[SI-LIST] Re: How to connect to GND planes


Johnni,

I think that you can get away with using the vias necessary at your
components.  You will need some ground vias there that will keep the two
planes at the same DC potential.  

If your traces change layers from referencing one ground plane to the next,
you may need to provide a return current path (ground via) near the layer
transition.

Out of curiosity, I notice that layers 3 and 4 are closer to each other than
the adjacent reference planes.  Is this done on purpose?  If not, I might
recommend changing your core and prepreg thicknesses such that each routing
layer is closer to a plane than another routing layer.

Hope this helps,
James R. Jones
Dell



-----Original Message-----
From: johnni.friis@xxxxxxxxx [mailto:johnni.friis@xxxxxxxxx]
Sent: Tuesday, October 29, 2002 3:44 AM
To: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx
Subject: [SI-LIST] How to connect to GND planes




Hi

I have a 6 layer stackup with 2 GND planes, how do I connect the 2 GND
planes together ?
E.g. what distance should I use between vias ? What  is the best patter=
n to
use ?

I have a MCU running at 100 MHz (C8051F126 until C8051F122 is relased, =
from
cygnal),  a K6R1008V1D (10 ns RAM), and a GAL16LV8-5 (5 ns PLD). And a =
lol
of slower devices.
I don't know the edge rates. I  don't have a simulator.
Address- and controlsignals are source terminated, datasignals are plan=
ed
to be routed as lumped elements. (Tr > 0,5 ns -->>  flightlength =3D 2.=
75
inch, a faktor of 4, gives a max treaclength of 690 mills).


Stackup:

Layer1: Components / routing
5.1 mill preprik
Layer2: GND plane
20 mill FR4 core
Layer3: routing
5.1 mill preprik
Layer4: routing
20 mill FR4 core
Layer5: GND plane
5.1 mill preprik
Layer6: 3V plane


Yours sincerely,

Johnni Friis


VELUX A/S
Accessories

B=E6kg=E5rdsvej 40
6900 Skjern


Telephone Direct:   +45 9980 6326
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e-Mail:                   johnni.friis@xxxxxxxxx
WWW:                   http://www.VELUX.com

=


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