What Is Drill File Generation From a Physical Board?
Drill file generation is the process of extracting every hole location, diameter, plating specification, and tool assignment from a physical PCB and encoding that data into an industry-standard NC drill file—typically Excellon 2 format. When original design files are lost, obsolete, or never available, this is the only reliable path to a fabrication-ready drill dataset. Our engineers routinely achieve positional accuracy within ±0.05 mm (±2 mil) and diameter tolerances of ±0.025 mm (±1 mil) across boards ranging from simple 2-layer designs to 20+ layer HDI stackups.
Why Drill Files Matter More Than Most Engineers Expect
A Gerber set without a matching drill file is unfabricable. The drill file tells the CNC drilling machine where to plunge, at what diameter, and whether the hole is plated (PTH) or non-plated (NPTH). Miss a single via or mis-assign one tool, and the entire board fails electrically or mechanically at assembly.
Common scenarios that trigger drill file generation from a physical board:
- Legacy equipment repair — original OEM dissolved or refuses to supply data.
- Second-source qualification — you need a fab-ready package to quote alternate suppliers.
- Design recovery after data loss — EDA archives corrupted, engineer departed, backup tapes unreadable.
- Competitive benchmarking — understanding hole density, via strategy, and drill complexity of a reference design.
In each case the drill file is not optional—it is the foundation that ties copper layers to physical connectivity. Understanding what a Gerber file contains helps clarify why drill data must ship alongside it as a separate, coordinated dataset.
How Our Engineers Extract Drill Data Step by Step
1. Board Intake and Optical Scan
We photograph the board at 2400+ DPI using calibrated flatbed scanners or structured-light inspection systems. Fiducial marks and board edges establish the coordinate origin. If the board is encapsulated, our potting removal process exposes the surface first.
2. Hole Detection and Measurement
Automated vision software identifies every hole centroid, then our engineers verify against the physical board under a toolmaker’s microscope at 30–80× magnification. We measure finished hole diameters with pin gauges accurate to 0.01 mm. For blind and buried vias on HDI boards, we use micro-sectioning or X-ray CT to confirm depth and target layer.
3. Tool Table Construction
Each unique diameter is assigned a tool number (T01, T02, …). We consolidate near-identical sizes using IPC-2221B preferred drill sizes where the board’s fab house clearly rounded to a standard tool. A typical 6-layer board yields 8–14 unique tools; complex HDI designs may reach 25+.
4. Plating Classification
Every hole is tagged PTH or NPTH. We determine plating status by checking barrel conductivity with a 4-wire micro-ohmmeter, cross-referencing annular ring presence on inner layers, and inspecting via fill or plug status under magnification.
5. File Export and Cross-Check
The completed dataset exports as Excellon 2 (ASCII), with an optional secondary format if the fab requires it. We overlay the drill file on the recovered Gerber layers in CAM software and run a DRC checking pad-to-hole registration, minimum annular ring (typically ≥ 0.1 mm for Class 2, ≥ 0.05 mm for Class 3), and hole-to-copper clearance. Any mismatch triggers a re-measure cycle.
Drill File Formats: What You Receive
| Format | Extension | Typical Use | Notes |
|---|---|---|---|
| Excellon 2 | .drl / .xln | Universal CNC drill | De facto standard; ASCII, human-readable |
| Excellon 1 | .drl | Older fab houses | Fixed-format; rarely needed today |
| Gerber X2 drill | .gbr | Integrated Gerber packages | Embeds drill as a Gerber layer with attributes |
| IPC-2581 | .xml / .cvg | Single-file fab+assembly | Drill data embedded in the ODB++ alternative |
| ODB++ | folder structure | Advanced fabs, DFM tools | Drill encoded within the step hierarchy |
By default we deliver Excellon 2 plus a Gerber-format drill drawing layer. If your fab workflow uses IPC-2581 packages, we can bundle drill data into that single deliverable instead.
Tolerances, Limits, and Honest Caveats
No extraction method is perfect. Here is what we guarantee—and where the boundaries lie:
| Parameter | Our Spec | Potential Issue |
|---|---|---|
| XY position accuracy | ±0.05 mm (±2 mil) | Warped or stretched boards may shift centroids; we compensate with multi-point registration |
| Diameter accuracy | ±0.025 mm (±1 mil) | Plating buildup inside barrels means finished hole ≠ drill diameter; we back-calculate using typical 25 µm Cu plating |
| Blind/buried via depth | Layer-accurate via X-ray or cross-section | Filled and capped microvias may require destructive sectioning of one sample |
| Slot / routed features | Captured as routed slots in Excellon | Irregular cutouts may need manual G-code pathing |
| Back-drill stubs | Identified if stub length > 0.2 mm | Sub-0.2 mm stubs may be indistinguishable from normal PTH |
Boards with heavy corrosion, fire damage, or missing sections present additional challenges. We assess feasibility before quoting and will flag any holes where confidence is below 95%.
How Drill Files Fit Into the Full Reverse Engineering Package
Drill file generation is one deliverable inside a broader PCB reverse engineering workflow. A complete fab-ready package typically includes:
- Gerber layers (copper, mask, silk, paste)
- NC drill file(s) — PTH, NPTH, and optionally blind/buried as separate files
- Board outline / mechanical layer
- Pick-and-place file for SMT assembly automation
- Bill of materials with manufacturer part numbers
- Netlist and optional schematic
For a detailed breakdown of every file in that package, see our full deliverable set documentation.
Drill Complexity by Board Class
Simple Through-Hole Boards (1–2 layers)
Typically 4–8 drill tools, all PTH or NPTH, no vias. Extraction takes 1–2 working days. These boards are straightforward, but legacy single-sided phenolic boards can be brittle—hole edges chip during measurement if handled roughly.
Standard Multilayer (4–8 layers)
Via counts jump to 200–2,000+. Buried vias between specific layer pairs require X-ray or cross-sectioning to confirm. Tool counts reach 10–18. Turnaround: 3–5 working days for drill data alone.
HDI and Microvia Boards (10+ layers)
Stacked and staggered microvias, laser-drilled holes as small as 0.075 mm (3 mil), via-in-pad, and back-drill features. We use X-ray CT at 5 µm resolution to map these structures non-destructively when possible. Tool tables can exceed 25 entries. Turnaround: 5–10 working days, depending on layer count and via density.
Common Mistakes That Ruin a Drill File
After reviewing thousands of drill files—both our own and those from other providers—these are the errors we see most often:
- Wrong zero-suppression setting — leading vs. trailing zero suppression in Excellon shifts every coordinate. Always confirm the header or use explicit decimal format (2:4 or 3:3).
- Metric/imperial mismatch — a file generated in mm but read as inches places holes 25.4× off. We embed unit declarations in every file header.
- PTH/NPTH merged into one file — many fabs require separate files. Merging them causes plating on mounting holes or missing plating on signal vias.
- Ignoring plating compensation — listing finished hole size instead of drill size means the fab drills too small after plating. We specify drill diameter, not finished diameter, per IPC-2221B Table 6-1.
Pricing Signals and Turnaround
Drill file generation as a standalone service starts around $150–$400 for a simple 2-layer board and scales with hole count, via complexity, and layer count. Most projects bundle drill extraction into a full Gerber recovery package. Turnaround ranges from 1 day (rush, simple boards) to 10 working days (complex HDI). We provide a firm quote within 24 hours of receiving your board or high-resolution scans.
Check feasibility for your project
Send the chip marking or board details and tell us what you need to recover. Add clear photos if available.
Request a feasibility reviewFrequently Asked Questions
Can you generate a drill file from board photos instead of the physical board?
High-resolution photos (2400 DPI minimum, calibrated scale reference in frame) allow us to extract hole positions and approximate diameters for through-holes. However, we cannot verify plating status, blind/buried vias, or exact finished-hole dimensions without the physical board or X-ray data. Accuracy drops to ±0.1 mm positional from photos alone.
Do you deliver separate drill files for PTH and NPTH holes?
Yes. By default we output two Excellon files: one for plated through-holes (including vias) and one for non-plated holes (mounting, tooling). If your fab requires a combined file with embedded attributes, we can provide that as well.
How do you handle slots and non-round holes?
Slots are encoded as routed paths (G85 or M15/M16 commands) within the Excellon file. Rectangular or irregular cutouts that exceed simple slot geometry are captured in the board outline / mechanical Gerber layer and noted in the drill drawing.
What if a hole on my board is damaged or plugged?
We cross-reference the damaged hole against the board’s pad pattern, net connectivity, and symmetry with identical circuit blocks. If sufficient evidence exists, we reconstruct the hole parameters with a confidence flag. If not, we mark it as unresolved and discuss options with you before finalizing.
Is drill file generation included in a full board copy project?
Always. Every electronic board copy engagement includes complete NC drill data as part of the standard deliverable set. You never need to order it separately unless you only need drill data and nothing else.
Working on a board like this?
Send the chip marking or two photos. You get feasibility, lead time and price within 24 hours, and the check costs nothing.
Get a free quote