1. Altium Gerber Files
RS-274-X Gerber file format is a defacto data sharing standard for PCB manufacturing. This is basically a printer or plotter language which is used for PCB CAM (Computer Aided Manufacturing) data generation. Almost everyone who uses Altium Designer software for PCB design, either hobbyist or commercial designer, may have used this feature. It is actually a 2D ASCII file format.
Gerber file format is evolved from applications where it is used to re-create images or graphics i.e., printers and plotters industry. In the same way it is used in electronics hardware industry to print PCB tracks, vias, pads, text, holes, clearances and all information which is contained in a *.PcbDoc design file. The Altium Designer software tool has a feature to create and gerbtool option to verify data as well.
Like other softwares outputs the Altium Designer gerber file can be divided into four subparts:
- Configuration Parameters
- Aperture Definitions
- Drawing Commands
- X/Y Coordinates
Each file extension denotes a specific layer such as:
Top Layer => *.gtl
Bottom Layer => *.gbl
Keepout Layer => *.gko
TopOverlay Layer => *.gto
BottomOverlay Layer => *.gbo etc.
2. Generating Gerbers in Altium Designer
Add layer stackup to any of the mechanical or other suitable layer.
Add other information like manufacturing notes, dimensions, cutouts etc., before generating gerber files.
In Altium Designer it is very easy to setup Gerber Files creation setup. It is done by two ways:
Generate through File>Fabrication Outputs> Gerber Files
It opens Gerber Setup dialogue box.
In Gerber setup dialogue box Set file producing unit system.
In layers pane add layers to be re-produced in gerber format.
In drill drawing pane click plot all used layer pairs on both of the boxes.
Set apertures box.
Set advanced parameters in advanced pane or otherwise keep default settings.
Click ok , it generates the gerber outputs in the project folder.
On same method NC drill files are created i.e., File>Fabrication Outputs> NC Drill Files and then adopt the same steps as above.
Or in other way it can be generated by following steps:
Output Job File to project > Fabrication Outputs> Gerber Files and then set path for files.
Double click “Gerber Files” it will open Gerber setup. Use the same steps as above and click ok.
Enable output generate option and set target folder location.
Clock Run or double click over generates content. The gerber file outputs will be generated.
Figure 1: Sample PCB Design file
In figure 1 different layers names are shown in their respective layer. The same layers can be viewed in the final view Figure 5 as Gerber output generated.
Figure 2: Gerbers Settings Dialogue Box
Figure 3: Gerber Setup Dialogue Box opens
Figure 4: Gerber Files generated and viewed in CAMTastic Bottom Layer view
Figure 5: CamTastic complete PCB view
3. What is Needed by Manufacturer
In a gerber file following layers and information should be added:
- 1- Enable all signal layers which have been used for routing in PCB design or those which have electrical signals routing should be enabled to re-produce in gerber format.
- 2- Enable all plane layers which are solid copper and distribute power to the circuit on PCB. These are printed as negative image of layer.
- 3- Enable Keepout layer, it is usually electrical boundary of the board. The keepout can also be asked to manufacturer for cutting boundary.
- 4- Enable required mechanical layers in gerber setup. A mechanical layer does not have any electrical information like in signal layer or plane layers. However, they can have some information about mechanical parameter like PCB cutting or, 3D PCB footprints information, assembly and fixing in enclosures etc.
- 5- Enable Top Overlay and Bottom Overlays which have information of components designators and PCB name, number, nomenclature debug information and test signal details etc.
- 6- Dimensional Information: PCB Dimensions information should be added on top overlay or mechanical or keepout layer of PCB design file before generating gerber files.
- 7- Layer PCB stackup: Before generating gerber files add layer stackup information in any enabled mechanical layers so that manufacturer can use information about PCB material such as base material thickness, pre-preg thickness type etc.
- 8- Preferably produce time and date stamped Gerber files so that they would be back traced for any query.
- 9- Recheck and verify the file types using any gerber viewer software tool.
- 10-If found accurate and forward to the manufacturer.
Figure 6: Gerber files enable and disable and extensions
Figure 6 shows the gerber files produced by Altium Designer software, produced time, type of layer etc.
4. Summary:
Gerber format is RS-274-X 2D ASCII file format. The gerber file format is a defacto standard of interface between a PCB Design engineer and manufacturer. It includes all conductive, mechanical, text and keepout layers information of a PCB design alongwith necessary notes for manufacturing.
The Altium Designer software produces RS-274-X format Gerber files by different methods. The latest software and updates about files generation are available on Altium ®. In this tutorial a complete yet comprehensive guide has been provide.
Introduction
Gerber files are the standard format used to transfer PCB design data to fabrication and assembly units. Altium Designer has robust capabilities to generate industry-standard Gerber files needed for board manufacturing. This article provides a detailed guide on the process of exporting Gerber files from an Altium PCB project, with additional tips for file settings and customization.
Gerber File Basics
Gerber files represent PCB layout data in a vector graphics format that can be interpreted by fabrication machines. Here are some key facts about Gerber files:
- Developed by Gerber Systems in the 1960s, hence the name.
- Provide image of PCB layers like copper, solder mask, silkscreen, drill files etc.
- Use RS-274X file format with .gbr extension.
- Contain vector-based information to image PCB layers.
- Used for photoplotting fabrication layers on film or directly on boards.
- Required by PCB manufacturer along with drill files for board fabrication.
Output Job File Settings
Before exporting Gerber files, the key output job settings in Altium must be configured. This is done through the OutJob editor by going to File > Fabrication Outputs > OutJob Editor.
The important parameters are:
| Parameter | Description |
|---|---|
| Output Location | Folder path to save Gerber files |
| Layer Stack Regions | Defines coverlay and multilayer regions |
| Layer Specs | Specifies layers included in outputs |
| File Naming | Sets filename prefixes and suffixes |
| Format | Gerber RS-274X, ODB++ etc. |
| Settings | Various options like coordinates, zero suppression etc. |
The most critical settings are layer stack and layer specifications which determine the actual layers output.
Generating Gerber Files
Once the OutJob is defined, we are ready to export the Gerber files. This involves simply running the output job to generate all the required layers.
The steps are:
- Open the PCB project in Altium and go to File > Fabrication Outputs > Generate Gerbers.
- Select the OutJob in the Gerber Job Editor window.
- Click on Validate outputs – this checks for any errors or missing data.
- If validation passes, click on Generate to run the job and output Gerber files.
- The Gerber files can be found in the specified output folder location.
- By default, a .PDF and .ZIP archive of the files is also generated.
For quick one-click Gerber generation, the OutJob can be added to the Project menu for the PCB. This automates opening the job editor and executing the output process.
Layer Stack Settings
The layer stack regions defined in the OutJob determine which layers are combined to generate the final Gerber files.
For a typical PCB, the layer stacks are:
| Layer Stack | Purpose |
|---|---|
| Top Layer | Images top copper layer |
| Bottom Layer | Images bottom copper layer |
| Internal Layers | Images inner signal layers |
| Drill Drawing | For NC drill files |
| Multi-Layer | Combines inner and outer layers |
| Top Solder | Solder mask on top side |
| Bottom Solder | Solder mask on bottom side |
| Top Paste | Solder paste layer for top side |
| Bottom Paste | Solder paste layer for bottom side |
| Top Overlay | Silkscreen and other markings on top side |
| Bottom Overlay | Silkscreen and markings on bottom side |
Using these layer stacks, all required Gerber files can be generated. Additional stack-ups can also be defined.
Layer Specifications
Layer specifications determine which layers actually get included in a layer stack while generating outputs.
Typical layer inclusions for standard PCB file outputs:
| Layer Stack | Layers Included |
|---|---|
| Top Layer | Top Layer + Multi-Layer |
| Bottom Layer | Bottom Layer + Multi-Layer |
| Internal Layers | Inner Layers + Multi-Layer |
| Top Solder | Top Solder + Coverlay Top |
| Bottom Solder | Bottom Solder + Coverlay Bottom |
| Top Overlay | Top Overlay + Coverlay Top |
| Bottom Overlay | Bottom Overlay + Coverlay Bottom |
The multi-layer and coverlay combinations merge the signals and plane layers appropriately. Additional specifications like keep-outs can also be added.
File Naming Conventions
Consistent file naming allows easy identification of Gerber files. Recommended naming conventions:
- File Prefix – Use project name or PCB code
- Layer identifier – TL for Top Layer, TS for Top Solder etc.
- File Suffix – Can include version number, date etc.
For example: ProjectABC_TL_Rev1.gbr
This provides a unique ID for each layer file. Similar naming can be applied to drill files.
Important Plot Layers
Some of the key Gerber layers required for fabrication are:
- Top and Bottom Copper Layers – Carry signals and traces
- Internal Plane Layers – Power, ground and routing layers
- Top and Bottom Solder Mask – Defines solderable areas
- Top and Bottom Silkscreen – Component markings and legends
- Board Outline – Dimensions of finished board
- Drill Drawing – For NC drill machine
- Drill Data – Size and location of drilled holes
Additional Outputs
Besides standard Gerber layers, additional outputs like the following can also be generated:
- Copper thickness table – Specifies finished copper thickness for each layer
- Netlist file – Connectivity information for test and analysis
- Assembly drawings – Help guide component placement
- PCB 3D model – For design visualization
- Fabrication and Assembly drawings – Includes callouts, notes, etc.
- Impedance information – For controlled impedance designs
- Stackup details – Layer materials, properties and sequence
File Validation
Before sending to PCB fabrication, the Gerber files must be thoroughly validated using the following checks:
- Visual examination – Open files in Gerber viewer to check if layers contain the expected images.
- Preflight tests – Use preflight tools to verify file format, aperture settings etc.
- CAM tool checks – Use CAM software to check file opening, merging and editing.
- Test photoplots – Get film photoplots made from files to validate image accuracy.
- Compare netlist – Use netlist file to check all connections in design are properly imaged.
- Design rule check – Ensure critical clearances are maintained in generated images.
File Optimization
Gerber file optimization involves tweaking settings to get smaller files while retaining image quality. Main techniques include:
- Selecting optimal resolution and image settings.
- Using zero suppression to reduce file size.
- Applying data compression while exporting files.
- Removing duplicate drawing data and unused apertures.
- Merging layers where possible to reduce file count.
Proper optimization ensures faster file transfers and processing while minimizing storage requirements.
Conclusion
Comprehensive Gerber file generation tools within Altium allow creating all fabrication data needed to manufacture a PCB easily and efficiently. Configuring suitable OutJobs, layer stacks and file settings produces industry-standard outputs that can be directly sent for board fabrication. Validation checks must be performed diligently before file release to avoid errors reaching manufacturing stage. Overall, mastery over the Gerber generation process is crucial to harness the full power of Altium and seamlessly progress from design to fabrication.
FAQs
- What are some common problems observed in Gerber files?
Missing copper, malformed apertures, incorrect filenames and layers in wrong files are common Gerber issues. Preflight tools help catch such errors.
- How to check if a specific layer is getting correctly output in Gerbers?
Open that Gerber file in viewer and check if key shapes or test structures added to the layer are present in output image.
- Why zipping is recommended for Gerber file transfer?
Zipped files occupy less storage space. Zipping also reduces chances of file corruption during internet transfer using protocols like FTP.
- What is the difference between PCB fabrication drawing and assembly drawing?
Fabrication drawing guides board manufacture while assembly drawing is used for component placement, annotations during PCB assembly.
- How can gaps be avoided between copper layers and planes in Gerber data?
Enable the Remove islands option in Layer Stack Regions. Use proper Positive and Negative layers to define extents.
