Control of electric field effects in a printed circuit board assembly using embedded nickel-metal composite materials

Abstract

A printed circuit board assembly (PCBA) controls an electrically-initiated device (EID) in an electric field. The PCBA includes a conductive layer, a dielectric layer, and a trans-conductive layer (TCL). The conductive layer of the PCBA designated protected areas. An electrical current with a predetermined current density is impressed in the conductive layer when the PCBA is in the electric field. The TCL is a nickel-metal composite metamaterial positioned between the conductive and dielectric layers and configured to change in shape or thickness in the electric field such that the impressed current is steered away from the conductive layer and into the dielectric layer to prevent premature activation of the EID. A system includes an outer housing, power supply, an EID such as a sonobuoy or medical device, and the PCBA, all of which are encapsulated in the housing. A method is also disclosed for manufacturing the PCBA.

Claims

1. A printed circuit board assembly (PCBA) for control of an electrically-initiated device (EID) operating in an externally generated electric field exterior to the EID and the PCBA, the PCBA comprising: a first conductive layer; a first dielectric layer attached to the first conductive layer; a second conductive layer attached to the first dielectric layer, wherein an electrical current is impressed on the second conductive layer when the PCBA is in the presence of the externally generated electric field; a pre-pregnated layer attached to the second conductive layer; a trans-conductor layer (TCL) attached to the second conductive layer and including a nickel-metal composite metamaterial; and a second dielectric layer attached to the TCL such that the TCL is positioned between the second conductive layer and the second dielectric layer, wherein the TCL includes a plurality of islands of the nickel-metal composite metamaterial, each of the islands having a distinct irregular shape providing a respective impedance value in response to a variation in an intensity and/or a wavelength of the externally generated electric field, and wherein the TCL has a surface roughness configured to change in proportion to an energy level of the externally generated electric field to thereby change an effective permittivity of the second dielectric layer and thereby direct the impressed electrical current away from the second conductive layer.

2. The PCBA of claim 1, wherein the nickel-metal composite metamaterial of the TCL includes a nickel-phosphorus (NiP) metamaterial.

3. The PCBA of claim 1, wherein the nickel-metal composite metamaterial of the TCL includes a nickel-chromium (NiCr) metamaterial.

4. The PCBA of claim 1, wherein a nickel content of the nickel-metal composite metamaterial of the TCL is between about 10% and about 45% by weight of the TCL.

5. The PCBA of claim 1, wherein the first and second conductive layers each includes a metallic foil sheet.

6. The PCBA of claim 1, wherein the pre-pregnated layer includes an uncured resin-treated glass or ceramic material.

7. The PCBA of claim 1, further comprising a plurality of circuit components surface mounted to one or both of the first and second conductive layers.

8. The PCBA of claim 1, characterized by an absence of an electromagnetic interference (EMI) shield and a Faraday cage mounted to the PCBA.

9. The PCBA of claim 1, wherein the first dielectric layer is mounted to an inside surface of the first conductive layer, the pre-pregnated layer is mounted to an inside surface of the first dielectric layer, the second conductive layer is mounted to an inside surface of the pre-pregnated layer, the TCL is mounted to an inside surface of the second conductive layer, and the second dielectric layer is mounted to an inside surface of the TCL.

10. The PCBA of claim 1, further comprising a third conductive layer attached to the second dielectric layer.

11. The PCBA of claim 1, further comprising a via electrically connecting the first and second conductive layers.

12. The PCBA of claim 1, wherein the plurality of islands includes a first TCL island spaced from a second TCL island, the first TCL island having a first irregular shape, and the second TCL island having a second irregular shape distinct from the first irregular shape.

13. A system comprising: a housing defining a cavity; a power supply located within the cavity of the housing; an electrically-initiated device (EID) located within the cavity of the housing and electrically connected to the power supply; and a printed circuit board assembly (PCBA) located within the cavity of the housing, separated from the EID and the power supply, and electrically connected to the power supply, wherein the PCBA includes: a first conductive layer; a second conductive layer with a designated protected area, wherein the PCBA is configured such that an electrical current is impressed on the second conductive layer in the presence of a resonant broadband electric field that is externally generated with respect to the EID and the PCBA; a first dielectric layer adjacent to the first conductive layer; a pre-pregnated layer adjacent to the first dielectric layer and the second conductive layer; a trans-conductor layer (TCL) adjacent to the second conductive layer and constructed with a nickel-metal composite metamaterial; and a second dielectric layer adjacent to the TCL such that the TCL is positioned between the second conductive layer and the second dielectric layer, wherein the TCL includes a plurality of islands of the nickel-metal composite metamaterial, each of the islands having a non-uniform length and a non-uniform width providing the TCL with multiple resistance values in response to a variation in an intensity and/or a wavelength of the resonant broadband electric field, and wherein the TCL has a surface roughness configured to change in proportion to an energy level of the resonant broadband electric field to thereby change an effective permittivity of the second dielectric layer and thereby direct the impressed electrical current through the PCBA and away from the designated protected area of the second conductive layer, thereby preventing an unintended activation of the EID due to the impressed electrical current.

14. The system of claim 13, wherein the EID is a controlled component of a sonobuoy or a medical device.

15. The system of claim 13, wherein the nickel-metal composite metamaterial of the TCL includes a nickel-phosphorus (NiP) metamaterial and/or a nickel-chromium (NiCr) metamaterial.

16. The system of claim 13, wherein a nickel content of the nickel-metal composite metamaterial of the TCL is between about 10% and about 45% by weight of the TCL.

17. The system of claim 13, wherein the first and second dielectric layers each includes an epoxy-resin fiberglass or a glass-reinforced epoxy laminate.

18. The system of claim 13, wherein the first and second conductive layers each includes a metallic foil sheet.

19. The system of claim 13, wherein the pre-pregnated layer includes an uncured resin-treated glass or a ceramic material.

20. The system of claim 13, further comprising a plurality of circuit components surface mounted to one or both of the first and second conductive layers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic perspective-view illustration of an example system having a printed circuit board assembly (PCBA) contained therein, with the PCBA constructed with embedded nickel-metal trans-conductor layers as set forth herein.

(2) FIG. 2 is schematic cross-sectional view of a PCBA usable within the system shown in FIG. 1.

(3) FIG. 2A is a schematic plan view illustration of a portion of the PCBA of FIG. 2 in a possible embodiment.

(4) FIG. 3 is a flow chart describing a method of constructing the PCBA shown in FIG. 1.

DETAILED DESCRIPTION

(5) Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, a system 10 is shown schematically in FIG. 1. The system 10 includes an outer housing 12 having a wall 14 that defines an internal cavity 15. While shown as an example cylinder, e.g., the shape typically assumed by the outer housing 12 when used in an example sonobuoy application, with the outer housing 12 being perforated or porous, as indicated generally at 12P in FIG. 1, in sonobuoy applications as noted above, the actual shape of the outer housing 12 may be expected to differ with the design. For instance, as an alternative to being configured as a sonobuoy system, the system 10 may be alternatively embodied as a medical device, such as a pacemaker, and thus may have a rectangular or an irregular shape in other embodiments. Other geometric shapes may be envisioned without departing from the intended inventive scope.

(6) A printed circuit board assembly (PCBA) 16 is encapsulated within the cavity 15, along with other possible components such as a power supply 18 such as a DC battery (BAT) and an electrically-activated device (EID) 19, both of which may be collocated with the PCBA 16 as shown, i.e., external to the PCBA 16 in proximity thereto as shown in FIG. 1. The PCBA 16 and the EID 19 are electrically connected to the power supply 18 via a conductor 17, for instance a length of wire. Example applications of the EIDs 19 may include deployment of a sonobuoy and activation of a pacemaker or other medical device as noted above.

(7) A sonobuoy may be a submarine, air, or surface-launched device used to detect acoustic emissions or reflections in a body of water, and to transmit the detected signals to a remote source for processing. A sonobuoy may employ acoustic sensors that aid in the detection, classification, and localization of targets in the body of water via determination of sonar propagation properties and acoustic range prediction. Thus, the EID 19 of FIG. 1 could be used as part of a launch device or other controlled component of such a sonobuoy. Example medical device applications that may embody the EID 19 of FIG. 1 include those used in critical care systems such as pacemakers, defibrillators, neuro-stimulator devices, and robotic surgical tools. While sonobuoy and medical devices are examples of systems 10 that may benefit from the design of the PCBA 16 disclosed herein, the system 10 is not intended to be limited to such devices.

(8) In general, the PCBA 16 of FIG. 1 may be constructed using, for instance, surface and/or bulk micromachining techniques such as chemical vapor deposition, etching, and/or other suitable processes, as is well understood in the art. The PCBA 16, the internal structure of which is described in further detail below with reference to FIG. 2, is a multi-layered circuit board. The various layers may be laminated together via pressure and heat to form the PCBA 16 as an integral piece. The PCBA 16 is characterized by an absence of a Faraday cage or other EMI shielding structure, as shown in the various Figures and noted above, with the TCL 20 replacing such shielding structure to a different effect.

(9) Instead, the PCBA 16 in all embodiments includes an embedded trans-conductor layer (TCL) 20. As explained in detail below, the TCL 20 is an embedded layer of a nickel-metal composite metamaterial, i.e., artificial materials that are structured on a size scale that is smaller than the wavelength of external stimuli, e.g., nanomaterials. Such materials may exhibit properties that are not typically found in nature. One such property used herein is the tendency to compress in the presence of energy from an externally-generated electric field, which is represented schematically in FIG. 1 by {right arrow over (a)}rrows E. The geometry of the TCL 20 may also vary with respect to at least one of the three primary dimensions of the PCBA 16, i.e., length, width, and height. That is, TCL 20 could be thicker, wider, or longer in certain locations relative to others.

(10) The TCL 20 as described herein is configured to act as a filter or waveguide of broad-band energy from the externally-generated electric field {right arrow over (E)}. The ability to change in shape or thickness in the presence of the electric field {right arrow over (E)} allows an impressed current in the conductive layer 30 to be steered or guided away from the conductive layer 30 and into the dielectric layer 40 to thereby prevent premature activation of the EID 19. As used herein, the term “broadband” refers to a sufficiently wide range of radio frequency (RF) energy, e.g., 2 MHz-20 GHz in an example embodiment, and any complex resonant fields associated with this incident energy. It is recognized herein that the electric field {right arrow over (E)} may induce a current with a current density J in the PCBA 16. The term “current density” refers to the electric current (I) per unit area (A) of cross section. The magnitude of the current density J, as measured in amperes/m.sup.2, may be given as:

(11) $J={\lim }_{A.fwdarw.0}\frac{I}{A}$

(12) In particular, the TCL 20 may be shaped, sized, and positioned, i.e., configured, to direct undesirable energy from the electric field {right arrow over (E)} through the PCBA 16 without penetrating into an any conductive layers. The TCL 20 is embedded in the PCBA 16 itself, and thus unlike Faraday cages and other EMI shielding designs does not cover the PCBA 16, i.e., the TCL 20 is not positioned between an uppermost surface 35 of the PCBA 16 and the incident electric field {right arrow over (E)}. Likewise, the TCL 20 does not reflect energy away from the PCBA 16 like a Faraday shield, and also does not suffer from the same Z-dimensional packaging issues of such shields.

(13) A key element of the present disclosure is the use of nickel in the TCL 20 in a particular manner, which is to control the undesirable effects of the electric field {right arrow over (E)}. The TCL 20, due to its nickel content, is configured to contract or otherwise change shape or deform in the presence of the electric field {right arrow over (E)}, which in turn allows the TCL 20 to be formed with a variable geometry and thus control the effects of the electric field {right arrow over (E)} on the performance of the PCBA 16. The particular design of the TCL 20 is both field and application specific. A general approach for achieving the desired end results via the TCL 20 is described below with reference to FIG. 3.

(14) Specifically, the TCL 20 is configured to reduce or eliminate the effects of high-intensity radiated broadband fields, including peak fields as high as 5000 volts per meter with vertical and horizontal polarization. Energy from the incident electric field {right arrow over (E)} is guided away from the EID 19 by passively controlling the internal complex impedance of the PCBA 16. The same electric field {right arrow over (E)} falls incident upon the PCBA 16 sets up an immediate electric field vector potential from a top side to a bottom side of the PCBA 16, with “top’ referring to the surface of the PCBA 16 facing the incident electric field {right arrow over (E)}.

(15) The true transverse electric field established by the electric field vector potential will change characteristics of the nickel-metal composite materials of the TCL 20, including a change in shape and/or thickness of the TCL 20, thereby changing the impedance of the PCBA 16. As will be appreciated by one of ordinary skill in the art, the impressed current will follow a path of least resistance away, which in the present construction is away from the conductive layer 30 or any protected areas in or on such a layer 30. In particular, the characteristic impedance of the nickel-metal composite materials changes by physically changing the natural surface roughness and physical size and/or shape of the nickel-metal composite materials of the TCL 20 throughout the PCBA 16. Such a change is caused by the high intensity of the magnetic field associated with the predefined polarization of the illuminating spherical electric field.

(16) As the impressed currents will tend to flow in the path of least resistance, such currents can be steered through the PCBA 16 using the TCL 20, and ultimately dissipated into the dielectric layers 40 shown in FIG. 2. Thus, characteristics of the TCL 20 can be chosen to provide a desired response to the electric field {right arrow over (E)} the EID 19 is expected to operate in, once again without EMI shielding of the PCBA 16. The dielectric material for the layers 40 is selected to create a dielectric waveguide which redirects unwanted field energy to the ends of the PCBA 16, e.g., into vias 36 (FIG. 2) or other structure. Such vias 36 then radiate trapped energy away from the EID 19 as dispersed, lower intensity fields. Therefore, directing the impressed currents into the dielectric layers 40 allows for amplitude and phase variations of impressed currents to effectively cancel each other out. The phase mismatch created by the different magnitudes and angles at which energy from the incident field {right arrow over (E)} is impressed onto the TCL 20 eliminates the need for EMI shield material, with operation of the EID 19 possible in incident electric fields {right arrow over (E)} of at least 2600 volts per meter.

(17) As used herein, the term “nickel-metal composite” refers to any alloy of nickel, with nickel phosphorus (NiP) and nickel chromium (NiCr) being two possible embodiments exhibiting desirable properties and control results. NiP, for instance, is highly resistive, and in a field such as the electric field {right arrow over (E)}, exhibits a measurable frequency response. This response can be employed to the desired effect as explained below. An alloy having an excessive amount of nickel, however, tends to behave too much like a conductor, and therefore the percentage of nickel by weight should be limited. An example range that achieves the desired effect is 10-45% of nickel by weight of the TCL 20.

(18) Additionally, the TCL 20 exhibits capacitance due in part to its surface roughness. For this reason, the TCL acts a transmission line, and for this reason is referred to herein as a Trans-Conductor Layer or TCL. In acting like a transmission line, the TCL 20 is able to reduce EMI effects from the externally-generated electric field via embedding of nickel-based metamaterials in a purposeful, design-specific manner. The TCL 20 guides unwanted current density flow away from any adjacent conductive layers 30 or other predetermined sensitive protected areas of the PCBA 16, with energy dissipated away from such areas via thermal conductance and reactance. In this manner, the internal traces of the PCBA 16 are prevented from inadvertently acting as fuses in the presence of the electric field {right arrow over (E)}, thereby avoiding prematurely firing or triggering some action via the PCBA 16, such as an activation of the EID 19.

(19) In the example system 10 shown in FIG. 1, the cavity 15 allows space for the PCBA 16 to be inserted in the housing 12 along with other necessary components, e.g., the power supply 18 and the EID 19. However, the same cavity 15 may serve to impinge energy from the electric field {right arrow over (E)}. Various cavity modes may result from this effect. Common cavity modes include coupling and cross-coupling, and thus traces of the PCBA 16 could pick up energy from the electric field {right arrow over (E)} or from energy trapped in the cavity 15, e.g., energy entering any external openings or passages of the housing 12.

(20) Referring to FIG. 2, an example embodiment of the PCBA 16 of FIG. 1 is shown in a schematic cross-sectional view. The thickness or z-dimension of the PCBA 16 is formed from a laminated stack-up of layers 20, 30, 40, and 50, i.e., TCL(s) 20, conductive layer(s) 30, dielectric layer(s) 40, and pre-pregnated layer(s) 50. The PCBA 16 in all embodiments includes at least one conductive layer 30, such as thin foil sheet of copper or another suitable conductor.

(21) Three conductive layers 30 are shown in the non-limiting example embodiment of FIG. 2, with a pair of the conductive layers 30 acting as outer layers of the PCBA 16 with outermost surfaces 35. Two dielectric layers 40 are shown in the same example embodiment, with the conductive outer layers 30 positioned adjacent to a corresponding one of the dielectric layers 40. The pre-pregnated layer 50 may be disposed between one of the conductive layers 30 and one of the dielectric layers 40.

(22) Suitable materials for the dielectric layers 40 include epoxy-resin fiberglass or a glass-reinforced epoxy laminate, e.g., FR-4, or any other application-suitable material. The pre-pregnated layer 50 may be formed as an uncured resin-treated glass or ceramic sufficient for filling any gaps or spacing between the outer layers, i.e., conductive layers 30 having the outermost surfaces 35. Use of the pre-pregnated layer(s) 50 may help to bond the various layers 20, 30, and 40 together, and also providing additional structural integrity for the PCBA 16.

(23) While the layers 20, 30, and 40 are shown with uniform distribution in FIG. 2 for illustrative clarity, the TCL 20 in an actual application will ordinarily have a variable geometry with respect to at least one of the thickness (z-dimension), width (x-direction), and length (y-direction) of the PCBA 16. An example of this variable geometry is shown via narrowed portion 21 in FIG. 2, which indicates z-dimension or thickness variation. A PCBA portion 16A is shown in the schematic plan view of FIG. 2A to show geometric variation with respect to the width/x-dimension and length/y-dimension of the PCBA 16 of FIG. 2. In FIG. 2A, the first four layers 30, 40, 50, and 30 of FIG. 2 are removed for illustrative clarity.

(24) Referring to FIG. 3, an example method 100 is shown that explains a process for designing and manufacturing a PCBA such as the PCBA 16 of FIG. 2 for use as an EMI broadband filter using the trans-conductor properties of the TCL 20 described above. The method 100 begins with step 102, wherein characteristics of the electric field {right arrow over (E)} are identified. Step 102 entails determining the type and intensity of the electric field {right arrow over (E)}, e.g., the far field, near far field, and near reactive field, as well as the polarization of these fields. Step 102 also includes determining the band of frequencies of exposure, whether broad, narrow, pulsed, or continuous.

(25) After this step is complete, the components of the PCBA 16 are identified that are susceptible to the identified properties of the electric field {right arrow over (E)}. These components of the conductive layer 30 are referred to hereinafter as the predetermined protected components or areas. Example components or areas can include traces, embedded vias, through vias, connectors, ribbon cable, wires, and the like. The method 100 proceeds to steps 104 and 106 when all of this is completed.

(26) At step 104, the method 100 includes determining the depth of penetration (DOP) of the expected portions of the electric field {right arrow over (E)} into the identified predetermined protected components from step 102, e.g., via direct measurement, modeling, or theoretical calculation. The end goal of step 104 is to determine the thickness of the TCL 20, which should be sufficient for conducting the required electrical current from the electric field {right arrow over (E)} having a predetermined current density J. The method 100 then proceeds to step 108.

(27) Step 106, which is performed in tandem with step 104, includes determining the maximum allowable resistance (R.sub.MAX) of the circuit trace being formed by the TCL 20. The circuit embodied as the PCBA 16 has an overall maximum resistance for implementation of the desired application, including control of the EID 19 of FIG. 1. The sheet resistance of the TCL 20 can be used to calculate the effective added impedance of the TCL 20 to the overall PCBA 16. The location of placement of the TCL 20 is also determined as part of step 106 using this information, with the electrical current I with the predetermined current density J directed around any protected components as noted above. The method 100 then proceeds to step 108.

(28) Step 108 entails determining the power loss (P.sub.LOSS) in the PCBA 16. Step 108 may entail solving the following equation:

(29) $P_{\mathrm{LOSS}}=2\left(\frac{R_S}{2}\right){\int }_{x=0}^{\infty }{\stackrel{.Math.}{J}}_S^2\mathrm{dx}$
where R.sub.S is the sheet resistance and J.sub.S is the current density of the current flowing the TCL 20. The impressed and conducted current densities are also determined, with impressed current being the current due to radiation from the electric field {right arrow over (E)} and the conducted current being the current due to any adjacent sources. The required maximum attenuation for controlling the current density J resulting from the electric field {right arrow over (E)} is ultimately determined as part of step 108. As the TCL 20 is not purely a capacitor, nor is it purely an inductor or a resistor, the embedded TCL 20 will change its impedance in the presence of the electric field {right arrow over (E)}. That is, the TCL 20 will react over a very broad band range of frequencies with variable attenuation. The method 100 proceeds to step 110 once the power loss and maximum attenuation have been determined.

(30) Step 110 includes defining the shape of the TCL 20. This includes defining the length, width, and thickness of the TCL 20. For commercially available sheets of NiP, for example, market standard sheet resistance R.sub.S is 10, 25, and 250 Ohms/meter, with various sheet thicknesses. For any of the suitable nickel-metal based materials used for construction of the TCL 20, as the magnetic field increases the nickel will contract. Although the nickel contracts, there is more phosphorus, in the example of NiP, so the surface roughness of the TCL 20 will change with the contraction. This in turn changes the capacitance and changes the effective permittivity of the dielectric material located adjacent to the TCL 20, for instance the dielectric layer 40 shown at that location in FIG. 2. Although the TCL 20 is not a pure resistor, the TCL 20 has various resistance values under varying electric fields, effective wavelengths, and penetration depths. The method 100 proceeds to step 112 after the shape of the TCL 20 has been defined.

(31) Step 112 includes constructing the TCL 20 with the determined shape from step 110. Constructing the TCL 20 with the desired shape may take place with the fabrication of the PCBA 16, including positioning the TCL 20 with the determined thickness and shape adjacent to the dielectric layer 40 and the protected areas of the conductive layer 30 to form the PCBA 16. The PCBA 16 thereafter can be installed in a system, such as the system 10 shown in FIG. 1, and used in the control of the EID 19.

(32) Aspects of the present disclosure have been described in detail with reference to the illustrated embodiments; those skilled in the art will recognize, however, that many modifications may be made thereto without departing from the scope of the present disclosure. The present disclosure is not limited to the precise construction and compositions disclosed herein; any and all modifications, changes, and variations apparent from the foregoing descriptions are within the spirit and scope of the disclosure as defined in the appended claims. Moreover, the present concepts expressly include any and all combinations and subcombinations of the preceding elements and features.