JP4325207B2 - Surface emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin surface light emitting device usable as a light source for a back light of a liquid crystal display. <P>SOLUTION: This surface light emitting device 1 is provided with a LED chip 11 and a light guide plate 12 having a light extracting face 12a and an end face 12b. A part of the LED chip 11 is embedded in the end face of the light guide plate 12, and the other part of the LED chip 11 is exposed from the end face 12b of the light guide plate 12. The LED chip 11 is disposed so that its face exposed from the end face 12b of the light guide plate 12 is disposed on a mounting substrate 17. The mounting substrate 17 is disposed on at least a part of the inner wall face of a casing 13. The surface light emitting device 1 is formed by filling a light guide plate forming material to form the light guide plate 12 in the casing 13 disposed on at least a part of the inner wall face of the mounting substrate 17 on which the LED chip 11 is disposed. <P>COPYRIGHT: (C)2004,JPO&amp;NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface emitting equipment available as a light source such as a backlight of a liquid crystal display, particularly to a surface emitting equipment thin that can reduce the thickness.
[0002]
[Prior art]
2. Description of the Related Art In recent years, a surface light-emitting device that emits light from a light-emitting diode, which is a light-emitting element that is a point light source, placed on a lead frame and sealed with a mold resin, is used as a light source for a liquid crystal display backlight or the like. It has been. This surface light emitting device is configured to allow light from one or more light emitting diodes to enter from one end surface of a light guide plate having opposing main surfaces and to emit light from the entire one main surface of the light guide plate. The
[0003]
As an example of such a surface light-emitting device, a schematic cross section is shown in FIG. In order to introduce light from the light-emitting diode into the plate-like light-transmitting member 504 that is a light guide plate, the light-emitting diode 502 is optically connected to the end face of the plate-like light-transmitting member 504. In addition, except for the end face to which the light-emitting diode is connected and the light extraction surface, the light-emitting diode disposed on the light guide and the mounting substrate 503 serves as a reflector made of a resin to which aluminum or a white pigment is added. A cover surface light emitting device is configured at 505. In particular, a light emitting diode capable of emitting mixed-color light such as white light by combining a blue LED chip and a phosphor that absorbs blue light emitted from the blue LED chip and converts it into yellow is used as a light source. Therefore, it can be used as a surface emitting device capable of emitting various emission colors. Such surface light emitting devices are rapidly spreading as liquid crystal backlights for mobile phones. Further, in the market, it is desired to reduce the thickness of the liquid crystal display, and accordingly, it is required to reduce the thickness of the surface light emitting device. Also, a surface light emitting device is known in which the entire light emitting diode is buried in a light guide plate, and a power connection terminal is drawn out from a side end surface near the buried light source (Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-127158
[Problems to be solved by the invention]
However, when the light emitting diode as described above is used in a surface light emitting device, there is a problem that it is difficult to make the surface light emitting device thinner than the light emitting diode. Therefore, an object of the present invention is to provide a thin surface light emitting device that can be used as a light source such as a backlight of a liquid crystal display.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a surface light emitting device according to a first aspect of the present invention includes a light guide plate having a light extraction surface and an end surface, and a portion embedded in the end surface and the other portion exposed from the end surface. The light guide plate has the light extraction surface, the first light guide plate containing a light transmissive diffusing material, the end surface, and the light emitted from the LED chip. A second light guide plate containing a phosphor to be converted , wherein the first light guide plate and the second light guide plate are in contact with each other at an interface, and the thickness of the light guide plate is equal to that of the light guide plate. It is less than twice the width of the LED chip in the thickness direction, and the light guide plate is formed of any one of acrylic resin, polycarbonate resin, amorphous polyolefin resin, and polystyrene resin . With this configuration, the light emitting element can be reliably positioned with respect to the mounting board attached to the end face of the light guide plate. Accordingly, it is possible to prevent a decrease in luminance caused by a poor positioning of the light emitting element. Furthermore, when a plurality of light emitting elements are arranged, the positioning between the light emitting elements can be reliably performed, and uneven luminance of the surface light emitting device can be prevented.
[0007]
Furthermore, the surface light emitting device according to claim 2 of the present invention is the surface light emitting device according to claim 1, wherein the surface light emitting device further includes a housing in which the light guide plate is disposed, and a light emitting surface of the LED chip. And the second light guide plate is disposed in a space formed by the casing and the light source cover. With this configuration, the mounting substrate can be reliably positioned with respect to the housing and the light guide plate. Therefore, it is possible to more surely prevent the luminance decrease and the luminance unevenness of the surface light emitting device due to the poor positioning of the light emitting element.
[0008]
Furthermore, in the surface light emitting device according to claim 3 of the present invention, in addition to the features of claim 1 or 2 , a light diffusion pattern is formed on the back surface of the light guide plate and the bottom surface of the housing. Features.
[0009]
In order to achieve the above object, a surface emitting equipment according to claim 4 of the present invention, in addition to any one of the features of claims 1 to 3, wherein the first light guide plate and the second light guide plate Has a light diffusion portion on the back surface .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments shown below are intended to illustrate the surface emission equipment for embodying the technical idea of the present invention, the present invention does not specify the surface emission equipment in the following.
[0011]
Further, the present specification by no means specifies the members shown in the claims to the members of the embodiments. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, in the following description, the same name and symbol indicate the same or the same members, and detailed description thereof will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing.
[0012]
The surface light-emitting device can select the shape of the light guide plate to be used according to its application and purpose.For example, when used for a backlight of a liquid crystal such as a personal computer, a substantially rectangular flat light guide plate is used. Moreover, when using for the backlight etc. of the panel meter of a motor vehicle, the light-guide plate of the shape according to the design is used.
[0013]
[Embodiment 1]
FIG. 1 is a schematic cross-sectional view of a surface light-emitting device 1 according to Embodiment 1 of the present invention as viewed from the side. The surface light emitting device 1 includes an LED chip 11 as a light emitting element, and a light guide plate 12 having a light extraction surface 12a and an end surface 12b. A part of the LED chip 11 is embedded in the end surface 12 b of the light guide plate 12, and the other part of the LED chip 11 is exposed from the end surface 12 b of the light guide plate 12. In the example of FIG. 1, in the drawing, the LED chip 11 is exposed so that the surface of the right end portion forms the same plane as the right end surface of the light guide plate 12, and the entire LED chip 11 excluding the surface of the right end portion. The light guide plate 12 is embedded so as to be sealed. The LED chip 11 has a surface exposed from the end surface of the light guide plate 12 disposed on the mounting substrate 17. The mounting substrate 17 is disposed on at least a part of the inner wall surface of the housing 13. In the example of FIG. 1, an example in which the mounting substrate 17 and the housing 13 are formed separately is shown, but the mounting substrate 17 and the housing 13 may be configured integrally. In this case, a wiring pattern is formed on at least a part of the inner wall surface of the housing 13. Furthermore, on the light guide plate 12, a diffusion sheet 14 that makes the light from the light guide plate 12 uniform, and a first prism sheet 15 and a second prism sheet 16 that direct the light in the observed direction are placed in order. .
[0014]
(LED chip 11)
Nitride compound semiconductors (general formula In _i Ga _j Al _k N, where 0 ≦ i, 0 ≦ j, 0 ≦ k, i + j + k = 1) that can be used in the present invention include InGaN and various impurities. There are various types, including doped GaN. The LED chip 11 is formed by growing a semiconductor such as InGaN or GaN as a light emitting layer on a substrate by MOCVD or the like. Examples of the semiconductor structure include a homostructure, a heterostructure, or a double heterostructure having a MIS junction, a PI junction, a PN junction, and the like. The nitride semiconductor layer can have various emission wavelengths depending on the material and the degree of mixed crystal. Moreover, it can also be set as the single quantum well structure and multiquantum well structure which formed the semiconductor active layer with the thin film which produces a quantum effect. In the present invention, as the LED chip 11, an yttrium / aluminum / garnet phosphor and / or a nitride phosphor having a semiconductor light emitting layer capable of emitting ultraviolet to blue light and activated by cerium described later is efficiently used. It is preferable to use an LED chip that can be excited.
[0015]
The LED chip 11 may have an electrode structure in which a semiconductor layer is formed on an insulating substrate such as a sapphire substrate, and a p-electrode and an n-electrode are formed on the same surface side. The LED chip 11 may be on a conductive or semiconductive substrate such as a GaN substrate. Alternatively, a counter electrode structure in which a semiconductor layer is formed and a p electrode and an n electrode are opposed to each other with the semiconductor layer interposed therebetween may be employed.
[0016]
(Light guide plate 12)
In the present invention, the material used for the light guide plate 12 is preferably a material excellent in light transmittance and moldability, and examples thereof include acrylic resin, polycarbonate resin, amorphous polyolefin resin, and polystyrene resin. The light guide plate 12 can be formed in various shapes such as a substantially rectangular flat plate shape, a panel shape of an automobile panel meter, and a pointer of a meter needle. The light guide plate 12 contains, for example, translucent fine particles having an average particle diameter of 3 to 20 μm made of benzoguanamine resin, PET, or the like as a diffusing material.
[0017]
(Case 13)
As a housing | casing used in this invention, the mounting substrate 17 and the light-guide plate 12 which have arrange | positioned the LED chip 11 at least can be hold | maintained. The housing 13 is preferably made of various materials such as resin and metal. In particular, in consideration of light reflection and heat dissipation of the LED chip 11, metals such as nickel, iron and copper, and various alloys such as stainless steel are more preferably used. Further, Ag vapor deposition is preferably performed on the inner wall surface of the housing 13. The size and shape of the housing 13 can be variously selected according to the light guide plate 12, the LED chip 11 and the space. Further, by forming irregularities on the bottom surface of the housing 13 and forming a light diffusion portion on the back surface of the light guide plate 12, a uniform light emitting surface free from luminance unevenness can be obtained. Such unevenness as the light diffusing portion forms a diffusion pattern (for example, a convex portion) in the vicinity of the LED chip 11 such that the interval is high when the luminance is high and the interval is dense when the luminance is low. It is preferable to make it. If such a diffusion pattern is formed, it is possible to further improve luminance unevenness in the vicinity of the LED chip.
[0018]
(Mounting board 17)
As the mounting substrate 17 used in the present invention, an insulating substrate having a conductive pattern formed on its surface can be used. One or more LED chips 11 are arranged on the mounting substrate 17, and the electrodes of the LED chips 11 and the conductive patterns are electrically connected directly or via wires or the like. Furthermore, this conductive pattern is electrically connected to a connection terminal (not shown), and power is supplied to the LED chip 11 from the outside via this connection terminal. The connection terminal may be extended from the opening direction of the housing 13 (upper side in FIG. 1), or an opening is provided in a part of the inner wall surface of the housing 13 so that the rear surface of the mounting substrate 17 (the surface on the right side in FIG. 1). ) May be exposed.
[0019]
When the LED chip 11 has a coplanar electrode structure in which a p-electrode and an n-electrode are formed on the same plane side, so-called flip chip bonding in which the electrodes are directly bonded to the conductive pattern may be used. It is good also as what is called wire bonding which fixes to the mounting substrate 17 and bonds to a conductive pattern via a wire. When flip chip bonding is used, heat generated in the LED chip electrodes and light emitting layer can be efficiently dissipated to the mounting substrate 17 side, and wire bonding is not required, so that the LED chips 11 are arranged with high density. Is possible. On the other hand, when wire bonding is used, short-circuiting between the electrodes of the LED chip 11 is unlikely to occur, so that mass productivity can be increased. In particular, by arranging the bonding position of the wire to the conductive pattern of the mounting substrate 17 between the LED chips 11, it is possible to prevent the thickness of the surface light emitting device from increasing. Similarly, when the LED chip 11 has a counter electrode structure in which a p-electrode and an n-electrode are formed to face each other, it is preferable that the position of wire bonding to the conductive pattern of the mounting substrate 17 is disposed between the LED chips 11.
[0020]
Further, the mounting substrate 17 and the housing 13 may be integrally formed by forming a conductive pattern on at least a part of the inner wall surface of the housing 13. When the housing 13 is formed of an insulating member such as resin, for example, a conductive pattern can be directly formed on at least a part of the inner wall surface. When the casing 13 is formed of a conductive member such as metal, for example, at least a part of the inner wall surface is punched and the punched portion is connected to other conductive members of the casing 13 via an insulating member. A conductive pattern can also be formed by embedding electrically insulated conductive members.
[0021]
(Phosphor)
In the present invention, the phosphor can be contained in the light guide plate 12, the diffusion sheet 14, or the like. Further, the phosphor sheet containing the phosphor in the translucent resin is arranged between the light guide plate 12 and the diffusion sheet 14 or between the diffusion sheet 14 and the first prism sheet 15. You can also. Examples of the phosphor used in the surface light emitting device of the present invention include a photoluminescence phosphor that emits light when excited by visible light or ultraviolet light. Specific examples of photoluminescent phosphors include yttrium, aluminum, and garnet fluorescence activated with cerium as a phosphor capable of emitting white light by complementary color with light from a nitride semiconductor LED chip capable of emitting blue light. And phosphors such as Mg ₅ Li ₆ Sb ₆ O ₁₃ : Mn, Mg ₂ TiO ₄ : Mn, and phosphors obtained by mixing a plurality of these phosphors. Can also be used.
[0022]
Here, a yttrium / aluminum / garnet phosphor activated with cerium as a more suitable phosphor is shown below. In the present invention, the yttrium-aluminum-garnet phosphor activated with cerium is to be interpreted in a broad sense, and at least one selected from the group consisting of Lu, Sc, La, Gd and Sm is part or all of yttrium. It is used to mean a phosphor that emits a fluorescent action by substituting with one element, or replacing part or all of aluminum with either or both of Ga and In.
[0023]
More specifically, the general formula _{(Y z Gd 1-z)} 3 Al 5 O 12: Ce ( where, 0 <z ≦ 1) photoluminescence phosphor and the general formula represented by _{(Re 1-a Sm a)} 3 Re ' ₅ O ₁₂ : Ce (where 0 ≦ a <1, Re is at least one selected from Y, Gd, La, and Sc, and Re ′ is at least one selected from Al, Ga, and In. ) Is a photoluminescent phosphor.
[0024]
In addition to the YAG phosphor, a nitride phosphor can be used alone. The nitride-based phosphor used in the present invention contains N and at least one element selected from Be, Mg, Ca, Sr, Ba, and Zn, and C, Si, Ge, Sn, Ti, Zr. And at least one element selected from Hf, and a phosphor activated by at least one element selected from rare earth elements. The nitride-based phosphor used here is excited and emits light by absorbing light emitted from the LED chip 11 from visible light, ultraviolet light, or YAG-based phosphor. Such nitride-based phosphors include, for example, Sr—Ca—Si—N: Eu, Mn added, Ca—Si—N: Eu, Sr—Si—N: Eu, Sr—Ca—Si—O. -N: Eu, Ca-Si-ON: Eu, Sr-Si-ON: Eu-based silicon nitride. The basic constituent element of this phosphor is the general formula L _X Si _Y N _{(2 / 3X + 4 / 3Y)} : Eu or L _X Si _Y O _Z N _{(2 / 3X + 4 / 3Y-2 / 3Z)} : Eu (L is Sr, Ca, or any one of Sr and Ca). In the general formula, X and Y are preferably X = 2, Y = 5, or X = 1, Y = 7. Specifically, the basic constituent elements, Mn is added _{(Sr X Ca 1-X)} 2 Si 5 N 8: Eu, Sr 2 Si 5 N 8: Eu, Ca 2 Si 5 N 8: Eu, Sr _{X Ca 1-X Si 7 N} 10: Eu, SrSi 7 N 10: Eu, CaSi 7 N 10: it is preferable to use a phosphor represented by Eu. In the composition of these phosphors, at least one selected from the group consisting of Mg, Sr, Ca, Ba, Zn, B, Al, Cu, Mn, Cr and Ni may be contained. The mixing ratio of Sr and Ca can be changed as desired.
[0025]
Such a nitride-based phosphor absorbs part of the blue light emitted by the LED chip 11 and emits light in the yellow to red region. By using the nitride-based phosphor together with the YAG-based phosphor, the blue light emitted from the LED chip 11, the yellow light from the YAG-based phosphor, and the red light from the nitride-based phosphor are mixed to produce a warm color system. A surface emitting device that emits white light can be obtained.
[0026]
[Embodiment 2]
FIG. 2 is a schematic cross-sectional view of the surface light-emitting device 2 according to Embodiment 2 of the present invention as viewed from the side. Members denoted by the same reference numerals in the drawings are the same as those in the first embodiment, and a description thereof is omitted. The second embodiment is different from the first embodiment in that a light source cover 18 is arranged on the light emitting surface side of the LED chip 11 (upper side in FIG. 2). By disposing the light source cover 18 on the light emitting surface side of the LED chip 11 as a light emitting element in this way, light emission from the LED chip 11 is not directly observed by an observer, so that the vicinity of the LED chip 11 is particularly bright. It is prevented from being observed. Therefore, more uniform surface emission can be obtained.
[0027]
As the light source cover 18, various types such as a resin and a metal can be preferably cited as in the case 13. In particular, in consideration of light reflection and heat dissipation of the LED chip 11, metals such as nickel, iron and copper, and various alloys such as stainless steel are more preferably used. Furthermore, Ag vapor deposition is preferably performed on the inner surface of the light source cover 18 (the lower surface in FIG. 2). Furthermore, by forming irregularities on the inner surface of the light source cover 18 to form a light diffusion portion, more uniform surface emission can be obtained. The light source cover 18 can be formed integrally with the housing 13.
[0028]
[Embodiment 3]
FIG. 3 is a schematic cross-sectional view of the surface light-emitting device 3 according to Embodiment 3 of the present invention as viewed from the side. Members denoted by the same reference numerals in the drawings are the same as those in the first and second embodiments, and a description thereof will be omitted. In the third embodiment, the light guide plate includes a first light guide plate 121 having a light extraction surface 121a and a second light guide plate 122 having an end surface 122b in which a part of the LED chip 11 is embedded. Is different. The first light guide plate 121 contains translucent fine particles having an average particle diameter of 3 to 20 μm made of benzoguanamine resin, PET, or the like as a diffusing material. The second light guide plate 122 contains at least the above-described phosphor. In the present embodiment, a part of the LED chip 11 is embedded in the end surface 122 b of the second light guide plate 122, and the other part of the LED chip 11 is exposed from the end surface 122 b of the second light guide plate 122. The surface light emitting device preferably includes a light source cover 18. The second light guide plate 122 is preferably arranged in a space formed by the housing 13 and the light source cover 18. According to the present embodiment, when performing color conversion using a phosphor, a surface light emitting device with little chromaticity unevenness can be obtained.
[0029]
【Example】
FIG. 4 schematically shows a method for manufacturing the surface light emitting device according to Embodiment 1 of the present invention described above. In the present embodiment, a casing 13 is used which is composed of four frames (inner wall surfaces) and a bottom surface formed of a metal having a thickness of 0.15 mm on which Ag is deposited. First, the mounting substrate 17 on which five LED chips are arranged is arranged in one of the four frames of the housing 13 (FIG. 4a). Next, a light guide plate forming material such as a resin for forming the light guide plate 12 is filled in the housing 13. Then, a diffusion sheet having a thickness of 65 μm, a first prism sheet having a thickness of 65 μm, and a second prism sheet having a thickness of 65 μm are sequentially placed on the light guide plate 12 (FIG. 4b).
[0030]
In this way, the surface light emitting device of the present invention is obtained. In the surface light emitting device according to the present invention, since the LED chip 11 itself is sealed by the light guide plate 12, the thickness of the conventional surface light emitting device is 0.8 to 1.0 mm. .25 to 0.35 mm. The thickness of the light guide plate 12 is preferably not more than 3 times, more preferably not more than 2 times the width of the LED chip 11 in the thickness direction of the light guide plate 12.
[0031]
Further, the light source cover 18 may be disposed after the formation as described above.
[0032]
In the method of manufacturing the surface light emitting device including the first light guide plate 121 and the second light guide plate 122, first, a part of the opening of the housing 13 is covered with the light source cover 18, and the housing 13 and the light source cover 18 are covered. A light guide plate forming material such as a resin for forming the second light guide plate 122 is filled in the space formed in step (b). Then, it can manufacture by filling light guide plate forming materials, such as resin which forms the 1st light guide plate 121, in the space in the remaining housings 13.
[0033]
【The invention's effect】
As described above, a thin surface light emitting device that can be used as a light source such as a backlight of a liquid crystal display can be provided. Since the LED chip is directly molded by the light guide plate in the surface light emitting device of the present invention, the LED chip and the light emitting diode made of a mold resin for sealing the LED chip are arranged on the light guide plate even if the chip size is the same. The surface light emitting device can be made thinner than the surface light emitting device.
[0034]
Further, in the surface light emitting device of the present invention, since the LED chip is directly molded by the light guide plate, a surface light emitting device with less luminance unevenness can be obtained as compared with a surface light emitting device using a light emitting diode with strong directivity. Furthermore, in the surface light-emitting device of the present invention, the other part of the light-emitting element is exposed from the end surface of the light guide plate, so that heat dissipation is achieved as compared with the surface light-emitting device in which the light-emitting diode is completely buried in the light guide plate. Is expensive.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a surface light-emitting device according to Embodiment 1 of the present invention as viewed from the side.
FIG. 2 is a schematic cross-sectional view of a surface light emitting device according to a second embodiment of the present invention as viewed from the side.
FIG. 3 is a schematic cross-sectional view of a surface light emitting device according to a third embodiment of the present invention as viewed from the side.
FIG. 4 is a schematic view showing a method for manufacturing a surface light emitting device according to the present invention.
FIG. 5 is a schematic cross-sectional view showing an example of a conventional surface light emitting device.
[Explanation of symbols]
1, 2, 3 ... Surface emitting device 11 ... LED chip 12 ... Light guide plate 13 ... Case 14 ... Diffusion sheet 15 ... First prism sheet 16 ... Second prism Sheet 17 ... Mounting substrate 18 ... Light source cover 121 ... First light guide plate 122 ... Second light guide plate

Claims (4)

A light guide plate having a light extraction surface and an end surface;
An LED chip partly embedded in the end face and the other part exposed from the end face;
With
The light guide plate is
A first light guide plate having the light extraction surface and containing a light transmissive diffusion material;
A second light guide plate having the end face and containing a phosphor that converts light emitted from the LED chip ;
The first light guide plate and the second light guide plate are in contact at the interface;
The thickness of the light guide plate is not more than twice the width of the LED chip in the thickness direction of the light guide plate,
The surface light-emitting device, wherein the light guide plate is formed of any one of an acrylic resin, a polycarbonate resin, an amorphous polyolefin resin, and a polystyrene resin . The surface emitting device further includes
A housing in which the light guide plate is disposed;
A light source cover disposed on the light emitting surface side of the LED chip;
Have
The surface light-emitting device according to claim 1, wherein the second light guide plate is disposed in a space formed by the casing and the light source cover. Bottom of the back and the housing of the light guide plate, a surface light-emitting device according to claim 1 or 2, characterized in that the light diffusion pattern is formed.   The surface light-emitting device according to any one of claims 1 to 3, wherein the first light guide plate and the second light guide plate have a light diffusion portion on a back surface.

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