GB2390755A

GB2390755A - Spring terminal

Info

Publication number: GB2390755A
Application number: GB0216110A
Authority: GB
Inventors: Ken Taylor
Original assignee: ITT Manufacturing Enterprises LLC
Current assignee: ITT Manufacturing Enterprises LLC
Priority date: 2002-07-11
Filing date: 2002-07-11
Publication date: 2004-01-14
Also published as: EP1381116A1; DE60220266T2; DE60220266D1; GB0216110D0; ATE363136T1; EP1381116B1

Abstract

A spring terminal 1 for mounting on a printed circuit board comprises a base strip 3 and a contact strip 5 extending from a fold region and defining a gap 43 between the strips 3,5. Blocking members 7,13,15 integrally formed from the same sheet as the sprung terminal impede access to the gap 43. In addition, the terminal has flaps 19,21 closing a gap at the end of the terminal, and fingers 23,25 restraining the contact strip so that the contact strip may be preloaded.

Description

Sprung Electrical Terminal This invention relates to electrical terminals,

and in particular to sprung electrical terminals for mounting on 5 printed circuit boards.

Electronic devices commonly have terminals for making electrically conductive paths between two components. Often, one of the two components is a printed circuit board, to 10 which the terminal is soldered, and the other component has contact pads which are urged against the terminal.

For example, the casing of a wireless communication device such as a twoway radio or mobile telephone may 15 comprise first and second lateral halves, with a printed circuit board assembled into the first half and components including a microphone, antennae or battery assembled into the second half. When the halves are mated, contact pads on the components in the second half are urged against terminals zo on the printed circuit board in the first half to make electrically conductive paths. Terminals are also used on the printed circuit boards of mobile telephones to make electrical contact with removable SIM (subscriber identity module) cards.

2s A known form of terminal is the sprung terminal.

Applying a force to a contact strip of the terminal displaces it, wherein the displacement is dependent on the magnitude of the force applied. A sprung terminal can provide a robust 30 and reliable electrical connection between a printed circuit board and a mating contact pad because, if a contact strip of the terminal is displaced, it reacts on the mating contact pad with a corresponding nominal force. A sprung terminal can also maintain the electrical connection between the

printed circuit board and mating contact pad of assemblies that have dimensional tolerances or are moving. This is because, if the contact strip is displaced, the tolerances or movement can either increase or reduce the displacement of 5 the contact strip without breaking the electrical connection with the contact pad.

Conventional sprung terminals are made from a strip of resilient, usually metallic, conductive material formed into lo a generally C-shaped configuration to provide two strips extending from a fold region. The first strip of the sprung i terminal is a base strip, which is soldered to a printed circuit board. The second strip of the sprung terminal is a contact strip, against which the contact pads of mating 15 components are urged. As a consequence of the resilience of the material, the contact strip acts as a spring when loaded in a direction normal to the plane of the printed circuit board. 20 The generally C-shaped cross-section of sprung terminals usually has complicated local geometry. For example, the contact strip of terminals often has an arcuately formed projection for making point contact with a mating contact pad. Sprung terminals may have a preloaded contact strip.

The primary advantage of a preloaded contact strip is that its displacement can give rise to Large reactive forces over relatively small displacements. The base strip of terminals 30 with preloaded contact strips is extended at its end to form a generally O-shaped cross-section. The extension to the base is perpendicular and engages the contact strip, acting on it to limit its travel in one direction. In its engaged condition, the contact strip is preloaded.

A problem associated with sprung terminals is that they tend to become tangled when loosely packaged together. The manual untangling of loosely packaged sprung terminals is a S time consuming task and their tendency to tangle effectively precludes the use of automated part loading on the assembly lines of devices that use them. A second problem associated with spring terminals is that interference between loosely packaged terminals during transit can cause their fragile 10 contact strips to become damaged, especially those that are preloaded in the manner described above.

There is thus a need for an improved sprung terminal that is less susceptible to tangling and damage.

According to the invention there is provided a sprung terminal formed from a single sheet of resilient material comprising: a base strip; a contact strip; a resilient fold region joining one end of the base strip to one end of the 20 contact strip, the base strip and the contact strip extending I longitudinally from the fold region, the base and contact strips defining a gap therebetween and further defining laterally opposed side faces of the gap, each side face extending between the corresponding sides of the base and 25 contact strips; and a pair of laterally opposed side flaps extending in the plane of one of the side faces transversely across the gap, the side flaps depending from laterally opposite sides of the base strip.

30 By providing flaps that impede access to the gap defined between the base and contact strips, the sprung terminals cannot become knitted and tangled when loosely packaged.

The sprung terminal is formed from a single blank of sheet material in order to minimize manufacturing costs.

The side flaps may also protect the delicate contact 5 strip of the sprung terminal from damage.

To block the end of the gap, a pair of end flaps may be provided, depending from the opposed side flaps, blocking the gap at the other end of the base and contact strips to the 10 fold region. The end flaps also assist in preventing other components from hooking up the contact strip and lifting the strip to cause damage.

The sprung terminal may further include a pair of 15 fingers extending laterally inwardly from respective side flaps, the contact strip being resiliently biased away from the base strip against the fingers. This allows the contact strip to be preloaded, i.e. to be resiliently biased in the initial position. This reduces the deformation of the 20 contact strip required, in use, to provide a particular force I on the contact strip, which in turn allows a better contact for small deformation. By preloading the contact strip from each of its sides, it is less prone to becoming damaged or twisted. In embodiments, at least one blocking element is a bent region of one of the base or contact strips bent into the gap towards the other of the base or contact strips, the bent region laterally spanning the gap between opposed side faces.

30 Such bent regions are particularly suitable as blocking elements near the fold regions where side flaps may interfere with the movement of the strips.

In embodiments, the sprung terminal may be of nickel plated beryllium copper alloy.

The contact strip may include a contact protrusion for 5 making contact with mating electrical components, the protrusion projecting away from the base strip. The contact protrusion optimizes the electrically conductive path to mating contact pads and allows the contact strip to stand proud of the side and end members. The external surface of 10 the contact protrusion may be gold plated.

The base strip may define at least one external contact region and the external surface of the contact protrusion and of the at least one external contact region may be gold 15 plated.

The invention also relates to a wireless communication device comprising at Least one sprung terminal as set out above. According to another aspect of the invention there is provided a sprung terminal comprising: a base strip; a contact strip; a resilient fold region joining one end of the base strip to one end of the contact strip, the base strip 25 and the contact strip extending longitudinally from the fold region of the strip, the base and contact strips defining a gap therebetween and further defining laterally opposed side faces of the gap, each side face extending between the corresponding sides of the base and contact strips; and a 30 plurality of blocking elements impeding another like sprung terminal from entering the gap through the side faces anywhere along the length of the side faces.

The blocking elements may include at least one side flap depending from one of the base or contact strips extending in the plane of one of the side faces transversely across the gap. Preferably, a pair of laterally opposed side flaps 5 depend from opposite sides of the base strip. In this way, the gap may be substantially blocked.

In another aspect, the invention relates to a method of forming a sprung terminal, including: forming a flat blank 10 from a sheet of resilient material to have a base strip and a contact strip longitudinally separated by a fold region, side flaps depending from the base strip and fingers depending from the side flaps; plating part of the base strip and part of the contact strip to define plated contact areas; folding 15 the side flaps to be perpendicular to the base strip; folding the fingers inwardly from the side flaps; and folding back the contact region to be resiliently biased against the fingers such that the plated contact areas are on the external surface of the base and contact strips.

The invention will now be described further with reference to the following drawings in which: Figure l shows a preferred embodiment of the invention; Figure 2 shows the shape of a single blank from which the preferred embodiment of the invention may be formed; Figure 3 shows a mobile phone comprising a plurality of 30 sprung terminals according to the invention; and Figure 4 shows a further use of a sprung terminal according to the invention.

Figure 1 shows a preferred embodiment of the sprung terminal 1. The sprung terminal 1 comprises a base strip 3, for soldering to a printed circuit board, and a resiliently biased contact strip 5, against which a mating contact pad of 5 another component is urged. The base strip 3 and contact strip 5 are formed from a resilient strip of nickel plated berillium copper alloy sheet and extend longitudinally from a fold region 9.

10 The base strip 3 and contact strip 5 define a gap 41 therebetween. The notional planes 43,45 extending between the lateral edges of the strips 3, 5 transversely across the gap 41 at the sides of the gap are referred to in this specification as side faces 43,45.

The base strip includes a bent region 7 which projects towards the contact strip 5 and is located near the fold region 9. The bent region 7 acts as a blocking region to impede objects such as other sprung terminals from entering 20 the gap 41 through the side faces 43,45 near the fold region 9 and becoming tangled.

The contact strip 5 includes a gold plated contact protrusion 11 located at its distal end. The contact 25 protrusion 11 projects away from the base strip 3. The gold plating forms a contact area 55 on the contact strip. The contact protrusion 11 provides a point contact against which a mating contact pad is urged, and ensures that the point contact stands proud of the rest of the sprung terminal 1. A 30 further gold plated contact area 53 (Figures 2,4) is formed on the underside of the base strip.

The sprung terminal 1 further comprises two laterally opposed side flaps 13, 15 which depend from the laterally

opposite sides of the base strip 3. The side flaps extend transversely across the gap 41 along part of the side faces 43, 45 and block other components entering the gap 41 through the side faces 43,45. The side flaps 13, 15 are formed from S the same piece of material that forms the base strip 3 and contact strip 5.

An end member 17 is formed from end flaps in the form of wing extensions 19, 21 to the side flaps 13,15 depending from 10 the distal ends of the side flaps. The wings 19,21 laterally span the gap 41 at the distal end of the gap. The side flaps 13, 15 and end member 17 impede the passage of objects into the gap 41 between the base strip 3 and contact strip 5, thus reducing tangling between a plurality of the sprung terminals 15 1 while loosely packaged. Furthermore, the side flaps 13, 15 and end member 17 provide some protection to the contact strip S and help to prevent it from becoming damaged, particularly damage caused by other components hooking under the contact strip and bending or twisting it.

The side flaps 13, 15 of the sprung terminal 1 have fingers 23, 25 that protrude towards each other in a direction perpendicular to the plane of the surface of the side flaps 13, 15. The fingers 23, 25 engage the contact 25 strip 5 to limit its movement. The fingers 23, 25 also act on the upper surface of the contact strip 5 to preload it.

The use of two fingers 23, 25, one on either side flap 13, 15 improves the balance of the preloaded contact strip 5 and reduces its susceptibility to twisting.

Figure 2 shows the shape of a single blank 39 from which the preferred embodiment of the sprung terminal 1 may be formed. The area 27 enclosed by dashed lines forms the base strip of the sprung terminal 1. Area 33 extends

longitudinally from area 27, for forming the contact strip 5.

Side flap 13 and side flap 15 are formed from the areas 29 and 31 which are joined to and arranged on either side of area 27. End regions 49, 51 and finger regions 35, 37 depend 5 from areas 29,31.

To form the sprung terminal, gold is plated onto contact areas 53,55. It will be noted that it is only necessary to plate on one side of the blank 39. The strip 33 is folded to 10 form the contact strip, with both contact areas 53, 55 facing outwards, and held in a preloaded condition. The areas 35,37 are folded to form fingers 23, 25, end regions 49, 51 are folded to form end flaps 19, 21 and the areas 29 folded down to form the side flaps 13,15. The fingers 23,25, end flaps 15 19, 21 and side flaps 13,15 may be folded in a single operation or in any order.

Figure 3 shows a mobile phone 47 that comprises a plurality of the sprung terminals 1. The sprung terminals 1 20 are used to provide electrical connections to the contact pads of a SIM card or rechargeable battery (not shown).

Figure 4 shows an alternative use of the sprung terminal 1. A sprung terminal 1 is mounted proud of a PCB 63 with the z5 gold contact area 53 of its base strip 3 soldered to a conductive track 65 on the PCB.

A device 61, for example a vibrator, microphone, speaker, antenna, or battery, is mounted in a mating housing 30 67, the mating housing defining a mating pad 69. When the mating housing 67 is brought into alignment with the PCB 63, for example by bringing two halves of a housing together, the mating pad 69 is brought into contact with the contact protrusion 11. This allows the device 61 to be connected to

the PCB without requiring the device or the housing 67 to be provided with its own integral sprung contacts. Since the PCB 63 needs to be populated with other components, adding one or more sprung terminals l to the PCB causes little 5 increase in manufacturing difficulty.

The invention is not limited to mobile telephone applications. Indeed, the sprung terminal can be applied to interconnect a variety of devices. Sprung terminals 10 according to the invention offer a flexible modular approach to PCB layout and component infrastructure.

The embodiments of the invention described using the drawings are purely preferred, and described by way of 15 example only. It will be apparent to one skilled in the art that there are many other embodiments of the invention not described. For example, the fingers that protrude from the side flaps of the sprung terminal may take the form of any type of protrusion capable of acting on, and preloading the 20 contact strip. It may be possible to provide different arrangements of blocking elements, for example the bent region 7 may be omitted in an arrangement with larger side flaps. The sprung terminal may be manufactured from any resilient conductive material, including copper beryllium 25 alloy substitutes. In some circumstances it may not be !necessary to preload the contact strip; in these circumstances fingers 23, 25 are unnecessary. Further, the form of fingers 23, 25 can be varied significantly

Claims

1. A sprung terminal formed from a single sheet of resilient material comprising: 5 a base strip; a contact strip; a resilient fold region joining one end of the base strip to one end of the contact strip, the base strip and the contact strip extending longitudinally from the fold region, 10 the base and contact strips defining a gap therebetween and further defining laterally opposed side faces of the gap, each side face extending between the corresponding sides of the base and contact strips; and a pair of laterally opposed side flaps extending in the 15 plane of one of the side faces transversely across the gap, the side flaps depending from laterally opposite sides of the base strip.

2. The sprung terminal of claim 1, further comprising a 20 pair of end flaps depending from the opposed side flaps blocking the gap at the other end of the base and contact strips-to the fold region.

3. The sprung terminal of claim 1 or 2, further comprising 25 a pair of fingers extending laterally inwardly from respective side flaps, the contact strip being resiliently biased away from the base strip against the fingers.

4. The sprung terminal of any preceding claim, including a 30 bent region of one of the base or contact strips bent into the gap towards the other of the base or contact strips, the bent region laterally spanning the gap between opposed side faces.

5. The sprung terminal of any preceding claim, wherein the sprung terminal is of nickel plated beryllium copper alloy.

6. The sprung terminal of any preceding claim, wherein the 5 contact strip comprises a contact protrusion for making contact with mating electrical components, the protrusion projecting away from the base strip.

7. The sprung terminal of claim 6, wherein the base strip lo defines at least one external contact and wherein the external surface of the contact protrusion and of the at least one external contact area are gold plated.

8. A sprung terminal comprising: IS a base strip; a contact strip; a fold region joining one end of the base strip to one end of the contact strip, the base strip and the contact strip extending longitudinally from the fold region of the -20 strip, the base and contact strips defining a gap therebetween and further defining laterally opposed side faces of the gap, each side face extending between the corresponding sides of the base and contact strips; and a plurality of blocking elements impeding another like 25 sprung terminal from entering the gap through the side faces anywhere along the length of the side faces.

9. The sprung terminal of claim 8, comprising a pair of laterally opposed side flaps depending from opposite sides of 30 the base strip, the side flaps extending transversely across the gap.

10. A wireless communication device comprising at least one sprung terminal according to any of the preceding claims.

11. A method of forming a sprung terminal, including: forming a flat blank from a sheet of resilient material to have a base strip and a contact strip longitudinally 5 separated by a fold region, side flaps depending from the base strip and fingers depending from the side flaps; plating part of the base strip and part of the contact strip to define plated contact areas; folding the side flaps to be perpendicular to the base 10 strip; folding the contact region such that the plated contact areas are on the external surface of the base and contact strips; and folding the fingers inwardly from the side flaps.

12. A sprung terminal substantially as hereinbefore described with reference to and as shown in the accompanying drawings.