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Via Fence/Fencing

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • Via fence/fencing is a technique that creates a barrier between sensitive circuitry or components and the rest of the PCB.

  • PCD designers consider factors such as cost, manufacturing constraints, and performance requirements when selecting the appropriate type of via fence/fencing.

  • Via fence/fencing techniques contribute to the overall PCB performance, reliability, and compliance by providing EMI isolation/compliance, noise reduction, signal integrity improvement, thermal management, design partitioning, and adequate grounding.

Example of via fence/fencing on a PCB

Example of via fence/fencing on a PCB

Via fence/fencing is a technique that creates a barrier between sensitive circuitry or components and the rest of the PCB. It involves surrounding an area of the PCB with a ring or series of vias to shield or prevent electromagnetic interference (EMI) from affecting the enclosed section.

Via fence/fencing is a technique that creates a barrier between sensitive circuitry or components and the rest of the PCB.

The vias used in a via fence are typically connected to a ground or power plane to provide a conductive path. Encircling the sensitive components or circuitry with these vias, electromagnetic waves or noise that would otherwise propagate through the PCB are intercepted and diverted around the fenced area.

The via fence technique helps to improve the signal integrity and reduce the noise coupling between different sections of the PCB. It is commonly employed in PCBs with critical analog or RF (radio frequency) circuits that require isolation from digital circuits or other noise sources.

Via fences can be created using vias placed in a regular pattern around the sensitive area, forming a continuous ring or multiple concentric rings. The density and spacing of the vias are determined based on the desired level of shielding and the frequency range of the signals involved.

In addition to EMI containment, via fences can provide a low-impedance return path for high-frequency currents, improving the overall performance and reducing the potential for signal degradation.

Types of Via Fence/Fencing

There are several types of via fence/fencing that can be implemented in PCBs. Some common types include:

  • Solid Copper Pour: In this technique, a continuous copper plane is created around the vias, connecting them. The entire area between the vias is filled with copper, forming a solid copper pour.
  • Thermal Relief Copper Pour: This type of via fence/fencing is commonly used in thermal management applications. The copper pour around the vias is modified to have thermal relief spokes or traces. These spokes or traces allow easier heat transfer between the vias and the surrounding copper plane, facilitating efficient thermal dissipation.
  • Hatched Copper Pour: In hatched copper pour, instead of a solid copper plane, the area between the vias is filled with a series of diagonal copper traces, forming a hatch pattern. This type of via fence/fencing reduces the amount of copper used, which can be beneficial in terms of cost and manufacturing constraints.
  • Stitching Vias: Stitching vias are additional vias placed around the PCB to create a continuous ring or grid of vias. These vias act as a fence, enclosing a specific region or separating different signal or power domains. They are primarily used to enhance the ground plane and minimize ground loops.
  • Partial Copper Pour: In some cases, only a portion of the area is filled instead of filling the entire area between vias with copper. This technique is known as partial copper pour. It provides localized shielding or grounding benefits while allowing greater flexibility in routing other traces.

What Role Does Via Fence/Fencing Play in PCB Design?

Via fence/fencing techniques contribute to the overall PCB performance, reliability, and compliance by providing EMI isolation/compliance, noise reduction, signal integrity improvement, thermal management, design partitioning, and adequate grounding. 

Role of Via Fence/Fencing in PCB Design

EMI Isolation/Compliance

Isolates sensitive components and helps achieve EMI compliance by minimizing PCB radiated and conducted emissions

Noise Reduction

Minimizes coupling of noise into sensitive components by diverting noise around the fenced area

Signal Integrity Boost

Provides a low-impedance return path for high-frequency currents, improving the overall signal integrity

Thermal Management

Spreads heat and reduces temperature rise in critical areas

Design Partitioning

Creates isolated sections within the PCB, separating different functional blocks or circuits

Grounding and Return Path

Establishes a low-impedance grounding system and provides an efficient return path for currents

Via fence/ fencing plays several essential roles in PCB design. Here are the key roles and benefits:

  • EMI Isolation: Via fences help isolate sensitive circuitry or components from electromagnetic interference. They act as a barrier that prevents EMI from propagating into or out of the fenced area, reducing the potential for signal degradation and ensuring better signal integrity.

  • EMI Compliance: Regulatory standards often require electronic devices to meet specific EMI emission and susceptibility criteria. Via fences can help achieve EMI compliance by containing and minimizing the radiated and conducted emissions from the PCB.

  • Noise Reduction: By diverting electromagnetic waves and noise around the fenced area, via fences minimize the coupling of noise into sensitive components, which helps reduce crosstalk, ground bounce, and other types of noise that could impact the circuit's performance.

  • Signal Integrity Improvement: Via fences provide a low-impedance return path for high-frequency currents, reducing the loop area and improving the overall signal integrity. This is particularly important for high-speed digital and RF designs, where maintaining clean and stable signals is crucial.

  • Thermal Management: Via fences can be used as thermal vias to improve heat dissipation in areas where components generate significant heat. Connecting the vias to a thermal plane or heat sink helps spread the heat and reduce the temperature rise in critical areas.

  • Design Partitioning: Via fences can create isolated sections within the PCB, separating different functional blocks or circuits, which allows for better organization and easier debugging, as well as providing a clear distinction between analog, digital, and RF sections.

  • Grounding and Return Path: Via fences connected to ground planes or power planes help establish a low-impedance grounding system and provide an efficient return path for currents. This helps reduce ground loops, improve power distribution, and minimize voltage fluctuations.

Leverage Via Fence/Fencing in Your PCB Design With Cadence Solutions

The choice of via fence/fencing technique depends on the requirements of the PCB design, such as EMI shielding, thermal management, and signal integrity. Designers often evaluate factors such as cost, manufacturing constraints, and performance requirements when selecting the appropriate type of via fence/fencing for a particular PCB design. Consulting with an experienced PCB design company like Cadence can provide valuable insights and guidance to ensure you use the right via fence/fencing technique for your PCB project.

You can leverage Cadence’s suite of PCB Design and Analysis Software tools to leverage via fence/fencing in your PCB design. When you are ready for prototyping, OrCAD PCB Designer's speed and comprehensive functionality accelerate board layout and reduce time-to-market.

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