Mr. Ross, 

I don't have any data on the surface tension requirements for optimal
comformal coating compatibility.  For this, I would suggest that you
contact Conap, Humiseal, Dow Corning or another conformal coating
manufacturer.

We have found that the method of application has a big impact on the
compatibility of the conformal coating and the solder mask.  A coating
that properly wets a surface when it is applied by dipping may exhibit
dewetting when it is thinned and sprayed.  The altered surface tension
of the solvent/coating mix is probably a key factor.

In addition, the mask cure conditions, the soldering conditions, the flux 
(and its residues) and the post clean process may affect the conformal
coating compatibility.  

Sorry I can't be of more help.

Regards,

Curt Lustig
Associate Scientist
Solder Mask R&D Group
Morton Electronic Materials
(714) 730-4511

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