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August 2008

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Wed, 20 Aug 2008 10:59:54 -0500
Content-Type:
text/plain
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text/plain (64 lines)
Polyimide flex has a great water retention capability. Storage over an
extended period of time could well reduce the overall dimensions.
Polyester and pen flex also have this propensity, but I believe it is
greatest with polyimide.   

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Anselmo
Sent: Wednesday, August 20, 2008 10:38 AM
To: [log in to unmask]
Subject: [TN] Flex Material Movement at Assembly

Hi All,

A couple of questions concerning flex panel movement at assembly.

We were assembling some 2 layer flex parts with a stiffener and noticed
some movement (or mis-alignment) of the stencil on the 2nd side.
After the 1st side was completed, the panels were stored in a McDry
cabinet for 5 weeks before we finished the lot.
When we finally did finish the 2nd side, we saw a progressively larger
mis-alignment as you went across the panel (from left to right).
The mis-alignment was 5 to 7 mils on a 13 mil wide rectangle pad.  These
parts are 10 up in a 7" x 8" panel (2 rows of 5). 

So, my questions are; is this type of movement typical?  Did storing
these in the McDry add to the problem?
They were stored on end, not lying flat.  Should they have been stored
flat?
Is there a way to reverse the material movement?  Or do we need to
complete the whole lot and not store any in the McDry?
What is the time limit (and conditions) for storing panels that haven't
been completed?

We washed a few panels then baked at low temp (50 deg C) for 15 minutes,
and this helped a little.  Just need to know if anyone else has
experienced this before.

Thanks,

John 

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