LIGHT-EMITTING DEVICE AND MANUFACTURING METHOD OF LIGHT-EMITTING DEVICE

A light-emitting device includes a package having a recessed portion, a light-emitting element placed on a bottom surface of the recessed portion at a position away from an inner lateral surface of the recessed portion, and a light-reflective member disposed between the light-emitting element and the inner lateral surface so as to surround the light-emitting element at a position away from the light-emitting element and having a light reflecting surface configured to reflect light emitted from the light-emitting element. The light reflecting surface is inclined with respect to the bottom surface in a direction from the inner lateral surface toward the light-emitting element, and has different light reflection characteristics at different positions with different heights from the bottom surface to the light reflecting surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2023-044913, filed on Mar. 22, 2023, the disclosure of which is hereby incorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to a light-emitting device and a manufacturing method of a light-emitting device.

In the related art, in order to improve efficiency of extracting light emitted from a light-emitting element included in a light-emitting device, a light-reflective member is used to reflect light emitted from the light-emitting element. For example, Japanese Unexamined Patent Application Publication No. 2008-098247 discloses a light-emitting device including a tapered light reflecting board for reflecting upwardly light emitted laterally from a light-emitting element.

SUMMARY

The light reflecting board disclosed in the Japanese Unexamined Patent Application Publication No. 2008-098247 has a reflection film made of a metal film formed by, for example, sputtering, vapor deposition, plating, or the like. However, the reflection film made of the metal film has uniform light reflection characteristics, and when light emitted from the light-emitting element is reflected by such a reflection film, luminance spots may occur.

There is a need to provide a light-emitting device that can reduce luminance spots of emitted light.

A light-emitting device according to an embodiment includes a package including a recessed portion, a light-emitting element placed on a bottom surface of the recessed portion at a position away from an inner lateral surface of the recessed portion, and a light-reflective member disposed between the light-emitting element and the inner lateral surface so as to surround the light-emitting element at a position away from the light-emitting element and including a light reflecting surface configured to reflect light emitted from the light-emitting element, wherein the light reflecting surface is inclined with respect to the bottom surface in a direction from the inner lateral surface toward the light-emitting element, and has different light reflection characteristics at different positions with different heights from the bottom surface to the light reflecting surface.

A method of manufacturing a light-emitting device according to an embodiment includes preparing a package including a recessed portion including an inner lateral surface and a bottom surface having a placement region on which a light-emitting element is placeable; mixing at least first particles comprising a light reflecting material and second particles having a smaller average particle diameter than the first particles, a lower average aspect ratio than the first particles, and a lower total reflectance than the first particles to prepare a mixture having thixotropy; applying the mixture to at least one of the bottom surface or the inner lateral surface; and curing the mixture to form a light-reflective member including a light reflecting surface inclined with respect to the bottom surface in a direction from the inner lateral surface toward the placement region so as not to reach the placement region.

In accordance with the light-emitting device according to the embodiment, the light reflecting surface that reflects light emitted from the light-emitting element is inclined in a direction from the inner lateral surface of the recessed portion toward the light-emitting element, and the light reflection characteristics of the light reflecting surface vary depending on a height from the bottom surface of the recessed portion to the light reflecting surface. Consequently, since the light reflecting surface has no uniform light reflection characteristics like a metal film, for example, and has different light reflection characteristics depending on the height from the bottom surface of the recessed portion to the light reflecting surface, so that luminance spots of light emitted from the light-emitting device can be reduced.

DETAILED DESCRIPTION

An embodiment of the present invention is described below with reference to the drawings. Note that a light-emitting device1and a manufacturing method of the light-emitting device1according to the present embodiment are intended to embody the technical concepts of the present invention, and the present invention is not limited to the following unless specifically stated. The sizes and positional relationships of members illustrated in the drawings may be appropriately exaggerated, or some of the members may be simplified or omitted.

In the present embodiment, XYZ orthogonal coordinates are employed for convenience of explanation. Specifically, a thickness direction of a light-emitting element3(details are described below) included in the light-emitting device1is referred to as a “Z axis”, and two directions respectively orthogonal to the thickness direction are referred to as an “X axis” and a “Y axis”. In the Z-axis, a direction on a side where light from the light-emitting device1mainly travels is referred to as “up”, and an opposite direction thereof is referred to as “down”. However, the expression of “up” and “down” is for convenience and is independent of the direction of gravity. An expression “in plan view” used in the present specification is assumed to indicate a case when viewed from above on the Z axis to below.

FIG.1is a schematic perspective view illustrating an example of the light-emitting device1according to an embodiment.FIG.2is a schematic plan view illustrating an example of the light-emitting device1according to an embodiment.FIG.3is a schematic cross-sectional view taken along line III-III illustrated inFIG.2.

The light-emitting device1according to the present embodiment includes a package2having a recessed portion22on an upper surface210side, the light-emitting element3placed on a bottom surface220of the recessed portion22at a position away from an inner lateral surface221of the recessed portion22, a protective element4placed on the bottom surface220of the recessed portion22at a position away from the light-emitting element3and the inner lateral surface221of the recessed portion22, a light-reflective member5disposed between the light-emitting element3and the inner lateral surface221of the recessed portion22so as to surround the light-emitting element3at a position away from the light-emitting element3and having a light reflecting surface53for reflecting light emitted from the light-emitting element3, and a cap6bonded to the upper surface210of the package2so as to close the recessed portion22.

The package2includes a base portion20having a flat plate shape and a lateral wall portion21disposed on the base portion20. The recessed portion22of the package2is formed by the base portion20and the lateral wall portion21.

The base portion20and the lateral wall portion21mainly comprise or are mainly formed of an insulating base material. Examples of the material of the insulating base material include ceramics, glass epoxy, and resin. Examples of the ceramics include alumina, aluminum nitride, and mullite. The base portion20and the lateral wall portion21may be integrated with each other or may be separated from each other.

The lateral wall portion21has a rectangular frame shape in plan view. Note that the lateral wall portion21may have no rectangular frame shape in plan view. The recessed portion22has the bottom surface220and the inner lateral surface221. The bottom surface220of the recessed portion22corresponds to a portion of an upper surface of the base portion20surrounded by the upper surface210of the lateral wall portion21in plan view. The bottom surface220of the recessed portion22has a placement region220aon which the light-emitting element3can be placed. The inner lateral surface221of the recessed portion22corresponds to an inner surface of the lateral wall portion21. Note that the recessed portion22may have a step. Furthermore, the bottom surface220and the inner lateral surface221of the recessed portion22may be covered with a protective film for preventing deterioration.

The package2includes positive and negative first wirings23on the bottom surface220of the recessed portion22(the upper surface of the base portion20) and positive and negative second wirings24on a lower surface200of the base portion20. The first wiring23and the second wiring24are connected to each other by, for example, an internal wiring penetrating the base portion20. Each of the positive and negative first wirings23is disposed in a range including the placement region220a, and the light-emitting element3is bonded thereto. The second wiring24is bonded to a pad of a mounting substrate when the light-emitting device1is surface-mounted. The first wiring23and the second wiring24are formed using, for example, a metal such as copper, aluminum, gold, silver or the like.

The dimensions of each part of the package2are appropriately determined in accordance with, for example, the dimensions and the like of the light-emitting element3. The length of each side of the package2in plan view is, for example, in a range from 0.3 mm to 10 mm. The height of the package2is, for example, in a range from 0.1 mm to 4 mm. The depth (height Hd inFIG.4) of the recessed portion22is, for example, in a range from 0.075 mm to 3 mm.

The light-emitting element3is an element that emits light having a predetermined wavelength. The light-emitting element3emits ultraviolet light or blue light, for example. The light-emitting element3mainly emits light from an upper surface thereof, but also emits light from a lateral surface thereof (may be a part thereof). The light-emitting element3may also emit light from a lower surface thereof (may be a part thereof). In the present embodiment, the light-emitting device1is described as a light-emitting device including one light-emitting element3, but may include a plurality of light-emitting elements3.

Examples of the light-emitting element3that can be used include a light-emitting diode and a laser diode. The light-emitting element3includes at least a semiconductor layer including an n-type semiconductor layer, a p-type semiconductor layer, a light-emitting device layer, and the like, and positive and negative electrodes. The light-emitting element3preferably uses a nitride semiconductor layer containing, for example, InXAlYGa1−X−YN (0≤X, 0≤Y, X+Y≤1).

The emission peak wavelength of light emitted by the light-emitting element3is in a range from 260 nm to 630 nm, for example; however, no such limitation is intended. The emission peak wavelength of the light-emitting element3that emits ultraviolet light may be, for example, in an ultraviolet region from or below 400 nm or in a deep ultraviolet region from or below 280 nm. By using the light-emitting element3that emits ultraviolet light, for example, the light-emitting device1can be used as a light source for sterilization, disinfection, or the like.

The light-emitting element3is placed on the bottom surface220of the recessed portion22(upper surface of the base portion20) at a position away from the inner lateral surface221of the recessed portion22. In the present embodiment, the light-emitting element3is placed on the placement region220aof the bottom surface220. The placement region220ais provided at the center of the bottom surface220. The placement region220aincludes the center of the bottom surface220. The light-emitting element3is flip-chip mounted on the package2. Specifically, the light-emitting element3includes the positive and negative electrodes (not illustrated) on the same surface side, and the positive and negative electrodes are electrically connected to the positive and negative first wirings23by conductive members, respectively. Examples of the conductive member that can be used include a conductive paste containing solder, copper, gold, palladium, or the like, and a bump containing silver, gold, or the like.

Note that, instead of the above flip-chip mounting, the light-emitting element3may be face-up mounted on the package2and the positive and negative electrodes may be connected to the positive and negative first wirings23by wires, respectively. The light-emitting element3may have one of the positive and negative electrodes on the upper surface thereof and the other electrode on the lower surface thereof. In such a case, the electrode on the upper surface may be connected to one of the positive and negative first wirings23by a conductive member, and the electrode on the lower surface may be connected to the other first wiring23by a wire.

The light-emitting element3is rectangular in plan view. The length of each side of the light-emitting element3in plan view is, for example, in a range from 100 μm to 3000 μm. The thickness (height He inFIG.4) of the light-emitting element3is, for example, in a range from 50 μm to 2000 μm. Note that the shape of the light-emitting element3in plan view may be, for example, a polygon such as a triangle or a hexagon; however, no such limitation is intended.

The protective element4is an element for protecting the light-emitting element3from a surge voltage or static electricity. Examples of the protective element4that can be used include a Zener diode. The protective element4is electrically connected in parallel with the light-emitting element3, for example. In the present embodiment, the light-emitting device1is described as including one protective element4, but may include a plurality of light-emitting elements3or may not include the protective element4.

The protective element4is placed on the bottom surface220of the recessed portion22(upper surface of the base portion20) at a position away from the light-emitting element3and the inner lateral surface221of the recessed portion22. In the present embodiment, the lower surface of the protective element4is connected to one of the positive and negative first wirings23by a conductive member, and the upper surface of the protective element4is connected to the other first wiring23by a wire40.

FIG.4is a cross-sectional view schematically illustrating an example of the light-reflective member5.FIG.5is an enlarged view schematically illustrating a portion V inFIG.4.FIG.6is an enlarged view schematically illustrating a portion VI inFIG.4.

The light-reflective member5is a member having light reflectivity that reflects light emitted from the light-emitting element3. The light-reflective member5is disposed between the light-emitting element3and the inner lateral surface221of the recessed portion22so as to surround the light-emitting element3at a position away from the light-emitting element3. At this time, the light-reflective member5is formed in contact with the bottom surface220and the inner lateral surface221of the concave portion22. The light-reflective member5is formed in a frame shape along the inner lateral surface221of the recessed portion22(inner surface of the lateral wall portion21) in plan view. Note that as illustrated inFIG.2, the light-reflective member5may cover a part of the protective element4or may cover the entire protective element4. The light-reflective member5may not cover the protective element4.

The light-reflective member5includes an inner peripheral edge portion50formed on a side close to the light-emitting element3, an outer peripheral edge portion51formed on a side close to the inner lateral surface221of the recessed portion22, and an intermediate portion52located between the inner peripheral edge portion50and the outer peripheral edge portion51. The light-reflective member5includes the light reflecting surface53that is an outer surface of the light-reflective member5. The light reflecting surface53is provided over the inner peripheral edge portion50, the intermediate portion52, and the outer peripheral edge portion51. Note that the intermediate portion52may be located between the inner peripheral edge portion50and the outer peripheral edge portion51, does not necessarily need to be located at the center between the inner peripheral edge portion50and the outer peripheral edge portion51, and may be specified at an approximate position. The inner peripheral edge portion50and the outer peripheral edge portion51do not necessarily need to be located on peripheral edges, and may be specified at approximate positions. Moreover, the inner peripheral edge portion50, the intermediate portion52, and the outer peripheral edge portion51may be defined as regions each having a predetermined width. In such a case, the inner peripheral edge portion50, the intermediate portion52, and the outer peripheral edge portion51may be separated from one another with a gap or may be separated with no gap.

The light reflecting surface53reflects upwardly light emitted from the light-emitting element3. The reflectance of the light reflecting surface53is preferably 60% or more, more, preferably 85% or more, with respect to the emission peak wavelength of the light-emitting element3.

The light reflecting surface53is inclined with respect to the bottom surface220of the recessed portion22in a direction from the inner lateral surface221of the recessed portion22toward the light-emitting element3. In a case in which a height from the bottom surface220to the light reflecting surface53is defined as a height H of the light reflecting surface53, when a height of the light reflecting surface53in the inner peripheral edge portion50is defined as H0, a height of the light reflecting surface53in the outer peripheral edge portion51is defined as H1, and a height of the light reflecting surface53in the intermediate portion52is defined as H2, a relationship of H0<H2<H1 is satisfied. As a distance from the light-emitting element3to the light reflecting surface53(distance in a left-right direction inFIGS.3and4) increases, the height H of the light reflecting surface53increases. That is, the height H of the light reflecting surface53increases from the inner peripheral edge portion50toward the intermediate portion52, and from the intermediate portion52toward the outer peripheral edge portion51. It can be said that the height H of the light reflecting surface53is also the thickness of the light-reflective member5, but in such a case, the thickness of the light-reflective member5increases in the order of the inner peripheral edge portion50, the intermediate portion52, and the outer peripheral edge portion51.

A distance WO from the inner lateral surface221to a distal end of the inner peripheral edge portion50is shorter than a distance Wd from this inner lateral surface221to the light-emitting element3. The bottom surface220has a portion not in contact with the light-reflective member5in a region located around the light-emitting element3, and a gap (distance Wg) exists between the light-emitting element3and the light-reflective member5. The height H of the light reflecting surface53is maximum at an upper end of the outer peripheral edge portion51, but a maximum height Ht of the light reflecting surface53is lower than the height Hd of the recessed portion22. Therefore, the inner lateral surface221located on the upper surface210side has a portion not in contact with the light-reflective member5, and a gap (distance Hg) exists between the upper surface210and an outer edge of the light-reflective member5in contact with the inner lateral surface221. The distance Hg can exceed 0 and be equal to or less than ½ of the height Hd. AlthoughFIG.4illustrates a case in which the maximum height Ht of the light reflecting surface53is higher than the height He of the light-emitting element3, the maximum height Ht may be lower than the height He of the light-emitting element3.

Note that when the inner peripheral edge portion50, the intermediate portion52, and the outer peripheral edge portion51are defined as regions each having a predetermined width, the maximum height and the minimum height of the light reflecting surface53are defined in each of the regions, and the maximum height and the minimum height are determined by the following values. The maximum height H0 of the inner peripheral edge portion50is equal to or less than ¼ of the maximum height Ht of the light reflecting surface53. The minimum height H1 of the outer peripheral edge portion51is equal to or greater than ⅔ of the maximum height Ht of the light reflecting surface53. The minimum height H2 of the intermediate portion52is greater than ¼ of the maximum height Ht of the light reflecting surface53, and the maximum height H2 of the intermediate portion52is less than ⅔ of the maximum height Ht of the light reflecting surface53. At this time, the region of the intermediate portion52may be defined so that the minimum height H2 of the intermediate portion52is equal to or greater than ⅓ of the maximum height Ht of the light reflecting surface53and the maximum height H2 of the intermediate portion52is equal to or less than ⅗ of the maximum height Ht of the light reflecting surface53.

As illustrated inFIGS.3and4, the light reflecting surface53is formed in a curved shape in cross-sectional view. In the present embodiment, the light reflecting surface53is described as being formed in a concave shape with respect to the bottom surface220of the recessed portion22, but may be formed in a convex shape with respect to the bottom surface220of the recessed portion22. The curvatures of the concave shape and the convex shape may not be constant, or may be a combination of the concave shape and the convex shape. Accordingly, a position where the height H of the light-reflective member5is maximum is not necessarily a position in contact with the inner lateral surface221.

Modified Example of Light-Reflective Member5

As a modified example of the light-reflective member5, the light-reflective member5may be formed in an asymmetrical shape.FIG.7is a schematic plan view illustrating an example of the light-emitting device1according to a modified example.FIG.8is a schematic cross-sectional view taken along line VIII-VIII illustrated inFIG.7.FIGS.7and8correspond toFIGS.2and3, respectively, and are different in that the shape of the light-reflective member5is different, but the other configurations of the light-emitting device1are in common.

As illustrated inFIG.7, the light-reflective member5according to the modified example can have an asymmetrical shape in plan view. As illustrated inFIG.8, the light-reflective member5may have an asymmetrical shape in cross-sectional view. The asymmetrical shape has unevenness on the outer surface or the outer contour line thereof, and includes, for example, a distorted shape, which is not defined by a straight line or a curve having a constant curvature, in at least a part thereof. Therefore, the light-reflective member5is formed in a shape at least partially including a shape not defined by line symmetry or point symmetry in plan view or cross-sectional view as an asymmetrical shape. For example, although the inner peripheral edge portion50is formed to be separated from the light-emitting element3and to surround the periphery of the light-emitting element3in plan view, the shape of the inner edge surrounding the light-emitting element3in plan view may not be a rectangular shape such as a rectangle or a square. Although the outer peripheral edge portion51is formed along the inner lateral surface221, the distance Hg may not be constant. The distance from the light reflecting surface53to the light-emitting element3at the same height may not be constant over the entire circumference surrounding the light-emitting element3.

Light Reflection Characteristics of Light-Reflective Member

The light reflecting surface53has different light reflection characteristics at positions where the height H (seeFIG.4) from the bottom surface220of the recessed portion22to the light reflecting surface53is different. The light reflection characteristics of the light reflecting surface53change from a position close to the light-emitting element3toward a position far from the light-emitting element3in a planar direction (for example, X direction or Y direction). The light reflection characteristics of the light reflecting surface53substantially continuously change as a whole. The “substantially” used herein means that the presence of a partial small region where the light reflection characteristics do not change is allowed when viewed locally.

The light reflection characteristics of the light reflecting surface53in the inner peripheral edge portion50are different from the light reflection characteristics of the light reflecting surface53in the intermediate portion52. The light reflection characteristics used herein include at least one of reflectance of light or a degree of diffusion of light (also referred to as a degree of light scattering). The light reflection characteristics used herein may also be defined as characteristics including at least the reflectance of light and the degree of diffusion of light. The reflectance of light reflected by the light reflecting surface53is higher in the inner peripheral edge portion50than in the intermediate portion52. Light emitted from the light-emitting element3is diffused and reflected by the light reflecting surface53. The intermediate portion52diffuses light at the light reflecting surface53more than the inner peripheral edge portion50. That is, it can be said that the degree of diffusion of light by the light reflecting surface53is higher in the intermediate portion52than in the inner peripheral edge portion50. The surface roughness of the light reflecting surface53is greater in the intermediate portion52than in the inner peripheral edge portion50.

As an example of a material for implementing the above light reflection characteristics, the light-reflective member5may comprise or be formed of a material including at least first particles54made of a light reflecting material and second particles55having a lower reflectance than the first particles54. The second particles are particles having a smaller average particle diameter and a lower average aspect ratio than the first particles54. In the present embodiment, a case in which an inorganic material is used as the material of the light-reflective member5is mainly described, but an organic material may be used.

When the light-emitting element3that emits ultraviolet light is used, the light-reflective member5preferably comprises or is formed of an inorganic material. In this case, the light-reflective member5may further contain an alkali metal, a scattering material, or a composition other than these materials, in addition to the first particles54and the second particles55.

As illustrated inFIGS.5and6, the first particle54is a scale-like or plate-like particle having two opposing main surfaces540and541. Note that the first particle54may be a primary particle, or a secondary particle obtained by aggregating a plurality of primary particles. The first particle54may also be a mixture of the primary particle and the secondary particle.

The first particles54comprise or are composed of, for example, at least one of boron nitride or alumina. Note that the first particles54may use another material as long as the material reflects light having the emission peak wavelength of the light-emitting element3.

The average particle diameter of the first particles54is in a range from 0.6 μm to 43 μm, for example. The average aspect ratio of the first particles54is, for example, 10 or more, preferably in a range from 10 to 70. A method for calculating the average particle diameter and the average aspect ratio is described below.

The second particles55are particles having a smaller average particle diameter, a lower average aspect ratio, and a lower reflectance than the first particles54.

The second particles55comprise or are composed of, for example, silica.

The average particle diameter of the second particles55is in a range from 0.1 μm to 10 μm, for example. For example, the average aspect ratio of the second particles55is in a range from 1 to 5, preferably in a range from 1 to 2. A method for calculating the average particle diameter and the average aspect ratio is described below.

An area or the number of particles per unit area occupied by the second particles55in the light reflecting surface53is smaller in the inner peripheral edge portion50(seeFIG.5) than in the intermediate portion52(seeFIG.6). This is because the first particles54have a larger average particle diameter and a higher average aspect ratio than the second particles55.

In the inner peripheral edge portion50where the thickness of the light-reflective member5(height H of the light reflecting surface53) is relatively small, as illustrated inFIG.5, the first particles54tend to be arranged in a lying state so that the main surfaces540and541of the first particles54follow the bottom surface220. This results in an increase in an area where the main surfaces540and541of the first particle54are exposed as the light reflecting surface53. As a result, since a gap between the first particles54into which the second particles55enter is reduced, the area or the number of the second particles55filling the gap is relatively reduced.

On the other hand, in the intermediate portion52where the thickness of the light-reflective member5is larger than in the inner peripheral edge portion50, as illustrated inFIG.6, the first particles54are randomly arranged in an arbitrary direction, and variations in an angle formed by the main surfaces540and541of the first particles54and the light reflecting surface53are greater than in the inner peripheral edge portion50. Therefore, compared to the inner peripheral edge portion50, the area of the first particles54where the main surfaces540and541are exposed as the light reflecting surface53is smaller. As a result, since the gap between the first particles54into which the second particles55enter is increased, the area or the number of the second particles55filling the gap is relatively increased.

Since the first particles54have a higher reflectance than the second particles55, it can be said that the reflectance of the light reflecting surface53per unit area is higher when the area where the first particles54are exposed is larger and the area where the second particles55are exposed is smaller as illustrated inFIG.5than when the area where the first particles54are exposed is smaller and the area where the second particles55are exposed is larger as illustrated inFIG.6. Furthermore, since the smoothness of the light reflecting surface53is higher and the surface roughness is smaller when the main surfaces540and541of the scale-like or plate-like first particles54are exposed as illustrated inFIG.5than when the distal end of the scale-like or plate-like first particles54are exposed as illustrated inFIG.6, it can be said that the degree of scattering is lower. Moreover, as illustrated inFIGS.5and6, in the light reflecting surface53per unit area, since the number of the first particles54and the number of the first particles54each exposed are different, the difference in the number of the particles may also affect the smoothness and the surface roughness of the light reflecting surface53.

The alkali metal is at least one of potassium or sodium. The alkali metal is a metal contained in an alkali solution used in a step of forming the light-reflective member5. The alkali solution is a solution in which the alkali metal is dissolved in a solvent. For example, water can be used as the solvent. The alkali solution in such a case is a potassium hydroxide solution or a sodium hydroxide solution, for example.

The scattering material is, for example, at least one of zirconia or titania. The scattering material preferably has a smaller average particle diameter and a lower average aspect ratio than the first particles54. When the light-emitting element3that emits ultraviolet light is used, zirconia that absorbs less light in the ultraviolet wavelength region is preferable. The light-reflective member5includes the scattering material, so that the light reflectance of the light-reflective member5can be improved.

The light-reflective member5is formed by curing a mixture obtained by mixing at least the powder of the first particles54and the powder of the second particles55in an alkali solution. For example, the content ratio of the first particles54and the second particles55included in the light-reflective member5is preferably in a range from 1:1 to 4:1 by weight ratio. The weight of the first particles54included in the light-reflective member5is, for example, in a range from one time to four times the weight of the second particles55included in the light-reflective member5.

Calculation Method of Average Particle Diameter

The average particle diameters of measurement targets (the first particles54, the second particles55, the scattering material, and the like) are measured using, for example, a scanning electron microscope. Specifically, the measurement target is attached to a tape or the like, and the surface of the tape is placed on a sample stage of the scanning electron microscope. The number of pixels of the scanning electron microscope is set to, for example, one million pixels, the magnification is set to, for example, 1000 times to 2000 times, and a predetermined number of (for example, 100) images of the measurement target are acquired by the scanning electron microscope. Subsequently, the particle diameter of each measurement target is measured with image analysis software. For example, when the measurement target is the first particle54, the particle diameter of the first particle54is the maximum diameter of the diameters of the first particle54when viewed from any one of the main surfaces540and541. Subsequently, the median diameter is calculated from the measured particle diameters of the measurement targets, and the calculated value is defined as the average particle diameter of the measurement target.

As another calculation method, an image of a cross-section obtained by cutting the light-reflective member5(performing mirror polishing) or an image of the outer surface (light reflecting surface53) of the light-reflective member5is acquired by a scanning microscope, and a predetermined number of images of the measurement target are acquired. Subsequently, the particle diameter of each measurement target may be measured by the image analysis software, and the average particle diameter of the measurement target may be calculated in the same manner as described above. As still another calculation method, the average particle diameter of the measurement target may be calculated by measuring the particle size distribution of the measurement target by a laser diffraction method.

Calculation Method of Average Aspect Ratio

The average aspect ratios of the measurement targets (the first particles54, the second particles55, the scattering material, and the like) are calculated by measuring the lateral widths and the thicknesses of the measurement targets or measuring the longitudinal dimensions and the lateral dimensions of the measurement targets by using, for example, a scanning electron microscope.

Specifically, an image of a cross-section obtained by cutting the light-reflective member5(performing mirror polishing) is acquired by a scanning microscope, and a measurement region including a predetermined number of (for example, 1000) cross-sections of the measurement target is selected. The number of pixels of the scanning microscope is set to, for example, 20 million pixels, and the magnification is set to, for example, 500 times to 3000 times. When the measurement target is the first particle54, the cross section of the measurement target is a plane substantially perpendicular to the main surfaces540and541. Subsequently, a lateral width (or longitudinal dimension) and a thickness (or lateral dimension) in each cross section of the measurement target are measured by image analysis software, and a ratio (aspect ratio) of the lateral width (or lateral dimension) to the thickness (or longitudinal dimension) is calculated. Subsequently, an average value of the aspect ratios of the measurement targets is set as an average aspect ratio.

Note that in a case in which the light-reflective member5contains an alkali metal, when a measurement target is a material that melts in an alkali container, the average particle diameter and the average aspect ratio of the measurement target are preferably measured before mixing with the alkali solution.

The cap6is a light-transmissive member that transmits light emitted from the light-emitting element3. As a material of the cap6, an inorganic material such as sapphire and glass can be used.

The cap6is bonded to the upper surface210of the package2(lateral wall portion21) by a bonding member so as to close the recessed portion22. Examples of applicable bonding member include solder, glass, and resin. Note that the cap6may be bonded to the package2so as to seal the concave portion22or may be bonded to the package2so as not to seal the concave portion22.

The cap6is rectangular in plan view. The length of each side of the cap6in plan view is longer than the length of each side of the inner lateral surface221of the recessed portion22(inner peripheral surface of the lateral wall portion21). The length of each side of the cap6in plan view may be shorter than or approximately the same as the length of each side of an outer peripheral surface211of the lateral wall portion21. The thickness of the cap6is in a range from 0.1 mm to 7 mm, for example. Note that the cap6may have a flat plate shape as in the present embodiment, or at least one of an upper surface or a lower surface thereof may have a lens shape.

As described above, in accordance with the light-emitting device1according to the present embodiment, the light reflecting surface53that reflects light emitted from the light-emitting element3is inclined in a direction from the inner lateral surface221of the recessed portion22toward the light-emitting element3, and the light reflection characteristics of the light reflecting surface53vary depending on the height H of the light reflecting surface53. Specifically, the light reflection characteristics of the light reflecting surface53in the inner peripheral edge portion50are different from the light reflection characteristics of the light reflecting surface53in the intermediate portion52in which the height H of the light reflecting surface53is higher than in the inner peripheral edge portion50. Consequently, the light reflecting surface53has no uniform light reflection characteristics like a metal film, for example, and has different light reflection characteristics depending on the height H of the light reflecting surface53, so that luminance spots of light emitted from the light-emitting device1can be reduced.

At this time, the reflectance of the light reflecting surface53is higher in the inner peripheral edge portion50than in the intermediate portion52. Thus, the light-reflective member5can reflect light more effectively in the inner peripheral edge portion50on a side closer to the light-emitting element3than in the intermediate portion52.

The degree of scattering (degree of diffusion) of the light reflecting surface53is higher in the intermediate portion52than in the inner peripheral edge portion50, and the intermediate portion52diffuses light more than the inner peripheral edge portion50. Thus, the light-reflective member5can reliably reduce luminance spots even in the intermediate portion52on a side farther from the light-emitting element3than the inner peripheral edge portion50.

Moreover, as an example of a material for implementing the above light reflection characteristics, the light-reflective member5may comprise or be formed of a material including at least the first particles54made of a light reflecting material and the second particles55having a smaller average particle diameter, a lower average aspect ratio, and a lower reflectance than the first particles54. Thus, the light reflection characteristics of the light reflecting surface53as described above can be implemented by a simple combination of materials. The first particles54function as aggregates of the light-reflective member5when the light-reflective member5is heated by heat generated from the light-emitting element3. Thus, shrinkage of the light-reflective member5due to the heat of the light-emitting element3is suppressed, so that heat resistance of the light-emitting device1can be improved.

The area or the number of particles per unit area occupied by the second particles55in the light reflecting surface53is smaller in the inner peripheral edge portion50than in the intermediate portion52. Therefore, the area or the number of exposed first particles54having a larger average particle diameter, a higher average aspect ratio, and a higher reflectance than the second particles55is larger in the inner peripheral edge portion50than in the intermediate portion52. Thus, the light-reflective member5can reflect light more effectively in the inner peripheral edge portion50on a side closer to the light-emitting element3than in the intermediate portion52, and can reliably reduce luminance spots even at the intermediate portion52on a side farther from the light-emitting element3than in the inner peripheral edge portion50.

When the light-emitting element3that emits light including ultraviolet light is used, the light-reflective member5preferably comprises or is formed of an inorganic material. The first particles54comprise or are composed of, for example, at least one of boron nitride or alumina, and the second particles55comprise or are composed of, for example, silica. Thus, deterioration of the light-reflective member5due to the ultraviolet light emitted from the light-emitting element3can be suppressed.

Note that the light reflection characteristics of the light-reflective member5are derived from the surface state of the light reflecting surface53related to a plurality of particles having different shapes and properties; however, no such limitation is intended and the light reflection characteristics of the light-reflective member5can be obtained by a known method that can derive, calculate, or measure the light reflection characteristic.

Manufacturing Method of Light-Emitting Device1

FIG.9is a flowchart illustrating an example of a manufacturing method of the light-emitting device1according to an embodiment. The manufacturing method of the light-emitting device1having the above configuration is described along steps S1to S4illustrated inFIG.9.

First, the package2formed with the recessed portion22is prepared. The light-emitting element3may or may not be placed on the placement region220aof the package2to be prepared. Note that when the package2on which the light-emitting element3is not placed is prepared, the light-emitting element3may be placed on the placement region220aafter step S4of forming the light-reflective member5is performed.

Subsequently, at least the first particles54and the second particles55having a smaller average particle diameter, a lower average aspect ratio, and a lower total reflectance than the first particles54are mixed to prepare the mixture7having thixotropy (also referred to as thixotropic property).

For example, a mixed powder obtained by mixing the first particles54and the second particles55is mixed with an alkali solution to prepare the mixture7. The mixed powder and the alkali solution are mixed to the extent that a uniform viscosity is obtained and are defoamed and mixed by a mixing and defoaming machine.

The first particles54comprise or are composed of, for example, boron nitride or alumina powder. The second particles55comprise or are composed of silica powder. The concentration of the alkali solution is in a range from 1 mol/L to 5 mol/L, for example. The thixotropy of the mixture7is adjusted by adjusting the concentration of the alkali solution with a solvent (for example, water). The viscosity characteristics of fluid representing the thixotropy of the mixture7can be measured by, for example, a B-type viscometer or an E-type viscometer. As the viscosity characteristics of the mixture7, a thixotropy index (TI value) is preferably in a range from 2 to 4, for example. The thixotropy index is obtained by dividing a measured value of viscosity at a low shear rate (for example, the number of revolutions of 10 rpm) by a measured value of viscosity at a high shear rate (for example, the number of revolutions of 50 rpm). For example, the TI value can be measured using a jig with an angle of 9.7°. Note that when the light-reflective member5includes a scattering material, the scattering material may be mixed with the mixture7.

Subsequently, the mixture7is applied to at least one of the bottom surface220or the inner lateral surface221of the recessed portion22formed in the package2.

FIG.10is a perspective view illustrating an example of step S3of applying the mixture7to the package2. For example, the mixture7is applied toward the inner lateral surface221at a position away from the placement region220aby using a dispensing nozzle70that can adjust discharge pressure and discharge diameter. At this time, the mixture7is continuously applied while the application position of the mixture7is moved along the inner lateral surface221so as to make one round around the light-emitting element3as indicated by a broken line arrow inFIG.10. Furthermore, the mixture7is continuously applied to make one round around the inner lateral surface221while aiming at a corner portion222formed by the bottom surface220and the inner lateral surface221. At this time, the mixture7is applied so that the height of the mixture7is in a range from ⅓ to ⅘ of a depth Hd of the concave portion22. Thus, when the mixture7is cured, the mixture7can be suppressed from protruding upward from the upper surface210.

As described above, when the mixture7is applied, the dispensing nozzle70may be moved in a state in which the package2is fixed, or the package2may be moved in a state in which the dispensing nozzle70is fixed. Note that after the mixture7is applied, the package2may be vibrated, or the mixture7may be applied while being vibrated. Before the mixture7is applied, a film may be formed on the bottom surface220and the inner lateral surface221of the recessed portion22by using silica, alumina, or the like. Thus, the adhesive force of the mixture7can be improved.

Since the mixture7has thixotropy, the mixture7immediately after being discharged from the dispensing nozzle70at a predetermined discharge pressure and a predetermined discharge meter and applied to the package2is in a state of low viscosity. Therefore, as indicated by a solid line arrow inFIG.10, an end portion of the mixture7on the bottom surface220side immediately after application moves on the bottom surface220so as to approach the placement region220a, and reaches the position of the inner peripheral edge portion50. Furthermore, an end portion of the mixture7on the inner lateral surface221side immediately after application moves along the inner lateral surface221due to surface tension, and reaches the position of the outer peripheral edge portion51. When the movement of the mixture7is stopped, since the viscosity characteristics of the mixture7transition to a state of high viscosity, the shape of the mixture7is maintained. The surface of the mixture7on the bottom surface220side (the inner peripheral edge portion50after curing) is in the same state as the state illustrated inFIG.5. The surface of the mixture7between the inner lateral surface221side and the bottom surface220side (the intermediate portion52after curing) is in the same state as the state illustrated inFIG.6.

Subsequently, the mixture7is cured to form the light-reflective member5including the light reflecting surface53inclined in a direction from the inner lateral surface221of the recessed portion22toward the placement region220aso as not to reach the placement region220a.

For example, the mixture7is heated at a predetermined temperature and cured to form the light-reflective member5. At this time, a temporary curing step of curing the mixture7at a first temperature T1and a main curing step of curing the mixture7at a second temperature T2higher than the first temperature T1may be performed. The temporary curing step is performed at the first temperature T1in a range from 80° C. to 100° C. for a range from 10 minutes to two hours, for example. The main curing step is performed at the second temperature T2in a range from 150° C. to 250° C. for a range from 10 minutes to three hours, for example. By performing the temporary curing step at a temperature lower than the temperature of the main curing step, cracks in the light-reflective member5can be suppressed. Note that when the mixture7is cured, the mixture7may be pressurized at a predetermined pressure. Alternatively, the mixture7may be cured by natural drying.

Note that the above steps S1to S4illustrated inFIG.9are main steps included in the manufacturing method of the light-emitting device1, and other steps may be included before or after each of the steps S1to S4. Examples of the other steps include a step of placing (mounting) the light-emitting element3on the placement region220aof the package2and a step of bonding the cap6to the upper surface210of the package2. Each of the steps S1to S4may be performed in an automated manner by various devices or may be performed by an operator.

As described above, in accordance with the manufacturing method of the light-emitting device1according to the present embodiment, the light-emitting device1including the light-reflective member5can be manufactured by applying and curing the mixture7having thixotropy. At this time, the light reflecting surface53as the outer surface of the light-reflective member5is inclined with respect to the bottom surface220of the concave portion22, and has different light reflection characteristics at different positions with different heights H of the light reflecting surface53. Thus, the light-emitting device1including the light-reflective member5as described above can be manufactured by a simple method.

OTHER EMBODIMENTS

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be appropriately changed without departing from the technical concepts of the present invention.

The light-emitting device1is a device used as a light source for any application. The light-emitting device1, for example, can be suitably used as a light-emitting device for various applications such as sterilization, disinfection, lighting, in-vehicle use, display devices, and electronic devices. The light-emitting device1may function not only as a single device but also in combination with other components or members.