[SI-LIST] Re: Layer Stackup
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "david.kaushansky@xxxxxxxxxxxx" <david.kaushansky@xxxxxxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Wed, 7 Jan 2004 08:02:36 -0800
David,
The problem you will have with this stackup is the lack of interplane
capacitance between power and ground planes. This will manifest itself in
several ways. Very high ripple on your power supplies when transmission
lines switch, potentially very high EMI, unstable operation.
It is imperative that you make sure that Vcc and ground planes are close to
each other. If you have several different supply voltages, this will mean
several pairs of power planes.
If you really need that many signal layers, it will be necessary to add
plane layers to get it right.
Lee
> [Original Message]
> From: <david.kaushansky@xxxxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Date: 1/7/2004 6:40:52 AM
> Subject: [SI-LIST] Layer Stackup
>
> The design I am working has a fairly dense placement. To try minimize my
> time in artwork, I would like to add as many routing layers as possible
to
> my layer stackup. I was thinking of using an 18 layer board of Nelco
> 4000-13, with the following stackup:
> Signal1
> GND
> Signal2
> Signal3
> PWR
> Signal4
> Signal5
> GND
> Signal6
> Signal7
> GND
> Signal8
> Signal9
> PWR
> Signal10
> Signal11
> GND
> Signal12
>
> The skinniest dielectric thickness is 4 mils, all signal layers are 0.5
Oz
> copper and plane layers are 1 Oz copper. The fastest signals are 100MHz,
> with rise times in 500ps range.
> My primary concern is the ratio of 6:12 of plane layers to signal
layers.
> I usually try to design for a ratio of about 8:10 or 9:9. I know I will
> have to be very careful about crosstalk on adjacent layers, but other
than
> that, what else should I be concerned about?
>
> Thanks
> Dave
>
>
>
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