WO2001016968A1

WO2001016968A1 - Sheet capable of absorbing heat and electromagnetic radiation

Info

Publication number: WO2001016968A1
Application number: PCT/JP2000/005641
Authority: WO
Inventors: Yasuji Nakayama; Makoto Ishikura; Junji Konda; Hiroaki Ono; Manabu Teranishi
Original assignee: Fdk Corporation
Priority date: 1999-08-26
Filing date: 2000-08-23
Publication date: 2001-03-08
Also published as: JP2001068312A

Abstract

The invention provides a wave-absorbing sheet that absorbs electromagnetic noise and has high thermal conductivity to dissipate heat. A sheet (1) is a soft sheet of 50 on a scale of rubber hardness and resistant to 150°C, whose surfaces are adhesive so that it can be directly attached between a semiconductor device such as a CPU (2) and a heat sink (3) with no adhesive material. Since the sheet is soft, its adhesion to the electric device improves, allowing heat and electromagnetic radiation from a semiconductor device to be absorbed efficiently. The sheet (1) preferably includes 100 parts by weight of liquid silicon resin, 300 parts by weight of magnetically soft powder, and 100 parts by weight of nonmagnetic inorganic powder in order to improve the electromagnetic absorption at 100 megahertz to several gigahertz as well as heat absorption.

Description

Specification

Radio wave absorption heat conduction sheet

Technical field

The present invention relates to a radio wave absorbing heat conductive sheet, and more specifically, to an improvement in a structure for removing heat and noise in an electronic circuit.

Background art

Various devices such as computers, home appliances, automobiles, and industrial devices incorporate electronic circuits using semiconductor elements for controlling the functions of the devices. By digitizing electronic circuits, circuits with even higher processing speed have been devised. With this high-speed processing, measures against radiated noise to the surroundings and noise countermeasures due to in-flight radio interference caused by the electromagnetic waves generated by itself will be required. In addition, the temperature of semiconductor devices such as CPU becomes high, so the importance of heat dissipation measures has increased more than ever.

Therefore, as a conventional noise countermeasure, for example, an insulating soft magnetic layer is laminated on the surface of a conductive support as shown in Japanese Patent Application Laid-Open No. There is a radio wave absorber having a structure in which a dielectric layer is formed on the surface of a conductive magnetic layer. The insulating soft magnetic layer is obtained by hardening the soft magnetic powder with an organic binder. This radio wave absorber is placed on a semiconductor device or the like that is subject to noise suppression.

As a measure for heat radiation, for example, as shown in JP-A-9-11-1124, a silica fine powder of 10 to 90% by weight having an average particle diameter of 0.1 to 50% is used. Containing 40 to 90% by weight of a thermally conductive filler composed of 90 to 10% by weight of alumina fine powder having an average particle size of 0.1 to 5m (excluding 5m). There is a thermally conductive silicone rubber composition formed by the heat treatment. Then, the silicone rubber obtained by curing the composition by an addition reaction curing type or condensation reaction curing type curing mechanism is attached to a semiconductor element or the like to be subjected to a heat radiation measure. However, the inventions disclosed in Japanese Patent Application Laid-Open No. Hei 7-212 979 and Japanese Patent Application Laid-Open No. Hei 9-111 1124 are applicable to both measures against radiated noise and in-machine failure and measures against heat radiation of semiconductor elements. It was not an invention that would take optimal measures.

In other words, the invention of Japanese Patent Application Laid-Open No. Hei 7-212,799 can reduce noise, but does not have sufficient heat conductivity, and can be mounted on a semiconductor device that requires heat radiation measures such as CPU. Have difficulty. On the other hand, in the invention of Japanese Patent Application Laid-Open No. 9-111124, the filler in the silicone is not a substance contributing to radio wave absorption, and it is not expected to reduce radiation noise due to radio wave absorption.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and has as its object to solve the above-described problems, to provide a radio wave absorbing property required as a noise countermeasure for a semiconductor device, and to generate a semiconductor device such as a semiconductor device. An object of the present invention is to provide a radio wave absorbing heat conductive sheet having both properties of high heat conductivity that absorbs heat and guides the heat to the outside.

Disclosure of the invention

In order to achieve the above-mentioned object, the radio wave absorbing heat conductive sheet according to the present invention is constituted by a soft sheet formed by mixing a soft magnetic powder with a silicone resin. In this configuration, the soft magnetic powder filled in the silicone resin allows a high complex magnetic permeability ('-jμ') to be obtained in a wide frequency band from DC to 20 GHz. In particular, from 100 MHz to several GHz, the imaginary part (;) of the complex permeability becomes large.

The imaginary term ") of the complex permeability is proportional to the resistance component (R) of the high-frequency impedance, and electromagnetic energy is easily converted to heat as the imaginary term (〃) increases. The conversion absorbs radio noise.

In addition, silicone-based resins have higher thermal conductivity and heat resistance than other resins, but by mixing with soft magnetic powders having higher thermal conductivity than organic substances, This sheet has a higher thermal conductivity than the silicone resin alone.

Therefore, when the radio wave absorbing heat conductive sheet of the present invention is brought into contact with the surface of a target article such as a semiconductor device, the heat generated from the target article is absorbed by the radio wave absorbing heat conductive sheet, heat is conducted inside the sheet, and the heat is transferred. Released outside. And, if the radio wave absorbing heat conductive sheet of the present invention is interposed between the heat radiating component such as a heat sink and the target article, the heat generated from the target article can be efficiently transmitted to the heat radiating component, and the heat radiating effect is improved. improves.

In addition, since radio wave noise emitted from the target article is absorbed in the radio wave absorption and heat conduction sheet, it does not leak out and does not reflect internally. Of course, radio wave noise from the outside is also absorbed by the radio wave absorbing heat conductive sheet, so that the noise is suppressed from entering the target article.

Further, since the radio wave absorbing heat conductive sheet of the present invention is made to be a soft sheet, when the radio wave absorbing heat conductive sheet of the present invention is brought into contact with the surface of the object by being pressed relatively, the surface of the soft sheet (adhesion) Surface) is also deformed and adheres without gaps. Therefore, the heat resistance at the contact surface is small, and the above-described measures for heat dissipation accompanying heat absorption are more remarkably exhibited. The same can be said for the absorption of radio noise. As the soft magnetic powder, at least one of a ferrite soft magnetic powder and a metal soft magnetic powder can be used. With this configuration, the thermal conductivity is improved. When ferrite-based soft magnetic powder is used, the volume resistivity is as high as 10 Ω · cm or more, which is effective when insulating properties are required. Become smaller. In the case of metal-based soft magnetic powder, the volume resistivity is lower than that of ferrite-based soft magnetic powder, and the reflection of radio waves increases. Therefore, an appropriate material is selected according to the required specifications and the like.

Preferably, the metal-based soft magnetic powder is at least one of permalloy, sendust, gay steel, permendur, pure iron, and magnetic stainless steel. Is composed of a spherical or flat particle shape.

Since the metal-based soft magnetic powder has a higher magnetic permeability than the ferrite-based soft magnetic powder and the shape of the powder particles can be easily adjusted, the radio wave absorbing heat conductive sheet is further improved in a predetermined frequency band. The imaginary term (複素) of the complex magnetic permeability can be shown. In particular, in the case of a flat particle shape, the flattened metal soft magnetic powder is oriented in the surface direction of the sheet to suppress the effect of the demagnetizing field in the surface direction, and the imaginary number of high complex permeability at a given frequency The term (〃) is obtained.

Furthermore, it is preferable that the surface of the flexible sheet has tackiness. With this configuration, the silicone resin itself can be mounted on the surface of the target article without using an adhesive due to its own adhesiveness. Further, when the use of the adhesive material is not required, the radio wave absorbing heat conductive sheet can be brought into direct contact with the target article on the circuit board, which is a noise transmission source, so that noise absorption is improved.

Further, the flexible sheet may be provided on both sides or one side of the conductive sheet. With this configuration, the conductive sheet enhances the shielding effect of radio waves, and is effective when shielding radiated noise to prevent leakage to the outside. Although the shielding effect can be obtained by using only the conductive sheet, there are problems such as the reflection of radio waves becoming large and the reflected wave adversely affecting the target article, and radiation noise from the target article being re-emitted by the conductive sheet. cause.

Here, the conductive sheet is made of, for example, a metal foil, a metal mesh, a metal-coated resin mesh, a conductive nonwoven fabric, a conductive woven fabric, a resin mixed with a conductive powder (carbon powder, metal powder, or the like).

Further, it is preferable that the conductive sheet is made of a soft magnetic metal. With this configuration, the shielding property in a low frequency band (1 MHz or less) is improved by the conductive sheet in the above-described radio wave absorbing heat conductive sheet.

Furthermore, the soft sheet may be mixed with a non-magnetic inorganic powder. It is good to configure. As the non-magnetic inorganic powder, for example, A l ₂ 〇 _3, Z N_〇, there are M n O, etc., since the non-magnetic inorganic powder is provided with a high heat transfer electrical resistance as compared with a silicone resin, these When mixed with the electromagnetic wave absorbing heat conductive sheet, the thermal conductivity of the electromagnetic wave absorbing heat conductive sheet is improved.

*Definition of terms

A “soft sheet” is a sheet that is elastically deformed when pressed against the surface of a target article, and has such a softness that the sheet surface is deformed into a shape along the surface shape of the target article. Then, it is not always necessary to have an elastic restoring force to return to the original sheet shape when separated from the target article. And, as an example, when evaluated in terms of rubber hardness, those having a hardness of 50 or less correspond. Of course, the rubber hardness is a standard, and any rubber having a higher hardness may have the above-mentioned properties.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view showing a first embodiment of a radio wave absorbing heat conductive sheet according to the present invention, and FIG. 2 (a) is a second embodiment of a radio wave absorbing heat conductive sheet according to the present invention. FIG. 2 (b) is a front view showing a second embodiment of the radio wave absorbing heat conductive sheet according to the present invention, and FIG. 3 is an implementation view of the radio wave absorbing heat conductive sheet according to the present invention. FIG. 4 is a front view showing a state in which the form is mounted on an electronic circuit, FIG. 4 is a cross-sectional view showing a state in which the embodiment of the radio wave absorbing heat conductive sheet according to the present invention is mounted on another electronic circuit, and FIG. Fig. 6 is a view showing a part of the results of an experiment conducted to determine an optimum component for the embodiment of the radio wave absorbing heat conducting sheet according to the present invention. FIG. 10 is a diagram illustrating a part of results of another experiment performed in order to obtain an optimal component.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows a first embodiment of a radio wave absorbing heat conductive sheet according to the present invention. As shown in the figure, the radio wave absorbing heat conductive sheet 1 of the present embodiment has It is composed of a flexible sheet 1a composed of a flat sheet piece. The soft sheet 1a is formed by mixing a soft magnetic powder with a liquid silicone resin. As the soft magnetic powder, either a ferrite soft magnetic powder or a metal soft magnetic powder may be used, or a mixture of both may be used. Various types such as Zn-based ferrite, Ni-based ferrite, and Mg-Ζη-based ferrite can be used. It is preferable to use Ni-based ferrite because heat conduction is best.

The mixing ratio of the soft magnetic powder to 100 parts by weight of the liquid silicone resin may be adjusted in the range of 100 parts by weight to 900 parts by weight. The mixing amount of the soft magnetic powder is from 200 parts by weight to 400 parts by weight. Furthermore, it may be mixed with non-magnetic inorganic powders such high A 1 ₂ 〇 ₃ thermal conductivity for the purpose of improving the thermal conductivity. Incidentally, the non-magnetic inorganic powder is not limited to A 1 ₂ 0 _3, high zinc oxide thermal conductivity may be used oxide powder and gold Shokukotai such copper oxide.

Furthermore, the surface of the flexible sheet 1a is made to have a sticky tackiness. In order to impart such tackiness, for example, it can be formed by selecting a silicone resin having viscosity after curing, or by adjusting the amount of a curing agent (vulcanizing agent) added.

The radio wave absorbing heat conductive sheet 1 having such components has a rubber hardness of 50 or less, a heat conductivity of 0.5 wZm 'k or more, and a heat resistant temperature of 150 or more. Can be.

FIG. 2 shows a second embodiment of the present invention. In the present embodiment, the soft sheet 1a is attached so as to sandwich the conductive sheet 1b such as a metal foil or a metal mesh from both sides. When the radio wave absorbing heat conductive sheet is configured in this way, noise absorption and thermal conductivity are improved, and the chip is generated from some chips in the electronic circuit. It has been confirmed that such electromagnetic waves are less likely to cause electromagnetic interference (in-machine interference) in equipment by wrapping around to other chips.

For the conductive sheet lb, in addition to the above, conductive non-woven fabric, conductive woven fabric, resin mixed with conductive powder, or the like may be applied, and carbon powder, metal powder, or the like may be used as the conductive powder. . When a soft magnetic metal or resin mixed with a soft magnetic powder is used as the conductive sheet, the effect is improved at a low frequency (1 MHz or less). Next, an actual use state of each of the above-described radio wave absorbing heat conductive sheets 1 will be described. As an example, as shown in FIG. 3, the radio wave absorbing heat conductive sheet 1 is disposed on the surface of the CPU 2 and is interposed between the CPU 2 and the heat sink 3.

With this configuration, the surface of the semiconductor component such as the CPU 2 and the both surfaces of the radio wave absorbing heat conductive sheet 1 that is in contact with the connection surface of the heat sink 3 are in close contact with the connection surfaces without any gap. Therefore, the thermal resistance at the connection portion is small, and the heat generated in CPU 2 is efficiently transmitted to heat sink 3 and radiated.

In addition, since the high frequency noise generated from the CPU 2 is also absorbed by the radio wave absorbing heat conductive sheet 1 which is in close contact with the high frequency noise, scattering to the outside as radiation noise can be suppressed as much as possible.

FIG. 4 shows a state where the radio wave absorbing heat conductive sheet 1 is mounted on an electronic component in which a substrate 5 on which a semiconductor chip 4 is mounted is housed in a case 6. The radio wave absorbing heat conductive sheet 1 is a soft flat sheet and its surface is sticky, so that it can be fixed simply by placing it between the upper surface 4 a of the semiconductor chip 4 or the like and the case 6. Is determined. That is, the configuration does not require a connection member such as an adhesive tape. In addition, by closing the gap between the semiconductor chip 4 and the case 6 for packing the electronic circuit in this manner, it is possible to suppress the occurrence of an in-flight failure due to the electromagnetic waves generated from one semiconductor chip being routed to another semiconductor chip. It will be easier. In particular, since the radio wave absorbing heat conductive sheet and the semiconductor chip 4 etc. are in close contact with each other, the gap formed between them is Noise is not propagated through, and the propagation of noise can be reliably suppressed.

Furthermore, when the case 6 is made of metal, the case 6 also functions as a heat sink, and a heat dissipation effect can be expected. Even if the case 6 does not have the function of a heat sink, the heat generated from the semiconductor chip 4 and the like proceeds in the thickness direction of the radio wave absorbing heat conductive sheet 1, so that the heat generated in the adjacent element Can be suppressed as much as possible (compared to those that propagate in the air).

Hereinafter, the manufacturing process of the radio wave absorbing heat conductive sheet of the present embodiment will be briefly described. The liquid silicone resin and the soft magnetic powder are uniformly mixed by a mixer. At this time, it may be mixed with a high thermal conductivity A 1 ₂ 0 ₃ or the like in order to improve the thermal conductivity.

The mixer performs mixing by rotating mixing wings in a closed stainless steel chamber. At the time of mixing, the pressure in the mixer should be lower than the atmospheric pressure, and care should be taken to prevent air bubbles from entering the liquid silicone resin. When the soft magnetic powder is ferrite, it is preferable to control the temperature of the mixture from 40 to 100 in order to adjust the viscosity of the mixture of the liquid silicone resin and the ferrite. .

As a mixing machine, a three-roll mill, a pressure roller, a twin-screw kneader, or the like can be used. However, the twin-screw extruder allows continuous mixing and improves productivity, but the dispersibility of the liquid silicone resin and ferrite powder is not sufficient, and simple kneading must be performed in advance.

The kneaded mixture is applied to the PET film at a thickness of 1 band by the doctor blade method. After coating, heat and cure to complete. In order to manufacture the second embodiment, a conductive sheet material prepared in advance is sandwiched between the coated sheets during or after the application by the doctor blade method.

When a flat metal-based soft magnetic powder is used, the thickness of one coating is 0.1 mm. Laminate while chopping below. That is, the metal-based soft magnetic powder is coated while being oriented in the plane direction to have a predetermined thickness. By orienting in the plane direction in this manner, a large projection area of the metal-based magnetic powder in the thickness direction of the sheet can be secured, and the electromagnetic wave absorbing function is improved.

By the way, the thermal conductivity of the radio wave absorbing heat conductive sheet manufactured as described above may be 0.5 w / m · k or more when used in a place having a relatively small calorific value. When it is applied to a mounting part where is large, it is more than 1.0 w / m * k, and preferably more than 1.5 w / m · k.

*Experimental result

Fig. 5 shows the rubber hardness and thermal conductivity of Samples A to D with different constituent components and their mixing amounts, and Fig. 6 shows the radio wave absorption characteristics of those samples for the coupling attenuation between the small antennas at each frequency. Shown as level (dB).

The amount of silicone resin in all samples is 100 parts by weight, sample A contains 400 parts by weight of Mn-Zn ferrite powder, and sample B contains Mn-Zn system. It contains 600 parts by weight of ferrite powder. Sample C contains 1 0 0 parts by weight of A 1 ₂ 0 ₃ powder in addition to 3 0 0 parts by weight of M n _ Z n ferrite powder. Sample D contains 400 parts by weight of Ni_Zn ferrite powder. However, none of the above samples used a conductive sheet. As shown in FIG. 5, the rubber hardness is particularly low when the content of the ferrite powder used as the soft magnetic powder is from 300 to 400 parts by weight. From the experimental results other than the sample shown in the figure, it was found that when the amount of the soft magnetic powder was 900 parts by weight or more, it was difficult to mix the powder with a resin matrix such as a liquid silicone resin.

On the other hand, when the soft magnetic powder was less than 100 parts by weight, it was found that the required magnetic wave absorption performance could not be obtained because the complex magnetic permeability was too low. Therefore, the manufacturing method of the embodiment As described in the description, the mixing amount of the soft magnetic powder with respect to 100 parts by weight of the liquid silicone resin was in the range of 100 to 900 parts by weight.

Also, even though Sample A and Sample D and the rubber hardness hardly changes, the thermal conductivity of the sample C with the children in the A 1 ₂ 0 ₃ powder is non-magnetic inorganic powder, other samples It can be seen that the thermal conductivity is higher. From various experiments, it was confirmed that the thermal conductivity can be easily increased to about 1.5 w / m · k by adding non-magnetic inorganic powder without deteriorating the rubber hardness or the bond attenuation level. ing. The thermal conductivity required by the user who needs the radio wave absorbing heat conductive sheet as in the present embodiment is about 0.5 to 1.5 w / m'k, depending on the member.

As shown in Fig. 4, when ferrite powder is mixed into each sample as a soft magnetic powder, good magnetic properties can be obtained with respect to in-machine failure of electronic equipment. As shown in the figure, in any band from 0 to 100 (MHz), a sufficient level of electromagnetic wave noise is absorbed for noise suppression of semiconductor chips such as CPU.

It has been found that this characteristic exhibits good noise absorption characteristics especially as a countermeasure against noise of an electronic circuit including a semiconductor chip such as CPU over a range of 100 MHz to several GHz. In addition, the electromagnetic energy of the absorbed electromagnetic waves is converted to heat, but the sample has a higher thermal conductivity and heat resistance than the radio-absorbing heat conductive sheet using other resins because the sample is based on silicone resin. .

As shown in the figure, the larger the amount of the soft magnetic powder, the higher the coupling attenuation level. However, as described above, mixing the metallic soft magnetic powder with the ferrite powder, etc. By changing the particle shape in a timely manner, a better coupling attenuation level can be obtained at a specific frequency.

Industrial applicability

As described above, in the radio wave absorbing heat conductive sheet according to the present invention, the silicone resin The structure consists of a soft sheet formed by mixing soft magnetic powder into the surface of a semiconductor chip. It can have good heat conductivity. In addition to having a high complex magnetic permeability, it has electromagnetic wave absorption that can absorb electromagnetic waves in an electronic circuit on which semiconductor elements are mounted over a wide band, and directly absorbs electromagnetic noise generated from such chips. Since heat can be efficiently converted to heat, good noise countermeasures can be taken.

When at least one of a ferrite soft magnetic powder and a metal soft magnetic powder is used as the soft magnetic powder, in the case of a ferrite, a radio wave absorbing heat conductive sheet having high thermal conductivity and insulation properties can be obtained. . In the case of a metal material, a radio wave absorbing heat conductive sheet having high heat conductivity and high radio wave absorption can be obtained. The metal-based soft magnetic powder is at least one of permalloy, sendust, gay steel, permendur, pure iron, and magnetic stainless steel, and has a spherical or flat particle shape. If this is the case, a radio wave absorbing heat conductive sheet having high electromagnetic wave absorption in a desired frequency band can be obtained.

If the surface of the flexible sheet is made sticky, the adhesiveness between the semiconductor chip in the electronic equipment to be mounted and the electromagnetic wave absorbing heat conductive sheet is improved, so that the heat generated from those chips can be transmitted to the outside. A radio wave absorbing heat conductive sheet that easily absorbs electromagnetic waves can be obtained. When the soft sheet is provided on both sides or one side of the conductive sheet, noise shielding characteristics are improved.

If the conductive sheet is made of a soft magnetic metal, the shielding effect in a low frequency band is further improved. Further, when a nonmagnetic inorganic powder is mixed with the soft sheet, a radio wave absorbing heat conductive sheet with further improved heat conductivity can be obtained.

Claims

The scope of the claims

1. A radio-wave-absorbing heat-conductive sheet, which is made of a soft sheet formed by mixing a soft magnetic powder with a silicone resin.

2. The radio wave absorption heat conduction sheet according to claim 1, wherein the soft magnetic powder is at least one of a ferrite soft magnetic powder and a metal soft magnetic powder.

3. The metal-based soft magnetic powder is at least one of Permalloy, Sendust, Ca steel, Permendur, Pure iron, Magnetic stainless steel,

3. The radio wave absorbing heat conductive sheet according to claim 2, wherein the shape is a spherical or flat particle shape.

4. The radio wave absorption heat conductive sheet according to any one of claims 1 to 3, wherein a surface of the flexible sheet has an adhesive property.

5. The radio wave absorbing heat conductive sheet according to any one of claims 1 to 4, wherein the soft sheet is provided on both sides or one side of the conductive sheet.

6. The radio wave absorbing heat conductive sheet according to claim 5, wherein the conductive sheet is made of a soft magnetic metal.

7. The radio wave absorption heat conductive sheet according to any one of claims 1 to 6, wherein a non-magnetic inorganic powder is mixed with the soft sheet.