Gerber vs. CAD: PCB File Formats Demystified

February 27, 2019 Cadence PCB Solutions

 

 

Today’s PCBs can be quite complex, there are multiple layers of traces, vias, and components that must fit together with a high degree of precision. One small error can turn a PCB into an inert slab of fiberglass and metal. Which is why it’s important that the machines in a fabrication house are able to follow the instructions laid out in your designs.

PCB file formats may not be the most exciting part of PCB design, but they play a critical role in communicating how your designs will be brought to life at a fabrication house. In this post we’ll cover the basics behind two of the most popular file formats you’ll encounter: Gerber vs. CAD.

What is a Gerber file?

Gerber is the standard file format of the PCB industry. It’s a 2-D ASCII file format that was originally designed for the now deprecated photoplotters which used to be mainstays of the PCB manufacturing process.

 

Like the electronics world equivalent of a PDF, Gerbers are treated as image files representing each manufacturing layer of a PCB. As a result, a typical PCB build can easily span ten files:

  1. Copper conductor (top)

  2. Copper conductor (bottom)

  3. Solder mask (top)

  4. Solder mask (bottom)

  5. Silkscreen (top)

  6. Silkscreen (bottom)

  7. Plated through holes (PTH)

  8. Non-plated through holes (NPTH)

  9. Board outline with machining operations (including cutouts, scoring, etc.)

  10. README file with the name and details for other files.

As you might imagine, keeping track of all those dimensions and tolerances across multiple files can be a lot of work, especially when you have little margin for error. It’s not unusual for Gerber files to make a few rounds between manufacturer and designer before a design can be manufactured.

That said, modern design software in conjunction with the newer backwards-compatible Gerber X2 file format somewhat mitigate the issue of Gerber data transcription errors that plagued designers of the past.

What is a CAD file in the context of PCB design?

We don’t need to tell you what a CAD file is, as you’ve likely worked with the files generated by CAD programs countless times in the past. While the file format extensions differ from software to software, the concept remains the same. A single file that contains all the information on how a PCB can be assembled.

The current standard for CAD files is ODB++, a proprietary CAD-to-CAM data exchange format. There is also an open-source standard called IPC-2581, and this ubiquity is its greatest advantage.

Modern manufacturing equipment can easily read a single CAD file and perform the appropriate operations to build a PCB. Eliminating the need to track multiple files simplifies things for both designer and manufacturer, reducing error rates.

More importantly, CAD files are more comprehensive than Gerber files, and can even contain useful information not found in Gerber files, such as electrical data, silkscreen color schemes, machine agnostic drilling information, and material specs.

Choose the file format that’s right for your needs

Since Gerbers have been the de facto file format of choice for most of the history of the electronics industry, virtually all PCB manufacturers support the file format, and this ubiquity is its greatest advantage. That said, the advantage of holding all your design data in a single file is hard to ignore. So how do you choose the right file format for your needs?

A good rule of thumb is to go by your preferred fabrication house. If the manufacturer you wish to work with doesn’t support CAD, it doesn’t make sense to let that stop you from working with them. Modern PCB software will perform a DFM check before breaking up your design into multiple Gerbers, which should mitigate many of the concerns with working with the older file format.

On the other hand, the CAD file format is truly comprehensive, and can streamline communications between designer and manufacturer. If your design is particularly complex, a modern fabrication house will know what to do with your single CAD file, and can take full advantage of the extra information included in the data.

Cadence PCB design software supports both Gerbers and CAD files to give you the freedom to use the fabrication house that best serves your needs.

 

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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