JP2007250275A - Backlight unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight unit including a flexible printed substrate for mounting an LED with an excellent radiation property, an LED assembling part with high intensity, and a flexible feed part to the LED. <P>SOLUTION: The backlight unit includes: a flexible printed substrate 2 with a plurality of the LEDs 3 mounted thereon; a light guide plate 4 for introducing light from the LEDs; reflecting and diffusing the light, and emitting the light from a light exiting surface; and casings 7, 8 for arranging the LEDs, substrate, and light guide plate in predetermined positions and housing them. The flexible printed substrate is formed of wiring patterns of a plurality of layers with different thicknesses, and the thickness of the layer of the largest thickness out of the wiring patterns of the plurality of layers is within 100-500 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a backlight unit in which a flexible wiring board is used for arrangement and power supply of LEDs serving as light sources.

  In a backlight unit using an LED as a light source, it is common to use a plurality of LEDs due to the problem of light quantity. A wiring board is indispensable for wiring and feeding power to a plurality of LEDs. For example, a backlight unit of a display unit of a mobile phone uses about 2 to 4 LEDs, and a flexible printed wiring board is used for wiring because of a demand for space saving. FIG. 4 shows the structure of a flexible printed circuit board 102 for LED mounting in a conventional backlight unit. The flexible printed circuit board 102 shown in FIG. 4 has a two-layer structure. The front cover film 121 and the front wiring pattern 122 constitute the first layer, and the back cover film 123 and the rear wiring pattern 124 constitute the second layer. A base film 125 is sandwiched between the first layer and the second layer.

  Further, in recent years, LEDs have begun to be used as light sources for medium- and large-sized liquid layer backlights due to the improvement of the light emission efficiency of LEDs and the increase in the amount of light emission per one. In LED, when the temperature of an element becomes high, problems such as a decrease in light amount due to a decrease in efficiency and a shortened life occur, and thus it is essential to take measures against heat dissipation.

  As a technique for improving the heat dissipation of the substrate, Japanese Patent Application Laid-Open No. 2001-160312 (Patent Document 1) uses a substrate on which an LED is mounted as a metal substrate, and conducts and dissipates heat generated in the LED to the substrate to prevent an increase in element temperature. The technology is described. However, even though the metal substrate is excellent in heat dissipation, it is difficult to reduce the thickness of the substrate, the area of the substrate, and the size of the power supply terminal in order to adopt it in a light guide plate type thin backlight unit. is there.

On the other hand, if a flexible printed wiring board is used, the problem of space saving can be solved, and it is not necessary to provide a terminal as external power feeding, and the problem of miniaturization of the power feeding terminal can also be solved. However, when a flexible printed wiring board is employed, there is another problem that it is difficult to effectively conduct and dissipate heat generated by the LED and prevent an increase in element temperature. In addition, it is necessary to use a reinforcing plate as necessary to secure the strength of the LED mounting portion, and there is a problem that heat conduction is further deteriorated. FIG. 5 shows the structure of a flexible printed circuit board 202 for LED mounting in a conventional backlight unit. The flexible printed circuit board 202 shown in FIG. 5 has a two-layer structure. The front cover film 221 and the front wiring pattern 222 constitute the first layer, and the back cover film 223 and the rear wiring pattern 224 constitute the second layer. A base film 225 is sandwiched between the first layer and the second layer, and a reinforcing plate 226 made of polyimide or polyester is attached to the lower surface side in the figure of the back cover film 223. For this reason, there existed a problem which heat conductivity fell and also manufacturing cost increased.
JP 2001-160312 A

  The present invention has been made in view of the above-described problems of the prior art, and the flexible printed circuit board for mounting LEDs has excellent heat dissipation, the strength of the LED assembly part, and the flexibility of the power supply part for the LED. It is another object of the present invention to provide a backlight unit that can reduce the thickness of the substrate, reduce the area, and reduce the size of the power supply terminal.

  The backlight unit of the invention of claim 1 introduces a plurality of LEDs, a flexible printed circuit board that is electrically connected to the plurality of LEDs and supplies power, and introduces light from the plurality of LEDs to reflect and diffuse. A light guide plate that guides light so as to be emitted from the light exit surface, and a housing that houses the LED, the substrate, and the light guide plate in a predetermined arrangement, and the flexible printed circuit board has a plurality of different thicknesses. It is composed of a wiring pattern, and the maximum thickness of the plurality of wiring patterns is in the range of 100 μm to 500 μm.

  According to a second aspect of the present invention, in the backlight unit of the first aspect, among the plurality of wiring patterns of the flexible printed circuit board, the thickness of the layers other than the maximum thickness layer is 50 μm or less. It is a feature.

  According to a third aspect of the present invention, in the backlight unit of the first or second aspect, the base of the flexible printed circuit board is made of a polyimide or polyester film.

  According to the backlight unit of the present invention, the flexible printed circuit board for LED mounting has excellent heat dissipation, the strength of the LED assembly part, the flexibility of the power feeding part for the LED, and the thin flexible printed circuit board In addition, the area can be reduced and the power supply terminal can be downsized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a backlight unit according to one embodiment of the present invention. The backlight unit according to the present embodiment includes an elongated flexible printed circuit board 2, a plurality of LEDs 3 that are light sources arranged on the flexible printed circuit board 2, and light from the plurality of LEDs 3 that are light sources. The light guide plate 4 is introduced from the light incident surface of the end surface, is reflected and diffused by the reflection surface on the lower surface side in the drawing, and is guided so as to be emitted from the light emission surface on the upper surface side, and leaks from the lower surface side of the light guide plate 4 A reflection plate 5 that reflects light back to the light guide plate 4; optical sheets 6 that diffuse and collect light emitted from the light exit surface of the light guide plate 4 to make it uniform and bright; It is composed of a front frame 7 and a back frame 8 which form a housing for assembling and housing all these elements.

  In the backlight unit of the present embodiment, the top view type LED 3 is used. For this type of LED 3, for example, a side view type LED used for a backlight of a mobile phone is used. You can also.

  As shown in FIG. 2, the flexible printed circuit board 2 has a two-layer structure, the front cover film 21 and the front wiring pattern 22 constitute the first layer, and the back cover film 23 and the back wiring pattern 24 form the second layer. The base film 25 is sandwiched between the first layer and the second layer. The front cover film 21, the back cover film 23, and the base film 25 are made of polyimide or polyester and have a thickness of 12.5 μm. Both the front wiring pattern 22 and the back wiring pattern 24 are made of copper foil, and the thickness of the front wiring pattern 22 is 50 μm or thinner, preferably about 18 μm. The back wiring pattern 24 has a thickness of 100 μm to 500 μm, preferably about 300 μm, for improving heat dissipation and strength.

  As shown in FIG. 3, the front and back wiring patterns 22 and 24 have the two-layer structure shown in FIG. 2 in the LED mounting portion 2a, but the power feeding portion 2b has a front cover film 21 and a thin front wiring. A single-layer structure is formed only with the pattern 22. Although the LED mounting portion 2a has a two-layer structure, the flexibility of the portion of the flexible printed circuit board 2 is impaired, but it is easy to mount the LED 3 on that portion in order to maintain the strength of the LED mounting portion. Further, the power supply portion 2b has a single-layer structure having only a thin layer so that external electrical connection is free and easy.

  In the conventional flexible printed circuit board 202 for LED mounting, a reinforcing plate 226 is attached as shown in FIG. 5. However, since the reinforcing plate 226 is made of polyimide or polyester, its thermal conductivity is low, and it is further manufactured. There was a problem that the cost increased. On the other hand, in the backlight unit of the present embodiment, in the flexible printed circuit board 2 for mounting LEDs, the back wiring pattern 24 having a large thickness replaces the reinforcing plate, thereby reducing the cost and heat conduction. There is a good advantage. Further, since the portion other than the LED mounting portion in the flexible printed circuit board 2 has a single-layer structure having only a thin layer, the flexible printed circuit board 2 has flexibility in the portion exposed to the outside from the casing of the backlight unit. There is an advantage that the degree of freedom in electrical connection with the outside is high.

The disassembled perspective view of the backlight unit of one embodiment of this invention. Sectional drawing of the flexible printed circuit board for LED mounting in the said embodiment. The front view and sectional drawing of a flexible printed circuit board which mounted LED in the said embodiment. Sectional drawing of the flexible printed circuit board for the conventional LED mounting. Sectional drawing of the flexible printed circuit board for LED mounting in which the conventional reinforcement board was provided.

Explanation of symbols

2 Flexible printed circuit board 3 LED
4 Light guide plate 7 Front frame 8 Back frame 21 Front cover film 22 Front wiring pattern 23 Back cover film 24 Back wiring pattern 25 Base film 2a LED mounting portion 2b Power feeding portion

Claims (3)

A plurality of LEDs, a flexible printed circuit board that is electrically connected to the plurality of LEDs to be fed, and light from the plurality of LEDs are introduced, reflected and diffused, and guided to be emitted from the light exit surface. A light guide plate, and a housing that houses the LED, the substrate, and the light guide plate in a predetermined arrangement,
The flexible printed circuit board includes a plurality of wiring patterns having different thicknesses, and the maximum thickness of the plurality of wiring patterns is in a range of 100 μm to 500 μm. Backlight unit.   2. The backlight unit according to claim 1, wherein a thickness of the plurality of wiring patterns of the flexible printed circuit board other than the maximum thickness layer is 50 μm or less.   The backlight unit according to claim 1, wherein a base of the flexible printed circuit board is made of a polyimide or polyester film.

Images