Abstract:
An FPCB includes a flexible base, a wiring layer formed on a top surface of the base, a covering layer formed on the wiring layer, and a shielding layer formed on a portion of the covering layer. The wiring layer includes a grounding line. The covering layer defines an opening to expose the grounding line to the outside. A portion of the shielding layer fills into the opening. The shielding layer is electrically connected to the grounding line through the opening.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to technologies for manufacturing printed circuit boards (PCBs), and particularly to a flexible PCB (FPCB) having a relatively low cost, and a method for making the FPCB. 
         [0003]    2. Description of Related Art 
         [0004]    With the progress of technology, more and more concentrated circuits are arranged on FPCBs. However, the concentrated circuits on the FPCB may induce electro-magnetic interference (EMI), which inhibits performance of the FPCB. A conductive fabric may be employed to shield the EMI. However, the conductive fabric usually has a complex structure and a high cost, which increases manufacturing difficulty and costs of the FPCB. 
         [0005]    Therefore, what are needed are an FPCB and a method for making the FPCB addressing the limitations described. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0006]    The components of the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments of the present disclosure. 
           [0007]      FIGS. 1-11  are schematic views of an embodiment of a method for making an FPCB. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.” The references “a plurality of” and “a number of” mean “at least two.” 
         [0009]      FIGS. 1-11  illustrate a method for making a flexible printed circuit board (FPCB)  100 . 
         [0010]      FIGS. 1-2  show that a flexible wiring board  10  is provided, wherein  FIG. 2  is a cross section view of the flexible wiring board  10  of  FIG. 1  taken along line II-II. The flexible wiring board  10  includes a flexible base  11 , a first wiring layer  12  formed on a top surface of the base  11 , a second wiring layer  13  formed on a bottom surface of the base  11 , a first covering layer  14  covering the first wiring layer  12 , and a second covering layer  15  covering the second wiring layer  13 . In one embodiment, the base  11  is made from flexible material, such as polyimide (PI), polyethylene terephthalate (PET), or polyethylene naphthalate (PEN). Alternatively, the flexible wiring board  10  can be a multi-layer board, which includes a number of alternately arranged bases and wiring layers. In one embodiment, the first wiring layer  12  and the second wiring layer  13  are made of copper and formed by a selective etching process. The flexible wiring board  10  includes an EMI shielding area  16  and a common area  17  outside the shielding area  16 . Portions of the first wiring layer  12  within the shielding area  16  are grounding lines  122 . 
         [0011]      FIG. 3  shows that a number of openings  142  are defined in the first covering layer  14  within the EMI shielding area  16 . Some of the grounding lines  122  are exposed to the outside through the openings  142 . In one embodiment, the openings  142  can be formed by a punching process before laminating on the first wiring layer  12 . In other embodiment, the opening  142  can be processed by a layer ablation process. 
         [0012]      FIG. 4  shows that a first seed layer  18  and a second seed layer  19  are formed. The first seed layer  18  covers the first covering layer  14 , inner surfaces of each of the openings  142 , and portions of the grounding lines  122  exposed through the openings  142 . The second seed layer  19  covers the second covering layer  14 . In one embodiment, the first seed layer  18  and the second seed layer  19  are formed by an electroless process, such as a chemical electroplating process, and the first seed layer  18  and the second seed layer  19  are made of copper. 
         [0013]    Before the first seed layer  18  and the second seed layer  19  are formed, surfaces of the flexible wiring board  10  to be covered by the first seed layer  18  and the second seed layer  19  undergo a pretreatment process. The pretreatment process removes pollutants from the surfaces, thereby enhancing an adhesive force of the first seed layer  18  and the second seed layer  19  on the corresponding surfaces of the flexible wiring board  10 . The pretreatment process can be a plasma treatment process, a pumice process, or other suitable process. 
         [0014]      FIG. 5  shows that a first photoresist layer  20  is formed on the first seed layer  18 , and a second photoresist layer  21  is formed on the second seed layer  19 . In one embodiment, the first photoresist layer  20  and the second photoresist layer  21  are made of a photosensitive material. 
         [0015]      FIG. 6  shows that a portion of the first photoresist layer  20  on the first seed layer  18  in the EMI shielding area  16  is removed. Thus, a portion of the first seed layer  18  in the EMI shielding area  16  is exposed to the outside. The portion of the first photoresist layer  20  is removed by an exposing/developing process. 
         [0016]      FIG. 7  shows that a shielding layer  22  is formed on the portion of the first seed layer  18  exposed to the outside. The openings  142  are filled with the shielding layer  22 . In one embodiment, the shielding layer  22  is formed by a electroplating process, and the shielding layer  22  is made of copper. 
         [0017]      FIG. 8  shows that the first photoresist layer  20  and the second photoresist layer  21  are removed. 
         [0018]      FIG. 9  shows that the first seed layer  18  in the common area  17 , as well as the second seed layer  19 , are removed. In one embodiment, the first seed layer  18  and the second seed layer  19  are removed by a micro-etching process. The first seed layer  18  in the EMI shielding area, together with the shielding layer  22 , form an EMI shielding structure  23 . The shielding layer  22  and the first seed layer  18  serve as EMI shielding layers  24  of the EMI shielding structure  23 . The openings  142  serve as vias  25  for electrically connecting the EMI shielding structure  23  to the grounding lines  122 . 
         [0019]      FIGS. 10-11  show that a solder resist layer  26  is formed on the EMI shielding layer  24  to form a final FPCB  100 , wherein  FIG. 11  is a plan view of the FPCB of the  FIG. 10 . The solder resist layer  26  protects the EMI shielding layer  24  from external impact. In one embodiment, the solder resist layer  26  covers a top surface and peripheral surfaces of the EMI shielding layer  24 . 
         [0020]    As described above, the EMI shielding structure  23  is formed on the first covering layer  14 . However, it is understood that in other embodiments, the EMI shielding structure  23  can also be formed on the second covering layer  15 . Furthermore, a shape and size of the EMI shielding area  16  can be adjusted according to different requirements. For example, the EMI shielding structure  23  can be formed on an entire surface of the first covering layer  14  and/or on the second covering layer  15 . 
         [0021]    It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being exemplary embodiments of the disclosure.