[PCB_FORUM] Re: Planes: Negative vs. Positive?

As Ed stated there are many ways to control the anti pad.
I use positive planes because they show split plane DRC's where negative
planes
don't.
   We have boards up to 80 Gig, so controlling the antipad is critical.
We can do it all with
positive planes and padstack definitions..  File size is irrelevant
these days.  ( yes we sometimes have very large boards with many
planes.).
 

Jerry 

 

________________________________

From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Ed Caldwell
Sent: Thursday, July 19, 2007 1:07 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Cc: icu-pcb-forum@xxxxxxxxxxxxx; icu-pcb-forum-bounce@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Planes: Negative vs. Positive?



Hi George, 

I may have misunderstood your statement... but doesn't the opening from
pin to positive plane follow the DRC settings (or exception clearances)?
And doesn't the opening in a negative plane ignore the DRC settings and
simply follow the anti-pad? 

Respectfully! 
Ed 

Ed Caldwell
PCB Designer
USA 678-473-8707
mailto:ed.caldwell@xxxxxxxxxx
EDS http://www.eds-pcb.com




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[PCB_FORUM] Re: Planes: Negative vs. Positive?

        




  
Positive plane layers have a much larger opening around pins.  This is
fine if you are doing low to medium speed boards (roughly < 200 MHz
clock speed), but on high-speed designs the impedance discontinuities
created by the huge opening around the pins are significantly greater on
a positive plane than on a negative plane. 
  
We use negative planes for this reason, and we always use Valor to check
our artworks to make sure we haven't shot ourselves in the foot :) 
  
YMMV 
  
-- 
George Patrick
Tektronix, Inc.
Central Engineering, EDS Applications Support 
P.O. Box 500, M/S 39-512
Beaverton, OR 97077-0001
* 503-627-5272 (voice)     * 503-627-5587 (fax)
http://www.tektronix.com <http://www.tektronix.com/>
http://www.pcb-designer.com <http://www.pcb-designer.com/>  
  
"Off-Grid and Proud of it!" 
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Bob McCreight
Sent: Thursday, July 19, 2007 06:51
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Planes: Negative vs. Positive?

The design team I work with is split one which to use, negative or
positive planes.
What are the pros and cons of each? What do most people prefer to  work
with?
We are currently using 15.5.1 but evaluating 16.x for possible future
migration.
  
 Thanks for your feedback.
  
 Bob McCreight, C.I.D.

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