Patent Publication Number: US-9890459-B2

Title: Roll-to-roll electroless plating system with spreader duct

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of prior U.S. patent application Ser. No. 14/484,866 (now U.S. Publication No. 2016/0076150), filed Sep. 12, 2014, which is hereby incorporated herein by reference in its entirety. 
     Reference is made to commonly-assigned, U.S. patent application Ser. No. 14/455,196 (now U.S. Publication No. 2016/0040292), entitled “Roll-to-roll electroless plating system with low dissolved oxygen content” by G. Wainwright et al.; to commonly-assigned, U.S. patent application Ser. No. 14/455,227 (now U.S. Publication No. 2016/0040293), entitled “Method for roll-to-roll electroless plating with low dissolved oxygen content” by G. Wainwright et al.; and to commonly-assigned, U.S. patent application Ser. No. 14/455,246 (now U.S. Publication No. 2016/0040291), entitled “Roll-to-roll electroless plating system with micro-bubble injector” by G. Wainwright et al., each of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention pertains to the field of roll-to-roll electroless plating, and more particularly to a system for replenishing the plating solution while inhibiting the trapping of gas bubbles beneath the web. 
     BACKGROUND OF THE INVENTION 
     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. 
     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. 
     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 16×14 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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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 to 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. Air can be added to the plating solution to increase the dissolved oxygen content. Alternatively, an inert gas such as nitrogen can be added to the plating solution to decrease the dissolved oxygen content. As disclosed in U.S. Pat. No. 5,284,520 to Tanaka, entitled “Electroless Plating Device,” for an immersion plating tank where air is blown into the plating solution, a shield plate having small perforations can be used to allow distribution of the oxygenated plating solution without allowing air bubbles to directly contact the object to be plated. 
     Roll-to-roll electroless plating systems are commercially available from Chemcut Corporation, for example. In such systems, a web of media is advanced substantially horizontally through a pan of plating solution. The plating solution in the pan is replenished from a sump. It has been found that in a roll-to-roll electroless plating system if the replenishment inlet to the pan is directly below the horizontal web of media, and if air or gas bubbles are injected into the plating solution shortly before entering the replenishment inlet to the pan, some of the bubbles can become trapped beneath the web of media, thereby interfering with uniform plating on the lower side of the web of media. What is needed is a system that allows the addition of air or gas into the plating solution being replenished into the pan and facilitates mixing of the replenished plating solution within the pan in such a way that bubbles are not trapped beneath the web of media. 
     SUMMARY OF THE INVENTION 
     The present invention represents a roll-to-roll electroless plating system, comprising: 
     a reservoir containing a volume of a plating solution; 
     a web advance system for advancing a web of substrate from an input roll though the plating solution in the reservoir along a web advance direction and to a take-up-roll, the web of substrate including a first edge and a second edge that is separated from the first edge along a cross-track direction perpendicular to the web advance direction, wherein a plating substance in the plating solution is plated onto predetermined locations on a surface of the web of substrate as it is advanced through the plating solution in the pan; 
     a pump for circulating plating solution, the pump having an inlet connected to an output of the reservoir and an outlet connected through a pipe to an inlet of the reservoir, the inlet of the reservoir being located in proximity to a bottom of the reservoir below the web of substrate; and 
     a spreader duct including a channel that is in fluidic communication with the inlet of the reservoir, wherein the channel is positioned below the web of substrate and includes at least one outlet disposed beyond the first edge or the second edge of the web of substrate, and wherein the channel has no outlets disposed immediately below the web of substrate. 
     This invention has the advantage that any bubbles of gas that are introduced in the plating solution upstream of the inlet of the reservoir are directed beyond the edges of the web of substrate so that they do not collect on a bottom surface of the substrate where they would impact the uniformity of the plating process. 
     It has the additional advantage that a plurality of outlets can be provided to control the distribution of the plating solution within the pan. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of a flexographic printing system for roll-to-roll printing on both sides of a substrate; 
         FIG. 2  is a schematic side view of a prior art roll-to-roll electroless plating system; 
         FIG. 3  is a schematic side view of a roll-to-roll electroless plating system; 
         FIG. 4  is a schematic side view of a roll-to-roll electroless plating system; 
         FIG. 5  is a schematic side view of a roll-to-roll electroless plating system including a pan inlet in the bottom of the pan; 
         FIG. 6  is a perspective of a prior art flood bar; 
         FIG. 7  is a perspective of a portion of a roll-to-roll electroless plating system having a spreader duct according to an embodiment of the invention; 
         FIG. 8A  is a cross-sectional view of a spreader duct according to an embodiment of the invention; 
         FIG. 8B  is a bottom view of a spreader duct with a channel and outlet geometry according to an exemplary embodiment of the invention; 
         FIG. 8C  is a bottom view of a spreader duct with a channel fluidically connected to manifolds according to an embodiment of the invention; 
         FIG. 9  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; 
         FIG. 10  is a side view of the touch sensor of  FIG. 9 ; 
         FIG. 11  is a top view of a conductive pattern printed on a first side of the touch sensor of  FIG. 10 ; and 
         FIG. 12  is a top view of a conductive pattern printed on a second side of the touch sensor of  FIG. 10 . 
     
    
    
     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 
     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. 
     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. 
     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. 
     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. 
     As described herein, the example embodiments of the present invention provide a roll-to-roll electroless plating system where air or gas are added to the plating solution in a manner that avoids bubbles becoming trapped beneath the web of media. 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. 
       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 . 
     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. 
     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. 
     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 . 
       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 . 
     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. 
     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 . 
       FIG. 3  is a schematic side view of an improved roll-to-roll electroless plating system  300  described in commonly-assigned, co-pending U.S. patent application Ser. No. 14/455,196, entitled “Roll-to-roll electroless plating system with low dissolved oxygen content” by G. Wainwright et al., which is useful for plating solutions  310  having a low level of dissolved oxygen content. As in the prior art roll-to-roll 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  horizontally 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 . 
     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. 
     A number of modifications were made relative to the prior art 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 . 
     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 . 
     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 ). 
     Modifications also 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  through tee  334  upstream of pan inlet  321 , forming gas bubbles  344  which are carried into the pan  320 . 
       FIG. 3  also shows gas 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 gas bubbles  344  are injected through a plumbing assembly  342  located near a bottom  339  of sump  330  so that the injected gas 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 . 
     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. 
     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 (e.g., using motor  362 ), 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). 
       FIG. 4  shows a schematic side view of another example of a roll-to-roll electroless plating system  300  described in commonly-assigned, co-pending U.S. patent application Ser. No. 14/455,196, entitled “Roll-to-roll electroless plating system with low dissolved oxygen content” by G. Wainwright et al., where micro-bubbles of inert gas are injected 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 gas 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 . 
     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  and upstream of pan inlet  321 . 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  at pan inlet  321 . A filter  348  can be used for further reducing the size of gas bubbles  344 . 
     In  FIGS. 3 and 4  pipe  333  delivers plating solution  310  to pan inlet  321  positioned near an end  327  of pan  320  and proximate to a bottom  325  of the pan  320 . Herein, “proximate to a bottom of the pan” is understood to mean “below the web of substrate  350 ”. 
       FIG. 5  shows a configuration for a roll-to-roll electroless plating system  300  which is similar to that shown in  FIG. 4  except that the pipe  333  delivers plating solution  310  to a pan inlet  321  centrally positioned in pan  320  in proximity to the bottom  325  of pan  320 . Furthermore, the pan inlet  321  is connected to a flood bar  322 . 
     Although in the examples described above, inert gas is added to the plating solution  310  re-entering the pan  320  at pan inlet  321 , in some embodiments, air or oxygen can be added to the plating solution  310  re-entering the pan  320  at pan inlet  321  as needed for adjusting the dissolved oxygen content in the plating solution  310  in the pan  320 . 
       FIG. 6  is a perspective of a prior art flood bar  322  extending along a cross-track direction  307  that is perpendicular to the web advance direction  305 . Inlet  323  of the flood bar  322  is fluidically connected to pan inlet  321  ( FIG. 5 ) below the web of substrate  350 . Conventional flood bar  322  includes an array of distribution orifices  324  for mixing the incoming plating solution  310  ( FIG. 5 ) with the plating solution  310  already in the pan  320  ( FIG. 5 ). For conventional roll-to-roll plating systems  200 , such as the one shown in  FIG. 2 , where gas is not added to the plating solution  310  in pipe  233  just upstream of the pan inlet, a conventional flood bar  322  can be used and typically functions satisfactorily without causing problems. However, in a roll-to-roll electroless plating system  300 , such as the one shown in  FIG. 5 , where the plating solution  310  contains gas bubbles  344  of gas as it enters the pan  320  below the horizontal web of substrate  350 , the gas bubbles  344  will be released through distribution orifices  324 , rise due to buoyancy, and be trapped beneath the web of substrate  350 . This can have the undesirable effect of causing non-uniform plating on the second surface  352  of the substrate  350 . 
       FIG. 7  is a perspective of a portion of a roll-to-roll electroless plating system  300  according to an embodiment of the invention. Relative to the roll-to-roll electroless plating system  300  shown in  FIG. 5 , the flood bar  322  has been replaced with a spreader duct  380  extending substantially along cross-track direction  307 . Spreader duct  380  includes a channel  381  that is in fluidic communication with pan inlet  321 , and has one or more outlets  382 ,  383  located beyond the edges  353 ,  354  of the web of substrate  350 . In the example shown in  FIG. 7 , web of substrate  350  has a first edge  353  and a second edge  354  that is separated from the first edge  353  by a width W along the cross-track direction  307 . Outlet  382  is located beyond the first edge  353  of the web of substrate  350 , and outlet  383  is located beyond the second edge  354  of the web of substrate  350 . In other words, a vertical projections from outlets  382 ,  383  do not intersect the web of substrate  350 . In this way, rather than directing the incoming plating solution  310  into pan  320  such that gas bubbles  344  are trapped beneath the web of substrate  350 , gas bubbles  344  are allowed to float freely to the surface of the plating solution  310  near the sides  326  of the pan  320 . 
     In the example shown in  FIG. 7  where the pan inlet  321  is in the bottom  325  of pan  320 , spreader duct  380  can simply include a rectangular body with a wide groove serving as the channel  381 . The spreader duct  380  is positioned in proximity to the bottom  325  of pan  320  with channel  381  sitting over the pan inlet  321 . If, as in the example of  FIG. 7 , the channel  381  includes a first end  387  and a second end  388  that is displaced from the first end  387  by a distance L that is greater than the width W between the first edge  353  and the second edge  354  of the web of substrate  350 , outlets  382 ,  383  at both ends of channel  381  will be beyond the edges of the web of substrate  350 . In this way plating solution  310  can be directed from pan inlet  321  toward both sides  326  of pan  320  in along cross-track direction  307  and release the gas bubbles  344  beyond the edges of the web of substrate  350  where they can rise freely to the surface of the plating solution  310  without being trapped beneath the substrate  350 . Furthermore, the flow of plating solution  310  toward sides  326  helps to mix the replenished plating solution  310  in non-turbulent fashion in the pan  320 . When the flow of plating solution  310  hits sides  326 , it is redirected into other portions of the pan  320 . 
       FIG. 8A  illustrates a cross-sectional view of the spreader duct  380  from  FIG. 7  in which the height h and width s of channel  381  are shown. In some embodiments the height h and width s of the channel  381  are constant throughout the length L ( FIG. 7 ) of the channel  381 . In other embodiments, in order to optimize the flow of plating solution  310 , the channel  381  can have a nonuniform cross-section with varying width s or height h, or a non-rectangular cross-section. 
     In still other embodiments, the channel  381  can have a variety of different outlet arrangements. For example,  FIG. 8B  shows a bottom view of a spreader duct  380  having a plurality of outlets  382   a ,  382   b ,  382   c  distributed across the first end  387 , and a second plurality of outlets  383   a ,  383   b ,  383   c  distributed across the second end  388 . In the illustrated embodiment, some of the outlets  382   a ,  382   c ,  383   a ,  383   c  are not directed either parallel to cross-track direction  307  nor parallel to web advance direction  305 . In this case, if the spreader duct  380  of  FIG. 8B  is used in the configuration of  FIG. 7 , the outermost outlets  382   a  and  383   a  that are closest to end  329  of pan  320  are oriented somewhat toward end  329 , and the outermost outlets  382   c  and  383   c  that are closest to end  327  of pan  320  are oriented somewhat toward end  327 . This configuration serves to direct the flow of replenished plating solution  310  to other portions of pan  320 . Innermost outlets  382   b  and  383   b  are oriented parallel to cross-track direction  307  to direct flow of replenished plating solution  310  directly toward the opposite sides  326  of pan  320 . 
     In other embodiments, as illustrated in the bottom view of spreader duct  380  shown in  FIG. 8C , the channel  381  can be connected to a manifold  385  at one or both ends, where the manifold  385  extends for a greater distance along the web advance direction  305  than the spreader duct  380 . In the illustrated example, the manifold  385  has a plurality of manifold outlets  386  distributed along the web advance direction  305 , all being located beyond the first and second edges  353  and  354  of the web of substrate  350  ( FIG. 7 ). 
     In the example shown in  FIG. 7 , spreader duct  380  has no outlets disposed below the web of substrate  350 . In other embodiments (not shown), the roof of channel  381  can include a plurality of small perforations that allow plating solution to pass through, but not gas bubbles  344  (in an analogous manner to that described for the immersion plating tank disclosed in U.S. Pat. No. 5,284,520 to Tanaka entitled “Electroless plating device,” which is incorporated herein by reference). 
     In the examples described above relative to  FIGS. 5, 7 and 8A-8C , the channel  381  of the spreader duct  380  is in fluid communication with a pan inlet  321  positioned in the bottom  325  of the pan  320 . For configurations as in  FIGS. 3 and 4  where the pan inlet  321  is positioned in an end  327  of the pan  320 , spreader duct  380  can have the form of a pipe (not shown) connected to pan inlet  321  and extending along cross-track direction  307  ( FIG. 7 ) to one or more outlets (not shown) that are beyond the first edge  353  or second edges  354  of web of substrate  350 . 
       FIG. 9  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  having a spreader duct  380  as described above. 
       FIG. 10  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 . 
       FIG. 11  shows an example of a conductive pattern  450  that can be printed on first side  441  ( FIG. 10 ) of substrate  440  ( FIG. 10 ) 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  having a spreader duct  380  as described above. 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. 9 ). 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 . 
       FIG. 12  shows an example of a conductive pattern  460  that can be printed on second side  442  ( FIG. 10 ) of substrate  440  ( FIG. 10 ) 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  having a spreader duct  380  as described above. 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. 9 ). 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 . 
     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  having a spreader duct  380  as described above. 
     With reference to  FIGS. 9-12 , 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. 
     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 
     
         
         
           
               100  flexographic printing system 
               102  supply roll 
               104  take-up roll 
               105  roll-to-roll direction 
               106  roller 
               107  roller 
               110  print module 
               111  plate cylinder 
               112  flexographic printing plate 
               113  raised features 
               114  impression cylinder 
               115  anilox roller 
               116  UV curing station 
               120  print module 
               121  plate cylinder 
               122  flexographic printing plate 
               124  impression cylinder 
               125  anilox roller 
               126  UV curing station 
               130  print module 
               131  plate cylinder 
               132  flexographic printing plate 
               134  impression cylinder 
               135  anilox roller 
               136  UV curing station 
               140  print module 
               141  plate cylinder 
               142  flexographic printing plate 
               144  impression cylinder 
               145  anilox roller 
               146  UV curing station 
               150  substrate 
               151  first side 
               152  second side 
               200  roll-to-roll electroless plating system 
               202  supply roll 
               204  take-up roll 
               205  web advance direction 
               206  drive roller 
               210  plating solution 
               220  pan 
               222  lower flood bar 
               224  upper flood bar 
               230  sump 
               232  lower lift pump 
               233  pipe 
               234  upper lift pump 
               235  pipe 
               236  freefall return 
               240  air inlet tube 
               250  substrate 
               251  first surface 
               252  second surface 
               300  roll-to-roll electroless plating system 
               302  supply roll 
               304  take-up roll 
               305  web advance direction 
               306  drive roller 
               307  cross-track direction 
               310  plating solution 
               315  controller 
               320  pan 
               321  pan inlet 
               322  flood bar 
               323  inlet 
               324  distribution orifices 
               325  bottom 
               326  side 
               327  end 
               328  pan cover 
               329  end 
               330  sump 
               331  inlet 
               332  pan-replenishing pump 
               333  pipe 
               334  tee 
               335  outlet 
               336  drain pipe 
               338  sump cover 
               339  bottom 
               340  inert gas source 
               341  inert gas inlet 
               342  plumbing assembly 
               344  gas bubbles 
               345  inert gas source 
               348  filter 
               350  substrate 
               351  first surface 
               352  second surface 
               353  edge 
               354  edge 
               360  oxygen sensor 
               362  motor 
               370  recirculation pump 
               372  inlet line 
               373  inlet 
               374  outlet line 
               375  outlet 
               376  inert gas source 
               377  filter 
               378  tee 
               379  plumbing assembly 
               380  spreader duct 
               381  channel 
               382  outlet 
               382   a  outlet 
               382   b  outlet 
               382   c  outlet 
               383  outlet 
               383   a  outlet 
               383   b  outlet 
               383   c  outlet 
               385  manifold 
               386  manifold outlet 
               387  end 
               388  end 
               400  apparatus 
               410  touch screen 
               420  display device 
               430  touch sensor 
               440  transparent substrate 
               441  first side 
               442  second side 
               450  conductive pattern 
               451  fine lines 
               452  grid 
               453  fine lines 
               454  channel pads 
               455  grid column 
               456  interconnect lines 
               458  connector pads 
               460  conductive pattern 
               461  fine lines 
               462  grid 
               463  fine lines 
               464  channel pads 
               465  grid row 
               466  interconnect lines 
               468  connector pads 
               480  controller 
             h height 
             L distance 
             s width 
             W width