JP2020181926A - Joining structure of high crystalline graphite, and joining method - Google Patents

Abstract

To provide a heat-dissipating joined body having a high strength and easy to manufacture, taking advantage of a high heat conductivity of a high crystalline graphite, such as graphite.SOLUTION: According to the present invention, a joining layer 3 made of metal or oxide is formed between lamination planes of a plurality of plate-like or sheet-like graphite sheets 1 made of high crystalline graphite, which serves to join the graphite sheets to each other. The metal is iron, cobalt or nickel, and the oxide is titanium oxide or vanadium oxide. By laminating the plurality of plate-like or sheet-like graphite sheets 1 made of high crystalline graphite are laminated, interposing a joining material 2 composed of a thin film made of metal or oxide between lamination planes of the graphite sheets 1, and heating and pressing the graphite sheets 1 thus laminated under a reduced pressure, carbide is produced between lamination planes of the graphite sheets 1 to form the joining layer 3 for joining the graphite sheets to each other.SELECTED DRAWING: Figure 1

Description

The present invention relates to, for example, a bonding structure and a bonding method of highly crystalline graphite used as a material for a heat spreader or a heat sink for heat dissipation and cooling of semiconductors and electronic components.

In recent years, automobiles have been electrified such as HVs and EVs, and power semiconductors capable of highly efficient output control have been improved in performance. As the performance of power semiconductors increases, the cooling of semiconductors has become an important issue. Increasing the thermal conductivity of the heat spreader in the immediate vicinity of the semiconductor is an important point for increasing the cooling efficiency, and at present, metals such as copper and aluminum have been used.

As described above, in the demand for a material having higher thermal conductivity, graphite-based materials such as highly crystalline pyrolytic graphite (PG) and high-purity carbon materials such as artificial graphite have been attracting attention. However, graphite shows strong anisotropy depending on the crystal structure in the heat conduction direction. That is, while the biaxial plane of the crystal ab axis shows a high thermal conductivity comparable to that of diamond and 3 to 4 times that of copper, the heat of about resin (1/100 or less of copper) in the direction of the crystal c axis. Shows only conductivity. Further, graphite is a material that is difficult to join, and it is very difficult to join without impairing thermal conductivity.

On the other hand, conventionally, as shown in Patent Document 1, a technique is known in which a binder containing silver, copper, and titanium is interposed between graphite members, and the graphite members are heat-bonded by heating and fusing the binder.

Further, as shown in Patent Document 2, a sheet-shaped bulk graphene material is inserted between a pair of metal or ceramic substrates, and titanium, zirconium or other carbides are formed on the overlapping surface of the bulk graphene material and the substrate. A technique for providing a heat-bonding layer of a metal material (silver, tin, etc.) containing a chemical and heat-bonding is known.

Japanese Unexamined Patent Publication No. 2017-11234 Japanese Unexamined Patent Publication No. 2015-532531

However, the thermal conductivity of titanium carbide (TiC) formed as a bonding layer in the invention of Patent Document 1 is as low as about 20 W / m / K. Therefore, due to the low thermal conductivity of the bonding layer material, the bonding layer If the thickness is not 5 μm or less, there is a drawback that the thermal conductivity of the entire joint is significantly impaired. Further, in the above invention, although it is described that a slurry may be used as the bonding material, the use of a metal foil is recommended, and it is difficult to make a foil of 10 μm or less because titanium has low malleability. On the other hand, slurries are made by kneading metal powder with an organic solvent, but compared to brittle ceramics, metal is more difficult to pulverize and the surface is easily oxidized, making it difficult to use as a starting material for bonding materials. Therefore, titanium carbide When is used as a bonding material by reaction with metallic titanium, it is difficult to make it sufficiently thin enough to withstand practical use. Incidentally, in Patent Document 1, a metal foil of 0.05 mm (= 50 μm) is used as a bonding material (see [0028]).

The invention of Patent Document 2 is to join a metal or ceramic substrate to both sides of a sheet-shaped bulk graphene (graphite) material, and although it is not to join graphite to each other, carbide is formed between the joining surfaces of both. A metal-based coating (thermally bonded layer) containing a chemical (or activator) made of titanium, zirconium, or the like is arranged and heat-bonded (see [0032]).

Considering that it is difficult to atomize a metal as described above, the metal-based coating material powder shown in Patent Document 2 is prepared by adding titanium or zirconium as a chemical to a metal such as silver, tin, or lead in advance. It is understood that the alloy (see [0033]) is processed and formed into a metal foil having a thickness of 0.01 to 1.0 mm (see [0034]).

This contrasts the invention of Cited Document 2 with the fact that when brazing or soldering, which is generally used for joining dissimilar materials, shows high thermal interface resistance due to the thermal barrier between graphene and brazing or soldering. It is also clear from this point (see [0040] and [0041]).

In the joining structure or joining method of the present invention for solving the above problems, first, graphite sheets are joined between laminated surfaces of a plurality of plate-shaped or sheet-shaped graphite sheets 1 made of highly crystalline graphite. It is characterized in that a bonding layer 3 made of metal or oxide is formed.

Secondly, the metal is iron, cobalt or nickel.

Thirdly, the oxide is titanium oxide or vanadium oxide.

Fourth, the bonding layer 3 is characterized in that the average film thickness is 0.5 to 20 μm.

Fifth, the metal is iron and the average film thickness of the bonding layer 3 is 50 μm or less.

Sixth, the average film thickness of the bonding layer is 0.5 to 5 μm.

Seventh, it is characterized in that the graphite sheets 1 of the laminated graphite sheets 1 are overlapped and joined in a state where the crystal orientations are crossed.

Eighth, a plurality of plate-shaped or sheet-shaped graphite sheets 1 made of highly crystalline graphite are laminated, and a thin bonding material 2 made of metal or oxide is interposed between the laminated surfaces of each graphite sheet 1. By heating and pressurizing the laminated graphite sheets 1 under reduced pressure, carbides are generated between the laminated surfaces of the graphite sheets 1 to form a bonding layer 3 for joining the graphite sheets to each other.

Ninth, it is characterized in that iron, cobalt, nickel or oxides thereof or titanium oxide or vanadium oxide is used for the bonding material 2.

Tenth, a fine powder of iron oxide, cobalt oxide, vanadium oxide, titanium oxide, or nickel as the bonding material 2 is adhered to the laminated surface of the graphite sheet 1 to form a film as the bonding layer 3. It is a feature.

Eleventh, it is characterized in that the finely powdered bonding material 2 is applied to the laminated surface of the graphite sheet 1 as a suspension to which a lower alcohol is added and dried.

The twelfth feature is that the bonding material 2 is adhered to the laminated surface of the graphite sheet 1 by sputtering or other physical vapor deposition method.

Thirteenth, the finely powdered bonding material 2 is characterized in that the particle size is 2 μm or less.

Fourteenth, it is characterized in that iron foil is used as the bonding material 2.

According to the present invention configured as described above, a large number of graphite sheets are bonded to each other with a thin film bonding layer to obtain a heat radiating member having a high thermal conductivity or an interfacial low thermal resistance value utilizing the characteristics of high crystalline graphite. Can be done. In particular, when a finely powdered bonding material is used, an ultrathin film bonding layer can be formed by suspending and coating on the bonding surface of a graphite sheet or by forming a film by sputtering or the like, so that a material for generating carbides. The alloy is not limited to the method of forming the alloy in advance or forming the alloy into a metal foil, and an ultra-thin film can be formed and the strength is high. In particular, iron has good compatibility with graphite (carbon) and a high-strength bonding layer can be obtained, and in the case of iron oxide, it is a thinner film and has higher strength.

When ethanol or other lower alcohol is used for the suspension, it has excellent drying properties after application, is superior in terms of safety and cost, and has a hydrophilic group and a new oil group. What is an oxide powder? In addition to being more familiar with the hydrophilic group, the new oil group is compatible with the surface of the graphite sheet, so uniform application is possible.
Other effects of the present invention will be described in the description of the embodiments.

(A) to (C) are schematic views explaining the joining process by the joining method of the present invention. It is a schematic diagram for explanation of the apparatus for carrying out the joining of this invention. It is explanatory drawing which shows the relationship between the cross-sectional view of a joint structure and the thermal resistance in a thickness direction. It is explanatory drawing which shows the relationship between the cross-sectional view of a junction structure and a thermal circuit. It is a graph which shows the relationship between the thickness of the bonding layer (membrane) in the bonding portion of a graphite sheet, and the apparent thermal conductivity when the total thickness of the bonded body is 2 mm. It is explanatory perspective view of the bonded body which shows the laminated (junction) structure which prevents the decrease of thermal conductivity of a graphite sheet which has anisotropy. It is a scanning electron micrograph of a cross section of a zygote according to Example 1 of the present invention. It is a scanning electron micrograph of a cross section of a zygote according to Example 2 of the present invention. It is a scanning electron micrograph of a cross section of a zygote according to Example 3 of the present invention. 6 is a scanning electron micrograph of a cross section of a bonded body according to Example 6 of the present invention. It is a scanning electron micrograph of a cross section of a zygote according to Example 7 of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Graphite has properties such as high heat resistance, high thermal conductivity, and good conductor, but as mentioned above, there are few practical joining methods that utilize these properties without impairing these properties. Since the inventors of the present invention have found that the use of some metals and oxides as a thin-layer bonded body is suitable for bonding graphite, they provide a graphite bonding structure and a bonding method thereof. Is what you do.

Highly crystalline graphite such as highly crystalline pyrolytic graphite (PG) and artificial graphite is high-purity carbon and has excellent thermal stability. In particular, the PG material is almost single crystal graphite and has a very high thermal conductivity of 1000 W / m / K or more in the plane along the crystal ab axis, while several W in the crystal c-axis direction. When trying to utilize the high thermal conductivity characteristics of highly crystalline graphite, which has a large anisotropy of / m / K, for heat dissipation of electronic devices, etc., the thermal resistance at the junction between PGs becomes a major problem. Become. The present invention mainly provides a bonding structure and a bonding method for bonding PGs to each other with low thermal resistance to form a high-performance heat dissipation mechanism, and attempts to alleviate the anisotropy of heat conduction by applying this method. It is a thing.

In the structure of the graphite junction of the present invention, the junction layer is composed of iron, cobalt, nickel, titanium oxide, and vanadium oxide, and the resulting junction layer is sufficiently thin, so that it can be used for heat dissipation later. As described in detail, it is desirable that the bonding layer is 20 microns or less when the bonding layer is a metal of iron, cobalt, or nickel, and 5 microns or less when the bonding layer is composed of an oxide of titanium oxide or vanadium oxide. By satisfying these above conditions, the thermal resistance (thermal resistance) per area of the bonding layer is 5 × 10 ^-7 K / m ² / W or less.

Sheet-shaped or plate-shaped graphite has a high thermal conductive surface that depends on the crystal orientation, but in the plate material in which two or more sheet-shaped graphite sheets of the present invention are joined, the high thermal conductive surface is set in the plate thickness direction and in the plate surface. By setting the high heat conduction direction of one direction and the next surface to the plate thickness direction and another direction in the plate surface, a laminated structure in which the heat conduction anisotropy of graphite is relaxed is formed.

As a typical embodiment, the substance that is the source of the bonding layer is supplied by spraying oxide powder as a suspension with a solvent onto graphite by spraying or the like. That is, unlike metals, oxides are brittle and therefore easily atomized, and by suspending them in an alcohol solvent and spraying them with an airbrush or the like, a thin and uniform bonding layer can be formed.

As another method, a substance that is the source of the bonding layer can be supplied by a film forming method such as sputtering. As for the state before bonding, iron, cobalt, and nickel may be metals or oxides, but titanium oxide and vanadium oxide are formed as oxides.

The bonding should be performed under vacuum, high temperature, and pressure treatment at 900 ° C or higher (1200 ° C or higher for iron oxide), and in the case of graphite with high crystallinity and close to single crystal such as PG, the crystal orientation should be controlled for bonding. A heat dissipation plate capable of heat diffusion can be constructed with. In addition to PG, high crystalline graphite such as polycrystalline graphite, graphene, and carbon fiber is targeted as graphite.

When joining graphite materials, the raw material that is the source of the bonding layer is first fixed to the surface of the graphite material. When an oxide-state ceramic powder is used for fixing, a method of applying by spraying as a suspension or a method of forming a film by a film forming method such as sputtering can be adopted. For joining, heat in a vacuum in the direction perpendicular to the joining surface while applying a load of several to several hundreds of kg per 1 cm ² . As a result, when the oxide bonding layer raw material is used, the oxide is completely or partially reduced by the carbon of the graphite material, and the graphite materials are bonded to each other.

1 (A) to 1 (C) are schematic views showing the above-mentioned bonding state, and as shown in the drawing, a pair of sheet-shaped or plate-shaped graphite sheets 1 and 1 made of highly crystalline graphite such as graphite are superposed. In this example, finely pulverized iron oxide (Fe ₂ O ₃ ) is interposed between the overlapping surfaces as the bonding material 2, and by heating and pressurizing in a vacuum environment, carbides are generated by the upper and lower graphite and iron oxide. As a result, the bonding layer 3 is generated between the upper and lower graphite sheets 1, 1 and the graphite sheets 1, 1 are integrally bonded to each other.

A discharge plasma sintering apparatus can be used for this joining operation. This device applies a large pulse current for heating directly to the sample, but the current promotes diffusion and allows various sintered bodies to be quickly sintered.

FIG. 2 is an explanatory view of a known discharge plasma sintering apparatus 4 used for carrying out the present invention, in which a large pulse current is generated up and down in a main body 6 composed of a vacuum vessel to energize and generate plasma. The apparatus 7 is provided with a conductive die 8 for positioning and accommodating the graphite sheets 1 and 1 stacked as shown in FIG. 2 (A) inside, and a punch for pressurizing the laminated graphite sheet 1 in the die 8. It is composed of a pressurizing device 9.

In the above discharge plasma sintering method, it is important to heat at a high temperature in a vacuum and carry out by uniaxial pressurization. As a device capable of realizing this condition, a hot press and an atmosphere control furnace (however, pressurization is a heavy stone). It is only weakly chipped due to such factors), HIP, etc.

The discharge plasma sintering method is similar to the hot press, except that a large pulse current is applied directly to the sample (the hot press is heated by an external heater), which results in fine plasma. Is generated, and impurities on the surface of the sample (the surface of the graphite material and the bonding material powder in the present invention) can be removed to improve the adhesion. Further, by promoting diffusion by an electric current, it can be expected that the porous powder bonding material is sintered to reduce pores, and the bonding material enters the unevenness of the graphite material to improve the bonding strength.

When spraying oxide powder is used to supply the raw material for the bonding layer as described above, various solvents can be used, but lower alcohols such as ethanol, methanol and propanol are particularly desirable, and ethanol is preferable from the viewpoint of safety. Is the most desirable. Alcohol has a hydrophilic group and a lipophilic group, and it is desirable to use an alcohol solvent for uniform coating because the oxide powder is more compatible with the hydrophilic group and the lipophilic group is compatible with the graphite surface.

When the vapor deposition method is used to supply the raw material for the bonding material, it is possible and desirable to use a physical vapor deposition method (PVD) such as sputtering. A variety of bonding materials can be selected depending on the type of target material, and in the case of bonding materials that form joints in metallic states such as iron, cobalt, and nickel, film formation in metal states other than oxides is also possible. Since the formed bonding material needs to be thinned as described later, a film forming method such as sputtering having excellent film thickness controllability is desirable.

When the bonding layer raw material is pressurized and heated while being fixed to the surface of the graphite material, iron oxide is reduced at 1200 ° C. or higher, cobalt oxide and nickel oxide are reduced at 900 ° C. or higher by carbon of graphite to become a metal. The valences of titanium oxide and vanadium oxide also change due to reduction at 900 ° C. or higher.

The heating temperature does not depend on the type of the bonding material, the bonding temperature is in the range of 700 ° C. to 1800 ° C., preferably 900 ° C. to 1500 ° C., and the bonding pressure is in the range of 1 MPa to 50 MPa, preferably 5 MPa to 30 MPa.

This is because the low temperature side is necessary for advancing the reduction reaction or sintering required for bonding. On the high temperature side, if the bonding equipment (furnace) has specifications above this temperature at 1500 ° C or higher (preferably), it will be expensive. Further, the temperature up to 1800 ° C is made of anisotropic graphite material or bonding layer material. This is because poor bonding is expected due to the difference in the coefficient of thermal expansion.

Those that form a bonding layer as a metal such as iron, cobalt, and nickel after the bonding work fill the space between the graphite plates by plastic flow at the bonding temperature, and carbon diffuses into the metal to create a strong bonding state. Become. Titanium oxide, vanadium oxide, and other oxides that form an additional bond after the bonding work fill the spaces between the particles and graphite plates by sintering, and are firmly bonded.

Here, it is extremely important whether or not the oxide is reduced by carbon (derived from the graphite material), and this point can be judged from the Ellingham diagram. That is, the reduction (metal) becomes stable when the temperature exceeds the intersection of the oxidation reaction lines of various metals in the Ellingham diagram and the carbon-carbon monoxide equilibrium line, and iron, cobalt, and nickel are 1000K (about 700 ° C). , V is 1800K (about 1500 ° C.), and titanium is 1900K (about 1600 ° C.).

The joint portion formed by the present invention has a joint structure as shown in FIG. For the bonded body in which the bonding layer 3 is formed between the two graphite sheets 1 and 1, the thermal resistance in the plate thickness direction is the thermal resistance of each of the graphite sheet and the bonding layer material, and the interfacial thermal resistance of the bonding material and graphite. It can be considered that it was synthesized by a series circuit. The thermal resistance Rx of the substance x is expressed as follows using the thermal conductivity λ (value peculiar to the substance).
Rx = t / (Sλ) (1)

Rx: Thermal resistance (K / W)
t: Thickness (length in heat transfer direction) (m)
S: Cross-sectional area (m ² )
λ: Thermal conductivity (W / m / K)

The thermal resistance Rj of the joint _j is expressed as follows using the thermal resistivity ρ _j of the joint.
R _j = ρ _j / S (2)

R _j : Thermal resistance of the joint (K / W)
S: Cross-sectional area (m ² )
ρ _j : Thermal resistance of the joint (Km ² / W)

Here, for graphite Gr having one layer of junction j between a certain thickness t _total , the thermal resistance R _{total in the} thickness direction uses the thermal conductivity λGr peculiar to graphite.
R _total = R _Gr1 + R _j + R _Gr2 = t _total / (Sλ _Gr ) + ρ _j / S (3)
It is expressed as.

On the other hand, if the apparent thermal conductivity λ _total obtained when the thermal conductivity is actually measured using the laser flash method or the like for this object is used.
R _total = t _total / (Sλ _total ) (4)
Also expressed as.
From equations (3) and (4), the thermal resistivity ρ _j of the joint is ρ _j = (1 / λ _total -1 / λ _Gr ) t _total (5)
Can be calculated by

The thermal resistance of the joint, which is a figure of merit of the member, can be evaluated by Eq. (5) from the measured value of thermal conductivity, but it can also be an index of the constituent requirements by examining the structure of the joint layer in more detail.

Fig. 4 shows the thermal circuit when the joint is formed using the bonding material. Ρ _j calculated by Eq. (5) with the apparent thermal conductivity λ _total is also called the interfacial thermal resistance R _i is also called the capitza resistance. It is expressed as follows from the interfacial heat transfer coefficient κi (value unique to the combination of substances).
Ri = 1 / (Sκ _i ) (6)
The thermal resistance due to the substance y used for bonding depends on the thermal conductivity λ _y.
R _y = t / (Sλ _y ) (7)
Will be.

Therefore, the total thermal resistance of the two Gr2 graphite plates (1 and 2) joined by the joining material y is
R _total = R _Gr1 + R _Gr2 + R _y + 2R _j = t ₁ / (Sλ _Gr ) + t ₂ / (Sλ _Gr ) + t _x / (Sλ _x ) + 2 / (Sκ)
Here, the joint layer thickness is sufficiently small.
t ₁ + t ₂ >> t _x
If
t _total = t ₁ + t ₂
Because it can be regarded as
R _total = t _total / (Sλ _Gr ) + t _x / (Sλ _x ) + 2 / (Sκ)
Will be.

Here, the thermal resistance of the bonding layer 3 is 10 ^-8 to 10 ^-7 K / m ² W for metals such as iron, cobalt, and nickel (thermal conductivity 50 to 100) when the bonding layer thickness is 1 to 20 μm. Oxides such as titanium oxide and vanadium oxide have a thermal resistance of 10 ^-7 to 10 ^-6 K / m ² W, whereas the interfacial thermal resistance of graphite and dissimilar materials is 10 ^-9 to 10 ^-8 K / m ² W (substance). -Calculated from the interfacial heat transfer coefficient data posted on the website of the Materials Research Organization, MatNavi), which is sufficiently smaller than the thermal resistance of the bonding layer and can be ignored. Then, the apparent thermal conductivity of this plate is λ _total = S / (t _total R _total ).
Can be calculated as.

PG has a very high thermal conductivity of 1400 W / (mK), which is more than three times that of silver and copper (about 400 W / (mK)), which are the highest in metals. In order to utilize the PG junction as a heat radiating plate utilizing high thermal conductivity, it is considered that at least an apparent thermal conductivity of 1000 W / (mK) or more is required.

Therefore, when the total thickness of the graphite-bonded plate was calculated as 2 mm (thickness often used as a substrate for semiconductor mounting), the thermal resistivity of the joint was calculated to keep the apparent thermal conductivity of the PG-bonded product at 1000 W / m / K or more. Must be 5.7 x 10 ^-7 (Km ² / W) or less, if the bonding material is iron, cobalt, nickel, the thickness is 20 μm or less, and if the bonding material is an oxide such as titanium oxide, vanadium oxide. Is preferably 5 μm or less in thickness.

In actual bonding, the ideal contact state may not be realized for both, such as the occurrence of vacancies due to the influence of the wettability of the material to be bonded and the material to be bonded, but based on the thermal conductivity of the material used for the bonding layer. The desired thickness is estimated as described above.

On the other hand, for the bonded body of FIG. 3, when the film thickness of the joint layer 3 is sufficiently smaller than the thickness of the entire bonded body, the overall apparent thermal conductivity is expressed by the following formula.
λ _total = t _total (t _total / λ _Gr ＋ t _j / λ _j ) ^-1

From this equation, when the total thickness of the bonded body is 2 mm, the apparent thermal conductivity of the bonded body when the thermal conductivity of the bonded layer is 10 W / m / K and 100 W / m / K is the joint layer thickness. The calculated figure is shown in FIG.

If the bonding layer is 100 W / m / K class (iron, cobalt, nickel) based on 1200 W / m / K, which is a 20% reduction as a numerical value that does not impair the high thermal conductivity of the original graphite (depending on the application). The upper limit is about 20 μm, and in the case of 10 W / m / K class (titanium, vanadium), the upper limit is considered to be about 5 μm. This calculation is ideal without considering interfacial thermal resistance and poor bonding.

The thinner the lower limit, the better, but there is a limit to improving the smoothness of graphite in the bonding material by processing, and the bonding material is expected to fill the gap, so the lower limit is about 0.5 μm. We can conclude that it is desirable.

When a junction having a sufficiently small thermal resistance can be realized in this way, it becomes possible to produce a structure in which the defects of graphite having a large anisotropy close to a single crystal such as PG are alleviated and overcome. FIG. 6 shows a schematic diagram thereof. In this example, pseudo-isotropic properties are formed by joining the graphite crystal orientations of the adjacent graphite sheets 1 to be laminated so as to intersect each other by approximately 90 °. With such a structure, the high thermal conductivity direction of PG is arranged in the plate thickness direction, and about half of the cross-sectional area is arranged in the high thermal conductivity direction in the horizontal direction, and the thermal conductivity is high in each of the thickness direction and the horizontal direction. Can be utilized.

In the above embodiment, an example in which a finely pulverized metal or oxide is used as the bonding material has been described, but as shown in Example 7 described later, it is easy to generate carbides at the time of bonding and processing in relation to graphite. Iron, which is superior in terms of properties and cost, can also be processed into a thin metal foil, and graphite sheets can be joined and laminated by heating and pressurizing under vacuum.

Further, in Examples 1 to 7 described below, the bonding layer of the bonded body is formed as a thin film in the range of 1.6 to 30 μm, and although there is a difference in thermal conductivity and interfacial thermal resistance, the heat radiating material It is considered that all of them can be sufficiently used depending on the application target of.
Hereinafter, examples of the present invention will be described in detail. In Examples 1 to 7, with respect to Examples 4 and 5, photographic data of the actual product could not be obtained due to a trouble in producing an observation sample, so attachment of micrograph data of the cross section of the joint of the actual product is omitted. did.

[Example 1]
Two sheets of graphite for electrodes processed to 20 × 20 × 1 mm (density: about 1.7 g / cm ³ , thermal conductivity: 91 W / m / K (actual measurement)) were prepared. A solution of Fe ₂ O ₃ powder (particle size 1 μm or less) suspended in ethanol was applied to one side of the graphite material for electrodes with an airbrush so as to be about 0.025 g per 1 cm ² after drying. Graphite for electrodes is cheaper than PG, but it is chemically the same substance, so it can be used for evaluation of joinability. Graphite for electrodes is also used as a bonded product with low thermal resistance.

A discharge plasma sintering device (SPS3.20 manufactured by Sumitomo Coal (currently Fuji Radio Industrial Co., Ltd.)) was used for heating. Align the Fe ₂ O ₃ coated surfaces of the graphite material for the electrode, insert the graphite material for the electrode inside the graphite mold with a 20 mm square through hole, and use a 20 mm square graphite punch from above and below to approximately 400 kgf (10 MPa as pressure). A load was applied. A pulse current was applied to the graphite mold in a vacuum of 10 Pa or less, the graphite mold was heated to 1300 ° C. at 50 ° C./min, held at 1300 ° C. for 10 minutes, and then cooled in a furnace. FIG. 7 shows a cross-sectional photograph thereof.

As a result, the graphite for the electrode was firmly bonded. When observing the cut surface, a bonding layer having a thickness of about 0.5 to 1 μm was observed at the bonding portion of graphite for electrodes.
The finished thickness was 1.90 mm, and the apparent thermal conductivity was measured by the laser flash method (NETZSCH, LFA457) and found to be 90 W / m / K, so the interfacial thermal resistance value was about 2.3 × 10 ^-7 Km. It was calculated as ² / W.

[Example 2]
Two sheets of graphite for electrodes (density of about 1.7 g / cm ³ , thermal conductivity of 91 W / m / K (actual measurement)) processed to 20 × 20 × 0.8 mm were prepared. A solution of Co ₂ O ₃ powder (particle size 1 μm or less) suspended in ethanol was applied to one side of the graphite material for electrodes with an airbrush so as to be about 0.025 g per 1 cm ² after drying.

A discharge plasma sintering device (SPS3.20 manufactured by Sumitomo Coal (currently Fuji Radio Industrial Co., Ltd.)) was used for heating. Align the Co ₂ O ₃ coated surfaces of the graphite material for the electrode, insert the graphite material for the electrode inside the graphite mold with a 20 mm square through hole, and use a 20 mm square graphite punch from above and below to approximately 400 kgf (pressure 10 MPa). A load was applied. A pulse current was applied to the graphite mold in a vacuum of 10 Pa or less, the graphite mold was heated to 900 ° C. at 50 ° C./min, held at 900 ° C. for 10 minutes, and then cooled in a furnace. FIG. 8 shows a cross-sectional photograph thereof.

As a result, the graphite for the electrode was firmly bonded. When observing the cut surface, a bonding layer having a thickness of about 1 μm was observed at the bonding portion of graphite for electrodes.
The finished thickness was 1.60 mm, and the apparent thermal conductivity was measured by the laser flash method (NETZSCH, LFA457) and found to be 90 W / m / K, so the interfacial thermal resistance value was approximately 1.0 x 10 ^-8 Km. It was calculated as ² / W.

[Example 3]
Two sheets of graphite for electrodes (density of about 1.7 g / cm ³ , thermal conductivity of 91 W / m / K (actual measurement)) processed to 20 × 20 × 0.8 mm were prepared. A solution of V ₂ O ₅ powder (particle size 1 μm or less) suspended in ethanol was applied to one side of the graphite material for electrodes with an airbrush so as to be about 0.02 g per 1 cm ² after drying.

A discharge plasma sintering device (SPS3.20 manufactured by Sumitomo Coal (currently Fuji Radio Industrial Co., Ltd.)) was used for heating. Align the V ₂ O ₅ coated surfaces of the graphite material for the electrode, insert the graphite material for the electrode inside the graphite mold with 20 mm square through holes, and use a 20 mm square graphite punch from above and below to approximately 400 kgf (10 MPa as pressure). A load was applied. A pulse current was applied to the graphite mold in a vacuum of 10 Pa or less, the graphite mold was heated to 900 ° C. at 50 ° C./min, held at 900 ° C. for 10 minutes, and then cooled in a furnace. FIG. 9 is a cross-sectional photograph thereof.

As a result, the graphite for the electrode was firmly bonded. When observing the cut surface, a bonding layer having a thickness of about 1 μm was observed at the bonding portion of graphite for electrodes.
The finished thickness was 1.61 mm, and the apparent thermal conductivity was measured by the laser flash method (NETZSCH, LFA457) and found to be 82 W / m / K, so the interfacial thermal resistance value was approximately 1.9 x 10 ^-6 Km. It was calculated as ² / W.

[Example 4]
Two sheets of graphite for electrodes (density of about 1.7 g / cm ³ , thermal conductivity of 91 W / m / K (actual measurement)) processed to 20 × 20 × 0.8 mm were prepared. A solution in which TiO ₂ powder (particle size 1 μm or less) was suspended in ethanol was applied to one side of a graphite material for electrodes with an airbrush so as to be about 0.02 g per 1 cm ² after drying.

A discharge plasma sintering device (SPS3.20 manufactured by Sumitomo Coal (currently Fuji Radio Industrial Co., Ltd.)) was used for heating. Align the TiO ₂ coated surfaces of the graphite material for the electrode, insert the graphite material for the electrode inside the graphite mold with a 20 mm square through hole, and use a 20 mm square graphite punch from above and below to obtain approximately 400 kgf (pressure of 10 MPa). A load was applied. A pulse current was applied to the graphite mold in a vacuum of 10 Pa or less, the graphite mold was heated to 900 ° C. at 50 ° C./min, held at 900 ° C. for 10 minutes, and then cooled in a furnace.

As a result, graphite for electrodes was bonded. When observing the cut surface, a bonding layer having a thickness of about 1 μm was observed at the bonding portion of graphite for electrodes.

The finished thickness was 1.6 mm, and the apparent thermal conductivity was measured by laser flash method (NETZSCH, LFA457) and found to be 77 W / m / K, so the interfacial thermal resistance value was approximately 3.3 x 10 ^-6 Km. It was calculated as ² / W.

[Example 5]
Two sheets of graphite for electrodes (density of about 1.7 g / cm ³ , thermal conductivity of 91 W / m / K (actual measurement)) processed to 20 × 20 × 0.8 mm were prepared. A solution of Ni powder (particle size 2 μm) suspended in ethanol was applied to one side of the graphite material for electrodes with an airbrush so as to be about 0.025 g per 1 cm ² after drying.

A discharge plasma sintering device (SPS3.20 manufactured by Sumitomo Coal (currently Fuji Radio Industrial Co., Ltd.)) was used for heating. Align the Ni-coated surfaces of the graphite material for the electrode, insert the graphite material for the electrode into the graphite mold with a 20 mm square through hole, and load about 400 kgf (10 MPa as pressure) with a 20 mm square graphite punch from above and below. Was applied. A pulse current was applied to the graphite mold in a vacuum of 10 Pa or less, the graphite mold was heated to 900 ° C. at 50 ° C./min, held at 900 ° C. for 10 minutes, and then cooled in a furnace.

As a result, graphite for electrodes was bonded. When observing the cut surface, a bonding layer having a thickness of about 1 μm was observed at the bonding portion of graphite for electrodes.

The finished thickness was 1.6 mm, and the apparent thermal conductivity was measured by the laser flash method (NETZSCH, LFA457) and found to be 89 W / m / K, so the interfacial thermal resistance value was approximately 5.34 x 10 ^-7 Km. It was calculated as ² / W.

[Example 6]
Two PGs (density of about 2.25 g / cm ³ , thermal conductivity of 1420 W / m / K (actual measurement)) processed to 20 × 20 × 1 mm were prepared. This PG plate is substantially single crystal graphite, and is cut out so that the graphite crystal ab axial direction is parallel to the thickness direction of the plate material and one side of the square surface. A solution of Fe ₂ O ₃ powder (particle size 1 μm or less) suspended in ethanol was applied to one side of the PG material with an airbrush so as to be about 0.025 g per 1 cm ² after drying.

A discharge plasma sintering device (SPS3.20 manufactured by Sumitomo Coal (currently Fuji Radio Industrial Co., Ltd.)) was used for heating. Align the Fe ₂ O ₃ coated surface of the PG material so that the in-plane graphite crystal ab axis direction is orthogonal, insert the graphite material for the electrode into the graphite mold with a 20 mm square through hole, and 20 mm square from the top and bottom. A load of about 400 kgf (10 MPa as a pressure) was applied to the graphite punch. A pulse current was applied to the graphite mold in a vacuum of 10 Pa or less, the graphite mold was heated to 1300 ° C. at 50 ° C./min, held at 1300 ° C. for 10 minutes, and then cooled in a furnace. FIG. 10 is a cross-sectional photograph thereof.

As a result, the PG material was firmly joined. When observing the cut surface, a joint layer having a thickness of about 1 μm was observed at the joint portion of the PG. As a result of analysis, this junction layer was iron.

The finished thickness was 1.93 mm, and the apparent thermal conductivity was measured by the laser flash method (NETZSCH, LFA457) and found to be 1360 W / m / K, so the interfacial thermal resistance value was approximately 6.0 x 10 ^-8 Km. It was calculated as ² / W.

[Example 7]
Two PGs (density of about 2.25 g / cm ³ ) processed to 20 × 20 × 1 mm were prepared. This PG plate is substantially single crystal graphite, and is cut out so that the graphite crystal ab axial direction is parallel to the thickness direction of the plate material and one side of the square surface.

A discharge plasma sintering device (SPS3.20 manufactured by Sumitomo Coal (currently Fuji Radio Industrial Co., Ltd.)) was used for heating. The PG materials were aligned so that the in-plane graphite crystal ab axial directions were orthogonal to each other, and an iron foil having a thickness of 30 μm was sandwiched between them. A graphite material for electrodes was inserted into a graphite mold having a 20 mm square through hole, and a load of about 400 kgf (10 MPa as a pressure) was applied from above and below with a 20 mm square graphite punch. A pulse current was applied to the graphite mold in a vacuum of 10 Pa or less, the graphite mold was heated to 1300 ° C. at 50 ° C./min, held at 1300 ° C. for 10 minutes, and then cooled in a furnace. FIG. 11 is a cross-sectional photograph thereof.

As a result, the PG material was firmly bonded. When observing the cut surface, a joint layer having a thickness of about 30 μm was observed at the joint portion of the PG. As a result of analysis, this junction layer was iron.

The finished thickness was 1.98 mm, and the apparent thermal conductivity was measured by the laser flash method (NETZSCH, LFA457) and found to be 890 W / m / K, so the interfacial thermal resistance value was approximately 8.2 x 10 ^-7 Km. It was calculated as ² / W.

[Comparison example]
Two PGs (density of about 2.25 g / cm ³ ) processed to 20 × 20 × 1 mm were prepared. This PG plate is substantially single crystal graphite, and is cut out so that the graphite crystal ab axial direction is parallel to the thickness direction of the plate material and one side of the square surface.

This PG material was coated with commercially available heat conductive grease and rubbed against each other so that the in-plane graphite crystal ab axis direction was orthogonal to each other, and integrated. When the thermal resistance was measured, the finished thickness was 2.00 mm, and the apparent heat was obtained. When the conductivity was measured by the laser flash method (NETZSCH, LFA457), it was 520 W / m / K, so the interfacial thermal resistance value was calculated to be about 2.4 × 10 ^-6 Km ² / W.

1 Graphite sheet 2 Bonding material 3 Bonding layer

Claims (14)

Highly crystalline graphite in which a bonding layer (3) made of metal or oxide that bonds graphite sheets to each other is formed between the laminated surfaces of a plurality of plate-shaped or sheet-shaped graphite sheets (1) made of highly crystalline graphite. Joint structure. The bonded structure of high crystalline graphite according to claim 1, wherein the metal is iron, cobalt or nickel. The bonded structure of highly crystalline graphite according to claim 1 or 2, wherein the oxide is titanium oxide or vanadium oxide. The bonded structure of high crystalline graphite according to claim 2, wherein the bonded layer (3) has an average film thickness of 0.5 to 20 μm. The bonded structure of high crystalline graphite according to claim 2, wherein the metal is iron and the average film thickness of the bonded layer (3) is 50 μm or less. The bonded structure of high crystalline graphite according to claim 3, wherein the average film thickness of the bonded layer is 0.5 to 5 μm. The bonded structure of high crystalline graphite according to any one of claims 1 to 6, wherein the laminated graphite sheet (1) is laminated and bonded in a state where the crystal orientations of graphite are crossed. A plurality of plate-shaped or sheet-shaped graphite sheets (1) made of highly crystalline graphite are laminated, and a thin bonding material (2) made of metal or oxide is interposed between the laminated surfaces of each graphite sheet (1). By heating and pressurizing the laminated graphite sheets (1) under reduced pressure, carbides are generated between the laminated surfaces of the graphite sheets (1) to form a bonding layer (3) for joining the graphite sheets to each other. A method for joining highly crystalline graphite. The method for joining highly crystalline graphite according to claim 8, wherein iron, cobalt, nickel or oxides thereof or titanium oxide or vanadium oxide is used as the bonding material (2). A fine powder of iron oxide, cobalt oxide, vanadium oxide, titanium oxide, or nickel as the bonding material (2) is adhered to the laminated surface of the graphite sheet (1) to form a film as the bonding layer (3). The method for joining highly crystalline graphite according to claim 8 or 9. The method for joining highly crystalline graphite according to claim 10, wherein the finely powdered bonding material (2) is applied to the laminated surface of the graphite sheet (1) as a suspension to which a lower alcohol is added and dried. The method for joining highly crystalline graphite according to claim 10, wherein the bonding material (2) is adhered to the laminated surface of the graphite sheet (1) by sputtering or other physical vapor deposition method. The method for joining highly crystalline graphite according to any one of claims 10 to 12, wherein the finely powdered bonding material (2) has a particle size of 2 μm or less. The method for joining high crystalline graphite according to claim 8 or 9, wherein an iron foil is used as the joining material (2).