[SI-LIST] Re: Layer Stackup
- From: "Chris McGrath" <chris.mcgrath@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 7 Jan 2004 08:23:06 -0800
David,
Just out of curiosity, why are you going to Nelco 4000-13? From your
original post it doesn't sound like you are overly concerned about
routing lengths and you are not dealing with excessively high speed
signals.
Regarding Lee's post, I think it is good practice to have at least one
pair of power and ground planes next to each other but having worked on
a 42 layer board (Nelco 4000-13SI, 4 mils) that had interfaces running
between 125 MHz and up to 1 GHz and routing it completely in a dual
stripline stackup without any adjacent power and ground planes I think
that proper coupling of the planes can be achieved without forcing you
to muck with your proposed stackup. I should add that the 42 layer
board carried a range of voltages including 0.9V from a daughter board
(through connectors) and had no problems passing the EMI qualifications.
Nothing involved with that board was easy, but it showed that what you
are proposing can be done.
-Chris
> -----Original Message-----
> From: Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx]=20
> Sent: Wednesday, January 07, 2004 11:03 AM
> To: david.kaushansky@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Layer Stackup
>=20
>=20
> David,
>=20
> The problem you will have with this stackup is the lack of=20
> interplane capacitance between power and ground planes. This=20
> will manifest itself in several ways. Very high ripple on=20
> your power supplies when transmission lines switch, =20
> potentially very high EMI, unstable operation.
>=20
> It is imperative that you make sure that Vcc and ground=20
> planes are close to each other. If you have several=20
> different supply voltages, this will mean several pairs of=20
> power planes.
>=20
> If you really need that many signal layers, it will be=20
> necessary to add plane layers to get it right.
>=20
> Lee=20
>=20
>=20
> > [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=20
> try minimize=20
> > my
> > time in artwork, I would like to add as many routing layers=20
> as possible
> to=20
> > 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=20
> > 0.5
> Oz=20
> > copper and plane layers are 1 Oz copper. The fastest signals are=20
> > 100MHz,
> > with rise times in 500ps range.=20
> > My primary concern is the ratio of 6:12 of plane layers to signal
> layers.=20
> > I usually try to design for a ratio of about 8:10 or 9:9. I know I=20
> > will
> > have to be very careful about crosstalk on adjacent layers,=20
> but other
> than=20
> > that, what else should I be concerned about?
> >
> > Thanks
> > Dave
> >
> >
> >
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