Gerber format

Gerber file format
Filename extension .gbr
Developed by Gerber Systems Corp.,
now Ucamco
Initial release August 27, 1980
Latest release
Extended Gerber
RS-274X Rev J4
(13 November 2014)
Type of format Image file format
Standard Ucamco Downloads

The Gerber format is an open 2D bi-level vector image file format.[1] It is the de facto standard used by printed circuit board (PCB) industry software to describe the printed circuit board images: copper layers, solder mask, legend, etc.[2][3][4]

The standard file extension is .GBR or .gbr[1] though other extensions are also used.

There are two major generations of Gerber format:

Usage

Gerber is the standard input format for photoplotters in PCB fabrication and all other fabrication equipment that needs digital images, such as legend printers, direct imagers or automated optical inspection (AOI) machines or for viewing reference data in different departments.

Gerber files also contains a 'stencil' layer for solder paste and the central locations of components to allow the PCB assembler to create the stencil and place and bond the components.

PCB fabrication data

A third usage of Gerber is in PCB fabrication data.[8] PCBs are designed on a specialized electronic design automation (EDA) or a computer-aided design (CAD) system.[9] The CAD systems output a Gerber file for each image layer (copper layers, solder mask, legend or silk...). Drilled hole information is also transferred in Gerber but for historic reasons the Excellon format is often used. (Using Excellon rather than Gerber usually leads to copper-drill registration problems.[8]) Typically, all these files are "zipped" into a single archive that is sent to the PCB bare board fabrication shop. The fabricator loads them into a computer-aided manufacturing (CAM) system to prepare data for each step of the PCB production process. [10][11] [12]

Each layer in the PCB must be linked with a Gerber file in the fabrication data. In Gerber version 2 the .FileFunction attribute provides a standardized method to do this.[1] In legacy files only informal methods are available. A straightforward informal method is to express the file function clearly in the file name. Sometimes, however, cryptic file names are used and then documented in a free-format text file. Sometimes even the file extension is abused to indicate the file function - e.g. .BOT for the bottom layer rather than the standard extension .GBR ; very unpractical as the format of the file can no longer be deducted from the extension. [6][13][14]

PCB Fabrication Data must comply with a number of rules: all layers must be aligned, a profile layer must be included, etc.

A Gerber file cannot represent the netlist; the netlist is usually specified in the IPC-D-356 format.[15]

The material stack up, components and finishes are typically provided in informal text files or drawings.[16] Ucamco recommends using a subset of IPC-2581 for this non-image information.[6][17]

Extended Gerber

The Gerber format, also known as RS-274X, extended Gerber or X-Gerber, is a 2D bi-level vector image description format.[1]

It is a human readable ASCII format.[18] It consists of a stream of commands generating an ordered stream of graphics objects. The graphics objects can be positive or negative. Superimposed in the correct order they create the final image.

A Gerber file contains the complete description of a PCB layer image without requiring any external files. It has all the imaging operators needed for a PCB image. Any aperture shape can be defined. Planes and pads can be specified without the need to paint or vector-fill as in Standard Gerber. (However painting is sometimes still used because implementations created for Standard Gerber and have not yet been upgraded to use the more powerful capabilities of Extended Gerber.)[19]

In February 2014 Ucamco extended the Gerber format with attributes (Gerber version 2). Attributes add meta-information to a Gerber file. These are akin to labels providing information associated with image files, or features within them. Examples of meta-information conveyed by attributes are:

For more information see the version 2 FAQ or intro video in the external links. [20] [1] [21] [22] [23]

Gerber is a complete, powerful and unambiguous standard to describe a PCB layer. It can be input and processed fully automatically. This makes it well suited for fast and secure data transfer and for reliable and automated workflows.

An example of a Gerber file:

G04 Short version a file taken from the Example Job 1, created by Filip Vermeire, Ucamco*
%TF.FileFunction,Copper,Bot,L4*%
%TF.Part,Single*%
%FSLAX35Y35*%
%MOMM*%
%TA.AperFunction,Conductor,NotC*%
%ADD10C,0.15000*%
%TA.AperFunction,ViaPad*%
%ADD11C,0.75000*%
%TA.AperFunction,ComponentPad*%
%ADD12C,1.60000*%
%ADD13C,1.70000*%
%SRX1Y1I0.00000J0.00000*%
G01*
G75*
%LPD*%
D10*
X7664999Y3689998D02*
X8394995D01*
X8439999Y3734999D01*
X9369999D01*
D11*
X7664999Y3689998D03*
X8359999Y1874998D03*
X9882998Y3650498D03*
D12*
X4602988Y7841488D03*
D13*
X10729976Y2062988D03*
X10983976D03*
X11237976D03*
M02*

The format specification is published.[1]

Standard Gerber

Standard Gerber was an NC format designed by Gerber Systems Corp to drive their vector photo plotters for the PCB industry in the 1960s and 1970s. As Gerber was the market leader its format became a de-facto standard.

Standard Gerber has been deprecated and declared obsolete. It no longer conforms to the Gerber format specification.[6][7] Standard was designed for a manual workflow. It is not suitable for automated data transfer between PCB designers and manufacturers. Vector photo plotters are replaced by raster photoplotters. Standard Gerber is superseded by extended Gerber.

Standard Gerber was a subset of the Electronic Industries Association RS-274-D specification,[24] a format to drive mechanical NC machines in a wide range of industries. The term RS-274-D, without the qualifying "Gerber" postfix, is sometimes used informally for the standard Gerber subset rather than full RS-274-D.

RS-274-D standard Gerber was a simple ASCII format consisting of commands and XY coordinates.[25] An example:

D11*
X1785250Y2173980D02*
X1796650Y2177730D01*
X1785250Y2181480D01*
X1796650Y2184580D01*
D12*
X3421095Y1407208D03*
X1785250Y2173980D03*
M02*

A Standard Gerber file on its own is not an image description because it does not contain all information: the coordinate unit and the definitions of the apertures are not defined in the RS-274-D file. (Apertures are the basic shapes, similar to fonts in a PDF file.) The coordinate units set manually by the operator of the plotter. They were described in a free-format text file, called an aperture file or a wheel file, intended for human reading. It was called a wheel file because the apertures were mounted on a rotating wheel and the operator defined the apertures by selecting a wheel and mounting it on the plotter. There are no standards for wheel files. The designer and the plotter operator had to agree on these case-by-case. Therefore standard Gerber is an NC standard but not an image definition standard.[1][25]

Standard Gerber supports only imaging operators to draw tracks and flash aperture as vector plotters were only capable of these operations. The only way to create large copper pours is to paint (aka stroke or vector-fill) them with a vast number or tracks. This creates very large files that take long time to process. Because of the difficulty and cost of creating apertures with all but the simplest and most standard shapes painting was also used to create all but the simplest pads. Painting creates the desired image but the original shape of the copper pour or pad and must be laboriously recovered in CAM.[8][19][26][27]

History

The Gerber file format was originally developed by the Gerber Systems Corp., a division of Gerber Scientific, founded by Joseph Gerber.[28] The Gerber file format is now owned by Ucamco through its acquisition of Barco ETS, a company that previously acquired Gerber Systems Corp.[10][29] The specification can be freely downloaded.[1]

Related formats

Over the years there have been several attempts to replace Gerber by formats containing more information than just the layer image, e.g. netlist or component information.[10] None of these attempts have been widely accepted within the electronics manufacturing industry, probably because the formats are complex.[6] Gerber remains the most widely used data transfer format.[2][3][4]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 "Gerber File Format Specification Rev. J2". Ucamco. June 2014. Retrieved 6 July 2014.
  2. ↑ 2.0 2.1 Williams, Al (2004). Build your own printed circuit board. McGraw-Hill Professional. p. 121. ISBN 978-0-07-142783-8. Retrieved April 2, 2011.
  3. ↑ 3.0 3.1 Schroeder, Chris (1998). Printed circuit board design using AutoCAD. Newnes. p. 283. ISBN 978-0-7506-9834-4. Retrieved April 2, 2011.
  4. ↑ 4.0 4.1 Blackwell, Glenn R. (2000). The electronic packaging handbook. 5.18: CRC Press. ISBN 978-0-8493-8591-9. Retrieved April 2, 2011.
  5. ↑ 5.0 5.1 "Ucamco Offers Latest Gerber Format Specification". ucamco.com. February 19, 2013. Retrieved February 15, 2013.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Tavernier, Karel (2011). "Improving CAD to CAM Data Transfer: A Practical Approach" (PDF). Journal of the HKPCA (40, 2Q). Retrieved 2 October 2011. Use of RS-274-D: Do not use it.
  7. ↑ 7.0 7.1 Tavernier, Karel. "Open Letter on Standard Gerber". Ucamco. Ucamco. Retrieved 7 July 2014.
  8. ↑ 8.0 8.1 8.2 Tavernier, Karel. "PCB Fabrication Data - A Guide". Ucamco. Retrieved 8 January 2015.
  9. ↑ "EDA: Where Electronics Begins". edac.org. Electronic Design Automation Consortium. Retrieved December 18, 2011.
  10. ↑ 10.0 10.1 10.2 Buetow, Mike (28 June 2011). "A Short History of Electronic Data Formats". Printed Circuit Design and Fab magazine. Retrieved December 18, 2011.
  11. ↑ "PCBexpress Printed Circuit Board Tutorial". PCBexpress.com. Retrieved December 18, 2011.
  12. ↑ "PCB Layout Data". Eurocircuits. Retrieved 26 November 2011.
  13. ↑ http://daycounter.com/LabBook/Protel-Layer-File-Extensions.phtml
  14. ↑ http://techdocs.altium.com
  15. ↑ "Using IPC-D-356 for Importing Net and Node". Retrieved 16 October 2011.
  16. ↑ IPC-2524 PWB Fabrication Data Quality Rating System, February 1999.
  17. ↑ Tavernier, Karel (January 2013). "IPC-2581 meets Gerber". PCB Design Magazine (January 2013). Retrieved 19 February 2013.
  18. ↑ Sinclair, Ian Robertson; Dunton, John (January 11, 2007). Practical electronics handbook. Elsevier. p. 543. ISBN 978-0-7506-8071-4. Retrieved April 2, 2011.
  19. ↑ 19.0 19.1 "RS-274X Painting Considered Harmful.pdf". Ucamco. June 2011. Retrieved 5 March 2012.
  20. ↑ "Gerber version 2 intro movie". Ucamco. Retrieved 20 November 2014.
  21. ↑ 21.0 21.1 21.2 Tavernier, Karel. "A proposal to extend the Gerber format with attributes". Ucamco. Ucamco. Retrieved 12 July 2013.
  22. ↑ "Gerber X2: New Paradigm in CAD-to-CAM Communication". Ucamco. PCB007. Retrieved 13 June 2014.
  23. ↑ "Gerber version 2 FAQ" (PDF). ucamco. Ucamco. Retrieved 21 December 2014.
  24. ↑ EIA Standard RS-274-D Interchangeable Variable Block Data Format for Positioning, Contouring, and Contouroring/Positioning Numerically Controlled Machines. Electronic Industries Association, Engineering Department, 2001 Eye Street, NW, Washington, D.C. 200006. February 1979.
  25. ↑ 25.0 25.1 DiBartolomeo, Steve (1991). "D-codes, Apertures and Gerber Files". Artwork Conversion Software, Inc. Retrieved 16 October 2011.
  26. ↑ Tavernier, Karel (November 2013). "Painting Pads". PCB Design Magazine (November 2013). Retrieved 23 November 2013.
  27. ↑ "PCB Layout Data". Eurocircuits. Retrieved 26 November 2011.
  28. ↑ "Gerber Scientific Instrument Company Records, 1911-1998".
  29. ↑ Tanghe, Jean-Pierre. "Barco acquires Gerber Systems Corp". Barco.com. Barco NV. Retrieved 26 November 2011.
  30. ↑ Google book entry on Gerber format: a subset of EIA RS-274-D ; plot data format reference book.
  31. ↑ Coombs, Clyde F. (September 2, 2007). Printed circuits handbook. McGraw-Hill Professional. p. 18.11. ISBN 978-0-07-146734-6. Retrieved April 3, 2011.
  32. ↑ "Ucamco announce a revision of the industry standard RS-274X Format Specification". ucamco.com. December 9, 2010. Retrieved February 15, 2013.
  33. ↑ "New Gerber Format Specification free at www.ucamco.com". ucamco.com. January 27, 2012. Retrieved February 15, 2013.
  34. ↑ "Ucamco's Revised Gerber Format Specification Now Online". ucamco.com. February 19, 2013. Retrieved February 15, 2013.
  35. ↑ "Ucamco Enhances Gerber File Format Specification". ucamco.com. November 22, 2013. Retrieved November 22, 2013.
  36. ↑ Santarini, Mike (2002-01-22). "ODB++ spec tapped for CAD-to-CAM data exchange". EE Times. Retrieved 29 September 2011.
  37. ↑ IPC-2581 Panel: A Spirited Discussion on PCB Data Transfer Formats, Richard Goering, Cadence Design Systems blog, October 2, 2011
  38. ↑ "JPCA Standards".

External links