PCBs have holes or vias that connect different layers of a PCB. They also enable PCB manufacturers to embed an electronic component on the PCB by placing the component pins in the vias.
In order to facilitate the connection of electronic components on the PCB with the circuit, there has to be a solder mask on the via. This solder mask should be in contact with a conductor, present on a hole, which is called an annular ring.
In this blog post, you’ll learn the importance of annular rings in PCB, calculating the right annular ring size, general troubleshooting, and more.
What are annular rings in PCB?
Each PCB vias on the PCB have conductive rings surrounding it, which ensures that the PCB solder mask, component pins, and traces are all in perfect contact with each other to facilitate flow of electricity. The metallic conductive ring plate that surrounds a via is called an Annular Ring. Since annular rings are one of the smallest components on a PCB, they’re often ignored by most people, but PCB manufacturers have to pay special attention to annular rings, their sizes, etc.
Importance of annular rings
The presence of annular rings on each vias holds utmost importance and this section expands on this.
●An annular ring is solely responsible for a valid connection of vias with the trace. (PCB trace)
●Annular rings make sure that the traces on different layers of a PCB stay in contact with the overall circuit on the PCB.
●Small ring that is required would cause interrupting or failing PCB due to low conductivity.
●Proper implementation of annular rings on the PCBs by a PCB manufacturer results in a high-quality PCB that ensures a high-quality electronics product.
●Poor implementation of annular ring can result in PCB overheating and/or short circuit or burnt PCB.
●To ensure long-lasting PCB, annular rings need to be properly implemented, which is a responsibility of a PCB manufacturer.
How to calculate annular rings sizes?
Annular ring size means the width of the ring from the outer end of the via. The annular ring expands outwards from the via and has a specific width according to the overall PCB. The formula for calculating the annular ring size is given as:
Annular ring = (pad’s diameter – finished hole’s diameter) / 2
●Here, pad’s diameter depends on the level of the PCB according to IPC-2221. Level A, Level B, and Level C pad’s diameters are 24 mil, 20 mil, and 16 mil, respectively.
●Finished hole’s diameter is the via size or via’s diameter.
Annular ring size is just the half of the difference between these two diameters.
Minimum annular rings size
Annular rings sizes are different for different layers of PCB. The minimum annular ring size for a single layer PCB will be 0.05mm. In case of a multi-layer PCB, the minimum annular ring size for internal layers and external layers are 0.1mm and 0.05mm, respectively.
Annular rings VS Through-hole
●Through holes are a type of hole that help in embedding the components on the PCBs. Annular ring is just a conduction plate surrounding the vias.
●Through-holes run from top to bottom of the PCB, piercing it to make a hole. You can see through the hole, hence the name “through-hole”.
●Through holes will have annular rings surrounding them for conductivity.
●Through holes will need a solder mask to create connection between the component and the trace.
●Annular rings will directly connect the components to the trace with the help of copper pads.
Also read: What is through hole technology and why is it important
Teardrop annular rings
Sometimes, drilling the holes can get off the course and may drill a part of annular rings. This can cause chaos, as the annular ring size will get reduced, causing improper conductivity. In order to overcome this issue, some PCB manufacturers prefer teardrop annular rings.
A teardrop annular ring has additional copper plating on the sides, in a teardrop shape, rather than a perfect circle.
As a result, even if the drilling drills down the annular ring a bit, the extra copper pad going outwards helps make up for the loss of the drilled annular ring.
Also read: PCB Drilling – What is it and how to minimize its cost during assembling
Annular rings rupture and how to avoid?
Annular ring rupture is a simple term to indicate any damage to the annular ring due to wear and tear.
Annular rings can get damaged over time, due to extensive use, or physical abuse to the PCB. To avoid annular ring rupture, you can:
●Use high-quality raw materials to make annular rings during the PCB manufacturing process.
●Consider replacing the PCB with a fresh piece, if there are any signs of breaking or rupturing annular ring.
●Using solder mask with flux over the ruptured annular ring will help in ensuring smooth conductivity and this acts as a repair to the annular ring.
General issues with annular rings
These are general issues with the annular rings:
1.Oversized Annular Rings
Annular rings, that are larger than required are a general problem that occurs especially in small PCBs. Large annular rings can interrupt the entire circuit and cause malfunctioning of the PCB.
- Overcoming Oversized Annular Rings
The PCB manufacturer should take extra precautions during the prototyping and designing stages to ensure that the annular rings sizes are calculated precisely.
2.Tangency
Tangency is a condition when the hole is drilled so off the course that it touches the outer edge of the annular ring. Moreover, if the annular ring ain’t wide enough to accommodate the hole, it’s called “Tangency”.
- Overcoming Tangency
Ensure that the drilling machine is properly aligned.
3.Breakout
An even chaotic version of tangency is breakout, when the hole is drilled in such a way that it goes out of the annular ring. As a result, the annular ring is cut off, causing a breakout.
- Overcoming Breakout
The drill machine needs to be readjusted.
4.Rupture
When the annular rings get damaged during drilling, or over time due to extensive use, it’s called Rupture.
- Overcoming Rupture
Use high-quality raw materials and thick copper pads.
Conclusion
After getting an idea of the annular rings, you might be wondering how to take care of so many complications in the process. You can stay tension-free by choosing IBE Electronics, who knows how to make perfect annular rings in the PCBs. IBE Electronics can take care of well-designed and implemented annular rings, so your PCB doesn’t fail even after decades.
In order to facilitate connection of electronic components on the PCB with the circuit, there has to be a solder mask on the via. This solder mask should be in contact with a conductor, present on a hole, which is called an annular ring.
●Use high-quality raw materials to make annular rings during the PCB manufacturing process.
●Consider replacing the PCB with a fresh piece, if there are any signs of breaking or rupturing annular ring.
●Using solder mask with flux over the ruptured annular ring will help in ensuring smooth conductivity and this acts as a repair to the annular ring.
- Oversized Annular Ring
- Tangency
- Breakout
- Rupture
