PATENT DOCUMENT

Publication Number: US-9116267-B2
Application Number: US-201313771473-A
Country: US
Kind Code: B2

Title: Backlight structures and assemblies for electronic device displays

Abstract:
Electronic devices may include displays. A display may include backlight components such as a light guide plate that distributes light from a light source across the display. The light source may include a plurality of light-emitting diodes mounted on a printed circuit substrate. A portion of the light guide plate may be attached to the printed circuit substrate using adhesive. The adhesive may be a supported adhesive that includes a lining of reflective material. A reflective coating such as a layer of white coverlay may be formed on the surface of the printed circuit substrate and may be configured to reflect light into the light guide plate. The reflective coating may serve as a solder mask. The printed circuit substrate may be attached to a metal display chassis using adhesive. A shim may be used to raise the height of the light source relative to the printed circuit substrate.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 display layers; 
 a light source configured to provide light; 
 a printed circuit substrate on which the light source is mounted; 
 a light guide plate configured to receive the light and to provide the light to the display layers as backlight illumination, wherein the light guide plate is adhered to the printed circuit substrate using adhesive; and 
 a reflector configured to reflect the light into the light guide plate, wherein the reflector is adhered to the printed circuit substrate using additional adhesive. 
 
     
     
       2. The electronic device defined in  claim 1  further comprising a plastic display chassis configured to receive the display layers, wherein the light guide plate is floating with respect to the plastic display chassis. 
     
     
       3. The electronic device defined in  claim 1  wherein the adhesive comprises a layer of reflective film interposed between first and second layers of optically clear adhesive. 
     
     
       4. The electronic device defined in  claim 1  wherein the adhesive is a supported adhesive that includes a layer of white polymer resin interposed between first and second layers of optically clear adhesive. 
     
     
       5. The electronic device defined in  claim 1  further comprising a metal display chassis that at least partially surrounds the light source, wherein the printed circuit substrate is adhered to metal display chassis. 
     
     
       6. The electronic device defined in  claim 5  wherein the metal display chassis comprises a bent portion that receives the light source, the electronic device further comprising:
 a friction-reducing material formed on a surface of the printed circuit substrate, wherein the friction-reducing material is configured to slide along the metal display chassis as the light source is received by the bent portion of the metal display chassis. 
 
     
     
       7. The electronic device defined in  claim 1  further comprising a layer of reflective coating formed on a surface of the printed circuit substrate, wherein the reflective coating is configured to reflect the light into the light guide plate. 
     
     
       8. A backlight assembly configured to provide backlight illumination for a display, comprising:
 a light guide plate having a surface from which the backlight illumination is provided to the display and having an edge into which light is launched to form the backlight illumination; 
 a printed circuit substrate; 
 a plurality of light-emitting diodes mounted on the printed circuit substrate; and 
 a coating of reflective material on a surface of the printed circuit substrate, wherein the coating of reflective material is configured to reflect the light into the light guide plate and wherein the coating of reflective material comprises white coverlay material. 
 
     
     
       9. A backlight assembly configured to provide backlight illumination for a display, comprising:
 a light guide plate having a surface from which the backlight illumination is provided to the display and having an edge into which light is launched to form the backlight illumination; 
 a printed circuit substrate; 
 a plurality of light-emitting diodes mounted on the printed circuit substrate; and 
 a coating of reflective material on a surface of the printed circuit substrate, wherein the coating of reflective material is configured to reflect the light into the light guide plate, wherein the coating of reflective material comprises a polymer based binder and a reflective additive, and wherein the reflective additive is configured to reflect the light into the light guide plate. 
 
     
     
       10. The backlight assembly defined in  claim 9  wherein the printed circuit substrate comprises a flexible printed circuit substrate. 
     
     
       11. The backlight assembly defined in  claim 9  further comprising a metal display chassis that at least partially surrounds the light source, wherein the printed circuit substrate is attached to the metal display chassis using adhesive. 
     
     
       12. The backlight assembly defined in  claim 9  further comprising a reflector configured to reflect the light into the light guide plate, wherein the light guide plate overlaps the reflector, wherein the reflector has a portion that is interposed between the light guide plate and the printed circuit substrate, and wherein the reflector is attached to the printed circuit substrate using adhesive. 
     
     
       13. A backlight assembly configured to provide backlight illumination for a display, comprising:
 a light guide plate having a surface from which the backlight illumination is provided to the display and having an edge into which light is launched to form the backlight illumination; 
 a printed circuit substrate; 
 a plurality of light-emitting diodes mounted on the printed circuit substrate; and 
 a shim interposed between the plurality of light-emitting diodes and the printed circuit substrate, wherein the shim is configured to raise the height of the plurality of light-emitting diodes relative to the printed circuit substrate. 
 
     
     
       14. The backlight assembly defined in  claim 13  wherein each light-emitting diode in the plurality of light-emitting diodes comprises at least one power supply terminal, wherein the printed circuit substrate comprises at least one solder pad, and wherein the at least one power supply terminal is electrically coupled to the at least one solder pad. 
     
     
       15. The backlight assembly defined in  claim 14  wherein the shim comprises a plurality of openings and wherein at least one opening in the plurality of openings aligns with the at least one power supply terminal and the at least one solder pad. 
     
     
       16. The backlight assembly defined in  claim 15  further comprising solder in the at least one opening, wherein the solder forms an electrical connection between the at least one power supply terminal and the at least one solder pad. 
     
     
       17. The backlight assembly defined in  claim 13  further comprising a reflector configured to reflect the light into the light guide plate, wherein the reflector has a portion adhered to the printed circuit substrate. 
     
     
       18. The backlight assembly defined in  claim 13  wherein a portion of the light guide plate is attached to the printed circuit substrate using adhesive.

Description:
This application claims the benefit of provisional patent application No. 61/707,724, filed Sep. 28, 2012, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, cellular telephones and portable computers often include displays for presenting information to a user. An electronic device may have a housing such as a housing formed from plastic or metal. Components for the electronic device such as display components may be mounted in the housing. 
     It can be challenging to incorporate a display into the housing of an electronic device. Size, weight, electrical grounding, robustness, ease of assembly, and light-tightness are often important considerations in designing electronic devices. If care is not taken, displays may be bulky, may exhibit undesired light reflections, or may be prone to damage during a drop event. The housing of an electronic device can be adjusted to accommodate a bulky display with large borders, but this can lead to undesirable enlargement of the size and weight of the housing and unappealing device aesthetics. 
     It would therefore be desirable to be able to provide improved ways to provide displays for electronic devices. 
     SUMMARY 
     An electronic device may be provided with a display. The display may have display layers for displaying images. Backlight structures may be included in the display. The backlight structures may provide backlight that illuminates the display layers in the display that are displaying an image for a user. 
     Display chassis structures may be used to support display layers and backlight structures. The display chassis structures may include a metal display chassis and a plastic display chassis. 
     A light source may launch light into an edge of a light guide plate in a display. The light source may include light-emitting diodes mounted on a printed circuit substrate. A portion of the light guide plate may be attached to the printed circuit substrate using adhesive. The adhesive may be a supported adhesive that includes a layer of reflective material interposed between first and second layers of optically clear adhesive. 
     The display may include a reflector that overlaps the light guide plate and is configured to reflect light into the light guide plate. The reflector may be adhered to the printed circuit substrate on which the light-emitting diodes are mounted. 
     A reflective coating may be formed on a surface of the flexible printed circuit and may be configured to reflect light into the light guide plate. The reflective coating may include a polymer based binder with a reflective additive such as a reflective pigment or dye. The reflective coating may be a layer of white coverlay that serves as a solder mask for the printed circuit on which light-emitting diodes are mounted. 
     A shim structure may be used to raise the height of light-emitting diodes with respect to the printed circuit substrate. The shim structure may be perforated to accommodate a solder connection between power supply terminals of the light-emitting diodes and solder pads on the printed circuit substrate. 
     The light-emitting diodes and the printed circuit substrate may be mounted within a bent portion of the metal display chassis. A friction-reducing material may be formed on the surface of the printed circuit substrate and may allow the printed circuit substrate to slide along the metal display chassis as the printed circuit substrate is received by the bent portion of the metal display chassis. The friction-reducing material may include a fluorocarbon based material or a low-friction shim structure. 
     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 perspective view of an illustrative electronic device such as a laptop computer with a display in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with a display in accordance with an embodiment of the present invention. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment of the present invention. 
         FIG. 4  is a schematic diagram of an illustrative electronic device with a display in accordance with an embodiment of the present invention. 
         FIG. 5  is a cross-sectional side view of an illustrative display in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of illustrative display layers and backlight structures in accordance with an embodiment of the present invention. 
         FIG. 7  is an exploded perspective view of a light guide plate and corresponding chassis structure in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of illustrative display layers, backlight structures, and chassis structures in accordance with an embodiment of the present invention. 
         FIG. 9  is a cross-sectional side view of an illustrative adhesive that includes a lining of reflective material in accordance with an embodiment of the present invention. 
         FIG. 10  is a cross-sectional side view of an illustrative printed circuit substrate that includes a coating of reflective material in accordance with an embodiment of the present invention. 
         FIG. 11  is a cross-sectional side view of illustrative display layers, backlight structures, and chassis structures in accordance with an embodiment of the present invention. 
         FIG. 12  is an illustrative diagram showing how a friction-reducing material may be formed on a printed circuit substrate and may be used to slide the printed circuit substrate and associated backlight components into a bent portion of a metal display chassis in accordance with an embodiment of the present invention. 
         FIG. 13  is a cross-sectional side view of an illustrative light-emitting diode that is mounted on elongated frame structures in accordance with an embodiment of the present invention. 
         FIG. 14  is a cross-sectional side view of an illustrative light-emitting diode that is mounted on a thickened portion of a printed circuit substrate in accordance with an embodiment of the present invention. 
         FIG. 15  is a cross-sectional side view of an illustrative light-emitting diode that is mounted on a shim in accordance with an embodiment of the present invention. 
         FIG. 16  is an exploded perspective view showing how a shim on which a light-emitting diode is mounted may be provided with openings to accommodate a solder connection between power supply terminals of the light-emitting diode and solder pads on a printed circuit substrate in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images to a user. Illustrative electronic devices that may be provided with displays are shown in  FIGS. 1 ,  2 , and  3 . 
       FIG. 1  shows how electronic device  10  may have the shape of a laptop computer having upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  may have hinge structures  20  that allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  may be mounted in upper housing  12 A. Upper housing  12 A, which may sometimes referred to as a display housing or lid, may be placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows how electronic device  10  may be 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  may have opposing front and rear surfaces. Display  14  may be mounted on a front face of housing  12 . Display  14  may, if desired, have a display cover layer or other exterior layer that includes openings for components such as button  26 . Openings may also be formed in a display cover layer or other display layer to accommodate a speaker port (see, e.g., speaker port  28  of  FIG. 2 ). 
       FIG. 3  shows how electronic device  10  may be a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  may have opposing planar front and rear surfaces. Display  14  may be mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  may have a cover layer or other external layer with an opening to accommodate button  26  (as an example). 
     The illustrative configurations for device  10  that are shown in  FIGS. 1 ,  2 , and  3  are merely illustrative. In general, electronic device  10  may be a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined or cast aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     Displays for device  10  may, in general, include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable image pixel structures. In some situations, it may be desirable to use LCD components to form display  14 , so configurations for display  14  in which display  14  is a liquid crystal display are sometimes described herein as an example. It may also be desirable to provide displays such as display  14  with backlight structures, so configurations for display  14  that include a backlight unit may sometimes be described herein as an example. Other types of display technology may be used in device  10  if desired. The use of liquid crystal display structures and backlight structures in device  10  is merely illustrative. 
     A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . A display cover layer or other outer display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     Touch sensor components such as an array of capacitive touch sensor electrodes formed from transparent materials such as indium tin oxide may be formed on the underside of a display cover layer, may be formed on a separate display layer such as a glass or polymer touch sensor substrate, or may be integrated into other display layers (e.g., substrate layers such as a thin-film transistor layer). 
     A schematic diagram of an illustrative configuration that may be used for electronic device  10  is shown in  FIG. 4 . As shown in  FIG. 4 , electronic device  10  may include control circuitry  29 . Control circuitry  29  may include storage and processing circuitry for controlling the operation of device  10 . Control circuitry  29  may, for example, include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Control circuitry  29  may include processing circuitry based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Control circuitry  29  may be used to run software on device  10 , such as operating system software and application software. Using this software, control circuitry  29  may present information to a user of electronic device  10  on display  14 . When presenting information to a user on display  14 , sensor signals and other information may be used by control circuitry  29  in making adjustments to the strength of backlight illumination that is used for display  14 . 
     Input-output circuitry  30  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output circuitry  30  may include communications circuitry  32 . Communications circuitry  32  may include wired communications circuitry for supporting communications using data ports in device  10 . Communications circuitry  32  may also include wireless communications circuits (e.g., circuitry for transmitting and receiving wireless radio-frequency signals using antennas). 
     Input-output circuitry  30  may also include input-output devices  34 . A user can control the operation of device  10  by supplying commands through input-output devices  34  and may receive status information and other output from device  10  using the output resources of input-output devices  34 . 
     Input-output devices  34  may include sensors and status indicators  36  such as an ambient light sensor, a proximity sensor, a temperature sensor, a pressure sensor, a magnetic sensor, an accelerometer, and light-emitting diodes and other components for gathering information about the environment in which device  10  is operating and providing information to a user of device  10  about the status of device  10 . 
     Audio components  38  may include speakers and tone generators for presenting sound to a user of device  10  and microphones for gathering user audio input. 
     Display  14  may be used to present images for a user such as text, video, and still images. Sensors  36  may include a touch sensor array that is formed as one of the layers in display  14 . 
     User input may be gathered using buttons and other input-output components  40  such as touch pad sensors, buttons, joysticks, click wheels, scrolling wheels, touch sensors such as sensors  36  in display  14 , key pads, keyboards, vibrators, cameras, and other input-output components. 
     A cross-sectional side view of an illustrative configuration that may be used for display  14  of device  10  (e.g., for display  14  of the devices of  FIG. 1 ,  FIG. 2 , or  FIG. 3  or other suitable electronic devices) is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  may include one or more layers of touch sensitive components such as touch-sensitive layers  47  that are attached to a cover layer such as cover layer  49 . Cover layer  49  may be formed from a sheet of rigid or flexible transparent material such as glass or plastic. 
     Touch-sensitive layers  47  may be attached to cover layer  49  using an adhesive material such as optically clear adhesive (OCA)  43 . Adhesive  43  may be a liquid adhesive, light-cured adhesive, pressure-sensitive adhesive or other suitable adhesive. Touch-sensitive layers  47  may include touch sensor components such as an array of capacitive touch sensor electrodes formed from transparent materials such as indium tin oxide. 
     Display  14  may include display layers such as layers  46  for generating images to be displayed on display  14 . Display layers  46  may include polarizer layers, color filter layers, transistor layers, adhesive layers, layers of liquid crystal material, or other layers for generating display images. Display layers  46  may be attached to touch-sensitive layers  43  using adhesive such as optically clear adhesive  45 . Adhesive  45  may be a liquid adhesive, light-cured adhesive, pressure-sensitive adhesive or other suitable adhesive. 
     Display layers  46  may use light generated by light-generating structures such as backlight structures  42  to form images to be viewed by a user of device  10 . Backlight structures  42  may include light-generating components such as light-emitting diodes, light guiding structures, reflective structures, optical films, etc. Backlight structures  42  may be attached to display layers  46  or may be mounted adjacent to layers  46  by attaching backlight structures  42  to one or more structural members. 
     A cross-sectional side view of an illustrative configuration that may be used for display layers  46  and backlight structures  42  of display  14  (e.g., for display layers  46  and backlight structures  42  of the display of  FIG. 5 , or other suitable display) is shown in  FIG. 6 . As shown in  FIG. 6 , display  14  may include backlight structures such as backlight unit  42  for producing backlight  44 . During operation, backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 6 ) and passes through display pixel structures 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 chassis structure and/or a metal 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 form a liquid crystal display or may be used in forming displays of other types. 
     In a configuration in which display layers  46  are used in forming a liquid crystal display, display layers  46  may include a liquid crystal layer such a liquid crystal layer  52 . Liquid crystal layer  52  may be sandwiched between display layers such as display layers  58  and  56 . Layers  56  and  58  may be interposed between lower polarizer layer  60  and upper polarizer layer  54 . If desired, upper polarizer layer  54  may be attached to an outer cover layer such as cover layer  49  ( FIG. 5 ). 
     Layers  58  and  56  may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers  56  and  58  may be layers such as a thin-film transistor layer and/or a color filter layer. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates of layers  58  and  56  (e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into layers such as layers  58  and  56  and/or touch sensor electrodes may be formed on other substrates. 
     With one illustrative configuration, layer  58  may be a thin-film transistor layer that includes an array of thin-film transistors and associated electrodes (display pixel electrodes) for applying electric fields to liquid crystal layer  52  and thereby displaying images on display  14 . Layer  56  may be a color filter layer that includes an array of color filter elements for providing display  14  with the ability to display color images. If desired, layer  58  may be a color filter layer and layer  56  may be a thin-film transistor layer. 
     During operation of display  14  in device  10 , control circuitry  29  (e.g., one or more integrated circuits such as components  68  on printed circuit  66  of  FIG. 6 ) may be used to generate information to be displayed on display (e.g., display data). The information to be displayed may be conveyed from circuitry  68  to display driver integrated circuit  62  using a signal path such as a signal path formed from conductive metal traces in flexible printed circuit  64  (as an example). 
     Display driver integrated circuit  62  may be mounted on thin-film-transistor layer driver ledge  82  or elsewhere in device  10 . A flexible printed circuit cable such as flexible printed circuit  64  may be used in routing signals between printed circuit  66  and thin-film-transistor layer  58 . If desired, display driver integrated circuit  62  may be mounted on printed circuit  66  or flexible printed circuit  64 . 
     Printed circuit  66  may be formed from a rigid printed circuit board (e.g., a layer of fiberglass-filled epoxy) or a flexible printed circuit (e.g., a flexible sheet of polyimide or other flexible polymer layer). However, these examples are merely illustrative. If desired printed circuits  64  and  66  may be formed from a combination of rigid and flexible printed circuit layers (e.g., printed circuit  66  may be formed from a rigid printed circuit board with a layer of flexible printed circuitry that extends from an edge of printed circuit  66  to form flexible printed circuitry  64  that attaches to thin-film-transistor layer  58 ). 
     Backlight structures  42  may include a backlight 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 source  72  may be coupled into edge surface  76  of light guide plate  78  and 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 or other light-scattering structures. 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, a layer of reflective film (e.g., a reflective film such as Vikuiti™ Enhanced Specular Reflector Film (ESR) or other suitable reflective film), 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. 6 , optical films  70  and reflector  80  may have a matching rectangular footprint. 
     Display structures such as light guide plate  78  may be received within a support structure such as display chassis  90  of  FIG. 7 . Display chassis  90  may include plastic chassis structures and metal chassis structures. Display chassis  90  may serve as an interface between the structures of display  14  and surrounding portions of housing  12 . If desired, display chassis  90  may include a ring of plastic (e.g., a plastic ring with a thickness of about 0.2 to 1.5 mm, as an example) or may be formed from a plate of material that includes a rectangular recess to accommodate display structures such as light guide plate  78 . Chassis structure  90  may be formed from housing structures (e.g., as part of a housing frame, part of a unibody housing such as a metal housing, etc.). 
     The arrangement of  FIG. 7  in which chassis structure  90  surrounds light guide plate  78  and is formed from a single contiguous structure is merely illustrative. If desired, chassis structure  90  may only partially surround light guide plate  78 , may be formed from multiple structures, and/or may be formed from different materials. 
     An illustrative arrangement in which display  14  is mounted in a chassis structure that includes multiple parts formed from different materials is shown in  FIG. 8 . As shown in  FIG. 8 , chassis structure  90  may include a plastic display chassis such as plastic chassis member  90 P (sometimes referred to as a p-chassis) and a metal display chassis such as metal chassis member  90 M (sometimes referred to as an m-chassis). Plastic chassis member  90 P and metal chassis member  90 M may each be formed from a single structure or may each include multiple parts. 
     Display structures such as display layers  46  may have a first end mounted on a planar portion such as portion  91  of plastic chassis  90 P. An adhesive such as adhesive  92  may be used in attaching an interior layer of display layers  46  such as lower polarizer  60  to planar surface  91  of plastic chassis  90 P. An opposing end of display layers  46  may be mounted on protruding portion  93  of chassis  90 P using adhesive  105 . Adhesives  92  and  105  may be liquid adhesives, light-cured adhesives, pressure-sensitive adhesives, or other suitable adhesives. If desired, adhesives  92  and  105  may be optically clear adhesives. 
     Plastic chassis  90 P may be formed from materials such as polycarbonate, polycarbonate acrylonitrile butadiene styrene (PC-ABS), nylon, glass-filled polycarbonate, glass-filled nylon, silicone, or other suitable materials. Using a glass-reinforced plastic may lower the thermal expansion coefficient of chassis  90 P. Chassis  90 P may include any suitable amount of glass fibers (e.g., 10%, 20%, 30%, 40%, or other suitable amount of glass). If desired, chassis  90  may contain a sufficient amount of glass to lower the thermal expansion coefficient to a desired level without causing chassis  90 P to be excessively rigid. If desired, chassis  90 P may be free of glass fibers. The example in which chassis  90 P is formed from glass-filled polycarbonate (e.g., a low-glass-filled polycarbonate) is merely illustrative. 
     Features such as low coefficient of thermal expansion and low rigidity may ensure that chassis  90 P provides structural support for display  14  without inducing undesired stress on display  14 . For example, the thermal expansion coefficient of chassis  90 P may be matched to that of other structures in device  10  such as device housing structures (e.g., housing  12  of  FIGS. 1 ,  2 , and  3 ). This may ensure that chassis  90 P and the surrounding structures such as housing  12  expand at similar rates when device  10  heats up. 
     Chassis  90 P may be provided with other features that may help minimize mechanical stress on display  14 . For example, chassis  90 P may have a minimized footprint in the X-Y plane. Wall sections such as wall section  95  of chassis  90 P may, for example, have a width W of about 0.1 mm, 0.2 mm, 0.3 mm, less than 0.3 mm, more than 0.3 mm, etc. 
     Chassis structure  90 P may be molded (e.g., using an injection molding process or other suitable molding process), machined, thermoformed, or may be formed using any other suitable fabrication process. Plastic chassis  90 P may, for example, be injection molded over metal chassis  90 M (e.g., at the corners of device  10  or at other suitable locations in device  10 ). In the example of  FIG. 8 , plastic chassis  90 P is attached to metal chassis  90 M at location  89 . 
     Metal chassis  90 M may be formed from stainless steel sheet metal or other suitable materials. Chassis  90 M may have a planar portion such as portion  97  that overlaps light guide plate  78  and a bent portion such as portion  99  that wraps around an edge portion of light guide plate  78  (e.g., using a C-shaped wrap). As shown in  FIG. 8 , backlight structures may be mounted in c-shaped portion  99  of chassis  90 M. For example, light-emitting diodes  72  may be mounted on a substrate such as substrate  88 . Light-emitting diodes  72  and substrate  88  may be mounted within c-shaped portion  99  of chassis  90 M (e.g., light-emitting diodes  72  and substrate  88  may be interposed between upper and lower layers of metal chassis  90 M). Substrate  88  may be formed from a rigid printed circuit board material (e.g., fiberglass-filled epoxy material such as FR4) or a flexible printed circuit substrate material such as polyimide or a sheet of other flexible polymer. Substrate  88  may be mounted on planar portion  97  of chassis  90 M. 
     Light guide plate  78  may have a locally thickened portion such as locally thickened portion  78 P. Locally thickened portion  78 P of light guide plate  78  may be formed along an edge of light guide plate  78  that is adjacent to light-emitting diodes  72 . Locally thickened portion  78 P may have a thickness T 1  that is greater than thickness T 2  of light guide plate  78 . Light guide plate  78  may have a tapered surface such as tapered surface  78 T that bridges the thinner portions of light guide plate  78  with locally thickened portion  78 P of light guide plate  78 . Tapered surface  78 T may be formed by stamping, molding, embossing, adding thermoplastic material to portion  78 P using heat, laminating additional film material, adding clear adhesive to light guide plate portion  78 P, or by otherwise enhancing the thickness of the light guide plate  78  in portion  78 P. 
     As shown in  FIG. 8 , reflector  80  may be interposed between metal chassis  90 M and light guide plate  78 . If desired, reflector  80  may be attached to plastic chassis  90 P using an adhesive such as adhesive  86  (e.g., a pressure sensitive or other suitable adhesive). This is, however, merely illustrative. If desired, reflector  80  may be floating with respect to plastic chassis  90 P and adhesive  86  may be omitted. 
     In conventional backlight arrangements, a light guide plate is often floating with respect to the light-emitting diodes that launch light into the light guide plate. To constrain the light guide plate, the light guide plate is sometimes attached to a plastic display chassis using adhesive. This type of attachment is typically made on a side of the light guide plate that opposes the light-emitting diodes. 
     This type of conventional backlight arrangement in which a light guide plate floats with respect to an array of light-emitting diodes can have an adverse impact on the optical efficiency of a display backlight. For example, during thermal expansion and contraction events, large air gaps may occur between light-emitting diodes and a light guide plate. The presence of large air gaps between light-emitting diodes and a light guide plate can result in poor backlight efficiency, which may in turn decrease power consumption efficiency and can reduce battery life in an electronic device. 
     A backlight arrangement of the type shown in  FIG. 8  may be used to ensure that gaps between light-emitting diodes  72  and light guide plate  78  are minimized. As shown in  FIG. 8 , light guide plate  78  may be attached to substrate  88  on which light-emitting diodes  72  are mounted. An adhesive such as adhesive  102  may be used in attaching portion  78 P of light guide plate  78  to substrate  88 . Reflector  80  may also be attached to substrate  88  using an adhesive such as adhesive  94 . Substrate  88  may in turn be attached to planar surface  97  of metal chassis  90 M using an adhesive such as adhesive  98 . Adhesives  102 ,  94 , and  98  may be liquid adhesives, light-cured adhesives, pressure-sensitive adhesives, other suitable adhesives, combinations of these adhesives, etc. If desired, adhesives  102 ,  94 , and  98  may be optically clear adhesives. 
     A friction-reducing material such as friction-reducing material  100  may attached to a lower surface of substrate  88  (e.g., friction-reducing material  100  may be interposed between substrate  88  and planar surface  97  of chassis  90 M). Friction-reducing material  100  may be used in mounting backlight structures within c-shaped portion  99  of chassis  90 M. 
     Adhesive  102  may be interposed between light-emitting diodes  72  and reflector  80 . Portions of light guide plate  78  which do not overlap reflector  80  may overlap a layer of reflective material such as reflective layer  96 . Reflective material  96  may help reflect light into light guide plate  78  at portions of light guide plate  78  that do not overlap reflector  80 . The presence of reflective material  96  may ensure that the transition from reflector  80  to light-emitting diodes  72  does not adversely affect backlight efficiency. 
     If desired, adhesive  102  may also be configured to reflect light into light guide plate  78 . For example, adhesive  102  may have a configuration of the type shown in  FIG. 9 . As shown in  FIG. 9 , adhesive  102  may be a supported adhesive that includes a lining of reflective material such as reflective layer  102 A interposed between layers of optically clear adhesive (OCA) such as optically clear adhesive layers  102 B. Reflective layer  102 A may be formed from a reflective polymer (e.g., a white polymer such as white polyethylene terephthalate or other suitable reflective polymer resin), may be formed from a reflective film (e.g., a reflective film such as Vikuiti™ Enhanced Specular Reflector Film (ESR) or other suitable reflective film), or may be formed from other suitable reflective materials. Lining adhesive  102  with a reflective material may ensure that the transition from reflector  80  to light-emitting diodes  72  does not have an adverse effect on backlight efficiency. 
     Reflective material  96  on the surface of substrate ( FIG. 8 ) may be formed from a reflective coverlay material (a white polyimide or polyester coverlay material), a layer of printed white ink, a layer of reflective film (e.g., a reflective film such as Vikuiti™ Enhanced Specular Reflector Film (ESR) or other suitable reflective film), a layer of white tape, or other suitable reflective materials. Reflective material  96  may formed on the surface of substrate  88  (e.g., interposed between adhesive  96  and substrate  88 ) using any suitable application process (e.g., laminating, screen printing, other suitable application processes, etc.). 
     As shown in  FIG. 10 , for example, reflective material  96  may be formed from a polymer-based binder such as polymer-based binder  96 P that includes a reflective additive such as reflective additive  96 A. Polymer-based binder  96 P may be a layer of polyimide, polyester, or other suitable polymer. Reflective additive  96 A may be a reflective dye or pigment (e.g., a titanium dioxide powder or other white or shiny material). As shown in  FIG. 10 , reflective additive  96 A may be configured to reflect light  103  upwards in the Z direction (e.g., towards light guide plate  78  of  FIG. 8 ). Reflective additive  96 A may be configured to reflect more than 30% of incident light, more than 50% of incident light, more than 70% of incident light, more than 90% incident light, etc. 
     Reflective coating  96  may be a coverlay material that serves as a solder mask for printed circuit substrate  88 . For example, reflective coating  96  may surround or partially surround solder pads such as solder pad  126  and may prevent solder from contaminating portions of substrate  88  (e.g., reflective coating  96  may prevent solder from bridging adjacent contact pads  126 ). 
     Another illustrative backlight arrangement that may help minimize gaps between light guide plate  78  and light-emitting diodes  72  is shown in  FIG. 10 . In the example of  FIG. 11 , reflector  80  extends to the edge of light guide plate  78 . Reflector  80  may be interposed between adhesive  120  and adhesive  122 . Adhesive  120  may be used in attaching an upper surface of reflector  80  to light guide plate  78 , whereas adhesive  122  may be used in attaching a lower surface of reflector  80  to substrate  88 . Adhesives  120  and  122  may be liquid adhesives, light-cured adhesives, pressure-sensitive adhesives, other suitable adhesives, combinations of these adhesives, etc. If desired, adhesives  120  and  122  may be optically clear adhesives. In one suitable embodiment, reflector  80  may be a layer of reflective film (e.g., a reflective film such as Vikuiti™ Enhanced Specular Reflector Film (ESR) or other suitable reflective film) that forms a lining between adhesives  120  and  122 , thereby forming a supported adhesive that attaches light guide plate  78  to substrate  88 . 
     If desired, a reflective coating may be formed on the upper surface of substrate  88  (e.g., interposed between light guide plate  78  and substrate  88 ) and may be used to reflect light into light guide plate  78 . For example, a layer of white coverlay material (e.g., similar to reflective material  96  of  FIG. 8 ) may be formed on the surface of printed circuit substrate  88 . This may ensure that the transition from reflector  80  to light-emitting diodes  72  does not have an adverse effect on backlight efficiency. This is, however, merely illustrative. If desired, substrate  88  may be free of reflective coatings. For example, edge  80 E of reflector  80  may be flush with edge  76  of light guide plate  78 , thereby providing a reflective surface that overlaps all or substantially all of light guide plate  78 . With this type of arrangement, white coverlay on the surface of substrate  88  may not be necessary. 
     In the examples of  FIGS. 8 and 11 , printed circuit substrate  88  is attached to planar surface  97  of chassis  90 M using an adhesive such as adhesive  98 . Prior to adhering substrate  88  to chassis  90 M, substrate  88  may be inserted into c-shaped portion  99  of chassis  90 M. In order to ensure that adhesive  98  does not adhere to planar surface  97  of chassis  90 M until substrate  88  is received within bent portion  99 , substrate  88  may slide on friction-reducing material  100  at an angle with respect to planar surface  97  until substrate  88  is received by bent portion  99 . 
     A diagram illustrating how friction-reducing material  100  of  FIGS. 8 and 11  may be used in mounting backlight structures (e.g., light-emitting diodes  72 , substrate  88 , and an edge portion of light guide plate  78 ) within bent portion  99  of chassis  90 M is shown in  FIG. 12 . 
     As shown in the upper portion of  FIG. 12 , backlight structures  42  may be mounted within c-shaped portion  99  of chassis  90 M by sliding substrate  88  on friction-reducing material  100  in direction  104 . An angle such as angle  125  may be formed between substrate  88  and planar portion  97  of chassis  90 M as substrate  88  slides into portion  99 . Friction-reducing material  100  may provide a low-friction interface between substrate  88  and chassis  90 M that allows substrate  88  to slide smoothly in direction  104 . By keeping substrate  88  at an angle with planar portion  97  of chassis  90 M, adhesive  98  may remain separated from chassis  90 M until backlight structures are received within portion  99  of chassis  90 M. Angle  125  between substrate  88  and planar surface  97  of chassis  90 M may be any suitable angle between 0° and 90° (e.g., 15°, 30°, etc.). 
     As shown in the lower portion of  FIG. 12 , once backlight structures  42  have been received within c-shaped opening  99  of chassis  90 M, substrate  88  may be pressed in direction  121  (e.g., to bring substrate  88  in parallel with planar portion  97  of chassis  90 M), thereby bringing adhesive  98  into contact with planar portion  97  of chassis  90 M and attaching substrate  88  to chassis  90 M. In arrangements where adhesive  98  is a pressure sensitive adhesive, the downward pressure provided by pressing light guide plate  78  in direction  124  may activate adhesive  98  to form a bond with chassis  90 M. 
     Friction-reducing material  100  may, for example, be formed from a corrugated surface on the underside of substrate  88  (e.g., to reduce the amount of surface area of substrate  88  in contact with chassis  90 M as substrate  88  slides into portion  99 ), may be formed from low-friction pads attached to the underside of substrate  88 , may be a low-friction shim structure attached to the underside of substrate  88  (e.g., a metal, glass, ceramic, or plastic shim structure), or may have other suitable forms. If desired, friction-reducing material  100  may be a coating of low-friction material, may be a low-friction film (e.g., a low-friction film deposited or applied to the underside of substrate  88 ), or may be a separate structure formed from low-friction material that is attached to substrate  88  (e.g., using adhesive or other attachment mechanisms). 
     Friction-reducing material  100  may be formed from a low-friction polymer such as a halogen based polymer or fluorocarbon based polymer (e.g., polytetrafluoroethylene), or may be formed from other suitable slick materials such as graphite, silicone based lubricants, etc. 
     As shown in  FIG. 12 , a gap of height H may be formed between light guide plate  78  and substrate  88  to accommodate reflector  80  and adhesive  102 . Light-emitting diodes  72  may emit light at a height relative to substrate  88  that is equal to or greater than height H. This may allow light emitted by light-emitting diodes  72  to enter light guide plate  78  at edge  76 . 
     To ensure that light-emitting diodes  72  emit light at a height relative to substrate  88  that is equal to or greater than height H, light-emitting diodes  72  may have a configuration of the type shown in  FIG. 13 . As shown in  FIG. 13 , each light-emitting diode  72  may include a semiconductor device such as diode die  110  mounted within a molded package such as package  72 P. Diode die  110  may be mounted on one or more lead frame structures such as lead frame structure  114 . A wire bond such as wire bond  112  may be used to electrically couple one of the diode&#39;s terminals to lead frame structure  114 . Lead frame structure  114  may extend out from package  72 P towards substrate  88  on which light-emitting diodes  72  are mounted. Lead frame structure  114  may be mounted to solder pad  118  on substrate  88  using solder  116 . 
     Lead frame structures  114  may be elongated to serve as stilts for light-emitting diodes  72 . For example, lead frame structures  114  may increase the height at which light is emitted from diode  110  relative to substrate  88  by a length L 1 . Elongated lead frame structures  114  may ensure that light emitted from diode die  110  is launched directly into the edge of light guide plate  78  even when a gap of height H ( FIG. 12 ) is present between light guide plate  78  and substrate  88 . 
     Another suitable arrangement that may be used to accommodate a gap between light guide plate  78  and substrate  88  is shown in  FIG. 14 . As shown in  FIG. 14 , a thickening layer such as layer  88 L may be added to portions of printed circuit substrate  88 . Portions of substrate  88  that include layer  88 L may have a thickness T 3  that is greater than a thickness T 4  of portions that do not include layer  88 L. Light-emitting diodes  72  may be mounted on additional layer  88 L. Mounting light-emitting diodes  72  on a thickened portion of substrate  88  may ensure that light emitted from diodes  72  is launched directly into the edge of light guide plate  78  even when a gap of height H ( FIG. 12 ) is present between light guide plate  78  and substrate  88 . 
     If desired, layer  88 L may also be used as a thermal management layer. For example, conductive structures such as copper traces may be formed on layer  88 L and may be configured to transfer heat away from light-emitting diodes  72 . 
     Another suitable arrangement that may be used to accommodate a gap between light guide plate  78  and substrate  88  is shown in  FIG. 15 . As shown in  FIG. 15 , a shim such as shim  106  may be interposed between light-emitting diodes  72  and substrate  88 . Shim  106  may be formed from plastic (e.g., polyimide or other suitable polymer-based material) or may be formed from other suitable material. Shim  106  may have a thickness T 5  and may therefore be used to raise the height of light-emitting diodes  72  relative to substrate  88  by length T 5 . 
     Shim  106  may be configured to accommodate an electrical connection between light-emitting diodes  72  and traces on substrate  88 . For example, as shown in the exploded perspective view of  FIG. 16 , shim  106  may include openings such as openings  108  (sometimes referred to as perforations) which may be used in providing an electrical path from light-emitting diodes  72  and contact pads such as contact pads  126  on substrate  88 . 
     As shown in  FIG. 16 , light-emitting diodes  72  may include terminals such as terminals  130 . Terminals  130  (sometimes referred to as lead frame structures) may extend out from under diodes  72 . This is, however, merely illustrative. If desired, terminals  130  may extend out the sides of diodes  72  or may extend out of the rear of diodes  72 . Terminals  130  may include positive and negative power supply terminals. A power supply signal may be supplied across the positive and negative terminals for each diode  72  to adjust the power of the emitted light from that diode. Metal traces such as illustrative trace  128  of  FIG. 16  may be formed on substrate  88  to provide power to terminals  130  of light-emitting diodes  72 . 
     Solder may be used to soldering light-emitting diodes  72  to substrate  88  (e.g., to solder lead frame structures  130  to solder pads  126  and other traces  128  on substrate  88 ). Openings  108  in shim  106  may be used to accommodate a solder connection between terminals  130  and contact pads  126 . For example, shim  106  may be placed on substrate  88  such that openings  108  align with contact pads  126 . Solder  109  may be applied over openings  108  and may fill openings  108  to make contact with solder pads  126 . Light-emitting diodes  72  may be mounted on shim  106  such that terminals  130  align with openings  108 . Solder  109  within openings  108  may be used in forming an electrical and mechanical connection between terminals  130  and contact pads  126 . 
     Mounting light-emitting diodes  72  on shim  106  may ensure that light emitted from diodes  72  is launched directly into the edge of light guide plate  78  even when a gap of height H ( FIG. 12 ) is present between light guide plate  78  and substrate  88 . This is, however, merely illustrative. If desired, light-emitting diodes  72  may be mounted within a plastic housing that is molded such that light emitted from diodes  72  is launched directly into the edge of light guide plate  78  even when a gap is present between light guide plate  78  and substrate  88  (e.g., such that the height increasing structures of  FIGS. 13-16  are not required). 
     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.

Metadata:
Filing Date: 20130220
Publication Date: 20150825
Grant Date: 20150825
Priority Date: 20120928
Inventors: FRANKLIN JEREMY C.
GIBBS KEVIN D.
QIAN AMY
RAFF JOHN
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/0031", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/009", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0031", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0091", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/009", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0031", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0091", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0083", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0083", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/009", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 50385018