What are Gerber Files and How to Use Them for PCB Fabrication

What exactly are Gerber files, and why are they so crucial in the world of printed circuit board design and manufacturing? These files bridge the gap between design and manufacturing, acting as the essential link that transforms a digital concept into a physical product. This article will explore the different formats of Gerber files, how they are used, and why they are so important in PCB fabrication.

What are Gerber Files

Gerber files are the lifeblood of PCB fabrication. They are the de facto standard file format used in the PCB industry to describe printed circuit board images. These open ASCII vector format files contain detailed information on each physical board layer of your PCB design, such as copper layers, solder mask, legend, drill data, and more.

Think of Gerber files as the electronics world equivalent of a PDF. Just as a PDF preserves the exact layout and formatting of a document, Gerber files preserve the precise design of a PCB. They are treated as image files representing each manufacturing layer of a PCB, ensuring that the manufacturer can accurately reproduce your design.

Each Gerber file typically represents a single layer of the PCB. For example, one file might contain information about the top copper layer, while another describes the bottom solder mask. This layered approach allows for incredibly detailed and precise PCB designs.

PCB manufacturers use these files to translate the intricate details of a design into the physical properties of the PCB. The data in Gerber files guides machines through every phase of the production process, from creating copper traces to applying solder mask.

Gerber files are typically generated by PCB design software (CAD). Once an engineer has finished their circuit design, they use this software to create the Gerber files that will be sent to the manufacturer. This process ensures that the designer’s vision is accurately communicated to the production team.

Gerber File Formats

The world of Gerber files has evolved over time, with several formats developed to meet the changing needs of the PCB industry.

RS-274-D

RS-274-D, also known as Standard Gerber, is one of the oldest Gerber file formats. It was originally used for numerical control machines and later adapted for photo-plotters. This format was a subset of the Electronic Industries Association RS-274-D specification.

Standard Gerber was a simple ASCII format consisting of commands and XY coordinates. While it served its purpose for many years, it had limitations. For instance, it didn’t include information about the coordinate unit or aperture definitions, which often led to confusion and errors.

It’s worth noting that RS-274-D is no longer supported by its developer UCAMCO and is considered obsolete. If you encounter this format, it’s best to convert it to a more modern version.

RS-274X

RS-274X, also known as Extended Gerber or X-Gerber, was developed to address the flaws of RS-274-D. Released in September 1998, this format significantly improved upon its predecessor.

RS-274X is a human-readable ASCII format that includes embedded units, aperture definitions, and other crucial information. This self-contained format allows for multiple-layer structures and special polygon fills, minimizing photo-plotting errors by eliminating manual data entry.

RS-274X contains the complete description of a PCB layer image without requiring any external files. This self-contained nature makes it much more reliable and easier to work with than its predecessor.

Gerber X2

Gerber X2 is the latest Gerber file format, released in 2014. It involves advanced CAM software and builds upon the strengths of RS-274X while adding new features.

The most significant improvement in Gerber X2 is the addition of metadata to the image. This allows designers to assign attributes to features within the Gerber file, providing even more detailed information about the PCB design.

Gerber X2 includes information such as layer function, object functions, and locations of impedance-controlled traces. This additional data makes the manufacturing process even more precise and reduces the chances of misinterpretation.

X2 files typically use the .GBR extension for all files, eliminating the need for intuitive file extensions. The actual location in the PCB stackup can be encoded as part of the data in the .GBR files, allowing Gerber viewer utilities to rebuild the stackup accurately.

ODB++

While not strictly a Gerber format, ODB++ is worth mentioning as it’s sometimes used alongside or instead of Gerber files. ODB++ is a self-extracting file format with an all-inclusive, standardized input format.

Developed to address some of the limitations of Gerber files, ODB++ helps automate stack-up, drill placements, and labeling. It’s designed to reduce human errors by automating most processes.

However, ODB++ is not as widely used as Gerber formats. While it offers some advantages, particularly for complex designs, many manufacturers still prefer the simplicity and universality of Gerber files.

Gerber File Extensions

Understanding Gerber file extensions is crucial for effective PCB design and manufacturing. These extensions indicate the layer or function each file represents, helping both designers and manufacturers with PCB fabrication.

The standard file extension for Gerber files is .GBR or .gbr, though you might also encounter extensions like .GB, .geb, or .gerber. However, it’s the specific extensions that provide more detailed information about each file’s content.

Common extensions include:

• .GTL (Top Layer)
• .GBL (Bottom Layer)
• .GTO (Top Silk Screen)
• .GBO (Bottom Silk Screen)
• .GTS (Top Solder Mask)
• .GBS (Bottom Solder Mask)
• .GKO (Board Outline)

Each of these extensions corresponds to a specific layer or function in the PCB design. For example, a file with the .GTL extension contains information about the top copper layer of the PCB.

In the latest Gerber X2 format, the .FileFunction attribute has become the standardized method to link each layer in the PCB with its corresponding Gerber file in the fabrication data. This attribute provides even more precise information about the file’s content and purpose.

RS-274-X files use extensions in the format “GXY” to denote specific functions and layer assignments. On the other hand, X2 files typically use the .GBR extension for all files, relying on embedded metadata to distinguish between layers.

Generating Gerber Files from CAD Software

Now that we understand what Gerber files are and their various formats, what is the process of generating these crucial files from CAD software? While the exact steps may vary depending on your specific software, the general process remains similar across platforms.

Step 1: Complete Your PCB Design

Before generating Gerber files, ensure your PCB design is complete and thoroughly checked for errors. This includes verifying all connections, component placements, and design rule checks.

Step 2: Access the Gerber File Generation Tool

In most PCB design software, you’ll find an option to generate or export Gerber files. This might be under a menu item like “File,” “Export,” or “Manufacturing Outputs.”

Step 3: Select the Layers to Export

You’ll need to export Gerber files for each layer of your PCB. This typically includes:

• Top and bottom copper layers
• Top and bottom solder mask
• Top and bottom silkscreen
• Board outline
• Drill files (often in Excellon format)

Ensure you select all necessary layers for your design.

Step 4: Choose the Gerber Format

Select the appropriate Gerber format. While you should check with your manufacturer, RS-274X or Gerber X2 are generally recommended for modern PCB fabrication.

Step 5: Set the Units and Precision

Choose the units (inches or millimeters) and set the precision. A common setting is 2:4 or 2:5, meaning 2 digits before the decimal point and 4 or 5 after.

Step 6: Configure Other Settings

Depending on your software, you may need to configure additional settings such as apertures, drill formats, and layer polarities. When in doubt, consult your software’s documentation or your manufacturer’s guidelines.

Step 7: Generate the Files

Once all settings are configured, generate the Gerber files. Your software will create a set of files, each representing a different layer or aspect of your PCB design.

Step 8: Verify the Output

Before sending the files to your manufacturer, it’s crucial to verify them. We’ll cover this process in the next section.

Remember, while this process may seem complex, it’s actually quite straightforward once you understand the key steps. Always double-check your export settings before generating Gerber files to ensure accuracy and prevent manufacturing issues.

Viewing and Verifying Gerber Files

Verifying your Gerber files before sending them to manufacturers is not optional—it’s essential. This step can significantly reduce manufacturing errors and delays. But how exactly do you go about viewing and verifying these files?

Step 1: Choose a Gerber Viewer

Several Gerber viewers are available, both as local software and online tools. Some popular options include:

• Gerbv (open-source, multi-platform)
• FlatCAM (open-source, multi-platform)
• ViewMate (free, Windows)
• GerberLogix (free, Windows)
• Online viewers like the one provided by JLCPCB

Choose a viewer that’s compatible with your operating system and the Gerber format you’re using.

Step 2: Load Your Gerber Files

Open your chosen Gerber viewer and load your Gerber files. Most viewers allow you to drag and drop the files or use a file selection dialog.

Step 3: Check Layer Ordering

Ensure that all layers are present and in the correct order. If your Gerber viewer doesn’t understand the Gerber format extension and can’t determine the location in the layer stack, it might cue up the layers out of order (usually in alphabetical order). In this case, you may need to manually arrange the layers.

Step 4: Verify Board Dimensions

Check that the board outline is correct and that all layers align properly with this outline.

Step 5: Inspect Each Layer

Carefully examine each layer:

• Copper layers: Check for broken traces, unintended connections, or missing pads.
• Solder mask: Ensure all pads that need to be exposed are indeed exposed.
• Silkscreen: Verify that all text is readable and doesn’t overlap with pads or vias.
• Drill layer: Confirm that all holes are present and correctly sized.

Step 6: Check for Design Rule Violations

Some Gerber viewers can perform basic design rule checks. Use this feature if available to catch any violations of minimum trace width, clearance, etc.

Step 7: Compare with Your Original Design

If possible, compare the Gerber view with your original CAD design. This can help catch any discrepancies that may have occurred during the export process.

Step 8: Address Any Issues

If you find any problems, return to your PCB design software, make the necessary corrections, and generate new Gerber files. Then repeat the verification process.

Using Gerber Files in PCB Fabrication

Have you ever wondered how a digital design becomes a physical PCB? This is where Gerber files truly shine. They are the crucial link between your PCB design and the manufacturing process, guiding every step of fabrication.

When you send Gerber files to a PCB manufacturer, you’re providing them with a detailed blueprint of your board. Each Gerber file represents one layer in the physical board, such as copper layers, solder mask, legend, or silk. Together, these files provide a complete picture of your PCB design.

The process typically unfolds as follows:

1. File Reception and Verification: The manufacturer first receives and verifies your Gerber files. They’ll check for any obvious errors or missing information.
2. Image Generation: The Gerber files are used to create photographic films or direct digital images for each layer of the PCB. These images guide the creation of each physical layer.
3. Layer Creation: Using the images generated from the Gerber files, the manufacturer creates each layer of the PCB. For copper layers, this involves etching away unwanted copper, leaving only the traces and pads defined in your design.
4. Drilling: While not strictly part of the Gerber files (drill data is usually in Excellon format), the drilling process is guided by data often submitted alongside Gerber files.
5. Layer Alignment and Pressing: The individual layers are carefully aligned and pressed together to form the complete PCB.
6. Solder Mask and Silkscreen Application: The solder mask and silkscreen layers, defined by their respective Gerber files, are applied to the board.
7. Final Inspection: The completed board is inspected to ensure it matches the specifications provided in the Gerber files.

Gerber files are remarkably versatile in guiding the PCB fabrication process. They provide precise instructions for creating each aspect of the board, from the width and location of traces to the size and shape of pads.

Gerber files can provide the most necessary information, but manufacturers may need additional details for certain specifications. For example, Gerber files typically don’t include information about the color of the solder mask and silkscreen, requirements for panelization, pad finish, copper weight, and board thickness. These details are usually provided separately or discussed with the manufacturer.

Troubleshooting Common Gerber File Issues

Ever encountered a mysterious Gerber file error? You’re not alone. Despite their crucial role in PCB fabrication, Gerber files can sometimes be a source of frustration. Let’s explore some common issues and how to resolve them.

Duplicated Layers

One frequent issue is the appearance of “duplicated layers” when submitting Gerber files to a manufacturer. This can occur if you output the zip file to the same directory as the Gerbers, or due to incorrect settings in your CAD software.

Solution: Always check the contents of your zipfile before submission. Ensure there are no duplicated files and that layer assignments are correct. If using KiCad, be careful not to tick any boxes under “Plot on All Layers” unless necessary.

Incorrect File Formats

Using an obsolete file format like Gerber 274D can cause issues with modern manufacturing processes.

Solution: Use Gerber X2 or at least Gerber 274X. Check with your manufacturer to confirm their preferred format.

Missing Board Outlines

The absence of a defined board outline can be a significant problem when manufacturing your PCB.

Solution: Ensure you include a board outline in your Gerber files. This can be its own independent file or included on each layer in the data set.

Confusing File Labels

Unclear or inconsistent file naming can lead to mistakes in the manufacturing process.

Solution: Use clear, consistent naming conventions for your Gerber files. Each file name should reflect the board layer it represents and be easily interpretable.

Incorrect Drill File Formats

Problems with drill file formats can cause issues when importing the file for manufacturing.

Solution: Use the NC Drill file format, which is the industry standard. Ensure the header in the file clearly indicates the format.

Misalignment of Layers

When layers aren’t properly aligned, it can require manual alignment by the manufacturer, introducing potential errors.

Solution: When possible, have your Gerber files registered to a common data point. This helps ensure proper alignment of all layers.

Vector Fills for Plane Layers

Using vector fills for plane layers or layers with shield areas can result in large Gerber file sizes and require additional processing.

Solution: For areas to be filled, use “raster” or “contour” data instead of vector fills.

Composite Layers

Some PCB design software uses composite layers to create one layer, which can cause confusion.

Solution: Combine all composite layers and output as a single Gerber layer.

Vectorized Pads

Pads composed of many small vectors can require additional processing time.

Solution: Use flash pads instead of vectorized pads when possible.

Empty or Corrupted Gerber Data

This can result from incorrect settings in your CAD software.

Solution: Always verify your Gerber files using a Gerber viewer before submission. Check your CAD software settings carefully.

Gerber Files vs. Other PCB File Formats

With so many PCB file formats available, why do Gerber files remain the industry standard? To answer this question, let’s compare Gerber files with other PCB file formats and understand their relative strengths and weaknesses.

Gerber vs. ODB++

ODB++ is one of the main competitors to the Gerber format. Developed in 1992, ODB++ aims to address some of Gerber’s limitations.

Gerber:

• Widely accepted and supported
• Simple and easy to interpret
• Contains only image data

ODB++:

• Contains more comprehensive information (electrical data, material specs)
• Supports automation in the manufacturing process
• Can reduce the number of files needed

While ODB++ offers some advantages, particularly for complex designs, Gerber files remain more widely used due to their simplicity and universal acceptance.

Gerber vs. IPC-2581

IPC-2581 is an open-source standard that, like ODB++, aims to provide more comprehensive PCB data.

Gerber:

• Industry standard with wide support
• Simpler format
• Requires separate files for different aspects of the design

IPC-2581:

• Single file format containing all PCB data
• Includes stackup information and material properties
• Open standard, not controlled by any single company

While IPC-2581 offers some compelling features, it has not yet achieved the widespread adoption of Gerber files.

Other Formats

Other PCB formats include:

• IPC-D-350 C
• DXF
• PDF
• EDIF
• GenCAM (IPC-2511A and IPC-2511B)
• STEP AP210

Each of these formats has its own strengths and use cases, but none have displaced Gerber as the de facto standard for PCB manufacturing.

Why Gerber Remains Dominant

Gerber files are remarkably resilient in the face of newer, more complex formats. This is due to several factors:

1. Universal Support: Virtually all PCB manufacturers support Gerber files, making them a safe choice for designers.
2. Simplicity: The relative simplicity of Gerber files makes them easy to generate, read, and troubleshoot.
3. History: As the long-standing industry standard, there’s a wealth of knowledge and tools available for working with Gerber files.
4. Continuous Improvement: The Gerber format hasn’t stood still. Updates like Gerber X2 have added features to address some of the format’s limitations.

A good rule of thumb is to go by your preferred fabrication house’s supported formats. If they accept Gerber files (which most do), there’s often little reason to complicate the process by using a different format.

Excellon Files for PCB Drilling

Ever wondered how PCB manufacturers know exactly where to drill holes in your board? Excellon files. While not strictly part of the Gerber format, Excellon files are crucial companions to Gerber files in the PCB fabrication process.

Excellon files are commonly used to describe the holes on a PCB, providing CNC (Computer Numerical Control) instructions for drilling machines. They are typically provided to PCB manufacturers along with a set of Gerber files, completing the information needed for board fabrication.

The format most commonly used is Enhanced Excellon (or Excellon Version 2). This format is designed to drive CNC drilling and routing machines efficiently and accurately.

Key components of Excellon files include:

1. Tool Definitions: These specify the sizes of drill bits to be used.
2. Hole Coordinates: Precise X and Y coordinates for each hole to be drilled.
3. Plated vs. Non-Plated Holes: Information on which holes should be plated through and which should not.

When generating Excellon files, key settings to consider include:

• Layers: Specify which layers contain drill information (e.g., Drills, Holes, Plated Vias, Unplated Vias).
• Tool Sizes: Ensure all necessary tool sizes are included.
• Zero Suppression: This should typically be set to “off”.
• Origin: Usually set to “absolute” for consistency with Gerber files.

Excellon files ensure accurate PCB drilling. They work in tandem with Gerber files to provide a complete set of instructions for PCB fabrication. While Gerber files define the copper traces, solder mask, and other layer information, Excellon files ensure that holes for vias, through-hole components, and mounting are placed precisely where they’re needed.