JP2022126535A - Method for manufacturing thermal conductive sheet and thermal conductive sheet - Google Patents

Abstract

To obtain a thermal conductive sheet having tackiness in an inexpensive step.SOLUTION: A method for manufacturing a thermal conductive sheet includes the steps of: preparing a thermal conductive composition by dispersing a first filler that is magnetic powder having a thin plate shape, a second filler that is a thermal conductive filler having a thin plate shape and a third filler that is a thermal conductive filler into a binder resin, and thereby preparing a thermal conductive composition; forming the thermal conductive composition into a sheet shape; applying a magnetic field to the sheet-shaped thermal conductive composition, orienting the first filler in a thickness direction of the thermal conductive composition, and orienting the second filler in the thickness direction; and curing the thermal conductive composition.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD Embodiments of the present invention relate to a method for manufacturing a thermally conductive sheet and the thermally conductive sheet.
Regarding.

2. Description of the Related Art In recent years, as electronic devices have become more sophisticated, the density and packaging of semiconductor elements have increased. Along with this, it has become important to more efficiently dissipate the heat generated from the electronic components that make up the electronic equipment.

In order to efficiently dissipate heat, the semiconductor element is attached to a heat sink such as a heat dissipating fan or a heat dissipating plate via a heat conductive sheet. As a thermally conductive sheet, a material in which a filler such as an inorganic filler is dispersed in silicone is widely used.

In such heat dissipating members, there is a demand for further improvement in thermal conductivity. there is

However, if the filling rate of the inorganic filler is increased, there is a possibility that flexibility may be impaired or powder may fall off. Therefore, there is a limit to increasing the filling rate of the inorganic filler.

Examples of inorganic fillers include alumina, aluminum nitride, and aluminum hydroxide. For the purpose of high thermal conductivity, the matrix may be filled with scaly particles such as boron nitride or graphite, carbon fibers, or the like. This is due to the anisotropy of the thermal conductivity of the scaly particles and the like.

For example, carbon fibers have a thermal conductivity of about 600-1200 W/mK in the fiber direction. Boron nitride has a thermal conductivity of about 110 W/mK in the plane direction and about 2 W/mK in the direction perpendicular to the plane direction, and is known to have anisotropy. .
In this manner, the surface direction of the carbon fibers and scale-like particles is made the same as the thickness direction of the sheet, which is the direction of heat transfer. That is, by orienting the carbon fibers and the scale-like particles in the thickness direction of the sheet, it is possible to dramatically improve the heat conduction.

Japanese Patent No. 5405890 JP-A-2009-94110 Japanese Patent No. 6200119

By the way, thermally conductive sheets are desired to be thin and have high thermal conductivity in order to reduce the thermal resistance between various heat sources and heat radiating members. Tackiness (adhesiveness) is required from the viewpoint of handling such as attaching to

However, in the above conventional technique, a thermally conductive sheet is manufactured by slicing a cured product of a thermally conductive resin composition, and there is a problem that the surface of the thermally conductive sheet formed by slicing has no tackiness. rice field.
The present invention has been made in view of the above, and an object of the present invention is to obtain a thermally conductive sheet having tackiness by an inexpensive process.

A method for producing a thermally conductive sheet according to an embodiment includes a first filler that is a magnetic powder having a thin plate shape, a second filler that is a thermally conductive filler that has a thin plate shape, and a third filler that is a thermally conductive filler. A step of preparing a thermally conductive composition by dispersing it in a binder resin, a step of forming the thermally conductive composition into a sheet, applying a magnetic field to the sheet-shaped thermally conductive composition, and dispersing the first filler. Orienting along the thickness direction of the thermally conductive composition to orient the second filler along the thickness direction, and curing the thermally conductive composition.

According to the method for producing a thermally conductive sheet of the embodiment, it is possible to obtain a thermally conductive sheet having tackiness at low cost with a small number of steps.

FIG. 1 is a manufacturing flow chart of the thermally conductive sheet of the embodiment. FIG. 2 is a schematic illustration of the state of fillers in a thermally conductive composition. FIG. 3 is a schematic explanatory diagram (part 1) of the state of the filler in the sheet-like thermally conductive composition. FIG. 4 is a schematic explanatory diagram (No. 2) of the state of the filler in the sheet-like thermally conductive composition. FIG. 5 is an explanatory diagram of the effect of the example and the comparative example.

Hereinafter, a method for manufacturing a thermally conductive sheet to which the present technology is applied will be described in detail with reference to the drawings. In addition, the present technology is not limited to the following embodiments, and various modifications are possible without departing from the gist of the present technology. Also, the drawings are schematic, and the ratio of each dimension may differ from the actual one. Specific dimensions and the like should be determined with reference to the following description. In addition, it goes without saying that there are portions with different dimensional relationships and ratios between the drawings.

FIG. 1 is a manufacturing flow chart of the thermally conductive sheet of the embodiment.
First, a first filler F1 that is a magnetic powder having a thin plate shape, a second filler F2 that is a thermally conductive filler that has a thin plate shape, and a third filler F3 that is a thermally conductive filler are combined with a binder resin (polymer matrix component ) Prepare a thermally conductive composition by dispersing it in BD (step S11).

FIG. 2 is a schematic illustration of the state of fillers in a thermally conductive composition.
As shown in FIG. 2, the thermally conductive composition 10 is in a state in which the first filler F1, the second filler F2 and the third filler F3 are dispersed in the binder resin BD.

In this case, since the first filler F1 and the second filler F2 are in a non-oriented state, they face various directions. In FIG. 1, the particles of the first filler F1 and the second filler F2 viewed from the side are shown in a rod shape, and the particles of the first filler F1 and the second filler F2 viewed from the surface direction are plate-shaped. shown in the form.

Here, the thin plate shape means a scale shape, a flat shape, a flake shape, and the like, and the thickness thereof is, for example, a flat plate shape of 1 μm or less.
The first filler F1 is a scale-like magnetic particle, and examples thereof include ferrite (Fe-based alloy), permalloy (Ni--Fe-based alloy), and sendust (Al--Si--Fe-based alloy).

In this case, the content of the first filler F1 in the thermal conductive sheet composition is preferably 5 to 30 vol % in order to ensure the orientation of the second filler F2.
Moreover, when ferrite is used as the first filler, insulation can be imparted to the thermally conductive sheet.

Examples of the second filler F2 include scaly particle materials such as scaly boron nitride (scaly BN), artificial graphite, scaly graphite, expansive graphite, and expanded graphite.
In this case, the thermal conductivity of the second filler F2 is preferably 10 W/m·K or more because it is necessary to have a sufficient thermal conductivity when used as a thermally conductive sheet.
Also, the content of the second filler F2 in the thermally conductive sheet composition is preferably 5 to 30 vol % in order to ensure sufficient thermal conductivity.

Further, as the third filler F3, zinc oxide particles, alumina particles, aluminum nitride particles, silicon carbide particles, silicon nitride particles, magnesium oxide particles, artificial graphite, natural graphite, acid-treated graphite, expandable graphite, expandable graphite, Examples include carbon black, carbon nanotubes, vapor-grown carbon fibers, and carbon fibers obtained by carbonizing organic fibers.

In this case, the particle diameter of the third filler is 0.2 to 0.2 so as to disperse uniformly in the binder resin BD and sufficiently conduct heat, and not to hinder the orientation of the first filler F1 and the second filler F2. 5 μm is preferred. For the same reason, the content of the third filler is preferably 10-60 vol %.

Examples of the binder resin BD include thermosetting polymers.
Examples of thermosetting polymers include crosslinked rubber, epoxy resin, polyimide resin, bismaleimide resin, benzocyclobutene resin, phenol resin, unsaturated polyester, diallyl phthalate resin, silicone resin, polyurethane, polyimide silicone, and thermosetting polyphenylene. Ethers, thermosetting modified polyphenylene ethers, and the like. These may be used individually by 1 type, and may use 2 or more types together.

In this case, the crosslinked rubber includes, for example, natural rubber, butadiene rubber, isoprene rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene propylene rubber, chlorinated polyethylene, chlorosulfonated polyethylene, butyl rubber, halogenated butyl rubber, Fluororubber, urethane rubber, acrylic rubber, polyisobutylene rubber, silicone rubber, and the like. These may be used individually by 1 type, and may use 2 or more types together.

Among these thermosetting polymers, it is preferable to use a silicone resin from the viewpoint of excellent moldability and weather resistance, as well as adhesion and conformability to electronic parts.
The silicone resin is not particularly limited, and the type of silicone resin can be appropriately selected according to the purpose. For example, from the viewpoint of obtaining molding processability, weather resistance, adhesion, etc., the silicone resin is preferably a silicone resin composed of a liquid silicone gel main agent and a curing agent. Examples of such silicone resins include addition reaction type liquid silicone resins, heat vulcanization type millable type silicone resins using peroxide for vulcanization, and the like.

Among these silicone resins, the addition reaction type liquid silicone resin is particularly preferable as a heat dissipation member for electronic devices, because the heat generating surface of the electronic component and the heat sink surface are required to have good adhesion. As the addition reaction type liquid silicone resin, for example, a two-liquid addition reaction type silicone resin or the like can be used in which polyorganosiloxane having a vinyl group is used as a main component and polyorganosiloxane having an Si—H group is used as a curing agent. is preferred.

Here, the liquid silicone component has a silicone A liquid component as a main agent and a silicone B liquid component containing a curing agent, and the silicone A liquid component and the silicone B liquid component are blended in a predetermined ratio.

Next, when forming the thermally conductive composition 10 into a sheet, the thermally conductive composition is passed through a narrow gap (clearance) by a bar coater or the like. As a result, the thin plate-shaped (scaly) first filler F1 and the second filler F2 are oriented along the surface direction of the sheet (step S12).

FIG. 3 is a schematic explanatory diagram (part 1) of the state of the filler in the sheet-like thermally conductive composition.
As shown in FIG. 3, in the heat conductive composition 10, the first filler F and the second filler F2 are oriented along the surface direction of the sheet in the binder resin BD.

FIG. 4 is a schematic explanatory diagram (No. 2) of the state of the filler in the sheet-like thermally conductive composition.
Subsequently, a magnetic field is applied to the sheet-shaped thermally conductive composition 10 so that the direction of the magnetic lines of force is in the thickness direction, and as shown in FIG. The second filler F2 is oriented along the thickness direction (step S13).
This is because the first filler F1 and the second filler F2 are oriented in a laminated state, so that the second filler F2 is also This is because it is physically oriented in the thickness direction.

For this reason, in order to orient the second filler F2 along with the orientation of the first filler F1, it is necessary to physically transmit the force at the time of orientation of the first filler F1 to the second filler F2. The particle size ratio of the first filler F1 and the second filler F2 is preferably in the range of 3:1 to 1:3.

Furthermore, in order to more reliably transmit the force of the orientation of the first filler F to the second filler F2, the second filler F2 needs to be positioned in the vicinity of the first filler F1. The volume ratio of the first filler F1 and the second filler F2 is preferably in the range of 3:1 to 1:3.

Here, as a method of applying a magnetic field, for example, a sheet-like thermally conductive composition is sandwiched between permanent magnets or electromagnets, but it is not limited to this.
Next, the sheet-like thermally conductive composition is cured by heating or the like to form the thermally conductive film 10F (step S14).

In this case, when a soft magnetic material is used as the first filler F1, there is a risk that the orientation in the thickness direction will return to the original orientation when the application of the magnetic field is stopped. The adhesive composition is cured by heating or the like.

According to the method for producing a thermally conductive sheet of the embodiment, since there is no step of slicing the cured product of the thermally conductive resin composition to produce a thermally conductive sheet, the surface of the thermally conductive sheet is given tackiness. be able to.
Moreover, since the number of manufacturing steps can be reduced, the manufacturing cost of the thermally conductive sheet can also be reduced.

Next, more specific examples will be described.

[1] Examples [1.1] First Example [1.1.1] Formulation In the first example, the following first formulation resin and filler were used.
(1st formulation)
Resin: Contains 35 vol% of silicone resin.
First filler: 10% by volume of scaly Sendust having a D50 (medium average diameter) of 70 µm.
Second filler: 10 vol% of scaly hexagonal BN with a D50 of 40 µm is blended Third filler: 35 vol% of spherical alumina with a D50 of 3 µm is blended

[1.1.2] Manufacturing Conditions First, the composition of the first formulation is applied to a thickness of 1 mm using a bar coater, and the first filler and the second filler are oriented in the plane direction (sheet forming step).
Subsequently, the sheet is sandwiched between permanent magnets and a magnetic field is applied to orient the first filler in the thickness direction. process).
Subsequently, it was held in an oven at 60° C. for 4 hours (curing step) to obtain a thermally conductive sheet of the first example.

[1.2] Second Example [1.2.1] Compounding In the second example, the following second compounding resin and filler were used.
(Second formulation)
Resin: Contains 35 vol% of silicone resin.
First filler: 10% by volume of scaly ferrite having a D50 (medium average diameter) of 70 µm.
Second filler: 10% by volume of scaly hexagonal BN having a D50 of 40 μm.
Third filler: 35 vol % of spherical alumina having a D50 of 3 µm.

[1.2.2] Manufacturing conditions The thermally conductive sheet composition of Formulation 2 above was applied with a bar coater to a thickness of 1 mm, the sheet was sandwiched between permanent magnets and subjected to magnetic field orientation, and then held in an oven at 60°C for 4 hours (curing step). , a heat conductive sheet of the second example was obtained.

[2] Comparative Example Next, a comparative example will be described.
[2.1] First Comparative Example [2.1.1] Formulation The same first formulation as in the first example was used.

[2.1.2] Manufacturing Conditions First, the composition of the first formulation was applied to a thickness of 1 mm using a bar coater.
Subsequently, it was held in an oven at 60° C. for 4 hours (curing step) to obtain a thermally conductive sheet of the first comparative example.

[2.2] Second Comparative Example [2.2.1] Formulation The same first formulation as in the first example was used.

[2.1.2] Manufacturing Conditions First, the composition of the first formulation was applied to a thickness of 1 mm using a bar coater.
Subsequently, it was held at 60° C. for 0.5 hours in an oven to obtain a semi-cured green sheet.
Subsequently, 50 green sheets obtained were laminated and held at 60° C. for 4 hours (curing step) to prepare a block-shaped compact, and the obtained compact was sliced perpendicular to the stacking direction. A heat conductive sheet of the second comparative example was obtained.

[3] Effect of Example FIG. 5 is an explanatory diagram of an example and a comparative example.
[3.1] Orientation Direction and Bulk Thermal Conductivity As shown in FIG. It is predicted that heat can be efficiently transferred from a heat source such as a semiconductor element to a heat dissipation member such as a heat dissipation fin, and the bulk thermal conductivity is also 4.0 [W / m K]. ], and it was found that the thermal conductivity was actually high.

On the other hand, in the thermally conductive sheet of the first comparative example, the orientation direction of the second filler, which is the thermally conductive filler, is the plane direction, and the bulk thermal conductivity is 2.0 [W/m K]. However, it was not practical due to its low thermal conductivity.

[3.2] Number of Processes and Cost The manufacturing cost was good (○) because there was little

On the other hand, the number of processes in the second comparative example was 6, and the manufacturing cost was high, so it was impossible (x).

[3.3] Tackiness With regard to tackiness, as shown in FIG. 5, the first, second and first examples are good (○) because they do not include a slicing step in the manufacturing process. there were.

On the other hand, the second comparative example, in which a block-shaped molded body was prepared and sliced from the obtained molded body, was unsatisfactory (x) as in the conventional example.

[3.4] Insulation With regard to insulation, as shown in FIG. The first example, the first comparative example, and the second comparative example, in which an insulating material is not used as a material, are not acceptable (x).

[3.5] Summary As described above, in the first and second examples, although there is a difference in the presence or absence of insulation due to the filler material, the number of processes, bulk thermal conductivity, tack It was preferable from the viewpoint of quality and manufacturing cost.

On the other hand, the first comparative example was not preferable as a thermally conductive sheet from the viewpoint of bulk thermal conductivity, and the second comparative example was not preferable as a thermally conductive sheet from the viewpoint of tackiness and manufacturing cost.

10 thermally conductive composition 10F thermally conductive sheet BD binder resin (polymer matrix component)
F1 First filler F2 Second filler F3 Third filler

Claims (14)

A thermally conductive composition is prepared by dispersing a first filler that is a magnetic powder having a thin plate shape, a second filler that is a thermally conductive filler that has a thin plate shape, and a third filler that is a thermally conductive filler in a binder resin. a step of preparing
A step of forming the thermally conductive composition into a sheet;
A magnetic field is applied to the sheet-like thermally conductive composition, the first filler is oriented along the thickness direction of the thermally conductive composition, and the second filler is oriented along the thickness direction. and orienting with
curing the thermally conductive composition;
A method for producing a thermally conductive sheet comprising The particle size ratio of the first filler and the second filler is in the range of 3:1 to 1:3,
The method for producing a thermally conductive sheet according to claim 1. The volume ratio of the first filler and the second filler is in the range of 3:1 to 1:3,
The method for producing a thermally conductive sheet according to claim 1 or 2. The first filler is an iron-based alloy,
The method for producing a thermally conductive sheet according to any one of claims 1 to 3. The first filler is ferrite,
The method for producing a thermally conductive sheet according to any one of claims 1 to 3. The thermal conductivity of the second filler is 10 W / m K or more,
The method for producing a thermally conductive sheet according to any one of claims 1 to 5. The second filler is a BN filler,
The method for producing a thermally conductive sheet according to any one of claims 1 to 6. The particle size of the third filler is 0.2 to 5 μm,
The method for producing a thermally conductive sheet according to any one of claims 1 to 7. The binder resin is a silicone resin,
The method for producing a thermally conductive sheet according to any one of claims 1 to 8. The content of the first filler in the thermally conductive sheet composition is 5 to 30 vol%.
The method for producing a thermally conductive sheet according to any one of claims 1 to 9. The method for producing a thermally conductive sheet according to any one of claims 1 to 10, wherein the content of the second filler in the thermally conductive sheet composition is 5 to 30 vol%. The method for producing a thermally conductive sheet according to any one of claims 1 to 11, wherein the content of the third filler in the thermally conductive sheet composition is 10 to 60 vol%. a first filler that is a magnetic powder that is oriented along the thickness direction and has a thin plate shape;
a second filler that is a thermally conductive filler having a thin plate shape oriented along the first filler;
a third filler that is a thermally conductive filler;
a binder resin that supports the first filler, the second filler, and the third filler in a dispersed state;
A thermally conductive sheet with The thermally conductive sheet is insulating,
The thermally conductive sheet according to claim 13.

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