Abstract:
Provided is a method of forming a fine pitch in a flexible printed circuit board (FPCB) having an increased adhesive property of wirings and an improved insulating property between the wirings. The method includes etching regions where wirings are to be formed on a base substrate; forming conductive layers on the etched regions; forming a photoresist film on a substrate between the etched regions; forming the wirings by forming the conductive layers on the etched regions to be higher than the substrate; and removing the photoresist film.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2008-0038952, filed on Apr. 25, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a flexible printed circuit board (FPCB) on which a semiconductor package or an integrated circuit chip is mounted, and more particularly, to a method of forming a fine pitch in a FPCB. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, conventional printed circuit boards (PCBs) are rigid products used for mechanically supporting and electrically connecting electronic components such as semiconductor packages or integrated circuit chips in various electronic products. However, as the electronic products are manufactured to have smaller sizes and more functions, flexible printed circuit boards (FPCBs), which can be installed in a small place and can accommodate thereon many electronic components, are widely used. 
         [0006]    Flexible printed circuit boards (FPCBs) include electric circuits having various patterns in order to mount thereon many electronic components. Thus, in order to increase the integration of the electronic components, a fine pitch should be realized in FPCBs. 
         [0007]    Conventionally, there are two methods of realizing a fine pitch in an FPCB. First, in order to form a terminal having a predetermined thickness in a FPCB, a copper layer is formed to a predetermined thickness in the FPCB, and then the copper layer is etched. Second, a thin copper seed is formed in a FPCB, and then a copper layer is formed in the copper seed by using an electroplating method. 
         [0008]    However, when wirings are formed using such conventional methods of forming a fine pitch, an adhesive property of the wirings can be decreased and an insulating property between wirings can be deteriorated. Thus, there is a need for new FPCB and a method of manufacturing the same that can address the above problems. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a method of forming a fine pitch in a flexible printed circuit board (FPCB) having an increased adhesive property of wirings and an improved insulating property between the wirings. 
         [0010]    The present invention also provides a FPCB manufactured by the above method. 
         [0011]    According to an aspect of the present invention, there is provided a method of forming a fine pitch in a flexible printed circuit board (FPCB), the method including: etching regions where wirings are to be formed on a base substrate; forming conductive layers on the etched regions; forming a photoresist film on a substrate between the etched regions; forming the wirings by forming the conductive layers on the etched regions to be higher than the substrate; and removing the photoresist film. 
         [0012]    According to another aspect of the present invention, there is provided a FPCB manufactured by a method including: etching regions where wirings are to be formed on a base substrate; forming conductive layers on the etched regions; forming a photoresist film on a substrate between the etched regions; forming the wirings by forming the conductive layers on the etched regions to be higher than the substrate; and removing the photoresist film. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0014]      FIG. 1  is a schematic view illustrating a method of manufacturing a FPCB according to an embodiment of the present invention; 
           [0015]      FIG. 2  is a cross-sectional view of a base substrate before a FPCB is completed, according to an embodiment of the present invention; 
           [0016]      FIG. 3  is a cross-sectional view of the base substrate on which a first photoresist film is formed, according to an embodiment of the present invention; 
           [0017]      FIG. 4  is a cross-sectional view of the base substrate undergoing a first masking process, according to an embodiment of the present invention; 
           [0018]      FIG. 5  is a cross-sectional view of the base substrate undergoing a first exposure process, according to an embodiment of the present invention; 
           [0019]      FIG. 6  is a cross-sectional view of the base substrate from which a first mask is removed, according to an embodiment of the present invention; 
           [0020]      FIG. 7  is a cross-sectional view of the base substrate undergoing an etching process, according to an embodiment of the present invention; 
           [0021]      FIG. 8  is a cross-sectional view of the base substrate from which all the first photoresist film is removed, according to an embodiment of the present invention; 
           [0022]      FIG. 9  is a cross-sectional view of the base substrate on which a first conductive layer is formed, according to an embodiment of the present invention; 
           [0023]      FIG. 10  is a cross-sectional view of the base substrate on which a second photoresist film is formed on the first conductive layer, according to an embodiment of the present invention; 
           [0024]      FIG. 11  is a cross-sectional view of the base substrate undergoing a second masking process, according to an embodiment of the present invention; 
           [0025]      FIG. 12  is a cross-sectional view of the base substrate undergoing a second exposure process, according to an embodiment of the present invention; 
           [0026]      FIG. 13  is a cross-sectional view of the base substrate from which a second mask is removed, according to an embodiment of the present invention; 
           [0027]      FIG. 14  is a cross-sectional view of the base substrate on which a second conductive layer is formed in an area where the second photoresist film is removed, according to an embodiment of the present invention; 
           [0028]      FIG. 15  is a cross-sectional view of the base substrate from which the second photoresist film is removed, according to an embodiment of the present invention; and 
           [0029]      FIG. 16  is a cross-sectional view of a completed FPCB of which wirings are capped, according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Hereinafter, the present invention will be described in detail by explaining exemplary embodiments of the invention with reference to the attached drawings. The same reference numerals in the drawings denote the same element. 
         [0031]      FIG. 1  is a schematic view illustrating a method of manufacturing a FPCB  165  according to an embodiment of the present invention. The FPCB  10  illustrated in  FIG. 1  may be manufactured by a roll-to-roll method or a sheet method. 
         [0032]    Referring to  FIG. 1 , a base substrate  10 , that is, a raw material in which an circuit pattern has not been formed, is unwound from a supplying roll  11  and wound up on a recovering roll  12 , is unwound from the supplying roll  11  while passing simultaneously through an exposure apparatus  2 , an etching apparatus  3 , and a deposition apparatus  4  for manufacturing the FPCB  165 . Then, the FPCB  165  is wound up on the recovering roll  12 . 
         [0033]    In order to manufacture the FPCB  165 , the exposure apparatus  2 , the etching apparatus  3 , and the deposition apparatus  4  are sequentially arranged in a moving direction of the base substrate from the supplying roll  11  to the recovering roll  12 . For example, the exposure apparatus  2 , the etching apparatus  3 , and the deposition apparatus  4  are sequentially arranged in an arrow direction as shown in  FIG. 1 . 
         [0034]    The exposure apparatus  2 , the etching apparatus  3 , and the deposition apparatus  4  of  FIG. 1  are schematically illustrated to describe a method of manufacturing the FPCB according to an embodiment of the present invention. However, the present invention is not limited thereto, and other various apparatuses may be arranged in various forms. 
         [0035]      FIGS. 2 through 16  are cross-sectional views for explaining a method of manufacturing a FPCB  165  of  FIG. 16 , according to an embodiment of the present invention. 
         [0036]      FIG. 2  is a cross-sectional view of the base substrate  10  before the FPCB  165  is manufactured, according to an embodiment of the present invention. Referring to  FIG. 2 , the base substrate  10  is made of an insulating material, such as a polyimide film or a polyester film. That is, the inside of the base substrate  10  may be formed of a composition of glass fiber and resin. The base substrate  10  may be manufactured to a predetermined thickness, for example, less than 0.15 mm so as to be flexible. Thus, the base substrate  10  can be wound up on the supplying roll  11  and the recovering roll  12  as illustrated in  FIG. 1 . 
         [0037]      FIG. 3  is a cross-sectional view of the base substrate  10  on which a first photoresist film  30  is formed, according to an embodiment of the present invention. Referring to  FIG. 3 , a photoresist is coated on the entire surface of the base substrate  10 , thereby forming the first photoresist film  30 . The first photoresist film  30  may be formed of dry film resist (DFR), and may be also formed of a photosensitive film or ink. In order to sufficiently adhere the first photoresist film  30  to the base substrate  10 , the first photoresist film  30  may be formed after heating the surface of the base substrate  10 . 
         [0038]      FIG. 4  is a cross-sectional view of the base substrate  10  undergoing a first masking process, according to an embodiment of the present invention. Referring to  FIG. 4 , the entire surface of the base substrate  10  is covered by a first mask  40  having a predetermined pattern. An operation for covering the entire surface of the base substrate  10  with the first mask  40  having a predetermined pattern is referred to as masking. The surface of the base substrate  10  is divided into a region where a wiring is to be formed, that is, a region which is to be etched to form the wiring, and a region where a wiring is not to be formed. Accordingly, the first mask  40  is not placed on the region where the wiring is to be formed, and is placed only on the region where the wiring is not to be formed, that is, a region which is not to be etched. The first mask  40  may be adhered to the base substrate  10  as illustrated in  FIG. 4 , and may be formed in a free state on the base substrate  10  without being adhered to the base substrate  10 . The first mask  40  may be made of a removable film, a photosensitive resin, or a dry film. 
         [0039]      FIG. 5  is a cross-sectional view of the base substrate  10  undergoing a first exposure process, according to an embodiment of the present invention. Referring to  FIG. 5 , when the base substrate  10  on which masking is performed enters the exposure apparatus  2  of  FIG. 1 , light, such as ultra-violet (UV) light, is irradiated to the base substrate  10 . Accordingly, the first photoresist film  30  in the region where the first mask  40  is not formed is removed, and the first photoresist film  30  in the region where the first mask  40  is formed is maintained as it is. A developing process may be additionally performed after performing the exposure process according to the type of the first photoresist film  30 , in order to remove the first photoresist film  30 . 
         [0040]      FIG. 6  is a cross-sectional view of the base substrate  10  from which the first mask  40  is removed, according to an embodiment of the present invention. Referring to  FIG. 6 , the first mask  40  is removed after removing the first photoresist film  30  in the region where the first mask  40  is formed after the exposure process is finished. When the first mask  40  is adhered to the base substrate  10 , the first mask  40  is removed by stripping or using an etching material. 
         [0041]      FIG. 7  is a cross-sectional view of the base substrate  10  undergoing the etching process, according to an embodiment of the present invention. Referring to  FIG. 7 , when the base substrate  10  enters the etching apparatus  3  of  FIG. 1 , an etching material is sputtered from an upper portion of the etching apparatus  3  on the base substrate  10 . Thus, the region of the base substrate  10  where the first photoresist film  30  is not formed is etched to a predetermined thickness, and the region where the first photoresist film  30  is formed is maintained as it is. 
         [0042]      FIG. 8  is a cross-sectional view of the base substrate  10  from which all the first photoresist film  30  is removed, according to an embodiment of the present invention. Referring to  FIG. 8 , when the base substrate  10  enters the etching apparatus  3 , an exfoliating material is sputtered on the base substrate  10  to exfoliate the first photoresist film  30 . 
         [0043]      FIG. 9  is a cross-sectional view of the base substrate  10  on which a first conductive layer  90  is formed, according to an embodiment of the present invention. Referring to  FIG. 9 , when the base substrate  10  enters the deposition apparatus  4  of  FIG. 1 , the deposition apparatus  4  deposits a material having electroconductivity, such as copper, nickel chrome, or an copper-nickel chrome alloy, on the base substrate  10  to form the conductive layer  90 . The conductive layer  90  may be formed to be thin. 
         [0044]      FIG. 10  is a cross-sectional view of the base substrate  10  when a second photoresist film  100  is formed on the first conductive layer  90 , according to an embodiment of the present invention. Referring to  FIG. 10 , the second photoresist film  100 , for example, dry film resist (DFR), is formed to a predetermined thickness on the entire surface of the conductive layer  90 . The predetermined thickness may be equal to that of a wiring to be formed on the base substrate  10 . The second photoresist film  100  may be formed by vapor deposition. 
         [0045]      FIG. 11  is a cross-sectional view of the base substrate  10  undergoing a second masking process, according to an embodiment of the present invention. Referring to  FIG. 11 , the second photoresist film  100  is divided into a region to be etched and a region not to be etched, and the region not to be etched is covered by a second mask  110 . The second mask  110  may be adhered to the base substrate  10  as illustrated in  FIG. 11 , and may be formed in a free state on the base substrate  10  without being adhered to the base substrate  10 . The second mask  110  may be made of a removable film, a photosensitive resin, or a dry film. 
         [0046]      FIG. 12  is a cross-sectional view of the base substrate  10  undergoing a second exposure process, according to an embodiment of the present invention. Referring to  FIG. 12 , when the base substrate  10  on which masking is performed enters the exposure apparatus  2  ( FIG. 1 ), the second photoresist film  100  of the region where the second mask  110  is not formed is removed, and the second photoresist film  100  of the region where the second mask  110  is formed is maintained as it is. A developing process may be additionally performed after performing the exposure process according to the type of the second photoresist film  100  in order to remove the second photoresist film  100 . 
         [0047]      FIG. 13  is a cross-sectional view of the base substrate  10  from which the second mask  110  is removed, according to an embodiment of the present invention. Referring to  FIG. 13 , after the second exposure process is finished, the second mask  110  of  FIG. 12  is removed by stripping or using an etching material.  FIG. 14  is a cross-sectional view of the base substrate  10  when wirings  140  are formed on a region where the second photoresist film  100  is removed, according to an embodiment of the present invention. Referring to  FIG. 14 , the wirings  140  are formed by growing a conductive material, for example, copper, in the region where the second photoresist film  100  is removed, by using an electroplating method. The wirings  140  may be formed to have the same height as the second photoresist film  100  remaining in the base substrate  10 . Since the conductive layer  90  is formed of a high adhesive material, the wirings  140  have high adhesive properties so as to be adhered to the base substrate  10  by the conductive layer  90 . 
         [0048]      FIG. 15  is a cross-sectional view of the base substrate  10  from which the second photoresist film  100  is removed, according to an embodiment of the present invention. Referring to  FIG. 15 , all the second photoresist film  100  of  FIG. 14  remaining in the base substrate  10  is removed by exfoliating using an exfoliating material. Accordingly, only the wirings  140  remain as illustrated in  FIG. 15 . The wirings  140  electrically connect each of electronic components mounted on the FPCB  165  of  FIG. 16 . In removing the second photoresist film  100  of  FIG. 14 , a part of side lower end portions of the wirings  140  is etched, thereby generating an undercut effect as illustrated in  FIG. 15 . Paths between the wirings  140  are extended due to the undercut effect, thereby increasing an insulating property between the wirings  140 . 
         [0049]    As such, according to the present invention, an insulating property between the wirings  140  and an adhesive property of the wirings  140  are increased, and thus a fine pitch can be formed. 
         [0050]      FIG. 16  is a cross-sectional view of a completed FPCB  165  when the wirings  140  are capped, according to an embodiment of the present invention. Referring to  FIG. 16 , in order to protect the wirings  140  from external factors, and increase the conductivity of the wirings  140 , a capping layer  160  is formed by capping an upper portion and a side portion of the wiring  140  with a conductive material, for example, tin (sn), silver (Au), gold (Ag), lead (Pd) or an alloy thereof. 
         [0051]    In order to form the capping layer  160 , an additional process may be performed as follows. A third photoresist film is formed on the entire surface of the FPCB  165 , and then masking is performed on the third photoresist film. Then, after the third photoresist film formed on the wirings  140  is removed, a conductive material is deposited on the entire surface of the FPCB  165  and the remaining portions of the third photoresist film are removed. 
         [0052]    Also, in order to protect the wirings  140  from external factors, a cover layer film or silicon may be additionally partially or entirely coated on the FPCB  165 , or the FPCB  165  may be gold-plated in order to increase the corrosion resistance of the FPCB  165 . 
         [0053]    Also, when the wirings  140  are formed only in an upper portion of the FPCB  165 , a stiffener may be adhered to the lower portion of the FPCB  165  in order to prevent the FPCB  165  from bending. 
         [0054]      FIGS. 2 through 16  illustrate a case where the wirings  140  are formed only in the upper portion of the FPCB  165 . However, the wirings  140  may be also formed in the lower portion of the FPCB  165  using the same method. 
         [0055]    The FPCB  165  can be used for electrical connections between a main circuit substrate, such as a cellular phone, a notebook computer, or a liquid crystal display (LCD) image display apparatus, and an LCD module, and for controlling signal transmission. 
         [0056]    According to the present invention, undercuts are formed in side lower end portions, so that an insulating property between wirings can be increased. Accordingly, a fine pitch in a FPCB can be formed. 
         [0057]    Also, a first conductive layer is formed so as to increase an adhesive property of wirings. 
         [0058]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.