PATENT DOCUMENT

Publication Number: US-8913390-B2
Application Number: US-201213536890-A
Country: US
Kind Code: B2

Title: Thermally conductive printed circuit board bumpers

Abstract:
An electronic device may have electrical components that generate heat. The components may be mounted on a printed circuit board having a peripheral edge with an edge surface. The edge surface may be coated with a layer of metal. Metal traces in the printed circuit board such as ground plane traces may be used to conduct heat from the electrical components to the layer of metal on the edge surface. The edge surface may be separated from an adjacent thermally conductive electronic device housing structure by an air gap. Thermally conductive elastomeric bumper structures may bridge the air gap between the edge surface of the printed circuit and the housing structure. The thermally conductive elastomeric bumper structures may conduct heat from the layer of metal on the edge surface to the housing structure and may serve as a cushioning interface between the printed circuit and the housing structure.

Claims:
What is claimed is: 
     
       1. Apparatus, comprising:
 an electrical component; 
 a printed circuit board to which the electrical component is mounted; 
 a thermally conductive electronic device housing structure; and 
 thermally conductive elastomeric structures interposed between the printed circuit board and the thermally conductive electronic device housing structure to conduct heat from the electrical component to the thermally conductive electronic device housing structure, wherein the printed circuit board has an edge and wherein the thermally conductive elastomeric structures are interposed between the edge and the thermally conductive electronic device housing structure. 
 
     
     
       2. The apparatus defined in  claim 1  further comprising a metal coating on the edge of the printed circuit board. 
     
     
       3. The apparatus defined in  claim 2  wherein the thermally conductive electronic device housing structure comprises a metal housing wall. 
     
     
       4. The apparatus defined in  claim 3  wherein the thermally conductive elastomeric structures comprise an elastomeric polymer with a thermally conductive additive. 
     
     
       5. The apparatus defined in  claim 4  wherein the elastomeric polymer comprises silicone. 
     
     
       6. The apparatus defined in  claim 4  wherein the elastomeric polymer has a Shore A hardness of less than 60. 
     
     
       7. The apparatus defined in  claim 4  wherein the thermally conductive elastomeric structures are configured to exhibit a thermal conductivity of greater than 1 W/mK. 
     
     
       8. The apparatus defined in  claim 1  wherein the printed circuit board has opposing first and second planar surfaces and has a metal trace on the first planar surface and wherein the thermally conductive elastomeric structures conduct heat from the metal trace to the thermally conductive electronic device housing structure. 
     
     
       9. Apparatus, comprising:
 an electrical component; 
 a printed circuit board to which the electrical component is mounted; 
 a thermally conductive electronic device housing structure; and 
 thermally conductive elastomeric structures interposed between the printed circuit board and the thermally conductive electronic device housing structure to conduct heat from the electrical component to the thermally conductive electronic device housing structure, wherein the thermally conductive elastomeric structures comprise at least one elastomeric member with a C-shaped cross section. 
 
     
     
       10. The apparatus defined in  claim 1 , wherein the edge has at least one recess, wherein the edge has an edge surface covered with an edge surface metal layer, and wherein the thermally conductive elastomeric structures are configured to conduct heat from the edge surface metal layer to the thermally conductive housing structure. 
     
     
       11. An electronic device, comprising:
 a printed circuit board that includes metal traces; 
 an integrated circuit mounted on the printed circuit board that generates heat that is conducted to the metal traces; 
 a thermally conductive housing structure; and 
 thermally conductive elastomeric bumper structures that are coupled between the printed circuit board and the thermally conductive housing structure to conduct heat from the metal traces to the thermally conductive housing structure, wherein the thermally conductive housing structure comprises a metal housing wall with an inner surface, wherein the metal traces include ground plane traces, wherein the printed circuit board includes an edge surface coated with a metal layer that contacts at least one of the ground plane traces, and wherein the thermally conductive elastomeric bumper structures contact the metal layer and contact the inner surface of the metal housing wall. 
 
     
     
       12. The electronic device defined in  claim 11  wherein the thermally conductive elastomeric bumper structures comprise an elastomeric member with a C-shaped cross section. 
     
     
       13. The electronic device defined in  claim 11  wherein the thermally conductive elastomeric bumper structures comprise thermally conductive silicone. 
     
     
       14. Apparatus, comprising:
 an integrated circuit that generates heat; 
 a printed circuit to which the integrated circuit is mounted; 
 a metal electronic device housing structure; and 
 a thermally conductive elastomeric member that physically contacts the printed circuit and that physically contacts the metal electronic device housing member, wherein the printed circuit has opposing upper and lower surfaces and has an edge surface that is perpendicular to the upper and lower surfaces, wherein the printed circuit includes metal traces coupled to a metal layer on the edge surface, and wherein the thermally conductive elastomeric member is configured to conduct heat from the metal layer of the edge surface to the metal electronic device housing structure to cool the electrical component. 
 
     
     
       15. Apparatus, comprising:
 an electrical component; 
 a printed circuit board to which the electrical component is mounted; 
 a thermally conductive electronic device housing structure; and 
 thermally conductive elastomeric structures interposed between the printed circuit board and the thermally conductive electronic device housing structure, wherein the thermally conductive elastomeric structures are in contact with more than one surface of the printed circuit board. 
 
     
     
       16. Apparatus, comprising:
 an electrical component; 
 a printed circuit board to which the electrical component is mounted; 
 a thermally conductive electronic device housing structure; and 
 thermally conductive elastomeric structures interposed between the printed circuit board and the thermally conductive electronic device housing structure, wherein the thermally conductive elastomeric structures are in contact with more than one surface of the thermally conductive electronic device housing structure.

Description:
BACKGROUND 
     This relates to electronic devices and, more particularly, to thermal and shock management features for electronic devices. 
     Electronic devices such as cellular telephones and other portable devices are often provided with components such as integrated circuits. During operation of an electronic device, these components may generate heat. A heat sink may be placed on top of a component such as an integrated circuit to help cool the component, but this can add undesirable bulk to a system or may be insufficient to completely cool a component. Printed circuit boards with components may also be subjected to damage during drop events. 
     It would therefore be desirable to be able to provide improved structures for cooling components and for preventing components from being damaged during impact events. 
     SUMMARY 
     An electronic device may have electrical components that generate heat such as integrated circuits. The components may be mounted on a printed circuit board. The printed circuit board may have signal lines formed from one or more layers of metal traces. The metal traces may include ground plane layers. 
     The printed circuit board may have a peripheral edge with an edge surface. The edge surface may be coated with a layer of metal. The metal traces in the printed circuit board such as the ground plane layers may be coupled to the metal layer on the edge surface. As heat is produced by the integrated circuits and other components on the printed circuit board, the ground plane traces and other metal traces may conduct heat from the components to the layer of metal on the edge surface. 
     The edge surface of the printed circuit board may be separated from adjacent thermally conductive electronic device housing structures by an air gap. The thermally conductive electronic device housing structures may include a metal housing wall. 
     Thermally conductive elastomeric bumper structures may be formed between the edge surface of the printed circuit and the housing structures, bridging the air gap. The thermally conductive elastomeric bumper structures may conduct heat from the layer of metal on the edge surface to the housing structures and may serve as a cushioning interface between the printed circuit and the housing structures. 
     Further features of the invention, its 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 front perspective view of an illustrative electronic device of the type that may be provided with thermally conductive bumper structures in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of a printed circuit board panel in accordance with an embodiment of the present invention. 
         FIG. 3  is a cross-sectional side view of a portion of a printed circuit board with edge plating that has been mounted to a housing wall using thermally conductive bumper structures in accordance with an embodiment of the present invention. 
         FIG. 4  is a cross-sectional side view of an illustrative printed circuit board with upper and lower pads that have been coupled to a housing wall using thermally conductive bumper structures in accordance with an embodiment of the present invention. 
         FIG. 5  is a cross-sectional side view of an edge portion of an illustrative printed circuit board coupled to a portion of a housing wall with a ledge in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of an edge portion of an illustrative printed circuit board coupled to a corner portion of a housing wall in accordance with an embodiment of the present invention. 
         FIG. 7  is a top view of a printed circuit coupled to a housing wall using a pair of bumpers that are attached along an edge of the printed circuit in accordance with an embodiment of the present invention. 
         FIG. 8  is a top view of a printed circuit coupled to a housing wall using bumper structures that run around the periphery of the printed circuit in accordance with an embodiment of the present invention. 
         FIG. 9  is an exploded perspective view of an illustrative printed circuit with bumpers in accordance with an embodiment of the present invention. 
         FIG. 10  is a perspective view of a printed circuit mounted within electronic device housing structures using bumper structures in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Components such as integrated circuits and other electrical components can be mounted on substrates such as printed circuit boards. The printed circuit boards may be mounted in electronic device housings. 
     To ensure that the components on a printed circuit are not damaged during a drop event, elastomeric bumper structures may be used to mount a printed circuit within an electronic device housing. 
     Integrated circuits and other electrical components generate heat. To help remove the heat, the bumper structures that are used to mount the printed circuit board to the device housing may be formed from a thermally conductive material. A layer of metal on the edge of the printed circuit board and metal traces such as ground plane traces in the printed circuit board may also be used in dissipating heat. 
     An illustrative electronic device of the type that may be provided with a printed circuit board that is mounted in an electronic device housing using thermally conductive bumper structures is shown in  FIG. 1 . Device  10  of  FIG. 1  may be a handheld device such as a cellular telephone or media player, a tablet computer, a notebook computer, other portable computing equipment, a wearable or miniature device such as a wristwatch or pendant device, a television, a computer monitor, or other electronic equipment. This equipment may include processors, memory, switches, sensors, wireless circuits, and other circuitry. 
     As shown in  FIG. 1 , electronic device  10  may include a display such as display  14 . Display  14  may be a touch screen that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components or may be a display that is not touch-sensitive. Display  14  may include an array of display pixels formed from liquid crystal display (LCD) components, an array of electrophoretic display pixels, an array of electrowetting display pixels, or display pixels based on other display technologies. 
     Display  14  may be protected using a display cover layer such as a layer of transparent glass or clear plastic. Openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button such as button  16  and an opening such as opening  18  may be used to form a speaker port. Device configurations without openings in display  14  may also be used for device  10 . 
     Device  10  may have a housing such as housing  12 . 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 may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     Device  10  may include components such as processor integrated circuits, memory integrated circuits, application-specific integrated circuits, and other integrated circuits and electrical components. These components may be mounted on substrates such as printed circuit boards (e.g., fiberglass-filled epoxy substrates such as FR4 substrates). 
     Printed circuit boards may be formed from panels of printed circuit board substrate material. An illustrative printed circuit board panel is shown in  FIG. 2 . As shown in  FIG. 2 , multiple printed circuit boards  22  may be formed within panel  20 . Printed circuit boards  22  may contain metal traces (sometimes referred to as interconnects). The metal traces may include patterned horizontal signal lines and vias for routing signals between components that are mounted on the printed circuit boards. The metal traces may include ground plane structures (e.g., blanket sections of metal traces that serve as ground). There may be any suitable number of layers of metal in a printed circuit such as printed circuit boards  22  of  FIG. 2 . For example, printed circuit boards  22  may contain two layers of metal, three layers of metal, four layers of metal, or more than four or fewer than four layers of metal. 
     To promote heat transfer through the edges of printed circuits  22 , the edges of printed circuits  22  may be coated with a layer of conductive material such as metal. As an example, grooves such as grooves  24  of  FIG. 2  may be formed by machining or laser cutting of printed circuit board panel  20 . The inner sides of grooves  24  may form vertical edge surfaces for the peripheral edges of printed circuit boards  22 . Electroplating techniques or other metal deposition techniques may be used to coat the peripheral edges of printed circuit boards  22 . Following metal coating of the edges or printed circuit boards  22 , a saw or other cutting tool may be used to singulate boards  22  (e.g., by forming cuts through board  20  such as cut  26  of  FIG. 2 ). 
     A cross-sectional side view of printed circuit board  22  in which edge surface  24  of printed circuit board  22  has been coated with metal layer  26  is shown in  FIG. 3 . As shown in  FIG. 3 , electrical component  28  may be mounted to printed circuit board  22  using solder  32 . Solder  32  may connect electrical paths in component  28  to traces in printed circuit  22  such as solder pads  32 . Solder pads  32  may be connected to other traces in printed circuit board  22  such as traces  34 . Traces  34  may include patterned signal lines, vias, and ground planes (as examples). At one or more peripheral edges of printed circuit  22  such as edge  24 , traces  34  (e.g., ground plane traces) may be coupled to edge metal  26  to promote heat transfer. 
     Bumper structures  38  may have portions such as portions  40  that enclose the edge of printed circuit  22  (e.g., bumper structures  38  may have a C-shaped cross section). Bumper structures  38  may be formed from an elastomeric material such as silicone or other polymers (e.g., a polymer with a Shore A hardness of 70 or less, 60 or less, 50 or less, 65-45, or 45 or less). The use of elastomeric materials in forming bumper structures  38  may allow bumper structures  38  to absorb shocks during impact events in which device  10  is struck against an external object. Bumper structures  38  may, for example, keep edge  24  of printed circuit  22  from contacting the opposing inner surface of housing  12 , thereby preventing printed circuit board  22  from becoming cracked. 
     A thermally conductive additive such as metal particles  36  may be incorporated into the silicone or other elastomeric polymer that is used in forming bumper structures  38 . The thermally conductive additive may ensure that bumper structures  38  exhibit a satisfactory thermal conductivity for helping to transfer heat from component  28  to housing  12  (e.g., a metal housing wall). For example, thermally conductive additives may be incorporated into bumper structures  38  at a level sufficient to cause bumper structures  38  to exhibit a thermal conductivity of greater than 0.5 W/mK, greater than 1 W/mK, greater than 1.5 W/mK, greater than 2 W/mK, greater than 4 W/mK, 1-2 W/mK, 0.5-3 W/mK, greater than 10 W/mK or other suitable amount. 
     During operation, heat from component  28  may be conducted through solder  30 , pads  32 , and traces  34  to edge metal layer  26 . From edge metal  26 , elastomeric thermally conductive bumper structures  38  may conduct the heat to housing  12  along contact surface  42  between bumper structures  38  and housing  12 . Housing  12  may be formed from one or more metal parts or other substances that exhibit a relatively high thermal conductivity (e.g., greater than 200 W/mK, as an example). Housing  12  may also have a relatively large surface area on exterior surface  44  that is exposed to the air surrounding device  10 , allowing housing  12  to effectively serve as a large heat sink. 
     The portion of housing  12  that is contacted by thermally conductive bumper structures  38  may be a housing sidewall, may be part of a rear or front planar housing wall, may be part of an internal frame structure that is coupled to a housing wall, or other suitable housing structures. The housing structures that are contacted by thermally conductive bumper structures  38  may be formed from a thermally conductive material such as metal (e.g., aluminum, stainless steel, copper, or other metals) or other thermally conductive structures (e.g., fiber-based composites, etc.). 
     If desired, thermally conductive bumper structures  38  may be mounted between printed circuit  22  and adjacent upper and lower housing structures using pads on printed circuit  22  such as pads  32 . This type of arrangement is shown in  FIG. 4 . As shown in  FIG. 4 , thermally conductive bumper structures  38  may include upper bumper structures  38 A and lower bumper structures  38 B. Upper bumper structures  38 A may be used to couple pad  32  on the upper surface of printed circuit  22  to an upper housing wall of housing  12 . Lower bumper structures  38 B may be used to couple pad  32  on the lower surface of printed circuit  22  to a lower housing wall of housing  12 . Pads  32  may be coupled to ground plane traces and other traces in printed circuit  22  to facilitate the flow of heat to thermally conductive bumper structures  38 . 
     As shown in the illustrative configuration of  FIG. 5 , printed circuit board  22  may be coupled to housing  12  using thermally conductive bumper structures  38  resting on ledge portion  12 L of housing  12 . This type of arrangement, in which thermally conductive bumper structures  38  contact more than one surface of housing  12 , may help facilitate heat transfer to housing  12  by enhancing the amount of contact surface area between thermally conductive bumper structures  38  and housing  12 . 
     As shown in  FIG. 6 , printed circuit board  22  may be coupled to a corner of housing  12  using thermally conductive bumper structures  38  that simultaneously form a thermal pathway between a surface pad on the upper surface of printed circuit  22  and an inner surface of a planar wall in housing  12  (e.g., an upper or lower housing wall) and between an edge conductor such as edge metal layer  26  and an inner surface of a side wall portion of housing  12 . Thermally conductive bumper structures  38  of  FIG. 6  may have an L-shaped cross section (as shown in  FIG. 6 ) or may have other cross-sectional shapes (e.g., C-shaped cross sections, etc.). The L-shaped cross-sectional shape of  FIG. 6  is merely illustrative. 
       FIG. 7  is a top view of an interior portion of device  10  in an illustrative configuration in which thermally conductive bumper structures  38  have been implemented using two separate bumpers ( 38 - 1  and  38 - 2 ). Bumper structures  38 - 1  and  38 - 2  may each be interposed between edge  24  of printed circuit  22  and inner surface  42  of housing  12 . Bumper structures  38  may bridge air gap  42 , thereby providing a cushioning feature that helps prevent edge  24  from contacting surface  42  during drop events in which device  10  is subjected to sharp impacts. Bumpers such as bumpers  38 - 1  and  38 - 2  may have C-shaped cross sections, L-shaped cross sections, or other suitable cross-sectional shapes. 
     Printed circuit board  22  may have a rectangular periphery as shown in  FIG. 7  (e.g., when viewed along the surface normal of the board as shown in  FIG. 7 ), may have a periphery with one or more curved edges, may have a periphery with straight edges, or may have a periphery with a combination of straight and curved edges. The rectangular footprint for board  22  that is shown in  FIG. 7  is merely illustrative. 
     Thermally conductive bumper members such as bumpers  38 - 1  and  38 - 2  may be located on one edge along the periphery of printed circuit board  22 , along two or more edges of printed circuit board  22 , along three or more peripheral edges of printed circuit board  22 , or along four or more peripheral edges of printed circuit board  22 . Each edge of printed circuit board  22  may, in general, be provided with no bumpers, one or more bumpers, two or more bumpers, three or more bumpers, or other suitable bumper structures. 
     As shown in  FIG. 8 , printed circuit board  22  may have a rectangular periphery. Thermally conductive bumper structures  38  may include a first U-shaped bumper member such as bumper member  38 TR and a second U-shaped bumper member such as bumper member  38 LR. Bumper structures  38 TR and  38 LR may be formed from a rectangular ring-shaped bumper structure that is separated into two segments (members  38 TR and  38 LR) by air gaps  46 . 
       FIG. 9  is an exploded perspective view of a printed circuit and associated bumper structures. As shown in  FIG. 9 , printed circuit board  22  may have an L-shaped footprint. Edge  24  may have recesses such as recesses  48 . Bumper structures  38 - 1  and  38 - 2  may have C-shaped cross-sections that fit over edge metal layers  26  in recesses  48 . 
       FIG. 10  is a perspective view of an interior portion of device  10  showing how an electrical component such as battery  50  may be mounted adjacent to printed circuit board  22 . If desired, other internal components in device  10  may be mounted adjacent to printed circuit board  22 . The configuration of  FIG. 10  is merely illustrative. 
     Printed circuit board  22  may have an L-shaped footprint and thermally conductive bumper structures  38 - 1  and  38 - 2  may have C-shaped cross sections that are received in recesses of the type shown in  FIG. 9 . When assembled into housing  12  as shown in  FIG. 10 , thermally conductive bumper structures  38 - 1  and  38 - 2  may help structurally cushion and isolate printed circuit board  22  from inner wall surface  42  of housing  12 . Thermally conductive bumper structures  38 - 1  and  38 - 2  may also help conduct heat from components  28  to the thermally conductive wall structures of housing  12 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20120628
Publication Date: 20141216
Grant Date: 20141216
Priority Date: 20120628
Inventors: MALEK SHAYAN
WITTENBERG MICHAEL B.
CHRISTOPHY MIGUEL C.
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K7/205", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K7/205", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 49777922