[SI-LIST] Re: 6 layers stackup
- From: Dave Pollum <vze24h5m@xxxxxxxxxxx>
- To: Fernando Yuitiro Mori <mori@xxxxxxxxxxxxx>
- Date: Thu, 21 Feb 2008 12:49:21 -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?=20
>
>Regards,
>
>Fernando Mori
>
With a "S1 G S2 S3 P S4" stackup, you won't get the helpful capacitance=20
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=20
High Speed PCB and System Design, Volume 2" he discusses a similar=20
problem with a 6 layer board (pg. 43). That board was flaky and failed=20
EMI testing. His solution was to copper flood all non-used board area=20
on each _signal_ layer, and then connect the flooded copper to the=20
appropriate power or ground plane. In your case, layers S1 and S2 are=20
adjacent to the Ground plane, so the copper flood on those layers must=20
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=20
the _ground_ plane. Make sure that there are "enough" vias to connect=20
the floods to the appropriate plane.
HTH
-Dave Pollum
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