Abstract:
Systems and methods for electroplating embossed features on substrates are disclosed. In an exemplary implementation, a method may include positioning a device in close proximity to an anode. The device may have embossed trenches. The method may also include delivering pressurized electrolyte to the anode. The method may also include activating electrical power between the anode and the device. The metal ions migrate into the embossed trenches to form electroplated metal traces on the device

Description:
BACKGROUND 
       [0001]    Electroplating is a well-known technique for covering surfaces of a substrate with a metal. In general, electroplating systems include a tank for holding a chemical solution or “plating bath” which contains the metal to be plated, an anode (positive charge), and a cathode (negative charge). A substrate to be electroplated is placed in the plating bath and a charge is applied, causing the metal to come out of solution and deposit on the substrate. 
         [0002]    Electroplating techniques arc used for a wide variety of applications, such as, in computers, mobile phones, and other electronic devices, to name only a few examples. Advanced techniques may be used to fabricate more elaborate devices. For example, to fabricate electrical circuits that drive a pixilated flexible display (or other flex circuits), a conductive substrate is first coated with a resin, patterned with traces by pressure-embossing, and then cured. The substrate is then placed into the plating bath so that the resin removed by the embossing is replaced with electroplated nickel (or other metal). 
         [0003]    It is often difficult, however, to maintain a uniform plating thickness along the traces on the substrate during the electroplating process because of radical asymmetry and/or variation in trace density inherent in more complicated circuit designs. Plating “shields” are physical, non-conductive obstructions that may be placed between the anode and cathode in the plating tank to affect more uniform plating thickness through current density redirection. Although reasonably effective, shields must be modeled, designed, and fabricated specifically for each substrate that is to be electroplated. Segmented anodes also may be used to help bias the current flow away from edges and toward areas of greater trace concentration, but with a similarly marginal effect. In general, these techniques rely on trial and error and are application specific. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIGS. 1   a - b  show a side, cross-sectional view of an exemplary planar electroplating system which may be implemented for electroplating embossed features on a substrate, wherein (a) shows a partially-plated metal trace, and (b) shows a completely-plated metal trace. 
           [0005]      FIG. 2  shows a side, cross-sectional view of an exemplary roll-to-roll electroplating system which may be implemented for electroplating embossed features on a substrate. 
           [0006]      FIG. 3  is a flowchart illustrating exemplary operations which may be implemented for electroplating embossed features on a substrate. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    Exemplary systems and methods described herein for electroplating embossed features on a substrate may be used to improve: plating thickness uniformity and enables greater flexibility in device design. The electroplating systems and methods use a conductive web substrate as the cathode, and replace the part-specific anode and shield combinations of conventional electroplating systems with a single, close-proximity anode that serves as both a current source and an electrolyte supply vessel. The anode “smooths out” both the current density and the metal ion flow to the device, and thus results in a more uniform metal buildup during the deposition process. The close-coupled anode configuration also enables the large volume, open plating bath to be reduced in size or even eliminated altogether. The conductive web substrate results in traces only where the web is exposed to the electrolyte (the bottom of the trenches), and nowhere else. 
       Exemplary System 
       [0008]      FIGS. 1   a - b  show a side, cross-sectional view of an exemplary planar electroplating system  100  which may be implemented for electroplating embossed features on a substrate  110 .  FIG. 1   a  shows a partially-plated metal trace  112  on the substrate  110  (e.g., during the electroplating procedure).  FIG. 1   b  shows a completely-plated metal trace  114  on the substrate  110  (e.g., following the electroplating procedure). 
         [0009]    In an exemplary embodiment, the substrate  110  may be prepared in advance for the electroplating procedure by coating the substrate with a dielectric resin  115  that protects the surface of the substrate  110  from being plated during the electroplating procedure. The resin may then be pressure-embossed to remove a portion of the resin and create “trenches”  117   a - b  exposing conductive portions  118   a - b  of the substrate  110  corresponding to the desired traces that are to be electroplated. After curing, the substrate is ready for the electroplating process, e.g., using system  100 . 
         [0010]    Exemplary system  100  may comprise a plating fixture  120 . The plating fixture  120  may be manufactured of a non-conductive material (e.g., plastic), and holds a small fluid plenum  122  of heated electrolyte  124 . The electrolyte  124  may be provided to the plating fixture  120  by an electrolyte supply system  130 . The supply system  130  may include an electrolyte reservoir  131 , a pump  132 , a valve  133 , a heater  134 , and a filter  135 . During operation, the supply system  130  provides a metered, pressurized supply of warm, particle-free electrolyte to the plating fixture  120 . 
         [0011]    It is noted that the components shown in  FIG. 1   a  are intended only to illustrate one example of a system  100  which may be implemented. Other embodiments are also contemplated and may include additional components, components comprised of multiple parts, and/or fewer components. The system  100  is not limited to those components shown. 
         [0012]    The plating fixture  120  is designed to support an anode device  140 . In an exemplary embodiment, the anode device  140  is a composite anode. As better shown in the cut-away  145  in  FIG. 1   a , the anode  140  may comprise a thick metal-doped porous ceramic layer  141 , sandwiched between two similar but thinner, non-conductive layers  142   a - b.    
         [0013]    The conductive porous ceramic material  141  has been used for some time in fuel cells, for the creation of hydrogen peroxide, and in metals production. Low flow-resistance to liquid, however, is a less-common attribute and requires a particularly suited material. By way of example, such a material is described, e.g., in U.S. Pat. No. 4,892,857 titled “Electrically Conductive Ceramic Substrate” of Tennent, et al. and assigned to Corning Incorporated (Corning, N.Y.). These and other materials now known or later developed may be used to implement the described systems and methods. 
         [0014]    It is noted that the anode  140  may be a “sacrificial” anode, wherein the anode itself provides at least some of the metal ions for the electroplating process and is disposed of when there are insufficient metal ions remaining in the anode for the electroplating process. Alternatively, the anode  140  may be a “non-sacrificial” anode, wherein the metal ions are provided primarily by the heated electrolyte  124 . In any event, use of a porous conductive ceramic as the anode enables the substrate  110  that is to be plated to be positioned against (or very close to) the anode  140  during the electroplating process. 
         [0015]    The system  100  may also comprise an electric power supply  150 . In an exemplary embodiment, the electric power supply  150  may be a regulated DC power supply selected to provide the electrical current necessary for the electroplating process. In any event, the electric power supply  150  electrically connects the anode  140  to the substrate  110  (which serves as the cathode in the electroplating circuit). 
         [0016]    During operation, a device (e.g., the resin-coated and embossed substrate described above) is placed over the anode  140  in the plating fixture  120 . The pump  132  is activated, providing a metered flow of heated electrolyte  124  to the small plenum  122  under the anode  140  in the plating fixture  120 . As the fluid level rises within the plating fixture  120 , air is forced out through the porous anode  140 . The electrolyte  124  reaches the anode  140 , and by virtue of its being hydrophilic, the anode  140  becomes fully wetted. The electrolyte  124  then wets the surface of the device. Flowing electrolyte  124  may be collected and returned to the main supply reservoir  131 . 
         [0017]    In some embodiments, a slight uniform pressure may be applied to the device to limit the fluid-filled gap between the device and anode  140  so that it is only a very thin film. The power supply  150  is then activated and the metal ions from the electrolyte  124  (e.g., when using a non-sacrificial anode  140 ) and/or from the doped internal layer of the anode (e.g., when using a sacrificial anode  140 ) migrate to the exposed surfaces  118   a - b  of the substrate  110  (e.g., in trenches  117   a - b  as illustrated by arrows  160 ). If the plating inadvertently makes contact with the anode  140 , the anode&#39;s outer layer  142   a - b  of non-conductive ceramic prevents short-circuiting of the electroplating circuit. 
         [0018]    The exposed conductive surfaces  117   a - b  on the device correspond to the embossed trenches  118   a - b  (e.g., the desired traces). Accordingly, the metal ions accumulate as electroformed features only in these trenches  118   a - b . When the desired plating thickness is achieved (e.g., when the metal has accumulated so that it is flush with the surrounding resin as shown in  FIG. 1   b ), the electrical power  150  may be disconnected (as indicated by the “X” in  FIG. 1   b ) and the device removed for rinsing and drying. 
         [0019]    The system  100  enables improved plating thickness uniformity. Proper electrical performance of the device depends on predictable trace resistance, which can only be achieved through predictable trace thickness. Embodiments described herein reduce or altogether eliminate the uncertainty inherent in conventional processes. The system  100  is also universally applicable. Predictable trace thickness may be achieved without regard to device design. The system  100  also reduces the size and complexity of the electroplating system. There is no need for a large open tank (less real estate, less environmental impact), no need for a large volume of plating solution (lower cost), and fewer accessories are needed (no shields or mixer is required). The system  100  also enables better temperature control. The temperature uniformity of the much-reduced, essentially enclosed volume of electrolyte is easier to maintain at a constant level. 
         [0020]    It is noted that the system  100  described above is shown for purposes of illustration only, and is not intended to be limiting. Other embodiments are also contemplated. For example, the electroplating system described above may also be effectively adapted to a high-throughput manufacturing environment, as described below with reference to  FIG. 2 . 
         [0021]    Previous roll-to-roll electroplating systems included a series of tanks through which the substrate is drawn. The anodes and shields within these tanks had to be sized and located somewhat generically to roughly achieve their intended purposes. However, the anodes and shields could not move with the substrate and therefore could not effectively accommodate the subtleties of multiple device designs. 
         [0022]      FIG. 2  shows a side, cross-sectional view of an exemplary roll-to-roll electroplating system  200  which may be implemented for electroplating embossed features on a substrate  210  in a high-throughput environment. It is noted that  200 -series reference numbers are used to refer to similar components already described above with reference to  FIGS. 1   a - b , and therefore may not be described again with reference to  FIG. 2 . 
         [0023]    In the exemplary embodiment of system  200  shown in  FIG. 2 , the anode  240  may be configured as a rotating electrolyte-filled “drum” or cylinder  270  to enable continuous roll-to-roll plating. A supply system  230  may be implemented to deliver electrolyte  224  into the drum  270  via piping  280 . In one embodiment, system  200  includes an electrolyte recovery system  285  to recycle the electrolyte. 
         [0024]    During operation, the supply system  230  pressurizes the electrolyte  224  in drum  270 , pushing the electrolyte  224  out from inside the drum  270  and into close proximity of the substrate  210 . The process is continuous as the substrate is wrapped around at least a portion of drum  270 . That is, the new substrate  210  with exposed metal portions  217  enters on one side of the drum (as shown in inset  290 ), contacts the drum  270  during the electroplating process, and is removed after the electrolyte has been deposited on exposed metal portions  217  (as shown in inset  291 ). It is noted that there is no relative motion between the anode and the device during the electroplating process, e.g., as indicated by contact points  275   a - g.    
       Exemplary Operations 
       [0025]      FIG. 3  is a flowchart illustrating exemplary operations which may be implemented for electroplating embossed features on a substrate. Operations  300  may be implemented by the system described above, e.g., by an electronic controller executing logic instructions on one or more computer-readable medium. When executed by the controller, the logic instructions may program the system as a special-purpose machine that implements the described operations. However, the operations are not limited to automatic implementation, and may also be implemented manually, or in a combination of manual and automatic process steps. In an exemplary implementation, the components and connections depicted in the figures may be used. 
         [0026]    In operation  310 , a device having embossed trenches may be positioned over an anode. For example, the device may be positioned in a planar production configuration (e.g., as shown in  FIGS. 1   a - b ). Or for example, the device may be positioned in a roll-to-roll production configuration (e.g., as shown in  FIG. 2 ). 
         [0027]    In operation  320 , a metered flow of heated electrolyte may be delivered under the anode. As the level of the heated electrolyte rises within the fixture, air is forced out through the porous anode. The heated electrolyte eventually reaches the anode, which becomes fully wetted. The heated electrolyte then wets the surface of the device. In some embodiments, excess heated electrolyte may be collected and returned to the main supply reservoir. Also in some embodiments, a slight uniform pressure may be applied to the device to limit the fluid-filled gap between the device and the anode. 
         [0028]    In operation  330 , electrical power may be activated between the anode and the device. When power is applied in operation  330 , metal ions migrate into the embossed trenches to form electroplated metal traces on the device. In an exemplary embodiment, metal ions may migrate from the electrolyte (e.g., where a non-sacrificial anode is used). In another exemplary embodiment, metal ions may migrate from a doped internal layer of the anode (where a sacrificial anode is used). In yet another exemplary embodiment, metal ions may migrate from both the electrolyte and a doped internal layer of the anode. 
         [0029]    Once the desired plating thickness has been reached (e.g., when the metal traces are flush with the surrounding resin), the power may be disconnected, and the device may be removed for rinsing and drying. 
         [0030]    The operations shown and described herein are provided to illustrate exemplary implementations for electroplating embossed features on a substrate. It is noted that the operations are not limited to the ordering shown. Still other operations may also be implemented. 
         [0031]    It is noted that the exemplary embodiments shown and described are provided for purposes of illustration and are not intended to be limiting. Still other embodiments are also contemplated for electroplating embossed features on a substrate.