Metal terminal

Abstract: A metal terminal (10) has a portion (12) with a slit (15) extending in a direction in which the terminal (10) is inserted into the installing hole (H) of a circuit substrate (P). The slit (15) allows the terminal (10) to be elastically deformable in the radial direction. The inserted portion has a tapered part (13) having a diameter decreasing gradually in the insertion direction. The maximum outer diameter portion (13L) of the tapered part (13) makes a circumferential linear elastic contact with a contact region (C). When the tapered part (13) is inserted into the hole (H), it contracts gradually elastically. The terminal (10) has a low insertion resistance. Further, if the terminal (10) becomes inclined with respect to the axis of the hole (H), the maximum outer diameter portion (13L) maintains a circumferential linear contact with the inner peripheral surface of the hole (H).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an electrical circuit substrate having a metal terminal installed on it. Description of the Related Art In U.S. Patent 4017143, a metal terminal is shown inserted into a circular installing hole of a circuit substrate so as to bring the metal terminal into contact with a contact region of a printed circuit formed on the inner surface of the installing hole. The metal terminal is of C-shape cross-section, with a slit extending in a direction in which the terminal is inserted into the installing hole to allow the metal terminal to elastically deform in its radial (transverse) direction so that the metal terminal makes elastic contact with the contact region. The outer diameter of the cylindrical metal terminal is axially (i.e. in the metal terminal insertion direction) uniform where it contacts the inner surface of the installing hole. Therefore, in the normally installed state, the metal terminal makes surface-to-surface contact with the contact region. However, if the metal terminal is inclined with respect to the axis of the installing hole, the outer surface of the metal terminal separates from the inner surface of the installing hole and makes point-contact with the edges of the substrate at the openings of the installing hole. Therefore, there may be defective contact between the metal terminal and the contact region on the inner surface of the installing hole. EP-A-0528108 discloses a printed circuit contact system which includes a generally tapered slotted socket made of conductive spring material. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrical circuit substrate with a metal terminal capable of maintaining the intended electrical connection even if the metal terminal is inclined with respect to the axis of an installing hole. According to the invention there is provided an electrical circuit substrate having a contact hole into which is inserted a metal terminal which makes electrical contact with an inner surface of the contact hole, the metal terminal having an insertion portion having a resiliently deformable outer wall which defines a central cavity with a slit which extends along the outer wall in the insertion direction of the terminal and allows the terminal to contract in the transverse direction, wherein the insertion portion comprises a tapered part which provides a widest portion of the metal terminal within the contact hole, and which narrows smoothly in the insertion direction. The outer peripheral surface of the tapered part at said widest portion bears resiliently on the inner surface of the contact hole along a linear contact region, whereby the metal terminal is inclinable with respect to the axis of the contact hole while maintaining a linear contact region. When the tapered part of the metal terminal is inserted into the contact hole, the tapered part gradually contracts elastically. That is, the diameter of the tapered part decreases gradually. Therefore, the metal terminal has a low insertion resistance and thus is easy to use. Further, if the metal terminal becomes inclined with respect to the axis of the contact hole, the outer peripheral surface of the tapered part can maintain a circumferential linear contact with the inner surface of the contact hole. It is preferable that said outer peripheral surface of the tapered at its widest portion is outwardly convex. Therefore if the metal terminal is inclined with respect to the axis of the contact hole, there is a reduced risk of the outer peripheral surface of the tapered part damaging the contact region formed on the inner surface of the contact hole. Typically the substrate has electrical circuit elements on at least one of its surfaces, and the terminal makes electrical contact with such a circuit element via conductive layer in the contact hole. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which:- Fig. 1 is a sectional view showing metal terminals inserted in a circuit substrate, in a first embodiment of the invention. Fig. 2 is an enlarged sectional view of part of Fig. 1 showing a part of one metal terminal inserted into a contact hole of the substrate. Fig. 3 is an enlarged sectional view corresponding to Fig. 2 in which the metal terminal becomes inclined in the contact hole. Fig. 4 is a perspective view of a part of one metal terminal shown in Fig. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to Figs. 1 through 4. Two metal terminals 10 of the first embodiment are shown installed on an electrical circuit substrate P, with each metal terminal 10 also mounted on a connector housing 20. The connector housing 20 is made of synthetic resin material and includes a rectangular hood part 21 open at a forward part (left side in Fig. 1) and a supporting wall part 22 which closes the rear end of the hood part 21. The metal terminals 10 are installed on the connector housing 20 by penetrating through the supporting wall part 22. The circuit substrate P is generally of electrically insulating material and has a printed circuit (not shown) formed on an upper surface thereof. The circuit substrate P has circular contact holes H (referred to below as installing holes) which perpendicularly penetrate the substrate. Each metal terminal 10 is inserted into the respective installing hole H from above. A contact region C continuous with the printed circuit is formed by plating the inner peripheral surface of the installing hole H with a metal. The metal terminal 10 is brought into contact with the contact region C. The elongate metal terminal 10 is made of a resiliently deformable electrically conductive metal which is bent in an L-shape. A tab part 11 of the metal terminal 10 penetrates horizontally through the supporting wall part 22. A substrate connection section 12 of the metal terminal 10 bent vertically downward from the rear end of the tab section 11 is inserted through the installing hole H of the circuit substrate P. The substrate connection section 12 has an outer wall which defines a central cavity. To allow its radial (transverse) elastic deformation, the substrate connection section 12 has a slit 15 extending along the direction in which the section 12 is inserted into the installing hole H. The section 12 is, apart from the slit 15, symmetrical about an axis which is parallel to the insertion direction. The upper part of the section 12 includes a tapered connection part 13 whose diameter decreases gradually in the forward (insertion) direction, i.e. downwardly in Figs. 1 and 2, of the section 12. The maximum outer-diameter portion 13L of the tapered connection part 13 makes an elastic circumferential linear contact with the contact region C of the installing hole H. The outer peripheral surface of the tapered connection part at the widest position thereof (referred to here as the maximum outer-diameter portion 13L) has an outwardly convex surface, as seen in axial section. In the uninstalled state, the outer diameter of the maximum outer-diameter portion 13L is larger than the inner diameter of the installing hole H. The minimum diameter of the tapered connection part 13 at its lower end is smaller than the inner diameter of the installing hole H. The substrate connection section 12 has a cylindrical leading part 14 extending from the lower end of the tapered connection part 13 to a tapered lower end. The outer diameter of the leading part 14 is smaller than the inner diameter of the installing hole H. The terminal 10 is made by punching and bending sheet metal having appropriate resilience in the shaped state. The operation of the first embodiment will be described below. In fixing the connector housing 20, on which the metal terminals 10 have been installed, to the upper surface of the circuit substrate P at a predetermined position thereof, the substrate connection section 12 of each metal terminal 10 is inserted downward into the installing hole H. On inserting the section 12 of the metal terminal 10 into the installing hole H, the leading part 14 penetrates the installing hole H, and then the tapered connection part 13 penetrates thereinto. During insertion of the metal terminal 10 into the installing hole H, the outer surface of the tapered connection part 13 contacts the upper surface of the substrate at the edge of the upper end of the installing hole H. As a result, the tapered connection part 13 is contracted elastically and its diameter decreases. The inclination of the outer surface of the tapered connection part 13 that contacts the upper edge is small relative to the insertion direction of the metal terminal 10. Thus, the tapered connection part 13 contracts smoothly without being snagged by the upper edge. Thus, the metal terminal 10 has a low insertion resistance. When the connector housing 20 has been fixed to the upper surface of the circuit substrate P, the operation of inserting the metal terminal 10 into the installing hole H is completed. It is to be noted that the metal terminal 10 is not soldered to the inner surface of the installing hole H. When the connector housing 20 has been fixed to the upper surface of the circuit substrate P, the maximum outer-diameter portion 13L of the tapered connection part 13 bears elastically on the contact region C of the inner surface of the installing hole H. Thus, the metal terminal 10 makes electrical contact with the contact region C with a predetermined contact pressure. As shown in Fig. 2, the maximum outer-diameter portion 13L of the tapered connection part 13 makes a linear contact with the contact region C with a contact pressure which is approximately uniform around the entire circumference of the maximum outer-diameter portion 13L. Further, because the tapered connection part 13 bears elastically on the inner surface of the installing hole H, the metal terminal 10 can be prevented from moving radially relative to the axis of the installing hole H. To remove the metal terminal 10 from the installing hole H, the substrate connection section 12 of the metal terminal 10 is pulled out from the installing hole H, with the connector housing 20 being lifted above the circuit substrate P. During the withdrawal operation, the outer surface of the tapered connection part 13 makes sliding contact with the edge of the upper end of the hole H, with the tapered connection part 13 being restored to its original state as its diameter increases. The elastic restoring force of the tapered connection part 13 urges the metal terminal 10 in the withdrawal direction, thus accelerating the withdrawal. In the prior art metal terminal which has a cylindrical part with a uniform outer diameter for making electrical contact, the outer surface of the cylindrical part separates from the inner surface of the installing hole when the metal terminal is inclined with respect to the axis of the installing hole. In this case, the outer surface of the cylindrical part may make only two-point contact, i.e. with the upper and lower edges of the installing hole. Thus, defective contact between the metal terminal and the inner surface of the installing hole can occur. On the other hand, the metal terminal 10 of the first embodiment does not have this disadvantage. The metal terminal 10 contacts the inner surface of the installing hole H, with the maximum outer-diameter portion 13L of the tapered connection part 13 making the circumferential linear contact with the inner surface of the installing hole H. Thus, when the metal terminal 10 is inclined with respect to the axis of the installing hole H, as shown in Fig. 3, the maximum outer-diameter portion 13L maintains linear contact around the entire circumference of the inner peripheral surface of the installing hole H, the tapered connection part 13 being slightly deformed into an elliptical cross-section. Accordingly, the metal terminal 10 and the contact region C are capable of maintaining the intended contact state. A displacement of the contact line between the outer surface of the maximum outer-diameter portion 13L and the inner surface of the installing hole H occurs when the metal terminal 10 inclines with respect to the axis of the installing hole H. However, because the maximum outer-diameter portion 13L of the tapered connection part 13 is not angular but has an outwardly convex surface, there is less possibility that the metal terminal 10 damages the contact region C on the inner surface of the installing hole H. The present invention is not limited to the above-described embodiment. For example, the following embodiments are within the technical scope of the present invention. (1) In the first embodiment, the outer surface of the maximum outer-diameter portion of the tapered connection part is outwardly convex as seen in axial section. But according to the present invention, the maximum outer-diameter portion may be angular, i.e. have an apex as seen in axial section. (2) In the first embodiment, it is possible to form a stop member on the metal terminal to prevent insertion of the metal terminal beyond a point where the stop member reaches the substrate surface at the edge of the end of the installing hole. (3) In the first embodiment, the connector housing on which the metal terminal is installed, is arranged to receive a mating connector to connect the metal terminal and a mating metal terminal. However, instead of this another electrical component, such as an electrical wire may be directly connected to the metal terminal. (4) In the first embodiment, the radius of curvature of the maximum outer-diameter portion of the tapered connection part is smaller than the radius of the installing hole. But according to the present invention, the radius of curvature of the maximum outer-diameter portion may be equal to the radius of the installing hole. In this case, irrespective of the inclination of the metal terminal with respect to the axis of the installing hole, the line of contact between the inner surface of the installing hole and the outer surface of the metal terminal is constantly maintained and the tapered connection part maintains a circular cross-section.

Claims: An electrical circuit substrate (P) having a circular contact hole (H) into which is inserted a metal terminal (10) which makes electrical contact with an inner surface of the contact hole (H), the metal terminal having an insertion portion (12) having a resiliently deformable outer wall which defines a central cavity with a slit (15) which extends along the outer wall in the insertion direction of the terminal and allows the terminal to contract in the transverse direction, the insertion portion (12) comprising a tapered part (13) which provides a widest portion of the metal terminal within the contact hole, and which narrows smoothly in the insertion direction, characterised in that the outer peripheral surface of said tapered part at said widest portion bears resiliently on the inner surface of the contact hole along a linear contact region, whereby the metal terminal is inclinable with respect to the axis of the contact hole while maintaining a linear contact region. An electrical circuit substrate according to claim 1 wherein said outer peripheral surface at the widest portion is outwardly convex as seen in axial cross-section.

Inventors: WRIGHT DAVID, WRIGHT, DAVID, Wright, David, c/o Sumitomo Wiring Systems, Ltd.
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 2000
Main classification: H01R12
IPC codes: H01R13, H05K3, H01R43, H01R12