The biggest problem is when high speed lines cross the split in the planes.
 The return currents follow directly under the traces, and if there is a
split in the plane, the currents have to flow around the split causing
emissions problems.  There is no real problem splitting the plane if high
speed lines do not cross that barrier.

Dave.

At 10:13 AM 7/21/98 -0700, you wrote:
>At the expense of sounding ignorant, what are the problems caused by
>splitting gnd planes?  I have to do this constantly, mainly under
>opto-isolators, to seperate the part of the board that is our product from
>the outside world.  I hope you can get some online answers so that everyone
>has a chance to check the data.  Thanks.
>Richard
>
> ----------
>From: dschaefer
>To: DesignerCouncil
>Subject: [DC] !!! SPLIT GROUND PLANES !!!
>Date: Tuesday, July 21, 1998 8:25AM
>
>I'm looking for information regarding SPLIT GROUND PLANES.
>
>Experts on grounding, EMI, EMC are teaching that gaps in ground planes
>create serious problems.  Component manufacturers, however, continue to
>recommend placing gaps under components (such as A/D's and D/A's).
>
>Can anyone:
>
> - point me in the direction of theoretical reference material
> - relate their experiences / practices
>
>Thanks,
> --
>Dave Schaefer                                                      Phone
>: (204)631-2298
>Senior PWB Designer                                         FAX :
>(204)631-2475
>NORTEL - Broadband Wireless Access          email : [log in to unmask]
>37 Stevenson Road
>Winnipeg, MB R3H 0H9
>
>################################################################
>DesignerCouncil E-Mail Forum provided as a free service by IPC using
>LISTSERV
>1.8c
>################################################################
>To subscribe/unsubscribe, send a message to [log in to unmask] with following
>text in the body:
>To subscribe:   SUBSCRIBE DesignerCouncil <your full name>
>To unsubscribe:   SIGNOFF DesignerCouncil
>################################################################
>Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section
>for additional information.
>For technical support contact Hugo Scaramuzza at [log in to unmask] or
>847-509-9700 ext.312
>################################################################
>
>################################################################
>DesignerCouncil E-Mail Forum provided as a free service by IPC using
LISTSERV 1.8c
>################################################################
>To subscribe/unsubscribe, send a message to [log in to unmask] with
following text in the body:
>To subscribe:   SUBSCRIBE DesignerCouncil <your full name>
>To unsubscribe:   SIGNOFF DesignerCouncil
>################################################################
>Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
section for additional information.
>For technical support contact Hugo Scaramuzza at [log in to unmask] or
847-509-9700 ext.312
>################################################################
>
>
>
____________________________________

   PCB Designs by Baldwin Tech.
(602) 539-4400  FAX (602) 539-4500
   http://www.neta.com/~btech
____________________________________

################################################################
DesignerCouncil E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE DesignerCouncil <your full name>
To unsubscribe:   SIGNOFF DesignerCouncil 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################