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Subject: FAB: MOISTURE CONTENT INNER LAYERS
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Subject: FAB: Moisture content Inner Layers
An inner layer engineer would like to ask technetters the
following:
1) Has anyone determined the % moisture content in inner layers, presumably
after oxide, that relates to potential delamination problems after
lamination?
2) How is this moisture content measured and/or monitored?
3) What resin types (ie multifunctional, polyimide etc) are applicable?
>>>>>>>>>>Dave, we have not baked FR4 inner layers after oxide (and
reduction) for at least 8 years, if not longer, and do not have a
delamination problem. We did try some experimental work on BT epoxy
without baking, and found in this case that it did make a (big) difference.
The problem with baking of reduced oxide layers, is to bake long enough
to remove moisture, but at a time/temperature that does not reoxidise the
copper.
Dougal Stewart
Exacta Circuits
Scotland
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======== Fwd by: Tony King / N ========
We do still bake after oxide/reduction prior to lamination, and hold inner
layers in a desiccater cabinet until laminated. I believe there are more
variables than just baking which determine if product will delaminate. Many
companies use vacuum lamination, many do not. Vacuum draw-down ? Moisture
can cause problems other than delamination, under cure for example. We did
perform weight loss tests to determine moisture loss with bake vs. vacuum
draw down and found that vacuum alone did not remove the moisture, baking
did remove the major percentage. Better to take control of the product
quality by insuring moisture removal than to roll the dice and wait for a
problem. Many of the people performing the assembly operation bake the
product prior, to insure moisture removal and therefore minimize the risk of
delamination caused by moisture. The first response from every board
fabricator referencing delamination at assembly is to bake the boards, and
in most cases this does eliminate the problem.
If there are any quick solutions to allow elimination of bake prior to
lamination without risk, I would like to know about it, the reduction of 1
or 2 hours of cycle time would be huge.
Tony King
Elexsys International Inc.
Nashua N.H.
Phone:603-886-0066 Fax:603-886-9724
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