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October 2012

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From:
Robert Kondner <[log in to unmask]>
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Date:
Mon, 8 Oct 2012 14:12:53 -0400
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Phil,

  I did a little looking around on the web about diffusion rates and plastic
bags. I did not find much but when I saw a demo of how fast iodine defused
through a plastic bag I figured I would stop looking. 

 Next chance I get I will place a moisture indicator in a plastic bag and
see what happens.

 A very important issue is the bag. There appears to be very specialized
metal coatings used in potato chip bags which are also back filled with
nitrogen. Folks expect potato chips to remain crunch in a bag over a long
period. 

The saving grace is that diffusion rates are very much related to
temperature. And what "Seeps In" over 2 years on a shelf can quickly be
baked out. The exception is a laminate coated with copper on both sides.
That is almost a hermetic seal and I wonder how much moisture is "Built In"
during board fabrication.

 Now take all this with a grain of hogwash because I cannot site any exact
experimental evidence. 

Bob K.



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Monday, October 08, 2012 1:45 PM
To: [log in to unmask]
Subject: [TN] board baking - thread continuation

Ok, you folks have been very helpful so far.  Now I need to pump you for a
little more information, but let me set the stage a little.

We typically build boards in small batches (25 to 50 boards at a time) but
we may buy bare boards in a larger quantity.  Historically we would slice
(or rip) open the sealed board package and remove the number needed for the
kit.  The remainder would sit in the parts bin in the stockroom with no
special handling.  Being in New England, summertime can get pretty humid.  I
maintain that we should seal the boards for the kit (build here or ship to a
CM) and the leftover boards in a bag or pouch with a desiccant.  I did order
IPC-1601 back in August, but it hasn't made it up to my office yet.

To properly store the boards is there a preferred plastic bag and desiccant
I should use?  I'm going to assume your basic grocery store "Zip-lock" type
bag is NOT the product to use.  I would think there are bags and desiccant
that are specifically for this application.

Thanks in advance,

Phil Nutting
Design for Manufacturing Engineer
Kaiser Systems, Inc.
126 Sohier Road
Beverly, MA 01915
Phone: 978-922-9300 x1310
Fax: 978-922-8374
e-mail: [log in to unmask]<mailto:[log in to unmask]>
www.kaisersystems.com<http://www.kaisersystems.com>
www.linkedin.com/in/philnutting<http://www.linkedin.com/in/philnutting>


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