What is an Annular Ring in PCB?
WHAT THIS VIDEO COVERS
The annular ring is the copper ring surrounding a drilled hole on a PCB — technically the distance from the edge of the finished hole to the edge of the pad. This video explains why this seemingly small dimension plays a major role in PCB fabrication success and long-term reliability.
It covers how drill bit misalignment during manufacturing can cause "breakout," where part or all of the annular ring is cut away, leading to weak or open connections. The content reviews IPC-recommended minimum annular ring sizes (typically 0.1 mm, with 0.125–0.15 mm preferred for higher reliability) and larger rings for through-hole components to improve mechanical strength.
Viewers also learn practical solutions like adding teardrops — small copper reinforcements at trace-to-pad junctions — to maintain connectivity even with slight drilling shifts. These design considerations are critical for via reliability, pad integrity, and overall board yield across FR4 PCB, HDI PCB, and multilayer designs used in aerospace, medical devices, and automotive electronics.
Get an instant PCB quote or explore PCB prototyping services and turnkey PCB assembly with expert DFM support.
KEY HIGHLIGHTS
- Definition & Function: The annular ring is the copper area between the drilled hole and pad edge, directly determining connection reliability after fabrication.
- Breakout Risk: Insufficient annular ring allows drill misalignment to cause partial or complete copper loss, leading to weak joints or open circuits.
- Design Best Practices: Follow IPC guidelines (min 0.1 mm, ideally 0.125–0.15 mm) and use teardrops to maintain connectivity under manufacturing tolerances.
FAQ
Q1: What is the recommended annular ring size for PCB designs?
A1: IPC standards recommend a minimum of 0.1 mm, but 0.125–0.15 mm provides better reliability. Use larger rings for through-hole components to enhance mechanical strength.
Q2: What causes annular ring breakout in PCBs?
A2: Drill bit misalignment during fabrication can cut into the pad if the annular ring is too small, resulting in partial copper loss and potential open or unreliable connections.
Q3: How do teardrops improve PCB reliability?
A3: Teardrops add extra copper reinforcement where traces meet pads, helping maintain electrical connectivity even if minor breakout occurs during drilling.
Look at this PCB hole.See the copper ring around it?
That ring is called the annular ring.
More precisely, the distance fdrom the edge of the hole to the edge of the pad.
Pad size = hole size + 2 × annular ring.
During manufacturing, drill bits can shift slightly.
If the annular ring is too small, the drill may cut into the pad.
This causes breakout—where part of the copper ring disappears.
And that can lead to unreliable connections or even open circuits.
According to IPC design recommendations, a common reference is at least 0.1 mm.
For better reliability, 0.125–0.15 mm is safer.
For through-hole components, designers often make it even larger to improve mechanical strength.
How to avoid breakout？A common trick is adding teardrops, small copper reinforcements where the trace meets the pad.
They help keep copper connected even if drilling shifts slightly.
So when designing vias or holes, don't just think about the drill size, a fraction of a millimeter can decide reliability.
