Open EXCELLON Drill File Online Free

The Excellon format, officially developed by the Excellon Automation Company, serves as the industry standard for Computer-Aided Manufacturing (CAM) data used in printed circuit board (PCB) production. Unlike graphical image formats, an Excellon file is a structured ASCII text document containing coordinate data and machine tool commands.

Technical Details

The internal architecture of an Excellon file relies on specific syntax blocks, primarily the Header, Tool Definitions, and the Body. The header establishes the unit of measurement—either absolute or incremental—and specifies the coordinate format (e.g., 2.4 leading or trailing zeros). This numerical precision is critical; a single misplaced decimal interpretation can shift drill hits by several millimeters, ruining a PCB batch.

Excellon files utilize NC (Numerical Control) code, specifically a subset of G-code. The file structure defines drill bit diameters using "T" codes (e.g., T01, T02) which correspond to specific tool sizes stored in the header metadata. Compression is non-existent as the files are raw text, but size considerations arise in high-density interconnect (HDI) boards where tens of thousands of via-hole coordinates can bloat the ASCII character count.

Compatibility issues usually stem from the "leading/trailing zero suppression" settings. If the software opening the file expects zero suppression but the file includes them, the board geometry will appear scaled incorrectly. Furthermore, modern variations include "XNC" formats which are more standardized but occasionally cause legacy parser errors in older CAM software.

Step-by-Step Guide

1. Verify Source Integrity: Ensure the .drl or .xln file is accompanied by a tool list. If the tool diameters are not embedded in the file header, you will need a separate report file to manually assign drill sizes.
2. Access a Specialized Parser: Traditional text editors like Notepad++ can view the code, but to visualize the drill hits, you must use a dedicated CNC or Gerber viewer like OpenAnyFile.app.
3. Configure Coordinate Formats: Before importing, check if the file uses Imperial (inches) or Metric (mm) units. Mismatching these will result in an unreadable or microscopic board layout.
4. Load the Tool Table: In your viewer, confirm that "T01" correctly maps to the physical diameter specified in the design phase. If the holes appear too large or small, adjust the aperture settings within the software interface.
5. Align with Gerber Layers: Overlay the Excellon drill data on top of the copper layers (typically .GTL or .GBL files). The drill hits must center perfectly within the copper pads to ensure electrical connectivity.
6. Check for "Double Hits": Use the analytical tools in your viewer to identify redundant coordinates. Overlapping drill commands can cause mechanical fatigue or breakage of the CNC drill bits during actual fabrication.

Real-World Use Cases

PCB Fabrication and Quality Control

In mass-production environments, CAM engineers utilize Excellon data to generate the physical pathing for CNC drilling machines. They analyze the file to optimize the "travel path" of the drill head, ensuring the machine moves in the most efficient pattern to reduce wear and heat buildup.

Aerospace Electronics Engineering

Designers working on high-reliability avionics use Excellon files to verify "aspect ratios"—the relationship between the board thickness and the smallest drill diameter. Detailed analysis of the drill file allows engineers to confirm that the manufacturer can successfully plate the through-holes with copper without risking structural failure under thermal stress.

Prototype Debugging and Failure Analysis

When a hardware prototype fails, electrical engineers compare the physical board under a microscope against the digital Excellon drill coordinates. This process helps identify "drill break-out," where the hole is misaligned with the internal copper traces, causing open circuits or intermittent signals.

FAQ

Can I modify an Excellon file using a standard text editor?

Yes, because the format is ASCII-based, you can manually edit coordinates or tool definitions in a text editor. However, this is risky as any accidental deletion of a single character like a "G05" or "M30" command can render the entire file unreadable by CNC machinery.

Why does my Excellon file look like a single dot when I open it?

This is almost always a coordinate scaling error related to leading or trailing zero suppression. If the file expects the software to "guess" where the decimal point goes (e.g., 0025 instead of 0.0025), the software may interpret the coordinates as being much smaller or larger than intended.

What is the difference between a Gerber file and an Excellon file?

While both are used in PCB manufacturing, Gerber files define the shapes and traces of the copper layers, whereas Excellon files specifically define the holes meant to be drilled through those layers. You need both to manufacture a complete, functional circuit board.

Do Excellon files support multi-depth drilling?

The standard format primarily focuses on through-holes, but advanced versions include "Z-axis" commands for blind and buried vias. These files require specific headers to tell the CNC machine exactly how deep to plunge the bit before retracting.