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May 2007

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Subject:
From:
John Burke <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, John Burke <[log in to unmask]>
Date:
Tue, 1 May 2007 15:34:46 -0700
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Why bother to use "near to" measurements for laminate I thought laminate
measurements were all in English anyway? Or was that when I was a lot
younger......8-)

 
 
John Burke
 
(408) 515 4992

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Tuesday, May 01, 2007 3:13 PM
To: [log in to unmask]
Subject: [TN] Laminate damage

We are writing an internal laminate damage standard, based on the 600
and the 610, but specifically dealing with only the types of material we
use and the class we build to, so it is easier to evaluate our products.
I know the IPC standards need to be a bit general or broad in their
descriptions because of the need to cover the whole industry, so we are
just clarifying the specific areas that apply for our workplace.  
This includes things like simplifying some of the dimensions.  2.5mm is
~ equal to 0.1", rather than stating 0.0984" (...you know someone would
spend 45 minutes trying to measure that...).  The 600 seems bad for that
- very literal dimension translations between units.  1.25mm has
[.04921in] after it.
My specific questions are regarding exposed fibres:
1. Exposed or disrupted fibres are acceptable according to the 600, if
conductor spacing is not reduced below minimum requirements.  However,
only unbroken exposed fibres are acceptable in the 610.  Why is there a
looser spec allowed at the bare board stage than at the assembled board
stage?  If a bare board was passed based on the 600, it would always
fail at assembly based on the 610.
2. Also, we have been told that exposed weave has a propensity for
drawing moisture into a board.  Just wondering, would this be any worse
for broken fibres than for unbroken?
3. Finally, we have been discussing:  why are disrupted and/or exposed
fibres such a danger, when you could consider the same condition
existing on every routed out or scored and cut board edge, or unplated
drill hole?

Thanks once again,
Genny


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