JP2011135109A - Heat dissipation substrate and substrate for light-emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that the deterioration of element functions is caused by the generation of heat in LEDs and high-density LSI chips, and light emission efficiency and a lifetime are reduced accompanied by an increase of the amount of heat generated especially when the LEDs are used for high luminance/high output applications. <P>SOLUTION: A substrate which is used as a heat dissipation substrate, especially as a substrate for mounting a light-emitting diode, comprises two or more layers composed of at least an isotropic heat conduction layer and an anisotropic heat conduction layer. The heat conductivity of the anisotropic heat conduction layer in a high heat conductivity direction is two or more times larger than that of the isotropic heat conduction layer, and the anisotropy of heat conductivity in the anisotropic heat conduction layer is ten times larger, thereby obtaining the substrate with a better heat dissipation effect than that obtained when the isotropic heat conductor is only used alone. Thus, heat generated from an LED chip is efficiently dissipated. The anisotropic heat conduction layer is a graphite layer having the anisotropy of heat conductivity, and the graphite has heat conductivity in the layer plane direction of 200 W/mK or higher. Even if a drive current is increase, the LED chip does not suffer from deterioration in light emission efficiency, and has a longer lifetime. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a substrate excellent in heat dissipation (thermal diffusion) characteristics. The present invention also relates to a mounting substrate having excellent heat dissipation (heat diffusion) characteristics effective for a light emitting diode.

  In recent years, the heat generation problem of light emitting diodes and high performance LSIs is becoming a very big problem, and how to dissipate the heat generated by these elements through the mounting board is becoming an important issue.

  In particular, light-emitting diodes are widely used as various display boards, traffic signals, and the like, and their uses are expanding for indoor lighting. It is known that this type of light emitting diode (LED) generates a large amount of heat, and the temperature of the LED rises due to the heat generation and the light emission characteristics deteriorate. For example, when the material of the circuit board on which the LED chip is mounted is a glass epoxy resin having poor thermal conductivity, the increased heat only dissipates through the plated surface of the electrode pattern, and the heat dissipation efficiency is poor. The problem of temperature rise occurs.

  For example, in order to improve the heat dissipation characteristics of LEDs and solve such problems, a display technology in which a large number of LEDs are arranged in a resin case and covered with a resin cap is disclosed (Patent Document 1). In this case, heat sinks are installed inside and outside the case and both are connected. However, in such a configuration, the two lead wires constituting the LED are not directly connected to the heat sink, but are thermally conducted to the instrument body via the silicone resin and radiated to the outside. It is considered that heat cannot be efficiently dissipated.

  Moreover, as an illuminating device having an LED aiming at improving heat dissipation, an instrument body having an opening, a printed circuit board disposed in the instrument body, and a light mounted toward the opening side mounted on the printed circuit board. An illumination device is disclosed which includes an LED that emits light, a protective resin that covers and protects a power supply terminal and a printed circuit board that are derived from the semiconductor light source, and an irradiation lens that is provided in an opening of the instrument body. (Patent Document 2). This is to conduct and dissipate a certain amount of heat from the energizing terminal and the printed circuit board, but it is considered that there is a limit to heat dissipation.

  Furthermore, for the purpose of improving heat dissipation from the lead terminals, a technique using graphite having high thermal conductivity has been proposed (Patent Document 3). This is because the light emitting part is arranged on one side of the board, the lead wire end is exposed and arranged on the other side of the board, and the LED is arranged on the other side of the board. A lighting circuit component, a heat conductive graphite provided so as to cover the LED lead wire end and the lighting circuit component, and to be in contact with the lead wire end, and directly or indirectly provided on the heat conductive graphite And an illuminating device. This is considered to have the effect of improving the heat dissipation effect by using thermally conductive graphite, but the heat dissipation is basically via the lead wire, and the heat dissipation capability is considered to be limited.

  In addition, for the purpose of providing an LED illumination light source in which LEDs are integrated at a high density with improved heat dissipation and light utilization efficiency, a detachable card-type LED illumination light source having LEDs mounted on one side of a substrate is provided. (Patent Document 4). The card-type LED illumination light source includes a metal base substrate and a plurality of LEDs mounted on one side of the metal base substrate, and the back surface of the metal base substrate on which the LEDs are not mounted is provided. The power supply terminal that is in thermal contact with a part of the lighting device and is electrically connected to the connector has a structure provided on one side of the metal base board on which the LED is mounted.

Japanese Utility Model Publication No. 1-153586. Japanese Patent Laid-Open No. 11-312403. JP2003-100110A. JP2003-124528A.

  An object of the present invention is to provide a mounting substrate that can effectively dissipate heat generated by a light emitting diode, a high performance LSI, or the like. In particular, it is to provide a substrate on which an LED chip on which heat dissipation is an important issue can be mounted.

  In the LED chip, the drive current and the luminance are in a substantially proportional relationship up to a certain operating region, and it is necessary to increase the drive current to obtain high luminance. However, when the drive current is increased, the power loss of the LED chip increases in proportion to it, and most of the energy is converted into heat, and the temperature of the LED chip rises. Since the LED chip has a higher luminous efficiency efficiency as the temperature is lower, there is a problem that the light emission luminance is lowered when the LED chip is at a higher temperature. Furthermore, the operating life of the LED chip is shortened as the operation is performed at a higher temperature, and there arises a problem that the translucent sealing resin that seals the LED chip deteriorates transparency due to discoloration due to heat. That is, in order to use the LED as a high-luminance and high-power application, how to suppress the temperature rise is a problem. In particular, such a problem becomes conspicuous when a large number of LEDs are mounted for illumination.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a mounting substrate capable of quickly diffusing the heat generation of the LED and consequently suppressing the temperature rise of the LED.

  As means for solving the problems, in the present invention, the mounting substrate has a structure of at least two layers of a layer having isotropic thermal conductivity and a layer having anisotropic thermal conductivity. The means of the present invention has been found that better heat dissipation characteristics can be obtained by using a multilayer structure with anisotropic heat conductive materials having certain characteristics than using these isotropic high heat conductive materials alone. The purpose of this is. In this case, when the anisotropic thermal conductivity of the anisotropic heat conduction layer is 10 times or more and the thermal conductivity in the high thermal conductivity direction is 2 times or more larger than that of the isotropic heat conduction layer Thus, it is possible to realize a substrate having a better heat dissipation effect than when only an isotropic heat conductor is used alone.

  In a preferred embodiment, the layer having thermal conductivity anisotropy is a graphite layer having at least thermal conductivity anisotropy, and the thermal conductivity in the surface direction of the graphite layer is 200 W / mK or more. By using such a graphite material, a substrate that realizes excellent heat dissipation characteristics can be obtained.

  Furthermore, in a preferred embodiment, the isotropic thermal conductivity layer includes a metal having a thermal conductivity of 100 W / mK or more.

  In a preferred embodiment, the isotropic thermal conductivity layer includes a ceramic having a thermal conductivity of 10 W / mK or more.

  In a preferred embodiment, the anisotropic heat conductive layer has a thickness of 1 mm or less.

  In a preferred embodiment, the isotropic heat conductive layer and the anisotropic heat conductive layer in the substrate are in direct contact. As a specific preferred embodiment, the isotropic heat conduction layer and the anisotropic heat conduction layer in the substrate are in direct contact without an adhesive layer. This is more preferable in order to realize better heat dissipation characteristics. Here, without an adhesive layer means that a metal layer or a ceramic layer is directly formed on the graphite layer by a chemical method such as plating or a physical method such as sputtering or vapor deposition. It is also in this category that it is mechanically caulked with screws or screws.

  It is a preferred embodiment of the present invention that the metal layer is formed on the surface of the graphite layer by an electroless plating method.

  In a preferred embodiment, the graphite having thermal conductivity anisotropy is obtained by heat-treating a polymer film selected from polyimide, polyoxazole, and polyparaphenylene vinylene in an inert gas at a temperature of 2400 ° C. or higher. It is what was done. The polymer film of the present invention has a broad concept including a resin film.

  In particular, as a means for solving the problem of heat generation in LEDs, in the present invention, the mounting substrate of the light emitting diode has a structure of at least two layers of a layer having isotropic thermal conductivity and a layer having anisotropic thermal conductivity. The means of the present invention has been found that better heat dissipation characteristics can be obtained by using a multilayer structure with anisotropic heat conductive materials having certain characteristics than using these isotropic high heat conductive materials alone. The purpose of this is. In this case, when the anisotropic thermal conductivity of the anisotropic heat conduction layer is 10 times or more and the thermal conductivity in the high thermal conductivity direction is 2 times or more larger than that of the isotropic heat conduction layer Thus, it is possible to realize a light emitting diode substrate that is more excellent in heat dissipation effect than when only an isotropic thermal conductor is used alone.

  In a preferred embodiment, the layer having thermal conductivity anisotropy is a graphite layer having at least thermal conductivity anisotropy, and the thermal conductivity in the surface direction of the graphite layer is 200 W / mK or more. By using such a graphite material, excellent heat dissipation characteristics can be realized.

  Furthermore, in a preferred embodiment, the isotropic thermal conductivity layer is a metal having a thermal conductivity of 100 W / mK or more.

  In a preferred embodiment, the isotropic thermal conductivity layer is a ceramic having a thermal conductivity of 10 W / mK or more.

  In a preferred embodiment, the anisotropic heat conductive layer has a thickness of 1 mm or less.

  In a preferred embodiment, the isotropic heat conductive layer and the anisotropic heat conductive layer in the substrate are in direct contact without an adhesive layer. This is more preferable in order to realize better heat dissipation characteristics. Here, without an adhesive layer means that a metal layer or a ceramic layer is directly formed on the graphite layer by a chemical method such as plating or a physical method such as sputtering or vapor deposition. This category also includes mechanically caulking with screws or screws.

  It is a preferred embodiment of the present invention that the metal layer is formed on the surface of the graphite layer by an electroless plating method.

  In a preferred embodiment, the light emitting diode chip is directly mounted on a substrate, and the outermost surface of the mounting substrate is a metal layer. This is to prevent the problem of powder falling due to peeling, which is peculiar to the graphite layer having thermal conductivity.

  In a preferred embodiment, the light emitting diode chip is directly mounted on a substrate, and the outermost surface of the mounting substrate is a ceramic layer. This is to prevent powder falling off due to peeling of the graphite layer as described above and to provide insulation.

  In a preferred embodiment, the isotropic heat conductive layer and the anisotropic heat conductive layer in the substrate are in direct contact without an adhesive layer. This is more preferable in order to realize better heat dissipation characteristics. Here, without an adhesive layer means that a metal layer or a ceramic layer is directly formed on the graphite layer by a chemical method such as plating or a physical method such as sputtering or vapor deposition. It is also in this category that it is mechanically caulked with screws or screws.

  In a preferred embodiment, the graphite having thermal conductivity anisotropy is obtained by heat-treating a polymer film selected from polyimide, polyoxazole, and polyparaphenylene vinylene in an inert gas at a temperature of 2400 ° C. or higher. It is what was done.

  According to the present invention, the rising temperature of the LED chip is suppressed by effectively radiating heat through the mounting substrate having the structure of the present invention, and even if the drive current is increased, the light emission efficiency and the operating life of the LED chip are not reduced. It is possible to provide a light emitting diode.

Sectional drawing of the light emitting diode concerning embodiment of this invention. Sectional drawing of the light emitting diode concerning embodiment of this invention. Sectional drawing of the light emitting diode concerning embodiment of this invention. Sectional drawing of the light emitting diode concerning embodiment of this invention. Sectional drawing of the light emitting diode concerning embodiment of this invention.

  Each component of the present invention will be described.

<Light emitting diode>
The light emitting part of the light emitting diode according to the present invention includes indium gallium nitride (InGaN), gallium phosphorus (GaP), aluminum indium gallium phosphorus (AlInGaP) and gallium phosphorus (GaP) or indium gallium. A light emitting diode made of phosphor having a nitride (InGaN) and YAG structure, a light emitting diode made of indium gallium nitride (InGaN) and a phosphor, or a light emitting diode made of zinc selenium (ZnSe). A plurality of these light emitting diodes may be connected in series or in parallel.

  In these light emitting diodes, in order to emit blue, green, yellow, red and white light, indium gallium nitride (InGaN) and aluminum indium gallium phosphorus (AlInGaP) and gallium phosphorus (GaP) are used. Each light emitting diode can be used. In order to emit blue to green light, an indium gallium nitride (InGaN) light emitting diode can be used. In order to emit yellow to red light, each of light emitting diodes of aluminum, indium, gallium, phosphorus (AlInGaP) and gallium, phosphorus (GaP) can be used. In order to emit infrared light from red, a light emitting diode in which zinc (Zn) is doped into gallium phosphorus (GaP) can be used. In order to emit white light, a phosphor (main wavelength: yellow) having a YAG structure was applied around a light emitting diode composed of indium, gallium, nitride (InGaN) and a phosphor having a YAG structure to form a chip. A light emitting diode, a light emitting diode combining indium gallium nitride (InGaN) that emits ultraviolet light and a phosphor, or a light emitting diode of zinc selenium (ZnSe) can be used.

<Isotropic heat conduction layer>
The isotropic heat conductive layer used in the present invention includes aluminum (thermal conductivity: 237 W / mK), copper (thermal conductivity: 398 W / mK), silver (thermal conductivity: 428 W / mK), nickel (thermal Metal materials with excellent thermal conductivity such as conductivity: 90 W / mK, silica (thermal conductivity: 1.5 W / mK), alumina (thermal conductivity: 20 W / mK), magnesium oxide (MgO) (heat Conductivity: 40 W / mK), boron nitride (BN) (thermal conductivity: 60 (200) W / mK), aluminum nitride (AlN) (thermal conductivity: 70 (270) W / mK), silicon carbide (SiC) ) (Thermal conductivity: 88 to 128 W / mK (depending on the crystal system)), or a substrate combining these materials.

<Anisotropic heat conduction layer>
The anisotropic thermal conductive layer used for the purpose of the present invention has an anisotropic thermal conductivity anisotropy of 10 times or more in the anisotropic thermal conductive layer, and the high thermal conductivity in the anisotropic thermal conductive layer. There is no particular limitation as long as the thermal conductivity in the direction is twice or more larger than the thermal conductivity of the isotropic thermal conductive layer.

  As the most preferable material used for such an anisotropic heat conductive layer, graphite can be mentioned. Graphite has a structure in which carbon atoms are spread in layers, and has excellent thermal conductivity in the surface direction. With ideal graphite, the thermal conductivity in the plane direction reaches 2000 W / mK, which is five times that of copper, 398 W / mK. Moreover, the thermal conductivity in the thickness direction of graphite is characterized by being about 1/400 in the plane direction. The graphite film used for the purpose of the present invention preferably has a thermal conductivity of 200 W / mK or more in the film surface direction and anisotropy of 10 times or more of the thermal conductivity in the direction perpendicular to the film surface. Furthermore, 20 times or more is preferable.

  However, the thermal conductivity of the graphite is a value of an ideal single crystal graphite, and the thermal conductivity of the graphite material actually obtained is inferior to the ideal value. As graphite that can be practically used for the purpose of the present invention, (1) a graphite film obtained by sheeting graphite powder such as natural graphite or artificial graphite, and (2) a graphite film obtained by heat-treating a polymer film Can be mentioned. The graphite film obtained by the production method (1) has a film surface thermal conductivity of 200 to 400 W / mK, a thickness direction thermal conductivity of 5 to 20 W / mK, and a thickness of 100 to 1000 μm. can get.

  The thermal conductivity of graphite has anisotropy of thermal conductivity derived from the original structure of graphite. The higher the thermal conductivity in the plane direction, the smaller the thermal conductivity in the thickness direction. Since the object of the present invention is diffusion of heat, it is extremely important for the present invention that the thermal conductivity in the surface direction is large. On the other hand, since the thermal conductivity in the thickness direction of the surface in the anisotropic heat conductive layer is small, it is preferable that the thickness in the thickness direction is as small as possible in the range in which sufficient heat diffusion is possible in the surface direction. In the case of using the graphite, the thickness of the anisotropic heat conductive layer is preferably 1 mm or less. When graphite of 1 mm or more is used, the heat dissipation characteristics are worse than when an isotropic heat conductive layer is used alone.

<Measurement and calculation of thermal conductivity anisotropy and thermal conductivity>
In the present invention, “anisotropy of thermal conductivity”
Between the value of the thermal conductivity in the plane direction and the value of the thermal conductivity in the thickness direction,
The value obtained by dividing the value of the larger thermal conductivity by the value of the smaller thermal conductivity is expressed.

  The thermal conductivity in the film surface direction (X direction, Y direction) and the thermal conductivity in the film thickness direction (Z direction) can be measured independently by the following methods.

  In the case of graphite, the thermal conductivity in the film surface direction is derived from the essential crystal structure of graphite, and there is no difference in the XY direction.

The thermal diffusivity was measured at 10 Hz in an atmosphere of 20 ° C. using a thermal diffusivity measuring apparatus (“LaserPit” available from ULVAC Riko Co., Ltd.) by an optical alternating current method. Thermal conductivity and thermal conductivity were calculated from the measured thermal diffusivity using the values of density and specific heat. The density of the graphite film was calculated by dividing the weight (g) of the graphite film by the volume (cm ³ ) calculated by the product of the vertical, horizontal and thickness of the graphite film. In addition, the average value measured by arbitrary 10 points | pieces was used for the thickness of a graphite film.

<Method for producing graphite film-1>
A method for producing the graphite will be described.

  The production method (1) is a graphite film obtained by pressing graphite powder into a sheet. In order for the graphite powder to be formed into a film, the powder needs to be in the form of flakes or flakes. The most common method for producing such graphite powder is a method called an expanding method. In this method, a graphite intercalation compound is produced by immersing in an acid such as graphite sulfuric acid, and thereafter, this is heat-treated and foamed to separate the graphite layers. After peeling, the graphite powder is washed to remove the acid to obtain a thin film graphite powder. The graphite powder obtained by such a method is further subjected to rolling roll molding to obtain film-like graphite. The graphite film obtained by such a method has flexibility and is preferably used for the purpose of the present invention because it has high thermal conductivity in the film surface direction.

<Method for producing graphite film-2>
The graphite film obtained by the method (2) has a thermal conductivity in the film surface direction of 400 to 1000 W / mK, a thermal conductivity in the thickness direction of 5 to 20 W / mK, and a thickness of 50 to 200 μm. It is done. Any of these is preferably used for the purpose of the present invention.

  This graphite is obtained by heat-treating a raw material film composed of a polymer film and / or a carbonized polymer film at a temperature of 2400 ° C. or higher. Polymer films that can be used in the present invention include polybenzoxazole (PBO), polybenzobisoxazal (PBBO), polythiazole (PT), polyimide (PI), polyamide (PA), and polyoxadiazole (POD). ), Polybenzoxazole (PBO), polybenzothiazole (PBT), polybenzobisthiazole (PBBT), polyparaphenylene vinylene (PPV), polybenzimidazole (PBI), and polybenzobisimidazole (PBBI). In particular, since the finally obtained graphite has high thermal conductivity, polyimide (PI), polyoxadiazole (POD), and polyparaphenylene vinylene (PPV) are preferably used as raw materials for producing graphite for this purpose. What is necessary is just to manufacture these films with a well-known manufacturing method. Above all, the polyimide described below is particularly suitable for this purpose because the film is more easily carbonized and graphitized than the polymer films made of other organic materials, and is easily converted to graphite having excellent crystallinity and thermal conductivity. Preferred starting material.

As graphite used for the purpose of the present invention, a polyimide film having an average linear expansion coefficient of 2.5 × 10 ⁻⁵ cm / cm / ° C. or less in the range of 100 to 200 ° C. is heat-treated at a temperature of 2400 ° C. or more. It is preferable that the graphite film is made to realize excellent thermal conductivity.

  In addition, it is preferable to use a graphite film by heat-treating a polyimide film having a birefringence of 0.13 or more at a temperature of 2400 ° C. or more in order to realize excellent thermal conductivity.

Of course, a polyimide film having an average linear expansion coefficient in the range of 100 to 200 ° C. of 2.5 × 10 ⁻⁵ cm / cm / ° C. or less and a birefringence of 0.13 or more is obtained at a temperature of 2400 ° C. or more. It is preferable to produce a graphite film by heat treatment in order to realize excellent thermal conductivity.

The polyimide preferably used for such graphitization is
Polyimide having at least one or more repeating units selected from the group consisting of repeating units represented by the following general formulas (1), (2) and (3), or the following general formulas (1) and (2 ), A polyimide copolymer film having at least two types of repeating units selected from the group consisting of repeating units represented by (3), or general formula (1), general formula (2), and general The object can be achieved by being a mixture film of at least two kinds of polyimide copolymers selected from the group consisting of polyimide copolymers represented by the formula (3).

It is. R ₁ is

A divalent organic group selected from the group consisting of: R ₂ is independently —CH ₃ , —Cl, —Br, —F, or —CH ₃ O.
R in the formula (3) is

Where n is an integer from 1 to 3. X and Y are each independently hydrogen, halogen, carboxyl group, lower alkyl group having 6 or less carbon atoms, or alkoxy group having 6 or less carbon atoms, and A is -O-, -S-, -CO- , -SO2-, or -CH2-.

  Moreover, the copolymer of the polyimide which has at least 2 or more types of repeating unit selected from the group which consists of the repeating unit represented by the said General formula (1), (2) and following General formula (6), (7) Or a mixture of at least three or more selected from the group consisting of polyimide copolymers represented by general formula (1), general formula (2), general formula (6), and general formula (7) Polyimide copolymers are particularly preferred for obtaining the intended graphite. The target graphite sheet can be obtained by heat-treating these polyimides at a temperature of 2400 ° C. or higher.

Furthermore, it is a polyimide copolymer polyimide film having a repeating unit represented by the general formulas (1) and (2), and 4 / 4′-oxydianiline and paraphenylenediamine are used in a molar ratio of 9/1 to 4 A polyimide film obtained by using a diamine containing at a ratio of / 6 is most preferably used for obtaining graphite for this purpose. By heat-treating these polyimide films at a temperature of 2400 ° C. or higher, the target graphite film of the present invention can be obtained. Above all, the polyimide is a polyimide copolymer having repeating units represented by the general formulas (1), (2), (6) and (7), and the number of each repeating unit is represented by a, b, When c, d and a + b + c + d is s, (a + b) / s, (a + c) / s, (b + d) / s, (c + d) / s is a polyimide film satisfying 0.25 to 0.75 Is most preferably used for the purpose of producing the graphite film of the present invention.

  By using the polyimide described above, the average linear expansion coefficient in the range of 100 to 200 ° C. is 2.5 × 10 −5 cm / cm / ° C. or less, preferably 2.0 × 10 −5 cm / cm / ° C. or less, A polyimide film that is preferably 1.5 × 10 −5 cm / cm / ° C. or less can be obtained. The linear expansion coefficient of the film was measured using a TMA (thermomechanical analyzer), first the sample was heated to 350 ° C. at a temperature increase rate of 10 ° C./min, then air-cooled to room temperature, and then increased again to 10 ° C./min. The temperature was increased to 350 ° C. at a temperature rate, and the average linear expansion coefficient was 100 ° C. to 200 ° C. from the second temperature increase. Further, the elastic modulus of the film is 200 kg / mm 2 or more, further 250 kg / mm 2 or more, more preferably 350 kg / mm 2 or more. The polyimide film used in the present invention has a birefringence Δn indicating in-plane orientation of 0.13 or more, preferably 0.15 or more, and most preferably 0.16 or more in any direction in the film plane. It is preferable. Birefringence here is the difference between the refractive index in the in-plane direction of the film and the refractive index in the thickness direction. In this specification, the birefringence Δnx in the in-plane direction of the film is given by Equation 1.

A specific measurement method will be described. When a film sample is cut into a wedge shape, sodium light is applied from a direction perpendicular to the X direction in the film plane, and observed with a polarizing microscope, interference fringes are observed. When the number of interference fringes is n, the birefringence Δnx in the X direction in the film plane is expressed by Equation 2.

Here, λ is the wavelength of sodium light 589 nm, and d is the width (width) (nm) of the sample. Details are described in "New Experimental Chemistry Course" Vol. 19 (Maruzen Co., Ltd.).

  The above-mentioned “birefringence Δn is in any direction in the film plane” means, for example, 0 ° direction, 45 ° direction, 90 ° direction, 135 ° in the plane with reference to the flow direction during film formation. It means in any direction.

<Graphitization process and structure of polymer film>
Next, the process of graphitization of the polymer film will be described. As an example, the process of graphitization of a polyimide film will be described, but the present invention is not limited to the following.

  In the present invention, the starting polyimide film is preheated in nitrogen gas to perform carbonization. The preheating is usually performed at a temperature of about 1000 ° C., and for example, when pretreatment is performed at a rate of temperature increase of 10 ° C./min, it is desirable to hold for about 30 minutes in a temperature range of 1000 ° C. In the pretreatment stage, it is effective to apply a pressure in the plane direction that does not cause the film to break so that the orientation of the starting polymer film is not lost.

  Next, the film carbonized by the above method is set in an ultrahigh temperature furnace, and graphite is performed. Graphitization is carried out in an inert gas, but argon is most suitable as the inert gas, and it is more preferable to add a small amount of helium to the argon. The treatment temperature is preferably 2400 ° C or higher, more preferably 2700 ° C or higher.

  The higher the treatment temperature is, the higher the quality of graphite can be converted, but from the viewpoint of economy, it is preferable that it can be converted to high quality graphite at the lowest possible temperature. In order to create an ultra-high temperature of 2500 ° C. or higher, an electric current is usually passed directly to a graphite heater, and overheating is performed using the juule heat. Graphitization occurs by converting the carbonized film prepared in the pretreatment to a graphite structure, and in that case, the carbon-carbon bond must be cleaved and recombined. In order for the graphitization to occur smoothly, the cleavage and recombination must occur with minimal energy, and the molecular orientation of the starting polyimide film affects the carbon alignment of the carbonized film, which is graphitization. This has the effect of reducing the energy of carbon-carbon bond cleavage and recombination. Therefore, by designing the molecules so that the molecules are oriented and realizing a high degree of orientation, graphitization at a low temperature and conversion to a high-quality graphite film becomes possible.

  The obtained graphite film may have an irregularly shaped pattern having a shortest diameter of 0.1 to 50 μm inside. In the graphite film having such a structure, the surface adhesive force measured based on the adhesive tape / adhesive sheet test method measured based on JIS Z 0237 is 3 N / cm or more, preferably 4 N / cm or more, more preferably 5 N / cm or more. At 3 N / cm or more, when the graphite and the heat-generating component are attached using an adhesive or a pressure-sensitive adhesive, the heat dissipation characteristics inherent to graphite can be exhibited without peeling. Further, the specific level of the appearance of the surface is 6 or more, preferably 8 or more, as measured based on the X-cut tape method measured based on JIS K 5400. When the appearance is 6 or more, graphite and exothermic parts will not peel off when attached using adhesive or adhesive, and the graphite will peel off from the surface due to the wind of the fan after contact with the equipment or after being installed in the device Will not contaminate the electronic equipment.

  Further, the graphite of the present invention may be a graphite film in which the cross-sectional pattern of the surface layer and the cross-sectional pattern other than the surface layer have at least different portions. Furthermore, a part of the cross-sectional pattern of the surface layer may be a graphite film having a substantially rectangular shape with a short side of 5 μm or more formed as a result of laminating substantially rectangular shapes having a thickness of less than 1 μm in parallel. Here, the “surface layer” refers to a range from both surfaces of the film, which is a portion having a thickness within 30% of the outer thickness of the entire film when the cross section of the graphite film is viewed. The structure of the graphite film is as follows: (1) Graphite crystallites develop in the plane direction, these are cross-sectional patterns of a high-density graphite layer laminated in parallel with the film surface shape, and (2) Graphite crystallites develop in the plane direction. Although these are laminated, the cross-sectional pattern of the high-density graphite layer that exists in a wavy state, not parallel to the film surface shape, (3) the graphite crystallites are developed in the plane direction, These are not laminated, and the cross-sectional pattern of the graphite layer rich in the low-density air layer that exists in parallel with the film surface shape. (4) Graphite crystallites are developed in the plane direction. Cross-sectional pattern of a graphite layer rich in low-density air layers that are not laminated and are not parallel to the film surface shape but exist in a wavy state. (5) A cross-sectional pattern of a flake-like graphite layer with no developed graphite crystallites. (6) Cross-sectional patterns other than the above (1) to (5), for example, those formed by the influence of impurities or the like in the graphitization step and not formed with a graphite layer such as a carbon block having no graphene structure can be exemplified. .

  Excellent thermal conductivity in the plane direction requires a high-density graphite layer in which graphite crystallites develop in the plane direction and are laminated. If it is a high-density graphite layer, there is little loss of heat conduction and efficiency is good. Accordingly, among the observed cross-sectional patterns (1) to (6), (1) and (2) are preferable as the cross-sectional pattern exhibiting high thermal conductivity, and (3) is the next preferable. And (4), the next preferred is (5), and the next preferred is (6). If the cross-sectional pattern of the surface layer and the cross-sectional pattern other than the surface layer are only the high-density graphite layer (1), the thermal diffusivity is excellent and the film strength is excellent. Since there is no portion to be buffered when bent, it becomes a graphite film with poor flexibility. Moreover, if the cross-sectional pattern of the surface layer and the cross-sectional pattern other than the surface layer are only the cross-sectional pattern of (3), which is a low-density graphite layer containing an air layer, the flexibility is excellent, but the thermal diffusivity It becomes a graphite film inferior to the strength of the film. Therefore, in the graphite film having both high thermal conductivity and flexibility, the cross-sectional pattern of the surface layer and the cross-sectional pattern other than the surface layer have different combinations in the observed cross-sectional patterns (1) to (6). preferable. There are cross-sectional patterns (1) and (2) in which graphite layers are laminated on the surface layer at high density, and there are cross-sectional patterns (3) and (4) that are graphite layers including an air layer other than the surface layer. It is preferable.

  The graphite film having an irregularly shaped pattern with a shortest diameter of 0.1 to 50 μm inside is heat-treated at a temperature of 2400 ° C. or higher before a raw material film made of a polymer film and / or a carbonized polymer film, and before the heat treatment and In contact with a substance containing metal during heat treatment. Specific methods include, for example, (1) a method in which a metal-containing substance is attached to the surface of the polymer film before heat treatment, and (2) a method in which the carbonized polymer film is graphitized before graphitization. Method of attaching and heat-treating a substance containing metal on the surface, (3) Method of heat-treating a polymer film or carbonized polymer film in a container containing metal, and adding a substance containing metal to the polymer film There are methods, etc.

  A graphite film is produced by holding a raw material film made of a polymer film and / or a carbonized polymer film in an energizable container (A), and applying a voltage to the container and graphitizing it while energizing. Is done.

<Combination of isotropic and anisotropic heat conduction layers>
In the present invention, the anisotropic heat conductive layer is combined with an isotropic heat conductive layer to form a heat dissipation substrate for LED. The large-area graphite has low mechanical strength and is difficult to use as a mounting board for electronic components due to the phenomenon that flake-like graphite peels off along the graphite layer. there were. The present invention compensates for the disadvantage of such graphite by making it a multilayer structure with metal and ceramic, and further realizes heat dissipation characteristics better than when using an isotropic heat conduction layer alone, and a light emitting diode mounting substrate It is used as

  As a composite method, an anisotropic heat conductive layer and an isotropic heat conductive layer can be bonded via an adhesive layer exhibiting excellent adhesion / adhesiveness to form a composite. For forming the adhesive layer, there are a coating method using a dip or a roll, a method of attaching a film-like adhesive material to a graphite film, etc., and any of them can be preferably used. Examples of preferable adhesives for such purposes include silicone adhesives, acrylic adhesives, polyimide adhesives, epoxy adhesives, and COPNA adhesives. These are appropriately selected depending on the temperature environment to be used, but silicone adhesives and polyimide adhesives are preferably used because of their excellent heat resistance.

  The heat radiation effect can be further enhanced by adding various fillers with excellent thermal conductivity to the adhesive / adhesive material when composite. Examples of fillers used for such purposes include silica, SiC, alumina, magnesium oxide, boron nitride, aluminum nitride, copper, aluminum, silver, nickel, and the like.

  Adhering the anisotropic heat conductive layer and the isotropic heat conductive layer without using an adhesive layer is a preferable method for realizing better heat dissipation characteristics.

  When the isotropic heat conduction layer is a metal and the anisotropic heat conduction layer is graphite, a metal layer is formed on the graphite surface by a metal chemical plating method, and thereafter, the metal layer is formed on the metal chemical plating layer by electroplating. It is preferable to form the metal layer to an arbitrary thickness. Examples of the metal for chemical plating used for such purposes include copper, nickel, chromium, silver, aluminum, zinc, and gold. The chemical plating process is performed through processes of degreasing, soft etching, applying a catalyst, and electroless plating.

  As a base metal forming method when forming a metal layer by electroplating, a physical method such as vapor deposition or sputtering may be used. In such a case, in order to realize a relatively strong connection, for example, a metal layer such as nickel may be further provided between the sputtered copper layer and the graphite layer.

  As a method of bonding the anisotropic heat conductive layer and the isotropic heat conductive layer without using an adhesive layer, it may be simply fixed by mechanical pressure. High quality graphite is basically soft and compressed in the film thickness direction, and such properties are used as packings and gaskets. Also in the present invention, it is possible to produce a high thermal conductive substrate by utilizing such inherent properties of graphite. For example, a graphite film may be sandwiched between various ceramic substrates and mechanically fixed. Of course, a metal may be used instead of ceramic, and one may be a metal and the other may be a ceramic structure.

<LED mounting structure>
The configuration shown in FIG. 1 is an example in which the heat dissipation substrate of the present invention is applied to the most basic mounting structure of LEDs. In general, a resin is used as a substrate material in an LED display. However, since the heat conductivity of a normal resin material is low and heat is easily trapped, it is not suitable for lighting at a high output. In the structure of the present invention (FIG. 1), the heat dissipation substrate has a three-layer structure of an insulating ceramic layer 16, an anisotropic heat conductive layer 15, and an isotropic heat conductive layer 17 as isotropic heat conductive layers. Yes. The isotropic heat conductive layer 17 may be an insulating ceramic or a conductive metal material. Although the internal structure of the LED bare chip is not shown, the n-type semiconductor layer of GaN, the active layer, and the p-type semiconductor layer are sequentially formed on an element substrate such as sapphire, SiC, GaAs, or GaP. Lead wires 13 drawn from the N-type semiconductor layer and the P-type semiconductor layer are connected to the circuit 14 formed on the insulating substrate from the bare chip. The bare chip 11 is mounted on an insulating ceramic substrate. In the conventional structure, the heat generated in the bare chip 11 is mainly dissipated through the lead wire. In the structure of the present invention, the heat generated in the bare chip is insulated. Is transmitted to the anisotropic heat conductive layer through the conductive ceramic substrate, where it quickly spreads over the entire substrate and dissipates heat. That is, in this structure, a means for radiating heat from the entire back surface of the substrate on which the LED is not mounted is provided. On the other hand, when the anisotropic heat conductive layer is not provided, the substrate back surface temperature immediately below the bare chip is high, but the temperature of the other portions is low, so the heat dissipation characteristics as a whole are inferior. .

  The configuration shown in FIG. 2 is a case where the isotropic thermal conductive layer 21 on which the bare chip is mounted is a conductive layer such as a metal. In such a case, the circuit 14 is formed on the substrate via the insulating layer 22. The lowest layer of the bare chip is an element substrate, and is mounted on the substrate via an insulator as necessary. Other structures and heat dissipation mechanisms are the same as in FIG.

  The configuration shown in FIG. 3 is a mounting structure employed in an LED dot matrix display. In the LED display, a plurality of LEDs are mounted. At this time, a partition wall 31 is provided between the elements. This partition functions to increase the contrast between the light emission and the non-light emitting portion of the LED. This partition is also important for the role of heat dissipation, and it is important to make the temperature of the plurality of LEDs as uniform as possible. Therefore, a metal or ceramic material having excellent heat dissipation characteristics is used as the partition wall. As this partition, it is useful to use the heat dissipation substrate material of the present invention comprising an isotropic heat conductive layer / an anisotropic heat conductive layer / isotropic heat conductive layer.

  FIG. 4 shows a structure in which a concave portion is provided in a heat-radiating substrate such as ceramic, an LED bare chip is mounted in the concave portion, and a circuit formed on the surface is connected with a lead wire. By adopting such a structure, the distance between the LED, which is a heating element, and the anisotropic heat conductive layer is shortened, and heat is diffused more effectively. In addition, the isotropic heat conductor surface cut obliquely contributes to the role of efficiently reflecting light.

  FIG. 5 shows an example of an LED mounting structure that radiates light to the front surface more efficiently. The bare chip 11 mounted on the insulating substrate 53 and the circuit 14 are directly bonded. The partition 52 is cut obliquely so that light reflection occurs effectively, and the light from the LED and the light reflected by the partition are radiated forward through the condenser lens 51. Needless to say, the heat generated in the bare chip at this time is efficiently dissipated through the substrate of the present invention.

  Hereinafter, the present invention will be described more specifically with reference to examples.

<Graphite film>
First, five types of graphite films used as anisotropic heat conductive layers in the examples of the present invention will be described, but the present invention is not limited to these examples.

(1) Graphite film-A
Manufactured by Graphtec (eGRAF-HiTherm, sales source Sakai Kogyo Co., Ltd., product number 710). Thickness 250 μm, surface direction thermal conductivity 240 W / mK, thickness direction thermal conductivity 6 W / mK.

(2) Graphite film-B
Made by Suzuki Sogyo Co., Ltd. (Super λ-GS-300). Thickness 300 μm, surface direction thermal conductivity 300 W / mK, thickness direction thermal conductivity 5-10 W / mK.

(3) Graphite film-C
Panasonic (PGS graphite sheet, product number: EYGS182310). Thickness 70 μm, plane direction thermal conductivity 700 W / mK, thickness direction thermal conductivity 5 W / mK.

(4) Graphite film-D
From 10 g of acetic anhydride and 10 g of isoquinoline to 100 g of a 18 wt% DMF solution of polyamic acid prepared by synthesizing pyromellitic dianhydride, 4,4′-diaminodiphenyl ether and p-phenylenediamine in a molar ratio of 4/3/1. The resulting curing agent was mixed, stirred, defoamed by centrifugation, and cast onto an aluminum foil. The process from stirring to defoaming was performed while cooling to 0 ° C. The laminate of the aluminum foil and the polyamic acid solution was heated at 120 ° C. for 150 seconds to obtain a gel film having self-supporting properties. This gel film was peeled off from the aluminum foil and fixed to the frame. This gel film was heated at 300 ° C., 400 ° C., and 500 ° C. for 30 seconds each to produce a polyimide film having an average linear expansion coefficient of 100 to 200 ° C. of 1.6 × 10 −5 cm / cm / ° C. The film thickness is 75 μm. The birefringence of the film produced by these methods was 0.14.

The obtained film was heated up to 1000 ° C. at a rate of 10 ° C./min in nitrogen gas using an electric furnace, and preliminarily treated at 1000 ° C. for 1 hour. The obtained carbonized film is set inside a cylindrical graphite heater so that it can be stretched and contracted freely, heated to 2800 ° C. at a heating rate of 20 ° C./min, held for 10 minutes, and then 40 ° C./min. The temperature dropped at a rate of. The treatment was performed under a pressure of 0.5 kg / cm ^{2 in} an argon atmosphere.

  It was found that this polyimide film can be converted to high-quality graphite at 2800 ° C. The obtained graphite film-D had a thickness of 40 μm, a plane direction thermal conductivity of 1200 W / mK, and a thickness direction thermal conductivity of 6 W / mK.

(5) Graphite film-E
From 10 g of acetic anhydride and 10 g of isoquinoline to 100 g of a 18 wt% DMF solution of polyamic acid synthesized from pyromellitic dianhydride, 4,4′-diaminodiphenyl ether and p-phenylenediamine in a molar ratio of 3/2/1. The resulting curing agent was mixed, stirred, defoamed by centrifugation, and cast onto an aluminum foil. The process from stirring to defoaming was performed while cooling to 0 ° C. The laminate of the aluminum foil and the polyamic acid solution was heated at 120 ° C. for 150 seconds to obtain a gel film having self-supporting properties. This gel film was peeled off from the aluminum foil and fixed to the frame. This gel film was heated at 300 ° C., 400 ° C., and 500 ° C. for 30 seconds each to obtain a polyimide film (thickness 75 μm) having an average linear expansion coefficient of 100 × 200 ° C. to 1.0 × 10 ⁻⁵ cm / cm / ° C. Manufactured. The birefringence of this film was in the range of 0.15 to 0.16. Using this film, graphitization was performed at 2800 ° C. as in the case of (4). The obtained graphite film-E had a thickness of 40 μm, a plane direction thermal conductivity of 1400 W / mK, and a thickness direction thermal conductivity of 10 W / mK. (6) Graphite film-F
A 10 wt% methanol solution of iron nitrate was applied to the carbonized product of the 125 μm polyimide film obtained in (5) above, and then sandwiched between graphite plates and set in a graphite container. The entire container was heated to 3000 ° C. under reduced pressure at 2100 ° C. or lower and argon atmosphere at 2100 ° C. or higher using a graphitization furnace, and then heat-treated at 3000 ° C. for 1 hour to prepare a graphite film F. . The obtained graphite film F had a thickness of 70 μm, a plane direction thermal conductivity of 1000 W / mK, and a thickness direction thermal conductivity of 5 W / mK.

<Method for measuring physical properties of graphite film>
The thermal diffusivity was measured at 10 Hz in an atmosphere of 20 ° C. using a thermal diffusivity measuring apparatus (“LaserPit” available from ULVAC Riko Co., Ltd.) by an optical alternating current method. Thermal conductivity and thermal conductivity were calculated from the measured thermal diffusivity using the values of density and specific heat. The density of the graphite film was calculated by dividing the weight (g) of the graphite film by the volume (cm ³ ) calculated by the product of the vertical, horizontal and thickness of the graphite film. In addition, the average value measured by arbitrary 10 points | pieces was used for the thickness of a graphite film.

  The obtained graphite film was cut with a cutter knife into a strip size of 20 mm long × 10 mm wide. Furthermore, a fine cut is made in the surface direction with a razor at one end of this film, a force is applied from the opposite side of the cut, and the cross section is taken out by cleaving the film. SEM (Hitachi scanning electron microscope S-4500 type, The cross section of the film was observed with an acceleration voltage of 5 kV.

  Graphite films A and B use natural graphite as a raw material, and the cross-sectional pattern other than the surface layer and the surface layer is a cross-sectional pattern of a low-density graphite layer including an air layer, where graphite crystallites are not developed. Met.

  It is presumed that the graphite film C is produced by heat-treating a polyimide film as a raw material, and the cross-sectional pattern other than the surface layer and the surface layer has developed graphite crystallites in the plane direction. It was a pattern of the cross section of the low-density graphite layer.

  In the graphite film D, the cross-sectional pattern other than the surface layer and the surface layer has graphite crystallites developed in the plane direction, but these are not laminated, and the cross-sectional pattern is the cross-sectional pattern of the graphite film C. It turns out that it is similar. However, the thermal diffusivity is superior to graphite films, A, B, and C.

In the cross section of the graphite film D, an irregularly shaped pattern (nonuniform layer) having a shortest diameter of 0.1 to 50 μm, which was not observed in the original raw material film, was formed inside the film. Further, there was no air layer between the layers such as the graphite films 1 to 3 and 5, but it was in a dense state. Since it has such a structure, in addition to excellent heat conduction characteristics, lead hardness is HB or higher, density is 1.9 g / cm ³ or higher, beer strength is 5.0 N / cm or higher, and appearance is 8 or higher. Excellent characteristics.

  The pencil hardness of the graphite film was evaluated in accordance with the test method 8.4.1 of “Paint General Test Method” of JIS K 5400 (1990) (JIS K 5600 (1999)). The peel strength of the graphite film was evaluated according to JIS Z 0237 (1980) “Testing method for adhesive tape / adhesive sheet”. A larger value means higher adhesion to the surface adhesive or pressure-sensitive adhesive. The appearance of the graphite film was evaluated in accordance with the 8.5.3 X-cut tape method of “JIS K 5400 (1990) (JIS K 5600 (1999))“ Paint General Test Method ”. A value is shown in the range of 0-10, and it means that there are few peeling of a surface, so that a value is large.

(Examples 1-6)
The six types of graphite (A, B, C, D, E, F) were used for electroless Cu plating on both surfaces. Tables 1 and 2 show pretreatment conditions and plating conditions for electroless plating. In order to form a stable chemical plating film, it is necessary to strictly select pretreatment conditions and plating conditions. In particular, pretreatment conditions are important for plating a chemically stable graphite layer surface.

After the electroless plating, a copper electrolytic plating film was formed in an arbitrary thickness using a normal electrolytic plating method. The sum of the thicknesses of the electroless plating and the electrolytic copper plating layer was set to 40 μm.

For the purpose of estimating the heat dissipation characteristics of the obtained substrate (area 10 × 10 cm ² ) composed of the first copper layer / graphite / second copper layer, a ceramic heater (a micro ceramic heater manufactured by Sakaguchi Electric Heat Co., Ltd., MS-3) (Size 10 × 10 mm ² ) was placed, a constant power (16 W) was applied, and the temperature rise of the heater was measured with a thermocouple (note that the measured value includes an error of about ± 2 to 3 ° C.) The better the heat conduction and the better the heat dissipation characteristics, the more the temperature of the ceramic heater will not rise, and the results obtained are shown in Table 3. For comparison, the same experiment was conducted using a copper plate of the same thickness. The temperature of the ceramic heater surface was measured, and the obtained results are shown in Table 4 as a comparative example, and the surface temperature of the heater alone is about 150 ° C. under the above conditions.

In the three-layer substrate of copper / graphite / copper according to the present invention, the temperature was 50 ° C. to 60 ° C., and a significant heat dissipation effect could be confirmed. Moreover, in the comparative example, the heater surface temperature when attaching a 120 μm thick copper substrate that is the same thickness as the substrates of Examples D and E is 85 ° C. (Comparative Example 3). The heater surface temperature when a copper substrate having a thickness of 150 μm, which is the same thickness as the substrate, is attached is 70 ° C. (Comparative Example 2) The substrate according to the present invention is compared with, for example, a substrate made only of copper. It can be seen that it has excellent heat dissipation characteristics. Further, when a 330 μm copper substrate having the same thickness as the substrate of Example A was used (Comparative Example 1), the temperature of the heater surface was 60 ° C., which was almost equivalent to Example 1. That is, in Examples C, D, E, and F, although the thickness thereof is less than half that in the case of Comparative Example 1, it has excellent heat dissipation characteristics that are equal or equal to or greater. It became clear and the usefulness of this invention was confirmed.

(Examples 7 to 12)
In the same manner as in Example 4, the thickness of the copper layer of the first layer and the second layer was changed using graphite D, and the heat dissipation effect was measured using the same ceramic heater. The results are shown in Table 5. The thickness of the first copper layer has a great influence on the heat dissipation characteristics. When the thermal conductivity in the plane direction is 1200 W / mK as in the case of the graphite D used in this study and is much larger than the thermal conductivity of copper 398 W / mK, the thinner the first layer is, The heat dissipation effect is excellent. Desirably, there is no first copper layer and graphite is the first layer in terms of characteristics. Graphite F can be preferably used when the graphite layer is used as the first layer because the graphite powder does not fall off.

  On the other hand, the influence of the second copper layer is not as great as that of the first layer. The role of the second layer is to dissipate heat spread over the entire substrate due to the effect of the graphite layer, and although there is an influence of the heat capacity, the influence will be small from the viewpoint of the heat dissipation effect.

(Examples 13 to 18)
The above three types of graphite (A, C, D) were used, and an aluminum layer was formed on the surface by vapor deposition. Next, the aluminum / graphite / aluminum three-layer plate thus obtained was press-bonded onto the aluminum plate. The heat dissipation characteristics of the obtained heat dissipation substrate were measured using the same ceramic heater as in Example 1. The results are shown in Table 6. For comparison, the heat dissipation characteristics were measured using a single aluminum plate having the same thickness, and the effects were compared. When aluminum having a thickness of 150 μm, 180 μm, and 1250 μm was used, the surface temperature of the ceramic heater was 98 ° C., 95 ° C., and 85 ° C., respectively. From this, it was confirmed that the method of the present invention using graphite has an excellent heat dissipation effect.

(Examples 17 to 19)
Two discs with a diameter of 100 mm and a thermal conductivity of 20 W / mK obtained by processing Nippon Tungsten Co., Ltd. alumina (trade name NPA-5) were prepared (each with a thickness of 2 mm and 10 mm). The periphery of the film (A, C, D) was clipped, and the same ceramic heater as in Example 1 was attached to the surface (2 mm thick plate side), and the surface temperature was measured. When the graphite film was not sandwiched, the heater surface temperature was 105 ° C., but when graphite A, C, and D were sandwiched, they were 95 ° C., 90 ° C., and 84 ° C., respectively. From this, it was found that excellent heat dissipation characteristics could be realized by sandwiching graphite.

(Examples 20 to 25)
TSE3080 silicone resin manufactured by GE Toshiba Silicone Co., Ltd. was applied to both surfaces of graphite (A, B, C, D, E, F), and two sheets of aluminum nitride manufactured by Nippon Tungsten Co., Ltd. (trade name NPL-2) ), A heat radiating substrate was produced by sandwiching it with a thickness of 3 mm, a diameter of 100 mm, and a thermal conductivity of 170 W / mK. The heat dissipation characteristics were examined by the same method, but graphite A and B did not show the effect of sandwiching the graphite. This is because the heat conduction in the surface direction of graphite A and B is 240 W / mK and 300 W / mK, respectively, which is larger than 170 W / mK of aluminum nitride, but the heat conduction in the thickness direction of graphite is 6 W / mK, respectively. It is thought that the influence appeared because it was as small as 5 to 10 W / mK.

  However, graphite C, D, E, and F were able to confirm heat dissipation characteristics that were 10 ° C. higher than that of aluminum nitride having the same thickness. This is presumably because the high thermal conductivity (700 W / mK or more) in the plane direction in these graphites contributed to the rapid diffusion of heat.

  From these facts, when an anisotropic heat conductor is used, it is desirable that the heat conductivity in the high heat conduction direction of the anisotropic heat conductor is preferably at least twice that of the isotropic heat conductor used. I understand.

(Example 26)
Based on the above examples, a verification test was conducted with LEDs. (1) Substrate mounting substrate with copper wiring on polyimide resin, (2) Substrate formed by baking copper paste on aluminum nitride substrate to form a circuit, (3) The outermost surface is the aluminum nitride circuit, and the back surface is graphite. A comparative experiment was performed with three types of substrates, D attached to the substrate. An element capable of applying a voltage of 3 V to the prepared light emitting diode and allowing a current of 200 mA to flow was used. When the increase in the junction temperature of the light emitting diode (LED) is increased, the light output is relatively decreased. On the contrary, if the emission intensity when each substrate is used is measured, the heat dissipation effect of the substrate can be estimated. As a result, assuming that (1) the emission intensity of the substrate is 100, the emission intensity of about 120 was obtained for the substrate of (2) and about 130 for the substrate of (3). From this, it was found that the junction temperature can be lowered by 30 ° C. or more by using the substrate (3).

11 LED chip 12 Transparent sealing resin 13 Lead wire 14 Wiring circuit 15 Anisotropic heat conduction layer (graphite layer)
16 Insulating Isotropic Thermal Conductive Layer 17 Insulating Isotropic Thermal Conductive Layer 21 Conductive Isotropic Thermal Conductive Layer (Metal Layer)
22 Insulating layer 23 Conductive isotropic thermal conductive layer (metal layer)
31 Anisotropic heat conduction layer (graphite layer)
32 Conductive isotropic heat conduction layer (metal layer)
41 Insulating Isotropic Thermal Conductive Layer 51 Transparent Sealing Resin 52 Insulating Isotropic Thermal Conductive Layer 53 Conductive Isotropic Thermal Conductive Layer (Metal Layer)

Claims (18)

It is a heat dissipation board having two or more layers including at least an isotropic heat conductive layer and an anisotropic heat conductive layer,
Anisotropy of thermal conductivity in the anisotropic heat conductive layer is 10 times or more,
A heat dissipation board having a thermal conductivity in the direction of high thermal conductivity in the anisotropic heat conductive layer that is at least twice as large as that of the isotropic heat conductive layer. The anisotropic heat conductive layer is a graphite layer having at least anisotropy of thermal conductivity;
The heat dissipation substrate according to claim 1, wherein the thermal conductivity in the plane direction of the graphite layer is 200 W / mK or more.   The heat dissipation substrate according to claim 1, wherein the isotropic heat conductive layer includes a metal having a thermal conductivity of 100 W / mK or more.   The heat dissipation substrate according to any one of claims 1 to 3, wherein the isotropic heat conductive layer includes a ceramic having a thermal conductivity of 10 W / mK or more.   The heat dissipation substrate according to any one of claims 1 to 4, wherein the anisotropic heat conduction layer has a maximum thickness of 1 mm or less.   The heat dissipation substrate according to claim 1, wherein the isotropic heat conductive layer and the anisotropic heat conductive layer in the substrate are in direct contact.   A heat dissipation substrate, wherein the metal according to claim 3 is formed on the surface of the graphite layer according to claim 2 by an electroless plating method.   The at least one polymer film selected from the group consisting of polyimide, polyoxazole, and polyparaphenylene vinylene is used as the graphite having thermal conductivity anisotropy according to claim 2 in an inert gas at a temperature of 2400 ° C or higher. The heat dissipation substrate according to any one of claims 2 to 7, which can be obtained by heat treatment. It is a configuration of two or more layers including at least an isotropic heat conductive layer and an anisotropic heat conductive layer,
Anisotropy of heat conduction in the anisotropic heat conduction layer is 10 times or more,
A substrate for a light emitting diode, wherein the thermal conductivity in the direction of high thermal conductivity in the anisotropic thermal conductive layer is at least twice as large as that of the isotropic thermal conductive layer. The anisotropic heat conductive layer is a graphite layer having at least anisotropy of thermal conductivity;
The light emitting diode substrate according to claim 9, wherein a thermal conductivity in a plane direction of the graphite layer is 200 W / mK or more.   The light-emitting diode substrate according to claim 9, wherein the isotropic heat conductive layer includes a metal having a thermal conductivity of 100 W / mK or more.   The light-emitting diode substrate according to claim 9, wherein the isotropic thermal conductivity layer includes a ceramic having a thermal conductivity of 10 W / mK or more.   The substrate for a light-emitting diode according to claim 9, wherein the anisotropic heat conductive layer has a maximum thickness of 1 mm or less.   The substrate for a light emitting diode according to claim 9, wherein the isotropic heat conductive layer and the anisotropic heat conductive layer in the substrate are in direct contact with each other.   A substrate for a light emitting diode, which can be obtained by forming the surface of the graphite layer according to claim 10 by electroless plating.   The one or more polymer films selected from the group consisting of polyimide, polyoxazole, and polyparaphenylene vinylene, wherein the graphite having thermal conductivity anisotropy according to claim 10 is at a temperature of 2400 ° C or higher in an inert gas. A substrate for a light-emitting diode, which can be obtained by heat treatment with. A light emitting diode mounting substrate, wherein the outermost surface includes a metal, and includes the light emitting diode substrate according to any one of claims 9 to 16, and a light emitting diode chip.
The light emitting diode chip is directly mounted on the substrate,
Light emitting diode mounting board. A light emitting diode mounting substrate, wherein the outermost surface includes ceramic, and includes the light emitting diode substrate according to any one of claims 9 to 16, and a light emitting diode chip.
The light emitting diode chip is directly mounted on the substrate,
Light emitting diode mounting board.