Patent Publication Number: US-2005133252-A1

Title: Printed circuit board noise suppression device and method of manufacturing

Description:
FIELD OF THE INVENTION  
      This invention relates generally to electrical and electromagnetic noise suppression and, in particular, to suppressing noise on printed circuit boards (PCBs).  
     BACKGROUND  
      PCBs used in noise-sensitive applications such as telecommunications are often connected to, or incorporate, electronic devices that generate, transmit, or both generate and transmit electrical signals that contain undesirable radio frequencies (RF). Such signals are considered to be “noisy”, and the undesirable frequencies are commonly referred to as conducted noise or spurious emissions. Radiated noise is a consequence of conducted noise and is generated by the flow of these undesired electrical signals through electronic components and/or interconnecting wires or printed circuit board traces. Both conducted noise and radiated noise can adversely affect the operation of electronic devices or particular electronic components. This is commonly referred as electromagnetic interference (EMI).  
      One known technique for suppressing noise generated or transmitted on a PCB is to provide a metal enclosure, connected to a ground plane on an external device to which the PCB is connected, to substantially enclose the entire PCB. Such a metal enclosure acts as a shield, reducing the amount of radiated noise that propagates away from the PCB. Signal filters can be used in conjunction with such a shielded PCB to further reduce the noise generated, transmitted or radiated by the PCB by reducing conducted noise.  
      However, in many applications, external physical access to PCB components must be provided. Although openings in conventional shield enclosures allow access to such components as optical fiber, buttons, shafts, actuators, and circuit breakers, for example, these same openings tend to reduce shielding effectiveness. In order to prevent significant degradation of shield performance, such openings/apertures should be smaller than a maximum size, which is determined by a wavelength of radiated noise to be suppressed, and is generally on the order of λ/10-λ/1000, depending upon the amplitude of each noise spectral component, the number of apertures, the shape of the apertures and the desired amount of suppression. As such, conventional shield enclosures may not satisfy both noise suppression and external access requirements where relatively high-frequency noise is to be suppressed. This is particularly challenging when the dimensions of apertures likely to incur significant degradation are at the limit of common manufacturing capabilities or impart severe design constraints at the outset. This is often the case when attempting to suppress noise at frequencies at or over 1 GHz, for example.  
     SUMMARY OF THE INVENTION  
      A noise suppression device for a PCB according to one aspect of the invention includes an electrically conductive sub-enclosure configured to at least partially enclose a portion of the PCB, a divider configured to extend electrically into a surface of the PCB along an edge of the at least partially enclosed portion, and electrical signal filters mounted on the sub-enclosure. The noise suppressing device thus suppresses both conducted noise and radiated noise but encloses only a section of a PCB.  
      In some embodiments, the divider is integrated with the sub-enclosure, or with one section of the sub-enclosure. The enclosed section of the PCB may be a clean side or a noisy side of the noise suppression device.  
      The divider may physically extend onto the circuit board, as a surface mounted component in electrical contact with conductive material in a plurality of through holes in the PCB, for example, or into the PCB. In one embodiment, the divider includes pins, with pin spacing being less than a maximum spacing based on a wavelength of radiated noise to be suppressed. The pins may be through hole pins or compliant pins.  
      In one embodiment, the sub-enclosure includes multiple sub-enclosure sections. Sub-enclosure sections may be adapted for mounting on surfaces of the PCB, including conductive surface plating or edge plating on the PCB, or on external devices in conjunction with which the PCB operates.  
      The invention also provides, in a further aspect, a conductive plate for use with a conductive sub-enclosure section for at least partially enclosing a section of a PCB and for connection to a suitable RF reference potential to suppress radiated noise. The conductive plate includes a divider configured to extend through the PCB to divide the partially enclosed section from a remainder of the PCB, and has openings for holding signal filters for suppressing conducted noise in electrical signals.  
      A device for suppressing noise on a PCB is also provided according to another aspect of the invention. The device includes means for at least partially enclosing a portion of the PCB, means for dividing the PCB into a noisy region and a clean region, the means for dividing extending electrically into a surface of the PCB, and means for filtering electrical signals to be transmitted from the noisy region to the clean region.  
      In accordance with a further aspect of the invention, a PCB includes an RF reference plane conductor and a noise suppression device in electrical contact with the RF reference plane conductor. The noise suppression device has a conductive sub-enclosure at least partially enclosing a portion of the PCB and forming a conductive barrier extending through the PCB, and filters for filtering electrical signals.  
      Yet another aspect of the invention provides a method of manufacturing a PCB. Drop-in components on a PCB substrate. A conductive divider is also placed on the PCB substrate to divide the PCB into separate areas. The conductive divider is configured for use with a conductive sub-enclosure to at least partially enclose one of the areas. The drop-in components and the conductive divider are then soldered onto the PCB substrate.  
      Other aspects and features of the present invention will become apparent, to those ordinarily skilled in the art, upon review of the following description of specific embodiments of the invention.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will now be described in greater detail with reference to the accompanying diagrams, in which:  
       FIG. 1  is an isometric view of a section of a sub-enclosure according to an embodiment of the invention;  
       FIG. 2  is a side elevation of the sub-enclosure section of  FIG. 1 ;  
       FIG. 3  is an isometric view of a section of a sub-enclosure according to another embodiment of the invention;  
       FIG. 4  is a side elevation of the sub-enclosure section of  FIG. 3 ;  
       FIG. 5  is a cross-sectional view along line  5 - 5  of  FIG. 4 ;  
       FIG. 6  is a top view of a base plate for use with the sub-enclosure section of  FIGS. 3 and 4 ;  
       FIG. 7  is an exploded view of a noise suppression device according to a further embodiment of the invention;  
       FIG. 8  is an expanded view of the section  8 - 8  of  FIG. 7 ;  
       FIGS. 9 and 10  are isometric views of a PCB having a noise suppression device in accordance with an embodiment of the invention; and  
       FIG. 11  is an isometric view of a backplane element and a PCB carrying a noise suppression device according to an embodiment of the invention.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      As described briefly above, known enclosure-type noise shields that substantially enclose an entire PCB have inherent drawbacks, particularly where external access to PCB components is required. Noise suppression devices in accordance with aspects of the invention significantly mitigate the need for any openings in the shield and substantially reduce any noise from migrating through interconnections which traverse the shield boundary. This facilitates the necessary shielding and filtering while enclosing only a portion of a PCB, thereby providing physical access to all PCB components that are outside the noise suppression device. A noise suppression device preferably divides or partitions a PCB into “noisy” and “clean” sides or areas, such that physical access to components on a clean side of a noise suppression device, or alternatively on a noisy side of a noise suppression device, is not restricted by the noise suppression device.  
       FIGS. 1 and 2  are, respectively, an isometric view and a side elevation of a section of a sub-enclosure according to an embodiment of the invention. The shape and structure of the sub-enclosure section  10  is intended solely for illustrative purposes, and the invention is in no way restricted thereto. It will be apparent to those skilled in the art that a sub-enclosure or any sections thereof may be sized and shaped in accordance with the physical requirements and restrictions of a particular device or environment in which the sub-enclosure will be implemented.  
      The sub-enclosure section  10  comprises a conductive material, preferably a metal such as aluminum or copper. A metal sub-enclosure section  10  may be fabricated by stamping from a metal sheet and subsequent forming of a stamped blank, casting, or tooling, for example. In other embodiments, conductive paints, coatings, or additives may be used in combination with non-conductive materials in the fabrication of the sub-enclosure section  10 . A plastic sub-enclosure section  10  may be formed using a mould, for instance, and then painted with a conductive paint. Other suitable materials and fabrication methods will be apparent to those skilled in the art.  
      With reference to both  FIGS. 1 and 2 , the sub-enclosure section  10  comprises a plurality of walls  12 ,  14 ,  16 ,  18 ,  20 ,  30 , and  32  for partially enclosing a portion of a PCB, and flanges or extensions  22  and  24 , having bores  26  and  28  therein. As shown most clearly in  FIG. 2 , the walls are oriented in a plurality of planes and define an interior space or cavity  34  within which a portion of a PCB may be partially enclosed, as described in further detail below.  
      Depending upon the method of fabrication, the sub-enclosure section  10  is not necessarily a continuous component. Although such fabrication techniques as casting and moulding can produce a continuous sub-enclosure section  10 , production of a continuous structure tends to be more difficult using other techniques. In a sub-enclosure section  10  formed from a stamped metal blank for instance, not all walls would be continuous with adjacent walls. Gaps between walls in a non-continuous structure that are smaller than a maximum allowable opening size, which is dependent upon the wavelength of radiated noise to be suppressed, should not significantly degrade the shielding effectiveness of the sub-enclosure section  10 . Any larger gaps are preferably closed with conductive material, such as a patch of the material from which the sub-enclosure section  10  was fabricated or conductive solder or welding, for example. One or both of adjacent but discontinuous walls may also or instead incorporate mating structures such as flanges to provide for electrical contact between the adjacent walls and thereby close gaps in the structure of the sub-enclosure section  10 .  
      As shown, the relative orientations of the walls of the sub-enclosure section  10  need not be consistent. In the sub-enclosure section  10 , the walls  16  and  20  are substantially parallel to each other and substantially perpendicular to the wall  12 . The walls  30  and  32  are similarly parallel to each other and substantially perpendicular to the wall  12 . However, the walls  14  and  18  have different orientations relative to each other and to the wall  12 . The walls  14  and  18  are not parallel to each other and are not perpendicular to the wall  12 . Those skilled in the art will appreciate that the edges between adjacent walls of the sub-enclosure section  10  are substantially connected using any of a number of common techniques (soldering, welding, for example) to minimise gaps.  
      The sub-enclosure section  10  also includes a plurality of extensions or flanges  22  and  24  for abutting other sub-enclosure sections or portions of a PCB or a device in conjunction with which a PCB operates. The flanges  22 A and  22 E include bores  26 A and  26 B and possibly additional bores, not shown, for receiving fasteners for mounting the sub-enclosure section  10  to a PCB or other structure. The bores  28 A,  28 B,  28 C,  28 D and  28 E in the flanges  22 B,  22 C, and  22 D are similarly configured to receive fasteners for fastening the sub-enclosure section  10  to another sub-enclosure section. In one embodiment of the invention described in further detail below, the flanges  24 A,  24 B, and  24 C contact a portion of an external device with which a PCB operates.  
      In one embodiment of the invention, a plurality of sub-enclosure sections are connected to form a sub-enclosure for at least partially enclosing a portion of a PCB. For example, the sub-enclosure section  10  is a first section of such a sub-enclosure. Other sections of the sub-enclosure are at least electrically, and preferably also physically, connected to the sub-enclosure section  10 .  
      For example, where radiated noise is to be suppressed, a second sub-enclosure section abuts the flanges  28 A,  28 B, and  28 C to close the cavity  34  along one side of the sub-enclosure section  10 , and electrically contacts the sub-enclosure section  10  through a low-impedance connection, either directly or through an intermediate conductive material such as a conductive gasket. A conductive gasket between sections of a sub-enclosure may provide for more continuous and thus more effective and reliable electrical contact along entire surfaces of the sub-enclosure sections. A compressible gasket will typically conform more efficiently than the slight irregularities along the surface of abutting flanges and thereby mitigate residual gaps.  
      Further sub-enclosure sections may also be provided to substantially enclose components or portions of a PCB or device. These further sub-enclosure sections are either distinct sub-enclosure sections or provided as elements of a shielded PCB or device. In some embodiments, conductors on a shielded PCB, or a plurality of PCBS, and an external device form such further sub-enclosure sections for substantially enclosing a portion of a PCB.  
      As described above, a sub-enclosure at least partially encloses only a portion of a PCB or device, and thus partitions the PCB or device into a plurality of areas or regions.  
      According to an aspect of the invention, a noise suppression device includes a divider for dividing a PCB into a plurality of structurally connected but distinct portions or areas. The separate portions form elements of the clean side and the noisy side, either of which may be the portion that is at least partially enclosed by a sub-enclosure. The divider may be carried by, integral with, or a separate element configured for attachment to one or more sub-enclosure sections. An illustrative example of a divider is described in further detail below, and comprises a plurality of pins that extend into holes in the PCB. The pins and holes are preferably sized and spaced such that gaps between the pins are smaller than a maximum allowable opening size associated with radiated noise frequencies to be suppressed.  
      Those skilled in the art will appreciate that “noisy” and “clean” are not intended as absolute terms. Electronic components and electrical signals are rarely, if ever, totally clean. Electronic components that have RF current flowing through or over them may generate some noise, and electrical signals often include noise in the form of unwanted or unnecessary spectral components/frequencies. Similarly, practical noise shields and signal filters are not perfect, such that a clean side of a shield is not free from noise. In general, the clean side of a noise suppression device according to an embodiment of the invention has a lower level of noise than the noisy side. Indeed, those skilled in the art will appreciate the degree of isolation will be characterized by an amount, commonly expressed in decibels (dB), of shielding and filtering effectiveness.  
      A conductive sub-enclosure as described above is suitable for implementations in which only radiated noise is to be suppressed.  FIGS. 3 and 4  are an isometric view and a side elevation, respectively, of a section of a sub-enclosure according to another embodiment of the invention, which provides for suppression of both radiated noise and conducted noise. It will be apparent from  FIGS. 1-4  that the sub-enclosure section  40  is adapted for use in conjunction with the sub-enclosure section  10 . The sub-enclosure section  40  is thus a further illustrative example of a second sub-enclosure section as described generally above. However, the invention is in no way limited to the specific sub-enclosure sections  10  and  40 . Sub-enclosure design is dependent upon noise suppression requirements, physical access requirements, and physical size and location restrictions, for example, of a particular PCB or device environment.  
      The sub-enclosure section  40  comprises a conductive plate  42  having extensions or flanges  44  with slots  46 . Signal filters, including a filtered connector  48  and a plurality of electrical power filters  50 , are carried by the plate  42 .  
      The plate  42  is made of a conductive material or a non-conductive material with a conductive coating, such as any of the materials described above for the sub-enclosure section  10 .  
      In an assembled sub-enclosure, the flanges  44 A,  44 B, and  44 C abut the flanges  22 B,  22 C, and  22 D of the sub-enclosure section  10 , or an intermediate conductive gasket. The slots  46 A,  46 B,  46 C,  46 D, and  46 E receive or accommodate fasteners that also pass through the corresponding bores  28 A- 28 E of the sub-enclosure section  10 . The slots  46  allow for a certain degree of misalignment with the bores  28  and adjustment of the relative positions of the sub-enclosure sections  10  and  40 . In addition, as described in further detail below, the slots  46  simplify the assembly of a sub-enclosure where sections are mounted to a PCB at different manufacturing stages. However, it should be appreciated that sections of a sub-enclosure may incorporate slots, bores, or any combination thereof.  
      Such fasteners as nuts and bolts, screws, clamps, and rivets, for example, are preferred for attachment of sub-enclosure sections. However, other suitable fastening techniques will be apparent to those skilled in the art, including soldering or deformation of parts of one or both of the sub-enclosure sections, such as for heat staking or crimping, for instance. Embodiments of the invention in which alternative fastening techniques are employed need not necessarily incorporate such bores or slots.  
      When assembled, the sub-enclosure sections  10  and  40  form a sub-enclosure that at least partially encloses a portion of a PCB or a device. In accordance with an aspect of the invention, the sub-enclosure section  40  incorporates a divider, in the form of a plurality of pins  52 , for dividing a PCB into a plurality of portions, including at least a clean side and a noisy side. The pins  52  are preferably either through-hole pins or compliant pins that extend into holes in the PCB. Through-hole pins are soldered into position in the holes, whereas compliant pins require no soldering. In a preferred embodiment, the pins extend from a first side of a PCB to a second, opposite side of the PCB via conductive through holes in a substrate of the PCB, and electrically connect with a ground plane conductor on the second side of the PCB.  
      In an alternate embodiment, the enclosure is surface mounted to a ground plane or RF reference plane along the periphery of the enclosure. Conductive “vias” or through holes connect this plane to a plane on the opposite side or an intermediate layer of the PCB which encloses the area encompassed by the enclosure.  
      Radiated noise suppression or shielding for a sub-enclosure comprising the sub-enclosure sections  10  and  40  is substantially as described above. The sub-enclosure forms a conductive barrier to reduce the amount of radiated noise that propagates from the noisy side of the sub-enclosure to the clean side of the sub-enclosure. The pins  52  and the holes in the PCB into which the pins extend are preferably sized and spaced such that gaps between the pins are smaller than a maximum allowable opening size for the radiated noise frequencies to be suppressed. By controlling the gap size in this manner, the conductive barrier effectively extends through the PCB between the clean side and the noisy side of the sub-enclosure.  
      In a sub-enclosure comprised of the sub-enclosure sections  10  and  40 , the pins  52  are positioned only on the sub-enclosure section  40 . The conductive barrier formed by the sub-enclosure and the pins therefore extends into and preferably through a PCB along a segment of an edge of the portion of the PCB that is at least partially enclosed by the sub-enclosure. In other embodiments, the conductive barrier extends into or through a PCB along an entire common edge between the at least partially enclosed portion and the remainder of the PCB, or possibly around an entire perimeter of the at least partially enclosed area.  
      The sub-enclosure section  40  also includes filters for filtering conducted noise from electrical signals, and may therefore be considered a filter plate. The filtered connector  48  and the plurality of filters  50  are illustrative examples of such filters. The electrical signals to be filtered may be power signals, control signals, data signals, or virtually any other type of electrical signal to be transferred from a noisy side of a noise suppressing device to a clean side of the device.  
      Filtered connectors are generally known in the art to which the present invention pertains. The connector  48  may be any such connector. In the example shown in  FIGS. 3 and 4 , the connector  48  is a 15-pin connector, although the invention is in no way limited to any specific size or type of connector.  
      Signal filters are also well-known. Common filter types that may be employed as the filters  50  include capacitive filters, inductive filters, and Pi filters, for example.  
      On filtered connections through the sub-enclosure section  40 , noise components are filtered out of noisy input signals to provide filtered or clean output signals. In this manner, signals that are to be transmitted from the noisy side to the clean side of a noise suppression device are routed off a PCB, through a filtered connection in the noise suppression device, and then onto the clean side of the sub-enclosure. As described above, portion of a PCB that is partially enclosed by a sub-enclosure is either the clean side or the noisy side, and the filters  50  and the filtered connector  48  are implemented accordingly.  
      The filtered connector  48  and the filters  50  are accommodated in openings in the conductive plate  42 . Given the typical sizes of such components, these openings may exceed a maximum allowable opening size, particularly where relatively high-frequency noise is to be suppressed. One possible solution to this potential problem is to locate the filtered connector  48  and the filters  50  on the noisy side of a noise suppression device. However, this creates a problem of transferring a filtered signal to the clean side. An alternative solution will now be described with reference to  FIG. 5 , which is a cross-sectional view along line  5 - 5  of  FIG. 4 .  
       FIG. 5  shows a filter  50 , comprising a threaded filter component  54  held in an opening in the plate  42  with a conductive nut  62 , preferably a metal nut. The filter component  54  has leads  56  and  58 , which may, for example, include surface-mount pins, through-hole pins, compliant pins, or direct hardwire connections to other components of a PCB or an external device in conjunction with which a PCB operates.  
      The component  54  is preferably a conductive bushing or may be a non-conductive material with a conductive coating  60  applied to a surface thereof. The nut  62  and the conductive coating  60  provide conductive paths around the filter component  54  and the opening therein. As shown at  64 , the coating  60  thereby reduces the effective size of a sub-enclosure opening. Although the conductive plate  42  includes an opening of sufficient size to required to accommodate the filter component  54 , the conductive coating  60  overlaps and substantially closes the larger opening to a much smaller size. The opening  64  need only be large enough to accommodate the lead  56 .  
      Conductive coatings may be provided on other surfaces of the filter component  54 , and on one or more surfaces of the filtered connector  48 . Where the filter component  54  is a capacitive filter, creating a conductive connection between the ground electrode of a capacitor in the filter component  54  and the conductive plate  42  may further reduce the effective opening size. Although not explicitly shown in  FIG. 5 , electrical contact between the conductive plate  42  and a conductive bushing or a conductive coating on a filter or filtered connector may be provided through a conductive gasket.  
       FIG. 5  also shows one of the pins  52  and a cooperating through hole  68  in a PCB  66 . The pin  52  extends into the through hole  68  from a first side of the PCB  66  to a second, opposite side  72  of the PCB  66 . In a preferred embodiment, each hole  68  is plated or stitched as shown at  70  to extend the conductive barrier through the PCB  66  to a second side of the PCB  66  as described above.  
      Insertion of components onto a PCB substrate in a direction that is substantially perpendicular to the substrate surface simplifies PCB fabrication. So-called “drop-in” components are therefore generally preferred. A primary challenge in adapting the sub-enclosure section  40  as a drop-in component is maintaining proper alignment of the leads for the filtered connector  48  and the filters  50 . In one embodiment, sub-enclosure section  40  is itself assembled on a non-conductive substrate or base plate. FIG.  6  is a top view of a base plate for use with the sub-enclosure section  40  of  FIGS. 3 and 4 .  
      The base plate  74  aligns the leads for filtered connections in the sub-enclosure section  40 , and includes through holes  76   a  and  76   b  for the filtered connector  48 , and through holes  78   a  and  78   b  for input and output leads of the filters  50 . The through holes  79 , for the pins  52 , allow the base plate  74  to pass from a clean side to a noisy side of the PCB without degrading shielding performance of a noise suppression device. As described above, the spacing of the pins  52  is preferably below a maximum allowed spacing for the noise frequencies to be suppressed.  
       FIGS. 3-6  relate to embodiments of the invention in which a divider, comprising the pins  52 , extends through a PCB. However, the invention is in no way limited to such dividers. A divider preferably electrically extends into or through the PCB, but need not physically extend into or through the PCB.  
      For example, the holes  68  are plated or stitched as shown at  70 , such that electrical contact between the conductive plate  42  and a conductive plating on the opposite surface  72  or an intermediate layer of the PCB  66  may be established with pins or other structures that do not necessarily extend through, or even into, the PCB  66 .  
      In one embodiment, the divider includes surface-mount components such as surface-mount pins or “feet” that extend onto the surface of a PCB to mount the conductive plate to the PCB. The surface-mount pins are preferably in electrical contact with conductive through hole plating such as shown at  70  in  FIG. 5 , or “vias” in the PCB. The vias are in turn preferably in electrical contact with conductive plating on an opposite surface of the PCB or an intermediate conductive layer of the PCB between its surfaces. This type of divider thereby electrically extends into or through the PCB without physically extending into the PCB.  
      It will be apparent from the foregoing that through hole pins and surface-mount pins represent two extreme cases of divider structure. Embodiments of the invention in which the divider physically extends into the PCB to an extent between these extremes are also contemplated.  
       FIG. 7  is an exploded view of a noise suppression device according to a further embodiment of the invention. The noise suppression device in  FIG. 7  includes sub-enclosure portions  80 ,  82 , and  92 , and is intended to be mounted along an edge of a PCB  86 . The sub-enclosure sections  80  and  82  are substantially similar to the sub-enclosure sections  10  and  40  described above. The sub-enclosure section  82  is preferably first assembled with a base plate  84  to maintain lead alignment for drop-in assembly of the sub-enclosure section  82  with the PCB  86 .  
      As shown in detail in  FIG. 8 , which is an expanded view of the section  8 - 8  in  FIG. 7 , the PCB  86  includes ground conductor plating  88 , preferably copper plating. The PCB  86  also includes plated through holes  96  and  98 , which provide an electrical connection between the ground conductor plating  88  and similar ground conductor plating on an opposite side (not shown) of the PCB  86 . The through holes  98  also receive the pins on the sub-enclosure section  82 , as described above. The through holes  96  and  98  may be of different sizes, and the through holes  96  may be designed as vias since they do not receive the pins of the sub-enclosure section  82  in the illustrated embodiment. As will be appreciated by those skilled in the art, the ground conductor plating  88  is electrically connected to ground.  
      Referring again to  FIG. 7 , it can be seen that although the pins of the sub-enclosure section  82  extend into or through the PCB  86  to divide the PCB  86  into clean and noisy areas when the sub-enclosure section  82  is assembled to the PCB  86 , the PCB  86  structurally remains a single board.  
      During manufacturing of a PCB, through-hole components are typically placed on a substrate such that pins extend into cooperating through holes on the PCB substrate and are then soldered into the through holes. The sub-enclosure section  82  is preferably assembled and soldered to the PCB  86  along with other drop-in components (not shown). The pins on the sub-enclosure section  82  thereby extend through the PCB  86  and are in electrical contact with the ground conductor plating  88 , as well as any ground conductor plating on the opposite side of the PCB  86 . This simplifies the manufacturing process in that such typical elements as a conductive gasket and separate fasteners are not needed to assemble the sub-enclosure section  82  to the PCB  86 . In a further preferred embodiment, integral through hole stitching as described above is performed during a soldering stage of PCB manufacturing.  
      The slots in the flanges of the sub-enclosure section  82  are for receiving or accommodating fasteners, as described above. As will be apparent from  FIG. 7 , the slots provide a further advantage during PCB manufacturing. In particular, the fasteners may be carried by the sub-enclosure section  80  and the sub-enclosure section  80 , with the fasteners, can be placed on the PCB  86  in a vertical direction relative to the surface of the PCB  86  after the sub-enclosure section  82  has been assembled to the PCB  86 . For example, according to one embodiment, screws are placed in bores in the sub-enclosure section  80 , clamps are placed on the screws, or alternatively the clamps and screws are provided as an integrated fastener, a conductive gasket is applied to surfaces of the sub-enclosure section  80  that mate with the sub-enclosure section  82 , and the sub-enclosure section  80  is placed on and fastened to the circuit board  86  such that the screws are received in the slots of the sub-enclosure section  82  and the clamps extend over the flanges of the sub-enclosure section  82 . The sub-enclosure sections  80  and  82  are then attached by tightening the screws to close the clamps. Each clamp extends over the sub-enclosure section  82  to “sandwich” the sub-enclosure section  82  between a portion of the clamp and the sub-enclosure section  80 . Electrical connection between the sub-enclosure section  80  and the ground conductor plating  88  is either through direct physical contact or a conductive gasket.  
      The portion of the PCB  86  bordered by the ground conductor plating  88  and partially enclosed by the sub-enclosure sections  80  and  82  may be either the clean side or the noisy side of the noise suppression device. For example, in one embodiment, the connector  90  receives noisy electrical input signals from an external device. The connector  90  is partially enclosed by the sub-enclosure sections  80  and  82  and the input signals are filtered by signal filters in the sub-enclosure section  82  before being transmitted to the clean side.  
      In  FIG. 7 , it is assumed that PCB component leads, including those for the filters and the filtered connection of the sub-enclosure section  82 , extend into through holes in a PCB substrate to an opposite side of the substrate. Thus, the opposite side of the PCB  86  may include leads that carry clean electrical signals and leads that carry noisy electrical signals. In order to suppress radiated noise generated by the noisy electrical signals or leads, a further sub-enclosure section  92  for mounting on the opposite side of the PCB  86  is provided. The sub-enclosure section  92  is a stamped metal or other type of conductive plate having a conductive gasket  94  for establishing an electrical connection between the conductive plate and ground copper plating on the opposite surface of the PCB  86 . The sub-enclosure section  92  at least partially encloses a portion of the opposite surface of the PCB  86 . In  FIG. 7 , the sub-enclosure section  92  encloses the noisy side on the opposite surface of the PCB  86 , which underlies the section of the PCB  86  that is at least partially enclosed by the sub-enclosure sections  80  and  82 .  
      It should be appreciated that the sub-enclosure section  92  is preferred where PCB components of the enclosed portion of the PCB  86 , or leads associated with such components, extend to the opposite side of the PCB  86 . If these PCB components are surface-mount components for example, then the ground conductive plating on the opposite side of the PCB  86  preferably covers an underside of the enclosed portion, thereby eliminating the separate sub-enclosure section  92 .  
      Although only the connector  90  is shown in an enclosed portion of the PCB  86 , those skilled in the art will appreciate that other PCB components that generate or transmit noise, or alternatively components that are to be protected from such noise, are located in an enclosed section of a PCB in other embodiments. It should also be appreciated that a PCB may include more than one noise suppression device, to provide different noisy and clean levels or to protect different components, for instance.  
      To ensure a highly continuous conductive contact through the mating surfaces formed by sub-enclosure section  82 , the PCB  86 , and the sub-enclosure section  92 , and their respective gaskets, an embodiment of the invention includes a PCB technique commonly referred as edge plating. This edge plating  86 A and  86 B when coplanar to flanges  80 A,  80 B,  80 C, and  92 A, forms a near-contiguous conductive surface that can mate to another sub-enclosure section to substantially enclose noisy or clean PCB components on PCB  86 .  
       FIGS. 9 and 10  are isometric views of a PCB having a noise suppression device in accordance with an embodiment of the invention. The PCB  100  includes a noise suppression device  102  and a bank of circuit breakers  104  to which external physical access is to be provided. Clearly, the noise suppression device  102 , by partitioning the PCB  100  into clean and noisy sides, provides virtually unobstructed access to the circuit breakers  104 . Physical access to the circuit breakers  104 , as well as any other components on a remainder of the PCB  100  outside a portion of the PCB  100  enclosed by a sub-enclosure of the noise suppression device  102 , does not require openings in the sub-enclosure.  
       FIG. 11  is an isometric view of a backplane element and a PCB carrying a noise suppression device according to an embodiment of the invention. In  FIG. 11 , the backplane element  116  includes a conductive gasket  118  that is electrically connected to ground, through a conductive plate or ground conductor plating, for example. The connectors  120  and  122  interface with corresponding connectors on the PCB  110 , one of which is shown at  124 . As in  FIGS. 9 and 10 , the PCB  110  includes a noise suppression device  112  and a bank of circuit breakers  114  as examples of PCB components.  
      The PCB  110  is configured to operate in conjunction with an external device through the backplane element  116 . The backplane element  116  may be connected to the external device or form a part of the external device. In one embodiment, the PCB  110  or a device incorporating the PCB  110  is adapted for insertion into a rack or other holder for blind mating with the backplane element  116 . When placed in an operative position with the backplane element, the connectors  120  and  122  connect to corresponding connectors on the PCB  110 , and the sub-enclosure of the noise-suppression device  112  is also in electrical contact with a grounded conductor on the backplane element  116  through the conductive gasket  118 . The grounded conductor on the backplane element may thus be considered a further sub-enclosure element of the noise suppression device  112 .  
      In this manner, a section of the PCB  112  may be substantially enclosed within a sub-enclosure of the noise suppression device  112 . The sub-enclosure may include sub-enclosure sections for placement on both surfaces of the PCB  110  and on an external device such as the backplane element  116 .  
      The connector  124  illustrates the fact that a noise suppression device on a PCB in no way precludes the implementation of conventional components on the same PCB. In  FIG. 11 , the connector  120  enters an enclosed portion of the PCB  110 , whereas the connector  122  interfaces with a connector  124  that is outside the enclosed area.  
      It will be particularly evident from  FIGS. 7-11  that many different configurations of a noise suppression device are possible in accordance with aspects of the invention. A noise suppression device according to aspects of the invention suppresses both conducted noise and radiated noise. A sub-enclosure of a noise suppression device encloses a section of a PCB to different degrees ranging from partial enclosure to substantially complete enclosure, depending upon the level of noise suppression desired. A sub-enclosure comprising sections such as  80  and  82  suppresses radiated noise in both directions, into and out of an enclosed section of a PCB, owing to the reciprocal nature of suppression devices. In certain embodiments, these sections may be fashioned to provide different degrees of suppression in each direction. The addition of further sections such as  92  or a ground conductor on an opposite side of a PCB provides more effective radiated noise suppression. Substantially complete enclosure of a portion of a PCB, with underside and backplane sub-enclosure sections, for example, provides an even higher level of radiated noise suppression.  
      Similarly, the extent to which a divider surrounds an enclosed portion of a PCB also affects noise suppression properties. As described above, a divider effectively extends a conductive barrier through a PCB. Therefore, a divider may extend through a PCB along only a segment of an edge of an enclosed section or along an entire perimeter of the enclosed section. In  FIG. 7 , the pins on the sub-enclosure section  82  provide a most effective radiated noise suppression function in a direction of the majority of the remainder of the PCB  86 , which may be sufficient in many applications of a noise suppression device. Other applications may warrant a more extensive divider.  
      What has been described is merely illustrative of the application of the principles of the invention. Other arrangements and methods can be implemented by those skilled in the art without departing from the spirit and scope of the present invention.  
      For example, a PCB may include more than one noise suppression device. A sub-enclosure in a noise suppression device may also include a plurality of enclosed sections, such as a first enclosed section for suppression of radiated noise only, and a second enclosed section for suppression of both radiated and conducted noise. In this case, signal filters are included only in a part of the sub-enclosure associated with the second enclosed section.  
      In addition, although signal filters have been shown in the drawings in only one wall of one section of a sub-enclosure, signal filters may be provided in any or all walls of a sub-enclosure, depending upon PCB layout.