JP2004266124A - Semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting device the entire profile of which is made low by surely carrying out flip chip mount of a semiconductor light emitting element. <P>SOLUTION: The semiconductor light emitting device includes a substrate 2 made of a ceramic raw material. The light emitting element 5 is mounted on the substrate 2 of the semiconductor light emitting device by joining an n-type electrode and a p-type electrode of the light emitting element 5 with two electrodes 3, 4 formed on the substrate 2 via micro bumps 8, 9 respectively. Since the ceramic raw material is used for the substrate 2, the substrate 2 is chemically stabilized and lead electrodes can be formed on the surface with high accuracy, the substrate 2 is not softened nor deformed even when heat is applied at joining of the micro bumps 8, 9, and the ultrasonic vibration is not absorbed to attain efficient joining of the micro bumps 8, 9. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor light emitting device using a gallium nitride-based compound used for an optical device such as a blue light or ultraviolet light emitting diode.
[0002]
[Prior art]
Gallium nitride-based compound semiconductors such as GaN, GaAlN, InGaN, and InAlGaN have been widely used as semiconductor materials for visible light emitting devices and high-temperature operating electronic devices, and are being developed in the field of blue light emitting diodes.
[0003]
In the production of this gallium nitride-based compound semiconductor, an insulating sapphire substrate is generally used as a crystal substrate for growing a semiconductor film. When an insulating crystal substrate such as a sapphire substrate is used, an electrode cannot be formed on the crystal substrate side, and thus the electrode is formed on a surface opposite to the crystal substrate.
[0004]
FIG. 4A is a front view of a conventional semiconductor light emitting device in which a gallium nitride-based compound semiconductor is flip-chip mounted, and FIG. 4B is a plan view of the semiconductor light emitting device.
[0005]
4A and 4B, lead electrodes 52a and 52b are formed on a resin-based insulating lead substrate 51 by a plating method, and one of the lead electrodes 52a and the n-electrode of the light-emitting element 53 and the other are formed. The lead electrode 52b and the p-electrode of the light emitting element 53 face each other, are conductively connected and fixed via the micro bumps 54a and 54b. Since the light emitting element 53 is flip-chip mounted, the sapphire substrate 55 side is the top surface and serves as a main light extraction surface for emitted light. Then, the entire surface of the light emitting element 53 is sealed by transfer molding with a transparent epoxy resin 56 (for example, Patent Document 1).
[0006]
FIG. 4 of the semiconductor light emitting device used here is a top view type semiconductor light emitting device. The top view type is a light emitting direction from a main light extraction surface of the light emitting device (a direction indicated by an arrow in FIG. 4A). ) Is perpendicular to the solder mounting surface, and this type of semiconductor light emitting device is used, for example, for a numeric keypad backlight of a mobile phone or the like. In order to be used in such applications, it is important to reduce the mounting volume by reducing the thickness and to widen the light distribution to illuminate a wide range of numeric keys.
[0007]
In the case of a semiconductor light emitting device using such a light emitting element 53, since wire bonding is not used for conduction between the electrode of the light emitting element and the lead electrode, a rising height of the wire is not required, and the thickness of the sealing resin is reduced. There is an advantage that it can be made thin. However, since the electrode of the light emitting element 53 and the lead electrode of the resin-based insulating lead substrate 51 are conductively fixed by the microbump, disconnection due to the difference in the coefficient of thermal expansion between the light emitting element 53 and the lead substrate 51 in a temperature cycle environment. You have to be careful about the modes.
[0008]
FIG. 5A is a front view of a side-view type semiconductor light emitting device having a conventional structure, and FIG. 5B is a plan sectional view of the semiconductor light emitting device. The side-view type refers to a type in which a light emitting direction from a main light extraction surface of a light emitting device is parallel to a solder mounting surface, and a semiconductor light emitting device of this type is, for example, a full-color type such as a mobile phone. It is used by being arranged on the side surface of a light guide plate for a backlight of a liquid crystal panel. In order to be used in such applications, the height t from the solder mounting surface (described in FIG. 5A) is reduced to reduce the mounting volume and to allow a large amount of light to enter the light guide plate. It is important to increase the on-axis luminosity.
[0009]
In FIGS. 5A and 5B, a metal lead frame 61 is formed by punching a copper-based plate-like substrate with a mold, applying Ag plating to the surface thereof, forming lead electrodes 62a and 62b, and forming a resin around the lead electrodes. The package 64 is formed by molding with a light-transmitting adhesive 65 or the like on one lead electrode 62a with the sapphire surface side opposite to the electrode forming surface of the light emitting element 63 as the bonding surface, and the light emission is performed. The n-electrode of the element 63 and the lead electrode 62a are electrically connected by a wire 66a, and the other lead electrode 62b and the p-electrode of the light-emitting element 63 are electrically connected by a wire 66b. Since the light emitting element 63 is mounted so that the surface on which the electrode is formed is used as the main light extraction surface, the light emitted is emitted through the transparent electrode 62c. Then, the entire surface of the light emitting element 63 is sealed with a transparent epoxy resin 68.
[0010]
The package 64 must reflect the light emitted from the side surface of the light emitting element 63 to the main light extraction surface side and also have a function of increasing the axial luminous intensity. It is molded into a shape with a taper of
[0011]
In the case of this structure, flip-chip mounting on the lead electrode is difficult (the reason will be described later). In order to flip-chip mount the light emitting element 53, as shown in FIGS. A composite light emitting element in which the light emitting element 53 is flip-chip mounted on the mount element 69 will be used.
[0012]
[Patent Document 1]
JP-A-11-121797 (paragraph numbers 0029 to 0030, FIG. 1)
[0013]
[Problems to be solved by the invention]
As shown in FIG. 4, in the case of a top-view type semiconductor light-emitting device in which a GaN-based light-emitting element is flip-chip mounted, the thickness T of the light-emitting device can be reduced to 300 μm or less. There is a problem.
[0014]
First, the first problem is that a thin film electrode cannot be formed by vapor deposition on a resin-based substrate, so that the pattern of the lead electrodes cannot be formed with high accuracy. This is necessary, and the shape of the lead electrode is not sharpened. For this reason, an error when recognizing the pattern of the lead electrode and performing flip-chip mounting increases, and mounting is performed at a position shifted from a predetermined mounting location, thereby causing a short circuit or open between the electrodes.
[0015]
The second problem is that when mounting a GaN-based light-emitting element, it is necessary to apply heat and ultrasonic waves to the micro-bumps to perform welding bonding. However, in the case of a resin-based substrate, the substrate is softened by heat. The bonding of the microbumps due to the transmission of the vibration of the sound wave becomes insufficient, and the disconnection occurs due to the opening of the bump portions, which causes a problem in reliability.
[0016]
A third problem is that since the p and n electrodes of the GaN-based light emitting device and the lead electrodes of the resin-based lead substrate are conductively fixed by micro-bumps, the sapphire substrate and the resin-based substrate that occupy most of the GaN-based light-emitting device. If the thermal expansion coefficients of the lead substrates are significantly different, the microbumps will crack due to repetitive stress in a temperature cycle environment, and breakage due to opening will occur.
[0017]
In this case, the thermal expansion coefficient of sapphire, against 7.2 × ^{10 -6} / ℃, thermal expansion coefficient of the BT resin glass cloth substrate normally used as the resin system lead board is 10.0 × 10 ^{- 6} / ° C., which is about 40% larger.
[0018]
As described above, the flip-chip mounting structure that is effective for thinning has several problems due to the resin-based lead substrate in mounting, and it is not practically used as a semiconductor light emitting device because sufficient reliability cannot be secured. Absent.
[0019]
Also in the case of the side-view type semiconductor light emitting device shown in FIG. 5, a resin substrate is used because the gap between the lead electrodes 62a and 62b cannot be made smaller than 100 μm and the molding resin comes under the lead electrodes. For the same reason as in the above-described top view type, flip chip mounting with micro bumps is difficult.
[0020]
In the case of using a composite light emitting element in which the light emitting element 53 is flip-chip mounted on the sub mount element 69 shown in FIGS. 6A and 6B, the sub mount element 69 needs to be larger than the light emitting element 53. Therefore, there is a problem that it is difficult to make the height t from the solder mounting surface, which is important in a side-view type semiconductor light emitting device, 750 μm or less.
[0021]
Therefore, the present invention provides a semiconductor light emitting device capable of reliably performing flip-chip mounting of a semiconductor light emitting element, securing reliability, and reducing the overall thickness (that is, the height from the solder mounting surface). The purpose is to provide.
[0022]
[Means for Solving the Problems]
The semiconductor light emitting device of the present invention is a semiconductor light emitting device using a ceramic material having heat resistance and capable of forming a thin film electrode on an insulating lead substrate.
[0023]
According to the present invention, it is possible to obtain a semiconductor light emitting device capable of reliably performing flip-chip mounting of a semiconductor light emitting element and securing reliability, and also capable of reducing the overall thickness.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention according to claim 1 of the present invention is characterized in that the p-side electrode and the n-side electrode of the light emitting element are respectively bonded to two lead electrodes formed on the substrate via microbumps, so that the two lead electrodes are formed on the substrate. In a semiconductor light emitting device equipped with a light emitting element,
The substrate is a semiconductor light emitting device characterized by being made of a ceramic material. Since the ceramic material is used for the substrate, the substrate is scientifically stable and the thin-film electrode lead electrode is accurately formed on the surface. In addition, even if heat is applied during the bonding of the microbumps, the microbumps are softened and do not deform, and the microbumps are efficiently bonded without absorbing ultrasonic vibration.
[0025]
In the case of the top-view type, the light-transmitting crystal substrate is mounted on the top surface, and since there is no rise of the wire, the thickness T of the semiconductor light-emitting device can be reduced. Since the substrate also serves as a part of the package and the submount element, the height t from the solder mounting surface can be reduced to 500 μm or less.
[0026]
According to a second aspect of the present invention, there is provided the semiconductor light emitting device according to the first aspect, wherein the lead electrode is vapor-deposited on a surface of the substrate. Since the thickness of the lead electrode formed by vapor deposition is smaller than that of the method described above, the step of the substrate is reduced, and the vibration by the ultrasonic wave is reliably transmitted.
[0027]
According to a third aspect of the present invention, the light emitting device is a gallium nitride-based light emitting device including a light transmitting crystal substrate, wherein the light transmitting crystal substrate is a main light extraction surface, and the light emitting device is a light transmitting device. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is sealed with an optical resin, and has an effect of improving luminous efficiency.
[0028]
According to a fourth aspect of the present invention, the substrate is provided with a reflecting member formed on an inner peripheral surface of the through hole, the reflecting wall reflecting light emitted laterally from the light emitting element in a main light extracting direction. 4. The semiconductor light emitting device according to claim 1, wherein light extracted laterally from the light emitting element is reflected in a main light extraction direction to extract the main light. This has the effect of increasing the intensity of light emitted in the direction.
[0029]
The invention according to claim 5, wherein the ceramic material constituting the substrate is mainly composed of any one of aluminum oxide, aluminum nitride, and barium titanate. The semiconductor light-emitting device described above has high heat resistance, does not soften even when heated, and is chemically stable, so that a fine pattern can be easily formed.
[0030]
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0031]
(First Embodiment)
FIG. 1A is a front view of a semiconductor light emitting device according to a first embodiment of the present invention, and FIG. 1B is a plan view of the semiconductor light emitting device.
[0032]
The semiconductor light emitting device 1 is a device in which a light emitting element 5 is mounted on a surface of a white substrate 2 made of a ceramic material.
[0033]
The n-side electrode 6 and the p-side electrode 7 of the light emitting element 5 are electrically connected to the two lead electrodes 3 and 4 of the substrate 2 via the micro bumps 8 and 9, respectively.
[0034]
At the time of connection, heat and ultrasonic vibrations are applied to the micro bumps 8 and 9 and the micro bumps 8 and 9 are joined by pressing.
[0035]
The ceramic material forming the substrate 2 can be mainly composed of, for example, aluminum oxide.
[0036]
This material has characteristics of excellent heat resistance and small deformation due to heat. Therefore, the micro-bumps 8 and 9 are not deformed by the heat (approximately 160 to 190 ° C.) applied at the time of connection and do not attenuate the ultrasonic vibration. Can be done.
[0037]
Note that the ceramic substrate 2 has not been used in a semiconductor light emitting device as shown in FIG. The reason is that transfer molding is used when sealing the light emitting element mounted on the substrate with resin.However, in the case of a ceramic substrate, the elasticity is insufficient when the mold is brought into close contact and the resin flows. Because of this, it cannot be sealed and resin leakage occurs.
[0038]
This time, by mounting the gallium nitride based light emitting element by flip chip mounting, the wires disappeared, so it became possible to perform resin molding by potting or screen printing from the top side of the light emitting element 5, and it was not necessary to perform transfer molding, Ceramic substrates can now be used.
[0039]
The substrate 2 is formed in a rectangular plate shape, and through-hole electrodes 10 and 11 are formed on opposing short sides, and lead electrodes 3 and 4 are connected to the back surface.
[0040]
The lead electrodes 3 and 4 are made of NiCr, Au (the outermost surface is Au), and are metal-deposited on the surface of the substrate 2. The two lead electrodes 3 and 4 are connected to the front side via the through-hole electrodes 10 and 11 from both ends on the back side of the substrate 2 which is conductively connected to an external wiring (not shown), and are opposed to each other at the center part on the front side. This opposing portion is formed in substantially the same shape as the n-side electrode 6 and the p-side electrode 7 of the light emitting element, and the gap width therebetween is formed to be 10 to 40 μm. Since the patterns of the lead electrodes 3 and 4 are formed on the ceramic substrate 2 by vapor deposition, the gap width can be formed very small and accurately.
[0041]
With such a configuration, recognition accuracy of the flip chip bonder on which the light emitting element 5 is mounted is improved, and even if the mounting position is slightly shifted, no open or short circuit occurs.
[0042]
The thickness of the lead electrodes 3 and 4 can be formed to 2 to 5 μm by using metal evaporation. When ultrasonic vibration is applied, pressure is applied to the substrate 2 from the light emitting element 5 side, but plating is applied to the resin substrate. When the lead electrode is formed by the method, the thickness of the lead electrode is increased, and the central portion of the back surface of the resin substrate floats from the support table, so that the resin substrate is bent. Then, the vibration transmitted from the microbump to the lead electrode is absorbed by the bending of the resin substrate. By reducing the thickness of the lead electrodes 3 and 4, the back surface of the substrate 2 is in close contact with the support table, and vibration is reduced from the micro bumps 8 and 9 to the lead electrodes 3 and 9 by using the ceramic substrate 2 with low internal friction. 4, the welding can be performed reliably.
[0043]
The light-emitting element 5 has a square plate shape in which a plurality of gallium nitride-based compound semiconductor films are laminated on a translucent crystal substrate 12, and the n-side electrode 6 and the p-side electrode 7 are formed on the gallium nitride-based compound semiconductor layer side. Are arranged respectively. The n-side electrode 6 and the p-side electrode 7 are flip-chip mounted on the lead electrodes 3 and 4 of the substrate 2 with the substrate facing the substrate 2.
[0044]
In the light emitting element 5, the epoxy resin 13 seals the space between the light emitting element 5 including the top surface and side portions of the gallium nitride-based compound semiconductor layer and the micro bumps 8 and 9 and the substrate 2.
[0045]
The blue or green light traveling from the light emitting layer included in the gallium nitride-based compound semiconductor layer of the light emitting element 5 toward the main light extraction surface or to the side passes through the epoxy resin 13 and is extracted to the outside.
[0046]
In addition, white light can be obtained by mixing a phosphor that converts blue light into its complementary color light into the sealing resin.
[0047]
(Second embodiment)
FIG. 2A is a front view of a semiconductor light emitting device according to a second embodiment of the present invention, and FIG. 2B is a plan sectional view of the semiconductor light emitting device. The semiconductor light emitting device according to the first embodiment is a top-view type, whereas the semiconductor light emitting device 20 according to the second embodiment is a side-view type light emitting device.
[0048]
The position of the through-hole electrode of the ceramic substrate 21 of the semiconductor light emitting device 20 is different from that of the substrate 2 of the semiconductor light emitting device 1 described above. New arc-shaped notches 24 and 25 (through-hole electrodes) are formed at two adjacent corners, and lead electrodes 22 and 23 formed by metal evaporation are formed on the surface.
[0049]
The semiconductor light emitting element 15 is mounted on the lead electrodes 22 and 23, and a reflecting member 27 having a through hole is externally mounted on the semiconductor light emitting element 15 and fixed to the substrate 21. The shape of the through hole of the reflection member 27 is a conical cross-sectional shape that spreads in the main light extraction direction, and efficiently reflects lateral light emitted from the semiconductor light emitting element 15 in the main light extraction direction to increase on-axis luminous intensity. For this purpose, it is made of a white resin molded product, or its inner peripheral surface 28 is plated with Ag having good reflectivity. The inside of the through hole is filled with a transparent epoxy resin 29.
[0050]
The portions of the side surfaces of the substrate 21 where the notches 24 and 25 are formed are connected to the lead electrodes 22 and 23, so that the side surface 26 of the substrate 21 on the side of the notches (through-hole electrodes) 24 and 25 is used as a mounting surface. The semiconductor light emitting device 20 can be used as a side view type.
[0051]
Further, after the semiconductor light emitting device is flip-chip mounted on the ceramic substrate, a resin paste containing a phosphor is applied around the semiconductor light emitting device by a screen printing method or the like (not shown), and the semiconductor light emitting device emits white light. It can also be a device.
[0052]
(Third embodiment)
FIG. 3A is a front sectional view of a semiconductor light emitting device according to a third embodiment of the present invention, and FIG. 3B is a plan view of the semiconductor light emitting device. This is a semiconductor light emitting device 30 formed by adding the reflecting member 27 of the semiconductor light emitting device 20 according to the second embodiment to the top view type semiconductor light emitting device 1 according to the first embodiment. is there.
[0053]
The semiconductor light emitting device 30 is different from the semiconductor light emitting device 1 according to the first embodiment, which is thin and has a wide light distribution, in that the lateral light emitted from the semiconductor light emitting element 5 is efficiently emitted in the main light extraction direction. It is made for the purpose of reflecting well and increasing on-axis luminous intensity, and is applied to a white LED for illumination.
[0054]
Also in this case, after the semiconductor light emitting device is flip-chip mounted on the ceramic substrate, a resin paste containing a phosphor is applied around the semiconductor light emitting device by a screen printing method or the like (not shown) to emit white light. Semiconductor light emitting device.
[0055]
In addition, as the ceramic material, for example, silicon nitride, barium titanate, or the like can be used in addition to the above materials.
[0056]
Further, the lead electrode of the substrate can be formed by firing.
[0057]
【The invention's effect】
As described above, according to the present invention, the ceramic material is used for the substrate, so that the substrate is chemically stable, and the lead electrode can be accurately formed on the surface. By efficiently joining the micro-bumps without being deformed and absorbing ultrasonic vibrations, flip chip mounting of the semiconductor light emitting element can be reliably performed and the whole can be reduced in thickness.
[0058]
When the lead electrode is deposited on the surface of the substrate, the step of the substrate becomes small, and the vibration by the ultrasonic wave is transmitted reliably, so that the bonding of the micro bumps can be performed more reliably.
[0059]
When a reflective member having a through hole is provided on a substrate, light extracted laterally from the light emitting element is reflected in a main light extraction direction, and luminous efficiency can be increased.
[0060]
When a substrate made of a ceramic material is mainly made of aluminum oxide, aluminum nitride, or barium titanate, it has high heat resistance, does not soften even when heated, and is chemically stable. It is easy to ensure the bonding of the micro bumps. In addition, aluminum nitride can improve heat radiation characteristics, and barium titanate can form a capacitor, and can protect the gallium nitride based semiconductor light emitting element from an electrostatic breakdown voltage of about 200 V.
[Brief description of the drawings]
FIG. 1A is a front view of a semiconductor light emitting device according to a first embodiment of the present invention; FIG. 1B is a plan view of the semiconductor light emitting device; FIG. FIG. 3B is a front sectional view of the semiconductor light emitting device according to the embodiment; FIG. 3A is a front sectional view of the semiconductor light emitting device according to the third embodiment of the present invention; FIG. 4 (A) is a plan view of the semiconductor light emitting device according to the related art; FIG. 4 (A) is a plan view of the semiconductor light emitting device according to the related art; FIG. FIG. 6B is a front view of a side-view type semiconductor light emitting device according to a conventional example. FIG. 6B is a plan sectional view of the semiconductor light emitting device. FIG. 6A is a side view type semiconductor according to a conventional example using a composite light emitting element. The front view (B) of the light emitting device is a plan sectional view of the semiconductor light emitting device.
DESCRIPTION OF SYMBOLS 1 Semiconductor light emitting device 2 Substrate 3, 4 Lead electrode 5 Light emitting element 6 n side electrode 7 p side electrode 8, 9 Micro bump 10, 11 Through hole electrode 12 Translucent crystal substrate 13 Epoxy resin 20 Semiconductor light emitting device 21 Substrate 22, 23 Lead electrode 24, 25 Notch (through-hole electrode)
26 side surface 27 reflective member 28 inner peripheral surface 29 epoxy resin

Claims (5)

In a semiconductor light emitting device having the light emitting element mounted on the substrate by bonding a p-side electrode and an n-side electrode of the light emitting element to two lead electrodes formed on the substrate via micro bumps,
A semiconductor light emitting device, wherein the substrate is made of a ceramic material. The semiconductor light emitting device according to claim 1, wherein the lead electrode is deposited on a surface of the substrate. The light-emitting element is a gallium nitride-based light-emitting element including a light-transmitting crystal substrate, wherein the light-transmitting crystal substrate is used as a main light extraction surface, and the light-emitting element is sealed with a light-transmitting resin. The semiconductor light emitting device according to claim 1, wherein: 2. The substrate according to claim 1, wherein a reflection member is provided on the inner peripheral surface of the through hole, the reflection wall reflecting light emitted laterally from the light emitting element in a main light extraction direction. 4. The semiconductor light-emitting device according to any one of items 3 to 3. 5. The semiconductor light emitting device according to claim 1, wherein the ceramic material forming the substrate is mainly made of one of aluminum oxide, aluminum nitride, and barium titanate. 6.

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