[SI-LIST] Re: Crosstalk between two planes

Your mileage may vary but for 8 layers with the digital ICs on the 
bottom, I would do this:


1. Top  Motor drive parts
    3-4 mil dielectric
2. Power
    =< 4 mil dielectric
3. Gnd1
    4 mil dielectric
4. S1
    >10 mil dielectric
5. S2
    4 mil dielectric
6. Gnd2
    match L2/L3 dielectric =< 4 mils
7. Atmel / SDRAM power
    3-4 mil dielectric
8. Bottom Atmel / SDRAM parts

For an 0.062" thick board it is easy to make the dielectric between 
layers 4 and 5 20 mils or thicker.  Cross talk will be a non-issue even 
for tandem lines.

Normally I would have put the digital ICs on top, in which case layer 2 
swaps with layer 7.  I don't know if you've placed the motor junk on top 
for heat sinking or other reasons.  Typically those sorts of things have 
the through hole connections which would favor flipping and bottom.

Steve

Jaison Fernandez (RBEI/EED2) wrote:
> Dear Experts,
> I have a layer stack up like  as follows:
>
> 1. Top
> 2. Gnd1
> 3. Power
> 4. Gnd2
> 5. Sig1
> 6. Sig2
> 7. Gnd3
> 8. Bottom
>
>
> My board is one which contains ATMEL AT91SAM9M10, 128MB SDRAM (166MHz), GPS 
> Chip solution, High current motor Drivers etc.
>
> I placed Atmel and SDRAM in bottom layer and routed the SDRAM signals in Sig1 
> and Sig2 planes.
> Could any one tell me the chances crosstalk between sig1 and Sig2 planes and 
> possible ways to avoid it.
> Due to some tool limitations I can't able to due any POST SI analysis.(Stack 
> up of Layer1 to Layer 3 is fixed due to some high current applications)
>
> Regards,
> Jaison Fernandez
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Steve Weir
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