JP4536171B2 - LED display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light-emitting device in which an LED chip is disposed inside a package, and more particularly to a light-emitting device that is extremely reliable with little damage due to static electricity, EMI (electromagnetic interference), and light irradiation.
[0002]
[Prior art]
Today, LEDs capable of emitting ultra-bright light with RGB (red, green, blue) light corresponding to the three primary colors of light reaching over 1000 mcd have been developed. Since a light emitting device using such an LED is a semiconductor element, it is small, light, highly reliable, and has low power consumption. For this reason, light emitting devices in which LEDs are arranged inside packages have been used in various fields such as backlights, printer heads, and LED displays.
[0003]
FIG. 5 shows a schematic perspective view of an LED display 510 as an example using a light emitting device 500 using LEDs. The LED display 510 can display various information by arranging a plurality of light emitting devices 500 in a dot matrix shape and controlling lighting of each light emitting device. By connecting a plurality of LED displays 510, image data of a desired size can be displayed. Specifically, display data is transferred from various information sources such as various computers, VTRs, DVDs, etc., and the display data is calculated as drive data. Based on the calculated data, the driver constituting the drive circuit is switched. By turning on each light emitting device for a desired time, desired image data or the like can be displayed. These drive circuits may be formed on the light emitting device arrangement substrate 501 on which the light emitting device 500 is arranged, or for reasons of space or the like, the drive circuit is provided on the back side with respect to the light emission observation surface of the light emission device arrangement substrate 501. The arranged driving substrate 502 may be configured. The light emitting device arrangement substrate 501 and the drive substrate 502 are electrically connected using pins 505.
[0004]
The LED display 510 is arranged not only outdoors but also indoors. In particular, depending on the size of the display and the installation location, it may be arranged not only at a relatively high position but also at a position touched by a person. In the light emitting device 500, an LED chip electrically connected to an external electrode is disposed in a concave portion of a package made of a liquid crystal polymer colored black. Further, the concave portion of the package is covered with a translucent epoxy resin to protect it. As a result, even if a person or the like hits the surface of the light emitting device, the LED chip disposed inside is not mechanically destroyed.
[0005]
[Problems to be solved by the invention]
However, by touching the LED display 510, even if the light emitting device 500 arranged on the light emitting device arrangement substrate 501 is covered with an insulating layer, the internal light emitting element may be destroyed. Therefore, the light emitting device having the above configuration is not sufficient and further improvement is demanded.
[0006]
As a result of various experiments, the inventors of the present invention have found that a high voltage charged on a human body or the like is discharged all at once by touching the light emitting device, and the surface shielding layer provided on the light emitting device causes the light emitting element to break down the light emitting device. It has been found that current can be passed without causing damage, and the present invention has been achieved.
[0007]
That is, the LED display can have various sizes depending on the number of light emitting devices arranged. It can also be placed in front of a person and touched by a hand. In particular, it can be used indoors where installation space is limited. In this case, static electricity tends to occur in a dry atmosphere such as winter. Therefore, there is a case where a human body or the like discharges to the LED display just by touching or approaching the LED display such as indoor use. A light emitting device such as a chip type LED has a short distance from the surface of the light emitting device to the substrate for arranging the light emitting device (the thickness of the light emitting device is thin), and is connected to the conductive pattern of the substrate on which the light emitting device is arranged. It is also conceivable that the discharge is concentrated. It is considered that the discharge to the conductive pattern causes the LED chip to be electrostatically broken by a current flowing locally through the LED chip. In particular, LED chips using nitride semiconductors tend to be easily electrostatically broken. Further, when the light emitting layer has a film thickness that is said to produce a quantum effect such as a single quantum well structure or a multi-quantum well structure, it tends to be more easily destroyed.
[0008]
Further, in the LED display, an image of nearly 60 frames is scanned per second. In the case of multi-color or full-color display, it is necessary to drive RGB light emitting devices corresponding to the three primary colors. Therefore, in a large display, each tens of thousands to hundreds of thousands of LED chips are switched and driven. Therefore, the waveguide frequency increases as the number of light emitting devices is increased and the size is increased. A high frequency may be radiated | emitted from the integrated circuit, wiring, etc. which comprise a drive circuit with the drive of a LED chip.
[0009]
The high frequency is unnecessary for the LED display, and it is considered that not only the malfunction of the light emitting device but also the malfunction is caused by being emitted from the LED display and entering another device. In an environment where many electronic devices are arranged in a sealed space such as indoors, EMI countermeasures are extremely important as a problem due to electromagnetic waves. The shield layer of the present invention can also reduce such unnecessary electromagnetic waves.
[0010]
[Means for Solving the Problems]
The LED display device of the present invention includes an LED and a ceramic package in which the LED is disposed in a recess. The ceramic package includes an electrode connected to the LED and an opening side of the ceramic package. A plurality of light emitting devices having a shield layer provided on the surface and serving also as a light absorption layer, and a GND electrode electrically connected to the shield layer, and a substrate on which the light emitting devices are disposed by soldering; And a driving board on which a driving circuit for driving the light emitting device is disposed on the back side of the board, and the board and the driving board are a multilayer board and are electrically connected to the shield layer. It has a GND layer. According to the present invention, damage due to static electricity, EMI countermeasures, and damage during repair can be prevented with a relatively simple configuration.
[0011]
Further, the light emitting device has a shield layer and a light absorption layer. Thus, even when external light is received, a light-emitting device with a high contrast ratio can be obtained.
[0012]
In the light emitting device, the shield layer has high thermal conductivity with respect to the package, but if it is a metal or alloy, the main material of the package is a glass epoxy resin, and the shield layer is a metal and the package is a glass epoxy resin. Is preferred. Thereby, damage to the light emitting device due to peeling of the glass epoxy resin or the like in the case of soldering or the like by light irradiation can be reduced. In particular, the effect of the present invention appears remarkably because the temperature rise is particularly remarkable on the surface side where the light absorption layer is provided.
[0013]
In the light emitting device, the shield layer connected to the GND electrode is electrically independent of the external electrode electrically connected to the LED. Thereby, a light-emitting device with higher reliability can be obtained.
[0014]
In the light emitting device, the LED is made of a nitride semiconductor. In particular, even when a nitride semiconductor that is weak against static electricity is used, a light-emitting device with higher reliability can be obtained.
[0015]
A driving substrate having a driving circuit for driving the light emitting device disposed on the back side of the substrate is provided, and the substrate and the driving substrate are a multilayer substrate and a GND layer electrically connected to the shield layer Have Thereby, even in a light emitting device touched by a person or the like, a light emitting device in which the LED chip is not broken can be obtained. In addition, a light-emitting device that does not emit image disturbance due to electromagnetic waves from the outside or electromagnetic waves from the internal drive circuit can be provided.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of the present invention is shown in FIGS. A light emitting device 300 having an LED chip 305 capable of emitting RGB light as shown in FIG. 3 is arranged on the substrate. The electrodes of the conductive pattern on the substrate 401 and the respective electrodes of the light emitting device 300 are electrically connected and fixed by the solder 408. On the substrate, light emitting devices are arranged in a 16 × 16 dot matrix. Next, on the back side of the light emitting device arrangement substrate 401 on which the light emitting device 300 is formed, this substrate and a driving substrate 402 in which a CPU or the like is arranged as a driving driver for driving each light emitting device are illustrated using pins 405. 4 is electrically connected.
[0017]
The package 303 of the light-emitting device 300 uses a green sheet before firing with a ceramic that is mainly made of alumina. A green sheet is laminated in multiple layers, and a metal layer serving as a conductive pattern in the light emitting device 300 after firing is formed by printing a tungsten-containing resin in a desired pattern. The opening of the package 303 in which the LED chip is disposed is formed by laminating a green sheet having a hole in advance on a green sheet on which a conductive pattern is formed with tungsten.
[0018]
In the present invention, ruthenium oxide that later functions as the shield layer 301 is applied to the outermost surface side of the green sheet together with the resin. When the green sheet is fired, the ceramic turns white, but the ruthenium oxide becomes dark. Further, the ruthenium oxide printed on the front surface is electrically connected to the back surface side through the through-hole 308 in the state of a green sheet. On the back side, an electrode 302 connected to ruthenium oxide on the front surface is provided in addition to an electrode for being electrically connected and fixed to the LED chip.
[0019]
When the green sheets thus laminated are fired in a furnace, various electrodes 302 and 306 having an opening inside and electrically connected from the bottom of the opening to the back surface are formed. The surface layer provided around the opening of the ceramic package 303 formed by firing functions as a shield layer / light absorption layer 301 and can improve the contrast ratio of the light emitting device.
[0020]
In addition, the shield layer on which ruthenium oxide is formed has electrodes 302 and 306 formed on the back surface side independently of the electrode for driving the LED chip. For this reason, even if a large voltage such as static electricity is applied from the surface side of the shield layer 301, a current is discharged to the ground line (ground) through an electrode independent of the LED chip. In particular, since the shield layer 301 is provided on the outermost surface side of the light emitting device, current flows preferentially and damage to the LED chip disposed inside is extremely reduced.
[0021]
Inside the opening, a GaN buffer layer formed on the sapphire substrate at a low temperature as an LED chip 305 capable of emitting B (blue), a contact layer / clad layer made of n-type GaN, a GaN layer and an InGaN layer The active layer having a multiple quantum well structure, a clad layer made of p-type AlGaN, and a contact layer made of p-type GaN are stacked. After each contact layer is exposed and an electrode is formed, an LED chip formed using a die-bonding device is placed in the opening of the package by a mounting member made of epoxy resin. After the mount member is cured, each electrode of the LED chip and the electrode on the surface of the package exposed in the opening are wire-bonded using a gold wire. Thereafter, an epoxy resin is filled in the opening of the package as a translucent mold member 304 to protect the LED and the wire from external force, dust, moisture, and the like.
[0022]
The LED chip 305 can emit light by supplying current to the external electrode 306 provided on the back side of the ceramic package 303. In addition, the GND electrode 302 provided on the back side through the shield layer 301 and the through hole 308 of the package 303 is dedicated to the ground line independently of the external electrode 306 that is electrically connected to the LED chip 305. Connected to. Hereafter, each structure of this invention is explained in full detail.
[0023]
(Shield layer 101, 301)
The shield layer 101 is provided on the light emission observation surface side surface of the package 103, and can discharge unnecessary current such as static electricity from the outside without damaging the LED chip 105. Alternatively, it is also possible to absorb electromagnetic waves from the drive circuit that is caused by controlling the light emission / non-light emission of the LED chip 105. Furthermore, the heat generated by the light irradiated on the package surface can be efficiently released to the outside. Therefore, the thing with high electrical conductivity and heat conductivity is preferable. Various materials can be selected as the material of the shield layer 101 depending on the main member of the package 103. Specifically, various metal films such as copper, gold and silver, refractory metals such as palladium and tungsten, and these These metal oxides and various metal leads can be suitably used.
[0024]
(Light absorption layer 107)
The light absorption layer 107 is preferably used on the shield layer 101. Since the shield layer 101 has good electrical conductivity, various metals can be used. In this case, those having a metallic luster tend to reduce the contrast ratio of the light emitting device because they reflect external light. Therefore, a dark paint or the like is formed as the light absorption layer 107 at least on the surface side of the package 103 which is a non-light emitting portion of the light emitting device 100. The light absorption layer 107 can improve the contrast ratio of the light emitting device 100 during light emission / non-light emission. When the light absorption layer 107 is insulative, it is not possible to efficiently supply external static electricity or the like. The current flows easily through the electrode for driving the LED chip or the like, and is easily destroyed. Therefore, the light absorption layer 107 itself preferably has high conductivity. Specific examples of the light absorbing layer 107 include metal oxides such as silver oxide and iron oxide, and various conductive pastes containing dark colored coloring dyes such as carbon, black, and amber. When the conductivity of the light absorption layer 107 is good, the shield layer 101 and the light absorption layer 107 can be used together.
[0025]
(GND electrodes 102 and 302)
The GND electrode 102 is provided on the back surface or side surface of the package 103 and connected to a ground line or the like. The GND electrode 103 is electrically connected to a shield layer 107 provided on the surface side of the package 103 through a through hole 108 and the like, and is supplied with an external current such as static electricity, an electromagnetic wave, and an electromagnetic wave from a driving circuit that drives the light emitting device. Can be prevented from radiating to the outside. Further, heat accompanying external light irradiation can be externally released from the shield layer 107 via the GND electrode 102 without being retained on the surface of the package 103.
[0026]
The GND electrode 102 can be used in common with the external electrode 106 for driving the LED chip 105, or can be used electrically independently. In order to flow external static electricity or the like without damaging the LED chip 105, it is preferable to dispose the LED chip 105 electrically independently from the external electrode 106. The GND electrode 102 and the shield layer 101 can be electrically connected by using a through hole 108 in which a conductive member is formed in a hole provided in the package 103 or a wiring provided outside the package. As a specific material of the GND electrode 102, a copper foil provided in a hole of a package using glass epoxy, tungsten formed in a package using ceramic, or the like can be preferably cited.
[0027]
(Package 103)
The package 103 used in the present invention has an LED chip 105 disposed therein as a light emitting element, and is intended to protect the LED chip 105 and the like from external forces in the external environment. Various LED chips 105 can be arranged in the package 13, and a plurality of LED chips can be arranged as desired. A recess is formed in the package 103, and wiring that can be electrically connected to each electrode of the LED chip is exposed at the bottom of the recess. The wiring exposed in the package 103 is electrically connected to the electrode on the back surface side of the package 103 and functions as an external electrode. In order to reduce the damage of the LED chip 105, the translucent resin 106 can be sealed in the opening of the package 103. For such a package 103, various packages such as those using an acrylic resin or a liquid crystal polymer, a glass epoxy resin, a ceramic material, etc. can be suitably used as being strong against external force and having high light resistance. it can.
[0028]
(LED105, 305)
Various LEDs 105 and 305 can be used as semiconductor light emitting elements. Specifically, not only LEDs capable of emitting monochromatic light in RGB (red, green, blue), but also LEDs capable of emitting Y (yellow) can be used. Moreover, it is also possible to use an LED that emits light by changing the color of the emission wavelength emitted from the LED 105 by using various fluorescent substances. Specific examples of such LEDs include those in which various materials such as InN, GaN, AlN, GaP, InGaN, AlInN, AlGaN, InAlGaN, GaAlAs, GaAsP, and AlInGaP are used for the light emitting layer. Examples of the light emitting layer include those using various types such as MOCVD, MBE, and CVD. The structure of the LED can be variously selected from a MIS junction, a PIN junction, a homostructure using a pn junction, a heterostructure, and a double heterostructure. Moreover, it can also be set as a single quantum well structure or a multiple quantum well structure.
[0029]
(External electrodes 106, 306)
The external electrode 106 is provided to connect to the LED chip 105 arranged inside the package 103 and to connect to an external power source (not shown). Therefore, since it can be formed on the back surface side or the side surface side of the package 103, it is desired that the adhesive property with the main member constituting the package 103 is high and the conductivity is good. Various materials can be selected for the material constituting the external electrode 106 depending on the main member of the package. However, when glass epoxy resin is used as the main member of the package, copper foil and ceramic are used as the main member of the package. In this case, when a refractory metal such as tungsten or a heat resistant resin such as liquid crystal polymer is used as a main member of the package, a metal lead such as iron plated with silver or the like can be preferably used.
[0030]
(Light Emitting Device Arrangement Substrate 401)
The light emitting device arrangement substrate 401 is a substrate on which the light emitting device 300 of the present invention is arranged. When it is used as an LED unit or the like, a desired number and arrangement such as a dot matrix can be used. In the present invention, the light emitting device 300 may have an independent GND electrode separately from that for driving the LED chip. In this case, it is desirable to form a conductive pattern exclusively for grounding, which is connected to the ground line, separately from the conductive pattern for supplying power to the LED chip on the light emitting device arrangement substrate 401 itself. Such a conductive pattern for the grounding wire is desirably formed as the GND layer 404 so as not to be damaged even when a large current flows.
[0031]
(Drive board 402)
The drive substrate 402 is suitably used for lighting the light emitting device 300 as desired. The driving substrate 402 can display desired image data depending on how much each LED chip of each light emitting device is lit by data input from the outside using a CPU or various memories. Specifically, after calculating image data from the outside, the driver is driven according to the calculation result. The current supplied to the LED chip is controlled by switching the driver. Each LED chip can be made to emit light by variously controlling the time and amount of current flowing. When each LED chip is RGB (red, green, blue) which is the three primary colors of light, full color display can be performed by utilizing the respective mixed color emission. In the LED display, the light emitting device can be formed in substantially the same size on the back side of the light emitting device substrate arranged in a dot matrix. By connecting a plurality of these, a display having a desired size can be configured relatively easily. Like the light emitting device arrangement substrate, it is preferable that a GND layer 406 be formed in the driver circuit.
[0032]
(GND layers 404 and 406)
The GND layers 404 and 406 can be suitably formed inside the drive substrate 402 and the light emitting device arrangement substrate 401. By using the conductive pattern formed inside the multilayer laminated substrate, for example, the shield layer of each of 16 × 16 light emitting devices can be connected at one place in the GND layer 404. The GND layer 404 in the multilayer laminated substrate can be relatively easily connected to the shield layer of each light emitting device 300 by using a through hole. Examples of the present invention will be described in detail below.
[0033]
【Example】
Example 1
A light emitting device package was formed using a glass epoxy resin substrate. The package is formed by laminating two layers of glass epoxy resin having copper foil formed in a desired pattern on both sides. The glass epoxy resin on the surface side, which is the light emission observation surface side, has 16 × 16 openings in a dot matrix in which LED chips are arranged. On the outermost surface of the glass epoxy resin around the opening, a copper foil having a thickness of 20 μm is formed over the entire rectangular shape that later becomes the size of each light emitting device except for the opening. This copper foil serves as a shield layer. On the copper foil, in order to improve the contrast ratio, a light absorption layer containing dark iron oxide in an epoxy resin is applied in a thin film having a thickness of about 30 μm.
[0034]
The glass epoxy resin on which the LED chip is mounted is connected to the external electrode (copper foil pattern) provided on the back surface side from the front surface of the opening in units of each opening. Specifically, it is electrically connected to the surface of a hole penetrating a package using a glass epoxy resin through a through hole made of copper foil and gold plating formed thereon. Similarly, on the back surface side, in addition to the external electrode, a GND electrode electrically connected to the shield layer through a through hole is formed using a copper foil. In addition, it cut | disconnected from the double-sided side of the glass epoxy resin so that it might isolate | separate into a rectangular shape for every opening part by which an LED chip is arrange | positioned later, and to become each light-emitting device.
[0035]
An LED chip having a single quantum well structure with a thickness of 3 nm using InGaN as a light emitting layer was used. LED chips of blue (main emission wavelength 470 nm) and green (main emission wavelength 555 nm) are formed by changing the composition of In. On the other hand, a red LED chip using AlGaInP as a light emitting layer is used. Since an LED chip using a nitride semiconductor to form InGaN having good crystallinity is formed on a sapphire substrate, a pair of electrodes are formed on the nitride semiconductor on sapphire.
[0036]
Each LED chip was placed on the bottom of the opening using Ag paste using a die-bonding device in the package opening. The LED chip was fixed by curing the Ag paste. Since the substrate of the red LED chip itself is conductive, the red LED chip can be disposed on the copper foil pattern on the bottom surface of the package opening, and one electrode of the LED chip can be electrically connected. On the other hand, an LED chip using a nitride semiconductor cannot take electrical continuity only by being fixed with Ag paste because sapphire is insulative. Therefore, wire bonding was performed using a gold wire on each electrode of the LED chip and the copper foil pattern exposed in the opening. Thereby, each LED chip and the external electrode of the package can be electrically connected. After confirming that each LED chip can emit light, an epoxy resin was applied and cured in the opening to form a mold for protecting the LED chip and the like. An individual light emitting device is formed by applying an external force to the glass epoxy resin along a notch provided in advance for each opening.
[0037]
The formed light emitting device is arranged in a dot matrix on a light emitting device mounting substrate using solder. A glass epoxy substrate on which a copper foil pattern formed in advance so that the light emitting device can be arranged in a dot matrix form was used. On the mounting substrate, other than the copper foil surface connected to each external electrode and the GND electrode of the light emitting device is coated in advance with a resist. Each light emitting device was arranged on the mounting substrate, fixed from above using a mold, and then passed through a flow soldering device to conduct and fix. The mounting substrate is also a multilayer substrate, and a GND layer connected only to the GND electrode is provided in the mounting substrate. All are connected to the shield layer of each light-emitting device through the GND layer.
[0038]
In addition, the drive substrate on which the driver for driving each light emitting device was mounted was made approximately the same size as the light emitting device mounting substrate, and the light emitting device mounting substrate and the drive substrate were connected and fixed using connection pins. One of the connection pins is connected to the shield layer of each light emitting device, and is connected to the GND layer of the driving substrate via the GND layer of the mounting substrate. The GND layer of the driving substrate is electrically connected to the ground independently of each LED chip. Thereby, even if a person with static electricity contacts the surface side of the light emitting device, the light emitting device can be driven without destroying the LED chip. Further, the shield layer provided on the surface of the light emitting device absorbs electromagnetic waves from the drive substrate disposed on the back side. Alternatively, by absorbing external electromagnetic waves without causing adverse effects on the drive circuit, an LED display with very little influence of EMI can be obtained.
[0039]
(Example 2)
Further, one of the light emitting devices arranged in a dot matrix shape was taken out by irradiating with a light beam and melting the solder. After applying the solder paste onto the electrode of the substrate from which the light emitting device was partially taken out, a new light emitting device was placed and irradiated with a light beam. With the irradiation, the solder melts and the light emitting device can be placed on the substrate.
[0040]
(Comparative Example 1)
The light emitting device was partially replaced and repaired in substantially the same manner as in Example 2 except that the shield layer was not provided. The repaired light-emitting device package made of glass epoxy resin and the resist film made of epoxy resin coated with silver oxide were deformed by heat at the time of light beam irradiation, and partially peeled off. For this reason, not only the contrast ratio is lowered due to damage to the surface resist, but also the LED chip becomes unlit.
[0041]
【The invention's effect】
The present invention can avoid damage to an LED due to static electricity or the like even in a light-emitting device that can be directly touched by a person such as indoors by providing an electrically conductive shield layer on the surface of the light-emitting device. It is possible to prevent malfunctions of various electronic devices due to electromagnetic waves or electromagnetic waves from an internal drive circuit.
[Brief description of the drawings]
FIG. 1 is a schematic plan view of a light emitting device of the present invention.
FIG. 2 shows an AA cross section in FIG.
FIG. 3 is a schematic plan view of another light emitting device of the present invention.
FIG. 4 is a partial cross-sectional view of an LED display using the light emitting device of the present invention.
FIG. 5 is a schematic perspective view showing a part of the LED display.
[Explanation of symbols]
100, 300... Light emitting device
101, 301 ... Shield layer
102, 302 ... GND electrode
103, 303 ... Package
104, 304 ... Mold member
105,305 ... LED
106,306 ... external electrode
107: Light absorption layer
108 ... Through hole
401... Light emitting device mounting substrate
402 ... Drive substrate
403... Conductive pattern for connecting GND electrode and GND layer
404 ... GND layer of substrate for mounting light emitting device
405 ... pin
406... GND layer for driving substrate
407 ... CPU mounted on the drive board
408 ... Solder
500... Light emitting device
501... Light emitting device arrangement substrate
502 ... Drive substrate
505 ... pin
510 ... LED display

Claims (1)

An LED and a package for disposing the LED in a recess, and the package is an electrode connected to the LED and a shield that serves as a light absorption layer provided on the surface of the opening side of the package A light emitting device having a layer and a GND electrode electrically connected to the shield layer;
A substrate on which the light emitting device is disposed;
A driving substrate on which a driving circuit for driving the light emitting device is disposed on the back side of the substrate;
The LED display device, wherein the substrate and the driving substrate are a multilayer substrate and have a GND layer electrically connected to the shield layer.

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