U.S. patent application number 12/115875 was filed with the patent office on 2009-04-30 for surface coating.
This patent application is currently assigned to Integrated Surface Technologies. Invention is credited to Adam Anderson, W. Robert Ashurst, Jeff Chinn.
Application Number | 20090110884 12/115875 |
Document ID | / |
Family ID | 40581356 |
Filed Date | 2009-04-30 |
United States Patent
Application |
20090110884 |
Kind Code |
A1 |
Chinn; Jeff ; et
al. |
April 30, 2009 |
Surface Coating
Abstract
A composite is provided, comprising a substrate and a film on
the substrate. The film has an RMS surface roughness of 25 nm to
500 nm, a film coverage of 25% to 60%, a surface energy of less
than 70 dyne/cm; and a durability of 10 to 5000 microNewtons.
Depending on the particular environment in which the film is to be
used, a durability of 10 to 500 microNewtons may be preferred. A
film thickness 3 to 100 times the RMS surface roughness of the film
is preferred.
Inventors: |
Chinn; Jeff; (Menlo Park,
CA) ; Ashurst; W. Robert; (Aubum, AL) ;
Anderson; Adam; (Auburn, AL) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Integrated Surface
Technologies
Menlo Park
CA
|
Family ID: |
40581356 |
Appl. No.: |
12/115875 |
Filed: |
May 6, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61029801 |
Feb 19, 2008 |
|
|
|
60983504 |
Oct 29, 2007 |
|
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Current U.S.
Class: |
428/147 ;
174/250; 428/141; 428/143; 428/148; 428/149 |
Current CPC
Class: |
Y10T 428/24372 20150115;
H05K 2201/0239 20130101; Y10T 428/24413 20150115; Y10T 428/24405
20150115; Y10T 428/24355 20150115; Y10T 428/24388 20150115; H05K
2201/0209 20130101; H05K 2201/0257 20130101; Y10T 428/2839
20150115; H01L 2924/00 20130101; H01L 2924/0002 20130101; H01L
23/49894 20130101; Y10T 428/24364 20150115; Y10T 428/24421
20150115; H05K 3/284 20130101; H01L 2924/0002 20130101; Y10T
428/269 20150115; H05K 2201/09872 20130101 |
Class at
Publication: |
428/147 ;
428/141; 428/143; 428/148; 428/149; 174/250 |
International
Class: |
B32B 27/00 20060101
B32B027/00; B32B 3/10 20060101 B32B003/10; B32B 5/16 20060101
B32B005/16; H05K 1/00 20060101 H05K001/00; B32B 15/02 20060101
B32B015/02; B32B 9/00 20060101 B32B009/00 |
Claims
1. A composite comprising: a substrate; a film on the substrate,
the film having: an RMS surface roughness of 25 nm to 500 nm; a
film coverage of 25% to 60% a thermodynamic surface energy of
<70 dyne/cm; and a durability of 10 to 5000 microNewtons.
2. The composite of claim 1, wherein the film has a durability of
10 to 500 microNewtons.
3. The composite of claim 2, wherein the film has a thickness 3 to
100 times the RMS surface roughness of the film.
4. The composite of claim 1, wherein the film comprises
non-conductive particles linked to each other and to the substrate
by linker molecules.
5. The composite of claim 4, wherein the non-conductive particles
are metal oxide or semiconductor oxide particles.
6. The composite of claim 5, wherein the non-conductive particles
are alumina or silica particles.
7. The composite of claim 5, wherein the non-conductive particles
are alumina particles have a particle size of about 40-60 nm.
8. The composite of claim 5, wherein the non-conductive particles
are silica particles have a particle size of about 10-20 nm.
9. The composite of claim 4, wherein the non-conductive particles
are latex particles.
10. The composite of claim 4, wherein the linker molecules are
selected from the group consisting of bi-functional linkers such as
bis-trichlorosilane-ethane, bis-trichlorosilane-butane,
bis-trichlorosilane-hexane, bis-trimethoxysilane-ethane,
bis-trimethoxysilane-butane, bis-trimethoxysilane-hexane,
bis-tris-dimethylaminosilane-ethane,
bis-tris-dimethylaminosilane-butane, and
bis-tris-dimethylaminosilane-hexane.
11. The composite of claim 10, wherein the linker molecules are
silanes with a reactive group at both ends.
12. The composite of claim 4, wherein the film further comprises a
low thermodynamic surface energy coating, having a surface energy
of less than 70 dyne/cm, disposed over the non-conductive particles
and linker molecules.
13. The composite of claim 12, wherein the low surface energy
coating comprises a material selected from the group consisting of
long chain hydrocarbons, long chain fluorocarbons, phosphonates,
thiols and ring structures.
14. The composite of claim 12, wherein the low surface energy
coating comprises a material selected from the group consisting of
C8, C10, C 11, C12, C14, C18, FDTS, FODCMS or FOTS.
15. The composite of claim 1, wherein the substrate is a printed
circuit board.
16. The composite of claim 1, wherein the substrate is a consumer
electronic device.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is related to and claims priority from
Provisional Application Ser. Nos. 61/029,801, filed Feb. 19, 2008
and 60/983,504, filed Oct. 29, 2007.
BACKGROUND
[0002] Today's conformal coatings include glob-top organic based
coatings. Such coatings include acrylics, epoxies, urethanes,
parylene or silicone materials. Such conformal coatings provide
limited environmental protection from moisture, dust, vibration,
and provide physical protection from handling.
[0003] Today's conformal coatings are typically several mils thick.
The thinnest conformal coating produced today is made of
vapor-deposited parylene and is about 15 .mu.m thick. Thick
conformal coatings can be problematic. For example, during any
rework of a printed circuit board, a previously applied thick
conformal coating may need to be removed (e.g., by dissolution or
physical abrasion). This is time consuming, expensive and
difficult. Also, thick conformal coatings can undesirably impede
the transfer of heat from an electrical apparatus such as a chip or
circuit substrate.
[0004] Conformal coatings are also not completely foolproof.
Conformal coatings are typically not applied over electrical
connectors as they affect the contact resistance. For example, if a
cell phone with a thick conformal coating is immersed in a body of
water, there is a high probability that the phone will not work.
This is because residues or contaminated liquids can form leakage
pathways between the various exposed components, connectors,
assemblies or surfaces not coated.
[0005] Improvements can be made to such coatings.
SUMMARY
[0006] Embodiments of the invention are directed to novel
films.
[0007] Embodiments of the invention are directed to surface
coatings, articles including such surface coatings, and methods for
forming surface coatings.
[0008] One embodiment of the invention is directed to a method
comprising: depositing nano-particles on a substrate surface using
a liquid deposition process, to form an ionic barrier with
anti-wetting or super-hydrophobic properties on the substrate.
[0009] Another embodiment of the invention is directed to an
article comprising: a substrate; and a coating on the substrate,
wherein the coating has a surface roughness between about 25-500 nm
RMS over an area of at least about 2500 .mu.m.sup.2.
[0010] These and other embodiments of the invention are described
in detail below.
[0011] One embodiment of the invention is directed to a composite
comprising: a substrate; and a film on the substrate, wherein the
film has at least two, and preferably all, of the following
properties a)-d):
TABLE-US-00001 a) Film Roughness: 25 < RMS (nm) < 1000
(preferably 30 < RMS (nm) < 150) (Average roughness).
Preferred ranges for RMS roughness also include 30 < RMS (nm)
< 1000 and 25 < RMS (nm) < 500. b) Film Coverage: 25 <
Coverage (%) < 60 (Average density) c) Film Durability: 10 <
Force (.mu.-Newtons) < 500 (Force) (it is noted that the film
durability may be greater than about 500 .mu.-Newtons in some
embodiments) d) Surface Energy: 15 < Energy (Dyne/cm) < 70
(Zisman Critical angle). Surface energy may be less than 15 dyne/cm
in some embodiments.
[0012] In one aspect, a composite is provided, comprising a
substrate and a film on the substrate. The film has an RMS surface
roughness of 25 nm to 500 nm, a film coverage of 25% to 60%, a
surface energy less than 70 dyne/cm, i.e., zero to 70 dyne/cm; and
a durability of 10 to 5000 microNewtons. Depending on the
particular environment in which the film is to be used, a
durability of 10 to 500 microNewtons may be preferred. A film
thickness 3 to 100 times the RMS surface roughness of the film is
preferred.
[0013] The film may comprise non-conductive particles linked to
each other and to the substrate by linker molecules. Preferred
non-conductive particles include metal oxide or semiconductor oxide
particles. Specific preferred materials for the non-conductive
particles include alumina and silica. Where the non-conductive
particles are alumina, a particle size of about 40-60 is preferred,
and more preferably 40-50 nm. Where the non-conductive particles
are silica, a particle size of about 10-20 nm. is preferred. The
nano-particles shape could be round spheres, flatten discs, rods,
nails, hollow spheres or other shapes with the preferred diameter.
Latex particles are also preferred. Preferred linker molecules
include those selected from the group consisting of bi-functional
linkers such as bis-trichlorosilane-ethane,
bis-trichlorosilane-butane, bis-trichlorosilane-hexane,
bis-trimethoxysilane-ethane, bis-trimethoxysilane-butane,
bis-trimethoxysilane-hexane, bis-tris-dimethylaminosilane-ethane,
bis-tris-dimethylaminosilane-butane, and
bis-tris-dimethylaminosilane-hexane. Preferred linker molecules
include silanes with a reactive group at both ends.
[0014] The film may further comprise a low surface energy coating,
having a thermodynamic surface energy of less than 70 dyne/cm,
disposed over the non-conductive particles and linker molecules.
Preferred materials for the low surface energy coating include
materials selected from the group consisting of long chain
hydrocarbons, long chain fluorocarbons, phosphonates, thiols and
rings. Specific preferred materials include C8
(n-Octyltrichlorosilane (C.sub.8H.sub.17Cl.sub.3Si)), C10
(n-Decyltrichlorosilane (C.sub.10H.sub.21Cl.sub.3Si)) or
n-Decyltriethoxysilane (C.sub.16H.sub.36C.sub.13Si), C11
(Undecyltrichlorosilane (C.sub.11H.sub.23Cl.sub.3Si)), C12
(Dodecyltrichlrosilane (C.sub.12H.sub.25Cl.sub.3Si)) or
Dodecylthriethoxysilane (C.sub.18H.sub.40O.sub.3Si)), C14
(Tetradecyltrichlorosilane (C.sub.14H.sub.25Cl.sub.3Si)), C18
(n-Octadecyltrichlorosilane (C.sub.18H.sub.37Cl.sub.3Si)) or
(n-Octadecyltrimethoxylsilane (C.sub.21H.sub.46O.sub.3Si)), FDTS
((Heptadecafluoro-1,1,2,2-TetraHydrodecyl)Trichlorosilane
(C.sub.10H.sub.4Cl.sub.3F.sub.17Si)), FODCMS
((Tridecafluor-1,1,2,2-Tetrahydro-Octyl)methyldichlorosilane)
(C.sub.9H.sub.7Cl.sub.2F.sub.13Si)), FOTS
((Tridecafluoro-1,1,2,2-Tetrahydro-Octyl)Trichlorosilane
C.sub.8H.sub.4Cl.sub.3F.sub.13Si)) or rings like structures
(Pentafluorophenylpropyl-trichlorosilane
(C.sub.9H.sub.6F.sub.5Cl.sub.3Si)).
[0015] Preferred substrates include a printed circuit board and a
consumer electronic device.
[0016] Methods of making a film are also provided. A film may be
made by depositing nanoparticles on a surface of a substrate using
a liquid deposition process, and linking the nanoparticles to each
other and to the surface using linker molecules. A coating having a
surface energy of less than 70 dyne/cm may be deposited over the
film to form a coated film. The film preferably has the surface
roughness, film coverage, surface energy and durability described
above. The materials and other parameters described above are also
preferred.
[0017] Preferably, the nanoparticles pre-treated with protected
linker molecules prior to deposition on a surface of a substrate,
and the nanoparticles are linked to each other and to the surface
using the linker molecules by deprotecting the linker
molecules.
[0018] Embodiments of the invention are directed to specific
combinations of these different aspects, as well as specific
embodiments related to those specific aspects. Further details
regarding embodiments of the invention are provided below in the
Detailed Description, Claims, and Appendix.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows a diagram illustrating components of a
composite film.
[0020] FIG. 2 shows an illustration of three surfaces having the
same RMS surface roughness but different surface coverages. Both
topographical and digital coverage views of the surfaces are
provided.
[0021] FIG. 3 shows surfaces for which surface coverage has been
calculated. FIGS. 3A, 3C and 3E show scanning electron microscope
(SEM) images of 3 different surfaces. FIGS. 3B, 3D and 3F show
digital images corresponding to the SEM images of FIGS. 3A, 3C and
3E, respectively.
[0022] FIG. 4 shows wear images.
[0023] FIG. 5 shows a table with test data of films which have been
treated with various low surface energy coatings.
[0024] FIG. 6 shows a Venn diagram illustrating an intersection
between preferred property ranges.
[0025] FIG. 7 shows a schematic of an apparatus that may be used to
fabricate coatings.
[0026] FIG. 8 shows an apparatus that may be used to fabricate
coatings.
[0027] FIG. 9 shows printed circuit boards with various coatings
after exposure to an ionic solution.
[0028] FIG. 10 shows atomic force microscopy measurements of
surfaces having a texturized coating applied using different
process parameters.
[0029] FIG. 11 shows USB memory devices with various coatings,
including no coating, and at various magnifications exposed to an
ionic electrolyte of Gatorade.RTM..
[0030] FIG. 12, including FIGS. 12A, 12B, 12C and 12D show scanning
electron micrographs (SEM) of coatings at different magnifications
which do not exhibit the desired properties due to a lack of
surface coverage.
[0031] FIG. 13, including FIGS. 13A, 13B, 13C and 13D show scanning
electron micrographs (SEM) of coatings at different magnifications.
The coating of FIG. 13 was fabricated differently from that of FIG.
12, and has a different surface coverage which does exhibit the
desired properties.
[0032] FIG. 14 shows several scanning electron micrographs (SEM) of
a cross section of a sample similar to that illustrated in FIG.
13.
[0033] FIG. 15, including FIGS. 15A and 15B show scratch test data
of two films in which one was treated with a linker chemistry.
[0034] FIG. 16, including FIGS. 16A, 16B, 16C and 16D shows surface
coverage measurements. FIGS. 16A and 16C show SEM micrographs at
different magnifications. FIGS. 16B and 16D are their corresponding
digitized coverage images.
[0035] FIG. 17, including FIGS. 17A, 17B and 17C show the results
of scratch testing on different films and/or with different testing
parameters.
DETAILED DESCRIPTION
[0036] Some aspects of the invention are directed to a new barrier
film, which can protect printed circuit boards and electronic
assemblies from failures caused by ionic materials. In some aspects
of the invention, a special textured surface is created on an
electrical apparatus such as a circuit substrate (e.g., a circuit
board, a circuit card, a connector, etc.). This textured surface
can be a barrier that can repel ionic contaminants. Most circuitry
failures occur when contamination results in leakage or where
conducting pathways form between the various electrical conductors
(e.g., leads on a printed circuit board). Some aspects of the
invention prevent such electrical leakage paths from forming.
[0037] FIG. 1 shows a diagram illustrating components of a
texturized, composite film. Nanoparticles 120 are linked to each
other and to a substrate 110 by linker molecules 130. A low surface
energy coating 140 is disposed over the nanoparticles 120 and the
linker molecules 630.
[0038] Nanoparticles 120 are preferably non-conductive. Metal oxide
or semiconductor oxide particles are preferred. Specifically,
alumina and silica particles are preferred. Where the nanoparticles
are alumina, a particle size of about 40-60 nm, more preferably
40-50 nm, is preferred, where particle size is according to
industry standard measurements that correlate more or less to the
particle diameter. Where the nanoparticles are silica, a particle
size of about 10-20 nm is preferred. Other types of nanoparticles
may be used, including but not limited to latex nanoparticles.
Hollow silica particles, which incorporate a substantial amount of
air, may improve resistance to oils and other solvents.
[0039] Process parameters may be controlled to obtain a film having
an RMS surface roughness of 25 nm to 500 nm, a film coverage of 25%
to 60%, a surface energy of less than 70 dyne/cm, and a durability
of 10 to 5000 microNewtons. Such a film is particularly desirable
for the following reasons.
[0040] First, the combination of surface roughness, film coverage,
and surface energy results in a film sufficiently resistant to
wetting by aqueous solutions (water, coffee, sodas) and organic
solvents to which electronics may be exposed during use. As a
result, the electronics may survive conditions that would otherwise
have rendered them inoperable. Each of the parameters is important.
For example, as illustrated in FIG. 2, surface roughness alone is
not sufficient to provide the type of surface desired, and two
surfaces having the same surface roughness but different film
coverage may have very different surface topography and, hence,
different resistance to wetting.
[0041] Second, the durability range results in a film that is
sufficiently durable to resist many of the environmental conditions
to which an electronic device might be exposed. Durabilities that
are too much lower may result in films that are removed during
normal use of a device. However, the durability is still low enough
to allow for convenient fabrication and rework. Specifically, the
film may be applied to different parts before an electrical
connection is made. Then, when the connection is made, the film has
a durability low enough that the film may be readily removed during
the connection process. A durability of 10 to 5000 microNewtons is
sufficiently low to allow for connections at the printed circuit
board level. Where a film that will allow for good electrical
connections at the chip level is desired (eg. thin film flex
circuit boards in which connections are spring-loaded contacts), a
durability having a lower top range is preferred, i.e., a
durability of 10 to 500 microNewtons is preferred.
[0042] A film thickness that is 3 to 100 times the surface
roughness of the film is preferred. Such a film is thick enough to
ensure that the underlying substrate is adequately protected from
moisture, but is not so thick that fabrication times increase,
excess material is present, or issues with electrical connections
arise. Depending upon the application, however, much thicker films
may be used, up to 10,000 times the RMS surface roughness, or even
greater.
[0043] Substrate 110 may be any electrical part that can benefit
from protection from fluids. A printed circuit board is one example
of such a substrate. More generally, any electronic device may be
used as a substrate. Consumer electronic devices, including flash
memory, MP3 players, cell phones, personal digital assistants
(PDAs), video game consoles, portable video game consoles,
computers, laptops, monitors, keyboards and others, may be used as
a substrate, where such devices have electronics that could benefit
from water resistance protection.
[0044] When an electrical assembly includes a film having a
texturized surface according to an embodiment of the invention, a
polluted or contaminated liquid cannot form a liquid-solid
interface, which can lead to shorts and low level leakage resulting
of device failure or reliability issues. The texturized film
provides liquid resistance for the electrical apparatus.
[0045] The film with the textured surface can be formed with
nanoparticles and can consequently be very thin. The film is
virtually invisible and does not affect the performance of the
electrical apparatus.
[0046] The underlying reasons for using the textured film according
to embodiments of the invention are different than the reasons for
using a thick glob-top conformal coating. For example, when a
glob-top coating is used, a thicker coating is generally better,
because of greater physical protection or a physical barrier is
provided with a thicker coating. In contrast, embodiments of the
invention use a thin film as a liquid repellant barrier. The thin
film can be effective, even though it is scratched. The same is not
true for other conformal films. Unlike a conformal coating, a thin
textured film according to an embodiment of the invention does not
interfere with the electrical conductivity of a conductor, but it
still protects the conductor from ionic solutions.
[0047] The textured films according to embodiments of the invention
are particularly useful directly on electrical connectors. Current
conformal coatings cannot be applied to electrical connectors since
they are non-conductive and will increase the resistance between
two conducting and contacting surfaces. However, in embodiments of
the invention, a male connector and/or a female connector can be
coated with the texturized films. Preferably both are coated. The
texturized films can protect the connector surfaces from ionic
contamination and shorts. If the female connector abrades the
texturized film on the male connector (or vice-versa), the abraded
texturized film would still protect conductors in the male
connector from shorting out if the male connector is exposed to an
ionic liquid such as water. The texturized films on the female and
male connectors are thin enough so that the abrasion of either
textured film can cut through the other film and provide for a low
resistance connection. Low electrical resistance is desirable,
since any increases in contact resistance can have a direct effect
on the battery life and device performance of portable and low
voltage electronic devices.
[0048] In addition, because some of the films disclosed herein may
have reduced interference with electrical connections, rework may
be significantly easier. With a glob-top coating, it may be
necessary to locally (or globally) remove the coating prior to
rework, and replace the coating after rework. With some of the
films described herein, however, it may be possible to simply
perform the rework without removing or replacing the film.
[0049] Because some of the films disclosed herein are significantly
thinner than glob-top coatings, heat entrapment issues may be
less.
[0050] Tests have shown that electronic devices (e.g., cell phones,
PDA's or MP3 players) that use the texturized coatings according to
embodiments of the invention can still function when they are
immersed in electrolyte solutions. For example, flash memory drives
(USB sticks) were coated with the texturized films using methods
according to embodiments of the invention. The processed flash
memory drives were tested by immersing them in Gatorade.RTM.
(potassium phosphate+citric acid). A control sample shorted out in
2 seconds, while the test samples worked for up to 10 minutes while
being immersed in Gatorade.RTM..
[0051] As noted above, the texturized films according to
embodiments of the invention are thin. They can be less than about
5000 .ANG. (typically at 1000 .ANG.). A coating according to an
embodiment of the invention can be about 1/250.sup.th the thickness
of a conventional parylene conformal coating.
[0052] Embodiments of the invention can also include coatings with
specific properties. For example, a textured film according to an
embodiment of the invention can have one, two, or more of the
following properties in Table 1. A variety of different methods may
be used to make textured films with such properties. It is also
possible to tune one or more of the properties (e.g., the physical
abrasion characteristics or durability of a textured film).
TABLE-US-00002 TABLE 1 Textured Roughness 25 < RMS (nm) < 500
(Average roughness) Textured Coverage 25 < Coverage (%) < 60
(Average density) Textured Durability 10 < Force (micro-Newtons)
< 5000 (or 500) (Force) Thermodynamic <70 (Zisman Critical
angle) Surface Energy
[0053] The composition of the textured film can vary. Since the
conformal coating covers a conducting surface, a non-conducting
material is generally used. In preferred embodiments of the
invention, non-conducting particles are attached to a surface of a
conductor such as a metal base (e.g., a copper line or copper pad).
Suitable particles may comprise ceramics such as aluminum oxide,
titanium oxide, silicon oxide, etc. In other embodiments of the
invention, the particles that form the textured film can be organic
latex spheres.
[0054] A textured film according to an embodiment of the invention
can be produced according to any suitable process. For example, the
textured film can be created using a subtractive process (e.g.,
etching, creating pits, etc.) or an additive process. Preferred
embodiments use additive processes to create the textured
films.
[0055] Additive processes include liquid and vapor deposition
processes. In a liquid deposition process, particles can be
suspended in a liquid medium and can then be transported to the
surface to be treated using a spray technique. In other
embodiments, the textured film can be created using chemicals that
react in a gaseous state or with chemically modified surfaces to
create particles. The particles can then be transported to the
surface to be treated by Van der Waals forces, gravity, or by fluid
transport in a gas stream.
[0056] A textured film with a nano-structure can be created by a
variety of methods, including dry and wet processing. One dry
method is an atomic layer deposition reaction (ALD). Precursors for
creating many materials via ALD are known to the art. For alumina,
useful precursors include trimethylaluminum or TMA (Me.sub.3Al),
diethyl aluminum ethoxide (C.sub.2H.sub.5).sub.2AlOC.sub.2H.sub.2,
and tris(diethylamino)aluminum. For silica, useful precursors
include silicon tetrachloride (SiCl.sub.4),
Tretraethylorthosilicate (TEOS) (Si(OC.sub.2H.sub.5).sub.4) and
disilane (Si.sub.2H.sub.6). For titania, useful precursors include
Titanium Tretrachloride (TiCl.sub.4) and
tetrakis(dimethylamino)titanium (C.sub.8H.sub.24N.sub.4Ti).
Oxidizing agents such as ozone (O.sub.3), oxygen plasma, or water
vapor (H.sub.2O) are often used in such ALD processes. ALD is used
in many applications to obtain atomically smooth surfaces and/or
coatings having an atomically uniform thickness, but can also be
readily used to obtain rougher surfaces. (References: U.S. Pat. No.
6,426,4307. N. P. Kobayashi et al./Journal of Crystal Growth 299
(2007) 218-222, Sandia National Labs: LDRD Project 52523 Final
Report, Atomic Layer Deposition of Highly Conformal Tribological
Coatings--2005) CVD is used in many application can be used to
create alumina nano-particles as noted by the work of Kim.
(Reference: Kim et al, J. Material Engineering, (1991) 13:199-205)
More generally, vapor flow-through technologies may be used as dry
methods of creating textured film with a nano-structure.
[0057] Wet methods for obtaining a film with a nano-structure
include applying a suspension of particles in a solution to a
surface. Nanoparticles having specified properties can be
commercially obtained from a number of sources. One such source is
Nanophase Technologies Corp. of Romeoville, Ill.,
www.nanophase.com. Application methods for wet sprays can be
obtained from many several commercially sources such as Asymtek
(www.asymtek.com), PVA (www.pva.net) or Ultrasonic Systems
(www.ultraspray.com)
[0058] Surface coverage requirements can also be taken into
consideration. Textured film coverage on the surface to be treated
can be controlled by controlling the flux of the various media,
which creates the particles, and controlling the time of the
particle flux. Rough surfaces may not be sufficient to provide
protection for the printed circuit boards. In some instances, a
device coated with a textured film had a rough surface as measured
with an AFM (atomic force microscopy), but the device could still
failed from an ionic (electrical) leakage.
[0059] The AFM technique for measuring roughness (RMS=root mean
square) does not capture all relevant topographical information. In
addition to a desired RMS roughness, a textured film preferably has
a sufficiently wide coverage area on the surface to be treated. It
is possible to define this as the "surface coverage" or "density"
of the nano-particles in the textured film. In FIG. 2, three
different cases provide the same RMS value of roughness, but the
coverage needs to be greater than 6% (preferably greater than 20%)
before the textured coating is deemed suitable for protecting the
surface (in this application).
[0060] A textured film having porosity may be useful. It is
believed that porosity in the textured film may help prevent fluids
from reaching a protected surface by creating an air boundary layer
between any liquid and the conducting surface.
[0061] FIG. 2 shows a digital map that is used to calculate the
surface coverage. As shown, specific surface coverage values can be
desirable. FIG. 3 also shows additional surface coverage data.
[0062] In some embodiments, the particles in the textured film can
be attached to a surface to be treated using a "glue." The "glue"
can provide the textured film with durability. Use of a "glue" type
surface chemistry can bind particles together and can make the
textured film more durable. The "glue" may be referred to as linker
molecules or coupling agents. Preferred linker molecules include
silanes with a reactive group at both ends. Suitable chemistries
include the use of bi-functional linkers such as
bis-trichlorosilane-ethane, bis-trichlorosilane-butane,
bis-trichlorosilane-hexane, bis-trimethoxysilane-ethane,
bis-trimethoxysilane-butane, bis-trimethoxysilane-hexane,
bis-tris-dimethylaminosilane-ethane,
bis-tris-dimethylaminosilane-butane, and
bis-tris-dimethylaminosilane-hexane. Methoxy-ethoxy type linkers
are particularly suitable for wet chemistry processes.
Dimethyl-amines may be preferred in some situations over
chloro-silanes, because the reaction product is a non-corrosive
di-methyl-amine as opposed to HCl, which may be corrosive when
exposed to water.
[0063] Since the distance or geometric distance of the
nano-particles in relation to each other can vary, and a
combination of different linker chemistries can be used to improve
durability (e.g., molecules of different lengths can be used to
bind nano-particles together and/or to the surface to be treated).
Durability is desirable, since the nano-particles in the textured
film are preferably stable enough to adhere to the surface to be
treated and also to each other. Some nano-particle based films are
so porous or loosely bound that they self-disintegrate or dissolve
with the slightest disturbance (e.g., a light air-stream). The
durability of the texturized film can be controlled by controlling
the exposure time of the chosen linking chemistry to particles
which increases the number of binding sites between neighboring
particles.
[0064] It is also possible to vary the gluing process. For example,
a surface to be treated can be exposed to gluing chemistries, and
the nanoparticles can be deposited thereon. In an alternative
embodiment, the nano-particles themselves may be exposed to the
gluing chemistries and the resulting intermediate product may then
be bound to the surface to be treated.
[0065] Preferably, the nanoparticle may be pre-treated with
protected linker molecules prior to deposition. A "protected"
linker will not link with other nanoparticles or is reacted to
other surfaces during the deposition process. Then, after the
pre-treated nanoparticles are deposited, the linker molecules may
be deprotected, such that they link the nanoparticles to each other
and to the surface. Examples of "protected" nanoparticle
chemistries include pretreated particles with Isocyanates which can
be deposited to the surface and then deprotected (or activated)
using heat to form a urethane bond to the surface. In another
chemical system, nanoparticles are treated with a surface chemistry
containing Biotin and are reacted with Avidin terminations. Other
possible protected binary reactions would include Epoxides and
Amines.
[0066] In the case of electrical connectors in particular, the
durability of the texturized films is preferably low enough so one
electrical conductor can cut through the texturized film on the
other conductor. This allows the electrical conductors of the
connectors to contact each other and to electrically communicate
with each other. Low resistance connections between conductors can
increase the battery life of portable electronic devices and the
like.
[0067] FIG. 4 illustrates the durability of texturized films using
a Hysitron scanning probe. Here, the surface of an AFM probe tip is
scrubbed against a texturized film with a known force. In some
embodiments of the invention, if the tested film is contacted with
a force of about 10 .mu.Newtons, then the film may not be stable
enough. If the film is intact with a force with a force of 500
.mu.N, then the film may be too durable to break through, depending
on the specific application.
[0068] It is desirable to change the energy of the surface to be
treated such that the critical energy is within a desired range,
i.e., to provide a low surface energy coating. One way to do this
is to expose the surface to be treated to long change hydrocarbons.
Examples include but not limited to C8, C10, C11, C12, C14, and
C18. Such long chain hydrocarbons may be derived from alkyl silanes
(e.g., n-octyltriclohorosilane for C8). It is also possible to
expose a surface to be treated to long chain fluorocarbons.
Examples include FOTS FODCMS, or FDTS. Surface energy reduction can
also be achieved with a wide variety of chemical treatments
including the use of phosphonates or thiols. Alkyl-monomers and
perfluoroalkyl monomers may be used to treat the surface, and may
result in water contact angles greater than 135.degree.. Ring
structures, such as fluorinated or hydrogenated rings, may also be
used like Pentafluorophenyl-trichlorosilane
(C.sub.9H.sub.6F.sub.5Cl.sub.3Si).
[0069] Various methods may be used to apply materials to change the
surface energy. One method is by the application of a
self-assembling monolayer. Vapor application of a self-assembling
monolayer is described in W. Robert Ashurst et al., Journal of
MicroElectroMechanical Systems, Vol. 10, No. 1, March 2001 and W.
Robert Ashurst et al., IEEE Transactions on Device and Materials
Reliability, Vol. 3, No. 4, December 2003. See also R. Maboudian,
Surface Science Reports, 30 (1998) 2007-269. Molecular Vapor
Deposition (MVD.RTM.) of a self-assembling monolayer is described
in B. Kobrin, et al., SEMI Technical Symposium: Innovations in
Semiconductor Manufacturing (STS:ISM), 2004.
[0070] A preferred solution based process for forming a texturized
film according to an embodiment of the invention may include first
obtaining alumina powder. Alumina powder can be produced or
purchased from a supplier such as Nanophase Technologies. The
alumina powder may have particle sizes of about 40-60 nanometers
and may have a surface area of about 32-40 m.sup.2/gram.
[0071] After the alumina powder is obtained, about 40 mg of powder,
for example, can be dispersed in 10 ml of methanol. An ultrasonic
process can be used to ensure complete dispersion. Once dispersed,
the solution can be sprayed onto a substrate to be treated at about
80.degree. C. using a spray bottle or other spraying apparatus.
Additional dilution of the stock solution with methanol or other
solvent may be used to help control the thickness of the overall
textured film being deposited. The resulting roughness of the film
can be about 25 rms (nm), with coverage estimated at 25%. To
improve the durability of the textured film, the surface to be
treated can be exposed to bis-chlorosilane-ethane (vapor), before,
after, or while the alumina particles are attached to the surface.
The surface energy can be changed by exposing the surface to be
treated with FDTS (vapor) or by a 0.5% solution of C18 in
iso-octane.
[0072] A preferred vapor deposition process can use a vapor
deposition chamber. Process conditions can include heating TMA to
50.degree. C., which results in about 42 T of vapor pressure. Then,
water is heated to 40.degree. C., and a needle valve is adjusted so
that the vapor pressure is about 55 Torr. Then, the substrate to be
treated is exposed to the vapor of water and TMA sequentially for
15 seconds using an N.sub.2 carrier gas (used in part for
dilution). This water followed by TMA exposure can be repeated to
increase the thickness. Then, the nano-particles are exposed to
bis-chlorosilane-ethane (vapor) using a carrier gas. The injection
process can be conducted for 30 seconds. Then, the surface energy
can be changed with exposure to FDTS or FODCMS (vapor) using a
carrier gas, again for 1 minute. Exposure to
bis-chlorosilane-ethane increases the durability of the film as
more links are created between the nano-particles.
[0073] In an alternative method for making the texturized film, it
is possible to spray or shower the surface of a substrate with
nano-particles. The nano-particles embed in the surface and dry
leaving the desired texture (i.e., sand-blast roughening of the
surface.). A low surface energy coating is applied to the circuit
board. Other process variations include the use of other linker
chemistries such as those listed above.
[0074] Other chemistries can be used to lower the surface energy of
a surface. Examples are provided in FIG. 5.
[0075] Embodiments of the invention preferably include a textured
surface which has one or more, and preferably all, of the following
properties:
TABLE-US-00003 a) Film Roughness: 25 < RMS (nm) < 500
(Average roughness) b) Film Coverage: 25 < Coverage (%) < 60
(Average density) c) Film Durability: 10 < Force (.mu.-Newtons)
< 500 (Force) d) Surface Energy: 0 < Energy (Dyne/cm) < 70
(Zisman Critical angle)
[0076] FIG. 6 graphically shows other ranges for the four textured
film properties described above, when used to protect a printed
circuit board or other type of electrical apparatus.
[0077] The film can have a thickness that is less than about 5000
.ANG. or less than about 5 microns, and the film can be used to
protect printed circuit boards and other electrical assemblies from
ionic contamination.
[0078] FIG. 7 shows an apparatus that may be used to fabricate
coatings. Other apparatus may also be used. The apparatus includes
a chamber 710. A substrate holder 720 and gas dispersion rods 730
are disposed within the chamber. Gas dispersion rods 730 are
connected to various material sources through valves and tubes. The
material sources may be heated. A heated stainless steel cylinder
containing the precursor source 740, and a source of nitrogen
carrier gas 741 are connected to a gas dispersion rod 730 by tubes
742 and valves 743. A heated water source 750, and a source of
nitrogen carrier gas 751 are connected to a gas dispersion rod head
730 by tubes 752 and valves 753. A heated first precursor source
760, and a source of nitrogen carrier gas 761 are connected to a
gas dispersion rod 730 by tubes 762 and valves 763. A heated second
precursor source 770, and a source of nitrogen carrier gas 771 are
connected to a gas dispersion rod730 by tubes 772 and valves 773.
The specific material sources illustrated in FIG. 7, including the
carrier gas source, are by way of example, and other material
sources may be substituted or added. A vacuum pump 780, in
conjunction with tubes 781, valves 782, filter 783 and manometer
784 are also connected to chamber 710, and may be used to control
the pressure within chamber 710 and to remove reaction byproducts
and excess reagents from chamber 710. The apparatus of FIG. 7 is
particularly well suited for wet methods for obtaining a film with
a nano-structure.
[0079] A coating may be fabricated by placing a substrate,
including an electronic device or the like, to be coated on
substrate holder 720. The substrate may be exposed to various
materials in desired combinations and/or sequences in a controlled
manner by operating the valves of the apparatus of FIG. 7.
[0080] An in-line continuous spray system may also be used for wet
methods for obtaining a film with a nano-structure. In that type of
system, a substrate on a conveyor apparatus is passed sequentially
under a number of shower heads or similar spray apparatus, and is
exposed to different materials or combinations of materials by each
shower head. Commercial spray coating equipment is available for
Asymtek (www.asymtek.com), (www.asymtek.com), PVA (www.pva.net) or
Ultrasonic Systems (www.ultraspray.com).
[0081] FIG. 8 shows an apparatus that may be used to fabricate
coatings. Other apparatus may be used. The apparatus includes a
chamber 810. Chamber 810 includes inlet tubes 820 through which gas
may be introduced into chamber 810. Inlet tubes 820 may be
connected to various material sources using connections know to the
art. Chamber 810 may be subjected to a vacuum using apparatus and
techniques known to the art. The apparatus of FIG. 8 is
particularly well suited for vapor deposition methods for obtaining
a film with a nano-structure.
[0082] Some desirable terms may include the following.
[0083] Film coverage definition: using a digital map to represent
the surface topography and surface density. As quantified herein
for purposes of defining which films have sufficient coverage, a
digital map similar to that shown in FIG. 2 may be generated for
any given surface. These areas are shown, for example, as black in
FIG. 2. Thus, a surface having few large protrusions may have a
surface roughness similar to that of a surface having many smaller
protrusions, but the surface with many smaller protrusions may have
a significantly greater coverage, as illustrated in FIG. 2.
[0084] IMAGE.J Software (versions 1.38) was used for computing the
digital surface coverage. ImageJ is a public domain, Java-based
image processing program developed at the National Institutes of
Health and is available on the internet. The source code has been
published by the NIH.
[0085] The following procedure was used to compute the digital
surface coverage. [0086] 1) Take the SEM image [0087] 2) Open the
image file in Image J software [0088] 3) Set scale in Image J to
match with scalebar (this allows for calculation of sizes in actual
physical units, as opposed to pixels) [0089] 4) Convert the image
to binary. The surface roughness now shows as black . . .
everything else is white. [0090] 5) Select the region of the image
that includes everything above the scale bar (including the scale
bar will cause erroneous calculations). Analyze the area--this
represents the total surface area (Call this number "A") [0091] 6)
Analyze particles, from 0 to infinity size. This counts all
particles, and calculates their individual areas. Copy and paste
the results into Excel. [0092] 7) Add up all the areas of the
particles. Call this number "B" [0093] 8) "B/A" represents the
fraction of the total surface that is occupied by particles. [0094]
9) The threshold is set using the publish Isodata Algorithm [T. W.
Ridler, S. Calvard, Picture thresholding using an iterative
selection method, IEEE Trans. System, Man and Cybernetics, SMC-8
(1978) 630-632.] which is included in the version 1.38 software
package. In the Isodata Algorithm, the procedure divides the image
into objects and background by taking an initial threshold, then
the averages of the pixels at or below the threshold and pixels
above are computed. The averages of those two values are computed,
the threshold is incremented and the process is repeated until the
threshold is larger than the composite average.
[0095] Film Durability: The film is subjected to testing in a
Hysitron scanning probe. A 1 .mu.m radius conical stylus with a
controlled reciprocating scratch with 100 cycles, a length of 3
.mu.m, at a rate of four seconds is applied to the film. The normal
load for these tests was 10 to 500 .mu.N. A profile map of the
scanned area shows if the film is still present or is removed.
Films which were removed with a 10 .mu.N load were observed to lack
coherence. These films could be easily removed or "blown away" or
would be removed by gravity. Films which were still present with a
500 .mu.N force are very durable and would not be removed from a
connector surface under normal contact pressures which would lead
to electrical conduction issues.
[0096] This texturized surface or conformal coating can include any
non-conductive material. Such materials include metal oxides such
as (aluminum oxide, titanium oxide, and silicon oxide). Other
materials may include organic latex spheres or other media. A
conformal coating with the above-described properties can suppress
electrical leakage from circuit leads by creating an ionic
barrier.
[0097] The above description is illustrative and is not
restrictive. Many variations of the invention will become apparent
to those skilled in the art upon review of the disclosure. The
scope of the invention should, therefore, be determined not with
reference to the above description, but instead should be
determined with reference to the pending claims along with their
full scope or equivalents. For example, while some examples may be
given with respect to a particular device or substrate,
[0098] One or more features from any embodiment may be combined
with one or more features of any other embodiment without departing
from the scope of the invention.
[0099] A recitation of "a", "an" or "the" is intended to mean "one
or more" unless specifically indicated to the contrary.
[0100] All patents, patent applications, publications, and
descriptions mentioned above are herein incorporated by reference
in their entirety for all purposes. None is admitted to be prior
art.
Experimental
[0101] For a Vapor deposition coating process: Nano-particles were
created using chemical reactions which consist of two self-limiting
process steps. The use of sequential chemical reactions ensures the
proper reaction at the surface. For alumina particles, the overall
reaction is.
2Al(CH.sub.3).sub.3+3H.sub.2O.fwdarw.Al.sub.2O.sub.3+6CH.sub.4
The two self-limiting process steps, which are surface reactions,
are: [0102] Surface Reaction #1:
2AlOH+2Al(CH.sub.3).sub.3=>2[Al--O--Al(CH.sub.3).sub.2]+2CH.sub.4
[0103] Surface Reaction #2:
2[Al--O--Al(CH.sub.3).sub.2]+3H.sub.2O=>Al.sub.2O.sub.3+2AlOH+4CH.sub.-
4
[0104] To impart durability into the film, a bi-functional linker
is applied to the particles. By introducing more linking agents,
the cohesion between the nano-particles is increased. To impart
super-hydrophobic qualities to a surface, we then apply an
organosilane-based self-assembled monolayer (SAM) that forms a
covalent bond nano-structure.
[0105] An example of an ALD process recipe is shown below in Table
3. The value of "1" indicates that the valve in the corresponding
vacuum diagram (FIG. 7) is open.
TABLE-US-00004 TABLE 3 Slow Note Step Time Gas 1 N2 1 Gas 2 N2 2
Gas 3 N2 3 Gas 4 N2 4 ISO ISO Vent Pump Down 1 60 1 Particle-Set-Up
#1 2 5 1 1 Water Injection 3 15 1 1 Purge #1 4 10 1 1 Metal
Precursor Setup 5 5 1 1 TMA Injection 6 15 1 1 React #1 7 15 1 1
Particle-Set-Up #2 8 5 1 1 Water Injection 9 15 1 1 Purge #2 10 10
1 1 Metal Precursor Setup 11 5 1 1 TMA Injection 12 15 1 1 React #2
13 15 1 1 Linker Treatment 14 5 1 1 Linker Chemistry Injection 15
30 1 1 Purge #4 16 10 1 Reaction 17 60 1 1 Set-Up Surface Treatment
18 5 1 1 Surface Treatment Injection 19 60 1 1 Reaction 20 60 Purge
21 30 1 Chamber Vent 22 260 1
[0106] Alternatives to the process include increasing or decreasing
the times of the chemical injection times. The water injection time
(Step #3 and Step #9 in the above Table) can vary from 1 to 30
seconds. The TMA or precursor injection time (Step #5 and Step #12)
can vary from 1 to 30 seconds. The purge times (Step #4, Step #10,
Step #16, Step #21) can be increased to decreased to control the
mixing of the residual vapors. As the purge time is increased, the
concentration of the adsorbed vapors onto the surface is reduced
which reduces the surface reactions and the number of
nano-particles. The above reaction was performed at pressure
between 1 torr to 100 torr. The temperature of the reaction was
performed at 35 C. By controlling the temperature, pressure, time,
and the timing sequence, the size and number of nano-particles can
be influenced. The timing and order of the linker chemistry
injection will affect the durability of the nano-composite
produced.
[0107] For a wet spray process: Alumina oxide particles with a
surface area of 3-5 meter.sup.2/gram and with a particle size
distribution between 40 to 60 nm were commercially purchased. A
solution of consisting of 40 mg of alumina powder was added to 10
ml of methanol. The solution was sonicated to insure complete
dispersion. The solution was sprayed onto the substrate @80.degree.
C. using a artist airbrush. Additional dilution of the stock
solution with methanol or other solvent can help control the
thickness of the overall textured film being deposited. Improve
durability with exposure to Bis-Chlorosilane-ethane (vapor). Change
surface energy with exposure to FDTS (vapor) or C18 in a solution
of iso-octane or hexane.
EXAMPLE 1
[0108] In FIG. 4A, the recipe shown in Table-3 using steps 1
through 13, 18 through 22 were used. The surface treatment
chemistry in Step #19 was FDTS. A wear load of 10 .mu.N was
applied. The AFM image shows that the nano-particles (texture) were
pushed around indicating the particles were loosely coherent or
just laying on the surface. In FIG. 4B, the deposition recipe shown
in Table-3 using steps 1 through 22 were used. The linker chemistry
in Step #15 was Bis-trichlorosilane-Ethane and the surface
treatment chemistry in Step #19 was FDTS. A wear load of 10 .mu.N
was used. The nano-particles were adherent of the surface and were
not pushed around by the loaded stylist. In FIG. 4C, the recipe
shown above using steps 1 through 22 were used expect the wear load
was increased to 50 .mu.N. The process recipe used for FIG. 4B was
used. The nano-film was completely removed.
EXAMPLE 2
[0109] A printed circuit board with various coatings are shown in
FIG. 9. The circuit boards consists of an inter-digitated comb
structures specifically designed for testing reliability after a
high temperature bake. The test boards were exposed to
Gatorade.RTM., which is an ionic solution that includes potassium
phosphate and citric acid. The contact angle of the Gatorade.RTM.
on each coating was measured by using a Rame-Hart Goniometer.
Contact angles were as follows: Example 1A, 70.degree.; Example 1B,
70.degree.; Example 1C, 110.degree.; Example 1D,
>165.degree..
EXAMPLE 2A
[0110] A printed circuit board of Example 2 shown in FIG. 9
consists a inter-digitated comb structures used for testing
reliability was provided, without any treatment. When the board is
exposed to Gatorade.RTM., the surface wets and dries with a
potassium phosphate/sugar residue. These residues result in
leakages between the inter-digitated surface wiring of the printed
circuit board.
EXAMPLE 2B
[0111] The printed circuit board of Example 2 was coated with
alumina particles having a diameter of approximately 40 to 60 nm.
The coating was performed via by a process of TMA and Water with a
recipe shown in Table 3 using steps 1 through 13. The contact angle
of a Gatorade.RTM. solution was .about.70 degrees. The solution
adheres to the surface and dries with a residue.
EXAMPLE 2C
[0112] A printed circuit board similar to Example 2A but
subsequently coated with a hydrophobic coat of FDTS (Step #19) with
a recipe shown in Table-3 using steps #18 through #22. The contact
angle of a Gatorade.RTM. solution was .about.110 degrees. The
Gatorade.RTM. solution would "bead-up" in clumps but when dried,
residues were still observed.
EXAMPLE 2D
[0113] The printed circuit board Example 2A was further treated by
applying alumina particles using a CVD reaction of TMA and Water
(Table #3, Steps #1 to Step #13) followed by a surface treatment of
FDTS (Steps #18 to #22). The Gatorade.RTM. contact angle was
>165 degrees. The surface does not wet and no residues were
observed. No electrical leakage could be measured using a
resistance Ohm meter.
EXAMPLE 3
[0114] Several samples were prepared by depositing alumina
particles over a 50.times.50 micron square and then treating with
FODCMS. These samples show how surface roughness and low surface
energy add to anti-wetting properties and ionic contamination
control.
EXAMPLE 3A
[0115] Alumina particles having a diameter of 40 to 60 nm were
deposited over a Silicon substrate by a recipe shown in Table 3.
BCTSE was used as the linker agent in Step #15 and FODCMS was used
as a low surface energy coating in Step #19. The resultant film is
illustrated in FIG. 10A, and was measured as having an average
roughness of 9.63 nm, an RMS roughness of 15.66 nm and a ten points
height of 280.72 nm. A water contact angle of 130.degree. was
observed.
EXAMPLE 3B
[0116] A sample was prepared using a method similar to that of
Example 3A, except the water injection time was increased two
times. The resultant film is illustrated in FIG. 10B, and was
measured as having an average roughness of 31.62 nm, an RMS
roughness of 40.77 nm, and a ten points height of 393.54 nm. A
water contact angle of 140.degree. was observed. As the surface
roughness increases, the contact angle increased.
EXAMPLE 3C
[0117] A sample was prepared using a method similar to that of
Example 3A, except the water injection was increased 4 times. The
resultant film is illustrated in FIG. 10C, and was measured as
having an average roughness of 43.43 nm, an RMS roughness of 55.17
nm, and a ten points height of 485.04 nm. The water contact angle
of >165.degree. was observed. When the surface roughness
increased further, the anti-wetting properties were observed.
EXAMPLE 4
[0118] Example 4 shows a USB 512 MB memory, both uncoated and
coated. FIG. 11A shows the USB 512 MB memory having a 1500 micron
pitch and 500 micron spacing between the leads. If the film
thickness plus the film's roughness is greater than 1/2 the
distance between the spacing, there is a potential for electrical
shorting. Thus the film thickness is preferably much less than the
spacing between the minimum features size.
EXAMPLE 4A
[0119] Gatorade.RTM. was applied to the USB 512 MB memory as
received. A water contact angle of <40.degree. was measured.
FIG. 11B shows the uncoated USB 512 MB memory at a greater
magnification than that of FIG. 11A. Gatorade.RTM. completely wets
the electrical circuit and any residuals between the electrical
leads from a drying solution could potential cause leakage
pathways.
EXAMPLE 4B
[0120] A USB 512 MB memory was treated per the recipe of Table 1
Steps #1 to 22. The linker chemistry in Step #15 was
Bis-trichlorosilane-ethane and the surface treatment chemistry in
Step #19 was FDTS. The alumina nano-particles were .about.40
.mu.m-60 .mu.m in size. A water contact angle of >165.degree.
was measured. FIG. 11C shows the coated USB 512 MB memory at the
same magnification as that of FIG. 11B. The coating is not visible.
No liquids were observed to adhere to the surface and accumulated
on the surface or between electrical leads.
EXAMPLE 5
[0121] Several samples were prepared, each using the same alumina
particles, linker molecules, and low surface energy coating. The
linker chemistry was Bis-Trichlorosilane-ethane and the surface
treatment chemistry was FODCMS. The differences were in the
parameters used to deposit the alumina particles, resulting in
different surface roughnesses.
EXAMPLE 5A
[0122] The deposition parameters were similar to Table 3. The
result is shown in FIG. 12, and has a RMS surface roughness of 15
nm. A water contact angle of 130.degree. was observed. FIGS. 12A,
12B, 12C and 12D are the same sample at different magnifications,
x2,700, x3,500, x20,000 and x65,000 respectively.
EXAMPLE 5B
[0123] The deposition parameters were similar to Table 3 but the
water vapor injection time during the coating process was increased
by 2 times. The result is shown in FIG. 13, and has a RMS surface
roughness of 55 nm. A water contact angle of >160.degree. was
observed. FIGS. 13A, 13B, 13C and 13D are the same sample at
different magnifications, x2,700, x3,500, x20,000 and x65,000
respectively. The increased surface roughness and density can be
observed.
[0124] FIG. 14 shows a scanning electron micrograph (SEM) of a
cross section of a sample similar to that illustrated in FIG.
13.
EXAMPLE 6
[0125] Critical surface tension was measured from four (4)
different surface coatings used to reduce the surface energy. The
measurement was performed by depositing a layer of the material on
a polished silicon surface. Table 2 shows the results. The "Contact
Angle" was measured using DI water. The contact angle was also
measured on alumina particles and measured it the resulting contact
angle was greater than 135 degrees. It was observed that if the
critical surface tension was >75 Dyne/cm, a contact angle
greater than 135 degrees could not be achieved and the film did not
exhibit an ionic barrier.
TABLE-US-00005 TABLE 2 SURFACE ENERGY WITH ROUGHNESS Critical
Contact Angle > Does it Chemistry Surface Tension* 135.degree.
Work? DDMS >75 dyne/cm NO NO (Dichlorodimethylsilane)
(Hydro-carbon) FDTS 15-20 dyne/cm YES YES (Perfluoronated) OTS
(C18) 20-25 dyne/cm YES YES (Hydro-carbon) Octyl-saline (C8) 25-35
dyne/cm YES YES (Hydro-carbon) *Critical Surface Tension measured
on polished silicon surface
EXAMPLE 7
[0126] A protective film was formed by a wet process as shown in
FIG. 15.
[0127] First, a silicon substrate was sprayed with a mixture of
alumina particles about 40 nm in diameter, suspended in methanol
and water, 0.5 wt % alumina in a solution of 1000 (volume)
methanol: 100 (volume) water. The surface was heated to 80.degree.
C. during the spray using an artist airbrush. The surface in FIG.
15B was subsequently treated with Bis-trichlorosilane-ethane vapor
coating followed by C18 in a solution. The final surface had a RMS
surface roughness of 25 nm, and a contact angle of about
135.degree. for water.
EXAMPLE 8
[0128] Films with improved durability were formed by exposing the
nano-particles to a linker chemistry.
EXAMPLE 8A
[0129] A film was formed by a process similar to Example 7. The
film was subjected to a mechanical scratch test by sliding the
surface of Teflon tweezers over the substrate. The result is
illustrated in FIG. 15A, showing that the film was removed where
scratched.
EXAMPLE 8B
[0130] A film was formed using a process similar to that of Example
8A, except nano-particles are exposed to Bis-Trichlorosilane-Ethane
after the formation of the nano-particles onto the surface and
before the surface treatment. The film was subjected to the same
scratch test described in Example 8A. The result is illustrated in
FIG. 15B, showing an improved film durability.
EXAMPLE 9
[0131] A sample was prepared using a method similar to that
described in Table 3.
EXAMPLE 9A
[0132] The resultant film is illustrated in FIG. 3A (a SEM
photograph) and FIG. 3B (a digitized image showing black where film
roughness protrudes from the surface. The film had a RMS roughness
of 9 nm. Based on FIG. 3B, the film has a coverage of 2.51
.mu.m.sup.2 over an area of 26.43 .mu.m.sup.2, for a film coverage
of 9.32%. This coating did not exhibit ionic barrier
properties.
EXAMPLE 9B
[0133] The resultant film is illustrated in FIG. 3C (a SEM
photograph) and FIG. 3D (a digitized image showing black where the
film roughness protrudes from the surface. The film had a RMS
roughness of .about.35 nm. Based on FIG. 3D, the film has a
coverage of 8.84 .mu.m.sup.2 over an area of 26.88 .mu.m.sup.2, for
a film coverage of 32.88%. This coating does exhibit ionic barrier
properties.
EXAMPLE 9C
[0134] The resultant film is illustrated in FIG. 3E (a SEM
photograph) and FIG. 3F (a digitized image showing black where the
film roughness protrudes from the surface. The film had a RMS
roughness of 30 mm. Based on FIG. 3F, the film has a coverage of
8.94 .mu.m.sup.2 over an area of 26.62 .mu.m.sup.2, for a film
coverage of 8.94%. This coating does not exhibit the ionic barrier
properties.
EXAMPLE 10A
[0135] A film was formed by the recipe shown in Table 3 using steps
1 through 13, 18 through 22 were used. The water injection time in
Step #3 and Step #9 was 30'' and surface treatment chemistry in
Step #19 was FODCMS.
[0136] The resultant film is illustrated in FIG. 16A (a SEM
photograph) and FIG. 16B (a digitized image showing black where the
film roughness protrudes from the surface. The film had a RMS
roughness of .about.50 nm. Based on FIG. 16A, the film has a
coverage of 296.08 .mu.m.sup.2 over an area of 899.99 .mu.m.sup.2,
for a film coverage of 32.92%.
EXAMPLE 10B
[0137] In FIG. 16B, the digital image of the SEM photograph is
shown which is converted to have a coverage of 296.08 .mu.m.sup.2
over an area of 899.99 .mu.m.sup.2, for a film coverage of
32.92%.
[0138] A higher resolution SEM of the same sample in FIG. 16A is
shown in FIG. 16C. In FIG. 16D (a digitized image showing black
where the film roughness protrudes from the surface). The film had
a RMS roughness of .about.50 nm Based on FIG. 16D, the film has a
coverage of 0.776 .mu.m.sup.2 over an area of 2.63 .mu.m.sup.2, for
a film coverage of 29.5%. This illustrates that the IMAGEJ digital
conversion process is independent of the magnification.
EXAMPLE 11A
[0139] A film was formed by the recipe shown in Table-3 using steps
1 through 13, 18 through 22 were used. The surface treatment
chemistry was FDTS in Step #19.
[0140] The resultant film was subjected to durability testing using
a Hysitron scanning probe. The film was subject to scrubbing from
the scanning probe with a force of 10 .mu.N. A 1 .mu.m radius
conical stylus with a controlled reciprocating scratch with 100
cycles, a length of 3 .mu.m, at a rate of four seconds is applied
to the film. The result is shown in FIG. 17A. The film was almost
entirely removed in the area subjected to testing.
EXAMPLE 11B
[0141] A film was formed by the process of EXAMPLE 11A using steps
#1 through step #22. The linker chemistry used in Step #15 was
Bis-Trichlorosilane-ethane.
[0142] The resultant film was subjected to the same testing as that
of Example 11A. The result is shown in FIG. 17B. While some
deterioration is observed in the tested area, the film is still
intact.
EXAMPLE 11C
[0143] A film was formed by the process of EXAMPLE 11A using steps
#1 through step #22. The linker chemistry used in Step #15 was
Bis-Trichlorosilane-ethane.
[0144] The film was subject to the same testing as that of Example
11A, but the applied pressure was 50 .mu.mN. The result is shown in
FIG. 17C. The film was entirely removed in the area subjected to
pressure.
* * * * *
References