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As a PCB designer, collaboration with your manufacturer is key to turning your vision into reality. Sending off your design files can feel like a leap of faith. How do you ensure the final boards match your creative efforts? This is where Gerber files become essential. In this comprehensive guide, we’ll demystify Gerber files so you can utilize them effectively.
You’ll discover what they contain, how they drive fabrication, best practices for generating and validating them, and more. Whether you’re new to PCB design or a seasoned veteran, this article will build your understanding and confidence working with this crucial file format.
What are Gerber Files?
Gerber files are a critical component in the PCB soldering process. Gerber files, also known as photolithography files, are a standard two-dimensional image file format widely used to depict the graphical data of a PCB, including pads, traces, vias, and all other physical levels of detail. It allows PCB manufacturers to understand exactly what the designer intended and to produce according to this design data.
Each physical layer or element of the PCB is represented by its own separate Gerber file. For example, there may be individual Gerber files for:
- Top and bottom copper layers
- Top and bottom solder mask
- Top and bottom silkscreen legend
- Drill holes
- Board outline
Gerber files use a simple ASCII text format consisting of basic commands like “flash”, “draw”, and “move”. The files were originally designed to drive photoplotters, which use light to optically transfer or “image” each layer onto film. The film is then used to produce the PCB etching, masking, and drilling templates needed for fabrication.
The Benefits of the Gerber File Format
The Gerber file plays a vital role in the PCB manufacturing process, and its main roles include:
Accurate Guidance for Production
Gerber documentation provides all the detailed specifications required to manufacture PCBs, ensuring accuracy during the production process. These specifications include but are not limited to, pad locations, lead widths, layer alignment, aperture sizes, and locations, as well as specific material and handling requirements for the various layers. Every detail is accurately labeled, thus ensuring that the PCBs produced are the same as the design drawings. This high degree of precision is particularly important for complex electronic devices, where even small deviations can lead to performance degradation or failure of the entire board.
Bridging Design and Manufacturing
Electronic equipment designers create PCB designs using CAD (Computer Aided Design) software and then export them as Gerber files. During this process, the designer considers some aspects of the circuit, including functional requirements, signal integrity, power distribution, thermal management, and mechanical construction. Once the design is complete, the designer performs a series of design rule checks (DRCs) and simulations to ensure that the design is theoretically feasible. The exported Gerber file is then sent to the PCB manufacturer and is key to the transition from design to manufacture. The manufacturer uses specialized CAM (Computer Aided Manufacturing) software to read the Gerber file, convert it into machine-recognizable instructions, and then complete the manufacture of the PCB. This process may include steps such as multi-layer lamination, copper foil etching, hole metallization, solder mask application, screen printing, etc., each of which requires precise graphic and dimensional information, all of which is contained in the Gerber file.
Standardised communication language
Because the Gerber format is a widely accepted standard in the industry, it allows seamless communication between different designers and manufacturers without having to worry about software or system compatibility issues. This standardized communication language streamlines the process from design to production, reducing delays and errors caused by format incompatibilities or misunderstandings. The standardization of Gerber files also means that manufacturers can easily handle design files from different designers around the world, and as long as they comply with the Gerber standard, they can be accurately converted into the final physical PCB. In addition, such standardization also supports the efficient operation of the global supply chain, as design can be done in one country and manufacturing can take place in another, as long as both parties follow the same Gerber standards. This interoperability is one of the key factors enabling rapid growth and innovation in modern electronics manufacturing.
A Brief History of Gerber Files
Gerber files were developed by the Gerber Systems Corporation, founded by Joseph Gerber in 1948. Gerber pioneered the use of photo plotters to automate the PCB design process.
Before Gerber files, there was no standard format for transferring PCB design data to manufacturers. Different CAD tools would output PCB layers in various incompatible graphic and text formats. This caused a lot of confusion and errors.
The introduction of the Gerber file standard finally allowed compatibility between PCB designers using any CAD system and their PCB production partners. For the first time, circuit designers could be assured their boards would meet the original specs, by providing manufacturers a complete set of instructions in a common file format.
Among the earliest versions of the Gerber standard was RS-274D, which evolved to meet the needs of increasingly sophisticated photo plotters. However, RS-274D had limitations due to needing separate aperture list files.
This was improved with RS-274X, which combined aperture definitions, commands, and coordinate data into a single, more complete Gerber file. The latest Gerber X2 standard adds even smarter metadata like pad types for more intelligent PCB fabrication.
Gerber File Composition
A Gerber file contains four key types of data:
- Configuration Parameters – Specifies settings like units of measurement, image polarity, and coordinates format. This ensures the manufacturer interprets the file correctly.
- Aperture Definitions – Defines “apertures” or standardized shapes/sizes for flashes and draws, similar to fonts. Circles, rectangles, polygons, and more complex apertures can be defined.
- Image Commands – Consists of simple commands like “D02” for draw, “D03” for flash, and “D01” for move. Draw traces out paths while flash fills in pads, vias, and regions.
- Coordinate Data – Lists X-Y coordinates locating where image commands like draw and flash are performed. Draw commands list a series of coordinate points to connect.
These four elements allow all the intricate details of each PCB layer to be described in a relatively simple ASCII text file. The precise sequences of commands at specific coordinates produce the pad and trace layout artwork. Let’s look at some of the common Gerber files found in a PCB design’s fabrication dataset:
Copper Layers
The top and bottom copper layers represent the conductive portions of the PCB – the circuitry. These are the most important files for defining electrical connectivity.
Solder Mask Layers
Solder mask is the protective coating on the PCB that prevents solder bridges between pads. The solder mask layers define the areas that are to be masked vs. exposed.
Silkscreen Legend Layers
Silkscreen applies component information, labels, logos, and other markings using ink. The silkscreen layers contain vector artwork for the silkscreen.
Drill Files
While not technically Gerber files, drill files are generated in a similar format. They specify hole sizes and locations to generate the PCB drilling coordinates.
Board Outline Layer
This layer defines the physical profile or edge shape of the final PCB. It is used for mechanical routing or cutting of the board outline.
Other Layers
Additional optional layers may include pastemasks, assembly drawings, fabrication drawings, etc. These provide extra instructions or information to the PCB manufacturer.
The Gerber File Format Explained
Although human-readable, Gerber files use a cryptic format not meant to be manually edited. The files are loaded directly into the manufacturer’s CAM software. Let’s take a quick look at some key characteristics of the Gerber file format:
- ASCII Text File – Gerber files are plain text files using ASCII characters to encode all data.
- Simple Graphics Primitives – Uses basic draw, flash, and move commands rather than higher-level graphics.
- Aperture Definitions – Apertures define the sizes and shapes of graphics primitives.
- Compact But Powerful – While terse and arcane, the format efficiently conveys all PCB visuals.
- Numeric Control Origins – Still contains syntax from its roots driving photoplotter numeric control.
For most designers, understanding the nuances of the Gerber format itself is unnecessary. It’s more important to master your CAD tool’s Gerber file export process and know how to validate the files.
Viewing and Validating Gerber Files
While the Gerber files contain all the data needed to manufacture the PCB, they can’t easily be visualized by the human eye. You’ll need to use Gerber viewer software to interpret the files and render the final PCB layout for display and inspection.
Most PCB design software includes standalone Gerber viewer tools. The manufacturer will also use Gerber viewing software to inspect the files. It’s critical to visually verify the exported Gerber files before sending them off for fabrication. Here are some things to check:
- Layer Accuracy – Do copper layers match schematics? Are mask and legend layers correct?
- Alignment – Are layers precisely lined up with no offsets?
- Completeness – Are all necessary layers included?
- Polarity – Are images of dark and light areas correct?
- Sizes and Shapes – Are apertures rendering correctly?
Since different Gerber viewers can interpret data slightly differently, it’s best to use the manufacturer’s viewer when possible. Many also provide online Gerber viewing tools to inspect designs before ordering.
Creating Gerber Files with CAD Software
Every PCB design software includes utilities to export design files into the standard Gerber format needed for fabrication. Key steps in the process include:
- Checking Settings – Confirm your design’s units, coordinates format, and other parameters match the output settings.
- Generating Layers – Export individual Gerber files for each physical layer of your board.
- File Naming – Name files appropriately according to their layer using extensions like .GBR or .GTS.
- Visual Verification – thoroughly inspect layers in a Gerber viewer before releasing.
- Outputting Drills – Include an NC drill file in addition to the Gerber layers.
- Additional Outputs – Fabrication drawings, BOMs, netlists, and other info as required.
- Archiving – Zip the Gerber dataset for simplified transfer and storage.
Don’t forget important design documentation like your bill of materials, assembly drawings, and ReadMe notes. These provide vital information to complement the fabrication dataset.
Gerber Files in PCB Manufacturing
For PCB fabricators, Gerber files are the primary method for transforming design data into physical circuit boards. Here are some of the ways Gerber files drive PCB manufacturing:
- Photoplotting – Originally for photoplotter film generation, now used in laser photoplotters.
- Direct Imaging-Gerber files are converted into images to drive direct laser imaging of PCB innerlayers.
- CAM processing – Gerber data is processed, optimized, and prepared for fabrication by CAM software tools.
- Solder Masking – The solder mask layer is used to image or pattern the solder mask onto raw PCBs through photolithography.
- Etching Copper – Copper layers image etch-resistant material to selectively remove copper during etching.
- Drilling Holes – Excellon drill files guide PCB drilling machinery.
- Routing – The board outline layer shapes mechanical routing or cutting bits.
- Visualization – Gerber viewers check files, and probe designs, view 3D models, and program AOI inspection systems.
- Layer Alignment – Gerber’s ensure accurate multi-layer board stacking and alignment throughout fabrication.
Conclusion
Gerber files play an indispensable role in taking your PCB design into fabrication and production. Understanding what these files contain and how they instruct manufacturing processes is key for both designers and producers.
With the right mastery of the ubiquitous Gerber file format, you gain confidence that your creative vision will materialize into a physical board that matches your original intent. Utilize this guide as a valuable reference for working effectively with Gerber files in your end-to-end PCB development workflow.
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