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    What Is a Gerber File in the PCB Fabrication Process?

    Altium Designer
    |  December 18, 2017

    Young women taking pictures of holiday lights

    Aside from the food, the sweaters, and the cheer, what is the most important part of a holiday party? Taking pictures, of course. So when I was getting ready for a holiday party, I retrieved my HD camera to get some better quality shots than what my phone might be able to give me. Though, as I pulled the camera out I realized just how long it’s been since I’ve used it. And just like any technology that you don’t use for a while, I had completely forgotten how to transfer image files to my computer.

    It didn’t take me long to remember the hidden USB port on the side, but it did bring up a funny thought: imagining someone involved in the world of PCB design, without being able to understand the back end of the process. All of those pads and traces in a CAD system will need to be turned into an actual printed board somehow. Just as I couldn’t remember how to access the pictures that I was going to take, I wonder how many people don’t understand what is involved in transferring Printed Board design data to a manufacturer.

    The most common way to get your design data to your manufacturer is through a file format called “Gerber.” Just like how you spend the first few hours of any holiday party reminiscing about the antics from last year’s, it’s best to go into the Gerber file with a little background knowledge. Having an idea for its history will enable you to have a better understanding of how it has grown and what its future may look like. After knowing its process and development, you’ll be best equipped to be the bridge to a manufacturer and design team.

    The Gerber File, the First Step of the PCB Fabrication Process

    When you design a printed board on a CAD system, you will see the metal of the board represented by different styles of lines and shapes. Somehow those graphical images need to be reformatted into data that the PCB manufacturer can use to create the board. This is the job of the Gerber file.

    What is Gerber Data?

    A Gerber file is an ASCII text file composed of four elements:

    1. Configuration parameters

    2. Aperture definitions

    3. XY coordinate locations for draw and flash commands

    4. Draw and flash command codes

    If you open up Gerber data in a text editor, you can read the ASCII data in the file and modify it on your own. Some manufacturers will do this by hand when correcting some design problems, and then they will check their changes with a Gerber viewer. If you use a Gerber viewer to recreate a board from your Gerber data, it might look something like this:

    Gerber data in a gerber viewer

    The exact view that you see depends on the viewer tool you use to recreate your board. Most PCB CAD systems have the ability to generate Gerber files from design data. The round pads of a thru-hole pin will be represented in a Gerber file by a flash command along with some location coordinates. A clock line trace will be represented by a draw command code along with a series of coordinate locations for each vertex of the trace.

    The reason for these command codes is that Gerber files were originally designed to drive a plotter that would create the layers of a Printed Circuit Board on film. This photoplotter would use light from a lamp or laser to expose film that would then be used to create the tooling needed by the PCB fabricator. The different codes would either flash the light, draw with the light, or move without the light. There were also codes to determine the size and shape of the light known as apertures. Although still widely used today, traditional photoplotters are beginning to be replaced by laser direct imaging (LDI) techniques where the Gerber information is imaged directly onto the circuit board materials.

    Laptop with blue file folders in it

    Gerber files get the data out of your CAD system and into the hands of the manufacturer

    The Gerber File Past, Present, and Future

    The original Gerber files were known as the RS-274-D format. Those early files were only made up of the XY coordinate locations and the draw & flash commands. As PCB designers, we had to manually assign aperture codes during the Gerber file creation process. Later on, we would then extract all the aperture data into a separate file along with the configuration parameters. You had to be diligent in assigning the correct codes in order to create accurate Gerber files.

    If you are creating Gerber files today from your CAD system, you probably are using the RS-274-X format. This version combines all four elements of the Gerber data (configuration parameters, apertures, XY coordinates, draw & flash commands) into one file. You will also notice that your CAD system will more than likely automatically assign aperture positions eliminating the chance for human input errors.

    Within the past few years, a new version of the Gerber format has become available that includes additional data. Gerber X2 files will include information such as the layer function of that file, object functions such as pad types, locations of impedance-controlled traces, and much more. The goal is to enhance the Gerber format to make it more like a database such as ODB++, while still having the legacy ability to drive photoplotters and LDI systems.

    Pile of PCBs

    Your Gerber files will be used to create bare PCBs like these

    What Does This Mean to You?

    The PCB designer, as well as all members of the PCB fabrication and design team, need to understand the needs of the manufacturer and create the Gerber and other output files accordingly. Some manufactures may still require separate aperture lists or other data files, and you need to know what those files do and how to create them. A lot of our design processes are automated these days, but it still is worth your time to have a better understanding of what is going on under-the-hood of your CAD system.

    One of the best things that you can do is to make sure that you are using the best CAD system available to design your board. Not only does it need to have state of the art place and route technologies, it also needs to be able to create your Gerber and other output files easily and without error in the latest formats.

    Altium Designer® is PCB Design Software that has standard Gerber RS-274-X and the new Gerber X2 already built into it. This will help you to deliver a design to your manufacturer that will work with whichever imaging system that they are using.

    Would you like to find out more about how Altium can help you to create these next generation output files? Talk to an expert at Altium.

     

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    About Author

    PCB Design Tools for Electronics Design and DFM. Information for EDA Leaders.

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