JP2024078299A - Heat radiation member and heat radiation member production method - Google Patents

Abstract

To provide a heat radiation member in which adhesion between a base material made of a composite material and a metal layer provided on the surface of the base material is high, and heat conductivity is high as well.SOLUTION: Provided is a heat radiation member which comprises: a base material composed of a composite material; and a metal layer provided at the surface of the base material. The base material comprises: plural covered diamond particles; and a binder phase for binding the plural covered diamond particles. The covered diamond particles each has: a core made of diamond; and a carbide layer for covering the surface of the core. The binder phase is composed of metals. In a cross section vertical to the surface of the metal layer, among the plural covered diamond particles, a coverage rate of the carbide layer in a first boundary between the first particles having a particle diameter of 80 μm or more and the metal layer is 80% or more. The content of silver to the total content of silver and copper in a boundary region between the base material and the metal layer is 98 atomic% or more. The heat conductivity is 780 W/m K or more.SELECTED DRAWING: Figure 2

Description

This disclosure relates to a heat dissipation member and a method for manufacturing a heat dissipation member.

Patent Documents 1 to 3 disclose a heat dissipation member including a substrate made of a composite material and a metal layer provided on the surface of the substrate. The composite material includes a plurality of diamond particles and a metal phase that bonds the plurality of diamond particles. Patent Document 1 discloses a composite material including coated diamond particles. The coated diamond particles include a carbide layer that covers the surface of the diamond particles. The constituent material of the metal phase is, for example, silver or a silver alloy. The metal layer is formed, for example, by bonding a metal material to the surface of the substrate. The metal material is, for example, a metal powder or a metal foil. Patent Document 1 and Patent Document 2 disclose a method of forming a metal layer using a metal powder. Patent Document 3 discloses a method of forming a metal layer using a metal foil.

International Publication No. 2016/035795 International Publication No. 2016/035796 International Publication No. 2020/084903

The coated diamond particles have a high wettability with metals due to the carbide layer. Therefore, the coated diamond particles have better adhesion with metals than diamond particles. In the manufacturing process of a composite material, foreign matter may adhere to the surface of the composite material. For example, this foreign matter is a release agent applied to the inner surface of a mold for molding the composite material. If foreign matter adheres to the surface of a substrate made of a composite material, the adhesion between the substrate and the metal layer decreases. This decrease in adhesion leads to peeling of the metal layer or bulging of the metal layer when an electronic component is brazed to the surface of the metal layer. When the surface of the composite material is polished or etched to remove foreign matter attached to the surface of the substrate, the carbide layer of the coated diamond particles exposed from the surface of the substrate is also removed together with the foreign matter. When a metal layer is formed on the surface of the substrate, the carbide layer of the coated diamond particles located on the surface of the substrate is lost, so the wettability between the coated diamond particles and the metal layer is poor. As a result, the adhesion between the substrate and the metal layer decreases.

When a metal layer is formed by the method described in Patent Document 3, the thermal conductivity may decrease in the boundary region between the substrate and the metal layer. The method of forming a metal layer described in Patent Document 3 forms a metal layer by joining a metal foil to the surface of the substrate with a brazing material. The metal foil is, for example, a silver foil. The brazing material is, for example, a eutectic alloy of silver and copper. When the substrate and silver foil are joined with the brazing material, copper contained in the brazing material may remain in the boundary region between the substrate and the metal layer. This reduces the silver content in the boundary region. As a result, there is a risk of a decrease in thermal conductivity in the boundary region.

One of the objectives of the present disclosure is to provide a heat dissipation member that has high adhesion between a substrate made of a composite material and a metal layer provided on the surface of the substrate, and that also has high thermal conductivity.

The heat dissipation member of the present disclosure includes:
A substrate made of a composite material;
A metal layer provided on a surface of the base material,
The substrate is
A plurality of coated diamond particles;
a binder phase bonding the plurality of coated diamond particles together;
The coated diamond particles are
A core made of diamond;
a carbide layer covering a surface of the core;
The binder phase is composed of a metal,
In a cross section perpendicular to the surface of the metal layer, a coverage rate of the carbide layer at a first interface between the metal layer and a first particle having a particle size of 80 μm or more among the plurality of coated diamond particles is 80% or more;
a ratio of silver to a total content of silver and copper in a boundary region between the substrate and the metal layer is 98 atomic % or more;
The thermal conductivity is 780 W/m·K or higher.

The heat dissipation member disclosed herein has high adhesion between the substrate and the metal layer and high thermal conductivity.

FIG. 1 is a schematic cross-sectional view of a heat dissipation member according to an embodiment. FIG. 2 is a schematic cross-sectional view showing an enlarged view of the vicinity of the interface between the base material and the metal layer in the heat dissipation member according to the embodiment. FIG. 3 is a schematic cross-sectional view showing an enlarged view of the vicinity of the interface between the substrate and the metal layer in the heat dissipation member according to the embodiment, illustrating the first interface between the first particle and the metal layer. FIG. 4 is a schematic cross-sectional view showing an enlarged view of the vicinity of the interface between the base material and the metal layer in the heat dissipation member according to the embodiment, and is a diagram illustrating a reference line. FIG. 5 is a schematic cross-sectional view showing an enlarged view of the vicinity of the interface between the substrate and the metal layer in the heat dissipation member according to the embodiment, illustrating the second interface between the coated diamond particles and the metal layer. 6 is a diagram showing an enlarged SEM image of the vicinity of the interface between the coated diamond particles and the metal layer in the cross section of the heat dissipation member of Sample No. 1-7. FIG. 7 is a diagram showing the results of EDX mapping analysis of titanium in the SEM image shown in FIG. FIG. 8 is a diagram showing the results of carbon mapping analysis by EDX in the SEM image shown in FIG. FIG. 9 is a diagram showing the results of EDX mapping analysis of silver in the SEM image shown in FIG. 10 is a diagram showing an enlarged SEM image of a part of the first interface between the first particle and the metal layer in a cross section of the heat dissipation member of Sample No. 1-7.

[Description of the embodiments of the present disclosure]
First, the embodiments of the present disclosure will be listed and described.

(1) A heat dissipation member according to an embodiment of the present disclosure includes:
A substrate made of a composite material;
A metal layer provided on a surface of the base material,
The substrate is
A plurality of coated diamond particles;
a binder phase bonding the plurality of coated diamond particles together;
The coated diamond particles are
A core made of diamond;
a carbide layer covering a surface of the core;
The binder phase is composed of a metal,
In a cross section perpendicular to the surface of the metal layer, a coverage rate of the carbide layer at a first interface between the metal layer and a first particle having a particle size of 80 μm or more among the plurality of coated diamond particles is 80% or more;
a ratio of silver to a total content of silver and copper in a boundary region between the substrate and the metal layer is 98 atomic % or more;
The thermal conductivity is 780 W/m·K or higher.

According to the heat dissipation member of the present disclosure, the coverage of the carbide layer at the first interface between the first particle and the metal layer is 80% or more, so the proportion of the core exposed at the first interface is small. With a coverage of the carbide layer of 80% or more, the wettability between the first particle and the metal layer is high. Therefore, the heat dissipation member of the present disclosure has high adhesion between the substrate and the metal layer. With high adhesion between the substrate and the metal layer, the heat conductivity of the entire heat dissipation member is high.

The silver content in the boundary region between the substrate and the metal layer is 98 atomic % or more, so the silver content in the boundary region is high. Silver has high thermal conductivity. By having a silver content of 98 atomic % or more, it is possible to suppress a decrease in thermal conductivity in the boundary region. Therefore, the heat dissipation member of the present disclosure has high thermal conductivity. The thermal conductivity of the heat dissipation member of the present disclosure is 780 W/m·K or more. Details of the "boundary region between the substrate and the metal layer" will be described later.

(2) In the heat dissipation member according to (1),
The carbide layer may be comprised of a carbide containing at least one first element selected from the group consisting of zirconium, chromium, titanium, silicon, tantalum and niobium.

The carbide layer made of the carbide of the first element has high adhesion to metals. According to the above configuration (2), the adhesion between the coated diamond particles and the metal is improved, resulting in high adhesion between the substrate and the metal layer.

(3) In the heat dissipation member according to (2),
In the cross section, the first element may be present between a reference line and a surface of the metal layer.
The reference line is a line segment that passes through the most protruding position of the first particle and is parallel to the surface of the metal layer.

According to the above configuration (3), a carbide layer is easily formed at the first interface between the first particles and the metal layer during the manufacturing process of the heat dissipation member.

(4) In the heat dissipation member according to (2) or (3),
The first element may be titanium.
The metal layer may be made of silver.
The binder phase may be made of silver.

When the first element is titanium, the carbide layer is composed of titanium carbide. A carbide layer composed of titanium carbide is easily formed on the surface of diamond particles during the manufacturing process of a composite material. When the first element is titanium, it is easy to manufacture a composite material containing coated diamond particles. In addition, when the constituent material of the binder phase is silver, the thermal conductivity of the substrate is high. When the constituent material of the metal layer is silver, the thermal conductivity of the metal layer is high. As a result, the thermal conductivity of the entire heat dissipation member is high.

(5) In any one of the heat dissipation members according to (1) to (4),
The content of the first element in the boundary region may be less than 1.2 atomic % relative to 100 atomic % of the composition of the boundary region.

The lower the content of the first element in the boundary region, the more the decrease in thermal conductivity in the boundary region can be suppressed. According to the above configuration (5), the thermal conductivity of the entire heat dissipation member is increased.

(6) In any one of the heat dissipation members according to (1) to (5),
The metal layer may have a surface having an arithmetic mean roughness Ra of 2.0 μm or less.

The above configuration (6) makes it easy to bond electronic components to the surface of the metal layer.

(7) In any one of the heat dissipation members according to (1) to (6),
The metal layer may have a thickness of 3 μm or more and 200 μm or less.

When the thickness of the metal layer is 3 μm or more, it is easy to bond electronic components to the surface of the metal layer. When the thickness of the metal layer is 200 μm or less, the decrease in the thermal conductivity of the entire heat dissipation component can be suppressed.

(8) In any one of the heat dissipation members according to (1) to (7),
the plurality of coated diamond particles includes second particles having a particle size of less than 80 μm;
In the cross section, the amount of protrusion of the first particles sandwiched between the second particles may be 10 μm or less.

The above configuration (8) makes it easier to reduce the thickness of the metal layer.

(9) A method for manufacturing a heat dissipation member according to an embodiment of the present disclosure includes:
Providing a substrate made of a composite material;
Supplying a mixed powder of a first powder made of a metal and a second powder containing a first element onto a surface of the base material;
and sintering the base material and the mixed powder,
The composite material in the step of preparing the substrate includes:
a plurality of coated diamond particles and a bonding phase bonding the plurality of coated diamond particles;
The plurality of coated diamond particles each have a diamond core and a carbide layer covering the core,
The binder phase is composed of a metal,
the plurality of coated diamond particles located on a surface of the composite material include particles having their cores exposed from the carbide layer;
The first element is at least one element selected from the group consisting of zirconium, chromium, titanium, silicon, tantalum and niobium.

According to the manufacturing method of the heat dissipation member disclosed herein, a carbide layer can be formed on the surface of the coated diamond particles whose cores are exposed from the carbide layer at the same time as the metal layer is formed. Therefore, the manufacturing method of the heat dissipation member disclosed herein can manufacture a heat dissipation member with high adhesion between the substrate and the metal layer.

[Details of the embodiment of the present disclosure]
Hereinafter, specific examples of heat dissipation members according to embodiments of the present disclosure will be described with reference to the drawings. The same reference numerals in the drawings denote the same or corresponding parts.
However, the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

<Heat dissipation material>
A heat dissipation member 1 according to an embodiment will be described with reference to Fig. 1. The heat dissipation member 1 includes a substrate 2 made of a composite material 10 and a metal layer 4 provided on the surface of the substrate 2. The shape and size of the heat dissipation member 1 can be appropriately selected depending on the application of the heat dissipation member 1. In this example, the shape of the heat dissipation member 1 is a flat plate. Fig. 1 shows a cross section of the heat dissipation member 1 cut in the thickness direction. The thickness direction here is the direction perpendicular to the surface of the heat dissipation member 1, i.e., the surface of the metal layer 4, and is the direction from the metal layer 4 toward the substrate 2.

(Base material)
The substrate 2 includes a plurality of coated diamond particles 20 and a binder phase 30 that bonds the plurality of coated diamond particles 20. The thickness of the substrate 2 is, for example, not less than 0.5 mm and not more than 5 mm.

(Coated diamond particles)
The coated diamond particle 20 has a core 21 made of diamond and a carbide layer 22 covering the surface of the core 21. In Fig. 1, the coated diamond particle 20 is shown in an exaggerated schematic view.

The shape of the coated diamond particle 20 can be various. In FIG. 1, the cross-sectional shape of the coated diamond particle 20 is circular, but the cross-sectional shape of the coated diamond particle 20 may be polygonal.

The content of the coated diamond particles 20 in the substrate 2 is, for example, 50 volume % or more and 90 volume % or less. The higher the content of the coated diamond particles 20, the higher the volume ratio of diamond contained in the substrate 2. Therefore, the thermal conductivity of the substrate 2 is higher. The higher the thermal conductivity of the substrate 2, the higher the thermal conductivity of the entire heat dissipation member 1. A substrate 2 containing 50 volume % or more of the coated diamond particles 20 has high thermal conductivity. On the other hand, the higher the content of the coated diamond particles 20, the less the bonding phase 30 contained in the substrate 2. When the content of the coated diamond particles 20 is 90 volume % or less, the bonding phase 30 easily bonds the coated diamond particles 20 together.

The particle size of the coated diamond particles 20 is, for example, 1 μm or more and 300 μm or less. If the content of the coated diamond particles 20 is the same, the larger the particle size of the coated diamond particles 20, the fewer the number of coated diamond particles 20 contained in the substrate 2. Since the grain boundaries of the coated diamond particles 20 are reduced, the grain boundary thermal resistance is reduced and the thermal conductivity of the substrate 2 is increased. By making the particle size of the coated diamond particles 20 1 μm or more and 300 μm or less, it is easy to increase the thermal conductivity of the substrate 2. The multiple coated diamond particles 20 may include coarse particles with a large particle size and fine particles with a small particle size. The multiple coated diamond particles 20 may be composed only of coarse particles with a particle size of 80 μm or more and 300 μm or less. The multiple coated diamond particles 20 may include fine particles with a particle size of 1 μm or more and less than 80 μm in addition to the coarse particles. In this case, the fine particles enter between the coarse particles, thereby increasing the density of the coated diamond particles 20 contained in the substrate 2.

The particle size of the coated diamond particles 20 is measured as follows. A cross section of the substrate 2 cut in the thickness direction is observed with a SEM (Scanning Electron Microscope). The coated diamond particles 20 present within the observation field are extracted. The diameter of a circle having an area equal to the cross-sectional area of the coated diamond particle 20 is regarded as the particle size of the coated diamond particle 20. The size of the observation field is set appropriately according to the size of the coated diamond particle 20. For example, the magnification is set so that 10 or more coated diamond particles 20 can fit in one observation field. This magnification may also be set so that 20 or more coated diamond particles 20 can fit in the observation field.

(Carbide layer)
The carbide layer 22 is made of carbide. The carbide layer 22 is made of, for example, a carbide of a first element. The first element is at least one element selected from the group consisting of zirconium (Zr), chromium (Cr), titanium (Ti), silicon (Si), tantalum (Ta) and niobium (Nb). The carbide constituting the carbide layer 22 is, for example, a carbide containing at least one element selected from the group consisting of Zr, Cr, Ti, Si, Ta and Nb. When the first element is Zr, the carbide layer 22 is made of a carbide of Zr (ZrC). When the first element is Cr, the carbide layer 22 is made of a carbide of Cr (Cr ₃ C ₂ ). When the first element is Ti, the carbide layer 22 is made of a carbide of Ti (TiC). When the first element is Si, the carbide layer 22 is made of a carbide of Si (SiC). When the first element is Ta, the carbide layer 22 is made of Ta carbide (TaC). When the first element is Nb, the carbide layer 22 is made of Nb carbide (NbC). The carbide layer 22 has high wettability with the binder phase 30. The coated diamond particles 20 having the carbide layer 22 have high adhesion with the binder phase 30. Since voids are unlikely to occur at the interface between the coated diamond particles 20 and the binder phase 30, the thermal conductivity of the substrate 2 is high. In this example, the carbide layer 22 is made of Ti carbide (TiC).

The thickness of the carbide layer 22 may be thin as long as it is effective in increasing the wettability between the coated diamond particles 20 and the binder phase 30. The carbide layer 22 has a lower thermal conductivity than the core 21 made of diamond. The thinner the carbide layer 22 is, the more the decrease in the thermal conductivity of the substrate 2 can be suppressed. The thickness of the carbide layer 22 may be, for example, 5 μm or less, 3 μm or less, or 1 μm or less. The thickness of the carbide layer 22 may be on the order of nanometers. How to determine the thickness of the carbide layer 22 will be described later.

(bonded phase)
The binder phase 30 is made of a metal having high thermal conductivity. The binder phase 30 is made of, for example, silver (Ag). Ag has high thermal conductivity. When the binder phase 30 is made of Ag, the thermal conductivity of the base material 2 is high. In this example, the binder phase 30 is made of Ag.

The bonding phase 30 may contain impurities other than Ag. The impurities include, for example, the first element, copper (Cu), and unavoidable impurities. The Ag content in the bonding phase 30 is, for example, 98 atomic % or more. The content of impurities other than Ag contained in the bonding phase 30 is less than 2 atomic %. The higher the Ag content, i.e., the lower the impurity content, the higher the thermal conductivity of the bonding phase 30. As a result, the thermal conductivity of the substrate 2 is high. The Ag content may further be 99 atomic % or more, 99.5 atomic % or more. The upper limit of the Ag content is, for example, 99.995 atomic %. The Ag content may be 98 atomic % or more and 99.995 atomic % or less, 99 atomic % or more and 99.995 atomic % or less, or 99.5 atomic % or more and 99.995 atomic % or less.

(Metal Layer)
The metal layer 4 only needs to cover at least a part of the surface of the base material 2. The surface of the base material 2 here means at least one of the two surfaces facing each other in the thickness direction of the base material 2, and does not include the side surfaces. In this example, the metal layer 4 is provided so as to cover the entire surface of the base material 2. The metal layer 4 is provided to bond an electronic component (not shown) to the heat dissipation member 1. The electronic component is, for example, a semiconductor element. The electronic component is bonded, for example, by soldering or brazing. Since the metal layer 4 is made of metal, it has high wettability with solder or brazing material. The heat dissipation member 1 can firmly bond the electronic component to the surface of the metal layer 4 by solder or brazing material.

The material constituting the metal layer 4 is, for example, Ag. Ag has a high thermal conductivity and a melting point higher than that of the solder or brazing material used to join electronic components. When the metal layer 4 is made of Ag, the thermal conductivity of the metal layer 4 is high. The higher the thermal conductivity of the metal layer 4, the higher the thermal conductivity of the entire heat dissipation member 1. If the material constituting the metal layer 4 is the same as the material constituting the bonding phase 30, the bonding strength between the metal layer 4 and the bonding phase 30 and the heat resistance can be increased. In this example, the metal layer 4 is made of Ag.

The metal layer 4 may contain impurities other than Ag. The impurities include, for example, the first element, copper (Cu), and unavoidable impurities. The Ag content in the metal layer 4 is, for example, 98 atomic % or more. The content of impurities other than Ag contained in the metal layer 4 is less than 2 atomic %. The higher the Ag content, i.e., the lower the impurity content, the higher the thermal conductivity of the metal layer 4. As a result, the thermal conductivity of the entire heat dissipation member 1 is high. The Ag content may further be 99 atomic % or more, 99.5 atomic % or more. The upper limit of the Ag content is, for example, 99.995 atomic %. The Ag content may be 98 atomic % or more and 99.995 atomic % or less, 99 atomic % or more and 99.995 atomic % or less, or 99.5 atomic % or more and 99.995 atomic % or less.

The arithmetic mean roughness Ra of the surface of the metal layer 4 is, for example, 2.0 μm or less. The smaller the surface roughness of the metal layer 4, the smoother the surface. A smooth surface of the metal layer 4 makes it easier to bond electronic components to the surface of the metal layer 4 with solder or brazing material. Furthermore, a smooth surface of the metal layer 4 makes it easier to adhere electronic components to the metal layer 4. As a result, heat from the electronic components is easily transferred to the heat dissipation member 1. The arithmetic mean roughness Ra of the surface of the metal layer 4 may further be 1.5 μm or less, or 1.0 μm or less. The lower limit of the arithmetic mean roughness Ra of the surface of the metal layer 4 is 0.005 μm. The arithmetic mean roughness Ra of the surface of the metal layer 4 may be 0.005 μm or more and 2.0 μm or less, 0.005 μm or more and 1.5 μm or less, or 0.005 μm or more and 1.0 μm or less. The arithmetic mean roughness Ra is the arithmetic mean roughness Ra defined in JIS B 0601:2001.

The thickness of the metal layer 4 is, for example, 3 μm or more and 200 μm or less. When the thickness of the metal layer 4 is 3 μm or more, the wettability with the solder or brazing material can be increased. Electronic components can be easily bonded to the surface of the metal layer 4. The thinner the metal layer 4, the easier it is to transfer heat from the electronic components to the substrate 2. When the thickness of the metal layer 4 is 200 μm or less, the decrease in the thermal conductivity of the entire heat dissipation member 1 can be suppressed. The thickness of the metal layer 4 may further be 5 μm or more and 150 μm or less, or 10 μm or more and 100 μm or less.

The thickness of the metal layer 4 is measured as follows. A cross section of the metal layer 4 cut in the thickness direction is observed with an SEM. Within one observation field, the coated diamond particle 20 closest to the surface of the metal layer 4 is identified. The shortest distance from the point on the contour of the coated diamond particle 20 closest to the surface of the metal layer 4 to the surface of the metal layer 4 is measured. The shortest distance is measured in the same manner for five or more different observation fields. The average of the measured shortest distances is regarded as the thickness of the metal layer 4. The size of the observation field is, for example, 400 μm or more in the vertical direction and 600 μm or more in the horizontal direction. The vertical direction here refers to the thickness direction. The horizontal direction refers to the direction perpendicular to the thickness direction, i.e., the direction along the surface of the metal layer 4. The observation magnification is, for example, 100 times.

One of the features of the heat dissipation member 1 of the embodiment is that a carbide layer 22 is present at at least a portion of the interface between the coated diamond particles 20 and the metal layer 4. Before going into a detailed description of the heat dissipation member 1 having this feature, a method for manufacturing the heat dissipation member 1 will be described.

<Method of Manufacturing Heat Dissipation Member>
The heat dissipation member 1 of the embodiment can be manufactured, for example, by the following manufacturing method. The manufacturing method of the heat dissipation member includes a first step of preparing a base material, and a second step of forming a metal layer on the surface of the base material.
Each step will be described in detail below.

(First process)
The first step is to prepare a substrate made of a composite material. The composite material includes a plurality of coated diamond particles and a binder phase that bonds the plurality of coated diamond particles. The plurality of coated diamond particles have a core made of diamond and a carbide layer covering the core. The binder phase is made of a metal. The plurality of coated diamond particles located on the surface of the composite material include particles whose cores are exposed from the carbide layer.

As described below, before forming the metal layer, the composite material to be prepared is subjected to a surface treatment such as polishing or etching on the surface of the substrate to remove foreign matter that has adhered to the surface of the composite material during the manufacturing process. This surface treatment removes the carbide layer of the coated diamond particles located on the surface of the substrate. In other words, the core of the coated diamond particles located on the surface of the substrate is exposed from the carbide layer. Since the carbide layer has been removed, no carbide layer is present at the interface between the coated diamond particles and the metal layer. In the manufacturing method of the embodiment, a carbide layer is formed on the surface of the core exposed from the carbide layer, as described below.

A known composite material can be used for the prepared composite material. The composite material can be manufactured by a known manufacturing method such as that described in Patent Document 1. An example of a manufacturing method for a composite material will be described. The manufacturing method for a composite material includes the following steps A, B, C, and D.

(Step A)
Step A is a step of preparing raw materials for the composite material. The raw materials are diamond powder, a powder containing a first element, and a metal powder. The diamond powder is composed of a plurality of diamond particles. The diamond particles constitute the core of the coated diamond particle. The powder containing the first element is a raw material that constitutes the carbide layer of the coated diamond particle. The metal powder is a raw material that constitutes the binder phase.

(Diamond powder)
The diamond particles contained in the diamond powder have a particle size of, for example, 1 μm or more and 300 μm or less. The content of diamond powder in the raw material of the composite material is, for example, 50 volume % or more and 90 volume % or less. The particle size of the coated diamond particles contained in the composite material finally manufactured is substantially equal to the particle size of the diamond particles contained in the diamond powder. The content of the coated diamond particles in the composite material is substantially equal to the content of diamond powder in the raw material of the composite material. The diamond powder may be a mixture of coarse diamond particles and fine diamond particles. The diamond powder may be composed only of coarse particles having a particle size of 80 μm or more and 300 μm or less. The diamond powder may contain fine particles having a particle size of 1 μm or more and less than 80 μm in addition to the coarse particles.

(Powder containing the first element)
The powder containing the first element may be a powder of the first element, or may be a powder of a compound containing the first element. The first element is an element that forms a carbide layer on the surface of the diamond particles contained in the diamond powder. The first element is at least one selected from the group consisting of Zr, Cr, Ti, Si, Ta and Nb. The compound containing the first element is, for example, at least one selected from the group consisting of sulfides, nitrides, hydrides and borides. When the first element is Zr, a carbide layer made of _ZrC is formed. When the first element is Cr, a carbide layer made of _Cr3C2 is formed. When the first element is Ti, a carbide layer made of TiC is formed. When the first element is Si, a carbide layer made of SiC is formed. When the first element is Ta, a carbide layer made of TaC is formed. When the first element is Nb, a carbide layer made of NbC is formed.

The content of the powder containing the first element may be appropriately selected so that a carbide layer is formed on the surface of the diamond particles. If the content of the powder containing the first element is too low, the carbide layer may not be formed sufficiently. If the content of the powder containing the first element is too high, the carbide layer may become too thick. The content of the powder containing the first element is, for example, 0.1 parts by mass or more and 5 parts by mass or less per 100 parts by mass of diamond powder.

(Metal powder)
The metal powder is, for example, Ag. The content of the binder phase in the final composite material is substantially equal to the content of the metal powder in the raw material of the composite material.

(Process B)
Step B is a step of filling the raw material of the composite material into the mold. In this step, for example, a mixed powder of diamond powder, a powder containing a first element, and a powder of a metal is filled into the mold. Alternatively, after filling the mixed powder of diamond powder and a powder containing a first element into the mold, a powder of a metal may be placed on the mixed powder. Alternatively, after filling the diamond powder into the mold, a mixed powder of a metal powder and a powder containing a first element may be placed on the diamond powder.

(Step C)
Step C is a step of heating the raw material of the composite material filled in the mold. This step combines diamond and metal. The heating temperature is equal to or higher than the melting point of the metal powder. For example, when the metal powder is made of Ag, the heating temperature is, for example, 980°C or higher and 1200°C or lower. The powder containing the first element dissolves in the molten metal, for example Ag.

The diamond powder and the powder containing the first element react by heating, and this reaction forms a carbide layer on the surface of the diamond particle. For example, when the first element is Ti, Ti bonds with the carbon (C) constituting the diamond particle when it comes into contact with the diamond particle to form TiC. When the first element is Zr, ZrC is formed. When the first element is Cr, _Cr3C2 is formed. When the first element is Si, _SiC is formed. When the first element is Ta, TaC is formed. When the first element is Nb, NbC is formed. The formation of the carbide of the first element forms a carbide layer on the surface of the diamond particle. As a result, a coated diamond particle having a carbide layer on the surface of the core made of diamond is formed. The carbide layer increases the wettability of the diamond particle and the metal, and the molten metal is infiltrated between the diamond particles.

The raw materials for the composite material are heated and then cooled. The molten metal solidifies to form a binder phase. As a result, a composite material is produced in which multiple coated diamond particles are bonded together by the binder phase. Some of the first element may not react with the diamond particles and remain in the binder phase.

(Step D)
Step D is a step of performing a surface treatment to remove foreign matter adhering to the surface of the composite material. For example, the surface of the composite material is polished or etched to remove the foreign matter adhering to the surface of the composite material. Foreign matter may adhere to the surface of the composite material during the manufacturing process. This foreign matter is, for example, a release agent applied to the inner surface of the mold. If foreign matter adheres to the surface of the substrate made of the composite material, the adhesion between the substrate and the metal layer will decrease when a metal layer is formed on the surface of the substrate in a later process. By removing the foreign matter adhering to the surface of the composite material, the decrease in adhesion between the substrate and the metal layer can be suppressed. By polishing or etching the surface of the substrate, the metal layer on the surface of the substrate is removed at the same time as removing the foreign matter, or the carbide layer of the coated diamond particles exposed from the surface of the substrate is removed. Therefore, the carbide layer of the coated diamond particles located on the surface of the substrate is removed by the above-mentioned surface treatment. In other words, in the composite material after the surface treatment, the cores of the multiple coated diamond particles located on the surface of the composite material are exposed from the carbide layer.

Abrasives such as grindstones or abrasive paper can be used to polish the surface of the composite material. When the surface of the composite material is polished with an abrasive containing diamond abrasive grains, not only the carbide layer but also the diamond core is polished. Therefore, the surface of the coated diamond particles exposed on the surface of the substrate becomes flat. When polishing the surface of the composite material, the bonding phase and the coated diamond particles may be polished until they are flush with each other, or they may not be polished until they are flush with each other. In the latter case, the time required for polishing can be shortened. An acid or alkali etching solution can be used to etch the surface of the composite material. A specific example of the etching solution is a cyanide (CN)-based etching solution. When etching the surface of the composite material, it is not necessary to roughen the surface until the coated diamond particles protrude significantly from the bonding phase to form irregularities that have an anchor effect with the metal layer. In this case, the time required for etching can be shortened.

(Second step)
The second step is a step of forming a metal layer on the surface of the substrate. In the manufacturing method of the embodiment, the metal layer is formed from metal powder. The hot pressing method described in Patent Document 1 or Patent Document 2 can be used as the method of forming the metal layer. The second step can be roughly divided into two steps, Step E and Step F, as shown below.

(E process)
Step E is a step of supplying the raw material of the metal layer to the surface of the substrate. In the manufacturing method of this embodiment, one of the features is that the powder containing the first element is mixed with the powder of the metal, which is the raw material of the metal layer. Specifically, in step E, a mixed powder of the first powder and the second powder is supplied to the surface of the substrate. The first powder is a powder made of metal. The second powder is a powder containing the first element. The first powder is the raw material of the metal layer. Here, the reason why the second powder is mixed with the raw material of the metal layer is to form a carbide layer on the surface of the particles whose cores are exposed from the carbide layer among the multiple coated diamond particles located on the surface of the substrate. In other words, the second powder is the raw material of the carbide layer.

The first powder is made of, for example, Ag. The average particle size of the metal particles constituting the first powder is, for example, 1 μm or more and 300 μm or less. The average particle size is the particle size (D50) at which the cumulative volume in the volumetric particle size distribution measured by a laser diffraction particle size distribution measuring device is 50%.

The second powder can be the same as the powder containing the first element used as the raw material of the composite material. The second powder can be a powder of the first element, or a powder of a compound containing the first element.

The content of the second powder in the raw material of the metal layer may be appropriately selected so that a carbide layer is formed on the surface of the coated diamond particle where the core is exposed from the carbide layer. If the content of the second powder is too low, the carbide layer may not be sufficiently formed on the surface of the particle where the core is exposed. If the content of the second powder is too high, the carbide layer may become too thick. The content of the second powder is, for example, 0.05 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the first powder.

When the raw material for the metal layer is supplied to the surface of the substrate, only the mixed powder may be supplied, or the raw material for the metal layer may be supplied in multiple batches. In the former case, only one layer of the mixed powder is placed on the surface of the substrate. In the latter case, after the mixed powder is supplied to the surface of the substrate, a first powder is supplied on the mixed powder. In other words, after a first layer made of the mixed powder is placed on the surface of the substrate, a second layer made of the first powder may be placed on the surface of the first layer. If the first layer placed on the surface of the substrate is composed of the mixed powder containing the second powder, a carbide layer can be formed on the surface of the particle whose core is exposed from the carbide layer by the first element contained in the second powder.

The F step is a step of sintering the raw materials of the substrate and the metal layer. Specifically, in the F step, the substrate and the mixed powder are sintered in a state where the mixed powder is arranged on the surface of the substrate, thereby forming a metal layer on the surface of the substrate. The sintering temperature is, for example, 600°C or more and 900°C or less. The holding time is, for example, 20 minutes or more and 180 minutes or less. For example, a hot pressing method can be used as the sintering method. By hot pressing the mixed powder on the surface of the substrate, the first powder contained in the mixed powder flows and enters the unevenness of the surface of the substrate. This makes it easy for the metal layer to adhere to the surface of the substrate. In addition, the first element contained in the second powder comes into contact with the coated diamond particles located on the surface of the substrate. The carbon on the core surface exposed from the carbide layer and the first element bond to form a carbide layer on the surface of the core. Therefore, a carbide layer can be formed on the surface of the coated diamond particle whose core is exposed from the carbide layer at the same time as the formation of the metal layer. A part of the first element does not react with the coated diamond particle and may remain in the metal layer.

The heat dissipation member 1 of the embodiment can be manufactured by the above-mentioned manufacturing method. The heat dissipation member 1 has a high coverage of the carbide layer 22 of the coated diamond particles 20 at the interface between the substrate 2 and the metal layer 4. Below, the characteristics of the heat dissipation member 1 of the embodiment will be described with reference to Figures 2 to 4.

2 to 4 are cross-sectional views perpendicular to the surface of the metal layer 4, and show the vicinity of the interface between the substrate 2 and the metal layer 4 in an enlarged manner. The substrate 2 shown in FIGS. 2 to 4 is made of a composite material 10. In this example, the substrate 2 includes a plurality of coated diamond particles 20 having different particle sizes. The plurality of coated diamond particles 20 include a first particle 20a having a particle size of 80 μm or more and a second particle 20b having a particle size of less than 80 μm. The plurality of coated diamond particles 20 may be composed of only the first particle 20a, or may include the first particle 20a and the second particle 20b as in this example. In FIGS. 2 to 4, the core 21 and the carbide layer 22 are illustrated only for the first particle 20a. The core 21 and the carbide layer 22 are omitted for the second particle 20b. Although not illustrated, the second particle 20b has a core 21 and a carbide layer 22, similar to the first particle 20a.

(Coverage of the carbide layer at the first interface) In the heat dissipation member 1, the coverage of the carbide layer 22 at the first interface between the first particle 20a and the metal layer 4 among the multiple coated diamond particles 20 is 80% or more. The first interface is a region of the contour of the first particle 20a where no other coated diamond particles 20 are present at a position closer to the surface of the metal layer 4 than the first particle 20a, as shown by the thick solid line in FIG. 3. Specifically, the coated diamond particles 20 close to the surface of the metal layer 4 are extracted, and the first particle 20a is identified from among the coated diamond particles 20. When the cross section of the heat dissipation member 1 is viewed in the thickness direction, the region of the contour of the first particle 20a that faces the metal layer 4 and does not overlap with the other coated diamond particles 20 is the first interface. For example, in a cross section perpendicular to the surface of the metal layer 4, there are second particles 20b on both sides of one first particle 20a, and when viewed from the metal layer 4, the second particles 20b partially overlap the first particle 20a in the thickness direction of the heat dissipation member 1. Two line segments perpendicular to the surface of the metal layer 4 and passing through the closest point in the horizontal direction on the contour of each second particle 20b are drawn. The horizontal direction is a direction perpendicular to the thickness direction of the heat dissipation member 1, i.e., a direction parallel to the surface of the metal layer 4. The intersection points of each of these two line segments and the contour of the first particle 20a are obtained. The line segment connecting the two intersection points along the surface of the first particle 20a is the first interface. On the other hand, when the second particles 20b are arranged in contact with each of the left and right sides of the first particle 20a, but each second particle 20b does not overlap with the first particle 20a in the thickness direction of the heat dissipation member 1, the line segment connecting the contact point between the first particle 20a and the left second particle 20b and the contact point between the first particle 20a and the right second particle 20b along the surface of the first particle 20a is the first interface. The coverage is the ratio of the length of the first interface covered with the carbide layer 22 to the length of the first interface.

The coverage is measured as follows. In a cross section perpendicular to the surface of the metal layer 4 in the heat dissipation member 1, the vicinity of the interface between the substrate 2 and the metal layer 4 is observed by SEM. The magnification is set so that three or more first particles 20a having a first interface are included in one observation field. The length of the first interface is measured for each of the three or more first particles 20a, and the total length Lt of the lengths is calculated. The length of the first interface is the length measured along the contour of the first particle 20a in the region that does not overlap with the other coated diamond particles 20 described above. The length of the first interface covered with the carbide layer 22 is measured for each of the three or more first particles 20a, and the total length Lc of the lengths is calculated. The coverage is calculated by (Lc/Lt) x 100.

The presence or absence of the carbide layer 22 can be checked using mapping analysis using EDX (Energy Dispersive X-ray Spectroscopy) or EPMA (Electron Probe Micro Analyzer). Because the carbide layer 22 is very thin, the mapping analysis is performed at a magnification of, for example, 700 times or more. The distribution of the first element at the first interface is confirmed by the mapping analysis. As a result of the mapping analysis, the area on the diamond surface where the first element is densely distributed is regarded as the carbide layer 22. The thickness of the carbide layer 22 is the average value of the thicknesses of five or more areas where the first element is densely distributed in a secondary electron image of an SEM taken at a magnification of, for example, 10,000 times or more.

When the coverage of the carbide layer 22 at the first interface is 80% or more, the wettability between the first particles 20a and the metal layer 4 is increased. Therefore, the adhesion between the first particles 20a and the metal layer 4 is improved. Since voids are unlikely to occur at the interface between the first particles 20a and the metal layer 4, the thermal conductivity of the entire heat dissipation member 1 is increased. In addition, peeling of the metal layer 4 from the substrate 2 can be suppressed. The higher the coverage, the better the adhesion between the first particles 20a and the metal layer 4. The coverage may be 85% or more, or 90% or more. The upper limit of the coverage is 100%. The coverage may be 80% or more and 100% or less, 85% or more and 100% or less, or 90% or more and 100% or less.

(Thermal conductivity of heat dissipation member)
The thermal conductivity of the heat dissipation member 1 is 780 W/m·K or more. The higher the thermal conductivity, the better the heat dissipation. The thermal conductivity of the heat dissipation member 1 may be 800 W/m·K or more, or 810 W/m·K or more. The upper limit of the thermal conductivity is, for example, 1000 W/m·K. The thermal conductivity may be 780 W/m·K or more and 1000 W/m·K or less, 800 W/m·K or more and 1000 W/m·K or less, or 810 W/m·K or more and 1000 W/m·K or less. The thermal conductivity was measured according to the measurement of thermal conductivity described in Test Example 1 below.

(Ag content in boundary region)
In the heat dissipation member 1, the Ag content in the boundary region between the base material 2 and the metal layer 4 is 98 atomic % or more. The Ag content in the boundary region is the atomic ratio to the total content of Ag and copper (Cu) in the boundary region. In other words, the Ag content is a value expressed in atomic percentage of the Ag content to the total content of Ag and Cu when the total content of Ag and Cu is 100 atomic %. The Cu content in the boundary region is less than 2 atomic %. The higher the Ag content in the boundary region, that is, the lower the Cu content, the more the thermal conductivity in the boundary region can be suppressed. As a result, the thermal conductivity of the entire heat dissipation member 1 is increased. The Ag content in the boundary region may be 99 atomic % or more. The boundary region may not contain Cu. In other words, the Cu content in the boundary region may be 0 atomic %. The upper limit of the Ag content in the boundary region is 100 atomic %. The Ag content in the boundary region may be 98 atomic % or more and 100 atomic % or less, or 99 atomic % or more and 99.999 atomic % or less.

(Content of first element in boundary region)
The content of the first element in the boundary region may be less than 1.2 atomic %, with the composition of the boundary region being 100 atomic %. The less the first element in the boundary region, the greater the Ag content, so that the decrease in thermal conductivity in the boundary region can be suppressed. As a result, the thermal conductivity of the entire heat dissipation member 1 is increased. The content of the first element in the boundary region may further be 1.1 atomic % or less, 0.9 atomic % or less, or 0.7 atomic % or less. The lower limit of the content of the first element in the boundary region is, for example, 0.02 atomic %. The content of the first element in the boundary region may be 0.02 atomic % or more and less than 1.2 atomic %, or 0.03 atomic % or more and 1.1 atomic % or less.

《Boundary Region》 The boundary region between the substrate 2 and the metal layer 4 is obtained as follows. In a cross section perpendicular to the surface of the metal layer 4 in the heat dissipation member 1, the vicinity of the interface between the substrate 2 and the metal layer 4 is observed with an SEM. The observation magnification is, for example, 100 times or more. In the observation field, the coated diamond particle 20 closest to the surface of the metal layer 4 is identified. Among the contours of the coated diamond particle 20, the point closest to the surface of the metal layer 4 is obtained. The line segment parallel to the surface of the metal layer 4 passing through this point is regarded as the boundary between the substrate 2 and the metal layer 4. The region closer to the surface of the metal layer 4 than this boundary and ranging from this boundary to 15 μm is defined as the first region. The region farther from the surface of the metal layer 4 than this boundary and ranging from this boundary to 15 μm is defined as the second region. The boundary region between the substrate 2 and the metal layer 4 is the region that combines the first region and the second region. In other words, the thickness of the boundary region is 30 μm. The coated diamond particle 20 may be included in the boundary region. In addition, when the thickness of the metal layer 4 is less than 15 μm, the first region is the range from the boundary to the surface of the metal layer 4. In other words, the first region includes the entire metal layer 4.

The composition of the boundary region can be determined by compositional analysis using EDX or EPMA. Compositional analysis of the boundary region measures the content of elements in the boundary region.

(Presence of the first element in the metal layer)
In the heat dissipation member 1 of the embodiment, the first element may be present between the reference line S shown in FIG. 4 and the surface of the metal layer 4 in a cross section perpendicular to the surface of the metal layer 4. As shown in FIG. 4, the reference line S is a line segment that passes through the most protruding position of the first particle 20a and is parallel to the surface of the metal layer 4. The reference line S is obtained as follows. In the cross section perpendicular to the surface of the metal layer 4 in the heat dissipation member 1, the vicinity of the interface between the base material 2 and the metal layer 4 is observed by SEM. The magnification is set so that three or more first particles 20a having a first interface are included in one observation field. Of the first particles 20a present in the observation field, the first particle 20a closest to the surface of the metal layer 4 is identified. Of the contours of the first particles 20a, the point closest to the surface of the metal layer 4 is found. The line segment that passes through this point and is parallel to the surface of the metal layer 4 is set as the reference line S. The presence or absence of the first element is examined using mapping analysis by EDX or EPMA. The distribution of the first element between the reference line S and the surface of the metal layer 4 is confirmed by mapping analysis.

The presence of the first element between the reference line S and the surface of the metal layer 4 indicates that, as explained in the manufacturing method described above, a mixed powder of a first powder made of metal and a second powder containing the first element was used as the raw material for the metal layer 4. Since the raw material for the metal layer 4 contained the first element, the coverage of the carbide layer 22 at the first interface between the first particle 20a and the metal layer 4 becomes high.

(Amount of protrusion of the first particle) In the embodiment of the heat dissipation member 1, the amount of protrusion of the first particle 20a sandwiched between the second particles 20b in a cross section perpendicular to the surface of the metal layer 4 may be 10 μm or less. The amount of protrusion of the first particle 20a is the difference between the most protruding position of the first particle 20a close to the surface of the metal layer 4 and the most protruding position of the second particle 20b adjacent to the first particle 20a in the horizontal direction. The horizontal direction is a direction parallel to the surface of the metal layer 4. The amount of protrusion is obtained as follows. In the cross section perpendicular to the surface of the metal layer 4 in the heat dissipation member 1, the vicinity of the interface between the substrate 2 and the metal layer 4 is observed with an SEM. The magnification is set so that three or more first particles 20a having the first interface are included in one observation field. The coated diamond particles 20 close to the surface of the metal layer 4 are extracted, and the second interface is obtained. The second interface is the interface between the coated diamond particles 20 and the metal layer 4, as shown by the dotted line in FIG. 5. The second interface is obtained as follows. The point closest to the surface of the metal layer 4 is obtained from the contour of each second particle 20b. Hereinafter, this point is referred to as the highest point. The highest points of adjacent second particles 20b are connected. When the second particle 20b is adjacent to the first particle 20a, the shortest distance between the highest point of the second particle 20b and the first interface of the first particle 20a is connected. The second interface includes the first interface. The first particle 20a sandwiched between the second particles 20b is identified. The highest point closest to the surface of the metal layer 4 is obtained from the contour of the first particle 20a. Also, the highest point of the second particle 20b adjacent to the first particle 20a is obtained. When the cross section of the heat dissipation member 1 is viewed in the thickness direction, the difference from the highest point of the second particle 20b to the highest point of the first particle 20a is the protrusion amount of the first particle 20a. For example, when there are second particles 20b on both the left and right sides of one first particle 20a, the difference from the highest point of each second particle 20b to the highest point of the first particle 20a is obtained. Of the two differences, the larger difference is taken as the protrusion amount of the first particles 20a. Here, the protrusion amount of the first particles 20a being 10 μm or less means that the protrusion amount of all the first particles 20a within the observation field of view is 10 μm or less.

The second interface is considered to roughly represent the surface of the substrate 2 before the metal layer 4 is formed. The smaller the amount of protrusion of the first particles 20a, the smaller the surface roughness of the substrate 2, i.e., the flatter the surface of the substrate 2. By making the amount of protrusion of the first particles 20a 10 μm or less, the thickness of the metal layer 4 can be made thinner. The amount of protrusion of the first particles 20a may further be 5 μm or less.

[Test Example 1]
A sample of a heat dissipation member having a metal layer on the surface of a substrate made of a composite material was prepared. The prepared sample of the heat dissipation member was evaluated.

A substrate made of a composite material was prepared. The substrate was produced by the composite material manufacturing method described in Patent Document 1. The diamond powder used as the raw material for the composite material was a fine-coarse mixed powder in which fine powder with a small average particle size was mixed with coarse powder with a large average particle size, as in Test Example 2 described in Patent Document 1.

The composite material produced is a composite material in which multiple coated diamond particles are bonded together by a binder phase. This composite material contains multiple coated diamond particles with different particle sizes. The multiple coated diamond particles are made of first particles with a particle size of 80 μm or more and second particles with a particle size of less than 80 μm. The coated diamond particles have a carbide layer on the surface of a core made of diamond. The carbide layer is made of TiC. The binder phase is made of Ag. The composite material has a flat plate shape.

The surface of the substrate made of the composite material was subjected to surface treatment to remove foreign matter adhering to the surface of the composite material. The surface treatment method was polishing or etching. The substrate surfaces of Samples No. 1-1 to 1-12 and Sample No. 1-21 shown in Tables 1 and 2 were polished. The substrate surfaces of Samples No. 1-13 and 1-22 were etched. Sample No. 1-20 was not surface treated. As shown in Table 1, Samples No. 1-1 to 1-8, Sample No. 1-10, Sample No. 1-12, and Sample No. 1-21 were polished using abrasive paper. The material of the abrasive grains in the abrasive paper was silicon carbide (SiC). Samples No. 1-9 and Sample No. 1-11 were polished using a grindstone. The grindstone was a diamond grindstone containing diamond abrasive grains. Sample No. Samples No. 1-13 and 1-22 were etched using a CN-based etching solution.

Next, a metal layer was formed on the surface of the substrate to produce a heat dissipation member. In Samples No. 1-1 to No. 1-13 and Samples No. 1-20 to No. 1-22, Ag powder was used as the raw material for the metal layer. The metal layer was formed as follows. Ag powder and powder of the first element were prepared. In Samples No. 1-1 to 1-13, a mixed powder of Ag powder and powder of the first element was used as the raw material for the metal layer. The type of the first element differed depending on the sample. In Samples No. 1-1 to 1-3 and Samples No. 1-9 to 1-13, the first element was Ti. In Sample No. 1-4, the first element was Zr. In Sample No. 1-5, the first element was Cr. In Sample No. 1-6, the first element was Si. In Sample No. In sample No. 1-7, the first element is Ta. In sample No. 1-8, the powder of the first element is Nb. The content of the powder of the first element in the mixed powder varies depending on the sample. The type of first element in each sample and the content of the powder of the first element are shown in Table 1. The content of the powder of the first element is expressed in parts by mass relative to 100 parts by mass of Ag powder. In sample No. 1-1 to sample No. 1-13, a first layer made of the mixed powder was placed on the surface of the substrate, and then a second layer made of Ag powder was placed on the surface of the first layer. In this state, the substrate was sintered at 800°C for 180 minutes to form a metal layer on the surface of the substrate. The average thickness of the metal layer was 50 μm to 100 μm.

In Sample No. 1-20 to Sample No. 1-22, only Ag powder was used as the raw material for the metal layer. In Sample No. 1-20 to Sample No. 1-22, Ag powder was placed on the surface of the substrate before sintering. In other words, Sample No. 1-1 to Sample No. 1-13 have two layers, a first layer made of mixed powder and a second layer made of Ag powder, while Sample No. 1-20 to Sample No. 1-22 have one layer made of only Ag powder.

Furthermore, a heat dissipation member was produced in which a metal layer was formed by the method described in Patent Document 3. In Sample No. 1-31 to Sample No. 1-33, Ag foil was used as the raw material for the metal layer, as in Test Example 1 described in Patent Document 3. In Sample No. 1-31 to Sample No. 1-33, Ag foil was joined to the surface of the substrate with a brazing material to form a metal layer. The average thickness of the metal layer was about 50 μm. Specifically, the brazing material was placed on the surface of the substrate, and the substrate was heated to the melting point of the brazing material or higher with Ag foil placed on the brazing material. The Ag foil was made of pure silver. The thickness of the Ag foil was 50 μm. The brazing material was a sheet material based on a eutectic alloy of Ag and Cu. The brazing material was an Ag alloy containing 30 mass% Cu and 1.5 mass% Ti. In Sample No. 1-31 to Sample No. In Sample No. 1-33, the conditions for joining using the brazing material were different for each sample, with at least one of the heating temperature and heating time. In Sample No. 1-31 to Sample No. 1-33, the surface of the substrate was polished using a grindstone. In Sample No. 1-31 to Sample No. 1-33, the "Content of first element" shown in Table 1 indicates the content of Ti in the brazing material. The content of Ti is based on 100 parts by mass of the entire brazing material.

(Carbide layer coverage and thickness)
The cross section perpendicular to the surface of the metal layer of the heat dissipation member sample was observed by SEM-EDX. The coverage of the carbide layer at the first interface between the first particle and the metal layer of the multiple coated diamond particles was obtained. The thickness of the carbide layer at the first interface was also obtained. The coverage and thickness of the carbide layer at the first interface are shown in Table 1.

(Evaluation of adhesion of metal layer)
The adhesion between the substrate and the metal layer was evaluated for the heat dissipation member samples prepared. The adhesion was evaluated by conducting a heating test and examining the presence or absence of peeling or blistering of the metal layer. Specifically, the heat dissipation member was held at 780° C. for 20 minutes in a hydrogen atmosphere, and then the presence or absence of peeling or blistering of the metal layer was visually confirmed. The adhesion was evaluated as "A" when there was no peeling or blistering of the metal layer, and "B" when there was. The results are shown in Tables 1 and 2.

(Measurement of thermal conductivity)
After the heating test, the thermal conductivity of the heat dissipation member was measured. The thermal conductivity was measured at room temperature using a laser flash type thermal conductivity measuring device. The results are shown in Tables 1 and 2.

(Composition of the Boundary Region)
The composition of the boundary region between the substrate and the metal layer was analyzed for the heat dissipation member sample produced. The composition of the boundary region was analyzed by setting a measurement region from the boundary region as follows, and the measurement region was analyzed. In a cross section perpendicular to the surface of the metal layer, the vicinity of the interface between the substrate and the metal layer was observed by SEM-EDX. In the boundary region within the observation field of view, a rectangular region with a short side of 30 μm and a long side of 300 μm was set as the measurement region. The length of the short side of the measurement region is the length in the vertical direction of the measurement region. The length of the short side of the measurement region is equal to the thickness of the boundary region. The length of the long side of the measurement region is the length along the surface of the metal layer 4. In other words, the length of the long side of the measurement region is the length in the horizontal direction of the measurement region. The composition in this measurement region was analyzed by EDX.

The composition of the boundary region was analyzed by measuring the elemental content in five different measurement regions for each sample using EDX. The elemental content is a value with the composition of the boundary region taken as 100 atomic %. Specifically, the elemental content is a value expressed as an atomic percentage with the total number of atoms of all detected elements taken as 100 atomic %. The elemental content in the boundary region is the average value of the elemental content in each measurement region. Here, the Ag content, Cu content, and first element content in the boundary region were determined. In addition, the Ag content ratio to the total content of Ag and Cu was determined. The results are shown in Table 2.

All of Samples No. 1-1 to No. 1-13 were rated an A for adhesion. All of Samples No. 1-20 to No. 1-22 were rated a B for adhesion. Furthermore, all of Samples No. 1-1 to No. 1-13 had a thermal conductivity of 780 W/m·K or higher after the heating test, which was higher than that of Samples No. 1-20 to No. 1-22.

All of Sample No. 1-31 to Sample No. 1-33 were rated A for adhesion. However, Sample No. 1-31 to Sample No. 1-33 had a thermal conductivity of 680 W/m·K or less. The thermal conductivity of Sample No. 1-31 to Sample No. 1-33 was lower than that of Sample No. 1-9 and Sample No. 1-11. Sample No. 1-31 to Sample No. 1-33 were surface-treated with a grindstone, like Sample No. 1-9 and Sample No. 1-11. The reason for the decrease in thermal conductivity of Sample No. 1-31 to Sample No. 1-33 is thought to be due to the inclusion of Cu in the boundary region. Sample No. 1-31 to Sample No. In sample No. 1-33, the Ag content in the boundary region is less than 92 atomic %, which is a low Ag content in the boundary region. Therefore, it is believed that the thermal conductivity in the boundary region is reduced in sample No. 1-31 to sample No. 1-33.

In contrast, Sample No. 1-1 to Sample No. 1-13 do not contain Cu in the boundary region. In Sample No. 1-1 to Sample No. 1-13, the Ag content in the boundary region is 98 atomic % or more. It is believed that the presence of such a boundary region suppresses the decrease in thermal conductivity in the boundary region. Furthermore, in Sample No. 1-1 to Sample No. 1-13, the content of the first element in the boundary region is 0.7 atomic % or less. All of these samples satisfy the requirement that the content of the first element in the boundary region is less than 1.2 atomic %.

In all of Sample No. 1-1 to Sample No. 1-13, the coverage of the carbide layer at the first interface was 80% or more. Specifically, the coverage of the carbide layer in all of these samples was 85% or more. In Sample No. 1-2 to Sample No. 1-13, the coverage of the carbide layer was approximately 100%. In addition, by mapping analysis using EDX, it was investigated whether the first element was present between the reference line and the surface of the metal layer. As a result, in all of Sample No. 1-1 to Sample No. 1-13, the first element was present between the reference line and the surface of the metal layer. Furthermore, the protrusion amount of the first particle sandwiched between the second particles was investigated. In Sample No. 1-1 to Sample No. 1-8, Sample No. 1-10, and Sample No. 1-12, in which the substrate was surface-treated with abrasive paper, the protrusion amount of the first particle was about 30 μm. In Sample No. 1-9 and Sample No. 1-2, in which the substrate was surface-treated with a grindstone, the protrusion amount of the first particle was about 30 μm. In sample No. 1-11, the amount of protrusion of the first particles was about 5 μm. In sample No. 1-13, in which the surface of the base material was etched, the amount of protrusion of the first particles was 30 μm. The amount of protrusion of the first particles was also examined for sample No. 1-31 to sample No. 1-33. In sample No. 1-31 to sample No. 1-33, in which the base material was surface-treated with a grindstone, the amount of protrusion of the first particles was about 5 μm.

The surface roughness of the metal layer was measured for Sample No. 1-1 to Sample No. 1-13. The arithmetic mean roughness Ra of the metal layer surface was 0.1 μm or less for all Sample No. 1-1 to Sample No. 1-13.

The cross section of the heat dissipation member was observed by SEM-EDX for Sample No. 1-20 to Sample No. 1-22. In Sample No. 1-20, the surface of the first particle was covered with a carbide layer, but it was found that a foreign matter was present at the first interface between the first particle and the metal layer. This foreign matter was thought to be a mold release agent for the molding die. In Sample No. 1-21 and Sample No. 1-22, the carbide layer was not present at the first interface between the first particle and the metal layer, and the core was exposed from the carbide layer. In other words, the coverage rate of the carbide layer at the first interface was 0. In both Sample No. 1-21 and Sample No. 1-22, the first element was not present between the reference line and the surface of the metal layer. In Sample No. 1-20, where the surface treatment of the substrate was not performed, the protrusion amount of the first particle was 20 μm. In Sample No. 1-21 and Sample No. In 1-22, the protrusion amount of the first particle was 30 μm.

Figure 6 shows an SEM image of the cross section of the heat dissipation member of sample No. 1-12, enlarging the vicinity of the interface between the coated diamond particle and the metal layer. The magnification of the SEM image is 700 times. In Figure 6, the black part indicates the core of the coated diamond particle, and the gray part indicates the metal. Figures 7 to 9 show the results of mapping analysis by EDX of the vicinity of the interface between the coated diamond particle and the metal layer in the SEM image shown in Figure 6. Figure 7 shows a mapping of only Ti. In Figure 7, the bright part indicates the presence of Ti. Figure 8 shows a mapping of only C. In Figure 8, the gray part is C. In Figure 9, the gray part is Ag. From the SEM image shown in Figure 6 and the mapping image of Ti shown in Figure 7, it can be seen that Ti is densely distributed on the surface of the core of the coated diamond particle in sample No. 1-12. It is considered that the area where Ti is densely distributed on the surface of the core is a carbide layer made of TiC. Additionally, Ti is scattered at positions away from the coated diamond particles, indicating that Ti is distributed throughout the metal layer.

Figure 10 shows an SEM image of a cross section of the heat dissipation member of sample No. 1-12, enlarging a portion of the first interface between the first particle and the metal layer. The magnification of the SEM image is 10,000 times. In Figure 10, the polygonal black portion is the core 21 of the first particle 20a, and the dark gray portion covering the surface of the core 21 is the carbide layer 22. The light gray area is the metal layer 4. As shown in Figure 10, it can be seen that in sample No. 1-12, the carbide layer 22 is present at the first interface between the first particle 20a and the metal layer 4.

REFERENCE SIGNS LIST 1 heat dissipation member 2 substrate 4 metal layer 10 composite material 20 coated diamond particle 20a first particle, 20b second particle 21 core 22 carbide layer 30 binder phase S reference line

Claims (9)

A substrate made of a composite material;
A metal layer provided on a surface of the base material,
The substrate is
A plurality of coated diamond particles;
a binder phase bonding the plurality of coated diamond particles together;
The coated diamond particles are
A core made of diamond;
a carbide layer covering a surface of the core;
The binder phase is composed of a metal,
In a cross section perpendicular to the surface of the metal layer, a coverage rate of the carbide layer at a first interface between the metal layer and a first particle having a particle size of 80 μm or more among the plurality of coated diamond particles is 80% or more;
a ratio of silver to a total content of silver and copper in a boundary region between the substrate and the metal layer is 98 atomic % or more;
The thermal conductivity is 780 W/m·K or more.
Heat dissipation material. The heat dissipation member according to claim 1, wherein the carbide layer is made of a carbide containing at least one first element selected from the group consisting of zirconium, chromium, titanium, silicon, tantalum, and niobium. the first element is present between a reference line and a surface of the metal layer in the cross section,
The heat dissipation member according to claim 2 , wherein the reference line is a line segment that passes through the most protruding position of the first particle and is parallel to a surface of the metal layer. the first element is titanium,
the metal layer is made of silver;
4. The heat dissipation member according to claim 2, wherein the binder phase is made of silver. The heat dissipation member according to claim 2 or 3, wherein the content of the first element in the boundary region is less than 1.2 atomic %, with the composition of the boundary region being 100 atomic %. The heat dissipation member according to claim 1 or 2, wherein the arithmetic mean roughness Ra of the surface of the metal layer is 2.0 μm or less. The heat dissipation member according to claim 1 or 2, wherein the thickness of the metal layer is 3 μm or more and 200 μm or less. the plurality of coated diamond particles includes second particles having a particle size of less than 80 μm;
3. The heat dissipation member according to claim 1, wherein a protrusion amount of the first particles sandwiched between the second particles in the cross section is 10 μm or less. Providing a substrate made of a composite material;
Supplying a mixed powder of a first powder made of a metal and a second powder containing a first element onto a surface of the base material;
and sintering the base material and the mixed powder,
The composite material in the step of preparing the substrate includes:
a plurality of coated diamond particles and a bonding phase bonding the plurality of coated diamond particles;
The plurality of coated diamond particles each have a diamond core and a carbide layer covering the core,
The binder phase is composed of a metal,
the plurality of coated diamond particles located on a surface of the composite material include particles having their cores exposed from the carbide layer;
The first element is at least one element selected from the group consisting of zirconium, chromium, titanium, silicon, tantalum and niobium;
A method for manufacturing a heat dissipation member.

Images