Circuit board, electrical connection box having the circuit board and method of making the circuit board

Abstract: A circuit board has an insulation board (11) and strip bus bars (14, 15) arranged on the opposite faces of board (11). On one face the bus bars (14) extend in parallel in a first direction, and on the second face the bus bars (15) extend in parallel in a second direction crossing said first direction, whereby so that there is an array of crossing points of the bus bars. The insulation board has holes (11d) at which the mutually crossing bus bars (14, 15) are bent towards each other and joined to establish electrical connection. In this way, a predetermined wiring pattern is obtained, and can be varied easily.

Description: FIELD OF THE 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. BACKGROUND OF THE INVENTION 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 constitution of inside 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 electric wire is wired in the pressure welding system becomes complicated, there are problems that the wiring work and the processing of an insulation board require a long time, so that the production cost increases. Further, when bus bars are used as an interior circuit, a mould for stamping must be made in accordance with the circuit, so that there are problems that the alternation of a circuit cannot be easily carried out and the costs of preparation of a mould costs high. Further, there are a lot of residual parts which are not used after stamping, so that the yield of the electro-conductive metal plate is poor, also raising cost. For example, if 7 or 8 sheets of bus bars must be arranged in multi-layer lamination with insulation boards between them because of a sharp increase of number of circuits accommodated in the inside of an electrical connection box, the cost is high. 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 1a, 1b are laminated on both sides of an electro-conductive member 3 which is made in a lattice shape by stamping out the removed parts 3a of an electro-conductive metal plate. The circuit is formed by cutting the unwanted connection points 3b. Wiring is connected to the electro-conductive member 3 to make connection with exterior circuits. Since the circuit is formed by cutting the points 3b, 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 3a, there remains a problem that the yield of the electro-conductive metal plate is not improved. US 2019625 describes a circuit board having an insulating panel carrying a set of parallel conductors on each of its two main faces, the sets of conductors extending orthogonally to each other. The insulating panel has apertures at points where the conductors cross, and the conductors have displaced portions which extend through the aperture and are welded together to make contact with each other. The contacting portions are displaced by the welding electrodes during welding. 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. Further, the subject is thirdly to design a cost reduction by being able to easily form insulation materials which lie between the third bus bars. In a first aspect the present invention provides a circuit board according to claim 1. 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. At the holes, the thickness of each of the mutually crossing bus bars in the direction of insulation board thickness 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 by stretching, in order to provide the bent portion. This can avoid disturbance of the ends of the bus bars. In a second aspect the invention provides a method of making a circuit board according to claim 7. In this method, step (iv) is 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 portion 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 thickness direction of the insulation board, in the range of 0.5mm to 1.0mm. 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 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 correspond with the terminal pitch of a relay. Some of the bus bars arranged in the other direction may correspond with the small pitch of a connector terminal hole, others correspond with a middle-size pitch, and the remainder 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 the circuit boards may be further arranged by lamination through insulation boards. BRIEF DESCRIPTION OF DRAWING Embodiments of the invention will now be described by way of non-limitative example 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), and 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), and 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), and 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). Figs. 7(A) and (B) show a prior art example discussed above. DESCRIPTION OF THE 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 11a, 11b in the upper and lower faces of the insulation board 11. As shown in Fig. 2, the ends of the bus bars 14 of the X direction are initially linked with the carriers 16A, 16B, and may be arranged on the upper face of the insulation board 11 in this condition, but as indicated by Fig. 1(A) in this embodiment the carrier 16B is cut off after the formation of the bent parts 14a described below and before the bus bars 14 are placed on the board 11. The width of the bus bars 14 is 2mm, and their nominal thickness is 0.64mm. 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 4mm, others a pitch of 10mm and yet others a pitch of 6.8mm, corresponding with the spacing of terminals of a connector, a fuse and a relay. The bus bars 15 of the Y direction are similar. Both ends in their longitudinal direction when formed are linked with the carriers 17A, 17B, and 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 2mm, a nominal thickness of 0.64mm and a uniform pitch of 4mm. Downwardly bent parts 14a formed by press molding are provided at requisite points on the bus bars 14. Similarly, upwardly bent parts 15a formed by press molding are provided on the bus bars 15. These bent parts 14a, 15a 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 11a and 11b on the insulation board 11, the board thickness of the parts 11c between the respective bottom faces of the grooves 11a and 11b are as thin as 0.8mm at the cross positions. At the crossing points where the upper and lower bus bars are to be connected penetration holes 11d are provided. As shown in Fig. 3, the penetration holes 11d provide a clearance since their upper parts 11d-1 are larger than the width of bus bars, and their lower parts 11d-2 are enlarged in a taper manner. The amount of protrusion of the bent parts 14a, 15a of the upper and lower bus bars 14, 15, which are resistance-welded through the penetration holes 11d, is thus fixed at half (0.4mm) of the board thickness of 0.8mm. The protruding faces are mutually brought in contact. To achieve this, the parts 14a, 15a are bent in an approximately arc shape so as to protrude by 0.4mm by press working. The bus bars 14, 15 are extended in length by this press working so as to be reduced in thickness by 15 to 25% (20% in the present embodiment) of their nominal thickness. The bent parts 14a, 15a 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 14b are formed by press working when both ends of the bus bars 14 of the X direction are linked to the carriers 16A, 16B. Even if the number of the bent parts 14b 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 16A, 16B. The same applies for the bus bars 15 of the Y direction and the carriers 17A, 17B. 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 16A, 16B, and the bus bars 15 can be arranged on the lower face of the insulation board 11 when linked with the carriers 17A, 17B. Then the bent parts 14a of the bus bars 14 protrude downwards in the penetration holes 11d, and the bent parts 15a of the bus bars 15 protrude upwards, to bring the faces of the upper and lower bent parts 14a, 15a 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 14a, 15a from above and below so that resistance welds 30 (see Fig. 1) are formed between the bus bars 14, 15. After resistance-welding of the bent parts 14a, 15a, the carriers 16A and 16B of the bus bars 14 and the carriers 17A, 17B 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 16A and 16B and the carriers 17A, 17B 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 0.3mm height are provided on the upper faces of the bent parts 15a of the bus bars 15 in the press working. Further, when the fine protrusions 20 are provided, the bent part 15a including the fine protrusion 20 is also formed by length extension so that that the thickness of the bus bar is reduced by 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 moulded 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, when the bent parts are formed by reducing the bus bar thickness by 15 to 25%, 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, so that 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 scope of the invention.

Claims: A circuit board having: an insulation board (11) having first and second main faces; a plurality of first strip bus bars (14) arranged on the first main face of the insulation board (11) and extending in parallel in a first direction; a plurality of second strip bus bars (15) arranged on the second main face of the insulation board (11) and extending in parallel in a second direction crossing said first direction so that, when seen in plan view on one of said main faces there is an array of crossing points of said bus bars (14, 15); and a plurality of holes (11d) through the insulation board (11) at a plurality of said crossing points, both the mutually crossing bus bars (14, 15) being bent each towards the other to be mutually joined at said holes (11d) to establish electrical connection between the bus bars (14, 15) to obtain a predetermined wiring pattern, characterised in that : at the holes (11d), the thickness of each of said mutually crossing bus bars (14, 15) in the direction of the insulation board thickness is reduced by 15 to 25%, compared with the thickness of adjacent portions of said bus bars. A circuit board according to claim 1, wherein at said holes (11d) said bus bars (14, 15) are joined by welding. A circuit board according to claim 2, wherein at said holes (11d) said bus bars (14, 15) are joined by resistance welding. A circuit board according to any one of claims 1 to 3, wherein said bus bars (14, 15) are located in grooves in said main faces of said insulation board. A circuit board according to any one of claims 1 to 4, wherein said bus bars have a nominal thickness of 0.5 to 1.0 mm. An electrical connection box containing a circuit board according to any one of claims 1 to 5. A method of making a circuit board, comprising the steps of:- (i) providing an insulation board (11) having a plurality of holes (11d) through it at locations at which electrical connection is to be made through the board; (ii) locating a plurality of first bus bars (14) on a first main face of said board (11) extending in parallel in a first direction; (iii) locating a plurality of second bus bars (15) on a second main face of said board (11) extending in parallel in a second direction crossing said first direction, whereby as seen in plan view on one of said main faces there is an array of crossing points of said bus bars, a plurality of said crossing points coinciding with said holes; (iv) providing bent portions (15a) of said bus bars (14, 15) such that, in the assembled circuit board, each of the mutually crossing pair of said bus bars (14, 15) at the position of each of said holes (11d) has a portion (15a) bent towards the other bus bar of said pair; (v) joining each said mutually crossing pair of bus bars (14, 15) at said holes (11d) to establish electrical connection between them, characterised in that : step (iv) is performed before locating said bus bars (14, 15) on said insulation board (11). A method according to claim 7, wherein said joining step (v) is carried out by welding.. A method according to claim 8, wherein said joining step (v) is carried out by resistance welding. A method according to any one of claims 7 to 9, wherein step (iv) includes the step of reducing the thickness of each of said mutually crossing bus bars at its bent portion, in the thickness direction of the insulation board, by 15 to 25% of the nominal thickness of the bus bar at adjacent portions of unreduced thickness. A method according to any one of claims 7 to 10, wherein, during step (iv) said first bus bars (14) and/or said second bus bars (15) are joined at opposite ends thereof to a pair of carrier members (16A, 16B; 17A, 17B) which maintain their relative positions. A method according to any one of claims 7 to 11, wherein, prior to said joining step (v), one of said bent portions (15a) has a protrusion (20) directed towards the other of said mutually crossing pair of bus bars.

Inventors: KASAI KOJI, KASAI, KOJI, Kasai, Koji, c/o Sumitomo Wiring Systems Ltd.
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 2001
Main classification: H05K1
IPC codes: H01R43, H05K1, H05K3, H01R9, H05K7, H01R4, H01R29