Surface-mounted component's contact having a soldering portion

Abstract: An electrical connector (1) (see Fig. 1) which is to be surface-mounted to a printed circuit board (6) has terminals (11) with inverted "T"-shaped soldering portions (12) to be electrically connected to conductors on the printed circuit board (6) each by soldering its soldering portion (12) to a conductor. The soldering portion comprises a flat foot (17) and a leg (18) which is integrally connected to and rising from the midportion of said foot (17). The relatively large foot (17) has an effect of causing substantial reduction of load per unit soldering area upon application of an undesired force to the terminal (11) and of increasing the strength of the soldering joint against removal from the conductor of the printed circuit board (6).

Description: The present invention relates to an electrical contact of an electric component to be mounted to a printed circuit board, such as electrical connector, carrier chip, switch, capacitor, electrical connection member or any other electrical part, and more particularly to an improved shape of the soldering portion of an electrical contact of such surface-mounted component. As is well known, a variety of electric components are mounted to a printed circuit board by soldering the lead wire terminals of such electrical components to the surface of the printed circuit or by connecting them to the surface of the printed circuit with the aid of lead-less means. In the former the strength with which the lead wire terminals are fixed to the surface of the printed circuit, and the quality with which the lead wire terminals are electrically connected to the surface of the printed circuit, depends on the shape of the lead wire terminal, and on the soldering condition resulting from the particular shape of the lead wire terminal. Therefore, the lead wire terminal shape and the soldering strength attained thereby have been studied, and these factors are taken into consideration in designing lead wire terminals. A conventional lead wire terminal is shown in Fig. 8. As shown, the soldering portion 2′ of the terminal 1′ is of rod shape. The end surface 3′ of the rod-shaped soldering portion 2′ is put on a conductor, and then its surface is joined to the surface of the conductor as indicated at 4′. As shown, the soldering skirts the lead wire terminal. Advantageously, the rod-shape of this lead wire terminal soldering portion 2′ makes it easy to produce a lot of such metal pieces by stamping metal sheets. When an exterior force is applied to the terminal 1′, the soldering skirt 4′ will be loaded from the soldering portion 2′. Disadvantageously, the load per unit soldering area will be great because of the relatively small contact area between the rod-shaped soldering portion 2′ and the surrounding soldering skirt 4′, and therefore, the soldering portion 2′ is liable to be removed from the conductor. Fig. 9 shows another conventional lead wire terminal 11′ having an "L"-shaped soldering portion 12′. It is composed of a horizontal foot 13′. As shown, the end surface 14′ of the foot 13′ of the "L"-shaped soldering portion 12′ is put on the conductor, and then the surface of the soldering portion 12′ is joined to the surface of the conductor as indicated at 15′. When an undesired exterior force is applied to the lead wire terminal 11′, the load per unit area on the soldering skirt 15′ will be relatively small because the end surface area 14′ is relatively large, accordingly increasing the resistance of the soldering portion against the exterior force to remove the lead wire terminal 11′ from the underlying conductor. In case that a strong pull is applied to the vertical leg 16′ of the lead wire terminal 11′, the pulling force is liable to concentrate to the bent portion "P" of the "L"-shaped soldering portion 12′. As a result a fatigue failure is liable to appear at this bent portion, allowing the soldering portion to be removed from the conductor. The jointing strength between the soldering and the conductor results only from the soldering around the bent portion of the "L"-shaped lead wire terminal. The remaining contact area of the "L"-shaped piece even though it is relatively large in area, has little effect of increasing the jointing strength. An improved soldering portion of an electrical connector is known from IBM Technical Disclosure Bulletin, Vol.21, no. 12, May 1979, New York, page 4805. The object of the present invention is to provide a surface-mounted component's contact having an improved soldering portion which is capable of preventing localized concentration of force in the soldering portion as is the case with a conventional "L"-shaped contact when pulled up, and is capable of minimizing the load per unit soldering area upon application of undesired external force to the contact, thereby preventing the fatigue failure or removal of the contact from the conductor, and assuring that sufficient jointing strength to the conductor is maintained at all times and that good electrical contact is kept at all times. To attain this object a surface-mounted component's contact having a soldering portion, according to the preamble of claim 1, is characterised by the features disclosed in the characterising portion of claim 1. The soldering portion of the contact has an extensive foot, and the soldering material will be applied over this extensive foot. When an undesired external force is applied to the contact, and hence the soldering skirt, the force will be distributed evenly over the extensive area of the contact foot, thus reducing the load per unit soldering area to possible minimum. In case that a strong pull is applied to the contact to raise it apart from the conductor, the force will be transmitted to the horizontal foot via the joint between the horizontal foot and the vertical leg of the contact, and will be evenly distributed in the surrounding soldering skirt in all directions thanks to the location of the joint in the midpoint of the foot. Thus, no fatigue failure will be caused in the soldering skirt, and the peeling-off of soldering material will be prevented. The inverted "T"-shape of the contact piece has the effect of holding the joint strength and electrical contact in good, reliable condition. The inverted "T"-shape of the contact piece permits the stamping-out of the contact from metal sheets. This assures that a metal piece has a strong joint between horizontal and vertical portions. One way of carrying out the present invention will now be described in detail by way of example with reference to drawings which show one specific embodiment. In the drawings: FIG. 1 is a plan view of an electrical contact assembly having an array of terminal structures according to the present invention; FIG. 2 is a front view of the electrical contact assembly; FIG. 3 is a perspective view of the electrical contact assembly with its midlength eliminated; FIG. 4 is an enlarged view of the portion of the contact assembly encircled and indicated by line A in Fig. 2; FIG. 5 is an enlarged sectional view of the portion of the contact assembly taken along the line B-B in Fig. 2 and seen from the direction as indicated by arrows; FIG. 6 is a sectional view showing the contact piece pair with its feet soldered to a conductor on a printed circuit board, said contact piece pair receiving and resiliently holding and contacting another printed circuit board between its contact arms; FIG. 7 is a perspective view of the portion at which the contact piece is soldered to a conductor; FIG. 8 is a similar perspective view, but showing the soldering of a conventional contact piece; and FIG. 9 is a similar perspective view, showing the soldering of another conventional contact piece. DESCRIPTION OF ILLUSTRATED EMBODIMENTS The present invention is described as being applied to an electrical connector. Figs. 1-5 show an electrical contact assembly having an array of terminal structures according to the present invention. As shown in these drawings, the electrical connector 1 comprises an elongated body 4 having extensions 2 and 3 integrally connected to the opposite ends of the elongated body 4. A plurality of terminals 11 according to the present invention are fixed to the elongated body 4 at regular intervals. As best seen from Fig. 5, each terminal 11 is integrally jointed to a counter terminal 11, and is fixed to the elongated body 4 to face the counter terminal 11. Particularly, referring to Figs. 5, 6 and 7, each terminal 11 comprises an inverted "T"-shaped soldering connecting portion 12, a trunk 13 integrally connected to the soldering connecting portion 12 and having an extended arm 16 to be inserted in a selected slot 15 of the elongated body 4 and a contact piece 14 integrally connected to the trunk 13. The terminal pair is a metal piece which is stamped out from a metal sheet. The inverted "T"-shaped soldering connecting portion 12 comprises a relatively large foot 17 and a leg 18 integrally connected to the foot 17 as indicated at 19 and rising from the foot 17. When in use, the foot 17 of each terminal 11 is soldered to a conductor on a printed circuit board 6 to joint the surface of the foot 17 to the surface of the conductor, as indicated at 21. The soldering metal is melted and is allowed to invade somewhat the gap remaining between the end surface 20 of the foot 17 and the conductor surface. When another circuit board 8 is inserted between the opposite extensions 2 and 3 of the elongated body 4, the contact 14 of each terminal 11 will be resiliently put in contact with a selected conductor on the printed circuit board 8. Likewise, the contact 14 of the counter terminal 11 will be sandwiched between these contacts 14. As already described, the foot 17 has a relatively large area. Assume that an undesired exterior force is applied to the contact 14 of the terminal 11 and that the force is transmitted to the soldering skirt 21 via the leg 18, thereby loading the soldering skirt 21. The load per soldering unit area of the foot will not be great because of the increased soldering area which surrounds the relatively large foot 17. When a printed circuit board 8 is inserted and then pulled up from the electrical connector 1, a raising force will be applied to the leg 18 of each terminal 11, and this force will be transmitted to the joint 19 between the leg 18 and the foot 17. The force will be distributed all the way from the mid-joint to each end 23 or 24 to evenly 20 stress the whole soldering skirt 21. This is because the leg 18 rises from the center 22 of the foot 17. The force cannot be localized to the portion of the soldering skirt 21 around the joint 19. The even distribution of an undesired force prevents fatigue failure of soldering at a localized point, and assures good mechanical and electrical connection. As described earlier, the terminal 11 is a metal piece stamped out from a metal sheet and therefore the foot-and-leg joint has an increased strength, compared with the one in which a separate leg is integrally connected to a separate foot. This particular embodiment is described as being applied to an electrical connector terminal but it should be understood that the present invention can be equally applied to lead wire terminals for carrier chips, switches, capacitors, resistors and any other components to be mounted to a printed circuit board. As may be understood from the above, the inverted "T"-shaped soldering portion of a terminal according to the present invention has a leg and a relatively large foot integrally connected to the center of the leg, thereby causing substantial reduction of load per unit soldering area upon application of an undesired force to the terminal, and increasing the resistivity of the soldering against removal from the conductor on a printed circuit board. The leg is integrally connected to the center of the foot, and therefore, an undesired external force when applied to the terminal will be transmitted to the foot and the surrounding soldering skirt so that the foot and the surrounding soldering skirt are evenly stressed, not localizing the force to particular points. Thus, the soldering strength will not be lowered, and the electrical connection will be kept in good condition. The terminal is a metal piece which is stamped out from a metal sheet. Therefore, the joint between the foot and the leg has an increased strength. This contributes the solidity with which the soldering portion of the terminal is fixed to the conductor on a printed circuit board.

Claims: Surface-mounted component's contact having a soldering portion, which contact is to be mounted to the surface of a printed circuit board (6) and is to be electrically connected to a conductor on said circuit board, said soldering portion (12) comprising an elongate flat foot (17) and a leg (18), which is integrally connected to and rising from the midportion of said foot (17), the cross section from the side view of the contact being thus substantially shaped in the form of an inverted "T", characterised in that said leg (18) and said foot (17) lie between two parallel planes, said planes being spaced apart by a distance equal to the thickness of both said leg and said foot. Surface-mounted component's contact according to claim 1 wherein said leg (18) is integrally connected to the midportion of said rectangular foot to rise upright therefrom, said leg (18) and said foot (17) having the same width in a direction perpendicular to said common plane. Surface-mounted component's contact according to claim 1 or 2 wherein said leg (18) is integrally connected to a trunk (13) which is integrally connected to a contact piece (14), thereby constituting together a terminal (11) of an electric connector. Surface-mounted component's contact according to claim 3 wherein said trunk (13) has an arm (16) extending parallel to said contact piece (14) and integrally connected to said trunk (13), said arm (16) being adapted to be inserted in a selected slot (15) of an elongated body (4). Surface-mounted component's contact according to claim 4 wherein said soldering portion (12) comprising said flat, rectangular foot (17) and said leg (18), said trunk (13), said contact piece (14) and said arm (16) are integrally connected together in a unitary form stamped out from a metal sheet. Surface-mounted component's contact according to claim 5 wherein a pair of terminals (11) each stamped out from a metal sheet are arranged with their contact pieces (14) facing each other at a predetermined interval, and their feet positioned relative to one another to be soldered to a conductor on said printed circuit board (6).

Inventors: YAMADA SHOJI, YAMADA TOMOO, YAMADA, SHOJI, YAMADA, TOMOO
Applicants: MOLEX INC, MOLEX INCORPORATED
Application year: 1989
Main classification: H01R23
IPC codes: H01R12, H05K1, H05K3, H01R33, H01R4