Abstract:
An electronic device including a substrate having opposing top and bottom surfaces is provided. A ground layer is disposed in the substrate. An electrically conductive chassis has a mounting surface to receive the bottom surface of the substrate and is in electrical contact with the ground layer by a ground stitch via. An electromagnetic shield is defined by the ground layer, the ground stitch via and the chassis to enclose the bottom surface of the substrate and protect the bottom surface from electromagnetic interference. A non-conductive cover is assembled to the substrate in tension so that an interior surface of the cover applies a force to the top surface of the substrate thereby ensuring the chassis maintains in electrical contact with the ground layer.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure generally relates to shielding devices for minimizing electromagnetic interference and susceptibility effects on electrical and electronic devices. More particularly, the present disclosure relates to a shielding device for a printed circuit board assembly having a transmission and/or receiver component and an enclosure. 
       BACKGROUND 
       [0002]    Electronic devices such as audio devices and infotainment systems, and other devices often contain circuitry and components that are susceptible to electromagnetic interference and require electromagnetic shielding. Generally, parasitic radiation is generated from electrical components or circuits during operation which may influence the electrical performance of other electrical components. Therefore, it is important to shield the electronic devices against electromagnetic interference. 
         [0003]    It can be costly to provide an electromagnetic shield to keep interfering noise out of a selected region of a device where it can cause harm to sensitive electrical components. To protect from electromagnetic interference, electronic circuits and electric components mounted on a printed circuit board are typically enclosed within metal enclosures that shield from electromagnetic radiation. In addition to being costly, conventional electromagnetic shield covers mounted to a printed circuit board can be undesirably bulky and time consuming to install. 
         [0004]    In some situations, the electronic device may include a component through which electromagnetic signals will be passed, such as for an antenna, transmitter, receiver, or transceiver. Providing an electromagnetic shield to printed circuit boards including an antenna, for example, may increase the complexity and cost of an electromagnetic shield because it must protect against parasitic electromagnetic radiation in one area of the printed circuit board while allowing transmission of electromagnetic radiation in another area. 
       SUMMARY 
       [0005]    In one embodiment, an electronic device is provided with a substrate having opposing top and bottom surfaces. A plurality of conductive pads and at least one first electrical component are mounted on the bottom surface of the substrate. A second electrical component is disposed in the substrate adjacent the top surface. A ground layer is disposed in the substrate between the second electric component and the bottom surface. A plurality of ground stitch vias are provided where via electrically connects the ground layer and one of the conductive pads. A metallic chassis has a mounting surface to receive the bottom surface of the substrate. The mounting surface includes a plurality of raised dimples that each contact one of the plurality of conductive pads. A plastic cover receives the top surface of the substrate and has a plurality of posts that contact the top surface of the substrate opposite the dimples. A fastener extends through the plastic cover and substrate into the chassis so that the posts engage the top surface of the substrate thereby ensuring electric contact between each of the pads and dimples along the bottom surface. A Faraday cage is a formed with the ground layer, the via and the chassis to enclose the bottom surface of the substrate and the first electrical component mounted thereto. The Faraday cage thereby defines a shielded enclosure that protects the first electrical component from electromagnetic interference. 
         [0006]    In another embodiment, the second electrical component is a transmission component whereby electromagnetic signals from the transmission component are not prevented by the Faraday cage. 
         [0007]    In a further embodiment, the second electrical component is an antenna. 
         [0008]    In another embodiment, a pair of fasteners is disposed at opposing sides of the substrate and defines a span there between. The posts of the plastic cover contact the substrate to produce a downward force and maintain the plastic cover in tension along the span between the pair of fasteners. 
         [0009]    In yet another embodiment, the plurality of raised dimples and conductive pads are disposed within the span between the pair of fasteners. Maintaining the plastic cover in tension ensures contact between each of the conductive pads and raised dimples in any environmental conditions. 
         [0010]    In still another embodiment, the conductive pads are spaced apart by a maximum distance based on an electromagnetic wavelength. 
         [0011]    In another embodiment, wherein the chassis is formed as a single metallic component. 
         [0012]    In another embodiment, the Faraday cage does not include any additional electromagnetic shield component to form the Faraday cage. 
         [0013]    In one other embodiment, an electronic device including a substrate having opposing top and bottom surfaces is provided. A ground layer is disposed in the substrate. An electrically conductive chassis has a mounting surface to receive the bottom surface of the substrate and is in electrical contact with the ground layer by a ground stitch via. An electromagnetic shield is defined by the ground layer, the ground stitch via and the chassis to enclose the bottom surface of the substrate and protect the bottom surface from electromagnetic interference. A non-conductive cover is assembled to the substrate in tension so that an interior surface of the cover applies a force to the top surface of the substrate thereby ensuring the chassis maintains in electrical contact with the ground layer. 
         [0014]    In another embodiment, the ground layer is disposed at a predetermined distance from a surface of the chassis. 
         [0015]    In still another embodiment, the ground layer is disposed in a layer of the substrate adjacent the top surface. 
         [0016]    In another embodiment, the interior surface of the cover includes a plurality of posts arranged along a perimeter, wherein the posts contact the top surface of the substrate. 
         [0017]    In yet another embodiment, the electromagnetic shield defines a Faraday cage for preventing electromagnetic interferences, wherein the electromagnetic shield does not include any additional components to form the Faraday cage. 
         [0018]    In another embodiment, the cover permits transmission of electromagnetic signals from an electrical component disposed in the substrate outboard of the ground layer. 
         [0019]    In one other embodiment, an electronic device is provided with a substrate having opposing top and bottom surfaces. A first electrical component is mounted on the bottom surface of the substrate. A ground layer is disposed in the substrate adjacent the top surface of the substrate. A chassis is formed as a single metallic component and has a mounting surface to receive the bottom surface of the substrate. A Faraday cage is defined by the ground layer and the chassis to enclose the bottom surface of the substrate and the first electrical component mounted thereto thereby protecting the at least one electrical component from electromagnetic interference. 
         [0020]    In another embodiment, the mounting surface includes a plurality of raised dimples that each contact one of a plurality of conductive pads disposed on the bottom surface of the substrate. The conductive pads are electrically connected to the ground layer by a via to define the Faraday cage. 
         [0021]    In a further embodiment, the mounting surface defines a datum plane, and the ground layer is disposed at a predetermined distance from the datum plane. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  illustrates an assembled perspective view of an electronic device package with electromagnetic interference shield. 
           [0023]      FIG. 2  illustrates an exploded view of the electronic device package of  FIG. 1 . 
           [0024]      FIG. 3  illustrates a cross-section of the electronic device package of  FIG. 1  taken along line  3 - 3 . 
           [0025]      FIG. 4  illustrates a cross-section of the electronic device package of  FIG. 1  taken along line  4 - 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0027]      FIG. 1  illustrates a perspective view of an assembled electronic device package  10 . The electronic device package  10  includes a top cover  12  and a bottom chassis or frame  14  that encloses an electronic device. The top cover  12  and bottom chassis  14  are joined together with a fastener  16  to form a mechanical enclosure assembly  18 . 
         [0028]      FIG. 2  illustrates an exploded view of the electronic device electronic device package  10  that encloses an electronic device being a rigid substrate  20  such a printed circuit board assembly. The electronic device package  10  and substrate  20  may be any suitable shape and are not limited to a generally rectangular shape, as illustrated. As shown, the fasteners  16  are threaded fasteners, such a screws; however, the fasteners  16  may be a suitable fastener for securing the electronic device package  10 . 
         [0029]      FIG. 3  illustrates a cross-section of the assembled electronic device package  10  taken along line  3 - 3  in  FIG. 1 . In particular,  FIG. 3  illustrates in more detail the substrate  20 . The schematic view of the substrate  20  is not necessarily to scale. As shown in more detail in  FIG. 3 , the substrate  20  has a top surface  24  and an opposing bottom surface  26 . The top surface  24  (A side) is defined as the most exterior plane of the substrate  20  while the bottom surface  26  (B side) is defined as the most interior plane of the substrate  20 . 
         [0030]    Various electrical components  28  may be mounted on a printed circuit board  22  along a top surface  24  of the substrate  20 . The printed circuit board  22  may be single sided, as illustrated in  FIG. 3 , double sided or multi-layer (outer and inner layer) or any configuration known by a person of ordinary skill in the art. The printed circuit board  22  may contain components  28  such as capacitors, resistors or active devices and the like. 
         [0031]    The printed circuit board  22  supports and electrically connects the electrical components  28  using conductive traces, or other features etched from copper sheets laminated onto substrate  20  along the bottom surface  26 . For example, the electrical components  28  may be surface-mount technology components that are mounted directly onto the printed circuit board  22  along the bottom surface  26 . The printed circuit board  22  and substrate  20  may be formed from rigid printed circuit board materials such as fiberglass-filled epoxy. 
         [0032]    The electrical components  28  may be sensitive to electromagnetic interference and may have the potential to generate electromagnetic interference for other components. At least one of the components  28  on the substrate  20  may need to be electromagnetically shielded from components that generate electromagnetic interference or from external sources of electromagnetic interference. 
         [0033]    The substrate  20  has a conductive ground layer  30  is disposed adjacent the top surface  24 . The ground layer  30  is ground plane that extends as a solid layer through the entire substrate. As shown in  FIG. 2 , the ground layer  30  extends as a continuous layer along the width and length of the substrate  20 . Additional routing layers  32  may be disposed in the substrate  20  between the ground layer  30  and the bottom surface  26  and the printed circuit board  22 . The substrate  20  may include any number of intermediate layers  32  such as the routing layers, dependent on the electronic device. 
         [0034]    The ground layer  30  is electrically connected bottom surface  26  with a ground stitch via  34 . The ground stitch via  34  electrically connects the ground layer  30  to conductive contact pads  36  disposed on the bottom surface  26 . The ground stitch via  34  may be formed as a conductive through-hole in the substrate  20 , or may be formed at the edge of the substrate  20 , as shown in  FIG. 3 . The ground stitch vias  34  are formed adjacent the perimeter of the substrate  20  and outboard of the printed circuit board  22  and any components  28 . 
         [0035]    The ground stitch vias  34  electrically connect the ground layer  30  to the bottom surface  26  and as such, the ground stitch vias  34  are only exposed on the bottom surface  26  of the substrate  20 . The contact pads  36  to which the ground stitch vias  34  are connected may be bare metallic pads mounted on the bottom surface  26  and are arranged along the perimeter of the bottom surface  26 . The contact pads  36  are positioned also outboard of the printed circuit board  22  and any components  28 . 
         [0036]    The bottom surface  26  of the substrate  20  mates to the chassis  14  along a mounting surface  40 . The mounting surface  40  defines a mounting datum plane  42  along the perimeter of the chassis  14 . A plurality of raised dimples  44  are formed along the mounting surface  40  and extend above the datum plane  42 . When the substrate  20  is mated to the chassis  14 , each dimple  44  contacts a contact pad  36 . The raised dimples  44  extend above any mounting bosses for the fasteners  16 . 
         [0037]    The chassis  14  is formed of conductive material such as a metallic material. The chassis  14  may be formed of cast metal, or machined metal or any suitable process to define the chassis  14  as a single piece metallic component. The chassis  14  has a cavity defined by side walls  46  and a distal wall  48 . When the dimples  44  on the metallic chassis  14  are aligned with the contact pads  36  around the perimeter of the substrate, an electromagnetic shield  50  is defined. The electromagnetic shield enclosure  50  is a Faraday cage that extends around and shields the substrate  20  between the ground layer  30  and the chassis  14 . In particular, the electromagnetic shield  50  blocks specific electromagnetic interference from the bottom surface  26  of the substrate  20 . 
         [0038]    Together with the conductive chassis  14 , the electromagnetic shield  50  is formed by the electrical contact along the contact pads  36 , the ground stitch via  34 , and the ground layer  30  to form the Faraday cage. AS such, the electromagnetic interference protection of the shield  50  is built into to the substrate construction without the need for extra components, such as EMI gaskets or shielding pads. By eliminating shielding gaskets and pads, material and installation costs are reduced. 
         [0039]    The electromagnetic shield  50  protects the electrical components  28  along the bottom surface  26  as well as the intermediate routing layers  32  from electromagnetic interference while permitting transmission of electromagnetic signals from a transmitting component  56  such as for an antenna, transmitter, receiver, or transceiver. The transmitting component  56  is not contained within the Faraday cage, and is not shielded. As such, the transmitting component  56  is disposed closer to the top surface  24  than the ground layer  30 . 
         [0040]    The electronic device package  10  also includes the cover  12  that mates to the top surface  24  of the substrate  20 . The cover  12  permits transmission of the electromagnetic signals from the transmitting component  56 . The cover  12  is non-conductive and may be formed of plastic or any suitable material suitably protects the substrate  20  while allowing transmission of electromagnetic signals. 
         [0041]    The electronic device package  10  is assembled with the fasteners  16  that extend through the plastic cover  12  and substrate  20  into the chassis  14 . The cover  12  includes a plurality of posts  60  that extend from an interior surface. When the cover  12  is assembled in the electronic device package  10 , the posts  60  contact the top surface  24  of the substrate  20 . The posts  60  may be aligned opposite the dimples  44  on the chassis  14 , as shown in  FIGS. 3-4 . The posts  60  extend from an interior surface of the cover  12  along the perimeter of the cover  12 . As illustrated, the posts  60  are formed as cylindrical protrusions, but any suitable shaped post may be used. 
         [0042]    The datum plane  42 , upon which the bottom surface  26  of the substrate  20  mates to the metallic chassis  14 , is a specified distance below a datum plane of the ground layer  30 . When the fasteners  16  are installed to secure the plastic cover  12  and the posts  60  contact the top surface  24  of the substrate  20 , the cover  12  is placed into tension in the span between the pair of fasteners  16  on laterally opposite sides of the package  10 . When the cover  12  is in tension, a force is applied to the substrate  20  by the cover  12  to ensure electric contact between each of the contact pads  36  and dimples  44 . 
         [0043]    The contact pads  36  may be spaced apart by relief cutouts  66  along the perimeter of the substrate  20 . The relief cutouts  66 , along with the cover  12  that is always in tension over the span of the substrate  20 , apply a force to the substrate  20  at the contact pads  36 . The contact pads  36  and relief cut outs  66  may be spaced apart by a distance that is defined as a ratio of the wavelengths sensitive harmonics, to the size of the aperture of electromagnetic radiation which is desired to be protected against. In one embodiment, the contact pads  36  and relief cutouts  66  may be spaced apart by a distance that is one-twentieth of the wavelength of electromagnetic radiation which is desired to be protected against. The distance between the contact pads  36  may be varied depending on the specific wavelength of electromagnetic interference that is of particular concern. 
         [0044]      FIG. 4  illustrates a line-to-line condition between each of the ground contact pads  36  and the dimples  44  of the chassis  14 , and between the top surface  24  of the substrate  20  and the cover  12 . A gap  70  is defined between the substrate  20  and the screw mounting boss  72  on the chassis  14 , and between the substrate  20  and the cover  12  at the fastener  16  locations. When the fasteners  16  are driven into the chassis  14 , the substrate  20  will deflect locally to reduce the gap outboard of the fasteners  16 . When the substrate  20  deflect while the posts  60  are in contact with the top surface  24 , the plastic cover  12  will be put into tension, thus guaranteeing electrical contact at every ground contact pad  36 , even during environmental stressors 
         [0045]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.