Abstract:
A maskless type exposure system using an exposure engine on which a digital micromirror device (DMD) is mounted includes an independent upper and lower side drive type double-sided simultaneous exposure system, in which a flexible object of exposure, including a flexible board, such as a chip-on-film (COF) or a lead frame, is fed in a rolled state, and is simultaneously exposed throughout an exposure pattern thereof on upper and lower sides thereof by independently driving a plurality of exposure engines in x, y and z axial directions in the case where the flexible exposure object has a large area or a restricted exposure region, thereby reducing costs based on minimized defective proportion and maximized productivity.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates, in general, to a maskless type exposure system using an exposure engine on which a digital micromirror device (DMD) is mounted and, more particularly, to an independent upper and lower side drive type double-sided simultaneous exposure system, in which a flexible object of exposure including a flexible board, such as a chip-on-film (COF) or a lead frame, which can be fed in a rolled state, and is simultaneously exposed with an entire exposure pattern thereof on upper and lower sides thereof by independently driving a plurality of exposure engines in x, y and z axial directions in the case of the flexible exposure object has a large area or a restricted exposure region, thereby reducing costs by minimizing a defective proportion and maximizing productivity. 
         [0003]    2. Description of the Related Art 
         [0004]    Generally, a semiconductor fabricating process includes an exposure process for forming a pattern on a printed board. 
         [0005]    This exposure process is classified into two types: a mask type using a mask, and a maskless type not using a mask. 
         [0006]    In this exposure process, it is more important than anything else that an exposure system be aligned before exposure in order to minimize the defective proportion of pattern exposure. Thereby, the pattern can be exposed with high precision. 
         [0007]      FIG. 1  is a conceptual diagram illustrating the alignment structure of a conventional mask type upper and lower exposure system. In this mask type, exposure is carried out in a manner such that the positions of reference marks  4  of upper and lower masks  3  and  3 ′ above and below an exposure stage  2  are checked, such that the positions of the upper and lower masks  3  and  3 ′ are aligned on the basis of the reference marks  4 , and such that the light from an UV lamp is applied en masse. 
         [0008]    This mask type does not use an exposure engine, so that it can directly conduct exposure after the alignment is completed using the reference marks. 
         [0009]    In this mask type, a rigid printed circuit board (PCB), which is categorized according to material, can be exposed on upper and lower faces thereof, but it is difficult to simultaneously expose upper and lower surfaces of a flexible PCB, i.e. a flexible object of exposure including a flexible board, such as a chip-on-film (COF) or a lead frame, using a mask. 
         [0010]    This mask-type exposure system is difficult to use for high-resolution exposure when a high-resolution micro circuit pattern is exposed due to increased mask fabrication and management costs. 
         [0011]    Thus, in order to solve the problem with the mask-type exposure system, recently, a maskless type exposure system for realizing high resolution capable of obtaining a submicron circuit line width and reducing the number of processes is being developed. 
         [0012]    This maskless type exposure system performs exposure in a manner such that a laser beam from a laser direct imaging system is applied to the unit pixel of a discrete exposure engine so as to align the unit pixels of upper and lower exposure engines of an exposure stage. 
         [0013]    One example of such a maskless type exposure system is disclosed in Korean Patent Application Publication No. 10-2006-51792. 
         [0014]    This maskless type exposure system performs exposure by winding a flexible object of exposure, that is, a flexible board such as a flexible PCB called a COF or a lead frame, around a roll, feeding the flexible exposure object to an exposure section by means of roll feeding, and projecting exposure patterns onto a photosensitive substance (e.g. dry film resist or photoresist) from a plurality of exposure engines disposed above and below the exposure section. 
         [0015]    At this time, since the light emitted from the exposure engines cannot expose the entire region of the photosensitive material at one time, part of the entire region of the photosensitive material moves toward the exposure engines, so that the entire region of the photosensitive material is exposed. 
         [0016]    In other words, when using this conventional exposure system, one has no choice but to install the plurality of exposure engines corresponding to the patterns to be exposed on the flexible exposure object, and thus the installation of such equipment at an enormous cost cannot be avoided. 
         [0017]    Thus, it takes a lot of time to perform the exposure, which leads to low productivity and a high defective proportion. 
         [0018]    In particular, the flexible exposure object moves to be exposed by the plurality of exposure engines in a stationary state. As such, in the case where the exposure region becomes wider, the number of exposure engines must be further increased. 
         [0019]    In other words, the problems with the above-mentioned convention exposure system are summarized as follows. 
         [0020]    First, the number of exposure engines and the exposure region must be increased. 
         [0021]    Second, workability is low because exposure is impossible while the flexible exposure object is moving on upper and lower sides thereof in longitudinal and transverse directions at the same time. 
         [0022]    Third, in the case in which the flexible exposure object, such as the COF or the lead frame, which is fed in a rolled state, is exposed, the number of exposure engines must be high in order for the entire region to be exposed in an exposure direction as well as in a direction perpendicular thereto. As a result, the volume of the equipment and the associated cost are increased. 
       SUMMARY OF THE INVENTION 
       [0023]    Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide an independent upper and lower side drive type double-sided simultaneous exposure system, in which a flexible object of exposure (photosensitive material) including a flexible board, such as a chip-on-film (COF) or a lead frame, which can be fed in a rolled state, is simultaneously exposed on upper and lower sides thereof in a fixed state by independently driving at least one set of exposure engines in x, y and z axial directions, thereby providing an optimal environment to the flexible exposure object, and maximizing exposure workability and productivity. 
         [0024]    In order to achieve the above object, according to one aspect of the present invention, there is provided an independent upper and lower side drive type double-sided simultaneous exposure system, which comprises: 
         [0025]    a base plate, which feeds a flexible object of exposure in a rolled state on both sides in one direction, and has a flexible exposure object fixing means fixing the flexible exposure object in position at an exposure processing section in the middle thereof; and independent upper and lower drivable exposure modules, which include: upper and lower x-axial movable stages, which are supported above and below the base plate, and are individually driven above and below the flexible exposure object fixing means in a x-axial direction; upper and lower y-axial movable stages, which are supported on the upper and lower x-axial movable stages, and are individually driven above and below the upper and lower x-axial movable stages in a y-axial direction; upper and lower exposing means, which are supported on the upper and lower y-axial movable stages, pass through the middles of the upper and lower y-axial movable stages and the upper and lower x-axial movable stages so as to be able to be elevated in a z-axial direction, and have at least one set of exposure engines; and z-axial driving means, which are installed on the respective upper and lower exposing means, and provide z-axial movement. 
         [0026]    Here, the upper and lower x-axial movable stages may be slidably guided on respective linear motion guides disposed therebetween by driving means, and the upper and lower y-axial movable stages may be slidably guided on respective linear motion guides disposed therebetween by driving means. 
         [0027]    Further, the z-axial driving means may include servo motors, ball screws elevated by driving the servo motors, and linear motion guides guiding stable elevation of the upper and lower exposing means on opposite sides thereof. 
         [0028]    Also, the upper and lower exposing means may include the at least one set of exposure engines, on each of which a digital micromirror device is mounted, installed parallel to each other in quadrilateral boxes, laser displacement sensors measuring an exposure distance from the flexible exposure object to correct an exposure height, and vision cameras checking a correct position of the flexible exposure object. 
         [0029]    Meanwhile, the exposure engines may include: collimators, which receive light beams from ultraviolet light sources through optical fibers connected to a control box; beam expander telescopes, which expand the light beams collimated by the collimators into light beams having a desired diameter; cube beam splitters, which split and supply the diameter-adjusted light beams into vertical and horizontal light beams having equal intensity; upper right-angled mirrors, which reflect and cast the vertical light beam split by the cube beam splitters at a right angle in a horizontal direction; upper and lower right-angled mirrors, which reflect and cast the horizontal light beam split by the cube beam splitters at a right angle in a vertical direction, and then reflect and cast the vertical light beam, which has been reflected and cast at a right angle, at a right angle in a horizontal direction. The upper right-angled mirrors may be disposed at an angle of 45° with respect to a plane such that the light beams are incident onto incident sections of the exposure engines disposed at an angle of 45° in the horizontal direction. 
         [0030]    Further, the flexible exposure object fixing means may include: an exposure plate; fixing plates, which closely fix the flexible exposure object from top to bottom on left-hand and right-hand sides of the exposure plate; and air cylinders, which are assembled with the fixing plates so as to control elevation of the fixing plates. 
         [0031]    According to the present invention, the independent upper and lower side drive type double-sided simultaneous exposure system has the following advantages. 
         [0032]    First, the upper and lower exposure engines can expose flexible exposure object such as the COF or the lead frame to form programmed patterns while moving in x, y and z axial directions in the state where the flexible exposure object is fixed at a preset position, so that the exposure system can improve the exposure workability and the resulting productivity. 
         [0033]    Second, the flexible exposure object can be more efficiently exposed over a large area using at most two exposure engines, so that the exposure system can be made compact and reduce its manufacturing cost. 
         [0034]    Third, the exposure engine can expose the flexible exposure object by controlling its movement in a three-dimensional direction, i.e. in three axial directions, so that the exposure system can be optimal for continuous exposure of the rolled flexible exposure object. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
           [0036]      FIG. 1  is  FIG. 1  is a conceptual diagram illustrating the alignment structure of a conventional mask type upper and lower exposure system; 
           [0037]      FIG. 2  is a perspective view illustrating an independent upper and lower side drive type double-sided simultaneous exposure system according to an exemplary embodiment of the present invention; 
           [0038]      FIG. 3  is an exploded perspective view illustrating an independent upper and lower side drive type double-sided simultaneous exposure system according to an exemplary embodiment of the present invention; 
           [0039]      FIG. 4  is a partial exploded perspective view illustrating an independent upper drivable exposure module according to an exemplary embodiment of the present invention; 
           [0040]      FIG. 5  is a partial exploded perspective view illustrating an independent lower drivable exposure module according to an exemplary embodiment of the present invention; 
           [0041]      FIG. 6  is a top plan view illustrating an independent upper and lower side drive type double-sided simultaneous exposure system according to an exemplary embodiment of the present invention; 
           [0042]      FIG. 7  is a front cross-sectional view illustrating an independent upper and lower side drive type double-sided simultaneous exposure system according to an exemplary embodiment of the present invention; 
           [0043]      FIG. 8  is a partial cross-sectional view illustrating an independent upper drivable exposure module according to an exemplary embodiment of the present invention; 
           [0044]      FIG. 9  is a partial enlarged view illustrating part F of  FIG. 8 ; 
           [0045]      FIG. 10  is a partial cross-sectional view illustrating an independent lower drivable exposure module according to an exemplary embodiment of the present invention; 
           [0046]      FIG. 11  is a partial enlarged view illustrating part G of  FIG. 10 ; 
           [0047]      FIG. 12  is a partial exploded perspective view illustrating upper (or lower) x-axial and y-axial movable stages according to an exemplary embodiment of the present invention; 
           [0048]      FIG. 13  is a partial exploded perspective view illustrating the state in which an upper (or lower) y-axial movable stage, an upper (or lower) exposing means, and a z-axial driving means are coupled with each other according to an exemplary embodiment of the present invention; 
           [0049]      FIG. 14  is a partial perspective view illustrating an upper (or lower) z-axial driving means according to an exemplary embodiment of the present invention; 
           [0050]      FIG. 15  is a partial exploded perspective view illustrating a base plate and a flexible exposure object fixing means according to an exemplary embodiment of the present invention; 
           [0051]      FIG. 16  is a partial exploded perspective view illustrating a flexible exposure object fixing means installed on a base plate according to an exemplary embodiment of the present invention; 
           [0052]      FIG. 17  is a perspective view illustrating the configuration of an upper (or lower) exposing means according to an exemplary embodiment of the present invention; 
           [0053]      FIG. 18  is a top plan view illustrating the configuration of an upper (or lower) exposing means according to an exemplary embodiment of the present invention; 
           [0054]      FIG. 19  is a conceptual view explaining exposure performed by an upper (or lower) exposing means according to an exemplary embodiment of the present invention; and 
           [0055]      FIG. 20  is a control block diagram illustrating the control process of an independent upper and lower side drive type double-sided simultaneous exposure system according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0056]    Reference will now be made in greater detail to an exemplary embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts. 
         [0057]    The present invention is characterized in that independent upper side and lower side exposure sections disposed on upper and lower sides of a base plate are independently controlled to simultaneously expose an object of exposure, such as a flexible board, fed in a rolled state on the upper and lower sides of the base plate. 
         [0058]    Hereinafter, the exemplary embodiment of the present invention will be described with reference to  FIGS. 2  through  20 . 
         [0059]    The exemplary embodiment of the present invention comprises: 
         [0060]    a base plate  300 , which feeds a flexible object of exposure such as a flexible board (F/B) in a rolled state on both sides in one direction, and has an F/B fixing means  350  fixing the F/B in position at an exposure processing section  310  in the middle thereof; and 
         [0061]    independent upper and lower drivable exposure modules  100  and  200 , which include upper and lower x-axial movable stages  110  and  210 , which are supported above and below the base plate, and are individually driven above and below the F/B fixing means  350  in a x-axial direction; upper and lower y-axial movable stages  130  and  230 , which are supported on the upper and lower x-axial movable stages  110  and  210 , and are individually driven above and below the upper and lower x-axial movable stages  110  and  210  in a y-axial direction; upper and lower exposing means  150  and  250 , which are supported on the upper and lower y-axial movable stages  130  and  230 , pass through the middles of the upper and lower y-axial movable stages  130  and  230  and the upper and lower x-axial movable stages  110  and  210  so as to be able to be elevated in a z-axial direction, and have at least one set of exposure engines  160  and  260  mounted therein; and z-axial driving means  180  and  280 , which are installed on the respective upper and lower exposing means  150  and  250 , and provide z-axial movement. 
         [0062]    As illustrated in  FIG. 15 , the base plate  300  is a metal table that has a very smoothly polished surface, and includes a guide channel  321  along which the F/B is guided in leftward and rightward directions, and an exposure processing section  310 , which has a through-hole passing through the middle of the guide channel  310  in a vertical direction and steps  322  recessed from the through-hole, and an F/B fixing means  350  assembled to the exposure processing section. 
         [0063]    As illustrated in  FIG. 16 , the F/B fixing means  350  includes: an exposure plate  351 , which is fixedly supported on the steps  322  of the base plate  300  and has an exposure hole  352  passing through the middle thereof; a pair of fixing plates  353  and  353  closely fixing the F/B from top to bottom on left-hand and right-hand sides of the exposure plate; and four air cylinders  354 , which have bodies  355  fixed to ends of the exposure plates  353  and  353 , and rods  356  moving from the respective bodies  355  in expanding and contracting directions and assembled with the fixing plates  353  and  353 . 
         [0064]    As illustrated in  FIG. 3 , the base plate  300  is supported at a predetermined height by a base  370 , which has a plurality of vertical frames  371  and a horizontal frame  372  supporting these vertical frames  371  thereon and assembled with support legs thereunder. 
         [0065]    Here, each vertical frame  371  of the base  370  is assembled with an absorber plate  375  thereon. These absorber plates  375  are disposed along the outer circumference of the lower surface of the base plate  300  at regular intervals, and thus absorb vibrations from the base plate  300 . 
         [0066]    As illustrated in  FIG. 2 , each air cylinder  354  of the F/B fixing means  350  is operated by controlling compressed air supplied from an air supply  376  installed on one side of the horizontal frame  372  constituting the base  370 . The operation of the air supply  376  is controlled by a control box (C/B) of the base plate  300 . 
         [0067]    As illustrated in  FIGS. 6 and 7 , the base plate  300  is equipped with an F/B feeding roll  330  and an F/B recovering roll  331  on the left-hand and right-hand sides thereof. The F/B is fed from the F/B feeding roll  330 , is guided between the exposure plate  351  and the fixing plates  353  and  353  of the F/B fixing means  350  through the guide channel  321 , and is wound around the F/B recovering roll  331 . 
         [0068]    At this time, the F/B is fed from left to right a predetermined amount by control of a servo motor  340  driving the F/B recovering roll  331 , and thus is partly disposed in the exposure hole  352  of the exposure plate  351 . Then, the part of the F/B can be closely fixed on the upper surface of the exposure plate  351  by controlling the F/B fixing means  350 , particularly by moving the rods  356  of the air cylinders  354  in a contracting direction, and then the fixing plates  353  and  353  disposed on the rods  356  in a downward direction. 
         [0069]    The independent upper and lower drivable exposure modules  100  and  200 , which are opposite to each other on the upper and lower sides of the base plate  300 , are adapted to simultaneously or individually expose the upper and lower surfaces of the F/B by control of the C/B. 
         [0070]    As illustrated in  FIGS. 8 through 14 , these independent upper and lower drivable exposure modules  100  and  200  are designed so that the upper and lower x-axial movable stages  110  and  210 , the upper and lower y-axial movable stages  130  and  230 , and the upper and lower exposing means  150  and  250  are sequentially disposed opposite each other, and so that the upper and lower exposing means  150  and  250  are elevated through through-holes  111  and  231 , and  211  and  231  formed in the middles of the upper and lower x-axial movable stages  110  and  210  and the upper and lower y-axial movable stages  130  and  230  by the z-axial driving means  180  and  280  coupled with the upper and lower y-axial movable stages  130  and  230 . 
         [0071]    As illustrated in  FIG. 12 , the upper and lower x-axial movable stages  110  and  210  are guided in leftward and rightward directions (x-axial direction) on upper and lower sides thereof by two pairs of LM guides  112  and  212 , in which linear motion (LM) rails coupled to upper and lower sides of the base plate  300  are assembled with LM blocks sliding on the LM rails, and are controlled and moved by two pairs of linear motors  115  and  215  attached to front and rear sides thereof. 
         [0072]    The linear motors  115  and  215  are designed so that movers are fixed to front and rear edges of the upper and lower x-axial movable stages  110  and  210 , and so that stators supporting the movers are fixed to the base plate  300 . Thus, movement distances of the upper and lower x-axial movable stages  110  and  210  are controlled by controlling the movement of the movers. 
         [0073]    Of course, the upper x-axial movable stage  110  and the lower x-axial movable stage  210  are individually driven in an x-axial direction according to exposed patterns of the F/B, so that x-axial movement distances of the upper and lower exposing means  150  and  250  are controlled. 
         [0074]    The upper and lower y-axial movable stages  130  and  230  are guided in forward and backward directions (y-axial direction) by two pairs of LM guides  132  and  232 , in which LM rails coupled to the upper and lower sides of the upper and lower x-axial movable stages  110  and  210  are assembled with LM blocks sliding on the LM rails, and are controlled and moved by two pairs of linear motors  135  and  235  assembled on left-hand and right-hand sides thereof. 
         [0075]    The linear motors  135  and  235  are designed so that movers are fixed to left-hand and right-hand edges of the upper and lower y-axial movable stages  130  and  230 , and so that stators supporting the movers are fixed to the upper and lower x-axial movable stages  110  and  210 . Thus, movement distances of the upper and lower y-axial movable stages  130  and  230  are controlled by controlling movement of the movers. 
         [0076]    Of course, the upper y-axial movable stage  130  and the lower y-axial movable stage  230  are individually driven in a y-axial direction according to exposed patterns of the F/B fed in a rolled state, so that forward and backward y-axial movement distances of the upper and lower exposing means  150  and  250  are controlled. 
         [0077]    The LM rails of LM guides  112  and  212 , and  132  and  232  are provided with stoppers (S/T) on opposite ends thereof, so as to restrict leftward and rightward movement of the upper and lower x-axial movable stages  110  and  210  and forward and backward movement of the upper and lower y-axial movable stages  130  and  230 . 
         [0078]    The upper and lower exposing means  150  and  250  are adapted to control an elevating distance (z-axial movement distance) through through-holes  111  and  211 ; and  131  and  231  formed in the middles of the upper and lower x-axial movable stages  110  and  210  and the upper and lower y-axial movable stages  130  and  230  by the two pairs of z-axial driving means  180  and  280  coupled with the upper and lower sides of the upper and lower y-axial movable stages  130  and  230 . 
         [0079]    As illustrated in  FIGS. 13 and 14 , the z-axial driving means  180  and  280  include servo motors  181  and  281 , ball screws  185  and  285 , elevated by driving the servo motors  181  and  281 , and LM guides  182  and  282 , guiding stable elevation of the upper and lower exposing means  150  and  250  on opposite sides thereof. 
         [0080]    The servo motors  181  and  281  are supported on the upper and lower exposing means  150  and  250  by support brackets  183  and  283 . The ball screws  185  and  285  are coupled to driving shafts of the servo motors  181  and  281  at one ends thereof, and are supported on the upper and lower y-axial movable stages  130  and  230  at the other ends thereof. In order to stably guide the elevation of the upper and lower y-axial movable stages, LM rails, fixed to the support brackets  183  and  283 , and LM blocks, sliding on the LM rails, are installed on the upper and lower exposing means  150  and  250 . 
         [0081]    As illustrated in  FIGS. 17 and 19 , the upper and lower exposing means  150  and  250  include a plurality of exposure engines  160  and  260  in quadrilateral boxes  151  and  251 , laser displacement sensors  170  and  270  for measuring the exposure distance from the F/B to correct the exposure height, and vision cameras  180  and  280  for checking the correct position of the F/B. 
         [0082]    The vision cameras  180  and  280  function to check whether or not the F/B is fed to the correct position when exposure is performed. 
         [0083]    The laser displacement sensors  170  and  270  are sensors, each of which measures the distance from the F/B using a laser and measures the distance between the F/B and each of the exposure engines  160  and  260  to correct the exposure height. 
         [0084]    The upper and lower exposing means  150  and  250  are designed so that light beams emitted from UV light sources (having a wavelength of 355 nm or 405 nm) by the C/B are incident onto collimators  153  and  253  through optical fibers  152  and  252 , so as to be changed into collimated light beams. 
         [0085]    The collimated light beams are expanded into light beams having a desired diameter through beam expander telescopes (BETs)  154  and  254 . 
         [0086]    Each of the adjusted light beams is split into two light beams, i.e. vertical and horizontal light beams, having the same intensity through cube beam splitters (BSs)  155  and  255 . 
         [0087]    The vertical and horizontal light beams split with the same intensity are reflected at a predetermined angle through three sets of right-angled mirrors  156  and  256 ;  157  and  257 ; and  158  and  258 , and are then incident onto the respective sets of exposure engines  160  and  260 ; and  161  and  261 . 
         [0088]    More specifically, one of the vertical and horizontal light beams is reflected in a horizontal direction by the upper right-angled mirrors  156  and  256  disposed on upper sides of the cube BSs  155  and  255 , and is incident onto one  160  and  260  of the exposure engine sets through incident sections disposed at an angle of 45° when viewed in the traveling direction of the reflected light beam. 
         [0089]    The other light beam is incident onto the lower right-angled mirrors  157  and  257  disposed in line with the cube BSs  155  and  255 , is reflected in a vertical upward direction, is reflected again in a horizontal direction using the upper right-angled mirrors  158  and  258  disposed in line with the lower right-angled mirrors  157  and  257 , and is incident onto the other set of exposure engines  161  and  261  through incident sections disposed at an angle of 45° when viewed in the traveling direction of the reflected light beam. 
         [0090]    The plurality of light beams incident onto the respective sets of exposure engines  160  and  260 ; and  161  and  261  are subjected to on/off modulation through a plurality of digital micromirror devices (DMDs), and the on/off modulated light beams (or images) travel to the F/B, such as the COF or the lead frame, through optical systems installed in the exposure engines in upward and downward directions, thereby performing exposure. 
         [0091]    In the upper and lower exposing means  150  and  250 , the above-mentioned sets of exposure engines  160  and  260 ; and  161  and  261  can remarkably reduce the volumes of the quadrilateral boxes  151  and  251 , and thus can be made compact. 
         [0092]    The operation of the present invention configured in this way will be described with reference to  FIG. 20 , illustrating a control block diagram. 
         [0093]    First, a worker sets a flexible object of exposure, that is, an F/B, such as a COF or a lead frame, which is wound around the F/B feeding roll  330  on one side of the base plate  300 , on the guide channel  321  by fixing a leading end of the F/B to the F/B recovering roll  331  on the other side of the base plate via the F/B fixing means  350 . 
         [0094]    In this state, the C/B drives the servo motor  340  to feed the F/B from the F/B feeding roll  330  to the F/B recovering roll  331 . Then, the F/B is fixed by the F/B fixing means  350 . 
         [0095]    In other words, the F/B is fed by a predetermined amount from the left to the right by control of the servo motor  34  driving the F/B recovering roll  311  via a belt, and then is positioned in the exposure hole  352  of the exposure plate  351 . Subsequently, the fixing plates  353  and  353  move downwards by means of control of the F/B fixing means  350 , particularly by means of operation of the air cylinders  354 , thereby closely fixing the F/B on top of the exposure plate  351 . 
         [0096]    In this state, the independent upper and lower drivable exposure modules  100  and  200  are controlled to expose the upper and lower surfaces of the F/B at the same time. 
         [0097]    Of course, if necessary, the upper and lower surfaces of the F/B may be selectively exposed. 
         [0098]    This exposure process includes a correcting process of controlling the upper and lower exposing means  150  and  250  constituting the independent upper and lower drivable exposure modules  100  and  200  using the C/B to set an exposure position and an exposure region. 
         [0099]    To this end, the upper and lower exposing means  150  and  250  measure the exposure position and height of the F/B using the laser displacement sensors  170  and  270  and the vision cameras  180  and  280 , and transmit the measured results to the C/B. The correction process of the upper and lower exposing means  150  and  250  is performed on these measured results. 
         [0100]    In detail, the C/B controls the upper and lower x-axial movable stages  110  and  210 , the upper and lower y-axial movable stages  130  and  230 , and the z-axial driving means  180  and  280  to correct the positions of the exposure engines  160  and  260  of the upper and lower exposing means  150  and  250 . 
         [0101]    The upper and lower x-axial movable stages  110  and  210  are guided on the respective LM guides  112  and  212  by the linear motors  115  and  215  driven by the C/B, thereby moving along an x axis in leftward and rightward directions. 
         [0102]    The upper and lower y-axial movable stages  130  and  230  are guided on the respective LM guides  132  and  232  by the linear motors  135  and  235 , thereby moving along a y axis in forward and backward directions. 
         [0103]    The upper and lower exposing means  150  and  250  are elevated by a predetermined height by control of the servo motors  181  and  281  of the z-axial driving means  180  and  280 . 
         [0104]    It should be understood that the above-mentioned control sequence is not always identical, but it is dependent on the positions of the upper and lower exposing means  150  and  250 , and is determined by control of the C/B based on the detected values of the laser displacement sensors  170  and  270  and the vision cameras  180  and  280 . 
         [0105]    In this manner, in the state in which the upper and lower exposing means  150  and  250  are corrected, the upper and lower exposing means  150  and  250  perform exposure throughout the upper and lower surfaces of the F/B in preset patterns using the built-in exposure engines  160  and  260  while simultaneously moving in the x-axial and y-axial directions by means of the C/B. 
         [0106]    It will be apparent that the heights of the upper and lower exposing means  150  and  250 , particularly the heights of the exposure engines  160  and  260 , are adjusted by control of the z-axial driving means  180  and  280  as described above when they need to be adjusted. 
         [0107]    In this exposing process of the upper and lower exposing means  150  and  250 , light beams emitted from UV light sources (having a wavelength of 355 nm or 405 nm) by control of the C/B are incident onto the collimators  153  and  253  through the optical fibers  152  and  252 , and are thereby changed into collimated light beams. 
         [0108]    The collimated light beams are expanded into light beams having a desired diameter through the BETs  154  and  254 . Each of the adjusted light beams is split into two light beams, i.e. vertical and horizontal light beams, having the same intensity through the cube BSs  155  and  255 . Here, one of the vertical and horizontal light beams is reflected in a horizontal direction by the upper right-angled mirrors  156  and  256  disposed above the cube BSs  155  and  255 , and is incident onto one set of exposure engines  160  and  260  through incident sections disposed at an angle of 45° when viewed in the traveling direction of the reflected light beam, while the other light beam is incident onto the lower right-angled mirrors  157  and  257  disposed in line with the cube BSs  155  and  255 , is reflected in a vertical upward direction, is reflected again in a horizontal direction through the upper right-angled mirrors  158  and  258  disposed in line with the lower right-angled mirrors  157  and  257 , and is incident onto the other set of exposure engines  161  and  261  through incident sections disposed at an angle of 45° when viewed in the traveling direction of the reflected light beam. 
         [0109]    The plurality of light beams incident onto the respective sets of exposure engines  160  and  260 ; and  161  and  261  are subjected to on/off modulation through the plurality of DMDs, and the on/off modulated light beams (or images) travel to the F/B, such as the COF or the lead frame, through the optical systems installed in the exposure engines in upward and downward directions, thereby performing exposure. 
         [0110]    Thus, the exposure regions of the F/B fixed to the F/B fixing means  350  are independently exposed on the upper and lower sides of the F/B, and then the C/B operates the F/B fixing means  350  to release the fixed state of the F/B. 
         [0111]    Simultaneously, the C/B controls the servo motor  340  to rotate the F/B recovering roll  331 . Thereby, the F/B is fed from the F/B feeding roll  330 , and the unexposed part of the F/B is positioned at the exposure processing section  310 . Then, the F/B is fixed by the F/B fixing means  350 . 
         [0112]    In this state, the above-mentioned processes, including the process of feeding the F/B, such as the COF or the lead frame, in a rolled state, and positioning the part of the F/B at the exposing position, are repeated. Thus, the exposure of the F/B is continuously carried out by feeding, exposing, and recovering processes. 
         [0113]    As is apparent from the above description, the independent upper and lower side drive type double-sided simultaneous exposure system according to the present invention can simultaneously expose the flexible exposure object, the F/B, such as the COF or the lead frame, which has a large area or a restricted exposure region, while continuously feeding the F/B in the rolled state. 
         [0114]    Although exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.