FR2741216A1 - SHIELDING OF A MEMBRANE - Google Patents

Abstract

A device (100) includes a keypad membrane (1600) having a conductive membrane layer (1608) above the bottom surface of the membrane body (1602). The conductive layer covers the membrane contact areas (217) and is connected to ground by an adhesive (1700). The grounded conductive layer placed over the membrane provides RF shielding to reduce unwanted coupling of RF energy through the key area of the device.

Description

I Title

SHIELDING OF A MEMBRANE

  Field of the Invention The present invention relates to shielding and more precisely shielding in a contact area of a membrane. BACKGROUND OF THE INVENTION A large variety of devices are known which include RF circuits, such as transmitters, receivers or transceivers making it possible to

  communicate with other compatible devices.

  Examples of this type of device include radio telephones, which can be

  cell or wireless phones, transmitters-

  receivers, paging devices,

  personal digital calendars (PDAs), or the like.

  These devices generally include keys that can be activated by the user to manually close the respective switches mounted on a circuit board. The switches are coupled to a controller that reacts to the activation of the keys to control the operation of the RF circuits. Shielding is often used in the area near the keys (the "key area") of these devices, in addition to other areas of the housing. Shielding isolates RF circuits from noise signals that can reduce the performance of these devices. In the past, shielding was done by spraying conductive material on the inner surface of the device housing around the key openings. The shielding was also carried out using a

  conductive layer on a printed circuit board.

  By connecting the conductive layers to ground, they become a shield by conducting the signals

RF to earth.

  Although each of these shielding techniques provides effective RF shielding in existing devices, it is desirable to provide smaller technologically improved devices. These new devices have been found to be even more sensitive to noise signals. A particularly advantageous new device comprises an antenna in a cover which pivots between an open position and a closed position. In the closed position, the protected antenna is placed above the keys near the circuits of the box. A passive antenna element is attached inside the housing to tune the protected antenna when the cover is open. This proximity to the protected antenna makes it very sensitive to the reception of noise from the circuits of the housing. It is particularly difficult to shield against this noise since the key openings make shielding difficult, and the passive element

  antenna is placed near the key openings.

  Therefore, there is a need for shielding

  improved the key area of a device.

Brief description of the drawings

  Figure 1 shows a front elevation view illustrating a radiotelephone having a cover in

an open position.

  Figure 2 shows a perspective view from above, side, front, fragmentary, exploded of

radiotelephone according to Figure 1.

  Figure 3 shows a fragmentary rear elevational view illustrating the rear of the front housing of the phone according to Figure 2, the cover being in

open position.

  Figure 4 is a top plan view illustrating a radiotelephone membrane according to the

Figure 1.

  Figure 5 is a bottom plan view

  illustrating the membrane according to Figure 4.

  Figure 6 is a cross-sectional view

  taken along plane 6-6 of Figure 4.

  Figure 7 is a side, rear and top perspective view illustrating a clip for the

radiotelephone according to Figure 2.

  Figure 8 is a rear elevation view

  illustrating the clip according to Figure 7.

  Figure 9 is a top plan view

  illustrating the clip according to Figure 7.

  Figure 10 is a fragmentary cross-sectional view taken along the plane 10-10 of Figure 1. Figure 11 is a perspective view from the right, front side and from above illustrating a membrane

  assembly and a printed logic board.

  Figure 12 is a fragmentary cross-sectional view taken along the plane 12-12 of Figure 1. Figure 13 is a side elevational view illustrating the relative position of a protected antenna, a passive antenna element , a membrane, a printed display card, a fastener, a shield and a printed RF card for the radiotelephone according to FIG. 1, when the cover is

in the closed position.

  Figure 14 is a circuit diagram partially in the form of a block diagram illustrating the electrical components of the radiotelephone. Figure 15 is an enlarged fragmentary view of Figure 10 and illustrating the connection between the fastener, the membrane shield and the conductor of

mass.

  Figure 16 is a perspective view from below of a membrane according to another embodiment.

realization of the invention.

  Figure 17 is a cross-sectional view of the membrane according to Figure 16 mounted on a circuit board and taken along a plane similar to that

in Figure 12.

  Figure 18 is a circuit diagram illustrating a key pad matrix and a microprocessor

  for the embodiment according to Figure 16.

Detailed description of the drawings

  A device has keys that can be activated by the user to control the operation of the device. A keypad membrane having contact areas associated with the keys of the device has a conductive layer on its bottom surface. The conductive layer covers the area under the contact. The membrane conductor is connected to ground to provide a shield that blocks the passage of RF signals through the key area. Since a grounded membrane conductor extends above the key contact area, the transmission of signals through the contact area is prevented. By installing the membrane conductor on the bottom of the membrane, it is easier to assemble the membrane shield and an associated printed circuit board in an electronic device. A radiotelephone, illustrated as a portable cellular telephone, 100 (Figure 1) has a body 101 and a keypad cover 103. A mast antenna 104 is placed on the body 101 and a protected antenna 106 (shown in dotted lines) is mounted inside the cover 103. The mast antenna communicates with a fixed site, or base station, 102, by means of RF signals represented by A, and the protected antenna 106 communicates with the base 102, via the RF signals represented by B. The cover pivots between the extended position illustrated in FIG. 1 and a closed position covering the keypad 108. The radiotelephone comprises a keypad 108, a

  display 107 and an opening for loudspeaker 112.

  Although a cellular telephone is illustrated, the invention can also be applied to cordless telephones, transceivers, paging devices and PDAs, and "device" as used herein can refer to each of these

  devices and their equivalents.

  The radiotelephone 100 includes a front housing 210 (Figure 2) and a rear housing 212. The front and rear housings are molded in one piece from a suitable material, such as a polymer. The keys 211 (only some of these are shown) are placed behind the front housing 210 and are made from a suitable material, such as a molded polymer. A respective key 211 is associated with each opening 214 of the front housing 210. A membrane 216 is placed behind the keys 211. The membrane has a respective region or contact zone 217 (only some are numbered) associated with each key 211. The membrane also has holes 215 which extend through the membrane to allow light to pass through. The contact area, or keys, 217 is illustrated in a curved portion. As used here, the curved part

  is equivalent to a dome in the body of the membrane.

  However, the contact zone can be flat or hollowed out, the only requirement being that it can return to its initial shape after having been flexed by the activation of the button 211. The contact zone is therefore deformable when it is pressed by the key 211 and sufficiently elastic to return to its initial position when it is released by the key 211. An assembly of display cards 218 is placed behind the membrane 216. The assembly of display cards comprises contacts 220 ( only some are numbered), light emitting diodes (LEDs) 223 (only some are numbered), a display 107 and a speaker 222 which are mounted on the display board 219. A shield 224 is placed between the assembly of display boards 218 and an assembly of RF printed boards 226. The RF circuits (not shown) are mounted on the assembly of RF printed boards which comprises an RF transceiver (not shown in the Figure 2), a controller (not shown) and other circuits (not shown specifically), which are mounted on a printed circuit board RF 227. Fasteners 228 and 230 are mounted on the display board to provide a connection membrane 216 to ground as described in more detail in this document. The radiotelephone has

  also a cap 324 and a connector 236.

  The radiotelephone 100 (Figure 1) has a protected antenna 106. The protected antenna 106 is a dipole antenna provided by two electrical conductors fixed to a plastic case 129. The conductors have respective high current sections 130 connected to the circuits of the radiotelephone transceiver (not shown in Figure 1, 1240 in Figures 12 and 14) through a power line and impedance transformer conductors 133, which extend through the

hinge 135 in body 101.

  A passive antenna element 310 (Figure 3) is

  connected to the internal surface 312 of the front housing 210.

  The passive antenna element is made from a suitable electrically conductive material, such as a copper alloy. Passive antenna 310

  has a shoulder 314 and two arms 316.

  The shoulder is placed so as to extend between two rows of openings 214. The arms are placed so as to extend along the sides 318 and 320 of the front housing. The shoulders and arms are connected by a junction element 315. The antenna passive element conductor is mounted inside the front housing 210 using an appropriate adhesive. Passive antenna 310 is designed to tune the antenna

  protected 106 (Figure 1) when the cover 103 is closed.

  The connection is ensured by an electrical coupling between the high current sections 130 of the protected antenna 106 and the shoulder 314 (FIG. 3) of the passive antenna element 310. The passive antenna element and the the protected antenna is not coupled when the cover 103 is open. When the passive antenna element 310 (FIG. 3) is mounted in a completely assembled radiotelephone 100, it is not directly connected either to another electrically conductive material or to circuit elements. Since the passive antenna element is not electrically connected directly to other circuits or to ground, the surface 312 which surrounds the openings of the keys 214 cannot be coated with an electrically conductive material, such as that was the case for radiotelephones of the prior art. The membrane 216 (Figure 4) has a respective contact area 217 for each key 211 of the keypad 108. Each illustrated contact area 217 is a domed portion, which is a dome in one piece which extends upwards from a flat rib 410. The bottom of each contact zone 217 has a contact 510 (Figure 5) allowing connection with a respective contact 220 (Figure 2) on the display card. When the contact area 217 is deformed downwards by the button 211, the contact 510 at the bottom of the membrane is pushed down to have an impact on the contact 220. This contact completes a circuit, thus indicating the closure of a switch. This provides a signal to the controller that a key is pressed, and the controller identifies which key has been pressed, in a conventional manner. The contact area returns to its initial position after releasing the button 211. The contact area gives the user a tactile sensation, once the button 211 is released. The planar rib 410 has holes 215 which extend through the membrane to allow the light coming from the LEDs 223 to pass through (Figure

2) to the bottom of the 211 keys.

  The inventors have discovered that placing the protected antenna 106 (Figure 1) near the display card assembly 218 (Figure 2) when the cover 103 is closed opens a path for RF signals between a clock of microprocessor (not shown in Figure 2, 1311 in Figure 13) and the protected antenna 106. The clock of the microprocessor produces clock signals having harmonic frequencies included in the frequency band of the transceiver (not shown in Figure 2, 1240 in Figure 13). These harmonics are detected by the protected antenna 106 when the cover 103 is closed. The area surrounding the passive antenna element 310 is not coated with a conductive material, as has been done in the past on radiotelephones.

  which do not have a passive antenna element.

  However, even if the interior was coated with a conductor, the key openings 214 open a passage for the RF signals. The inventors have discovered that the contacts 220, 510 (Figures 2 and 5 providing the key activated switch) emit considerable amounts of noise energy. Therefore, shielding the interior surface of the front housing or providing a ground layer which does not extend over the contact areas 217 will not provide effective shielding to the protected antenna 106 since noise from contacts forming circuit traces 220, 510 pass through the

openings 214.

  To overcome this problem discovered with prior shielding techniques, the membrane 216 is provided with at least two layers. The membrane comprises a non-conductive membrane body 624 (FIG. 6) and a membrane conductor 626, the membrane conductor covering the entire upper surface of the

  membrane body comprising the contact zones 217.

  The membrane body 624 is made from a suitable material, such as a solid polyester fabric, and may for example be that known under the trade name of MylarTM. The body is elastic, so that it oscillates between a dome position (not deformed) and a closed position (collapsed). The Mylar provides users with a tactile sensation when the

key 211 is pressed.

  Membrane conductor 626 (Figure 6) is a conductive layer applied using an appropriate technique, such as vaporization. The membrane conductor 626 is preferably a commercially available conductor such as the conductor composition

  flexible polymer number 5007 available from DuPont '.

  The 510 contacts are made from any suitable means, such as silver paint

  applied using screening techniques.

  Fasteners 228 (Figure 2) and 230 are provided to connect the membrane conductor 626 (not identified in Figure 2) to ground. These fasteners are identical. Therefore, only the fastener 228

  is described in more detail in this document.

  The fastener 228 has parallel arms 710 (Figures 7 to 9, only some are numbered in each figure) which extend from the shoulder 712. Each arm has a fold 713 (only some are numbered). 716 upper rods protrude

  outward from the bottom of the shoulders 712.

  Each of the upper rods has a curvature 715. The middle rods 718 protrude from the middle of the shoulder 712. Legs 720 extend perpendicularly from the opposite ends of each shoulder 712. The fasteners are made from 'a suitable electrically conductive material, and can for example be made from beryllium copper with a tin on nickel plating. The fastener is electrically conductive and elastic so that it can be deformed and

return to its original position.

  The cap 234 (Figure 2) and the connector 236 are made from a suitable electrically conductive material, such as an aluminum alloy or a copper alloy. The cap has rods 1212 (Figure 12), 1214 and 1216 which extend outward from the body 1218. The connector 236

  (Figure 2) has a plate 240 and springs 242.

  To assemble the radiotelephone 100 (FIG. 10), the membrane 216 is placed on the display card 219 so that the contacts 510 placed on the bottom of the contact areas 217 are aligned with the contacts

  220 placed on the display card 219.

  When placed correctly, the LEDs 223 (Figure 11) are visible through the holes 215 in the membrane 216. The clip 228 (Figure 10) is attached to the display board 219 and to the membrane 216, from so that the upper rods 716 come into contact with the membrane conductor 626. The tabs 720 are placed against the walls 1112 (Figure 11) to place the fastener 228 in an appropriate position on the circuit board. The curvature 715 (Figure 10) comes into contact with the membrane conductor 626 and exerts a force on the layer so as to ensure a connection with the membrane conductor 626 of the membrane 216. The intermediate rod 718 engages with the surface of the display card 219. The display card is pinched between the upper rod 716 and the rod

intermediate 718.

  The clip 228 (Figure 10) is connected to the conductive strips 1010. The clip 228 can be soldered to the strip 1010 so as to provide an electrical connection between the two. The strips extend along the perimeter of the display card 219 and are electrically connected to a conductive layer 1012 (Figure 15) of the display card 219 via a direct conductor 1018. The conductive layer 1012 is placed between the insulating layers 1014 and 1016, and extends over the entire display card 219. This electrically conductive layer 1012 constitutes a ground conductor for the display card 219. The clip 238 thus connects the membrane conductor 626 to the ground conductor, to the conductive layer 1012, of the display card 219. The arms 710 of the clip 238 extend outward from the shoulder 712 to connect to the shield 224. The fold 713 of the arm 710 engages the shield 224. The fold 713 presses on the shield 224 so as to ensure an electrical connection between the shield 224 and the fastener. Thus, the clip electrically connects the conductor of

membrane 626 to shield 224.

  The shield 224 is electrically connected to a conductive layer 1220 (Figure 12) of the printed circuit board RF 227 by a direct conductor 1222. The conductive layer of the printed circuit board RF 1220 is sandwiched between the electrical insulators 1224 and 1226. The layer conductor 1220 extends over the entire printed circuit board RF 227, and constitutes the ground conductor for the printed circuit board RF 227. The shield 224 and the conductive layer 1220 provide a grounding box around the circuits RF. Since the arms 710 of the clip 228 connect to the shield 224 when the display card 219 and the printed circuit board RF 227 are assembled in the radiotelephone 100, as best represented in FIG. 10, the clip 228 is connected to layer

  conductor of the printed circuit board RF 1220.

  Although it is not specifically described in this document, the clip 230 is assembled in the radiotelephone 100 in a manner identical to

  the fastener 228. The description of the fixing of

  fastener 230 is therefore omitted for the purpose of

brevity.

  The internal surface of the front housing 210 and the rear housing 212 is vaporized with a conductive material in the area of the speaker 222. The cap 234 and the connector 236 connect the conductive layer 1220 of the printed circuit board RF 227 to the surface of the housing. front 210 and rear housing 212 when the radiotelephone housings are assembled over the printed circuits. This layer of the telephone case and the connection to the conductive layer 1220 provide ground conductors

  additional to the radiotelephone.

  When the housing is completely assembled, the LEDs 223 are placed in holes 215 (Figure 11) to

  provide light on the back of the 211 keys.

  This light illuminates the keys 211 of the keypad 108 during operation. The inventors have discovered that the LED areas (holes 215) do not allow considerable amounts of RF energy of the type which manages the operation of the light to pass through.

  RF 1240 transceiver circuit (Figure 13).

  The relative position of the components of the radiotelephone 100 when the cover is closed is illustrated in FIG. 13. In this position, the protected antenna 106 is placed substantially parallel to the membrane 216. The passive antenna element 310 is placed between the membrane 216 and the protected antenna 106. The arms 316 of the passive antenna element extend along the sides of the radiotelephone circuits. The display card 219 is placed behind the membrane, the shield 224 is placed under the display card and the shield is mounted on the printed circuit board RF 227. The clip 230 is electrically connected to the conductive layer of the membrane 216 and to the shield 224. The microprocessor 1310 of the radiotelephone is mounted in the lower part of the display card 219 and is shielded from the RF card by the shield grounded 224. The high current sections 113 of the protected antenna 106 are coupled to the shoulder 314 of the passive antenna element 310. The shoulder 314 is the

  high current section of the passive antenna element.

  This high current section of the passive antenna element extends to the junction element 315, which is coupled to the arms 316. The junction element 315 extends along the fasteners 228, 230, so that

  fasteners provide additional shielding.

  Clip 228 (not shown in Figure 13) is placed similarly to the element

junction 315.

  It will be recognized that the passive antenna element 310 (Figure 3) is mounted in the internal surface of the front housing 210 and that it is spaced from the fasteners 228 (Figure 2) and 230, mounted on the card assembly. display 218, so that the clips 228, 230 do not come into contact with the passive antenna element. The fasteners 228 and 230 are both located on the display card 219, so that they are placed between the junction elements 315 of the passive antenna element and the side of the card

display 219.

  When in operation, microprocessor 1310 (Figure 14) supplies RF noise signals, which include harmonics of clock signals, to contacts 510. Contacts 510, 220 act as an antenna element and transmit these RF noise signals. The grounded membrane conductor 626 provides shielding that prevents RF signals from reaching the protected antenna 106 when the cover is closed. This prevents RF signals from reaching the RF 1240 transceiver circuit. As a result, background noise is reduced for the transceiver, reducing the minimum amplitude of B signals.

  (Figure 1) which is necessary for the transmitter-

  RF receiver receives an identifiable signal when the

cover 103 is closed.

  It is particularly advantageous to use

  the invention with a protected antenna 106 (Figure 14).

  Although the protected antenna 106 is located near the display card assembly 218 when the cover 103 is closed, the shield provided by the grounded membrane conductor 626 blocks the transmission of signals between the traces of circuit, which form the contacts 220, 510 and the protected antenna 106. Thus, the high order harmonics and the clock signals generated by the clock of the microprocessor 1311, and any other source of signal which produces present signals on the contacts 220, 510 which are in the frequency band of the circuit of the transceiver RF 1240, are blocked by the membrane conductor grounded 626. Consequently, the reception by the antenna 106 of signals noise emitted by the contacts 220, 510 is significantly reduced and practically eliminated. In addition, the large surface area shielded by the grounded membrane conductor 626 provides improved shielding for the key area of the radiotelephone 100. A membrane 1600 (FIG. 16) according to another embodiment of the invention, comprises a generally planar membrane body 1602. Although the membrane body 1602 is illustrated in rectangular form, it will be recognized that the body can be advantageously formed so that it adapts to the device in which it is used, and that 'It can have the same shape and the same construction as the membrane body 624 (Figure 6). The planar body has contact zones 1606 (Figure 16), the contact zones being able to

  be curved as illustrated in Figures 16 and 17.

  The membrane body 1602 is made from a suitable elastic, deformable material such as a polymeric material. A conductive membrane layer 1608 is mounted on a lower surface of the membrane body 1602. The conductive membrane layer 1608 is composed of any suitable material, such as a silver paint sprayed on a lower surface of the membrane body 1602. The conductive membrane layer 1608 is flexible, so that

  do not interfere with the handling of the keys 211.

  The conductive membrane layer 1608 extends over

  above and beyond the lower surface of the contact areas 1606, and may extend advantageously above the entire lower surface of the

diaphragm body 1602.

  A conductive adhesive 1700 (Figure 17) is provided between a circuit board 1702 and the conductive membrane layer 1608. The conductive adhesive can be composed of any suitable material, such as a fluid polymer impregnated with an electrical conductor, a transfer band comprising an electrically conductive material, such as the transfer band N

  9703 from the Scotch brand, or similar.

  The printed board 1702 (Figure 17) has a first non-conductive outer layer 1706. The openings 1712 made in this outer layer 1706 provide access to the conductive layer 1704. Thus, an air pocket 1720 present in the adhesive 1700 surrounds the contacts 220. The air pocket is preferably open to the surrounding air, and can for example be perforated to facilitate sagging of the contact areas. This adhesive 1700 establishes a reliable connection between the conductive membrane layer 1608 and the conductive layer of the printed circuit board 1704. Another non-conductive layer 1714 extends above the lower part of the conductive layer 1704. The conductive layer is connected to a ground conductor on the internal surface of the body 101 (Figure 1) and / or to the ground conductor

  mass of printed circuit board assembly 226.

  The contacts of the keypad 220 are physically organized in rows and columns. A contact 220 associated with each key of the first column is connected to the conductor 1820. A contact 220 associated with each key of the second column is connected to the conductor 1822. A contact 220 associated with each key of the third column is connected to the conductor 1824 A contact 220 associated with each key

  of the first line is connected to the conductor 1826.

  A contact 220 associated with each key of the second line is connected to the conductor 1828. A contact 220 associated with each key of the third line is connected to the conductor 1830. A contact 220 associated with each key of the fourth line is connected to the conductor 1832 The conductors 1820, 1822 and 1824 are connected to the column inputs 1802, 1804 and 1806 of the microprocessor 1310 via the resistors 1834, 1836 and 1838, respectively. The conductors 1826, 1828, 1830 and 1832 are connected to the line inputs 1810, 1812, 1814 and 1816 of the microprocessor 1310 via the

  resistors 1840, 1842, 1844 and 1846, respectively.

  Each of the line inputs 1810, 1812, 1814 and 1816 is connected via a respective isolation diode 1850 to 1853 to interrupt

  input 1808 of microprocessor 1310.

  To assemble the membrane 1600 to the printed board 1702, the transfer tape or the fluid adhesive is placed between the membrane 1600 and the printed board 1702. If the transfer tape is used, the transfer tape is first applied to the conductive layer 1704 of the membrane 1600. The layer

  adhesive is then attached to the printed board 1702.

  The adhesive of the transfer tape 1700 circulates in the openings 1712 when the membrane is fixed to the printed board 1702. According to another solution, the fluid adhesive 1700 is applied to one of the membrane 1600 and printed circuit 1702. The the membrane is then fixed to the printed circuit 1702. The fluid must be applied with care, so that it does not connect to the contact 220. The fluid adhesive 1700 circulates in the openings 1712 when the membrane is fixed to the printed circuit 1702. The adhesive 1700 physically and electrically connects the conductive membrane layer 1608 to the conductive printed circuit layer 1704 so as to form a one-piece assembly when the fluid hardens. 1700 adhesive is not applied in the area surrounding the contacts

220.

  In the embodiment of Figures 1 to 15, pressing a button 211 (Figure 10) connects the contact 510 to two contacts 220, thus shorting the two contacts 220. Those skilled in the art will recognize that this causes an interruption of the material, which results in a scanning of the columns and of the rows of a matrix associated with the pairs of contacts, or sets of contacts, 220. The closed contact will cause a row and a column to have a voltage level unique, which identifies the

key activated.

  In the embodiment of Figures 16 to 18, activating the key 211 (Figure 17) pushes the grounded layer 1608 (Figure 1) into the associated contacts 220. The connected contacts 220 are pulled towards the ground by the conductive membrane layer grounded 1608. This connection to the ground causes an interruption of the material at the entry 1808. The entry of the rows and columns having a contact drawn towards the ground identifies which curved part is closed ( i.e. which key 211 is activated). The embodiment of Figures 16 and 17 has the following advantage: the adhesive is used to connect the membrane shielding, provided by the membrane layer, to the ground of the circuit. This simplifies manufacturing, since fasteners 228 and 230 may require manual welding. In such circumstances, the use of the membrane on the bottom surface eliminates the need for a fastener to connect the grounded layer to the circuit ground. Therefore, it can be seen that improved shielding of the key area has been described. Shielding provides protection above the surface of the keypad, and prevents the keypad switches from emitting RF energy through the key openings toward an antenna

located near them.

Claims (10)

  1. A keypad membrane, comprising: a substantially planar elastic body (624) made from an elastic foldable non-conductive member and having respective contact areas, the contact areas being resiliently deformable so as to sag and return to their original position; and characterized in that it comprises: a membrane conductor (626) placed on a lower surface of the substantially planar elastic body and covering a lower surface of the contact areas and extending beyond the lower surface of the contact areas contact, the membrane conductor connecting to ground to provide a conductor which   acts as a shield in contact areas.   2. The keypad membrane of claim 1, further characterized in that the   membrane conductor is flexible.   The device comprising the keypad membrane of claim 1, further characterized in that the device comprises: a plurality of keys (211) to be activated by a user; a printed card (218) comprising at least one contact (220) associated with each key; and the membrane (216) being placed between said keys and said printed card, said contact areas having a shape which changes and which recovers its   initial shape after pressing a key.   4. Device according to claim 3, further characterized in that the printed card comprises a conductive layer of card (1702), and in that said device further comprises an adhesive (1700) connected to said conductive layer of card and   to said layer of conductive membrane.   5. Device according to claim 4, further characterized in that the printed card further comprises a non-conductive layer, said non-conductive layer comprising openings (1712) through which said adhesive extends to   connect to said layer of conductive membrane.   6. Device according to claim 3, further characterized in that said contact zones comprise respective convex parts (1720).   7. Device according to claim 3, further characterized in that the membrane layer conductive is flexible.   8. Device according to claim 3, further characterized in that the device is a radiotelephone comprising: a housing having a body (101); the printed card placed in the body; and the keys placed so as to extend across the body, the keys to be activated by an user.   9. Radiotelephone according to claim 8, further characterized in that the radiotelephone comprises a mobile keypad cover (103) and an antenna (106) placed on the cover, the membrane being placed between the contacts and the cover when the cache is closed.   10. Radiotelephone according to claim 9, further characterized in that it comprises a second printed card (226) comprising RF circuits, the first printed card being placed between the membrane and the second printed map.