Gerber Files for printed circuit boards (PCB) are the set of instructions that are used to manufacture electrical engineering PCB designs. After a PCB is designed, your contract manufacturer must be given these files in order to accurately build your boards to spec. Having errors in these files may lead to faulty boards and wasted budget. Therefore, all documentation must be complete and accurate.
To help you to be better positioned for success, here’s a look at what exactly Gerber files are and how they’re used in the manufacturing of your circuit board.
Gerber Files Explained: What Is a Gerber File?
Gerber files are created through PCB design software and are open ASCII vector format files. These files contain information on each physical board layer of your PCB design. The components of a circuit board like copper traces, vias, pads, solder mask and silkscreen, are all represented by a flash or draw code, and defined by a series of vector coordinates. These files are used by PCB fabricators to program equipment and translate your design into the physical properties of the PCB.
PCB Design software widely ranges in terms of functionality and pricing but at the end of the day, this CAD software is a requirement in order to create gerber files. The majority of today’s Gerber files are generated according to the RS-274X Gerber format, which supersedes obsolete formats such as the RS-274-D Gerber standard. As a text file, Gerber data does not have to have a specific identifying file name but is often given a common extension such as .gb, or .gbr.
Gerber Files and How They Are Used In PCB Manufacturing
The PCB manufacturing technology used today has advanced greatly since the first PCB. Back in the old days, vector photoplotters were used to create the tooling film required in the PCB manufacturing process. This focused light was conducted through a small aperture in order to expose the film to create the flashes and draws for each individual pad and trace.
Since there was only a minimal set of apertures available, engineers and designers had to be resourceful in restricting their flashes and lines to only the available apertures. Since those old days, the older vector machines have now been replaced by new equipment that uses a raster laser process to expose the film. With this new laser plotter technology, the process has been exponentially faster, especially for larger pieces of film with a lot of line drawings on it.
The history of gerber files can be traced back to the original needs of vector photoplotters. For the required instructions given to the plotter, a Gerber file was provided containing minimal plotter configuration information, and X-Y coordinates followed by a flash or drawing command and which aperture position to use. Gerber technology has increased in functionality since then. The current gerber files can now include additional configuration information as well as macro and aperture definitions.
Todays laser plotters still use the same Gerber information, but the difference is that the aperture restrictions of the older vector plotters no longer are a handicap. Laser plotters now convert the Gerber coordinates into a raster file, and that information instructs the laser plotter equipment on how, where, and what exactly is to be created on the films. These aperture definitions can convey information such as the thickness and size of the traces and pads while the drawing commands define whether lines, polygon fills or flashes are to be created. Then the laser sweeps across the film exposing the image as it goes.
Gerber files, their CAD software, and manufacturing processes continue to improve and innovate. Some circuit board manufacturers have even begun using direct laser imaging to create circuit board images directly onto the copper and completely bypassing the need for film! Despite these advances, gerber files will remain the standard for board fabrication for years to come. This is why it is important to have a full understanding of these files.
Generating Gerber Files for a PCB Design
After your design is complete and you’ve reviewed it and then reviewed it again, the next step will be to create the actual Gerber files for your manufacturer. This process really is dependent on the PCB design software that you choose to use. Some older tools may be clunky and take many steps to set up and generate files, but nowadays most CAD packages have simplified that process.
The Gerber files that need to be produced will be individual files for each physical layer of your board. This means that if your board design is a six-layer board with four signal layers and two planes for power and ground, then your software must output those layers into six separate Gerber files. On top of that, the top and bottom solder mask layers will also require their own files, the top and bottom silkscreen layers, and the top and bottom solder paste layers. Not all board will require both top and bottom silkscreen and paste layers. This will be dependent on design. Some manufacturers may need additional Gerber layers for the board outline or extra fabrication and assembly information, but that’s usually dependent on unique information.
Before sending over the files to the board house, make sure the units, formats, and standards are set up in a way that is consistent with design and manufacturing standards. Separate of the Gerber file, a NC drill file is usually created and accompanying the Gerber files. This instructs the board house’s drilling machines where to drill the holes in the board. This file is similar to a Gerber formatted file since it also contains drill size information and vector data for the different drill locations.
Additional Documentation for Manufacturing
Before sending files over, make sure to document your Gerber, NC Drill, and other manufacturing files in a way so that your contract manufacturer can build your design according to specifications. Fabrication and assembly drawings may be useful as well as pick and place data, test data, a schematic netlist, along with a readme file for additional notes. The best to mitigate errors is to collaborate with your manufacturing partner ahead of time in case something does come up. Vinatronic has been helping designers and engineers get their projects to market in California for over 25 years. Feel free to reach out to our staff in case you have any project questions or manufacturing needs!
