GB2505176A

GB2505176A - Security wrap for protecting electronic device with x-ray impervious screen or x-ray invisible conductive tracks

Info

Publication number: GB2505176A
Application number: GB1214818.5A
Authority: GB
Inventors: Libing Zhang; Dominic John Ward
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 2012-08-20
Filing date: 2012-08-20
Publication date: 2014-02-26
Also published as: GB201214818D0

Abstract

An electronic device is protected from unauthorized access by use of a security film wrap 20 having at least one security screen 30 connected to an alarm circuit of the electronic device. The security screens 30 have a number of serpentine conductive paths 46 to trigger an alarm response when the security wrap 20 is tampered with. The security wrap 20 has a layer 40 which is at least partly impervious to x-rays to hide the configuration of the security screen when the device is x-rayed. The x-ray impervious layer is preferably sandwiched between two security screen layers. The security screen may be formed by etching a flexible printed circuit FPC. In an alternative arrangement the conductive tracks of the security screens are formed from a conductive ink which is invisible to x-rays.

Description

TITLE

[0001] Security Wrap

FIELD OF THE INVENTION

[0002] This invention relates to a security device for an electronic circuit and in particular, to an improved security wrap for preventing unauthorized access to a designated portion of the circuit.

BACKGROUND OF THE INVENTION

[0003] Protecting electronic circuits from unauthorized access is an important consideration when designing apparatus that use electronic circuits that have or may have sensitive andlor confidential information. For example, point of sale (POS) devices collect confidential information about credit cards or bank account details when a purchase is being made.

[0004] Recently, security wraps have been used for the protection of such devices.

Thc security wrap forms a part of the device's security system and identifies an attempt to physically access the protected portion of the device. The security wrap physically covers the electronic components being protected. referred to as the parent device, which may be a portion of a PCB, the entire PCB or components Uke a smart card connector, a secure microprocessor and the like. The security wrap may be flexible so as to be able to be wrapped around the parent device, further reducing the opportunities to access the components.

[0005] The security wrap has one or more conductors which connect between corresponding pairs of screen terminals, forming a security screen. The screen terminals are connected to terminals of an alarm circuit of the parent device. Severing a connector triggers an alarm condition. The function of the alarm circuit is not a part of the instant invention and depends on the security response of the device being protected which may range from a visual andJor audible indication, to shutting down of the device, disabling the device or in an extreme response to total destruction of the device or the components being protected.

[0006] Prior art security wraps are made with etched copper circuitry or flexible printed circuits (FPC). They can also be fabricated by additive method such as polymer thick film (PTF) technology using printed conductors. Typically the circuits consist of substrate, conductor layers, adhesive layer, and/or dielectric ayers.

[0007] However, the use of x-ray detection methods can be used to reveal the conductor traces, the circuitry layout and the location of terminal contact points. With this information, hackers may use a drill or laser cutting to by-pass the security circuitry to access IC chips and other sensitive electronic components on the board.

[0008] Another problem with existing products is that a flexible security wrap is a relatively simp'e circuitry; a single layer conductor ayout typically satisfies the design requirements. While in theory it is possible to use a thick metal plate to block x-ray detection, this method is not practical in point of sale (POS) devices due to both weight, space and flexibility constraints, hi order to improve the security coverage by conductors, one approach is to use double-layer or multi-layer circuitry, or stack several security screens together. While the security level indeed can increase, the circuitry cost increases significantly with each additional security screen layer. In addition, multi-layer or multi-stacking of circuitry leads to reduced flexibility due to added thickness. It may pose refiability issues when wrapping or bending around a board or component.

SUMMARY OF THE INVENTION

[0009] Hence, there is a need for a new security wrap in which the design of the security screen can not be determined using known x-ray detection methods.

[0010] This is achieved by the present invention by combing both actual flexible security conductor layers with non-conductive layers, with both showing under x-ray detection. In this case, it would effectively increase the circuitry coverage and add circuitry layout complexity, which renders more challenges for hackers to decipher the true conductor layout. Aliernatively, this is also achieved by using a security screen composed of conductors which are transparent to x-rays.

[0011] Accordingly, in one aspect thereof, the present invention provides a security wrap, for preventing unauthorized access to a component of an electronic device having an alarm circuit, comprising: a substrate; a security screen composed of at least one conductive path fixed to a first side of the substrate, said conductive path having a pair of screen terminals arranged to make contact with alarm terminals of the alarm circuit; a layer of adhesive applied to the security screen and arranged to fix the security wrap to the component; and a layer which is at least parfly impervious to x-rays and arranged to obscure an x-ray image of the security screen.

[0012] Preferably, the impervious layer is the substrate.

[0013] Alternatively, the impervious layer is a separate layer configured to overlay at least a part of the component to be secured.

[0014] Alternatively, the impervious layer is a separate layer configured to overlay at least a part of the security screen and is disposed between the substrate and the security screen.

[0015] Preferably. the security wrap includes at least one additiona] security screen.

[0016] Preferably. each additional security screen is formed on a dielectric layer and each dielectric layer is formed on a preceding security screen.

[0017] Preferably, each dielectric layer is formed by a printing process and each additional security screen is formed by pnnting a conductive ink on to the preceding dielectric layer.

[0018] Preferably, at least one of the dielectric layers is at least partly impervious to x-rays.

[0019] Preferably, the or each conductive path of the security screen is made with a frangible conductor that is readily broken when the security wrap is disturbed after being fitted to the electronic device.

[0020] Preferably. an intermittent layer of adhesive modifier is disposed between the or each security screen and the substrate dielectric layer to modify the adhesion of portions of the or each conductive path to create the frangible conductor.

[0021] Preferably. the impervious layer is intermittently impervious to x-rays so as to create a predetermined image when x-rayed.

[0022] According to a second aspect thereof, the present invention provides a secunty wrap, for preventing unauthorized access to a component of an electronic device having an alarm circuit, comprising: a substrate; a security screen fixed to the substrate on a first side thereof, the security screen having a number of conductive paths extending between and dectrically interconnecting a corresponding pair of screen terminals arranged to make contact with alarm terminals of the alarm circuit; and a layer of adhesive applied to the security screen and arranged to fixed the security wrap to the component, wherein the conductive paths of the security screen are formed by a conductive ink that is invisible to x-rays.

[0023] Preferably, the component to be secured is an electronic component mounted on a PCB and the security wrap is fixed to the PCB and covers the component.

[0024] Alternatively, the component to be secured is a flexible circuit.

[0025] Preferably. the conductive paths are formed from a thermoset conductive ink.

[0026] Preferably, the substrate and the security screen are be produced as a flexible printed circuit (FPC), with the security screen being formed by etching a copper layer fixed on the substrate.

[0027] Preferably, a dielectric layer is applied over the copper traces, and exposed copper pads are surface-treated with tin, nickel or gold.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Preferred embodiments of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labelled with a same reference numeral in all the figures in which they appear.

Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed bdow.

[0029] Figure 1 is illustrates an electronic device inside which is fitted a security wrap; [0030] Figure 2 illustrates a single surface security wrap applied to a circuit board of the device of Fig. 1; [0031] Figure 3 is a schematic illustration showing an exemplary full face security wrap in an unwrapped form; [0032] Figure 4 is a schematic illustration showing an exemplary circuitry layout revealed under x-ray detection; [0033] Figure 5 is a schematic illustration showing a single-layer metallic conductor with a non-conductive layer, which under x-ray is displayed as complex stacked circuits; [0034] Figure 6 is a schematic illustration showing a single-layer non-metallic conductor with a non-conductive layer, which under x-ray only displays the non-conductive layout; [0035] Figure 7 is a schematic illustration showing a single-layer conductor with a non-conductive layer, which under x-ray is displayed as overlapped circuits; [0036] Figure 8 is a schematic illustration showing a single-layer conductor with a complementary non-conductive layer, which under x-ray is displayed as a nearly fully covered security circuit; [0037] Figure 9A is an optical photograph taken of a sample substrate having a single-layer conductor (vertical lines) with non-conductive layer (horizontal lines) printed over an opaque substrate; [0038] Figure 9B is an x-ray image taken of the sample of Fig. 9A; [0039] Fig. 10 is an exploded view of a two layer security wrap; [0040] Fig. 11 is an exploded schematic view of a security wrap according to the second embodiment; [0041] Fig. 12 is an exploded schematic view of a security wrap according to a third embodiment; 0042J Fig. 13 is an exploded schematic view of a security wrap according to a fourth embodiment; and [0043] Fig. 14 is an exploded view of a security wrap according to a further embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] Fig. 1 illustrates a POS device 10 as an example of where the security wrap is used. The POS has a slot for receiving a card 12 containing confidential infoimation such as account details, etc. The device also has buttons 14 for entering details and instructions for controlling the device. Inside the P05 is an electronic circuit comprising circuit board 16 with a memory chip and/or a microprocessor (Mcli) which may contain or momentarily access confidential information. The security wrap 20 may be placed over the entire circuit board or over just a portion of the board, as will be described herein after, depending on system requirements. Fig. 2 shows the security wrap 20 as a single suiface version, covering a large portion of the PCB 16 of the POS device. The PCB forms the parent device to be protected and the security wrap is bonded to the PCB. Alternate forms of security wraps may be used depending on the situation and desired security lev&, such as open face or frill face. An open face wrap is adhered to a device with a top face and sides only.

[0045] Fig. 3 is a schematic illustration showing an exemplary full face security wrap in an unwrapped form. The illustration is a plan view of the security wrap using opaque substrate where the conductor layers are on the reverse side and remain hidden after assemNy to a parent device. A fufl face wrap is adhered around a device with top and bottom faces and sides.

[0046] Fig. 4 is a schematic illustration showing an exemplary circuitry ayout revealed under x-ray detection. For this single layer conductor, there are plenty spaces between the traces, which makes it vulnerable for hackers to cut or drill in the non-covered areas.

[0047] Fig. 5 is a schematic illustration showing a single-layer metallic conductor with a non-conductive layer, which under x-ray is displayed as complex stacked circuits. In Fig. 5, the use of metallic conductors combined with x-ray imagable non-conductive patterns, produce multi-layer circuit patterns in the x-ray image. This would give increase the tamper difficulty significantly and deter hackers' attempt to bypass them with mechanical methods.

[0048] Fig. 6 is a schematic illustration showing a single-layer non-metallic conductor with a non-conductive layer, which under x-ray only displays the non-conductive layout. In Fig. 6, the use of non-metallic conductors combined with x-ray imagable non-conductive patterns, produce an image of only the non-conductive patterns in x-ray image. This would give false information to hackers attempting to tamper the security circuit.

[0049] Fig. 7 is a schematic illustration showing a single-layer conductor with a non-conductive ayer, which under x-ray is displayed as overlapped circuits. In Fig. 7.

a single-layer metallic conductor is combined with a non-conductive layer, in which case, the selected or all non-conductor traces is broadly based on conductor layer design. Under x-ray the image is displayed as a fattened traced with very narrow spaces. With less space between traces, it means harder access by mechanical dnlling or laser cutting.

[0050] Fig. 8 is a schematic illustration showing a single-layer conductor with a complementary non-conductive layer, which under x-ray is displayed as nearly fully-covered security circuit. In Fig. 8, a single-layer meta'lic conductor is used with a complementary non-conductive layer. In other words, non-conductor x-ray layer is designed as negative image of the conductive layer. By precision registration, the conductor patterns and non-conductive patterns are over-laid to provide nearly iOO% coverage under x-ray detection.

[0051] Figures 9A and 9B are images of an actual circuitry sample made with a silver conductive ink and a non-conductive zinc ink. Visually a single-layer conductor (Ivettical lines) with non-conductive layer (horizontal lines) can be seen if they are viewed from the circuit side. The substrate here is a white coloured PET, so the circuit patterns are invisible if viewing from the PET side. Under x-ray detection, both conductor and non-conductive layers are shown in the x-ray image. Although electrically this is a single layer circuit, it exhibits as cross-overed double layer circuit under x-ray. hi Fig. 9B x-rays were emitted from the circuit side and the image was recorded from the substrate side, thus Fig. 9A and 9B appear as mirror images.

[0052] Figs 10 to 12 illustrate the stack up of three embodiments of a security wrap using a decoy layer. The figures are exploded schematic views and not drawn to scale.

[0053] In Fig. 10. the substrate 26 is on the bottom, the security screen 30 is printed or formed on the substrate and the decoy layer 40 is formed on the security screen. The adhesive layer 28 is on top.

[0054] In Fig. 11, the substrate 26 is on the bottom, the decoy layer 40 is formed on the substrate and the security screen 30 is printed or formed on the decoy layer. The adhesive layer 28 is on top.

[0055] In Fig. i2, the security screen 30 is printed or formed on a first side of the substrate 26 and the decoy hyer 40 is formed on a second side of the substrate remote from the security screen. The adhesive layer 28 is on top of the security screen.

[0056] For a multi-layer security wrap 20, meaning a security wrap with more than one security screen, as shown for example in Fig. 13, the arrangement is similar, except that each additional security screen 30 is printed on to a dielectric layer 36 printed on the preceding security screen 30. In this case the substrate 26 and first security screen 30 may be a flexible printed circuit (FPC) with the subsequent security screens 30 being formed using the printed conductive inks technology. For a multi-layer security wrap with breakable conductors, an intermittent layer of adhesive modifier 38 is applied between the substrate 26 and the first security screen 30 and between the dielectric layers 36 and the subsequent security screens 30.

[0057] The decoy byer 40 may be applied to the first or second security screen as per the Fig. 10 embodiment, applied between the substrate and the first secunty screen as per the Fig. II embodiment, between the dielectric layer and the second security screen as shown in Fig. i3, or to the outer sm-face of the substrate as per the Fig. 12 embodiment.

[0058] The decoy layer may be formed using a pnnting process to deposit lines or areas of x-ray impervious ink on a dielectric layer covering the security screen, or if the ink is non-conductive, the decoy layer may be printed directly onto the security screen or the substrate. As an aliernative, the decoy layer may be applied to the outer surface of the substrate, remote from the security screen.

[0059] In Fig. 14, the decoy layer is a solid layer of conductive material. This has the advantage of not only shielding the security screen and component layout from x-ray imaging but also provides a shield against electromagnetic WM) or radio frequency (RE) signals, thus preventing a hacker from listening' to the information being transferred to or read by the MCU.

[0060] The general principles of construction are common for each embodiment.

The security wraps 20 have a substrate 26, a security screen 30, a decoy layer 40 and a layer of adhesive 28 to bond the security wrap to the parent device 16. The order and number of the layers may change depending on the application and security level required. Additionally, in some embodiments a dielectric layer 36 may be used to provide insulation between adjacent conductive layers.

[0061] The substrate 26 is preferably flexible to allow it to wrap around the parent device. Typically the substrate 20 is a PET film but other polymer films such as polycarbonate, PEN, polyimide and PVC may be used. The substrate may be clear or opaque and pigmented, for example black or white.

[0062] The security screen 30 is preferably composed of a pattern of one or more conductive traces or conductors 46 formed by thermoset or thermoplastic conductive ink printed over the substrate 26 in variable trace widths and serpentine mesh patterns forming an electrically conductive path between a pair of screen terminals 48.

Preferably, the screen terminds are simply the ends of the conductors 46. A sing'e layer security screen may have one, two or more conductors interconnecting respective pairs of screen terminals. The fillers in the conductive ink can be silver, silver coated copper or gold etc., which are x-ray detectable.

[0063] The conductive inks can be silver, silver-coated copper or gold containing conductive or resistive ink, each with specific properties that suit the necessary requirement for the operation and functionality of the security wrap flexible circuit.

Multiple layers can be printed in total isolation or connected at specific points depending on the intended functionality of the security wrap flexible circuit. With metallic powder, the conductive ink is x-ray imagable.

[0064] The conductive ink can also be carbon, graphite, clear conductive polymer or other conductive or resistive ink, each with specific properties that suit the necessary requirement for the operation and functionality of the security wrap flexible circuit.

With these non-metallic conductive particles, the conductive ink and thus the security screen, is invisible under x-ray.

[0065] The dielectric layer 36 is preferably, a UV curable ink system with electrically insulative properties and is used as a separating medium to permit multiple layers of conductive ink or multiple security screens to be printed on a single substrate.

For example, the dielectric layer may be applied directly over a first security screen by a printing process to insulate the first security screen from a second security screen or from other conductive circuit components, either of the security wrap or the parent device. The dielectric layer is not necessary in a security wrap having a single layer secunty screen and a non-conductive decoy layer.

[0066] The dielectric layer, depending on security wrap functionality, can be printed partially or fully over the top of a conductive ink trace pattern to enable a subsequent conductive layer to be printed but remain electrically isolated from the first where necessary. A number of conductive ink/dielectric ink layers can be pnnted in succession. The dielectric layer is typically not detectable under x-ray.

[0067] The decoy layer 40 may be a layer of ink applied in a predetermined pattern to the substrate 26 or security screen 30. Preferably the decoy layer is disposed between the substrate and the security screen. The ink may be conductive or non-conductive. Where the decoy layer is conductive, it needs to be isolated from the security screens preferably by a dielectric layer 36. Conductive inks may be similar to the inks used for the security screen.

[0068] The non-conductive ink, which is x-ray irnagable, is preferably a UY or thermal-curable screen ink system with electrically insulative properties and used as an x-ray irnagable medium to hide the actua' conductive layout when hacked by x-ray detection. The non-conductive ink typically consists of filler and polymer binders.

There are three type of fillers that can be used for this invention: [0069] 1) Non-conductive metal powders, which include but not limited to zinc, iron, copper etc. Although these materials are conductive in bdk, they become non-conductive in the fine powder form due to surface oxidation. The filler loading range in the ink could be from 1-99% by weight. 40-90% is preferred to achieve both good x-ray image quality arid ink printability.

[0070] 2) Non-metallic but x-ray imagable materials, which include Barium sulphate etc. The filler loading range could be from 1-99% by weight. 40-90% is preferred to achieve both good x-ray image quality and ink printability.

[0071] 3) Conductive metals but use lower loading below percolation threshold, so the formulated ink is non-conductive after curing. For silver, the percolation threshold is around 40-60% depending on different polymers. To achieve non-conductive furicdon, less than 40% loading is preferred.

[0072] The adhesive layer 28 is preferaNy a pressure-sensitive adhesive (PSA).

typically an acrylic adhesive that forms a bond between surfaces when pressure applied. The adhesive may be applied as an adhesive ink or as a laminate. Depending on the parent substrate to which the security wrap is adhered a variant PSA with specific adhesion properties can be used. This can be a bespoke PSA specifically developed for a specific bondthg requirement. The adhesive layer is typically not visible under x-ray.

[0073] Dunng assembly, the conductive traces 46 are attached to the substrate 26 via screen printing methods. Although non-conductive x-ray irnagable ink can be printed before or after the conductive ink traces are laid down, it is preferred to print the non-conductive ink over the conductive inlc, so it has no impact on the conductivity of conductive traces.

[0074] The adhesive layer 28 is attached by applying pressure. The secunty wrap is attached to the parent device via the adhesive layer 28 by applying pressure.

[0075] As shown in Figure 5-8, the non-conductive x-ray imagable layers (decoy layers) can be printed partially or fully over the top of a conductive silver trace pattern.

In all cases, the trace coverage on the substrate 26 appears to be increased under x-ray detection, which helps hide the actual circuitry layout and provides increased difficulty against tampering.

[0076] Alternatively, the substrate and the security screen can be produced as a flexible printed circuit (EPC), with the security screen being formed by etching a copper layer fixed on the substrate. To prevent copper oxidation, a dielectric layer such as solder mask or overlay is applied over copper traces, and exposed copper pads are typically surface-treated with tin, nickel or gold etc. Similarly the x-ray irnagable, non-conductive ink can be printed on solder mask or overlay to form a decoy layer.

[0077] In case of assemNy design with breakable conductors, the security function against peeling is not affected by adding the non-conductive x-ray layers. When hackers attempt to remove the security wrap 20 from the parent device 16, the conductive ink traces 46 are disturbed, thus creating a resistance change or a complete open circuit at the weak points. This occurrence effectively changes the electrical state of the conductive trace and prompts the monitoring systems of the parent device to initiate an alairn response which may include erasure of secure or personal data as necessary.

[0078] In operation. a conductive ink is screen printed onto a substrate, in a pattern to meet specific dectrical requirements. A non-conductive x-ray imagable ink is prhned subsequently over the conductive traces. A pressure-sensitive adhesive (PSA) is laminated over both the conductive and non-conductive ink patterns by means of a laminating roller. The security wrap is profile cut to a custom-made shape ready to be assembled to a parent device which might be in the form of a printed circuit board, an open face or a complete plastic enclosure. The security wrap is assembled to a device either by hand or some mechanical means dependant on the assembly process.

[0079] When the circuits of the security screen are detected by x-ray, the x-ray images of the decoy layer can hide the actual conductive traces of the security screen.

[0080] Security wraps with decoy layers which modify and thus falsify or hide x-ray images of the circuitry of the security wrap renders x-ray hacking ineffective. When both non-conductive and actual conductive layers are formed on a flexible substrate, the x-ray images could display like multi-layer designs, or form broadened conductor traces, or appear as a completely sohd coverage.

[0081] Increased security can be achieved by printing one or more non-functional layers. For a security screen using printed silver for its conductor, the non-functional decoy layers can be printed using similar equipment and process. In case of copper-based FPC circuit, the non-functional decoy layer can be printed over FPC layers after wet-chemistry process is complete. These x-ray irnagable non-functional layers (decoy layers) use no precious metal, and the applying method is an environrnenta friendly additive process, which is cost-effective to improve the security level against x-ray detection.

[0082] It was disclosed by our commonly assigned, co-pending application (patent application #), the contents of which are fully incorporated herein by reference, that a security wrap may consist of breakable conductors, which are to designed to prevent circuitry tampering by mechanic peel or shearing. The method described here against x-ray tampering can also be applied on flexible circuits or security wraps with breakable conductors, by which the final circuitry would have combined security features.

[0083] In the description and claims of the present application, each of the verbs "comprise", "include", "contain" and "have", and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items.

0084J Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow.

[0085] For example, although the invention has been described using a decoy layer providing a false x-ray image of the security screen layout. if the screen is made using non-metal or x-ray invisible conductive ink to form the conductive traces, no decoy layer would be required.

Claims

CLAiMS: 1. A security wrap, for preventing unauthorized access to a component of an electronic device having an alarm circuit, comprising: a substrate; a security screen composed of at least one conductive path fixed to a first side of the substrate, said conducfive path having a pair of screen terminals ananged to make contact with alarm terminals of the alarm circuit; a layer of adhesive applied to the security screen and arranged to fix the security wrap to the component; and a layer which is at least partly impervious to x-rays and ananged to obscure an x-ray image of the security screen.
2. A security wrap according to Claim 1, wherein the impervious layer is the substrate.
3. A security wrap according to Claim 1, wherein the impervious layer is a separate layer configured to overlay at least a part of the component to be secured.
4. A security wrap according to Claim 1, wherein the impervious layer is a separate layer configured to overlay at least a part of the security screen and is disposed between the substrate and the security screen.
5. A security wrap according to any one of the preceding claims, further comprising at least one additional security screen.
6. A security wrap according to Claim 5, wherein each additional security screen is formed on a dielectric layer and each dielectric layer is fotmed on a preceding security screen.
7. A security wrap according to Claim 6, wherein each dielectric layer is formed by a printing process and each additional security screen is formed by printing a conductive ink on to the preceding dielectric layer.
8. A security wrap according to Claim 6 or 7, wherein at least one of the dielectric layers is at least partly impervious to x-rays.
9. A security wrap according to any one of the preceding claims, wherein the or each conductive path of the security screen is made with a frangible conductor that is readily broken when the security wrap is disturbed after being fitted to the electronic device.
10. A security wrap according to Claim 9, wherein an intermittent layer of adhesive modifier is disposed between the or each security screen and the substrate dielectric layer to modify the adhesion of portions of the or each conductive path to create the frangible conductor.
11. A security wrap according to any one of the preceding claims, wherein the impervious layer is intermittently impervious to x-rays so as to create a predetermined image when x-rayed.
12. A security wrap, for preventing unauthorized access to a component of an electronic device having an alarm circuit, comprising: a substrate; a security screen fixed to the substrate on a first side thereof, the security screen having a number of conductive paths extending between and electrically interconnecting a corresponding pair of screen terminals arranged to make contact with alarm terminals of the alarm circuit; and a layer of adhesive applied to the security screen and arranged to fixed the security wrap to the component, wherein the conductive paths of the security screen are formed by a conductive ink that is invisible to x-rays.
13. A security wrap according to any one of the preceding claims, wherein the component to be secured is an electronic component mounted on a PCB and the security wrap is fixed to the PCB and covers the component.
14. A security wrap according to any one of Claims 1 to 12, wherein the component to be secured is a flexible circuit.
15. A security wrap according to any one of the preceding claims, wherein the substrate and the security screen are be produced as a flexible printed circuit (FPC), with the security screen being formed by etching a copper layer fixed on the substrate.
16. A security wrap according to Claim 15, wherein a dielectric layer is apphed over the copper traces, and exposed copper pads are surface-treated with tin, nickel or gold.
17. A security wrap according to any one of the preceding claims, wherein the conductive paths are formed from a thermoset conductive ink.
18. A security wrap, for preventing unauthorized access to an electronic device having an alarm circuit, substantially as herein before described with reference to the accompanying drawings.