JP4452464B2 - Light emitting diode - Google Patents

Description

The present invention relates to light emitting diodes, and more particularly that Hassu the light emitted from the light emitting diode chip, any emission color by additive color mixing of the wavelength converted light by the phosphor is emitted from the light emitting diode chip emitting The present invention relates to a photodiode.

  A light-emitting diode (LED) is a light-emitting element made of a semiconductor. By applying a bias voltage in the forward direction by bonding a p-type semiconductor and an n-type semiconductor, electrical energy is converted into light energy at the junction (active layer). It is based on the principle that it is converted to emit light. The peak emission wavelength of the LED varies depending on the semiconductor material, but is in the near ultraviolet to visible light to near infrared region, and the emission spectrum has a steep characteristic.

  The LED light emitter (LED chip) has a hexahedron shape with a side length of about 0.5 mm, which is small, has a small amount of emitted light, and has optical characteristics close to a point light source. Have. Therefore, when designing and manufacturing a display element using an LED chip having such characteristics as a light source, the light is emitted from the light emitting surface of the LED chip to the outside of the LED chip with respect to the amount of light emitted from the active layer of the LED chip. A technique has been applied in which the ratio of the amount of light (external quantum efficiency) is increased and the light emitted from the LED chip is collected in one direction to increase the on-axis luminous intensity of the LED.

  Specifically, an LED chip is placed on one of a pair of electrodes disposed on a substrate via a conductive adhesive to achieve electrical conduction, and one end of the other electrode is an LED chip. The other end of the wire connected to is connected to achieve electrical conduction in the same manner. Then, a lens is formed above the LED chip with a light-transmitting resin having a refractive index higher than that of the semiconductor material forming the light emitting surface that emits light from the LED chip, and the LED chip and the wire are resin-sealed. Here, the purpose of sealing the LED chip and the wire with a light-transmitting resin is to protect the LED chip and the wire from mechanical conditions such as vibration and impact and environmental conditions such as moisture, and to emit light in the active layer of the LED chip. The ratio (external quantum efficiency) of the amount of light emitted outside the LED chip from the light emitting surface of the LED chip to the amount of light is increased, and the light emitted from the light emitting surface of the LED chip is guided inside the light-transmitting resin. The light reaching the inner surface of the lens is refracted by the light exit surface of the lens and emitted so as to be collected in one direction, thereby increasing the brightness in the optical axis direction of the LED.

Based on such a basic configuration of an LED, a forward voltage is applied to the LED chip through a pair of electrodes, and the phosphor emits light emitted from the LED chip and emitted from the LED chip to excite the phosphor. There has been proposed an LED that exhibits a white light color by additive color mixing of light that has been converted to a wavelength longer than the wavelength of the irradiated light and light emitted from the LED chip. The specific structure is that one of a pair of electrodes for supplying power to the LED chip from the outside is bonded with an inorganic member such as gold, silver, copper, or aluminum dispersed in a binder such as epoxy resin, silicone resin, polyimide resin, etc. At the same time as placing the LED chip via the agent, one end of a pair of wires connected to each of the pair of electrodes (anode and cathode) provided on the upper surface of the LED chip is connected to the same electrode to Electrical conduction is achieved by connecting the end of the other wire to the other electrode. The LED chip is covered with a wavelength conversion member in which a phosphor is dispersed in a binder such as an elastomer or a gel-like silicone resin, an amorphous fluororesin, or a polyimide resin, and further a mold member made of a light-transmitting resin so as to cover it. It is what is sealed. The external shape of the LED having such a configuration is such that an LED chip is placed on one end of a pair of leads, sealed with a bullet-shaped light-transmitting resin lens, and the lead is inserted into the through hole of the printed circuit board. The LED chip is mounted on a flat board and sealed with a light-transmitting resin, and soldered to the component side of the printed circuit board. It is roughly divided into two types, that is, a fixed mounting type (surface mounting type LED).
(For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 10-228249 (page 2-7, FIG. 1 to FIG. 2)

  The LED emitting white light color described above is different in the material of the binder in which the phosphor is dispersed and the material of the mold member that contacts the binder to form the interface (the material of the light-transmitting resin that becomes the mold member is Separation occurs at the interface between the binder and the mold member due to the difference in shrinkage when the mold member is heated and cured and cooled. As a result, a gap is generated between the binder and the mold member, and the light emitted from the LED chip and the light emitted from the LED chip and wavelength-converted by the phosphor are transmitted along the optical path to the entrance surface of the mold member. As a result, the amount of light decreases until reaching the inner surface of the lens. In addition, the mechanical strength is weakened due to the peeling of the interface between the binder and the mold member, which may cause damage depending on the use environment, and the reliability is impaired.

  Further, optical characteristics for evaluating the performance of the light emitting diode include luminous intensity, luminance, luminous flux divergence, and the like. These photometric quantities indicate how much the luminous flux emitted from the light source exists within a certain range (luminosity and luminance per unit solid angle, and luminous flux divergence per unit area). If the luminous flux is the same, the light emitted from the light source is collected more efficiently as the value of these photometric quantities increases. When this is applied to the vertical LED of the white light color described above, the emission direction of the light emitted from the LED chip extends over the entire upper area of the light emission surface of the LED chip, and the inner surface is defined as the reflection surface. By placing the LED chip on the bottom surface of the bowl-shaped recess, the light that is emitted in the direction substantially perpendicular to the optical axis of the LED chip (substantially lateral direction) and directed toward the bowl-shaped reflection surface is reflected by the reflection surface. It is a general technique to increase the extraction efficiency of light emitted from the LED to the outside in the direction of the lens.

  In this case, the light emitted from the LED chip directly reaches the inner surface of the lens, refracted at the lens-air interface, and emitted to the outside from the light emitting surface of the lens has a substantially line-symmetric distribution around the optical axis. ing. On the other hand, the light emitted from the LED chip, reflected by the bowl-shaped reflecting surface, and emitted to the outside from the light emitting surface of the lens travels in various directions regardless of the optical axis. Therefore, although the extraction efficiency of the light emitted from the LED chip is increased, the light emitted from the LED chip does not contribute to the luminance in the optical axis direction or the luminous flux divergence, so the luminance or luminous flux divergence is insufficient. I have to say that.

  Further, in order to efficiently collect light by using a spherical lens or an aspheric lens, the light source is required to be a point light source, and a hexahedral (dice-shaped) LED chip having an optical system of about 0.5 mm is used as the point light source. To be considered, it is said that the limit of the distance from the LED chip serving as the light source to the lens needs to be 5 mm or more, which is 10 times or more of 0.5 mm, and in the lens, as the distance from the LED chip becomes longer The lens surface area must be large, and the radius of curvature must be large enough to ensure efficient light collection. Therefore, in order to ensure such conditions required for the LED, it is necessary to go back to the downsizing of the LED.

  On the other hand, the surface mount type LED has a very small size as compared with the vertical type LED, so even if a resin lens is formed above the LED chip, the distance from the LED chip to the lens and the radius of curvature are satisfied as an optical system. It cannot be secured as much. Therefore, the lens effect of condensing is small, and the photometric quantity such as luminous intensity, luminance, luminous flux divergence and the like becomes insufficient.

  The present invention has been made in view of the above problems, and provides a light-emitting diode having high light extraction efficiency and high light collection efficiency.

In order to solve the above-mentioned problems, the invention described in claim 1 of the present invention is to seal a light emitting diode chip placed on a substrate with a wavelength conversion member in which a phosphor is dispersed in a first light transmitting resin. sealed, wherein at least the light emitting surface of the wavelength conversion member, Kutsugae設the first light transmitting resin and the second light transmitting resin having a refractive index than that of the second light transmitting resin is dispersed a small number of microbeads However, the brightness is improved .

  For the purpose of improving the light extraction efficiency and light collection efficiency of a small white light emitting diode, a large number of microbeads are placed on the light emitting surface of a light transmitting resin in which a phosphor encapsulating a light emitting diode chip is dispersed. It was realized.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIG. 1 to FIG. 8 (the same parts are given the same reference numerals). The embodiments described below are preferable specific examples of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. As long as there is no description of the effect, it is not restricted to these aspects.

  FIG. 1 is a sectional view showing a first embodiment of the present invention. The LED chip 6 is placed on one of a pair of electrodes 4 for supplying power to the LED chip on the bottom surface 3 of the substrate 2 having a bowl-shaped recess having the inner side surface 1 as a reflection surface via a conductive adhesive 5. The other electrode (not shown) is connected to the other end of the wire 7 whose one end is connected to the LED chip 6 to achieve the same electrical continuity. Then, the wavelength conversion member 9 in which the phosphor 8 is dispersed in the binder of the first light transmitting resin having a refractive index closer to that of the semiconductor material that forms the light emitting surface 11 that emits the light emitted from the LED chip 6 is used as the LED. The LED 12 is formed by filling the mortar-shaped recess on which the chip 6 is placed and sealing the LED chip 6 and the wire 7. At this time, the light emission surface 13 from which the light emitted from the LED chip 6 is guided through the wavelength conversion member 9 and emitted to the outside is formed with continuous unevenness.

  In such an LED 12, by applying a directional voltage to the LED chip 6 through a pair of electrodes 4 electrically connected to a pair of (anode and cathode) electrodes provided on the LED chip 6, The light emitted from the active layer and reaching the light emitting surface 11 is refracted at the interface between the light emitting surface 11 and the first light-transmitting resin having a refractive index closer to the semiconductor material forming the light emitting surface 11. The light is often emitted into the first light transmissive resin, most of which excites the phosphor 8 dispersed in the first light transmissive resin, undergoes wavelength conversion, and reaches the light emission surface 13 of the wavelength conversion member 9. On the other hand, light that is emitted from the LED chip 6 into the first light-transmitting resin and does not contribute to excitation of the phosphor is guided through the first light-transmitting resin and reaches the light emitting surface 13 of the wavelength conversion member 9. Here, the light emitting surface 13 of the wavelength conversion member 9 has an interface formed by the first light-transmitting resin and air, and the refractive index of the first light-transmitting resin is larger than that of air. Therefore, when the light emitting surface 13 of the wavelength converting member 9 is a flat surface, the angle of incidence (incident angle) with the normal of the interface at the incident point out of the incident light rays that are emitted from the LED chip 6 and reach the light emitting surface 13 is critical. When the angle is larger than the angle, the refracted light is totally reflected by the light emitting surface 13 and is not emitted from the LED 12, and the light extraction efficiency is not good. On the other hand, in the first embodiment of the present invention, the light emitting surface 13 of the wavelength conversion member 9 has a continuous uneven shape, and most of the light emitted from the LED chip 6 and reaching the light emitting surface 13. Is emitted from the light emitting surface 13 to the outside of the LED 12. Therefore, an LED having a high light extraction efficiency is made possible.

  As is common to all the embodiments, when the light emitted from the LED chip 6 is blue light, the light emitted from the LED chip 6 and wavelength-converted by the phosphor 8 and the light not wavelength-converted. The color of light emitted from the LED 12 due to the additive color mixture with the white color is white. However, the present invention is not limited to this, and the light emitted from the LED chip 6 may be other colors of visible light, infrared light, or ultraviolet light. You may make it get.

  FIG. 2 is a sectional view showing a second embodiment of the present invention. The basic configuration of the present embodiment is the same as that of the first embodiment, except that the light emitting surface of the wavelength conversion member 9 in which the phosphor 8 is dispersed in the binder of the first light transmitting resin. 13 is that an indeterminate transparent diffusion piece 15 such as powder or flake made of a light transmissive member such as glass or silicone resin is directly covered. In this case, the transparent diffusion piece 15 may be covered on the light emission surface 13 or may be covered in a state where a part of the transparent diffusion piece 15 is embedded in the wavelength conversion member 9 from the light emission surface 13. However, the latter is preferable in consideration of the purpose of covering the transparent diffusion piece 15. As a result, the light emitted from the LED chip 6 and excited by the phosphor 8 and subjected to wavelength conversion, and the light emitted from the LED chip 6 and guided through the first light-transmitting resin are transparent diffusion pieces 15. It is incident on the inside, refracted and emitted to the outside of the LED 12. Therefore, since the ratio of the light that reaches the planar light emitting surface 13 is totally reflected by the light emitting surface 11, the LED 12 with high light extraction efficiency is possible. In this case, the light extraction efficiency is improved as the refractive indexes of the first light-transmitting resin and the transparent diffusion piece 15 are closer.

  FIG. 3 is a sectional view showing a third embodiment of the present invention. In this embodiment, the wavelength changing member in which the transparent diffusion piece 15 of the second embodiment is dispersed in the binder of the second light transmissive resin 16 such as silicone resin and the phosphor 8 is dispersed in the first light transmissive resin binder. 9 is covered with the light emission surface 13. In this case, the light extraction efficiency improves as the refractive index of the first light transmissive resin constituting the wavelength conversion member 9 and the second light transmissive resin 16 serving as the binder of the transparent diffusion piece 15 and the transparent diffusion piece 15 are closer. . The configuration of the present embodiment is an effective method when it is difficult to directly cover the transparent diffusion piece 15 on the light emitting surface 13 of the wavelength conversion member 9.

  FIG. 4 is a sectional view showing a fourth embodiment of the present invention. In this embodiment, a large number of substantially spherical lenses (microbeads) 17 made of a light transmissive member such as glass or silicone resin are dispersed in the binder of the second light transmissive resin 16 in place of the transparent diffusion piece 15 of the third embodiment. It is a thing. In this case, unlike the amorphous transparent diffusion piece 15, light incident on a large number of microbeads at a certain angle is refracted and emitted in a certain direction, so that the light extraction efficiency is good and the light collection efficiency is also high. It will improve. In this case as well, the light extraction efficiency improves as the refractive index between the first light-transmitting resin constituting the wavelength conversion member 9 and the second light-transmitting resin 16 serving as the binder of the microbeads 17 and the microbeads 17 is closer. .

  FIG. 5, FIG. 6 and FIG. 7 show the relationship between the amount of exposure of the microbeads 17 to the air and the light extraction efficiency with respect to the second light-transmitting resin 16 serving as the binder of the microbeads 17 based on the structure of this embodiment. The conditions and results of simulating the above are shown. FIG. 5 shows the simulation conditions. The refractive index of the first light-transmitting resin that disperses the phosphor 8 is 1.50, and the refractive index of the second light-transmitting resin 16 that disperses the microbeads is 1. 50A shows a state in which 25% of the diameter of the microbead having a diameter of 100 μm is exposed from the second light-transmitting resin 16 to the air, and FIG. (C) shows a state in which 75% of the diameter of the microbead having a diameter of 100 μm is exposed in the air from the second light transmissive resin 16. .

  FIG. 6 shows a simulation result (1) of the light extraction efficiency. The light extraction efficiency when the microbeads 17 are not covered is 1.0, and the exposure amount of the microbeads 17 in the air is used as a parameter. The refractive index of beads is plotted on the horizontal axis and the light extraction efficiency is plotted on the vertical axis. The convexity of 50%, the convexity of 25%, and the convexity of 75% indicate that the exposure amount of the microbeads 17 in the air is 50%, 25%, and 75% of the diameter of the microbeads 17, respectively. As a result, the light extraction efficiency is best when 50% of the diameter of the microbeads 17 is exposed to the air, and the refractive index of the first light-transmitting resin and the second light-transmitting resin 16 is particularly high. It can be seen that the light extraction efficiency is better when the refractive index of the microbeads 17 is smaller.

  FIG. 7 shows the simulation result (2). The light extraction efficiency when the microbeads 17 are not covered is 1.0, and the exposure amount of the microbeads 17 in the air is 50% of the diameter of the microbeads 17 ( Convex 50%), the refractive index of the microbeads is plotted on the horizontal axis, the light extraction efficiency is plotted on the vertical axis, and the relationship between the luminous flux emitted from the microbeads 17 and the maximum luminance with respect to the refractive index of the microbeads 17 is shown. is there. The reason why the maximum luminance is used is that the luminance varies depending on the direction in which the light source is observed. As a result, it can be seen that when the refractive index of the microbeads 17 is smaller than the refractive index of the first light-transmitting resin 16 and the second light-transmitting resin 16, more light is emitted from the microbeads 17. This shows the same content as the graph with the exposure amount (convex 50%) of the microbeads 17 in FIG. 6 as a parameter. However, the maximum luminance is maximum when the refractive index of the microbeads 17 is 1.45. This indicates that the refractive index of the microbeads 17 exhibiting the maximum luminance is not determined by the absolute value, but is determined by the relative relationship between the refractive indexes of the first light transmitting resin and the second light transmitting resin 16. .

  In any case, by covering the light emitting surface 13 of the wavelength converting member 9 in which the phosphor 8 is dispersed with the microbeads 17, the total amount of light (light flux) emitted from the LED 12 and the amount of collected light (brightness) are reduced to micro. It has been verified that the increase is 10% or more when the beads 17 are not covered.

  FIG. 8 is a sectional view showing a fifth embodiment of the present invention. The present embodiment shows the configuration of the LED 12 when the microbeads 17 are covered on the outer peripheral portion of the flip chip type LED chip 6. In this structure, a pair of electrodes (bumps) 21 provided on the LED chip 6 are connected and fixed to a pair of electrodes 4 provided on the mounting substrate 20 of the LED 12 to achieve electrical conduction. Then, the outer peripheral portion of the LED chip 6 is sealed with a wavelength conversion member 9 in which the phosphor 8 is dispersed in the first light-transmitting resin, and the microbeads 17 dispersed in the second light-transmitting resin 16 are further provided on the outer side. The microbeads 17 are covered so that 50% of the diameter is exposed to the air.

  As described above in Examples 1 to 5, the high-brightness LED of the present invention has an interface between a wavelength conversion member in which a phosphor is dispersed using a light-transmitting resin as a binder and a Mole resin lens having a different heat shrinkage rate. Therefore, a decrease in light extraction efficiency and a decrease in reliability caused by mechanical vibration, impact, etc. caused by peeling occurring at the interface are avoided. In order to promote downsizing of the LED, a lens having a large radius of curvature is disposed with a distance from the LED chip serving as a light source in order to improve light extraction efficiency and light condensing performance as in the past. If this is difficult, for example, a surface-mount type LED is applicable. However, by making the LED have the configuration of the present invention, light extraction efficiency and light condensing performance comparable to those of the conventional configuration of the LED are ensured. It has excellent effects such as.

1 is a cross-sectional view of a high brightness light emitting diode according to a first embodiment of the present invention. It is sectional drawing of the high-intensity light emitting diode concerning 2nd Example of this invention. It is sectional drawing of the high-intensity light emitting diode concerning 3rd Example of this invention. It is sectional drawing of the high-intensity light emitting diode concerning 4th Example of this invention. It is a fragmentary sectional view showing conditions of simulation, (a) shows the state where 25% of the diameter of the micro lens was exposed in the air, and (b) shows the state where 50% of the diameter of the micro lens was exposed in the air. (C) shows a state in which 75% of the diameter of the microlens is exposed to the air. A simulation result (1) is shown. A simulation result (2) is shown. It is sectional drawing of the high-intensity light emitting diode concerning 5th Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner side surface 2 Board | substrate 3 Bottom surface 4 Electrode 5 Conductive adhesive 6 LED chip 7 Wire 8 Phosphor 9 Wavelength conversion member 11 Light-emitting surface 12 LED
13 Light emission surface 15 Transparent diffusion piece 16 Second light transmitting resin 17 Microbead 20 Mounting substrate 21 Bump

Claims (1)

A light-emitting diode chip placed on a substrate is sealed with a wavelength conversion member in which a phosphor is dispersed in a first light-transmitting resin, and the first light-transmitting resin is formed on at least a light emission surface of the wavelength conversion member. And a light-emitting diode, wherein the second light-transmitting resin in which a large number of microbeads having a refractive index smaller than that of the second light-transmitting resin is dispersed is covered to improve luminance .

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