JP3309939B2 - Light emitting diode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gallium nitride compound on a sapphire substrate semiconductor _{(In X Al Y Ga 1- XY} N, 0
A light emitting diode (LE) having a structure in which a light emitting chip composed of ≤X, 0≤Y, X + Y≤1) is bonded to a support with a sapphire substrate as an adhesive 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-based compound semiconductor as a light emitting chip have just been put into practical use. FIG. 3 shows the structure of the LED. The light emitting chip is formed by forming a gallium nitride based compound semiconductor layer 2 having a pn junction on a sapphire substrate 1, and the sapphire substrate 1 and the lead frame 4 are bonded with an adhesive 3, and the whole is molded with a resin 5. I have. Epoxy resin is used for the adhesive 3 and the mold resin 5. The adhesive 3 reflects the light emitted from the gallium nitride-based compound semiconductor layer 2 transmitted through the sapphire substrate 1 on the surface of the lead frame 4 and takes it out to the light emission observation surface side. A transparent and insulating epoxy resin is used for the purpose of not causing a short circuit between the electrodes even when it goes around the surface of the compound semiconductor layer 2. The gallium nitride-based compound semiconductor layer 2 includes, in order from the sapphire substrate 1, a buffer layer made of GaN, an n-type layer made of GaN, an n-type clad layer made of AlGaN,
An active layer made of N, a p-type clad layer made of AlGaN, and a p-type contact layer made of GaN have a double hetero structure in which layers are sequentially stacked.
The LED has a forward voltage (Vf) of 3.6 V and a peak emission wavelength of 450 to 520 at a forward current (If) of 20 mA.
nm, a luminous intensity of 1 cd or more, and a light emission output of 1.2 mW or more.

[0003]

Although the characteristics of the blue LED and the blue-green LED sufficiently satisfy the specifications under ordinary use conditions, there are still insufficient points. For example, when a continuous lighting test is performed under a high-temperature and high-humidity condition such as 85 ° C. and 85% RH, there is a disadvantage that the output greatly decreases. For example, in some of them, the output after 500 hours elapse is 6
In some cases, it drops to 0%. Since the LED is a highly reliable light emitting device, it is necessary to realize a blue LED that can maintain a stable output even under the above-mentioned high temperature and high humidity.

Therefore, the present invention has been made to solve this problem, and an object of the present invention is to improve the reliability of an LED using a gallium nitride-based compound semiconductor as a light emitting chip. An object of the present invention is to realize an LED in which the output hardly decreases even when used under severe conditions.

[0005]

According to the present invention, there is provided a light emitting chip comprising a gallium nitride-based compound semiconductor laminated on a sapphire substrate, the sapphire substrate surface being placed on a support via an adhesive, and In a light emitting diode in which the entire chip is molded with a resin, the light emitting chip is bonded with an adhesive covering at least the entire exposed surface of a sapphire substrate made of a resin having a lower hardness than the molded resin. Light emitting diode. The invention according to claim 2 of the present invention is the light emitting diode according to claim 1, wherein a difference in hardness between the adhesive and the mold resin is 10 or more in Rockwell hardness at 25 ° C. The invention described in claim 3 of the present invention provides:
The light emitting diode according to claim 1, wherein the adhesive is a rubber-like elastic resin, and the mold resin is a resin having a Rockwell hardness at 25 ° C of 80 or more. The invention according to claim 4 of the present invention is the light emitting diode according to any one of claims 1 to 3, wherein the adhesive contains rubber-like elastic fine particles. is there.

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 property of the adhesive 13 for bonding the sapphire substrate 1 of the light emitting chip and the lead frame 14 is smaller than the hardness of the mold resin 15. Material.

For the adhesive 13, it is necessary to select a material having a hardness lower than that of the mold resin 15. For example, the mold resin 15 has a Rockwell (M) hardness (hereinafter referred to as a Rockwell hardness of 25 ° C. in the present specification). When the epoxy resin of 120 is used, 12
Use a soft material smaller than 0, such as an epoxy resin, a urea resin, an acrylic resin, or a silicone resin. For a rubber-like elastic material such as silicone resin, its hardness is not represented by Rockwell hardness.
A silicone resin represented by the value of SA and having a value of less than 60 can be preferably used. It is desirable to select the adhesive 13 having a Rockwell hardness of 10 or more, more preferably 20 or more, in hardness difference from the mold resin 15. By selecting those having a large difference in hardness, the stress applied to the chip is reduced and L
The reliability of the ED is improved. Specifically, even when used under severe conditions, the output rarely drops.

Furthermore, since the above-mentioned adhesive 13 is transparent and has insulating properties, as shown in FIG.
Does not short-circuit between the electrodes even if it reaches the pn junction interface of the semiconductor layer along the side surface of the light emitting chip. Moreover, since the light is transmitted, the light transmitted through the sapphire substrate 1 is transmitted through the adhesive 13 and is reflected on the lead frame 14, which is the bonding surface, so that the light can be effectively extracted to the outside. Further, in order to increase the adhesive strength of the chip, it is possible to intentionally increase the amount of the adhesive. From the above, as the material used for the adhesive 13, the most elastic, insulating and transparent silicone resin can be particularly recommended.

[0009]

The sealing resin thermally expands due to the heat generated by the light emitting chip,
Strain due to expansion and contraction adversely affects the light emitting chip, and LE
It is known to reduce the output of D. Conventionally, as a countermeasure, a resin (for example, a silicone resin) having a different coefficient of thermal expansion is coated on the surface of the light emitting chip as a buffer layer, and an epoxy resin is molded on the resin.
ED.

However, in the present invention, a buffer layer is provided not on the front surface of the chip but on the bonding surface by using a structure specific to a gallium nitride-based compound semiconductor light emitting chip having an insulating and transparent substrate called sapphire. As a result, the stress on the chip was reduced and the output of the LED was prevented from being reduced.

In the LED according to the first aspect of the present invention, a buffer material is provided between the sapphire substrate and the support by selecting a resin material for bonding the chip having a hardness lower than that of the mold resin. The stress on the chip can be reduced.

According to a third aspect of the present invention, as the most effective combination, the adhesive is made of a resin having rubber-like elasticity such as silicone resin, and the mold resin is selected from resins such as epoxy and acrylic which can express the hardness by Rockwell hardness. I have.
A rubber-like resin having a large elasticity has a large absorptivity, 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 not suitable as an LED sealing resin.

Further, even if rubber-like fine particles are added to the material of the adhesive, elasticity can be imparted to the adhesive. Rubber microparticles have a particle size of 0.5μ
m or less, more preferably 0.1 μm or less. If the thickness is larger than 0.5 μm, the adhesive becomes opaque and it becomes difficult to transmit light.
Therefore, it is preferable to select transparent or white rubber-like fine particles. However, in the present specification, “transparent” means that the emission wavelength of the gallium nitride-based compound semiconductor layer is transmitted, and does not necessarily mean colorless and transparent. Further, white means white having a reflectivity for reflecting light emitted from the gallium nitride-based compound semiconductor layer.

The rubber fine particles may be mixed with the adhesive according to the first aspect to impart elasticity and serve as a filler. Further, the fine particles may be mixed into the rubbery adhesive having elasticity from the beginning. Then, it may be used as a filler. Preferably, the material of the rubber fine particles is selected to have a higher thermal conductivity than the material used for the adhesive, so that the heat generated by the chip can be efficiently transmitted to a support such as a lead frame, thereby improving the life of the chip. I do.

Further, 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 increase the adhesive strength. LED with excellent reliability because the element does not break down even if the adhesive touches the pn junction interface on the semiconductor layer side
Can be provided.

[0016]

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

An L having a structure as shown in FIG.
A lead frame to be assembled 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 after curing (JI
SA) 32, a colorless and transparent silicone resin having a coefficient of thermal expansion of 3 × 10 ⁻⁴ / ° C. was used. After the LED chip was die-bonded in the cup, the adhesive 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 using a wire bonder.

Finally, the lead frame to which the LED chip is adhered is transferred to a molding device, and the entire chip is molded with the resin 15, and then heated at 120 ° C. to cure the resin 15, thereby obtaining a structure as shown in FIG. LED lamp 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 prepared as described above was turned on at room temperature, Vf was obtained at If mA of 20 mA.
3.6 V, peak emission wavelength 450 nm, luminous intensity 1200 m
cd and the light emission output were 1.8 mW. Separately, as an acceleration test, 100 of these LED lamps were randomly extracted, subjected to 40 mA under high temperature and high humidity conditions of 85 ° C. and 85% RH, lit continuously for 500 hours, and compared with the initial output. There was no sharp drop in output, and the output was all within the range of 95% ± 3% as compared to the initial output.

Example 2 An adhesive to be filled into a dispenser at the time of die bonding was applied to a Rockwell hardness of 9 after curing.
7. Thermal expansion coefficient 8.5 × 10 ^-5 / ° C, colorless and transparent epoxy resin, and mold resin of 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. Similarly, 100 lamps were extracted and 4 lamps were extracted.
When a high-temperature and high-humidity test was performed at 0 mA for 500 hours, there was no sudden decrease in output, and all were within the range of 87% ± 4%.

Example 3 The adhesive to be filled in the dispenser at the time of die bonding was applied to a Rockwell hardness of 9 after curing.
7. One white rubber-like fine particle having an average particle size of 0.1 μm is added to a colorless and transparent epoxy resin having a thermal expansion coefficient of 8.5 × 10 ⁻⁵ / ° C.
A mixture of 0% by weight was used. Further, the molding resin is made of a Rockwell hardness of 117 and a thermal expansion coefficient of 7.8 × 10 ^−5.
An LED lamp was prepared in the same manner as in Example 1, except that the colorless transparent epoxy resin was used. This lamp 100
The test pieces were similarly subjected to a high-temperature and high-humidity test at 40 mA for 500 hours.
% Range.

Embodiment 4 Embodiment 4 will be described with reference to FIG. The basic configuration is not particularly different from FIG.
The support for the LED chips is a ceramic substrate 24. An electrode pattern is formed on the ceramic substrate 24 in advance, and the electrodes of the LED chip are wire-bonded to the patterned electrodes.

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

Next, after connecting the electrode of the LED chip and the electrode of the ceramic substrate with a wire bonder, the LED chip was sealed with a 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.

One hundred LED lamps were extracted from the LED lamps prepared as described above, and were extracted under the conditions of 40 mA, high temperature and high humidity.
When the light was continuously lit for 0 hours, there was no sudden decrease in output, and the output was all within the range of 95% ± 4% as compared with the initial output.

Comparative Example An LED was obtained in the same manner as in Example 1, except that the same resin as the mold resin was used as the adhesive at the time of die bonding. When 100 LED lamps were similarly subjected to a high-temperature and high-humidity test, the output was 7 in 500 hours.
It decreased to 0% ± 10%.

[0027]

As described above, in the LED of the present invention, since the adhesive for bonding the chip is a resin having a lower hardness than the molding resin, the stress applied to the chip due to the heat generated by the chip is reduced by the adhesive layer. Therefore, the reliability of the chip can be remarkably improved.
As another technique, it is also possible to form a resin layer serving as a buffer layer of a conventional silicone resin or the like as a buffer layer between the gallium nitride-based compound semiconductor layer of the chip and the mold resin. .

[Brief description of the drawings]

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

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

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

[Explanation of symbols]

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

(56) References JP-A-62-101090 (JP, A) JP-A-61-34085 (JP, A) JP-A-61-5530 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H01L 33/00 H01L 21/56 H01L 23/28 JICST file (JOIS)

Claims (4)

(57) [Claims] 1. A light emitting chip in which a gallium nitride-based compound semiconductor is laminated on a sapphire substrate, the sapphire substrate surface is placed on a support via an adhesive, and the entire light emitting chip is molded with a resin. The light emitting diode according to claim 1, wherein the light emitting chip is bonded with an adhesive made of a resin having a hardness lower than that of a molded resin and covering at least an entire exposed surface of the sapphire substrate. 2. The hardness difference between the adhesive and the mold resin is 2
The light-emitting diode according to claim 1, wherein the light-emitting diode 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 a resin of 0 or more. 4. The light emitting diode according to claim 1, wherein the adhesive contains rubber-like elastic fine particles.