Impact of Via Stitching on PCB EMI

I’ve been exploring the concept of via stitching for the ground planes surrounding the perimeter of my PCB. While researching, I’ve found various resources suggesting guidelines like maintaining a specific spacing distance, typically equal to the smallest dominant wavelength divided by 20. However, I’ve encountered conflicting information stating that placing vias too close together could potentially worsen electromagnetic emissions compared to having no vias at all. I’m curious about the mechanism behind this phenomenon and how an excessive number of vias could worsen EMI

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That’s not normally a problem. It can be a problem when you have a lot of vias close together and end up have a plane cut or divided by anti-pads. Normally however if you follow the spacing rules you’ll be just fine.

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In most cases, the presence of additional vias shouldn’t pose a problem unless they are spaced in a manner that coincides with a significant harmonic of your board’s emission profile. It’s worth noting that symmetry, often considered advantageous, can actually be problematic. The equidistant placement of elements may create a resonant structure, leading to nulls and peaks at specific frequencies.

To mitigate this, you have two options:

  • Place the vias at semi-random intervals. This approach ensures that any resonance will be shallower and occur at a minimum common multiple of the spacing. Prime number spacing is often favored for this reason.
  • Adopt a technique commonly used in high-frequency PCBs: employ two separate rows of vias with varying spacing and via sizes. This setup ensures that the resonances of one structure are counteracted by the nulls of the other, minimizing the risk of interference.
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Via stitching is normally not a problem. However keep in mind that depending on board shop you use, too many holes may increase the cost if vias are too small.

With that said, I havent seen any significant evidence that via stitching improves EMI by certain dB. So overall you would be okay with via stitching. As other suggested, you can place them at certain distance of wavelength etc… here is a good video on altium channel