Is conformal coating a good protection against dendrites?  I read that
ionic contamination can cause dendrites, if a board has ionic
contamination,
will conformal coating prevent dendrites?

*In a word, NO, and I can't stress that enough.  To get dendrites, you need
three things:  electrical potential (voltage), moisture, and an ionic
contaminant.  All conformal coatings are water permeable to a certain
degree, some are better than others in this respect.  You can count on
moisture going through the coating, combining with the ionic residues to
form electrolytes.  Then dendrites can grow.

I had a number of situations in a former life where a client would be told
he had ionically dirty boards.  They did not want to go to the hassle of
cleaning the assemblies and decided to coat over the boards "so that the
environment can't get to the contaminant".  We told them that it would not
work, for the reasons above.  But to no avail.  9-12 months later they came
back "It didn't work".  At best, it only bought them a little time.

Doug Pauls
Rockwell Collins

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