A PCB drill file tells manufacturing equipment where holes belong and which tool diameter to use. It commonly ends in .drl,.xln, or .txt and usually uses an Excellon-style format. The file can describe component lead holes, vias, mounting holes, and, in supported exports, slots or routed features.
Drill data is not a substitute for the Gerber layers. Gerber files describe copper, solder mask, silkscreen, paste, and the board profile; the drill file supplies hole locations and sizes. To check a board properly, load both kinds of manufacturing data and confirm that the holes align with pads, vias, clearances, and the outline.
You can load an Excellon file and its companion layers in this online Gerber viewer. For a broader explanation of the two formats, read the Gerber versus drill file guide.
Quick answer
Open a .drl, .xln, or Excellon .txt file by loading it into a PCB viewer that supports drill data. Add the matching Gerber files at the same time, then inspect the drill overlay. If holes appear offset or incorrectly sized, verify units, coordinate precision, zero suppression, and that every file came from the same export revision.
What is an Excellon drill file?
Excellon is a coordinate-based format used for PCB drilling and routing data. A typical file defines a tool table, assigns a diameter to each tool, and lists the coordinates where that tool is used. Depending on the exporter and format version, the file may include a header with units and other settings, comments, repeat commands, and slot or route instructions.
The format is text-based in many modern workflows, so a text editor can reveal commands such as a tool definition and X/Y coordinates. That does not make a text editor a reliable visual checker. Coordinates may omit decimal points and zeros, and the intended geometry only becomes clear after a drill-aware parser applies the correct format settings.
Filename extensions are clues rather than proof. .drl and.xln strongly suggest drill data, while .txtcan contain almost anything. A drill map or drill report may look related but is not necessarily the machine-coordinate file. Keep the complete EDA export package whenever possible.
How to view a drill file with Gerber layers
- Open the free PCB manufacturing file viewer in your browser.
- Drag in the original fabrication ZIP if you have it. Otherwise, select the
.drl,.xln, or relevant.txtfile together with all matching Gerber files. - Let the viewer parse and overlay the layers. Do not judge the drill file in isolation if copper and outline data are available.
- Compare holes with top and bottom copper pads. Via holes should sit inside their annular rings, and through-hole component drills should match the expected pad locations.
- Check mounting holes, board-edge clearances, slots, and internal cutouts. Confirm that the profile and drill data share the same origin and scale.
- If separate plated and non-plated drill files are present, load both and use their filenames, documentation, and rendered geometry to keep their manufacturing intent clear.
A visual match is an important sanity check, but it does not prove that every fabrication setting is correct. The manufacturer still needs unambiguous plated/non-plated intent, finished-hole requirements where applicable, and a complete package. The PCB manufacturing file checklist explains the wider handoff.
Common unit and coordinate problems
Excellon coordinates may use inches or millimeters. They may also use an implied decimal format, meaning the coordinate digits do not contain a literal decimal point. The parser must know the coordinate precision to place the decimal correctly. A wrong assumption can make a pattern ten, one hundred, or one thousand times too large or too small.
Leading-zero and trailing-zero suppression create another source of ambiguity. With leading zeros omitted, digits missing from the left are implied; with trailing zeros omitted, missing digits are implied on the right. Terminology and file declarations must be interpreted together with the coordinate format. Guessing can produce geometry that looks regular but has the wrong scale or offset.
Modern exports often declare enough information in the header, but not every legacy file is self-describing. A sidecar report, CAM notes, or the original EDA export settings may be required. If the file is ambiguous, the safest solution is to regenerate it with explicit units and a format accepted by the chosen PCB manufacturer.
Why drill holes may not line up
- The drill and Gerber files were generated from different board revisions or exported with different origins.
- Inch data was interpreted as metric, or metric data as inches.
- The coordinate precision or zero-suppression mode was missing or interpreted incorrectly.
- Only one of multiple drill files was loaded, such as plated holes but not non-plated holes.
- A drill drawing was mistaken for the actual Excellon coordinate file.
- Slots or routed features use commands that were exported incorrectly or are not represented as expected in the selected file.
Do not repair a questionable manufacturing package by manually shifting or renaming files. Return to the source PCB project and create one clean export. Then reopen the complete set and repeat the alignment check. If Gerber layers are also unfamiliar, follow the guide to opening Gerber files.
FAQ
- What program opens a .drl file?
- A PCB CAM or Gerber viewer with Excellon support can open a .drl file. This online viewer can load the drill file together with its related Gerber layers for visual inspection.
- Is an Excellon drill file a Gerber file?
- No. Gerber describes two-dimensional layer artwork, while Excellon describes drill tools, hole coordinates, and sometimes routed slots. They are separate manufacturing formats that are normally reviewed together.
- Can an Excellon drill file use a .txt extension?
- Yes. Some EDA exports name Excellon data .txt, but .txt is generic and does not guarantee that a file contains drill data. Check the file content, export documentation, and rendered result.
- Why are the holes the wrong size or position?
- The viewer may be interpreting the wrong units, coordinate precision, or leading/trailing-zero convention, or the drill file may come from a different board revision. Regenerate an explicit, matching export when the format is ambiguous.
- Should plated and non-plated holes be separate files?
- Many exports separate plated through holes and non-plated holes, which makes fabrication intent clearer. Other workflows include them in one file with suitable metadata or accompanying documentation; follow the fabricator requirements.