Gerber-Format

The Gerber format is a standard file structure in ASCII format, which allows the exchange of data between CAD (development) and CAM ( production). It is especially in the area of electronic CAD programs (EDA - Electronic Design Automation) used to output the data layout on PCBs.

It was developed in 1980 by the company Gerber Scientific to control the Photoplotter this company. It became the de facto standard for PCB data exchange. Gerber Scientific was acquired in 1998 by Barco ETS, which published the RS- 274X Format User's Guide. This Extended Gerber or RS- 274X is the current standard.

All popular CAD programs allow export of design in Extended Gerber format, and all common CAM programs an import. The outdated standard Gerber (RS -274 -D) should not be exported. Several vendors also offer Extended Gerber viewer.

After various restructuring the Gerber format is now maintained by Ucamco NV. Ucamco published from time to time revised revisions; current J1 is the revision of the specification from the February 2014 that extends the Gerber file format attributes. The specification is available on the download page Ucamco freely available.

3.1 Using
3.2 Additional Data
3.3 Gerber file extensions

Construction

Each Gerber file always contains only one layer (fachsprachlich "Layer "). Is there a circuit board of several layers, for example, two layers for mapping the electrical connections in copper, two layers for the solder mask and a layer for the text printed on the circuit board, five different Gerber files are necessary in total.

Structure

The individual elements ( traces, pads, etc. ) of a circuit board can be positioned with xy coordinates. The coordinates can be specified in absolute or incremental values. As units of mm or inch are possible. The coordinates are expressed in whole numbers, for finer structures must be specified scaling. Leading or trailing zeros can be suppressed to save space. The basic structure of a Gerber file is:

The choice of the control function and the tool is via the D- Code List (also: aperture table ). The D- Code List describes the employed in a Gerber File graphical tools ( circles, rings, rectangles). It describes the assignment of all present in the Gerber data D codes to a geometric aperture shape and a mechanical aperture size. D1 to D3 are reserved codes; they do not denote a visor, but the switching on or off the light source of the photoplotters. Where:

D1: draw a line with the lights on. Note: this does not mean simply " light on", but rather " draw a line ", which is an important difference.
D2: light source
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 the control of NC machines in many industries. Note that the term RS -274- D is often used incorrectly ( without the " Gerber " addition), to refer to the Gerber subset rather than the original RS -274 -D. Standard Gerber is used to control vector photo plotters, which are actually 2D NC machines. It is a simple ASCII format consisting of commands and the 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 sixties and seventies to control numerical machine as vector photoplotters. These are all now been replaced by raster Photoplotter. An RS -274- D file is not an image description file itself. It contains no unit or aperture. These are standard forms, similar to a font for text processing, and should be manually set by Plotterbediener. They were written in a plain ASCII file, called aperture table or Aperturetabelle. The operator then fitted a circular disc with apertures, as described in the Table, which were rotated during the exposure of the film in the light beam. There is no standard for these tables, so each has its own formatting.

In order to represent shapes that can not be described with the limited aperture size, the coloring (vector -fill ) this form is used. Standard Gerber is well suited to the limited possibilities at the disposal a vector-oriented Photoplotter exploit. It was designed for manual operation and thus is not suitable for a fully automated data transfer between PCB designers and manufacturers.

The full file set for the description of a circuit board consists of the files of the individual layers, one or more files with a D- Code List and a file that describes the layer structure.

RS- 274X Gerber extended

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

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

An example of an RS- 274X file:

G04 Movie Name: paste_top * G04 Origin Date: Thu Sep 20, 2007 15:54:22 * G04 Layer: PIN / PASTEMASK_TOP * MOIN *% * % FSLAX26Y26 IPPOS % *% % ADD28R, .11 X.043 *% ADD39O %, .07 x .022 *% ... % AMMACRO19 * 21.1, .0512, .0512,0.0,0.0,45. *% ADD19MACRO19 % *% % LPD *% G75 * D10 * X17625170Y1175000D03 * Y1300000D03 * Y1637508D03 * ... D39 * X4962517Y1425000D02 * Y1375000D01 * Y1325000D01 * Y1275000D01 * M02 * An RS - 274X file contains the complete unambiguous description of a circuit board location. There are no extra files needed. Hide and operators are included, surfaces can be specified to be filled without need as RS-274 -D. Since it can be processed automatically, it is well suited for secure data transfer and reliable and automated workflows.

The specification is freely available and there is a tutorial.

Use

Gerber files are usually written by PCB Layout Electronic Design Automation ( EDA) or PCB CAD software. These files are sent to PCB manufacturers, where they are read into a CAM system to generate data for each production step. They are also used for bore holes, which can be seen as a drilling location; normally but a drilling format as Excellon is used. Gerber files are also used to control testing machines, as well as for automatic optical inspection.

The RS- 274X format does not describe which layer is displayed. Therefore, the position function should be included in the file name, the format of the file extension, for example ". Gbx " (Extended Gerber ). Some Entflechter use cryptic file names, which are documented in a separate file, or misuse the file extension, such as. " Ls " on the solder side.

Additional data

An RS - 274X file describes, inter alia, a copper layer or mask. However, PCB manufacturing and testing need even more information. RS- 274X may represent drilling data, usually but these are specified in IPC -NC -349 or Excellon format. RS- 274X can not contain netlist; if needed, it is usually depicted in IPC- D -356. Location names and material composition are normally included in text files or drawings. However Ucamco recommends using the use of a part of the IPC - 2581st Normally, all files are in a zip archive. This is then sent to PCB manufacturers.

Gerber file extensions

A Gerber file contains, for example, a copper layer, mask or silkscreen. Thus, a plurality of Gerber data is required for a circuit board. There is no naming convention for these files, but the extension usually used for Gerber RS- 274X, the extension " gbx. ": For Gerber RS -274 -D " gbr ".. The file name can include the function, for example Lage1.gbx or mask - top.gbx.

For historical reasons ( DOS 8.3 format) the file extensions used as a feature in some CAD packages ( Altium / Protel ). Thus inevitably arise over 50 different extensions. Today's operating systems usually have an extension to a file type. This mechanism works here but not.

Preferred file extension:

. GBX - function of the position in the file name

MS- DOS legacy file extensions:

GBL, SOL - solder side ( Gerber Bottom Layer)
GTL, CMP - component side ( Gerber Top Layer )
GBS, STS - solder resist mask for the bottom ( Gerber Bottom Solder resist)
GTS, STC - mask for solder mask above ( Gerber Top Solder resist)
GBO, PLS - Silkscreen below ( Gerber Bottom Overlay )
GTO, PLC - Silkscreen above ( Gerber Top Overlay )

GTP - ( Gerber Top Paste Mask)
GBP - ( Gerber Bottom Paste Mask)
GM1 - ( Gerber Mechanical Layer 1)
GM2 - ( Gerber Mechanical Layer 2), etc.
GDD - ( Gerber Drill Drawing )
GD1 - ( Gerber Drill Drawing, Top To Mid 1 )
GD2 - ( Gerber Drill Drawing, Mid 1 To Mid 2 ), etc.
GDG - ( Gerber Drill Guide)
GG1 - ( Gerber Drill Guide, Top To Mid 1 )
GG2 - ( Gerber Drill Guide, Mid 1 To Mid 2 ), etc.
GPT - ( Gerber Top Pad Master)
GPB - ( Gerber Bottom Pad Master)
GKO - ( Gerber Keepout )
PO1 - ( Gerber panels)
REP - (report file)
TXT - (ASCII NC Drill )
DRL - (EIA NC Drill )
DRR - (NC Drill Report)
Apr - ( Aperature File)

Computer-aided design Computer-aided manufacturing Physical design (electronics)

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