WO2011101989A1 - Thermally conductive sheet - Google Patents

Thermally conductive sheet Download PDF

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Publication number
WO2011101989A1
WO2011101989A1 PCT/JP2010/052643 JP2010052643W WO2011101989A1 WO 2011101989 A1 WO2011101989 A1 WO 2011101989A1 JP 2010052643 W JP2010052643 W JP 2010052643W WO 2011101989 A1 WO2011101989 A1 WO 2011101989A1
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Prior art keywords
sheet
magnetic metal
particles
heat conductive
heat
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PCT/JP2010/052643
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French (fr)
Japanese (ja)
Inventor
佑介 久保
久村　達雄
義寛 加藤
鈴木　和彦
Original Assignee
ソニーケミカル＆インフォメーションデバイス株式会社
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Priority to CN201080064549.7A priority Critical patent/CN102763216B/en
Priority to KR1020127024765A priority patent/KR101511417B1/en
Priority to PCT/JP2010/052643 priority patent/WO2011101989A1/en
Publication of WO2011101989A1 publication Critical patent/WO2011101989A1/en

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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
    • H05K7/00—Constructional details common to different types of electric apparatus
    • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
    • 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
    • H05K7/00—Constructional details common to different types of electric apparatus
    • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
    • H05K7/2039—Modifications to facilitate cooling, ventilating, or heating characterised by the heat transfer by conduction from the heat generating element to a dissipating body
    • H05K7/20436—Inner thermal coupling elements in heat dissipating housings, e.g. protrusions or depressions integrally formed in the housing
    • H05K7/20445—Inner thermal coupling elements in heat dissipating housings, e.g. protrusions or depressions integrally formed in the housing the coupling element being an additional piece, e.g. thermal standoff
    • H05K7/20472—Sheet interfaces
    • H05K7/20481—Sheet interfaces characterised by the material composition exhibiting specific thermal properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
    • H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
    • H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
    • H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
    • H01L23/3737—Organic materials with or without a thermoconductive filler
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/552—Protection against radiation, e.g. light or electromagnetic waves
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/0001—Technical content checked by a classifier
    • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Definitions

  • the present invention relates to a heat conductive sheet disposed between an electronic component such as a semiconductor package and a metal heat dissipating member that dissipates heat generated by the electronic component.
  • heat dissipation plate, a heat pipe, a heat sink, or the like made of a metal material having high thermal conductivity such as copper or aluminum is widely used.
  • These heat dissipating parts having excellent thermal conductivity are arranged 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 achieve a heat dissipation effect or temperature relaxation in the device.
  • 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 large electric field strength or magnetic field strength that can be a component of unwanted radiation. For this reason, when a heat dissipating part made of metal is disposed in the vicinity of an electronic part, there are often cases where a harmonic component of an electric signal flowing in the electronic part is picked up together with heat.
  • the heat dissipating part is made of a metal material, a phenomenon occurs in which the heat dissipating part itself functions as a harmonic component antenna or a harmonic noise component transmission path.
  • a thermal conductive sheet containing a magnetic material in order to suppress the heat radiation component from acting 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 heat conductive sheet having the functions of both the heat conduction characteristics and the electromagnetic wave suppression characteristics described above vary 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. Rate.
  • 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)
  • 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 volume ratio of the magnetic material [nu 2 is the base material The volume ratio.
  • 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.
  • a conventional heat conductive sheet having an electromagnetic wave suppressing function flat magnetic powder or crushed magnetic powder is used as a magnetic material.
  • the present invention has been proposed in view of such a situation, and by achieving high packing of magnetic metal particles and thermally conductive particles having higher thermal conductivity than magnetic metal particles, An object is to provide a heat conductive sheet having both functions of electromagnetic wave suppression characteristics.
  • Means for Solving the Problems As described above, in order to increase the filling amount of both the magnetic metal particles and the heat conductive particles for the purpose of suppressing electromagnetic waves while having high heat conduction characteristics, the inventor Have invented the following thermal conductive sheet. That is, the present invention provides a heat conductive sheet disposed between an electronic component and a metal heat dissipating member that dissipates heat generated by the electronic component.
  • the volume ratio is 55 vol% or more.
  • the magnetic metal particles, which are electromagnetic wave absorbing materials have a spherical shape, and the average particle diameter of the magnetic metal particles is larger than the average particle diameter of the heat conductive particles, thereby making the magnetic metal particles and the heat conductive It is possible to increase the filling with particles, and furthermore, the value of the imaginary part of the complex relative permeability can be increased with increasing the filling of magnetic metal particles, so both functions of heat conduction characteristics and electromagnetic wave suppression characteristics A good heat conductive sheet can be provided.
  • FIG. 1 is a diagram showing a configuration of a circuit board on which a thermally conductive sheet to which the present invention is applied is mounted.
  • FIG. 2 is a graph showing the frequency characteristics of the far field strength in the circuit board.
  • FIG. 3 is a graph showing the frequency characteristics of the far field strength in the circuit board according to the characteristics of the heat conductive sheet.
  • FIG. 4 is a graph showing the change of the imaginary part of the complex relative permeability at 500 MHz according to the volume ratio of spherical Sendust and spherical amorphous (Fe—Si—B—Cr) as magnetic metal particles.
  • FIG. 5 is a graph in which the relationship between the filling amount of the thermally conductive material in the sheet and the thermal conductivity of the entire sheet is calculated.
  • the thermally conductive sheet to which the present invention is applied is disposed between an electronic component such as a semiconductor package and a metal heat radiating member that radiates heat generated by the electronic component.
  • a heat conductive sheet to which the present invention is applied is attached to a circuit board 1 as shown in FIG. That is, the heat conductive sheet 11 shown in FIG.
  • the heat conductive sheet 11 has a circuit in which one surface 11a is in close contact with the resin mold 13 for sealing the semiconductor package constituting the high-frequency substrate 17, and the other surface 11b is in close contact with the heat radiating metal plate 12. Affixed to the substrate 1.
  • the high-frequency substrate 17 comprises a copper foil 15 serving as a GND electrode on one surface of the dielectric substrate 16 and a copper signal line 14 formed by patterning on the other surface to constitute a microstrip line. .
  • the high-frequency substrate 17 is designed so that the far field intensity 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 picks up harmonic components of the electric signal flowing in the signal line 14 of the high-frequency substrate 17 opposed via the heat conductive sheet 11, It functions as an antenna for harmonic components, resulting in an increase in the far field strength.
  • the thermally conductive sheet 11 contains spherical magnetic metal particles so that the volume ratio of the sheet occupies a predetermined value or more.
  • the heat conductive sheet 11 contains the heat conductive particle whose heat conductivity is higher than a spherical magnetic metal particle.
  • FIG. 2 compares the frequency characteristics of the far field strength with and without the heat radiating metal plate 12 with the heat conductive sheet 11 omitted in the circuit board 1.
  • FIG. 2 when the heat radiating metal plate 12 is laminated on the high frequency substrate 17 without the heat conductive sheet 11 interposed, due to electromagnetic coupling between the high frequency substrate 17 and the heat radiating metal plate 12. Parallel plate resonance occurs, and the electric field is radiated at a frequency corresponding to the resonance.
  • strong electric field radiation is observed when the frequency of the harmonics transmitted from the high-frequency substrate 17 is in the vicinity of 1.1 [GHz] and 2.1 [GHz].
  • FIG. 3 shows a distant view when the real part of the complex relative permeability of the heat conductive sheet 11 is fixed to 10 and only the value of the imaginary part is changed in the state including the heat conductive sheet 11 in the circuit board 1.
  • the frequency characteristics of electric field strength are compared. Comparing the analysis results of FIG. 2 and FIG. 3, the peak of the radiated electric field intensity can be suppressed when the value of the imaginary part is 1, but the radiated electric field intensity is increased over the entire frequency as compared with the result without the radiating metal plate of FIG. high.
  • the value of the imaginary part is 3
  • the radiated electric field peak of the frequency described above is completely suppressed, and the electric field strength characteristic is almost equivalent to the result without the radiating metal plate in FIG. 2 over the entire frequency.
  • the value of the imaginary part is 5
  • the radiation electric field strength further decreases.
  • the larger the complex relative permeability imaginary part of the thermal conductive sheet the greater the reduction effect on the radiation electric field.
  • the value of the imaginary part is 3 or more
  • the heat conductive sheet 11 can remove the influence of parallel plate resonance, and even if the heat radiating metal plate 12 is brought close to the high frequency substrate 17, it does not increase unnecessary radiation. Can be.
  • a change in magnetic characteristics according to the filling amount of the magnetic metal particles in the heat conductive sheet 11 will be described.
  • a specific example will be described using a sheet in which the following two kinds of magnetic metal particles are actually filled in a range of 20 vol% to 70 vol%.
  • FIG. 4 shows the change in the imaginary part of the complex relative permeability at 500 MHz according to the volume fraction of spherical sendust and spherical amorphous (Fe—Si—B—Cr) as magnetic metal particles.
  • Spherical magnetic metal particles have a low magnetic permeability as compared with flat magnetic metal particles, but have high dispersibility and can be highly filled. Further, as apparent from FIG. 4, as the volume ratio of the magnetic metal particles increases, the magnetic permeability of the entire sheet also increases. Therefore, the spherical magnetic metal particles can be highly filled in the sheet, and as a result, high magnetic permeability and high thermal conductivity can be realized.
  • the thermal conductive sheet 11 is filled with spherical magnetic metal particles at 55 vol% or more, so that unnecessary radiation is not increased even if the heat radiating metal plate 12 is brought close to the high frequency substrate 17.
  • the change of the heat conductivity according to the filling amount of the heat conductive material in the heat conductive sheet 11 is demonstrated. According to the Bruggeman equation, the thermal conductivity has the following relationship.
  • FIG. 5 shows a graph in which the relationship between the filling amount of the thermally conductive material in the sheet and the thermal conductivity of the entire sheet is calculated using the above Bruggeman equation.
  • the thermal conductivity of the base polymer material was 0.2 W / mK
  • the thermal conductivity of the thermally conductive material was 10, 30, 50, and 70 W / mK.
  • the heat conductive sheet 11 contains both the magnetic metal particles having high magnetic properties and the heat conductive particles having higher heat conductivity than the magnetic metal particles as the heat conductive material, the inclusion thereof. Due to the ratio, the thermal conductivity when virtually regarded as one type of thermal conductive material changes. For this reason, although the thermal conductivity changes according to the content ratio, as is clear from FIG. 5, the thermal conductivity of the entire sheet increases monotonously with the increase in the filling amount of the thermal conductive material, When the filling amount of the conductive material is about 65% or more, the thermal conductivity of the entire sheet also increases rapidly. In particular, in order to realize high thermal conductivity in the entire sheet, it is desirable that the thermal conductive material is filled so as to be 70 vol% or more.
  • the inventors of the present application conducted research on the optimal blending to achieve good heat conduction characteristics and good electromagnetic wave suppression simultaneously using spherical magnetic powder. It has been found that it is necessary to contain 55 vol% or more of magnetic metal particles with respect to a flexible resin such as silicon resin in order to satisfy the good characteristics of the heat conductive sheet 11. Further, as the heat conductive material, 3 vol% or more of heat conductive particles having higher heat conductivity than the magnetic metal particles are contained, and 70 vol% or more in total of the magnetic metal particles and the heat conductive particles. It has been found that it is preferable from the viewpoint of increasing the thermal conductivity of the thermal conductive sheet 11.
  • the thermally conductive sheet 11 includes spherical magnetic metal particles that are electromagnetic wave absorbing materials that absorb electromagnetic waves emitted from electronic components such as the high-frequency substrate 17 and thermally conductive particles that have higher thermal conductivity than the magnetic metal particles. It consists of the flexible resin to contain, the average particle diameter of a magnetic metal particle is larger than the average particle diameter of a heat conductive particle, and the volume ratio of the magnetic metal particle which occupies for this heat conductive sheet 11 is 55 vol% or more.
  • the heat conductive sheet 11 having such a configuration enables high filling of magnetic metal particles and heat conductive particles, and further, the imaginary number of the complex relative magnetic permeability in the sheet as the magnetic metal particles increase. Since the value of the portion can be increased, it is possible to achieve good heat conduction characteristics and electromagnetic wave suppression effects. Moreover, the heat conductive sheet 11 contains a heat conductive particle having a volume fraction of 3 vol% or more, and thus has a higher heat conduction characteristic than a heat conductive sheet using, for example, flat magnetic metal particles. Can be realized. The heat conductive sheet 11 is filled with magnetic metal particles and heat conductive particles so that the sum of the volume ratios is 70 vol% or more, thereby realizing particularly good heat conduction characteristics and electromagnetic wave suppression effect. can do.
  • the heat conductive sheet 11 adjusts the average particle diameter ratio between the magnetic metal particles and the heat conductive particles, thereby making use of the good dispersibility of the spherical magnetic metal particles to Magnetic metal particles and thermally conductive particles can be contained so that the sum is about 80 vol% at maximum. Further, the heat conductive sheet 11 realizes good heat conduction characteristics and electromagnetic wave suppression characteristics regardless of the presence or absence of the coupling treatment, but contains a coupling agent that performs the coupling treatment on the heat conductive particles. Therefore, dispersibility in the sheet is improved, and particularly good heat conduction characteristics can be realized.
  • the thermal conductive sheet 11 is filled with a plurality of types of thermal conductive particles having a higher thermal conductivity than the magnetic metal particles, thereby maintaining various thermal conductivity and electromagnetic wave suppression characteristics while maintaining various heat The characteristics can be easily changed by adjusting the filling amount of the conductive particles.
  • the heat conductive sheet 11 is formed by containing the following particulate powder in a flexible resin such as a silicon resin. That is, the thermal conductive sheet 11 is boron (B) or carbon (C), which has good permeability characteristics and is relatively easy to produce as magnetic metal particles satisfying the requirements of the above-mentioned electromagnetic wave suppression characteristics from the viewpoint of powder production. It contains magnetic metal amorphous powder to which etc. are added.
  • the magnetic metal amorphous powder examples include Fe—Si—B, Fe—Si—B—C, Co—Si—B, Co—Zr, Co—Nb, and Co—Ta.
  • the magnetic metal particles contained in the heat conductive sheet 11 are not limited to the above-described magnetic metal amorphous, but may be, for example, crystalline magnetic powder such as spherical sendust. That is, as crystallized metal powder and metal alloy powder, Fe-based, Co-based, Ni-based, Fe-Ni-based, Fe-Co-based, Fe-Al-based, Fe-Si-based, Fe-Si-Al-based, etc.
  • a microcrystalline material refined by adding a small amount of N, C, or O may be used as the magnetic metal particles.
  • the thermally conductive sheet 11 increases the thermal conductivity of the sheet, so that the thermally conductive particles having higher thermal conductivity than the magnetic metal particles are alumina, boron nitride, silicon nitride, nitride It contains highly thermally conductive ceramics such as aluminum and silicon carbide, and powders of copper and aluminum coated with an insulator.
  • the heat conductive particles are not limited to those described above, and any material having a higher thermal conductivity than the magnetic metal particles may be used. In particular, particles having an average particle size smaller than that of the magnetic metal particles are used.
  • Example 1 Next, as Example 1 of the heat conductive sheet 11, the following sheets A to D were used to evaluate the heat conduction characteristics and the electromagnetic wave suppression effect. ⁇ Sheet A> Sheet A was produced as follows.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 21 g of a coupling agent for applying a coupling treatment to the thermally conductive particles were used as a flexible resin material.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 35 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 66 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 18 g of a coupling agent for applying a coupling treatment to the thermally conductive particles were used as a flexible resin material.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 13 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 5.3 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 5.3 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material.
  • the imaginary part ⁇ ′′ of the complex relative permeability was measured under the following conditions. That is, with respect to a sample prepared by punching each sheet into a ring-shaped body having an outer diameter of 20 mm and an inner diameter of 6 mm, the measurement frequency “Agilent 4291B RF Impedance / Material Analyzer” manufactured by Agilent Technologies, Inc. The imaginary part of the complex relative permeability at 500 MHz was measured. In addition, the thermal conductivity was calculated under the following conditions as an evaluation index of thermal conductivity characteristics.
  • each sheet is cut into a size of about 1 cm square, sandwiched between a metal heat sink and a metal heater case, pressed and contacted with a force of 1 kgf, and heated by applying electric power to the metal heater case. Then, when the temperature of the metallic heater case and the metallic heat sink became constant, the temperature difference between them was measured.
  • the imaginary part ⁇ ′′ of the complex relative permeability measured under the above conditions and the calculated thermal conductivity are shown in the following Table 1. In Table 1, the thickness of the sheet, the volume ratio of the magnetic metal particles, and the thermal conductivity are shown. The volume ratio of the active particles.
  • the sheets A to D have an imaginary part ⁇ ′′ of complex relative permeability of 3 or more, and even if the heat radiating metal plate 12 is brought close to the high-frequency substrate 17, unnecessary radiation increases. I was able to avoid it.
  • those excluding the sheet F had a value of the imaginary part ⁇ ′′ of the complex magnetic permeability of 3 or less and could not sufficiently suppress the electromagnetic wave.
  • Sheet F had an imaginary part ⁇ ′′ value of complex permeability of 3 or more and was excellent in electromagnetic wave suppression effect, but its thermal conductivity was low and sufficient thermal conductivity characteristics could not be realized.
  • the sheet E is superior in thermal conductivity to the sheets A, C, and D, but the imaginary part ⁇ ′′ of the complex permeability is very small and the electromagnetic wave cannot be sufficiently suppressed.
  • the magnetic metal particles and the heat conductive particles can be highly filled with each other because of the flat shape contained in the sheets F to H to be compared. This is because the spherical magnetic metal particles are more excellent in dispersibility than the magnetic metal particles.
  • the magnetic metal particles and the heat conductive particles could be highly filled with each other because the average particle diameter of the magnetic metal particles was larger than that of the heat conductive particles.
  • the average particle size of the heat conductive particles is larger than the average particle size of the magnetic metal particles. It is also clear from the point that the electromagnetic wave suppression effect is not sufficient because it cannot be filled. In addition, in the sheets A to D, it was possible to achieve high filling regardless of whether the heat conductive particles were spherical or crushed powder, because the dispersibility of the spherical magnetic metal particles was high, and the average of the magnetic metal particles This is because the particle size is larger than the average particle size of the heat conductive particles.
  • the sheet B can contain two types of thermally conductive particles because the magnetic metal particles are highly dispersible and can be filled with various thermally conductive particles.
  • the sheets A to D are formed of spherical magnetic metal particles as the electromagnetic wave absorbing material, so that the magnetic metal particles and the thermal conductivity are, for example, 70 vol% or more in terms of the sum of volume ratios. Higher packing with particles, and with increased packing of magnetic metal particles, the value of the imaginary part of the complex relative permeability in the sheet could be increased, so good heat conduction characteristics and electromagnetic wave suppression effect And was able to be realized.
  • the sheets A to D can be highly filled with the heat conductive particles by using the dispersibility of the magnetic metal particles. As a result, it was possible to realize high heat conduction characteristics while maintaining a high electromagnetic wave suppression effect.
  • the sheet B since the sheet B has high dispersibility of the magnetic metal particles, it was possible to highly fill various heat conductive particles regardless of whether it was a spherical powder or a crushed powder. For this reason, the sheet B clearly shows that the characteristics could be easily changed by adjusting the filling amount of various heat conductive particles while maintaining sufficient heat conduction characteristics and electromagnetic wave suppression characteristics. Yes.
  • Example 2 Next, as Example 2 of the heat conductive sheet 11, the heat conductive particles having a volume ratio of 3 vol% or more are higher in heat conductivity than the heat conductive sheet using flat magnetic metal particles. What is desirable for realizing the above will be described using the following sheets I and J. ⁇ Sheet I> Sheet I was produced as follows.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 12.8 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 20.5 g of a coupling agent for coupling the thermally conductive particles were used as a flexible resin material.
  • Example 3 As shown in Table 2 above, although the characteristics change according to the volume ratio of the magnetic metal particles, the thermal conductivity value is 3 vol% or more, so that the value of the thermal conductivity is increased. It became 2 or more. As is apparent from the evaluation results, the sheets I and J have a volume ratio of 3 vol% or more of the heat conductive particles, so that, for example, compared with a heat conductive sheet using flat magnetic metal particles, for example. High heat conduction characteristics could be realized.
  • Example 3 of the heat conductive sheet 11 by adjusting the average particle size ratio of the magnetic metal particles and the heat conductive particles, the sum of the volume ratio in the sheet is about 80 vol% at the maximum.
  • Sheet K was produced as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 27 g of a coupling agent for applying a coupling treatment to the thermally conductive particles were used as a flexible resin material.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 20 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material.
  • Example 4 As shown in Table 3 above, in the sheets K and L, by adjusting the average particle size ratio between the magnetic metal particles and the heat conductive particles, the good dispersibility of the spherical magnetic metal particles is utilized. Magnetic metal particles and heat conductive particles can be contained so that the sum of the volume fraction in the sheet is about 80 vol% at maximum, and as a result, good heat conduction characteristics and electromagnetic wave suppression characteristics can be realized. It was.
  • Example 4 of the heat conductive sheet 11 a change in characteristics depending on the presence or absence of the coupling treatment will be described using the following sheets M and N. ⁇ Sheet M> As a specific example where the coupling treatment was not performed, a sheet M was manufactured as follows.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture was used as a flexible resin material.
  • a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 31 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material.
  • this flexible resin material 2650 g (60 vol%) of spherical amorphous alloy (Fe—Si—B—Cr) having an average particle diameter of 26 ⁇ m as magnetic metal particles, and spherical alumina having an average particle diameter of 3 ⁇ m as thermally conductive particles
  • spherical amorphous alloy Fe—Si—B—Cr
  • spherical alumina having an average particle diameter of 3 ⁇ m as thermally conductive particles
  • both the heat conductive sheets M and N were able to realize good heat conduction characteristics and electromagnetic wave suppression characteristics regardless of the presence or absence of the coupling treatment.
  • the heat conductive sheet N contains a coupling agent that applies a coupling treatment to the heat conductive particles, thereby improving dispersibility in the sheet and realizing particularly good heat conduction characteristics. I was able to.

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Abstract

The disclosed thermally conductive sheet, which is excellent in both the functions of thermal conductivity and electromagnetic wave suppression attributes, is provided by causing the high packing of magnetic metal particles and thermally conductive particles of which the thermal conductivity is more favorable than that of the magnetic metal particles. The thermally conductive sheet (11), which is disposed between an electronic component (14) and a metallic radiator member (12) that radiates the heat given off by the electronic component (14), is characterized: by comprising a flexible resin containing both spherical magnetic metal particles that absorb electromagnetic waves emitted from the electronic component (14) and thermally conductive particles that have a higher thermal conductivity than the magnetic metal particles; by the average particle size of the magnetic metal particles being greater than the average particle size of the thermally conductive particles; and by the volume fraction of the magnetic metal particles in said thermally conductive sheet being at least 55 vol%.

Description

熱伝導性シートThermally conductive sheet
　本発明は、半導体パッケージなどの電子部品と、この電子部品が発熱する熱を放熱させる金属製放熱部材との間に配置される熱伝導性シートに関する。 The present invention relates to a heat conductive sheet disposed between an electronic component such as a semiconductor package and a metal heat dissipating member that dissipates heat generated by the electronic component.
　近年、電子機器は小型化の傾向をたどる一方、アプリケーションの多様性のために電力消費量はそれほど変化させることができないため、機器内における放熱対策がより一層重要視されている。
　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、放熱効果又は機器内の温度緩和を図るため、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。
　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、不要輻射の成分となりうる電界強度又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辺に配置すると、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も拾ってしまうケースがしばしば見られる。
　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働いてしまうことや、高調波ノイズ成分の伝達経路として働いてしまうという現象が生じる。
　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働い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。 In recent years, electronic devices have been trending toward miniaturization, but the power consumption cannot be changed so much due to the variety of applications, and therefore heat radiation countermeasures in the devices have become more important.
As a heat dissipation measure in the electronic devices described above, a heat dissipation plate, a heat pipe, a heat sink, or the like made of a metal material having high thermal conductivity such as copper or aluminum is widely used. These heat dissipating parts having excellent thermal conductivity are arranged 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 achieve a heat dissipation effect or temperature relaxation 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 large electric field strength or magnetic field strength that can be a component of unwanted radiation. For this reason, when a heat dissipating part made of metal is disposed in the vicinity of an electronic part, there are often cases where a harmonic component of an electric signal flowing in the electronic part is picked up together with heat.
Specifically, since the heat dissipating part is made of a metal material, a phenomenon occurs in which the heat dissipating part itself functions as a harmonic component antenna or a harmonic noise component transmission path.
With such a background, there is a thermal conductive sheet containing a magnetic material in order to suppress the heat radiation component from acting 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。
　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） The characteristics of the heat conductive sheet having the functions of both the heat conduction characteristics and the electromagnetic wave suppression characteristics described above vary greatly depending on the filling amount of the target powder contained in the polymer material as the base material.
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
 　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率である。
　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。この磁性特性についても、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）
Figure JPOXMLDOC01-appb-M000001
 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. Rate.
In general, the imaginary part μ r ″ of the complex relative permeability (μ r = μ r ′ −jμ r ″) is used as an index of the 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
 　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は磁性材料の体積率、ν２は母材の体積率である。
　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。
　しかしながら、このような熱伝導性シートの作製に当たり、任意の金属粉末と樹脂を単に混ぜるだけでは、シートに充填する磁性材料と熱伝導性材料の充填量に限界がある。
　従来の電磁波抑制機能を有する熱伝導性シートには、磁性材料として、偏平状磁性粉末、又は破砕磁性粉末が使用されている。偏平状磁性粉末、破砕磁性粉末は透磁率が大きいが比表面積が大きい。このため、樹脂とこれらの粉末を練るという単純な混合プロセスによってシート内に最密充填させることが困難であり、高充填化に限界がある。また熱伝導性を高めるため、偏平状磁性粉末又は破砕磁性粉末と充填性の高い球状の熱伝導性粉末とを混合させる場合も、これらの形状から最密充填させることが困難であり、高充填化に限界がある。磁性材料を高充填するためには熱伝導性材料を高い割合で充填することを要するが、この結果、磁性材料の充填量が減り、高い透磁率を得ることができない。
　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、磁性金属粒子と、磁性金属粒子より熱伝導性が高い熱伝導性粒子との高充填化を図ることで、熱伝導特性と電磁波抑制特性の両者の機能が良好な熱伝導性シートを提供することを目的とする。
課題を解決するための手段
　上記のように、高い熱伝導特性を有しながら電磁波を抑制するという目的にて、磁性金属粒子と熱伝導性粒子との両者の充填量を増やすために、発明者らは下記の熱伝導性シートを発明するに至った。
　すなわち、本発明は、電子部品と、この電子部品が発熱する熱を放熱させる金属製放熱部材との間に配置される熱伝導性シートにおいて、球状の磁性金属粒子と、磁性金属粒子よりも熱伝導性が高い熱伝導性粒子とを含有する可撓性樹脂からなり、磁性金属粒子の平均粒径は、熱伝導性粒子の平均粒径よりも大きく、当該熱伝導性シートに占める磁性金属粒子の体積率は５５ｖｏｌ％以上であることを特徴とする。
　本発明は、電磁波吸収性材料である磁性金属粒子の形状を球状とし、磁性金属粒子の平均粒径を、熱伝導性粒子の平均粒径よりも大きくすることで、磁性金属粒子と熱伝導性粒子との高充填化を可能にし、さらに、磁性金属粒子の高充填化に伴い複素比透磁率の虚数部の値を高めることができるので、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。
Figure JPOXMLDOC01-appb-M000002
 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 volume ratio of the magnetic material, [nu 2 is the base material The volume ratio.
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.
However, in the production of such a heat conductive sheet, there is a limit to the amount of magnetic material and heat conductive material to be filled in the sheet simply by mixing arbitrary metal powder and resin.
In a conventional heat conductive sheet having an electromagnetic wave suppressing function, flat magnetic powder or crushed magnetic powder is used as a magnetic material. Flat magnetic powder and crushed magnetic powder have a large magnetic permeability but a large specific surface area. For this reason, it is difficult to close-pack the sheet with a simple mixing process of kneading the resin and these powders, and there is a limit to high filling. In addition, in order to increase the thermal conductivity, even when flat magnetic powder or crushed magnetic powder is mixed with spherical heat conductive powder with high filling property, it is difficult to close-pack from these shapes, and high filling There is a limit to conversion. In order to highly fill the magnetic material, it is necessary to fill the heat conductive material at a high rate. However, as a result, the filling amount of the magnetic material is reduced, and high magnetic permeability cannot be obtained.
The present invention has been proposed in view of such a situation, and by achieving high packing of magnetic metal particles and thermally conductive particles having higher thermal conductivity than magnetic metal particles, An object is to provide a heat conductive sheet having both functions of electromagnetic wave suppression characteristics.
Means for Solving the Problems As described above, in order to increase the filling amount of both the magnetic metal particles and the heat conductive particles for the purpose of suppressing electromagnetic waves while having high heat conduction characteristics, the inventor Have invented the following thermal conductive sheet.
That is, the present invention provides a heat conductive sheet disposed between an electronic component and a metal heat dissipating member that dissipates heat generated by the electronic component. Magnetic metal particles made of a flexible resin containing highly conductive heat conductive particles, and the average particle size of the magnetic metal particles is larger than the average particle size of the heat conductive particles, and occupies the heat conductive sheet The volume ratio is 55 vol% or more.
In the present invention, the magnetic metal particles, which are electromagnetic wave absorbing materials, have a spherical shape, and the average particle diameter of the magnetic metal particles is larger than the average particle diameter of the heat conductive particles, thereby making the magnetic metal particles and the heat conductive It is possible to increase the filling with particles, and furthermore, the value of the imaginary part of the complex relative permeability can be increased with increasing the filling of magnetic metal particles, so both functions of heat conduction characteristics and electromagnetic wave suppression characteristics A good heat conductive sheet can be provided.
図１は、本発明が適用された熱伝導性シートが実装される回路基板の構成を示す図である。FIG. 1 is a diagram showing a configuration of a circuit board on which a thermally conductive sheet to which the present invention is applied is mounted. 図２は、回路基板における遠方電界強度の周波数特性を示すグラフである。FIG. 2 is a graph showing the frequency characteristics of the far field strength in the circuit board. 図３は、熱伝導性シートの特性に応じた回路基板における遠方電界強度の周波数特性を示すグラフである。FIG. 3 is a graph showing the frequency characteristics of the far field strength in the circuit board according to the characteristics of the heat conductive sheet. 図４は、磁性金属粒子として、球状センダストと球状アモルファス（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）とにおける体積率に応じた、５００ＭＨｚにおける複素比透磁率の虚数部の変化を示すグラフである。FIG. 4 is a graph showing the change of the imaginary part of the complex relative permeability at 500 MHz according to the volume ratio of spherical Sendust and spherical amorphous (Fe—Si—B—Cr) as magnetic metal particles. 図５は、シートにおける熱伝導性材料の充填量とシート全体の熱伝導率との関係を算出したグラフである。FIG. 5 is a graph in which the relationship between the filling amount of the thermally conductive material in the sheet and the thermal conductivity of the entire sheet is calculated.
　以下、本発明を実施するための最良の形態について、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。
　本発明が適用された熱伝導性シートは、半導体パッケージなどの電子部品と、この電子部品が発熱する熱を放熱させる金属製放熱部材との間に配置される。
　＜熱伝導性シートが貼着される回路基板＞
　例えば本発明が適用された熱伝導性シートは、図１に示すような、回路基板１に貼着される。すなわち、図１に示す熱伝導性シート１１は、発熱部である高周波基板１７と、高周波基板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、熱伝導性シート１１は、一方の面１１ａが高周波基板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１に貼着される。
　高周波基板１７は、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。
　高周波基板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。このような高周波基板１７を有する回路基板１では、放熱金属板１２が、熱伝導性シート１１を介して対向する高周波基板１７の信号線１４内を流れる電気信号の高調波成分を拾ってしまい、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。熱伝導性シート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ため、シートに占める体積率が所定の値以上になるように、球状の磁性金属粒子が含有されている。また、熱伝導性シート１１には、良好な熱伝導特性を実現するため、球状の磁性金属粒子よりも熱伝導率が高い熱伝導性粒子が含有されている。
　＜シミュレーション＞
　本発明が適用された熱伝導性シート１１の具体的な構成を説明する前に、十分な熱伝導特性と電磁波吸収特性とを発揮するために必要な条件について説明する。
　第１に、遠方電界強度と熱伝導性シート１１の磁気特性との関係について説明する。上述した回路基板１を解析用モデルとし、シミュレーションにはアンソフト社製の電磁界シミュレーターＨＦＳＳを用い、次のように各条件を設定して３ｍ遠方での電界強度を算出した。
　図２は、回路基板１において、熱伝導性シート１１を省いた状態で、放熱金属板１２がある場合とない場合の遠方電界強度の周波数特性を比較したものである。図２から明らかなように、高周波基板１７に熱伝導性シート１１を介さない状態で放熱金属板１２が積層されていると、高周波基板１７と放熱金属板１２の間での電磁気的な結合により平行平板共振が発生し、この共振に対応した周波数で電界の放射が強くなる。本例では、高周波基板１７から発信される高調波の周波数が１.１［ＧＨｚ］、２.１［ＧＨｚ］付近で強い電界放射が見られる。
　図３は、回路基板１において熱伝導性シート１１を含めた状態で、熱伝導性シート１１の複素比透磁率の実数部を１０に固定して虚数部の値のみを変えたときの、遠方電界強度の周波数特性を比較したものである。図２と図３との解析結果を比較すると、虚数部の値が１では放射電界強度のピークを抑制できるが、図２の放射金属板無しの結果と比べると周波数全体に亘り放射電界強度が高い。これに対して、虚数部の値が３では上述した周波数の放射電界ピークは完全に抑えられ、また周波数全体に亘り図２の放射金属板無しの結果とほぼ同等な電界強度特性となっている。また、虚数部の値が５の場合は、更に放射電界強度が下がる。以上の解析結果から、熱伝導性シートの複素比透磁率虚数部が大きいほど、放射電界に対する低減効果が大きい傾向がある。特に、熱伝導性シート１１は、虚数部の値が３以上であれば平行平板共振の影響を取り除くことができ、放熱金属板１２を高周波基板１７に近接させたとしても、不要輻射を増大させないようにすることができる。
　第２に、熱伝導性シート１１における磁性金属粒子の充填量に応じた磁気特性の変化について説明する。
　ここでは、具体例として実際に次の２種類の磁性金属粒子を２０ｖｏｌ％～７０ｖｏｌ％の範囲で変化させて充填させたシートを用いて説明する。図４は、磁性金属粒子として、球状センダストと球状アモルファス（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）とにおける体積率に応じた、５００ＭＨｚにおける複素比透磁率の虚数部の変化を示している。球状の磁性金属粒子は、偏平形状の磁性金属粒子に比べて、粒子単体での透磁率は低いが、分散性が高く高充填することが可能である。また、図４から明らかなように、磁性金属粒子の体積率が大きくなるのに伴って、シート全体での透磁率も大きくなる。よって、球状の磁性金属粒子は、シート内に高充填可能であり、その結果として高透磁率、高熱伝導率を実現することができる。
　図２、図３で示される解析結果を踏まえると、２種類の磁性金属粒子において両方とも複素比透磁率の虚数部の値が３以上となる条件は、体積率が５５ｖｏｌ％である。したがって、熱伝導性シート１１は、球状の磁性金属粒子が５５ｖｏｌ％以上で充填されていることで、放熱金属板１２を高周波基板１７に近接させたとしても、不要輻射を増大させないようにすることができる。
　第３に、熱伝導性シート１１における熱伝導性材料の充填量に応じた熱伝導率の変化について説明する。
　熱伝導率は、Ｂｒｕｇｇｅｍａｎの式によると以下のような関係がある。 Hereinafter, the best mode 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.
The thermally conductive sheet to which the present invention is applied is disposed between an electronic component such as a semiconductor package and a metal heat radiating member that radiates heat generated by the electronic component.
<Circuit board to which the thermally conductive sheet is attached>
For example, a heat conductive sheet to which the present invention is applied is attached to a circuit board 1 as shown in FIG. That is, the heat conductive sheet 11 shown in FIG. 1 is disposed between the high-frequency substrate 17 that is a heat generating portion and the heat radiating metal plate 12 that dissipates heat generated by the high-frequency substrate 17. Specifically, the heat conductive sheet 11 has a circuit in which one surface 11a is in close contact with the resin mold 13 for sealing the semiconductor package constituting the high-frequency substrate 17, and the other surface 11b is in close contact with the heat radiating metal plate 12. Affixed to the substrate 1.
The high-frequency substrate 17 comprises a copper foil 15 serving as a GND electrode on one surface of the dielectric substrate 16 and a copper signal line 14 formed by patterning on the other surface to constitute a microstrip line. .
The high-frequency substrate 17 is designed so that the far field intensity 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 having such a high-frequency substrate 17, the heat radiating metal plate 12 picks up harmonic components of the electric signal flowing in the signal line 14 of the high-frequency substrate 17 opposed via the heat conductive sheet 11, It functions as an antenna for harmonic components, resulting in an increase in the far field strength. In order to suppress the heat radiating metal plate 12 from acting as an antenna, the thermally conductive sheet 11 contains spherical magnetic metal particles so that the volume ratio of the sheet occupies a predetermined value or more. Moreover, in order to implement | achieve a favorable heat conductive characteristic, the heat conductive sheet 11 contains the heat conductive particle whose heat conductivity is higher than a spherical magnetic metal particle.
<Simulation>
Before describing the specific configuration of the heat conductive sheet 11 to which the present invention is applied, conditions necessary for exhibiting sufficient heat conduction characteristics and electromagnetic wave absorption characteristics will be described.
First, the relationship between the far field strength and the magnetic properties of the thermal conductive sheet 11 will be described. The above-described circuit board 1 was used as an analysis model, and an electromagnetic field simulator HFSS manufactured by Ansoft was used for the simulation. Each field was set as follows, and the electric field strength at a distance of 3 m was calculated.
FIG. 2 compares the frequency characteristics of the far field strength with and without the heat radiating metal plate 12 with the heat conductive sheet 11 omitted in the circuit board 1. As is clear from FIG. 2, when the heat radiating metal plate 12 is laminated on the high frequency substrate 17 without the heat conductive sheet 11 interposed, due to electromagnetic coupling between the high frequency substrate 17 and the heat radiating metal plate 12. Parallel plate resonance occurs, and the electric field is radiated at a frequency corresponding to the resonance. In this example, strong electric field radiation is observed when the frequency of the harmonics transmitted from the high-frequency substrate 17 is in the vicinity of 1.1 [GHz] and 2.1 [GHz].
FIG. 3 shows a distant view when the real part of the complex relative permeability of the heat conductive sheet 11 is fixed to 10 and only the value of the imaginary part is changed in the state including the heat conductive sheet 11 in the circuit board 1. The frequency characteristics of electric field strength are compared. Comparing the analysis results of FIG. 2 and FIG. 3, the peak of the radiated electric field intensity can be suppressed when the value of the imaginary part is 1, but the radiated electric field intensity is increased over the entire frequency as compared with the result without the radiating metal plate of FIG. high. On the other hand, when the value of the imaginary part is 3, the radiated electric field peak of the frequency described above is completely suppressed, and the electric field strength characteristic is almost equivalent to the result without the radiating metal plate in FIG. 2 over the entire frequency. . Further, when the value of the imaginary part is 5, the radiation electric field strength further decreases. From the above analysis results, the larger the complex relative permeability imaginary part of the thermal conductive sheet, the greater the reduction effect on the radiation electric field. In particular, if the value of the imaginary part is 3 or more, the heat conductive sheet 11 can remove the influence of parallel plate resonance, and even if the heat radiating metal plate 12 is brought close to the high frequency substrate 17, it does not increase unnecessary radiation. Can be.
Secondly, a change in magnetic characteristics according to the filling amount of the magnetic metal particles in the heat conductive sheet 11 will be described.
Here, a specific example will be described using a sheet in which the following two kinds of magnetic metal particles are actually filled in a range of 20 vol% to 70 vol%. FIG. 4 shows the change in the imaginary part of the complex relative permeability at 500 MHz according to the volume fraction of spherical sendust and spherical amorphous (Fe—Si—B—Cr) as magnetic metal particles. Spherical magnetic metal particles have a low magnetic permeability as compared with flat magnetic metal particles, but have high dispersibility and can be highly filled. Further, as apparent from FIG. 4, as the volume ratio of the magnetic metal particles increases, the magnetic permeability of the entire sheet also increases. Therefore, the spherical magnetic metal particles can be highly filled in the sheet, and as a result, high magnetic permeability and high thermal conductivity can be realized.
Based on the analysis results shown in FIG. 2 and FIG. 3, the condition that the value of the imaginary part of the complex relative permeability is 3 or more in both of the two types of magnetic metal particles is 55 vol%. Therefore, the thermal conductive sheet 11 is filled with spherical magnetic metal particles at 55 vol% or more, so that unnecessary radiation is not increased even if the heat radiating metal plate 12 is brought close to the high frequency substrate 17. Can do.
3rdly, the change of the heat conductivity according to the filling amount of the heat conductive material in the heat conductive sheet 11 is demonstrated.
According to the Bruggeman equation, the thermal conductivity has the following relationship.
Figure JPOXMLDOC01-appb-M000003
 　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率である。
　図５は、上記のＢｒｕｇｇｅｍａｎの式を用い、シートにおける熱伝導性材料の充填量とシート全体の熱伝導率との関係を算出したグラフを示している。母材の高分子材の熱伝導率を０．２Ｗ／ｍＫとし、熱伝導性材料の熱伝導率を１０、３０、５０、７０Ｗ／ｍＫとした。ここで、熱伝導性シート１１は、磁気特性が高い磁性金属粒子と、磁性金属粒子よりも熱伝導率が高い熱伝導性粒子との両方を、熱伝導性材料として含有するため、これらの含有比率に起因して、仮想的に１種類の熱伝導性材料としてみなしたときの熱伝導率が変化する。このため、含有比率に応じて熱伝導率が変化するが、図５から明らかなように、シート全体の熱伝導率は熱伝導性材料の充填量の増加に応じて単調増加し、特に、熱伝導性材料の充填量が約６５％以上になると、シート全体の熱伝導率も急激に増加する。特に、シート全体で高い熱伝導率を実現するためには、７０ｖｏｌ％以上となるように熱伝導性材料が充填されていることが望ましい。
　上述した解析結果を踏まえ、本願の発明者らは、球状の磁性粉末を使用して良好な熱伝導特性と良好な電磁波抑制を同時に実現するために最適な配合の研究を行った結果、球状の磁性金属粒子を、シリコン樹脂などの可撓性樹脂に対して５５ｖｏｌ％以上含有されていることが、熱伝導性シート１１の良好な特性を満たす上で必要であるということを見出した。さらに熱伝導性材料として、磁性金属粒子より熱伝導率が高い熱伝導性粒子を３ｖｏｌ％以上含有されていること、及び、磁性金属粒子と熱伝導性粒子との合計で７０ｖｏｌ％以上含有されていることが、熱伝導性シート１１の熱伝導率を高めるという観点から好ましいことを見出した。
　＜熱伝導性シート＞
　次に、本願の発明者らが見出した良好な特性を実現する熱伝導性シート１１の具体的な構成について説明する。
　熱伝導性シート１１は、高周波基板１７などの電子部品から放出される電磁波を吸収する電磁波吸収材料である球状の磁性金属粒子と、磁性金属粒子よりも熱伝導性が高い熱伝導性粒子とを含有する可撓性樹脂からなり、磁性金属粒子の平均粒径が熱伝導性粒子の平均粒径よりも大きく、この熱伝導性シート１１に占める磁性金属粒子の体積率が５５ｖｏｌ％以上である。このような構成からなる熱伝導性シート１１は、磁性金属粒子と熱伝導性粒子との高充填化を可能にし、さらに、磁性金属粒子の高充填化に伴いシート内の複素比透磁率の虚数部の値を高めることができるので、良好な熱伝導特性と電磁波抑制効果とを実現することができる。
　また、熱伝導性シート１１は、熱伝導性粒子の体積率が３ｖｏｌ％以上が含有されていることによって、例えば偏平形状の磁性金属粒子を用いた熱伝導性シートと比べて高い熱伝導特性を実現することができる。
　また、熱伝導性シート１１は、体積率の和で７０ｖｏｌ％以上となるように磁性金属粒子と熱伝導性粒子が充填されていることによって、特に良好な熱伝導特性と電磁波抑制効果とを実現することができる。なお、熱伝導性シート１１は、磁性金属粒子と熱伝導性粒子との平均粒径比を調節することにより、球状の磁性金属粒子の分散性の良さを利用して、シートに占める体積率の和が最大８０ｖｏｌ％程度となるように、磁性金属粒子と熱伝導性粒子とを含有することができる。
　また、熱伝導性シート１１は、カップリング処理の有無に拘わらず、良好な熱伝導特性と電磁波抑制特性を実現するが、熱伝導性粒子に対してカップリング処理を施すカップリング剤が含有されていることによって、シート内での分散性が向上し、特に良好な熱伝導特性を実現することができる。
　また、熱伝導性シート１１は、磁性金属粒子より熱伝導率が高い複数種類の熱伝導性粒子が充填されていることによって、十分な熱伝導特性と電磁波抑制特性と維持しつつ、種々の熱伝導性粒子の充填量を調整することにより容易に特性を変更することができる。
　次に熱伝導性シート１１に用いられる具体的な材料について説明する。
　熱伝導性シート１１は、シリコン樹脂などの可撓性樹脂に、下記のような粒子状の粉末が含有されることにより形成されている。
　すなわち、熱伝導性シート１１は、透磁率特性が良く、かつ上記の電磁波抑制特性の要求を満たす磁性金属粒子として、粉末作製の観点から比較的作製しやすい、ボロン（Ｂ）や炭素（Ｃ）などを添加した磁性金属アモルファス粉末を含有している。磁性金属アモルファス粉末は、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。
　また、熱伝導性シート１１に含有される磁性金属粒子は、上述した磁性金属アモルファスのみに限らず、例えば、球状センダストなどの結晶系磁性粉末であってもよい。すなわち、結晶化した金属粉末、金属合金粉末として、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系などがあげられ、これにＮ、Ｃ、Ｏを微量加えて微細化させた微結晶材料を磁性金属粒子として用いてもよい。
　また、熱伝導性シート１１は、上述した磁性金属粒子とともに、シートの熱伝導率を高めるため、磁性金属粒子よりも熱伝導率が高い熱伝導性粒子として、アルミナ、窒化ホウ素、窒化珪素、窒化アルミ、炭化珪素などの高熱伝導性セラミックス、また銅やアルミなどに絶縁体をコーティングした粉末を含有している。なお、熱伝導性粒子は、上述したものに限定されず、磁性金属粒子よりも熱伝導率が高い材料であればよいが、特に、平均粒径が磁性金属粒子に比べてより小さいものを用いることで、更なる高充填化が実現される。一般に熱伝導性シートの厚みにも依存するが、更なる高充填化を実現するには、熱伝導性粒子の平均粒径が磁性金属粒子の平均粒径よりも小さいことを前提として、磁性金属粒子の粒径が４～１００μｍの範囲であり、熱伝導性粒子の粒径が０．１～２０μｍの範囲が好ましい。
実施例１
　次に、熱伝導性シート１１の実施例１として、下記のシートＡ～Ｄ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。
　＜シートＡ＞
　シートＡを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと、熱伝導性粒子にカップリング処理を施すためのカップリング剤２１ｇとを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が１０μｍの球状アモルファス合金（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）を２０００ｇ（６５ｖｏｌ％）、熱伝導性粒子として平均粒径が３μｍの球状アルミナ粉末１０６ｇ（６ｖｏｌ％）の合計７１ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが１．５ｍｍのシートにし、１００度で６０分間加熱して硬化させることにより、シートＡを作製した。
　＜シートＢ＞
　シートＢを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤３５ｇとを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が１０μｍの球状アモルファス合金（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）を３１００ｇ（６２ｖｏｌ％）、熱伝導性粒子として平均粒径が１μｍの窒化アルミ破砕粉末３８０ｇ（１６ｖｏｌ％）、熱伝導性粒子として平均粒径が０．２μｍの球状アルミナ８７ｇ（２ｖｏｌ％）の合計８０％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させることによりシートＢを作製した。
　＜シートＣ＞
　シートＣを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤６６ｇとを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が１０μｍの球状アモルファス合金（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）を４２００ｇ（６７ｖｏｌ％）、熱伝導性粒子として平均粒径が１μｍの窒化アルミ破砕粉末を３００ｇ（１０ｖｏｌ％）の合計７７ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させることによりシートＣを作製した。
　＜シートＤ＞
　シートＤを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤１８ｇとを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が１０μｍの球状センダスト１６１５ｇ（５５ｖｏｌ％）、熱伝導性粒子として平均粒径が１μｍの窒化アルミ破砕粉末２０５ｇ（１５ｖｏｌ％）の合計７０ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させることによりシートＤを作製した。
　このような４種類のシートＡ～Ｄに対し、比較対象として次の４種類のシートＥ～Ｈを用いた。
　＜シートＥ＞
　シートＥを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤１３ｇとを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が１０μｍの球状アモルファス合金（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）を６００ｇ（２２ｖｏｌ％）、熱伝導性粒子として平均粒径が１μｍの窒化アルミ破砕粉末１００ｇ（８ｖｏｌ％）、熱伝導性粒子として平均粒径が４５μｍの球状アルミナ６２０ｇ（４０ｖｏｌ％）の合計７０ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させることによりシートＥを作製した。
　＜シートＦ＞
　シートＦを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒１％未満を含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤３ｇとを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が６０μｍの偏平形状センダスト２６５ｇ（２４ｖｏｌ％）、熱伝導性粒子として平均粒径が５μｍの窒化アルミ破砕粉末５０ｇ（８ｖｏｌ％）の合計３２ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させることによりシートＦを作製した。
　＜シートＧ＞
　シートＧを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤５．３ｇとを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が６０μｍの偏平形状センダスト２３０ｇ（１５ｖｏｌ％）、熱伝導性粒子として平均粒径が５μｍの球状アルミナ粉末２８０ｇ（３２ｖｏｌ％）、熱伝導性粒子として平均粒径が０．２μｍの球状アルミナ粉末３５ｇ（３ｖｏｌ％）の合計５０ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させることによりシートＧを作製した。
　＜シートＨ＞
　シートＨを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤５．３ｇとを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が２０μｍの偏平形状のＦｅ－Ｓｉ－Ｃｒ－Ｎｉ２３０ｇ（１５ｖｏｌ％）、熱伝導性粒子として平均粒径が５μｍの球状アルミナ粉末２８０ｇ（３２ｖｏｌ％）、熱伝導性粒子として平均粒径が０．２μｍの球状アルミナ粉末３５ｇ（３ｖｏｌ％）の合計５０ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させることによりシートＨを作製した。
　＜評価＞
　以上のような合計８種類のシートの電磁波吸収特性を評価するための指標として、次のような条件下で複素比透磁率の虚数部μ”を測定した。
　すなわち、各シートを外径２０ｍｍ、内径６ｍｍのリング状体に打ち抜いて作製したサンプルについて、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、電磁波の発振周波数が５００ＭＨｚでの複素比透磁率の虚数部を測定した。
　また、熱伝導特性の評価指標として、次のような条件下で熱伝導率を算出した。
　すなわち、各シートを１ｃｍ角程度の大きさに切り出し、これ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、金属製ヒータケースに電力をかけて加熱して、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。ここで、熱伝導率は下記の式より算出した。
　熱伝導率＝（電力×サンプル厚み）／（温度差×測定面積）
　上記の条件下で測定した複素比透磁率の虚数部μ”と、算出した熱伝導率とを下記の表１に示す。表１においては、シートの厚みと磁性金属粒子の体積率と熱伝導性粒子の体積率とを示す。
Figure JPOXMLDOC01-appb-M000003
 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. Rate.
FIG. 5 shows a graph in which the relationship between the filling amount of the thermally conductive material in the sheet and the thermal conductivity of the entire sheet is calculated using the above Bruggeman equation. The thermal conductivity of the base polymer material was 0.2 W / mK, and the thermal conductivity of the thermally conductive material was 10, 30, 50, and 70 W / mK. Here, since the heat conductive sheet 11 contains both the magnetic metal particles having high magnetic properties and the heat conductive particles having higher heat conductivity than the magnetic metal particles as the heat conductive material, the inclusion thereof. Due to the ratio, the thermal conductivity when virtually regarded as one type of thermal conductive material changes. For this reason, although the thermal conductivity changes according to the content ratio, as is clear from FIG. 5, the thermal conductivity of the entire sheet increases monotonously with the increase in the filling amount of the thermal conductive material, When the filling amount of the conductive material is about 65% or more, the thermal conductivity of the entire sheet also increases rapidly. In particular, in order to realize high thermal conductivity in the entire sheet, it is desirable that the thermal conductive material is filled so as to be 70 vol% or more.
Based on the analysis results described above, the inventors of the present application conducted research on the optimal blending to achieve good heat conduction characteristics and good electromagnetic wave suppression simultaneously using spherical magnetic powder. It has been found that it is necessary to contain 55 vol% or more of magnetic metal particles with respect to a flexible resin such as silicon resin in order to satisfy the good characteristics of the heat conductive sheet 11. Further, as the heat conductive material, 3 vol% or more of heat conductive particles having higher heat conductivity than the magnetic metal particles are contained, and 70 vol% or more in total of the magnetic metal particles and the heat conductive particles. It has been found that it is preferable from the viewpoint of increasing the thermal conductivity of the thermal conductive sheet 11.
<Thermal conductive sheet>
Next, a specific configuration of the heat conductive sheet 11 that realizes good characteristics found by the inventors of the present application will be described.
The thermally conductive sheet 11 includes spherical magnetic metal particles that are electromagnetic wave absorbing materials that absorb electromagnetic waves emitted from electronic components such as the high-frequency substrate 17 and thermally conductive particles that have higher thermal conductivity than the magnetic metal particles. It consists of the flexible resin to contain, the average particle diameter of a magnetic metal particle is larger than the average particle diameter of a heat conductive particle, and the volume ratio of the magnetic metal particle which occupies for this heat conductive sheet 11 is 55 vol% or more. The heat conductive sheet 11 having such a configuration enables high filling of magnetic metal particles and heat conductive particles, and further, the imaginary number of the complex relative magnetic permeability in the sheet as the magnetic metal particles increase. Since the value of the portion can be increased, it is possible to achieve good heat conduction characteristics and electromagnetic wave suppression effects.
Moreover, the heat conductive sheet 11 contains a heat conductive particle having a volume fraction of 3 vol% or more, and thus has a higher heat conduction characteristic than a heat conductive sheet using, for example, flat magnetic metal particles. Can be realized.
The heat conductive sheet 11 is filled with magnetic metal particles and heat conductive particles so that the sum of the volume ratios is 70 vol% or more, thereby realizing particularly good heat conduction characteristics and electromagnetic wave suppression effect. can do. In addition, the heat conductive sheet 11 adjusts the average particle diameter ratio between the magnetic metal particles and the heat conductive particles, thereby making use of the good dispersibility of the spherical magnetic metal particles to Magnetic metal particles and thermally conductive particles can be contained so that the sum is about 80 vol% at maximum.
Further, the heat conductive sheet 11 realizes good heat conduction characteristics and electromagnetic wave suppression characteristics regardless of the presence or absence of the coupling treatment, but contains a coupling agent that performs the coupling treatment on the heat conductive particles. Therefore, dispersibility in the sheet is improved, and particularly good heat conduction characteristics can be realized.
In addition, the thermal conductive sheet 11 is filled with a plurality of types of thermal conductive particles having a higher thermal conductivity than the magnetic metal particles, thereby maintaining various thermal conductivity and electromagnetic wave suppression characteristics while maintaining various heat The characteristics can be easily changed by adjusting the filling amount of the conductive particles.
Next, specific materials used for the heat conductive sheet 11 will be described.
The heat conductive sheet 11 is formed by containing the following particulate powder in a flexible resin such as a silicon resin.
That is, the thermal conductive sheet 11 is boron (B) or carbon (C), which has good permeability characteristics and is relatively easy to produce as magnetic metal particles satisfying the requirements of the above-mentioned electromagnetic wave suppression characteristics from the viewpoint of powder production. It contains magnetic metal amorphous powder to which etc. are added. Examples of the magnetic metal amorphous powder include Fe—Si—B, Fe—Si—B—C, Co—Si—B, Co—Zr, Co—Nb, and Co—Ta.
Further, the magnetic metal particles contained in the heat conductive sheet 11 are not limited to the above-described magnetic metal amorphous, but may be, for example, crystalline magnetic powder such as spherical sendust. That is, as crystallized metal powder and metal alloy powder, Fe-based, Co-based, Ni-based, Fe-Ni-based, Fe-Co-based, Fe-Al-based, Fe-Si-based, Fe-Si-Al-based, etc. A microcrystalline material refined by adding a small amount of N, C, or O may be used as the magnetic metal particles.
In addition to the above-described magnetic metal particles, the thermally conductive sheet 11 increases the thermal conductivity of the sheet, so that the thermally conductive particles having higher thermal conductivity than the magnetic metal particles are alumina, boron nitride, silicon nitride, nitride It contains highly thermally conductive ceramics such as aluminum and silicon carbide, and powders of copper and aluminum coated with an insulator. The heat conductive particles are not limited to those described above, and any material having a higher thermal conductivity than the magnetic metal particles may be used. In particular, particles having an average particle size smaller than that of the magnetic metal particles are used. As a result, further higher filling is realized. Generally, depending on the thickness of the heat conductive sheet, in order to realize further high filling, it is assumed that the average particle size of the heat conductive particles is smaller than the average particle size of the magnetic metal particles. The particle diameter is preferably in the range of 4 to 100 μm, and the heat conductive particle diameter is preferably in the range of 0.1 to 20 μm.
Example 1
Next, as Example 1 of the heat conductive sheet 11, the following sheets A to D were used to evaluate the heat conduction characteristics and the electromagnetic wave suppression effect.
<Sheet A>
Sheet A was produced as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 21 g of a coupling agent for applying a coupling treatment to the thermally conductive particles were used as a flexible resin material. In this flexible resin material, 2000 g (65 vol%) of a spherical amorphous alloy (Fe—Si—B—Cr) having an average particle diameter of 10 μm as magnetic metal particles and spherical alumina having an average particle diameter of 3 μm as heat conductive particles A total of 71 vol% of 106 g (6 vol%) of powder was stirred with a vacuum stirrer, and then made into a sheet having a thickness of 1.5 mm, and heated and cured at 100 degrees for 60 minutes to prepare sheet A.
<Sheet B>
Sheet B was produced as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 35 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material. In this flexible resin material, 3100 g (62 vol%) of a spherical amorphous alloy (Fe—Si—B—Cr) having an average particle diameter of 10 μm as magnetic metal particles and aluminum nitride having an average particle diameter of 1 μm as heat conductive particles A total of 80% of pulverized powder 380 g (16 vol%) and 87 g (2 vol%) of spherical alumina having an average particle diameter of 0.2 μm as heat conductive particles were stirred with a vacuum stirrer, and then a sheet with a thickness of 2 mm was obtained. Sheet B was produced by heating and curing at 60 ° C. for 60 minutes.
<Sheet C>
Sheet C was produced as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 66 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material. In this flexible resin material, 4200 g (67 vol%) of a spherical amorphous alloy (Fe—Si—B—Cr) having an average particle diameter of 10 μm as magnetic metal particles and aluminum nitride having an average particle diameter of 1 μm as thermally conductive particles A total of 77 vol% of 300 g (10 vol%) of the crushed powder was stirred with a vacuum stirrer, and then the sheet was made into a sheet having a thickness of 2 mm, and heated and cured at 100 ° C for 60 minutes to prepare a sheet C.
<Sheet D>
Sheet D was produced as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 18 g of a coupling agent for applying a coupling treatment to the thermally conductive particles were used as a flexible resin material. In this flexible resin material, a total of 70 vol% of spherical sendust 1615 g (55 vol%) having an average particle diameter of 10 μm as magnetic metal particles and 205 g (15 vol%) of aluminum nitride crushed powder having an average particle diameter of 1 μm as thermally conductive particles. After being stirred with a vacuum stirrer, a sheet having a thickness of 2 mm was prepared, and the sheet D was prepared by heating at 100 ° C. for 60 minutes to cure.
For the four types of sheets A to D, the following four types of sheets E to H were used as comparison objects.
<Sheet E>
Sheet E was produced as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 13 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material. In this flexible resin material, 600 g (22 vol%) of a spherical amorphous alloy (Fe—Si—B—Cr) having an average particle diameter of 10 μm as magnetic metal particles and aluminum nitride having an average particle diameter of 1 μm as heat conductive particles A total of 70 vol% of crushed powder 100 g (8 vol%) and spherical alumina 620 g (40 vol%) having an average particle diameter of 45 μm as heat conductive particles was stirred with a vacuum stirrer, and then a sheet with a thickness of 2 mm was obtained at 100 ° C. Sheet E was produced by heating and curing for 60 minutes.
<Sheet F>
Sheet F was produced as follows. That is, an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, a methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a silicone containing less than 1% of a platinum group addition reaction catalyst 100 g of the mixture and 3 g of a coupling agent for applying a coupling treatment to the thermally conductive particles were used as a flexible resin material. In this flexible resin material, 265 g (24 vol%) of flat sendust having an average particle diameter of 60 μm as magnetic metal particles and 50 g (8 vol%) of aluminum nitride crushed powder having an average particle diameter of 5 μm as heat conductive particles are a total of 32 vol. % Was stirred with a vacuum stirrer, and then a sheet having a thickness of 2 mm was formed. The sheet F was prepared by heating at 100 ° C. for 60 minutes to cure.
<Sheet G>
Sheet G was produced as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 5.3 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material. In this flexible resin material, 230 g (15 vol%) of flat sendust having an average particle diameter of 60 μm as magnetic metal particles, 280 g (32 vol%) of spherical alumina powder having an average particle diameter of 5 μm as thermal conductive particles, and thermal conductivity A total of 50 vol% of spherical alumina powder 35 g (3 vol%) having an average particle diameter of 0.2 μm is stirred as a particle with a vacuum stirrer, and then a sheet with a thickness of 2 mm is formed and heated at 100 ° C. for 60 minutes to be cured. Thus, a sheet G was produced.
<Sheet H>
Sheet H was produced as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 5.3 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material. In this flexible resin material, 230 g (15 vol%) of flat Fe—Si—Cr—Ni having an average particle diameter of 20 μm as magnetic metal particles and 280 g (32 vol) of spherical alumina powder having an average particle diameter of 5 μm as heat conductive particles are used. %), A total of 50 vol% of 35 g (3 vol%) of spherical alumina powder having an average particle diameter of 0.2 μm as heat conductive particles was stirred with a vacuum stirrer, and then a sheet with a thickness of 2 mm was formed at 100 ° C. for 60 minutes. Sheet H was produced by heating and curing.
<Evaluation>
As an index for evaluating the electromagnetic wave absorption characteristics of a total of eight types of sheets as described above, the imaginary part μ ″ of the complex relative permeability was measured under the following conditions.
That is, with respect to a sample prepared by punching each sheet into a ring-shaped body having an outer diameter of 20 mm and an inner diameter of 6 mm, the measurement frequency “Agilent 4291B RF Impedance / Material Analyzer” manufactured by Agilent Technologies, Inc. The imaginary part of the complex relative permeability at 500 MHz was measured.
In addition, the thermal conductivity was calculated under the following conditions as an evaluation index of thermal conductivity characteristics.
That is, each sheet is cut into a size of about 1 cm square, sandwiched between a metal heat sink and a metal heater case, pressed and contacted with a force of 1 kgf, and heated by applying electric power to the metal heater case. Then, when the temperature of the metallic heater case and the metallic heat sink became constant, the temperature difference between them was measured. Here, the thermal conductivity was calculated from the following equation.
Thermal conductivity = (power × sample thickness) / (temperature difference × measurement area)
The imaginary part μ ″ of the complex relative permeability measured under the above conditions and the calculated thermal conductivity are shown in the following Table 1. In Table 1, the thickness of the sheet, the volume ratio of the magnetic metal particles, and the thermal conductivity are shown. The volume ratio of the active particles.
Figure JPOXMLDOC01-appb-T000004
 　上記の表１を見ると、シートＡ～Ｄは、複素比透磁率の虚数部μ”の値が３以上であり、放熱金属板１２を高周波基板１７に近接させたとしても、不要輻射を増大させないようにすることができた。
　これに対して、比較対象であるシートＥ～Ｈのうち、シートＦを除くものは、複素透磁率の虚数部μ”の値が３以下であり、十分に電磁波を抑制させることができなかった。シートＦは、複素透磁率の虚数部μ”の値が３以上であり電磁波抑制効果に優れているが、熱伝導率が低く十分な熱伝導特性を実現することができなかった。シートＥは、シートＡ、Ｃ、Ｄに比べて熱伝導性に優れているが、複素透磁率の虚数部μ”が非常に小さく電磁波を十分に抑制させることができなかった。
　この結果から明らかなように、シートＡ～Ｄにおいて、磁性金属粒子と、熱伝導性粒子とを互いに高充填することができたのは、比較対象のシートＦ～Ｈに含有されている偏平形状の磁性金属粒子に比べて、球状の磁性金属粒子の方が分散性に優れているからである。
　また、シートＡ～Ｄにおいて、磁性金属粒子と、熱伝導性粒子とを互いに高充填することができたのは、磁性金属粒子の平均粒径が熱伝導性粒子に比べて大きいからである。これは、比較対象であるシートＥにおいて、磁性金属粒子の形状が球形であっても、磁性金属粒子の平均粒径に比べて熱伝導性粒子の平均粒径が大きいため、磁性金属粒子を高充填できず電磁波抑制効果が十分ではない点からみても明らかである。
　また、シートＡ～Ｄにおいて、熱伝導性粒子が球状であるか破砕粉末であるかに拘わらず高充填できたのは、球状の磁性金属粒子の分散性が高く、さらに、磁性金属粒子の平均粒径が熱伝導性粒子の平均粒径に比べて大きいからである。
　また、シートＢにおいて、２種類の熱伝導性粒子を含有することができたのは、磁性金属粒子の分散性が高いので、種々の熱伝導性粒子を充填できるからである。
　以上の評価から明らかなように、シートＡ～Ｄは、電磁波吸収性材料を球状の磁性金属粒子にしたことで、例えば体積率の和で７０ｖｏｌ％以上となるように磁性金属粒子と熱伝導性粒子との高充填化を可能にし、さらに、磁性金属粒子の高充填化に伴いシート内の複素比透磁率の虚数部の値を高めることができたので、良好な熱伝導特性と電磁波抑制効果とを実現することができた。
　また、シートＡ～Ｄは、磁性金属粒子の平均粒径が、熱伝導性粒子の平均粒径よりも大きいので、磁性金属粒子の分散性を利用して熱伝導性粒子を高充填化でき、結果として高い電磁波抑制効果を維持しつつ、高い熱伝導特性を実現することができた。
　また、シートＢは、磁性金属粒子の分散性が高いので、球状粉末であるか破砕粉末であるかに拘わらず、種々の熱伝導性粒子を高充填することができた。このため、シートＢは、十分な熱伝導特性と電磁波抑制特性と維持しつつ、種々の熱伝導性粒子の充填量を調整することにより容易に特性を変更することができたことを明示している。
実施例２
　次に、熱伝導性シート１１の実施例２として、熱伝導性粒子の体積率が３ｖｏｌ％以上であることが、偏平形状の磁性金属粒子を用いた熱伝導性シートと比べて高い熱伝導特性を実現するために望ましいことを、下記のシートＩ、Ｊを用いて説明する。
　＜シートＩ＞
　シートＩを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤１２．８ｇとを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が２６μｍの球状アモルファス合金（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）を２５００ｇ（７３ｖｏｌ％）、熱伝導性粒子として平均粒径が３μｍの球状アルミナ粉末６０ｇ（３ｖｏｌ％）の合計７６ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させることによりシートＩを作製した。
　＜シートＪ＞
　シートＪを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤２０．５ｇを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が５０μｍの球状アモルファス合金（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）を２０００ｇ（６７ｖｏｌ％）、熱伝導性粒子として平均粒径が３μｍの球状アルミナ粉末５０ｇ（３ｖｏｌ％）の合計７０ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させることによりシートＪを作製した。
　＜評価＞
　これら２種類の熱伝導性シートＩ、Ｊに対して、上述した実施例１において行った条件下で、複素比透磁率の虚数部μ”を測定し、熱伝導率を算出した。
　測定した複素比透磁率の虚数部μ”と、算出した熱伝導率を、下記の表２に示す。
Figure JPOXMLDOC01-appb-T000004
 As can be seen from Table 1 above, the sheets A to D have an imaginary part μ ″ of complex relative permeability of 3 or more, and even if the heat radiating metal plate 12 is brought close to the high-frequency substrate 17, unnecessary radiation increases. I was able to avoid it.
On the other hand, among the sheets E to H to be compared, those excluding the sheet F had a value of the imaginary part μ ″ of the complex magnetic permeability of 3 or less and could not sufficiently suppress the electromagnetic wave. Sheet F had an imaginary part μ ″ value of complex permeability of 3 or more and was excellent in electromagnetic wave suppression effect, but its thermal conductivity was low and sufficient thermal conductivity characteristics could not be realized. The sheet E is superior in thermal conductivity to the sheets A, C, and D, but the imaginary part μ ″ of the complex permeability is very small and the electromagnetic wave cannot be sufficiently suppressed.
As is clear from this result, in the sheets A to D, the magnetic metal particles and the heat conductive particles can be highly filled with each other because of the flat shape contained in the sheets F to H to be compared. This is because the spherical magnetic metal particles are more excellent in dispersibility than the magnetic metal particles.
In addition, in the sheets A to D, the magnetic metal particles and the heat conductive particles could be highly filled with each other because the average particle diameter of the magnetic metal particles was larger than that of the heat conductive particles. This is because, in the sheet E that is the object of comparison, even though the shape of the magnetic metal particles is spherical, the average particle size of the heat conductive particles is larger than the average particle size of the magnetic metal particles. It is also clear from the point that the electromagnetic wave suppression effect is not sufficient because it cannot be filled.
In addition, in the sheets A to D, it was possible to achieve high filling regardless of whether the heat conductive particles were spherical or crushed powder, because the dispersibility of the spherical magnetic metal particles was high, and the average of the magnetic metal particles This is because the particle size is larger than the average particle size of the heat conductive particles.
In addition, the sheet B can contain two types of thermally conductive particles because the magnetic metal particles are highly dispersible and can be filled with various thermally conductive particles.
As is apparent from the above evaluation, the sheets A to D are formed of spherical magnetic metal particles as the electromagnetic wave absorbing material, so that the magnetic metal particles and the thermal conductivity are, for example, 70 vol% or more in terms of the sum of volume ratios. Higher packing with particles, and with increased packing of magnetic metal particles, the value of the imaginary part of the complex relative permeability in the sheet could be increased, so good heat conduction characteristics and electromagnetic wave suppression effect And was able to be realized.
In addition, since the average particle diameter of the magnetic metal particles is larger than the average particle diameter of the heat conductive particles, the sheets A to D can be highly filled with the heat conductive particles by using the dispersibility of the magnetic metal particles. As a result, it was possible to realize high heat conduction characteristics while maintaining a high electromagnetic wave suppression effect.
In addition, since the sheet B has high dispersibility of the magnetic metal particles, it was possible to highly fill various heat conductive particles regardless of whether it was a spherical powder or a crushed powder. For this reason, the sheet B clearly shows that the characteristics could be easily changed by adjusting the filling amount of various heat conductive particles while maintaining sufficient heat conduction characteristics and electromagnetic wave suppression characteristics. Yes.
Example 2
Next, as Example 2 of the heat conductive sheet 11, the heat conductive particles having a volume ratio of 3 vol% or more are higher in heat conductivity than the heat conductive sheet using flat magnetic metal particles. What is desirable for realizing the above will be described using the following sheets I and J.
<Sheet I>
Sheet I was produced as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 12.8 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material. In this flexible resin material, 2500 g (73 vol%) of a spherical amorphous alloy (Fe—Si—B—Cr) having an average particle diameter of 26 μm as magnetic metal particles and spherical alumina having an average particle diameter of 3 μm as heat conductive particles A total of 76 vol% of 60 g (3 vol%) of the powder was stirred with a vacuum stirrer, and then a sheet having a thickness of 2 mm was prepared and heated at 100 ° C. for 60 minutes to be cured to produce Sheet I.
<Sheet J>
Sheet J was prepared as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 20.5 g of a coupling agent for coupling the thermally conductive particles were used as a flexible resin material. In this flexible resin material, 2000 g (67 vol%) of a spherical amorphous alloy (Fe—Si—B—Cr) having an average particle diameter of 50 μm as magnetic metal particles and spherical alumina having an average particle diameter of 3 μm as heat conductive particles A total of 70 vol% of 50 g (3 vol%) of the powder was stirred with a vacuum stirrer, and then a sheet having a thickness of 2 mm was formed and heated at 100 ° C. for 60 minutes to be cured to produce a sheet J.
<Evaluation>
With respect to these two types of thermal conductive sheets I and J, the imaginary part μ ″ of the complex relative permeability was measured under the conditions performed in Example 1 described above, and the thermal conductivity was calculated.
Table 2 below shows the measured imaginary part μ ″ of the complex relative permeability and the calculated thermal conductivity.
Figure JPOXMLDOC01-appb-T000005
 　上記の表２に示されるように、磁性金属粒子の体積率に応じて特性が変化するものの、熱伝導性粒子の体積率が３ｖｏｌ％以上を含有されていることにより、熱伝導率の値が２以上となった。
　この評価結果から明らかなように、シートＩ、Ｊは、熱伝導性粒子の体積率が３ｖｏｌ％以上含有されていることによって、例えば偏平形状の磁性金属粒子を用いた熱伝導性シートと比べて高い熱伝導特性を実現することができた。
実施例３
　次に、熱伝導性シート１１の実施例３として、磁性金属粒子と熱伝導性粒子との平均粒径比を調節することにより、シートに占める体積率の和が最大８０ｖｏｌ％程度となるように、磁性金属粒子と熱伝導性粒子とを高充填することができることを、下記のシートＫ、Ｌを用いて説明する。
　＜シートＫ＞
　シートＫを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤２７ｇを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が２６μｍの球状アモルファス合金（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）を２３５０ｇ（６０ｖｏｌ％）、熱伝導性粒子として平均粒径が３μｍの球状アルミナ粉末３５５ｇ（１６ｖｏｌ％）の合計７６ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させることによりシートＫを作製した。
　＜シートＬ＞
　シートＬを、次のようにして作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤２０ｇを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が５０μｍの球状アモルファス合金（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）を２４３５ｇ（５８ｖｏｌ％）、熱伝導性粒子として平均粒径が３μｍの球状アルミナ粉末５２５ｇ（２２ｖｏｌ％）の合計８０ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させることにより熱伝導性シートＬを作製した。
　＜評価＞
　これら２種類のシートＫ、Ｌに対して、上述した実施例１及び２で行ったときと同様の条件下で複素比透磁率の虚数部μ”を測定し、熱伝導率を算出した。
　測定した複素比透磁率の虚数部μ”と、算出した熱伝導率を、下記の表３に示す。
Figure JPOXMLDOC01-appb-T000005
 As shown in Table 2 above, although the characteristics change according to the volume ratio of the magnetic metal particles, the thermal conductivity value is 3 vol% or more, so that the value of the thermal conductivity is increased. It became 2 or more.
As is apparent from the evaluation results, the sheets I and J have a volume ratio of 3 vol% or more of the heat conductive particles, so that, for example, compared with a heat conductive sheet using flat magnetic metal particles, for example. High heat conduction characteristics could be realized.
Example 3
Next, as Example 3 of the heat conductive sheet 11, by adjusting the average particle size ratio of the magnetic metal particles and the heat conductive particles, the sum of the volume ratio in the sheet is about 80 vol% at the maximum. The fact that magnetic metal particles and thermally conductive particles can be highly filled will be described using the following sheets K and L.
<Sheet K>
Sheet K was produced as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 27 g of a coupling agent for applying a coupling treatment to the thermally conductive particles were used as a flexible resin material. In this flexible resin material, 2350 g (60 vol%) of spherical amorphous alloy (Fe—Si—B—Cr) having an average particle diameter of 26 μm as magnetic metal particles, and spherical alumina having an average particle diameter of 3 μm as heat conductive particles A total of 76 vol% of 355 g (16 vol%) of powder was stirred with a vacuum stirrer, and then a sheet with a thickness of 2 mm was prepared. The sheet K was prepared by heating at 100 ° C. for 60 minutes to cure.
<Sheet L>
Sheet L was produced as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 20 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material. In this flexible resin material, 2435 g (58 vol%) of spherical amorphous alloy (Fe—Si—B—Cr) having an average particle diameter of 50 μm as magnetic metal particles and spherical alumina having an average particle diameter of 3 μm as heat conductive particles A total of 80 vol% of 525 g (22 vol%) of the powder was stirred with a vacuum stirrer, and then a sheet having a thickness of 2 mm was prepared and heated and cured at 100 ° C. for 60 minutes to prepare a heat conductive sheet L.
<Evaluation>
For these two types of sheets K and L, the imaginary part μ ″ of the complex relative permeability was measured under the same conditions as those performed in Examples 1 and 2 described above, and the thermal conductivity was calculated.
Table 3 below shows the imaginary part μ ″ of the measured complex relative permeability and the calculated thermal conductivity.
Figure JPOXMLDOC01-appb-T000006
 　上記の表３に示すように、シートＫ、Ｌでは、磁性金属粒子と熱伝導性粒子との平均粒径比を調節することにより、球状の磁性金属粒子の分散性の良さを利用して、シートに占める体積率の和が最大８０ｖｏｌ％程度となるように、磁性金属粒子と熱伝導性粒子とを含有することができ、結果として良好な熱伝導特性及び電磁波抑制特性を実現することができた。
実施例４
　次に、熱伝導性シート１１の実施例４として、カップリング処理の有無による特性の変化について、下記のシートＭ、Ｎを用いて説明する。
　＜シートＭ＞
　カップリング処理が施されていない具体例として、シートＭを次のように作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇとを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が２６μｍの球状アモルファス合金（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）を１９７０ｇ（６０ｖｏｌ％）、熱伝導性粒子として平均粒径が３μｍの球状アルミナ粉末３３５ｇ（１８ｖｏｌ％）の合計７８ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化して、シートＭを作製した。
　＜シートＮ＞
　カップリング処理が施されている以外を熱伝導性シートＭと同様にして、シートＮを作製した。すなわち、分子鎖両末端にのみアルケニル基を含有するオルガノポリシロキサンと側鎖にのみケイ素原子に直接結合した水素原子をもつメチルハイドロジェンポリシロキサンと白金族系付加反応触媒を１％未満含んだシリコーン混合物１００ｇと熱伝導性粒子にカップリング処理を施すためのカップリング剤３１ｇを可撓性樹脂材料とした。この可撓性樹脂材料に、磁性金属粒子として平均粒径が２６μｍの球状アモルファス合金（Ｆｅ－Ｓｉ－Ｂ－Ｃｒ）を２６５０ｇ（６０ｖｏｌ％）、熱伝導性粒子として平均粒径が３μｍの球状アルミナ粉末４５０ｇ（１８ｖｏｌ％）の合計７８ｖｏｌ％を真空攪拌機にて攪拌した後に、厚さが２ｍｍのシートにし、１００℃で６０分間加熱して硬化させてシートＮを作製した。
　＜評価＞
　これら２種類のシートＭ、Ｎに対して、上述した実施例１～３で行ったときと同様の条件下で、複素比透磁率の虚数部μ”を測定し、熱伝導率を算出した。
　測定した複素透磁率の虚数部μ”と、算出した熱伝導率を、下記の表４に示す。
Figure JPOXMLDOC01-appb-T000006
 As shown in Table 3 above, in the sheets K and L, by adjusting the average particle size ratio between the magnetic metal particles and the heat conductive particles, the good dispersibility of the spherical magnetic metal particles is utilized. Magnetic metal particles and heat conductive particles can be contained so that the sum of the volume fraction in the sheet is about 80 vol% at maximum, and as a result, good heat conduction characteristics and electromagnetic wave suppression characteristics can be realized. It was.
Example 4
Next, as Example 4 of the heat conductive sheet 11, a change in characteristics depending on the presence or absence of the coupling treatment will be described using the following sheets M and N.
<Sheet M>
As a specific example where the coupling treatment was not performed, a sheet M was manufactured as follows. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture was used as a flexible resin material. In this flexible resin material, 1970 g (60 vol%) of a spherical amorphous alloy (Fe—Si—B—Cr) having an average particle diameter of 26 μm as magnetic metal particles and spherical alumina having an average particle diameter of 3 μm as heat conductive particles A total of 78 vol% of 335 g (18 vol%) of powder was stirred with a vacuum stirrer, and then a sheet having a thickness of 2 mm was cured by heating at 100 ° C. for 60 minutes to produce a sheet M.
<Sheet N>
A sheet N was produced in the same manner as the heat conductive sheet M except that the coupling treatment was performed. That is, a silicone containing less than 1% of an organopolysiloxane containing an alkenyl group only at both ends of a molecular chain, methylhydrogenpolysiloxane having a hydrogen atom directly bonded to a silicon atom only in a side chain, and a platinum group addition reaction catalyst 100 g of the mixture and 31 g of a coupling agent for applying a coupling treatment to the heat conductive particles were used as a flexible resin material. In this flexible resin material, 2650 g (60 vol%) of spherical amorphous alloy (Fe—Si—B—Cr) having an average particle diameter of 26 μm as magnetic metal particles, and spherical alumina having an average particle diameter of 3 μm as thermally conductive particles After stirring a total of 78 vol% of 450 g (18 vol%) of the powder with a vacuum stirrer, the sheet was made into a sheet having a thickness of 2 mm and cured by heating at 100 ° C. for 60 minutes to prepare a sheet N.
<Evaluation>
For these two types of sheets M and N, the imaginary part μ ″ of the complex relative permeability was measured under the same conditions as those performed in Examples 1 to 3 described above, and the thermal conductivity was calculated.
Table 4 below shows the measured imaginary part μ ″ of the complex magnetic permeability and the calculated thermal conductivity.
Figure JPOXMLDOC01-appb-T000007
 　上記の表４から明らかなように、カップリング処理の有無に拘わらず、熱伝導性シートＭ、Ｎ両者とも良好な熱伝導特性と電磁波抑制特性を実現することができた。また、熱伝導性シートＮは、特に熱伝導性粒子に対してカップリング処理を施すカップリング剤を含有することで、シート内での分散性が向上し、特に良好な熱伝導特性を実現することができた。
Figure JPOXMLDOC01-appb-T000007
 As is clear from Table 4 above, both the heat conductive sheets M and N were able to realize good heat conduction characteristics and electromagnetic wave suppression characteristics regardless of the presence or absence of the coupling treatment. Further, the heat conductive sheet N contains a coupling agent that applies a coupling treatment to the heat conductive particles, thereby improving dispersibility in the sheet and realizing particularly good heat conduction characteristics. I was able to.

Claims (5)

  1. 電子部品と、この電子部品が発熱する熱を放熱させる金属製放熱部材との間に配置される熱伝導性シートにおいて、
    　球状の磁性金属粒子と、上記磁性金属粒子よりも熱伝導性が高い熱伝導性粒子とを含有する可撓性樹脂からなり、
    　上記磁性金属粒子の平均粒径は、上記熱伝導性粒子の平均粒径よりも大きく、
    　当該熱伝導性シートに占める上記磁性金属粒子の体積率は５５ｖｏｌ％以上であることを特徴とする熱伝導性シート。     In the heat conductive sheet disposed between the electronic component and the metal heat radiating member that radiates the heat generated by the electronic component,
    It consists of a flexible resin containing spherical magnetic metal particles and heat conductive particles having higher heat conductivity than the magnetic metal particles,
    The average particle size of the magnetic metal particles is larger than the average particle size of the thermally conductive particles,
    The volume ratio of the said magnetic metal particle which occupies for the said heat conductive sheet is 55 vol% or more, The heat conductive sheet characterized by the above-mentioned.
  2. 上記熱伝導性粒子の体積率は、３ｖｏｌ％以上であることを特徴とする請求項１記載の熱伝導性シート。 The heat conductive sheet according to claim 1, wherein the volume ratio of the heat conductive particles is 3 vol% or more.
  3. 当該熱伝導性シートに占める上記磁性金属粒子の体積率と、当該熱伝導性シートに占める上記熱伝導性粒子の体積率との和は、７０ｖｏｌ％以上であることを特徴とする請求項２記載の熱伝導性シート。 The sum of the volume fraction of the magnetic metal particles in the thermally conductive sheet and the volume fraction of the thermally conductive particles in the thermally conductive sheet is 70 vol% or more. Thermally conductive sheet.
  4. 上記熱伝導性粒子には、カップリング処理が施されていることを特徴とする請求項１記載の熱伝導性シート。 The heat conductive sheet according to claim 1, wherein the heat conductive particles are subjected to a coupling treatment.
  5. 上記熱伝導性粒子は、２種類以上の熱伝導性材料から構成されている請求項１記載の熱伝導性シート。 The thermally conductive sheet according to claim 1, wherein the thermally conductive particles are composed of two or more kinds of thermally conductive materials.
PCT/JP2010/052643 2010-02-22 2010-02-22 Thermally conductive sheet WO2011101989A1 (en)

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KR102009416B1 (en) * 2016-12-01 2019-08-12 율촌화학 주식회사 Composition for complex sheet with emi shields and absorbing and thermal dissipation, and complex sheet comprising the same
US11985805B2 (en) * 2020-03-31 2024-05-14 3M Innovative Properties Company Thermally conductive electromagnetically absorptive material

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JP3608612B2 (en) * 2001-03-21 2005-01-12 信越化学工業株式会社 Electromagnetic wave absorbing heat conducting composition, heat softening electromagnetic wave absorbing heat radiation sheet, and heat radiation construction method
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JP2006310812A (en) * 2005-03-30 2006-11-09 Yasuyuki Agari Thermally conductive sheet

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