Abstract:
A circuit board has an insulation board and strip bus bars arranged on the opposite faces of the board. On one face, the bus bars extend in parallel in a first direction. On the second face, the bus bars extend in parallel in a second direction crossing the bars extending in said first direction, so that there is an array of crossing points of the bus bars. The insulation board has holes at which the mutually crossing bus bars are bent towards each other and joined to establish electrical connection. In this way, a predetermined wiring pattern is obtained, which can be varied easily.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to a circuit board and to an electrical connection box containing such a circuit board, e.g. an electrical connection box for use in an automobile or other vehicle. The invention also relates to a method of making such a circuit board. 
     2. Description of Related Art 
     To form a circuit board constituting the interior circuit of an electrical connection box, e.g. a junction box for an automobile and the like, there has conventionally been used a pressure welding system of wiring a wire, such as a single core wire or the like, along a circuit on an insulation board and connecting a pressure welding terminal on said wire by pressure welding. It is also known to use bus bars formed by stamping an electro-conductive metal plate into a circuit board shape. 
     When a pressure welding system is used for the formation of an interior circuit, circuits accommodated in an electrical connection box have recently increased in accordance with a large increase of electric parts to be connected. Since the shape of an insulation board where an electric wire is wired in the pressure welding system becomes complicated, problems occur such that the wiring work and the processing of an insulation board require a long time, resulting in increased production costs. 
     Further, when bus bars are used as an interior circuit, a mold for stamping must be made in accordance with the circuit. As a result, the alteration of a circuit cannot be easily carried out and the costs of preparation of a mold are high. Further, because a lot of residual parts are not used after stamping, the yield of the electro-conductive metal plate is poor, which also raises costs. For example, if seven or eight sheets of bus bars were arranged in multi-layer lamination with insulation boards between them, the cost is high, because of a sharp increase of the number of circuits accommodated in the inside of an electrical connection box. 
     A circuit board  2  for the interior of an electric connection box, shown in present FIGS.  7 (A) and  7 (B), is proposed in JP-A-56-130989, in view of the above problems. Insulation sheets  1   a ,  1   b  are laminated on both sides of an electro-conductive member  3 , which is made in a lattice shape by stamping out the removed parts  3   a  of an electro-conductive metal plate. The circuit is formed by cutting the unwanted connection points  3   b . Wiring is connected to the electro-conductive member  3  to make connection with exterior circuits. Since the circuit is formed by cutting the points  3   b , variation of the circuit is easily achieved. However, since the lattice-shape is formed by stamping and there are a lot of the removed parts  3   a , there remains the problem that the yield of the electro-conductive metal plate is not improved. 
     SUMMARY OF THE INVENTION 
     The present invention has as a first object to reduce the cost related to forming the interior circuit. Another object is to permit easy variation of a circuit. A third object is to design a cost reduction by easily forming insulation materials which lie between the third bus bars. 
     In a first aspect of the invention, a circuit board is provided having an insulation board with first and second opposite main faces. A plurality of first strip bus bars are arranged on the first main face. The first strip bus bars extend in parallel in a first direction. A plurality of second strip bus bars are arranged on the second main face. The second strip bus bars extend in parallel in a second direction crossing the first strip bus bar extending in the first direction, whereby, as seen in plan view, on one of the main faces there is an array of crossing points of the first and second bus bars. The insulation board has a plurality of holes through it at a plurality of the crossing points. The mutually crossing bus bars are bent each towards each other at the holes and mutually joined through the board to establish electrical connection between them, whereby a predetermined wiring pattern is obtained. 
     Preferably, at the holes the bus bars are joined by welding, but other joining methods are possible. Resistance welding is most preferred. 
     Preferably the first bus bars are located in grooves in the first main face of the insulation board, and the second bus bars are located in grooves in the second main face. 
     Suitably at the holes, the thickness of each of the mutually crossing bus bars in the direction of the insulation board is reduced, compared with the thickness of adjacent portions, by 15 to 25%. In the manufacture of the circuit board, this thickness reduction is accompanied by elongating the bus bar via stretching, to provide the bent portion. This can avoid disturbance of the ends of the bus bars. 
     A second aspect of the invention provides a method of making a circuit board, comprising the steps of: 
     (i) providing an insulation board having first and second opposite main faces and a plurality of holes at locations through which electrical connection is made through the board; 
     (ii) locating a plurality of first bus bars on the first main face extending in parallel in a first direction; 
     (iii) locating a plurality of second bus bars on the second main face extending in parallel in a second direction crossing the first direction, whereby as seen in plan view on one of the main faces there is an array of crossing points of the bus bars, a plurality of said crossing points coinciding with said holes; 
     (iv) providing each of the mutually crossing pair of the bus bars at the position of each of the holes with a portion bent towards the other bus bar of the pair; 
     (v) joining the mutually crossing pair of bus bars at said holes to establish electrical connection between them. 
     In this method, step (iv) is preferably performed to provide the bent portions at the appropriate positions, before locating the bus bars on the insulation board. Preferably, during step (iv), at least one of said first bus bars and said second bus bars are joined at opposite ends thereof to a pair of carrier members which maintain their relative positions. 
     Prior to the joining step (v), one of the bent portions may have a protrusion directed towards the other of said mutually crossing pair of bus bars. 
     Within the invention the use of material of the bus bars can be efficient, so that the yield of the material can be improved. Further, stamping by a mold which has been specifically designed for the individual circuit required is unnecessary. Therefore the cost for formation of the circuit board can be greatly reduced. 
     The bus bars respectively arranged in parallel in the two directions, which are typically orthogonal, may have a nominal thickness, in the direction of the insulation board, in the range of 0.5 mm to 1.0 mm. Both ends thereof may be linked with carriers, and the carriers are cut to be removed after the bent parts are joined, e.g. resistance-welded. 
     After the bus bars of the two directions are assembled on the insulation board, portions of them which are unnecessary in the circuit may be cut, after joining of the upper and lower bent parts, to form the requisite circuit. It is possible to use standard sets of the bus bars for both of the two directions, to simplify and reduce cost. 
     Further, the pitches (spacing) of the strip bus bars can be selected to correspond with the spacings of terminals of exterior components, such as a connector, a fuse and a relay. For example, some of the bus bars arranged in parallel in one direction may correspond with the terminal pitch of a fuse, while others may correspond with the terminal pitch of a relay. Some of the bus bars arranged in the second direction may correspond with the small pitch of a connector terminal hole, while others may correspond with a middle-size pitch, and the remainder may correspond with a large pitch. 
     Thus, tabs connected with these bus bars can be directly connected with the connector, the fuse and the relay, etc. 
     Further, the present invention provides an electric connection box including the above circuit board. The circuit board of the above-described construction may be arranged as a single layer in the electric connection box, or a plural number of circuit boards may be further arranged by lamination through insulation boards. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described by way of non-limiting examples with reference to the accompanying drawings, in which: 
     FIG.  1 (A) is a plan view of a circuit board which is a first embodiment of the present invention; 
     FIG.  1 (B) is a sectional view on line I—I of FIG.  1 (A); 
     FIG.  1 (C) is an enlarged sectional view of a portion of FIG.  1 (B); 
     FIG.  2 (A) is a plan view of the bus bars of the X direction in the circuit board of FIG.  1 (A); 
     FIG.  2 (B) is a plan view of the bus bars of the Y direction; 
     FIG.  3 (A) is a plan view of the insulation board of the circuit board of FIG.  1 (A); 
     FIG.  3 (B) is a sectional view on line II—II of FIG.  3 (A); 
     FIG.  3 (C) is an enlarged sectional view of a portion of FIG.  3 (B); 
     FIG. 4 is a plan view showing the assembled state of the bus bars of the X direction and the Y direction, in the circuit board of FIG.  1 (A); 
     FIG. 5 is a sectional view showing the resistance welding of the bus bars of the X and Y directions, in the circuit board of FIG.  1 (A); 
     FIGS.  6 (A) and (B) are sectional views showing modified examples of the circuit board of FIG.  1 (A); and 
     FIGS.  7 (A) and (B) show a prior art example discussed above. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     One embodiment of the present invention is shown in FIGS. 1 to  5  which illustrate the circuit board  10 . Strip bus bars  14  are provided as parallel discrete spaced metal strips extending in an X direction on the upper face of an insulation board  11 . Strip bus bars  15  are similarly provided as parallel discrete spaced metal strips extending in a Y direction, orthogonal to the X direction, on the lower face of the insulation board  11  at regular spacings. The strip bus bars  14 ,  15  of the X and Y directions are thus arranged crosswise through the insulation board  11  so as to form a lattice with mutual crossing points of the bus bars. As FIG.  1 (B) shows, the bus bars  14 ,  15  are located in recesses or grooves  11   a ,  11   b  in the upper and lower faces of the insulation board  11 . 
     As shown in FIG.  2 (A), the ends of the bus bars  14  of the X direction are initially linked with the carriers  16 A,  16 B, and may be arranged on the upper face of the insulation board  11  in this condition. However, as indicated by FIG.  1 (A) in this embodiment, the carrier  16 B is cut off after the formation of the bent parts  14   a  described below and before the bus bars  14  are placed on the board  11 . The width of the bus bars  14  is, for example, 2 mm, and their nominal thickness is, for example, 0.64 mm. The spacings (pitches) of the parallel bus bars  14  of the X direction may, as desired, be varied. For example, some may have a pitch of 4 mm, others a pitch of 10 mm and yet others a pitch of 6.8 mm, corresponding with the spacing of terminals of a connector, a fuse and a relay. 
     As shown in FIG.  2 (B), the bus bars  15  of the Y direction are similar. Both ends in their longitudinal direction when formed are linked with the carriers  17 A,  17 B. The bus bars  15  are arranged on the lower face of the insulation board  10  in this condition. The bus bars  15  have a width of, for example, 2 mm, a nominal thickness of, for example, 0.64 mm and a uniform pitch of, for example, 4 mm. 
     Downwardly bent parts  14   a  formed by press molding are provided at requisite points on the bus bars  14 . Similarly, upwardly bent parts  15   a  formed by press molding are provided on the bus bars  15 . These bent parts  14   a ,  15   a  are provided at the positions where the bus bars of the X and Y directions cross and where conductive connection is to be made. 
     Since there are grooves  11   a  and  11   b  on the insulation board  11 , the board thickness of the parts  11   c  between the respective bottom faces of the grooves  11   a  and  11   b  are as thin as, for example, 0.8 mm at the cross positions. At the crossing points where the upper and lower bus bars are to be connected penetration holes  11   d  are provided. 
     As shown in FIGS.  3 (A)-(C), the penetration holes  11   d  provide a clearance since their upper parts  11   d - 1  are larger than the width of bus bars, and their lower parts  11   d - 2  are enlarged in a taper manner. 
     The amount of protrusion of the bent parts  14   a ,  15   a  of the upper and lower bus bars  14 ,  15 , which are resistance-welded through the penetration holes  11   d , is thus fixed, for example, at half (0.4 mm) of the board thickness of 0.8 mm. The protruding faces are mutually brought in contact. To achieve this, the parts  14   a ,  15   a  are bent in an approximately arc shape so as to protrude by 0.4 mm by press working. The bus bars  14 ,  15  are extended in length by this press working so as to be reduced in thickness by, for example, 15 to 25% (20% in the present embodiment) of their nominal thickness. The bent parts  14   a ,  15   a  are made so that the dimension between the two ends of each bus bar before formation and after formation of the bent part may be the same. 
     The bent parts  14   b  are formed by press working when both ends of the bus bars  14  of the X direction are linked to the carriers  16 A,  16 B. Even if the number of the bent parts  14   b  are different in each bus bar  14 , the deviation in the end positions of the respective bus bars  14  does not occur, and distortion and cracking do not occur in the carriers  16 A,  16 B. The same applies for the bus bars  15  of the Y direction and the carriers  17 A,  17 B. 
     As shown in FIG. 4, the bus bars  14  can be arranged on the upper face of the insulation board  11  when linked with the carriers  16 A,  16 B, and the bus bars  15  can be arranged on the lower face of the insulation board  11  when linked with the carriers  17 A,  17 B. Then the bent parts  14   a  of the bus bars  14  protrude downwards in the penetration holes  11   d , and the bent parts  15   a  of the bus bars  15  protrude upwards to bring the faces of the upper and lower bent parts  14   a  and  15   a , respectively, in contact. 
     As shown in FIG. 5, the resistance welding is carried out by pressing the electrodes  50 ,  51  of a resistance welder on the bent parts  14   a ,  15   a  from above and below, respectively, so that resistance welds  30  (see FIG. 1) are formed between the bus bars  14 ,  15 . After resistance-welding of the bent parts  14   a ,  15   a , the carriers  16 A and  16 B of the bus bars  14  and the carriers  17 A,  17 B of the bus bars  15  are separated collectively. 
     Thus, in the present invention, as the parallel sets of bus bars  14 ,  15  are linked with the carriers  16 A and  16 B and the carriers  17 A,  17 B, respectively, until the resistance welding is completed, the manufacturing operation is extremely simple. 
     In a variation of this embodiment shown in FIG. 6, fine protrusions  20  of, for example, 0.3 mm height are provided on the upper faces of the bent parts  15   a  of the bus bars  15  in the press working. Further, when the fine protrusions  20  are provided, the bent part  15   a  including the fine protrusion  20  is also formed by length extension so that that the thickness of the bus bar is reduced by, for example, 15 to 25%, and the dimension between the two ends of each bus bar  15  is the same as that before the formation of the bent part. 
     When the fine protrusions  20  are provided on the contact face as described above, the welding zone can be concentrated at a small area in resistance welding, so that heat generation occurs easily, and the welding quality can be raised. 
     The circuit board  10  formed as described above is for example accommodated in the lower casing part of an electrical connection box and assembled by placing an upper casing part thereon. The casing is typically of molded plastics material and has lateral openings to receive components which have terminals to engage the ends of the bus bars  14 ,  15  e.g. connectors, fuses and relays. Further, a plurality of the circuit boards  10  may be arranged in a stack in a box by lamination through a further insulation board or boards. 
     As the above embodiment illustrates, according to the present invention, for an interior circuit of an electrical connection box, the arrays of strip bus bars are arranged to give a lattice shape on the upper and lower faces of an insulation board. Penetration holes are provided on the insulation board at intersection points where conduction is required, and bent parts provided on the upper and lower bus bars are mutually joined through the penetration holes. The bus bars  14 ,  15  are in the form of parallel spaced discrete metal strips. They are preferably joined without use of bonding material, e.g. by resistance-welding. Thereby, the connection of the upper and lower bus bars can be securely and easily obtained, and variation of the circuits is simple to achieve. Further, the bent parts are formed by reducing the bus bar thickness by, for example, 15 to 25%, such that the dimension between the ends of the bus bars is the same before and after the formation of bent parts. Therefore, the parallel bus bars can be processed when they are joined with the carriers. Accordingly, their installation on the insulation board is easy and the resistance welding can be carried out in a condition in which the positioning of the bus bars was accurately carried out. As a result, the quality of the resistance welding can be high. 
     While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.