KR20140070692A - Back light unit - Google Patents

Abstract

The present invention relates to a backlight unit having a wide light-guiding angle and a uniform brightness, and in accordance with an embodiment of the present invention, a curved substrate having at least one upward projecting portion formed of a pair of inclined surfaces; An LED chip provided on one side of the inclined surface; And a diffusing plate disposed on an upper portion of the bending substrate and having a reflective pattern formed on one side thereof so as to reflect a part of light emitted from the LED chip.

Description

Backlight unit {BACK LIGHT UNIT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit, and more particularly, to a backlight unit capable of increasing a light directing angle of an LED chip to achieve a uniform luminance even with a smaller number of LED chips.

Generally, indoor and outdoor lighting facilities such as street lamps and security lamps are mainly used filament and discharge lamp type lamps such as metal halide lamps, mercury lamps, sodium lamps and the like.

However, since the conventional filament and discharge light bulb have a disadvantage in that they have high power consumption and poor durability, and since a substantial part of the supplied power is discharged as heat, the energy output to the visible light used in actual lighting is not used Which is about 5 ~ 28% of the energy efficiency.

On the other hand, LED (Light Emitting Diode) has many merits such as high brightness in terms of size and power consumption, long service life, low manufacturing cost, etc., .

Meanwhile, in recent years, display devices capable of visually displaying information together with development of information technology and mobile communication technology have been developed. Since LED has advantages such as small size, low power consumption and high reliability , And a liquid crystal display (LCD) device that does not have its own luminescent characteristics.

That is, since the LCD device does not have a self-luminous element, a separate light source is required. Accordingly, a backlight unit having a light source on the back surface thereof is provided to irradiate light toward the liquid crystal panel, An image is realized. At this time, an LED is used as the display light source.

Here, the general backlight unit is divided into an edge type and a direct type according to the arrangement structure of the light sources. The edge type has a structure in which one or a pair of light sources are disposed on one side of the light guide plate or two or two pairs of light sources are arranged on both sides or four corner sides of the light guide plate, Light sources are disposed at the lower portion of the optical sheet.

In recent years, researches on a large-sized liquid crystal display device have been actively carried out according to the demand of a consumer. In addition, direct-type liquid crystal display devices can be dividedly driven to realize delicate images. More suitable.

FIG. 1 is a cross-sectional view of a direct-type backlight unit using a general LED as a light source, and FIGS. 2a and 2b are schematic views showing an arrangement of LED chips according to a change in a light directing angle.

1, the backlight unit 1 includes a substrate 2 serving as a reflector, and a plurality of LED chips 3 are arranged side by side on the upper side of the substrate 2, A diffuser plate 4 and a plurality of optical sheets 5 are disposed apart from the upper portion of the LED chip 3.

As a method of mounting the LED chip 3 on the substrate 2, there are a package mounting method in which the LED chip 3 is placed in the LED package and the LED package itself is mounted on the substrate 2, There is a COB (Chip-On-Board) method in which the substrate 3 is directly mounted on the substrate 2 and is sealed in a dome form using a resin or the like for protection.

However, in the case where the directivity angle A of the light emitted from the LED chip 3 is narrow as shown in FIG. 2A, in order to illuminate a certain area, as compared with the case where the light directivity angle B shown in FIG. , There is a disadvantage that more LED chips 3 must be densely arranged on the substrate 2 having the same area.

Therefore, in order to increase the directivity angle of the LED light source, in the case of the package mounting method, the reflector of the LED package is arranged along the periphery of the LED chip. However, in the case of the COB method, since the LED chip is mounted directly on the substrate without a separate package, it is difficult to apply the reflector, and in the case of the package mounting method, the manufacturing cost increases as the number of steps for forming the reflector increases .

On the other hand, recent liquid crystal display devices such as computer monitors and wall-mounted televisions are required to have a thin display while having a wide display area, and this demand is also applicable to LED lights used for tubes, flat panels, or signboards.

Accordingly, attempts have been made to provide a thin backlight unit by reducing the width of the optical gap or air gap of the backlight unit, that is, the space between the reflector and the diffuser plate.

However, in order to supply a high quality surface light source, which is the most important role of the backlight unit, various optical designs are considered, and maintenance of the gap between the reflection plate and the diffusion plate is an important factor.

That is, when the distance between the reflection plate and the diffusion plate is small, the light of the LED light source is concentrated at the upper center of the LED light source, and a hot spot phenomenon in which the center corresponding to the LED light source is bright, A mura phenomenon occurs.

As a result, a method for preventing the occurrence of the hot spot phenomenon and the chromatic phenomenon described above has been studied while thinning the backlight unit. For example, Korean Patent Laid-Open No. 10-2009-0026671 (Patent Document 1) 10-1131152 (Patent Document 2), a diffusing lens is provided to prevent hot spots from being generated while light is evenly distributed. However, the application of such a diffusion lens has a problem that manufacturing time and cost are increased due to an increase in the number of steps.

As another method, it is possible to eliminate the blurring phenomenon by increasing the number of the optical sheets. However, if the number of the optical sheets to be stacked is increased, the production cost of the backlight unit increases and the manufacturing cost increases.

Patent Document 1: Korean Patent Laid-Open No. 10-2009-0026671 (published on Mar. 13, 2009) Patent Document 2: Korean Patent No. 10-1131152 (registered on March 21, 2012)

SUMMARY OF THE INVENTION The present invention has been conceived in order to solve the problems as described above, and one embodiment of the present invention is to provide a liquid crystal display device in which the light directing angle is increased and hot spot phenomenon and mura phenomenon are prevented from occurring, The present invention provides a backlight unit that can be used as a backlight unit.

In order to achieve the above-mentioned object, according to a preferred embodiment of the present invention, there is provided a bending board comprising: at least one upward protrusion formed of a pair of inclined surfaces; An LED chip provided on one side of the inclined surface; And a diffusion plate spaced apart from the upper portion of the bending substrate and having a reflective pattern formed on one side thereof so as to reflect a part of the light emitted from the LED chip, There is provided a backlight unit which is formed at a position spaced apart from a central axis extending vertically by a predetermined angle in a direction in which the inclined surface is inclined.

In the backlight unit according to an embodiment of the present invention, the reflection pattern is formed along the shape of light that is obliquely projected from the LED chip to the diffusion plate.

In the backlight unit according to an embodiment of the present invention, the LED chip may include a semiconductor layer including an active layer; And a light-transmitting layer that transmits light output from the active layer on the semiconductor layer, wherein the light-transmitting layer has a thickness of 150 mu m to 300 mu m.

In the backlight unit according to an embodiment of the present invention, the LED chip is a frameless LED chip having a light directing angle of 140 degrees or more.

In the backlight unit according to an embodiment of the present invention, the light transmitting layer is a growth substrate of a transparent material.

A backlight unit according to an embodiment of the present invention is characterized in that a remote phosphor layer is formed on one side of the diffusion plate.

In the backlight unit according to an embodiment of the present invention, the reflection pattern may be conical or elliptical.

In the backlight unit according to an embodiment of the present invention, the upward protrusions are formed continuously along one direction of the bending substrate.

In the backlight unit according to another embodiment of the present invention, the upward protruding portions are formed apart from each other along one direction of the bending substrate.

The backlight unit according to an embodiment of the present invention provides an effect of widening the light directing angle by providing the LED chip on the inclined surface of the bending substrate.

The backlight unit according to an embodiment of the present invention prevents a hot spot phenomenon and a mura phenomenon by forming a reflection pattern on one side of a diffusion plate spaced from an axis extending perpendicularly from an LED chip to a diffusion plate, It is possible to secure the uniformity of the magnetic field.

The backlight unit according to an embodiment of the present invention provides an effect of enhancing aesthetics in appearance when the backlight unit is turned off as the remote fluorescent material layer is formed on the diffusion plate.

1 is a sectional view of a direct-type backlight unit using a general LED as a light source.
2A is a schematic view showing the arrangement of LED chips when a light directing angle is narrow.
2B is a schematic view showing the arrangement of the LED chips when the light directing angle is wide.
3 is a cross-sectional view of a backlight unit according to an embodiment of the present invention.
Figure 4 is a partial enlarged view of Figure 3;
FIG. 5A is a graph illustrating a simulation result of brightness uniformity of a backlight unit to which a conventional flat panel substrate is applied. FIG.
5B is a graph illustrating simulation results of brightness uniformity of a backlight unit according to an embodiment of the present invention.
6 is a cross-sectional view illustrating an example in which a remote fluorescent material layer is formed on a diffuser plate according to another embodiment of the present invention.
7 is a cross-sectional view of a frameless LED chip;
FIG. 9 is a graph showing a change in the orientation angle characteristic of the frameless LED chip according to the change of the light transmission layer thickness. FIG.
9 to 12 are graphs showing the orientation angle characteristics when the thickness of the transparent layer of the frameless LED chip is 120 탆, 150 탆, 250 탆 and 400 탆, respectively.

Hereinafter, preferred embodiments of a backlight unit according to an embodiment of the present invention will be described with reference to the accompanying drawings. In this process, the thicknesses of the lines and the sizes of the components shown in the drawings may be exaggerated for clarity and convenience of explanation.

In addition, the terms described below are defined in consideration of the functions of the present invention, which may vary depending on the intention or custom of the user, the operator. Therefore, definitions of these terms should be made based on the contents throughout this specification.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, Embodiments that include components replaceable as equivalents in the elements may be included within the scope of the present invention.

Further, it should be understood that the "backlight unit" used herein is not limited to the parts used in the flat panel display device but includes a surface emitting illumination used for illumination.

The term "frame-less LED chip " used herein is used to distinguish the LED chip from a conventional LED chip. The frame-less LED chip is a body that forms an outer shape of the LED chip, a reflector And a package not including the lead frame means a package in which the LED chip except for the lens portion forms the outer shape of the LED chip. Is referred to as a wafer level package in that a package of a lead frame or a submount is formed, and also referred to as a chip scale package in that the external shape of the package is close to the size of the LED chip, A "chipless board" LED package is also referred to as a "COB (chip on board) type LED package" in which an LED chip is mounted on a substrate without a component. A chip having an LED package that does not include a main body, a lead frame that forms a key figure, a reflector, and a main body. As such a frameless LED chip, a light emitting diode disclosed in Korean Patent Application No. 10-2011-0139385 .

Since the frameless LED chip does not include additional components and most processes are completed in the semiconductor production process, the time and cost required for manufacturing can be reduced, and reliability is improved. In addition, since there is no constituent element for forming the external shape of the package, there is an effect that the size of the package can be reduced, and the LED chip is mounted close to the substrate.

Example

FIG. 3 is a cross-sectional view of a backlight unit according to an embodiment of the present invention, and FIG. 4 is a partially enlarged view of FIG.

3 and 4, a backlight unit (hereinafter, referred to as a 'backlight unit') 10 according to an embodiment of the present invention includes a bending substrate 20, an inclined surface 21 of the bending substrate 20 And a diffusion plate 40 provided on an upper portion of the bending substrate 20.

The bent substrate 20 is a substrate on which a plurality of LED chips 30 are arranged side by side. For example, an electrical connecting means such as an FR-4 (Flame Resistant 4) based substrate, an Al based substrate, Alternatively, a flexible substrate 20 may be prepared by using a plastic or metal material, and a separate substrate (not shown) provided with electrical connection means such as a wiring pattern may be used. The substrate may be bonded onto the bending substrate 20.

That is, the LED chip 30 to be described later may be directly mounted on the bending substrate 20, or may be mounted on a separate substrate coupled to the bending substrate 20.

At this time, at least one upward protruding portion 22 is formed on the bending substrate 20 so that the surface is bent. The upward protruding portion 22 is formed by, for example, an upwardly inclined face 21a and a downwardly inclined face 21b And a plurality of upwardly projecting portions 22 are formed side by side along the width direction or the longitudinal direction of the bending substrate 20.

At this time, the plurality of upward protrusions 22 may be formed consecutively according to design conditions such as the distance between the LED chips 30, the brightness of the light, the size of the bending substrate, or may be spaced apart from each other by a predetermined distance.

On the other hand, when the thin plate is bent several times at a predetermined interval to form the bent substrate 20, the heat generated by the LED chip 30 is dissipated to the outside due to the increase of the surface area of the bending substrate 20 ).

The LED chip 30 is mounted on the bendable substrate 20 or the separate substrate provided on the bendable substrate 20.

The LED chip 30 may be mounted by a package mounting method and a COB method. According to a preferred embodiment of the present invention, in order to avoid an increase in the thickness of the backlight unit 10 due to the height of the package itself, It is preferable to follow the COB method in which the substrate is mounted on the substrate in a flip chip form.

More preferably, in accordance with an embodiment of the present invention, a frame-less LED chip is mounted on the flex board 20, in which case the orientation angle of the frameless LED chip exhibits a maximum of 140 degrees , The light directing angle improving effect is remarkably superior to that of the LED chip having the 120 ° directing angle characteristic. This will be described later with reference to Figs. 7 to 12.

A plurality of LED chips 30 are arranged at predetermined distances from each other along the longitudinal direction of each of the inclined faces 21 of the upward protruding portion 22. For protection of the LED chip 30, It is preferable to be sealed in a dome form by silicone or epoxy resin or the like.

As described above, when the LED chip 30 is disposed on both inclined faces 21 of the upward protruding portion 22 of the bending substrate 20, the LED chips 30 on both sides of the upward protruding portion 22 are positioned outside As the light is diverged at an oblique angle, a wider light directing angle is exhibited as compared with a pair of LED chips arranged at the same pitch on a conventional flat substrate.

Therefore, as described above with reference to FIG. 2B, in the backlight unit 10 according to the embodiment of the present invention, when illuminating the same area, a smaller number of LEDs Since the chip 30 can be used, the light efficiency is improved.

If the inclination angle is less than 5 degrees, the effect of improving the light directing angle is insufficient as compared with the flat board substrate. If the inclination angle exceeds 30 degrees, the backlight unit 10 is increased and the light efficiency of the backlight unit 10 is lowered.

The diffusion plate 40 is installed at a predetermined distance from the upper portion of the bending substrate 20 and diffuses the light emitted from the LED chip 30 to uniformly distribute the brightness.

At this time, the distance between the LED chip 30 and the diffuser plate 40 is set to be equal to or smaller than the number of the LED chips 30, So that it is possible to make the backlight unit 10 thinner.

Here, if the distance between the bending substrate 20 and the diffuser plate 40 is too close, a portion of the diffuser plate 40 corresponding to the vertical upper portion of the LED chip 30 becomes hot-spot ) Phenomenon may occur.

However, since the LED chip 30 according to the embodiment of the present invention is disposed on the inclined surface 21 of the bending substrate 20 and forms a predetermined angle with the diffusion plate 40, The distance to the diffusing plate 40 corresponding to the light source is formed to be farther than when the flat substrate is applied, and thus a more uniform luminance distribution is obtained than when the flat substrate is used.

4, the central axis l 'of the LED chip 30 is spaced apart from the extension line 1 extending vertically from the LED chip 30 to the diffusion plate 40 by an angle? The distance r 'from the LED chip 30 to the diffusion plate 40 corresponding to the vertical upper portion of the LED chip 30 along the central axis 1' (R) to the diffuser plate 40 extending along the extension line 1 perpendicular to the diffuser plate 40, and as a result, the optical uniformity is further improved as compared with the example in which the flat panel substrate is applied .

FIGS. 5A and 5B are graphs showing simulation results showing that the optical uniformity is further improved as compared with the example in which the flat panel substrate is applied, when the backlight unit according to the embodiment of the present invention is applied, as described above.

5A is a graph illustrating a result of simulation of luminance uniformity of a backlight unit to which a conventional flat panel substrate is applied, and FIG. 5B is a graph illustrating simulation results of luminance uniformity of a backlight unit according to an exemplary embodiment of the present invention.

In the case of the flat substrate shown in FIG. 5A, the luminance of the central portion of the light emitted from each LED chip is higher than that of the surroundings. However, in the case of the embodiment of FIG. 5B, .

In addition to this, in order to prevent the light projected onto the diffusion plate 40 along the center axis l 'of the LED chip 30 from becoming brighter than the surrounding area, 40, and reflects the incident light back toward the bending substrate 20.

4, the reflection pattern 41 corresponds to a point at which the central axis l 'of the LED chip 30 meets the diffusion plate 40, that is, the vertical upper portion of the LED chip 30 The reflection pattern 41 is formed on the bottom surface of the diffusion plate 40 while the reflection pattern 41 is formed on the bottom surface of the diffusion plate 40. Alternatively, It is possible.

The reflection pattern 41 is preferably formed in a conical shape or an elliptical shape along the shape of the light projected obliquely from the LED chip 30 toward the diffusion plate 40.

At this time, the light reflected by the reflection pattern 41 in the direction of the bending substrate 20 is reflected again on the bottom surface of the diffusion plate 40 (when the reflection pattern is formed on the upper surface or the inside of the diffusion plate) 20, and then travels toward the diffusion plate 40. [0050]

If all the light incident in the direction of the reflection pattern 41 is reflected, a dark mura phenomenon occurs in the region corresponding to the reflection pattern 41 in the illumination projected through the diffusion plate 40.

Therefore, it is preferable that the reflection pattern 41 allows a part of the light emitted from the LED chip 30 to pass therethrough and reflects a part of the light. In this case, the reflection pattern 41 may include SiO2 or TiO2, Acrylate, acrylate, acrylate, acrylate, acrylate, acrylate, acrylate, acrylate, acrylate, acrylate,

The light transmittance and the light reflectance of the reflection pattern 41 can be appropriately selected in consideration of the brightness of the light emitted from the LED chip 30 and the distance between the LED chip 30 and the diffusion plate 40.

6 is a cross-sectional view showing an example of a backlight unit 10 'in which a remote fluorescent material layer is formed on a diffusion plate according to another embodiment of the present invention. The same reference numerals are assigned to the same components as in the above- Duplicate description will be omitted.

According to another embodiment of the present invention, the remote phosphor layer 42 may be formed by spraying, coating, or attaching a film such as a film or the like in order to prevent the feeling of rejection as the appearance of the LED is turned off when the LED is turned off. And is formed on one side of the diffuser plate 40 in a manner as shown in Fig.

In this case, the remote fluorescent material layer 42 is formed on the upper surface of the diffusion plate 40. Alternatively, the remote fluorescent material layer 42 may be formed on the inner or bottom surface of the diffusion plate 40 Of course.

Meanwhile, when a frame-less LED chip is mounted on the bending board 20 according to an embodiment of the present invention, the light directing angle is much wider than that of a conventional LED chip. This is because the frameless LED chip exhibits a directivity angle characteristic of 140 degrees at maximum, which will be described below with reference to Figs. 7 to 12. Fig.

7 is a cross-sectional view of the frameless LED chip.

7, the frame-less LED chip 30 'includes a semiconductor layer 31' including an active layer, and a light transmission layer formed on the semiconductor layer 31 'and transmitting light output from the active layer Layer 32 '.

At this time, the light transmitting layer 32 'is made of a growth substrate made of a transparent material such as sapphire. By controlling the thickness of the light transmitting layer 32', the directing angle characteristic can be adjusted, The chip 30 'has a wider light directing angle than the conventional LED chip.

FIG. 8 is a graph showing a change in the directional angle characteristic of the frame-less LED chip according to the change in the thickness of the light-transmitting layer. As the thickness of the light-transmitting layer 32 'increases, the directivity angle widens.

At this time, the thickness of the light transmitting layer 32 'of the frameless LED chip 30' is preferably 150 μm to 300 μm. If the thickness of the light transmitting layer 32 'is less than 150 μm, °, and when the thickness of the light-transmitting layer 32 'is more than 300 μm, the change is slowed at a directivity angle of 140 °.

Therefore, according to an embodiment of the present invention, a frame-less LED chip 30 'having a directional angle characteristic of maximum 140 ° can be mounted on the bending substrate 20, and in this case, , The effect of increasing the light directing angle is further doubled.

9 to 12 are graphs showing the orientation angle characteristics when the thicknesses of the light transmitting layers of the frameless LED chip are 120 μm, 150 μm, 250 μm and 400 μm, respectively, wherein the thickness of the light transmitting layer 32 ' When the thickness of the light transmitting layer 32 'is 400 μm, the difference is not remarkable as compared with the case where the thickness of the light transmitting layer 32' is 250 μm. However, when the thickness of the light transmitting layer 32 'is 120 μm, 150 μm, As a result, it can be seen that as the thickness of the light transmitting layer 32 'is thicker, the directing angle characteristics are improved.

10, 10 ': backlight unit 20: bent substrate
21: inclined surface 21a: upward inclined surface
21b: downward slope 22: upward protrusion
30: LED chip 30 ': frameless LED chip
31 ': semiconductor layer 32': light-transmitting layer
40: diffusion plate 41: reflection pattern
42: remote phosphor layer

Claims (9)

A bent substrate on which at least one upward protruding portion made up of a pair of inclined surfaces is formed;
An LED chip provided on one side of the inclined surface; And
And a diffusing plate disposed on an upper portion of the bending substrate and having a reflective pattern formed on one side thereof so as to reflect a part of light emitted from the LED chip,
The reflection pattern
Wherein the light guide plate is formed at a position spaced apart from the LED chip by a predetermined angle in a direction in which the inclined surface is inclined from a central axis extending perpendicularly to the diffusion plate.
[2] The method according to claim 1,
Wherein the LED chip is formed along a shape of light projected obliquely from the LED chip to the diffusion plate.
The LED package according to claim 1,
A semiconductor layer including an active layer; And
And a light-transmitting layer that transmits light output from the active layer on the semiconductor layer,
Wherein the thickness of the light transmitting layer is 150 mu m to 300 mu m.
4. The LED chip according to claim 3,
And the light directing angle is not more than 140 degrees.
4. The light-emitting device according to claim 3,
Wherein the backlight unit is a growth substrate of a transparent material.
The method according to claim 1,
Wherein a remote phosphor layer is formed on one side of the diffusion plate.
The optical device according to claim 2,
And is formed into a conical shape or an elliptical shape.
[2] The apparatus according to claim 1,
Wherein the plurality of light emitting units are continuously formed along one direction of the bending substrate.
[2] The apparatus according to claim 1,
Wherein the first and second flexible substrates are spaced apart from each other along one direction of the bending substrate.

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