U.S. patent application number 14/455246 was filed with the patent office on 2016-02-11 for roll-to-roll electroless plating system with micro-bubble injector.
The applicant listed for this patent is Shawn A. Reuter, Gary P. Wainwright. Invention is credited to Shawn A. Reuter, Gary P. Wainwright.
Application Number | 20160040291 14/455246 |
Document ID | / |
Family ID | 55266974 |
Filed Date | 2016-02-11 |
United States Patent
Application |
20160040291 |
Kind Code |
A1 |
Wainwright; Gary P. ; et
al. |
February 11, 2016 |
ROLL-TO-ROLL ELECTROLESS PLATING SYSTEM WITH MICRO-BUBBLE
INJECTOR
Abstract
A roll-to-roll electroless plating system including a reservoir
containing plating solution. A web advance system advances a web of
media though the plating solution in the reservoir, wherein a
plating substance in the plating solution is plated onto
predetermined locations on a surface of the web of media. A
distribution system injects an inert gas into the plating solution
to reduce the amount of dissolved oxygen. The distribution system
includes an injector having a converging tube segment, a diverging
tube segment downstream of the converging tube segment, a throat
formed at a junction of the converging tube segment and the
diverging tube segment, and an inlet for the inert gas in proximity
to the throat.
Inventors: |
Wainwright; Gary P.;
(Fairport, NY) ; Reuter; Shawn A.; (Rochester,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wainwright; Gary P.
Reuter; Shawn A. |
Fairport
Rochester |
NY
NY |
US
US |
|
|
Family ID: |
55266974 |
Appl. No.: |
14/455246 |
Filed: |
August 8, 2014 |
Current U.S.
Class: |
428/544 ;
118/600; 118/602; 118/612; 118/712; 420/441; 420/463; 420/469;
420/501 |
Current CPC
Class: |
C23C 18/1608 20130101;
C22C 5/04 20130101; C22C 19/03 20130101; C23C 18/1617 20130101;
C23C 18/1669 20130101; C23C 18/1683 20130101; C23C 18/1619
20130101; C23C 18/1628 20130101; C22C 5/06 20130101; C23C 18/163
20130101; C22C 9/00 20130101 |
International
Class: |
C23C 18/16 20060101
C23C018/16; C22C 5/04 20060101 C22C005/04; C22C 19/03 20060101
C22C019/03; C22C 9/00 20060101 C22C009/00; C22C 5/06 20060101
C22C005/06 |
Claims
1. A roll-to-roll electroless plating system, comprising: a
reservoir containing plating solution; a web advance system for
advancing a web of media from an input roll through the plating
solution in the reservoir to a take-up roll, wherein a plating
substance in the plating solution is plated onto predetermined
locations on a surface of the web of media as it is advanced
through the plating solution in the reservoir; and a distribution
system for injecting an inert gas into the plating solution,
wherein the distribution system includes an injector for injecting
the inert gas into the plating solution, wherein the injector
includes: a converging tube segment; a diverging tube segment
downstream of the converging tube segment; a throat formed at a
junction of the converging tube segment and the diverging tube
segment; and an inlet for the inert gas in proximity to the
throat.
2. The roll-to-roll electroless plating system of claim 1, wherein
diameters of the converging and diverging tube segments increase
with distance from the throat.
3. The roll-to-roll electroless plating system of claim 1, wherein
the injector is located downstream of a pump which pumps the
plating solution through the injector.
4. The roll-to-roll electroless plating system of claim 1, wherein
the injector injects micro-bubbles of the inert gas into the
plating solution, wherein the micro-bubbles have a diameter between
about one micron and one millimeter.
5. The roll-to-roll electroless plating system of claim 1, wherein
the plating substance is copper, silver, nickel or palladium.
6. The roll-to-roll electroless plating system of claim 1, wherein
the inert gas is nitrogen or argon.
7. The roll-to-roll electroless plating system of claim 1, further
including a recirculation system including: a recirculation pump
including an inlet and an outlet; an inlet line for moving plating
solution from the reservoir to the pump inlet; and an outlet line
for returning plating solution from the pump outlet to the
reservoir.
8. The roll-to-roll electroless plating system of claim 7, wherein
the distribution system is configured to inject the inert gas into
the outlet line.
9. The roll-to-roll electroless plating system of claim 7, further
comprising a filter in the outlet line.
10. The roll-to-roll electroless plating system of claim 1, wherein
the distribution system includes a plumbing assembly having a
plurality of distributed orifices for providing bubbles of inert
gas into the reservoir.
11. The roll-to-roll electroless plating system of claim 10,
wherein the plumbing assembly is disposed proximate to a bottom of
the sump.
12. The roll-to-roll electroless plating system of claim 1, further
comprising an oxygen sensor.
13. The roll-to-roll electroless plating system of claim 12,
further comprising a controller, wherein the controller is
configured to receive data from the oxygen sensor and to control a
rate of injection of the inert gas into the plating solution in
response to the data received from the oxygen sensor.
14. The roll-to-roll electroless plating system of claim 13,
wherein a dissolved oxygen content of the plating solution is
controlled to be between 0.5 and 2 parts per million.
15. The roll-to-roll electroless plating system of claim 1, wherein
the reservoir further includes a reservoir cover.
16. The roll-to-roll electroless plating system of claim 1, wherein
the distribution system further includes a static mixer.
17. The roll-to-roll electroless plating system of claim 1, wherein
the predetermined locations include features printed onto the web
of media with ink including a catalyst for plating.
18. An article having features that were plated using the
roll-to-roll electroless plating system of claim 1.
19. The article of claim 18, wherein at least some of the features
have widths between 2 microns and 10 microns.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Reference is made to commonly-assigned, co-pending U.S.
patent application Ser. No. ______ (Docket K001833), entitled
"Roll-to-roll electroless plating system with low dissolved oxygen
content" by G. Wainwright et al.; and to commonly-assigned,
co-pending U.S. patent application Ser. No. ______ (Docket
K001834), entitled "Method for roll-to-roll electroless plating
with low dissolved oxygen content" by G. Wainwright et al., each of
which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention pertains to the field of roll-to-roll
electroless plating, and more particularly to a system and method
for providing low dissolved oxygen content in the plating
solution.
BACKGROUND OF THE INVENTION
[0003] Electroless plating, also known as chemical or
auto-catalytic plating, is a non-galvanic plating process that
involves chemical reactions in an aqueous plating solution that
occur without the use of external electrical power. Typically, the
plating occurs as hydrogen is released by a reducing agent and
oxidized, thus producing a negative charge on the surface of the
part to be plated. The negative charge attracts metal ions out of
the plating solution to adhere as a metalized layer on the surface.
Using electroless plating to provide metallization in predetermined
locations can be facilitated by first depositing a catalytic
material in the predetermined locations. This can be done, for
example by printing features using an ink containing a catalytic
component.
[0004] Touch screens are visual displays with areas that may be
configured to detect both the presence and location of a touch by,
for example, a finger, a hand or a stylus. Touch screens may be
found in televisions, computers, computer peripherals, mobile
computing devices, automobiles, appliances and game consoles, as
well as in other industrial, commercial and household applications.
A capacitive touch screen includes a substantially transparent
substrate which is provided with electrically conductive patterns
that do not excessively impair the transparency--either because the
conductors are made of a material, such as indium tin oxide, that
is substantially transparent, or because the conductors are
sufficiently narrow that the transparency is provided by the
comparatively large open areas not containing conductors. For
capacitive touch screens having metallic conductors, it is
advantageous for the features to be highly conductive but also very
narrow. Capacitive touch screen sensor films are an example of an
article having very fine features with improved electrical
conductivity resulting from an electroless plated metal layer.
[0005] Projected capacitive touch technology is a variant of
capacitive touch technology. Projected capacitive touch screens are
made up of a matrix of rows and columns of conductive material that
form a grid. Voltage applied to this grid creates a uniform
electrostatic field, which can be measured. When a conductive
object, such as a finger, comes into contact, it distorts the local
electrostatic field at that point. This is measurable as a change
in capacitance. The capacitance can be measured at every
intersection point on the grid. In this way, the system is able to
accurately track touches. Projected capacitive touch screens can
use either mutual capacitive sensors or self capacitive sensors. In
mutual capacitive sensors, there is a capacitor at every
intersection of each row and each column. A 16.times.14 array, for
example, would have 224 independent capacitors. A voltage is
applied to the rows or columns. Bringing a finger or conductive
stylus close to the surface of the sensor changes the local
electrostatic field which reduces the mutual capacitance. The
capacitance change at every individual point on the grid can be
measured to accurately determine the touch location by measuring
the voltage in the other axis. Mutual capacitance allows
multi-touch operation where multiple fingers, palms or styli can be
accurately tracked at the same time.
[0006] WO 2013/063188 by Petcavich et al. discloses a method of
manufacturing a capacitive touch sensor using a roll-to-roll
process to print a conductor pattern on a flexible transparent
dielectric substrate. A first conductor pattern is printed on a
first side of the dielectric substrate using a first flexographic
printing plate and is then cured. A second conductor pattern is
printed on a second side of the dielectric substrate using a second
flexographic printing plate and is then cured. The ink used to
print the patterns includes a catalyst that acts as seed layer
during subsequent electroless plating. The electrolessly plated
material (e.g., copper) provides the low resistivity in the narrow
lines of the grid needed for excellent performance of the
capacitive touch sensor. Petcavich et al. indicate that the line
width of the flexographically printed material can be 1 to 50
microns.
[0007] Flexography is a method of printing or pattern formation
that is commonly used for high-volume printing runs. It is
typically employed in a roll-to-roll format for printing on a
variety of soft or easily deformed materials including, but not
limited to, paper, paperboard stock, corrugated board, polymeric
films, fabrics, metal foils, glass, glass-coated materials,
flexible glass materials and laminates of multiple materials.
Coarse surfaces and stretchable polymeric films are also
economically printed using flexography.
[0008] Flexographic printing members are sometimes known as relief
printing members, relief-containing printing plates, printing
sleeves, or printing cylinders, and are provided with raised relief
images onto which ink is applied for application to a printable
material. While the raised relief images are inked, the recessed
relief "floor" should remain free of ink.
[0009] Although flexographic printing has conventionally been used
in the past for printing of images, more recent uses of
flexographic printing have included functional printing of devices,
such as touch screen sensor films, antennas, and other devices to
be used in electronics or other industries. Such devices typically
include electrically conductive patterns.
[0010] To improve the optical quality and reliability of the touch
screen, it has been found to be preferable that the width of the
grid lines be approximately 2 to 10 microns, and even more
preferably to be 4 to 8 microns. In addition, in order to be
compatible with the high-volume roll-to-roll manufacturing process,
it is preferable for the roll of flexographically printed material
to be electroless plated in a roll-to-roll electroless plating
system. More conventionally, electroless plating is performed by
immersing the item to be plated in a tank of plating solution.
However, for high volume uniform plating of features on both sides
of the web of substrate material, it is preferable to perform the
electroless plating in a roll-to-roll electroless plating
system.
[0011] Roll-to-roll electroless plating systems are commercially
available from Chemcut Corporation, for example. However,
commercially available roll-to-roll electroless plating systems are
adapted to be used with plating solutions that include a relatively
high amount of dissolved oxygen, for example greater than three
parts per million. Such plating solutions can work well for plating
copper in the context of printed circuit board manufacture where
the minimum line width is on the order of 100 microns. However, it
has been found that such oxygen-rich plating solutions do not
provide uniform metallization at high yield on features having line
widths of 10 microns or less.
[0012] Dissolved oxygen content of an electroless plating solution
influences the rate and quality of the plating. As indicated in
U.S. Pat. No. 4,616,596 Helber Jr. et al., entitled "Electroless
plating apparatus," U.S. Pat. No. 4,684,545 to Fey et al., entitled
"Electroless plating with bi-level control of dissolved oxygen,"
and U.S. Patent Application Publication No. 2011/0214608 to Ivanov
et al., entitled "Electroless Plating System," increased oxygen
content tends to stabilize plating and decrease the plating rate.
Decreased oxygen content tends to increase plating activity.
[0013] It has been found that a copper electroless plating solution
made by Enthone is well-suited to provide high quality plating on
features having minimum line widths of 10 microns or less in a low
dissolved oxygen content tank plating system, but not in a
commercially available roll-to-roll electroless plating system.
What is needed is a roll-to-roll plating system and method that can
provide and maintain low dissolved oxygen content in the plating
solution.
SUMMARY OF THE INVENTION
[0014] The present invention represents a roll-to-roll electroless
plating system, comprising:
[0015] a reservoir containing plating solution;
[0016] a web advance system for advancing a web of media from an
input roll through the plating solution in the reservoir to a
take-up roll, wherein a plating substance in the plating solution
is plated onto predetermined locations on a surface of the web of
media as it is advanced through the plating solution in the
reservoir; and
[0017] a distribution system for injecting an inert gas into the
plating solution, wherein the distribution system includes an
injector for injecting the inert gas into the plating solution,
wherein the injector includes: [0018] a converging tube segment;
[0019] a diverging tube segment downstream of the converging tube
segment; [0020] a throat formed at a junction of the converging
tube segment and the diverging tube segment; and [0021] an inlet
for the inert gas in proximity to the throat.
[0022] This invention has the advantage that the inert gas for
reducing the amount of dissolved oxygen can be injected from a low
pressure gas source into the plating solution downstream of a
pump.
[0023] It has the additional advantage that the injector can form
micro-bubbles of the inert gas which are more efficient at reducing
the dissolved oxygen content in the plating solution.
[0024] It the further advantage that the injection of the inert gas
reduces the amount of dissolved oxygen in the plating solution to
provide dissolved oxygen levels appropriate for use with plating
solutions whose performance degrades at higher levels of dissolved
oxygen.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a schematic side view of a flexographic printing
system for roll-to-roll printing on both sides of a substrate;
[0026] FIG. 2 is a schematic side view of a prior art roll-to-roll
electroless plating system;
[0027] FIG. 3 is a schematic side view of a roll-to-roll
electroless plating system according to an embodiment of the
invention;
[0028] FIG. 4 is a schematic side view of a roll-to-roll
electroless plating system according to another embodiment of the
invention;
[0029] FIG. 5A is a top view of an exemplary embodiment of a
plumbing assembly for distributing inert gas bubbles into the
plating solution;
[0030] FIG. 5B is a top view of another exemplary embodiment of a
plumbing assembly for distributing inert gas bubbles into the
plating solution;
[0031] FIG. 6 is a side view of an injector for injecting inert gas
at a localized low pressure region;
[0032] FIG. 7 is a high-level system diagram for an apparatus
having a touch screen with a touch sensor that can be printed using
embodiments of the invention;
[0033] FIG. 8 is a side view of the touch sensor of FIG. 7;
[0034] FIG. 9 is a top view of a conductive pattern printed on a
first side of the touch sensor of FIG. 8; and
[0035] FIG. 10 is a top view of a conductive pattern printed on a
second side of the touch sensor of FIG. 8.
[0036] It is to be understood that the attached drawings are for
purposes of illustrating the concepts of the invention and may not
be to scale.
DETAILED DESCRIPTION OF THE INVENTION
[0037] The present description will be directed in particular to
elements forming part of, or cooperating more directly with, an
apparatus in accordance with the present invention. It is to be
understood that elements not specifically shown, labeled, or
described can take various forms well known to those skilled in the
art. In the following description and drawings, identical reference
numerals have been used, where possible, to designate identical
elements. It is to be understood that elements and components can
be referred to in singular or plural form, as appropriate, without
limiting the scope of the invention.
[0038] The invention is inclusive of combinations of the
embodiments described herein. References to "a particular
embodiment" and the like refer to features that are present in at
least one embodiment of the invention. Separate references to "an
embodiment" or "particular embodiments" or the like do not
necessarily refer to the same embodiment or embodiments; however,
such embodiments are not mutually exclusive, unless so indicated or
as are readily apparent to one of skill in the art. It should be
noted that, unless otherwise explicitly noted or required by
context, the word "or" is used in this disclosure in a
non-exclusive sense.
[0039] The example embodiments of the present invention are
illustrated schematically and not to scale for the sake of clarity.
One of ordinary skill in the art will be able to readily determine
the specific size and interconnections of the elements of the
example embodiments of the present invention.
[0040] References to upstream and downstream herein refer to
direction of flow. Web media moves along a media path in a web
advance direction from upstream to downstream. Similarly, fluids
flow through a fluid line in a direction from upstream to
downstream.
[0041] As described herein, the example embodiments of the present
invention provide a roll-to-roll electroless plating system and
methods for providing and maintaining low dissolved oxygen content
in the plating solution. The roll-to-roll electroless plating
system is useful for metalizing printed features in sensor films
incorporated into touch screens. However, many other applications
are emerging for printing and electroless plating of functional
devices that can be incorporated into other electronic,
communications, industrial, household, packaging and product
identification systems (such as RFID) in addition to touch screens.
In addition, roll-to-roll electroless plating systems can be used
to plate items for decorative purposes rather than electronic
purposes and such applications are contemplated as well.
[0042] FIG. 1 is a schematic side view of a flexographic printing
system 100 that can be used in embodiments of the invention for
roll-to-roll printing of a catalytic ink on both sides of a
substrate 150 for subsequent electroless plating. Substrate 150 is
fed as a web from supply roll 102 to take-up roll 104 through
flexographic printing system 100. Substrate 150 has a first side
151 and a second side 152.
[0043] The flexographic printing system 100 includes two print
modules 120 and 140 that are configured to print on the first side
151 of substrate 150, as well as two print modules 110 and 130 that
are configured to print on the second side 152 of substrate 150.
The web of substrate 150 travels overall in roll-to-roll direction
105 (left to right in the example of FIG. 1). However, various
rollers 106 and 107 are used to locally change the direction of the
web of substrate as needed for adjusting web tension, providing a
buffer, and reversing the substrate 150 for printing on an opposite
side. In particular, note that in print module 120 roller 107
serves to reverse the local direction of the web of substrate 150
so that it is moving substantially in a right-to-left
direction.
[0044] Each of the print modules 110, 120, 130, 140 includes some
similar components including a respective plate cylinder 111, 121,
131, 141, on which is mounted a respective flexographic printing
plate 112, 122, 132, 142, respectively. Each flexographic printing
plate 112, 122, 132, 142 has raised features 113 defining an image
pattern to be printed on the substrate 150. Each print module 110,
120, 130, 140 also includes a respective impression cylinder 114,
124, 134, 144 that is configured to force a side of the substrate
150 into contact with the corresponding flexographic printing plate
112, 122, 132, 142. Impression cylinders 124 and 144 of print
modules 120 and 140 (for printing on first side 151 of substrate
150) rotate counter-clockwise in the view shown in FIG. 1, while
impression cylinders 114 and 134 of print modules 110 and 130 (for
printing on second side 152 of substrate 150) rotate clockwise in
this view.
[0045] Each print module 110, 120, 130, 140 also includes a
respective anilox roller 115, 125, 135, 145 for providing ink to
the corresponding flexographic printing plate 112, 122, 132, 142.
As is well known in the printing industry, an anilox roller is a
hard cylinder, usually constructed of a steel or aluminum core,
having an outer surface containing millions of very fine dimples,
known as cells. Ink is provided to the anilox roller by a tray or
chambered reservoir (not shown). In some embodiments, some or all
of the print modules 110, 120, 130, 140 also include respective UV
curing stations 116, 126, 136, 146 for curing the printed ink on
substrate 150.
[0046] FIG. 2 is a schematic side view of a prior art roll-to-roll
electroless plating system 200, similar to a configuration
available from Chemcut Corporation, for use with a plating solution
210. The roll-to-roll electroless plating system 200 performs well
with plating solutions 210 that are formulated for optimized
plating with relatively high dissolved oxygen content (e.g.,
greater than 3 parts per million). Substrate 250 is fed as a web of
media from supply roll 202 to take-up roll 204. Drive rollers 206
advance the web in a web advance direction 205 from the supply roll
202 through a reservoir of the plating solution 210 to the take-up
roll 204. In the configuration shown in FIG. 2, a sump 230 contains
a large volume of the plating solution 210, and a pan 220
positioned above the sump contains a smaller volume of the plating
solution 210.
[0047] As the substrate 250 is advanced through the plating
solution 210 in the pan 220, a metallic plating substance such as
copper, silver, nickel or palladium is electrolessly plated from
the plating solution 210 onto predetermined locations on one or
both of a first surface 251 and a second surface 252 of the
substrate 250. As a result, the concentration of the metal in the
plating solution 210 in the pan 220 decreases and the plating
solution 210 needs to be refreshed. To refresh the plating solution
210, it is recirculated between the sump 230 and the pan 220. A
lower lift pump 232 moves plating solution 210 from the sump 230
through a pipe 233 to a lower flood bar 222 for distribution into
the pan 220 below the substrate 250. Likewise, an upper lift pump
234 moves plating solution 210 from the sump 230 through a pipe 235
to an upper flood bar 224 for distribution into the pan 220 above
the substrate 250. Excess plating solution 210 waterfalls back into
the sump 230 at freefall return 236. Occasionally the plating
solution 210 is chemically analyzed, for example by titration, and
fresh plating solution 210, or components of the plating solution
210, are added to the sump 230 as needed. Air inlet tubes 240 are
provided to provide additional oxygen to the plating solution 210
in sump 230 as needed.
[0048] Although the prior art roll-to-roll electroless plating
system 200 shown in FIG. 2 works well for plating solutions 210
that are designed to plate at relatively high levels of dissolved
oxygen, for example greater than 3 parts per million, it has been
found that it does not work well for plating solutions 210 that are
designed to plate at a lower level of dissolved oxygen, for example
between about 0.5 parts per million and about 2 parts per million.
Not adding air through the air inlet tubes 240 is an obvious
measure for reducing the dissolved oxygen content in the plating
solution 210. However, in order to control the dissolved oxygen
content at the desired low level, it is necessary to make
significant modifications to the roll-to-roll electroless plating
system 200.
[0049] FIG. 3 is a schematic side view of an improved roll-to-roll
electroless plating system 300 which is useful for plating
solutions 310 having a low level of dissolved oxygen content. As in
the prior art electroless plating system 200, a substrate 350 is
fed as a web of media from a supply roll 302 to a take-up roll 304.
Drive rollers 306 advance the web of substrate 350 along a web
advance direction 305 from the supply roll 302 through a reservoir
of plating solution 310 to the take-up roll 304. A sump 330
contains a large volume of the plating solution 310 and a pan 320
positioned above the sump contains a smaller volume of the plating
solution 310. The term "reservoir" can be used to refer to either
the sump 330 or the pan 320.
[0050] As the substrate 350 is advanced through the plating
solution 310 in pan 320, a metallic plating substance such as
copper, silver, nickel or palladium is electrolessly plated from
the plating solution 310 onto predetermined locations on one or
both of a first surface 351 and a second surface 352 of the
substrate 350. The predetermined locations can be provided, for
example, by the prior printing of a catalytic ink.
[0051] A number of modifications have been made relative to the
prior art similar to a configuration available from roll-to-roll
electroless plating system 200 of FIG. 2 to control the amount of
dissolved oxygen in the plating solution within a lower range of
about 0.5 to about 2 parts per million. The modifications include
measures to a) reduce the amount of turbulence in the plating
solution 310 in portions of the roll-to-roll electroless plating
system 300 that are exposed to air, b) reduce the exposure of the
plating solution 310 to ambient air, c) displace dissolved oxygen
from the plating solution 310, and d) sense the amount of dissolved
oxygen in the plating solution 310.
[0052] Modifications for reducing turbulence in the roll-to-roll
electroless plating system 300 of FIG. 3 relative to the prior art
roll-to-roll electroless plating system 200 of FIG. 2 include
replacing the freefall return 236 (FIG. 2) with a more controlled
flow of the plating solution 310 through a drain pipe 336;
eliminating the lower flood bar 222 and the upper flood bar 224
(FIG. 2); and removing the upper lift pump 234 and its associated
plumbing. Instead, in roll-to-roll electroless plating system 300,
there is only a single pan-replenishing pump 332 that moves plating
solution 310 from the sump 330 to the pan 320 through a pipe 333
connected to an outlet 335 of the pan-replenishing pump 332.
Plating solution 310 enters the pan-replenishing pump 332 from sump
330 via an inlet 331.
[0053] In addition to reducing splashing and other forms of
turbulence, drain pipe 336 also reduces the exposure of plating
solution 310 to ambient air. The top of drain pipe 336 is within
the plating solution 310 in pan 320, and the bottom of drain pipe
336 is within the plating solution 310 in sump 330. Other measures
for reducing the exposure of plating solution 310 to ambient air
include providing a sump cover 338 and optionally providing a pan
cover 328 (see FIG. 4).
[0054] Preferred embodiments of the invention also include
modifications that provide for the displacement of dissolved oxygen
from the plating solution 310. This is done by injecting an inert
gas into the plating solution 310 via a distribution system. As
used herein, the term inert gas refers to a gas that does not take
part in the chemical reactions necessary for electroless plating.
Nitrogen is an example of such an inert gas. Another example of an
inert gas would be argon. In various embodiments, the inert gas can
also be injected into one or both of the sump 330 and pan 320. FIG.
3 shows inert gas being injected into the pan 320 from an inert gas
source 345. In the illustrated embodiment, the inert gas from the
inert gas source 345 is inserted into pipe 333 at through tee 334,
forming bubbles 344 which are carried into the pan 320.
[0055] FIG. 3 also shows bubbles 344 of inert gas being injected
into the sump 330 from inert gas source 340. As the inert gas is
dissolved in the plating solution 310, the amount of dissolved
oxygen decreases. To facilitate dissolution of the inert gas, it is
advantageous to inject the inert gas as micro-bubbles and to
distribute the inert gas in such a way as to promote longer paths
through the plating solution 310 before exiting. In the embodiment
of FIG. 3, the bubbles 344 are injected through a plumbing assembly
342 located near a bottom 339 of sump 330 so that the injected
bubbles 344 will rise through nearly the entire height of the
plating solution 310. The inert gas enters the plumbing assembly
342 from the inert gas source 340 through an inert gas inlet 341.
As shown in the top view of FIG. 5A, in an exemplary embodiment the
plumbing assembly 342 has a network of distributed orifices 343, so
that the inert gas bubbles 344 enter the plating solution 310 more
uniformly, thereby facilitating dissolution by avoiding forming a
few regions of inert-gas-saturated plating solution 310.
[0056] Within the context of the present invention, micro-bubbles
are defined as bubbles having a diameter between about one micron
(one thousandth of a millimeter) and one millimeter. Since the
ratio of surface area to volume of a sphere is inversely dependent
upon diameter, micro-bubbles have a larger surface area to volume
ratio than larger bubbles, thereby facilitating efficient
dissolution into the plating solution 310. In addition,
micro-bubbles tend to stay suspended longer in the plating solution
310 rather than rising and bursting rapidly. As described below,
there are a variety of ways to inject the inert gas into the
plating solution 310 in the form of micro-bubbles.
[0057] It is also advantageous to control the amount of flow of
inert gas into the plating solution 310 according to a measured
amount of dissolved oxygen in the plating solution 310. An oxygen
sensor 360 can be immersed into, or periodically dipped into, the
plating solution 310 to measure the dissolved oxygen content. The
data from the oxygen sensor 360 can be provided to a controller 315
to control the rate of flow of inert gas injected into plating
solution 310 from inert gas source 340 or inert gas source 345, for
example by controlling flow rate through a needle valve (not
shown).
[0058] FIG. 4 shows a schematic side view of an alternate
embodiment of a roll-to-roll electroless plating system 300 that
injects micro-bubbles of inert gas into the sump 330 by means of a
recirculation system including a recirculation pump 370 having an
inlet 373 and an outlet 375; an inlet line 372 for moving plating
solution 310 from the sump 330 to the pump inlet 373; and an outlet
line 374 for returning plating solution 310 from the pump outlet
375 to the sump 330. In the example shown in FIG. 4, inert gas is
injected into the low pressure inlet 373 of the recirculation pump
370 from an inert gas source 376 connected to inlet 373 by tee 378.
Mechanical action within recirculation pump 370 tends to break
inert gas bubbles into micro-bubbles, which then flow together with
plating solution 310 from the pump outlet 375 into the sump 330
through a plumbing assembly 342 located near bottom 339 of sump 330
providing the bubbles 344. Furthermore, a filter 377 can be
disposed in the outlet line 374 for removing particulates so that
they do not re-enter the sump 330. A second function of filter 377,
which may have a pore size on the order of one micron, can
optionally be used to break up bubbles of inert gas into
micro-bubbles. Thus, inert gas is injected into the plating
solution 310 outside the sump 330 to provide an inert-gas-rich
plating solution 310, and the inert-gas-rich plating solution 310
is delivered into the sump 330.
[0059] FIG. 5B shows a top view of an exemplary embodiment of the
plumbing assembly 379, where the inert gas is injected from the
inert gas source 376 into the inlet line 372 to the recirculation
pump 370. The inert gas bubbles pass through a filter 377 before
entering plumbing assembly 379. The bubbles of inert gas have a
long flow path within plumbing assembly 379 before exiting at
distributed orifices 371, thereby aiding dissolution of the inert
gas into the plating solution 310 (FIG. 4) within the plumbing
assembly 379.
[0060] An advantage of injecting inert gas on the low pressure
inlet side of a pump is that the inert gas source 376 can be a low
pressure source for improved flow control. However, a potential
disadvantage of injecting inert gas into a pump inlet is cavitation
damage within the pump. FIG. 4 also shows inert gas flowing from
inert gas source 345 through a tee 334 into pipe 333 downstream of
the outlet 335 of pan-replenishing pump 332. Thus, inert gas is
injected into the plating solution 310 outside the pan 320 to
provide an inert-gas-rich plating solution 310, and the
inert-gas-rich plating solution 310 is delivered into the pan 320
through the pipe 333. A filter 348 can be used for further reducing
the size of bubbles.
[0061] In some embodiments, a static mixer (not shown) having a
tortuous flow path around baffles can be inserted in-line with pipe
333 to facilitate dissolution of the inert gas micro-bubbles within
the plating solution 310 being returned to pan 320 through pipe
333.
[0062] Although FIG. 4 shows inert gas provided upstream of the
inlet 373 of recirculation pump 370, and shows inert gas provided
downstream of the outlet 335 of pan-replenishing pump 332,
alternatively inert gas could be provide downstream of outlet 375
of recirculation pump 370 or upstream of inlet 331 of
pan-replenishing pump 332.
[0063] For configurations where the inert gas is provided
downstream of the outlet of a pump (i.e., on the high pressure side
of the pump), it is advantageous to provide a local low pressure
region where the inert gas can be injected. For example, in FIG. 4,
it can be useful to provide a local low pressure region where the
inert gas is injected downstream of the outlet 335 of the
pan-replenishing pump 332. FIG. 6 is a side view of an injector 380
(sometimes called a Venturi injector) for providing a local low
pressure region at a gas injection site. The injector 380 can be
used at the position of the tee 334 in FIG. 4. Injector 380
includes a throat 386; converging tube segment 382 upstream of the
throat 386 having a diameter D1 that decreases from an upstream
portion to a downstream portion; and a diverging tube segment 384
downstream of the throat 386 having a diameter D2 that increases
from an upstream portion to a downstream portion. The throat 386 is
formed by the junction of the converging tube segment 382 and the
diverging tube segment 384. The plating solution 310 flows through
the injector 380 from upstream to downstream in flow direction 385.
Due to the Venturi effect, a localized low pressure region is
formed at the throat 386. By providing an inlet 388 for inert gas
389 in proximity to the throat 386, a low pressure source of inert
gas, such as inert gas sources 340, 345 (FIG. 4) can be used. In
some operating conditions it has been found that micro-bubbles tend
to be formed when the inert gas is injected using injector 380,
thereby providing an additional advantage for the use of this
device. In some embodiments, an injector 380 can be also be used to
inject inert gas downstream of the outlet 375 of the recirculation
pump 370 (FIG. 4).
[0064] Having described exemplary embodiments of the roll-to-roll
electroless plating system 300, a context has been provided for
describing further details of methods for controlling the dissolved
oxygen content to be at its desired low range (e.g., in the range
of about 0.5 to about 2 parts per million). As described above, an
amount of dissolved oxygen in the plating solution 310 is measured
using oxygen sensor 360. The measured amount of dissolved oxygen is
compared to a target range of dissolved oxygen. If the measured
amount of dissolved oxygen is greater than the target range of
dissolved oxygen, then the rate of injecting the inert gas is
increased, for example by further opening a needle valve through
which the inert gas flows to increase the flow rate. If the
measured amount of dissolved oxygen is less than the target range
of dissolved oxygen, then the rate of injecting the inert gas is
decreased, for example by further closing a needle valve through
which the inert gas flows to decrease the flow rate.
[0065] In some embodiments, the measuring of the amount of
dissolved oxygen can be repeated at specified time intervals, for
example once every five minutes or once every hour. During start-up
of the electroless plating process, prior to injecting inert gas,
the plating solution 310 tends to be somewhat oxygen rich.
Therefore, it can be advantageous to measure the dissolved oxygen
content at a relatively high repetition frequency (e.g., once every
five minutes) during a start-up phase, and then to measure the
dissolved oxygen content at a lower repetition frequency (e.g.,
once per thirty minutes) after the system has stabilized and the
dissolved oxygen content has reached the target range.
[0066] In some embodiments, measurement of dissolved oxygen content
can also be initiated by the controller 315 if it detects that an
environmental condition has changed. For example, a measurement can
be initiated if the controller 315 senses that the temperature of
the plating solution 310 has changed by more than a predetermined
threshold, as gas solubility is a function of temperature.
[0067] In some embodiments, measurement of dissolved oxygen content
can also be initiated when a system operating condition changes.
For example, a measurement can be initiated if the pan cover 328 is
removed for service, thereby exposing the surface of the plating
solution 310 to the air. Likewise, a measurement can be initiated
when fresh plating solution 310, or components of the plating
solution 310, are added to the sump 330.
[0068] In some embodiments, measurement of dissolved oxygen content
can also be initiated when an indication is detected that the
system may not be performing in the intended manner. For example, a
measurement can be initiated if it is observed that elements of the
plating solution 310 are plating onto extraneous surfaces other
than the intended features on the substrate 250.
[0069] In some embodiments, a user interface can be provided to
enable the measurement of dissolved oxygen to be manually initiated
by an operator. For example, if it is observed that the system
performance has been degraded.
[0070] For embodiments where the inert gas is injected into the
plating solution 310 for delivery into both the sump 330 and the
pan 320, the rates of injection can be independently controlled by
controller 315. For example, the injection of the inert gas into
the plating solution 310 for delivery into the sump 330 can be done
at a first rate, and the injection of inert gas into the plating
solution 310 for delivery into the pan 320 can be done at a second
rate that is different from the first rate.
[0071] FIG. 3 shows the oxygen sensor 360 submerged within the
plating solution 310 in pan 320. In some embodiments, if the oxygen
sensor 360 is kept within the plating solution 310, metal can
deposit on it, thereby affecting its performance. FIG. 4 shows an
embodiment where the oxygen sensor 360 is configured to be
repositionable. Under control of controller 315, a motor 362
controllably lowers the oxygen sensor 360 to dip it into the
plating solution 310 (e.g., through an opening in the pan cover
328) in order to measure dissolved oxygen content. The controller
315 can then control the motor 362 to raise the oxygen sensor 360
to remove it from the plating solution after the measurement is
made. Data indicating the measured amount of dissolved oxygen can
be sent to controller 315 either before or after the oxygen sensor
360 is removed from the plating solution 310.
[0072] FIG. 7 shows a high-level system diagram for an apparatus
400 having a touch screen 410 including a display device 420 and a
touch sensor 430 that overlays at least a portion of a viewable
area of display device 420. Touch sensor 430 senses touch and
conveys electrical signals (related to capacitance values for
example) corresponding to the sensed touch to a controller 480.
Touch sensor 430 is an example of an article that can be printed on
one or both sides by the flexographic printing system 100 and
plated using an embodiment of roll-to-roll electroless plating
system 300 with low dissolved oxygen content described above.
[0073] FIG. 8 shows a schematic side view of a touch sensor 430.
Transparent substrate 440, for example polyethylene terephthalate,
has a first conductive pattern 450 printed and plated on a first
side 441, and a second conductive pattern 460 printed and plated on
a second side 442. The length and width of the transparent
substrate 440, which is cut from the take-up roll 104 (FIG. 1), is
not larger than the flexographic printing plates 112, 122, 132, 142
of flexographic printing system 100 (FIG. 1), but it could be
smaller than the flexographic printing plates 112, 122, 132,
142.
[0074] FIG. 9 shows an example of a conductive pattern 450 that can
be printed on first side 441 (FIG. 8) of substrate 440 (FIG. 8)
using one or more print modules such as print modules 120 and 140
of flexographic printing system (FIG. 1), followed by plating using
an embodiment of roll-to-roll electroless plating system 300 (FIGS.
3 and 4). Conductive pattern 450 includes a grid 452 including grid
columns 455 of intersecting fine lines 451 and 453 that are
connected to an array of channel pads 454. Interconnect lines 456
connect the channel pads 454 to the connector pads 458 that are
connected to controller 480 (FIG. 7). Conductive pattern 450 can be
printed by a single print module 120 in some embodiments. However,
because the optimal print conditions for fine lines 451 and 453
(e.g., having line widths on the order of 4 to 8 microns) are
typically different than for printing the wider channel pads 454,
connector pads 458 and interconnect lines 456, it can be
advantageous to use one print module 120 for printing the fine
lines 451 and 453 and a second print module 140 for printing the
wider features. Furthermore, for clean intersections of fine lines
451 and 453, it can be further advantageous to print and cure one
set of fine lines 451 using one print module 120, and to print and
cure the second set of fine lines 453 using a second print module
140, and to print the wider features using a third print module
(not shown in FIG. 1) configured similarly to print modules 120 and
140.
[0075] FIG. 10 shows an example of a conductive pattern 460 that
can be printed on second side 442 (FIG. 8) of substrate 440 (FIG.
8) using one or more print modules such as print modules 110 and
130 of flexographic printing system (FIG. 1), followed by plating
using an embodiment of roll-to-roll electroless plating system 300
(FIGS. 3 and 4). Conductive pattern 460 includes a grid 462
including grid rows 465 of intersecting fine lines 461 and 463 that
are connected to an array of channel pads 464. Interconnect lines
466 connect the channel pads 464 to the connector pads 468 that are
connected to controller 480 (FIG. 7). In some embodiments,
conductive pattern 460 can be printed by a single print module 110.
However, because the optimal print conditions for fine lines 461
and 463 (e.g., having line widths on the order of 4 to 8 microns)
are typically different than for the wider channel pads 464,
connector pads 468 and interconnect lines 466, it can be
advantageous to use one print module 110 for printing the fine
lines 461 and 463 and a second print module 130 for printing the
wider features. Furthermore, for clean intersections of fine lines
461 and 463, it can be further advantageous to print and cure one
set of fine lines 461 using one print module 110, and to print and
cure the second set of fine lines 463 using a second print module
130, and to print the wider features using a third print module
(not shown in FIG. 1) configured similarly to print modules 110 and
130.
[0076] Alternatively, in some embodiments conductive pattern 450
can be printed using one or more print modules configured like
print modules 110 and 130, and conductive pattern 460 can be
printed using one or more print modules configured like print
modules 120 and 140 of FIG. 1 followed by plating using an
embodiment of roll-to-roll electroless plating system 300 (FIGS. 3
and 4).
[0077] With reference to FIGS. 7-10, in operation of touch screen
410, controller 480 can sequentially electrically drive grid
columns 455 via connector pads 458 and can sequentially sense
electrical signals on grid rows 465 via connector pads 468. In
other embodiments, the driving and sensing roles of the grid
columns 455 and the grid rows 465 can be reversed.
[0078] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
PARTS LIST
[0079] 100 flexographic printing system [0080] 102 supply roll
[0081] 104 take-up roll [0082] 105 roll-to-roll direction [0083]
106 roller [0084] 107 roller [0085] 110 print module [0086] 111
plate cylinder [0087] 112 flexographic printing plate [0088] 113
raised features [0089] 114 impression cylinder [0090] 115 anilox
roller [0091] 116 UV curing station [0092] 120 print module [0093]
121 plate cylinder [0094] 122 flexographic printing plate [0095]
124 impression cylinder [0096] 125 anilox roller [0097] 126 UV
curing station [0098] 130 print module [0099] 131 plate cylinder
[0100] 132 flexographic printing plate [0101] 134 impression
cylinder [0102] 135 anilox roller [0103] 136 UV curing station
[0104] 140 print module [0105] 141 plate cylinder [0106] 142
flexographic printing plate [0107] 144 impression cylinder [0108]
145 anilox roller [0109] 146 UV curing station [0110] 150 substrate
[0111] 151 first side [0112] 152 second side [0113] 200
roll-to-roll electroless plating system [0114] 202 supply roll
[0115] 204 take-up roll [0116] 205 web advance direction [0117] 206
drive roller [0118] 210 plating solution [0119] 220 pan [0120] 222
lower flood bar [0121] 224 upper flood bar [0122] 230 sump [0123]
232 lower lift pump [0124] 233 pipe [0125] 234 upper lift pump
[0126] 235 pipe [0127] 236 freefall return [0128] 240 air inlet
tube [0129] 250 substrate [0130] 251 first surface [0131] 252
second surface [0132] 300 roll-to-roll electroless plating system
[0133] 302 supply roll [0134] 304 take-up roll [0135] 305 web
advance direction [0136] 306 drive roller [0137] 310 plating
solution [0138] 315 controller [0139] 320 pan [0140] 328 pan cover
[0141] 330 sump [0142] 331 inlet [0143] 332 pan-replenishing pump
[0144] 333 pipe [0145] 334 tee [0146] 335 outlet [0147] 336 drain
pipe [0148] 338 sump cover [0149] 339 bottom [0150] 340 inert gas
source [0151] 341 inert gas inlet [0152] 342 plumbing assembly
[0153] 343 orifices [0154] 344 bubbles [0155] 345 inert gas source
[0156] 348 filter [0157] 350 substrate [0158] 351 first surface
[0159] 352 second surface [0160] 360 oxygen sensor [0161] 362 motor
[0162] 370 recirculation pump [0163] 371 orifices [0164] 372 inlet
line [0165] 373 inlet [0166] 374 outlet line [0167] 375 outlet
[0168] 376 inert gas source [0169] 377 filter [0170] 378 tee [0171]
379 plumbing assembly [0172] 380 injector [0173] 382 converging
tube segment [0174] 384 diverging tube segment [0175] 385 flow
direction [0176] 386 throat [0177] 388 inlet [0178] 389 inert gas
[0179] 400 apparatus [0180] 410 touch screen [0181] 420 display
device [0182] 430 touch sensor [0183] 440 transparent substrate
[0184] 441 first side [0185] 442 second side [0186] 450 conductive
pattern [0187] 451 fine lines [0188] 452 grid [0189] 453 fine lines
[0190] 454 channel pads [0191] 455 grid column [0192] 456
interconnect lines [0193] 458 connector pads [0194] 460 conductive
pattern [0195] 461 fine lines [0196] 462 grid [0197] 463 fine lines
[0198] 464 channel pads [0199] 465 grid row [0200] 466 interconnect
lines [0201] 468 connector pads [0202] 480 controller [0203] D1
diameter [0204] D2 diameter
* * * * *