Heat sink, semiconductor device and method for manufacturing heat sink

Abstract

To provide a heat sink, a semiconductor device, and a method for manufacturing the heat sink that is thinner and can improve yield.SOLUTION: It is characterized that a heat sink consists of copper layers, and a graphite-copper composite material containing flake-shaped graphite particles laminated through the copper layers, and the flake-shaped graphite particles are stacked in a direction perpendicular to the thickness of the heat sink, and the median diameter of the flake-shaped graphite particles is 50 μm or more and 800 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a heat sink, a semiconductor device, and a method for manufacturing a heat sink. [Background technology]

[0002] Materials for heat dissipation components of semiconductor devices are required to have high thermal conductivity. Copper has high thermal conductivity but also a high coefficient of thermal expansion. A metal-graphite composite has been proposed as a composite material that can reduce the coefficient of thermal expansion of copper without impairing its high thermal conductivity and can be manufactured at low cost (see, for example, Patent Document 1). The metal-graphite composite material in Patent Document 1 is disclosed to have high cooling reliability and a low coefficient of linear expansion.

[0003] Furthermore, Patent Documents 2 and 3 propose a graphite-copper composite material as a composite material. Patent Document 3 describes that the thermal conductivity of the flake graphite particles constituting this composite material in directions (X, Y) perpendicular to the stacking direction (Z) is greater than the thermal conductivity in the stacking direction (Z). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-128802 [Patent Document 2] Japanese Patent Application Publication No. 2023-056481 [Patent Document 3] Japanese Patent Application Publication No. 2023-126049 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, advances in new technologies such as IoT, AI, and electric vehicles have led to the miniaturization of semiconductor devices, necessitating the development of thinner heat dissipation components (heat sinks) with improved heat dissipation. However, reducing the thickness of the heat sink raises concerns that its strength will decrease, resulting in lower yields. Furthermore, when graphite-copper composites are used as heat sink materials, depending on the stacking direction of the flake graphite particles, heat conduction may be poor, potentially reducing heat dissipation performance. Therefore, an object of the present disclosure is to provide a heat sink, a semiconductor device, and a method for manufacturing a heat sink that are thinner and can improve yield, and also to provide a heat sink, a semiconductor device, and a method for manufacturing a heat sink that can further improve heat dissipation. [Means for solving the problem]

[0006] As a result of investigations conducted by the present inventors to solve the above problems, it was found that by using flake graphite particles that are stacked in a direction intersecting the thickness direction of the heat sink and have a median diameter of 50 μm or more and 800 μm or less, a heat sink that is thinner and can improve yield can be obtained.

[0007] That is, the present disclosure provides a heat sink made of a graphite-copper composite material including a copper layer and flake graphite particles stacked via the copper layer, wherein the flake graphite particles are stacked in a direction intersecting the thickness direction of the heat sink, and the median diameter of the flake graphite particles is 50 μm or more and 800 μm or less.

[0008] The present disclosure also provides a semiconductor device including the heat sink described above, and a semiconductor element in contact with a main surface of the heat sink that intersects with the thickness direction.

[0009] The present disclosure also provides a method for manufacturing a heat sink made of a graphite-copper composite material containing a copper layer and flake graphite particles stacked via the copper layer, the method comprising the steps of: pretreating graphite particles to obtain the flake graphite particles having a median diameter of 50 μm or more and 800 μm or less; mixing the flake graphite particles with copper particles to obtain a molding raw material; molding the molding raw material and sintering the molded body obtained by molding the molding raw material under pressure using a multi-axis current sintering method to obtain a sintered body in which the flake graphite particles are stacked in a predetermined direction; and processing the sintered body to obtain the heat sink so that the stacking direction of the flake graphite particles is perpendicular to the thickness direction of the heat sink. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide a heat sink, a semiconductor device, and a method for manufacturing a heat sink that are thinner and can improve yield, and it is also possible to provide a heat sink, a semiconductor device, and a method for manufacturing a heat sink that can further improve heat dissipation. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic diagram showing a heat sink according to the present disclosure. [Figure 2] FIG. 1 is a schematic diagram illustrating an example of a semiconductor device. [Figure 3] FIG. 1 is a schematic diagram showing a semiconductor package as an example of a semiconductor device. [Figure 4] 1 is a schematic diagram showing a light source device as an example of a semiconductor device. [Figure 5] FIG. 1 is a schematic diagram showing a semiconductor laser unit as an example of a semiconductor device. [Figure 6] 1 is a schematic diagram showing a power semiconductor module as an example of a semiconductor device. [Figure 7] FIG. 2 is a diagram illustrating an example of pretreatment of graphite particles. [Figure 8] FIG. 10 is a diagram illustrating another example of pretreatment of graphite particles. [Figure 9] FIG. 1 is a schematic diagram illustrating a multi-axis electric current sintering apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0012] Embodiments of the present disclosure will be described in detail below. Note that the heat sink, semiconductor device, and method for manufacturing a heat sink described below are intended to embody the technical concept of the present disclosure, and unless otherwise specified, the present disclosure is not limited to the following. In each drawing, components having the same function may be assigned the same reference numeral. The size and positional relationship of components shown in each drawing may be exaggerated for clarity of explanation.

[0013] <Heat sink> As shown in FIG. 1, the heat sink 14 of the present disclosure is a plate-like body having a certain thickness. The heat sink 14 has a main surface 14a that contacts a semiconductor element (heat-receiving member) 18 (see FIG. 2), which will be described later, and a side surface 14b that intersects with the main surface 14a. The main surface 14a and the side surface 14b are one of multiple surfaces of the heat sink 14. The main surface 14a is a square with one side in the direction of the arrow X and the other side in the direction of the arrow Y. In another embodiment, the main surface may be a rectangle with the long side in the direction of the arrow X and the short side in the direction of the arrow Y.

[0014] In heat sink 14, the "thickness direction" is the direction perpendicular to main surface 14a (the direction of arrow Z). The thickness (length in the thickness direction) of heat sink 14 may be 0.05 mm or more and less than 1.0 mm, preferably 0.075 mm or more, more preferably 0.1 mm or more, and preferably 0.75 mm or less, and more preferably 0.7 mm or less.

[0015] The thermal diffusivity of the heat sink 14 is 380 mm 2 / s or more is preferable, 410mm 2 / s or more is preferable, and 440mm 2 / s or more is even more preferable. The thermal diffusivity in this specification is the average value measured at three locations on the heat sink using a laser spot periodic heating radiation thermometry method (JIS R 7240:2018). If the thickness and thermal diffusivity are within these ranges, the heat sink 14 can be used in miniaturized semiconductor devices and can have improved heat dissipation properties.

[0016] The heat sink 14 is a heat dissipation member that dissipates heat generated from a semiconductor element 18 in, for example, a semiconductor device 10 (see FIG. 2) described later. The shape of the heat sink 14 is not limited to that of the present embodiment, and may be a plate-like shape such as a cube, a rectangular parallelepiped, or a cylinder, a stepped shape, a sloped shape, or a combination of multiple shapes.

[0017] From the viewpoint of thermal resistance between the heat sink and the heat-receiving member, the main surface 14a of the heat sink 14 is preferably a smooth surface with small surface roughness. The surface roughness (Ra) of the main surface 14a is preferably 1 μm or less, and more preferably 0.5 μm or less.

[0018] <Graphite-copper composite material> The heat sink 14 is made of a graphite-copper-graphite-copper composite material (hereinafter simply referred to as a composite material) containing a copper layer and flake graphite particles laminated with the copper layer interposed therebetween. The heat sink 14 includes a graphite-copper composite material that has been plated with Ni, Au, Ag, or the like by a known method. The graphite-copper composite material is a sintered body obtained from flake graphite particles and copper particles as raw materials. The flake graphite particles are laminated with a copper layer having an average thickness of 15 μm or less interposed therebetween. "With a copper layer interposed" means that the flake graphite particles (hereinafter simply referred to as graphite particles) are connected by adjacent copper layers. The graphite particles within the composite material are electrically continuous. The composite material has high thermal conductivity due to the continuous graphite particles with high thermal conductivity.

[0019] 1, graphite particles 23 are indicated by dashed lines. Heat sink 14 includes a plurality of graphite particles 23. The plurality of graphite particles 23 are stacked in a direction (arrow X direction) intersecting the thickness direction (arrow Z direction) of the heat sink (the stacking direction of the plurality of graphite particles 23 is the same as the arrow X direction). Each graphite particle 23 is roughly in the shape of a scale spreading on the plane formed by the arrow Y direction and the arrow Z direction, and the arrow X direction is the thickness direction of graphite particle 23.

[0020] The value obtained by measuring the graphite particles 23 using a method conforming to particle size analysis - laser diffraction and scattering method (JIS Z 8825:2022) is defined as the "median diameter of the graphite particles." This median diameter may be 50 μm or more and 800 μm or less, preferably 75 μm or more, more preferably 100 μm or more, preferably 700 μm or less, and more preferably 600 μm or less. Within such a range, the strength of the heat sink is ensured, the thickness of the heat sink can be processed to be thinner, and the yield can be improved. Furthermore, the heat sink can have improved heat dissipation properties.

[0021] The average thickness of the copper layer may be 15 μm or less. This reduces the coarse copper layers that exist locally between the graphite particles. Since copper has a lower thermal conductivity than graphite, reducing the coarse copper layers results in a composite material with high thermal conductivity. Furthermore, the thickness of the copper layer decreases as the volume fraction of copper in the composite material decreases.

[0022] The volume fraction of copper in the entire composite material may be 3% or more and 30% or less, preferably 10% or more, more preferably 13% or more, and may be 20% or less, more preferably 18% or less. The volume ratio of graphite to copper (graphite:copper) in the composite material may be 70:30 to 97:3, preferably 80:20 to 90:10, and more preferably 82:18 to 87:13. Within these ranges, the thermal conductivity of the heat sink can be increased and its processability can be improved. Copper acts as a binder in the composite material and prevents the heat sink from breaking during processing, thereby improving the processability of the heat sink.

[0023] <Semiconductor device> 2 shows an example of a semiconductor device 10. The semiconductor device 10 includes at least a heat sink 14, a semiconductor element 18, and a cooler 12.

[0024] The semiconductor element 18 is not particularly limited, but examples thereof include power semiconductor elements such as transistors, diodes, integrated circuits, and memories, as well as semiconductor light-emitting elements such as LEDs and laser diodes. The semiconductor element 18 is in contact with at least a main surface 14a (top surface in FIG. 2) of the heat sink 14 that intersects with the thickness direction. The semiconductor element 18 may also be housed in a semiconductor package, which will be described later.

[0025] The cooler 12 is not particularly limited as long as it cools the heat generated by the semiconductor element 18, but examples thereof include a heat sink. The heat sink may have a plate-like shape (e.g., cube, rectangular parallelepiped, or cylindrical), a stepped shape, a pinholder shape, a bellows-like slope, or a fin shape, or may be a combination of several shapes. A heat sink with plate-like fins may have multiple fins on a flat metal heat-receiving plate. The thickness of the heat sink can be selected appropriately depending on the material and structure, but is typically approximately 0.5 mm to 5.0 mm. The cooler 12 may have a channel through which a refrigerant flows and cooling fins formed inside. The refrigerant may be a liquid such as water or ethylene glycol liquid.

[0026] The material of the cooler 12 is preferably a material with high thermal conductivity, such as copper, copper alloy, graphite-copper composite material, etc., but other metal materials such as aluminum material and stainless steel material can also be used.

[0027] <Semiconductor package> As an example of a semiconductor device, a semiconductor package 110 is shown in Fig. 3. The semiconductor package 110 includes at least a heat sink 14, a base 20, and a lid 30, and contains a semiconductor element 18 therein.

[0028] The semiconductor package 110 has a configuration in which two bases 20 are mounted on a heat sink 14, and the two bases 20 and the lid 30 are joined together by a joining member 25. The heat sink 14 and the base 20 may be joined together by a joint (adhesive) not shown. The semiconductor element 18 is in contact with at least the main surface (top surface in FIG. 3) of the surface of the heat sink 14 in the semiconductor package 110 that intersects with the thickness direction.

[0029] The semiconductor package 110 accommodates a semiconductor element 18 electrically connected to a control device external to the semiconductor package 110. The semiconductor element 18 is, for example, a laser diode, and its light emission is controlled by an external control device. The semiconductor element 18 is not limited to a laser diode, and may be, for example, a power device composed of a power MOSFET or a diode, an LED, or may include a semiconductor having another function. The semiconductor package 110 may accommodate multiple semiconductor elements. The semiconductor package 110 electrically connects the semiconductor element 18 to the external control device and dissipates heat generated by the semiconductor element 18 to the outside via the heat sink 14.

[0030] The base 20 is a frame-shaped member and may be made of a material such as alumina, AlN, or SiC.

[0031] The lid 30 is made of, for example, translucent glass. The lid 30 is joined to the base 20 via a joining member 25. As a result, the lid 30, together with the base 20 and the heat sink 14, maintains the airtightness of the space in which the semiconductor element 18 is housed. Note that the material from which the lid 30 is made is not limited to glass as long as it is translucent, and may be sapphire.

[0032] The bonding members 25 may be made of tungsten (W), nickel (Ni), and gold (Au), or may be made of chromium (Cr), nickel, and gold, or may be made of gold-tin solder (e.g., Au 80 wt%-Sn 20 wt%). The bonding members 25 may also be made of two or more types of metal films.

[0033] Specific examples of the semiconductor device include a light source device and a power supply device.

[0034] <Light source device> 4 shows a light source device 210 as an example of a semiconductor device. The light source device 210 includes at least a semiconductor light emitting element 218, a heat sink 14, a cooler 12, and a substrate 50.

[0035] The substrate 50 is a module substrate, and is made of a glass epoxy substrate, a metal substrate, a ceramic substrate, etc. Suitable examples of the semiconductor light emitting element 218 include an LED, a laser diode, etc.

[0036] <Semiconductor laser module> A semiconductor laser module 310 is shown as an example of a light source device (semiconductor device). As shown in Fig. 5, the semiconductor laser module 310 includes at least a heat sink (cooler) 312, a heat sink 14, and a semiconductor laser element (semiconductor light-emitting element) 318. The semiconductor laser element 318 is an example of a semiconductor element. The structure of the semiconductor laser module 310 is not particularly limited, but examples include a TO-Can package type and a surface-mount type. In Fig. 5, graphite particles 23 are indicated by dashed lines.

[0037] The semiconductor laser module 310 has a package made up of a housing (case) 60 and a window member 66. A semiconductor laser unit 11 having a semiconductor laser element 318 and optical components 62 are mounted on the housing (case) 60 in this package. The semiconductor laser element 318 is joined to the heat sink 14 by joints (adhesive) (not shown) arranged on the upper and lower surfaces (front and back surfaces) in the direction of the arrow Z.

[0038] The shape, position, relative arrangement, and dimensions of each part of the semiconductor laser module 310 are not limited. For example, a semiconductor laser module having a structure similar to a semiconductor laser array in which the semiconductor laser element has multiple optical resonators can be adopted. A semiconductor laser stack may also be formed using the semiconductor laser unit 11. In this case, a semiconductor laser stack can be obtained by stacking heat sinks via spacers made of, for example, silicone resin. The thickness of the spacer can be selected appropriately depending on the configuration of the semiconductor laser unit, and is, for example, about 0.01 mm.

[0039] An optical component 62 and a light-transmitting window member 66 are attached to the emission side of the semiconductor laser element 318 in the housing (case) 60. This allows the emitted light from the semiconductor laser element 318 to pass through the window member 66 and be emitted to the outside of the semiconductor laser module 310.

[0040] The material forming the housing (case) 60 is not particularly limited, but may be, for example, metal, etc. The housing (case) 60 may be configured as a package using a plurality of members such as a base and a terminal holding member (outer peripheral wall).

[0041] The optical component 62 may be, for example, a lens, which controls the light distribution of the laser light 64 emitted by the semiconductor laser element 318 and transmits the laser light 64. The laser light 64 is emitted through a window member 66. The material from which the window member 66 is made is not particularly limited as long as it is a light-transmitting material, and examples thereof include known glass materials and resin materials.

[0042] <Semiconductor laser unit> The semiconductor laser unit according to the present disclosure includes a heat sink, a heat dissipation plate, and a semiconductor laser element, and constitutes the main configuration of the semiconductor device according to the present disclosure.

[0043] As shown in FIG. 5, the semiconductor laser unit 11 includes a heat sink 312, a heat sink 14 disposed on the upper surface of the heat sink 12, and a semiconductor laser element 318 in contact with the heat sink 14 (principal surface 14a). The heat sink 14 is sometimes called a submount, and both are aspects of the heat sink in the present technology. The heat sink 14 efficiently transfers heat generated by the semiconductor laser element 318 to the heat sink 312. Note that "in contact" may refer to a state in which two members (e.g., the heat sink 14 and the semiconductor laser element 318) are in direct contact with each other, or a state in which the two members are bonded together via an adhesive. In this embodiment, the semiconductor laser element 318 and the heat sink 14 are bonded together via an adhesive such as solder.

[0044] <Semiconductor laser element> In short, the semiconductor laser element according to the present disclosure refers to an element that oscillates as a laser when a current is passed through a circuit element made of a semiconductor material, thereby emitting light.

[0045] The semiconductor laser element 318 is not particularly limited, but examples thereof include nitride semiconductor laser elements, GaAs-based semiconductor laser elements, and InP-based semiconductor laser elements. The wavelength of the emitted light can be, for example, wavelengths ranging from the ultraviolet region to the red region and the infrared region, but is not limited thereto, and semiconductor laser elements of any wavelength region can be used depending on the application. The output of the semiconductor laser element 318 may be appropriately selected depending on the application, but is preferably, for example, 3 watts or more. The output of the semiconductor laser element 318 is more preferably 5 watts or more, even more preferably 10 watts or more, and even more preferably 15 watts or more.

[0046] An insulating film (not shown) may be formed on the semiconductor laser element 318. The insulating film is made of, for example, SiO2 or the like. Metal wiring electrically connecting to the semiconductor laser element 318 may be formed on the heat sink 14 and the heat dissipation plate 14 and the heat sink 12. For example, the semiconductor laser element 318 emits light when power is supplied via the metal wiring and wiring (not shown) formed on the housing (case) 60.

[0047] <Power semiconductor module> FIG. 6 shows a power semiconductor module 410 as an example of a power supply device (semiconductor device). The power semiconductor module 410 includes at least a power semiconductor element 418, a heat sink 14, an insulating heat sink 451, and a cooler 12. The power semiconductor module 410 is a module equipped with a power semiconductor element 418 (e.g., a SiC semiconductor as a powered bandgap semiconductor) and constitutes, for example, an inverter circuit in an inverter device. The power semiconductor element 418 is an example of a semiconductor element. The power semiconductor element 418 is bonded to the upper surface of the heat sink 14. An insulating heat sink 451 is bonded to the lower surface of the heat sink 14. The cooler 12 is bonded to the lower surface of the insulating heat sink 451. The insulating heat sink 451 must have a certain degree of thermal conductivity while maintaining electrical insulation. The insulating heat sink 451 is made of, for example, a silicon sheet or a ceramic sheet. The cooler 12 is made of, for example, aluminum and is provided with heat dissipation fins. The power semiconductor element 418, the heat sink 14, and the insulating heat dissipation member 451 are sealed in an insulating mold 452 (for convenience, the mold 452 is shown in a see-through manner in FIG. 6).

[0048] <Heat sink manufacturing method> The method for manufacturing a heat sink includes the steps of pretreating graphite particles to obtain graphite particles with a predetermined median diameter, mixing the graphite particles with copper particles to obtain a molding raw material, sintering the molded body obtained by molding the molding raw material under pressure using a multi-axis current sintering method to obtain a sintered body in which the graphite particles are stacked in a predetermined direction, and processing the sintered body so that the stacking direction of the graphite particles is perpendicular to the thickness direction of the heat sink to obtain the heat sink. Each step is described below.

[0049] (Graphite pretreatment) The pretreatment of graphite particles (hereinafter sometimes referred to as "thinning") is carried out by applying shear force to the graphite particles to reduce their thickness. The graphite particles used are not particularly limited, but generally have a long side of about 10 μm to 2000 μm and a thickness of about 20 μm to 200 μm. Examples of graphite that can be used include "+3299" (manufactured by Ito Graphite Industries Co., Ltd.).

[0050] For example, as shown in FIG. 7, the pretreatment can use a sieve 21 on which graphite particles 23 are placed and a grindstone 22 that can move back and forth horizontally in contact with the graphite particles 23. The size of the graphite particles obtained can be selected depending on the mesh size of the sieve 21 used. The mesh size of the sieve 21 can be, for example, about 53 μm. The grindstone 22 is preferably a coarse to medium grindstone, and preferably uses alundum or natural diamond as abrasive grains. The graphite particles 23 are placed on the sieve 21, and the grindstone 22 is moved back and forth horizontally to apply shear force, thereby reducing the thickness of the graphite particles 23.

[0051] Sieve 21 removes particles that have internal cavities due to shear force and particles that are brittle and easily crumble. As a result, the thickness of the resulting graphite particles is reduced and the density is increased. Furthermore, impurities in the graphite particles are removed, leading to improved purity. Note that graphite particles of various sizes can be obtained by changing the size of the abrasive grains used in the process and the opening size of the sieve.

[0052] For the pre-treatment of graphite particles, two grindstones 30a, 30b can also be used, as shown in Fig. 8. Grindstones 30a, 30b have metal plates 31a, 31b, respectively, with abrasive grains 33a, 33b, such as diamond, provided on opposing surfaces. Abrasive grains 33a, 33b are fixed by bonding metal members 32a, 32b, such as plated metal members, and graphite particles 23 to be treated are placed between abrasive grains 33a, 33b. When graphite particles 23 are pre-treated using grindstones 30a, 30b, relatively small and thin graphite particles can be obtained efficiently.

[0053] The pretreatment described above produces graphite particles with a thickness of 50 μm or less. The thickness shown here is the average thickness of 50 graphite particles after pretreatment. Graphite particles have a structure in which multiple graphite flakes are stacked on top of each other. The thinner the graphite particles, the smaller the gaps between the graphite flakes within the graphite particles, resulting in better thermal conductivity and mechanical properties. The thickness of the graphite particles can be adjusted by the graphite particles used and the pretreatment conditions. The thinner the graphite particles, specifically when the thickness is 30 μm or less, the higher the thermal conductivity and the better the processability of the resulting composite material.

[0054] The median diameter of the graphite particles obtained by the pretreatment may be 50 μm or more and 800 μm or less, preferably 75 μm or more, more preferably 100 μm or more, and preferably 700 μm or less, and more preferably 600 μm or less. Within these ranges, the graphite particles are less likely to be cut during machining, and cracks and fractures in the heat sink are less likely to occur, thereby improving processing yield. Furthermore, in order to further increase thermal conductivity and improve processability, the median diameter of the graphite particles may be smaller than the thickness of the heat sink.

[0055] (Preparation of copper particles) The copper particles used as the raw material for the copper layer are not particularly limited, and for example, copper particles having a volume-based median diameter (median diameter measured according to a method in accordance with JIS Z 8825:2022) of 1.5 μm or less can be used. The median diameter of the copper particles is preferably 1.0 μm or less. When small copper particles having a median diameter of 1.5 μm or less are used, a composite material with stable thermal conductivity and processability can be obtained. The copper particles can be produced by any method. For example, the desired copper particles can be obtained by a chemical reduction method or a physical production method.

[0056] (mixture) The graphite particles obtained by pretreatment and copper particles are blended in a predetermined ratio, and wet-mixed in an organic solvent to obtain a molding raw material. The blending ratio of the raw materials is selected so that the volume ratio of graphite to copper in the composite material, graphite:copper, is the aforementioned volume ratio (e.g., 70:30 to 97:3). Specific examples of suitable organic solvents include toluene and xylene.

[0057] (sintering) First, the molding raw materials are filled into a predetermined mold and compacted at a pressure of 3 MPa to 15 MPa using, for example, a hydraulic hand press. By repeating the filling and compacting of the molding raw materials, a compact of the desired size is produced. The resulting compact is then sintered using a multi-axis current sintering method to obtain a sintered body that will become the desired composite material.

[0058] Here, an outline of a multi-axis electric current sintering apparatus will be described with reference to Fig. 9. In a multi-axis electric current sintering apparatus 40, a carbon mold 44 containing a compact can be fixed in a vacuum container 42 by vertical pressure shafts 45a, 45b and horizontal heating shafts (A) 47a, 47b and heating shafts (B) 49a, 49b. The heating shafts (A) 47a, 47b and heating shafts (B) 49a, 49b are configured so that electricity can be applied alternately. Electricity is applied to the heating shaft (A) in the directions of arrows x1, x2, and to the heating shaft (B) in the directions of arrows y1, y2.

[0059] In the multi-axis electric current sintering apparatus 40, the pressure application axes 45a, 45b and the heating axes 47a, 47b, 49a, 49b are separate. Specifically, the pressure application axes 45a, 45b are in the z-axis direction, the heating axes (A) 47a, 47b are in the x-axis direction, and the heating axes (B) 49a, 49b are in the y-axis direction. This makes it possible to control pressure application and heating independently, resulting in a uniform temperature distribution in the radial direction of the sintered portion.

[0060] During sintering, the carbon mold 44 containing the compact is fixed inside the vacuum container 42, and the pressure inside the vacuum container 42 is then reduced to 100 Pa or less, preferably to 50 Pa or less to prevent oxidation and deterioration of components inside the device. Next, while applying pressure up to 10 MPa in the directions of arrows z1 and z2 using the vertical pressure shafts 45a and 45b, electricity is passed through the heating shafts (A) 47a and 47b to heat the material to 650°C or higher and 750°C or lower (preferably 670°C or higher, or 730°C or lower).

[0061] Thereafter, the heating shafts (B) 49a and 49b are switched to heat the material to 930°C or higher and 980°C or lower (preferably 940°C or higher and 970°C or lower). Furthermore, pressure is applied in the directions of arrows z1 and z2 by the vertical pressure shafts 45a and 45b. The pressure applied is preferably 10 MPa or higher and 100 MPa or lower, more preferably 30 MPa or higher and 50 MPa or lower.

[0062] The multi-axis current sintering method allows for uniform temperature distribution, making it possible to produce composite materials of stable quality. Moreover, because the material is produced using the specified graphite particles and copper particles obtained through pretreatment as raw materials, the resulting composite material has a higher and more stable thermal conductivity, a higher and more stable bending strength, and a lower coefficient of thermal expansion.

[0063] (Processing into heat sink) The heat sink is manufactured by, for example, cutting the sintered body into a plate-like body of a predetermined thickness. At this time, the cutting direction of the sintered body is adjusted, for example, so that the plurality of graphite particles 23 contained in the heat sink 14 are stacked in a direction (arrow X direction) that intersects with the thickness direction (arrow Z direction) of the heat sink 14, as shown in Figure 1, and the sintered body is processed into the plate-like body 14.

[0064] <Method of manufacturing a semiconductor device> In manufacturing the semiconductor device of the present disclosure, assembly is performed, for example, in the following procedure. First, heat sink 14 (see FIG. 2) containing a graphite-copper composite material is joined to the upper surface of heat sink 12 using solder or the like. Next, semiconductor element 18 is joined to main surface 14a of heat sink 14 using solder or the like. At this time, from the perspective of improving heat dissipation, semiconductor element 18 is arranged so as to be positioned in the thickness direction of heat sink 14 (a direction intersecting the stacking direction of graphite particles 23). [Example]

[0065] Next, the present invention will be specifically explained by way of examples, but the present invention is not limited to the following examples.

[0066] Example 1 Commercially available graphite particles were pretreated (thinned) using the method described with reference to Figure 7 to obtain graphite particles with a thickness of 50 μm or less. The grinding wheel 22 used a grinding wheel using alundum or natural diamond as abrasive grains. The obtained graphite particles were dried in a dryer. The graphite particles were measured using a method conforming to particle size analysis - laser diffraction and scattering method (JIS Z 8825:2022), and the median diameter was found to be 770 μm. This measurement was performed using an LA-950V2 manufactured by Horiba, Ltd. Meanwhile, copper particles produced by a chemical reduction method and with a median diameter of 1.5 μm were prepared.

[0067] The molding raw material was adjusted so that the volume fraction of copper in the composite material after the subsequent sintering process would be 16%. Specifically, 558.23 g of graphite particles that had been pretreated and dried as described above and 421.55 g of copper particles were blended to obtain the molding raw material. These powders were placed in a 2 L plastic bottle and mixed using a ball mill.

[0068] 979.78 g of molding material was placed into a 120 mm diameter stainless steel mold and compacted at 5 MPa using a hydraulic hand press. The process of adding molding material and compacting was repeated more than 10 times, and the compact was then removed from the stainless steel mold. The removed compact was placed in a cylindrical carbon mold and sintered using multi-axis electric current sintering. The carbon mold 44 was placed in the vacuum chamber 42 of the multi-axis electric current sintering apparatus 40 shown in Figure 9 and secured in place by two diagonal heating shafts (A) 47a and 47b and two pressure shafts 45a and 45b. The pressure inside the vacuum chamber 42 was reduced to 5 Pa using a rotary pump, and the pressure was increased to 10 MPa in the directions indicated by arrows z1 and z2 using the vertical pressure shafts 45a and 45b. The temperature was then raised by increasing the output of the power supply. The heating shafts (A) 47a and 47b heated the material to 600 °C, after which the temperature was maintained for 5 minutes. The temperature was then raised to 700°C, and while applying a pressure of 50 MPa in the directions of arrows z1 and z2 using the vertical pressure shafts 45a and 45b, the heating shafts (B) 49a and 49b were used to heat the compact to 950°C. After reaching 950°C, the temperature was maintained for 30 seconds. By performing these heating and pressure processes to sinter the compact, the graphite particles in the compact are stacked in a predetermined direction (stacking direction). Next, the power output was reduced and the device was cooled. After cooling, the carbon mold 44 was removed from the device, and a cylindrical sintered body was obtained from the mold.

[0069] The sintered body was cut out to a plate material having a thickness (distance in the direction of arrow Z shown in FIG. 1) of 2 mm. Next, this plate material was processed to obtain plate materials having a width of 20 mm (direction of arrow X in FIG. 1) and a length of 20 mm (direction of arrow Y in FIG. 1). A plurality of such plate materials (e.g., 36 pieces) were produced. Next, this plate material was ground to obtain a heat sink having a thickness (distance in the direction of arrow Z shown in FIG. 1) of 0.80 mm. This was used as the heat sink of Example 1. The grinding was performed using a surface grinder PSG-52DX manufactured by Okamoto Machine Tools Works, Ltd. Furthermore, a superabrasive wheel manufactured by A.L.M.T. was used as the wheel for the surface grinder.

[0070] Example 2 The heat sink of Example 2 was prepared in the same manner as Example 1, except that graphite particles with a median diameter of 520 μm were used as the raw material in the pretreatment and were ground to a thickness of 0.60 mm in the plate-shaped body by grinding.

[0071] Example 3 The heat sink of Example 3 was prepared in the same manner as Example 1, except that graphite particles with a median diameter of 270 μm were used as the raw material in the pretreatment and were ground to a thickness of 0.30 mm in the plate-shaped body by grinding.

[0072] Example 4 The heat sink of Example 4 was prepared in the same manner as Example 1, except that graphite particles with a median diameter of 150 μm were used as the raw material in the pretreatment and were ground to a thickness of 0.15 mm in the plate-shaped body by grinding.

[0073] (Comparative Example 1) A heat sink of Comparative Example 1 was prepared in the same manner as in Example 1, except that graphite particles with a median diameter of 900 μm were used as raw material in the pretreatment and ground to a thickness of 0.80 mm in the plate-shaped body by grinding.

[0074] (Comparative Example 2) A heat sink of Comparative Example 2 was prepared in the same manner as in Example 1, except that graphite particles with a median diameter of 40 μm were used as the raw material in the pretreatment and were ground to a thickness of 0.04 mm in the plate-shaped body by grinding.

[0075] <Evaluation of processability> The shape of the heat sinks obtained in each example and comparative example was observed, and cracks and splits were visually checked to evaluate workability. If cracks or splits were found in approximately 20% or more (7 or more) of the total number of heat sinks obtained (36), the result was marked "X", and if not, the result was marked "O". The results are shown in Table 1 below. In Table 1, the value for "graphite particle size" indicates the median diameter of the graphite particles.

[0076] <Measurement of thermal diffusivity> The heat sinks obtained in each example and comparative example were prepared, and their thermal diffusivities were measured using a laser spot periodic heating radiation thermometer (JIS R 7240:2018). A Thermowave Analyzer TA3 manufactured by Bethel Corporation was used as the measuring device. Each measurement was performed at three locations, and the average value of the thermal diffusivity of the heat sink was calculated. The results are shown in Table 1 below.

[0077] [Table 1]

[0078] In Examples 1 to 4, by setting the median diameter of the graphite particles to 50 μm or more and 800 μm or less, it was possible to process the heat sink into a thickness in the range of 0.05 mm or more and less than 1.0 mm. Such a heat sink has excellent thermal diffusivity and can be cut to any thickness. When a heat source (a member to be heat-dissipated) is arranged on the main surface of this heat sink, heat is conducted effectively in the vertical direction (thickness direction of the heat sink), which is the direction intersecting the stacking direction of the graphite particles, which is preferable. Looking at Examples 2 to 4, by setting the median diameter of the graphite particles to 520 μm or less, it was possible to make the heat sink into a thickness of 0.60 mm or less and a thermal diffusivity of 460 mm or less. 2 / s or more. In Example 4, by setting the median diameter of the graphite particles to 150 μm, the thickness of the heat sink could be set to 0.15 mm. On the other hand, in Comparative Examples 1 and 2, cracks and splits occurred, and it was not possible to process the heat sink into the desired shape. Therefore, it was not possible to measure the thermal diffusivity.

[0079] <Other embodiments> The present disclosure is not limited to the embodiments described above and in the drawings, and for example, the following embodiments are also included within the technical scope of the present disclosure. Furthermore, various modifications other than those described below can be made without departing from the spirit of the present disclosure.

[0080] The graphite particles may be stacked in the direction of arrow Y (see FIG. 1), which is a direction intersecting the thickness direction (direction of arrow Z) of the heat sink. In this case, each graphite particle is roughly in the shape of a scale spreading on the plane formed by the directions of arrow X and arrow Z, and the direction of arrow Y is the thickness direction of the graphite particle.

[0081] In the above embodiment, the submount in contact with the semiconductor laser element is exemplified as one aspect of the heat sink, but the present disclosure is not limited thereto. For example, the heat sink in contact with the submount may be applied to the heat sink.

[0082] This technology can be applied to light source components and light source devices for various optical devices such as light sources for processing, projectors, light sources for LCD backlights, lighting light sources, light sources for various indicators, automotive light sources, light sources for displays, traffic lights, etc., as well as heat sinks used in high-power laser devices, semiconductor packages, power supplies, power semiconductor modules, etc. [Explanation of symbols]

[0083] 10, 110, 210, 310, 410... semiconductor device, 14... heat sink, 18, 218, 318, 418... semiconductor element (heat dissipation member), 23... graphite particles

Claims

1. A heat sink made of a graphite-copper composite material including a copper layer and flake graphite particles laminated via the copper layer, the flake graphite particles are stacked in a direction intersecting the thickness direction of the heat sink, A heat sink characterized in that the median diameter of the flake graphite particles is 50 μm or more and 800 μm or less.

2. The heat sink according to claim 1 , wherein the thickness of the heat sink is equal to or greater than 0.05 mm and less than 1.0 mm.

3. 3. The heat sink according to claim 1, wherein the volume fraction of copper in the graphite-copper composite material is 3% or more and 30% or less.

4. The heat sink according to claim 1 or 2; a semiconductor element in contact with a main surface of the heat sink that intersects with the thickness direction.

5. A method for producing a heat sink made of a graphite-copper composite material including a copper layer and flake graphite particles laminated via the copper layer, comprising: A step of pretreating graphite particles to obtain the flake graphite particles having a median diameter of 50 μm or more and 800 μm or less; a step of mixing the flake graphite particles and copper particles to obtain a molding raw material; a step of sintering a compact obtained by molding the molding raw material under pressure by a multi-axis current sintering method to obtain a sintered body in which the flake graphite particles are stacked in a predetermined direction; and processing the sintered body to obtain the heat sink so that the stacking direction of the flake graphite particles is a direction intersecting the thickness direction of the heat sink.

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