WO2013024809A1 - Electromagnetically absorbing, thermally conductive sheet and electronic instrument - Google Patents

Electromagnetically absorbing, thermally conductive sheet and electronic instrument Download PDF

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Publication number
WO2013024809A1
WO2013024809A1 PCT/JP2012/070465 JP2012070465W WO2013024809A1 WO 2013024809 A1 WO2013024809 A1 WO 2013024809A1 JP 2012070465 W JP2012070465 W JP 2012070465W WO 2013024809 A1 WO2013024809 A1 WO 2013024809A1
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magnetic metal
metal particles
electromagnetic wave
conductive sheet
magnetic
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PCT/JP2012/070465
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French (fr)
Japanese (ja)
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久村　達雄
佑介 久保
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デクセリアルズ株式会社
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00—Screening of apparatus or components against electric or magnetic fields
    • H05K9/0073—Shielding materials
    • H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
    • H05K9/0083—Electromagnetic shielding materials, e.g. EMI, RFI shielding comprising electro-conductive non-fibrous particles embedded in an electrically insulating supporting structure, e.g. powder, flakes, whiskers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
    • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
    • H01F1/20—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of particles, e.g. powder
    • H01F1/22—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together
    • H01F1/24—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together the particles being insulated
    • H01F1/26—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of particles, e.g. powder pressed, sintered, or bound together the particles being insulated by macromolecular organic substances

Definitions

  • the present invention efficiently transfers heat from an electronic component such as a semiconductor package to a heat radiating component such as a heat sink, a heat pipe, and a heat sink in the vicinity of a signal transmission unit that transmits a high-frequency signal inside the electronic device. It is related with the electromagnetic wave absorptive heat conductive sheet which can absorb.
  • a heat sink, a heat pipe, a heat sink, or the like made of a metal material having a high thermal conductivity such as copper or aluminum is widely used.
  • These heat dissipating parts having excellent thermal conductivity are disposed so as to be close to an electronic part such as a semiconductor package which is a heat generating part in the electronic device in order to reduce the heat dissipation effect or the temperature rise in the device. Further, these heat dissipating parts having excellent thermal conductivity are arranged from the electronic part as the heat generating part to a low temperature place. Further, in order to fill a space generated when the electronic component and the metal heat dissipation component are bonded, a flexible heat conductive sheet is disposed between the electronic component and the metal heat dissipation component.
  • the heat generating part in the electronic device is an electronic component such as a semiconductor element having a high current density.
  • a high current density means a high electric field strength or magnetic field strength that can cause unwanted radiation. For this reason, when a heat dissipating component made of metal is disposed in the vicinity of an electronic component, there are often cases where a harmonic component of an electric signal flowing in the electronic component is received with heat.
  • the heat dissipating part since the heat dissipating part is made of a metal material, it may function as a harmonic component antenna itself or as a harmonic noise component transmission path. .
  • thermal conductive sheet that contains a magnetic material in order to prevent the heat dissipation component from functioning as an antenna, that is, to cut off the coupling of the magnetic field
  • Patent Document 1 a thermal conductive sheet that contains a magnetic material in order to prevent the heat dissipation component from functioning as an antenna, that is, to cut off the coupling of the magnetic field.
  • Such a heat conductive sheet includes a magnetic material having a high magnetic permeability such as ferrite in a polymer material such as silicone or acrylic, thereby providing both functions of heat conductivity and electromagnetic wave suppression. Realized.
  • the characteristics of the above-described heat conductive sheet having both the heat conduction characteristics and the electromagnetic wave suppression characteristics change greatly depending on the filling amount of the target powder contained in the polymer material as the base material.
  • the thermal conductivity has the following relationship according to the Bruggeman equation. (Reference: "High heat conductivity of heat dissipation materials for electronic equipment parts and measurement / evaluation technology for heat conductivity", Technical Information Association, 2003)
  • ⁇ e is the thermal conductivity of the entire sheet
  • ⁇ d is the thermal conductivity of the thermally conductive material
  • ⁇ c is the thermal conductivity of the base polymer material
  • ⁇ is the volume of the thermally conductive material in the sheet. It is a fraction.
  • This magnetic characteristic also has the following relationship, for example, according to the Lichtenecker equation. (Reference: “Studies on low-loss, high-permittivity magnetic materials”, IEICE Transactions C, Vol. J86-C, No. 4, pp. 450-456, 2003)
  • mu r1 is the complex relative permeability of the magnetic material
  • mu r2 are complex relative permeability of the preform
  • [nu 1 is the volume fraction of the magnetic material
  • [nu 2 Mother This is the volume fraction of the material.
  • the heat conduction characteristics and the electromagnetic wave suppression characteristics vary greatly depending on the amounts of the magnetic material and the heat conductive material filled in the sheet.
  • the maximum filling rate is 74 vol%.
  • small spherical magnetic powder is sequentially packed in the gap between the previously filled spherical magnetic powder.
  • the present invention has been proposed in view of such circumstances, and an electromagnetic wave-absorbing heat conductive sheet having good functions of both heat conduction characteristics and electromagnetic wave absorption characteristics and the electromagnetic wave-absorbing heat conduction sheet are mounted.
  • An object is to provide electronic equipment.
  • the present invention provides an electromagnetic wave absorbing heat conductive sheet disposed in the vicinity of a signal transmission unit that transmits a high-frequency signal inside an electronic device. It contains particles and second magnetic metal particles having an average particle size smaller than that of the first magnetic metal particles and smaller electric resistivity than that of the first metal particles.
  • the electronic apparatus includes a signal transmission unit that transmits a high-frequency signal and an electromagnetic wave absorbing heat conductive sheet disposed in the vicinity of the signal transmission unit, and the electromagnetic wave absorbing heat conductive sheet is flexible.
  • the resin material contains first magnetic metal particles and second magnetic metal particles having an average particle size smaller than that of the first magnetic metal particles and lower electric resistivity than that of the first metal particles.
  • the present invention provides a flexible resin material comprising a first magnetic metal particle and a second magnetic material having an average particle size smaller than that of the first magnetic metal particle and lower electrical resistivity than that of the first metal particle. Since the metal particles are contained, it is possible to provide a heat conductive sheet having both functions of heat conduction characteristics and electromagnetic wave suppression characteristics. Furthermore, it is possible to provide an electromagnetic wave suppressing and radiating sheet having high thermal conductivity and a high electromagnetic wave suppressing effect and also having flexibility.
  • FIG. 1A shows a configuration of an electronic device on which an electromagnetic wave absorbing heat conductive sheet to which the present invention is applied is mounted
  • FIG. 1B is a diagram showing a modification thereof.
  • FIG. 2 is a diagram for explaining electromagnetic wave absorption characteristics of the electromagnetic wave absorbing heat conductive sheet to which the present invention is applied.
  • FIG. 3 is a diagram for explaining frequency characteristics related to electromagnetic wave absorption characteristics of an electromagnetic wave absorbing heat conductive sheet to which the present invention is applied.
  • the electromagnetic wave absorptive heat conductive sheet to which the present invention is applied is disposed in the vicinity of a signal transmission unit that transmits a high frequency signal inside an electronic device.
  • This electromagnetic wave absorptive heat conductive sheet efficiently transfers heat from an electronic component such as a semiconductor package to a heat radiating component such as a heat radiating plate, a heat pipe, and a heat sink, and absorbs electromagnetic waves.
  • the electromagnetic wave absorptive heat conductive sheet to which the present invention is applied is attached to a circuit board 1a inside the electronic apparatus 1 as shown in FIG. 1A, for example. That is, the sheet 11 having electromagnetic wave absorption and thermal conductivity as shown in FIG. 1A includes a high-frequency signal transmission board 17 that transmits a high-frequency signal and a heat-dissipating metal plate 12 that dissipates heat generated by the high-frequency signal transmission board 17. Between.
  • the sheet 11 has a circuit board such that one surface 11a is in close contact with the resin mold 13 for sealing the semiconductor package constituting the high-frequency signal transmission substrate 17, and the other surface 11b is in close contact with the heat dissipation metal plate 12. Affixed to 1a.
  • the high-frequency signal transmission substrate 17 is a specific example of a signal transmission unit that transmits a high-frequency signal inside the electronic device 1.
  • the dielectric substrate 16 has a copper foil 15 serving as a GND electrode on one surface and a second surface.
  • a microstrip line is constituted by the copper signal line 14 formed by patterning.
  • the high-frequency signal transmission board 17 is designed so that the far field strength when operating itself is suppressed to a predetermined value or less in order to prevent the influence of unnecessary radiation.
  • the heat radiating metal plate 12 receives a harmonic component of an electric signal flowing in the signal line 14 of the high-frequency signal transmission board 17 facing through the sheet 11. It functions as an antenna for harmonic components, and as a result, the far field strength is increased.
  • the magnetic metal particles are adjusted so that the volume fraction in the sheet 11 is equal to or greater than a predetermined value. Is contained.
  • the sheet 11 having an electromagnetic wave absorbing heat conduction function to which the present invention is applied may not be brought into close contact with the heat radiating metal plate 12 as shown in FIG. 1B, for example. 1B, the sheet 11 absorbs electromagnetic waves emitted from the high-frequency signal transmission board 17 without deteriorating the heat dissipation efficiency of the heat generated in the high-frequency signal transmission board 17. Can do.
  • the sheet 11 includes a flexible resin material, a first magnetic metal particle, and a second magnetic metal having an average particle size smaller than that of the first magnetic metal particle and lower electrical resistivity than that of the first magnetic metal particle. It contains particles.
  • the sheet 11 having such a configuration can achieve both good heat conduction characteristics and good electromagnetic wave suppression characteristics, as is apparent from the performance evaluation described later.
  • the sheet 11 prepared under the following conditions was used to evaluate the heat conduction characteristics and the electromagnetic wave suppression effect.
  • a silicone resin is used for the flexible resin material
  • a spherical magnetic amorphous alloy having an average particle size of 6 ⁇ m is used for the first magnetic metal particles
  • a spherical iron powder having an average particle size of 1.5 ⁇ m is used for the second magnetic metal particles.
  • the “average particle diameter” in the present embodiment specifically refers to the median diameter (also referred to as D50) in which the large side and the small side are equal when the powder is divided into two from a certain particle diameter. For example, in this embodiment, it can be calculated by a laser diffraction / scattering method.
  • the electrical resistivity is 0.5 ⁇ m.
  • the above materials it is particularly preferable to use a material having an electrical resistivity of 0.8 ⁇ m or more from the viewpoint of increasing the average particle size and improving the filling property.
  • the electrical resistivity of the second magnetic metal particles may be lower than 0.5 ⁇ m, which is smaller than that of the first magnetic metal particles, but in order to achieve particularly good thermal conductivity. Is preferably 0.3 ⁇ m or less.
  • magnetic metal amorphous particles having a high electrical resistivity are suitable.
  • the magnetic metal amorphous particles include Fe—Si—B, Fe—Si—B—C, Co—Si—B, Co—Zr, Co—Nb, and Co—Ta. However, it is not limited to these.
  • Crystalline magnetic metals include Fe, Co, Ni, or Fe—Ni, Fe—Co, Fe—Al, Fe—Si, Fe—Si—Al, Fe—Ni—Si. -Al type and the like.
  • the microcrystalline magnetic metal is a material obtained by finely crystallizing these crystalline materials by adding a small amount of N, C, O, B or the like.
  • the electrical resistivity is 0.5 ⁇ m or more, and at least one kind of substantially spherical magnetic particles such as a sphere and a polyhedron is the first magnetic metal particle,
  • the second magnetic metal particle at least one kind of magnetic particles having an average particle size smaller than that of one magnetic metal particle and an electrical resistivity smaller than 0.5 ⁇ m is used.
  • the average particle diameter of the second magnetic metal particles can be set in plural if the particle diameter ratio is in the range of 5 to 50% with respect to the first magnetic metal particle diameter. That is, the second magnetic metal particles can be used in combination of a plurality of materials, compositions and particle sizes.
  • heat conductive particles such as alumina, boron nitride, silicon nitride, aluminum nitride, silicon carbide, etc. are added. You can also. Such heat conduction particles are preferably smaller in particle size than the first magnetic metal particles and have a shape close to a sphere.
  • the flexible resin examples include resins such as epoxy resin, phenol resin, melamine resin, urea resin, and unsaturated polyester, and rubber such as silicone rubber, urethane rubber, acrylic rubber, butyl rubber, and ethylene propylene rubber.
  • resins such as epoxy resin, phenol resin, melamine resin, urea resin, and unsaturated polyester
  • rubber such as silicone rubber, urethane rubber, acrylic rubber, butyl rubber, and ethylene propylene rubber.
  • surface treatment agents such as a flame retardant, a reaction regulator, a crosslinking agent, and a silane coupling agent, can be further added and used.
  • the complex relative permeability was measured as follows.
  • the produced sheet was punched into a ring shape having an outer diameter of 20 mm and an inner diameter of 6 mm to produce a measurement sample.
  • the complex relative permeability of this measurement sample was measured using a measuring instrument “Agilent 4291B RF Impedance / Material Analyzer” manufactured by Agilent Technologies.
  • thermal conductivity was calculated as follows. The produced sheet is cut into a size of about 1 cm square, and the cut sample is sandwiched between a metal heat sink and a metal heater case, and is pressed into contact with a force of 1 kgf. Heat with power. When the temperature of the metal heater case and the metal heat sink became constant, the temperature difference between them was measured. The thermal conductivity was calculated from the following formula.
  • FIG. 2 shows the measurement result of the imaginary part of the complex relative permeability. Since the imaginary part of the complex relative permeability is a magnetic loss term of permeability, it can be used as an evaluation index of magnetic absorption characteristics. As is clear from FIG. 2, a large magnetic loss is observed around 2 GHz.
  • Such magnetic loss at high frequencies of magnetic metal materials mainly includes eddy current loss and loss due to ferromagnetic resonance.
  • FIG. 3 shows a case where the electrical resistivity is changed with the average particle diameter of the spherical magnetic metal particles being 6 ⁇ m and the initial permeability ⁇ i being 40 in order to evaluate the deterioration of the magnetic permeability due to the eddy current loss in the spherical magnetic metal particles.
  • the frequency characteristic of the imaginary part ⁇ r ′′ of the complex relative permeability is calculated.
  • the imaginary part ⁇ r ′′ of the complex relative permeability is shown normalized by the initial permeability ⁇ i .
  • the electric resistivity when the electrical resistivity is low, the magnetic loss greatly shifts to the low frequency side.
  • the electric resistivity In a sheet using spherical magnetic metal particles having an average particle diameter of 6 ⁇ m, the electric resistivity must be 0.5 ⁇ m or more in order to bring the peak of magnetic loss to the GHz band.
  • the electrical resistivity is 1.1 ⁇ m
  • the average particle diameter needs to be 9 ⁇ m, 8 ⁇ m and 2.8 ⁇ m, respectively.
  • the material has a high electrical resistivity, it is possible to obtain a frequency characteristic that absorbs electromagnetic waves in a good high frequency band even if the particle size is increased, and if the material has a low electrical resistivity, the particle size Unless it is made small, it is impossible to obtain frequency characteristics that absorb electromagnetic waves in a good high frequency band.
  • the flexible resin material in order to realize the frequency characteristics of absorbing electromagnetic waves in the high frequency band as described above, is highly filled with magnetic metal particles having different average particle diameters in consideration of the following points.
  • the particle size that can be produced is generally several ⁇ m to several tens of ⁇ m, which is the minimum particle size of commercially available materials. Is about 5-6 ⁇ m.
  • Such a material intended to absorb electromagnetic waves in the GHz band is used as the first magnetic metal material, and magnetic metal particles having a small average particle diameter are used as the second magnetic metal material. If it arrange
  • the particle size of the second magnetic metal particles is 5 to 50% of the average particle size of the first magnetic metal particles, and the second magnetic metal particles have a second magnetic particle size relative to the first magnetic metal particles.
  • the mixing ratio of the metal particles is 10 to 60 vol%, the filling of the magnetic metal particles in the flexible resin can be increased.
  • the second magnetic metal particles are small in size and are not easily affected by eddy current loss, it is not necessary to increase the electrical resistivity, and from the viewpoint of increasing the thermal conductivity, the second magnetic metal particles have a small electrical resistivity. Is selected. This is because the movement of free electrons in the metal affects the thermal conductivity, so that a metal material having a higher electrical conductivity, that is, a lower electrical resistivity can increase the thermal conductivity.
  • a spherical magnetic amorphous alloy having an electrical resistivity of 1.1 ⁇ m and an average particle size of 6 ⁇ m is used as the first magnetic metal.
  • a spherical iron powder having an electrical resistivity of 0.15 ⁇ m and an average particle size of 1.5 ⁇ m is selected as the second magnetic metal particle.
  • the sheet according to the example has a high thermal conductivity of 2.0 W / m ⁇ K, and has excellent thermal conductivity characteristics.
  • the thermal conductivity of is evaluated.
  • the thermal conductivity of the sheet according to the comparison target was 1.71 W / m ⁇ K.
  • the sheet 11 according to the example uses about 18% of the thermal conductivity as the second magnetic metal particle by using iron powder having a lower electrical resistivity than the amorphous powder. was able to improve.
  • the thermal conductivity of the finished product sheet can be greatly improved.
  • the electromagnetic wave absorptive heat conductive sheet to which the present invention is applied has the first magnetic metal particles and the first magnetic metal particles having a smaller average particle size than the first magnetic metal particles. Since the second magnetic metal particles having an electric resistivity smaller than that of the metal particles are contained, it is possible to provide a heat conductive sheet having both functions of heat conduction characteristics and electromagnetic wave suppression characteristics. Furthermore, it is possible to provide an electromagnetic wave suppressing and radiating sheet having high thermal conductivity and a high electromagnetic wave suppressing effect and also having flexibility.
  • a material in which the electrical resistivity of the first magnetic metal particles is 0.5 ⁇ m or more is selected, and a material in which the electrical resistivity of the second magnetic metal particles is less than 0.5 ⁇ m is selected.
  • 1 Electronic device 1a circuit board, 11 sheet, 12 heat dissipation metal plate, 13 resin mold, 14 signal lines, 15 copper foil, 16 dielectric substrate, 17 high frequency signal transmission board

Abstract

Provided is an electromagnetically absorbing, thermally conductive sheet having excellent heat conducting characteristics and electromagnetic absorbing characteristics. An electromagnetically absorbing, thermally conductive sheet (11) disposed near a high-frequency-signal-transmitting substrate (17) for transmitting a high-frequency signal, the substrate being disposed inside an electronic instrument (1), wherein the sheet is characterized in that first magnetic metallic particles and second magnetic metallic particles are included on a flexible resin material. The second magnetic metallic particles have a smaller average particle diameter and a lower electrical resistivity than first magnetic metallic particles.

Description

電磁波吸収性熱伝導シート及び電子機器Electromagnetic wave absorbing heat conductive sheet and electronic device
　本発明は、電子機器内部の高周波信号が伝送する信号伝送部の近傍、例えば、半導体パッケージなどの電子部品から、放熱板や、ヒートパイプ、ヒートシンク等といった放熱部品へ効率よく熱を伝え、かつ電磁波を吸収することが可能な電磁波吸収性熱伝導シートに関する。
　本出願は、日本国において２０１１年８月１８日に出願された日本特許出願番号特願２０１１－１７８８５４を基礎として優先権を主張するものであり、この出願は参照されることにより、本出願に援用される。 The present invention efficiently transfers heat from an electronic component such as a semiconductor package to a heat radiating component such as a heat sink, a heat pipe, and a heat sink in the vicinity of a signal transmission unit that transmits a high-frequency signal inside the electronic device. It is related with the electromagnetic wave absorptive heat conductive sheet which can absorb.
This application claims priority on the basis of Japanese Patent Application No. 2011-178854 filed on August 18, 2011 in Japan. This application is incorporated herein by reference. Incorporated.
　近年、電子機器は、小型化の傾向をたどる一方、アプリケーションが多様化しているため電力消費量をそれほど変化させることができず、機器内における放熱対策がより一層重要視されている。 In recent years, electronic devices have been trending toward miniaturization, but since the applications have diversified, the power consumption cannot be changed so much, and heat radiation countermeasures in the devices have become more important.
　上述した電子機器における放熱対策として、銅やアルミなどといった熱伝導率の高い金属材料で作製された放熱板やヒートパイプ、あるいはヒートシンクなどが広く利用されている。これらの熱伝導性に優れた放熱部品は、放熱効果または機器内の温度上昇の緩和を図るため、電子機器内における発熱部である半導体パッケージなどの電子部品に近接するようにして配置される。また、これらの熱伝導性に優れた放熱部品は、発熱部である電子部品から低温場所へ亘って配置される。また、電子部品と金属放熱部品とを接着させたときに生じる空間を埋めるため、可撓性を有する熱伝導性シートが、電子部品と金属放熱部品との間に配置される。 As a heat dissipation measure in the electronic devices described above, a heat sink, a heat pipe, a heat sink, or the like made of a metal material having a high thermal conductivity such as copper or aluminum is widely used. These heat dissipating parts having excellent thermal conductivity are disposed so as to be close to an electronic part such as a semiconductor package which is a heat generating part in the electronic device in order to reduce the heat dissipation effect or the temperature rise in the device. Further, these heat dissipating parts having excellent thermal conductivity are arranged from the electronic part as the heat generating part to a low temperature place. Further, in order to fill a space generated when the electronic component and the metal heat dissipation component are bonded, a flexible heat conductive sheet is disposed between the electronic component and the metal heat dissipation component.
　これらのような熱伝導性に優れた放熱部品は、金属であるが故にその副作用として電気信号の高調波成分を受けることによって生じる電磁誘導により、結果的に不要電磁波の輻射の原因となってしまうことがしばしばある。 These heat-dissipating parts with excellent thermal conductivity are metal, and as a result, electromagnetic induction caused by receiving harmonic components of electric signals as a side effect results in unnecessary electromagnetic radiation. There is often.
　また、電子機器内における発熱部は、電流密度が高い半導体素子などの電子部品である。電流密度が高いということは、不要輻射の原因となりうる電界強度または磁界強度が大きい。このため金属で作製された放熱部品を電子部品の近傍に配置すると、熱とともに電子部品内を流れる電気信号の高調波成分を受けるケースがしばしば見られる。 Also, the heat generating part in the electronic device is an electronic component such as a semiconductor element having a high current density. A high current density means a high electric field strength or magnetic field strength that can cause unwanted radiation. For this reason, when a heat dissipating component made of metal is disposed in the vicinity of an electronic component, there are often cases where a harmonic component of an electric signal flowing in the electronic component is received with heat.
　具体的には、放熱部品は、金属材料で作製されているため、それ自体が高調波成分のアンテナとして機能してしまうことや、高調波ノイズ成分の伝達経路として機能してしまうという現象が生じる。 Specifically, since the heat dissipating part is made of a metal material, it may function as a harmonic component antenna itself or as a harmonic noise component transmission path. .
　このような背景により、熱伝導性シートは、放熱部品がアンテナとして機能してしまうのを抑制するため、すなわち磁界のカップリングを断ち切るために、磁性材料を含有するものがある（特許文献１）。このような熱伝導性シートは、例えばフェライトなどの高透磁率を有する磁性材料を、シリコーン系やアクリル系などの高分子材に含有させることにより、熱伝導特性と電磁波抑制特性の両者の機能を実現している。 With such a background, there is a thermal conductive sheet that contains a magnetic material in order to prevent the heat dissipation component from functioning as an antenna, that is, to cut off the coupling of the magnetic field (Patent Document 1). . Such a heat conductive sheet, for example, includes a magnetic material having a high magnetic permeability such as ferrite in a polymer material such as silicone or acrylic, thereby providing both functions of heat conductivity and electromagnetic wave suppression. Realized.
特開２００６－３１０８１２号公報JP 2006-310812 A
　上述した熱伝導特性と電磁波抑制特性の両者の機能を有する熱伝導性シートは、母材となる高分子材に含まれる目的粉末の充填量に応じて大きく特性が変化する。 The characteristics of the above-described heat conductive sheet having both the heat conduction characteristics and the electromagnetic wave suppression characteristics change greatly depending on the filling amount of the target powder contained in the polymer material as the base material.
　例えば、熱伝導率は、Ｂｒｕｇｇｅｍａｎの式によると以下のような関係がある。（参考：“電子機器部品用放熱材料の高熱伝導化および熱伝導性の測定・評価技術”，技術情報協会，２００３年出版） For example, the thermal conductivity has the following relationship according to the Bruggeman equation. (Reference: "High heat conductivity of heat dissipation materials for electronic equipment parts and measurement / evaluation technology for heat conductivity", Technical Information Association, 2003)
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　ここで、λｅはシート全体の熱伝導率、λｄは熱伝導性材料の熱伝導率、λｃは母材の高分子材の熱伝導率、φは熱伝導性材料のシートに占める体積分率である。 Here, λ e is the thermal conductivity of the entire sheet, λ d is the thermal conductivity of the thermally conductive material, λ c is the thermal conductivity of the base polymer material, and φ is the volume of the thermally conductive material in the sheet. It is a fraction.
　また、電磁波抑制特性の指標として、一般的には複素比透磁率（μｒ=μｒ'－ｊμｒ”）の虚部μｒ”が用いられる。この磁気特性についても、例えばＬｉｃｈｔｅｎｅｃｋｅｒの式によると以下のような関係がある。（参考：“低損失高誘電率磁性体に関する研究”,電子情報通信学会論文誌　C, Vol. J86-C, No. 4, pp. 450-456, 2003） In general, the imaginary part μ r ″ of the complex relative permeability (μ r = μ r ′ −jμ r ″) is used as an index of electromagnetic wave suppression characteristics. This magnetic characteristic also has the following relationship, for example, according to the Lichtenecker equation. (Reference: “Studies on low-loss, high-permittivity magnetic materials”, IEICE Transactions C, Vol. J86-C, No. 4, pp. 450-456, 2003)
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
　ここで、μｒはシート全体の複素比透磁率、μｒ１は磁性材料の複素比透磁率、μｒ２は母材の複素比透磁率、ν１は磁性材料の体積分率、ν２は母材の体積分率である。 Here, the complex relative permeability of mu r entire sheet, mu r1 is the complex relative permeability of the magnetic material, mu r2 are complex relative permeability of the preform, [nu 1 is the volume fraction of the magnetic material, [nu 2 Mother This is the volume fraction of the material.
　上述のように、熱伝導特性と、電磁波抑制特性とは、それぞれシートに充填される磁性材料と熱伝導性材料との充填量に応じて大きく変化する。 As described above, the heat conduction characteristics and the electromagnetic wave suppression characteristics vary greatly depending on the amounts of the magnetic material and the heat conductive material filled in the sheet.
　しかしながら、このような電磁波吸収性熱伝導シートの作製にあたり、任意の磁性粉末と樹脂をただ混ぜるだけでは、粉末の充填量に限界がある。 However, in the production of such an electromagnetic wave absorbing heat conductive sheet, there is a limit to the amount of powder filling only by mixing arbitrary magnetic powder and resin.
　同一サイズの球状の磁性粉末を最密充填した場合、その最大の充填率が７４ｖｏｌ％である。これよりも多くの磁性粉末を充填する場合、先に充填した球状の磁性粉末の隙間に小径の球状の磁性粉末を順次詰め込んでいくようにする。 When the spherical magnetic powder of the same size is packed most closely, the maximum filling rate is 74 vol%. When a larger amount of magnetic powder is filled, small spherical magnetic powder is sequentially packed in the gap between the previously filled spherical magnetic powder.
　このようにして、樹脂の中に物質を充填していく場合は、樹脂とのなじみが問題となり充填物質の比表面積が小さいほうが高充填でき、一般的に、粒子径の大きなものは体積当りの比表面積が小さいことから高充填し易い。 In this way, when a substance is filled in a resin, familiarity with the resin becomes a problem, and the smaller the specific surface area of the filling substance, the higher the filling can be. Since the specific surface area is small, high filling is easy.
　しかし、充填物質として粒子径の大きい金属磁性粒子を用いると表皮効果の影響により高い周波数帯では透磁率が低下して、良好な磁気吸収特性を実現できない。このような表皮効果を軽減させるために電気抵抗率の高い金属材料を用いると、一般に熱伝導率が小さくなり、熱伝導性が損なわれるという問題が生じる。 However, when metal magnetic particles having a large particle diameter are used as the filling material, the magnetic permeability decreases at a high frequency band due to the skin effect, and good magnetic absorption characteristics cannot be realized. When a metal material having a high electrical resistivity is used in order to reduce the skin effect, there is a problem that the thermal conductivity is generally reduced and the thermal conductivity is impaired.
　本発明は、このような実情に鑑みて提案されたものであり、熱伝導特性と電磁波吸収特性の両者の機能が良好な電磁波吸収性熱伝導シート及びこの電磁波吸収性熱伝導シートが実装された電子機器を提供することを目的とする。 The present invention has been proposed in view of such circumstances, and an electromagnetic wave-absorbing heat conductive sheet having good functions of both heat conduction characteristics and electromagnetic wave absorption characteristics and the electromagnetic wave-absorbing heat conduction sheet are mounted. An object is to provide electronic equipment.
　上述した課題を解決するため、本発明は、電子機器内部の高周波信号が伝送する信号伝送部の近傍に配置される電磁波吸収性熱伝導シートにおいて、可撓性樹脂材料に、第１の磁性金属粒子と、第１の磁性金属粒子よりも平均粒径が小さく第１の金属粒子よりも電気抵抗率が小さい第２の磁性金属粒子とを含有することを特徴とする。 In order to solve the above-described problem, the present invention provides an electromagnetic wave absorbing heat conductive sheet disposed in the vicinity of a signal transmission unit that transmits a high-frequency signal inside an electronic device. It contains particles and second magnetic metal particles having an average particle size smaller than that of the first magnetic metal particles and smaller electric resistivity than that of the first metal particles.
　また、本発明に係る電子機器は、高周波信号が伝送する信号伝送部と、信号伝送部の近傍に配置される電磁波吸収性熱伝導シートとを備え、電磁波吸収性熱伝導シートは、可撓性樹脂材料に、第１の磁性金属粒子と、第１の磁性金属粒子よりも平均粒径が小さく第１の金属粒子よりも電気抵抗率が小さい第２の磁性金属粒子とを含有することを特徴とする。 The electronic apparatus according to the present invention includes a signal transmission unit that transmits a high-frequency signal and an electromagnetic wave absorbing heat conductive sheet disposed in the vicinity of the signal transmission unit, and the electromagnetic wave absorbing heat conductive sheet is flexible. The resin material contains first magnetic metal particles and second magnetic metal particles having an average particle size smaller than that of the first magnetic metal particles and lower electric resistivity than that of the first metal particles. And
　本発明は、可撓性樹脂材料に、第１の磁性金属粒子と、該第１の磁性金属粒子よりも平均粒径が小さく該第１の金属粒子よりも電気抵抗率が小さい第２の磁性金属粒子とが含有しているので、熱伝導特性と電磁波抑制特性との両者の機能が良好な熱伝導性シートを提供することができる。さらに、高い熱伝導性と高い電磁波抑制効果を有していながら、かつフレキシブル性も兼ね備えた電磁波抑制放熱シートを提供することができる。 The present invention provides a flexible resin material comprising a first magnetic metal particle and a second magnetic material having an average particle size smaller than that of the first magnetic metal particle and lower electrical resistivity than that of the first metal particle. Since the metal particles are contained, it is possible to provide a heat conductive sheet having both functions of heat conduction characteristics and electromagnetic wave suppression characteristics. Furthermore, it is possible to provide an electromagnetic wave suppressing and radiating sheet having high thermal conductivity and a high electromagnetic wave suppressing effect and also having flexibility.
図１Ａは、本発明が適用された電磁波吸収性熱伝導シートが実装される電子機器の構成を示し、図１Ｂは、その変形例を示す図である。FIG. 1A shows a configuration of an electronic device on which an electromagnetic wave absorbing heat conductive sheet to which the present invention is applied is mounted, and FIG. 1B is a diagram showing a modification thereof. 図２は、本発明が適用された電磁波吸収性熱伝導性シートの電磁波吸収特性について説明するための図である。FIG. 2 is a diagram for explaining electromagnetic wave absorption characteristics of the electromagnetic wave absorbing heat conductive sheet to which the present invention is applied. 図３は、本発明が適用された電磁波吸収性熱伝導性シートの電磁波吸収特性に関する周波数特性について説明するための図である。FIG. 3 is a diagram for explaining frequency characteristics related to electromagnetic wave absorption characteristics of an electromagnetic wave absorbing heat conductive sheet to which the present invention is applied.
　以下、本発明を実施するための形態について、図面を参照しながら詳細に説明する。なお、本発明は、以下の実施形態のみに限定されるものではなく、本発明の要旨を逸脱しない範囲内において種々の変更が可能であることは勿論である。 Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the present invention.
　本発明が適用された電磁波吸収性熱伝導シートは、電子機器内部の高周波信号が伝送する信号伝送部の近傍に配置されるものである。この電磁波吸収性熱伝導シートは、例えば、半導体パッケージなどの電子部品から、放熱板や、ヒートパイプ、ヒートシンク等といった放熱部品へ効率よく熱を伝え、かつ電磁波を吸収する。 The electromagnetic wave absorptive heat conductive sheet to which the present invention is applied is disposed in the vicinity of a signal transmission unit that transmits a high frequency signal inside an electronic device. This electromagnetic wave absorptive heat conductive sheet efficiently transfers heat from an electronic component such as a semiconductor package to a heat radiating component such as a heat radiating plate, a heat pipe, and a heat sink, and absorbs electromagnetic waves.
　＜熱伝導性シートが貼着される回路基板＞
　本発明が適用された電磁波吸収性熱伝導シートは、例えば図１Ａに示すような、電子機器１内部の回路基板１ａに貼着される。すなわち、図１Ａに示すような電磁波吸収性と熱伝導性とを有するシート１１は、高周波信号が伝送する高周波信号伝送基板１７と、高周波信号伝送基板１７が発熱する熱を放熱させる放熱金属板１２との間に配置される。具体的に、シート１１は、一方の面１１ａが高周波信号伝送基板１７を構成する半導体パッケージを封止する樹脂モールド１３と、他方の面１１ｂが放熱金属板１２とそれぞれ密着するように、回路基板１ａに貼着される。 <Circuit board to which the thermally conductive sheet is attached>
The electromagnetic wave absorptive heat conductive sheet to which the present invention is applied is attached to a circuit board 1a inside the electronic apparatus 1 as shown in FIG. 1A, for example. That is, the sheet 11 having electromagnetic wave absorption and thermal conductivity as shown in FIG. 1A includes a high-frequency signal transmission board 17 that transmits a high-frequency signal and a heat-dissipating metal plate 12 that dissipates heat generated by the high-frequency signal transmission board 17. Between. Specifically, the sheet 11 has a circuit board such that one surface 11a is in close contact with the resin mold 13 for sealing the semiconductor package constituting the high-frequency signal transmission substrate 17, and the other surface 11b is in close contact with the heat dissipation metal plate 12. Affixed to 1a.
　高周波信号伝送基板１７は、電子機器１内部の高周波信号が伝送する信号伝送部の具体例であって、誘電体基板１６の一方の面にＧＮＤ電極となる銅箔１５と、もう一方の面にパターニングにより構成された銅の信号線１４からなるものでマイクロストリップラインを構成している。 The high-frequency signal transmission substrate 17 is a specific example of a signal transmission unit that transmits a high-frequency signal inside the electronic device 1. The dielectric substrate 16 has a copper foil 15 serving as a GND electrode on one surface and a second surface. A microstrip line is constituted by the copper signal line 14 formed by patterning.
　高周波信号伝送基板１７は、不要輻射の影響が生じないようにするため、それ自体が動作した際の遠方電界強度が所定の値以下に抑制するように設計されている。このような高周波信号伝送基板１７を有する回路基板１ａでは、放熱金属板１２が、シート１１を介して対向する高周波信号伝送基板１７の信号線１４内を流れる電気信号の高調波成分を受けてしまい、高調波成分のアンテナとして機能し、結果的に遠方電界強度を増大させてしまう。シート１１には、放熱金属板１２がアンテナとして作用するのを抑制するとともに、良好な熱伝導特性を実現するため、シート１１に占める体積分率が所定の値以上になるように、磁性金属粒子が含有されている。 The high-frequency signal transmission board 17 is designed so that the far field strength when operating itself is suppressed to a predetermined value or less in order to prevent the influence of unnecessary radiation. In the circuit board 1 a having such a high-frequency signal transmission board 17, the heat radiating metal plate 12 receives a harmonic component of an electric signal flowing in the signal line 14 of the high-frequency signal transmission board 17 facing through the sheet 11. It functions as an antenna for harmonic components, and as a result, the far field strength is increased. In order to prevent the heat radiating metal plate 12 from acting as an antenna on the sheet 11 and to achieve good heat conduction characteristics, the magnetic metal particles are adjusted so that the volume fraction in the sheet 11 is equal to or greater than a predetermined value. Is contained.
　なお、本発明が適用された電磁波吸収性熱伝導の機能を有するシート１１は、例えば図１Ｂに示すように、放熱金属板１２に密着させないようにしてもよい。すなわち、図１Ｂに示すような使用をすることで、シート１１は、高周波信号伝送基板１７で発生する熱の放熱効率を悪化させることなく、高周波信号伝送基板１７から放出される電磁波を吸収することができる。 Note that the sheet 11 having an electromagnetic wave absorbing heat conduction function to which the present invention is applied may not be brought into close contact with the heat radiating metal plate 12 as shown in FIG. 1B, for example. 1B, the sheet 11 absorbs electromagnetic waves emitted from the high-frequency signal transmission board 17 without deteriorating the heat dissipation efficiency of the heat generated in the high-frequency signal transmission board 17. Can do.
　次に本発明が適用されたシート１１の具体的な構成について説明する。シート１１は、可撓性樹脂材料に、第１の磁性金属粒子と、第１の磁性金属粒子よりも平均粒径が小さく第１の磁性金属粒子よりも電気抵抗率が小さい第２の磁性金属粒子とが含有されたものである。 Next, a specific configuration of the sheet 11 to which the present invention is applied will be described. The sheet 11 includes a flexible resin material, a first magnetic metal particle, and a second magnetic metal having an average particle size smaller than that of the first magnetic metal particle and lower electrical resistivity than that of the first magnetic metal particle. It contains particles.
　このような構成からなるシート１１は、後述する性能評価から明らかなように、良好な熱伝導特性と良好な電磁波抑制特性とを両立することができる。 The sheet 11 having such a configuration can achieve both good heat conduction characteristics and good electromagnetic wave suppression characteristics, as is apparent from the performance evaluation described later.
　次に、電磁波吸収性熱伝導シートの実施例として、次のような条件で作成したシート１１を用いて、熱伝導特性と電磁波抑制効果について評価した。 Next, as an example of the electromagnetic wave absorbing heat conductive sheet, the sheet 11 prepared under the following conditions was used to evaluate the heat conduction characteristics and the electromagnetic wave suppression effect.
　まず、可撓性樹脂材料にシリコーン樹脂を、第１の磁性金属粒子に平均粒径が６μｍの球状磁性アモルファス合金を、第２の磁性金属粒子に平均粒径が１．５μｍの球状鉄粉を用いた。本実施の形態における「平均粒径」とは、具体的には、粉体を、ある粒子径から２つに分けたときに大きい側と小さい側が等量となるメディアン径（Ｄ５０ともいう。）によって定義される値であって、例えば当該実施例においては、レーザー回折・散乱法によって算出することができる。 First, a silicone resin is used for the flexible resin material, a spherical magnetic amorphous alloy having an average particle size of 6 μm is used for the first magnetic metal particles, and a spherical iron powder having an average particle size of 1.5 μm is used for the second magnetic metal particles. Using. The “average particle diameter” in the present embodiment specifically refers to the median diameter (also referred to as D50) in which the large side and the small side are equal when the powder is divided into two from a certain particle diameter. For example, in this embodiment, it can be calculated by a laser diffraction / scattering method.
　１００ｇのシリコーン樹脂に、カップリング剤を１０ｇ、球状磁性アモルファス合金を５０ｖｏｌ％、及び球状鉄粉を２４ｖｏｌ％加え、真空攪拌機にて攪拌した後に、１.５ｍｍ厚のシート形状にし、１００℃、３０分の環境下で硬化させて、電磁波吸収性熱伝導シートを作製した。 To 100 g of silicone resin, 10 g of a coupling agent, 50 vol% of spherical magnetic amorphous alloy, and 24 vol% of spherical iron powder were added, and after stirring with a vacuum stirrer, a 1.5 mm thick sheet was formed at 100 ° C., 30 It was made to harden | cure in the environment of minutes, and the electromagnetic wave absorptive heat conductive sheet was produced.
　ここで、実施例に係るシートでは、高周波信号から放出される電磁波の吸収性、例えば１ＧＨｚ帯以上での電磁波吸収性を実現するため、第１の磁性金属粒子として、電気抵抗率が０．５μΩｍ以上の材料を用いているが、平均粒径を大きくして充填性を高めるという観点から、特に電気抵抗率が０．８μΩｍ以上の材料を用いるのが好ましい。また、実施例に係るシートでは、第２の磁性金属粒子の電気抵抗率が、第１の磁性金属粒子よりも小さい０．５μΩｍを下回ればよいが、特に良好な熱伝導性を実現するためには０．３μΩｍ以下が好ましい。 Here, in the sheet according to the example, in order to realize the absorptivity of the electromagnetic wave emitted from the high-frequency signal, for example, the absorptivity of the electromagnetic wave in the 1 GHz band or more, as the first magnetic metal particle, the electrical resistivity is 0.5 μΩm. Although the above materials are used, it is particularly preferable to use a material having an electrical resistivity of 0.8 μΩm or more from the viewpoint of increasing the average particle size and improving the filling property. Further, in the sheet according to the example, the electrical resistivity of the second magnetic metal particles may be lower than 0.5 μΩm, which is smaller than that of the first magnetic metal particles, but in order to achieve particularly good thermal conductivity. Is preferably 0.3 μΩm or less.
　第１及び第２の磁性金属粒子としては、電気抵抗率の高い磁性金属アモルファス粒子が適している。磁性金属アモルファス粒子は、例えば、Ｆｅ－Ｓｉ－Ｂ系、Ｆｅ－Ｓｉ－Ｂ－Ｃ系、Ｃｏ－Ｓｉ－Ｂ系、Ｃｏ－Ｚｒ系、Ｃｏ－Ｎｂ系、Ｃｏ－Ｔａ系などがあげられるが、これらに限るものではない。 As the first and second magnetic metal particles, magnetic metal amorphous particles having a high electrical resistivity are suitable. Examples of the magnetic metal amorphous particles include Fe—Si—B, Fe—Si—B—C, Co—Si—B, Co—Zr, Co—Nb, and Co—Ta. However, it is not limited to these.
　なお、磁性金属アモルファスのみに限らず、結晶系、微結晶系の磁性材料を用いることもできる。結晶系の磁性金属としては、Ｆｅ系、Ｃｏ系、Ｎｉ系、あるいはＦｅ－Ｎｉ系、Ｆｅ－Ｃｏ系、Ｆｅ－Ａｌ系、Ｆｅ－Ｓｉ系、Ｆｅ－Ｓｉ－Ａｌ系、Ｆｅ－Ｎｉ－Ｓｉ－Ａｌ系などがあげられる。微結晶系の磁性金属としては、これら結晶系材料にＮ、Ｃ、Ｏ、Ｂ等を微量加えて微細結晶化させた材料である。 It should be noted that not only the magnetic metal amorphous but also crystalline and microcrystalline magnetic materials can be used. Crystalline magnetic metals include Fe, Co, Ni, or Fe—Ni, Fe—Co, Fe—Al, Fe—Si, Fe—Si—Al, Fe—Ni—Si. -Al type and the like. The microcrystalline magnetic metal is a material obtained by finely crystallizing these crystalline materials by adding a small amount of N, C, O, B or the like.
　実施例に係るシートでは、これらの複数の材料のうち、電気抵抗率が０．５μΩｍ以上で、球、多面体などの略球状の磁性粒子の少なくとも一種類以上を第１の磁性金属粒子とし、第１の磁性金属粒子よりも平均粒径が小さく、電気抵抗率が０．５μΩｍよりも小さい磁性粒子の少なくとも一種類以上を第２の磁性金属粒子として用いる。 In the sheet according to the example, among the plurality of materials, the electrical resistivity is 0.5 μΩm or more, and at least one kind of substantially spherical magnetic particles such as a sphere and a polyhedron is the first magnetic metal particle, As the second magnetic metal particle, at least one kind of magnetic particles having an average particle size smaller than that of one magnetic metal particle and an electrical resistivity smaller than 0.5 μΩm is used.
　また、第２の磁性金属粒子の平均粒径は、第１の磁性金属粒子径に対して粒径比率が５～５０％の範囲内であれば複数設定することができる。すなわち、第２の磁性金属粒子としては複数の材料、組成、粒径のものを組み合わせて使用することができる。 Also, the average particle diameter of the second magnetic metal particles can be set in plural if the particle diameter ratio is in the range of 5 to 50% with respect to the first magnetic metal particle diameter. That is, the second magnetic metal particles can be used in combination of a plurality of materials, compositions and particle sizes.
　また、実施例に係るシートでは、熱伝導率をあげるために、第２の磁性金属粒子の粉状体以外にアルミナ、窒化ホウ素、窒化珪素、窒化アルミ、炭化珪素などの熱伝導粒子を加えることもできる。このような熱伝導粒子は、第１の磁性金属粒子よりも小さい粒径のもので、形状も球形に近いものが望ましい。 In addition, in the sheet according to the example, in order to increase the thermal conductivity, in addition to the powder of the second magnetic metal particles, heat conductive particles such as alumina, boron nitride, silicon nitride, aluminum nitride, silicon carbide, etc. are added. You can also. Such heat conduction particles are preferably smaller in particle size than the first magnetic metal particles and have a shape close to a sphere.
　また、可撓性樹脂としては、例えば、エポキシ樹脂、フェノール樹脂、メラミン樹脂、ユリア樹脂、不飽和ポリエステル等の樹脂や、シリコーンゴム、ウレタンゴム、アクリルゴム、ブチルゴム、エチレンブロピレンゴム等のゴムが挙げられるが、これらに限定されない。また、実施例に係るシートでは、更に、難燃剤、反応調整剤、架橋剤、シランカップリング剤などの表面処理剤を適量加えて使うことができる。 Examples of the flexible resin include resins such as epoxy resin, phenol resin, melamine resin, urea resin, and unsaturated polyester, and rubber such as silicone rubber, urethane rubber, acrylic rubber, butyl rubber, and ethylene propylene rubber. For example, but not limited to. Moreover, in the sheet | seat which concerns on an Example, surface treatment agents, such as a flame retardant, a reaction regulator, a crosslinking agent, and a silane coupling agent, can be further added and used.
　このようにして作成したシートの性能を調べるために、複素比透磁率と熱伝導率を測定した。 In order to investigate the performance of the sheet thus prepared, the complex relative permeability and the thermal conductivity were measured.
　まず、複素比透磁率の測定は、次のようにして行った。作製したシートを外径２０ｍｍ、内径６ｍｍのリング形状に打ち抜いて測定用のサンプルを作製した。この測定用のサンプルを、アジレントテクノロジー社製の測定器「Ａｇｉｌｅｎｔ　４２９１Ｂ　ＲＦインピーダンス／マテリアル・アナライザ」を使用して複素比透磁率を測定した。 First, the complex relative permeability was measured as follows. The produced sheet was punched into a ring shape having an outer diameter of 20 mm and an inner diameter of 6 mm to produce a measurement sample. The complex relative permeability of this measurement sample was measured using a measuring instrument “Agilent 4291B RF Impedance / Material Analyzer” manufactured by Agilent Technologies.
　また、熱伝導率の測定は、次のようにして行った。作製したシートを１ｃｍ角程度の大きさに切り出し、この切り出したサンプルを金属性ヒートシンクと金属製ヒータケースの間に挟んで、１ｋｇｆの力で加圧して接触させた状態で、金属製ヒータケースに電力をかけて加熱する。金属製ヒータケースと金属性ヒートシンクの温度が一定になったところで、この間の温度差を計測した。熱伝導率は下記の式より算出した。 Moreover, the measurement of thermal conductivity was performed as follows. The produced sheet is cut into a size of about 1 cm square, and the cut sample is sandwiched between a metal heat sink and a metal heater case, and is pressed into contact with a force of 1 kgf. Heat with power. When the temperature of the metal heater case and the metal heat sink became constant, the temperature difference between them was measured. The thermal conductivity was calculated from the following formula.
　熱伝導率＝（電力×サンプル厚み）／（温度差×測定面積）
　上記のような測定により、図２に示すような複素比透磁率の測定結果が得られた。すなわち、図２は、複素比透磁率の虚数部の測定結果を示すものである。複素比透磁率の虚数部は、透磁率の磁気損失項であるため、磁気吸収特性の評価指標として用いることができる。図２から明らかなように、２ＧＨｚを中心に大きな磁気損失がみられる。 Thermal conductivity = (power × sample thickness) / (temperature difference × measurement area)
The measurement result of the complex relative permeability as shown in FIG. 2 was obtained by the above measurement. That is, FIG. 2 shows the measurement result of the imaginary part of the complex relative permeability. Since the imaginary part of the complex relative permeability is a magnetic loss term of permeability, it can be used as an evaluation index of magnetic absorption characteristics. As is clear from FIG. 2, a large magnetic loss is observed around 2 GHz.
　このような、磁性金属材料の高周波での磁気損失は、主に渦電流損失と強磁性共鳴による損失がある。 Such magnetic loss at high frequencies of magnetic metal materials mainly includes eddy current loss and loss due to ferromagnetic resonance.
　このうち、強磁性共鳴は、磁性材料の飽和磁化が高いほど、そのピーク周波数が高周波側にずれる。これは、初透磁率をμｉ、共鳴周波数をｆｒ、及び飽和磁化をＩｓとしたとき、（μｉ－１）ｆｒとＩｓとが比例関係にあるからである。このように磁性粒子を高充填したシート状の成型品では、磁性粒子間の磁気的結合により反磁界の影響が激減し、透磁率が高くなり、共鳴周波数が低い周波数側へずれるが、磁性体の飽和磁化が１００Ａ・ｍ２／ｋｇ以上では、共鳴周波数をＧＨｚ帯域にもっていくことができる。このため、この共鳴周波数よりも低い周波数帯では渦電流損失が磁気損失の主体となる。参考文献としては、久村、久保、加藤：「電磁ノイズ抑制熱伝導シート」、第３３回日本磁気学会学術講演会概要集、１４ｐＦ－１４、（２００９）が挙げられる。 Of these, the peak frequency of ferromagnetic resonance shifts to the high frequency side as the saturation magnetization of the magnetic material increases. This is because (μ i −1) fr is proportional to Is, where μ i is the initial permeability, fr is the resonance frequency, and Is is the saturation magnetization. In such a sheet-like molded product highly filled with magnetic particles, the influence of the demagnetizing field is greatly reduced due to the magnetic coupling between the magnetic particles, the magnetic permeability is increased, and the resonance frequency is shifted to the lower frequency side. When the saturation magnetization is 100 A · m 2 / kg or more, the resonance frequency can be brought to the GHz band. For this reason, in the frequency band lower than the resonance frequency, eddy current loss becomes the main magnetic loss. References include Hisamura, Kubo, Kato: “Electromagnetic Noise Suppressing Thermal Conductive Sheet”, Summary of the 33rd Annual Meeting of the Magnetic Society of Japan, 14pF-14, (2009).
　また、球状磁性金属粒子での渦電流損失による透磁率の劣化は、ミーの散乱をベースにした複素渦電流ファクタ（Ｒ．Ｒａｍｐｒａｓａｄ　ａｎｄ　ｅｔ　ａｌ：　Ｊ．Ａｐｐｌ．Ｐｈｕｓ，９６５１９（２００４)）を評価指標として用いることができる。 Moreover, the deterioration of the magnetic permeability due to the eddy current loss in the spherical magnetic metal particles was evaluated by a complex eddy current factor (R. Ramprasad and et al: J. Appl. Phus, 96519 (2004)) based on Mie's scattering. It can be used as an indicator.
　図３は、球状磁性金属粒子での渦電流損失による透磁率の劣化を評価するため、球状磁性金属粒子の平均粒径６μｍ、初透磁率μｉを４０として、電気抵抗率を変えた場合の複素比透磁率の虚部μｒ”の周波数特性を計算したものである。 FIG. 3 shows a case where the electrical resistivity is changed with the average particle diameter of the spherical magnetic metal particles being 6 μm and the initial permeability μ i being 40 in order to evaluate the deterioration of the magnetic permeability due to the eddy current loss in the spherical magnetic metal particles. The frequency characteristic of the imaginary part μ r ″ of the complex relative permeability is calculated.
　ここでは、複素比透磁率の虚部μｒ”は初透磁率μｉで規格化して示している。図３から明らかなように、電気抵抗率が低いと磁気損失が低周波側に大きくずれていく。平均粒径が６μｍの球状磁性金属粒子を用いたシートでは、磁気損失のピークをＧＨｚ帯にもっていくために、電気抵抗率が０．５μΩｍ以上でなければならない。 Here, the imaginary part μ r ″ of the complex relative permeability is shown normalized by the initial permeability μ i . As is apparent from FIG. 3, when the electrical resistivity is low, the magnetic loss greatly shifts to the low frequency side. In a sheet using spherical magnetic metal particles having an average particle diameter of 6 μm, the electric resistivity must be 0.5 μΩm or more in order to bring the peak of magnetic loss to the GHz band.
　また、電気抵抗率が０．５μΩｍ、平均粒径が６μｍ、初透磁率μｉが４０の磁性金属粒子を用いたシートと同等な周波数特性を得るためには、電気抵抗率が１．１μΩｍ、０．９μΩｍ、０．１μΩｍの磁性金属粒子を用いたシートでは、それぞれ平均粒径を９μｍ、８μｍ、２．８μｍにする必要がある。このように、電気抵抗率の高い材料であれば、粒径を大きくしても良好な高周波帯域の電磁波を吸収する周波数特性を得ることができ、電気抵抗率の低い材料であれば、粒径を小さくしなければ、良好な高周波帯域の電磁波を吸収する周波数特性を得ることができない。 In addition, in order to obtain frequency characteristics equivalent to a sheet using magnetic metal particles having an electrical resistivity of 0.5 μΩm, an average particle size of 6 μm, and an initial permeability μ i of 40, the electrical resistivity is 1.1 μΩm, In the sheet using magnetic metal particles of 0.9 μΩm and 0.1 μΩm, the average particle diameter needs to be 9 μm, 8 μm and 2.8 μm, respectively. Thus, if the material has a high electrical resistivity, it is possible to obtain a frequency characteristic that absorbs electromagnetic waves in a good high frequency band even if the particle size is increased, and if the material has a low electrical resistivity, the particle size Unless it is made small, it is impossible to obtain frequency characteristics that absorb electromagnetic waves in a good high frequency band.
　実施例に係るシートでは、上記のような高周波帯域の電磁波を吸収する周波数特性を実現するため、次の点を考慮して、平均粒径の異なる磁性金属粒子を可撓性樹脂材料に高充填させる。 In the sheet according to the example, in order to realize the frequency characteristics of absorbing electromagnetic waves in the high frequency band as described above, the flexible resin material is highly filled with magnetic metal particles having different average particle diameters in consideration of the following points. Let
　まず、磁性金属粒子の作製によく使われている方法としてアトマイズ法があるが、作製できる粒子径は一般的に数μｍ～数十μｍであり、商業的にラインナップされている材料の最小粒径は約５～６μｍである。 First, the atomization method is often used for the production of magnetic metal particles. The particle size that can be produced is generally several μm to several tens of μm, which is the minimum particle size of commercially available materials. Is about 5-6 μm.
　したがって、ＧＨｚ帯での電磁波吸収を目的とした電磁波吸収性シートの磁性金属粒子として、例えば平均粒径５～６μｍの粒子を使う場合、電気抵抗率０．５μΩｍ以上の材料を用いる必要がある。 Therefore, for example, when using particles having an average particle diameter of 5 to 6 μm as magnetic metal particles of the electromagnetic wave absorbing sheet for the purpose of absorbing electromagnetic waves in the GHz band, it is necessary to use a material having an electrical resistivity of 0.5 μΩm or more.
　このようなＧＨｚ帯での電磁波吸収を目的とした材料を第１の磁性金属材料として、さらに平均粒径の小さい磁性金属粒子を第２の磁性金属材料として、第１の磁性金属材料の間に充填するように配置すると、粒子全体の充填率を向上させることができる。 Such a material intended to absorb electromagnetic waves in the GHz band is used as the first magnetic metal material, and magnetic metal particles having a small average particle diameter are used as the second magnetic metal material. If it arrange | positions so that it may fill, the filling rate of the whole particle | grain can be improved.
　特に、第２の磁性金属粒子の粒径は、第１の磁性金属粒子の平均粒径に対して、５～５０％の大きさを用い、また第１の磁性金属粒子に対し第２の磁性金属粒子の混合比率が１０～６０ｖｏｌ％にすることで、可撓性樹脂に占める磁性金属粒子の充填を高くすることができる。 In particular, the particle size of the second magnetic metal particles is 5 to 50% of the average particle size of the first magnetic metal particles, and the second magnetic metal particles have a second magnetic particle size relative to the first magnetic metal particles. When the mixing ratio of the metal particles is 10 to 60 vol%, the filling of the magnetic metal particles in the flexible resin can be increased.
　ここで、第２の磁性金属粒子は、粒径が小さいため渦電流損失の影響を受けにくいので電気抵抗率を高くする必要はなく、熱伝導率を高くするという観点から電気抵抗率の小さなものが選択される。これは、金属における自由電子の移動が熱伝導率に影響するため、電気伝導度の高い、つまり電気抵抗率の小さい金属材料の方が熱伝導率を高くできるからである。 Here, since the second magnetic metal particles are small in size and are not easily affected by eddy current loss, it is not necessary to increase the electrical resistivity, and from the viewpoint of increasing the thermal conductivity, the second magnetic metal particles have a small electrical resistivity. Is selected. This is because the movement of free electrons in the metal affects the thermal conductivity, so that a metal material having a higher electrical conductivity, that is, a lower electrical resistivity can increase the thermal conductivity.
　良好な高周波数帯域での電磁波吸収性と熱伝導性とを両立するため、上記の実施例では、電気抵抗率が１．１μΩｍ、平均粒径が６μｍの球状磁性アモルファス合金を第１の磁性金属粒子として選択し、電気抵抗率が０．１５μΩｍ、平均粒径が１．５μｍの球状鉄粉を第２の磁性金属粒子として選択している。このため、実施例に係るシートでは、図３に示されるようなＧＨｚ帯域で大きな磁気損失が得られ、良好な電磁ノイズ抑制効果が実現できる。 In order to achieve both good electromagnetic wave absorptivity and thermal conductivity in a high frequency band, in the above embodiment, a spherical magnetic amorphous alloy having an electrical resistivity of 1.1 μΩm and an average particle size of 6 μm is used as the first magnetic metal. A spherical iron powder having an electrical resistivity of 0.15 μΩm and an average particle size of 1.5 μm is selected as the second magnetic metal particle. For this reason, in the sheet | seat which concerns on an Example, a big magnetic loss is obtained in a GHz band as shown in FIG. 3, and the favorable electromagnetic noise suppression effect is realizable.
　また、実施例に係るシートでは、熱伝導率も２．０Ｗ／ｍ・Ｋと高く、優れた熱伝導特性を併せ持つ。 In addition, the sheet according to the example has a high thermal conductivity of 2.0 W / m · K, and has excellent thermal conductivity characteristics.
　ここで、比較対象として実施例と同組成のアモルファス粉を磁性金属粒子に用いて、平均粒径が１０μｍ、３μｍの粒子を、それぞれ実施例と同様に５０ｖｏｌ％、２４ｖｏｌ％配合して作製したシートの熱伝導率について評価する。比較対象に係るシートの熱伝導率は、１．７１Ｗ／ｍ・Ｋであった。このような比較対象に係るシートと比べて、実施例に係るシート１１は、第２の磁性金属粒子として、アモルファス粉より電気抵抗率の低い鉄粉を使うことで、１８％程度、熱伝導率を向上させることができた。 Here, as an object for comparison, a sheet prepared by using amorphous powder having the same composition as that of the examples for the magnetic metal particles and blending particles having an average particle size of 10 μm and 3 μm in the same manner as in the examples of 50 vol% and 24 vol%, respectively. The thermal conductivity of is evaluated. The thermal conductivity of the sheet according to the comparison target was 1.71 W / m · K. Compared with the sheet according to the comparison object, the sheet 11 according to the example uses about 18% of the thermal conductivity as the second magnetic metal particle by using iron powder having a lower electrical resistivity than the amorphous powder. Was able to improve.
　このように、実施例に係るシートでは、高周波数帯域での電磁波吸収性を実現する観点から表皮効果を抑制するために、第１の磁性金属粒子に電気抵抗率の高い材料を用いても、第２の磁性金属粒子に電気抵抗率の低い材料を用いることで、完成品シートの熱伝導率を大きく向上させることができる。 Thus, in the sheet according to the example, in order to suppress the skin effect from the viewpoint of realizing electromagnetic wave absorbency in a high frequency band, even if a material having a high electrical resistivity is used for the first magnetic metal particles, By using a material having a low electrical resistivity for the second magnetic metal particles, the thermal conductivity of the finished product sheet can be greatly improved.
　以上のようにして、本発明が適用された電磁波吸収性熱伝導シートは、可撓性樹脂材料に、第１の磁性金属粒子と、第１の磁性金属粒子よりも平均粒径が小さく第１の金属粒子よりも電気抵抗率が小さい第２の磁性金属粒子とが含有しているので、熱伝導特性と電磁波抑制特性との両者の機能が良好な熱伝導性シートを提供することができる。さらに、高い熱伝導性と高い電磁波抑制効果を有していながら、かつフレキシブル性も兼ね備えた電磁波抑制放熱シートを提供することができる。 As described above, the electromagnetic wave absorptive heat conductive sheet to which the present invention is applied has the first magnetic metal particles and the first magnetic metal particles having a smaller average particle size than the first magnetic metal particles. Since the second magnetic metal particles having an electric resistivity smaller than that of the metal particles are contained, it is possible to provide a heat conductive sheet having both functions of heat conduction characteristics and electromagnetic wave suppression characteristics. Furthermore, it is possible to provide an electromagnetic wave suppressing and radiating sheet having high thermal conductivity and a high electromagnetic wave suppressing effect and also having flexibility.
　特に、電磁波吸収性熱伝導シートは、第１の磁性金属粒子の電気抵抗率が０．５μΩｍ以上の材料を選択し、第２の磁性金属粒子の電気抵抗率が０．５μΩｍより小さい材料を選択することで、ＧＨｚ帯域が伝送される信号伝送部から放射される電磁波を効率よく吸収しつつ、良好な熱伝導性を得ることができる。 In particular, for the electromagnetic wave absorbing heat conductive sheet, a material in which the electrical resistivity of the first magnetic metal particles is 0.5 μΩm or more is selected, and a material in which the electrical resistivity of the second magnetic metal particles is less than 0.5 μΩm is selected. By doing so, it is possible to obtain good thermal conductivity while efficiently absorbing the electromagnetic wave radiated from the signal transmission unit transmitting the GHz band.
　１　電子機器、１ａ　回路基板、１１　シート、１２　放熱金属板、１３　樹脂モールド、１４　信号線、１５　銅箔、１６　誘電体基板、１７　高周波信号伝送基板 1 Electronic device, 1a circuit board, 11 sheet, 12 heat dissipation metal plate, 13 resin mold, 14 signal lines, 15 copper foil, 16 dielectric substrate, 17 high frequency signal transmission board

Claims (5)

  1. 　電子機器内部の高周波信号が伝送する信号伝送部の近傍に配置される電磁波吸収性熱伝導シートにおいて、
    　可撓性樹脂材料に、第１の磁性金属粒子と、該第１の磁性金属粒子よりも平均粒径が小さく該第１の磁性金属粒子よりも電気抵抗率が小さい第２の磁性金属粒子とを含有することを特徴とする電磁波吸収性熱伝導シート。     In the electromagnetic wave absorptive heat conductive sheet disposed in the vicinity of the signal transmission unit that transmits high frequency signals inside the electronic device
    The flexible resin material includes first magnetic metal particles, and second magnetic metal particles having an average particle size smaller than the first magnetic metal particles and smaller electric resistivity than the first magnetic metal particles, An electromagnetic wave absorptive heat conductive sheet comprising:
  2. 　上記信号伝送部は、１ＧＨｚより高い高周波信号が伝送し、
    　上記第１の磁性金属粒子は、その電気抵抗率が０．５μΩｍ以上で、
    　上記第２の磁性金属粒子は、その電気抵抗率が０．５μΩｍより小さいことを特徴とする請求項１記載の電磁波吸収性熱伝導シート。     The signal transmission unit transmits a high frequency signal higher than 1 GHz,
    The first magnetic metal particle has an electrical resistivity of 0.5 μΩm or more,
    2. The electromagnetic wave absorbing heat conductive sheet according to claim 1, wherein the second magnetic metal particles have an electrical resistivity smaller than 0.5 [mu] [Omega] m.
  3. 　上記第１の磁性金属粒子は、球状の粒子であることを特徴とする請求項１記載の電磁波吸収性熱伝導シート。 The electromagnetic wave-absorbing heat conductive sheet according to claim 1, wherein the first magnetic metal particles are spherical particles.
  4. 　上記第１の磁性金属粒子に対する上記第２の磁性金属粒子の混合比率が、１０～６０ｖｏｌ％であり、かつ、該第１の磁性金属粒子に対する該第２の磁性金属粒子の粒径比率が５～５０％であることを特徴とする請求項３記載の電磁波吸収性熱伝導シート。 The mixing ratio of the second magnetic metal particles to the first magnetic metal particles is 10 to 60 vol%, and the particle size ratio of the second magnetic metal particles to the first magnetic metal particles is 5 The electromagnetic wave absorptive heat conductive sheet according to claim 3, characterized in that it is -50%.
  5. 　高周波信号が伝送する信号伝送部と、
    　上記信号伝送部の近傍に配置される電磁波吸収性熱伝導シートとを備え、
    　上記電磁波吸収性熱伝導シートは、可撓性樹脂材料に、第１の磁性金属粒子と、該第１の磁性金属粒子よりも平均粒径が小さく該第１の磁性金属粒子よりも電気抵抗率が小さい第２の磁性金属粒子とを含有することを特徴とする電子機器。     A signal transmission unit for transmitting high-frequency signals;
    An electromagnetic wave absorptive heat conductive sheet disposed in the vicinity of the signal transmission unit,
    The electromagnetic wave absorptive heat conductive sheet comprises a flexible resin material, first magnetic metal particles, and an electrical resistivity lower than that of the first magnetic metal particles, having an average particle size smaller than that of the first magnetic metal particles. And a second magnetic metal particle having a small diameter.
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CN115335487B (en) * 2020-03-31 2024-03-08 3M创新有限公司 Heat-conducting electromagnetic absorbing material

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