U.S. patent application number 11/220360 was filed with the patent office on 2006-02-16 for tray carrier with ultraphobic surfaces.
This patent application is currently assigned to Entegris, Inc.. Invention is credited to Charles W. Extrand.
Application Number | 20060032781 11/220360 |
Document ID | / |
Family ID | 33162174 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060032781 |
Kind Code |
A1 |
Extrand; Charles W. |
February 16, 2006 |
Tray carrier with ultraphobic surfaces
Abstract
A tray carrier with ultraphobic surfaces for promoting more
effective cleaning and drying of the tray carrier. In the
invention, entire surfaces or portions of surfaces of a tray
carrier are made ultraphobic. The ultraphobic surfaces of the tray
carrier cause liquids that may come in contact with the surface,
such as may be used in cleaning, to quickly and easily "roll off"
without leaving a liquid film or substantial quantity of liquid
droplets. As a result, less time and energy is expended in drying
the surfaces, and redeposited residue is minimized, thereby
improving overall process quality and facilitating economical reuse
of the tray carrier. In addition, the ultraphobic surfaces may be
resistant to initial deposition of contaminants, where the
contaminants may be in liquid or vapor form.
Inventors: |
Extrand; Charles W.;
(Minneapolis, MN) |
Correspondence
Address: |
Patterson, Thuente, Skaar & Christensen, P.A.
4800 IDS Center
80 South 8th Street
Minneapolis
MN
55402-2100
US
|
Assignee: |
Entegris, Inc.
|
Family ID: |
33162174 |
Appl. No.: |
11/220360 |
Filed: |
September 6, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10454740 |
Jun 3, 2003 |
6938774 |
|
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11220360 |
Sep 6, 2005 |
|
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60462963 |
Apr 15, 2003 |
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Current U.S.
Class: |
206/564 ;
206/454; 206/711; 211/41.18 |
Current CPC
Class: |
B01L 2300/166 20130101;
B01L 13/02 20190801; B65G 2201/0258 20130101; B08B 17/06 20130101;
B01L 3/5027 20130101; B01L 9/52 20130101; F15D 1/065 20130101; B08B
17/065 20130101; B01L 9/527 20130101; B01L 3/502707 20130101 |
Class at
Publication: |
206/564 ;
206/454; 206/711; 211/041.18 |
International
Class: |
A47G 19/08 20060101
A47G019/08; B65D 85/48 20060101 B65D085/48; B65D 1/34 20060101
B65D001/34; B65D 85/00 20060101 B65D085/00 |
Claims
1. A tray carrier for articles comprising: a body having a
substrate portion with a surface, at least a portion of said
surface having a multiplicity of substantially uniformly shaped
asperities thereon to form an ultraphobic surface, each asperity
having a common asperity rise angle relative to the substrate
portion, the asperities positioned so that the ultraphobic surface
defines a contact line density measured in meters of contact line
per square meter of surface area equal to or greater than a contact
line density value ".LAMBDA..sub.L" determined according to the
formula: .LAMBDA. L = - P .gamma.cos .function. ( .theta. a , 0 +
.omega. - 90 .times. .degree. ) ##EQU10## where .gamma. is the
surface tension of a liquid in contact with the surface in Newtons
per meter, .theta..sub.a,0 is the experimentally measured true
advancing contact angle of the liquid on the asperity material in
degrees, .omega. is the asperity rise angle in degrees, and P is a
predetermined liquid pressure value in kilograms per meter, wherein
the ultraphobic surface exhibits a liquid-solid-gas interface with
the liquid at liquid pressures up to and including the
predetermined liquid pressure value.
2. The tray carrier of claim 1, wherein the body has a plurality of
pockets, each pocket adapted to receive a component.
3. The carrier of claim 1, wherein the asperities are
projections.
4. The carrier of claim 3, wherein the asperities are polyhedrally
shaped.
5. The carrier of claim 3, wherein each asperity has a generally
square transverse cross-section.
6. The carrier of claim 3, wherein the asperities are cylindrical
or cylindroidally shaped.
7. The carrier of claim 1, wherein the asperities are cavities
formed in the substrate.
8. The carrier of claim 1, wherein the asperities are positioned in
a substantially uniform array.
9. The carrier of claim 8, wherein the asperities are positioned in
a rectangular array.
10. The carrier of claim 1, wherein the asperities have a
substantially uniform asperity height relative to the substrate
portion, and wherein the asperity height is greater than a critical
asperity height value "Z.sub.c" in meters determined according to
the formula: Z c = d .function. ( 1 - cos .function. ( .theta. a ,
0 + .omega. - 180 .times. .degree. ) ) 2 .times. sin .function. (
.theta. a , 0 + .omega. - 180 .times. .degree. ) ##EQU11## where d
is the distance in meters between adjacent asperities,
.theta..sub.a,0 is the experimentally measured true advancing
contact angle of the liquid on the asperity material in degrees,
and .omega. is the asperity rise angle in degrees.
11. A process of making a tray carrier with an ultraphobic surface
portion, the process comprising: providing a tray carrier including
a substrate having an outer surface; and forming a multiplicity of
substantially uniformly shaped asperities on the outer surface of
the substrate, each asperity having a common asperity rise angle
relative to the substrate portion, the asperities positioned so
that the surface has a contact line density measured in meters of
contact line per square meter of surface area equal to or greater
than a contact line density value ".LAMBDA..sub.L" determined
according to the formula: .LAMBDA. L = - P .gamma. .times. .times.
cos .function. ( .theta. a , 0 + .omega. - 90 .times. .degree. )
##EQU12## where .gamma. is the surface tension of a liquid in
contact with the surface in Newtons per meter, .theta..sub.a,0 is
the experimentally measured true advancing contact angle of the
liquid on the asperity material in degrees, .omega. is the asperity
rise angle in degrees, and P is a predetermined liquid pressure
value in kilograms per meter, wherein the ultraphobic surface
exhibits a liquid-solid-gas interface with the liquid at liquid
pressures up to and including the predetermined liquid pressure
value.
12. The process of claim 11, wherein the asperities are formed by
photolithography.
13. The process of claim 11, wherein the asperities are formed by a
process selected from the group consisting of nanomachining,
microstamping, microcontact printing, self-assembling metal colloid
monolayers, atomic force microscopy nanomachining, sol-gel molding,
self-assembled monolayer directed patterning, chemical etching,
sol-gel stamping, printing with colloidal inks, and disposing a
layer of parallel carbon nanotubes on the substrate.
14. A process for producing a tray carrier having a surface with
ultraphobic properties at liquid pressures up to a predetermined
pressure value, the process comprising: selecting an asperity rise
angle; determining a critical contact line density ".LAMBDA..sub.L"
value according to the formula: .LAMBDA. L = - P .gamma. .times.
.times. cos .function. ( .theta. a , 0 + .omega. - 90 .times.
.degree. ) ##EQU13## where P is the predetermined pressure value,
.gamma. is the surface tension of the liquid, .theta..sub.a,0 is
the experimentally measured true advancing contact angle of the
liquid on the asperity material in degrees, and .omega. is the
asperity rise angle; providing a carrier with a substrate portion;
and forming a multiplicity of projecting asperities on the
substrate portion so that the surface has an actual contact line
density equal to or greater than the critical contact line
density.
15. The process of claim 14, wherein the asperities are formed
using photolithography.
16. The process of claim 14, wherein the asperities are formed
using wherein the asperities are formed using nanomachining,
microstamping, microcontact printing, self-assembling metal colloid
monolayers, atomic force microscopy nanomachining, sol-gel molding,
self-assembled monolayer directed patterning, chemical etching,
sol-gel stamping, printing with colloidal inks, or by disposing a
layer of parallel carbon nanotubes on the substrate.
17. The process of claim 14, further comprising the step of
selecting a geometrical shape for the asperities.
18. The process of claim 14, further comprising the step of
selecting an array pattern for the asperities.
19. The process of claim 14, further comprising the steps of
selecting at least one dimension for the asperities and determining
at least one other dimension for the asperities using an equation
for contact line density.
20. The process of claim 14, further comprising the step of
determining a critical asperity height value "Z.sub.c" in meters
according to the formula: Z c = d .function. ( 1 - cos .function. (
.theta. a , 0 + .omega. - 180 .times. .degree. ) ) 2 .times. sin
.function. ( .theta. a , 0 + .omega. - 180 .times. .degree. )
##EQU14## where d is the distance in meters between adjacent
asperities, .theta..sub.a,0 is the true advancing contact angle of
the liquid on the surface in degrees, and .omega. is the asperity
rise angle in degrees.
21. A tray carrier for articles comprising: a body having a
substrate and a polymer outer layer on the substrate, the outer
layer having a surface with a multiplicity of asperities thereon
forming an ultraphobic surface for contacting a liquid, the
asperities distributed so that the surface has an average contact
line density equal to or greater than a critical contact line
density value, and wherein the ultraphobic surface exhibits a
liquid-solid-gas interface with the liquid at liquid pressures up
to and including a predetermined liquid pressure value.
22. The carrier of claim 21, wherein the critical contact line
density value ".LAMBDA..sub.L" is determined according to the
formula: .LAMBDA. L = - P .gamma. .times. .times. cos .function. (
.theta. a , 0 + .omega. - 90 .times. .degree. ) ##EQU15## where
.gamma. is the surface tension of a liquid in contact with the
surface in Newtons per meter, .theta..sub.a,0 is the experimentally
measured true advancing contact angle of the liquid on the asperity
material in degrees, .omega. is the asperity rise angle in degrees,
and P is the predetermined liquid pressure value in kilograms per
meter.
23. The carrier of claim 21, wherein the liquid contacting the
surface is in the form of droplets, and the critical contact line
density ".LAMBDA..sub.L" is determined according to the formula:
.LAMBDA. L = - .rho. .times. .times. g .function. ( V ) 1 3 .times.
( ( ( 1 - cos .times. .times. .theta. a ) sin .times. .times.
.theta. a ) .times. ( 3 + ( ( 1 - cos .times. .times. .theta. a )
sin .times. .times. .theta. a ) 2 ) ) 2 3 ( 36 .times. .times. .pi.
) 1 3 .times. .gamma. .times. .times. cos .function. ( .theta. a ,
0 + .omega. - 90 .times. .degree. ) , ##EQU16## where V is the
volume of the droplet in cubic meters, g is the density (.rho.) of
the liquid in kilograms per cubic meter, (g) is the acceleration
due to gravity in meters per second squared, (h) is the depth of
the liquid in meters, (.gamma.) is the surface tension of the
liquid in Newtons per meter, .omega. is the average rise angle of
the side of the asperities relative to the substrate in degrees,
.theta..sub.a is the apparent advancing contact angle of the
droplet on the surface, and (.theta..sub.a,0) is the experimentally
measured true advancing contact angle of the liquid on the asperity
material in degrees.
24. The carrier of claim 21, wherein the polymer outer layer
includes a fluoropolymer.
25. The carrier of claim 21, wherein the polymer outer layer
includes alkylketene dimer.
26. A process of making a tray carrier with an ultraphobic surface
portion, the process comprising: providing a tray carrier including
a substrate having an outer surface; and forming the ultraphobic
surface portion by depositing a layer of polymer material on the
outer surface using a chemical vapor deposition process, the layer
of polymer material having an outer surface with a multiplicity of
asperities, the asperities distributed so that the ultraphobic
surface has a contact line density measured in meters of contact
line per square meter of surface area equal to or greater than a
critical contact line density value, wherein the ultraphobic
surface exhibits a liquid-solid-gas interface with the liquid at
liquid pressures up to and including a predetermined liquid
pressure value.
27. The process of claim 26, wherein the critical contact line
density value ".LAMBDA..sub.L" is determined according to the
formula: .LAMBDA. L = - P .gamma. .times. .times. cos .function. (
.theta. a , 0 + .omega. - 90 .times. .degree. ) ##EQU17## where
.gamma. is the surface tension of a liquid in contact with the
surface in Newtons per meter, .theta..sub.a,0 is the experimentally
measured true advancing contact angle of the liquid on the asperity
material in degrees, .omega. is the asperity rise angle in degrees,
and P is the predetermined liquid pressure value in kilograms per
meter.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. patent
application Ser. No. 10/454,740, entitled "Tray carrier With
Ultraphobic Surfaces", filed Jun. 3, 2003, and U.S. Provisional
Patent Application Ser. No. 60/462963, entitled "Ultraphobic
Surface for High Pressure Liquids", filed Apr. 15, 2003, hereby
fully incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to tray carriers for
delicate electronic components, and more particularly to a tray
carrier having ultrahydrophobic or ultralyophobic surfaces formed
thereon.
BACKGROUND OF THE INVENTION
[0003] Trays are used in the micro-electronic industry for storing,
transporting, fabricating, and generally holding small components
such as, but not limited to, semi-conductor chips, ferrite heads,
magnetic resonant read heads, thin film heads, bare dies, bump
dies, substrates, optical devices, laser diodes, preforms, and
miscellaneous mechanical articles such as springs and lenses.
[0004] Semi-conductor chips (chips) are illustrative of the issues
associated with handling the above-defined components.
Semi-conductor chips are very small electronic devices which, for
purposes of economy and scale, are manufactured en-masse from a
larger semi-conductor wafer (wafer). Typically, a single wafer will
yield several tens or hundreds of chips. Often, after the wafer has
been segmented into individual chips, additional processing is
necessary. This usually entails transporting a plurality of chips
from one workstation to another for processing by specialized
equipment.
[0005] To facilitate processing of chips on a large scale,
specialized carriers called matrix trays (trays) have been
developed. These trays are designed to hold a plurality of chips in
individual processing cells or pockets arranged in a matrix or
grid. The size of the matrix or grid can range from two to several
hundred, depending upon the size of the chips to be processed.
Examples of specialized chip carriers are disclosed in U.S. Pat.
Nos. 6,079,565 and 5,791,486 assigned to the owner of the present
invention, and which are hereby fully incorporated herein by
reference.
[0006] Electronic device fabrication processes, particularly where
semiconductors are involved, are often extremely sensitive to
contamination. Contamination and contaminants can be generated in
many different ways. For example, particulates can be generated
mechanically by wafers as they are processed, or they can be
generated chemically in reaction to different processing fluids.
Contamination can also be the result of out-gassing from chemical
fabrication processes, or biological in nature due to human
activity.
[0007] As a tray carrier is used through a fabrication process, it
will generally accumulate some amount of contamination. After use,
the carrier may be discarded or recycled, or the contamination may
be cleaned off and the carrier reused. In the past, cleaning of
tray carriers has often been considered uneconomical in view of the
relatively low cost of new tray carriers and the relatively high
cost and difficulty of cleaning and reusing contaminated tray
carriers.
[0008] Previously, cleaning of tray carriers has been made more
difficult and expensive due to the need to dry the tray after
cleaning with water or other solvents. The tray carrier may have
intricate arrangements of surfaces that are difficult to dry. In
addition, a residual amount of the cleaning fluid may adhere to the
surfaces of a carrier as a film or in a multiplicity of small
droplets after the washing step. Any contaminants suspended in the
residual cleaning fluid may be redeposited on the surface as the
fluid dries, leading to contaminant carryover when the carrier is
reused. Consequently, process efficiency and effectiveness is
diminished overall. Reuse of tray carriers is discouraged, leading
to environmentally undesirable proliferation of solid waste.
[0009] What is still needed in the industry is a tray carrier with
features that promote more effective cleaning and drying of the
carrier with reduced levels of residual process contamination.
SUMMARY OF THE INVENTION
[0010] The present invention includes a tray carrier with
ultraphobic surfaces for promoting more effective cleaning and
drying of the carrier. In the invention, entire surfaces or
portions of surfaces of a carrier are made ultraphobic. The
ultraphobic surfaces of the carrier cause liquids that may come in
contact with the surface, such as may be used in cleaning, to
quickly and easily "roll off" without leaving a liquid film or
substantial number of liquid droplets. As a result, less time and
energy is expended in drying the surfaces, and redeposited residue
is minimized, thereby improving overall process quality. In
addition, the ultraphobic surfaces may be resistant to initial
deposition of contaminants, where the contaminants may be in liquid
or vapor form.
[0011] In a particularly preferred embodiment of the invention, the
ultraphobic surface includes a multiplicity of closely spaced
microscale to nanoscale asperities formed on a substrate. For the
purpose of the present application, "microscale" generally refers
to dimensions of less than 100 micrometers, and "nanoscale"
generally refers to dimensions of less than 100 nanometers. The
surface is designed to maintain ultraphobic properties up to a
certain predetermined pressure value. The asperities are disposed
so that the surface has a predetermined contact line density
measured in meters of contact line per square meter of surface area
equal to or greater than a contact line density value
".LAMBDA..sub.L" determined according to the formula: .LAMBDA. L =
- P .gamma.cos .function. ( .theta. a , 0 + .omega. - 90 .times.
.degree. ) ##EQU1## where P is the predetermined pressure value,
.gamma. is the surface tension of the liquid, and .theta..sub.a,0
is the experimentally measured true advancing contact angle of the
liquid on the asperity material in degrees, and .omega. is the
asperity rise angle. The predetermined pressure value may be
selected so as to be greater than the anticipated liquid pressures
expected to be encountered during cleaning or use of the
carrier.
[0012] The asperities may be formed in or on the substrate material
itself or in one or more layers of material disposed on the surface
of the substrate. The asperities may be any regularly or
irregularly shaped three dimensional solid or cavity and may be
disposed in any regular geometric pattern or randomly. The
asperities may be formed using photolithography, or using
nanomachining, microstamping, microcontact printing,
self-assembling metal colloid monolayers, atomic force microscopy
nanomachining, sol-gel molding, self-assembled monolayer directed
patterning, chemical etching, sol-gel stamping, printing with
colloidal inks, or by disposing a layer of parallel carbon
nanotubes on the substrate.
[0013] Alternatively, randomly patterned surfaces may be produced
by any of a variety of known processes, including chemical vapor
deposition (CVD),
[0014] The invention may also include a process for producing a
tray carrier with surfaces having ultraphobic properties at liquid
pressures up to a predetermined pressure value. The process
includes steps of selecting an asperity rise angle; determining a
critical contact line density ".LAMBDA..sub.L" value according to
the formula: .LAMBDA. L = - P .gamma.cos .function. ( .theta. a , 0
+ .omega. - 90 .times. .degree. ) ##EQU2## where P is the
predetermined pressure value, .gamma. is the surface tension of the
liquid, and .theta..sub.a,0 is the experimentally measured true
advancing contact angle of the liquid on the asperity material in
degrees, and .omega. is the asperity rise angle; providing a
carrier with a surface portion; and forming a multiplicity of
projecting asperities on the surface portion so that the surface
has an actual contact line density equal to or greater than the
critical contact line density.
[0015] The process may further include the step of determining a
critical asperity height value "Z.sub.c" in meters according to the
formula: Z c = d .function. ( 1 - cos .function. ( .theta. a , 0 +
.omega. - 180 .times. .degree. ) ) 2 .times. sin .function. (
.theta. a , 0 + .omega. - 180 .times. .degree. ) ##EQU3## where d
is the distance in meters between adjacent asperities,
.theta..sub.a,0 is the true advancing contact angle of the liquid
on the surface in degrees, and .omega. is the asperity rise angle
in degrees.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1a is a perspective view of one embodiment of a tray
carrier with ultraphobic surfaces thereon according to the present
invention;
[0017] FIG. 1b is a side elevation view of the tray carrier of FIG.
1a;
[0018] FIG. 1c is a partial cross-sectional view of the tray
carrier of FIG. 1a;
[0019] FIG. 1d is a perspective, enlarged view of an ultraphobic
surface according to the present invention, wherein a multiplicity
of nano/micro scale asperities are arranged in a rectangular
array;
[0020] FIG. 2 is a top plan view of a portion of the surface of
FIG. 1;
[0021] FIG. 3 is a side elevation view of the surface portion
depicted in FIG. 2;
[0022] FIG. 4 is a partial top plan view of an alternative
embodiment of the present invention wherein the asperities are
arranged in a hexagonal array;
[0023] FIG. 5 is a side elevation view of the alternative
embodiment of FIG. 4;
[0024] FIG. 6 is a side elevation view depicting the deflection of
liquid suspended between asperities;
[0025] FIG. 7 is a side elevation view depicting a quantity of
liquid suspended atop asperities;
[0026] FIG. 8 is a side elevation view depicting the liquid
contacting the bottom of the space between asperities;
[0027] FIG. 9 is a side elevation view of a single asperity in an
alternative embodiment of the invention wherein the asperity rise
angle is an acute angle;
[0028] FIG. 10 is a side elevation view of a single asperity in an
alternative embodiment of the invention wherein the asperity rise
angle is an obtuse angle;
[0029] FIG. 11 a partial top plan view of an alternative embodiment
of the present invention wherein the asperities are cylindrical and
are arranged in a rectangular array;
[0030] FIG. 12 is a side elevation view of the alternative
embodiment of FIG. 11;
[0031] FIG. 13 is a table listing formulas for contact line density
for a variety of asperity shapes and arrangements;
[0032] FIG. 14 is a side elevation view of an alternative
embodiment of the present invention;
[0033] FIG. 15 is a top plan view of the alternative embodiment of
FIG. 14; and
[0034] FIG. 16 is a top plan view of a single asperity in an
alternative embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Referring to FIGS. 1a, 1b and 1c, an example of a tray
carrier for processing and transporting a plurality of electronic
devices such as semi-conductor chips is shown and generally
designated by the numeral 100. The tray 100 comprises a first
peripheral frame 102 having a first end 104, a second end 106, and
sides 108, 110. Sides 108, 110 include rails 112, 114 and notches
116, 118, 120, and 122, located at the ends of rails 112 and 114,
respectively. Tabs 124, 126, 128, and 130 project into notches 116,
118, 120, and 122 for engagement with flanges (not depicted). Note
that the tabs 124, 126, 128, and 130 project in the same direction
relative to the tray 100. Together, first end 104, second end 106
and the rails 112, 114 extend substantially around the perimeter of
a chip support surface 132. The chip support surface 132 is of a
conventional design and is depicted as a matrix of lands 134 which
define pockets or cells 136 which hold individual chips. Referring
to FIG. 1b, the peripheral frame 102 forms a support base which is
vertically offset with respect to a chip support surface 132. This
creates a space or plenum beneath the chips to facilitate
processing.
[0036] Surfaces resistant to wetting by liquids may be referred to
as hydrophobic where the liquid is water, and lyophobic relative to
other liquids. The surface may be generally referred to as an
ultrahydrophobic or ultralyophobic surface if the surface resists
wetting to an extent characterized by any or all of the following:
very high advancing contact angles of liquid droplets with the
surface (greater than about 120 degrees) coupled with low contact
angle hysteresis values (less than about 20 degrees); a markedly
reduced propensity of the surface to retain liquid droplets; or the
presence of a liquid-gas-solid interface at the surface when the
surface is completely submerged in liquid. For the purposes of this
application, the term ultraphobic is used to refer generally to
both ultrahydrophobic and ultralyophobic surfaces.
[0037] As depicted in FIGS. 1a-c, ultraphobic surfaces 20 are
formed on all outer surfaces of tray carrier 100. Ultraphobic
surfaces 20 may be formed in any of a variety of configurations and
using a variety of processes as described hereinbelow. It will of
course be appreciated that ultraphobic surfaces 20 may be
selectively formed on any desired portion of tray carrier 100. For
example, if desired, ultraphobic surface 20 may cover only the chip
support surface 132.
[0038] Although a matrix tray is depicted herein, it will be
appreciated that the present invention includes any tray carrier
for electronic or mechanical articles with an ultraphobic surface
thereon, whether for a single electrical or mechanical article or
for multiple articles.
[0039] A greatly enlarged view of one preferred embodiment of an
ultraphobic surface 20 according to the present invention is
depicted in FIG. 1d. The surface 20 generally includes a substrate
22 with a multiplicity of projecting asperities 24. Each asperity
24 has a plurality of sides 26 and a top 28. Each asperity 24 has a
width dimension, annotated "x" in the figures, and a height
dimension, annotated "z" in the figures.
[0040] As depicted in FIGS. 1d-3, asperities 24 are disposed in a
regular rectangular array, each asperity spaced apart from the
adjacent asperities by a spacing dimension, annotated "y" in the
figures. The angle subtended by the top edge 30 of the asperities
24 is annotated .phi., and the rise angle of the side 26 of the
asperities 24 relative to the substrate 22 is annotated .omega..
The sum of the angles .phi. and .omega. is 180 degrees.
[0041] Generally, surface 20 will exhibit ultraphobic properties
when a liquid-solid-gas interface is maintained at the surface. As
depicted in FIG. 7, if liquid 32 contacts only the tops 28 and a
portion of the sides 26 proximate top edge 30 of asperities 24,
leaving a space 34 between the asperities filled with air or other
gas, the requisite liquid-solid-gas interface is present. The
liquid may be said to be "suspended" atop and between the top edges
30 of the asperities 24.
[0042] As will be disclosed hereinbelow, the formation of the
liquid-solid-gas interface depends on certain interrelated
geometrical parameters of the asperities 24 and the properties of
the liquid. According to the present invention, the geometrical
properties of asperities 24 may be selected so that the surface 20
exhibits ultraphobic properties at any desired liquid pressure.
[0043] Referring to the rectangular array of FIGS. 1d-3, surface 20
may be divided into uniform areas 36, depicted bounded by dashed
lines, surrounding each asperity 24. The area density of asperities
(.delta.) in each uniform area 36 may be described by the equation:
.delta. = 1 2 .times. y 2 , ( 1 ) ##EQU4## where y is the spacing
between asperities measured in meters.
[0044] For asperities 24 with a square cross-section as depicted in
FIGS. 1d-3, the length of perimeter (p) of top 28 at top edge 30:
p=4x, (2) where x is the asperity width in meters.
[0045] Perimeter p may be referred to as a "contact line" defining
the location of the liquid-solid-gas interface. The contact line
density (.LAMBDA.) of the surface, which is the length of contact
line per unit area of the surface, is the product of the perimeter
(p) and the area density of asperities (.delta.) so that:
.LAMBDA.=p.delta.. (3) For the rectangular array of square
asperities depicted in FIGS. 1d-3: .LAMBDA.=4x/y.sup.2. (4)
[0046] A quantity of liquid will be suspended atop asperities 24 if
the body forces (F) due to gravity acting on the liquid are less
than surface forces (f) acting at the contact line with the
asperities. Body forces (F) associated with gravity may be
determined according to the following formula: F=.rho. gh, (5)
where g is the density (.rho.) of the liquid, (g) is the
acceleration due to gravity, and (h) is the depth of the liquid.
Thus, for example, for a 10 meter column of water having an
approximate density of 1000 kg/m.sup.3, the body forces (F) would
be: F=(1000 kg/m.sup.3)(9.8 m/s.sup.2)(10 m)=9.8.times.10.sup.4
kg/m.sup.2-s.
[0047] On the other hand, the surface forces (f) depend on the
surface tension of the liquid (.gamma.), its apparent contact angle
with the side 26 of the asperities 24 with respect to the vertical
.theta..sub.s, the contact line density of the asperities
(.LAMBDA.) and the apparent contact area of the liquid (A):
f=-.LAMBDA. A .gamma. cos .theta..sub.s. (6)
[0048] The true advancing contact angle (.theta..sub.a,0) of a
liquid on a given solid material is defined as the largest
experimentally measured stationary contact angle of the liquid on a
surface of the material having essentially no asperities. The true
advancing contact angle is readily measurable by techniques well
known in the art.
[0049] Suspended drops on a surface with asperities exhibit their
true advancing contact angle value (.theta..sub.a,0) at the sides
of the asperities. The contact angle with respect to the vertical
at the side of the asperities (.theta..sub.s) is related to the
true advancing contact angle (.theta..sub.a,0) by .phi. or .omega.
as follows: .theta..sub.s=.theta..sub.a,0+90
.degree.-.phi.=.theta..sub.a,0+.omega.-90.degree.. (7)
[0050] By equating F and f and solving for contact line density
.LAMBDA., a critical contact line density parameter .LAMBDA..sub.L
may be determined for predicting ultraphobic properties in a
surface: .LAMBDA. L = - .rho. .times. gh .gamma.cos .function. (
.theta. a , 0 + .omega. - 90 .times. .degree. ) , ( 8 ) ##EQU5##
where g is the density (.rho.) of the liquid, (g) is the
acceleration due to gravity, (h) is the depth of the liquid, the
surface tension of the liquid (.gamma.), .omega. is the rise angle
of the side of the asperities relative to the substrate in degrees,
and (.theta..sub.a,0) is the experimentally measured true advancing
contact angle of the liquid on the asperity material in
degrees.
[0051] If .LAMBDA.>.LAMBDA..sub.L, the liquid will be suspended
atop the asperities 24, producing an ultraphobic surface.
Otherwise, if .LAMBDA.<.LAMBDA..sub.L, the liquid will collapse
over the asperities and the contact interface at the surface will
be solely liquid/solid, without ultraphobic properties.
[0052] It will be appreciated that by substituting an appropriate
value in the numerator of the equation given above, a value of
critical contact line density may be determined to design a surface
that will retain ultraphobic properties at any desired amount of
pressure. The equation may be generalized as: .LAMBDA. L = - P
.gamma.cos .function. ( .theta. a , 0 + .omega. - 90 .times.
.degree. ) , ( 9 ) ##EQU6## where P is the maximum pressure under
which the surface must exhibit ultraphobic properties in kilograms
per square meter, .gamma. is the surface tension of the liquid in
Newtons per meter, .theta..sub.a,0 is the experimentally measured
true advancing contact angle of the liquid on the asperity material
in degrees, and .omega. is the asperity rise angle in degrees.
[0053] It is generally anticipated that a surface 20 formed
according to the above relations will exhibit ultraphobic
properties under any liquid pressure values up to and including the
value of P used in equation (9) above. The ultraphobic properties
will be exhibited whether the surface is submerged, subjected to a
jet or spray of liquid, or impacted with individual droplets. It
will be readily appreciated that the pressure value P may be
selected so as to be greater than the largest anticipated liquid or
vapor pressure to which the carrier will be subjected during use or
cleaning.
[0054] It will be generally appreciated that the value of P should
be selected so as to provide an appropriate safety factor to
account for pressures that may be momentarily or locally higher
than anticipated, discontinuities in the surface due to tolerance
variations, and other such factors.
[0055] If the surface 20 is intended for very low values of P where
the liquid contact may be in the form of droplets on the surface,
the value of P must be selected to account for the smaller apparent
contact area of a droplet as opposed to a uniform layer of liquid.
In general, the apparent contact area (A) in square meters of a
small droplet on the surface is given by the relation: A = .pi. 1 3
.function. ( 6 .times. V ) 2 3 .times. ( ( ( 1 - cos .times.
.times. .theta. a ) sin .times. .times. .theta. a ) .times. ( 3 + (
( 1 - cos .times. .times. .theta. a ) sin .times. .times. .theta. a
) 2 ) ) - 2 3 , ( 10 ) ##EQU7## where V is the volume of the
droplet in cubic meters, and .theta..sub.a is the apparent
advancing contact angle of the droplet on the surface. The critical
contact line density .LAMBDA..sub.L parameter for suspending a
droplet on the surface becomes: .LAMBDA. L = - .rho. .times.
.times. g .function. ( V ) 1 3 .times. ( ( ( 1 - cos .times.
.times. .theta. a ) sin .times. .times. .theta. a ) .times. ( 3 + (
( 1 - cos .times. .times. .theta. a ) sin .times. .times. .theta. a
) 2 ) ) 2 3 ( 36 .times. .pi. ) 1 3 .times. .gamma.cos .function. (
.theta. a , 0 + .omega. - 90 .times. .degree. ) , ( 11 ) ##EQU8##
where V is the volume of the droplet in cubic meters, g is the
density (.rho.) of the liquid, (g) is the acceleration due to
gravity, (h) is the depth of the liquid, the surface tension of the
liquid (.gamma.), .omega. is the rise angle of the side of the
asperities relative to the substrate in degrees, .theta..sub.a is
the apparent advancing contact angle of the droplet on the surface,
and (.theta..sub.a,0) is the experimentally measured true advancing
contact angle of the liquid on the asperity material in degrees.
Equation 11 may be useful to check the value of P selected for low
pressure ultraphobic surfaces to ensure that the surface will
suspend droplets.
[0056] Once the value of critical contact line density is
determined, the remaining details of the geometry of the asperities
may be determined according to the relationship of x and y given in
the equation for contact line density. In other words, the geometry
of the surface may be determined by choosing the value of either x
or y in the contact line equation and solving for the other
variable.
[0057] The liquid interface deflects downwardly between adjacent
asperities by an amount D.sub.1 as depicted in FIG. 6. If the
amount D.sub.1 is greater than the height (z) of the asperities 24,
the liquid will contact the substrate 22 at a point between the
asperities 24. If this occurs, the liquid will be drawn into space
34, and collapse over the asperities, destroying the ultraphobic
character of the surface. The value of D.sub.1 represents a
critical asperity height (Z.sub.c), and is determinable according
to the following formula: D 1 = Z c = d .function. ( 1 - cos
.function. ( .theta. a , 0 + .omega. - 180 .times. .degree. ) ) 2
.times. sin .function. ( .theta. a , 0 + .omega. - 180 .times.
.degree. ) , ( 12 ) ##EQU9## where (d) is the distance between
adjacent asperities, .omega. is the asperity rise angle, and
.theta..sub.a,0 is the experimentally measured true advancing
contact angle of the liquid on the asperity material. The height
(z) of asperities 24 must be at least equal to, and is preferably
greater than, critical asperity height (Z.sub.c).
[0058] Although in FIGS. 1d-3 the asperity rise angle .omega. is 90
degrees, other asperity geometries are possible. For example,
.omega. may be an acute angle as depicted in FIG. 9 or an obtuse
angle as depicted in FIG. 10. Generally, it is preferred that
.omega. be between 80 and 130 degrees.
[0059] It will also be appreciated that a wide variety of asperity
shapes and arrangements are possible within the scope of the
present invention. For example, asperities may be polyhedral,
cylindrical as depicted in FIGS. 11-12, cylindroid, or any other
suitable three dimensional shape. In addition, various strategies
may be utilized to maximize contact line density of the asperities.
As depicted in FIGS. 14 and 15, the asperities 24 may be formed
with a base portion 38 and a head portion 40. The larger perimeter
of head portion 40 at top edge 30 increases the contact line
density of the surface. Also, features such as recesses 42 may be
formed in the asperities 24 as depicted in FIG. 16 to increase the
perimeter at top edge 30, thereby increasing contact line density.
The asperities may also be cavities formed in the substrate.
[0060] The asperities may be arranged in a rectangular array as
discussed above, in a polygonal array such as the hexagonal array
depicted in FIGS. 4-5, or a circular or ovoid arrangement. The
asperities may also be randomly distributed so long as the critical
contact line density is maintained, although such a random
arrangement may have less predictable ultraphobic properties, and
is therefore less preferred. In such a random arrangement of
asperities, the critical contact line density and other relevant
parameters may be conceptualized as averages for the surface. In
the table of FIG. 13, formulas for calculating contact line
densities for various other asperity shapes and arrangements are
listed.
[0061] Generally, the substrate material may be any material upon
which micro or nano scale asperities may be suitably formed and
which is suitable for use in the processing environment in which
the carrier is used. The asperities may be formed directly in the
substrate material itself, or in one or more layers of other
material deposited on the substrate material, by photolithography
or any of a variety of suitable methods. A photolithography method
that may be suitable for forming micro/nanoscale asperities is
disclosed in PCT Patent Application Publication WO 02/084340,
hereby fully incorporated herein by reference.
[0062] Other methods that may be suitable for forming asperities of
the desired shape and spacing include nanomachining as disclosed in
U.S. patent application Publication No. 2002/00334879,
microstamping as disclosed in U.S. Pat. No. 5,725,788, microcontact
printing as disclosed in U.S. Pat. No. 5,900,160, self-assembled
metal colloid monolayers, as disclosed in U.S. Pat. No. 5,609,907,
microstamping as disclosed in U.S. Pat. No. 6,444,254, atomic force
microscopy nanomachining as disclosed in U.S. Pat. No. 5,252,835,
nanomachining as disclosed in U.S. Pat. No. 6,403,388, sol-gel
molding as disclosed in U.S. Pat. No. 6,530,554, self-assembled
monolayer directed patterning of surfaces, as disclosed in U.S.
Pat. No. 6,518,168, chemical etching as disclosed in U.S. Pat. No.
6,541,389, or sol-gel stamping as disclosed in U.S. patent
application Publication No. 2003/0047822, all of which are hereby
fully incorporated herein by reference. Carbon nanotube structures
may also be usable to form the desired asperity geometries.
Examples of carbon nanotube structures are disclosed in U.S. patent
application Publication Nos. 2002/0098135 and 2002/0136683, also
hereby fully incorporated herein by reference. Also, suitable
asperity structures may be formed using known methods of printing
with colloidal inks. Of course, it will be appreciated that any
other method by which micro/nanoscale asperities may be formed with
the requisite degree of precision may also be used.
[0063] In some applications, particularly where the carrier will
not be subjected to high fluid pressures or where the surface is
intended to repel droplets of liquid that may precipitate or
condense on the surface, ultraphobic surface 20 may be formed with
a coating of polymer material applied using known chemical vapor
deposition techniques. For example, a thin layer of PFA, PTFE, or
other polymer material may be applied to the polycarbonate surfaces
of a carrier using gas phase polymerization. The resulting
ultraphobic surface 20 will be generally characterized by randomly
shaped and arranged asperities formed in the PFA material, and will
be ultraphobic at low fluid pressures.
[0064] In another embodiment for low fluid pressure applications, a
fractal ultraphobic surface may be formed as a layer of material on
the substrate. In one such embodiment, a layer of alkylketene dimer
(AKD) or similar material may be melted or poured on the polymer
substrate and allowed to harden in a nitrogen gas atmosphere. One
suitable method for forming an AKD surface is more fully described
by T. Onda, et.al., in an article entitled "Super Water Repellant
Fractal Surfaces", Langmuir, Volume 12, Number 9, May 1, 1996, at
page 2125, which article is fully incorporated herein by
reference.
[0065] In another embodiment suitable for low fluid pressure
applications, polymer material, such as polypropylene, may be
dissolved in a solvent, such as p-xylene. A quantity of non-solvent
such as methyl ethyl ketone may be added to the solution, and the
solution deposited on the carrier substrate. When the solvent is
evaporated, a porous, gel-like ultraphobic surface structure will
result.
[0066] In each of the above polymer layers, the resulting surface
will be generally characterized by randomly shaped and arranged
micrometer scale asperities. Although the actual contact line
density and critical contact line density values for such surfaces
are difficult to determine due to the variations in individual
asperities, these surfaces will exhibit ultraphobic properties if
the contact line density value for the surface equals or exceeds
the critical contact line density for the surface. For such
surfaces, the actual contact line density will necessarily be an
average value for the surface due to the variability of dimensions
and geometry of individual asperities. In addition, asperity rise
angle .omega. in equations 9 and 11 should be an average value for
the surface.
[0067] The present invention may be embodied in other specific
forms without departing from the spirit or essential attributes
thereof, and it is, therefore, desired that the present embodiment
be considered in all respects as illustrative and not
restrictive.
* * * * *