Radio wave-absorbing thermally-conductive composition and sheet of same

Abstract

This radio wave-absorbing thermally-conductive composition comprises a silicone resin (A), a radio wave-absorbing material (B), and a thermally-conductive substance (C). The radio wave-absorbing material (B) is a helical structure having a metal plated layer, and is contained in an amount of 0.1-50 parts by mass with respect to 100 parts by mass of the silicone resin (A). The thermally-conductive substance (C) is preferably inorganic particles of a metal oxide, a metal nitride, a metal carbide, a metal boride, an elemental metal, or the like, is contained in an amount of 50-3000 parts by mass with respect to 100 parts by mass of the silicone resin (A), and preferably has a thermal conductivity rate of 0.8 W / mK or more. As a result, provided are: a radio wave-absorbing thermally-conductive composition that achieves both thermal conductivity and radio wave-absorbing ability for terahertz waves; and a sheet of the same.

Description

Radio wave absorbing thermally conductive composition and sheet thereof

[0001] The present invention relates to a radio wave absorbing thermally conductive composition capable of efficiently absorbing radio wave noise in a specific frequency range, and a sheet thereof.

[0002] In recent years, the increasing integration and density of electronic components in devices such as personal computers and automobiles has led to an increase in the amount of heat generated per unit area. This has led to a growing demand for highly thermally conductive materials that can dissipate heat more quickly than conventional heat-dissipating materials, thereby improving thermal conductivity. Furthermore, applications requiring insulation require stable, high-performance insulation, even at high operating temperatures. Meanwhile, the demand for faster processing speeds in central processing units (CPUs) has led to a dramatic increase in operating frequencies, generating high-frequency components (radio wave noise). This radio wave noise can be transmitted to signals in communication lines and can cause adverse effects, such as malfunctions. To address this issue, methods have been adopted to efficiently dissipate heat generated by CPUs to metal heat sinks using heat-dissipating media such as thermally conductive silicone grease or thermally conductive silicone rubber. However, these methods are unable to avoid problems such as malfunctions due to radio wave noise, because thermally conductive silicone rubber lacks the radio wave absorption (radio wave noise suppression) effect.

[0003] As prior art, Patent Document 1 proposes a silicone composition having thermal conductivity and radio wave absorption properties in a portion of the millimeter wave band from 60 to 90 GHz. Patent Document 2 proposes a λ / 4 type radio wave absorber including a resistive film, a dielectric layer, and a reflective layer. Another radio wave absorber has been proposed that has thermal conductivity and radio wave absorption properties in the millimeter wave band. Patent Document 3 proposes a radio wave absorber for the millimeter wave to terahertz band. Patent Document 4 proposes a terahertz wave absorber containing a carbon fiber system. Patent Document 5 proposes forming a metal plating layer on phytoplankton, a type of blue-green algae known as spirulina, and turning it into a microcoil.

[0004] JP 2023-028969 A JP 2021-136447 A JP 2023-133360 A JP 2022-029057 A Japanese Patent No. 5606572

[0005] However, the conventional techniques have not yet achieved a radio wave absorbing, thermally conductive composition that is both radio wave absorbing and thermally conductive for terahertz waves.

[0006] In order to solve the above-mentioned problems of the related art, the present invention provides a radio wave absorbing and thermally conductive composition that achieves both radio wave absorption and thermal conductivity in the terahertz wave region, and a sheet thereof.

[0007] One embodiment of the present invention relates to a radio wave absorbing thermally conductive composition comprising a silicone resin (A), a radio wave absorber (B), and a thermally conductive substance (C), wherein the radio wave absorber (B) has a helical structure having a metal plating layer, and the radio wave absorbing material (B) is contained in an amount of 0.1 to 50 parts by mass per 100 parts by mass of the silicone resin (A).

[0008] Another embodiment of the present invention relates to a radio wave absorbing thermally conductive sheet, in which the radio wave absorbing thermally conductive composition is formed into a sheet and cured.

[0009] According to the present invention, a radio wave absorbing thermally conductive composition and sheet thereof can be provided, which contain a silicone resin (A), a radio wave absorber (B), and a thermally conductive substance (C), wherein the radio wave absorber (B) has a helical structure having a metal plating layer, and which contains 0.1 to 50 parts by mass of the radio wave absorber (B) per 100 parts by mass of the silicone resin (A). The thermally conductive substance (C) functions as a thermal interface material (TIM) between the heat-generating and heat-dissipating parts of electronic components such as semiconductors, and also transfers heat generated when absorbed by the radio wave absorber (B) to the heat-dissipating parts, thereby efficiently protecting the electronic components.

[0010] FIG. 1 is a schematic cross-sectional view showing a method of using a radio wave absorbing thermally conductive sheet according to one embodiment of the present invention. FIGS. 2A and 2B are explanatory diagrams showing a method of measuring thermal conductivity used in one embodiment of the present invention. FIG. 3 is an enlarged photograph of an assembly of helical structures according to one embodiment of the present invention. FIG. 4 is a further enlarged photograph of a single helical structure according to one embodiment of the present invention. FIG. 5 is an enlarged photograph showing the plated portion of a helical structure according to one embodiment of the present invention. FIG. 6 is a graph showing the transmittance of Examples 1-2 of the present invention. FIG. 7 is a graph showing the transmittance of Examples 3-4 of the present invention. FIG. 8 is a graph showing the transmittance of Comparative Examples 1-2 of the present invention. FIG. 9 is a graph showing the reflectance of Examples 1-2 of the present invention. FIG. 10 is a graph showing the reflectance of Examples 3-4 of the present invention. FIG. 11 is a graph showing the reflectance of Comparative Examples 1-2 of the present invention. FIG. 12 is a graph showing the transmittance of Examples 5-6 of the present invention. FIG. 13 is a graph showing the reflectance of Examples 5-6 of the present invention.

[0011] The present invention relates to a radio wave absorbing, thermally conductive composition comprising a silicone resin (A), a radio wave absorbing material (B), and a thermally conductive substance (C). The silicone resin (A) is also called a silicone polymer, and includes properties such as rubber, gel, grease, putty, and liquid. Silicone polymers have high heat resistance and are suitable as a matrix material for thermally conductive materials: TIMs (Thermal Interface Materials). Examples of preferred silicone polymers include addition-cured silicone polymers, peroxide-cured silicone polymers, and condensation-cured silicone polymers. These may be used alone or in combination. Commercially available silicone polymers can be used.

[0012] The radio wave absorber (B) has a helical structure having a metal plating layer. The helical structure is obtained by forming a metal plating layer on phytoplankton of cyanobacteria called spirulina. The cyanobacteria called spirulina is a group of helical-shaped cyanobacteria phytoplankton belonging to the genus Arthrospira, including Arthrospira platensis, Arthrospira maxima, and Arthrospira subsalsa.

[0013] The metal plating layer is preferably made of a metal with good conductivity, such as nickel, gold, copper, or silver. The thickness of the metal plating layer is preferably 0.1 to 5 μm. The wire diameter of the helical structure is preferably 1 to 10 μm, the helix diameter is preferably 10 to 50 μm, and the length of the helix major axis is preferably 30 to 300 μm. Examples of such configurations are shown in Figures 3-5. Figure 3 is an enlarged photograph of an assembly of helical structures according to one embodiment of the present invention. Figure 4 is a further enlarged photograph of a single helical structure according to one embodiment of the present invention. Figure 5 is an enlarged photograph showing the plated portion of a helical structure according to one embodiment of the present invention. A method for manufacturing a helical structure is described in Patent Document 5.

[0014] The amount of the helical structure added is preferably 0.1 to 50 parts by mass, more preferably 0.5 to 40 parts by mass, and even more preferably 0.8 to 30 parts by mass per 100 parts by mass of the silicone resin (A). Within this range, the radio wave absorption for terahertz waves can be efficiently improved. Specifically, the radio wave absorption for terahertz waves of 0.1 THz to 2.4 THz is achieved.

[0015] The thermally conductive material (C) is preferably at least one inorganic particle selected from the group consisting of metal oxides, metal nitrides, metal carbides, metal borides, elemental metals, and carbon materials. Examples include aluminum oxide (alumina), aluminum hydroxide, magnesium oxide, magnesium hydroxide, zinc oxide, aluminum nitride, boron nitride, silicon nitride, silicon carbide, graphite, graphene, and carbon black. These particles may be used alone or in combination of two or more. The average particle size of the thermally conductive particles is preferably in the range of 0.01 to 100 μm. The particle size is measured by a laser diffraction / light scattering method, measuring the D50 (median diameter) of the cumulative particle size distribution based on volume. An example of such a measuring device is the LA-950S2 laser diffraction / scattering particle distribution analyzer manufactured by Horiba, Ltd.

[0016] The thermally conductive substance (C) is preferably contained in an amount of 50 to 3,000 parts by mass, more preferably 100 to 2,000 parts by mass, and even more preferably 200 to 1,800 parts by mass per 100 parts by mass of the silicone resin (A). This amount increases the thermal conductivity of the composition, making it suitable for use as a thermal interface material (TIM).

[0017] The thermal conductivity of the radio wave absorbing thermally conductive composition is preferably 0.8 W / m K or more, more preferably 1 to 20 W / m K, and even more preferably 2 to 20 W / m K. This provides high thermal conductivity and makes the composition suitable as a heat dissipation sheet: TIM (Thermal Interface Material). Furthermore, the radio wave absorption in the terahertz wave region is preferably a maximum transmittance of -15 dB or less. This makes it possible to provide a radio wave absorbing thermally conductive composition and a sheet thereof that combine radio wave absorption and thermal conductivity in the terahertz wave region.

[0018] The radio wave absorbing thermally conductive composition may further contain soft magnetic metal particles. An example of the soft magnetic metal particles is iron particles such as carbonyl iron particles. The carbonyl iron particles preferably have an average particle size of 0.1 μm or more and 100 μm or less, more preferably 1 μm or more and 20 μm or less. The amount of the carbonyl iron particles added is preferably 1 to 50 parts by mass per 100 parts by mass of the radio wave absorbing thermally conductive composition. The inclusion of soft magnetic metal particles can absorb electromagnetic waves of less than 100 GHz and prevent the adverse effects of radio wave noise.

[0019] At least one substance selected from the group consisting of the radio wave absorber (B) and the thermally conductive substance (C) is preferably surface-treated with a silane compound, a titanate compound, an aluminate compound, or a partial hydrolyzate thereof. This can prevent the deactivation of the curing catalyst or the crosslinking agent, and improve storage stability. Examples of the silane compound include R ａ Si(OR') ４－ａ (R is an unsubstituted or substituted alkyl group having 1 to 20 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is 0 to 3), or a partial hydrolyzate thereof. ａ Si(OR') ４－ａ Examples of alkoxysilane compounds (hereinafter simply referred to as "silanes") represented by the formula (where R is an unsubstituted or substituted alkyl group having 1 to 20 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is an integer from 0 to 3) include methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, pentyltrimethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, and octadecyltriethoxysilane. These silane compounds can be used alone or in combination. Alkoxysilanes and single-terminated silanol siloxanes can also be used as surface treatment agents. The surface treatment here includes not only covalent bonding but also adsorption.

[0020] The thermally conductive material (C) contains two or more types of inorganic particles with an average particle diameter D50 (median diameter) of 2 μm or more and less than 2 μm, and the inorganic particles with an average particle diameter D50 (median diameter) of less than 2 μm are preferably surface-treated with a silane compound, a titanate compound, an aluminate compound, or a partial hydrolyzate thereof. The combined use of two or more types of inorganic particles with an average particle diameter D50 (median diameter) of 2 μm or more and less than 2 μm allows small particles to be packed between large particles, resulting in close packing and high thermal conductivity. Furthermore, inorganic particles with an average particle diameter D50 (median diameter) of less than 2 μm have a high specific surface area, which can adsorb and deactivate curing catalysts, crosslinking agents, etc., preventing this.

[0021] The radio wave absorbing thermally conductive composition of the present invention is formed into a sheet and cured. The sheet is highly versatile and suitable as a TIM. The thickness of the sheet is preferably in the range of 0.2 to 10 mm.

[0022] The sheet manufacturing method of the present invention involves vacuum degassing the composition, rolling it, and forming it into a sheet. Vacuum degassing involves reducing the pressure of the composition (compound) to -0.08 to -0.1 Pa and leaving it for approximately 5 to 10 minutes to degas it. Rolling can be done by roll rolling or press working, but roll rolling is preferred because it allows for continuous production. The resulting sheet has a substantially uniform composition from the inside to the outside. A sheet with a uniform composition will exhibit uniform physical properties even after being mounted on an electrical or electronic component as a TIM. In roll rolling, for example, the compound is sandwiched between two synthetic resin films and then rolled with a roll. The heat curing conditions for the molded sheet are preferably a temperature of 90 to 120°C and a time of 5 to 180 minutes. In this specification, curing and crosslinking are synonymous. The radio wave absorbing thermally conductive composition of the present invention is molded into a desired shape by a method such as press molding, vacuum press molding, injection molding, extrusion molding, calendar molding, or roll molding.

[0023] The following description will be made with reference to the drawings. In the following drawings, the same reference numerals indicate the same components. FIG. 1 is a schematic cross-sectional view of a heat dissipation structure 10 incorporating a radio wave absorbing thermally conductive sheet according to one embodiment of the present invention. The radio wave absorbing thermally conductive sheet 11b dissipates heat generated by an electronic component 13, such as a semiconductor device. The radio wave absorbing thermally conductive sheet 11b is fixed to a main surface 12a of the heat spreader 12 facing the electronic component 13, and is sandwiched between the electronic component 13 and the heat spreader 12. The radio wave absorbing thermally conductive sheet 11a is sandwiched between the heat spreader 12 and a heat sink 15. The radio wave absorbing thermally conductive sheets 11a and 11b, together with the heat spreader 12, constitute a heat dissipation member that dissipates heat from the electronic component 13. The heat spreader 12 is formed, for example, in the shape of a rectangular plate and has a main surface 12a facing the electronic component 13 and a side wall 12b extending along the outer periphery of the main surface 12a. The heat spreader 12 has a main surface 12a surrounded by side walls 12b, on which a radio wave absorbing thermally conductive sheet 11b is provided, and a heat sink 15 is provided on the other surface 12c opposite to the main surface 12a, via the radio wave absorbing thermally conductive sheet 11a. The electronic component 13 is, for example, a semiconductor element such as a BGA, and is mounted on a wiring board 14.

[0024] The following examples are provided for illustrative purposes only. The present invention is not limited to these examples. Various parameters were measured using the methods described below. <Thermal Conductivity> The thermal conductivity of the radio wave absorbing thermally conductive sheet was measured using a hot disk (in accordance with ISO 22007-2:2008). As shown in FIG. 2A, this thermal conductivity measuring device 1 sandwiches a polyimide film sensor 2 between two samples 3a and 3b. A constant power is applied to the sensor 2 to generate a constant amount of heat, and the thermal characteristics are analyzed based on the temperature rise of the sensor 2. The sensor 2 has a 7 mm diameter tip 4 and, as shown in FIG. 2B, has a double spiral electrode structure with an applied current electrode 5 and a resistance electrode (temperature measurement electrode) 6 located at the bottom. The thermal conductivity is calculated using the following formula (Equation 1): <Radio Wave Absorption Properties> The radio wave absorption properties of the radio wave absorbing thermally conductive sheet can be measured by a technique called terahertz time-domain spectroscopy. Terahertz time-domain spectroscopy involves irradiating a test object with a terahertz pulse wave, measuring the waveform of the terahertz pulse wave after it has passed through or been reflected from the sample, and then performing a Fourier transform on the waveform to obtain the amplitude and phase for each frequency. In this example, measurements were performed using a terahertz spectroscopy and imaging system "TAS7500TS" manufactured by ADVANTEST. The radio wave absorption properties were evaluated as follows: in the range of 0.1 THz to 2.4 THz, a maximum transmittance of less than -15 dB was evaluated as A, and a maximum transmittance of -15 dB or greater was evaluated as B.

[0025] (Examples 1-6, Comparative Examples 1-2) <Matrix Resin> 10.4 g of commercially available addition-curing liquid silicone resin A liquid (containing a platinum-based catalyst) and 10.4 g of liquid silicone resin B liquid (containing a crosslinking agent) were mixed and degassed using a planetary centrifugal mixer (Mazerustar KK-400W, manufactured by Kurabo Industries, Ltd.), and then sandwiched between polyester (PET) films and press-rolled to a thickness of 2.0 mm at 100°C for 10 minutes for heat curing. The thermal conductivity and radio wave absorption characteristics of the resulting sheet were measured. The silicone polymer (matrix resin) used in each example and comparative example was CY52-276A / B, a two-component addition-curing dimethylpolysiloxane resin manufactured by Dow-Toray Industries, Inc. <Thermally Conductive Inorganic Particles> The thermally conductive inorganic particles were as follows.・Boron nitride: HSL (manufactured by DCEI, plate-like, D50 = 30 μm) ・Alumina A: AKP30 (manufactured by Sumitomo Chemical Co., Ltd., amorphous, D50 = 0.3 μm) dry-treated with octyltriethoxysilane ・Alumina B: AZ2L-75 (manufactured by Nippon Steel Chemical & Material Co., Ltd., spherical, D50 = 2 μm) ・Aluminum nitride: TFZ-S20P (manufactured by Toyo Aluminum K.K., amorphous, D50 = 20 μm) <Radio wave absorber> The helical structure shown in Figure 3-5 was used for the radio wave absorber. The metal plating layer was a copper plating layer with an average film thickness of 0.3 to 0.4 μm, the microcoil wire diameter was 5 to 8 μm, the helix diameter was 20 to 40 μm, and the length of the helix major axis was 50 to 200 μm.

[0026] The physical properties of the obtained sheet are as shown in Table 1-2. Figure 6 is a graph showing the transmittance of Examples 1-2 of the present invention, Figure 7 is a graph showing the transmittance of Examples 3-4 of the present invention, Figure 8 is a graph showing the transmittance of Comparative Example 1-2, Figure 9 is a graph showing the reflectance of Examples 1-2 of the present invention, Figure 10 is a graph showing the reflectance of Examples 3-4 of the present invention, Figure 11 is a graph showing the reflectance of Comparative Example 1-2, Figure 12 is a graph showing the transmittance of Examples 5-6 of the present invention, and Figure 13 is a graph showing the reflectance of Examples 5-6 of the present invention. The maximum transmittance and the frequency at that time, and the maximum reflectance and the frequency at that time, read from the range of 0.1 THz to 2.4 THz in the graphs of Figures 6 to 12, are respectively listed in Table 1-2.

[0027]

[0028] As is clear from Table 1, it was confirmed that Examples 1 to 4 had high terahertz wave absorption and thermal conductivity. In contrast, Comparative Example 1 had good wave absorption properties, but was undesirably low in thermal conductivity because no thermally conductive particles were added. Comparative Example 2 had high thermal conductivity, but was undesirably low in terahertz wave absorption because no helical structure was added.

[0029]

[0030] Example 5 in Table 2 is the same as Example 1 except that the thermally conductive inorganic particles were changed to alumina, and Example 6 is the same as Example 1 except that the thermally conductive inorganic particles were changed to alumina and aluminum nitride, and it was confirmed that they had high radio wave absorption and thermal conductivity for terahertz waves.

[0031] The radio wave absorbing thermally conductive composition and sheet thereof of the present invention are highly useful because they can simultaneously address the two problems of heat dissipation and radio wave noise in applications such as LEDs, electronic components for home appliances, information and communication modules including optical communication devices, and in-vehicle components.

[0032] REFERENCE SIGNS LIST 1 Thermal conductivity measuring device 2 Sensor 3a, 3b Sample 4 Sensor tip 5 Electrode for applied current 6 Electrode for resistance value (electrode for temperature measurement) 10 Heat dissipation structure 11a, 11b Radio wave absorbing thermally conductive sheet 12 Heat spreader 13 Electronic component 14 Wiring board 15 Heat sink

Claims

1. A radio wave absorbing, thermally conductive composition comprising a silicone resin (A), a radio wave absorbing material (B), and a thermally conductive substance (C), wherein the radio wave absorbing material (B) has a helical structure having a metal plating layer, and is contained in an amount of 0.1 to 50 parts by mass per 100 parts by mass of the silicone resin (A).

2. The radio wave absorbing thermally conductive composition according to claim 1, wherein the radio wave absorbing properties of the radio wave absorbing thermally conductive composition are such that the maximum transmittance for terahertz waves in the range of 0.1 THz to 2.4 THz is -15 dB or less.

3. The radio wave absorbing and thermally conductive composition according to claim 1 or 2, wherein the metal plating layer of the spiral structure is at least one metal selected from the group consisting of nickel, gold, copper, silver and alloys thereof.

4. The radio wave absorbing and thermally conductive composition according to any one of claims 1 to 3, wherein the metal plating layer of the helical structure has a thickness of 0.1 to 5 μm.

5. The radio wave absorbing thermally conductive composition according to any one of claims 1 to 4, wherein the thermally conductive substance (C) is at least one inorganic particle selected from the group consisting of metal oxides, metal nitrides, metal carbides, metal borides, elemental metals, and carbon materials.

6. The radio wave absorbing thermally conductive composition according to any one of claims 1 to 5, wherein the thermally conductive substance (C) is contained in an amount of 50 to 3,000 parts by mass per 100 parts by mass of the silicone resin (A).

7. The radio wave absorbing thermally conductive composition according to any one of claims 1 to 6, which has a thermal conductivity of 0.8 W / mK or more.

8. The radio wave absorbing thermally conductive composition according to any one of claims 1 to 7, wherein the helical structure has a wire diameter of 1 to 10 μm, a helix diameter of 10 to 50 μm, and a length of the helix major axis of 30 to 300 μm.

9. The radio wave absorbing and thermally conductive composition according to any one of claims 1 to 8, which further contains soft magnetic metal particles.

10. The radio wave absorbing thermally conductive composition according to any one of claims 1 to 9, wherein at least one substance selected from the group consisting of the radio wave absorbing material (B) and the thermally conductive substance (C) is surface-treated with a silane compound, a titanate compound, an aluminate compound, or a partial hydrolyzate thereof.

11. A radio wave absorbing thermally conductive composition according to any one of claims 1 to 10, wherein the thermally conductive substance (C) contains two or more types of inorganic particles, one having an average particle size D50 (median size) of 2 μm or more and the other having an average particle size D50 (median size) of less than 2 μm, and the inorganic particles having an average particle size D50 (median size) of less than 2 μm have been surface treated with a silane compound, a titanate compound, an aluminate compound, or a partial hydrolyzate thereof.

12. At least one substance selected from the group consisting of the radio wave absorbing material (B) and the thermally conductive material (C) is R ａ Si(OR') ４－ａ 12. The radio wave absorbing thermally conductive composition according to claim 1, which has been surface-treated with a silane compound represented by the following formula: (R is an unsubstituted or substituted alkyl group having 1 to 20 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is an integer of 0 to 3), or a partial hydrolyzate thereof.

13. A radio wave absorbing, thermally conductive sheet in which the radio wave absorbing, thermally conductive composition according to any one of claims 1 to 12 is formed into a sheet and cured.

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