[SI-LIST] Re: Ground vias around signal via
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 15 Oct 2014 14:13:30 -0700
Very little signal energy travels through metal. Almost all signal
energy is in the dielectric. The signal vias that penetrate and power
node vias that stitch the cavity act as reflection boundaries for the
signal energy. If you use a TDR or VNA to look at a single signal
penetrating a cavity you won't see much S21 impact at all. But that
does not tell you what you need to know. You need to know that for a
set of signals that the noise and cross talk will not be excessive.
Steve
On 10/15/2014 1:58 PM, Aaditya K wrote:
> Thanks Lee.
> I think (I am not an expert), discontinuity itself is enough to distort
> signal(to whatever extent). By placing ground vias around the signal via
> does not by itself significantly improve signal quality. Assuming the
> return current flows through these vias, the length of this Vias are so
> short comparatively that placing ground vias doesn't matter.
>
> Am I correct?
>
> Thanks,
> Aaditya.
>
> On Wed, Oct 15, 2014 at 1:48 PM, Kelvin Harding <
> kelvin.harding@xxxxxxxxxxxxxxx> wrote:
>
>> Hi Lee and All,
>>
>> Why are some very concerned about stitching vias at layer transitions
>> and some not.
>> What results are available to show what happen when there is a
>> transition with / without stitching vias.
>> There are usually lots of ground vias at say an FPGA or connector so it
>> really applies to a transition where
>> the signal reference planes change.
>>
>> Regards,
>>
>> Kelvin
>>
>> On 15/10/2014 20:32, Lee wrote:
>>> You are correct. Can't think of any case where they add value
>> commensurate
>>> with their cost.
>>>
>>> Lee
>>>
>>> -----Original Message-----
>>> From: Aaditya K
>>> Sent: Wednesday, October 15, 2014 10:41 AM
>>> To: si-list
>>> Subject: [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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