JP2007217206A - Graphite film, thermal diffusion film using the same and thermal diffusion method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the thermal resistance of a graphite film and a heating element, and to provide a film capable of dissipating heat without impairing thermal conductivity characteristics peculiar to the graphite film. <P>SOLUTION: Part of a graphite film having a compression rate of ≥20% and anisotropy of thermal conductivity between film plane and film thickness directions is compressed by application of pressure so that apparent difference in thickness is produced, and an uncompressed part and a heating element are brought into contact with each other in such a way that the uncompressed part is pressurized. An adhesive layer (layer having adhesion function) is attached to the compressed part and this compressed part is stuck to a heat sink. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heat diffusing film (also referred to as a heat radiating film) and a heat diffusing method, which are excellent in heat dissipation characteristics and have a reduced thermal resistance with a heat source.

  In recent years, the performance of electronic devices such as personal computers, mobile phones, and PDAs has improved significantly, which is due to the significant improvement in CPU performance. Along with such improvement in CPU performance, the amount of heat generated by the CPU also increases remarkably, and how to dissipate heat in electronic devices is an important issue.

  As heat countermeasures, there are methods such as air cooling with fans, heat pipes, water cooling with water, etc., but these all require new heat dissipation devices, which not only increase the weight of the equipment, but also noise and There is a disadvantage that it causes an increase in the amount of electricity used.

  On the other hand, the method of diffusing the heat generated by the CPU to a large area as quickly as possible aims to increase the cooling efficiency, and is the most realistic cooling method for electronic devices such as mobile phones and personal computers. It is.

  In recent years, sheet-like graphite has attracted much attention as a heat conductive sheet used for such purposes. The reason is that a high-quality graphite sheet has a very high thermal conductivity of 100 to 1000 W / mK, and the thermal conductivity (0.8 to 6.5 W / mK) of other gel-like or sheet-like heat dissipation materials. This is because it is optimal for diffusing heat with remarkably high performance compared to the characteristics of

  The first method for producing an artificial graphite film used for such a purpose is a method called an expanded graphite method. This is produced by immersing natural graphite in a mixed solution of concentrated sulfuric acid and concentrated nitric acid and then rapidly heating it. The graphite produced in this way is processed into a film after removing the acid by washing. While the thermal conductivity value of the graphite film produced in this manner is about 100 to 400 W / mK, the mechanical strength is weak, and the graphite powder has a problem of peeling off (expressed as powder falling), It is used as a heat conductive sheet because it is cheap and easy to manufacture thick materials.

  The second method for producing an artificial graphite film is a method in which a special polymer is graphitized by direct heat treatment. Polymers used for this purpose include polyoxadiazole, polyimide, polyparaphenylene vinylene and the like. This method is essentially a method that does not contain impurities such as an acid, and further has a feature that a very excellent thermal conductivity in the plane direction (300 to 1000 W / mK) can be obtained. (For example, there are patent documents (1), (2), (3), (4), (5)).

In addition, a composite of a graphite film and an adhesive polymer material having adhesiveness, insulation, and flexibility has been performed. Natural rubber and acrylic are the most common adhesive materials used as the adhesive layer for thermally conductive graphite sheets. Silicone rubber and polyimide adhesives with excellent heat resistance and adhesiveness may be used as required. . For example, a heat conductive sheet for electric parts (Patent Documents (6), (7), (8)) characterized in that a silicone rubber is applied to one or both surfaces of a graphite sheet, and polyurethane or a polyurethane derivative is formed on the graphite sheet. A heat-dissipating component (Patent Document (10)) having a primer layer and a technique for firmly bonding graphite and the silicone composition (Patent Document (9)), a graphite sheet and an adhesive layer having a thickness of 100 μm or less provided on the surface of the graphite sheet. )) And the like are disclosed.
Japanese Patent Publication No. 1-49642. Japanese Patent Publication No. 1-57044. Japanese Patent Laid-Open No. 4-310569. JP-A-3-75211. JP 2000-247740 A. Publication No. 3-51302. JP-A-8-83990. JP-A-9-17923. JP 2001-287298 A. Japanese Patent Laid-Open No. 11-317480. JP 2002-160970 A.

<Problems remaining in the prior art>
The graphite film heat-dissipating sheets described in the above-mentioned Patent Documents (1) to (5) have a drawback that they do not have adhesiveness and cannot be connected to a heating element or a cooling body as they are. For heat dissipation / heat diffusion applications, it is necessary to make sufficient contact between the heat source such as the CPU and the graphite film, which is the heat conductor, and it is also necessary to make sufficient contact with the cooling / heat dissipating member such as cooling fins and housings. Also occurs. Especially when the heat source or radiator has an uneven surface, sufficient contact cannot be obtained, increasing the thermal resistance at the joint surface and taking advantage of the high thermal conductivity of the graphite film. Can not.

  In order to solve such a problem of the heat-dissipating graphite film, a composite of a graphite film and an adhesive polymer material having adhesiveness, insulating properties and flexibility has been performed. Natural rubber and acrylic are the most common adhesive materials used as the adhesive layer for thermally conductive graphite sheets. Silicone rubber and polyimide adhesives with excellent heat resistance and adhesiveness may be used as required. . For example, a heat conductive sheet for electric parts (Patent Documents (6), (7), (8)) characterized in that a silicone rubber is applied to one or both surfaces of a graphite sheet, and polyurethane or a polyurethane derivative is formed on the graphite sheet. A heat-dissipating component (Patent Document (10)) having a primer layer and a technique for firmly bonding graphite and the silicone composition (Patent Document (9)), a graphite sheet and an adhesive layer having a thickness of 100 μm or less provided on the surface of the graphite sheet. )) And the like are disclosed.

  However, all of these examples have a drawback that the thermal conductivity of the insulating layer is low, and therefore, the excellent thermal conductivity characteristic of the graphite film is impaired.

<Problem of the present invention>
An object of the present invention is to provide a heat diffusion film that can reduce heat resistance between the graphite film and the heating element and can radiate heat without impairing the heat conduction characteristics of the graphite film.

(1) The first of the present invention is
“A part of the graphite film having a compression ratio of 20% or more and anisotropy of thermal conductivity in the film surface direction and the film thickness direction is compressed by the pressure treatment in the thickness direction,
A graphite film characterized in that portions having different compression states coexist in the graphite film. "
It is.

(2) The second aspect of the present invention is
"The graphite film in which the different compression states coexist,
At least the apparent thickness of any one of two or more portions selected from the group consisting of an uncompressed portion, a low-compressed portion of the pre-compressed portion, and a high-compressed portion of the pre-compressed portion and having different compression states. The graphite film according to (1), characterized in that a difference of "
It is.

(3) The third aspect of the present invention is
“A graphite film having a compressibility of 20% or more and anisotropy of thermal conductivity in the film surface direction and the film thickness direction.”
It is.

(4) The fourth aspect of the present invention is
“A graphite film having a compression ratio of 20% or more and having anisotropy of thermal conductivity in the film surface direction and the film thickness direction,
A graphite film that can be obtained by treating a raw material film composed of a polymer film and / or a carbonized film in an inert gas or in vacuum at a temperature of 2400 ° C. or higher,
The graphite film according to any one of (1) to (3), which is a graphite film expanded to 80% or more of the thickness of the raw material film. "
It is.

(5) The fifth aspect of the present invention is
“The graphite film according to any one of (1) to (4);
A heat diffusion film comprising a layer having an adhesive function,
A thermal diffusion film, wherein the layer having an adhesive function is provided on a part of the film surface of the graphite film. "
It is.

(6) The sixth aspect of the present invention is
“The layer having an adhesive function described in (5) is formed on a low compression portion and / or a high compression portion of the precompressed portion of the graphite film according to any one of (1) to (2). A heat diffusion film characterized by being formed. ",
It is.

(7) The seventh of the present invention is
“A layer having an adhesive function and / or an electrically insulating function is formed on the surface of the low-compressed part and / or the high-compressed part of the pre-compressed part of the graphite film,
On at least one surface of the uncompressed portion of the graphite film,
The heat diffusion film according to (5), wherein a layer having the adhesion function and / or the electrically insulating function is not formed. "
It is.

(8) The eighth aspect of the present invention is
“The thermal diffusion film according to any one of (5) to (7), wherein the thermal conductivity in the plane direction of the graphite film is 100 W / mK or more.”
It is.

(9) The ninth of the present invention is
"The polymer film described in (4)
The thermal diffusion film according to any one of (5) to (8), which is at least one selected from the group consisting of polyimide, polyoxadiazole, and polyparaphenylene vinylene. "
It is.

(10) The tenth aspect of the present invention is
“(5) to (9), wherein the polyimide film according to (9) has an average linear expansion coefficient in the range of 100 to 200 ° C. of 2.5 × 10 −5 cm / cm / ° C. or less. The thermal diffusion film according to any one of the above ”.
It is.

(11) The eleventh aspect of the present invention is
“The thermal diffusion film according to any one of (5) to (10), wherein the birefringence of the polyimide film according to (9) is 0.13 or more.”
It is.

(12) The twelfth aspect of the present invention is
“The uncompressed portion of the graphite film according to any one of (1), (2), and (4) is brought into contact with a heating element, and further connected so that the uncompressed portion is pressurized. And thermal diffusion method. ",
It is.

(13) The thirteenth aspect of the present invention is
“The thermal diffusion method according to (12), wherein the already compressed portion of the graphite film according to any one of (1), (2), and (4) is provided with a heat dissipation portion through a layer having an adhesive function. A thermal diffusion method characterized by being joined. ",
It is.

  According to the present invention, the thermal resistance between the graphite film and the heating element can be reduced, and the excellent heat conduction characteristics inherent in the graphite film can be effectively utilized. As a result, the heat of the heating element can be diffused smoothly.

According to the second configuration of the present invention,
The uncompressed portion is used for joining with the heating element, and a connection with low thermal resistance can be realized by compressing at the time of joining. The compressed portion has a role of diffusing the heat transferred from the heating element to the graphite, and this portion can enhance the heat diffusion performance by being compressed.

According to the fifth configuration of the present invention,
The portion of graphite that is not provided with a layer having an adhesive function is mainly used for joining to the heating element. In this case, the graphite layer has a compression ratio of 20% or more, so that it is compressed. It is possible to maintain a good connection by pressing and joining to the heating element. A portion provided with a layer having an adhesion function of graphite is used by being joined to a portion that plays a role of heat dissipation.

According to the configuration (6) of the present invention,
As described in the second section of the present invention, the compressed portion has excellent thermal diffusivity, so it is possible to remarkably improve the heat radiation efficiency by sticking it to the necessary part of the heat radiator (such as the bottom of the heat sink). I can do it.

  The compressed portion that contributes to heat dissipation plays a role of heat diffusion, but at the same time, it is necessary that the portion other than the heating element is not affected by heat or electrical influence. Therefore, it is preferable to provide an insulating layer for the compressed portion. According to the (7) configuration of the present invention, the compression portion contributing to heat dissipation plays a role of heat diffusion, but at the same time, it is possible to prevent heat and electrical influences on portions other than the heating element.

  As already described in the background section, the graphite film has excellent heat conduction characteristics in the plane direction, while the heat conduction in the thickness direction of the film is about 10 W / mK. With the configuration (8) of the present invention, a graphite film having such anisotropy of thermal conductivity is preferable for the thermal diffusion film of the present invention.

According to the ninth configuration of the present invention,
By using these polymer films as raw materials, a heat-dissipating graphite film that meets this purpose can be obtained.

According to the tenth configuration of the present invention,
By using such a polyimide film as a raw material, a graphite thermal diffusion film meeting this purpose can be obtained.

With the (11) configuration of the present invention,
By using such a polyimide film as a raw material, a graphite thermal diffusion film meeting this purpose can be obtained.

  By adopting the heat dissipation method described in item (13) of the present invention, the heat resistance of the heat generating element and graphite is reduced, and the performance of the heat dissipating element can be improved by using such a method. The heat dissipation effect can be realized.

  Each component of the present invention will be described.

<Graphite film>
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. Furthermore, the thermal conductivity in the thickness direction of graphite is characterized by being about 1/400 in the plane direction. Since the object of the present invention is thermal diffusion (heat dissipation), 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 film is small, the thickness in the thickness direction is preferably as small as possible, and the method of joining with the heating element is important. In other words, how to reduce the thermal resistance is important.

  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. The graphite film used for the purpose of the present invention preferably has a thermal conductivity in the film surface direction of 100 W / mK or more and anisotropy with the thermal conductivity in the direction perpendicular to the film surface of 10 times or more. As a practical method for producing graphite that can be 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) heat treating a polymer film. Can be mentioned graphite film.

  As the graphite film obtained by the production method of (1), a film having a thermal conductivity in the film surface direction of 100 to 400 W / mK, a thermal conductivity in the thickness direction of 5 to 20 W / mK, and a thickness of 100 to 1000 μm is obtained. It is done. This manufacturing method 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, and the obtained graphite powder is further subjected to rolling roll molding or press compression to obtain film-like graphite.

  On the other hand, in the method (2), a graphite film having 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 is obtained. Any of these is preferably used for the purpose of the present invention. This graphite film is obtained by heat-treating a raw material film made 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, polyimide is easy to progress graphitization of the film, it is easy to become graphite with excellent thermal conductivity, and furthermore, an expanded graphite film can be obtained by controlling the process of carbonization and graphitization. Preferred raw material.

  As the graphite used for the purpose of the present invention, heat-treating 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 at a temperature of 2400 ° C. or more It is preferable for producing an expanded graphite film by realizing excellent thermal conductivity.

  In addition, it is preferable to heat-treat a polyimide film having a birefringence of 0.13 or more at a temperature of 2400 ° C. or more in order to produce a graphato film having excellent thermal conductivity and an expanded state.

  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 heat-treated at a temperature of 2400 ° C. or more. It is preferable to produce a graphite film in order to achieve excellent thermal conductivity and to produce an expanded graphite film.

The polyimide preferably used for such graphitization is
A polyimide having at least one repeating unit selected from the group consisting of repeating units represented by the following formulas (1), (2), (3), and (4), or the following formula (1) , (2), (3), and a polyimide copolymer film having at least two types of repeating units selected from the group consisting of repeating units represented by (4), or Formula (1), Formula The object is achieved by being a mixture film of at least two kinds of polyimide copolymers selected from the group consisting of polyimide copolymers represented by (2), formula (3) and formula (4). I can do it.

@ 0001

@ 0002

@ 0003

@ 0004

It is. R1 is

@ 0005

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

@ 0006

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-.

  Also, a polyimide copolymer having at least two types of repeating units selected from the group consisting of the repeating units represented by the above formulas (1) and (2) and the following formulas (7) and (8), or The polyimide copolymer containing a mixture of at least three or more selected from the group consisting of polyimide copolymers represented by formula (1), formula (2), formula (7), and formula (8) It is particularly preferable for obtaining the target graphite.

@ 0007

@ 0008

Furthermore, it is a polyimide copolymer polyimide film having a repeating unit represented by formulas (1) and (2), wherein 4,4′-oxydianiline and paraphenylenediamine are in a molar ratio of 9/1 to 4 /. A polyimide film obtained by using a diamine containing 6 is most preferably used to obtain 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), (7) and (8), 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 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. The birefringence referred to 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 X direction is given by the following formula 1.
Birefringence Δnx = (In-plane X direction refractive index Nx) − (Thickness direction refractive index Nz) (Formula 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 the interference fringes is n, the birefringence Δnx in the in-plane X direction is expressed by the following formula 2.
Δnx = nx × λ / d (Formula 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.

<Film in which portions with different compression states coexist (in one aspect, a film in which a high compression portion and a low compression portion coexist, and in one aspect, a film in which an already compressed portion and an uncompressed portion coexist)>
As a practical method for producing graphite that can be used for the purposes of the 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.

  The graphite film obtained by the production method of (1) above is obtained by further forming a graphite film by rolling or press-compressing graphite powder. Therefore, by changing the pressure applied in this rolling roll forming process or pressing process, a strongly compressed part (as an aspect, an already compressed part) and a weakly compressed part (as an aspect, an uncompressed part or also as an aspect) In addition, a graphite film suitable for the purpose of the present invention can be obtained by forming an already compressed portion that is compressed weaker than a strongly compressed already compressed portion.

  On the other hand, in the case of the production method (2), in order to obtain a graphite film that meets the object of the present invention, it is first necessary to produce a graphite film in an expanded (foamed) state.

  To specifically illustrate the process for producing graphite from a polymer, the polyimide film is preheated in nitrogen gas and carbonized. 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, pressure in the surface direction may be applied 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. 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 heating is performed using the juule heat. Graphitization is performed by converting the carbonized film prepared in the pretreatment to a graphite structure, but the molecular orientation of the starting polyimide film affects the carbon alignment of the carbonized film, which is carbon-carbon during graphitization. Reduce the energy of 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 expanded graphite film can be obtained by controlling the graphitization process. Conditions for obtaining an expanded film and conditions for controlling the degree of expansion vary depending on the type of polyimide used and the thickness of the film. As an example, a cross-sectional photograph of a graphite film in an expanded (foamed) state is shown in FIG.

  As shown in FIG. 1, the expanded graphite film can be regarded as an aggregate of extremely thin graphite thin films. For comparison, a cross section of graphite not in an expanded state is shown in FIG.

  From the comparison of both cross sections, the difference between the two is remarkable.

  In order to quantitatively estimate the degree of expansion of the obtained graphite film, the graphite film obtained in a foamed state may be compressed under pressure and its compression rate may be measured. The compression rate is the ratio of the amount of deformation caused by short-time compression to the original thickness. Strictly speaking, it is determined by comparing the volume of an object under an isotropic pressure with the original volume. However, in the case of high-quality graphite, the C-axis direction (the C-axis direction is the film thickness direction) of graphite is a structure that is coupled by a weak van der Waals force. It is much larger than the compression rate in the ab plane direction (ab direction is the film plane direction), and the properties of graphite can be judged only by considering the compression rate in this direction.

  Therefore, in this patent, the compressibility was defined by applying a 17 MPa load in the thickness direction (that is, the axial direction) of the graphite sheet and the amount of deformation as a ratio to the original thickness. 17 MPa has no particular academic significance, but was usually selected as a pressure that could remove the internal air layer present in the foamed state without destroying the graphite structure.

  That is, the compression rate in the present invention is, for example, that the compression rate is 20% or more, when the thickness before pressure compression is 1, the thickness when pressurized at 17 MPa for 1 minute is 0. It refers to a graphite film that is 8 or less. For the purpose of the present invention, the compression ratio is preferably 20% or more, more preferably 30% or more (the thickness after pressing is 0.7 or less with respect to the thickness 1 before pressing). preferable.

  When the pressure of 17 MPa is removed, the thickness of the graphite increases due to the force for returning to the original thickness. Here, the ratio between the thickness at this time and the thickness at the time of compression is defined as the restoration rate. For example, when the thickness of the film in the compressed state is 1, the restoration rate is 10% when the thickness when the pressure is released is 1.1. For the purpose of the present invention, it is preferable for graphite to have a property of restoring, in order to reduce the thermal resistance. For the purpose of the present invention, it is preferable that the restoration rate is 5% or more. The above is more preferable.

  Low compression portion (uncompressed portion as one aspect or precompressed portion compressed weakly than strongly compressed portion) and high compression portion (in one aspect, precompressed portion) of the present invention In order to produce a film coexisting with the above, a pressure is applied to the film in the above-mentioned expanded state, and the magnitude of the pressure may be changed. Of course, the low compression portion may not be subjected to any compression operation (uncompressed portion). Alternatively, the high compression portion may be prepared by pressurizing and compressing a high compression portion at a relatively weak pressure in advance and then producing a low compression portion and then compressing and compressing a part of the film at a higher pressure. . For example, the pressure compression method may be mechanical press compression, or rolling using a roll or the like.

<Join with heating element>
In the present invention, for the purpose of thermal diffusion (heat dissipation), using a graphite film in which parts with different compression states coexist,
As one aspect thereof,
A high-compression part (in one aspect, a pre-compressed part) and a low-compression part (in one aspect, an uncompressed part or, in another aspect, a pre-compressed part that is compressed weaker than a strongly compressed part) While using a graphite film (in one aspect, a graphite film characterized by the presence of an already compressed portion and an uncompressed portion)
The low-compression portion is used for joining with the heating element, and is used for the purpose of reducing the thermal resistance of the joint portion by forming the joint so that the low-compression portion is further compressed when the joint portion is formed.

  Since it is used for such a purpose, the low compression portion of graphite may be formed in any portion of the graphite film according to the purpose of thermal diffusion, and the low compression portion (or uncompressed portion) is the graphite film. There may be more than one. Further, the shape of the low compression portion is arbitrarily selected so that the thermal resistance with the heating element becomes small.

  For joining to the heating element, there are methods called dry connection and wet connection in which contact is made directly without using the adhesive layer (layer having an adhesive function) as described above. In the case of dry connection, if the method of the present invention is used, it is possible to realize a joint with low thermal resistance by simply pressing it with mechanical pressure. This is mainly because high quality graphite is basically soft. There is. In the present invention, a graphite film having further compression and restoration ability in addition to the original properties of graphite is used. By using such a film and press-connecting it, it is possible to follow the uneven portion of the heating element to follow it, and it is considered that the thermal resistance can be further reduced.

  Of course, even in the case of wet bonding, by using the graphite of the present invention, it is possible to realize bonding with low thermal resistance with the heating element. Wet bonding is a method of connecting via connecting grease called heat-dissipating grease or oil compound, but by applying heat-dissipating grease to the graphite part that does not have an adhesive layer (layer having an adhesive function) of the present invention, a smaller thermal resistance is achieved. Can be realized. This method is particularly effective when the heating element is so uneven that the graphite of the present invention cannot follow it. Commercially available thermal grease can be used as the thermal grease used for such purposes. As such examples, there are many examples such as Three Bond Co., Ltd .: heat dissipation silicon gel sheet, Geltech Co., Ltd .: Lambda GEL paste, RTE Co., Ltd .: heat dissipation silicon, Fuji Polymer Industries.

  For example, FIG. 3 shows a connection state when cooling is performed by bringing a heat sink into contact with a heating element such as a CPU.

  In FIG. 3 (a), (1) is a graphite film (20) having anisotropy of thermal conductivity in the film surface direction and the film thickness direction and having a compressibility of 20% or more according to the present invention. %, And a graphite film having anisotropy of thermal conductivity in the film surface direction and the film thickness direction). Further, (2) is an adhesive layer (a layer having an adhesive function), and no adhesive layer (a layer having an adhesive function) is provided at the center of the graphite film. FIG. 3B shows a joined state between the heat sink and the heating element. The heating element (4) is pressed against the heat sink and pressed into the graphite so that it is hard to get into the graphite. By doing so, a connection with low thermal resistance can be made between the graphite and the heat sink.

  Although there is no restriction | limiting in particular as an adhesive layer (layer which has an adhesive function) used for such a purpose, Acrylic resin, silicon resin, an epoxy resin, etc. are used preferably. Among these, acrylic resins are preferably used for this purpose. Of course, a filler having excellent thermal conductivity may be added to these adhesives. Examples of the filler include metal powders such as copper, silver, and aluminum, carbon powders, and inorganic / ceramic powders such as silica and aluminum nitride.

  FIG. 4 shows that by compressing and compressing a part of the graphite of the present invention, an apparent thickness difference occurs between a compressed part (precompressed part) and an uncompressed part (uncompressed part). It is an example of the manufacturing method of the manufactured graphite film. In this example, by compressing graphite having a compression ratio of 20% or more with a pressing jig having a hole in the center, it is possible to produce graphite in which the periphery of the graphite is strongly compressed. By selecting various pressurizing pressures, the difference in apparent thickness can be controlled to a desirable level.

  FIG. 5 and FIG. 6 are examples of simultaneously producing a graphite film and forming an adhesive layer (layer having an adhesive function) so that an apparent thickness difference is generated by press molding. As shown in FIG. 5 (b), the graphite film is pressed together with an adhesive layer (layer having an adhesive function) with a release paper (7) at the time of pressing, so that the object of the present invention as shown in FIG. 5 (c) is achieved. A heat diffusion film can be obtained. FIG. 6D shows an adhesion state with the heat sink. The CPU core is pressed so that the graphite film is compressed, and a good connection with the heat sink becomes possible. At this time, applying the above heat dissipation grease to the interface part (central part) where the graphite and the heat sink are in direct contact or the interface part where the CPU core and the graphite are in direct contact realizes a further low thermal resistance. This is preferable. Such a connection situation is shown in FIG. Examples of the heat dissipating grease are as described above.

  For example, as another usage, there is a method in which both ends of the ribbon-like graphite are in a low compression state and the other portion is in a high compression state, and the low compression portion at one end is used for joining with a heating element such as a CPU. . In this case, the high compression portion is used for heat transport, and the low compression portion at the other end is used for joining with a cooling body such as a heat sink.

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

<Graphite film>
First, four types of graphite films used as examples of the present invention will be described, but the present invention is not limited to these examples.

(1) Graphite film-A
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 pretreated by raising the temperature in a nitrogen gas to 1200 ° C. using an electric furnace and keeping the temperature at 1200 ° C. for 1 hour. The obtained carbonized film was set inside a cylindrical graphite heater so that it could freely expand and contract, and treated at 2800 ° C.

  It was found that this polyimide film can be converted to high-quality graphite at 2800 ° C. The obtained graphite film-A was in a foamed state. The thickness in the foamed state was 80 μm, and the thickness when compressed at 17 MPa was 32 μm (that is, the compression rate was 60%). When the pressure of the film is released, the thickness is 48 μm (that is, the restoration rate of the graphite thus treated is 50%), and the plane direction thermal conductivity of the compressed graphite film is 1200 W / mK, the thickness direction. The thermal conductivity was 6 W / mK.

(2) Graphite film-B
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 produce a polyimide film (thickness 75 μm) having an average linear expansion coefficient of 100 × 200 ° C. to 1.0 × 10 −5 cm / cm / ° C. did. 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 (1). The obtained graphite film-B is in a foamed state, the thickness in the foamed state is 75 μm, the thickness when compressed at 17 MPa is 35 μm (that is, the compressibility is 53%), and the thickness when the pressure is released is The restored graphite film had a thermal conductivity in the plane direction of 1400 W / mK and a thermal conductivity in the thickness direction of 10 W / mK.

(3) Graphite film-C
A PGS graphite sheet (product number: EYGS182310) manufactured by Panasonic was prepared with a thickness of 70 μm, a surface direction thermal conductivity of 700 W / mK, and a thickness direction thermal conductivity of 5 W / mK. The compression rate was 35%.

(4) Graphite film-D
A graphite sheet (Super λGS) manufactured by Suzuki Sogyo Co., Ltd. was prepared with a thickness of 120 μm, a surface direction thermal conductivity of 250 W / mK, and a thickness direction of 5 W / mK. The compression rate was 30%.

<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 device (ULVAC Riko Co., Ltd. “LaserPit”) by an optical alternating current method. The thermal conductivity was calculated from the measured thermal diffusivity using 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 (cm3) calculated by the product of the vertical, horizontal and thickness of the graphite film.

  The cross section of the film was observed using a SEM (Hitachi Scanning Electron Microscope S-4500, acceleration voltage 5 kV) by cleaving the film.

The specific method of cleaving is as follows. The obtained graphite film was cut with a cutter knife into a strip size of 20 mm long × 10 mm wide. Furthermore, put a small cut with a razor in the surface direction at one end of this film, apply force from the opposite side of the cut, and cut the film to give a cross section,
<Measurement method of thermal resistance>
The measurement of the thermal resistance at the joint between the heating element and the graphite film was carried out by producing a simulated cell as shown in FIG. 3B or FIG.

  That is, the graphite sheet of the present invention was sandwiched between a CPU core and a heat sink, a constant pressure was applied, and then a constant power was applied to the transistor to cause it to generate heat (heat generation amount W). The experimental environment this time is as follows. CPU: P3 (800 MHz), heat sink: FC-PAL35T, memory: SDRAM 128 MB, OS: Windows (registered trademark) me, measurement conditions: temperature measurement after completion of Loop of Super PI 209,000 lines. The temperature measurement point is a part of the CPU core.

  The value of thermal resistance was estimated as follows. That is, the temperature of the CPU core part is set to (Th), the temperature (Tf) of a specific place in the heat radiating fin is measured with a CA thermocouple, and the thermal resistance (unit: ° C./W) is measured according to the following formula-3 did. The lower the temperature of the heating element and the higher the temperature of the radiation fin, the smaller the thermal resistance.

Thermal resistance Hr = (Th−Tf) / W (Formula-3)
The value of thermal resistance varies depending on the performance of the heat dissipation fins, the heat generation characteristics of the heating element, the size of the graphite film, etc., so it cannot be regarded as an absolute value, but by making these conditions constant, the thermal resistance characteristics It is possible to make a relative comparison.

(Examples 1-4)
Four types of graphite films -A, -B, -C, -D are cut to the size of the bottom surface of the heat sink, and only the portion corresponding to the top surface of the CPU core is cut out so that there is no adhesive layer (layer having an adhesive function) The adhesive sheet was bonded together with a pressure press, and was bonded to the bottom surface of the heat sink. The adhesive sheet is an acrylic adhesive layer (layer having an adhesive function) with a thickness of 30 μm (acrylic adhesive layer 5603 manufactured by Nitto Denko Corporation).

  CPU core temperature and thermal resistance were measured by the method described in the above measurement method. Table 1 shows the result of measuring the value of thermal resistance by changing the pressing pressure from 2 N / cm 2 to 20 N / cm 2 at four points.

@ 0009

It was found that with any graphite, the CPU temperature was kept at 65 ° C. or lower, and a good connection could be realized with a relatively weak pressure of about 5 N / cm 2. In particular, it was found that graphite A, B, and C excellent in compressibility showed an excellent heat dissipation effect, and graphite A and B excellent in heat conduction in the surface direction had a further excellent heat dissipation effect.

(Comparative Example 1)
An adhesive layer (layer having an adhesive function) was formed on the entire surface of the graphite film using the graphite film-A, and this was attached to the bottom surface of the heat sink, and the thermal resistance was measured in the same manner as in Example 1. The obtained results are shown in Table 1.

(Comparative Example 2)
A copper foil having a thickness of 45 μm was used to form an adhesive layer (layer having an adhesive function) on the entire surface of the foil, which was attached to the bottom surface of the heat sink, and the thermal resistance was measured in the same manner as in Example 1. The obtained results are shown in Table 1.

  From the comparison between Comparative Example 1 and Examples 1 to 4, the heat dissipation method of the present invention is a method of directly joining a heating element (CPU here) and a cooling fin (without an adhesive layer (layer having an adhesive function)). The advantage of was revealed. Furthermore, the excellent heat dissipation characteristics of the graphite sheet of the present invention were clarified by comparing the results obtained in Comparative Example 2 and the results of Examples 1 to 4.

(Examples 5 and 6)
The graphite films -A and -B are cut into the size of the bottom surface of the heat sink by the same method as in Examples 1 and 2, and only the portion corresponding to the top surface of the CPU core is cut out so that there is no adhesive layer (layer having an adhesive function) The adhesive sheet was joined together with a pressure press. At this time, an extremely thin (about 1 μm) silicon grease (Shin-Etsu Chemical G765: thermal conductivity 2.9 W / mK (catalog value)) is applied to the graphite surface where the adhesive layer (layer having an adhesive function) does not exist. I left it. Similarly, an extremely thin (about 1 μm) silicon grease (Shin-Etsu Chemical G765) was applied to the upper surface of the CPU, and then the CPU was pressure-bonded to the graphite surface. Next, the CPU core temperature and thermal resistance were measured in the same manner as in Example 1. Table 2 shows the results of measuring the value of thermal resistance while changing the pressing pressure from 2 N / cm 2 to 20 N / cm 2. From this result, it became clear that the contact resistance can be further reduced by applying silicon grease. Such an effect becomes remarkable particularly in a region where the pressure when the CPU is pressure-bonded is relatively small (2 to 5 N / cm 2 in this experiment).

The cross-sectional SEM photograph of the graphite film (expanded state) of this invention. The cross-sectional SEM photograph of the graphite film which is not an expanded state. Example in which an adhesive layer (layer having an adhesive function) is formed on a part of the graphite film of the present invention (a) Embodiment of the thermal diffusion film of the present invention (b) Together with the heat sink, the thermal diffusion film is used for cooling the CPU. Example used Example of production of graphite film having portions having different thicknesses (a) Graphite film having a compression rate of 20% or more (b) A method of compressing and compressing a part of the graphite film. (C) Graphite film having portions with different thicknesses by pressure compression Example of simultaneously forming a graphite film having a difference in thickness and an adhesive layer (layer having an adhesive function) (a) Graphite film having a compression rate of 20% or more (b) An adhesive layer with release paper (adhesive function) (C) Example of graphite having a graphite film having a difference in thickness and an adhesive layer (layer having an adhesive function) Example of simultaneously forming a graphite film having a difference in thickness and an adhesive layer (layer having an adhesive function) (d) Adhesion state between the film and the heat sink shown in FIG. (E) Example of applying thermal grease to the contact interface between CPU and graphite

Explanation of symbols

1 Graphite film 2 Adhesive layer (layer with adhesive function)
3 Heat sink 4 Heating element (CPU core)
5 Compression jig 6 Graphite film of the present invention 7 Release paper 8 Heat radiation grease

Claims (13)

A part of the graphite film having a compressibility of 20% or more and having anisotropy of thermal conductivity in the film surface direction and the film thickness direction is compressed by the pressure treatment in the thickness direction,
A graphite film characterized in that portions having different compression states coexist in the graphite film. A graphite film in which the portions having different compression states coexist,
At least the apparent thickness of any one of two or more portions selected from the group consisting of an uncompressed portion, a low-compressed portion of the pre-compressed portion, and a high-compressed portion of the pre-compressed portion and having different compression states. The graphite film according to claim 1, wherein the difference is generated.   A graphite film having a compressibility of 20% or more and anisotropy of thermal conductivity in the film surface direction and the film thickness direction. A graphite film having a compression ratio of 20% or more and having anisotropy of thermal conductivity in the film surface direction and the film thickness direction,
A graphite film that can be obtained by treating a raw material film composed of a polymer film and / or a carbonized film in an inert gas or in vacuum at a temperature of 2400 ° C. or higher,
The graphite film according to any one of claims 1 to 3, wherein the graphite film is expanded to 80% or more of the thickness of the raw material film. The graphite film according to any one of claims 1 to 4,
A heat diffusion film comprising a layer having an adhesive function,
A thermal diffusion film, wherein the layer having an adhesive function is provided on a part of the film surface of the graphite film. The layer having an adhesive function according to claim 5 is formed in a low compression portion and / or a high compression portion of the precompressed portion of the graphite film according to any one of claims 1 and 2. A heat diffusion film characterized by A layer having an adhesive function and / or an electrically insulating function is formed on the surface of the low-compression part and / or the high-compression part of the pre-compression part of the pre-compression part of the graphite film,
On at least one surface of the uncompressed portion of the graphite film,
6. The thermal diffusion film according to claim 5, wherein a layer having the adhesive function and / or an electrically insulating function is not formed.   The thermal diffusion film according to any one of claims 5 to 7, wherein the thermal conductivity in the surface direction of the graphite film is 100 W / mK or more. The polymer film according to claim 4,
The thermal diffusion film according to any one of claims 5 to 8, which is at least one selected from the group consisting of polyimide, polyoxadiazole, and polyparaphenylene vinylene. The average linear expansion coefficient in the range of 100-200 degreeC of the polyimide film of Claim 9 is 2.5 * 10 < ^-5 > cm / cm / degrees C or less, The any one of Claims 5-9 characterized by the above-mentioned. The heat diffusion film described in 1. The thermal diffusion film according to any one of claims 5 to 10, wherein the birefringence of the polyimide film according to claim 9 is 0.13 or more.   A thermal diffusion method comprising contacting an uncompressed portion of the graphite film according to any one of claims 1, 2, and 4 with a heating element, and further connecting the uncompressed portion so as to be pressurized. .   The thermal diffusion method according to claim 12, wherein the already compressed portion of the graphite film according to any one of claims 1, 2, and 4 is joined to the heat dissipation portion via a layer having an adhesive function. A thermal diffusion method characterized by the above.