KR20040057269A - Backlight unit - Google Patents

Abstract

PURPOSE: A backlight unit is provided to add a heatproof structure to a PCB(Printed Circuit Board) and thereafter attach a light emitting device to the P.B, thereby emitting the heat and then stabilizing the luminance and optical characteristics. CONSTITUTION: The backlight unit is comprised of a heatproof plate(31), the PCB substrate(32) adhered to the heatproof plate(31) and a plurality of light emitting devices(33) adhered to the PCB substrate(32) with a constant interval. The heatproof plate(31) has an area which is, about four times as much, larger than that of the PCB substrate(32). The PCB substrate(32) and the heatproof plate(31) are adhered by using a both side tape. The light emitting device(33) includes a light emitting unit(33a) comprised of a light emitting chip and a transparent mold, a cathode(33b) adhered to the light emitting unit(33a), and a lead frame(33c) connected to both ends of the cathode(33b). The lead frame(33c) is adhered to the PCB substrate(32) by soldering. The heatproof plate(31) comprises a connection surface(31a) connected to the PCB substrate(32) and a plurality of heatproof pins(31b) constructed to a lower portion of the connection surface(31a) with a constant interval.

Description

Backlight unit

TECHNICAL FIELD The present invention relates to a backlight unit, and more particularly to a backlight unit suitable for stabilizing brightness and optical characteristics.

CRT (Cathode Ray Tube), one of the commonly used display devices, is mainly used for monitors such as televisions, measuring devices, information terminal devices, etc., but the miniaturization of electronic products due to the CRT's own weight and size It was unable to actively respond to the demand for weight reduction.

Therefore, in the trend of miniaturization and light weight of various electronic products, CRT has a certain limit in weight and size, and is expected to be replaced. Liquid crystal display (LCD) and gas discharge using electro-optic effects Plasma Display Panel (PDP) and Electro Luminescence Display (ELD) using the electroluminescent effect, among others, are being actively studied for the liquid crystal display device.

In order to replace the CRT, a liquid crystal display device having advantages such as small size, light weight, and low power consumption has recently been developed to be able to perform a sufficient role as a flat panel display device. As used in monitors and large information display devices, the demand for liquid crystal display devices continues to increase.

The liquid crystal display may be classified into a liquid crystal panel displaying an image and a driving unit for applying a driving signal to the liquid crystal panel. The liquid crystal panel may include first and second glass substrates bonded to each other with a predetermined space, and It consists of the liquid crystal layer injected between the 1st, 2nd glass substrate.

The first glass substrate (TFT array substrate) may include a plurality of gate lines arranged in one direction at a predetermined interval, a plurality of data lines arranged at regular intervals in a direction perpendicular to the gate lines, A plurality of pixel electrodes formed in a matrix form in each pixel region defined by crossing gate lines and data lines, and a plurality of thin films that are switched by signals of the gate lines to transfer signals of the data lines to the pixel electrodes Transistors are formed.

The second glass substrate (color filter substrate) includes a black matrix layer for blocking light in portions other than the pixel region, an R, G and B color filter layer for expressing color colors, and a common electrode for implementing an image. Is formed.

The first and second glass substrates are bonded to each other by a seal material having a predetermined space by a spacer and having a liquid crystal injection hole, so that the liquid crystal is injected between the two substrates.

On the other hand, since most of the liquid crystal display devices are light-receiving elements that display an image by controlling the amount of light source coming from the outside, a separate light source, that is, a backlight, is required for irradiating light to the liquid crystal panel. It is divided into edge type and direct type according to the location where the lamp unit is installed.

The light source includes EL (Electro Luminescence), LED (Light Emitting Diode), CCFL (Cold Cathode Fluorescent Lamp), HCFL (Hot Cathode Fluorescent Lamp), etc., especially long life, low power consumption and thin can be formed. CCFL is widely used in large color TFT LCDs.

The CCFL method uses a fluorescent discharge tube in which mercury gas containing argon, neon, or the like is sealed at a low pressure in order to use a penning effect. Electrodes are formed at both ends of the tube, and the cathode is formed in a wide plate shape.When voltage is applied, as in the sputtering phenomenon, charged particles in the discharge tube collide with the plate-shaped cathode to generate secondary electrons, which excite surrounding elements to excite the plasma. To form.

These elements emit strong ultraviolet light, which in turn excites the phosphor, causing the phosphor to emit visible light.

In the double-edge method, the lamp unit is installed on the side of the light guide plate for guiding the light, and the lamp unit covers a lamp emitting light, a lamp holder inserted at both ends of the lamp to protect the lamp, and an outer circumferential surface of the lamp, and one side It is provided with a lamp reflector plate fitted to the side of the light guide plate to reflect the light emitted from the lamp toward the light guide plate.

The edge method in which the lamp unit is installed on the side of the light guide plate is applied to a relatively small liquid crystal display device such as a monitor of a laptop computer and a desktop computer, and has good uniformity of light and a long service life. It is advantageous to thin the liquid crystal display device.

On the other hand, the direct method began to develop mainly as the size of the liquid crystal display device became larger than 20 inches, and arranged a plurality of lamps in a row on the lower surface of the diffusion plate to direct light directly to the front of the liquid crystal panel. will be.

The direct method is mainly used for a large screen liquid crystal display device requiring high luminance because the light utilization efficiency is higher than that of the edge method.

However, the liquid crystal display device adopting the direct method is used as a large monitor or a television, which takes longer to use than a laptop computer, and because the number of lamps is larger, the failure and life of the lamp in the direct method than the edge method. It is more likely that a lamp that will not turn on appears.

In the direct method, because a plurality of lamps are installed on the bottom of the screen, for example, due to the life and failure of the lamp, if one lamp does not light up, the part where the lamp does not light up becomes significantly darker than the other part. The part will appear immediately on the screen.

For this reason, since the lamp is frequently replaced in the direct method, the lamp unit should be easily disassembled and assembled.

As described above, the liquid crystal display device uses a liquid crystal to control the amount of light transmitted through the screen, and uses the light to determine the contrast and the color of the screen.

For example, the viewing angle of which the image quality varies greatly depending on the viewing angle, the transmittance according to the projection light emitting display, and the transmitted light pass through the color filter to display the red (R), green (G), and blue (B) colors. These include color reproducibility depending on how much they are reproduced, luminance representing the contrast of the image, and afterimages in which the traces of the image remain long when the same image is continued for a long time.

Currently, liquid crystal displays are expanding from display of portable products to monitors for desktop PCs and home TVs. Although the liquid crystal display has the physical advantages of light and thin, the color reproducibility and luminance, among the above characteristics, are particularly weak compared to the CRT.

Conventional LCD monitors have 40-50% color reproducibility compared to the NTSC system adopted by the National Television System Committee for color television broadcasting. Could meet.

However, in the case of a TV which is attracting attention as a market for a new liquid crystal display device, it is required to develop a liquid crystal display device capable of realizing color reproducibility of CRT level or higher.

A typical multi-color liquid crystal display device is largely composed of a liquid crystal panel, a backlight, and a color filter. That is, by using a backlight composed of a three-wavelength fluorescent lamp as a light source, the white light emitted from the color filter is separated into three colors of red, green, and blue in the color filter, and then added and mixed again to realize various colors.

The color of the light source is determined by chromaticitycordinates determined by the International Lighting Commission. That is, after calculating tristimulus values X, Y and Z from the spectra of an arbitrary light source, color coordinates x, y and z of red, green and blue are obtained from the tristimulus values using the transformation matrix. Subsequently, when the x, y values of red, green, and blue are expressed in Cartesian coordinates, a horn-shaped spectral trajectory is drawn, which is called a CIE chromaticity diagram. All common light sources have their color coordinates inside these horseshoe shapes.

In this case, a triangular region formed by each color coordinate of red, green, and blue becomes a color reproduction region, and as the triangle region becomes larger, color reproducibility is increased. Color reproducibility depends on color purity and luminance, and color reproducibility increases as color purity and luminance increase.

Here, the tristimulus values X, Y, and Z represent weights of individual color-matching functions close to a spectrum, and particularly Y represents a stimulus value for brightness.

On the other hand, the color temperature of the white color based on the color change of the light emitted according to the temperature of the heat source is called the color temperature, the color temperature on the monitor is represented by three, that is, 9300K, 6500K and 5000K.

The closer the color temperature is to 9000K, the more white is added to the blue color. If the color temperature is 6500K, the red color is added to the white. If the color temperature is 5000K, the color becomes neutral. The color temperature is obtained from the color coordinates (x, y) of white. As the color temperature is around 9000K, the European broadcasting union (EBU) standard can be satisfied.

In the case of the liquid crystal display device described above, the emission spectrum of the backlight is combined with the transmission spectrum of the color function and the color filter to determine tristimulus values for each wavelength of the visible light region. Correlation between extremes should be adjusted accordingly. That is, in order to optimize color reproducibility and color temperature, the emission spectrum of the backlight should be changed, and the transmission spectrum of the color filter should be adjusted to maximize the emission efficiency.

If a white, blue, green, and red LEDs must be used at the same time, many application problems occur. In particular, when using blue, green, and red LEDs at the same time, it is difficult to apply them realistically because of a technical problem of gathering different colors coming out according to the position of each LED to make white.

Therefore, in order to realize white light, it is required that all three wavelengths of one LED emit light with a predetermined intensity or more.

As such, there is an urgent need for the development of a backlight capable of utilizing the advantages of the backlight of the SMD (Surface Mounting Device) LED of the mobile phone, which is not only small and cold, but also has a small power consumption.

Meanwhile, the configuration of a general backlight assembly is as follows.

1 is a view for explaining the structure of a general backlight assembly.

As shown in FIG. 1, the fluorescent lamp 1, the light guide plate 2, the diffusion material 3, the reflection plate 4, the diffusion plate 5, the prism sheet 6, and the like are constituted.

First, when the voltage is applied to the fluorescent lamp 1, residual electrons present in the fluorescent lamp 1 move to the anode, and the moving residual electrons collide with argon (Ar) to excite argon to proliferate cations, The multiplying cations collide with the cathode to release secondary electrons.

When the emitted secondary electrons flow through the tube to initiate discharge, the flow of electrons by the discharge collides with, and ionizes, the mercury vapor to emit ultraviolet rays and visible light, and the emitted ultraviolet rays excite the phosphor coated on the inner wall of the lamp to display visible light. It emits light and emits light.

Subsequently, the light guide plate 2 is a wave guide for injecting the light emitted from the fluorescent lamp 1 into the surface to emit a surface light source to the top, and has excellent light transmittance. PMMA (Poly Methyl Meth Acrylate) ) Resin is used.

Factors related to light incidence efficiency of the light guide plate 2 include light guide plate thickness versus lamp diameter, the distance between the light guide plate and the lamp, the shape of the lamp reflector, and the like. In general, the fluorescent lamp 1 is thicker than the center of the light guide plate 2. By inclining in the direction, the light incidence efficiency is increased.

The light guide plate 2 of the backlight unit for an LCD includes a printing light guide plate, a V-cut light guide plate, and a scattering light guide plate.

Subsequently, the diffusion material 3 is composed of Si0 ₂ , particles, PMMA, solvent, and the like. At this time, the Si0 ₂ particles described above are used for light diffusion and have a porous particle structure. PMMA is also used to attach Si0 ₂ particles to the lower surface of the light guide plate 2.

The diffusion material 3 is applied to the lower surface of the light guide plate in the form of a dot, and the area of the dot is gradually increased in order to obtain a uniform surface light source on the light guide plate 2. That is, the area ratio occupied by the dot per unit area is smaller in the one closer to the fluorescent lamp 1, and the area ratio occupied by the dot per unit area is larger in the far side from the fluorescent lamp 1.

In this case, the shape of the dot may have various shapes. If the area ratio of the dots per unit area is the same, the same brightness effect may be obtained on the light guide plate regardless of the shape of the dot.

Subsequently, the reflector 4 is installed at the rear end of the light guide plate 2 so that the light emitted from the fluorescent lamp 1 is incident into the light guide plate 2.

The diffusion plate 5 is installed on the light guide plate 2 to which the dot pattern is applied to obtain uniform luminance according to a viewing angle. As the material of the diffusion plate 5, PET or PC (Poly) is used. Carbonate) resin is used, and the upper part of the diffusion plate 5 has a particle coating layer that serves as a diffusion.

Subsequently, the prism sheet 6 is to increase the front luminance of the light that is transmitted through the diffusion plate 5 and reflected. The prism sheet 6 allows only the light of a specific angle to pass therethrough and the light incident at the remaining angle. Total internal reflection occurs and returns back to the bottom of the prism sheet 6. As described above, the returning light is reflected by the reflecting plate 4 attached to the lower part of the light guide plate 2.

The backlight assembly configured as described above is fixed to the mold frame, and the display unit disposed on the upper surface of the backlight assembly is protected by the top chassis, and the top chassis and the mold frame are coupled while receiving the backlight assembly and the display unit therebetween.

2 is a perspective view illustrating a backlight unit using a general fluorescent lamp.

As shown in FIG. 2, the fluorescent lamp 11 is coated on the inner surface to emit light, and the fluorescent lamp 11 is fixed, and the light emitted from the fluorescent lamp 11 is in one direction. A lamp housing 12 for condensing, a light guide plate 13 for supplying the light emitted from the fluorescent lamp 11 to the liquid crystal panel side of the backlight, and light leaking to the opposite side of the liquid crystal panel attached to the lower part of the light guide plate 13 Reflector 14 reflecting light to the light guide plate 13, a diffuser plate 15 positioned above the light guide plate 13 to uniformly diffuse the light emitted from the light guide plate 13, and the diffuser plate 15 A prism sheet 16 positioned above and condensing light diffused from the diffusion plate 15 to a liquid crystal panel, and a protective sheet positioned above the prism sheet 16 to protect the prism sheet 16. 17, storing the components It consists of a main support (18) that secure.

In the backlight unit configured as described above, the light emitted from the fluorescent lamp 11 is focused on the light incident surface of the light guide plate 13, and then passes through the light guide plate 13 through the diffuser plate 15 and the prism sheet 16 to the liquid crystal panel. Delivered.

However, as described above, the backlight unit using the conventional fluorescent lamp has low color reproducibility due to the light emission characteristics of the light source itself. In addition, it is difficult to obtain a high brightness backlight unit due to constraints of the size and capacity of the fluorescent lamp.

On the other hand, in recent years, the backlight unit has been used as a function for reading information displayed on the screen of a liquid crystal display in a dark place, but recently, the light guide plate has been formed thinner due to various requirements such as design, low power, and thinning. In addition to the ability to express various colors, technologies for reducing power consumption using LEDs (Light Emitting Diodes) are being made.

Hereinafter, a backlight unit of a conventional liquid crystal display device will be described with reference to the accompanying drawings.

3A is a side view illustrating a conventional backlight unit, and FIG. 3B is a top view illustrating a conventional backlight unit.

As shown in Figs. 3A and 3B, a plurality of light emitting elements 21 are arranged on the PCB substrate 22 made of Al at regular intervals.

That is, in a state in which the plurality of light emitting elements 21 are arranged on the front surface of the PCB substrate 22, the PCB substrate 22 is positioned under the light guide plate (not shown) to directly illuminate the liquid crystal panel.

The light emitting device 21 attached to the PCB substrate 22 may include a light emitting part 21a formed of a light emitting chip and a transparent mold, a cathode 21b attached to the light emitting part 21a, and the cathode ( The lead frame 21c connected to both ends of 21b) and the lead frame 21c are attached to the PCB substrate 22 by soldering or the like.

However, in the conventional backlight unit as described above, since a large amount of light emitting elements are used in a single area by directly attaching a plurality of light emitting elements on an PCB substrate made of Al, heat is emitted and a fatal weakness that the optical characteristics are changed by the radiating heat. There is this.

In other words, when the light emitting device chips are directly mounted on a PCB board and used as a signal lamp or lighting equipment, the light emitting device chips emit more heat, and the amount of heat dissipation increases in proportion to the total light emitting area. Defects will occur.

The present invention provides a backlight unit to stabilize the brightness and optical properties by adding a heat dissipation structure to the PCB substrate and then attaching a light emitting device to release the heat dissipated to solve the conventional problems as described above. The purpose is.

1 is a view for explaining the structure of a typical backlight assembly

2 is a perspective view showing a backlight unit using a conventional fluorescent lamp

Figure 3a is a side view showing a conventional backlight unit

Figure 3b is a top view showing a conventional backlight unit

Figure 4a is a side view showing a backlight unit according to the present invention

Figure 4b is a top view showing a backlight unit according to the present invention

Explanation of symbols for the main parts of the drawings

31 heat sink 32 PCB substrate

33: light emitting element 34: double-sided tape

The backlight unit according to the present invention for achieving the above object is characterized in that it comprises a heat sink, a PCB substrate bonded to the heat sink, and a light emitting element attached to the PCB substrate.

Here, the heat sink is made of alumina.

In addition, the heat sink has a larger area than the PCB substrate.

In addition, the heat sink and the PCB substrate are bonded using a double-sided tape.

The heat dissipation plate may include a connection surface to which the PCB substrate is connected, and a plurality of heat dissipation fins configured to have a predetermined distance below the connection surface.

Hereinafter, a backlight unit according to the present invention will be described in detail with reference to the accompanying drawings.

4A is a side view illustrating the backlight unit according to the present invention, and FIG. 4B is a top view illustrating the backlight unit according to the present invention.

As shown in FIGS. 4A and 4B, a heat-radiating plate made of alumina, a PCB substrate 32 adhered to the heat sink 31, and a plurality of light emitting layers attached to the PCB substrate 32 at regular intervals. The element 33 is comprised.

Here, the heat sink 31 is configured to have a larger area about four times larger than the PCB board 32.

On the other hand, the PCB substrate 32 and the heat sink 31 is bonded using a double-sided adhesive tape (tape).

In addition, the light emitting device 33 attached to the PCB substrate 32 includes a light emitting part 33a made of a light emitting chip and a transparent mold, a cathode 33b attached to the light emitting part 33a, and the cathode ( The lead frame 33c and the lead frame 33c connected to both ends of 33b) are attached to the PCB board 32 by soldering or the like.

Therefore, as described above, the PCB substrate 32 is adhered to the predetermined region on the heat sink 31 using the double-sided tape 34, and the plurality of light emitting elements 33 are soldered onto the PCB substrate 32. Attach.

Here, the PCB substrate 32 may be any substrate capable of mounting the light emitting element 33 at a high density.

For example, the PCB substrate 32 may include alumina, quartz, calcium zirconate, forsterite, SiC, graphite, fused silica, and mullite. ), Cordierite, zirconia, beryllia, aluminum nitride, and the like.

Therefore, the material of the PCB substrate 32 is not particularly limited, and among them, alumina or SiC material is suitable. More preferably, alumina is used.

The alumina ceramic has high electrical insulation and high thermal conductivity. In addition, alumina ceramics have excellent heat resistance, chemical resistance, and mechanical strength, and particularly, have low radiation emission.

In addition, the heat dissipation plate 31 is configured to include a connection surface 31a to which the PCB substrate 32 is connected, and a plurality of heat dissipation fins 31b formed at regular intervals under the connection surface 31a. By increasing the heat dissipation surface can maximize the heat dissipation effect.

On the other hand, the present invention described above is not limited to the above-described embodiment and the accompanying drawings, it is possible that various substitutions, modifications and changes within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

As described above, the backlight unit according to the present invention has the following effects.

That is, by adhering the PCB substrate on the heat sink made of alumina and attaching the light emitting device, it is possible to effectively emit heat emitted from the light emitting device, thereby improving brightness and optical characteristics.

Claims (5)

With heat sink, A PCB substrate bonded to the heat sink; And a light emitting device attached to the PCB substrate. The backlight unit of claim 1, wherein the heat sink is made of alumina. The backlight unit of claim 1, wherein the heat sink has a larger area than the PCB substrate. The backlight unit of claim 1, wherein the heat sink and the PCB substrate are bonded using double-sided tape. The backlight unit of claim 1, wherein the heat dissipation plate comprises a connection surface to which the PCB board is connected, and a plurality of heat dissipation fins configured to have a predetermined distance below the connection surface.