WO2022060581A1

WO2022060581A1 - Integrated lcd backlight units with glass circuit boards

Info

Publication number: WO2022060581A1
Application number: PCT/US2021/048955
Authority: WO
Inventors: Dmitri Vladislavovich Kuksenkov; Young Suk Lee; Hyung Soo Moon
Original assignee: Corning Incorporated
Priority date: 2020-09-18
Filing date: 2021-09-03
Publication date: 2022-03-24
Also published as: CN116368412A; TW202215128A; KR20230070471A; JP2023543185A

Abstract

Display devices are disclosed comprising a backlight unit, wherein the light sources illuminating the display panel, for example LEDs, are integrated into the light board assembly, and more specifically on the light board substrate. The light board substrate can be a glass circuit board.

Description

INTEGRATED LCD BACKLIGHT UNITS WITH GLASS CIRCUIT BOARDS

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Serial No. 63/080,276 filed on September 18, 2020, the content of which is relied upon and incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure is directed to a display device, and in particular a display device comprising a backlight unit with light sources integrated onto a glass circuit board.

BACKGROUND

[0003] TFT LCD displays are the most widespread type of flat panel display technology. To stay competitive against OLED displays and various emerging display technologies such as QD-OLED display, micro-LED displays, etc., TFT LCD display technology continues to innovate, resulting in improved picture quality, including higher resolution and brightness, wider color gamut, as well as aesthetics - narrow (or zero) bezel and thin form factors.

Recently, mini-LEDs have drawn attention, especially in backlight applications, because they can enable thin form factor by reducing OD (Optical Distance), high contrast by increased the number of dimming zones, high peak brightness for HDR, and narrow bezel or bezel-less designs. With rapid decreases in the price of mini-LEDs, the overall cost is dominated by surface mounting technology (SMT) processes. Accordingly, IT display (monitors, notebook, etc.) and TV set manufacturers are adopting direct-lighted backlight units (BLU) with mini-LEDs.

[0004] The advent of mini-LED adaptation in BLU modules requires new materials and stack designs. Shorter ODs and narrow pitch distance between LEDs eliminate the need for a 2^nd lens for additional light spreading. At the same time, the diffuser plate needs higher thermal stability against heat generated by LEDs. Smaller bond pads of mini-LEDs and higher SMT equipment positioning accuracy require high pattern accuracy of LED circuit boards, down to < 20 micrometers (pm), compared to approximately 50 pm for conventional PCBs.

SUMMARY

[0005] Liquid crystal displays are commonly used in various electronics, such as cell phones, laptops, electronic tablets, televisions, and computer monitors. Liquid crystal displays are light valve-based displays in which the display panel includes an array of individually addressable light valves. Liquid crystal displays may include a backlight for producing light that may then be wavelength converted, filtered, and/or polarized to produce an image from the LCD panel. Backlights may be edge-lit or direct-lit. Edge-lit backlights may include a light emitting diode (LED) array edge-coupled to a light guide plate that emits light from its surface. Direct-lit backlights may include a two-dimensional (2D) array of LEDs behind the LCD panel.

[0006] Recently, glass has become available for hybrid glass and/or plastic diffuser plates in premium ultra-narrow bezel TFT-LCD TVs. Improved mechanical properties and/or reduced thickness compared to polymer materials can be achieved using glass materials for multiple layers and/or functions such as glass circuit boards and glass diffusers or light guide plates, or by integrating functions of multiple layers in a single glass plate. Such integrated glass circuit boards are expected to eliminate one or more layers in the BLU design and may present an additional cost reduction opportunity.

[0007] Accordingly, a display device is disclosed, comprising a display panel and a backlight unit arranged adjacent the display panel. The backlight unit comprises a light board assembly comprising: a light board substrate comprising a first major surface facing the display panel and a second major surface opposite the first major surface, a plurality of patterned reflectors disposed on the first major surface of the light board substrate, an electrically conductive layer disposed over the second major surface, and a plurality of light sources disposed on the second major surface, the plurality of light sources in electrical connection with the electrically conductive layer. The electrically conductive layer may comprise, for example, a plurality of electrical traces that provide electrical power to the light sources.

[0008] The display device may further comprise a reflective layer disposed over the electrically conductive layer. The reflective layer may comprise a polymeric layer, for example an epoxy layer.

[0009] The display device may include a reflective layer disposed between the light board substrate and the electrically conductive layer. The reflective layer may be a metallic layer. In some embodiments, the display device can comprise an adhesion layer disposed between the light board substrate and the electrically conductive layer. The adhesion layer can comprise a metal, a metal oxide, or a metal nitride. For example, in some embodiments, the adhesion layer can comprise titanium, chromium, zinc, or manganese.

[0010] In some embodiments, the display device may comprise a first reflective layer disposed over the electrically conductive layer and a second reflective layer disposed between the light board substrate and the electrically conductive layer. The first reflective layer may comprise a polymeric layer and the second reflective layer may comprise a metallic layer, although in further embodiments, the first reflective layer may comprise a polymeric layer and the second reflective layer may comprise a polymeric layer or a dielectric layer.

[0011] In some embodiments, the display device may include a light extraction layer on the second major surface of the light board substrate. For example, the light extraction layer may be disposed between the light board substrate and the electrically conductive layer.

[0012] In some embodiment, the plurality of light sources can be optically coupled to the light board substrate with an optical adhesive.

[0013] In some embodiments, the plurality of light sources can be electrically connected to the electrically conductive layer by wire leads.

[0014] In some embodiments, the electrically conductive layer comprises a raised electrical contact pad adjacent each light source of the plurality of light sources, each light source electrically connected to the raised electrical contact pad by an electrically conductive bridge. [0015] In some embodiments, the light board substrate can comprise a plurality of cavities, the plurality of light sources disposed in the plurality of cavities.

[0016] In some embodiments, the light board substrate comprises glass.

[0017] Both the foregoing general description and the following detailed description present embodiments intended to provide an overview or framework for understanding the nature and character of the embodiments disclosed herein.

[0018] The drawings illustrate various embodiments of the disclosure and, together with the description, explain the principles and operations thereof, and are incorporated into and constitute a part of this specification. As such, it should not be assumed that the relative size of different regions, portions, substrates, or other components are shown in the drawings are proportional to its actual relative size, unless explicitly indicated otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. l is a cross-sectional side view (exploded) of an exemplary display device;

[0020] FIG. 2 is a cross-sectional side view of an embodiment of a light board assembly according to the present disclosure;

[0021] FIG. 3 is a cross-sectional side view of another embodiment of a light board assembly according to the present disclosure, wherein an adhesion layer is disposed between an electrically conductive layer and a light board substrate;

[0022] FIG. 4 is a cross-sectional side view of an embodiment of a light board assembly according to the present disclosure wherein light sources are electrically connected to an electrically conductive layer with wire bonds; [0023] FIG. 5 is a cross-sectional side view of an embodiment of a light board assembly according to the present disclosure wherein an electrically conductive layer comprises raised pads to which light sources are electrically connected;

[0024] FIG. 6 is a cross-sectional side view of an embodiment of a light board assembly according to the present disclosure wherein light sources are disposed in cavities in a light board substrate;

[0025] FIG. 7 is a cross-sectional side view of an embodiment of a light board assembly according to the present disclosure wherein a reflective layer is disposed over an electrically conductive layer;

[0026] FIG. 8 is a cross-sectional side view of an embodiment of a light board assembly according to the present disclosure wherein a reflective layer is disposed between a light board substrate and an electrically conductive layer;

[0027] FIG. 9 is a bottom view of an exemplary light board assembly showing apertures in the reflective layer of FIG. 8 that allow light to transmit from a plurality of light sources through the reflective layer;

[0028] FIG. 10 is a cross-sectional side view of an embodiment of a light board assembly according to the present disclosure wherein a first reflective layer is disposed over an electrically conductive layer and a second reflective layer is disposed between a light board substrate and the electrically conductive layer;

[0029] FIG. 11 is a cross-sectional side view of the embodiment of FIG. 10 and comprising a light extraction layer disposed between the second reflective layer and the light board substrate;

[0030] FIG. 12 is a cross-sectional side view of portion A of the light board substrate from FIG. 2 showing a patterned reflector disposed on a first major surface of the light board substrate;

[0031] FIG. 13 is a top view of an embodiment of a light board assembly according to the present disclosure showing an exemplary distribution of patterned reflectors; and [0032] FIG. 14 is a top view of another exemplary patterned reflector according to the present disclosure.

DETAILED DESCRIPTION

[0033] Reference will now be made in detail to embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. However, this disclosure can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0034] As used herein, the term “about” means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art.

[0035] Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value to the other particular value. Similarly, when values are expressed as approximations by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0036] Directional terms as used herein — for example, up, down, right, left, front, back, top, bottom — are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

[0037] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus, specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification.

[0038] As used herein, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise.

[0039] The word “exemplary,” “example,” or various forms thereof are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” or as an “example” should not be construed as preferred or advantageous over other aspects or designs. Furthermore, examples are provided solely for purposes of clarity and understanding and are not meant to limit or restrict the disclosed subject matter or relevant portions of this disclosure in any manner. It can be appreciated that a myriad of additional or alternate examples of varying scope could have been presented but have been omitted for purposes of brevity.

[0040] As used herein, the terms “comprising” and “including,” and variations thereof, shall be construed as synonymous and open-ended, unless otherwise indicated. A list of elements following the transitional phrases comprising or including is a non-exclusive list, such that elements in addition to those specifically recited in the list may also be present.

[0041] The terms “substantial,” “substantially,” and variations thereof as used herein are intended to note that a described feature is equal or approximately equal to a value or description. For example, a “substantially planar” surface is intended to denote a surface that is planar or approximately planar. Moreover, “substantially” is intended to denote that two values are equal or approximately equal. In some embodiments, “substantially” may denote values within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

[0042] As used herein and unless otherwise indicated, the word “on” means in close proximity to and does not necessarily mean in contact with. Thus, a first layer on a surface does not preclude the existence of intervening layers between the first layer and the surface.

[0043] FIG. 1 is a cross-sectional side view of an exemplary display device 10 according to embodiments of the present disclosure. Display device 10 comprises a display panel 12, e.g., a liquid crystal display (LCD) panel, and a backlight unit 14 arranged to illuminate display panel 12. That is, backlight unit 14 is positioned behind display panel 12 relative to a viewer 16 of display device 10. Backlight unit 14 comprises light board assembly 18 and may further include various light modifying films or layers disposed between light board assembly 18 and display panel 12. For example, in some embodiments, backlight unit 14 may comprise any one or more of a prism film 20, one or more brightness enhancement films 22, a quantum dot layer 24, and/or a diffusion layer 26 in any needed order.

[0044] Turning now to FIG. 2, an exemplary light board assembly 18 is shown comprising light board substrate 28 including a first major surface 30 and a second major surface 32 opposite first major surface 30. First major surface 30 is a front-facing surface. That is, first major surface 30 faces display panel 12 and viewer 16. Light board substrate 28 may be a rigid substrate or a flexible substrate. Light board substrate 28 may be a flat substrate or a curved substrate. A curved light board substrate may have a radius of curvature less than about 2000 mm, such as less than about 1500 mm, less than about 1000 mm, less than about 500 mm, less than about 200 mm, or less than about 100 mm. In various embodiments, first major surface 30 and second major surface 32 may be parallel surfaces. A thickness of light board substrate 28, e.g., in a direction orthogonal to one or both of first major surface 30 and second major surface 32, may be in a range from about 100 micrometers (pm) to about one millimeter (mm). [0045] Light board substrate 28 may be a transparent substrate. As used herein, the term “transparent” denotes an internal optical transmission greater than about 70 percent over a length of 500 millimeters in the visible region of the spectrum (about 420-750 nanometers) when measured with a spectrophotometer. Transmittance is the ratio of the intensity of incident light on a sample to the intensity of light passing through the sample. In certain embodiments, light board substrate 28 may have an optical transmittance greater than about 50 percent in the ultraviolet (UV) region (about 100-400 nanometers) over a length of 500 millimeters. According to various embodiments, light board substrate 28 may include an optical transmittance of at least 95 percent over a path length of 50 millimeters for wavelengths ranging from about 450 nanometers to about 650 nanometers. Light board substrate 28 may have a refractive index ranging from about 1.3 to about 1.8. In various embodiments, light board substrate 28 may have a low level of light attenuation (e.g., due to absorption and/or scattering). The light attenuation a of light board substrate 28 may be less than about 5 decibels per meter for wavelengths ranging from about 420-750 nanometers.

[0046] Light board substrate 28 may include polymeric materials, such as plastics (e.g., polymethyl methacrylate (PMMA), methylmethacrylate styrene (MS), polydimethylsiloxane (PDMS), polycarbonate (PC)), or other similar materials). However, in further embodiments, light board substrate 28 may include a glass material, such as an aluminosilicate glass, an alkalialuminosilicate glass, a borosilicate glass, an alkali-borosilicate glass, an aluminoborosilicate glass, an alkali-aluminoborosilicate glass, a soda lime glass, or other suitable glasses. Nonlimiting examples of commercially available glasses suitable for use as a glass light board substrate include EAGLE XG®, Lotus™, Willow®, Iris™, and Gorilla® glasses from Coming Incorporated. In some embodiments, light board substrate 28 may be a laminate and include both one or more glass layers and on or more polymer layers in any arrangement.

[0047] Light board assembly 18 comprises a plurality of light sources 34 disposed on second major surface 32. Each light source 34 of the plurality of light sources may be an LED (e.g., having a size larger than about 0.5 millimeters), a mini -LED (e.g., having a size between about 0.1 millimeters and about 0.5 millimeters), a micro-LED (e.g., having a size smaller than about 0.1 millimeter), an organic LED (OLED), or any other suitable light source. Light sources 34 may emit light with a wavelength ranging from about 400 nanometers to about 750 nanometers. In other embodiments, each light sources 34 may emit light at a wavelength shorter than 400 nanometers and/or longer than 750 nanometers.

[0048] Light sources 34 may emit light with a Lambertian distribution pattern. However, in other embodiments, light sources 34 can emit light at an angular distribution different from a Lambertian distribution. For example, the angular distribution of the light emitted from light sources 34 may have a full width half maximum intensity of 90 degrees, 100 degrees, 110 degrees, 130 degrees, 140 degrees, 150 degrees, 160 degrees, larger than 160 degrees, or smaller than 90 degrees. The angular distribution may have a peak intensity along 0 degrees, 10 degrees, 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, or 80 degrees, where the 0-degree direction corresponds to the normal direction of light board substrate 28. Light sources 34 may be arranged in any of a variety of array patterns over second major surface 32. For example, in some embodiments, light sources 34 may be arranged in a rectangular array comprising rows and columns of light sources. However, in further embodiments, light sources 34 may be arranged in other geometric patterns, such as a hexagonal array.

[0049] Light board assembly 18 further comprises an electrically conductive layer 36 disposed on or over second major surface 32. Electrically conductive layer 36 need not be a continuous layer. For example, electrically conductive layer 36 can comprise a plurality of electrical traces (electrical conductors) arranged over second major surface 32 and configured to supply electrical current to the plurality of light sources 34. In some embodiments, electrically conductive layer 36 can comprise copper. However, in further embodiments, electrically conductive layer 36 may comprise a material more reflective to light than copper, such as aluminum, gold, or silver.

[0050] As shown in FIG. 3, in some embodiments, an adhesion layer 38 may be used between electrically conductive layer 36 and second major surface 32 to promote adhesion between the electrically conductive layer 36 and second major surface 32. For example, adhesion layer 38 can include a metal layer such as a titanium layer, a chromium layer, or a manganese layer, a metal oxide layer such as titanium oxide (e.g., TiOx), or a zinc oxide layer (ZnO), or a metal nitride layer such as titanium nitride (TiN).

[0051] In some embodiments, light sources 34 may be optically coupled to light board substrate 28 with an index-matched optically clear adhesive (OCA) 40 such that light sources 34 emit into and through light board substrate 28. Solder connections 42 can be provided that directly attach each light source 34 to electrically conductive layer 36. In various embodiments, so-called bottom emission light sources (e.g., bottom emission LEDs) may be used, such that they can be flip-chip bonded (surface mounted by soldering) at second major surface 32, e.g., to electrically conductive layer 36. Alternatively, top-emitting light sources can be adapted for the purpose.

[0052] In some embodiments, as shown in FIG. 4, light sources 34 may be mounted to light board substrate 28 with wire bonds 44 that can be used to deliver a driving current from electrically conductive layer 36 (e.g., at solder joints 46 on electrical traces) to the light sources, e.g., to contact pads 48 on each light source 34. Although the embodiment of FIG. 4 is shown without adhesion layer 38, adhesion layer 38 can be used as indicated in FIG. 3 and described above if needed.

[0053] In still other embodiments, raised contact pads 50 can be fabricated on the electrically conductive layer 36, as shown in FIG. 5. Printed conductive ink or jetted solder bridges 52 can then be used to contact the light sources and deliver a driving current from electrically conductive layer 36 (e.g., electrical traces) to light sources 34. Although the embodiment of FIG. 5 is shown without adhesion layer 38, adhesion layer 38 can be used as indicated in FIG. 3 and described above if needed.

[0054] In still other embodiments, illustrated in FIG. 6, cavities 54 can be pre-machined (or pre-etched) in light board substrate 28. Cavities 54 can be any suitable geometric shape necessary to accommodate light sources 34. For example, cavities 54 can be rectangular or rounded. Light sources 34, for example top-emission LED chips, can be embedded in the cavities, for example with index-matched optically clear adhesive 40. Light efficiency can be further improved because light emitted not only from the light source top face (the face of the light source facing display panel 12) but also laterally from the sides of the light source can be effectively injected into light board substrate 28. Light sources 34 can be electrically connected to electrically conductive layer 36 via solder pads 56. Additionally, since the bottom surface (the surface of the light source facing away from display panel 12, where solder pads 56 are located) of light sources 34 can be made approximately flush with second major surface 32 of light board substrate 28. Thus, implementing an electrical contact technique as illustrated in FIG. 6 can be employed without a need for raised contact pads. Although the embodiment of FIG. 6 is shown without adhesion layer 38, adhesion layer 38 can be used as indicated in FIG. 3 and described above if needed.

[0055] In general, it is desirable that second major surface 32 be highly reflective, to allow for light “recycling” from optical films positioned above the glass light guide (between light board substrate 28 and display panel 12). The spectral reflectivity of copper, typically used for electrical traces, is relatively low, especially at blue and green wavelengths, which may negatively impact overall light efficiency and color shift of the backlight. For improved light efficiency and color uniformity, highly reflective metals such as aluminum or silver can be selected for electrical traces. Alternatively, a thin layer of a more reflective material can be deposited between the light board substrate and the electrical traces to increase reflectivity. In some embodiments, it may be sufficient to pattern the conductive traces with minimal gaps therebetween such that most of second major surface 32 is covered with metal to avoid a significant light efficiency loss while light is guided through the light board substrate. For additional efficiency, a reflective film or coating can be added over the LEDs and/or the electrical traces. Such a reflective coating can be a multi-layer dielectric reflector, or a multilayer dielectric or metal reflector, or in a simplest case a layer of highly reflective white ink or paint.

[0056] Accordingly, in some embodiments, for example any one or more of the preceding embodiments, light board assembly 18 may comprise a reflective layer 58 overtop electrically conductive layer 36. By way of example and not limitation, FIG. 7 depicts the embodiments of FIG. 2 including a reflective layer 58. Reflective layer 58 may be an epoxy, such as an epoxy solder mask material. In some embodiments, reflective layer 58 may comprise a liquid photoimageable solder mask (LPSM or LPI) ink or a dry film photoi ageable solder mask (DFSM) or a laminate dry film resist (DFR). Reflective coating materials suitable for reflective layer 58 and applied over electrically conductive layer 36 (e.g., electrical traces) can be other materials as long as they are highly reflective and can survive subsequent chemical and thermal processes such as acid etch and reflow processes. In embodiments, reflective layer 58 is not an electrically conductive layer, thereby avoiding electrical shorts across the electrical traces. Accordingly, reflective layer 58 can coat the entire back side of the light board substrate, including light sources 34. In some embodiments, reflective layer 58 can be white in color, such as a white ink, e.g., a white epoxy material.

[0057] As shown in FIG. 8, in some embodiments, for example any one or more of the preceding embodiments, a reflective layer 60 may be disposed between second major surface 32 and electrically conductive layer 36. Reflective layer 60 can comprise a reflective metal such as aluminum, gold, or silver, although in further embodiments, reflective layer 60 can comprise a dielectric layer or an ink layer (e.g., epoxy layer). Reflective layer 60 can exhibit a reflectivity greater than 70%, for example greater than 80%, over a wavelength range from about 450 nanometers (nm) to about 700 nm, with a variation in reflectivity no greater than 10% over that wavelength range, when measured with a spectrophotometer. Reflectance is the ratio of the intensity of light incidence on a surface to the intensity of light reflected at the surface. Reflective layer 60 can be applied to the light board substrate prior to metallization (e.g., depositing of electrical traces). In case of direct printing of the electrical traces, highly reflective white polymer materials may be selected to promote adhesion, and/or a catalytic ink may be used, for subsequent electroless plating of the electrically conductive layer. If reflective layer 60 is a metallic layer, reflective layer 60 can be patterned together with electrically conductive layer 36. That is, reflective layer 60 can be deposited, then electrically conductive layer 36 can be deposited overtop reflective layer 60, then the combined reflective layer and electrically conductive layer can be patterned, such as with photolithography. Thus, the reflective layer 60 may exhibit the same pattern as the electrically conductive layer 36 (e.g., electrical traces), minimizing the possibility the metallic reflective layer creates shorts between the electrical traces. On the other hand, this opens spaces between adjacent traces so that reflection in the open spaces is reduced. Accordingly, in other embodiments, as described above, reflective layer 60 can be a non-electrically conductive layer that is deposited prior to metallization. Care should be taken to ensure apertures are created such that light from light sources 34 can be successfully injected into light board substrate 28. For example, FIG. 9 is a bottom view of an exemplary light board assembly 18 showing a plurality of apertures 62 positioned in a rectangular array of rows and columns to match a rectangular array of light sources (not shown), the apertures 62 extending through reflective layer 60. Accordingly, light sources 34 are mounted to light board substrate 28 at locations coinciding with apertures 62. [0058] In some embodiments, as shown in FIG. 10, light board assembly may comprise both a first reflective layer 58 overtop electrically conductive layer 36 and a second reflective layer 60 between electrically conductive layer 36 and second major surface 32.

[0059] Turning now to FIG. 11, in some embodiments, including any one or more of the preceding embodiments, light board assembly 18 may include a light extraction layer 63 on second major surface 32. For example, by way of illustration and not limitation, FIG. 11 depicts the embodiment of FIG. 10 including a light extraction layer 63 disposed between electrically conductive layer 36 and light board substrate 28. Light extraction layer 63 can include a plurality of reflective dots deposited on second major surface 32. In some embodiments, light extraction layer 63 can be a paint or an ink, such as a white paint or ink. The reflective paint or ink can be deposited, for example by screen printing, by ink-jet printing, or by any other suitable deposition method as is known in the art. Alternatively, or in addition, depending on the material of the light board substrate (e.g., an etchable material such as a silicate glass), light extraction layer 63 can be an etched layer, wherein a top surface of second major surface 32 is etched with a suitable etchant to roughen the second surface and produce a light scattering surface. Other methods of roughening the surface as may be known in the art may be used. In various embodiments, light extraction layer 63 can be positioned between electrically conductive layer 36 and light board substrate 28, for example between reflective layer 60 and light board substrate 28.

[0060] In some embodiments, including any one or more of the preceding embodiments, light board assembly 18 may comprise a plurality of discrete patterned reflectors 64 deposited on first major surface 30 of light board substrate 28. In some embodiments, patterned reflectors 64 may be deposited directly on an in contact with first major surface 30. In some embodiments, the plurality of patterned reflectors 64 can be optically coupled to first major surface 30 with an adhesive, while in other embodiments, the plurality of patterned reflectors 64 can be deposited directly on first major surface 30, such as by printing. The plurality of patterned reflectors 64 may include, for example, metallic foils, such as silver, platinum, gold, copper, and the like; dielectric materials (e.g., polymers such as polytetrafluoroethylene (PTFE)); porous polymer materials, such as polyethylene terephthalate (PET), Poly(methyl methacrylate) (PMMA), polyethylene naphthalate (PEN), polyethersulfone (PES), etc.; multilayer dielectric interference coatings, or reflective inks, including inks containing white inorganic particles such as titania, barium sulfate, etc., or other materials suitable for reflecting light and tuning the color of the reflected and transmitted light, such as colored pigments.

[0061] As best seen in FIG. 12, in some embodiments, each patterned reflector 64 may comprise a thickness profile including a substantially flat section 66 and a curved section 68. That is, curved section 68 can represent a thickness variation of the patterned reflector. FIG. 12 illustrates a portion of an exemplary light board substrate 28 (portion A of FIG. 2) and depicts a single patterned reflector 64 with a thickness variation deposited on first major surface 30. The substantially flat section 66 may be more reflective than the curved section 68, and the curved section 68 may be more transmissive than the substantially flat section 66. Each curved section 68 may have properties that change in a continuous, smooth way with distance from the substantially flat section 66. In some embodiments, patterned reflectors 64 may comprise a plurality of discrete reflective dots arranged in a predetermined pattern, while in other embodiments, the discrete reflective dots may be randomly distributed. Each patterned reflector 64 can be circular in shape, while in other embodiments each patterned reflector 64 may have another suitable shape (e.g., rectangular, hexagonal, etc.). Patterned reflectors 64 fabricated directly on first major surface 30 of light board substrate 28 diffusely reflect light back toward light sources 34 as well as to the sides to be guided in the light board substrate. Away from the light source positions, the patterned reflectors extract light guided in light board substrate 28. Patterned reflectors 64 can hide light sources 34 from viewer 16 of display device 10 and fabricating patterned reflectors 64 directly on first major surface 30 of light board substrate 28 may also save space in a thickness direction of backlight unit 14 (orthogonal to either one or both of first major surface 30 or second major surface 32). As shown in FIG. 4, light board assembly 18 may further include individual (discrete) reflective spots 70 disposed on first major surface 30 of light board substrate 28. FIG. 13 is a top view of a light board substrate 28 comprising a plurality of patterned reflectors 64 deposited thereon in an array (e.g., rectangular array, hexagonal array, etc.) and randomly distributed reflective spots 70. Reflective spots 70 may be at least partially transmissive. Reflective spots 70 may exhibit uniform reflectivity. Reflective spots 70 can function as a light extraction layer.

[0062] Each patterned reflector 64 or discrete reflective spot 70 may be formed, for example, by printing (e.g., inkjet printing, screen printing, microprinting, etc.) a pattern with white ink, black ink, metallic ink, or other suitable ink depending on desired function. Each patterned reflector 64 or discrete reflective spot 70 may also be formed by first depositing a continuous layer of a white or metallic material, for example by physical vapor deposition (PVD) or another coating technique, such as, for example, slot die or spray coating, and then patterning the layer by photolithography or other known methods of area-selective material removal.

[0063] As shown in FIG. 14, in other embodiments, each patterned reflector 64 can include a first (central) solid section 72, a plurality of second solid sections 74 surrounding the first solid section 72, and a plurality of open sections 76 interleaved with the plurality of second solid sections 74. Each second solid section 74 and each open section 76 may be ring-like, such as circular, elliptical, or another suitable shape. For example, in various embodiments, second solid sections 74 and open sections 76 may be annular and concentric with first solid section 72.

[0064] An area ratio A(r) of each second solid section 74 may equal As(r) / (As(r) + Ao(r)), where r is the distance from the center of the corresponding patterned reflector, As(r) is the area of the corresponding second solid section 74, and Ao(r) is the area of the corresponding open section 76. The area ratio A(r) of each second solid section 74 decreases with the distance r, and a rate of the decrease decreases with the distance r.

[0065] The size (i.e., width or diameter) of each first solid section 72 as indicated at 80 (in a plane parallel to light board substrate 28) may be greater than the size (i.e., width or diameter) of each corresponding light source 34. The size 80 of each first solid section 72 may be less than the size of each corresponding light source 34 multiplied by a predetermined value. In certain exemplary embodiments, when the size of each light source 34 is greater than or equal to about 0.5 millimeters, the predetermined value may be about two or about three, such that the size of each first solid section 72 is less than three times the size of each light source 34. When the size of each light source 34 is less than about 0.5 millimeters, the predetermined value may be determined by the alignment capability between the light sources 34 and the patterned reflectors 64, such that the size of each first solid section 72 of each patterned reflector 64 is within a range between about 100 micrometers and about 300 micrometers greater than the size of each light source 34. Each first solid section 72 is large enough that each patterned reflector 64 can be aligned to the corresponding light source 34 and small enough to achieve suitable luminance uniformity and color uniformity.

[0066] As used herein, the term “aligned” and variations as used in respect of light sources and patterned reflectors denotes a patterned reflector positioned over (coincident with) a particular light source and positioned such that a center of the patterned reflector lies on a line through the center of the light source light output distribution and orthogonal to the light board substrate surface to which the light source is coupled (e.g., deposited on). One or more patterned reflectors may be aligned with one or more light sources, one patterned reflector aligned to one light source. Similarly, a patterned reflector “corresponding” to a particular light source is that patterned reflector positioned over a particular light source.

[0067] Patterned reflectors 64 may have both the layer thickness and the surface coverage varying, which can serve two distinct purposes. Immediately above the light sources, the pattern can suppress a “hot spot” from the corresponding light source by diffusely reflecting light back towards the light source as well as to the sides to be guided in light board substrate. Away from the light source positions, the pattern can serve to extract light guided in the light board substrate. The overall function of the backlight unit is to make the brightness of light emitted from the backlight toward the display panel uniform over the entire emission surface of the backlight unit.

[0068] It will be apparent to those skilled in the art that various modifications and variations can be made to embodiments of the present disclosure without departing from the spirit and scope of the disclosure. Thus, it is intended that the present disclosure cover such modifications and variations provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A display device, comprising: a display panel; a backlight unit arranged adjacent the display panel, the backlight unit comprising: a light board assembly comprising: a light board substrate comprising a first major surface facing the display panel and a second major surface opposite the first major surface; a plurality of patterned reflectors disposed on the first major surface of the light board substrate; an electrically conductive layer disposed over the second major surface; and a plurality of light sources disposed on the second major surface, the plurality of light sources in electrical connection with the electrically conductive layer.

2. The display device of claim 1, further comprising a reflective layer disposed over the electrically conductive layer.

3. The display device of claim 2, wherein the reflective layer comprises a polymeric layer.

4. The display device of claim 3, wherein the reflective layer comprises an epoxy.

5. The display device of claim 1, further comprising a reflective layer disposed between the light board substrate and the electrically conductive layer.

6. The display device of claim 5, wherein the reflective layer comprises a metallic layer.

7. The display device of claim 1, further comprising a first reflective layer disposed over the electrically conductive layer and a second reflective layer disposed between the light board substrate and the electrically conductive layer.

8. The display device of claim 7, wherein the first reflective layer comprises a polymeric layer and the second reflective layer comprises a metallic layer.

9. The display device of claim 7, wherein the first reflective layer comprises a polymeric layer and the second reflective layer comprises a polymeric layer.

10. The display device of claim 1, further comprising a light extraction layer on the second major surface of the light board substrate.

11. The display device of claim 1, wherein the plurality of light sources are optically coupled to the light board substrate with an optical adhesive.

12. The display device of claim 1, wherein the plurality of light sources are electrically connected to the electrically conductive layer by wire leads.

13. The display device of claim 1, wherein the electrically conductive layer comprises a raised electrical contact pad adjacent each light source of the plurality of light sources, each light source electrically connected to the raised electrical contact pad by an electrically conductive bridge.

14. The display device of claim 1, wherein the light board substrate comprises a plurality of cavities, the plurality of light sources disposed in the plurality of cavities.

15. The display device of claim 1, further comprising an adhesion layer disposed between the light board substrate and the electrically conductive layer.

16. The display device of claim 15, wherein the adhesion layer comprises a metal, a metal oxide, or a metal nitride.

17. The display device of claim 16, wherein the adhesion layer comprises titanium, chromium, zinc, or manganese.

18. The display device of claim 1, wherein the electrically conductive layer comprises a plurality of electrical traces.

19. The display device of claim 1, wherein the light board substrate comprises glass.