plot. The person generating the plot file had responsibility to ensure that the aperture list used positions that were actually available and matched the plot file.
* In 1986 the GERBER Format was extended to support apertures with variable sizes to produce rectangles of arbitrary sizes within a given range and tapered lines. This functionality is not in practical use any more.
* On 1991-04-26 with the availability of raster-scan capability the GERBER Format was then again extended for polygon areas and Extended Mass Parameter, allowing to dynamically define apertures of different shape and sized and more.
* The last edition of the GERBER FORMAT, Plot Data Format Reference Book was published on 1993-01-31 by Gerber Systems Corporation.
* Later the Gerber Systems Corporation joined with Barco Graphics, Gent, Belgium, and on 1998-09-21 the RS-274X Format User’s Guide was published by the Barco Gerber Systems Corporation.
* Again sometime later the rights on the specification turned over to ManiaBarco GmbH, Germany
* On 2003-01-01 ManiaBarco GmbH, Germany was taken over by MANIA Technologie AG, Germany. Since then no "official" public documentation on the GERBER Format is any longer available.
* Today, the Gerber Scientific Instruments Company, a pioneer in photoplotter manufacturing, and a former division of Gerber Scientific, Inc. is no longer in the business of photoplotter for printed circuit board

Around the year 1990 the GERBER Format was adopted by several other photoplotter vendors and also Computer-aided manufacturing tools for PCBs. It became a de-facto standard even if no official documentation is any longer available.

Usage of the GERBER Format

These files are produced by PCB designers using specialized Electronic Design Automation (EDA) software, such as OrCAD Layout, Altium Designer, Mentor Expedition, Cadence Allegro, CadSoft EAGLE, TARGET 3001!, Sunstone PCB123, Number One System Easy-PC, PADS, Zuken Cadstar or Zuken CR5000.

Since a PCB may have many layers, the older Gerber format EIA RS-274D 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". A standard for the latter was never established so every EDA software had its own file format which caused problems for the manufacturers. Often the aperture information had to be re-entered manually.

The newer Gerber format RS-274X, also known as X-Gerber or Extended Gerber, includes the aperture information into the file headers. With embedded apertures, this makes every X-Gerber file complete as to how each PCB layer should look. However, there are still problems with the interpretation of these files, such as on polygons, or the question of which file to use for which layer. Gerber file extensions are often .GBR, .GBX, .PHD, .SPL or .ART. Sometimes extensions such as .TOP and .BOT are used instead.

Some common XGerber extensions are:
*.GBL - Gerber Bottom Layer
*.GTL - Gerber Top Layer
*.GBS - Gerber Bottom Solder Resist
*.GTS - Gerber Top Solder Resist
*.GBO - Gerber Bottom Overlay
*.GTO - Gerber Top Overlay
*.GBP - Gerber Bottom Paste
*.GTP - Gerber Top Paste
*.GKO - Gerber Keep-Out Layer
*.GM1 - Gerber Mechanical 1
*.GM2 - Gerber Mechanical 2
*.GPT - Gerber Top Pad Master
*.GPB - Gerber Bottom Pad Master

Alternatives

Over the years there have been several attempts to replace Gerber by more powerful or more consistent formats. But none of these have (yet) been able to replace the dominance of Gerber:

* IPC-D-350 C "Printed Board Description in Digital Format"', 1989. This specification was standardized as IEC 61128 in 1992 and withdrawn in 2001
* "Dynamic Process Format", DPF Format Description, Version 5, 1998, Barco Graphics
* The "Electronic Design Interchange Format", EDIF
* ODB++ from Valor Computerized Systems Ltd, Israel
* GenCAM: IPC-2511A "Generic Requirements for Implementation of Product Manufacturing Description Data and Transfer Methodology", 2000
* GenCAM: IPC-2511B "Generic Requirements for Implementation of Product Manufacturing Description Data and Transfer XML Schema Methodology", 2002
* Offspring: IPC-2581 "Generic Requirements for Printed Board Assembly Products Manufacturing Description Data and Transfer Methodology", 2004
* STEP AP210: ISO 10303-210, Electronic assembly interconnect and packaging design", first edition 2001, second edition 2008 (to be published)

ee also

*G-code
*GDS II stream format
* [http://www.rulabinsky.com/cavd/text/chapa.html Computer Aids for VLSI Design - Appendix A: Gerber Format by Steven M. Rubin]

External links

* [http://www.artwork.com/gerber/appl2.htm D-codes, Apertures & Gerber Plot Files]
* [http://www.artwork.com/gerber/274x/rs274xrevd_e.pdf RS-274X Gerber format]
* [http://www.gerberscientific.com Gerber Scientific, Inc]
* [http://geda.seul.org/ gEDA] , open source (GPL) EDA suite including Gerber viewer.
* [http://gerbv.sourceforge.net/ gerbv] , open source (GPL) Gerber viewer. Part of gEDA.
* [http://www.lis.inpg.fr/realise_au_lis/kicad/ Kicad] , open source (GPL) CAD suite
* [http://www.graphicode.com/ GC-Prevue] , freeware, closed-source Gerber file viewer
* [http://www.softwarecompanions.com/ GerbView] , trialware, closed-source Gerber file viewer.
* [http://www.pentalogix.com/ Viewmate] , freeware, closed-source Gerber file viewer
* [http://www.circuitpeople.com/ CircuitPeople] , free web-based Gerber file viewer.
* [http://www.gerber-viewer.com/ Gerber Viewer Online] , multicolored online Gerber viewer.
* [http://www.numericalinnovations.com/ Fab-It] , trialware, closed-source Gerber file viewer.