PCB Annular Ring

What is a PCB Annular Ring

An annular ring is a circular metal pad on a PCB that resembles a doughnut. The inner hole is used to insert a wire or component pin. After soldering, the annular ring connects to the component pin inserted into the inner hole, thus achieving an electrical connection between components on the PCB.
The design and manufacturing quality of the annular ring are crucial for stable and reliable electrical connections on the PCB.

PCB Annular Ring

Possible Forms of PCB Annular Rings
Sometimes, a drilled hole is not centered on the pad. When the inner ring touches the edge of the pad, it is considered tangent. If the wire is broken, it is not encircling the ring. The specific examples are as follows:

1. Normal
   A via is considered a good via when it is centered on the pad or within the specified restricted area. A good via will form a complete annular ring and provide a good electrical connection.
2. Tangent
   When the drill bit is not aligned with the mark, the completed via will be off-center and closer to the side of the pad. Tangent occurs when a portion of the via touches the edge of the pad. 3. Broken Via
   Broken vias occur when a via deviates significantly and may ultimately extend beyond the pad boundary.
   Tangency and broken vias should be avoided during PCB design and manufacturing.
3. How to Calculate the Annular Ring Size?
4. Outer Annular Ring Size
   Ideally: Outer Annular Ring (OAR) = (Outer Pad Diameter – Plated Aperture Diameter) / 2
   Actually: Plated Aperture Diameter = Finished Aperture Diameter + 0.10mm (for all PTHs) + 0.00mm (for all NPTHs).
   Example: Calculating the IAR for a 0.60mm copper pad thickness and a 0.30mm finished hole diameter (PTH):
   OAR = [0.60mm – (0.30mm + 0.10mm)] / 2 = 0.10mm

Outer Annular Ring

2. Inner Ring
   Ideal: Inner Annular Ring (IAR) = (Inner Pad Diameter – Plated Hole Diameter) / 2
   Practical: Plated Hole Diameter = Hole Diameter + 0.10mm (for all PTHs), + 0.00mm (for all NPTHs)
   Example: Calculating the IAR for a 0.50mm copper pad and a 0.20mm finished hole diameter (PTH): IAR = [0.50mm – (0.20mm + 0.10mm)] / 2 = 0.10mm
   

Finished Area Annular Ring (FAR)

The area between the outer edge of the pad and the hole. The annular ring may break due to slight deviations in the hole center during drilling. This depends on the ratio of the nominal outer diameter of the pad to the nominal diameter of the solder hole.

4. Minimum Annular Ring

The minimum thickness (AR) on a printed circuit board (PCB) refers to the minimum copper thickness between the edge of the land (pad) and the edge of the plated through hole (also known as a support hole). The minimum annular ring width should be greater than or equal to the value defined in the PCB design.

Minimum Annular Ring

When the annular ring is smaller than the specified width, component attachment may be affected and the pad may crack. In this case, the circuit enters the pad, minimizing the circuit’s current-carrying capacity.

Sometimes, a trace on a circuit board needs to connect to another layer. In this case, the trace ultimately connects to a pad. A through-hole in the pad facilitates the trace’s exit from the pad and connection to another layer.

Minimum Annular Ring

t1: Minimum annular ring on an outer layer, must be greater than or equal to 0.05mm on the finished board.
t2: Minimum annular ring on an inner layer, must be greater than or equal to 0.01mm on the finished board.

5. Teardrop Rings
   Teardrop rings are primarily used to repair damaged vias and strengthen electrical connections. When a via is broken at the connection between the conductor and the pad, adding copper around the via can reestablish the broken connection, repairing the short and ensuring that the signal still reaches its intended destination.

Teardrop Rings
This concludes a brief introduction to PCB annular rings.