Re: [SI-LIST] : Regarding plane splits

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From: Ritchey Lee (leeritchey@earthlink.net)
Date: Tue Jan 02 2001 - 08:33:14 PST


Without knowing hte thickness of the dielectrics between power and ground
planes, it's tough to assess why one was better than the other, but my bet is
the better performing stackup had more interplane capacitance.

Lee

Dennis Yarak wrote:

> I haven't been following threads recently (too busy) but I do have a mildly
> interesting result to report in re: split planes.
>
> After discussions with our EMI experts we decided to do two different stack
> ups with the same gerber files. This is a 10 layer/50 ohm board with
> s-g-s-s-g-pslit-psplit-s-g-s, and the alternative was
> s-g-s-psplit-g-psplit-s-g-s.
>
> The first stack optimized for signal return path (only one signal layer sees
> the power split, and layer 8 was routed carefully) while the second
> optimized for VDD decoupling to ground.
>
> Even though this was as controlled an experiment for EMI as we could do, the
> specifics of the situation determine whether the result would be applicable
> in general. We didn't have the luxury of trying to reroute layer 3 to be
> better behaved across the new plane splits it sees in the alternate stack,
> for example.
>
> We found the first stack was a few dB better pretty much across the board.
>
> Dennis Yarak
>
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