Abstract:
An RFPCB includes a reinforcement layer and at least two FPCBs spliced together to match the reinforcement layer in shape and size. The FPCBs are adhered onto the reinforcement layer. The reinforcement layer includes circuits connected with the FPCB and has portions removed to obtain a desired flexibility.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to rigid-flex printed circuit boards (RFPCBs), and particularly to an RFPCB of low cost and a method for making the RFPCB. 
         [0003]    2. Description of Related Art 
         [0004]    To form RFPCBs, raw boards of flexible printed circuit boards (FPCBs) and rigid printed circuit boards (RPCBs) are provided and formed with respective circuits to obtain the FPCBs and the RPCBs. Then, the FPCBs are combined with the RPCBs to obtain the RFPCBs. However, both the raw boards of the FPCBs and the RPCBs have standard lengths and widths, which may not match each other. Thus, portions of the FPCBs or of the RPCBs may be wasted, which increases a cost of the RFPCBs. 
         [0005]    Therefore, it is desirable to provide an RFPCB and a method for making the RFPCB to overcome the above-mentioned problems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. 
           [0007]      FIG. 1  is a top view of an embodiment of a first FPCB. 
           [0008]      FIG. 2  is a cross-sectional view of the first FPCB of  FIG. 1 . 
           [0009]      FIG. 3  is a top view of an embodiment of a second FPCB. 
           [0010]      FIG. 4  is a cross-sectional view of the second FPCB of  FIG. 3 . 
           [0011]      FIG. 5  is a top view of a third FPCB formed from the first FPCB of  FIG. 1  and the second FPCB of  FIG. 3 . 
           [0012]      FIG. 6  is a top view of a first semifinished board of the third FPCB of  FIG. 5 . 
           [0013]      FIG. 7  is a cross-sectional view of the first semifinished board of  FIG. 6 . 
           [0014]      FIG. 8  is a cross-sectional view of a second semifinished board made from the first semifinished board of  FIG. 7 . 
           [0015]      FIG. 9  is a cross-sectional view of RFPCBs made from the second semifinished board of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    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.” 
         [0017]    Embodiments of the present disclosure will be described with reference to the drawings. 
         [0018]    A method for making a first RFPCB  310  and a second RFPCB  320  (both shown in  FIG. 9 ) includes the following steps: 
         [0019]    In step  1 , referring to  FIGS. 1-2 , a substantially rectangular first FPCB  11  is provided. A number of substantially C-shaped cutouts  117  are defined in a side of the first FPCB  11  by stamping. 
         [0020]    In one embodiment, the first FPCB  11  includes from top to bottom, a first cover layer  111 , a first inner circuit layer  112 , a first flexible isolative layer  113 , a second inner circuit layer  114 , and a second cover layer  115 . Thus, the first FPCB  11  includes two inner circuit layers (the first inner circuit layer  112  and the second inner circuit layer  114 ). In other embodiments, the first FPCB  11  can include only one or more than two inner circuit layers according to actual needs. 
         [0021]    In one embodiment, the first FPCB  11  is divided into two first engaging portions  116  and one first FPCB unit  12 , such that the first FPCB unit  12  is located between the two first engaging portions  116 . In the two first engaging portions  116 , portions of the first FPCB  11  are disabled. 
         [0022]    A first conductive scrap  1121  of the first inner circuit layer  1121  located within the first engaging portions  116  is disabled from transmitting electric signals. A second conductive scrap  1141  of the second inner circuit layer  114  located within the first engaging portions  116  is also disabled from transmitting electric signals. 
         [0023]    In one embodiment, the first FPCB  11  is made from a raw board (not shown) cut from a flexible board tape (not shown) having a standard width, such as about 250 millimeters (mm) or about 500 mm. The first FPCB  11  includes two opposite first sides  1101  and two opposite second sides  1102 . A length of the first sides  1101  can be changed according to actual needs. In one embodiment, a size of the first FPCB  11  is about 250 mm*350 mm. 
         [0024]    In one embodiment, a number of the cutouts  117  is three. The cutouts  117  are equidistantly arranged along one of the first sides  1101  and located within the corresponding first engaging portion  116 . 
         [0025]    In the illustrated embodiment, the cutouts  117  are defined through the first cover layer  111 , the first conductive scrap  1121 , the first flexible isolative layer  113 , the second conductive scrap  1141 , and the second cover layer  115 . In another embodiment, the cutouts  117  are defined through the first cover layer  111 , the first conductive scrap  1121 , the first flexible isolative layer  113 , and the second cover layer  115 . In another embodiment, the cutouts  117  are defined through the first cover layer  111 , the first flexible isolative layer  113 , the second conductive scrap  1141 , and the second cover layer  115 . 
         [0026]    The cutouts  117  are substantially circular, and a central angle of a circular side of each of the cutouts  117  is larger than about  180  degrees. Each cutout  117  satisfies the following condition: Lo&lt;2Rc, wherein Rc is a radius of the cutout  117 , and Lo is a length of an opening  1172  of the cutout  117  at the first side  1101 . As such, the opening  1172  is shorter than a diameter of the cutout  177 , and thus can function as an engaging structure. In one embodiment, Lo is about 1 mm. 
         [0027]    In step  2 , referring to  FIGS. 3-4 , a substantially rectangular second FPCB  21  is provided. In one embodiment, the second FPCB  21  is divided into two second engaging portions  216  and one second FPCB unit  22 , such that the second FPCB unit  22  is located between the two second engaging portions  216 . A number of substantially C-shaped protrusions  217  is formed in a side of the second FPCB  21  by stamping. The C-shaped protrusions  217  correspond to the C-shaped cutouts  117 . 
         [0028]    In one embodiment, the second FPCB  21  includes from top to bottom, a third cover layer  211 , a third inner circuit layer  212 , a second flexible isolative layer  213 , a fourth inner circuit layer  214 , and a fourth cover layer  215 . Thus, the second FPCB  21  is a two-layer FPCB having two circuit layers (the third and the fourth inner circuit layers  212 ,  214 ). In one embodiment, the second FPCB  21  can include one or more than two inner circuit layers according to actual needs. 
         [0029]    A third conductive scrap  2121  of the third inner circuit layer  212  located within the second scrap zones  216  is disabled from transmitting electric signals. A fourth conductive scrap  1141  of the fourth inner circuit layer  214  located within the second engaging portions  216  is also disabled from transmitting electric signals. 
         [0030]    The second FPCB  21  is made in substantially a similar manner as the first FPCB  11 . The second FPCB  21  includes two opposite third sides  2101  and two opposite fourth sides  2102 . A length of the third sides  2101  can be changed according to actual needs. In one embodiment, a size of the second FPCB  21  is about 250 mm*350 mm. 
         [0031]    In the illustrated embodiment, a number of the protrusions  217  is three. The protrusions  217  are equidistantly arranged along one of the third sides  2101  and located within the corresponding second engaging portion  216 . Each protrusion  217  spatially corresponds to one cutout  117  in shape and size. 
         [0032]    To form the protrusions  217 , an actual length of the fourth sides  2102  is slightly shorter than an actual length of the second sides  1102 . 
         [0033]    Each protrusion  217  is substantially circular and includes a straight side  2171  and a circular portion  2172  connected to the straight side  271 . A central angle of the circular side  2172  is substantially equal to the central angle of the cutout  117 . Each protrusion  217  satisfies the following condition: Ls&lt;2Ri and 0&lt;Rc−Ri≦0.1 mm, wherein Ri is a radius of the protrusion  217 , and Ls is a length of the straight side  2171 . Thus, a length of the radius Ri of the protrusion  217  is slightly smaller than a size of the radius Rc of the cutout  117 . 
         [0034]    The second FPCB  21  includes a first trapezoidal zone  2173  and a second trapezoidal zone  2174 , both of which have a common side  2175  and are symmetrical about the common side  2175 . A long side  2176  of the first trapezoidal zone  2173  opposite to the common side  2175  is located within the protrusion  217 , and is substantially equal to or slightly smaller than a diameter of the protrusion  217 . The long side  2176  and the common side  2175  are substantially parallel to the straight side  2171 . The common side  2175  is located outside the protrusion  217 . The first trapezoidal zone  2173  satisfies the following condition: 0≦Ds≦50 micrometers (μm), wherein Ds is a distance between the common side  2175  and the straight side  2171  of the first trapezoidal zone  2173 , to leave a gap between the protrusion  217  and the cutout  117  when the protrusion  217  is received in the cutout  117 , such that the protrusion  217  is not forced out of the cutout  117  in case of thermal expansion of the protrusions  217 . 
         [0035]    In the illustrated embodiment, the first trapezoidal zone  2173  includes, in this order from a side to another, the third cover layer  211 , the third conductive scrap  2121 , the second flexible isolative layer  213 , the fourth conductive scrap  2141 , and the fourth cover layer  215 . In another embodiment, each first trapezoidal zone  2173  includes from top to bottom, the third cover layer  211 , the third conductive scrap  2121 , the second flexible isolative layer  213 , and the fourth cover layer  215 . In another embodiment, the first trapezoidal zone  2173  includes, in this a side to another, the third cover layer  211 , the second flexible isolative layer  213 , the fourth conductive scrap  2141 , and the fourth cover layer  215 . Thus, the first trapezoidal zone  2173  is reinforced by the third conductive scrap  2121 , the fourth conductive scrap  2141 , or both. Because the third conductive scrap  2121  and the fourth conductive scrap  2141  are made of metal, deformation of the protrusion  217  is avoided. Thus, the protrusion  217  is stably received into the cutout  117 . 
         [0036]    The second trapezoidal zone  2174  is substantially similar to the first trapezoidal zone  2173 . 
         [0037]    In one embodiment, materials of portions of the protrusions  217  can be changed to reinforce the protrusions  217  in the cutouts  117 . 
         [0038]    In step  3 , referring to  FIG. 5 , the protrusions  217  are received into the cutouts  117 . Thus, the second FPCB  21  and the first FPCB  11  cooperatively form a third FPCB  31 . The third FPCB  31  is substantially rectangular. A width of the third PFCB  31  is substantially equal to the lengths of the first side  1101  and of the third side  2101 . A length of the third FPCB  31  is slightly smaller than a total length of the second side  1102  and the fourth side  2102 . 
         [0039]    In other embodiments, each of the first FPCB  11  and the second FPCB  21  can form the cutouts  117  and the protrusions  217  in more than one side thereof, and thus can be combined with more than one of the first FPCB  11  or the second FPCB  21 . 
         [0040]    In step  4 , referring to  FIGS. 6-7 , a first reinforcement layer  61  and a second reinforcement layer  71  are provided. The third FPCB  31  is located between the first and second reinforcement layers  61 ,  71  to form a first semifinished board  100  of the RFPCBs  310 ,  320 . In one embodiment, the first semifinished board  100  is formed by a thermal pressing technology and is substantially rigid. 
         [0041]    The first reinforcement layer  61  includes a first copper foil  611  and a first adhesive layer  41 . The first adhesive layer  41  binds the copper foil  611  to the third FPCB  31 . The second reinforcement layer  71  includes a second copper foil  711  and a second adhesive layer  51 . The second adhesive layer  51  binds the second copper foil  711  to the third FPCB  31 . 
         [0042]    The first reinforcement layer  61  and the second reinforcement layer  71  are substantially identical to each other in shape and size and are slightly larger than the third FPCB  31 . 
         [0043]    The first adhesive layer  41  and the second adhesive layer  51  can be separately formed and then combined with the first copper foil  611  and the second copper foil  711 , respectively. In one embodiment, the first adhesive layer  41  and the second adhesive layer  51  are semi-cured before being applied to the first copper foil  611  and the second copper foil  711 , and can be epoxy, acrylic resin, fiberglass cloth resin, or other suitable adhesive. The first adhesive layer  41  and the second adhesive layer  51  are fully cured after they are applied. 
         [0044]    To increase a binding strength between the third FPCB  31  and the first and second adhesive layers  41 ,  51 , the third FPCB  31  can be plasma-treated before being bound to the first and second adhesive layers  41 ,  51 . 
         [0045]    In other embodiments, the first reinforcement layer  61  or the second reinforcement layer  71  can be omitted, such that only the first reinforcement layer  61  or the second reinforcement layer  71  is applied. 
         [0046]    In step  5 , referring to  FIG. 8 , a first via  101  and a second via  102  are defined through the first semifinished board  100 . A first circuited layer  210  is formed from the first copper foil  611 , and a second circuited layer  710  is formed from the second copper foil  711 . The first circuited layer  210  includes a first circuit pattern  201  and a second circuit pattern  202 . The second circuited layer  710  includes a third circuit pattern  203  and a fourth circuit pattern  204 . The first via  101  electrically connects the first circuit pattern  201 , the first inner circuit layer  112 , the second inner circuit layer  114 , and the third circuit pattern  203  to each other. The second via  102  electrically connects the second circuit pattern  202 , the third inner circuit layer  212 , the fourth inner circuit layer  214 , and the fourth circuit pattern  204  to each other. Thus, a second semifinished board  200  is formed from the first semifinished board  100 . In one embodiment, the second semifinished board  200  is substantially rigid. 
         [0047]    In one embodiment, lithophotography and etching technologies are employed to form the first circuited layer  210  and the second circuited layer  710 . In one embodiment, each first circuit pattern  201  and each third circuit pattern  203  corresponds to one first FPCB unit  12 . Likewise, each second circuit pattern  202  and each fourth circuit pattern  204  corresponds to one second FPCB unit  22 . 
         [0048]    In other embodiments, numbers of the first through fourth circuit patterns  201 - 204  can be more than one, and can be identical or not identical to each other. 
         [0049]    In another embodiment, the first via  101  and the second via  102  selectively connect the first circuit pattern  201  and the first inner circuit layer  112  together. 
         [0050]    In another embodiment, the first via  101  and the second via  102  selectively connect the first circuit pattern  201 , the first inner circuit layer  112 , and the second inner circuit layer  114  together. 
         [0051]    In another embodiment, the first via  101  and the second via  102  selectively connect the first circuit pattern  201 , the first inner circuit layer  112 , the second inner circuit layer  114 , and the third circuit pattern  203  together. 
         [0052]    In another embodiment, the first via  101  and the second via  102  selectively connect the second circuit pattern  202  and the third inner circuit layer  212 . 
         [0053]    In another embodiment, the first via  101  and the second via  102  selectively connect the second circuit pattern  202 , the third inner circuit layer  212 , and the fourth inner circuit layer  214 . 
         [0054]    In another embodiment, the first via  101  and the second via  102  selectively connect the second circuit pattern  202 , the third inner circuit layer  212 , the fourth inner circuit layer  214 , and the fourth circuit pattern  204 . 
         [0055]    The first-fourth circuit patterns  201 - 204  of the second semifinished board  200  can be coated with solder resisting patterns (not shown) and/or plated with gold. 
         [0056]    In step  6 , referring to  FIG. 9 , portions of the first reinforcement layer  61  and of the second reinforcement layer  71  are removed to expose corresponding portions of the first FPCB unit  12  and of the second FPCB unit  22 , to obtain a desired flexibility. In one embodiment, the first and second RFPCBs  310 ,  320  are formed by cutting along a boundary line between the first FPCB unit  12  and the second FPCB unit  22 . The RFPCB  310  includes the first FPCB unit  12 , and the second RFPCB  320  includes the second FPCB unit  22 . 
         [0057]    In other embodiments, the semifinished board  200  just includes one RFPCB. As such, the cutting process in step  6  is omitted after the desired parts of the first reinforcement layer  61  and of the second reinforcement layer  71  are removed. 
         [0058]    Because the FPCBs (the first FPCB  11  and the second FPCB  21 ) are first spliced and then combined with RPCBs (the first reinforcement layer  61  and the second reinforcement layer  71 ), size matching between the FPCBs and the corresponding RPCBs is achieved. As such, an amount of wasted material and cost are reduced. 
         [0059]    It will be understood that the above particular embodiments are shown and described by way of illustration only. The principles and the features of the present disclosure may be employed in various and numerous embodiments thereof without departing from the scope of the disclosure. The above-described embodiments illustrate the possible scope of the disclosure but do not restrict the scope of the disclosure.