TW201619401A - Copper powder - Google Patents

Abstract

The copper powder according to the present invention has an X-ray photoelectron spectroscopy (XPS) spectrum, which is obtained by measuring the surface of copper particles using an X-ray photoelectron spectroscope, in which the ratio P2/(P1+P0), which is the ratio of the peak intensity P1 of Cu(I) and the peak intensity P0 of Cu(0) to the peak intensity P2 of Cu(II), is 0.15-1. The proportional content of oxygen is preferably 0.15-1.2 mass%. The volume accumulation particle diameter D50 at an accumulation volume of 50 vol.%, as measured by the light scattering particle sizing technique, is preferably 0.3-10 [mu]m.

Description

Copper powder

The present invention relates to a copper powder.

Copper powder is now used as a raw material for a conductive composition such as a conductive paste. The conductive composition is obtained by dispersing copper powder in a medium containing a binder resin and an organic solvent. The conductive composition is used, for example, for formation of a circuit, formation of an external electrode of a ceramic capacitor, or the like.

In recent years, as circuits and the like have progressed in the direction of micro-pitching, copper powder for conductive compositions has also been micronized, and the specific surface area of copper powder has been increasing. As a result, the copper powder gradually becomes a state of being more easily oxidized. Therefore, various techniques for preventing oxidation of copper powder have been proposed. For example, when copper powder is produced by the atomization method, boron is added in an amount of 0.01 to 0.1% by weight based on copper, thereby reducing the occurrence of an oxide film (see Patent Document 1). Patent Document 2 describes copper powder containing any of Al, Mg, Ge, and Ga.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2008-95169

Patent Document 2: Japanese Patent Laid-Open No. 2011-6739

In the copper powder described in the above Patent Documents 1 and 2, oxidation of copper is prevented by including an element other than copper in the copper powder. Therefore, the element contained in the copper powder remains in the conductor formed of the conductive composition containing the copper powder. Depending on the state of use of the conductor or the location of use, this element may adversely affect joint reliability or continuity characteristics. The use of copper powder is limited.

Therefore, an object of the present invention is to improve copper powder, and more particularly to provide excellent surface stability even when no different element is used, and the denseness of the conductive composition or the adhesion to the oxygen-containing insulating material, Copper powder with excellent uniformity of distribution.

The present invention provides a copper powder having a peak intensity P ₂ of Cu(II) relative to a peak intensity P _{1 of} Cu(I) in an X-ray photoelectron spectroscopy spectrum obtained by measuring a surface using an X-ray photoelectron spectroscopy device (XPS). The ratio of the peak intensity P ₀ of Cu(0), that is, the ratio of P ₂ /(P ₀ +P ₁ ) is 0.15 or more and 1 or less.

Further, the present invention provides the following method as a suitable method for producing the above copper powder: The dried raw material copper powder is allowed to stand for 20 minutes or more and 650 minutes or less in an atmosphere having a relative humidity of 40% RH or more and 80% RH or less and a temperature of 20° C. or more and 120° C. or less.

Hereinafter, the present invention will be described based on the preferred embodiments. The copper powder of the present invention contains a collection of copper particles. Although the copper powder of the present invention contains substantially only copper particles, it is allowed to contain unavoidable impurities. Further, the copper powder of the present invention may contain other powders or the like as needed.

One of the characteristics of the copper powder of the present invention is the oxidation state of copper present on the surface of the copper particles. Specifically, the copper particles constituting the copper powder of the present invention become metallic copper (i.e., Cu(0)), monovalent copper (i.e., Cu(I)), and divalent copper (i.e., Cu(II)) on the surface of the copper particles. The ratio of existence is specific. The ratio of the presence of these various valences of copper can be measured using an X-ray photoelectron spectroscopy device (XPS). X-ray photoelectron spectroscopy spectra of various elements were obtained according to XPS measurement. In XPS, the elemental composition from the surface of the copper particles to a depth of about ten nm can be quantitatively analyzed. In the X-ray photoelectron spectroscopy spectrum obtained by measuring the surface state of the copper particles constituting the copper powder of the present invention by XPS, the peak intensity P ₂ of Cu(II) is relative to the peak intensity P ₁ and Cu of Cu(I). The ratio of the peak intensity P ₀ of 0), that is, the value of P ₂ /(P ₀ +P ₁ ) is preferably 0.15 or more and 1 or less, more preferably 0.3 or more and 0.9 or less, still more preferably 0.4 or more and 0.7 or less. . Hereinafter, the value of P ₂ /(P ₁ +P ₀ ) is referred to as "copper oxidation rate". Furthermore, the so-called peak intensity refers to the height of the peak.

In the X-ray photoelectron spectroscopy spectrum, the peak of Cu(II) is mainly derived from CuO and Cu(OH) ₂ , and is observed in the range of 934.0 eV or more and 936.0 eV or less. These peaks cannot be distinguished because they are observed at the same position. The peak of Cu(I) is mainly derived from Cu ₂ O. Further, the peak of Cu(0) is derived from metallic copper. The peak of Cu(I) and the peak of Cu(0) are observed at the same position in the range of 930.0 eV or more and 933.5 eV or less, so that it is impossible to separate the two. Therefore, in the present invention, the copper oxidation rate is defined as described above.

The amount of Cu(II) is less or the same as the total amount of Cu(I) and Cu(0) present on the surface of the copper particles in the copper powder containing copper particles having a copper oxidation rate within the above range. The conductor obtained from the conductive composition containing the copper powder of the present invention can be made into a dense structure by appropriately setting the amount of Cu(II). Moreover, since the affinity between the conductive composition and the oxygen-containing insulating material is high, the adhesion to the substrate or the dielectric material of the electronic component is improved, and an electronic component having high adhesion reliability can be obtained. Therefore, the electrode for an electronic component can be suitably manufactured using the copper powder of this invention. Further, when the conductive composition contains a glass frit, when the conductive composition is used as the electrode of the ceramic electronic component, since the affinity between the copper particles and the ceramic material and the glass frit is good, it is required as needed. When it is used as a conductive composition for sintered ceramic electronic parts, it is possible to effectively prevent segregation of glass components during sintering. Thereby, it is also possible to form the conductor into a dense structure. Further, since the copper powder of the present invention does not substantially contain a different element other than copper, it has an advantage in that it is less restrictive in use. The term "substantially free of heterogeneous elements" means heterogeneous elements other than copper and oxygen when performing elemental analysis on copper powder. The total content ratio is 0.1% by mass or less. A suitable production method of the copper powder satisfying the above copper oxidation rate will be described below.

Further, the ratio of the peak intensities P ₀ , P ₁ and P ₂ , P ₂ :(P ₀ + P ₁ ) is 15:85 to 50:50, particularly 23:77 to 47:53, especially 29: From 71 to 41:59, the viewpoint of improving the oxidation resistance of copper powder is also preferable.

The method for measuring the copper oxidation rate of copper particles by XPS is as follows. The device can use, for example, Quantum 2000 manufactured by ULVAC-PHI Co., Ltd. The X-ray source can use an Al-Kα line (1486.8 eV). The condition of the X-ray source can be, for example, 17 kV × 0.023 A. The charge correction can be performed by setting the bond energy of SiO ₂ to 103.2 eV. Further, the beam diameter was set to 200 μm (40 W), and the measurement was carried out in the range of about 300 × 900 μm. Regarding the peak intensities P ₀ , P ₁ and P ₂ , Cu(II) is in the range of 934.0 eV or more and 936.0 eV or less, and Cu(0) and Cu(I) are in the range of 930.0 eV or more and 933.5 eV or less. It is calculated from the highest count number (c/s). In addition to the measurement of the copper particle alone, it is also possible to measure a mixture with the binder component of the conductive composition. In this case, it may be measured by washing with an alcohol organic solvent such as rosin alcohol to expose the copper particles. Further, in the case where the electrode for the following electronic component is formed, it can be measured by the following processor: the electrode member is made of a neutral organic solvent (ether, ketone) for the electrode in which the copper particles are not sintered, melted, or welded. a mixed solution of lactone, aromatic hydrocarbon, rosinol, carbitol acetate, etc., which is boiled under high temperature and high pressure to swell the resin, thereby exposing the surface of the copper particles, and exposing the copper particles on the surface The individual bodies were taken out, filtered, and air dried.

Regarding the copper powder of the present invention, in addition to the surface oxidation state of the copper particles as described above, the low content ratio of oxygen is also one of the characteristics. Specifically, the copper powder of the present invention preferably has an oxygen content of 0.15% by mass or more and 1.2% by mass or less, more preferably 0.4% by mass or more and 1.0% by mass or less. When a conductive composition is prepared using the copper powder of the present invention in which the oxygen content ratio is within this range, and a conductor is formed from the conductive composition, the conductor becomes a denser having less voids in the calcined film. Further, the conductive composition of the copper powder of the present invention in which the oxygen content is contained in this range is high in affinity with the oxygen-containing insulating material, and the adhesion is likely to be high. Further, when the glass frit is contained in the conductive composition, the affinity between the copper particles and the glass frit is good, and the presence of the glass in the conductor is likely to be uniform. An oxide ceramic is exemplified as an example of the oxygen-containing insulator. Examples of the oxide ceramics include oxide ceramics of a single metal species such as alumina, zirconia, titania, ferrite, magnesia, and cerium oxide, or a mixture thereof, and barium titanate or barium titanate. Such as composite metal oxide ceramics. Examples of other oxygen-containing insulators include resins containing oxygen in the structure. Examples of the oxygen-containing resin include an epoxy resin, a cyanate resin, and a bis-n-butylene diimide. Resin (BT resin), polyphenylene ether resin, phenol resin, polyimide resin or polyamide resin, unsaturated polyester resin, liquid crystal polymer, polyethylene terephthalate resin, polyethylene naphthalene resin, etc. Insulating resin. In addition, when a filler particle containing various oxides such as cerium oxide or aluminum oxide is contained in the resin, the resin is excellent in adhesion to the conductive composition using the copper powder of the present invention.

The content ratio of oxygen in the copper powder of the present invention is measured by the following method. As the apparatus, for example, an oxygen/nitrogen analyzer EMGA-620 manufactured by Horiba, Ltd. can be used. 0.1 g of copper powder was weighed and placed in a nickel capsule, and then burned in a graphite crucible to determine the oxygen content ratio.

With respect to the copper powder of the present invention, it is preferred that the volume cumulative particle diameter D ₅₀ at 50% by volume of the cumulative volume measured by the laser diffraction scattering particle size distribution measurement is 0.3 μm or more and 10 μm or less, especially 1.0. Μm or more and 5.5 μm or less. When the particle diameter of the copper particles constituting the copper powder is reduced to such an extent, the copper particles are easily oxidized due to an increase in the specific surface area. With regard to the copper powder of the present invention, the oxidation state of the copper on the surface of the copper particles is The control is appropriate, so that oxidation due to changes over time can be prevented.

The measurement of the volume cumulative particle diameter D ₅₀ described above can be carried out, for example, by the following method. 0.1 g of the measurement sample was mixed with 100 ml of a 20 mg/L aqueous solution of sodium hexametaphosphate, and dispersed by an ultrasonic homogenizer (US-300T manufactured by Nippon Seiki Co., Ltd.) for 10 minutes. Thereafter, the particle size distribution is measured using a laser diffraction scattering type particle size distribution measuring apparatus, for example, Microtrac MT-3000 manufactured by Nikkiso Co., Ltd.

The copper powder of the present invention may be used by sintering it or may be used in the state of an unsintered powder. When the copper powder of the present invention is used for sintering, the copper powder preferably has a shrinkage start temperature of 480 ° C or more and 620 ° C or less. More preferably, it is 500 ° C or more and 580 ° C or less. When a conductive composition is prepared using the copper powder of the present invention having a shrinkage start temperature within the range, and a conductor is formed from the conductive composition, a "dent" of the baked film due to low-temperature shrinkage can be formed, or vice versa. A calcined film having less "neck failure" due to insufficient calcination. As a result, the calcined film becomes a denser with less pores. Further, when the glass frit is contained in the conductive composition, the affinity between the copper particles and the glass frit is good, and it is easy to obtain a baked film in which the presence of the softened glass in the conductor is uniform. The shrinkage onset temperature can be measured using a thermomechanical analysis device (TMA). As the measuring device, for example, EXSTAR 6000 TMA/SS6200 manufactured by Seiko Instruments Co., Ltd. can be used. As a sample for measuring the shrinkage start temperature, for example, a cylindrical formed body in which 0.2 g of pre-weighed copper powder is placed in an inner diameter of 3.8 mm is used. In the aluminum case, a load of 4835 N is applied to form. The cylindrical molded body was attached to a thermomechanical analysis device (TMA), and the thermal expansion coefficient (%) in the longitudinal direction when the temperature was raised at a rate of 10 ° C/min under a nitrogen atmosphere and a nitrogen atmosphere was measured, and the expansion behavior was measured from the first to the positive Negative temperature (°C). This temperature can be defined as the shrinkage start temperature.

The shape of the copper particles constituting the copper powder of the present invention is not particularly limited, and various shapes such as a spherical shape, a flake shape, a plate shape, and a dendritic shape can be used. The shape of the copper particles to be used can be appropriately judged according to the specific use of the copper powder of the present invention. The shape of the copper particles generally depends on the method of manufacture. The spherical copper particles can be produced, for example, by an atomization method or a wet reduction method. The flaky particles can be produced, for example, by a method of mechanically plastically deforming spherical particles. The plate-like particles can be produced, for example, by a wet reduction method. The dendritic copper particles can be produced, for example, by electrolysis. The copper powder of the invention can also be a mixture of copper particles of various shapes. Fit.

In addition, the copper particles constituting the copper powder of the present invention have the above-described respective shapes, and when the copper powder of the present invention is observed by an electron microscope observation (for example, 1000 times), the particles having the above-described respective shapes occupy 80 on a number basis. More than %.

Next, a suitable method for producing the copper powder of the present invention will be described. The copper powder of the present invention is suitably produced by subjecting the raw material copper powder produced by various methods to oxidation under appropriate conditions under appropriate conditions. The method for producing the raw material copper powder is not particularly limited. However, in the case of producing a copper powder containing spherical copper particles, it is preferable to use, for example, an atomization method to produce a copper powder of fine particles having an average particle diameter of 3 μm or less. Suitable for wet method.

As the atomization method, a gas atomization method or a water atomization method can be preferably employed. In the case where the particle shape is uniformized, it is preferred to use a gas atomization method. On the other hand, in the case of purifying the particles, it is preferred to employ a water atomization method. In the gas atomization method and the water atomization method, it is particularly preferable because the high-pressure atomization method can produce particles finely and uniformly. The high-pressure atomization method is a method in which atomization is performed under a water pressure of 50 MPa or more and 150 MPa or less in a water atomization method. The gas atomization method is a method of atomizing at a gas pressure of about 0.5 MPa or more and 3 MPa or less.

As the wet method, a reduction precipitation method may be employed in which a reducing agent is added to a slurry in which an aqueous alkaline solution is added to a copper salt aqueous solution. In the case of obtaining a specific particulate copper powder, it is preferred to add a reducing agent such as reducing sugar or hypophosphorous acid or sodium sulfite to prepare a cuprous oxide slurry, and then add a cerium compound such as cerium hydrate or barium sulfate or boron. A two-stage reduction method such as a strong alkaline reducing agent such as sodium hydride.

The raw material copper powder may also be classified before being subjected to oxidation treatment. This classification can be easily carried out by separating the coarse powder or the fine powder from the obtained raw material copper powder by using an appropriate classification device in such a manner as to be the target particle size. The classification is preferably carried out in such a manner that the value of D ₅₀ of the raw material copper powder is within the range described above.

The raw material copper powder thus obtained is supplied to the oxidation treatment. Suitable as an oxide strip The material may be, for example, a condition in which the relative humidity is 40% RH or more and 80% RH or less, and the temperature is 60° C. or more and 120° C. or less in an atmosphere to be left as an industrial processing condition. From the viewpoint of uniformity of oxidation treatment of copper powder and prevention of particle agglomeration accompanying an increase in Cu(II) due to excessive treatment, the conditions of the atmospheric environment are within the above range as conditions. It is preferably 20 minutes or longer and 650 minutes or shorter, more preferably 30 minutes or longer and 600 minutes or shorter, and still more preferably 30 minutes or longer and 180 minutes or shorter. In the case where the relative humidity is low, since the oxidation rate tends to be slow, in this case, the temperature may be set higher. For example, when the relative humidity is 40% or more and 60% or less, the treatment temperature is preferably 70° C. or higher and 130° C. or lower, and the relative humidity is more than 60% and 80% or less, and the treatment temperature is preferably 60° C. or higher. Below 90 °C. In the treatment, it is preferred to keep the relative humidity and temperature of the atmospheric environment constant, that is, constant temperature and humidity, but it is also possible to treat the relative humidity and/or temperature as needed.

As the copper powder to be subjected to the oxidation treatment, for example, a dry powder having a low moisture content can be used. In this case, the moisture content ratio can be set to, for example, 0.1% by mass or less. In the case where the relative humidity is low, although the oxidation rate tends to be slow, the oxidation rate can be increased by adding water to the copper powder. For example, the oxidation treatment of the copper powder can be carried out in a state where water is added in a range of 1% by mass or more and 5% by mass based on the mass of the dry copper powder.

By the above method, the target copper powder can be manufactured smoothly and smoothly. The copper powder obtained in this manner is preferably sealed in a container of a moisture impermeable material and kept at a temperature of room temperature (25 ° C) or less for the purpose of maintaining the oxidation state of the surface of the copper particles.

The copper powder of the present invention is excellent in electrical conductivity, has high oxidation resistance, and has good affinity with a glass frit. Therefore, it can be suitably used as a conductive resin composition such as a conductive paste or a conductive adhesive or conductivity. It is used as a main constituent material of various conductive materials such as paints.

For example, in order to prepare a conductive paste, the copper powder of the present invention may be mixed with a binder and a solvent. Thus, a high-temperature baking type conductive paste can be obtained. Alternatively, the invention may also be The copper powder is mixed with a binder and a solvent, and further, if necessary, a hardener or a coupling agent, a hardening accelerator, or the like, to prepare a resin-curable conductive paste.

Examples of the above-mentioned binder include a liquid epoxy resin, an acrylic resin, a phenol resin, and an unsaturated polyester resin, but are not limited thereto. Examples of the solvent include rosin alcohol, ethyl carbitol, carbitol acetate, butyl cellosolve, and butyl carbitol acetate. Examples of the curing agent include 2-ethyl-4-methylimidazole and the like. Examples of the curing accelerator include tertiary amines, tertiary amine salts, imidazoles, phosphines, and phosphonium salts.

Further, when the conductive paste is used for an oxide ceramic electronic component to be sintered, it is preferable to further mix the glass frit in the conductive paste in order to improve the adhesion to the oxide ceramic. Examples of the glass frit include cerium oxide as an essential component and addition of aluminum oxide, boron oxide, calcium carbonate, titanium oxide, zinc oxide, cerium oxide, vanadium oxide, phosphoric acid, cerium oxide, iron oxide, cerium oxide, and the like. A mixture of at least one oxide of a group consisting of tin oxide, cerium oxide, cerium oxide, and tin oxide is heated, melted, and pulverized.

The conductive paste containing the copper powder of the present invention can be suitably used, for example, for forming a conductor circuit for screen printing or an electrical contact member for various electronic parts. For example, an internal electrode of a multilayer ceramic capacitor, a wafer component such as an inductor or a temporary memory, a single-plate capacitor electrode, a tantalum capacitor electrode, a resin multilayer substrate, a low-temperature simultaneous-fired ceramic (LTCC) multilayer substrate, an antenna switch module, and a PA Modules such as modules or high frequency active filters. Examples of the insulating material of the ceramic electronic component include oxide ceramics such as alumina, zirconia, titania, ferrite, magnesia, and cerium oxide, and ceramic composite oxides such as barium titanate and barium titanate. In addition, it can be used for a PDP (plasma display panel) front panel and a flexible printed circuit board (FPC) for electronic components using a resin as an insulating material, and an electrode for a printed wiring board such as a stacked multilayer wiring board. Electromagnetic shielding filter for back panel or PDP color filter, surface electrode and back electrode of crystalline solar cell, conductive adhesive, EMI (electromagnetic interference) shielding, RF-ID (radio-frequency identification) , radio frequency identification), and PC (personal computer, personal computer) keyboard and other membrane switches, anisotropic conductive film (ACF / ACP). In the case where a resin is used as the insulating material, examples of the specific resin include epoxy resin, cyanate resin, and bis-cis-butylimine. Resin (BT resin), polyphenylene ether resin, phenol resin, polyimide resin or polyamide resin, unsaturated polyester resin, liquid crystal polymer, polyethylene terephthalate resin, polyethylene naphthalene resin, etc. Insulating resin. Further, a case where a filler particle containing various oxide inorganic particles such as cerium oxide or aluminum oxide is contained in the resin may be mentioned.

[Examples]

Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the invention is not limited to the embodiments. Prior to the examples and comparative examples, the production of the raw material copper powder will be described.

(Manufacture of raw material copper powder A)

Electrolytic copper (copper purity: Cu 99.95%) was heated in a gas furnace to prepare a melt. Then, 100 kg of the melt was poured into the feed tank in the water atomizing device, and the molten metal was poured from the nozzle (caliber of 5 mm) at the bottom of the feed tank, and the water was sprayed from the nozzle of the full-cone type nozzle (bore diameter: 26 mm). The molten metal was sprayed (water pressure: 100 MPa, water amount: 350 L/min) to the molten metal in the shape of an inverted cone shape, and water atomization was carried out to produce copper powder.

Then, the copper powder obtained was classified by the classification apparatus (Turbo Classifier (trade name) TC-25 (model)) manufactured by Nissin Engineering Co., Ltd.), and the graded person was used as the raw material copper powder A. The raw material copper powder A is a spherical dry powder, and the ratio of D _{50 to} oxygen is shown, for example, in Table 1 below.

(Manufacture of raw copper powder B)

In the production of the raw material copper powder A, the raw material copper powder B was obtained in the same manner as the raw material copper powder A except that the classification point of the classifying device was changed. The raw material copper powder B is a spherical dry powder, and the ratio of D _{50 to} oxygen is shown, for example, in Table 1 below.

(Manufacture of raw material copper powder C)

In the production of the raw material copper powder A, the raw material copper powder C was obtained in the same manner as the raw material copper powder A except that the classification point of the classifying device was changed. The raw material copper powder C is a spherical dry powder, and the ratio of D _{50 to} oxygen is shown, for example, in Table 1 below.

(Manufacture of raw material copper powder D)

After dissolving 100 kg of copper sulfate (pentahydrate salt) to prepare an aqueous solution of 200 L, while maintaining this at 60 ° C, 125 L of a 25 mass% sodium hydroxide aqueous solution and 80 L of a 450 g/L glucose aqueous solution were added to form a cuprous oxide slurry. material. Further, 20% by weight of hydrazine hydrate 100 L was further added to the slurry, whereby the raw material copper powder D was obtained. The raw material copper powder D is a spherical dry powder, and the ratio of D _{50 to} oxygen is shown, for example, in Table 1 below.

(Example 1)

1000 g of the raw material copper powder A was allowed to stand in a constant temperature and humidity chamber adjusted to 80 ° C ̇ 80% RH for 30 minutes, and subjected to oxidation treatment in an atmospheric environment. The target copper powder is obtained in this way.

(Examples 2 to 10)

The target copper powder was obtained in the same manner as in Example 1 except that the oxidation treatment of the raw material copper powder shown in the same table was carried out under the conditions shown in Table 2 below.

(Examples 11 and 12)

In the state where the raw material copper powder is wetted by adding 3 mass% of water to the mass of the raw material copper powder shown in Table 2, the oxidation treatment is performed under the conditions shown in the same table, and The target copper powder was obtained in the same manner as in Example 1.

(Example 13)

In the state in which 1% by mass of water was added to the mass of the raw material copper powder shown in Table 2, and the raw material copper powder was wetted, oxidation treatment was carried out under the conditions shown in the same table, and Example 1 was carried out. The target copper powder is obtained in the same manner.

(Comparative Examples 1 to 4)

Raw material copper powders A to D are used directly.

(Comparative Examples 5 to 7)

The target copper powder was obtained in the same manner as in Example 1 except that the oxidation treatment of the raw material copper powder shown in the same table was carried out under the conditions shown in Table 2 below.

(Comparative Example 8)

In the state in which the raw material copper powder was wetted by adding 3 mass% of water to the mass of the raw material copper powder shown in the following Table 2, the oxidation treatment was carried out under the conditions shown in the same table, and other methods were carried out. Example 1 obtained the same target copper powder.

(Evaluation)

The copper oxide ratio, the oxygen content ratio, and D ₅₀ of the copper powder obtained in the examples and the comparative examples were measured by the above methods. Moreover, the shrinkage start temperature was measured by the following method, and the compactness of the baked film and the glass uniformity in the baked film were evaluated. Also, a comprehensive evaluation was conducted. The results are shown in Table 2 below.

(shrinkage start temperature)

The shrinkage initiation temperature of the copper powder was measured by the above method by thermomechanical analysis (TMA).

(The compactness of the calcined film I)

To the copper powder obtained in the examples and the comparative examples, rosin alcohol and an acrylic resin were added and mixed to prepare a conductive paste (1). The proportion of copper powder in the conductive paste (1) is 70% by mass, the ratio of rosinol is 25% by mass, and the ratio of acrylic resin is 5 mass. %. The conductive paste was applied to an alumina substrate at a film thickness of 50 μm to form a coating film. The coating film was baked at 845 ° C for 20 minutes under a nitrogen atmosphere to obtain a baked film. The surface of the obtained calcined film was magnified by a scanning electron microscope (1000 times), and images of 10 fields of view were taken. The images of the 10 fields of view were analyzed, and the compactness was evaluated based on the following criteria. In addition, the pore area ratio is obtained by image analysis to obtain an area of pores (5 μm or more) included in one field of view, and arithmetically average the values of the ten fields of view. If the pore area is too large, the denseness is insufficient, and if it is too small, the denseness is too high, which adversely affects the uniformity of the glass distribution described below. The quality of the compactness is evaluated based on the following three levels.

◎: The pore area ratio is 3% or more and 7% or less.

○: The void area ratio is 1% or more and less than 3%, or more than 7% and 10% or less.

×: The pore area ratio is less than 1%, or more than 10%.

(Adhesion of baked film II)

With respect to the above calcined film, the adhesion was evaluated based on another viewpoint. Specifically, the calcined film was immersed in the ultrasonic cleaning machine together with the substrate for 30 seconds, and the surface of the baked film was observed by a scanning electron microscope (1000 times), and was observed in the observation field of about 100 μm square based on the following three levels. The adhesion of the baked film was evaluated.

◎: Peeling of the baked film was not observed at all.

○: 70% or more of the area of the calcined film was in close contact with each other.

×: The area of the baked film which is in close contact is less than 30%.

(glass distribution uniformity in the calcined film)

To the copper powder obtained in the examples and the comparative examples, rosin alcohol, an acrylic resin (KWE-250T manufactured by Daisei Fine Chemicals Co., Ltd.), and a glass frit (ASF1891F manufactured by Asahi Glass Co., Ltd.) were added and mixed to prepare a conductive paste (2). . The proportion of the copper powder in the conductive paste (2) was 70% by mass, the ratio of rosinol was 22% by mass, the ratio of the acrylic resin was 3% by mass, and the ratio of the glass frit was 5% by mass. Except for this, the calcined film was obtained in the same manner as the evaluation of the compactness of the above calcined film. For the surface of the baked film, with a field of view The image was obtained at about 100 μm square and 1000 times, and EDX (energy dispersive X-ray) analysis was performed on the image, and the glass distribution uniformity was evaluated based on the amount of Si derived from the glass frit. The evaluation criteria are as follows. Further, the amount of Si is an amount defined by Si × 100 / (Si + Cu). In the formula, Si and Cu represent the peak intensities of Si and Cu in the EDX analysis.

◎: The amount of Si is 1% or more and 10% or less.

○: The amount of Si is 0.5% or more and less than 1%, or more than 10% and 20% or less.

×: The amount of Si is less than 0.5%, or more than 20%.

(Overview)

In the above evaluation, the following evaluation was performed as a comprehensive evaluation.

◎: In the evaluation of compactness I, compactness II, and homogeneity, two or more were ◎.

○: In the evaluation of the compactness I, the compactness II, and the uniformity, one or more of them were ○.

×: In the evaluation of the density I, the compactness II, and the uniformity, there are × in one or more items.

As is clear from the results shown in Table 2, the copper powder obtained in each of the examples had higher oxidation initiation temperature and more excellent oxidation resistance than the copper powder of the comparative example. Moreover, it is understood that the calcined film produced by using the copper powder obtained in each of the examples as a raw material has a higher density of the film than the calcined film produced by using the copper powder of the comparative example as a raw material, and the copper powder and the glass are more Affinity has become better.

[Industrial availability]

According to the present invention, copper powder excellent in shrinkage temperature control can be provided. Since the copper powder has a good affinity with the glass frit at the time of baking, a baked film excellent in compactness can be obtained by using the copper powder. Further, when the copper powder is used as a conductive composition, the affinity with the oxygen-containing insulating material is high, and an electronic component having high adhesion reliability can be obtained.

Claims (7)

A copper powder having a peak intensity P ₂ of Cu(II) relative to a peak intensity P ₁ and Cu of Cu(I) in an X-ray photoelectron spectroscopy spectrum obtained by measuring a surface using an X-ray photoelectron spectroscopy device (XPS) The ratio of the peak intensity P ₀ of 0), that is, the value of P ₂ /(P ₀ + P ₁ ) is 0.15 or more and 1 or less. The copper powder according to claim 1 has a oxygen content of 0.15% by mass or more and 1.2% by mass or less. The copper powder according to claim 1 which has a volume cumulative particle diameter D ₅₀ of 50% by volume cumulative volume obtained by a laser diffraction scattering particle size distribution measurement of 0.3 μm or more and 10 μm or less. A conductive composition comprising the copper powder according to any one of claims 1 to 3, and a binder. An electrode for an electronic component, comprising the copper powder according to any one of claims 1 to 3. A method for producing a copper powder according to claim 1, which is characterized in that the dried raw material copper powder is in an atmosphere having a relative humidity of 40% RH or more and 80% RH or less and a temperature of 20 ° C or more and 120 ° C or less. Oxidation treatment was carried out by allowing to stand for 20 minutes or more and 650 minutes or less. The method of producing copper powder according to claim 6, wherein the oxidation treatment is carried out in a state where water is added in an amount of 1% by mass or more and 3% by mass based on the mass of the raw material copper powder.