JP2018186110A - Light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting device having a phosphor layer with a resin as a base material and having a high heat dissipation efficiency from the phosphor layer.SOLUTION: In a light emitting device including a light emitting element mounted on a substrate, a phosphor layer covering a light extraction surface of the light emitting element, and a reflective material covering a surface other than the light extraction surface of the light emitting element, the phosphor layer includes an inorganic filler and a phosphor using a resin as a base material. This increases the thermal conductivity of the phosphor layer, such that heat generated from the phosphor is more easily transferred to the light-emitting element and the substrate, and heat radiation efficiency from the phosphor can be improved.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light emitting device.

  In recent years, light emitting devices using light emitting diode (LED) elements have been widely used. Among such light emitting devices, there is one in which an LED chip is flip-chip mounted on a substrate or a case, and a phosphor layer including a phosphor is disposed on the light extraction surface side of the LED chip. The phosphor in the phosphor layer is excited by the light emitted from the LED chip and emits fluorescence having a wavelength different from that of the emitted light (that is, wavelength-converted light). Take out to the outside. An example of such a light emitting device is described in Patent Document 1 (Japanese Patent Laid-Open No. 2007-19096). The phosphor layer described in Patent Document 1 uses a resin as a base material (see paragraph [0015] of the specification of Patent Document 1).

JP 2007-19096 A Japanese Patent Application Laid-Open No. 2014-140014

When a high current is passed through such a light-emitting device to obtain high-luminance light, the phosphor generates heat due to energy loss during wavelength conversion, and the amount of heat generated from the phosphor layer increases. Therefore, considering the reliability of the phosphor layer, an inorganic substance (glass, alumina, phosphor sintered body, etc.) is used as a base material instead of the phosphor layer using a resin as a base material as in Patent Document 1. A phosphor plate may be used (see, for example, paragraph [0020] of Patent Document 2).
However, a phosphor plate using an inorganic material as a base material is relatively expensive, and an adhesive is applied to join the phosphor plate and the LED chip, and the phosphor plate is mounted on the LED chip and bonded. A process of curing the material is required. For this reason, the manufacturing cost of the light emitting device has become a factor.

  In view of the above, it is an object of the present invention to provide a light-emitting device that can improve the efficiency of heat dissipation from a phosphor in a light-emitting device having a phosphor layer using a resin as a base material. Another object is to improve the light extraction efficiency from the light source.

The inventor of the present invention has intensively studied to solve the above-mentioned problems, and as a result, has arrived at each aspect of the present invention as follows.
That is, the light emitting device according to the first aspect of the present invention includes a light emitting element mounted on a substrate, a phosphor layer that covers a light extraction surface of the light emitting element, and a reflective material that covers a surface other than the light extraction surface of the light emitting element. The phosphor layer is a light-emitting device containing a phosphor and an inorganic filler using a resin as a base material.

  In the light-emitting device according to the above aspect, the phosphor layer includes a resin as a base material and contains an inorganic filler having a high thermal conductivity in addition to the phosphor having a high thermal conductivity, so that the thermal conductivity of the phosphor layer is increased. Has been increased. Accordingly, heat generated from the phosphor is easily transmitted to the light emitting element and the substrate, and the efficiency of heat dissipation from the phosphor can be improved. In particular, it becomes easy to keep the temperature rise of the phosphor layer below the heat-resistant temperature of the resin that forms the phosphor layer, and it is possible to prevent cracks and the like from being generated in the phosphor layer when the light emitting element is energized for a long time. Therefore, the reliability is improved, and the reliability of the phosphor layer is improved even when a large current is supplied. Since the base material of the phosphor layer is a resin, an adhesive for adhering the phosphor layer to the light emitting element can be omitted, which can contribute to a reduction in manufacturing cost of the light emitting device.

  According to the second aspect of the present invention, in the light emitting device, the reflecting material contains a phosphor. Thereby, a part of the light emitted from the surface other than the light extraction surface of the light emitting element is converted into long wavelength light by the phosphor contained in the reflecting material, and the light is absorbed again into the light emitting element or applied to the substrate. Light absorption can be suppressed. As a result, a light emitting device having a high luminous flux can be provided.

  According to the third aspect of the present invention, in the light emitting device, the light emitting element is mounted on the substrate via the joint, and the median diameter of the phosphor contained in the reflector is smaller than the thickness of the joint. . As a result, the phosphor contained in the reflective material easily enters the gap between the light emitting element and the substrate. Accordingly, part of the light traveling from the light emitting element toward the substrate can be converted into long wavelength light by the phosphor, and reabsorption of light into the light emitting element and absorption of light into the substrate can be suppressed. As a result, a light emitting device having a high luminous flux can be provided.

  According to the fourth aspect of the present invention, in the light emitting device, the median diameter of the phosphor contained in the phosphor layer is larger than the median diameter of the phosphor contained in the reflector. Since the phosphor tends to have higher wavelength conversion efficiency and heat transfer efficiency as the particle size increases, it is advantageous to set the particle size of the phosphor contained in the phosphor layer to be larger than the particle size of the phosphor contained in the reflector. It is.

FIG. 1 is a cross-sectional view of a light emitting device according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view of a light emitting device according to a second embodiment of the present invention. FIG. 3 is a cross-sectional view of a light emitting device according to a third embodiment of the present invention. FIG. 4 is a graph showing an example of the relationship between the volume ratio of the phosphor and inorganic filler in the phosphor layer and the thermal conductivity of the phosphor layer.

Hereinafter, light emitting devices according to a plurality of embodiments of the present invention will be described with reference to the accompanying drawings.
(First embodiment)
FIG. 1 shows a cross-sectional view of a light emitting device 1 according to a first embodiment of the present invention. A light emitting device 1 shown in FIG. 1 includes a substrate 10 such as aluminum nitride (AlN), an LED chip (light emitting element) 20 bonded and mounted on the substrate 10, and an upper surface of the LED chip 20 opposite to the substrate 10. A phosphor layer 30 that covers (light extraction surface) and a reflector 40 that covers the outer surface of the LED chip 20 and other surfaces (side surfaces and lower surface) than the light extraction surface. The LED chip 20 is mounted on the substrate 10 in such a manner that the LED chip 20 is electrically connected to an electrode (not shown) on the surface of the substrate 10 through the joint portion 50. The light emitting device 1 may further include a member such as a dam surrounding the outer periphery of the phosphor layer 30 and the reflecting material 40.

(LED chip 20)
The LED chip 20 is preferably a flip-chip type, and a gallium nitride (GaN) -based semiconductor layer (epitaxial layer) formed on a sapphire substrate can be employed. However, the embodiment of the present invention is not limited to this, and a zinc oxide (ZnO) -based, zinc selenide (ZnSe) -based, silicon carbide (SiC) -based, or the like may be used as the semiconductor layer of the LED chip 20 in addition to the above. In addition, a substrate suitable for each substrate can be used. The emission color of the LED chip 20 is preferably blue, purple, or ultraviolet light that can excite a phosphor and extract white color by synthesis with fluorescence, but is not limited thereto. In the following description of the present embodiment, the LED chip 20 that emits blue light will be described as an example.

(Phosphor layer 30)
The phosphor layer 30 has a light emission surface exposed to the light extraction side, and is configured to cover the entire light extraction surface of the LED chip 20. The phosphor layer 30 is mainly composed of a base material 31 made of a resin such as a high heat-resistant silicone resin, a particulate phosphor 32 and an inorganic filler 33 dispersed in the base material 31.
An arbitrary phosphor can be used as the phosphor 32 included in the phosphor layer 30. However, the LED chip 20 that emits blue light is excited by receiving emitted light (blue light) from the LED chip 20. Thus, by using a yellow phosphor such as YAG or BOS that emits wavelength-converted light (yellow light), the light emitting device 1 is mixed with the blue light of the LED chip 20 and the wavelength-converted light by the phosphor 32. Thus, it can be configured as a white LED package that emits white light. The phosphor 32 has a higher thermal conductivity than the resin constituting the base material 31.
As the inorganic filler 33 contained in the phosphor layer 30, alumina, aluminum nitride, magnesium oxide, boron nitride, silicon dioxide, silicon nitride, or the like having higher thermal conductivity than the base material 31 can be used. Further, as the other inorganic filler 33, a host crystal of a phosphor that does not contain an activator such as europium or cerium can be used. As the host crystal, YAG, α-sialon, β-sialon, CaASiN ₃ , Ca ₂ Si ₅ N _8, or the like can be used.

(Reflecting material 40)
The reflective material forming the reflective material 40 may be a resin in which light reflecting particles are contained, and the light reflecting particles are emitted from the side surface and the lower surface of the LED chip 20 by light emission of the light emitting layer of the LED chip 20. It has a function of receiving leaked light and reflecting it into the LED chip 20. As the resin, silicone resin, epoxy resin, acrylic resin, or the like can be used. As light reflecting particles, oxides such as titanium (Ti), zirconium (Zr), niobium (Nb), aluminum (Al), and silicon (Si), and particles such as aluminum nitride and magnesium fluoride (MgF) should be used. Can do. In particular, a combination of a silicone resin and titanium oxide (TiO ₂ ) is preferable from the viewpoint of heat resistance to heat generated in the LED chip 20 and light reflectivity.

(Operation of the light emitting device 1)
When a voltage is applied from the power source to the LED chip 20, light is emitted from the light emitting layer, and this emitted light is emitted from the light extraction surface of the LED chip 20 through the phosphor layer 30 as first emitted light to the light extraction side, and also to the LED. The light is emitted from the chip 20 into the reflector 40 as second radiated light (leakage light). Of these radiated lights, the second radiated light emitted from the LED chip 20 into the reflector 40 is reflected by the light reflecting particles in the vicinity of the LED chip 20, and most of the reflected light is reflected in the LED chip 20. Returning, it is radiate | emitted via the fluorescent substance layer 30 from the light extraction surface with 1st emitted light. In this case, the phosphor layer 30 emits yellow wavelength-converted light by receiving the first radiated light and the second radiated light (both blue light) emitted from the LED chip 20 and exciting the phosphor 32. To do. For this reason, the blue radiation light radiated from the LED chip 20 and the yellow wavelength converted light radiated from the phosphor layer 30 are mixed to form white light.

  In the present embodiment, the case where the light emitting device 1 includes the flip chip type LED chip 20 has been described. However, the present invention is not limited thereto, and the light emitting device including the face up type LED chip may be used. Good. However, the flip chip type LED chip 20 is easier to form a configuration in which the light extraction surface is covered with the phosphor layer 30.

(Method for manufacturing light emitting device)
Below, an example of the manufacturing method of the light-emitting device 1 of this embodiment is demonstrated.
First, the electrode on the surface of the substrate 10 and the electrode of the LED chip 20 are bonded (Au—Sn bonding) with an alloy of gold (Au) and tin (Sn) to form the bonding portion 50, and flip chip mounting is performed. . For example, the Au electrode on the surface of the substrate 10 and the AuSn electrode of the LED chip 20 can be alloyed by thermocompression bonding and can be employed.
As a method of bonding the electrode on the surface of the substrate 10 and the electrode of the LED chip 20, any appropriate and arbitrary method can be selected from conventionally known bonding methods.

Next, the reflective material 40 is formed inside the dam provided on the substrate 10 so as to cover the side surface and the lower surface of the LED chip 20. The reflective material 40 is formed by potting or the like.
After the reflecting material 40 is cured, the phosphor layer 30 is formed so as to cover the light extraction surface of the LED chip 20. The phosphor layer 30 is formed by applying a base material 31 in which a phosphor 32 and an inorganic filler 33 are dispersed onto the LED chip 20 and the reflector 40 by potting or the like.
Next, it is divided into product sizes by dicing or the like.

(Effect of 1st Embodiment)
In the light emitting device 1 having the above-described configuration, the phosphor layer 30 contains the inorganic filler 33 in addition to the phosphor 32, thereby increasing the thermal conductivity of the phosphor layer 30. The heat generated from the LED can be easily transmitted to the LED chip 20 and the substrate 10, and the light emitting device 1 that is advantageous for heat dissipation can be obtained. Examples of the contents of the phosphor 32 and the inorganic filler 33 for achieving such an effect will be described later with reference to examples. If an inorganic filler 33 having the same base crystal as that of the phosphor 32 is employed, the specific gravity of both is substantially the same, so that both are easily dispersed uniformly in the base material 31. Moreover, since the base material 31 of the phosphor layer 30 is made of resin, an adhesive for adhering the phosphor layer 30 to the LED chip 20 can be omitted, which can contribute to a reduction in manufacturing cost of the light emitting device 1.

(Second Embodiment)
FIG. 2 shows a cross-sectional view of a light emitting device 1A according to the second embodiment of the present invention. In comparison with the light emitting device 1 according to the first embodiment, the light emitting device 1A according to the second embodiment is such that the particles of the phosphor 41 are uniformly dispersed in the reflector 40 that covers the side surface of the LED chip 20. Different. Thereby, a part of blue light emitted from the side surface of the LED chip 20 can be converted into long wavelength light by the phosphor 41 contained in the reflector 40, thereby suppressing reabsorption of light in the LED chip 20. it can. Further, light absorption by the substrate 10 made of aluminum nitride can also be suppressed. As a result, the light emitting device 1A having a high luminous flux can be provided.

(Third embodiment)
FIG. 3 shows a cross-sectional view of a light emitting device 1B according to the third embodiment of the present invention. In the light emitting device 1B according to the third embodiment, in comparison with the light emitting device 1 according to the first embodiment, the phosphors 42 are uniformly dispersed in the reflector 40 that covers the side surface and the lower surface of the LED chip 20. It is different. In order to put the phosphor 42 under the LED chip 20 (that is, between the LED chip 20 and the substrate 10), it is desirable that the particle size of the phosphor 42 is smaller than the thickness of the bonding portion 50. Thereby, a part of the light traveling below the LED chip 20 can be converted into long-wavelength light by the phosphor 42, so that re-absorption to the LED chip 20 and light absorption by the substrate 10 can be suppressed, and light emission with high luminous flux can be achieved. The apparatus 1B can be provided. In addition, the thinner the joint portion 50 is, the easier it is to transmit the heat from the LED chip 20 to the substrate 10 side, and the light emitting device 1B is advantageous for heat dissipation. In addition, since the wavelength conversion efficiency and the heat transfer efficiency tend to be higher as the particle size of the phosphor is larger, the particle size of the phosphor 32 included in the phosphor layer 30 is larger than the particle size of the phosphor 42 included in the reflector 40. It is advantageous to set it large. As an example, when the thickness of the junction 50 is about 5 μm, the median diameter (d50) of the phosphor 42 included in the reflector 40 is about 3 μm, and the median diameter of the phosphor 32 included in the phosphor layer 30 is 10 μm. Can be about. For example, it is possible to set the median diameter of the phosphor 32 included in the phosphor layer 30 within a range of about 6 μm to about 20 μm and the median diameter of the phosphor 42 included in the reflector 40 within a range of about 3 μm to about 5 μm. It is preferable in terms of increasing the luminous flux of 1B.

(Example)
Next, examples of the light emitting device 1 according to the first embodiment of the present invention will be described. The conditions of this example are shown below.

Target mixed color (light emitting color of light emitting device 1): amber color Material of base material 31: high heat resistant silicone resin, thermal conductivity 0.2 W / m · K
Material of phosphor 32: α-sialon phosphor, emission center wavelength 597 to 603 nm, thermal conductivity 10 W / m · K
Material of the inorganic filler 33: silicon dioxide (SiO ₂ )
Content of inorganic filler 33: 1 wt% of the entire phosphor layer 30
Thickness of phosphor layer 30: 60 μm to 160 μm
Reflective material 40: silicone resin + titanium oxide

上記式（１）における各記号の定義は次の通りである。
Φ：蛍光体３２と無機フィラー３３の体積充填率（体積率）
λｃ：蛍光体層３０の熱伝導率
λｆ：蛍光体３２と無機フィラー３３の平均の熱伝導率
λｍ：母材３１の熱伝導率 FIG. 4 shows the volume ratio Φ (vol%) of the phosphor 32 and the inorganic filler 33 occupying the phosphor layer 30 of this embodiment and the thermal conductivity λc (W / m · K) of the phosphor layer 30. It is a graph showing a relationship. This graph plots the values calculated by the following Bruggeman equation (1).

The definition of each symbol in the above formula (1) is as follows.
Φ: Volume filling rate (volume ratio) of phosphor 32 and inorganic filler 33
λc: thermal conductivity of phosphor layer 30 λf: average thermal conductivity of phosphor 32 and inorganic filler 33 λm: thermal conductivity of base material 31

From FIG. 4, the higher the content of the phosphor 32 and the inorganic filler 33, the higher the thermal conductivity of the phosphor layer 30, and it becomes easier to transfer heat generated from the phosphor 32 to the LED chip 20 and the substrate 10, which is advantageous for heat dissipation. It turns out that it becomes. Therefore, the relationship between the content of the phosphor 32 and the inorganic filler 33 and the temperature of the phosphor layer 30 was confirmed by simulation. The model used for the simulation is a flat heat conduction model, and it is assumed that the phosphor 32 generates heat from the surface of the phosphor layer 30. The thickness of the phosphor layer 30 was 100 μm, the calorific value of the phosphor layer 30 was 0.563 W / mm ² , and the junction temperature Tj was 150 ° C. The results of the simulation are shown in the following table (in the table, the phosphor 32 and the inorganic filler 33 are collectively referred to as “phosphor etc.”). Considering that the heat resistant temperature of the resin is 250 ° C., it is considered that the volume ratio of the phosphor 32 and the inorganic filler 33 is desirably 35 vol% or more.

  However, when the volume ratio of the phosphor 32 and the inorganic filler 33 is 50 vol% or more, the mixture of the resin (base material 31), the phosphor 32, and the inorganic filler 33 that becomes the phosphor layer 30 is not in a slurry state. Layer 30 could not be formed.

In addition, when aiming at white light as the luminescent color of the light-emitting device 1, in order to improve the heat dissipation from the fluorescent substance layer 30, the volume ratio of the fluorescent substance 32 and the inorganic filler 33 in the fluorescent substance layer 30 is set based on the said Example. If a large amount of the phosphor 32 is contained so as to be 35 vol% or more, it is considered that the mixed color is too yellow and white light cannot be obtained. In such a case, it can be considered that the chromaticity is adjusted by further replacing a part of the phosphor 32 included in the phosphor layer 30 with the inorganic filler 33.
In the second embodiment and the third embodiment, part or all of the phosphors 41 and 42 included in the reflector 40 are replaced with an inorganic filler made of the material described as the material of the inorganic filler 33 of the first embodiment. Also good.

The elements of the different embodiments of the present invention described above may be implemented in combination with each other except where it is impossible to implement, and such embodiments are also included in the scope of the present invention.
The present invention is not limited to the description of each aspect and embodiment of the above-described invention and modifications thereof. Various modifications are also included in the present invention as long as those skilled in the art can easily conceive without departing from the scope of the claims.

DESCRIPTION OF SYMBOLS 1, 1A, 1B Light-emitting device 10 Board | substrate 20 LED element 30 Phosphor layer 31 Base material 32 Phosphor 33 Inorganic filler 40 Reflective material 41 Phosphor 42 Phosphor 50 Joint part

Claims (4)

A light emitting device mounted on a substrate;
A phosphor layer covering a light extraction surface of the light emitting element;
A reflective material that covers a surface other than the light extraction surface of the light emitting element, and a light emitting device comprising:
The phosphor layer is a light-emitting device containing a phosphor and an inorganic filler using a resin as a base material.   The light emitting device according to claim 1, wherein the reflecting material contains a phosphor. The light emitting element is mounted on the substrate via a joint,
The light-emitting device according to claim 2, wherein a median diameter of the phosphor contained in the reflecting material is smaller than a thickness of the joint portion. 4. The light-emitting device according to claim 2, wherein a median diameter of the phosphor contained in the phosphor layer is larger than a median diameter of the phosphor contained in the reflector.

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