A display having a direct-illumination type backlight unit

Abstract

This application is titled "Display with Direct-Illumination Backlight Unit". A display may have a pixel array such as a liquid crystal pixel array. The pixel array may be illuminated by backlight from a backlight unit. The backlight unit may include: a printed circuit board; a plurality of light-emitting diodes mounted on the printed circuit board; at least one light-diffusion layer formed over the printed circuit board, the at least one light-diffusion layer diffusing light received from the plurality of light-emitting diodes; a partial-reflection layer formed over the at least one light-diffusion layer; a color-conversion layer formed over the partial-reflection layer; a collimation layer formed over the color-conversion layer; a brightness-enhancing film formed over the collimation layer; and a diffuser formed over the brightness-enhancing film. The at least one light-diffusion layer may include two light-diffusion layers having elongated protrusions that are rotated relative to each other.

Description

[0001] This application is a divisional application of a patent application for an invention named "Display with Direct Illumination Backlight Unit", with application number 201910143649.1, priority date of March 13, 2018, and filing date of February 27, 2019.

[0002] This patent application claims the priority of U.S. Provisional Patent Application No. 62 / 642,539, filed on March 13, 2018, which is hereby incorporated by reference in its entirety. Technical Field

[0003] This application generally relates to displays, and more particularly to backlit displays. Background Art

[0004] Electronic devices generally include a display. For example, computers and cellular phones sometimes have backlit liquid crystal displays. Edge-lit backlight units have light-emitting diodes that emit light onto the edge surface of a light guide plate. The light guide plate then laterally distributes the emitted light over the display for use as backlight illumination.

[0005] Direct illumination backlight units have an array of light-emitting diodes that emit light vertically through the display. However, if not carefully designed, direct illumination backlighting can be bulky or may produce uneven backlight illumination. Summary of the Invention

[0006] A display may have a pixel array such as a liquid crystal pixel array. The pixel array may be illuminated by backlight from a backlight unit. The backlight unit may include an array of light-emitting diodes and a light reflector that helps reflect light from the light-emitting diodes through the pixel array. Each light-emitting diode may be placed in a corresponding cell.

[0007] The backlight unit may include: a printed circuit board; a plurality of light-emitting diodes mounted on the printed circuit board; at least one light diffusion layer formed over the printed circuit board, the at least one light diffusion layer diffusing light received from the plurality of light-emitting diodes; a partial reflection layer formed over the at least one light diffusion layer; a color conversion layer formed over the partial reflection layer; a collimating layer formed over the color conversion layer; a brightness enhancement film formed over the collimating layer; and a diffuser formed over the brightness enhancement film. Brief Description of the Drawings

[0008] Figure 1 Illustrates an exemplary electronic device having a display according to one embodiment.

[0009] Figure 2 Is a cross-sectional side view of an exemplary display according to one embodiment.

[0010] Figure 3 Top view of an exemplary light-emitting diode array for a direct-illumination backlight unit according to one embodiment.

[0011] Figure 4 Cross-sectional side view of an exemplary light-emitting diode array according to one embodiment, the exemplary light-emitting diode array having a heat-conducting layer and light-emitting diodes adhered to a printed circuit board.

[0012] Figure 5 Cross-sectional side view of an exemplary light-emitting diode array according to one embodiment, the exemplary light-emitting diode array having a radiative cooling coating and light-emitting diodes on a printed circuit board.

[0013] Figure 6 Top view of an exemplary light-emitting diode array for a direct-illumination backlight unit according to one embodiment, the exemplary light-emitting diode array having four rectangular light-emitting diodes in each unit.

[0014] Figure 7 Top view of an exemplary light-emitting diode array for a direct-illumination backlight unit according to one embodiment, the exemplary light-emitting diode array having light-emitting diodes with different properties in each unit.

[0015] Figure 8 Cross-sectional side view of an exemplary light-emitting diode array according to one embodiment, the exemplary light-emitting diode array having a light redirecting layer between the light-emitting diodes.

[0016] Figure 9 and Figure 10 Cross-sectional side view of exemplary light-emitting diodes according to one embodiment, the exemplary light-emitting diodes having or not having a reflector layer such as a distributed Bragg reflector.

[0017] Figure 11 Cross-sectional side view of an exemplary light-emitting diode array according to one embodiment, the exemplary light-emitting diode array having a reflective layer.

[0018] Figure 12 Cross-sectional side view of an exemplary light-emitting diode array according to one embodiment, the exemplary light-emitting diode array having a encapsulant with a flat upper surface over the light-emitting diodes.

[0019] Figure 13 Cross-sectional side view of an exemplary light-emitting diode array according to one embodiment, the exemplary light-emitting diode array having a encapsulant with a curved upper surface over each light-emitting diode.

[0020] Figure 14 A cross-sectional side view of an exemplary light-emitting diode array according to one embodiment, the exemplary light-emitting diode array having an encapsulant with a curved upper surface and a recessed portion over each light-emitting diode.

[0021] Figure 15 A cross-sectional side view of an exemplary light-emitting diode array according to one embodiment, the exemplary light-emitting diode array having an encapsulant with dopants uniformly distributed throughout the encapsulant material.

[0022] Figure 16 A cross-sectional side view of an exemplary light-emitting diode array according to one embodiment, the exemplary light-emitting diode array having an encapsulant with dopants at the upper surface of the encapsulant material.

[0023] Figure 17 A cross-sectional side view of an exemplary light-emitting diode array according to one embodiment, the exemplary light-emitting diode array having an encapsulant with dopants at the lower surface of the encapsulant material.

[0024] Figure 18 A cross-sectional side view of an exemplary dopant according to one embodiment, the exemplary dopant having different densities.

[0025] Figure 19 A cross-sectional side view of an exemplary dopant according to one embodiment, the exemplary dopant having a shape for controlling the orientation of dopants in the encapsulant material.

[0026] Figure 20 A cross-sectional side view of an exemplary backlight unit according to one embodiment, the exemplary backlight unit having a patterned layer formed on the encapsulant material.

[0027] Figure 21 A cross-sectional side view of an exemplary light-emitting diode array according to one embodiment, the exemplary light-emitting diode array having an encapsulant with a textured upper surface over the light-emitting diodes.

[0028] Figure 22 A cross-sectional side view showing a method for heating solder in a backlight unit according to one embodiment.

[0029] Figure 23 A cross-sectional side view of an exemplary backlight unit according to one embodiment, the exemplary backlight unit having a light-diffusing layer coupled to the encapsulant.

[0030] Figure 24A cross-sectional side view of an exemplary backlight unit according to an embodiment, the exemplary backlight unit having a first light-diffusing layer below a second light-diffusing layer.

[0031] Figure 25 A cross-sectional side view of an exemplary backlight unit according to an embodiment, the exemplary backlight unit having a first light-diffusing layer below a second light-diffusing layer and an intervening waveguide layer.

[0032] Figure 26 A cross-sectional side view of an exemplary backlight unit according to an embodiment, the exemplary backlight unit having a sealant having a respective portion of a parabolic upper surface over each light-emitting diode.

[0033] Figure 27 A cross-sectional side view of an exemplary backlight unit according to an embodiment, the exemplary backlight unit having a light leakage promoting structure between each light-emitting diode.

[0034] Figure 28 A cross-sectional side view of an exemplary display according to an embodiment, the exemplary display having a light-diffusing layer with microlenses on upper and lower surfaces thereof.

[0035] Figure 29 A cross-sectional side view of an exemplary display according to an embodiment, the exemplary display having two light-diffusing layers rotated relative to each other.

[0036] Figure 30 A cross-sectional side view of an exemplary light-diffusing layer according to an embodiment, the exemplary light-diffusing layer having protrusions.

[0037] Figure 31 A cross-sectional side view of an exemplary light-diffusing layer according to an embodiment, the exemplary light-diffusing layer having recesses.

[0038] Figure 32 A top view of an exemplary light-diffusing layer according to an embodiment, the exemplary light-diffusing layer having protrusions or recesses.

[0039] Figure 33 and Figure 34 A top view of an exemplary light-diffusing layer according to an embodiment, the exemplary light-diffusing layer having protrusions formed by a partial cubic structure.

[0040] Figure 35 A perspective view of an exemplary protrusion of a light-diffusing layer according to an embodiment, the exemplary protrusion being in a polyhedral pyramid shape.

[0041] Figure 36A cross-sectional side view of an exemplary backlight unit according to an embodiment, the exemplary backlight unit having microlenses on a lower surface of a partial reflection layer and a encapsulant having a flat upper surface over the light-emitting diodes.

[0042] Figure 37 A cross-sectional side view of an exemplary backlight unit according to an embodiment, the exemplary backlight unit having microlenses on a lower surface of a partial reflection layer and a encapsulant having a flat upper surface over each light-emitting diode.

[0043] Figure 38 A cross-sectional side view of an exemplary backlight unit according to an embodiment, the exemplary backlight unit having microlenses on a lower surface of a partial reflection layer and an encapsulant portion having a curved upper surface over each light-emitting diode.

[0044] Figure 39 A cross-sectional side view of an exemplary backlight unit according to an embodiment, the exemplary backlight unit having microlenses on a substrate, the microlenses being separated from the light-emitting diodes by an air gap.

[0045] Figure 40 A cross-sectional side view of an exemplary separately formed backlight enhancement film and collimating layer according to an embodiment.

[0046] Figure 41 A cross-sectional side view of an exemplary optical film according to an embodiment, the exemplary optical film serving simultaneously as a backlight enhancement film and a collimating layer.

[0047] Figure 42 A cross-sectional side view of an exemplary display having an edge coating according to an embodiment. DETAILED DESCRIPTION

[0048] An electronic device may be provided with a backlit display. The backlit display may include a liquid crystal pixel array or other display structure backlit by light from a direct-lit backlight unit. Figure 1 A perspective view of an exemplary electronic device of a type that may be provided with a display having a direct-lit backlight unit is shown. Figure 1The electronic device 10 can be a computing device such as a laptop computer, a computer monitor including an embedded computer, a tablet computer, a cellular phone, a media player, or other handheld or portable electronic devices, smaller devices (such as a wristwatch device), a hanging device, a headset or earpiece device, a device embedded in glasses or other devices worn on a user's head, or other wearable or miniature devices, a television, a computer monitor without an embedded computer, a gaming device, a navigation device, an embedded system (such as a system in which an electronic device with a display is installed in a kiosk or a vehicle), a device that implements two or more of these device functions, or other electronic devices.

[0049] As Figure 1 shown, the device 10 can have a display such as display 14. The display 14 can be mounted in a housing 12. The housing 12, which can sometimes be referred to as a case, can be formed of plastic, glass, ceramic, fiber composite material, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. The housing 12 can be formed using a one-piece construction in which part or all of the housing 12 is machined or molded into a single structure, or can be formed using multiple structures (e.g., an internal frame structure, one or more structures forming an outer housing surface, etc.).

[0050] The housing 12 can have a stand, can have multiple components (e.g., housing parts that move relative to each other to form a laptop computer or other device with movable parts), can have the shape of a cellular phone or a tablet computer, and / or can have other suitable configurations. Figure 1 The illustrated arrangement of the housing 12 is exemplary.

[0051] The display 14 can be a touchscreen display incorporating a conductive capacitive touch sensor electrode layer or other touch sensor components (e.g., a resistive touch sensor component, an acoustic touch sensor component, a force-based touch sensor component, a light-based touch sensor component, etc.) or can be a non-touch-sensitive display. The capacitive touchscreen electrodes can be formed by an array of indium tin oxide pads or other transparent conductive structures.

[0052] The display 14 can include an array of pixels 16 formed by liquid crystal display (LCD) components or can have an array of pixels based on other display technologies. Figure 2 A cross-sectional side view of the display 14 is shown.

[0053] As Figure 2 shown, the display 14 can include an array of pixels such as pixel array 24. The pixel array 24 can include such as Figure 1A pixel array of pixel 16 (e.g., a pixel array having rows and columns of pixel 16). The pixel array 24 can be formed by a liquid crystal display module (sometimes referred to as a liquid crystal display or liquid crystal layer) or other suitable pixel array structures. A liquid crystal display used to form the pixel array 24 can include, for example, upper and lower polarizers, a color filter layer, a thin film transistor layer inserted between the upper and lower polarizers, and a liquid crystal material layer inserted between the color filter layer and the thin film transistor layer. If desired, other types of liquid crystal display structures can be used to form the pixel array 24.

[0054] During operation of the display 14, an image can be displayed on the pixel array 24. A backlight unit 42 (which can sometimes be referred to as a backlight, backlight layer, backlight structure, backlight module, backlight source system, etc.) can be used to generate backlight illumination 45 that passes through the pixel array 24. This illuminates any image on the pixel array 24 for viewing by a viewer 20, such as a viewer viewing the display 14 in direction 22.

[0055] The backlight unit 42 can include a plurality of optical films 26 formed over a light emitting diode array 36. The light emitting diode array 36 can comprise a light source such as a two-dimensional array of light emitting diodes 38 that generate the backlight illumination 45. The light emitting diodes 38 can be arranged in rows and columns, for example, and can be in the Figure 2 X-Y plane. The light emitting diodes 38 can be mounted on a printed circuit board 50 (sometimes referred to as a substrate 50) and can be encapsulated by an encapsulant 52 (sometimes referred to as a transparent encapsulant 52).

[0056] The light emitting diodes 38 can be uniformly controlled by a control circuit in the device 10 or can be individually controlled (e.g., to implement a local dimming scheme that helps improve the dynamic range of the image displayed on the pixel array 24). The light generated by each light emitting diode 38 can propagate upward in the direction Z through the optical film 26 before passing through the pixel array 24.

[0057] The optical film 26 can include films such as a light diffusion layer 28, a partial reflection layer 30, a color conversion layer 34 (which can include a phosphor layer 40 and a partial reflection layer 41), a collimating layer 44, a brightness enhancement film 46, a diffuser layer 48, and / or other optical films.

[0058] The light-emitting diode 38 can emit light of any suitable color (e.g., blue, red, green, white, etc.). In one exemplary configuration described herein, the light-emitting diode 38 emits blue light. To help provide uniform backlighting on the backlight unit 42, the light from the light-emitting diode 38 can be diffused by the light diffusion layer 28. After passing through the light diffusion layer 28, the light from the light-emitting diode 38 can pass through the partial reflection layer 30. The partial reflection layer 30 (sometimes referred to as a dichroic layer 30 or a dichroic color filter layer 30) can be configured to reflect a portion of the light from the LED and transmit a portion of the light from the LED. In one possible embodiment, the partial reflection layer can include a multi-Bragg reflector and a diffuser layer. The light reflected out of the partial reflection layer 30 can be recycled (e.g., the reflected light will reflect off other layers such as the substrate 50 before reaching the partial reflection layer 30 again). Then, the light transmitted through the partial reflection layer 30 passes through the color conversion layer 34 (which can sometimes be referred to as a photoluminescent layer).

[0059] The transmittance of the partial reflection layer 30 can be selected to maximize the efficiency of the display 14. Reducing the transmittance of blue light (e.g., from the light-emitting diode) passing through the partial reflection layer will increase the amount of blue light recycled. However, recycling more light can cause more light to be absorbed by the printed circuit board 50 (or other layers below the partial reflection layer 30). However, increasing the transmittance of blue light can result in more visual artifacts. Therefore, the transmittance of the partial reflection layer can be selected to optimize the efficiency and uniformity of the display. The reflectivity of the printed circuit board 50 can affect the transmittance of the partial reflection layer 30. In one exemplary embodiment, the printed circuit board 50 can have a reflectivity of about 90%, and the partial reflection layer 30 can reflect 50% of the blue light from the light-emitting diode 38. Increasing the reflectivity of the printed circuit board 50 will increase the optimal reflectivity of the partial reflection layer 30.

[0060] The color conversion layer 34 can convert the light from the LED 38 from a first color to other colors. For example, when the LED emits blue light, the color conversion layer 34 can include a phosphor layer 40 (e.g., a white phosphor material or other photoluminescent material layer) that converts the blue light to white light. If desired, other photoluminescent materials can be used to convert the blue light to light of different colors (e.g., red, green, white, etc.). For example, layer 34 can have a phosphor layer 40 that includes quantum dots that convert blue light into red and green light (e.g., to produce white backlighting including red, green, and blue components, etc.). Configurations can also be used in which the light-emitting diode 38 emits white light (e.g., such that layer 34 can be omitted if desired). In addition to the phosphor layer 40, the color conversion layer 34 can include a partial reflection layer 41. For example, the partial reflection layer 41 (sometimes referred to as a dichroic layer or a dichroic color filter layer) can reflect all red and green light and partially reflect blue light.

[0061] If desired, the color conversion layer 34 and the partially reflective layer 30 can be formed as a single integral layer. This can reduce the thickness of the optical film stack.

[0062] When the light from the light emitting diode 38 reaches the collimating layer 44, the light has been converted from blue light to white light and is homogenized (e.g., achieved by a light diffusing layer). The collimating layer 44 (sometimes referred to as the microlens layer 44 or the microlens array diffuser 44) can collimate off-axis light. One or more brightness enhancement films 46 can be included to further assist in collimating the light 45, thereby increasing the brightness of the display 14 for the user 20. Finally, the backlight unit 42 can include a diffuser layer 48 to homogenize the light from the light emitting diode array.

[0063] Figure 3 FIG. [ID number] is a top view of an exemplary light emitting diode array for the backlight 42. As Figure 3 shown, the light emitting diode array 36 can include rows and columns of light emitting diodes 38. Each light emitting diode 38 can be associated with a corresponding unit (chip area) 38C. The edge length D of the unit 38C can be 2 mm, 18 mm, 1 - 10 mm, 1 - 4 mm, 10 - 30 mm, greater than 5 mm, greater than 10 mm, greater than 15 mm, greater than 20 mm, less than 25 mm, less than 20 mm, less than 15 mm, less than 10 mm, less than 1 mm, less than 0.1 mm, greater than 0.01 mm, greater than 0.1 mm, or other desired dimensions. If desired, a hexagonal tiling array and an array having light emitting diodes 38 organized in other suitable array patterns can be used. In an array having rectangular units, each unit can have two sides of equal length (e.g., each unit can have a square profile, where four unit edges of equal length surround the corresponding light emitting diode) or each unit can have sides of different lengths (e.g., a non-square rectangular shape). The configuration in which the light emitting diode array 36 has a square light emitting diode area such as rows and columns of units 38C is Figure 3 merely exemplary.

[0064] If desired, each unit 38C can have a light source formed by an array of light emitting diode dies (e.g., a plurality of individual light emitting diodes 38 arranged in an array, such as a 2x2 cluster of light emitting diodes located at the center of each unit 38C). For example, Figure 3The light sources 38' in the leftmost and bottommost cells 38C have been formed by an array of 2x2 light-emitting diodes 38 (e.g., four individual light-emitting diode dies). Generally, each cell 38C may include a light source 38 having a single light-emitting diode 38, a pair of light-emitting diodes 38, two to ten light-emitting diodes 38, at least two light-emitting diodes 38, at least four light-emitting diodes 38, at least eight light-emitting diodes 38, fewer than five light-emitting diodes 38, or any other suitable number of light-emitting diodes. A configuration in which each cell 38C has a single light-emitting diode 38 may sometimes be described herein as an example. However, this is merely illustrative. Each cell 38C may have a light source 38 having any suitable number of one or more light-emitting diodes 38. The diodes 38 in the light-emitting diode array 36 may be mounted on a printed circuit board substrate extending across the array 36, or may be mounted in the array 36 using any other suitable arrangement.

[0065] The light-emitting diodes 38 in the light-emitting diode array 36 may generate heat. If not carefully managed, the resulting thermal gradient (e.g., the temperature of the array region closer to the light-emitting diodes is higher than the temperature of the array region between the light-emitting diodes) may cause a thermal gradient to form in the pixel array 24. The color of the light emitted by the pixel array 24 may depend on the temperature. Thus, a higher thermal gradient in the pixel array may have a negative impact on display performance.

[0066] Figure 4 and Figure 5 is a cross-sectional side view of exemplary light-emitting diode arrays having layers that help dissipate heat from the light-emitting diodes 38 (and prevent a thermal gradient from forming in the pixel array 24). As Figure 4 shown, the light-emitting diodes 38 may be connected to conductive pads 54 (e.g., pads) of a printed circuit board 50 using a conductive material (e.g., solder) 56. A thermal conductive layer 60 may be connected to the bottom surface of the printed circuit board 50 using an adhesive layer 58. The adhesive layer 58 may conduct heat to the thermal conductive layer 60 in the negative Z direction (e.g., from the printed circuit board 50). The thermal conductive layer 60 may then dissipate heat in the XY plane.

[0067] The thermal conductive layer 60 may be formed of any desired material. For example, the thermal conductive layer 60 may be formed of aluminum, graphite, carbon fiber reinforced sheet, carbon nanotubes, or metal particles. The thermal conductive layer 60 may have a thermal conductivity greater than 200 W / mK, greater than 300 W / mK, greater than 400 W / mK, between 200 W / mK and 400 W / mK, or any other desired thermal conductivity. The thermal conductive layer 60 may have a thickness 62 less than 0.1 mm, less than 0.2 mm, about 55 microns, greater than 20 microns, or any other desired thickness.

[0068] The adhesive layer 58 can be a pressure-sensitive adhesive layer. If desired, the adhesive layer 58 can include an additive 64 (e.g., metal particles) to increase the thermal conductivity of the adhesive layer.

[0069] In another embodiment, as Figure 5 shown, the radiative cooling coating can be attached to the printed circuit board 50. As Figure 5 shown, a layer 66 (sometimes referred to as a coating, radiative cooling layer, or radiative cooling coating) can be attached to the bottom surface of the printed circuit board 50 (e.g., using an adhesive 58). The layer 66 can include metal particles embedded in a polymer sheet. The metal particles can, for example, emit infrared light, thereby cooling the adjacent layer.

[0070] As Figure 4 and Figure 5 shown, the light-emitting diode 38 is connected to a pad on the printed circuit board 50 using solder. If the overlap area between the solder and the light-emitting diode is low, the bonding strength between the solder and the light-emitting diode may be low. To increase the overlap area between the solder and the light-emitting diode (and thereby improve the bonding strength and SMT yield), the light-emitting diode can have a rectangular design, as Figure 6 shown.

[0071] Figure 6 FIG. is a top view of an exemplary light-emitting diode having a rectangular (non-square) shape. As shown, each light-emitting diode in the light-emitting diode array 36 can have a width (W) and a length (L) that is longer than the width (e.g., greater than the width, at least 2 times the width, at least 1.5 times the width, at least 3 times the width, less than 3 times longer than the width, etc.). In other words, each light-emitting diode can have a non-square rectangular shape. Each unit (die area) 38C can have four associated light-emitting diodes 38-1, 38-2, 38-3, and 38-4. As Figure 6As shown, light-emitting diodes 38-1, 38-2, 38-3, and 38-4 are arranged in a 2x2 grid within cell 38C. Light-emitting diode 38-1 is at the upper left corner of the grid, light-emitting diode 38-2 is at the upper right corner of the grid, light-emitting diode 38-3 is at the lower left corner of the grid, and light-emitting diode 38-3 is at the lower right corner of the grid. Light-emitting diodes 38-1 and 38-4 may have a length parallel to the Y-axis, while light-emitting diodes 38-2 and 38-3 may have a length parallel to the X-axis (and rotated 90° with respect to the length direction of 38-1 and 38-4). In this arrangement, each light-emitting diode may have a non-square rectangular profile (for increasing the bonding strength), while ensuring uniform backlighting (since the four light-emitting diodes in each sheet will emit uniform backlighting together). The light-emitting diodes in each sheet may be controlled together. Each light-emitting diode in a given cell may have any desired positioning and orientation. Each light-emitting diode in a given cell may have any desired solder pattern. Each light-emitting diode in a given cell may have any desired encapsulant additive, and these encapsulant additives have any desired particle size and distribution.

[0072] Another arrangement of the light-emitting diodes in the light-emitting diode array 36 is as Figure 7 shown. As Figure 7 shown, each sheet 38C may have a plurality of (e.g., two, three, more than three, etc.) associated light-emitting diodes. In Figure 7 the example of Figure 7 , each sheet 38C includes light-emitting diodes 38-1, 38-2, and 38-3. These light-emitting diodes may have different properties to help tune the light emitted by the cell. In Figure 7 the example where each light-emitting diode has a non-square rectangular shape is only illustrative, and each light-emitting diode may have any desired shape. In another possible embodiment, the light-emitting diodes may emit light of different peak wavelengths. Additionally, as Figure 2 shown, each light-emitting diode may be covered by an encapsulant 52. Each light-emitting diode in sheet 38C may be covered by an encapsulant with a different shape or an encapsulant with different dopants.

[0073] Generally, multiple light-emitting diodes in a given die may have different properties to tune the light emitted by the die. These properties may include location, orientation, properties of solder connected to the light-emitting diodes, particle size of encapsulant additives, and distribution of encapsulant additives. In an illustrative example, light-emitting diodes 38-1, 38-2, and 38-3 may be red, blue, and green light-emitting diodes respectively (and die 38C emits white light).

[0074] Figure 2 Shows a light diffusion layer 28 for diffusing light from light-emitting diodes 38 in a light-emitting diode array 36. Figure 8 Is a cross-sectional side view of an illustrative light-emitting diode array having a light redirecting layer adjacent to the light-emitting diodes on a printed circuit board. As Figure 8 shown, light-emitting diodes 38 are mounted on the upper surface of a printed circuit board 50. The light redirecting layer 68 is also mounted on the upper surface of the printed circuit board 50. The light redirecting layer 68 may be a prism reflector that helps redirect light emitted from the edges of the light-emitting diodes 38. The layer 68 may be a separate film laminated to the printed circuit board 50, or may be a UV curable or thermally curable coating imprinted on the printed circuit board.

[0075] The layer 68 may be designed to direct light in a specific direction to improve optical uniformity and efficiency. The layer may include diffusive, refractive, and / or diffractive optical properties. The layer 68 may include microstructures, parabolic reflectors, imprinted structures that diffract specific wavelengths, or prism structures that emit light at a defined cone angle. The layer 68 may be used in combination with the light diffusion layer 28, or may replace the light diffusion layer 28. In Figure 8 the example, the layer 68 includes two protrusions between each adjacent light-emitting diode 38.

[0076] Figure 9 and Figure 10 Are cross-sectional side views showing how the light-emitting diodes 38 in the light-emitting diode array 36 may or may not include a reflector layer. As Figure 9 shown, the light-emitting diodes may include a reflector layer 70 (e.g., a distributed Bragg reflector) to help direct the emitted light of the light-emitting diodes 38 laterally. This may reduce the coaxial intensity of the light emitted by the light-emitting diodes 38. However, this will increase the amount of light incident on the upper surface of the printed circuit board 50, the pads 54, and the solder 56. The printed circuit board 50, the pads 54, and the solder 56 may not have a high reflectivity. Therefore, the presence of the reflector layer 70 may result in higher light losses. To reduce light losses, the light-emitting diodes may not include a reflector layer 70 (as Figure 10 shown).

[0077] Additionally, Figure 10Shows various ways to reduce the solder thickness and the corresponding height of the light-emitting diode relative to the printed circuit board and to improve the solder quality by reducing the air encapsulated under the light-emitting diode. As Figure 10 shown, the pad 54 may have recesses 53B (e.g., on the upper surface of the pad), which receive portions of the solder 56. The recesses 53B enable the solder 56 to better attach to the pad 54 due to capillary action and gravity. Similarly, the lower surface of the light-emitting diode 38 may have one or more recesses 53A, which receive portions of the solder 56. Likewise, the recesses 53A may enable the solder 56 to better attach to the light-emitting diode 38. If desired, one or more of the recesses may be coated with a conductive coating.

[0078] Additionally, a coating 57 may be included on the printed circuit board 50 below the light-emitting diode 38. The coating 57 may be a dielectric (e.g., non-conductive) coating. The coating 57 may be hydrophobic, enabling the solder 56 to flow across the coating. When depositing the solder 56, the excess solder may flow across the coating 57 into the recesses 55 of the printed circuit board 50. The recesses 55 may partially extend through the printed circuit board 50 or may completely extend through (e.g., from the upper surface to the lower surface) the circuit board. Vacuum suction may also be applied (e.g., during the solder deposition process) to align the die and remove excess air. Flowing the excess solder into the recesses 55 as described herein may improve the solder quality and placement reliability, reduce die tilt, and reduce the air under the die.

[0079] Figure 11 Shows ways to reduce light loss by increasing the reflectivity of the printed circuit board and other adjacent layers. As Figure 11 shown, a solder mask 72 (sometimes referred to as a solder mask reflector or reflective layer) may be included in the light-emitting diode array 36. The solder mask 72 may be formed of a highly reflective material to reduce the loss when light from the light-emitting diode 38 impinges on the solder mask 72. The solder mask may include titanium dioxide (TiO2) (e.g., titanium dioxide particles dispersed in a polymer) or other desired materials to increase the reflectivity. The particle size of the titanium dioxide and the refractive index of the polymer in the tunable solder mask are adjusted to optimize the reflectivity. In one embodiment, the solder mask may be directly laminated onto the upper surface of the printed circuit board. In another embodiment, the solder mask may be a thermosetting coating or an ultraviolet light-curable coating. The solder mask may have any desired thickness (e.g., 50 microns, greater than 50 microns, less than 100 microns, less than 50 microns, etc.).

[0080] The properties of the printed circuit board 50 can also be optimized to obtain a high reflectivity. For example, a fiberglass material or a polyimide polymer can form the core of the printed circuit board 50. The reflectivity of the solder mask and the printed circuit board can be the same or different (e.g., greater than 80%, greater than 50%, greater than 90%, greater than 92%, greater than 94%, between 85% and 95%, less than 90%, less than 99%, between 80% and 95%, etc.). Thermal conductive fillers can also be added to the printed circuit board 50 to tune the thermal conductivity of the printed circuit board.

[0081] There are various possible embodiments for the encapsulant (e.g., conforming to) the light-emitting diodes on the printed circuit board 50. Figure 12 FIG. is a cross-sectional side view of an exemplary light-emitting diode array having an encapsulant 52 with a flat upper surface. As Figure 12 shown, the encapsulant 52 can have a flat upper surface 74 that extends over the light-emitting diodes. The encapsulant 52 (sometimes referred to as the encapsulant flat in this embodiment) provides additional structural integrity to the light-emitting diodes 38. Additionally, to reduce total internal reflection at the interface between the light emitted by the light-emitting diodes 38 and the adjacent material 76 (e.g., air) between the encapsulant 52 and the adjacent material 76, the refractive index of the encapsulant 52 can be between the refractive indices of the light-emitting diodes 38 and the material 76. For example, the encapsulant 52 can have a refractive index between 1.2 and 1.5, between 1.3 and 1.4, less than 1.4, less than 1.5, greater than 1.1, greater than 1.2, greater than 1.3, about 1.35. As Figure 12 shown, the encapsulant 52 flat can cover all the light-emitting diodes in the light-emitting diode array 36. The encapsulant 52 can have any desired thickness 78 (e.g., between 0.1 mm and 0.4 mm, less than 0.5 mm, less than 0.3 mm, between 0.2 mm and 0.4 mm, between 0.15 mm and 0.25 mm, between 0.25 mm and 0.35 mm, about 0.2 mm, about 0.3 mm, etc.).

[0082] Figure 13 FIG. is a cross-sectional side view of an exemplary light-emitting diode array having an encapsulant 52 with a curved upper surface. As Figure 13As shown, the encapsulant 52 may have a curved upper surface 80 (e.g., a convex upper surface). The encapsulant may form a dome shape over the light-emitting diode. In this embodiment, the encapsulant may be referred to as a droplet lens. The encapsulant 52 provides additional structural integrity to the light-emitting diode 38. Additionally, to reduce total internal reflection at the interface between the light emitted by the light-emitting diode 38 and the adjacent material 76 (e.g., air), the refractive index of the encapsulant 52 may be between the refractive indices of the light-emitting diode 38 and the material 76. For example, the encapsulant 52 may have a refractive index between 1.2 and 1.5, between 1.3 and 1.4, less than 1.4, less than 1.5, greater than 1.1, greater than 1.2, greater than 1.3, about 1.35. Each light-emitting diode may have a corresponding encapsulant portion (e.g., each light-emitting diode may have an encapsulant dome). The encapsulant 52 may have any desired thickness 82 (e.g., between 0.1 mm and 0.4 mm, less than 0.5 mm, less than 0.3 mm, between 0.2 mm and 0.4 mm, between 0.15 mm and 0.25 mm, between 0.25 mm and 0.35 mm, about 0.2 mm, about 0.3 mm, etc.) and any desired width 84 (e.g., between 0.3 mm and 2.5 mm, between 0.3 mm and 0.7 mm, between 0.8 mm and 0.9 mm, greater than 0.5 mm, greater than 1.0 mm, greater than 2.0 mm, less than 2.0 mm, etc.). The ratio of the width to the thickness may be greater than 5:1, greater than 3:1, between 4:1 and 6:1, less than 10:1, etc.

[0083] Figure 14 FIG. is a cross-sectional side view of an exemplary light-emitting diode array having an encapsulant 52 with a curved upper surface and a recess. Figure 14 The encapsulant in Figure 13 is similar to the encapsulant in Figure 14 (e.g., having a dome shape). However, in Figure 13 , the encapsulant 52 also has a recess 86 formed over the light-emitting diode 38. The recess 86 may also be referred to as a depression. The recess 86 may have any desired shape (e.g., a pyramid shape). Compared to the embodiment in Figure 13 without the recess, the recess 86 may further improve uniformity by reducing the intensity of coaxial (e.g., zero-order) light.

[0084] Figures 15 - 17 FIG. shows an example of a dopant included in the encapsulant 52. Figure 15A cross-sectional side view showing a light-emitting diode 38 covered by a sealant 52 including a dopant 88. The dopant 88 (sometimes referred to as an additive 88) can be a scattering dopant. The presence of the dopant 88 can increase the light-emitting area of the light-emitting diode 38. If there is no scattering dopant, the light emitted by the light-emitting diode 38 will be directly concentrated above the light-emitting diode 38. However, the scattering dopant can spread the light from the light-emitting diode 38 throughout the sealant 52. Therefore, the sealant 52 area will emit light from the light-emitting diode 38. For example, this light scattering can be used in combination with or in place of the light diffusing layer 28 in Figure 2 or replace the light diffusing layer 28 in Figure 2 .

[0085] Any desired dopant can be used as the dopant 88. For example, the dopant 88 can include polymer nanoparticles, inorganic nanoparticles, pores (e.g., air bubbles), or any other desired dopant. The distribution of the dopant in the sealant 52 can be controlled by the buoyancy of the dopant in the encapsulating material (e.g., encapsulating resin). For example, Figure 15 shows an example of neutral buoyancy. Therefore, Figure 15 the dopant 88 in is uniformly distributed in the sealant 52 (e.g., the dopant can be suspended anywhere in the encapsulating material). Figure 16 shows an example in which the dopant 88 has high buoyancy and thus tends to distribute along the upper surface of the sealant (e.g., because the dopant floats to the top of the sealant). In contrast, Figure 17 shows an example in which the dopant 88 has low buoyancy and thus tends to distribute along the lower surface of the sealant (e.g., because the dopant sinks to the bottom of the sealant).

[0086] If desired, the position of the dopant 88 can be controlled. For example, the dopant can be placed directly on top of the light-emitting diode 38. The dopant 88 can also be designed such that the orientation of the dopant 88 in the sealant 52 can be controlled. In one example, as Figure 18 shown, the dopant 88 (e.g., a specific particle) can have two parts with two different densities. As Figure 18 shown, the dopant 88 can include part 88-1 and part 88-2. Part 88-2 can have a different density (e.g., higher) from part 88-1. In another example, as Figure 19 shown, the shape of the dopant 88 can be designed to control the orientation of the dopant 88. Figure 19 The shape shown in (sometimes referred to as a mushroom shape) can allow control of the orientation of the dopant 88 in the sealant 52.

[0087] The foregoing example of the dopant 88 in the dome-shaped sealant area is merely illustrative. Generally, any desired sealant (e.g., Figure 12a sealant having a flat upper surface and Figure 14 a sealant having a recessed portion) may include a dopant.

[0088] Figure 20 is a cross-sectional side view of an exemplary backlight unit, showing how a light-emitting diode array 36 may include a patterned layer 90 on a sealant 52. The patterned layer 90 may help to spread light from the light-emitting diodes 38 (e.g., in combination with or in place of the light-diffusing layer 28 in Figure 2 ). The patterned layer 90 may also help to maintain a gap 92 (e.g., an air gap) between the optical film 26 and the sealant 52. The patterned layer 90 may be a separate film attached to the upper surface of the sealant 52. Alternatively, the patterned layer 90 may be formed by a patterned portion of the sealant material (e.g., the patterned layer 90 may be part of the sealant 52).

[0089] Figure 21 is a cross-sectional side view of an exemplary backlight unit, showing how a light-emitting diode array 36 may include a sealant 52 having a textured surface. As Figure 21 shown, the sealant 52 has a textured upper surface 94. The textured upper surface 94 may generally be planar (e.g., the sealant forms a flat plate). However, the upper surface may be rough (as opposed to smooth). The textured upper surface may prevent total internal reflection of light emitted by the light-emitting diodes 38, thereby improving efficiency. The texture of the upper surface may be random.

[0090] To increase the reflectivity of a printed circuit board in a backlight unit, a reflective layer may be used. For example, a reflective material may be laminated to the printed circuit board. However, care must be taken to ensure that the reflective material is not damaged during the solder reflow process. The melting point of the reflective material may be less than or equal to the melting point of the solder. Thus, the solder reflow may melt (and damage) the reflective material.

[0091] To prevent damage to the reflective layer, the reflective layer may be laminated to the circuit board after the solder reflow. Alternatively, the reflective layer may be connected to the printed circuit board before the solder reflow. Then, a solder mask may be used to prevent damage to the reflective layer during the solder reflow process. An arrangement of this type is shown in Figure 22 .

[0092] As Figure 22As shown, a reflective layer 96 can be formed on the printed circuit board 50 (e.g., on the upper surface of the printed circuit board 50). The reflective layer can be formed of any desired material. The reflective layer can be formed of one or more layers. The reflective layer can have a high reflectance at the wavelength emitted by the light-emitting diode. For example, if the light-emitting diode emits blue light, the reflective layer 96 can have a high reflectance for blue light (e.g., greater than 80%, greater than 90%, greater than 92%, greater than 94%, greater than 96%, less than 99%, etc.). Solder 56 can also be formed on the printed circuit board 50 (e.g., on the conductive pads on the upper surface of the printed circuit board that are not covered by the reflective layer). A heat source 100 can be used to heat the reflowing solder 56. The heat source 100 can heat the solder 96 by emitting energy (e.g., infrared light) through the solder mask 98. The solder mask 98 can have an opening that overlaps with the solder 56. The portion of the printed circuit board 50 that is not covered by the solder 56 can be covered by the solder mask 98. In this way, the solder mask 98 can prevent the reflective layer 96 from being damaged during the heating of the solder 56. The solder mask 98 can be formed of any material that is opaque or tolerant to the energy 102 emitted by the heat source 100. The heat source 100 can be, for example, a laser that emits infrared light.

[0093] In some embodiments, the backlight unit 42 can include a polarization grating that helps increase the point spread function (PSF) width of the light emitted by the light-emitting diode 38. Increasing the PSF width can reduce the dependence on reflections from the printed circuit board for recycling. Figures 23 - 25 FIG. is a cross-sectional side view of an exemplary backlight unit having a polarization grating layer (sometimes referred to as a diffraction layer, a light diffusion layer, a polarization phase grating layer, a polarization grating, or a polarization phase grating). As Figure 23 shown, the backlight unit 42 includes a light-emitting diode 38 covered by an encapsulant 52 on a printed circuit board 50. The backlight unit can also have optical films 26, which include a light diffusion layer 28. However, the backlight unit can include an additional light diffusion layer 104. The polarization grating layer 104 (sometimes referred to as a diffraction layer, a light diffusion layer, a polarization phase grating layer, a polarization grating, or a polarization phase grating) can divide the light received from the light-emitting diode 38 into two different polarization states. The light diffusion layer 104 can reduce the coaxial intensity peak associated with the light-emitting diode.

[0094] As Figure 23 shown, the light diffusion layer 104 can be coupled to the encapsulant 52 covering the light-emitting diode (e.g., the light diffusion layer 104 can directly contact the encapsulant 52). This example is only illustrative. In Figure 24In another example shown, a light diffusion layer 104 is formed on the lower surface of the light diffusion layer 28. The light diffusion layer 28 and the light diffusion layer 104 can be connected together in any desired manner. The light diffusion layer 28 can have uniformly patterned protrusions on the upper surface of the light diffusion layer. In another embodiment, as Figure 25 shown, a waveguide layer 106 (sometimes referred to as a light guide layer) can be interposed between the light diffusion layer 28 and the light diffusion layer 104. In this embodiment, the light diffusion layer 28 can have non-uniform spacing on the upper surface of the light diffusion layer (e.g., having statistical spacing to control waveguide dispersion).

[0095] Other structures can be used to increase the point spread function (PSF) width of the light emitted by the light emitting diode 38. Figure 26 And Figure 27 are cross-sectional side views of backlight units that include structures used in combination with a high-reflectivity printed circuit board to increase the point spread function (PSF) width of the light emitted by the light emitting diode 38. As Figure 26 shown, the light emitting diode 38 can be positioned on the printed circuit board 50 and can be covered by an encapsulant 52. Each light emitting diode 38 can be covered by a corresponding portion of the encapsulant having a corresponding parabolic upper surface 108. The parabolic upper surfaces of adjacent encapsulant portions can meet at a vertex 110. This portion can be referred to as a shallow recess or depression portion of the encapsulant 52.

[0096] The light 112 emitted by the light emitting diode 38 can be reflected back to the vertex 110 by total internal reflection (TIR). When the light 112 reaches the vertex 110 (sometimes referred to as the light leakage promoting structure 110), the light is more likely to exit the encapsulant 52 in the direction of the observer. In this way, the light from the light emitting diode can be directed and exit from the region between adjacent light emitting diodes (thereby increasing the PSF width). This type of arrangement relies on the light reflected from the printed circuit board 50 (e.g., the light is emitted by the light emitting diode, reflected from the parabolic upper surface of the encapsulant due to total internal reflection, and then reflected from the upper surface of the printed circuit board). Therefore, if the reflectivity of the printed circuit board is low, then the Figure 26 efficiency of the backlight unit with this arrangement may be low. Therefore, Figure 26 this arrangement can be applicable to embodiments in which the printed circuit board has a high reflectivity (e.g., greater than 90%, greater than 94%, greater than 96%, etc.).

[0097] In another embodiment, as Figure 27 shown, the light emitting diode 38 is likewise positioned on the printed circuit board 50 and can be covered by the encapsulant 52. In this embodiment, the light emitting diode is covered by an encapsulant having a flat upper surface (e.g., an encapsulant flat). A light leakage promoting structure 114 can be interposed between each light emitting diode.Figure 27 The light leakage promoting structure 114 in [[ ]] can be formed by an opaque white structure. In another embodiment, the light leakage promoting structure 114 can be an air gap (sometimes referred to as a pore) in the encapsulant 52.

[0098] The light emitted by the light emitting diode 38 can be reflected back to the light leakage promoting structure 114 by total internal reflection (TIR). When the light reaches the light leakage promoting structure 114, the light is more likely to exit the encapsulant 52 in the direction of the observer. In this way, the light from the light emitting diode can be directed and exit from the region between adjacent light emitting diodes (thereby increasing the PSF width). This type of arrangement relies on the light reflected from the printed circuit board 50 (for example, the light is emitted by the light emitting diode, reflected from the upper surface of the encapsulant due to total internal reflection, and then reflected from the upper surface of the printed circuit board). Therefore, Figure 27 the arrangement can be applicable to embodiments in which the printed circuit board has a high reflectivity (for example, greater than 90%, greater than 94%, greater than 96%, etc.).

[0099] The light diffusion layer 28 (for example, as [[ ]] Figure 2 shown) has various possible ways to diffuse light. Figure 28 is a cross-sectional side view of an exemplary display that has a light diffusion layer with microlens structures on both the upper and lower surfaces. As [[ ]] Figure 28 shown, the light diffusion layer 28 has an upper surface 116 and a lower surface 118. The upper surface 116 has a plurality of microlenses 120 formed by depressions in the upper surface of the light diffusion layer. The microlenses 120 can be formed by spherical depressions or depressions having any other desired shape in the upper surface 116. The lower surface 118 also has a plurality of microlenses 122 formed by depressions in the lower surface of the light diffusion layer. The microlenses 122 can be formed by spherical depressions or depressions having any other desired shape in the lower surface 118. The microlenses 122 can be larger than the microlenses 120 (as [[ ]] Figure 28 shown). However, this example is only illustrative, and the size of the microlenses 122 can also be the same as or smaller than the microlenses 120. Additionally, each microlens in the microlens array 120 can have the same size or different sizes, and each microlens in the microlens array 122 can have the same size or different sizes.

[0100] Another arrangement of the light diffusion layer 28 is as [[ ]] Figure 29 shown. As [[ ]] Figure 29 shown, the light diffusion layer can include two membranes (layers). In [[ ]] Figure 29In the example, the light diffusing layer 28-1 is positioned above the light diffusing layer 28-2. For example, the light diffusing layer 28-1 and the light diffusing layer 28-2 can be attached together using an adhesive 128 (e.g., a pressure-sensitive adhesive). If desired, the adhesive 128 can have diffusing properties.

[0101] As Figure 29 shown, the light diffusing layer 28-2 has an upper surface that has microlenses 132. The microlenses 132 can be formed by a plurality of depressions in the upper surface of the light diffusing layer 28-2. The light diffusing layer 28-2 can also include a plurality of protrusions 130. The protrusions 130 can protrude toward the light emitting diode. The protrusions 130 can be elongated protrusions (sometimes referred to as ridges) that extend along the longitudinal axis of the layer (e.g., parallel to Figure 29 the Y-axis in). The light diffusing layer 28-1 can be the same as the light diffusing layer 28-2, except that it is rotated 90° relative to the light diffusing layer 28-2. For example, the light diffusing layer 28-1 also has a plurality of protrusions that extend along the longitudinal axis of the layer. However, the protrusions of the light diffusing layer 28-1 can extend parallel to the X-axis (perpendicular to the protrusions of the light diffusing layer 28-2). The light diffusing layer 28-1 also includes microlenses 126. The microlenses 126 can be formed by a plurality of depressions in the upper surface 124 of the light diffusing layer 28-1.

[0102] The light emitted by the light emitting diode 38 will diffuse relative to a first axis (e.g., from a point source to two points) when it reaches the light diffusing layer 28-2. The microlenses 132 can reduce total internal reflection to facilitate the transmission of light to the light diffusing layer 28-1. The light diffusing layer 28-1 will diffuse the incident light relative to a second axis (from two points to four points), the second axis being perpendicular to the first axis (since the protrusions of layer 28-1 are perpendicular to the protrusions of layer 28-2). The microlenses 126 can reduce total internal reflection to facilitate the leakage of light out of layer 28-1 and toward layer 30. The layers 28-1 and 28-2 can each have any desired thickness (e.g., between 20 microns and 30 microns, between 20 microns and 25 microns, less than 50 microns, less than 25 microns, about 22 microns, greater than 15 microns, less than 100 microns, etc.). The thicknesses of the layers 28-1 and 28-2 can be the same.

[0103] The example of the light diffusing layer 28 having elongated protrusions that extend along the longitudinal axis (and dividing the incident point source into two points) is merely illustrative. If desired, the light diffusing layer 28 can instead include an array of protrusions or depressions. Each protrusion can divide the incident point source into two or more points. Figure 30A cross-sectional side view of the light diffusing layer 28 including the protrusion 134. The protrusion 134 can have any desired shape. For example, the protrusion can have a pyramid shape (e.g., having a square base and four triangular faces meeting at the apex 136) or a triangular pyramid shape (e.g., having a triangular base and three triangular faces meeting at the apex 136). The pyramid protrusion can divide a point light source into four points, while the triangular pyramid protrusion can divide a point light source into three points. In another embodiment, as Figure 31 shown, the light diffusing layer 28 can include a plurality of recesses 138. The recesses 138 can have any desired shape. For example, the recess can have a pyramid shape (e.g., having a square base and four triangular faces meeting at the apex 140) or a triangular pyramid shape (e.g., having a triangular base and three triangular faces meeting at the apex 140). The pyramid recess can divide a point light source into four points, while the triangular pyramid recess can divide a point light source into three points. Figure 32 A top view of the light diffusing layer 28 showing the arrangement of the protrusions 134 (or recesses 138) in an array. The protrusions and / or recesses can have any desired shape and can be arranged in any desired type of array.

[0104] Figure 33 A top view of the light diffusing layer having protrusions 134 formed by a partial cubic structure (sometimes referred to as a pyramid). As shown, each protrusion (or recess) can be formed by three square faces (e.g., a pyramid) meeting at the apex 136. In Figure 34 , each protrusion 134 is formed by two pyramid structures offset from each other. Thus, Figure 34 each protrusion 134 in has six faces (and divides an incident point light source into six points).

[0105] In Figure 35 another embodiment shown, the protrusion 134 can be formed by a multi-pyramid structure. As Figure 35 shown, the protrusion has four faces 142 meeting at the apex 148. Each face can have a lower portion 144 and an upper portion 146, which are angled 150 relative to each other. The angle 150 can be selected to optimize the light diffusion function of the light diffusing layer.

[0106] Additional embodiments for diffusing light from the light emitting diode 38 are as Figures 36 - 39 shown. Figure 36A cross-sectional side view of an exemplary backlight unit is shown, which has a microlens array formed on the lower surface of a partial reflection layer 30. The microlenses 152 may protrude from the lower surface of the partial reflection layer 30. The microlenses may assist in diffusing the light received from the light-emitting diodes 38. The microlenses 152 may have an associated focal length (f). The thickness 154 of the encapsulant 52 may be a function of the focal length (e.g., t = n × f, where t is the thickness 154 and n is the refractive index of the encapsulant material).

[0107] Figure 37 A layout similar to Figure 36 is shown. However, in Figure 36 , an encapsulant 52 (e.g., an encapsulant flat plate) is formed over all the light-emitting diodes in the array. In Figure 37 , each light-emitting diode has a corresponding portion of the encapsulant 52. In Figure 37 , the thickness 154 of each encapsulant portion may still be selected based on the focal length of the microlenses 152 and the refractive index of the encapsulant material.

[0108] Figure 38 Another embodiment is shown in which the microlenses 152 are on the lower surface of the partial reflection layer 30. In Figure 38 , each light-emitting diode may be covered by an encapsulant portion 52 having a curved upper surface (instead of the flat upper surface in Figure 37 ). In Figure 38 , the thickness 154 of each encapsulant portion may be selected based on the focal length of the microlenses 152 (e.g., t = f, where t is the thickness 154 and f is the focal length of the microlenses 152).

[0109] Figures 36 - 38 The example of the microlenses 152 formed on the lower surface of the partial reflection layer 30 shown in Figure 39 is merely illustrative. If desired, the microlenses 152 may be formed at other locations on the display.

[0110] In Figures 36 - 39 , the light diffusion layer 28 is omitted (since the microlenses 152 diffuse the light from the light-emitting diodes). However, this is merely illustrative. If desired, the light diffusion layer 28 may be included in any of the embodiments in Figures 36 - 39 (and cooperate with the microlenses 152 to diffuse light).

[0111] Figure 2 An example is shown in which the backlight unit 42 includes a brightness enhancement film 46 and a collimating layer 44. Examples of these layers are also inFigure 40 is shown. As Figure 40 shown, the brightness enhancement film 46 may include protrusions 160 on the upper surface of the film. The collimating layer 44 may include an array of microlenses 162 on the lower surface of the film. To reduce the number of layers in the backlight unit 42, the brightness enhancement film 46 and the collimating layer 44 may be combined into a single film. Figure 41 is a cross-sectional side view of an exemplary optical layer 164 having protrusions 160 (serving as a brightness enhancement film) on the upper surface and microlenses 162 (serving as a collimating layer) on the lower surface.

[0112] Light leaking from the edge of the optical film 26 may cause the edge of the display to have an undesirable blue tint (due to the pixel array 24 receiving excess blue light from the light-emitting diodes 38). To mitigate this problem, one or more coatings may be included in the edge of the display. As Figure 42 shown, the display 14 may include a coating 168 on the lower layer of the pixel array 24. The display may include a chassis 166 (e.g., a plastic chassis sometimes referred to as a p-chassis) that supports one or more other layers of the display 14. One or more surfaces of the chassis (e.g., the edge surface 176) are coated with a coating 174. The upper surface of the optical layer is coated with a coating 170. The edge surface of the optical layer is coated with a coating 172. The coatings 168, 170, 172, and 174 (all at the edge of the display) may be formed of a black material, a gray material, a yellow material, or a phosphor material. The black material, the gray material, and the yellow material may adjust or eliminate the reflection of blue light (thereby reducing the excess blue light at the edge of the display). The phosphor material may convert blue light into white light (thereby reducing the excess blue light at the edge of the display).

[0113] According to one embodiment, a display is provided that includes: a plurality of pixels; and a backlight configured to generate backlight illumination for the plurality of pixels and including: a light source configured to emit light and disposed in a plurality of respective units; a first light diffusing layer that receives light from the light source and has a first plurality of elongated protrusions extending in a first direction; and a second light diffusing layer that receives light from the first light diffusing layer and has a second plurality of elongated protrusions extending in a second direction perpendicular to the first direction.

[0114] According to another embodiment, the light source includes light-emitting diodes mounted on a printed circuit board.

[0115] According to another embodiment, the backlight includes a heat-conducting layer that is attached to the lower surface of the printed circuit board by an adhesive.

[0116] According to another embodiment, the adhesive includes a heat-conducting additive.

[0117] According to another embodiment, the backlight includes a radiative cooling coating on the lower surface of the printed circuit board.

[0118] According to another embodiment, the backlight includes a encapsulant layer having a flat upper surface formed over the light emitting diodes.

[0119] According to another embodiment, the backlight includes an encapsulant, and each light emitting diode is covered by a respective encapsulant portion having a curved upper surface.

[0120] According to another embodiment, the curved upper surface of each respective encapsulant portion has a respective recess over the light emitting diode.

[0121] According to another embodiment, the backlight includes an encapsulant layer that is formed over the light emitting diodes and includes a scattering dopant.

[0122] According to another embodiment, the backlight includes an encapsulant, and each light emitting diode is covered by a respective encapsulant portion having a parabolic upper surface.

[0123] According to another embodiment, the backlight includes a light leakage promoting structure that is interposed between adjacent light emitting diodes.

[0124] According to another embodiment, each respective unit includes four light emitting diodes having a non-square rectangular shape.

[0125] According to another embodiment, each respective unit includes a first light emitting diode having a first size and a second light emitting diode having a second size different from the first size.

[0126] According to another embodiment, each respective unit includes a red light emitting diode, a blue light emitting diode, and a green light emitting diode.

[0127] According to another embodiment, a first plurality of elongated protrusions extend from the lower surface of a first light diffusing layer having a first microlens array formed on the upper surface of the first light diffusing layer, a second plurality of elongated protrusions extend from the lower surface of a second light diffusing layer, and the second light diffusing layer has a second microlens array formed on the upper surface of the second light diffusing layer.

[0128] According to one embodiment, a display is provided that includes: a plurality of pixels; and a backlight configured to generate backlight illumination for the plurality of pixels and including: a printed circuit board; a plurality of light-emitting diodes mounted on the printed circuit board; at least one light-diffusing layer formed over the printed circuit board, the at least one light-diffusing layer diffusing light received from the plurality of light-emitting diodes; a partial reflection layer formed over the at least one light-diffusing layer; a color conversion layer formed over the partial reflection layer; and a collimating layer formed over the color conversion layer.

[0129] According to another embodiment, the color conversion layer includes a phosphor layer formed over an additional partial reflection layer.

[0130] According to another embodiment, the at least one light-diffusing layer includes: a first light-diffusing layer that receives light from the plurality of light-emitting diodes and has a first plurality of elongated protrusions extending in a first direction; and a second light-diffusing layer that receives light from the first light-diffusing layer and has a second plurality of elongated protrusions extending in a second direction perpendicular to the first direction.

[0131] According to one embodiment, a display is provided that includes: a plurality of pixels; and a backlight configured to generate backlight illumination for the plurality of pixels and including: a light-emitting diode array including a plurality of light-emitting diodes that emit light; a plurality of optical films formed over the light-emitting diode array; and a coating formed on an edge of the plurality of optical films, the coating receiving light emitted by the plurality of light-emitting diodes and changing the color of the light.

[0132] According to another embodiment, the coating includes a coating selected from the group consisting of: a black material, a gray material, a yellow material, or a phosphor material.

[0133] The foregoing is merely illustrative and various modifications may be made to the embodiments. The foregoing embodiments may be implemented independently or in any combination.

Claims

1. A display, comprising: a plurality of pixels; and a backlight configured to generate backlight illumination for the plurality of pixels, wherein the backlight includes: a printed circuit board; light sources configured to emit light and arranged in a plurality of corresponding units, wherein the light sources include light emitting diodes mounted on the printed circuit board, and wherein the light emitting diodes have a first refractive index; at least one light diffusion layer formed on the printed circuit board, the at least one light diffusion layer receiving light from the light emitting diodes, diffusing the light and reducing total internal reflection to facilitate light leakage; a light leakage facilitating structure located on the printed circuit board and interposed between adjacent light emitting diodes, wherein the light leakage facilitating structure includes a first material having a second refractive index; and a encapsulant plate covering the light emitting diodes and the light leakage facilitating structure, wherein the encapsulant plate includes a second material having a third refractive index, and wherein the third refractive index is between the first refractive index and the second refractive index.

2. The display according to claim 1, wherein The backlight further includes a thermal conductive layer attached to the lower surface of the printed circuit board by an adhesive.

3. The display according to claim 2, wherein, The adhesive includes a thermally conductive additive.

4. The display according to claim 1, wherein, The backlight further includes a radiative cooling coating on the lower surface of the printed circuit board.

5. The display according to claim 1, wherein, The backlight further includes: a patterned layer formed directly on the flat upper surface of the encapsulant plate.

6. The display according to claim 1, wherein, The encapsulant plate includes scattering dopants.

7. The display according to claim 1, wherein Each corresponding unit includes four light emitting diodes having a non-square rectangular shape.

8. The display according to claim 1, wherein, Each corresponding unit includes a first light emitting diode having a first size and a second light emitting diode having a second size different from the first size.

9. The display according to claim 1, wherein, Each corresponding unit includes a red light emitting diode, a blue light emitting diode and a green light emitting diode.

10. The display according to claim 1, wherein, The at least one light diffusion layer includes: a first light diffusion layer receiving light from the light source and having a first plurality of elongated protrusions extending in a first direction; and a second light diffusion layer receiving light from the first light diffusion layer and having a second plurality of elongated protrusions extending in a second direction perpendicular to the first direction.

11. The display according to claim 10, wherein, The first plurality of elongated protrusions extend from the lower surface of the first light diffusion layer, wherein the first light diffusion layer has a first microlens array formed on the upper surface of the first light diffusion layer, wherein the second plurality of elongated protrusions extend from the lower surface of the second light diffusion layer, and wherein the second light diffusion layer has a second microlens array formed on the upper surface of the second light diffusion layer.

12. The display according to claim 1, wherein, The encapsulant plate has a flat upper surface, and wherein light emitted by the light emitting diodes is reflected back to the light leakage facilitating structure by total internal reflection from the flat upper surface.

13. The display according to claim 1, wherein, The first material is air.

Images