[SI-LIST] Re: 6 layers stackup
- From: Dave Pollum <vze24h5m@xxxxxxxxxxx>
- To: Fernando Yuitiro Mori <mori@xxxxxxxxxxxxx>
- Date: Thu, 21 Feb 2008 18:11:13 -0500
Fernando Yuitiro Mori wrote:
> Hi,
> I normally use S1 S2 G P S3 S4 for the 6 layers stackup. I need the 4
> layer with 60 ohms, so there are some problem if I use S1 G S2 S3 P S4?
> Regards,
>
> Fernando Mori
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>
With a "S1 G S2 S3 P S4" stackup, you won't get the helpful capacitance
between the Power and Ground planes because to planes are too far away.
In Lee Ritchie's book "Right the First Time - A Practical Handbook on
High Speed PCB and System Design, Volume 2" he discusses a similar
problem with a 6 layer board (pg. 43). That board was flaky and failed
EMI testing. His solution was to copper flood all non-used board area
on each _signal_ layer, and then connect the flooded copper to the
appropriate power or ground plane. In your case, layers S1 and S2 are
adjacent to the Ground plane, so the copper flood on those layers must
be connected to the _power_ plane. Layers S3 and S4 are adjacent to the
Power plane, so the copper flood on these layers must be connected to
the _ground_ plane. Make sure that there are "enough" vias to connect
the floods to the appropriate plane.
HTH
-Dave Pollum
>
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