Circuit Boards
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 Parylene was developed over thirty
years ago primarily to provide a conformal coating for printed
circuit boards. It provided benefits which made parylene unique
compared to other dip, spray or brushed liquid conventional
conformal coatings.
Parylene is the commercial name of the ply-para-xylylene polymeric
family. It is applied by vapor depositionunder a vacuum in
a room temperature coating chamber. The coating process exposes
objects to the gas-phase monomer (see
process) at low pressure. Through vacuum deposition, parylene
condenses and polymerizes on the object’s surface in
a polycrystalline fashion, providing a coating that is truly
conformal and pin-hole free. Compared to liquid processes,
the effects of gravity and surface tension are negligible,so
there is no bridging, thin-out, pinholes, puddling, run-off
or sagging. And with the process taking place at room temperature,
there’s no thermal or mechanical stress on the object.
Parylene films ranging from 0.25 to 1.5 mils in thickness
provide a barrier which is equivalent or superior to 2 to
6 mils of other conventional coatings. Parylene does not pull
away from edges or exhibit meniscus forces as do conventional
liquid coatings applied by spraying, dipping or brushing.
Because parylene is in a molecular state and builds from the
surface up, board components are coated evenly and consistently,
thus electrical protection can be achieved with a thinner
layer than that of the conventional coatings. The dielectric
constant and dissipation factor are practically insensitive
to changes in frequency.
Given its resistance to humidity, barrier properties, physical
and thermal properties and its unique molecular structure,
parylene is practically insoluble in all known organic and
inorganic solvents including strong acids and alkali. Parylene
proves to be an effective barrier to corrosive agents and
does not out-gas. With parylene meeting mil spec 46058C criteria,
it is an excellent choice when it comes to conformally coating
printed circuit boards for military and aerospace applications.
When looking at the total cost of protecting your parts in
a hazardous or contaminated environment, parylene is typically
the least expensive option for coating electronics.
See Technical Information for details.
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