Don't Trust Your Gerber Files

03 June, 2012

By Simon Garrison, Numerical Innovations

WARNING: The Gerber files exported from your PCB Layout software may be Incorrect!  Your Design may already be compromised and contain hundreds of hidden mistakes before it ever reaches manufacturing.

 

 What are Gerber files?

For the past 30 years, Gerber 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 essentially 4 flavors of Gerber data: RS-274D, RS-274X, Fire9000, and the new X2 format.

Sample screen capture of Gerber data inside FAB 3000 software.

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 photo-plotter. Virtually every PCB CAD system generates Gerber data because all photo-plotters 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.

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)

Many gerber software tools have a hard time loading, & rendering gerber files attributes properly (ie. rounded paths, custom flashes, composite layers, and step/repeat). When loading gerber files, make sure to use a commercial quality tool (with thousands of hours invested refining & perfecting the gerber import process) to ensure your gerber data files load successfully.

 

 Protect Yourself Against Common Gerber File Mistakes

Let's compare the benefits between using a Gerber Viewer and CAM Software to protect yourself against common Gerber file mistakes.

 Gerber Viewer:  

Almost every PCB designer has used a Gerber viewer before to look for problems in their Gerber files before sending them out... but unless you have eyes like a hawk, simply staring at Gerber files inside a Gerber viewer (especially with hundreds of signals & drilled holes) is just an invitation for mistakes. It may have been understandable in the past for a designer to rely solely on a Gerber viewer but nowadays in these competitive economic times you can't afford to just stare at Gerber files and assume everything will be okay. Using a Gerber Viewer is at best an average solution, and prone to mistakes.

 CAM Software:  

CAM Software is to Gerber files what Print Preview is to Word Processor documents. Just as you wouldn't think of printing (or publishing) your documents without previewing them first, the exact same should be held true with your Gerber files.  CAM Software automates all Gerber file checks to ensure your PCB design integrity.  Should any mistakes be detected, reports can be generated making it easy to go back to your original PCB layout and correct any problems.  Using CAM Software will protect you from unknown mistakes hidden in your Gerber files, improve yields, lower manufacturing costs, and increase your time to market.

Every Year PCB Designers waste over $30 Million (USD) on failures & repairs that could have been prevented with CAM Software. That averages to $500 (USD) lost each year per PCB designer!

Avoid the Mistakes When there are shorts, weak track/pad connections, wrong part footprint used, silkscreen over mask openings, etc.
Avoid the Frustration When PCB boards comes back wrong or they fail out in the field.
Avoid the Embarrassment When projects are delayed and thousands of dollars are wasted.

  

 

Buy Numerical Cloud for only $75/month.  Includes FAB 3000 (CAM Software) on up to 3 computers. Easily perform all Design Integrity Checks on your Gerber and ODB++ files. No contracts and cancel anytime.

 

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