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April 1998

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Mon, 13 Apr 1998 08:05:12 -0700
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I would bet that the coating is being cured at too high of a temperature
which causes the surface of the coating to skin over and trap the volatiles
inside of the conformal coating.

Brian Stumm
ETS, LLC
Manufacturer of the Nordson Select Coat Cure ovens


>I don't have the IPC document in front of me either, but I believe a good case
>could be argued that the coating does not meet class 3 requirements due to the
>necessarily diminished film thickness due to the bubbles, depending on the
>amount present. I would like to add that bubbles are usually symptomatic of
>improper reduction of the coating. Bubbles are generated whenever a coating is
>sprayed on with traditional air-spray, air-assisted airless or HVLP spray.
>They disappear unless: (1) the coating is too thick to let the bubbles rise to
>the surface and pop prior to the coating hardening, (2) the reducer or thinner
>used is evaporating too quickly to allow the bubbles to escape (even if it's
>thin enough), or (3) heat is being applied prior to the solvent's escape from
>the coating (insufficient flash time).
>I agree that baking prior to coating is a good precaution, and with acrylic
>coatings, it can be beneficial to coat boards while still warm. The trick is
>to use a sufficiently slowly evaporating solvent.
>
>Mike Moninger
>Thermospray Company, Inc.
>www.thermospray.com
>
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