Patent Publication Number: US-2020296821-A1

Title: Reducing Capacitive Coupling On Metal Core Boards

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119 to U.S. Provisional Patent Application Ser. No. 62/816,669, titled “Reducing Capacitive Coupling on Metal Core Boards” and filed on Mar. 11, 2019, the entire contents of which are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     Embodiments described herein relate generally to electrical devices such as light fixtures, and more particularly to systems, methods, and devices for improving the performance and functionality of metal core boards used in such electrical devices. 
     BACKGROUND 
     Electrical devices, such as light fixtures, often include one or more circuit boards on which multiple components (e.g., integrated circuits, resistors, diodes, transistors, hardware processors, capacitors, sensors) are disposed. There are a number of different types of circuits boards, including but not limited to printed circuit boards and metal core circuit boards, and there can be multiple divisions within each type of circuit board. Each type of circuit board has advantages and disadvantages. One common disadvantage of a metal core board (also called, among other names, a metal core circuit board, a metal core PCB, and an insulated metallic substrate circuit board) is capacitive coupling, which facilitates electronic noise, causes poor voltage and current regulation, and causes an unstable electrical environment for the components on the metal core board. 
     SUMMARY 
     In general, in one aspect, the disclosure relates to a metal core board assembly that includes a metal base layer upon which at least one electrical component is disposed. The metal core board assembly can also include a circuit assembly disposed proximate to the metal base layer, where the circuit assembly is isolated from the metal base layer, where the circuit assembly is electrically coupled to the at least one electrical component. Separating the circuit assembly from the metal base layer can reduce effects of capacitive coupling on the circuit assembly. 
     These and other aspects, objects, features, and embodiments will be apparent from the following description and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate only example embodiments of devices and methods for reducing capacitive coupling and shielding small signal circuits on multi-layer metal core boards and are therefore not to be considered limiting of its scope, as devices and methods for reducing capacitive coupling on metal core boards may admit to other equally effective embodiments. The elements and features shown in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the example embodiments. Additionally, certain dimensions or positions may be exaggerated to help visually convey such principles. In the drawings, reference numerals designate like or corresponding, but not necessarily identical, elements. 
         FIG. 1  shows an exploded view of a light fixture with a circuit board assembly currently used in the art. 
         FIG. 2  shows a cross-sectional side view of a metal core circuit board assembly currently used in the art. 
         FIGS. 3A and 3B  show a top view and a cross-sectional side view, respectively, of a metal core circuit board assembly in accordance with certain example embodiments. 
         FIGS. 4A and 4B  show a top view and a cross-sectional side view, respectively, of another metal core circuit board assembly in accordance with certain example embodiments. 
         FIG. 5  shows a cross-sectional side view of yet another metal core circuit board assembly in accordance with certain example embodiments. 
         FIGS. 6A and 6B  show a top view and a cross-sectional side view, respectively, of still another metal core circuit board assembly in accordance with certain example embodiments. 
         FIGS. 7A and 7B  show a top view and a cross-sectional side view, respectively, of yet another metal core circuit board assembly in accordance with certain example embodiments. 
         FIGS. 8A and 8B  show a top view and a cross-sectional side view, respectively, of still another metal core circuit board assembly in accordance with certain example embodiments. 
         FIG. 9  shows a top view of a metal core circuit board assembly that is a physical representation of the metal core circuit board assembly of  FIG. 8  in accordance with certain example embodiments. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     The example embodiments discussed herein are directed to systems, methods, and devices for reducing capacitive coupling on metal core boards in electrical devices. Such electrical devices can include light fixtures. In such a case, example embodiments can be used with any type of light fixture. For instance, example devices can be used with new light fixtures or retrofitted to existing light fixtures. Further, light fixtures with which example embodiments can be used can be located in any environment (e.g., indoor, outdoor, high humidity, low temperature, sterile, high vibration). 
     Further, light fixtures described herein can use one or more of a number of different types of light sources, including but not limited to light-emitting diode (LED) light sources, organic LEDs, fluorescent light sources, organic LED light sources, incandescent light sources, and halogen light sources. Therefore, light fixtures described herein should not be considered limited to having a particular type of light source. When a light fixture described herein uses LED light sources, those LED light sources can include any type of LED technology, including, but not limited to, chip on board (COB) and discrete die. 
     A light fixture described herein can be any type fixture, including but limited to a street light, a troffer, a down can fixture, an under cabinet light fixture, a pendant light, a table lamp, a floodlight, a spot light, and a high-bay fixture. Also, example embodiments can be used with electrical devices other than light fixtures. Specifically, any electrical device that includes a circuit board can use example devices described herein. Examples of such electrical devices can include, but are not limited to, a computer (e.g., a desktop, a laptop, a tablet), a stereo, a control panel, a digital display, a television set, an appliance (e.g., a clothes dryer, a dish washing machine, a toaster, an oven), and a motor control station. 
     A user may be any person that interacts with an electrical device. Examples of a user may include, but are not limited to, a homeowner, a tenant, a landlord, a property manager, an engineer, an electrician, a lineman, an instrumentation and controls technician, a consultant, a contractor, and a manufacturer&#39;s representative. Example metal core circuit boards used in electrical devices (including components thereof) described herein can be made of one or more of a number of materials, including but not limited to plastic, thermoplastic, copper, aluminum, rubber, stainless steel, and ceramic. 
     Capacitive coupling is the transfer of energy within an electrical network or between distant networks by means of displacement current, induced by an electric field, between two or more circuit nodes. This capacitive coupling can have an adverse effect on the operation of one or more components on a circuit board, as discussed above. Example embodiments are designed to reduce or eliminate capacitive coupling and its adverse effects. 
     In certain example embodiments, electrical devices (e.g., light fixtures) that include example metal core circuit boards are subject to meeting certain standards and/or requirements. For example, the National Electric Code (NEC), the National Electrical Manufacturers Association (NEMA), the International Electrotechnical Commission (IEC), the California Energy Commission (CEC), Underwriters Laboratories (UL), and the Institute of Electrical and Electronics Engineers (IEEE) set standards as to electrical enclosures (e.g., light fixtures), wiring, and electrical connections. Use of example embodiments described herein meet and/or allow the associated electrical device to meet such standards when required. 
     Any electrical devices (e.g., light fixtures), or components thereof (e.g., example metal core circuit boards), described herein can be made from a single piece (e.g., as from a mold, injection mold, die cast, 3-D printing process, extrusion process, stamping process, or other prototype methods). In addition, or in the alternative, an electrical device (or components thereof) can be made from multiple pieces that are mechanically coupled to each other. In such a case, the multiple pieces can be mechanically coupled to each other using one or more of a number of coupling methods, including but not limited to epoxy, welding, soldering, etching, fastening devices, compression fittings, mating threads, tabs, and slotted fittings. One or more pieces that are mechanically coupled to each other can be coupled to each other in one or more of a number of ways, including but not limited to fixedly, hingedly, removeably, slidably, and threadably. 
     Components and/or features described herein can include elements that are described as coupling, fastening, securing, abutting, or other similar terms. Such terms are merely meant to distinguish various elements and/or features within a component or device and are not meant to limit the capability or function of that particular element and/or feature. For example, a feature described as a “coupling feature” can couple, secure, fasten, abut, and/or perform other functions aside from merely coupling. 
     A coupling feature (including a complementary coupling feature) as described herein can allow one or more components and/or portions of an example metal core circuit board to become coupled, directly or indirectly, to another portion of the metal core circuit board and/or a component (e.g., an enclosure wall) of the electrical device. A coupling feature can include, but is not limited to, a snap, a clamp, a portion of a hinge, an aperture, a recessed area, a protrusion, a slot, a spring clip, a tab, a detent, and mating threads. One portion of an example metal core circuit board can be coupled to another component of the metal core circuit board or another component of the electrical device by the direct use of one or more coupling features. 
     In addition, or in the alternative, a portion of an example metal core circuit board can be coupled to another portion of the metal core circuit board or another component of the electrical device using one or more independent devices that interact with one or more coupling features disposed on a component of the electrical device. Examples of such devices can include, but are not limited to, a pin, a hinge, a fastening device (e.g., a bolt, a screw, a rivet), epoxy, a sealing member (e.g., an O-ring, a gasket), glue, adhesive, tape, and a spring. One coupling feature described herein can be the same as, or different than, one or more other coupling features described herein. A complementary coupling feature (also sometimes called a corresponding coupling feature) as described herein can be a coupling feature that mechanically couples, directly or indirectly, with another coupling feature. 
     If a component of a figure is described but not expressly shown or labeled in that figure, the label used for a corresponding component in another figure can be inferred to that component. Conversely, if a component in a figure is labeled but not described, the description for such component can be substantially the same as the description for the corresponding component in another figure. The numbering scheme for the various components in the figures herein is such that each component is a three-digit number, and corresponding components in other figures have the identical last two digits. For any figure shown and described herein, one or more of the components may be omitted, added, repeated, and/or substituted. Accordingly, embodiments shown in a particular figure should not be considered limited to the specific arrangements of components shown in such figure. 
     Further, a statement that a particular embodiment (e.g., as shown in a figure herein) does not have a particular feature or component does not mean, unless expressly stated, that such embodiment is not capable of having such feature or component. For example, for purposes of present or future claims herein, a feature or component that is described as not being included in an example embodiment shown in one or more particular drawings is capable of being included in one or more claims that correspond to such one or more particular drawings herein. 
     Example embodiments of reducing capacitive coupling and shielding of small signal circuits on metal core boards in electrical devices be described more fully hereinafter with reference to the accompanying drawings, in which example embodiments of reducing capacitive coupling on metal core boards in electrical devices are shown. Reducing capacitive coupling on metal core boards in electrical devices may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of reducing capacitive coupling on metal core boards in electrical devices to those or ordinary skill in the art. Like, but not necessarily the same, elements (also sometimes called components) in the various figures are denoted by like reference numerals for consistency. 
     Terms such as “first”, “second”, “top”, “bottom”, “outer”, “inner”, “height”, “width”, thickness”, “lower”, “upper”, “side”, “front”, “distal”, “proximal”, and “within” are used merely to distinguish one component (or part of a component or state of a component) from another. Such terms are not meant to denote a preference or a particular orientation. Such terms are not meant to limit embodiments of reducing capacitive coupling on metal core boards in electrical devices. In the following detailed description of the example embodiments, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description. 
       FIG. 1  shows an exploded view of a light fixture  100  with a circuit board assembly  110  currently used in the art. As discussed above, the light fixture  100  is a type of electrical device. In this case, the light fixture  100  of  FIG. 1  is a street light. In addition to the circuit board assembly  110 , the light fixture  100  of  FIG. 1  includes an upper housing  105  that is coupled to a lower housing  108  and a door  107 . Disposed within a cavity formed by the upper housing  105 , the lower housing  108 , and the door  107  is the circuit board assembly  110 , an optic  101 , a sensor module  162 , a retaining clip  166  for the sensor module  162 , a driver  175  (a form of power supply), a transformer  170 , a clamp  171  for the transformer  170 , a terminal block  172 , a surge module  177 , and a clamp  109  for a pole (not shown) for mounting. A sensor  160  is disposed on an outer (bottom) surface of the lower housing  108 , and another sensor  165  is disposed on an outer (upper) surface of the upper housing  105 . A sensor receptacle  167  can be used to couple the sensor  165  to the upper housing  105 . 
     The circuit board assembly  110  can include one or more of a number of components. Among these components is a circuit board. As discussed above, the circuit board of the circuit board assembly  110  can have any of a number of configurations and be made of any of a number of materials. A circuit board can have any of a number of layers and/or have any of a number of substrates disposed thereon. In addition to the circuit board, the circuit board assembly  110  can include one or more of a number of different components (e.g., integrated circuits, resistors, diodes, transistors, hardware processors, capacitors, sensors, heat sinks, terminal blocks) disposed on the circuit board. 
     In this case, where the electrical device is a light fixture  100 , particularly using LED technology, such luminaires typically consist of an assembly of mechanical and electrical components. The components of the light fixture  100  shown in  FIG. 1  typically are packaged as independent units, each having their own support electronics, connector interfaces, wire harnesses, and mechanical housings. The light fixture  100  is assembled by using multiple coupling features (e.g., fasteners, clamps) to attach these various components to each other. One or more of these components of the light fixture  100  are also coupled to an outer housing (which in this case includes the upper housing  105 , the lower housing  108 , and the door  107 ). 
     To interconnect the various electrical/electronic sub-assemblies, numerous internal wiring harnesses with connectors are required. To minimize the number of connections and associated mechanical housings, integration of many components into a single sub-assembly is desirable. The benefits associated with this approach include a lower number of components, lower cost of assembly, and improved electrical/electronic performance and reliability. The circuit board assembly  110  is a principal way to embody this integration and achieve these benefits. When the circuit board of the circuit board assembly  110  includes metal or is a metal core circuit board, capacitive coupling can result, resulting in electronic noise, poor voltage and current regulation, and an unstable electrical environment for the components mounted on the circuit board. 
       FIG. 2  shows a cross-sectional side view of a metal core circuit board assembly  210  currently used in the art. Referring to  FIGS. 1 and 2 , the metal core circuit board assembly  210  of  FIG. 2  includes a metal base  215 , on top of which is disposed an insulative layer  214  (also called an insulative substrate  214  and a dielectric layer  214 ), on top of which is disposed a conductive layer  212  (also called a conductive substrate  212 ). While the insulative layer  214  and the conductive layer  212  can have thermal properties (e.g., thermally conductive, thermally non-conductive), the insulative layer  214  is designed to electrically isolate the conductive layer  212  from the metal base  215 . Further, the conductive layer  212  can be designed to be electrically conductive. 
     Since the metal base  215  is made, at least in part, of metal, the metal base  215  is designed to be electrically conductive. The metal base  215  can also be thermally conductive. In fact, thermal management is one principal reason for using a metal core board, as some components (e.g., resistors, diodes, integrated circuits, driver circuitry) disposed, directly or indirectly, on a circuit board (e.g., metal base  215 ) can operate at higher temperatures, which can adversely affect the performance and longevity of adjacent components on the circuit board. The metal base  215  acts as a very large and effective heat sink to absorb heat generated by such heat-generating components disposed on the conductive layer  212  and subsequently dissipate that heat away from those heat-generating components. Other reasons for using the metal base  215  can include improved stability (e.g., structural integrity), a reduced footprint, higher packing density, more stable operating parameters, higher operational safety, and a reduced failure rate of electrical components. 
     With these benefits of using metal core boards (a name used herein for circuit board assemblies that include a metal base  215 ), there are also some drawbacks. For example, a common problem that occurs with metal core boards is capacitive coupling (also called parasitic capacitance) generated between switching that occurs on the circuit board assembly, relatively high voltage power that can commonly be used, and the interaction of those factors with the metal base  215 . The result is induced current into the low voltage circuitry (used in the control circuits) of the circuit board assembly that generates noise at the outputs of and within the circuit board assembly. 
     As a more specific explanation, using the metal base  215  for driver circuitry (and other components that generate heat) is desirable because the metal base  215  provides a built-in heat sink and/or acts as a heat spreader. The insulative layer  214  provides electrical insulation and thermal conductivity between the metal base  215  and the power circuits disposed on the conductive layer  212 . This configuration of the insulative layer  214  allows even dissipation in the metal base  215  of heat generated by the driver circuits and/or other heat-generating components disposed on the conductive layer  212 , resulting in higher reliability and functionality compared to using polymer-based (e.g., epoxy laminate FR4) substrates. 
     For metal core circuit board assemblies  210 , it is desirable to have the insulative layer  214  separating the conductive layer  212  (on which the circuitry is disposed) and the metal base  215  to be as thin as possible (e.g., 50 μm-200 μm) to minimize thermal impedance of the insulative layer  214 . However, because of the layered structure of the metal core circuit board assembly  210  shown in  FIG. 2 , the dielectric layer  214  and the metal base  215  electrically form a capacitor. Because the dielectric layer  214  is thin, capacitive coupling between the metal base  215  and the components disposed atop the conductive layer  212  can occur if high speed switching of power is functionally realized. 
     This parasitic capacitance is observed at the output of the driver (or other power supply) in the form of electronic noise generation, which decreases the efficiency of the circuit disposed atop the conductive layer  212  to power the LED&#39;s or other load of the electrical device. In many cases, this noise has inhibited or prevented the integration of the power supply and the associated electrical load using a metal base  215  for the circuit board assembly  210 . By contrast, in polymer-based boards (e.g., FR4) used as a base, there may be capacitive coupling in a localized area only near the traces through which the high power flows. For the metal base  215 , the parasitic capacitance couples the entire metal substrate to the whole power supply (e.g., driver circuit). 
     A typical circuit integrating these functions consists of a high voltage section and a small signal control section, both of which are on the primary input side of the power supply (e.g., driver). The switched high voltage of the power supply induces current spikes in nearby traces due to the parasitic capacitance between the high voltage switched node and any conductive trace near it. The presence of the electrically-conductive metal in the metal base  215  spreads this effect through the entire metal base  215 , not just the nearby traces. The resulting induced current is injected into the small signal control circuit, which masks the small signal (on the order of millivolts) or induces false signals. This results in poor regulation and unstable output. Example embodiments shown and described herein greatly reduce or eliminate parasitic capacitance, thereby also reducing or eliminating the adverse effects caused by such parasitic capacitance. 
       FIGS. 3A and 3B  show a top view and a cross-sectional side view, respectively, of a metal core circuit board assembly  310  in accordance with certain example embodiments. Referring to  FIGS. 1 through 3B , the metal core circuit board assembly  310  of  FIGS. 3A and 3B  include a metal base  315  that has an aperture  331  that traverses the thickness of part (in this case, the approximate lower middle) of the metal base  315 . The aperture  331  is defined by an edge  317  of the metal base  315  and in this case is the shape of a rectangle, although the aperture  331  can have any of a number of other shapes (e.g., circle, triangle, square, hexagon, random). In some cases, there can be multiple apertures  331 . 
     Disposed within the aperture  331  is a circuit assembly  320 . The circuit assembly  320  has a width (when viewed from above) that is less than the width of the aperture  331  formed by the edge  317 . Similarly, the circuit assembly  320  also has a height (when viewed from above) that is less than the height of the aperture  331  formed by the edge  317 . In this way, the circuit assembly  320  can fit entirely within the aperture  331  without making physical contact with any of the edge  317 . The shape of the circuit assembly  320  can be the same as, or different than, the shape of the aperture  331  defined by the edge  317 . In any case, the circuit assembly  320  is positioned in such a way within the aperture  331  as to avoid making any direct physical contact with the metal base  315 . Specifically, there are gaps  330  that are formed between the circuit assembly  320  and the metal base  315 . 
     Disposed between the circuit assembly  320  and the metal base  315  can be one or more isolation tabs  325 , which each make a connection between the circuit assembly  320  and the metal base  315 . These isolation tabs  325  can be formed in any of a number of ways, including but not limited to with tooling when the outline of the metal base  315  and the aperture  331  are punched to their shape, punched in a secondary operation, or separately machined. An isolation tab  325  can also be an electrical conductor, with one end coupled to a component disposed on or part of the metal base  315 , and with the other end coupled to the circuit assembly  320  (or component thereof). 
     The isolation tabs  325  can be permanent or temporary (e.g., removable). In practice, the circuitry of the metal base  315  and the circuit assembly  320  can be configured relative to each other in any of a number of ways. For example, the circuitry of the metal base  315  and the circuit assembly  320  can be formed using standard PCB methods, where thin copper (or similar electrically-conductive metal) foil is laminated to the base substrate (e.g., the metal base  315 , the circuit board of the circuit assembly  320 ) and then chemically etched (subtractive process) to form the circuit traces. 
     Alternatively, an additive process can be used by printing layers (e.g., screen, ink jet, aerojet, flexographic, printing) of dielectric and electrically-conductive materials. Typically, the printing step is followed by a film drying step (to remove inorganic solvents and vehicles), and then a firing step (at high temperature) to sinter the inorganic constituents of the ink together, thereby forming a continuous film while creating a metallurgical bond with the substrate. Any of these various methods of applying one or more layers directly or indirectly atop a metal base (e.g., metal base  315 ) can be used in any of the example embodiments described herein. Once the metal base  315  and/or the circuit board of the circuit assembly  320  is fabricated with the circuit traces, components can then be placed (electrically attached using solder, electrically-conductive adhesive, or some other method) on the metal base  315  and/or the circuit board. At this point, the isolation tabs  325  can be removed. 
     The circuit board assembly  310  can also include an optional support  314  mounted on a bottom surface of the metal base  315 . The support  314  is designed to help anchor the circuit assembly  320  relative to the metal base  315  within the aperture  331 . The support  314  can have any of a number of forms and configurations. For example, in this case, the support  314  is a solid, electrically non-conductive layer that covers the aperture  331 . As another example, the support  314  can be an electrically non-conductive mesh that covers the aperture  331 . 
     As still another example, the support  314  can be an electrically insulative tape or film that can be adhesively bonded, molded, printed (using dielectric inks), or otherwise disposed on the circuit assembly  320  and at least portions of the metal base  315 . In any case, if the support  314  exists, it is coupled to both the circuit assembly  320  (in this case, on the back side) and at least the portions of the metal base  315  (also on the back side in this case) adjacent to the aperture  331 . In addition to being electrically non-conductive, the support  314  can have any type of thermal property (e.g., thermally conductive, thermally non-conductive). 
     The circuit assembly  320  can include a control circuit that is disposed on a circuit board (e.g., another metal base  315 , a polymer-based circuit board). Similarly, a power supply can be disposed on the metal base  315 . The isolation tabs  325  can be coupled to the circuit board of the circuit assembly  320  or directly to one or more components disposed on the circuit board of the circuit assembly  320 . As discussed above, capacitive coupling caused by the power supply can have an adverse effect on the control circuit of the circuit assembly  320  when these two circuits are mounted on the same metal base  315 . By using the system and method for physically and, aside from the isolation tabs  325 , electrically isolating the circuit assembly  320  from the rest of the metal base  315 , the adverse effects associated with capacitive coupling can be greatly reduced or eliminated. 
       FIGS. 4A and 4B  show a top view and a cross-sectional side view, respectively, of another metal core circuit board assembly  410  in accordance with certain example embodiments. Referring to  FIGS. 1 through 4B , the metal core circuit board assembly  410  of  FIGS. 4A and 4B  shows an example where there is no aperture (such as aperture  331  of  FIG. 3 ) in the metal base  415  for receiving the circuit assembly  420 . Instead, isolation and shielding of the circuit assembly  420  is achieved by using a number of dielectric layers and a printed electrically-conductive ground plane  461 . 
     The metal core circuit board assembly  410  of  FIGS. 4A and 4B  includes the metal base  415  (e.g., aluminum), in this case having no aperture (e.g., aperture  331 ) that traverses the thickness of the metal base  415 . As a result, there is no support (e.g., support  314 ) that is coupled to the bottom surface of the metal base  415 . In addition, there are multiple layers disposed atop the metal base  415  that were not disposed atop the metal base  315  of  FIGS. 3A and 3B . Specifically, dielectric layer  451  (also called an isolation plane  451 ) is disposed atop the entire metal base  415 . Also, an electrically-conductive layer  465  is disposed atop the entire dielectric layer  451 . 
     In certain alternative embodiments, an optional secondary isolation plane (similar to dielectric layer  451 ) can be added on top of the dielectric layer  451  to increase the dielectric thickness and minimize or limit capacitive coupling. As an example, this additional isolation plane could be printed with a low temperature, polymer-based ink, and the same (or the use of different methods) could be done for the successive layers. The circuit assembly  420  is disposed atop a portion of the electrically-conductive layer  465 , and the remainder of the electrically-conductive layer  465  has no other layers disposed atop it. Instead, the various components (e.g., resistors, diodes, integrated circuits, capacitors, transistors) of the power supply  449  (also sometimes called a power circuit  449 ) are disposed atop the electrically-conductive layer  465  in areas not occupied by the circuit assembly  420 . 
     As discussed above, the circuit assembly  420  is layered atop an isolated portion of the electrically-conductive layer  465 . Specifically, disposed atop a portion of the electrically-conductive layer  465  is another dielectric layer  454 . Disposed (e.g., printed) atop the second dielectric layer  454  on the portion of the electrically-conductive layer  465  that hosts the circuit assembly  420  is the electrically-conductive ground plane  461 , atop of which is disposed (e.g., printed) another dielectric layer  463  (also called an isolation plane  463 ). Disposed (e.g., printed) within one or more portions of the dielectric layer  463  are one or more vias  466 , which provide electrical connectivity between the control circuit  440  and the power supply  449 . 
     In some cases, a via  466  is electrically conductive. In other cases, a via  466  (also called an opening  466 ) is electrically non-conductive but designed into the dielectric layer  463  so that an electrical conductor can be deposited into the via  466 , either during a separate conductor print or while printing the electrically-conductive traces of the control circuit  440 . In any case, the vias  466  provide a conductive conduit between the control circuit  440  and the electrically-conductive ground plane  461  such that the electrically-conductive ground plane  461  can be polarized (usually with a negative electrical bias), causing it to act as a ground shield and eliminate (or at least greatly reduce) any capacitive coupling to the power supply  449 . 
     Disposed atop parts of the dielectric layer  463  and/or the vias  466  are multiple electrically-conductive traces  455 . The discrete components of the control circuit  440  of the circuit assembly  420  have electrically-conductive leads that are disposed on and make contact with the traces  455 , using the traces  455  as electrical conductors to carry low voltage and/or control signals. Any of the printing techniques and/or materials described herein or known in the art can apply to any of the layers of the circuit board assembly  410  of  FIGS. 4A and 4B . 
       FIG. 5  shows a cross-sectional side view of yet another metal core circuit board assembly  510  in accordance with certain example embodiments. Referring to  FIGS. 1 through 5 , the metal core circuit board assembly  510  of  FIG. 5  shows an example where a shielding plane is built using an additive process. The metal core circuit board assembly  510  (including components thereof) of  FIG. 5  is similar to the metal core circuit board assembly  310  (including corresponding components thereof) of  FIGS. 3A and 3B , with added features discussed below. 
     For example, the metal core circuit board assembly  510  of  FIG. 5  includes a metal base  515  that has an aperture  531  that traverses the thickness of part (in this case, the approximate lower middle) of the metal base  515 . The aperture  531  is defined by an edge  517  of the metal base  515  and in this case is the shape of a rectangle. Disposed within the aperture  531 , and without physically contacting the metal base  515 , is a circuit assembly  520  that includes a circuit board  521  having a rectangular shape with a width that is less than the width of the aperture  531  formed by the edge  517  and a height that is less than the height of the aperture  531  formed by the edge  517 . There is a continuous gap  530  or multiple gaps  530  that are formed between the circuit assembly  520  and the metal base  515 . The circuit board assembly  510  in this case also includes a support  514  (similar to support  314  of  FIGS. 3A and 3B  above) that is coupled to the bottom surfaces of the metal base  515  and the circuit board  521  of the circuit assembly  520 . 
     In addition, there are multiple layers disposed atop the metal base  515  and the circuit board  521  of the circuit assembly  520 . Specifically, a dielectric layer  551  is disposed atop both the metal base  515  and the circuit board  521  of the circuit assembly  520 , but not in any of the gaps  530  therebetween. On top of the dielectric layer  551  on the circuit board  521  of the circuit assembly  520  is disposed a localized, electrically-conductive electronic shield  553 . Disposed atop the electrically-conductive electronic shield  553  on the circuit assembly  520  is another dielectric layer  554 . Finally, atop the dielectric layer  554  on the circuit assembly  520  are multiple electrically-conductive traces  555 . 
     Disposed atop these traces  555  are the various discrete components of the control circuit  540  of the circuit assembly  520 , where the traces  555  serve as electrical conductors to carry low voltage and/or control signals to and from those components of the control circuit  540 . These layers of the circuit assembly  520  disposed on the circuit board  521  to not extend beyond the edges of the circuit board  521 , so that the gap  530  is maintained for all of the layers. 
     On top of the portion of the dielectric layer  551  that is not disposed on the circuit board  521  of the circuit assembly  520  (e.g., directly atop the metal base  515 ) are disposed multiple electrically-conductive traces  552 . Disposed atop these traces  552  are the various discrete components that make up the power supply  549 , using the traces  552  as electrical conductors to carry voltage and/or control signals to and from those components of the power supply  549 . Example thicknesses for these layers are 4 μm-60 μm for the dielectric layers  551  and/or  554 , and 10 μm-15 μm for the electrically-conductive conductive traces  552  and/or  555 . The thickness of any of these layers can be adjusted to allow for improved electrical performance (e.g., higher current carrying capability) and/or some other desired effect. 
       FIGS. 6A and 6B  show a top view and a cross-sectional side view, respectively, of still another metal core circuit board assembly  610  in accordance with certain example embodiments. Referring to  FIGS. 1 through 6B , the metal core circuit board assembly  610  of  FIGS. 6A and 6B  shows an example where a high-current trace  645  is integrated with the circuit assembly  620 . The metal core circuit board assembly  610  (including components thereof) of  FIGS. 6A and 6B  is similar to the metal core circuit board assembly  510  (including corresponding components thereof) of  FIG. 5 , with added/different features as discussed below. 
     For example, the metal core circuit board assembly  610  of  FIGS. 6A and 6B  includes a metal base  615  that has an aperture  631  that traverses the thickness of part (in this case, the approximate lower middle) of the metal base  615 . The aperture  631  is defined by an edge  617  of the metal base  615  and in this case is the shape of a rectangle. Disposed within the aperture  631 , and without physically contacting the metal base  615 , is a circuit assembly  620  that includes a circuit board  621  having a rectangular shape with a width that is less than the width of the aperture  631  formed by the edge  617  and a height that is less than the height of the aperture  631  formed by the edge  617 . There can be one continuous gap  630  or multiple gaps  630  that are formed between the circuit assembly  620  and the metal base  615 . The metal core circuit board assembly  610  in this case also includes a support  614  that is coupled to the bottom surfaces of the metal base  615  and the circuit board  621  of the circuit assembly  620 . 
     In addition, there are multiple layers disposed atop the metal base  615  and the circuit board  621  of the circuit assembly  620 . Specifically, dielectric layer  651  is disposed atop both the metal base  615  and the circuit board  621  of the circuit assembly  620 , but not in any of the gaps  630  therebetween. Also, there are gaps  699  in the dielectric layer  651  atop the circuit board  621  of the circuit assembly  620 . In other words, the dielectric layer  651  is not disposed over the entire top surface of the circuit board  621  of the circuit assembly  620 . These gaps  699  physically separate the high-current trace  645  from the shield  653 . Specifically, aside from where the high-current trace  645  is disposed atop the dielectric layer  651  on the circuit board  621  of the circuit assembly  620 , a localized, electrically-conductive electronic shield  653  is disposed atop the dielectric layer  651  on the circuit board  621 . The electrically-conductive electronic shield  653  is separated from the high-current trace  645  by the gaps  699 . 
     Disposed atop the electrically-conductive electronic shield  653  on the portion of the circuit assembly  620  that includes the control circuit  640  is another dielectric layer  654 . Finally, disposed atop the second dielectric layer  654  on the portion of the circuit assembly  620  that includes the control circuit  640  are multiple electrically-conductive traces  655 . The discrete components of the control circuit  640  of the circuit assembly  620  have electrically-conductive leads that are disposed on and make contact with the traces  655 , using the traces  655  as electrical conductors to carry low voltage and/or control signals. 
     These layers disposed on the circuit board  621  of the circuit assembly  620  do not extend beyond the edges of the circuit board  621 , so that the gap  630  is maintained for all of the layers. Similarly, the gaps  699  that are formed at various points above the circuit board  621  of the circuit assembly  620  can be maintained vertically through all of the various layers. In this example, there are no additional layers disposed atop the electrically-conductive electronic shield  653  at some portions of the circuit assembly  620 . Also, there are no additional layers disposed atop the electrically-conductive electronic shield  653  on the metal base  615  in this example. 
     The power supply  649  is disposed on the electrically-conductive electronic shield  653  atop the metal base  615  and is connected to the circuit assembly  620  by a power FET  648 . In this example, the power FET  648  has one pin connected to the high-current trace  645  disposed (e.g., printed) within the electrically-conductive electronic shield  653  and another pin connected to a lead that connects to the control circuit  640 . The distal end of the high-current trace  645  in this example is connected to a sense resistor  646 , which in turn is connected to an electrically-conductive electronic shield  647 , which can be the same as or different than the electrically-conductive electronic shield  653 . 
     In some cases, the same material family for the printed electronic inks is used for all of the aforementioned layers. Certain types of printed inks are capable of carrying high current but must be processed at high temperatures. When there are multiple layered structures with these inks, the repeated high temperature processing may cause conductor ions to diffuse into the dielectric, resulting in a dielectric with poor electrical properties. In such a case, the high-temperature ink can be used to form the electrically-conductive electronic shield  653  (and any conductors requiring high current carrying capability) of the isolated circuit assembly  620 . 
     Subsequently, the second dielectric layer  654  and conductor could be deposited using lower cure temperature materials (e.g., polymer-based electronic inks). Such materials sinter at much lower temperatures, which minimizes any diffusion. As a result, this deposition approach can be well suited for the configuration of the metal core circuit board assembly  610  shown in  FIGS. 6A and 6B . One potential draw-back is that the polymer-based conductors have much higher electrical resistivity than their high temperature counterparts, and so the polymer-based conductors are best suited for low current-carrying circuits. 
       FIGS. 7A and 7B  show a top view and a cross-sectional side view, respectively, of yet another metal core circuit board assembly  710  in accordance with certain example embodiments. Referring to  FIGS. 1 through 7B , the metal core circuit board assembly  710  of  FIGS. 7A and 7B  shows an example where there is no aperture in the metal base  715  for receiving the circuit assembly  720 . Instead, isolation and shielding of the circuit assembly  720  is achieved by using a dielectric layer and a printed electrically-conductive electronic shield  753 . The metal core circuit board assembly  710  (including components thereof) of  FIGS. 7A and 7B  is similar to the metal core circuit board assemblies (including corresponding components thereof) discussed above, with added/different features as discussed below. 
     The metal core circuit board assembly  710  of  FIGS. 7A and 7B  includes the metal base  715 , in this case having no aperture (e.g., aperture  631 ) that traverses the thickness of the metal base  715 . As a result, there is no support (e.g., support  614 ) that is coupled to the bottom surface of the metal base  715 . In addition, there are multiple layers disposed atop the metal base  715 . Specifically, dielectric layer  751  is disposed atop the entire metal base  715 . Also, an electrically-conductive electronic shield  753  is disposed atop the dielectric layer  751 , but there are gaps  799  in the electrically-conductive electronic shield to physically separate the circuit assembly  720  from the rest of the metal base  715 . In this example, there are no other layers disposed atop the electrically-conductive electronic shield  753  outside of the gaps  799  on the rest of the metal base  715 . 
     Disposed atop the electrically-conductive electronic shield  753  on the portion of the metal base  715  that hosts the circuit assembly  720  is another dielectric layer  754 . Finally, disposed atop the second dielectric layer  754  on the portion of the metal base  715  that hosts the circuit assembly  720  are multiple electrically-conductive traces  755 . The discrete components of the control circuit  740  of the circuit assembly  720  have electrically-conductive leads that are disposed on and make contact with the traces  755 , using the traces  755  as electrical conductors to carry low voltage and/or control signals. 
     In some cases, the first dielectric layer  751  is printed in the same step as the dielectric that is printed to form the power supply of the circuit assembly  720 . The material of the dielectric layer  751  electrically insulates the subsequent layers from the metal base  715 . Next, the electrically-conductive electronic shield  753  can be printed on top of the dielectric layer  751 , including the traces (e.g., traces  755 ) of the power supply of the circuit assembly  720 . This electrically-conductive electronic shield  753  can be electrically connected to the proper shield polarity defined in the power supply (like the negative or ground trace) during the deposition of the electrically-conductive electronic shield  753 . Alternatively, the electrically-conductive electronic shield  753  can be connected using a discrete jumper later in the process. 
     The second dielectric layer  754  can be printed over the electrically-conductive electronic shield  753  to isolate the control circuit  740 . The control circuit  740  can then be printed on top of the dielectric layer  754 , and one or more jumpers  725 ,  726  can be used to connect the control circuit  740  to the power supply  749 , the components for which are disposed on the other side of the gap  799  atop the electrically-conductive electronic shield  753 . In some cases, in addition to or as an alternative to jumpers  725 ,  726 , one or more vias (such as those shown in  FIG. 4  above) can be incorporated into one or more of the multi-layered structures to provide connectivity between the control circuit  740  and the power supply  749 . 
     As discussed above, many different materials and/or deposition techniques can be used for each layer. For example, ceramic-based materials can be used for the power supply  749 , the dielectric layer  754 , and the electrically-conductive electronic shield  753 , while polymer-based materials can be used for the control circuit  740 . One rationale for this arrangement is that the higher temperatures required for processing of the ceramic-based materials result in migration of those conductors into the dielectric layer  754 , resulting in sub-optimal dielectric properties. The polymer-based materials are processed at a much lower temperature, and so they will not migrate. The main issue with the polymer-based materials is that the conductor resistivity is much higher than for the ceramic-based materials, and so the power supply  749  may be difficult to fabricate. 
       FIGS. 8A and 8B  show a top view and a cross-sectional side view, respectively, of still another metal core circuit board assembly  810  in accordance with certain example embodiments. Referring to  FIGS. 1 through 8B , the metal core circuit board assembly  810  of  FIGS. 8A and 8B  shows an example where there is no aperture in the metal base  815  for receiving the circuit assembly  820 . Instead, isolation and shielding of the circuit assembly  820  is achieved by using a number of dielectric layers. The metal core circuit board assembly  810  (including components thereof) of  FIGS. 8A and 8B  is similar to the metal core circuit board assemblies (including corresponding components thereof) discussed above, with added/different features as discussed below. 
     The metal core circuit board assembly  810  of  FIGS. 8A and 8B  includes the metal base  815  (e.g., made of aluminum). In this example, there is no aperture (e.g., aperture  331 ) that traverses the thickness of the metal base  815 . As a result, there is no support (e.g., support  314 ) that is coupled to the bottom surface of the metal base  815 . In addition, there are multiple layers disposed atop the metal base  815 . Specifically, dielectric layer  851  (also called an isolation plane  851 ) is disposed atop the entire metal base  815 . Also, an electrically-conductive layer  865  is disposed atop the entire dielectric layer  851  (or at least the majority of the dielectric layer  851 ). 
     In this case, the electrically-conductive layer  865  is disposed atop all but a small area in the middle of the dielectric layer  851 . In other words, there is an aperture  831  that traverses part of the electrically-conductive layer  865 , inside of which the dielectric layer  854  that supports the circuit assembly  820  is disposed. As shown in  FIGS. 8A and 8B , within the aperture  831  in this case is disposed (e.g., printed, adhesively bonded) the optional dielectric layer  854 , which is also disposed atop the dielectric layer  851 . The various components of the power supply  849  are disposed atop the electrically-conductive layer  865 , separate from the circuit assembly  820 . 
     As discussed above, the circuit assembly  820  is layered atop the dielectric layer  854 , which is disposed within the aperture  831  in the dielectric layer  851 . Disposed atop the dielectric layer  854  is a circuit board  821  of the circuit assembly  820 . The circuit board  821  can be electrically conductive or electrically non-conductive. If the circuit board  821  is a metal core type of board, the optional dielectric layer  854  can be applied before bonding to increase the separation between the metal base  815  and the circuit board  821 , which will minimize or eliminate the capacitive coupling. If the circuit board  821  is made of a polymer-based material, the thickness of the circuit board  821  should be sufficiently large so as to minimize or eliminate the capacitive coupling. For example, the thickness of the circuit board  821  can be ≥0.002″, but it should be noted that this determination is dependent on the material used in the circuit board  821 . 
     Atop the circuit board  821  in this example is disposed (e.g., printed) another dielectric layer  863  (also called an isolation plane  863 ). Finally, disposed atop the dielectric layer  863  are multiple electrically-conductive traces  855 . The discrete components of the control circuit  840  of the circuit assembly  820  have electrically-conductive leads that are disposed on and make contact with the traces  855 , using the traces  855  as electrical conductors to carry low voltage and/or control signals. One or more jumpers  825  are used to connect the control circuit  840  to the power supply  849 , which is disposed atop the electrically-conductive layer  865 . The combination of the traces  855 , the dielectric layer  863 , and the circuit board  821  make up the control circuit substrate  868 , which can be electrically conductive or electrically non-conductive. Any of the printing techniques and/or materials described herein or known in the art can apply to any of the layers of the metal core circuit board assembly  810  of  FIGS. 8A and 8B . 
       FIG. 9  shows a top view of a metal core circuit board assembly  910  that is a physical representation of the metal core circuit board assembly  810  of  FIG. 8 . The components of the metal core circuit board assembly  910  of  FIG. 9  can be substantially the same as the corresponding components of the metal core circuit board assemblies discussed above. Referring to  FIGS. 1 through 9 , the metal core circuit board assembly  910  of  FIG. 9  includes a metal base  915  that in this case has no aperture (e.g., aperture  331 ) that traverses the thickness of part of the metal base  915 . Disposed on top of part of the metal base  915  is the circuit assembly  920 . The circuit assembly  920  includes a circuit board  921  having a rectangular shape. The circuit assembly  920  has disposed thereon the control circuit  940 , which is made of multiple discrete components (e.g., resistors, capacitors, diodes). 
     Disposed between the circuit assembly  920  and the rest (e.g., the power supply  949 ) of the metal core circuit board assembly  910  is a dielectric isolation plane  951 . In this way, there is no direct physical contact (aside from jumpers, such as jumpers  925 ,  926 ) between the circuit assembly  920  and the rest (e.g., the power supply  949 ) of the metal core circuit board assembly  910 . The power supply  949  in this case is made up of a number of discrete components (e.g., diodes, resistors, transistors, capacitors) that are disposed on the metal base  915 . 
     Jumpers  925  (in this case electrical conductors) bridge the gap  930  formed between the circuit board  921  of the circuit assembly  920  and the power supply  949  disposed on the metal base  915 , thereby providing electrical connectivity between the two. The circuit board assembly  910  in this case also includes a support  914  in the form of electrically non-conductive tape that is adhered to the top (and also possibly the bottom) surfaces of the metal base  915  and the circuit board  921  of the circuit assembly  920 . 
     In the configuration shown in  FIG. 9 , the circuit board  921  of the circuit assembly  920  includes a metal substrate, and so the circuit board  921  becomes a functional, electronic shielding element of the circuit assembly  920  by maintaining a different polarity than the portion of the metal base  915  on which the power supply  949  is disposed. The control circuit  940  of the circuit assembly  920  needs to be shielded from the induced current that is capacitively coupled between the metal base  915  and the high-switched voltage of the power supply  949 . The shield in this case is connected to the DC negative of the primary circuit power supply  949 , which establishes a well-defined zero-volt reference (DC Ground) and is electrically isolated from the metal base  915 . Any induced current in the DC ground shield will be sunk into the DC ground, and any resulting voltage will be clamped to zero volts. 
     Example embodiments show, describe, and contemplate various ways to isolate a power supply and/or control circuit from a circuit assembly of a metal core circuit board assembly for an electrical device. Example embodiments greatly reduce or eliminate capacitive coupling that occurs in the current art. By greatly reducing or eliminating capacitive coupling in the power and control circuitry used on metal-based circuit boards, the control signals can be unaltered, and the occurrence of false control signals can be eliminated. 
     Accordingly, many modifications and other embodiments set forth herein will come to mind to one skilled in the art to which example embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that example embodiments are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this application. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.