JP2012053988A - Backlight unit and image display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a side-light type backlight unit of a thin shape with an LED as a light source and having superir efficiency of using light from the light source.SOLUTION: The LED 1 is arranged on a substrate 2 with an emitting surface 1b inclined upward. The inclination is formed by loading an end of the LED 1 on paint 2a on the substrate 2. A light-incident surface 3a formed on a side face of a light guide plate 3 has an enough breadth to accept light from the LED 1. As a volume of light from the LED 1 emitted on the substrate 2 decreases, the efficiency of using light is increased. With this arrangement, a backlight unit with large brightness can be achieved.

Description

  The present invention relates to a backlight unit configured to irradiate a liquid crystal panel with light from a light source such as a light emitting diode (LED), and an image display device using the backlight unit.

  An image display device using a liquid crystal panel includes a liquid crystal panel and a backlight unit for illuminating the liquid crystal panel from the back side. As this backlight, for example, as described in Patent Document 1 below, a plurality of LEDs are arranged as light sources on the end surface (side surface) of a light guide plate made of transparent resin or the like, and light from the LEDs is guided to the light guide plate. A side light type is known in which multiple reflections are made to emit light as a planar light source from the surface of the light guide plate (light exit surface) on the liquid crystal panel side.

JP 2009-37212 A

  In recent years, liquid crystal display devices have been required to be thin (reduced in the depth direction of the device), and thinning has also been achieved in liquid crystal panels, backlight units, and other members constituting the liquid crystal display device. In order to cope with such thinning, it is necessary to reduce the thickness of the light guide plate corresponding to the depth direction of the apparatus. Decreasing the thickness of the light guide plate reduces the height direction dimension of the light incident surface of the light guide plate, and narrows the incident range of light from the LED in the thickness direction of the light guide plate.

  For this reason, when the LED is mounted on the circuit board, the displacement (tilt) of the LED in the falling direction greatly affects the utilization efficiency of the light from the LED. For example, when the optical axis of the LED is inclined to the back side of the display device with respect to the direction parallel to the light exit surface of the light guide plate, the light use efficiency is greatly reduced, and the luminance of the light emitted from the light guide plate is reduced. . In Patent Document 1, no consideration is given to the inclination of the LED and the decrease in light use efficiency due to the inclination.

  The present invention has been made in view of such a conventional technical problem, and provides a technique suitable for improving the utilization efficiency of light from an LED.

  The present invention includes an LED as a light source and a light guide plate. Light from the LED is incident on a light incident surface of the light guide plate, and the incident light is used as planar light from the light exit surface of the light guide plate to the liquid crystal panel side. In the backlight unit configured to irradiate, the LED is arranged so as to be inclined so that the emitted light of the LED is directed obliquely upward, that is, in the direction of the light exit surface of the light guide plate.

  ADVANTAGE OF THE INVENTION According to this invention, the influence of the inclination of LED can be suppressed, and the backlight unit with sufficient light utilization efficiency, and a thin and high-intensity image display apparatus can be provided.

It is sectional drawing of the part by which LED of the backlight unit which concerns on 1st Example of this invention is arrange | positioned. It is the figure which looked at LED from the joint surface side. It is explanatory drawing of the LED mounting part of the circuit board by 1st Example. It is the figure which showed the state which mounted LED by 1st Example in the circuit board. It is explanatory drawing of the mounting process to the circuit board of LED by 1st Example. It is a figure which shows the relationship between the joining angle (alpha) in the 1st Example, and the brightness | luminance of the light from a backlight unit. It is a disassembled perspective view of the liquid crystal display device to which this embodiment is applied. It is AA sectional drawing of the liquid crystal display device of FIG. It is a figure which shows the relationship between joining angle (alpha) and the brightness | luminance of the light from a backlight unit. It is sectional drawing of the part by which LED of the backlight unit which concerns on 2nd Example of this invention is arrange | positioned.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Elements having the same function and action are denoted by the same reference numerals, and redundant description is omitted.

  First, the overall configuration of a liquid crystal display device as an image display device to which the present invention can be applied will be described with reference to FIG. FIG. 7 is an exploded perspective view of the liquid crystal display device, where the upper side of the paper is the front side (image viewing side) and the lower side of the paper is the back side. In FIG. 7, a liquid crystal display panel 30 incorporates a TFT substrate, a color filter, a counter substrate, a polarizing plate (none of which are shown), and the like.

  On the back side of the liquid crystal display panel 30, a backlight unit 31 for irradiating the liquid crystal display panel 30 with light from the back side of the liquid crystal display panel 30 is disposed. The backlight unit 31 includes a circuit board 2 on which a plurality of LEDs 1 as light sources are arranged, a light guide plate 3, a reflection sheet 5, and an optical sheet 6.

  On the circuit board 2, a plurality of LEDs 1 as light sources are linearly arranged along the side of one end thereof, and circuit components such as an LED driver for driving the LEDs 1 are mounted. The LED 1 is a side-view type LED that emits white light in a direction parallel to the electrode surface. In this example, the LED 1 is a direction orthogonal to the arrangement direction of the LEDs 1 and substantially parallel to the surface of the circuit board 2. Light is emitted in the direction of the arrow in the figure. In addition, the arrow in a figure shall correspond with the optical axis direction of each LED.

  On the circuit board 2, the light guide plate 3 is placed via the reflection sheet 5. In a state where the light guide plate 3 is placed on the circuit board 2, along one side surface of the light guide plate 3, Several LED1 is arrange | positioned in a line so that this side surface and the output surface of LED1 may oppose. The side surface of the light guide plate 3 becomes the light incident surface 3 a, and the light emitted from the LED 1 enters the light incident surface 3 a and is guided into the light guide plate 3. The light guide plate 3 has a rectangular shape when viewed from the front side, and a cross section perpendicular to the light exit surface 3b and parallel to the optical axis direction of the LED 1 gradually extends from the light incident surface 3a to the front end portion facing it. The wedge shape is made thinner. The light guided into the light guide plate 3 is reflected by the back surface of the light guide plate 3 (the surface facing the reflection sheet 5) and the back surface of the light guide plate 3, and emitted from the light exit surface 3b. Is done.

  Light emitted from the light exit surface 3 b of the light guide plate 3 enters the optical sheet 6. The optical sheet 6 includes, for example, a diffusion sheet, a prism sheet, a reflective polarizing plate, etc., and diffuses and equalizes the light from the light guide plate 3 and improves the luminance of the light toward the front side, thereby increasing the liquid crystal display panel 30. Is irradiated.

  Further, a front frame 32 made of, for example, a resin as a bezel is disposed on the front side of the liquid crystal display panel 30, and a back cover 33 made of, for example, a resin as a rear housing is provided on the back side of the backlight unit 31. The liquid crystal display panel 32 and the backlight unit 31 are accommodated in the interior by the front frame 32 and the back cover 33. In addition, illustration of electric circuits etc., such as a signal board | substrate for driving the liquid crystal display panel 30 and LED1, and a power supply board | substrate, is abbreviate | omitted here.

  In this example, the light guide plate 3 uses a wedge type whose thickness decreases from the light emitting surface 3a to the tip as described above. However, the light guide plate 3 is not a wedge type but has a substantially constant thickness. May be used. Further, although the number of optical sheets 6 is three, it is not necessary to be limited to this. Moreover, although LED1 is arrange | positioned at the side surface side of 1 side of the light-guide plate 3, it is good also as a structure arrange | positioned at the side surface side of 2 or more sides. Further, in FIG. 7, a sidelight type backlight is configured by using only one light guide plate 3, but a plurality of sets of the light guide plate 3 and LEDs 1 having a relatively small area (for example, 10 cm × 10 cm) are provided. A so-called tandem backlight arranged in two dimensions may be configured. In this way, the brightness of light can be controlled for each light guide plate 3 having a small area.

  FIG. 8 is a cross-sectional view of the liquid crystal display device of FIG. For simplicity of illustration, the front frame 32 and the back cover 33 are not shown. As shown in FIG. 8, the optical sheet 6, the light guide plate 3, the reflection sheet 5, the LED 1, and the circuit board 2 on which the optical sheet 6 is mounted are arranged on the back side of the liquid crystal display panel 30 in order from the front side to the back side. ing. In FIG. 8, the light guide plate 3 and the reflection sheet 5 are drawn in close contact with each other, but in reality, a slight gap often occurs.

  Next, the details of the LED 1 and the light guide plate 3 shown in FIGS. 7 and 8 and the characteristic part of this embodiment will be described with reference to FIG. FIG. 1 is an enlarged cross-sectional view of the periphery of a portion where LEDs are arranged in the backlight unit according to this embodiment.

  In FIG. 1, an LED 1 includes an LED chip 1 a that is a light emitting unit, and light emitted from the LED chip 1 a is emitted from the emission surface 1 b toward the light incident surface 3 a of the light guide plate 3 in the direction of the optical axis 1 d. . Here, the optical axis 1d passes through the center of the LED chip 1a and is orthogonal to the emission surface 1b, and the light intensity in the direction of the optical axis 1d is the highest.

  The lower surface of the LED 1 is a bonding surface 1 c that is bonded to the circuit board 2. As shown in FIG. 2, the bonding surface 1c is provided with LED electrode portions 1e that are not electrically connected to each other. By passing a current through the LED electrode portion 1e, the light emitting portion 1a inside the LED 1 emits light. In FIG. 2, two LED electrode portions 1e are provided at both ends of the bonding surface 1c. However, depending on a circuit inside the LED, three or more LED electrode portions 1e may be provided on the LED bonding surface 1c.

  In this example, the LED 1 is a side-view type white light emitting LED having a size including a surface including the emission surface 1b of about 2 mm × 3 mm and a depth (horizontal direction in the drawing) of about 1.5 mm.

  The circuit board 2 includes a base material 2b, a wiring land 8 disposed on the base material 2, and a substrate printing paint 2a such as a resist. The circuit board 2 is provided on the bonding surface 1c of the LED 1 and the substrate 2. The wiring lands 8 are joined and fixed using a joining member 7 such as solder.

  In FIG. 1, the bonding surface 1c of the LED 1 and the direction of the optical axis 1d are parallel to each other. This type of LED 1 is referred to as a side view type LED. In the top view type LED described later, the joint surface 1c and the optical axis 1d are orthogonal to each other.

  The light guide plate 3 is made of, for example, a transparent resin, and the side surface on the LED 1 side is a light incident surface 3a. Light emitted from the LED 1 is incident on the light incident surface 3 a of the light guide plate 3 through the air layer 9. The light guide plate 3 has a light exit surface 3b on the front side (surface facing the liquid crystal display panel 30) and a reflection surface 3c on the back side (surface facing the reflection sheet). The light output surface 3b and / or the reflection surface 3c are both. Further, a diffusion pattern formed by printing of white ink or a white sheet, or a minute lens unevenness pattern having a shape optically designed to make the in-plane brightness uniform is applied. The light from the LED 1 incident on the light incident surface 3a of the light guide plate 3 travels inside the light guide plate 3, and part of the light is emitted from the light exit surface 3b. The light reflected by the light exit surface 3b and traveling toward the reflective surface 3c, and the light traveling directly from the light incident surface 3a toward the reflective surface 3c are diffused and reflected by the pattern formed on the reflective surface 3c, and emitted from the light exit surface 3b. The In addition, the light that is transmitted without being reflected by the reflecting surface 3c of the light guide plate 3 and traveling downward is reflected back to the inside of the light guide plate 3 by the reflecting sheet 5 installed below the reflecting surface 3c. The light diffused and reflected by 3c is emitted from the light exit surface 3b. Thereby, planar light whose luminance is substantially uniform is obtained over the entire surface from the light incident surface 3a of the light guide plate 3 to the tip portion facing the light incident surface 3a. The light emitted from the light exit surface 3b is further uniformed by the optical sheet 6 as described above, and the luminance is improved.

In this embodiment, a white light emitting LED is used as the LED 1, but white may be obtained by combining red, blue, and green colored LEDs, or a combination of white light emitting and colored light emitting LEDs. Also good. Although it is preferable to use a glass epoxy substrate as the base material 2b of the circuit board 2, a flexible substrate or a metal base substrate can also be used. The number of LEDs 1 used is determined by the size of the target backlight unit 31. The light guide plate 3 is generally manufactured by injection molding a transparent resin such as acrylic or polycarbonate. However, the light guide plate 3 can also be manufactured by cutting or creating a surface pattern by laser marking. The joining member 7 is a conductive resin, solder, or the like, and is a member that can electrically connect the LED 1 and the wiring land 8 and can fix and hold the LED 1.
In the backlight unit having such a configuration, in this embodiment, the optical axis 1d of the LED 1 is above a predetermined angle α1 with respect to the axis L in a direction parallel to the surface of the circuit board 2 or the light output surface 3b of the light guide plate 3 (liquid crystal display). The LED 1 is attached to the circuit board 2 so as to incline toward the panel 3a or the light exit surface 3b side of the light guide plate 3). Hereinafter, the inclination angle α1 is referred to as a “joining angle”. In addition, the state in which the optical axis 1d of the LED 1 is inclined upward from the axis L is referred to as a positive inclination, and the state in which the optical axis 1d is downward from the axis L (circuit board 2 side) is referred to as a negative inclination. To do. Mounting the LED 1 to the circuit board 2 with the bonding angle α1 can be realized by the following configuration. That is, as shown in FIG. 1, when the LED 1 is fixedly held on the circuit board 2, a part 2 c of the board printing paint 2 a is interposed between the bonding surface 1 c on the emission surface 1 b side of the LED 1 and the wiring land 8. Furthermore, the lower part on the opposite side (left side in the figure) of the emission surface 1b of the LED 1 falls to the wiring land 8 side. As a result, the LED 1 can be fixedly held on the circuit board 2 in a state where the LED 1 is inclined at the bonding angle α1. That is, in this embodiment, the emission surface 1b side of the side view type LED is made higher by partially using the substrate printing paint.

  As described above, the light emitted from the LED 1 enters the light incident surface 3 a of the light guide plate 3 through the air layer 9. In order to receive light from the LED 1 with high efficiency, the light guide plate light incident surface 3a must have a sufficiently large area. If the optical axis 1d of the LED 1 is parallel to the axis L, a part of the light traveling downward from the LED 1 (on the circuit board 2 side) hits the reflection sheet 5 or the circuit board 2 before reaching the light guide plate 3, and partially In many cases, the reflected light does not reach the light incident surface 3a, and most of the other is converted into heat energy and lost, and cannot be used as light. Such a loss becomes more prominent when the thickness of the light guide plate 3, that is, the height of the light incident surface 3a is reduced.

  Furthermore, the above-mentioned loss is also caused when a minus-direction inclination occurs due to an attachment error or positional deviation when mounting the LED 1 on the circuit board 2 or a variation in the spatial melting degree of the bonding member 7 such as solder. growing. Here, FIG. 9 shows a simulation result of the relationship between the bonding angle α and the luminance of the light emitted from the backlight unit. As is apparent from FIG. 9, the junction angle α and the luminance of light from the backlight unit are in a substantially proportional relationship, and the luminance decreases when the junction angle is negative, that is, when a negative inclination occurs.

  Further, when the LED 1 is to be mounted on the circuit board 2 on the basis of the bonding angle of 0 °, the actual bonding angle is in the range of about 0 ° due to the above-described error and positional deviation as shown in FIG. Variations occur in B, and accordingly, the luminance of the backlight unit also varies within the range C. Therefore, when the LED 1 is mounted on the circuit board 2 with a bonding angle of 0 ° as a reference, there is a possibility that a backlight having a low luminance or a low luminance as a whole is manufactured. For this reason, even if the light incident surface 3a of the light guide plate is enlarged, there is an upper limit in optical efficiency.

  On the other hand, in the configuration of this embodiment shown in FIG. 1, the light traveling downward from the LED 1 hardly hits the reflection sheet 5 or the circuit board 2 and reaches the light incident surface 3 a of the light guide plate 3. For this reason, the light from LED1 can be utilized with high efficiency. In addition, it is possible to prevent the negative direction from being tilted due to an attachment error or a positional deviation of the LED 1, and to suppress the above-described loss.

  Next, the shape, process, and the like for tilting and holding the LED 1 will be described in detail with reference to FIGS.

  FIG. 3 is an explanatory diagram of the LED mounting portion of the circuit board 2. In FIG. 3, the substrate printing paint 2a is not applied to a part between the plurality of wiring lands 8, and the base material 2b is exposed. On the other hand, in the portion 2c, the substrate printing paint 2a is applied so as to cover the wiring land 8. That is, in the AA sectional view in FIG. 3, the base material 2b is exposed between the left and right wiring lands 8, and in the BB sectional view, the substrate printing paint 2b ( 2c) is applied.

  FIG. 4 is a diagram showing a state in which the LED 1 is mounted on the circuit board 2. The board printing paint 2a (2c) is disposed on the light emitting surface 1b side of the LED bonding surface 1c, and the board printing paint 2a is not provided on the opposite side. 2 is fixedly held. By doing so, the LED 1 is inclined, and the emission surface 1 b of the LED 1 faces upward as compared to the parallel direction of the circuit board 2. In other words, a bonding angle α1 in the + direction is generated.

  The mounting process of the LED 1 according to this embodiment on the circuit board 2 will be described with reference to FIG. Here, the case where the coupling member 7 is paste-like solder will be described.

  In the first step, the coupling member 7 is applied on the wiring lands 8 provided on the circuit board 2 by a normal printing step.

  Next, in the second step, the LED 1 is placed on the wiring land 8. At this time, one end on the light emitting surface 1 b side of the bonding surface 1 c of the LED 1 is placed on the board printing paint 2 a (2 c) of the circuit board 2. In FIG. 4, the other end of the bonding surface 1 c is on the solder of the wiring land 8, but may be on the base material 2 b of the circuit board 2.

  Subsequently, in the third step, the bonding member 7 is melted by the solder reflow step. At that time, the LED 1 comes into contact with the printed board 2a (2c) on the light emitting surface 1b side of the bonding surface 1c from its own weight, while the opposite side is the wiring land. 8 is closely attached. As a result, as shown in the figure, the emission surface 1b of the LED 1 is fixedly held on the circuit board 2 with an upward inclination with respect to the circuit board 2, that is, with an inclination α1 in the + direction. Can do.

The inclination in the + direction can be adjusted by the thickness of the substrate printing paint 2c. For example, when the depth of the LED 1 (dimension in the left-right direction in FIG. 5) is 1.5 mm and the thickness of the substrate printing paint 2c is 0.1 mm, the bonding angle α1 of the LED 1 is tan ⁻¹ (0.1 / 1.5) = An inclination of 3.8 °. Variations during the reflow process vary around α1.

  FIG. 6 shows the result of simulating the relationship between the joining angle α and the luminance of light from the backlight unit when this embodiment is applied. In this embodiment, the joining angle α varies in the range D with α1 as the center, and the luminance as the backlight at that time is in the range E. For comparison, a range B and a range C when the LED 1 is mounted on the circuit board 2 on the basis of the bonding angle α = 0 shown in FIG. 9 are also illustrated. As shown in the figure, the luminance range E when mounted at the junction angle α1 as in the present embodiment is higher than the luminance range C when mounted with the junction angle α = 0 as a reference. It can also be seen that the variation in luminance is small.

  That is, when LEDs having the same light amount are used, the liquid crystal display device according to the present embodiment can have higher luminance, and can prevent local or overall luminance from being lowered. Further, even if the light amount of the LED is reduced, the same luminance as that obtained when the bonding angle α = 0 is used as a reference can be obtained, so that power consumption can be reduced.

  Note that, as is apparent from FIGS. 6 and 9, even if the bonding angle α <b> 1 is too large, the light use efficiency is lowered. In addition to the tilting of the LED 1 in the + direction, the incident efficiency may be further increased by making the light incident surface 3a of the light guide plate 3 tilted toward the LED 1 side.

  As described above, according to the present embodiment, since the optical axis 1d of the LED 1 is arranged to be inclined upward, the backlight unit that can improve the light use efficiency and improve the luminance, and the image display using the backlight unit. An apparatus can be provided. Further, according to the present embodiment, it is possible to suppress variations in luminance, and it is possible to display a higher quality image.

  FIG. 12 is an enlarged cross-sectional view of the vicinity of the portion where the LEDs are arranged in the backlight unit according to the second embodiment of the present invention. Whereas the first embodiment uses side view type LEDs, the second embodiment is characterized by the use of top view type LEDs. In the second embodiment, the surface of the circuit board 2 on which the LED 1 is mounted is parallel to the light incident surface 3a in order to direct light from the top view type LED in a direction parallel to the light exit surface 3a of the light guide plate 3. Thus, the circuit board 2 is mounted upright on a flat metal chassis 12 provided on the back side of the backlight unit. Here, the LED 1 is a top-view type white light emitting LED having a size including a surface including the emission surface 1b of 2 mm × 3 mm and a depth of about 1.5 mm.

  The method and configuration for mounting the LED 1 on the circuit board 2 are basically the same as those described in the first embodiment. However, in this embodiment, a top-view type LED is used. Since the circuit board 2 on which is mounted is provided upright with respect to the chassis 12, the mounting method is partially different. That is, in this embodiment, first, the surface of the circuit board 2 is leveled and the bonding member 7 such as solder is applied, and the circuit board 2 is placed with the emission surface 1b of the LED 1 facing up. At this time, the circuit board 2 is placed in a state where one end of the LED 1 rides on the board printing paint 2a and the other end is dropped on the wiring land 8 where the board printing paint 2a is not applied. By mounting in this way, the optical axis 1d of the LED 1 can be inclined in advance by an angle α2 with respect to the direction orthogonal to the surface of the circuit board 2. Subsequently, the LED 1 is fixedly held on the circuit board 2 through a process of dissolving the coupling member 7. Thereafter, the LED 1 is mounted on the chassis 12 with the circuit board 2 standing up (that is, the surface of the circuit board 2 is perpendicular to the surface of the chassis 12). As a result, the joining angle of the optical axis 1d of the top view type LED 1 becomes α2 in the + direction.

  As described above, according to the second embodiment, even in the case of a top view type LED, the junction angle can be set in the + direction. Therefore, similarly to the first embodiment, the light use efficiency can be improved and the luminance can be improved. It is possible to provide an improved backlight unit and an image display device using the backlight unit. Further, according to the present embodiment, it is possible to suppress variations in luminance, and it is possible to display a higher quality image.

1 ... LED
DESCRIPTION OF SYMBOLS 2 ... Circuit board 3 ... Light guide plate 5 ... Reflective sheet 6 ... Optical sheet 7 ... Bonding member 8 ... Wiring land 9 ... Air layer 12 ... Chassis 30 ... Liquid crystal display panel 31 ... Backlight unit 32 ... Front frame 33 ... Back cover

Claims (8)

A light-emitting diode, a substrate provided with the light-emitting diode, and a light guide plate placed on the substrate, and light from the light-emitting diode is incident on a side surface of the light guide plate, and the incident light is In the backlight unit configured to irradiate the liquid crystal panel side from the light exit surface of the light guide plate as planar light,
The backlight unit, wherein the light emitting diodes are inclined and arranged such that the light emitting diode emitting surface faces the light emitting surface of the light guide plate.   2. The backlight unit according to claim 1, wherein the light-emitting diode is a side-view type light-emitting diode, and is arranged so that an emission surface of the side-view type light-emitting diode faces a light-incident surface of the light guide plate. Backlight unit characterized by that.   3. The backlight unit according to claim 2, wherein a member for incliningly arranging the light emitting diode is interposed between an emission surface of the side view type light emitting diode and the substrate. Backlight unit to be used.   4. The backlight unit according to claim 3, wherein the member is a printing paint applied to the substrate.   2. The backlight unit according to claim 1, wherein the light-emitting diode is a top-view type light-emitting diode, and is disposed so that an emission surface of the top-view type light-emitting diode faces a light-incident surface of the light guide plate. Backlight unit characterized by that.   6. The backlight unit according to claim 5, wherein the circuit board is provided so as to be perpendicular to a chassis disposed on a back side of the backlight unit. A light-emitting diode, a substrate provided with the light-emitting diode, and a light guide plate placed on the substrate, and light from the light-emitting diode is incident on a side surface of the light guide plate, and the incident light is In the backlight unit configured to irradiate the liquid crystal panel side from the light exit surface of the light guide plate as planar light,
The backlight unit, wherein the light emitting diode is arranged so that an optical axis of the light emitting diode is inclined to the light emitting surface side by a predetermined angle with respect to a direction parallel to the light emitting surface of the light guide plate.   The image display apparatus carrying the backlight unit in any one of Claims 1-7.

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