PATENT DOCUMENT

Publication Number: US-10571743-B2
Application Number: US-201715688736-A
Country: US
Kind Code: B2

Title: Electronic devices with backlit displays

Abstract:
A display may have a backlight unit that provides backlight illumination. The backlight unit may include a light guide that distributes light through the display. Light-emitting diodes may emit light into the light guide. A reflector that is overlapped by the light guide may help reflect light upwards through an array of pixels. The backlight unit may have a chassis that receives the reflector, light guide, light-emitting diodes, and optical films such as diffusers and prism films. Optical and mechanical features in the backlight unit may enhance color and intensity uniformity for the backlight illumination and may help enhance durability.

Claims:
What is claimed is: 
     
       1. Apparatus, comprising:
 display layers that form an array of pixels configured to display images; and 
 backlight structures that provide backlight illumination that passes through the array of pixels, wherein the backlight structures include:
 a chassis; 
 a reflector overlapping the chassis, wherein the reflector has an edge; 
 a printed circuit; 
 a light-emitting diode mounted on the printed circuit; 
 a strip of reflective tape having a first portion that overlaps the printed circuit and a second portion that contacts the chassis, wherein the strip of reflective tape has an edge that is separated by a gap from the edge of the reflector, and wherein the gap exposes a portion of the chassis; and 
 a light guide layer that overlaps the reflector and that entirely overlaps the strip of reflective tape. 
 
 
     
     
       2. The apparatus defined in  claim 1  further comprising:
 clear adhesive that attaches an edge portion of the light guide layer to the strip of reflective tape and that is configured to allow light to leak out of the light guide layer. 
 
     
     
       3. The apparatus defined in  claim 2  wherein the backlight structures include a film overlapping the light guide layer, wherein a portion of the film adjacent to an edge portion of the light guide layer is coated with light-absorbing material. 
     
     
       4. The apparatus defined in  claim 3  wherein the film forms a diffuser and wherein the light-absorbing material comprises black material. 
     
     
       5. The apparatus defined in  claim 4  further comprising colored material adjacent to the edge portion of the light guide layer. 
     
     
       6. The apparatus defined in  claim 5  wherein the colored material comprises a material selected from the group consisting of: blue material, yellow material, red material, and orange material. 
     
     
       7. The apparatus defined in  claim 6  wherein the colored material comprises tape selected from the group consisting of: blue tape, yellow tape, red tape, and orange tape. 
     
     
       8. The apparatus defined in  claim 7  wherein the portion of the film adjacent to the light guide layer that is coated with the light-absorbing material comprises a surface of the film facing the tape. 
     
     
       9. The apparatus defined in  claim 6  further comprising a strip of foam interposed between a sidewall portion of the chassis and the light guide layer. 
     
     
       10. The apparatus defined in  claim 2  wherein the light guide layer has an edge surface with an average roughness characterized by an Ra value of less than 0.2 microns. 
     
     
       11. The apparatus defined in  claim 2  wherein the light guide layer comprises:
 a first surface facing the display layers; and 
 an opposing second surface facing the reflector; 
 light-scattering features on the second surface having a first peak-to-valley distance; and 
 antifriction protrusions on the second surface having a second peak-to-valley distance that is greater than the first peak-to-valley distance. 
 
     
     
       12. The apparatus defined in  claim 2  wherein the light guide layer has a pencil hardness of at least H. 
     
     
       13. The apparatus defined in  claim 2  wherein the chassis includes a metal chassis layer, the apparatus further comprising a reflector layer that is interposed between the metal chassis layer and the light-emitting diode. 
     
     
       14. Apparatus, comprising:
 display layers that form an array of pixels configured to display images; and 
 backlight structures that provide backlight illumination that passes through the array of pixels, wherein the backlight structures include:
 a chassis; 
 a reflector overlapping the chassis, wherein the reflector has an edge; 
 a printed circuit; 
 a light-emitting diode mounted on the printed circuit; 
 a strip of reflective tape that overlaps the printed circuit and that has an edge that is separated by a gap from the edge of the reflector, wherein the gap exposes a portion of the chassis; 
 a light guide layer overlapping the reflector and the strip of reflective tape; 
 a strip of foam interposed between a sidewall portion of the chassis and the light guide layer; and 
 a first layer of adhesive between the strip of foam and the sidewall portion, a layer of polymer, a second adhesive layer that attaches the layer of polymer to the strip of foam, and a white paint layer on a side of the layer of polymer facing away from the sidewall portion. 
 
 
     
     
       15. Apparatus, comprising:
 display layers that form an array of pixels configured to display images; and 
 backlight structures that provide backlight illumination that passes through the array of pixels, wherein the backlight structures include:
 a metal chassis layer, wherein the metal chassis layer has a planar rear wall portion that lies in a plane and has an edge portion that is bent out of the plane toward the display layers at an angle of 0.1-0.7°; 
 a reflector overlapping the metal chassis layer, wherein the reflector has an edge; 
 a printed circuit; 
 a light-emitting diode mounted on the printed circuit; 
 a strip of reflective tape that overlaps the printed circuit and that has an edge that is separated by a gap from the edge of the reflector, wherein the gap exposes a portion of the metal chassis layer; and 
 a light guide layer overlapping the reflector and the strip of reflective tape. 
 
 
     
     
       16. An electronic device, comprising:
 an array of pixels configured to display images; 
 control circuitry; and 
 backlight structures that provide backlight illumination for the array of pixels, wherein the backlight structures include:
 a light guide layer having an edge, 
 a first reflector that is overlapped by the light guide layer and that has an edge, 
 a metal chassis structure configured to receive the light guide layer and the first reflector, 
 a printed circuit board, 
 a light-emitting diode that is mounted on the printed circuit board and that emits light into the light guide layer, 
 a second reflector that is interposed between the metal chassis and the light-emitting diode, 
 a third reflector having a first portion that is mounted to the printed circuit board, a second portion that is mounted to the metal chassis, and an edge that is separated by a gap from the edge of the first reflector to expose a strip of the metal chassis, and 
 at least one optical film, wherein the second reflector is interposed between the light guide layer and the at least one optical film. 
 
 
     
     
       17. The electronic device defined in  claim 16  further comprising:
 clear adhesive that attaches the light guide layer to the third reflector.

Description:
This application claims the benefit of provisional patent application No. 62/487,082, filed on Apr. 19, 2017, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices with displays, and, more particularly, to backlit displays. 
     Electronic devices often include displays. Backlit displays such as backlit liquid crystal displays include backlight units. A backlight unit produces light that travels outwardly through an array of pixels in a display. The pixels modulate the intensity of the light from the backlight unit to create images on the display. 
     Backlight units help ensure that displays can display images in a wide variety of ambient lighting conditions. If care is not taken, however, the backlight illumination from a backlight unit will not be uniform and the structures in the backlight unit will not be sufficiently robust. 
     SUMMARY 
     A display may have a backlight unit that provides backlight illumination. The backlight unit may include a light guide that distributes light through the display. Light-emitting diodes may emit light into the light guide. A reflector that is overlapped by the light guide may help reflect light upwards through an array of pixels. The backlight unit may have a chassis that receives the reflector, light guide, light-emitting diodes, and optical films such as diffusers and prism films. Optical and mechanical features in the backlight unit may enhance color and intensity uniformity for the backlight illumination and may help enhance durability. 
     A black paint layer and blue material may be placed along an edge of the light guide to reduce light reflections and color-correct backlight illumination that has reflected from the chassis. The black paint layer may be formed on the underside of a portion of a diffuser. The blue material may be provided in the form of blue tape affixed to the chassis. If desired, materials of other colors may be placed along the edge of the light guide for color correction (e.g., yellow material such as yellow paint, yellow tape, yellow plastic, red material such as red paint, red tape, red plastic, orange material such as orange paint, orange tape, orange plastic, etc.). The use of blue color corrective material is sometimes described herein as an example. In general, material of any suitable color for color correction may be used. 
     A reflector strip may overlap a printed circuit to which the light-emitting diodes are mounted. The reflector strip may have an edge that is separated by a gap from an edge of the reflector under the light guide. The gap may expose a portion of a metal layer in the chassis. Optically clear adhesive may be used to attach the light guide layer to the reflector strip. The optically clear adhesive may give rise to light leakage from the light guide that helps eliminate a dark band in the backlight illumination that might otherwise arise from the exposure of the metal layer by the presence of the gap. 
     An additional reflector strip may be interposed between a metal portion of the chassis that overhangs the light-emitting diodes and the light-emitting diodes. The additional reflector strip may help prevent moisture from reaching the light-emitting diodes and potentially damaging phosphor on the light-emitting diodes. 
     A layer of foam may be interposed between the edge of the light guide layer and the chassis. The foam layer may be overlapped by a polymer layer and may be attached using adhesive. During drop events, the foam layer may help cushion light guide layer impacts with the chassis and may help to reduce particle formation. 
     The light guide layer may have upper and lower coating layers with light scattering features. The light scattering features on the lower coating layer may be characterized by a first peak-to-valley distance. Antifriction protrusions on the lower coating layer may be characterized by a second peak-to-valley distance that is larger than the first peak-to-valley distance. The antifriction protrusions may help prevent sticking between the light guide layer and the reflector. 
     The light guide layer and/or an adjacent diffuser layer in the backlight unit may be configured to reduce white spots by forming one or both of these layers from hard materials. The light guide layer may also be intentionally cupped with a concave surface facing the pixel array and the chassis may be provided with a matting curvature near the edges of the display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of an illustrative display in accordance with an embodiment. 
         FIG. 4  is an exploded perspective view of illustrative backlight structures in accordance with an embodiment. 
         FIG. 5  is a top view of an edge portion of an illustrative diffuser layer in accordance with an embodiment. 
         FIG. 6  is a top view of an edge portion of an illustrative light guide layer in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of an illustrative edge portion of a backlight in accordance with an embodiment. 
         FIG. 8  is a cross-sectional side view of an illustrative backlight and associated light source in accordance with an embodiment. 
         FIG. 9  is a perspective view of an illustrative edge of a backlight layer such as a light guide layer and an associated backlight chassis structure in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of an illustrative foam layer of the type that may be mounted adjacent to an edge of a light guide layer and/or other backlight layers in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of an illustrative light guide layer and associated light source such as a light-emitting diode in accordance with an embodiment. 
         FIG. 12  a cross-sectional side view of a light guide layer with illustrative friction-reducing protrusions in accordance with an embodiment. 
         FIG. 13  is a cross-sectional end view of the illustrative light guide layer of  FIG. 12  in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of a portion of a backlight in accordance with an embodiment. 
         FIG. 15  is a side view of illustrative cupped and planar light guide layers in accordance with embodiments. 
         FIGS. 16 and 17  are cross-sectional side views of portions of illustrative backlight units with cupped light guide layers in accordance with embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device of the type that may be provided with a display is shown in  FIG. 1 . Electronic device  10  may be a computing device such as 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, a device embedded in eyeglasses or other equipment worn on a user&#39;s head, or other wearable or miniature device, a computer display that does not contain an embedded computer, a computer display that includes 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. In the illustrative configuration of  FIG. 1 , device  10  is a portable device such as a cellular telephone, media player, tablet computer, watch or other wrist device, or other portable computing device. Other configurations may be used for device  10  if desired. The example of  FIG. 1  is merely illustrative. 
     In the example of  FIG. 1 , device  10  includes a display such as display  14  mounted in housing  12 . Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     Display  14  may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.) or may be a display that is not touch-sensitive. Capacitive touch screen electrodes may be formed from an array of indium tin oxide pads or other transparent conductive structures. A touch sensor may be formed using electrodes or other structures on a display layer that contains a pixel array or on a separate touch panel layer that is attached to the pixel array (e.g., using adhesive). 
     Display  14  may include an array of pixels  22 . The array of pixels in display  14  may form an active area such as rectangular active area AA of  FIG. 1  in which images are displayed for a user. One or more edges of active area AA may be bordered by an inactive area that is free of pixels such as inactive areas IA. Borderless designs for display  14  and arrangements in which active area AA is bordered only on two sides by inactive areas IA may be used, if desired. 
     Pixels  22  may be formed from liquid crystal display (LCD) components, an array of electrophoretic pixels, an array of electrowetting pixels, or pixels based on other display technologies. Configurations in which display  14  is a liquid crystal display with a backlight are sometimes described herein as an example. This use of liquid crystal display technology for forming display  14  is merely illustrative. Display  14  may, in general, be formed using any suitable type of pixels. 
     Display  14  may be protected using a display cover layer such as a layer of transparent glass or clear plastic. Openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button, a speaker port, or other component. Openings may be formed in housing  12  to form communications ports (e.g., an audio jack port, a digital data port, etc.), to form openings for buttons, etc. 
       FIG. 2  is a schematic diagram of device  10 . As shown in  FIG. 2 , electronic device  10  may have control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may 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. Processing circuitry in control circuitry  16  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  18  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 devices  18  may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors (e.g., ambient light sensors, proximity sensors, orientation sensors, magnetic sensors, force sensors, touch sensors, pressure sensors, fingerprint sensors, etc.), light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  18  and may receive status information and other output from device  10  using the output resources of input-output devices  18 . Input-output devices  18  may include one or more displays such as display  14 . 
     Control circuitry  16  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  16  may display images on display  14  using an array of pixels in display  14 . While displaying images, control circuitry  16  may control the transmission of each of the pixels in the array and can make adjustments to the amount of backlight illumination for the array that is being produced by backlight structures in display  14 . 
     Display  14  may have a rectangular shape (i.e., display  14  may have a rectangular footprint and a rectangular peripheral edge that runs around the rectangular footprint) or may have other suitable shapes. Display  14  may be planar or may have a curved profile. 
     A cross-sectional side view of display  14  is shown in  FIG. 3 . As shown in  FIG. 3 , display  14  may include backlight structures such as backlight unit (backlight)  42  for producing backlight such as backlight illumination  44 . During operation, backlight illumination  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 3 ) 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 illumination  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 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 . 
     Layers  58  and  56  may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers  58  and  56  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 pixel circuits based on thin-film transistors and associated electrodes (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. Configurations in which color filter elements are combined with thin-film transistor structures on a common substrate layer in the upper or lower portion of display  14  may also be used. 
     During operation of display  14  in device  10 , control circuitry (e.g., one or more integrated circuits on a printed circuit) may be used to generate information to be displayed on display  14  (e.g., display data). The information to be displayed may be conveyed to one or more display driver integrated circuits such as illustrative circuit  62 A or illustrative circuit  62 B using a signal path such as a signal path formed from conductive metal traces in a rigid or flexible printed circuit such as printed circuit  64  (as an example). 
     Backlight structures  42  may include a light guide layer such as light guide layer  78  (sometimes referred to as a light guide structure or light guide). Light guide layer  78  may be formed from one or more layers of transparent material such as clear glass or plastic. For example, light guide layer  78  may be a molded polymer that forms a light guide plate or may be a thin flexible polymer film produced in a roll-to-roll process or other process. Light guide layer  78  may be coated on one or both sides with polymer coating layers to form features such as light scattering features. During operation of backlight structures  42 , light sources such as light source  72  may generate light that creates backlight illumination  44 . In the example of  FIG. 3 , light source  72  is located along the left edge of display  14 . If desired, light sources can be provided along two or more edges of display  14 . 
     Light source  72  may include an array of light-emitting diodes. The light-emitting diodes may run along one or more edges of light guide layer  78  such as edge  76  of light guide layer  78  (i.e., into the page along the X axis in the orientation of  FIG. 3 ). Light-source  72  may emit light  74  into edge  76  of light guide layer  78 . Light  74  may be distributed throughout light guide layer  78  due to the principal of total internal reflection. In the arrangement of  FIG. 3 , light  74  propagates to the right (in the positive Y direction) in light guide layer  78  and spreads out in dimension X. Light scattering features (protrusions, recesses, etc.) may be incorporated into light guide layer  78  (e.g., on the upper and/or lower surface of layer  78 ) to scatter light from layer  78 . For example, bumps, ridges, and other protrusions, indentations, grooves, and other recesses, and/or other irregular surface features may be provided on the upper surface and/or lower surface of light guide layer  78  (e.g., in coating layers on the upper and lower surfaces of layer  78 ) to serve as a light scattering features. 
     Light that is scattered upwards in direction Z from light guide layer  78  may serve as backlight illumination  44  for display  14 . Light 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 plastic covered with a dielectric mirror thin-film coating. 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 illumination  44  and thereby reduce hotspots and light collimating films such as prism films (sometimes referred to as brightness enhancement films) for directing backlight illumination  44  towards direction Z. Optical films  70  may overlap the other structures in backlight unit  42  such as light guide layer  78  and reflector  80 . For example, if light guide layer  78  has a rectangular footprint in the X-Y plane of  FIG. 3 , optical films  70  and reflector  80  may have a matching rectangular footprint. If desired, films such as compensation films may be incorporated into other layers of display  14  (e.g., a reflective polarizer layer). With one illustrative configuration, there are four films  70  in backlight  42 . The lowermost of the four films and the uppermost of the four films may be diffuser layers (sometimes referred to as diffusers) and the middle two films may be prism films. Other arrangements for films  70  may be used, if desired. 
     The structures of backlight  42  may be mounted in a chassis or other support structures (e.g., portions of housing  12 , etc.). As shown in  FIG. 4 , for example, backlight layers  82  (e.g., films  70 , light guide layer  78 , and/or reflector  80 ) may be received within rectangular opening  84  of backlight chassis  86 . Chassis  86  may have a rectangular ring shape and may be formed from materials such as metal (e.g., a sheet metal structure with features formed by bending and/or cutting) and/or polymer (e.g., plastic that is molded over the metal). Edge portions of one or more of the layers of display  14  (e.g., layers  82 ) may protrude under one or more structures along edge portion  86 E of chassis  86  (e.g., under overhanging metal chassis and/or plastic chassis structures). A strip of light-emitting diodes in light source  72  may also be mounted under overlapping portions of chassis  86  such as chassis structures in edge portion  86 E. 
     If desired, one or more of the layers in backlight  42  may have notches. As shown in  FIG. 5 , for example, diffuser layers such as diffuser  70 D may have left and right protrusions separated by a central notch. In some embodiments, protruding edge portions of diffuser  70 D may be captured under an overhanging portion of edge  86 E of chassis  86 . Light guide  78  may, if desired, have left and right notches separated by a central protrusion. In some embodiments, a central protruding edge portion of light guide  78  may protrude under an overhanging portion of edge portion  86 E of chassis  86  and may be coupled to underlying structures in backlight  42 . 
       FIG. 7  is a cross-sectional side view of an edge portion of backlight  42  showing how diffuser  70 D (e.g., one of the protruding portions of diffuser  70 D of  FIG. 5 ) may overlap the edge of light guide plate  78 . Inner surface  86 I of chassis  86  may be formed from metal (e.g., sheet metal) and may be reflective. To prevent excess light reflection that could give rise to a bright band in backlight illumination  44  along the peripheral edge of display  14 , inner (lower) surface  70 DL of diffuser  70 D may be covered with light absorbing coating  100 . Coating  100  may, for example, be a layer of black paint (ink) or other light-absorbing material. The presence of coating  100  may suppress excessive light reflections from surface  86 I. 
     Exposed chassis surfaces (e.g., metal surfaces such as inner surface  86 I) may absorb more blue light than red light, causing reflected light to be reddish or to have other undesired color casts. Colored material such as blue material may be formed on chassis  86  or other structures along the edge of light guide layer  78  to help color correct backlight illumination  44  along the edge of display  14 . As shown in  FIG. 7 , color correcting material may be provided as a coating (coating  104 ) on tape  102 . Tape  102  (e.g., single sided adhesive tape with a downwardly-facing adhesive layer  102 A on carrier layer  102 C) may, for example, be provided with a color-correcting coating such as blue paint (e.g., blue paint forming coating  104 ) or paint of other suitable colors. Blue coating material such as coating  104  may help color correct the reflecting light (making the reddish light bluer) so that backlight illumination  44  has a desired white color along the edge of backlight  42 . If desired, tape  102  and blue coating  104  may be attached to other portions of chassis  86  along the edge of backlight  42 , black coating  100  may be formed on other portions of chassis  86  along the edge of backlight  42 , the positions of coating  100  and coating  104  may be swapped, and/or other configurations may be used for incorporating stray light color and stray light intensity adjustment structures into display  14  to adjust the light intensity and color of peripheral portions of backlight illumination  44  in backlight  42 . The configuration of  FIG. 7  is illustrative. 
     A cross-sectional side view of backlight  42  is shown in  FIG. 8 . In the example of  FIG. 8 , light source (light-emitting diode)  72  is soldered to flexible printed circuit  94  using solder  92 . Inactive area IA of display  14  may overlap the outer edge of light guide  78 . Top reflector  90  may be formed from a strip of reflective material (e.g., white reflective tape formed from a polymer layer with a white ink coating, a strip of a polymer sheet with a white coating, and/or other reflective structures). Top reflector (reflector strip)  90  may have an outer edge that faces an outer wall of chassis  86  and may have an opposing inner edge that is aligned with or that slightly overlaps edge  80 E of reflector  80 . In this configuration, at least some of top reflector  90  overlaps light source (light-emitting diode)  72  and is interposed between the overhanging portion (metal chassis portion) of edge  86 E of chassis  86  and each light-emitting diode in source  72 . When top reflector  90  is interposed between light-emitting diodes  72  and chassis  86  in this way, moisture (e.g., water drops) that might condense on the inner surface of the overhanging chassis portion and that therefore might damage phosphor on light-emitting diodes  72  may be prevented from reaching light-emitting diodes  72 . 
     Light guide fixing tape  98  may have a width (in dimension Y) of about 0.5-2 mm, about 1 mm, at least 0.4 mm, or less than 2.5 mm. Tape  98  (sometimes referred to as optically clear adhesive tape, optically clear adhesive, transparent adhesive, or clear adhesive) may have a transparent carrier layer such as polymer film layer  98 - 2  and opposing upper and lower clear adhesive coating layers  98 - 1 . The upper adhesive coating layer  98 - 1  attaches tape  98  to light guide  78 . The lower adhesive coating layer attaches tape  98  to a strip of reflective tape  96  (sometimes referred to as a reflector, reflective strip, reflector layer, reflector strip, etc.). 
     Reflective tape  96  may be formed form a white reflective tape or other reflective structure. The outer edge of reflective tape  96  may overlap flexible printed circuit  94  and may help enhance the reflectively of printed circuit  94  so that light is reflected upwards through layers  70  without excess light absorption near the periphery of backlight  42 . The inner edge of reflective tape is separated by a gap G from opposing edge  80 E of reflector  80 . Gap G may have a width of 0.3 mm, at least 0.1 mm, at least 0.2 mm, at least 0.3 mm, less than 1 mm, less than 0.7 mm, 0.1-2 mm, or other suitable size. The presence of gap G may help satisfy assembly tolerances during manufacturing of backlight  42 . At the same time, gap G may expose underlying metal portions of chassis  86  that absorb more light than reflector  80  and that therefore have the potential to create a dark band in backlight illumination  44  along the edge of display  14 . The presence of tape  98  in a location that overlaps a portion of reflective tape  96  helps create light leakage from light guide  78  that counteracts the absorption of the exposed metal chassis layer in gap G and thereby helps prevent any dark bands from forming in backlight illumination  44  along the peripheral edge of display  14 . 
     To prevent particles from being formed in the event that device  10  is inadvertently dropped, the inner surface of chassis  86  (e.g., the inner surface of a plastic portion of chassis  86 , a metal portion of chassis  86 , and/or other portions of chassis  86 ) may be provided with a layer of compressible material such as compressible layer  120  of  FIG. 9 . As shown in  FIG. 9 , compressible layer  120  (e.g., a layer of foam, a layer of elastomeric material, and/or other compressible material) may have one surface that is coupled to an inner sidewall surface of chassis  86  (e.g., with adhesive) and may have an opposing surface that faces the surface of the peripheral edge of light guide  78  and/or other backlight unit layers. This suppresses the formation of particles that might otherwise be formed (e.g., by chipping off of light guide  78 ) if light guide  78  were forced against chassis  86  directly during a drop event. 
     An illustrative configuration that may be used for forming compressible layer  120  is shown in the cross-sectional side view of  FIG. 10 . As shown in  FIG. 10 , layer  120  may be formed from a coated adhesive tape layer. The tape layer may have a first adhesive layer such as adhesive layer  122  for attaching layer  120  to the inner surface of chassis  86 . Foam layer  124  may be formed from a compressible closed cell or open cell foam. Foam  124  may be black or other suitable color. Adhesive layer  126  may be used to couple foam layer  124  to polymer layer  128 . Polymer layer  128  may be formed from a flexible sheet of polymer material such as a layer of polyethylene terephthalate (PET). Coating layer  130  may be formed from a reflective material such as white paint and may help match the appearance and reflectivity of layer  120  to the appearance and reflectivity of chassis  86  (e.g., plastic portions of chassis  86  such as white plastic portions). The presence of polymer layer  128  may help protect foam  124  and thereby reduce the likelihood of the formation of foam particles during drop events. 
     By using computer-numerical-controlled polishing techniques, the edge roughness of light guide layer  78  may be reduced relative to that of raw die cut films. Die cut films may, as an example, have edge surfaces with a roughness average value (Ra value) of 0.3 microns. By using a polishing tool such as a computer numerical control (CNC) machine with a polishing head to polish edge  76  of light guide  78 , the roughness of surfaces such as surface  76  of light guide  78  of  FIG. 3  may be reduced to a roughness average value (Ra value) of less than 0.2 microns, less than 0.1 microns, less than 0.05 microns, 0.001-0.15 microns, or other suitable value). An Ra value of 0.3 microns is illustrated by surface  76 PA of  FIG. 11 , whereas an Ra value of 0.2 microns or less is illustrated by surface  76  of  FIG. 11 . Reduced surface roughness may enhance coupling of light  74  into edge  76  by 7-10%. 
       FIGS. 12 and 13  are cross-sectional side views of an illustrative light guide layer  78 . As shown in  FIGS. 12 and 13 , light guide layer  78  may have a transparent film, molded light guide plate, or other transparent layer such as layer  78 - 2 . Layer  78 - 2  may be a transparent polymer such as a layer of polycarbonate, a layer of polymethyl methacrylate (acrylic), or other clear plastic for guiding light  74  from light source  72  throughout display  14 . 
     Layer  78 - 2  may have opposing outwardly facing and inwardly facing surfaces. An upper (outer) layer such as upper coating  78 - 1  may be formed the outwardly facing side of layer  78 - 2  (e.g., the side of layer  78  facing away from reflector  80 ). A lower (inner) layer such as lower coating  78 - 3  may be formed on the inwardly facing side of layer  78 - 2  (e.g., the side of layer  78  facing reflector  80 ). Coatings  78 - 1  and  78 - 3  may, if desired, be applied to layer  78 - 2  as liquid polymers in a roll-to-roll coating process. Following ultraviolet light curing or curing with other techniques, coating  78 - 1  and/or coating  78 - 3  may form solid layers on the opposing surfaces of layer  78 - 2  with recesses and/or protrusions that form light-scattering features. The light-scattering features may be patterned using embossing (stamping) during and/or after roll-to-roll processing, may be pattered using laser processing techniques, and/or may be formed using other processing techniques. These light-scattering structures may help extract light from layer  78 - 2  for use as backlight illumination  44 . 
     As shown in  FIG. 13 , for example, upper coating  78 - 1  may have light-scattering features such as ridges or other protrusions to help scatter light  74  outwardly as backlight illumination  44 . Lower coating  78 - 3  may also have light-scattering features (e.g., prism structures or other protruding and/or recessed light-scattering structures) to help scatter light  74  outwardly as backlight illumination  44 . The ridges in upper coating  78 - 1  may, as an example, include elongated raised ridges that extend along light guide layer  78  away from light source  72 . The light-scattering structures in lower coating  78 - 3  may be characterized by peak-to-valley distances of about 2-3 microns and lateral dimensions of about 10-30 microns (as an example). 
     To help reduce the coefficient of friction between coating  78 - 3  and surface  80 T of reflector  80 , coating  78 - 3  may be provided with additional protrusions (sometimes referred to as antifriction protrusions) such as protrusions  78 A of height H. Protrusions  78 A may be elongated ridges, bumps, and/or other features of height H. Height H, which represents a peak-to-valley distance associated with antifriction protrusions  78 A, may have a value of about 4-7 microns, 5-7 microns, at least 2 microns, at least 4 microns, at least 5 microns, at least 6 microns, at least 7 microns, 5-10 microns, less than 20 microns, less than 10 microns, or other suitable size greater than the maximum peak-to-valley distance of the light-scattering structures in coating layer  78 - 3 . There may be any suitable density of protrusions  78 A on light guide layer  78  (e.g., 19 protrusions per square mm, 5-30 protrusions per square mm, at least 5 protrusions per square mm, at least 10 protrusions per square mm, fewer than 20 protrusions per square mm, fewer than 30 protrusions per square mm, or other suitable number of protrusions per square mm). In the presence of excessive friction between reflector  80  and layer  78 , there is a risk that light guide layer  78  could stick to reflector  80  and drag reflector  80  laterally during thermal expansion. The use of antifriction protrusions  78 A helps reduce friction between upper surface  80 T of reflector  80  and the opposing lower surface of coating layer  78 - 3  and thereby helps prevent binding between reflector  80  and light guide layer  78  during expansion and contraction of light guide plate  78 . The density and size of antifriction protrusions  78 A generally makes these protrusions unsuitable for use as light-scattering features (e.g., light scattering is primarily performed by the prism structures in coating  78 - 3 , not by protrusions  78 A). At the same time, the greater height of protrusions  78 A than the light-scattering features in layer  78 - 3  allows protrusions  78 A to serve as effective antifriction structures. 
       FIG. 14  shows how components  140  (integrated circuits, discrete components, etc.) may be mounted on a substrate such as printed circuit  142  under backlight  42 . During use of device  10 , printed circuit  142  may be pressed upwards in the +Z direction, which may cause components  140  to press against certain areas of chassis  86  (e.g., certain portions of a sheet metal layer forming a rear wall of chassis  86 ). This can give rise to different pressures on different areas of light guide layer  78  and can cause the ridges or other light scattering features of coating  78 - 1  to wet out where these features contact lower surface  70 DL of diffuser  70 D. Selective wetting out of light guide layer  78  against diffuser  70 D creates a risk that undesirable white spots may become visible in active area AA of display  14 . To prevent white spots, light guide layer  78  and/or lower diffuser  70 D may have a hardness that is relatively high (e.g., pencil hardness values of H to 3H, at least H, at least 2H, or at least 3H). Layers  78  and/or  70 D may, for example, be formed from polymers of H to 3H hardness. If desired, the hardness of layer  70 D may be enhanced by using light-scattering particles  70 P (e.g., polymer or glass beads) formed from hard materials (e.g., pencil hardness of at least H, at least 2H, or at least 3H). 
       FIG. 15  shows how light guide layer  78  (e.g., a layer of molded acrylic or other clear plastic) may be flat (as shown by layer  78 F), may be cupped downwardly (as shown by layer  78 D, which has a convex surface facing outwardly toward display layers  46  and an opposing concave surface facing inwardly toward reflector  80 ), or may be cupped upwardly (as shown by layer  78 U, which has a concave surface facing outwardly toward display layers  46  and a convex surface facing inwardly toward reflector  80 ). Due to the presence of moisture and heat, layer  78  will tend to bend and therefore form either the upward or downward cupping shapes of  FIG. 15 . To ensure that layer  78  has a desired shape (e.g., to avoid Moiré effects that might arise if layer  78  were raised towards films  70  in the center of device  10 ), layer  78  may be manufactured with a slight downward cup. This downward cupping bias ensures that any additional cupping of layer  78  will be in the downwards direction. 
       FIG. 16  shows how the left edge of downwardly cupped light guide layer  78 D will tend to separate from a reflector such as reflector  80  that is flat. This can arise when chassis  86  is bend downwardly to accommodate the thickness of adhesive tape  150  and thereby allows reflector  80  to assume a planar shape. In planar shape for reflector  80  of  FIG. 16 , an air gap AG develops between reflector  80  and light guide layer  78 D that can lead to nonuniformity in the intensity of emitted backlight illumination  44 . 
     To avoid non-uniformity in backlight illumination  44 , chassis  86  may have bent edge portions (portions along the periphery of display  14 ) such as metal chassis rear wall portion  86 EB. Portion  86 EB is angled at a non-zero angle A with respect to the XY plane and with respect to planar metal rear wall portion  86 R of chassis  86 , as shown in  FIG. 17 . The value of A may be, for example, 0.1-0.7°, at least 0.05°, at least 0.1°, at least 0.2°, at least 0.3°, less than 2°, less than 1°, less than 0.8°, or other suitable non-zero angle. As shown in  FIG. 17 , adhesive tape  150  may be used to help attach reflector  80  to chassis  86 . Edge portion  86 EB of chassis  86  is overlapped by tape  150 , a corresponding edge portion of reflector  80 , and a corresponding edge portion of layer  78 D. Because at least edge portion  86 EB is angled by at least non-zero angle A with respect to the XY plane, air gap AG is minimized or is absent and backlight nonuniformity is reduced. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20170828
Publication Date: 20200225
Grant Date: 20200225
Priority Date: 20170419
Inventors: KO, BYUNGSOO
Xu, Daming
SUH, HEESANG
TOM, MICHAEL
LU, SHIN-YING
MUELLER, THOMAS
ZHU, WENYONG
YIN, VICTOR H.
SON, Mookyung
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B6/0028", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0031", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0073", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133611", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0036", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0025", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0088", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0028", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0031", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0073", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0025", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133611", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0036", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0088", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0055", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0073", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0036", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0088", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 63854340