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PCB Design Tools

ANNULAR RING CALCULATOR

Calculate annular ring width from pad and drill sizes, or find the required drill size for a target annular ring. Includes IPC-6012 class requirements.

Calculate annular ring width from pad and drill dimensions, or determine the maximum drill size for a target annular ring. Results include IPC-6012 class compliance checks. All values update in real time.

Calculation Mode

Units

Quick Presets

Dimensions

Annular Ring Results

Annular Ring Width

6.00 mil

Pad Diameter

40.00 mil

Drill Diameter

28.00 mil

Annular Ring

6.00 mil

Drill-to-Pad Ratio

70.0%

IPC-6012 Compliance

Class 1 (General Electronics)
Ext: 2 mil PASS
Class 2 (Dedicated Service)
Ext: 2 mil PASS
Class 3 (High Reliability)
Ext: 2 mil PASS

Cross-Section View

Pad: 40.00 milDrill: 28.00 milAnnular Ring6.00 milHOLE

Formulas Used

The calculator supports both annular-ring solve mode and maximum-drill solve mode using the same geometric relationship.

\[AR = \frac{D_{pad} - D_{drill}}{2}\]

\[D_{drill,\text{max}} = D_{pad} - 2AR_{target}\]

\[\text{Drill-to-pad ratio} = \frac{D_{drill}}{D_{pad}} \times 100\%\]

AR = annular ring width
Dpad = pad diameter
Ddrill = finished drill diameter.

What Is an Annular Ring?

The annular ring is the area of copper pad that remains around a drilled hole on a PCB. It is calculated as (Pad Diameter − Drill Diameter) / 2. A sufficient annular ring ensures reliable solder joints and electrical connectivity between the pad and the internal barrel of the via or through-hole.

If the drill hole is too large relative to the pad, the annular ring becomes too thin or even breaks out (the hole extends beyond the pad edge). Breakout compromises both the mechanical and electrical integrity of the connection, which is especially critical in aerospace and defense applications governed by IPC-6012 Class 3 requirements.

IPC-6012 Annular Ring Requirements

IPC-6012 "Qualification and Performance Specification for Rigid Printed Boards" defines minimum annular ring requirements based on product class:

ClassApplicationExternal MinInternal Min
Class 1General Electronics2 mil (0.050 mm)Breakout allowed
Class 2Dedicated Service2 mil (0.050 mm)1 mil (0.025 mm)
Class 3High Reliability2 mil (0.050 mm)2 mil (0.050 mm)

*Values per IPC-6012 Rev D. Class 3 boards (aerospace, military) require the tightest tolerances. Always confirm requirements with your fabricator.

Common Pad & Drill Sizes

ComponentPad (mil)Drill (mil)Annular Ring (mil)
Standard Via402010
Small Via28147
Micro Via (HDI)2086
0805 Pad603612
SOIC Lead502811
Through-Hole704214

Annular Ring Design Tips

Drill Tolerance

Fabricators typically have ±2-3 mil drill tolerance. Add this margin to your minimum annular ring to avoid breakout after drilling.

Registration

Layer-to-layer misregistration can reduce effective annular ring. Budget ±2 mil for standard processes, ±1 mil for HDI.

Teardrops

Adding teardrops where traces meet pads increases effective annular ring and improves manufacturability, especially for tight designs.

Understanding Breakout

  • Tangent condition: The drill hole edge touches the pad edge (annular ring = 0). This is the boundary between acceptable and breakout.
  • Partial breakout: The drill hole extends slightly beyond the pad on one side. IPC-6012 Class 1 allows 90° breakout on external layers and 180° on internal layers.
  • Full breakout: The drill completely misses the pad. This is a defect in all IPC classes and will cause open circuits.
  • Prevention: Use adequate pad sizes, specify tight drill tolerances, and add registration allowance. Most CAD tools have DRC rules to flag insufficient annular rings.

Calpak USA's engineering team can review your PCB design for annular ring compliance and manufacturability. Request a design review today.

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