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[SOLVED] Placing Ground Vias To Improve EMI

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yolco

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Placing ground vias all over the PCB (stiching) to improve the EMI.
  • Have all ground vias to be spaced the same distance? Or may they be separated different distances if it is under lambda/8?

I mean, I have to place ground vias all over the PCB edge to reduce EMI. The space between these ground vias are below lambda/20, around the edge. But the doubt comes from the ground vias which are not at the edge.
  • Have these ground vias to maintain the same distance between them? How can I calculate the maximum number of them?
  • Is there any rule of thumb to do it manually?
 

marce

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Throw them down randomly..... its harder for resonances to occur.
You quote Lamba/20 of what frequency though.... main clock, main clock harmonic, some other dominant frequency observed.....
 
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yolco

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Hi Marce,

thanks for your answer.

The circuit I'm working in has 2.4 GHz and other frequencies as clock or high speed digital lines.
But I'm refering to 2.4 GHz with lambda/20 (~2.98 mm) of spacing.

Moreover, I've got two different parts at my PCB, one analog (power supply), and other with RF subsystem. So, I need to place them in order to improve EMI and shield both parts from each other (as much as possible).

Regards.
 

marce

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Generally any RF feed lines will have closely spaced via's either side, round the edge of the board will stop noise from the edge...I've got a headache so I will dig out some info on this that I have floating about...
Generally though I just throw down random stitching vias apart from round the board edges and to isolate say an RF area where I will space them out equally cos it looks nice and I have OCD. :-D
The biggest problem with GHz stuff and RF can be capacitive coupling, check the RF and anything associated with it isn't going to couple to other areas......
 
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isphu

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Placing ground vias all over the PCB (stiching) to improve the EMI.
  • Have all ground vias to be spaced the same distance? Or may they be separated different distances if it is under lambda/8?

I mean, I have to place ground vias all over the PCB edge to reduce EMI. The space between these ground vias are below lambda/20, around the edge. But the doubt comes from the ground vias which are not at the edge.
  • Have these ground vias to maintain the same distance between them? How can I calculate the maximum number of them?
  • Is there any rule of thumb to do it manually?

-The space of Vias GND for reduce EMI around the edge of PCB : 2.54mm or 5mm or 5.08mm ( 2.54mm for High speed)
- Vias GND for free space is 5mm (5.08mm for inch unit). There are no rules for this and you need to input more via in free space as much as possible. The space of Via GND can reduce to 4mm if you want.
- For analog designs: the space of Via GND maybe reduce to 1mm.
 

marce

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Why.... The more GND vias you add the more you create holes in other power planes and reduce routing paths, it is not that critical or has that much of an effect on EMI unless it is an RF board, where it becomes more critical.
 
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