JP2014239236A - Thermally conductive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermally conductive sheet having good functions from the viewpoint of both the thermal conduction property and the electromagnetic wave-suppression property by performing the higher-density packing of magnetic metal particles, and thermally conductive particles better than the magnetic metal particles in thermal conductivity.SOLUTION: A thermally conductive sheet 11 is placed between an electronic component 14 and a metal heat dissipation member 12 for dissipating heat generated by the electronic component 14. The thermally conductive sheet 11 comprises a flexible resin including spherical magnetic metal particles for absorbing electromagnetic waves radiated by the electronic component 14, and thermally conductive particles higher than the magnetic metal particles in thermal conductivity. The magnetic metal particles are larger than the thermally conductive particles in average particle diameter. The volume fraction which the magnetic metal particles account for in the thermally conductive sheet is 55 [vol.%] or larger. The total volume fraction of the magnetic metal particles and the thermally conductive particles is larger than 70 [vol.%].

Description

  The present invention relates to a thermally conductive sheet disposed between an electronic component such as a semiconductor package and a metal heat radiating member that radiates heat generated by the electronic component.

  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 disposed so as to be close to electronic parts such as a semiconductor package, which is a heat generating part in the electronic equipment, in order to achieve a heat radiation effect or temperature relaxation in the equipment. 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.

JP 2006-310812 A

  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)

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.

Further, as an index of the electromagnetic wave suppressing properties, generally _"imaginary part mu _r of the complex relative permeability _{(μ r = μ r '-jμ} r)" is used. 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)

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, the amount of magnetic material and heat conductive material filled in the sheet is limited by simply mixing an 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.

  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 inventors have the following heat conductivity. Invented the 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, and the total volume ratio of the magnetic metal particles and the heat conductive particles is larger than 70 [vol%].

  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.

It is a figure which shows the structure of the circuit board with which the heat conductive sheet to which this invention was applied is mounted. It is a graph which shows the frequency characteristic of the far field intensity in a circuit board. It is a graph which shows the frequency characteristic of the far field intensity in the circuit board according to the characteristic of a heat conductive sheet. It is a graph which shows the change of the imaginary part of the complex relative magnetic permeability in 500 MHz according to the volume ratio in spherical sendust and spherical amorphous (Fe-Si-B-Cr) as magnetic metal particles. It is the graph which computed the relationship between the filling amount of the heat conductive material in a sheet | seat, and the thermal conductivity of the whole sheet | seat.

  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 therebetween, the electromagnetic coupling between the high frequency substrate 17 and the heat radiating metal plate 12 is caused. 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 near 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 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 types of magnetic metal particles are actually filled in a range of 20 vol% to 70 vol%. FIG. 4 shows 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. 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.

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 is made of a flexible resin, and the average particle diameter of the magnetic metal particles is larger than the average particle diameter of the heat conductive particles, and the volume ratio of the magnetic metal particles in the heat conductive sheet 11 is 55 [vol%] or more. It is. 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 a crystallized metal powder or metal alloy powder, Fe-based, Co-based, Ni-based, or 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 size is preferably in the range of 4 to 100 μm, and the heat conductive particle size is preferably in the range of 0.1 to 20 μm.

  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 heat 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 such four types of sheets A to D, the following four types of sheets E to H were used as comparison targets.

<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 size of 10 μm as magnetic metal particles and aluminum nitride having an average particle size 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 %), 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 was used to determine the oscillation frequency of electromagnetic waves. 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.

  As can be seen from Table 1 above, the sheets A to D have an imaginary part μ ″ value of complex relative permeability of 3 or more, and increase the unnecessary radiation even when the heat radiating metal plate 12 is brought close to the high-frequency substrate 17. 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 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 in the flat shape contained in the comparison sheets F to H. This is because the spherical magnetic metal particles are more excellent in dispersibility than the magnetic metal particles.

  Moreover, 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 size 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, the highly conductive particles can be filled regardless of whether the thermally conductive particles are spherical or crushed powder, and the dispersibility of the spherical magnetic metal particles is high. 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 clear from the above evaluation, the sheets A to D are formed of spherical magnetic metal particles as the electromagnetic wave absorbing material, so that, for example, the magnetic metal particles and the thermal conductivity are 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 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.

  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.

  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.

  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 thermally 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.

  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.

  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 a spherical alumina having an average particle diameter of 3 μm as thermally 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 heat 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.

  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.

DESCRIPTION OF SYMBOLS 1 Circuit board, 11 Thermal conductive sheet, 12 Heat dissipation metal plate, 13 Resin mold, 14 Signal line, 15 Copper foil, 16 Dielectric board, 17 High frequency board

Claims (6)

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 magnetic metal particles in the thermally conductive sheet is 55 [vol%] or more,
The heat conductive sheet, wherein the total volume ratio of the magnetic metal particles and the heat conductive particles is greater than 70 [vol%].   The heat conductive sheet according to claim 1, wherein a volume ratio of the heat conductive particles is 3 vol% or more.   The heat conductive sheet according to claim 1, wherein the heat conductive particles are subjected to a coupling treatment.   The thermally conductive sheet according to claim 1, wherein the thermally conductive particles are composed of two or more kinds of thermally conductive materials.   The heat conductive sheet according to claim 1, wherein the total volume ratio of the magnetic metal particles and the heat conductive particles is 76 vol% or more.   The thermally conductive sheet according to claim 1, wherein the thermally conductive particles are spherical.

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