Gerber Files: A Step by Step Guide on How to Generate Gerber Files

What are Gerber Files?

Gerber files are the standard file format used to describe the printed circuit board (PCB) layers and drilling information needed for PCB fabrication. They are named after the Gerber Scientific Instrument Company which originally developed the file format. Gerber files provide a clear, unambiguous, and standardized way to communicate PCB design information between PCB design and manufacturing.

A complete set of Gerber files will include individual files for each copper layer, the solder mask, silkscreen legend, drill drawing, and drill data. Each Gerber file represents a single PCB layer or manufacturing function. Here are the common types of Gerber files:

Why Are Gerber Files Important?

Gerber files are crucial because they provide the essential fabrication data needed to reliably manufacture PCBs. Using Gerber files eliminates ambiguity by providing a clear, standard data format that PCB manufacturers can use directly without conversion or re-interpretation. This streamlines communication between PCB designers and manufacturers and helps avoid manufacturing errors.

Well-structured, complete Gerber files allow PCB fabrication to be highly automated. PCB manufacturers can take a set of Gerber files and use them to directly drive their fabrication equipment with little manual intervention. This improves manufacturing speed and quality.

Gerber is an open ASCII vector format that is compact and easy to read, modify, and manipulate. Virtually all PCB design software can export Gerber files, and all PCB manufacturers accept Gerber files as input. This makes Gerber a universally supported PCB data transfer standard.

Step-by-Step Process to Generate Gerber Files

Here is a general step-by-step process for generating manufacturing-ready Gerber files from a PCB design:

1. Complete PCB Design

Before generating Gerber files, your PCB design should be complete and ready for manufacturing. This means:

• Schematic capture is finished
• PCB layout is final with no design rule check (DRC) errors
• Component footprints are correct
• Copper layers, drill holes, solder mask, and silkscreen are properly defined
• Board outline is present
• All necessary mechanical features (mounting holes, cutouts, etc.) are in place

2. Define Layer Stackup

Clearly define and document your intended layer stackup, including:

• Number, order and type of layers (signal, power, ground planes)
• Layer copper weights
• Dielectric substrate material and thicknesses

Communicate this layer stackup to your manufacturer. Many design tools allow embedding the stackup data in the fabrication files.

3. Set Up Design Rules

Set up appropriate design rules in your PCB layout software according to your manufacturer’s capabilities and requirements. Key design rules to consider:

• Minimum trace width and spacing
• Minimum drill hole size and annular rings
• Solder mask expansion
• Silkscreen clearances
• Acceptable fonts and line widths for text and graphics

Running a design rule check (DRC) will verify your layout meets these constraints.

4. Specify Physical PCB Parameters

Define key physical PCB parameters such as:

• Final board thickness
• Copper weights for outer and inner layers
• Surface finish for exposed copper (HASL, ENIG, OSP, etc.)
• Solder mask color and finish (matte/glossy)
• Silkscreen color

5. Generate Drill Files

Generate the following drill file outputs:

• NC drill file (.DRL) containing hole sizes and XY coordinates
• Drill map drawing (.PDF) showing hole sizes and locations
• Drill tool list (.TXT) detailing the hole sizes and quantities

Typically configure the drill file generation to output plated holes and non-plated holes as separate files/drawings.

6. Generate Gerber Files

Configure and generate the complete set of required Gerber files for your design. This typically involves:

1. Set up the Gerber file output configuration in your PCB design tool. Specify:

2. Gerber format (RS-274X extended format is current standard)

3. Output directory
4. Desired file extensions
5. Plot scale and offset

6. Aperture list control

7. Select all required plot layers, including:

8. Top and bottom copper (.GTL, .GBL)

9. Inner signal layers (.G1, .G2, etc.)
10. Solder mask (.GTS, .GBS)
11. Silkscreen (.GTO, .GBO)
12. Solder paste (.GTP, .GBP)

13. Board outline on a mechanical layer (.GKO)

14. Initiate Gerber File Generation. The result will be a complete set of Gerber files for your design, usually zipped into a single archive file.

7. Review and Verify Gerber Files

Always carefully review your generated Gerber files before submitting them for manufacturing. Common checks include:

• Inspect Gerber layers in a Gerber viewer to confirm accuracy to original design
• Verify presence of all expected files (copper layers, masks, silkscreens, drills, etc.)
• Check for any missing features or discrepancies
• Ensure board outline is present
• Confirm drill holes are correct sizes and in proper locations

Many free and commercial Gerber file viewer tools are available for this purpose. Reviewing Gerber files in a neutral viewer outside your primary PCB design environment is a good validation practice.

8. Generate Assembly Outputs (Optional)

If you require PCB Assembly in addition to fabrication, generate and include the following files:

• Bill of Materials (BOM): Complete parts list
• Pick-and-Place File: Component locations and rotations
• Assembly Drawing: Component placement overview

These files are not technically part of the Gerber file set, but are usually included in the fabrication package if assembly is required.

9. Send Files for Manufacturing

Once your Gerber files are generated and verified, package them (usually in a .ZIP archive) and send them to your manufacturer for fabrication. Clearly communicate any special instructions, requirements, or questions to your manufacturer.

Common Gerber File Errors and Solutions

Certain errors in Gerber file generation are common. Be aware of these potential issues:

Careful layer checks and Gerber file review in a neutral viewer can identify most of these common errors before submitting files for manufacturing.

Gerber File Generation FAQs

What is the current Gerber file format standard?

The current Gerber file format standard is RS-274X, also known as Extended Gerber or X-Gerber. It is an enhancement of the older RS-274-D Gerber format that adds embedded aperture definitions and simplifies file structure. Always use RS-274X Gerber file format unless otherwise specified by your manufacturer.

What is an aperture list?

An aperture list is a definition of the aperture shapes and sizes used to interpret the vectors in the Gerber file. In older Standard Gerber RS-274-D, the aperture list was a separate file that needed to be included with the Gerber files. In Extended Gerber RS-274X, the aperture list is embedded in the Gerber file itself with the %AD parameters, simplifying file structure.

How do I verify my Gerber files are correct?

Always review your Gerber files in a neutral Gerber file viewer before submitting them for manufacturing. This allows you to confirm the files accurately represent your design intent outside of your primary PCB design tool environment. Visually inspect and compare each layer and feature to your original design. Many free Gerber viewers are available for this purpose.

What resolution should I use for Gerber files?

For best compatibility with manufacturing equipment, output Gerber files at the highest resolution supported by your PCB design software, typically 1.5 or 3.6 decimal places. Avoid imperial units and use metric (mm) units instead. Most modern vector photoplotters support 1.5 or 3.6 resolution in metric.

Should I use Gerber files or ODB++ for manufacturing?

While ODB++ is an alternative intelligent CAD-to-CAM data transfer format, Gerber is by far the most widely supported and universally accepted fabrication data format. Unless your manufacturer specifically requests ODB++, Gerber is the safest choice for ensuring compatibility and painless data transfer. Gerber is the lingua franca of PCB fabrication.

Conclusion

Generating accurate, complete Gerber files is a critical step in the PCB design-to-manufacturing process. By following the steps outlined here and carefully validating your outputs, you can ensure a smooth handoff to fabrication and minimize the risk of manufacturing errors. As an open, simple, and near-universally accepted standard, Gerber continues to be the most reliable choice for PCB fabrication data exchange.