Abstract:
An electronic system including an electronic circuit, an actuation device, a spacer and a protection device. The electronic circuit has a surface on which at least two first conductive tracks are arranged. The actuation device includes at least one first bearing element. The spacer is interposed between the electronic circuit and the actuation device and includes at least one opening at least partially receiving the bearing element. The protection device is interposed between the electronic circuit and the spacer and includes at least one second conductive track having ends respectively connected to first conductive portions of first deformable regions of the protection device. Each first portion is capable of contacting one of the first conductive tracks of the electronic circuit to electrically supply the second track under the effect of a deformation of first regions.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for protecting an electronic system, for example, a banking card reader, especially a chip card reader, against intrusions. 
     DISCUSSION OF PRIOR ART 
     A banking card reader generally comprises a package containing a printed circuit on which electronic components are connected. The reader comprises a keyboard corresponding to a flexible membrane partially covering the printed circuit and at the level of which the keys of a keyboard are formed. Each key generally comprises, on the printed circuit side, a conductive land. The separate ends of two conductive tracks are arranged on the printed circuit under each key. These ends for example correspond to interdigitated combs. 
     In the absence of an external action on the keyboard, each key is in an idle position where it is distant from the printed circuit. When a user presses a key, said key moves until the associated conductive land creates an electric contact between the ends of the two underlying metal tracks. The key and the underlying printed circuit tracks thus behave as a generally off switch which is turned on when a user presses the key. 
     The card reader generally comprises a device of protection against intrusions formed of one or several dummy keys provided at the level of the keyboard membrane and which are not visible from the outside of the package. Each dummy key is maintained in permanent contact with the printed circuit by the reader package so that it creates a permanent electric connection between two tracks of the printed circuit. 
     When someone tries to open the package, the dummy key is no longer actuated by the package and moves away from the printed circuit. The dummy key and the underlying tracks of the printed circuit thus behave as a switch which is on when the reader package is properly closed and which is off when the package is open. The turning-off of this switch is detected by a specific electronic circuit provided at the printed circuit level. 
     The use of dummy keys may not provide a sufficient protection, especially in the case where a spacer is interposed between the keyboard membrane and the underlying printed circuit, for example, to behave as a light diffuser to light the keyboard membrane from the inside of the package (backlighting of the keys). The spacer comprises openings enabling the passing of the normal and dummy keys of the keyboard membrane. A disadvantage of such a reader structure is that it may be relatively easy to fill the spacer openings associated with the dummy keys with glue so that the dummy keys remain permanently glued to the printed circuit. The reader package can then be opened without interrupting the contact between the dummy keys and the printed circuit. 
     Document US-A-2007/152042 describes a keyboard for a chip card reader equipped with a light guide and with a membrane of protection against the introduction of the needle of a hypodermic syringe enabling to short-circuit safety keys (dummy keys). 
     Document DE-A-4312905 describes a device for protecting the keyboard of a chip card reader comprising a conductive track supplied by a peripheral connector. The device is intended to be folded up around the electronic circuit of the keyboard. The use of a conductive track protects the electronic circuit against possible intrusions. However, the presence of a peripheral connector to power the conductive track creates a weak point in the system security. 
     FIELD OF THE INVENTION 
     The present invention aims at a device for protecting an electronic system comprising a package containing a keyboard membrane separated from a printed circuit by a spacer against intrusion attempts. 
     Thus, an embodiment of the present invention provides an electronic system, comprising: 
     an electronic circuit having a surface on which at least two first conductive tracks are arranged; 
     an actuation device comprising at least one first bearing element; 
     a spacer interposed between the electronic circuit and the actuation device and comprising at least one opening at least partially receiving the bearing element; and 
     a protection device interposed between the electronic circuit and the spacer and comprising at least one second conductive track having ends respectively connected to first conductive portions of first deformable regions of the protection device, each first portion being capable of contacting one of the first conductive tracks of the electronic circuit to electrically supply the second track under the effect of a deformation of said first regions. 
     According to an embodiment of the present invention, said first deformable regions are arranged outside of the periphery of the protection device. 
     According to an embodiment of the present invention, said first conductive portions are distant from the first conductive tracks in the absence of an external action exerted on the first deformable region, the first bearing elements being capable of deforming the first deformable regions to put the first conductive portions in contact with the first conductive tracks, whereby the respective ends of the second track are connected to the first conductive tracks. 
     According to an embodiment of the present invention, the protection device comprises a deformed area, the electronic circuit comprising electronic components covered by said area, the second conductive track extending at the level of said area. 
     According to an embodiment of the present invention, the protection device further comprises at least one second conductive portion supported by a second deformable region and separated from the second conductive track by an insulating region, the second conductive portion being, in the absence of an external action exerted on the second deformable region, distant from the third and fourth conductive tracks supported by the electronic circuit, at least one second bearing element being capable of deforming the second deformable region to put the second conductive portion in contact with the third and fourth conductive tracks, whereby the third and fourth conductive tracks are electrically connected. 
     According to an embodiment of the present invention, the protection device comprises a stack of first, second, and third insulating films, the second conductive track being arranged between the first and second insulating films, the third film being in contact with the electronic circuit and comprising openings at least in front of the first conductive tracks, exposing the conductive portions. 
     According to an embodiment of the present invention the spacer is formed of a material capable of diffusing light and comprises a first surface on the side of the actuation device and a second surface on the side of the electronic circuit, the electronic circuit comprising at least one light source, and the spacer comprising a non-through recess on the side of the second surface, containing said light source. 
     According to an embodiment of the present invention, the spacer comprises a first planar surface on the side of the actuation device and a second planar surface on the side of the electronic circuit, the first surface being tilted with respect to the second surface by an angle ranging between 1° and 20°. 
     According to an embodiment of the present invention, the actuation device comprises a membrane covering the spacer, the membrane comprising at least one key which is mobile with respect to the electronic circuit, capable of being displaced by a user and extending in one of the second bearing elements. 
     According to an embodiment of the present invention, the actuation device comprises a package containing the electronic circuit, the spacer, and the protection device, the package comprising an internal surface and a portion projecting from the internal surface and being capable of holding the first bearing elements against the first deformable regions of the protection device when the package is closed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features, and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings: 
         FIG. 1  is a simplified perspective view of an example of a card reader; 
         FIG. 2  is a perspective view of an embodiment of some internal elements of the reader of  FIG. 1 ; 
         FIGS. 3 and 4  are respective exploded perspective three-quarter top and bottom views of the elements of  FIG. 2 ; 
         FIGS. 5 and 6  are perspective views of the two surfaces of the protection device shown in  FIG. 2 ; 
         FIGS. 7 and 8  are simplified cross-section views of the reader of  FIG. 1  at the level of a keyboard key at two stages of the reader operation; 
         FIGS. 9 and 10  are simplified cross-section views of the reader of  FIG. 1  at the level of a dummy key respectively when the reader package is open and closed; 
         FIGS. 11 and 12  are cross-section views similar to  FIGS. 9 and 10  at the level of a power supply contact area of the protection device; 
         FIG. 13  is a bottom view of an example of distribution of internal conductive tracks of a variation of the protection device shown in  FIG. 6 ; and 
         FIG. 14  is a perspective view showing a cross-section of the elements shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     For clarity, the same elements have been designated with the same reference numerals in the different drawings. Further, only those elements which are necessary to the understanding of the present invention will be described. 
     The present invention provides, in an electronic circuit comprising a package containing a printed circuit separated from a keyboard membrane by a spacer, to interpose a protection device between the spacer and the printed circuit. The protection device corresponds to a flex circuit formed of a layer stack. The flex circuit comprises conductive elements on the printed circuit side, which form switches with conductive tracks of the printed circuit. Further, one or several conductive tracks are arranged in a lattice in the layer stack and are connected to an electronic safety circuit provided at the printed circuit level. The safety circuit is capable of detecting a modification of the electric voltage of the conductive tracks of the protection device. 
       FIG. 1  schematically shows an embodiment of an electronic circuit  10 , for example, a banking card reader. Reader  10  comprises a package  12  formed of an upper package portion  14  connected to a lower package portion  16 . Openings  17  are provided at the level of upper package portion  14  for a display  18  and keys  20  belonging, for example, to a keyboard. Further, an opening, not shown, is provided in package  12  to enable to introduce cards. 
       FIGS. 2 ,  3 , and  4  respectively are a general perspective view, an exploded three-quarter top view and an exploded three quarter bottom view of an embodiment of some internal elements of reader  10  of  FIG. 1 . Reader  10  contains a printed circuit  22  on which electronic components are connected, only a few electronic components being shown in  FIG. 3 . Printed circuit  22  comprises a surface  23  partially covered with a protection device  24  which will be described in further detail hereafter. In the present embodiment, protection device  24  is covered with a spacer  26  behaving as a light diffuser. Spacer  26  is covered with a flexible membrane  28  forming a keyboard, at the level of which keys  20  are formed. Keyboard membrane  28  comprises nineteen keys  20 . 
     Printed circuit  22  comprises conductive tracks, not shown, for example, made of copper, on the side of surface  23 . Only some locations of conductive tracks of printed circuit  22  forming switches of power supply contact areas have been shown in the form of ellipses  31 . A switch corresponds, for example, to the different ends of two conductive tracks which correspond, for example, to interdigitated combs. A power supply contact area corresponds, for example, to a comb. 
     Spacer  26  comprises an upper surface  33  covered with keyboard membrane  28  and a lower surface  34  resting on protection device  24 . According to the present embodiment, surfaces  33  and  34  are not parallel and form an angle of a few degrees, for example ranging between 1° and 20°, preferably between 2° and 6°. 
     Keyboard membrane  28 , for example made of silicone or polyurethane, comprises a base  35  having a surface  36  resting on spacer  26  and a surface  37  oriented towards upper package portion  14 . Each key  20  has a substantially parallelepipedal shape and is connected to base  35  by a thinned-down upper lip  38 . Further, each key  20  in continued on the side of surface  36  by a pin  40  which projects substantially perpendicularly to the plane of base  35 . Keyboard membrane  28  further comprises pins  41  which project from surface  36  substantially perpendicularly thereto and which are connected to base  35  by a thinned-down peripheral lip  42 . Keyboard membrane  28  also comprises lugs  43  distributed on surface  36  of base  35 . The length of pins  40 ,  41  is not uniform. More specifically, the length of pins  40 ,  41  increases along with the thickness of the portion of spacer  26  located close to the considered pins. In the present embodiment, keyboard membrane  28  comprises nineteen pins  40 , eight pins  41 , and ten lugs  43 . 
     Spacer  26  is crossed by nineteen cylindrical openings  44  intended to receive pins  40  of keyboard membrane  28  and eight cylindrical openings  45 , of same diameter or of smaller diameter than openings  44  and intended to receive pins  41 . Further, spacer  26  is crossed by ten cylindrical openings  46  of smaller diameter intended to receive lugs  43 . In the present embodiment, openings  44 ,  45 ,  46  have axes perpendicular to surface  33  of spacer  26 . Spacer  26  comprises through openings  49  intended for the passing of elements of reader  10 , for example, means for fastening package  12 . Spacer  26  comprises non-through recesses  50 ,  51  on the side of surface  34 . 
       FIGS. 5 and 6  show more detailed perspective views of protection device  24 . Reference numeral  53  is used to designate the surface of protection device  24  in contact with spacer  26  and reference numeral  54  is used to designate the surface of protection device  24  covering printed circuit  22 . Surface  53  cannot extend under the entire surface  33  of spacer  26 . In particular, the peripheral shape of protection device  24  may enable the passing of electronic components connected to surface  23  of printed circuit  22 . 
     Protection device  24  has a resilient structure. It is capable of being locally deformed and takes, in the absence of external action, a generally planar shape except for indentations  56  which project on the side of surface  53 . Each indentation  56  is arranged at the level of one of recesses  50  of spacer  26  and may have a shape substantially complementary to the associated recess  50 . Each indentation  56  may be obtained by plastic deformation of protection device  24 . Electronic components  57  may be provided on printed circuit  22  at the level of at least some of indentations  56  of protection device  24 . 
     Through openings  58 ,  60  may be provided in protection device  24 . More specifically, each opening  58  is provided substantially as an extension of one of openings  49  of spacer  26  and is intended to enable the passing of elements of the reader, for example means for fastening upper and lower package portions  14 ,  16 . Openings  60  are provided substantially as an extension of recesses  51  of spacer  26  and are intended to enable the passing of light-emitting diodes  61  connected to surface  23  of printed circuit  22 . 
     Protection device  24  comprises, on the side of surface  54 , planar conductive lands  66 , for example, made of carbon, for each of keys  20 . Protection device  24  further comprises, on the side of surface  54 , domed conductive elements  68 A and  68 B, called domes. Each dome  68 A,  68 B is associated with a pin  41 . Domes  68 A and  68 B have slightly different structures, as will be described in further detail hereafter. 
       FIGS. 7 to 12  show partial simplified cross-section views of the stack formed by printed circuit  22 , protection device  24 , spacer  26 , and keyboard membrane  28  at the level of a carbon land  66 , of a dome  68 A, and of a dome  68 B. In the drawings, the ratios between dimensions are not kept with respect to the preceding drawings. According to the present embodiment, protection device  24  is a flex circuit formed of a substrate  78  made of a resilient material, for example, a thermoplastic resin such as polyethylene therephtalate (PET) having a thickness, for example, on the order of 0.1 mm. One or several conductive tracks  80  are formed on substrate  78  on the side of printed circuit  22 . Tracks  80  are, for example, made of silver ink and are obtained by serigraphy. Tracks  80  and substrate  78  are covered with a varnish layer  92 , for example, formed of a dielectric material. A stack  93  of three layers  94 ,  96 , and  98 , forming a separator, covers varnish layer  92 . Separator  93  has, for example, a thickness on the order of 0.2 mm. It is possible for separator  93  not to be present at the level of each indentation  56 . Spacer  26  may be held on protection device  24  via a gluing material  99 . Separator  93  comprises an opening  100  at the level of each switch or power supply contact area  31 . For  FIGS. 7 to 10 , a switch  31  has been shown in the form of two separate conductive tracks  101 ,  102  formed on printed circuit  22  substantially at the level of opening  100  of separator  93  and, for  FIGS. 11 and 12 , a power supply contact area  31  has been shown in the form of a conductive track  103 . 
       FIGS. 7 and 8  are cross-section views at the level of a conductive land  66  respectively in the absence of any action on key  20  and when key  20  is pressed. Carbon land  66  covers varnish layer  92  and opening  100  of separator  93  at least partially exposes carbon land  66 . As appears in  FIG. 8 , when key  20  is pressed, lip  38  deforms to enable the key to move down along an axis D substantially perpendicular to surface  33 . Pin  40  causes a local deformation of protection device  24  along axis D′ perpendicularly to surface  34  at the level of opening  100  of separator  93  so that carbon land  66  comes into contact with tracks  101  and  102  and provides an electric connection between the tracks. When no further pressure is exerted on key  20 , protection device  24  resiliently returns to its neutral position in which it takes a planar configuration at the level of pin  40 , land  66  being then separated from conductive tracks  101 ,  102 . 
       FIGS. 9 and 10  are cross-section views at the level of a conductive dome  68 A respectively in the absence and in the presence of upper package portion  14 . Dome  68 A is a metal part having, for example, a 0.05-mm thickness corresponding, for example, to a portion of a sphere or of an ellipsoid. Dome  68 A is formed, for example, by deformation of a spring steel plate. The peripheral edge of dome  68 A may be located in a housing  110  provided in separator  93 . When upper package portion  14  is arranged, a finger  112  provided at the level of the internal surface of upper package portion  14  bears against pin  41 , which is displaced and bears against dome  68 A. Dome  68 A deforms to come into contact with conductive tracks  101 ,  102 , creating an electric contact between them. The deformed state of dome  68 A corresponds to an unstable position thereof so that, as soon as the action of finger  112  on pin  41  stops, dome  68 A takes back its domed shape and breaks the electric contact with tracks  101 ,  102 . 
       FIG. 11  is a view similar to  FIG. 9  at the level of a dome  68 B. As compared with what has been previously described in relation with  FIG. 9 , varnish layer  92  comprises an opening  113  which exposes one or several sections of track  80  substantially at the level of dome  68 B. Thereby, when flex circuit  24  and dome  68 B are deformed under the action of pin  41 , dome  68 B comes into contact, on the one hand, with track  80  and, on the other hand, with track  103  of printed circuit  22 . Such a contact is used to supply track  80 . The deformed state of dome  68 B corresponds to an unstable position thereof so that, as soon as the action of finger  112  on pin  41  stops, dome  68 B takes back its domed shape and breaks the electric contact between track  103  and track  80 . 
       FIG. 13  is a bottom view of protection device  24  showing an example of distribution of conductive tracks  80  on substrate  78 . Domes  68 A and  68 B have been shown in the form of circles. In the present example, a single track  80  extends on substrate  78 . Track  80  comprises a first end pad  104  at the level of one of domes  68 B and a second end pad  105  at the level of the other dome  68 B. Track  80  substantially zigzags across the entire surface of protection device  24 . In particular, track  80  extends at the level of domes  68 A and of conductive lands  66 , not shown. Conductive track  80  also extends at the level of indentations  56 . 
     Preferably, the section of track  80  brought by deformable dome  68 B into contact with a conductive track  103  of circuit  22  corresponds to an end of track  80 . Thus, both ends of track  80  are connected to conductive portions of deformable regions (domes  68 B) of the protection device. 
     Although this is not clearly shown in  FIGS. 11 and 12 , deformable conductive region  68 B is only in contact with the end point of track  80  by an opening through insulating layer  92 . Indeed, it is not desirable for the contact to short-circuit several sections since this risks to “blind” some areas of the protection device and then to adversely affect the reliability of the detection. 
     To avoid a pirate supply of track  80 , domes  68 B for supplying track  80  (and thus end pads  104  and  105 ) are placed outside of the periphery of the protection device. Thus, conductive track  80  protects not only against an intrusion attempt by means of a probe or the like, but also against a displacement of the system. The corresponding detections are performed by one or several adapted electronic circuits, supported by the printed circuit. 
     The width of conductive track  80  may be variable but preferably remains much lower (preferably, by a factor greater than 5) than the diameter of a dome. The narrower track  80  and the lower the intervals between sections, the better the sensitivity of the detection device. Further, the pattern followed by track  80  may take different shapes (coils, combs, curved sections, etc.). In the case where several tracks  80  are provided, they may be supplied by same deformable regions of the protection device and corresponding tracks of the printed circuit, or be associated with different deformable regions. 
       FIG. 14  is a view similar to  FIG. 2  in which a cross-section has been made. Lugs  43  of keyboard membrane  28  are held in the corresponding openings  46  of spacer  26  and hold keyboard membrane  28  in position with respect to spacer  26 . 
     The present embodiment enables to prevent the access to metal tracks  101 ,  102  of printed circuit  22  while preserving the switch function of pins  40 ,  41 . 
     The present embodiment enables to protect some electronic components  57  present on printed circuit  22  against an intrusion by encapsulating these components  57  with protection device  24 . 
     In the present embodiment, the two surfaces  33 ,  34  of spacer  26  may be tilted with respect to each other and not parallel. Spacer  26  enables to tilt the displacement axes of keys  20  of the keyboard with respect to the displacement axes of the deformable portions of protection device  24 . Keys  20  can thus be oriented to obtain the simplest and most natural possible motions for a user. 
     In the present embodiment, for each key  20 , protection device  24  is planar in the absence of an external action and is deformed to provide the electric connection between conductive land  66  and conductive tracks  101 ,  102 . The travel of protection device  24  is on the order of 1 mm. The switching speed is thus privileged. For pins  41 , protection device  24  has, in the absence of an external action, a domed shape due to resilient conductive element  68 A and is deformed to provide the electric connection between conductive element  68 A and conductive tracks  101 ,  102 . 
     Specific embodiments of the present invention have been described. Various alterations and modifications will occur to those skilled in the art. In particular, it may be provided to associate with keys  20  of keyboard membrane  28  the structure of protection device  24  shown in  FIGS. 9 and 10  where protection device  24  comprise a resilient conductive element  68 A having a domed shape in the absence of an external action. In this case, when key  20  is pressed, pin  40  continuing key  20  deforms conductive element  68 A to provide the electric connection between conductive tracks  101 ,  102  of printed circuit  22 . Further, a protection device in which membrane  28  would be used as a substrate for track  80  and where conductive lands  66  and domes  68 A and  68 B would be directly placed on membrane  28 , may be envisaged. Further, the resilient function of domes  68 A and  68 B may be achieved by thermoforming of protection device  24  above areas  31 .