PATENT DOCUMENT

Publication Number: US-9739929-B2
Application Number: US-201314132346-A
Country: US
Kind Code: B2

Title: Electronic device with light-emitting diode array

Abstract:
Electronic devices may be provided with displays. A display may have a light guide plate. Backlight for the display may be launched into the light guide plate from an array of light-emitting diodes. The light-emitting diodes may be mounted on a metal core printed circuit board having a dielectric layer and a metal layer. The metal core printed circuit board may have an elongated shape that extends along the surface of a metal structure. A weld may be formed along a seam between the metal layer of the metal core printed circuit board and the metal structure. The metal structure may be an electronic device housing, a display chassis member, a heat spreader, a heat pipe, or other structures in an electronic device.

Claims:
What is claimed is: 
     
       1. Apparatus, comprising:
 a metal core printed circuit board having a dielectric layer on a metal layer; 
 a light-emitting diode mounted to the dielectric layer; 
 a metal structure welded to the metal layer; and 
 a display backlight, wherein the display backlight includes a light guide plate into which light is emitted from the light-emitting diode. 
 
     
     
       2. The apparatus defined in  claim 1  wherein the metal structure comprises an electronic device housing. 
     
     
       3. The apparatus defined in  claim 2  wherein the electronic device housing is formed from aluminum, and wherein the metal layer is an aluminum layer. 
     
     
       4. The apparatus defined in  claim 3  wherein the electronic device housing comprises a housing selected from the group consisting of: a laptop computer housing, a computer monitor housing, and a television housing. 
     
     
       5. The apparatus defined in  claim 1  wherein the metal structure comprises a display chassis. 
     
     
       6. The apparatus defined in  claim 5  wherein the display chassis and the metal layer are formed from a common metal. 
     
     
       7. The apparatus defined in  claim 1  wherein the metal structure comprises a copper heat spreader, and wherein the apparatus further comprises an electronic device housing to which the copper heat spreader is mounted. 
     
     
       8. The apparatus defined in  claim 1  wherein the metal structure comprises a heat pipe. 
     
     
       9. The apparatus defined in  claim 8  wherein the light-emitting diode comprises one of a plurality of light-emitting diodes arranged in an array along the heat pipe. 
     
     
       10. The apparatus defined in  claim 1  wherein the light-emitting diode comprises one of a plurality of light-emitting diodes arranged in an array. 
     
     
       11. The apparatus defined in  claim 1  wherein the metal structure comprises a display chassis, and wherein the display chassis is welded to the metal layer. 
     
     
       12. An electronic device, comprising:
 a metal housing; 
 a metal core printed circuit board having a dielectric layer on a metal layer; 
 an array of light-emitting diodes mounted on the dielectric layer, wherein the metal layer is welded to the metal housing; and 
 a display backlight, wherein the display backlight has a light guide plate into which light from the array of light-emitting diodes is launched. 
 
     
     
       13. The electronic device defined in  claim 12  wherein the light-emitting diodes comprise surface-emitting light-emitting diodes and wherein the metal layer comprises an elongated metal strip that is welded to the metal housing along a seam between the elongated metal strip and the metal housing. 
     
     
       14. The electronic device defined in  claim 13  wherein the metal housing comprises aluminum and wherein the metal strip comprises aluminum. 
     
     
       15. The electronic device defined in  claim 12 , wherein the metal housing forms at least a portion of an exterior of the electronic device. 
     
     
       16. Apparatus, comprising:
 an elongated metal core printed circuit board having a dielectric layer on a metal layer, wherein the dielectric layer includes metal traces used for routing signals that are separate from the metal layer; 
 an array of light-emitting diodes extending along the elongated metal core printed circuit board and soldered to contacts on the dielectric layer; and 
 a metal structure attached to the metal layer with a weld along a seam between the metal layer and the metal structure. 
 
     
     
       17. The apparatus defined in  claim 16  further comprising a display, wherein the display has a transparent light guide plate with an edge surface and wherein the array of light-emitting diodes emit light into the edge surface of the light guide plate. 
     
     
       18. The apparatus defined in  claim 17  wherein the metal structure comprises a metal display chassis in the display. 
     
     
       19. The apparatus defined in  claim 17  wherein the metal structure comprises an electronic device housing.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to electronic devices with light-emitting diode arrays. 
     Electronic devices often include light-emitting diodes. For example, cellular telephones, computers, and televisions have displays that are backlit using light-emitting diodes. A typical backlight includes light-emitting diodes that launch light into the edge of a rectangular light guide plate. Scattered light from the light guide plate serves as backlight for the display. 
     It can be challenging to provide sufficient backlight illumination in a display. For example, in large displays, backlight requirements scale with increasing area, whereas the space available for light-emitting diodes along the edges of a light guide plate tends to scale only with the edge length of the light guide plate. There may therefore be a need to closely space light-emitting diodes, leading to heat buildup during operation. 
     Light-emitting diode lifetimes can be significantly affected by changes in operating temperature. High temperatures can degrade performance rapidly. For example, an operating temperature increase of 20° C. may reduce light-emitting diode lifetime by a factor of two or more. 
     It would therefore be desirable to be able to provide an electronic device with improved light-emitting diode heat sinking capabilities. 
     SUMMARY 
     An electronic device may have light-emitting diodes. The light-emitting diodes may be mounted to a metal core printed circuit board that is attached to a metal structure using a weld. The electronic device may have a display. The display may have a backlight. The backlight may illuminate an array of display pixels in the display. The backlight may have a light guide plate that distributes light across the display. The light guide plate may be formed form a rectangular plastic member having an edge surface. Backlight for the display may be launched into the edge surface of the light guide plate from the light-emitting diodes. 
     The light-emitting diodes may be mounted in an array on the metal core printed circuit board. The metal core printed circuit board has a dielectric layer and a metal layer. The metal core printed circuit board may have an elongated shape that extends along the surface of the metal structure. A weld may be formed along a seam between the metal layer of the metal core printed circuit board and the metal structure. The metal structure may be an electronic device housing, a display chassis member, a heat spreader, a heat pipe, or other structures in an electronic device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a display for a computer or television in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative display illuminated with light-emitting diodes in accordance with an embodiment. 
         FIG. 6  is a cross-sectional side view of a light-emitting diode mounted to a metal core printed circuit board in accordance with an embodiment. 
         FIG. 7  is a perspective view of an illustrative light-emitting diode array mounted to a metal core printed circuit board that is welded to a metal structure such as an electronic device housing or a display chassis in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative light-emitting diode array mounted to a metal core printed circuit board that is welded to an electronic device housing in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of an illustrative light-emitting diode array that is mounted to a metal core printed circuit board that is welded to a metal chassis structure in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of an illustrative light-emitting diode array that is mounted to a metal core printed circuit board that is soldered to a metal structure such as a heat spreader that is mounted to an electronic device housing in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of an illustrative heat pipe to which a metal core printed circuit board carrying a light-emitting diode has been welded in accordance with an embodiment. 
         FIG. 12  is a cross-sectional side view of an illustrative heat pipe to which a metal core printed circuit board with an array of light-emitting diodes has been mounted in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with light-emitting diodes. An electronic device may have a display with a backlight. The backlight may include one or more arrays of the light-emitting diodes. 
     The light-emitting diodes in a backlight for a display may launch light into one or more edges of a light guide plate. The light guide plate may laterally distribute the light across the display. Light that is scattered outwards from the light guide plate may serve as backlight for the display. 
     Illustrative electronic devices that may be provided with displays having arrays of light-emitting diodes that provide light for a display backlight are shown in  FIGS. 1, 2, 3, and 4 . 
     Electronic device  10  of  FIG. 1  has the shape of a laptop computer and has upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  has hinge structures  20  (sometimes referred to as a clutch barrel) to allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  is mounted in housing  12 A. Upper housing  12 A, which may sometimes be referred to as a display housing or lid, is placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows an illustrative configuration for electronic device  10  based on a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  has opposing front and rear surfaces. Display  14  is mounted on a front face of housing  12 . Display  14  may have an exterior layer that includes openings for components such as button  26  and speaker port  28 . 
     In the example of  FIG. 3 , electronic device  10  is a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  has opposing planar front and rear surfaces. Display  14  is mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  has an opening to accommodate button  26 . 
       FIG. 4  shows an illustrative configuration for electronic device  10  in which device  10  is a computer monitor (display), a computer that has an integrated computer display, or a television. Display  14  is mounted on a front face of housing  12  (i.e., a computer monitor housing, a computer housing, a television housing, etc.). With this type of arrangement, housing  12  for device  10  may be mounted on a wall or may have an optional structure such as support stand  30  to support device  10  on a flat surface such as a tabletop or desk. 
     Display  14  may be a liquid crystal display, an electrophoretic display, an electrowetting display, a display using other types of display technology, or a display that includes display structures formed using more than one of these display technologies. Display  14  may have light-emitting diodes for producing backlight. Light-emitting diodes may also be used as status indicators, camera flash elements, or as other components in device  10 . Illustrative configurations for device  10  in which light-emitting diodes are used for producing backlight in a backlight liquid crystal display are sometimes described herein as an example. 
     A cross-sectional side view of an illustrative configuration for display  14  of device  10  (e.g., a liquid crystal display for the devices of  FIG. 1 ,  FIG. 2 ,  FIG. 3 ,  FIG. 4  or other suitable electronic devices) is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  may include backlight structures such as backlight structures  42  for producing backlight  44 . During operation, backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 5 ) and travels away from backlight  42  through display pixels  90  in display layers  46 . This illuminates any images that are being produced by the display pixels for viewing by a user. For example, backlight  44  may illuminate images on display layers  46  that are being viewed by viewer  48  in direction  50 . 
     Display layers  46  may be mounted in chassis structures such as a plastic display chassis structure and/or a metal display chassis structure to form a display module for mounting in housing  12  or display layers  46  may be mounted directly in housing  12  (e.g., by stacking display layers  46  into a recessed portion in housing  12 ). 
     Display layers  46  may include a liquid crystal layer. The liquid crystal layer may be sandwiched between display layers such as a color filter layer and a thin-film transistor layer. The color filter layer, liquid crystal layer, and the thin-film transistor layer may be sandwiched between a lower (innermost) polarizer layer and an upper (outermost) polarizer layer. 
     The color filter layer and thin-film transistor layer may be formed from transparent substrate layers such as clear layers of glass or plastic. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates (e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into display layers  46 . 
     During operation of display  14  in device  10 , control circuitry (e.g., one or more integrated circuits on a printed circuit) may be used to generate information to be displayed on display  14  (e.g., display data). The information to be displayed may be conveyed to display driver circuitry. The display driver circuitry may display corresponding images on an array of display pixels  90 . Backlight  44  may pass through display pixels  90  to illuminate display  14 . 
     Backlight structures  42  may include a light guide plate such as light guide plate  78 . Light guide plate  78  may be formed from a transparent material such as clear glass or plastic. During operation of backlight structures  42 , a light source such as light source  72  may generate light  74 . Light source  72  may be, for example, an array of light-emitting diodes. 
     Light  74  from light sources such as light source  72  may be coupled into one or more edges of light guide plate  78 . In the example of  FIG. 5 , light  74  is coupled into the left-hand edge of rectangular light guide plate  78 . If desired, light  74  may be coupled into a pair of opposing edges of a rectangular light guide plate from a pair of light sources  72  or may be coupled into all four edges of a rectangular light guide plate using four respective light sources. The example of  FIG. 5  is merely illustrative. 
     As shown in  FIG. 5 , light  74  may be coupled into the interior of light guide plate  78  through edge surface  76  of light guide plate  78 . Once inside of light guide plate, light  74  may be distributed laterally in dimensions X and Y throughout light guide plate  78  due to the principal of total internal reflection. Light guide plate  78  may include light-scattering features such as pits or bumps. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide plate  78 . 
     Light  74  that scatters upwards in direction Z from light guide plate  78  may serve as backlight  44  for display  14 . Light  74  that scatters downwards may be reflected back in the upwards direction by reflector  80 . Reflector  80  may be formed from a reflective material such as a layer of white plastic or other shiny materials. 
     To enhance backlight performance for backlight structures  42 , backlight structures  42  may include optical films  70 . Optical films  70  may include diffuser layers for helping to homogenize backlight  44  and thereby reduce hotspots, compensation films for enhancing off-axis viewing, and brightness enhancement films (also sometimes referred to as turning films) for collimating backlight  44 . Optical films  70  may overlap the other structures in backlight unit  42  such as light guide plate  78  and reflector  80 . For example, if light guide plate  78  has a rectangular footprint in the X-Y plane of  FIG. 5 , optical films  70  and reflector  80  may have a matching rectangular footprint. 
     Light-emitting diodes  72  may be mounted on metal core printed circuit boards such as metal core printed circuit board  100  of  FIG. 6 . As shown in  FIG. 6 , metal core printed circuit board  100  may have a metal layer such as metal layer  102 . Metal layer  102  may be formed from a metal such as aluminum or copper. Dielectric  104  may be formed on metal layer  102 . Dielectric layer  104  may include metal traces such as metal traces  108  and multiple sublayers  106 . Metal traces  108  may include horizontal metal traces extending horizontally across layers  106 , surface traces for forming contacts, and vertical via structures running vertically through layers  106 . Metal traces  108  may be formed form a metal such as copper (as an example). The metal traces in dielectric layer  104  may be used for routing signals within metal core printed circuit board  100  (e.g., power signals for powering light-emitting diodes such as diode  72 ). 
     The dielectric material that forms dielectric layer  104  preferably has a high thermal conductivity to help conduct heat away from light emitting diodes  72 . For example, the dielectric material that forms dielectric layer  104  may be a polymer that is filled with a filler having a high thermal conductivity. The filler may be, as an example, particles of boron nitride, aluminum oxide, or aluminum nitride or other particles that have high thermal conductivity and that can be embedded within the polymer to enhance the thermal conductivity of dielectric layer  104 . 
     Light-emitting diodes such as light-emitting diode  72  may have contacts such as contacts  112 . Contacts  112  may be soldered to contacts such as traces  108  of  FIG. 6  on metal core printed circuit board  100 . For example, solder  110  may be used in soldering an array of light-emitting diodes  72  to metal core printed circuit board  100 . Printed circuit  100  may have an elongated shape that extends into the page of  FIG. 6  and an array of light-emitting diodes  72  on printed circuit  100  may likewise extend into the page of  FIG. 6 . 
     The presence of metal layer  102  (i.e., a metal core) in metal core printed circuit board  100  helps conduct heat away from light-emitting diode  72  during operation. To effectively conduct heat away from metal layer  102 , metal layer is preferably thermally coupled to metal structures in device  10  such as housing  12 , internal frame or chassis structures, a heat pipe, a heat sink, or other thermally conductive structures. Thermal coupling may be accomplished using thermal compound, thermally conductive adhesive, screws or other mechanical fasteners, solder, or welds. An advantage of using welds is that welds are mechanically stable and exhibit superior thermal conductivity compared to other coupling mechanisms. 
     Welds may be formed using laser welding equipment or other suitable welding tools. An illustrative welding arrangement is shown in  FIG. 7 . As shown in  FIG. 7 , light-emitting diodes  72  may be soldered to metal core printed circuit board  100 . Metal core printed circuit board  100  may have an elongated shape supporting an array of light-emitting diodes  72  that extend along the length of metal core printed circuit board  100 . In this type of configuration, metal layer  102  is an elongated metal layer (i.e., an elongated metal strip having a width in dimension Z of 0.2 to 4 mm or other suitable width, a thickness in dimension Y of 0.02 to 2 mm or other suitable thickness, and a length in dimension X of 2 to 3000 cm or other suitable length) and dielectric layer  104  is a correspondingly elongated dielectric layer. Light-emitting diodes in display  14  may be edge-emitting diodes or surface-emitting diodes. In the example of  FIG. 7 , light-emitting diodes  72  are surface-emitting light-emitting diodes that emit light horizontally along the X-axis of  FIG. 7 . 
     Laser welding tool  128  may have a computer-controlled positioner such as positioner  122  that controls the position of laser  118 . Laser  118  may be a visible laser, an infrared laser, a gas laser, a solid state laser, a diode laser, a pulsed laser, a continuous wave laser, or other suitable laser. With one suitable arrangement, laser  118  is a Nd:YAG (neodymium-doped yttrium aluminum garnet) laser operating at a wavelength of 1064 nm with a power of about 400-600 W. During operation, positioner  122  may move laser  118  so that laser beam  120  runs along seam  124  between metal layer  102  and metal structure  114  in direction  126  (i.e., a direction parallel to the longitudinal axis of elongated metal core printed circuit board  100 ), thereby creating weld  116  along the seam between layer  102  and structure  114 . Focusing optics may be used to focus beam  120  to a spot size of about 40 to 100 microns. Application of laser light  120  to the seam between metal layer  102  and metal structure  114  welds the metal core of metal core printed circuit board  100  to metal structure  114 , forming a welded seam that is characterized by good mechanical strength and high thermal conductivity. 
     To form satisfactory welds  116 , it may be desirable to weld structures together that are formed from identical metals. For example, if metal layer  102  is formed from aluminum, it may be desirable to weld layer  102  to a metal structure  114  that is also formed from aluminum. If metal layer  102  is formed from copper, welds  116  can be formed to weld layer  102  to a copper metal structure  114 . Other welding arrangements may be used if desired (e.g., other arrangements in which metal layer  102  and metal structure  114  are formed from the same metal). 
     Metal structure  114  may be a structure such as electronic device housing (case)  12 , an internal frame or chassis structure such as a metal display chassis (sometimes referred to as an m-chassis), a heat pipe, a heat sink, a metal structure such as a housing, chassis, heat spreader, or heat pipe having integral heat sink fins or other structures to enhance heat dissipation, or other thermally conductive structures. 
     In the illustrative configuration of  FIG. 8 , an array of light-emitting diodes  72  (i.e., an array extending into the page of  FIG. 8 ) is shown that has been mounted on a metal core printed circuit board  100  that is welded to housing  12  using welds  116 . Light  74  is launched horizontally into edge  76  of light guide plate  78 . In this configuration, metal housing  12  serves as metal structure  114  of  FIG. 7 . Housing  12  may be a laptop computer housing, a computer monitor housing, a display housing for a display that includes and integrated computer, a television housing, or other electronic device housing. 
     Components  130  may be mounted within housing  12  (e.g., components  130  may be mounted under light guide plate  78 ). Components  130  may include batteries, printed circuit boards, integrated circuits, switches, sensors, input-output devices, etc. 
     It may be desirable to form housing  12  from a material such as aluminum that can form an aesthetically pleasing enclosure for device  10 . It may also be desirable to form metal layer  102  from aluminum, because aluminum may serve as an effective thermal conductor for metal core printed circuit board  100 . When aluminum is used to form both layer  102  and housing  12 , welds  116  may be effectively formed to weld layer  102  to housing  12 . During operation of light-emitting diodes  72 , heat is conducted to housing  12 . The size and surface area of housing  12  helps draw heat away from light-emitting diodes  72 . In this way, housing  12  can serve as a heat sink that dissipates heat and cools light-emitting diodes  72 . 
     In the illustrative configuration of  FIG. 9 , light-emitting diodes  72  are edge-emitting light-emitting diodes that extend in an array into the page of  FIG. 9 . Edge-emitting light-emitting diodes on a metal core printed circuit board may be mounted on a metal housing structure, a metal display chassis, or other metal structures. In the example of  FIG. 9 , metal core printed circuit board  100  is mounted on recessed portion  132  of metal display chassis structure  134  (i.e., metal chassis structure  134  serve as metal structure  114  of  FIG. 7 ). Laser welding or other welding techniques may be used to form a weld such as weld  116  that runs along the seam between metal layer  102  and portion  132  of metal chassis  134 . 
       FIG. 10  shows an illustrative arrangement for device  10  in which metal layer  102  of metal core printed circuit board  100  has been attached to internal metal structure  138  (i.e., metal structure  114  of  FIG. 7 ). Metal layer  102  and metal structure  138  may be formed form a material such as copper or other suitable metal. Solder  136  or other coupling structures (e.g., welds, screws, thermally conductive adhesive, etc.) may be used in mounting layer  102  to structure  138 . Metal core printed circuit board  100  may be an elongated structure that runs along a longitudinal axis that extends into the page of  FIG. 10 . 
     Structures  138  may serve as a heat sink or heat spreader that helps draw heat away from light-emitting diodes  72 . As shown in the illustrative configuration of  FIG. 10 , structure  138  may be attached to housing  12  (e.g., an aluminum electronic device housing for device  10 ) using welds  140  or other suitable coupling mechanisms (solder, thermally conductive adhesive, screws, etc.). With an arrangement of the type shown in  FIG. 10 , heat may be efficiently drawn away from diodes  72  by using a high conductivity material such as copper for layer  102 . Compatibility between layers  102  and  138  to facilitate coupling (e.g., welding) of layers  102  and  138  together may be achieved by forming structure  138  from the same material as layer  102  (e.g., by forming structure  138  from copper in this example). A metal such as aluminum or other suitable material may be used for forming housing  12 . Housing  12  may be coupled to heat spreader  138  using connections  140 , thereby allowing housing  12  to help draw away heat from diodes  72 . 
     Heat pipes may be used in conducting heat away from light-emitting diodes  72 . This type of configuration is shown in  FIG. 11 . As shown in  FIG. 11 , an array of light-emitting diodes  72  may be mounted on metal core printed circuit  100 . Metal core printed circuit board  100  may have an elongated shape running along a longitudinal axis that extends into the page of  FIG. 11 . The array of light-emitting diodes on printed circuit  100  may likewise extend into the page of  FIG. 11 . 
     Heat pipe  142  of  FIG. 11  may have a metal wall such as wall  144  that surrounds an inner cavity  146 . Fluid in inner cavity  146  may facilitate heat transfer by pipe  142  in direction  150  from light-emitting diode  72  to heat sink  148 . Metal layer  102  of metal core printed circuit board  100  and optional heat sink structure  148  may be attached to heat pipe  142  using welds, solder, fasteners, thermal compound, thermally conductive adhesive, etc. Heat pipe  142  may have the shape of a plate, a series of wound coils, or other suitable shape. 
     In the example of  FIG. 11 , heat sink  148  has fins for dissipating heat. If desired, the metal structure to which metal layer  102  is attached may be provided with integral fins. For example, heat pipe  142  may be provided with integral fins, metal housing  12  may be provided with integral heat sink fins, integral heat sink fins may be formed in a heat spreader, in a metal display chassis, or other metal structures  114  may be provided with integral heat sink structures such as fins. 
     If desired, heat pipe  142  may be used to help equalize the operation temperature of diodes  72  in an array of light-emitting diodes. As shown in  FIG. 12 , for example, metal layer  102  of metal core printed circuit board  100  may be welded or otherwise attached to metal wall  144  of heat pipe  142 . Heat pipe  142  may be welded to housing  12  or other metal structure in device  10  or may be otherwise mounted in device  10 . During operation of light-emitting diodes  72 , heat is distributed laterally along the X-axis of  FIG. 12 . This helps ensure that all of diodes  72  are operating at substantially similar temperatures. In the absence of heat pipe  142 , central diode  72 M may become hotter than end diodes  72 E, because end diodes  72 E are not surrounded on both sides by adjacent heat-producing diodes. When heat pipe  142  is used, however, heat is distributed evenly along the length of heat pipe  142  and metal layer  104 , so that diodes  72  such as diodes  72 E and  72 M are maintained at the same operating temperature. Premature aging of a subset of diodes  72  such as diodes  72 M is thereby avoided. 
     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: 20131218
Publication Date: 20170822
Grant Date: 20170822
Priority Date: 20131218
Inventors: GARELLI ADAM T.
BOITNOTT CHRISTOPHER L.
MATHEW DINESH C.
QI JUN
RUNDLE NICHOLAS A.
YIN VICTOR H.
GUPTA NATHAN K.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/0073", "inventive": false, "first": false, "tree": "[]"}, {"code": "F21K9/61", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": false, "first": false, "tree": "[]"}, {"code": "F21Y2115/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0083", "inventive": true, "first": true, "tree": "[]"}, {"code": "F21Y2115/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0073", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": false, "first": false, "tree": "[]"}, {"code": "F21K9/61", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0083", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 53367931