I think that's standard double sided rigid thickness tolerance for .040"
material

Regards
Ian Fox
Lead Materials and Process Engineer
Aero Engine Controls
A Rolls-Royce plc and Goodrich Corporation Joint Venture
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden
Sent: 09 January 2009 13:42
To: [log in to unmask]
Subject: [TN] PCB thickness tolerance question...Am I losing it?

We have a small PCB that is less than 2" x 2" square.  Material is
IPC-4101/21 FR4 with 2 oz copper.  2 layers.  Finish is Tin-Lead HASL.
 
Total thickness is specified as .040" +/- .005", and the supplier is
requesting increase to .040" +/- .006".  Is it me, or is +/- .006"
excessive for a 2 layer .040" thick PCB?  I was always taught a "rule of
thumb" that the PCB thickness tolerance is +/- 10% of the specified
nominal thickness.
Is this a bad "rule of thumb"?  Even +/- .005" is 12.5%!  Is this a sign
of a problem with the supplier's process?
 
Thanks!
 
Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.

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Registered Office: Moor Lane, PO Box 31, Derby, DE24 8BJ.
Registered in England No. 06686268.
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