Excellon Drill File Format – PCB NC Drill Files Explained

The Excellon drill file format is one of the most common formats used to describe drilled holes and routing information for printed circuit board manufacturing. Excellon files are normally used together with Gerber files, ODB++ data or other PCB fabrication data to define how a circuit board should be produced.

Typical file extensions: .drl, .drd, .xln, .txt, .tap
Format type: PCB NC drill and routing format
Common use: PCB drilling, plated holes, non-plated holes, vias and board fabrication

What Is an Excellon Drill File?

An Excellon drill file is a machine-readable text file that describes where holes should be drilled in a printed circuit board. The file usually contains a list of drill tool definitions followed by X and Y coordinates for each drilled hole.

During PCB manufacturing, these files help drilling and routing machines place holes for vias, component leads, mounting holes and other mechanical features. The drill file must align correctly with the Gerber copper layers and the board outline to avoid manufacturing errors.

How Excellon Files Relate to Gerber Files

Gerber files describe the visual PCB production layers, such as copper, solder mask, silkscreen, paste and mechanical outlines. Excellon drill files describe hole and drill information. A complete PCB manufacturing job will often include both Gerber files and one or more Excellon drill files.

Gerber files: define PCB layer artwork.
Excellon drill files: define drilled holes and tool positions.
ODB++: can package many PCB manufacturing details in a structured dataset.

Because drill data and Gerber layers are separate in many workflows, it is important to verify that all files use the correct units, coordinate format, zero suppression and origin.

What Information Does an Excellon File Contain?

The exact content of an Excellon file can vary, but a typical file may contain header information, units, coordinate format settings, drill tool definitions and drilling coordinates.

Common Drill File Data

Drill tool numbers
Tool diameters
X and Y hole coordinates
Units, such as inch or millimeter
Coordinate format information
Plated and non-plated hole data
Routing or slot information in some files

Typical PCB Hole Types

Vias
Through-hole component pins
Mounting holes
Tooling holes
Non-plated mechanical holes
Slots and routed features

Simple Excellon Drill File Example

A simplified Excellon file may look like this:

M48
METRIC,TZ
T01C0.500
T02C0.900
%
T01
X010000Y015000
X020000Y015000
T02
X030000Y025000
M30

In this simplified example, the header defines metric units and two drill tools. The following coordinate lines define where each selected tool should drill holes. Real-world files may contain more commands and may depend on the CAD system or CAM output settings used to generate them.

Common Problems with Drill Files

Drill files can be easy to misinterpret if important information is missing or inconsistent. A drill file without clear units, tool sizes or coordinate formatting can create uncertainty during PCB production.

Wrong units, such as inch instead of millimeter.
Incorrect zero suppression settings.
Missing drill tool sizes.
Drill holes not aligned with Gerber layers.
Separate plated and non-plated files not clearly identified.
Slots or routed features interpreted incorrectly.

This is why drill files should always be visually checked together with the corresponding Gerber layers before a PCB design is sent to manufacturing.

View, Inspect and Convert Excellon Drill Files with GerbView

GerbView can open Excellon drill files together with Gerber, ODB++, PDF, DXF, HPGL/2 and other supported formats. This allows you to inspect the complete PCB manufacturing data before production or documentation.

Open Excellon Drill Files with GerbView

With GerbView you can view drill holes together with the rest of your PCB manufacturing layers, making it easier to verify hole placement, tool sizes, board alignment and output quality before fabrication.

Learn more about GerbView

What Can GerbView Do with Excellon Files?

View and Inspect Drill Data

Open Excellon drill files in Windows
Load drill files together with Gerber PCB layers
Inspect hole positions and drill patterns
Verify alignment between drill data and copper layers
Review PCB manufacturing data before production

Convert and Document PCB Data

Convert PCB manufacturing data to PDF
Export drill and board data to DXF
Create SVG or image output for documentation
Print PCB layers and drill information
Create documentation from Gerber and drill files

Useful for PCB Review and Documentation

Excellon files are an important part of a PCB fabrication package. GerbView helps engineers, PCB designers and manufacturing teams review drill data alongside Gerber or ODB++ layers, reducing the risk of sending incomplete or misaligned data to production.

Conversion to PDF, DXF and Other Formats

GerbView can convert PCB manufacturing data to widely used formats such as PDF, DXF, SVG and image formats. This is useful for documentation, inspection, customer communication, mechanical design workflows and archiving.

Best Practices for Excellon Drill Files

Always include drill files together with the matching Gerber layers.
Check that units and coordinate format are correct.
Confirm that plated and non-plated holes are clearly identified.
Verify that drill holes align with pads, vias and the board outline.
Include drill tool sizes in the file header whenever possible.
Inspect the complete PCB manufacturing package before sending it to production.

Excellon Drill File Format FAQ

What is an Excellon drill file?

An Excellon drill file is a PCB manufacturing file that contains drilling information, including hole locations and drill tool numbers. It is commonly used together with Gerber files to manufacture printed circuit boards.

What is an NC drill file?

An NC drill file is a numerical control file used to describe drilling or routing operations for PCB manufacturing. Excellon is one of the most common NC drill file formats.

Are Excellon and Gerber files the same?

No. Gerber files describe PCB image layers such as copper, solder mask and silkscreen, while Excellon drill files describe drilled holes and sometimes routing information.

What information is stored in an Excellon file?

An Excellon file normally stores drill coordinates, tool numbers, drill sizes, units and formatting information. Some files may require additional information if the header is incomplete.

Can GerbView open Excellon drill files?

Yes. GerbView can open Excellon drill files together with Gerber and other PCB manufacturing files, making it possible to inspect drill holes together with the PCB layers.

Can Excellon drill files be converted to PDF or DXF?

Yes. GerbView can convert Excellon drill data and PCB manufacturing layers to formats such as PDF, DXF, SVG and image formats.

Why should drill files be checked before PCB manufacturing?

Drill files should be checked to confirm that hole positions, tool sizes, units, scaling and alignment match the Gerber layers before the board is sent for manufacturing.

Related Information

Note: Excellon files may vary depending on the PCB design software, CAM system or manufacturing export settings used to create them.