PCB Technology

Annular Ring Explained by a PCB Manufacturer

To ensure the smooth flow of electricity and proper function of the circuit, it is important to maintain a uniform annular ring width. This width is the distance between the edge of the drilled hole and the outer edge of the copper pad surrounding it.

Welcome to our comprehensive guide to understanding and designing annular rings. As an essential element in printed circuit board design, annular rings are widely used in electronic devices for establishing electrical connections between different layers of the PCB. In this article, we will cover the fundamental concepts, design principles, manufacturing processes, quality controls, and practical applications of annular rings. Whether you are an experienced PCB designer or a curious beginner, you will find valuable insights and tips to enhance your knowledge and skills. Let’s dive into the world of annular rings and explore their mysteries!

Table of Contents

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What is Annular Ring?

Annular Ring is a term used in PCB design and manufacturing. It refers to the area of copper that surrounds the hole drilled in the PCB. Simply put, the Annular Ring is the donut-shaped copper area that sits around the drill hole.

What is Outer Annular Ring?

Outer Annular Ring Calculation:

Outer Layer Annular Ring (OAR) = (Outer Layer Pad Diameter – Plated Hole Diameter)/2,
OAR = (Copper Pad Diameter – Tool Size)/2,
Tool Size = End Size + 0.10mm for all PTHs, +0.00mm for all NPTHs.
Calculation for IAR on a copper pad of 0.60mm and finished hole size diameter of 0.30mm (PTH):
IAR=[0.60mm–(0.30mm+0.10mm)]/2=0.10mm

What is Inner Layer Annular Ring?

Inner Layer Annular Ring Calculation:

Inner Layer Annular Ring (IAR) = (Inner Layer Pad Diameter – Plated Hole Diameter)/2,
IAR = (Copper Pad Diameter – Tool Size)/2,
Tool Size = End Size + 0.10mm for all PTHs, +0.00mm for all NPTHs.
Calculation for IAR on a copper pad of 0.50mm and finished hole size diameter of 0.20mm (PTH):
IAR=[0.50mm–(0.20mm+0.10mm)]/2=0.10mm

The Structure & Characteristics of Annular Ring

Annular rings are circular copper pads surrounding vias and through-holes on printed circuit boards PCBs. They have several important characteristics, including:

Diameter: The diameter of an annular ring is the distance between the edge of the copper pad and the edge of the hole it surrounds. The diameter is determined by the size of the via or hole, as well as the amount of space needed for routing traces.
Width: The width of an annular ring is the thickness of the copper pad. It is important to ensure that the width is wide enough to provide sufficient electrical contact between the via or hole and the trace, while still leaving enough space for routing.
Clearance: The clearance is the space between the edge of the annular ring and any adjacent copper or non-conductive features, such as other pads, traces, or the board edge. It is important to ensure that the clearance is sufficient to prevent any unintended electrical connections or short circuits.
Plated or Non-Plated: Annular rings can be either plated or non-plated, depending on their intended use. Plated annular rings have a thin layer of metal deposited on top of the copper pad to improve electrical contact and prevent corrosion.

These characteristics are important to consider when designing annular rings on a PCB, as they can significantly impact the performance and reliability of the circuit.

Design Principles

Principles for Designing Annular Rings
When designing annular rings on printed circuit boards, the following principles should be considered:

The annular ring width should be sufficient to ensure the reliability and proper functioning of the PCB.
The minimum annular ring size should meet industry-standard specifications to avoid potential signal integrity issues and other problems.
The annular ring size should be appropriate for the intended application of the PCB, taking into account the required connection reliability and signal integrity.

Considerations for Designing Annular Rings
In addition to the above principles, the following considerations should also be taken into account when designing annular rings:

The annular ring width should be calculated based on the thickness of the PCB, the size of the drill hole, and the type of plating used.
The minimum annular ring size should be carefully selected to avoid problems such as short circuits and open circuits.
When designing annular rings for through-hole components, it is important to consider the component pin size, the drill size, and the pad size to ensure proper functionality.
The use of smaller annular rings can increase the risk of manufacturing defects and signal integrity issues, which should be taken into account when designing PCBs.
Overall, careful consideration of these principles and considerations can ensure the reliable performance of PCBs and prevent potential issues from arising.

FAQs

What is the role of the PCB annular ring?

The annular ring on a PCB serves several important functions. It provides a connection point for components or wires to the PCB, and it also helps to increase the strength of PCB through-holes, especially in high-stress applications. Additionally, in high-speed circuit design, the annular ring plays a critical role in the impedance matching and signal integrity of the circuit by providing a path for return signals and minimizing electromagnetic interference (EMI).

How to Calculate the PCB Annular Ring?

To calculate the annular ring for a PCB, you need to consider several factors, including the hole size, board thickness, solder mask, and drill tolerance. Here is the basic formula for calculating the minimum annular ring width:

Minimum Annular Ring Width = [(Finished Hole Size + (2 x Annular Ring Width)) - Pad Diameter] / 2

You can use this formula to calculate the minimum annular ring width needed for your specific PCB design requirements. It is also important to note that different manufacturing processes and equipment can affect the precision of the finished hole size and the tolerance for the annular ring width. Therefore, it is recommended to consult with your PCB manufacturer to ensure that the annular ring width meets your design specifications.

What is the difference between an annular ring and a though-Hole?

An annular ring and a through-hole are both elements of a printed circuit board (PCB), but they serve different purposes.

A through-hole is a hole that passes through the entire board and is typically used to mount components, such as resistors or capacitors, that have wire leads that extend through the hole and are soldered on the other side.

An annular ring, on the other hand, is the circular area of copper that surrounds the edge of a drilled hole on the surface layer of the PCB. The purpose of an annular ring is to provide a conductive connection between the drilled hole and the surface layer copper traces. This connection is important for many reasons, including providing mechanical strength to the hole and allowing for the flow of current between the surface layer traces and the component leads.

So, in summary, a through-hole is a hole that passes through the entire board and provides a mounting point for components, while an annular ring is a circular area of copper that surrounds the edge of a drilled hole on the surface layer of the board and provides a conductive connection between the hole and the surface layer copper traces.

What is meant by the term 'Teardrop Annular Ring'?

Teardrop annular rings are so named because their shape resembles that of a teardrop. This shape helps maintain structural integrity against mechanical stress. Teardrop pads can be utilized to add extra copper to the junction of annular rings.

What is the Minimum Annular Ring for PCBs?

The minimum annular ring for internal and external PCB layers is different. Typically, the standard minimum annular ring is 0.1 mm for inner layers and 0.05 mm for external layers. However, smaller annular rings can be created based on the tight spacing of surrounding elements. It's important to consider the drawbacks of small annular rings, including an increased likelihood of drilled vias being too close to the edge and breaking out of the annular ring, resulting in a broken trace connection. Additionally, small annular rings can lead to a fragile relationship and hinder the PCB's functionality. Although the smallest annular ring is -1 mil, it's not recommended as it increases the chances of a breakthrough.

Whar are the common annular ring issues?

Common annular ring issues