JP4233941B2 - Display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a display device used for a mobile phone, a PDA, or the like.
[0002]
[Prior art]
The liquid crystal display panel changes the alignment and phase of liquid crystal molecules depending on the electric field, current, or temperature, and changes optical properties such as light interference, scattering, diffraction, optical rotation, selective scattering, and absorption in the liquid crystal state. This is the principle of operation. Usually, display is performed on a liquid crystal display panel by applying a voltage between opposing electrodes to control the liquid crystal layer. Since the liquid crystal display panel is non-self-luminous, it is necessary to use external light or backlight emission to visualize the display.
[0003]
In general, a backlight used for a liquid crystal display or the like is a planar light source, and a light guide system is currently mainstream. EL, LED, CCFL, etc. are used as the light source of the backlight. In a light guide type backlight, a light scatterer is provided on the back surface of the light guide so that light from the light source irradiates the light emitting surface uniformly. The light scatterer is formed by an uneven scatterer such as a pattern by printing or a groove pattern by molding. In the backlight having such a configuration, light from the light source travels inside the light guide, for example, is scattered by a printed dot pattern that is a light scatterer, and the scattered light is emitted from the light guide. At this time, a part of the light scattered by the light scatterer is emitted from the surface of the light guide, but a part of the other light leaks to the back and side surfaces of the light guide. An optical design has been made in which a sheet-like reflector having a high reflectance of 90% or more is attached to the side surface and bottom surface (opposite side of the light emitting surface) of the light guide so that the leaked light enters the light guide again. (For example, refer to Patent Document 1).
[0004]
In general, a side-view type LED unit using a chip LED applies a voltage to the LED chip mounted on the chip substrate, a transparent mold portion provided on the chip substrate so as to cover the LED chip, and the LED chip. For this purpose, an electrode portion formed on the chip substrate is provided. Such an LED unit is mounted on the surface of the circuit board, and the electrodes of the circuit board are electrically connected to the electrodes of the chip board. When a driving voltage is applied from the electrode part to the LED chip, the LED chip emits light, and this light is emitted to the outside through the mold part. In the case of obtaining pseudo white light emission using the LED unit having such a configuration, it is known to combine a blue LED chip and a transparent mold portion in which a phosphor emitting yellow light is mixed (for example, Patent Documents). 2).
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-245827 (page 2, FIG. 9)
[0006]
[Patent Document 2]
JP 2002-343123 A (2nd page, FIG. 10)
[0007]
[Problems to be solved by the invention]
The backlight having the conventional structure described above has low light reuse efficiency that does not enter the light guide from the LED but reflects at the interface of the light entrance portion of the light guide plate. Further, in order to increase the luminance, an expensive reflector is required, making it difficult to reduce the thickness and cost of the module. In addition, when a packaged LED is used, it becomes a point light source, so that a large diffusion from a point to a surface is necessary, leading to a decrease in light utilization efficiency.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problem, the display device of the present invention includes a flexible substrate connected to the display element and disposed on the back side thereof, a light guide provided between the display element and the flexible substrate, The light guide is provided with a light source that emits light, and a reflective layer is formed on the surface of the flexible substrate facing the light guide. With such a configuration, the reuse efficiency of the light leaked without entering the light guide is improved. Furthermore, the reflective layer was formed of a metal reflective film, and a light source was connected to the pattern formed using this metal reflective film.
[0009]
Furthermore, the light source is not a package body but a chip-like LED element. Therefore, it becomes a state close to a surface light source, and both light diffusibility and utilization efficiency are improved.
[0010]
Further, the LED chip is arranged on the flexible substrate so that light is incident on the light guide from the side surface of the light guide, and the reflective film is also provided on the portion where the flexible substrate is folded. Both diffusibility and reuse efficiency are improved.
[0011]
In addition, the flexible substrate is provided with a portion extending from the portion connected to the display panel to the end side, and the extended portion, the portion connected to the display panel, and the folded portion are continuous with the reflective film. It was decided to provide a reflective film. Thereby, since the LED chip is configured to be covered with the reflective layer except for the light emitting part to the light guide, the light of the LED chip can be efficiently condensed on the light incident part of the light guide.
[0012]
In addition, the LED chip can be arranged on a flexible substrate directly below the light guide. At this time, a concave portion was formed in the light guide facing the LED chip, and a dot pattern having a higher density than the dot patterns in other areas was provided on the bottom surface of the concave portion.
[0013]
Further, by connecting a metal reflective film used as a reflective layer to the ground (terminal), it is possible to function as a shield against static electricity or electromagnetic waves.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The display device of the present invention has a configuration in which a flexible printed circuit board (hereinafter referred to as FPC) having a thickness of 10 to 100 microns, on which a circuit component such as a semiconductor chip is mounted, is provided on the back side of the display element. A reflective layer is provided in a portion facing the display element of the FPC. Since the display element is a type that does not emit light, it is necessary to provide a light source for illuminating the display element. A light guide for irradiating the display element with light from the light source is provided between the reflective layer and the display element. The light emitted from the light source is optically designed so as to be repeatedly reflected by the reflection layer and condensed on the light incident portion of the light guide. Part of the light scattered by the pattern formed inside the light guide is directed toward the display element. The remaining light is reflected by the reflective layer and enters the light guide again. In this way, most of the light from the light source reaches the display element by repeating scattering and reflection.
[0015]
Here, a metal reflective film can be used as the reflective layer. In this case, since the wiring can be formed using a part of the metal reflective film, a light source such as an LED can be directly mounted on the FPC. That is, the metal reflection layer has a function as a current path to the light source and a function as a reflection layer. Furthermore, by connecting the metal reflective film to the ground terminal, a function as a shield for preventing static electricity and electromagnetic waves is generated.
[0016]
Wiring is formed on the surface opposite to the surface facing the display element of the FPC, and circuit components are mounted. In general, a diffusion sheet or a prism sheet is often installed between the display element and the light guide.
[0017]
Hereinafter, the case of a bare chip LED will be described. Bumps made of gold or solder are formed on the bare chip LED, and face-down mounting is performed on the FPC using the bumps. The bump and the aluminum layer are connected by a eutectic bond of metal or an anisotropic conductive film. Further, by potting a molding agent for adding a light emitter onto the bare chip LED, it is possible to protect the chip and control the emission wavelength.
[0018]
【Example】
Below, the Example using a liquid crystal panel as a display element is described based on FIGS.
[0019]
Example 1
FIG. 1 shows a schematic cross section of the display device of this example. The liquid crystal panel 1 has a configuration in which a pair of transparent substrates on which an ITO pattern is formed are arranged so that the pattern surfaces face each other, a liquid crystal is provided between the substrates, and an optical plate such as a polarizing plate is provided above and below the substrate. A film is provided. The connection terminal of the liquid crystal panel 1 and the FPC are joined by hot pressing through an anisotropic conductive film. In this embodiment, a glass substrate having a thickness of 0.5 mm is used as the transparent substrate. The FPC uses a polyimide film 3 having a thickness of 25 μm as a base film, and has a structure in which a Cu pattern 2 having a thickness of 8 μm is formed on one surface of the polyimide film 3 and a metal reflective film is formed on the other surface. Yes. Here, an Al thin film 4 by vapor deposition is used as the metal reflective film. The Cu pattern 2 is subjected to electroless tin plating on the surface. On the Cu pattern 2, chip parts (not shown) such as resistors and capacitors are mounted. The LED unit 5 that is a light source is configured to package an LED chip and emit light from one direction. The LED unit is surface-mounted on the FPC. A pattern for surface mounting the LED unit 5 is formed on the FPC using the Al thin film 4.
[0020]
As shown in the figure, the FPC is bent so as to be arranged on the back side (the counter-observer side) of the liquid crystal panel 1. A light guide 6 is provided in the gap between the liquid crystal panel and the FPC. The FPC and the light guide are arranged so that the light emission from the LED unit 5 provided on the FPC efficiently enters the light guide 6. In many cases, a diffusion sheet or a prism sheet is provided between the display element and the light guide. The Al thin film 4 provided on the side of the FPC facing the liquid crystal panel functions as a reflective layer for reusing light scattered by the light guide 6. Therefore, it is necessary to provide an Al thin film at least at a site corresponding to the display range or parting range of the display panel. In order to increase the light utilization efficiency, it is preferable to provide an Al thin film 4 having a size that covers the entire light guide.
[0021]
On the other hand, wiring is provided on the surface opposite to the surface on which the Al thin film of FPC is provided, and circuit components are mounted thereon. The wiring is formed of a thin copper layer, and several types of resistors, capacitors, and ICs are mounted.
[0022]
A light scatterer (print pattern, uneven scatterer) is formed on the surface of the light guide 6 and adjusted so that the luminance of the light emitting surface is uniform. If the light scatterer is formed on both sides of the light guide plate, the diffusibility is improved, but either one may be used. In general, it is often formed on the liquid crystal panel side. According to such a configuration, the light emitted from the LED unit 5 is repeatedly refracted and reflected by the light scatterer of the light guide 6 and the Al thin film 4, and 75% or more can be used as a surface light source of the liquid crystal panel 1.
[0023]
Furthermore, the Al thin film 4 can also be provided in the portion where the FPC is bent. Light from the light source is normally emitted from one direction surface of the LED unit 5 and enters the light guide 6. At this time, part of the light does not enter the light guide plate and is reflected at the interface of the light incident portion of the light guide plate. The Al thin film 4 is also provided at the portion where the FPC is bent so that the reflected light is reflected and directed toward the light guide again. With such a configuration, the light from the LED unit 5 can be efficiently condensed on the light incident portion of the light guide 6. It is also possible to function as a shield against static electricity and electromagnetic waves by connecting the Al thin film 4 to the ground terminal 7 of the power source.
[0024]
According to the configuration using the Al thin film described above, the reflection sheet that is conventionally disposed on the bottom surface of the light guide is not necessary. Therefore, for example, cost reduction of about 1 yen / cm ² can be expected. Furthermore, if used as a static electricity or electromagnetic wave shield, both yield and market failure rate are improved. Moreover, since an adhesive layer required when using a reflective sheet can be omitted, there is also an effect of thinning.
[0025]
(Example 2)
The display device of this embodiment will be described with reference to FIGS. FIG. 2 is a schematic cross-sectional view showing a partially enlarged display device of this embodiment, and FIG. 3 is a schematic view partially showing a plane of the FPC of this embodiment. In this embodiment, an example in which the LED chip 9 is mounted on an FPC as a bare chip will be described. The description overlapping with the first embodiment will be omitted as appropriate.
[0026]
The FPC of this embodiment shown in FIG. 2 also has a sandwich structure in which the polyimide film 15 is sandwiched between the Cu circuit pattern 16 and the deposited Al thin film 13 in the same manner as in the first embodiment. The Cu circuit pattern 16 is connected to the terminal portion of the liquid crystal panel 12 through the anisotropic conductive film 8. In this embodiment, the FPC is formed so as to extend from the part connected to the liquid crystal panel to one end side. As shown in the figure, the surplus area which is an extended portion is provided so as to wrap the LED chip 9. With such a configuration, leakage of light emitted from the LED chip 9 can be prevented, which contributes to an increase in luminance. In the present embodiment, the length from the outer end of the connecting portion to the end of the FPC was set to 2.0 mm with respect to the length of 1.5 mm at the portion where the FPC and the liquid crystal panel are connected. That is, the LED 9 was wrapped in a 2.0 mm surplus area of the FPC.
[0027]
The gold bumps 10 of the LED chip 9 are eutectic bonded to the pattern of the FPC Al thin film 13. The LED chip 9 is potted with a molding agent 11 to which a color conversion element is added. When a voltage of 3 to 5 V is applied to the LED chip 9, light is emitted with a peak wavelength of 460 nm. When the color conversion element added to the molding agent 11 adds a peak wavelength of 580 nm, pseudo white light emission is emitted.
[0028]
Even if the light emission of the LED chip does not have the directivity toward the light guide 14, the light emission of the LED chip is reflected by the reflection layer by forming the reflection layer on the FPC in the part that wraps the LED. Come to the body. That is, by continuously providing an Al thin film as a metal reflective film on the back surface of the FPC where the FPC is bent, the surplus area, and the portion connected to the liquid crystal panel, the light from the LED chip 9 is guided to the light guide 14. Can be efficiently condensed on the light incident portion. Thus, the pseudo white light emitted from the entire surface of the molding agent 11 enters the light guide 14 and is reflected and scattered by the Al thin film 13 and the light guide 14 provided on the FPC surface facing the light guide 14. By repeating, it can be used as a surface light source of the liquid crystal panel 1 as in the first embodiment.
[0029]
FIG. 3 is a partial plan view showing an outline of the FPC on which the LED chip 9 is mounted. The conductive aluminum pattern 17 connected to the LED chip 9 is electrically connected to the Cu pattern on the back surface side through the through hole 18. Or you may wire only on the surface using the wiring which patterned the aluminum thin film 13 without providing a through hole.
[0030]
As described above, by directly mounting the LED chip on the FPC, the light emitting area of the packaged LED unit of Example 1 is about 1.4 mm ² , and the light emitting area is about 3 mm ^{2, which} is about 2.14 times. It is in. Therefore, the light conversion efficiency is also increased by multiplying the area. Furthermore, since the package is unnecessary, there is an effect of reducing the thickness.
[0031]
(Example 3)
The display device of this embodiment will be described with reference to FIGS. FIG. 4 is a cross-sectional view schematically showing the main configuration of the display device of this embodiment, and FIG. 5 is a schematic view showing the plane of the FPC of this embodiment. In this embodiment, a direct type structure in which the LED chip 26 is disposed on the back surface of the light guide 28 is used. Similar to the second embodiment, the LED chip 26 is mounted face-down on the FPC as a bare chip that is not packaged. In addition, the description which overlaps with each above-mentioned Example is abbreviate | omitted suitably. The FPC of the present embodiment shown in FIG. 4 has a sandwich structure in which the polyimide film 20 is sandwiched between the Cu circuit pattern 19 and the deposited Al thin film 21 as in the first embodiment. The Cu circuit pattern 19 is connected to the electrodes of the liquid crystal panel 24 through the anisotropic conductive film 22.
[0032]
The gold bumps 27 of the LED chip 26 are eutectic bonded to the pattern of the Al thin film 21 of the FPC. The LED chip 26 is potted with a molding agent 25 to which a color conversion element is added. When a voltage of 3 to 5 V is applied to the LED chip 26, light is emitted at a peak wavelength of 460 nm. When the color conversion element added to the molding agent 25 adds a peak wavelength of 580 nm, pseudo white light is emitted.
[0033]
On the light guide just above the position where the LED chip 26 is provided, a dot pattern that is 2 to 4 times higher in density than the dot patterns in other areas is formed. Furthermore, as shown in the drawing, a recess is formed in the light guide 28 directly above the LED chip. Among the recesses, a dot pattern is formed in the diffusion area 23 of the light guide facing the LED chip. Due to the dot pattern in the diffusion area 23, the light incident on the diffusion area is strongly diffused and emitted to the display panel 24 side. At this time, the light reflected by the light guide and returned to the FPC side is reflected by the Al thin film 21 and enters the light guide again. As described above, the pseudo white light emitted from the entire surface of the molding agent 25 is repeatedly reflected and scattered by the Al thin film 21 and the light guide 28 and can be used as a surface light source of the liquid crystal panel 24.
[0034]
FIG. 5 is a plan view showing an outline of the appearance of the FPC on which the LED chip 26 is mounted. The conductive aluminum pattern 30 connected to the LED chip 26 is electrically connected to the Cu pattern on the back surface side through the through hole 29. Or you may wire only on the surface using the pattern which patterned the aluminum thin film 21 without providing a through hole. According to such a configuration, since a plurality of LED light sources can be installed, the surface brightness increases.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a display device according to a first embodiment of the present invention.
FIG. 2 is a partially enlarged cross-sectional view of a display device according to a second embodiment of the present invention.
FIG. 3 is a plan view schematically showing an FPC used in Example 2 of the present invention.
FIG. 4 is a cross-sectional view showing a schematic configuration of a display device according to a third embodiment of the present invention.
FIG. 5 is a plan view schematically showing an FPC mounted with an LED light source used in Example 3 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 2 FPC Cu pattern 3 Polyimide film 4 Al thin film 5 LED unit 6 Light guide 7 Power supply ground terminal 8 Anisotropic conductive film 9 LED chip 10 Gold bump 11 Molding agent

Claims (2)

A non-self-luminous display element;
In order to illuminate the display element, a light guide provided on the back side of the display element ;
An LED chip that emits light incident from a light incident portion of the light guide;
A connection part connected to the terminal portion of the display element; a chip mounting part on which the LED chip is mounted; and a flexible substrate having a surplus area formed extending from the connection part to the side opposite to the mounting part. Prepared,
The flexible substrate is folded to the back side of the light guide, and the light guide is configured to be between the flexible substrate and the display element.
The flexible substrate has an Al thin film formed as a metal reflection layer on the side facing the light guide, and the gold bump provided on the LED chip and the Al thin film are directly connected by eutectic bonding at the chip mounting site. And
A surplus area of the flexible substrate is formed so as to enclose the LED chip, and an Al thin film is formed as a metal reflective layer on a side of the surplus area of the flexible substrate facing the LED chip. . The display device according to claim 1, wherein the LED chip emits light having no directivity toward the light guide.

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