Introduction
EAGLE (Easily Applicable Graphical Layout Editor) is a popular PCB design software used by engineers, hobbyists and students. It provides a seamless workflow from schematic capture to PCB layout and includes powerful features for generating manufacturing files. This article provides a comprehensive guide on exporting Gerber files from an EAGLE PCB project.
Overview of Gerber Files
Gerber files are the industry standard for transferring PCB design data to fabrication and assembly units. Here are some key facts about Gerber files:
- Contain vector image data of PCB layers like copper, mask, silkscreen, drill files etc.
- Use RS-274X file format with .gbr extension.
- Provide image plots of fabrication layers for photoploting.
- Required by PCB manufacturer along with drill files to manufacture the board.
- EAGLE uses extended Gerber format RS-274X with additional features.
CAM Processor Settings
Before generating Gerber files, the CAM processor settings must be configured in EAGLE to specify file outputs. This is done through the CAM editor.
The important CAM job settings are:
- File Format – Extended Gerber RS-274X.
- Coordinates – Absolute or Incremental depending on manufacturer requirements.
- Leading and trailing zeros – For consistent file formatting.
-asymperc Output directory – Location to save output files.
- File naming convention – Unique names for identification.
- Layer mapping – Links board layers to Gerber files.
- Additional outputs – Like drill files, drawings etc.
Properly setting up the CAM job is essential for clean and error-free Gerber generation.
Generating Gerber Files
Once the CAM processor settings are configured, we are ready to export the Gerber files. The steps are outlined below:
- Open the PCB project in EAGLE.
- Run the Design Rule Check to ensure the layout passes all checks.
- Open the CAM processor window from the File menu.
- Select the configured CAM job and click on the Process Job button.
- Specify an output directory when prompted.
- Review the final summary and click on OK.
- The Gerber files are generated in the defined output folder location.
- Additionally, a job report is created detailing file outputs.
This completes the generation of fabrication-ready Gerber files along with drill, mask and other layers as specified in the CAM job.
Layer Mapping
A key aspect of the CAM job settings is mapping the PCB layers correctly to the desired Gerber files. The typical layer mapping is:
| PCB Layer | Gerber File |
|---|---|
| Top Copper | gt[name].gbr |
| Bottom Copper | gb[name].gbr |
| Pads | gp[name].gbr |
| Vias | gv[name].gbr |
| Top Soldermask | gts[name].gbr |
| Bottom Soldermask | gbs[name].gbr |
| Top Silkscreen | gto[name].gbr |
| Bottom Silkscreen | gbo[name].gbr |
| Board Outline | gko[name].gbr |
| Drill Holes | [name].xln / [name].drd |
where [name] is the file name prefix. Additional inner layers are mapped similarly.
Important File Outputs
Some of the key Gerber files needed for PCB fabrication are:
- Top and Bottom Copper Layers – Contain signals and traces.
- Solder Mask Layers – Define solderable areas on the PCB.
- Silkscreen Layers – Include component designators, values, logos etc.
- Drill Files – For creating NC drill machine program.
- Board Outline – Dimensions of final PCB profile.
- Inner Layers – Used for multilayer boards.
- Assembly Drawings – Help guide component placement.
File Generation Tips
Here are some useful tips to generate clean Gerber files from EAGLE:
- Always run DRC and ERC checks before generating Gerbers to avoid errors.
- Ensure all design data is on specified layers to be correctly output.
- Confirm board outline is closed polygon without gaps or missing segments.
- Use unique and intuitive names for file identification.
- Enable zipping of output files for compressed transfer.
- Specify consistent number of decimal places for file formatting.
- Round hole sizes to match manufacturer drill sizes to avoid errors.
File Validation
Before releasing Gerber files for fabrication, they should be thoroughly validated:
- Visually inspect files in a Gerber viewer to ensure proper images.
- Use pre-flight tools to verify file format, apertures, parameters etc.
- Get test film photoplots made from files to validate accuracy.
- Compare the images with board layout to catch any missing data.
- Confirm critical clearances are maintained in files through measurement.
- Check if generated drill file matches holes designed in PCB.
Thorough file validation prevents costly errors from propagating to manufacturing stage.
Panelization
For assembly of multiple PCBs, the boards need to be arranged in a panel to optimize manufacturing. Steps:
- Create the required panel layout by arranging board outlines.
- Generate a new Gerber file containing just the panel outline.
- Modify main board outline file to remove outline.
- Include the panel file along with other layers for manufacturing.
- Add fiducials, tooling holes, breakaway tabs etc.
Panelization streamlines assembly by allowing multiple boards to be populated and assembled together.
Version Control
Maintaining proper version control of Gerber files is essential:
- Increment version number in CAM job file naming convention.
- Include version number in file name or as comment within file.
- Track versions in documentation.
- Save prior versions in archive directory.
Proper versioning avoids mix up or use of outdated files.
Conclusion
The CAM processor in EAGLE provides a streamlined workflow to generate industry-standard Gerber files from a PCB design. Configuring appropriate settings and layer mapping produces a fabrication-ready set of Gerber images and drill data. Proper validation ensures accuracy while features like panelization and version control enhance manufacturability. A sound understanding of the Gerber file generation process enables PCB designers to hand-off error-free files to fabrication, leading to smooth prototype builds or production.
FAQs
- What are some common issues observed in Gerber files?
Missing copper or silkscreen details, incorrect apertures, wrong polarity and layers mapped to incorrect files are frequent Gerber issues.
- How can panelization help reduce PCB assembly cost?
Panelizing allows multiple boards to be populated and assembled together. This lowers setup overheads and improves throughput, reducing overall cost.
- What information should be included in Assembly drawings?
Assembly drawings include component outlines, designators, polarity markings, fabrication notes and other build instructions.
- Why is validation of drill files important?
Drill files must match hole sizes and locations designed in PCB to avoid incorrect drilling. This can lead to lack of hole alignment during assembly.
- How can Gerber files be compressed?
EAGLE CAM allows zipping output files. Gerber data can also be compressed after generation using utilities like gzip.
1.PCB Manufacturing Pre-requisites
The Gerber RS-274X file format is used for PCB manufacturing data submission to fabrication house. This is output of PCB design file. Why not PCB Design file handed over to manufacturer? One of the reasons is almost all product hardware concept related information is present in PCB design file. For example, Bill of Material can be very easily generated from this PCB design file. It contains active connectivity information from where entiredesign can be copied. The gerber files do not include BOM and active connectivity information. The gerber files are image of active layers and connections but they are just “images of all active PCB layers”.
So they are relatively safe to submit to third parties such as PCBs fabrication houses etc.The gerber format was emerged from applications where it was applied to re-generategraphics or images i.e., from plotters industry. It isused in electronics PCBs manufacturing industry in the same way. It generates PCB traces, pads, vias, clearances and all other electrical and non-electrical information contained in a design file. All PCB CAD softwares are capable to generate gerber files.All the electronics engineers who have designedand manufactured PCBs will have used this option.
Gerber file outputs these four parts:
- X/Y Coordinates
- Configuration Parameters
- Drawing Commands
- Aperture Definitions
The PCB manufacturer creates photo plots from the given Gerber files data. The higher the resolution of gerber files data the better the plots created for PCB fabrication.
2.What should include in Gerbers
The gerber data is very critical to produce. It should be generated very carefully. Usually, any layer missed during gerber files generation will interpreted by manufacturer that there was no layer in the original design. The PCB produced will be off course faulty and cannot be used. A faulty gerber data will produce faulty PCB output.Before generating gerber files in Eagle software the PCB design engineer should very clear to include necessary layers ad information in Gerber CAM processor of Eagle software.
3.Eagle Output File Format
The eagle PCB Design software generates gerber files on popular RS-274X format however it is slightly tricky to understand the file extensions. The drill files are created and saved separately in Exelon format. For gerber files creation it provides a separate software utility called CAM (Computer Aided Manufacturing) processor or only processor.
In eagle there are two main terms the processor and the job. The processor is explained already. The job is a set of tasks composed so that each task reads specific layer information from PCB design file and creates gerber file.
CAD softwares create one file for each PCB design layer. So for 20-conductive layers PCB design there will be 20 gerber files, additive to top and bottom legend, keepout, top and bottom paste, top and bottom solder mask layers. When it is to submit data for manufacturing or quotation purposes the Gerber files folder should be in*.zip or *.rar format.In Eagle software the following extension for layers are produced in gerber generation.
- GTL Top Copper Layer
- GTS Top Soldermask Layer
- GTO Top Silkscreen Layer
- GBL Bottom copper Layer
- GBS Bottom Soldrmask Layer
- GBO Bottom Silkscreen Layer
- TXT Drills Layer
- GML/GKO *Board Outline or Keepout Layer
- 6 layer board also need internal layers information also
- GL2 Inner Layer2
- GL3 Inner Layer3
- GL4 Inner Layer4
- GL5 Inner Layer5
Along with layers information, holes location and size of drills also part of gerber data produced before submission to a manufacturer. It is called NC drill file and data is incomplete without these files. The purpose of Gerber files is to create X/Y Coordinates, Configuration Parameters, Drawing Commands and Aperture Definitions of each layer mentioned in software. The Eagle software scans the each layer entire PCB file to create these four parameters for each separate layer.
4.CAM Processor
However, to generate a PCB Design file into CAM Processor:
Usually, the CAM processor is a dialog box that takes design file as an input and allows optional settings and generates output files.
To open CAM Processor click File> CAM Processor
OR alternatively, in Control Panel’s main menu File > New > CAM Job
thenselect PCB board: go to file> selecta job file>execute the job.
to load a PCB design file.
Figure 1: Eagle PCB software CAM Processor
Start CAM processor from Eagle software as shown in Figure 1.
Figure 2: Selecting CAM Processor File Format
Select format of output files and necessary options in the CAM processor as in Figure 2.
Figure 3: Layer names in Eagle CAM Processor
Produce output files as shown in Figure 3.
Summary:
For fabrication data to be handed over to manufacturer it is necessary that it should be accurate and complete. Ay missing information will cause a faulty and hence garbage PCB.Eagle software like other softwares produces files in Gerber RS-274X format. For successful gerber files creation one should have clear knowledge of Eagle CAM processor. It is a good practice to verify metadata files against each layer with their three charactersextension.For gerber data verification known online and offline installable softwares are available which show the exact image what data is generated. Verify and match gerber data before submitting it to fabrication house. Besides PCB layers metadata NC drill files are also required by the PCB fabrication house so produce separately, verify and match with original design file before forwarding it.3
