JP2000247740A - Graphite sheet having insulated surface and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a graphite sheet capable of preventing the elimination of graphite powder from the surface thereof while maintaining the heat conductivity and flexibility and having electrical insulating properties of the surface. SOLUTION: This method for producing a graphite sheet comprises a pretreating step for heating up a polyimide film having <=300 μm film thickness from room temperature in an inert gas and baking the polyimide film at a temperature within the range of 1,000 to 1,600 deg.C, a regular treating step for heating up the polyimide film after the pretreating step from the room temperature to a temperature of >=2,500 deg.C and providing a graphite sheet, a rolling treatment step for carrying out the rolling treatment of the graphite sheet obtained in the regular treating step, and a step for forming an insulating material layer on the surface of the graphite sheet after the rolling treatment step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a graphite sheet, and more particularly to a method for producing a graphite sheet having an insulating layer on a surface.

[0002]

2. Description of the Related Art It has been known that a flexible graphite film is directly obtained by heat-treating a polyimide film and then rolling.

The physical properties of this film are similar to those of single-crystal graphite, and it does not cause flake-like exfoliation or residual acid phenomena. An excellent graphite film can be obtained.

[0004] On the other hand, in recent years, as electronic devices have become smaller and more sophisticated, how to release heat generated from a CPU or the like integrated at a high density has become an important consideration. In addition to heat dissipation, it is also important how to reduce temperature variations depending on the location.

Heretofore, at present, a metal plate such as an aluminum plate or a copper plate having excellent heat conductivity is appropriately processed or combined with a cooling fan to take measures against heat radiation.

Under such circumstances, the graphite sheet is
Compared to a metal plate, it has good thermal conductivity, and is light and flexible. Therefore, it is beginning to be expected as a heat conductive material for electronic devices, devices and equipment.

[0007]

However, when the graphite sheet is used as it is as a heat conductive material inside an electronic device, an electrical short is generated between the electronic components due to its excellent electrical conductivity. There are cases.

[0008] Further, when brought into direct contact with a metal, a thermal reaction occurs, which may result in alteration or the like.

In order to prevent these disadvantages, it has been proposed to attach an organic polymer film to a graphite sheet. However, applying an organic polymer thin film
When the heating element is brought into contact with the graphite, heat conduction to the graphite is hindered.

[0010] Accordingly, there is a need for a graphite sheet having excellent insulating properties, being chemically stable, and having a surface with reduced thermal resistance.

[0011]

In order to solve the above-mentioned problems, the present invention relates to a method for producing a polyimide film having a thickness of 300 μm or less from room temperature in an inert gas at 1000 ° C.
A preliminary processing step of firing at a temperature range of 600 ° C., a main processing step of raising the temperature from room temperature after the preliminary processing step to firing at a temperature of 2500 ° C. or higher to obtain a graphite sheet, A method for producing a graphite sheet, comprising: a rolling step of rolling the obtained graphite sheet; and a step of providing an insulating material layer on the surface of the graphite sheet after the rolling step.

With such a configuration, a chemically stable graphite sheet having excellent insulation properties can be realized.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claim 1 has a thickness of 3 mm.
A pretreatment step of raising the temperature of the polyimide film of not more than 00 μm from room temperature in an inert gas to a temperature range of 1000 ° C. to 1600 ° C., and after the pretreatment step, raising the temperature from room temperature to a temperature of 2500 ° C. or higher. This processing step of firing at a temperature to obtain a graphite sheet, a rolling processing step of rolling the graphite sheet obtained in the main processing step, and a step of providing an insulating material layer on the surface of the graphite sheet after the rolling processing step Thus, a graphite sheet whose surface is formed into an insulating layer and a method of manufacturing the same.

With such a structure, the surface of the graphite sheet is insulated, the chemical stability is improved, and the graphite powder is prevented from desorbing.

In many cases, the surface of the graphite sheet has a laminar structure, so that the chemical reaction is often limited to only one surface. In order to make the reaction proceed to the inside, fine scratches can be made on the surface of the graphite sheet as described in claim 2.

Here, the step of providing the insulating material layer is a step of insulating the surface of the graphite sheet.

With such a structure, there is no danger that thermal contact will be deteriorated as in the case of insulation by wrapping with a polymer film, and the high thermal conductivity of the graphite sheet can be effectively utilized.

As the insulating layer for forming such a structure, basically, any insulating layer can be used as long as it can maintain characteristics suitable for the use of the graphite sheet.

Further, in order to form an insulating layer on the surface of the graphite sheet, it is effective to make a layer having a certain thickness on the surface of the graphite sheet chemically insulative. The carbon on the graphite surface may be bonded to, for example, hydrogen or halogen atoms, so that the surface layer has no double bond.

Here, as described in claim 4, the thickness of the insulating material layer formed on the surface of the graphite sheet is 0.1 mm.
It is preferably in the range of 1 μm to 50 μm.

That is, in order to exhibit the basic characteristics of the graphite sheet, it is preferable that the insulating material layer is thin. If the insulating material layer is thicker than the above range, it takes a long time to exhibit good heat conduction characteristics. On the other hand, if it is too thin, it is not preferable from the viewpoint of mechanical strength and the like.

According to a fifth aspect of the present invention, the insulating material layer comprises carbon atoms constituting the original graphite sheet and fluorine bonded thereto.
It is suitable in terms of conditions often used for applications such as insulation, heat resistance, and mechanical strength.

Further, the step of providing the insulating material layer may be a step of exposing the graphite sheet to fluorine gas for a certain period of time while maintaining the graphite sheet in a specific temperature range. The thickness of the formed insulating material layer can be defined by this temperature and time.

In order for the surface of the graphite sheet to react with fluorine gas, it is not always necessary to set the temperature to a high temperature, and a plasma containing fluorine may be used. In the case where fluorine is introduced using plasma and the insulating treatment is performed, the temperature of the graphite sheet may be lowered.

In order to form a plasma containing fluorine, not only a fluorine gas but also a hydrogen fluoride gas may be used. Of course, a diluent gas such as argon may be used to generate the plasma.

As described in claim 8, chlorine or bromine may be used to convert the surface of the graphite sheet into an insulating material, but since it does not form an insulating layer by a heating reaction, as described in claim 9, Preferably, plasma is used.

Here, the region of the insulating material layer formed on the surface of the graphite sheet, which is sufficiently thinner than the thickness of the insulating material layer, may be activated by oxygen plasma. it can.

Then, a conductive wiring circuit formed of a conductive thin film of metal or the like can be provided on the activated insulating material layer.

Alternatively, as described in claim 12, an insulating polymer film such as polyimide provided with a conductive wiring circuit formed of a conductive thin film of metal or the like is attached to the graphite sheet. May go.

Hereinafter, a more detailed description will be given in accordance with each embodiment of the present invention.

(Embodiment 1) In this embodiment, a polyimide film having a thickness of 75 μm manufactured by Dupont Toray (trade name: Kapton) was used.

Next, in order to obtain foamability by heat treatment,
Preliminary baking using such a polyimide film is performed by raising the temperature in nitrogen at a rate of 5 ° C./min.
The test was performed at 200 ° C.

Then, the main firing is performed in an Ar gas atmosphere.
The temperature was raised at a rate of 20 ° C / min, and the maximum processing temperature was 28
The test was performed at 00 ° C.

The film after the main baking was a graphite sheet, was in a foamed state, had a thickness of 250 to 300 μm, had no flexibility, and was hard and brittle.

Therefore, in order to make the graphite sheet flexible, rolling was performed using a roller.

Specifically, the graphite sheet was sandwiched on both sides by a polyimide film having a thickness of 125 μm, and was rolled by a rolling roller set at a roller interval of 50 μm.

The film thickness after the rolling was 95 μm, and had sufficient flexibility and flexibility.

The above-described conditions for graphitization and rolling conditions are typical examples, and it is a matter of course that the conditions are not limited as long as the graphitization is performed and the rolling process is performed without fail.

The graphite sheet thus obtained was used as a raw material, and was reacted with fluorine in a nickel-made reaction tube at 350 ° C. for 1 hour to fluorinate the graphite sheet to a thickness of about 5 μm from the surface of the graphite sheet. The thickness of the fluorinated layer was not necessarily uniform because the surface of the graphite sheet was foamed and was not flat even after rolling, but all parts showed insulation.

Of course, if the temperature for reacting fluorine is increased, or if the time is increased, the fluorinated layer becomes thicker. As a result of various studies, the inventors have found that the thickness of the fluorinated insulating material layer that can withstand use is practically preferably 0.5 to 50 μm, and for that purpose, the reaction conditions are 320 ° C. to 630 ° C. At a temperature between 350 ° C. and 430 ° C., preferably between 0.5 and 12 hours.

In the present embodiment, the temperature of the heat source is set to 100 ° C., only the graphite sheet of 5 cm square is used, and the insulating layer is fluorinated to a thickness of 5 μm on both sides in the same manner as described above. Are prepared by using only one graphite sheet, using two graphite sheets, and using three graphite sheets, and contacting the heat source to reach a steady state. The temperature at was measured.

As a result, the temperature was 87 ° C. for the raw graphite sheet alone, and 87 ° C. for the graphite sheet whose surface was insulated by fluorine treatment, which was substantially the same as the temperature.

Further, the graphite sheet having the insulating layers formed on both sides thereof has the same flexibility and flexibility as a single graphite sheet, and even if the graphite sheet is lightly brought into contact with an iron plate and relatively moved, graphite powder is generated. Did not.

Further, the graphite sheet having the insulating layers formed on both surfaces did not cause any breakage such as peeling or cracking even when it was bent 100 times in each of the front and back directions.

Therefore, the graphite sheet according to the present embodiment, whose both surfaces are covered with the insulating layer, can improve the mechanical strength while maintaining the original thermal conductivity, flexibility and flexibility of the graphite sheet, and improve the graphite powder. It can be said that it has realized prevention of desorption and insulation of the surface.

When the graphite sheet of the present embodiment is cut, trimmed, drilled for mounting, etc. in order to mount the graphite sheet in the electronic apparatus, it is needless to say that the processing is the same as the processing of the graphite sheet. is there.

(Embodiment 2) In the present embodiment, when a graphite sheet of the same material as that of Embodiment 1 is produced, when rolling with a roller, sandpaper No. 600 is attached to the surface of the roller. Rolling was performed. As a result, it was possible to give flexibility to the graphite sheet and to form extremely fine indentations on the surface. When the graphite sheet was reacted with fluorine in the same manner as in Embodiment 1, fluorination was able to be performed very easily to a thickness of 10 μm on the surface. According to this method, the chemical reaction can easily proceed into the graphite sheet.

Further, when various tests were conducted on the particle size of the sandpaper to be used, it was found that a particle size of about 400 (50 microns) to about 1000 (15 microns) was preferable. As a result, a flaw having a depth of about 15 to 50 microns is formed on the sheet.

Also, if the rotational speeds (peripheral speeds) of the upper and lower rollers are made different during rolling, they become rubbed and become fine scratches instead of indentations, and the reaction proceeds more easily than in the case of indentations. Become. Sandpaper particles may be as fine as 5 microns or more than in the case of indentations.

If sandpaper is attached to only one of the upper and lower rollers used for rolling, fine scratches can be made only on one surface of the graphite sheet, and the fluorination reaction can be made thicker only on that surface.

In this embodiment, as a method of making a scratch,
Sandpaper was used, but the present invention is not limited to this, and it is not performed at the same time as rolling.
Obviously, a method of scratching the surface with a particle size of 50 microns may be used.

(Embodiment 3) In this embodiment, after a graphite sheet made of the same material as that of Embodiment 1 is produced, this sheet is set in a plasma generator and fluorine diluted with argon at room temperature is used. One side exposed to the plasma containing gas was fluorinated to prepare a graphite sheet having a 1.5 μm-thick insulating layer formed thereon.

With respect to the graphite sheet thus obtained, the same result as in the first embodiment was confirmed with respect to the insulation of the surface while maintaining the original thermal conductivity of the graphite sheet. Further, as described in Embodiment 1, the thickness of the fluorinated layer that can withstand use is 0.5 to 50 μm, and the step for obtaining the same is performed by reducing the graphite sheet between −200 ° C. and + 250 ° C. And preferably at a temperature between minus 50 ° C and plus 100 ° C.
Exposure to a plasma containing fluorine for 0 to 200 minutes has been found to be appropriate.

When the insulating layer is formed by plasma, the insulating layer is formed only on one side, and when the insulating layer is formed on both sides, two reactions must be performed. However, it is not always necessary to make both surfaces insulative, and only one surface may need to be made insulative as a conductive material.

Therefore, the graphite sheet according to the present embodiment, whose both surfaces are covered with the ceramic thin film, can improve the mechanical strength, prevent the desorption of the graphite powder, and maintain the surface thermal conductivity while maintaining the original thermal conductivity of the graphite sheet. It can be said that insulation has been achieved, and the one further covered with a polymer thin film can also exhibit the original flexibility and flexibility of a graphite sheet.

Although argon has been used as a method for forming the insulating layer, it is not necessarily limited to this. For example, nitrogen gas can be used to dilute the fluorine gas, in which case the insulating layer also contains a carbon nitride component. Nitrogen carbon is hard and wear-resistant and is effective for protecting the surface of the graphite sheet. Since such carbon nitride is dispersed in the fluorinated carbon layer, it does not impair the original flexibility of the graphite sheet.

(Embodiment 4) In this embodiment, after a single graphite sheet similar to that of Embodiment 1 is produced, the graphite sheet is placed in a plasma apparatus,
Exposure to oxygen plasma for 20 minutes at room temperature. By this operation, the insulating layer made of carbon fluoride formed on the surface of the graphite sheet became hydrophilic. In addition, the surface of the insulating layer subjected to such a treatment became familiar with the adhesive, and the adhesive strength was increased. Further, it was found that when a metal was deposited, a film having uniform and sufficient adhesion was obtained.

When the graphite sheet of the present embodiment was used to confirm and compare the physical properties in the same manner as that of the first embodiment, the adhesiveness was particularly improved. The phenomenon that the insulating layer peeled off from the graphite sheet surface did not occur at all.

Therefore, it goes without saying that the modification of the surface of the insulating layer according to the present embodiment can be applied to the insulating layer formed by the plasma method according to the third embodiment.

(Embodiment 5) In this embodiment, chlorine or bromine is used in place of fluorine in bonding a reactive element to the surface of a graphite sheet by plasma as in Embodiment 2. Chlorine, bromine and iodine do not react only by heating the graphite sheet. For this reason, it was necessary to make the plasma into a state of high energy and react. Of these, iodine was not practical because the reaction did not proceed to the inside. Also, when comparing chlorine and bromine, it was found that the reaction proceeded more easily with chlorine. That is, when the film was exposed to plasma at plus 100 ° C. for 3 hours, the thickness of the formed insulating layer was about 1 μm in the case of chlorine and 0.6 μm in the case of bromine. However, none of them exhibited insulating properties and did not impair the original flexibility of the graphite sheet.

Using the graphite sheet of the present embodiment, the physical properties were confirmed and compared in the same manner as in the first embodiment. Especially, the adhesiveness was improved, and even if the sheet was excessively bent, The phenomenon that the insulating layer peeled off from the graphite sheet surface did not occur at all.

Further, with respect to the insulating layer obtained in this embodiment,
It should be noted that the oxygen plasma treatment shown in Example 3 was similarly effective.

(Embodiment 6) In this embodiment, copper is vapor-deposited to a thickness of 1 μm on a graphite sheet having an insulating layer whose surface reactivity is increased according to Embodiment 4 and having a size of 10 cm × 10 cm. Further, the copper vapor deposition film was formed into a circuit pattern for a power IC by lithography. An IC chip was directly bonded thereon by a flip chip method. When this was compared with the case where a similar circuit was formed on a polyimide film of the same size and the IC chip was bonded, the temperature when the IC chip was operated and reached a steady state was 85% on the graphite sheet. On the other hand, on polyimide, the temperature exceeded 97 ° C.

According to the present embodiment, a circuit can be formed directly on a graphite sheet having excellent thermal conductivity via a thin insulating layer, and an element generating a large amount of heat can be efficiently cooled. . Further, since the graphite sheet itself is flexible, it is possible to realize new functions exceeding those of the conventionally used polyimide.

(Embodiment 7) In this embodiment, a graphite sheet surface-treated according to Embodiment 3
Alternatively, a film made of a polymer such as polyimide having an electronic circuit formed thereon was adhered to a graphite sheet having no insulating material layer formed on the surface thereof by an appropriately selected adhesive.

Using such a flexible electronic circuit, an electronic circuit of the same size was made in the same manner as in the fifth embodiment, and the temperature of the IC was about 88 ° C.
According to this embodiment, as a base film of an electronic circuit,
Because the 50μm polyimide film is interposed,
Although the effect of removing heat generated from components mounted on the circuit, particularly transistors, ICs and the like, is inferior to that of the sixth embodiment, it can be used without significantly changing the conventionally used circuit material configuration.

By using a configuration in which the electronic circuit of the polymer film of the present embodiment is attached to a graphite sheet in a portion where heat generation is a problem in a circuit using only the polymer film, a simple solution can be obtained. can do.

[0068]

As described above, according to the present invention, a polyimide film is fired by pre-firing and main firing, and after firing, the insulating material layer is formed on the surface of the graphite sheet rolled using a rolling roller. By providing flexibility,
It is possible to obtain a graphite sheet of good quality, which is excellent in electrical insulation and has improved characteristics such that graphite powder is not easily detached. Further, by treating the surface of the insulating layer, an electronic circuit can be directly formed.

Continuation of the front page (72) Inventor Akira Taomoto 3-10-1, Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa F-term in Matsushita Giken Co., Ltd. 4G032 AA13 BA04 GA11 GA19 4G046 EA03 EB01 EB06 EC03 EC05 5F036 AA01 BB21 BD11

Claims (10)

[Claims] 1. A polyimide film having a thickness of 300 μm or less is heated from room temperature in an inert gas to 1000 ° C.
A preliminary processing step of firing at a temperature range of 600 ° C., a main processing step of raising the temperature from room temperature after the preliminary processing step to firing at a temperature of 2500 ° C. or higher to obtain a graphite sheet, A method for producing a graphite sheet having an insulating layer formed on the surface thereof by a rolling step of rolling the obtained graphite sheet and a step of providing an insulating material layer on the surface of the graphite sheet after the rolling step. 2. The method for producing a graphite sheet according to claim 1, further comprising a rolling treatment step or a step of making fine scratches on the surface thereafter. 3. The method for producing a graphite sheet according to claim 1, wherein the step of providing the insulating material layer is a step of reacting fluorine on the surface of the graphite sheet. 4. The method for producing a graphite sheet according to claim 1, wherein the step of providing the insulating material layer is a step of reacting chlorine or bromine on the surface of the graphite sheet. 5. A graphite sheet obtained by calcining and rolling a polyimide film having a thickness of 300 μm or less in an inert gas, wherein an insulating material layer is formed on the surface of the graphite sheet after the rolling. 6. The graphite sheet has fine scratches on its surface after or after the rolling process.
The described graphite sheet. 7. The graphite sheet according to claim 5, wherein the insulating material layer is formed by reacting fluorine on the surface of the graphite sheet. 8. The graphite sheet according to claim 5, wherein the insulating material layer mainly comprises carbon and fluorine. 9. The graphite sheet according to claim 5, wherein the insulating material layer is formed by reacting chlorine or bromine on the surface of the graphite sheet. 10. The graphite sheet according to claim 6, wherein an electronic circuit is formed by a thin film of a conductive material on the insulating material layer formed on the surface of the graphite sheet.