WO2024142895A1

WO2024142895A1 - Heat transfer member and device

Info

Publication number: WO2024142895A1
Application number: PCT/JP2023/044322
Authority: WO
Inventors: 健夫木戸
Original assignee: 富士フイルム株式会社
Priority date: 2022-12-26
Filing date: 2023-12-12
Publication date: 2024-07-04

Abstract

The present invention addresses the problem of providing a heat transfer member and a device using the same, the heat transfer member exhibiting excellent adhesion to a heat-dissipating member even when exposed to a process in which heating and cooling are repeated. The heat transfer member according to the present invention satisfies at least one of requirements 1 and 2.　Requirement 1: Contains 40 to 99% by volume of metal nanowire.　Requirement 2: Contains 70 to 99 % by mass of metal nanowire.

Description

Thermal Conductive Materials and Devices

The present invention relates to a thermally conductive member and device.

In recent years, devices using semiconductor elements have rapidly become more functional and smaller. As a result, the amount of heat generated by the semiconductor elements in the devices has increased, and there is an increasing need to dissipate the generated heat to the outside.
Known methods for dissipating heat generated inside a device to the outside include using a heat dissipation member (e.g., a heat spreader, a heat sink, a thermal diffusion sheet, etc.) Also known is a method for bonding a heat source (heat generating element) of the device and the heat dissipation member with a thermally conductive member in order to efficiently transfer heat to the heat dissipation member.

For example, Patent Document 1 describes such a thermally conductive member that uses a thermally conductive resin composition containing easily deformable aggregates including thermally conductive particles and thermally conductive fibers, a binder resin, and a solvent, and is obtained by removing the solvent ([Claim 1], [Claim 4], [Claim 7], etc.).

JP 2014-201687 A

The inventors have studied the thermally conductive member described in Patent Document 1 and have found that after the thermally conductive member is placed between the heat dissipation member and the heat generating body, the adhesion between the heat dissipation member and the thermally conductive member decreases when the member is exposed to repeated heating and cooling processes in a semiconductor manufacturing process or the like. The inventors have also found that the aforementioned decrease in adhesion is a problem that becomes apparent when metal nanowires are used as the thermally conductive fibers. This is believed to be because metal nanowires are more likely to aggregate than metal fibers with diameters on the order of micrometers or millimeters.

The present invention aims to provide a thermally conductive member that maintains good adhesion to a heat dissipation member even after being exposed to repeated heating and cooling processes, and a device that uses the same.

As a result of intensive research to solve the above problems, the inventors discovered that a thermally conductive member containing metal nanowires in accordance with certain requirements maintains good adhesion to a heat dissipation member even after being exposed to repeated heating and cooling processes, and thus completed the present invention.
That is, the present inventors have found that the above problems can be solved by the following configuration.

[1] A thermally conductive member satisfying at least one of the following requirements 1 and 2:
Requirement 1: The metal nanowires are contained at 40 to 99 volume %.
Requirement 2: The metal nanowires are contained in an amount of 70 to 99 mass %.
[2] The heat conductive member according to [1], wherein the metal constituting the metal nanowires is at least one metal selected from the group consisting of silver and copper.
[3] The thermal conductive member according to [1] or [2], further comprising a resin.
[4] The heat conductive member according to [3], wherein the resin is a crosslinked resin.
[5] The heat conductive member according to [3] or [4], which is in a sheet form.
[6] A device comprising a heat generating body, the heat conducting member according to any one of [1] to [5], and a heat dissipating member.
[7] The device according to [6], comprising a heat generating element, a thermally conductive member, and a heat dissipating member adjacent to each other in this order.

The present invention provides a thermally conductive member that has good adhesion to a heat dissipation member even after being exposed to repeated heating and cooling processes, and a device using the same.

FIG. 1A is a schematic cross-sectional view of a valve metal substrate prior to an anodization step in a procedure showing an example of a method for producing metal nanowires. FIG. 1B is a schematic cross-sectional view of a structure after an anodization step in the procedure showing an example of a method for producing metal nanowires. FIG. 1C is a schematic cross-sectional view of a structure after a metal filling step in the procedure showing an example of a method for producing metal nanowires. FIG. 1D is a schematic cross-sectional view of the structure after the isolation step in the procedure showing one example of a method for producing metal nanowires. FIG. 1E is a schematic cross-sectional view of a structure (metal nanowires) after a crushing step in the procedure showing an example of a method for producing metal nanowires.

The present invention will be described in detail below.
The following description of the components may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.
In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.
In addition, in this specification, "(meth)acrylic" is a notation representing "acrylic" or "methacrylic".

[Heat conductive material]
The thermally conductive member of the present invention is a thermally conductive member that satisfies at least one of the following

requirements

1 and 2, and is preferably a thermally conductive member that satisfies at least the following requirement 2, and is more preferably a thermally conductive member that satisfies both of the following

requirements

1 and 2, because this provides better adhesion to the heat dissipation member.
Requirement 1: The metal nanowires are contained at 40 to 99 volume %.
Requirement 2: The metal nanowires are contained in an amount of 70 to 99 mass %.
Here, the "volume percentage" in requirement 1 can be determined by measuring the mass of each component contained in the thermal conductive member and calculating the volume of each component by dividing the mass of each component by the specific gravity of each component.

In the present invention, as described above, a thermally conductive member that satisfies at least one of

requirements

1 and 2 maintains good adhesion to a heat dissipating member even after being subjected to a process in which heating and cooling are repeated.
Here, the reason why the adhesion to the heat dissipation member is good even after exposure to the process of repeated heating and cooling is not clear in detail, but is presumed to be as follows.
In other words, by satisfying at least one of

requirements

1 and 2, the strength is improved by the metal nanowires becoming entangled with each other, and the content of components other than the metal nanowires (e.g., resin, metal particles, etc.) is reduced. As a result, the thermal expansion difference with the heat dissipation member (e.g., a heat spreader made of a copper plate, etc.) is reduced, and it is believed that the adhesion to the heat dissipation member is good even after being exposed to repeated heating and cooling processes.

The heat conductive member of the present invention preferably satisfies at least one of the following requirements 1-1 and 2-1, and more preferably satisfies at least one of the following requirements 1-2 and 2-2.
Furthermore, it is more preferable that the heat conductive member of the present invention satisfy both of the following requirements 1-1 and 2-1, and it is particularly preferable that the heat conductive member of the present invention satisfy both of the following requirements 1-2 and 2-2.
Furthermore, the thermally conductive member of the present invention preferably contains more than 50 volume % and not more than 99 volume % of metal nanowires, for the reason that this provides better adhesion to the heat dissipation member.
Requirement 1-1: The metal nanowires are contained at 45 to 90 volume %.
Requirement 2-1: The metal nanowires are contained in an amount of 75 to 99 mass %.
Requirement 1-2: The metal nanowires are contained at 50 to 80 volume %.
Requirement 2-2: The metal nanowires are contained in an amount of 80 to 98 mass %.

[Metal Nanowires]
The metal nanowires contained in the heat conducting member of the present invention are conductive substances made of metal, having a needle-like or thread-like shape, and having a diameter on the order of nanometers.
The metal nanowires may be either straight or curved.
Furthermore, the material of the metal nanowires is not particularly limited as long as it contains a metal, and may contain components other than metals in addition to the metal.

The specific surface area per unit mass of the metal nanowires is preferably 100 to 50,000 m ² /kg, more preferably more than 100 m ² /kg and not more than 50,000 m ² /kg, even more preferably more than 1,000 m ² /kg and not more than 50,000 m ² /kg, particularly preferably more than 2,000 m ² /kg and not more than 30,000 m ² /kg, and most preferably more than 3,000 m ² /kg and not more than 20,000 m ² /kg.
Here, the specific surface area per unit mass of the obtained metal nanowires can be measured by known analytical methods, but in the present invention, a value measured by a krypton gas adsorption method is used.

In the present invention, the metal constituting the above-mentioned metal nanowires is not particularly limited, but it is preferable that the metal be a material having an electrical resistivity of 10 ³ Ω·cm or less, and specific examples of such metals include gold (Au), silver (Ag), copper (Cu), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), etc.
Among these, at least one metal selected from the group consisting of Ag and Cu is preferable, and Cu is more preferable, because of its particularly high thermal conductivity.

The diameter (arithmetic mean value) of the metal nanowires is preferably 10 to 200 nm, more preferably 10 to 100 nm, and even more preferably 10 to 50 nm.
The length (arithmetic mean value) of the metal nanowires is preferably 0.3 to 300 μm, more preferably 0.5 to 200 μm, and even more preferably 1 μm to 100 μm.
Here, the diameter and length of the metal nanowire can be determined, for example, by observing an SEM image at a magnification of 100 to 500 times using a field emission scanning electron microscope (FE-SEM). Specifically, the diameter and length of the metal nanowire are determined by observing 10 metal nanowires randomly selected from an SEM image taken at a magnification of 100 to 500 times, measuring their diameters and lengths, and performing this in 10 fields of view, and averaging the measured values of the diameters and lengths of a total of 100 metal nanowires.

The ratio of the length to the diameter (length/diameter) of the metal nanowire (hereinafter also abbreviated as "aspect ratio") is preferably 10 or more, and more preferably 100 to 1000.

<Method of Producing Metal Nanowires>
The method for producing the metal nanowires contained in the heat conduction member of the present invention (hereinafter also formally abbreviated as "the production method of the present invention") is preferably a method having an anodization process for forming an anodized film having pores on ^the surface of a valve metal substrate, a metal filling process for filling the pores with metal, an isolation process for isolating the filled metal from the anodized film and the valve metal substrate, and a crushing process for crushing the isolated metal (hereinafter also abbreviated as "isolated metal") to obtain metal nanowires, because this makes it easy to adjust the specific surface area per unit mass to 100 to 50,000 m2/kg.

Next, we will use Figures 1A to 1E to provide an overview of each step in the manufacturing method of the present invention, and then provide a detailed description of each processing step.

As shown in FIGS. 1A and 1B, in the anodizing step, the surface of a valve metal substrate 1 is anodized to form an anodized film 3 having pores (micropores) 2 on the surface of the valve metal substrate 1.
Next, as shown in FIG. 1C, in a metal filling step, the pores 2 are filled with a metal 4.
Next, as shown in Fig. 1D, in the isolation step, the filled metal 4 is isolated from the anodized film 3 and the valve metal substrate 1. The embodiment shown in Fig. 1D shows the state in which the isolated metal 5 obtained in the isolation step is collected (a part of the isolated metal is adhered).
Next, as shown in FIG. 1E, in a crushing step, metal nanowires 10 in which the isolated metal 5 is crushed can be obtained.

(Valve metal substrate)
The valve metal substrate used in the manufacturing method of the present invention is not particularly limited as long as it is a substrate containing a valve metal.
Specific examples of the valve metal include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, etc. Among these, aluminum is preferable because it has good dimensional stability and is relatively inexpensive.
Therefore, in the manufacturing method of the present invention, it is preferable to use a base material containing aluminum (hereinafter, abbreviated as "aluminum base material") as the valve metal base material.

The aluminum substrate is not particularly limited, and specific examples include pure aluminum plates; alloy plates containing aluminum as the main component and trace amounts of other elements; substrates in which high-purity aluminum is vapor-deposited onto low-purity aluminum (e.g., recycled materials); substrates in which the surfaces of silicon wafers, quartz, glass, etc. are coated with high-purity aluminum by methods such as vapor deposition and sputtering; and resin substrates laminated with aluminum.

The surface of the valve metal substrate that is anodized in the anodizing process described below preferably has a valve metal purity of 99.5% by mass or more, more preferably 99.9% by mass or more, and even more preferably 99.99% by mass or more. When the valve metal purity is within the above-mentioned range, the arrangement of the through passages is sufficiently regular.

In addition, the surface of the valve metal base material that is to be anodized in the anodizing step described below is preferably previously subjected to a heat treatment, a degreasing treatment and a mirror finish treatment.
Here, the heat treatment, degreasing treatment and mirror finish treatment can be the same as those described in paragraphs [0044] to [0054] of JP-A-2008-270158.

(Anodizing process)
The anodizing step is a step of forming a porous anodized film on the surface of the valve metal base by subjecting the surface of the valve metal base to an anodizing treatment.

The anodizing treatment carried out in the anodizing step can be a conventionally known method, but it is preferable to use a self-ordering method or a constant voltage treatment because this makes it possible to isolate the filled metal with less variation in diameter in the isolation step described below.
Here, the self-ordering method of the anodizing treatment and the constant voltage treatment can be the same as the treatments described in paragraphs [0056] to [0108] and in FIG. 3 of JP-A-2008-270158.

The anodizing treatment can be carried out, for example, by passing a current through a valve metal substrate as an anode in a solution having an acid concentration of 1 to 10% by mass.
The solution used in the anodizing treatment is preferably an acid solution, more preferably sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid, amidosulfonic acid, glycolic acid, tartaric acid, malic acid, citric acid, etc., and among these, sulfuric acid, phosphoric acid, and oxalic acid are further preferable, and oxalic acid is particularly preferable. These acids can be used alone or in combination of two or more kinds.

The conditions for the anodizing treatment vary depending on the electrolyte used and cannot be determined in general, but generally, the electrolyte concentration is preferably 0.1 to 20% by mass, the solution temperature is -10 to 30°C, the current density is 0.01 to 20 A/ ^dm2 , the voltage is 3 to 300 V, and the electrolysis time is 0.5 to 30 hours, more preferably the electrolyte concentration is 0.5 to 15% by mass, the solution temperature is -5 to 25°C, the current density is 0.05 to 15 A/ ^dm2 , the voltage is 5 to 250 V, and the electrolysis time is 1 to 25 hours, and even more preferably the electrolyte concentration is 1 to 10% by mass, the solution temperature is 0 to 20°C, the current density is 0.1 to 10 A/ ^dm2 , the voltage is 10 to 200 V, and the electrolysis time is 2 to 20 hours.

The anodizing treatment time is preferably 0.5 minutes to 16 hours, more preferably 1 minute to 12 hours, and even more preferably 2 minutes to 8 hours.

The thickness of the anodized film formed by the anodization process is not particularly limited, but from the viewpoint of adjusting the length of the metal nanowires, it is preferably 0.3 to 300 μm, more preferably 0.5 to 120 μm, and even more preferably 0.5 to 100 μm.
The thickness of the anodic oxide film can be calculated as the average value of 10 measurements taken by cutting the anodic oxide film in the thickness direction with a focused ion beam (FIB), taking surface photographs (magnification: 50,000 times) of the cross section with a field emission scanning electron microscope (FE-SEM).

The density of the pores formed by the anodization process is not particularly limited, but is preferably 2 million pores/ ^mm2 or more, more preferably 10 million pores/ ^mm2 or more, even more preferably ⁵⁰ million pores/mm2 or more, and particularly preferably 100 million pores/ ^mm2 or more.
The density of the pores can be measured and calculated by the method described in paragraphs [0168] and [0169] of JP-A-2008-270158.

The average opening diameter of the pores formed by the above-mentioned anodization process is not particularly limited, but from the viewpoint of adjusting the diameter of the metal nanowires, it is preferably 5 to 500 nm, more preferably 20 to 400 nm, even more preferably 40 to 200 nm, and particularly preferably 50 to 100 nm.
The average opening diameter of the pores can be calculated as the average value of measurements taken at 50 points on a surface photograph (magnification: 50,000 times) taken with an FE-SEM.

(Metal filling process)
The metal filling step is a step of filling the inside of the pores with a metal after the anodization step.

The above metals can be the same as those described above as the metals that make up the metal nanowires.

Methods for filling the interior of the pores with the metal include, for example, methods similar to those described in paragraphs [0123] to [0126] and [Figure 4] of JP 2008-270158 A.

In the manufacturing method of the present invention, it is preferable that the metal filling step includes a plating step, because this makes it difficult for the produced metal nanowires to contain hollow portions.
Specifically, it is preferable to use an electrolytic plating method as a method for filling the inside of the pores with the metal, and for example, an electrolytic plating method or an electroless plating method can be used.
Here, it is difficult to selectively deposit (grow) a metal in a hole with a high aspect ratio using a conventional electrolytic plating method used for coloring, etc. This is thought to be because the deposited metal is consumed in the hole and the plating does not grow even if electrolysis is performed for a certain period of time or more.
Therefore, in the manufacturing method of the present invention, when filling metal by electrolytic plating, it is necessary to provide a rest period during pulse electrolysis or constant potential electrolysis. The rest period must be 10 seconds or more, and is preferably 30 to 60 seconds.
It is also preferable to apply ultrasonic waves to promote stirring of the electrolyte.
Furthermore, the electrolysis voltage is usually 20 V or less, and preferably 10 V or less, but it is preferable to measure the deposition potential of the target metal in the electrolyte solution to be used in advance and perform constant-potential electrolysis at a potential within +1 V of that potential. When performing constant-potential electrolysis, it is preferable to use a device that can also be used with cyclic voltammetry, and a potentiostat device manufactured by Solartron, BAS, Hokuto Denko, IVIUM, etc. can be used.

As the plating solution, a conventionally known plating solution can be used.
Specifically, when copper is precipitated, an aqueous solution of copper sulfate is generally used, and the concentration of the copper sulfate is preferably 1 to 300 g/L, and more preferably 100 to 200 g/L. Precipitation can be promoted by adding hydrochloric acid to the electrolyte. In this case, the concentration of hydrochloric acid is preferably 10 to 20 g/L.
When gold is to be deposited, it is preferable to use a sulfuric acid solution of gold tetrachloride and to perform plating by AC electrolysis.

In addition, since it takes a long time to completely fill the pores of high aspect ratio pores with metal using electroless plating, it is preferable to fill the metal using electrolytic plating in the manufacturing method of the present invention.

In the manufacturing method of the present invention, it is preferable to use, as the electrolytic plating method, a treatment method in which AC electrolytic plating and DC electrolytic plating are combined in this order.
Here, in the AC electrolytic plating method, for example, a voltage is applied modulated into a sine wave at a predetermined frequency. Note that the waveform of the voltage modulation is not limited to a sine wave, and may be, for example, a square wave, a triangular wave, a sawtooth wave, or an inverse sawtooth wave.
In addition, the DC electrolytic plating method can appropriately use the treatment methods in the electrolytic plating method described above.

In the manufacturing method of the present invention, because it is possible to shorten the time required to manufacture metal nanowires, as shown in FIG. 1C, it is preferable that the metal filling step is a process that is performed on the region from the bottom of the hole to halfway through the opening, out of the entire region from the bottom of the hole to the opening.

(Isolation step)
The isolation step is a step of isolating the filled metal from the anodized film and the valve metal substrate after the metal filling step.
Here, the method of isolating the filled metal from the anodized film and the valve metal base material is not particularly limited, and for example, the method of removing (for example, dissolving, peeling, etc.) the anodized film and the valve metal base material and isolating the filled metal can be preferably mentioned.Therefore, the embodiment after the above-mentioned isolation process also includes, for example, the embodiment in which the filled metal is dispersed in an isolated state in the treatment liquid used in the dissolution process (dissolution treatment) described later.

In the manufacturing method of the present invention, the method for removing the anodic oxide film and the valve metal substrate is not particularly limited, and may be, for example, by polishing. However, in order to ensure that the length of the produced metal nanowires is uniform, it is preferable that the isolation process includes a dissolution process, that is, that at least a portion of the anodic oxide film and the valve metal substrate is removed by a dissolution process.

In the manufacturing method of the present invention, in order to maintain the shape and size of the metal nanowires produced, it is preferable that the isolation process includes a one-step removal process of removing the anodic oxide film and the valve metal substrate, and it is more preferable that the removal of the anodic oxide film is a process in which the anodic oxide film is removed by a dissolution treatment.
For the same reason, the isolation step may include a two-step removal step of removing the valve metal base material and then removing the anodic oxide film, and in this case, it is more preferable that both of the two removal steps are performed by dissolution treatment.

The removal of the valve metal substrate is preferably carried out by a dissolution treatment using a treatment liquid which does not easily dissolve the anodized film but easily dissolves the valve metal.
The dissolution rate of such a treatment solution for valve metal is preferably 1 μm/min or more, more preferably 3 μm/min or more, and even more preferably 5 μm/min or more.Similarly, the dissolution rate of anodized film is preferably 0.1 nm/min or less, more preferably 0.05 nm/min or less, and even more preferably 0.01 nm/min or less.
Specifically, the treatment liquid preferably contains at least one metal compound having a lower ionization tendency than the valve metal, and has a pH of 4 or less or 8 or more, more preferably a pH of 3 or less or 9 or more, and even more preferably a pH of 2 or less or 10 or more.

Such a treatment liquid is preferably based on an acid or alkaline aqueous solution and contains, for example, compounds of manganese, zinc, chromium, iron, cadmium, cobalt, nickel, tin, lead, antimony, bismuth, copper, mercury, silver, palladium, platinum, and gold (e.g., chloroplatinic acid), their fluorides, or their chlorides.
Among these, an acid aqueous solution base is preferred, and a chloride blend is preferred.
In particular, a treatment solution in which mercury chloride is blended into an aqueous hydrochloric acid solution (hydrochloric acid/mercury chloride) and a treatment solution in which copper chloride is blended into an aqueous hydrochloric acid solution (hydrochloric acid/copper chloride) are preferred from the viewpoint of treatment latitude.
The composition of such a treatment liquid is not particularly limited, and for example, a bromine/methanol mixture, a bromine/ethanol mixture, aqua regia, etc. can be used.

The acid or alkali concentration of such a treatment solution is preferably from 0.01 to 10 mol/L, and more preferably from 0.05 to 5 mol/L.
Furthermore, the processing temperature when using such a processing solution is preferably from -10°C to 80°C, and more preferably from 0°C to 60°C.

The valve metal substrate is removed by contacting the valve metal substrate after the metal filling step with the treatment liquid described above. The contact method is not particularly limited, and examples include the immersion method and the spray method. Of these, the immersion method is preferred. The contact time is preferably 10 seconds to 5 hours, and more preferably 1 minute to 3 hours.

To remove the anodic oxide film, a solvent that does not dissolve the metal filled in the pores but selectively dissolves the anodic oxide film can be used, and either an alkaline aqueous solution or an acid aqueous solution can be used.

When an alkaline aqueous solution is used, it is preferable to use an aqueous solution of at least one alkali selected from the group consisting of sodium hydroxide, potassium hydroxide, and lithium hydroxide, and it is more preferable to use an aqueous solution of potassium hydroxide. The concentration of the alkaline aqueous solution is preferably 1 to 30 mass %. The temperature of the alkaline aqueous solution is preferably 10 to 60°C, more preferably 20 to 60°C, and even more preferably 30 to 60°C.
On the other hand, when an aqueous acid solution is used, it is preferable to use an aqueous solution of an inorganic acid such as chromic acid, sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, oxalic acid, or a mixture thereof, and it is more preferable to use an aqueous solution of chromic acid. The concentration of the aqueous acid solution is preferably 1 to 30 mass %. The temperature of the aqueous acid solution is preferably 15 to 80°C, more preferably 20 to 60°C, and even more preferably 30 to 50°C.

The anodic oxide film is removed by contacting the above-mentioned alkaline aqueous solution and acid aqueous solution after the metal filling step (preferably after the valve metal substrate is removed). The contacting method is not particularly limited, and examples include immersion and spraying. Of these, the immersion method is preferred. The immersion time in the alkaline aqueous solution and acid aqueous solution is preferably 1 to 120 minutes, more preferably 2 to 90 minutes, even more preferably 3 to 60 minutes, and particularly preferably 3 to 30 minutes. Of these, 3 to 20 minutes is preferred, and 3 to 10 minutes is more preferred.

(Crushing process)
The crushing step is a step of crushing the isolated metal after the isolation step.
The method for crushing the isolated metal is not particularly limited, but a suitable example is a method in which the isolated metal is crushed by applying an impact to the isolated metal in a liquid.
The liquid (solvent) used for disintegration is not particularly limited as long as it does not alter or dissolve the isolated metal, and examples thereof include water, ethanol, methanol, acetone, methyl ethyl ketone, butanol, ethyl acetate, butyl acetate, tetrahydrofuran, toluene, dimethylformamide, cyclohexane, cyclohexanone, etc. Among these, water is preferred from the viewpoint of safety.
In addition, the crushing step is preferably carried out in water or in an aqueous solution having an alkali or acid concentration of less than 1 mass %, from the viewpoint of producing metal nanowires having higher bonding strength when bonded.
Examples of the crushing treatment include a crushing treatment using cavitation and a crushing treatment using ceramic balls, and devices such as an ultrasonic cleaner, an ultrasonic homogenizer, a jet mill, a wet type micronizer, etc. Among these, a crushing treatment using cavitation or a crushing treatment using ceramic balls is preferred, and a crushing treatment using cavitation is more preferred.

In the present invention, the concentration of the isolated metal in the liquid during pressure disintegration in the liquid is preferably 0.1 to 50 mass % because this makes the treatment uniform and improves productivity.
Furthermore, the concentration of the isolated metal in the liquid when the pressure is released in the liquid is more preferably 0.5 to 30 mass%, and even more preferably 1 to 10 mass%, because this allows for the production of metal nanowires having higher bonding strength upon bonding.

(Drying process)
The manufacturing method of the present invention preferably further includes a drying step for drying the isolated metal between the isolation step and the crushing step, since this makes apparent the effect of the present invention, that is, the ability to obtain metal nanowires having high bonding strength when bonded.
Here, the method for drying the isolated metal is not particularly limited, but after removing the anodized film and the valve metal substrate, the isolated metal can be recovered and dried by performing a separation operation such as filtration using a filter or centrifugation.

(Protective layer forming process)
Because the manufacturing method of the present invention can obtain metal nanowires with low connection resistance, it is preferable that the manufacturing method of the present invention further includes a step of forming a protective layer containing a corrosion inhibitor on the isolated metal after the isolation step (or after the drying step if the drying step is included).

The corrosion inhibitor is not particularly limited, and any known corrosion inhibitor can be used.
Examples of the corrosion inhibitor include compounds containing at least one of a nitrogen atom, an oxygen atom, and a sulfur atom.
From the viewpoint of durability, the corrosion inhibitor is preferably a heterocyclic compound containing at least one of a nitrogen atom and an oxygen atom, more preferably a compound containing a five-membered ring structure containing one or more nitrogen atoms, and particularly preferably at least one compound selected from the group consisting of a compound containing a triazole structure, a compound containing a benzimidazole structure, and a compound containing a thiadiazole structure. The five-membered ring structure containing one or more nitrogen atoms may be a monocyclic structure or a partial structure constituting a condensed ring.

In addition, the corrosion inhibitor is preferably a compound containing at least one of a polar group-containing acid and a polar group-containing base, because this makes it easier for the corrosion inhibitor to be adsorbed onto the surface of the isolated metal.
Examples of the polar group contained in the polar group-containing acid and the polar group-containing base include a carboxylic acid group (carboxy group), a sulfonic acid group (sulfo group), a phosphonic acid group, a phosphoric acid group, a primary to quaternary ammonium base, a carboxylate group, a sulfonate group, a phosphonate group, and a phosphate group.

In addition, the corrosion inhibitor is preferably a compound containing a carboxy group, because it bonds with metal ions to form complex ions, which makes it easier to protect the surface of the isolated metal.

Specific examples of the corrosion inhibitors include imidazole, benzimidazole, 1,2,4-triazole, benzotriazole (BTA), tolyltriazole (TTA), butylbenzyltriazole, alkyldithiothiadiazole, alkylthiol, 2-aminopyrimidine, 5,6-dimethylbenzimidazole, 2-amino-5-mercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole (DMTDA), 2-mercaptopyrimidine, 2-mercaptobenzoxazole, 2-mercaptobenzothiazole (MBT), 2-mercaptobenzimidazole, etc.

Other specific examples of the corrosion inhibitors include aliphatic carboxylic acids such as acetic acid, propionic acid, palmitic acid, stearic acid, lauric acid, arachidic acid, terephthalic acid, and oleic acid; carboxylic acids such as glycolic acid, lactic acid, oxalic acid, malic acid, tartaric acid, and citric acid; aminopolycarboxylic acids such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), ethylenediaminediacetic acid (EDDA), and ethylene glycol diethyl ether diaminetetraacetic acid (GEDA); uric acid; and gallic acid.

The corrosion inhibitors may be used alone or in appropriate combination of two or more kinds.
In addition, for the reason that the stability over time is good, the corrosion inhibitor preferably contains a compound containing a nitrogen atom (nitrogen-containing compound), more preferably is a nitrogen-containing compound, and further preferably is a heterocyclic compound containing at least one of a nitrogen atom and a sulfur atom.

The method for forming such a protective layer containing a corrosion inhibitor is not particularly limited, and examples include a method in which the isolated metal recovered in the drying process is added to an aqueous solution containing a corrosion inhibitor and stirred; a method in which the corrosion inhibitor is added to a washing solvent that washes the isolated metal recovered in the drying process; etc.

(Reduction or Removal Step)
Because the manufacturing method of the present invention can obtain metal nanowires with low connection resistance, it is preferable that the manufacturing method of the present invention further includes a step of reducing or removing the surface oxide layer of the isolated metal between the isolation step and the crushing step (or before the drying step, if the drying step is included).
The reduction or removal step may be, for example, a step of carrying out an immersion treatment using an aqueous alkaline solution or an aqueous acid solution as described above in the removal treatment of the anodic oxide film.

〔resin〕
It is preferable that the heat conductive member of the present invention further contains a resin, because by filling the gaps between the metal nanowires, the heat conductivity can be increased compared to when there are gaps.
The resin is preferably a resin other than a fluororesin, and examples thereof include an epoxy resin, an acrylic resin, a urethane resin, a maleimide resin, an itaconimide resin, and a nadimide resin.
Among these, a crosslinked resin is preferable, and an epoxy resin is more preferable, because the strength of the heat conductive member is improved by crosslinking of the resin in addition to entanglement of the metal nanowires.
Specific examples of the epoxy resin include epoxy resins having a naphthalene skeleton, bisphenol A type epoxy resins, bisphenol F type epoxy resins, phenol novolac type epoxy resins, alicyclic epoxy resins, siloxane type epoxy resins, biphenyl type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, and hydantoin type epoxy resins. These may be used alone or in combination of two or more.
In particular, from the viewpoint of film formability, the epoxy resin is preferably an epoxy resin having a naphthalene skeleton, a bisphenol A type epoxy resin, or a bisphenol F type epoxy resin that is liquid at room temperature.

Resins other than the above-mentioned epoxy resins include water-soluble polymers and oil-soluble polymers.
Here, "water-soluble" in the case of a water-soluble polymer means that the amount of the target substance dissolved in 100% by mass of water at 25°C is 5% by mass or more, and a more preferred water-soluble polymer means that the amount dissolved is 10% by mass or more.
Moreover, the term "oil-soluble" in the context of an oil-soluble polymer means that the amount of the target substance dissolved in 100% by mass of water at 25°C is less than 5% by mass.

Water-soluble polymers include polyvinyl alcohol (unmodified polyvinyl alcohol and modified polyvinyl alcohol), polyacrylic acid amide and its derivatives, ethylene-vinyl acetate copolymer, styrene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, polyvinylpyrrolidone, ethylene-acrylic acid copolymer, vinyl acetate-acrylic acid copolymer, carboxymethylcellulose, methylcellulose, casein, gelatin, starch derivatives, gum arabic, and sodium alginate.

Examples of oil-soluble polymers include (meth)acrylic acid ester polymers having an alkyl group having 12 to 30 carbon atoms in the side chain described in paragraphs [0009] to [0051] of WO 2018/207387, polymers having heat storage properties described in JP 2007-031610 A, and olefin copolymers described in paragraphs [0019] to [0021] of WO 2018/066605, the descriptions of which are incorporated herein. In particular, olefin copolymers having 3 to 8 carbon atoms are preferred, and copolymers of ethylene and olefins having 3 to 8 carbon atoms are more preferred.

Among the water-soluble polymers and oil-soluble polymers described above, water-soluble polymers are preferred, polyols are more preferred, polyvinyl alcohol is even more preferred, and modified polyvinyl alcohol is particularly preferred.

Among polyvinyl alcohols, unmodified polyvinyl alcohol is obtained, for example, by substituting at least a part of the acetate groups of polyvinyl acetate with hydroxyl groups by a saponification reaction. The polyvinyl alcohol may be polyvinyl alcohol in which only a part of the acetate groups of polyvinyl acetate are substituted with hydroxyl groups (partially saponified polyvinyl alcohol), or polyvinyl alcohol in which all of the acetate groups of polyvinyl acetate are substituted with hydroxyl groups (fully saponified polyvinyl alcohol).
The modified polyvinyl alcohol means polyvinyl alcohol having a modifying group. The modifying group is preferably at least one group selected from the group consisting of a carboxy group or a salt thereof, and an acetoacetyl group, and more preferably at least one group selected from the group consisting of a carboxy group or a salt thereof, and an acetoacetyl group.
As the salt of the carboxy group, a metal salt of the carboxy group is preferred, and a sodium salt of the carboxy group is more preferred.
The modified polyvinyl alcohol can be obtained, for example, by saponifying a polymer obtained by copolymerizing a monomer having a modifying group with a vinyl ester (e.g., vinyl acetate, etc.). The modified polyvinyl alcohol may also be obtained by reacting a hydroxyl group or acetate group in unmodified polyvinyl alcohol with a compound having a modifying group.
Examples of polyvinyl alcohol include the Kuraray Poval series manufactured by Kuraray Co., Ltd. (e.g., Kuraray Poval PVA-217E, Kuraray Poval KL-318, etc.), the Gohsenx series manufactured by Mitsubishi Chemical Corporation (e.g., Gohsenx Z-320, etc.), and the A series manufactured by Nippon Vinyl Acetate & Poval Co., Ltd. (e.g., AP-17, etc.).
The polymerization degree of polyvinyl alcohol is preferably from 500 to 5,000, more preferably from 1,000 to 3,000, and even more preferably from 2,000 to 3,000.

The number average molecular weight (Mn) of the water-soluble polymer and oil-soluble polymer described above is not particularly limited, but from the viewpoint of film strength, it is preferably from 20,000 to 300,000, and more preferably from 20,000 to 150,000.
The molecular weight is a value measured by gel permeation chromatography (GPC).
Measurement by gel permeation chromatography (GPC) is performed using an HLC (registered trademark)-8020GPC (Tosoh Corporation) as a measuring device, three TSKgel (registered trademark) Super Multipore HZ-H (4.6 mm ID x 15 cm, Tosoh Corporation) as columns, and THF (tetrahydrofuran) as an eluent. The measurement conditions are a sample concentration of 0.45 mass%, a flow rate of 0.35 ml/min, a sample injection amount of 10 μl, and a measurement temperature of 40° C., and the measurement is performed using an RI (differential refractive index) detector.
The calibration curve is prepared from eight samples of "Standard Sample TSK standard, polystyrene" from Tosoh Corporation: "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene".

When the thermally conductive member of the present invention contains a resin, the amount of resin contained is not particularly limited, but is preferably 1 to 50 parts by mass, and more preferably 2 to 30 parts by mass, per 100 parts by mass of the metal nanowires.

[Epoxy resin hardener]
When the heat conductive member of the present invention contains an epoxy resin, it is preferable that the heat conductive member of the present invention contains an epoxy resin curing agent, that is, a catalyst that promotes the curing reaction of the epoxy resin.
As the epoxy resin curing agent, for example, imidazole-based, phenol-based, amine-based, acid anhydride-based, organic peroxide-based, etc. can be used. In particular, the epoxy resin curing agent is preferably a latent curing agent from the viewpoint of the storage stability (life) of the composition of the present invention at room temperature, and more preferably an encapsulated imidazole-based curing agent with latent properties. By improving the storage stability at room temperature, it is possible to more easily manage the supply and use of the heat conductive member of the present invention. Specifically, as the epoxy resin curing agent, a microencapsulated latent curing agent in which a latent imidazole modified body is used as a core and the surface is coated with polyurethane can be used. As a commercially available product, for example, Novacure 3941 (manufactured by Asahi Kasei E-Materials Corporation) can be used. The epoxy resin curing agent may be used alone or in combination of two or more types.

When the thermally conductive member of the present invention contains an epoxy resin and an epoxy resin curing agent, the total content of these is preferably 50 mass% or less, more preferably 30 mass% or less, and even more preferably 10 to 20 mass%, relative to the total mass of the thermally conductive member of the present invention.

[Elastomer]
The heat conductive member of the present invention may further contain an elastomer.
Examples of the elastomer include acrylic rubber (e.g., a copolymer of (meth)acrylate and acrylonitrile), SB (polystyrene-polybutadiene), SBS (polystyrene-polybutadiene-polystyrene), SIS (polystyrene-polyisoprene-polystyrene), SEBS (polystyrene-polyethylene/polybutylene-polystyrene), ABS (acrylonitrile butadiene styrene copolymer), ACM (acrylic acid ester rubber), ACS (acrylonitrile chlorinated polyethylene styrene copolymer), acrylonitrile styrene copolymer, syndiotactic 1,2-polybutadiene, polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate, and the like.
When the thermal conductive member of the present invention contains an elastomer, the content of the elastomer is not particularly limited, but is preferably 0.5 to 15 parts by mass, and more preferably 1 to 10 parts by mass, per 100 parts by mass of the metal nanowires.

[Coupling Agent]
The heat conductive member of the present invention may further contain a coupling agent.
Suitable examples of the coupling agent include silane coupling agents such as γ-ureidopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, 3-phenylaminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, etc. These may be used alone or in combination of two or more.
When the thermally conductive member of the present invention contains a coupling agent, the content of the coupling agent is not particularly limited, but is preferably 0.01 to 0.2 parts by mass, and more preferably 0.015 to 0.15 parts by mass, per 100 parts by mass of the metal nanowires.

[Curing Accelerator]
The heat conductive member of the present invention may further contain a curing accelerator.
Examples of the curing accelerator include imidazoles and derivatives thereof, organic phosphorus compounds, secondary amines, tertiary amines, quaternary ammonium salts, etc. These may be used alone or in combination of two or more.
Among these, imidazoles and derivatives thereof are preferred from the viewpoint of reactivity.
Examples of imidazoles include 2-methylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, etc. These may be used alone or in combination of two or more.
When the thermal conductive member of the present invention contains a curing accelerator, the content of the curing accelerator is not particularly limited, but is preferably 0.001 to 0.1 parts by mass, and more preferably 0.005 to 0.05 parts by mass, per 100 parts by mass of the metal nanowires.

[Metal Particles]
The heat conducting member of the present invention may further contain metal particles in addition to the metal nanowires.
Here, the metal particles preferably contain at least one metal selected from the group consisting of gold, silver, copper, aluminum, nickel, zinc and cobalt.
The metal particles may also contain one or more conductive components other than metals.

In the present invention, the shape of the metal particles is not particularly limited, and they may be either solid or hollow.
The average major axis of the minimum enclosing ellipsoid of the metal particle is preferably 0.01 μm or more and 50 μm or less, and more preferably 0.1 μm or more and 20 μm or less.
In addition, the average major axis of the minimum enclosing ellipsoid of the metal particles is preferably 1 to 10 times the average minor axis, for the reason of selecting a shape that efficiently fills the space.
Here, the minimum enclosing ellipsoid refers to the ellipsoid that has the smallest volume among the ellipsoids that enclose a metal particle therein, and includes an ellipsoid whose major axis and minor axis are the same (i.e., a sphere).
The average major axis of the minimum enclosing ellipsoid can be obtained by observing the cross section of the layer formed using the dispersion in the thickness direction with a microscope (e.g., electron microscope), measuring the major axis of 100 arbitrary fine particles, and calculating and averaging them. Similarly, the average minor axis of the minimum enclosing ellipsoid can be obtained by observing the cross section of the layer formed using the dispersion in the thickness direction with a microscope (e.g., electron microscope), measuring the minor axis of 100 arbitrary fine particles, and calculating and averaging them.

When the heat conductive member of the present invention contains metal particles, the content of the metal particles is not particularly limited, but is preferably 1 to 30 parts by mass, and more preferably 2 to 20 parts by mass, per 100 parts by mass of the metal nanowires.

The shape of the heat conductive member of the present invention is not particularly limited, but a sheet-like shape is preferable because it can make the heat transfer uniform within the contact surface and also improves the adhesion with the heat dissipation member. Hereinafter, the sheet-like heat conductive member will be abbreviated as "heat conductive sheet".
The size of the heat conductive sheet is not particularly limited, and can be processed to a size according to the size of the heat generating member. Similarly, the thickness is not particularly limited, but is preferably 20 to 200 μm, and more preferably 30 to 150 μm.

<Method of manufacturing the sheet>
The method for producing the thermal conductive member of the present invention in sheet form is not particularly limited, but examples include a method in which a coating liquid containing each of the above-mentioned components contained in the thermal conductive member of the present invention and an organic solvent is prepared and supplied onto a substrate.

The organic solvent contained in the coating liquid may be, for example, aromatic hydrocarbons such as toluene, xylene, mesitylene, cumene, and p-cymene; aliphatic hydrocarbons such as hexane and heptane; cyclic alkanes such as methylcyclohexane; cyclic ethers such as tetrahydrofuran and 1,4-dioxane; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and 4-hydroxy-4-methyl-2-pentanone; esters such as methyl acetate, ethyl acetate, butyl acetate, methyl lactate, ethyl lactate, γ-butyrolactone, butyl carbitol acetate, and ethyl carbitol acetate; carbonates such as ethylene carbonate and propylene carbonate; amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; and alcohols such as butyl carbitol and ethyl carbitol. These may be used alone or in combination of two or more.

The substrate to which the coating liquid is applied is not particularly limited, but examples of the material include polyethylene terephthalate, polytetrafluoroethylene, polyimide, PEEK (polyether ether ketone), aluminum, glass, alumina, silicon nitride, and stainless steel. Note that cloth coated or impregnated with the above material may be used as the substrate. The substrate may also be a temporary support that can be peeled off after the composition is applied.

Methods for supplying the coating liquid onto the substrate include, for example, inkjet printing, screen printing, jet printing, dispenser, jet dispenser, comma coater, slit coater, die coater, gravure coater, slit coat, letterpress printing, intaglio printing, gravure printing, stencil printing, bar coating, applicator, spray coater, and electrocoating.

The method for producing the sheet may include a step of drying the coating liquid supplied onto the substrate. By drying the coating liquid, the sheet can be separated from the substrate as a free-standing sheet.
The drying method may be drying at room temperature, drying by heating, or drying under reduced pressure. For drying by heating or drying under reduced pressure, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared ray dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, a steam heating furnace, a hot plate press device, or the like may be used. It is preferable to appropriately adjust the temperature and time of drying according to the type and amount of the dispersion medium used, and for example, it is preferable to dry at 50 to 300° C. for 1 to 180 minutes.
From the viewpoint of suppressing oxidation of the metal, drying may be performed in a non-oxidizing atmosphere or a reducing atmosphere, for example, by substitution or blowing with a non-oxidizing gas such as argon, nitrogen, or water vapor, or with hydrogen or formic acid.

<Storage method>
The heat conductive sheet is preferably stored in a sealed container or bag containing an oxygen scavenger to prevent oxidation. The sheet may also be stored with an easily peelable protective film attached to one or both sides.

<Bringing to the mounting process>
The thermally conductive sheet may be brought into the mounting process in any of the following forms: a thermally conductive sheet alone; a thermally conductive sheet having an easily peelable protective film attached to one side thereof; a thermally conductive sheet having an easily peelable protective film attached to both sides thereof; or a support having an adhesive layer provided on top thereof and attached to the thermally conductive sheet.

<Thermal conductive sheet mounting process 1>
In actual use, the thermally conductive sheet can be mounted on, for example, electronic components such as semiconductor devices, or various heat dissipation components such as heat spreaders.
The thermally conductive sheet alone or the thermally conductive sheet with a protective film attached thereto is cut to a predetermined size. In the case of a thermally conductive sheet with a protective film attached thereto, the sheet may be cut either before or after the protective film is peeled off.
A thermally conductive sheet that has been cut to a specified size, or a thermally conductive sheet with the protective film removed, is used to bring each side of the thermally conductive sheet into contact with an electronic component such as a semiconductor device, which is a heat generating body, and a heat spreader, which is a heat dissipating body.
The method of contacting the heat generating body with one side of the heat conductive sheet and the method of contacting the heat dissipating body with the other side of the heat conductive sheet are not particularly limited as long as they can be fixed in a state of sufficient adhesion. For example, a method of placing a heat conductive sheet between the heat generating body and the heat dissipating body, fixing them with a pressurizable jig, and causing the heat generating body to generate heat in this state; a method of heating with an oven, etc.; and the like can be mentioned. Another example is a method of using a press machine that can apply heat and pressure.

<Thermal conductive sheet mounting process 2>
Another mounting method includes a dicing/die bonding method using a thermally conductive sheet in a form in which an adhesive layer is provided on a support and the thermally conductive sheet is attached to the adhesive layer.
A semiconductor wafer is attached to the above-mentioned thermally conductive sheet, and then diced to produce a plurality of individual semiconductor chips with thermally conductive sheet pieces. These are then attached to a heat dissipation member such as a heat spreader via the thermally conductive sheet.

[device]
The device of the present invention is a device having a heat generating body, the heat conductive member of the present invention described above, and a heat dissipation member, and it is preferable that the device has a heat generating body, the heat conductive member of the present invention described above, and a heat dissipation member adjacent to each other in this order.
Here, "adjacent in this order" means that there are no other layers between the heat generating element and the heat conducting member, and that they are in contact with each other; similarly, it means that there are no other layers between the heat conducting member and the heat dissipation member, and that they are in contact with each other.

[Heater]
The heating element of the device of the present invention is not particularly limited as long as it is a component in the device that may generate heat, and examples thereof include a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an SRAM (Static Random Access Memory), an SoC (Systems on a Chip) such as an RF (Radio Frequency) device, a camera, an LED (Light Emitting Diode) package, power electronics, and a battery (particularly a lithium ion secondary battery).

[Heat dissipation member]
Examples of the heat dissipation member included in the device of the present invention include a heat spreader, a heat sink, and a thermal diffusion sheet.
Moreover, the heat dissipation member is preferably made of a heat conductive material.
The thermally conductive material is preferably a material having a thermal conductivity of 10 Wm ⁻¹ K ⁻¹ or more. The thermal conductivity (unit: Wm ⁻¹ K ⁻¹ ) is a value measured by a flash method at a temperature of 25° C. according to a method in accordance with Japanese Industrial Standards (JIS) R1611.
Examples of such thermally conductive materials include carbon materials (eg, graphite), metals (eg, silver, copper, aluminum, iron, platinum, stainless steel, nickel), and silicon.

In the present invention, the heat dissipation member is preferably a heat spreader made of metal.
The heat dissipation member is preferably in the form of a sheet, and the thickness thereof is preferably from 10 to 500 μm, and more preferably from 20 to 300 μm.

The device of the present invention is preferably used in electronic devices such as mobile phones (particularly smartphones), personal digital assistants, personal computers (particularly portable personal computers), cameras, game consoles, and remote controls.
Specifically, the device of the present invention is applicable to logic integrated circuits such as application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and application specific standard products (ASSPs).
The device of the present invention is also applicable to microprocessors such as CPUs and GPUs.
In addition, the device of the present invention can also be applied to memories such as dynamic random access memory (DRAM), hybrid memory cube (HMC), magnetoresistive random access memory (MRAM), phase-change memory (PCM), resistance random access memory (ReRAM), ferroelectric random access memory (FeRAM), and flash memory.
The device of the present invention can also be applied to analog integrated circuits such as LEDs, power devices, DC (Direct Current)-DC (Direct Current) converters, and insulated gate bipolar transistors (IGBTs).
Furthermore, the device of the present invention can also be applied to MEMS (Micro Electro Mechanical Systems) such as acceleration sensors, pressure sensors, vibrators, and gyro sensors.
In addition, the device of the present invention can also be applied to wireless elements such as Global Positioning System (GPS), Frequency Modulation (FM), Near field communication (NFC), RF Expansion Module (RFEM), Monolithic Microwave Integrated Circuit (MMIC), Wireless Local Area Network (WLAN), discrete elements, Complementary Metal Oxide Semiconductor (CMOS), CMOS image sensors, camera modules, passive devices, Surface Acoustic Wave (SAW) filters, Radio Frequency (RF) filters, Integrated Passive Devices (IPDs), and the like.

The final products in which the device of the present invention is mounted are not particularly limited, and examples include smart TVs, mobile communication terminals, mobile phones, smartphones, tablet terminals, desktop PCs (Personal Computers), notebook PCs, network equipment (routers, switching), wired infrastructure equipment, digital cameras, game consoles, controllers, data centers, servers, mining PCs, HPCs (High Performance Computing), graphic cards, network servers, storage, chipsets, in-vehicle equipment (electronic control equipment, driving assistance systems), car navigation systems, PNDs (Portable Navigation Devices), lighting (general lighting, in-vehicle lighting, LED lighting, OLED (Organic Light Emitting Diode) lighting), televisions, displays, display panels (liquid crystal panels, organic EL (Electro Luminescence) panels, electronic paper), music playback terminals, industrial equipment, industrial robots, inspection equipment, medical equipment, white goods, space or aircraft equipment, wearable devices, etc.

In addition to electronic device applications, the device of the present invention can also be used in applications such as building materials (e.g., flooring, roofing, wall materials, etc.) suitable for temperature control during sudden daytime temperature increases or indoor heating and cooling; clothing (e.g., underwear, jackets, winter clothing, gloves, etc.) suitable for temperature control in response to changes in environmental temperature or changes in body temperature during exercise or at rest; bedding; and exhaust heat utilization systems that store unnecessary exhaust heat and use it as thermal energy.

The present invention will be described in more detail below based on examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the examples shown below.

[Fabrication of Metal Nanowires]
<Preparation of Aluminum Substrate>
A molten metal was prepared using an aluminum alloy containing 0.06 mass% Si, 0.30 mass% Fe, 0.005 mass% Cu, 0.001 mass% Mn, 0.001 mass% Mg, 0.001 mass% Zn, 0.001 mass% Ti, and the remainder being Al and unavoidable impurities. The molten metal was treated and filtered, and an ingot having a thickness of 500 mm and a width of 1,200 mm was produced by a DC (Direct Chill) casting method.
Next, the surface was scraped off by an average thickness of 10 mm using a facing machine, and then the plate was soaked at 550°C for about 5 hours. When the temperature was lowered to 400°C, the plate was rolled into a 2.7 mm thick plate using a hot rolling machine.
Further, the sheet was heat-treated at 500° C. using a continuous annealing machine, and then cold-rolled to a thickness of 1.0 mm to obtain an aluminum substrate of JIS (Japanese Industrial Standards) 1050 material.
The aluminum substrate was formed into a wafer having a diameter of 200 mm (8 inches) and then subjected to the following treatments.

<Electrolytic polishing treatment>
The above-mentioned aluminum substrate was subjected to electrolytic polishing treatment using an electrolytic polishing solution having the following composition under conditions of a voltage of 25 V, a solution temperature of 65° C., and a solution flow rate of 3.0 m/min.
The cathode was a carbon electrode, and the power source was GP0110-30R (manufactured by Takasago Manufacturing Co., Ltd.) The flow rate of the electrolyte was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE Corporation).
(Electrolytic polishing solution composition)
85% by weight phosphoric acid (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 660 mL
・160mL of pure water
・150mL sulfuric acid
・30mL ethylene glycol

<Anodizing process>
Next, the aluminum substrate after the electrolytic polishing treatment was subjected to anodizing treatment by a self-ordering method according to the procedure described in JP-A-2007-204802.
The aluminum substrate after electrolytic polishing was subjected to a pre-anodizing treatment for 5 hours in an electrolytic solution of 0.50 mol/L oxalic acid under conditions of a voltage of 40 V, a solution temperature of 16° C., and a solution flow rate of 3.0 m/min.
Thereafter, the aluminum substrate after the pre-anodizing treatment was subjected to a coating removal treatment by immersing it in a mixed aqueous solution of 0.2 mol/L chromic anhydride and 0.6 mol/L phosphoric acid (liquid temperature: 50° C.) for 12 hours.
Thereafter, re-anodization was performed for 5 hours in an electrolyte of 0.50 mol/L oxalic acid under conditions of a voltage of 40 V, a liquid temperature of 16° C., and a liquid flow rate of 3.0 m/min, to obtain an anodized film with a thickness of 40 μm.
In both the pre-anodizing treatment and the re-anodizing treatment, the cathode was a stainless steel electrode, and the power source was GP0110-30R (manufactured by Takasago Manufacturing Co., Ltd.). The cooling device was NeoCool BD36 (manufactured by Yamato Scientific Co., Ltd.), and the stirring and heating device was Pair Stirrer PS-100 (manufactured by EYELA Tokyo Rikakikai Co., Ltd.). Furthermore, the flow rate of the electrolyte was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE Corporation).

<Metal filling process>
Next, electrolytic plating was carried out using the aluminum substrate as the cathode and platinum as the anode.
Specifically, a copper plating solution having the composition shown below was used and constant current electrolysis was carried out to produce a metal-filled microstructure in which the inside of the pores (micropores) was filled with copper.
Here, the constant current electrolysis was performed using a plating device manufactured by Yamamoto Plating Tester Co., Ltd. and a power supply (HZ-3000) manufactured by Hokuto Denko Corporation. After confirming the deposition potential by carrying out cyclic voltammetry in the plating solution, the treatment was performed under the conditions shown below.
(Copper plating solution composition and conditions)
・Copper sulfate 100g/L
Sulfuric acid 50g/L
Hydrochloric acid 15g/L
Temperature: 25℃
Current density 10A/ ^dm2

The surface of the anodized film after the pores were filled with metal was observed with an FE-SEM to determine whether 1,000 pores were sealed with metal. The sealing rate (number of sealed pores/1,000) was calculated to be 96%.
In addition, after filling the holes with metal, the anodized film was cut in the thickness direction using an FIB, and the cross section was photographed with an FE-SEM (magnification 50,000x) to check the inside of the holes. It was found that the filling height from the bottom of the sealed holes was 35 μm.

<Isolation step>
The filled metal was isolated from the anodized film and the aluminum base material by immersing the aluminum base material in an aqueous potassium hydroxide solution (concentration: 5 mol/L) at 60° C. for 300 seconds, to obtain an isolated metal. Specifically, the anodized film was dissolved by immersing the aluminum base material in an aqueous potassium hydroxide solution (concentration: 5 mol/L) at 60° C. for 300 seconds, and the filled metal was isolated by peeling off the aluminum base material at the same time as the anodized film was dissolved (after 300 seconds had elapsed).

<Drying process>
Next, the isolated metal was recovered by suction filtration using a membrane (0.4 μm, PTFE, manufactured by Omnipore), and the isolated metal was dried.

<Cleaning/Protective Layer Forming Step/Reduction or Removal Step>
Next, the isolated metal recovered on the membrane was washed for 1 minute using the washing solvent shown below. In Example 1, since a corrosion inhibitor was added to the washing solvent, a protective layer was formed at the same time as washing. In Example 1, since citric acid was used as the corrosion inhibitor, the surface oxide layer of the isolated metal was also removed at the same time as the protective layer was formed.
The isolated metals on the membrane were then collected.
(Washing Solvent)
An aqueous solution containing 1% by weight of citric acid

<Crushing process>
Next, the recovered isolated metal was added to water at 1 mass %, and the mixture was subjected once to a cavitation-based crushing treatment (pressure: 50 MPa) using a Starburst Mini manufactured by Sugino Machine Ltd.
Thereafter, the crushed isolated metal was collected by suction filtration using a membrane (0.4 μm, PTFE, manufactured by Omnipore Corporation) and dried under reduced pressure for 12 hours to produce metal nanowires.
Here, after carrying out a reduced pressure treatment at 50° C. for 60 minutes using a BELSORP-max manufactured by Microtrac-Bel, the specific surface area was measured by a krypton gas adsorption method and found to be 7000 m ² /kg.

[Examples 1 to 4]
[Preparation of Varnish]
A raw varnish was prepared by adding components (A), (B), (C), (D), and (E) according to the symbols and composition ratios (unit: parts by mass) shown in Table 1 below.
Next, the prepared raw varnish was stirred at 100 rpm for 12 hours at room temperature using a mix rotor (VMR-3R, manufactured by AS ONE Corporation) to prepare a varnish.

[Preparation of Coating Solution]
Next, component (F) in the composition ratio (parts by mass) shown in Table 1 below and cyclohexanone as an organic solvent were added to the prepared varnish, and the mixture was stirred twice for 2 minutes at room temperature at 800 rpm using a Thinky Mixer (ARE-400TWIN, manufactured by Thinky Corporation), to prepare coating solutions with solid contents of 61% by mass for Examples 1 to 4.

The symbols of the components shown in Table 1 below have the following meanings.
Component (A): Resin Bisphenol F type epoxy resin (product name: EXA-830CRP, manufactured by DIC Corporation)
Component (B): Hardener Phenolic resin (product name: SK Resin HE100C-30, manufactured by Air Water Performance Chemicals Inc.)
Component (C): Elastomer acrylic rubber (product name: SG-P3, manufactured by Nagase ChemteX Corporation)
Component (D): Coupling agent γ-ureidopropyltriethoxysilane (product name: KBE-585A, manufactured by Shin-Etsu Chemical Co., Ltd.)
Component (E): Curing accelerator 1-cyanoethyl-2-phenylimidazole (product name: 2PZ-CN, manufactured by Shikoku Chemical Industry Co., Ltd.)
Component (F): Metal Nanowire The metal nanowire prepared above

[Preparation of thermally conductive member]
The prepared coating solution was applied onto a polyethylene terephthalate (PET) film (thickness: 100 μm) that had been subjected to a release treatment as a support film.
The coated sample was then dried by heating in two stages, first at 90° C. for 10 minutes and then at 140° C. for 10 minutes, to form a sheet (thickness 330 μm) in a B-stage state on the support film.
Next, the sheet peeled off from the support film was sandwiched between two polyimide films (50 μm) and subjected to heat pressing at 180° C. for 5 minutes. After pressing, the polyimide films were removed to produce the thermal conductive members of Examples 1 to 4 in sheet form with a thickness of 100 μm.

[Comparative Example 1]
A thermally conductive adhesive sheet was produced by the method described in paragraphs [0078], [0081], [0085] and [0101] of Patent Document 1 (JP 2014-201687 A).

[Comparative Example 2]
A thermally conductive member was produced in the same manner as in Example 1, except that the (F) component was changed to copper microwires having a diameter of 15 μmφ and a length of 40 μm, and a coating liquid prepared by blending the components in the composition ratio (parts by mass) shown in Table 1 below was used.

[Example 5]
A thermally conductive member was produced in the same manner as in Example 1, except that the component (A) used in preparing the varnish was changed to polyvinylidene fluoride (PVDF) (product name: Solef 1006, manufactured by Solvay Specialty Polymers Japan, Inc.) and the component (F) used in preparing the coating liquid was changed to a mixed solvent of dimethylformamide and methyl ethyl ketone (mixing ratio by volume: 38:62).

[Evaluation of Adhesion]
The CTE (coefficient of linear expansion) in the in-plane direction of the sheets produced in Examples 1 to 5 and Comparative Examples 1 and 2 was measured using a thermal mechanical analyzer (TMA, manufactured by Shimadzu Corporation).
Specifically, a sample cut to a width of 4 mm and a length of 14 mm was set on a measuring jig so that the chuck distance was 10 mm, and the temperature was raised and lowered while a tensile load of 1 gf was applied, and the amount of expansion of the sample was measured.
The temperature control for heating and cooling was performed by heating from 25° C. to 200° C. at a rate of 5° C./min, then cooling to 25° C. at a rate of 2° C./min, and then heating again from 25° C. to 200° C. at a rate of 5° C./min.
The linear expansion coefficient was calculated by measuring the elongation (L50, L150) of the sample at two temperatures (50° C., 150° C.) during the second heating on the TMA curve and using the following formula. The results are shown in Table 1 below.
Linear expansion coefficient [ppm/°C] = (L150-L50)/Lo/(150-50)
Lo: Initial sample length (= chuck distance)
The adhesion was then evaluated according to the following criteria, and the results are shown in Table 1 below.
<Standards>
The difference between the calculated linear expansion coefficient of each sheet and the linear expansion coefficient (18.0 ppm/° C.) of a heat spreader (heat dissipation member) made of a copper plate was calculated, and the adhesion was evaluated as follows.
AAA: Within 3.0 AA: Over 3.0 and within 7.0 A: Difference is over 7.0 and within 10.0 B: Difference is over 10.0 and within 30.0 C: Difference is over 30.0

From the results shown in Table 1, it was found that when the content of metal nanowires does not satisfy either

requirement

1 or 2, the difference in the linear expansion coefficient between the heat conduction member and the heat dissipation member becomes large, and when exposed to a process of repeated heating and cooling, the adhesion between the heat conduction member and the heat dissipation member becomes poor (Comparative Examples 1 to 2).
In contrast, when the content of metal nanowires satisfies at least one of

requirements

1 and 2, the difference in the linear expansion coefficient between the heat conduction member and the heat dissipation member becomes small, and it was found that the adhesion between the heat conduction member and the heat dissipation member becomes good when exposed to a process of repeated heating and cooling (Examples 1 to 5).
In particular, by comparing Examples 1 and 2 with Examples 3 and 4, it was found that when the content of metal nanowires satisfies both

requirements

1 and 2, the adhesion between the thermal conduction member and the heat dissipation member is better.
Furthermore, a comparison between Example 1 and Example 2 revealed that when the content of metal nanowires was more than 50% by volume, the adhesion between the heat conducting member and the heat dissipating member was further improved.
Furthermore, a comparison between Example 1 and Example 5 reveals that the adhesion between the heat conducting member and the heat dissipating member is improved when a resin other than a fluororesin is used.

1 Valve metal substrate 2 Porous (micropore)
3 Anodic oxide film 4 Metal 5 Isolated metal 10 Metal nanowire

Claims

A thermally conductive member that satisfies at least one of the following requirements 1 and 2:
Requirement 1: The metal nanowires are contained at 40 to 99 volume %.
Requirement 2: The metal nanowires are contained in an amount of 70 to 99 mass %.
The heat conducting member according to claim 1, wherein the metal constituting the metal nanowires is at least one metal selected from the group consisting of silver and copper.
The heat conductive member according to claim 1, further comprising a resin.
The thermal conductive member according to claim 3, wherein the resin is a cross-linked resin.
The thermally conductive member according to claim 3, which is in sheet form.
A device having a heating element, a heat conduction member according to any one of claims 1 to 5, and a heat dissipation member.
The device according to claim 6, comprising the heat generating element, the heat conducting member, and the heat dissipating member, arranged adjacent to each other in this order.