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Date: | Fri, 9 Jan 2009 14:12:41 -0000 |
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Kevin,
The supplier is right to ask if you have stated you want the laminate at
class A tolerance. If you want your 10% for this particular material you
should specify class B or C. IPC 4101/B section 1.1.4, and table 3.7
regards
Dougal
-----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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