Abstract:
A method for manufacturing a rigid-flex board is disclosed. After the formation of each layer of the rigid-flex board, a laser-etched groove is formed at the interface between a rigid part and a bending area of the rigid-flex board. After the laser etching process, a circuit-board routing process is performed to remove materials along the sideward perimeter of the bending area. The exposed copper layer is then removed from inside the laser-etched groove. Thereafter, a redundancy rigid structure within the bending area is readily removed to expose the flex board within the bending area.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to the field of printed circuit board (PCB) technology. More particularly, the present invention relates to a method for manufacturing a rigid-flex circuit board. 
         [0003]    2. Description of the Prior Art 
         [0004]    Rigid-flex printed circuit boards or rigid-flex boards are known in the art, which allow integrated interconnection between several rigid boards. This technology helps to reduce the number of soldered joints and plug-in connections and also the number of wires and cables, thus improving quality and reliability. For this reason, the rigid-flex board has become firmly established in many sectors of industry, notably automotive, telecommunications, medical, sensor technology, mechanical engineering and military electronics. 
         [0005]    Typically, the fabrication of a rigid-flex board may start with a flex circuit board or flex board as core material. Rigid circuit board process such as build-up method or core-lamination method is then performed to form multi-layer circuit on the core flex board. Eventually, a redundancy rigid part that is directly above a pre-determined area to be bent is removed by a mechanical depth-controlled routing technique. 
         [0006]    However, the prior art method for fabricating rigid-flex boards has shortcomings. Because of the difficulty of precise control of the routing depth, the aforesaid mechanical depth-controlled routing technique for removing the redundancy rigid part above a bending area may have potential risks of damaging the flex board, particularly at the interface between the flex and rigid parts. Further, expensive, custom-made fixtures or molds are ordinarily required in the mechanical depth-controlled routing process, thus increasing the production cost. The custom-made fixtures or molds are also time-consuming, which decreases the production throughput. Therefore, there is a strong need in this industry to provide an improved method for manufacturing rigid-flex boards in order to solve the above-mentioned problems. 
       SUMMARY OF THE INVENTION 
       [0007]    It is one object of the present invention to provide an improved method for manufacturing rigid-flex boards, particularly focusing on the improvement of the step of removing the redundancy rigid part above a bending area, thereby solve the above-mentioned prior art problems. 
         [0008]    According to the claimed invention, a method for manufacturing rigid-flex board is provided. A flex board is provided. The flex board comprises an intermediate base layer and copper circuit pattern layers disposed on an upper side and bottom side of the intermediate base layer. A protective cover layer is laminated on the copper circuit pattern layers. A pre-routed dielectric layer is laminated on the protective cover layer, wherein the pre-routed dielectric layer comprises at least one pre-routed opening that defines a bending area between two rigid parts. A copper foil is laminated on the pre-routed dielectric layer. A rigid circuit board structure is formed within the rigid parts. Concurrently, the bending area is covered with at least one dielectric material. A first cutting process is performed to remove the dielectric material at the interface between the bending area and the rigid part, thereby forming a first groove exposing a portion of the copper foil. A second cutting process is performed to remove an extra, sideward rigid board and flex board at two opposite sides of the bending area. A copper etching process is performed to remove the exposed copper foil from inside the first groove, thereby forming a second groove connected to the pre-routed opening and a redundancy rigid structure within the bending area. The redundancy rigid structure within the bending area is then removed. 
         [0009]    These and other objectives of the present invention will no doubt become obvious 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 
         [0010]      FIGS. 1-7  are schematic diagrams illustrating the method for manufacturing a rigid-flex board in accordance with one preferred embodiment of this invention, wherein  FIGS. 1-3  and  5 - 7  are cross-sectional views of the rigid-flex board, while  FIG. 4  is a schematic top view showing the rigid-flex board after performing a second cutting process. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Please refer to  FIGS. 1-7 .  FIGS. 1-7  are schematic diagrams illustrating the method for manufacturing a rigid-flex board in accordance with one preferred embodiment of this invention, wherein  FIGS. 1-3  and  5 - 7  are cross-sectional views of the rigid-flex board, while  FIG. 4  is a schematic top view showing the rigid-flex board after performing a second cutting process. 
         [0012]    As shown in  FIG. 1 , a flex board  10  comprising an intermediate base layer  12 , a copper circuit pattern layer  22  and a copper circuit pattern layer  32  is provided. The intermediate base layer  12  may be composed of dielectric materials. The dielectric materials may include but not limited to polyimide. 
         [0013]    A protective cover layer  26  and a protective cover layer  36  are formed on the first side  10   a  and second side  10   b  of the flex board  10 , respectively. The protective cover layers  26  and  36  may be composed of polyimide or any other suitable materials. The protective cover layers  26  and  36  protect the underlying copper circuit pattern layer  22  and copper circuit pattern layer  32  from the corrosion of etchant solution that is used during the fabrication of the rigid-flex board. 
         [0014]    In addition, the protective cover layer  26  may be boned to the first side  10   a  of the flex board  10  by using an adhesive layer  24  and pressing methods, and the protective cover layer  36  may be boned to the second side  10   b  of the flex board  10  by using an adhesive layer  34  and pressing methods. 
         [0015]    Subsequently, a pre-routed dielectric layer  28  and a pre-routed dielectric layer  38  such as low-flow prepreg (abbr. of pre-impregnated) are laminated on the protective cover layer  26  and the protective cover layer  36 , respectively. Prepreg is the abbreviation of pre-impregnated fibers, which include but not limited to reinforcing glass fibers or other fibers pre-impregnated with a polymer matrix resin system that is typically incompletely cured (B-stage) thermosetting resin system. 
         [0016]    The pre-routed dielectric layer  28  and the pre-routed dielectric layer  38  have an opening  128  and an opening  138 , respectively. The position and area of the openings  128  and  138  in the pre-routed dielectric layer  28  and the pre-routed dielectric layer  38  are pre-determined and pre-routed according to the position and area of the bending area  100  between a rigid area  102  and a rigid area  104 . 
         [0017]    From one aspect, the dielectric layer  28  and  38  merely covers the rigid areas  102  and  104 , while exposes the bending area  100 . The pre-routed dielectric layers  28  and  38  may have a plurality of pre-routed openings. 
         [0018]    Thereafter, a copper foil  30  and a copper foil  40  are laminated on the pre-routed dielectric layer  28  and the pre-routed dielectric layer  38  respectively. 
         [0019]    Subsequently, as shown in  FIG. 2 , circuit build-up process is carried out to form additive circuit layers on the copper foils  30  and  40  respectively. The involved intermediate process includes but not limited to plating, etching, through-hole or blind-via drilling and solder-resist coating. At this point, rigid board circuit structures  232  and  242  and plated through holes  520  and blind via  521  for electrically connecting circuit layers (including the flex board) are formed within the rigid areas  102  and  104  respectively. After the circuit build-up process, the bending area  100  is covered and filled with dielectric layers  262  and  264 . 
         [0020]    According to the preferred embodiment of this invention, the rigid board circuit structure  232  comprises a copper circuit layer  321 , a copper circuit layer  322  and a solder resist layer  323 . The rigid board circuit structure  242  comprises a copper circuit layer  421 , a copper circuit layer  422  and a solder resist layer  423 . However, it is understood that the rigid board circuit structures  232  and  242  may comprise only one single layer or may comprise a plurality of circuit layers. 
         [0021]    At this point, the area within the bending area  100  and above the copper foils  30  and  40  is filled with dielectric material  262  and dielectric material  264  such as prepreg but not limited thereto. 
         [0022]    As shown in  FIG. 3 , a first cutting process, such as a laser cutting process that employs a laser beam with a pre-selected energy and wavelength, is carried out to remove a portion of the dielectric material  262  and a portion of the dielectric material  264  from the interface between the bending are  100  and the rigid area  102  and from the interface between the bending are  100  and the rigid area  104 , thereby forming laser grooves  362  and  364  respectively. 
         [0023]    As shown in  FIG. 3 , the laser grooves  362  and  364  expose a portion of the underlying copper foils  30  and  40  respectively. During the aforesaid first cutting process, the copper foils  30  and  40  protect the flex board  10  from laser-induced damage. 
         [0024]      FIG. 4  is a schematic top view (not to scale) showing the rigid-flex board after performing a second cutting process. As shown in  FIG. 4 , a second cutting process is performed to remove an extra, sideward rigid board and flex board at two opposite sides of the bending area  100 , thereby forming gap  302  traversing the thickness of the rigid board and flex board at two opposite sides of the bending area  100 . The second cutting process may include mechanical routing methods or laser methods. The gap  302  is connected with the laser grooves  362  and  364 . 
         [0025]    As specifically indicated in  FIG. 4 , in accordance with the preferred embodiment of this invention, supporting bars  304  are provided for temporarily sustaining a redundancy rigid structure situated directly above the flex board  10  within the bending area  100 . One of the supporting bars  304  is enlarged in the circle. Preferably, the supporting bars  304  are slender and thin such that they can be easily manually snapped off. According to the preferred embodiment, at least one explosion-proof aperture  306  is provided at one end of the supporting bar  304 . However, it is understood that depending upon the design requirements, the explosion-proof aperture  306  may be omitted in other cases. The explosion-proof aperture  306  can prevent undesirable damage to the rigid-flex board during the removal of the redundancy rigid structure. 
         [0026]    As shown in  FIG. 5 , after the second cutting process, a copper etching process is performed to remove the exposed copper foil  30  and copper foil  40  from inside the laser grooves  362  and  364 , respectively, thereby forming a groove  362   a  connected to the opening  128  and a groove  364   a  connected to the opening  138 . At this point, a redundancy rigid structure  462  and a redundancy rigid structure  464  to be removed are floating within the bending area  100 . As previously mentioned, the redundancy rigid structures  462  and  464  are sustained through the supporting bars  304 , which is not explicitly shown in  FIG. 5 , but shown in  FIG. 4 . 
         [0027]    Further, according to this invention, the manufacturing sequence may be adjusted depending upon the process designs. For example, the second cutting process and the copper etching process may be swapped in another embodiment. The adjustment of the manufacturing sequence of the above-described process steps may increase the design flexibility. In addition, swapping the second cutting process and the copper etching process may have the advantage of omitting the step of manually removing the redundancy rigid structures. 
         [0028]    In accordance with the preferred embodiment of this invention, the redundancy rigid structure  462  comprises dielectric material  262  and the copper foil  30  that is directly under the dielectric material  262 . The redundancy rigid structure  464  comprises dielectric material  264  and the copper foil  40  that is directly under the dielectric material  264 . 
         [0029]    It is noteworthy that during the copper etching process, the inner-layer circuit formed on the flex board  10  is fully protected by the protective cover layers  26  and  36 , thus avoiding the corrosion of etchant solution, which is one of the germane features of the present invention. 
         [0030]    As shown in  FIG. 6 , subsequently, by snapping the supporting bars  304  with manual or any suitable physical methods, the redundancy rigid structures  462  and  464  are readily removed from the bending area  100 , thereby exposing the flex board  10  within the bending area  100 . 
         [0031]    As shown in  FIG. 7 , optionally, after exposing the flex board  10  within the bending area  100 , depending upon the customer&#39;s requirements, a portion of the protective cover layers  26  and  36  and the underlying adhesive layers  24  and  34  within the bending area  100  may be removed by laser methods, in order to expose a portion of the copper surfaces  22   a  and  32   a  on the flex board  10 . Thereafter, for assembly purposes, surface treatments may be carried out on the exposed copper surfaces  22   a  and  32   a  on the flex board  10  within the bending area  100 . 
         [0032]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.