JP2001168398A - Light emitting diode and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting diode having excellent heat resistance by reducing a thermal stress applied to an LED chip in the diode using the LED chip usable for a writing light source, a light source for a back light or the like of various type indicators, displays or optical printers and a method for manufacturing it. SOLUTION: The light emitting diode comprises conductive wires for respectively electrically connecting at least one of a pair of lead electrodes to the electrodes of an LED chip, and a translucent sealing resin covering the chip and the wires. In this diode, the resin has a first site containing an inorganic filler covering the LED chip and operating as a buffer layer, and a higher translucent second site than that of the first site on the first site.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to various indicators,
The present invention relates to a light emitting diode using an LED chip that can be used as a display, a light source for writing in an optical printer, a light source for a backlight, and the like, and in particular, relates to a light emitting diode excellent in heat resistance that reduces thermal stress applied to the LED chip and a method for manufacturing the same. .

[0002]

2. Description of the Related Art Today, various light emitting devices such as a surface mount type and a shell type are used in various fields. A light emitting diode, which is an example of a light emitting device, has an LED on a substrate serving as a support.
The chip is die-bonded with resin. In addition, each electrode of the LED chip is electrically connected to each other using a wire or the like, and is covered with a translucent sealing resin for protecting the LED chip as required.

As the sealing resin injected into the concave portion of the substrate after die bonding and wire bonding of the LED chip, generally, a resin that is insulative and translucent and is liquid at room temperature is used. As a specific example, a thermosetting resin such as an epoxy resin, an acrylate resin, a urethane resin, a silicone resin, or a polyimide resin, or a thermoplastic resin such as an acrylic resin, a polycarbonate resin, or a polynorbornene resin is used. When a thermosetting resin is used, a light-transmitting resin can be formed by heating for curing the resin.
When a thermoplastic resin is used, a light-transmitting resin can be formed by evaporating the solvent.

A characteristic of the thermosetting resin is that it can be molded by a simple method such as compression molding with a thermosetting reaction at the time of molding, and a hard and strong resin can be obtained. In terms of heat resistance, it is generally superior to thermoplastic resins. As a characteristic of the thermoplastic resin, it is a linear polymer in chemical structure. Further, it can be efficiently processed by extrusion molding and injection molding, and defective moldings can be recycled. Further, it is easier to mold a transparent resin than a thermosetting resin, and is excellent in light transmission.

Next, the LED chips are made of GaAs, Ga
P, GaAlAs, GaN, InGaN, InGaAl
It is composed of a semiconductor light emitting layer such as N. Since the LED substrate made of these semiconductor light emitting layers uses a light-transmitting sealing resin, it is particularly vulnerable to heat compared to an IC substrate or the like among semiconductors, and the generation of thermal stress has been a serious problem. Therefore, improvement has been made by forming a lead electrode or the like which plays a role of heat release.

[0006]

However, in the case of forming a light emitting diode having good mass productivity and high heat resistance in the LED chip used in the present invention and the like, the above method may not be sufficient. For this reason, reflow heat during mounting causes wire opening due to separation due to the difference in thermal expansion coefficient between the LED chip, substrate, and lead electrode and the translucent sealing resin, and the heat cycle performance of other surface-mounted components Inferiority is considered a problem, and an object of the present invention is to improve heat resistance.

[0007]

SUMMARY OF THE INVENTION The present invention provides an LED chip / substrate / substrate on which the reliability of the light emitting diode is a heat conduction path.
Focusing on the thermal stress generated at the interface between the lead electrode and the translucent resin, the components of the translucent sealing resin are changed.

The object of the present invention can be achieved by the following structures (1) to (7) described in more detail. (1) The light-transmitting sealing resin contains an inorganic filler for covering the LED chip and the wire and serves as a buffer layer, and has a higher light-transmitting property on the first portion than on the first portion. A light emitting diode having a second portion. (2) The buffer layer has a linear expansion coefficient of 2 × 10 ⁻⁵ (1 / ° C.).
The light-emitting diode according to (1), wherein the light-emitting diode is not less than 6 × 10 ⁻⁵ (1 / ° C.) and the thickness of the buffer portion is not less than 20 μm and not more than 400 μm on the LED chip. (3) The light emitting diode according to (1), wherein the buffer portion contains at least one inorganic filler selected from silica, boron nitride, calcium phosphate, and a rare earth compound. (4) The light emitting diode according to (1), wherein the LED chip is disposed on a substrate having a concave portion on a surface having a lead electrode, and the translucent sealing resin is disposed in the concave portion. (5) The light emitting diode according to (1), wherein the translucent sealing resin is at least one selected from an epoxy resin, an acrylate resin, a urethane resin, a polyimide resin, an acrylic resin, a polycarbonate resin, and a polynorbornene resin. (6) The buffer has a density gradient of the inorganic filler,
The light emitting diode according to (1), wherein the coefficient of linear expansion continuously approaches the coefficient of linear expansion of the lead electrode as approaching the lead electrode. (7) wire bonding with the lead electrode, the LED chip, and the conductive wire, and the LED chip And a step of causing the inorganic filler in the thermosetting or plastic resin having a lower specific gravity than the inorganic filler obtained by mixing and stirring the inorganic filler on the conductive wire to settle on the LED chip side.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of various experiments, the present inventor has found that when a light-emitting diode in which an LED chip is arranged on a substrate having a concave portion is filled with a light-transmitting sealing resin containing an inorganic filler, the inorganic filler is injected. The present inventors have found that the heat resistance is rapidly improved by sedimentation on the LED chip side to form a buffer layer, and the present invention has been accomplished.

That is, in the light emitting diode according to one embodiment, since the thermal expansion coefficient of the translucent sealing resin is larger than that of the LED chip, the substrate, and the lead electrode, expansion and contraction behavior due to thermal shock occurs, and desired reliability is obtained. Is not obtained, L
The thermal stress generated at the interface between the ED chip / substrate / lead electrode and the translucent resin is suppressed by molding a translucent sealing resin having a buffer portion to improve heat resistance.

Hereinafter, a surface mount type LED will be briefly described as an example of the light emitting diode of the present invention. FIG. 1 shows a schematic sectional view of the present invention. The light-emitting diode 100 in which the LED chip 103 is covered by using a heat-resistant resin that can be insert-molded is used for the substrate 106. Substrate 10 as support
6 is fitted with an internal electrode 105b for electrically connecting the LED chip 103 and the outside. The external electrode 105a is plated with silver to enhance light reflectivity. The LED chip 103 is fixedly locked by die bonding. After that, the electrode provided on the LED chip 103 and the electrode of the substrate are wire-bonded with the gold wire 104, and the light-transmitting resin is injected into the concave portion of the substrate to form the light emitting diode 100.

Since the LED chip used in the present invention has a double hetero structure, a large amount of light is emitted from the light emitting portion. Further, since an LED chip using a nitride semiconductor is difficult to grow a crystal, it is generally formed on a sapphire substrate due to the properties of the nitride semiconductor. Therefore, a positive electrode and a negative electrode are formed on the semiconductor lamination surface side formed on the sapphire substrate. In addition, a full-surface electrode covering almost the front surface of the light emitting layer is formed. The electrode material that can make such ohmic contact is limited, and light is extracted through this metal electrode layer. As the surface-mounted light-emitting diode used in the present invention, a light-emitting diode having a side wall on a substrate and a light-emitting diode having different directivity characteristics by removing the side wall on the substrate can be used. Hereinafter, one embodiment of the present invention will be described in more detail.

The structure of the light emitting diode used in the present invention is as follows.
First, a substrate 106 as a support is made of a heat-resistant resin that can be insert-molded, and a lead electrode 105 is provided as a conductive portion. The lead electrode includes an external electrode 105a and an internal electrode 105b. The lead electrode 105 uses an Ag-plated copper electrode so as not to impair the light extraction efficiency. Next, Al was used as a light emitting element in the concave portion of the substrate 106.
The LED chip 103 made of GaInP is mounted with an Ag paste conductive adhesive using a die bonding device.

Next, the electrode on the light emitting surface side of the mounted LED chip 103 and the lead electrode 105 of the substrate 106 are wire-bonded using a wire bonding device. The wire used is a gold wire 104.

Next, a thermosetting or thermoplastic resin is used as the light-transmitting sealing resin in the present invention, and then the light-transmitting sealing resin containing a sedimentable inorganic filler is disposed on an LED chip. Is implanted into the recessed portion of the substrate 106 thus formed. The sedimentable inorganic filler sediments due to the properties of wettability, particle size, specific gravity, and viscosity and covers the bottom surface of the recess. The sedimentable inorganic filler is more likely to sediment as the wettability with the translucent sealing resin is lower. Further, the sedimentation property increases as the particle size or specific gravity increases and the viscosity of the translucent resin decreases. Further, the smaller the difference in refractive index from the translucent sealing resin, the better the transmittance tends to be.
Refractive index (n _D =
1.50), the refractive index of silica (n _D = 1.46),
Since the refractive index is close to the refractive index of alumina (n _D = 1.56), the buffer layer can be formed without impairing the light transmittance. Further, the difference in the refractive index between the other translucent resin and the sedimentable inorganic filler also shows an approximation. As a result, a light-emitting diode having high heat resistance can be obtained without significantly impairing the light extraction efficiency. Hereinafter, the constituent members of the present invention will be described in detail.

(Buffer layer 101) The buffer layer 101 of the present invention
By injecting a translucent resin containing a settling inorganic filler into the substrate recess, at least the LED chip 10
3 is covered. Further, the sedimentable inorganic filler contains at least one selected from silica, boron nitride, calcium phosphate, and a rare earth compound, which is insulating, has a large specific gravity, low expansion, and high thermal conductivity. The buffer layer 101 in the present invention reduces thermal stress generated at the interface between the substrate 106, the lead electrode 105, and the translucent sealing resin, which is a heat conduction path in the LED chip 103. Further, since the buffer layer 101, which is an insulating heat conductive layer, is provided between the substrate 106 and the lead electrode 105, heat is radiated only from the chip mounting side. It also has the effect of reducing the element thermal resistance.

It is preferable that the buffer layer 101 in the present invention has high translucency with respect to light from the LED chip 103, and has high adhesion and heat resistance with the translucent sealing resin material and the substrate 106. The buffer layer 101 can be formed relatively easily by pouring it into a concave portion of the substrate 106 on which the LED chips 103 are arranged in advance and curing it.

(Translucent Sealing Resin Layer 102) The translucent sealing material is provided in the concave portion of the substrate.
3 efficiently transmits the light to the outside and protects the LED chip 103, the gold wire 104, and the like from external force, dust, and the like. As such a translucent sealing material, a thermosetting resin such as an epoxy resin, an acrylate resin, a urethane resin, a silicone resin, and a polyimide resin, or a thermoplastic resin such as an acrylic resin, a polycarbonate resin, and a polynorbornene resin. Used.

(LED chip 103) LED chip 10
Reference numeral 3 denotes GaP, G by MOCVD or liquid phase epitaxy.
aAlAs, GaAlInP, InN, GaN, Al
It can be formed by stacking a semiconductor light emitting layer of N, InGaN, InGaAlN, or the like on a substrate.
Examples of the structure of the LED chip include a homostructure having a MIS junction, a PIN junction and a PN junction, a heterostructure, and a double heterostructure. In particular, in the case of the double heterostructure through the active layer, light generated in the active layer is easily propagated in the active layer like a waveguide and emitted from the end face of the active layer.

A nitride semiconductor (In _X Ga _Y Al _{1 -XYN} ,
(0 ≦ X, 0 ≦ Y, 0 ≦ X + Y ≦ 1) are formed on an insulating sapphire substrate that is difficult to grow. In order to supply power to the nitride semiconductor formed on the sapphire substrate, the positive electrode and the negative electrode must be formed on the same surface side. A gold thin film or the like is used as an electrode for the above. Although such an electrode is formed as a thin film and has translucency, it is made of metal, so that light generated in the active layer of the LED chip is partially reflected.

Such an LED chip 103 can be mounted on a substrate by using a die bonding device. Further, the electrode provided on the LED chip 103 can be electrically connected to the electrode using the gold wire 104.

(Substrate 106) On the substrate 106, the LED chip 103 is disposed, and an external current is supplied to the LED chip 10.
3 is provided with a lead electrode 105 to be supplied. Therefore, a substrate having heat resistance and insulating properties is preferably used as the substrate 106. Specific examples of such a material for the substrate 106 include glass epoxy, bismaleimide triazine (hereinafter also referred to as BT resin), ceramics, liquid crystal polymer, and polybutylene terephthalate resin (PBT resin). The light emitting diode 100 according to the present invention has a light emitting diode having a substrate side wall portion 106a for efficiently extracting light from the LED chip 103, and a light emitting device having the substrate side wall portion 106b removed after the light-transmitting sealing resin is injected. And light emitting diodes having different directivity characteristics. Further, in order to efficiently reflect the light from the LED chip, a white pigment such as titanium oxide can be mixed with the resin constituting the substrate.

When the substrate 106 is molded with resin, the lead electrode 105 for supplying power to the LED chip 103 disposed inside can be formed relatively easily by insert molding or the like. The lead electrode 105 can be formed of a good electrical conductor such as copper and a copper alloy. The lead electrode 105 of the light emitting diode according to the present invention preferably emits heat efficiently, and a copper electrode is used. In order to improve the reflectivity of light from the LED chip 103, the surface of the lead electrode 105 may be plated with a smooth metal such as silver, aluminum, or gold.

When a substrate is made of glass epoxy and BT resin, chemical etching is performed on the BT resin to which copper-clad glass epoxy and copper foil are pressed to form a desired pattern. A glass epoxy and a BT resin having a hole serving as a side wall formed by drilling and punching press processing are bonded together with an adhesive. When the substrate is made of ceramic, a conductive paste containing a high melting point metal is printed in a desired pattern on a green sheet as a raw material before firing the ceramic. A plurality of green sheets are laminated to form a substrate shape and then fired to form a ceramic substrate. During firing, the conductive paste jumps out of the resin component and remains as an electrode layer that can be electrically connected to the outside. Hereinafter, specific examples of the present invention will be described in detail, but the present invention is not limited thereto.

[0025]

Embodiment 1 As a chip type LED, blue (470
LE with a nitride semiconductor capable of emitting light in the light emitting layer
The D chip was arranged on the substrate by die bonding.
The LED chip has a buffer layer made of gallium nitride, an n-type contact and clad layer made of GaN, a p-type clad layer made of GaAlN, and a p-type contact layer made of GaN laminated on a sapphire substrate. An InGaN layer having a single quantum well structure is formed between the n-type contact layer and the p-type cladding layer. In order to form positive and negative electrodes from the semiconductor layer side formed on the sapphire substrate, a part of the nitride semiconductor is etched to expose the n-type contact layer. A gold thin film is formed on the p-type contact layer as an ohmic electrode.

The substrate was formed by placing a lead electrode formed in advance in a mold and injecting and curing an epoxy resin. The molded substrate has a smooth surface with a part of the lead electrode exposed at the bottom of the opening. In addition, the bottom surface of the smooth substrate is an LED that enters from a certain direction like a mirror surface.
A plane that can reflect most of the light from the chip in a specific direction. Vertical light emitted from the LED chips arranged on such a plane can be efficiently emitted to the front surface. Therefore, the surface of the lead electrode, the bottom surface and the side surface of the substrate can efficiently reflect light from the LED chip.

The above-described LED chip was mounted in the opening of the substrate using a translucent epoxy resin using a die bonding apparatus. Each electrode of the LED chip and a lead electrode in the opening of the substrate are wire-bonded using a gold wire to establish electrical continuity.

It is preferable that the coefficient of linear expansion of the member serving as the buffer layer be closer to the coefficient of linear expansion of the lead electrode. The measurement of the linear expansion coefficient in Example 1 was performed by TMA (thermomechanical analyzer). The epoxy resin, which is a translucent resin, has a linear expansion coefficient of 6 × 10 ⁻⁵ (1 / ° C.) or more and 2 × 10 ⁻⁴ (1 / ° C.) or less, and a linear expansion coefficient of a lead electrode of 1.3 × 10 ^−5. (1 /
° C) or more and 2.0 × 10 ⁻⁵ (1 / ° C.) or less, so that the coefficient of linear expansion of the member serving as the buffer layer is 2 × 10 ⁻⁵ or more and 6 × 10 ^−5.
It is preferable to set the following. More preferably, the coefficient of linear expansion of the member to be the buffer layer is 2 × 10 ⁻⁵ (1 / ° C.) or more and 5 × 1.
0 to ^-5.

A mixed resin containing 5.4 parts by weight of silica per 100 parts by weight of liquid epoxy resin as a buffer layer was injected into the opening of the substrate while stirring. After injection, 8
By curing at 5 ° C for 3 hours and 140 ° C for 4 hours, L
A first portion serving as a buffer layer containing an inorganic filler for covering the ED chip was formed, and a second portion having higher light transmission than the first portion was formed on the first portion. In this way, 50 chip type LEDs were formed and the heat resistance was examined.

In FIG. 4, for comparison, 50 chip-type LEDs were formed in the same manner as the chip-type LED of the present invention except that no inorganic filler was contained and the buffer layer was not formed.

Each of the formed chip type LEDs is
A liquid-phase thermal shock test at -40 ° C on the low temperature side and 100 ° C on the high-temperature side was performed 5000 times in order to check the environmental resistance using 0 pieces. When the chip type LED provided with the buffer layer did not show any non-light failure. On the other hand, a chip type LED without a buffer layer has a non-light failure more than 1500 times.
At the time of 0 times, 30 non-lights occurred. Further, with respect to the chip type LED from which the substrate side wall shown in FIG. 3 was removed, the same liquid phase thermal shock test as the light emitting diode having the side wall shown in FIG. 1 was performed. It has been found that it can be greatly improved. The same effect was obtained by using another translucent sealing resin and a sedimentable inorganic filler according to claims 4 and 6.

[0032]

Example 2 A liquid phase thermal shock test was conducted under the same conditions as in Example 1 at five concentrations of the sedimentable inorganic filler added to the liquid epoxy resin, and the heat resistance due to the difference in the thickness of the buffer layer was examined. .
Silica was used as the sedimentable inorganic filler, and the five concentrations were 1 part by weight, 3 parts by weight, 5.4 parts by weight, 8 parts by weight, and 11 parts by weight with respect to 100 parts by weight of the liquid epoxy resin. The mixture was dispersed by a ball mill for 6 hours, and each was injected into a concave portion of the substrate by a dispenser. 3 hours at 85 ° C +
After curing at 140 ° C. for 4 hours, and forming an external electrode, a chip type LED was obtained. When the environmental resistance of the light emitting diode was examined, it was found that the amount of the precipitated inorganic filler added was large.
No lighting failure was observed from 11 parts by weight to 11 parts by weight. However, for the light-emitting diode of 1 part by weight with the smallest addition amount, no light was generated from the 3500th time, and
In the case of 00 times, 24 defects occurred. Also, the side surface of each light emitting diode was cut, and as a result of measuring the thickness of the buffer layer, the thickness of the buffer layer was determined to be 1 part by weight, 3 parts by weight, 5.4 parts by weight, 8 parts by weight, and 11 parts by weight. 20μ each
m, 66 μm, 150 μm, 250 μm, and 400 μm. Next, when the luminous intensity was measured using a photodiode, the luminous intensity for the buffer layer of 1 to 8 parts by weight was maintained at 180 mcd, while the luminous intensity was significantly reduced to 100 mcd at a film thickness of 400 μm, which was 11 parts by weight. all right. As described above, the thickness of the buffer layer in the light emitting diode according to the present invention is set to 20 μm or more having heat resistance and 400 μm or less without impairing the light extraction efficiency.

[0033]

According to the structure of the present invention, the thermal stress generated at the interface between the LED chip / substrate and the translucent sealing resin is reduced. This reduces wire open due to peeling due to reflow heat during mounting. LED
Since the heat dissipation from only the chip mounting side is achieved by providing a buffer layer that is an insulating heat conductive layer between the chip and the board, the heat dissipation from all the LED chips and the board in the element can be obtained. Can also be reduced.

According to the structure of the present invention, the luminance of light emitted from the end of the light emitting layer can be maintained without lowering the light extraction efficiency from the LED chip.

[Brief description of the drawings]

FIG. 1 shows a chip type LED according to an embodiment of the present invention.
1 shows a schematic sectional view of FIG.

FIG. 2 shows a chip type LED according to an embodiment of the present invention.
1 shows a schematic sectional view of FIG.

FIG. 3 shows a chip type LED according to an embodiment of the present invention.
1 shows a schematic sectional view of FIG.

FIG. 4 shows a chip type LE shown for comparison with the present invention.
D shows a schematic sectional view.

[Explanation of symbols]

100, 200, 300, 400 ... light emitting diode 101, 201, 301 ... buffer layer 102, 202, 302, 402 ... translucent sealing resin layer 103, 203, 303, 403 ... LED Chips 104, 204, 304, 404: Gold wire 105, 205, 305, 405: Lead electrode 105a, 405a: External electrode 105b, 405b: Internal electrode 106, 206, 306, 406 ..Substrate 206a ... Substrate side wall 206b, 306b ... Substrate support 207, 307 ... Insulating resin

Continued on the front page (72) Inventor Masafumi Kuramoto 491-1100, Kaminakamachioka, Anan-shi, Tokushima Nichia Chemical Industry Co., Ltd.F-term (reference) 5F041 AA25 AA33 AA40 AA43 CA05 CA34 CA36 CA37 CA40 CA46 DA02 DA07 DA20 DA44 DA46 DA58

Claims (8)

[Claims] A first lead electrode connected to at least one of a pair of lead electrodes;
In a light emitting diode having a conductive wire electrically connected to an electrode of an ED chip, respectively, and a light transmitting sealing resin covering the LED chip and the conductive wire, the light transmitting sealing resin is an LED. A light emission characterized by having a first portion containing an inorganic filler for covering the chip and serving as a buffer layer, and a second portion having a higher light transmitting property than the first portion on the first portion. diode. 2. The buffer layer has a linear expansion coefficient of 2 × 10.
The light emitting diode according to claim 1, wherein the light emitting diode has a temperature of not less than ^-5 (1 / ° C) and not more than 6 × 10 ^-5 (1 / ° C). 3. The thickness of the buffer layer is 2 mm on the LED chip.
The light emitting diode according to claim 1, wherein the light emitting diode has a thickness of 0 μm or more and 400 μm or less. 4. The buffer section contains silica as an inorganic filler,
The light emitting diode according to claim 1, wherein the light emitting diode contains at least one selected from boron nitride, calcium phosphate, and a rare earth compound. 5. The light emitting diode according to claim 1, wherein the LED chip is disposed on a substrate having a concave portion on a surface having a lead electrode, and the translucent sealing resin is disposed in the concave portion. 6. The translucent sealing resin is an epoxy resin,
Acrylate resin, urethane resin, silicone resin, polyimide resin, acrylic resin, polycarbonate resin,
The light emitting diode according to claim 1, wherein the light emitting diode is at least one selected from polynorbornene resins. 7. The light emitting diode according to claim 1, wherein the buffer portion has a density gradient of an inorganic filler, and the linear expansion coefficient continuously approaches the linear expansion coefficient of the lead electrode as approaching the lead electrode. 8. At least one of a pair of lead electrodes and L
A method for forming a light emitting diode, comprising: a conductive wire electrically connected to an electrode of an ED chip; and a light-transmitting sealing resin covering the LED chip and the conductive wire. A step of wire bonding an electrode of the chip with a conductive wire; and a step of disposing a thermosetting or thermoplastic resin having a lower specific gravity than the inorganic filler obtained by mixing and stirring the inorganic filler on the LED chip and the conductive wire. The inorganic filler in the thermosetting or plastic resin is LE
Forming a light-emitting diode on the D-chip side.