JP3399342B2 - Method of forming light emitting diode - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-emitting diode that emits light by converting at least a part of the emission wavelength emitted from a light-emitting element with a fluorescent substance, and more particularly to uneven light emission. ,
The present invention relates to a light-emitting diode having a high yield with little color unevenness and light-emitting variation between formed light-emitting diodes. 2. Description of the Related Art A semiconductor light emitting device is small and efficiently emits bright colors. In addition, the ball is not broken because it is a semiconductor element. It has excellent drive characteristics and is resistant to vibration and ON / OFF lighting. Therefore, it is used as various indicators and various light sources. However, since such a light emitting element has a monochromatic peak wavelength, even when only white light (white, pink, light bulb color, etc.) is obtained, two or more kinds of light emitting elements have to be used. Was. Further, various luminescent colors could not be easily obtained. [0003] Japanese Patent Application Laid-Open Nos. 5-152609 and 7-99345 have disclosed light-emitting diodes that emit light of various colors using an LED chip emitting a monochromatic peak wavelength and a fluorescent substance. Things are known. In these light emitting diodes, a light emitting chip is mounted on the bottom of a cup that reflects light emitted from the light emitting chip toward a light emission observation surface side, and a resin filled inside the cup is provided;
It can be made of resin that covers the whole. The resin filled therein contains a fluorescent substance that absorbs light from the light emitting chip and converts the wavelength. [0005] A resin containing a fluorescent substance is dropped and poured into the upper portion of a cup on which a light emitting element is mounted, such as a liquid thermosetting epoxy resin, and is heated and cured to form a color conversion member. The resin other than the inside of the cup is immersed in the casting case where liquid epoxy resin or the like is cast, and the color conversion member and the tip of the frame member on which the light emitting chip is formed are immersed,
This is formed by placing it in an oven and curing by heating. [0006] Thus, a light emitting diode that emits light by converting the wavelength of light emitted from the light emitting chip with the fluorescent substance can be obtained. For example, a white light-emitting diode can be obtained by mixing blue light from an LED chip with light from a phosphor that absorbs the blue light and emits a yellow light having a complementary color relationship. [0007] In order to emit a desired white light or the like using such a light emitting diode, it is necessary to emit each light with extremely high accuracy and to adjust the color mixture. LE
The light from the D-chip can be adjusted relatively easily by its semiconductor and driving current. On the other hand, the wavelength-converted light from the fluorescent substance can also be adjusted to some extent by controlling the composition and particle size of the fluorescent substance. However, since the fluorescent substance itself has no or weak adhesion, it is difficult to arrange and fix the fluorescent substance on the light emitting element. It must be contained in a binder having an adhesive property capable of emitting light. Regarding the fluorescent substance contained in such a binder, the amount of light emitted from the LED chip and the amount of light emitted from the fluorescent substance largely depend on the content and distribution of the fluorescent substance. If these cannot be controlled, and the light emitted from the light emitting element and the light emitted from the fluorescent substance are visible light, and the colors are expressed by their respective colors, the difference in the amount of light poses a particularly serious problem. In particular, the white system is a big problem because human eyes can identify even a slight color temperature difference. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a light-emitting diode having a high yield, excellent uniform light-emitting characteristics, a uniform content and distribution of a fluorescent substance, and a method of forming the same. As a result of various experiments, the inventor of the present invention has found that, in a light emitting diode using a fluorescent substance, variations between the light emitting diodes, uneven color of the light emitting diode, and uneven light emission are found in the distribution of the fluorescent substance. The present invention has been found to be largely caused by the fact that unevenness in light emission can be controlled by a forming method using a specific resin. That is, when a liquid resin containing a fluorescent substance is cast and cured, a liquid epoxy resin having a low viscosity of about 500 to 1000 cps is used in consideration of filling properties. Since the specific gravity of the fluorescent substance and the specific gravity of the resin are greatly different, when a fluorescent substance is mixed as a filler in such a resin, the two are easily separated. Therefore, when a light organic fluorescent substance is used, it floats, and when a heavy inorganic fluorescent substance is used, it sinks. Such separation results in non-uniform dispersion of the phosphor. In particular, in the case of repeatedly producing a mixture in which a resin and a fluorescent substance are mixed in a batch manner by small amounts, the separation of the resin and the fluorescent substance in the mixture proceeds with time. Therefore, the content of the fluorescent substance tends to be different between a light emitting diode manufactured by casting immediately after mixing and a light emitting diode manufactured by casting a while after mixing. Further, when the light-emitting diode after casting is cured by heating, the viscosity decreases with the temperature rise until the resin solidifies, so that separation due to the difference in specific gravity between the resin and the fluorescent substance easily occurs. There is a tendency. In particular, in a light-emitting diode that emits mixed light of light emitted from a light-emitting element and fluorescence from a fluorescent substance, the change in the content of the fluorescent substance and the non-uniform arrangement in the sealing resin are all changes in the color temperature of the emission color. Appears prominently. The method for forming a light emitting diode according to the present invention comprises the steps of:
It contains a light emitting element composed of a compound semiconductor, an inorganic fluorescent substance which emits fluorescence of longer wavelength than the light emitting wavelength and absorbing at least a portion of the emission wavelength from the light emitting element, the inorganic fluorescent substance
A method of forming a light emitting diode having a quality and density of different resins, the photocurable resin photocuring catalyst are uniformly mixed is added the inorganic fluorescent substance is coated on the light emitting element while stirring, the photocurable Curing by irradiating the light energy of the light emitting element to the conductive resin. Thereby, the fluorescent substance in the resin can be uniformly maintained, and thus a light emitting diode having extremely little unevenness in light emission and uneven color can be obtained. Further, the light emitting element is yttrium aluminum garnet-based phosphor fluorescent material is cerium-activated with a nitride semiconductor If it is (hereinafter, sometimes referred to as YAG phosphors.), It is formed In addition, a light emitting diode capable of emitting white light with less variation between the light emitting diodes and less uneven light emission and uneven color can be obtained. According to the forming method of the present invention , a fluorescent substance is mixed very uniformly in the sealing resin of the formed light emitting diode, and a light emitting diode having stable optical characteristics can be formed relatively easily. In particular, there is little variation between the formed light emitting diodes, and the yield can be improved. FIG. 2 is a schematic sectional view of a white light emitting diode as an embodiment of the present invention. The package 205 has a configuration in which an external electrode 206 is coupled to an insulating support member such as a ceramic, a liquid crystal polymer, or a PBT resin. Examples of the material of the external electrode include a metallized material such as nickel and tungsten or an electrically conductive material such as phosphor bronze. The external electrode 206 is formed integrally with the insulating support member by insert molding or the like. The surface of the external electrode is preferably plated with silver, gold, aluminum, or the like in order to improve reflectivity. Also,
The package has a concave portion at the center thereof, and a part of the external electrode is exposed on the bottom surface of the concave portion. An LED chip capable of emitting blue light is die-bonded to the bottom surface of the recess as the light emitting element 204. Each electrode of the light emitting element and the external electrode are wire-bonded to each other by a wire 203 such as a gold wire which is a good electrical conductor. A light-curable resin 201 having excellent translucency and heat resistance is applied onto the light-emitting element bonded by wire bonding while stirring to cover the light-emitting element. The photocurable resin is obtained by adding a photocuring catalyst such as an aromatic diazonium salt, an aromatic iodonium salt, a sulfonium salt, an aluminum complex or a silanol compound to a modified acrylic, epoxy or silicone resin. The resin is uniformly mixed with about 5% by mass of a YAG phosphor 202 which emits yellow fluorescence when irradiated with blue light. After the resin is dropped into the concave portion of the package, UV or blue visible light for irradiating a photo-curing catalyst is applied. In the light emitting diode of the present invention, the resin containing the fluorescent substance solidifies in about 10 seconds after being injected into the package. The time during which the fluorescent substance-containing resin is present in a liquid state (that is, the time when the fluorescent substance is in a non-uniform distribution state in the resin) is several tens of times when the thermosetting resin cures the fluorescent substance-containing resin. Very few compared to the order of minutes to several hours. Therefore, after the dropping, the distribution of the fluorescent substance in the resin hardly becomes nonuniform, and the variation in the optical characteristics of the light emitting diode due to this is remarkably reduced. According to the present invention, the phosphor is rapidly cured before the distribution gradient of the phosphor in the resin starts without causing a decrease in viscosity when the resin is cured. Thereby, in the light emitting diode of the present invention, the light emitting diode can be uniformly dispersed in the resin regardless of the specific gravity difference between the resin and the fluorescent substance. In particular, in the case of the present invention, in the case of a light emitting diode capable of emitting white light containing a YAG phosphor as a fluorescent substance in a sealing resin, the distribution of the YAG phosphor can always be extremely uniform. Therefore, a light emitting diode having a uniform color temperature can be stably manufactured. Hereinafter, each configuration used in the present invention will be described in detail. (Photo-Curable Resin 201) The photo-curable resin used in the present invention efficiently supplies the emission wavelength from the light emitting element to the fluorescent substance and emits the fluorescence from the fluorescent substance to the outside. It is a resin that can be photocured before the distribution gradient of the fluorescent substance caused by the difference in specific gravity between the fluorescent substance and the resin increases. Specific resins include modified acrylic resins,
Epoxy or silicone resins are preferred. A photocurable resin can be obtained by adding a photocuring catalyst such as an aromatic diazonium salt, an aromatic iodonium salt, a sulfonium salt, an aluminum complex or a silanol compound to these resins. When such a photo-curable resin is irradiated with relatively high energy such as ultraviolet light or visible violet or blue light as light energy, the photo-curing catalyst functions as a photo-polymerization initiator. Therefore, the light applied to the resin containing the photocuring catalyst can be variously selected depending on the type of the resin containing the fluorescent substance or the photocuring catalyst. As a high energy source for irradiating light energy, a light source such as a high-pressure mercury lamp, a low-pressure mercury lamp, a metal halide lamp, a xenon lamp, a carbon arc lamp, a chemical lamp and the like are preferably exemplified. Further, in addition to the photo-curing catalyst, a thermosetting catalyst can be added. Specific examples of such a thermosetting catalyst include amine compounds and acid anhydride compounds. This makes it possible to more effectively suppress the non-uniform distribution of the fluorescent substance. In particular, a light-emitting element using a nitride semiconductor is preferable because it can have a wide band gap and can be irradiated with a relatively high-energy light at a wavelength at which a photocuring catalyst acts. In the case where the light emitting element is a nitride semiconductor that emits ultraviolet light, if the ultraviolet curable resin contains a fluorescent substance, the ultraviolet curable resin itself easily transmits ultraviolet light, so that the fluorescent substance can be efficiently excited. (Fluorescent Substance 202) The fluorescent substance used in the present invention refers to a fluorescent substance that emits fluorescence when excited by an electromagnetic wave emitted from a light emitting element. Examples of the fluorescent substance include yttrium-aluminum-garnet-based phosphor activated with cerium, perylene-based derivatives, zinc selenide activated with copper, and the like. In particular, when a nitride semiconductor is used for a light emitting element, yttrium / aluminum / garnet-based phosphors are particularly preferable in terms of light resistance and efficiency. The yttrium-aluminum-garnet-based phosphor activated with cerium has a garnet structure, so it is resistant to heat, light and moisture, and can have an excitation spectrum peak near 450 nm. In addition, the emission peak is around 530 nm, and a broad emission spectrum that extends to 700 nm can be obtained. In the present invention, the yttrium / aluminum / garnet-based phosphor activated with cerium is, in the broadest sense, interpreted from Lu, Sc, La, Gd, and Sm in place of yttrium (Y) of Y3Al5O12: Ce. It can be replaced with at least one selected. Ga instead of aluminum (Al);
It can be replaced with at least one selected from In, B, and Tl. The emission color can be continuously adjusted by changing the composition. That is, there is an ideal condition for converting blue light emission of the nitride semiconductor into white light emission such that the intensity on the long wavelength side can be continuously changed by the composition ratio of Gd. Similarly, Lu, Lc, Sc and S
The desired characteristics may be obtained by adding m or the like. Such fluorescent materials include Y, Gd, Ce,
An oxide or a compound which easily becomes an oxide at a high temperature is used as a raw material of Sm, La, Al and Ga, and these are sufficiently mixed in a stoichiometric ratio to obtain a raw material. Or Y, Gd,
A co-precipitated oxide obtained by co-precipitating a solution obtained by dissolving a rare earth element of Ce, Sm, La in an acid at a stoichiometric ratio with oxalic acid, and aluminum oxide and gallium oxide are mixed and mixed. Get the raw materials. An appropriate amount of a fluoride such as ammonium fluoride is mixed as a flux into the crucible, and calcined in air at a temperature in the range of 1350 to 1450 ° C. for 2 to 5 hours to obtain a calcined product. It can be obtained by ball milling, washing, separating, drying and finally passing through a sieve. In the method for forming a light emitting diode of the present invention, such a fluorescent substance may be a mixture of two or more fluorescent substances. Specifically, Al, Ga, Y and Gd,
The wavelength components of RGB can be increased by mixing two or more types of yttrium / aluminum / garnet-based phosphors activated with cerium having different La and Sm contents. In such a case, even if the specific gravities of the different fluorescent materials are different, it is possible to form a light emitting diode with uniform light emitting characteristics with good mass productivity. (Light-Emitting Element 204) The light-emitting element used in the present invention is a semiconductor light-emitting element having a light-emitting layer capable of emitting an emission wavelength capable of exciting a fluorescent substance. As such a semiconductor light emitting device, a nitride semiconductor (InXAlYGa1-X-YN, 0 ≦ X, 0 ≦
Y, 0 ≦ X + Y ≦ 1) and the like. Examples of the semiconductor structure include a homo structure, a hetero structure, and a double hetero structure having an MIS junction, a PIN junction, a pn junction, and the like. Various emission wavelengths can be selected depending on the material of the semiconductor layer and the degree of mixed crystal thereof. Also,
A single quantum well structure or a multiple quantum well structure in which the semiconductor active layer is formed as a thin film in which a quantum effect occurs can be used. When a gallium nitride compound semiconductor is used, sapphire, spinel, SiC,
Materials such as Si and ZnO are preferably used. In order to form gallium nitride having good crystallinity, a sapphire substrate is preferably used. MOC on this sapphire substrate
A nitride semiconductor can be formed using a VD method or the like. GaN, AlN, GaAIN on sapphire substrate
And the like, and a gallium nitride semiconductor having a pn junction is formed thereon. As an example of a light emitting device having a pn junction using a nitride semiconductor, a first contact layer formed of n-type gallium nitride and a first clad formed of n-type aluminum / gallium nitride on a buffer layer Layer, an active layer formed of indium gallium nitride, a second cladding layer formed of p-type aluminum gallium nitride, and a double hetero structure in which a second contact layer formed of p-type gallium nitride is sequentially stacked. No. The gallium nitride-based semiconductor shows n-type conductivity without being doped with impurities. When a desired n-type gallium nitride semiconductor is formed, for example, to improve luminous efficiency, Si, Ge, Se, Te, C
It is preferable to introduce such as appropriate. On the other hand, in the case of forming a p-type gallium nitride semiconductor, doping is performed with a p-type dopant such as Zn, Mg, Be, Ca, Sr, and Ba. Since gallium nitride-based compound semiconductors are difficult to become p-type only by doping with a p-type dopant, it is preferable to reduce the resistance by introducing a p-type dopant and then performing heat treatment by heating in a furnace, plasma irradiation, or the like. After the electrodes are formed, an LED chip made of a nitride semiconductor can be formed by cutting the semiconductor wafer into chips. In the case where the light emitting diode of the present invention emits white light, the emission wavelength of the light emitting element is preferably 400 nm or more and 530 nm or less in consideration of the complementary color relationship with the emission wavelength from the fluorescent substance and the deterioration of the thermoplastic resin. , 420
The thickness is more preferably from 490 nm to 490 nm. In order to further improve the excitation and emission efficiency of the light emitting element and the fluorescent substance, respectively, the thickness is more preferably 450 nm or more and 475 nm or less. Hereinafter, specific reference examples of the present invention will be described in detail, but it goes without saying that the present invention is not limited thereto. REFERENCE EXAMPLE ( Reference Example 1) The LED chip has an emission peak of 450 nm as a light emitting layer.
In0.2Ga0.8N semiconductor was used. The LED chip is formed by flowing a TMG (trimethyl gallium) gas, a TMI (trimethyl indium) gas, a nitrogen gas and a dopant gas on a cleaned sapphire substrate together with a carrier gas, and forming a nitride semiconductor film by MOCVD. Was. SiH4 and Cp as dopant gas
By switching between 2Mg, an n-type or p-type conductive semiconductor is formed. As the light-emitting element, a contact layer made of a gallium nitride semiconductor having n-type conductivity, a clad layer made of an aluminum gallium nitride semiconductor having p-type conductivity, and a contact layer made of gallium nitride having p-type conductivity were formed. . An InGaN active layer having a thickness of about 3 nm and a single quantum structure is formed between the n-type contact layer and the p-type cladding layer. (Note that gallium nitride is formed at a low temperature on the sapphire substrate to serve as a buffer layer. The p-type semiconductor is heat-treated at 400 ° C. or more after film formation.) After exposing the surface of the semiconductor contact layer, each electrode was formed by sputtering. After the scribe line was drawn on the semiconductor wafer thus completed, it was divided by an external force to form LED chips. On the other hand, an iron-containing copper lead frame is formed by punching and stamping, which is connected by a tie bar and has a cup formed at the tip of a mount lead. Using an epoxy resin, the LED chip was die-bonded into the tip cup of a copper lead frame containing iron, which was silver-plated with a die bonding device. Each electrode of the LED chip was mounted on a mount lead or an inner lead provided with a cup by wire bonding with a gold wire to establish electrical continuity. As a fluorescent substance, a solution obtained by dissolving rare earth elements of Y, Gd and Ce in an stoichiometric ratio in an acid was coprecipitated with oxalic acid. This is mixed with a coprecipitated oxide obtained by calcination and aluminum oxide to obtain a mixed raw material. This was mixed with ammonium fluoride as a flux, packed in a crucible, and fired in air at a temperature of 1400 ° C. for 3 hours to obtain a fired product. The calcined product was ball milled in water, washed, separated, dried, and finally formed through a sieve. (Y0.8Gd0.2) 3Al formed
5O12: 25 parts by weight of Ce fluorescent material, epoxy resin 10
0 parts by weight and 1 mol% of aromatic sulfonium as a photocuring catalyst. While mixing this, it was applied and covered as a photocurable resin containing a fluorescent substance on the LED chip. In this state, the resin containing the fluorescent substance was cured with a low-pressure halogen lamp. Next, the tip end of the lead terminal in which the LED chip was covered with a resin containing a fluorescent substance was placed in a casting case. An epoxy resin was poured into the casting case and cured to form a light emitting diode having a shell-shaped mold. By taking out the lead from the casting case and cutting the tie bar, it is possible to obtain a light emitting diode having an LED chip covered with a photocurable resin containing a fluorescent substance and having a shell type mold. The dispersion was measured by forming 500 such light emitting diodes. The chromaticity point of the obtained light emitting diode capable of emitting white light was measured and plotted on CIE coordinates. In addition, it was confirmed that there was no uneven light emission in the appearance of each light emitting diode. Comparative Example A light-emitting diode was formed in the same manner as in the reference example except that a thermosetting epoxy resin was used as the fluorescent material-containing resin and the resin was cast . An average of 500 formed light emitting diodes of the comparative example was compared with the light emitting diode of the reference example 1 to examine the manufacturing variation of the color temperature. In the light emitting diode of the reference example , the manufacturing variation of the color temperature was reduced by 30% or more as compared with the light emitting diode of the comparative example. According to the present invention, it is possible to form a light emitting diode having a fluorescent material with stable light emission characteristics with good mass productivity, and to obtain a light emitting diode with reduced light emission unevenness on the light emission observation surface side relatively easily. Can be formed. Further, even during long-term mass production, variation in light emission between a light emitting diode formed first and a light emitting diode formed later can be extremely reduced, so that mass productivity and yield can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view showing a light emitting diode of the present invention. FIG. 2 is a schematic sectional view showing a chip type LED which is another light emitting diode of the present invention. [Description of Reference Numerals] 101: Photo-curable resin containing a fluorescent substance 102: Light-emitting element 103: Mount lead 104 having a concave portion for disposing the light-emitting element 104: Inner lead 105 Wire 106 Mold 201 Photocurable resin 202 Fluorescent substance 203 Wire 204 Light emitting element 205 Package 206 External electrode

Claims (1)

(57) and Patent Claims 1. A light emitting device comprising a nitride semiconductor, a longer wavelength than the light emitting wavelength and absorbing at least a portion of the emission wavelength from the onset <br/> optical device A method for forming a light-emitting diode comprising an inorganic fluorescent substance that emits fluorescent light, and a resin having a specific gravity different from that of the inorganic fluorescent substance, wherein a light-curing catalyst is added, and the light-curing resin uniformly mixes the inorganic fluorescent substance. coated on the light-emitting element with stirring, a method of forming the light-emitting diodes, characterized in that is cured by irradiating light energy of the light emitting element to the light-curable resin.