Patent Publication Number: US-2007114125-A1

Title: System and method for electroplating flexible substrates

Description:
FIELD OF THE INVENTION  
      This invention relates generally to electroplating systems, and in particular, to a system and method for electroplating flexible substrates.  
     BACKGROUND OF THE INVENTION  
      The electroplating of a flexible substrate typically involves a two step process. First, an electrically-conductive seed layer is formed on the flexible substrate. Typically, this is accomplished by subjecting the substrate to a vacuum sputtering process to form a thin layer of metallization on the substrate (typically referred to as a “seed layer”). For example, a copper seed layer having a thickness between 500 and 2000 Angstroms may be formed on a polyimide or polyethylene substrate. The seed layer serves as an electrically-conductive layer on which further deposition may be formed by a subsequent electroplating process.  
      Second, the flexible substrate having the seed layer thereon is subjected to an electroplating process to increase the thickness of the metallization layer to a desired level. In some systems, the flexible substrate is fed into an electroplating apparatus in a vertical orientation. Near a loading station, electrically-conductive clips make contact to upper portions of the flexible substrate in order to provide a cathode potential to the substrate. The flexible substrate is transported horizontally from the loading station, through one or more pre-treatment cells, one or more electroplating cells, and one or more post-treatment cells, to an unloading station. This process and equipment are further explained with reference to the following example.  
       FIG. 1A  illustrates a top view of a conventional electroplating system  100  for electroplating flexible substrates. The electroplating system  100  includes a loading station  102 , a pre-treatment cell  104 , an electroplating cell  106 , a post-treatment cell  108 , and an unloading station  110 . The electroplating system  100  further includes a substrate transportation subsystem  120  including an input spool  122  oriented to have a vertical rotational axis, an output spool  124  also oriented to have a vertical rotational axis, and a drive motor (not shown) to cause the rotation of the input and output spools such that the flexible substrate S is transported laterally from the input spool  122  to the output spool  124  by way of the pre-treatment cell  104 , electroplating cell  106 , and post-treatment cell  108 .  
      The conventional electroplating system  100  further includes a cathode contact system  140  comprising an idle wheel  142  oriented to have a vertical rotational axis, a drive wheel  144  also oriented to have a vertical rotational axis, and an electrically-conductive belt  146  situated around and adapted to rotate in the counter-clockwise direction with the idle and drive wheels  142  and  144 . The drive motor that drives the substrate transportation system  120  may also serve to drive the cathode contact system such that the movement of both are in synchronization. The belt  146  supports a plurality of equally spaced-apart, electrically-conductive clips  148  adapted to make cathode contact to upper portions of the flexible substrate S while it travels from the loading station  102  to the unloading station  110 . The electroplating system  100  further includes a clip strip cell  112  adapted to remove residual plating which forms on the clips during the electroplating process.  
      In operation, the drive motor is operated to cause the clockwise movement of the drive wheel  124  of the substrate transportation system  120 , and the counter-clockwise movement of the cathode contact system  140  such that the movement of both subsystems  120  and  140  are in synchronization. Near the loading station  102 , the clips  148  are operated to engage the top portion of the flexible substrate S. The clips  148  move in synchronization with the flexible substrate S maintaining a fixed cathode contact to the flexible substrate S as it moves from the loading station  102  to the unloading station  110 . The substrate S undergoes the various processes provided by the pre-treatment cell  104 , electroplating cell  106 , and post-treatment cell  108 , wherein the clips  148  provide the cathode contact for the electroplating process. Near the unloading station  110 , the clips  148  are operated to disengage from the substrate S, and subsequently move to the clip strip cell  112  for removal of residual plating formed on the clips  148 . The processed substrate S is continuously rolled onto the output spool  124 .  
       FIG. 1B  illustrates a side view of the conventional electroplating cell  106  including a normally situated flexible substrate S. The conventional cell  106  includes a container  150  adapted to support a bath of electroplating fluid  152 , one or more anode electrodes  154  situated within the container  150  and adapted to make contact with the plating fluid bath  152 , and a sparger  156  adapted to introduce fresh plating fluid into the plating fluid bath  152  in the direction of the substrate S. In normal operations, the flexible substrate S is oriented substantially vertical within the electroplating cell  106 . Generally, the weight of the flexible substrate S keeps it substantially vertical.  
       FIG. 1C  illustrates a side view of a conventional electroplating cell  106  including an abnormally situated flexible substrate S. When the thickness of the flexible substrate S becomes relatively small, the stability of the substrate S as it travels through the electroplating cell  106  typically degrades. As a result, the orientation of the flexible substrate S is no longer substantially vertical, and may warp as shown. Since the spatial distance between the anode  154  and the flexible substrate S is no longer consistent due to the warping of the substrate S, a non-uniform plating forms on the surface of the flexible substrate S.  
       FIG. 1D  illustrates a side view of the conventional electroplating cell  106  including another abnormally situated flexible substrate S. Another problem associated with thin flexible substrates is that the bottom portion of the substrate tends to float. As shown, the bottom portion of the flexible substrate S curves upwardly due to the buoyancy of the substrate S. Similarly, because the spatial distance between the anode  154  and the flexible substrate S is no longer consistent due to the buoyancy of the substrate S, a non-uniform plating forms on the surface of the flexible substrate S.  
      In the past, some electroplating systems, especially those designed and manufactured in Japan and Korea, include cathode contact rollers located at the entrance and exit of an electroplating cell. The contact rollers maintain the material in a vertical orientation while providing a cathode contact to the material. These cathode contact rollers need to be located at intervals along the length of the flexible substrate. Typically, the cathode contact rollers are designed to provide a cathode potential to about two ( 2 ) meters length of material. Normally, the effective cell length range from 10 to 30 meters. Accordingly, five (5) to 15 electroplating cells need to be provided to effectively plate 10 to 30 meters of material, which translates to five (5) to 15 sets of cathode contact rollers along the length of the material. The large number of cathode contact rollers making contact to the substrate typically causes considerable damage to the material.  
     SUMMARY OF THE INVENTION  
      A processing system for processing flexible substrates or other types of articles is disclosed. The system includes a loading station having an input spool adapted to provide an unprocessed flexible substrate; a processing station adapted to perform one or more predetermined processes on the flexible substrate; an unloading station having an output spool adapted to receive the processed flexible substrate; and a substrate stability subsystem adapted to maintain the flexible substrate in a substantially stable vertical orientation while the substrate undergoes the one or more processes performed by the processing station. The substrate stability subsystem includes a plurality of movable upper clips adapted to engage with respective upper portions of the flexible substrate, and a plurality of movable lower clips adapted to engage with respective lower portions of the flexible substrate as it is being transported into and out of the processing station. Also disclosed is a unique shield for the cathode clips to improve the uniformity of the deposition formed on the flexible substrate, and a unique seal to allow the transportation of the lower clips into and out of a processing cell while reducing leakage of fluid from the cell.  
      Other aspects, features, and techniques of the invention will be apparent to one skilled in the relevant art in view of the following detailed description of the exemplary embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  illustrates a top view of a conventional electroplating system for electroplating flexible substrates;  
       FIG. 1B  illustrates a side view of a conventional electroplating cell including a normally situated flexible substrate;  
       FIG. 1C  illustrates a side view of a conventional electroplating cell including an abnormally situated flexible substrate;  
       FIG. 1D  illustrates a side view of a conventional electroplating cell including another abnormally situated flexible substrate;  
       FIG. 2A  illustrates a top view of an exemplary electroplating system in accordance with an embodiment of the invention;  
       FIG. 2B  illustrates a side view of an exemplary electroplating cell in accordance with another embodiment of the invention;  
       FIG. 3A  illustrates a right side view of the exemplary substrate stability subsystem in accordance with another embodiment of the invention;  
       FIG. 3B  illustrates a left side view of the exemplary substrate stability subsystem in accordance with another embodiment of the invention;  
       FIG. 4A  illustrates a front view of an exemplary upper clip in accordance with another embodiment of the invention;  
       FIG. 4B  illustrates a side view of the exemplary upper clip in accordance with another embodiment of the invention;  
       FIG. 5A  illustrates a side view of an exemplary lower clip in a closed position in accordance with another embodiment of the invention;  
       FIG. 5B  illustrates a side view of the exemplary lower clip in an open position in accordance with another embodiment of the invention;  
       FIG. 6  illustrates a front view of the exemplary upper and lower clips engaged with a flexible substrate in accordance with another embodiment of the invention;  
       FIG. 7A  illustrates a side view of an exemplary seal in accordance with another embodiment of the invention;  
       FIG. 7B  illustrates a front view of the exemplary seal in accordance with another embodiment of the invention; and  
       FIG. 7C  illustrates a top view of the exemplary seal in accordance with another embodiment of the invention;  
       FIG. 7D  illustrates a top view of the lower portion of the exemplary seal in accordance with another embodiment of the invention;  
       FIG. 7E  illustrates a side view of the lower portion of the exemplary seal in accordance with another embodiment of the invention; and  
       FIG. 7F  illustrates a front view of the lower portion of the exemplary seal in accordance with another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS  
       FIG. 2A  illustrates a top view of an exemplary electroplating system  200  in accordance with an embodiment of the invention. The electroplating system  200  is particularly useful for electroplating a flexible substrate S. The flexible substrate S includes a seed layer disposed on either or both its sides. The electroplating system  200  forms one or more metallization layers on top of the seed layer by one or more electroplating processes, respectively. The flexible substrate S is fed into the electroplating system in a substantially vertical orientation.  
      As discussed in more detail below, the electroplating system  200  comprises a unique substrate stability subsystem including upper and lower clips adapted to engage upper and lower portions of the flexible substrate S to maintain the substrate in a substantially stable vertical orientation as it moves through the various processing cells. Accordingly, the substrate stability subsystem maintains the flexible substrate S a predetermined distance from the anode electrode to ensure a desirable uniformity of the plating deposition on the surface of the flexible substrate S. Another feature of the electroplating system  200  includes a unique seal for the electroplating cell that allows the passage of the lower clips into and out of the cell, while reducing leakage of plating fluid from the cell. Additionally, in the case where the upper and/or lower clips also function as a cathode contact to the flexible substrate S, the electroplating system  200  includes a clip shield adapted to further improve the uniformity of the plating deposition on surface of the flexible substrate S.  
      In particular, the electroplating system  200  comprises a loading station  202 , one or more pre-treatment cells  204 , one or more electroplating cells  206 , and one or more post-treatment cells, including a post-treatment wet cell  210  and a post-treatment drying cell  212 , and an unloading station  214 . The electroplating system  200  further comprises a substrate stability subsystem  250  adapted to maintain the flexible substrate S in a substantially stable vertical orientation as the flexible substrate S travels through the various processing cells. The substrate stability subsystem  250  may also serve to provide a continuous cathode contact to the flexible substrate S as it travels through the various processing cells.  
      More specifically, the loading station  202  comprises an input spool  202   a  around which the unprocessed, flexible substrate S is wound, and one or more tension rollers  202   b  and  202   c  to apply tension to the flexible substrate S, and also guide the flexible substrate S toward the processing area of the electroplating system  200 . In this example, the input spool  202   a  and the tension rollers  202   b  and  202   c  are oriented such that their respective rotational axes extend substantially vertical. Although only two tension rollers  202   b  and  202   c  are shown, it shall be understood that the electroplating system  200  may include more or less tension rollers. The number of tension rollers needed depends on the thickness, physical size, and weight of the substrate material, so that the material properly unwinds from the input spool  202   a.    
      The pre-treatment cell  204  is adapted to perform one or more pre-treating processes on the flexible substrate S prior to it undergoing the electroplating processes performed by the electroplating cell  206 . The purpose of the pre-treatment cell  204  is to clean and remove oxides (e.g., copper oxides) from the flexible substrate S before the substrate S undergoes the electroplating processes performed by the electroplating cell  206 . Such pre-treating processes may include an alkaline cleaning, acid cleaning, a de-ionized (DI) water rinsing, and/or others.  
      The electroplating cell  206  is adapted to perform one or more electroplating processes to form one or more metallization layers on the flexible substrate S. For example, the electroplating cell  206  may be configured to perform an electroplating process to form a layer of copper (Cu) on the flexible substrate S. In this example, the electroplating cell  206  is U-shaped to reduce the overall length of the electroplating system  200 .  
      As discussed in more detail below, the substrate stability subsystem  250  includes lower clips that engage with lower portions of the flexible substrate S as it moves into and out of the electroplating cell  206 . In the electroplating cell  206 , which performs electroplating of the flexible substrate S by immersing it in a bath of plating fluid, the lower clips traverse a bottom portion of the liquid bath. As discussed in more detail below, the electroplating cell  206  includes input and output seals  205   a  and  205   b  that allows the passage of the lower clips into and out of the electroplating cell  206 , while reducing the amount of leakage. Some leak will occur, though. Accordingly, the electroplating cell  206  also includes an input drain  206   a  and an output drain  206   b  to receive the leakage of the plating fluid through the entrance and exit openings.  
      The post-treatment wet cell  210  is adapted to perform one or more post-treating processes on the flexible substrate S after it has undergone the electroplating processes performed by the electroplating cell  206 . The purpose of the “wet” post-treating process is to remove residual plating fluid left on the flexible substrate S from the prior electroplating process, and to apply an anti-tarnish protective coating. Such post-treating processes may include an acid rinse, a DI water rinse, an anti-tarnish rinse, a warm DI water rinse, and/or others. After the post-treatment cell  210 , the flexible substrate S is subjected to a drying process performed by the post-treatment dry cell  212 . The purpose of the drying process is to substantially dry the flexible substrate S before it goes into the unloading station  214 .  
      The unloading station  214  comprises an output spool  214   a  around which the processed flexible substrate S is wound, and one or more tension rollers  214   b  and  214   c  to apply tension to the flexible substrate S, and also guide the flexible substrate S from the processing area to the output spool  214   a.  In this example, the output spool  214   a  and the tension rollers  214   b  and  214   c  are oriented such that their respective rotational axes extend substantially vertical. Although only two tension rollers  214   b  and  214   c  are shown, it shall be understood that the electroplating system  200  may include more or less tension rollers, as discussed above with reference to the tension rollers of the loading station.  
      A drive motor may be coupled to the input and output spools  202   a  and  214   a  (as well as the tension rollers  202   b - c  and  214   b - c ) to cause the rotation thereof in order to transport the flexible substrate S from the loading station  202  to the unloading station  214  by way of the various processing cells of the electroplating system  200 .  
      The substrate stability subsystem  250  comprises upper and lower, movable support structures  252   a  and  252   b  (e.g., a belt, cable, chain, etc.) adapted to respectively support a plurality of upper and lower clips  254   a  and  254   b.  The upper and lower, support structures  252   a  and  252   b  are positioned around a plurality of conveyor wheels (e.g., upper wheels  256   a,    258   a,  and  260   a ) and (e.g., lower wheels  256   b  and  258   b ). As discussed in more detail below, the upper and lower conveyor wheels are coupled to one or more drive motors for rotating the upper and lower wheels along with the upper and lower support structures  252   a  and  252   b  in a counter-clockwise direction. The drive motor for the substrate stability subsystem  250  may be the same or different than the drive motor for the transportation of the flexible substrate S. If different, the drive motors would be synchronized together so that the flexible substrate S moves at substantially the same speed as the support structures  252   a  and  252   b.    
      As discussed in more detail below, the upper and lower clips  254   a  and  254   b  of the substrate stability subsystem  250  engage with upper and lower portions of the flexible substrate S to maintain the substrate S in a substantially vertical orientation as the substrate S moves through the various processing cells of the electroplating system  200 . This helps to improve the uniformity of the plating formed on the surface of the flexible substrate S by keeping the substrate S substantially fixed with respect to the anode. The upper and lower clips  254   a  and  254   b  may be configured to be substantially equally spaced along the upper and lower support structures  252   a  and  252   b,  respectively. The spacing between adjacent clips may be, for example, three (3) to six (6) inches. In general, the spacing may depend on the width of the flexible substrate S and the desired current density.  
      In addition to applying vertical tension to the flexible substrate S, the upper and lower clips  254   a  and  254   b  may be used to apply a cathode contact to the flexible substrate S. In this regard, a cathode potential may be applied to the upper and/or lower support structures  252   a  and  252   b  in order to provide a cathode potential to the upper and/or lower clips  254   a  and  254   b.  Accordingly, the upper and/or lower support structures  252   a  and  252   b  along with the upper and/or lower clips  254   a  and  254   b  may be made of an electrically-conductive material (e.g., a metal). In this example, only the upper clips are used to provide a cathode contact to the flexible substrate S. The plating of the substrate S may cause residual plating to form on the upper clips  254   a.  Thus, the electroplating system  200  further includes a clip strip cell  262  to remove residual plating off of the upper clips  254   a.    
      In operation, the drive motor of the substrate transportation system is operated to transport the flexible substrate S from the loading station  202  to the unloading station  214  through the various processing cells  204 ,  206 ,  210 , and  212  of the electroplating system  200 . If separate, the drive motor of the substrate stability system  250  is also operated to cause the upper and lower support structures  252   a  and  252   b  including the upper and lower clips  254   a  and  254   b  to move substantially in synchronous with the flexible substrate S. At a region immediately downstream of the loading station  202 , the upper clips  254   a  are operated to engage the flexible substrate S. At a region immediately downstream of the region in which the upper clips  254   a  first engage the flexible substrate S, the lower clips  254   b  are operated to engage the flexible substrate S. Having the upper clips  254   a  engage the flexible substrate S prior to the lower clips  254   b,  prevents sagging of the flexible substrate S. This is because the substrate S is allowed to be initially suspended by the upper clip and therefore the weight of the material prevents it from sagging; then the lower clip is allowed to engage the suspended substrate S.  
      After the upper and lower clips  254   a  and  254   b  are engaged with the flexible substrate S, the clips and the substrate S move substantially together through the various processing cells of the electroplating system  200 . While in transit, the upper and lower clips  254   a  and  254   b  apply vertical tension to the substrate S so that the flexible substrate S remains substantially vertically oriented within the various processing cells, and in particular, within the electroplating cell  206 . As previously discussed, the stable, vertical orientation of the flexible substrate S improves the uniformity of the plating deposition across the substrate S. In addition, as previously discussed, the upper and/or lower clips  254   a  and  254   b  may also serve as a cathode contact to the flexible substrate S while the substrate S undergoes an electroplating process within the electroplating cell  206 .  
      At a region downstream of the post-treatment dry cell  212 , the upper and lower clips  254   a  and  254   b  clips disengage from the flexible substrate S to allow it to be unloaded onto the output spool  214   a  in the unloading station  214 . In this example, the upper and lower clips  254   a  and  254   b  disengage from the flexible substrate S at substantially the same region (e.g., at substantially the same time). Alternatively, the upper and lower clips  254   a  and  254   b  may be disengaged at a location upstream of the post-treatment cell. In this manner, the clips would not contaminate the substrate S by allowing drainage to contaminate the plating finish on the substrate S. The upper clips  254   a  are subsequently transported into the clip strip cell  262  to remove residual plating formed thereon during the electroplating process.  
       FIG. 2B  illustrates a side view of an exemplary electroplating cell  206  in accordance with another embodiment of the invention. The electroplating cell  206  comprises a container  220  adapted to support a bath of plating fluid  224 , one or more anode electrodes  226  situated within the container  220  and adapted to make contact with the plating fluid bath  224 , and a sparger  228  adapted to introduce fresh plating fluid into the plating fluid bath  224  in the direction of the substrate S. As illustrated in this figure, the upper and lower clips  254   a  and  254   b  are engaged with upper and lower portions of the flexible substrate S to ensure that the substrate S is oriented substantially vertical within the electroplating cell  206 . As previously discussed, this improves the uniformity of the plating deposition across the flexible substrate S.  
       FIG. 3A  illustrates a right side view of the exemplary substrate stability subsystem  250  in accordance with another embodiment of the invention. As shown, the substrate stability subsystem  250  comprises an upper drive motor  274 , an upper gear reducer  276 , a drive shaft  278 , the upper drive wheel  256   a,  the lower idle wheel  256   b,  a turning drum  280 , the upper supporting structure  252   a  (in this example, a belt) supporting a plurality of the upper clips  254   a,  and the lower supporting structure  252   b  (in this example, a belt) supporting a plurality of the lower clips  254   b.  The upper gear reducer  276  reduces the rotational speed of the drive shaft  278  as compared to the rotational speed of the upper drive motor  274 . The drive shaft  278  is rotatably coupled to the upper drive wheel  256   a  and turning drum  280 , and may extend coaxially through the lower idle wheel  256   b  and separated therefrom by a bearing. The upper drive wheel  256   a  assists in the movement of the upper supporting structure  256   a  including the upper clips  254   a  thereon. The lower idle wheel  256   b  assists in the movement of the lower supporting structure  256   b  including the lower clips  254   b  thereon. The turning drum  208  laterally supports the flexible substrate S through the turn.  
       FIG. 3B  illustrates a left side view of the exemplary substrate stability subsystem  250  in accordance with another embodiment of the invention. The substrate stability subsystem  250  further comprises the upper idle wheel  260   a,  which rotates around a shaft  282 . The substrate stability subsystem  250  further comprises the lower drive wheel  252   b  rotatably coupled to a lower drive motor  290  by way of a gear reducer  292 . The lower drive motor  290  may be coupled to the upper drive motor  272  by way of servos and/or encoders, so that the movement of the upper and lower belts  252   a  and  252   b  are substantially synchronous. In this example, the upper drive motor  272  may serve as the master which sets the speed for the bottom conveyor as well as the speed for the conveyor that transports the flexible substrate S. Similar to the upper clips  254   a,  the lower clips  254   b  are spring-biased in the closed position, and opened by a clip actuator at any desired location along their movement.  
       FIGS. 4A-4B  illustrate front and side views of an exemplary upper clip  400  in accordance with another embodiment of the invention. The clip  400  may be a detailed version of the upper clip  254   a  discussed above. In particular, the clip  400  comprises a fixed member  402  including an upper back end for attaching to the upper supporting structure  252   a,  an upper front end attached to an end of a torsional spring  404 , and a lower end attached to a first clip member  406 . The first clip member  406  includes a first lip  408  at its lower end for making contact to one side of the flexible substrate S. As shown in  FIG. 4A , the sides of the first clip member  406  are tapered, such that its upper end is wider than its lower end.  
      The clip  400  further comprises a pivoting member  420  including an upper back end attached to the other end of the torsional spring  404 , an upper front end attached to a cam wheel  422 , and a lower end attached to a second clip member  424 . The second clip member  424  includes a second lip  426  at its lower end for making contact to the other side of the flexible substrate S. The sides of the second clip member  424  are tapered, such that its upper end is wider than its lower end. A lower portion of the pivoting member  420  and the second clip member  424  extend substantially parallel with the fixed member  402  and the first clip member  406 . The remaining portion of the pivoting member  420  extends upwardly at an acute angle with that of the fixed member  402 .  
      The lower portion of the pivoting member  420  is also attached to a shield  428  used to improve the uniformity of the plating formed on the flexible substrate S. The shield  428  is attached to the lower end of the pivoting member  420 , at approximately the region which the second clip member  424  is attached to the pivoting member  420 . The shield  428  extends downward from that region to below the lower end of the clip members  424  and  406 . The shield  428  is configured to completely laterally shield the clip members  424  and  406 . It shall be understood that if both sides of the flexible substrate S were to be plated, there would also be a corresponding shield attached to the fixed member  402  at substantially the same location and with substantially the same position and orientation.  
      Without the shield  428 , there would typically be a build up of plating near the point of contact of the clip  400  to the flexible substrate S. This is because the current density is typically much higher at that region. To reduce the current density at that region in order to better equalize the current density throughout the width of the flexible substrate S, the shield  428  operates to reduce the current density at the region for that purpose. It shall be understood that the configuration of the shield  428  may vary with the article undergoing plating, the plating solution, the specified current density, the configuration of the anode electrode, and other factors.  
      In operation, the torsional spring  404  biases the pivoting member  420  with respective to the fixed member  402  such that the clip  400  is in a normally closed position. The cam wheel  422  rides along a clip actuator (e.g., a rail) which controls the pivoting of the pivoting member  420  (against the bias force of the torsional spring  404 ) to provide the desired opening or closing of the clip  400  at designated regions along the movement of the clip  400 . For example, the clip actuator may control the pivoting member  420  such that the clip  400  is in a closed position while it is engaged with the flexible substrate S during transportation through the electroplating system. When disengaging from the flexible substrate S, the clip actuator may control the pivoting member  420  such that the clip  400  is fully opened. When the clip  400  enters the clip strip cell, the clip actuator may control the pivoting member  420  such that the clip  400  is slightly opened. It shall be understood that the location of the opening and closing of the clip  400  along its movement, and the degree to which the clip  400  is opened may vary substantially depending on the particular processing strategy.  
       FIG. 5A  illustrates a side view of an exemplary lower clip  500  in a closed position in accordance with another embodiment of the invention. The lower clip  500  comprises a fixed clip member  502  and a pivoting clip member  504  pivotable about a substantially horizontal axis. A torsional spring  506  positioned substantially coaxial with the pivot axis of the pivoting clip member  504  applies a biasing force to the pivoting clip member  504  such that the top portions of the fixed and pivoting clip members  502  and  504  are urged together to engage with the lower portion of the flexible substrate S. Thus, the biasing force of the torsional spring  506  sets the lower clip  500  in a normally-closed configuration. The pivoting clip member  504  further includes a cam surface adapted to engage with a clip actuator to control the opening and closing of the lower clip  500 .  
      The lower portion of the lower clip  500  is attached to the lower support structure  252   b,  which, in this example, is a belt. The substrate stability system further includes a belt guide  520  to guide the movement of the belt within the electroplating system. In particular, the belt guide  520  includes a narrow opening in which a lower portion of the belt  252   b  is situated. The substrate stability system further includes a roller guide  522  to assist in the guiding of rollers connected to the lower belt to improve the vertical stability of the belt  252   b  while it moves.  
       FIG. 5B  illustrates a side view of the exemplary lower clip  500  in an open position in accordance with another embodiment of the invention. As previously discussed, the pivoting clip member  504  of the lower clip  500  includes a cam surface  508  adapted to engage with a clip actuator  540  in order to control the opening and closing of the lower clip  500  as desired. As shown in this figure, the clip actuator  540  has urged the cam surface  508  of the pivoting clip member  504  to cause the opening of the lower clip  500 .  
      In operation, the clip actuator  540  acts to open the lower clip  500  to disengage the clip  500  from the lower portion of the flexible substrate S. This may be performed immediately upstream of the unloading station, or immediately upstream of the post-processing section, or at any other location pursuant to the processing strategy. In this example, the clip actuator  540  keeps the lower clip  500  in the open position until it is to be engaged again with the flexible substrate S near the loading station. Again, the clip actuator  540  may be configured to open and close the lower clip  500  as desired pursuant to the processing strategy.  
       FIG. 6  illustrates a side view of the exemplary upper and lower clips  400  and  500  engaged with the flexible substrate S in accordance with another embodiment of the invention. As shown, the upper clip  400  is adapted to engage with an upper portion of the flexible substrate S. In this example, the upper portion of the flexible substrate S is relatively small (e.g., seven (7) millimeters) as compared to the width W of the flexible substrate S. Similarly, the lower clip  500  is adapted to engage with a lower portion of the flexible substrate S. In this example, the lower portion of the flexible substrate S is also relatively small (e.g., seven (7) millimeters) as compared to the width W of the flexible substrate S. Having the upper and lower clips  400  and  500  contact only a relatively small portion of the flexible substrate S substantially maximizes the platable surface of the flexible substrate S.  
       FIGS. 7A-7C  illustrate side, front, and top views of an exemplary seal  700  in accordance with another embodiment of the invention. The seal  700  may be an exemplary detailed version of the seals  205   a  and  205   b  discussed above with reference to the electroplating system  200 . As previously discussed, the lower clips  254   b  traverse a bottom portion of the fluid bath contained in the electroplating cell  206 . To enter and exit the electroplating cell  206 , the lower clips  254   b  enter and exit through corresponding openings. Such openings are near the bottom of the fluid-containing cell  206 . Accordingly, the seal  700  is configured to allow the passage of the lower clips through the openings, while reducing leakage of plating fluid from the electroplating cell  206 .  
      For explanation purposes, the seal  700  shown is an exemplary detailed version of the input seal  205   a  to the electroplating cell  206 , and is situated between the pre-treatment cell  204  and the electroplating cell  206 . It shall be understood that the seal  700  may also serve as the output seal  205   b  of the electroplating cell  206 . In particular, the seal  700  comprises an upper portion  702  and a lower portion  750 . The upper portion  702  of the seal  700  is primarily configured to allow the passage of the top clips  254   a  and the flexible substrate S into (and out of) the electroplating cell  206 , while reducing leakage of plating fluid from the electroplating cell  206 . The lower portion  750  of the seal  700  is primarily configured to allow the passage of the lower clips  254   b  and the lower support structure  252   b  into (and out of) the electroplating cell  206  while reducing leakage of plating fluid from the electroplating cell  206 . The lower portion  750  of the seal  700  also assists in guiding the leaked plating fluid to the drain  206   a  via a spill out area  770 . The drain  206   a,  in turn, routes the leaked plating fluid to a reservoir (not shown) to collect the fluid for recycling purposes.  
      The upper portion  702  of the seal  700  comprises support structures  704   a - b  for supporting a plurality of opposed glass rods  708   a - b,    712   a - b,    716   a - b,  and  720   a - b.  More specifically, the support structure  704   a  includes a plurality of rod supports  706   a,    710   a,    714   a,  and  718   a  including respective grooves to respectively receive the elongated cylindrical glass rods  708   a,    712   a,    716   a,  and  720   a.  The grooves of the rod supports  706   a,    710   a,    714   a,  and  718   a  are configured to expose the center sides (i.e., the sides facing the flexible substrate) of the elongated cylindrical glass rods  708   a,    712   a,    716   a,  and  720   a.  The support structure  704   b,  in turn, includes a plurality of rod supports  706   b,    710   b,    714   b,  and  718   b  including respective grooves to respectively receive the elongated cylindrical glass rods  708   b,    712   b,    716   b,  and  720   b.  The grooves of the rod supports  706   b,    710   b,    714   b,  and  718   b  are configured to expose the center sides (i.e., the sides facing the flexible substrate) of the elongated cylindrical glass rods  708   b,    712   b,    716   b,  and  720   b.    
      This configuration defines elongated gaps between opposed glass rods  708   a - b,    712   a - b,    716   a - b,  and  720   a - b,  respectively. The elongated gaps are configured to allow the passage of the flexible substrate S therethrough, while reducing contact of the flexible substrate S to the glass rods. That is, the elongated gaps are configured such that leaked plating fluid situated between the rods and the flexible substrate S further inhibits the flexible substrate S from contacting the rods in order to reduce contact damages to the flexible substrate S. As discussed, the rods are made of glass material or other non-scratching material, which reduces or eliminates surface damage to the flexible substrate S in case the substrate S makes contact with the rods.  0065   
      The first three sets of rods  708   a - b,    712   a - b,  and  716   a - b  (from the left as shown) are inclined such that their upper portions are situated further downstream along the movement of the flexible substrate S than their respective lower portions. This makes it more difficult for plating fluid to leak through the elongated gaps. The fourth set of rods  720   a - b  (from the left as shown) is oriented substantially vertical to provide a vertical interface to the electroplating cell  206 . As shown in  FIG. 7B , the support structures  704   a - b  be are recessed near the top to define a groove  722  through which the upper clips  254   b  travel.  
      The lower portion  750  of the seal  700  includes a chamber  752  having a lower opening  754 . The chamber  752  includes an inlet  756  to receive the incoming lower clips  254   b,  and an outlet  758  to allow the lower clips  254   b  to pass through into the electroplating cell  206 . Situated inside the chamber  752  is a first set of opposed doors  760   a - b  (e.g., similar to saloon doors). The doors  760   a - b  are spring biased against an inside wall of the chamber  752  to normally occlude the inlet  756 . Situated on the outside of the chamber  752  is a second set of doors  762   a - b  (e.g., similar to saloon doors). The doors  762   a - b  are spring biased against an outside wall of the chamber  752  to normally occlude the outlet  758 . As discussed in further detail below, the movement of the lower clips  254   b  forces the doors to open. The lower portion  750  of the seal  700  further includes a buffer area  764  to allow the doors  762   a - b  to swing outwardly without penetrating the electroplating cell  206 .  
      In operation, as the flexible substrate S is being transported through the seal  700 , the flexible substrate S moves through the elongated gaps between the respective opposed glass rods  708   a - b,    712   a - b,    716   a - b,  and  720   a - b.  The fourth set of glass rods  720   a - b  operate to perform a first stage seal. Some plating fluid from the electroplating cell  206  leaks through the fourth set of rods  720   a - b  as represented by the four (4) arrows as depicted in  FIG. 7A . The third set of glass rods  716   a - b  operate to perform a second stage seal. Less plating fluid leaks through the rods  716   a - b  as represented by the three (3) arrows depicted in  FIG. 7B . The remaining sets of rods  712   a - b  and  708   a - b  operate as third and fourth seal stages to further reduce leakage; two (2) arrows shown through rods  712   a - b  and one (1) arrow shown through rods  708   a - b.  Thus, only a relatively small amount of plating fluid leaks through the rods  708   a - b.  The leakage of plating fluid through the rods  708   a - b,    712   a - b,    716   a - b,  and  720   a - b  flows down to the spill out area  770  directly and through the chamber  752  of the lower portion  750  of the seal  700 .  
      With reference to FIGS.  7 D-F, as a lower clip  254   b  enters the seal  700 , the movement of the lower clip  254   b  forces the first set of doors  760   a - b  to open, while the second set of doors  762   a - b  remain closed. When the lower clip  254   b  moves passed the doors into the chamber  752 , the spring bias of the doors  760   a - b  forces the doors closed. In this state, both sets of doors  760   a - b  and  762   a - b  are in their closed position, thereby substantially reducing or eliminating leakage from the electroplating cell  206 . The lower clip  254   b  then moves further and forces the second set of doors  762   a - b  to open. In this state, plating fluid from the electroplating cell  206  leaks into the chamber  752  by way of the outlet  758 . Also, in this state, the first set of doors  254   b  are in their closed position, thereby substantially reducing or eliminating leakage of plating fluid through the inlet  756 . The leaked plating fluid flows down into the lower opening  754  of the chamber  752 , and subsequently to the spill out area  770  and drain  206   a.    
      After the lower clip  254   b  moves pass the second set of doors  762   a - b,  the spring bias of the doors  762   a - b  forces the doors  762   a - b  in their closed position. In this state, both sets of doors  760   a - b  and  762   a - b  remain closed. Then, the next lower clip  254   b  moves to open the first set of doors  760   a - b,  and sealing cycle is repeated. Thus, at any given time, at least one set of doors is closed in order to reduce of plating fluid through the seal  700 .  
      Although the various embodiments of the invention have been described with reference to performing an electroplating process, it shall be understood that these embodiments may be configured for implementing other types of processes including electroless plating, developing, stripping, cleaning, and others. In addition, although the various embodiments have been described with reference to performing a process on a flexible substrate, it shall be understood that the embodiments may be configured to process other types of articles.  
      While the invention has been described in connection with an exemplary embodiment, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptation of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within the known and customary practice within the art to which the invention pertains.