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 What Is The Annular Ring in PCB ?

What Is The Annular Ring in PCB ?

Introduction:

The annular ring are an important part of both PCBs and flex PCBs. In such a sophisticated PCB design and production work. it makes the designers’ job more difficult. because drilling holes in the post-production can easily lead to errors. which can lead to failures of the board itself.

Thus PCB designers must be careful when calculating sizes and locations. In this article, we’ll explore everything you need to know about circular holes. the unique challenges they present, and how to drill them properly.

What Is The Annular Ring in PCB?

The annular ring in a printed circuit board (PCB) refers to the circular ring. -shaped copper area surrounding a hole or via in the PCB. The size and shape of the annular ring are crucial factors in PCB design. They must be carefully considered to ensure proper electrical connections. mechanical stability, and the ability to solder components effectively. Designers need to take into account factors like the component size, and lead spacing. and the PCB’s layer stacks up when determining the dimensions of the annular ring. The annular ring’s diameter depends on the specific requirements of the PCB.

What is the annular ring in PCB
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Why Does Annular Ring Size Vital?

※ Electrical Connection:

The annular ring provides the electrical connection between the component lead or via and the PCB traces. If the annular ring is too small, it may not provide a reliable electrical connection. which can lead to intermittent connections or signal integrity issues.

※ Soldering Reliability:

During the soldering process, the annular ring is where solder applied. to create a solid connection between the component lead and the PCB. If the annular ring is too small, it can lead to insufficient solder coverage. resulting in poor solder joints, weak connections, or solder bridges (short circuits).

※ Mechanical Stability:

The annular ring serves as a mechanical support for components, especially through-hole components. If the annular ring is too small, it may not adequately support the component. leading to mechanical instability, which can result in components coming loose or breaking off.

※ Component Size and Lead Spacing:

The size of the annular ring should be compatible with the size. and lead spacing of the components used. Different components may have varying lead diameters and spacings. so the annular ring size chosen to accommodate these variations.

※ Manufacturing Tolerances:

Stiffeners can help maintain consistent electrical performance. by reducing the risk of signal interference. or impedance changes caused by flexing or bending of the PCB.

※ Signal Integrity:

In high-frequency or high-speed PCB designs. the size and shape of the annular ring can affect signal integrity. An incorrectly sized annular ring can introduce impedance mismatches. and signal reflections, leading to signal degradation.

※ Assembly Process:

The assembly process, including automated soldering and inspection equipment. may have specific requirements for annular ring size. Using the correct annular ring size can facilitate the assembly process. and ensure consistent and reliable soldering.

※ Thermal Considerations:

In power electronics or components that generate heat. a larger annular ring can help dissipate heat more effectively. preventing overheating and potential damage to the PCB or components.

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How To Calculate the Annular Size?

To calculate the annular ring size, you can use the following formula:

Annular Ring Size = (Lead Diameter + Manufacturing Tolerance) – Hole Diameter

Keep in mind that this formula is a simplified approach and doesn’t account for all design considerations. It’s important to follow industry standards and consult with your PCB manufacturer. to ensure your design meets all requirements and manufactured reliably. Additionally, specific design software or guidelines. To provide more precise methods for calculating annular ring size.

Annular Ring for flexible PCB

Outer Ring Dimensions

  • Ideal: Outer Annular Ring (OAR) = (Outer Pad Diameter – Plated Hole Diameter)/2
  • Actual: Plated Aperture = Finished Aperture + 0.10mm (for all PTH) + 0.00mm (for all NPTH).
  • Example: Calculation of IAR for a copper pad thickness of 0.60mm and a finished hole diameter of 0.30mm (PTH):
  • OAR=[0.60mm-(0.30mm+0.10mm)]/2=0.10mm

Inner Ring

inner Annular Ring
  • Ideally: Inner Annular Ring (IAR) = (Inner Pad Diameter – Plated Hole Diameter)/2
  • Actual: Plated Hole Diameter Pin Hole Size + 0.10mm (for all PTH), +0.00mm (for all NPTH)
  • Example: Calculation of IAR on 0.50mm Copper Pad and 0.20mm Finished Hole Size Diameter (PTH)
  • IAR=[0.50mm-(0.20mm+0.10mm)]/2=0.10mm
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How To Choose The Right Annular Ring Size ?

Choosing the right annular ring size for your PCB design. That is essential for ensuring the reliability, manufacturability, and functionality of the PCB. Here’s a step-by-step guide to help you select the appropriate annular ring size:

Component and Hole Information:

  • Identify the components that mounted on the PCB. And their respective lead or pin diameters. Consult the datasheets of these components for lead diameter specifications.
  • Determine the hole sizes required for these components. The hole size should match the component lead diameter.

Manufacturing Capability:

  • Contact your chosen PCB manufacturer or fabrication service. To inquire about their manufacturing capabilities. especially regarding minimum and maximum annular ring sizes they can reliably produce.
  • Consider the manufacturing tolerances for hole drilling. and copper plating that your manufacturer can achieve. Factor in these tolerances when calculating the annular ring size. A typical tolerance range is 0.1 to 0.15 mm (4 to 6 mils).

IPC Standards:

Refer to industry standards, such as IPC-2221. which provides recommendations for minimum annular ring sizes. based on lead diameter and other design factors. IPC standards can serve as a useful guideline.

Design Requirements:

  • Consider the specific requirements of your PCB design. For high-speed or high-frequency applications, impedance control. or RF circuits, the annular ring size may need to adjusted. to maintain signal integrity and minimize signal reflections.
  • Be aware of any special requirements imposed by your design. such as minimum clearances, spacing, or thermal considerations.

Layer Stackup:

If your PCB has multiple layers, ensure that the annular ring is large enough. To maintain electrical connections through all layers. The annular ring should extend to the desired signal or ground plane on the inner layers.

Design Software:

Use PCB design software, which often provides design rule checks (DRC). to ensure that the annular ring sizes follow design rules and industry standards.

Margin for Reliability:

Consider providing a margin beyond the minimum requirements for annular ring size. This added margin can enhance the reliability of your PCB design. and account for potential variations in the manufacturing process.

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What Is the Minimum Annular Ring in PCB?

The minimum annular ring size in a PCB determined by various factors. including the manufacturing capabilities of the PCB fabrication service. industry standards, and design considerations. There isn’t a universally fixed minimum annular ring size, as it can vary depending on these factors. However, there are general guidelines and standards that provide recommendations.

min annular ring

For many PCB manufacturers, the minimum annular ring size typically falls within the range of 0.1 to 0.15 mm (4 to 6 mils). It’s important to note that this is a general guideline. and some manufacturers may have even more stringent requirements.

Industry standards, such as IPC (Association Connecting Electronics Industries) standards. provide specific recommendations for minimum annular ring sizes. based on the component lead size and other design factors. For example, IPC-2221, which is often referenced in PCB design. offers guidelines for minimum annular ring sizes based on the lead diameter. via type, and other design considerations.

Keep in mind that while you may aim for the minimum annular ring size. to maximize component placement density on your PCB.

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Annular Ring in Flexible PCBs

Flex PCBs have unique considerations when it comes to annular rings. A flexible PCB designed to bend and conform to the shape of the application. and this flexibility can affect how you calculate and specify annular ring sizes. Here are some considerations specific to annular rings in flexible PCBs:

Flexibility and Bending Radius:

The annular ring designed to accommodate flexibility. and bending radius of the flexible PCB. When the PCB bent or flexed, the annular ring should not crack. delaminate, or compromise the electrical connection.

Material Selection:

The choice of flexible PCB material is crucial. Flexible PCBs are often made from materials like polyimide (PI) or polyester (PET). The material’s flexibility and thermal play a role in determining the appropriate annular ring size.

Layer Stackup:

In multi-layer flexible PCBs, the layer stackup and adhesive materials. used between layers needs to be carefully considered to ensure the annular ring. maintains its integrity when the PCB flexed.

Bending and Stress Points:

Identify the areas where the flexible PCB will experience the most bending and stress. These areas may require larger annular rings. or additional support to prevent damage or signal integrity issues.

Smaller Radii:

Flexible PCBs often have smaller bend radii compared to rigid PCBs. The annular ring must be able to maintain its integrity. when subjected to these smaller bend radii.

Soldering Considerations:

For components mounted on a flexible PCB, soldering may pose unique challenges. The annular rings designed to allow for effective and reliable soldering in the context of a flexible substrate.

Industry Standards:

While there may not be specific industry standards for flexible PCB annular rings. you should still follow general PCB design standards. and consult with your PCB manufacturer for guidelines and recommendations.

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Annular Ring in Aluminium PCB

In aluminum-based printed circuit boards (Aluminum PCBs or Metal Core PCBs). the concept of an annular ring is slightly different from that in traditional FR-4 PCBs. Aluminum PCBs are often used in applications that require excellent thermal conductivity . such as LED lighting, power electronics, and automotive systems. These PCBs have a metal core (usually aluminum or copper) that acts as a heat sink. which affects the annular ring design:

Component Attachment:

In Aluminum PCBs, components attached using thermal vias. The annular ring, in this context, is typically a circular pad surrounding a via. that connects a component to the metal core for heat dissipation.

Thermal Considerations:

The primary function of the annular ring in Aluminum PCBs is to facilitate efficient thermal transfer. The annular ring must be appropriately sized to ensure good thermal conductivity. between the component and the metal core. A larger annular ring can enhance heat dissipation.

Thermal Vias:

These vias often have a larger diameter than signal vias in traditional PCBs. The size of the annular ring around a thermal via based on factors like the via diameter. the thermal pad size of the component, and the required thermal performance.

Signal Routing:

While the primary purpose of the annular ring in Aluminum PCBs is thermal. signal traces still need to routed on the board. The design must take into account the annular ring’s size in relation to the pad size. and copper weight to ensure proper electrical connections.

High-Power Components:

Aluminum PCBs are often used for high-power applications. In these cases, the annular ring size becomes especially important. to ensure that the components can dissipate heat effectively. The size of the annular ring designed to handle the thermal requirements of the specific components.

Mounting Components:

If you’re mounting components directly onto the aluminum core without vias. the annular ring designed to provide a secure and thermally efficient connection.

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Annular Ring Vs Through-Hole

Here are the main differences between annular rings and through-holes:

Function:

Annular rings provide electrical connections, mechanical support and soldering points. whereas through-holes are primarily used for component mounting. and electrical connections through the PCB.

Design:

Annular rings are part of the component pad or via design and surround the hole. while through-holes are the holes themselves, drilled completely through the PCB.

Usage:

In summary, annular rings are copper rings surrounding holes. used for both electrical and mechanical connections. as well as soldering points, while through-holes are the holes. that go through the PCB and used for component placement. and electrical connections, particularly for through-hole components. Both play important roles in PCB design and assembly.

In summary, annular rings are copper rings surrounding holes. used for both electrical and mechanical connections. as well as soldering points, while through-holes are the holes. that go through the PCB and used for component placement. and electrical connections, particularly for through-hole components. Both play important roles in PCB design and assembly.

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What Is the Teardrop Annular Ring?

Teardrops are a design feature in PCBs where the copper trace or pad connected to a through-hole. or via is intentionally widened in a teardrop shape as it connects to the hole. This design element used to improve the reliability of soldered connections. and to prevent issues like cracks and open circuits in high reliability. or high-vibration environments. Teardrops offer benefits like improved mechanical strength. better solder adhesion, and reduced stress at the connection point.

Teardrop Annular Ring

The teardrop shape resembles a teardrop or pear, with a wider end connected to the pad. or trace and a narrower end extending to the hole. This wider shape distributes mechanical and thermal stress more effectively. reducing the risk of failure in the connection.

To clarify, there is no “teardrop annular ring.” The “annular ring” typically refers to the copper ring around a through-hole or via. and “teardrops” refer to the enlarged trace or pad that connects to this annular ring. The two concepts related because teardrops are often used in conjunction with annular rings. to improve the reliability of the connections on a PCB.

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FAQs About PCB Annular Rings

As we mentioned at the beginning, toroids can be tricky to fabricate correctly. pcb designers may encounter the following problems related to toroid construction.

Undesirable toroids

On smaller PCBs, oversized rings may interfere with board functionality. Especially if the copper pads are small, the toroidal ring may cause problems.

The easiest way to solve this problem is to ensure that prototypes used in the design and fabrication of the PCB.

Wire Cutting

Forms of PCB Annual Rings
  • Tangent occurs when you accidentally drill a hole off-center. If the off-center is so bad that the hole touches the edge of the pad, a tangent will occur.
  • Another cause of tangent lines is that the ring holes are not wide enough.
  • Tangent lines can disrupt connectivity and can even be dangerous.

Breakout

  • Breakout is the next stage of tangent and occurs when the hole pushed beyond the ring and copper pad edge. It is literally a protrusion.
  • Breakout occurs when the layers of the board are poorly matched to each other. and the holes cannot aligned between each layer.
  • Again, the best way to prevent breakouts is to make sure the ring is wide enough to accommodate the holes.

Rupture

Ring seals, like anything else, are subject to stress and deterioration over time. When a ring breaks or cracks, we call it a rupture. Ruptures can caused by long-term aging, mechanical stress, or even environmental stress.

The best way to deal with ruptures is to use high-quality materials and replace deteriorated PCBs over time.

Final Thoughts

Ring collars are an important part of any printed circuit board, but they can be difficult to use correctly. Use our guide above to learn the ins and outs of toroidal rings and how to design them.

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Conclusion

The annular ring enables PCB and FPCs to function more efficiently in the assembly. Annular rings are a crucial part of any printed circuit board, but they can be tricky to get right. If you have more comments about the rings you’d like to discuss with us. Please contact GESFLEX and our experts will glad to contact you. Please Contact GESFLEX today via e-mail at marketing@gespcb.com for more information.

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