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

Abstract

To provide a graphite-copper composite material with higher thermal conductivity than conventional, a heat sink member using the same, and a method for producing the graphite-copper composite material.SOLUTION: A graphite-copper composite material includes a copper layer and flaky graphite particles laminated via the copper layer and having a copper volume fraction of 3 to 30%, and the thickness of the copper oxide layer at the interface between the copper layer and the flaky graphite particles is up to 100 nm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a graphite-copper composite material, a heat sink member using the same, and a method for producing the graphite-copper composite material. [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 material has been proposed as a composite material that can be obtained at low cost and has a lower coefficient of thermal expansion without impairing the high thermal conductivity of copper (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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-128802 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the recent advances in new technologies such as IoT, AI, and electric vehicles, the demand for heat dissipation is increasing. Specifically, there is a demand for graphite-copper composite materials with high heat dissipation and stable thermal conductivity, exceeding the current 600W / (m·K) to around 700W / (m·K) or even 850W / (m·K). Therefore, an object of the present invention is to provide a graphite-copper composite material having a higher thermal conductivity than conventional materials, a heat sink member using the same, and a method for producing the graphite-copper composite material. [Means for solving the problem]

[0005] As a result of investigations conducted by the present inventors to solve the above problems, they found that by limiting the thickness of the copper oxide layer at the interface between the graphite particle and the copper layer to 100 nm or less, a graphite-copper composite material with higher thermal conductivity than conventional materials can be obtained.

[0006] That is, the present invention provides a graphite-copper composite material comprising a copper layer and flake graphite particles stacked via the copper layer, with a copper volume fraction of 3 to 30%, characterized in that the thickness of a copper oxide layer at the interface between the copper layer and the flake graphite particles is a maximum of 100 nm.

[0007] The present invention also provides a heat sink member using the above-mentioned graphite-copper composite material.

[0008] Furthermore, the present invention provides a method for producing the aforementioned graphite-copper composite material, comprising the steps of: pretreating graphite particles to obtain flake graphite particles; mixing the flake graphite particles with copper particles having an oxygen concentration of 0.40% or less to obtain a forming raw material; and sintering the formed body obtained by forming the forming raw material by a multi-axis electric current sintering method. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a graphite-copper composite material having a higher thermal conductivity than conventional materials, a heat sink member using the same, and a method for producing the graphite-copper composite material. [Brief explanation of the drawings]

[0010] [Figure 1] This is an example of EDS mapping of a laminate cross section of a graphite-copper composite material. [Figure 2] FIG. 1 is a diagram illustrating an example of a method for forming a thin layer of graphite particles. [Figure 3] FIG. 10 is a diagram illustrating another example of a method for forming a thin layer of graphite particles. [Figure 4] FIG. 1 is a schematic diagram illustrating a multi-axis electric current sintering apparatus. [Figure 5] FIG. 2 is a schematic diagram illustrating a cooling substrate. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail.

[0012] <Graphite-copper composite material> The graphite-copper composite material of the present invention (hereinafter also simply referred to as the composite material) is a sintered body obtained using flake graphite particles and copper particles as raw materials. The flake graphite particles are stacked with copper layers interposed between them. Here, "with copper layers interposed" means that the flake graphite particles are connected by adjacent copper layers. In other words, the flake graphite particles in the composite material are electrically continuous. The thickness of the copper layer in the composite material is not particularly limited, but is generally about 3 to 25 μm.

[0013] The volume fraction of copper in the composite material is 3 to 30%. Because the content of graphite, which has high thermal conductivity, is as high as 70 to 97%, the thermal conductivity of the composite material of the present invention is very high. Copper acts as a binder in the composite material. Considering the need to avoid fracture of the composite material during processing, the volume ratio of graphite to copper (graphite:copper) in the composite material is preferably 70:30 to 97:3. To ensure a high thermal conductivity of 780 W / (m·K) or higher and good processability, the volume ratio (graphite:copper) is more preferably 84:16 to 95:5. The volume fraction of copper in the composite material can be adjusted by the blending ratio of the raw materials used during production.

[0014] Furthermore, in the composite material of the present invention, the thickness of the copper oxide layer at the interface between the copper layer and the flake graphite particles is 100 nm or less. Copper oxide refers to copper (II) oxide, copper (I) oxide, etc., and may be generated at the interface between the copper layer and the flake graphite particles due to oxygen in the copper particles used as a manufacturing raw material. The inventors focused on the copper oxide layer in the composite material and made it possible to increase thermal conductivity by limiting the thickness of this copper oxide layer.

[0015] To clearly investigate the interface between the copper layer and the flake graphite particles, a cross-section of the composite was prepared using a cross-section polisher, and carbon deposition was then performed on the cross-section. The thickness of the copper oxide layer at the interface was determined by observing the cross-section with a field emission scanning electron microscope (FE-SEM) and elemental mapping using energy dispersive X-ray analysis (EDS). The laminated cross section is a cross section in which stacked flake graphite particles can be observed, and specifically, it is a plane that includes the direction in which the stacked flake graphite particles are pressed when a molding raw material containing the flake graphite particles is sintered to produce a composite material. When the composite material is cylindrical, the vertical direction of the cylinder corresponds to the stacking direction of the flake graphite particles, so a plate material with a thickness of about 2 mm is cut out in the vertical direction of the cylinder to prepare the laminated cross section.

[0016] The method for determining the thickness of the copper oxide layer is explained below. First, an arbitrary region (approximately 3.2 μm × 4.2 μm) of the laminate cross section of the composite material is designated as the observation region. The observation region is observed using FE-SEM, and an FE-SEM image is taken at an accelerating voltage of 3 kV and an imaging magnification of 30,000x. Cu-mapping and O-mapping are obtained by EDS in the same field of view as this FE-SEM image. Furthermore, by overlaying these two mapping data, the copper oxide layer at the interface between the copper layer and the flake graphite particles can be confirmed.

[0017] An example of the obtained EDS mapping is shown in Figure 1. As shown in Figure 1, a copper oxide layer 16 with a maximum thickness of approximately 100 nm is observed at a portion of the interface between the flake graphite particles 12 and the copper layer 14. Ten or more observation areas are similarly observed to confirm the thickness of the copper oxide layer 16 at the interface. In the composite material of the present invention, a copper oxide layer 16 with a thickness of approximately 50 to 90 nm is observed at some portions of the interface between the copper layer 12 and the flake graphite particles 14, but no copper oxide layer exceeding 100 nm is observed. The thickness of the copper oxide layer 16 is preferably 90 nm or less, and more preferably 50 nm or less.

[0018] The composite material of the present invention preferably has a thermal conductivity of 850 W / (m·K) or more. The thermal conductivity is a value measured in a direction perpendicular to the direction in which the flake graphite particles are stacked. For use in high-power electronic components, the thermal conductivity is more preferably 880 W / (m·K) or more. The thermal conductivity is measured by cutting a sample of specified dimensions (outer diameter 10 mm x thickness 2.5 mm) from the center of the composite material using a NETZSCH LFA447 in accordance with the laser flash method (JIS H 7801:2005), and the average thermal conductivity of five samples cut from the composite material is used.

[0019] <Manufacturing method> The composite material of the present invention can be produced by pretreating graphite particles to obtain flake graphite particles, mixing them with predetermined copper particles to form a molding raw material, molding this, and sintering it under predetermined conditions. Each step is described below. (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 2000 to 10 μm and a thickness of about 200 to 20 μm. Examples of graphite that can be used include +3299 (manufactured by Ito Graphite Industries Co., Ltd.).

[0020] For example, as shown in FIG. 2, 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 length of the long side of the resulting scaly graphite particles 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 is preferably one that 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.

[0021] Sieve 21 removes particles that have internal cavities due to shear force or are brittle and easily crumble. As a result, the thickness of the resulting flake graphite particles is reduced and the density is increased. Furthermore, impurities in the graphite particles are removed, leading to improved purity. Note that flake 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.

[0022] For the pre-treatment of graphite particles, two grindstones 30a, 30b can also be used, as shown in FIG. 3. The grindstone 30b is a rotatable rotary grindstone. The grindstones 30a, 30b have metal plates 31a, 31b, respectively, with abrasive grains 33a, 33b, such as diamond, provided on opposing surfaces. The abrasive grains 33a, 33b are fixed by bonding metal members 32a, 32b, such as plated metal members, and the graphite particles 23 to be treated are placed between the abrasive grains 33a, 33b. When the graphite particles 23 are pre-treated using the grindstones 30a, 30b, relatively small and thin flake graphite particles can be efficiently obtained.

[0023] The above-described pretreatment produces flake graphite particles with reduced thickness. The flake graphite particles have a structure in which multiple graphite flakes are stacked on top of each other. The thinner the flake 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 flake graphite particles can be adjusted by the type of graphite particles used, the pretreatment conditions, and other factors.

[0024] To obtain a composite material with higher thermal conductivity and good processability, the thickness of the flake graphite particles is preferably 30 μm or less. This pretreatment fixes the shape of the flake graphite particles. For example, when a sieve 21 with a mesh size of 53 μm is used, flake graphite particles with a long side of 60 μm or more are obtained.

[0025] (Preparation of copper particles) The copper particles used have an oxygen concentration of 0.40% or less. Conventionally, copper particles used in the manufacture of composite materials have an oxygen concentration of approximately 0.42%. The oxygen concentration in the copper particles can be confirmed by high-frequency combustion-infrared absorption. Since the thermal conductivity of the composite material improves as the oxygen concentration decreases, the oxygen concentration in the copper particles is preferably 0.35% or less, and more preferably 0.25% or less.

[0026] The copper particles are not particularly limited in other conditions as long as the oxygen concentration is 0.40% or less. For example, the volume-based median diameter of the copper particles can be approximately 1.5 μm or less. When small copper particles with a median diameter of 1.5 μm or less are used, a composite material with stable thermal conductivity and processability can be obtained. Copper particles with a median diameter of 1.5 μm or less can be produced by any method. For example, copper particles of the desired particle size can be obtained by chemical reduction or physical production methods.

[0027] (mixture) The flake graphite particles obtained by pretreatment and predetermined copper particles are blended in a predetermined ratio and mixed to obtain a molding raw material. The blending may be performed by either dry blending or wet blending. The blending ratio of the raw materials is selected so that the volume ratio of graphite to copper (graphite:copper) in the composite material is 70:30 to 97:3. From the viewpoint of thermal conductivity and processability, the volume ratio (graphite:copper) is preferably selected so that it is 84:16 to 95:5.

[0028] (sintering) First, a small amount (approximately 40 g or less) of molding raw material is filled into a predetermined mold and compressed at a pressure of approximately 3 to 15 MPa using, for example, a hydraulic hand press. The mold can be, for example, a SUS mold with a diameter of 30 mm. By repeating the process of filling with the molding raw material and compressing, a molded body of the desired size is produced. The obtained molded body is sintered by multi-axis current sintering to obtain a sintered body that will become the composite material of the present invention.

[0029] Here, an outline of a multi-axis electric current sintering apparatus will be described with reference to Fig. 4. In the multi-axis electric current sintering apparatus 40 shown in Fig. 4, 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.

[0030] In the multi-axis electric current sintering apparatus 40, the pressure application axes 45a and 45b and the heating axes 47a, 47b, 49a, and 49b are separate. Specifically, the pressure application axes 45a and 45b are in the z-axis direction, the heating axes (A) 47a and 47b are in the x-axis direction, and the heating axes (B) 49a and 49b are in the y-axis direction. This makes it possible to control pressure application and heating independently, thereby achieving a uniform temperature distribution in the radial direction of the compact.

[0031] 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 about 650 to 750°C, preferably about 670 to 730°C.

[0032] Thereafter, the heating shafts (B) 49a and 49b are switched to apply pressure of 30 to 100 MPa in the directions of arrows z1 and z2 by the vertical pressure shafts 45a and 45b, while heating to about 930 to 980° C., preferably about 940 to 970° C. The pressure at this time is preferably about 30 to 100 MPa, more preferably about 40 to 70 MPa.

[0033] The conditions for pressurization and heating during sintering are not limited to those described above and can be set as appropriate. For example, after applying a pressure of 10 MPa in the directions of arrows z1 and z2 using vertical pressure shafts 45a and 45b, electricity is applied to heating shafts (A) 47a and 47b to heat the mixture to approximately 650 to 750°C, preferably approximately 670 to 730°C. Then, heating shafts (B) 49a and 49b are switched to apply a pressure of 30 to 100 MPa using vertical pressure shafts 45a and 45b in the directions of arrows z1 and z2, while heating the mixture to approximately 930 to 980°C, preferably approximately 940 to 970°C. The pressure during this process is preferably approximately 30 to 100 MPa, more preferably approximately 40 to 70 MPa.

[0034] Alternatively, electricity is applied to heating shafts (A) 47a and 47b to heat the material to about 650 to 750°C, preferably about 670 to 730°C. Thereafter, heating shafts (B) 49a and 49b are switched to heat the material to about 930 to 980°C, preferably about 940 to 970°C, while applying pressure of 30 to 100 MPa in the directions of arrows z1 and z2 using vertical pressure shafts 45a and 45b. The pressure at this time is preferably about 30 to 100 MPa, more preferably about 40 to 70 MPa.

[0035] Regardless of the conditions for pressure application and temperature increase, multi-axis current sintering results in uniform temperature distribution, making it possible to produce composite materials of consistent quality. Furthermore, because copper particles with an oxygen concentration of 0.40% or less are used together with the flake graphite particles as raw materials, the composite material of the present invention has a copper oxide layer at the interface between the copper layer and the flake graphite particles that is 100 nm or less in thickness. By having a copper oxide layer thickness of 100 nm or less, the composite material of the present invention has an increased thermal conductivity without impairing any of the conventional properties.

[0036] The composite material of the present invention can be suitably used as a heat sink (heat sink member). Heat sink members are used in a wide range of fields, including wireless communication, electronic control, and optical communication. Specific applications include power semiconductor modules, optical communication modules, projectors, Peltier coolers, water-cooled coolers, and LED heat dissipation fans.

[0037] FIG. 5 shows an example of a cooling substrate using a heat sink. Cooling substrate 55 includes heat sink 50 and cooling layer 54. Heat sink 50 has an electrical insulating layer 52 and a wiring layer 51 laminated in this order on a stress buffer layer 53. A heat-generating element such as a semiconductor element is mounted on mounting surface 51a on the upper surface of wiring layer 51. The composite material of the present invention can be used for at least one of stress buffer layer 53 and wiring layer 51.

[0038] Heat generated in a heat-generating element mounted on mounting surface 51a of heat sink 50 is conducted in this order to wiring layer 51, electrical insulating layer 52, stress buffer layer 53, and cooling layer 54, and is dissipated from cooling layer 54. The composite material of the present invention has higher thermal conductivity than conventional materials, and is therefore able to cool heat-generating elements more efficiently than conventional materials, thereby lowering their temperature. [Example]

[0039] Next, the present invention will be specifically explained by way of examples, but the present invention is not limited to the following examples.

[0040] Example 1 Commercially available raw graphite was pretreated using the method described with reference to Figure 3. The upper and lower grinding wheels were equipped with diamond abrasive grains, and 5 g of graphite particles were inserted between them along with 2 mL of water. The grinding wheels were rotated at 10 Hz, and the graphite particles were pretreated for approximately 20 seconds under a pressure of 0.5 MPa.

[0041] The graphite particles after the treatment were classified using a sieve with 500 μm openings, and the graphite particles remaining on the sieve were removed and dried to obtain the raw material flake graphite particles.On the other hand, commercially available copper particles with an oxygen concentration of 0.22% were prepared as copper particles.

[0042] A molding raw material was obtained by blending 11.0 g of pretreated and dried flake graphite particles and 19.0 g of copper particles so that the volume fraction of copper after sintering would be 30%. These powders were placed in a 250 mL plastic bottle and mixed using a ball mill. 3 g of the molding raw material was placed in a 30 mm diameter SUS mold and compressed at a pressure of 5 MPa using a hydraulic press. The process of adding the molding raw material and compressing the powder was repeated more than 10 times, and the compact was then removed from the SUS mold.

[0043] The removed compact was placed in a cylindrical carbon mold and sintered by multi-axis electric current sintering. A carbon mold 44 was placed in a vacuum chamber 42 of a multi-axis electric current sintering apparatus 40 shown in Figure 4 and fixed with two diagonal heating shafts (A) 47a and 47b and two pressure shafts (B) 45a and 45b. The pressure inside the vacuum vessel 42 was reduced to 5 Pa using a rotary pump, and the temperature was raised by increasing the output of the power supply while pressurizing the vessel 42 to 10 MPa in the directions of arrows z1 and z2 using the vertical pressure shafts 45a and 45b. After heating the vessel 42 to 700°C using heating shafts (A) 47a and 47b, the vessel 42 was heated to 950°C using heating shafts (B) 49a and 49b while pressurizing the vessel 42 to 50 MPa in the directions of arrows z1 and z2 using the vertical pressure shafts 45a and 45b.

[0044] After reaching 950°C, the temperature was maintained for 30 seconds, and the power output was reduced to cool the device. After cooling, the carbon mold 44 was removed from the device, and a cylindrical sintered body was obtained from the mold. The same procedure was repeated five times to prepare five sintered bodies, and the composite material of Example 1 was obtained.

[0045] Example 2 A composite material of Example 2 was produced in the same manner as Example 1, except that the molding raw materials were changed so that the volume fraction of copper after sintering would be 16%.

[0046] Example 3 A composite material of Example 3 was produced in the same manner as Example 1, except that the molding raw material was changed so that the volume fraction of copper after sintering was 5%.

[0047] (Comparative Example 1) A composite material of Comparative Example 1 was produced in the same manner as in Example 1, except that copper particles with an oxygen concentration of 0.42% were used. The copper particles used here correspond to those conventionally used in the production of composite materials.

[0048] (Comparative Example 2) A composite material of Comparative Example 2 was produced in the same manner as in Example 2, except that copper particles with an oxygen concentration of 0.42% were used.

[0049] (Comparative Example 3) A composite material of Comparative Example 3 was produced in the same manner as in Example 3, except that copper particles with an oxygen concentration of 0.42% were used.

[0050] For the composite materials of the examples and comparative examples, the thickness of the copper oxide layer at the interface between the copper layer and the flake graphite particles was measured, and the thermal conductivity was evaluated. Measurements were made for five composite materials in each case, and the average was calculated.

[0051] <Thickness of copper oxide layer> As described above, the thickness of the copper oxide layer at the interface between the copper layer and the flake graphite particles in the composite material was determined.

[0052] <Thermal conductivity> To prepare samples for measuring thermal conductivity, plates were first cut lengthwise from the center of cylinders of the composite materials of the Examples and Comparative Examples. The lengthwise direction of the cylinder was the direction in which the flake graphite particles were stacked. These plates were then processed to obtain samples for measuring thermal conductivity, each with an outer diameter of 10 mm and a thickness of 2.5 mm. The thickness direction of the sample was perpendicular to the direction in which the flake graphite particles were stacked (the pressure direction). The thermal conductivity of the sample was measured in this thickness direction in accordance with the "Method for measuring thermal diffusivity of metals by the laser flash method (JIS H 7801:2005)."

[0053] The results obtained are summarized in Table 1 below, along with the volume fraction of copper and the oxygen concentration in the copper particles used as raw material. [Table 1]

[0054] As shown in Table 1 above, composite materials produced using copper particles with an oxygen concentration of 0.22% have a copper oxide layer thickness of 85 nm or less at the interface between the copper layer and the flake graphite particles (Examples 1 to 3). It has been shown that by controlling the oxygen concentration in the copper particles to less than 0.40%, the thickness of the copper oxide layer can be controlled to 100 nm or less. The composite materials of these examples have a thermal conductivity of 780 W / mK or more, which is higher than conventional materials.

[0055] In contrast, in the composite materials (Comparative Examples 1 to 3) using copper particles with an oxygen concentration of 0.40%, the thickness of the copper oxide layer at the interface between the copper layer and the flake graphite particles exceeds 100 nm, reaching a maximum of 148 nm.Compared to the composite materials of the Examples containing copper at the same volume fraction, it is clear that the composite materials of the Comparative Examples have inferior thermal conductivity regardless of the volume fraction.

[0056] Since more than 70% of the volume of a composite material is graphite, it is thought that the thermal conductivity of the composite material depends on the thermal conductivity of the graphite. Although it is unlikely that the oxygen concentration in the copper layer affects the thermal conductivity, it is presumed that the interface between the copper layer and the flake graphite particles has a significant effect on the thermal resistance of the composite material. From these results, it was confirmed that by reducing the thickness of the copper oxide layer at the interface between the copper layer and the flake graphite particles, rather than the oxygen content of the entire copper layer in the composite material, it is possible to obtain a lead-copper composite material with reduced thermal resistance and higher thermal conductivity than conventional materials. [Explanation of symbols]

[0057] 12...Graphite particles 14...Copper layer 16...Copper oxide layer 21...sieve 22...grindstone 23...graphite particles 30a, 30b...grindstone 31a, 31b... Metal plates 32a, 32b... Metal members for joining 33a, 33b... Abrasive grains 40...Multi-axis current sintering device 42...Vacuum container 44...Carbon mold 45a, 45b...pressure shaft 47a, 47b...heating shaft 49a, 49b...heating shaft 50...heat sink 51...wiring layer 52...electrical insulating layer 53...stress buffer layer 54...cooling layer 55...Cooling substrate

Claims

1. A graphite-copper composite material comprising a copper layer and flake graphite particles laminated via the copper layer, the volume fraction of copper being 3 to 30%, A graphite-copper composite material, characterized in that the thickness of a copper oxide layer at the interface between the copper layer and the flake graphite particles is 100 nm at most.

2. 2. The graphite-copper composite material according to claim 1, wherein the thermal conductivity in a direction perpendicular to the direction in which the flake graphite particles are stacked is 850 W / (m·K) or more.

3. A heat sink material using the graphite-copper composite material according to claim 1 or 2.

4. A method for producing the graphite-copper composite material according to claim 1, comprising: A step of pretreating graphite particles to obtain flake graphite particles; a step of mixing the flake graphite particles with copper particles having an oxygen concentration of 0.40% or less to obtain a forming raw material; a step of sintering the molded body obtained by molding the molding raw material by a multi-axis electric current sintering method; A manufacturing method comprising:

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