PCB Drill Tolerance: Hole Size, Position Accuracy & Manufacturing Standards

I’ve lost count of how many times a designer has called me asking why their components don’t fit into the board holes—only to discover they specified ±0.001″ tolerance on a plated through-hole. That tolerance doesn’t exist in the real world of PCB manufacturing. Understanding PCB hole tolerance isn’t optional; it’s fundamental to getting boards that actually work.

This guide covers everything you need to know about PCB hole tolerance from a practical engineering perspective. I’ll walk through the IPC standards, explain what tolerances are actually achievable, and share the design guidelines that will keep your boards manufacturable and reliable.

What is PCB Hole Tolerance?

PCB hole tolerance defines the acceptable variation in drilled hole characteristics from the designed specifications. When you specify a 0.8mm finished hole, the manufacturer can’t deliver exactly 0.8mm every time—there will be variation within an acceptable range.

Hole tolerance encompasses three distinct specifications:

• Diameter tolerance: The allowable variation in the hole’s finished size after all processing is complete.
• Position tolerance: How accurately the hole center is placed relative to its designed location.
• Plating tolerance: The variation in copper thickness deposited inside the hole barrel.

Plated vs. Non-Plated Hole Tolerances

The tolerance you can expect depends fundamentally on whether the hole will be plated.

Plated Through-Hole (PTH) Tolerances

Plated holes undergo multiple processing steps after drilling: cleaning, electroless copper deposition, electrolytic copper plating, and surface finishing. Each step introduces variation.

Finished Hole Size	Standard Tolerance	Notes
≤0.8mm (≤31 mil)	±0.08mm (±3 mil)	Small vias, tight tolerance
0.8-2.5mm (31-100 mil)	±0.10mm (±4 mil)	Most component holes
2.5-6.3mm (100-250 mil)	±0.15mm (±6 mil)	Larger mounting holes
>6.3mm (>250 mil)	±0.20mm (±8 mil)	Routed, not drilled

Non-Plated Through-Hole (NPTH) Tolerances

Non-plated holes are simpler—what you drill is essentially what you get, minus minor drill wear effects. This allows tighter tolerances:

Hole Type	Standard Tolerance	Achievable Tight Tolerance
Standard NPTH	±0.05mm (±2 mil)	±0.03mm (±1.2 mil)
Press-fit NPTH	±0.05mm (±2 mil)	±0.025mm (±1 mil)
Tooling holes	±0.05mm (±2 mil)	±0.025mm (±1 mil)

Hole Position Tolerance and Registration

Position accuracy is often more critical than diameter accuracy. A perfectly sized hole in the wrong location can break annular rings, cause shorts, or make component insertion impossible.

Position Tolerance by Hole Type

Hole Type	Position Tolerance	Notes
Mechanical drill	±0.075mm (±3 mil)	Typical production
Mechanical drill (tight)	±0.05mm (±2 mil)	Premium process
Laser drill (microvia)	±0.025mm (±1 mil)	HDI processes
Laser drill location	±0.13mm (±5 mil)	Per IPC guidelines

Factors Affecting Position Accuracy

Hole position accuracy degrades through the manufacturing process due to cumulative tolerances:

• Material variation: FR4 substrate varies ±0.005mm per inch from lot to lot
• Imaging registration: LDI systems achieve ±0.025mm front-to-back registration
• Lamination: Pin registration during lamination adds ±0.025mm
• Drill accuracy: CNC drill machines contribute ±0.025mm positioning error
• Drill wander: As drills penetrate through layers, they can wander from the ideal path

Annular Ring and Its Relationship to PCB Hole Tolerance

The annular ring—the copper pad remaining around a drilled hole—is directly impacted by both hole diameter and position tolerance.

IPC-6012 Annular Ring Requirements

IPC Class	External Min	Internal Min	Breakout?
Class 1	0mm (breakout OK)	0mm (breakout OK)	Yes, 90° max
Class 2	0mm (breakout OK)	0mm (breakout OK)	Yes, 90° max
Class 3	0.05mm (2 mil)	0.025mm (1 mil)	No

Practical Annular Ring Recommendations

Application	Recommended Ring	Notes
Standard via (single lam)	0.15mm (6 mil)	Class 2, safe margin
Standard via (multiple lam)	0.18mm (7 mil)	Additional registration
Class 3 via	0.15-0.18mm (6-7 mil)	No breakout allowed
Component holes	0.18mm (7 mil) min	Improves soldering

IPC Standards for PCB Hole Tolerance

IPC-6012: Rigid Board Performance Specification

IPC-6012 is the primary acceptance standard for rigid PCBs. It defines three product classes with different requirements:

Parameter	Class 2	Class 3
Min hole wall plating	20μm (0.8 mil)	25μm (1 mil)
Min annular ring (ext)	Breakout to 90°	0.05mm (2 mil)
Min annular ring (int)	Breakout to 90°	0.025mm (1 mil)

Mechanical Drilling vs. Laser Drilling Tolerances

Mechanical Drilling Specifications

Parameter	Standard Capability	Advanced Capability
Min drill diameter	0.15mm (6 mil)	0.10mm (4 mil)
Diameter tolerance	±0.08mm (±3 mil)	±0.05mm (±2 mil)
Position tolerance	±0.075mm (±3 mil)	±0.05mm (±2 mil)
Max aspect ratio	10:1	12:1

Laser Drilling Specifications

Parameter	CO2 Laser	UV Laser
Min hole diameter	0.075mm (3 mil)	0.025mm (1 mil)
Diameter tolerance	±0.025mm (±1 mil)	±0.013mm (±0.5 mil)
Position tolerance	±0.025mm (±1 mil)	±0.013mm (±0.5 mil)
Max aspect ratio	1:1 typical	1:1 typical

Design Guidelines for Managing PCB Hole Tolerance

The 7-Mil Rule and When to Use It

The rule of thumb for through-hole components: make the finished hole 0.18mm (7 mil) larger than the component lead diameter. This accounts for lead diameter tolerance (typically ±0.075mm), PCB hole tolerance (typically ±0.1mm), and minor plating variations.

Specifying Tolerances in Fabrication Drawings

Be explicit in your documentation:

Feature	Good Specification	Poor Specification
Component hole	0.9mm ±0.08mm FINISHED	0.9mm
Via hole	0.3mm +0.05/-drill size	0.3mm ±0.001mm
Press-fit hole	1.0mm ±0.05mm NPTH	1.0mm
Mounting hole	3.2mm ±0.10mm NPTH	3.2mm NPTH

Common Mistakes and How to Avoid Them

Mistake 1: Specifying Unrealistic Tolerances

Specifications with ±0.001″ (±0.025mm) tolerances on plated holes aren’t achievable in standard manufacturing. The plating process alone introduces more variation than this. For standard plated holes, specify ±0.08mm (±3 mil) minimum.

Mistake 2: Ignoring Plating Copper Consumption

Designers sometimes specify the drill size as the finished hole size, forgetting that plating reduces the hole diameter by 0.05-0.10mm (2-4 mil) total. Always specify FINISHED hole size and let the fabricator determine the appropriate drill size.

Mistake 3: Insufficient Annular Ring for Layer Count

A 4-layer design might work fine with 0.13mm (5 mil) annular ring, but the same design at 12 layers will have breakout issues. Add 0.025mm (1 mil) to annular ring for every lamination cycle beyond the first.

Useful Resources

IPC Standards

• IPC-6012: Qualification and Performance Specification for Rigid Printed Boards
• IPC-2221: Generic Standard on Printed Board Design
• IPC-A-600: Acceptability of Printed Boards (visual inspection criteria)
• IPC Standards Portal: https://shop.ipc.org

Manufacturer Resources

• Sierra Circuits: https://www.protoexpress.com/kb/manufacturing-tolerances/
• Eurocircuits: https://www.eurocircuits.com/pcb-design-guidelines/drilled-holes/
• PCBWay: https://www.pcbway.com/pcb_prototype/PCB_Manufacturing_tolerances.html

Frequently Asked Questions

What is the standard PCB hole tolerance for plated through-holes?

The standard PCB hole tolerance for plated through-holes is ±0.08mm (±3 mil) for holes up to 0.8mm diameter, and ±0.10mm (±4 mil) for holes between 0.8mm and 2.5mm. These tolerances apply to the finished hole size after plating. Specifying tighter tolerances like ±0.05mm (±2 mil) is possible but requires premium processing and increases cost.

How much larger should a PCB hole be than the component lead?

A PCB hole should be approximately 0.18mm (7 mils) larger than the component lead diameter. This accounts for lead tolerance (typically ±0.075mm), PCB hole tolerance (±0.08-0.10mm), and allows for easy component insertion during assembly. For example, a component with 0.56mm leads should have a finished hole size of approximately 0.74mm.

What causes hole breakout and how can I prevent it?

Hole breakout occurs when the drilled hole extends beyond the copper pad boundary, typically due to drill position tolerance exceeding the available annular ring. Prevention requires designing adequate annular rings that account for both diameter and position tolerances. For Class 2 designs, use minimum 0.13mm (5 mil) annular ring for simple boards, increasing to 0.15-0.18mm (6-7 mil) for boards with 8+ layers.

What’s the difference between IPC Class 2 and Class 3 hole requirements?

IPC Class 2 allows 90-degree breakout on both external and internal layers, while Class 3 requires minimum annular rings of 0.05mm (2 mil) external and 0.025mm (1 mil) internal with no breakout permitted. Class 3 also requires thicker minimum hole wall plating (25μm vs. 20μm for Class 2). Class 2 is appropriate for most commercial applications, while Class 3 is required for aerospace, medical, and military electronics.

Can I specify different tolerances for different holes on the same board?

Yes, you can and should specify different tolerances for different hole types. Component holes that require specific fit (like press-fit connectors) may need tighter tolerances than standard vias. Document this clearly in your fabrication drawing with a drill chart that lists each hole size, quantity, tolerance, and whether it’s PTH or NPTH. Discuss with your fabricator before finalizing specifications.

Conclusion

PCB hole tolerance is a multifaceted specification that requires understanding the interplay between drilling, plating, registration, and design requirements. Standard plated hole tolerance is ±0.08-0.10mm (±3-4 mil)—don’t specify tighter without good reason. Position tolerance accumulates through manufacturing, especially on high layer count boards.

Always specify FINISHED hole sizes and clearly distinguish between PTH and NPTH requirements. The 7-mil-over-lead-size rule provides adequate margin for most through-hole components. Work with your fabricator early to understand their specific capabilities, and you’ll get reliable boards without unnecessary cost premiums.