Ken, I agree you did not. But rightly or wrongly it is easily inferred from some statements of others. Since we all agree that is a bad extreme, I think it is reasonable that Chris objects to it. Regards, Steve. At 09:09 AM 7/26/2006, Ken Cantrell wrote: >Steve - >I never said or implied that arbitrarily traversing any cavity with any >combination of signals without concern for the Z-axis return path was >acceptable. I do agree about the silly extreme. > >Ken > >-----Original Message----- >From: steve weir [mailto:weirsi@xxxxxxxxxx] >Sent: Wednesday, July 26, 2006 9:47 AM >To: Ken.Cantrell@xxxxxxxxxxxxxxxx; Chris.Cheng@xxxxxxxxxxxx; Ken >Cantrell; si-list@xxxxxxxxxxxxx >Subject: Re: [SI-LIST] Re: Current Return Vias > > >Ken, I disagree. I think that Chris' examples graphically >demonstrate the fact that we cannot arbitrarily traverse any cavity >with any combination of signals without concern for the Z axis return >path and yield desired results. I find it very much in context with >the original discussion of the what is for many cases at current >signaling edge rates an equally silly extreme in the form of an >individual return stitch via per signal via. > >Regards, > > >Steve. > >At 07:32 AM 7/26/2006, Ken Cantrell wrote: > >Chris - > >That was my point, the example was extreme and didn't address the issue. > >Ken > > > >-----Original Message----- > >From: si-list-bounce@xxxxxxxxxxxxx > >[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Chris Cheng > >Sent: Tuesday, July 25, 2006 6:05 PM > >To: Ken Cantrell; si-list@xxxxxxxxxxxxx > >Subject: [SI-LIST] Re: Current Return Vias > > > > > >How stupid it is for the design below vs. statements like "all you need = > >is the power/ground plane and decoupling capacitance for the return = > >current path, no vias needed". Wait, aren't they the same stupid concept = > >? > >While the example is extremely, I have been called to fix package = > >designs (not my own) that conveniently forgot to provide return vias = > >between upper and lower power/gnd planes because package designers want = > >to steal those large core via locations for their signal escapes to = > >bottom layers. If you read Larry's reply carefully, you will see similar = > >experiences he refers to. Some highspeed signals experience a huge = > >glitch everytime some slow JTAG signals toggles hundreds of mils away on = > >a package. As it turns out, the package designer forgot to provide the = > >through vias for the reference planes and the return current decided to = > >take the nearest return via as return path which is on the highspeed = > >signal area hundreds of mils away. > >At the end, talk is cheap. If you truly believe return via is useless = > >and plane and decoupling capacitance is good enough, why border to drill = > >those vias on packages. Put your money where your mouth is. And if you = > >are too chicken to do so, you are not practicing what you preach. > > > >-----Original Message----- > >From: Ken Cantrell [mailto:Ken.Cantrell@xxxxxxxxxxxxxxxx] > >Sent: Tuesday, July 25, 2006 6:49 AM > >To: Chris Cheng; si-list@xxxxxxxxxxxxx > >Subject: RE: [SI-LIST] Re: Current Return Vias > > > > > >Chris, > >Nobody said it was OK to do stupid stuff. > >Ken > > > >-----Original Message----- > >From: si-list-bounce@xxxxxxxxxxxxx > >[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Chris Cheng > >Sent: Monday, July 24, 2006 5:15 PM > >To: si-list@xxxxxxxxxxxxx > >Subject: [SI-LIST] Re: Current Return Vias > > > > > >Ok, I'll give you an evidence if you dare to take it up and try on your = > >=3D > >clients design and see if you can keep your job after that. > > > >In a typical multi-layer BGA design, the signal fan out is almost =3D > >entirely done on the top half of the package and reference to the planes = > >=3D > >on top. The power and ground planes are connected through blind and =3D > >buried vias through the package to the PCB. As such a package design can = > >=3D > >therefore stop the via connection at any plane he/she desire. > > > >My challenge to you is just connnect all those power/ground pin on the = > >=3D > >peripheral (not directly underneath the die) to the bottom half of the = > >=3D > >package only and not to the top half where the signals are reference to. = > >=3D > >Let's see how much ground/power bounce you will observe. > > > >BTDT, have you ? > > > >-----Original Message----- > >From: si-list-bounce@xxxxxxxxxxxxx > >[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Lee Ritchey > >Sent: Monday, July 24, 2006 3:46 PM > >To: Ken Cantrell; kenny_frohlich@xxxxxxxxx; si-list@xxxxxxxxxxxxx > >Subject: [SI-LIST] Re: Current Return Vias > > > > > >Ken, > > > >Well put. When someone makes the statement that ground vias are =3D > >required > >to provide a path for return currents, it needs to be accompanied with = > >=3D > >some > >evidence. > > > > > > > [Original Message] > > > From: Ken Cantrell <Ken.Cantrell@xxxxxxxxxxxxxxxx> > > > To: <kenny_frohlich@xxxxxxxxx>; <leeritchey@xxxxxxxxxxxxx>; > ><si-list@xxxxxxxxxxxxx> > > > Date: 7/24/2006 6:51:24 AM > > > Subject: [SI-LIST] Re: Current Return Vias > > > > > > Kenny, > > > At 133MHz, and assuming your edge rates are > 500ps, you aren't going = > >=3D > >to > > > need them, even if you have twice as many layers. It's an important > >effect, > > > but at 133MHz it's not relevant. What is important, as Lee indicated, = > >=3D > >is > > > your PDS design. > > > > > > Ken > > > > > > -----Original Message----- > > > From: si-list-bounce@xxxxxxxxxxxxx > > > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Kenny Frohlich > > > Sent: Saturday, July 22, 2006 1:56 PM > > > To: leeritchey@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx > > > Subject: [SI-LIST] Re: Current Return Vias > > > > > > > > > Lee, > > > I'm not talking about jumping from one layer to the next adjacent = > >=3D > >layer > > > which shares the same referrence plane. In this case, I do not need a > > > ground via. But I'm asking about jumping from one layer to another = > >=3D > >layer > > > that has a differrent reference ground plane. For example, on an 8 = > >=3D > >layer > > > PCB stackup where the two ground planes are layers 2 and 7, the =3D > >signal > > > jumps from the top layer (layer 1) to the bottom layer (layer 8). > > > > > > Thank you > > > Kenny > > > Lee Ritchey <leeritchey@xxxxxxxxxxxxx> wrote: > > > Kenny, > > > > > > It is not true that you need a "return current" via next to each layer > > > changing signal via. I continue to be amazed that engineers who are > > > looked upon as SI experts say such things. > > > > > > Imagine you have a 4 layer PCB, such as the mother board in a PC, =3D > >where > > > there are only two planes, one Vdd and one ground, where would such = > >=3D > >vias > > > connect? There have been billions of these made to date that work just > > > fine and have very fast signals on them. The return currents you are > > > concerned about find their way from plane to plane through the =3D > >collection > > > of decoupling capacitors and interplane capacitance that you had to > > > engineer into the power delivery system in order to make it stable. = > >=3D > >Focus > > > on this and the return currents take care of themselves. EMI is =3D > >minimized > > > he same way.. > > > > > > > > > > > > > > > > [Original Message] > > > > From: Kenny Frohlich > > > > To: > > > > Date: 7/22/2006 6:45:56 AM > > > > Subject: [SI-LIST] Current Return Vias > > > > > > > > Dear Experts, > > > > I understand that I need to provide ground vias next to via =3D > >explictly > > > for the purpose of letting return currents jump between layers. I know > > > it's a requirement for high speed signals, especially differrential > > > signals. Is this also required for low speed single-ended signals =3D > >(133Mhz > > > or slower)? > > > > If this is a requirement, what would be a good signal via to ground = > >=3D > >via > > > ratio? For example, there are five signal vias within a 1 inch area, = > >=3D > >how > > > many ground vias do I need? > > > > > > > > Thank you > > > > Kenny > > > >------------------------------------------------------------------ > >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 > > > > > > > >______________________________________________________________________ > >All email being sent to or from SRC Computers, Inc. will be scanned by a > >third party scanning service. > >______________________________________________________________________ > > > >------------------------------------------------------------------ > >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 > > > > >______________________________________________________________________ >All email being sent to or from SRC Computers, Inc. will be scanned by a >third party scanning service. >______________________________________________________________________ > >------------------------------------------------------------------ >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