impedance control specsBrandon..

    I have always giving the finished board thickness requirement, minimum
   finished copper width, copper weight and the layers that require impedance.  
  I would do a rough lay-up to determine if it "seems realistic"  and then let my 
  drawing reflect any other end product requirements.  Don't try to be a pwb 
  fabricator- they know their fab. processes better then you and they all differ 
  slightly.  Hope this helps. P.S. Talk to you fabricators also.  Hope this helps.

  Bob Vanech
  BVAN Enterprise, LLC.   
  ----- Original Message ----- 
  From: Luther, Brandon 
  To: [log in to unmask] 
  Sent: Monday, April 16, 2001 1:47 PM
  Subject: [DC] impedance control specs


  Good Day!

    We are having a raging debate about specifying controlled impedance on our fabrication drawings.

    The main part of the debate is over laminate thickness specifications.  I would like to know how other companies are handling these issues.  

          Are you specifying the individual laminate thickness?

          Are you specifying the individual laminate thickness tolerance?   If so, how do you handle deviations between different fab houses beyond the tolerance?

  It seems that every time we use a different fab house, they like to use their standard laminates.  While this is also a benefit to us, it causes problems when our boards are microsectioned and the board doesn't agree with the print.  

  We will continue to specify trace width, copper thickness and impedance, all with tolerances.

  Any input will be appreciated!

          Brandon Luther 

          Dataram Corp.

  (609) 799-007  x2310