PATENT DOCUMENT

Publication Number: US-9618689-B2
Application Number: US-201313770817-A
Country: US
Kind Code: B2

Title: Electronic devices with displays having attached optical films

Abstract:
Electronic devices may include displays having backlight structures that include optical films. The optical films may help guide light from the backlight structures to display layers that generate display images using the light. The optical films may be attached together at one or more locations. The optical films may be attached to a structural member of the backlight structures. The structural member may be formed along each edge of the optical films and prevent the optical films from sliding within the display. Each optical film may be designed to expand to a common lateral size when the display is operated at a display operating temperature. The optical films may each include an elongated opening such as a slot through which a pin can be placed to partially constrain the movement of the optical films while allowing the optical films to expand or contract under changing thermal conditions in the display.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 backlight structures comprising:
 a light guide plate; 
 a plurality of light-emitting diodes that emit light into the light guide plate; and 
 first and second optical films on the light guide plate, wherein light that has passed through the light guide plate passes through the first and second optical films during operation of the display, wherein the first optical film has a first coefficient of thermal expansion, wherein the second optical film has a second coefficient of thermal expansion that is different from the first coefficient of thermal expansion, and wherein the first and second optical films are configured to expand to a common lateral size when the display is operating at a display operating temperature; and 
 a structural member having an opening, wherein the first and second optical films are mounted within the opening and wherein the structural member holds the first and second optical films together. 
 
 
     
     
       2. The display defined in  claim 1 , the backlight structures further comprising:
 third and fourth optical films on the light guide plate, wherein light that has passed through the light guide plate passes through the first, second, third, and fourth optical films during operation of the display, wherein the third and fourth optical films are mounted within the opening, and wherein the structural member holds the third and fourth optical films together. 
 
     
     
       3. The display defined in  claim 1  wherein the structural member includes portions formed adjacent to each edge of the first and second optical films. 
     
     
       4. The display defined in  claim 1 , wherein the structural member comprises a plastic structural member. 
     
     
       5. The display defined in  claim 4 , further comprising a metal support member, wherein the plastic structural member is insert-molded onto the metal support member. 
     
     
       6. The display defined in  claim 1  wherein a portion of the first optical film is attached to a corresponding portion of the second optical film. 
     
     
       7. The display defined in  claim 2 , wherein the third optical film has a third coefficient of thermal expansion, wherein the fourth optical film has a fourth coefficient of thermal expansion, and wherein the third and fourth optical films are configured to expand to the common lateral size when the display is operating at a display operating temperature. 
     
     
       8. A display, comprising:
 a plurality of display layers; and 
 a backlight unit that generates light for the display, wherein the plurality of display layers generate images to be displayed to a user using the light, wherein the backlight unit comprises at least one structural member and a plurality of optical films that are interposed between the plurality of display layers and the backlight unit and wherein each of the plurality of optical films has first and second opposing parallel edges, wherein the plurality of optical films are attached together along their respective first edges, and wherein the plurality of optical films are free to move relative to each other along their respective second edges. 
 
     
     
       9. The display defined in  claim 8  wherein the plurality of optical films are attached to the at least one structural member. 
     
     
       10. The display defined in  claim 9  wherein the at least one structural member comprises a plastic structural member that is insert molded onto the edge of the optical films. 
     
     
       11. The display defined in  claim 8  wherein the at least one structural member comprises a metal structural member. 
     
     
       12. The display defined in  claim 11  wherein the backlight unit comprises a reflective layer and a light guide layer that are supported by the metal structural member. 
     
     
       13. The display defined in  claim 12  wherein the at least one structural member further comprises an insert molded plastic member on the metal structural member that includes first, second, and third portions that are adjacent to the second respective edges and third and fourth additional respective edges of the plurality of optical films. 
     
     
       14. The display defined in  claim 13  wherein the insert molded plastic member includes a ridge and wherein the plurality of display layers are attached to the ridge. 
     
     
       15. The display defined in  claim 8  wherein the plurality of display layers comprises a layer of liquid crystal material. 
     
     
       16. A display, comprising:
 a backlight assembly comprising:
 a metal backlight chassis; 
 a light guide plate mounted on the metal backlight chassis; 
 a plastic backlight chassis attached to the metal backlight chassis that at least partially surrounds the light guide plate; 
 a plurality of optical films disposed over the light guide plate, wherein the plurality of optical films forms an optical film stack having first and second opposing surfaces and a peripheral edge formed between the first and second opposing surfaces; and 
 a plastic support structure that attaches the plurality of optical films together, wherein the plastic support structure forms at least one edge of the plastic backlight chassis, and wherein the plastic support structure overlaps the first and second opposing surfaces of the optical film stack without overlapping the light guide plate. 
 
 
     
     
       17. The display defined in  claim 16  wherein the plastic support structure has a recess, and wherein the plurality of optical films are attached together within the recess. 
     
     
       18. The display defined in  claim 16  wherein the plastic support structure surrounds at least a portion of the first and second opposing surfaces and the peripheral edge. 
     
     
       19. The display defined in  claim 16  wherein the plastic support structure is attached to a portion of the metal backlight chassis that extends laterally beyond a peripheral edge of the light guide plate. 
     
     
       20. The display defined in  claim 19  wherein the second opposing surface is interposed between the first opposing surface and the light guide plate, wherein a portion of the plastic support structure extends below the second opposing surface, and wherein the portion of the plastic support structure is attached to the portion of the metal backlight chassis that extends laterally beyond a peripheral edge of the light guide plate. 
     
     
       21. The display defined in  claim 16  wherein the plastic support structure is insert-molded onto the plurality of optical films. 
     
     
       22. A display, comprising:
 a plurality of display layers; and 
 a backlight unit that generates light for the display, wherein the plurality of display layers generate images to be displayed to a user using the light, wherein the backlight unit comprises at least one structural member and a plurality of optical films that are interposed between the plurality of display layers and the backlight unit and wherein the plurality of optical films are attached together along an a first edge of the plurality of optical films and are free to move relative to each other along a second edge of the plurality of optical films, wherein the at least one structural member comprises a metal structural member, wherein the backlight unit comprises a reflective layer and a light guide layer that are supported by the metal structural member, and wherein the at least one structural member further comprises an insert molded plastic member on the metal structural member that includes first, second, and third portions that are adjacent to respective first, second, and third additional edges of the plurality of optical films. 
 
     
     
       23. The display defined in  claim 22  wherein the insert molded plastic member includes a ridge and wherein the plurality of display layers are attached to the ridge. 
     
     
       24. The display defined in  claim 22  wherein the plurality of display layers comprises a layer of liquid crystal material.

Description:
This application claims priority to U.S. provisional patent application No. 61/707,777 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. 
     Displays often include one or more optical films that help distribute light from a light source for the display. These films often have a coefficient of thermal expansion that is high enough that the films expand when the temperature of the display rises during operation of the display. It can be therefore be challenging to secure optical films in a display while allowing the films to expand when exposed to rising temperatures. However, optical films that are unsecured may be prone to damage during a drop event or during assembly of the display. 
     It would therefore be desirable to be able to provide improved displays with optical films 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. 
     The backlight structures may include optical films such as light diffusing films, light-redirecting films, light-collimating films or other films for distributing light from the backlight to other portions of the display. 
     The optical films may be formed from materials having different coefficients of thermal expansion. A given optical film may therefore expand more or less or in different dimensions than another optical film when display temperatures rise when a display is powered on. The optical films may therefore be designed to expand to a common lateral size at a given temperature such as a nominal operating temperature of the display. 
     The edges of the optical films may be surrounded by a support structure that constrains the movement of the optical films. The optical films may be attached together at one or more locations such as along an edge of the optical films. Other portions of the optical films may be free to move with respect to each other so that the optical films can expand or contract when the operating temperature of the display rises or falls. 
     The portions of the optical films that are attached together may be attached together using adhesive or a pin, may be melted together using a hot bar, may be heat staked, may be spiral bound, may be thread bound, or may be attached together using other binding members or binding methods. An additional portion of the optical films may be constrained by providing a pin through a slot such as an elongated opening in each optical film that is aligned with a slot in each other film. The slot in each film may have an elongated dimension along a dimension in which that film exhibits maximum expansion under heat exposure. In this way, movement of the films may be partially constrained while allowing the films to expand and contract when exposed to changing temperatures. 
     The backlight structures may include support structures such as a metal support structure and a plastic support structure. The optical films may be placed in the display adjacent to the plastic support structure or a portion of the plastic support structure may be attached or insert molded onto the portion of the optical films that is attached together. 
     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 a cross-sectional side view of an illustrative display showing how backlight structures and display layers may be mounted to support structures in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional top view of an illustrative display showing how a support structure for a display may include openings that receive extended tabs on optical films in accordance with an embodiment of the present invention. 
         FIG. 9  is a cross-sectional top view of an illustrative display showing how optical films having a common lateral size at a given temperature may be mounted within a cavity between structural members for the display in accordance with an embodiment of the present invention. 
         FIG. 10A  is a cross-sectional side view of illustrative optical films for a display having various lateral sizes in accordance with an embodiment of the present invention. 
         FIG. 10B  is a cross-sectional side view of illustrative optical films of the type shown in  FIG. 10A  showing how the optical films may expand to have a common lateral size at a particular temperature in accordance with an embodiment of the present invention. 
         FIG. 11  is a cross-sectional side view of illustrative optical films that are attached together using adhesive in accordance with an embodiment of the present invention. 
         FIG. 12  is a top view of illustrative optical films that are attached together showing various possible locations at which the films can be attached together in accordance with an embodiment of the present invention. 
         FIG. 13  is a cross-sectional side view of illustrative optical films that are attached together using a hot bar in accordance with an embodiment of the present invention. 
         FIG. 14  is a cross-sectional side view of illustrative optical films that are attached together using pins in accordance with an embodiment of the present invention. 
         FIG. 15  is a cross-sectional side view of illustrative optical films that are attached together using a clamping structure such as a book-binding structure in accordance with an embodiment of the present invention. 
         FIG. 16  is a cross-sectional side view of illustrative optical films that are heat staked together in accordance with an embodiment of the present invention. 
         FIG. 17  is a cross-sectional side view of illustrative optical films that are attached together using binding structures that pass through openings in a portion of the films in accordance with an embodiment of the present invention. 
         FIG. 18  is a cross-sectional side view of illustrative optical films that are attached together and placed in backlight structures adjacent to a structural member in accordance with an embodiment of the present invention. 
         FIG. 19  is a cross-sectional side view of illustrative optical films that are attached together showing how a plastic structural member may be molded onto the attached portion of the films in accordance with an embodiment of the present invention. 
         FIG. 20  is a perspective view of illustrative backlight structures showing how optical films that are attached together may be mounted on a metal structural member with insert molded structural members on three sides in accordance with an embodiment of the present invention. 
         FIG. 21  is a cross-sectional side view of illustrative optical films that are partially constrained by a pin that passes through slots in the films in accordance with an embodiment of the present invention. 
         FIG. 22  is a top view of illustrative optical films showing how slots in the films may be oriented in various directions 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  14  (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 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 substantially similar rectangular footprint. 
     As shown in  FIG. 7 , display  14  may include structural members such as support structures  100 ,  102 , and  104 . Member  100  may, for example, be a metal support member such as a metal chassis. Members  102  and  104  may, for example, be plastic support members that are molded onto metal member  100  or otherwise attached to member  100 . Members  102  and  104  may be separate members or may be portions of a common structure (e.g., a plastic chassis structure that surrounds the edges of display layers  46 ). Members  102  and  104  may each include a recess such as a ridge. Display layers  46  may be attached to the ridge on members  102  and  104 . 
     Backlight structures  42  may be mounted between members  102  and  104 . Backlight structures may be attached to member  100  or to members  102  and/or  104 . Optical films  70  (see, e.g.,  FIG. 6 ) may be constrained within display  14  at least partially by structural members such as members  102  and  104 . As examples, films  70  may be placed within a space between members  102  and  104 , may be molded into one or more of members  104 , may include one or more portions (e.g., tabs) that extend into cavities in members  102  and/or  104  or may be otherwise mounted in display  14 . 
     In the example shown in  FIG. 8 , optical films  70  include protruding portions such as tabs  106  along edges of films  70  that extend into cavities  108  in structures  102  and  104 . Optical films  70  may include tabs  106  along one edge, along two edges, along three edges, or along all edges of films  70 . During a drop event in which device  10  receives an impact, tabs  106  may move into contact with sidewalls of cavities  108 , thereby preventing films  70  from sliding out of position and negatively affecting the performance of display  14 . The size of members  102  and/or  104  may be increased in order to accommodate cavities  108 . This may create an undesirable increase in peripheral support portions of display  14 . If desired, optical films  70  may therefore be provided without any tabs  106 . 
     In the example of  FIG. 9 , optical films  70  are provided without any tabs  106 . As shown in  FIG. 9 , films  70  may be mounted in an opening such as opening  112  between a structural member such as support structure  110 . In the example of  FIG. 9 , member  110  includes members  102  and  104  along two edges of films  170  and additional portions  114  and  116  along respective top and bottom edges of films  70 . Structures  102 ,  104 ,  114 , and  116  may be formed from plastic, glass, ceramic or other materials and may form a single continuous structure or structures  102 ,  104 ,  114 , and  116  may be one or more separate structures. 
     Multiple optical films  70  may be placed separately into opening  112  or optical films  70  may be attached to each other prior to placement in opening  112 . Optical films  70  may be attached to one or more of members  102 ,  104 ,  114 , and/or  116  or may be able to move within opening  112 . Each optical film  70  may have an associated coefficient of thermal expansion (CTE) that indicates the extent to which that optical film expands when the temperature of the film rises. 
     Opening  112  may have a lateral width WS and a lateral height HS. Optical films  70  may each be designed so that, at a given temperature, t (e.g., a common operating temperature of display  14 ), all optical films  70  have a common lateral width WFt and a common lateral height HFt. Each optical film  70  may have a lateral width and a lateral height that is different from WFt and HFt at other temperatures. Operating temperature t may be, as examples, between 70 C. and 80 C., between 60 C. and 90 C., between 70 C. and 100 C., between 75 C. and 85 C., less than 120 C., or greater than 10 C. 
     Common lateral width WFt and a common lateral height HFt of films  70  at temperature t may be respectively smaller than lateral width WS and a lateral height HS by a predetermined amount. In this way, films  70  may be constrained within opening  112  and protected from damage during a drop event while allowing films  70  to expand and contract within opening  112 . 
       FIG. 10A  shows an exemplary set of optical films  70  at a temperature t′ that is different from temperature t. At temperature t′, each film  70  may have a lateral width that is different from lateral width WFt. When the temperature of films  70  is raised to temperature t, each optical film  70  may expand to have to a lateral width that is substantially equal to lateral width WFt as shown in  FIG. 10B . 
     During assembly of backlight structures such as backlight structures  42 , optical films such as films  70  may be prone to damage (e.g., scratching) if the films are free to move with respect to one another. In order to prevent excessive movement of films  70  with respect to each other, optical films  70  may be attached to each other. Each optical film  70  may have one or more portions that are attached to a corresponding portion of another film  70  and other portions that remain unattached so that films  70  are able to expand and contract under changes in display temperature. 
     As shown in  FIG. 11 , a portion such as portion  120  of films  70  may be attached together using adhesive such as adhesive  122  that is interposed between each film in region  120 . Portion  120  of films  70  may be a portion that is located along an edge of films  70  as shown in  FIG. 11 , or films  70  may be attached together at one or more other locations such regions  120 ′ of  FIG. 12 . 
     As shown in  FIG. 12 , films  70  may be attached in a region  120  that extends along substantially all of one edge of films  70  or films  70  may be attached together in one or more other regions such regions  120 ′. Regions  120 ′ may include a region along a portion of an edge such as a portion of a side edge, a portion of a top edge and/or a portion of a bottom edge. 
     If desired, films  120  may include openings such as one or more slots  124 . Slots  124  may be used to receive a pin that passes through slots  124  in order to help constrain films  70  within backlight structures  42 . Slots  124  may have a size and a shape that is larger than the pin that passes through the slot. In this way, pins in slots  124  may partially constrain the movement of films  70  while allowing for some expansion and contraction of films  70 . 
     If desired, films  70  may be attached together in portion  120  and/or portions  120 ′ using adhesive as described above in connection with  FIG. 11 . However, this is merely illustrative. If desired, films  70  may be attached together in portion  120  and/or portions  120 ′ using other attachment structures or attachment methods as shown in  FIGS. 13, 14, 15, 16, and 17 . 
     In the example of  FIG. 13 , films  70  are attached together in region  120  (or one or more of regions  120 ′) using hot bars  126  to melt films  70  together in that region by pressing hot bars  126  against films  70  as indicated by arrows  136 . 
     In the example of  FIG. 14 , films  70  are attached together in region  120  (or one or more of regions  120 ′) using a fastening member such as pin  128  that passes through openings in films  70  in that region and fastens the films together. 
     In the example of  FIG. 15 , films  70  are attached together in region  120  (or one or more of regions  120 ′) using a binding structure such as clamping structure  130  (e.g. a structure such as a book-binding structure that binds together pages of a book) that provides a squeezing force that attaches films  70  together in that region. 
     In the example of  FIG. 16 , films  70  are attached together in region  120  (or one or more of regions  120 ′) by heat staking the films together in that region. Heat staking films  70  together in region  120  may include providing some films with protruding portions  132  that fit into openings  134  in adjacent films and pressing films  70  in region  120  using hot bars  126  as indicated by arrows  136  so that protruding portions  132  expand to fill openings  134 ). 
     In the example of  FIG. 17 , films  70  are attached together in region  120  (or one or more of regions  120 ′) using binding members  140  that pass through openings  138  in films  70  and wrap around an outside edge of films  70  in that region. Binding members  140  may be formed from wire, thread or other materials. Binding members  140  may be a single continuous binding member that wraps around the edge of films  70  and through multiple openings  138  in a spiral pattern or films  70  may be provided with a binding member  140  associated with each opening  138 . 
     As shown in  FIG. 18 , optical films  70  that are attached together in region  120  (or in one or more regions  120 ′) may be mounted in display  14  so that region  120  is adjacent to plastic structural member  102 . Other backlight structures  142  (e.g., light guide  78  and reflector  80 ) may be interposed between films  70  and metal structural member  100 . In the example of  FIG. 18 , films  70  are attached together but are free of attachments to structural member  102 . However, this is merely illustrative. If desired, portion  120  of films  70  may be attached to member  102 . 
     As shown in  FIG. 19 , some or all of portion  120  of films  70  may be attached to member  102  by molding (e.g., insert molding) member  102  onto portion  120  of films  70 . Other portions of films  70  (e.g., an opposing edge of films  70 ) may be free of attachments to structural members of display  14 . In this way, films  70  may be secured within display  14  while allowing films  70  to expand and/or contract when the temperature of display  14  changes. 
       FIG. 20  is a perspective view of a portion of display  14  during assembly operations for display  14  showing how films  70  may be attached (e.g., insert molded or otherwise attached) to a structural member such as support structure  144  prior to being placed over other backlight structures  142  (e.g., light guide  78  and reflector  80 ). 
     As shown in  FIG. 20 , a structural member such as metal support structure  100  may have insert-molded plastic structural members  104 ,  114  and  116  formed along three edges of member  100 . Member  144  may be fourth plastic structural member (e.g., member  144  may be member  102  of  FIGS. 7, 8, 9, 19 , and/or  20 ). Member  144  and films  70  may be lowered together in direction  148  onto other backlight structures  142  and metal member  100 . If desired, member  144  may include portions such as portion  146  that extend beyond films  70  so that member  144  may be attached to metal member  100  while films  70  rest on structures  142 . However, this is merely illustrative. If desired, metal member  100  may have light sources such as LEDs  72  (see  FIG. 6 ) mounted to member  100  adjacent to structures  142  (e.g., in a light bar containing multiple LEDs that extends along the edge of structures  142 ) that emit light into structures  142 . Member  144  may be attached to the light bar or to other portions of member  100  and/or structures  142 . 
     When assembled, structures  144 ,  104 ,  114 , and  116  may form a structural member such as member  110  of  FIG. 9  that has portions formed along each edge of optical films  70 . 
       FIG. 21  is a cross-sectional side view of a portion of a stack of optical films  70  showing how display  14  may include a pin such as pin  150  that passes through an opening  124  in films  70 . As shown in  FIG. 20 , each optical film  70  may have an opening that, when aligned with corresponding openings in other optical films  70  forms opening  124 . Pin  150  may be formed from metal, plastic, glass, ceramics, polymers, combinations of these materials or other suitable materials. 
     Openings in optical films  70  may be elongated openings such as slots so that, when viewed from a particular direction (e.g., the direction shown in  FIG. 21 ), some openings appear to have a width that is larger than the width of the openings in other films. Films  70  may include openings of various sizes that correspond to the coefficient of thermal expansion (CTE) of that film. For example, a film with a larger CTE may be provided with a larger opening. A film with a smaller CTE may be provided with a smaller opening. However, this is merely illustrative. If desired, films  70  may be provided with openings having a common size with openings in other films. For example, each film  70  may be provided with an elongated opening such as elongated openings  124 - 1 ,  124 - 2 , and  124 - 3  of  FIG. 22 . 
     As shown in  FIG. 22 , pin  150  may pass through openings  124 - 1 ,  124 - 2 , and  124 - 3  in three respective films  70 . Openings  124 - 1 ,  124 - 2 , and  124 - 3  may have a common overlapping portion and portions that do not overlap due to the orientation of the elongated axis of the openings. 
     Each optical film  70  may have a preferred direction of thermal expansion (i.e., a direction in which that particular film expands more relative to expansions in other directions when the film is heated). As an example, films  70  of  FIG. 22  may include three films having respective preferred directions of thermal expansion PD- 1 , PD- 2 , and PD- 3 . Each film  70  may include an elongated opening that is elongated along the preferred direction of thermal expansion. In the example of  FIG. 20 , films  70  include a first film having an elongated opening  124 - 1  that is elongated along preferred direction of thermal expansion PD- 1  for that film, a second film having an elongated opening  124 - 2  that is elongated along preferred direction of thermal expansion PD- 2  for that film, and a third film having an elongated opening  124 - 3  that is elongated along preferred direction of thermal expansion PD- 3  for that film. 
     Providing optical films  70  with elongated openings that are elongated along the preferred direction of thermal expansion for each film and a pin in the elongated openings may help partially constrain the movement of films  70  within display  14  while allowing the films to expand and/or contract when the temperature of the display changes. 
     The example of  FIG. 22  in which films  70  include three optical films having elongated openings is merely illustrative. Films  70  may include more than three optical films having elongated openings, less than three optical films having elongated openings, films with openings having other shapes, and/or optical films without any elongated openings. 
     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: 20130219
Publication Date: 20170411
Grant Date: 20170411
Priority Date: 20120928
Inventors: FRANKLIN JEREMY C.
GIBBS KEVIN D.
QIAN AMY
RAFF JOHN
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133602", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0088", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133602", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0088", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 50384846