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Forget Gerbers; Intelligent CAD Files are Better for PCB Assembly

The Gerber file format was first defined in 1980 for vector photoplotters. As the use of computer aided manufacturing (CAM) for printed circuit board (PCB) fabrication grew during the eighties, the Gerber file format was adopted by most manufacturers as the de facto standard for CAD-to-CAM data exchange. In the nearly 40 years since it was first defined, the Gerber file format has evolved and improved some, but newer formats exist that are far superior. It’s time for the industry to take a leap forward and leave Gerbers behind.

 

What are Gerber files?

Gerbers are actually a package of individual files, one for each layer of the PCB.  Each file defines a two-dimensional image of that layer of the design.  Because the format was originally designed for photoplotters, the files actually contain instructions, in ASCII, for a machine to “plot” the required image.  There are usually many files for even simple designs – one for each copper layer, plus files for solder mask, paste mask, silkscreens, etc.  The unnecessary complexity of multiple “dumb” files is one of the drawbacks of Gerber files.  Other drawbacks of Gerbers are that they lack of 3D information such as hole definitions and they are not human readable so they are difficult to review.  For the level of difficulty they present, Gerbers offer few benefits compared to modern file formats. 

 

What are intelligent CAD files, and why are they better?

Modern electronic design automation (EDA) or computer aided design (CAD) tools used to draw schematics and layout PCB boards can all output Gerber files, but they can also all output much more intelligent design databases.  The most common of these today is the ODB++ format, though IPC-2581 and a few other formats are also used by some software packages.  These files are more intelligent than Gerbers, while being structured more simply.  ODB++ files, for example, include all design information is in one file, including fabrication, component, and assembly information.  They also contain electrical connectivity information, net names, and reference designators.  All of this information is invaluable to your PCB assembly house.

 

Intelligent CAD files are easier to understand Because they contain net names and component reference designators, intelligent CAD files enable assembly engineers and technicians to understand the intent of the design, not just where copper should go.
Intelligent CAD files are easier to review Because they are easier to understand, engineers and assemblers are able to more easily, quickly, and thoroughly review intelligent CAD files.  Automated design for assembly reviews also use these files.
Intelligent CAD files are easier to build to Because they are easier to understand and review, they are easier to build with.  The assembly house has all the information they need in an easily accessible format to identify, locate, and place every component.
Intelligent CAD files are easier to debug with Intelligent CAD files allow the assembly house to debug failures on assembled PCBAs much more efficiently.  Quick and easy access to the design intent contained in these files greatly reduces time and cost.

 

Why are Gerber files still used?

You may be wondering why the 40-year old Gerber format is still used if newer, better, file formats exist.  A catch-22 exists. Because all PCB fabricators accept Gerber files, all CAD software packages support exporting the design database in that format… and because all CAD software packages support exporting the design database as Gerber files, all PCB fabricators have traditionally continued to accept the format.  But that is finally starting to change, as more assembly manufacturers are requiring intelligent CAD files.


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