Area and real estate ? Many boards are very small and very dense having not the space to place the "ideal" GND via (or any via at all). The Routing space gets reduced ... I guess there are always two sides of a medal .. Hermann EKH - EyeKnowHow Hermann Ruckerbauer www.EyeKnowHow.de Hermann.Ruckerbauer@xxxxxxxxxxxxx Itzlinger Strasse 21a 94469 Deggendorf Tel.: +49 (0)991 / 29 69 29 05 Mobile: +49 (0)176 / 787 787 77 Fax: +49 (0)3212 / 121 9008 Am 17.10.2014 um 17:24 schrieb Grasso, Charles: > Surely there has been sufficient research published that quantifies the use > of ground > vias for single ended, differential pairs(as recently as DesignCon 2013) and > cavities? > Besides - what's the downside? > > > Best Regards > Charles Grasso > Compliance Engineer > Echostar Communications > (w) 303-706-5467 > (c) 303-204-2974 > (t) 3032042974@xxxxxxxxx > (e) charles.grasso@xxxxxxxxxxxx > (e2) chasgrasso@xxxxxxxxx > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On > Behalf Of Havermann, Gert > Sent: Friday, October 17, 2014 1:47 AM > To: Lee ; scott@xxxxxxxxxxxxx; Yishan.Li@xxxxxxxxxxxxxxxxxxxx > Cc: aaditya.kandibanda@xxxxxxxxx; si-list > Subject: [SI-LIST] AW: Re: AW: Ground vias around signal via > > Lee, > When talking about stitching vias I'm not always talking about complete plane > stitching with via patterns. The rule of thumb is just about creating at > least one GND return path for a signal transition, and I don't think that > anyone of us needs proof that changing signal layers without a GND return > path is big trouble. Thus there must be a GND via somewhere when signals > switch Layers and reference planes. > You are correct in regards to via pattern stitching. There is no general > proof that these are always necessary, or even beneficial. > Usually there are many GND vias in each design, and if they are not too far > away from the signal via then there is a decent GND return and you don't need > any additional vias. If the GND vias are well distributed (which is the case > in 90% of the Designs), then you usually don't need to stitch the complete > plane using via patterns. But that’s also just a rule of thumb. > > My two cents here are: > The question wasn't specific enough to create a single complete answer. The > best answer then is to give guidance and provide some insights that allow > engineers to think into the right direction. That’s what we all did. > > BR > Gert > > > > ---------------------------------------- > Absender ist HARTING Electronics GmbH, Marienwerderstraße 3, D-32339 > Espelkamp; Registergericht: Amtsgericht Bad Oeynhausen; Register-Nr.: HRB > 8808; Vertretungsberechtigte Geschäftsführer: Dipl.-Kfm. Edgar-Peter Düning, > Dipl.-Ing. Torsten Ratzmann, Dipl.-Wirtschaftsing. Ralf Martin Klein > > -----Ursprüngliche Nachricht----- > Von: Lee [mailto:leeritchey@xxxxxxxxxxxxx] > Gesendet: Donnerstag, 16. Oktober 2014 19:16 > An: scott@xxxxxxxxxxxxx; Yishan.Li@xxxxxxxxxxxxxxxxxxxx > Cc: Havermann, Gert; aaditya.kandibanda@xxxxxxxxx; si-list > Betreff: Re: [SI-LIST] Re: AW: Ground vias around signal via > > This discussion seems to be terribly theoretical. We all know that there are > thousands, perhaps tens of thousands of assemblies shipped every day with > differential signals as high as 28 Gb/S on them that work just fine without > the need to put in "ground vias" nearby. > > What comes to my mind when I read discussions such as this is that old Burger > King commercial where Clara Peller asks "where's the beef?" > > For all of the postulated problems mentioned in these discussions, "where's > the proof?" > > We do too much speculating on this forum and not enough proving! > > My position on this whole thing as well as many others that appear on this > discussion group is, if you are going to put forth a rule, be prepared to > offer the proof that the rule is valid as well as where it is valid. If you > are not prepared to do this, it is a disservice to those who are asking for > advice to make such a posting. > > -----Original Message----- > From: Scott McMorrow > Sent: Thursday, October 16, 2014 3:29 AM > To: Yishan.Li@xxxxxxxxxxxxxxxxxxxx > Cc: Gert.Havermann@xxxxxxxxxxx ; aaditya.kandibanda@xxxxxxxxx ; si-list > Subject: [SI-LIST] Re: AW: Ground vias around signal via > > Gert has good advice about the distance of the ground via to the signal via, > but I would like to modify it a bit. A well-referenced set of ground planes > will have ground stitch vias that are separated by no more than 1/10 the > wavelength of the Nyquist frequency of the highest differential bit rate, or > the bandwidth of the signal edge rate of the fastest single ended driver. > So for some numbers in the English system. > > Let Dk = 4 > Tdelay = 170 ps/inch > > For DDR3/4 with 100 ps driver edge rates BW = .35/100ps = 3.5 GHz lambda = > 285 ps > 1/10 lambda = 28.5 ps > In Dk = 4 ground vias should be separated by a maximum of 167 mil to maintain > a good return path for these singled-ended DDR signals. > > For 10 Gbps > Nyquist is 5 GHz > lambda = 200 ps > 1/10 lambda = 20 ps117 > In Dk = 4 ground vias should be separated by a maximum of 117 mil for 10 > Gbps signalling to maintain a good return path. > > For 28 Gbps > Nyquist is 14 GHz > lambda is 71 ps > 1/10 lambda is 7.1 ps > In Dk = 4 ground vias should be separated by a maximum of 42 mil for 28 Gbps > signalling. > > These recommendations apply to the region in proximity of the signal > transition vias. They serve to tie the ground cavities together, provide > shielding for the power/ground cavities, eliminate resonances in the signal > passband and first harmonic, and reduce via-to-via crosstalk. If the signal > transition is at the balls of a semiconductor device, or in the pin field of > a connector, there are "usually" enough ground vias in these regions to meet > these requirements. If that is the case, then no additional grounds are > required. But, there are often cases that we encounter at Teraspeed > Consulting where these rules are violated. Here are some common areas to > look at. > > Via transitions around dc blocking capacitors. > > Boards with outer layer buildup microvias, where drilled vias do not carry > the package or connector grounds down through the board. > > Areas with asymmetric stripline crossing power splits on the distant plane > side of the stripline (the stripline is close to ground.) > > In all these regions it is necessary to close the return path loop with > ground vias as described above. Use the above as a guide to current and > future designs. > > best regards, > > Scott > > > > > > Scott McMorrow > Teraspeed® Consulting - A Division of Samtec > 16 Stormy Brook Rd > Falmouth, ME 04105 > (401) 284-1827 Business > http://www.teraspeed.com > > On Thu, Oct 16, 2014 at 3:39 AM, LI Yishan <Yishan.Li@xxxxxxxxxxxxxxxxxxxx> > wrote: > >> 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: 2014å¹´10月16æ—¥ 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 >> >> >> ---------------------------------------- >> Absender ist HARTING Electronics GmbH, Marienwerderstraße 3, D-32339 >> Espelkamp; Registergericht: Amtsgericht Bad Oeynhausen; Register-Nr.: >> HRB 8808; Vertretungsberechtigte Geschäftsführer: Dipl.-Kfm. >> Edgar-Peter Düning, Dipl.-Ing. Torsten Ratzmann, >> Dipl.-Wirtschaftsing. Ralf Martin Klein >> >> -----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 >> >> >> ------------------------------------------------------------------ >> 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 forum is accessible at: >> http://tech.groups.yahoo.com/group/si-list >> >> List archives are viewable at: >> //www.freelists.org/archives/si-list >> >> 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 forum is accessible at: >> http://tech.groups.yahoo.com/group/si-list >> >> List archives are viewable at: >> //www.freelists.org/archives/si-list >> >> 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 forum is accessible at: >> http://tech.groups.yahoo.com/group/si-list >> >> List archives are viewable at: >> //www.freelists.org/archives/si-list >> >> 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 forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2014.0.4765 / Virus Database: 4040/8400 - Release Date: 10/16/14 > > ------------------------------------------------------------------ > 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 forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > List archives are viewable at: > //www.freelists.org/archives/si-list > > 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 forum is accessible at: > http://tech.groups.yahoo.com/group/si-list > > List archives are viewable at: > //www.freelists.org/archives/si-list > > 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 forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu