JP6800034B2 - Interlayer bonding part, interlayer thermal bonding member, interlayer thermal bonding method, and method for manufacturing interlayer thermal bonding member - Google Patents

Description

The present invention relates to an interlayer bonding portion, an interlayer thermal bonding member, an interlayer thermal bonding method, and a method for manufacturing an interlayer thermal bonding member for rapidly transferring heat from a heat generation source to a cooling / heat dissipation portion.

In recent years, the problem of heat in electronic devices and LED lighting has become a major issue to be solved. There are methods that use heat conduction, heat radiation, and heat convection for heat dissipation and cooling. To effectively dissipate and cool the heat of the heat generation source, combine these heat dissipation and cooling methods to dissipate the heat of the heat generating part. It is necessary to efficiently transmit heat to the heat dissipation / cooling parts such as the circuit board, cooling fins, and heat sink, and for that purpose, it is important to reduce the heat resistance between the heat generation part and the heat dissipation / cooling part.

Even if hard members such as metal and ceramic are simply joined together, the bonding between the layers becomes point contact due to the unevenness of the member surface, and as a result, an air layer with low thermal conductivity (thermal conductivity: 0.02 W) / MK) is present, which causes a large thermal resistance. An interlayer thermal bonding member (Thermal Interface Material, hereinafter abbreviated as TIM) is used to reduce the thermal resistance between such interlayers, and is used by sandwiching the metal with each other or between a member such as a metal and a ceramic. In this case, it is important that the thermal conductivity of the TIM itself is high and that the thermal resistance at the interface between each member and the TIM is small. In order to reduce the interfacial thermal resistance, it is necessary to increase the contact area of the interface and bring it closer to surface contact. For this purpose, conventionally, a mixture of a fluid substance such as a flexible polymer material for surface contact and a highly thermally conductive inorganic filler for making the TIM itself highly thermally conductive has been used ( Hereinafter, it is abbreviated as composite TIM).

Examples of the high thermal conductive filler include fused silica (1 to 2 W / mK), aluminum oxide (20 to 35 W / mK) hexagonal boron nitride (30 to 60 W / mK), magnesium oxide (45 to 60 W / mK), and the like. There are aluminum nitride (150 to 250 W / mK), graphite (described later) and the like. Further, as the flexible substance as the matrix, a flexible polymer such as an acrylic resin, an epoxy resin, or a silicone resin is often used. The interface is in surface contact with the composite TIM, and the air layer is removed from the layers, so that the thermal resistance between the layers can be reduced. However, in such a composite type TIM, if the amount of the high thermal conductive inorganic filler added is increased in order to realize high thermal conductivity, the fluidity is impaired and the thermal resistance at the interface is increased. Therefore, in the composite type TIM, the thermal conductivity of the TIM itself is only about 1 to 2 W / mK for the normal product and about 5 W / mK for the high thermal conductive product. The general thickness of the composite TIM is about 0.5 to 5 mm. The reason why such a thickness is necessary is that the TIM needs to enter the surface unevenness of the member to be heat-bonded.

The thermal resistance value, which is a practical characteristic of TIM, is the sum of the thermal resistance of TIM itself and the thermal resistance at the interface, and is usually about 0.4 to 4.0 K · cm ² / W. Since this thermal resistance value changes depending on the magnitude of the pressure applied to the joint surface, it is necessary to indicate the magnitude of the pressure together in order to display the thermal resistance value.

A typical composite TIM is shown in FIG. FIG. 1A shows a case where the filler added to the flexible polymer is in the form of particles, and FIG. 1B shows a case where the filler added to the flexible polymer is in the form of flakes. (C) aims to improve the thermal resistance characteristics by orienting the flaky filler in the direction perpendicular to the film surface (hereinafter referred to as vertical orientation).

FIG. 2 shows a joining state when the various composite TIMs shown in FIG. 1 are actually sandwiched between the members. FIG. 2A shows a case where heat bonding is performed using only a flexible substance (not containing a heat conductive filler). Even in such a case, the thermal resistance can be reduced by allowing the flexible substance to enter the surface irregularities, and especially when the surface of the member is close to a mirror surface with few irregularities, the thickness of the TIM can be made very thin by pressurization. Therefore, a small thermal resistance can be realized. However, it is known that such a flexible substance-only system decomposes or diffuses the flexible substance due to partial heat concentration (called bleeding), and it is difficult to use it as a TIM. There is a problem to say. (B) is a case of thermal bonding using a composite TIM containing a granular filler. Further, (c) is a case of thermal bonding using a composite type TIM containing a furnishing granular filler. (D) is a case of thermal bonding using a composite type TIM containing a vertically oriented scaly filler. In addition to the purpose of improving thermal conductivity, these fillers also have the purpose of preventing heat concentration and avoiding the bleeding phenomenon that occurs in the case of FIG. 2A.

Graphite is used in a wide range of fields such as energy, space, and medicine due to its excellent heat resistance, chemical resistance, high thermal conductivity, and high electrical conductivity, and occupies an important position as an industrial material. Therefore, the present inventors have a thickness of 10 nm to 15 μm, a thermal conductivity in the film surface direction of 500 W / mk or more, and an anisotropy of the thermal conductivity in the film surface direction and the thickness direction of 100 or more. Was developed. This graphite TIM has excellent thermal resistance characteristics of 0.98 K · cm ² / W (thickness 13 μm) to 0.33 K · cm ² / W (thickness 105 nm) under a pressure of, for example, 1.0 kgf / cm ^2. Shown. (Patent Document 1)

Japanese Unexamined Patent Publication No. 2014-133669

However, such a graphite TIM exhibits excellent characteristics when the surface of the member is considered to be substantially a mirror surface, but the characteristics are deteriorated when the member is a practical member having irregularities on the surface of the member.
Therefore, the present invention provides an interlayer thermal bonding member, an interlayer thermal bonding method, and an interlayer thermal bonding that can deal with unevenness of a member that is thermally bonded with high performance (low thermal resistance) as compared with a conventional composite TIM. It is an object of the present invention to provide a method for manufacturing a member.

The present inventors have promoted the improvement of the prior invention (Patent Document 1), and have developed a TIM having a structure completely different from that of the conventional composite TIM as shown in FIG. 3A, and have completed the present invention. .. In FIG. 3A, 3a is a flexible substance and 3b is a graphite film. The TIM of the present invention comprises a graphite film having special physical properties and a fluid substance that coats the surface thereof. FIG. 3 (b) shows a joining state when the TIM of the present invention is sandwiched between uneven members. The convex portion on the surface of the member forms an internal recessed thermal contact of the graphite film. On the other hand, a fluid substance enters the recess of the member and fills the recess. As a result, the air layer in the recess is removed. As will be described later, since the graphite film used in the present invention has extremely high thermal conductivity in the film surface direction, the heat flowing from one junction immediately diffuses and heat is generated from many other contacts facing each other. Can be shed. That is, it is considered that the TIM of the present invention can realize excellent thermal resistance characteristics because it can be joined at multiple points. If multi-point bonding can be realized, the thermal bonding can have the same effect as surface bonding. Such a heat conduction mechanism is completely different from the heat conduction mechanism of the conventional TIM shown in FIGS. 2 (b), 2 (c) and 2 (d) above.

Further, it was found that the graphite film TIM of the present invention has superior durability to that of the conventional composite TIM. This is because the graphite film has high thermal conductivity in the plane direction and is evenly present throughout the TIM, which prevents bleeding due to heat concentration compared to the filler used in conventional composite TIMs. By having an excellent effect on. Furthermore, a new fact that has not been known at all in the past has been clarified that the graphite film TIM of the present invention has extremely small pressure dependence of thermal resistance. For example, according to the present invention, the pressure dependence (R _0.1P / R _0.5P ) of the thermal resistance value when pressurized (loaded) at the magnitudes of 0.1 MPa and 0.5 MPa is 2.0 or less. Can be done. The fact that the pressure dependence of the thermal resistance value is extremely small and that it exhibits low thermal resistance characteristics with a small pressing force means that strong mechanical tightening is not required, and even if the mechanical tightening is loosened, It is a practically extremely useful property that its thermal resistance is hardly affected.

That is, the interlayer heat bonded portion of the present invention is a interlayer heat bonded portion for transferring heat between the layers of the two members,
The interlayer bonding portion includes an interlayer thermal bonding member sandwiched between the two members.
The interlayer thermal bonding member contains a graphite film and a fluid material that coats the graphite surface.
The fluid material layer is a layer of fluid material and
The thickness of the graphite film is more than 15 μm and 50 μm or less, the density of the graphite film is 1.40 g / cm ^{3 to} 2.26 g / cm ³ , and the thermal conductivity of the graphite film in the plane direction is 500 W / mK to 2000 W. / a mK, the ratio of the weight of the flowable material and the weight (B) of the graphite film (a) (a / B) is Ri der 0.01 to 4.0, further,
The surface of at least one of the two members has a concave portion and a convex portion, the arithmetic average roughness Ra value is 0.1 μm to 10 μm, and the ten-point average roughness Rz value is 1.0 μm to It is 30 μm, and further
The convex portion is an interlayer thermal joint portion in which the inside of the graphite film is formed into a thermal contact, and the concave portion is filled with the fluid substance .
In this way, since it is much thinner than the composite TIM, the thermal resistance of the bulk is small, and by providing a flexible material layer with fluidity, the interfacial thermal bonding between the members having irregularities is extremely small. You can.

The present invention is formed from the above-mentioned graphite film and a fluid substance, and the fluid substance is used for reducing the interfacial thermal resistance with a member. The fluid substance referred to in the present invention is divided into a flexible substance that is solid at room temperature and a fluid substance that is liquid. A flexible substance that is solid at room temperature refers to a substance that is deformed by heating, pressurization at room temperature, or both pressurization and heating to exhibit fluidity. Such substances include gel-like, grease-like, and wax-like substances in addition to soft polymer materials. In the present invention, the room temperature means 20 ° C., and when the flexible substance is a substance that is solid at room temperature, the thickness of the substance shown when there is no load at room temperature is the specified temperature. It is deformed when a load is applied by pressure, and the thickness after deformation is 1/2 or less of the thickness before deformation. In a substance that is solid at room temperature, the preferable pressure for developing fluidity according to such a definition is 0.5 MPa or less, and the preferable temperature for developing fluidity is 100 ° C. or less under the above pressure.

The TIM of the present invention penetrates into the pressure at the time of forming a thermal bond, or the unevenness of a member to be thermally bonded by pressure and heating. As a result, the air layer existing in the space is removed, and excellent thermal resistance characteristics are realized. The optimum thickness of the fluid material layer depends on the size of the unevenness of the member to be held, the required fluid layer is thicker for the member with large unevenness, and the required fluid layer is thin for the member with less unevenness. Become. Therefore, in the present invention, the amount (thickness) of the fluid layer formed on the surface is important for realizing excellent thermal resistance characteristics. As a result of the examination, it was found that the fluid substance used in the present invention has a relatively small effect depending on the type and a large effect on the amount. The weight ratio of preferred (fluid material / graphite film) in the present invention is in the range of 0.01 to 4.0. In the present invention, it is preferable to provide fluid layers on both sides of the graphite surface, so that a fluid layer having a maximum weight twice that of graphite is formed on one surface of the graphite film. In order to realize the low thermal resistance characteristic, the weight ratio of (fluid substance / graphite) is more preferably in the range of 0.02 to 3.0, further preferably in the range of 0.04 to 2.0. Most preferably, it is in the range of 0.05 to 1.0.

As a material for forming a fluid layer, it is also possible to use a liquid substance such as oil that exhibits fluidity at room temperature. In the present invention, when the fluid substance is liquid at room temperature, it means a liquid substance having a boiling point of 150 ° C. or higher. Such a liquid substance cannot be used as a matrix in a normal composite TIM. This is because, in the case of a normal composite TIM, it is necessary to form a film with a polymer layer. However, in the case of the TIM of the present invention, since a film-like graphite layer as a core already exists, such a liquid substance can be used.

When the surface unevenness of the member becomes larger, the thickness of the graphite film TIM of the present invention (in the range of more than 15 μm to 50 μm) may not be sufficient even if the fluidized layer is provided. In such a case, it is effective to stack and use a plurality of interlayer thermal bonding members of the present invention. FIG. 3C shows a TIM when three sheets are stacked as an example. At this time, the fluid layer between the graphite films may be thinner than the outermost layer. It is that the outermost fluid layer needs to correspond to the unevenness of the member, but the fluid layer between the graphite films is only used for bonding and does not need such a role (corresponding to the unevenness of the substrate). Because. In this way, by laminating, it is possible to heat-bond between members having a wide range of irregularities, but if the number of laminated members becomes too large, the thermal resistance value of the TIM itself becomes too large. In the case of the TIM of the present invention, the thickness of the TIM capable of achieving excellent thermal resistance characteristics (heat resistance value when heated at 0.2 MPa is 2.0 ° C. cm ² / W or less) is 400 μm or less. If it is 400 μm or more, the bulk thermal resistance becomes too large and good thermal resistance characteristics cannot be realized. The thickness of 400 μm is the maximum thickness for the present invention, but it goes without saying that even such a thickness is sufficiently thin as compared with the conventional composite TIM.

The thermal resistance characteristics of TIM are also affected by the unevenness of the member as described above. Since the graphite TIM of the present invention has a thickness of 400 μm or less, it cannot cope with unevenness of all sizes of members. The range in which the characteristics of 2.0 ° C. cm ² / W or less can be realized when pressurized at 0.2 MPa is that the surface unevenness of the member is 10 μm or less in the arithmetic average roughness Ra display and 30 μm in the ten-point average roughness Rz display. In the following cases.

It is difficult to realize the characteristics of 2.0 ° C. cm ² / W or less even by using the graphite TIM of the present invention for the unevenness exceeding such unevenness. On the other hand, when the unevenness of the member surface is 0.2 μm or less in Ra display and 1.0 μm or less in Rz display, the fluidity layer as in the present invention is not always required, and even if there is no fluidity layer. In some cases, characteristics of 2.0 ° C. cm ² / W or less can be realized. That is, the present invention is a TIM preferable for performing thermal bonding between two members having a Ra value of 0.1 μm to 10 μm and an Rz value of 1.0 μm to 30 μm or less, which represents the roughness of the surface of at least one member. Therefore, by using the TIM of the present invention, the thermal resistance value can be set to 2.0 ° C. cm ² / W or less (however, when pressurized at 0.2 MPa).

The method for producing the graphite TIM of the present invention is not particularly limited, but the graphite film portion is preferably produced by a step of carbonizing or graphitizing the polymer film. Further, in at least one treatment step of carbonization and graphitization, the polymer film, carbonized film, or graphite film may be held at a plurality of points and heat-treated while being pressurized. Further, in at least one of the carbonization and graphitization treatment steps, a spacer may be laminated on at least one surface of the polymer film, the carbonized film, or the graphite film, and heat treatment may be performed while applying pressure. The spacer is not particularly limited as long as it has the necessary unevenness, durability, and heat resistance, but it is an example of a preferable spacer that the spacer is felt made of a carbon material such as carbon fiber or graphite fiber.

The type of the polymer raw material is not particularly limited, but it is preferable that the polymer raw material contains a condensed aromatic polymer. Further, the condensed aromatic polymer is an aromatic polyimide film having a thickness in the range of 30 μm to 100 μm, and it is preferable to heat the polyimide film at a temperature of 2400 ° C. or higher.

That is, the present invention that has solved the above problems is as follows.
(1) An interlayer thermal bonding member that transfers heat between layers of two members. The interlayer thermal bonding member contains a graphite film and a fluid substance that covers the surfaces of the graphite film, and the graphite film has a thickness of more than 15 μm. and it is 50μm or less, the density of the graphite film was ^{1.40g / cm 3 ~2.26g / cm 3} , the plane direction of the thermal conductivity of the graphite film is 500W / mK~2000W / mK, graphite film An interlayer thermal bonding member in which the ratio (A / B) of the weight (B) to the weight (A) of the fluid substance is 0.01 to 4.0.
(2) A fluid substance is a substance that is solid at 20 ° C and is deformed by applying a load of 0.5 MPa in an environment of 20 ° C, and the thickness after deformation becomes 1/2 or less of the thickness before deformation. The interlayer thermal bonding member according to (1).
(3) The interlayer thermal bonding member according to (1), wherein the fluid substance is liquid at 20 ° C. and the boiling point of the fluid substance is 150 ° C. or higher.
(4) The interlayer thermal bonding member according to (1) or (2), wherein the fluid substance contains at least one selected from an acrylic polymer, an epoxy resin, or a silicon polymer.
(5) An interlayer thermal bonding member obtained by laminating a plurality of interlayer thermal bonding members according to any one of (1) to (4) and having a total thickness of 400 μm or less.
(6) The thermal resistance value when a load of 0.2 MPa is applied is 2.0 ° C. cm ² / W or less, and the thermal resistance value (R _0.1P ) and 0 when a load of 0.1 MPa is applied. Any of (1) to (5) in which the ratio (R _0.1P / R _0.5P ) of the thermal resistance value (R _0.5P ) when a load of _.5 MPa is applied is 1.0 to 2.0. The interlayer thermal bonding method using the interlayer thermal bonding member according to one of the above.
(7) The interlayer thermal joining method for joining by the interlayer thermal joining member according to any one of (1) to (5), wherein the surface of at least one of the two members has an arithmetic mean roughness Ra value. Is 0.1 μm to 10 μm, and the ten-point average roughness Rz value is 1.0 μm to 30 μm.
(8) The method according to any one of (1) to (5), which has a carbonization step of carbonizing a polymer film to obtain a carbonized film and a graphitization step of graphitizing the carbonized film to obtain a graphite film. A method for manufacturing an interlayer thermal bonding member.
(9) The method for producing an interlayer thermal bonding member according to (8), wherein the polymer film contains a condensed aromatic polymer and the temperature in the graphitization step is 2400 ° C. or higher.
(10) In at least one step of the carbonization step and the graphitization step, at least one of the polymer film, the carbonized film, and the graphite film is sandwiched by a spacer, pressed with the spacer, and heat-treated (8). ) Or (9). The method for manufacturing an interlayer heat-bonded member.
(11) The method for manufacturing an interlayer thermal bonding member according to (10), wherein the arithmetic mean roughness Ra of the spacer is 0.1 μm to 20 μm.

According to the present invention, there is provided an interlayer thermal bonding member that can be applied to a member having irregularities, has excellent thermal bonding characteristics, has excellent durability, and has a small pressure dependence of thermal resistance characteristics.

Examples of various composite TIMs. (A) TIM composed of granular thermally conductive filler and flexible polymer, (b) TIM composed of flint-like filler and flexible polymer, (c) TIM composed of longitudinally oriented fluffy filler and flexible polymer Joining state between members using various TIMs. (A) When heat-bonding is performed only with a fluid substance, (b) When heat-bonding is performed using a composite TIM containing a granular fuller, (c) When heat-bonding is performed using a composite TIM containing a flaky granular fuller , (D) In the case of thermal bonding using a composite TIM containing a vertically oriented scaly filler. (A) Structure of the TIM of the present invention, (b) Image of the case where the TIM of the present invention is sandwiched between members. (C) An example of the TIM of the present invention laminated in multiple layers, in which the concave portion of the member is filled with a fluid substance. The figure of the thermal resistance measurement method (1) between members having different surface roughness. The figure of the principle (2) of the method of measuring the thermal resistance characteristic between members having different surface roughness. A copper foil having defined irregularities on one surface is used, and a graphite TIM is sandwiched between the copper foils for measurement. The other surface of the copper foil is considered to be almost a mirror surface and is a copper foil, and this surface is joined to the heat measurement rod via silicon grease. The figure of the principle (3) of the method of measuring the thermal resistance characteristic between members having different surface roughness.

Hereinafter, embodiments of the present invention will be described in detail. All academic and patent documents described in the present specification are incorporated herein by reference. Further, unless otherwise specified in the present specification, "A to B" representing a numerical range means "A or more (including A and larger than A) and B or less (including B and smaller than B)".

(A) Graphite film The thickness of the graphite film used in the present invention is in the range of more than 15 μm to 50 μm. The thickness is preferably 16 μm or more, most preferably 18 μm or more. Further, the graphite film of the present invention is preferably 50 μm or less. With a thickness of 50 μm or more, it becomes difficult to satisfy the following heat conduction characteristics (heat transfer characteristics) and density characteristics of the graphite film.

Graphite film of the present invention is in the range density of 1.40~2.26g / cm ^3, the density that is more preferably in the range of 1.60~2.26g / cm ^3, 1.80~2. Most preferably, it is in the range of 26 g / cm ³ . The density of 2.26 g / cm ³ is the density of graphite that does not contain an air layer at all, and whether or not the graphite film contains an air layer can be confirmed by measuring the density of the graphite film. Since the thermal conductivity of the air layer is extremely low, it is desirable that the air layer does not exist inside the graphite film as much as possible, and the density condition is a guide for knowing the existence of the air layer.

Further, the thermal conductivity in the graphite film surface direction of the present invention is preferably 500 W / mK or more, more preferably 600 W / mK or more, further preferably 800 W / mK or more, and 1000 W / mK or more. Something is most preferable. Since the maximum value of the thermal conductivity of the graphite ab surface is 2000 W / mK, the preferable thermal conductivity in the film surface direction in the present invention is 500 W / mK to 2000 W / mK. The large thermal conductivity is a characteristic necessary to realize excellent thermal resistance characteristics by the multi-point bonding effect described above.

(B) Method for Producing Polymer Film The method for producing a graphite film of the present invention is not particularly limited, but can be obtained by, for example, a method for heat-treating a polymer film. The polymer film is preferably a condensed aromatic polymer. Among them, polyamide, polyimide, polyquinoxaline, polyoxadiazole, polybenzimidazole, polybenzoxazole, polybenzthiazole, polyquinazolinedione, polybenzoxazineone, polyquinazoline, benzimidazolobenzophenanthroline ladder polymer, and derivatives thereof. It is preferable that it is at least one kind.

Among the above-mentioned polymer films, a polyimide film having a condensed aromatic substance is preferable because it can be converted into high-quality graphite. Further, among the polyimide films, a film having a controlled molecular structure and its higher-order structure and excellent orientation is preferable because it is easier to convert to graphite. Such an aromatic polyimide film can be produced by a known method. For example, it can be produced by casting an organic solvent solution of polyamic acid, which is a polyimide precursor, on a support such as an endless belt or a stainless steel drum, and drying and imidizing the solution.

The method for imidizing the polyamic acid is not particularly limited, and is a thermal cure method in which the precursor polyamic acid is imide-converted by heating, a dehydrating agent typified by an acid anhydride such as acetic anhydride, picolin, and quinoline. , Isoquinoline, pyridine and other tertiary amines are used as imidization accelerators, and a chemical cure method for imid conversion can be mentioned.

Specific methods for producing a film by the chemical cure method include the following methods. First, a dehydrating agent having a stoichiometry or higher and an imidization accelerator having a catalytic amount are added to the polyamic acid solution, and the solution is cast or applied onto an organic film such as a support plate or PET, or a support such as a drum or an endless belt. A film having a self-supporting property is obtained by forming a film and evaporating an organic solvent. Next, this is further heated and dried while being imidized to obtain a polyimide film made of a polyimide polymer. The temperature during heating is preferably in the range of 150 ° C. to 550 ° C. The rate of temperature rise during heating is not particularly limited, but it is preferable to gradually heat the temperature continuously or intermittently so that the maximum temperature reaches the above temperature. Further, it is preferable that the polyimide manufacturing process includes a step of fixing or stretching the film in order to prevent shrinkage. By such a treatment, the orientation can be increased.

The thickness of the graphite film finally obtained varies depending on the type of the starting polymer film, but in the case of aromatic polyimide, when the thickness is 1 μm or more, it is about 60 to 40% of the thickness of the original polymer film. In many cases. Therefore, in order to finally obtain a graphite film having a thickness of 15 μm to 50 μm, the thickness of the starting polymer film is preferably in the range of 25 nm to 125 μm.

(C) Method for Producing Graphite Film The method for producing a graphite film TIM (interlayer thermal bonding member) of the present invention is not particularly limited as long as it can obtain graphite having required characteristics, but carbonization of the polymer film is not particularly limited. , It is preferable to produce by graphitization. Such carbonization and graphitization steps may be carried out continuously in a single furnace or in individual furnaces. Here, a method for carbonizing and graphitizing a polymer film will be described. The method of carbonization is not particularly limited, and for example, a polymer film as a starting material is preheated in an inert gas or in a vacuum to perform carbonization. As the inert gas, nitrogen, argon or a mixed gas of argon and nitrogen is preferably used. Preheating is usually performed at a temperature of about 1000 ° C. At the stage of preheating, it is effective to apply tension in the plane direction to the extent that the film does not break so that the orientation of the starting polymer film is not lost.

The method of graphitization is not particularly limited, and for example, the film carbonized by the above method is set in a high-temperature furnace to perform graphitization. Graphitization is performed in an inert gas, but argon is the most suitable as the inert gas, and a small amount of helium may be added to argon. The higher the treatment temperature, the higher the quality of graphite that can be converted, preferably 2400 ° C. or higher, more preferably 2600 ° C. or higher, and most preferably 2800 ° C. or higher.

The graphite film produced by the above general method may have wrinkles over the entire surface of the film. When carbonizing using an aromatic polyimide as the polymer film, the carbonized film often shrinks to about 75 to 85% of the original polymer film at the time of carbonization. In addition, when the shrinkage and expansion of the film during carbonization and graphitization are left to nature, the finally obtained graphite film in the film surface direction is 85 to 95, which is the size of the original polymer film. It is often about%. Wrinkles occur due to such natural contraction and expansion. Such wrinkles of the graphite film may affect the characteristics of TIM, and it is preferable to prepare a graphite film having controlled wrinkles. The method for forming wrinkles of an appropriate size is not particularly limited, but in at least one step of the carbonization step or the graphitization step, a spacer having an uneven size of an appropriate size is formed on a polymer film, a carbonized film, or the like. Appropriate wrinkles can be obtained by laminating with at least one surface of a sample such as a graphite film, sandwiching it with a smooth substrate, and applying pressure from both sides at an appropriate pressure while treating at carbonization temperature and graphitization temperature. Can be formed. However, unlike the case where the graphite film is used alone as a TIM, the TIM of the present invention has a multi-layer structure with a flexible layer, so that the size and uniformity of wrinkles do not have a great influence on the thermal resistance characteristics. ..

In order to control natural shrinkage and natural expansion by pressing with a spacer to form appropriate wrinkles, unevenness of appropriate size is required on both sides of the polymer film, carbonized film, or graphite film. Appropriate wrinkles can be formed by laminating spacers having the above, sandwiching them with a smooth press plate, pressing them from both sides at an appropriate pressure, and treating them at a carbonization temperature and a graphitization temperature. The carbonization step is a step performed on the polymer film, and the graphitization step is a step performed on the carbonized film. Moreover, you may perform a regraphitization step if necessary. The regraphitization step is a step performed on the graphite film. When the polymer film is carbonized and then graphitized, the press treatment may be performed by either carbonization or graphitization, or the press treatment may be performed by both.

(D) Formation of fluid layer When a solid fluid layer is formed (coated) on the surface of the graphite film prepared by the above method at room temperature, a flexible acrylic polymer or epoxy-based polymer used in composite TIM. Resins and silicon-based polymers are materials for forming a particularly preferable fluid layer. The material forming the fluid layer is deformed by pressurization at room temperature or both pressurization and heating, and enters the unevenness of the two members to be thermally joined. As a result, the air layer existing in the space is removed, and excellent thermal resistance characteristics are realized. The fluidity referred to here means that the thickness of the substance is halved or less when pressurized at a specified temperature and pressure, but as described above, fluidity is exhibited at room temperature. The preferable pressure for this is 0.5 MPa or less, more preferably 0.4 MPa or less, further preferably 0.3 MPa or less, and most preferably 0.2 MPa or less. The temperature at which fluidity develops is preferably 80 ° C. or lower, more preferably 60 ° C. or lower, and most preferably 40 ° C. or lower under the above pressure environment. That is, the fluid substance is a substance that is solid at 20 ° C. and is deformed by applying a load of 0.5 MPa in an environment of 20 ° C., and the thickness after deformation becomes 1/2 or less of the thickness before deformation. Is preferable.

The method of forming the fluid layer on the surface of the graphite film is not particularly limited. For example, a flexible polymer layer in the form of a film may be pressure-bonded by a laminating method, and a polymer dissolved in a solvent is applied. Alternatively, a molten polymer may be applied. Further, the fluid layer may be formed in advance on the two members to be heat-bonded, and may be pressurized at the time of heat-bonding to finally form the TIM structure of the present invention. If the TIM formed in this way is eventually formed from a graphite film and a fluid material within the scope of the present invention, such TIM is included in the scope of the present invention.

The weight ratio of the graphite film of the present invention to the fluid substance (fluid substance / graphite) is preferably in the range of 0.01 to 4.0. The weight ratio of (fluid substance / graphite) is 4, which means that the fluid layer is basically applied to both sides of graphite, so if the same amount of fluid substance is applied to both sides, the graphite film A fluid material layer twice as heavy as the graphite film is formed on one surface.

The layer formed on the surface of the graphite film may be a liquid fluid substance. When the fluid is a liquid, it is preferably mineral oil, vegetable oil, synthetic oil, essential oil edible oil, animal oil, and mixtures thereof. For example, in the case of oil, mineral oil, synthetic hydrocarbon oil, ester oil, polyglycol oil, silicon oil, fluorine oil, canola oil and mixtures thereof can be preferably used. Alternatively, it may be a modified oil. For example, in the case of silicone oil, an epoxy-based modified silicone oil, a polyether-modified silicone oil, an amino-modified silicone oil, or an epoxy-based modified silicone oil can be used. In order not to lose the heat resistance and high durability characteristics which are one of the features of the TIM of the present invention, it is desirable that the substance has a low vapor pressure, and the fluid substance referred to in the present invention has a boiling point of 150 ° C. or higher. Say the substance of. The boiling point of the fluid substance is more preferably 200 ° C. or higher, more preferably 250 ° C. or higher, and most preferably 300 ° C. or higher.

(E) Fabrication of Multilayer TIM As described above, when the surface roughness of the two members to be heat-bonded is large, a plurality of TIMs of the present invention can be laminated and used. In order to laminate a plurality of sheets, the TIM of the present invention may be simply laminated and press-pressed, and it is preferable to apply temperature at the time of crimping. Further, instead of press crimping, roll crimping may be performed through rolls provided with a certain gap. At this time, the fluid layer formed on the bonding surface between the brafite films may be thinner than the fluid layer on the outermost surface, and a thickness of several μm is sufficient, and the thinner the film, the smaller the bulk resistance.

(F) Interlayer Thermal Bonding Method The interlayer thermal bonding method using the TIM of the present invention includes a step of installing the TIM between two members to be thermally bonded. By sandwiching the TIM of the present invention between layers, interlayer thermal bonding is performed to transfer heat from a heat generating source or a member thermally bonded to the heat generating source to a second member having a temperature lower than that. Can be done. The graphite film is sandwiched between a member close to the heat source and a member far from the heat source, and the graphite film and each member are in direct contact with each other. As a joining method, it may be fixed by simply mechanical pressure. It is effective and preferable to mechanically tighten with screws, screws, springs, or the like. However, considering that low thermal resistance can be realized under low pressure, which is a feature of the present invention, and that the pressure dependence of thermal resistance is small, it is not always necessary to tighten strongly, and even if the tightening pressure changes. Since the influence is small, it is possible to realize a practically extremely effective interlayer thermal bonding.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples, and is carried out with appropriate modifications to the extent that it can be adapted to the gist of the above and the following. It is also possible and they are within the technical scope of the invention.
<Measurement method of physical properties>

First, the method for measuring physical properties in the following examples is shown below.
(1) Thickness of Graphite Film The thickness of the graphite film cut into 5 cm squares was measured at arbitrary 5 points with a contact type thickness gauge, and the average value was taken as the thickness of the graphite film.

(2) Density of graphite film The density of graphite film was measured using a dry automatic densitometer Accupic II 1340 (manufactured by Shimadzu Corporation). The densities of the five graphite films cut into 5 cm squares were measured one by one, and the average value was taken as the density.

(3) the thermal diffusivity of the thermal conductivity of the graphite film of the graphite film, using a thermal diffusivity measuring apparatus due to the periodic heating method (ULVAC-RIKO Co. "LaserPit" device), 25 ° C., under vacuum (10 ^- (Approximately ² Pa), the measurement was performed using a frequency of 10 Hz. This is a method in which a thermocouple is attached at a point separated from the point of laser heating by a certain distance and the temperature change is measured.

(4) Thermal resistance measurement of TIM The thermal resistance measurement of the graphite TIM of the present invention was carried out using a precision thermal resistance measuring device manufactured by Hitachi Technology and Service. This measuring device is a device capable of precise thermal resistance measurement, and the error is ± 0.002 ° C. cm ² / W. The sample size is 10 x 10 mm ² . Range of applied pressure is 10 to 50 N (approximately equivalent to ^{1.0kgf / cm 2 ~5.0kgf / cm 2} ), measurement temperature was 60 ° C.. Specifically, first, the wattage (W) to be added was adjusted so that the interface temperature became 60 ° C., and the measurement was performed 10 times after the temperature change became constant, and the average value was used as the measured value.

The above is a standard method for measuring a thermal resistance value, but the measurement rod surface of the thermal resistance measuring device is mirror-finished, which is different from the practical member surface having irregularities. The value we want to know is the value of the thermal resistance value at the uneven interface as shown in FIG. The TIM is sandwiched between members having surface roughness (unevenness) and its thermal resistance is measured. In order to measure the thermal resistance between the uneven members using the above measuring device, we conducted the following experiments.

FIG. 5 shows a method for measuring the thermal resistance value when members having different surface roughness are used. Reference numeral 5a is a rod for measuring thermal resistance of the precision thermal resistance measuring device manufactured by Hitachi Technology and Service. Reference numeral 5b is silicon grease, and 5c is a copper foil having irregularities of a size on one side. The copper foil is bonded to the thermal resistance measuring rod 5a by using the silicon grease 5b. Reference numeral 5d is a graphite TIM sample (interlayer thermal bonding member) of the present invention. First, the thermal resistance characteristics are measured while changing the load using copper foils having different surface roughness without sandwiching the graphite TIM. Let x be the measured value at this time. The measurement conditions are as described above. Next, the graphite TIM of the present invention is sandwiched as shown in FIG. 5, and the thermal resistance value in each case is measured. Let y be the measured value at this time. However, the thermal resistance value measured by this method includes the thermal resistance values between 5a-5b and 5b-5c (two places each), and the thermal resistance between 5c-5d-5c to be measured is included. It is not a value that indicates only the value. In order to know the thermal resistance value between 5c-5d-5c, it is necessary to estimate the thermal resistance value between 5a-5b and 5b-5c from the measured value and subtract the value. Therefore, the thermal resistance values between 6a-6b and 6b-6c were measured by the method shown in FIG. The value at this time is z. Note that 6a is a rod for measuring thermal resistance, 6b is silicon grease, and 6c is a mirror-surfaced copper foil. The value measured by this method was subtracted from the thermal resistance value measured by the method of FIG. 5 (that is, the value of yz was taken as the thermal resistance value to be obtained. The value of xx and the value of yz The effect of the graphite TIM of the present invention can be estimated by comparison. Such a method includes some assumptions and does not directly measure the thermal resistance value of the TIM, but is a correct evaluation in principle. It is a method and is considered to be a sufficient evaluation method for evaluating the practical characteristics of TIM.

(5) Arithmetic mean roughness Ra and ten-point average roughness Rz of the member
If necessary, the surface roughness (arithmetic mean roughness) Ra and the ten-point average roughness Rz of the heat-bonded members were measured. The measurement was based on JIS B 0601, and the value was measured in a normal temperature atmosphere using a surface roughness measuring machine Surfcom DX (manufactured by Tokyo Seimitsu Co., Ltd.).

(6) Preparation of Graphite Films Used in Examples and Comparative Examples The following describes seven types of graphite films having different thicknesses and maximum treatment temperatures (HTT) used in Examples and Comparative Examples.

Acetic anhydride 20 g in 100 g of a 18 wt% DMF solution of polyamic acid prepared from pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and p-phenylenediamine (4/3/1 in molar ratio). A curing agent consisting of 10 g of isoquinoline was mixed, stirred, defoamed by centrifugation, and then cast and coated on 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 self-supporting gel film. 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 have an average linear thermal expansion coefficient of 1.6 × ^10-5 cm / cm / ° C. and a birefringence of 0.14 at 100 to 200 ° C. Polyimide films with different thicknesses were manufactured.

The obtained polyimide film was heated to 1000 ° C. in nitrogen gas at a rate of 10 ° C./min using an electric furnace, and kept at 1000 ° C. for 1 hour for pretreatment. Next, the obtained carbonized film was sandwiched between spacers made of graphite fiber felt having a surface roughness Ra value of 5 μm, which was further placed between surface-polished graphite blocks and set in a graphite heater furnace. The temperature was raised to HTT at a rate of temperature rise of 20 ° C./min, held at HTT for 10 minutes, and then lowered at a rate of 40 ° C./min. The graphitization treatment was performed in an argon atmosphere. At this time, a load was applied to the sample so as to be 100 gf / cm ² .

The HTT, thickness, thermal conductivity in the film surface direction, and density of the obtained seven types of graphite films were as follows.
(A-1) HTT: 2900 ° C., thickness 48 μm, thermal conductivity in the film surface direction: 1500 W / mK, density 2.0 g / cm ³
(B-1) HTT: 2900 ° C., thickness: 35 μm, thermal conductivity in the film surface direction: 1650 W / mK, density 2.1 g / cm ³
(C-1) HTT: 2900 ° C., thickness: 24 μm, thermal conductivity in the film surface direction: 1700 W / mK, density 2.1 g / cm ³
(C-2) HTT: 2700 ° C., thickness: 25 μm, thermal conductivity in the film surface direction: 1400 W / mK, density 1.9 g / cm ³
(C-3) HTT: 2500 ° C., thickness: 25 μm, thermal conductivity in the film surface direction: 1000 W / mK, density 1.8 g / cm ³
(D-1) HTT: 2900 ° C., thickness: 19 μm, thermal conductivity in the film surface direction: 1760 W / mK, density 2.14 g / cm ³
(E-1) HTT: 2900 ° C., thickness, 16 μm, thermal conductivity in the film surface direction: 1780 W / mK, density 2.15 g / cm ³

[Examples 1 to 7]
Flexible acrylic polymer layers were formed on both sides of the above seven types of graphite films. As a result of weight measurement, the thickness of the formed flexible acrylic polymer was estimated to be about 5 μm (both sides combined) in all samples. The thermal resistance characteristics and the pressure dependence thereof when TIM was used were measured, and the results are shown in Table 1.

From this result, it was found that all of the above TIMs exhibited excellent thermal resistance characteristics and pressure dependence of the thermal resistance characteristics. The obtained characteristics are such that the thermal resistance value when pressurized at 0.2 MPa is 2.0 ° C. cm ² / W or less, and the thermal resistance value when pressurized at 0.1 MPa (R _0.1P ). It was found that the ratio (R _0.1P / R _0.5P ) of the thermal resistance value (R _0.5P ) to that at the time of pressurization at 0.5 MPa can be set to 2 or less.

[Examples 8 to 12]
Table 2 shows the characteristics when the flexible acrylic polymer is formed on both sides of the D-1 graphite film by changing the thickness (weight) and used as TIM. From this result, if the weight ratio of (flexible polymer / graphite) is in the range of 0.01 to 4.0, the thermal resistance value when pressurized at 0.2 MPa is 2.0 ° C. cm ² / W or less. , The ratio of the thermal resistance value (R _0.1P ) when pressurized at 0.1 MPa and the thermal resistance value (R _0.5P ) when pressurized at 0.5 MPa (R _0.1P / R _0.5P ) It turned out that it can be done within 2.

[Examples 13 to 17]
Five types of samples (F to J) were prepared by laminating a plurality of the above graphite films, and the thermal resistance characteristics when used as TIM were measured. The flexible layer used is an acrylic polymer. Table 3 shows the name of the prepared sample, the sample structure, the measured thermal resistance value, and the pressure dependence (R _0.1P / R _0.5P ) value thereof. However, A described in the section of sample structure in the table means a flexible acrylic polymer, G represents the type of graphite used, and () indicates the thickness represented by μm. From this result, if the total thickness of the TIMs when laminated is 400 μm or less, the thermal resistance value when pressurized at 0.2 MPa is 2.0 ° C cm ² / W or less, when pressurized at 0.1 MPa. the thermal resistance _{(R 0.1P)} and heat resistance of the pressurization at 0.5 MPa _{(R 0.5P)} ratio _(R 0.1P _/ R _0.5P) a can be to within two I found out.

[Examples 18 to 24]
Among the above samples, three types of TIMs, A-1, G, and I, were used to measure the thermal resistance characteristics using a copper foil having a relatively large surface roughness. The measurement was carried out by the experimental method shown in FIGS. 4 to 6 and the results are shown in Table 4. From this result, according to the present invention, the range of surface roughness of a member capable of achieving a thermal resistance of 2.0 ° C. cm ² / W or less under a pressure of 0.2 MPa is 10 μm or less in Ra value on the surface of at least one member. , It was estimated that the Rz value was in the range of 30 μm or less.

[Example 25] [Comparative example 1]
For comparison, a composite TIM (acrylic resin / graphite) having a weight ratio of 0.2 using flake graphite and a flexible acrylic resin (the same as the resin used in Example 3). Sample name X, thickness: about 30 μm) was prepared. The durability of both samples was compared using sample C-1, which has almost the same composition as this composite TIM. In the experiment, first, the upper and lower sides of C-1 and X were sandwiched between copper foils (both sides were approximately mirror surfaces, thickness 50 μm), and the thermal resistance values of C-1 and X (under a pressure of 0.2 MPa) were determined. At this time, the rod for measuring the thermal resistance and the copper foil were joined with a thin silicon grease. Next, a sample composed of copper foil / TIM / copper foil was placed in a furnace at 150 ° C. (in air) and heated for 6 hours. The thermal resistance value after heating was measured, and the change was investigated by comparing with the thermal resistance value before heating. The results are shown in Table 5. The increase in the thermal resistance value of C-1 was + 1.0%, but in the case of X, which is a composite TIM, an increase in the thermal resistance value was observed by + 11.3%. From this, it was judged that the TIM of the present invention is improved in heat resistance as compared with the conventional composite TIM.

[Examples 26 to 29]
The graphite film (C-1) was immersed in canola oil, the surface was wiped with gauze, and the weight ratio was changed by changing the degree of wiping. In Examples 26 to 28, the weight ratio of canola oil / graphite (C) is about 0.2, and in Example 29, it is about 1.0. Using these, the thermal resistance characteristics were measured using three types of copper foils having different surface roughness. The measurement results are shown in Table 6. From this result, it is possible to use a fluid substance that is liquid at room temperature, such as canola oil, between members with irregularities, and it is excellent at 2.0 ° C. cm ² / W or less between such members. It was found that the thermal resistance characteristics can be realized.

3a Flexible material 3b Graphite film 4a First member 4b Interlayer heat bonding member 4c Second member 5a Thermal resistance measurement rod 5b Silicon grease 5c Copper foil 5d Interlayer heat bonding member with irregularities on one side 6a Thermal resistance measurement rod 6b Silicon grease 6c Mirror surface copper foil

Claims (11)

In layers of the two members a interlayer heat bonded portion for transferring heat,
The interlayer bonding portion includes an interlayer thermal bonding member sandwiched between the two members.
The interlayer thermal bonding member includes a graphite film and a fluid material layer covering the surface of the graphite film.
The fluid material layer is a layer of fluid material and
The graphite film has a thickness of more than 15 μm and less than 50 μm.
Density of the graphite film was ^{1.40g / cm 3 ~2.26g / cm 3} ,
The thermal conductivity of the graphite film in the plane direction is 500 W / mK to 2000 W / mK.
The ratio of the weight of the graphite film (B) to the weight of the flowable material (A) (A / B) is Ri der 0.01 to 4.0, further,
The surface of at least one of the two members has a concave portion and a convex portion, the arithmetic average roughness Ra value is 0.1 μm to 10 μm, and the ten-point average roughness Rz value is 1.0 μm to It is 30 μm, and further
The convex portion forms a recessed thermal contact inside the graphite film, and the fluid substance enters the concave portion to fill the concave portion.
Interlayer thermal joint . Claimed that the fluid substance is a solid at 20 ° C. and is deformed by applying a load of 0.5 MPa in an environment of 20 ° C. so that the thickness after deformation becomes 1/2 or less of the thickness before deformation. Item 2. The interlayer thermal junction according to item 1 . The interlayer thermal junction according to claim 1, wherein the fluid substance is liquid at 20 ° C. and the boiling point of the fluid substance is 150 ° C. or higher . The interlayer thermal junction according to claim 1 or 2, wherein the fluid substance contains at least one selected from an acrylic polymer, an epoxy resin, or a silicon polymer . An interlayer thermal bonding member constituting the interlayer thermal bonding portion according to any one of claims 1 to 4 . The interlayer thermal bonding member according to claim 5.
An interlayer thermal bonding member having a total thickness of 400 μm or less by laminating a plurality of the interlayer thermal bonding members. The interlayer thermal bonding method using the interlayer thermal bonding member according to claim 5 or 6, wherein the thermal resistance value when a load of 0.2 MPa is applied is 2.0 ° C. cm ² / W or less.
The ratio (R0.1P / R0.5P) of the thermal resistance value (R0.1P) when a load of 0.1 MPa is applied and the thermal resistance value (R0.5P) when a load of 0.5 MPa is applied is 1. A method of interlaminar thermal bonding , which is 0 to 2.0. The method for manufacturing an interlayer thermal bonding member according to claim 5 or 6.
A method for manufacturing an interlayer thermal bonding member , which comprises a carbonization step of carbonizing a polymer film to obtain a carbonized film and a graphitization step of graphitizing the carbonized film to obtain a graphite film. The polymer film comprises a condensed aromatic polymer, the temperature of the graphitization process is 2400 ° C. or more, the manufacturing method of the interlayer heat bonded member according to claim 8. In at least one of the carbonization step and the graphitization step, the polymer film, the carbonized film, or at least one of the graphite films is sandwiched by a spacer, and is pressurized with the spacer and heat-treated. The method for manufacturing an interlayer thermal bonding member according to claim 8 or 9. Arithmetic average roughness Ra of the spacer is 0.1Myuemu～20myuemu, manufacturing method of the interlayer heat bonded member according to claim 10.