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

MessageHi 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.

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