WO2021100595A1

WO2021100595A1 - Copper powder and method for producing the same

Info

Publication number: WO2021100595A1
Application number: PCT/JP2020/042217
Authority: WO
Inventors: 諒太小林; 貢吉田
Original assignee: 東邦チタニウム株式会社
Priority date: 2019-11-22
Filing date: 2020-11-12
Publication date: 2021-05-27
Also published as: KR20220070003A; JP6704083B1; TWI763135B; TW202120225A; CN114786839B; CN114786839A; JP2021080549A

Abstract

This copper powder is configured such that the average particle diameter D₅₀ is 100-500 nm, the sintering start temperature is 450°C or higher, and the peak degassing temperature is 150-300°C. The copper powder may be configured such that the ratio (W₁/W₀) of the total amount of gas (W₁), which is desorbed at a temperature range between 600°C and 950°C, to the total amount of gas (W₀), which is desorbed at a temperature range of 60-950°C, is 0.6 wt% or less. The ratio D/D₅₀ of the average crystallite diameter (D) of the copper powder to the average particle diameter (D₅₀) may be 0.10 to 0.50.

Description

Copper powder and its manufacturing method

One of the embodiments of the present invention relates to copper powder and a method for producing copper powder.

Metal powder, which is an aggregate of fine metal particles, and paste containing metal powder are various electrons such as wiring and terminals of low-temperature simultaneous firing ceramics (LTCC) substrate, internal electrodes and external electrodes of multilayer ceramic capacitors (MLCC). It is widely used as a raw material for manufacturing parts. In particular, copper powder has been widely used in the past because of the high conductivity of copper, which enables thinning of the internal electrode of MLCC, miniaturization of the external electrode, and significant improvement of frequency characteristics. It is expected as a material to replace nickel powder and silver powder (see Patent Documents 1 to 5).

JP-A-2015-36439 International Publication No. 2015/137015 JP-A-2018-076597 Japanese Unexamined Patent Publication No. 2016-108649 Japanese Unexamined Patent Publication No. 2004-211108

One of the objects of the embodiment of the present invention is to provide a copper powder and a method for producing the copper powder. For example, one of the embodiments of the present invention is to provide a copper powder having a high sintering start temperature and controlled degassing behavior during sintering, and a method for producing the same.

One of the embodiments according to the present invention is copper powder. This copper powder has an average particle size D ₅₀ of 100 nm or more and 500 nm or less, a sintering start temperature of 450 ° C. or more, and a degassing peak temperature of 150 ° C. or more and 300 ° C. or less.

One of the embodiments according to the present invention is a method for producing copper powder. In this production method, copper chloride gas is produced by the reaction of metallic copper and a chlorine-containing gas, primary powder containing copper is produced by the reaction of copper chloride gas and a reducing gas, and the primary powder is produced. Includes treatment with nitrogen-containing heteroaromatic compounds.

The copper powder according to one of the embodiments according to the present invention not only exhibits a high firing start temperature, but also has a small amount of gas desorbed during sintering. For this reason, this copper powder can provide a copper film whose structure is clearly defined by sintering, making various functional elements such as MLCCs thinner and smaller, and wiring and terminals for electronic components. It can contribute to miniaturization and the like.

A flow for producing copper powder according to one of the embodiments of the present invention.

Hereinafter, each embodiment of the present invention will be described with reference to drawings and the like. The present invention can be carried out in various aspects without departing from the gist thereof, and is not construed as being limited to the description contents of the embodiments and examples illustrated below. The drawings may schematically represent the width, thickness, shape, etc. of each part as compared with the actual embodiment in order to clarify the explanation, but this is merely an example and the interpretation of the present disclosure is limited. It's not something to do.

1. 1. Method for Producing Copper Powder One of the embodiments of the present invention is a copper powder containing a plurality of copper particles. An example of the method for producing the present copper powder will be described with reference to the flow shown in FIG. Here, a method for producing copper powder using the so-called vapor phase growth method will be described, but the method for producing copper powder is not limited to the vapor phase growth method, and the copper powder is produced by using a wet method, a plasma method, or the like. It may be manufactured.

1-1. Production of copper chloride First, copper chloride gas is produced by reacting metallic copper with chlorine gas. This method is not only cost-effective in that metallic copper, which is cheaper than copper chloride, can be used, but also can stabilize the supply amount of copper chloride gas. As a specific method for producing copper chloride gas, copper chloride gas is produced by reacting metallic copper with chlorine gas at a melting point or lower (for example, 800 ° C. or higher and 1000 ° C. or lower). The chlorine gas may be a gas containing substantially only chlorine, or may be a mixed gas of chlorine containing an inert gas for dilution and an inert gas for dilution. By using the mixed gas, it is possible to easily and precisely control the amount of chlorine that reacts with metallic copper.

1-2. Reduction of Copper Chloride The produced copper chloride gas is reacted with the reducing gas to produce copper powder. As the reducing gas, for example, hydrogen, hydrazine, ammonia, methane and the like can be used. The reducing gas can be used in a stoichiometric amount or more with respect to the copper chloride gas. For example, when the copper chloride gas is entirely composed of monovalent copper chloride and the reducing gas is hydrogen, the amount of the reducing gas introduced is 50 mol% or more and 10000 mol% or less, 500 mol% with respect to the copper chloride gas. It can be 10000 mol% or more, or 1000 mol% or more and 10000 mol% or less. By this reaction, copper chloride is reduced to copper, and the copper element grows into copper particles to become copper powder as an aggregate. The copper powder produced by this reduction reaction is hereinafter referred to as a primary powder.

1-3. Reduction of Chlorine Component The chlorine component may be reduced by treating the primary powder obtained by the above production method with an aqueous solution or suspension of a base.

1-4. Reduction of oxygen component After treating the primary powder obtained by the above production method with a solution or suspension containing ascorbic acid, hydrazine, citric acid, etc. as a cleaning solution in order to reduce the oxygen component. , It may be washed with water, filtered and dried.

1-5. Surface treatment A predetermined surface treatment may be applied to the primary powder obtained by the above production method. As the surface treatment agent, benzotriazole and its derivative, triazole and its derivative, thiazole and its derivative, benzothiazole and its derivative, imidazole and its derivative, and nitrogen-containing heteroaromatic compounds such as benzimidazole and its derivative are used. can do.

1-6. Other Treatments The copper powder obtained by the above production method may be subjected to treatments such as drying, classification, crushing, and sieving. The classification may be dry classification or wet classification, and in the dry classification, any method such as air flow classification, gravitational field classification, inertial force field classification, and centrifugal force field classification can be adopted. Similarly, in wet classification, methods such as gravitational field classification and centrifugal force field classification can be adopted. Crushing can be performed using, for example, a jet mill. Sieve separation can be performed by vibrating a sieve having a desired mesh size and passing copper powder through the sieve. By performing classification, crushing, and sieving, the particle size distribution of copper powder can be made smaller.

2. Characteristics of copper powder 2-1. The copper powder produced by the steps having a particle size or larger has a small average particle size and a narrow distribution due to the production of the primary powder by the vapor phase growth method. Here, the average particle size of the copper powder means the particle size when the cumulative frequency in the volume-based particle size histogram of the copper powder becomes 50%. The volume-based particle size of the copper powder is a particle size weighted by the volume of each particle contained in the copper powder. As expressed by the following formula, the total volume of particles having a particle size di (i is a natural number from 1 to k, i ≦ k) is divided by the total volume of all particles contained in the powder body. The frequency F of the particles having the particle size di is obtained. The particle size when the frequency F is accumulated and reaches 50% is the median diameter D ₅₀ . Here, the average particle size is also expressed as _{D 50.}

Here, Vi is the volume of copper particles having a particle size di, and ni is the number of copper particles having a particle size di.

The method of calculating the volume Vi and the particle size di will be described below. In a micrograph of copper powder observed with an optical microscope or an electron microscope, copper particles having confirmed contours (for example, 100 to 10,000, typically 500) are visually observed. Next, the particle size of the copper particles is calculated as the diameter of an assumed circle having the same area as the surface area from the visually observed surface area Si of the copper particles. Specifically, the particle size di is calculated by the following formula. ..
Si = π (di) ²

Next, the volume Vi of the copper particles is calculated from the calculated particle diameter di by the following formula.
Vi = 4π (di / 2) 3/3

_{The average particle size D 50} of the copper powder, which is one of the embodiments of the present invention, is specifically 100 nm or more and 500 nm or less, 100 nm or more and 300 nm or less, or 100 nm or more and 200 nm or less. By sintering this copper powder that satisfies this range, a metal film with a small thickness can be provided, which contributes to, for example, thinning of MLCC electrodes and miniaturization of wiring and terminals of other electronic components. be able to. In addition, agglomeration of copper particles can be suppressed, which facilitates the handling of copper powder. The average particle size D ₅₀ of copper powder is the temperature at the time of chloride of metallic copper, the flow rate of chlorine gas, the ratio of chlorine gas and diluted gas, the temperature at the time of reduction of copper chloride, and the flow rate ratio of copper chloride gas and reducing gas. By appropriately setting such conditions, control can be performed within the above-mentioned range.

2-2. Average crystallite diameter One of the features of the copper powder, which is one of the embodiments of the present invention, is that the average crystallite diameter D is large due to the production of the primary powder by the vapor phase growth method. .. Here, the crystallite is an index showing the length of a region that can be regarded as a single crystal. Each copper particle has a single crystallite or multiple crystallites. The average crystallite diameter D includes various parameters (wavelength λ of X-rays used, half-value width β of spread of diffracted X-rays, Bragg angle θ) obtained by measuring X-ray diffraction with respect to copper powder. It can be obtained by substituting into the Scherrer's equation (Equation 1) shown. Here, K is a Scheller constant. For example, the half width of the diffraction peaks of the (111) plane, (200) plane, and (220) plane of the copper crystal can be obtained using an X-ray diffractometer, and the average crystallite diameter D can be calculated according to the following equation 1. .. The average crystallite diameter D is a parameter that reflects the crystallite size of each copper particle.
D = (K × λ) / (β × cos θ) ・・・ Equation 1

Due to the small average particle size D ₅₀ and larger average crystallite diameter D, embodiment copper powder average crystallite diameter The average ratio D / D ₅₀ for the particle diameter D ₅₀ of D which is one of the present invention, It can be 0.10 or more and 0.50 or less. Due to such a large D / D ₅₀ , this copper powder exhibits a high sintering start temperature. As one of the methods for producing copper powder, there is a method (wet method) in which a solution or suspension of a copper salt such as copper chloride, copper hydroxide, copper sulfate, or copper nitrate is treated with a reducing agent. .. However, it is difficult to obtain such a large D / D _{50 by the wet method.} The reason for this is that in the vapor phase growth method, copper particles grow at a high temperature, and the growth of the grown copper particles can be stopped by rapidly cooling the grown copper particles with nitrogen gas or the like.

2-3. Average circularity Copper particles of copper powder are close to a true sphere in shape. More specifically, the average circularity of the copper powder, that is, the average circularity C of the copper particles is, for example, 0.85 or more and 0.95 or less, or 0.87 or more and 0.95 or less. The average circularity is one of the parameters representing the shape of each particle contained in the powder, and the image obtained by observing the powder under a microscope is analyzed, and the circularity C is obtained for a plurality of (for example, 500) particles. Is calculated and averaged. Circularity C is expressed by the following equation. Here, A is the perimeter of the projection plane of each particle in the microscope image, and B is the perimeter of a circle having an area equal to the area of the projection plane. Due to the high average circularity, the copper powder exhibits high filling properties. Therefore, by using this copper powder, it is possible to form high-density and low-resistance electrodes and wiring.

2-4. Degassing behavior The copper powder, which is one of the embodiments of the present invention, has a highly controlled degassing behavior during sintering, and as a result, the structure is clearly defined by sintering as described later. It is possible to give a copper film. The method for evaluating the degassing behavior is not limited, but a method called a throughput method or a conductance method can be used. In this method, the copper powder is heated in a depressurized chamber at a constant temperature rise rate in a predetermined temperature range, and the amount of desorbed gas is estimated based on the pressure change in the chamber. For example, using a heated desorption gas analysis (TDS) device, a stage on which copper powder is placed under reduced pressure is placed at a constant temperature rising rate (for example, 30 ° C./min) in a predetermined temperature range (for example, 60 ° C. to 950 ° C.). Heat with and monitor pressure changes. The desorbed gas can be analyzed by a mass spectrometer, whereby the desorbed gas can be identified and its composition ratio can be determined. Examples of the desorbed gas include water, hydrogen, carbon dioxide, carbon monoxide, nitrogen, hydrogen cyanide and the like. Since nitrogen and carbon monoxide have the same molecular weight, they are evaluated as a mixed gas.

Copper powder, which is one of the embodiments of the present invention, shows a degassing peak at a relatively low temperature. Here, the degassing peak temperature is a temperature at which a peak is observed in the plot of the amount of degassed gas with respect to the temperature or the heating time when the copper powder is heated at a constant heating rate. Specifically, the degassing peak of the copper powder when heated from 60 ° C. to 950 ° C. at a heating rate of 30 ° C./min is observed at 150 ° C. or higher and 300 ° C. or lower, or 150 ° C. or higher and 260 ° C. or lower. To. Further, based on the total amount of gas desorbed by heating in the temperature range of 60 ° C. or higher and 950 ° C. or lower (W ₀ ), the ratio (W ₁ ) of the amount of gas desorbed at 600 ° C. or higher and 950 ° C. or lower (W 1). ₁ / W ₀ ) is 0.6% by weight or less, preferably 0.4% by weight or less, and more preferably 0.3% by weight or less. W ₁ / W ₀ may be 0.1% by weight or more. These characteristics show that in copper powder, which is one of the embodiments of the present invention, most of the gas is desorbed at a low temperature (150 ° C or higher and 300 ° C or lower), and sintering proceeds (for example, 600 ° C or higher). ) Means that degassing is significantly suppressed.

2-5. Carbon Concentration and Sintering Start Temperature As described above, the copper powder, which is one of the embodiments of the present invention, is produced by surface-stabilizing the primary powder obtained by the vapor phase growth method. Therefore, the copper particles contain a trace amount of carbon derived from the surface treatment agent on the surface thereof. The carbon concentration in the copper powder is, for example, 0.04% by weight or more and 1.00% by weight or less, 0.04% by weight or more and 0.90% by weight or less, or 0.04% by weight or more and 0.80% by weight or less. is there.

The carbon concentration in the copper powder can be measured by using, for example, the combustion / infrared absorption method. In this case, the carbon concentration may be measured by a method compliant with JIS H1617, JIS Z2615, and ASTM E1941. Specifically, carbon dioxide is generated from carbon in the copper powder by burning the copper powder in a combustion furnace under an oxygen stream. The generated carbon dioxide is introduced into an infrared analyzer using oxygen gas, and its absorption is measured with a detector to determine the concentration of carbon dioxide. The carbon concentration in the copper powder is quantified from this carbon dioxide concentration.

As shown in the examples, the copper powder of the present embodiment contains a small amount of carbon on the surface of the copper particles, so that the sintering start temperature of the copper powder can be significantly improved. Further, by controlling the residual carbon concentration, it is possible to control the sintering start temperature. Specifically, it is possible to provide a copper powder having a sintering start temperature of 450 ° C. or higher or 740 ° C. or higher. The method for evaluating the sintering start temperature is not limited, but for example, the shrinkage rate of pellets containing copper powder is measured by thermomechanical analysis, and the temperature at which the shrinkage rate reaches a constant value (for example, 5%) is determined. Can be adopted.

2-6. Impurity Concentration As described above, the method for producing copper powder, which is one of the embodiments of the present invention, includes a surface stabilization treatment of primary particles, and further includes a treatment for reducing chlorine components and oxygen components. it can. This manufacturing method does not need to include a step that causes contamination of transition metals such as aluminum, titanium, zirconium, and cerium, or impurities such as silicon. Therefore, the copper powder is substantially free of these impurities that can adversely affect the electrical properties of the copper film formed by sintering. The concentration of the above-mentioned element is preferably less than the detection limit value in the elemental analysis measurement using, for example, inductively coupled plasma (ICP) emission spectroscopy. The term "less than the detection limit" in the present invention means that aluminum is less than 1 ppm, silicon is less than 1 ppm, titanium is less than 10 ppm, and zirconium is less than 1 ppm.

The high sintering start temperature of the copper powder according to the present embodiment improves the reliability and yield of the electronic components when the copper powder is used as a material for electrodes, other wirings, and terminals of electronic components such as MLCCs. Contributes greatly to. Such characteristics are particularly remarkable when used as an electrode material for MLCCs. The reason for this is as follows. As the MLCC becomes smaller, the electrodes are required to be thinner, and for this purpose, reducing the average particle size of the copper powder is one of the effective methods. However, as the average particle size of the copper powder decreases, the specific surface area increases, so that the sintering start temperature decreases. MLCC is produced by alternately applying a dispersion containing a dielectric and a dispersion containing a copper powder and then heating the mixture to sinter the copper powder and the dielectric. The sintering start temperature of the copper powder The decrease causes an increase in the difference in the sintering start temperature between the copper powder and the dielectric, and as a result, a large difference occurs in the sintering start time between the copper powder and the dielectric. Therefore, the copper powder shrinks due to sintering before the dielectric starts sintering, and a gap is generated between the electrode formed by sintering the copper powder and the dielectric, which is caused by this gap. Peeling occurs between the electrode and the dielectric film. On the other hand, the copper powder, which is one of the embodiments of the present invention, _{has a high sintering start temperature even though it has a small average particle diameter D 50} , so that the difference between the sintering start temperature and the dielectric is small. As a result, peeling of the electrode during sintering can be suppressed. Therefore, by using this copper powder, it is possible to provide a highly reliable MLCC with a high yield.

Further, as described above, the copper powder according to the present embodiment gives a degassing peak at a relatively low temperature, and the amount of gas degassed at 600 ° C. or higher and 950 ° C. or lower is relatively small. Therefore, the degassing peak of the present copper powder is observed at a temperature lower than the sintering start temperature. This means that most of the gas is desorbed before the start of sintering and the process of forming the copper film, and almost no degassing occurs near the sintering start temperature or after sintering. .. Therefore, the generation and deformation of voids due to degassing are prevented, and the shape change before and after sintering is small. Therefore, it is possible to provide a copper film having a controlled structure, that is, a copper film having a well-defined structure.

As a method for improving the sintering start temperature of copper powder, for example, a method of pulverizing molten copper containing silicon or carbon by an atomizing method, aluminum, titanium, zirconium, cerium, tin, or silicon is applied to the surface of copper particles. A method of forming a film containing the mixture, a method of forming a film of silicon oxide on the surface of copper particles, and the like are known. However, since these elements are insulating or have higher electrical resistance than copper, they adversely affect the electrical properties of the copper film obtained by sintering copper powder. Further, if the copper powder is formed so that a relatively large amount of these elements are contained inside or on the surface of the copper particles, a large amount of gas is desorbed at the time of sintering, so that voids are generated due to degassing and the copper film is formed. It is difficult to prevent deformation.

On the other hand, the copper powder, which is one of the embodiments of the present invention, contains a trace amount of carbon derived from the surface treatment agent, but the above-mentioned contents of the transition metal and silicon are negligible. Therefore, the copper film obtained by sintering exhibits high conductivity. This means that this copper powder can be used as an effective material for thinning and miniaturizing various functional elements such as MLCCs, and for wiring and terminal miniaturization of electronic components.

Hereinafter, examples according to the embodiment of the present invention will be described. In this example, the results of producing copper powder according to the above-mentioned method and evaluating its characteristics will be described.

1. 1. Example 1
Spherical copper was installed in the chlorination furnace, and the chlorination furnace was heated to 900 ° C. At this temperature, a mixed gas of chlorine gas and nitrogen gas was supplied from chlorine introduction pipes (hereinafter referred to as upper introduction pipe and lower introduction pipe, respectively) connected to the upper part and the lower part of the chloride furnace. The volume ratio of the chlorine gas and nitrogen gas in the mixed gas introduced through the upper inlet (V _Cl2: V _N2) is 29:61, the chlorine gas and nitrogen gas in the mixed gas introduced through the lower inlet pipe volume ratio (V _Cl2: V _N2) was 2:98. _{The volume ratio (V u} : V _l ) of the mixed gas introduced through the upper introduction pipe and the mixed gas introduced through the lower introduction pipe was 1: 0.17.

Copper chloride gas generated by the reaction of metallic copper and chlorine is led to a reduction furnace heated to 1150 ° C., and hydrogen is added so that hydrogen gas and nitrogen gas are 4600 mol% and 24600 mol%, respectively, with respect to the copper chloride gas. Gas and nitrogen gas were introduced into the reduction furnace. The copper powder obtained by the reaction of copper chloride gas and hydrogen gas was cooled with nitrogen gas to obtain a primary copper powder.

Subsequently, the obtained primary powder was treated to reduce chlorine and oxygen components. Specifically, the oxygen component was reduced by using a 40% by weight sodium hydroxide aqueous solution and a 10% by weight ascorbic acid aqueous solution with respect to the primary powder.

After that, surface stabilization treatment was performed. Specifically, an aqueous solution containing 1.0% by weight of benzotriazole as a surface treatment agent was added to the primary powder treated with an aqueous ascorbic acid solution, and the obtained mixture was stirred for 30 minutes. After the stirring was completed, the mixture was allowed to stand, the supernatant was removed, and the mixture was dried to obtain the copper powder of Example 1.

2. Reference example 1
The copper powder was prepared under the same conditions as in Example 1 except that the concentration of the aqueous solution of benzotriazole when the copper powder was surface-treated was 0.33% by weight.

3. 3. Reference example 2
The copper powder was prepared under the same conditions as in Example 1 except that the concentration of the aqueous solution of benzotriazole when the copper powder was surface-treated was 0.05% by weight.

4. Comparative Example The copper powder of Comparative Example 1 was prepared by using the wet reduction method disclosed in Patent Document 3.

5. Evaluation Example 1, Reference Examples 1 and 2, and Comparative Example 1 copper powder average particle size D ₅₀ , average crystallite diameter D, average circularity, sintering start temperature, carbon concentration, and aluminum, silicon, titanium , And the concentration of zirconium was measured. Furthermore, the throughput method was applied to evaluate the degassing behavior.

The average particle size D ₅₀ was measured as follows. Using a scanning electron microscope (SEM: Hitachi High-Technologies Co., Ltd., SU5000, the same applies hereinafter), image analysis of 500 copper particles existing in one field of view of the SEM image of copper powder at a magnification of 15,000 times. The analysis was performed using software (Macview 4.0 manufactured by Mountech Co., Ltd.). _{The average particle size D 50} was calculated from the particle size of each copper particle obtained by this analysis.

The average crystallite diameter D is the (111) plane of the copper crystal obtained by CuKα rays generated under the conditions of an acceleration voltage of 45 kV and a discharge current of 40 mA using an X-ray diffractometer (X'PertPro manufactured by Spectris Co., Ltd.). , (200) plane, (220) plane, half-value width of the diffraction peak and Scherrer's formula.

The average circularity was measured as follows. Using SEM, about 500 copper particles existing in one field of view of an SEM image at a magnification of 15,000 were analyzed using image analysis software (Macview 4.0 manufactured by Mountech Co., Ltd.), and about 500 copper particles were analyzed. The circularity C was obtained, and the average value, that is, the average circularity was calculated.

The degassing behavior was evaluated using a heated degassing gas analyzer (manufactured by Electronic Science Co., Ltd., TDS-1200). Specifically, copper powder (0.6 mg) was placed on quartz glass installed in the chamber of the temperature-temperature desorption gas analyzer. ^{The inside of the chamber was depressurized to 2 × 10 -7} Pa using a turbo molecular pump, and then heated from room temperature to 950 ° C. The temperature rise during heating was 30 ° C./min. While monitoring the pressure in the chamber during heating with a vacuum gauge, the discharged gas was analyzed using a mass spectrometer. The amount of gas desorbed was estimated from the pressure change in the chamber. The amount of gas desorbed from the copper powder was quantified by heating the chamber under the same conditions in the absence of the copper powder and subtracting the amount of gas desorbed as a blank. .. In addition, the composition of the desorbed gas was calculated using a mass spectrometer.

The sintering start temperature was determined by the following method. Copper powder was filled into a cylindrical cylinder having a diameter of 5 mm and a height of about 40 mm. The punch was pushed in from the upper part of the housing and pressed at 0.87 ton / cm ² for 10 seconds to form a copper powder into a columnar shape having a height of about 5 mm. This molded product was arranged so that the long axis was in the vertical direction, and was heated in a heating furnace while applying a load of 98.0 mN in the long axis direction. Heating was carried out from room temperature to 1000 ° C. under a stream of nitrogen gas containing 2% by volume of hydrogen gas (flow rate 300 mL / min) at a heating rate of 5 ° C./min. During heating, the height change (expansion / contraction) of the molded product was monitored, and a thermomechanical analysis curve was obtained. Based on this thermomechanical analysis curve, the temperature at which the height change (shrinkage) of the molded product started and the shrinkage rate reached 5% was adopted as the sintering start temperature.

The carbon concentration was measured by a combustion / infrared absorption method using a carbon / sulfur analyzer (EMIA-920V2 manufactured by HORIBA, Ltd.).

The concentrations of aluminum, silicon, titanium, and zirconium were measured using an ICP emission spectrophotometer (SPS3100) manufactured by SII Nanotechnology Co., Ltd. Specifically, about 1.0 g of copper powder was added to a mixed solution of ultrapure water (30 mL), nitric acid (10 mL), and hydrochloric acid (10 mL), and dissolved while heating using a hot plate. After cooling the obtained solution to room temperature, pure water was added to make the total volume 100 mL, and ICP emission spectroscopic analysis was performed using this. The concentrations of aluminum, silicon, titanium, and zirconium were evaluated using emission wavelengths of 396.15 nm, 251.61 nm, 334.94 nm, and 339.20 nm, respectively.

The evaluation results are summarized in Table 1. The copper powder of Example 1 is produced by the vapor phase growth method, and therefore, the average particle diameter D ₅₀ is small and the average crystallite diameter D is large. The result is a large D / D ₅₀ . This result is in contrast to the result of the copper powder of Comparative Example 1 produced by the wet method. Further, as compared with Comparative Example 1, the copper powder of Example 1 has a higher average circularity.

As shown in Table 1, it was confirmed that the copper powders of Examples 1 and Reference Examples 1 and 2 contained carbon at a concentration of 0.04% by weight or more and 1.00% by weight or less. Comparing Example 1, Reference Example 1, and Reference Example 2, it can be seen that the carbon concentration increases as the concentration of the aqueous solution containing the surface treatment agent increases. This indicates that the carbon concentration can be controlled by the concentration of the solution or suspension containing the surface treatment agent.

From the results of Example 1 and Reference Examples 1 and 2, it was found that the sintering start temperature increases as the carbon concentration increases. In particular, it is noteworthy that even the copper powder of Reference Example 1 having a carbon concentration of only 0.04% by weight shows a high starting temperature of 450 ° C. or higher. On the other hand, it was found that the copper powder of Comparative Example 1 having a carbon concentration of 0.19% by weight had a lower sintering start temperature than Reference Example 1 and was less than 400 ° C. It was. The concentrations of aluminum, silicon, titanium, and zirconium in the copper powders of Example 1, Reference Examples 1 and 2, and Comparative Example 1 were all below the detection limit. This means that the sintering start temperature does not simply depend on the carbon concentration, but the ratio of the average crystallite _{diameter D to the average particle size D 50} _{(D / D 50} ) has a large effect, and D / D ₅₀ is 0. It is considered that the temperature of .10 or more also contributes to the increase in the sintering start temperature. It is presumed that this is probably _{because the larger the D / D 50, the} higher the proportion of copper present in the crystalline state.

It was found that the copper powder of Example 1 not only showed a degassing peak temperature below the sintering start temperature, but also had a temperature difference of 300 ° C. or more (Table 1). This suggests that degassing is almost complete before sintering begins. Therefore, a large amount of gas is not desorbed in the process of sintering progressing and the film is formed, and by using the copper powders of Examples 1 to 3, voids are formed in the copper film and the copper thin film is formed. It can be said that deformation can be suppressed. On the other hand, in the copper powder of Comparative Example 1, although the peak temperature of degassing was lower than the sintering start temperature, the difference was found to be as small as about 240 ° C. This suggests that when the copper powder of Comparative Example 1 is used, the gas is desorbed even in the process of sintering progressing and the film is formed, and voids are formed in the formed copper film. It can be said that there is an extremely high possibility that it will occur or that the copper film will be deformed.

_{The ratio (W 1} / W ₀ ) of the amount of desorbed gas at 600 ° C. or higher and 950 ° C. or lower to the total amount of gas desorbed by heating at 60 ° C. or higher and 950 ° C. or lower is significantly larger in Example 1 than in Comparative Example 1. It is understood from Table 1 that it is very low. From this, when the copper powder of Example 1 is sintered, a large amount of gas is not desorbed in the process of forming the film, and void generation and deformation of the copper film are effectively prevented. It can be said that it is possible.

The above-described embodiments of the present invention can be appropriately combined and implemented as long as they do not contradict each other. Further, based on each embodiment, those skilled in the art who appropriately add, delete, or change the design, or add, omit, or change the conditions of the process also have the gist of the present invention. As long as it is, it is included in the scope of the present invention.

Of course, other effects different from those brought about by the aspects of each of the above-described embodiments, which are clear from the description of the present specification or which can be easily predicted by those skilled in the art, are described in the present invention. It is understood that it is brought about by the invention.

Claims

The average particle size D 50 is 297 nm or more and 500 nm or less.
The average crystallite diameter (D) is 92.3 nm or more and 250 nm or less.
The ratio D / D 50 of the average crystallite diameter (D) to the average particle size (D 50 ) is 0.31 or more and 0.50 or less.
Copper powder having a carbon concentration of 0.73% by weight or more and 1.00% by weight or less.
For 60 ° C. or higher 950 ° C. or less of the total amount of gas desorbed at a temperature range (W 0), the ratio of the amount of gas desorbed at a temperature range of 600 ° C. or higher 950 ° C. or less (W 1) (W 1 / W 0 ) Is the copper powder according to claim 1, which is 0.6% by weight or less.
The copper powder according to claim 1 or 2, wherein the sintering start temperature is 450 ° C. or higher.
The copper powder according to any one of claims 1 to 3, wherein the degassing peak temperature is 150 ° C. or higher and 300 ° C. or lower.