Abstract:
A circuit which is to be protected contains a substrate which includes a recoiling area is surrounded by protruding areas. A hardware protection system is provided as half-shells and includes conductor structures arranged on and/or in the substrate to detect access to the circuit which is protected.

Description:
BACKGROUND 
       [0001]    Electronics modules for highly sensitive data processing and data backup, of the kind used, for example, in tachographs for commercial vehicles but also in financial institutions, ATMs, aircraft and wherever sensitive data is being handled, must have hardware protection to prevent external tampering, such as chemical or physical attacks (e.g. mechanical, laser, fire, etc.), so that data cannot be fraudulently manipulated. 
         [0002]    The existing solution is for the electronics module requiring protection to be wrapped all round in a sheet of so-called anti-drilling foil. Such anti-drilling foil is available e.g. from Gore as a finished product or from Freudenberg as a foil with conductive silver paste print. The inside of the foil is electrically connected to the module. After the electronics module has been three-dimensionally wrapped, it is then synthetic resin encapsulated in a container. In the event of an attempt to open the package, the electrical conductor runs or resistive lines on the foils are sure to be damaged or broken at the locations at which the attacks take place, causing the data to be immediately erased in the electronics module. This means that the data cannot be tampered with and the external attack is therefore detectable by appropriate monitoring agencies. 
         [0003]    There are two problems with this known method. On the one hand, the use of foil does not conform to any electronics assembly process. Second, the foil is often damaged even during assembly, resulting in high wastage. 
       SUMMARY 
       [0004]    An aspect is therefore to specify a hardware protection system for electronics modules which can be incorporated into electronics production. 
         [0005]    To achieve this, a hardware protection system for a circuit to be protected has a conductive or non-conductive planar substrate. However, the planar substrate is not flat, but has a set-back central region which is enclosed, preferably completely, by projecting regions. Conductive patterns for detecting access to the circuit to be protected are disposed on and/or in the substrate. In the event of unauthorized access to the circuit, the conductive patterns are damaged, so that a contact is made or broken and access to the circuit is thereby detected. 
         [0006]    The projecting regions preferably have an edge running parallel to the set-back central region. This edge enables the hardware protection system to be disposed on a circuit carrier in a planar manner where it can be bonded or soldered or generally contacted. 
         [0007]    In particular the substrate is implemented in the form of a half-shell. 
         [0008]    The substrate is preferably a deep-drawn circuit board and/or a foil. 
         [0009]    Advantageously the conductive patterns and the isolation spacings of the area sensor form a tightly meshed entity in the form of a grid, in the form of a network, with meanders and/or with sectors in which the conductive patterns run e.g. in the form of geometrical features, the isolation spacings between two runs of the conductive pattern in the form of conductor runs or conductor tracks (the mesh size) corresponding to known HDI (high density interconnection) structures. The same applies to the width of the runs of the conductive patterns. 
         [0010]    The conductive patterns can be produced particularly simply and inexpensively by printing. This is preferably performed while the planar substrate is still flat, i.e. not yet deep-drawn. 
         [0011]    In particular the hardware protection system has connections for connecting detectors for detecting conductive pattern damage. 
         [0012]    In a method for producing a hardware protection system of one of the above described types, a planar substrate is provided with conductive patterns for detecting access to a circuit to be protected. Previously or preferably subsequently, the substrate is formed into a shape in which it has a set-back central region enclosed by projecting regions. Advantageous embodiments of the method result from the advantageous embodiments of the hardware protection system and vice versa. 
         [0013]    A device has a hardware protection system of one of the above described types and a circuit carrier for a circuit to be protected. The hardware protection system is disposed with the projecting regions of its substrate on the circuit carrier, so that space for the circuit to be protected is created between the set-back central region and the circuit carrier. 
         [0014]    The circuit carrier preferably is or contains a circuit carrier PCB, the back side of which often has to be protected also. For this purpose the device has in particular a second hardware protection system according to one of the previously described types which is disposed on the side of the circuit carrier opposite the first hardware protection system. 
         [0015]    In addition, the device preferably contains detectors for detecting conductive pattern damage due to illegal access and/or tampering. To ensure that the detectors are also protected, they can be implemented as part of the circuit to be protected. 
         [0016]    The complete module with the circuit carriers is used particularly in a tachograph, a driving data recorder and/or a railborne or non-railborne vehicle. However, it can also be used in ATMs, systems of financial institutions and aircraft. In particular, the use of the complete module with circuit carriers is advantageous whenever cryptographic keys (RSA, DES) to be protected are used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    These and other aspects and advantages will become more apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
           [0018]      FIG. 1  is a cross section of an embodiment of a device with a circuit carrier, on one side of which a hardware protection system is disposed and on the opposite side of which a second hardware protection system is disposed; 
           [0019]      FIG. 2  is a cross section of an alternative embodiment of a device with a circuit carrier, on one side of which a hardware protection system is disposed and on the opposite side of which a second hardware protection system is disposed; 
           [0020]      FIG. 3  is a cut-away plan view of a conductive patterned substrate from which a hardware protection system is produced. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
         [0022]      FIG. 1  shows a hardware protection system  10  having a planar substrate  11 ,  12  having a set-back central region  11  which is completely enclosed by projecting regions  12 . Conductive patterns  13 ,  14  are disposed on and in the substrate  11 ,  12 . For this purpose the substrate  11 ,  12  contains two prepregs  15 ,  16 . The first prepreg  15  forms the side of the substrate  11 ,  12  which faces in the direction in which the central region  11  is set back. The first conductive structure  13  of the two above mentioned conductive patterns  13 ,  14  is disposed on the side of the prepreg  15  facing in the direction in which the regions  12  enclosing the central region  11  project. 
         [0023]    In turn disposed thereon is the second prepreg  16  on whose side opposite the first conductive pattern  13  the second conductive pattern  14  is disposed. 
         [0024]    The hardware protection system  10  has connections  17  for contacting the conductive patterns  13 ,  14  with other hardware protection conductive patterns and with detectors for detecting damage to the conductive patterns  13 ,  14 . 
         [0025]    The hardware protection system  10  is disposed with its projecting regions  12 , in particular with their edges, on a circuit carrier  20  for a circuit  21  to be protected. In the example shown in  FIG. 1 , the circuit carrier  20  is embodied as a multilayer circuit board. 
         [0026]    In the area in which the edges of the projecting regions  12  running parallel to the central region are disposed on the circuit carrier  20 , the circuit carrier  20  for its part, to protect the circuit  21  to be protected, has circuit carrier conductive patterns  22  by which frontal drilling into the circuit carrier  20  can be registered. These are connected via the connections  17  to the conductive patterns  13 ,  14  of the hardware protection system  10 . 
         [0027]    The circuit carrier  20  also has input and output connections  23  outside the protection area which are connected to the circuit  21  to be protected via lines which are routed through the layers of the circuit carrier conductive patterns  22 . 
         [0028]    A second hardware protection system  30  is disposed on the circuit carrier  20  on the side opposite the first hardware protection system. The second hardware protection system  30  is of similar design to the first hardware protection system  10  and likewise has a set-back central region  31  enclosed by projecting regions  32 . Its substrate is made up e.g. of prepregs  35 ,  36  between which a first conductive pattern  33  is disposed which is connected via connections  37  to a second conductive pattern  34  which is disposed on the side of the prepreg  36  facing away from the prepreg  35  and the conductive pattern  33 . The second hardware protection system  30  is disposed rotated by a defined angle with respect to the first hardware protection system  10 . 
         [0029]    The embodiment shown in  FIG. 2  differs from that shown in  FIG. 1  in that the two hardware protection systems  10 ,  30  are not disposed on the multilayer circuit board of the circuit carrier  20 , but directly adjacent to one another. The circuit carrier  20  in this case contains, in addition to its multilayer circuit board, further carriers  24  with which the circuit  21  to be protected and the multilayer circuit board of the circuit carrier  20  are retained in the space produced between the set-back central regions  11 ,  31  of the hardware protection systems  10 ,  30 . 
         [0030]      FIG. 3  depicts a planar substrate  41 ,  42 ,  44  with a square central region  41  which is enclosed at its four edges by regions  42 ,  44 . The regions  42 ,  44  for their part each have, adjacent to the central region  41 , a region which is angled thereto in a deep-drawing process, and an edge which is non-adjacent to the region  42  and which, for its part, is angled to the region of the region  42  that is adjacent to the central region  41  in such a way that it again runs parallel to the central region  41 . Between the regions  42  enclosing the central region  41 , cutouts  43  are provided which open up on deep-drawing of the regions  42 ,  44  so that they can be welded together at their abutting edges. The entire substrate  41 ,  42 ,  44  in the form of pre-patterned and subsequently deep-drawn anti-drilling layers is imprinted with a meandering conductive pattern. 
         [0031]    The anti-tamper hardware protection is therefore incorporated into one or two three-dimensional half-shells which are formed e.g. as a deep-drawn part or deep-drawn parts and either completely surround the circuit to be supported with its module ( FIG. 2 ) or are mounted on the circuit board  20  of the module to be protected of the circuit  21  ( FIG. 1 ). 
         [0032]    If in a particular embodiment only one three-dimensional half-shell is used, in place of the second half-shell the flat circuit board  20  can be used as a substitute for the second half-shell. The electronic components are then disposed on the side facing the first half-shell and the hardware with its conductive patterns is disposed on the side facing away therefrom. 
         [0033]    For the last-mentioned case, an additional hardware protection system must also be incorporated in the circuit board used for the module, e.g. by the latter itself having a conductive pattern network  22  in the regions in which it is soldered or bonded to the hardware protection system. This can be realized, for example, by the circuit board  20  being implemented as a multilayer circuit board which contains, in the regions in question, a plurality of conductor layers disposed one above the other which provide protection from frontal spot drilling. 
         [0034]    The design of the half-shells  11 ,  12 ;  31 ,  32  of the hardware protection system  10  can, on the one hand, be executed in such a way that they are produced from a deep-drawn circuit board material such as glass fiber reinforced FR4 prepreg which is not yet cured in its initial state. On the other hand, the use of foils is possible, particularly RCC foils (resin coated copper, partially copper pre-patterned) or otherwise deep-drawn foils with or without metal coating. 
         [0035]    Prior to deep-drawing and subsequent curing, a tightly meshed conductive or resistive network is patterned onto one or both sides. The protection network made up of conductive patterns  13 ,  14 ;  33 ,  34  can be embodied, on the one hand, as a patterned metal line network e.g. lithographically by etching or other suitable processes. On the other hand, it can also be implemented as a resistive network, carbon-filled resin systems preferably being screen or resistance printed onto one or both sides to produce the protective pattern. 
         [0036]    However, such a resistive network can also be applied by direct printing with carbon ink or similar suitable methods. 
         [0037]    The design of the deep-drawn parts  11 ,  12 ;  31 ,  32  for the hardware protection system can be such that, on the one hand, they are similar to multilayer circuit boards, the lines necessary for the protective wiring facing the module side and having no electrical vias through to the outside of the half-shells. For this purpose, all the vias necessary for the functions of the hardware protection shells and the module are inside the protection network and are implemented either as buried vias, and/or the necessary build-up layers for sub-module wiring are implemented as SBUs (sequential build-ups) with laser-drilled or otherwise produced micro-via through holes. 
         [0038]    Should the deep-drawn hardware protection shells be applied on one or both sides to the circuit board  20  of the circuit carrier of the circuit to be protected, the circuit board must, as in the above implementations, be designed as a multilayer circuit board with a corresponding hardware protection network  22  against frontal attacks. 
         [0039]    The conductive patterns of the shell-shaped hardware protection system have an array of contacting pads which are subsequently used either to connect the two hardware protection shells enclosing the circuit to be protected to the circuit carrier of the circuit to be protected or to electrically interconnect them on the multilayer circuit board of the circuit carrier of the circuit to be protected. 
         [0040]    The hardware protection shells contain one or more conductive layers. These are implemented e.g. as multiple copper layers each containing very fine-line traces of the conductive patterns  13 ,  14 ;  33 ,  34  which, on the one hand, cover the entire layer surface in a tightly meshed manner but also extend from layer to layer contingent upon the design of the conductor runs. 
         [0041]    The conductor widths of one layer thereby cover isolation spaces and some of the associated conductor tracks of the layers associated therewith and separated by the dielectric. 
         [0042]    They are likewise again through-wired inward to the module via buried vias or μm-vias. 
         [0043]    The design embodying a layer e.g. in the X-direction with such a meander pattern of thin copper conductor tracks and the under- or overlying layer in the Y-direction separated by the dielectric layer provides the circuit with hardware protection against mechanical tampering due to the fact that these conductor runs are wired inwardly to the module and are therefore damaged due to the ultrafine patterning. This causes a line break which is registered in the circuit. Alternatively, two networks can also be used and short-circuiting of the two networks due to tampering can be registered. 
         [0044]    The conductive patterns  13 ,  14 ;  33 ,  34  can preferably be implemented as ultrafine conductors using carbon printing (resistive paste printing), as conductive paste (conductive silver paste) or as ink printing using carbon ink in all conceivable patterns which produce a tightly meshed network on a wide-area basis over at least one layer and which are electrically connected inwardly to the circuit. 
         [0045]    At least one of the hardware protection shells  11 ,  12 ;  31 ,  32  can also be realized in “flex-rigid” technology or a flex line for data transfer can be added. 
         [0046]    The dielectric spacing of the hardware protection layers in the hardware protection shells shall be selected such that, also in the event of frontal spot drilling, the over- and underlying protection layer will be damaged, thereby triggering the protection mechanism. 
         [0047]    The electrical and mechanical connection of the hardware protection shells to one another or to the circuit carrier of the circuit to be protected can be established by soldering with subsequent sealing of the solder gap by adhesives, laminating, contact bonding or a similar method. Known connection methods can likewise be used. 
         [0048]    One advantage of the hardware protection system described is that it provides a sensor system which is incorporated in the hardware protection shells and possibly in the multilayer circuit board of the circuit carrier of the circuit to be protected and which can be produced using virtually conventional “high-tech” circuit board technology and populated and processed on conventional component placement lines and electronic module production facilities. Another advantage is that it provides and incorporates directly in the electronics module a security system for reliably detecting hardware attacks that is secure, inexpensive and does not entail additional assembly costs. 
         [0049]    The system also includes permanent or removable storage, such as magnetic and optical discs, RAM, ROM, etc. on which the process and data structures of the present invention can be stored and distributed. The processes can also be distributed via, for example, downloading over a network such as the Internet. The system can output the results to a display device, printer, readily accessible memory or another computer on a network. 
         [0050]    A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide v. DIRECTV,  358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).