What is a PCB Gerber File?

Introduction to PCB Gerber Files

A PCB Gerber file is a standard file format used in the electronic design automation (EDA) industry for the fabrication of printed circuit boards (PCBs). It contains all the necessary information required to manufacture a PCB, including the layout, dimensions, and materials. Gerber files are named after their creator, H. Joseph Gerber, who developed the format in the 1960s.

What Information is Contained in a PCB Gerber File?

A PCB Gerber file typically contains the following information:

1. Layer data: This includes the copper layers, solder mask, silkscreen, and drill layers.
2. Aperture definitions: These define the shapes and sizes of the pads, traces, and vias on the PCB.
3. Coordinate data: This specifies the locations of the various elements on the PCB.
4. Drill data: This includes the locations and sizes of the holes to be drilled in the PCB.

Why are PCB Gerber files Important?

PCB Gerber files are essential for the following reasons:

1. They provide a standardized format for communicating PCB design information between designers and manufacturers.
2. They ensure that the manufactured PCB matches the original design intent.
3. They reduce the risk of errors and misinterpretations during the manufacturing process.
4. They allow for automated manufacturing processes, which increases efficiency and reduces costs.

Understanding the Structure of a PCB Gerber File

Gerber File Extensions

PCB Gerber files typically have the following file extensions:

Aperture Definitions

Aperture definitions specify the shapes and sizes of the pads, traces, and vias on the PCB. They are defined using a specific format called the Aperture Definition (AD) format. The AD format consists of the following:

1. Aperture number: A unique identifier for each aperture definition.
2. Aperture type: The shape of the aperture (e.g., circle, rectangle, oblong).
3. Aperture size: The dimensions of the aperture (e.g., diameter, width, height).

Example AD format:

%ADD10C,0.5*%

In this example, %ADD indicates the start of an aperture definition, 10 is the aperture number, C indicates a circular aperture, and 0.5 is the diameter of the circle.

Coordinate Data

Coordinate data specifies the locations of the various elements on the PCB. Gerber files use a coordinate system based on the X and Y axes, with the origin (0,0) typically located at the bottom-left corner of the PCB.

Example coordinate data:

G54D10*
X1000Y1500D03*

In this example, G54 selects the aperture defined by D10, X1000Y1500 specifies the location of the element (1000 units in the X direction and 1500 units in the Y direction), and D03 indicates a flash command (i.e., place the aperture at the specified location).

Drill Data

Drill data specifies the locations and sizes of the holes to be drilled in the PCB. It is typically contained in a separate file with a .DRL extension.

Example drill data:

X1000Y1500T01
X2000Y2500T02

In this example, X1000Y1500 specifies the location of the first hole, T01 indicates the drill tool to be used (defined elsewhere in the file), X2000Y2500 specifies the location of the second hole, and T02 indicates the drill tool to be used for the second hole.

Creating PCB Gerber Files

EDA Software

PCB Gerber files are typically created using electronic design automation (EDA) software. Some popular EDA software packages include:

1. Altium Designer
2. KiCad
3. Eagle
4. OrCAD
5. Cadence Allegro

These software packages allow designers to create PCB layouts, define apertures, and generate Gerber files for manufacturing.

Gerber File Generation

Once the PCB layout is complete, the designer can generate Gerber files using the EDA software. The process typically involves the following steps:

1. Select the layers to be included in the Gerber files (e.g., copper layers, solder mask, silkscreen).
2. Define the apertures to be used for each layer.
3. Specify the coordinate format and units to be used.
4. Generate the Gerber files for each layer.

Best Practices for Creating PCB Gerber Files

To ensure that the PCB Gerber files are accurate and complete, designers should follow these best practices:

1. Use a consistent naming convention for the Gerber files (e.g., .GTL for top copper layer, .GBL for bottom copper layer).
2. Include all necessary layers in the Gerber files (e.g., copper layers, solder mask, silkscreen, drill data).
3. Use standard aperture sizes and shapes whenever possible.
4. Verify that the Gerber files match the original PCB layout before sending them to the manufacturer.
5. Communicate any special requirements or considerations to the manufacturer (e.g., material specifications, surface finishes).

Verifying and Inspecting PCB Gerber Files

Gerber Viewers

Gerber viewers are software tools that allow designers to visualize and inspect PCB Gerber files. Some popular Gerber viewers include:

1. GC-Prevue
2. ViewMate
3. Ucamco UcamX
4. Pentalogix ViewMate Pro
5. Aegis CAM350

These tools allow designers to check the Gerber files for errors, inconsistencies, or missing information before sending them to the manufacturer.

Common Errors in PCB Gerber Files

Some common errors that can occur in PCB Gerber files include:

1. Missing layers (e.g., forgetting to include the solder mask or silkscreen layers).
2. Incorrect aperture definitions (e.g., using the wrong size or shape for a pad or trace).
3. Overlapping or conflicting elements (e.g., traces that cross or overlap each other).
4. Incorrect coordinate data (e.g., placing elements in the wrong location on the PCB).
5. Incomplete or missing drill data (e.g., forgetting to include the drill file or using incorrect drill sizes).

By carefully inspecting the Gerber files using a Gerber viewer, designers can catch and correct these errors before sending the files to the manufacturer.

Communicating with PCB Manufacturers

When sending PCB Gerber files to a manufacturer, it is important to communicate any special requirements or considerations. This may include:

1. Material specifications (e.g., FR-4, Rogers, Isola).
2. Surface finishes (e.g., HASL, ENIG, OSP).
3. Impedance control requirements.
4. Special handling or packaging requirements.
5. Desired quantities and lead times.

By clearly communicating these requirements upfront, designers can ensure that the manufactured PCBs meet their specific needs and expectations.

Frequently Asked Questions (FAQ)

1. What is the difference between a Gerber file and a drill file?

A Gerber file contains information about the copper layers, solder mask, and silkscreen of a PCB, while a drill file contains information about the locations and sizes of the holes to be drilled in the PCB.

2. Can I use any EDA software to create PCB Gerber files?

Most EDA software packages support the creation of PCB Gerber files, including Altium Designer, KiCad, Eagle, OrCAD, and Cadence Allegro. However, the specific process for creating Gerber files may vary depending on the software being used.

3. What should I do if I find an error in my PCB Gerber files?

If you find an error in your PCB Gerber files, you should correct the error using your EDA software and regenerate the Gerber files. It is important to carefully inspect the updated Gerber files using a Gerber viewer to ensure that the error has been fully resolved before sending the files to the manufacturer.

4. How do I know what aperture sizes and shapes to use in my PCB Gerber files?

Aperture sizes and shapes are typically defined by the component manufacturer or the PCB design standards being followed (e.g., IPC-2221). EDA software packages often include libraries of standard aperture sizes and shapes that can be used in PCB designs.

5. What happens if I send incomplete or incorrect PCB Gerber files to a manufacturer?

If you send incomplete or incorrect PCB Gerber files to a manufacturer, it may result in delays, additional costs, or even the production of incorrect or non-functional PCBs. To avoid these issues, it is important to carefully verify and inspect your Gerber files before sending them to the manufacturer and to communicate any special requirements or considerations upfront.

Conclusion

PCB Gerber files are an essential tool for communicating PCB design information between designers and manufacturers. By understanding the structure and contents of Gerber files, using EDA software to create accurate and complete files, and carefully verifying and inspecting the files before production, designers can ensure that their PCBs are manufactured to their exact specifications and requirements. With the right tools and best practices, PCB Gerber files can help streamline the PCB manufacturing process and bring innovative electronic products to market faster and more efficiently.