JP2002329989A - Heat-softening heat dissipation sheet - Google Patents

Abstract

(57) [Summary] [Problem] At normal temperature, it is a solid sheet, easy to attach and detach to electronic components and heat sink, and softens by the heat generated during operation of electronic components to achieve a negligible level of interfacial contact thermal resistance. Further, the present invention provides a heat radiating sheet that exhibits excellent heat radiating performance over a long period of time without pumping out. A heat radiation sheet to be mounted and used between an electronic component and a heat dissipating member, wherein (A) a metal foil having a thickness of 1 to 50 μm and a thermal conductivity of 10 to 500 W / mK or An intermediate layer made of a metal mesh, and (B) a softening point formed on both surfaces thereof is 40 ° C or more, and the viscosity at 80 ° C is
It is in the range of 1 × 10 ² to 1 × 10 ⁵ Pas, and the thermal conductivity is 1.0
A laminated structure including a layer made of a resin-based heat conductive composition having a W / mK or more, wherein the thickness of the entire sheet is 40 to 500 μm.
m, a heat-softening heat dissipation sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat radiating sheet used for cooling a heat-generating electronic component, and in particular, reversibly changes its property from a solid to a paste or liquid as the temperature of the electronic component rises. The present invention relates to a heat-softening heat-dissipating sheet that is a laminated structure that changes.

[0002]

2. Description of the Related Art In recent years, LSIs such as CPUs, driver ICs, and memories used in electronic devices such as personal computers, digital video disks, and mobile phones have increased power consumption as the degree of integration and operation speed have increased. At the same time, the calorific value also increases, which causes malfunction of electronic devices and damage to electronic components.

Conventionally, in electronic devices and the like, a heat sink using a metal plate having high thermal conductivity, such as brass, has been used in order to suppress a rise in the temperature of electronic components during use. The heat sink conducts heat generated by the electronic component and releases the heat from the surface due to a temperature difference from the outside air.

In order to efficiently transfer the heat generated from the electronic components to the heat sink, the heat sink must be in close contact with the electronic components. However, due to differences in the height of each electronic component and tolerances due to assembling processing, flexibility is increased. A heat conductive sheet or a heat conductive grease is interposed between the electronic component and the heat sink, and heat conduction from the electronic component to the heat sink is realized through the heat conductive sheet or the heat conductive grease. . As the heat conductive sheet, a heat conductive sheet (heat conductive silicone rubber sheet) formed of a heat conductive silicone rubber or the like is used, and as the heat conductive grease, a heat conductive silicone grease is used. .

[0005]

However, in the conventionally used thermally conductive silicone rubber sheet, there is a limit in thermal conduction performance due to the existence of contact thermal resistance at the interface with the electronic component. This means that high-frequency driving, which generates a large amount of heat,
Cooling the CPU is a major problem, and it is desired to reduce the interfacial contact thermal resistance.

On the other hand, thermal conductive silicone grease has almost negligible interfacial contact thermal resistance due to its properties close to a liquid, and has good thermal conductivity, but requires a dedicated device such as a dispenser. However, there is a problem that workability is poor when collecting. Further, the thermal conductive grease has a problem that a pump-out problem occurs when subjected to a heat cycle from room temperature to an electronic component operating temperature (60 to 120 ° C.) for a long period of time. Pump-out is a phenomenon in which the liquid oil component contained in grease separates and exudes from between the electronic component and the heat dissipating member, solidifying the grease and generating cracks and voids. This leads to an increase in resistance, which makes it impossible to radiate heat from the electronic component.

[0007] In order to improve some of the above problems, a phase-change heat-dissipating sheet (solid-state sheet at room temperature) which is softened by heat generated during the operation of electronic components and has a negligible interfacial contact thermal resistance. Phase change sheet) has been proposed. The following are proposed as prior art of those phase change seats. US Patent No. 4466
No. 483 discloses forming a phase-change wax layer on both sides of a non-metallic sheet. US Patent No. 59
Japanese Patent No. 04796 discloses a metal foil in which a phase-change paraffin or petroleum jelly is formed on one side and an adhesive is formed on the other side. Japanese Unexamined Patent Publication No. 2000-509209 discloses a phase change sheet comprising an acrylic pressure-sensitive adhesive, a wax, and a thermally conductive filler and having no intermediate layer such as a network structure or a film. However, these prior arts do not propose any effective solution for pump-out.

Accordingly, an object of the present invention is to solve the above-mentioned problems, and is a solid sheet at room temperature, which can be easily attached to and detached from an electronic component or a heat sink, and is softened by heat generated at the time of operation of the electronic component. An object of the present invention is to provide a heat radiating sheet having a contact heat resistance at a negligible level and exhibiting excellent heat radiating performance for a long time without pumping out.

[0009]

That is, the present invention relates to a heat-dissipating sheet to be mounted and used between an electronic component and a heat-dissipating member, wherein (A) the thickness is 1 to 50 μm and the thermal conductivity is Is 1
(B) formed on both surfaces of the intermediate layer which is a metal foil or a metal mesh of 0 to 500 W / mK, and is heat-softened at 40 ° C. or more, and has a viscosity of 1 × 10 ² to 1 × 10 ^{5 at} 80 ° C. A laminated structure including a layer made of a resin-based heat conductive composition having a Pa · s range and a thermal conductivity of 1.0 W / mK, and a thickness of the entire sheet in a range of 40 to 500 μm. A heat-softening heat-dissipating sheet characterized by the above.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION [Thermosoftening Heat Dissipating Sheet] The total thickness of the heat softening heat dissipation sheet as a laminated structure is 40 to 500.
It is preferred that the thickness be in the range of μm, especially 40 to 250 μm.
If the thickness is less than 40 μm, the rigidity is insufficient, so that there is a problem that the heat-softening heat-dissipating sheet is deformed when it is manually handled. On the other hand, if it exceeds 500 μm, it is disadvantageous in terms of thermal resistance.

[Intermediate Layer (A)] The metal foil or metal mesh of the intermediate layer (A) of the heat-softening heat-dissipating sheet functions as a support to increase the strength of the sheet. When mounting on and removing from the heat dissipating member, the handleability is improved.

Further, the thickness of the intermediate layer (A) is 1 to 50 μm,
In particular, the thickness is preferably in the range of 5 to 25 μm, and if it is less than 1 μm, the strength of the sheet cannot be sufficiently increased as a support. This may cause air to be trapped between the heat dissipation sheets.

The metal constituting the intermediate layer (A) is a metal having a high thermal conductivity of 10 to 500 W / mK, preferably a metal of 20 to 500 W / mK. Specifically, aluminum alloys, magnesium alloys, copper, iron,
Examples include stainless steel, silver, and gold. Further, in the case of a metal mesh, a metal foil having a plurality of holes formed by punching or a metal wire formed into a woven fabric is used.

The above-mentioned metal foil or metal mesh also has a function of suppressing pump-out of the resin-based thermally conductive composition. Generally, the heat dissipation sheet is incorporated so as to receive a compressive stress from the electronic component and the heat dissipation member. The resin-based thermally conductive composition of the present invention is thermally softened at 40 ° C. or higher, but at that time, the resin-based thermally conductive composition protrudes from the contact surface between the electronic component and the heat dissipation member due to compressive stress and has a small thickness. However, at this time, the frictional force acts between the intermediate layer and the resin-based heat conductive composition, so that the above-mentioned protrusion can be suppressed as compared with the case where there is no intermediate layer. In addition, it is possible to suppress the liquid component from oozing out (pump-out) due to the same frictional force. Further, when the intermediate layer is a metal mesh, since the resin-based heat conductive composition is embedded in the openings of the metal mesh,
Further, pump-out can be suppressed more effectively.

[Resin-based thermal conductive composition layer (B)] The thermal conductivity of the resin-based thermal conductive composition of the present invention must be 1.0 W / mK or more, preferably 20 to 50 W / mK. is there.
If the thermal conductivity is less than 1.0 W / mK, the thermal conductivity between the electronic component and the heat sink will be low, and sufficient heat radiation performance will not be exhibited.

Further, the resin-based heat conductive composition of the present invention comprises:
Although it is solid at room temperature, it is thermally softened by the heat generated by the electronic components, and the viscosity at 80 ° C. is preferably in the range of 1 × 10 ² to 1 × 10 ⁵ Pa · s, more preferably ² × 10 ⁵ Pa · s. 10 ² ~
It is better to be 5 × 10 ⁴ Pa · s. If the viscosity is less than 1 × 10 ² Pa · s, there is a problem that the liquid component is pumped out from between the electronic component and the heat sink, and the viscosity is 1 × 10 ⁵ Pa · s
Exceeding the range, the contact thermal resistance increases, the thermal conductivity between the electronic component and the heat sink decreases, and sufficient heat radiation performance cannot be exhibited. That is, the resin-based thermally conductive composition of the present invention is adjusted to a viscosity range (1 × 10 ² to 1 × 10 ⁵ Pa · s) that suppresses pump-out and does not impair heat radiation performance.

[Resin Component of Resin-Based Thermal Conductive Composition] The above-mentioned resin-based thermal conductive composition comprises a mixture of a thermosoftening resin and a thermally conductive filler. The heat-softening resin is a heat-softening component of the heat-softening heat radiating sheet. Even if the resin itself is critically heat-softened (melted) at the operating temperature of the electronic component (for example, 40 to 100 ° C.), the critical heat is not applied. A material that does not have softening properties but that thermally softens as a thermally conductive composition may be used. Specifically, polyolefins such as polyethylene and polypropylene, fluorine resins such as polyvinylidene fluoride, polyamide resins such as nylon 6, nylon 66, polyester resins such as polyethylene terephthalate, and silicone resins such as paraffin and diorganopolysiloxane. Illustrated, polyolefins are preferred. The polyolefin is preferably selected from α-olefin polymers, ethylene / α-olefin copolymers and ethylene / α-olefin / non-conjugated polyene random copolymers, more preferably those containing α-olefin polymers. , Especially α-olefin polymer, ethylene α
-Olefin copolymer and ethylene / α-olefin /
The one containing a non-conjugated polyene random copolymer is preferable, and the compounding ratio in that case is 100 parts by weight of the α-olefin polymer, and 10 to 100 parts of the ethylene / α-olefin copolymer.
It is preferably 0 parts by weight and 10 to 1000 parts by weight of an ethylene / α-olefin / non-conjugated polyene random copolymer. The heat conductive filler is preferably selected from metals, inorganic oxides, and inorganic nitrides.

[Polyolefin] The α-olefin polymer is preferably represented by the following general formula (1): CH ₂ CH (CH ₂ ) _n CH ₃ (1) Here, n is a range in which the heat conductive composition is solid or waxy at room temperature and usually softens in the range of 40 ° C. to 100 ° C., which is the heat generation temperature of electronic components, and n = 16 to 50. preferable. If n is too small, it may bleed from the heat dissipation sheet because it is liquid at room temperature, and if n is too large, it does not melt below the operating temperature (100 ° C) of the electronic component and the heat softening property of the heat dissipation sheet becomes poor. May worsen. Further, when a mixture of those derived from two or more α-olefins is used as the α-olefin polymer, the melting temperature has a wider range than when a single α-olefin is used. Can do
(Because the thermal softening temperature can have a certain range), there is an advantage that a stable heat dissipation can be obtained due to gradual hardening and softening even with a rapid temperature change, and at the same time, it is difficult to pump out. Examples of the α-olefin polymer include Dialen (trade name, manufactured by Mitsubishi Chemical Corporation).

The above-mentioned ethylene / α-olefin copolymer imparts flexibility and tackiness to the sheet (necessary from the necessity of temporarily fixing the heat dissipation sheet to an electronic component or a heat sink). The following general formula (2): [(CH ₂ -CH ₂ ) _x- (CH ₂ -CRH) _Y ] _p (2) is preferable. Here, R is an alkyl group represented by C _n H _{2n + 1} , and X, Y, P and n are positive integers.

The ethylene / α-olefin copolymer is preferably a liquid at room temperature, and has a viscosity at 25 ° C. of 200 to 100,000,000 cS.
Those in the range of t are preferred. If it is less than 200 cSt, the heat dissipation sheet has insufficient green strength, so that the handleability becomes poor,
If it exceeds 1000000 cSt, the sheet workability of the heat radiation sheet may deteriorate. More preferably, it is 300 to 300,000 cSt. In addition, a polymer having a single viscosity may be used.However, when a mixture of two or more polymers having different viscosities is used, a heat dissipation sheet having an excellent balance between flexibility and tackiness can be obtained. It is advantageous.

As an example of the ethylene / α-olefin copolymer, Lucant (trade name, manufactured by Mitsui Chemicals, Inc.) can be mentioned. Further, the ethylene / α-olefin / non-conjugated polyene random copolymer is an effective component for maintaining the strength of the sheet. The non-conjugated polyene has the following general formula (3) or
It is preferable that the rubber is an ethylene / α-olefin / non-conjugated polyene random copolymer rubber comprising at least one kind of norbornene compound having a terminal vinyl group represented by (4).

[0022]

Embedded image (In the formula, n is an integer of 0 to 10, R ¹ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ² is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.)

[0023]

Embedded image (In the formula, R ³ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.) Examples of the non-conjugated polyene include 5-vinyl-norbornene and 5
-Methylene-norbornene is preferred.

The ethylene / α-olefin / non-conjugated polyene random copolymer is a solid at room temperature, but has a Mooney viscosity (JIS K 6395) of 5 to 50 at 100 ° C. and has fluidity. If it is less than 5, the green strength of the heat radiating sheet is insufficient and the handleability is poor, and if it exceeds 50, the green strength is not improved, and the sheet workability is deteriorated and the flexibility of the sheet is insufficient. More preferably, it is in the range of 5 to 25. Furthermore, the ethylene content is the main factor that determines the crystallinity in the polymer and affects the green strength of the polymer. When the ethylene content is less than 63%, the green strength is weak, and when the ethylene content exceeds 63%, the green strength sharply increases. Strength increases. In the present invention, a single polymer having an ethylene content may be used, but more preferably, when two or more polymers having different ethylene contents are used, it is possible to balance the workability and flexibility of the sheet. It is possible and advantageous.

An example of the ethylene / α-olefin / non-conjugated polyene random copolymer is Mitsui EPT (trade name, manufactured by Mitsui Chemicals, Inc.). Although the polyolefin-based thermally conductive composition of the present invention thermally softens at 40 ° C or higher,
In a system to which an organohydrogenpolysiloxane and a platinum-based catalyst are added or a system to which an organic peroxide is added, ethylene-α-
Since the olefin / non-conjugated polyene random copolymer can be crosslinked, pump-out can be more effectively prevented.

[Thermal conductive filler] The thermal conductive filler is a metal powder such as iron, aluminum, nickel, silver and gold, or an inorganic powder such as silicon oxide, aluminum oxide, zinc oxide, iron oxide and magnesium oxide. An oxide powder or an inorganic nitride powder such as aluminum nitride or boron nitride is used. The compounding amount varies depending on the type of the heat conductive filler, but it is necessary to set the amount so that the heat conductivity of the resin-based heat conductive composition is at least 1.0 W / mK.

[Other optional components] Further, additives or fillers to be added to the synthetic rubber as optional components can be used. Specifically, silicone oil, a fluorine-modified silicone surfactant as a release agent, carbon black and titanium dioxide as a coloring agent, a halogen compound as a flame retardant, a carbon functional silane as a processability improver, and the like are added. You may.

[Formation of heat-softening sheet] The resin-based heat conductive composition is prepared by using the above-mentioned components in a rubber kneading machine such as a two-roll mill, a Banbury mixer, a dough mixer (kneader), a gate mixer, and a planetary mixer. And can be obtained by uniform mixing.

Next, the heat-softening sheet can be obtained by forming the above-mentioned resin-based heat conductive composition and a metal foil or a metal mesh into a composite sheet by coextrusion, press molding and coating molding. In the case of coating molding, it is preferable to heat and melt the resin-based heat conductive composition or to dissolve it in a solvent to form a coating liquid, and the solvent can be toluene, xylene, thinner, rubber rubber, or the like. .

[0030]

EXAMPLES [Description of Raw Materials] In the following examples, the following materials were used. [Resin-based thermally conductive composition layer (B)] 1) The ethylene / α-olefin / non-conjugated polyene random copolymer is as follows under the trade name of Mitsui Chemicals, Inc.

[0031]

[Table 1]

2) Lucant HC40 (350 cSt), HC3000X (2500
0cSt) and HC10 (140cSt) are ethylene / α-olefin copolymers, trade names of Mitsui Chemicals, Inc., and the values in parentheses are viscosities at 25 ° C. 3) Dialen 30 (30 to 40), Dialen 208 (17 to 25), Dialen 18 (15) (the values in parentheses are the values of n in the general formula <1>) are α-olefin polymers, and Mitsubishi Chemical ( 4) Ag-E-100 is silver powder, Fukuda Metal Foil Powder Co., Ltd. product name 5) AS30 is alumina powder, Showa Denko Co., Ltd. product name 6) Crystallite VXS Is silica powder, product name of Tatsumori 7) KBN- (h) -10 is boron nitride powder, product name of Shin-Etsu Chemical Co., Ltd. 8) KBM3103 carbon functional silane and Shin-Etsu Chemical Co., Ltd. Product name

[Intermediate layer (A)] Aluminum foil: Fukuda Metal Foil & Powder Co., Ltd. thickness 30 μm, thermal conductivity 205 W / mK. Aluminum mesh: manufactured by Vacuum Metallurgy Co., Ltd., thickness 50 μm, thermal conductivity 205 W / mK. Copper foil: Fukuda Metal Foil & Powder Co., Ltd. thickness 35μm, thermal conductivity
372W / mK. Copper mesh: manufactured by Vacuum Metallurgy Co., Ltd., thickness 50 μm, thermal conductivity 372 W / mK.

-Examples 1 to 12- [Procedure for preparing heat-softening heat-radiating sheet] Raw materials having the formulation shown in Tables 1 to 3 were put into a planetary mixer,
Stir and mix for hours. Next, the mixture was degassed and mixed with two rolls at room temperature, and the obtained compound was dissolved in xylene at a concentration of solid content of 75%. Thereafter, a heat-softening sheet was processed by coating the both surfaces of a metal film or a metal mesh having a width of 500 mm using a coater so that the finished film thickness of the composite sheet was 200 μm. The obtained heat-softening sheet was stamped and formed into a predetermined shape.

[Evaluation means] Pump-out property, flexibility, tackiness, and handleability are ◎ (excellent), ○ (good), Δ (somewhat good), ×.
(Poor) was evaluated. 1) Pump-out property: Two sheets of glass (L × W × H = 50)
× 50 × 1mm) Heat-softening heat dissipation sheet (L × W × H)
(10 × 10 × 0.2mm) sandwiched between the oil components after 50 cycles of a heat shock test in which 125 ° C × 10 minutes and −50 ° C. × 10 minutes are alternately repeated with a load of 0.2 MPa applied. The condition was observed. 2) Flexibility: Evaluated by the state of crack generation when the sheet was bent at 90 °. 3) Tackability: A heat radiating sheet 2 is placed on the bottom surface of the heat sink 1 having the shape shown in FIG.
It was left in the air for 5 minutes and evaluated by the presence or absence of peeling and falling off. 4) Handling properties: The ease of attachment to the heat sink was evaluated by manual work.

[Performance Evaluation Measuring Method] 1) Plasticity measuring method: Measured by a plasticity test according to JIS-K-6249. 2) Thermal conductivity measurement method: Measured with a thermal conductivity meter QTM-500 (trade name, manufactured by Kyoto Denki). 3) Thermal resistance measurement method: A 0.5 mm thick sample punched into a transistor TO-3 shape was placed between the transistor 2SD923 (trade name of Fuji Electric) and the heat sink FBA-150-PS (trade name of OS Co., Ltd.). A load is applied with a compression load of 300 gf / cm ² sandwiched therebetween. The heat sink is placed in a thermostatic water bath and kept at 60 ° C. Next, supply 10 V, 3 A power to the transistor, measure the temperature of the thermocouple embedded in the transistor (temperature T ₁ ) and the heat sink (temperature T ₂ ) after 5 minutes, and measure the thermal resistance R _{s of the} sample from the following equation. (° C./W) is calculated. R _s = (T ₁ -T ₂ ) / 30 4) Viscosity measuring method: Measured with ARES viscoelastic system (manufactured by Rheometric Scientific). 5) Thermal softening point measurement method: Measured by the Vicat softening temperature test method of J1S-K7206.

[0037]

[Table 2]
(Blending amount is parts by weight)

[0038]

[Table 3]
(Blending amount is parts by weight)

[0039]

[Table 4]
(Blending amount is parts by weight)

Comparative Examples 1-4 A single-layer phase-change sheet (heat-softening heat-dissipating sheet: 0.2 mm thick) commercially available for comparison.
3) and the measurement results of the thermal resistance of grease (Comparative Example 4),
Table 4 shows the results of the viscosity measurement at 80 ° C, the results of the pump-out property test, and the handling properties. In addition, the manufacturer and brand name of the sheet used in each comparative example are as follows.

Comparative Example 1: “X-65-705B” manufactured by Shin-Etsu Chemical Co., Ltd. Comparative Example 2: “T-725” manufactured by Commerics Company Comparative Example 3: “1060” manufactured by Furon Company Comparative Example 4: GE Toshiba "YG626" manufactured by Silicone Corporation
0 "

[0042]

[Table 5]

From these results, the heat-softening heat radiating sheet according to the embodiment of the present invention can be compared with the conventional heat radiating sheet and grease.
It was proved to be excellent in pump-out property, and it was found to be effective for heat radiation of electronic components.

[0044]

The heat-softening heat radiating sheet of the present invention is solid at room temperature, so that it can be easily attached to and detached from electronic parts and heat sinks. Thermal resistance is reduced to a negligible level, and excellent heat dissipation performance is exhibited over a long period without pumping out.

[0045]

[Brief description of the drawings]

FIG. 1 is an elevational view showing a state in which a heat-softening heat radiating sheet of the present invention is attached to a heat sink surface in order to measure tackiness.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 23/00 C08L 23/00 H01L 23/36 H01L 23/36 D 23/373 M (72) Inventor Yoneyama Tsutomu 1-10, Hitomi, Matsuida-cho, Usui-gun, Gunma Prefecture F-term (reference) 4E100 AA12A AA12C AA12H AA17A AA17C AA17H AB01B AB03B AB04B AB09B AB10B AB17B AB24B AB31B AB33B ABABAB ABA AK62C AK63A AK63C CA23A CA23C GB41 JA04A JA04C JA06A JA06C JJ01 JJ01A JJ01B JJ01C JJ01H YY00A YY00C 4J002 BB031 BB051 BB121 BB151 BD076 DA086 DA096 DE076 DE106 DE116 DE016 DF016 A01601016

Claims (5)

[Claims] 1. A heat-dissipating sheet mounted between an electronic component and a heat-dissipating member, wherein (A) a metal foil having a thickness of 1 to 50 μm and a thermal conductivity of 10 to 500 W / mK. Or an intermediate layer made of a metal mesh, and (B) a softening point formed on both surfaces thereof is 40 ° C. or more, and the viscosity at 80 ° C.
It is in the range of 1 × 10 ² to 1 × 10 ⁵ Pas, and the thermal conductivity is 1.0
A laminated structure including a layer made of a resin-based heat conductive composition having a W / mK or more, wherein the thickness of the entire sheet is 40 to 500 μm.
m, a heat-softening heat dissipation sheet. 2. The heat conductive composition according to claim 1, wherein the resin heat conductive composition constituting the layer (B) is a polyolefin heat conductive composition containing a polyolefin and a heat conductive filler. Heat-softening heat dissipation sheet. 3. The method according to claim 1, wherein the polyolefin is an α-olefin polymer, an ethylene / α-olefin copolymer and ethylene / α-olefin.
The heat-softening heat-dissipating sheet according to claim 2, wherein the heat-softening heat-dissipating sheet is at least one selected from the group consisting of an α-olefin and a non-conjugated polyene random copolymer. 4. The method according to claim 1, wherein the metal foil or the metal mesh constituting the layer (A) is an aluminum alloy, a magnesium alloy,
The heat-softening heat-dissipating sheet according to any one of claims 1 to 3, comprising a material selected from copper, iron, stainless steel, silver, gold, and tungsten. 5. The method according to claim 1, wherein the heat conductive filler contained in the resin heat conductive composition constituting the layer (B) is selected from metals, inorganic oxides and inorganic nitrides. 4
The heat-softening heat dissipation sheet according to any one of the above items.