Graphite-copper composite, heat sink member using the same, and method for manufacturing graphite-copper composite

Abstract

A graphite-copper composite material comprising a copper layer and flake-like graphite particles deposited between the copper layer and the copper layer, wherein the volume fraction of copper is 3-30%, characterized in that: in the deposited cross-section, the number N of interparticle gaps obtained by the following steps (1a) to (1c) is 5 or less. (1a) Five measurement fields of 930 μm × 1230 μm are defined in the above-mentioned deposited cross-section. (1b) For each of the five measurement fields, the number of gaps with a width of 2-5 μm within the flake-like graphite particles is counted and set as N. 1 ~N 5 (1c) Calculate the average number of gaps (N) 1 +N 2 +N 3 +N 4 +N 5 The number of interstitial spaces N within the particle is obtained by ) / 5).

Description

Graphite-copper composite material, heat sink components using the same, and method for manufacturing graphite-copper composite material. Technical Field

[0001] This invention relates to a graphite-copper composite material, a heat sink component using the same, and a method for manufacturing the graphite-copper composite material. Background Technology

[0002] Materials used for heat dissipation components in semiconductor machines require high thermal conductivity. While copper has high thermal conductivity, it also has a high coefficient of thermal expansion. A metal-graphite composite material has been proposed as a way to reduce the coefficient of thermal expansion without compromising copper's high thermal conductivity and at low cost (see, for example, Patent Document 1: Japanese Patent Application Publication No. 2017-128802). Patent Document 1 discloses that the metal-graphite composite material has high cooling reliability and a low coefficient of linear expansion. Summary of the Invention

[0003] [The problem that the invention aims to solve]

[0004] When metal-graphite composites are used as heat dissipation materials, they are sometimes subjected to temperature cycling ranging from a minimum of approximately -40°C to a maximum of approximately 125°C. Suppressing the thermal degradation of composites caused by temperature cycling has been a long-standing issue, but it remains largely unresolved.

[0005] Therefore, the object of the present invention is to provide a graphite-copper composite material in which thermal degradation after temperature cycling is suppressed, a heat sink component using the same, and a method for manufacturing the graphite-copper composite material.

[0006] [Technical means to solve the problem]

[0007] In order to solve the above-mentioned problems, the inventors conducted research and found that by using flake-shaped graphite particles obtained by subjecting graphite particles to specific pretreatment together with copper particles as raw materials, a graphite-copper composite material in which thermal degradation after temperature cycling is suppressed can be obtained.

[0008] That is, the present invention is a graphite-copper composite material comprising a copper layer and flake-like graphite particles deposited between the copper layer and the copper volume fraction being 3 to 30%, and characterized in that: in the deposited cross section, the number N of interparticle gaps obtained by (1a) to (1c) below is 5 or less.

[0009] (1a) Five measurement fields of 930 μm × 1230 μm were delineated within the above-mentioned lamination profile.

[0010] (1b) For each of the five measurement fields, the number of gaps with a width of 2 to 5 μm in the scaly graphite particles was counted and set as N1 to N5.

[0011] (1c) Calculate the average number of gaps ((N1+N2+N3+N4+N5) / 5) to obtain the number of gaps N inside the particle.

[0012] Furthermore, the present invention is a heat sink component using the above-mentioned graphite-copper composite material.

[0013] Furthermore, the present invention is a manufacturing method for the aforementioned graphite-copper composite material, characterized by comprising the following steps: inserting graphite particles between a pair of grinding stones arranged vertically, rotating the upper grinding stone at a frequency of 12 Hz or less, thereby pre-treating the graphite particles to obtain flake-shaped graphite particles; mixing the aforementioned flake-shaped graphite particles with copper particles to obtain a molding material; and sintering the molded body obtained by shaping the aforementioned molding material using a multi-axis electric sintering method.

[0014] [The effects of the invention]

[0015] According to the present invention, a graphite-copper composite material in which thermal degradation after temperature cycling is suppressed, a heat sink component using the same, and a method for manufacturing the graphite-copper composite material are provided. Attached Figure Description

[0016] Figure 1 is a diagram showing the defined field of view in an SEM image of a laminated profile of a graphite-copper composite material.

[0017] Figure 2 illustrates the gaps within the flake-like graphite particles;

[0018] Figure 3 illustrates the pretreatment method for graphite particles;

[0019] Figure 4 is a schematic diagram illustrating the multi-axis energized sintering apparatus;

[0020] Figure 5 is a schematic diagram illustrating the cooling substrate;

[0021] Figure 6 is an example of the progression of thermal degradation rate during temperature cycling tests.

[0022] Explanation of reference numerals in the attached figures

[0023] 12: Flake-like graphite particles; 14: Copper layer

[0024] 16: Gap 23: Graphite particles

[0025] 30a, 30b: Grinding stone; 31a, 31b: Metal plate

[0026] 32a, 32b: Metal components for joining; 33a, 33b: Abrasive grains

[0027] 40: Multi-axis energized sintering device; 42: Vacuum container

[0028] 44: Carbon die; 45a, 45b: Pressure shaft

[0029] 47a, 47b: Heating shafts 49a, 49b: Heating shafts

[0030] 50: Heat sink 51: Wiring layer

[0031] 52: Electrical insulation layer; 53: Stress buffer layer

[0032] 54: Cooling layer 55: Cooling substrate Detailed Implementation

[0033] The embodiments of the present invention will now be described in detail.

[0034] <Graphite-copper composite materials>

[0035] The graphite-copper composite material of the present invention (hereinafter referred to as the composite material) is a sintered body obtained by using flake graphite particles and copper particles as raw materials. The flake graphite particles are stacked in layers separated by copper layers. Here, "separated by copper layers" means that the flake graphite particles are connected through adjacent copper layers. That is, the flake graphite particles in the composite material are electrically continuous. The thickness of the copper layer in the composite material is not particularly limited, but is generally about 3 to 25 μm.

[0036] The volume fraction of copper in the composite material is 3-30%. Since the content of graphite, which has high thermal conductivity, is as high as 70-97%, the composite material of this invention has very high thermal conductivity. Copper acts as a binder in the composite material. To avoid breakage of the composite material during processing, the volume ratio of graphite to copper in the composite material (graphite:copper) is preferably 70:30-97:3. To ensure a high thermal conductivity of over 750 W / (m·K) and good processability, the volume ratio (graphite:copper) is more preferably 84:16-95:5. The volume fraction of copper in the composite material can be adjusted by the blending ratio of the raw materials during manufacturing.

[0037] Furthermore, the number N of interparticle gaps obtained by a specific method in the laminated profile of the composite material of the present invention is 5 or less. The laminated profile refers to a cross-section for observing the flake-like graphite particles of the laminate, specifically, it refers to the surface in which the flake-like graphite particles of the laminate are pressurized when the composite material is manufactured by sintering the molding raw material containing flake-like graphite particles.

[0038] When the composite material is cylindrical, the longitudinal direction of the cylinder corresponds to the stacking direction of the flake-like graphite particles. Therefore, firstly, a sheet with a thickness of about 2 mm is cut along the longitudinal direction of the cylinder. After grinding the surface of the cut sheet, a cross section polisher (CP) is used to obtain the stacking profile of the analytical area.

[0039] The number of interstitial spaces N within a particle can be obtained through the following (1a) to (1c).

[0040] (1a) Five 930 μm × 1230 μm measurement fields were defined within the lamination profile of the composite material. The measurement fields could be arbitrarily defined in an SEM image obtained by observing the lamination profile of the composite material at 100x magnification using a scanning electron microscope (SEM). In the measurement fields, as shown in Figure 1, the flake-like graphite particles 12 were laminated with copper layers 14 as intersperses, and gaps 16 were confirmed within the flake-like graphite particles 12.

[0041] (1b) For each of the five measurement fields, the number of gaps with a width of 2–5 μm within the flake-shaped graphite particles was counted and designated as N1–N5. The width of the gap within the flake-shaped graphite particles was defined as shown in Figure 2. That is, a gap 16 in any of the flake-shaped graphite particles 12 was selected and adjusted so that the gap 16 crosses the image. The maximum distance between the upper and lower edges L1 and L2 of the defined gap 16 was defined as the width w of the gap. The width w was measured using commercially available image processing software, and the number of gaps 16 with a width of 2–5 μm was counted to determine N1–N5. The contrast of the SEM image was adjusted appropriately as needed before observation.

[0042] (1c) Calculate the average number of gaps in the 5 measured fields of view ((N1+N2+N3+N4+N5) / 5) to obtain the number of gaps N inside the particle.

[0043] In this invention, the number of interparticle gaps N obtained by this method is specified to be 5 or less. The inventors have discovered that flake-like graphite particles with 5 or less interparticle gaps have the effect of suppressing the thermal degradation of composite materials after temperature cycling. Preferably, the number of interparticle gaps N is 5.0 or less, more preferably 3.5 or less, and even more preferably 2.3 or less.

[0044] The composite material of the present invention preferably has a thermal conductivity of 700 W / (m·K) or higher. Thermal conductivity is a value measured in a direction perpendicular to the stacking direction of the flake-like graphite particles. For use in high-output electronic components, a thermal conductivity of 750 W / (m·K) or higher is more preferred. Regarding thermal conductivity, a sample of a specific size (outer diameter 10 mm × thickness 2.5 mm) was cut from the center of the composite material, and the thermal conductivity was measured using the laser flash method (JIS H 7801:2005) and an LFA447 manufactured by NETZSCH Corporation. The average thermal conductivity of five samples cut from the composite material was used.

[0045] Furthermore, the composite material of the present invention preferably has a thermal degradation rate of 10% or less obtained by the following (2a) to (2c).

[0046] (2a) A plate is cut along the stacking direction of the flake graphite particles to prepare a sample.

[0047] The sample can be obtained by processing the above plate into, for example, an outer diameter of 10 mm and a thickness of 2.5 mm.

[0048] (2b) After determining the thermal diffusivity TD0 of the above sample, the temperature was repeatedly increased and decreased from -40℃ to 220℃, and the thermal diffusivity TD0 after 500 cycles was determined. 500 ;

[0049] Thermal diffusivity can be determined by laser flash method (JIS H 7801:2005) using LFA447 manufactured by NETZSCH.

[0050] (2c) via ((TD0-TD) 500 The thermal degradation rate is obtained by calculating () / TD0×100).

[0051] The thermal degradation rate is an indicator of the thermal diffusivity resistance of a composite material; the lower the value, the better the properties. If the thermal degradation rate reaches 10%, the material can be considered as having suppressed thermal degradation after temperature cycling. Ideally, the thermal degradation rate should be below 5%.

[0052] <Manufacturing Method>

[0053] The composite material of the present invention can be manufactured by the following method: performing specific pretreatment on graphite particles to obtain the desired flake-shaped graphite particles, mixing them with copper particles to form a molding raw material, shaping it, and sintering it under specific conditions. The steps are described below.

[0054] (Graphite pretreatment)

[0055] The pretreatment of graphite particles is performed by applying stress to the graphite particles. Due to the stress applied during the manufacturing process, graphite particles are inherently prone to having internal gaps. The inventors have discovered that the thermal degradation of composite materials containing graphite particles is related to the number of gaps within the graphite particles, and that by using flake-like graphite particles obtained through specific pretreatment, the thermal degradation of the composite material after temperature cycling can be suppressed.

[0056] As shown in Figure 3, two grinding stones 30a and 30b can be used in the pretreatment of graphite particles. Grinding stone 30b is a rotatable grinding stone. Grinding stones 30a and 30b each have metal plates 31a and 31b, respectively, and abrasive grains 33a and 33b, such as diamond, are provided on their opposing surfaces. The abrasive grains 33a and 33b are fixed by bonding metal components 32a and 32b, such as plating, and the graphite particles 23 to be processed are arranged between the abrasive grains 33a and 33b. The rotating grinding stone 30b is rotated at a speed of 12 Hz or less to apply stress to the graphite particles 23. If the rotational speed of the rotating grinding stone 30b is 12 Hz or less, the desired effect can be obtained.

[0057] Applying stress to graphite particles creates gaps, as if a single graphite particle were becoming multiple particles. It is hypothesized that by setting the rotational speed of the rotating grinding stone 30b to below 12 Hz, suitable stress can be applied to the graphite particles, resulting in flake-like graphite particles with fewer gaps. Pretreatment also causes the graphite particles to become thin films, hence the term flake-like graphite particles. Furthermore, the rotational speed of the rotating grinding stone 30b is preferably below 10 Hz, and more preferably below 6 Hz.

[0058] As a pretreatment condition for graphite particles, if the rotation speed of the rotating grinding stone 30b is specified to be below 12Hz, then there are no other special requirements. For example, the pressure can be set to about 0.2 to 0.8 MPa, and the time can be set to about 10 to 30 seconds.

[0059] (Preparation of copper particles)

[0060] There are no specific requirements for the copper particles; for example, copper particles with a median particle size of 1.5 μm or less based on volume can be used. The median particle size of the copper particles is preferably 1.0 μm or less. When using smaller copper particles with a median particle size of 1.5 μm or less, composite materials with stable thermal conductivity or processability can be obtained. Copper particles with a median particle size of 1.5 μm or less can be manufactured by any method. For example, the desired copper particles can be obtained by chemical reduction or physical methods.

[0061] (mix)

[0062] Pre-treated flake-like graphite particles are blended with copper particles in a specific ratio and wet-mixed using an organic solvent to obtain a molding raw material. The blending ratio is selected to achieve a graphite:copper volume ratio (graphite:copper) of 70:30 to 97:3 in the composite material. From the viewpoint of thermal conductivity and processability, a volume ratio (graphite:copper) of 84:16 to 95:5 is preferred. Suitable organic solvents include, specifically, toluene or xylene.

[0063] (sintering)

[0064] First, a small amount (less than 40g) of molding material is filled into a specific molding die, for example, by pressing the powder using a manual hydraulic press at a pressure of about 3 to 15 MPa. For example, a SUS die with a diameter of 30 mm can be used as the molding die. The filling and pressing of the molding material is repeated to produce a molded body of the desired size. The obtained molded body is sintered using a multi-axial electro-sintering method, thereby obtaining a sintered body that is the composite material of the present invention.

[0065] Here, referring to Figure 4, a general description of the multi-axis energized sintering apparatus is provided. The multi-axis energized sintering apparatus 40 shown in Figure 4 fixes a carbon mold 44 containing a shaped body within a vacuum container 42 via vertical pressure shafts 45a and 45b, and horizontal heating shafts (A) 47a and 47b and heating shafts (B) 49a and 49b. The heating shafts (A) 47a and 47b and heating shafts (B) 49a and 49b are configured to be alternately energized. Heating shaft (A) is energized in the directions of arrows x1 and x2, and heating shaft (B) is energized in the directions of arrows y1 and y2.

[0066] In the multi-axis sintering apparatus 40, the pressure shafts 45a and 45b are separated from the heating shafts 47a, 47b, 49a, and 49b. Specifically, the pressure shafts 45a and 45b are located in the z-axis direction, the heating shafts (A) 47a and 47b are located in the x-axis direction, and the heating shafts (B) 49a and 49b are located in the y-axis direction. This allows for independent control of pressure and heating, resulting in a uniform temperature distribution in the radial direction of the formed body.

[0067] During sintering, after fixing the carbon mold 44 containing the shaped body inside the vacuum container 42, the pressure inside the vacuum container 42 is reduced to below 100 Pa. To suppress the oxidation and deterioration of the parts inside the device, it is preferable to reduce the pressure to below 50 Pa. Then, the heating shafts (A) 47a and 47b are first energized and heated to about 650 to 750°C, preferably about 670 to 730°C.

[0068] Subsequently, the heating shafts (B) 49a and 49b are switched on, and the temperature is heated to approximately 930–980°C, preferably approximately 940–970°C. Then, pressure is applied via the vertical pressure shafts 45a and 45b along the directions of arrow z1 and arrow z2. The pressure at this point is preferably approximately 10–100 MPa, more preferably approximately 30–50 MPa.

[0069] Because sintering is performed under a uniform temperature distribution using a multiaxial electrosintering method, composite materials with stable quality can be manufactured. Furthermore, the raw material used with copper particles is flake-shaped graphite particles obtained through specific pretreatment; therefore, the number of interparticle gaps in the composite material of the present invention, determined by a specific method, is 5 or less. By reducing the number of interparticle gaps to 5 or less, the composite material of the present invention suppresses thermal degradation after temperature cycling and exhibits higher thermal conductivity.

[0070] The composite material of this invention is suitable for use as a heat sink (heat radiator component). The heat sink component can be used in a wide range of fields, including wireless communication, electronic control, and optical communication. Specific applications include: power semiconductor modules, optical communication modules, projectors, Peltier coolers, water-cooled coolers, and LED cooling fans.

[0071] Figure 5 shows an example of a cooling substrate using a heat sink. The cooling substrate 55 includes a heat sink 50 and a cooling layer 54. The heat sink 50 has an electrical insulating layer 52 and a wiring layer 51 sequentially deposited on a stress buffer layer 53. A heat-generating element, such as a semiconductor element, is mounted on the mounting surface 51a of the upper surface of the wiring layer 51. The composite material of the present invention can be used in at least one of the stress buffer layer 53 and the wiring layer 51.

[0072] The heat generated by the heating element mounted on the mounting surface 51a of the heat sink 50 is sequentially conducted to the wiring layer 51, the electrical insulation layer 52, the stress buffer layer 53, and the cooling layer 54, and dissipated from the cooling layer 54. Because the composite material of the present invention suppresses thermal degradation after temperature cycling, it can efficiently cool the heating element and lower its temperature; furthermore, it can maintain stable performance over a long period.

[0073] [Example]

[0074] The present invention will then be specifically described by way of examples, but the present invention is not limited to the following examples.

[0075] Example 1

[0076] Commercially available raw graphite was pretreated using the method illustrated in Figure 3. Diamond abrasive grains were used as the upper and lower grinding stones, and 5g of graphite particles were inserted between them along with 2mL of water. The grinding stones were rotated at 10Hz to pretreat the graphite particles for approximately 20 seconds. The pressure was set to 0.5MPa during this process.

[0077] The processed graphite particles are separated using a 500μm mesh sieve. The graphite particles remaining on the surface of the sieve are removed and dried, becoming flake-shaped graphite particles used as raw materials. On the other hand, copper particles with a median particle size of 1.5μm are prepared as copper particles.

[0078] To obtain a molding raw material, 11.0 g of pretreated and dried flake graphite particles and 19.0 g of copper particles were mixed in such a manner that the volume fraction of sintered copper was 30%. The powder was then contained in a 250 mL eggplant-shaped flask along with 50 mL of toluene as a solvent, and the mixture was desolvated and mixed using an evaporator.

[0079] 3g of molding material is placed into a 30mm diameter SUS mold and pressed into powder using a hydraulic press at a pressure of 5MPa. The molding process of adding molding material and pressing powder is repeated more than 10 times, and the molded body is removed from the SUS mold.

[0080] The removed molded body is housed in a cylindrical carbon mold and sintered using a multi-axis electric sintering method. The carbon mold 44 is placed inside the vacuum container 42 of the multi-axis electric sintering apparatus 40 shown in Figure 4 and is fixed by two diagonally opposite heating shafts (A) 47a and 47b and two pressure shafts (B) 45a and 45b.

[0081] The vacuum container 42 is depressurized to 5 Pa by a rotary pump, and the power output of the device is increased to raise its temperature. After heating to 700°C by heating shafts (A) 47a and 47b, the temperature is changed to heating shafts (B) 49a and 49b and heated to 950°C.

[0082] After reaching 950℃, pressure is applied to 50MPa via pressure shafts 45a and 45b. Once the displacement of the cylinder caused by the pressure application stops, it is held for 30 seconds to allow the power output to decrease and the device to cool. After cooling, the carbon mold 44 is removed from the device, and a cylindrical sintered body is obtained from the mold.

[0083] Five sintered bodies were produced by performing the same operation five times, thereby obtaining the composite material of Example 1.

[0084] Example 2

[0085] The forming material was changed so that the volume fraction of copper after sintering was 16%, and the composite material of Example 2 was otherwise manufactured in the same manner as in Example 1.

[0086] Example 3

[0087] The forming material was changed so that the volume fraction of copper after sintering was 5%, and the composite material of Example 3 was manufactured in the same manner as in Example 1.

[0088] Example 4

[0089] The rotation speed of the rotating grinding stone in the pretreatment of graphite particles was changed to 5 Hz, and the composite material of Example 4 was manufactured in the same manner as in Example 2.

[0090] Comparative Example 1

[0091] The rotation speed of the rotating grinding stone in the pretreatment of graphite particles was changed to 20 Hz, and the composite material of Comparative Example 1 was manufactured in the same manner as in Example 1.

[0092] Comparative Example 2

[0093] The rotation speed of the rotating grinding stone in the pretreatment of graphite particles was changed to 20 Hz, and the composite material of Comparative Example 2 was manufactured in the same manner as in Example 2.

[0094] Comparative Example 3

[0095] The rotation speed of the rotating grinding stone in the pretreatment of graphite particles was changed to 20 Hz, and the composite material of Comparative Example 3 was manufactured in the same manner as in Example 3.

[0096] Comparative Example 4

[0097] The composite material of Comparative Example 4 was prepared using untreated graphite particles, except that it was prepared in the same manner as in Example 2.

[0098] For the composite materials of the examples and comparative examples, the number of interparticle gaps was determined, and the thermal conductivity and thermal degradation rate were evaluated. For each item, five composite materials were measured, and the average value was calculated.

[0099] <Number of interstitial spaces within flaky graphite particles>

[0100] As described above, a laminated profile in the composite material is prepared, and the number of interstitial spaces N within the particles is determined according to (1a) to (1c).

[0101] Thermal conductivity

[0102] When preparing the specimen for thermal conductivity measurement, firstly, a plate is cut longitudinally from the center of the cylinder of the composite material in the examples and comparative examples. The longitudinal direction of the cylinder is the stacking direction of the flake graphite particles. The plate is processed to obtain a specimen for thermal conductivity measurement with an outer diameter of 10 mm and a thickness of 2.5 mm. The thickness direction of the specimen is perpendicular to the stacking direction of the flake graphite particles (the direction of pressure). In this thickness direction, the thermal conductivity of the specimen is measured according to the "Method for Determination of Thermal Diffusivity of Metals by Laser Flash Method (JISH 7801:2005)".

[0103] <Temperature Deterioration Rate>

[0104] The thermal degradation rate was determined based on the decrease in thermal diffusivity caused by temperature cycling tests. Thermal diffusivity was measured using the same sample shape and method as in the laser flash method. After determining the thermal diffusivity TD0 for each sample, a repeated temperature increase and decrease cycle from -40℃ to 220℃ was performed to determine the thermal diffusivity TD after 500 cycles. 500 Through ((TD0-TD) 500 ) / TD0×100), calculate the thermal degradation rate.

[0105] The results obtained, along with the volume fraction of copper and the rotational speed during the pretreatment of graphite particles, are summarized in Table 1 below.

[0106] Table 1

[0107]

[0108] As shown in Table 1 above, the composite materials manufactured using pretreated flake graphite particles at a rotation speed of 10 Hz all had 4.8 or fewer interparticle gaps (Examples 1-4). In contrast, the composite materials using pretreated flake graphite particles at a rotation speed of 20 Hz (Comparative Examples 1-3) and the composite materials using untreated graphite particles (Comparative Example 4) had 7.0 or more interparticle gaps.

[0109] The number of interparticle gaps in flake graphite particles obtained by pretreatment at a speed below 12 Hz was limited to less than 5. This result indicates that the rotational speed of the grinding stone during pretreatment affects the number of interparticle gaps in the treated flake graphite particles.

[0110] The thermal conductivity of the composite material depends on the ratio of graphite to copper. Therefore, as shown in Examples 1-3, if the volume fraction of copper decreases and the content of graphite, which contributes to thermal conductivity, increases, the thermal conductivity improves. However, a comparison between Examples 1-3 and Comparative Examples 1-3 shows that if the rotational speed of the grinding stone during pretreatment increases, the thermal conductivity decreases. It is speculated that graphite particles pretreated at speeds exceeding 12 Hz will pass between the grinding stones without being subjected to sufficient stress.

[0111] Shape observation using an optical microscope confirmed that the flake-like graphite particles in Comparative Examples 1-3 were untreated. The thermal conductivity of the composite material using untreated graphite particles (Comparative Example 4) was slightly lower than that of the composite material with the same copper volume fraction (Comparative Example 2).

[0112] As shown in Examples 1-4, the thermal degradation rate of the composite material using pretreated flake graphite particles at a rotation speed of 10 Hz was less than 4.8%. Figure 6 shows the progression of the thermal degradation rate during temperature cycling tests on the composite material of Example 1. Although the thermal degradation rate increased significantly after 100 temperature cycles, it remained relatively constant thereafter without significant increase even after repeated temperature cycling. The composite materials of Examples 2-4 also exhibited the same trend.

[0113] The thermal degradation rates of composite materials using pretreated flake graphite particles at a rotation speed of 20 Hz (Comparative Examples 1-3) and composite materials using untreated graphite particles (Comparative Example 4) were 18% or more, with a maximum of 25.5%.

[0114] These results indicate that the thermal degradation rate of the composite material is caused by the number of gaps within the flake-shaped graphite particles. It was confirmed that the number of gaps within the flake-shaped graphite particles can be controlled through appropriate pretreatment, and graphite-copper composite materials with suppressed thermal degradation after temperature cycling can be obtained using these flake-shaped graphite particles.

Claims

1. A graphite-copper composite material comprising a copper layer and flake-like graphite particles deposited between the copper layer and the copper volume fraction of 3-30%, characterized in that: In the lamination profile, the number N of interstitial spaces within the particles obtained by the following steps (1a) to (1c) is 5 or less: (1a) Five measurement fields of 930 μm × 1230 μm are defined in the above lamination profile; (1b) For each of the five measurement fields, the number of interstitial spaces with a width of 2 to 5 μm within the flake graphite particles is counted and set as N1 to N5; (1c) The number N of interstitial spaces within the particles is obtained by calculating the average value of the number of interstitial spaces ((N1+N2+N3+N4+N5) / 5).

2. The graphite-copper composite material according to claim 1, wherein the thermal conductivity in the direction perpendicular to the stacking direction of the above-mentioned flake graphite particles is 700 W / (m·K) or higher.

3. The graphite-copper composite material according to claim 2, wherein the thermal degradation rate obtained by the following (2a) to (2c) is less than 10%: (2a) a sample is prepared by cutting a plate along the lamination direction of the above-mentioned flake graphite particles; (2b) after determining the thermal diffusivity TD0 of the above-mentioned sample, the sample is repeatedly subjected to a temperature increase and decrease cycle from -40°C to 220°C, and the thermal diffusivity TD after 500 cycles is determined. 500 (2c) via ((TD0-TD) 500 The thermal degradation rate is obtained by calculating () / TD0×100).

4. A heat sink component using a graphite-copper composite material according to any one of claims 1 to 3.

5. A method for manufacturing the graphite-copper composite material of claim 1, characterized in that... The method comprises the following steps: inserting graphite particles between a pair of grinding stones arranged vertically, rotating the upper grinding stone at a frequency of 12 Hz or less, thereby pre-treating the graphite particles to obtain flake-shaped graphite particles; mixing the flake-shaped graphite particles with copper particles to obtain a molding material; and sintering the molded body obtained by shaping the molding material using a multi-axis electric sintering method.

Images