JP2012084455A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat dissipation structure of a light source capable of thinning and achieving low cost in the light source of a liquid crystal display device using surface-mounting type point light sources (LEDs).SOLUTION: In a light source unit wherein a plurality of light sources 8 mounted on a wiring board 9 and a light guide plate 11 for guiding light of the light sources to a direction of a liquid crystal panel are assembled, a mounted surface side of the light sources 8 on the wiring board 9 and a heat diffusion plate 10 are pinched by an approximately U-shaped member 101 via a thermal conductive sheet 91 in order to radiate heat generated from the light sources 8 from the heat diffusion plate 10 to the atmosphere.

Description

  The present invention relates to a liquid crystal display device. For example, the present invention relates to a liquid crystal display device that can efficiently exhaust heat generated in a housing.

  In recent years, as a display device, a light-emitting plasma display device or a non-light-emitting liquid crystal display device is increasingly used in place of a CRT (Cathode Ray Tube). Among these, a liquid crystal display device uses a liquid crystal panel as a transmissive light modulation element, and includes a lighting device (hereinafter referred to as a backlight device) on the back thereof to irradiate the liquid crystal panel with light. The liquid crystal panel forms an image by controlling the transmittance of the light emitted from the backlight device.

  The following two systems are mainly known as a backlight device system for irradiating a liquid crystal panel with light. One is a sidelight system in which light sources are arranged on the left and right or upper and lower ends of the liquid crystal panel, and light is incident through a light guide plate for emitting light incident from the side surface in a plane direction. This is a direct system that irradiates light from the back of the panel. One feature of the liquid crystal display device is that the outer shape can be thinned. In recent years, a liquid crystal display device that is thinner and consumes less power is desired. If the liquid crystal display device is made thin, it will be difficult to secure an air flow path for exhausting heat generated inside the housing that forms the outer shape of the liquid crystal display device. The problem of rising will arise.

  Therefore, for example, in Patent Document 1, an LED (Light Emitting Diode) is used as a light source of a backlight device in a sidelight type liquid crystal display device, and heat generated from the LED is promptly transmitted from the wiring board through a pair of heat transfer members. The configuration to be diffused is described.

  On the other hand, as a direct cooling structure, Patent Document 2 describes a structure in which a fluorescent tube type light source is disposed on the back side of a liquid crystal panel, a back wall surface is used as a heat radiating surface, and cooling is performed by air flow on the back surface. Has been.

Japanese Patent No. 4525492 JP 2009-252724 A

  The technique described in Patent Document 1 is a technique in which heat generated from an LED is transmitted to an outer frame by being coupled by a thermally conductive member that connects the surface of the substrate and the outer frame, and the surrounding air is radiated. However, this structure is effective for the sidelight system in which LED rows are installed on the upper and lower ends of the light guide plate or on the edges including the left and right ends. However, a light source unit is arranged in the middle of the light guide plate, It cannot be used for an area control type backlight structure in which the luminance is changed by an image. In addition, since the outer frame and the substrate are connected by members, the deformation of the outer frame causes an inclination in the substrate installation direction. This inclination causes an optical axis shift with respect to the light guide plate, and affects optical performance such as a decrease in brightness and unevenness.

  Accordingly, an object of the present invention is to radiate heat generated from the LED to the air with a small temperature difference after securing the optical axis deviation between the LED and the light guide plate within a predetermined range in the area control type backlight structure. . For this reason, when the liquid crystal display device is required to be thin with a support structure for the substrate in consideration of alignment accuracy and heat dissipation performance of the substrate on which the LED is mounted and the light guide plate, the length of the substrate support structure in the screen depth direction is also required. It is an object of the present invention to provide a liquid crystal display device structure that can be shortened, further improves assembly workability, and can reduce material costs as much as possible.

  In order to solve the above problems, for example, the configuration described in the claims is adopted.

  The present application includes a plurality of means for solving the above-described problems. For example, a liquid crystal panel, a backlight device including a light source that illuminates the liquid crystal panel from the back, and a chassis that holds the backlight device are provided. And the backlight device has a light source that emits light in a direction parallel to a display surface of the liquid crystal panel, a wiring board on which the light source is mounted, and translucency for guiding the light of the light source toward the liquid crystal panel. In a liquid crystal display device having a plurality of light source units combined with a light guide plate, the mounting surface of the wiring board on which the light source is mounted and the heat diffusion plate are brought into contact with each other via a heat conductive sheet, and the wiring board and the heat diffusion plate are sandwiched between them. There is a liquid crystal display device including a member.

  Further, for example, the member that sandwiches the wiring board and the heat diffusion plate by bringing the mounting surface of the wiring board and the heat diffusion plate into contact with each other through a heat conductive sheet is a member having a substantially U-shaped cross section.

  Further, for example, a member that sandwiches the wiring board and the heat diffusion plate by bringing the mounting surface of the wiring board and the heat diffusion plate into contact with each other via a heat conductive sheet can be attached with screws.

  Further, for example, the member that sandwiches the wiring board and the heat conductive sheet by bringing the mounting surface of the wiring board and the heat diffusion plate into contact with each other through the heat conductive sheet is a heat diffusion plate that is partially molded into a substantially U shape. It is.

  Further, for example, the heat diffusion plate connected to the wiring board is a plate material having a thermal conductivity higher than that of the wiring board.

  Furthermore, for example, the wiring board is a printed wiring board made of paper base phenolic resin or a laminated wiring printed board made of glass cloth base epoxy resin.

  Further, for example, the heat diffusion plate provided on the wiring board is a plate material mainly composed of aluminum or iron.

  Further, for example, at least two wiring boards are attached to one light guide plate.

  According to the present invention, it is possible to provide a structure capable of cooling an LED stably without reducing the image quality while enabling a thin liquid crystal display device.

It is the figure which looked at the liquid crystal display device of the 1st example from the front. It is AA sectional drawing in FIG. 1 of a 1st Example. It is a figure of the combination of the wiring board and thermal diffusion board in a 1st Example. It is an expanded sectional view of a wiring board and a heat diffusion plate used in the first embodiment. It is a top view by the side of the light source mounting surface of the wiring board of a 1st Example. It is a top view of the light source non-mounting surface side of the wiring board of the first embodiment. It is an expanded sectional view of a wiring board and a heat diffusion plate used in the second embodiment. It is a figure of the combination of the wiring board and thermal diffusion board of a 3rd Example. It is a figure of the combination of the wiring board of 4th Example, and a thermal-diffusion board.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings as appropriate.

A liquid crystal television which is an embodiment of a liquid crystal display device to which the present invention is applied is shown in FIGS.
FIG. 1 is a front view on the side of displaying an image of the liquid crystal television of the first embodiment. FIG. 2 is a part of a cross-sectional view taken along the line AA in FIG. 1, and the right side of FIG.

  As shown in FIG. 2, the liquid crystal television 1 according to the present embodiment includes a liquid crystal panel 2 as a passive display device, a backlight unit 3 for irradiating the liquid crystal panel 2 with light, a liquid crystal panel 2 and a back panel. An optical sheet 4 that is disposed between the light unit 3 and diffuses the light of the backlight unit 3 is provided. The liquid crystal panel 2 may be provided with a color filter, may be monochrome, or may be an IPS system or a VA system. The backlight unit 3 is assembled in a metal chassis 5 formed into a box shape with a metal such as an aluminum plate or a steel plate. Further, on the rear surface of the metal chassis 5, a circuit board 6 and a circuit board 6 ′ such as a signal control circuit, a power supply circuit, and a panel drive circuit are mounted, and includes a housing 7 for housing these elements. Shall. Although the optical sheet 4 is schematically shown as one sheet in FIG. 2, it is actually configured by combining any of a diffusion sheet, a prism sheet, a diffusion plate, a polarization selective reflection film, and the like. Since these sheets reflect a part of the light emitted from the light source 8 and reflect the light toward the backlight unit 3, the light reflected again from the backlight unit 3 is transmitted and diffused, and the luminance is uniform. There is an effect to increase.

  As shown in FIG. 2, the backlight unit 3 includes a wiring board 9 on which a light source 8 including a plurality of light emitting elements such as light emitting diodes (LEDs) is mounted, and a light emitting element mounting surface of the wiring board 9 and a plane perpendicular to the plane. And the heat diffusion plate 10 provided in a plane parallel to the liquid crystal panel 2. Light emitted from the light source 8 in the direction of the arrow B (that is, the direction parallel to the liquid crystal panel 2) is incident, and this is bent in the direction of the arrow C (that is, the direction orthogonal to the display surface of the liquid crystal panel 2). A light guide plate 11 for guiding to the liquid crystal panel 2 disposed in front of the light unit 3 is combined.

  As shown in a lattice shape in the front view of FIG. 1, the backlight unit 3 is divided into a plurality of areas as a light source unit 12. As shown in FIGS. 1 and 2, a plurality of elements are arranged in the direction of arrow B and the direction of arrow C, that is, in the direction parallel to the display surface of the liquid crystal panel 2. The illuminance of the light source 8 (intensity of light emitted from the light source 8) is controlled for each light source unit 12 using the luminance information of the video signal, for example, as the unit of the light source of each optical unit 12 via the circuit board 6. You may make it do. In this case, the brightness and color of the display image on the liquid crystal panel 2 can be locally controlled corresponding to the light source unit 12. As a result, the contrast and color purity of the display image can be improved. As the number of light source units 12 increases, finer control can be performed. For example, as shown in FIG. 1, when six light source units 12 are arranged in the vertical direction and sixteen in the horizontal direction, the display area of the liquid crystal panel 2 is divided into 96 areas corresponding to each light source unit 12. The brightness and color can be controlled for each divided area. Of course, the number of light source units 12 (the number of divisions of the display area) is not limited to this. As described above, finer control is possible as the number of light source units 12 is larger. However, if the number is too large, the number of parts and cost are significantly increased, so an appropriate number is set according to the size of the liquid crystal panel 2. It is desirable. In FIG. 2, the light guide plate 11 having a uniform thickness is provided with six groove portions in the direction perpendicular to the paper surface, and the light source 8 enters the groove portions, and light is emitted upward. Although the light guide plate 11 is shown as a single structure in the drawing, the effects of the present invention can be achieved even if the thicknesses are partially different or divided in the vertical direction or the horizontal direction. As shown in FIG. 2, the heat generated by the light source 8 is transferred to the heat diffusion plate 10 by heat conduction through a heat conductive sheet 91 provided on the wiring board 9. The heat spread to the heat diffusing plate 10 is transferred to the air in the air ventilation path 14.

  FIG. 3 shows an enlarged main part of FIG. A feature of the first embodiment is that a thermal conductive sheet 91 is provided in a portion where the light source 8 on the light source mounting surface side of the wiring board 9 is not mounted, and a thermal diffusion plate having a right angle portion in parallel with the wiring board. 10 is in surface contact and thermally coupled. Then, the wiring board 9 and the heat diffusing plate 10 are sandwiched simultaneously via the heat conductive sheet 91 using the member 101 having a substantially U-shaped cross section. The heat conductive sheet 91 is preferably made of a material having a predetermined heat conductivity and a high flexibility and a high compression recovery rate. The light guide plate 11 and the resin rivet 111 will be described with reference to FIG.

  FIG. 4 shows a main enlarged view of a combination of one set of the wiring board 9, the light source 8 and the heat diffusion plate 10 in FIG. 3. On the wiring substrate 9, a copper layer (light source mounting surface side) 900 on the mounting surface D side of the light source 8 covers the surface of the wiring substrate 9 widely including the light source 8 part. A copper wiring layer (light source non-mounting surface side) 901 is wired on the opposite surface E side of the wiring substrate 9 so as to be electrically connected to the light sources 8 arranged in the direction perpendicular to the paper surface. The copper wiring layer (light source non-mounting surface side) 901 and the light source 8 are electrically connected through a through hole (not shown) that penetrates the insulating portion of the wiring board 9. The substantially U-shaped member 101 is advantageous because a structure for generating an elastic force by sheet metal processing can be configured at a relatively low cost. The heat diffusing plate 10 and the light guide plate 11 are fixed by fitting a resinous rivet 111. The heat diffusion plate 10 is preferably made of a material such as aluminum having a high thermal conductivity from the viewpoint of heat dissipation, but may be a steel plate or the like with an emphasis on cost depending on the amount of heat generated by the light source 8.

  5 and 6 show the wiring board 9 in a plan view. FIG. 5 shows a D surface of the mounting surface of the light source 8, and FIG. 6 shows an E surface on the opposite side. On the D surface, a light source 8 having a metal electrode portion is mounted by reflow soldering with a predetermined gap in consideration of the necessary light quantity. On the surface of the substrate, a copper layer is provided in a relatively wide area as long as there is no problem in electrode formation. The thickness of the copper layer can be selected according to standards such as 18, 35, and 70 microns. However, when the temperature of the light source 8 is further reduced, it is desirable that the copper layer be a thick copper layer. In addition, from the viewpoint of ensuring electrical insulation and optical performance, a thin white resist layer having a high reflectance is provided on the surface of the copper layer. The surface D shown in FIG. 6 shows a case where a plurality of light sources 8 are connected by serial wiring as shown by 8a, 8b and 8c in the figure. By providing the copper wiring layer (on the light source non-mounting surface side) 901 that can control the current of each of the three light sources, it is possible to control the backlight in which the screen is divided into areas. In this case, when a large current is required for the light source 8 in relation to the amount of light, it is desirable to set the wiring width of the copper wiring layer (light source non-mounting surface side) 901 wider so as not to generate Joule heat. Although not shown in the drawing, a connector is connected to the end of the wiring layer to be coupled to the wiring from the driver circuit board. Since the heat diffusion plate 10 is connected to the area D shown in FIG. 5 via the heat conductive sheet in the region indicated by the broken line, it can be connected with a relatively low thermal resistance near the light source 8. Further, since it is not necessary to conduct the heat generated by the light source 8 to the E surface on the back surface, the number and arrangement of the through holes connecting the D surface and the E surface with an emphasis on electrical characteristics may be sufficient. A good point in the pattern design of the wiring mainly of the electric circuit within the dimensions is a high degree of freedom of design.

  Next, the operation of the structure of this embodiment will be described. By supplying power to the liquid crystal television 1, current is supplied to the light source 8 including a light emitting element such as a light emitting diode (LED), and the light source 8 starts to emit light. Along with light emission, Joule heat is generated inside the light source 8 and the temperature starts to rise. The heat generated by the light source 8 is spread over a wide area of the wiring board 9 by the copper layer (light source mounting surface side) 900 on the surface of the wiring board 9. The heat spread over a wide area is transferred to the heat diffusion plate 10 by heat conduction through the heat conductive sheet 91 provided on the same surface. The heat spread to the heat diffusing plate 10 is transferred to the air in the air ventilation path 14. The air warmed by the housing 7 has buoyancy due to a decrease in density, and is discharged from the upper exhaust port. At the same time, low-temperature air is sucked from the lower intake port. The heat generated by the light source 8 due to the air flow is finally radiated to the outside.

  The wiring board 9 can be configured as a thin backlight unit 3 by ensuring a heat connection area with the heat diffusion plate 10 together with the wiring area and by making the wiring board 9 as short as possible in the horizontal direction of the drawing. The heat transferred to the heat diffusing plate 10 becomes a ventilation path 14 in the space provided on the back side thereof, and natural convection occurs due to the density difference of the air. Finally, the heat of the LED is discharged to the outside of the liquid crystal display device.

  As described above, the thermal diffusion plate is thermally connected to the mounting surface side of the light source 8 of the wiring board 9 so that the connection can be made with a low thermal resistance without being affected by the thermal resistance in the thickness direction of the wiring board 9. Further, since the heat conductive sheet 91 is compressed by the elastic force of the substantially U-shaped member 101, the contact surface between the heat conductive sheet 91 and the wiring board 9 can have high adhesion. Furthermore, since the substantially U-shaped member is inserted from the side, the assembly workability is high unlike the screw tightening structure.

  Further, according to the present invention, since the copper layer (light source mounting surface side) 900 on the surface of the wiring board 9 is used as a main heat conducting member, the double-sided glass cloth base is very inexpensive compared with a base board made of aluminum or the like. It is advantageous for cost reduction in that a material epoxy substrate or the like can be used.

  Moreover, the cost of the light guide plate of the injection-molded product can be suppressed by a structure in which a plurality of wiring boards in which light sources are mounted on one large light guide plate is attached as in this embodiment.

  FIG. 7 shows another embodiment of the present invention. The difference from the invention of FIG. 4 is that a substantially U-shaped member 101 is fastened from above and below with screws 102. With such a configuration, even when the compressive elastic force of the substantially U-shaped member 101 is reduced due to the creep phenomenon, the substantially U-shaped member 101 can be prevented from falling off by tightening the screws, and the long-term reliability of the apparatus is improved. . The number of screws 102 may be the minimum number necessary to prevent falling off, and the assembling workability is not greatly impaired.

  FIG. 8 shows another embodiment of the present invention. In the embodiment of FIG. 3, the wiring substrate 9 and the heat diffusion plate 10 are fixed by the elastic force of the substantially U-shaped member 101, but in the embodiment of FIG. Even in such a structure, since the thermal diffusion plate 10 is thermally connected to the mounting surface of the light source 8, it can be coupled with a low thermal resistance.

  FIG. 9 shows still another embodiment of the present invention. In the embodiment of FIG. 3, the substantially U-shaped member 101 is a separate member. In the embodiment in FIG. 9, the substantially U-shaped member 101 of FIG. 3 is formed by the same parts as the heat diffusion plate 10. With such a structure, the number of parts can be reduced, and it can be configured at a lower cost. Further, in this case, by using a drawn material such as aluminum, the accuracy of the squareness of the right-angle portion of the heat diffusion plate is increased, and even when the connection width with the wiring board 9 is small, the installation position and angle of the wiring board are set to a predetermined value. Since the range can be set, the influence on the optical performance can be reduced.

  As described above, the heat diffusion plate 10 is thermally connected through the heat conductive sheet 91 by using the heat conduction of the copper layer 900 (not shown) on the light source 8 mounting surface side of the wiring board 9. . For this reason, a glass base epoxy laminated substrate having a relatively low thermal conductivity of the insulating portion can be used for the wiring substrate 9, which is very advantageous in terms of cost compared to an aluminum substrate or the like. Moreover, since the elastic force of the substantially U-shaped member shaped with the same parts as the heat diffusion plate 10 is used as a method of fixing the wiring board 9, the number of fixing screws used can be reduced as much as possible, so that a structure with high workability is achieved. realizable.

  As shown in the embodiment of the present invention described with reference to FIGS. 1 to 9, the wiring board 9 is divided into at least two pieces with respect to one light guide plate in the vertical direction of the screen, Although not shown, the wiring board 9 is divided into at least two pieces in the horizontal direction of the screen. Thereby, even when elongation due to linear expansion occurs in the light guide plate, it is possible to obtain an effect capable of absorbing the positional deviation between the light guide plate and the light source 8.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. In addition, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Liquid crystal television 2 Liquid crystal panel 3 Backlight unit 4 Optical sheet 5 Metal chassis 6 Circuit board 7 Housing 8 Light source (LED)
9 Wiring board 10 Heat diffusion plate 11 Light guide plate 12 Light source unit 14 Air ventilation path 91 Thermal conductive sheet 92 Screw 101 Substantially U-shaped member 111 Rivet 900 Copper layer (light source mounting surface side)
901 Copper wiring layer (light source non-mounting surface side)

Claims (8)

A liquid crystal panel, a backlight device for illuminating the liquid crystal panel from the back, and a chassis for holding the backlight device;
The backlight device has a light source that emits light in a direction parallel to a display surface of the liquid crystal panel, a wiring board on which the light source is mounted, and a light-transmissive guide that guides light from the light source toward the liquid crystal panel. In a liquid crystal display device having a plurality of light source units combined with an optical plate,
A liquid crystal display device, wherein a member for sandwiching the wiring board and the heat diffusion plate is provided by contacting a mounting surface of the wiring substrate on which the light source is mounted and a heat diffusion plate via a heat conductive sheet.   The member that sandwiches the wiring board and the heat diffusion plate by bringing the mounting surface of the wiring board and the heat diffusion plate into contact with each other via the heat conductive sheet is a member having a substantially U-shaped cross section. The liquid crystal display device according to claim 1.   2. The liquid crystal according to claim 1, wherein a member that sandwiches the wiring board and the thermal diffusion plate by bringing the mounting surface of the wiring substrate and the thermal diffusion plate into contact with each other through the thermal conductive sheet is a screw. Display device.   The member that sandwiches the wiring board and the heat conductive sheet by bringing the mounting surface of the wiring board and the heat diffusion plate into contact with each other via the heat conductive sheet is a heat diffusion plate formed in a substantially U shape. The liquid crystal display device according to claim 1.   The liquid crystal display device according to claim 1, wherein the heat diffusion plate provided on the wiring board is a plate material having a thermal conductivity higher than that of the wiring board.   2. The liquid crystal display device according to claim 1, wherein the wiring board is a printed wiring board made of a paper base phenolic resin or a laminated wiring printed board made of a glass cloth base epoxy resin.   2. The liquid crystal display device according to claim 1, wherein the heat diffusion plate provided on the wiring board is a plate material mainly composed of aluminum or iron.   The liquid crystal display device according to claim 1, wherein at least two wiring boards are attached to one light guide plate.

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