Parylene
conformal
coatings
are
applied
at
surrounding
temperatures
with
specialized
vacuum
deposition
equipment.
Parylene
polymer
deposition
takes
place at
the
molecular
level,
where
films
essentially
‘grow’ a
molecule
at a
time on
the
surface
being
coated
(See
Figure
1).
A solid,
granular
raw
material,
called
dimer,
is
heated
under
vacuum
and
vaporized
into a
dimeric
gas. The
gas is
then
pyrolyzed
to
cleave
the
dimer to
its
monomeric
form
which is
a
molecule
of low
molecular
weight
capable
of
reacting
with
identical
or
different
molecules
of low
molecular
weight
to form
a
polymer.
In the
ambient
temperature
deposition
chamber,
the
monomer
gas
deposits
on all
surfaces
as a
thin,
transparent
polymer
film.
Because
Parylene
conformal
coating
is
applied
as a
gas, the
coating
penetrates
any
crevices
and
tight
areas on
multi-layer
components,
providing
complete
and
uniform
encapsulation
(See
Figure
2).
Optimal
thickness
of the
polymer
coatings
is
determined
based on
the
application
and the
coating
properties
desired.
While
Parylene
coatings
can
range in
thickness
from
hundreds
of
angstroms
to
several
mils, a
typical
thickness
is in
the
microns
range.
Substrate
Material:
Optimal
adhesion
of
Parylene
conformal
coating
to a
wide
variety
of
substrates
which
are
materials
which
provide
the
surface
on which
something
is
deposited
or
inscribed,
for
example
the
silicon
wafer
used to
manufacture
integrated
circuits.
Substrate
Preparation:
One of
the
defining
characteristics
of
Parylene
conformal
coating
is its
ability
to coat
all
surfaces,
including
deep
into
multi-layers
and
crevices.
All
surfaces
in the
deposition
chamber
are
coated
with
Parylene,
unless
technicians
carefully
protect,
or mask,
any
areas
that are
not to
be
coated.
MORE
INFORMATION
HERE ON
VAPOR
DEPOSTIED
CONFORMAL
COATING
FOLLOW
THIS
LINK:
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
|
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.
Figure
2
|