WO2010128939A1 - Arrangement for cooling tamper protected circuitry - Google Patents

An arrangement for enclosing electronic circuitry is disclosed. The arrangement comprises tamper protection means being arranged to form an interior space for keeping the electronic circuitry and an exterior space, and such that any straight line from the interior space to the exterior space intersects the tamper protection means. The arrangement also comprises a static heat conductive medium extending continuously from the interior space to the exterior space for leading heat from the electronic circuitry to the exterior space.

ARRANGEMENT FOR COOLING TAMPER PROTECTED CIRCUITRY

Technical Field

The present invention relates generally to the field of tamper protection of electronic circuitry. More particularly, it relates to cooling of tamper protected electronic circuitry.

Background

Tamper protection of electronic circuitry may involve prevention of access to the electronic circuitry, any information comprised in the electronic circuitry (such as program code or configurations of the circuitry), or any internal signals generated by the electronic circuitry. Additionally or alternatively, tamper protection of electronic circuitry may involve that attempts to access the electronic circuitry, information, or signals are detected. Tamper protection of electronic circuitry is known, for example, from www.gore.com where a tamper respondent envelope that can surround an entire module or a few chips is disclosed. The anti-tamper system surrounds the module or chips physically and electronically. A problem with such enclosure is that excess heat generated by the entirely enclosed circuitry cannot be efficiently disposed with. JP 2008/065401 A discloses a tamper protection arrangement where an airflow is provided to cool enclosed circuitry. A problem with air-cooling is that means must be provided to ensure a sufficient airflow to enable satisfactory cooling of the circuitry. For example, some type of fan and a sufficiently wide air-canal passing by the circuitry may be required. This makes such a solution ungainly for many purposes. Thus, if the circuitry is to be comprised in, for example, portable devices, small-sized devices, or hermetically sealed devices air-cooling may be cumbersome or even impossible. Another disadvantage with air-cooling is that the heat conductivity of air is relatively poor.

Therefore, there is a need for improved arrangements for tamper protection of electronic circuitry wherein cooling of the circuitry may be achieved. Summary

It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

It is an object of the invention to obviate at least some of the above disadvantages and to provide a tamper proof arrangement that enables cooling of the protected circuitry.

According to a first aspect of the invention, this is achieved by an arrangement for enclosing electronic circuitry comprising: tamper protection means being arranged to form an interior space for keeping the electronic circuitry and an exterior space, and such that any straight line from the interior space to the exterior space intersects the tamper protection means. The arrangement also comprises a static heat conductive medium extending continuously from the interior space to the exterior space for leading heat from the electronic circuitry to the exterior space.

In some embodiments, the arrangement may further comprise detecting means adapted to detect an alteration of the tamper protection means. The detecting means may comprise a detector (such as, for example, an impedance detector or an impulse response detector). The tamper protection means may comprise a tamper protection enclosure forming the interior space. The tamper protection means may, in some embodiments, further comprise a detector adapted to detect an alteration of the tamper protection means.

In some embodiments, the tamper protection means may comprise a raster having an impendence property, and the detecting means may be adapted to detect a change of the impedance property.

In some embodiments, the static heat conductive medium may be a one-piece block.

In some embodiments, the static heat conductive medium may be made of metal or a metal alloy. The metal may be aluminium. The tamper protection means may, in some embodiments, comprise a first tamper protection sheet arranged on a first side of the static heat conductive medium and a second tamper protection sheet arranged on a second side of the static heat conductive medium, the second side being opposite to the first side. The tamper protection means may further comprise a third tamper protection sheet part associated with and protruding from the first tamper protection sheet and arranged in a first groove in the first side of the static heat conductive medium, and a fourth tamper protection sheet part associated with and protruding from the second tamper protection sheet and arranged in a second groove in the second side of the static heat conductive medium. In some embodiments, the third and fourth tamper protection sheet parts may be flexible circuit card parts.

In some embodiments, the third and fourth tamper protection sheet parts may be arranged one outside the other and overlapping each other.

The third and fourth tamper protection sheet parts may, in some embodiments, each encircle the interior space.

In some embodiments, the third and fourth tamper protection sheet parts may comprise third and fourth tamper protection sheets.

The third and fourth tamper protection sheet parts may, in some embodiments, comprise third and fourth printed circuit card parts. In some embodiments, the first and second tamper protection sheets may comprise first and second printed circuit cards.

In some embodiments, the first printed circuit card may comprise a first raster arranged along the first groove and the second printed circuit card may comprise a second raster arranged along the second groove, and the static heat conductive medium may be fixed to the first and second printed circuit cards on their respective raster. In such embodiments, the alteration may comprise a tear in any of the first and second rasters. The static heat conductive medium may be fixed to the first and second printed circuit cards by an adhesive.

In some embodiments, the third and fourth printed circuit card parts may comprise third and fourth rasters and the alteration may comprise a tear in any of the third and fourth rasters. According to some embodiments, the arrangement further comprises means configured to, in response to a detected alteration of the tamper protection means, permanently erase information comprised in the electronic circuitry and/or means configured to permanently destroy the electronic circuitry. The means configured to permanently erase information comprised in the electronic circuitry may, for example, comprise a memory over-write functionality.

The means configured to permanently destroy the electronic circuitry may, for example, comprise a functionality configured to expose the electronic circuitry to a voltage and/or current spike. The arrangement may, in some embodiments, further comprise the electronic circuitry.

A second aspect of the invention is a device comprising the arrangement if the first aspect of the invention. In some embodiments, the device may be an electronic storage module, an electronic encryption module, an electronic authentication module, a communication device, a personal computer extension board, an automated teller machine - ATM, a lottery machine, an electronic voting machine, a cash register, a tachograph or a fight recorder.

In some embodiments, the second aspect of the invention may additionally have features identical with or corresponding to any of the various features as explained above for the first aspect of the invention.

An advantage of some embodiments of the invention is that tamper protection is achieved while still allowing excess heat to be lead away from a tamper protected electronic circuit.

Another advantage of some embodiments of the invention is that it enables use of powerful, but heat generating, circuitry in tamper-protected applications.

Another advantage of some embodiments of the invention is that the tamper protection and cooling arrangement may be made small and easy to handle.

Another advantage of some embodiments of the invention is that there is a possibility to make the arrangement hermetically sealed. This possibility in turn has the advantage that dirt particles and other impurities or pollutions cannot enter the interior space of the arrangement. Another advantage of some embodiments of the invention is that there is a possibility to make the arrangement waterproof (and/or tight against other liquids). This possibility in turn has the advantage that water (and/or other liquids) cannot enter the interior space of the arrangement even if the arrangement is exposed to or submerged into the liquid.

Another advantage of some embodiments of the invention is that there is no need for any fans (or other means for providing circulation of the heat conductive medium) or filters (e.g. particle filters) as may be the case for air-cooled arrangements. Thus, there is also the advantage that not filter changes are required to keep the cooling effective. Further, the arrangement does not generate any noise as is the case for air- cooled arrangements comprising a fan.

Brief Description of the Drawings

Further objects, features and advantages of the invention will appear from the following detailed description of embodiments of the invention, with reference being made to the accompanying drawings, in which:

Fig. 1 is an exploded view illustrating an example arrangement according to some embodiments of the invention;

Fig. 2 is a cutaway view illustrating an example arrangement according to some embodiments of the invention; and

Fig. 3 is a cutaway view illustrating details of an example arrangement according to some embodiments of the invention.

Detailed Description In the following, embodiments of the invention will be described where an aluminium frame is used to lead away excess heat from tamper protected electronic circuitry. It is noted however, that the use of aluminium as heat conductive material is merely used as an example to illustrate embodiments of the invention. Any other static heat conductive material may be used, such as other metals or metal alloys. Examples of heat conductive material that may be used include, but are not limited to: silver, copper, aluminium, gold, platinum, brass, and non-metallic heat-conductive materials (e.g. heat- conductive adhesives). The heat conductive medium being static makes unnecessary any means for providing circulation of the heat conductive medium and thus simplifies implementation.

Embodiments of the invention will be described with reference to Figures 1-3, which all illustrate schematically an example arrangement according to some embodiments of the invention. Figure 1 is an exploded view and Figure 2 is a cutaway view of the example arrangement, while Figure 3 is a cutaway view of details of the example arrangement.

The arrangement of Figures 1-3 is suitable for enclosing one or more electronic circuits or circuitry 110 to protect it from tampering and to detect tampering attempts. In the example arrangement, the tamper protection means that enclose the electronic circuitry 110, comprise a printed circuit board 111, whereupon the electronic circuitry 110 is mounted. The printed circuit board may comprise one or more internal conductive rasters (e.g. a mesh) in one or more layers and thereby provides tamper protection on a first side of the electronic circuitry 110. The tamper protection means further comprise a printed circuit board 116 arranged opposite to the printed circuit board 111. The printed circuit board 116 may be similar to the printed circuit board 111 in terms of its tamper protection properties and thereby provides tamper protection on a second side of the electronic circuitry 110. Such raster arrangements of the printed circuit boards 111 and 116 provide tamper protection in that, if an attempt is made to penetrate or otherwise invade the arrangement via either of the printed circuit boards 111, 116, one or more tears will appear in the respective raster. The tears will change the impedance properties of the raster, which makes the tamper attempt detectable. To this end, an impedance detector 150 is provided in association with the rasters. In the space between the two printed circuit boards 111 and 116, an aluminium frame 120 is mounted. The aluminium frame 120 has a cavity fitting to the electronic circuitry 110.

The tamper protection means of the example arrangement also needs to avoid tampering and detect tampering attempts via the space between the two printed circuit boards 111 and 116 (through the aluminium frame 120). To this end the tamper protection means comprise two flexible printed circuit cards 131, 141, each enclosing the electronic circuitry in the space between the two printed circuit boards 111 and 116. The two flexible printed circuit cards 131, 141 are arranged in respective grooves 130,

140 in the aluminium frame. The grooves 130, 140 are arranged on opposite sides of the aluminium frame. Thus, each of the flexible printed circuit cards or boards 131, 141 is associated with and protrudes from a respective printed circuit board 111, 116. The grooves 130, 140, and thereby the flexible printed circuit cards 131, 141, are arranged one inside the other and in an overlapping fashion.

In Figures 1-3, the flexible printed circuit boards 131, 141 are each arranged to form a substantially square form. However, other forms may be equally applicable, for example, circular or elliptic forms, or a substantially square form with rounded corners.

Furthermore, a single flexible printed circuit board may be used. In such embodiments, the single flexible printed circuit board may extend in a groove corresponding to the groove 140, via a passage through the aluminium frame to a groove corresponding to the groove 130 such that it encircles the interior space in an overlapping fashion. In other embodiments, more than two flexible printed circuit boards may be used to create the encircles of the interior space. In such embodiments, it is also possible to use non- flexible boards and arrange them with a suitable overlap.

The printed circuit boards 111, 116 and the flexible printed circuit boards 131,

141 create an interior space that has the property that any straight line from the interior space to the exterior intersects the tamper protection means. Thereby efficient tamper protection is provided. At the same time a passage (thermal bridge) for excess heat to be lead away form the interior space is provided by means of the overlapping arrangement of the flexible printed circuit boards 131, 141.

The aluminium frame 120 serves to hold together the assembly and also leads excess heat away from the electronic circuitry 110, thereby providing cooling of the electronic circuitry. To this end, the aluminium frame extends from the interior space created by the tamper protection means to the exterior space via the passage to enable excess heat to be conducted from the interior space.

The assembly maybe held together by gluing the aluminium frame to the printed circuit boards 111, 116. Any suitable adhesive or other fastening means may be used for fixing the aluminium frame to the printed circuit boards 111, 116. The printed circuit boards 111, 116 may be provided with respective rasters 112, 117 on the side facing the aluminium frame 120. The rasters may be arranged along the respective grooves 130, 140 of the aluminium frame. The fastening means provided to hold together the assembly may be arranged in particular on the aluminium frame 120 and the printed circuit boards 111, 116 at the location of the respective rasters 112, 117. A raster may, for example, comprise a mesh, a wiring, a tinplate arrangement, or similar. The material of the raster may, for example, be copper or silver. Any material having measurable impedance properties may be used (for example, the tamper respondent material ofwww.gore.com). Such a raster arrangement provides a further tamper protection in that, if an attempt is made to remove either of the printed circuit boards 111, 116, one or more tears will appear in the respective raster. The tears will change the impedance properties of the raster, which makes the tamper attempt detectable. To this end, the impedance detector 150 is additionally provided in association with the rasters. It is noted that even though this embodiment has been described as having one impedance detector 150, several impedance detectors may be used, each provided in association with one or more of the rasters.

The flexible printed circuit boards 131, 141 may also comprise respective rasters similar to those described above. This raster arrangement also provides a further tamper protection in that, if an attempt is made to access the interior space via the space between the two printed circuit boards 111 and 116 (e.g. by drilling or other invasive techniques), one or more tears will appear in the rasters of the flexible printed circuit boards 131, 141. As above, the tears will change the impedance properties of the raster, which makes the tamper attempt detectable. Thus, the impedance detector 150 may be associated also with the rasters of the flexible printed circuit boards 131, 141.

The arrangement may additionally have means configured to permanently erase part or all of the information of the electronic circuitry 110 and/or completely destroy the electronic circuitry 110 in response to a detection of an attempt to access the interior space. Information that may be erased includes, but is not limited to, code controlling the operation of the circuitry (e.g. program code, configurations, etc) and data stored in the circuitry (e.g. encryption keys, military secrets, or any other sensible data).

For example, information and/or program code may be stored in a battery- backed-up memory. If a tamper attempt is detected the memory may be actively over- written. Alternatively or additionally, the memory may be passively erased by cutting off the battery power supply.

Numerous variations to the arrangement of Figures 1-3 may be envisioned while not departing from the scope of the invention. For example, the geometry and the use of two printed circuit boards and two flexible printed circuit boards as in the described embodiment is merely an example and by no means limiting. In other embodiments, the tamper protection means may comprise other materials than printed circuit boards, for example sheets of the tamper responsive material ofwww.gore.com. Furthermore, the parts of the tamper protection means and their geometry relative each other may be selected and arranged in any way that forms an interior space for keeping the electronic circuitry and an exterior space, and such that any straight line from the interior to the exterior intersects the tamper protection means to provide efficient tamper protection. An additional criterion is that a passage must be provided that extends from the interior space to the exterior space to provide a possibility of leading heat from the electronic circuitry to the exterior space. The aim of the tamper protection means may be one or both of: render it impossible (or at least very cumbersome) to access the interior space and hence the electronic circuitry, and detecting an attempt to access the interior space such that information may be erased and/or the circuitry be destroyed. For fulfilling the first purpose, the material of the tamper protection means should be hard to penetrate, and any joints between sheets of material should be firmly fixed. For fulfilling the second purpose the tamper protection means should be such that an attempt to penetrate the material or loosen the joints results in a measurable alteration of the tamper protection means.

As described above, the alteration of the tamper protection means may be a change in an impedance property of a raster. The raster may be arranged as in the embodiments described in Figures 1-3 or in any other suitable way. For example, the raster may be provided on the entire tamper protection means. A change of impedance property may, for example, be caused by a break of the raster (e.g. a tear), a shortcut in the raster, or any other impedance change (e.g. a partial break of the raster). In such embodiments, an impedance detector may be provided in association with the raster to detect the impedance change. The impedance detector may take any suitable form. For example, it may be an analog or a digital impedance detector. In some embodiments, the impedance detector may be adapted to measure voltage and current and perform complex division to estimate the impedance. A memory and comparison function may be implemented to determine whether there is a change in impedance. The memory and comparison function may be integral with or external to the impedance detector.

However, it is to be understood that other measurable alterations of the tamper protection means, and other detection means may fulfill the same purpose. For example, the detection means may comprise a detector adapted to evaluate a response to an impulse (or other signal) emitted by the detector. A memory and comparison function may be implemented to determine whether there is a change in the response. The memory and comparison function may be integral with or external to the detector.

The heat conductive medium has been described as a one-piece aluminium frame having a specific geometry. However, other materials may be used as mentioned above. Furthermore, the heat conductive medium may in some embodiments comprise two or more separate or connected parts as long as it extends continuously from the interior space to the exterior space.

The invention may be embodied within a device (e.g. an electronic apparatus) comprising an arrangement according to any of the embodiments of the invention. The electronic apparatus may, for example, be a portable or handheld mobile radio communication equipment, a mobile radio terminal, a mobile telephone, a computer, an encryption device for communication and/or storage, an electronic storage module (for example for storing of secret information such as encryption keys, symmetric keys, asymmetric private keys, etc.), an electronic encryption module, an electronic authentication module, a certificate authority (CA) device, a personal computer extension board, an automated teller machine (ATM), a lottery machine, an electronic voting machine, a cash register, a tachograph or a fight recorder. The invention has been described herein with reference to various embodiments. However, a person skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the invention. For example, it should be noted that in the description of embodiments of the invention, the partition of functional blocks into particular units is by no means limiting to the invention. Contrarily, these partitions are merely examples. Functional blocks described herein as one unit may be split into two or more units. In the same manner, functional blocks that are described herein as being implemented as two or more units may be implemented as a single unit without departing from the scope of the invention. Hence, it should be understood that the limitations of the described embodiments are merely for illustrative purpose and by no means limiting. Instead, the scope of the invention is defined by the appended claims rather than by the description, and all variations that fall within the range of the claims are intended to be embraced therein.

1. An arrangement for enclosing electronic circuitry (110) comprising: tamper protection means (111, 112, 116, 117, 131, 141) being arranged to form an interior space for keeping the electronic circuitry and an exterior space, and such that any straight line from the interior space to the exterior space intersects the tamper protection means; characterized by a static heat conductive medium (120) extending continuously from the interior space to the exterior space for leading heat from the electronic circuitry to the exterior space.

2. The arrangement of claim 1, further comprising detecting means (150) adapted to detect an alteration of the tamper protection means.

3. The arrangement of claim 2, wherein the tamper protection means comprises a raster having an impendence property, and wherein the detecting means is adapted to detect a change of the impedance property.

4. The arrangement of any of claims 1 through 3 wherein the static heat conductive medium is a one-piece block.

5. The arrangement of any of claims 1 through 4 wherein the static heat conductive medium is made of metal or a metal alloy.

6. The arrangement of claim 5 wherein the metal is aluminium.

7. The arrangement of any of claims 1 through 6, wherein the tamper protection means comprises: a first tamper protection sheet (111) arranged on a first side of the static heat conductive medium; a second tamper protection sheet (116) arranged on a second side of the static heat conductive medium, the second side being opposite to the first side; a third tamper protection sheet part (131) associated with and protruding from the first tamper protection sheet and arranged in a first groove (130) in the first side of the static heat conductive medium; and a fourth tamper protection sheet part (141) associated with and protruding from the second tamper protection sheet and arranged in a second groove (140) in the second side of the static heat conductive medium.

8. The arrangement of claim 7, wherein the third and fourth tamper protection sheet parts are flexible circuit card parts.

9. The arrangement of any of claims 7 through 8, wherein the third and fourth tamper protection sheet parts are arranged one outside the other and overlapping each other.

10. The arrangement of any of claims 7 through 9, wherein the third and fourth tamper protection sheet parts each encircles the interior space.

11. The arrangement of any of claims 7 through 10 wherein the third and fourth tamper protection sheet parts comprise third and fourth tamper protection sheets.

12. The arrangement of any o f claims 7 through 11 , wherein the third and fourth tamper protection sheet parts are third and fourth printed circuit card parts.

13. The arrangement of any of claims 7 through 12, wherein the first and second tamper protection sheets are first and second printed circuit cards.

14. The arrangement of claim 13, wherein the first printed circuit card comprises a first raster (112) arranged along the first groove and the second printed circuit card comprises a second raster (117) arranged along the second groove, and wherein the static heat conductive medium is fixed to the first and second printed circuit cards on their respective raster.

15. The arrangement of claim 14, wherein the static heat conductive medium is fixed to the first and second printed circuit cards by an adhesive.

16. The arrangement of claims 3 and 14, wherein the alteration comprises a tear in any of the first and second rasters.

17. The arrangement of claims 3 and 12, wherein the third and fourth printed circuit card parts comprise third and fourth rasters and the alteration comprises a tear in any of the third and fourth rasters.

18. The arrangement of any of claims 2, 3, 16 or 17, further comprising means configured to, in response to a detected alteration of the tamper protection means, permanently erase information comprised in the electronic circuitry and/or means configured to permanently destroy the electronic circuitry.

19. An arrangement according to any of the preceding claims, further comprising the electronic circuitry (110).

20. A device comprising the arrangement according to any of the preceding claims.

21. The device according to claim 20, wherein the device is an electronic storage module, an electronic encryption module, an electronic authentication module, a communication device, a personal computer extension board, an automated teller machine - ATM, a lottery machine, an electronic voting machine, a cash register, a tachograph or a fight recorder.