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Subject:	Re: [pcdlist] RE: controlled impedance
From:	"McGlaughlin, Jeffrey A" <[log in to unmask]>
Reply To:	DesignerCouncil E-Mail Forum.
Date:	Wed, 27 Jun 2001 07:29:36 -0400
Content-Type:	text/plain
Parts/Attachments:	text/plain (57 lines)

Louis -

  1% tolerances will be difficult if not impossible to hold on a PCB. A
variance of less than 1/2 mil in any of the primary variables, trace width,
dielectric spacing, or trace thickness will be enough to put your impedance
out of tolerance. A variation of 0.2 in dielectric constant will also put
you out of tolerance.  I have done designs at 5%, and 10% but never 1%.  Is
this tolerance really necessary?


Jeffrey A. McGlaughlin, C.I.D.
Sr. PCB Designer
Battelle Memorial Institute
Columbus Ohio
[log in to unmask]



-----Original Message-----
From: Louis T Dallara [mailto:[log in to unmask]]
Sent: Wednesday, June 27, 2001 6:27 AM
To: [log in to unmask]
Subject: Re: [DC] [pcdlist] RE: controlled impedance


Do any one know what the type tolerance is for a controlled impedance board?
+/- 1% of a 100 ohm trace??
TIA
Lou Dallara
Infincon Systems

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