JP2013197505A - Light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting device comprising a particle layer in which light absorption by a lead frame is suppressed and light emission from an LED chip is not shaded.SOLUTION: A light-emitting device 1 comprises a lead frame 2, an LED chip 4 which is formed on the lead frame 2 and includes a light-emitting layer 13, and a particle layer 3 which is formed on the lead frame 2 and comprised of a group of inorganic filler particles of which the light absorption rate is lower than that of the lead frame 2, and in which a height of a top face of a portion right above the lead frame 2 is lower than a height of a bottom face of the light-emitting layer 13.

Description

  The present invention relates to a light emitting device.

  Conventionally, a light-emitting device in which an LED chip is mounted on a lead frame is known. However, if a part of light emitted from the LED chip is absorbed by the lead frame, there is a problem in that the light emission intensity of the light-emitting device decreases. is there.

  As a conventional light emitting device, a substrate having a recess, a light emitting element disposed in the recess of the substrate, and a reflectance of a member formed on at least a part of the exposed portion in the recess to form the recess There is known a light emitting device including a particle layer made of particles having a higher reflectance (see, for example, Patent Document 1).

  According to Patent Document 1, the light extraction efficiency of the light emitting device can be improved by using a particle layer made of particles having a high reflectance.

JP 2007-173408 A

  However, in the light emitting device described in Patent Document 1, since a highly reflective particle layer is formed on the upper surface of the LED chip, the light emitted upward from the LED chip is blocked, and the light emission intensity of the light emitting device. Has the disadvantage of lowering.

  Accordingly, one object of the present invention is to provide a light emitting device having a particle layer that suppresses light absorption by the lead frame and does not block light emission from the LED chip.

  To achieve the above object, according to one embodiment of the present invention, a lead frame, an LED chip having a light emitting layer formed on the lead frame, and a light absorption layer formed on the lead frame that absorbs light more than the lead frame. There is provided a light emitting device comprising a group of inorganic filler particles having a low rate, and a particle layer in which a height of an upper surface of a portion immediately above the lead frame is lower than a height of a bottom surface of the light emitting layer.

  In the light emitting device, the particle layer preferably does not contact a side portion of the LED chip.

  In the light emitting device, the LED chip may be formed on the lead frame via the particle layer.

  In the light emitting device, the particle layer may include at least one kind of particles of barium sulfate particles, barium carbonate particles, magnesium carbonate particles, and silicon oxide particles as the inorganic filler particles.

  ADVANTAGE OF THE INVENTION According to this invention, the light-emitting device which has a particle layer which suppresses the light absorption by a lead frame and does not block light emission from an LED chip can be provided.

FIG. 1 is a vertical sectional view of a light emitting device according to an embodiment. FIG. 2A is a vertical cross-sectional view when the LED chip is a face-up type. FIG. 2B is a vertical cross-sectional view when the LED chip is a flip chip type. 3A and 3B are vertical cross-sectional views illustrating an example of the positional relationship between the particle layer and the LED chip according to the embodiment. FIG. 4 is a graph showing the relationship between the application rate of the particle layer composed of barium sulfate and the increase rate of the light extraction efficiency of the light emitting device according to the example.

Embodiment
FIG. 1 is a vertical sectional view of a light emitting device according to an embodiment. The light-emitting device 1 includes a reflector 6 having a recess, a lead frame 2 formed on the bottom of the recess of the reflector 6, an LED chip 4 formed on the lead frame 2, and a particle layer formed on the lead frame 2. 3 and a sealing resin 7 which is formed in the recess of the reflector 6 and seals the LED chip 4.

  The lead frame 2 is made of Ag, for example.

  The particle layer 3 is composed of a group of inorganic filler particles having a light absorption rate lower than that of the lead frame 2. For example, when the lead frame 2 is made of Ag with a light absorption rate of 11.8% at a wavelength of 450 nm, the particle layer 3 is a group of inorganic filler particles whose light absorption rate at a wavelength of 450 nm is lower than 11.8%. Consists of.

When the lead frame is made of Ag, the inorganic filler particles of the particle layer 3 are barium sulfate (BaSO ₄ ) particles, barium carbonate (BaCO ₃ ) particles, magnesium carbonate (MgCO ₃ ) particles, and silicon oxide (SiO ₂ ) particles. At least one kind of particles can be used.

Here, the absorptance of light (blue light) with a wavelength of 450 nm of Ag, BaSO ₄ , BaCO ₃ , MgCO ₃ , and SiO ₂ is 11.8%, 0.0%, 1.0%, 3.8, respectively. % And 1.9%. Moreover, the absorptance of light (green light) with a wavelength of 550 nm of Ag, BaSO ₄ , BaCO ₃ , MgCO ₃ , and SiO ₂ is 8.0%, 0.0%, 1.4%, and 0.4%, respectively. 1.8%. These absorptances are obtained by dividing the difference between the number of photons of incident light and reflected light by the number of photons of incident light.

  In order for the particle layer 3 not to disturb the light emission of the LED chip 4, the height of the upper surface of the portion immediately above the lead frame 2 of the particle layer 3 is lower than the height of the bottom surface of the light emitting layer 13 of the LED chip 4 described later. For this reason, for example, the particle layer 3 does not reduce the light emission intensity of the LED chip 4 by covering the side surface of the light emitting layer 13 or the upper surface of the LED chip 4.

  The particle size of the inorganic filler particles constituting the particle layer 3 is smaller than the height from the top surface of the lead frame 2 to the bottom surface of the light emitting layer 13 of the LED chip 4 in order to satisfy the above conditions.

  The particle layer 3 is formed, for example, by applying a mixed liquid containing inorganic filler particles onto the lead frame 2 and drying it. The liquid mixture is applied onto the lead frame 2 by, for example, application using a needle, spraying of the liquid mixture by an ink jet method, and potting of a slurry solution.

  The LED chip 4 has a light emitting layer sandwiched between an n-type semiconductor layer and a p-type semiconductor layer. The LED chip 4 may be a face-up type or a flip chip type.

  FIG. 2A is a vertical sectional view when the LED chip 4 is a face-up type. FIG. 2B is a vertical cross-sectional view when the LED chip 4 is a flip chip type. The LED chip 4 includes a substrate 11 made of sapphire, an n-type semiconductor layer 12, a light emitting layer 13, a p-type semiconductor layer 14, an electrode 15, and pad electrodes 16a and 16b.

  The substrate 11 is, for example, a sapphire substrate.

  The n-type semiconductor layer 12 has, for example, a stacked structure including an n-type contact layer, an n-type ESD layer, and an n-type cladding layer, and each of these layers is made of n-type GaN containing an n-type dopant such as Si.

  The light emitting layer 13 has, for example, a multiple quantum well structure in which quantum well layers and barrier layers are alternately stacked and each quantum well layer is sandwiched between barrier layers. The quantum well layer is made of InGaN, and the barrier layer is made of GaN or AlGaN.

  The p-type semiconductor layer 14 has, for example, a stacked structure including a p-type cladding layer and a p-type contact layer, and each of these layers is formed of p-type GaN containing a p-type dopant such as Mg.

  In the case where the LED chip 4 is a face-up type, the electrode 15 is formed of a material having excellent light transmittance, such as ITO (Indium Tin Oxide). Further, when the LED chip 4 is a flip chip type, it is formed of Ag or the like, for example.

  The pad electrodes 16a and 16b have, for example, a structure in which an Au film is plated on a Ni film. When the LED chip 4 is a face-up type, the pad electrodes 16a and 16b are connected to the lead frame 2 via wires 17, and when the LED chip 4 is a flip-chip type, the lead frame is connected via bumps 18. 2 is connected.

  A dotted line in FIGS. 2A and 2B represents the height of the bottom surface of the light emitting layer 13. As described above, the height of the upper surface of the portion immediately above the lead frame 2 of the particle layer 3 is lower than the height of the bottom surface of the light emitting layer 13. The height of the bottom surface of the light emitting layer 13 when the LED chip 4 is a face-up type is, for example, 150 μm, and the height of the bottom surface of the light emitting layer 13 when the LED chip 4 is a flip chip type is, for example, 50 μm.

  FIGS. 3A and 3B are vertical sectional views showing an example of the positional relationship between the particle layer 3 and the LED chip 4. FIG. 3A shows a configuration in which the LED chip 4 is formed on the lead frame 2 via the particle layer 3.

  FIG. 3B shows a configuration in which the particle layer 3 is in contact with the side portion of the LED chip 4. In this case, since the distance between the portion of the particle layer 3 in contact with the side portion of the LED chip 4 and the light emitting layer 13 is short, the light reflected from this portion is easily incident on the light emitting layer 13 and absorbed. Therefore, it is preferable that the particle layer 3 does not contact the side part of the LED chip 4 as in the configuration shown in FIGS. 2 (a) and 2 (b) and FIG. 3 (a).

  The sealing resin 7 is made of a transparent resin such as a silicone resin or an epoxy resin. Further, the sealing resin 7 may include dispersed phosphors 8 as shown in FIG. In addition, the fluorescent substance 8 may be arrange | positioned so that it may sink on the particle layer 3 of the bottom of the sealing resin 7, and what was disperse | distributed and what was sunk may coexist.

  Using a particle layer composed of barium sulfate particles, the relationship between the coverage of the particle layer and the luminous efficiency of the light emitting device was investigated. As a comparative example, the luminous efficiency of the light emitting device was examined using a particle layer composed of titanium oxide particles.

(Manufacture of light emitting devices)
First, 13 light emitting devices having a reflector, a face-up type LED chip, and a lead frame made of Ag were prepared.

  Next, 0.2 g of barium sulfate particles, 0.4 g of water, and 0.4 g of ethanol were mixed to obtain a mixed solution containing barium sulfate particles. Moreover, 0.2 g of titanium oxide particles, 0.4 g of water, and 0.4 g of ethanol were mixed to obtain a mixed solution containing titanium oxide particles.

  The particle diameters of the barium sulfate particles used in this example were D10, D50, D90, and the maximum particle diameters were 1.6 μm, 2.8 μm, 5.5 μm, and 15.2 μm, respectively. The particle diameters of the titanium oxide particles were D10, D50, D90, and the maximum particle diameters were 0.4 μm, 1.1 μm, 3.1 μm, and 34.3 μm, respectively. Here, D10, D50, and D90 represent the particle sizes when the undersize accumulation (cumulative total from those having a small particle size) is 10%, 50%, and 90%.

  Next, the obtained liquid mixture was apply | coated on the lead frame using the needle. At this time, the mixed liquid containing barium sulfate particles is applied to the lead frames of the ten light emitting devices at different application rates, and the titanium oxide is applied to the lead frames of the two light emitting devices at different application rates. A mixed solution containing particles was applied. None of the mixed solutions was applied to the lead frame of the remaining one light emitting device.

  Next, the light emitting device was dried at room temperature. Next, after prebaking at 140 ° C. for 40 minutes to the light emitting device, the LED chip was sealed with a sealing resin made of silicone resin. The sealing resin was cured by heat treatment at 150 ° C. for 2 hours.

  As a result, one light emitting device as a reference having no particle layer, and the coating rate of the particle layer composed of barium sulfate particles are 48%, 50%, 65%, 66%, 69%, 74%, Ten light emitting devices of 78%, 82%, 86%, and 100% and two light emitting devices having a coating rate of 60% and 62% of the particle layer composed of titanium oxide particles were obtained.

  Here, the coating rate is the ratio (%) of the particle layer that occupies a region other than the region where the LED chip is mounted from the outside to the center of the surface of the lead frame exposed at the bottom of the concave portion of the reflector. . Of the twelve light emitting devices having a particle layer, those having a particle layer application rate of 100% also formed a particle layer on the LED chip. No particle layer was formed on the LED chips of the remaining 11 light emitting devices.

(Measurement of light emitting device output)
For the 13 light emitting devices described above, output measurement was performed before the particle layer formation and after the resin sealing. The measurement results are shown in Table 1. “Voltage (V)” and “emission wavelength (nm)” in Table 1 are the voltage applied to the LED chip and the emission wavelength of the LED during each measurement.

  The “output ratio” in Table 1 is the ratio between the output after resin sealing and the output before formation of the particle layer. The larger the “output ratio” value, the greater the increase in output due to particle layer formation. The “reference ratio” represents the ratio of the “output ratio” of each light emitting device to the “output ratio” of the light emitting device that does not include a particle layer as a reference.

  As can be seen from Table 1, when a particle layer composed of barium sulfate particles is used, the output of the light emitting device is higher than when the particle layer is not used, and the output is improved as the coating rate of the particle layer increases. However, when the particle layer is formed on the LED chip, the output is lower than when the particle layer is not used even though the coating rate is the highest. As the main cause, it is considered that the particle layer on the LED chip blocks light emitted upward from the light emitting layer of the LED chip.

  Also, when a particle layer composed of titanium oxide particles is used, the output is lower than when no particle layer is used. This is considered to be because the light absorption rate of titanium oxide is higher than the light absorption rate of Ag constituting the lead frame of this example.

  FIG. 4 is a graph showing the relationship between the coating rate of the particle layer composed of barium sulfate and the rate of increase in the light extraction efficiency of the light emitting device. Here, the “increase rate of light extraction efficiency” is a value representing the increase from the “reference ratio” in Table 1 as a percentage. FIG. 4 shows that the rate of increase in light extraction efficiency approaches about 9.4% when the coating rate of the particle layer composed of barium sulfate is brought close to 100%.

  Note that the increase rate of the light extraction efficiency starts to increase from the vicinity of the application rate of 40% because the particle layer is applied from the outer region on the lead frame toward the center. This is probably because there is no particle layer near the chip, and light emitted from the LED chip cannot be efficiently reflected.

  The present invention is not limited to the embodiments and examples described above, and various modifications can be made without departing from the spirit of the invention.

  Moreover, said embodiment and Example do not limit the invention which concerns on a claim. It should be noted that not all combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention.

DESCRIPTION OF SYMBOLS 1 Light emitting device 2 Lead frame 3 Particle layer 4 LED chip 13 Light emitting layer

Claims (4)

A lead frame;
An LED chip having a light emitting layer formed on the lead frame;
Particles formed on the lead frame and made of a group of inorganic filler particles having a light absorption rate lower than that of the lead frame, and the height of the upper surface of the portion immediately above the lead frame is lower than the height of the bottom surface of the light emitting layer Layers,
A light emitting device. The particle layer does not contact the side of the LED chip;
The light emitting device according to claim 1. The LED chip is formed on the lead frame through the particle layer.
The light emitting device according to claim 2. The particle layer includes, as the inorganic filler particles, at least one kind of particles of barium sulfate particles, barium carbonate particles, magnesium carbonate particles, and silicon oxide particles.
The light-emitting device of any one of Claims 1-3.

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