[SI-LIST] Re: Ground vias around signal via
- From: Sanjeev Gupta <skgupta.sanjeev@xxxxxxxxx>
- To: Scott McMorrow <scott@xxxxxxxxxxxxx>
- Date: Thu, 16 Oct 2014 08:12:40 +0530
Aaditya,
you may be meeting all your SI specs without stitching via but these
stitching via are important from EMI reduction point of view at design
stage itself. so they are very important. Scott explanation further gives
strong reason of using such via.
Thanks
On Thu, Oct 16, 2014 at 2:58 AM, Scott McMorrow <scott@xxxxxxxxxxxxx> wrote:
> When you ask these sorts of questions you need to specify "at what
> frequency?" You also need to specify the signaling type. Otherwise the
> question is ill defined.
> In fact, stitch vias to the planes that are called ground are important.
> They are very important for single ended signaling, highly important for
> high bandwidth differential signaling, and less important for lower
> bandwidth differential. Where I define low bandwidth as anything below 10G.
>
> Ground planes on multiple layers are only at an equipotential at stitch
> vias. Between the stitch vias those very same ground planes float and
> resonate. Single ended ddr signals are notorious for lighting up ground
> cavities. differential signals with high bandwidth, such as 28G can pump
> significant energy into unstitched ground cavities, causing unwanted
> insertion loss, return loss, and crosstalk.
>
> Don't let anyone tell you that ground stitch vias are not important. Such a
> blanket statement is dangerous and reckless. It is bad engineering.
>
> Regards,
>
> Scott
> On Oct 15, 2014 7:45 PM, "Aaditya K" <aaditya.kandibanda@xxxxxxxxx> wrote:
>
> > 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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--
Thanks
Sanjeev
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