JP2007194383A - Optical member and backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep a conductive adhesive applied on the undersurfaces of LEDs uniform in thickness so as to satisfy requirements, such as a density enhancement and an improvement in heat dissipation properties, for LEDs mounted on a sub-mount, and to prevent an electrical short circuit from occurring between interconnections due to the fact that the conductive adhesive spreads too wide. <P>SOLUTION: Columnar bumps having each a smooth outer shape are provided at the periphery of a die bonding region on a sub-mount, so that the thickness and wetting spread of the conductive adhesive can be controlled when a die bonding process is carried out. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a submount on which a semiconductor light emitting element is mounted. Furthermore, another aspect of the present invention relates to a backlight. The submount can be used effectively. In addition, this backlight is extremely useful for LCD (Liquid Crystal Display).

  In recent years, high-performance light-emitting diodes (hereinafter abbreviated as LED (Light Emitting Diode)) characterized by high brightness, high luminous efficiency, and long life have been put into practical use. Various displays, traffic lights, backlights for liquid crystal displays, It has begun to be used for printer heads and lighting.

  While there is a trend toward miniaturization and high density of light source modules, the heat generated from the LED chip tends to increase in conjunction with an increase in power consumption due to higher brightness.

  Normally, when the current flowing through the LED is increased, the light emission luminance increases relatively linearly up to a certain current value, but the light emission efficiency decreases in inverse proportion to the temperature increase of the LED. In addition, the operating characteristics become unstable, for example, the spectrum of light emitted from the light emitting element shifts with increasing temperature. In some cases, thermal stress may cause partial destruction of the light emitting device. Therefore, in order to drive the LED stably, it is important to suppress a temperature rise during driving, and a structure that efficiently dissipates heat generated in the LED is desired. In mounting a semiconductor laser diode, it is common to interpose a submount rather than mounting a chip directly on a mounting substrate from the viewpoint of heat dissipation characteristics and handling. The submount has a role of expanding a heat radiation cross section from the semiconductor light emitting element to the substrate, and heat generated from the LED is efficiently transmitted to the mounting substrate.

  The connection between the LED and the submount includes a method of connecting Au electrodes to each other by ultrasonic waves or thermocompression bonding, and a method of connecting by soldering such as AuSn by thermocompression bonding or reflow. In the case of ultrasonic connection or thermocompression bonding, it takes time to apply ultrasonic waves or pressure to each element, which hinders increase in throughput. In the case of solder reflow, the chips can be mounted together, but the connection is performed at a high temperature of 200 ° C. or higher.

  On the other hand, when the Ag paste is used, the module on which the LED chip is mounted can be collectively heated at a temperature of about 150 ° C.

  From the viewpoint of LED heat dissipation, the Ag paste conventionally used for die bonding has a thermal conductivity that is one to two orders of magnitude smaller than metal materials such as solder, and is several W / mK. In general, conductive pastes such as Ag pastes are blended with resin in the base material, and the reason is that the thermal conductivity of these resins is lower than that of metals. In order to make lead-free solder materials, development of alternative solder materials is progressing, and the performance of Ag paste, a kind of conductive adhesive, is also improving. Ag pastes with a silver filler filling rate of up to about 90% and a thermal conductivity of up to about 30 W / mK have been produced, and the possibility of application to LED chip die bonding has emerged. Dispensing and printing techniques are used to supply the Ag paste. In order to reduce the size and increase the density of the package, it is necessary to control the amount of paste supplied to prevent short-circuiting between electrodes due to excessive spreading of the paste agent and insufficient wetting. Several ideas have been proposed for these problems.

  Japanese Patent Laid-Open No. 9-223846 (Patent Document 1) discloses that when an LED is flip-chip connected with a conductive material, the anode and cathode electrodes are prevented from being short-circuited. A method of forming a concave groove by etching is shown. Moreover, the following fact is shown in the Example of Unexamined-Japanese-Patent No. 2002-299747 (patent document 2). That is, after ultrasonically connecting the Au electrodes of the submount and the motherboard, when injecting the heat conductive paste into the gap, if there is a region where it is not desirable for the paste to spread, a convex frame or the like is previously formed on the substrate. This is a method of providing a dike and pouring paste into it.

  In JP-A-2005-183899, an example in which a plurality of hemispherical convex portions are provided on the upper surface of a conductor layer located inside the outside of the light emitting element, or rectangular convex portions are parallel to the outer periphery of the light emitting element. The example provided so that it may become is shown (patent document 3).

Japanese Patent Application Laid-Open No. 9-223846 (FIG. 2) JP 2002-299747 A (paragraph <0083>) JP 2005-183899 A (claim 1, paragraph <0036>)

  Ag paste has been studied as a die-bonding agent instead of solder. However, when the application amount of the Ag paste is small, a gap is generated between the LED chip and the submount substrate, or the chip is inclined. In addition, since the film thickness is not uniform, there is a concern that the heat dissipation characteristics may be degraded. On the other hand, when there is too much application quantity of a die-bonding agent, there exists a possibility of contacting with an adjacent LED chip and a wiring pattern.

  In order to satisfy the demands for high density and high heat dissipation of LED mounting, it is necessary to develop a die bond system that does not cause a short circuit between electrodes while maintaining a uniform film thickness.

  Currently used LED chips are about 1 mm square at most. When the amount of Ag paste corresponding to this area is supplied by printing or dispensing, one or several points are placed in a circle or ellipse. On top of this, when an LED chip is mounted using a chip bonder, the Ag paste is crushed, and excess Ag paste protrudes from the outer periphery of the chip. Here, in order to sufficiently spread the Ag paste to the four corners of the chip, it is necessary to increase the amount of the Ag paste or scrub the chip.

  In the present invention, the problem is solved by devising the structure on the submount side on which the LED chip is mounted.

  As a first method, convex bumps having a smooth curve around a height of several to several tens of μm, for example, cylindrical bumps, are formed on the electrodes of the submount. By arranging these bumps in a staggered manner rather than linearly at the inner side of the LED mounting position, it is more preferable that the Ag paste moves in the four corner directions while suppressing the protrusion from the four sides and the film thickness becomes uniform. Further, by using convex bumps having a smooth curve around the periphery, Ag paste can easily flow around the back side of the bumps. A typical example of this bump is, for example, a cylindrical or elliptical bump. In addition, by arranging a bump having a certain height below the LED chip, the gap between the electrode on the submount and the back surface of the LED is determined by the height of the bump. By optimizing the supply amount of the Ag paste, generation of voids can be suppressed, and both uniformity of film thickness and improvement of heat dissipation can be achieved.

  The second method is a method in which elongated frame-like bumps having a height of several tens of μm are arranged on the submount so as to surround the LED chip. The elongated bumps do not completely surround the LED chip, but provide gaps at positions close to the four corners of the LED. Furthermore, the width of the frame is reduced as it approaches the four corners. By doing so, the Ag paste spread when the chip is mounted is dammed by the bumps and driven to the four corners of the chip. It is possible to sufficiently spread the Ag paste to the four corners of the LED chip while preventing the Ag paste from spreading too much.

  Next, various aspects related to the backlight according to the present application are as follows. There are two main methods for configuring the backlight. Since the basic configuration other than the optical member according to the present invention is sufficient, the detailed description thereof will be omitted.

  The first form is a form incident from the side surface of the LCD panel. That is, a backlight substrate, a plurality of optical members disposed on the backlight substrate, a translucent member provided so as to cover the plurality of optical members, and optically attached to the translucent member A backlight including a light guide plate connected to supply light to the side surface of the LCD panel.

  The second form is a form incident from the back surface of the LCD panel. That is, a backlight substrate, a plurality of optical members disposed on the backlight substrate, a translucent member provided to cover the plurality of optical members, and a translucent member are provided. And a diffuser for supplying diffused light to the back surface of the LCD panel. In any form, any one of the optical members described so far is employed as the optical member.

  The present invention can prevent electrical shorting between wirings due to excessive spreading of the conductive adhesive while keeping the thickness of the conductive adhesive on the lower surface of the LED uniform.

  Prior to describing the embodiments of the present invention, the embodiments of the invention will be described, including a comparison with known techniques.

  As described above, a representative embodiment of the present invention includes at least a substrate having a substrate-side electrode and a semiconductor light-emitting element bonded to the substrate using a conductive adhesive, and the substrate on the substrate is An optical member having a plurality of columnar bumps having a smooth outer peripheral shape in a peripheral portion of a die bond region with respect to the semiconductor light emitting element and not having the columnar bumps in a central portion of the die bond region. In many cases, the semiconductor light emitting device is a quadrilateral. In this case, the plurality of columnar bumps are preferably provided in a staggered arrangement corresponding to each side of the quadrilateral. By the way, in the said Unexamined-Japanese-Patent No. 2005-183899 (patent document 3), the example in which several hemispherical convex parts were provided in the upper surface of the conductor layer located inside rather than the outer side of a light emitting element is shown. On the other hand, in the example of the present application, a configuration is adopted in which a plurality of columnar bumps having a smooth outer peripheral shape are provided in the peripheral portion of the die bond region, and the columnar bumps are not provided in the central portion of the die bond region. On the other hand, in the example of Patent Document 3, the hemispherical convex portions are uniformly arranged in the region of the light emitting element. The form in which the convex portion does not exist in the central portion of the die bond region as in this example is extremely preferable for allowing the conductive adhesive before solidification to have a uniform film thickness and spread to the four corners.

  Another form of this example includes at least a substrate having a substrate-side electrode and a semiconductor light emitting element bonded to the substrate using a conductive adhesive, and corresponds to a corner portion of the semiconductor light emitting element. The optical member has a frame-like bump having a gap at the corner and a width narrowing toward the corner. In many cases, the semiconductor light emitting element has a quadrangular shape, and the frame-shaped bumps are arranged corresponding to the sides of the quadrilateral.

  By the way, in the said Unexamined-Japanese-Patent No. 2005-183899 (patent document 3), the example provided so that a rectangular convex part might become parallel with respect to the outer periphery of a light emitting element was shown. However, in the example of the present invention, a frame-like bump whose width is narrowed toward the corner of the semiconductor light emitting element is used. That is, the conductive adhesive before solidification easily moves along the bumps in the four corner directions, and excess conductive adhesive is pushed out from the gaps between the bumps.

  Based on the above-described representative form, the optical member according to the present invention can be described as follows. That is, at least a substrate having a substrate-side electrode and a semiconductor light-emitting element bonded to the substrate by using a conductive adhesive, and a semiconductor light-emitting element on the periphery of a die bond region with respect to the semiconductor light-emitting element on the substrate A bump having a function of suppressing the spread of the conductive adhesive in the die bond area other than the corner of the semiconductor light emitting element and promoting the spread of the conductive adhesive in the corner of the semiconductor light emitting element; It is an optical member which does not have the said columnar bump in the center part.

  Next, the structure and manufacturing method of the submount according to the present invention will be specifically described.

<Example 1>
FIG. 1 is a schematic cross-sectional view of this example. An LED chip 5 is die-bonded using a conductive adhesive 7 on a submount substrate 1 with cylindrical bumps. Al ₂ O ₃ , SiC, and Si are used for the substrate of the LED chip. In this embodiment, a Si substrate is used from the viewpoint of cost and mass productivity. When a silicon substrate is used for the submount substrate 1, an insulating layer is formed in advance on this upper surface. When the substrate 1 is an insulating substrate, it is not necessary to provide this insulating layer. A Cu wiring 2 is formed on the substrate 1, and cylindrical bumps 3 are formed on the wiring 2. And Ag paste 7 is supplied on it and LED chip 5 is mounted. The upper and lower electrodes of the LED element are connected to an external circuit by Au wires. A Cu layer 11 is disposed at one connection portion to the external circuit, and an upper electrode conductor (Au electrode) 12 is formed thereon. The upper electrode portion of the LED chip and the upper electrode conductor 12 are connected by an Au wire 6-1. The other electrode of the LED chip is formed as a conductor layer 4 at one end of the wiring 2, and is led out to the conductor layer 4 by an Au wire 6-2. In FIG. 1, the external circuit is omitted.

  FIG. 2 is a top view of the submount. A Cu wiring 2 is provided on the Si substrate 1, and a cylindrical bump 3 made of Cu is disposed thereon. By arranging these cylindrical bumps in a staggered arrangement at the positions where the LED chips are mounted, excess Ag paste protrudes from the four corners.

  FIG. 3 is a top view in which the LED element 5 is die-bonded. 1 denote the same members as in FIG. Wirings 2 are formed on the substrate 1, and cylindrical bumps 3 are arranged at locations corresponding to the peripheral edge of the LED chip 5. Further, the lower electrode 4 of the LCD is disposed at the end of the wiring 2. In FIG. 3, the code | symbol 7 has shown the state by which Ag paste was spread | expanded favorably.

  FIG. 7 is a cross-sectional view of a comparative example showing an example of spreading of the conductive adhesive when the bump according to the present invention is not used. The same reference numerals as those in FIG. 1 are used for the respective parts in the drawings. For example, the conductive adhesive 7 expands to the surroundings, and for example, a situation occurs in which the upper electrode of the light emitting element 5 comes into contact with a conductor layer (Cu layer) 11 used for connecting to an external circuit. In this case, both electrodes of the light emitting element are connected. Further, there is a great possibility that the thickness of the conductive adhesive 7 under the light emitting element (5) is not uniform.

  Next, the manufacturing process of the columnar bump-equipped submount will be described with reference to FIGS. First, the insulating film 13 is formed on the surface of the silicon substrate 1. As a method for manufacturing this insulating film, there are a method of forming a thermal oxide film by leaving it at a high temperature of about 1000 ° C. in an oxygen or water vapor atmosphere, and a method of applying an organic resin. Next, in order to perform Cu plating for electric wiring, a power feeding film is formed on the insulating film. A vapor deposition method, a sputtering method, a CVD method, an electroless plating method, or the like can be used as a method for manufacturing the power supply film. As the power supply film in this example, a Cu / Cr double-layer film made of a sputtered film was used. The function of Cr here is to ensure adhesion between the insulating film and the Cu wiring film. Ti or W may be used instead of Cr.

  On the other hand, the sputtering film thickness of Cu is preferably a minimum film thickness that does not cause a film thickness distribution at the time of electrolytic Cu plating to be carried out later. Determine the thickness. When the copper film thickness is increased more than necessary, for example, when the film thickness exceeds 1 μm, the sputtering time becomes long and the production efficiency decreases. In addition to this, it is inevitable that the power supply film etching removal process to be performed later will be prolonged, and as a result, side etching of the rewiring layer becomes large.

  Next, a plating resist having a pattern opposite to that of the wiring is formed by using a normal photolithography technique. For electrolytic copper plating, a sulfuric acid / copper sulfate plating solution is used. After washing with a surfactant, washing with water, washing with dilute sulfuric acid, and washing with water, an electrolytic copper plating film for wiring is formed.

  After removing the resist used for plating the wiring layer, a plating resist for the cylindrical bump pattern and the wire bonding electrode pattern is formed again by the photolithography technique. The height of the bump is set to a height of 10 μm to 20 μm in this embodiment in consideration of the thermal resistance at the time of heat dissipation and the plating time. Similar to the copper plating process for wiring, copper plating and gold plating for bumps and electrodes are performed.

  After removing the plating resist, the Cu / Cr power supply film formed in advance is removed by wet etching. There are various types of etching of Cu, such as iron chloride and an alkaline etching solution. In this embodiment, an etching solution mainly containing sulfuric acid / ammonium persulfate is used. Practically, it is desirable to control with an etching time of 10 seconds or more. However, when etching is performed for a long time, for example, exceeding 5 minutes, there arises a problem that side etching becomes large and tact becomes long. Therefore, the etching solution and the etching conditions are preferably obtained by experiments as appropriate.

  For the subsequent etching of the feeding film Cr portion, an etching solution mainly composed of potassium permanganate and metasilicic acid is used. Soak in hydroxyamine hydrochloride for several minutes for reduction treatment.

  Finally, back grinding and dicing are performed to divide into submount pieces. In mounting LEDs, Ag paste is supplied by a dispenser or printing technology. The film thickness of the Ag paste after die bonding is made uniform. For this reason, it is preferable to place the chip on a plurality of points instead of one point. However, by forming bumps as in this embodiment, it is possible to easily obtain a uniform film thickness even in the case of single point application. it can.

  In addition, when an LED having a size exceeding 1 mm is mounted, in order to reduce the generation of voids due to the solvent in the Ag paste, the Ag paste is not heated rapidly to a high temperature at 10 minutes per minute. It is desirable to raise the temperature gently at an increase rate of about ° C.

<Example 2>
FIG. 4 is a schematic cross-sectional view showing an example using a frame-type bump. This is an example in which the LED chip 5 is die-bonded to a submount in which elongated bumps 8 are formed around the mounting portion of the LED element 5.

  Similar to the first embodiment, Cu wiring 2 is formed on the Si substrate 1 having the insulating film 13 on the surface, and frame-shaped bumps 8 are formed around the LED chip 5 mounting portion. The planar shape of the frame-like bump 8 will be described later with reference to FIG. An Ag paste 7 is filled between the LED chip 5 and the Cu wiring 2. The Ag paste protruding from the LED is dammed up by the frame-like bumps 8 and crawls up to the side surface of the LED chip. At this time, there is too much scooping up of the Ag paste, and if it reaches the light emitting layer of the LED, it causes a lighting failure, so attention should be paid to the supply amount of the Ag paste. In FIG. 4 and FIG. 5, the same symbols are used for the same parts as in the previous figures.

  FIG. 5 is a schematic top view of the submount with frame-shaped bumps. Cu wirings 2 are formed on the Si substrate 1 and frame-like bumps 8 are formed around the Cu wirings 2. The positions corresponding to the four corners of the LED are in an open state, and the width of the bump is narrowed as the four corners are approached. As described above, in this example, it is important to use a shape in which the width of the bump becomes narrower as the frame-type bump approaches the four corners. By adopting this configuration, it is possible to sufficiently spread the Ag paste to the four corners of the LED chip while preventing the Ag paste from spreading too much for the first time. FIG. 6 is a top view in which the LED element 5 is mounted in the state of FIG. The Ag paste 7 moves along the bumps toward the four corners, and the excess Ag paste is pushed outward from the gaps between the bumps. Such a submount can be manufactured by the same process as in the first embodiment.

<Example 3>
The submount according to the present invention is very useful, for example, for a backlight of a liquid crystal display (LCD). This application form will be described. 8 and 9 are diagrams showing two examples of the LCD display. FIG. 8 is a plan view illustrating a method of introducing light from the side surface of the LED screen using a light guide plate, and FIG. 9 is a side view of a method of irradiating light from the back surface of the LED screen.

  An example of side incidence illustrated in FIG. 8 will be described. A plurality of submounts 22 on which the semiconductor light emitting elements described so far are mounted are arranged on the backlight substrate 21. When the metal substrate 21 is used as the backlight substrate, an insulating film 33 is formed on the upper surface thereof. The detailed structure of these submounts 22 is sufficient using the form described in the previous embodiments. Reference numeral 26 denotes an LED chip. In this example, each LED is connected in series. For this connection, an insulating layer 27 is formed between the LEDs on the backlight substrate 21. The wiring layer 2 is formed on the insulating layer 27, and external lead lines from each LED are connected. A protective insulating film 28 is formed on the wiring layer 2. Other detailed description of the LED section is omitted because it is the same as the configuration of the previous embodiments. Each of these LED portions is covered with a translucent sealing resin 23. The backlight substrate 21 thus prepared is covered with a transparent cap 24 and connected to the light guide plate 25. Thus, the light from each LED is introduced into the light guide plate 25 and used for the backlight of the LCD panel 31. The basic configuration of such a liquid crystal display is the same as the conventional one except for the configuration of the LED section.

  Next, an example of back incidence in FIG. 9 will be described. The LED submount 22 is disposed on the back panel 30 of the backlight. The parts related to the LED submount 22 are basically the same as those described so far. The same parts are indicated by the same reference numerals. Light is diffused on the upper surface of the backlight by a diffusion plate 32 or the like. Such various diffusion plates are known. It goes without saying that a further film for improving the brightness, which has been used so far, may be used on the surface of the diffusion plate 32. The back surface or side wall of the backlight is made highly reflective. The LCD panel 31 is disposed in front of the backlight via the diffusion plate 32. In this example as well, the basic configuration of such a liquid crystal display is the same as the conventional one except for the configuration of the LED section. Therefore, detailed description thereof is omitted.

FIG. 1 is a sectional view in which an LED is mounted on a submount with a cylindrical bump. FIG. 2 is a plan view of a submount with cylindrical bumps. FIG. 3 is a plan view of an LED element mounted on a submount with cylindrical bumps. FIG. 4 is a cross-sectional view in which an LED element is mounted on a submount with a frame-like bump. 烏 z5 is a plan view of the submount with frame-shaped bumps. FIG. 6 is a plan view of LED elements mounted on a submount with a frame-like bump. FIG. 7 is a cross-sectional view of an optical member when the present invention is not used. FIG. 8 is a top view of an example of a backlight. FIG. 9 is a cross-sectional view of another example of a backlight.

Explanation of symbols

1: substrate, 2: wiring, 3: bump, 4: Au electrode, 5: LED chip (element), 6, 6-1, 6-2: gold wire, 7: conductive adhesive, 8: frame-shaped bump 11: Conductor layer, 12Au layer, 13: Insulating layer, 21: Substrate for backlight, 22: Submount for LED, 23: Translucent sealing resin, 24: Transparent cap, 25: Light guide plate, 26: LED Chip: 27: insulating layer, 28: protective insulating layer, 31: LCD panel, 32: diffuser, 33: insulating film.

Claims (8)

At least a substrate having a substrate side electrode and a semiconductor light emitting element bonded on the substrate using a conductive adhesive,
A plurality of columnar bumps having a smooth outer peripheral shape are provided in a peripheral portion in a die bond region with respect to the semiconductor light emitting element on the substrate, and the columnar bumps are not provided in a central portion of the die bond region. Optical member to be used.   The optical member according to claim 1, wherein the semiconductor light emitting element is a quadrilateral. The semiconductor light emitting element is a quadrilateral,
The optical member according to claim 1, wherein the plurality of columnar bumps are provided in a staggered arrangement corresponding to each side of the quadrilateral. At least a substrate having a substrate side electrode and a semiconductor light emitting element bonded on the substrate using a conductive adhesive,
An optical member comprising a frame-like bump having a gap in a region corresponding to a corner of the semiconductor light emitting element and having a width narrowed toward the corner.   The optical member according to claim 4, wherein the semiconductor light emitting element is a quadrilateral, and the frame-shaped bumps are arranged corresponding to the sides of the quadrilateral. At least a substrate having a substrate side electrode and a semiconductor light emitting element bonded on the substrate using a conductive adhesive,
A corner portion of the semiconductor light emitting element while suppressing spreading of the conductive adhesive in the die bond region other than the corner portion of the semiconductor light emitting element at a peripheral portion in the die bond region with respect to the semiconductor light emitting element on the substrate An optical member comprising: a bump having a function of promoting the spread of the conductive adhesive at a portion; and the columnar bump not provided in a central portion of the die bond region. A backlight substrate, a plurality of optical members disposed on the backlight substrate, a translucent member provided to cover the plurality of optical members, and optically connected to the translucent member A light guide plate for supplying light to the side of the LCD panel,
The said optical member is an optical member in any one of Claims 1-6, The backlight characterized by the above-mentioned. Backlight substrate, a plurality of optical members arranged on the backlight substrate, a translucent member provided to cover the plurality of optical members, and a diffusion member provided on the translucent member A diffuser for supplying light to the back of the LCD panel;
The said optical member is an optical member in any one of Claims 1-6, The backlight characterized by the above-mentioned.

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