U.S. patent application number 11/280033 was filed with the patent office on 2007-03-01 for conformal coverings for electronic devices.
This patent application is currently assigned to Honeywell International Inc.. Invention is credited to William J. Dalzell, Kenneth H. Heffner.
Application Number | 20070045001 11/280033 |
Document ID | / |
Family ID | 37663369 |
Filed Date | 2007-03-01 |
United States Patent
Application |
20070045001 |
Kind Code |
A1 |
Dalzell; William J. ; et
al. |
March 1, 2007 |
CONFORMAL COVERINGS FOR ELECTRONIC DEVICES
Abstract
Stand-alone conformal coverings for electronic devices and
methods of making and using such coverings.
Inventors: |
Dalzell; William J.;
(Parrish, FL) ; Heffner; Kenneth H.; (Largo,
FL) |
Correspondence
Address: |
Honeywell International Inc.;Law Dept. AB2
101 Columbia Rd.
Morristown
NJ
07962
US
|
Assignee: |
Honeywell International
Inc.
|
Family ID: |
37663369 |
Appl. No.: |
11/280033 |
Filed: |
November 16, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60712768 |
Aug 31, 2005 |
|
|
|
Current U.S.
Class: |
174/350 ;
257/E23.114; 264/272.11 |
Current CPC
Class: |
H01L 2924/16152
20130101; H01L 21/4817 20130101; H01L 23/552 20130101; C23C 4/185
20130101 |
Class at
Publication: |
174/350 ;
264/272.11 |
International
Class: |
B29C 45/14 20060101
B29C045/14; H05K 9/00 20060101 H05K009/00 |
Claims
1. A method of making a conformal covering for an electronic
device, the method comprising the steps of: providing a template
representative of the shape of at least a portion of an electronic
device; forming a radio-opaque coating on at least a portion of a
surface of the template; and separating at least a portion of the
coating from the template.
2. The method of claim 1, wherein the template comprises a replica
of the electronic device.
3. The method of claim 2, comprising masking at least a portion of
the electronic device.
4. The method of claim 1, wherein the step of forming a coating
comprises a thermal spraying process.
5. The method of claim 1, wherein the step of separating at least a
portion of the coating from the template comprises chemically
dissolving at least a portion of the template.
6. A method of providing a protective covering on an electronic
device, the method comprising the steps of: providing a template
representative of the shape of at least a portion of an electronic
device; forming a radio-opaque coating on at least a portion of a
surface of the template; separating at least a portion of the
coating from the template; and attaching the separated portion of
the coating to an electronic device.
7. The method of claim 6, comprising attaching the separated
portion of the coating to an electronic device with an epoxy.
8. The method of claim 6, comprising positioning the separated
portion of the coating with respect to the electronic device so
that the separated portion of the coating functions as an
electromagnetic radiation shield.
9. The method of claim 6, comprising positioning the separated
portion of the coating with respect to the electronic device so
that the separated portion of the coating protects the electronic
device from tampering or unauthorized access.
10-20. (canceled)
21. A method of making a conformal covering for an electronic
device, the method comprising the steps of: thermally spraying a
radio-opaque composition onto a template to form a radio-opaque
coating on the template wherein the template has a topography
substantially corresponding with an electronic device; separating
at least a portion of the coating from the template to form a
covering for the electronic device; and attaching the covering to
the electronic device.
22. The method of claim 21, wherein the template comprises a
replica of the electronic device.
23. The method of claim 21, wherein the step of separating at least
a portion of the coating from the template comprises chemically
dissolving at least a portion of the template.
24. The method of claim 21, further comprising providing a release
layer on the template before thermally spraying the radio-opaque
composition.
Description
[0001] This application claims the benefit of U.S. Provisional
Patent Application having Ser. No. 60/712,768, filed on Aug. 31,
2005, entitled "Conformal Coverings for Electronic Devices," the
entire disclosure of which is incorporated herein by reference for
all purposes.
TECHNICAL FIELD
[0002] The present invention relates to conformal coverings for use
with electronic devices. Such coverings can be used, for example,
to protect electronic devices from the environment, block or help
shield energy or radiation emitted from or received by electronic
devices, and to help protect electronic devices from security
breaches such as tampering and reverse engineering.
BACKGROUND
[0003] Specialized coatings are often used with electronic devices,
especially microelectronic devices. Such coatings are used to
provide shielding or blocking functions with respect to potentially
harmful energy or electromagnetic radiation, for example. Such
shielding can be used to protect a device from external energy
sources and/or help contain energy emitted by an internal source.
Thus, these coatings are often referred to as radio-opaque.
Coatings can also be used to protect against tampering or reverse
engineering. In this regard, these coatings are usually designed to
cover all or some portion of an electronic device. Moreover, these
coatings are usually designed to conform to weight and size
restrictions and to minimize the number and complexity of steps to
form the coating.
[0004] Various techniques can be used to provide coatings on
electronic devices, one of which is known as thermal spraying.
Examples of thermal spraying or coating processes include arc
spraying, flame spraying, and plasma spraying. Thermal spraying
generally refers to any process where metallic and/or non-metallic
materials are deposited, in a molten or semi-molten condition, on a
surface to form a coating of the material with a desired thickness.
In this process, a thermal spraying nozzle provides a heated zone.
The material to be deposited, in a powder or finely divided form,
is passed through the heated zone of the spray nozzle under the
force of a flowing gas or the like. As the materials are heated,
they change to a plastic or molten state and are accelerated by the
flowing gas. The particles are then directed to the surface to be
coated. The particles strike the surface where they flatten and
form thin platelets that conform and adhere to the irregularities
of the surface and to each other. As the sprayed particles impinge
upon the surface they coalesce, cool, build-up, and form a coating.
Exemplary thermal spraying systems and processes for coating
electronic devices are described in U.S. Pat. Nos. 5,762,711;
5,877,093; 6,110,537; 6,287,985; and 6,319,740 to Heffner et al.,
the entire disclosures of which are incorporated by reference
herein for all purposes.
[0005] Well-known thermal spraying processes can be used to provide
high quality functional coatings on surfaces of electronic devices
without damaging such devices. However, such thermal spraying
processes have some shortcomings in some applications. Thermal
spraying processes for certain electronic devices typically deposit
such coatings at a deposition efficiency level less than about
thirty percent. One reason for this is that many electronic devices
are sensitive to heat and deposition efficiency decreases with
deposition temperature. Thus, the deposition temperature for a
thermal spraying process cannot be so high as to damage the
electronic device being coated and deposition efficiency suffers
from lower deposition temperatures. Moreover, the density of the
coating is also related to deposition temperature. Specifically,
coating density decreases with decreasing temperature. Yet, many
coatings for electronic devices, such as those that are desired to
be radio-opaque, would have improved shielding properties with
higher density but practical restrictions on deposition temperature
limit the density by which shield coatings can be formed on devices
using thermal spraying.
SUMMARY
[0006] The present invention provides conformal coverings, methods
of forming such coverings, and methods of using such coverings with
electronic devices. A covering in accordance with the present
invention comprises a preformed structure, such as a stand-alone
shell, for example, that can be bonded, adhered, or otherwise
attached to an electronic device. In one aspect of the present
invention, such a covering can be made by thermally spraying a
conformal coating on a template that substantially represents the
shape of the electronic device to be covered. The template
preferably comprises a copy or replica of the electronic device or
may be a sacrificial electronic device. The coating can be
separated from the template to form a distinct stand-alone covering
for the electronic device. The separated covering can then be
attached, mechanically or adhesively, for example, to the
electronic device.
[0007] Coating a template representative of the shape of an
electronic device, rather than the actual device itself, provides
many advantages. First, potential damage to sensitive electronic
devices can be avoided because the device itself is not exposed or
subject to the coating process. In this respect, coatings can be
formed at higher temperatures and deposition efficiency can be
increased. This also can provide coatings with improved properties
such as increased density as compared to those formed at lower
temperatures. Generally, denser materials are better at blocking
harmful energy or electromagnetic radiation, for example.
[0008] In one aspect of the present invention a method of making a
conformal covering for an electronic device is provided. The method
comprises the steps of providing a template representative of the
shape of at least a portion of an electronic device, forming a
radio-opaque coating on at least a portion of a surface of the
template, and separating at least a portion of the coating from the
template.
[0009] In another aspect of the present invention, a method of
providing a protective covering on an electronic device is
provided. The method comprises the steps of providing a template
representative of the shape of at least a portion of an electronic
device, forming a radio-opaque coating on at least a portion of a
surface of the template, separating at least a portion of the
coating from the template, and attaching the separated portion of
the coating to an electronic device.
[0010] In another aspect of the present invention, an electronic
assembly comprising an electronic device and a conformal covering
attached to at least a portion of the electronic device is
provided. The conformal covering comprises a shell having a shape
that substantially corresponds with the shape of the electronic
device wherein the covering is capable of blocking reception and
emission of electromagnetic radiation from a predetermined portion
of the electromagnetic spectrum.
[0011] In yet another aspect of the present invention, a method of
making a conformal covering for an electronic device is provided.
The method comprising the steps of, thermally spraying a
radio-opaque composition onto a template to form a radio-opaque
coating on the template wherein the template has a topography
substantially corresponding with an electronic device, separating
at least a portion of the coating from the template to form a
covering for the electronic device, and attaching the covering to
the electronic device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] These and other features, aspects, and advantages of the
present invention will become better understood with regard to the
following description, appended claims, and accompanying drawings
where:
[0013] FIG. 1 is a schematic cross-sectional view of an electronic
assembly comprising an electronic device and a covering in
accordance with the present invention;
[0014] FIG. 2 is a schematic cross-sectional view of a template
that is substantially representative of the outside shape of the
electronic device of FIG. 1;
[0015] FIG. 3 is a schematic cross-sectional view of the template
of FIG. 2 having a coating formed on the template in accordance
with the present invention;
[0016] FIG. 4 is a schematic cross-sectional view of a covering in
accordance with the present invention formed by separating the
coating from the template of FIG. 3;
[0017] FIG. 5 shows an illustrative apparatus for creating
coverings in accordance with the present invention using thermal
spray techniques;
[0018] FIG. 6 is a front view of the thermal spray gun used in FIG.
5 showing the nozzle configuration; and
[0019] FIG. 7 is a schematic illustration of an alternative
apparatus for creating coverings in accordance with the present
invention using thermal spray techniques.
DETAILED DESCRIPTION
[0020] Referring to FIG. 1, electronic assembly 10 of the present
invention is schematically illustrated in cross-section and
comprises covering 12 positioned on electronic device 14.
Electronic device 14 comprises packaged device 16 on substrate 18.
Packaged device 16, as shown, comprises body 20, lid 22, and
electronic circuitry 24 enclosed therein. Electronic device 14 may
be in the form of electronic devices such as microelectronic
devices, semiconductor chips, micro-electro-mechanical-systems,
medical devices, and the like. Preferably, as illustrated, covering
12 is attached with adhesive layer 26. Exemplary adhesives that can
be used include epoxy, polyurethane, polyamide, polyester,
inorganic cement, combinations of these, and the like. Covering 12
may also be attached by using mechanical fasteners or welding such
as laser or ultrasonic welding, for example.
[0021] Referring to FIG. 2, a template 28 that can be used to form
covering 12 in accordance with the present invention is
schematically shown in cross-section. Template 28 is preferably
designed so that covering 12 can be formed on template 28 such as
by a thermal spray process as described in detail below. After
covering 12 is formed on template 28, covering 12 is separated from
the template 28 to form stand-alone covering 12, as shown in FIG.
4. Covering 12 can then be incorporated with the electronic device
14 as shown in FIG. 1 in accordance with the present invention.
[0022] As illustrated, template 28 is designed to substantially
represent the shape of the electronic device 14 and is preferably a
copy or replica of at least a portion of electronic device 14. In
one aspect of the present invention, a mold can be made from the
electronic device 14, which mold can be used to form the template
28. In another aspect of the present invention, a sacrificial
electronic device otherwise identical to device 14 can be used as
template 28.
[0023] As illustrated, template 28 comprises a base portion 32 and
a raised portion 34. The base portion 32 corresponds with the
substrate 28 and the raised portion 34 corresponds with the
packaged device 16. In this way, the template 28 provides a replica
or copy of the electronic device 14 and can be used to form
covering 12 as a near net shape covering.
[0024] Template 28 is preferably designed so that the template 28
can be separated from the covering 12. In those instances in which
a sacrificial device constitutes template 28, certain areas or
regions, such as voids or openings, of such a sacrificial
electronic device are preferably filled in with a suitable material
before forming a coating on the electronic device 14. This
preparation of template 28 makes it easier to remove covering 12
after covering 12 is formed. In any event, any known or future
developed molding, die making, prototype making, model making, or
forming techniques can be used to form the template 28. In other
representative modes of practice, template 28 can be made from a
material that can be selectively etched away with respect to
covering 12 or otherwise easily separated therefrom. One exemplary
material that can be used for the template 28 comprises aluminum in
as much as reagents can be used to selectively etch aluminum with
respect to a typical covering material such as tungsten.
Optionally, a release layer can be provided on the template 28 that
can allow easier separation of covering 12 from template 28.
[0025] Any material(s) that are compatible with the particular
deposition process used to form the covering 12 can be used to form
the template 28. In particular, template 28 is preferably designed
in light of the temperature range it may be exposed to in a
particular deposition process. Other considerations that may be
used in selecting a material(s) for template 28 include cost,
formability, and thermal expansion compatibility with a coating
formed thereon.
[0026] Template 28 may comprise a single replica of electronic
device 14, as illustrated, or may comprise plural replicas of
electronic device 14 or any other electronic device(s). A template
having plural replicas can be used for volume manufacturing and can
take advantage of economies of scale with respect to a deposition
process, for example. If a template having plural replicas of an
electronic device is used, such template can be coated and the
coating can be subsequently separated from the template as
described below to form plural coverings in accordance with the
present invention.
[0027] Covering 12 can be provided by any thin-film deposition
technique. Masking techniques can be used during the deposition
process to separate individual covering from each other or such
coverings can be separated by saw or laser cutting after being
separated from the template. Preferred deposition techniques
include thermal spraying, chemical vapor deposition and combustion
chemical vapor deposition. A preferred thermal spraying process is
described in detail below. Other thermal spraying processes that
can be used are described in U.S. Pat. Nos. 5,762,711; 5,877,093;
6,110,537; 6,287,985; and 6,319,740, the disclosures of which are
fully incorporated herein for all purposes. Chemical vapor
deposition is well known in the semiconductor processing arts and
an example of a combustion chemical vapor deposition process can be
found in U.S. Pat. No. 6,013,318 to Hunt et al., the disclosure of
which is incorporated herein by reference for all purposes.
[0028] Covering 12 may comprise any material capable of being
coated on template 28 and subsequently separated from template 28
to form covering 12 in accordance with the present invention.
Covering 12 may comprise a single layer of material, plural layers
of the same material, or plural layers of different materials.
[0029] Covering 12 may be formed from any material or combination
of materials that help provide such a coating with radiation
shielding characteristics. Radiation shielding relates to the use
of a material(s) that can alter some characteristic of a source of
particles and/or photons (such as spectrum, fluence, intensity, or
the like) through physical interaction between the atomic structure
of the atoms of the material and the incident photons or particles
striking the material. The net reduction in such a characteristic
of the incident particles or photons and any contribution by
secondary radiation can be used to assess the shielding
effectiveness of the material. For applications related to
shielding harmful energy and/or electromagnetic radiation,
preferred materials include refractory metals such as tungsten,
molybdenum, niobium, and tantalum, for example. Representative
examples of materials with radiation shielding characteristics
include elements having an atomic number of 39 or greater,
preferably 56 or greater, more preferably 72 or greater, compounds
of such elements, alloys incorporating such elements, admixtures
incorporating such elements, combinations of these and the like.
Elements with low atomic numbers (hydrogen and carbon, for example)
also have the capacity to shield radiation effectively. However, it
typically takes more material to provide effective shielding.
Representative examples of preferred elements include Hf, Ta, W,
Re, Os, Ir, Pt, Au, Tl, Pb, Bi, and Ba. Heavier elements and
materials incorporating such heavier elements, such as W, are more
preferred singly or in combination, as these tend to provide more
shielding capability at a given coating thickness than lighter
elements. Carbon-based materials such as polyethylene may also be
used. Polyethylene, for instance, is a suitable shielding material
inasmuch as polyethylene coatings are highly dense due to favorable
packing density characteristics.
[0030] For applications related to security, materials may be
polymeric or otherwise organic, inorganic, metals, metal alloys,
intermetallic compositions, semiconductor materials, combinations
of these and the like. One or more piezoelectric materials are
preferred for such security applications. Materials that can be
used for security applications are described in Applicant's
copending U.S. provisional patent application entitled "Security
Techniques for Electronic Devices," filed on 15 Jul. 2005 in the
name of William J. Dalzell, and having attorney docket number
H0006637-1628 (HON0028/P1), the entire disclosure of which is
incorporated by reference herein for all purposes.
[0031] The thickness of covering 12 can vary over a wide range
depending on the desired functionality for the covering 12. When
used for applications related to shielding electromagnetic
radiation, for example, thickness of covering 12 is preferably
sufficient to block such radiation as desired for the particular
application. Generally, covering 12 can have a thickness suitable
to the radiation spectrum, fluence and intensity of the operational
environment. Proton and particle radiation spectra can be
attenuated and shifted as a function of the coating material,
coating thickness, and coating density. In one example tungsten
metal can be applied to a thickness of 1 mil to 100 mils, more
preferably 10 mils to 50 mils, even more preferably 20 mils to 30
mils. Such a coating preferably has a density of about 14 to 18
grams per cubic centimeter. In one preferred aspect of the present
invention, thickness of covering 12 would be suitable for
substantially shielding most spacecraft electronics from total dose
in medium earth orbit natural space radiation environment.
[0032] Where covering 12 is desired to provide security functions,
factors that can be used to determine thickness of covering 12 are
described in Applicant's copending U.S. provisional patent
application entitled "Security Techniques for Electronic Devices,"
filed on 15 Jul. 2005 in the name of William J. Dalzell, and having
attorney docket number H0006637-1628 (HON0028/P1), the entire
disclosure of which is incorporated by reference herein for all
purposes. In any event, the thickness of covering 12 is preferably
uniform but may vary based on factors such as design, the nature of
the item(s) on which the coating is formed, the deposition process
used, and/or the like.
[0033] In accordance with the present invention, covering 12 as
formed on template 28, can have increased density as compared to
directly coating electronic device 14 with a coating. This is
because higher density can be achieved at higher temperatures. By
using a template as an intermediary in accordance with the present
invention instead of coating directly onto a device, it is possible
to use higher coating temperatures without the risk of thermal
damage to the device. This in turn enhances the density of the
resultant covering 12. For example, the theoretical density of
tungsten is about 19 grams per cubic centimeter. Coverings formed
by directly coating an electronic device with tungsten have a
density of about 14-15 grams per cubic centimeter. In accordance
with the present invention, tungsten coverings with a density
greater than 16 grams per cubic centimeter have been made.
[0034] In preferred modes of practice, coverings of the present
invention advantageously are formed on templates using thermal
spray techniques. Generally, thermal spraying involves causing a
substrate to be coated to pass through a plume of a spray
comprising molten particles of the coating composition. In
preferred modes of practice, a line of sight coating process uses
heat energy to heat the coating material to a molten state. The
molten material typically is caused to be atomized or otherwise
converted into molten droplets. The molten material is carried to
the substrate by a carrier gas or jet. The molten droplets are
preferably finely sized. During coating, the substrate is
preferably moved in and out of the hot spray to minimize thermal
risk to the substrate. The desired coating thickness desirably is
built up using multiple passes. The substrate optionally may be
thermally coupled to a heat sink and/or chilling media during
thermal spraying in order to help carry away thermal energy
imparted to the substrate.
[0035] One embodiment of a thermal spray system 300 useful to carry
out thermal spraying is illustrated in FIGS. 5 and 6. Particles,
e.g., a fine powder, of a coating composition are supplied from a
composition feedstock supply 302 to thermal spray gun 304. The gun
304 is mounted on an X-Y positioning rack 306. Thermal spray gun
304 may be of a variety of types, including a flame gun, plasma
gun, electric arc, gun or the like. For purposes of illustration,
spray gun 304 is a flame-type gun. In such an embodiment, fuel and
oxygen are supplied to the gun 304 from a fuel/oxidant supply 308
and air is supplied from an air supply 310. The air is ejected
through annular nozzle 312, and a flame 316 is emitted from nozzles
314 located centrally inside annular nozzle 312. The air carries
entrained particles (not shown), which are melted by the flame 316
as the particles exit the gun 304. The air acts not only as a
carrier gas to help transport the molten particles to the substrate
(not shown) to be coated, but the air also acts as a nozzle
coolant.
[0036] The molten particles are aimed at a pair of rotatable arms
318. Arm ends 320 each receive one or more corresponding substrates
to be coated. By rotating arms 318, the substrates repeatedly move
in an out of the spray plume. In this way, the thermal spray
coating can be applied without excessively heating the substrates
if desired. Each substrate generally may be planar and may be
fixedly mounted to an arm end 320. However, three dimensional
substrates may also be coated. These would be mounted onto arms 318
so that the three dimensional substrate could be spun in several
axis modes while the gun 304 sprays molten material onto the
surfaces of the substrate in line of sight fashion.
[0037] The arms 318 are rotated by an electric motor 322. A
coolant, such as compressed air, is pumped into the arms 318 from a
coolant supply 324 through a pipe or hose 326 that connects to a
coolant slip ring 328 located generally at the central axis of
rotation of arms 318. The coolant flows from the slip ring to
coolant passages (not shown) inside arms 318. Those passages
desirably extend radially along the interior of arms 318 and each
arm end 320.
[0038] The arms 318 rotate at a suitable rate, sweeping the mounted
substrates through the spray of molten particles. As general
guidelines, rotational rates within the range of 1 to 500 rpm, more
desirably 300 to 350 rpm would be suitable. With each pass, the
coating builds up on the surface(s) of the substrate in line of
sight coating fashion. As a practical matter, the deposition of
coating material tends to be a small swath along the substrate
surfaces in the direction of rotation R, and as the arms 318
rotate. Accordingly, the gun 304 is indexed in the radial direction
(X direction) with respect to the arms 318 so that the coating
covers the entire surfaces to be coated. The speed of movement in
the X direction optionally may be adjusted so that the deposition
rate of material onto the substrate is constant. Otherwise, faster
moving portions of the surfaces radially farther from the center of
rotation may receive less material per unit time than those closer
to the center of rotation.
[0039] The distance from the gun 304 to the arms 318 also is
adjustable in the Y direction. A desired distance can be one at
which substrate heating is below a desired threshold, yet the
composition is still molten when it impacts the substrate. Thus, if
gun 304 were to be too close to a substrate, the substrate might
get too hot. If too far, the molten droplets might solidify too
much before reaching the substrate surfaces, impairing the quality
of the resultant coating.
[0040] FIG. 7 schematically shows a thermal spray system 400
similar to system 300 of FIGS. 5 and 6, except system 400 of FIG. 7
is adapted for automated processing of larger batches of substrates
(not shown) in a protected environment 402 defined by housing 404.
Particles, e.g., a fine powder, of a coating composition are
supplied from a composition feedstock supply 406 to the thermal
spray gun 408. A carrier gas supply (not shown) and heat energy
source (not shown) such as fuel, electricity, or the like, are also
coupled to gun 408. As shown, gun 408 is a plasma gun, facilitating
thermal spraying of materials such as tungsten, which become molten
at very high temperatures, e.g., temperatures above about 3400 C.
Supply 406 preferably includes an automated powder feeder that is
outside environment 402 to facilitate convenient loading of powder
feedstock. Gun 408 is generally aimed toward rotatable substrate
mounting platform 410 including a plurality of arms 412 extending
from centrally positioned rotor 414. Platform 410 rotates about
central axis 416. System 400 also includes an exhaust system 418
includes a powder particulate collection system 420.
[0041] The movement of both gun 408 and rotatable substrate
mounting platform 410 are automated and controlled via computer
422. An operator interfaces with the computer 422 and system 400
via console 424. Rotor 414 desirably has at least a
computer-controlled rotation rate and rotation direction. Gun 408
is mounted on robotic manipulation system 426 which can control the
distance between gun 408 and arms 412, the height of gun 408
relative to platform 410, the position of gun 408 relative to
central axis 416, and the relative angle at which material is
sprayed toward platform 410. The supply 406 of material to gun 408
is also automated and may be held constant or varied during the
course of a coating operation as desired.
[0042] In a typical coating operation, the desired coating material
is loaded into automated powder feeder of supply 406. One or more
substrates (not shown) to be coated are positioned on one or more
of arms 412. Desirably, the substrates are positioned in a balanced
manner so that platform 410 rotates smoothly. Thus, pairs of
substrates may be positioned in balanced fashion on opposed arms
412 symmetrically about central axis 416. If an odd number of
substrates is being processed, a dummy substrate may also be used
for balance. As is the case with arms 318 of apparatus 300 of FIGS.
5 and 6, arms 412 of system 400 can be designed to act as a heat
sink to help draw thermal energy away from substrates being coated.
Cooling media (not shown) may also be circulated through arms 412
to help cool the substrates if desired.
[0043] The powder is supplied to gun 408 and is sprayed from gun
408 toward rotating platform 410. During spraying, platform 410
rotates at a suitable rotational speed, such as a speed in the
range of 100 to 500 rpm. Typically, gun 408 may be indexed radially
back and forth relative to platform 410 to help ensure full
coverage of surfaces to be coated. The speed at which gun 408 is
indexed may be adjusted based upon the position of gun 408 relative
to central axis 416 so that coating coverage is uniform
notwithstanding the changing relative speed between arms 412 and
gun 408 as the radial position of gun 408 with respect to central
axis 416 changes. The heat source, in this case a plasma, provides
enough heat energy to melt the sprayed particles. Typically, the
heat source provides a suitable temperature in the range of 7000 C
to about 20000 C. The carrier gas helps to transport the sprayed
particles to the substrates. The carrier gas may be any gas such as
nitrogen, carbon dioxide, argon, air, combinations of these, and
the like. A preferred carrier gas comprises argon and optionally at
least one other gas such as hydrogen, helium, nitrogen, carbon
dioxide, or the like. A gas such as argon is favored because argon
heats quickly in the flame of the gun 408.
[0044] A typical supply pressure for the carrier gas is in the
range of 30 psi. The preferred primary (argon) and secondary gas
(hydrogen) pressures are 75 psi and 50 psi respectively. The molten
particles impact on the substrates, where they coalesce and form a
coating. Areas of the substrates may be masked if those areas are
desired to be uncoated after treatment. A suitable process time may
be in the range of a few seconds to 600 seconds or more. A
satisfactory coating thickness generally would be in the range of 5
micrometers to about 400 micrometers. Excess spray material is
exhausted through exhaust system 418, where entrained particles in
the exhaust are collected.
[0045] Methods and equipment used to carry out thermal spraying
suitable in the practice of the present invention also have been
described in U.S. Pat. Nos. 5,762,711; 5,877,093; 6,110,537;
6,287,985; and 6,319,740. Each of these patent documents is
incorporated herein by reference.
[0046] After the covering 12 is separated from the template 28,
processes such as cleaning, trimming, and/or post-machining or the
like can be performed, as needed or desired. For example, the
covering 12 may be polished to enhance gloss and surface finish as
desired. In other modes of practice, the covering 12 may receive a
protective overcoat (not shown) to protect the covering 12 from
damage, oxidation, or the like. Examples of materials that would be
suitable to form an overcoat include Al, W, Rh, reactive
di-xylylene precursors applied by chemical vapor deposition,
combinations of these, and the like.
[0047] The present invention has now been described with reference
to several embodiments thereof. The entire disclosure of any patent
or patent application identified herein is hereby incorporated by
reference. The foregoing detailed description and examples have
been given for clarity of understanding only. No unnecessary
limitations are to be understood therefrom. It will be apparent to
those skilled in the art that many changes can be made in the
embodiments described without departing from the scope of the
invention. Thus, the scope of the present invention should not be
limited to the structures described herein, but only by the
structures described by the language of the claims and the
equivalents of those structures.
* * * * *