JP2011230472A - Heat conductive sheet with high insulating property and heat radiator using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat conductive sheet which maintains high heat conductivity and further has additional characteristics such as an insulating property and an adhesive property.SOLUTION: In the heat conductive sheet which has multilayered structure of two or more layers including a layer (A) and a layer (B) formed by lamination in a sheet thickness direction, the layer (A) includes a composition including an organic polymer compound and an insulating aspherical particles with a volume resistivity of ≥10Ω m and the insulating aspherical particles are oriented in a longitudinal direction toward a thickness direction of the layer (A), and the layer (B) includes an insulating resin composition of ≥10 kV/mm.

Description

  The present invention relates to a heat conductive sheet having high insulating properties and a heat dissipation device using the same.

  In recent years, the wiring density and the mounting density of electronic components in multilayer wiring boards and semiconductor packages have increased, and semiconductor elements have been highly integrated, and the amount of heat generated per unit area of such heating elements has increased. Therefore, a technique for improving the efficiency of heat dissipation from the heating element is desired.

  As a general method of heat dissipation, a heat transfer grease or heat transfer sheet is sandwiched and adhered between a heating element such as a semiconductor package and a heat dissipation element made of aluminum or copper to transfer heat to the outside. Has been. From the viewpoint of workability when assembling the heat dissipation device, the heat conductive sheet is superior to the heat conductive grease. For this reason, various developments for heat conductive sheets have been studied.

  For example, for the purpose of improving thermal conductivity, various thermal conductive composite compositions in which thermally conductive inorganic particles are blended in a matrix material and molded products thereof have been proposed. Substances used as thermally conductive inorganic particles are roughly classified into electrically conductive substances such as carbon, silver and copper, and electrically insulating substances such as alumina, silica, aluminum nitride and boron nitride. .

Electrically conductive substances may cause a short circuit if they are used in the vicinity of wiring. Considerations for providing electrical insulation such as providing an electrical insulation layer on one or both sides of electrical conductivity. (For example, refer to Patent Documents 1 and 2).
Moreover, in order to fundamentally solve such a problem of electrical insulation, a method of using an electrically insulating substance for the thermally conductive inorganic particles can be mentioned. For example, an insulating heat dissipation sheet made of a composition in which inorganic particle powder such as boron nitride is blended has been proposed (see, for example, Patent Document 3).
Furthermore, the proposal which raises insulation by providing the insulating synthetic resin film layer in the intermediate | middle layer of a heat conductive sheet is made | formed (for example, refer patent document 4).

  High current applications such as power devices are required to have high heat dissipation to cope with an increase in the amount of heat generated and high electrical insulation that can ensure insulation when used with a large current. However, in the conventional heat conductive sheet, since it is difficult to achieve both high thermal conductivity and electrical insulation at a high level, further development is required.

JP 2000-191812 A JP 2007-1038 A JP 2008-280496 A JP 2004-122664 A

  For example, in the heat conductive sheets disclosed in Patent Document 1 and Patent Document 2, a metal, graphite, or the like having excellent heat conductivity is used in order to ensure high heat conductivity. However, since these are electrically conductive substances, it is difficult to provide high electrical insulation even if consideration is given to providing electrical insulation.

On the other hand, in the heat conductive sheet disclosed in Patent Document 3, since electrically insulating inorganic particles are used as the heat conductive material, a certain electric insulating property can be ensured, but in applications where a large current is used. Anxiety remains for high electrical insulation.
Moreover, in the heat conductive sheet disclosed in Patent Document 4, high electrical insulation can be ensured by the synthetic resin film layer of the intermediate layer, but high heat conductivity is ensured because the intermediate layer having low heat conductivity is provided. It ’s difficult.

As described above, various studies have been made toward the heat conductive sheet, but none of the methods is satisfactory from the viewpoint of achieving both high levels of thermal conductivity and electrical insulation of the sheet.
In view of such circumstances, an object of the present invention is to provide a heat conductive sheet that maintains high thermal conductivity and has high electrical insulation. Another object of the present invention is to provide a heat dissipation device that uses such a heat conductive sheet and has a high heat dissipation capability and has a low risk of short-circuiting nearby circuits.

The present invention is as follows.
(1) In the heat conductive sheet having a multilayer structure of two or more layers including the layer (A) and the layer (B) so as to be laminated in the sheet thickness direction, the layer (A) has a volume of 10 ⁹ Ω · m or more. It is a layer made of a composition comprising insulating non-spherical particles having resistivity and an organic polymer compound, and the insulating non-spherical particles are oriented in the major axis direction with respect to the thickness direction of the layer (A). ,
The heat conductive sheet, wherein the layer (B) is a layer made of an insulating resin composition of 10 kV / mm or more.

(2) The heat conductive sheet according to (1), wherein the insulating non-spherical particles are boron nitride particles.
(3) The heat conductive sheet according to (1) or (2), wherein the insulating non-spherical particles are plate-like boron nitride particles.

(4) The thermal conductive sheet according to any one of (1) to (3), wherein the insulating resin composition includes at least one of a polyamideimide resin and an epoxy resin.
(5) The above (1) to (4), wherein the layer (B) contains particles having a volume resistivity of 10 ⁹ Ω · m or more and a thermal conductivity of 10 W / mK or more in the resin composition. The heat conductive sheet as described in any one of these.

(6) The heat conductive sheet according to any one of (1) to (5), wherein the layer (A) is obtained by a production method including the following steps (a) to (d): .
(A) mixing at least the insulating non-spherical particles and the organic polymer compound to prepare a composition for the layer (A);
(B) using the composition, forming a primary sheet oriented in a direction substantially parallel to the main surface of the insulating non-spherical particles;
(C-1) a step of laminating the primary sheets to form a molded body having a multilayer structure;
(D) A step of slicing the molded body at an angle of 0 degree to 30 degrees with respect to a normal line extending from the main surface.

(7) The heat conductive sheet according to any one of (1) to (5), wherein the layer (A) is obtained by a production method including the following steps (a) to (d): .
(A) mixing at least the insulating non-spherical particles and the organic polymer compound to prepare a composition for the layer (A);
(B) using the composition, forming a primary sheet oriented in a direction substantially parallel to the main surface of the insulating non-spherical particles;
(C-2) forming a molded body having a multilayer structure by winding around the orientation direction of the insulating non-spherical particles;
(D) A step of slicing the molded body at an angle of 0 degree to 30 degrees with respect to a normal line extending from the main surface.
(8) A heat dissipation device having a structure in which the heat conductive sheet according to any one of (1) to (7) is interposed between a heating element and a heat dissipation element.

  The heat conductive sheet of the present invention can have both high heat conductivity and high electrical insulation. In addition, since it is possible to easily add performance such as adhesiveness as needed, they are applied to, for example, heat dissipation applications in the vicinity of electric / electronic circuits to achieve efficient heat dissipation from the heat generating part. It becomes possible.

In addition, the thermal conductive sheet of the present invention is advantageous in terms of productivity, cost, energy efficiency, and certainty compared to the conventional method, and is a thermal conductive sheet having both high thermal conductivity and high flexibility. It becomes possible to provide.
Furthermore, according to the heat dissipating device of the present invention, the possibility of causing a short circuit near the circuit becomes extremely low, and it is possible to realize complete and efficient heat dissipation.

The schematic sectional drawing of the heat conductive sheet obtained in Example 1 and Example 2 is shown.

Hereinafter, the present invention will be described in detail.
The heat conductive sheet of the present invention is a heat conductive sheet having a multilayer structure of two or more layers including a layer (A) and a layer (B) so as to be laminated in the sheet thickness direction, wherein the layer (A) is 10 ^A layer comprising a composition comprising insulating non-spherical particles having a volume resistivity of ⁹ Ω · m or more and an organic polymer compound, and the insulating non-spherical particles are long in the thickness direction of the layer (A). It is oriented in the axial direction, and the layer (B) is a layer made of an insulating resin composition of 10 kV / mm or more.

<Layer (A)>
The layer (A) in the present invention is a layer made of a composition containing insulating non-spherical particles having a volume resistivity of 10 ⁹ Ω · m or more and an organic polymer compound.
In the present invention, the use of insulating non-spherical particles having a volume resistivity of 10 ⁹ Ω · m or more has a sufficient effect on the thermal conductivity of the layer (A).

Specifically, the non-spherical particles are those having a ratio of the major axis direction to the minor axis direction of 1.5 or more as “non-spherical” in the present invention. In the present invention, it is sufficient that non-spherical particles in this range are contained, and particles outside this range can be added as necessary. Since the higher aspect ratio of the non-spherical particles is more advantageous for orientation, the particle shape is preferably a needle shape or a plate shape. Furthermore, the spherical particles can be used as non-spherical particles by pulverization, pulverization, or the like.
The insulating non-spherical particles in the present invention have a volume resistivity of 10 ⁹ Ω · m or more, and more preferably 10 ¹¹ Ω · m or more. Insulating non-spherical particles having a volume resistivity in the above range can be appropriately selected and used.
Moreover, the preferable thermal conductivity of a non-spherical particle is 10 W / mK or more.
Examples of the insulating non-spherical particles having a volume resistivity of 10 ⁹ Ω · m or more that can be used for the layer (A) in the present invention include the following.
Alumina (10 ⁹ to 10 ¹² Ω · m, 21 to 40 W / mK), magnesium oxide (10 ¹² to 10 ¹³ Ω · m, 60 W / mK), beryllium oxide (> 10 ¹⁰ Ω · m, 130 W / mK), Aluminum nitride (10 ¹¹ to 10 ¹² Ω · m, 70 to 200 W / mK), boron nitride (10 ¹² to 10 ¹⁴ Ω · m, 40 to 60 W / mK), silicon nitride (10 ¹² to 10 ¹⁴ Ω · m, 25-155 W / mK).

  Specific examples of the insulating non-spherical particles that can be used in the layer (A) of the present invention include alumina, magnesium oxide, beryllium oxide, aluminum nitride, boron nitride, silicon nitride and the like. Although not particularly limited, the present invention uses at least one particle selected from the group consisting of boron nitride and alumina from the viewpoint of high water resistance and low harmfulness to human body. Is preferred. Furthermore, their shape is preferably scaly, plate-like, needle-like, oval, rod-like or plate-like, more preferably plate-like. In particular, plate-like boron nitride particles are preferable as the insulating non-spherical particles.

  Although the compounding quantity of an insulating non-spherical particle is not specifically limited, The range of 30-80 volume% is preferable on the basis of the volume of the composition for a layer (A). When the blending amount is less than 30% by volume, the thermal conductivity tends to be low, and when the blending amount exceeds 80% by volume, the cohesive force of the composition for the layer (A) tends to be reduced, and the layer There is a high possibility that the strength of (A) will decrease. A more preferable blending amount of the insulating non-spherical particles is 45 to 75% by volume based on the volume of the composition for the layer (A).

In the present invention, the blending amount (volume%) of the insulating non-spherical particles in the layer (A) is a value determined by the following formula.
Content (volume%) of insulating non-spherical particles (A) =
(Aw / Ad) / ((Aw / Ad) + (Bw / Bd) + (Cw / Cd) +...) × 100
Aw: mass composition (% by mass) of insulating non-spherical particles (A)
Bw: mass composition (mass%) of the organic polymer compound (B)
Cw: mass composition (mass%) of other optional components (C)
Ad: Specific gravity of insulating non-spherical particles (A) (In the present invention, in the case of boron nitride particles, Ad is calculated as 2.3. In addition, alumina: 3.97, aluminum nitride: 3.26, silicon nitride: 3. (Calculate with 2)
Bd: Specific gravity of organic polymer compound (B) Cd: Specific gravity of other optional component (C)

When the insulating non-spherical particles in the layer (A) are plate-like boron nitride particles, the average particle size is preferably more than 10 μm and 60 μm or less. For example, an aggregate-like material can be obtained as non-spherical particles by pulverization, pulverization, or the like. In addition, when the average particle size is outside the range of more than 10 μm and 60 μm or less, it can be adjusted within a specific average particle size range by removing particles that are too large or too small by crushing, sieving, etc. Is possible.
The average particle diameter is a value of D50 when measured by a laser diffraction / scattering method.

In the present invention, specific examples of the plate-like boron nitride particles (A) preferably used as the insulating non-spherical particles are not particularly limited, but “PT-110 (trade name)” (Momentive Performance Materials). Made by Japan GK, average particle size: 45 μm, volume resistivity: 10 ¹² to 10 ¹⁴ Ω · m, ratio of major axis direction to minor axis direction: 20), “HP-1CAW (trade name)” (Mizushima Alloy Iron Manufactured by Co., Ltd., average particle diameter: 16 μm, volume resistivity: 10 ¹² to 10 ¹⁴ Ω · m, ratio of major axis direction to minor axis direction: 13), “PT-110 Plus (trade name)” (Momentive performance Materials Japan LLC, Ltd., average particle size of 45μm, volume ^{resistivity: 10 12 ~10 14 Ω · m} , the long axis direction and a minor axis direction of the ratio: 20), "HP-1CA (trade name)" ( Island alloy steel, the average particle diameter of 16 [mu] m, major axis and minor axis ratio: 13), and the like.
Examples of the plate-like aluminum nitride particles include “Toyalnite FLX (trade name)” (manufactured by Toyo Aluminum, average particle diameter of 16 μm, volume resistivity of 10 ¹² Ω · m), and the like.

In the layer (A) in the present invention, the insulating non-spherical particles are oriented in the major axis direction with respect to the thickness direction of the layer (A).
In the present invention, “orientation in the major axis direction with respect to the thickness direction of the layer (A)” means that when a cross section of the heat conductive sheet is observed with respect to 50 arbitrary particles using an SEM (scanning electron microscope). It means a state in which the average value of the angles of the spherical particles with respect to the surface of the heat conductive sheet in the major axis direction (a complementary angle is adopted when 90 degrees or more) is in the range of 70 degrees to 90 degrees.
In the present invention, sufficient thermal conductivity cannot be obtained unless the insulating non-spherical particles exhibit the above-described orientation. In order to show the orientation as described above, the layer (A) in the present invention may be produced by the production process. Details will be described later.

  In the layer (A) of the present invention, an organic polymer compound can be used without any particular limitation. Specific examples of the organic polymer compound include a poly (meth) acrylate polymer compound (so-called acrylic rubber) and a polydimethylsiloxane structure mainly composed of butyl acrylate, 2-ethylhexyl acrylate, and the like. Polymer compound having main structure (so-called silicone resin), polymer compound having polyisoprene structure in main structure (so-called isoprene rubber, natural rubber), polymer compound having polychloroprene as main raw material component (polychloroprene, so-called neoprene) Rubber) and polymer compounds having a polybutadiene structure as a main structure (so-called butadiene rubber), etc., and flexible organic polymer compounds generally referred to as “rubber”. Among these, in particular, a poly (meth) acrylic acid ester-based polymer compound containing butyl acrylate or 2-ethylhexyl acrylate as a main raw material component easily obtains high flexibility, chemical stability and It is preferable because it is excellent in workability and relatively inexpensive.

The organic polymer compound preferably has a weight average molecular weight of 10,000 to 1,000,000. The weight average molecular weight can be measured by gel permeation chromatography using a standard polystyrene calibration curve.
Furthermore, the organic polymer compound preferably has a glass transition temperature (Tg) of 50 ° C. or lower.
The glass transition temperature (Tg) can be measured with a dynamic viscoelasticity measuring device (DMA). As the dynamic viscoelasticity measuring device (DMA), for example, ARES-2KSTD manufactured by TA Instruments can be used. The measurement conditions are a temperature rising rate: 5 ° C./min and a measurement frequency: 1.0 Hz.

Although it does not specifically limit, As an organic high molecular compound which can be used conveniently by this invention, for example, acrylate ester copolymer resin "HTR-811DR (trade name)" manufactured by Nagase ChemteX Corporation (butyl acrylate) / Ethyl acrylate / acrylic acid 2-ethylhexyl copolymer, Mw 420,000, Tg-43 ° C. solid), acrylic ester copolymer resin “HTR-280DR (trade name)” manufactured by Nagase ChemteX Corporation (acrylic acid Butyl / acrylonitrile / acrylic acid copolymer, Mw 900,000, Tg-37 ° C., 30 mass% toluene / ethyl acetate = 1: 1 solution) and the like.
The blending amount of the organic polymer compound is preferably 10 to 40% by volume. There exists a tendency for sufficient sheet | seat strength to be acquired as it is 10 volume% or more. If it is 40 volume% or less, a sufficient amount of non-spherical particles can be contained, and sufficient thermal conductivity tends to be obtained.

  Various additives can be added to the composition constituting the layer (A) of the present invention, if necessary. In the preferable form of this invention, it is preferable to use a flame retardant for the purpose of improving the flame retardance of a heat conductive sheet. Although not particularly limited, the layer (A) composed of a composition containing a phosphate ester flame retardant is advantageous not only in terms of flame retardancy and flexibility but also in productivity and cost. . It is preferable to make content of a flame retardant into the range of 5-50 volume% of a composition, and it is more preferable to set it as the range of 10-40 volume%. If the content of the flame retardant is 5% by volume or more, sufficient flame retardancy can be obtained in the heat conductive sheet. If it is 50 volume% or less, it can prevent that the intensity | strength of a sheet | seat falls.

  In addition, in the composition constituting the layer (A) in the present invention, if necessary, a toughness improving agent such as urethane acrylate, a silane coupling agent, a titanium coupling agent, an adhesive strength improving agent such as an acid anhydride, It is also possible to add various additives such as wetting improvers such as nonionic surfactants and fluorine surfactants, antifoaming agents such as silicone oil, and ion trapping agents such as inorganic ion exchangers.

The layer (A) preferably has a thermal conductivity of 10 W / mK. In order to set the thermal conductivity of the layer (A) within the above range, the layer (A) may be formed from a composition containing the above-mentioned insulating non-spherical particles and organic polymer compound in a specific blending amount.
A specific method for producing the layer (A) will be described later.

<Layer (B)>
In the present invention, the layer (B) is characterized by comprising an insulating resin composition of 10 kV / mm or more.

As long as the insulating resin composition used for the layer (B) is 10 kV / mm or higher, any resin may be used, and if necessary, the insulating resin composition may include particles for setting to 10 kV / mm or higher. You may make it contain in an insulating resin composition.
Examples of the particles for achieving 10 kV / mm or more include insulating non-spherical particles used in the layer (A), but the shape is not limited to non-spherical.
The insulating resin composition used for the layer (B) preferably contains an insulating resin.
Here, the “insulating resin” is 10 kV / mm or more, and specific examples include polyamide resin, polyamideimide resin, polyimide resin, silicone resin, epoxy resin, phenol resin, melamine resin, urea resin, polyester. , Polyurethane, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, Teflon (registered trademark), ABS resin (acrylonitrile butadiene styrene resin), AS resin, NBR resin, acrylic resin, nylon, polyacetal, polycarbonate , Modified polyphenylene ether, polybutylene terephthalate, polyethylene terephthalate, cyclic polyolefin, polyphenylene sulfide, polytetrafluoroethylene, polysulfone, polyethersulfur O emissions, acrylate polymer, liquid crystal polymer, fluororesin, polyether ether ketone.

  Although not particularly limited, in the present invention, from the viewpoint of high adhesiveness, heat resistance and insulation, it is possible to use at least one resin selected from the group consisting of polyamideimide resins and epoxy resins. preferable.

The insulating resin composition of the layer (B) in the present invention preferably contains particles satisfying a volume resistivity of 10 ⁹ Ω · m or more and a thermal conductivity of 10 W / mK or more. Specific examples include alumina, magnesium oxide, beryllium oxide, aluminum nitride, boron nitride, silicon nitride, and the like. Although not particularly limited, in the present invention, alumina is preferable from the viewpoint of high water resistance and cost.

Although the compounding quantity of the said particle | grain is not specifically limited, The range of 20-90 volume% is preferable on the basis of the volume of the insulating resin composition used for a layer (B). If the blending amount is less than 20% by volume, the thermal conductivity of the heat conductive sheet tends to be reduced, and if the blending amount exceeds 90% by volume, the cohesive strength of the resin composition tends to be reduced, and the layer (B) There is a high possibility that the strength of the material will decrease.
The insulating resin composition according to the present invention includes a curing accelerator, a rubber elastomer, a phosphorus compound as a flame retardant, an inorganic filler, a coupling agent, a pigment, a leveling agent, an antifoaming agent, and an ion trap as necessary. You may mix | blend an agent etc.

  Examples of the method for forming the layer (B) in the present invention include rolling, pressing, extrusion, and coating. In order to facilitate handling, it is also possible to form the layer (B) by dissolving the insulating resin composition in an organic solvent, applying it to a support, and removing the organic solvent. Moreover, it is also possible to apply | coat directly to other layers, such as a layer (A) and a layer (B), instead of a support body. The direct application to the layer (B) is a case in which two or more layers (B) are provided. From the viewpoint of improving the adhesion of the first layer, the viewpoint of improving the thermal conductivity of the second layer. Set up from.

Examples of the support include polyethylene, polyvinyl chloride, polyethylene terephthalate, polycarbonate, tetrafluoroethylene film, release paper, metal foil such as copper foil and aluminum foil, and the thickness of the support is 10 to 150 μm. Preferably there is. The support may be subjected to mud treatment, corona treatment, mold release treatment, and the like.
From the viewpoints of storage stability, productivity, and workability, it is preferable to further store a protective film on the layer (B) for storage. Examples of the protective film include polyethylene, polyvinyl chloride, polyethylene terephthalate, release paper, and the like, and mat treatment, embossing, and release treatment may be performed. Peeling of the support and the protective film may be performed before the layer (B) or the like is laminated on another layer, or after the lamination.

  The organic solvent to be used is not particularly limited, but ketones such as acetone, methyl ethyl ketone, and cyclohexanone, acetates such as ethyl acetate, butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate, carbitol acetate, cellosolve, butyl cellosolve And the like, carbitols such as carbitol and butyl carbitol, aromatic hydrocarbons such as toluene and xylene, dimethylformamide, dimethylacetamide, N-methylpyrrolidone and the like, and one or more of these Can be used.

<Heat conduction sheet>
The heat conductive sheet of the present invention is characterized by having a multilayer structure of two or more layers including the layer (A) and the layer (B) so as to be laminated in the sheet thickness direction. The method for forming the multilayer structure is not particularly limited. Specific examples include a method in which the sheet-like layer (A) and the layer (B) are superposed and pressure-bonded using a press or a laminating machine, and the resin in the layer (B) is applied to the sheet-like layer (A). Examples thereof include a method of applying the composition solution.

The thickness of the layer (B) in the heat conductive sheet of the present invention is desirably as thin as possible within a range in which insulation can be ensured. This is because as the thickness of the layer (B) increases, the insulating properties improve, but the thermal conductivity decreases.
Moreover, when forming a multilayer structure, it is also possible to include layers other than a layer (A) and a layer (B). Examples of the layer other than the layer (A) and the layer (B) include a layer for enhancing the sheet strength and a layer for adjusting the total thickness of the sheet.
The layers (A) and (B) need not be alternated, but are preferably alternated from the viewpoint of the balance between thermal conductivity and insulation. The layer (A) and the layer (B) do not need to be the outermost layer, but the layer (B) is preferably the outermost layer from the viewpoint of adhesiveness.

  In the present invention, it is preferable to protect the outermost surface prior to the use of the heat conductive sheet from the viewpoint of maintaining the shape of the heat conductive sheet of the present invention and preventing foreign matter contamination. The outermost surface is protected by, for example, providing a protective film on the outermost surface when forming the heat conductive sheet.

  Examples of the material for the protective film include resins such as polyethylene, polyester, polypropylene, polyethylene terephthalate, polyimide, polyetherimide, polyether naphthalate, and methylpentene film, and metals such as coated paper, coated cloth, and aluminum. These protective films may be a multilayer film composed of two or more kinds of films, and a film whose surface is treated with a release agent such as silicone or silica is preferably used.

<Manufacturing process of layer (A)>
The manufacturing process of the layer (A) is also within the scope of the present invention. The heat conductive sheet of the present invention is characterized in that the layer (A) is obtained by a production method including the following steps.
(A) mixing insulating non-spherical particles and the organic polymer compound to prepare a composition for the layer (A);
(B) using the composition, forming a primary sheet oriented in a direction substantially parallel to the main surface of the insulating non-spherical particles;
(C-1) a step of laminating the primary sheets to form a molded body having a multilayer structure;
(D) A step of slicing the molded body at an angle of 0 degree to 30 degrees with respect to a normal line extending from the main surface.

Instead of the step (c-1),
(C-2) The primary sheet may be wound around the orientation direction of the insulating non-spherical particles as an axis to form a molded body having a multilayer structure.

Hereinafter, each step will be described.
In the step (a), the composition constituting the layer (A) is prepared by any method as long as predetermined insulating non-spherical particles can be uniformly mixed in the composition. May be. Although not particularly limited, for example, a solution is formed by previously dissolving an organic polymer compound in a solvent, and other additives such as the insulating non-spherical particles and flame retardant are added to the solution, and they are mixed. The composition can be prepared by a method of drying after stirring or a method of mixing each component using roll kneading, kneader, brabender, or an extruder.

The solvent used is not particularly limited as long as it can be removed by drying after mixing and stirring. For example, acetone, methyl ethyl ketone, methyl butyl ketone, hexane, cyclohexane, ethyl acetate, butyl acetate, benzene, toluene, xylene Etc.
In the step of forming the primary sheet (b), a conventional film forming technique can be applied, but at least one forming method selected from the group consisting of rolling, pressing, extrusion, and coating is used. It is preferable to carry out using. By selecting at least one of rolling and pressing as the forming method, the non-spherical particles can be more reliably oriented in a direction substantially parallel to the main surface. In addition, when these methods are selected, pressure is applied during the formation of the primary sheet, whereby the insulating non-spherical particles are likely to come into contact with each other, and high thermal conductivity tends to be easily achieved. In addition, the thinner one is preferable from the viewpoint of thermal conductivity. When the thickness of the primary sheet is increased, the orientation of the insulating non-spherical particles becomes insufficient, and the thermal conductivity of the finally obtained thermal conductive sheet tends to deteriorate.

  The “state in which the non-spherical particles are oriented in a direction substantially parallel to the main surface of the sheet” refers to a state in which the non-spherical particles are oriented so as to lie on the main surface of the sheet. The orientation of the non-spherical particles in the sheet surface is controlled by adjusting the direction in which the composition flows when the composition is molded. That is, the direction of the non-spherical particles is controlled by adjusting the direction in which the composition is passed through a rolling roll, the direction in which the composition is pressed, the direction in which the composition is extruded, and the direction in which the composition is applied. Since the non-spherical particles are basically anisotropic particles, the orientation of the non-spherical particles is usually aligned by rolling, pressing, extrusion, or coating the composition. .

  The confirmation of “the state in which the non-spherical particles are oriented in a direction substantially parallel to the main surface of the layer (A)” is the confirmation method of the above-mentioned “orientation in the major axis direction with respect to the thickness direction of the layer (A)” Similarly, the cross section of the sheet is observed by observing 50 arbitrary particles using the SEM. Specifically, the cross section of the primary sheet is observed using an SEM, and for any 50 particles, the angle of the non-spherical particles in the major axis direction with respect to the primary sheet surface (a complementary angle is adopted when 90 degrees or more) Confirm that the average value of is in the range of 0 to 20 degrees.

The step of forming the molded body having the multilayer structure of (c-1) or (c-2) can be performed by laminating the primary sheet obtained in the previous step. The form of lamination is not particularly limited. For example, it is not limited to a form in which a plurality of independent sheets are sequentially stacked, and a form in which one sheet is folded without cutting its end may be used. Further, as another form of lamination, it is possible to form a compact by winding one sheet. The form of winding is not limited to the shape of the molded body being a cylindrical shape, and may be another shape such as a rectangular tube shape. The shape of the molded body may be any shape as long as there is no inconvenience when slicing the molded body at an angle of 0 to 30 degrees with respect to the normal line from the main surface in the subsequent step (d). Good.
For example, the shape of each sheet is formed into a circular shape, and a cylindrical shaped body is produced by laminating them, and the subsequent slicing in the step (d) may be performed by a method such as “wig removal”. Is possible.

  In the step (c-1) or (c-2), the pressure at the time of lamination and the pulling force at the time of winding are performed later. It is desirable to adjust the strength so that the orientation does not collapse and to the extent that the sheets in the molded body are appropriately bonded to each other. Usually, it is possible to obtain sufficient adhesion between the sheets by adjusting the pressure and tensile force when forming the molded body. However, when the adhesive force between the sheets is insufficient, lamination or winding may be performed after thinly applying a solvent or an adhesive to the sheet surface.

  In the step of slicing the molded body of (d), the molded body is sliced at an angle of 0 degree to 30 degrees with respect to the normal line coming out from the main surface so that the layer (A) has a predetermined thickness. To be implemented. Although the cutting tool which can be used at the time of a slice is not specifically limited, It is preferable to use a slicer, a cannula, etc. provided with a sharp blade. By using a cutting tool provided with a sharp blade, it is possible to easily produce a sheet having a small thickness, in which the particle orientation in the vicinity of the surface of the sheet obtained after slicing is hardly disturbed.

  When the slicing angle is 30 degrees or less, the thermal conductivity of the obtained thermal conductive sheet is good. When the molded body is a laminated body, it may be sliced (within the above angle range) so as to be perpendicular or substantially perpendicular to the lamination direction of the primary sheet. Further, when the molded body is a wound body, it may be sliced (within the above angle range) so as to be perpendicular or substantially perpendicular to the winding axis. As described above, in the case of a columnar molded body in which circular primary sheets are laminated, they may be sliced like a wig within the above angle range.

  (D) The slicing step is performed at a temperature (Tg + 50 ° C.) higher than the glass transition temperature (Tg) of the organic polymer compound constituting the layer (A) by 20 ° C. (Tg−20 ° C.). It is preferable to carry out within a range. When the temperature at the time of slicing is Tg + 50 ° C. or lower, not only does the molded body become flexible and it becomes difficult to perform slicing, but also the orientation of the particles in the layer (A) is prevented from being disturbed. On the other hand, when the temperature at the time of slicing is Tg−20 ° C. or higher, the molded body becomes hard and brittle, and it is difficult to perform slicing, and it is easy to avoid the layer (A) from being cracked immediately after slicing. A more preferable temperature for slicing is a temperature range of Tg + 40 ° C. to Tg−10 ° C.

  In addition, as thickness of a preferable layer (A), it is 200 times or less (preferably 100 times or less) of the average particle diameter more than the average particle diameter of the nonspherical particle contained. When the average particle size is larger than the average particle size, it is considered that non-spherical particles can be prevented from falling off the sheet. When the average particle size is 200 times or less, the number of passes through the non-spherical particles is reduced, and the thermal conductivity is improved.

<Heat dissipation device>
The present invention also includes a heat dissipation device. The heat dissipating device of the present invention has a structure in which the heat conductive sheet of the present invention is interposed between the heat generating body and the heat dissipating body.
The heating element that can be used in the heat dissipation device of the present invention has at least a surface temperature not exceeding 200 ° C, and the temperature at which the heat conductive sheet of the present invention can be suitably used is in the range of -10 ° C to 120 ° C. is there. There is a high possibility that the surface of the heating element exceeds 200 ° C., for example, in the vicinity of the nozzle of a jet engine, around the inside of a kiln pot, around the inside of a blast furnace, around the inside of a nuclear reactor, outer space shell, etc. Since there is a high possibility that the organic polymer compound in the sheet is decomposed, it tends to be unsuitable. Examples of the heating element suitable for the heat dissipation device of the present invention include a semiconductor package, a display, an LED, and an electric lamp.

  On the other hand, the heat radiator that can be used in the heat radiating device of the present invention is not particularly limited, and may be a typical one that is applied to the heat radiating device. For example, a heat sink using aluminum or copper fins or plates, an aluminum or copper block connected to a heat pipe, an aluminum or copper block in which cooling liquid is circulated by a pump, a Peltier element and this Examples include aluminum and copper blocks.

Instead of aluminum or copper, materials with a thermal conductivity of 10 W / mK or more, such as metals such as silver, iron, indium, graphite, diamond, aluminum nitride, boron nitride, silicon nitride, silicon carbide, aluminum oxide, etc. Those utilized are also preferred.
The heat dissipating device of the present invention is established by installing the heat conductive sheet of the present invention between the above-described heat generating body and the heat dissipating body and fixing each surface in contact. The heat conductive sheet is not particularly limited as long as it can be fixed in a state where the contact surfaces are sufficiently adhered, and any method may be used. However, from the viewpoint of maintaining sufficient contact between the contact surfaces, a method in which the pressing force is maintained is preferable. For example, the method of screwing using a spring and the method of inserting | pinching using a clip are mentioned. According to the heat dissipating device of the present invention, high heat dissipating efficiency can be achieved, and there is little risk of shorting nearby circuits.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.
In each example, the thermal conductivity as an index of thermal conductivity and the dielectric breakdown voltage as an index of insulation were obtained by the following methods.

(Measurement of thermal conductivity)
The heat conductive sheet to be measured was cut into a size of 1 cm × 1 cm with a cutter, and the cut piece was placed so that one surface was in contact with the transistor (2SC2233) and the other surface was in contact with the aluminum heat dissipation block, thereby preparing a test sample. . Next, while pressing the transistor, current is passed through the test sample to measure the temperature of the transistor (T1, unit ° C) and the temperature of the heat dissipation block (T2, unit ° C). From the measured value and the applied power (W, unit W), The thermal resistance (X, unit ° C / W) was measured according to the following formula.
As an evaluation standard, 10 W / mK or more was rated as ◯, and less than 10 W / mK was rated as x.

  From the obtained thermal resistance (X), the thickness of the cut piece (d, unit μm), and the correction coefficient C based on a known sample of thermal conductivity, the thermal conductivity (Tc, unit W / mK) was ) Was estimated.

(Measurement of dielectric breakdown voltage: short time breakdown method)
It conformed to ASTM D149 and JIS C2110.
A heat conductive sheet to be measured was cut into a size of 5 cm × 5 cm with a cutter, and a test sample was prepared so that one side had a circular copper layer of φ20 mm and the other side had an entire copper layer. The electrodes were arranged so as to sandwich the test sample, and the voltage of the test sample was increased from 0 to a constant rate so that dielectric breakdown occurred in an average of 10 to 20 seconds in electric insulating oil. The dielectric breakdown voltage (unit: kV / mm) was determined by dividing the voltage (unit: kV) when dielectric breakdown occurred by the film thickness (unit: mm) of the heat conductive sheet.
As an evaluation standard, 10 kV / mm or more was rated as ◯, and less than 10 kV / mm was rated as x.

Example 1
Plate-shaped boron nitride powder “PT-110 (trade name)” (Momentive Performance Materials Japan G.K., average particle size: 45 μm, volume resistivity: 10 ¹² to 10 ¹⁴ Ω · m, long axis direction and short axis Direction ratio: 20) 457.8 g, acrylate copolymer resin “HTR-811DR (trade name)” (manufactured by Nagase ChemteX Corp., butyl acrylate / ethyl acrylate / methacrylic acid 2-hydroxyethyl copolymer) Coalescence, Mw: 420,000, Tg: −29.4 ° C.) 89.6 g, and phosphate ester flame retardant “CR-741 (trade name)” (manufactured by Daihachi Chemical Industry Co., Ltd.) 69.7 g A composition was prepared by heating to 120 ° C. and kneading.
The composition prepared above is sandwiched between the release-treated PET films, and is pressed using a press machine under the conditions of a tool pressure of 10 MPa and a tool temperature of 120 ° C. for 10 seconds. A primary sheet was obtained. By repeating this operation, a large number of primary sheets were produced.

In the primary sheet, “a state in which the non-spherical particles are oriented in a direction substantially parallel to the main surface of the layer (A)” was confirmed as follows.
The cross section of the obtained primary sheet was observed using an SEM (scanning electron microscope), and the surface of the primary sheet in the major axis direction of the plate-like boron nitride particles from the direction seen for any 50 plate-like boron nitride particles The average value was determined to be 5 degrees, and the long axis direction of the plate-like boron nitride particles was observed to be oriented in a direction substantially parallel to the main surface of the primary sheet.

  Each of the obtained primary sheets was cut into a size of 4 cm × 20 cm with a cutter, the 40 sheets were laminated, and lightly pressed by hand to adhere the layers of the respective primary sheets, thereby obtaining a molded body having a thickness of 4 cm. After cooling this molded body with dry ice, a laminated cross section of 4 cm × 20 cm was scraped with a plane at a temperature of −10 ° C. (sliced at an angle of 5 degrees with respect to the normal line coming out from the primary sheet surface), and the size was 4 cm × A 20 cm × 0.25 mm layer (A) sheet (hereinafter also referred to as “BN sheet”) was obtained.

  The cross section of the sheet of the layer (A) is observed using an SEM (scanning electron microscope), and the heat conduction in the major axis direction of the plate-like boron nitride particles from the direction seen for any 50 plate-like boron nitride particles When the angle with respect to the sheet surface was measured and the average value was determined, it was 85 degrees, and it was confirmed that the major axis direction of the plate-like boron nitride particles was oriented in the thickness direction of the heat conductive sheet.

The adhesive sheet (trade name: KS7003, manufactured by Hitachi Chemical Co., Ltd., thickness: 12 μm, dielectric breakdown voltage: 95 kV / mm, alumina (10 ⁹ to 10 9-) on both surfaces of the layer (A) sheet. 10 ¹² Ω · m, 21 to 40 W / mK)) is formed by vacuum hot pressing to form a 0.012 mm layer (B) on both sides of the layer (A), and laminated together with a 105 μm copper foil. A cured product was prepared by heat treatment at 140 ° C. for 2 hours and 190 ° C. for 2 hours, and the copper foil was removed by etching treatment to obtain a heat conductive sheet of Example 1. A schematic sectional view of the obtained heat conductive sheet is shown in FIG. The heat conductive sheet 1 has a layer (B) 3a formed of an adhesive layer on both sides of a layer (A) 2 formed of a BN sheet layer.
The obtained thermal conductive sheet had a thermal conductivity of 13 W / mK and a dielectric breakdown voltage of 40 kV / mm.

(Example 2)
An adhesive resin solution (trade name: KS6003, manufactured by Hitachi Chemical Co., Ltd., dielectric breakdown voltage: 95 kV / mm) on both sides of the BN sheet layer of the layer (A) obtained in Example 1 Alumina (containing 10 ⁹ to 10 ¹² Ω · m, 21 to 40 W / mK) is applied and dried with a hot air dryer at 120 to 140 ° C. for 15 minutes, and a 0.012 mm layer on both sides of layer (A) ( B) was formed, and a cured product was prepared by heat treatment at 140 ° C. for 2 hours and 190 ° C. for 2 hours to obtain a heat conductive sheet of Example 2. The schematic cross-sectional view of the obtained heat conductive sheet is the same as that of Example 1 (FIG. 1).
The obtained heat conductive sheet had a good thermal conductivity of 10 W / mK and a dielectric breakdown voltage of 35 kV / mm.

(Comparative Example 1)
Only the layer (A) obtained in Example 1 was evaluated as a heat conductive sheet of Comparative Example 1.
The thermal conductivity of the obtained thermal conductive sheet was as good as 14 W / mK, but the dielectric breakdown voltage was as low as 8 kV / mm.

(Comparative Example 2)
Adhesive resin solution of layer (B) used in Example 2 (trade name: KS6003, manufactured by Hitachi Chemical Co., Ltd., dielectric breakdown voltage: 95 kV / mm, alumina (10 ⁹ to 10 ¹² Ω · m, 21 to 21) 40W / mK) containing) is applied to a PET film, dried with a hot air dryer at 140 ° C for 15 minutes, then peeled off from the PET film, and both sides are sandwiched with copper foil by hot pressing, and heated at 150 ° C for 1 hour. Then, the copper foil was removed by etching, and only the layer (B) having a thickness of 0.05 mm was obtained as the heat conductive sheet of Comparative Example 2.
The obtained thermal conductive sheet had a dielectric breakdown voltage of 95 kV / mm and a thermal conductivity of 0.3 W / mK.

  ADVANTAGE OF THE INVENTION According to this invention, the heat conductive sheet which has high heat conductivity and high electrical insulation can be provided. In addition, the present invention can provide a complete and efficient heat dissipation device that is extremely unlikely to cause a short circuit near the circuit.

1: Thermal conductive sheet 2: Layer (A) (BN layer)
3a: Layer (B) (adhesive layer)

Claims (8)

In the heat conductive sheet having a multilayer structure including two or more layers including the layer (A) and the layer (B) so as to be laminated in the sheet thickness direction, the layer (A) has a volume resistivity of 10 ⁹ Ω · m or more. The insulating non-spherical particles and a layer comprising a composition containing an organic polymer compound, and the insulating non-spherical particles are oriented in the major axis direction with respect to the thickness direction of the layer (A),
The heat conductive sheet, wherein the layer (B) is a layer made of an insulating resin composition of 10 kV / mm or more.   The heat conductive sheet according to claim 1, wherein the insulating non-spherical particles are boron nitride particles.   The heat conductive sheet according to claim 1, wherein the insulating non-spherical particles are plate-like boron nitride particles.   The heat conductive sheet according to any one of claims 1 to 3, wherein the insulating resin composition contains at least one of a polyamideimide resin and an epoxy resin. 5. The layer (B) contains particles having a volume resistivity of 10 ⁹ Ω · m or more and a thermal conductivity of 10 W / mK or more in the resin composition. The heat conductive sheet as described. The said layer (A) is obtained by the manufacturing method containing the following (a)-(d) process, The heat conductive sheet as described in any one of Claims 1-5 characterized by the above-mentioned.
(A) mixing the insulating non-spherical particles and the organic polymer compound to prepare a composition for the layer (A);
(B) using the composition, forming a primary sheet oriented in a direction substantially parallel to the main surface of the insulating non-spherical particles;
(C-1) a step of laminating the primary sheets to form a molded body having a multilayer structure;
(D) A step of slicing the molded body at an angle of 0 degree to 30 degrees with respect to a normal line extending from the main surface. The said layer (A) is obtained by the manufacturing method containing the following (a)-(d) process, The heat conductive sheet as described in any one of Claims 1-5 characterized by the above-mentioned.
(A) mixing the insulating non-spherical particles and the organic polymer compound to prepare a composition for the layer (A);
(B) using the composition, forming a primary sheet oriented in a direction substantially parallel to the main surface of the insulating non-spherical particles;
(C-2) forming a molded body having a multilayer structure by winding around the orientation direction of the insulating non-spherical particles;
(D) A step of slicing the molded body at an angle of 0 degree to 30 degrees with respect to a normal line extending from the main surface.   A heat dissipation device having a structure in which the heat conductive sheet according to any one of claims 1 to 7 is interposed between a heating element and a heat dissipation element.

Images