[SI-LIST] Re: 6 Layer Stack-up
- From: steve weir <weirsp@xxxxxxxxxx>
- To: vishrampandit@xxxxxxxxxxx, larry.smith@xxxxxxx
- Date: Fri, 12 Sep 2003 11:53:22 -0700
Vishram,
Inductance is the enemy. You definitely want to go with stack-up #2. Any
disadvantages are greatly outweighed by the dramatic reduction in
inductance versus #1.
Regards,
Steve
At 06:14 PM 9/10/2003 +0000, Vishram Pandit wrote:
>
>
>
>
>
>We have been using the stackup S-G-S-S-P-S.(stack up no. 1). Now, with
>suggestion from SI-List, on newer high speed designs, I would like to use G
>adjacent to P with 4-6 mils of separation. It will give me very good
>decoupling. However, I have only 6 layers so I have to have my stack-up as
>S-S-G-P-S-S (stack up no. 2). Will it be okay?
>
>Here are pros and cons as per my analysis:
>
>1] Stack up no. 1 gives you poor P/G decoupling, wheras stack up no. 2 gives
>you very good P/G decoupling.
>
>2] P/G Decoupling caps at higher frequencies (>500MHz) are not required for
>stack up no. 2
>
>3]Stack up no. 1 will shield the EMI radiation from internal traces because
>of G(Layer 2) and P(Layer 5).we will loose this benefit for the stack up no.
>2.
>
>4] For stack up no. 1, signals on Layer 1, 3, 4, and 6 had a reference
>plane.For stack up no. 2, only signals on Layer 2 and 5 have reference
>planes. So I have to be careful routing high speed signals on Layer 1 and
>Layer 6.
>
>Has anyone implemented stack up no. 2 on 6 layer board? Which stack up is
>advisible for 6 layer board? What are pros and cons for stack up no. 1 and 2
>for a 6 layer board?
>
>
>Thanks,
>
>Vishram
> >From: Larry Smith >Reply-To: larry.smith@xxxxxxx >To:
>vishrampandit@xxxxxxxxxxx >CC: si-list@xxxxxxxxxxxxx,
>Charles.Grasso@xxxxxxxxxxxx >Subject: [SI-LIST] Re: Power Integrity (was:
>UltraCAD ESR and Bypass Capacitor Caculator) >Date: Mon, 18 Aug 2003
>09:11:42-0700 >>Vishram - I agree. My general approach is to address the PI
>problem first >and make sure that the silicon circuits have clean power.
>Thisinvolves >management of capacitance and inductance at the PCB, package
>and chip levels. >Next, address the SI problems by making sure that all high
>speed signals have >a good return current path. After doing these two
>things,many EMI problems >will be eliminated. >>I have also been able to fix
>EMI problems at multiple 100's of MHz by >using decoupling capacitors. But
>the higher the frequency gets, the >harder it is to do this. Capacitors at
>this frequency usually will not affect >the quality of the power as measured
>at the silicon circuit terminals (PI), >but they might effect emmissions.
> >>After we began using thin power plane >dielectrics, I don't believe we
>havefound any EMI problems that can >be fixed with discrete decoupling
>capacitors. But if your product does >not have thin power plane dielectrics
>(4 mil or less) for cost or >other reasons, EMI problems can _sometimes_ be
>fixed with caps. If >this works, it is usually not a very robust solution.
>Ifsome little >thing changes, the EMI problem often crops back up again.
> >>regards, >Larry Smith >Sun Microsystems >>Vishram Pandit wrote:
> >>>>>>Larry, >>>>Very nice explanation. PI influences SSN, and SSN
>influencesEMI. EMI is >>influenced by PI and SI. If we have sound PI and
>also, reduce the SSN, then >>EMI (due to that aspect of the circuit) is
>mitigated. Would you agree? >>>>As mentioned in my pevious mails, I have
>seenimprovements in EMI at higher >>frequencies (as high as 800MHz) with
>decoupling capacitors, and changing the >>P/G structure to improve the
>impedance. Your email states that PI is >>characterized by P/G impedance and
>decaps for PI are effective up to 100MHz. >>However, in my case, I reduced
>the 800MHz impedance further by decaps >>betweenP/G, and by improving the
>P/Gstrucutre, and it helped improve the >>EMI. Thus, improving PI at 800MHz
>improved the EMI.Apart from chaning the >>structure of P/G, decaps (value,
>ESL, locations) played important part in >>it. >>>>I will appreciate your
>comments. >>>>Thanks, >>>>Vishram Pandit >>>>Senior Member Techincal Staff
> >>>>Hughes Network Systems >>>>>From: Larry Smith >Reply-To:
>Larry.Smith@xxxxxxx >To: >>si-list@xxxxxxxxxxxxx,
>Charles.Grasso@xxxxxxxxxxxx>Subject: [SI-LIST] Power >>Integrity (was:
>UltraCAD ESR and Bypass Capacitor Caculator) >Date: Fri, 15 >>Aug 2003
>14:04:39 -0700 (PDT) >>I changed the thread name to better reflect >>the
>subject.. >>Some of us at Sun have begun using a different word for the
> >>power >distribution problem, "power integrity." This phrase helps to
> >>>distinguish three major topics: power integrity (PI), signal integrity
> >>>(SI)and EMI. Power integrity is the issue that Charles is addressing >and
> >>signal integrity is what Kim is addressing in his very nice web >posting.
>A>>lot of the confusion could be eliminated by using clearer >terminology.
> >>I>>think of the "power integrity" problem as having only two nodes: Vdd
> >and >>Gnd. There are no signals involved. For the power integrity >problem,
>we are >>concerned with delivering many watts of power, often at >low
>voltageand >>highcurrent, to modern digital technology. The big >issues are
>transient >>current and DC loss. A good example is an >advanced micro
>processor that >>draws as much as 100 watts of power at 1 >volt (100 amps).
>The processor can >>go from an idle state to a fully >active state in just a
>few clock cycles (1 >>nSec). The silicon circuits >may consume 50 amps and
>then 100 amps just a >>fewcycles later. >Delivery of this 50 watt transient
>through the various >>timeconstants, >which range from nSec to mSec (chip,
>package, PCB, VRM, AC >>toDC >converter), is very much a part of the power
>integrity problem. Note >>>that 1 mOhm of DC resistance in this circuit
>consumes 10 watts of power >>>(I^2*R) and renders our delivery system only
>90% efficient. Power >>>Integrityinvolves delivering high current with huge
>transients. It is >best >>understood and managed by the concept of target
>impedance in the >frequency >>domain. >>Signal integrity, on the other hand,
>always involves signal nodes. >>A >few years ago, at the 50 MHz level,
>signalintegrity basically meant >the >>waveform quality and timing on ideal
>transmission lines. Before >that, all >>wehad to worry about (at the 5 MHz
>level) was RC time >constants. Now we are >>beyond 500MHz where we must be
>concerned with >frequency dependent loss and >>return current paths. Several
>years ago, >SSN (simultaneous switch noise) >>wasmostly an L*di/dt problem
>that >created ground bounce in the DIP's (dual >>inline packages, lead
> >frames). After we started including ground planes in >>our packages,
> >replaced wire bonds with solder bumps and started using just >>as many
> >ground pins as signal pins, the SSN problem changed to a power
> >>plane>bounce and return current problem. This is how power integrity keeps
> >>>getting mixed up with signal integrity. The return current for signals
> >is>>on power and/or ground planes. But we can avoid a lot of confusion >if
>we >>usethe term "power integrity" for topics that involve just Vdd >and
>ground >>and reserve "signal integrity" for topics that involve >signal
>nodes. >>>>Decoupling capacitors play a role in all three topics. For the
>power >>>integrity problem, they are energy storage devices that mitigate
>power >>>transients. They deliver energy when the voltage droops and store
> >energy >>when the voltage spikes. For the signal integrity problem, they
> >enable >>return current to jump from one node to another (i.e. Vdd1 to
> >Vdd2or Vdd >>toGnd) when packages, vias or connectors require signal
> >returncurrent to >>make the jump. For the EMI problem, they provide low
> >impedance and energy >>absorption at frequencies where the product
> >naturally has a lot of energy >>(clock) or frequencies where the product
> >has a very efficient resonator or >>radiator. >>Decoupling capacitors are
>effective for the power integrity >>problem in >the 100 kHz to 100 MHz
>frequency band. Below 100 kHz it takes >>toomany >uF for them to be
>effectiveand above 100 MHz their inductance gets >>in >the way. However,
>decoupling capacitors may be used to complete return >>>current paths (SI)
>orabsorb noise (EMC/EMI) up to much higher >>>frequencies.Below 50 MHz,
>position on the PCB is not very important >but >>above 200 MHz, position
>often becomes critical. Thin power plane >>>dielectricsare a good
>replacementfor discrete decoupling >capacitors that >>are aimed at
>frequencies above 100 MHz. Power plane >capacitance is "broad >>band" but
>theQ of discrete capacitors becomes >sharp and limits their >>effectiveness
>as frequency increases. >>Very few topics on SI-list seem to >>evoke as many
>emotions as decoupling >capacitors. That is probably because >>people view
>them from so many >different perspectives. Vastly different >>conclusions
>canbe drawn for >decoupling capacitors depending on the problem >>you are
>trying to solve >(PI, SI or EMI) and other variables such as power >>plane
>dielectric >thickness. Some of this can be helped by clearly defining >>the
> >terminology and use conditions. >>regards, >Larry Smith >Sun >>Microsystems
> >>>Delivered-To: si-list@xxxxxxxxxxxxx >>From: "Grasso, >>Charles">>To:
>"'si@xxxxxxxxxxxx'" , "'si-list@xxxxxxxxxxxxx'" >>>Subject: >>[SI-LIST] Re:
>UltraCAD ESR and Bypass Capacitor Caculator >>Date: Thu, 14 >>Aug2003
>15:39:34 -0600 >>MIME-Version: 1.0 >>Content-Transfer-Encoding: 8bit
> >>>>X-archive-position: 7937 >>X-ecartis-version: Ecartis v1.0.0
> >>>>X-original-sender: Charles.Grasso@xxxxxxxxxxxx >>X-list: si-list >>>>Hi
> >>Kim, >>First - thanks for putting the slides up on the bweb for >>all to
> >>see.I think that you may have missed the point >>a little. In your
>scenario>>(a signal trace switching >>planes )the location of the caps is
>vital. >>>>>>The discussion was centered on the location of caps >>wrt power
> >>distribution. The location of the capacitors >>(within reason) will not
> >>affect a S11/S21 measurement >>that much. >>>>Fancy tackling that little
> >>problem? >>>>Best Regards >>Charles Grasso >>Senior Compliance Engineer
> >>>>Echostar Communications Corp. >>Tel: 303-706-5467 >>Fax: 303-799-6222
> >>>>Cell: 303-204-2974 >>Email: charles.grasso@xxxxxxxxxxxx; >>Email
> >>Alternate:chasgrasso@xxxxxxxx
> >>>>------------------------------------------------------------------ >To
> >>unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with
>'unsubscribe'>>in the Subject field >>or to administer your membership from
>aweb page, go >>to: >//www.freelists.org/webpage/si-list >>For help:
> >>>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field >>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
> >>>>>>----------------------------------------------------------------------
>------ >>Tired of spam? Get advanced junk mail protection[1] with MSN 8.
> >>>>--- Links --- >>1 http://g.msn.com/8HMWENUS/2734??PS=
> >>------------------------------------------------------------------ >>To
>unsubscribe from si-list: >>si-list-request@xxxxxxxxxxxxx with 'unsubscribe'
>in the Subject field >>>>or to administer your membership from a web page,
>goto: >>//www.freelists.org/webpage/si-list >>>>For help:
> >>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field >>>>List
>archives are viewable at: >>//www.freelists.org/archives/si-list >>or
>atour 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
>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 >>
>
>----------------------------------------------------------------------------
>Fast, faster, fastest: Upgrade to Cable or DSL today! [1]
>
>--- Links ---
> 1 http://g.msn.com/8HMQENUS/2740??PS=
>------------------------------------------------------------------
>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 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 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
Other related posts:
