FR2908552A1 - Electronic system e.g. chip card read/write system, has conductive portion remote from conductors when external action is not exerted on deformable region, and key to deform region for permitting portion to contact with conductors - Google Patents

Abstract

The system has conductors (18) placed on a surface of a printed circuit board (16). A lattice type protection device (40) has a deformable region (49) covering the conductors. A conductor (46) is placed between insulating films (42, 44), and a conductive portion (50) is placed opposite to the conductors (18). The portion is remote from the conductors (18) when an external action is not exerted on the deformable region. A key (22) deforms the region for permitting the conductive portion to contact with the conductors (18).

Description

B7844 - 13737 1 ELECTRONIC CIRCUIT INTERRUPTER PROTECTED AGAINST

  BACKGROUND OF THE INVENTION The present invention relates to a switch of an electronic circuit with which is associated a protective device for preventing access to the electronic circuit or to information contained in the electronic circuit. DESCRIPTION OF THE PRIOR ART FIG. 1 is a diagrammatic section of a system or device for reading / writing smart cards. The device comprises a housing 11 consisting of a lower housing portion 12 and a housing upper portion 14. A display screen 15 is attached to the housing top portion 14. The device 10 includes a printed circuit board 16 on which are made conductive tracks 18. The metal tracks 18 are connected to electronic components, not shown. In addition, the means for reading and writing data on a smart card are not represented. The device 10 comprises a flexible membrane 20, for example made of silicone or polyurethane, at the level of which are formed keys 22 of a keyboard, each key 22 corresponding to a portion of the membrane connected to the remainder of the membrane by a peripheral lip 24. Each key 22 comprises, on the printed circuit side 16, a conductive portion 26, for example a metal region. Under each key 22 are disposed opposite two ends each belonging to a metal track 18. In the absence of external action on the keyboard, each key 22 is remote from the median plane of the membrane 20 and is remote from the conductive tracks 18. When a user exerts a pressure on a key 22, the associated lip 24 allows a movement of the key 22 until the conductive portion 26 comes into contact with the ends of the metal tracks 18 underlying, then establishing an electrical contact between the two metal tracks 18. The key 22 therefore acts as a switch which is generally open and which is closed when a user presses the key 22.

The read / write system 10 may optionally include an anti-intrusion device consisting of a dummy key 30 provided at the membrane 20 and which is not visible from outside the housing 11. The dummy key 30 is similar to the keys 22, connected to the rest of the membrane 20 by a peripheral lip 31 and comprises a conductive portion 32 on the side of its underside. The ends of two metal tracks 18 of the printed circuit 16 are disposed vis-à-vis under the fingertip 30. The conductive portion 32 and the associated metal tracks 18 form a safety circuit. When the upper housing portion 14 is fixed to the lower housing portion 12, the dummy key 30 is permanently biased by the housing upper portion 14 so as to bear against the printed circuit board 16. In this case, the portion conductive 32 of the dummy key 30 comes into contact with the ends of the two tracks 18. The electrical connection between the two metal tracks 18 is detected by a not shown processing circuit. When an individual attempts to access the contents of the housing 11 by removing the upper housing portion 14, the dummy key 30 is no longer biased by the housing upper portion 14 and is returned by the housing portion 14. action of the lip 31 to a rest position at which the conductive portion 32 is no longer in contact with the metal tracks 18. The processing circuit is adapted to detect a change in the resistance of the safety circuit, indicating that an attempt to open the device 10 takes place. The dummy key 30 thus acts as a switch which is closed when the housing top portion 14 is in a normal position and is open when the housing top portion 14 is removed. The use of dummy keys 30 may not provide sufficient protection. Indeed, a user could, without moving the upper housing portion 14 and 15 by eliminating, for example by scraping, cutting, machining, grinding, etc., a portion of the membrane 20, to access the metal tracks 18, 34, 36 and therefore to information contained in the circuit 16. It may therefore be desirable to provide additional protection to prevent access to the metal tracks 18 of the printed circuit 16. A possibility would be to cover the printed circuit 16, the side its opposite side to the keys 22, 30 of a lattice type protection device. Such a protective device corresponds to a stack of flexible and insulating films 25 containing one or more conductive tracks, for example made of copper. The tracks form security lines connected to a processing circuit. The processing circuit is adapted to determine if a safety line has been interrupted, for example by measuring the resistance at the terminals of the safety line, the interruption of a line that may correspond to an attempt to access the circuit board 16. However, the presence of a lattice between the printed circuit 16 and the membrane 20 would isolate the conductive portions 26, 32 of the corresponding metal tracks 18. It would then be no longer possible to use the keys 22, 30 as switches. SUMMARY OF THE INVENTION The present invention is directed to an electronic circuit switch protected against access attempts. According to another object, the switch has a particularly simple structure. To achieve all or part of these and other objects, one aspect of the present invention provides an electronic system comprising an electronic circuit having a face on which at least first and second conductive tracks are disposed; a protection device comprising a deformable region covering the electronic circuit at least at the first and second conductive tracks, the protective device comprising at least two insulating films between which is disposed at least a third conductive track and a conductive portion; opposite the first and second conductive tracks, the conductive portion being at a distance from the first and second conductive tracks in the absence of external action exerted on the deformable region; and a support member adapted to deform the deformable region to contact the conductive portion with the first and second conductive tracks. According to an exemplary embodiment, the third conductive track 25 extends at least between the support element and the first and second conductive tracks. According to an exemplary embodiment, the electronic circuit is flat and the deformable region has, in the absence of external action, a curved shape, the conductive portion being disposed at the center of the curved region. According to an exemplary embodiment, the electronic circuit is a printed circuit comprising a stack of at least first and second layers, the first and second conductive tracks being arranged on the first layer, the second layer comprising an opening releasing the first and 2908552 B7844 - 13737 5 second conductive tracks, the protective device covering the opening. According to an exemplary embodiment, the support element is a movable key relative to the electronic circuit that can be moved by a user. According to an exemplary embodiment, the electronic system comprises a housing containing the electronic circuit and the support element belongs to the housing. According to an exemplary embodiment, the electronic system comprises a housing containing the electronic circuit and a membrane comprising a body and at least a first key movable relative to the body and capable of being moved by a user and at least one second movable key relative to the body, the second key being held 15 against the deformable region by the housing. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features, and advantages of the present invention will be set forth in detail in the following description of particular embodiments given without limitation in connection with the accompanying figures in which: Figure 1, previously described, is a schematic section of a conventional read / write system; Figures 2 and 3 show, in two states of operation, an embodiment of a switch protected against access attempts according to the invention; Figures 4 and 5 show another embodiment of a switch according to the invention with two operating states; FIG. 6 represents another embodiment of a switch according to the invention; and Figure 7 shows another embodiment of a switch according to the invention.

2908552 B7844 - 13737 6 Detailed Description For the sake of clarity, the same elements have been designated with the same references in the various figures. The present invention consists in arranging a trellis-type protection device between the electronic circuit of an electronic system and the keys of the electronic system keyboard and / or the housing containing the electronic circuit, the protection device also playing the the role of an electrical switch electrically connecting the metal tracks of the electronic circuit when pressure is exerted on the keys and / or when the housing is put in place. FIGS. 2 and 3 show a partial schematic section of an exemplary embodiment of a switch according to the invention protected against access attempts from the outside and fitted to an electronic system, for example a reading system / smart card writing. In the present embodiment, the read / write system has the same structure as that of the system shown in FIG.

However, unlike that shown in FIG. 1, a protection device 40 is provided between the printed circuit 16 and the membrane 20. The protection device 40 is of the trellis type and consists of the stack of at least two insulating and flexible films 42, 44, 25 having several tens of micrometers in thickness, and made for example of polyethylene terephthalate (PET), polyethylene naphthalate (PEN) or polyimide, for example the product marketed by DuPont under the Kapton appellation. One of the films 42, 44 may correspond to a flexible layer of insulating varnish. Conductive tracks 46, for example copper, are sandwiched between the films 42, 44. The tracks 46 form one or more security lines connected at their end to a not shown processing circuit. The processing circuit is adapted to detect an interruption of the safety lines, corresponding to an attempt to access the printed circuit 16. The upper housing portion 14 may comprise studs or ribs 47 which the membrane of the keyboard 20 against the printed circuit 16, the protection device 40 then being sandwiched between the membrane 20 and the printed circuit 16. The printed circuit 16 may be covered with a protective layer 48 which is not This protective device 40 has a substantially flat general shape except at the level of each key 22 where the protection device 40 comprises a deformable region 49 which, in the absence of external action, has a convex shape. According to a first example, the convex region 49 has an outer diameter of 8 mm and a height, relative to the mean plane of the films 42, 44 of the order of 0.3 mm. According to a second example, the convex region 49 may have an outside diameter of 4 to 6 mm and a height, relative to the mean plane of the films 42, 44 of the order of 0.3 mm to 0.5 mm. The first example advantageously makes it possible to reduce the stresses to be applied to deform the convex region 49 and to increase the service life of the protection device 40. At each deformable region 49, a conductive portion 50 is provided on the face of the The conductive portion 50 is, for example, made of silver or carbon and has a thickness of a few micrometers, for example of the order of 10 μm. The operation of this exemplary embodiment will now be described. In FIG. 2, the protection device 40 is represented when no action is exerted on the key 22.

The key 22 is then separated as much as possible from the median plane of the membrane 20 under the action of the lip 24. The key 22 then exerts little or no effort on the deformable region 49. The latter then has a curved shape so that the conductive portion 50 is remote from the metal tracks 18.

2908552 B7844 - 13737 8 The assembly formed by the metal tracks 18 and the protection device 40 then corresponds to an open switch. In FIG. 3, the same structure is shown when a user exerts pressure on the key 22. The key 22 in turn presses on the protection device 40 at the convex region 49. The curved region 49 is then deformed until the conductive portion 50 comes into contact with the metal tracks 18 providing the electrical connection therebetween. The assembly formed by the metal tracks 18 and the protection device 40 then corresponds to a closed switch. The key 22 may comprise a pin 56 on the side facing the protection device 40. This facilitates the deformation of the curved region 49 of the protection device 40 when pressure is exerted on the key 22. An example of a method The protective device 40 is formed by forming the conductive tracks 46 on the film 44 which is initially completely flat. The photographic transfer of the desired electric circuit and the dissolution of the excess copper make it possible to obtain the conductive tracks 46. The film 42, which may be a varnish, is then deposited on the film 44 and the tracks 46. The conductive portions 50 are then deposited. Finally, the deformable regions 49 of convex shape are obtained by thermoforming the films 42, 44 and 25 of the conductive portions 50. The present embodiment thus makes it possible to prevent access to the metal tracks 18 while retaining the function of a switch A further advantage of the present exemplary embodiment is that the protection device 40 can easily be provided only where it is needed, for example at the keys 22 of the electronic system keyboard. FIGS. 4 and 5 are views similar to FIGS. 2 and 3 of another embodiment of an electronic system, for example a chip card reader / writer system, comprising a protected switch according to the invention. In such an embodiment, the protection device 40 is integrated in the printed circuit. More precisely, the printed circuit 16 'consists of the stack of several rigid layers, for example epoxy, three layers 60, 62, 64 being represented in FIGS. 4 and 5, the layer 64 being disposed on the side of the upper portion 14 and the layer 62 being disposed between the layers 60 and 64. The protective device 40 is then fixed, for example by gluing, to the upper layer 64 of the printed circuit 16 '. The metal tracks 18 associated with the key 20 are formed on the intermediate layer 62 of the printed circuit 16 '. An opening 66 is provided in the layer 64 of the printed circuit 16 'at the key 20. This opening 66 releases the metal tracks 18. The protective device 40 covers the openings 66 and delimits a cavity 67 at the level of the opening 66. In a similar manner to the previously described embodiment, the protection device 40 comprises, at each opening 66, a conductive portion 50 on the face of the film 42 vis-à-vis the metal tracks 18 The printed circuit board 16 'may also comprise, on the opposite side to the protection device 40, an additional protection device 70 corresponding to a stack of 25 rigid or flexible films at which one or more conductive tracks 72 are arranged. represents the structure obtained when the key 22 is remote from the protection device 40. The elasticity of the films 42, 44 constituting the protection device 40 tends to cause the protective device 40 substantially planar. The conductive portion 50 is then remote from the metal tracks 18. In this configuration, the printed circuit 16 'corresponds to an open switch. FIG. 5 shows the structure obtained when pressure is exerted on the key 22. The key presses on the protection device 40 at its turn. The latter deforms locally at the level of the opening 66. until the conductive portion 50 comes into contact with the metal tracks 18. In this configuration, the printed circuit 16 'corresponds to a closed switch. A manufacturing method of the present embodiment is to form the conductive tracks 18 on the layer 62, to form the openings 66 in the layer 64, to bond the layers 62, 64, 66 to each other by a hot-bonding assembly. under pressure (or hot rolling), and to stick the protective devices 40, 70, made beforehand, on the layers 60 and 64. The present embodiment thus makes it possible to prevent access to the metal tracks 18 while The additional advantage of the present exemplary embodiment is that the metal tracks 18 and the conductive portion 50 are contained in a closed and dust-tight cavity 67. FIG. 6 represents a variant of the embodiment described above with reference to FIGS. 2 and 3 adapted to a dummy key 30 of the electronic system 10. In this case, when the upper housing portion 14 is in the normal position, it exerts a constant pressure on the key 30 which, in turn, presses the protection device 40. The conductive portion 50 then provides the electrical connection between the metal tracks 18. Of course, the embodiment described above in relation to FIGS. 4 and 5 may also be implemented for a dummy key 30.

FIG. 7 represents a variant of the embodiment previously described with reference to FIGS. 2 and 3. According to this variant, the membrane 20 is not present at least locally. The housing upper portion 14 comprises a pin 60 which, when the housing upper portion 14 is in the normal position, permanently presses on the protective device 40. The conductive portion 50 then provides the electrical connection between Of course, the embodiment described above with reference to FIGS. 4 and 5 can also be adapted to this configuration. Of course, the present invention is susceptible of various variations and modifications which will be apparent to those skilled in the art.

Claims (7)

  An electronic system (10) comprising: an electronic circuit (16, 16 ') having a face on which at least first and second conductive tracks (18) are disposed; a protection device (40) comprising a deformable region (49) covering the electronic circuit at least at the first and second conductive tracks, the protection device comprising at least two insulating films (42, 44), between which is disposed at at least one third conductive track (46), and a conductive portion (50) vis-à-vis the first and second conductive tracks, the conductive portion being at a distance from the first and second conductive tracks in the absence of external action exerted on the deformable region; and a support member (22; 30; 60) adapted to deform the deformable region to contact the conductive portion with the first and second conductive tracks.   The system of claim 1, wherein the third conductive track (46) extends at least between the support member (22; 30; 60) and the first and second conductive tracks (18).   3. System according to claim 1 or 2, wherein the electronic circuit (16) is flat and in which the deformable region (49) has, in the absence of external action, a curved shape, the conductive portion (50). being arranged in the center of the domed region.   System according to claim 1 or 2, wherein the electronic circuit (16 ') is a printed circuit comprising a stack of at least first and second layers (62, 64), the first and second conductive tracks (18). being disposed on the first layer, the second layer comprising an opening (66) releasing the first and second conductive tracks, the protection device (40) covering the opening. 2908552 B7844 - 13737 13   5. System according to any one of the preceding claims, wherein the support element (22) is a movable key relative to the electronic circuit (16, 16 ') can be moved by a user. 5   6. System according to any one of the preceding claims, comprising a housing (11) containing the electronic circuit (16, 16 ') and wherein the support element (60) belongs to the housing.   7. System according to any one of the preceding claims, comprising a housing (11) containing the electronic circuit (16, 16 ') and a membrane (20) comprising a body and at least a first movable key (22) relative to to the body and can be moved by a user and at least one second key (30) movable relative to the body, the second key 15 being held in abutment against the deformable region (49) by the housing.