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 = 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 = entirely done on the top half of the package and reference to the planes = on top. The power and ground planes are connected through blind and = buried vias through the package to the PCB. As such a package design can = 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 = peripheral (not directly underneath the die) to the bottom half of the = package only and not to the top half where the signals are reference to. = 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 = required to provide a path for return currents, it needs to be accompanied with = 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 = 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, = 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 = 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 = layer > that has a differrent reference ground plane. For example, on an 8 = layer > PCB stackup where the two ground planes are layers 2 and 7, the = 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, = where > there are only two planes, one Vdd and one ground, where would such = 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 = collection > of decoupling capacitors and interplane capacitance that you had to > engineer into the power delivery system in order to make it stable. = Focus > on this and the return currents take care of themselves. EMI is = 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 = 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 = (133Mhz > or slower)? > > If this is a requirement, what would be a good signal via to ground = via > ratio? For example, there are five signal vias within a 1 inch area, = how > many ground vias do I need? > > > > Thank you > > Kenny > > > > __________________________________________________ > > Do You Yahoo!? > > Tired of spam? Yahoo! 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