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

You're kidding, right Austin?

 

With negative planes, the clearance is determined by the padstack and
with positive planes, the clearance is determined by the shape
parameters (changeable on a shape by shape basis).

 

  

Gary E. MacIndoe
PCB Design Engineer
Fort Collins, Colorado

amd.com

gary.macindoe@xxxxxxx

________________________________

From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Austin Franklin
Sent: Thursday, July 19, 2007 11:20 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Planes: Negative vs. Positive?

 

Hi George,

 

Why would the openings around pins be any different between positive and
negative planes?

 

Regards,

 

Austin

        -----Original Message-----
        From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of
george.h.patrick@xxxxxxxxxxxxxx
        Sent: Thursday, July 19, 2007 12:58 PM
        To: icu-pcb-forum@xxxxxxxxxxxxx
        Subject: [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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