All About Parylene Coating Process

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All About Parylene Coating Process
The parylene coating process takes place at room
temperature so that there is no thermal stress on
the product. The same is physically stable and an
inert product within the temperature range. It
also provides a friction coefficient of 0.25-0.30
along with excellent protection from salt spray,
moisture, corrosive elements, etc. existing in
the work environment. The polymers are deposited
from the vapor phase where all sides of the
object are encapsulated to achieve a uniform
coated surface. This helps to deliver a truly
conformal coating.
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 The Parylene Coating Process Includes Three
Stages - Sublimation at vacuum at 120 C. This is
done by using the stable crystalline dimer
di-p-xylylene that delivers vapors of the
material in question. Pyrolysis phase that has
vapors at 650 C to form a reactive monomer of
p-xylylene. This is succeeded by the deposition
and polymerization of p-xylylene to attain
Parylene. The process also requires proper
cleaning, activation, and masking of the product
before placing it inside the deposition chamber.
Such product remains at room temperature during
the entire process. Dimer di-p-xylylene is placed
in a glass tube at the opposite end of the
deposition chamber in an aluminum cup called a
boat. The thickness of the coating is determined
by the actual volume of the dimer placed in the
boat.
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Once the process initiates, the end cap is placed
on the tube, and the vaporizer radiant heater
cycles using a pressure safety interlock to
ensure a safe operational limit. Slowly, the
dimer takes a vapor state and the molecules
travel down the tube using reduced pressure at
the opposite end. The dimer then moves into the
pyrolysis zone where the high temperature cleaves
the dimer into radical monomers. When these
molecules enter the deposition chamber, they form
a long chain polymer on the surfaces of the
chamber. A cold trap is utilized between the
deposition chamber and vacuum pump as it prevents
the parylene molecules that have not been
deposited on the product from getting into the
vacuum pump. This prevents oil molecules from
back streaming into the chamber. However, the
complete process takes place minus a catalyst or
solvent.
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