JP3316838B2 - Light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device used as a light source or an indicator of various sensors such as a display capable of displaying various data, a line sensor, etc. The present invention relates to a highly reliable light emitting device.

[0002]

2. Description of the Related Art At present, LED chips capable of emitting ultra-high brightness of over 1000 mcd in RGB (red, green, blue) have been developed. Along with this, an LED display capable of full-color display can be provided by using LED chips capable of emitting light of RGB (red, green, and blue) to emit mixed colors. More specifically, it is being used for full-color large-sized video devices and character display boards used indoors and outdoors. In order to display complicated characters such as JIS second-level kanji, a particularly high-definition display is required. In addition, for applications such as destination display boards both indoors and outdoors, it is required that the display be visible from a fairly wide angle.

A light emitting device in which an LED chip is arranged in a ceramic package can be considered as a light emitting device capable of achieving high definition, a high viewing angle, and being small and thin. FIG. 1 is a schematic perspective view of a dot matrix LED display using such a ceramic substrate. A ceramic-based package can be formed relatively easily by firing a multilayered raw material called a green sheet. A light emitting device having an LED bare chip mounted on the bottom of the package can achieve a high definition of 6 mm pitch or less by mounting the LED chips at high density.

[0004] In addition, the higher the definition, the larger the amount of heat generated from the LED chip. However, since the heat dissipation of the ceramic is good, the reliability of the LED chip can be ensured. Further, in the case of using ceramic, wiring can be easily formed simultaneously with package formation by printing tungsten paste or the like on a green sheet. Therefore, high-density wiring can be performed in a relatively high-definition dot matrix shape or the like. Since a concave opening is easily formed in a ceramic substrate, there is an advantage that resin sealing for protecting an LED chip mounting portion can be easily performed. By directly mounting the LED bare chip, the omnidirectional light emission of the LED chip can be used as compared with the shell type LED lamp, so that a display with a high viewing angle can be manufactured.

[0005]

However, due to the ceramic composition and the denseness of the sintered body, the ceramic transmits a certain amount of light. Therefore, as shown in FIG.
Light emitted in the direction of the D chip side surface partially enters the ceramic side wall portion. Light that has entered the ceramic side wall portion is transmitted through the surface layer while being scattered. for that reason,
When a light emitting device such as a display is observed from the front, a weak ring-shaped light emission is observed on the outer periphery of the concave opening. This causes a decrease in contrast in a light emitting device using a ceramic package.

[0006] Similarly, it is considered that light loss in the ceramic package increases. Further, the ceramic package and the organic resin as the coating member have poor adhesion. Further, ceramic has a significantly different coefficient of thermal expansion from the coating member. Therefore, there is a problem that the coating material is easily prevented from peeling off due to thermal stress during the temperature cycle. Therefore, an object of the present invention is to solve the problems in a light emitting device using a ceramic substrate and provide a highly reliable light emitting device having high contrast, excellent light emission rate, and high reliability.

[0007]

According to the present invention, there is provided a substrate having a conductor wiring disposed therein and having a concave opening, an LED chip electrically connected to the conductor wiring in the concave opening,
A light emitting device in which the concave opening is sealed with a coating member, wherein a first metal layer composed of high melting point metal particles is formed on a side wall of the concave opening, and a first metal layer is formed on the first metal layer. This is a light emitting device having two metal layers. Further, the first metal layer is a deposition of refractory metal particles, and the second metal layer is a metal plating layer that reflects at least 90% or more of light from the LED chip. Further, the light-emitting device is a light-emitting device in which the average particle diameter of the high-melting-point metal particles is 0.3 to 100 μm, and the light-emitting device in which the conductor wiring and the first metal layer material are substantially the same.

[0008]

According to the present invention, a metal layer that reflects light from an LED chip is functionally separated into adhesion and reflection with ceramics and the like. Specifically, the adhesion can be improved by using the metal particles as the first metal layer. Moreover, the second metal layer provided on the side wall of the concave opening can improve the light reflection efficiency. That is, by providing the first and second metal layers on the side wall of the concave opening, light loss that has entered the ceramic package can be reduced. Also, since light emission other than inside the concave opening is prevented,
It has become possible to improve the contrast of displays and the like.

In printing the side wall of the green sheet opening, the viscosity of the paste containing the refractory metal is adjusted so that the side wall conductor layer for reflection is not only in a vertical shape but also in a concave tape shape. Alternatively, by forming a concave curved surface shape, it is possible to further improve the reflection efficiency and the like. Similarly, the flatness of the reflective layer surface can be changed by adjusting the particle size of the metal powder contained in the conductor paste at the time of side wall printing. Thereby, a light scattering effect can also be provided.

Although the adhesion between the ceramic substrate and the organic resin as the coating member is originally poor, the adhesion can be improved by controlling the surface roughness of the side wall portion of the present invention. As a result, it is possible to expect an effect of improving reliability such as improvement of sealing airtightness and prevention of peeling of a coating material due to thermal stress during a temperature cycle.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of various experiments, the inventor of the present invention has found that by performing wall surface treatment inside a concave opening in a ceramic package, the light emission characteristics and reliability can be significantly improved. It came to be.

That is, in a light emitting device using a ceramic material for a package, a metal layer is formed on at least a part of an opening wall surface of the light emitting device to control ring-shaped light emission that passes through the ceramic and occurs on a light emission observation surface side. it can. In particular, when a metal layer is formed integrally with the ceramic, it is preferable to use a high melting point metal. However, the refractory metal does not always reflect light from the LED chip efficiently. According to the present invention, efficient light emission and reliability can be achieved by separating the function of adhesion and reflection with ceramic. In addition, by selecting the unevenness of the side wall surface, the adhesiveness with the coating member can be controlled, and even when the resin is thermally expanded, peeling of the coating portion is small and reliability is improved.

[0013] Specifically, a resin paste containing tungsten is printed in a desired shape on a green sheet. A green sheet having the openings aligned is laminated in multiple layers and heated and pressed in a vacuum to form a concave opening. A resin paste containing tungsten is applied to the side wall of the concave opening. By adjusting the viscosity, a concave curved surface shape opened to the outside can be obtained. By firing such a green sheet, a ceramic package is formed. An LED chip is die-bonded to the bottom of the concave opening of the ceramic package with an epoxy resin. The electrode of the LED chip and the conductive pattern provided on the ceramic package are wire-bonded. The light emitting element of the present invention can be formed by injecting and curing an epoxy resin in the opening. Hereinafter, constituent elements of the present invention will be described in detail.

(Ceramic packages 201, 301)
Ceramic package 201, 3 used in the present invention
01 means that the LED chips 206, 30
6 is made of a ceramic material to protect the LED chip 6, and has a LED chip disposed therein and a member for electrically connecting the LED chip to the outside. Specifically, 90 to 96% by weight of the raw material powder is alumina, and 4 to 10% by weight of viscosity, talc, magnesia, calcia, silica or the like is added as a sintering aid.
40-60% by weight of ceramics and raw material powder sintered in the temperature range of 500-1700 ° C. are alumina, and 60-40% by weight as a sintering aid are added borosilicate glass, cordierite, forsterite, mullite, etc. 800
Ceramics sintered in the temperature range of -1200 ° C are exemplified.

Such a package can take various shapes at the green sheet stage before firing. The wiring in the package is screen-printed into a desired shape using a paste-like material in which a high-melting-point metal such as tungsten or molybdenum is contained in a resin binder. This becomes wiring by ceramic firing. By laminating the opened green sheets in multiple layers, the openings for containing the LED chips can be freely formed. Therefore, it is also possible to form a stepped side wall of the opening by laminating green sheets having different circular or elliptical shapes or different hole diameters when viewed from the light emission observation surface side. The first metal can also be formed by applying, for example, a resin paste containing a high melting point metal that forms the wiring to the side wall. By sintering such a green sheet, a package formed of ceramics can be obtained. The green sheet itself can be made darker by including Cr ₂ O ₃ , MnO ₂ , TiO ₂ , Fe ₂ O _3, etc. in the green sheet itself.

The concave opening of the package has an LED chip, a conductive wire and the like arranged therein.
Therefore, it is only necessary that the LED chip be large enough to be directly mounted on the die bonding device or the like, and be electrically connected to the LED chip by wire bonding or the like. Two or more concave openings can be provided as desired. Specifically, 16x16 or 24x2
Various selections such as a dot matrix of 4 or a linear shape can be made. When the dot pitch of the concave opening is 4 mm or less, the dot pitch can be greatly reduced as compared with the case where a bullet-type LED lamp is mounted. Further, the configuration of the present invention can solve various problems related to the heat radiation from the LED chip even in such a high minuteness. The bonding between the LED chip and the bottom of the package can be performed with a thermosetting resin or the like. Specifically, an epoxy resin, an acrylic resin, an imide resin, and the like can be given. In order to electrically connect to a wiring such as a face-down LED chip, an Ag paste, an ITO paste, a carbon paste, a metal bump, or the like can be used.

(First Metal Layers 202 and 302) The first metal layers 202 and 302 are formed in direct contact with the ceramic package and serve as a base for forming the second metal layer. Therefore, it is necessary that the first metal layer formed at the same time as the ceramic firing as described above does not melt at the time of forming the ceramic. Such first
Examples of the high melting point metal used for the metal layer include tungsten, chromium, titanium, cobalt, molybdenum, and alloys thereof. The first metal layer can be formed by mixing these metal particles with the resin paste, applying or printing on the side wall of the concave opening of the green sheet, and firing the green sheet together with the green sheet. By controlling the particle size of the metal particles, it is possible to control the adhesion to the ceramic, the second metal formed on the first metal, and also the coating member formed thereon. The surface roughness of the second metal formed thereon can be controlled by the metal particle size used for the first metal. Therefore, the particle diameter of the first metal particles is 0.3
To 100 μm, preferably 1 to 20 μm
Is more preferred.

Further, by adjusting the viscosity of the resin paste containing the metal particles used for the first metal layer, the shape of the side wall of the ceramic package can be variously controlled. That is, as long as the ceramic package is a stack of green sheets, it is difficult to make the opening side walls tapered. Therefore, even if a metal layer is simply formed, it is not possible to form a shape having high reflectance over the entire surface.

In the present invention, by adjusting the viscosity of the paste containing the high melting point metal particles according to the viscosity, the ceramic package can be formed into a linear taper shape or a concave curved surface shape opened from the inside to the outside of the ceramic package. .
The side wall extending toward the opening can further improve the reflectance. The side wall shape of the concave opening is LED
In order to avoid loss of light emission from the chip, it may have a linear taper angle or curved surface suitable for optical reflection, or a stepped shape. In order to make the shape of such a side wall reflective layer into a tapered shape or a concave curved surface shape, a viscosity of 5000 to 2
In the range of 0000 ps, it is possible to suitably form by adjusting the printing speed variously.

As a method of forming the reflective conductor layer other than the side wall printing, the center of the opening is opened with a laser to the extent that the conductor layer is left on the side wall after the conductor paste is completely flowed into and embedded in the opening of the green sheet. A method of opening may be used. In this case, as the laser light source, a carbon dioxide gas laser, a YAG laser, an excimer laser, and the like are preferably mentioned. Further, the first metal layer does not necessarily need to be formed on the entire side wall. By not forming the first and second metal layers partially, light is reflected only in a desired direction. The portion where the metal layer is not formed appears to spread light through the ceramic. By partially forming the metal layer formed on the side wall in this manner, the viewing angle can be widened in a desired direction.

(Second Metal Layers 203 and 303) The second metal layers 203 and 303 of the present invention correspond to the first metal layer 20.
2, 302, and has a reflection function for efficiently extracting the light emitted from the LED chips 206, 306 to the outside. Such a second metal layer can be relatively easily formed on the first metal layer by using plating, vapor deposition, or the like. As the second metal layer, specifically, 90% of the light emitted from the LED chip such as gold, silver, platinum, copper, aluminum, nickel, palladium, their alloys, and their multilayer films is used.
A metal having the above-mentioned reflectance is preferably exemplified.

The second metal layer can be formed simultaneously with the surface treatment of the conductor wiring pattern wired in the ceramic package. That is, the conductor wiring provided on the ceramic package is formed of Ni
/ Ag or Ni / Au may be plated simultaneously with the formation of the second metal layer. Alternatively, electroplating may be performed separately on the formation of the second metal layer and the surface of the conductive wiring.

(LED Chips 206, 306) The LED chips 206, 306 used in the present invention are formed on a substrate by GaAlN, ZnS, ZnSe, SiC, GaP, Ga
AlAs, AlN, InN, AlInGaP, InGa
A light emitting layer formed of a semiconductor such as N, GaN, or AlInGaN is used. As a semiconductor structure,
Homo structure having MIS junction, PIN junction and PN junction,
Examples include a heterostructure or a double heterostructure. The emission wavelength can be variously selected from ultraviolet light to infrared light depending on the material of the semiconductor layer and the degree of mixed crystal thereof. The light-emitting layer may have a single quantum well structure or a multiple quantum well structure in which a quantum effect occurs.

In consideration of outdoor use, it is preferable to use a gallium nitride-based compound semiconductor for green and blue as a high-luminance semiconductor material, and a gallium-aluminum-arsenic-based semiconductor or aluminum-indium-based semiconductor for red. It is preferable to use a gallium-phosphorus semiconductor, but it goes without saying that various semiconductors can be used depending on the application.

When a gallium nitride compound semiconductor is used, sapphire, spinel, SiC, S
Materials such as i, ZnO, and GaN single crystal are used. In order to form gallium nitride having good crystallinity with good mass productivity, a sapphire substrate is preferably used. An example of an LED chip using a nitride-based compound semiconductor will be described. A buffer layer such as GaN or AlN is formed on a sapphire substrate. A first contact layer of N- or P-type GaN, an active layer of an InGaN thin film having a quantum effect,
Or a cladding layer of N-type AlGaN, P or N
It is possible to adopt a configuration in which the second contact layers of GaN are sequentially formed. Gallium nitride-based compound semiconductors exhibit N-type conductivity without being doped with impurities. When a desired N-type gallium nitride semiconductor is formed, such as to improve luminous efficiency, Si,
It is preferable to appropriately introduce Ge, Se, Te, C, and the like.

On the other hand, when a P-type gallium nitride semiconductor is formed, a P-type dopant such as Zn, Mg, Be, C
a, Sr, Ba and the like are doped. Gallium nitride based semiconductors are difficult to become P-type only by doping with a P-type dopant, and thus, after introducing the P-type dopant, annealing by heating in a furnace, low electron beam irradiation, plasma irradiation, or the like is performed.
It needs to be typed. The semiconductor wafer thus formed is partially etched to form positive and negative electrodes. Thereafter, the semiconductor wafer is cut into a desired size to form LED chips.

A plurality of such LED chips can be used as desired, and the combination thereof can improve the color mixing in white display. For example, two LED chips that can emit green light and one LED chip that can emit blue light and red light can be used. In order to use the device as a full-color light emitting device for a display device, the emission wavelength of red light is 610n.
m to 700 nm, green emission wavelength from 495 nm to 565 nm, blue emission wavelength from 430 nm to 490
It is preferably nm.

(Coating members 205 and 305) The coating members 205 and 305 are disposed in the openings of the ceramic package, and protect the LED chips from external force or moisture from the external environment and light from the LED chips. Is to be efficiently released to the outside. As a specific material constituting such a coating member, a transparent resin having excellent weather resistance, such as an epoxy resin, a urea resin, or silicone, or glass is preferably used. When the LED chips are arranged at a high density, it is more preferable to use an epoxy resin, a silicone resin, or a combination thereof in consideration of the disconnection of the conductive wire due to thermal shock. Further, a diffusing agent may be contained in the coating member in order to further increase the viewing angle. As a specific diffusing agent, barium titanate, titanium oxide, aluminum oxide, silicon oxide, or the like is suitably used. In addition, an organic or inorganic coloring dye or coloring pigment can be contained for the purpose of cutting off an undesired wavelength. Further, a fluorescent substance that converts the wavelength of at least a part of the light from the LED chip can be included.

(Conductive Wire) The conductive wire is one kind of an electrical connection member for connecting the electrode of the LED chip and the conductor wiring provided on the ceramic package. Good conductivity and heat conductivity are required. The thermal conductivity is 0.
It is preferably at least 01 cal / cm ² / cm / ° C., more preferably at least 0.5 cal / cm ² / cm / ° C.
Also, considering the workability, etc., the diameter of the conductive wire is
Preferably, it is Φ10 μm or more and Φ45 μm or less.
Specifically, as such a conductive wire, gold, copper,
Examples include conductive wires using metals such as platinum and aluminum and alloys thereof. Such a conductive wire can easily connect an electrode of each LED chip to a conductive pattern or the like provided on a substrate by a wire bonding device. Hereinafter, specific examples of the present invention will be described in detail, but it goes without saying that the present invention is not limited thereto.

[0030]

【Example】

(Embodiment 1) As a light-emitting device, one dot matrix was used.
A ceramic package having a 6 × 16 concave opening was used. The concave opening was formed by laminating a perforated green sheet having no wiring layer when forming the ceramic package. The wiring layer was formed by screen-printing a tungsten-containing resin paste into a desired shape. (Note that tungsten has an average particle size of about 1 μm. The viscosity of the resin paste is about 3000.
0 ps. )

The green sheets having the aligned openings were superimposed and heated and pressed in a vacuum to form them temporarily. After the opening was formed, a tungsten resin paste for forming the first metal layer was applied to the side wall of the opening. For the first metal layer, the same tungsten particles as those used for the wiring layer were used. The viscosity of the tungsten paste printed on the side wall was about 10,000 ps, and the viscosity was slightly reduced so that it could easily flow in during the side wall printing. The green sheet for electrically insulating the first metal layer and the conductor wiring pattern has a thickness of 15 mm.
The configuration was such that the reflectance did not decrease at about 0 μm.

By sintering this, a ceramic package having the first metal layer formed thereon was formed. Next, as a second metal layer, a Ni / Ag multilayer film was electroplated on the exposed surfaces of the first metal layer and the conductor wiring pattern, respectively. Thereby, the dot pitch of the concave opening is 3.0 mm, the opening diameter is 2.0 mm, and the opening depth is 0.8.
A ceramic package having a total length of 48 mm square of a 16 mm × 16 × 16 dot matrix was formed. A partial cross section of the ceramic package had a concave curved surface shape opened outward as shown in FIG. For electrical extraction from the ceramic package to external electrodes, connection pins made of metal Kovar were formed by silver brazing.

On the other hand, an InGaN semiconductor having a main emission peak of 450 nm was used as an LED chip as a semiconductor light emitting element. In the LED chip, a TMG (trimethyl gallium) gas, a TMI (trimethyl indium) gas, a nitrogen gas, and a dopant gas are flowed together with a carrier gas on a cleaned sapphire substrate, and a gallium nitride-based compound semiconductor is formed by MOCVD. Formed. By switching between SiH ₄ and Cp ₂ Mg as the dopant gas, a gallium nitride semiconductor having N-type conductivity and a gallium nitride semiconductor having P-type conductivity were formed, and a PN junction was formed. (Note that the P-type semiconductor is annealed at 400 ° C. or higher after film formation.)

After exposing the surface of each PN semiconductor by etching, each electrode was formed by sputtering. After a scribe line was drawn on the semiconductor wafer thus completed, the wafer was divided by external force to form LED chips as light emitting elements. The LED chip capable of emitting blue light was die-bonded with epoxy resin to a predetermined bottom in the opening of the ceramic package, and then fixed by thermosetting. Thereafter, the gold wire was wire-bonded to each electrode of the LED chip and the wiring on the substrate to establish electrical connection. LED silicone resin
The chips were respectively injected into the concave openings where the chips were arranged. After the injection, the silicone resin was cured at 130 ° C. for 1 hour to form a coating member. At this time, the light emitting device has a ceramic package thickness of about 2.0 mm.
However, it was possible to significantly reduce the thickness as compared with a display device using a bullet-type LED lamp.

The light emitting device and a RAM (Random, Acces) for temporarily storing input display data.
s, Memory) and data stored in the RAM, a gradation control circuit for calculating a gradation signal for lighting the LED chip to a predetermined brightness, and each LED chip is switched by an output signal of the gradation control circuit. The drive means of the CPU provided with a driver for turning on the light is electrically connected. Even if power was continuously supplied to the light emitting device for 500 hours, there was almost no change in the light emitting characteristics. Next, the driving circuit was removed, and a gas phase thermal shock test was performed using only the light emitting device. Gas phase thermal shock test, temperature -40 ℃ time 30m
500 cycles of gas phase thermal shock were performed with one cycle of in and temperature of 100 ° C. for 30 min. Peeling of the coating member in the opening after the gas phase thermal shock test was not confirmed. Peeling was not confirmed in all the openings, and the device could be driven again as an LED display device.

Comparative Example 1 A gas-phase thermal shock test was conducted in the same manner as in Example 1 except that the second metal layer was formed by vapor deposition without forming the first metal layer of the present invention. Was. The metal layer was formed on the vapor deposition surface in a stepwise manner, and there was a portion that did not light up after the gas phase thermal shock test. As a result of examining the unlit portion, it was confirmed that the coating portion was floating and the conductive wire was broken.

[0037]

According to the present invention, a light emitting device having a high viewing angle, a high definition, a small size and a low thickness, and a high reliability can be obtained.
In particular, by adopting the structure of the first aspect, it is possible to provide a light emitting device that efficiently reflects light from the LED chip and is compatible with adhesion to a coating portion or the like. Therefore, it has the effects of improving the adhesion between the coating resin and the ceramic package, such as water resistance and relaxing stress during temperature cycling.

By adopting the structure described in claim 2 of the present invention, a light emitting device having a high luminous efficiency and good mass productivity can be obtained.

According to the third aspect of the present invention, a highly reliable light emitting device can be obtained.

By adopting the structure described in claim 4 of the present invention, a light emitting device with higher mass productivity can be obtained.

[0041]

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a ceramic package.

FIG. 2 is a partial cross-sectional view of the light emitting device of the present invention in the cross-sectional direction of FIG. 1A-A.

FIG. 3 is a partial sectional view of another light emitting device used in the present invention.

FIG. 4 is a partial cross-sectional view of a light emitting device shown for comparison with the present invention.

[Description of sign]

 201, 301 ... ceramic package 202, 302 ... first metal layer 203, 303 ... second metal layer 204, 304 ... conductor wiring 205, 305 ... coating member 206, 306 ..LED chip 401 ・ ・ ・ Ceramic package 404 ・ ・ ・ Conductor wiring 405 ・ ・ ・ Coating member 406 ・ ・ ・ LED chip

Claims (4)

(57) [Claims] 1. A ceramic package having a conductive wiring disposed therein and having a concave opening, an LED chip electrically connected to the conductive wiring in the concave opening, and the concave opening formed by a coating member. A sealed light emitting device, comprising: a first metal layer composed of high melting point metal particles on the side wall of the concave opening; and a second metal layer on the first metal layer. Light emitting device. 2. The light emitting device according to claim 1, wherein said first metal layer is a deposition of refractory metal particles, and said second metal layer is a metal plating layer which reflects at least 90% or more of light from an LED chip. apparatus. 3. The high melting point metal particles have an average particle size of 0.3.
The light emitting device according to claim 2, wherein the thickness of the light emitting device is from 100 μm to 100 μm. 4. The light emitting device according to claim 1, wherein said conductor wiring and said first metal layer material are substantially the same.