WO2007037605A1

WO2007037605A1 - Led board and illumination unit having the same

Info

Publication number: WO2007037605A1
Application number: PCT/KR2006/003798
Authority: WO
Inventors: Sung-Ha Park
Original assignee: Jahwa Electronics Co., Ltd.
Priority date: 2005-09-30
Filing date: 2006-09-25
Publication date: 2007-04-05
Also published as: KR100664349B1

Abstract

An illumination unit is provided, including: a casing; a plurality of LED boards each including a graphite sheet adjacent to inside of the casing to diffuse heat, a non-conductive layer stacked on the graphite sheet, and a conductive thin-film formed on the non-conductive layer; and a plurality of LEDs that is regularly arranged to receive an electrical drive signal from the conductive thin-film and to emit light. Accordingly, since the illumination unit includes the graphite sheet that is higher in thermal conductivity, lower in production cost, and more flexible than the metal PCB, it is possible to efficiently dissipate heat produced by the LEDs and to prevent the illumination unit from being deteriorated. Further, it is possible to produce it at a lower cost and to achieve a high heat-dissipation efficiency since the graphite sheet has a high thermal conductivity and a high sealing property even though it is directly attached to the casing.

Description

LED BOARD AND ILLUMINATION UNIT HAVING THE SAME

Technical Field

[1] The present invention relates to a light-emitting diode (LED) board and an illumination unit having the same and, more particularly, to a technology of efficiently dissipating heat produced by LEDs. Background Art

[2] Among display devices such as cathode ray tube (CRT), plasma display panel

(PDP), liquid crystal display (LCD), and organic electro-luminescence (EL) display, a thin-film transistor LCD (TFT-LCD) has emerged as one of leading display devices. The TFT-LCD is mainly divided into three units: a panel in which liquid crystal is injected between boards, a printed circuit board (PCB) having a driver LSI for driving the panel and other circuit elements, and a chassis including a backlight unit.

[3] The backlight unit includes a light source such as a fluorescent lamp and an LED lamp. A cold cathode fluorescent lamp (CCFL), one of the fluorescent lamps, has been widely used as a light source of the backlight unit. Recently, the LED lamp is popular as a light source of the backlight unit since it has a wide color gamut, high light efficiency, long life, low power consumption, light weight, and slim thickness. However, there is a problem in that the LED lamp radiates heat hotter than the fluorescent lamp. The LED lamp has a power consumption of about IW, more than 70% of which is turned into heat. A backlight unit incorporated in a 30-inch TFT-LCD normally has about 200 LED lamps, which produce a heat of about 140W. The heat raises the temperature of the backlight unit, which may cause elements constituting the backlight unit to be deteriorated, or the backlight unit to be deformed.

[4] Accordingly, it is necessary to lower the temperature raised due to the heat produced by the LED lamps in the backlight unit. In general, electronic appliances or telecommunications apparatuses use heat sinks, heat pipes or fans to solve the heat problem. However, the heat sink is not proper for use in the backlight unit since the size of the backlight becomes large to accommodate the heat sink. The heat pipe is not proper since it is expensive and the size of the backlight becomes large to accommodate the heat pipe.

[5] In addition, since the board of the backlight unit is made of metal, it is expensive and hard, and it is difficult to keep the board flat. Accordingly, a deviation in temperature occurs in the backlight unit and a manufacture process is complex.

[6] On the other hand, Korean Patent Application Publication No. 2005-36789, published on April 20, 2005, discloses a technology of using a graphite sheet to diffuse heat produced in a display device. The graphite sheet has anisotropy characteristic that is efficient in heat transfer in a surface direction, such that it is proper to diffuse heat produced in a display device that needs to have thin thickness. However, the above- mentioned publication discloses a technology of using the graphite sheet in an emissive display device such as a PDP. In more detail, the above-mentioned technology is limited to an emissive display device including at least one sheet that has a surface area larger than that of a discharge cell facing a rear side of the emissive display device, and that is formed of exfoliated, compressed graphite particles.

[7] The present invention discloses a technology of using graphite sheets in illumination units having LEDs as well as non-emissive TFT-LCDs to efficiently diffuse the heat produced therein.

[8] Fig. 1 shows a cross-sectional view of a light-emitting diode (LED) board according to an example of the invention. A graphite sheet 12 is attached to a lower side of a bottom chassis of a casing 10 of a backlight unit. The graphite sheet 12 has a high thermal conductivity and a high sealing property even though it is directly attached to the casing 10. A plurality of metal PCBs 14 is stacked on the casing 10. An LED 16 is provided on each of the metal PCBs 14. A gap pad 18 is provided between each of the metal PCBs 14 and the casing 10. The gap pad 18 is made of rubber with high thermal conductivity. Since the graphite sheet 12 is attached to the lower side of the casing 10, it is possible to produce a backlight unit that is thinner and has increased heat dissipation efficiency. However, there is a problem in that the backlight unit becomes more complicated since the backlight unit further includes the graphite sheet 12, and a scratch may occur during a manufacture process since the graphite sheet 12 is provided outside.

[9] Fig. 2 shows a cross-sectional view of an LED board according to an example of the invention. A graphite sheet 32 is stacked on an upper side of a bottom chassis of a casing 30 of a backlight unit. A plurality of metal PCBs 34 is stacked on the graphite sheet 32. An LED 36 is provided on each of the metal PCBs 34. Since the graphite sheet 32 is more flexible than metal, no gap pad is required between the graphite sheet 32 and each of the metal PCBs 34.

[10] However, the use of the metal PCBs causes a high production cost and a complex structure of the illumination unit. Disclosure of Invention Technical Solution

[11] The present invention provides an LED board and an illumination unit that has improved heat-dissipation efficiency. [12] Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention.

Advantageous Effects

[13] As apparent from the above description, since the illumination unit includes the graphite sheet that is higher in thermal conductivity, lower in production cost, and more flexible than the metal PCB, it is possible to efficiently dissipate heat produced by the LEDs and to prevent the illumination unit from being deteriorated. Further, it is possible to produce it at a lower cost and to achieve a high heat-dissipation efficiency since the graphite sheet has a high thermal conductivity and a high sealing property even though it is directly attached to the casing. Accordingly, no gap pad is required between the graphite sheet and the casing. However, the gap pad may be provided to improve an adhesive property between them.

[14] In addition, since the reflective layer reflects light that is emitted from an LED and reflected by a light-guide plate, a diffusion plate, and the like, it is possible to improve the luminance of display.

[15] In addition, since the illumination unit further includes the upper graphite sheet, it is possible to efficiently dissipate the heat.

[16] In addition, it is possible to minimize differences in temperature between the upper and lower sides of the casing, thereby preventing the illumination unit from being deformed.

[17] In addition, it is possible to efficiently dissipate the heat in a thickness direction as well as in a surface direction. Brief Description of the Drawings

[18] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention.

[19] Fig. 1 shows a cross-sectional view of an LED board according to an example of the present invention.

[20] Fig. 2 shows a cross-sectional view of an LED board according to another example of the present invention.

[21] Fig. 3 shows a cross-sectional view of an LED board according to an embodiment of the present invention.

[22] Fig. 4 shows a plan view of an illumination unit having the LED board shown in

Fig. 3.

[23] Fig. 5 shows a cross-sectional view taken along line A-A'of Fig. 4.

[24] Fig. 6 shows a plan view of a non-conductive layer having a conductive thin-film formed thereon according to an embodiment of the present invention.

[25] Fig. 7 shows a backlight unit according to an embodiment of the present invention.

[26] Fig. 8 shows a cross-sectional view taken along line A-A'of Fig. 4.

[27] Fig. 9 shows an upper graphite sheet of Fig. 8.

[28] Fig. 10 shows a backlight unit according to an embodiment of the present invention.

[29] Figs. 11 to 13 show cross-sectional views taken along line B-B' of Fig. 4.

[30] Fig. 14 shows a plan view of a graphite sheet unitarily formed according to an embodiment of the present invention.

[31] Fig. 15 shows a cross-sectional view taken along line C-C of Fig. 14.

[32] Fig. 16 shows metal mesh sheets.

[33] Fig. 17 shows a graphite sheet having a metal mesh sheet inserted therein.

Best Mode for Carrying Out the Invention

[34] According to an aspect of the present invention, there is provided a light-emitting diode (LED) board including: a graphite sheet to diffuse heat; a non-conductive layer stacked on the graphite sheet; and a conductive thin-film formed on the non-conductive layer and having a circuit configured to apply an electrical drive signal to LEDs.

[35] According to another aspect of the present invention, there is provided an illumination unit including: a casing; a plurality of LED boards each including a graphite sheet adjacent to inside of the casing to diffuse heat, a non-conductive layer stacked on the graphite sheet, and a conductive thin-film formed on the non-conductive layer; and a plurality of LEDs that is regularly arranged to receive an electrical drive signal from the conductive thin-film and to emit light.

[36] Since the illumination unit includes the graphite sheet that is higher in thermal conductivity, lower in production cost, and more flexible than the metal PCB, it is possible to efficiently dissipate heat produced by the LEDs and to prevent the illumination unit from being deteriorated. Further, it is possible to produce it at a lower cost and to achieve a high heat-dissipation efficiency since the graphite sheet has a high thermal conductivity and a high sealing property even though it is directly attached to the casing. Accordingly, no gap pad is required between the graphite sheet and the casing. However, the gap pad may be provided to improve an adhesive property between them.

[37] According to another aspect of the present invention, there is provided an illumination unit including: a graphite sheet to diffuse heat; a non-conductive layer stacked on the graphite sheet; a conductive thin-film formed on the non-conductive layer; and a plurality of LEDs that is regularly arranged to receive an electrical drive signal from the conductive thin-film and to emit light.

[38] The illumination unit may further include a reflective layer coated on the conductive thin-film.

[39] Since the reflective layer reflects light that is emitted from an LED and reflected by a light-guide plate, a diffusion plate, and the like, it is possible to improve the luminance of display.

[40] The illumination unit may further include an upper graphite sheet stacked on the conductive thin-film except on the LEDs.

[41] Since the illumination unit further includes the upper graphite sheet, it is possible to efficiently dissipate the heat.

[42] A graphite sheet adjacent to an upper side of the casing may be thicker in thickness or higher in density than a graphite sheet adjacent to a lower side of the casing.

[43] Accordingly, it is possible to minimize differences in temperature between the upper and lower sides of the casing, thereby preventing the illumination unit from being deformed.

[44] The graphite sheet may include a metal mesh sheet.

[45] Accordingly, it is possible to efficiently dissipate the heat in a thickness direction as well as in a surface direction.

[46] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. Mode for the Invention

[47] The invention is described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like reference numerals in the drawings denote like elements.

[48] Fig. 3 shows a cross-sectional view of a light-emitting diode (LED) board according to an embodiment of the present invention. The LED board includes a graphite sheet 100, a non-conductive layer 200 that is stacked on the graphite sheet 100, and a conductive thin-film 300 that is formed on the non-conductive layer 200 and has a circuit designed to supply an electrical drive signal to an LED. The graphite sheet 100 is one made of pure graphite that is subjected to acid treatment and high temperature treatment, such that it has excellent heat resistance, flexibility, and force of restitution. The graphite sheet 100 is formed of layers of carbon of which molecules are chemically bonded by covalent bonding, such that it efficiently diffuses heat on each of the layers of carbon. The non-conductive layer 200 is stacked on the graphite sheet 100, and the conductive thin-film 300 is formed on the non-conductive layer 200. The conductive thin-film 300 has a conductive pattern and supplies an electrical drive signal to the LED through the conductive pattern. The non-conductive layer 200 prevents the graphite sheet 100 from being electrically connected to the conductive pattern of the conductive thin-film 300.

[49] Fig. 4 shows a plan view of an illumination unit having the LED board of Fig. 3. A plurality of LED boards is joined to a bottom chassis of a casing 500. A plurality of LEDs 400 is arranged in parallel with one another on the LED board. The LED boards are electrically connected to one another through jump wires. The casing 500 and the LED boards may be fixed by bolt-nut connection (indicated by circles of Fig. 4).

[50] Fig. 5 shows a cross-sectional view taken along line A-A' of Fig. 4 according to an embodiment of the present invention. The graphite sheet 100 is stacked on the bottom chassis of the casing 500. Since the graphite sheet 100 is flexible, it is tightly attached to the casing 500 without any intermediate such as rubber pad. The non-conductive layer 200 is stacked on the graphite sheet 100, and the conductive thin-film 300 is formed on the non-conductive layer 200. Fig. 6 is a plan view of the non-conductive layer 200 and the conductive thin-film 300 formed on the non-conductive layer 200. The LEDs 400 are soldered into gaps between the conductive patterns of the conductive thin-film 300.

[51] This structure features that the graphite sheet 100 is used as a board without using an additional metal PCB. That is, since the non-conductive layer 200 and the conductive pattern of the conductive thin-film 300 are formed on the graphite sheet 100, an electrical drive signal can be supplied to the LEDs 400, and the graphite sheet 100 can be used as a heat-dissipation means. A metal PCB is typically formed of aluminum sheet, silicon steel sheet, or galvanized steel sheet, which has a relatively high thermal conductivity of 100 to 240W/mk. However, the graphite sheet 100, which is formed by rolling expandable graphite, has a thermal conductivity of 220 to 370W/mk. The graphite sheet 100 is less expensive (about a half price of metal) and is flexible. Accordingly, since the LEDs 400 are arranged on the graphite sheet 100 in the present embodiment of the invention, it is possible to lower the temperature of the LED board by about 3 to 4°C compared to a case where the metal PCB is used. In addition, it is possible to produce the LED board at a lower cost.

[52] Fig. 7 shows a backlight unit according to an embodiment of the present invention.

The LED board further includes a reflective layer 600. The reflective layer 600 is coated on the conductive thin-film 300. The reflective layer 600 re-reflects light that is irradiated from the LEDs 400 to an LCD panel 910 and reflected by a prism sheet 920, a diffusion sheet 930, a light-guide plate 940, and a reflective sheet 950, thereby enhancing luminance. Accordingly, in a case where the illumination unit having the reflective layer 600 is used for a flat-panel display panel, the reflective layer 600 re- reflects light that is irradiated from the LEDs 400 to an LCD panel and reflected by elements between the LEDs 400 and the LCD panel, such as a diffusion sheet and a light-guide plate, thereby enhancing luminance.

[53] Fig. 8 shows a cross-sectional view taken along line A-A' of Fig. 4 according to an embodiment of the present invention. The illumination unit shown in Fig. 8 further includes an upper graphite sheet 700, compared to the illumination unit shown in Fig. 5. Fig. 9 shows a perspective view of the upper graphite sheet 700 shown in Fig. 8 according to an embodiment of the present invention. The LEDs 400 are put in holes formed on the upper graphite sheet 700. Similarly to the graphite sheet 100, the upper graphite sheet 700 diffuses heat produced by the LEDs 400. Accordingly, it is possible to efficiently dissipate the heat by using the two graphite sheets. That is, it is possible to lower the temperature of the LED board by about 4 to 5°C compared to a case where the metal PCB is used.

[54] Fig. 10 shows a backlight unit according to an embodiment of the present invention.

The LED board further includes a reflective layer 800. The reflective layer 800 is coated on the upper graphite sheet 700. The reflective layer 800 re-reflects light that is irradiated from the LEDs 400 to the LCD panel 910 and reflected by the prism sheet 920, diffusion sheet 930, light-guide plate 940, and reflective sheet 950, thereby enhancing luminance. Accordingly, in a case where the illumination unit having the reflective layer 800 is used for a flat-panel display panel, the reflective layer 800 re- reflects light that is irradiated from the LEDs 400 to an LCD panel and reflected by elements between the LEDs 400 and the LCD panel, such as the diffusion sheet and light-guide plate, thereby enhancing luminance.

[55] Figs. 11 to 13 show cross-sectional views taken along line B-B' of Fig. 4 according to different embodiments of the present invention. The more closely the graphite sheet 100 is located towards an upper side of the bottom chassis of the casing, the thicker the graphite sheet 100. That is, the graphite sheets 100 have different thicknesses to prevent deviations in temperature from occurring. In general, an illumination unit has higher temperature on its upper side than on its lower side due to the process of thermal convection. Accordingly, the graphite sheet 100 adjacent to an upper side of the casing is thicker in thickness than the graphite sheet 100 adjacent to a lower side of the casing.

[56] Referring to Fig. 11, the LEDs 400 are positioned at different heights from one another, causing deviations in luminance. In this case, the bottom chassis of the casing 500 may be formed in an inclined manner as shown in Fig. 12, or in a step shape as shown in Fig. 13 so that the LEDs can have the same height. Although not shown, the upper graphite sheets 700 may have different thicknesses from one another. In this case, it is possible to minimize differences in temperature in the illumination unit.

[57] The graphite sheets 100 may have different densities from one another. For example, the graphite sheet 100 adjacent to the upper side of the casing 500 is higher in density than the graphite sheet 100 adjacent to the lower side of the casing 500. The density of the graphite sheet 100 can be adjusted by the condensed amount of the graphite sheet 100. Although not shown, the upper graphite sheets 700 may have different densities from one another. In this case, it is possible to minimize differences in temperature in the illumination unit.

[58] Fig. 14 shows a plan view of a graphite sheet according to an embodiment of the present invention. Fig. 15 shows a cross-sectional view taken along line C-C of Fig. 14. The graphite sheet 100 is unitarily formed differently from Fig. 11. In this case, no jump wires 990 shown in Figs. 11 to 13 are required, thus reducing the production cost.

[59] Although not shown in Fig. 15, the reflective layer 100 shown in Fig. 7 may be coated on the conductive thin-film 300 formed on the non-conductive layer 200 that is stacked on the graphite sheet 100. The graphite sheet 100 may be configured to have different thicknesses or densities on its upper and lower sides to prevent deformation caused by the deviation in temperature. When the graphite sheet 100 has different thicknesses on its upper and lower sides, the casing 500 is preferably formed as shown in Fig. 12 or 13. The upper graphite sheet 700 may be unitarily formed. The reflective layer 100 shown in Fig. 10 may be coated on the upper graphite sheet 700. Similarly to the graphite sheet 100, the upper graphite sheet 700 may have different thicknesses or densities on its upper and lower sides.

[60] The LEDs 400 may directly contact the graphite sheet 100. In this case, the conductive thin-film 300 and the non-conductive layer 200 preferably have holes formed thereon so that the LEDs 400 and the graphite sheet 100 can directly contact to each other. Accordingly, heat produced by the LEDs 400 is directly transmitted to the graphite sheet 100, causing the heat to be efficiently dissipated.

[61] The graphite sheet 100 may have a metallic net 150. Fig. 16 illustrates the metal mesh sheet 150. The metal mesh sheet 150 may be meshes woven from wires, a metal mesh sheet having holes formed thereon, or an uneven metal mesh sheet. The metal mesh sheet 150 is preferably made of copper, stainless steel, platinum, aluminum, titanium, or nickel, which has high thermal conductivity. Since the metal mesh sheet 150 is flexible, the graphite sheet 100 is flexible even though the metal mesh sheet 150 is inserted in the graphite sheet 100. As shown in Fig. 17, the graphite sheet 100 including the metal mesh sheet 150 is formed by rolling process.

[62] The metal mesh sheet 150 is inserted in the graphite sheet 100 to improve the heat- dissipation effect. The graphite sheet 100 efficiently diffuses the heat produce by the LEDs 400 in a surface direction but not in a thickness direction. Accordingly, the graphite sheet 100 can efficiently diffuse the heat in the thickness direction as well as in the surface direction by inserting the metal mesh sheet 150 in the graphite sheet 100.

[63] As apparent from the above description, since the LED board uses the graphite sheet that is higher in thermal conductivity, lower in cost and more flexible than the metal PCB, it is possible to dissipate the heat produced by the LEDs more efficiently, to prevent damage due to the heat or stress, to produce the LED board at a lower cost, and to improve the heat-dissipation effect due to a close contact between the graphite sheet and the casing. In addition, the production process is simplified, thereby increasing the production yield.

[64] In addition, since the LED board includes two graphite sheets, it is possible to obtain a more efficient heat-dissipation effect.

[65] In addition, since light that is irradiated from the LEDs to the LCD panel and reflected by the light-guide plate, diffusion sheet and other components is re-reflected by the reflective layer, it is possible to increase the luminance.

[66] It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. Industrial Applicability

[67] The present invention can be applied to a light-emitting diode (LED) board and an illumination unit having the LED.

Claims

[I] A light-emitting diode (LED) board comprising: a graphite sheet to diffuse heat; a non-conductive layer stacked on the graphite sheet; and a conductive thin-film formed on the non-conductive layer and having a circuit configured to apply an electrical drive signal to LEDs. [2] The LED board of claim 1, further comprising a reflective layer coated on the conductive thin-film. [3] The LED board of claim 1, further comprising an upper graphite sheet stacked on the conductive thin-film except on the LEDs. [4] The LED board of claim 3, further comprising a reflective layer coated on the upper graphite sheet. [5] The LED board of any one of claims 1 to 4, wherein the graphite sheet comprises a metal mesh sheet. [6] An illumination unit comprising: a casing; a plurality of LED boards each including a graphite sheet adjacent to inside of the casing to diffuse heat, a non-conductive layer stacked on the graphite sheet, and a conductive thin-film formed on the non-conductive layer; and a plurality of LEDs that is regularly arranged to receive an electrical drive signal from the conductive thin-film and to emit light. [7] The illumination unit of claim 6, wherein each of the LED boards further comprises a reflective layer coated on the conductive thin-film. [8] The illumination unit of claim 6, wherein each of the LED boards further comprises an upper graphite sheet stacked on the conductive thin-film except on the LEDs. [9] The illumination unit of claim 8, wherein each of the LED boards further comprises a reflective layer coated on the upper graphite sheet. [10] The illumination unit of claim 6, wherein a graphite sheet adjacent to an upper side of the casing is thicker in thickness or higher in density than a graphite sheet adjacent to a lower side of the casing.

[II] The illumination unit of claim 6, wherein the graphite sheets constituting the LED boards are unitarily formed with one another.

[12] The illumination unit of claim 11, wherein the LED boards further comprise upper graphite sheets stacked on the conductive thin-film except on the LEDs and unitarily formed with one another.

[13] The illumination unit of claim 11, further comprising a reflective layer coated on the conductive thin-film. [14] The illumination unit of claim 12, further comprising a reflective layer coated on the upper graphite sheets unitarily formed with one another. [15] The illumination unit of claim 11, wherein the unitarily formed graphite sheets are thicker in thickness or higher in density on an upper side of the casing than on a lower side of the casing. [16] The illumination unit of claim 12, wherein the unitarily formed upper graphite sheets are thicker in thickness or higher in density on an upper side of the casing than on a lower side of the casing. [17] The illumination unit of claim 6, wherein the LEDs directly contact the graphite sheet. [18] The illumination unit of any one of claims 6 to 17, wherein the graphite sheet comprises a metal mesh sheet. [19] An illumination unit comprising : a graphite sheet to diffuse heat; a non-conductive layer stacked on the graphite sheet; a conductive thin-film formed on the non-conductive layer; and a plurality of LEDs that is regularly arranged to receive an electrical drive signal from the conductive thin-film and to emit light. [20] The illumination unit of claim 19, further comprising a reflective layer coated on the conductive thin-film. [21] The illumination unit of claim 19, further comprising an upper graphite sheet stacked on the conductive thin-film except on the LEDs. [22] The illumination unit of claim 21, further comprising a reflective layer coated on the upper graphite sheet. [23] The illumination unit of claim 19, wherein the LEDs directly contact the graphite sheet. [24] The illumination unit of any one of claims 19 to 23, wherein the graphite sheet comprises a metal mesh sheet.