Re: [SI-LIST] : Board Stackup Question

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From: David Heald (daveheald@mediaone.net)
Date: Wed Mar 21 2001 - 07:39:34 PST


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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