Abstract:
There is provided a composite wiring board that occupies a small space and is low in price and a manufacturing method thereof; the composite wiring board comprises at least two rigid wiring boards on end faces of which connection portions are formed, in which each of the rigid wiring boards is arranged so that each of the connection portions is situated on a plane and each of corresponding connection portions is connected with each other in the plane.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a composite wiring board in which at least two rigid wiring boards are joined and a manufacturing method thereof.  
           [0003]    2. Description of the Related Art  
           [0004]    Conventionally, a composite wiring board in which at least two rigid wiring boards are disposed substantially in parallel to each other and are joined to each other for attaining to be small in size and excellent in function has been used.  
           [0005]    [0005]FIG. 1A is a side view showing a first example of the conventional composite wiring board.  
           [0006]    The composite wiring board  10  has a structure that connectors  13 ,  14  are respectively mounted on two rigid wiring boards  11 ,  12  and a lead wire or a flexible wiring board  15  are inserted into each of the connectors  13 ,  14  to join each of the rigid wiring board  11 ,  12 .  
           [0007]    Because the connectors  13 ,  14  need to have a height and an area to a certain extent owing to the necessity of a pitch of a connector pin or other necessities, the composite wiring board  10  having the aforesaid structure has a fault that it is not suitable for high density mounting.  
           [0008]    [0008]FIG. 1B is a side view showing a second example of the conventional composite wiring board.  
           [0009]    The composite wiring board  20  has a structure that counterparts  23 ,  24  of a board-to-board connector capable of being divided into the two counterparts  23 ,  24  are mounted on two rigid wiring boards  21 ,  22 , respectively, and that the counterparts  23 ,  24  of the board-to-board connector are fit to each other and thereby each of the rigid wiring boards  21 ,  22  is joined to each other.  
           [0010]    The composite wiring board  20  having such a structure does not need any lead wires and thereby does not require any troubles of the connection of the two rigid wiring boards  21 ,  22 . However, because the composite wiring board  20  has the structure formed by the simple pressing to each other of the counter parts  23 ,  24  of the board-to-board connector for joining them, the composite wiring board  20  has a disadvantage that the counterparts  23 ,  24  of the board-to-board connector are easy to come off owing to vibrations and other forces at the time of the usage thereof.  
           [0011]    [0011]FIG. 1C is a side view showing a third example of the conventional composite wiring board.  
           [0012]    The composite wiring board  30  has a structure that a lead wire or a flexible wiring board  33  is directly soldered on two rigid wiring boards  31 ,  32  for joining each of the rigid wiring boards  31 ,  32 .  
           [0013]    The composite wiring board  30  having such a structure becomes less expensive in costs because it has not the aforesaid connectors  13 ,  14 ,  23  and  24 , but it has a disadvantage that it is not suitable for high density mounting because it has a necessity of widening the pitches of the circuit patterns on the rigid wiring boards  31 ,  32  for preventing the bridging of solder.  
           [0014]    [0014]FIG. 1D is a side view showing a fourth example of the conventional composite wiring board.  
           [0015]    The composite wiring board  40  is a flex rigid wiring board that has a structure using two rigid wiring boards  41 ,  42  that put a flexible wiring board  43  at the center part of each of them.  
           [0016]    Because the flexible wiring board  43  is put in each of the rigid wiring boards  41 ,  42  in the composite wiring board  40  having such a structure, the joining of each of the rigid wiring boards  41 ,  42  is strong. Moreover, because the decrease of the mounting area is not produced like in each of the aforesaid composite wiring boards  10 ,  20  and  30 , the composite wiring board  41  is suitable for high-density mounting.  
           [0017]    Because it is needed for the aforesaid fourth example of the conventional composite wiring board  40  to put and fix the flexible wiring board  43  having flexibility between the rigid wiring boards  41 ,  42 , a specific adhesive is needed, and the gluing processes thereof are complicated, and further the coefficient of utilization of the material is also decreases. Consequently, the composite wiring board  40  has a disadvantage that it becomes very expensive. Moreover, because the composite wiring board  40  has a necessity to bend the flexible wiring board  43  between the rigid wiring boards  41  and  42 , the composite wiring board  40  has another disadvantage that it needs a space for the bending.  
         SUMMARY OF THE INVENTION  
         [0018]    Accordingly, an object of the present invention is to solve the aforementioned problems and to provide a composite wiring board that occupies a small space and is low in price and a manufacturing method thereof.  
           [0019]    According to the present invention, the foregoing and other objects and advantages are attained by a composite wiring board comprising at least two rigid wiring boards on an end face of each of which a connection portion is formed, wherein each of the rigid wiring boards is arranged so that each of the connection portions is situated on a plane and each of corresponding connection portions is connected with each other in the plane.  
           [0020]    Because the connection portions are formed on the end faces of the rigid wiring boards according to the aforesaid structure of the invention, the plural rigid wiring boards can be joined by the connection of each of the corresponding connection portions at the side face of each of the rigid wiring boards. Consequently, existing connection means can be applied to the connection of each of the connection portions, and thereby the composite wiring board can be manufactured inexpensively in cost. Moreover, because the connection means can be arranged in one plane, it is possible to attain the decrease of the space of the composite wiring board.  
           [0021]    As described above, according to the invention, a composite wiring board that is inexpensive and occupies a small space can be provided. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    The above and other objects, features and advantages of the present invention will become more apparent from the following description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:  
         [0023]    FIGS.  1 A- 1 D are side vies showing conventional composite wiring boards;  
         [0024]    FIGS.  2 A- 2 F are first process drawings showing a part of an embodiment of a method for manufacturing a composite wiring board of the present invention;  
         [0025]    FIGS.  3 A- 3 F are second process drawings showing another part of the embodiment of the method for manufacturing the composite wiring board of the invention; and  
         [0026]    [0026]FIGS. 4A and 4B are perspective views showing a further part of the embodiment of the method for manufacturing the composite wiring board of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    Hereinafter, a preferable embodiment of the present invention will be described in detail on the basis of the attached drawings.  
         [0028]    Incidentally, the following embodiment includes various technically preferable limitations because the embodiment is a suitable concrete example of the present invention. However the scope of the present invention is not limited to the forms except a case where a specific mention of the limitation of the invention to the described form is made in the following description.  
         [0029]    FIGS.  2 A- 2 F,  3 A- 3 F and FIGS. 4A, 4B are process drawings and perspective views, respectively, showing an embodiment of a method for manufacturing a composite wiring board of the present invention. The method will be described by reference to each of the drawings.  
         [0030]    At first, through holes to be interstitial blind via holes  52  are drilled in a double-sided copper-clad laminate  51  (FIG. 2A), and copper plating is performed on both surfaces of the double-sided copper-clad laminate  51  and an inner surfaces of the interstitial blind via holes  52  to form a copper foil  53  (FIG. 2B).  
         [0031]    Then, copper paste  54  is embedded in prescribed interstitial blind via holes  52 , and both of the surfaces of the double-sided copper-clad laminate  51  including the end faces of the copper paste  54  are polished (FIG. 2C). Incidentally, any conductive material such as solder may be used instead of the copper paste  54 .  
         [0032]    Next, the copper foil  53  on one surface of the double-sided copper-clad laminate  51  is etched, and a prescribed inner layer pattern is formed to be a first layer wiring board  55  (FIG. 2D). At this time, wirings to be used for the connection between rigid wiring boards  63  and  65 , which will be described later, are formed up to the end of the first layer wiring board  55 , although they are not shown in the figure.  
         [0033]    Then, a second layer wiring board  56  is manufactured in conformity with the processes similar to those described above. The patterned surface of each of the wiring boards  55 ,  56  is opposed to each other with a prepreg  57  put between them (FIG. 2E). Then, each of the wiring boards  55 ,  56  and the prepreg  57  is bonded by the thermo-compression bonding by being heated under pressure from the outer side surface of each of them to be formed as a laminated wiring board  58  (FIG. 2F). Through holes to be formed as thorough holes  59  are drilled in the laminated wiring board  58 . Copper plating is performed to the inner surfaces of the through holes  59  to form a copper foil  60  (FIG. 3A), and copper paste  61  is embedded in prescribed through holes  59  (FIG. 3B). Incidentally, any conductive material such as solder may be used instead of the copper paste  61 .  
         [0034]    Next, after the upper surfaces of the copper foils  53  on both of the surfaces of the laminated wiring board  58  including the end faces of the copper paste  61  have been polished, the copper foils  53  on both of the surfaces of the laminated wiring board  58  are etched to form prescribed outer layer patterns (FIG. 3C). In this case also, the wirings to be used for the connection between the rigid wiring boards  63  and  65 , which will be described later, are formed up to the end of the laminated wiring board  58 , although they are not shown in the figure. Then, solder resist  62  is applied on the outer layer patterns (FIG. 3D), and the laminated wiring board  58  is cut with a rooter or punched out by a pressing machine to be a four-layer rigid wiring board  63  having a predetermined outer shape (FIG. 3E).  
         [0035]    Next, the end face of the rigid wiring board  63  is cut with a dicer, a rooter or a rotary cutter, and connection portions  64  that are ends of the wirings to be used for the connection of the rigid wiring board  63  are formed on the cut end face (FIG. 3F). Then, a rigid wiring board  65 , on an end face for the joining with the aforesaid rigid wiring board  63  of which connection portions  66  are formed, is manufactured in conformity with the processes similar to those described above.  
         [0036]    That is, for example, as shown in FIG. 4A, connection portions  64   a ,  64   c  and  64   b ,  64   d  are formed on an end face  63   a  of the rigid wiring board  63  by cutting a wiring part or one of the interstitial blind via holes  52  in which copper paste  54  is embedded. And, connection portions  66   a ,  66   b ,  66   c  and  66   d  are formed on an end face  65   a  of the rigid wiring board  65  by cutting one of the through holes  59  in which the copper paste  61  is embedded.  
         [0037]    It is desirable to form the width of the wiring part thick to improve the reliability of connection by the setting of the areas of the connection portions formed by cutting the wiring part to be as large as possible. Moreover, the end faces of the rigid wiring boards  63  and  65  may be cut obliquely for the decrease of loads at the connection parts together with the increase of the areas of the connection portions as large as possible for the increase of the reliability. Moreover, because the connection portions formed by cutting the interstitial blind via holes  52  or the through holes  59  become hollow parts to decrease the reliability of connection, it is desirable to embed a conductive material such as copper paste and solder for preventing the formation of the hollow parts.  
         [0038]    Then, each of the rigid wiring boards  63 ,  65  are arranged in parallel to each other and the end faces  63   a ,  65   a  are arranged to be flush with each other. That is, each of the rigid wiring boards  63 ,  65  are arranged so that each of the connection portions  64   a ,  64   b ,  64   c ,  64   d ,  66   a ,  66   b ,  66   c  and  66   d  are situated on a plane.  
         [0039]    Next, a flexible wiring board  67  on which leads  68   a ,  68   b ,  68   c  and  68   d  are formed for connecting corresponding connection portions on each of the rigid wiring boards  63 ,  65 , namely connection portions  64   a  and  66   a ,  64   b  and  66   b ,  64   c  and  66   c , and  64   d  and  66   d  in the present example, is manufactured.  
         [0040]    Then, as shown in FIG. 4B, the flexible wiring board  67  is pasted to the end faces  63   a ,  65   a  of each of the rigid wiring boards  63 ,  65  in a state of being held to be flat, and the corresponding connection portions  64   a  and  66   a ,  64   b  and  66   b ,  64   c  and  66   c , and  64   d  and  66   d  are connected to each other with the leads  68   a ,  68   b ,  68   c  and  68   d , respectively. Then, the composite wiring board  69  is completed. Incidentally, lead wires may used for connecting the corresponding connection portions  64   a  and  66   a ,  64   b  and  66   b ,  64   c  and  66   c , and  64   d  and  66   d  in place of the flexible wiring board  67 .  
         [0041]    Now, the reliability of the connection of each of the leads  68   a ,  68   b ,  68   c  and  68   d  of the flexible wiring board  67  or the lead wires with each of the connection portions  64   a ,  64   b ,  64   c ,  64   d ,  66   a ,  66   b ,  66   c  and  66   d  can be increased by the formation of bumps  68   aa ,  68   ba ,  68   ca  and  68   da  on both of the ends of each of the leads  68   a ,  68   b ,  68   c  and  68   d  or the lead wires in advance.  
         [0042]    There are the following three methods as the connection methods of the aforesaid connection portions  64   a ,  64   b ,  64   c ,  64   d ,  66   a ,  66   b ,  66   c  and  66   d  with the leads  68   a ,  68   b ,  68   c  and  68   d  or the lead wires. That is, the methods are: a method in which a resin paste or a resin film is applied to the connection portions  64   a ,  64   b ,  64   c ,  64   d ,  66   a ,  66   b ,  66   c  and  66   d  and the flexible wiring board  67  or the lead wires are connected with the connection portions  64   a ,  64   b ,  64   c ,  64   d ,  66   a ,  66   b ,  66   c  and  66   d  by heating and pressuring, or by exciting by ultrasonic waves; a method in which a high voltage is imposed on the lands on the upper surfaces of the rigid wiring boards  63 ,  65  and the flexible wiring board  67  or the lead wires to join them; and a method in which solder is heated to be fused for joining.  
         [0043]    Because in the aforesaid composite wiring board  69  the flexible wiring board  67  and other connection members for joining are prepared as separated members and join the rigid wiring boards  63  and  65  in a state of being flat, the costs of the manufacture of it can be decreased and the space for the composite wiring board  69  can be decreased. Moreover, because the area for mounting connectors or other connecting members becomes unnecessary, the area for the mounting of parts can be used most effectively. Moreover, because the rigid wiring boards can be connected only by the drawing out of the wiring for connection to their side faces, the extra via holes and through holes become unnecessary and the high density mounting of the parts becomes possible.