Annular Ring Width

AR = (Dpad − Ddrill) / 2

Quick answer

This calculator solves AR = (D_pad − D_drill) / 2 for Annular Ring. With Pad Diameter 4.7 cm, Drill Diameter 2.2 cm, the result is 12.5 mm. It solves in 3 directions, so you can enter the values you have and get the one you need.

Calculator

Annular Ring (mm)
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Formula

AR = (D_pad − D_drill) / 2

Description

The annular ring is the width of copper remaining around a drilled hole after drilling. It must be large enough to ensure reliable electrical connection between the copper pad and the barrel plating of the via. IPC-6012 Class 2 (standard commercial) requires a minimum annular ring of 0.05 mm (2 mils) after all manufacturing tolerances. Class 3 (high reliability, aerospace, medical) requires 0.05 mm minimum with additional requirements. Insufficient annular ring can lead to broken connections, intermittent contacts, and reliability failures.

Variables

  • AR — Annular ring width (m)
  • D_pad — Copper pad diameter (m)
  • D_drill — Finished drill hole diameter (m)

Practical Notes

The finished hole diameter is the nominal drill size minus plating thickness (typically 50 µm total). Account for drill registration tolerance (typically ±0.05-0.075 mm). For a Class 2 board with 0.075 mm registration tolerance, the minimum pad diameter is D_drill + 2 × (0.05 + 0.075) = D_drill + 0.25 mm. HDI boards with laser-drilled microvias have tighter registration, allowing smaller annular rings.

Symbols and units

Symbol Meaning Default unit Accepted units
AR Annular Ring mm mm, cm, m, km
Dpad Pad Diameter mm mm, cm, m, km
Ddrill Drill Diameter mm mm, cm, m, km

Step by step

  1. 1. What you know: Pad Diameter 4.7 cm, Drill Diameter 2.2 cm
  2. 2. The relation: AR = (D_pad − D_drill) / 2
  3. 3. Substitute: Dpad = 4.7 cm, Ddrill = 2.2 cm
  4. 4. Result: Annular Ring = 12.5 mm

Worked examples

Minimum range

Given: Pad Diameter 0.47 mm, Drill Diameter 0.22 mm

Result: Annular Ring = 0.125 mm

Low range

Given: Pad Diameter 4.7 mm, Drill Diameter 2.2 mm

Result: Annular Ring = 1.25 mm

Typical

Given: Pad Diameter 4.7 cm, Drill Diameter 2.2 cm

Result: Annular Ring = 12.5 mm

High range

Given: Pad Diameter 47 cm, Drill Diameter 22 cm

Result: Annular Ring = 12.5 cm

Maximum range

Given: Pad Diameter 4.7 m, Drill Diameter 2.2 m

Result: Annular Ring = 1.25 m

Solving for each variable

Solve for Annular Ring

Pad Diameter 0.47 mm, Drill Diameter 0.22 mm → 0.125 mm

Solve for Pad Diameter

Annular Ring 0.1 mm, Drill Diameter 0.47 mm → 0.67 mm

Solve for Drill Diameter

Annular Ring 0.1 mm, Pad Diameter 0.22 mm → 0.02 mm

How Annular Ring changes with Pad Diameter

Pad Diameter (input) Annular Ring (result)
2.35 cm 0.75 mm
3.525 cm 6.625 mm
4.7 cm 12.5 mm
7.05 cm 2.425 cm
9.4 cm 3.6 cm
18.8 cm 8.3 cm
32.9 cm 15.35 cm
47 cm 22.4 cm

The same result in other units

Unit Value
mm 12.5
cm 1.25
m 0.0125

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Frequently asked questions

How do you calculate Annular Ring Width?

Use AR = (D_pad − D_drill) / 2. With Pad Diameter 4.7 cm, Drill Diameter 2.2 cm, Annular Ring works out to 12.5 mm.

What is the formula for Annular Ring Width?

The formula is AR = (D_pad − D_drill) / 2. The annular ring is the width of copper remaining around a drilled hole after drilling.

How do you find Pad Diameter when you know the other values?

Rearrange for Pad Diameter: with Annular Ring 0.1 mm, Drill Diameter 0.47 mm, Pad Diameter is 0.67 mm.

How do you find Drill Diameter when you know the other values?

Rearrange for Drill Diameter: with Annular Ring 0.1 mm, Pad Diameter 0.22 mm, Drill Diameter is 0.02 mm.

What units does Annular Ring Width use?

Annular Ring is shown in mm, cm, m. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

Related Concepts

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