WO2022176748A1

WO2022176748A1 - Heat conductive sheet and method for manufacturing heat conductive sheet

Info

Publication number: WO2022176748A1
Application number: PCT/JP2022/005216
Authority: WO
Inventors: 圭佑武笠; 佑介久保; 慶輔荒巻
Original assignee: デクセリアルズ株式会社
Priority date: 2021-02-19
Filing date: 2022-02-09
Publication date: 2022-08-25

Abstract

A heat conductive sheet of an embodiment comprises a heat conductive filler including carbon fibers and at least one of aluminum nitride, aluminum oxide and aluminum hydroxide as an inorganic filler, and a two-component addition reaction silicone having a volume ratio of 30-45%, so that a heat conductive sheet having a small amount of creep, while having a low residual stress, a low thermal resistance value and good tackiness can be obtained by a simple process.

Description

Thermally conductive sheet and method for producing thermally conductive sheet

Embodiments of the present invention relate to a thermally conductive sheet and a method for manufacturing a thermally conductive sheet.

In recent years, as electronic devices have become more sophisticated, semiconductor devices have become more dense and highly mounted. Along with this, it has become important to more efficiently dissipate the heat generated from the electronic components that make up the electronic equipment.

In order to efficiently dissipate heat, the semiconductor element is attached to a heat sink such as a heat dissipation fan or a heat dissipation plate via a thermally conductive sheet. As a thermally conductive sheet, a material in which a filler such as an inorganic filler is dispersed in silicone is widely used.

In such heat dissipating members, there is a demand for further improvement in thermal conductivity. there is

However, if the filling rate of the inorganic filler is increased, there is a risk that the flexibility will be impaired or that powder will fall off. Therefore, there is a limit to increasing the filling rate of the inorganic filler.

Examples of inorganic fillers include alumina, aluminum nitride, and aluminum hydroxide. For the purpose of high thermal conductivity, the matrix may be filled with scaly particles such as boron nitride or graphite, carbon fibers, or the like. This is due to the anisotropy of the thermal conductivity of the scaly particles and the like.

For example, carbon fibers have a thermal conductivity of about 600-1200 W/mK in the fiber direction. Boron nitride has a thermal conductivity of about 110 W/mK in the plane direction and about 2 W/mK in the direction perpendicular to the plane direction, and is known to have anisotropy. .
In this manner, the surface direction of the carbon fibers and scale-like particles is made the same as the thickness direction of the sheet, which is the direction of heat transfer. That is, by orienting the carbon fibers and the scale-like particles in the thickness direction of the sheet, it is possible to dramatically improve the heat conduction.

Further, in Patent Document 1, a sheet obtained by slicing a block of a composition containing a fibrous filler is pressed to promote contact between the fibrous fillers, thereby improving thermal conductivity. is described.
Further, it is described that as a result of the press treatment, the smoothness of the sheet surface is improved, and the adhesion to the heating element and the heat radiating element is improved.

Japanese Patent No. 5541401

By the way, using press technology improves the adhesion to the radiator and promotes the contact between the fillers, but at the same time, it requires greater pressure to further compress the pressed sheet, which has a dense interior. There was a problem of needing
The present invention has been made in view of the above, and it is an object of the present invention to obtain a thermally conductive sheet with a low residual stress, a small amount of creep, a low thermal resistance value, and tackiness by a simple process.

In order to solve the above problems, the thermally conductive sheet of the embodiment includes a thermally conductive filler containing carbon fiber and at least one of aluminum nitride, aluminum oxide and aluminum hydroxide as an inorganic filler, and a volume ratio of 30 to 45% two-part addition-cure silicone.

According to the thermally conductive sheet of the embodiment, it is possible to obtain a thermally conductive sheet that has a low residual stress, a small amount of creep, a low thermal resistance value, and tackiness.

FIG. 1 is a manufacturing flow chart of the thermally conductive sheet of the embodiment. FIG. 2 is an explanatory diagram of the effect of the embodiment.

A method for manufacturing a thermally conductive sheet to which this technology is applied will be described in detail below with reference to the drawings. In addition, the present technology is not limited to the following embodiments, and various modifications are possible without departing from the gist of the present technology. Also, the drawings are schematic, and the ratio of each dimension may differ from the actual one. Specific dimensions and the like should be determined with reference to the following description. In addition, it goes without saying that there are portions with different dimensional relationships and ratios between the drawings.

First, the thermally conductive sheet of the embodiment will be described.
The thermally conductive sheet of the embodiment contains at least one of carbon fiber, aluminum nitride, aluminum oxide, and aluminum hydroxide in a volume ratio of 55 to 70% as a thermally conductive filler.
Furthermore, the thermally conductive sheet contains 30 to 45% by volume of a two-liquid addition reaction type silicone as a polymer matrix component.

FIG. 1 is a manufacturing flow chart of the thermally conductive sheet of the embodiment.
First, a predetermined amount of two-liquid addition reaction type liquid silicone resin is mixed at a predetermined ratio to prepare (step S11).

Here, the reason for using a two-liquid addition reaction type liquid silicone resin as the polymer matrix component will be explained.
Thermosetting polymers are used as the polymer matrix component. Among thermosetting polymers, silicone resins are preferred because of their excellent moldability and weather resistance, as well as adhesion and conformability to electronic parts. It is preferable to use
There are various types of silicone resins, but the reason for using a two-liquid addition reaction type liquid silicone resin as a polymer matrix component is that, among silicone resins, it is used as a heat dissipation member for electronic devices. This is because adhesion between the heat generating surface and the heat sink surface is required.
This is because an addition reaction type liquid silicone resin is particularly preferable as the silicone resin for this purpose.

Here, the liquid silicone component has a silicone A liquid component as a main agent and a silicone B liquid component containing a curing agent, and the silicone A liquid component and the silicone B liquid component are blended in a predetermined ratio.
In parallel with this, one or more thermally conductive fillers are prepared (step S12).

In this case, a surface-treated filler can be used as the thermally conductive filler. When the thermally conductive filler is treated with a coupling agent as this surface treatment, the dispersibility of the thermally conductive filler is improved, and the flexibility of the thermally conductive sheet is improved.

At least one of carbon fiber, aluminum nitride, aluminum oxide, and aluminum hydroxide is used as the thermally conductive filler.
Subsequently, the prepared thermally conductive filler is added to and dispersed in the two-liquid addition reaction type liquid silicone resin to prepare a silicone resin composition (thermally conductive resin composition) (step S13).

Next, the obtained silicone resin composition is extruded into a mold whose inner wall is release-treated to create a silicone molded body (step S14).

The obtained silicone molding is heat-treated at a predetermined temperature for a predetermined time to obtain a cured silicone product (step S15).
Subsequently, the obtained silicone cured product is sliced (cut) with an ultrasonic cutter to obtain a molded sheet having a predetermined thickness (for example, 0.33 mm) (step S16).

Furthermore, after sandwiching the resulting molded sheet with release-treated PET films, a spacer of a predetermined thickness is inserted and press-treated at a predetermined pressure for a predetermined time to obtain a desired thickness (for example, a thickness of 0.30 mm). A conductive sheet was obtained (step S17).

The thermally conductive sheet is obtained by slicing a mixture of carbon fibers, an inorganic filler, and a binder, and orienting the carbon fibers in the thickness direction of the sheet.
According to the obtained thermally conductive sheet, the effective thermal conductivity was 10 W/m·K or more.
Furthermore, the heat resistance when a thermally conductive sheet having a thickness of 0.35 mm or less is pressed at 2.81 kgf/cm ² is 0.20° C. cm ² /W or less, and the sheet is 50% thicker than the initial thickness. The residual stress when compressed was 276 kPa or less.

In addition, when pressurized at 100 kPa for 1000 hours, the deformation rate in the x and y directions within the sheet surface was 15% or less.

After pressing the pressed thermally conductive sheet with a 5.1 mmφ probe at 2 mm/sec at 200 gf, the tack force was 80 gf or more when peeled off at 10 mm/sec.

As described above, according to the thermally conductive sheet of the present embodiment, the residual stress is low, the amount of creep is small, and it has both high flexibility and high elasticity.
Furthermore, it had low heat resistance and had tackiness.

From these results, it can be seen that the thermally conductive sheet of the present embodiment reduces the risk of damaging a heating element such as an IC even when pressure is applied due to the property of low residual stress.

In addition, since the thermally conductive sheet of the present embodiment has a small amount of creep, it is possible to prevent short circuits that may occur due to creep.
Furthermore, since it has tackiness, it becomes a thermally conductive sheet capable of preventing misalignment during mounting, and the adhesiveness to the adherend increases.
Due to this high adhesiveness, a low thermal resistance of 0.20° C.·cm ² /W or less could be achieved with a sheet as thin as 0.3 mm.

Next, specific examples and comparative examples will be described.
[1] Examples [1.1] First Example First, the production of the thermally conductive sheet of the first example will be described.
In Example 1, 36% by volume of a two-liquid addition reaction type liquid silicone resin was prepared.

Here, the two-liquid addition reaction type liquid silicone resin is a mixture of 20% by volume of silicone A liquid and 16% by volume of silicone B liquid.

In parallel with this, as a thermally conductive filler, 5% by volume of aluminum oxide particles (thermally conductive particles, manufactured by Denki Kagaku Kogyo Co., Ltd.) having a volume average particle size of 15 μm and having been subjected to coupling treatment with 0.1% by volume of a coupling agent. And, 33% by volume of aluminum nitride particles (thermally conductive particles, manufactured by Tokuyama Co., Ltd.) having a volume average particle size of 1 μm that are coupled with 0.9% by volume of a coupling agent, and pitch-based carbon fibers (thermally conductive fibers, Average fiber length 120 μm, average fiber diameter 9 μm, manufactured by Nippon Graphite Fiber Co., Ltd.) was adjusted to 25% by volume.

Subsequently, a thermally conductive filler was mixed with the addition reaction type liquid silicone resin and dispersed to prepare a silicone resin composition (thermally conductive resin composition).

Next, the obtained silicone resin composition was extruded into a rectangular parallelepiped mold (50 mm x 50 mm) with a release-treated polyethylene terephthalate (PET) film attached to the inner wall to mold a silicone molded body.

The resulting silicone molded product was cured in an oven at 100°C for 6 hours to obtain a silicone cured product.

Then, the cured silicone product obtained was cut with an ultrasonic cutter to obtain a molded sheet with a thickness of 0.33 mm. The slicing speed of the ultrasonic cutter was 50 mm per second. At this time, the ultrasonic vibration applied to the ultrasonic cutter had an oscillation frequency of 20.5 kHz and an amplitude of 60 μm.

After sandwiching the resulting molded sheet between release-treated PET films, a 0.30 mm thick heat conductive sheet was obtained by inserting a 0.3 mm thick spacer and pressing. The pressing conditions were 0.5 MPa and 30 seconds.
According to the first embodiment, the total filler content is 63 [volume %], the average sheet thickness is 0.29 [mm], the thermal resistance value is 0.181 [°C cm / W], and the tack force is 83 [gf]. , a thermally conductive sheet having a deformation rate of 11% in the x direction and a deformation rate of 11% in the y direction was obtained.

[1.2] Second Example Next, a second example will be described.
First, the manufacture of the thermally conductive sheet of the second embodiment will be described.
The second embodiment differs from the first embodiment in that, first, 31% by volume of a two-liquid addition reaction type liquid silicone resin is coupled with 0.4% by volume of a coupling agent, and a volume average particle diameter of 1 μm is obtained. 10% by volume of aluminum oxide particles (thermally conductive particles: manufactured by Nippon Light Metal Co., Ltd.) and 8% by volume of aluminum oxide particles (thermally conductive particles: manufactured by Denki Kagaku Kogyo Co., Ltd.) with a volume average particle size of 4 μm, and a coupling agent 25% by volume of aluminum nitride particles (thermally conductive particles, manufactured by Tokuyama Co., Ltd.) having a volume average particle size of 1 μm, which are coupled at 0.6% by volume, and pitch-based carbon fibers (thermally conductive fibers, average fiber length of 120 μm, In the same manner as in Example 1, except that a silicone resin composition (thermally conductive resin composition) prepared by dispersing 25% by volume of an average fiber diameter of 9 μm (manufactured by Nippon Graphite Fiber Co., Ltd.) was used. A thermally conductive sheet of the second example was obtained.

The two-liquid addition reaction type liquid silicone resin is a mixture of 16% by volume of silicone A and 15% by volume of silicone B.

[1.3] Third Example Next, a third example will be described.
-Preparation of Thermally Conductive Sheet- In Example 1, aluminum oxide having a volume average particle diameter of 1 μm was obtained by coupling 30% by volume of a two-liquid addition reaction type liquid silicone resin with 0.5% by volume of a coupling agent. 20% by volume of particles (thermally conductive particles: manufactured by Denki Kagaku Kogyo Co., Ltd.) and aluminum nitride particles with a volume average particle diameter of 1 μm (thermally conductive particles, Tokuyama Corporation) that are coupled with 0.5% by volume of a coupling agent. A silicone resin composition ( A thermally conductive sheet of Example 3 was obtained in the same manner as in Example 1, except that the thermally conductive resin composition) was used.
The two-liquid addition reaction type liquid silicone resin is a mixture of 16% by volume of silicone A and 14% by volume of silicone B.

[1.4] First Comparative Example Next, a first comparative example will be described.
-Preparation of Thermally Conductive Sheet- In Example 1, 49% by volume of a two-liquid addition reaction type liquid silicone resin was added to aluminum oxide particles (thermally conductive particles: Denki Kagaku Kogyo Co., Ltd.) 31% by volume and pitch-based carbon fiber (thermal conductive fiber, average fiber length 120 μm, average fiber diameter 9 μm, Nippon Graphite Fiber Co., Ltd.) 20% by volume were dispersed. A thermally conductive sheet of Comparative Example 1 was obtained in the same manner as in Example 1, except that a silicone resin composition (thermally conductive resin composition) was used.
The two-liquid addition reaction type liquid silicone resin is a mixture of 26% by volume of silicone A and 23% by volume of silicone B.

[1.5] Second Comparative Example Next, a second comparative example will be described.
-Preparation of Thermally Conductive Sheet- In Example 1, aluminum oxide having a volume average particle diameter of 1 μm was obtained by coupling 28% by volume of a two-liquid addition reaction type liquid silicone resin with 0.5% by volume of a coupling agent. 22% by volume of particles (thermally conductive particles: manufactured by Denki Kagaku Kogyo Co., Ltd.) and aluminum nitride particles with a volume average particle diameter of 1 μm that are coupled with 0.5% by volume of a coupling agent (thermally conductive particles, Tokuyama Corporation) A silicone resin composition ( A thermally conductive sheet of the first comparative example was obtained in the same manner as in the first example except that the thermally conductive resin composition) was used.
The two-liquid addition reaction type liquid silicone resin is a mixture of 14% by volume of silicone A and 14% by volume of silicone B.

[1.6] Effect of Example [1.6.1] Sheet thickness The average sheet thickness of the first to third examples is 0.29 to 0.32 mm, and the overall example is was 0.3 mm.
On the other hand, the average sheet thicknesses of the first comparative example and the second comparative example were 0.30 mm and 0.31 mm, respectively, and the total thickness of the comparative example was 0.31 mm.

[1.6.2] Thermal resistance When the thermal conductive sheets of Examples 1 to 3 were pressed at 2.81 kgf/cm ² , the sheet thermal resistance values were 0.181 to 0.189°C. · cm ² /W, and a thin sheet with a thickness of about 0.3 mm achieved a low thermal resistance value of 0.20°C·cm ² /W or less.
On the other hand, the thermal resistance value of the thermally conductive sheet of the first comparative example was as high as 0.48·cm ² /W.

[1.6.3] Thermal conductivity The effective thermal conductivity of the thermally conductive sheets of Examples 1 to 3 is 14.5 to 16.3 W / m K, and the thermal conductivity of the thermally conductive sheet is It had sufficient thermal conductivity. The heat conductive sheet of the first comparative example had a low heat conductivity of 3.5 W/m·K.

[1.6.4] Residual stress When the thermally conductive sheets of Examples 1 to 3 were compressed to a thickness of 50% of the initial thickness, the residual stress was 238 to 269 kPa. It was 276 kPa or less, which is sufficient for a thermally conductive sheet.
On the other hand, when the heat conductive sheet of the second comparative example was compressed to a thickness of 50% of the initial thickness, the residual stress was as high as 537 kPa.

[1.6.5] Tack force The thermally conductive sheets of Examples 1 to 3 were pressed with a probe of 5.1 mmΦ at 2 mm/sec at 200 gf, and then peeled off at 10 mm/sec. The force was 83 to 93 gf and had sufficient tackiness (80 gf or more).
On the other hand, when the thermally conductive sheets of the first and second comparative examples were pressed with a probe of 5.1 mmΦ at 2 mm/sec at 200 gf and then peeled off at 10 mm/sec, the tack force was 49 gf, respectively. It was 40 gf, and the tack force was insufficient.

[1.6.6] Sheet deformation ratio When the thermally conductive sheets of Examples 1 to 3 were pressed at 100 kPa for 1000 hours, the deformation ratio in the x direction in the sheet plane was 4.8 to 11. %, and the deformation rate in the y direction was 5.1 to 11%, achieving 15% or less, which is sufficient for a thermally conductive sheet, and the result was that the amount of creep was small.
On the other hand, when the thermally conductive sheet of the first comparative example was pressurized at 100 kPa for 1000 hours, the deformation rate in the x direction in the sheet plane was 30%, the deformation rate in the y direction was 33%, and the creep amount was A lot of results were obtained.

[1.6.7] Summary As described above, according to each example, a thermally conductive sheet having both high flexibility and high elasticity, which has low residual stress and a small amount of creep, has low thermal resistance and high elasticity. It also has properties such as tack. Due to the property of low residual stress, the risk of damaging a heating element such as an IC is reduced even when pressure is applied.

Moreover, it is a thermally conductive sheet that can prevent a short circuit that may occur due to creep.
Furthermore, the sheet has tackiness to prevent misalignment at the time of mounting, and the adhesion to the adherend is improved. Due to the high adhesion, a thin sheet with a thickness of about 0.3 mm achieved a low thermal resistance of 0.20° C.·cm ² /W or less.

Claims

a thermally conductive filler having a volume ratio of 55 to 70% and containing carbon fiber and at least one of aluminum nitride, aluminum oxide and aluminum hydroxide as an inorganic filler;
a two-liquid addition reaction silicone having a volume ratio of 30 to 45%;
A thermally conductive sheet containing.
Thermal conductivity is 10 W / m K or more,
The thermally conductive sheet according to claim 1.
The heat conductive sheet having a thickness of 0.35 mm or less has a thermal resistance value of 0.20° C. cm 2 /W or less when pressurized at 2.81 kgf/cm 2 ,
The residual stress when compressed to a thickness of 50% of the initial thickness is 276 kPa or less.
The thermally conductive sheet according to claim 1.
The deformation rate in the x and y directions in the sheet plane is 15% or less when pressurized at 100 kPa for 1000 hours.
The thermally conductive sheet according to claim 1.
After pressing the pressed thermally conductive sheet with a probe of 5.1 mmΦ at 200 gf at 2 mm / sec, the tack force when peeling off at 10 mm / sec is 80 gf or more.
The thermally conductive sheet according to claim 1.
A heat conductive filler containing carbon fiber, at least one of aluminum nitride, aluminum oxide and aluminum hydroxide as an inorganic filler, and a two-liquid addition reaction type silicone having a volume ratio of 30 to 45% are mixed and heated. creating a conductive sheet composition;
a step of thermosetting the thermally conductive sheet composition to form a block;
creating the thermally conductive sheet by slicing the block body so that the carbon fibers are oriented in the thickness direction of the thermally conductive sheet;
A method for producing a thermally conductive sheet comprising