Abstract:
The invention relates to a protection device fixed to a support and covering an electronic component. The protection device comprises at least a first wall corresponding to a first portion of printed circuit comprising at least a first conductive track, the first wall comprising at least a first mechanical guide element; at least a second wall corresponding to a second portion of printed circuit comprising at least a second conductive track, the second wall comprising at least a second mechanical guide element which interacts with the first guide element; and spot welds connecting the first wall to the second wall, at least one of the spot welds also electrically connecting the first conductive track to the second conductive track.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for protecting an electronic component, for example, an electronic component attached to a printed circuit, to avoid for anyone to have access to said electronic component or to data contained in said electronic component. 
     DISCUSSION OF PRIOR ART 
     Some electronic components, for example, a chip card or magnetic card reader, comprise a printed circuit contained in a package. Electronic components may be welded on both surfaces of the printed circuit. They may for example be a display screen, a serial link connector, a connector intended to be connected to the telephone network, a memory card connector, etc. The printed circuit surface on which the display screen is attached is called the front surface and the printed circuit surface opposite to the front surface is called the rear surface. 
     The security rules prescribed by accrediting bodies generally impose to provide protection devices enabling to prevent the access to certain electronic components attached to the printed circuit. In particular, for certain electronic components attached to the rear surface of the printed circuit, the security rules may impose the presence of specific protection devices for these components. Indeed, such components are more “sensitive” to fraud attempts since a user who manipulates the electronic system generally faces the screen and cannot notice that a fraud attempt has been carried out by tapping of the package on the rear surface side of the printed circuit. The printed circuit may integrate a track used as a protection mesh. This mesh blocks the access to the front surface components by its position on one of the lower layers of the printed circuit. A conventionally-used protection device corresponds to an enveloping flexible circuit (stamped or deformed) comprising a track intended to serve as an intrusion detection mesh, called flexible protection circuit hereafter. The flexible protection circuit is formed of the stacking of several flexible films between which are arranged interconnected conductive tracks forming at least one security circuit. The flexible protection circuit covers the electronic components to be protected and the security circuit is connected at its ends to a processing circuit, provided at the printed circuit level. The processing circuit is capable of detecting the rupture of a conductive track of the security circuit, which may correspond to an intrusion attempt. However, the protection provided by a flexible protection circuit may in certain cases be insufficient. 
       FIG. 1  shows a simplified example of a printed circuit  10  on which a memory card connector  12  is attached. Memory card connector  12  is arranged along the side of printed circuit  10 . Indeed, connector  12  must generally be accessible from an opening provided in the package containing the printed circuit to enable the introduction of a memory card into the connector and the retrieval of a memory card from the connector. The protection provided by a flexible protection circuit covering connector  12  may be insufficient. Indeed, someone could lift or deform the flexible protection circuit to have access to connector  12  without interrupting any conductive track of the security circuit of the flexible protection circuit. Such an intrusion would then not be detected. 
       FIG. 2  shows an example of protection device  20  conventionally used to protect memory card connector  12 . It is a rigid cage  20 , attached to printed circuit  10 , and covering connector  12  while providing access to connector  12  along the side of printed circuit  10 . Cage  20  being rigid and attached to printed circuit  10 , it cannot be easily displaced or deformed. Further, a mesh security circuit is generally provided on the internal surfaces of cage  20  to enable the detection of an attempt to drill cage  20 . 
     An example of a conventional method for manufacturing protection device  20  comprises stamping a thin plate corresponding to an insulating film, covered with an electrically conductive material (for example, copper) on both surfaces. The mesh security circuit is formed on one of the surfaces of the stamped thin plate. 
     It would be desirable to be able to further simplify the manufacturing method of such a protection device. 
     SUMMARY OF THE INVENTION 
     The present invention aims at an electronic component protection device, forming a rigid cage covering the electronic component and comprising a security circuit, which is particularly simple to manufacture. 
     According to another object, the protection device may be manufactured at a low cost. 
     To achieve all or part of these and other objects, an aspect of the present invention provides a protection device intended to be attached to a support and to at least partially cover at least one electronic component. The protection device comprises at least a first wall corresponding to a first printed circuit portion comprising at least one first conductive track at its surface, the first wall comprising at least a first mechanical guide element; at least a second wall corresponding to a second printed circuit portion comprising at least one second conductive track at its surface, the second wall comprising at least a second mechanical guide element which cooperates with the first mechanical guide element; and weld spots connecting the first wall to the second wall, at least one of the weld spots further electrically connecting the first conductive track to the second conductive track. 
     According to an embodiment, the clearance between the first wall and the second wall is smaller than 0.5 millimeter. 
     According to an embodiment, the first and/or the second printed circuit portion corresponds to a stacking of at least two rigid insulating layers, conductive tracks being arranged on a surface of the stacking and additional conductive tracks being arranged between the layers. 
     According to an embodiment, the second wall further comprises a third mechanical guide element and the first wall further comprises fourth and fifth mechanical guide elements. The device further comprises a third wall corresponding to a third printed circuit portion comprising at least one third conductive track at its surface, the third wall comprising at least a sixth mechanical guide element, which cooperates with the third mechanical guide element, a seventh mechanical guide element which cooperates with the fourth mechanical guide element, and an eighth mechanical guide element. The device further comprises a fourth wall corresponding to a fourth printed circuit portion comprising at least one fourth conductive track at its surface, the fourth wall comprising at least a ninth mechanical guide element which cooperates with the eighth mechanical guide element, and a tenth mechanical guide element which cooperates with the fifth mechanical guide element; and additional welding portions connecting the first wall to the third wall and to the fourth wall. 
     According to an embodiment, at least one of the additional weld spots electrically connects the third printed circuit portion to the first printed circuit portion and the fourth printed circuit portion to the first printed circuit portion. 
     According to an embodiment, all the weld spots ensuring an electric connection are intended to face the electronic component. 
     According to an embodiment, all the weld spots which are intended to be accessible from the outside of the protection device when the protection devices covers the electronic component only ensure a mechanical connection between the first wall and the second wall, between the first wall and the third wall, and between the first wall and the fourth wall. 
     The present invention also provides an electronic circuit comprising a printed circuit; at least one electronic component attached to the printed circuit; and at least one electronic component protection device such as defined previously. 
     According to an embodiment, the second wall comprises at least one protruding element, the printed circuit comprising an opening at least partially receiving the protruding element. 
     The present invention also provides a method for manufacturing a protection device intended to be attached to a support and to at least partially cover at least one electronic component. The method comprises the steps of providing at least a first wall corresponding to a first printed circuit portion comprising at least one first conductive track at its surface, the first wall comprising at least a first mechanical guide element, and at least a second wall corresponding to a second printed circuit portion comprising at least one second conductive track at its surface, the second wall comprising at least a second mechanical guide element; connecting the first wall to the second wall by having the first mechanical guide element cooperate with the second mechanical guide element; and forming weld spots connecting the first wall to the second wall, at least one of the weld spots further electrically connecting the first conductive track to the second conductive track. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing objects, features, and advantages of the present invention, as well as others, will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, among which: 
         FIG. 1 , previously described, shows a simplified example of an electronic component attached to a printed circuit; 
         FIG. 2 , previously described, schematically shows a conventional example of a device for protecting the electronic component of  FIG. 1 ; 
         FIGS. 3 and 4  respectively are an exploded view and a perspective view of an embodiment of a protection device according to the present invention; 
         FIGS. 5 and 6  respectively are a simplified cross-section view and a detail view of the protection device of  FIG. 4 ; 
         FIG. 7  shows the protection device of  FIG. 4  once attached to a printed circuit; and 
         FIGS. 8 and 9  are perspective views of other embodiments of the protection device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     For clarity, the same elements have been designated with the same reference numerals in the different drawings. 
       FIGS. 3 and 4  respectively are an exploded view and a perspective view of an embodiment of a protection device  30  according to the invention. Protection device  30  corresponds to a cage comprising: 
     a planar bottom plate  32  of rectangular general shape, comprising four edges  33 A,  33 B,  33 C, and  33 D, parallel two by two, edges  33 A and  33 D being however slightly tapered at one end, for example, to adapt to bulk constraints; 
     a first planar lateral plate  34  of rectangular general shape, comprising four edges  35 A,  35 B,  35 C, and  35 D, parallel two by two, edge  35 A being in contact with plate  32 ; 
     a second planar lateral plate  36  of rectangular general shape, adjacent to plate  34 , comprising four edges  37 A,  37 B,  37 C, and  37 D, parallel two by two, edge  37 A being in contact with plate  32 ; and 
     a third planar lateral plate  38  of rectangular general shape, adjacent to plate  36 , comprising four edges  39 A,  39 B,  39 C, and  39 D, parallel two by two, edge  39 A being in contact with plate  32 . 
     Plates  32 ,  34 ,  36 ,  38  correspond to cut portions of a printed circuit formed of a stacking of epoxy layers at the level of which conductive tracks are provided. 
     Bottom plate  32  comprises two oblong holes  40 ,  42 , which each extend along one of parallel edges  33 A,  33 C close to hole  33 D. Hole  40  receives a slug  44  which projects from edge  35 A of lateral plate  34  and hole  42  receives a slug  46  which projects from edge  39 A of lateral plate  38 . Lateral plate  34  comprises a notch  50  which extends along edge  35 B and emerges on edge  35 C. Notch  50  cooperates with a notch  52  of complementary shape provided at the level of lateral plate  36 , which extends along edge  37 D and which emerges on edge  37 A. Similarly, lateral plate  38  comprises a notch  54  which extends along edge  39 B and emerges on edge  39 C. Notch  54  cooperates with a notch  56  of complementary shape provided at the level of lateral plate  36 , which extends along edge  37 B and which emerges on edge  37 A. 
     Lateral plate  36  comprises two slugs  58 ,  60  which project from edge  37 A at the level of edges  37 D and  37 B, each cooperating with a notch  62 ,  64  provided on bottom plate  32 , notches  62 ,  64  extending along edge  33 B and respectively emerging on edges  33 A and  33 C. Plate  38  comprises a hook-shaped protrusion  65  which projects from edge  39 C. Protection device  30  further comprises a connector  66  attached to bottom plate  32 . 
     The assembly of protection device  30  may be performed by connecting plates  34 ,  36 ,  38  to one another by having notch  50  of plate  34  cooperate with notch  52  of plate  36  and by having notch  54  of plate  38  cooperate with notch  56  of plate  36 . The assembly formed by the three plates  34 ,  36 ,  38  is then placed on bottom plate  32  by introducing slug  44  of plate  34  into hole  40  of bottom plate  32 , by introducing slug  46  of plate  38  into hole  42  of bottom plate  32 , and by introducing slugs  58 ,  60  of plate  36  into notches  62 ,  64  of bottom plate  32 . The cooperation of slugs  44 ,  46 ,  58 ,  60  and of the corresponding holes  40 ,  42  and notches  62 ,  64  and of notches  50 ,  52 ,  54 ,  56  together enables to obtain an automatic alignment of plates  32 ,  34 ,  36 ,  38  with respect to one another with clearances that may be smaller than 0.5 mm, preferably smaller than 0.2 mm. Plates  32 ,  34 ,  36 ,  38  are then welded to one another, for example, according to a reflow welding method. Such a method comprises only arranging solder paste portions on plate  32  at the junctions between plates  32 ,  34 ,  36 ,  38 . The solder paste for example corresponds to a tin-based mixture of viscous texture. As an example, each solder paste portion has a thickness of several hundreds of micrometers. Protection device  30  is then heated in a reflow furnace to bring the solder paste portions to a liquid phase. At the next cooling step, a solidification of the solder paste portions, which form welds, is obtained. Connector  66  may also be welded to bottom plate  32  during the reflow welding operation. 
       FIG. 5  is a simplified cross-section view of plates  32  and  34  at the connection between these plates.  FIG. 5  is not drawn to scale. As an example, each plate  32 ,  34  corresponds to a printed circuit portion comprising a stacking of three insulating layers  70 ,  72 ,  74 , for example, epoxy layers, each having a 150-μm thickness. Conductive tracks  75 ,  76 ,  78 , for example, made of copper, are respectively arranged at the surface of layers  70 ,  72 ,  74 . As described hereafter, some of tracks  75  are used as bonding points for the forming of weld spots. The tracks  75  of plate  32  used as bonding points for the forming of weld spots are designated with reference  75   a  and the tracks  75  of plate  34  used as bonding points for the forming of weld spots are designated with reference  75   b . Further, for plates  34 ,  36 ,  38 , conductive tracks  80 , for example, made of copper, are also provided at the surface of insulating layer  74  on the side opposite to conductive tracks  78 . 
     Vias  81 , formed in layer  70 , made each connect one of tracks  75  to one of tracks  76 . Plate  34  is laid along edge  35 A against plate  32  and defines with plate  32  two junction regions  82 ,  83  on either side of plate  34 . A weld spot  84 , provided at the level of junction region  82 , electrically connects a track  75   a  of plate  32  to a track  75   b  of plate  34 . Another weld spot  86 , provided at the level of junction region  83 , electrically connects a track  75   a  of plate  32  to a track  80  of plate  34  and only ensures a function of mechanical connection between plates  32  and  34 . 
     The position of conductive tracks  75   a ,  75   b , and  80  used as bonding points for weld spots  84 ,  86  is an important parameter for the proper operation of the reflow welding method. Indeed, tracks  75   a  of plate  32  must be close to tracks  75   b  and  80  of plates  34 ,  36 ,  38 . For this purpose, tracks  75   b  and  80  of plates  34 ,  36 ,  38  are located at the end of the plate and tracks  75   a  of plate  32  partly extend under the edges of plates  34 ,  36 ,  38 . 
       FIG. 6  is a simplified view at the junction of plates  32 ,  34 , and  36 . Weld spots  84  are distributed along the contact regions between each pair of adjacent plates. The weld spots  84  which ensure an electric connection between tracks  75  of two adjacent plates are arranged inside of protection device  30 , that is, they face the component to be protected once protection device  30  is attached to the printed circuit. Some of weld spots  84  may only ensure a mechanical connection. Weld spots  86  which only ensure a mechanical connection between two adjacent plates are, as for them, provided outside of protection device  30 , that is, they are visible from the outside once protection device  30  has been attached to the printed circuit. This gives the assembly a mechanical strength greater than that provided by the sole weld spots  84  located on the inside. 
     Conductive tracks  75 ,  76 ,  78  of plates  32 ,  34 ,  36 ,  38 , interconnected especially by vias  81  and weld spots  84 , form at least one mesh-type security circuit. The ends of the security circuit emerge at the level of connector  66 . 
       FIG. 7  shows protection device  30  once assembled on a printed circuit  10 . Protection device  30  is assembled on printed circuit  10  by introduction of hook  65  into an opening  87  provided at the level of printed circuit  10 . This enables to properly position protection device  30  with respect to printed circuit  10 . Protection device  30  is then manually welded to printed circuit  10  by weld spots distributed at the periphery of device  30 . 
     Generally, protection device  30  may be electrically connected to printed circuit  10  via connector  66  or via the welds performed when protection device  30  is positioned on printed circuit  10 . In the second case, among the welds connecting protection device  30  to printed circuit  10 , some welds electrically connect the security circuit of protection device  30  to that of printed circuit  10  and other welds ensure a mechanical hold of protection device  30 . 
     More specifically, in the present embodiment, the electric connection between the security circuit of protection device  30  and a processing circuit provided at the level of printed circuit  10  is obtained by providing a connection plug, not visible in  FIG. 7 , at the level of printed circuit  10  capable of cooperating with connector  66  when device  30  is attached to printed circuit  10 . An attempt to remove or degrade device  30  then results in a rupture of a conductive track of the security circuit, which is detected by the processing system. The security circuit may also extend all the way to hook  65  to be able to detect a possible rupture thereof. 
       FIG. 8  shows another embodiment of protection device  100  according to the invention. As compared with protection device  30 , protection device  100  comprises, in addition to hook  65 , an additional hook  102  which projects from edge  35 C of plate  34 . Additional hook  102  is for example arranged symmetrically to hook  65 . Connector  66  may also be omitted. The electric connection between the security circuit of device  100  and printed circuit  10  can then be obtained by weld spots connecting the ends of hooks  65 ,  102  to printed circuit  10 . Such weld spots may be formed at the surface of printed circuit  10  which faces protection device  100 . This enables to make any attempt to neutralize protection device  100  even more difficult. 
       FIG. 9  shows another embodiment of device  103  according to the invention. As compared with protection device  30 , instead of hook  65 , four slugs  104 ,  106 ,  108 ,  110 , one slug  104  which projects from edge  35 C of plate  34 , two slugs  106 ,  108  which project from edge  37 C of plate  36 , and one slug  110  which projects from edge  39 C of plate  38 , are provided. The security circuit extends at least all the way to the end of two of slugs  104 ,  106 ,  108 ,  110 . The assembly of protection device  103  is obtained by introducing slugs  104 ,  106 ,  108 ,  110  into holes provided at the level of printed circuit  10 . Once the security device has been installed, at least two of slugs  104 ,  106 ,  108 ,  110  protrude from the surface of printed circuit  10  facing protection device  103 . The electric connection between the security circuit of device  103  and printed circuit  10  can then be obtained by weld spots connecting the printed circuit to the slug portions protruding from the surface of the printed circuit facing protection device  103 . This enables to make an attempt to neutralize protection device  103  even more difficult. 
     Of course, the present invention is likely to have all various alterations and modifications which will occur to those skilled in the art. In particular, although in the previously-described embodiments, the protection device is formed of four plates, it should be clear that the protection device may be formed of a different number of plates. Further, only some of the plates forming the protection device may correspond to printed circuit portions, the other plates being then formed of a rigid insulating material.