Light-emitting device and method for manufacturing a light-emitting device

Abstract

To fabricate a light emitting device having a light reflective coating material with high performance.SOLUTION: It has a light emitting element and a light reflective coating material containing plate-shaped light reflecting material 11, silica, and alkali metal to cover the light emitting element, and the average particle size of the light reflective material is equal to or more than 0.6 μm and equal to or more than 43 μm, and the average aspect ratio of the light reflective material is equal to or more than 10.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a light-emitting device and a method for manufacturing the same.

Background Art

[0002] Some light-emitting devices such as LEDs have a light-emitting element and a light-reflective coating member that covers a part of the light-emitting element. For example, Patent Document 1 discloses a light-reflective coating member that contains a reflective material including a white pigment such as titanium oxide, zinc oxide, tantalum oxide, niobium oxide, zirconia, or aluminum oxide in a base material of a heat-resistant resin such as silicone resin or an inorganic binder.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, there is still room for improvement in the light-reflective coating member formed of such an inorganic material in order to improve the performance of the light-emitting device. The performance of the light-emitting device in this specification is, for example, heat resistance, luminous flux, luminance, sharpness (cut-off property) of the luminance difference between the light-emitting surface of the light-emitting device and the non-light-emitting surface surrounding the light-emitting surface, reliability (life), and the like.

[0005] Therefore, an object of the present disclosure is to provide a light-emitting device including a light-reflective coating member having high performance, particularly heat resistance, of the light-emitting device, and a method for manufacturing the light-emitting device.

Means for Solving the Problems

[0006] The light-emitting device according to this disclosure comprises a light-emitting element and a light-reflective covering member that covers the light-emitting element and includes a plate-shaped light-reflective material, silica, and an alkali metal, wherein the average particle size of the light-reflective material is 0.6 μm or more and 43 μm or less, and the average aspect ratio of the light-reflective material is 10 or more.

[0007] Furthermore, the method for manufacturing a light-emitting device according to this disclosure includes the steps of: mixing silica powder, a plate-shaped light-reflecting material powder having an average particle size of 0.6 μm or more and 43 μm or less and an average aspect ratio of 10 or more, and an alkaline solution to form a mixture; applying the mixture to a light-emitting element; and curing the mixture by heating to form a light-reflecting coating member. [Effects of the Invention]

[0008] According to one embodiment of the present disclosure, a light-emitting device and a method for manufacturing the light-emitting device can be provided, which have high performance, particularly heat resistance, and are equipped with a light-reflecting coating member, as well as a method for manufacturing the light-emitting device. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view of a light-emitting device according to one embodiment of the present disclosure. [Figure 2] This is an enlarged cross-sectional view of a portion of the light-reflective coating material of the light-emitting device shown in Figure 1. [Figure 3] Figure 1 is an example of a schematic perspective view of the light-reflective powder that forms the light-reflective coating member of the light-emitting device shown in Figure 1. [Figure 4A] Figure 1 is a schematic cross-sectional view showing one step in the first manufacturing method of the light-emitting device. [Figure 4B] Figure 1 is a schematic cross-sectional view showing one step in the first manufacturing method of the light-emitting device. [Figure 4C] Figure 1 is a schematic cross-sectional view showing one step in the first manufacturing method of the light-emitting device. [Figure 5] This is a schematic cross-sectional view showing another step in the first manufacturing method. [Figure 6A]Figure 1 is a schematic cross-sectional view showing one step in the second manufacturing method of the light-emitting device. [Figure 6B] Figure 1 is a schematic cross-sectional view showing one step in the second manufacturing method of the light-emitting device. [Figure 6C] Figure 1 is a schematic cross-sectional view showing one step in the second manufacturing method of the light-emitting device. [Figure 6D] Figure 1 is a schematic cross-sectional view showing one step in the second manufacturing method of the light-emitting device. [Figure 7] This is a schematic cross-sectional view of a light-emitting device according to another embodiment of the present disclosure. [Figure 8A] Figure 7 is a schematic cross-sectional view showing an example of the manufacturing process of the light-emitting device shown. [Figure 8B] Figure 7 is a schematic cross-sectional view showing an example of the manufacturing process of the light-emitting device shown. [Figure 8C] Figure 7 is a schematic cross-sectional view showing an example of the manufacturing process of the light-emitting device shown. [Figure 9] This is an enlarged cross-sectional view of a part of the light-emitting device according to Example 10 during the manufacturing process. [Figure 10] This is an enlarged cross-sectional view of a part of the covering member of the light-emitting device according to Example 11. [Modes for carrying out the invention]

[0010] The embodiments and examples for carrying out the present invention will be described below with reference to the drawings. The light-emitting device and the method for manufacturing the light-emitting device described below are intended to embody the technical concept of the present invention, and the present invention is not limited to the following unless otherwise specified. In each drawing, members having the same function may be denoted by the same reference numeral. For the sake of easy explanation or understanding of the gist, the embodiments or examples may be shown separately for convenience, but partial substitution or combination of the configurations shown in different embodiments or examples is possible. In the embodiments and examples described below, descriptions of matters common to the foregoing are omitted, and only the different points are explained. In particular, the same operational effects due to the same configuration are not sequentially mentioned for each embodiment or example. The size, positional relationship, etc. of the members shown in each drawing may be exaggerated for clarity of explanation.

[0011] Embodiment 1 As shown in FIG. 1, the light-emitting device 1 according to the present embodiment includes a light-emitting element 4, a translucent member 6, and a light-reflective coating member 5 that covers the light-emitting element 4. The light-emitting element 4 includes a semiconductor laminate 2 and a pair of electrodes 3 provided on the lower surface of the semiconductor laminate 2. The translucent member 6 is disposed to cover the upper surface 4a of the light-emitting element 4. A part of the surface of the translucent member 6 is exposed from the coating member 5, and the surface of the translucent member 6 exposed from the coating member 5 includes the light-emitting surface 1a of the light-emitting device 1. The coating member 5 is disposed to cover a part of the side surface and the bottom surface of the light-emitting element 4 and a part of the side surface and the bottom surface of the translucent member 6. The coating member 5 contains a plate-like light-reflective material 11, silica, and an alkali metal. The average particle diameter of the light-reflective material 11 is 0.6 μm or more and 43 μm or less, and the average aspect ratio of the light-reflective material 11 is 1 or more.

[0012] (Light-emitting element) The semiconductor laminate 2 included in the light-emitting element 4 comprises, for example, an n-type semiconductor layer, a p-type semiconductor layer, and a light-emitting portion disposed between the n-type and p-type semiconductor layers. The light-emitting element 4 includes a growth substrate 7 (for example, a sapphire substrate) for growing the semiconductor layer on the side of the semiconductor laminate 2 opposite to the side where the electrode 3 is formed. However, the growth substrate may be removed after the semiconductor layer has been formed. The peak wavelength of the light emitted by the semiconductor laminate 2 is, for example, in the range of 260 nm to 630 nm. The light-emitting element 4 emits, for example, ultraviolet light or blue light. The pair of electrodes 3 provided on the lower surface of the semiconductor laminate 2 are a p electrode and an n electrode. In the growth substrate 7, the width of the growth substrate 7 (the length of the longest side of the polygonal growth substrate 7 when viewed from above) is preferably 2.5 times or more and 3.5 times or less the thickness of the growth substrate 7. With such a relationship between the thickness and width of the growth substrate 7, the light extraction efficiency from the light-emitting element 4 is improved.

[0013] (Translucent member) The translucent member 6 may contain resin or be an inorganic material. If the translucent member 6 is an inorganic material, it has higher heat resistance than a translucent member containing resin, making it possible to manufacture a light-emitting device with high heat resistance. For example, glass can be used as the inorganic material. The translucent member 6 can contain a wavelength-converting material such as a phosphor. If the translucent member 6 contains a phosphor in an inorganic material base, for example, YAG (yttrium aluminum garnet) can be used as the phosphor, and alumina or silica can be used as the base material. Note that the translucent member 6 does not have to contain a wavelength-converting material. In this case, the light from the light-emitting element is emitted to the outside without wavelength conversion.

[0014] (Covering material) In this embodiment, the covering member 5 covers the light-emitting element 4 and the light-transmitting member 6 by exposing the lower surface 3a of the electrode 3 of the light-emitting element 4 and the upper surface 6a of the light-transmitting member 6. Here, "covering" includes not only the state in which the covering member 5 is in contact with the light-emitting element 4 and / or the light-transmitting member 5, but also the state in which the covering member 5 is positioned between the light-emitting element 4 and / or the light-transmitting member 5 with another member or space (e.g., an air layer) in between. In this specification, expressions such as "cover," "cover," and "being covered" also include the same state as "being covered." When another member or space (e.g., an air layer) is positioned between the side surface of the light-emitting element 4 and the covering member 5, the inner surface of the covering member 5 facing the side surface of the light-emitting element 4 may have an inclined surface in cross-sectional view that moves away from the side surface of the light-emitting element 4 as it moves from the lower surface to the upper surface of the light-emitting element 4. In cross-sectional view, this inclined surface may be, for example, straight or curved. The upper surface 6a of the translucent member 6 exposed from the covering member 5 is the light-emitting surface 1a of the light-emitting device 1. However, the translucent member 6 is not an essential component of the light-emitting device 1 according to this embodiment. If the translucent member 6 is not provided, the covering member 5 is arranged to expose, for example, the upper surface 4a of the light-emitting element 4 and the lower surface 3a of the electrode 3. In this case, the upper surface 4a of the light-emitting element 4 is the light-emitting surface.

[0015] The covering member 5 is a mixture of multiple inorganic materials. The coating member 5 includes a light-reflecting material 11 and a support member 12 that supports the light-reflecting material 11. The support member 12 contains silica and alkali metal. The coating member 5 is formed by a heating process in which a mixture of powder of the light-reflecting material 11, powder of silica, and an alkali solution is heated, as will be described later. The covering member 5 may be composed solely of inorganic materials, or it may be composed mainly of inorganic materials. In this embodiment, the covering member 5 is used as a covering member for the light-emitting element 4 and the light-transmitting member 6, but it can be used for other purposes. The covering member 5 according to this embodiment can be used, for example, as a light-reflecting layer placed on the surface of a mounting substrate to reflect light traveling from the light-emitting element towards the mounting substrate. Furthermore, the mixture 50 according to this embodiment is not limited to being used as a material for the covering member 5, but can also be used, for example, as a material for constituting a reflective wall surrounding a light-emitting element in an LED package.

[0016] (light reflective material) The powder of the light-reflecting material 11 is a plate-shaped particle having two opposing main surfaces 11a and 11b, as shown in Figure 3, for example. The two opposing main surfaces 11a and 11b of the light-reflecting material 11 can also be called the top and bottom surfaces of the light-reflecting material 11. The powder of the light-reflecting material 11 can also be called a flake-shaped particle. Note that Figure 3 is merely a schematic diagram showing the powder of the light-reflecting material 11, for example, as a thin cylindrical shape, in order to facilitate the explanation of the shape of the powder of the light-reflecting material 11. The light reflecting material 11 is, for example, boron nitride or alumina. These materials can reflect light of the peak wavelength from the light-emitting element.

[0017] The light-reflecting material 11 may consist of primary particles, or it may consist of secondary particles formed by the aggregation of two or more primary particles. Furthermore, primary and secondary particles may be present in a mixture.

[0018] The average aspect ratio of the light-reflecting material 11 is 10 or greater, preferably between 10 and 70. The average aspect ratio of the light-reflecting material 11 is calculated by the following method.

[0019] <Method for calculating the average aspect ratio> The average aspect ratio of the light-reflecting material 11 is calculated by measuring the thickness and width of the light-reflecting material 11 contained in the covering member 5 in the cross-section of the light-emitting device 1. First, a cross-section is exposed that passes through the center of the light-emitting surface 1a of the light-emitting device 1 and is substantially perpendicular to the light-emitting surface 1a. This cross-section is exposed by cutting the light-emitting device 1.

[0020] Next, the exposed cross-section is mirror-polished. The mirror-polished cross-section is photographed with a scanning microscope (SEM) to extract the cross-sections of the light-reflecting material 11, and a measurement area containing approximately 1000 cross-sections of the light-reflecting material 11 is selected. The number of pixels of the microscope is set to approximately 20 million pixels, and the magnification is set to 500x to 3000x. In this specification, the cross-section of the light-reflecting material 11 is a surface that is substantially perpendicular to one main surface 11a and / or the other main surface 11b of the light-reflecting material 11. Due to its shape, the plate-shaped light-reflecting material 11 tends to be arranged within the covering member 5 so that their main surfaces 11a or 11b face each other and overlap. Therefore, by appropriately selecting the cross-section to be exposed by the light-emitting device 1, the cross-sections of the light-reflecting material 11 can be appropriately extracted by the SEM.

[0021] Next, using image analysis software, the width (length in the longitudinal direction of the cross-section of the light-reflective material) and thickness (length in the transverse direction of the cross-section of the light-reflective material) of each cross-section of the extracted light-reflective material 11 are measured one point at a time, and the average value of the width relative to the thickness is calculated. Then, the average of these measured values ​​for 100 light-reflective materials 11 is taken as the average aspect ratio. When the light reflecting material 11 is boron nitride, the average aspect ratio of the light reflecting material 11 is, for example, between 16.5 and 19.2. When the light reflecting material 11 is alumina, the average aspect ratio of the light reflecting material 11 is, for example, between 10 and 70.

[0022] Furthermore, the average particle size of the light-reflecting material 11 is between 0.6 μm and 43 μm. Here, the fusion of the light-reflecting material 11 powder and the silica powder due to the heating process, and the elution of the light-reflecting material 11 powder into the alkaline solution due to the heating process, are minimal. Therefore, the shape and dimensions of the light-reflecting material 11 powder and the shape and dimensions of the light-reflecting material 11 contained in the coating member 5 formed after the heating process are substantially the same. For this reason, the average particle size of the light-reflecting material 11 is calculated by measuring the particle size of the light-reflecting material 11 powder using the following method.

[0023] <Method for calculating average particle size> The particle size of the light-reflecting material 11 powder is calculated, for example, using a scanning electron microscope "TM3030Plus" manufactured by Hitachi High-Technologies Corporation. First, one side of a carbon fiber double-sided tape is attached to the sample stage of the microscope, and then the light-reflecting material 11 powder is placed on the other side of the double-sided tape. The microscope's pixel count is set to 1.23 million pixels, and the magnification is set to 1000x to 2000x to acquire images of 100 light-reflecting material 11 powders (particles). Then, the particle size of each particle is measured using image analysis software. In this specification, the particle size of the light-reflecting material 11 powder is the largest diameter when viewed from the main surface 11a or 11b of the light-reflecting material 11. Next, the median diameter of the measured particles is calculated, and this calculated value is taken as the average particle size of the light-reflecting material 11. Alternatively, the particle size of the light-reflecting material 11 powder may be calculated by extracting a cross-section of the coating member using a SEM and measuring it using image analysis software.

[0024] When the light reflector 11 is boron nitride, the average particle size of the light reflector 11 is, for example, 6 μm to 43 μm. When the light reflector 11 is alumina, the average particle size of the light reflector 11 is, for example, 0.6 μm to 10 μm.

[0025] (silica) The weight ratio of silica to light-reflecting material 11 in the coating member 5 is, for example, 1:4 or more and 1:1 or less. That is, the weight of the light-reflecting material 11 in the coating member 5 is, for example, 1 to 4 times the weight of the silica in the coating member 5. Within this range, shrinkage during curing of the mixture can be reduced. If the amount of light-reflecting material is too high, the curability may decrease. On the other hand, if the amount of silica is too high, shrinkage due to curing will be large, and cracks may occur during curing. The average particle size of silica is, for example, between 0.1 μm and 10 μm. Within this range, the density per unit volume of raw materials (light reflector and silica) can be improved, thereby ensuring the strength of the coating material. The average particle size of the silica powder should preferably be smaller than the average particle size of the light-reflecting material. This allows the silica powder to fill the voids that form between the light-reflecting materials during mixing. The average particle size of the silica powder is calculated by measuring the particle size distribution of the silica powder using laser diffraction. The average particle size of the silica is measured before mixing with the alkaline solution. This is because the silica powder melts when mixed with the alkaline solution, making it difficult to confirm the particle size from the coating material 5. Alternatively, the content ratio of silica to light-reflecting material from the coating material can be calculated by observing a cross-section of the coating material extracted by SEM, for example, and calculating it based on the occupancy rate of silica and light-reflecting material.

[0026] (Alkali metals) Alkali metals are those contained in the alkaline solution described above. Examples of alkali metals include potassium and / or sodium.

[0027] The light-reflecting material 11 having the average particle size and average aspect ratio described above functions as aggregate for the coating member 5 when the coating member 5 is heated by the heat generated from the light-emitting element 4. This suppresses the shrinkage of the coating member 5 due to the heat from the light-emitting element 4, resulting in a light-emitting device 1 with high heat resistance. Such a light-emitting device 1 has a longer service life. In addition, the coating member 5 can reflect light from the light-emitting element by utilizing the refractive index difference between the light-reflecting material and silica. Furthermore, by obtaining a covering member 5 whose shrinkage is suppressed by the heat of the light-emitting element 4, it becomes possible to use the light-emitting device 1 even under conditions where the heat generated from the light-emitting element is large (for example, when a large amount of power is supplied to the light-emitting element). By increasing the amount of power supplied to the light-emitting element, the amount of light per light-emitting device can be increased. In addition, light-emitting elements that emit ultraviolet light have a larger amount of light energy than light-emitting elements that emit visible light, and are more susceptible to photodegradation of the resin, so they are sometimes mounted in ceramic packages that have high durability against light energy. However, by using the covering member 5 according to this embodiment, it is possible to provide a light-emitting device in which a light-emitting element that emits ultraviolet light is covered with the covering member 5 without using a ceramic package. In this way, a light-emitting device equipped with the covering member 5 can reduce manufacturing costs and be miniaturized compared to a light-emitting device that includes a ceramic package.

[0028] The linear thermal expansion coefficient of the coating member 5 is preferably 0.0.5 ppm / °C to 5 ppm / °C in the temperature range of 40°C to 300°C. This suppresses the expansion of the coating member even when the temperature of the coating member 5 rises when the light-emitting device is used, thereby improving reliability. In this embodiment, the linear thermal expansion coefficient of the coating member 5 is approximately 1 ppm.

[0029] Furthermore, it is desirable that the coating member 5 includes a scattering material. The scattering material is, for example, mainly zirconia or titania. If the light-emitting element emits ultraviolet light, zirconia, which has low light absorption in the ultraviolet wavelength region, is desirable. By including a scattering material in the coating member 5, the light reflectivity of the coating member 5 is improved. As a result, the brightness difference between the light-emitting surface of the light-emitting device 1 and the coating member 5 (non-light-emitting surface) surrounding the light-emitting surface becomes steeper. In other words, the clarity of the light-emitting surface 1a of the light-emitting device 1 is improved.

[0030] The light scattering material may be titania alone, or it may be titania with various surface treatments such as silica, alumina, zirconia, zinc, or organic materials applied to its surface. Furthermore, the light scattering material may be zirconia alone, or zirconia with various surface treatments such as silica, alumina, zinc, or organic materials applied to its surface may be used. In addition, stabilized zirconia with calcium, magnesium, yttrium, aluminum, etc., or partially stabilized zirconia may be used.

[0031] When a scattering material is added to the coating material, the scattering material is dispersed within the silica.

[0032] The average particle size of the scattering material is preferably smaller than the average particle size of the light-reflecting material 11. This ensures that the scattering material is positioned in the gaps between the light-reflecting materials 11, thereby suppressing the emission of light from the light-emitting element 4 to the outside of the light-emitting device 1 through these gaps. As a result, the clarity of the light emission surface 1a of the light-emitting device 1 is improved. The average particle size of the scattering material is measured by laser diffraction.

[0033] In Embodiment 1, a light-emitting device equipped with a light-transmitting member 6 was described, but a light-emitting device without a light-transmitting member 6 may also be described. In a light-emitting device equipped with a light-transmitting member 6 as in Embodiment 1, the upper surface of the light-transmitting member 6 and the upper surface of the covering member 5 are on the same plane. In contrast, in a light-emitting device without a light-transmitting member 6, the upper surface of the light-emitting element and the upper surface of the covering member are on the same plane.

[0034] Manufacturing method <First manufacturing method> Next, an example of a manufacturing method (first manufacturing method) for the light-emitting device 1 according to this embodiment will be described with reference to Figures 4A to 4C.

[0035] (The process of mounting the light-emitting element onto the substrate.) First, a plurality of light-emitting elements 4 are prepared, each having a translucent member 6 positioned on its upper surface 4a. The translucent member contains a phosphor. Next, the light-emitting elements 4 are mounted on the mounting substrate 20 at predetermined intervals, as shown in Figure 4A.

[0036] (A process of mixing light-reflecting powder, silica powder, and an alkaline solution to form a mixture.) Next, a mixture of light-reflecting material 11 powder and silica powder is mixed with an alkaline solution to prepare mixture 50. The mixture of powder and alkaline solution is mixed, for example, until a uniform viscosity is obtained, and then degassed and stirred using a stirring and degassing machine that can stir under reduced pressure. The powder of the light reflector 11 has an average particle size of 0.6 μm or more and 43 μm or less, and an average aspect ratio of 10 or more, preferably 10 or more and 70 or less. The powder of the light reflector 11 is, for example, boron nitride powder or alumina powder. The silica powder, for example, has an average particle size of 0.1 μm to 10 μm. The concentration of the alkaline solution is, for example, between 1 mol / L and 5 mol / L. If the concentration of the alkaline solution is too low, the curing properties will be poor, which may lead to a decrease in the strength or decomposition of the coating member 5. On the other hand, if the concentration of the alkaline solution is too high, excess alkali metal may precipitate, which may reduce the reliability of the light-emitting element. The alkaline solution is, for example, a potassium hydroxide solution or a sodium hydroxide solution. The silica powder and the light-reflecting material 11 powder are mixed in a weight ratio of, for example, 1:4 to 1:1. That is, the silica powder and the light-reflecting material 11 powder are mixed in such a way that the weight of the light-reflecting material 11 is between 1 and 4 times the weight of the silica powder. The alkaline solution and the mixed powder are mixed in a weight ratio of, for example, 2:10 to 8:10. That is, the alkaline solution and the mixed powder are mixed in such a way that the weight of the mixed powder is between 1.25 and 5 times the weight of the alkaline solution. If there is too little alkaline solution, multiple small clumps will form when mixed, making molding difficult. On the other hand, if there is too much alkaline solution, cracks may occur during curing, or the strength of the resulting coated member may decrease.

[0037] Furthermore, if the coating member 5 of the manufactured light-emitting device 1 is to contain a scattering material, the scattering material is mixed into this mixture 50. The average particle size of the scattering material is smaller than, for example, the average particle size of the powder of the light-reflecting material 11. The scattering material mainly consists of, for example, zirconia or titania.

[0038] (Step of applying the mixture to hibi) In this step, the mixture 50 is applied to at least the side surface of the light-emitting element 4. In this manufacturing method for producing the light-emitting device 1, as shown in Figure 4B, the mixture 50 is applied to the mounting substrate 20 so as to cover the light-emitting element 4 and the light-transmitting member 6. It is desirable to vibrate the mounting substrate 20 while applying the mixture 50 and / or after applying it. This makes it possible to easily spread the mixture 50 over a wide area. In the case of a light-emitting device that does not have a light-transmitting member 6, in this step, the mixture 50 should be placed on the mounting substrate 20 so as to cover only the light-emitting element 4. Alternatively, instead of vibrating the mounting substrate, the mixture 50 may be applied while being vibrated.

[0039] Furthermore, a protective film can be formed on the electrode 3 and / or the wiring electrodes of the mounting substrate 20 before applying the mixture 50. This prevents the electrode 3 and / or the wiring electrodes of the mounting substrate 20 from being damaged by corrosion or other damage caused by the alkaline solution contained in the mixture 50. Also, by forming a protective film on the electrode 3 and / or the wiring electrodes of the mounting substrate 20, damage from corrosive gases in the atmosphere can be prevented during use of the manufactured light-emitting device 1. In other words, the gas barrier properties of the light-emitting device 1 can be improved. The protective film described above can be formed using atomic layer deposition (ALD). Furthermore, the protective film on the electrode 3 and / or the wiring electrodes of the mounting substrate 20 may be applied after coating the mixture 50, or it may be applied before and after coating the mixture 50. By applying the protective film on the electrode 3 and / or the wiring electrodes of the mounting substrate 20 before and after coating the mixture 50, the gas barrier properties of the light-emitting device 1 can be further improved.

[0040] Furthermore, after placing the mixture 50 on the mounting substrate 20, the mixture can be pressed using, for example, a glass plate to form the upper surface of the mixture 50 into a flat shape. By pressing the upper surface of the mixture 50 in this manner to flatten it, in the light-emitting device 1 that is manufactured, the light-reflecting material 11 located in the vicinity region R1 (see Figure 9) of the light-emitting element 4 and the translucent member 6 is positioned at an angle of 0° to 45° from the surfaces of the light-emitting element 4 and the translucent member 6. This arrangement of the light-reflecting material 11 will be demonstrated in the embodiments described later. The vicinity region R1 (see Figure 9) is, for example, a region within 10 μm from the surfaces of the light-emitting element 4 and the translucent member 6. Furthermore, if the surfaces of the light-emitting element 4 and / or the translucent member 6 are not flat, the surface obtained by averaging the irregularities of the surface is made the plane of the translucent member. Thus, when the light-reflecting material 11 located in the vicinity region R1 is positioned at an angle of 0° to 45° from the surface of the light-emitting element 4 and the translucent member 6, the light-reflecting materials 11 can be positioned in close proximity with their main surfaces 11a and 11b facing each other. In other words, the density of the light-reflecting material 11 in the vicinity region R1 can be increased. Therefore, if the light-reflecting material 11 is a highly thermally conductive material, such as boron nitride or alumina, it can promote the dissipation of heat generated from the light-emitting element 4 and the translucent member 6.

[0041] Furthermore, silica or alumina can be formed on the mounting substrate 20 before applying the mixture 50. This improves the adhesion between the mounting substrate 20 and the mixture 50.

[0042] (A process of heating a mixture to form a light-reflective coating member / heating process) Next, the mixture 50 is heated to cure it and form a light-reflective coating member 5. This process includes a preliminary curing step in which the mixture 50 is cured at a first temperature T1, and a main curing step in which the mixture 50 is cured at a second temperature T2 that is higher than the first temperature T1. The preliminary curing step is performed, for example, at a first temperature T1 of 80°C to 100°C for 10 minutes to 2 hours. The main curing step is performed, for example, at a second temperature T2 of 150°C to 250°C for 10 minutes to 3 hours. By performing a preliminary curing process at a lower temperature than the main curing process, cracks are less likely to occur in the formed coating member 5. Furthermore, performing the preliminary curing process and the main curing process under pressure increases the light reflectivity of the formed coating member 5. This is thought to be because the pressure applied to the mixture causes the light-reflecting materials within the mixture to become more densely packed during curing. The pressure applied during the main curing process is, for example, 1 MPa.

[0043] (Step to expose the light-transmitting material) Next, as shown in Figure 4C, the covering member 5 is ground down to expose the upper surface 6a of the translucent member 6. The exposed upper surface 6a of the translucent member 6 becomes the light-emitting surface 1a of the light-emitting device 1.

[0044] (Singulation process) Next, the material is pieced along a predetermined cutting position CL to include one light-emitting element 4, thereby obtaining a light-emitting device 1. The pieced-out process is carried out, for example, using a blade.

[0045] In the first manufacturing method, the mixture 50 is applied to cover the upper surface 6a of the translucent member 6 during the coating step, and the upper surface 6a of the translucent member 6 is exposed in the subsequent step of exposing the translucent member. However, the upper surface 6a of the translucent member 6 may be exposed during the coating step and the mixture 50 may be placed on the mounting substrate 20. This makes it possible to omit the step of exposing the translucent member.

[0046] Thus, when applying the mixture 50 with the upper surface 6a of the translucent member 6 exposed during the mixture application process, it is desirable to form grooves 90 in the mixture 50 after the mixture application process but before the heating process, as shown in Figure 5. It is desirable that the grooves 90 be positioned along the cutting position CL in the piece formation process. It is also desirable that the coating member is divided by the formation of the grooves 90. This directs the shrinkage stress generated during curing from the grooved area towards the light-emitting element 4, thereby preventing the light-emitting element 4 and the mixture 50 from peeling off during curing. As a result, the adhesive strength between the coating member 5 formed by the curing of the mixture 50 and the light-emitting element 4 can be increased. Grooves are cut, for example, using a blade.

[0047] As mentioned above, in the individualization process, individualization is carried out so that one light-emitting element is included in one light-emitting device. However, this is not limited to this, and individualization can also be carried out so that two or more light-emitting elements are included in one light-emitting device. The same applies to the second manufacturing method described later.

[0048] <Second manufacturing method> Next, with reference to Figures 6A to 6D, here is another example of a method for manufacturing the light-emitting device 1 according to this embodiment. The second manufacturing method will be explained.

[0049] (A step to prepare mixture 50 by mixing light-reflecting powder, silica powder, and an alkaline solution.) A mixture of light-reflecting material 11 powder and silica powder is mixed with an alkaline solution to prepare a mixture 50. This step is the same as the step in the first manufacturing method in which light-reflecting material powder, silica powder, and an alkaline solution are mixed to form a mixture 50.

[0050] (Step of preparing a translucent member on which the mixture 50 is placed on the side) As shown in Figure 6A, a translucent member 6 on which the mixture 50 is arranged on its side is prepared. The translucent member 6 on which the mixture 50 is arranged on its side can be manufactured, for example, as follows. First, one or more through holes are made in the prepared layered mixture 50, and the layered mixture 50 with the through holes is formed. If multiple through holes are provided, it is desirable that the multiple through holes be provided at predetermined intervals. Next, the translucent member 6 is placed in the through holes. This makes it possible to manufacture a translucent member 6 on which the mixture 50 is arranged on its side. The translucent member may or may not contain a wavelength conversion member (e.g., a phosphor). The mixture 50 placed on the side surface of the light-transmitting member 6 may be heated at this stage, or it may be heated after the mixture 50 has been coated onto the light-emitting element 4, which will be described later. The through holes may be formed by punching after the layered mixture 50 has been formed.

[0051] (Step of placing the light-emitting element on the first light-transmitting member) Next, as shown in Figure 6B, multiple light-emitting elements 4 are placed so that their upper surfaces 4a are in contact with the translucent member 6. Here, the upper surface 4a is defined as the surface of the light-emitting element 4 opposite to the surface on which the electrodes are formed. Also, the upper surface 6a is defined as the surface of the translucent member 6 opposite to the surface on which the light-emitting elements are located.

[0052] (Step of applying the mixture to hibi) Next, as shown in Figure 6C, the mixture 50 is applied in layers to cover the light-emitting element 4. Similar to the first manufacturing method, it is desirable to vibrate the mounting substrate during and / or after the application of the mixture 50 in this manufacturing method as well. Also, similar to the first manufacturing method, a protective film may be placed on the electrode 3 surface using the atomic layer volume method before and / or after the application of the mixture 50 in this manufacturing method as well.

[0053] (A process of heating a mixture to form a light-reflective coating member / heating process) Next, the mixture 50 is heated to harden it and form the coating member 5. This step is the same as the step (heating step) in the first manufacturing method in which the mixture is heated to form a light-reflective coating member.

[0054] (Step to expose the electrodes) Next, as shown in Figure 6D, the covering member 5 is ground to expose the lower surface 3a of the electrode 3 of the light-emitting element 4. Here, the lower surface 3a is defined as the surface of the electrode 3 opposite to the surface facing the light-emitting element 4.

[0055] (Singulation process) Next, the material is pieced along a predetermined cutting position CL to include one light-emitting element 4, thereby obtaining a light-emitting device 1. The pieced-out process is carried out, for example, using a blade.

[0056] In this example, the mixture 50 is placed on the side surface of the translucent member 6, but instead of the mixture 50, a white resin containing titanium dioxide may be used.

[0057] <Other embodiments and their manufacturing methods> In the light-emitting device 1 according to Embodiment 1, the upper surface 6a of the translucent member 6 is exposed from the covering member 5, and the upper surface of the light-emitting device 1 includes the upper surface 6a of the translucent member 6 and the upper surface of the covering member 5, but is not limited to this. For example, as shown in Figure 7, the upper surface 106a and side surface 106b of the translucent member 106 are exposed from the covering member 5, and the upper surface of the light-emitting device 100 may consist only of the upper surface 106a of the translucent member 106. The upper surface 106a of the translucent member 106 is the light-emitting surface 100a of the light-emitting device 100. The translucent member 106 may or may not include a wavelength conversion member (e.g., a phosphor).

[0058] Such a light-emitting device 100 is manufactured by the following manufacturing method. First, as shown in Figure 8A, multiple light-emitting elements 4 are placed on the translucent sheet 60 at predetermined intervals. The light-emitting elements 4 are placed on the translucent sheet 60 so that their upper surfaces face the translucent sheet 60. Next, as shown in Figure 8B, the mixture 50 is placed on the translucent sheet 60 so as to cover the light-emitting element 4. Then, the mixture 50 is heated to form a light-reflective coating member 5. This step is carried out in the same manner as the step (heating step) of heating the mixture to form a light-reflective coating member in the first and second manufacturing methods. Next, as shown in Figure 8C, the lower surface 3a of the electrode 3 is exposed and it is separated into individual pieces along a predetermined cutting position CL. This allows the light-emitting device 100 to be manufactured. In this embodiment, a metal film can be placed on each of the exposed lower surfaces 3a of the pair of electrodes 3. It is desirable that the metal film cover not only the lower surface 3a of the electrode 3 but also the lower surface of the covering member 5 surrounding the lower surface 3a. In other words, it is desirable that the area of ​​the lower surface of the metal film be larger than the area of ​​the exposed lower surface 3a of the electrode 3. This improves the electrical connection between the light-emitting device 1 and the wiring board. Furthermore, if the electrode 3 contains Cu and the Cu is exposed, oxidation of the Cu may cause mounting defects when mounting to the wiring board. However, this risk is avoided because the electrode 3 is covered with a metal film that is less susceptible to oxidation than Cu. As such a metal film, one in which Ni, Ru, and Au are layered sequentially from the electrode 3 side can be used. If the outermost surface is Au, it is less susceptible to oxidation than Cu, thus suppressing oxidation of the metal film. Also, by using Ni as the metal that bonds with the electrode 3 in the metal film, the adhesion between the electrode 3 and the metal film can be improved. The metal film can be formed, for example, as follows: A metal film is sputtered onto the lower surface 3a of the electrode 3 and the lower surface of the covering member, and the metal film is removed by laser ablation so that the pair of electrodes 3 are electrically separated.

[0059] Examples and Reference Examples Examples and reference examples are described below. In Reference Example 1, Reference Example 2, and Examples 1 to 9, a coated member was fabricated, and the shrinkage retention rate was measured after heating the coated member at 1000°C for 1 hour. The amount of alkaline solution added was adjusted as appropriate to achieve a viscosity suitable for molding.

[0060] The covering member 5 of Reference Example 1 was manufactured as follows. First, a mixed powder was prepared by mixing powder of light-reflecting material 11, which has an average particle size of 1 μm and an average aspect ratio of 4.6, with silica powder, which has an average particle size of 0.4 μm in median diameter. The powder of light-reflecting material 11 was boron nitride powder. The silica powder and boron nitride powder were mixed in a weight ratio of 4:5. A mixture was prepared by mixing the powder with an alkaline solution with a concentration of 3 mol / L. The alkaline solution was potassium hydroxide solution. The alkaline solution and the powder were mixed in a weight ratio of 5.8:9. Next, the mixture 50 was heated at a first temperature of 90°C and under a pressure of 1 MPa for 1 hour to partially cure it. Next, the mixture 50 was heated at a second temperature of 200°C and a pressure of 1 MPa for 2 hours to cure it completely, thereby producing the coating member 5.

[0061] In Reference Example 2 and Examples 1 to 9, the coating member 5 was manufactured by changing the material of the light reflector, the average particle size of the light reflector, the aspect ratio of the light reflector, and the weight ratio of silica powder to the light reflector as shown in Table 1. Except for the conditions described in Table 1, it was manufactured using the same method as in Reference Example 1.

[0062] The covering material 5 from Reference Example 1, Reference Example 2, and Examples 1 to 9 was divided into two from a plate-like shape with a diameter of approximately 3 cm and a thickness of approximately 1 mm. One of the two divided covering materials was heated at 1000°C for 1 hour. Subsequently, the ratio of the length of one side of the divided cross-section of the heated covering material to the length of one side of the divided cross-section of the unheated covering material (shrinkage retention rate) was calculated. The results are shown in Table 1.

[0063] [Table 1]

[0064] Based on the results from Reference Example 1, Reference Example 2, and Examples 1 to 9, the shrinkage retention rate of Examples 1 to 9 was 99.00% or higher, which was greater than that of Reference Example 1 and Reference Example 2. Therefore, it was revealed that the coating members 5 of Examples 1 to 9, which include silica, alkali metals, and a light-reflecting material with an average particle size of 0.6 μm to 43 μm and an aspect ratio of 10 or higher, have high heat resistance.

[0065] In Examples 10 to 13, light-emitting devices equipped with a coating member 5 were fabricated, and their luminous flux, light-emitting surface brightness, visibility, and reliability were evaluated. In Example 10, the cross-section of the coating member 5 applied to the light-emitting element 4 was observed when pressed. In Example 11, the cross-section of the fabricated light-emitting device was observed using a scanning electron microscope (SEM).

[0066] Example 10 The light-emitting device of Example 10 was fabricated as follows. A light-emitting element (LED) was formed by bonding a plate-shaped translucent member 6 containing YAG to an adhesive sheet, with the translucent member 6 facing the adhesive sheet. The LED 4 had a rectangular shape of 1 mm × 1 mm when viewed from above, and a peak wavelength of 450 nm to 455 nm. The LEDs 4 were arranged on the adhesive sheet at a pitch of 1.8 mm in both the X and Y directions (width and depth). A heat-resistant sheet with polyimide as the base material was used as the adhesive sheet, but any adhesive sheet with heat resistance above the pre-curing temperature may be used. The translucent member 6 had a rectangular shape of 1.1 mm × 1.1 mm when viewed from above, and a thickness of 180 μm. The thickness of the LED 4 was 200 μm. The electrode 3 of the LED 4 contained Cu with a height of approximately 50 μm. A mixed powder was prepared by mixing boron nitride with an average particle size of 10 μm and an average aspect ratio of approximately 17 with silica with an average particle size of 0.4 μm in a weight ratio of 1:1. Then, 3.4 g of a 3 mol / L potassium hydroxide solution was added to 10 g of the prepared mixed powder, and after mixing with a stirring rod, the mixture was defoamed and stirred using a stirring and defoaming machine that can stir under reduced pressure to obtain a white, uniform, viscous mixture 50. The resulting mixture 50 was applied to cover the light-emitting element 4 and the light-transmitting member 6. Then, the mixture 50 was pressed using a glass plate to form a flat shape with a thickness of approximately 1 mm. Figure 9 shows a cross-section that passes through the center of the upper surface 6a of the translucent member 6 and is substantially perpendicular to the upper surface 6a. As shown in Figure 9, the light-reflecting material 11 located near the light-emitting element 4 and the translucent member 6 among the light-reflecting material 11 contained in the mixture 50 tends to be positioned at an angle of 0° to 45° from the sides of the light-emitting element 4 and the translucent member 6, with the longitudinal direction of the light-reflecting material 11 being. This positioning tendency is thought to have been achieved by increasing the aspect ratio of the plate-shaped light-reflecting material 11 and slowing down the flow velocity of the mixture 50 flowing near the light-emitting element 4 and the translucent member 6 when the mixture 50 is applied to the light-emitting element 4. Next, the mixture 50 was heated to cure it and obtain a light-reflective coating member 5. For the curing conditions, preliminary curing was performed for 60 minutes in a pressurized nitrogen atmosphere at 1 MPa using a pressure oven. After peeling off the sheet, final curing was performed again in a pressurized nitrogen atmosphere at 1 MPa using the pressure oven for 40 minutes. The temperature during final curing was 200°C. Next, the covering member 5 was ground down to expose the electrode 3. Finally, the material was fragmented using a 100 μm thick blade. After fragmentation, a light-emitting device was obtained that emitted white light, with a top-view shape of 1.7 mm × 1.7 mm rectangle and a thickness of approximately 0.4 mm.

[0067] Example 11 The light-emitting device of Example 11 was fabricated as follows. A light-emitting device was obtained in the same manner as in Example 10, except that 4 g of a 3 mol / L potassium hydroxide solution was added to 13 g of a powder material prepared by mixing boron nitride with an average particle size of 10 μm and an average aspect ratio of about 17, silica with an average particle size of 0.4 μm, and titania with an average particle size of 0.25 μm in a weight ratio of 5:5:3. The cross-section of this light-emitting device was observed using a scanning electron microscope (SEM). Figure 10 shows a portion of the covering member 5 in a cross-section that passes through the center of the upper surface 6a of the translucent member 6 and is substantially perpendicular to the upper surface 6a. From Figure 10, it is clear that voids 13 exist in the covering member 5, and that a portion of the voids 13 is in contact with the light-reflecting material 11. By creating voids 13 locally in this way, it is possible to suppress shrinkage when the covering member 5 is heat-cured. Furthermore, by adding titania as a scattering material 14, the light-emitting device according to this embodiment achieved improved reflectivity and light-shielding properties compared to one without titania.

[0068] Example 12 The light-emitting device of Example 12 was fabricated as follows. A light-emitting device was obtained in the same manner as in Example 10, except that 4.8 g of a 3 mol / L potassium hydroxide solution was added to 14 g of a powder material prepared by mixing boron nitride with an average particle size of 10 μm and an average aspect ratio of about 17, silica with an average particle size of 0.4 μm, and zirconia in a weight ratio of 5:5:4. The light-emitting device according to this embodiment achieved improved reflectivity and light-shielding properties compared to one without zirconia by adding zirconia as a scattering material. In particular, zirconia has low absorption and good reflection properties in the wavelength range of 250 nm to 420 nm, which is the wavelength range of light-emitting devices that emit ultraviolet light, thus improving the characteristics of the light-emitting device that emits ultraviolet light.

[0069] The luminous flux, luminous surface brightness, visibility, and reliability of the light-emitting devices of Examples 10 to 12, which were fabricated as described above, were compared and evaluated. <Luminous flux> The luminous flux of each light-emitting device in Examples 10 to 12 was evaluated using an integrating sphere. The luminous flux of the light-emitting device in Example 10 was 161 [lm]. The luminous flux of the light-emitting device in Example 11 was 162 [lm]. The luminous flux of the light-emitting device in Example 12 was 162 [lm]. The forward current supplied to the light-emitting devices in Examples 10 to 12 was 350 [mA].

[0070] <Brightness of the luminous surface> When using a light-emitting device in combination with an optical system such as a lens, the brightness of a specific light-emitting area (in this disclosure, the light-emitting surface of the translucent member) is important. For the light-emitting devices of Examples 10 to 12, the brightness of the light-emitting surface (exposed surface) of the translucent member 6 was evaluated using a 2D colorimeter manufactured by Radiant Vision Systems. The brightness of the light-emitting device of Example 10 was 33.7 [cd / cm²]. 2 The luminance of the light-emitting device in Example 11 was 37.3 [cd / cm²]. 2 The luminance of the light-emitting device in Example 12 was 35.8 [cd / cm²]. 2 The forward current supplied to the light-emitting devices of Examples 10 to 12 was 350 [mA].

[0071] <Easy to decide when to cut your losses> In car headlights and the like, safety standards apply to light components that leak outside the light-emitting area, so a reduction in light components outside the light-emitting area (visibility) is required. When the brightness of the light leaking from the translucent member covering member was divided by the average brightness of the light emitted from the translucent member 6 as an indicator of visibility, values ​​of 7.2% were obtained in Example 10, 2.2% in Example 11, and 3.6% in Example 12. Note that the light leaking from the covering member is the light measured at a point 125 μm away from the boundary between the translucent member and the covering member in a top view.

[0072] <Vitality> A life test was conducted for 1000 hours by applying a current of 1.5A to the light-emitting devices of Examples 11 and 12 in a high-temperature environment of 85°C. The junction temperature during operation was approximately 175°C. The "junction temperature" refers to the temperature of the active layer, which is the region of the light-emitting device that emits light. When a current of 700mA was applied, the output maintenance rate after 1000 hours was 102% of the initial value for the light-emitting device in Example 11, and 101% for the light-emitting device in Example 12. Furthermore, no cracks were observed or propagated during testing for the light-emitting devices of Example 11 and Example 12.

[0073] Example 13 The light-emitting device of Example 13 was fabricated as follows. On an adhesive polyimide sheet, light-emitting elements 4, each having a peak wavelength of 280 nm and a rectangular shape of 1 mm × 1 mm when viewed from above, were arranged at a pitch of 2.2 mm with the sapphire substrate side facing the sheet side. The thickness of the light-emitting elements 4 is 700 μm. The electrodes 3 of the light-emitting elements 4 include Au bumps with a height of approximately 30 μm. To 10 g of a mixed powder consisting of boron nitride with an average particle size of 10.5 μm and an average aspect ratio of 16.5, and silica with an average particle size of 0.4 μm, in a weight ratio of 1:1, 3 g of a 3 mol / L potassium hydroxide solution was added and mixed in a container. Subsequently, the mixture was further kneaded using a vacuum stirring and degassing machine to obtain mixture 50. The resulting mixture 50 was applied to cover the light-emitting element 4 and the light-transmitting member 6. Then, the mixture 50 was pressed using a glass plate and molded into a flat shape with a thickness of approximately 2 mm. Next, a preliminary curing was performed in an oven in air for 60 minutes. The temperature during the preliminary curing was 95°C. After that, the polyimide adhesive sheet that held the light-emitting element 4 was peeled off. After peeling off the sheet, the final curing was performed in a pressurized oven in a 1 MPa N2 atmosphere for 40 minutes. The temperature during the final curing was 200°C. Next, the covering member 5 was ground down to expose the electrode 3. Finally, the material was fragmented using a 100 μm thick blade. After fragmentation, a light-emitting device was obtained that emitted ultraviolet light with a top-view shape of 2.1 mm × 2.1 mm and a thickness of approximately 720 μm.

[0074] <Vitality> Reliability tests were conducted on the light-emitting device fabricated as described above. A 1000-hour life test was conducted under room temperature conditions of 25°C with a current of 500mA applied. The junction temperature during operation was approximately 100°C. When a current of 350mA was applied, the output retention rate after 1000 hours was 92% of the initial value. No deterioration such as discoloration or cracks was observed in the appearance after the test.

[0075] While embodiments, modifications, examples, and reference examples of this disclosure have been described above, the disclosure may be modified in detail, and changes in the combinations and order of elements in the embodiments, modifications, examples, and reference examples can be realized without departing from the claimed scope and spirit of this disclosure. [Explanation of symbols]

[0076] 1,100 Light-emitting device 1a, 100a Light emission surface 2 Semiconductor laminate 3 Electrode 3a Lower surface 4 Light-emitting element 4a Top surface 5 Covering members 6, 106 Light-transmitting members 6a, 106a Top surface 7 Growth substrate 106b Side 11 Light reflective material 11a, 11b Main surface 12 Support member 13 Void 14 Scattering material 20 Mounting substrate 50 Mixture 60 Translucent sheet 90 Groove

Claims

1. Light-emitting element and The device comprises a light-reflecting material made of boron nitride or alumina, silica, and an alkali metal, and a light-reflecting covering member that covers the side surface of the light-emitting element, The covering member includes a plurality of voids, In the coating member, the density of the light-reflecting material is higher in the region near the light-emitting element, and the light-reflecting material located in the region near the element has an aspect ratio of 10 or more and is arranged at an angle of 0° to 45° with respect to the surface of the light-emitting element, in a light-emitting device.

2. Implemented circuit board and A light-emitting element arranged on the aforementioned mounting substrate, The device comprises a light-reflective coating member that covers the mounting substrate and contains a light-reflective material made of boron nitride or alumina, silica, and alkali metals, The covering member includes a plurality of voids, In the coating member, the density of the light-reflecting material is higher in the region near the light-emitting element, and the light-reflecting material located in the region near the element has an aspect ratio of 10 or more and is arranged at an angle of 0° to 45° with respect to the surface of the light-emitting element, in a light-emitting device.

3. The light-emitting device according to claim 1 or 2, wherein the covering member is a reflective wall surrounding the light-emitting element.

4. A portion of the void is in contact with the light-reflecting material, as described in any one of claims 1 to 3.

5. The light-emitting device according to claim 4, wherein the portion of the void is located between adjacent light-reflecting materials.

6. The light-emitting device according to any one of claims 1 to 5, wherein the light-reflecting material is in the form of a plate.

7. The light-emitting device according to any one of claims 1 to 6, wherein the covering member includes a scattering material.

8. The light-emitting device according to any one of claims 1 to 7, wherein the covering member is made of an inorganic material.

Images