JP6325186B2 - Thermally conductive sheet - Google Patents

Description

  The present invention relates to a heat conductive sheet that efficiently transfers heat by interposing between a heat generator such as a semiconductor element and a heat sink such as a heat sink in an electronic device.

A heat conductive sheet is used to release heat generated from a heating element such as a semiconductor element inside an electronic device to a housing or a heat sink. This heat conductive sheet is often used as a structure that covers a plurality of heat generating elements and releases heat to a common heat dissipating element.
In a configuration in which a plurality of heating elements are covered with a single heat conductive sheet, the height differs for each heating element. Therefore, if the heat conductive sheet is in close contact with all the heating elements, the heat conductive sheet is attached to the heating element. It is necessary to compress and use.

In such a use form, when the area to which the heating element is compressed is large, the compression load becomes large and a load is applied to the heating element or the substrate, so that the heating element is damaged or the substrate is distorted and the circuit is damaged. There is.
In order to reduce such a problem, a study has been made to reduce the compressive load. For example, Japanese Utility Model Registration No. 3023821 (Patent Document 1) reduces the compressive load by softening the hardness of the heat conductive sheet. It is described. However, when the hardness of the sheet itself is softened, the strength of the heat conductive sheet is remarkably lowered, and there is a problem that the workability is liable to be easily damaged or deformed.

  As a technique that does not deteriorate the workability while reducing the compressive load, for example, there is a technique in which a hard reinforcing layer is provided on the front and back of a heat-dissipating sheet described in JP-A-2002-33427 (Patent Document 2). However, when a hard reinforcing layer is provided, the thermal resistance increases and the deformation of the flexible heat conductive layer is hindered.

Utility Model Registration No. 3023821 JP 2002-33427 A

  The present invention provides a thermally conductive sheet having a low thermal resistance without reducing the load during compression, and without impairing workability, by a method completely different from the above-described conventional technology.

  That is, a heat conductive sheet composed of an adhesive layer containing a heat conductive filler in an adhesive polymer matrix and interposed between a heat generator and a heat radiator, and a plurality of blades inserted in the thickness direction of the sheet Provided is a thermally conductive sheet having a cut surface and one side and the other side divided by each one cut surface attached and integrated.

This thermally conductive sheet has a plurality of cut surfaces that are cut in the thickness direction of the sheet, and one side and the other side divided by one cut surface are attached and integrated.
In a use state where the heat conductive sheet covers a plurality of heating elements on the uneven substrate and is compressed by being sandwiched between the heat dissipation elements, the portion of the heat conductive sheet that presses the heating element having a height, and The portion of the heat conductive sheet that presses the heating element having a low height can be relatively displaced via the cut surface. Therefore, it can compress partially larger than the case where the heat conductive sheet which does not have a cut surface is used. In other words, when following a plurality of uneven heating elements, the heating elements can be pressed with a relatively lower load than when a heat conductive sheet having no cut surface is used.

  In addition, this heat conductive sheet covers a heating element without unevenness and is relatively compressed even when used in a state where the heat conductive sheet is sandwiched between the heat dissipation body and compressed without using a cut surface. The heating element can be pressed with a low load. The thermal conductive sheet is deformed so as to spread outward when it is sandwiched between objects without unevenness, but by having a cut surface at this time, the binding force that regulates the outward spreading of the polymer matrix is weakened. This is considered to be because the deformation stress is relieved.

  Further, since the one side and the other side separated by the cut surface are attached and integrated, they are not substantially divided by the cut surface and can be handled as a single sheet. Therefore, when sticking a heat conductive sheet to a heat generating body or a heat radiator, it has the same workability as handling a single sheet. Moreover, since it can be set as a comparatively hard heat conductive sheet compared with the conventional heat conductive sheet which does not have a cut surface, workability | operativity can also be improved.

  A hard layer harder than the adhesive layer may be further provided. Since the hard layer harder than the adhesive layer is further provided, the integrity of the sheet can be improved and the handleability can be improved.

The cut surface may be a cut surface that penetrates the sheet thickness or a cut surface that partially cuts the sheet thickness.
When the cut surface is a cut surface that penetrates the sheet thickness, a plurality of divided pieces divided by the plurality of cut surfaces are formed, and the adjacent divided pieces adhere to each other so that the heat conductivity is integrated. It can be a sheet.

  If the cut surface penetrates the sheet thickness to form the divided pieces, it is possible to increase the displacement of both side portions sandwiching the cut surface as compared with the case where the cut surface does not penetrate the sheet thickness. Further, depending on the degree of difference in the uneven height of the heat generating body, both sides of the cut surface can be completely divided when the heat radiating body is covered.

  The distance between the cut surfaces is preferably 0.05 mm to 5 mm. If the distance between the cut surfaces is less than 0.05 mm, the compressive load is reduced. However, even if it is made finer, the width of the decrease in the compressive load is small, but the processing cost is improved. On the other hand, when the distance exceeds 5 mm, the effect of reducing the compressive load is reduced.

  The depth of the cut surface is preferably 50% to 100% with respect to the sheet thickness. By setting the depth of the cut surface to 50% or more with respect to the sheet thickness, the effect of reducing the load can be enhanced. On the other hand, if it is less than 50%, the effect of reducing the load is reduced. Further, when the sheet is configured as 100% with respect to the thickness of the sheet, that is, a surface penetrating the sheet, the effect of reducing the load can be maximized.

  The cut surface can penetrate the hard layer. Since the cut surface penetrates the hard layer, the compressive load that is increased by the expansion of the hard layer can be kept low.

  The heat conductive sheet of the present invention is a heat conductive sheet that can suppress a load during compression, has excellent workability, and has low heat resistance.

It is a perspective view which shows the heat conductive sheet of 1st Embodiment. It is a top view of the heat conductive sheet of FIG. It is the SA-SA line sectional view of the heat conductive sheet of FIG. It is sectional drawing which shows the state which mounted | wore the electronic device with the heat conductive sheet of FIG. It is sectional drawing of the compressed heat conductive sheet shown in FIG. It is sectional drawing equivalent to FIG. 4 which shows the state with which the conventional heat conductive sheet was mounted | worn with the electronic device. It is sectional drawing of the compressed heat conductive sheet shown in FIG. It is a top view of the heat conductive sheet of 2nd Embodiment. It is a top view of the heat conductive sheet of 3rd Embodiment. It is a top view of the heat conductive sheet of 4th Embodiment. It is sectional drawing equivalent to FIG. 3 of the heat conductive sheet of 5th Embodiment. It is sectional drawing equivalent to FIG. 3 of the heat conductive sheet of 6th Embodiment. It is sectional drawing equivalent to FIG. 3 of the heat conductive sheet of 7th Embodiment. It is sectional drawing equivalent to FIG. 4 which shows the state with which the heat conductive sheet of FIG. 13 was mounted | worn with the electronic device. FIG. 5 is a cross-sectional view corresponding to FIG. 4 showing a state where a conventional heat conductive sheet having a two-layer structure is mounted on an electronic device.

  The present invention will be described in more detail based on embodiments. Components common to the following embodiments are denoted by the same reference numerals, and redundant description is omitted. In addition, overlapping descriptions of common materials, manufacturing methods, effects, and the like are omitted.

First Embodiment [FIGS. 1 to 5] :
The heat conductive sheet 11 of this embodiment is composed of a pressure-sensitive adhesive layer 1 containing a heat conductive filler in an adhesive polymer matrix, and is interposed between the heat generating element and the heat radiating element to generate heat generated from the heat generating element. Is a member that transmits heat to the radiator. In this embodiment, as shown in FIG. 1, the sheet is formed as a rectangular sheet as a whole.
The adhesive layer 1 has a plurality of cut surfaces 2 inserted in the thickness direction of the sheet, and one side and the other side divided by one cut surface 2 are attached and integrated.

  As shown in FIG. 2, the cut surface 2 formed on the heat conductive sheet 11 has a grid-like shape in two directions orthogonal to each other, and each cut surface 2 is shown in FIG. It penetrates the thickness of the sheet. Therefore, a plurality of divided pieces 3 divided by these cut surfaces 2 are formed. However, the divided piece 3 is adhered to the divided piece 3 adjacent to the divided piece 3 by an adhesive force.

The polymer matrix is thermoplastic or thermosetting, photocuring depending on the re-adhesion (adhesiveness) after entering the sword, the mechanical strength, heat resistance, and electrical properties of the heat conductive sheet. Selected from the functional polymer materials.
A thermoplastic elastomer can be used as the thermoplastic polymer material. Specific examples include a styrene-butadiene block copolymer and a hydrogenated polymer thereof, a styrene-isoprene block copolymer and a hydrogenated polymer thereof, and a styrene-based polymer. Examples thereof include thermoplastic elastomers, olefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, and polyamide-based thermoplastic elastomers.

  Specific examples of the thermosetting or photocurable polymer material include a crosslinked rubber, a polyurethane resin, an acrylic copolymer, and the like. Specific examples of the crosslinked rubber include natural rubber, acrylic rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene copolymer rubber, chlorinated polyethylene rubber, Examples thereof include chlorosulfonated polyethylene rubber, butyl rubber, halogenated butyl rubber, fluorine rubber, urethane rubber, and silicone rubber.

Among these, a silicone-based polymer material is preferable in consideration of heat resistance, adhesion to the heating element and the radiator, followability to the surface shape of the heating element and the radiator, and durability against temperature change. In consideration of bleeding such as a plasticizer, an acrylic copolymer is preferable. Moreover, the polymer alloy which consists of a several polymeric material selected from each said polymeric material may be sufficient.
The viscosity of the polymer matrix at normal temperature is preferably 1,000 mPa · s or less, and more preferably 500 mPa · s or less. If it exceeds 1,000 mPa · s, preparation of the composition may be difficult. The lower limit of the viscosity of the polymer matrix at room temperature is not particularly limited. The normal temperature is a temperature at which the composition is usually prepared, and is, for example, 25 ° C.

The thermally conductive filler is a material that imparts thermal conductivity performance to the thermally conductive sheet. Examples of the fibrous heat conductive filler include carbon fiber, metal fiber, glass fiber, and the like, and carbon fiber is preferable in terms of high thermal conductivity. Examples of the thermally conductive filler such as granular materials include aluminum oxide, boron nitride, aluminum nitride, silicon carbide, and silicon dioxide.
The average particle diameter or average fiber length of such a heat conductive filler is preferably 0.1 μm to 100 μm, and more preferably 1 μm to 50 μm. If it is less than 0.1 μm, the viscosity of the raw material composition becomes high and it becomes difficult to disperse it in the polymer matrix. If it exceeds 100 μm, the flatness of the surface when formed on the sheet may be deteriorated.
The content of the thermally conductive filler in the total solid content is preferably 90% by weight or less. If it exceeds 90% by weight, the flexibility may be reduced and the sheet may become brittle.

The heat conductive sheet 11 is manufactured by mixing and dispersing a heat conductive filler in a polymer matrix, orienting the heat conductive filler in a certain direction, if necessary, and forming it into a sheet shape.
Although heat conductivity can be given by containing a predetermined amount of heat conductive filler, the heat conductivity in the front and back direction of the sheet is enhanced by orienting the heat conductive filler in the thickness direction of the sheet. A heat conductive sheet can be obtained. The orientation of the thermally conductive filler can be performed by using magnetic particles for the thermally conductive filler and applying a magnetic field before the polymer matrix is cured.
For forming into a sheet, the polymer matrix is cured with the thermally conductive filler oriented in the mold, or the raw material composition is applied to a flat surface when orientation of the thermally conductive filler is not required. Then, it can be performed by a method of curing.

In order to install the heat conductive sheet 11 in an electronic device, for example, as shown in FIG. 4, the heat conductive sheet 11 is placed on a substrate 5 having a heating element (semiconductor element) 4 and heat is dissipated thereon. Place the body (heat sink) 6. In this way, the heating element 4 is pressed and covered on one side of the heat conductive sheet 11 and is in contact with the radiator 6 on the other side.
A state in which the heating element 4 is pressed by the heat conductive sheet 11 will be described with reference to FIG. For comparison, reference is made to the thermally conductive sheet 101 (prior art; FIGS. 6 and 7) having no cut surface. First, in the conventional heat conductive sheet 101, when the heat conductive sheet 101 is put on the substrate 5 having the semiconductor element 4 and then compressed by the heat sink 6, the heat conductivity is caused by the unevenness of the semiconductor element 4 having various heights. It deform | transforms so that the surface of the sheet | seat 101 may be extended (refer FIG. 6). A heat conductive sheet 101 shown in FIG. 7 is obtained by taking out the compressed heat conductive sheet 101 shown in FIG. ing. A region R1 in FIG. 7 represents the vicinity of the end portion of the semiconductor element 4a having the highest height, and shows that the thermally conductive sheet 101 is greatly stretched to generate an elongated portion 101a deformed in a curved shape. It is considered that having the elongated portion 101a that is partially deformed in this way increases the compressive load.

On the other hand, in the heat conductive sheet 11 having the cut surface 2 penetrating in the sheet thickness direction, the elongation in the vicinity of the end portion of the semiconductor element 4 is small (see FIG. 4). That is, as shown in a region R2 which is a partially enlarged view of FIG. 5, the heat conductive sheet 11 has cut surfaces 2a and 2b, and the divided pieces 3a and 3b are separated through the cut surface 2a. Relative displacement. More specifically, the divided piece 3a is greatly compressed by the protrusion of the semiconductor element 4a. However, since the cut surface 2a exists in the vicinity of the end portion, only the elongated portion 11a with small deformation is generated.
At this time, the cut surface 2a has a reattached surface that has been reattached and an exposed exposed surface after being relatively displaced as the divided piece 3a is compressed.

  Although the above description is about the vicinity that covers the semiconductor element 4a that protrudes greatly, the compressive load is reduced even when the plurality of semiconductor elements 4 on the substrate 5 are arranged flat. This is considered to be because the stress generated in the adhesive layer 1 is relaxed by the cut surface 2 when the heat conductive sheet 11 is compressed.

  The thickness of the heat conductive sheet is preferably 0.5 mm to 6.0 mm. When the thickness is less than 0.5 mm, the depth of the cut surface itself becomes shallow and the effect of reducing the compression load is small. On the other hand, if the thickness exceeds 6.0 mm, even if the cut surface is not provided, the amount of deformation is small with respect to the thickness, so the effect of reducing the load due to the provision of the cut surface is small.

Second Embodiment [FIG. 8] :
The heat conductive sheet 12 of this embodiment is different from the heat conductive sheet 11 provided with the cut surface 2 along two orthogonal directions in that it includes the cut surface 2 along one direction.
Even when the cut surface 2 is provided along one direction, the compression load by which the heat conductive sheet 12 is compressed when the heating element 4 is compressed can be reduced. Further, since it is only necessary to form the cut surface 2 along one direction, the manufacturing is easy.

Third Embodiment FIG. 9:
The heat conductive sheet 13 of this embodiment includes a frame-shaped frame portion 1a that does not form a cut surface on the outer periphery of the sheet. This is because, since the heat conductive sheet is generally arranged so that the heat generating element 4 is located near the center of the heat conductive sheet, it is rare that the end of the heat generating element 4 hits the outer periphery of the heat conductive sheet.
Since the frame portion 1a is provided, it is easy to keep the heat conductive sheet 13 together, and it can be suitably used when a polymer matrix having a low adhesive force is used as a raw material. Further, since the frame portion 1a is provided, the integrity of the sheet is hardly lost even when a large external force is applied to the outer periphery of the sheet, and the handling property can be improved.

  As a modified example of this embodiment, the frame portion 1 a can be a heat conductive sheet provided on a portion other than the outer periphery of the heat conductive sheet 13. It is also possible to form the cut surface 2 only at a location corresponding to the protruding portion of the semiconductor element 4 to be covered, and to make the periphery of the cut surface 2 a.

  As another modification, instead of forming the portion without the cut surface 2 in a frame shape, any one of the four corners of the sheet can be provided as the portion without the cut surface 2. In many cases, the sheet is held by holding the four corners, and handling in such a case can be improved.

Fourth Embodiment [FIG. 10] :
Although the heat conductive sheet 14 of this embodiment is provided with the several parallel cut surface 2 along one direction, not only the direction perpendicular | vertical to the surface direction of a cut surface but another cut surface also in the surface direction of a cut surface. 2 has. In other words, the connecting portion 1b is provided between the cut surfaces 2 adjacent to each other in the surface direction.
Since the divided pieces 3 are not formed in the heat conductive sheet 14 and the whole sheet is connected via the connecting portion 1b, the heat conductive sheet 14 can be easily kept in one body and excellent in handleability.

Fifth Embodiment [FIG. 11] :
In the heat conductive sheet 15 of the present embodiment, a plurality of cut surfaces 2 that are inserted from one surface of the sheet and do not penetrate the sheet thickness are provided.
Since the cut surface 2 is provided only on one surface side of the heat conductive sheet 15, the entire sheet is integrally formed on the other surface side, and the sheet is highly integrated and easy to handle.

Sixth Embodiment [FIG. 12] :
The heat conductive sheet 16 of the present embodiment has a two-layer configuration including a hard layer 7 that is harder than the adhesive layer 1.
As the material of the hard layer 7, a material that can be used in the adhesive layer 1 can be used, but it is preferable that the material is the same type as that of the adhesive layer 1 and has high hardness. This is because the adhesive layer 1 and the hard layer 7 can be easily fixed if they are of the same type. For example, when the adhesive layer 1 is silicone rubber, the hard layer 7 is also silicone rubber. Alternatively, the hard layer 7 can also be formed of a material having low extensibility such as a resin film. When the hard layer 7 is formed of a resin film, it is thin and the integrity as a sheet can be enhanced.
Although the thickness of each of the adhesive layer 1 and the hard layer 7 can be set to an appropriate thickness, since the hard layer 7 has a higher compressive load than the adhesive layer 1, the thickness of the hard layer 7 should be reduced. Is preferred.

  In the heat conductive sheet 16, the cut surface 2 which penetrates the adhesive layer 1 but does not penetrate the hard layer 7 is formed. Since it has the cut surface 2 which penetrated the adhesion layer 1, even if the surface with a large unevenness | corrugation is covered with the heat conductive sheet 16, the adhesion layer 1 divided by the cut surface 2 can be largely displaced with a low load. The compressive load on the semiconductor element 4 can be kept low. On the other hand, since the hard layer 7 is integrated without being cut, even if an excessive force is applied at the time of handling, the heat conductive sheet 16 is not easily broken or divided.

Seventh Embodiment [FIG. 13] :
The heat conductive sheet 17 according to the present embodiment includes the adhesive layer 1 and the hard layer 7, enters the hard layer 7 from the hard layer 7 side, penetrates the hard layer 7, and has a cut surface 72 extending to a part of the adhesive layer 1. Have.

  A state in which the heat conductive sheet 17 is mounted on the electronic device will be described. As shown in FIG. 14, when the heat conductive sheet 17 is compressed, a force that tends to extend in the vicinity of the end of the semiconductor element 4 works due to the unevenness of the semiconductor element 4 disposed on the substrate 5. However, since the hard layer 7 has the cut surface 2 penetrating therethrough, the hard layer 7 can follow the uneven surface together with the adhesive layer 1 with almost no deformation. Therefore, if the thermally conductive sheet 102 not provided with the cut surface 2 penetrating the hard layer 7 is attached to an electronic device (see FIG. 15), the hard layer 7 that is less likely to be stretched than the adhesive layer 1 tends to stretch. As a result, the compressive load can be greatly reduced as compared with the case where a large compressive load is applied.

The components shown in each of the above embodiments can be changed as appropriate to the components described in the other embodiments without departing from the spirit of the present invention, and a part of them can be applied in combination. Such modifications and combinations are also included in the scope of the technical idea of the present invention.
For example, the connection part 1b which the heat conductive sheet 14 has is provided on the cut surface 2 of the heat conductive sheet 13 provided with the frame part 1a, or the heat conductive sheet 11 has a two-layer structure like the heat conductive sheet 16. Examples of such cases are illustrated.

Next, further description will be made based on examples.
(Production of sheet compact)
100 parts by weight of liquid silicone rubber as a polymer matrix and 360 parts by weight of aluminum hydroxide powder as a heat conductive filler and mixed until uniform, and 100 parts by weight of liquid silicone rubber, heat conduction A mixed composition B was prepared by mixing 360 parts by weight of aluminum hydroxide powder as a conductive filler and mixing them until uniform. When this mixed composition A is cured, it becomes a cured product having a hardness of E60, and when the mixed composition B is cured, it becomes a cured product having a hardness of E5.

  Next, the mixed composition A is applied onto a release film (released PET film) with a blade coater so as to have a thickness of 0.25 mm, and the mixed composition B is coated thereon with a total thickness (mixed composition). The coating was applied with a blade coater so that the total thickness of A and the mixed composition B was 2 mm. Subsequently, the mixed composition A and the mixed composition B are solidified by heating at 100 ° C. for 10 minutes, and a hard layer made of a cured body of the mixed composition A and an adhesive layer made of a cured body of the mixed composition B are laminated. A sheet compact was obtained.

(Preparation of each sample)
Next, various samples (thermal conductive sheets) serving as examples or comparative examples were produced by imparting (or not imparting) various cut surfaces to the sheet compact.
Sample 1 was cut in the same way by cutting the previous sheet compact with a cutter knife at 1 mm intervals, changing the direction 90 degrees, and having a cut surface in a grid pattern with one side as viewed from the surface. A sheet was made. Sample 1 had split pieces formed but had cut surfaces attached to each other, and could be handled as an integral sheet.
In addition, although the adhesive force of a cut surface is substantially the same as the adhesive force of the surface which each mixed composition hardened independently, in this Example, the adhesive force of the surfaces of the mixed composition B in a cut surface is strong. , Greatly contributed to the integration.

Sample 2 is a thermally conductive sheet produced by the same method as Sample 1 except that the cut surface penetrating the sheet thickness is formed in a grid pattern with an interval of 0.5 mm and one side of 0.5 mm.
Sample 3 is a thermally conductive sheet produced by the same method as Sample 1 except that the cut surface penetrating the sheet thickness is formed in a grid pattern with an interval of 0.25 mm and one side of 0.25 mm.
Sample 4 was cut to a depth of 1 mm from the mixed composition B (adhesive layer) side without penetrating the sheet thickness, and a cut surface was formed in a grid pattern having one side of 0.5 mm when viewed from the adhesive layer side. Other than the above, it is a heat conductive sheet manufactured by the same method as Sample 1.

Sample 5 was cut to a depth of 1 mm from the mixed composition A (hard layer) side without penetrating the sheet thickness, and a cut surface was formed in a grid pattern having one side of 0.5 mm when viewed from the hard layer side. Other than the above, it is a heat conductive sheet manufactured by the same method as Sample 1.
Sample 6 is a thermally conductive sheet produced by the same method as Sample 1 except that the cut surface penetrating the sheet thickness is formed in a grid pattern with an interval of 5 mm and a side of 5 mm.
In Sample 7, a cut surface is not formed, and the sheet molded body is directly used as a heat conductive sheet.

(Measurement of compressive load, etc.)
The compression load when each sample was compressed (50% compression) until the thickness was halved was measured. Moreover, when thermal resistance was measured about each sample, as a thermal resistance value, all the samples were in the range of 0.32 degreeC / W-0.45 degreeC / W.
The form of each sample and the value of 50% compressive load are shown in Table 1 below.

(Test results and discussion)
First, Sample 1 to Sample 6 had cut surfaces attached to each other, and could be handled as an integral sheet.
Samples 1 to 3 and sample 6 provided with cut surfaces penetrating in a grid pattern had a 50% compressive load reduced to half or less as compared with sample 7 without a cut surface. Further, the value of the 50% compressive load was greatly reduced as the distance between the cut surfaces was narrowed.
Sample 4 and sample 5, which formed a cut surface that did not penetrate the sheet thickness and cut a part of its thickness, had a 50% compressive load higher than that of sample 1 provided with a cut surface that penetrated. It was found that it was lower than the 50% compressive load of Sample 7 without a surface and had the effect of reducing the compressive load.

DESCRIPTION OF SYMBOLS 1 Adhesive layer 1a Frame part 1b Connecting part 2, 2a, 2b Cut surface 3, 3a, 3b Divided piece 4 Heating element (semiconductor element)
5 Substrate 6 Radiator (heat sink)
7 Hard layer 11, 12, 13, 14, 15, 16, 17 Thermal conductive sheet 11a Elongation part
101,102 Thermal conductive sheet (prior art)
101a Elongation R1, R2 region

Claims (4)

A substrate having a heating element composed of an adhesive layer containing a thermally conductive filler in an adhesive polymer matrix, and a thermally conductive sheet interposed between the heating element and the radiator,
Having a plurality of cut pieces divided by a single cut surface and having a plurality of cut surfaces along the thickness direction of the sheet,
The depth of the cut surface, seat 50% to 100% der of the thickness, deeper than the height of the heating element,
Adjacent divided pieces can be relatively displaced with compression in the intervening state, and in the state after relative displacement, the cut surface has a reattached surface reattached to the adjacent divided piece and an exposed exposed surface, and is greatly compressed. The reattachment surface of the divided piece on the side that is adjacent has an extending portion that adheres to the adjacent divided piece on the smaller compression side, so that the adjacent divided pieces are attached and integrated.   The thermally conductive sheet according to claim 1, further comprising a hard layer harder than the adhesive layer.   The thermally conductive sheet according to claim 1 or 2, wherein an interval between one cut surface and a cut surface adjacent thereto is 0.05 mm to 1 mm. The thermally conductive sheet according to claim 2, wherein the cut surface penetrates the hard layer.

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