PATENT DOCUMENT

Publication Number: US-9048124-B2
Application Number: US-201213623436-A
Country: US
Kind Code: B2

Title: Heat sinking and electromagnetic shielding structures

Abstract:
An electronic device may be provided with electronic components such as radio-frequency transceiver integrated circuits and other integrated circuits that are be sensitive to electromagnetic interference. Metal structures are configured to serve both as heat sinking structures for the electrical components and electromagnetic interference shielding. Components are mounted to the substrate using solder. Metal fence structures are also soldered to the substrate. Each metal fence has an opening that covers a respective one of the components. A thermally conductive elastomeric gap filler pad is mounted in the opening. A metal heat spreading structure is electrically shorted to the fence using a conductive gasket that surrounds the gap filler pad so that the structure serves as an electromagnetic interference shield. Heat from the component travels through the gap filler pad to the metal heat spreading structure so that the heat spreading structure may laterally spread and dissipate the heat.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a housing with first and second opposing planar surfaces, wherein the electronic device has an exterior, and wherein the housing forms the entire exterior of the electronic device; 
 a dielectric substrate; 
 at least one electrical component mounted on the dielectric substrate; and 
 a metal heat spreader structure that is configured to dissipate heat from the electrical component and that is configured to serve as part of an electromagnetic interference shield for the electrical component, wherein the component comprises a radio-frequency transceiver integrated circuit, and wherein the metal heat spreader structure forms the first surface of the housing. 
 
     
     
       2. The electronic device defined in  claim 1  further comprising:
 a metal fence surrounding the electrical component, wherein the metal heat spreader structure is shorted to the metal fence. 
 
     
     
       3. The electronic device defined in  claim 2  further comprising a conductive gasket that is interposed between the metal heat spreader structure and the metal fence and that electrically shorts the metal structure to the metal frame. 
     
     
       4. The electronic device defined in  claim 3  wherein the conductive gasket comprises a conductive material selected from the group consisting of: conductive foam, conductive fabric, and conductive adhesive. 
     
     
       5. The electronic device defined in  claim 3  wherein the metal heat spreader structure comprises aluminum coated with aluminum oxide, wherein the aluminum has an exposed portion that is free of the aluminum oxide, and wherein the conductive gasket electrically shorts the metal frame to the exposed portion. 
     
     
       6. The electronic device defined in  claim 5  further comprising a thermally conductive elastomeric gap filler pad interposed between the component and the metal heat spreader structure. 
     
     
       7. The electronic device defined in  claim 6  wherein the metal fence has an opening over the electrical component and wherein the thermally conductive elastomeric gap filler pad is received within the opening. 
     
     
       8. The electronic device defined in  claim 2  further comprising solder pads on the dielectric substrate and solder with which the metal fence is soldered to the solder pads. 
     
     
       9. The electronic device defined in  claim 2  wherein the dielectric substrate comprises a printed circuit. 
     
     
       10. An electronic device, comprising:
 a printed circuit having solder pads; 
 an integrated circuit mounted on the printed circuit, wherein the integrated circuit comprises a radio-frequency transceiver; 
 a metal fence structure soldered to the solder pads, wherein the metal fence structure has an opening that overlaps the integrated circuit; 
 a thermally conductive layer of material in the opening that contacts the integrated circuit; and 
 a metal heat sink structure that contacts the thermally conductive layer of material, wherein the metal heat sink structure comprises aluminum covered at least partly with an insulating coating, and wherein a portion of the aluminum is free of the insulating coating and is electrically shorted to the metal fence structure. 
 
     
     
       11. The electronic device defined in  claim 10  further comprising a compressible conductive gasket interposed between the portion of the aluminum that is free of the insulating coating and the metal fence structure. 
     
     
       12. Apparatus, comprising:
 a printed circuit board; 
 at least one trace on the printed circuit board; 
 an electrical component mounted on the substrate; 
 a metal fence mounted to the at least one trace to surround the electrical component; 
 a metal heat spreader structure that is configured to dissipate heat from the electrical component and configured to serve with the metal fence as part of an electromagnetic shield for the electrical component, wherein the metal heat spreader structure comprises aluminum coated with aluminum oxide, wherein the aluminum has an exposed portion that is free of the aluminum oxide; and 
 a conductive gasket that electrically shorts the metal frame to the exposed portion of the metal heat spreader structure. 
 
     
     
       13. The apparatus defined in  claim 12  further comprising a thermally conductive elastomeric gap filler pad interposed between the electrical component and the metal heat spreader structure. 
     
     
       14. The apparatus defined in  claim 12  wherein the electrical component comprises a radio-frequency transceiver.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to radio-frequency shielding and thermal management structures for components in electronic devices. 
     Electronic devices often contain components such as radio-frequency transmitters and other circuits that use electromagnetic interference (EMI) shielding structures. Electromagnetic interference shielding structures may help prevent radio-frequency signals that are generated by one component from disrupting the operation of another component that is sensitive to radio-frequency interference. Electromagnetic shielding structures may be formed from metal shielding cans soldered to printed circuit boards. A typical shielding has an inner metal fence and an outer metal lid structure. 
     The operation of integrated circuits such as radio-frequency transmitters and other circuitry tends to generate heat. To properly dissipate heat that is generated during operation, heat sink structures may be thermally coupled to the exterior of an electromagnetic shielding can. To ensure satisfactory heat transfer from a shielded integrated circuit to a heat sink, a thermally conductive elastomeric pad may be interposed between the integrated circuit and the shielding can to fill air gaps between the integrated circuit and the shielding can and another thermally conductive elastomeric pad may be interposed between the shielding can and the heat sink. The use of multiple thermally conductive paths and separate heat sink and electromagnetic interference shielding structures tends to make designs of this type complex and costly and may reduce the efficacy of the overall structure in removing heat from a component during operation. 
     It would therefore be desirable to be able to provide improved ways in which to provide components in electronic devices with heat sinking and electromagnetic interference shielding structures. 
     SUMMARY 
     An electronic device may be provided with electronic components such as radio-frequency transceiver integrated circuits and other integrated circuits that are sensitive to electromagnetic interference. Metal heat spreading structures can be configured to serve both as heat sinking structures for the electrical components and electromagnetic interference shielding. 
     The electronic components are mounted to a dielectric substrate using solder. The dielectric substrate is formed from a rigid or flexible printed circuit or other dielectric material. Metal fence structures are soldered to the substrate over the components. Each metal fence has an opening that overlaps a respective one of the components. A thermally conductive structure such as an elastomeric gap filler pad is mounted in each opening. 
     The metal heat spreading structures are electrically shorted to each fence structure using a conductive gasket that surrounds the gap filler pad in that fence. This allows the metal heat spreading structure to serve as part of an electromagnetic interference shield. 
     Heat from the components travels through the gap filler pads on the components to the metal heat spreading structure. The heat spreading structure may laterally spread and dissipate the heat. 
     If desired, a heat spreading structure may be mounted directly over a component. In this type of configuration, sidewall portions of the heat spreading structure are shorted to traces on the substrate. A recess in the heat spreading structure is configured to receive the component. A gap filler or other thermally conductive structure is interposed between the component and the upper surface of the recess. 
     Further features, their nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device of the type that may be provided with electromagnetic interference shielding and thermal management structures in accordance with an embodiment. 
         FIG. 2  is an exploded perspective view of an illustrative electronic device with electromagnetic interference shielding and thermal management structures in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of electromagnetic interference shielding and thermal management structures in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of an electronic device having a housing in which electromagnetic interference shielding and thermal management structures have been installed in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an electronic device having a housing that is used in forming electromagnetic interference shielding and thermal management structures in accordance with an embodiment. 
         FIG. 6  is an exploded rear perspective view of an illustrative electronic device with electromagnetic interference shielding and thermal management structures in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of electromagnetic interference shielding and thermal management structures that have been coupled to a printed circuit substrate and that include a recess for accommodating a component in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of electromagnetic interference shielding and thermal management structures that have been coupled to a metal fence structure on a printed circuit substrate in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An electronic device may be provided with electronic components such as integrated circuits. These components may be provided with electromagnetic interference and heat sinking structures (sometimes referred to as heat spreading structures, heat spreaders, heat spreader structures, or thermal management structures). An illustrative electronic device is shown in  FIG. 1 . Electronic device  10  of  FIG. 1  has openings  14  in housing  12 . Openings  14  form connector ports for connectors such as Ethernet plugs, Universal Serial Bus connectors, power connectors, audio jacks, and other connectors. Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or can be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     Electronic device  10  of  FIG. 1  is a set-top box that provides video signals to a television or other display. If desired, electronic device  10  may be implemented using other types of equipment such as cellular telephones, media players, other handheld portable devices, somewhat smaller portable devices such as wrist-watch devices, pendant devices, or other wearable or miniature devices, gaming equipment, tablet computers, notebook computers, desktop computers, televisions, computer monitors, computers integrated into computer displays, wireless access points, or other electronic equipment. The use of a set-top box form factor in implementing device  10  is merely illustrative. 
     An exploded perspective view of device  10  is shown in  FIG. 2 . As shown in  FIG. 2 , device  10  has housing base structure  16 . Housing structure  16  has sidewall portions  46  that surround recessed rear portion  44 . Housings with other shapes and sizes may be used for device  10  if desired. 
     Components  20  are mounted on dielectric substrate  18 . Components  20  may include integrated circuits, discrete components such as resistors, capacitors, and inductors, connectors, and other circuitry. Examples of integrated circuits that may be used in forming components  20  include memory circuits, clock circuits, display driver circuits, radio-frequency integrated circuits such a radio-frequency transceiver circuitry associated with cellular telephone communications, radio-frequency transceiver circuitry associated with wireless local area network (WLAN) communications, satellite navigation system integrated circuits such as a Global Positioning System receiver, wireless radio-frequency transceiver circuitry for Bluetooth® communications, processors, power amplifiers, timing circuits, wireless circuits, and other circuitry. Substrate  18  may be a printed circuit board, a flexible printed circuit such as a printed circuit formed from a flexible sheet of polyimide or a layer of other polymer material, a rigid printed circuit board formed from fiberglass-filled epoxy or other printed circuit board substrate material, a dielectric such as plastic, glass, or ceramic, or other insulating material. Configurations in which dielectric substrate  18  is a printed circuit are sometimes described herein as an example. 
     Components  20  are soldered on printed circuit substrate  18  using solder. Fences  26  have leg portions  24  that are soldered to printed circuit substrate  22  using solder on solder pads  22 . Fences  26  are formed from metal. Other types of materials may be used to form fences if desired. Fences  26  have openings  28 . Openings  28  overlap components  20  and have shapes and sizes that are configured to expose upper surfaces  48  of components  20 . 
     Thermally conductive elastomeric pads  30 , which may sometimes be referred to as gap-filling pads or gap pads, have shapes such as rectangular shapes that are configured to be received within openings  28 . Elastomeric pads  30  are formed from elastomeric polymer material filled with thermally conductive material such as metal particles. During operation of device  10 , thermally conductive pads  30  are compressed between upper surfaces  48  of components  20  and the lower surface of structures  36 . Structures  36  are formed from metal and are therefore thermally and electrically conductive. With one illustrative configuration, structures  36  are formed from aluminum. Examples of other materials that may be used in forming structures  36  include stainless steel and carbon-fiber composites or other fiber-based composites. 
     Conductive structures such as conductive gaskets  32  are used to couple fences  26  to metal structure  36 . Conductive gaskets  32  have shapes that are configured to match the outlines of fences  26 . Conductive gaskets  32  may, as an example, have rectangular ring shapes with outlines that match the rectangular outlines of fences  26  and openings  34  that match the shape of gap pads  30  and openings  28 . Examples of materials that may be used in forming conductive gaskets  26  include compressible materials such as conductive foam, conductive adhesive, and conductive fabric (e.g., fabric formed from thin metal wires and/or plastic wires coated with metal). 
     Because metal structures  36  are sufficiently thermally conductive to spread and help dissipate heat, metal structures  36  may sometimes be referred to as metal heat spreader structures, metal thermal management structures, or metal heat sink structures. Metal structures  36  can be configured to mate with structures  16  so that structures  36  and  16  form some or all of a metal housing for device  10  (i.e., so that structures  36  and  16  form housing  12  of  FIG. 1 ). If desired, optional housing structure  38  can be configured to mate with structures  16 . Optional housing structures  38  may be formed from plastic, metal, or other materials and may have a shape that covers metal structure  36 . In configurations in which housing structures  38  and structure  16  form housing  12  in this way, housing structures  38  can be provided with a recess or other shape that receives heat spreader  36 . 
     When assembled to form device  10 , electromagnetic shielding functions are provided by the metal of fences  26 , conductive gasket structures  32 , and the metal of structures  36 . Ground plane metal (e.g., ground traces) in substrate  18  and/or metal in housing portion  16  may also be used in forming electromagnetic shielding functions. Thermal conduction is provided by gap pads  30  and metal structure  36 . Metal structure  36  therefor serves both as an electromagnetic shielding structure that prevents interference from disruption device operation and as a heat sink that dissipates heat from underlying components  20 . 
     A cross-sectional view of device  10  of  FIG. 2  taken along line  40  and viewed in direction  42  is shown in  FIG. 3 . As shown in  FIG. 3 , vertically extending leg portions  24  of fence  26  are soldered to metal solder pads  54  on substrate  18  using solder  56 . Electrical component  20  (e.g., an integrated circuit) is soldered to metal solder pads  22  on substrate  18  using solder  50 . 
     Metal structure  36  of  FIG. 3  is formed from aluminum and has a thin insulating coating. Coating  36 C in the  FIG. 3  example is formed from aluminum oxide. Other insulating coatings may be formed on metal structure  36  and metal structure  36  may be formed from materials other than aluminum, if desired. 
     To ensure that metal structure  36  is electrically connected to gasket  32  and fence  26  (and, if desired, to internal metal traces such as metal ground traces  60  in substrate  18 ), insulating coating  36 C is removed (e.g., by laser etching or other suitable removal techniques) from regions  52  on the underside of metal structure  36 . Because regions  52  are free of insulating material (i.e., because regions  52  are associated with exposed metal), conductive gasket  32  electrically shorts fence  26  to metal structures  36 . This allows metal structures  36  (in combination with fence  26  and, if desired, traces  60 ) to form an electromagnetic interference shield for component  20 . 
     Gap filler pad  30  is compressed between upper surface  48  of component  20  and the opposing lower surface of metal structure  36 . This provides a thermal path between component  20  and structure  36 . Gap pad  30  has a relatively high thermal conductivity. The high thermal conductivity of gap pad  30  (e.g., 0.3 W/mK or more, 1 W/mK or more, or 2.5 W/mK or more) allows heat to flow from component  20  to structure  36  in vertical dimension Z and to spread laterally outward in the X-Y plane of  FIG. 3 , as illustrated by lines  58 . Lines  62  show how the heat that has been spread throughout structure  36  in this way dissipates outwards into the surrounding environment. Structure  36  therefore serves not only as an electromagnetic interference shield for component  20 , but also serves as a heat sinking structure for component  20 . The configuration used for the metal structures of  FIG. 3  therefore integrates thermal management features and electromagnetic shielding. 
     If desired, housing  12  may be formed from structures that are separate from metal structure  36 . This type of configuration is shown in  FIG. 4 . As shown in  FIG. 4 , multiple components  20  may be mounted on substrate  18 . Housing  12  of  FIG. 4  includes upper structure  38  and lower structure  16 . Upper structure  38  and lower structure  16  are formed from a material such as metal, plastic, or fiber-based composite material (as examples). Metal structure  36  overlaps one or more components  20 . Upper housing structure  38  serves as a cover that overlaps and covers the upper surface of metal structure  36 . Upper housing structure  38  of  FIG. 4  also have sidewalls that cover the edges of device  10  and that mate with the peripheral edges of lower housing structure  16 . 
     In the illustrative configuration of  FIG. 5 , housing  12  is formed from metal structure  36  and structure  16 . Metal structure  36  has sidewall portions  36 W that serve as housing sidewalls. Metal structure  36  mates with housing structure  16  along the lower edges of sidewalls  36 W. Because no separate housing structure is used to cover the exposed upper surface of metal structure  36  in the configuration of  FIG. 5 , heat  62  may be radiated directly into the surrounding environment from metal structure  36  without passing through intermediate housing structures. 
       FIG. 6  is an exploded rear perspective view of device  10  (with lower housing portion  16  removed) in a configuration in which screws  90  are used to attach substrate  18  to device  10 . Substrate  18  has screw holes  92  through which the shafts of screws  90  pass. Screws  96  are used to attach metal structure  36  to housing structure  38 . Screws  96  have threaded holes  94  that are configured to receive the threaded shafts of screws  90 . Portions  36 C of metal structure  36  are coated with an insulating coating such as aluminum oxide, but portions  52  are free of insulating coating. When substrate  18  is screwed into place on metal structure  52 , gasket structures  32  are compressed against bare metal portion  52  of metal structure  36 . Housing  38  of  FIG. 6  contains components  98  in addition to the components that are covered with metal structure  36 . 
     If desired, metal structure  36  may be mounted directly to substrate  18 . This type of configuration is shown in  FIG. 7 . As shown in  FIG. 7 , metal structure  36  has one or more recesses (cavities) such as recess  100  that are configured to receive components such as component  20 . Thermally conductive gap filler pad  30  is coupled between component  20  and the inner surface of recess  100  to transfer heat from component  20  to metal structure  36  during operation. 
     Portions  36 V of metal structure  36  form sidewalls that help enclose and electromagnetically shield component  20 . To electrically couple metal structure  36  to metal traces in substrate  18  such as metal trace (solder pad)  102  and internal traces  60  (e.g., ground traces), conductive structures  104  are coupled between metal structures  36  (i.e., portions  36 V) and traces  102 . Conductive structures  104  may be formed from conductive adhesive, conductive fabric (e.g., metal wool or plastic fibers covered with metal), conductive foam, conductive elastomeric material, other compressible conductive materials, solder, welds, metal springs, or combinations of these structures. Metal structure  36  is formed from a metal such as aluminum and is covered with an insulating coating such as aluminum oxide. Portion  52  of metal structure  36  is free of aluminum to allow metal structure  36  to be electrically shorted to metal traces such as metal trace  102  through conductive structures  104 . 
       FIG. 8  is a cross-sectional side view of device  10  in a configuration of the type shown in  FIG. 7  where metal structure  36  contacts protruding portions  108  of fence  26 . Component  20  may protrude into a recess in the lower portion of metal structure  36  or may lie flush with the lower surface of metal structure  36 . A thermally conductive gap filler pad (see, e.g., pad  30  of  FIG. 2 ) is interposed between component  20  and metal structure  36  to enhance thermal conductivity. Metal protrusions  108  (e.g., metal spring structures) may be located no more than a quarter of a wavelength apart at radio-frequency operating frequencies of interest, to ensure that fence  26  and metal structure  36  provide satisfactorily shielding for electromagnetic interference. If desired, protrusions  108  may be supplemented by or replaced by conductive structures such as conductive adhesive, conductive fabric, conductive foam, conductive elastomeric material, other compressible conductive materials, solder, welds, or combinations of these materials. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20120920
Publication Date: 20150602
Grant Date: 20150602
Priority Date: 20120920
Inventors: DOLCI DOMINIC E.
SMEENGE JAMES G.
DIEP VINH H.
GOH CHIEW-SIANG
Assignee: APPLE INC
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Family ID: 48916187