[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
Å 503-627-5272 (voice)     Æ 503-627-5587 (fax)
http://www.tektronix.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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