What is a Drill File?

A drill file, also known as an NC drill file or Excellon file, is a machine-readable file format that contains information about the holes to be drilled in a PCB. It includes the following data:

• Hole coordinates (X and Y positions)
• Hole sizes
• Hole types (plated or non-plated)
• Tool sizes and definitions
• Drilling parameters (feed rates, speeds, etc.)

Drill files are typically generated from PCB design software and are used by CNC drilling machines to accurately drill holes in the PCB during manufacturing.

Drill File Formats

There are two main drill file formats used in the PCB industry:

Excellon Format

The Excellon format, named after the Excellon Automation company, is the most widely used drill file format. It has two main versions:

1. Excellon 1: This older version uses inch units and has limited tool definitions.
2. Excellon 2: This newer version supports both inch and metric units, as well as advanced tool definitions and drilling parameters.

Excellon files have a .drl or .txt file extension and follow a specific structure:

• Header section: Contains information about units, tool definitions, and coordinate format.
• Body section: Lists the hole coordinates and tool numbers.
• End-of-file marker: Indicates the end of the file.

Here’s an example of an Excellon 2 drill file:

M48
METRIC,TZ
T1C0.8
T2C1.2
%
T1
X10.5Y15.2
X22.0Y30.0
T2
X45.0Y20.0
X67.5Y42.8
M30

Sieb & Meyer Format

The Sieb & Meyer format, while less common, is still used by some manufacturers. It has a simpler structure compared to Excellon and uses a .smd file extension.

Generating Drill Files

To generate a drill file, you’ll need to use PCB design software that supports drill file export. Most popular PCB design tools, such as Altium Designer, KiCad, and Eagle, have built-in features for generating drill files.

Step 1: Design Your PCB

Start by designing your PCB in your chosen software. Ensure that all holes are properly defined, including their sizes, types, and layers.

Step 2: Set Up Drill File Export Settings

Before exporting the drill file, configure the export settings in your PCB design software. This typically involves:

• Selecting the drill file format (Excellon or Sieb & Meyer)
• Choosing the unit system (inch or metric)
• Specifying the coordinate format (absolute or incremental)
• Defining the tool sizes and parameters

Step 3: Export the Drill File

Once the export settings are configured, generate the drill file by selecting the appropriate export option in your software. The exported file will be saved in the specified format and location.

Step 4: Verify the Drill File

After generating the drill file, it’s crucial to verify its accuracy. You can use a drill file viewer or a Gerber Viewer that supports drill files to check for any errors or discrepancies. Ensure that the hole positions, sizes, and tool assignments match your PCB design.

Some common issues to look out for include:

• Missing or duplicate holes
• Incorrect hole sizes or types
• Misaligned or shifted hole coordinates
• Incorrect tool assignments

If any issues are found, make the necessary corrections in your PCB design software and regenerate the drill file.

Best Practices for Drill File Generation

To ensure optimal results and minimize issues during PCB manufacturing, follow these best practices when generating drill files:

1. Use a consistent unit system: Choose either inch or metric units and stick to that system throughout your design and drill file generation process.

2. Adhere to manufacturer specifications: Consult with your PCB manufacturer for their specific requirements regarding drill file formats, tool sizes, and parameters.

3. Keep tool sizes to a minimum: Minimize the number of unique tool sizes in your design to reduce setup time and cost during manufacturing.

4. Optimize hole placement: Avoid placing holes too close to the edge of the PCB or other components to prevent mechanical stress and drilling issues.

5. Follow naming conventions: Use clear and descriptive names for your drill files, including the PCB version, date, and any other relevant information.

6. Verify and double-check: Always verify your drill files before sending them to the manufacturer to catch any errors or discrepancies early in the process.

Tools for Drill File Generation and Verification

In addition to PCB design software, there are several dedicated tools available for generating, viewing, and verifying drill files:

• NCViewer: A free, cross-platform drill file viewer that supports Excellon and Sieb & Meyer formats.
• GC-Prevue: A professional Gerber and drill file viewer with advanced features for analysis and verification.
• PCB Toolkit: A collection of utilities for PCB design, including a drill file editor and converter.

These tools can help streamline your drill file generation process and ensure the accuracy of your files.

Troubleshooting Drill File Issues

Despite following best practices, issues may still arise during drill file generation or PCB manufacturing. Here are some common problems and their solutions:

1. Incorrect hole sizes: Double-check your hole size definitions in your PCB design software and ensure they match the manufacturer’s specifications. Regenerate the drill file with the correct sizes.

2. Misaligned holes: Verify that your hole coordinates are accurate and that the drill file matches your PCB design. Check for any shifts or offsets in the coordinates and adjust them in your design software.

3. Incompatible file format: Ensure that you are generating the drill file in a format compatible with your manufacturer’s requirements. Convert the file to the appropriate format using a drill file converter if necessary.

4. Missing or duplicate holes: Carefully review your PCB design and drill file for any missing or duplicate holes. Make the necessary corrections in your design software and regenerate the drill file.

5. Incorrect tool assignments: Verify that the tool numbers and sizes in your drill file match the definitions in your design. Update the tool assignments in your PCB design software and regenerate the file.

If you encounter persistent issues or need further assistance, consult with your PCB manufacturer or a PCB design expert for guidance.

Frequently Asked Questions (FAQ)

1. What is the difference between plated and non-plated holes in a drill file?
   Plated holes have a conductive coating on their inner walls to electrically connect different layers of the PCB, while non-plated holes are used for mechanical purposes and do not have a conductive coating.

2. Can I use different unit systems for my PCB design and drill file?
   It’s recommended to use a consistent unit system (either inch or metric) throughout your design and drill file generation process to avoid confusion and errors.

3. How do I choose the appropriate tool sizes for my drill file?
   Consult with your PCB manufacturer for their recommended tool sizes based on your PCB design requirements. Minimize the number of unique tool sizes to reduce setup time and cost.

4. What should I do if I find an error in my drill file after sending it to the manufacturer?
   Contact your manufacturer immediately and provide them with an updated and corrected drill file. The sooner you catch and address the error, the less impact it will have on your PCB production timeline.

5. Can I generate a drill file without using PCB design software?
   While it’s theoretically possible to create a drill file manually using a text editor, it’s highly recommended to use PCB design software for accuracy, efficiency, and compatibility with industry standards.

Conclusion

Generating accurate and compatible drill files is a critical step in the PCB manufacturing process. By understanding drill file formats, using the right tools, and following best practices, you can ensure that your PCBs are manufactured correctly and efficiently.

Remember to:

• Choose the appropriate drill file format based on your manufacturer’s requirements
• Configure your export settings correctly in your PCB design software
• Verify your drill files for accuracy and compatibility before sending them to the manufacturer
• Follow best practices for hole placement, tool sizes, and file naming conventions
• Troubleshoot any issues that arise during drill file generation or PCB manufacturing

By mastering the art of drill file generation, you can streamline your PCB design and manufacturing process, reduce errors and delays, and ultimately create high-quality, reliable printed circuit boards.