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

MessageHi 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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