Friday, June 25, 2010

What is Gerber data?

For the past 30 years, Gerber data has been the de-facto standard file format used to manufacture all PCB’s (printed circuit boards). The Gerber format itself is simply an ASCII text file containing X,Y coordinates, and shapes (i.e apertures/dcodes). There are essientially 4 flavors of Gerber data: RS-274D, RS-274X, Fire9000, and BarcoDPF.

(Sample screen capture of Gerber data inside FAB 3000.)

Gerber data is a simple, generic means of transferring printed circuit board information to a wide variety of devices that convert the electronic PCB data to artwork produced by a photoplotter. Virtually every PCB CAD system generates Gerber data because all photoplotters read it. It is a file structure consisting of X,Y coordinates supplemented by commands that define where the PCB image starts, what shape it will take, and where it ends. In addition to the coordinates, Gerber data contains aperture information, which defines the shapes and sizes of lines, holes, and other features.

Gerber RS-274X: Extended Gerber Format, which is also called RS-274X, provides enhancements that handle polygon fill codes, positive/negative image compositing, and custom apertures, and other features. RS-274X also encapsulates the aperture list in the header of the Gerber data file and therefore allows files to pass from one system to another without the need to re-input the aperture table. RS-274X produces a variety of Gerber data called X data.

The Problem - Gerber files can be Difficult to Handle: Gerber data is unique in the fact that each file usually represents a single layer, something different from most other EDA formats that may contain multiple layers & designs/blocks all inside a single file. Many Gerber files are not written to specification; Thus many "unwritten rules" must be made to properly load in these files to the authors intention. For more information about these problems read the article: Don't trust your Gerbers.

Here is a list of some common difficulties found inside Gerber files: Transcoding of apertures - when multiple gerber files define the same aperture dcode, but require different shapes, Handle complex custom aperture definitions. Handle 'user-defined' custom aperture macros ($). Circular Interpolation: Arcs (G75), & Quadrant Arcs(G74) Poly-Fill routines(G36,G37) Support composite merging(LPD/LPC) Photo Expose mode (G55) Step/repeat codes(SR) Offsets(OF),Units(G70,G71),Mirror(MI) Zero Suppression with leading or trailing zeros. Format type: Incremental(G91)

Choosing the right Gerber Editor/Viewer. Gerber data may seem like a simple format to comprehend, however "in the real world" almost every PCB layout software tool outputs gerber data with their own unique set of rules (in many cases these gerber files are invalid). For success in manufacturing, the Gerber tool must interpret what the "PCB layout software" meant and correctly display all geometries.

Also, many gerber software tools found on the internet are not complete, and have a hard time loading & viewing complex gerber files properly; some common mistakes involve the display of custom flashes, composite layers, large polygons, step/repeat, rounded/square paths, and more.

It takes thousands of hours testing, refining, & perfecting the gerber import process to ensure that a gerber software tool will successfully load all types of gerber data files (no matter where they originated or what tool has generated them). Make sure to choose a software vendor with an established gerber viewer, who constantly makes updates to their gerber software (because the gerber format is always evolving). Remember a free Gerber Viewers is not always free, and one mistake can cost thousands of dollars. If you work with gerber data you are better served investing in a professional gerber solution.

1 comment:

  1. Hello, have you try ViewMate Deluxe? or any of the pentalogix gerber solutions?

    What do you think about those software?