Thermally conductive composition having electromagnetic interference suppression capability

Abstract

Provided is a thermally conductive composition which exhibits effective electromagnetic interference suppression capability even in a higher frequency band, and has high thermal conductivity, thereby enabling the stable industrial manufacture of members capable of solving both electromagnetic interference and heat dissipation in recent electronic devices which are highly advanced. A thermally conductive composition according to the present invention has an electromagnetic interference suppression capability and contains one or more types of powder, the thermally conductive composition being characterized in that: one of the powders is α-type silicon carbide powder; and in powder X-ray diffraction of the thermally conductive composition using Cu-Kα as a radiation source, a value I4H / I6H, obtained by dividing a peak intensity I4H derived from 4H-SiC appearing at 2θ=34.4-35° by a peak intensity I6H derived from 6H-SiC appearing at 2θ=35-36°, is 0.01 or more.

Description

Thermally conductive composition with electromagnetic interference suppression capability

[0001] The present invention relates to a thermally conductive composition having electromagnetic interference suppression capabilities.

[0002] As communications become more advanced, electronic device circuits are becoming increasingly highly integrated and dense. As a result, the amount of heat generated by devices on the circuit increases, making heat dissipation measures important. Thermally conductive materials can solve this problem. Thermally conductive materials are made of soft resins containing highly thermally conductive fillers, and come in grease, putty, and sheet forms depending on the application. Thermally conductive materials fill the spatial gap between devices on the circuit and the heat sink, transferring heat from the device to the heat sink. For this reason, the development of thermally conductive materials is becoming increasingly important as a heat dissipation measure for electronic devices. Because thermally conductive materials come into direct contact with devices on the circuit, materials with high electrical resistance are preferred.

[0003] As electronic device circuits become more highly integrated and denser, electromagnetic interference (EMI) issues are becoming more serious, in addition to heat dissipation issues. For example, while mobile communications have traditionally used frequency bands ranging from several hundred MHz to 3 GHz, fifth-generation mobile systems (5G) are expected to use frequencies up to 60 GHz, which are higher than these. Furthermore, as electronic devices become lighter, thinner, and smaller, the space available within their internal structures is becoming increasingly limited, making EMI problems in electrical and electronic circuits even more serious. Noise suppression sheets offer a solution to this EMI problem. Noise suppression sheets are made of resin containing fillers such as soft magnetic powder, which convert noise into heat through electromagnetic loss.

[0004] The noise suppression performance of a noise suppression sheet depends on the magnetic permeability of the soft magnetic powder contained in it. Generally, magnetic permeability is expressed as complex permeability μ = μ' - jμ", where μ' is a measure of noise absorption and μ" is a measure of noise conversion to heat. When utilizing magnetic loss, such as in noise suppression sheets, μ" is important. That is, it is important that μ" is distributed across the frequency range of the radio noise to be suppressed. Meanwhile, when considering an electromagnetic interference suppression sheet for devices that utilize millimeter-wave radio waves, it may be possible to achieve greater design freedom by incorporating a nonmagnetic conductive material into a resin substrate to introduce electrical loss, rather than using a magnetic filler as a loss material, which does not offer high magnetic permeability in the millimeter-wave band.

[0005] To solve the two problems of heat and electromagnetic interference in electronic devices, thermally conductive materials and noise suppression sheets are often used in close proximity within electronic devices. Recently, due to the aforementioned shrinking space within electrical devices and the need for functional integration of components from a cost perspective, there has been a growing need for hybrid materials that combine thermally conductive materials and noise suppression sheets, and thermally conductive materials with electromagnetic interference suppression capabilities exist. Among these, as mentioned above, with the increasing use of higher frequencies in electronic devices, there is a growing need for thermally conductive sheets with electromagnetic interference suppression capabilities in the millimeter wave band. For example, Patent Document 1 (Japanese Patent No. 6737979) discloses a thermally conductive composition and sheet thereof with electromagnetic interference suppression capabilities compatible with frequencies from 18 to 26.5 GHz. Patent Document 1 claims that by incorporating a predetermined amount of carbonyl iron powder and thermally conductive powder in a resin matrix, the imaginary part of the magnetic permeability can be made 0.9 or greater in at least a portion of the 18 to 26.5 GHz band.

[0006] Patent Document 2 (JP 2022-052761 A) discloses a thermally conductive electromagnetic interference (EMI) absorber that has high thermal conductivity and efficiently absorbs microwaves. The thermally conductive electromagnetic interference (EMI) absorber is said to have a thermal conductivity of at least 6 watts per meter per Kelvin (W / mK) and an attenuation of more than 15 decibels per centimeter (dB / cm) at frequencies of 10 gigahertz (GHz) or higher.

[0007] However, Patent Document 1 does not mention the effectiveness of electromagnetic interference suppression in high-frequency bands such as frequencies above 26.5 GHz, nor does it describe specific solutions, so it cannot be expected to be effective in suppressing noise in electronic devices that use up to the millimeter wave band. Regarding thermal conductivity, while it claims that a thermal conductivity of 2 W / mK or more can be achieved in sheet form, the examples only disclose thermal conductivities of less than 3 W / mK. Today's electronic devices, which generate increasing amounts of heat, sometimes require a thermal conductivity of 3 W / mK or more, but Patent Document 1 does not provide a structure that can meet this requirement. Patent Document 2 adds more than 80% by volume of filler, which reduces flexibility and may make it impractical for use as a sheet or grease.

[0008] Patent No. 6737979 Publication Special Publication No. 2022-052761

[0009] In view of the above problems, the present invention aims to provide a thermally conductive composition having electromagnetic interference suppression properties that exhibits effective electromagnetic interference suppression even in higher frequency bands, while at the same time having high thermal conductivity, thereby enabling the industrially stable production of components that can simultaneously solve the electromagnetic interference and heat dissipation problems of today's increasingly sophisticated electronic devices.

[0010] The present inventors have conducted extensive research to solve the above problems and have discovered the following: By using a powder mainly composed of α-type silicon carbide (SiC), which provides light weight and high insulation, as the dielectric loss material to be supported on a substrate, and by using α-type silicon carbide (SiC) whose X-ray diffraction data falls within predetermined conditions, it is possible to provide a thermally conductive composition that exhibits effective electromagnetic interference suppression even in higher frequency bands and has high thermal conductivity.

[0011] The present invention, which was completed based on the above findings, has the following key features: [1] A thermally conductive composition having electromagnetic interference suppression capability, which contains one or more types of powder, one of which is an α-type silicon carbide powder, and in powder X-ray diffraction of the thermally conductive composition using Cu-Kα as a radiation source, a peak intensity I attributable to 4H-SiC, which appears at 2θ=34.4 to 35°, is ４Ｈ is the peak intensity I due to 6H—SiC appearing at 2θ=35 to 36°. ６Ｈ The value I divided by ４Ｈ / I ６Ｈ A thermally conductive composition having electromagnetic interference suppression capability, wherein the ratio of the thermal conductivity of the thermal conductive composition to the total thermal conductivity of the thermal conductive composition is 0.01 or more.

[0012] [2] The thermal conductive composition having electromagnetic interference suppression ability according to [1] above, characterized in that the average particle size of the α-type silicon carbide powder is 1 μm or more and 180 μm or less, and the volume ratio of the entire powder to the entire thermal conductive composition is 45% or more and 80% or less.

[0013] [3] The thermal conductive composition having electromagnetic interference suppression ability according to [1] above, characterized in that the powder further contains one or more powders of either a metal magnetic powder or a thermally conductive powder, the average particle size of the α-type silicon carbide powder is 30 μm or more and 180 μm or less, and the volume ratio of the α-type silicon carbide powder to the entire thermal conductive composition is 10% or more and 75% or less.

[0014] [4] The thermal conductive composition having electromagnetic interference suppression ability according to [3] above, characterized in that the powder contains the metal magnetic powder, the particle size of the metal magnetic powder is 1 μm or more and 7 μm or less, the volume ratio of the metal magnetic powder to the entire thermal conductive composition is 5% or more and 65% or less, and the ratio of the average particle size of the α-type silicon carbide powder to the average particle size of the metal magnetic powder is 4 or more.

[0015] [5] The thermal conductive composition having electromagnetic interference suppression ability according to [3] or [4] above, characterized in that the powder contains the thermal conductive powder, the average particle size of the thermal conductive powder is 0.1 μm or more and 1 μm or less, and the volume ratio of the thermal conductive powder to the entire thermal conductive composition is 1% or more and 15% or less.

[0016] [6] A thermal conductive composition having electromagnetic interference suppression ability according to any one of [1] to [5] above, characterized in that the thermal conductivity of the thermal conductive composition measured by a hot disc method is 1 W / mK or more.

[0017] [7] I ４Ｈ / I ６Ｈ The thermally conductive composition having electromagnetic interference suppression capability according to any one of [1] to [6] above, wherein is 0.1 or more.

[0018] [8] The thermal conductive composition having electromagnetic interference suppression capability according to any one of [1] to [7] above, characterized in that the thermal conductive composition is in the form of a sheet, putty, or grease.

[0019] [9] A thermally conductive composition having electromagnetic interference suppression capability according to any one of [1] to [8] above, which is used for near-field noise suppression.

[0020]

[10] A thermally conductive composition having electromagnetic interference suppression capability, comprising one or more types of powder, the thermally conductive composition being used for near-field noise suppression, characterized in that the thermally conductive composition has a radio wave attenuation of more than 1 dB / cm at 40 GHz, and a thermal conductivity of 3 W / mK or more as measured by a hot disk method.

[0021] The thermally conductive composition of the present invention exhibits effective electromagnetic interference suppression even in higher frequency bands, and at the same time has high thermal conductivity, making it possible to industrially and stably produce components that can simultaneously solve the electromagnetic interference and heat dissipation issues of today's increasingly sophisticated electronic devices.

[0022] 1 shows an example of a scanning electron microscope image of a sheet made using the thermally conductive composition of the present invention.

[0023] Hereinafter, an embodiment of the present invention will be described.

[0024] (Thermal Conductive Composition) The thermal conductive composition of the present invention is a thermal conductive composition having electromagnetic interference suppression capability, which contains one or more types of powder, one of which is an α-type silicon carbide powder, and in powder X-ray diffraction of the thermal conductive composition using Cu-Kα as a radiation source, a peak intensity I 2 originating from 4H—SiC, which appears at 2θ=34.4 to 35°, is ４Ｈ is the peak intensity I due to 6H—SiC appearing at 2θ=35 to 36°. ６Ｈ The value I divided by ４Ｈ / I ６Ｈ The thermal conductive composition may be characterized in that the ratio of the thermal conductivity of the thermal conductive material to the thermal conductive material is 0.01 or more.

[0025] Furthermore, the thermal conductive composition of the present invention preferably has electromagnetic interference suppression capability at 40 GHz, and has a radio wave attenuation at 40 GHz of more than 1 dB / cm. The thermal conductive composition of the present invention may also be a thermal conductive composition with electromagnetic interference suppression capability that contains one or more types of powder, characterized in that the radio wave attenuation at 40 GHz exceeds 1 dB / cm and the thermal conductivity of the thermal conductive composition measured by the hot disk method is 3 W / mK or more. In this case, the thermal conductive composition of the present invention can be suitably used for suppressing near-field noise.

[0026] The thermally conductive composition of the present invention generally comprises one or more types of powders as described above and a base resin, with the powders being supported in the base resin.

[0027] [Base Resin] The base resin used in the present invention is preferably a thermosetting resin, and examples thereof include silicone resin, acrylic resin, epoxy resin, and urethane resin. Among these, silicone resin or acrylic resin, which have excellent heat resistance, are particularly preferred as the base resin used, as the heat resistance temperature inside electronic devices is now often over 100°C. There are no particular limitations on the form of the resin raw material, and either millable or liquid forms can be used. However, the form can be selected according to the form of the final thermal conductive composition. For example, if a grease-like thermal conductive composition is to be obtained, a liquid form should be used. Here, as a representative example, an embodiment using a liquid silicone resin as the resin base raw material will be described.

[0028] Commercially available liquid silicones for general industrial use can be used. Silicones are available in one-component and two-component types (main component and curing agent), and curing types include condensation reaction and addition reaction types. Either type can be used in the present invention. While condensation reaction types require time to cure, addition reaction types can be expected to cure in a relatively short time by adding a heating step. Therefore, when obtaining a sheet- or putty-like thermal conductive composition, the addition reaction type is preferable from a productivity perspective. On the other hand, when obtaining a grease-like thermal conductive composition, if an addition reaction type is used, the heating step is not performed, and the mixture with powder filler is filled into a dispenser tube to form the final product. Liquid silicones with a viscosity of 1 to 10 Pa·s are preferred because a liquid silicone with a viscosity that is too low will have poor shape retention during sheet molding, while a liquid silicone with a viscosity that is too high will make it difficult to uniformly disperse the powder filler.

[0029] [Powder] The powder is usually supported in a base resin. The powder may contain α-type silicon carbide powder as described below. When the powder contains α-type silicon carbide powder, it may further contain other types of powder, such as a metal magnetic powder, a thermally conductive powder, a flame retardant, etc.

[0030] [Silicon carbide powder] When the thermal conductive composition of the present invention contains silicon carbide powder, the silicon carbide powder plays a role in controlling the thermal conductivity and electromagnetic interference suppression ability of the thermal conductive composition. Therefore, the present invention can be achieved by simply supporting a predetermined silicon carbide powder as the powder.

[0031] The average particle size of the silicon carbide powder is preferably 1 μm or more, more preferably 30 μm or more, and may be 65 μm or more, 90 μm or more, or 105 μm or more. The average particle size of the silicon carbide powder is preferably 180 μm or less, more preferably 120 μm or less. When only silicon carbide powder is used as the powder, it is preferable to use multiple types of silicon carbide powder with different particle sizes so that the powder approaches a close-packed structure. In addition, to obtain a thermally conductive composition with high thermal conductivity, it is necessary to use a predetermined amount of filler with high thermal conductivity and large particle size. In the present invention, silicon carbide powder is used whose average particle size is preferably 1 μm or more, more preferably 30 μm or more, and preferably 180 μm or less. If the average particle size is less than 1 μm or less than 30 μm, the desired thermal conductivity cannot be obtained. Furthermore, because silicon carbide is a material with extremely high hardness, if the average particle size exceeds 180 μm, there is a risk of damage to the surface of the device with which the thermal conductive composition comes into contact, and if the thermal conductive composition is in putty or sheet form, the substrate is likely to tear when bent. Furthermore, silicon carbide powders with large particle sizes such as those used in the present invention are generally specified by particle size rather than average particle size, and the particle size of the silicon carbide powder used in the present invention is preferably #320 to #80.

[0032] In this specification, the "average particle size" of various powders (e.g., silicon carbide powder, metal magnetic powder, and thermally conductive powder) is determined by the following procedure. First, a backscattered electron image of the thermal conductive composition is captured using a scanning electron microscope. When the thermal conductive composition is in sheet or putty form, a cross section of the thermal conductive composition is ion-milled and then photographed. To improve measurement accuracy, the magnification is set to 150 to 10,000 times according to the powder particle size. 10,000 times is preferable when the powder particle size is mainly small, such as 1 μm, and 150 times is preferable when the powder particle size is mainly large, such as 180 μm. Next, the maximum diameter of each powder in the captured image is defined as the particle size of that powder, and the average value of the particle sizes of all the various powders in the field of view is defined as the "average particle size" of the various powders contained in the thermal conductive composition. Note that powders approaching the edge of the captured image and powders with a particle size (maximum diameter) of less than 0.1 μm in the captured image are excluded from the measurement. Furthermore, when there are multiple types of powder, the types of powder are identified to distinguish them.

[0033] Industrially usable silicon carbide powders include those with an α-type structure for grinding and polishing applications and those with a β-type structure for sintering applications. The present invention uses α-type silicon carbide powder. Alpha-type silicon carbide powders are available in high-purity green and lower-purity black varieties. The present invention can use either green or black silicon carbide powders, which are characterized by their crystalline structure. Pure silicon carbide is an insulator, but the inclusion of impurities can cause it to exhibit semiconducting properties. Semiconducting silicon carbide exhibits relatively large dielectric loss in the millimeter-wave band, making it suitable for use in electromagnetic interference suppressors used in the millimeter-wave band. Therefore, the desired thermal conductive composition can be obtained by controlling the crystalline structure, particle size, and additive amount of the silicon carbide powder. The black type is characterized by a higher content of the impurity elements Al and Fe compared to the green type. Generally, the black type contains 0.1 to 0.2 mass% Al and 0.1 to 0.3 mass% Fe, while the green type contains 0.01 to 0.1 mass% Al and 0.02 to 0.03 mass% Fe. In the present invention, it is preferable to use a low-purity black silicon carbide powder as the filler. It is also possible to identify the content of Al and Fe, which are impurity elements in silicon carbide. In this case, for example, the Al and Fe contents can be detected by surface analysis of the silicon carbide powder using EPMA (WDS: wavelength dispersive X-ray spectroscopy) on the polished surface (e.g., ion-milled surface) of the thermal conductive composition.

[0034] In the present invention, silicon carbide powder having an α-type crystal structure may be used, and in powder X-ray diffraction of the thermal conductive composition using Cu-Kα as a radiation source, the peak intensity I due to 4H—SiC appears at 2θ=34.4 to 35°. ４Ｈ is the peak intensity I due to 6H—SiC appearing at 2θ=35 to 36°. ６Ｈ The value I divided by ４Ｈ / I ６Ｈis preferably 0.01 or more, more preferably 0.1 or more, even more preferably 0.2 or more, and even more preferably 0.3 or more. Furthermore, the upper limit is not particularly limited, but is preferably 0.5 or less. The crystal structure of silicon carbide is mainly a regular tetrahedron with a minimum structure, and 4H type (4H-SiC) and 6H type (6H-SiC) are mainly present due to the stacking structure of the regular tetrahedron. High-purity green-type silicon carbide is dominated by the 6H structure, with a small proportion of 4H type. On the other hand, low-purity black-type silicon carbide is a mixture of 4H type and 6H type, with a high proportion of 4H type. I ４Ｈ / I ６Ｈ The larger the value of , the greater the dielectric loss, and the more excellent the electromagnetic interference suppression effect can be expected. The α-type silicon carbide powder contained in the thermal conductive composition of the present invention can be identified by X-ray diffraction on the surface of the thermal conductive composition using Cu-Kα as a radiation source. The X-ray diffraction measurement conditions in the present invention are as follows:

[0035] <Apparatus> Manufacturer: Rigaku Instrument name: Fully automated horizontal multipurpose high-power X-ray diffraction instrument SmartLab (9 kW) Tube: Cu <Optical system conditions> CBO selection slit: BB Incident parallel slit (Soller / PSC): 5.0 deg Length limiting slit (IS length): 10.0 mm Receiving optical element (PSA): None Receiving parallel slit (Soller): 5.0 deg <Measurement conditions> Scan axis: 2θ / θ, Mode: Continuous, Range specification: Absolute Speed ​​counting time: 3.0 deg / min Scan: 20 deg to 80 deg Data collection interval: 0.01 deg IS: 1 / 2 deg, Receiving slit RS1: 8.0 mm Receiving slit RS2: 13.0 mm Attenuator: Open

[0036] The procedure for analyzing the measurement data is as follows. Using the integrated powder X-ray analysis software PDXL manufactured by Rigaku, the diffraction intensity data yobs minus bkg was used to eliminate the background effect of the obtained data. The peak intensity I derived from 4H—SiC was calculated by subtracting the minimum value of yobs−bkg from the maximum value in the range of 2θ = 34.4 to 35°.４Ｈ Similarly, in the range of 2θ=35 to 36°, the peak intensity I derived from 6H—SiC is calculated by subtracting the minimum value from the maximum value of yobs−bkg. ６Ｈ Let's say.

[0037] When the thermal conductive composition contains only α-type silicon carbide powder as the powder (filler), the volume ratio of the silicon carbide powder to the entire thermal conductive composition is preferably 45% or more, more preferably 50% or more, and preferably 80% or less, more preferably 75% or less. When the thermal conductive composition containing only α-type silicon carbide powder as the powder (filler) is used as a grease, the volume ratio of the silicon carbide powder to the entire thermal conductive composition can be 45% or more. When the thermal conductive composition containing only α-type silicon carbide powder as the powder (filler) is used as a sheet, the volume ratio of the silicon carbide powder to the entire thermal conductive composition can be 64% or more, preferably 70% or more. On the other hand, when the thermal conductive composition contains other powders (e.g., metal magnetic powder, thermally conductive powder, etc.) in addition to the α-type silicon carbide powder as powders (fillers), the volume ratio of the silicon carbide powder to the entire thermal conductive composition may be preferably 10% or more, more preferably 30% or more, and preferably 75% or less, more preferably 40% or less.

[0038] In this specification, the "volume ratio" of various powders (e.g., silicon carbide powder, metal magnetic powder described below, thermally conductive powder) is determined by the following procedure. Using the backscattered electron image used to determine the "average particle size" of the various powders described above, the colors of the images of the various powders and the substrate are binarized to separate the various powders from the substrate. After separation is complete, the types of the various powders are identified, and the area ratios of the various powders are determined according to the type of powder, which is defined as the "volume ratio (volume ratio to the entire thermal conductive composition)" of the various powders. Note that when performing binarization, appropriate settings can be made so that the boundaries between the various powders and the substrate are clear. Furthermore, when there are multiple types of powder, the types of the various powders are separated by performing multi-value processing to identify them, and the "volume ratio" of each can be determined by determining the area ratio of the various powders according to their particle size.

[0039] [Metal Magnetic Powder] In the present invention, the metal magnetic powder plays a role in controlling the thermal conductivity and electromagnetic interference suppression ability of the thermal conductive composition, but its role in controlling the electromagnetic interference suppression ability is more important. As the metal magnetic powder, for example, carbonyl iron powder can be used. However, other than carbonyl iron powder, any metal magnetic powder that exhibits μ″ in the high frequency band (e.g., frequencies of 26.5 GHz or higher) can be used. For example, FeSiAl alloys, FeSi alloys, FeSiCr alloys, FeSiB-based amorphous alloys, and FeSiBNbCu-based nanocrystalline alloys can also be used. Among these, carbonyl iron powder is preferred because (1) it has a high saturation magnetization due to its iron concentration of 95% or more, and is expected to have a higher magnetic permeability than other materials in the high frequency band, and (2) technology has been established for industrially producing powders with an average particle size of 7 μm or less. Magnetic materials with high saturation magnetization tend to have higher magnetic permeability at high frequencies.

[0040] In order to minimize the influence of the skin effect in the high frequency band, the particle size of the metal magnetic powder is preferably 1 μm or more, more preferably 3 μm or more, and preferably 7 μm or less, more preferably 4 μm or less. If the average particle size is less than 1 μm, there is no established industrially inexpensive manufacturing method, and the small particle size will result in a low thermal conductivity of the thermal conductive composition.

[0041] The volume ratio of the metal magnetic powder to the entire thermal conductive composition is preferably 5% or more, more preferably 30% or more, and preferably 65% ​​or less, more preferably 40% or less. Furthermore, the ratio of the average particle size of the α-type silicon carbide powder to the particle size of the metal magnetic powder is preferably 4 or more, more preferably 9 or more, which makes it easier for heat conduction paths to be formed by the filler distributed in the composition, thereby improving thermal conductivity.

[0042] [Thermal Conductive Powder] In the present invention, the desired thermal conductive composition can be obtained by using, for example, silicon carbide powder and metal magnetic powder as fillers. However, if further enhancement of thermal conductivity is desired, a thermal conductive powder with a particle size smaller than that of the metal magnetic powder can be added to fill the gaps between the metal magnetic powder. From the viewpoint of enhancing thermal conductivity, the thermal conductive composition may contain silicon carbide powder and a thermal conductive powder, but not metal magnetic powder. For example, aluminum oxide powder can be used as the thermal conductive powder. However, other materials with high thermal conductivity, such as silicon carbide, aluminum nitride, boron nitride, magnesium oxide, and barium titanate, can also be used as long as they function in the same way as aluminum oxide powder. Fine-grained aluminum oxide powder is widely used in known thermal conductive compositions, and aluminum oxide powder is preferred from the viewpoint of availability.

[0043] The average particle size of the aluminum oxide powder is preferably 0.1 μm or more, more preferably 0.3 μm or more, and preferably 1 μm or less, more preferably 0.9 μm or less, from the viewpoint of filling the gaps between the metal magnetic powder particles.

[0044] The volume ratio of the thermally conductive powder to the entire thermally conductive composition is preferably 1% or more, more preferably 5% or more, and preferably 15% or less, more preferably 10% or less. If the volume ratio of the thermally conductive powder is too large, the volume ratio of the silicon carbide powder and the carbonyl iron powder will decrease, resulting in a decrease in the thermal conductivity of the thermally conductive composition. The ratio of the average particle size of the metal magnetic powder to the average particle size of the thermally conductive powder is preferably greater than 1, more preferably greater than 4, which makes it easier for the filler distributed in the composition to form a thermal conduction path, thereby improving thermal conductivity.

[0045] [Other Additives] In addition to the silicon carbide powder, metal magnetic powder, and thermally conductive powder, additives such as flame retardants, bulking agents, plasticizers, dispersants, and antioxidants may be added to the base resin as needed, as long as they do not reduce thermal conductivity or the electromagnetic interference suppression effect. For example, flame retardants that do not constitute environmentally hazardous substances are preferred, and examples of such additives include hydroxyl compounds such as aluminum hydroxide and magnesium hydroxide, and nitrogen-based compounds such as melamine cyanurate. Furthermore, red phosphorus, which serves as a flame retardant aid, can also be added as needed.

[0046] [Other Features of the Thermal Conductive Composition] The volume ratio of all the powders to the entire thermal conductive composition may be preferably 45% or more, more preferably 50% or more, and preferably 80% or less, more preferably 75% or less. When the thermal conductive composition is used as a grease, the volume ratio of all the powders to the entire thermal conductive composition may be 45% or more. When the thermal conductive composition is used as a sheet, the volume ratio of all the powders to the entire thermal conductive composition may be 64% or more, preferably 70% or more.

[0047] The thermal conductivity of the thermally conductive composition of the present invention may be preferably 1 W / mK or more, more preferably 3 W / mK or more, and even more preferably 4 W / mK or more. The thermal conductivity is measured by the hot disk method. The measurement of thermal conductivity by the hot disk method conforms to ISO 22007-2. The apparatus and measurement sensor used in the hot disk method may be, for example, those described in the examples.

[0048] The thermally conductive composition of the present invention exhibits effective electromagnetic interference suppression capability even in high frequency bands. As an indicator of electromagnetic interference suppression capability in high frequency bands, the thermally conductive composition of the present invention preferably has a large value of radio wave attenuation at 40 GHz, specifically, preferably greater than 1 dB / cm, more preferably greater than 11 dB / cm, and even more preferably greater than 20 dB / cm. Measurement of radio wave attenuation at 40 GHz can be performed, for example, in accordance with the method described in the Examples.

[0049] (Method for Manufacturing Thermally Conductive Composition) The thermally conductive composition of the present invention can be obtained by mixing one or more of the powders with a base resin, for example, by kneading. The kneading process for mixing the base resin with the powder is described below. Kneading can be achieved using any method, such as a planetary mixer, kneader, three-roll mill, Banbury mixer, or twin-screw mixer. If the materials heat up during kneading and hardening progresses, kneading must be performed under cooling. Furthermore, to obtain a final product free of air bubbles, it is preferable to degas the material by reducing the pressure at any time during the kneading process. If the thermally conductive composition obtained after kneading is to be used as a grease product, it is filled into a dispenser tube. On the other hand, if it is in a putty or sheet form, the molding process described below is carried out.

[0050] The resulting kneaded material can be molded into a putty or sheet by any of a variety of methods, including compression molding, extrusion molding, and roll molding. In the case of compression molding, for example, the kneaded material is placed in a mold with a groove formed so that the molded putty or sheet-like thermal conductive composition has a predetermined thickness (typically 25 to 5,000 μm), and compression molding is performed under conditions that promote silicone vulcanization (temperature 80 to 200°C, time 5 to 60 minutes). To improve the releasability of the molded product from the mold, the mold may be coated with a release agent (preferably a fluorine-based one for silicone) beforehand, or the kneaded material may be sandwiched between PET films coated with a release agent and then molded in the mold.

[0051] (Uses of Thermally Conductive Composition) The thermally conductive composition of the present invention can be suitably used for suppressing near-field noise. In particular, it can be suitably used as a thermally conductive near-field noise suppression sheet, near-field noise suppression putty, near-field noise suppression grease, etc. Note that the thermally conductive composition of the present invention is specialized for thermal conduction applications, and applications other than thermal conduction, such as radio wave absorption applications (e.g., radio wave absorbing sheets), are excluded from the present invention. Note that by adjusting the particle size and additive amount of the material configuration of the present invention, it can also be used as a radio wave absorber for far-field applications, and therefore can be applied in cases where both thermal conduction and far-field radio wave absorption are required.

[0052] The present invention will be described below with reference to examples of sheet-type and grease-type thermal conductive compositions, but the present invention is not limited to these examples.

[0053] <Characteristics Evaluation> "Average particle size" The measurement conditions and analysis procedures were as described in the embodiment. When multiple types of silicon carbide powders with different average particle sizes were used (see Tables 1 and 4 below), the average particle sizes of the various silicon carbide powders as raw materials before mixing were shown.

[0054] "Volume % (volume ratio to the entire thermal conductive composition)" The measurement conditions and analysis procedures were as described in the embodiment. When multiple types of silicon carbide powders with different average particle sizes were used (Tables 1 and 4 below), the volume ratios of the various silicon carbide powders as raw materials before mixing were shown.

[0055] "I calculated from X-ray diffraction measurement ４Ｈ / I ６Ｈ The measurement conditions and analysis procedures were as described in the embodiment, and the results are shown in Tables 1 to 5.

[0056] "Thermal conductivity" Measurement of thermal conductivity using the hot disk method complies with ISO 22007-2. The thermal conductivity measurement results were rated as C for 1.0 W / mK or more and less than 2.5 W / mK, B for 2.5 W / mK or more and less than 4.0 W / mK, and A for 4.0 W / mK or more. [Device] Manufacturer: Hot Disk AB Device name: TPS2500 [Measurement sensor] Manufacturer: Hot Disk AB Sensor name: RTK sensor φ7

[0057] "Radio wave attenuation" [Apparatus] Manufacturer: KEYSIGHT TECHNOLOGY Apparatus name: Vector Network Analyzer P5008A [Waveguide] Manufacturer: EM Lab Apparatus name: R-band waveguide sample holder fixture WSF-R [Measurement conditions] Frequency: 40 GHz [Measurement method] A rectangular sample of 7.112 x 3.556 mm was cut out from the prepared sheet, and the sample was inserted into the R-band waveguide sample holder fixture to measure S11 and S21. The absorption of the sample was measured and divided by the sample thickness to obtain the radio wave attenuation (dB / cm). The measurement results of radio wave attenuation were rated as follows: X for 1 dB / cm or less, C for more than 1 dB / cm and 11 dB / cm or less, B for more than 11 dB / cm and 20 dB / cm or less, and A for more than 20 dB / cm.

[0058] (Examples 1 to 12, Comparative Examples 1 and 2) Alpha-type silicon carbide powders of different particle sizes were added to a liquid silicone resin. The mixture was mixed using a planetary mixer and placed in a mold with a groove formed so that the molded sheet would have a predetermined thickness. Compression molding was performed at a mold temperature of 160°C for 20 minutes to produce a sheet with a thickness of 1,000 μm. Ten sheets were stacked and their thermal conductivity was measured using the hot disk method. A rectangular sample measuring 7.112 x 3.556 mm was cut from one of the sheets, and the radio wave attenuation (dB / cm) at 40 GHz was measured using a waveguide. Examples 1 to 4, Examples 8 to 12, and Comparative Examples 1 to 2 used green silicon carbide powder, while Examples 5 to 7 and Example 11 used black silicon carbide powder. For example, Examples 5 to 7 showed a higher thermal conductivity than Examples 1 to 4. ４Ｈ / I ６Ｈ The value of I was large and the amount of radio wave attenuation was also large. ４Ｈ / I ６Ｈ The higher the value of I, the greater the amount of radio wave attenuation. When the total amount of silicon carbide powder was less than 70%, the thermal conductivity was relatively low. ４Ｈ / I ６Ｈ The value was below 0.01, and the amount of radio wave attenuation was also small.

[0059]

[0060] Examples 13-23: Alpha-type silicon carbide powder, carbonyl iron powder, and aluminum oxide powder of different particle sizes were added to a liquid silicone resin. Except for Example 22, the amount of each powder added was 35% silicon carbide powder, 35% carbonyl iron powder, and 5% aluminum oxide powder, by volume, relative to the total sheet substrate. The kneaded mixture mixed with a planetary mixer was placed in a mold with an indentation so that the molded sheet would have a predetermined thickness, and compression molding was performed at a mold temperature of 160°C for 20 minutes to produce a sheet with a thickness of 1000 μm. Ten sheets prepared were stacked, and the thermal conductivity was measured using the hot disk method. A rectangular sample measuring 7.112 x 3.556 mm was cut from one of the prepared sheets, and the radio wave attenuation (dB / cm) at 40 GHz was measured using a waveguide.

[0061]

[0062] (Examples 24 to 35) The sheet production and evaluation methods were the same as those of Examples 13 to 23. When the amount of aluminum oxide added exceeded 15%, the thermal conductivity became relatively low.

[0063]

[0064] Examples 36-38: Alpha-type silicon carbide powders of different particle sizes were added to a liquid silicone resin (grease base). Each powder was added at a volume ratio of 50% of the total grease base. The mixture was mixed using a planetary mixer and filled into a dispenser container. The kneaded grease was then poured from the dispenser into a hot disk liquid sample measuring jig to measure thermal conductivity. The kneaded grease was also filled into a 7.112 x 3.556 mm rectangular sample, and the radio wave attenuation (dB / cm) at 40 GHz was measured using a waveguide. All of Examples 36-38 exhibited thermal conductivities exceeding 1 W / mK and radio wave attenuation exceeding 5 dB / cm, demonstrating practical electromagnetic interference suppression capabilities.

[0065]

[0066] Examples 39-41: Alpha-type silicon carbide powder, carbonyl iron powder, and aluminum oxide powder of different particle sizes were added to a liquid silicone resin. The amounts of each powder added were 30% silicon carbide powder, 15% carbonyl iron powder, and 5% aluminum oxide powder, by volume, relative to the total sheet substrate. The mixture was mixed using a planetary mixer and filled into a dispenser container. The kneaded grease was then poured from the dispenser container into a hot disk liquid sample measuring jig to measure thermal conductivity. Additionally, the kneaded grease was filled into a 7.112 x 3.556 mm rectangular sample, and the radio wave attenuation (dB / cm) at 40 GHz was measured using a waveguide. All of Examples 39-41 exhibited thermal conductivities exceeding 1 W / mK and radio wave attenuation exceeding 5 dB / cm, demonstrating practical electromagnetic interference suppression capabilities.

[0067]

[0068] The thermally conductive composition of the present invention is attached to electronic devices and the like, and exhibits effective electromagnetic interference suppression even in higher frequency bands, while also having high thermal conductivity. Therefore, it is possible to industrially stably produce components that can simultaneously solve the electromagnetic interference and heat dissipation issues of today's increasingly sophisticated electronic devices, making it industrially useful.

Claims

1. A heat conduction composition having electromagnetic interference suppression ability, comprising one or more types of powders, One of the aforementioned powders is α-type silicon carbide powder. In powder X-ray diffraction using Cu-Kα as a source in the aforementioned heat conductive composition, the peak intensity I, which originates from 4H-SiC, appears at 2θ = 34.4 to 35°. ４Ｈ The peak intensity I, which appears at 2θ = 35-36°, originates from 6H-SiC. ６Ｈ The value I obtained by dividing by ４Ｈ / I ６Ｈ However, it is characterized by being 0.01 or greater. A heat-conducting composition having electromagnetic interference suppression capabilities.

2. The average particle size of the α-type silicon carbide powder is 1 μm or more and 180 μm or less. The volume ratio of the entire powder to the entire heat-conducting composition is 45% or more and 80% or less. A heat conduction composition having electromagnetic interference suppression ability as described in claim 1.

3. The powder further comprises one or more powders that are either metallic magnetic powder or thermally conductive powder. The average particle size of the α-type silicon carbide powder is 30 μm or more and 180 μm or less. The volume ratio of the α-type silicon carbide powder to the total heat-conducting composition is 10% or more and 75% or less. A heat conduction composition having electromagnetic interference suppression ability as described in claim 1.

4. The powder includes the metal magnetic powder, The particle size of the aforementioned metal magnetic powder is 1 μm or more and 7 μm or less. The volume ratio of the metal magnetic powder to the total heat conductive composition is 5% or more and 65% or less. The ratio of the average particle size of the α-type silicon carbide powder to the average particle size of the metal magnetic powder is 4 or more. A heat conduction composition having electromagnetic interference suppression ability as described in claim 3.

5. The powder includes the thermally conductive powder, The average particle size of the thermally conductive powder is 0.1 μm or more and 1 μm or less. The thermal conductive powder is characterized in that its volume ratio to the entire thermal conductive composition is 1% or more and 15% or less. A heat conduction composition having electromagnetic interference suppression ability according to claim 3 or 4.

6. A heat-conducting composition having electromagnetic interference suppression ability according to any one of claims 1 to 4, characterized in that the thermal conductivity of the heat-conducting composition measured by the hot disk method is 1 W / mK or more.

7. The above I ４Ｈ / I ６Ｈ A heat conduction composition having electromagnetic interference suppression ability according to any one of claims 1 to 4, characterized in that the value is 0.1 or greater.

8. A heat conduction composition having electromagnetic interference suppression ability according to any one of claims 1 to 4, characterized in that the heat conduction composition is in the form of a sheet, putty, or grease.

9. A thermal conductive composition having electromagnetic interference suppression ability according to any one of claims 1 to 4, for use in near-field noise suppression applications.