Susan,

As to applying thick unfilled (20 mil) acrylic, epoxies, urethanes etc.
coatings that may have a high CTE and may become very rigid when subjected to
cold temperature, not only do the solder joints crack, so do some of the
components .  Some of the silicones are more forgiving, but some of them can
cause problems also as they shrink/expand differently that the board or
components.  Encapsulating the board in heavy coatings, in my experience has
led to early failure when assemblies are subjected wide thermal changes.
Most of the office environment equipment is not harmed by using heavier
coatings, but again there is no need to do so unless you live in some of the
more humid climes.  I have found failures cause by some coatings when a faily
benign environment of -30 to + 80'C was used.

Phil Hinton

    .

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