GB2309128A

GB2309128A - A cantilever spring contact

Info

Publication number: GB2309128A
Application number: GB9700408A
Authority: GB
Inventors: Klaus Mayer; Helmut Brantsch
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1996-01-12
Filing date: 1997-01-10
Publication date: 1997-07-16
Anticipated expiration: 2017-01-10
Also published as: KR970060577A; DE19600966C2; DE19600966A1; GB2309128B; KR100393241B1; GB9700408D0

Description

1 2309128 C2NTACT SPRING FOR ELECTRICALLY CONTACTING A COMPONENT The

invention relates to a contact spring for electrically contacting a component. An electrical contact, preferably with a battery or an accumulator, but also with other electrical components, is established by way of such a contact spring.

Contact springs are used in many electrical devices, preferably in mobile, battery-operated or accumulator-operated devices, such as, for example, portable computers, mobile telephones, portable electronic entertainment devices, clocks/wrist-watches or even hand-held transmitters, which are used, for example, to open a locking system of a motor vehicle or to open a garage door.

The component, which is to be contacted, advantageously is arranged close to an associated electrical circuit arrangement. It is known that the component can be set directly upon a copper contact surface of the associated circuit carrier. Such contacting is not, however, reliable, as even the smallest impurities on the contact surfaces of the component or of the circuit carrier can result in a break in the electrical contact or in an "intermittent contact". Mounting the component on the contact surface of the circuit carrier also has a disadvantageous effect upon the reliability of the electrical contacting of the component since even a slight slippage of the component or of the circuit carrier can bring about a break in the electrical contact.

Furthermore, a plug-in contact spring arranged between a circuit carrier and a component has been known for a long time. Such a contact spring is plugged with a holding arm into a bore in the circuit carrier. The holding arm is soldered together with circuit carrier on the rear side of the latter.

1 is Securement of the contact spring is effected manually or by means of a special automatic fitting machine. Fitting the circuit carrier with the known contact spring by means of a standard automatic SMD (Surface Mounting Device)-fitting machine is not possible.

The invention therefore seeks to avoid the disadvantages of the known concepts/arrangements for contacting components and to provide a contact spring which guarantees a reliable electrical contact with a component and has small dimensions so that it can also be used in electrical devices which have very small dimensions, such as hand-held transmitters. The invention also seeks to form the contact spring in such a way that it can be arranged and secured on a circuit carrier by means of a standard automatic SMD-fitting machine.

According to the present invention, there is provided a contact spring for electrically contacting a component, the contact spring having a base with a planar underside and having spring arms at least part of which project out of a plane defined by the base, so that a component, which is placed upon free end sections of the spring arms, is resiliently supported.

A preferred embodiment of the contact spring according to the invention contains a base plate from which a plurality of spring arms branch off. When such a contact spring is arranged on a circuit carrier, the base plate rests with its underside, which is formed so as to be planar, on the circuit carrier. At least one section of each spring arm extends obliquely upwards, out of the plane of the base plate. Placed upon free end sections of the spring arms there is, if required, a component, which is resiliently mounted so as to be perpendicular to the base plate, and in consequence of this form of mounting is reliably connected to the contact spring in an electrically conductive manner, 1 even in the case of relative movement or play between the component and the circuit carrier or between the contact spring and the component. The contact spring can be arranged on a circuit carrier by means of a standard automatic SMD-fitting machine. In this connection, a vacuum pipette of the automatic SMDfitting machine is positioned on the upper side of the base plate and the contact spring drawn up by auction is set down with its underside on a contact surface of the circuit carrier, which surface is coated with a solder paste. A soldered connection between the circuit carrier and the contact spring is established by means of an infrared soldering tool of the automatic SMD-fitting machine.

The contact spring preferably has holding arms which project out of the plane of the base plate but which contain a portion which is arranged in the plane of the base plate. By means of these holding arms, the contact spring is supported, when secured on a circuit carrier, against the latter and cannot tilt. Furthermore, the holding arms present points of attachment for securing the contact spring to the circuit carrier. A soldered connection for the purposes of mechanical securement can be provided between the holding arms and the contact surfaces of the circuit carrier, which soldered connection can also be simultaneously used for the electrically conductive connection between the contact spring and the circuit carrier.

In a base plate that has small dimensions, the holding arms are used in particular to provide points of attachment for a soldered connection with the circuit carrier, which points are at the greatest possible distance from the spring arms and in particular from the points at which the latter emerge from the plane of the base plate. If the base plate 1 provides the points of attachment, there is a great risk that the spring arms will become contaminated with solder paste, in particular at the points at which they emerge from the plane of the base plate, or even that they will in part be soldered onto the circuit carrier. This would impair the spring force of the spring arms and thus the reliability of the electrical contacting of the component. Thirdly, as a result of the holding arms a stable position of the contact spring that is required for a reliable contact with the component is effected, even given the effect of force on the contact spring which is secured to the circuit carrier.

If a free end section of each holding arm is provided with a layer of tin on its underside, the contact spring can be mechanically and electrically connected to a circuit carrier by way of soldered connections between these free end sections of the holding arms and contact surfaces on said circuit carrier. In the case of this advantageous further development of the invention, the points of attachment are thus arranged on the free end sections of the holding arms and are arranged on the holding arms far away from the spring arms and the points at which the latter emerge from the base plate, this resulting in the afore-mentioned advantages.

Such provision of points of attachment as a result of fitting the holding arms on the base plate or preparation of a soldered connection as a result of applying the layer of tin at these points of attachment - namely the free end sections of the holding arms---is advantageous if the base plate, the spring arms and also the holding arms are formed in one piece and the spring arms are guided in particular laterally out of the base plate.

The one-piece formation of the base plate with the spring arms and the holding arms is advantageous, as 1 the whole contact spring can be stamped, for example, out of a chromium- nickel spring steel sheet in one production step and thereupon merely the spring arms need to be bent obliquely upwards. As a result of applying a layer of tin at least to the underside of the free end sections of the holding arms, preparations are made for a soldered connection at these points. For reasons of economy in terms of production, it is also possible to coat the whole underside of the securement arms and the base plate with tin.

If the holding arms of the contact spring are formed in such a way that initial sections.- which are arranged close to the base plate, have a smaller crosssectional area than the free end sections, by way of which the contact spring is soldered, for example, to a circuit carrier, during the soldering process as little heat as possible is transferred to the base plate and the spring arms of the contact spring.

The free end section of each holding arm is preferably bent off obliquely upwards, relative to the plane of the base plate. During a soldering process there thus develop between the free end section of the holding arm and a contact surface of the circuit carrier a soldering cone and with that a soldered connection which is of a high grade in terms of quality and is durable and which can also be checked visually in an advantageous manner for possible breakage points.

The contact spring is preferably formed in an axially symmetrical manner so that the contact spring is aligned by means of a gripper tool of the automatic SMD-fitting machine, after it (the spring) has been removed from a delivery belt with the aid of a vacuum pipette. In this aligned position, the contact spring is arranged on the circuit carrier. The contact spring preferably contains at least two holding arms which are arranged on opposing sides of the base plate so that is the gripper tool can act on the free end sections of' the holding arms.

The free end sections of the spring arms are preferably arranged such that their projection into the plane of the base plate falls outside the base plate. In this way, the contact spring can be compressed to the thickness of the sheet-metal by means of the component. With this development, the overall height of the contact spring is kept low whilst providing a maximum spring range.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 shows a contact spring according to the invention, in a perspective view obliquely from abovei; Figure 2 shows the contact spring of Figure 1 on a circuit carrier, in a perspective view obliquely from above; Figure 3 shows the contact spring of Figure 1, in a perspective view obliquely from below; and Figure 4 shows a holding arm of a contact spring on a circuit carrier, in a longitudinal section.

Identical elements in the figures have the same reference numerals.

Figure 1 shows a contact spring according to the invention having a base plate 1, four spring arms 2 which are formed in one piece with the base plate 1, with each spring arm 2 having at least one section 21 which is directed obliquely upwards - relative to a plane E defined by the base plate 1 - and also a freoi end section 22. Four triangular holding arms 3 are also formed in one piece with the base plate 1 and together with the base plate 1 form a planar surface. The holding arms 3 are arranged so as to be staggered relative to each other by, in each case, 90 degrees, as is are the spring arms 2. Alternately one spring arm 2. and/or one holding arm 3 may be provided on the base plate 1. The contact spring is axially symmetrical. A component, for example a battery, is laid upon the free end sections 22 of the spring arms. This exemplary embodiment allows there to be very good stable mounting and contacting of the component on/with the contact spring on account of the four spring arms 2, a very good stable position of the contact spring on a circuit carrier on account of the four holding arms 3, and soldered connections with a circuit carrier at the free end sections of the holding arms 3, without the spring arms 2 being soldered onto the circuit carrier as well, and allows a circuit carrier to be fitted with the contact spring by means of an automatic SMD-fitting machine.

Figure 2 shows the contact spring according to Figure 1 arranged on a circuit carrier 4. In this connection, the contact spring lies with the undersides of the holding arms 3 and the underside of the base plate 1 on the circuit carrier. Soldering cones 41 at the free end sections 33 of the holding arms 3 are indicated. Initial sections 31 of the holding arms 3 have a smaller cross-sectional area than the free end sections 33 of the holding arms 3.

Figure 3 shows the contact spring according to the invention in accordance with Figure 1, in a perspective view obliquely from below. In this connection, in particular the one-piece development of the holding arms 3 with the base plate 1 can be seen, as can the planar supporting surface, consisting of the undersi1es 31 of the holding arms 3 and the underside 11 of the base plate 1, which guarantees stable support of the contact spring on a circuit carrier.

Figure 4 is a longitudinal section through a holding arm 3 with a bentoff free end section 33, with the contact spring being arranged with a section 32 of this holding arm 3 on a circuit carrier 4. Applied to the underside 34 of the free end section 33 there is a layer of tin 35 which, by way of the soldering cone 41, establishes a soldered connection with the contact surface 42 of the circuit carrier 4.

In order to contact a component in a reliable manner and in order to apply the necessary contact pressure to the component, the contact spring preferably has three, four or more spring arms. However, if the component is held in a defined position by a carrier, even one or two spring arms will suffice.

is

Claims

1. A contact spring for electrically contacting a component, the contact spring having a base plate with a planar underside and having spring arms at least part of which project out of a plane defined by the base plate so that a component, which is placed upon free end sections of the spring arms, is resiliently supported.

2. A contact spring according to claim 1, having holding arms which project from the base plate and which have a section which is arranged in the plane of the base plate.

3. A contact spring according to claim 2, wherein each holding arm has a layer of tin on the underside of at least its free end section.

4. A contact spring according to claim 2 or 3, wherein the free end section of each holding arm is bent off obliquely upwards relative to the plane of the base plate.

5. A contact spring according to any one of claims 2 to 4, wherein each holding arm has a smaller cross-sectional are.. in its initial section close to the base plate than in its free end section.

6. A contact spring according to any one of claims 2 to 5, wherein the spring arms and the holding arms are formed in one piece with the base plate and are guided laterally out of the base plate.

7. A contact spring according to any one of the preceding claims, which is formed in an axially symmetrical manner.

8. A contact spring according to claim 7, having two holding arms which are guided out of the base plate on opposing sides of the base plate.

9. A contact spring according to any one of the preceding claims, wherein, if the spring arms are projected onto the plane defined by the base plate, the free end sections of the spring arms are arranged outside the base plate.

10. A circuit carrier on which a contact spring according to any one of the preceding claims is arranged, wherein the contact spring is connected to the circuit carrier by way of soldered connections at the free end sections of the holding arms.

11. A contact spring substantially as described herein, with reference to and as shown in Figures 1 to 3 or Figure 4 of the accompanying drawings.