Abstract:
Disclosed herein is a rigid flexible printed circuit board (PCB) including: a flexible area having a flexible copper foil laminate in which circuit layers are formed on an insulating material, and cover lays formed on the laminate; and rigid areas having insulating layers and copper layers built-up on both sides of the flexible area, and flattening materials to flatten outer surfaces of the insulating layers.

Description:
CROSS REFERENCE(S) TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit under 35 U.S.C. Section 119 of Korean Patent Application Serial No. 10-2013-0104834, entitled “Rigid Flexible PCB and Method for Manufacturing the Same” filed on Sep. 2, 2013, which is hereby incorporated by reference in its entirety into this application. 
       BACKGROUND OF THE INVENTION  
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a rigid flexible PCB and a method for manufacturing the same, and more particularly, to a rigid flexible PCB with improved flatness and a method for manufacturing the same. 
         [0004]    2. Description of the Related Art 
         [0005]    Recently, mobile electronic devices have evolved to have high performance and to support the Internet, video and massive data transmission. Accordingly, the design of the printed circuit board becomes more complicated, and highly densed and smaller circuits are increasingly required. 
         [0006]    Therefore, printed circuit boards incorporated in electronic devices become thinner and smaller, and thus the width of wiring on the printed circuit boards also becomes smaller in order to implement the functions of the printed circuit boards. The structure of the printed circuit boards is changing from a single layer to multiple layers. 
         [0007]    Currently, in the process of manufacturing a rigid flexible printed circuit board, a cover lay, an electromagnetic interference (EMI) filter and the like are manufactured on the flexible board in separate processes, and stacked on the insulating material to be cured. 
         [0008]    Further, in the process of manufacturing a rigid flexible printed circuit board, cover lays are applied on the surface of a flexible copper clad laminate (FCCL), then they are compressed at a high temperature of approximately 170° C. by the substrate molding members, and the cover lays and the FCCL are integrally molded. 
         [0009]    When the cover lays and the FCCL are integrally molded by the substrate molding members, however, smooth waves are formed on the surfaces of the cover lays conforming to the shape of the circuit layers. Thus, Layers such as prepreg and copper layers are formed on the wave surfaces, the surface of the rigid board becomes uneven, thereby decreasing product value. 
       RELATED ART DOCUMENT  
     Patent Document  
       [0010]    (Patent Document 1) Cited Reference: Korean Patent Laid-Open Publication No. 2012-0007444 
       SUMMARY OF THE INVENTION  
       [0011]    An object of the present invention is to provide a rigid flexible PCB capable of improving deviations in the overall thickness of the board by way of adding a rigid flattening material in the board when the rigid board is manufactured, and a method for manufacturing the same. 
         [0012]    Another object of the present invention is to provide a rigid flexible PCB capable of suppressing warpage by virtue of a rigid flattening material stacked in the rigid board. 
         [0013]    According to an exemplary embodiment of the present invention, there is provided a rigid flexible printed circuit board (PCB) including: a flexible area having a flexible copper foil laminate in which circuit layers are formed on an insulating material, and cover lays formed on the laminate; and rigid areas having insulating layers and copper layers built-up on both sides of the flexible area, and flattening materials to flatten outer surfaces of the insulating layers. 
         [0014]    The flattening material may be stacked between the insulating layers and the copper layers and may be formed of a copper foil laminate. 
         [0015]    The circuit layers and the copper layers may be electrically connected via a through via penetrating through the flattening materials and the insulating layers, and the flattening material may be formed of a rigid insulating material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]      FIG. 1  is a cross-sectional view of a manufactured rigid flexible PCB according to an exemplary embodiment of the present invention; and 
           [0017]      FIGS. 2A to 2F  are views showing a manufacturing process of the rigid flexible PCB according to an exemplary embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
         [0019]      FIG. 1  is a cross-sectional view of a manufactured rigid flexible PCB according to an exemplary embodiment of the present invention; and  FIGS. 2A to 2F  are views showing a manufacturing process of the rigid flexible PCB according to an exemplary embodiment of the present invention. 
         [0020]    As shown in  FIG. 1 , the rigid flexible PCB  100  according to the exemplary embodiment of the present invention includes a flexible area  10  and rigid areas  30  on both sides of the flexible area  10 . 
         [0021]    The flexible area  10  includes an insulating material  13  formed of polyimide or prepreg, a flexible copper foil laminate  12  having circuit layers  14  formed on both surfaces of the insulating material  13 , and cover lays stacked on the flexible copper foil laminate  12 . 
         [0022]    Preferably, the insulating material  13  is thinner than or equal to the circuit layers  14 . This is to prevent the circuit layers  14  from being readily delaminated from the insulating material  13  by ensuring sufficient tension against impact from the outside. 
         [0023]    The circuit layers  14  are formed by performing etching on copper foils formed the both surfaces of the insulating material  13  and may be formed of a material having good conductivity such as copper. 
         [0024]    Further, over the circuit layers  14 , the cover lays  15  are thermo-compression molded at high temperature by substrate molding members  20 . 
         [0025]    The cover lays  15  are thermo-compression molded by the substrate molding members  20  under a pressure of approximately 25 kg/cm 2  or greater at a temperature of approximately 170° C. or higher and then the substrate molding members  20  are separated from the cover lays  15  and the cover lays  15  are cured. 
         [0026]    Here, when the substrate molding members  20  are separated from the cover lays  15 , waves are made on the outer surfaces of the cover lays  15 . This is because the portions on the upper surfaces of the cover lays  15  where the circuit layers  14  are formed protrude than the portions where the circuit layers  14  are not formed depending on the shapes and locations of the circuit layers  14  when the cover lays  15  are pressed by the substrate molding members  20 . 
         [0027]    After the cover lays  15  are thermo-compression molded as described above, the rigid areas  30  are formed on both sides of the flexible area  10 . 
         [0028]    The rigid areas  30  include insulating layers  32 , copper layers  34 , and flattening material  36  interposed between the copper layers  34  and the insulating layers  32 . 
         [0029]    Further, the rigid areas  30  may further include photo solder resist (PSR) layers  38  applied on the copper layers  34 . 
         [0030]    The insulating layers  32  may be applied on both surfaces of the cover lays  15  and may be formed of prepreg. The insulating layers  32  are designed to have such a thickness as to maintain rigidity sufficient to suppress warpage. 
         [0031]    After the insulating layers  32  are stacked on the cover lays  15  as described above, the flattening materials  36  are stacked on the insulating layers  32 . 
         [0032]    The flattening materials  36  may be a copper foil laminate formed by laminating copper foils on insulating materials and, if necessary, may be a rigid insulating material having a melting point higher than that of the insulating layers  32 . 
         [0033]    That is, after the insulating layers  32  and the flattening materials  36  are stacked on the cover lays  15  in this order, by performing thermo-compression molding at a high temperature while bringing the substrate molding members  20  into close contact with the flattening material  36 , part of the insulating layers  32  is melted so as to fill the space on the recessed portions on the cover lays  15 . 
         [0034]    Here, although the upper surfaces of the insulating layer  32  may have a smooth wave as the circuit layers  14  during the compression molding process, since the upper surfaces of the insulating layers  32  are in close contact with the flattening material  36  while they are compression molded, the smooth wave on the upper surfaces of the insulating layers  32  do not affect the copper layers  34  stacked on the flattening materials  36 . 
         [0035]    The copper layers  34  are formed on the flattening materials  36  and formed by performing etching process or the like after copper foils are formed. After the copper layers  34  are formed, photo solder resist layers  38  are formed. 
         [0036]    Here, electrical connections between the layers are made by through vias  40 . That is, the circuit layers  14  and the copper layers  34  are electrically connected through the through vias  40  penetrating through the flattening materials  36  and the insulating layers  32 . The through vias  40  may be formed by being penetrated by laser to form a hole and then being plated. 
         [0037]    The rigid flexible PCB thus configured may be manufactured according to the following process. 
         [0038]    As shown in  FIGS. 2A and 2B , copper foils are formed on both surfaces of the insulating layer  13 , and then an etching process is performed on the copper foils to form circuit layers  14 . 
         [0039]    After flexible copper foil laminate  12  is manufactured by forming the circuit layers  14 , cover lays  15  are applied on both surfaces of the circuit layers  14 . The cover lays  15  are thermo-compression molded by the substrate molding members  20  under a pressure of approximately 25 kg/cm 2  or greater at a temperature of approximately 170° C. or higher. 
         [0040]    After the cover lays  15  are thermo-compression molded for a certain period of time by the substrate molding members  20 , the substrate molding members  20  are separated from the cover lays  15 , and the cover lays  15  are air-cooled and cured, to manufacture a flexible area  10 . 
         [0041]    Once the flexible area  10  is manufactured as described above, the insulating layers  32  and the flattening materials  36  are stacked on both surfaces of the flexible area  10  in this order. Here, the insulating layers  32  may be formed of an insulating material such as prepreg, and the flattening materials  36  may be formed of a rigid material such as a copper foil laminate. 
         [0042]    After the insulating layers  32  and the flattening materials  36  are stacked, they are thermo-compression molded by the substrate molding members  20  at a high temperature. After a certain period of time for the compression, the substrate molding members  20  are separated from the flattening materials  36  and air-cooling is performed. 
         [0043]    After air-cooling is completed, copper layers  34  are formed on the flattening materials  36 , and photo solder resist layers  38  are formed on the copper layers  34 . Here, electrical connections between the layers are made by through vias  40 . The through vias  40  may be formed according to a method well known in the art for providing electrical connections between layers, and thus detail description thereon will not be given. 
         [0044]    Accordingly, in the rigid flexible PCB  100  according to the exemplary embodiment of the present invention, waves formed between the cover lays  15  and the insulating layers  32  conforming to the shape of the circuit layers  14  can be flattened by the rigid flattening materials  36 . As a result, overall warpage of the board can be suppressed and thus product value can be improved. 
         [0045]    According to the exemplary embodiments of the present invention, a rigid flattening material is added in the board when the rigid board is manufactured, so that deviations in the overall thickness of the board is improved, as well as warpage is suppressed by virtue of a rigid flattening material. Therefore, product value can be improved. 
         [0046]    Thus far, although the rigid flexible PCB and the method for manufacturing the same have been described according to the exemplary embodiment of the present invention, the present invention is not limited thereto, but may be variously modified and altered by those skilled in the art.