WO2006001663A1

WO2006001663A1 - A circuit board having heat sink layer

Info

Publication number: WO2006001663A1
Application number: PCT/KR2005/001984
Authority: WO
Inventors: Young Mo Hwang
Original assignee: Sld Co., Ltd.
Priority date: 2004-06-24
Filing date: 2005-06-24
Publication date: 2006-01-05
Also published as: KR100660126B1; KR20050122365A

Abstract

The invention is to provide a structure of a circuit board which can maximize a heat discharging efficiency. The structure according to the invention includes a device, a circuit board having lead wire patterns on a first surface thereof for supplying electric current to the device, a first metallic heat sink layer formed over the entire first surface of the circuit board and formed between the device, the lead wire patterns and the circuit board for discharging heat generated from the device to the air upon receipt of the same, and an insulation layer formed over the entire surface of the first metallic heat sink layer and formed between the first metallic heat sink layer and the lead wire patterns for electrically insulating the first metallic heat sink layer and the lead wire patterns.

Description

A CIRCUIT BOARD HAVING HEAT SINK LAYER

Technical Field This invention relates to a circuit board for packaging electronic device, and in particular, a structure of a circuit board which is constructed to promptly discharge heat generated at the time of operating an optical device or an electronic device mounted on the circuit board.

Background Art Optical devices or electronic devices commonly generate a considerable amount of heat at the time of operation due to internal resistance, etc. The most outstanding device of this kind is a CPU in a computer. An exclusive cooler is separately mounted to this kind of device generating strong heat over a limited area. However, it is not only the CPU but also other devices mounted on the circuit board that generate the heat at the time of operation. Under the circumstances, heat released from a circuit board carrying such devices has emerged as a very serious technological problem. Such problem has particularly become a factor to be considered more seriously with the introduction of an array structure adopted in light emitting devices (LED) that are widely used in diverse applicable fields in recent days. In general, luminance with thousands of candela per unit area is required so as to use an LED as an illumination lamp. However, a single LED chip is insufficient to satisfy such luminance. Therefore, a number of LED are collectively constructed to be as an array to acquire the required luminance. The most difficult tasks to be achieved in forming an array in the conventional art are to maximize light emitting efficiency by reducing heat, which has been converted from the generated light as well as to discharge the heat outward from the circuit board within a shortest period of time. FIG. l is a cross-sectional view illustrating a structure of a printing circuit board, on which LED arrays are mounted according to the conventional art. FIG. 1 does not include any protection film or other structures not directly related to a subject matter of the present invention. Specifically referring to FIG. 1 , lead wire patterns 120 such as printed copper wires are mounted on a circuit board 130 composed of polychloiϊnated biphenyl (PCB). LED chips 110 are mounted on the lead wire patterns 120. If an LED with high luminance is mounted on the printed lead wire, a partial amount of heat 140 generated from the LED per se is discharged upward through volume of the LED, while the remaining heat 150 is discharged toward the lead wire per se or toward PCB downward through the lead wire. In the above structure, the PCB 130 is generally composed of a plastic material. Because of its poor heat discharging characteristics, relatively a small amount of heat 150 is discharged through the circuit board. Thus, when a device generating a notably large amount of heat is mounted on the circuit board, the suspended heat causes malfunction or decrease in lifespan of the device. The same phenomenon occurs in case of an LED with high luminance, a laser diode (LD) or in their arrays. One of the conventional methods to solve this problem is to mount a heat discharging structure, which is designed to enhance heat discharging efficiency, on each device in advance to its fabrication, and mounting the device on the printed circuit board in FIG. 1. However, such individual heat discharging structure mounted on each device is problematic and disadvantageous not only in terms of fabricating costs and efficiency but also in terms of integration because it requires excessively large packaging volume or area in each device for sufficient discharge of heat. Therefore, no satisfactory result has yet been achieved.

SUMMARY OF THE INVENTION To solve the above problems, it is an object of the invention to provide a structure for a circuit board that can package multiple electronic devices with high integrity without relying on any additional measures. The heat discharging structure installed in the circuit board solves the heat problem generated from the devices. In other words, it is an object of the invention to provide a structure of a circuit board maximizing the heat discharging efficiency. It is another object of the invention to provide a structure of a circuit board, on which the electronic devices can be fabricated or packaged with simpler fabricating process but with higher fabricating efficiency than the conventional art of fabricating the heat discharging structure on each device. It is still another object of the invention to provide a heat discharging structure on a surface, which is opposed to the surface carrying the devices, of a circuit board.

DETAILED DESCRIPTION OF THE INVENTION To achieve the above objects according to one aspect of the invention, there is provided a structure of a circuit board, comprising: a device; a circuit board having a first surface, on which lead wire patterns are mounted to supply electric current to the device; a first metal heat sink layer formed over the entire first surface of the circuit board between the device, the lead wire patterns and the circuit board to discharge heat generated from the device to the air upon receipt of the same; and an insulation layer formed over the first metal heat sink layer between the first metal heat sink layer and the lead wire patterns to electrically insulate the first metal heat sink layer and the lead wire patterns. According to another aspect of the invention, there is also provided a structure of a circuit board, comprising: a device; a circuit board having a first surface, on which lead wire patterns are mounted to supply electric current to the device; a first metal heat sink layer formed over the entire first surface of the circuit board among the device, the lead wire patterns and the circuit board to discharge heat generated from the device to the air upon receipt of the same. According to another aspect of the invention, there is also provided a structure of a circuit board, comprising: a device; lead wire patterns formed on a first surface of the circuit board; a first heat sink layer formed over entire surface of a first surface of the circuit board between the lead wire patterns and the circuit board to discharge heat generated from the device to the air upon receipt of the same. According to another aspect of the invention, there is also provided a structure of a circuit board, comprising: a device; a first metal heat sink layer formed over an entire first surface of the circuit board between the device, the lead wire patterns and the circuit board to discharge heat generated from the device to the air upon receipt of the same; and an insulation layer formed over the first metal heat sink layer between the first metal heat sink layer and the lead wire patterns to electrically insulate the first metal heat sink layer and the lead wire patterns, the insulation layer comprising at least one of BN, TiN, AIN, CNT or diamond powder. The invention relates to a heat discharging structure included in a circuit board per se to drastically increase the heat discharging area in comparison with the conventional structure. The invention has an advantageous effect of more efficiently discharging the heat. The efficient discharge of the heat serves to notably improve integrity of the electronic devices on the circuit board and operational electric current as well as to drastically stabilize the devices in comparison with the conventional art. If the invention is especially applied to an LED, and if a reflective layer is constructed on the circuit board in addition to the heat sink layer, more enhanced productivity and operational efficiency can be anticipated in comparison with the case of forming a reflective layer on each device. The invention also presents a heat discharging structure of a metal circuit board. The metal circuit board and the insulation layer formed on an upper portion thereof result in a prompter discharge of heat downward owing to the high thermal conductivity of the metal circuit board.

Brief Description of the Drawings The above objects, features and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a cross-sectional view of a structure of the conventional circuit board; FIG. 2 is a cross-sectional view of a structure of a circuit board according to the invention; FIG. 3 is a cross-sectional view of a structure of a circuit board having via-holes according to the invention; FIG. 4 is a cross-sectional view of a structure of a circuit board having via-holes and prominence and depression according to the invention; FIG. 5 is a cross-sectional view of a structure of a circuit board having a reflective layer according to the invention; FIG. 6 is a cross-sectional view of a structure of a circuit board having a reflective layer and via-holes according to the invention; FIG. 7 is a cross-sectional view of a structure of a circuit board having a reflective layer, via-holes and prominence and depression according to the invention; FIG. 8 is a cross-sectional view of a structure of a circuit board having an insulation layer/heat sink layer according to the invention; FIG. 9 is a cross-sectional view of a structure of a circuit board having an insulation layer/heat sink layer and a reflective layer according to the invention; FIG. 10 is a cross-sectional view of a structure of a circuit board additionally having via-holes to FIG. 8; FIG. 11 is cross-sectional view of a structure of a circuit board additionally having prominence and depression to FIG. 10; FIGS. 12 to 14 are schematic diagrams exemplifying applications of the circuit board according to the invention to a variety of optical devices; FIG. 15 is a schematic diagram exemplifying applications of the circuit board according to the invention to a variety of electric devices; FIG. 16 is a cross-sectional view of a structure of a dual-face circuit board; FIG. 17 is a cross-sectional view of a structure of a metal circuit board according to the invention; FIG. 18 is a schematic diagram illustrating heat discharging characteristics of an epoxy insulation layer; FIG. 19 is a cross-sectional view of a structure of a circuit board with dual insulation layers according to the invention; FIG. 20 is a cross-sectional view of a structure of a circuit board additionally having a heat sink layer at the bottom to FIG. 17; FIG. 21 is a cross-sectional view of a structure of a circuit board having an insulation layer surrounding the metal circuit board according to the invention; FIG. 22 is a cross-sectional view of a structure of a circuit board additionally having prominence and depression at the bottom to FIG. 17; FIG. 23 is a cross-sectional view of a structure of a circuit board having prominence and depression on the insulation layer at the bottom to increase a contact area between the circuit board and the insulation layer according to the invention; FIG. 24 is a cross-sectional view of a structure of a circuit board having dual heat sink layers at the bottom thereof; and FIG. 25 is a cross-sectional view of a structure of a circuit board having prominence and depression and dual heat sink layers at the bottom thereof.

Best Modes for Carrying out the Invention Best modes for carrying out the invention will now be described with reference to the accompanying drawings. In the following description, same drawing reference numerals are used for the same elements even in different drawings. The matters defined in the description are nothing but the ones provided to assist in a comprehensive understanding of the invention. Also, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. FIG. 2 is a cross-sectional view exemplifying one of the best modes for carrying out the invention. FIG. 2 shows a structure, under which a heat sink layer 210 plainly covering the entire circuit board is located between a PCB circuit board 200 and lead wire patterns 220 and devices 230 are also located above the heat sink layer 210. If the heat sink layer 210 is made of a metallic material, electric short can occur between the adjacent devices due to electric conductivity of the metallic material. Hence, a thin insulation layer 240 is additionally formed between the heat sink layer 210 and the lead wire patterns 220. In FIG. 2, the left and right side tips were drawn to be separated from the other portions of the circuit board for the sake of convenience. However, it would be apparent to those skilled in the art that all the drawings including FIG. 2 represent a magnified partial portion of a circuit board, and that each two-dimensional layer such as a heat sink layer or an insulation layer is formed over the entire surface of the circuit board. The most distinctive feature of the best mode as shown in FIG. 2 is that the heat sink layer 210 is formed over the entire surface of the circuit board 200. Unlike the conventional art, the heat generated at the time of operating the device 230 is not discharged only through the lower part of the PCB circuit board 200, which has low thermal conductivity, or toward the narrow copper lead wire 220. The heat is first spread over the entire heat sink layer of wide area, and discharged through the entire circuit board. Thus, the structure in FIG. 2 has a notably improved heat discharging efficiency compared with the conventional one. In particular, the heat can be discharged outward through the surface gap area 250 between the devices. The surface gap area has not contributed to thermal discharge efficiency in the conventional art because no structure similar to the heat sink layer 210 of this invention has been available to cover entire surface of the board. Therefore, the adjacent devices can be more rapidly cooled down. Such rapid cooling is a quite significant factor in improving integrity of the devices and their operational electric current as well as in solving the problem of heat accumulation in the board. Accordingly, the invention having such structure can serve to fabricate highly integrated device arrays. If the heat sink layer 210 at the lower portion of the circuit board is made of a metallic material, and if the device on the upper portion of the circuit board is an LED, the heat sink layer 210 can also perform the function of a light reflection layer or a light reflection plate due to its metallic reflectivity, thereby improving the luminance of the array as well. The heat sink layer 210 may be made of a metallic material of high electric and thermal conductivity such as Al or Cu. The insulation layer 240 may be fabricated with epoxy film of high thermal conductivity at the thickness of about 5μm ~ 30μm. The epoxy film may be thermally hardened resin or UV hardened resin and glass bead. The materials also available for the heat sink layer or the insulation layer are BN, TiN, AlN, CNT, diamond powder or an appropriate combination or compound of the same. FIG. 3 exemplifies another mode for carrying out the invention, in which via-holes are formed on a circuit board. In general, the via-hole means a hole perforated in a semiconductor structure, etc. In FIG. 3, a number of via-holes 310 are perforated on the circuit board 300 to physically link an upper heat sink layer 320-A with a lower heat sink layer 320-B. Other elements such as the device and the insulation layer on the PCB circuit board 300 are similar to those depicted in FIG. 2. If the upper heat sink layer 320-A is linked with the lower heat sink layer 320-B through the via-holes, the heat not discharged from the upper heat sink layer 320-A descends to the lower heat sink layer 320-B and is dispersed so as to be discharged according to the thermal gradient. Therefore, the structure having via-holes creates an effect of doubling the heat sinking area in the board, thereby enhancing the heat discharging efficiency in proportion to the prior art. FIG. 4 is a cross-sectional view of a structure of a circuit board having prominence and depression 410 in addition to the lower heat sink layer depicted in FIG. 3 to increase the heat sinking area. The prominence and depression 410 may be formed in diverse cross sectional shapes such as a triangle, a triangular cone or a rectangular cone. It may also be formed in a cylindrical shape. FIG. 5 exemplifies another mode of the structure according to the invention when applied to optical devices such as LD or LED, etc. In FIG. 5, a reflective layer 520 is additionally formed between the device 500 and the circuit board 510 to enhance luminance of the optical devices. In general, partial light generated from an active layer of an LED may progress toward a side surface or a bottom surface of the LED. Unless such light is reflected toward the front surface of the LED, the temperature of the LED may be elevated, and its lifespan can be critically shortened. Moreover, such light does not contribute to any luminance of the LED. Hence, it is necessary to enhance the light extracting efficiency comprehensively by reflecting the light toward the front surface of the LED which is a light emitting surface. Therefore, a reflective layer is a structure indispensable to an LED. In the conventional art, however, the reflective layer is installed at each LED per se, thereby decreasing productivity of the LED. For this reason, the structure according to the invention did not install the reflective layer at each LED but did at the circuit board per se. In FIG. 5, an insulation layer 530 and a heat sink layer 540 may be identical or similar to those in FIGS. 3 and 4. However, the insulation layer 530 is preferably made of a material having appropriate band gap so as to pass the light from the LED. The reflective layer 520 is deposited on the heat sink layer 540 by means of sputtering, CVD or electrically plating Ag, Al or highly reflective dye, etc. Sufficient reflectivity and heat discharging effects can be achieved by simply arraying the LEDs on the circuit board having a reflective layer without installing any other structures on each LED. Hence, there is no need to construct a heat sinking or reflecting structure on each device, unlike the conventional art, and it is possible to enhance an efficiency of fabrication and integrity, as well as to heighten luminance of the array. FIGS. 6 and 7 illustrate structures of a circuit board having via- holes 620 and prominence and depression 630 in addition to a reflective layer 600 as shown in FIG. 5. These structures are also to maximize an efficiency of heat discharge.

Other Modes for Carrying out the Invention <Structure of Integrating the Insulation/Heat Sink Layer> FIG. 8 exemplifies another mode of the structure of a circuit board according to the invention. The structure in FIG. 8 has a single layer of high thermal conductivity and non-conductivity so as to perform the functions of an insulation layer and a heat sink layer at the same time. This heat sink layer of non-conductivity will be referred to as the insulation/heat sink layer. If a material is thermally conductive but electrically non- conductive, there is no need to separately form the insulation layer and the heat sink layer within a structure. A single layer is sufficient to perform dual functions at the same time, thereby enhancing the processing efficiency and operational stability of the device. In FIG. 8, a single insulation/heat sink layer 730 is formed between a conductive lead pattern 710 and a circuit board 720 to perform dual functions of the heat sinking and electrical insulation. The aforementioned insulation/heat sink layer 730 may be formed by dispersing AlN nano powder of high non-conductivity and thermal conductivity into epoxy and solidifying the same. In that case, because the AlN powder is surrounded by the nonconductive epoxy, the thermal conductivity of the insulation/heat sink layer is almost the same as that of AlN, while its electrical insulation property is superior thereto. Other materials available for the insulation/heat sink layer 730 are BN, TiN, AlN, CNT₅ diamond powder or an appropriate combination or a compound of the same. The aforementioned epoxy substrate, in which AlN nano powder is dispersed, rarely absorbs the light within the visible range generated by the LED above the epoxy substrate because the epoxy per se is transparent and the band gap of AlN is too large to absorb such light. Therefore, as shown in FIG. 9, a reflective layer 830 is formed under AlN powder dispersed epoxy film 810 to reflect the light from the LED 820 upward. Then, the light passing AlN powder dispersed epoxy substrate is rarely absorbed but reflected, thereby maximizing an effect of the reflective layer. As in the case of FIG. 3 or 4, it is out of question that the via-hole structure or the via-hole/prominence and depression structure can also be employed in the case of using the AlN nano powder dispersed epoxy film as an insulation/heat sink layer. FIGS. 10 and 11 are cross-sectional views briefly illustrating such structures. Also, the AlN powder dispersed epoxy film can be used as a material of the insulation layer, which is separately employed from the heat sink layer. If this structure is applied to an optical device such as an LED, the reflective layer may also be constructed because epoxy has an excellent optical transmissivity in the visible range. In that case, the reflective layer may be formed under the AlN power dispersed epoxy film. Though FIGS. 3 and 4 exemplify the structure applied to an LED, the structure may also be applied to electronic devices in general. When applied to other than the LED, the reflective layer 830 may not be required. In the above structure, the insulation/heat sink layer may be formed with AlN alone instead of the AlN nano powder dispersed epoxy film. In that case, the reflective layer may be formed above the AlN layer, i.e., between the LED with the lead wire and the AlN layer. The above modes are applicable to LEDs and LDs of diverse shapes as shown in FIGS. 12 to 14, in addition to the surface mounting device (SMD) LEDs in general. In other words, the structural characteristics of the invention is also applicable to the flip-chip bonding structure 1010 (of a mesa type) as shown in FIG. 12, or in the LED 1020 having lead wire patterns on a side surface of the chip rather than under the chip as shown in FIG. 13. Since the heat sink layer is used in the array of the mesa type LD 1030 as shown in FIG. 14, the invention is applicable to the optical devices in general including the LEDs and the LDs. In addition, applicability of the invention is not limited to such optical devices but is extended to all kinds of electronic circuit board necessitating thermal discharge. If the invention is applied to a circuit board of the devices in general, heat can be effectively discharged as in the aforementioned cases by employing the heat sink layer 1160 and the insulation layer 1170 formed over the entire surface of the circuit board, in the case where the device 1130 is mounted above the lead wire patterns 1120, which is formed on one surface of the circuit board 1110 as shown in FIG. 15, or in the case where the device 1150 is mounted on side surfaces of the lead wire patterns 1140. For reference, FIG. 15 illustrates two different kinds of device structures on one circuit board for the sake of convenience. It is out of question that the via-hole structure and the via- hole/prominence and depression structure are also applicable to the circuit board in FIG. 15. If the aforementioned heat sink layer 1160 is made of AlN or AlN powder dispersed epoxy, the insulation layer 1170 is not required unlike the case of using a metal plate. Instead, a single layer can perform dual functions of the insulation/heat sink layer as described above. FIG. 16 shows another mode for carrying out the invention. In FIG. 16, a device is mounted to a dual-plated circuit board. A device and lead wire patterns 1220-A, 1220-B are arrayed on both surfaces of the circuit board 1210, and heat sink layers 1230-A, 1230-B are formed adjacent thereto. If applied to an LED, such structure may be used to a traffic signal light that needs to emit light from two surfaces. <Structure of Using a Metal Plate> FIG. 17 shows another mode for carrying out the invention, in which, a main body of the circuit board 1700 is made of metal with high thermal conductivity. In this mode, the conventional plastic material is replaced with a metallic material in composing the main body of the circuit board to drastically enhance thermal discharging characteristics of the circuit board. The metallic material constituting the main body of the circuit board 1700 may be Al or an alloy thereof. However, the material is not limited to such metal but is extended to all kinds of widely known metal with high thermal conductivity. Since the main body of the circuit board is made of a metallic material, an insulation layer needs to be formed between the circuit board and the lead wire 1720, such as copper wiring, for the purpose of insulation. In FIG. 17, the insulation layer 1710 should have high electrical resistance and thermal conductivity because it needs to promptly discharge the heat generated from the device 1730. In most of the materials, however, the electrical conductivity tends to be proportional to the thermal conductivity. For this reason, it was difficult for those skilled in the conventional art to conceive a metallic circuit board and an insulation/heat sink layer, which can insulate the metallic circuit board with its high electrical resistance but has high thermal conductivity as well. The invention has shifted such conventional paradigm by employing BN, TiN, AlN, CNT, diamond powder or an appropriate combination or a compound of the same for the insulation/heat sink layer with high thermal conductivity and with high electrical resistance. BN, TiN, AlN, CNT, diamond powder or an appropriate combination or a compound of the same has excellent electrical resistance and thermal conductivity. If 70 w/o of TiN and 30 w/o of CNT are deposited at the thickness of about 1 - 100 μm by means of CVD, for example, excellent thermal conductivity and electrical resistance can be achieved as a result. As another mode of making the insulation layer 1710, it is possible to mix BN powder, TiN powder, CNT powder, diamond powder, AlN powder, nano silver powder, or an alloy or a combination of the same with epoxy or liquefied silica. FIG. 18 is a schematic diagram illustrating a mixture of epoxy 1800 with powder particle 1810 of the above materials. The epoxy or the liquefied silica is electrically nonconductive or electrically resistant per se. If the above powder particles, which are also electrically non conductive, are mixed with the epoxy or the liquefied silica, the entire mixture becomes electrically nonconductive as described above. Since the powder particles have good thermal conductivity and the average distance between the powder particles is very short, heat can be rapidly discharged outward through the powder particles. For example, the aforementioned powder may be the powder of nano size. In short, the structure shown in FIG. 18 has high electrical resistance while it has excellent thermal conductivity. FIG. 19 shows another embodiment of the invention, in which dual insulation layers are constructed. Of the dual insulation layers 1910, 1920 in FIG. 19, the first insulation layer 1910 comprises at least one of BN, TiN, AlN, CNT or diamond powder. The second insulation layer 1920 comprises at least one of BN, TiN, AlN, CNT or diamond powder, excluding the materials included in the first insulation layer 1910. To be specific, the embodiment in FIG. 19 is a structure of enhancing the electrical resistance of the circuit board by constituting at least one of BN, AlN, CNT or diamond powder for the dual insulation layers 1910, 1920, either of which precluding the composition included in the other. FIG. 20 shows another embodiment of the invention. A second heat sink layer with excellent heat discharging characteristics is additionally mounted at the bottom of the circuit board. The second heat sink layer 2000 at the bottom may comprise at least one of BN, TiN, AlN, CNT or diamond powder, as in case of the insulation layers 1910, 1920 at the top. These materials have high thermal conductivity. Meanwhile, the insulation layer 2000 at the bottom does not necessarily be in dual forms and may be embodied in a single layer. FIG. 21 is a schematic diagram illustrating another embodiment of the invention. In FIG. 21, a single insulation /heat sink layer 2110 surrounds the entire metal circuit board 1700. One of the characteristics of this embodiment lies in that the insulation/heat sink layer 2110 covers the entire surfaces of the metal circuit board including the side surfaces. This structure has an advantage of being easily fabricated by plating, spray coating, etc. In other words, this structure improves productivity by skipping a complicated process of vacuum deposition. The insulation/heat sink layer 2110 may also comprise at least one of BN, TiN, AlN, CNT and diamond powder. FIG. 22 shows another embodiment of the invention, in which the structure has prominence and depression at the bottom for thermal discharge in addition to any one of the preceding embodiments. The function and effect of the prominence and depression are the same as described with reference to the other embodiments. The prominence and depression 2210 are mainly classified into two types: a type separately mounted on the metal circuit board 1700; and a type integrally formed on the circuit board as a unit. For the former type, a metallic material of high thermal conductivity may be used for the prominence and depression 2210. However, it is also possible to separately fabricate the prominence and depression 2210 by using a thin layer comprising at least one of BN, TiN₅ AlN, CNT or diamond powder, and to adhere the same to the bottom of the circuit board 1700. The latter type of prominence and depression 2210 may be formed on the circuit board by means of pressing at the time of fabricating the circuit board. Another method of fabricating the integrated type is to etch the bottom of the circuit board by means of dry etching or wet etching. One skilled in the art would easily understand the detailed steps of such process. FIG. 23 shows another embodiment of the invention, in which the prominence and depression 2320 are integrated with the heat sink layer 2310 at the bottom. The prominence and depression 2320 are used to increase the contact area between the heat sink layer 2310 at the bottom having high thermal conductivity and the metal circuit board 1700. FIG. 24 shows another embodiment of the invention, in which the heat sink layer is constructed in dual forms at the bottom for more effective thermal discharge than the one depicted in FIG. 23. In other words, a second heat sink layer 2410 is formed in addition to a first heat sink layer 2310. The first and the second heat sink layers 2310, 2410 may comprise at least one of BN, TiN, AlN, CNT, diamond powder or nano silver powder, either of which precluding the composition included in the other. The heat sink layers 2310, 2410 may be formed at least one of BN, TiN, AlN, CNT, diamond powder and nano silver powder. It may also take a form of epoxy film or silica film, in which at least one of BN powder, TiN powder, AlN powder, CNT powder, diamond powder and nano silver powder is dispersed. FIG. 25 shows another structure according to the invention, in which dual heat sink layers are formed at the top and the bottom of the structure in FIG. 21 , and the prominence and depression are additionally formed. The functions, the fabricating materials and the methods for making of each layer are the same or similar to the preceding embodiments. In the preceding embodiments, the heat sink layer and the insulation layer at the top or bottom may be constructed in the form of dual or multiple layers. Also, the preceding embodiments may be combined so as to be used in various shapes.

Industrial Applicability The invention can be used for the circuit boards in general. In particular, the invention can be used for analog and digital circuit boards which are apt to generate heat of high temperature due to their high integrity density. The invention can be particularly used for the circuit boards, in which optical devices or LEDs are intensely arrayed. The circuit boards for such LEDs include the SMD structure or the flip chip bonding structure. The invention is applicable not only to each LED but also to an array of LEDs. While the invention has been shown and described with reference to certain embodiments to carry out the invention, it will be understood by those skilled in the art who have understood the technical concept of the invention that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

What Is Claimed Is: 1. A circuit board assembly comprising: a device; , a circuit board having lead wire patterns on a first surface thereof for supplying electric current to the device; a first metallic heat sink layer formed over the entire first surface of the circuit board and formed between the device, the lead wire patterns and the circuit board, for discharging heat generated from the device to the air; and an insulation layer formed over the entire surface of the first metallic heat sink layer and formed between the first metallic heat sink layer and the lead wire patterns for electrically insulating the first metallic heat sink layer and the lead wire patterns. 2. The circuit board assembly of claim 1, wherein the device is an optical device, the circuit board further comprising a reflective layer formed over the entire surface of the first metallic heat sink layer between the first metallic heat sink layer and the optical device. 3. The circuit board assembly of claim 1 , further comprising a second metallic heat sink layer formed over an entire second surface of the circuit board opposed to the first surface thereof so as to be physically in contact with the first metallic heat sink layer through a plurality of via-holes formed in the circuit board. 4. The circuit board assembly of claim 3, wherein a plurality of prominence and depression are formed on a surface of the second metallic heat sink layer for increasing a heat discharging area. 5. The circuit board assembly of claim 1, wherein the insulation layer comprises at least one of BN, TiN, AlN, CNT and diamond powder. 6. A circuit board assembly comprising: 5 a device; a circuit board having lead wire patterns on a first surface thereof for supplying electric current to the device; a first electrically resistant heat sink layer formed over the entire first surface of the circuit board and formed between the device, the lead ) wire patterns and the circuit board for discharging heat generated from the device to the air upon receipt of the same; and 7. • The circuit board assembly of claim 6, wherein the first electrically resistant heat sink layer comprises at least one of BN, TiN, AlN, CNT and diamond powder. ) 8. The circuit board assembly of claim 6, wherein the device is an optical device, the circuit board further comprising a reflective layer formed over the entire surface of the first electrically resistant heat sink layer and formed between the first electrically resistant heat sink layer and the optical device. ) 9. The circuit board assembly of claim 6, wherein the device is an optical device, the circuit board further comprising a reflective layer formed over the entire surface of the first electrically resistant heat sink layer and formed between the first electrically resistant heat sink layer and the optical device for reflecting light generated from the optical 5 device upward, if the first electrically resistant heat sink layer is transparent with respect to the light generated from the optical device. 10. The circuit board assembly of any one of claims 6 to 9, further comprising a second electrically resistant heat sink layer formed over an entire second surface of the circuit board opposed to the first surface thereof so as to be physically in contact with the first electrically resistant heat sink layer through a plurality of via-holes formed in the circuit board. 11. The circuit board assembly of claim 10, wherein a plurality of prominence and depression are formed on a surface of the second electrically resistant heat sink layer. 12. A circuit board assembly comprising: a device; a circuit board having lead wire patterns on a first surface thereof for supplying electric current to the device; a first heat sink layer formed over the entire first surface of the circuit board and formed between the device, the lead wire patterns and the circuit board for discharging heat generated from the device to the air upon receipt of the same 13. The circuit board assembly of claim 12, further comprising ) a second heat sink layer formed over the entire surface of a second surface opposed to the first surface of the circuit board so as to be physically in contact with the first heat sink layer through a plurality of via-holes formed in the circuit board. 14. The circuit board assembly of claim 12, further comprising an insulation layer formed between the first heat sink layer and the lead wire patterns for electrically insulating the same if the first heat sink layer is a conductor. 15. The circuit board assembly of claim 12, wherein the first heat sink layer comprises at least one of BN₅ TiN, AlN, CNT and 5 diamond powder. 16. The circuit board assembly of claim 12, wherein the device is an optical device, the circuit board further comprising a reflective layer formed over the entire first surface of the circuit board for reflecting rather than absorbing light. ) 17. A circuit board assembly comprising: a device; a metallic circuit board having lead wire patterns on a first surface thereof for supplying electric current to the device; and an insulation layer formed over the entire surface of the metallic 5 circuit board and formed between the metallic circuit board and the lead wire patterns for electrically insulating the metallic circuit board and the lead wire patterns, the insulation layer including at least one of BN, TiN, AlN, CNT and diamond powder. 18. The circuit board assembly of claim 17, wherein the 3 insulation layer is formed by dispersing powder particles comprising at least one of BN, TiN, AlN, CNT and diamond powder into epoxy. 19. The circuit board assembly of claim 17, wherein the insulation layer is formed by dispersing powder particles comprising at least one of BN, TiN, AlN, CNT and diamond powder into silica. 5 20. The circuit board assembly of claim 17, wherein the insulation layer is a multiple layer. 21. The circuit board assembly of claim 17, further comprising a heat sink layer at the bottom of the metallic circuit board, the heat sink layer including at least one of BN, TiN, AlN, CNT, diamond powder and nano silver. 22. The circuit board assembly of claim 17, wherein the insulation layer is formed over the entire surface of the metallic circuit board. 23. The circuit board assembly of claim 17, further comprising prominence and depression formed at the bottom of the metallic circuit board for heat discharge. 24. The circuit board assembly of claim 21 , further comprising prominence and depression formed between the heat sink layer and the metallic circuit board for increasing a contact area between the same. 25. The circuit board assembly of claim 21, wherein the heat sink layer at the bottom of the circuit board is multiple layers. 26. The circuit board assembly of any one of claims 1 to 24, wherein the circuit board is a dual-face circuit board.