JP2012032722A - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To release heat from a light emitting element into air while avoiding influence of heat deformation of a metal chassis and a light emitting element substrate.SOLUTION: A liquid crystal display comprises: light source units each of which comprises combination of a light source 8 which is mounted on a wiring substrate 9 and composed of multiple light emitting elements and a light guide plate 11 for guiding light from the light source 8 toward a liquid crystal panel; and a metal chassis 5 comprising a positioning member for holding the light source units. The liquid crystal display also includes: a heat diffusion plate 10 provided on a surface of the opposite side to a mounting surface of the light source 8 on the wiring substrate 9 comprising the light source; and a gap d between the heat diffusion plate 10 and the chassis 5.

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 by the LED passes through a pair of heat transfer members from a drive circuit board. A configuration that is quickly dissipated 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.

JP 2007-12416 A JP 2009-252724 A

  Among the backlight methods for irradiating the liquid crystal panel with light, when the direct method is adopted, as in Patent Document 2, the chassis serving as the wall surface on the back surface of the backlight has a large area and can be used as a heat dissipation surface. When an LED that is a point light source is used, it is important as an issue how to spread heat from an LED that generates heat to a wide area and dissipate heat to the air. Therefore, in order to dissipate heat from the LED mounted on the substrate, a structure in which the substrate on which the LED is mounted is fixed and brought into contact with the chassis via a heat conductive sheet or the like can be considered. However, there is a temperature difference between the chassis and the substrate as the LEDs generate heat. Due to this temperature difference, the chassis and the substrate are warped due to the difference in their linear expansion coefficients. Due to this warpage, there is a problem that the adhesion between the chassis and the substrate is partially deteriorated. Further, the warpage of the substrate changes the inclination of the mounted LED. As a result, there is a problem that the predetermined optical axis of the irradiation light is shifted from the LED and the screen brightness is lowered.

  Further, in the case of a metal press-processed chassis or the like, securing the flatness of the surface with a large area in order to improve the adhesion to the substrate has a problem that hinders cost reduction of the chassis itself.

  The present invention has been made in view of the above-described problems of the prior art, and enables stable cooling without causing deterioration in image quality even when the chassis and the substrate are thermally deformed while enabling the liquid crystal display device to be thinned. It provides a possible structure.

  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 liquid crystal display device includes a heat diffusion plate provided on a surface opposite to a light source mounting surface of a wiring board on which the light source is mounted, and the heat diffusion plate A gap is provided between the chassis and the chassis.

  Further, for example, the heat diffusing plate is arranged on the entire plane of the wiring substrate or partially in the vicinity of the individual light source mounting surface.

  Further, for example, the metal chassis constitutes a minute gap with the heat diffusion plate provided on the entire or part of the wiring board.

  Furthermore, for example, the heat diffusion plate provided on the wiring board is a plate material having a higher thermal conductivity than the wiring board such as aluminum, iron, or graphite sheet.

  Further, 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 gap provided between the heat diffusion plate and the chassis is larger than the amount of thermal deformation of the wiring board.

  According to the present invention, it is possible to provide a structure in which a liquid crystal display device can be thinned and can be stably cooled without deterioration in image quality. For example, it is possible to provide a structure capable of stably cooling a light source even when a mounted wiring board is thermally deformed due to heat generated by a point light source of a light source unit of a 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 a component diagram of the wiring board used for a 1st Example. It is sectional drawing of the liquid crystal display device of a 2nd Example. It is sectional drawing of the liquid crystal display device of a 3rd Example. It is sectional drawing of the liquid crystal display device of a 4th Example. It is a component figure of the wiring board of a 1st Example, a 2nd Example, and a 4th Example. It is a figure explaining an example of the thermal radiation performance of this invention.

  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, and 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 or a circuit board 6 'such as a signal control circuit, a power supply circuit, and a panel drive circuit is mounted, and includes a housing 7 for storing 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 uniformity. 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 surface opposite to the light emitting element mounting surface of the wiring board 9. And a heat diffusing plate 10 provided on the surface. 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 through the circuit board 6 for each light source unit 12 using the luminance information of the video signal, for example, as a unit. 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, as the number of the light source units 12 increases, fine control is possible. However, if the number is too large, the number of parts and the cost are significantly increased, so an appropriate number is set according to the size of the liquid crystal panel 2. It is desirable to do.

  A feature of this embodiment is that a heat diffusion plate 10 is provided on the back surface of the wiring board 9 on which the light source 8 is mounted. This heat diffusion plate spreads local heat generation over a wide area. A minute gap d of about 1 mm or less is provided between the heat diffusion plate 10 and the metal chassis 5 via a spacer 13.

  Next, the operation of the structure of this embodiment will be described. By supplying power to the liquid crystal television 1 which is a liquid crystal display device, a 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 simultaneously. Along with light emission, Joule heat is generated inside the light source 8 and the temperature starts to rise. Next, heat is transmitted to the wiring board 9 serving as a heat conduction path. A heat diffusion plate 10 made of a material having a relatively high thermal conductivity such as aluminum is attached to the back surface of the wiring board 9. Therefore, heat is widely spread in the surface direction of the heat diffusing plate 10. Heat is transmitted to the metal chassis 5 provided with a certain gap d by the spacer 13 by heat conduction and heat radiation of air existing in the gap d. The heat transferred to the metal chassis 5 is a natural air convection due to the air density difference in the space provided on the back side of the air, and the air flows into and out of the liquid crystal television 1. Finally, the heat of the LED is discharged to the outside of the liquid crystal display device.

  When the wiring board 9 and the metal chassis 5 are fixed with pins or the like without the gap d, heat is generated due to the power supply to the light source 8, and due to the difference in coefficient of linear expansion between the metal chassis 5 and the wiring board 9 material, Curvature warpage occurs due to thermal deformation. Depending on how the wiring board 9 and the metal chassis 5 are fixed, a forcible force is applied from the metal chassis 5 side and the wiring board 9 is deformed more than necessary. When this deformation is significant, the fatigue strength of the connection portion such as solder of the light emitting element is reduced. Due to the deformation of the wiring board 9, the mounting angle of the light emitting element of the mounted light source 8 is shifted, and the irradiation light angle to the light guide plate 11 is shifted. As a result, the luminance uniformity of the liquid crystal display screen eventually deteriorates, resulting in a reduction in image quality.

  As described above, even when the wiring board 9 is thermally deformed in the direction approaching the metal chassis 5 due to the gap d between the heat diffusion plate 10 and the metal chassis 5 provided in the present embodiment, the wiring board 9 is formed on the metal chassis 5. Therefore, the optical axis is not greatly displaced more than the thermal deformation of the wiring board 9 alone.

  Further, when the screen size is a large screen size such as 37 inches or more, it is difficult to ensure the flatness of the surface within a certain range with a large area of the metal chassis 5. The point which should just manage only the flatness of the opposing surface part with respect to the heat | fever diffusion plate like this point can suppress the raise of the cost of a metal chassis.

  FIG. 3 is a view of the wiring board 9 of the embodiment of FIGS. 1 and 2 as viewed from the back side. A heat diffusion plate 10 is provided over the entire surface of the wiring board 9 on which the light source 8 is mounted. Reference numeral 9 'denotes a copper layer pattern used for the purpose of thermal diffusion when the wiring board is a glass epoxy base material or the like and has a low thermal conductivity. The thicker the copper layer pattern, the greater the thermal diffusion effect. The wiring board 9 and the heat diffusing plate 10 can be connected with a lower thermal resistance by sticking and fixing with a sticky material such as a heat conductive tape.

  FIG. 4 shows a second embodiment of the present invention. FIG. 4 shows only the right side portion from the portion corresponding to the backlight unit 3 of FIG. In the embodiment of FIG. 2, the heat diffusion plate 10 is shown as a size approximately equal to the size of the wiring board 9, but in the embodiment of FIG. 4, the heat diffusion plate is provided only in a limited portion near the light emitting element of the light source 8. 10 is provided. With such a configuration, the heat diffusing plate 10 can be reduced in size and weight, and an increase in cost can be suppressed. Moreover, since the facing area is small, the restriction on the flatness of the metal chassis 5 is further expanded. Other configurations have the same functions as the configurations denoted by the same reference numerals shown in FIG. 1 and FIG. 2 described above, and thus description thereof is omitted.

  FIG. 5 shows a third embodiment of the present invention. FIG. 5 depicts only the right side portion from the portion corresponding to the backlight unit 3 of FIG. In the embodiment of FIG. 5, the heat diffusion plate 5 'is also provided on the metal chassis 5 side. With such a configuration, even if the metal chassis is a material having a relatively low thermal conductivity, such as iron, a material having a relatively high thermal conductivity, such as aluminum, is selected for the heat diffusion plate 5 '. The amount of heat dissipation can be obtained. Accordingly, an increase in cost can be suppressed by using an inexpensive material having a low thermal conductivity for a large area and a small amount of an expensive material having a high thermal conductivity. The metal chassis-side heat diffusion plate 5 'and the metal chassis 5 are achieved by fixing with a heat conductive adhesive or rivets. Further, even if the metal chassis 5 is not a metal but a resin material such as ABS, the effect is achieved. Other configurations have the same functions as the configurations denoted by the same reference numerals shown in FIG. 1 and FIG. 2 described above, and thus description thereof is omitted.

  FIG. 6 shows a fourth embodiment of the present invention. FIG. 6 depicts only the right side portion from the portion corresponding to the backlight unit 3 of FIG. 4 differs from the embodiment of FIG. 4 in the embodiment of FIG. 4 in that the wiring board 9 is composed of six in the vertical direction, but in the embodiment of FIG. 5, it is composed of three. Even in such a configuration, the present invention can be applied. Other configurations have the same functions as the configurations denoted by the same reference numerals shown in FIG. 1 and FIG. 2 described above, and thus description thereof is omitted.

  FIG. 7 is a plan view showing a part of the wiring board 9 and the heat diffusion plate 10 in the structure of FIGS. In the structure of FIG. 2, as shown in FIG. 7A, the light-emitting elements of the light source 8 are arranged on a part of each wiring board, and the heat diffusion plate 10 is provided. In the structure of FIG. 4, the structure is as shown in FIG. 7B and in FIG. 6 is as shown in FIG. 7C.

  FIG. 8 is a component diagram of the wiring board of the first embodiment, the second embodiment, and the fourth embodiment. In FIG. 8, the configurations denoted by the same reference numerals as those already described have the same functions, and thus description thereof is omitted.

  FIG. 8A shows an enlarged view of a partial cross section of the combination of the thermal diffusion plate 10 and the metal chassis 5 in FIG. The heat diffusion plate 10 is disposed so that the inner surface of the metal chassis 5 faces in parallel.

  FIG. 8B shows another embodiment. The heat diffusion plate 10 and the surface of the metal chassis 5 are devised to increase the emissivity. Specifically, as indicated by reference numeral 5 'or reference numeral 10', a black tape is applied, or a black paint is applied partially or entirely. With such a configuration, the amount of radiant heat transfer can be increased as compared with the case of a metal base surface, and the amount of heat transfer from the light emitting element of the light source 8 to the metal chassis 5 can be increased. Further, the emissivity of the surface can be increased by a process such as coating the surface of the metal chassis 5 with the resin 5 '. For example, the surface emissivity can be as wide as 0.05 (polished surface) to 0.95 (black alumite treatment) in the case of metal, so a structure that increases the emissivity of the surface as described above. desirable.

  In FIG. 8 (c), the metal chassis 5 is drawn and deformed so as to partially approach the heat diffusion plate 10. With such a configuration, only the portion of W ′ that is convex when viewed from the display surface side is configured to have a gap d between the heat diffusion plate 10 and the metal chassis 5, so that only the portion of W ′ is made of metal. It is sufficient to ensure the flatness of the chassis 5, which is effective for reducing the cost of the metal chassis 5.

  FIG. 9 is a diagram for explaining an example of the effect of the present invention. The heat diffusion plate 10 is made of aluminum, iron, or resin, and the relationship between the gap d between the iron chassis 5 and the temperature of the light emitting element connection portion is a value calculated by three-dimensional thermal fluid analysis. From the point indicated by “reference” in FIG. 9, the gap d between the heat diffusion plate 10 and the metal chassis 5 is widened, so that air is interposed in the gap d, so that the thermal resistance is increased, and the temperature of the connection portion of the light emitting element is increased. An increase is seen. However, by using a material having a relatively high thermal conductivity such as aluminum as the heat diffusion plate 10, the degree of temperature rise can be suppressed to some extent as compared with the case of using a resin sheet or an iron plate. For example, when an aluminum plate is used as the heat diffusion plate 10, the temperature is about several degrees C with a gap d of 1 mm. As a result, heat transfer is possible while absorbing the amount of thermal deformation of the metal chassis 5 and the wiring board 9 in the gap d. In addition, as a material of the thermal diffusion plate 10, other than aluminum, copper having a high thermal conductivity, an alloy thereof, a flexible graphite sheet, or the like is an effective material. For example, a graphite sheet has a higher thermal conductivity in the lateral direction than aluminum, and is particularly effective for thermal diffusion in the lateral direction. Since the thermal conductivity in the thickness direction is about the same as that of iron, it is desirable that the graphite portion has a predetermined thickness. Moreover, since the graphite sheet is an electrically conductive material of the member itself, a laminate structure is desirable.

  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 Thermal diffusion plate 11 Light guide plate 12 Light source unit 13 Spacer 14 Air ventilation path

Claims (7)

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;
The backlight device includes a light source that emits light in a direction parallel to a display surface of a liquid crystal panel, a wiring board on which the light source is mounted, and a light guide plate having translucency for guiding 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
A liquid crystal display device comprising: a heat diffusion plate provided on a surface opposite to a light source mounting surface of a wiring board on which the light source is mounted, wherein a gap is provided between the heat diffusion plate and the chassis.   2. The liquid crystal display device according to claim 1, wherein the heat diffusion plate is disposed on the entire surface facing the plane of the wiring board or partially in the vicinity of each light source mounting surface.   The liquid crystal display device according to claim 1, wherein the chassis forms a gap with a heat diffusion plate provided on the wiring board or on the entire surface or partially.   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 a gap provided between the heat diffusion plate and the chassis is larger than a thermal deformation amount of the wiring board.   2. The liquid crystal display device according to claim 1, wherein the heat diffusion plate provided on the wiring substrate is a plate material mainly composed of aluminum, iron, or graphite sheet.

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