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

Let me throw in my two cents.

 

I have been using Allegro for a long time and I found ways to use
negative planes efficiently without errors or unexpected results during
Gerber generation, most long time users on the forum will probably feel
the same way.  On older versions, positive shape generation was
available but was very painful so the lesser of two evils was to use
negative planes as much as possible and developed the padstack library
to take advantage of negative planes.  Old habits never die.

 

Dynamic positive planes are certainly more flexible and have their on
set of problems but it comes down to a personal preference on whether
Negative planes or Dynamic positive planes are used.

 

Personally, I still use Negative planes for my dedicated plane layers
and only switch to Dynamic positive planes when it is a combination
layer with planes and traces. One thing that I did recently adopt was
the use of Dynamic shapes for Negative plane layers to automatically
void for keepouts and vias / pins which are too close to a split.  In
changing to Dynamic shapes I did see a slight performance hit but it is
worth it to avoid the false DRCs generated on plane edges. 

Hope this helps,
Michael Catrambone
UTStarcom, Inc.

________________________________

From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of
gnieski_mike@xxxxxxx
Sent: Thursday, July 19, 2007 1:18 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Planes: Negative vs. Positive?

 

        Isnt the beauty of the positive planes the fact that you have
multiple choices of control not only at the parameter (local and

        global shape parameters) level, but at the pin/via level with
properties. For pins/vias you can control spoke width and direction,

        oversize on the gap clearances and whether you want a void per
drc, anti-pad or no void. 8 diiferent parameters for a pin.

 

        thanks,

        Mike Gnieski

 

 

________________________________

From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Austin Franklin
Sent: Thursday, July 19, 2007 2:06 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Planes: Negative vs. Positive?

Hi Gary,

 

No, I'm not kidding.  I wasn't aware that the two were determined by
entirely different criteria.  To me, that is not intuitive, and
certainly isn't the same with other tools I've used.  IMO, they both
should give the same results ultimately, or at least should be able to
be configured so that they do.  But, thanks for the explanation.  I use
positive planes now, I used negatives in the past, but in other tools I
used them in, they didn't DRC correctly.

 

Regards,

 

Austin

 

        -----Original Message-----
        From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of Macindoe, Gary
        Sent: Thursday, July 19, 2007 1:52 PM
        To: icu-pcb-forum@xxxxxxxxxxxxx
        Subject: [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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