PCB tooling holes are non-plated holes that locate the board or panel on pins during drilling, assembly, testing and depaneling. Most designs need three or four of them, usually in the panel rails rather than the board itself, with diameters in the 1–3 mm range; one widely used EDA guide lists 1 to 3 mm in 0.5 mm steps, or 0.062, 0.093 and 0.125 inch. The PCB tooling holes requirements that belong on the drawing are which holes are yours (fixed by your fixture) and which the fabricator may add, the finished diameter and tolerance for the ones you control, and that they are unplated.
| Requirement | Typical entry | Who decides |
|---|---|---|
| Plating | NPTH (non-plated) | Designer |
| Diameter | 1–3 mm; match the fixture pin | Fixture owner |
| Count and pattern | 3–4 holes, asymmetric so the panel loads one way only | Designer or assembler |
| Location | Panel rails; in the board only if the product needs them | Designer |
| Position tolerance | From the datum used by the fixture | Designer |
| Extra rail holes | Allowed or not | Designer, stated on the drawing |
What Are PCB Tooling Holes Used For?
They give machines and fixtures a mechanical reference. The fabricator pins panels through tooling holes for drilling, imaging and routing; the assembler uses them to seat the panel in printers, pallets and test fixtures; a bed-of-nails tester relies on them to bring probes onto test pads. In each case the hole is a datum, not an electrical feature, which is why it is drilled without plating and kept away from copper.
IPC-2221C, the generic design standard, treats tooling holes as unsupported (non-plated) holes and covers their location tolerance and the datum features they relate to in separate clauses (IPC-2221C contents, December 2023). The Gerber format has a dedicated attribute for them, MechanicalDrill with the Tooling function, so the fabricator can tell a tooling hole from a component hole in the data (Gerber format specification, May 2026).
What Size Should a Tooling Hole Be?
The size of the pin it goes on. When you own the fixture, the hole diameter and tolerance come from the fixture drawing. When you do not, a hole between 1 and 3 mm is what assembly lines usually expect; the Altium guide gives 1 to 3 mm in 0.5 mm increments and the imperial sizes 0.062, 0.093 and 0.125 inch (Altium on tooling holes).
A real drawing shows how this is written. TI’s fabrication drawing for one of its LaunchPad reference panels calls out four 3 mm tooling holes, marked non-plated, on a 1.6 mm board, with three 1.5 mm fiducials on both sides (TI TIDA-010024 drawing, 2018). Treat that as an example of a complete callout, not a size every line uses.
Write the finished size, not the drill size. The fabricator chooses the drill to land the finished hole within tolerance, and for a hole that has to fit a pin, the tolerance matters more than the nominal. Tooling holes for a press-fit pin or a precise test fixture need a tighter tolerance than a hole that only stops the panel from sliding.
Where Should Tooling Holes Go?
In the panel rails or breakaway frame, near the corners, in an asymmetric pattern. Rails keep the holes off the product, so they disappear when the panel is separated; corners give the widest spacing and the best angular accuracy; an offset in one hole stops an operator from loading the panel rotated by 180°.
Keep them away from features that weaken the rail: V-score lines, tab routes and mouse bites. Leave copper clear around each hole, and keep it far enough from the panel edge that the rail does not crack when the pin takes load. Put tooling holes in the board itself only when the finished product needs them, for example to locate it in an enclosure or a production test fixture after depaneling. Our article on panelization for assembly covers rail width and break-off methods.
How Are Tooling Holes Different From Fiducials and Mounting Holes?
They locate mechanically; fiducials locate optically; mounting holes hold the finished board. An SMT line uses tooling pins to seat the panel and then reads fiducials, small copper targets with a clear ring of solder mask, to correct the placement position. A panel normally needs both, and the fiducials should be offset from the tooling holes so the camera does not confuse the two.
| Feature | Purpose | Plated? | Where |
|---|---|---|---|
| Tooling hole | Mechanical location on pins | No | Panel rails, sometimes the board |
| Fiducial | Optical reference for placement | No hole; copper target | Panel and board corners, near fine-pitch parts |
| Mounting hole | Fastens the finished board | Either, by design | In the board |
Mounting holes are sized for the screw. ISO 273 lists clearance holes for metric screws in fine, medium and coarse series: for an M3 screw, 3.2, 3.4 and 3.6 mm; for M2.5, 2.7, 2.9 and 3.1 mm; for M4, 4.3, 4.5 and 4.8 mm. A plated mounting hole also grounds the board to the chassis; an unplated one keeps it isolated. Keep copper clear of the screw head and washer; our guide to copper-to-edge clearance covers the related edge rules.
Which Tooling Holes Should the Designer Control?
The ones a downstream fixture depends on. If your assembler, test house or product enclosure uses specific pins, give their positions from a datum, the finished diameter and the tolerance on the panel or board drawing, and mark them “do not move”. Everything else can be left to the fabricator.
Fabricators add their own holes to rails and production panels for registration in drilling and imaging. That is normal and does not affect the product, as long as the drawing says whether added rail holes are allowed and the board outline stays untouched. Problems start when the two sets are not separated: a supplier moves a fixture hole to suit its panel, or adds a hole inside the board, and the parts no longer fit the customer’s fixture.
What Should the Drawing and RFQ Include?
| Item | Example | Why |
|---|---|---|
| Controlled holes | “4× Ø3.0 mm NPTH, positions per panel drawing, do not move” | Protects the fixture interface |
| Tolerance | Diameter and position tolerance from datum A | Sets the pin fit |
| Plating | “Tooling holes non-plated” | Prevents a plated hole on a datum |
| Supplier holes | “Additional rail holes permitted outside the board outline” | Lets the fabricator panelize freely |
| Fiducials | Size, mask opening and positions | Keeps optical and mechanical datums separate |
| Panel drawing | Rails, break method, panel size | Shows where the holes live |
Send the panel drawing with the Gerber and drill files, and label tooling holes in the drill data rather than leaving them as unlabeled drill hits. If an assembly house will receive the panels, include its fixture requirements before the fabricator builds the first panel. A free DFM check catches holes too close to V-scores or copper before production.
How Can We Help?
QueenEMS drills to a hole position accuracy of ±0.025 mm and mechanical holes down to 0.15 mm, so tooling holes for tight-fitting fixture pins are within normal capability. Send the panel drawing with your controlled holes marked; we keep those positions as given and tell you, in the quote, which rail holes we plan to add for our own process. Bare-board quotes are returned within 2 hours.
Conclusion
| Situation | Tooling-hole rule |
|---|---|
| Bare boards, no customer fixture | Let the fabricator place rail holes |
| SMT assembly in panels | 3–4 NPTH holes in rails, asymmetric, plus fiducials |
| Customer test or assembly fixture | Diameter, tolerance and position on the drawing, “do not move” |
| Holes needed after depaneling | Place in the board and approve as product features |
Mark which holes you own, give them a finished size and tolerance, and keep them unplated. Contact us with the Gerber and drill files, the panel drawing and any fixture requirements.
FAQ
What does a PCB drill do? It makes the holes in the board: plated holes for components and vias, and unplated holes for tooling and mounting.
What are the standard sizes for PCB mounting holes? They follow the screw. For M3, ISO 273 gives clearance holes of 3.2, 3.4 or 3.6 mm depending on the fit series.
Are tooling holes plated? No. They are drilled as non-plated holes because they serve as mechanical datums.
How many tooling holes does a panel need? Usually three or four, placed so the panel can only be loaded one way.
Can tooling holes be inside the board? Yes, when the finished product needs them for a fixture or enclosure; otherwise keep them in the rails.
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