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January 1999

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Subject:
From:
"Vascukynas, Brian" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 8 Jan 1999 16:03:56 -0500
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Hello,

We have been experiencing warping on certain PWB's from a specific
supplier.
I am curious on what the causes could be.

In each instance, the PWB design layout was checked and found to be
well balanced. Also our SMT Reflow Profiles were looked at for each PWB
and found
to be typical. The boards sometimes exhibit a slight warp right out of
the MFG
packaging and will warp out of spec on the first run.

1. We looked at dwell times, ramp up rate, actual temp, speed of PWB
going thru the
oven and all appears to be typical per each individual case. Is there
anything else we
could be checking for?

2. Is moisture absorption a concern - could it cause warping ?

3. Currently we do not bake PWB's prior to SMT Reflow - Is this
something we should
consider.

Thanks in advance.

Brian V.

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