Gerber files are the primary manufacturing data files used to fabricate and assemble printed circuit boards. They define the layer-by-layer PCB artwork, including copper circuitry, solder mask, silkscreen, drilling information, and board profiles required for production.
Accurate, organized Gerber data helps manufacturers convert PCB designs into production-ready printed circuit boards while reducing the risk of manufacturing errors.
What Are Gerber Files?
After a PCB schematic has been completed in a design software package such as Altium, Eagle, or OrCAD, the design data is exported into a collection of Gerber files that define the physical circuit board.
Gerber files contain the information required to manufacture a PCB. Each conductive layer, copper pattern, power plane, ground plane, solder mask layer, silkscreen layer, and drill program is represented by its own file. Together, these files provide the manufacturing instructions needed to create the finished circuit board.
Gerber files have become the traditional format used throughout the PCB industry because they provide a consistent and reliable method for communicating design intent from engineering to manufacturing.
What Information Is Included in a Gerber Data Package?
Gerber files are commonly grouped into a single compressed package and delivered to the PCB manufacturer. Depending on the complexity of the design and stack-up, the package may contain numerous manufacturing files.
Gerber files have become the traditional format for consistent production of circuit boards.
A typical Gerber package may include:
- Copper layer artwork
- Power and ground plane layers
- Top and bottom solder mask layers
- Silkscreen layers
- Paste layers for assembly
- Drill files
- Fabrication drawings
- Board array layouts
- PCB stack-up information
- Board outline and machining profile data
- README documentation
Each layer required to fabricate the PCB must be represented by a corresponding Gerber file.
PCB Layers, Solder Mask, and Assembly Data
The outer layers of a PCB are typically identified as top and bottom layers or by layer numbering. Associated manufacturing data is also provided for non-conductive layers required during fabrication and assembly.
These files commonly include:
- Solder mask layers
- Silkscreen layers
- Paste layers for assembly operations
- Array step-and-repeat information
Together, these files ensure that copper features, surface finishes, assembly locations, and identification markings are produced correctly during manufacturing.
Solder Mask Considerations
Solder mask layers define the areas of the PCB that receive protective solder mask coverage and the locations where copper features must remain exposed. Separate solder mask files are typically provided for the top and bottom sides of the circuit board.
Drill Files and Board Profile Information
Drill programs are a critical part of the Gerber data package. These files provide the information needed to create holes and features throughout the PCB.
Drill files contain X and Y coordinate data referenced to a common 0,0 origin. Depending on the PCB design, separate drill files may be used to identify:
- Plated through-holes
- Non-plated holes
- Blind vias
- Buried vias
- Slots
Manufacturing data should also include a detailed 1:1 board outline that defines the finished profile and any required internal cutouts.
What Should I Know About Vias?
Vias provide electrical connections between PCB layers and are frequently identified within dedicated drill data. Blind vias and buried vias may be separated into different manufacturing files to support accurate fabrication.
Gerber File Naming Conventions
Gerber file names are typically labeled so manufacturers can easily identify the board and layer represented by each file.
Many PCB manufacturers encounter naming conventions such as:
- .TOP
- .BOT
- .SMT
- .SMB
The exact extensions are determined by the PCB CAD or CAM software being used. While naming conventions can vary, clearly identifying each layer and providing a corresponding stack-up improves manufacturing efficiency and reduces interpretation errors.
Gerber File Processes
Once Gerber data is received, PCB manufacturers import the files into CAM engineering software that converts the design into production-ready manufacturing data.
The CAM system uses the imported information to:
- Create PCB manufacturing layouts
- Define copper circuitry and traces
- Generate component pad structures
- Establish drilling operations
- Create board profile information
- Prepare arrays and panel layouts
The imported files are labeled, aligned to a common origin, archived, and preserved in their original state before manufacturing preparation begins.
Manufacturing Data Verification
Before production, engineers perform cleanup and verification procedures to ensure the data accurately represents the intended design.
Typical activities include:
- Design rule checks
- Manual cleanup
- Automated cleanup
- Array preparation
- Production layout optimization
Throughout this process, engineers compare working files against the archived originals to verify that no unintended electrical changes have been introduced.
Why Accurate Gerber Data Matters
Gerber files are used during both PCB fabrication and PCB assembly. Because they communicate design intent throughout the manufacturing process, accuracy and consistency are critical.
Well-organized Gerber data can help:
- Reduce manufacturing delays
- Minimize interpretation errors
- Improve production efficiency
- Support accurate PCB fabrication
- Streamline PCB assembly
Engineers working with the data must follow the guidelines and references included within the Gerber package when preparing files for production.
Gerber File Formats
Several Gerber formats have been used throughout the evolution of PCB manufacturing. Each format was developed to improve data transfer, reduce manual processing, or provide additional manufacturing information.
RS274-D
RS274-D, often called the Standard Gerber format, was the original format developed by Gerber Scientific.
This format was based on numerical control (NC) data and was compatible with photoplotters used during the 1970s. Because it relied on manual entry of d-codes and greater user interpretation, limitations in the format eventually led to newer solutions.
RS274X
RS274X has been in use since 1998 and remains one of the most widely used Gerber formats.
Gerber file format RS247X has been used since 1998.
Key capabilities include:
- Embedded format information
- Embedded unit information
- Embedded aperture definitions
- Standard and custom aperture support
- Film control
- Polygon fill commands
- Polarity controls
By embedding critical manufacturing information directly within the file, RS274X significantly reduced manual data entry and made photoplotting errors far less common.
ODB++
ODB++ was developed by Valor as an all-inclusive, self-extracting, standardized manufacturing data format.
The format was designed to automate processes associated with:
- Stack-up definition
- Drill placement
- Layer labeling
ODB++ also includes design, fabrication, and netlist information within a single package, reducing reliance on manual file naming and helping minimize opportunities for human error. Although not universally preferred, it remains a useful format throughout the PCB industry.
Gerber X2
Gerber X2 is the newest Gerber format discussed in this article and was developed to support advanced CAM software environments.
The format allows attributes to be assigned directly to features within a Gerber file, enabling additional information to be transferred to both the fabricator and CAM operator.
Gerber X2 remains compatible with the earlier X1 format while allowing designers to communicate additional design information through the manufacturing data.
Summary
Gerber files are the foundational manufacturing data used to fabricate and assemble printed circuit boards. They contain the layer-by-layer information needed to create copper circuitry, solder mask openings, silkscreen markings, drill programs, vias, and board profiles. Formats such as RS274-D, RS274X, ODB++, and Gerber X2 each provide different levels of automation and manufacturing intelligence, while accurate file preparation and CAM verification help ensure the finished PCB matches the original design intent.
Contact Epec's engineering team for assistance reviewing Gerber data and preparing PCB designs for manufacturing.
Key Takeaways
- Gerber files are essential for PCB manufacturing: They contain detailed layer-by-layer information of a printed circuit board design, including copper layers, solder masks, silkscreens, and drill data used for both fabrication and assembly.
- Each PCB layer and function has a corresponding Gerber file: Files are organized and labeled to match specific board functions, like top copper, bottom solder mask, and drill programs, and are often zipped together for submission to manufacturers.
- There are multiple Gerber file formats, with RS274X being the most common: RS274X is widely used due to its embedded design data, reducing manual input errors. More advanced formats like Gerber X2 and ODB++ provide extended design metadata and automation benefits.
- CAM software translates Gerber data into manufacturable layouts: Engineers at the fabrication house import and clean up the files, run design rule checks, and prep the board for panelization and production, ensuring accuracy and performance.
- Accurate Gerber data streamlines production and minimizes errors: Whether you're building a single board or an array, well-organized Gerber files reduce production delays, prevent mistakes, and ensure the final PCB matches the design intent.
