U.S. patent application number 13/618322 was filed with the patent office on 2013-10-10 for pcb droplet actuator fabrication.
This patent application is currently assigned to Advanced Liquid Logic Inc. The applicant listed for this patent is Vamsee K. Pamula, Michael G. Pollack, Vijay Srinivasan. Invention is credited to Vamsee K. Pamula, Michael G. Pollack, Vijay Srinivasan.
Application Number | 20130264010 13/618322 |
Document ID | / |
Family ID | 40342076 |
Filed Date | 2013-10-10 |
United States Patent
Application |
20130264010 |
Kind Code |
A1 |
Srinivasan; Vijay ; et
al. |
October 10, 2013 |
PCB Droplet Actuator Fabrication
Abstract
Alternative approaches to fabricating printed circuit boards for
use in droplet actuator operations are provided. In one embodiment,
a method of manufacturing a droplet actuator for conducting droplet
operations includes positioning a dielectric material between a
first metal layer configured to include an electrode and a second
metal layer configured to include an interconnect pad. The method
additionally includes forming a connection between the first and
second metal layers. Droplet actuators and methods of fabricating
and supporting printed circuit boards of droplet actuators are also
provided.
Inventors: |
Srinivasan; Vijay; (Durham,
NC) ; Pamula; Vamsee K.; (Durham, NC) ;
Pollack; Michael G.; (Durham, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Srinivasan; Vijay
Pamula; Vamsee K.
Pollack; Michael G. |
Durham
Durham
Durham |
NC
NC
NC |
US
US
US |
|
|
Assignee: |
Advanced Liquid Logic Inc
Research Triangle Park
NC
|
Family ID: |
40342076 |
Appl. No.: |
13/618322 |
Filed: |
September 14, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12531794 |
Oct 15, 2009 |
8268246 |
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PCT/US2008/072770 |
Aug 11, 2008 |
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13618322 |
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60954841 |
Aug 9, 2007 |
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Current U.S.
Class: |
156/247 ; 156/60;
239/690; 29/846; 29/852 |
Current CPC
Class: |
B01L 3/502784 20130101;
H05K 3/0058 20130101; Y10T 29/49124 20150115; H05K 1/113 20130101;
Y10T 29/49155 20150115; H05K 2201/09527 20130101; B01L 3/502792
20130101; B01L 3/502707 20130101; H05K 3/0067 20130101; B01L
2400/0427 20130101; B01L 2300/089 20130101; H05K 3/28 20130101;
H05K 3/4038 20130101; H05K 3/427 20130101; Y10T 29/49165 20150115;
Y10T 156/10 20150115; H05K 3/421 20130101; B01L 2300/12
20130101 |
Class at
Publication: |
156/247 ; 156/60;
29/846; 29/852; 239/690 |
International
Class: |
H05K 3/40 20060101
H05K003/40; H05K 3/28 20060101 H05K003/28 |
Claims
1. A method of manufacturing a droplet actuator for conducting
droplet operations, the method comprising: (a) positioning a
dielectric material between a first metal layer configured to
include an electrode and a second metal layer configured to include
an interconnect pad; and (b) forming a connection between the first
and second metal layers.
2. The method of claim 1 further comprising applying a photoresist
layer onto the first metal layer.
3. The method of claim 1 further comprising stripping a photoresist
layer from the first metal layer.
4. The method of claim 1, wherein forming the connection further
comprises forming a via connection between the first and second
metal layers.
5. The method of claim 1, wherein forming the connection further
comprises forming an opening through both the dielectric material
and the second metal layer through to the first metal layer.
6. The method of claim 5 further comprising applying a photoresist
layer onto the second metal layer in such a manner as to leave the
opening exposed.
7. The method of claim 6 further comprising applying a metal
plating into the opening to form the connection.
8. The method of claim 7 further comprising stripping the
photoresist layer from the second metal layer.
9. The method of claim 1 further comprising forming the electrode
from the first metal layer.
10. The method of claim 1 further comprising forming the
interconnect pad from the second metal layer.
11. The method of claim 1 further comprising laminating a rigid
structure onto the second metal layer using a bonding layer.
12. The method of claim 1 further comprising attaching a rigid
structure onto the second metal layer.
13. The method of claim 12, wherein attaching the rigid structure
further comprises attaching a glass structure to the second metal
layer.
14. The method of claim 1 further comprising applying an
electrowetting layer onto the first metal layer.
15. The method of claim 14, wherein applying the electrowetting
layer to the first metal layer further comprises applying a
dielectric substance onto the first metal layer.
16. The method of claim 14, wherein applying the electrowetting
layer onto the first metal layer further comprises applying at
least one of a liquid photoimageable soldermask and a
non-florescent material onto the first metal layer.
17. The method of claim 1 further comprising applying a photoresist
layer onto the second metal layer.
18. The method of claim 1 further comprising stripping a
photoresist layer from the second metal layer.
19. The method of claim 1 further comprising forming the dielectric
material from non-florescent material.
20. The method of claim 1 further comprising positioning a first
plate proximate a second plate comprising the first and second
metal layers, the dielectric material and the connection to form a
gap between the two plates that provides a fluid flow path for a
droplet operations.
21. The method of 20 further comprising forming the first
plate.
22. A droplet actuator for conducting droplet operations,
comprising: (a) a first plate that includes: (i) a first metal
layer comprising an electrode; (ii) a second metal layer comprising
an interconnect pad; (iii) a dielectric material positioned between
the first and second metal layers; and (iv) a via connecting the
electrode to the interconnect; and (b) a second plate proximate the
first plate and forming a gap therebetween that provides a fluid
flow path for the droplet operations.
23. The droplet actuator of claim 22 further comprising an
electrowetting layer positioned on at least one of the first and
second metal layers proximate the gap.
24. The droplet actuator of claim 22, wherein the via comprises
metal applied in a hole formed through the second metal layer and
the dielectric material.
25. The droplet actuator of claim 24, further comprising a
photoresist layer protecting the second metal layer from the
applied metal.
26. A method of fabricating and supporting a printed circuit board
of a droplet actuator for conducting droplet operations, the method
comprising: (a) providing a core printed circuit board by
positioning a dielectric material between a first metal layer
configured to include an electrode and a second metal layer
configured to include an interconnect pad; (b) applying a
photoresist layer onto the first metal layer and forming one or
more openings in the dielectric material and the second metal
layer; (c) applying a photoresist layer onto the second metal layer
and plating the one or more openings to form one or more blind
vias, thereby forming a connection between the first and second
metal layers; (d) stripping the photoresist layer from both the
first metal layer and the second metal layer; (e) patterning the
features on both the first metal layer and the second metal layer;
(f) applying an electrowetting dielectric layer to the first metal
layer; and (g) bonding a rigid support structure to the second
metal layer.
Description
1 RELATED APPLICATIONS
[0001] This patent application is a continuation of and
incorporates by reference U.S. patent application Ser. No.
12/531,794, entitled "PCB Droplet Acutator Fabrication", filed Oct.
15, 2009, which is a national stage entry of International Patent
Application No. PCT/US2008/072770, filed Aug. 11, 2008, which and
claims priority to U.S. Provisional Patent Application No.
60/954,841, filed on Aug. 9, 2007, entitled "PCB Droplet Actuator
Fabrication," the entire disclosure of which is incorporated herein
by reference.
2 FIELD OF THE INVENTION
[0002] The present invention generally relates to the field of
conducting droplet operations in a droplet actuator. In particular,
the present invention is directed to alternative approaches to
fabricating printed circuit boards for use in droplet actuator
operations.
3 BACKGROUND OF THE INVENTION
[0003] Droplet actuators are used to conduct a wide variety of
droplet operations. A droplet actuator typically includes two
plates separated by a gap. The plates include electrodes for
conducting droplet operations. The space is typically filled with a
filler fluid that is immiscible with the fluid that is to be
manipulated on the droplet actuator. The formation and movement of
droplets is controlled by electrodes for conducting a variety of
droplet operations, such as droplet transport and droplet
dispensing. One or both of the plates of the droplet actuator may
be manufactured using a printed circuit board ("PCB"). As the
functionality of the droplet actuator is dependent on, for example,
the surface smoothness, topology, planarity, and florescence of the
PCB layers that form the gap, there is a need for alternative
approaches to fabricating PCBs to provide PCB droplet actuators
with more desirable characteristics.
4 BRIEF DESCRIPTION OF THE INVENTION
[0004] The present invention is directed to alternative approaches
to fabricating printed circuit boards for use in droplet actuator
operations.
[0005] In one embodiment, a method of manufacturing a droplet
actuator for conducting droplet operations is provided. The method
comprises positioning a dielectric material between a first metal
layer configured to include an electrode and a second metal layer
configured to include an interconnect pad. The method additionally
comprises forming a connection between the first and second metal
layers.
[0006] In another embodiment, a droplet actuator for conducting
droplet operations is provided. The droplet actuator comprises a
first plate that includes a first metal layer comprising an
electrode, a second metal layer comprising an interconnect pad, a
dielectric material positioned between the first and second metal
layers, and a via connecting the electrode to the interconnect. The
droplet actuator additionally comprises a second plate proximate
the first plate and forming a gap therebetween that provides a
fluid flow path for the droplet operations.
[0007] In a further embodiment, a method of fabricating and
supporting a printed circuit board of a droplet actuator for
conducting droplet operations is provided. The method comprises
providing a core printed circuit board by positioning a dielectric
material between a first metal layer configured to include an
electrode and a second metal layer configured to include an
interconnect pad, applying a photoresist layer onto the first metal
layer and forming one or more openings in the dielectric material
and the second metal layer, applying a photoresist layer onto the
second metal layer and plating the one or more openings to form one
or more blind vias, thereby forming a connection between the first
and second metal layers. The method further comprises stripping the
photoresist layer from both the first metal layer and the second
metal layer, patterning the features on both the first metal layer
and the second metal layer, applying an electrowetting dielectric
layer to the first metal layer, and bonding a rigid support
structure to the second metal layer.
5 DEFINITIONS
[0008] As used herein, the following terms have the meanings
indicated.
[0009] "Activate" with reference to one or more electrodes means
effecting a change in the electrical state of the one or more
electrodes which results in a droplet operation.
[0010] "Droplet" means a volume of liquid on a droplet actuator
that is at least partially bounded by filler fluid. For example, a
droplet may be completely surrounded by filler fluid or may be
bounded by filler fluid and one or more surfaces of the droplet
actuator. Droplets may take a wide variety of shapes; nonlimiting
examples include generally disc shaped, slug shaped, truncated
sphere, ellipsoid, spherical, partially compressed sphere,
hemispherical, ovoid, cylindrical, and various shapes formed during
droplet operations, such as merging or splitting or formed as a
result of contact of such shapes with one or more surfaces of a
droplet actuator.
[0011] "Droplet operation" means any manipulation of a droplet on a
droplet actuator. A droplet operation may, for example, include:
loading a droplet into the droplet actuator; dispensing one or more
droplets from a source droplet; splitting, separating or dividing a
droplet into two or more droplets; transporting a droplet from one
location to another in any direction; merging or combining two or
more droplets into a single droplet; diluting a droplet; mixing a
droplet; agitating a droplet; deforming a droplet; retaining a
droplet in position; incubating a droplet; heating a droplet;
vaporizing a droplet; cooling a droplet; disposing of a droplet;
transporting a droplet out of a droplet actuator; other droplet
operations described herein; and/or any combination of the
foregoing. The terms "merge," "merging," "combine," "combining" and
the like are used to describe the creation of one droplet from two
or more droplets. It should be understood that when such a term is
used in reference to two or more droplets, any combination of
droplet operations that are sufficient to result in the combination
of the two or more droplets into one droplet may be used. For
example, "merging droplet A with droplet B," can be achieved by
transporting droplet A into contact with a stationary droplet B,
transporting droplet B into contact with a stationary droplet A, or
transporting droplets A and B into contact with each other. The
terms "splitting," "separating" and "dividing" are not intended to
imply any particular outcome with respect to size of the resulting
droplets (i.e., the size of the resulting droplets can be the same
or different) or number of resulting droplets (the number of
resulting droplets may be 2, 3, 4, 5 or more). The term "mixing"
refers to droplet operations which result in more homogenous
distribution of one or more components within a droplet. Examples
of "loading" droplet operations include microdialysis loading,
pressure assisted loading, robotic loading, passive loading, and
pipette loading.
[0012] The terms "top" and "bottom" are used throughout the
description with reference to the top and bottom substrates of the
droplet actuator for convenience only, since the droplet actuator
is functional regardless of its position in space.
[0013] When a given component, such as a layer, region or
substrate, is referred to herein as being disposed or formed "on"
another component, that given component can be directly on the
other component or, alternatively, intervening components (for
example, one or more coatings, layers, interlayers, electrodes or
contacts) can also be present. It will be further understood that
the terms "disposed on" and "formed on" are used interchangeably to
describe how a given component is positioned or situated in
relation to another component. Hence, the terms "disposed on" and
"formed on" are not intended to introduce any limitations relating
to particular methods of material transport, deposition, or
fabrication.
[0014] When a liquid in any form (e.g., a droplet or a continuous
body, whether moving or stationary) is described as being "on",
"at", or "over" an electrode, array, matrix or surface, such liquid
could be either in direct contact with the
electrode/array/matrix/surface, or could be in contact with one or
more layers or films that are interposed between the liquid and the
electrode/array/matrix/surface.
[0015] When a droplet is described as being "on" or "loaded on" a
droplet actuator, it should be understood that the droplet is
arranged on the droplet actuator in a manner which facilitates
using the droplet actuator to conduct droplet operations on the
droplet, the droplet is arranged on the droplet actuator in a
manner which facilitates sensing of a property of or a signal from
the droplet, and/or the droplet has been subjected to a droplet
operation on the droplet actuator.
6 BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 illustrates a side view of a portion of an example
droplet actuator formed by a PCB fabrication process described in
accordance with the present invention;
[0017] FIG. 2 illustrates an example of a first process step of
fabricating a bottom plate of a droplet actuator by providing a
core PCB that is formed of a core dielectric layer that has metal
layers on both sides, e.g., an electrode side metal layer and a
non-electrode side metal layer;
[0018] FIG. 3 illustrates an example of a next process step of
fabricating a bottom plate of a droplet actuator by applying a
photoresist layer on the electrode side metal layer of the core PCB
and forming one or more openings in the core dielectric layer and
the non-electrode side metal layer;
[0019] FIG. 4 illustrates an example of a next process step of
fabricating a bottom plate of a droplet actuator by applying a
photoresist layer on the non-electrode side metal layer of the core
PCB and plating the one or more openings, in order to form one or
more blind vias;
[0020] FIG. 5 illustrates an example of a next process step of
fabricating a bottom plate of a droplet actuator by stripping the
photoresist layer from both the electrode side metal layer and the
non-electrode side metal layer of the core PCB;
[0021] FIG. 6 illustrates an example of a next process step of
fabricating a bottom plate of a droplet actuator by patterning the
features on both the electrode side metal layer and the
non-electrode side metal layer of the core PCB; and
[0022] FIG. 7 illustrates an example of a next process step of
fabricating a bottom plate of a droplet actuator by applying an
electrowetting dielectric layer to the electrode side metal layer
of the core PCB and bonding a rigid support structure to the
non-electrode side metal layer of the core PCB.
7 DETAILED DESCRIPTION OF THE INVENTION
[0023] The invention provides an improved PCB fabrication process
for forming a PCB for a droplet actuator that has certain
characteristics and properties for ensuring a desired functionality
thereof. In particular, the PCB fabrication process of the
invention provides PCB layers that have, for example, but not
limited to, a certain surface smoothness, topology, planarity, and
low florescence that are suited to ensure a desired functionality
in the electrowetting process, which is used for performing droplet
operations. Additionally, the invention provides a nonlimiting
example of a droplet actuator that is formed by the improved PCB
fabrication process of the invention.
[0024] 7.1 PCB Fabrication Process for Forming Droplet
Actuators
[0025] FIG. 1 illustrates a side view of a portion of a droplet
actuator 100, which is a nonlimiting example of a droplet actuator
that is formed by the improved PCB fabrication process of the
invention. Droplet actuator 100 includes a first plate, such as a
top plate 110, and a second plate, such as a bottom plate 114.
[0026] Top plate 110 may be formed of a core PCB 118 that is formed
of a core dielectric layer 122 that is sandwiched between a first
metal layer 126 and a second metal layer 130. One side of core PCB
118 of top plate 110 is coated with an electrowetting dielectric
layer 134. The opposite side of core PCB 118 is laminated to a
rigid support structure 138 by use of a bonding layer 142.
[0027] Bottom plate 114 may be formed of a core PCB 148 that is
formed of a core dielectric layer 152 that is sandwiched between a
first metal layer within which is formed one or more electrodes 156
and a second metal layer within which is formed one or more
interconnect pads 160. Additionally, each electrode 156 of core PCB
148 may be electrically connected to a respective interconnect pad
160 by use of a via structure 162 that is commonly known as a
"blind via," "hidden via," or "micro-via" structure. One side of
core PCB 148 of bottom plate 114 is coated with an electrowetting
dielectric layer 164. The opposite side of core PCB 148 is
laminated to a rigid support structure 168 by use of a bonding
layer 172.
[0028] Top plate 110 and bottom plate 114 are arranged one to
another such that there is a gap therebetween that provides a fluid
flow path for conducting droplet operations. In particular, first
metal layer 126 of top plate 110 that is coated with electrowetting
dielectric layer 134 is oriented toward the gap and, thus, acts as
the ground electrode. Additionally, the one or more electrodes 156
of bottom plate 114 that are coated with electrowetting dielectric
layer 164 are oriented toward the gap and, thus, may act as
transport electrodes.
[0029] A droplet actuator, such as droplet actuator 100, that is
formed by the improved PCB fabrication process of the invention,
has a certain desired surface smoothness, surface topology, surface
planarity, and low florescence. By way of example, more details of
the materials and the step-by-step fabrication of a bottom plate,
such as bottom plate 114, by use of the improved PCB fabrication
process of the invention are found with reference to FIGS. 2
through 7.
[0030] FIG. 2 illustrates a nonlimiting example of a first process
step of fabricating a bottom plate of a droplet actuator, such as
bottom plate 114 of droplet actuator 100 of FIG. 1, by use of the
improved PCB fabrication process of the invention. More
specifically, a first step may include the acquisition of core PCB
148 that includes a core dielectric layer 210 that is sandwiched
between a first metal layer 214 and a second metal layer 218. In
one example, core PCB 148 may be acquired commercially in an
assembled form, i.e., first metal layer 214 and second metal layer
218 that is bonded already to core dielectric layer 210 in an
unpatterned and unprocessed state. In another example, core
dielectric layer 210 may be formed of a commercially available
dielectric material, such as Kapton.RTM.; liquid crystal polymer
(LCP); standard FR4, which is general purpose epoxy/fiberglass
woven material; and any polymer (e.g., Mylar.RTM.). Additionally,
the thickness of core dielectric layer 210 is selected to permit
droplet operations and in some cases may be up to about 50 microns.
See section 7.2 "Fabrication Materials" for examples of materials
that are suitable for the core dielectric layer of a droplet
actuator PCB.
[0031] First metal layer 214 and second metal layer 218 are formed
of any electrically conductive material, such as copper. In one
example, first metal layer 214 may be the copper layer within which
one or more electrodes, such as electrode 156 of FIG. 1, are
formed, and may have any thickness suitable to the purpose of the
droplet actuator. In one example, second metal layer 218 may be the
copper layer within which one or more interconnect pads, such as
interconnect pad 160 of FIG. 1, are formed, and may have a
thickness suitable to the purpose of the droplet actuator. In
another example, first metal layer 214 may have a thickness which
is less than the thickness of second metal layer 218.
[0032] FIG. 3 illustrates a nonlimiting example of a next process
step of fabricating a bottom plate of a droplet actuator, such as
bottom plate 114 of droplet actuator 100 of FIG. 1, by use of the
improved PCB fabrication process of the invention. More
specifically, a next step may include applying a photoresist layer
310 on the metal layer within which the one or more electrodes are
to be formed, i.e., the electrode side of core PCB 148. In one
example, photoresist layer 310 is applied to first metal layer 214
using standard processes, in order to protect first metal layer 214
during other process steps. Photoresist is a photo-sensitive
material used in photolithography.
[0033] In this process step, FIG. 3 shows an opening 314 that is
formed using standard processes in core dielectric layer 210 and
second metal layer 218, but not in first metal layer 214. Opening
314 is formed as a first step in forming a blind via, such as via
structure 162 of FIG. 1.
[0034] FIG. 4 illustrates a nonlimiting example of a next process
step of fabricating a bottom plate of a droplet actuator, such as
bottom plate 114 of droplet actuator 100 of FIG. 1, by use of the
improved PCB fabrication process of the invention. More
specifically, a next step may include applying a photoresist layer
414 on the metal layer within which the one or more interconnect
pads are to be formed, i.e., the non-electrode side of core PCB
148. In one example, photoresist layer 414 is applied to second
metal layer 218 using standard processes, in preparation for
plating opening 314 as a next step in forming a blind via, such as
via structure 162 of FIG. 1. More specifically, an opening in
photoresist layer 414 at opening 314 allows metal plating 418 to be
applied, as shown in FIG. 4, using standard processes, while
protecting second metal layer 218 in all areas away from opening
314. In doing so, an electrical connection is made between first
metal layer 214 and second metal layer 218.
[0035] FIG. 5 illustrates a nonlimiting example of a next process
step of fabricating a bottom plate of a droplet actuator, such as
bottom plate 114 of droplet actuator 100 of FIG. 1, by use of the
improved PCB fabrication process of the invention. More
specifically, a next step may include the stripping of photoresist
layer 310 and photoresist layer 414 using standard processes. The
result is a full metal layer on the electrode side of core PCB 148,
a full metal layer on the non-electrode side of core PCB 148, and
one or more blind vias fabricated therebetween.
[0036] FIG. 6 illustrates a nonlimiting example of a next process
step of fabricating a bottom plate of a droplet actuator, such as
bottom plate 114 of droplet actuator 100 of FIG. 1, by use of the
improved PCB fabrication process of the invention. More
specifically, a next step may include the "patterning" of both
metal layers of core PCB 148. In one example, the metal features
that form one or more electrodes 156 are patterned in first metal
layer 214, using standard processes. Additionally, the metal
features that form one or more interconnect pads 160 are patterned
in second metal layer 218, using standard processes.
[0037] FIG. 7 illustrates a nonlimiting example of a next process
step of fabricating a bottom plate of a droplet actuator, such as
bottom plate 114 of droplet actuator 100 of FIG. 1, by use of the
improved PCB fabrication process of the invention. More
specifically, a next step may include laminating the support
mechanism to the non-electrode side of core PCB 148 and applying
the electrowetting dielectric. For example, the non-electrode side
of core PCB 148 is laminated to support structure 168 by use of
bonding layer 172 and electrowetting dielectric layer 164 is
applied atop the one or more electrodes 156. In one example, the
thickness of electrowetting dielectric layer 164 is selected to
facilitate use of the device for conducting droplet operations. The
material that forms electrowetting dielectric layer 164 is selected
for certain desired properties, such as a certain surface
smoothness. In one example, electrowetting dielectric layer 164 may
be formed of a commercially available polyimide of liquid
photoimageable (LPI) soldermask that, when applied, has low
roughness. In one example the roughness is less than about 50
nanometers. In another example, the roughness is less than less
than about 10 nanometers. In yet another example, the roughness is
less than less than about 1 nanometer. Because the irregular metal
features are substantially on the non-electrode side of core PCB
148, the smoothness of the electrode side of core PCB 148, which is
oriented in the gap of the droplet actuator, may be enhanced and
held to a certain desired specification that is suitable for
ensuring proper droplet operations. Furthermore, because the
thickness of the metal on the electrode side of core PCB 148 is
known and uniform, the electrowetting dielectric layer may me
applied uniformly and planar. In this way, the electrowetting
dielectric layer, upon which a droplet is manipulated, is suitably
smooth and flat.
[0038] LPI soldermask may be applied by, for example, but not
limited to, print screening, dip coating, and spin coating
techniques. See section 7.2 "Fabrication Materials" for examples of
materials that are suitable for forming electrowetting dielectric
layer 164.
[0039] In one example, support structure 168 is a rigid glass
plate. In one example, bonding layer 172 is a high flow material
that flows easily along the topology of the non-electrode side of
core PCB 148 in order to efficiently fill the volume around all
metal features. Examples of high flow materials include, but are
not limited to, thin FR4 Pregreg, which is partially cured epoxy,
and partially cured silicone. See section 7.2 "Fabrication
Materials" for examples of materials that are suitable for forming
bonding layer 172.
[0040] Warping is avoided by use of a rigid support structure, such
as glass, and a non-adhesive bonding layer, as an adhesive bonding
layer is weak. The combination of the rigid support structure and
the smoothness and planarity of the electrode side of the core PCB
provides a gap tolerance of less than 10% of the expected droplet
height. In one example, the gap tolerance may be from about 1% to
about 5% of the expected droplet height. In another example, the
gap tolerance may be about 1% of the expected droplet height.
[0041] 7.2 Fabrication Materials
[0042] Nonlimiting examples of materials that are suitable for
forming the core dielectric layer of a PCB may include, but are not
limited to, Kapton.RTM. Polyimide Film supplied by DuPont
(Wilmington, Del.), liquid crystal polymer (LCP), standard FR4, and
Mylar.RTM. Polyester Film supplied by DuPont (Wilmington, Del.).
Furthermore, the material forming the core dielectric layer of a
PCB may be a non-florescent material.
[0043] Nonlimiting examples of materials that are suitable for
forming the electrowetting dielectric layer, such as electrowetting
dielectric layer 164, may include, but are not limited to, liquid
photoimageable (LPI) soldermask. Additionally, the material forming
the electrowetting dielectric may be a non-florescent material.
[0044] Nonlimiting examples of materials that are suitable for
forming the bonding layer between the PCB and the support, such as
bonding layer 172, may include, but are not limited to, FR4
Pregreg. Furthermore, the material forming the bonding layer may be
a non-florescent material.
[0045] 7.3 Droplet Actuator
[0046] For examples of droplet actuator architectures that are
suitable for use with the present invention, see U.S. Pat. No.
6,911,132, entitled, "Apparatus for Manipulating Droplets by
Electrowetting-Based Techniques," issued on Jun. 28, 2005 to Pamula
et al.; U.S. patent application Ser. No. 11/343,284, entitled,
"Apparatuses and Methods for Manipulating Droplets on a Printed
Circuit Board," filed on filed on Jan. 30, 2006; U.S. Pat. Nos.
6,773,566, entitled, "Electrostatic Actuators for Microfluidics and
Methods for Using Same," issued on Aug. 10, 2004 and 6,565,727,
entitled, "Actuators for Microfluidics Without Moving Parts,"
issued on Jan. 24, 2000, both to Shenderov et al.; and Pollack et
al., International Patent Application No. PCT/US 06/47486,
entitled, "Droplet-Based Biochemistry," filed on Dec. 11, 2006, the
disclosures of which are incorporated herein by reference.
[0047] 7.4 Fluids
[0048] For examples of fluids that may subjected to droplet
operations using the approach of the invention, see the patents
listed in section 7.3, especially International Patent Application
No. PCT/US 06/47486, entitled, "Droplet-Based Biochemistry," filed
on Dec. 11, 2006. In some embodiments, the fluid includes a
biological sample, such as whole blood, lymphatic fluid, serum,
plasma, sweat, tear, saliva, sputum, cerebrospinal fluid, amniotic
fluid, seminal fluid, vaginal excretion, serous fluid, synovial
fluid, pericardial fluid, peritoneal fluid, pleural fluid,
transudates, exudates, cystic fluid, bile, urine, gastric fluid,
intestinal fluid, fecal samples, fluidized tissues, fluidized
organisms, biological swabs and biological washes. In some
embodiment, the fluid that is loaded includes a reagent, such as
water, deionized water, saline solutions, acidic solutions, basic
solutions, detergent solutions and/or buffers. In some embodiments,
the fluid includes a reagent, such as a reagent for a biochemical
protocol, such as a nucleic acid amplification protocol, an
affinity-based assay protocol, a sequencing protocol, and/or a
protocol for analyses of biological fluids.
[0049] 7.5 Filler Fluids
[0050] The gap is typically filled with a filler fluid. The filler
fluid may, for example, be a low-viscosity oil, such as silicone
oil. Other examples of filler fluids are provided in International
Patent Application No. PCT/US 06/47486, entitled, "Droplet-Based
Biochemistry," filed on Dec. 11, 2006.
[0051] 7.6 Method of Processing a PCB of a Droplet Actuator
[0052] A method of fabricating and supporting a PCB of a droplet
actuator may include, but is not limited to, one or more of the
following steps: (1) providing a core PCB that is formed of a core
dielectric layer that has metal layers on both sides, e.g., an
electrode side metal layer and a non-electrode side metal layer;
(2) applying a photoresist layer on the electrode side metal layer
of the core PCB and forming one or more openings in the core
dielectric layer and the non-electrode side metal layer; (3)
applying a photoresist layer on the non-electrode side metal layer
of the core PCB and plating the one or more openings, in order to
form one or more blind vias, respectively; (4) stripping the
photoresist layer from both the electrode side metal layer and the
non-electrode side metal layer of the core PCB; (5) patterning the
features on both the electrode side metal layer and the
non-electrode side metal layer of the core PCB; (6) applying an
electrowetting dielectric layer to the electrode side metal layer
of the core PCB; and (7) bonding a rigid support structure to the
non-electrode side metal layer of the core PCB.
8 CONCLUDING REMARKS
[0053] The foregoing detailed description of embodiments refers to
the accompanying drawings, which illustrate specific embodiments of
the invention. Other embodiments having different structures and
operations do not depart from the scope of the present
invention.
[0054] This specification is divided into sections for the
convenience of the reader only. Headings should not be construed as
limiting of the scope of the invention.
[0055] It will be understood that various details of the present
invention may be changed without departing from the scope of the
present invention. Furthermore, the foregoing description is for
the purpose of illustration only, and not for the purpose of
limitation, as the present invention is defined by the claims as
set forth hereinafter.
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