Tamper Responsive Assembly and Method of Manufacturing a Tamper Responsive Assembly (Tamper Responsive Assembly Having a Structural Material Within a Sealed Internal Compartment)

Abstract

To provide a novel tamper-respondent assembly and a method of manufacture which provide enhanced tamper-proof protection for electronic components within a secure volume in order to cope with increased use of encryption and decryption in a computing system.SOLUTION: Tamper-respondent assemblies are provided which include a circuit board, an enclosure assembly mounted on the circuit board, and a pressure sensor. The circuit board includes an electronic component, and the enclosure assembly is coupled to the circuit board to enclose the electronic component within a secure volume. The enclosure assembly includes an enclosure with a sealed inner compartment, and a structural material within the sealed inner compartment of the enclosure. The structural material within the enclosure inhibits deflection of the enclosure. The pressure sensor senses pressure within the sealed inner compartment of the enclosure to facilitate identifying a pressure change indicative of a tamper event.SELECTED DRAWING: Figure 1A

Description

[Background technology]

[0001] Many activities require secure electronic communications. To facilitate secure electronic communications, encryption / decryption systems may be implemented in electronic or circuit board assemblies included in devices connected to communication networks. Such electronic assemblies are attractive targets for criminals because they may contain codes or keys for decrypting intercepted messages or encoding fraudulent messages. To prevent this, the electronic assembly may be mounted in an enclosure, then encapsulated in a security sensor and encapsulated in a polyurethane resin. In one or more embodiments, the security sensor may be a web or sheet of insulating material with circuit elements fabricated thereon, with closely spaced conductive traces. The circuit elements may be sensed to interrupt if the sensor is damaged, generating an alarm signal. The alarm signal may be sent to a monitoring circuit to reveal an attack on the integrity of the assembly and trigger the erasure of the encryption / decryption key stored within the electronic assembly. Summary of the Invention [Problem to be solved by the invention]

[0002] With the increasing use of encryption and decryption in computing systems, novel tamper-responsive assemblies and methods of manufacture that provide enhanced tamper-evident protection for electronic components within secure volumes are desirable. [Means for solving the problem]

[0003]

[0009] In one or more embodiments herein, a tamper-responsive assembly is provided, including a circuit board, an enclosure assembly attached to the circuit board, and a pressure sensor. The circuit board includes an electronic component, and the enclosure assembly is attached to the circuit board to enclose the electronic component within a secure volume. The enclosure assembly includes an enclosure and a structural material. The enclosure includes a sealed internal compartment within the enclosure, and the structural material is within the sealed internal compartment of the enclosure. The structural material within the enclosure inhibits deflection of the enclosure due to a pressure difference between the pressure in the sealed internal compartment and the ambient pressure in at least a portion of the enclosure. The pressure sensor senses pressure within the sealed internal compartment of the enclosure to facilitate identification of a pressure change indicative of a tamper-evident event.

[0004] In another aspect, a tamper-responsive assembly is provided, including a circuit board, a plurality of electronic components, a first enclosure assembly, a second enclosure assembly, and a pressure sensor. The circuit board includes a first side and a second side, the first side and the second side being opposite sides of the circuit board. The plurality of electronic components includes at least one first electronic component coupled to the first side of the circuit board and at least one second electronic component coupled to the second side of the circuit board. The first enclosure assembly is attached to the first side of the circuit board and encloses the at least one first electronic component coupled to the first side of the circuit board within a first chamber of a safety volume. The first enclosure assembly includes an enclosure and a structural material. The enclosure has a sealed internal compartment within the enclosure, and the structural material is within the sealed internal compartment of the enclosure. The structural material within the enclosure inhibits deflection of the enclosure due to a pressure differential between the pressure in the sealed internal compartment and the ambient pressure in at least a portion of the enclosure. A second enclosure assembly is attached to the second side of the circuit board and encloses at least one second electronic component coupled to the second side of the circuit board within a second chamber of the safety volume. A pressure sensor senses pressure within the sealed internal compartment of the enclosure of the first enclosure assembly to facilitate identifying pressure changes indicative of a tamper event.

[0005] In a further aspect, a method of manufacturing a tamper respondent assembly is provided. The method includes providing a circuit board with an electronic component and attaching an enclosure assembly to the circuit board to enclose the electronic component within a secure volume. The enclosure assembly includes an enclosure and a structural material. The enclosure includes a sealed internal compartment within the enclosure, and the structural material is within the sealed internal compartment of the enclosure. The structural material within the enclosure inhibits deflection of the enclosure due to a pressure difference between pressure in the sealed internal compartment and ambient pressure in at least a portion of the enclosure. The method further includes providing a pressure sensor that senses pressure within the sealed internal compartment of the enclosure to facilitate identification of a pressure change indicative of a tamper event.

[0006] Additional features and advantages are realized through the techniques described herein. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed aspects. [Brief explanation of the drawings]

[0007] One or more aspects of the present invention are particularly pointed out and distinctly claimed as examples in the claims at the conclusion of this specification. The foregoing and other objects, features, and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

[0008] [Figure 1A] 1 is a cross-sectional elevation view of one embodiment of a tamper-evident electronic package, or tamper-responsive assembly, including (in part) an enclosure and a multi-layer circuit board with embedded tamper detection circuitry.

[0009] [Figure 1B] FIG. 1B is a plan view of the multilayer circuit board of FIG. 1A.

[0010] [Figure 2]1 illustrates one embodiment of a tamper respondent sensor with conductive traces that at least partially form at least one tamper detection circuit.

[0011] [Figure 3] 1C is a partial cross-sectional elevation view of a more detailed embodiment of the tamper respondent assembly of FIGS. 1A and 1B including (in part) an enclosure and a multi-layer circuit board with embedded tamper detection circuitry; FIG.

[0012] [Figure 4] 1 illustrates one embodiment of a process for manufacturing a multi-layer circuit board with embedded tamper detection circuitry in accordance with one or more aspects of the present invention.

[0013] [Figure 5] FIG. 1 is an isometric view of one embodiment of a tamper respondent assembly in accordance with one or more aspects of the present invention.

[0014] [Figure 6A] 1 shows one embodiment of a tamper respondent assembly illustrating deflection of the enclosure that can occur upon application of positive or negative pressure to the sealed interior compartment of the enclosure. [Figure 6B] 1 shows one embodiment of a tamper respondent assembly illustrating deflection of the enclosure that can occur upon application of positive or negative pressure to the sealed interior compartment of the enclosure. [Figure 6C] 1 shows one embodiment of a tamper respondent assembly illustrating deflection of the enclosure that can occur upon application of positive or negative pressure to the sealed interior compartment of the enclosure.

[0015] [Figure 7A] 6 is a cross-sectional elevation view of a further embodiment of a tamper respondent assembly (such as that shown in FIG. 5) with a structural material within a sealed internal compartment, in accordance with one or more aspects of the present invention. [Figure 7B]6 is a cross-sectional elevation view of a further embodiment of a tamper respondent assembly (such as that shown in FIG. 5) with a structural material within a sealed internal compartment, in accordance with one or more aspects of the present invention.

[0016] [Figure 8A] 1 is a partial illustration of materials of construction of a tamper respondent assembly in accordance with one or more embodiments of the present invention.

[0017] [Figure 8B] 8B is a magnified view of one embodiment of the structural material of FIG. 8A in accordance with one or more aspects of the present invention.

[0018] [Figure 9A] 7C illustrates one embodiment of a process for manufacturing an enclosure for a tamper respondent assembly with a structural material, such as that shown in FIG. 7B, in accordance with one or more aspects of the present invention. [Figure 9B] 7C illustrates one embodiment of a process for manufacturing an enclosure for a tamper respondent assembly with a structural material, such as that shown in FIG. 7B, in accordance with one or more aspects of the present invention. [Figure 9C] 7C illustrates one embodiment of a process for manufacturing an enclosure for a tamper respondent assembly with a structural material, such as that shown in FIG. 7B, in accordance with one or more aspects of the present invention. [Figure 9D] 7C illustrates one embodiment of a process for manufacturing an enclosure for a tamper respondent assembly with a structural material, such as that shown in FIG. 7B, in accordance with one or more aspects of the present invention.

[0019] [Figure 10A] 10 illustrates another embodiment of an epoxy-coated structural material defining an enclosure for a tamper respondent assembly in accordance with one or more aspects of the present invention.

[0020] [Figure 10B]10B is a cross-sectional elevation view of another embodiment of a tamper respondent assembly with an enclosure such as that shown in FIG. 10A in accordance with one or more aspects of the present invention.

[0021] [Figure 11] 10 is a cross-sectional elevation view of a further embodiment of a tamper respondent assembly with an enclosure having multiple sealed internal compartments with structural material in accordance with one or more aspects of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0022] Aspects of the present invention and specific features, advantages, and details thereof are described in more detail below with reference to non-limiting examples shown in the accompanying drawings. Descriptions of well-known materials, manufacturing tools, processing techniques, and the like are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and specific examples, while illustrating aspects of the present invention, are given by way of illustration only and not by way of limitation. Various substitutions, modifications, additions, or adjustments, or combinations thereof, within the spirit and / or scope of the underlying inventive concept, will become apparent to those skilled in the art from this disclosure. Furthermore, while reference is made below to the figures, it should be noted that, for ease of understanding, the figures are not drawn to scale and that the same reference numerals used in different figures indicate the same or similar components. It should also be noted that many aspects and features of the invention are disclosed herein and, to the extent not inconsistent, each disclosed aspect or feature can be combined with other disclosed aspects or features, for example, as desired for a particular application of a tamper-responsive assembly.

[0023] 1A and 1B show one embodiment of a tamper-evident electronic package or tamper-responsive assembly 100 that includes one or more electronic components, such as a circuit 115 coupled to a multilayer circuit board 110, or an electronic device (or element) 102, or both.

[0024] 1A and 1B together, circuit 115 is mounted or embedded within multilayer circuit board 110 and also has an embedded tamper-responsive sensor 111 that (in one or more embodiments) extends into multilayer circuit board 110 and facilitates partially defining a secure volume 101 associated with multilayer circuit board 110. Notably, in the embodiment of FIGS. 1A and 1B, secure volume 101 may reside partially within multilayer circuit board 110 and partially above multilayer circuit board 110. One or more electronic devices 102 are attached to multilayer circuit board 110 within secure volume 101 and may include, for example, one or more encryption modules, decryption modules, or associated components, or a combination thereof, to be protected within a tamper-evident electronic package. In one or more implementations, the one or more electronic components to be protected may include, for example, components of a secure communication card of a computer system.

[0025] The tamper-evident electronic package 100 further includes an enclosure 120, such as a pedestal-type enclosure, attached to the multilayer circuit board 110 within a continuous groove (or trench) 112 formed in the top surface of the multilayer circuit board 110 and secured to the multilayer circuit board 110 via, for example, a structural adhesive disposed within the continuous groove 112. In one or more embodiments, the enclosure 120 is made of a thermally conductive material and may act as a heat sink to facilitate cooling of one or more electronic components 102 within the secure volume. A security mesh or tamper-responsive sensor 121 may be associated with the enclosure 120, for example, enveloping the inner surface of the enclosure 120, to facilitate defining the secure volume 101 in combination with the tamper-responsive sensor 111 embedded within the multilayer circuit board 110. In one or more implementations, the enclosure 120 may be affixed to the surface of the multilayer circuit board 110 (without the continuous groove) using a bonding material such as, for example, epoxy or other adhesive.

[0026] The briefly described tamper respondent sensor 121 may, in one or more examples, include one or more tamper detection layers including circuit lines or traces provided on one or both sides of a structural layer, which in one or more implementations may be a flexible insulating layer or film. The circuit lines on one or both sides of the flexible layer have a line width and a pitch or spacing such that perforation of the layer at any point can result in damage to one or more circuit lines or traces. In one or more implementations, the circuit lines may define one or more conductors that can be electrically connected in a network to, for example, an enclosure monitor or detector 103 that monitors the resistance on the lines. Detection of a change in resistance caused by disconnection or damage to one or more lines triggers automatic erasure of the information within the secure volume. The conductive lines of the tamper respondent sensor may be any desired pattern, such as a sinusoidal pattern, making it more difficult to compromise the tamper detection layer without detection.

[0027] For resistance monitoring, a variety of materials can be employed to form the circuit lines. For example, the circuit lines can be formed of metal or metal alloys such as copper or silver, or can be formed of, for example, inherently conductive polymers, carbon ink, or nickel-phosphorus (NiP), or Omega-ply®, available from Omega Technologies, Inc., Culver City, California (USA), or Ticer™, available from Ticer Technologies, Chandler, Arizona (USA). The process employed to form the delicate circuit lines or traces depends in part on the selection of material used for the circuit lines. For example, if copper circuit lines are fabricated, additive processes such as plating the copper traces or subtractive processes such as etching away unwanted copper between the trace lines can be employed.

[0028] As described above, in one or more implementations, the circuit lines of the tamper-responsive sensor lining the inner surface of the enclosure 120, or even the circuit lines printed directly on one or more layers formed on the inner surface of the enclosure 120, may be connected to define one or more detection networks.

[0029] If a flexible layer is used on the interior surface of the enclosure 120, the flexible layer may be formed of a crystalline polymer material. For example, the crystalline polymer may include polyvinylidene fluoride (PVDF), or Kapton, or other crystalline polymer material. Advantageously, the crystalline polymer can be made fairly thin while maintaining the structural integrity of the flexible substrate, which also allows for stronger folding and greater reliability of the sensor after folding.

[0030] 1B , one or more external circuit connection vias 113 may be provided within the multilayer circuit board 110 to electrically connect to one or more electronic components within the safety volume 101. These one or more external circuit connection vias 113 may be electrically connected to one or more external signal lines or planes (not shown) embedded within the multilayer circuit board 110, for example, extending to (or below) a safe base region of the safety volume 101. Electrical connections to and from the safety volume 101 may be provided by coupling to such external signal lines or planes within the multilayer circuit board 110.

[0031] As noted above, secure volume 101 may be sized to house one or more electronic components to be protected and may be configured to extend into multi-layer circuit board 110. In one or more implementations, multi-layer circuit board 110 includes electrical interconnects within secure volume 101 defined within the board to electrically connect, for example, one or more tamper detection layers of embedded tamper respondent sensor 111, along with one or more daughter cards such as memory DIMMs, PCIe cards, processor cards, etc., to associated monitoring circuitry also disposed within secure volume 101.

[0032] 1A and 1B are presented by way of example only. Other configurations of enclosure 120 or multilayer circuit board 110 may be employed, and / or other approaches for coupling enclosure 120 and multilayer circuit board 110 may be used. For example, in one or more alternative implementations, enclosure 120 may be affixed to the top surface of multilayer circuit board 110 (without the continuous groove) using a structural bonding material such as, for example, epoxy or other adhesive.

[0033] Figure 2 shows one embodiment of a tamper detection layer 205 (or laser and perforation responsive layer) of a tamper responsive sensor 200 or security sensor. In Figure 2, the tamper detection layer 205 includes circuit lines or traces 201 provided on one or both of opposing sides of a layer, such as a flexible layer 202, which in one or more embodiments may be a flexible insulating layer or film.

[0034] 2 shows, for example, circuit lines 201 on one side of flexible layer 202, with traces on the opposing side of the film having the same pattern but (in one or more embodiments) offset between circuit lines 201 so as to lie directly beneath spaces 203. As noted above, the circuit lines on one side of the flexible layer have a line width W such that perforation of layer 205 at any point will result in damage to at least one of the line traces 201. l The pitch or spacing between the wires is W sIn one or more implementations, the circuit lines may be electrically connected in series or parallel to define one or more conductors that may be electrically connected in a network to an enclosure monitor, which may monitor the resistance of the lines in one or more implementations. Detection of an increase in resistance or other change caused by cutting or damaging one of the traces may cause the erasure of information in the encryption module, the decryption module, or both. Providing the conductive lines 201 in a pattern, such as a sinusoidal pattern, may advantageously make the tamper-evident layer 205 more difficult to compromise without detection. It should be noted that, in this regard, the conductive lines 201 may be provided in any desired pattern. For example, in an alternative implementation, the conductive lines 201 may be provided as parallel, straight conductive lines if desired, and the pattern or pattern orientation may vary between layers, or between layers, or both.

[0035] As noted above, as intrusion technologies continue to evolve, anti-intrusion technology must continue to improve to stay ahead. In one or more implementations, the tamper respondent sensor 200 of FIG. 2 , summarized above, may cover or line the interior surface of an enclosure to provide a secure volume around at least one electronic component to be protected. Additionally, the tamper respondent sensor, or more specifically, the sensor's tamper detection circuitry, may be embedded within a multi-layer circuit board, as described below.

[0036] It should also be noted that when implemented using resistance monitoring, a variety of materials may be advantageously employed to form the circuit lines. For example, the circuit lines may be formed of a conductive ink (such as a carbon-doped conductive ink) printed on one or both opposing sides of one or more such flexible layers 202 in a stack of such layers. Alternatively, metals or metal alloys such as copper, silver, and the like, inherently conductive polymers, carbon inks, nickel-phosphorus (NiP) such as Omega-Ply® offered by Omega Technologies, Inc., Culver City, California (USA), or Ticer® offered by Ticer Technologies, Chandler, Arizona (USA), or nickel-chromium may be used to form the circuit lines. It should be noted that the process employed to form the delicate circuit lines or traces in the sequence described herein depends in part on the selection of material used for the circuit lines. For example, if copper circuit lines are fabricated, additive processes such as plating the copper traces or subtractive processes such as etching away unwanted copper between the trace lines may be employed.

[0037] By way of further example, FIG. 3 shows a partial cross-sectional elevation view of a more detailed embodiment of the tamper-evident electronic package 100, and in particular the multilayer circuit board 110 to which the enclosure 120 is affixed. In this configuration, the embedded tamper-responsive sensor includes multiple tamper-detection layers, illustratively including at least one tamper-detection mat (or base) layer 300 and at least one tamper-detection frame 301. In this illustrated example, two tamper-detection mat layers 300 and two tamper-detection frames 301 are shown by way of example only. The bottom tamper-detection mat layer 300 may be a continuous sensing portion or may detect layers that extend completely below the secure volume defined within and / or above the multilayer circuit board 110. One or both tamper-detection mat layers 300 below the secure volume 101 may be partitioned into multiple circuit zones, if desired. Within each tamper evident mat layer, or more particularly within each circuit zone of each tamper evident mat layer, a plurality of circuits or conductive traces may be provided in any desired configuration. Furthermore, the conductive traces within the tamper evident layer may be implemented as a resistive layer, for example.

[0038] As shown, one or more external signal wires or planes 305 may enter the secure volume 101 between two tamper detection mat layers 300 in one embodiment and electrically connect upward into the secure volume 101 through one or more conductive vias positioned at any desired location. In the configuration shown, one or more tamper detection frames 301 are disposed at least inside the area defined by the continuous groove 112 that receives the base of the enclosure 120. The tamper detection frames 301 and tamper detection mat layers 300, together with the tamper respondent sensors 121 associated with the enclosure 120, define the secure volume 101 that may extend partially into the multi-layer circuit board 110. With the secure volume 101 defined partially within the multi-layer circuit board 110, the external signal wires 305 may be securely and electrically connected, for example, to one or more electronic components mounted on the multi-layer circuit board 110 within the secure volume 101 or to one or more components of the multi-layer circuit board 110 within the secure volume 101. Additionally, the secure volume 101 may house the electrical interconnection of the conductive traces of the multiple tamper evident layers 300, 301, for example, via appropriate monitoring circuitry.

[0039] Additional security may be provided by extending the tamper detection mat layer 300 (and tamper detection frame 301, if desired) outward beyond the perimeter of the enclosure 120. In this manner, a series of attacks at the interface between the enclosure 120 and the multilayer circuit board 110 may be made more difficult because an attack would require, for example, clearing the tamper detection mat layer 300, the enclosure 120, and the tamper detection frame 301 of the embedded tamper detection circuitry.

[0040] 1A-2 are possible. For example, in one embodiment, the embedded tamper detection circuit may include one or more tamper detection mat layers 300 and one or more tamper detection frames 301, as described above, and a triplate structure with one or more external signal lines or layers sandwiched between upper and lower ground planes. In this configuration, high-speed transmission of signals to and from the secure volume, and particularly to and from one or more electronic components within the secure volume, may be facilitated.

[0041] Additionally, once the security volume is defined, the conductive vias within the security volume between layers of the multilayer circuit board 110 can be either aligned or off-centered as desired depending on the implementation. Aligning the conductive vias can, for example, facilitate providing the shortest connection path, while off-centering the conductive vias between layers can further enhance the security of the tamper-evident electronic package by making attacks into the security volume through or around one or more of the multiple tamper-evident layers more difficult.

[0042] A tamper detection layer of an embedded tamper detection circuit formed within a multilayer circuit board of an electronic circuit or package may include, for example, a plurality of conductive traces or lines formed between respective sets of input and output contacts or vias at the trace terminating points. Any pattern and number of conductive traces or circuits may be employed in defining a tamper detection layer or tamper detection circuit zone within the tamper detection layer. For example, four, six, eight, etc. conductive traces may be formed in parallel (or otherwise) within a given tamper detection layer or circuit zone between respective sets of input and output contacts to those conductive traces.

[0043] In one or more implementations, the multilayer circuit board may be, for example, a multilayer wiring or printed circuit board, or a card, formed by building up multiple layers of substrate. Figure 4 illustrates one embodiment for forming and patterning a tamper-detecting layer in such a multilayer circuit board.

[0044] 4 , in one or more implementations, a tamper detectable layer, such as a tamper detectable mat layer or tamper detectable frame disclosed herein, may be formed, at least in part, by providing a material stack including a structural layer 401, such as a prepreg (or pre-impregnated) material layer, a trace material layer 402 used to define a desired trace pattern, and an overlying conductive material layer 403 patterned to define conductive contacts or vias, for example, that electrically connect to the pattern of traces formed in trace material layer 402 at trace termination points. In one or more implementations, trace material layer 402 may include nickel-phosphorus (NiP), and overlying conductive layer 403 may include copper. Note that these materials are identified by way of example only, and other trace and / or conductive materials may be used in buildup 400.

[0045] A first photoresist 404 is provided on the build-up 400 and patterned with one or more openings 405 through which the overlying conductive layer 403 can be etched. Depending on the materials employed and the etching process used, a second etching process may be desired to remove portions of the trace material layer 402 to define the conductive traces of the target tamper-detectable layer. The first photoresist 404 is then removed, and a second photoresist 404' may be provided on the conductive layer 403, leaving features such as input and output contacts. The exposed portions of the conductive layer 403 are then etched, as shown, and the second photoresist 404' may be removed, with any openings in the layer filled, such as with adhesive (or prepreg) 406, and the next build-up layer is provided. Note that in this implementation, at the end of the traces formed in the layer by patterning the trace material layer 402, most of the overlying conductive layer 403 is etched away, leaving only conductive contacts or conductive vias, if desired. Note that any of a variety of materials may be employed to form the conductive lines or traces in the tamper-evident layer. Nickel-phosphorus (NiP) is particularly advantageous as a material because it is resistant to solder contact or bonding using a conductive adhesive, making it more difficult to bridge from one circuit or trace to the next during an attempt to penetrate the protected safety volume of the electronic circuit. Other materials that may be employed include OhmegaPly®, available from Ohmega Technologies, Inc. of Culver City, California (USA), or Ticer™, available from Ticer Technologies of Chandler, Arizona (USA).

[0046] The traces or circuits within the tamper detection layer, and particularly within the tamper detection circuit zone, of the embedded tamper detection circuit may be electrically connected to detect or compare circuitry provided within, for example, the secure volume 101 (FIG. 1A) of the tamper-resistant electronic package, along with a tamper detector monitoring the enclosure. The detection or monitoring circuitry may include various bridge or comparison circuits and conventional printed wiring board electrical interconnections within the secure volume 101 (FIG. 1A) located within the secure volume defined by, for example, the tamper detection frame 301 (FIG. 3) and the tamper detection mat layer 300 (FIG. 3).

[0047] It should be noted that different tamper detection circuit zones on different tamper detection layers may advantageously be electrically interconnected, for example, to the same detection circuit. Thus, any number of interconnection configurations may be possible. For example, if two tamper detection mat layers each contain 30 tamper detection circuit zones and two tamper detection frames each contain 4 tamper detection circuit zones, the resulting 68 tamper detection circuit zones may be connected in any configuration within the secure volume to create any desired arrangement of circuit networks within the secure volume that are monitored for resistance changes or tampering. In this regard, it should be noted that the power supply or battery for the tamper respondent sensor may be located inside or outside the secure volume, with the sensor configured to trip or destroy any protected or critical data if the power supply or battery is tampered with.

[0048] By way of further example, an isometric view of one embodiment of a tamper-evident electronic package, or tamper-responsive assembly, is shown in FIG. 5 , with enclosure 500 (such as enclosure 120 of FIG. 1A or an enclosure described below in connection with FIGS. 6A-11 ) shown sealed to multilayer circuit board 110 to define a secure volume around one or more electronic components. In the illustrated embodiment, enclosure 500 is formed of a thermally conductive material and has a major surface 501 and a sidewall 502 including a sidewall angle 503. The interior surface of enclosure 500 may have an inner major surface and an inner sidewall corresponding to major surface 501 and sidewall 502, respectively, and in one embodiment, the inner major surface and inner sidewall surface are covered by one or more tamper-responsive sensors in embodiments such as those described above in connection with FIGS. 1A-2 . The power supply 505 or battery for the tamper sensitive sensor may be located inside or outside the secure volume as shown in this embodiment, and the tamper detector is configured to trip or destroy any protected or critical data if the power supply or battery is tampered with. The enclosure 500 may be adhered to the multi-layer circuit board 110, which has its own tamper protection as described herein.

[0049] With the increasing use of encryption and decryption in computing systems, novel tamper-responsive assemblies and methods of manufacture that provide enhanced tamper-evident protection for electronic components within secure volumes are desirable.

[0050] When considering tamper-resistant packaging, electronic packages must achieve defined tamper-resistance requirements, such as those described in Federal Information Processing Standards (FIPS) 140-2, a U.S. government computer security standard used to certify cryptographic modules, promulgated by the National Institute of Standards and Technology (NIST). NIST FIPS 140-2 defines four levels of security, designated Level 1 through Level 4, with Security Level 1 providing the lowest level of security and Security Level 4 providing the highest level of security. At Security Level 4, physical security mechanisms are provided to create a complete protective envelope around the cryptographic module, intended to detect and respond to any unauthorized attempts at physical access. Penetration of the cryptographic module enclosure from any direction has a very high probability of being detected, resulting in the immediate erasure of all plaintext critical security parameters (CSPs).

[0051] To meet the demand for ever-improving anti-intrusion technology and higher performance encryption / decryption functionality, enhanced security level 4 tamper-resistant, tamper-evident packaging for one or more electronic components or assemblies is desired.

[0052] Disclosed below with reference to Figures 6A-11 herein are various tamper-resistant assemblies and methods of manufacture that provide a security volume, e.g., security level 4, for housing one or more electronic components, such as one or more encryption modules, or decryption modules, or both, and associated components, e.g., communications cards or other electronic assemblies to be protected, and that provide enhanced conduction of heat generated within the security volume outward from the enclosure.

[0053] By way of reinforcement, FIG. 6A illustrates one embodiment of a tamper respondent assembly 600 that uses pressure sensing or monitoring to detect a tamper event. In this embodiment, the tamper respondent assembly 600 includes a multilayer circuit board 610 with one or more electronic components 602, 602′ coupled to a first side and a second side of the circuit board. In one or more implementations, the multilayer circuit board 610 and the one or more electronic components 602, 602′ are similar to the multilayer circuit board 110 and the one or more electronic components 102, respectively, as described above in connection with FIGS. 1A-5. For example, the multilayer circuit board 610, in one or more embodiments, includes embedded tamper respondent sensors 611, 611′ similar to the embedded tamper respondent sensor 111 described above in connection with FIGS. 1A-4. In one or more implementations, the electronic components 602, 602′ include one or more application-specific integrated circuits to be protected. As shown, in one or more embodiments, a peripheral component interconnect (PCI) tab or bus 613 may be provided from the multilayer circuit board 610 to connect to internal components and / or circuits on the multilayer circuit board. Also, in this embodiment, the embedded tamper-responsive sensors 611, 611′ need only occupy a portion of the multilayer circuit board 610 near a trench such as that shown. Together, the first enclosure 620 and the second enclosure 620′ define secure volumes 601, 601′ on opposing sides of the circuit board, with the embedded tamper-responsive sensors providing tamper protection along the enclosure-substrate interface.

[0054] As described above, the tamper respondent assembly 600 also includes a first enclosure 620, a second enclosure 620′ attached to opposing sides of the circuit board 610, such as within respective continuous grooves (or trenches) formed within the first and second sides of the multilayer circuit board 610, and secured to the multilayer circuit board 610 via, for example, structural adhesive 625, 625′ disposed within the continuous grooves. In one or more embodiments, the enclosures 620, 620′ are made of a thermally conductive material, such as metal, and may act (in part) as a heat sink to facilitate cooling of the electronic components 602, 602′ within the respective first and second chambers of the defined safety volume 601, 601′. In one or more embodiments, the enclosures 620, 620′ may be made of a plastic material, such as a polymeric material, as described further below.

[0055] In the illustrated embodiment, tamper detection is implemented using pressure sensing, and specifically detecting changes in pressure or changes in pressure differential. This pressure sensing approach is an alternative to the security mesh or tamper-responsive sensors associated with the interior surfaces of the enclosures of FIGS. 1A-2. For example, in one or more embodiments, the enclosures 620, 620′ include respective sealed interior compartments 623, 623′ between respective interior and exterior walls 621, 621′ and 622, 622′, which are pressurized or depressurized at the time of manufacture to facilitate monitoring of pressure changes.

[0056] In one embodiment, the sealed interior compartments 623, 623′ may each be defined as a gap between the respective interior wall 621, 621′ and exterior wall 622, 622′. As described below, in one embodiment, the enclosures 620, 620′ may be fabricated from base and top metal elements sealed together, such as by solder or braze 632, 632′, resulting in the interior walls 621, 621′, exterior walls 622, 622′, and sealed interior compartments 623, 623′. Other enclosure implementations, such as those described herein, are also possible.

[0057] As shown in FIG. 6A , pressure sensors 640, 640′ are provided where pressure sensor 640 is positioned to monitor the pressure within sealed interior compartment 623 of enclosure 620 and pressure sensor 640′ is positioned to monitor the pressure within sealed interior compartment 623′ of enclosure 620′. In one or more embodiments, if desired, pressure sensors (not shown) can be provided within the first and second chambers of secure volumes 601, 601′ on the first and second sides of the multilayer circuit board. Additionally, one or more monitoring circuits or modules 603, 603′ are provided within or on multilayer circuit board 610. Pressure sensors 640, 640′ provide sensed pressure data that is monitored by monitoring circuits 603, 603′ to identify changes in pressure or pressure differentials indicative of a tamper event. For example, a change in pressure within sealed interior compartment 623 would occur if there was an attempt to access the secure volume by piercing enclosure 620. Those skilled in the art will appreciate that such pressure changes can be detected or identified in a variety of ways.

[0058] In one or more implementations, positive pressure may be applied during manufacturing to sealed interior compartment 623, or sealed interior compartment 623', or both. Depending on the applied positive pressure and the ambient pressure outside enclosure 620, 620' and the pressure within the safety volume, interior walls 621, 621', or exterior walls 622, 622', or both, may bulge as shown in FIG. 6B. FIG. 6C illustrates the expected wall deflection of the tamper respondent assembly upon application of negative pressure during manufacturing of sealed interior compartment 623, 623'.

[0059] The potential deflection of the inner and outer walls shown in FIGS. 6B and 6C can negatively impact the performance and / or life cycle of the tamper-responsive assembly. For example, in one or more embodiments, a thermal interface material (not shown) can be provided to couple the electronic components 602, 602′ to the respective inner walls 621, 621′ of the enclosures 620, 620′ to facilitate heat conduction from the electronic components outward from the enclosure. Deflection of the enclosure walls shown in FIGS. 6B and 6C can interfere with this heat conduction. Furthermore, in the case of positive pressure, the inward deflection of the inner walls 621, 621′ can exert sufficient force against one or more electronic components within the safety volume, potentially negatively impacting the operation of the components, the overall system, or both.

[0060] Additionally, in one or more embodiments, the manufacture of pressure-sensitive, tamper-responsive assemblies disclosed herein may involve providing random pressurization or vacuum to the internal sealed compartment 623, 623′, resulting in internal pressures that vary from one tamper-responsive assembly to another, or (if desired) between enclosures of a particular tamper-responsive assembly, e.g., causing the pressure within each sealed internal compartment to be unknown and unpredictable. Deflection of the enclosure walls shown in Figure 6B or 6C may be a signal that the internal sealed compartment has been pressurized or vacuumed, information that is desired to remain confidential.

[0061] 7A-11 illustrate further embodiments of tamper respondent assemblies in accordance with one or more aspects of the present invention.

[0062] 7A and 7B illustrate further embodiments of tamper respondent assemblies 700, 700′ according to one or more aspects of the present invention. As shown in FIG. 7A, tamper respondent assembly 700 is similar to tamper respondent assembly 600 of FIG. 6A. In tamper respondent assembly 600 of FIG. 6A, an enclosure 620 is provided on one side of multilayer circuit board 610 to facilitate defining a secure volume 601 for one or more electronic components 602 mounted on the top surface of multilayer circuit board 610, for example. As shown, multilayer circuit board 610 includes, in one or more embodiments, an embedded tamper respondent sensor 611 similar to embedded tamper respondent sensor 111 described above in connection with FIGS. 1A-4.

[0063] In one or more implementations, the enclosure 620 is the same as or similar to the enclosure 620 discussed above in connection with FIG. 6A , with the addition of a structural material 701 provided within the sealed interior compartment 623 of the enclosure 620. This structural material 701 is selected and configured to substantially fill the interior compartment (in one embodiment only) and to facilitate inhibiting deflection of the walls of the enclosure due to a pressure differential between the pressure within the sealed interior compartment and the pressure surrounding the enclosure, as described herein.

[0064] 7B illustrates another embodiment of a tamper respondent assembly 700′ that includes an enclosure assembly attached to both a first side and a second side of a multilayer circuit board 610, similar to the tamper respondent assembly 600 of FIG. 6A. In this embodiment, a structural material 701 is provided within the sealed interior compartments 623, 623′ of both enclosures 620, 620′. The structural material is provided to substantially fill each interior compartment (in one embodiment only) and inhibit deflection of the enclosure walls due to a pressure differential between the pressure within the sealed interior compartment and the pressure surrounding at least a portion of the enclosure.

[0065] Also, in the embodiment of Figures 7A and 7B, the structural material 701 is configured to prevent the inner and / or outer walls of each enclosure from expanding upon application of positive pressure to the sealed internal compartment, and to prevent the inner and / or outer walls from collapsing upon application of negative pressure to the sealed internal compartment, while enabling pressure-sensing tamper detection.

[0066] 6A , the tamper respondent assembly 600 of FIG. 6A , as well as the tamper respondent assembly 700, 700′ of FIGS. 7A and 7B , use pressure sensing to implement tamper detection, and particularly detection of changes in pressure or pressure differentials. To facilitate this, sensors 640, 640′ are provided within the sealed internal compartments 623, 623′ of the enclosures 620, 620′, respectively. As described above, the structural material 701 substantially fills the available space within the respective sealed internal compartments. To facilitate pressure sensing, the structural material 701 is porous. For example, the porous material can have a porosity of 80 percent or more, such as 90 percent or more. In one or more implementations, the structural material is a metal foam with interconnected pores.

[0067] 8A and 8B illustrate one embodiment of the structural material 701 as a metal foam with interconnected porosity 800. The metal foam advantageously provides structural rigidity to the enclosure assembly when secured within the enclosure between the inner and outer walls and also allows for rapid pressure changes resulting from, for example, an attempted tamper event by drilling through the enclosure into the metal foam. As noted above, during manufacturing, the sealed internal compartment can be pressurized or depressurized. This pressurization or depressurization provides a pressure differential between the pressure within the sealed internal compartment and the ambient pressure outside the enclosure or even the pressure within the safety volume of the tamper-responsive assembly. In one embodiment, all of the porosity in the metal foam is interconnected, allowing for control of pore size for a desired application. In one or more embodiments, the porosity is micron-sized. Furthermore, in one or more embodiments, the physical strength of the metal foam can be controlled, for example, by adjusting the porosity of the metal foam. In just one embodiment, the metal foam may be Duocel® Aluminum Foam (nominal consistency 6101-T6 8%) from ERG Aerospace Corporation of Oakland, California (USA).

[0068] As noted above, during manufacturing, the sealed internal compartment may be pressurized or depressurized in pressure-sensing implementations such as those disclosed herein. This pressurization or depressurization may provide a pressure differential between the pressure within the sealed internal compartment and the ambient pressure outside the enclosure or even the pressure within the safety volume of the tamper respondent assembly. Furthermore, as noted above, in one or more implementations, the pressurization or depressurization of the sealed internal compartment may be random and may even vary between compartments of a particular tamper respondent assembly or between chambers of a particular enclosure of a tamper respondent assembly, as described further below. Advantageously, providing structural material 701 within the enclosure having structural material affixed to the enclosure walls inhibits any deflection of the enclosure walls due to a pressure differential between the pressure within the sealed internal compartment and at least a portion of the periphery of the enclosure.

[0069] 9A-9D illustrate one embodiment of a process for manufacturing a tamper respondent assembly with a structural material, such as that shown in FIGS. 7A and 7B. As shown in FIG. 9A, a structural material 701, such as a metal foam, can be preformed to a desired size and shape, such as by machining, trenching, or other forming operations. In the embodiment shown, the structural material has an interior space 900 formed therein that facilitates defining a portion of the safety volume. In one particular embodiment, the interior space (or depth) of the channel can be in the range of 4-5 mm, for example.

[0070] As shown in FIG. 9B , a base element 901, such as a base metal element, can be preformed by extrusion to contain the structural material 701 within channels or gaps that will form a portion of the sealed interior compartment of the enclosure once assembled. Additionally, a top element 902, such as a top metal element, is sized and configured to be attached to the base element 901 and secured in place via solder 632, braze 632, or both, with the resulting enclosure assembly shown in FIG. 9C . As shown, the enclosure assembly includes an enclosure 620 having an inner wall 621 and an outer wall 622 that define a sealed interior compartment therebetween and, in the illustrated embodiment, are filled with the structural material 701. In only one embodiment, the thickness of the top plate-metal foam-base plate combination can be 1 mm-1 mm-1 mm. Additionally, in one or more embodiments, the structural material 701 is diffusion bonded to the base element and to the top element, forming the inner and outer walls and firmly bonding the structural material to the walls of the enclosure.

[0071] The pressure sensor 640 is implanted inside the structural material (in one embodiment), and the interior walls are sealed around the sensor wire using fasteners, adhesive, or both. The sealed interior compartment is then randomly pressurized (e.g., to 1.5-2 atmospheres) or depressurized (e.g., to 0-0.5 atmospheres) as desired through a fill port (not shown). Once pressurized or depressurized, the fill port can be plugged or sealed using, for example, a solder or braze material.

[0072] Once manufactured, any attempt to puncture the enclosure assembly will cause a pressure change within the sealed internal compartment of the enclosure that is detected via the pressure sensor, facilitating identification of a tamper event. Based on the identification of a tamper event, a trigger signal or alarm can be issued by the monitoring circuitry to protect any confidential data within the secure volume of the tamper respondent assembly.

[0073] As shown in Figure 9D, the enclosure assembly of Figure 9C is attached to a surface of a circuit board, such as multi-layer circuit board 610 described above, to enclose one or more electronic components within a secure volume as described above. In Figure 9D, two enclosure assemblies fabricated as described in connection with Figures 9A-9C are attached to opposite sides of multi-layer circuit board 610, resulting in an embodiment of the two-sided tamper-responsive assembly described above in connection with Figure 7B.

[0074] 10A-10B illustrate an alternative tamper-responsive assembly approach. In FIG. 10A, an enclosure 1000 is fabricated by starting with a structural material 701, such as a metal foam, and applying a polymer coating 1001, such as an epoxy coating, around the entire perimeter of the structural material. For example, the polymer coating 1001 can be a polyimide film that is heated and physically wrapped around the structural material and then cured. If desired, an appropriate force can be applied during curing to help secure the coating to the structural material. In one implementation, the polymer material is wrapped around the structural material, heated, and an appropriate force is applied to compress the coating while adhering the layers together within the structural material. By wrapping the coating around the entire perimeter of the structural material and sealing it to the structural material, the polymer coating itself becomes the enclosure, defining a sealed internal compartment that is filled or substantially filled with the structural material 701. One or more pressure sensors 640 may be provided within the structural material either before or after sealing the polymer-coated structural material to define a sealed internal compartment.

[0075] Figure 10B shows one embodiment of a tamper respondent assembly 1010 with an enclosure assembly that uses enclosures 1000, 1000' such as those described above in connection with Figure 10A. As shown, enclosure 1000 replaces enclosures 620, 620' of the above-described two-sided pressure sensitive tamper respondent assembly of Figure 7B and is similar or the same as tamper respondent assembly 700' described above in connection with Figure 7B, except for the tamper respondent assembly 1010.

[0076] FIG. 11 illustrates another embodiment of a tamper respondent assembly 1100, similar to the tamper respondent assembly 700′ described above in connection with FIG. 7B. In this embodiment, the tamper respondent assembly 1100 is substantially identical to the tamper respondent assembly 700′ described above, but with the addition of at least one dividing wall 1101 separating the sealed interior compartment 623 into two or more separate sealed interior chambers 1102, 1103, each containing a structural material 701 as described herein. In one embodiment, this allows different portions of the enclosure 620 to be pressurized differently, further inhibiting the ability to tamper with the enclosure. For example, the first sealed interior chamber 1102 can be at a first pressure and the second sealed interior chamber 1103 can be at a second pressure, where the first pressure and the second pressure are different pressures. Furthermore, in one embodiment, the first pressure and the second pressure are each randomly selected pressures. Also, one or more dividers 1101 may be provided in both enclosures 620, 620′, if desired. In this manner, many different positive and / or negative pressures may be used in different versions of the tamper respondent assembly, which may advantageously inhibit any attempts to open or puncture the enclosure. In one embodiment, each sealed internal chamber of the sealed internal compartment of the enclosure has an associated pressure sensor 640 operatively coupled to one or more monitoring circuits 603, 603′ within the secure volume of the tamper respondent assembly. Any attempt to puncture the respective sealed internal chamber causes a pressure change that triggers a response within the secure volume to maintain the security of the confidential information, for example, by erasing the secure information.

[0077] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, singular forms such as "a," "an," and "the" are intended to include the plural unless the context clearly dictates otherwise. It will be further understood that "comprises" (and other variations of comprise such as "comprises" and "comprised"), "have" (and variations of have such as "have" and "have"), "includes" (and variations of include such as "includes" and "including"), and "contains" (and variations of contain such as "contains" and "containing") are open-ended linking verbs. Consequently, a method or device that "comprises," "has," "includes," or "contains" one or more steps or elements possesses those one or more elements, but is not limited to possessing only those one or more elements. Similarly, a method step or device element that "comprises," "has," "includes," or "contains" one or more features has those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a particular way is configured in at least that way, but may also be configured in other ways not listed.

[0078] The corresponding structure, material, and acts of any means or step-plus-function element in the following claims, and their equivalents, where available, are intended to include that structure, material, or act for performing a function as specifically claimed in combination with other claimed elements. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or to limit the invention to the form disclosed. Many modifications and variations that do not depart from the scope and spirit of the invention will be apparent to those skilled in the art. The embodiments were chosen and described to best explain the concepts of one or more aspects of the invention and to enable others skilled in the art to understand one or more aspects of the invention, since various embodiments, with various modifications where appropriate, are contemplated for particular uses.

Claims

1. 1. A tamper respondent assembly comprising: a circuit board, the circuit board having electronic components; an enclosure assembly attached to the circuit board to enclose the electronic component within a safety volume, the enclosure assembly comprising: an enclosure having an outer wall and an inner wall, the inner wall and the outer wall having a gap therebetween that defines a sealed interior compartment of the enclosure, the enclosure being attached to the circuit board to facilitate defining the safety volume between the enclosure and the circuit board, the sealed interior compartment of the enclosure being pressurized or depressurized; a structural material within the sealed interior compartment of the enclosure, the structural material within the enclosure inhibiting deflection of the enclosure due to a pressure differential between a pressure in the sealed interior compartment and an ambient pressure in at least a portion of the enclosure, the pressure differential resulting from pressurization or depressurization of the sealed interior compartment of the enclosure; an enclosure assembly having a pressure sensor that senses pressure within the sealed interior compartment of the enclosure to facilitate identification of pressure changes indicative of a tamper event; 1. A tamper respondent assembly comprising:

2. 1. A tamper respondent assembly comprising: a circuit board, the circuit board having electronic components; an enclosure assembly attached to the circuit board to enclose the electronic component within a safety volume, the enclosure assembly comprising: an enclosure having a sealed internal compartment within the enclosure; a structural material within the sealed interior compartment of the enclosure, the structural material within the enclosure inhibiting deflection of the enclosure due to a pressure differential between the pressure in the sealed interior compartment and the ambient pressure in at least a portion of the enclosure; an enclosure assembly having a pressure sensor that senses pressure within the sealed interior compartment of the enclosure to facilitate identification of pressure changes indicative of a tamper event; Equipped with the structural material comprises a metal foam having interconnected pores; The enclosure includes a polymer coating surrounding the metal foam. Tamper Responsive Assembly.

3. 3. The tamper respondent assembly of claim 1 or 2, wherein the structural material substantially fills the sealed interior compartment of the enclosure.

4. 4. The tamper respondent assembly of claim 1, wherein the structural material has a porous structure.

5. 5. The tamper respondent assembly of claim 4, wherein the porous structure has a porosity of 80 percent or greater.

6. 10. The tamper respondent assembly of claim 1, wherein the structural material comprises a metal foam of interconnected pores.

7. 7. The tamper respondent assembly of claim 6, wherein the enclosure comprises a metal enclosure with an inner wall and an outer wall, and the metal foam within the sealed interior compartment is diffusion bonded to the inner wall and to the outer wall.

8. 8. The tamper respondent assembly of claim 1, wherein the sealed internal compartment has a first sealed internal chamber and a second sealed internal chamber, the first sealed internal chamber and the second sealed internal chamber being separate sealed internal chambers, and the structural material is within the first sealed internal chamber and the second sealed internal chamber.

9. 9. The tamper respondent assembly of claim 8, wherein the first sealed interior chamber is at a first pressure and the second sealed interior chamber is at a second pressure, the first pressure and the second pressure being different pressures.

10. 10. The tamper respondent assembly of claim 9, wherein the first pressure and the second pressure are each random pressures.

11. 11. A tamper respondent assembly according to any one of claims 1 to 10, further comprising a monitoring circuit located within the safety volume that monitors pressure within the sealed interior compartment via the pressure sensor to identify the pressure change indicative of the tamper event.

12. 1. A tamper respondent assembly comprising: a circuit board having a first surface and a second surface, the first surface and the second surface being opposite surfaces of the circuit board; a plurality of electronic components having at least one first electronic component coupled to the first side of the circuit board and at least one second electronic component coupled to the second side of the circuit board; a first enclosure assembly attached to the first surface of the circuit board and enclosing the at least one first electronic component coupled to the first surface of the circuit board within a first chamber of a safety volume, the first enclosure assembly comprising: an enclosure having an outer wall and an inner wall, the inner wall and the outer wall having a gap therebetween that defines a sealed interior compartment of the enclosure, the enclosure being attached to the circuit board to facilitate defining the safety volume between the enclosure and the circuit board, the sealed interior compartment of the enclosure being pressurized or depressurized; a structural material within the sealed interior compartment of the enclosure, the structural material within the enclosure inhibiting deflection of the enclosure due to a pressure differential between a pressure within the sealed interior compartment and an ambient pressure within at least a portion of the enclosure, the pressure differential resulting from pressurization or depressurization of the sealed interior compartment of the enclosure; a first enclosure assembly having: a second enclosure assembly attached to the second side of the circuit board to enclose the at least one second electronic component coupled to the second side of the circuit board within a second chamber of the safety volume; and a pressure sensor that senses pressure within the sealed interior compartment of the enclosure to facilitate identification of pressure changes indicative of a tamper event; 1. A tamper respondent assembly comprising:

13. 1. A tamper respondent assembly comprising: a circuit board having a first surface and a second surface, the first surface and the second surface being opposite surfaces of the circuit board; a plurality of electronic components having at least one first electronic component coupled to the first side of the circuit board and at least one second electronic component coupled to the second side of the circuit board; a first enclosure assembly attached to the first surface of the circuit board and enclosing the at least one first electronic component coupled to the first surface of the circuit board within a first chamber of a safety volume, the first enclosure assembly comprising: an enclosure having a sealed internal compartment within the enclosure; a structural material within the sealed interior compartment of the enclosure, the structural material within the enclosure inhibiting deflection of the enclosure due to a pressure differential between a pressure within the sealed interior compartment and an ambient pressure within at least a portion of the enclosure; a first enclosure assembly having: a second enclosure assembly attached to the second side of the circuit board to enclose the at least one second electronic component coupled to the second side of the circuit board within a second chamber of the safety volume; and a pressure sensor that senses pressure within the sealed interior compartment of the enclosure to facilitate identification of pressure changes indicative of a tamper event; Equipped with the structural material includes a metal foam having interconnected porosity; The metal foam substantially fills the sealed interior compartment of the enclosure. The enclosure includes a polymer coating surrounding the metal foam. Tamper Responsive Assembly.

14. 13. The tamper respondent assembly of claim 12, wherein the structural material comprises a metal foam having interconnected porosity.

15. 15. The tamper respondent assembly of claim 14, wherein the metal foam substantially fills the sealed interior compartment of the enclosure.

16. 16. The tamper respondent assembly of claim 15, wherein the enclosure comprises a metal enclosure having an inner wall and an outer wall, the metal foam within the sealed interior compartment being diffusion bonded to the inner wall and to the outer wall.

17. 14. The tamper respondent assembly of claim 12 or 13, wherein the structural material comprises a porous structure, the porous structure having a porosity of 80 percent or greater.

18. 1. A method of manufacturing a tamper respondent assembly, comprising: providing a circuit board, the circuit board including electronic components; attaching an enclosure assembly to the circuit board to enclose the electronic component within a safety volume, the enclosure assembly comprising: an enclosure having an outer wall and an inner wall, the inner wall and the outer wall having a gap therebetween that defines a sealed interior compartment of the enclosure, the enclosure being attached to the circuit board to facilitate defining the safety volume between the enclosure and the circuit board, the sealed interior compartment of the enclosure being pressurized or depressurized; a structural material within the sealed interior compartment of the enclosure, the structural material within the enclosure inhibiting deflection of the enclosure due to a pressure differential between a pressure in the sealed interior compartment and an ambient pressure in at least a portion of the enclosure, the pressure differential resulting from pressurization or depressurization of the sealed interior compartment of the enclosure; an attaching step including: providing a pressure sensor that senses pressure within the sealed interior compartment of the enclosure to facilitate identification of pressure changes indicative of a tamper event; A method comprising:

19. 1. A method of manufacturing a tamper respondent assembly, comprising: providing a circuit board, the circuit board including electronic components; attaching an enclosure assembly to the circuit board to enclose the electronic component within a safety volume, the enclosure assembly comprising: an enclosure including a sealed internal compartment within the enclosure; a structural material within the sealed interior compartment of the enclosure, the structural material within the enclosure inhibiting deflection of the enclosure due to a pressure differential between the pressure in the sealed interior compartment and the ambient pressure in at least a portion of the enclosure; an attaching step including: providing a pressure sensor that senses pressure within the sealed interior compartment of the enclosure to facilitate identification of pressure changes indicative of a tamper event; Equipped with the structural material comprises a metal foam having interconnected pores; The enclosure includes a polymer coating surrounding the metal foam. method.

20. The method of claim 18 , wherein the structural material comprises a metal foam with interconnected pores.

21. 21. The method of claim 19 or 20, wherein the metal foam substantially fills the sealed interior compartment of the enclosure.

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