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

MessageHi Gary,

No problem.  Long time PADS, shorter time Allegro user (about four years?).
Long time ago...long time SciCards user.  Long time high speed digital
designer.

Am I right that positive planes can also have a larger, same or even smaller
opening than negative planes, depending on how you set it up?

This is great info, at least for me, thanks!  Sometimes the subtleties of
things like this across different tools escape me until I bump my head.

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 3:00 PM
  To: icu-pcb-forum@xxxxxxxxxxxxx
  Subject: [PCB_FORUM] Re: Planes: Negative vs. Positive?


  Hey Austin,



  Sorry, I guess I got the impression that you were also a long time Allegro
user.



  George mistakenly said "Positive plane layers have a much larger opening
around pins."



  With positive planes, when the shape is created, all clearances, thermal
ties and more is determined by your setup in the Global Dynamic Shape
Parameters form.  After the shape is created, you can change all of this for
each shape separately with the shapes individual Dynamic Shape Instance
Parameters form.



  Starting to make sense yet?



  Gary







  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 12:15 PM
  To: icu-pcb-forum@xxxxxxxxxxxxx
  Subject: [PCB_FORUM] Re: Planes: Negative vs. Positive?



  Hi Gary,



  I understand why they *could* be different, but...given your explanation,
and more to my confusion, your explanation doesn't say why positive planes
would *always* (which is what was said) have a larger opening.  They could
be configured to be smaller couldn't they?  It's all in how you set it up?



  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
      A 503-627-5272 (voice)     A 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.

GIF image

Other related posts: