How To Avoid Common Problems With Gerber File During PCB Manufacturing Process

What is a Gerber File?

A Gerber file is a standard file format used in the printed circuit board (PCB) industry to describe the printed circuit board images: copper layers, solder mask, legend, drill data, etc. It is the universal language for PCB fabrication data exchange.

Gerber files are ASCII vector image description files. They are 2D binary vector images, which means that only the image outlines are considered without any thickness information. The files describe each PCB layer using a photo plotter language containing commands (G-codes) and coordinates (X, Y).

Why are Gerber Files Important?

Gerber files are essential for PCB manufacturing because they contain all the necessary information for fabricating the circuit board. The PCB manufacturer uses these files to create the photomasks and stencils needed for the various steps in the manufacturing process, such as etching, drilling, and solder mask application.

Accurate and properly formatted Gerber files are crucial for ensuring that the manufactured PCB matches the design intent. Errors or inconsistencies in the Gerber files can lead to manufacturing defects, delays, and increased costs.

Common Pitfalls with Gerber Files

Despite being a standard format, there are several common issues that can arise with Gerber files during the PCB manufacturing process. These pitfalls can lead to problems such as manufacturing defects, delays, and increased costs.

1. Missing or Incorrect Layers

One of the most common issues with Gerber files is missing or incorrect layers. A complete set of Gerber files should include all the necessary layers for manufacturing the PCB, such as:

• Copper layers (top, bottom, and inner layers)
• Solder mask layers (top and bottom)
• Silkscreen layers (top and bottom)
• Drill files (plated and non-plated holes)
• Outline layer

If any of these layers are missing or incorrect, it can lead to manufacturing errors and delays.

2. Incorrect File Extensions

Another common problem is using incorrect file extensions for the Gerber files. The standard file extensions for Gerber files are:

Using non-standard file extensions can cause confusion and lead to errors in the manufacturing process.

3. Incorrect Aperture Definitions

Gerber files use apertures to define the shapes and sizes of the features on the PCB layers. Aperture definitions are typically included in a separate file or embedded within the Gerber files.

Incorrect aperture definitions can cause issues such as:

• Incorrect feature sizes (e.g., trace widths, pad sizes)
• Missing or extra features
• Incorrect solder mask or silkscreen openings

To avoid these issues, ensure that the aperture definitions are correct and consistent across all the Gerber files.

4. Overlapping or Conflicting Features

Overlapping or conflicting features in the Gerber files can cause manufacturing issues, such as short circuits or open circuits. Common examples include:

• Overlapping traces or pads on the same layer
• Traces or pads too close to the board edge
• Silkscreen or solder mask features overlapping with pads or vias

To avoid these issues, ensure that the design adheres to the PCB manufacturer’s design guidelines and that the Gerber files are thoroughly checked for any overlapping or conflicting features.

5. Incorrect Units or Coordinate Format

Gerber files can use either metric (millimeters) or imperial (inches) units, and the coordinates can be either absolute or incremental. Inconsistencies in the units or coordinate format can lead to manufacturing errors.

To avoid these issues, ensure that all the Gerber files use the same units and coordinate format, and that they match the intended design. Most PCB design software allows you to specify the desired units and coordinate format when exporting Gerber files.

Best Practices for Creating Gerber Files

To minimize the risk of common pitfalls and ensure a smooth PCB manufacturing process, follow these best practices when creating Gerber files:

1. Use a reputable PCB design software that supports the latest Gerber file format (RS-274X).
2. Ensure that all the necessary layers are included in the Gerber files and that they use the correct file extensions.
3. Double-check the aperture definitions to ensure they are correct and consistent across all the files.
4. Adhere to the PCB manufacturer’s design guidelines to avoid overlapping or conflicting features.
5. Use consistent units and coordinate format across all the Gerber files.
6. Generate a complete set of Gerber files, including drill files and outline layer.
7. Thoroughly review the Gerber files before submitting them to the PCB manufacturer, using a Gerber viewer to check for any errors or inconsistencies.

FAQ

1. What is the difference between Gerber files and ODB++ files?

Gerber files and ODB++ (Open Database++) files are both used for PCB fabrication data exchange, but they have some key differences:

• Gerber files are a 2D vector image format, while ODB++ is a more comprehensive database format that includes both 2D and 3D data.
• ODB++ files contain additional information such as layer stackup, materials, and design intent, which is not included in Gerber files.
• ODB++ is a proprietary format developed by Mentor Graphics, while Gerber is an open standard.

2. Can I use different units for different layers in Gerber files?

No, it is not recommended to use different units for different layers in Gerber files. Inconsistencies in units can lead to manufacturing errors. Always use the same units (either metric or imperial) for all the layers in a set of Gerber files.

3. What should I do if I find an error in my Gerber files after submitting them to the PCB manufacturer?

If you discover an error in your Gerber files after submitting them to the PCB manufacturer, contact them immediately to inform them about the issue. Provide the corrected Gerber files as soon as possible to minimize delays in the manufacturing process.

4. Can I include multiple PCB designs in a single set of Gerber files?

No, each PCB design should have its own complete set of Gerber files. Including multiple designs in a single set of files can cause confusion and lead to manufacturing errors.

5. Are there any tools available for checking Gerber files for errors?

Yes, there are several tools available for checking Gerber files for errors, such as:

• GerberLogix
• CAM350
• ViewMate
• GC-Prevue

These tools can help identify common issues such as missing layers, incorrect aperture definitions, and overlapping features. Many PCB manufacturers also offer Gerber file checking services as part of their fabrication process.

Conclusion

Gerber files are essential for the PCB manufacturing process, as they contain all the necessary information for fabricating the circuit board. However, common pitfalls such as missing layers, incorrect file extensions, and overlapping features can lead to manufacturing defects, delays, and increased costs.

To avoid these issues, it is crucial to follow best practices when creating Gerber files, such as using a reputable PCB design software, ensuring all necessary layers are included, double-checking aperture definitions, and adhering to the manufacturer’s design guidelines.

By understanding the common problems that can arise with Gerber files and taking steps to prevent them, you can ensure a smooth and efficient PCB manufacturing process.