JP5013524B2 - Backlight unit and liquid crystal display device - Google Patents

Description

  The present invention relates to a backlight unit including a point light source device such as an LED, and further relates to a liquid crystal display device incorporating the backlight unit.

  In recent years, liquid crystal display devices having features such as light weight, thinness, and low power consumption are widely used as display devices for information devices such as personal computers and word processors, and display devices for video devices such as televisions, video movies, and car navigation systems. . In many cases, such a liquid crystal display device adopts a configuration in which a backlight unit (surface light source device) for applying illumination light from behind the liquid crystal panel is incorporated in order to realize a bright display screen.

  Here, the backlight unit is classified into an edge light system and a direct system according to the location of the light source. For example, the edge light system is a system in which a point light source device such as an LED is disposed on the edge of a light guide plate facing a liquid crystal panel. The direct method is a method in which a plurality of straight tubular light sources such as fluorescent discharge tubes are arranged on the back surface of the liquid crystal panel, and a diffusion plate is arranged between the liquid crystal panel and the light source. Among these methods, the edge light method is advantageous in terms of thinning, and can be said to be a method suitable for a display device of a portable electronic device or a notebook personal computer, for example.

  By the way, when assembling the edge light type backlight unit, it is necessary to consider light leakage from a point light source device (LED or the like) mounted on a flexible substrate. The flexible substrate is formed of, for example, a polyimide resin and has a certain degree of light transmittance. Therefore, light emitted from the LED passes through the flexible substrate and is irradiated onto, for example, an LSI mounted on a liquid crystal panel, which causes a malfunction. In addition, light leakage also causes the quality of the liquid crystal display device to deteriorate.

  As a technique for preventing light leakage, for example, a technique of attaching a light shielding sheet to a flexible substrate on which an LED is mounted is known (see, for example, Patent Document 1). In the liquid crystal display device according to the invention described in Patent Document 1, the light shielding sheet is fixed to the upper surfaces of the end portions of the flexible substrate and the light guide plate via an adhesive.

Alternatively, it has been studied to form a light shielding pattern on a flexible substrate (see, for example, Patent Document 2). In the liquid crystal display device of the invention described in Patent Document 2, a light shielding pattern is formed on the back surface side corresponding to the mounting position of the light emitting diodes on the flexible wiring board. For example, the light shielding pattern is formed as a solid pattern over the entire position corresponding to the LED mounting position. This light-shielding pattern can surely prevent light leakage from the LED, and since there is no need for a light-shielding tape or the like, there is also an advantage that the manufacturing cost can be reduced.
Japanese Patent Laid-Open No. 2003-156739 JP 2003-344851 A

  However, for example, the method of adhering the light shielding sheet as in the invention described in Patent Document 1 leads to an increase in the thickness of the entire liquid crystal display device, which is disadvantageous when considering thinning of the device. Also, the use of the light shielding sheet leads to an increase in the number of parts, which not only makes the assembly work complicated, but also increases the manufacturing cost.

  On the other hand, if the light leakage is prevented by forming a light shielding pattern on the flexible substrate as in the invention described in Patent Document 2, a light shielding sheet as a separate member is not necessary, and the liquid crystal display device This is advantageous in reducing the thickness. Further, since a light shielding sheet or the like is unnecessary, the cost can be reduced accordingly. However, in the invention described in Patent Document 2, since the light shielding pattern is formed on the back side of the flexible substrate, it is necessary to use an expensive double-sided substrate for the flexible substrate, and the light shielding sheet is unnecessary. Even if cost reduction is taken into consideration, an increase in manufacturing cost is inevitable.

  The present invention has been proposed in view of such a conventional situation. That is, an object of the present invention is to provide a backlight unit and a liquid crystal display device that can surely prevent light leakage without hindering thickness reduction. Another object of the present invention is to provide a backlight unit and a liquid crystal display device that do not require the addition of a member such as a light shielding sheet and that do not require the use of an expensive double-sided substrate as a flexible substrate. The objective is to significantly reduce costs.

In order to achieve the above-described object, a backlight unit according to the present invention is a backlight unit in which a light output surface of an LED , which is a point light source device installed on a flexible substrate, is arranged to face an end surface of a light guide plate. Te, wherein the flexible substrate state, and are not the wiring pattern electrically connected to each LED is enlarged so as to have an area of more than the projected area of LED, the wiring pattern for each LED chip is mounted It is composed of each land part to be connected to the terminal and a lead-out wiring part, and each land part is similar to the LED mounting surface and is formed as a solid pattern larger than the LED mounting surface and functions as a light shielding pattern. Features.

  The wiring pattern on the flexible substrate is formed of copper foil or the like and has a very high light shielding property. In the present invention, since the area of the wiring pattern is enlarged and used as a light shielding pattern, light leakage of a point light source device such as an LED is reliably eliminated. Further, in the present invention, it is not necessary to add a member for preventing light leakage, and it is not necessary to use an expensive double-sided substrate for the flexible substrate.

  According to the present invention, it is possible to reliably prevent light leakage without hindering thickness reduction. Further, according to the present invention, it is not necessary to add a member such as a light shielding sheet, and it is not necessary to use an expensive double-sided substrate for the flexible substrate, so that the manufacturing cost can be greatly reduced.

  Hereinafter, a backlight unit according to the present invention and a liquid crystal display device using the same will be described.

  FIG. 1 shows a basic configuration of a backlight unit 1 to which the present invention is applied. As shown in FIG. 1, the backlight unit 1 of the present embodiment includes a flexible substrate 3 on which an LED chip 2 that is a point light source device is mounted and a light guide plate 4, and the LED chip 2 that is a point light source. Is converted into a surface light source by the light guide plate 4.

  The LED chip 2 is, for example, a so-called side-view type LED chip in which a light-emitting diode element (LED) is embedded in a sealing resin, and irradiates light parallel to the mounting surface of the flexible substrate 3 from the side surface. is there. In the case of this example, a plurality (three) of LED chips 2 are arranged along the longitudinal direction of the flexible substrate 3, and the LED chips 2 are arranged at substantially equal intervals.

  The LED chip 2 emits light from its one side surface (side surface on the light guide plate 4 side) 2A. That is, the side surface 2A is a light exit surface. Then, the end surface 4a of the light guide plate 4 and the light exit surface (side surface 2A) of the LED chip 2 are in contact with each other, so that the light emitted from the LED chip 2 is guided to the light guide plate 4 and converted into planar light. .

  Each LED chip 2 has an electrode soldered to a terminal portion of a wiring formed on the flexible substrate 3, and is electrically connected to an external drive circuit via the flexible substrate 3. The flexible substrate 3 is composed of a strip-shaped LED chip mounting portion 3a having a length substantially equal to the width of the light guide plate 4, and a lead-out wiring portion 3b drawn in a direction orthogonal thereto, and the LED chip mounting portion 3a. The LED chips 2 are mounted in a state of being arranged at equal intervals. The lead wiring part 3 b is connected to, for example, a power supply part that drives the LED chip 2.

  A wiring pattern for electrically connecting the LED chip 2 and a power supply circuit or the like is formed on one surface of the flexible substrate 3 described above. In the present invention, by increasing the area of these wiring patterns, they are used as light shielding patterns.

  FIG. 2 shows a wiring pattern 5 formed on the flexible substrate 3. In the flexible substrate, a wiring pattern having a predetermined shape is formed by etching a copper foil or the like, and is usually composed of a thin line-shaped wiring pattern and a land portion for connecting to the terminal of the LED chip 2. In the present embodiment, as shown in FIG. 2, the area of the land portion 5 a in the wiring pattern 5 is larger than usual, and is a rectangular pattern having a larger area than the projected area of the LED chip 2. .

  FIG. 3 shows a mounting state of the LED chip 2 on the wiring pattern 5. As described above, the area of the land portion 5a in the wiring pattern 5 is enlarged, and the vertical dimension L1 and the horizontal dimension W1 of the land portion 5a are larger than the vertical dimension L2 and the horizontal dimension W2 of the LED chip 2. ing. By mounting the LED chip 2 so as to fit on the land portion 5a of the wiring pattern 5 whose area is thus enlarged, the back surface side of the LED chip 2 is shielded by the wiring pattern 5 (rectangular land portion 5a). become.

  The wiring pattern 5 needs to fulfill the function as the wiring of the LED chip 2. Therefore, the wiring pattern 5 is composed of a land portion 5a on which each LED chip 2 is placed and connected to a terminal, and a lead-out wiring portion 5b. Each wiring pattern connected to each LED chip 2 individually. 5 need to be electrically separated from each other.

  FIG. 4 shows an example in which the wiring pattern 5 is enlarged to the maximum within such restrictions. In the example shown in FIG. 4, the wiring pattern 5 is formed as a substantially solid pattern, and the minimum slits 6 for electrically separating the land portions 5a and the lead-out wiring portions 5b are formed. Thereby, the light-shielding pattern is formed on almost the entire surface of the flexible substrate 3, and light leakage from the LED chip 2 can be reliably prevented.

  In the present embodiment, the land portion 5a of the wiring pattern 5 is enlarged and used as a light shielding pattern. However, the invention is not limited to this. For example, an independent pattern that does not participate in electrical connection is added to the wiring pattern. However, it may be used for light shielding. Moreover, the patterning method of the wiring pattern 5 is also arbitrary.

  The backlight unit having the above configuration is incorporated as a surface light source device in a liquid crystal display device. Next, a liquid crystal display device incorporating the above-described backlight unit will be described.

  FIG. 5 shows an exploded view of a liquid crystal display device in which a backlight unit, which is a surface light source device, is incorporated. As shown in FIG. 5, the liquid crystal display device of this embodiment includes a liquid crystal panel 11 and the backlight unit 1 described above, and these are held by a metal frame 12.

  The liquid crystal panel 11 is configured, for example, by enclosing a liquid crystal material between an array substrate and a counter substrate, and pixel electrodes and switching elements (thin film transistors) corresponding to display pixels are formed in a matrix on the array substrate. . In addition, a signal line for sending an electric signal to the pixel electrode and a gate line for supplying a switching signal to the thin film transistor which is a switching element are wired on the array substrate at right angles to each other. On the other hand, on the counter substrate, the counter electrode is formed on almost the entire surface with a transparent electrode material (for example, ITO), and a color filter layer is formed corresponding to each pixel. Further, polarizing plates are bonded to the outer surfaces of the array substrate and the counter substrate so that the polarization axes are orthogonal to each other.

  An LSI 13 for supplying a drive signal is mounted on the liquid crystal panel 11, and an image is displayed by driving the switching element based on the drive signal from the external circuit board. A region where this image display is performed is a display region, and the liquid crystal panel 11 has a display region in which a large number of pixels are arranged.

  The backlight unit 1 is incorporated as a backlight of the liquid crystal panel 11, a light guide plate 4 for irradiating light from the LED chip 2 as a light source to the back surface of the liquid crystal panel 11, and the light guide plate 4. And a reflection sheet 14 disposed on the back side of the optical plate 4. The LED chip 2 as a light source is provided along at least one side of the light guide plate 4. In the case of this embodiment, the flexible substrate 3 on which the LED chip 2 is mounted is installed on the short side of the light guide plate 4. ing.

  The light emitted from the LED chip 2 that is a light source is reflected directly or by the reflection sheet 14 and guided to the light guide plate 4, passes through the light guide plate 4, and is then applied to the liquid crystal panel 11. The irradiated light is transmitted through the liquid crystal panel 11, and images such as characters and videos are displayed with a predetermined brightness.

  The frame 12 is formed of a metal material such as stainless steel and has an outer frame portion that is substantially perpendicular to the main surfaces of the liquid crystal panel 11 and the light guide plate 4. The liquid crystal panel 11 and the light guide plate 4 are formed by the outer frame portion. Hold the outer periphery of.

  A plurality of optical sheets (here, three optical sheets 15, 16, and 17) are interposed between the light guide plate 4 and the liquid crystal panel 11, and are fixed to the frame 12 in a state where they are overlapped. ing. The liquid crystal panel 11 is fixed by using a frame-like double-sided adhesive sheet 18, and the liquid crystal panel 11 is bonded and fixed to the frame 12 by the double-sided adhesive sheet 18, so The optical board 4 and the flexible substrate 3 on which the LED chip 2 is mounted are sandwiched between the liquid crystal panel 11 and the frame 12 and fixed.

In the liquid crystal display device having the above-described configuration, the LSI 13 mounted on the liquid crystal panel 11 is disposed on the backlight unit 1. If light leaks from the backlight unit 1 in such an arrangement, not only the quality of the liquid crystal display device is lowered but also the malfunction of the LSI 13 is caused. Here, in the liquid crystal display device of this embodiment, the wiring pattern 5 formed on the flexible substrate 3 functions as a light-shielding pattern, so as to prevent light leakage of the LED chip 2, enters carelessly light to LSI13 The LSI 13 will not malfunction.

It is a schematic perspective view of the backlight unit to which the present invention is applied. It is a schematic perspective view which shows an example of the wiring pattern formed on a flexible substrate. It is a schematic plan view which shows the dimensional relationship between a wiring pattern and an LED chip. It is a schematic plan view which shows the other example of the wiring pattern formed on a flexible substrate. It is a disassembled perspective view which shows an example of a liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Backlight unit, 2 LED chip, 2A Side surface (light emission surface), 3 Flexible board, 4 Light guide plate, 4a End surface, 5 Wiring pattern, 5a Land part, 5b Lead-out wiring part, 6 Slit, 11 Liquid crystal panel, 12 Frame, 13 LSI, 14 Reflective sheet, 15, 16, 17 Optical sheet, 18 Double-sided adhesive sheet

Claims (3)

A backlight unit in which a light exit surface of an LED , which is a point light source device installed on a flexible substrate, is disposed to face an end surface of a light guide plate,
Wherein the flexible substrate state, and are not the wiring pattern electrically connected to each LED is enlarged so as to have an area of more than the projected area of LED, the wiring pattern is pin connected is placed each LED chip Each land portion and a lead-out wiring portion, and each land portion is similar to the LED mounting surface and is formed as a solid pattern larger than the LED mounting surface, and functions as a light shielding pattern. Backlight unit to be used. The backlight unit according to claim 1, wherein a land portion of the wiring pattern and a mounting surface of the LED have a similar rectangular shape, and the projection of the LED is directly above the land portion . A liquid crystal display device comprising a liquid crystal panel, wherein the backlight unit according to claim 1 or 2 is incorporated, and an LSI is mounted at a position facing the flexible substrate .

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