Structure for welding electrical connecting portions to each other using laser light beam

Abstract: An arrangement and method for establishing an electrical and mechanical connection between electrically conductive members. The arrangement includes an electrically conductive connecting member, two electrically conductive metallic members disposed opposite each other, flanking the connecting member, and clamping the connecting member therebetween, and a source of laser energy oriented such that an output beam therefrom is incident on an outer surface of one of the metallic members and directed towards the underlying connecting member to establish a weld connection at zones of mutual contact between the connecting member and the respective metallic members. The connecting member includes a cable or the like and the metallic members include contact terminals, busbars or the like. In the method, the connecting member is positioned between the metallic members and the output beam is radiated on one of the metallic members in the direction of the connecting member so as to weld the connecting member to the metallic members.

Description: The present invention relates to a structure and method for firmly and electrically welding an electrically conductive connecting member, such as a sheathed conductor having a small diameter, a flexible printed wiring board or the like, to an electrically conductive metallic member, such as a terminal, a busbar or the like, by using a laser light beam. Background Fig. 17 is a perspective view of a conventional structure employable for welding electrical connecting portions to each other using a laser light beam. This conventional structure is designed such that a conductor portion (consisting of a bundle of lead wires) 82 of a sheathed cable 81 is placed on the surface of an electrically conductive metallic plate 80 such as a terminal, a busbar or the like and a laser beam 83 is irradiated on the conductor portion from above so as to weld the conductor portion 82 to the electrically conductive metallic plate 80. Referring to Fig. 18, when a polyurethane sheathed conductor 86, having a small diameter, is connected to an electrically conductive metallic plate 88, a laser light beam 87 is irradiated directly on the sheathed conductor 86 without the sheath 91 peeled away therefrom. With the conventional structures mentioned above, there arises a problem in that the welded portion 84, 89 of the cable 81, 86 is largely recessed as illustrated by reference numeral 85, 90, causing the tensile strength of cable 81. 86 to be remarkably reduced. Moreover, in the case where the sheathed conductor 86 is welded directly to the electrically conductive metallic plate 88 as shown in Fig. 18, vapor resulting from vaporization of the sheath part 89 generates a number of voids, or bubbles, 92 which in turn cause a substantial reduction of the strength of the welded structure. The document "Kußmaul et al: Laserstrahlschweißverbindungen von lackisolierten Kupferdrähten mit Anschlußteilen aus NE-Metallen, Verbindungstechnik in der Elektronik, Heft 4, 1990, pages 179 to 184" according to the pre-characterizing parts of claims 1, 4, 6, 8 and 10, discloses an electrical and mechanical connection between a folded metal sheet with a copper wire clamped therebetween. A weld connection is provided between the folded metal sheet and the wire by means of a laser beam. EP-A-304593 discloses a SMD component including a terminal which is bent in a U-shaped form, wherein a wire is clamped therebetween to form an electrical and mechanical connection between the terminal and the wire. A weld connection between the wire and the folded terminal is provided by means of a laser beam. From US-A-4,978,835 it is known to provide a weld connection at zones of mutual contact between leads and bumps positioned onto an integrated circuit die. The weld connection is carried out by means of a laser beam. The weld connection provides an electrical as well as a mechanical connection between the leads and the bumps. SUMMARY OF THE INVENTION The present invention has been made with the following background in mind and its object resides in providing a structure and method for firmly welding an electrically conductive metallic plate, such as a terminal, busbar or the like, using laser light beam without the formation of a recessed portion at the welded part and the generation of voids. To accomplish the above object, the present invention provides an electrical and mechanical connection according to claims 1, 4, 6, 8, 10 and 12. As the laser light beam is irradiated, one of the electrically conductive metallic member becomes molten, causing the inner electrically conductive connecting member and the other electrically conductive metallic member to be heated, whereby the three members are welded to each other. Since the laser light beam is not irradiated directly on the electrically conductive connecting member, there does not arise the problems discussed above concerning the welded portion becoming recessed or generating the voids. Thus, the strength of the welded structure is remarkably increased. When a disconnecting force is applied to the electrically conductive connecting member, the connecting member counteracts the disconnecting force by bending at the opposite edge portions of the connecting member. Therefore, the disconnecting force is not imparted directly to the welded part, resulting in the strength of the welded structure against the disconnecting force being improved. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a welded structure, particularly illustrating a basic technical concept of welding electrical connecting portions to each other using a laser light beam; Fig. 2 is a vertical sectional view of the welded structure, particularly illustrating the welded state of the welded structure shown in Fig. 1; Fig. 3 is a perspective view schematically illustrating a method of testing the tensile strength of a cable; Fig. 4 is a perspective view schematically illustrating a method of testing the tensile strength of the conventional structure discussed above; Fig. 5 is a perspective view schematically illustrating a method of testing the tensile strength of a cable connecting structure in accordance with Fig. 1; Fig. 6 is a perspective view illustrating a first embodiment of the present invention; Fig. 7 is a perspective view illustrating a second embodiment of the present invention; Fig. 8 is a sectional view illustrating a third embodiment of the present invention; Fig. 9 is a perspective view illustrating a fourth embodiment of the present invention; Fig. 10 is a perspective view of the structure shown in Fig. 9 with the structure being illustrated in the assembled state; Fig. 11 is a sectional view of the structure taken along line A - A in Fig. 10; Fig. 12 is a perspective view illustrating a fifth embodiment of the present invention wherein essential components are shown in the exploded state; Fig. 13 is a perspective view illustrating an embodiment wherein essential components are shown in the exploded state; Fig. 14 is a perspective view illustrating a sixth embodiment of the present invention wherein essential components are shown in the disassembled state; Fig. 15 is a perspective view of the structure shown in Fig. 14 with the structure being illustrated in the assembled state; Fig. 16 is a sectional view of the structure taken along line B - B in Fig. 15 illustrating the welded state of a cable; Fig. 17 is a perspective view of a conventional structure wherein a sheathed cable is welded using laser light beam and a part of a sheath is removed therefrom; and Fig. 18 is a vertical sectional view of a conventional structure wherein a sheathed conductor is welded using a laser light beam. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a perspective view illustrating a structure designed for welding electrical connecting portions to each other using a laser light beam. This structure is embodied such that a sheathed conductor 1, having a small diameter of 1 mm or less, is clamped between two electrically conductive metallic plates 2 and 3 such as terminals, busbars or the like. Thereafter, a laser light beam is directed toward the central axis of the conductor 1 so as to be irradiated onto the upper metallic plate in a perpendicular direction. As a result, the sheathed conductor 1 and the electrically conductive metallic plates 2 and 3 are welded to each other. Each of the electrically conductive metallic plates 2 and 3 is made of a metallic material which is compatible to the sheathed conductor 1, e.g., a phosphor bronze, a beryllium copper or the like. With this construction, the upper metallic plate 2 is molten and develops a recessed portion, as shown in Fig. 2. Simultaneously, the sheathed conductor 1 and the lower conductive metallic plate 3 are heated together so that the sheathed conductor 1 is firmly welded to the upper and lower electrically conductive metallic plates 2 and 3 without the formation of any recessed portion in the conductor such that the diameter of the conductor is not reduced. Table 1 shows results obtained from tests conducted for measuring the strength of the welded conductor 1, as seen in the pulling direction. As is apparent from the table, the average value X of the tensile strength of the conductor alone is 3.1 Kgf, the average value of the tensile strength of the conventional connecting structure, discussed above and illustrated in Figs. 17 and 18, is only 1.2 Kgf, and the average value of tensile strength of the structure of Fig. 1 is a relatively high 2.9 Kgf. In addition, the average deviation σ of the conventional structure is 0.17 Kgf and that of the structure of Fig. 1 is 0.07 Kgf, which is less than half of the average deviation of the conventional structure. Accordingly, the structure of Fig. 1 is more uniform in respect to tensile strength. Tensile Strength of Conductor Itself (Kgf) Welded Strength of Conventional Structure (Kgf) Welded Strength of Structure of Fig. 1 (Kgf) No. 1 3.17 1.27 2.95 No. 2 3.10 1.46 2.73 No. 3 3.15 1.02 2.94 No. 4 3.15 1.56 3.00 No. 5 3.15 1.21 2.96 No. 6 3.01 1.08 2.94 No. 7 3.21 1.17 2.89 No. 8 3.16 1.05 2.94 No. 9 3.15 1.30 2.92 No. 10 3.13 1.11 2.99 X 3.138 1.223 2.926 σ n 0.050 0.169 0.072 Measuring methods employed for the aforementioned measurements are schematically illustrated in Fig. 3 through Fig. 5. Fig. 3 shows a tensile test for measuring a tensile strength of the conductor 1 alone, Fig. 4 shows a tensile test for measuring a tensile strength of the conventional welded structure, and Fig. 5 shows a tensile test for measuring a tensile strength of the welded structure of Fig. 1. When a certain disconnecting force is exerted on the sheathed conductor 1 in the disconnecting direction as represented by arrow A in Fig. 2, the sheathed conductor 1 is bent around the edge portions 5 of the upper electrically conductive metallic plate 2 so that a direct tensile force is not applied to the portions 6. Thus, any applied force is not exerted directly on the welded part 7, resulting in the strength of the welded structure against the disconnecting force being improved. Fig. 6 is a perspective view of a structure employable for welding electrical connecting portions to each other in accordance with a first embodiment of the present invention wherein a sheathed conductor is welded to a busbar. This structure is embodied such that a projecting portion 9 is formed at the intermediate portion of a busbar 8, and a resilient clamping piece 12 is formed by forwardly bending a projection piece 11 extending upright from an upper wall 10 of the bent portion 9 so as to clamp a sheathed conductor 13 between the clamping piece 12 and the upper wall 10 of the bent portion 9. The clamping piece 12, the sheathed conductor 13, and the upper wall 10 are welded to each other by irradiating a laser light beam 14 on the clamping piece 12 from above with the beam oriented toward the sheathed conductor 13. A foremost end 15 of the clamping piece 12 is upwardly bent to serve as a tapered guide for receiving the sheathed conductor 13. Additionally, a position determining piece 16 is formed on the upper wall 10 for the sheathed conductor 13 by upwardly bending a part of the upper wall 10. The position determining piece fixes the specific position of the conductor. Fig. 7 is a perspective view of a structure employable for welding electrical connecting portions to each other in accordance with a second embodiment of the present invention wherein a contact terminal 18 is formed by welding a sheathed cable to a base plate. The contact terminal 18 is constructed such that a forwardly sloped ceiling plate 20 is formed opposite to the base plate 19 at the fore end part of an electrically conductive metallic plate by cutting and bending it to a predetermined configuration to establish electrical contact therebetween. Additionally , a pair of cable tightening pieces 21 extend upwardly from the base plate 9 at the rear end thereof. With such construction, an exposed conductor portion 23, consisting of a bundle of wires, of a sheathed cable 22 is inserted and clamped between the ceiling portion 20 and the base plate 19. Thereafter, the ceiling portion 20, the conductor portion 23, and the base plate 19 are welded to each other by irradiating a laser light beam 24 toward the conductor portion 23 from above. Fig. 8 is a sectional view illustrating a structure employable for welding electrical connecting portions to each other using a laser light beam in accordance with a third embodiment of the present invention wherein a cable is welded to electrically conductive metallic plates. According to this embodiment of the invention, a lower electrically conductive metallic plate 28 is received in a groove 27 of a base board 26 molded of a synthetic resin or a ceramic material. A sheathed conductor 29 is then placed on the lower plate 28 and an upper electrically conductive metallic plate 32 is firmly placed on the sheathed cable 29 by engaging a pair of engagement pawls 31 of the upper plate 32 with corresponding through holes 30 in the base board 26 to clamp the sheathed conductor 29 between the upper and lower plates 32 and 28. A recess, or hollowed portion, 34 is centrally formed in the groove 27 of the base board 26 at a position coincident with an extension line along which laser light beam 33 is irradiated on the upper metallic plate 32. In addition, a position determining groove 35 is formed on the lower electrically conductive metallic plate 28 for correctly locating the sheathed conductor 29. It is noted that it is possible that another sheathed conductor 36 may be placed on the sheathed conductor 29 so as to intersect the latter at a right angle so that both the sheathed conductors 29 and 36 may be welded together between the upper and lower electrically conductive metallic plates 32 and 28. In this case, it is recommended that a position determining groove 37 is formed on the bottom surface of the upper metallic plate 32. Figs. 9 through 11 illustrate a structure for welding electrical connecting portions to each other using a laser light beam in accordance with a fourth embodiment of the present invention wherein a longitudinally extending busbar is welded to a sheathed cable. According to this embodiment of the invention, a longitudinally extending busbar 40 is positioned in a slot of a base board 39 so as to protrude therefrom. The base board is molded of an electrical insulating synthetic resin in the form of an electrical connection box or the like. The sheathed portion of a cable 43 is removed so as to expose the conductor portion 44, consisting of a bundle of wires. The wires of the conductor portion 44 are then uniformly distributed over an upper end surface 41 and opposite side surfaces 42 of the busbar 40, as specifically illustrated in Figs 10 and 11. Thereafter, an inverted U-shaped electrically conductive metallic cover 45 is placed over the wires in a press-fit manner, and the electrically conductive metallic cover 45, the conductor portion 44 and the busbar 40 are welded to each other by irradiating a laser light beam 47 on an upper wall 46 of the cover 45 from above with the beam directed toward the conductor portion 44. As a result, a portion of the electrically conductive metallic cover 45 is melted and the molten metal flows down along the busbar 40 such that the wires of the conductor portion 44 are uniformly welded to the busbar 40 and the metallic conductive metallic cover 45 with the aid of the molten metal. It is noted that the electrically conductive metallic cover 45 is correctly located by fitting a fore end part 49 of the cover 45 into an engagement groove 48 on the base board 39. Fig. 12 shows by way of a perspective view a structure employable for welding electrical connecting portions to each other using a laser light beam in accordance with a fifth embodiment of the present invention wherein a flexible printed circuit board (hereinafter referred to simply as FPC) is used as a cable to be welded. The FPC 53 includes a plurality of circuit conductors 52 arranged in parallel with each other on the surface of a flexible sheet 51 molded of an electrical insulating synthetic resin. The FPC 53 is clamped between a busbar 54 and a base plate portion 56 of a pressure contact terminal 55. Thereafter, the base plate portion 56, the circuit conductors 52 and the busbar 54 are welded to each other by irradiating a laser light beam 57 on the base plate portion 56 from above with the beam directed toward the circuit conductors 52. Although the circuit conductors 52 constituting the FPC 53 are dimensioned to have a very small thickness, they are heated and fused together with the base board portion 56 of the pressure contact terminal 55. In this manner the circuit conductors 52 are firmly welded to the pressure contact terminal 55 and the busbar 54 while they are clamped therebetween. When a disconnecting force is exerted on the FPC 53, the FPC 53 is bent at edge portions 58 of the base plate portion 56 to counteract against the disconnecting force in the same manner as the sheathed cable described above in the preceding embodiments. Thus, the disconnecting force is not exerted directly on welded portions 59. Accordingly, the FPC 53 has a high strength against a disconnecting force. Fig. 13 illustrates a structure employable for welding electrical connecting portions to each other using a laser light beam wherein two busbars each having a small thickness are welded to each other in an overlapped state. In this embodiment, the fore end portion of an upper busbar 61 is folded to form a double-layered structure. Thereafter, the upper busbar 61 is welded to the folded portion 62 and to a lower busbar 64 so as to be disposed and retained therebetween by irradiating a laser light beam 63 on the folded portion 62. Finally, Figs. 14 to 16 illustrate a structure employable for welding electrical connecting portions using a laser light beam in accordance with a sixth embodiment of the present invention wherein a plurality of sheathed conductors are welded to a pressure contact terminal to provide a relay base board for a flat circuit system. In Fig. 14, reference numeral 66 designates a terminal board having plurality of pressure contact terminals 67 standing upright thereon, reference numeral 68 designates a plurality of sheathed conductors arranged opposite to base plates 69 of the pressure contact terminals 67, and reference numeral 70 designates a base board having a plurality of circular disc-shaped electrically conductive metallic tips 71 placed over through holes 72 while facing the sheathed conductors 68. Fig. 15 is a perspective view which illustrates the manner in which the aforementioned components are assembled together, and Fig. 16 is a fragmentary sectional view of the assembled structure taken along line B - B in Fig. 15. Referring to Fig. 15 again, a connector (not shown), used for the purpose of connection to an external unit, is secured to a terminal end 68a of each sheathed conductor 68, and an external cable (not shown) is connected to each pressure contact terminal 67. As shown in Fig. 16, while the sheathed conductor 68 is clamped between the base plate 69 of the pressure contact terminal 67 and the electrically conductive metallic plate 71, a laser light beam 73 is irradiated on each of the electrically conductive metallic tips 71 through the hole 72 on the base board 70 while being directed toward the sheathed conductor 68. As a result, the electric conductive metallic tip 71, the sheathed conductor 68 and the bottom plate 69 of the pressure contact terminal 67 are welded to each other. It is noted that the pressure contact terminal 67 is not connected to the sheathed conductor 68 via pressure contact but, rather, is connected by welding. Therefore, the resulting relay base board 74 is compact. As is apparent from the above description, according to the present invention, while an electrically conductive connecting member such as a sheathed cable, a sheathed conductor, an FPC or the like is clamped between electrically conductive metallic members located opposite to each other, the electrically conductive connecting member and the electrically conductive metallic members are welded to each other by irradiating a laser light beam on one of the electrically conductive metallic members while avoiding direct irradiation of the laser light beam on the electrically conductive connecting member. Thus, the strength of the welded part can be improved without forming recesses or voids in the welded part. Even when a certain intensity of disconnecting force is exerted on the electrically conductive connecting member, the electrically conductive connecting member serves to counteract the force by bending the cable around the edge portions of the electrically conductive metallic members. Consequently, the welded part can exhibit a high strength against the disconnecting force without direct exertion of the disconnecting force on the welded portion.

Claims: An electrical and mechanical connection between electrically conductive members comprising: an electrically conductive cable (68); two electrically conductive metallic members (67,71) disposed opposite each other, flanking said cable (68) and clamping said cable (68) therebetween; and a weld connection (7) which includes zones of mutual contact between said cable (68) and both metallic members (68,71), said weld connection (7) being provided by means of a laser beam (73) characterized in that said one metallic member is a base member (71) and the other one of said metallic members is a contact terminal (67) having a base portion (69), wherein said cable (68) is a sheathed conductor disposed between said base member (71) and said base portion (69), wherein said connection comprises a base plate (70) supporting said metallic base member (71) and having a hole (72) adjacent said base member (71) through which said laser beam (73) passes, and wherein said contact terminal (67) is provided for a connection to an external cable. The connection according to claim 1, further comprising a terminal board (66) in which said contact terminal (67) is disposed with said base portion (69) being exposed on one side of the terminal board (66) and an opposite end of said contact terminal (67) being exposed on an opposite side of said terminal board (66). The connection according to claim 2, wherein a plurality of sets of base members (71), contact terminals (67) and sheathed conductors (68) are provided. An electrical and mechanical connection between electrically conductive members comprising: an electrically conductive cable (13); two electrically conductive metallic members (8,12) disposed opposite each other, flanking said cable (13) and clamping said cable (13) therebetween; and a weld connection (7) which includes zones of mutual contact between said cable (13) and both metallic members (8,12), said weld connection (7) being provided by means of a laser beam (14) characterized by a bus bar (8) having an intermediate portion with a projecting portion (9), an upright extending projecting portion (11) and a resilient clamping piece (12) for clamping the cable being a sheathed conductor (13), wherein a position determining piece (16) is formed on the upper wall (10) of said projecting portion (9) by upwardly bending a part of the upper wall (10) for fixing the specific position of the conductor (13). The connection as claimed in Claim 4, wherein the foremost end (15) of the clamping piece (12) is upwardly bent to serve as a tapered guide for receiving the sheathed conductor (13). An electrical and mechanical connection between electrically conductive members comprising: an electrically conductive cable (29); two electrically conductive metallic members (28,32) disposed opposite each other, flanking said cable (29) and clamping said cable (29) therebetween; and a weld connection (7) which includes zones of mutual contact between said cable (29) and both metallic members (28,32), said weld connection (7) being provided by means of a laser beam (33) characterized in that said one metallic member being a first plate (28) is received in a base board (26), said cable being a sheathed conductor (29) is placed on said first plate (28), said other metallic member being a second plate (32), said second plate (32) has engagement pawls (31) for engaging through holes (30) disposed in said base board (36). The connection as claimed in claim 6, wherein said first plate (28) has a position determining groove (35). An electrical and mechanical connection between electrically conductive members comprising: an electrically conductive cable (43); two electrically conductive metallic members (40,45) disposed opposite each other, flanking said cable (43) and clamping said cable (43) therebetween; and a weld connection (7) which includes zones of mutual contact between said cable (13) and both metallic members (40,45), said weld connection (7) being provided by means of a laser beam (47) characterized in that the one metallic member is a longitudinally extending bus bar (40) positioned in a slot of a base board (39) so as to protrude therefrom, the cable being a sheathed conductor (43) has an exposed conductor portion (44) consisting of a bundle of wires, said wires are uniformly distributed over an upper end surface (41) and opposite side surfaces of the bus bar (40), the other metallic member is an inverted U-shaped cover (45), which is placed over the wires in a press-fit manner, wherein the laser light beam (47) is irradiated on an upper wall (46) of the cover (45) from above with a beam (47) directed toward the conductor portion (44). The connection as claimed in claim 8, wherein said base board (39) has an engagement groove (48) for fitting the fore end part (49) of the the cover (45). An electrical and mechanical connection between electrically conductive members comprising: an electrically conductive cable (22); two electrically conductive metallic members (19,20) disposed opposite each other, flanking said cable (22) and clamping said cable (22) therebetween; and a weld connection (7) which includes zones of mutual contact between said cable (22) and both metallic members (19,20), said weld connection (7) being provided by means of a laser beam (24) characterized in that said metallic members are formed by a base plate (19) having at the fore end part thereof a forwardly sloped ceiling plate (20) opposite to said base plate (19), an exposed conductor portion (23) of said sheathed cable (22) being clamped between the ceiling plate (20) and the base plate (19) by insertion of the cable (22) in the direction of the slope. The connection as claimed in claim 10, further including cable tightening pieces (21) extending upwardly from the base plate (19) at the rear end thereof. An electrical and mechanical connection between electrically conductive members, comprising: a plurality of circuit conductors (52) arranged on the surface of a flexible sheet (51) of a flexible printed circuit board (53), a first electrically conductive member being a bus bar (54), a second electrically conductive member being a terminal (55), said electrically conductive metallic members being disposed opposite to each other and flanking and clamping said flexible printed circuit board (53) therebetween, and a weld connection (59) at zones of mutual contact between said circuit conductors (52) and said metallic members (54,55), said weld connection (59) being provided by means of a laser beam (57).

Inventors: NISHITANI KEIZO, SAIMOTO TETSUROU, SUGIURA MASUOC, TAKIGUCHI ISAO, NISHITANI, KEIZO, SAIMOTO, TETSUROU, SUGIURA, MASUO, TAKIGUCHI, ISAO, NISHITANI, KEIZO C/O YAZAKI CORPORATION, SAIMOTO, TETSUROU C/O YAZAKI PARTS CO., LTD., SUGIURA, MASUOC/O YAZAKI CORPORATION, TAKIGUCHI, ISAO C/O YAZAKI CORPORATION
Applicants: YAZAKI CORP, YAZAKI CORPORATION
Application year: 1992
Main classification: B23K1
IPC codes: B23K26, H01R43, H01R4, H05K3