Electrical switch, of the normally-closed type, especially for a portable communication device

The switch includes a printed circuit, of generally plane shape, and comprising a first face bearing a first contact pad, a second face, opposite the first, bearing a second contact pad, and a through-orifice allowing access between the first face and the second face. The switch also includes a conductor, having a first part, which cooperates with the first contact pad, and a second part, which extends between a first end, fixed to the first part, and a free second end, passing through the orifice. The second part is elastically deformable between a rest position, in which its second end cooperates with the second contact pad, and a stressed position, in which its second end is moved away from the second contact pad.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of International Application PCT/FR2011/051196 filed May 26, 2011. The PCT application published as WO 2011/148105 on Dec. 1, 2011. The PCT application claims priority to French Application No. 1002193 filed on May 26, 2010 and French application Ser. No. 10/05040 filed Dec. 22, 2010. The present application claims priority to and incorporates by reference all of the above applications.

The present invention relates to an electrical push button switch, of the normally closed type, in particular intended for use with the keypad of a portable communication device. The invention also relates to the manufacture of a flexible electrical contact keypad of the normally closed type, the corresponding flexible keypad, the key and contact strip.

It should be reminded that a switch may flip between a closed position in which it allows an electric current to pass, and an open position, in which it interrupts the flow or passage of this electric current. A push button switch is said to be of the normally closed type when it is brought back to its closed position in the absence of external stress, and when it passes into its open position when actuated by a user, particularly by means of the push button.

The current membrane keypads that are extremely fine and inexpensive are manufactured by printing silver based conductive ink tracks on plastic substrates in order to create extra fine circuits.

The keys of the keypad thus formed are all executed according to the same principle: at least two tracks are arranged facing one another and are contacted when the key is pressed. These keys are therefore normally open type electrical contact keys.

The electrically conductive member that enables the contacting is, as appropriate, either a metal cup forming a cup contact, or a silver dot printed on the back of the upper circuit or the back of the decorative face placed on the circuit. This type of contact is thus designated as comb contact with flat or thermoformed front face.

The above techniques enable the production of membrane keypads, which have reduced thicknesses of the order of 1 to 1.5 mm, or in the most elaborate cases, even of 0.6 to 0.7 mm.

The development of the aforementioned techniques has made it possible, more recently to integrate extra fine components into membrane keypads, components such as light emitting diodes LED or small resistors, whose thickness of the order of 0.5 mm allows their integration in these fabrications.

However, when the use of more complex components appears to be necessary, it is imperative to change the technology. Larger circuits are then most often bonded on to machined metal plates, which are used to support the integration of buttons, switches, emergency stop buttons or other elements.

When integrators of such circuits or keypads wish to take advantage in this type of circuit or keypad of one or more normally closed type electric contact keys, in which two or more conductive tracks are in permanent contact, the action of an operator on one of the keys serving to open the contact, it is now necessary to either integrate buttons that are bulky and constraining in terms of implementation costs, or to introduce electronic management of this type of contact, which many integrators do not want to or cannot execute.

For example, from the technical state of the art, in particular from EP 0 793 246, an electric push button switch, of the normally closed type is already known. Such a switch conventionally comprises a printed circuit, comprising first and second contact pads, and an electrical conductor for electrically connecting the first and second contact pads.

Such a switch of the normally closed type has numerous elements, and therefore is particularly costly and complex to implement. Moreover, on account of its complexity and size, such a switch is not generally suitable for the keypad of a portable communication device.

The present invention aims to overcome these drawbacks by providing an electric push button switch, of the normally closed type, having a structure that is simple, economical and compact.

Specifically, the invention relates in particular to the implementation of a process for the manufacture of a flexible electrical contact keypad of the normally closed type, of a normally closed type contact key and a keypad having at least one such key, while retaining the advantages inherent in the flexible keypad technology, namely:maintaining a very thin keypad, its thickness not exceeding 1 to 1.5 mm, according to the construction;conservation of the operating principle of cup or thermoformed keys that are used in membrane keypads at the present time;maintaining a manufacturing cost structure that is competitive and compatible with the specifications of existing markets that are seeking quality products at low costs;obtaining a type of key that can function hundreds of thousands of times, or more, without any reasonably foreseeable problems;making available a semi finished product that is easy to implement for integrators without additional constraints related to adaptation of their working methodsproducing a final product, that is a flexible membrane keypad, durable enough to withstand sometimes difficult conditions of use such as vibration, shock or other conditions.

An object of the present invention is in particular the implementation of a method for the manufacture of a flexible membrane keypad comprising of at least one normally closed type contact key.

This method is remarkable in that it consists at minimum, of equipping the keypad with at least one circuit board printed on both sides comprising of at least one front contact face and one back contact face; of providing in the printed circuit, between the front contact face and the back contact face, an insertion slot; of inserting into the slot one flexible conducting strip forming a normally closed electrical contact between the front contact face and the back contact face, this flexible conducting strip having a pressure point so as to enable the exertion of a force for breaking the normally closed electrical contact.

Advantageously, the flexible conducting strip comprises of a flexible center tab that includes the pressure point, which is electrically and mechanically joined and adjacent to a first side tab and a second side tab by a common point, the first and the second side tabs being placed in one and the same plane and the center tab being arranged in an offset position in an orthogonal direction to said plane so as to form a first and a second insertion space for inserting the flexible strip in the slot, the operation consisting of inserting includes at least one step consisting of inserting said flexible strip into the slot by clipping of the first and second insertion space on the opposite edges of the slot, in a manner so as to bring the flexible center tab to rest and respectively at least one of the first or second side tabs in electrical contact with the back contact face and respectively the front contact face or vice versa.

Preferably, the pressure point provided on the center tab is placed in distant offset position on the center tab in relation to the common point so as to form a cross-force lever between the contact point of the center tab on the back or front contact face and the common point.

Another object of the present invention is the implementation of a flexible contact strip of normally closed type for the double sided printed circuit board.

Such a flexible contact strip is remarkable in that it comprises at least one flexible center tab, and a first side tab and a second side tab that are electrically and mechanically joined to the same common point. The electrically and mechanically joined first side tab and second side tab are substantially placed in the same plane, laterally adjacent to the flexible center tab. The center tab is arranged in offset position in an orthogonal direction to the plane so as to form a first and a second insertion space for inserting the printed circuit board that is provided with one slot and at least one front contact face and one back contact face each disposed in the vicinity of one of the two opposite edges of the slot.

Advantageously, the contact face of the flexible center tab is formed by a boss, and, optionally, the contact faces of the first side tab and the second side tab are also formed by a boss.

Preferably, the flexible center tab is offset at rest in an oblique plane in relation to the plane containing the first flexible side tab and the second flexible side tab to form by opposite constrained rotation of the flexible center tab, the first and second insertion spaces of the printed circuit board between this flexible center tab and the first and second side tabs, respectively.

Advantageously, the strip has been derived from the cutting/stamping of a sheet of conductive material.

Another object of the present invention is the implementation of a contact key for the flexible membrane keypad, such a contact key being remarkable in that it comprises of at least one printed circuit board provided with at least one front contact face and one back contact face, each placed in the vicinity of one of the opposite edges of a slot provided in the printed circuit board, and a flexible contact strip according to the invention inserted into the slot and forming a normally closed electrical contact between the front contact face and the back contact face. The flexible strip includes a pressure point for enabling the exertion of a force for breaking the normally closed electrical contact.

Advantageously, the pressure point can be actuated by pressure on a cup or a touch pad disposed over it.

The invention also relates to a flexible membrane keypad having at least one corresponding key and/or one flexible contact strip of the normally closed type.

The manufacturing process, the corresponding keypad and the normally closed type electrical contact key, objects of the invention, find application in the manufacture of keypads of all sizes, in particular small size keypads for mobile portable phone devices, personal digital assistants (PDAs) and keypads and keyboards of larger dimensions such as keypads and keyboards for laptops or desk top computers, musical instruments or the like.

The invention also relates to an electrical push button switch, of the normally closed type, in particular intended for a portable communication device keypad, comprising of:a printed circuit board, including first and second contact pads, andan electrical conductor, designed for electrically connecting the first and second contact pads,

characterised in that:the printed circuit has at least locally a generally plane shape and comprises of a first face bearing a first contact pad, a second face, opposite the first, bearing a second contact pad, and a through-orifice allowing access between the first face and the second face,the conductor comprises of a first part, which cooperates with the first contact pad, andthe conductor comprises of a second part, which extends between a first end, fixed to the first part, and a free second end, passing through the orifice, the second part is elastically deformable between a rest position, in which its second end cooperates with the second contact pad, and a stressed position, in which its second end is moved away from the second contact pad.

Such a switch has a particularly simple structure, wherein the conductor cooperates with the two contact pads without any intermediary and for which it is sufficient to apply a force on the second part of the conductor in order to move this second part away from the second contact pad, and thus open the switch.

Such simplicity of structure is possible in particular thanks to the contact pads arranged on the opposite faces of the printed circuit.

In an optional manner, an electric switch according to the invention may include one or more of the following characteristics, taken alone or based on any of the technically feasible combinations:the switch comprises of a metal cup pusher, accessible from the side of the first face of the printed circuit, and movable between a rest position, in which the second part of the conductor is in its rest position, and an engaged position, in which the metal cup cooperates with the second part of the conductor in order to keep it in its stressed position,the second part of the conductor has a boss provided between its first and second ends, meant for cooperating with the metal cup when the metal cup is in its engaged position,the first part of the conductor comprises of two branches and a base, so as to have a U-shape, the two branches being arranged on either side of the orifice of the printed circuit,the second part of the conductor forms a small strip extending the base of the first part, and extending longitudinally between the two branches of the first part,the first and second parts are formed integrally, with the conductor for example, being of sheet metal, andthe switch comprises of means for backlighting, arranged on the side the second face of the printed circuit, andthe switch includes sealing means covering at least the metal cup and the conductor.

In the above mentioned figures the relative proportions of the elements have not necessarily been respected, so as not to affect the overall clarity of the illustrations.

The method of manufacturing a flexible membrane keypad according to the object of the present invention is now described in a detailed manner in connection withFIGS. 1ato1d.

In step1, shown inFIG. 1a, the method according to the invention consists in providing and equipping the keypad with at least one double sided printed circuit board CI comprising of at least one front contact face PR and one back contact face PV.

The double sided printed circuit board CI can be formed by a printed circuit board of any type, a double faced circuit or otherwise.

Step1is followed by a step2, shown inFIG. 1b, consisting of providing, in the printed circuit CI, between the front contact face PR and the back contact face PV, an insertion slot. Preferably, but without being limited thereto, the insertion slot F is formed by a slot with parallel edges, going through the entire thickness of the printed circuit board CI.

Step2is followed by a step3comprising of a sub step3(1), shown inFIG. 1c, consisting of inserting in the insertion slot F one flexible conducting strip LS forming a normally closed electric contact between the front contact face PR and the back contact face PV.

As further shown in the drawings, the flexible strip LS has a pressure point PA that enables the exertion of a force for breaking the normally closed electrical contact.

Moreover, in sub step3(2), represented inFIG. 1d, in a cross sectional view along the AA sectional plane of the printed circuit board CI ofFIG. 1c, the normally closed electrical contact type contact key obtained upon insertion of the flexible strip LS has been shown. It is understood, in particular, that the insertion operation consists of introducing the flexible strip LS by clipping, or by any other means, on each of the parallel edges of the slot F, as will be described below.

For this purpose, during step3(1) shown inFIG. 1c, the flexible strip LS may include, preferably, a flexible center tab LC including the pressure point PA, to which is electrically and mechanically joined by a common point PC, and a first side tab LL1and a second side tab LL2. The flexible center tab LC is adjacent and parallel to the first side tab and the second side tab LL1and LL2and joined to the latter by the common point PC. Preferably, the first and second side tabs LL1and LL2are placed substantially in the same plane P but the center tab LC is arranged in an offset position in an orthogonal direction to said plane P, in order to form a first insertion space EI1and a second insertion space EI2, each included between the second flexible tab LC and the opposite ends of the two side tabs LL1and LL2.

It is thus understood that, in step3(1) shown inFIG. 1c, the operation of insertion of the flexible strip LS in the slot F is carried out by insertion and clipping of respectively the first insertion space EL1and the second insertion space EL2on one of the opposite edges of the slot F, in a manner so as to bring to rest the center tab LC, respectively the two side tabs LLl and LL2electrically contacting respectively the back contact face PV and the front contact face PR or vice versa.

Finally it can thus also be observed inFIG. 1, that the pressure point PA provided on the center tab LC is placed in distant offset position on the center tab in relation to the common point PC so as to form a cross-force lever between the contact point of the first center tab on the back or front contact face and the common point CP.

A more detailed description of a normally closed type flexible electric contact strip specially designed for the implementation of the process, of a contact key and a flexible membrane keypad in accordance with the object of the present invention will now be given in connection withFIGS. 2 and 3.

InFIG. 2is shown the normally closed flexible contact strip according to the object of the invention comprising of at least one flexible center tab LC, to which it is electrically and mechanically joined at the common point PC.

The flexible strip LS further consists of the first side tab LL1and the second side tab LL2each being electrically and mechanically joined by the common point PC.

The first and the second side tabs are adjacent and parallel to the flexible center tab LC, but are arranged to be offset in position in an orthogonal direction to the plane P so as to form the first insertion space EI1and the second insertion space EI2for the printed circuit board CI that is provided with the slot F, and the front contact face and the back contact face disposed in the vicinity of the two opposite edges of this slot. With reference toFIG. 2, it is understood that the plane P substantially including the side tabs is none other than the plane of the sheet carrying the above mentionedFIG. 2and that the insertion spaces EI1and EI2shown between the parallel tabs onFIG. 2, however, extend in a direction that is orthogonal to the plane of the same sheet, as will be explained below in connection withFIG. 3.

With reference to the above mentioned figure, it is clear that the flexible center tab LC is offset at rest in an oblique plane PO in relation to the plane P containing the first flexible side tab LL1and the second flexible side tab LL2in order to form, through opposite constrained rotation of this flexible center tab LC, the first insertion space EI1of the printed circuit board CI between this flexible center tab LC and the first and second side tabs LL1and LL2. The angle of inclination of the oblique plane PO in relation to the above mentioned plane P may be between 10° and 20°, depending on the elasticity characteristics of the metallic material constituting the flexible strip LS.

InFIG. 3, the movement of the center tab LC is shown in dotted lines, in opposite constrained rotation f so as to form the first insertion space EI1mentioned above.

The flexible strip LS can thus be clipped at its insertion spaces EI2and EI2by performing opposite constrained rotation on the flexible center tab LC in order to enable this center tab to pass under the printed circuit CI, the latter entering, by the corresponding edge of the slot F, in the first insertion space EI1; and to enter into electrical contact with the back contact face PV, then, by displacement of the flexible strip LS, towards the opposite edge of the slot F, so as to bring the latter into the second insertion space EI2and make electrical contact between the front contact face PR and the flexible side tab or tabs LL1, LL2.

Thus, it is to be understood that the center tab LC makes it possible to ensure the function of breaking of the normally closed electrical contact by applying a stress on the pressure point PA in cooperation with the flexible side tabs LLI1and LL2.

The flexible strip as shown inFIGS. 2 and 3above, is advantageously derived from cutting/stamping of a sheet of conductive material such as a soft metal like copper-beryllium alloy, steel or some other similar materials.

In particular the pressure point PA provided on the center tab LC is advantageously formed by a boss, for example. Similarly, the contact face PcC1of the flexible center tab LC is formed, for example, by a boss. In addition, optionally, the contact faces PcL1, PcL2respectively of side tabs LL1are also formed by a boss, according to the present embodiment.

A contact key for flexible membrane keypad, according to the object of the invention is now described in connection withFIG. 4.

With reference to the above mentioned figure, the contact key comprises of the printed circuit board CI equipped with the front contact face PR and the back contact face PV each placed in the vicinity of one of the opposite edges of the slot F provided in the printed circuit board. A flexible contact strip LS, as previously described in connection withFIGS. 2 and 3, is inserted into the slot F so as to form the normally closed electrical contact between the front contact face PR and the back contact face PV. The flexible strip includes the pressure point PA for enabling the exertion of the force for breaking the normally closed electrical contact. As was additionally also shown inFIG. 4, the above mentioned pressure point can be activated by exerting pressure either on a cup C that is round in shape or on a touch pad PT, arranged above it. The connection between the pressure point PA and the cup C or the touch pad PT is made in the conventional manner.

Finally, the invention relates to a flexible membrane keypad provided with a contact key forming a normally closed type electrical contact as described in connection withFIG. 4. It is to be understood in particular that the key shown in the above mentioned figure can be integrated to form a flexible keypad compatible with all types of materials for the front face FA, such as polyethylene terephthalate (PET), elastomer, Polyurethane (PU), Polycarbonate (PC) or other similar materials.

Shown inFIGS. 5-8is an example of push button electric switch10, of the normally closed type. Such a switch is for example, designed to equip a keypad of a portable communication device, such as in particular mobile phones or portable radios.

The switch10includes a printed circuit12of generally plane shape, having a first face12A and a second face12B opposite to the first face12A.

The first face12A is generally an upper face intended to be turned towards the exterior of the portable communication device. This first face12A is in particular shown in theFIG. 1.

The second face12B is generally a lower face, intended to be turned towards the inside of the portable communication device. This second face12B is shown in particular inFIG. 2.

The printed circuit12has a through orifice14, allowing access between the first face12A and the second face12B. In the example shown, the orifice14has a generally rectangular shape in the plane of the printed circuit12.

As shown inFIG. 1, the printed circuit board has on its first face12A, a first contact pad16, also known as contact face. This first contact pad16has for example a U-shape and is arranged around the orifice14in such a manner that the orifice14is partially framed by this first pad16, along the lengthwise sides and one breadthwise side of this rectangular orifice14.

As is shown inFIG. 2, the printed circuit12includes, on its second face12B, a second contact pad18, also known as the contact face, for example of generally rectangular shape. Preferably, the second contact pad18is arranged close to the second breadthwise side of the rectangular orifice14.

The switch10also includes a conductor20, in the form of a flexible conducting strip, designed for electrically connecting the first16and second contact pads18.

The conductor20comprises a first part22, such as shown inFIG. 1, cooperating with the first contact pad16. Preferably, this first part22comprises of two branches22A, forming the side tabs, and a base22B, forming a common point between the side tabs, so as to have a U-shape also The branches22A are arranged on both sides of the orifice14of the printed circuit12, along its lengthwise sides, in such a manner that the orifice14is partially framed by this first part22in the plane of the orifice14.

The conductor20includes, in addition, a second part24extending between a first end24A connected to the first part22, and a second free end24B designed to cooperate with the second contact pad18.

Preferably, the conductor20is made of sheet metal, the first22and second24parts having been formed integrally.

In the example shown, the second part24of the conductor forms a strip (or flexible center tab) extending the base22B of the first part22, and extending longitudinally between the two branches22A of this first part22. This strip24passes through the orifice14so as to electrically connect the first part22with the second contact pad18.

The second part24is elastically deformable between a rest position, shown inFIG. 3, in which its second end24B cooperates with the second contact pad18, and a stressed position, shown inFIG. 4, in which its second end24B is moved away from the second contact pad18. Thus, the switch10is in the closed position when the second part24is in its rest position, and it is in its open position when the second part24is in its stressed position.

Advantageously, the second part24comprises, at its second end24B, of a boss25, also called contact face, facilitating contact with the second pad18.

It should be noted, that due to the elastically deformable structure of the conductor20, this conductor20can be assembled on the printed circuit board12by the pinching of the printed circuit12between the first22and second24parts of the conductor20. This assembly is particularly stable, thanks to the U-shape of the first part22. This structure thus facilitates the assembly of the switch10.

The switch10also comprises a metal cup26of conventional type, forming a pusher/push button, accessible from the side of the first face12A of the printed circuit12. This metal cup26is arranged above the conductor20, so that it is capable of cooperating with the second part24of the conductor20. To this end, as shown inFIG. 1, the metal cup26is for example arranged in abutment on the first part of the conductor20.

Such a metal cup26can be pushed by a user, in a manner so as to be deformed elastically between a rest position as shown inFIG. 3, and an engaged position as shown inFIG. 4.

In its rest position, the metal cup26is held away from the second part24of the conductor, which is also found in its resting position. The switch10is therefore closed. It should be noted that the height of the metal cup26in its position of rest is usually about 1 millimeter. Thus, the switch10is compact and can be easily integrated into a compact portable communication device.

In its engaged position, the metal cup26cooperates with the second part24of the conductor to maintain it in its stressed position. The switch10is thus opened.

Advantageously, the second part24of the conductor20includes a boss28, forming a pressure point, provided between its first24A and second24B ends and intended to cooperate with the metal cup26when the metal cup26is in its engaged position. This boss28makes it possible to ensure contact between the metal cup26and the second part24. Alternatively, the metal cup26could bear a similar boss meant for cooperating with the second part24.

It should be noted that when the user releases the metal cup26, the metal cup26and the second part24of the conductor20return by elasticity to their respective rest positions.

Preferably, the metal cup26is designed to form a hard point, in order to provide a tactile sensation to the user when he actuates the switch10by pressing the metal cup26with a finger.

The switch10preferably comprises some sealing means (not shown), for example of plastic material, covering at least the metal cup26and the conductor20. The sealing means may also include, on the user-side, an inscription relating to the operation of the switch10.

Such sealing means preferably cover the entire keypad of the communication device so that the device can be used in wet and aggressive environments.

On an optional basis, the switch10may also include means for back lighting, arranged on the side of the second face12B of the printed circuit12. Indeed, thanks to the orifice14, it is possible to provide the switch10with back lighting in a simple and effective manner.

The previously described switch10comprises of few elements, and thus it has a low weight, as well as a low cost.

It should be noted that the invention is not limited to the embodiment that has been described above, but may be presented in different variants without departing from the scope of the claims. In particular, the characteristics of each embodiment described above may be implemented in a manner equivalent to the other embodiment described.