Gerber format

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Gerber File Format
GbrX2 128x128 white bg.png
File extension : .gbr
Developed by: Gerber Scientific,
now Ucamco
Initial release: 1980
Current version: The Gerber Format Specification
Revision 2018.11 (as of June 2019)
Standard (s) : Ucamco downloads
Website : Reference Gerber Viewer


The Gerber format is a standard file structure in ASCII format, which enables data exchange between CAD (development) and CAM (production). It is mainly used in the area of ​​electronic CAD programs (EDA - Electronic Design Automation ) to output the layout data for printed circuit boards .

It was developed in 1980 by Gerber Scientific to control their photo plotters. It became the quasi-standard for circuit board data. Gerber Scientific was acquired by Barco ETS in 1998, which published the RS-274X Format User's Guide . This Extended Gerber or RS-274X is today's standard.

All common CAD programs allow the design to be exported in Extended Gerber format and all common CAM programs allow an import. The old standard Gerber (RS-274-D) is hardly used today. Various providers also offer Extended Gerber Viewers.

After various restructuring, the Gerber format has been maintained by Ucamco NV since 2007. Ucamco publishes revisions to the Gerber format specification from time to time; the current revision is 2018.11 from November 2018.

So far there are three major stages of development in Gerber format:

  • Gerber RS-274-D (Obsolete)
  • Gerber RS-274-X
  • Gerber X2, a compatible extension to RS-274-X

A file in Gerber Job Format can be used for the purpose of clear transmission of circuit board metadata (e.g. mask color, material, IPC standard, etc.). For this purpose, Ucamco provides the format description and a free editor.

construction

Each Gerber file always contains only one layer (technically "layer"). If a circuit board consists of several layers, e.g. For example, two layers for mapping the electrical connections in copper, two layers for the solder mask and one layer for printing text on the circuit board, five different Gerber files are required in total.

Four layers in Gerber format

structure

The individual elements (conductor tracks, pads, etc.) of a circuit board are positioned with xy coordinates. The coordinates can be given in absolute or incremental values. The units can be mm or inches . The coordinates are given in whole numbers; a scaling must be given for finer structures. Leading or trailing zeros can be suppressed to save storage space. The basic structure of a Gerber file is: 

 Format description (absolute or incremental, suppression of zeros)
 Unit description (mm / inch, scaling)
 Plot instructions
  1st block
  | Tool | X, Y coordinate | Control functions | End of block |
  2nd block
  | Tool | X, Y coordinate | Control functions | End of block |
 etc…

D code list

The control function and the tool are selected using the D code list (also known as the aperture table). The D code list describes the graphic tools used in a Gerber file (circles, circular rings, rectangles). It describes the assignment of all D codes in the Gerber data to a geometric aperture shape and a mechanical aperture size. D1 through D3 are reserved codes; they do not designate a shutter, but rather the switching on and off of the light source of the photoplotter. There are:

  • D1: draw a line with the light on. Warning: this does not just mean “light on”, but rather “draw a line”, which is an important difference.
  • D2: light source off
  • D3: light pulse ( flash )

RS-274-D standard Gerber

Standard Gerber has been replaced by Extended Gerber RS-274X. It describes a subset of the Electronic Industries Association RS-274-D Specification, a format for controlling NC machines in many industries. The term RS-274-D is often used incorrectly (without the “Gerber” suffix) to refer to the Gerber subset rather than the original RS-274-D. Standard Gerber is used to control vector photoplotters, which are actually 2D NC machines. It is a simple ASCII format consisting of commands and X and Y coordinates. An example of a Gerber RS-274-D file: 

 D11 *
 X1785250Y2173980D02 *
 X1796650Y2177730D01 *
 X1785250Y2181480D01 *
 X1796650Y2184580D01 *
 D12 *
 X3421095Y1407208D03 *
 X3422388Y1406150D03 *
 M02 *

RS-274-D was designed in the 1960s and 70s to control numerical machines such as vector photo plotters. These have now been replaced by raster photo plotters. An RS-274-D file is not an image description file in and of itself. It does not contain any unit or bezels . These are standard forms, similar to a font for word processing, and should be set manually by the plotter operator. They were written in an unformatted ASCII file, called an aperture table or aperture table . The operator then fitted a circular disk with openings, as described in the table, which were rotated into the light beam during the exposure of the film. There is no standard for these tables, so each has its own formatting.

In order to represent shapes that cannot be described with the limited amount of aperture, the coloring (vector-fill) of this shape is used. Standard Gerber is well suited to take advantage of the limited capabilities available to a vector-oriented photoplotter. It was designed for manual operation and is therefore not suitable for a completely automated data transfer between circuit board designer and manufacturer.

The complete set of files for describing a circuit board consists of the files for the individual layers, one or more files with a D-code list and a file that describes the layer structure.

RS-274X Extended Gerber

The RS-274X Gerber format, also known as Extended Gerber or X-Gerber, is a 2D bi-level vector-oriented image description format. It is an extension of the RS-274-D standard Gerber format, which in turn is a subset of the EIA RS-274-D format.

It is written in ASCII text and consists of a series of commands and coordinates. The basic functions are " Draw line" ( Draw ) and " Draw point" ( Flash ) with predefined shapes at a certain position and the filling of a contour. Positive and negative objects can be combined.

An example of an RS-274X file: 

 G04 Shorter version of Gerber X2 Example Job 1, created by Filip Vermeire, Ucamco*
 %TF.FileFunction,Copper,L4*%
 %TF.Part,Single*%
 %FSLAX35Y35*%
 %MOMM*%
 %TA.AperFunction,Conductor*%
 %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*

An RS-274X file contains the complete, unambiguous description of a printed circuit board layer. No additional files are required. Apertures and operators are included, areas can be specified without having to be filled, as in RS-274-D. Since it can be processed automatically, it is well suited for secure data transfer and reliable and automated work processes.

use

Gerber files are typically written by PCB layout Electronic Design Automation (EDA) or PCB CAD software. These files are sent to the circuit board manufacturers, where they are read into a CAM system in order to generate data for each production step. They are also used for drilled holes, which can be seen as drill locations; however, a drilling format such as Excellon is normally used. Gerber files are also used to control testing machines and for automatic optical inspection.

The RS-274X format does not describe which position is represented. Therefore, the layer function should be included in the file name, which is the format of the file extension .gbr. Some disentanglers use cryptic filenames, which are documented in a separate file, or misuse the file extension, e.g. B. .lsfor the solder side.

additional data

An RS-274X file describes, among other things, A. a layer of copper or a mask. However, PCB manufacturing and testing require more information. RS-274X can display drilling data, but these are usually specified in IPC-NC-349 or Excellon format. RS-274X cannot contain a netlist ; if required, this is usually shown in IPC-D-356. Layer names and material composition are usually supplied in text files or drawings. However, Ucamco recommends using part of the IPC-2581 for this. Normally, all files are combined in a zip archive. This is then sent to the circuit board manufacturer.

Gerber file extensions

A Gerber file contains, for example, a copper layer, mask or assembly print. This means that several Gerber files are required for one circuit board. There is no naming convention for these files, but the preferred file extension is .gbr . The file name can contain the function, for example Lage1.gbr or Mask-top.gbr . The extension .gbx is also used for Gerber RS-274X (Extended Gerber).

For historical reasons ( DOS , 8.3 format), the file extensions are used as a function in some CAD packages (Altium / Protel). This results in over 50 different extensions. A list can be found at Altium. Today's operating systems usually assign a file type to an extension. However, this mechanism does not work here.

Gerber X2

In revision J4 new commands for the use of attributes have been introduced. The attributes can relate to the file level, aperture level or object level.

Among other things, there are predefined attributes for:

  • Layer position within the structure of the circuit board: z. B. "Soldermask on Top".
  • Function of the individual objects and apertures: e.g. B. "Copper pad for SMD component"
  • Netlist and component information

The complete list of attributes is described in the freely available specification and instructions for use are provided.

See also

Web links

Individual evidence

  1. ↑ The Gerber Job Format Specification ( English , PDF) Ucamco. Retrieved July 3, 2019.
  2. ↑ Gerber Job EditorFAQ ( English , PDF) Ucamco. Retrieved July 3, 2019.
  3. ↑ EIA Standard RS-274-D Interchangeable Variable Block Data Format for Positioning, Contouring, and Contouring / Positioning Numerically Controlled Machines . Electronic Industries Association, Engineering Department, Washington, DC February 1979.
  4. ^ A b Steve DiBartolomeo: D-codes, Apertures and Gerber Files. Artwork Conversion Software, Inc., 1991, accessed October 16, 2011 .
  5. ↑ a b c RS-274X Gerber Format Specification. Ucamco, December 2016, accessed November 28, 2016 .
  6. ^ Ian Robertson Sinclair, John Dunton: Practical electronics handbook . 6th edition. Elsevier, Amsterdam / Boston 2007, ISBN 978-0-7506-8071-4 , pp. 543 .
  7. ↑ PCB layout data. (No longer available online.) Eurocircuits, archived from the original on December 6, 2011 ; Retrieved November 26, 2011 .
  8. ↑ a b Karel Tavernier: Improving CAD to CAM Data Transfer: A Practical Approach. (PDF; 93 kB) In: Journal of the HKPCA. No. 40/2011 / 2Q. 2011, accessed October 2, 2011 : "RS-274-D: Do not use it."
  9. ↑ Using IPC-D-356 for Importing Net and Node. Retrieved October 16, 2011 .
  10. ↑ IPC-2524 PWB Fabrication Data Quality Rating System, February 1999
  11. ^ Altium Gerber Output Options. (PDF) Retrieved January 9, 2015 .
  12. ↑ Steve DiBartolomeo: What's all this about RS274X Anyway? Artwork Conversion Software, Inc., 1995, accessed November 3, 2011 .