[SI-LIST] Re: Stack up for EMI reduction, plane resonance and u-strip radiation etc etc

From: "Ken Cantrell" <Ken.Cantrell@xxxxxxxxxxxxxxxx>
To: <lenaw@xxxxxxxxx>, <istvan.novak@xxxxxxxxxxxxxxxx>,"Chris Cheng" <Chris.Cheng@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
Date: Thu, 12 Feb 2004 08:32:26 -0700
MC,
Can you rephrase?  I think you just said you wanted greater Lmutual, but you
disagreed with bringing the planes closer together??
Ken

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of lenaw
Sent: Wednesday, February 11, 2004 9:23 PM
To: istvan.novak@xxxxxxxxxxxxxxxx; Chris Cheng; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Stack up for EMI reduction, plane resonance and
u-strip radiation etc etc


Istvan:
           On (b) my opinion is that if you want to reduce the power/ground
bounce, you have to reduce the total effective inductance of the
power/ground planes ( assume you have no bond wire and use flip-chip
technology to connect the die to the package ) and it depends on what kind
of buffer technology you are using, signals on top of a pair of closely
coupled power/ground reference may not be the best solution because you need
the strong mutual inductance between the signal and power or ground planes
to reduce your total effective inductance during SSO. Just my 2cents.


Regards,
MC

----- Original Message -----
From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
To: "Chris Cheng" <Chris.Cheng@xxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
Sent: Wednesday, February 11, 2004 9:59 PM
Subject: [SI-LIST] Re: Stack up for EMI reduction, plane resonance and
u-strip radiation etc etc


> Chris,
>
> > a) If your plane reference is so limited and crowed with highspeed
traces
> > that it can not provide the effective capacitance, it will exhibit
itself
> as
> > both xtalk and power/gnd bounce problem. The image current starts to
> overlap
> > each other and either add or subtract from each other. This is an
> observable
> > problem in most signal traces in organic packages. But I will turn the
> table
> > around and ask you, how could your fancy capacitor or thin core plane
help
> > if they are electrically further from the reference planes ? It's like
> > challenging my Covertte saying "hey, I bet you can't drive this car at
> > 300mph" while you are sitting on a pintle.
>
> So I think we are in agreement here that if trace density is increases,
> beyond
> a certain point we will have power/ground bounce issues on the planes.
> You are correct that crosstalk among traces will probably go up at
> a similar rate, but it is a matter of system design, which will pose a
> limitation first.
> If you hit the power/ground bounce limit first, and crosstalk is still not
> harmful,
> a thinner power/ground laminate may help to reduce power/ground bounce.
> If in the new stackup you still reference the same power plane, what has
> changed is that the traces will be 'outside' of the power/ground cavity,
not
> inside as before.  In this case only the ground reference plane for the
> traces is
> what is further away from the power/ground plane pair.  If the components
> on the board force you to have a large number of ground vias anyway, you
> can get the sufficiently tight stitching between the ground planes without
> extra
> expence.
>
>
> > b) At extreme high edge rate, the skin effect is limiting both the
signal
> > trace and the image current that flows on the reference plane, your
> infinity
> > argument doesn't exist. I can't answer an argument that cannot exist.
>
> OK, let me rephrase the question that may be easier to answer.  Say you
> have a working board, and you are satisfied with it.  It has a given
number
> of traces referencing the correct plane.  Say the transition times on
those
> traces are all around 1 nsec.  And lets suppose the power/gnd bounce
> is acceptable: not much lower than your target, but safely below your
> limit.  Suppose the only thing you change next is the silicon, and it puts
> out
> 200psec transition times instead of 1nsec.  There is no other change
> on the board.
> The 200psec edges are 'slow' enough that within an inch radius we cant
> really
> expect any absorption due to skin effect, and the one inch radius
> approximately
> represents the distance the signals can go within 200psec.  So the
> question is: if you want to maintain about the same level of power/ground
> bounce,
> would you change the plane structure; would you put the power/ground
planes
> closer, further apart, or leave them where they are?
>
> Regards,
> Istvan
>
>
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References:
- [SI-LIST] Re: Stack up for EMI reduction, plane resonance and u-strip radiation etc etc
  - From: lenaw
[SI-LIST] Re: Stack up for EMI reduction, plane resonance and u-strip radiation etc etc

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