THERMAL CONDUCTIVITY, THERMAL CONDUCTIVITY BODY, METHOD FOR PRODUCING A THERMAL CONDUCTIVITY BODY AND METHOD FOR FORMING A THERMAL CONDUCTIVITY

Abstract

One object of the present invention is to provide a heat conduction structure that is in close contact with opposing surfaces of two elements, such as a heating element and a heat sink, even if the opposing surfaces have fine irregularities, can achieve high heat transfer efficiency, is easy to handle, can maintain assembly accuracy and can maintain stable quality even after assembly.The heat conduction structure comprises: a heat-conducting porous base plate 2, which has a front and a back plate surface, each facing two elements 91 and 92, and has a plurality of through holes 20 extending in a thickness direction and opening on both the front and back plate surfaces; and a heat-conducting material 3, which retains a flowability at least under an operating temperature environment in which the heat conduction is carried out, fills the through holes 20 of the porous base plate 2 and is in close contact with opposing surfaces of the two elements.

Description

Thermal interface structure, thermal interface structure, method for manufacturing a thermal interface structure, and method for forming a thermal interface structure

[0001] The present invention relates to a thermal interface structure that is provided between two members and promotes thermal conduction between the two members.

[0002] Conventionally, this type of thermal interface structure involves providing a thermal interface material such as a thermally conductive silicone sheet, a thermally conductive tape, or a thermally conductive paste between a heat-generating element such as a semiconductor chip and a heat sink that acts as a cooler for the element (see, for example, Patent Document 1).

[0003] Thermally conductive silicone sheets and tapes retain their shape and are easy to handle. However, if there are minute irregularities on the opposing surfaces of a heating element or heat sink, air gaps form, resulting in increased and varying thermal resistance and reduced heat transfer efficiency. On the other hand, thermally conductive pastes are fluid and can adhere to opposing surfaces with such irregularities, but if the applied thickness is uneven, air gaps are likely to form and assembly accuracy will be reduced. Furthermore, such pastes alone will result in a film thickness of at least 50 to 100 μm, unavoidably generating high interfacial thermal resistance. Furthermore, there is a risk of the paste running off after assembly, making them difficult to handle, unstable, and prone to quality variations.

[0004] Japanese Patent Application Publication No. 11-58591

[0005] Therefore, in view of the above-mentioned situation, the present invention aims to solve the problem of providing a thermal interface structure that adheres to the opposing surfaces of two components, such as a heating element and a heat sink, even if the opposing surfaces have minute irregularities, thereby achieving high heat transfer efficiency, is easy to handle, maintains assembly accuracy, and maintains stable quality even after assembly.

[0006] The present invention encompasses the following inventions: (1) A thermal interface structure provided between two members to promote heat conduction, comprising: a porous base plate with good thermal conductivity having front and back plate surfaces facing each of the two members and having a plurality of through holes extending in the thickness direction and opening in both the front and back plate surfaces; and a thermally conductive material that has fluidity at least under an operating temperature environment in which the heat conduction occurs, filled in the through holes of the porous base plate, and in close contact with the opposing surfaces of the two members.

[0007] (2) The thermal interface structure according to (1), wherein the thermally conductive material is in a state of a liquid, semi-solid, particle aggregate, or a combination thereof, which has good thermal conductivity under the operating temperature environment.

[0008] (3) The thermal interface structure according to (1) or (2), wherein the thermally conductive material is in a solid state with good thermal conductivity at room temperature.

[0009] (4) A thermal interface structure provided between two members to promote heat conduction, comprising: a porous base plate with good thermal conductivity having front and back plate surfaces facing each of the two members and a plurality of through holes extending in the thickness direction and opening on both the front and back plate surfaces; and a thermally conductive material made of a fusible alloy having a melting point of 150°C or less, filled in the through holes of the porous base plate and in close contact with the opposing surfaces of the two members, the thermal interface structure being used in a temperature environment below the melting point of the thermally conductive material.

[0010] (5) The thermal interface structure according to (1) or (4), wherein the heat-conducting material is also interposed between the surface of the perforated base plate around the openings and the member.

[0011] (6) The thermal interface structure according to (1) or (4), further comprising a clamping means for elastically clamping the porous base plate between the two members.

[0012] (7) A thermal interface structure used in the thermal interface structure described in any one of (1) to (3), comprising: the porous base plate; and a thermal conductive material that is filled in the through holes of the porous base plate and is also present on the front and back plate surfaces, is in a solid state with good thermal conductivity at room temperature, and has fluidity under a temperature environment in which the heat is conducted.

[0013] (8) A thermal interface structure for use in the thermal interface structure described in (4), comprising the porous base plate and a thermal conductive material made of a fusible alloy having a melting point of 150°C or less, the thermal conductive material being filled in the through holes of the porous base plate and also present on the front and back plate surfaces, and being in a solid state with good thermal conductivity at room temperature, the thermal interface structure being used in a temperature environment below the melting point of the thermal conductive material.

[0014] (9) A method for manufacturing a thermal interface structure according to (7) or (8), wherein the thermal conductive material is heated to fluidize it, thereby filling it into the through holes of the porous base plate, and then the material is returned to room temperature to solidify.

[0015] (10) A method for forming a thermal interface structure using the thermal interface structure according to (7) or (8), comprising providing the thermal interface structure between two members, heating at least one of the members to fluidize the thermally conductive material of the thermal interface structure, bringing the thermal interface structure into close contact with the opposing surfaces of the two members, and then returning the material to room temperature to solidify it.

[0016] According to the thermal interface structure of the present invention, even if there are minute irregularities on the opposing surfaces of two components such as a heating element and a heat sink, the thermally conductive material adheres to each opposing surface, and the thermally conductive material transfers heat, which is also transferred to the porous base plate filled with the thermally conductive material.This allows heat to be transferred efficiently through the porous base plate, which has good thermal conductivity, and overall high heat transfer efficiency is achieved.

[0017] Furthermore, since the porous base plate functions as a core material with shape retention, it is easy to handle and can be assembled with high precision. Furthermore, since the thermally conductive material is filled into the through holes of the porous base plate, even if the thermally conductive material has fluidity, it is prevented from flowing out after assembly, thereby maintaining stable quality, i.e., excellent heat transfer efficiency over a long period of time. Furthermore, since the thermally conductive material enters the through holes, it is possible to avoid an excessive thickness of the thermally conductive material being present between the porous base plate and the component, thereby preventing an increase in contact thermal resistance.

[0018] A conceptual diagram showing the thermal interface structure of the present invention. An explanatory diagram showing a procedure for configuring the thermal interface structure. An explanatory diagram showing another procedure for configuring the thermal interface structure. An explanatory diagram showing yet another procedure for configuring the thermal interface structure. An explanatory diagram showing yet another procedure for configuring the thermal interface structure. An explanatory diagram explaining a thermal resistance measurement experiment conducted on various samples of the thermal interface structure. An explanatory diagram showing yet another procedure for configuring the thermal interface structure.

[0019] Next, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0020] 1, the thermal interface structure S according to the present invention is provided between two members, for example, a heat generating element 91 such as a semiconductor chip, and a heat sink 92, which is a cooler, to promote thermal conduction between them. Specifically, the thermal interface structure S is formed of a thermal interface structure 1 including a porous base plate 2 with good thermal conductivity, having front and rear plate surfaces 21 and 22 facing the two members (91 and 92), and a plurality of through holes 20 extending in the thickness direction and opening in both the front and rear plate surfaces, and a thermally conductive material 3 filled in the through holes 20 of the porous base plate 2 and in close contact with the opposing surfaces 91 a and 92 a of the two members (91 and 92). The thermally conductive material 3 in this example maintains fluidity at least under the operating temperature environment where the thermal conduction occurs.

[0021] In the thermal interface structure S of the present invention, even if the opposing surfaces of the two components (91, 92) have minute irregularities, the thermally conductive material 3 adheres to the opposing surfaces 91a, 92a, and the thermally conductive material 3 transfers heat. Heat is also transferred to the perforated base plate 2 filled with the thermally conductive material 3, allowing for efficient heat transfer through the perforated base plate 2. In this example, the two components 91, 92 are connected by a mounting member 8, sandwiching the thermal interface structure S between them and applying surface pressure. The illustrated mounting member 8 is an example, and a preferred example is a clamping means having a leaf spring, wire spring, or the like, which elastically clamps the thermal interface structure 1, consisting of the perforated base plate 2 and the thermally conductive material 9, between the two components 91, 92. A structure connected by such a mounting member 8 allows for easy removal. Of course, instead of using such a detachable mounting structure, soldering or welding may be used.

[0022] A wide variety of metal materials and alloys thereof with excellent thermal conductivity, such as aluminum, iron, and copper, can be used for the porous base plate 2. In the case of copper, a porous base plate is preferably used, which is formed by a metal solidification method into a lotus-type porous metal compact having a plurality of pores extending in one direction and then cut in a direction perpendicular to the direction in which the pores extend. However, the porous base plate of the present invention also includes a base plate in which through-holes are formed using a drill, laser, or the like.

[0023] The lotus-type porous metal compact can be formed by known methods such as the pressurized gas method (e.g., the method disclosed in Japanese Patent No. 4235813) or the thermal decomposition method. The through-holes of the perforated plate cut out from the lotus-type porous metal compact are the pores separated by the cutting process. In addition to the through-holes, there are also bottomed holes that do not penetrate (holes that are cut at the position where the pores are interrupted), but these bottomed holes also have the effect of increasing the contact area with the thermal conductive material 3. By using a perforated plate cut out from the lotus-type porous metal compact, the perforated base plate 2 can be obtained easily and at low cost.

[0024] Such a porous base plate 2 functions as a core material having shape retention, is easy to handle, and enables good assembly accuracy. Furthermore, since the thermally conductive material 3 is filled into the through holes 20 of the porous base plate 2, the thermally conductive material is retained within the through holes 20 even after assembly, preventing it from flowing out, and maintaining excellent heat transfer efficiency for a long period of time.

[0025] The thermally conductive material 3 may be, for example, a liquid such as a liquid metal with good thermal conductivity that maintains fluidity from room temperature to the operating temperature environment, a gel or sol-like semi-solid such as a thermally conductive gel sheet or thermally conductive grease (including a thermally conductive filler mixed in), a particle aggregate such as fine metal powder, or a combination of these. A wide range of well-known fillers can be used, including graphite, metal powder (including columnar structures), and ceramic powder. In other words, the term "fluidity" in this invention includes deformable semi-solids, particle aggregates, and the like.

[0026] The thermally conductive material 3 is preferably solid at room temperature. This allows the thermal interface structure 1 to be configured as shown in FIG. 7( a) , which is composed of a porous base plate 2 and a thermally conductive material 3 that is solid at room temperature, dramatically improving ease of handling. For example, a fusible alloy having a melting point of 150°C or less is suitable, and the thermally conductive material can be used in a temperature environment below the melting point of the material. Specifically, an alloy containing one or more low-melting-point metals selected from Bi (bismuth), Pb (lead), Cd (cadmium), Sn (tin), In (indium), and Ga (gallium) is preferred as such a fusible alloy.

[0027] As shown in the partially enlarged view of Figure 1, it is preferable that such thermal conductive material 3 is also interposed between the plate surface 22 (21) around the opening of the through hole 20 of the porous base plate 2 and the opposing surface 92a (91a) of each opposing member, thereby preventing the formation of an air layer between the two surfaces due to fine irregularities.

[0028] Next, the procedure for forming the thermal interface structure S will be described with reference to the example of Fig. 2. First, as shown in (a), the porous base plate 2 is placed on one member 91, and the thermal conductive material 3, which is fluid at room temperature, is poured into the through-holes 20 from the openings on the top surface to fill them. At this time, the thermal conductive material 3 is supplied so that it overflows from the openings.

[0029] Next, as shown in (b), the other member 92 is placed on the upper surface of the porous base plate 2. This brings the portion of the thermally conductive material 3 above the opening into close contact with the lower surface of the member 92. Then, as shown in (c), the two members 91 and 92 are connected using the mounting member 8, and the thermal interface structure S is sandwiched between them and maintained in a state where surface pressure is applied. This forms the thermal interface structure S in a stable state. Even if the thermally conductive material 3 is in a form other than a liquid, such as a sol or powder aggregate, it can be similarly formed by pouring it from the upper surface of the porous base plate 2.

[0030] 3(a), before placing the porous base plate 2 on one member 91, a thermally conductive material 3 in the form of a liquid, sol, or powder aggregate may be laid on the member 91 in an area corresponding to the underside of the porous base plate 2, and the porous base plate 2 may then be placed on top of this, so that the thermally conductive material 3 fills the through holes 20 in the porous base plate 2 from the openings on the underside. The steps (b) and (c) are the same as those shown in FIG. 2 above.

[0031] 4 and 5, in particular when the thermally conductive material 3 is a gel-like material with a certain degree of viscosity, it is also possible to prepare the thermally conductive material 3 in a plate shape and place it on one or both sides of the porous base plate 2 placed on one member 91 (on both sides in FIG. 4, and on the top side only in FIG. 5), and then press the other member 92 downward from above, so that the thermally conductive material 3 fills the interior through the openings in the porous base plate 2. The procedure after filling is the same as that shown in FIG. 2 above.

[0032] Another method is to fabricate a thermal interface structure 1 consisting of a perforated base plate 2 and a thermally conductive material 3 that is solid at room temperature, as shown in Figure 7(a). This structure is then sandwiched between components 91 and 92 as shown in (b) and (c). Heating the structure fluidizes the thermally conductive material 3, resulting in the thermally conductive material 3 adhering to the components 91 and 92 as shown in (d). After returning the structure to room temperature and solidifying it, the two components 91 and 92 are connected using mounting members 8 as shown in (e). The thermal interface structure S is sandwiched between the components and maintained under surface pressure. Specifically, for example, the thermally conductive material 3 is a low-melting-point metal with a melting point of 80°C. The thermal interface structure 1 is placed between two components, a CPU and a cooling component (e.g., fins). The structure is heated to the CPU's upper operating temperature (e.g., 80°C) to fluidize the low-melting-point metal, and the CPU temperature is then maintained below its melting point. Because the low-melting-point metal maintains its solid state, leakage of the material 3 from between the components is suppressed. Before returning to room temperature, surface pressure may be applied using the mounting member 8.

[0033] Here, the thermal interface structure 1 is formed by heating and fluidizing a thermally conductive material 3, such as a low-melting-point metal with a melting point of 80°C, to fill the through-holes of the porous base plate 2, and then returning it to room temperature to solidify. This allows such a thermal interface structure 1 to be prepared in advance and attached between the two members 91, 92, improving management, ease of construction, safety, and the like.

[0034] Although the embodiments of the present invention have been described above, the present invention is not limited to these examples, and it goes without saying that the present invention can be embodied in various forms without departing from the spirit of the present invention.

[0035] The results of thermal resistance measurement experiments on various samples of thermal interface structures will be described below.

[0036] (Samples) As shown in FIG. 6, the thermal interface structures prepared were Example 1 in which a thermal interface structure consisting of a porous base plate and a thermally conductive material according to the present invention was interposed between two members (between the heater and the copper block), Comparative Example 1 in which only silicone oil was interposed between the members, Comparative Example 2 in which only liquid metal was interposed between the members, and Comparative Example 3 in which only the porous base plate was interposed between the members.

[0037] The porous base plate used in Example 1 and Comparative Example 3 was a 0.2 mm thick porous plate cut out from a lotus-type porous copper compact. The liquid metal used in Example 1 and Comparative Example 2 was Thermalright Silverking liquid metal compound (thermal conductivity 79 W / mk).

[0038] (Method of Measuring Thermal Resistance) As shown in FIG. 6, a structure was formed in which a sample of a thermal interface structure (Example 1 / Comparative Example 1 / Comparative Example 2 / Comparative Example 3) was interposed between a heater and a copper block, and the thermal resistance value (R ｔ The thermal resistance is calculated using the following formula:

[0039] R ｔ = (T １ -T ２ ) / (Q-Q Leak ) R ｔ :Thermal resistance (K / W) T １ : Heater temperature (K) T２ : Cooling fin temperature (K) Q: Power consumption (W) Q Leak : Leakage power (w)

[0040] The specifications of each part are as follows:・Axial fan: NMB 06025SA-12T-AA, outer diameter 60 mm, thickness 25 mm, DC12V ・Heat sink: outer diameter 60 mm x 60 mm x 2 mm, central heat receiving surface 30 mm x 30 mm x 2 mm ・Heater: sheathed heater: 100 V-150 W, 3 pieces, leakage heat coefficient: 0.07771 ・Temperature sensor: heater section: sheathed thermocouple, T-type Class 2 φ0.5, copper block section: sheathed thermocouple, T-type Class 2 φ1.0, cooling fin inlet (air temperature) glass-coated thermocouple, T-type, Class 2 φ0.5 ・Axial fan: DC power supply, Texio PW24-1.5AQ ・Heater power supply: DC power supply, Texio PSW-720M160 ・Data logger: Graphic Graphtec GL840

[0041] As a result, as shown in Table 1 below, the structure of Example 1 had the lowest thermal resistance, confirming the effectiveness of the present invention. Comparative Example 1, which used only silicone oil, and Comparative Example 2, which used only liquid metal, had higher thermal resistance than the porous base plate, and it was unavoidable that a certain degree of film thickness would occur, which is thought to have resulted in higher thermal resistance than Example 1. Comparative Example 3, which used only the porous base plate, is thought to have had a small gap, i.e., an air layer, between the two members (between the heater and the copper block), resulting in higher thermal resistance than the other examples.

[0042]

[0043] REFERENCE SIGNS LIST 1 Thermal interface structure 2 Perforated base plate 3 Thermally conductive material 8 Mounting member 20 Through-hole 21, 22 Plate surface 91, 92 Member 91a, 92a Opposing surface S Thermal interface structure

Claims

1. A thermal interface structure provided between two components to promote thermal conduction, comprising: a porous base plate with good thermal conductivity having front and back plate surfaces facing each of the two components and having a plurality of through holes extending in the thickness direction and opening into both the front and back plate surfaces; and a thermally conductive material that has fluidity at least under the operating temperature environment in which the thermal conduction occurs, which is filled into the through holes of the porous base plate and is in close contact with the opposing surfaces of the two components.

2. The thermal interface structure according to claim 1, wherein the thermally conductive material is in a state of liquid, semi-solid, particle aggregate, or a combination thereof, having good thermal conductivity in the operating temperature environment.

3. The thermal interface structure according to claim 1 or 2, wherein the thermally conductive material is in a solid state with good thermal conductivity at normal (room) temperature.

4. A thermal interface structure provided between two components to promote thermal conduction, comprising: a porous base plate with good thermal conductivity having front and back plate surfaces facing each of the two components and having a plurality of through holes extending in the thickness direction and opening into both the front and back plate surfaces; and a thermally conductive material made of a fusible alloy having a melting point of 150°C or less, filled in the through holes of the porous base plate and in close contact with the opposing surfaces of the two components; and the thermal interface structure is used in a temperature environment below the melting point of the thermally conductive material.

5. A thermal interface structure according to claim 1 or 4, wherein the heat conductive material is also interposed between the plate surface surrounding the openings of the porous base plate and the member.

6. A thermal interface structure according to claim 1 or 4, further comprising a clamping means for elastically clamping said porous base plate between said two members.

7. A thermal interface structure for use in the thermal interface structure according to any one of claims 1 to 3, comprising: the porous base plate; and a thermal conductive material filled in the through holes of the porous base plate and present on both the front and back plate surfaces, which is in a solid state with good thermal conductivity at normal (room) temperature and has fluidity under a usage temperature environment in which the heat conduction takes place.

8. A thermal interface structure for use in the thermal interface structure according to claim 4, comprising: the porous base plate; and a thermal conductive material which is made of a fusible alloy having a melting point of 150°C or less, which is filled in the through holes of the porous base plate and is also present on the front and back plate surfaces, and which is in a solid state with good thermal conductivity at room temperature (room temperature), and which is used in a temperature environment below the melting point of the thermal conductive material.

9. A method for manufacturing a thermal interface structure according to claim 7 or 8, comprising heating and fluidizing the thermally conductive material to fill the through holes of the porous base plate, and then cooling the material to room temperature to solidify it.

10. A method for forming a thermal interface structure using the thermal interface structure according to claim 7 or 8, comprising the steps of: providing the thermal interface structure between two members; heating at least one of the members to fluidize the thermally conductive material of the thermal interface structure, bringing the thermal interface structure into intimate contact with the opposing surfaces of the two members; and returning the thermal interface structure to room temperature to solidify it.

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