Istvan, if you have multiple plane pairs then yes there should be lots of vias breaking-up the space. But for four and six layer boards, that is reduced to vias supporting the decoupling capacitors. Regards, Steve. At 10:31 PM 2/11/2004 -0500, Istvan NOVAK wrote: >Steve, > >Something is not clear to me in this argument. Via fence stitches planes >on the same DC voltage; mostly people stitch the ground planes. >Are you concerned about the cavity formed of GND-GND planes? >This might be a concern on boards where there are very few >components which would break the cavity with their vias. >On boards where you have many components, the necessary >ground vias will create probably sufficiently small sub cavities. > >Regards, > >Istvan > > >----- Original Message ----- >From: "steve weir" <weirsp@xxxxxxxxxx> >To: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>; ><Chris.Cheng@xxxxxxxxxxxx>; "'Istvan NOVAK'" <istvan.novak@xxxxxxxxxxxxxxxx> >Cc: <si-list@xxxxxxxxxxxxx> >Sent: Wednesday, February 11, 2004 12:13 PM >Subject: RE: [SI-LIST] Re: Stack up for EMI reduction, plane resonance and >u-s trip radiation etc etc > > > > Charles, sure. First, because of the ESD issue, I also favor fences. > > > > The problem with fences comes back to plane resonance. Fences do a really > > great job of setting up big standing waves on the planes as they make near > > perfect transmission line reflectors. We can mitigate this somewhat by > > avoiding evenly spaced vias. The advocates of 20H who know their stuff, > > rightly point out that 20H sets up a controlled leak, thereby effectively > > dissipating energy that would otherwise resonate in the planes. 20H is > > controversial, because that "dissipation" is release of energy outside the > > board. > > > > As I said before, if the planes were sealed tight, this would not be an > > issue. But vias carry energy to the surface and features above the >surface > > then become radiators. DET that Istvan has written about is one way to > > mitigate the problem. There are some other interesting ideas around, but > > at least at this time, I don't have the resources to pursue them. > > > > Steve. ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu