Thanks everyone for sharing valuable information. To get to a conclusion, I will articulate my opinion (Intuition). Assuming I am routing TX-RX lanes for USB 3.0 (5 Gbps). Considering the following stackup: TOP GND_1 HS1 GND_2 POWER HS2 GND_3 . . . Instead of using USB 3.0 Standard A connector, if I am routing signals to a SMP connectors. Assumptions (for argument sake): 1) SMP is not edge connector. 2) Good quality Dielectric 3) Ignore coupling from other sources. 4) board size is 5"x5" Question 1: a) If I am routing from HS1 to TOP b) GND_1 and GND_2 are stitched (not close to SMP signal pins). My point is, it doesn't matter to have ground vias next to signal Vias. Will it make a LOT OF DIFFERENCE if I route signal from HS2 to TOP under same conditions? Thanks Aaditya On Thu, Oct 16, 2014 at 12:13 PM, Rick Brooks (ricbrook) <ricbrook@xxxxxxxxx > wrote: > The counter argument is that anyone who says that GND stitching vias do > nothing or are not needed under any conditions, is also suggesting a "rule" > which should be proved for all possible cases. > Honestly, I do not remember anyone saying on this thread that having close > GND stitching vias is required in every conceivable place or scenario. > > I have certainly seen specific designs where the location and number of > GND stitching vias made a big difference with signals containing even mode. > Obviously, that does not mean they are a must have for every via on every > board that is built or shipped. > It also does not mean that I am willing to share the actual data, because, > like others, there may be confidential aspects to it. > > I have also seen conditions where right angle bends on traces creates no > visible problems. > That does not mean you should use right angle bends, or that there aren't > an infinite number of cases where right angle bends would be a disaster. > > As always, "it depends" > > This forum is for people to put forth their ideas and experience. > I, for one, welcome their comments, with or without proof. > cheers > > > > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] > On Behalf Of Lee > Sent: Thursday, October 16, 2014 10:16 AM > To: scott@xxxxxxxxxxxxx; Yishan.Li@xxxxxxxxxxxxxxxxxxxx > Cc: Gert.Havermann@xxxxxxxxxxx; aaditya.kandibanda@xxxxxxxxx; si-list > Subject: [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 > Teraspeedî 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´10æÅË16æâÂ¥ 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. > > Thatââ¬â¢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