Did you ever lose track of the wedding ring? We certainly did because we often took it off during gym. When we finally realized we couldn’t remember where we had put it, frightening thoughts of what we might find at home flooded our mind. However, after nearly hours of searching, we discovered the ring was in the same condition.
Misplacing the wedding ring is a significant concern, but encountering problems with annular rings on a printed circuit board (PCB) can be just as problematic. When there are issues with annular rings, it can break the flow of the electrical path and affect how well the circuit works as a whole.
What Is An Annular Ring Via?
The technical term used to describe the region between the drilled hole of a via & the border of the copper pad is an annular ring. Vias act as connection points linking various layers on the printed circuit board.
It is necessary to know about the construction of a via to comprehend the fundamentals of annular rings. When a PCB is manufactured, the process involves etching the board, leaving via pads aligned on various layers. Subsequently, the pad is drilled to create a hole, where copper is precipitated through electroplating.
Upon observing the printed circuit board from above, the drilled through-holes present themselves as circular-shaped patterns referred to as annular rings. These rings can vary in size, with some PCB designers choosing thicker rings while others may opt for thinner ones due to spatial limitations.
Common Issues With Annular Ring Via
Although vias are an integral component of printed circuit board manufacturing, it is a fallacy to presume that annular rings are infallible. Misshapen annular rings can arise, which may impede trace continuity.
Theoretically, the ideal circular ring is achieved by drilling precisely at the via pad. However, in practice, the accuracy of drilling hinges on a machine used by the printed circuit board manufacturer. These manufacturers have a particular tolerance for annular rings, typically around five miles. In simpler terms, there exists a likelihood of drilling being slightly off-target within the designated limit.
In the event of a missed target during drilling, the ending hole may shift towards the side of a pad, leading to tangency between the hole and the pad. Should the drilling stray even further from the mark, a breakout will occur. A breakout condition arises when a hole part surpasses the designated pad area.
Annular breakout can impede the via continuity, reducing the copper area linking the hole & pad, thereby affecting the current flow. This issue is more noticeable when the affected area channels a significant amount of current. To address the problem of the annular breakout, the exposed area is typically remedied by adding more copper padding, a process known as tear-dropping.
There are certain scenarios where an annular breakout can lead to irreparable issues. For instance, if a hole deviates to the extent that it pierces an adjacent trace, an unintentional short circuit may occur on the printed circuit board. This problem is challenging to resolve as it necessitates isolating the shortened trace & via.
Getting The Annular Ring Via Size Right
Although PCB manufacturers are responsible for creating precise annular rings, designers can contribute by selecting the appropriate size for a layout. It is advisable to allocate extra space beyond the manufacturer’s tolerance level to ensure accuracy. A general thumb rule is to increase the size of the annular ring by 1 mil, which can prevent potential problems in the future.
How to Get the Annular Ring Via Size Right?
Every PCB manufacturer has a specified tolerance for an annular ring in the printed circuit board manufacturing process. Nevertheless, it is prudent to allocate more space to be cautious.
We advise to enlarge the 1.0mm size from the producer’s specifications. This minor increase in width can assist in avoiding any potential problems in the future.
The specific purpose of the PCB design influences the annular ring size. PCB institute has established three classifications for PCBs: Class 2, Class 1, & Class 3. PCBs designed for high-stress applications necessitate large annular rings to accommodate the wider diameter. Class 3 PCBs, in particular, demand heavier annular rings to withstand rigorous usage.
Minimum Annular Ring Via in PCB
Certain PCBs accommodate large and heavy equipment, while others are essential to be highly compact. For instance, PCBs in small technological devices need to be extremely space-efficient.
In such scenarios, the annular ring size needs to be proportionally small. However, what is the smallest possible size that we can achieve?
There is a variation in the limit for outer and inner annular rings per the industry’s design standards.
- In an annular ring, the minimum width on the inner side of a printed circuit board is 0.1mm.
- In annular rings, the minimum width on the outer side of a printed circuit board is 0.05mm.
Difference Between a PCB Annular Ring Via and a Through-Hole
The term PCB often evokes thoughts of the via method, which involves mounting electronic components onto a printed circuit board. This technique entails inserting the components into drilled holes on the board.
Through-holes are created by inserting leads into drilled holes and then soldering them onto copper traces to establish conductivity.
In contrast, annular rings establish conductivity by linking the Plated through-hole to a copper trace.
Teardrop Annular Ring Via
A teardrop annular ring has a shape resembling a teardrop. Rather than being a circle, extra copper is there to connect the outer edges of the ring, providing it with additional strength.
Teardrop annular rings are primarily utilized when there is a risk of the drill head deviating from its intended path during drilling. So this issue can result in the removal of excess copper, which may compromise the connection.
Teardrop Annular Ring Via can:
- · Minimize the hazard of cracks on thin copper
- Alleviate thermal or mechanical stress
- Take precautions to prevent small deviations in the positioning of a drill hole.
Best Designs of Annular Ring Via for Your PCB
Manufacturing processes generate annular rings, and as a result, the standards that oversee board construction also outline specifications for these rings. These standards include IPC-2221, a generic standard for printed board layout; IPC-A-600, which specifies acceptable standards for printed boards; and IPC-6012, which provides performance and qualification specifications for rigid printed circuit boards. The standards generally establish the minimum dimensions or the lowest tolerances based on the IPC categorization, which is determined by the intended use and location of your PCBA. By following these standards, a series of crucial steps can be generated to produce a board that meets regulatory compliance and is of high quality. These essential steps are:
Essential Steps for Annular Ring PCB Design
- Identify the IPC of your board and familiarize yourself with the corresponding standards for its development.
- Find out the necessary clearance specifications for the annular ring.
- Then, find the minimum required width for the annular (circular) ring.
- Moreover, find the minimum required thickness for the via (if it is applicable)
- Choose the appropriate size and placement of the(circular) annular ring.
For optimal annular ring printed circuit board design, ensure your specifications comply with the contract manufacturer’s DFM guidelines and rules. Failure to do so may lead to issues such as breakout, solder expansion, or solder bridging.
Recommended PCB Annular Ring Via Size
In general, we advise that the diameter of your annular ring be at least as big as most force-exposed parts, such as a switch. The optimal diameter for an annular ring typically falls around 0.25mm. If you are uncertain about the size of your via, using this diameter as a fallback is a viable option.
The PCB manufacturer typically sets the minimum dimensions for vias and annular rings. It’s important to follow their specifications and ensure that your annular ring meets or exceeds the smallest size requirement. If the annular ring is smaller than its specified size, it could lead to inadequate connectivity for the components.
When contemplating the size of your drill, it is important to consider several factors, including the method of tenting, plugging, or filling your via, the amount of board space available, and your PCB’s current capacity. These are all critical considerations to make.
It’s advisable to check the copper traces and aim to make the diameter of the hole half of the copper lad’s area size. It can help ensure optimal results.
If you’ve arrived at this part of the article, it indicates that you have a good grasp of the basics of the annular ring. We covered the definition of the annular ring and guided how to determine its dimensions. Besides we also delved into the connection between vias and annular rings and explained why their sizes are crucial. RayPCB trusts that you have found this guide informative and beneficial. Thanks for your interest!