Thermally conductive composition

Abstract

The present invention provides a thermally conductive composition that exhibits excellent thermal conductivity, superior adhesion to adjacent components, and excellent stability of properties, enabling stable use. [Solution] A thermally conductive paste comprising a base material made of liquid metal and a filler, wherein the base material comprises gallium and one or both of indium and tin, the base material is liquid at atmospheric pressure and 25°C, the filler is structured not to react with the base material at 100°C, and the proportion of the filler in the thermally conductive composition is in the range of more than 0 mass% and 45 mass% or less.

Description

Technical Field

[0001] The present invention relates to a thermally conductive composition disposed between, for example, a heating element and a heat radiating member, and efficiently transferring heat generated from the heating element to the heat radiating member.

Background Art

[0002] In recent years, with the progress of high performance and integration of various electronic devices, a structure with enhanced heat dissipation has been demanded so that heat generated during the operation of component parts (heating elements) can be radiated to the outside using a heat radiating member. Therefore, in order to reduce the thermal resistance between the heating element and the heat radiating member, a thermally conductive paste may be disposed between the heating element and the heat radiating member. By using the above-mentioned thermally conductive paste, for example, heat generated in the heating element can be efficiently radiated to a heat radiating member such as a metal casing or a heat sink. Such a heat transfer material can reduce the thermal resistance between the heating element and the heat radiating member by being installed between them.

[0003] Here, as the heat transfer material (thermally conductive composition), for example, as shown in Patent Documents 1 and 2, a material in which a filler (such as silver, alumina, silica, boron nitride, aluminum nitride, etc.) having excellent thermal conductivity is added to a base material made of a resin material has been proposed. However, in these Patent Documents 1 and 2, the resin material itself serving as the base material has low thermal conductivity, and the structure is such that heat is mainly transferred by the filler. Therefore, in order to improve the thermal conductivity, it is necessary to contain a large amount of the filler, which may reduce the fluidity and make it impossible to ensure the adhesion between the heating element and the heat radiating member.

[0004] For example, Patent Documents 3 and 4 propose a thermally conductive composition using liquid metal as a base material. In Patent Document 3, a paste containing 50 mass% of tungsten as a filler in a 50 mass% Ga-In-Sn ternary eutectic alloy (liquid metal) is disclosed. Patent Document 4 discloses a heat dissipation grease composition comprising an alloy as a base material, which contains gallium (Ga), indium (In), and / or tin (Sn) and has a melting point of 16°C or lower under normal pressure, and a fine powder filler consisting of a metal (e.g., silver, copper, etc.) included in 2 to 40 mass%, with a consistency in the range of 200 to 400. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 3283455 [Patent Document 2] Patent No. 4351239 [Patent Document 3] Special Publication No. 07-029213 [Patent Document 4] Patent No. 5542280 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, in the paste described in Patent Document 3, the tungsten content, which is a filler, is high at 50 mass%, which reduces fluidity and may prevent proper adhesion between the heating element and the heat dissipation member. Furthermore, in the heat dissipation grease composition described in Patent Document 4, the metal contained as a filler (for example, silver, copper, etc.) may react with the alloy base material, potentially leading to instability in various properties.

[0007] This invention has been made in view of the circumstances described above, and aims to provide a thermally conductive composition that has excellent thermal conductivity, excellent adhesion to adjacent components, excellent stability of properties, and can be used stably. [Means for solving the problem]

[0008] To solve the above-mentioned problems, the thermal conductive composition of embodiment 1 of the present invention is a thermal conductive composition comprising a base material made of a liquid metal and a filler, wherein the base material comprises gallium and one or both of indium and tin, the base material is liquid at atmospheric pressure and 25°C, the filler has a structure that does not react with the base material at 100°C, and the proportion of the filler in the thermal conductive composition is in the range of more than 0 mass% and 45 mass% or less.

[0009] According to the thermally conductive composition of embodiment 1 of the present invention, the base material is composed of a liquid metal that is liquid at atmospheric pressure and 25°C, a filler is added to this base material, and the proportion of the filler in the thermally conductive composition is in the range of more than 0 mass% and 45 mass% or less, so that it is in a paste-like state, is easy to handle, and has excellent adhesion to adjacent members. Furthermore, since the filler is structured so that it does not react with the substrate at 100°C, its composition and properties do not change, resulting in excellent stability.

[0010] The thermally conductive composition of embodiment 2 of the present invention is characterized in that, in the thermally conductive composition of embodiment 1, the filler is one or more selected from tungsten, silicon carbide, carbon fiber, and boron nitride. According to the thermally conductive composition of embodiment 2 of the present invention, the filler is one or more selected from tungsten, silicon carbide, carbon fiber, and boron nitride, so it does not react with the liquid metal base material and has particularly excellent stability. Furthermore, because the composition is paste-like due to the inclusion of the filler in a range of more than 0 mass% and 45 mass% or less, it is easy to handle and has excellent adhesion to adjacent components. Furthermore, tungsten, silicon carbide, carbon fiber, and boron nitride have excellent thermal conductivity, which can further improve the thermal conductivity of the thermal conductive composition itself.

[0011] The thermal conductive composition of embodiment 3 of the present invention is characterized in that, in the thermal conductive composition of embodiment 1 or embodiment 2, the filler has an average particle diameter in the range of 0.1 μm or more and 50 μm or less. According to the thermally conductive composition of embodiment 3 of the present invention, since the average particle size of the filler is in the range of 0.1 μm to 50 μm, by incorporating it into a substrate made of liquid metal in a range of more than 0 mass% to 45 mass%, it can be reliably made into a paste, which is easy to handle and has excellent adhesion to adjacent members.

[0012] The thermal conductive composition of embodiment 4 of the present invention is characterized in that, in the thermal conductive composition of embodiment 1 or embodiment 2, the filler is fibrous, and the ratio L / D of fiber length L to fiber diameter D is in the range of 2 to 200. According to the thermally conductive composition of aspect 4 of the present invention, the filler is fibrous, and the ratio L / D of fiber length L to fiber diameter D is in the range of 2 to 200. By incorporating it into a substrate made of liquid metal in an amount exceeding 0 mass% and within 45 mass%, it can be reliably made into a paste, which is easy to handle and has excellent adhesion to adjacent members.

[0013] The thermal conductive composition of embodiment 5 of the present invention is a thermal conductive composition according to any one of embodiments 1 to 4, wherein the viscosity at a measurement temperature of 25°C and a shear rate of 0.1 (1 / s) is 10 Pa·s or more (1 × 10⁻¹⁶). 6 It is characterized by being within the range of Pa·s or less. According to the thermally conductive composition of embodiment 5 of the present invention, the viscosity at a measurement temperature of 25°C and a shear rate of 0.1 (1 / s) is 10 Pa·s or more (1 × 10⁻¹⁶). 6 Since it is within the range of Pa·s or less, it has a paste-like consistency and is easy to handle. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a thermally conductive composition that has excellent thermal conductivity, excellent adhesion to an adjacent member, excellent stability of properties, and can be stably used.

Brief Description of the Drawings

[0015] [Figure 1] It is a flowchart showing an example of a method for manufacturing a thermally conductive composition which is an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0016] Embodiments of the present invention will be described below. Each of the embodiments shown below is specifically described in order to better understand the gist of the invention, and does not limit the present invention unless otherwise specified.

[0017] The thermally conductive composition which is an embodiment of the present invention is, for example, disposed between a heating element and a heat radiating member, and transmits heat generated from the heating element to the heat radiating member. The thermally conductive composition of this embodiment has a base material made of a liquid metal and a filler dispersed in the base material.

[0018] The liquid metal constituting the base material is an alloy having a composition containing gallium (Ga) as an alloy element and one or both of indium (In) and tin (Sn), and is supposed to be in a liquid state at atmospheric pressure and 25°C. As the composition of the liquid metal constituting the base material, the content of Ga is preferably in the range of 60 mass% or more and 80 mass% or less, the content of In is preferably in the range of 0 mass% or more and 25 mass% or less, the content of Sn is preferably in the range of 0 mass% or more and 20 mass% or less, and the total content of In and Sn is preferably in the range of 20 mass% or more and 39 mass% or less.

[0019] Furthermore, other alloying elements other than gallium (Ga), indium (In), and tin (Sn) may be included. For example, zinc (Zn) may be included in an amount between 0 mass% and 5 mass%, and bismuth (Bi) may be included in an amount between 0 mass% and 5 mass%. Furthermore, it is preferable that the total content of impurity elements other than the alloying elements mentioned above be 5 mass% or less.

[0020] In the case of the liquid metal used as the base material, the surface tension is high, and the liquid metal alone will form droplets rather than a paste, making it impossible to ensure proper adhesion with components such as heating elements and heat dissipation members. Therefore, in this embodiment, the liquid metal base material is made into a paste by incorporating a filler.

[0021] In this embodiment, "paste-like" means that at a measurement temperature of 25°C and a shear rate of 0.1 (1 / s), the viscosity is 10 Pa·s or more (1 × 10⁻¹⁶). 6 This refers to a state where the value is less than or equal to Pa·s. "Solid state" is 1 × 10 6 A viscosity exceeding Pa·s is defined as "liquid," while "liquid" refers to a viscosity below 10 Pa·s. A parallel plate rheometer (in this embodiment, Discovery HR 20: manufactured by TA Instruments Corporation) was used for viscosity measurement.

[0022] In this embodiment, the filler content in the thermally conductive composition is within the range of more than 0 mass% and 45 mass% or less. If the filler content in a thermally conductive composition exceeds 45 mass%, the composition becomes solid, making it impossible to ensure proper adhesion to components such as heat-generating elements and heat-dissipating members. On the other hand, if the filler content in a thermally conductive composition is 0 mass%, as described above, it becomes liquid, making it impossible to ensure proper adhesion to components such as heat-generating elements and heat-dissipating members. The lower limit of the filler content in the thermally conductive composition is preferably 2 mass% or more, and more preferably 20 mass% or more. On the other hand, the upper limit of the filler content in the thermally conductive composition is preferably 45 mass% or less, and more preferably 40 mass% or less.

[0023] Furthermore, in this embodiment, the filler is structured so as not to react with the substrate (liquid metal) at 100°C. That is, at least the surface of the filler is made of a material that does not react with the liquid metal constituting the substrate. In this embodiment, the filler is preferably one or more selected from tungsten, silicon carbide, carbon fiber, and boron nitride. Fillers made of these materials do not react with gallium (Ga), indium (In), and tin (Sn), which constitute the liquid metal.

[0024] In this embodiment, there are no particular restrictions on the shape of the filler; it can be in the form of powder, crushed pieces, flakes, granules, or fibers, and these may be mixed together.

[0025] In the case of fillers other than fibrous fillers (powdered, crushed, flaky, or granular fillers), it is preferable that the average particle size of the filler is within the range of 0.1 μm to 50 μm. In this embodiment, the average particle diameter of the filler was determined by measuring the equivalent spherical diameter using a laser diffraction scattering particle size distribution analyzer (for example, MT3300EXII: manufactured by Microtrac-Bell Co., Ltd.).

[0026] When the average particle size of the filler is within the range of 0.1 μm to 50 μm, it will be dispersed relatively uniformly within the substrate, allowing the thermally conductive composition to be stably formed into a paste. Furthermore, the average particle size of the filler is more preferably 0.5 μm or larger, and even more preferably 3 μm or larger. On the other hand, the average particle size of the filler is more preferably 40 μm or smaller, and even more preferably 30 μm or smaller.

[0027] In the case of fibrous fillers, it is preferable that the ratio L / D of fiber length L to fiber diameter D is within the range of 2 to 200. In this embodiment, the fiber length L and fiber diameter D of the fibrous filler were measured using a microscope (for example, VHX-970F: manufactured by Keyence Corporation) in accordance with JIS H 7402.

[0028] When the ratio L / D of the fiber length L to fiber diameter D of the fibrous filler is within the range of 2 to 200, it will be dispersed relatively uniformly in the substrate, and the thermally conductive composition can be stably formed into a paste. Furthermore, the ratio L / D of the fiber length L to fiber diameter D of the fibrous filler is more preferably 2 or more and 100 or less, and even more preferably 2 or more and 50 or less.

[0029] Next, an example of a method for manufacturing the thermally conductive composition according to this embodiment will be described with reference to the flowchart in Figure 1. In this embodiment, as shown in Figure 1, the process includes a substrate forming step S01 and a filler mixing step S02.

[0030] (Base material formation step S01) First, the raw materials for the elements that make up the base liquid metal are prepared. In this embodiment, gallium (Ga) raw material, indium (In) powder, and tin (Sn) raw material are prepared and weighed out to a predetermined content ratio. By mixing these raw material powders while heated, a substrate made of liquid metal of a predetermined composition is formed. Preferably, the heating temperature in the substrate formation step S01 is within the range of 80°C to 200°C, and the holding time at the heating temperature is within the range of 5 minutes to 30 minutes. The formed substrate becomes liquid at atmospheric pressure and 25°C.

[0031] (Filler mixing process S02) Next, prepare the filler as described above and mix it with the base material. At this time, the filler should be added to the base material in small amounts and mixed. Preferably, the amount added at one time should be within the range of 0.5 parts by weight to 2.0 parts by weight of filler per 100 parts by weight of base material. There are no particular restrictions on the mixing method; it may be mixed manually or using a self-rotating mixer or the like. By mixing a predetermined amount of filler with the base material, the material changes from a liquid to a paste, and the thermally conductive composition of this embodiment is produced.

[0032] In this embodiment of the thermally conductive composition, the base material is composed of a liquid metal that is liquid at atmospheric pressure and 25°C, and a filler is added to this base material. Since the proportion of the filler in the thermally conductive composition is in the range of more than 0 mass% and 45 mass% or less, the composition becomes paste-like, is easy to handle, and has excellent adhesion to adjacent components (heat-generating element and heat-dissipating element). Therefore, the thermal resistance between the heat-generating element and the heat-dissipating element can be reduced. Furthermore, since the filler is structured so that it does not react with the substrate at 100°C, its composition and properties do not change, resulting in excellent stability.

[0033] In the thermally conductive composition of this embodiment, when the filler is one or more selected from tungsten, silicon carbide, carbon fiber, and boron nitride, it does not react with the liquid metal base material and exhibits particularly excellent stability. Furthermore, when contained in a range of more than 0 mass% and 45 mass% or less, it becomes paste-like, resulting in excellent handling and superior adhesion to adjacent components (heat-generating elements and heat-dissipating elements). Furthermore, tungsten, silicon carbide, carbon fiber, and boron nitride have excellent thermal conductivity, which can further improve the thermal conductivity of the thermal conductive composition itself.

[0034] In the thermally conductive composition of this embodiment, when the average particle size of the filler is in the range of 0.1 μm to 50 μm, by incorporating it into a substrate made of liquid metal in a range of more than 0 mass% to 45 mass%, it can be reliably made into a paste, which is easy to handle and has excellent adhesion to adjacent components.

[0035] Although one embodiment of the present invention has been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. [Examples]

[0036] The results of the verification experiments conducted to confirm the effects of the present invention are described below.

[0037] A substrate consisting of liquid metal with the composition shown in Tables 1 and 2 was prepared. The fillers listed in Tables 1 and 2 were mixed into this substrate. The average particle size of the filler was measured using a laser diffraction scattering particle size distribution analyzer (MT3300EXII: manufactured by Microtrac-Bell Co., Ltd.). For the fibrous filler, the fiber length L and fiber diameter D were measured using a microscope (VHX-970F: manufactured by Keyence Corporation) in accordance with JIS H 7402, and the ratio L / D of fiber length L to fiber diameter D was determined.

[0038] In the present invention examples 1-3, 6, 9, 12-17, and comparative examples 1, 3, and 4, the filler and base material were manually mixed using a spatula, and then mixed for 1 minute at 2000 rpm using a rotary mixer to obtain a thermally conductive composition. Furthermore, in Examples 4-5, 7-8, 10-11, and Comparative Example 2 of the present invention, a thermally conductive composition was obtained by adding 5 parts by mass of filler and mixing it for 1 minute at 2000 rpm using a rotary mixer, and repeating this until a predetermined content was reached.

[0039] The thermal conductivity, stability, and adhesion of the obtained thermally conductive compositions were evaluated as follows. The evaluation results are shown in Tables 1 and 2.

[0040] (Thermal conductivity) The thermal conductivity of the thermally conductive composition was measured using a thermal conductivity measuring device (TRM-046RHHT: manufactured by Hitachi Technology & Services, Ltd.) by a steady-state method.

[0041] (stability) The stability of the thermally conductive compositions was evaluated using SEM (JSM-IT200: manufactured by JEOL Ltd.). Compositions in which alloying between the filler and the substrate was not confirmed by EDS analysis were rated as "○" and those in which alloying was confirmed were rated as "×".

[0042] (Adhesion) One g of the thermally conductive composition was placed between glass slides and evaluated visually or using a microscope (VHX-970F: manufactured by Keyence Corporation). A "○" was given if there were no non-adhering surfaces with a diameter of 5 mm or more on the contact surface, and a "×" was given if non-adhering surfaces with a diameter of 5 mm or more were observed.

[0043] [Table 1]

[0044] [Table 2]

[0045] In Comparative Examples 1 and 2, the tungsten content as a filler was high at 66.6 mass%, resulting in insufficient fluidity and poor adhesion. Note that thermal conductivity was not measured in Comparative Examples 1 and 2. In Comparative Examples 3 and 4, copper was used as the filler, and the liquid metal base material reacted with the filler, resulting in a "×" (indicating poor) stability.

[0046] In contrast, in Example 1-17 of the present invention, the material was in paste form, resulting in excellent adhesion. Furthermore, the filler did not react with the liquid metal base material, resulting in excellent stability. In addition, the thermal conductivity was sufficiently high.

[0047] From the above, it has been confirmed that the present invention provides a thermally conductive composition that exhibits excellent thermal conductivity, excellent adhesion to adjacent components, excellent stability of properties, and can be used stably.

Claims

1. A thermally conductive composition comprising a base material made of liquid metal and a filler, The said substrate comprises gallium and one or both of indium and tin. The aforementioned substrate is liquid at atmospheric pressure and 25°C. The filler is structured so that it does not react with the substrate at 100°C. A thermally conductive composition characterized in that the proportion of the filler in the thermally conductive composition is in the range of more than 0 mass% and 45 mass% or less.

2. The thermally conductive composition according to claim 1, characterized in that the filler is one or more selected from tungsten, silicon carbide, carbon fiber, and boron nitride.

3. The thermal conductive composition according to claim 1 or 2, characterized in that the filler has an average particle diameter in the range of 0.1 μm to 50 μm.

4. The thermal conductive composition according to claim 1 or 2, characterized in that the filler is fibrous, and the ratio L / D of fiber length L to fiber diameter D is in the range of 2 to 200.

5. Viscosity of 10 Pa·s or more at a measurement temperature of 25°C and a shear rate of 0.1 (1 / s) is 1 × 10 ６ The thermally conductive composition according to claim 1 or 2, characterized in that it is within the range of Pa·s or less.

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