Deposition Process - Parylene
The
parylene
polymers
are
deposited
from
the
vapor
phase
by a
process
which
in
some
respects
resembles
vacuum
metalizing.
Unlike
vacuum
metalization,
however,
which
is
conducted
at
pressures
of
10-5
torr
or
below,
the
parylenes
are
formed
at
around
0.1
torr.
Under
these
conditions
the
mean
free
path
of
the
gas
molecules
in
the
deposition
chamber
is
in
the
order
of
0.1
cm.
Therefore,
unlike
vacuum
metalizing,
the
deposition
is
not
line-of-sight
and
all
sides
of
an
object
to
be
encapsulated
are
uniformly
impinged
by
the
gaseous
monomer.
This
is
responsible
for
the
truly
conformal
nature
of
the
coating.
The
process
consists
of
three
distinct
steps
as
shown
in
Figure
1.
Figure
1
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Since
parylene
is
non-liquid,
it
does
not
pool,
bridge,
or
exhibit
meniscus
properties
during
application.
No
catalysts
or
solvents
are
involved,
and
no
foreign
substances
are
introduced
that
could
contaminate
coated
specimens.
In
contrast
to
parylene,
the
thickness
of
liquid
coatings
is
related
to
viscosity,
working
temperature/humidity,
and
application
process
(spray
or
dip),
and
can
only
be
controlled
to a
tolerance
of
approximately
+/-
50%
of
final
thickness.
Parylene
thickness
is a
function
of
the
amount
of
vaporized
dimer
and
chamber
dwell
time
and
can
be
controlled
accurately
to
within
+/-
5%
of
targeted
thickness
for
most
typical
applications.
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