[SI-LIST] Re: PCB STACKUP
- From: steve weir <weirsp@xxxxxxxxxx>
- To: alexander.nosovitski@xxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Wed, 21 Jan 2004 14:10:27 -0800
Alexander,
The problem is that inside all of your mixed-signal IC's those 'analog' and
'digital' grounds are connected. The digital current that you think you
are isolating will flow through the analog ground pins due to coupling
between the AGND and GND planes. The only effective isolation geometry is
planar.
It is then possible to improve isolation with selective moating if you know
what you are doing. If not, moating can get you into trouble in a hurry,
and continuous planes of one ground is the safest way to go. That provides
the lowest impedance.
Steve
At 01:02 PM 1/21/2004 -0800, Nosovitski, Alexander (Contr) wrote:
>Hello si-list,
>
>
>The design I am working on has a dense placement.
>
>The proposed stack up looks as follow:
>
>TOP
>POWER_ANALOG
>DIFF_SIGNAL (Gb/s signals)
>AGND
>
>GND
>POWER
>S
>S
>GND
>POWER
>S
>S
>GND
>SPLIT_POWER
>GND
>S
>S
>POWER
>GND
>S
>S
>GND
>
>AGND
>DIFF_SIGNAL_ANALOG (Gb/s signals)
>POWER ANALOG
>
>BOTTOM
>
>
>
>All signal layers are 0.5 Oz copper and
>
>All planes are solid ( except one in the middle) with 0.5 Oz copper.
>
>The diff. signals are running at 2.5Gb/s.
>
>
>There are different opinions about analog plane location.
>
>Could the arrangement above cause a problem?
>
>What else should I be concern about?
>
>
>
>Any help or suggestion is appreciated!
>
>
>Regards,
>
>Alexander Nosovitski
>
>
>
>
>
>
>
>
>
>
>
>
>
>-----Original Message-----
>From: Salkow, Steven [mailto:steven.salkow@xxxxxxxx]
>Sent: Wednesday, January 21, 2004 1:57 PM
>To: weirsp@xxxxxxxxxx; fred@xxxxxxxxxxxxx; kar_thik_v1@xxxxxxxxx
>Cc: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Looking for thin dielectric tape
>
>
>4 mil prepreg (pcb laminate) is generally available from anyone doing
>multilayer PCB. You may also get samples from laminate vendors (dupont,
>Norplex) (sprayed with Scotch 444 adhesive for cold adhesion to copper
>foils)
>3M (tape division) have exactly what your looking for up to 36" wide
>slit to any width but they have minimum qtys
>
>see
>http://products3.3m.com/catalog/us/en001/utilities_telecom/oem_electrica
>l/node_R5MTBSFVGPbe/root_GST1T4S9TCgv/vroot_GSHBRQT7DVge/gvel_BBGZX3B1QG
>gl/theme_us_oemeletrical_3_0/command_AbcPageHandler/output_html
>
>Catalog on the above page for download
>
>Steve Salkow
>Lockheed Martin
>3200 Zanker Road
>San Jose, CA 95134
>(408) 473-4058 (san Jose)
>(408) 742-4162 (Sunnyvale)
>steven.salkow@xxxxxxxx
>salkow@xxxxxxxxxxxx
>(925) 462-1075 Home
>(925-) 487-5946 Cell
>(408) 468-7271 Numeric Pager
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of steve weir
>Sent: Tuesday, January 20, 2004 11:17 PM
>To: fred@xxxxxxxxxxxxx; kar_thik_v1@xxxxxxxxx
>Cc: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Looking for thin dielectric tape
>
>
>If you want to lay out a board, onesy, twosy, Express PCB is not a bad
>way
>to go. www.expresspcb.com It sure beats the Bishop Graphics adhesive
>backed Cu tape, or a bathroom full of ferric chloride.
>
>Steve.
>At 01:44 PM 1/20/2004 -0800, Fred Townsend wrote:
> >The last time I check you could still get mylar sheeting at most
> >drafting and staionary stores. You would to apply your own adhesive.
> >Comes in 4 and 7 mil thicknesses. You can also get polyester sheeting
> >frosted one side and adhesive on the other for making labels. Failing
> >that how about 3M's double sticky magic tape?
> >
> >Fred Townsend
> >
> >Karthik V wrote:
> >
> > >Hello,
> > >
> > > I am a student at the State University of New York. I am
> > looking for a double sided sticky dielectric tape (more like a sheet )
>of
> > thickness about 4mils (0.1mm) and with a dielectric constant of
> > around 4, to use between copper sheets - to make a "temporary board".
>I
> > tried things like epoxy, but it's almost impossible to get it so thin
>and
> > still provide infinite DC resistance.
> > >
> > > Could anyone point me to places where I could look for this
>
> > kind of stuff. Is there anything else I could try to get the
>dielectric
> > (with Dk around 4) so thin ( apart from elaborate processes ) .
> > >
> > >thanks in advance,
> > >Karthik,
> > >
> > >---------------------------------
> > >Do you Yahoo!?
> > >Yahoo! Hotjobs: Enter the "Signing Bonus" Sweepstakes
> > >
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