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Vias construction on a PCB for current to ground

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FANT

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A question that I cannot answer:

I have a PCB working on the microwave field; between upper and lower layer there are some vias that are used to continue the ground reference from bottom to upper layer.
If the vias are open, the current ( that travels on the surface, due the skin effect ) passes through the hollow tube made by the metallization of the via.

But what happens if the via is completely filled with copper ?
The upper surface is a continuous plane and it should not pass the current to the bottom plane.

But if I think on a DC frequency, the via filled with copper is a better solution for resistance.

Help please.

Thank you

Mandi
 

KlausST

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Hi,

If you look into a via you see the inner side of the via, but with high frequencies the curren runs on the outer surface of the via. You can't see, because it is the side that meets the pcb material.
Whether you fill the via or not doesn't have any influence for very high frequencies.
But it may improve DC resistance.

Klaus
 

FvM

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I don't see how you would "fill a via completely with copper". In so far the question seems purely theoretical. Via metallisation is created together with additive plating of top/bottom layers, the thickness can't be controlled independent of layer copper weight.

In RF circuits, you have usually ground via fences instead of individual ground vias. They also act as a perfect DC connection.
 

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