[SI-LIST] Re: AW: Ground vias around signal via

  • From: LI Yishan <Yishan.Li@xxxxxxxxxxxxxxxxxxxx>
  • To: "Gert.Havermann@xxxxxxxxxxx" <Gert.Havermann@xxxxxxxxxxx>, "aaditya.kandibanda@xxxxxxxxx" <aaditya.kandibanda@xxxxxxxxx>, si-list <si-list@xxxxxxxxxxxxx>
  • Date: Thu, 16 Oct 2014 07:39:50 +0000

Hi, Aaditya:
  According to 3D simulation, ground vias around signal via deeply effect high 
frequency impedance. If your signal is low speed signal, it seems the ground 
vias are not necessary.

Best regards
Li Yishan
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
Behalf Of Havermann, Gert
Sent: 2014年10月16日 14:59
To: aaditya.kandibanda@xxxxxxxxx; si-list
Subject: [SI-LIST] AW: Ground vias around signal via

Aaditya: My opinion is, if we have a proper return path,  they are not 
necessary.

-> As Wolfgang said, GND vias are needed for proper return path because without 
any GND via there will be no proper return path. You don't have to put multiple 
of those around the signal via. with proper placement one is enough even for 
very high speeds.

Aaditya: Any situations they are useful other than shielding?

-> Placing many stitching vias doesn't necessarily provide any shielding. 
That’s an old Myth. Take a look at waveguide filters. The placement of screws 
into the dielectric (air) looks and functions very similar to a PCB where the 
energy also travels in the dielectric. Stitching vias can act as a filter, 
meaning that some frequencies are not shielded but guided to the outside.

Aaditya: How will they help? When do we need them?

-> As already said, use GND vias to provide a proper GND return. as a rule of 
thumb there should be a return via within the range of 1/8 wavelength (Nyquist) 
to the signal via.

BR
Gert


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-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im 
Auftrag von Aaditya K
Gesendet: Mittwoch, 15. Oktober 2014 19:42
An: si-list
Betreff: [SI-LIST] Ground vias around signal via

Hello Experts,
I have a question on ground vias placement around signal via.

My opinion is, if we have a proper return path,  they are not necessary. Am I 
correct?

Any situations they are useful other than shielding?

How will they help? When do we need them?

Please help.

Thanks
Aaditya


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