Hi Bill,

I'd take a very close look at the adhesive you're using under your SMT
devices.  You may be having some out-gas or other reactive products getting
trapped under your coating and causing your problems.  Make sure the
adhesive is fully cured before you seal it under the conformal coating.
You might want to try a different adhesive or a board without adhesive and
see if it plays.  Make sure your adhesive is compatible with your application.

BTW, meals in your conformal coat indicate the coating is not bonding well
to your boards.  You may need to look at your coating process (cleanliness,
dryness).  Mealing doesn't necessarily mean you'll have a reliability
problem, unless of course the mealing is due to a contaiminant under the
coating.

-Gregg
[log in to unmask]

At 03:13 PM 11/3/97 -0500, BROMLEY, Bill wrote:
>Fellow technetters:
>
>        I would appreciate any help in the following subject....
>
...
>the temperature range. Uncoated assemblies will pass the temperature
>cycle test. It is suspected that small bubbles in the conformal coating
>(within allowable size per specification criteria) are accumulating
>condensation during temperature transitions, causing bridging between
>conductive surfaces on the SMT components. The surface mount components
>that we are using are attached to the board with a small dab of adhesive
>in the middle of the component.  Then, after the components are wave
...

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