Abstract:
A flexible printed circuit board includes a substrate, signal lines, a first reinforcing layer, and a second reinforcing layer. The first surface of the substrate includes a layout zone and a reinforcing zone disposed nearby the layout zone. The signal lines are disposed on the layout zone. The first reinforcing layer is disposed on the reinforcing zone. The second reinforcing layer is disposed on the second surface of the substrate.

Description:
1. CLAIM OF PRIORITY 
       [0001]    This application claims priority to Taiwanese Patent Application No. 098111547 filed on Apr. 7, 2009 and Taiwanese Patent Application No. 098137853 filed on Nov. 6, 2009. 
       BACKGROUND OF THE INVENTION 
       [0002]    2. Field of the Invention 
         [0003]    The present invention relates to a flexible printed circuit board (FPC), and more particularly, to a flexible printed circuit board that is not inclined to fracture. 
         [0004]    3. Description of Prior Art 
         [0005]    Functionally advanced display devices have gradually been one of the important characteristics of current consumer electronics products. Among these display devices, liquid crystal display panels (LCD panels) have gradually been extensively applied to all kinds of electronic devices, such as television sets, cell phones, personal digital assistants (PDAs), digital cameras, computer screens, and notebook screens. Because of the characteristics of lightness, thinness, shortness, smallness, and flexibility, FPCs are more suitable to be a medium of LCD devices to cause different parts of circuits to be coupled to each other. 
         [0006]    Referring to  FIG. 1  illustrating a conventional FPC  12  utilized in an LCD device, the FPC  12  comprises a substrate  14  and a plurality of signal lines  16 . The plurality of signal lines  16  on the substrate  14  is utilized to transmit electrical signals. However, when a backlight module is assembled, the bent portion of the FPC  12  nearby the light source would endure larger amounts of stress and then cause to fracture, which affects luminous efficiency of backlight modules. In order to reinforce the tolerance of the FPC  12 , a polyimide structure layer or a layer of tape is usually attached to the FPC  12 . But, both of the methods increase not only an additional process step but also an overall thickness of the FPC  12  so that it cannot be placed into a backlight module, even resulting in incrementing the cost. 
       SUMMARY OF THE INVENTION 
       [0007]    It is therefore an object of the present invention to provide a flexible printed circuit board (FPC) which is set with a first reinforcing layer and a second reinforcing layer. The first reinforcing layer and the second reinforcing layer can effectively endure stress produced during FPC bending and further, weaken stress that signal lines endure. Consequently, the mechanical strength of the FPC can be enhanced, so that the FPC is not too inclined to fracture to cause malfunctions. 
         [0008]    Briefly summarized, a flexible printed circuit board comprises a substrate, a plurality of signal lines, a first reinforcing layer, and a second reinforcing layer. The substrate comprises a first surface and a second surface opposite to the first surface. A layout zone and a reinforcing zone disposed nearby the layout zone are on the first surface. The plurality of signal lines are disposed on the layout zone. The first reinforcing layer is disposed on the reinforcing zone. The second reinforcing layer is disposed on the second surface of the substrate. 
         [0009]    In one aspect of the present invention, the first substrate comprises a first structure layer, the second substrate comprises a second structure layer, and both the first and the second structure layers are polyimide structure layers. 
         [0010]    In another aspect of the present invention, the plurality of signal lines, the first reinforcing layer, and the second reinforcing layer are made of metal. 
         [0011]    In yet another aspect of the present invention, an area of the second reinforcing layer is larger than an area of the layout area of the plurality of the signal lines. 
         [0012]    In still another aspect of the present invention, a third structure layer disposed on the second connection layer, and the third structure layer is a polyimide structure layer. 
         [0013]    These and other objectives of the present invention will become apparent to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  illustrates a conventional FPC utilized in an LCD device. 
           [0015]      FIG. 2  illustrates the FPC of an LCD device according to a first embodiment of the present invention. 
           [0016]      FIG. 3  demonstrates a cross-section view of lines  2 - 2 ′ along the FPC shown in  FIG. 2 . 
           [0017]      FIG. 4  illustrates a cross-section view of a FPC according to a second embodiment of the present invention. 
           [0018]      FIGS. 5A-5E  illustrate patterns of the second reinforcing layer and its position relative to the first reinforcing layer. 
           [0019]      FIG. 6  shows a cross-section view of the FPC according to a third embodiment of the present invention. 
           [0020]      FIG. 7  showing a cross-section view of the FPC according to a fourth embodiment of the present invention 
           [0021]      FIG. 8  shows a cross-section view of the FPC according to a fifth embodiment of the present invention 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    Referring to the attached figures, the following embodiments are illustrated to exemplify certain embodiments that the present invention can be applied to. The directional terms adopted in the present invention, such as upper, lower, front, back, left, right, top, and bottom, are defined merely according to the attached figures. Hence, the usage of the directional terms is to assist in elaborating, instead of confining, the present invention for better understanding. 
         [0023]    Referring to  FIG. 2  and  FIG. 3 ,  FIG. 2  illustrates the FPC  110  of an LCD device according to a first embodiment of the present invention, and  FIG. 3  demonstrates a cross-section view of lines  2 - 2 ′ along the FPC  110  shown in  FIG. 2 . The FPC  110  for use in the LCD device comprises a first substrate  120 , a first wiring layer  122 , a first reinforcing layer  124 , a first connection layer  126 , a second substrate  130 , a second reinforcing layer  132 , a second connection layer  134 , and a third structure layer  150 . A layout zone  160  and a reinforcing zone  162  are set on the first substrate  120 . The first wiring layer  122  includes a plurality of signal lines  122   a - 122   d,  setting on the layout zone  160  of the first substrate  120 , are mostly made of conductive metals, such as gold, copper, or silver, to transmit electrical signals. To simplify the illustration, only four signal lines  122   a - 122   d  are drawn in  FIG. 3 . In practice, the numbers of the signal lines are not limited to four lines but can be adjusted according to individual demands. When the FPC  110  is bent, the bent portion  303  without any circuit thereon is most possible to fracture. So the reinforcing zone  162 , which the first reinforcing layer  124  is placed on, is set alongside the signal line  122   a  or the signal line  122   d.  In this embodiment, the reinforcing zone  162  is disposed outside the layout zone  160  and near the signal line  122   d,  as well as on the bent portion  303 , but the reinforcing zone  162  can be disposed on the area adjacent to the side-most signal line  122   a.  The first reinforcing layer  124  is laid on the reinforcing zone  162 , and is made of metal with its thickness of 12 ρm-35 μm. The first reinforcing layer  124  is an enclosed region that is not coupled to any electrical signal and is preferably parallel to the signal lines  122   a - 122   d,  so that it can be employed to enhance the mechanical strength of the FPC  110 . The first connection layer  126  is set on the first substrate  120  and overlays the plurality of signal lines  122   a - 122   d  and the first reinforcing layer  124 , which is utilized to insulate the plurality of signal lines  122   a - 122   d  and the first reinforcing layer  124 . The second substrate  130  covers the first connection layer  126 . 
         [0024]    In order to enhance the mechanical strength of the FPC  110 , the second reinforcing layer  132  is laid on the second substrate  130 . Preferably, the second reinforcing layer  132  is made of metal with its thickness of 12 μm-35 μm, and the area overlaid by the second reinforcing layer  132  is greater than that laid by the signal lines  122   a - 122   d.  Because the second reinforcing layer  132  is a piece of a continuous metal film or a metal layer with multiple holes, it is able to endure larger amounts of stress so as to enhance more mechanical strength of the FPC  110 . The second reinforcing layer  132  is disposed corresponding to the layout zone  160  and the reinforcing zone  162 , in other words, the second reinforcing layer  132  covers larger area than the signal lines  122   a - 122   d.  The second reinforcing layer  132  is disposed over the signal lines  122   a - 122   d  and the first reinforcing layer  124 . In another embodiment, the second reinforcing layer  132  can be disposed only on the reinforcing zone  162 . In order to prevent the second reinforcing layer  132 , which is made of metal, from contacting other conductors, the second connection layer  134  covers the second reinforcing layer  132  to insulate the latter with other conductors. 
         [0025]    The first substrate  120  comprises a first structure layer  140  and a third connection layer  142 . The second substrate  130  comprises a second structure layer  144  and a fourth connection layer  146 . Both of the first structure layer  140  and the second structure layer  144  are polyimide structure layers. The first structure layer  140  is utilized to prevent the signal lines  122   a - 122   d  and the third connection layer  142  from direct exposure. The third connection layer  142  is utilized to couple the signal lines  122   a - 122   d  and the first reinforcing layer  124  to the first structure layer  140 . The fourth connection layer  146  is utilized to couple the second reinforcing layer  132  to the second structure layer  144 . 
         [0026]    In addition, the FPC  110  comprises a third structure layer  150 , which is set on the second connection layer  134 . The third structure layer  150 , which is a polyimide structure layer, is applied to preventing the second reinforcing layer  132  and the second connection layer  134  from direct exposure. Preferably, the first structure layer  140 , the second structure layer  144 , and the third structure layer  150  are roughly from 12.5 um to 25 um in thickness. 
         [0027]    In the above-mentioned embodiment, the second reinforcing layer  132  and the second substrate  130  are positioned over the first substrate  120 , but the second reinforcing layer  132  and the second substrate  130  also can be positioned under the first substrate  120 . In another embodiment, the first substrate  120  are sandwiched between two second substrates  130  each of which sticks to the second reinforcing layers  132 . 
         [0028]    It is allowed to use the same equipment to lay the plurality of signal lines  122   a - 122   d  and the first reinforcing layer  124  on the first substrate  120  at the same time. In other words, both of the plurality of signal lines  122   a - 122   d  and the first reinforcing layer  124  have not only the same materials but the same manufacturing processes, so nearly no additional operations are required to finish manufacturing the FPC  110 . 
         [0029]    Referring to  FIGS. 2 and 4 ,  FIG. 4  illustrates a cross-section view of a FPC  210  according to a second embodiment of the present invention. The FPC  210  for use in the LCD device comprises a substrate  230 , a first wiring layer  222 , a first reinforcing layer  224 , a second reinforcing layer  232 , a first structure layer  240 , a second structure layer  244 , a third structure layer  250 , a first connection layer  226 , a second connection layer  234 , and a third connection layer  242 . The substrate  230  is formed by the third structure layer  250 , the third connection layer  242 , and a fourth connection layer  246 . The third connection layer  242  and the fourth connection layer  246  are disposed on the first surface (bottom surface) and the second surface (top surface) of the substrate  230 , respectively. The first wiring layer  222 , the first reinforcing layer  224 , the first connection layer  226 , and the first structure layer  240  are also on the first surface of the substrate  230 . The second reinforcing layer  232 , the second structure layer  244 , and the second connection layer  234  are disposed on the second surface of the substrate  230 . 
         [0030]    The first surface of the substrate  230  is divided into a layout zone  260  and a reinforcing zone  262 . A plurality of signal lines  222   a - 222   d,  setting on the layout zone  260  of the substrate  230 , are mostly made of metals, such as gold, copper, or silver, to transmit electrical signals. To simplify the illustration, only four signal lines  222   a - 222   d  are drawn in  FIG. 4 . In practice, the numbers of the signal lines are not limited to four lines but can be adjusted according to individual demands. The reinforcing zone  262  is set outside the layout zone  260  and alongside the signal line  222   d.  The first reinforcing layer  224  is laid on the reinforcing zone  262 , and is made of metal with its thickness of 12 μm-35 μm. The first reinforcing layer  224  is an enclosed region that is not coupled to any electrical signal so that it can be employed to enhance the mechanical strength of the FPC  210 . Besides, the first reinforcing layer  224  is preferably parallel to the signal lines  222   a - 222   d.  The first connection layer  226  is set on the substrate  230  and overlays the plurality of signal lines  222   a - 222   d  and the first reinforcing layer  124 , which is utilized to insulate the plurality of signal lines  222   a - 222   d  and the first reinforcing layer  224 . The third connection layer  242  is utilized to couple the signal lines  222   a - 222   d  and the first reinforcing layer  224  to the third structure layer  250 . The first structure layer  240  covers the first connection layer  226 . 
         [0031]    In order to enhance the mechanical strength of the FPC  210 , the second reinforcing layer  232  is laid on the second surface (top surface) of the substrate  230 . Preferably, the second reinforcing layer  232  is made of metal with its thickness of 12 μm-35 μm, and the area overlaid by the second reinforcing layer  232  is greater than that laid by the signal lines  222   a - 222   d.  Because the second reinforcing layer  232  is a piece of a continuous metal film or a continuous metal layer with multiple holes, it is able to endure larger amounts of stress so as to enhance more mechanical strength of the FPC  210 . The second reinforcing layer  232  corresponds to the layout zone  260  and the reinforcing zone  262 , in other words, the second reinforcing layer  232  covers larger area than the signal lines  222   a - 222   d.  The second reinforcing layer  232  is disposed over the signal lines  222   a - 222   d  and the first reinforcing layer  224  to enhance not only more mechanical strength of the FPC  210  but also that of the layout area  260 . In order to prevent the second reinforcing layer  232  from contacting other conductors, the second connection layer  234  covers the second reinforcing layer  232  to insulate the latter with other conductors. 
         [0032]    The first reinforcing layer  224  comprises a first edge near the edge of substrate  230 , and the second reinforcing layer  232  comprises a second edge near the edge of substrate  230 . A distance D 1  from the edge of substrate  230  to the first edge can be longer than a distance D 2  from the edge of substrate  230  to the second edge. In other words, in contrast to the first edge of the first reinforcing layer  224 , the second edge of the second reinforcing layer  232  is closer to the substrate  230 . Therefore, when the FPC  210  is applied by a shear stress, the second reinforcing layer  232  serves as a first wall to resist the shear stress, and the first reinforcing layer  224  serves as a second wall to resist the shear stress. In another embodiment, the first edge is substantially flush with the second edge, i.e. D 2  equals to D 1 , so that the first reinforcing layer  224  and the second reinforcing layer  232  serves jointly as wall to resist shear stress applied on the FPC  210 . In addition, the second structure layer  244  covers the second connection layer  234  to prevent the second connection layer  234  from scratching. 
         [0033]    Referring to  FIGS. 5A-5E ,  FIGS. 5A-5E  illustrate the top view of the patterns of the second reinforcing layer  232  and its position relative to the first reinforcing layer  224 . It is noted that for convenience of description, the first reinforcing layer  224  and the second reinforcing layer  232  overlap in  FIGS. 5A-5E , but the first reinforcing layer  224  is not disposed on the same layer with the second reinforcing layer  232 . Preferably, the first reinforcing layer  224  is a piece of a metal film and the second reinforcing layer  132  is a piece of a continuous metal film or a continuous metal layer with multiple holes. The first reinforcing layer  224  and the second reinforcing layer  232  are made of metal with its thickness of 12 μm-35 μm. As shown in  FIG. 5A , the first reinforcing layer  224  and the second reinforcing layer  232  both shaped as bars. The first reinforcing layer  224  and the second reinforcing layer  232  correspond to the reinforcing zone  262 . The second edge of the second reinforcing layer  232  is closer to the edge of the substrate  230  than the first edge of the first reinforcing layer  224  is. Or, as shown in  FIG. 5B , the second reinforcing layer  232  is a piece of a metal film and corresponds to the reinforcing zone  262  and the layout zone  260 . The second edge of the second reinforcing layer  232  is closer to the edge of the substrate  230  than the first edge of the first reinforcing layer  224  is. Or, as shown in  FIGS. 5C-5E , the second reinforcing layer  232  is a continuous metal film with holes which are shaped as various patterns such as bars, circles, squares, ellipses, hexagons, irregular polygons and so on. In order to reinforce the mechanical strength of the FPC, any first reinforcing layer  124  and second reinforcing layer  132  which are made of metal to form an continuous construction belong to the scope of the present invention. Preferably, the layout area of the signal lines and the first reinforcing layer  224  on the first surface of the substrate  230  substantially equals to that of the second reinforcing layer  232  on the second surface of the substrate  230 . In other words, a metal coverage ratio (i.e. a ratio of the metal area and the substrate area) of the first surface of the substrate  230  substantially equals to that of the second surface. If the metal coverage ratios of the two surfaces are not uniform, the FPC  210  intends to bend due to a heat effect. As a result, it suggests that the metal coverage ratios of the two surfaces of the substrate  230  are nearly identical to avoid bent phenomenon of the FPC  210 . 
         [0034]    In this embodiment, the structure layers  240 ,  244 , and  260  are polyimide layer and are roughly from 12.5 um to 25 um in thickness. 
         [0035]    It is allowed to use the same equipment to lay the plurality of signal lines  222   a - 222   d  and the first reinforcing layer  224  on the substrate  230  at the same time. In other words, both of the plurality of signal lines  222   a - 222   d  and the first reinforcing layer  224  have not only the same materials but the same manufacturing processes, so nearly no additional operations are required to finish manufacturing the FPC  210 . 
         [0036]    Referring to  FIG. 6  showing a cross-section view of the FPC  310  according to a third embodiment of the present invention, for simplicity, elements in  FIG. 6  that have the same function as that illustrated in  FIG. 4  are provided with the same item numbers as those used in  FIG. 4 . Differing from FPC  210  in  FIG. 4 , the substrate is the third structure layer  250 . In addition, the signal lines  222   a - 222   d  and the first reinforcing layer  224  are directly formed on the third structure layer  250  by sputtering without needing the third connection layer  242 . 
         [0037]    Referring to  FIG. 7  showing a cross-section view of the FPC  410  according to a fourth embodiment of the present invention, for simplicity, elements in  FIG. 7  that have the same function as that illustrated in  FIG. 4  are provided with the same item numbers as those used in  FIG. 4 . Differing from FPC  210  in  FIG. 4 , a ground wire  223  is substitute for the signal line  222   d  of the FPC  410 , and the second reinforcing layer  232  electrically connects to the ground wire  223  through a first via  270 . As a result, not only the second reinforcing layer  232  and the ground wire  223  are coupled to ground, but also heat generated from the signal lines  222   a - 222   c  can be transferred to an ambient environment or to a heat-dissipation system through the second reinforcing layer  232 . 
         [0038]    Referring to  FIG. 8  showing a cross-section view of the FPC  510  according to a fifth embodiment of the present invention, for simplicity, elements in  FIG. 8  that have the same function as that illustrated in  FIG. 4  are provided with the same item numbers as those used in  FIG. 4 . Differing from FPC  210  in  FIG. 4 , a ground wire  223  is substitute for the signal line  222   d  of the FPC  510  is coupled to ground, and the second reinforcing layer  232  electrically connects to the ground wire  223  through a first via  270 , and a second reinforcing layer  232  electrically connects to a first reinforcing layer  224  via a second via  272 . As a result, not only the first reinforcing layer  224 , the second reinforcing layer  232 , and the ground wire  223  are coupled to ground, but also heat generated from the signal lines  222   a - 222   c  can be transferred to an ambient environment or to a heat-dissipation system through the second reinforcing layer  232  and the first reinforcing layer  224 . 
         [0039]    Comparing with Prior Art, the characteristic of the FPC in the present invention is that a first reinforcing layer and a second reinforcing layer are set outside of signal lines that transmit electrical signals. So, when the FPC endures repeated bending several times, the first reinforcing layer and the second reinforcing layer are able to effectively endure stress produced during bending and further, to weaken stress that the signal lines endured. Hence, the first reinforcing layer and the second reinforcing layer in the present invention can reinforce the mechanical strength of the FPC to protect the FPC from fracturing and then lapsing easily. In addition, the materials used in the first reinforcing layer are the same as those used in the signal lines, so both of the first reinforcing layer and the signal lines can be produced in the same manufacturing processes without increasing cost too much. Attributing to the design that the first reinforcing layer and the second reinforcing layer reinforce the FPC, the degree of bending of the FPC can be effectively enhanced, and the service life of the FPC can be extended as well. 
         [0040]    It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.