Abstract:
A security wrap ( 20 ) for protecting an electronic component ( 16 ) having a bonding surface includes a substrate ( 22 ) having a first side and a second side opposite to each other. A first security screen ( 26 ) is disposed over the first side of the substrate ( 22 ) and includes a first pair of screen terminals ( 48 ) and a first conductive track ( 46 ) between the first pair of screen terminals ( 48 ). A second security screen ( 26 ) includes a second pair of screen terminals ( 48 ) and a second conductive track ( 46 ) between the second pair of screen terminals ( 48 ) and overlaying the first conductive track ( 46 ) on the first security screen ( 26 ). A layer of adhesive ( 30 ) is over a side of the second security screen ( 26 ) remote from the substrate ( 22 ) and bonds the second security screen ( 22 ) to the bonding surface of the electronic component ( 16 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 1213447.4 filed in United Kingdom on Jul. 27, 2012. 
     FIELD OF THE INVENTION 
     This invention relates to a tamper indication device and in particular to a security wrap for an electronic circuit to protect against tampering. 
     Although this invention will be described in relation to security wraps as an example of the invention, the invention can be used with any printed electronics (PE) flex requiring a need for detection of removal or tampering. 
     BACKGROUND OF THE INVENTION 
     Security wraps form a solid security screen masking an area of the electronics to be protected. Removal of security wrap is physically difficult due to the manner in which the security wrap is attached to the device, usually by gluing, soldering or encapsulation with a resin material. However, they offer little in tamper resistance or indication of tampering except by visual inspection. Some systems have an alarm circuit which may disable the device or simply give a visual indication that the security wrap has been removed, but there is no detection of an attempt to remove or bypass the security wrap by drilling a hole through it or simply lifting up a corner of the wrap. 
     In addition, coating with resins or encapsulating the security wrap creates a heavier and thicker construction whilst industry is striving to develop thinner and lighter devices to maximize internal space for more components to add greater functionality into portable electronic devices such as point of sale (POS) terminals and other applications and/or to make the devices smaller and lighter. 
     Further, for some devices, such as credit card readers, there is a need to operate pre-assembled components of the device, for example curved metal discs known as metal domes for keypad buttons and so it is not feasible to encapsulate or coat the security wrap with resins. Resins create a hard shell that prevents the mechanical operation or tactile feedback of such components. The resin typically forms a permanent coating such that repair of the PCB or components is no longer possible. 
     SUMMARY OF THE INVENTION 
     In one aspect thereof, the present invention provides a security wrap for protecting an electronic component having a bonding surface, comprising: a substrate having a first side and a second side opposite to each other; a first security screen disposed over the first side of said substrate and including a first pair of screen terminals and a first conductive track between the first pair of screen terminals; a second security screen including a second pair of screen terminals and a second conductive track between the second pair of screen terminals and overlaying the first conductive track on said first security screen; and a layer of adhesive over a side of said second security screen remote from said substrate and bonding said second security screen to the bonding surface of the electronic component. 
     Preferably, said second security screen is disposed over the second side of said substrate. 
     Preferably, further comprising a dielectric layer over a side of said first security screen remote from said substrate, wherein said second security screen is disposed over said dielectric layer. 
     Preferably, further comprising an adhesion modification layer having intermittent pattern formed between the first side of said substrate and said first security screen, wherein said first security screen has a bonding strength to said substrate in the intermittent pattern of said adhesion modification layer different than a bonding strength between said first security screen and said substrate outside the intermittent pattern of said adhesion modification layer. 
     Preferably, the electronic component includes an alarm circuit having a plurality of terminals; and the first pair of screen terminals on said first security screen is coupled to two of the plurality of terminals of the alarm circuit of the electronic component. 
     Preferably, the second pair of screen terminals of said second security screen is coupled to another two of the plurality of terminals of the alarm circuit of the electronic component. 
     Preferably, second conductive track between the second pair of screen terminals of said second security screen is connected in series with the first conductive track between the first pair of screen terminals of said first security screen between the two of the plurality of terminals of the alarm circuit of the electronic component. 
     Preferably, further comprising a conductive via connecting a terminal in the first pair of screen terminals on said first security screen to a terminal in the second pair of screen terminals on said second security screen. 
     Preferably, the alarm circuit of the electronic component is sensitive to a variation in a resistance between the two of the plurality of terminals; and the second conductive track between the second pair of screen terminals of said second security screen is connected in parallel with the first conductive track between the first pair of screen terminals of said first security screen between the two of the plurality of terminals of the alarm circuit of the electronic component. 
     Preferably, the electronic component further includes a conductive pad formed on the bonding surface and coupled to one of the two terminals of the plurality of terminals; and said layer of adhesive includes a conductive plug formed therein and connecting one of the second pair of screen terminals on said second security screen to the conductive pad on the bonding surface of the electronic component. 
     Preferably, the electronic component further includes a conductive dome formed on the bonding surface and coupled to one of the two terminals of the plurality of terminals; said second security screen further includes a conductive extension connected to one of the second pair of the screen terminal and over the conductive dome in the bonding surface of the electronic component; said layer of adhesive has a void surrounding the conductive dome on the bonding surface of the electronic component and the conductive extension on said second security screen; and the conductive extension of said second security screen is configured to contact the conductive dome on the bonding surface of the electronic component in response to a force applied on the said substrate over the conductive extension. 
     Preferably, said first security screen further includes an additional pair of screen terminals and an additional conductive track between the additional pair of screen terminals. 
     Preferably, the first conductive track on said first security screen is formed from a conductive ink in a printing process. 
     Preferably, the first conductive track on said first security screen has a first pattern: and the second conductive track on said second security screen has a second pattern different from the first pattern. 
     In another aspect thereof, the present invention provides a security wrap for protecting a device having an alarm circuit by bonding to the device, comprising: a substrate having a first side and a second side opposite to each other; a first security screen disposed over the first side of said substrate and including a first conductive track coupled to the alarm circuit of the device; a second security screen including a second conductive track overlaying the first conductive track on said first security screen and coupled to the alarm circuit of the device; and a layer of adhesive over the a side of said second security screen remote from said substrate and bonding the said second security screen to the device. 
     Preferably, said second security screen is disposed over the second side of said substrate. 
     Preferably, further comprising a dielectric layer over a side of said first security screen remote from said substrate, wherein said second security screen is disposed over said dielectric layer. 
     Preferably, the first conductive track on said first security screen has a first pattern: and the second conductive track on said second security screen has a second pattern different from the first pattern. 
     Preferably, the first conductive track on said first security screen and the second conductive track on said second security screen are connected in series between two terminals of the alarm circuit of the device. 
     Preferably, said first security screen further includes an additional conductive track between the additional pair of screen terminals coupled to the alarm circuit of the device. 
     By overlaying screens composed of conductors arranged according to different predetermined patterns, the gaps between the circuitry of the security wrap can be significantly reduced or even eliminated, depending on the number of screens used. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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 below. 
         FIG. 1  illustrates a point of sale (POS) device as an example of a device which uses a security wrap in accordance with the present invention; 
         FIG. 2  illustrates the security wrap fitted to a PCB of the device of  FIG. 1 ; 
         FIG. 3  is an exploded view of a security wrap in accordance with an embodiment of the present invention; 
         FIG. 4  is an exploded view of a security wrap according to another embodiment; 
         FIG. 5A-C  are schematic representations of three screens have different conductor patterns in accordance with the present invention; 
         FIG. 6  is a schematic view showing the three screens of  FIG. 5  overlaid to form a three layer security screen; 
         FIG. 7  is an exploded view of a two layer security wrap; 
         FIG. 8  is an exploded view of a three layer security wrap; 
         FIG. 9  is a sectional view of a two screen, single circuit security wrap, assembled to a parent device; 
         FIG. 10  is a sectional view of a two screen, double circuit security wrap, assembled to a parent device; 
         FIG. 11  is a sectional view of a two screen security wrap having a metal tactile dome; 
         FIG. 12  is a sectional view of a two screen security wrap using a conductive material member as a connection element; 
         FIG. 13  is a sectional view of a two screen security wrap having a carbon pad as a connection element; 
         FIG. 14  is a simplified sectional view of the security wrap of  FIG. 10  showing separation of a conductive trace; 
         FIG. 15  is a schematic view of a partially separated security wrap; 
         FIGS. 16 and 16A  illustrate a resilient connection method between a security wrap and a parent device; and 
         FIG. 17  is a schematic illustration of a screen having two conductive traces. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates an electronic device, by way of example, in the form of a point of sale (POS) device  10 . The POS device  10  is arranged to read details from a card  12 , such as a credit card and has a key pad  14  for entering information and giving instructions to the POS device  10 . A security wrap is used to protect the data stored in the memory of the POS device  10 , generally some form of a memory chip. If unprotected, a perpetrator may access the contents of the memory in the POS device  10 . 
     A PCB  16  of device  10  is shown in  FIG. 2  with the a security wrap  20  fitted thereon. Security wrap  20  appears as a flexible sheet overlaying PCB  16 . In accordance with a preferred embodiment of the present invention, a substrate of the security wrap  20  is opaque so as to hide the layout or pattern of a screen (not shown in  FIG. 2 ) and the underlying circuitry on PCB  16 . Holes  18  in security wrap  20  and PCB  16  facilitate the mounting of the PCB  16  to a housing of device  10 . 
     By way of example,  FIG. 3  is an exploded view of a two layer security wrap  20 , meaning a security wrap with two screens, having breakable conductors (also referred to as conductive track).  FIG. 4  is an exploded view of a similar two layer security wrap  20 . The security wrap has a substrate  22 , a first screen  26  bonded to the substrate  22  and composed of a first conductor  46  having ends forming a pair of first screen terminals  48 , and a dielectric layer  28  formed on the first screen  26 . In the embodiment of  FIG. 3 , a second screen  26  is bonded to the dielectric layer  28  and composed of a second conductor  46  having ends forming a pair of second screen terminals  48 , and a layer of adhesive  30  is disposed on the second screen  26  for bonding the security wrap  20  to a parent device  16  such as a PCB, housing or similar. In the embodiment of  FIG. 4 , a second screen  26  is bonded to the other surface of the substrate  22  and composed of a second conductor  46  having ends forming a pair of second screen terminals  48 . A layer of adhesive  30  is disposed on the second screen  26  for bonding the security wrap  20  to a parent device  16  such as a PCB, housing or similar. 
     For a multi-layer security wrap with breakable conductors, an intermittent layer of adhesive modifier  24  is applied between the substrate  22  and the first screen  26  and between the dielectric layers  28  and the subsequent screens  26 . It should be noted that the use of breakable conductors is optional and that breakable conductors can be formed using different method not involving a release layer. Hence no release layer is shown in  FIG. 4 . 
     The general principles of construction are common for each embodiment. The security wraps  20  have a substrate  22 , at least two screens  26 , and a layer of adhesive  30  to bond the security wrap  20  to the parent device  16 . Dielectric layers  28  may be used to provide insulation between adjacent conductive layers  26 . The order and number of the layers may change depending on the application and security level required. As mentioned about, optional release layers  24  may be used. 
     The substrate  22  is preferably a polymer film, typically a polyethylene terephthalate (PET or commonly referred to as polyester) film, that provides a base for a security wrap  20  circuit. Optionally the substrate  22  is flexible, being a film of thickness between 25 μm and 175 μm but can be greater depending on functional requirements and may include other variants of polymer film including, but not limited to, polycarbonate, PEN, polyimide and PVC. The substrate  22  may be clear but preferably is opaque and pigmented, for example black or white. 
     The screens  26  are composed of a pattern of one or more conductive traces or conductors  46  preferably formed by thermoset or thermoplastic conductive ink printed over the substrate  22  in variable trace widths and serpentine mesh patterns forming an electrically conductive path between a pair of screen terminals  48 . Preferably, the screen terminals  48  are simply the ends of the conductors  46 . A single screen  26  may have one, two or more conductors interconnecting respective pairs of screen terminals  48 , as graphically shown in  FIG. 17 . 
     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  20  flexible circuit. Multiple layers  26  can be printed in total isolation or connected at specific points depending on the intended functionality of the security wrap  20  flexible circuit. 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 circuit. 
     The dielectric layer  28  is preferably, a UV curable ink system with electrically insulative properties and is used as a separating medium to permit multiple layers  26  of conductive ink or screens to be printed on a single substrate  22 . For example, the dielectric layer  28  may be applied directly over the first screen  26  by a printing process to insulate the first security screen  26  from the second screen  26  or from other conductive circuit components, either of the security wrap  20  or the parent device  16 . 
     Depending on security wrap  20  functionality, the dielectric layer  28  can be printed partially or fully over the top of a conductive trace pattern of a screen to enable a subsequent screen to be printed but remain electrically isolated from the first where necessary. A number of screen/dielectric layers can be printed in succession. 
     The adhesive layer  30  is preferably a pressure-sensitive adhesive (PSA), typically an acrylic adhesive that forms a bond between surfaces when pressure is applied. The adhesive may be applied as an adhesive ink or as a laminate. The adhesive layer  30  is used to bond the security wrap  20  to the parent device  16 . Alternatively, the adhesive maybe a liquid adhesive such as an epoxy, or moisture-cure urethane etc. which is dispensed or printed between the security wrap  20  and the PCB  16 , which is then cured by moisture, thermal or UV energy and forms a permanent bond between wrap and PCB. This type of adhesive is not pressure sensitive, but could work under the same disclosed principle. 
     Depending on the material of the parent device  16  to which the security wrap  20  is adhered a variant PSA with specific adhesion properties could be used. Specifically the adhesion to the parent device  16  must be stronger than the adhesion to the substrate  22 , so that on separation of the security wrap  20  from the parent device  16 , the adhesive layer  30  will remain adhered to the parent device  16  in order to break the conductive tracks  46  of the screens  26 . 
     The release layer  24  is preferably, an ultra-violet (UV), infra-red (IR) or thermally cured ink system used to provide a different adhesion level between the substrate  22  and the security screen  26 . The ink is thus an adhesion modifier. The release layer  24  is intermittent and applied to the substrate in a predetermined pattern by a printing process and is not a complete layer such that there are areas of substrate  22  which are not covered by the adhesion modifier ink. Optionally, the pattern of the release layer  24  is simple stripes or dots. 
     By way of example,  FIGS. 5A-C  illustrate three possible patterns of conductors  46  for use as screen  26 .  FIG. 5A , illustrates a first pattern, in which screen  26  is formed by one conductor  46  that terminates at two screen terminals  48 . The screen terminals  48  may be simply the ends of the conductor  46 . Additional screen terminals  48  may be formed between the ends of the conductor  46 , depending on the requirements of the alarm circuit. Likewise,  FIG. 5B  illustrates a second pattern, in which the screen  26  is formed by one conductor  46  that terminates at two screen terminals  48 . The pattern shown in  FIG. 5B  is formed by flipping the first pattern shown in  FIG. 5A  about a diagonal passing through the two terminals.  FIG. 5C  illustrates a third pattern, in which the screen  26  is formed by one conductor  46 , terminating at a pair of screen terminals  48 . The third pattern is different from the other two patterns. In accordance with an embodiment of the present invention, screen terminals  48  may function as contact pads. Each of the screens  26  should have a conductor pattern which is different from the pattern of the other screens used in the security wrap. 
     Ideally, the conductor patterns are designed to form a conductor that is as thin as reliably possible and arranged so that portions of the conductor are spaced apart by a minimum spacing that is reliably reproducible and reliably separated so as not to short out sections of the conductor  46 . The conductor pattern need not completely fill the wrap  20 . Indeed, the wrap  20  may be used to visually obscure or hide other parts of the PCB  16  with the conductor only being used to protect a small portion of the PCB  16 , such as the portion supporting the memory chip or microprocessor. 
       FIG. 6  illustrates a multi-layer security wrap  20 . In this embodiment, all three screens of  FIG. 5  are overlaid to form a three layer security wrap  20 . As shown in  FIG. 6 , the spaces between adjacent potions of the conductors  46  in one layer overlap portions of the conductors  46  of the other layers, thus significantly increasing the difficulty to find a clear path through the security wrap  20 . In the simple embodiment shown in  FIG. 6 , each screen  26  has two screen terminals  48  interconnected by a single conductor  46 . Depending on the alarm circuit, the screens may be connected to respective alarm terminals, connected in series to a single alarm circuit, or connected in parallel to a single alarm circuit. For the parallel connection, in one specific embodiment, the screens have a predetermined, definite resistance and the alarm circuit is able to monitor changes in the resistance of the connection across the alarm terminals indicating tampering of the security wrap  20 . The three screens  26  each have a conductor pattern  46  chosen from a predetermined set of patterns and each of the conductor patterns of the security screens of any security wrap are different. 
     Breaking any one of the three conductors  46  would change the current signal in the corresponding pair of terminals  48 . Overlaying multiple screens having conductors  46  with patterns not coinciding with each other significantly increases the circuitry density of security wrap  20  beyond what is otherwise achievable by a single screen. 
     A screen with a denser pattern of conductor provides a higher security level because it would be more difficult to penetrate screen  26  without breaking conductor  46 . Therefore, it is preferable to have a thin conductor  46  spreading densely throughout the area of the screen. It is also preferable for conductor  46  to be made of an easily breakable material or so arranged that the conductor is readily broken should someone attempt to remove the security wrap  20 , to further increase the sensitivity of screen  26 . 
       FIG. 7  illustrates a multilayer security wrap  20  having two screens  26  both of which are printed on to the substrate  22 , over a release layer  24  such that the substrate  22  has a screen on both surfaces. The outer screen  26  is covered by a dielectric layer  28  and the inner screen  26  is covered by the adhesive layer  30 . 
       FIG. 8  illustrates a multilayer security wrap  20  having three screens  26 . First screen  26  is printed on to the substrate  22  over a intermittent release layer  24 . A first dielectric layer  28  is printed over the first screen  26 . A second release layer  24  is printed on the dielectric layer  28  and a second screen  26  is printed on the first dielectric layer  28  over the second release layer  24 . A second dielectric layer  28  is printed over the second screen  26  and a third release layer  24  is formed on the second dielectric layer  28  and a third screen  26  is printed on the second dielectric layer  28  over the third release layer  24 . In this manner a security wrap  20  with any number of screens  26  can be formed. An adhesive layer  30  is applied to the last screen (in this example the third screen)  26  to bond the security wrap  20  to the parent device  16 . 
       FIG. 9  is a sectional view showing main components in a double screen, single circuit construction of a security wrap  20  assembled to parent device  16 . The security wrap  20  has a substrate  22 , a release layer  24 , a first screen  26 , a dielectric layer  28 , a second screen  26  and a layer of adhesive  30  bonding the security wrap  20  to the parent device  16 . The conductive traces of the first and second screens  26  are electrically interconnected by a hole  32  in the dielectric layer  28  which is filled with conductive ink during the printing of the second screen. Such holes are known as a via. In this case it is a printed via as the connection is made using a printing process. Plated vias are also known. 
       FIG. 10  is a sectional view showing main components in a double screen, double circuit construction of either an open or full face security wrap  20  when assembled to parent device  16 . The security wrap  20  has a substrate  22 , a release layer  24 , a first screen  26 , a dielectric layer  28 , a second release layer  24 , a second screen  26  and a layer of adhesive  30  bonding the security wrap to the parent device  16 . The conductive traces of the first and second screens  26  are electrically isolated by the dielectric layer  28 . Suitable means for connecting the first screen  26  to the alarm circuit of the parent device  16  are provided which pass through the second screen without being electrically connected. 
       FIG. 11  is a sectional view showing main components in a double screen construction of a single surface security wrap  20  utilizing a metal dome  34 , as a conductive element to connect security wrap  20  traces to a device  16  and where the parent surface is for example a rigid or flexible PCB. This drawing illustrates the addition of metal domes  34 ,  35  to the security wrap of  FIG. 9 . A similar arrangement can be made for the double screen, double circuit construction of the security wrap of  FIG. 10  by deletion of the vias  32  interconnecting the conductive layers  26  and providing isolated through connections for the screen terminals  48 . The second screen  26  is formed with an extension  36  which forms a screen terminal  48 . The adhesive layer  30  does not cover the extension and a void is formed below the extension to accommodate a curved metal disc known as a dome  34 . The dome  34  connects the screen terminal  48  to the parent device  16 , in particular, to an alarm terminal. A further void is shown accommodating a second dome  35  which is insulated for the conductive layer  26  by the adhesive layer  30 . Dome  35  is an example of how the security wrap  20  can be applied over switches. Dome  35  is an ancillary conductive element used to close a two pole switch on the surface of the parent device  16  which is operated by applying external downward pressure on the security wrap directly above the dome  35 . 
       FIG. 12  is a sectional view showing main components in a double screen construction of a single surface security wrap  20  utilizing a conductive material  40  to connect security wrap  20  traces to the parent device  16  and where the surface of the parent device  16  is for example a rigid or flexible PCB. This material can include anisotropic or isotropic conductive adhesives, depending on connection design, in resin or film form. Connection is established by means of polymerization of the adhesive or pressure applied from a protrusion of a device enclosure. The conductive material  40  replaces the metal domes  34  and the extensions  36  of the conductive layer  26  and connect the screen terminals  48  to the alarm circuit. A similar arrangement can be made for the double screen, double circuit construction of the security wrap  20  of FIG.  10  by deletion of the vias  32  interconnecting the conductive layers and providing isolated through connections for the screen terminals  48 . 
       FIG. 13  is a sectional view showing main components in a double screen construction of a single surface security wrap  20  utilizing a printed carbon pad  42  to connect security wrap  20  traces to the parent device  16  and where the surface of the parent device  16  is for example a rigid or flexible PCB. The carbon pad  42  replaces the conductive material  40  used in the embodiment of  FIG. 12 . A similar arrangement can be made for the double screen, double circuit construction of the security wrap  20  of  FIG. 10  by deletion of the vias  32  interconnecting the conductive layers  26  and providing isolated through connections for the screen terminals  48 . 
     The carbon pads  42  preferably do not fill the void formed in the adhesive layer  30  such that, in the relaxed state, there is no direct electrical connection between the screen terminals  48  and the alarm terminals. However, by applying a force to the security wrap  20  directly above the carbon pads  42  to resiliently deform the security wrap the carbon pads come into contact with the parent device  16  and electrically connect the screen terminals  48  to the alarm terminals. Typically the carbon pad  42  connection is established by means of pressure applied from a protrusion of a device enclosure. In this way, an alarm condition is triggered by mere opening of the device enclosure before any direct attempt to remove the security wrap  20  is made. 
       FIG. 14  is a simplified sectional view showing separation of conductive layers in a double conductive layer construction: As shown, in the corner of the security Wrap  20  where the substrate  22  has been lifted, the conductive traces  46  of the screens  26  have been torn into pieces damaging the conductive traces  46  and alerting the resistance between the screen terminals  48 . In the example shown the conductive traces  46  have been completely severed in several places. Portions of the conductive trace of the first screen  26  applied directly to the substrate  22  remains bonded to the substrate  22  but portions of the conductive trace applied to the release layer  24  remain bonded to the dielectric layer  28 . An additional separation occurs between the second screen  26  and the dielectric layer  28 , due to the reduced adhesion provided by the second release layer  24  applied to the dielectric layer  28  creating areas of weakened adhesion between the dielectric layer  28  and the conductive trace of the second screen  26 . Thus portions of the conductive trace of the second screen  26  applied directly to the dielectric layer  28  remains bonded to the dielectric layer  28  but portions of the conductive trace applied to the release layer  24  remain bonded to the adhesive layer  30  which also remains bonded to the parent layer  16 , due to the reduced strength of the bond between the release layer  24  and the dielectric  28  and the lower bond strength between the adhesive layer  30  and the conductive trace compared with the bond strength between the conductive trace and the dielectric layer  28 . Thus the conductive traces of both screens  26  are severed as the substrate  22  is prised from the parent device  16 . 
     It should be noted that in the sectional views of  FIGS. 9 to 14 , the section is cut along a conductor of the security screen  26  for convenience. It will be understood that the areas of the screen  26  where there is no trace, will be filled with material of the overlaying layer, i.e. either dielectric material or adhesive material, both of which are electrically insulative. 
       FIG. 15  illustrates an attempt to remove a security wrap  20  having breakable conductors, as described above, after it has been fitted to the PCB  16 . As the corner of the security wrap  20  is lifted from the PCB  16 , the conductor  46  is torn apart, with part of the conductor remaining glued to the PCB  16  and part of the conductor remaining attached to the substrate  22  or dielectric  28 . Actually, the pattern created by the conductor  46  on the substrate  22  and the PCB  16  conforms to the pattern of the release layer  24 . The bond between the conductor  40  and the substrate  22  is stronger than the bond between the conductor  46  and the adhesive  30 . However, the bond between the conductor  46  and the release ink is weaker than the bond between the conductor  46  and the adhesive  30 . Hence the conductor  46  remains bonded to the adhesive layer  30  where the release ink pattern was applied and remains bonded to the substrate  22  where the adhesion modifier pattern was not applied. Thus after separation, the connection between the two screen terminals  48  is open circuited. 
       FIGS. 16 and 16A , illustrate an additional security measure briefly described herein before. At least one of the screen terminals  48  is connected to an alarm terminal by a resilient or spring loaded connection which is biased to the open condition.  FIG. 16  shows a parent device  16  in the form of a PCB having a security wrap  20  fitted there to.  FIG. 16A  is a enlarged, exploded view of two connections between the security wrap  20  and the PCB  16 . Metal domes  34  are used for the connection between the security wrap  20  and the PCB  16  but in their relaxed state they resiliently lift off the PCB terminal pads. Spigots  60  formed on a part of the housing for the PCB  16  are arranged to bear down on the security wrap  20  so as to press the screen terminals  48  against the domes  34  and the domes  34  against the PCB terminals to establish an electrical connection, as the housing is closed. When the housing is opened, the spigots  60  separate from the security wrap and the domes  34  relax and the connection is broken, raising an alarm condition. The domes  34  are one example of a resilient connector and the carbon pads of  FIG. 13  are another. 
       FIG. 17  illustrates a screen  26  having two conductive traces or conductors  46 , each having two ends forming a pair of screen terminals  48 . Depending on the complexity of the alarm circuit, a screen may have any number of conductors  46 . 
     While, the drawings have been enlarged for better clarity of observation and description, in the preferred embodiments, the width of the conductive traces and the spaces there between are in the range of 1 to 1,000 microns. The preferred embodiment uses a trace width between 200 and 300 microns. This produces a good compromise between costs and security level as the finer the widths the higher the security level but the more expensive is the printing process. 
     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. 
     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.