I imagine that you'd need to get to/from the L2 high speed pairs with blind vias in order to avoid via stubbing problems. Mike - - - - - steve weir wrote: >John in capping the tracks go on layer 2. ( At least that is the way that >I understand it. ) The microstrip plate up, and SM problems are simply >avoided. > >Steve. >At 12:39 PM 6/1/2005 +1000, Jon Keeble wrote: > > >>I'm still struggling to understand exactly what is "capping", and how it >>differs from simply being another layer, despite Steve's kind attempts to >>explain it. >> >>.. do the tracks remain on the outer layer ie do not require vias? >> >>The particular case that interests me is the multiGbit connections between >>Virtex4 MGT IO and SFP connectors. >>Xilinx have arranged for this to happen on the outer layer, i.e. no vias. >>Is "capping" going to help? i.e. mitigate the uncertainties of outlayer >>plating and soldermask on Zo? >> >>Regards >> >>Jon >> >> >>----- Original Message ----- >>From: "Istvan Novak" <istvan.novak@xxxxxxx> >>To: <weirsi@xxxxxxxxxx> >>Cc: <jkeeble@xxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx> >>Sent: Tuesday, May 31, 2005 11:23 AM >>Subject: Re: [SI-LIST] Re: High speed signal on top layer >> >> >> >> >>>Steve, John, >>> >>>Tradeoff with capping is it also means an extra layer (and for symmetry >>>reasons, >>>probably two layers) in the PCB . >>> >>>Regards, >>>Istvan >>> >>> >>>steve weir wrote: >>> >>> >>> >>>>John, that is where dielectric caps the uppermost signal etch. This >>>>controls the copper dimensions, affording much better impedance control. >>>> >>>>Regards, >>>> >>>>Steve. >>>>At 07:41 AM 5/31/2005 +1000, Jon Keeble wrote: >>>> >>>> >>>> >>>> >>>>>Hi Steve .. >>>>> >>>>>What is 'capping'? >>>>> >>>>>Regards >>>>> >>>>>Jon Keeble >>>>> >>>>>----- Original Message ----- >>>>>From: "steve weir" <weirsi@xxxxxxxxxx> >>>>>To: <george_dai@xxxxxxx>; <si-list@xxxxxxxxxxxxx> >>>>>Sent: Tuesday, May 31, 2005 6:49 AM >>>>>Subject: [SI-LIST] Re: High speed signal on top layer >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>>>George, >>>>>> >>>>>>1. Possible, but there are several pitfalls, including control over >>>>>>plate-up and solder mask. Capping could help with those. >>>>>> >>>>>> >>>>>> >>>>>> >>>>>------------------------------------------------------------------ >>>>>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 FAQ wiki page is located at: >>>>> http://si-list.org/wiki/wiki.pl?Si-List_FAQ >>>>> >>>>>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 >>>>> >>>>> >>>>> >>>>> >>>>> >>>>------------------------------------------------------------------ >>>>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 FAQ wiki page is located at: >>>> http://si-list.org/wiki/wiki.pl?Si-List_FAQ >>>> >>>>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 >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>-------------------------------Safe >>> >>> >>Stamp----------------------------------- >> >> >>>Your Anti-virus Service scanned this email. It is safe from known viruses. >>>For more information regarding this service, please contact your service >>> >>> >>provider. >> >> >>------------------------------------------------------------------ >>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 FAQ wiki page is located at: >> http://si-list.org/wiki/wiki.pl?Si-List_FAQ >> >>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 >> >> >> > > >------------------------------------------------------------------ >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 FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > >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 > > > > > > ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ 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