Uniform thickness
and true
conformality
- the established
process guarantees
precise control of
thickness and
inherent uniformity,
especially critical
in microelectronics
applications; no
bridging, thin-outs,
puddlings, run-offs
which are common
problem with other
coating materials.
Since it is based on
a gas, Parylene can
penetrate spaces
which typical
conventional
coatings can not
cover: small
recesses, crevices
and holes and even
the edges and the
inside spaces of
very fine tubes.
Pin-hole Free
- tough coatings as
thin as 0.1 microns
can be achieved
without any voids.
Chemical, fungus and
bacteria resistance. Parylene resists
attack from exposure
to most acids, bases
and solvents. It is
an excellent
inhibitor to the
growth of fungus and
bacteria.
Superior barrier
properties
- Parylene provides
exceptional
corrosion protection
from moisture, salt
spray, corrosive
vapors and other
hostile
environments. Its
water vapor
transmission rate
has been found to be
significantly lower
than most
conventional
coatings. With
respect to migrating
ionic species,
Parylene coatings
have been proven to
act as barrier to
extractable metals
which otherwise will
contaminate
substrates.
Impressive
mechanical strength
- since it has high
tensile and yield
strength, Parylene
conformal coating
is used for
encapsulating
microcircuits
because it increases
the pull strength of
wire and lead bonds,
face bonded chips
and conductor
bridges and
therefore
contributes
significantly to
device integrity.
Since its specific
gravity is low, the
Parylene layers are
typically lighter
than most other
functional coatings.
High dielectric
characteristics
- its extremely high
dielectric strength
combined with its
electrical stability
in various media
provide unique
insulating property.
The dielectric
constant and
dielectric losses
are low and
unaffected by
absorption of water
vapors. Its volume
and surface
resistivities are
advantageously high
because of the
purity, low affinity
to moisture and in
particular its
freedom from trace
ionic impurities
present in
conventional
coatings.
Thermal stability
- Parylene
coatings remain
stable at continuous
temperatures as high
as 130 deg.C in air,
or 220 deg.C in the
absence of oxygen.
It has good
mechanical
properties from -200
to 275 C.
Stress-free
- since the
polymerization of
the film takes place
on the substrate
surface at room
temperature, there
is no thermal or
mechanical stress
introduced during
application, hence
original performance
parameters of coated
subjects are
basically
unaffected.
Particle
immobilization
- assures circuit
integrity,
preventing mobility
of loose solder,
wire particles or
other mobile debris
left from
manufacture. Pressed
powder parts,
ferrites, ceramics,
corrosive metals,
glass and epoxy
particulates can be
positively
stabilized.
Dry film lubricant
-inherent excellent
dry lubricity, as
indicated by
coefficient of
friction
measurements make
Parylene a valuable
asset as a dry film
lubricant,
particularly as a
coating for surgical
instruments.
Compared to
fluoropolymers,
Parylene conformal
coating has also
the
ability to provide
wear and abrasion
resistance.
Sterilization
- due to their
thermal and chemical
resistance, Parylene
coatings can survive
the conditions of
many common
sterilization
techniques (e.g.
autoclave,
radiation, ethylene
oxide).
Film Description
Thin, transparent
Parylene film is
unique in that it is
applied to
substrates in an
evacuated chamber by
a process called
gas-phase
polymerization. The
dry, powdered raw
material, or dimer
which is a compound of two
identical monomers
is converted by
heat to a dimeric
gas and ultimately
to a monomeric gas,
after which it is
deposited on
substrates at room
temperature. The
coating grows as a
uniform, conformal
film
(poly-para-xylylene)
on all exposed
surfaces including
edges and in
crevices. Parylene
deposition has no
liquid phase or
gaseous byproducts
and no solvents or
environmentally
restricted materials
are required.
There are four
primary variants of
the polymer:
Parylenes N, C, D
and HT. Each has its
own molecular form
that results in
unique
characteristics. The
optimum selection of
a Parylene variant
depends on the exact
nature of the
intended
application. Other
qualities:
-
Parylene film
has useful
dielectric and
barrier
properties, as
well as extreme
chemical
inertness and
freedom from the
pinholes typical
of liquid
coatings. It
resists organic
solvents,
inorganic
reagents and
acids. Because
Parylene is not
liquid at any
stage in the
process, it does
not pool, bridge
or exhibit
meniscus
properties.
-
Because of the
thinness of its
coating,
Parylenes
mechanical
dampening and
loading effects
are minimal. The
material can be
coated on
diverse
substrates
including glass,
metal, paper,
resin, plastics,
ceramic,
ferrites and
elastomers, as
well as powdered
and granular
substances.
-
Parylenes static
and dynamic
coefficient of
friction values
are in the range
of 0.25 to 0.33,
its dry-film
lubricity being
an important
attribute for
some coating
applications.
Current Uses
Today, the use of
Parylene ranges from
the common to the
arcane and
encompasses markets
from deep-space
vehicles to
automobile engines
to heart pacers to
military
electronics. In
every case, the
selection of
Parylene is based on
the importance of
one or more of its
basic properties.
The breadth of
applications can be
attributed to the
availability of
automated deposition
equipment, increased
familiarity with the
polymer across
technical
disciplines and
continuing
improvements in
coating efficiency.
Following is
representative of
current
applications:
Electronic sensors
benefit from
Parylene coatings by
providing
environmental
protection without
physically loading
delicate transducer
surfaces. Examples
include various
industrial
components and
automotive sensors.
Metering devices.
The use of remote
circuitry that
reports on utility
consumption is
growing. These
circuits must
operate dependably
under demanding
environmental
conditions, which
Parylene coatings
provide as long-term
protection against
moisture, solvents
and other
contaminants,
including metered
gases.
Aerospace
applications
for Parylene make
use of its unique
properties for space
hardening,
protection against
condensation
resulting from
extreme temperature
changes and
restricting
outgassing. For
example, the
material can protect
high voltage-control
units used on
communication
satellites from
arcing and damaging
corona discharge.
Military
electronics.
Parylene coats
circuits for
aircraft
communication and
navigation
equipment,
satisfying
requirements similar
to those for
aerospace
applications.
Military field
computers that are
transported, stored
and used under
rigorous weather
conditions must be
ruggedized for
dependable
operation; Parylene
is a key component
in that process in
places where
alternate liquid and
spray coatings have
not proven
satisfactory for
moisture protection.
Electronic-access
systems circuitry
for hotel security
is protected from
condensation and
corrosion by
Parylene film. This
is particularly
important in coastal
areas where the
combination of salt
air, high humidity
and heat quickly
degrade unprotected
electronics.
Medical devices
used in surgical
procedures are
selectively coated
with Parylene to
improve their
lubricity and to
provide selective
electrical
insulation. The
coating also
protects and
lubricates
hypodermic needles
and can create a
biocompatible
barrier on
implantable devices
and prosthetic
hardware.
Silicone keypads.
Many systems, such
as cellular
telephones and
specialized computer
equipment, use
silicone rubber
keypads for data
input. Parylene
coating often is
used for silicone
keypad surfaces,
protecting printed
legends and sealing
surfaces against
finger oils and
other contaminants.
Ferrite cores
are coated with
Parylene to serve
several purposes.
The coating provides
dielectric
insulation to avoid
electrical loss
without appreciable
change to physical
dimensions. Parylene
film consolidates
the surface of
ferrites and
pressed-metal
components, which
eliminates dust and
contamination.
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