JPH0878727A - Light emitting diode - Google Patents

Abstract

(57) [Summary] [Objective] To realize a highly reliable LED that can maintain stable output even under high temperature and high humidity. [Structure] A surface of a sapphire substrate 1 of a light emitting chip in which a gallium nitride-based compound semiconductor 2 is laminated on a sapphire substrate 1 is placed on a support 14 with an adhesive 13, and the entire light emitting chip is molded with a resin 15. In the light emitting diode formed as described above, the light emitting chip is bonded with the adhesive 13 made of a resin having a hardness lower than that of the molding resin 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a gallium nitride-based compound semiconductor (In _X Al _Y Ga _{1- XY} N, 0) on a sapphire substrate.
A light emitting diode (LE having a structure in which a light emitting chip consisting of ≦ X, 0 ≦ Y, X + Y ≦ 1) is adhered on a support body with a sapphire substrate as an adhesion surface and is entirely molded with resin.
D).

[0002]

2. Description of the Related Art Recently, blue LEDs and blue-green LEDs using a gallium nitride compound semiconductor as a light emitting chip have just been put into practical use. The structure of the LED is shown in FIG. The light emitting chip comprises a sapphire substrate 1 on which a pn-junction gallium nitride-based compound semiconductor layer 2 is formed. The sapphire substrate 1 and the lead frame 4 are bonded with an adhesive 3, and the whole is molded with a resin 5. There is. An epoxy resin is used for the adhesive 3 and the mold resin 5. The adhesive 3 is for the purpose of reflecting the emitted light of the gallium nitride-based compound semiconductor layer 2 that has passed through the sapphire substrate 1 on the surface of the lead frame 4 and extracting it to the emission observation surface side. A transparent and insulating epoxy resin is used for the purpose of preventing short-circuiting between electrodes even if it goes around the compound semiconductor layer 2 surface. The gallium nitride-based compound semiconductor layer 2 includes, in order from the sapphire substrate 1 side, a buffer layer made of GaN, an n-type layer made of GaN, an n-type clad layer made of AlGaN, and InGa.
An active layer made of N, a p-type clad layer made of AlGaN, and a p-type contact layer made of GaN are sequentially stacked to form a double hetero structure. With this structure,
The LED has a forward current (If) of 20 mA, a forward voltage (Vf) of 3.6 V, and a peak emission wavelength of 450 to 520.
nm, luminous intensity of 1 cd or more, and light emission output of 1.2 mW or more, showing the highest performance ever for blue LEDs and blue-green LEDs.

[0003]

The characteristics of the blue LED and the blue-green LED sufficiently satisfy the specifications under normal use conditions, but there are still insufficient points. For example, when a continuous lighting test is performed under high temperature and high humidity conditions such as 85 ° C. and 85% RH, there is a drawback that the output is greatly reduced. For example, in some of them, the output after 500 hours is 6
There are some things that decrease to 0%. Since the LED is a highly reliable light emitting device, it is necessary to realize a blue LED capable of maintaining stable output even under high temperature and high humidity as described above.

Therefore, the present invention has been made to solve this problem, and an object thereof is to improve the reliability of an LED using a gallium nitride-based compound semiconductor as a light emitting chip. It is to realize an LED whose output is less likely to decrease even when used under severe conditions.

[0005]

In the LED of the present invention, a sapphire substrate surface of a light emitting chip in which a gallium nitride compound semiconductor is laminated on a sapphire substrate is placed on a support through an adhesive, and In a light emitting diode in which the entire light emitting chip is molded with a resin, the light emitting chip is bonded with an adhesive made of a resin having a hardness lower than that of the molded resin.

FIG. 1 shows the structure of the LED of the present invention. The basic structure of the light emitting chip is the same as that of the conventional LED shown in FIG. 5, and the adhesive 13 for bonding the sapphire substrate 1 of the light emitting chip and the lead frame 14 has a property that the hardness thereof is smaller than that of the molding resin 15. It is used as a material.

It is necessary to select a material having a hardness smaller than that of the mold resin 15 for the adhesive agent 13. For example, the mold resin 15 has a Rockwell (M) hardness (hereinafter, Rockwell hardness is 25 ° C. in this specification). When the epoxy resin of 120 is used, it is 12
A soft material such as an epoxy resin, a urea resin, an acrylic resin, or a silicone resin smaller than 0 is used. In a material having rubber-like elasticity such as a silicone resin, its hardness is not expressed by Rockwell hardness, and for example, JI
A silicone resin represented by the value of S-A and having a value smaller than 60 can be preferably used. For the adhesive 13, it is desirable to select a material having a Rockwell hardness of 10 or more, more preferably 20 or more, which is different from that of the mold resin 15. By selecting the ones that have a large hardness difference, the stress on the chip is reduced and L
The reliability of the ED is improved. Specifically, the output is less likely to decrease even when used under severe conditions.

Further, since the adhesive 13 as described above is transparent and has an insulating property, as shown in FIG.
Does not cause a short circuit between the electrodes even when the electric field reaches the pn junction interface of the semiconductor layer along the side surface of the light emitting chip. Moreover, since it is transparent, the light emitted from the sapphire substrate 1 is transmitted through the adhesive 13 and reflected by the surface of the lead frame 14 which is the adhesive surface, so that the light emitted can be effectively extracted to the outside. It is also possible to intentionally increase the amount of the adhesive in order to increase the adhesive force of the chip. From the above, the most elastic, insulating and transparent silicone resin can be particularly recommended as the material used for the adhesive 13.

[0009]

[Function] The heat generated by the light emitting chip causes the sealing resin to thermally expand,
Distortion due to expansion and contraction adversely affects the light emitting chip, and LE
It is known to reduce the output of D. As a countermeasure against this, conventionally, by coating a resin (for example, silicone resin) having a different thermal expansion coefficient as a buffer layer on the surface of the light emitting chip, and molding an epoxy resin on the resin, L
It was ED.

However, in the present invention, the buffer layer is provided not on the front surface of the chip as in the prior art but on the bonding surface by utilizing the structure unique to the gallium nitride compound semiconductor light emitting chip having the insulating and transparent substrate called sapphire. As a result, it has succeeded in reducing the stress on the chip and preventing the LED output from decreasing.

In the LED according to the first aspect, a buffer layer is provided between the sapphire substrate and the support by selecting a resin material for bonding the chip that has a hardness lower than that of the molding resin. Stress related to the chip can be relieved.

According to a third aspect of the present invention, as the most effective combination, the adhesive is a resin having rubber-like elasticity such as a silicone resin, and the molding resin is a resin such as epoxy or acrylic which can express hardness in Rockwell hardness. There is.
A resin having rubber-like elasticity has a large absorbing power and is most suitable as an adhesive in the LED of the present invention. A mold resin having a Rockwell hardness of less than 80 is unsuitable as an LED sealing resin.

Further, even if rubber-like fine particles are added to the material of the adhesive as described in claim 4, elasticity can be imparted to the adhesive. The particle size of rubber particles is 0.5μ
It is preferable to select one having a thickness of m or less, more preferably 0.1 μm or less. This is because if it is larger than 0.5 μm, the adhesive becomes opaque and it becomes difficult to transmit light emission.
Therefore, it is preferable to select transparent or white rubber-like fine particles. However, in this specification, “transparent” means transmitting the emission wavelength of the gallium nitride-based compound semiconductor layer, and does not necessarily mean colorless and transparent. Further, white means white having a reflectance that reflects the light emitted from the gallium nitride-based compound semiconductor layer.

The rubber fine particles may be mixed with the adhesive according to claim 1 to give elasticity and serve as a filler. Further, as in claim 3, the rubber fine particles are mixed with the rubber-like adhesive having elasticity from the beginning. Then, it may be used as a filler. If you select a material that has a higher thermal conductivity than the material that uses rubber particles as the adhesive, it is possible to efficiently transfer heat from the chip to a support such as a lead frame, improving the chip life. To do.

Furthermore, since the adhesive is a resin having an insulating property, it is possible to intentionally increase the amount of the adhesive as shown in FIG. 1 to enhance the adhesive force. An LED with excellent reliability because the element will not be destroyed even if the adhesive contacts the pn junction interface on the semiconductor layer side.
Can be provided.

[0016]

【Example】

[Example 1] On the surface of a 2-inch φ sapphire substrate, G
aN buffer layer, Si-doped n-type GaN layer, Si-doped n-type AlGaN cladding layer, Si + Zn-doped I
nGaN active layer, Mg-doped p-type AlGaN layer, M
A wafer in which a g-doped p-type GaN layer was sequentially stacked was prepared. After etching the gallium nitride compound semiconductor layer side of this wafer in a predetermined shape, n-type G
An n-electrode was formed on the aN layer and a positive electrode was formed on the p-type GaN layer. After forming the electrodes, the wafer was broken into 350 μm squares by a scriber to obtain LED chips. Next, this LED chip was set in a die bonder together with the wafer.

The die bonder has an L structure as shown in FIG.
A lead frame for assembling into the ED was set, and the adhesive 13 was injected into the cup of the lead frame 14 with a dispenser. The adhesive 13 has a hardness (JI
S-A) 32, a thermal expansion coefficient of 3 × 10 ⁻⁴ / ° C., and a colorless transparent silicone resin were used. After the LED chip was die-bonded in the cup, it was heated at 150 ° C. to cure the adhesive. After the adhesive was cured, wire bonding was performed on the electrodes of the LED chip with a wire bonder.

Finally, the lead frame to which the LED chip is adhered is transferred to a molding device, the entire chip is molded with the resin 15, and then the resin 15 is cured by heating at 120 ° C., and the structure as shown in FIG. The LED lamp of was obtained.
As the resin 15, a colorless and transparent epoxy resin having a Rockwell hardness of 115 after curing and a thermal expansion coefficient of 7.8 × 10 ⁻⁵ / ° C. was used.

When the LED lamp produced as described above was lit at room temperature, Vf at If 20 mA
3.6V, peak emission wavelength 450nm, luminous intensity 1200m
cd, and the light emission output was 1.8 mW. Separately, as an acceleration test, 100 LED lamps were randomly sampled, 40 mA was applied under the conditions of high temperature and high temperature of 85 ° C. and 85% RH, and continuously lit for 500 hours, and compared with the first output, There was no sudden decrease in output, and all were in the range of 95% ± 3% compared to the initial output.

[Embodiment 2] The adhesive to be filled in the dispenser at the time of die bonding was set to have Rockwell hardness of 9 after curing.
7. Thermal expansion coefficient 8.5 × 10 ^-5 / ° C, colorless and transparent epoxy resin, and mold resin with Rockwell hardness 1
17, an LED lamp was prepared in the same manner as in Example 1 except that a colorless and transparent epoxy resin having a thermal expansion coefficient of 7.8 × 10 ⁻⁵ / ° C. was used. Extract 100 lamps in the same way and
When a high-temperature high-humidity test was performed at 0 mA for 500 hours, the output did not suddenly decrease, and all were in the range of 87% ± 4%.

[Embodiment 3] The adhesive to be filled in the dispenser at the time of die-bonding was hardened with Rockwell hardness 9
7. A colorless rubber-like epoxy resin having a thermal expansion coefficient of 8.5 × 10 ⁻⁵ / ° C. and white rubber-like fine particles having an average particle diameter of 0.1 μm
A mixture of 0% by weight was used. Further, the molding resin is Rockwell hardness 117, thermal expansion coefficient 7.8 × 10 ^-5
An LED lamp was prepared in the same manner as in Example 1 except that the epoxy resin was colorless and transparent at / ° C. This lamp 100
Similarly, when a high temperature and high humidity test was conducted at 40 mA for 500 hours, none of the outputs suddenly dropped, and all were 92% ± 3
It was in the range of%.

[Fourth Embodiment] A fourth embodiment will be described with reference to FIG. Although the basic structure is not particularly different from that in FIG. 1,
The ceramic substrate 24 serves as a support for the LED chip. An electrode pattern is previously formed on the ceramic substrate 24, and the electrode of the LED chip is wire-bonded to the patterned electrode.

The sapphire substrate of the LED chip of Example 1 was die-bonded with the adhesive 23 to a predetermined position on the ceramic substrate installed in the die bonder. The adhesive 35 has a hardness (JIS-A) 32 after curing and a thermal expansion coefficient of 3 × 10.
^A colorless and transparent silicone resin mixed at ⁻⁴ / ° C. with 5% by weight of white rubber fine particles having a particle size of 0.1 μm was used as a filler.

Next, after the electrode of the LED chip and the electrode of the ceramic substrate were connected with a wire bonder, the LED chip was sealed with resin 25 by a molding device. Resin 2
For No. ^5, a colorless and transparent epoxy resin having a Rockwell hardness of 110 after curing and a thermal expansion coefficient of 7.8 × 10 ⁻⁵ / ° C. was used.

100 pieces were extracted from the LED lamps prepared as described above, and 50 pieces were extracted under the conditions of 40 mA and high temperature and high humidity.
When the lamps were continuously turned on for 0 hours, none of the outputs drastically decreased, and all were within the range of 95% ± 4% compared to the initial output.

[Comparative Example] An LED was obtained in the same manner as in Example 1 except that the same resin as the molding resin was used as the adhesive at the time of die bonding. When 100 high-temperature and high-humidity tests were conducted on 100 of these LED lamps, the output was 7 hours after 500 hours
It decreased to 0% ± 10%.

[0027]

As described above, in the LED of the present invention, the adhesive for adhering the chip is a resin having a hardness lower than that of the molding resin, so that the stress on the chip due to heat generation of the chip is relieved by the adhesive layer. Therefore, the reliability of the chip can be significantly improved.
As another technique, it is possible to form a resin layer serving as a buffer layer such as a conventional silicone resin as a buffer layer between the gallium nitride compound semiconductor layer of the chip and the mold resin. .

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of an LED lamp according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing the structure of an LED lamp according to another embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing the structure of a conventional LED lamp.

[Explanation of symbols]

 1 ... Sapphire substrate 2 ... Gallium nitride compound semiconductor layer 13, 23 ... Adhesive agent 15, 25 ... Mold resin 14, 24 ... Support

Claims (4)

[Claims] 1. A light emitting chip having a gallium nitride-based compound semiconductor laminated on a sapphire substrate, the sapphire substrate surface of which is placed on a support through an adhesive, and the entire light emitting chip is molded with a resin. In the light emitting diode, the light emitting chip is bonded with an adhesive made of a resin having a hardness lower than that of the molded resin. 2. The hardness difference between the adhesive and the mold resin is 2
The light emitting diode according to claim 1, which has a Rockwell hardness of 10 or more at 5 ° C. 3. The adhesive is a rubber-like elastic resin, and the mold resin has a Rockwell hardness of 8 at 25 ° C.
The light emitting diode according to claim 1, wherein the light emitting diode is 0 or more resin. 4. The light emitting diode according to claim 1, wherein the adhesive contains rubber-like elastic fine particles.