A BOX FOR ENCAPSULATING AN ELECTRONIC DEVICE, AND A METHOD FOR GLUING A CIRCUIT BOARD ONTO THE INNER SURFACE OF A BOX

Abstract: The present invention relates to a box (1) for protective encapsulation of electronic circuits (7) carrying confidential information such as passwords, encryption codes etc. The box (1) comprises means for detecting penetration of the box (1) caused by chemical or corrosive destruction of the walls. It also comprises means for deleting confidential information carried by said electronic circuits (7) upon detection of penetration. Said means for detecting the penetration comprises an electronic circuit (3) provided in the box (1), said electronic circuit (3) comprising at least one electrical conductive path being exposed towards said chemical matter penetrating the box (1). The invention also relates to a method for gluing a circuit board (3) onto the inner circuit of the box (1) so that through-holes are provided in the glue (2).

Description: A BOX FOR ENCAPSULATING AN ELECTRONIC DEVICE, AND A METHOD FOR GLUING A CIRCUIT BOARD ONTO THE INNER SURFACE OF A BOX Field of the Invention 5 The present invention relates to a box for protective encapsulation of electronic circuits carrying confidential information such as passwords, encryption codes etc. Such encapsulation is used e.g. in connection with circuits for encryption of codes in ATM machines and in similar devices carrying confidential information. 10 Description of the Prior Art In general electronic circuits carrying confidential information such as passwords, encryption codes etc. are protected against intrusion by encapsulating the circuits mechanically in a box protected by electronic sensors. The sensors are adapted in order 15 to detect intrusion into the box, e.g. penetration through a wall of the box or opening of the box. Typically the intrusion results in deletion of the confidential information. One method of sensing intrusion through the walls of the box is by fastening a printed circuit board (PCB) to the inner surface of the box. The PCB has a pattern of conductive paths closely arranged side by side. In the case of mechanical intrusion through the wall, one or more 20 of the conductive paths will either break or be connected to an adjacent path, both situations resulting in the deletion of the confidential information. By means of the known sensors it has been relatively easy to detect mechanical intrusion. As an example it is relatively easy to detect destruction of the box by drilling, milling or 25 simply by crushing the walls of the box. On the other hand it is difficult to detect intrusion caused by a chemical or corrosive destruction of the walls. When the walls or parts of the walls are removed, the intruder can manipulate the exposed conductive paths of the PCB so that further intrusion in the box is possible without the release of the sensor and thus without the deletion of the confidential information. 30 Description of the Invention It is an object of the present invention to provide a method and a box for encapsulation of an electronic circuit and which will enable detection of chemical destruction of the box. Accordingly the present invention relates to a box for encapsulating an electronic device, said box comprising - means for detecting penetration of the box, and - means for deleting confidential information carried by the electronic device upon detection of the penetration, said means for detecting the penetration comprising an electronic circuit provided in the box, the electronic circuit comprising at least one electrical conductive path being exposed towards a chemical matter penetrating the box. The box could be of any shape and of any size. As an example the box could be used for encapsulation of a printed circuit board for encryption of pin codes. As an example such circuit boards are being used in connection with ATM machines for the encryption of the pin codes entered by the customers of the machines. The printed circuit board is carrying vital and of course confidential information that may be retrieved by examining the printed circuit board. An electrical signal transmitted from the keyboard is then transferred directly to the box. The box is provided with means for transferring the signal from the outside of the box to the inside of the box, wherein the signal is received by the printed circuit board. The encryption takes place and the encrypted signal is again transferred from the inside of the box to the outside of the box where the signal is transferred to means for further processing of the transaction. The means for detecting penetration of the box will react upon a chemical or a mechanical destruction of the box. The means for detecting penetration comprises an electrically conductive path or a plurality of electrically conductive paths encircling the printed circuit board that carries the confidential information. As an example the conductive path could be a wire glued onto the inner surface of the box or moulded into the box. The conductive path could also be a conductive material printed onto the inner surface of the box or printed directly onto the outer surface of the circuit carrying the confidential information. The conductive path could also be a conductive material evaporated onto the inner surface of the box or the outer surface of the circuit carrying the confidential information or it could be a number of conductive fibres moulded into the box. The conductive path(s) is being arranged so that any attempt to reach the circuit carrying the confidential information, will result in, that either one or more paths are broken or a number of paths are being interconnected, both results causing that the confidential information is being deleted or causing that the entire circuit carrying the confidential information is being destroyed. The deletion of the information or the destruction of the circuit carrying the information will be carried out by an electronic device connected to the conductive path(s). The path(s) according to the present invention will be exposed towards a chemical matter penetrating the box, such as towards an acid or a base of any kind or having any form - liquid or gas. Such chemical matter could be used for decomposing the box so as to reach the circuit carrying the confidential information. As the chemical matter enters the box, the conductive path(s) will be decomposed or destroyed so that the conductivity stops or conductance will occur between a number of paths. Conductance between a number of paths may occur e.g. if the chemical matter is conductive in it self - which typically would be the case for many liquid phase acids. Conductance between a number of paths may also occur e.g. if the chemical matter is decomposing an isolating material arranged between the conductive paths so that the ability of isolating the conductive paths changes. The electronic device can easily measure the change of the isolation and delete the confidential information. Preferably the conductive path(s) is made from a material, such as a soft metal, which easily is destroyed by a chemical matter. In that way it may be ensured that even acids in a very low concentration will destroy a path. The conductive path(s) may as an example be provided as a conductive powder suspended in a binder. The binder may be chosen so that it easily dissolves in any liquid which of course leads to a destruction or at least a change in the conductivity. According to a preferred embodiment, a number of paths are being arranged in an isolating matter which is easily dissolved in the chemical matter or which at least absorbs the chemical matter and thus becomes conductive. As an example, the paths could be arranged in a spongy tissue or in similar materials providing isolation sensitive towards the chemical matter. As another example the conductive paths could be arranged in a suspension comprising an isolating powder bound by an easily dissolvable binder. The isolating material could also be provided with through-holes so as to allow the chemical matter to penetrate through the isolating material. In that way the chemical matter would have free access to destroy the conductive path(s), or the chemical matter would more easily be able to conduct an electrical current between a number of paths. According to a preferred embodiment of the invention the conductive path(s) may be attached to the inner surface of the box by means of an adhesive. The path(s) could preferably be provided on or in a circuit board or a number of circuit boards of either a soft or hard type. As an example, a circuit board with a plurality of conductive paths could be glued onto each inner side of the box. Each of the circuit boards could be electrically interconnected so as to transfer an electrical current from one path to another, across the circuit boards and one of the circuit boards could then be connected to the electronic device for deletion of the information upon detection of intrusion. A protective coating may protect the path(s) of the circuit boards, e.g. a varnish sprayed onto the surface of the circuit board. In that case it will be preferred that the protective coating easily dissolves in the chemical matter or that through-holes are provided in the coating so as to allow the chemical matter to reach the path(s) or that the protective coating easily absorbs the chemical matter and thus becomes conductive. The path(s) of the circuit board could either be printed onto the circuit board or the path(s) could be evaporated onto the circuit board. According to a preferred embodiment of the invention, at least one conductive path could be provided in one layer of the circuit board whereas a conductive surface is provided in another layer of the circuit board. The layers are being isolated from each other by a material, which easily dissolves in a liquid, which would then cause a short circuit between the path and the surface. According to another preferred embodiment, a number of paths could be arranged in individual layers of the circuit board, isolated by layers of an isolating material that easily dissolves in a liquid. Preferably the glue or similar adhesive used to attach the circuit board with the path(s) to the inner surface of the box is permeable towards the chemical matter, absorbs the chemical matter or in any similar way allows the chemical matter to reach the circuit board with the path(s). As an example the glue may be provided discontinuously over the inner surface of the box so as to allow the chemical matter to penetrate. According to a preferred embodiment the glue is provided with through-holes, provided with a density in the size of 1-100 holes pr. cm 2 , such as in the size of 10-90 holes pr cm 2 , such as in the size of 20-80 holes pr cm 2 , such as in the size of 30-70 holes pr cm 2 , such as in the size of 40-60 holes pr cm 2 . The holes may be uniformly distributed in the adhesive but it is even more advantageous if the holes are provided randomly. In that way it is very difficult for an intruder to predict where the glue will protect the path(s) from the chemical matter and thus where the box may be destroyed without deleting the confidential information. The glue may preferably comprise a substance selected from the group consisting of: - epoxy, - acrylic, and - polyurethan. The box may preferably be made from a material or a composition of materials selected from the group consisting of: - metal, - plastic, and - ceramics. According to another aspect the present invention relates to a method for gluing a circuit board onto the inner surface of a box so that through-holes are provided in the glue, said method comprising providing a perforated sheet of glue between the circuit board and the inner surface of the box and by influence of heat, gluing the circuit board onto the inner surface of the box. The sheet of glue could be provided with holes either uniformly or randomly distributed in the sheet of glue. The heating of the glue could preferably be combined with providing a pressure in order to press the circuit board against the inner surface of the box. Detailed description of the invention A preferred embodiment of the invention will now be described in details with reference to the drawing in which: Fig. 1 shows an exploded view of a half side of a box according to the present invention, and Fig. 2 shows an exploded view of a half side of the box including an electronic circuit carrying the confidential information. Referring to Fig. 1 the box comprises a plate 1; in the shown example the plate is the closure of the box. The sensor PCB in the form of a flexible PCB 3 is glued onto the plate by the use of a glue-plate 2. Preferably the plate 1 is made from moulded zinc while the flexible printed circuit board is made from Kapton. The glue-plate is a pre-preg type comprising fibreglass-reinforced tissues with an epoxy hardener. The glue-plate is positioned against the zinc plate and the flexible PCB is positioned above the glue-plate. Influenced by a high pressure and temperature the PCB will be glued together with the zinc plate. The glue-plate is provided with a plurality of small holes in a suitable mutual distance and the flexible printed circuit board is covered with a soldering mask also provided with holes. The holes of the soldering mask are arranged adjacent to the holes of the glue-plate. Thereby it is achieved that the pattern of conductive path arranged in the PCB is exposed in the direction towards the zinc plate. The thickness of the glue-plate prevents the conductive path from being in contact with the zinc plate. Fig. 2 shows another exploded view of the box including a closure 1 of the box, a glue- plate 2, the flexible print 3, a guiding plate 4, a pair of two elastomer connectors 5 and 6 and a PCB 7 comprising the circuit that carries the information which is to be protected. On the side facing the closure 1 , the flexible PCB 3 is covered with a pattern of conductive paths having two through-going conductive paths in a complex arrangement. A plan ground-connection surface is arranged on the rear-side of the flexible PCB. The elastomer connectors 5 and 6 provides a contact between the flexible PCB 3 and the PCB 7. The guiding plate 4 provides a correct positioning of the elastomer connectors 5 and 6. A circuit arranged on the PCB 7 constantly measures that the paths of the PCB 3 are conductive and that the isolation between the individual path of the PCB 3 or the isolation between the paths and the ground-connection surface is above a pre-determined value. The circuit will detect any interruption of the conductivity of the paths or detect changes of the isolation value and react by deleting the confidential information. The plate 1 could be made of any material such as metal, plastic or ceramics. The glue- plate could be made with a glue comprising epoxy, acrylic, polyurethane or adhesive rubber or any other means of adhesive. Additionally the sensor PCB could be of a flexible or non-flexible type and the soldering mask could be omitted in the area where the sensor PCB is in contact with the glue.

Claims: CLAIMS 1. A box for encapsulating an electronic device, said box comprising - means for detecting penetration of the box, and - means for deleting confidential information carried by the electronic device upon detection of the penetration, said means for detecting the penetration comprising an electronic circuit provided in the box, the electronic circuit comprising at least one electrical conductive path being exposed towards a chemical matter penetrating the box. 2. A box according to claim 1 , wherein the at least one electrical conductive path is degradable towards the chemical matter and wherein penetration is detected by means of an interruption of the electrical conduction of at least one of the at least one conductive path, the interruption being caused by the chemical matter. 3. A box according to claim 1 or 2, wherein at least two conductive paths is provided electrically isolated from each other and wherein the penetration is detected by means of a change of the isolation between the at least two conductive paths. 4. A box according to claim 3, wherein the isolation provided by an isolating material being permeable towards the chemical matter so as to make the isolation sensitive towards the chemical matter. 5. A box according to claim 4, wherein the isolating material is provided with through- holes so as to make the isolation sensitive towards the chemical matter. 6. A box according to any of the preceding claims, wherein the at least one conductive path is provided integrated in the box. 7. A box according to any of the preceding claims, wherein the at least one conductive path is provided on an inner surface of the box. 8. A box according to claim 7, wherein the at least one conductive path is attached to the inner surface of the box by means of an adhesive. 9. A box according to any of the preceding claims, wherein the at least one conductive 5 path is provided in at least one flexible circuit board. 10. A box according to any of claims 1-8, wherein the at least one conductive path is provided in at least one non-flexible circuit board. 10 11. A box according to any claim 9 or 10, wherein the circuit board is attached to the inner surface of the box by means of an adhesive. 12. A box according to any of claims 9 - 11 , wherein the at least one conductive path of the at least one circuit board is printed onto the circuit board. 15 13. A box according to any of claims 9 - 11 , wherein the at least one conductive path of the at least one circuit board is evaporated onto the circuit board. 14. A box according to any of the preceding claims, wherein the at least one conductive 20 path is protected by a protective coating being permeable towards chemical matter. 15. A box according to claim 14, wherein the protective coating is made permeable by providing the coating with through-holes. 25 16. A box according to claim 14 or 15, wherein the adhesive is permeable towards the chemical matter. 17. A box according to any of claims 14 -16, wherein the adhesive is provided discontinuously over the inner surface of the box so as to allow the chemical matter to 30 penetrate. 18. A box according to any of claims 14-17, wherein the glue is provided with through- holes, provided with a density in the size of 1-100 holes pr. cm 2 , such as in the size of 10- 90 holes pr cm 2 , such as in the size of 20-80 holes pr cm 2 , such as in the size of 30-70 35 holes pr cm 2 , such as in the size of 40-60 holes pr cm 2 . 19. A box according to claim 18, wherein the through-holes are substantially uniformly distributed in the adhesive. 5 20. A box according to claim 18, wherein the through-holes are provided randomly in the adhesive. 21. A box according to any of the claims 8-20, wherein the adhesive is glue comprising a substance selected from the group consisting of: 10 - epoxy, - acrylic, and - polyurethan. 15 22. A box according to any of the preceding claims, made from a material or a composition of materials selected from the group consisting of: - metal, - plastic, and 20 - ceramic. 23. A method for gluing a circuit board onto the inner surface of a box so that through- holes are provided in the glue, said method comprising providing a perforated sheet of glue between the circuit board and the inner surface of the box and by influence of heat 25 and pressure, gluing the circuit board onto the inner surface of the box.

Inventors: GADGAARD OLE, RASMUSSEN JAN, GADGAARD, OLE, RASMUSSEN, JAN
Applicants: ASCOM DANMARK AS, GADGAARD OLE, RASMUSSEN JAN, ASCOM DANMARK A/S, GADGAARD, OLE, RASMUSSEN, JAN
Application year: 2001
Main classification: H05K5
IPC codes: E05G1, G07F7, H05K5