Method for manufacturing composite material

Abstract

A method for producing a composite material according to the present disclosure includes: a step for preparing a mixed powder of diamond particles and copper powder particles; and a step for producing, from the mixed powder, a composite material containing diamond and copper through a pulsed electric current sintering method, in which the mixed powder is maintained at a temperature of 500°C or higher to lower than 800°C, while being subjected to a pressure of 5 MPa to 100 MPa.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a composite material containing diamond particles and copper (Cu).

Background Art

[0002] As the light output of semiconductor light-emitting devices increases, heat dissipation of semiconductor devices has become an important issue. Heat dissipation of semiconductor devices is an important issue not only for semiconductor light-emitting devices but also for semiconductor integrated circuit devices that execute arithmetic processing at high speed and monolithic microwave integrated circuit devices that oscillate microwaves.

[0003] In order to dissipate heat from semiconductor devices that generate heat during operation in this way, the development of heat dissipation members such as heat dissipation substrates that dissipate the heat of semiconductor devices has been promoted. The heat dissipation member is required to have a high thermal conductivity. As a promising material for the heat dissipation substrate, the development of a composite material containing diamond and metal has been promoted. This composite material has a structure in which diamond particles having a higher thermal conductivity than metal are dispersed in a metal such as Cu.

[0004] Patent Document 1 discloses an example of producing a composite material containing diamond particles, chromium (Cr), and Cu by pulse electric current sintering at 800°C or higher. Patent Document 2 discloses an example of producing a composite material by coating diamond particles with Cu or aluminum (Al) in advance and then pulse electric current sintering at 900°C.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present disclosure provides a new manufacturing method of a composite material suitable for a heat dissipation member.

Means for Solving the Problems

[0007] In one aspect, the manufacturing method of the composite material of the present disclosure includes a step of preparing a mixed powder of diamond particles and copper powder particles, and a step of generating a composite material containing diamond and copper from the mixed powder by holding the mixed powder at a temperature of 500°C or higher and lower than 800°C while applying a pressure of 5 MPa or higher and 100 MPa or lower by a pulse electric current sintering method.

Advantages of the Invention

[0008] According to an embodiment of the present disclosure, a new manufacturing method of a composite material suitable for a heat dissipation member is provided.

Brief Description of the Drawings

[0009]

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MODE FOR CARRYING OUT THE INVENTION

[0010] Before explaining the embodiments of the present disclosure, the findings discovered by the present inventor and the technical background thereof will be explained.

[0011] FIG. 1 is a graph plotting the linear expansion coefficient and the thermal conductivity for materials such as diamond and Cu. The horizontal axis of the graph is the linear expansion coefficient, and the vertical axis is the thermal conductivity. The linear expansion coefficient is the coefficient of thermal expansion per unit length, and the unit is [10 -6 / K]. The unit of the thermal conductivity is [W / mK (watts per meter per kelvin)].

[0012] Single crystal diamond has the highest level of thermal conductivity among substances and ideally shows an extremely high value exceeding 2000 [W / mK]. The thermal conductivity of polycrystalline diamond particles is, for example, about 900 to 1800 [W / mK]. The thermal conductivity of diamond particles produced by the CVD method or the like is, for example, about 900 to 1800 [W / mK].

[0013] FIG. 2 is a perspective view schematically showing an example of diamond particles 10. The diamond particles 10 in the example of FIG. 2 have, for example, a polyhedral shape having hexagonal and square faces (facets) on the surface. In actual diamond particles, other polygonal faces may appear on the surface or a part may be missing, and they may have more complex and diverse shapes. The thermal conductivity of individual diamond particles may have different values depending on the presence of crystal defects or impurities present on the surface or inside.

[0014] On the other hand, the thermal conductivity of Cu, which is a metal, is about 400 [W / mK], and the thermal conductivity of silver (Ag) is about 420 [W / mK]. Therefore, the thermal conductivity of a composite material in which diamond particles are dispersed in a metal such as Cu shows an intermediate value between the thermal conductivity of the metal and the thermal conductivity of the diamond particles. The higher the volume ratio of the diamond particles contained in the composite material, the higher the theoretical value of the thermal conductivity of the composite material. However, in reality, the thermal conductivity of the composite material is not simply determined only by the volume ratio of diamond, and it is considered that the state of the interface between Cu and the diamond particles also has an influence. The interface between Cu and diamond can vary due to defects and damages that can occur in the diamond particles during the manufacturing process.

[0015] When a semiconductor element is bonded to a heat dissipation substrate and used, if the difference in the linear expansion coefficient existing between the member in contact with the heat dissipation substrate on the semiconductor element side and the heat dissipation substrate is large, problems such as peeling may occur. Therefore, it is desirable that the linear expansion coefficient of the composite material used for the heat dissipation substrate is close to the linear expansion coefficient of the member to be bonded.

[0016] A composite material containing diamond particles and Cu has an excellent property of having a higher thermal conductivity than Cu. Note that a composite material having a metal as a matrix may sometimes be called a metal matrix composite (MMC). Therefore, in this specification, a composite material in which diamond particles are dispersed in Cu may sometimes be referred to as "Cu-diamond MMC". Also, it may sometimes be simply referred to as "Cu diamond composite material" or "composite material".

[0017] As one of the methods for manufacturing Cu-diamond MMC, the "pulse electric current sintering method" is known. The details of the pulse electric current sintering method will be described later.

[0018] Generally, since the adhesion between Cu and diamond is poor, it is known that the thermal resistance or contact resistance increases at the interface between diamond particles and Cu in Cu-diamond MMC. Conventionally, in order to increase the thermal conductivity of Cu-diamond MMC, it has been considered necessary to reduce the thermal resistance at the interface between diamond particles and Cu. Therefore, in Patent Documents 1 and 2 described above, it is disclosed that a composite material is obtained by the pulse electric current sintering method performed at a high temperature of 800 °C or higher, or 900 °C or higher.

[0019] However, according to the experiments and studies by the present inventors, even when the sintering temperature when performing the pulse electric current sintering method is maintained below 800 °C, a finding not expected from the conventional technical common sense was obtained, that is, a Cu-diamond MMC having high thermal conductivity can be obtained.

[0020] The method for manufacturing a composite material of the present disclosure was completed based on the above new finding. Hereinafter, embodiments of the method for manufacturing a composite material in the present disclosure will be described.

[0021] <Embodiment 1> FIG. 3 is a flowchart showing the main steps in a method for manufacturing a Cu-diamond composite material according to an embodiment of the present disclosure. As shown in FIG. 3, the method for manufacturing the composite material in the present embodiment includes a step S10 of preparing a mixed powder of diamond particles and Cu powder particles, and a step S20 of generating a composite material containing diamond and Cu from the mixed powder by holding the mixed powder at a temperature of 500° C. or higher and lower than 800° C. while applying a pressure of 5 MPa or higher and 100 MPa or lower by pulse electric current sintering. This "temperature" is the "temperature" directly or indirectly measured by a temperature measuring device such as a radiation thermometer or a thermocouple. The "temperature" in the present disclosure is the measured value of the temperature of die 30 in an SPS apparatus as shown in FIG. 5 described later. Note that the sintering peak temperature Ts described later means the temperature of die 30 measured by a radiation thermometer or a thermocouple, which is held for a total of 1 minute or more at a predetermined pressure. For example, in the case of FIG. 6, in the sintering process, the temperature maintained at the highest temperature is called the sintering peak temperature Ts, which is distinguished from the temperature that transiently changes during the temperature rise and fall.

[0022] FIG. 4 is a photograph showing an example of diamond particles contained in the mixed powder of step S10. In one embodiment, the average particle size of the diamond particles is 40 μm or more and 500 μm or less. The particle size distribution of the diamond particles does not necessarily have to be a unimodal type with a single peak, and there may be a plurality of peaks. By setting the average particle size of the diamond particles to 40 μm or more, the thermal conductivity can be increased while manufacturing the Cu-diamond MMC at low cost. By setting the average particle size of the diamond particles to 500 μm or less, the manufacturing cost of the diamond particles themselves can be reduced. Further, the particle size distribution of the diamond particles is preferably 200 μm or more and 400 μm or less. Within this range, the thermal conductivity can be further improved. In one embodiment, the diamond particles in the mixed powder may include particles having an average particle size of 200 μm or more and 400 μm or less, and particles having an average particle size of 40 μm or more and 80 μm or less. In this specification, particles having an average particle size of 200 μm or more and 400 μm or less are referred to as "large particles", and particles having an average particle size of 40 μm or more and 80 μm or less are referred to as "small particles". Since particles having a relatively small average particle size can be arranged so as to fill the gaps formed by particles having a relatively large average particle size, the filling amount of diamond having a thermal conductivity higher than that of Cu can be increased. Thereby, the thermal conductivity of the Cu-diamond MMC can be further improved. Such a mixed powder having a bimodal particle size distribution is referred to as a "bimodal mixed powder" in this specification. In the bimodal mixed powder, the ratio of the particles having an average particle size of 200 μm or more and 400 μm or less to the total diamond particles is preferably 50% or more by mass ratio. This is because the larger the average particle size, the smaller the total surface area of the diamond particles, and the smaller the contribution of the thermal resistance at the interface between the diamond particles and Cu.

[0023] The average particle size of the Cu powder particles is, for example, 3 μm or more and 10 μm or less. The Cu powder may contain Cu fine powder with a particle size of 1 μm or less that can be generated by pulverization or the like. The Cu powder particles may contain inevitable impurities. However, since impurities such as oxygen and nitrogen cause a decrease in thermal conductivity, it is desirable to remove them as much as possible. For example, the content of impurities in the Cu powder particles is preferably 2% by mass or less. Such Cu powder particles may be those produced by known production methods. Also, commercially available Cu powder particles may be used.

[0024] Note that the "average particle size" in the present disclosure means the "median diameter" in the particle size distribution measured by a laser diffraction particle size distribution measuring device.

[0025] In Embodiment 1, no metal other than the Cu powder particles is intentionally added to enhance wettability. Conventionally, since the wettability between Cu and diamond is poor, it was considered necessary to improve the wettability with an additive metal. However, in Embodiment 1, such an additive metal is unnecessary. By not intentionally adding a metal other than the Cu powder particles, sintering inhibition can be reduced. In one embodiment, the amount of metal other than Cu in the mixed powder is 1% or less by mass ratio.

[0026] Also, for the purpose of enhancing the adhesion between the diamond particles and Cu, there is a possibility of coating each diamond particle with a metal layer such as copper as described above. However, in Embodiment 1, the diamond particles are not coated with a metal layer. This is because by not coating the diamond particles with a metal layer such as Cu in advance, the sintering activity can be enhanced compared to the case of coating the diamond particles with a metal layer such as Cu in advance. When the diamond particles are coated with a metal layer such as Cu in advance, the sintering activity decreases, and firing at a high temperature is required as in the case of adding a metal.

[0027] In this embodiment, the mass ratio of Cu powder particles in the mixed powder is preferably, for example, 60% or more and 85% or less, and the mass ratio of diamond particles in the mixed powder is preferably, for example, 15% or more and 40% or less. In other words, the mass ratio of Cu powder particles to diamond particles is selected within the range of 60:40 to 85:15, for example 80:20. The higher the mass ratio of diamond particles, the higher the thermal conductivity of the composite material. By setting the mass ratio of Cu powder particles to 60% or more and 85% or less, a sufficient amount of copper is arranged around the diamond, and gaps that inhibit heat conduction are less likely to occur in the Cu-diamond MMC. In other words, if the mass ratio of Cu powder particles is within the above range, Cu can have a volume sufficient to be arranged around the diamond, so that the gaps between diamond particles can be effectively filled. Also, if the amount of Cu is too large, since the thermal conductivity of Cu is lower than that of diamond, the thermal conductivity of the Cu-diamond MMC may decrease, but if it is within the above range, a Cu-diamond MMC having a high thermal conductivity can be manufactured. Also, as will be described later, according to the experiments of the present inventors, even when the mass ratio of diamond particles is the same, a bimodal mixed powder is more likely to achieve a high thermal conductivity.

[0028] The pulse electric current sintering method in step S20 can be carried out using a sintering apparatus 100 as shown in FIG. 5, for example. The pulse electric current sintering method is sometimes referred to as a discharge plasma sintering method (Spark·Plasma·Sintering: SPS) method. For this reason, the sintering apparatus 100 in FIG. 5 may be called an "SPS apparatus". The sintering apparatus 100 in FIG. 5 includes a die 30 having a through hole forming a cavity 20, and an upper punch 40 and a lower punch 50 that can move relatively up and down along the through hole of the die 30. The sintering apparatus 100 in this example can perform sintering using self-heating under uniaxial pressure in the vertical direction. The upper punch 40 is electrically connected to the first electrode 51, and the lower punch 50 is electrically connected to the second electrode 52. The first electrode 51 and the second electrode 52 are electrically connected to the power supply unit 60.

[0029] The die 30 can be formed from a material with excellent heat resistance, such as graphite. The upper punch 40 and the lower punch 50 can be formed from a material having conductivity and heat resistance, such as graphite. In heat conductivity measurement, the flatter the sample is, the higher the reliability of the measured thermal diffusivity can be. Therefore, when it is difficult to ensure the flatness of the sintered body to be manufactured, it is preferable to insert a hard material between the upper punch 40 and the sample and between the lower punch 50 and the sample to obtain a sintered body having a flat surface. The hard material is preferably a cemented carbide, for example, tungsten carbide (WC) or titanium carbide (TiC). Also, the materials of the upper punch 40 and the lower punch 50 may be changed to this material. The cavity 20 is a space defined by the inner wall surface of the through hole of the die 30, the lower end surface of the upper punch 40, and the upper end surface of the lower punch 50. The above-described mixed powder is loaded into the cavity 20. By moving at least one of the upper punch 40 and the lower punch 50 in the vertical direction, the distance between the upper punch 40 and the lower punch 50 is reduced, and pressure is applied to the mixed powder in the cavity 20. The upper punch 40 and the lower punch 50 are driven, for example, by a hydraulic device (not shown). The pressure applied to the mixed powder in the cavity 20 can be arbitrarily adjusted, for example, in the range of 5 MPa or more and 100 MPa or less.

[0030] In the pulse electric current sintering method, pulse electric current is passed between the upper punch 40 and the lower punch 50 while applying pressure to the mixed powder by the sintering apparatus 100. The pulse electric current is applied by repeatedly applying a DC pulse voltage from the power supply unit 60 between the first electrode 51 and the second electrode 52. In the mixed powder pressurized by the upper punch 40 and the lower punch 50, since the Cu powder particles are in contact with each other, several local current paths are formed in the mixed powder, and current flows. Due to such pulse electric current, Joule heat is generated, and the temperature of the mixed powder rises to a predetermined sintering temperature.

[0031] FIG. 6 schematically shows an example of how the temperature and pressure of the mixed powder change over time from the start to the end of the pulse current sintering process. The temperature is indicated by a dashed line, and the pressure is indicated by a solid line. The horizontal axis represents time, the left vertical axis represents temperature, and the right vertical axis represents pressure. By moving the upper punch 40 and / or the lower punch 50, the pressure reaches the sintering pressure Ps in, for example, several seconds, and the sintering pressure Ps is maintained for, for example, 60 to 1800 seconds. When the pulse current starts, the temperature of the mixed powder rises at a rate of, for example, 10 to 150 [°C / min] or more. After reaching a predetermined sintering peak temperature Ts, by adjusting the voltage application conditions of the pulse current, the sintering peak temperature Ts is maintained within ±5 °C of the target temperature. The control of the sintering temperature can be executed by the feedback of the measurement by the temperature measuring device attached to the die 30 in FIG. 5.

[0032] After a predetermined sintering time has elapsed and the composite material is produced from the mixed powder, the pulse current is stopped and the temperature reduction is started. Also, by moving the upper punch 40 and / or the lower punch 50, the application of pressure to the composite material is stopped. After the temperature of the composite material has sufficiently decreased, for example, to 50 °C or less, the composite material is taken out of the die 30.

[0033] In FIG. 6, the temperature and pressure are shown as rising and being maintained linearly over time for the sake of easy explanation. However, the actual transitions of temperature and pressure may include slight overshoots, curved changes, small vibrations, etc.

[0034] In this embodiment, the voltage for maintaining the sintering temperature is adjusted in the range of 1.0 V or more and 3.0 V or less, and the pulse current is adjusted in the range of 400 A or more and 800 A or less. The duty ratio of the pulse current is, for example, 10 to 80%, and the pulse width is, for example, 1 to 500 milliseconds. After holding at a predetermined sintering peak temperature Ts for a predetermined time, the pulse current is stopped. Note that these values vary depending on various conditions such as the weight of the mixed powder, the sintering temperature, and the material of the punch, and are not limited to the above ranges and can be changed as appropriate.

[0035] When the sintering temperature is set to 600°C, for example, the time from room temperature to reach the sintering temperature is about several minutes to 20 minutes, for example. The cavity 20 is located in a decompression chamber (not shown). The atmospheric pressure in the decompression chamber is, for example, 100 Pa or less. Thus, it is possible to prevent the powder particles from being oxidized or nitrided during the sintering process by pulse energization.

[0036] As described above, the sintering peak temperature Ts in the embodiment according to the present disclosure is 500°C or more and less than 800°C. Within this range, a Cu-diamond MMC having excellent thermal conductivity can be manufactured. Further, the preferable sintering peak temperature Ts is 500°C or more and 750°C or less. More preferably, it is 550°C or more and 700°C or less. Particularly preferably, it is 600°C or more and 700°C or less. Within the above range, a Cu-diamond MMC having further excellent thermal conductivity can be obtained. The range of the sintering time also depends on the sintering peak temperature Ts and is, for example, in the range of 1 minute or more and 30 minutes or less. When the sintering peak temperature Ts is, for example, 550°C or more and 650°C or less, the sintering time can be 5 minutes or more and 20 minutes or less, for example, about 10 minutes.

[0037] When the pressure applied to the mixed powder at the above sintering peak temperature Ts is maintained at a constant pressure, it is 5 MPa or more and 100 MPa or less. By setting the applied pressure to 5 MPa or more and 100 MPa or less, a Cu-diamond MMC having excellent thermal conductivity can be manufactured. The preferable pressure range is 10 MPa or more and 90 MPa. A more preferable pressure range is 20 MPa or more and 90 MPa or less. Further preferably, it is 25 MPa or more and 75 MPa or less. Particularly preferably, it is 25 MPa or more and 50 MPa or less. Within these pressure ranges, a Cu-diamond MMC having excellent thermal conductivity can be manufactured. As described above, applying a constant pressure at the sintering peak temperature Ts is referred to as "continuous pressurization" in this specification.

[0038] Note that although the case of continuous pressure application has been described so far, the above pressure does not necessarily have to be constant at all times. The applied pressure may be increased or decreased stepwise or continuously according to the progress of sintering.

[0039] FIG. 7 is a perspective view schematically showing an example of the outer shape of the composite material 80 manufactured according to the present embodiment. In this example, the composite material 80 has a disk shape with a thickness of T [mm] and a radius of R [mm]. The thickness T is, for example, 0.2 mm or more and 20.0 mm or less. Also, the radius R is, for example, 3 mm or more and 300 mm or less. The shape of the composite material 80 immediately after sintering is not limited to a disk shape, and it may have a rectangular parallelepiped shape or other polyhedron shape, or may have a shape with stripe grooves or a regular uneven pattern on the surface. The shape of the composite material 80 in a top view immediately after sintering is defined by the shape of a cross section perpendicular to the axial direction of the cavity 20 in FIG. 5. For example, when the die 30 in FIG. 5 has a through-hole in the shape of a prism and the lower end surface of the upper punch 40 and the upper end surface of the lower punch 50 are flat rectangular surfaces, the composite material 80 taken out from the sintering apparatus 100 may have a thin plate shape with a rectangular top view. After being taken out from the sintering apparatus 100, the composite material 80 may be subjected to machining such as cutting and polishing, or various treatments such as laser processing. It is also possible to separate a plurality of heat dissipation members from one composite material 80.

[0040] FIG. 8 is a schematic diagram showing a partially enlarged cross section of the composite material 80 thus manufactured. FIG. 8 is based on cross-sectional observation by an optical microscope or a scanning electron microscope (SEM). The composite material 80 shown in FIG. 8 contains Cu70, which is a metal matrix, and a large number of diamond particles 10 dispersed in Cu70. Cu70 is a metal body formed by sintering and integrating Cu powder particles contained in the mixed powder by pulse energization. Each diamond particle 10 contained in the composite material 80 is a diamond particle contained in the mixed powder. Although a part of the diamond particles 10 may be chipped during the pulse energization sintering process, the plurality of diamond particles do not combine and grow into a new single particle.

[0041] According to Embodiment 1, by fabricating a Cu-diamond composite material at a lower temperature compared to the prior art, the thermal conductivity of the composite material can be made, for example, a value of 460 [W / mK] or more. Further, a composite material having a thermal conductivity of 500 [W / mK] or more can also be obtained. Furthermore, it is possible to make the value 600 [W / mK], preferably 690 to 710 [W / mK] or more. This is considered to be because by making the sintering temperature lower than the value conventionally considered necessary, it was possible to suppress or avoid the deterioration of thermal conductivity at the diamond particles or the Cu / diamond interface that occurred during high-temperature sintering.

[0042] According to Embodiment 1, the temperature difference until the Cu-diamond MMC is cooled to room temperature after pulse electric current sintering is smaller than that of the conventional example. In Embodiment 1, the amount of expansion and contraction of copper and diamond respectively depending on the difference in the coefficient of linear expansion becomes smaller than that of the conventional example. That is, since copper and diamond are less likely to peel due to the difference in the coefficient of linear expansion, a decrease in thermal conductivity can be reduced.

[0043] <Embodiment 2> In Embodiment 2, the same effects as those of Embodiment 1 can be obtained. The manufacturing method of the composite material according to Embodiment 2 is substantially the same as the matters described in Embodiment 1 except as described below.

[0044] The manufacturing method of the composite material in Embodiment 2 is different from Embodiment 1 in terms of the method of applying pressure in the pulse electric current sintering method. In the present embodiment, the pressure applied to the mixed powder of diamond particles and Cu powder particles does not need to be constant. As shown in FIG. 9A, while repeatedly applying a first pressure and a second pressure higher than the first pressure to the mixed powder at the sintering temperature, pulse electric current is applied. Such a pressurization form will be referred to as "cycle pressurization" in this specification.

[0045] FIG. 9B is a diagram showing another example of "cycle pressing" during sintering. As shown in FIG. 9B, the first pressure and the second pressure higher than the first pressure may be repeatedly applied to the mixed powder from the temperature rising stage. Further, the first pressure and the second pressure can be repeatedly applied even during the holding time of the sintering peak temperature Ts.

[0046] As described above, in the cycle pressing, by repeatedly applying the first pressure and the second pressure higher than the first pressure, a Cu-diamond MMC having a high thermal conductivity can be manufactured. This is considered to be due to a mechanism as described below, for example.

[0047] There is a difference in the absolute value between the first pressure and the second pressure. When these pressures are repeatedly applied, there is a step of applying the first pressure after applying the second pressure. At this time, since the relatively low pressure is applied after the relatively high pressure, the degree of freedom of the diamond particles in the die increases compared to when the second pressure is applied, when the first pressure is applied. Thus, it is considered that the arrangement of the diamond particles or the state of the interface between Cu and the diamond particles can be more advantageous for heat conduction. There is also a possibility of removing oxygen present on the Cu surface and inhibiting heat conduction. As a result, it is considered that the Cu-diamond MMC manufactured by cycle pressing has an improved thermal diffusivity and a higher thermal conductivity compared to the case where only the first pressure is applied.

[0048] The pressures applied to the mixture of the diamond particles and the Cu powder particles can be set to the first pressure and the second pressure, respectively, in the range of 5 MPa or more and 100 MPa or less under the condition that the second pressure is greater than the first pressure. The first pressure may be 5 MPa or more and 60 MPa or less, and the second pressure may be 20 MPa or more and 100 MPa or less. Preferably, the first pressure is 5 MPa or more and less than 20 MPa, and the second pressure is 20 MPa or more and 40 MPa or less. By setting the first pressure and the second pressure in the above ranges, the thermal conductivity can be further improved.

[0049] <Example 1> Cu powder particles with an average particle size of 5 μm and diamond particles with an average particle size of 250 μm were mixed to obtain a mixed powder. The total weight of the mixed powder was 6.24 grams. With respect to the entire mixed powder, the Cu powder particles were 80 mass percent, and the diamond particles were 20 mass percent. Next, a Cu-diamond MMC with a thickness of 3 mm was fabricated using a sintering apparatus (model number SPS-515S) manufactured by SPS Syntex. The sintering peak temperature Ts was 500 °C, and the applied pressure was 36 MPa. The holding time of the sintering peak temperature Ts was 10 minutes. Also, the degree of vacuum at the start of sintering was 10 Pa. The magnitudes of the voltage and current during sintering vary depending on the weight and thickness of the sample, the target sintering peak temperature Ts, etc. In the examples and comparative examples, the current value while maintaining the sintering peak temperature Ts was in the range of 350 A or more and 700 A or less. The pulse width of the applied voltage was 3.3 milliseconds.

[0050] <Examples 2 to 12> In Examples 2 to 12, as shown in Table 1 below, only the sintering temperature, or both the sintering peak temperature Ts and the applied pressure, were changed with respect to Example 1 to obtain a Cu-diamond MMC. In Example 6, the average particle size of the diamond was further changed to 60 μm. Also, in Example 9, the diamond particles were made into a bimodal mixed powder. With respect to the entire Cu-diamond MMC, the diamond particles with an average particle size of 60 μm were 10 mass percent, and the diamond particles with an average particle size of 250 μm were 20 mass percent.

[0051] <Comparative Examples 1 to 4> Also in Comparative Examples 1 to 4, as shown in Table 1, only the sintering temperature, or both the sintering peak temperature Ts and the peak pressure, were changed with respect to Example 1 to obtain a Cu-diamond MMC.

[0052] <Thermal conductivity> The thermal conductivity was estimated for each of the examples and comparative examples. The thermal conductivity can be determined as the product of the specific heat, density, and thermal diffusivity. Specifically, the thermal conductivity is expressed by the following equation. Thermal conductivity [W / m·K] = Thermal diffusivity [m 2 / s] × Specific heat [J / K·kg] × Density [kg / m 3

[0053] The specific heat was obtained for each of the examples and comparative examples by weighting the literature values of the specific heat of diamond and Cu in the mixed mass ratio. The density was measured by the Archimedes method. The thermal diffusivity was obtained by the flash method using a xenon lamp with a measuring device (model number LFA-447) manufactured by Netch Japan. The measurement temperature was 25°C, and the thickness of the Cu-diamond MMC during measurement was 3 mm. The "thermal conductivity" in Table 1 is an estimated value from these literature values and measured values.

[0054]

Table 1

[0055] Composite materials in Examples 1 to 12 obtained by preparing a mixed powder of diamond particles and Cu powder particles and holding the mixed powder at a temperature of 500°C or higher and less than 800°C while applying a pressure of 5 MPa or higher and 100 MPa or lower by the pulse electric current sintering method had a higher thermal conductivity than any of the composite materials in Comparative Examples 1 to 4. For example, in Comparative Example 4, a higher pressure than any of the examples was applied, but instead, the thermal conductivity decreased. Generally, an increase in pressure is considered to densify the composite material, but from this experiment, it was found that when the pressure exceeds 100 MPa and becomes high, the thermal conductivity decreases.

[0056] Examples 5 and 6 differ in the average particle size of the diamond constituting the Cu-diamond MMC. Comparing Examples 5 and 6, the thermal conductivity of the Cu-diamond MMC in Example 5 was higher.

[0057] ​Comparing Example 9 and Example 10, the composite material in Example 9 had a higher thermal conductivity. Example 9 included diamond particles with an average particle size of 60 μm and diamond particles with an average particle size of 250 μm, and the proportion of diamond particles in the composite material was larger than that in Example 10 which included only diamond particles with an average particle size of 250 μm.

[0058] <Example 13> A composite material was obtained in the same manner as in Example 1 except for the following points. The sintering temperature was 600 °C, the first pressure was 10 MPa, and the second pressure was 36 MPa, and these were repeatedly applied. The holding time of the applied pressure was 15 seconds for the first pressure, 20 seconds for the second pressure, the total switching time of the pressure was 50 seconds, and the total time for one cycle was 85 seconds. The number of repeated cycles was 25. Also, the holding time of the sintering peak temperature Ts was 20 minutes.

[0059] <Examples 14 to 16> As shown in Table 2, by changing each condition, Cu-diamond MMCs were obtained respectively.

[0060] <Thermal conductivity> The thermal conductivities of the Cu-diamond MMCs according to Examples 13 to 16 were estimated in the same manner as in Example 1 described above. The results are shown in Table 2. In Table 2, Examples 3, 5, and 9 are all shown.

[0061]

Table 2

[0062] The thermal conductivities of the composite materials in Examples 13 to 16 obtained by preparing a mixed powder of diamond particles and Cu powder particles and holding the mixed powder at a temperature of 500 °C or higher and less than 800 °C while applying a pressure of 5 MPa or higher and 100 MPa or lower by the pulse electric current sintering method were higher than the thermal conductivities of any of the composite materials in Comparative Examples 1 to 4.

[0063] When comparing Example 13 with Example 3 and Example 13 with Example 5, in both cases, the thermal conductivity of the Cu-diamond MMC in Example 13 was higher. Also, from this result, it can be seen that the thermal conductivity of the Cu-diamond MMC obtained by cyclic pressing is higher compared to the case of continuous pressing.

[0064] When comparing Example 14 with Example 9, the thermal conductivity of the Cu-diamond MMC in Example 14 was higher. From this result, it can be seen that even when the diamond is in bimodal mixed powder, the thermal conductivity of the Cu-diamond MMC obtained is higher when the pressing method is cyclic pressing.

[0065] When comparing Example 14 with Example 16, the thermal conductivity of the Cu-diamond MMC in Example 14 was higher.

[0066] Figure 10 is a diagram showing an optical micrograph of a cross-section of a part of a composite material manufactured in the same manner as in Example 5 of Table 1. Figure 11 is a diagram showing an optical micrograph of a cross-section of a part of a composite material manufactured in the same manner as in Example 14 of Table 2. In each photograph, the region with relatively high brightness is the Cu part, and the region with relatively low brightness is the diamond particles. In the composite material of Figure 11, relatively small diamond particles with an average particle size of 60 μm are located in the gaps between relatively large diamond particles with an average particle size of 250 μm. Compared with the composite material of Figure 10, in the composite material of Figure 11, the number of diamond particles has increased, and the total surface area of the surface has also increased. This means that the area of the interface between Cu and diamond has increased. When this interface area increases, there is a possibility that voids and thermal resistance increase in parts with poor adhesion, resulting in a decrease in thermal conductivity, but in this example, such a phenomenon was not observed.

[0067] As can be seen from Figures 10 and 11, the composite materials in the examples are dense.

[0068] <Application Example> Embodiments of the method for manufacturing a composite material in the present disclosure provide a composite material that can be used as various heat dissipation members. Hereinafter, a configuration example of a light-emitting device including a heat dissipation substrate using the composite material manufactured in this embodiment will be described.

[0069] FIG. 12 is a perspective view schematically showing a configuration example of a light-emitting device 200 including a flip-chip type light-emitting element 22 and a heat dissipation substrate 24 that supports the light-emitting element 22. The heat dissipation substrate 24 is formed from a composite material manufactured by the manufacturing method in the above embodiment. On the upper surface of the heat dissipation substrate 24, an insulating layer 26 such as ceramic aluminum nitride (AlN) is formed. On the insulating layer 26, a p-side wiring 28p and an n-side wiring 28n are formed, and are electrically connected to the p-side electrode and the n-side electrode of the light-emitting element 22, respectively. The lower surface of the heat dissipation substrate 24 is in thermal contact with a heat sink or a cooling device (not shown). The heat generated in the light-emitting element 22 by operation spreads through the insulating layer 26 and then dissipates to the outside through the heat dissipation substrate 24.

[0070] Note that the above configuration example of the light-emitting device 200 is an example of a semiconductor device that uses the composite material according to the embodiment of the present disclosure as a heat dissipation member. In addition to this, this composite material can be used for various applications.

Industrial Applicability

[0071] The method for manufacturing a composite material according to the present disclosure provides a composite material that can be used as various heat dissipation members. Examples of the heat dissipation members include heat dissipation substrates, submounts, heat spreaders, packages, and heat sinks that are in thermal contact with elements such as semiconductor light-emitting elements, semiconductor integrated circuit elements, and monolithic microwave integrated circuit elements.

Explanation of Reference Numerals

[0072] 10... diamond particles, 20... cavity, 30... die, 40... upper punch, 50... lower punch, 60... power unit (Power), 100... sintering device

Claims

1. A step of preparing a mixed powder of diamond particles and copper powder particles; A step of generating a composite material containing diamond and copper from the mixed powder by holding the temperature at 500°C or higher and less than 800°C while applying a pressure of 5 MPa or higher and 100 MPa or lower to the mixed powder by a pulse electric current sintering method; including, The step of generating the composite material includes a step of repeatedly applying a first pressure and a second pressure higher than the first pressure to the mixed powder at the temperature, a method for manufacturing a composite material.

2. The method for manufacturing a composite material according to claim 1, wherein the addition amount of metals other than copper in the mixed powder is 1% or less by mass ratio.

3. The method for manufacturing a composite material according to claim 1 or 2, wherein in the step of preparing the mixed powder, the diamond particles are not coated with a metal layer.

4. The mass ratio of the copper powder particles in the mixed powder is 60% or more and 85% or less, The mass ratio of the diamond particles in the mixed powder is 15% or more and 40% or less, the method for manufacturing a composite material according to any one of claims 1 to 3.

5. The average particle size of the diamond particles in the mixed powder is 200 μm or more and 400 μm or less, the method for manufacturing a composite material according to any one of claims 1 to 4.

6. The diamond particles in the mixed powder include particles having an average particle size of 200 μm or more and 400 μm or less and particles having an average particle size of 40 μm or more and 80 μm or less, the method for manufacturing a composite material according to any one of claims 1 to 4.

7. The temperature is 500°C or higher and 750°C or lower, the method for manufacturing a composite material according to any one of claims 1 to 6.

8. The method for manufacturing a composite material according to any one of claims 1 to 7, wherein the pressure is 10 MPa or more and 90 MPa or less.

9. The method for manufacturing a composite material according to any one of claims 1 to 7, wherein the first pressure is 5 MPa or more and less than 20 MPa, and the second pressure is 20 MPa or more and 40 MPa or less.

10. The method for manufacturing a composite material according to any one of claims 1 to 9, wherein the average particle diameter of the copper powder particles is 3 μm or more and 10 μm or less.

11. A step of preparing a mixed powder of diamond particles and copper powder particles, A step of producing a composite material containing diamond and copper from the mixed powder by holding the mixed powder at a temperature of 500°C or more and less than 800°C while applying a pressure of 5 MPa or more and 100 MPa or less by pulse electric current sintering method, comprising In the step of preparing the mixed powder, the diamond particles are not coated with a metal layer. A method for manufacturing a heat radiating member.

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