Re: [SI-LIST] : Board Stackup Question

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From: Chandan Das (chandan_career@yahoo.com)
Date: Sat Mar 31 2001 - 01:37:19 PST


Hi,

David, why would you like to stay away from increasing
power planes? What effect does it have on EMC?

Patel, why do you prefer to increase the number of
ground planes?

Both of your e-mails show a preference for additional
grind planes. Subramanya's aim is to design a board
that is superior in terms of EMC performace. At those
frequecies, the power plane as well as the ground
plane are the same. Then, as far as radiations & EMC
effects are concerned, it should not matter whether he
has several ground planes or power planes.

Please explain.

Thanks,
Chandan

--- David Heald <daveheald@mediaone.net> wrote:
> Greetings Subramanya, all:
> I would stay away from increasing power planes, but
> the addition of
> another ground plane or two would do wonders for
> you. If you ould get
> away with only one power plane, you could reap
> additional benefits as
> well.
>
> I would recommend the following stackup:
>
> S1 G S2 S3 G S4 S5 G S6 P G S7
>
> If you need 2 power planes, try this
>
> S1 G S2 P G S3 S4 G P S5 G S6 or
> S1 G P S2 G S3 S4 G S5 P G S6 (I forget right now
> which is better, but I
> think the first - anyone else??)
>
> In the first case, use S4 and S5 for your highest
> speed signals and try
> to keep individual signals solely on S4 or S5 (for
> second case, layers
> S3, S4 are the corresponding layers). If you do
> have to jump between
> layers, add an additional ground via adjacent to the
> jump (this also is
> a good idea when returning to the outer layers.)
> Adding the via
> minimizes return current loop size and reduces
> overall emissions.
> Finally, bypass the power and ground planes often
> and tie the ground
> planes together with a good number of vias to
> minimize return current
> paths.
> Feel free to contact me if you have any questions
> about my reasoning
> for the above recommendations.
>
> Regards,
> Dave Heald
>
>
> subramanya C K wrote:
> >
> > Hello all ,
> > I have the following query regarding the Board
> stackup:
> >
> > If U were supposed to design a 12 layer board with
> superior EMC, which
> > stackup among the following would U prefer and why
> ?
> >
> > STACKUP-1: S1 G S2 S3 P S4 S5 G S6 S7 P S8
> > STACKUP-2: S1 P S2 S3 G S4 S5 G S6 S7 P S8
> > *S = Circuit (routing) Layer ; P = Power Plane ; G
> = Ground Plane
> >
> > Next, is there any hazzard due to the power noise
> in 3rd and 4th circuit
> > layers (S3 and S4) of the first topology ? if yes,
> what's the reason
> > behind that and how do U overcome it ?
> > (same for S7 and S8 of second stackup)
> >
> > Finally, if I am given the liberty of increasing
> the number of power
> > planes on the cost of circuit layers (say 4:4),
> will it create any
> > crosstalk among the tarces on the four circuit
> layers ? (because now
> > there are more number of high speed tracks bunched
> nearer than before)
> > If yes, is there any go for that ?
> >
> > Thanks and Regards,
> >
> > Subramanya C K
> > Tel: +91-80-8520408 Ext: 4179
> >
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