Steven Unfortunately, both the the paper and Dr Johnson's work are accurate only in the quasi-static domain. Our work on launches has shown that quasi-static analysis and models for vias are not very useful, except as a first order approximation. By using full-wave techniques, we can push via cutoff frequencies up to 40 GHz. We have a few slides on our website under publications that discuss high-performance via and launch issues. *Evaluation of a Single Via in the Frequency Domain **Hybrid Solver and Measurement Based Design **Electrically Transparent 50 Gbps Board-to-Board Interconnect best regards, Scott * Scott McMorrow Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 (401) 284-1827 Business (401) 284-1840 Fax http://www.teraspeed.com Teraspeed® is the registered service mark of Teraspeed Consulting Group LLC Salkow, Steven wrote: > These links will help > > > characterization_of_a_printed_circuit_board_via > > > > http://www.coe.montana.edu/ee/lameres/vitae/publications/1_thesis/thesis > _002_msee.pdf > > > > > > Dr. Johnson constructs a working large scale model of a via, large > enough so the he can reach into the board and modify the structure from > within while observing, in real-time, the electrical behavior of the > via. > > http://www.sigcon.com/SiLab/Via_clip.wmv > > > > 3D field solvers versus Network Analyzer and real models > > Many of you are already using coupons to assess the quality of your > boards. For those they are not familiar, Test coupons are typically > small sections around the periphery of a board with exactly the same > layers stackup as the main PCB that are fabricated at the same time as > the PCB. Coupons are or may be used to test a number of PCB features > that determine impedance, design integrity, etc. > > > > The opportunity exists to assess via-model-designs at practically no > cost to the project other than the via design time and lab assessment to > characterize the results: > > I envision a series of coupon with the various vias and anti-pads as > well as guard grounds place so these may be connectorized with surface > mount sma or sna connectors compatible with your Network analyzer. This > will allow an engineer to extract an S parameter model from each > physical module which may be useful for further simulation. (Most high > speed circuit simulators will be able to use S parameter model in > simulations.) This may seem, on the face of it, an expensive approach. > In reality, it is cheaper and quicker than 3D field solving but DOES NOT > produce an exact solution. > > > > Understand this: > > The optimum via design is rarely the one used as board space is not > available to contain all the signals and all the grounds in the same > area. As density of vias go up, the ground planes are literally carved > away near the BGAs where circuit density is the highest. What also goes > away is exact prediction of circuit behavior without exact 3D modeling > which is time intensive and uses expensive software tools. > > > > Steven Salkow > > Lockheed IS&S > > 3130 Zanker Rd, San Jose > > Ca. 94588 > > steven.salkow@xxxxxxxx > > salkow@xxxxxxxxxxxx > > > > > > > > > > ________________________________ > > From: chand basha [mailto:chand_374@xxxxxxxxx] > Sent: Tuesday, December 12, 2006 12:03 AM > To: Salkow, Steven; PaulClarke@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx > Subject: Re: [SI-LIST] Re: ROOKIE: Anti-Pad Size Effect On Signal > Integrity:By the formula, as F goes up, Xc goes down (was up by typo) > > > > > > Steven Salkow, > > > > its an excellent presentation, very simple really very simple, > > > > I have a dought in the last para i.e > > How do we tune via impedance? We use ground vias nearby and 3D Modeling > tools that exist to fufill this purpose but that is beyond the scope of > a short answer. > > > > if you can explain a littile bit about tuning the impedance with ground > vias will be very much > > help full. > > > > > > Thanks in advance. > > > > chand > > > > > > "Salkow, Steven" <steven.salkow@xxxxxxxx> wrote: > > > > -----Original Message----- > From: Salkow, Steven > Sent: Monday, December 11, 2006 1:59 PM > To: 'PaulClarke@xxxxxxxxxxxxx'; 'si-list@xxxxxxxxxxxxx' > Subject: RE: [SI-LIST] ROOKIE: Anti-Pad Size Effect On Signal > Integrity > > Paul: > I will make this simple are seems reasonable. It does, however, > seem to > me quite extraordinary that a mechanical fellow might be getting > involved with Gigahertz design of vias. > > You're correct the effect does depend on speed. The "anti-pad" > is used > when building plane layers (i.e.: solid layers) using negative > planes. > It is the VOID area between the pad and the copper of the plane. > The > effect is to provide a capacitive reactive effect given by the > formula > Xc= 1/(2*pi*F*C) where f is frequency and C is capacitance. By > the > formula, as F goes up, Xc goes down (was up by typo). The C > capacitance > is given by the formula C = (Area*k*e)/length where length is > really the > distance the two areas are apart (in this case the width of the > anti-pad > (the bigger the gap, the smaller the capacitance). The effects > of C is > cumulative for multiple planes. > > If the anti-pad size is very large, are we out of the woods. NO! > All signals used in modern design as transmission lines have a > certain > desirable impedance. The is the effective "resistance" of the > line that > best matches the driver electronics. When effective "resistance" > of the > line does not match the driver electronics one of two > possibilities > happen: > The signal has energy reflected back to the source > Or excessive energy is absorbed by the circuit a too little gets > to the > load. > Anti-pads are designed to maintain the required effective > "resistance" > (impedance) of a transmission line at a matching value. What's > that > mean? > If the line impedance and the driver impedance and the load > impedance > are all 50 ohms, then the via should be tuned to the same value. > > How do we tune via impedance? We use ground vias nearby and 3D > Modeling > tools that exist to fufill this purpose but that is beyond the > scope of > a short answer. > > Steven Salkow > Lockheed IS&S > 3130 Zanker Rd, San Jose > Ca. 94588 > steven.salkow@xxxxxxxx > salkow@xxxxxxxxxxxx > > > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx > [mailto:si-list-bounce@xxxxxxxxxxxxx] > On Behalf Of Clarke, Paul > Sent: Monday, December 11, 2006 1:25 PM > To: 'si-list@xxxxxxxxxxxxx' > Subject: [SI-LIST] ROOKIE: Anti-Pad Size Effect On Signal > Integrity > > Hello, > > Before you read the question please keep in mind that I am just > a lowly > Mechanical guy that has better odds of selecting the right bolt > than I > do > designing an LED circuit. > > I have a question about how the size of an anti-pad can effect > signal > integrity. The example application could be a backplane @ 5, 10, > 20, 40, > or > 80 [G] (I am asking for this range because I anticipate the > answer may > depend on the speed). > > If you have a BP via for a signal pair of .025" with a pad of > .044", how > much impact can an antipad have on the impendance through a > range of > sizes > of let's say .054-.060"? Center-Center distance could be 2.1 > [mm]. > > In the case described above, would the antipad size range really > have > any > effects or is it negligible? > Is an anti-pad just to keep solder off the pad if you flood the > plane? > Or is > there an actual SI reason for those things? > How sensitive is the SI to changes in antipad size? > Any concerns regarding manufacturing tolerances on antipads? > > Thank you for any information and your patience explaining any > of the > above > questions to a mechanical guy. > > Paul Clarke > > > > ------------------------------------------------------------------ > 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 > > > > > > __________________________________________________ > Do You Yahoo!? > Tired of spam? Yahoo! Mail has the best spam protection around > http://mail.yahoo.com > > > > ------------------------------------------------------------------ > 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