It is possible that the conformal coating you want to use is not compatible
with the particular solder mask on the boards you have. To check for this,
may ZI suggest:

1. Take a small section of a board and clean it thoroughly with an alkaline
cleaner (Joy dishwasher miracle can work), rinse, clean with isopropyl
alchohol, rinse and dry thoroughly.

2. Dip the cleaned board sample in the conformal coating to be tested and
dry/cure according to the manufacturers spec sheet.

3. Look for a smooth, continuous coating of the conformal coating over the
entire surface of the sample board and conduct a cross hatch adhesion test,
For this, take a razor blade, cut 6 parrallel lines about 1/8" apart, cut 6
more parallel lines (perpendicular to the 1st 6 lines) about 1/8" apart and
then apply a strip of 1" Scotch transparent tape to the grid pattern you have
made. Pull the tape up sharply and look for any lifting of the conformal
coating.

4. If everything looks okay, you can say that the conformal coating is
compatible with the solder mask. If there is adhesion loss, then the
conformal coating is not compatible and either the conformal coating or the
solder mask must be changed.

Since most conformal coating manufacturers offer many different types
(acrylics, epoxies, urethanes, silicones, etc.) of conformal coatings and
different formulas in each type range, I.m sure that if you contact the
specific conformal coating manufacturer, they would be able to give you the
right direction to go.

Hope this information helps.

Larry Fisher
Dexter Electronic Materials
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