JP2015194415A - Nickel fine particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide nickel fine particles capable of forming a fusion state at a temperature as low as possible and forming a connection layer having conductivity and high shear strength.SOLUTION: The nickel fine particles having a bulk density of 0.5-3.5 g/cm, a carbon element content of 0.3-1.0 mass% and an oxygen element content of 0.5-2.5 mass% satisfies that (1) when measured using a time-of-flight type secondary ion mass spectroscopy, a fragment derived from an organic material consisting of C and H is not detected in a mass number (m/z)≥80; (2) when measured using the time-of-flight type secondary ion mass spectroscopy, a fragment of CHCHO is detected in a mass number (m/z)=45; and (3) in a chromatogram obtained by measuring a mass spectrum in a mass number (m/z)=45 using a gas chromatography mass spectrometry, three or more kinds of spectra are identified.

Description

  The present invention relates to nickel fine particles that can be used for manufacturing electronic components and the like.

  Metal fine particles have physical and chemical properties different from those of bulk metals, and are therefore used in various industrial materials. In recent years, with the downsizing and thinning of electronic devices, the particle diameter of industrial metal fine particles has been reduced to about several tens to several hundreds of nanometers. For example, Patent Document 1 proposes a bonding material for electronic components using a nickel material that is relatively inexpensive and can be used at high temperatures. The bonding material of Patent Document 1 uses metal nanoparticles that include metal fine particles composed of nickel or a nickel alloy and an oxygen-containing film that covers the metal fine particles, and have an average particle diameter of 100 nm or less. .

  When metal fine particles are used for the bonding material, a baking process is required in which a bonding material containing metal fine particles is disposed between the members to be bonded and heated at a temperature of, for example, 300 ° C. The behavior of the metal fine particles in the firing step (hereinafter, sometimes referred to as “sinterability”) greatly affects the conductivity and shear strength of the bonding layer. For example, if the bonding layer after the firing step is in a state where the particle interface of many metal fine particles is confirmed, the conductivity and shear strength of the bonding layer are not sufficiently increased. On the other hand, when the bonding layer after the firing step is in a fused state in which the particle interface of the metal fine particles is not confirmed at all, it has conductivity and high shear strength.

International Publication WO2012 / 173187 Pamphlet

  When nickel fine particles are used as a bonding material, it is necessary that the nickel fine particles are fused to become conductive by firing and have electrical conductivity, and the bonding layer needs to have a sufficiently high shear strength. Factors that affect the conductivity and shear strength of the bonding layer include the average particle size of the metal fine particles used as a raw material, the particle size distribution, the dispersion / aggregation state, the surface modification state, and the firing conditions of the firing step. However, these factors are related to each other. For example, the optimum firing conditions vary depending on other factors, that is, the type and average particle size of the raw metal fine particles, the particle size distribution, the dispersion / aggregation state, the surface modification state, and the like.

  An object of the present invention is to provide nickel fine particles that can be fused at a temperature as low as possible and can form a bonding layer having electrical conductivity and high shear strength.

The nickel fine particles of the present invention have a bulk density in the range of 0.5 to 3.5 g / cm ³ , a carbon element content in the range of 0.3 to 1.0 mass%, and an oxygen element content. Is in the range of 0.5 to 2.5 mass%, and the following conditions (1) and (2) or (3),
(1) When measured using time-of-flight secondary ion mass spectrometry (TOF-SIMS), a fragment derived from an organic substance consisting of C and H is not detected at a mass number (m / z) ≧ 80;
(2) a CH ₂ CH ₂ O fragment is detected at a mass number (m / z) = 45 as measured using time-of-flight secondary ion mass spectrometry (TOF-SIMS);
(3) Three or more types of spectra are confirmed in a chromatogram obtained by measuring a mass spectrum at the mass number (m / z) = 45 using gas chromatography mass spectrometry (GC-MS). about;
Satisfied.

  The nickel fine particles of the present invention have an average primary particle diameter in the range of 10 to 150 nm, a particle diameter variation coefficient (standard deviation / average particle diameter) of 0.25 or less, and a crystallite calculated by the Scherrer method The diameter may be 15 nm or less.

  The nickel fine particles of the present invention can be sintered and heat-sealed at a low temperature of about 150 ° C. in a uniformly dispersed state. Therefore, the nickel fine particles of the present invention can be suitably used as a die bonding material that can be sintered at a low temperature, for example, for high-temperature applications that cannot be used with conventional Si devices.

2 is a SEM photograph of nickel fine particles obtained in Example 1. 2 is a chart showing measurement results of powder X-ray diffraction (XRD) of nickel fine particles obtained in Example 1. FIG. 2 is a chart showing measurement results of a thermal mechanical analyzer (TMA) of nickel fine particles obtained in Example 1. FIG. 2 is a SEM photograph of nickel fine particles obtained in Example 2. 4 is a chart showing measurement results of powder X-ray diffraction (XRD) of nickel fine particles obtained in Example 2. FIG. 6 is a chart showing measurement results of a thermal mechanical analyzer (TMA) of nickel fine particles obtained in Example 2. FIG. 4 is an SEM photograph of nickel fine particles obtained in Example 3. 6 is a chart showing measurement results of powder X-ray diffraction (XRD) of nickel fine particles obtained in Example 3. FIG. 4 is a chart showing measurement results of thermomechanical analysis (TMA) of nickel fine particles obtained in Example 3. FIG. 4 is a chart showing measurement results of time-of-flight secondary ion mass spectrometry (TOF-SIMS) of nickel fine particles obtained in Example 3. 4 is a SEM photograph of nickel fine particles obtained in Example 4. 6 is a chart showing measurement results of powder X-ray diffraction (XRD) of nickel fine particles obtained in Example 4. FIG. 6 is a chart showing measurement results of thermomechanical analysis (TMA) of nickel fine particles obtained in Example 4. FIG. It is a chart which shows the measurement result of the gas chromatography mass spectrometry (GC-MS) of the nickel fine particle obtained in Example 4. 2 is a SEM photograph of nickel fine particles obtained in Comparative Example 1. 6 is a chart showing measurement results of powder X-ray diffraction (XRD) of nickel fine particles obtained in Comparative Example 1. 4 is a chart showing measurement results of thermomechanical analysis (TMA) of nickel fine particles obtained in Comparative Example 1. 4 is a SEM photograph of nickel fine particles obtained in Comparative Example 2. 6 is a chart showing measurement results of powder X-ray diffraction (XRD) of nickel fine particles obtained in Comparative Example 2. 7 is a chart showing measurement results of thermomechanical analysis (TMA) of nickel fine particles obtained in Comparative Example 2. 4 is an SEM photograph of nickel fine particles obtained in Comparative Example 3. 10 is a chart showing measurement results of powder X-ray diffraction (XRD) of nickel fine particles obtained in Comparative Example 3. 10 is a chart showing the measurement results of thermomechanical analysis (TMA) of nickel fine particles obtained in Comparative Example 3. 6 is a SEM photograph of nickel fine particles obtained in Comparative Example 4. 6 is a chart showing measurement results of powder X-ray diffraction (XRD) of nickel fine particles obtained in Comparative Example 4. 10 is a chart showing measurement results of thermomechanical analysis (TMA) of nickel fine particles obtained in Comparative Example 4. 6 is a SEM photograph of nickel fine particles obtained in Comparative Example 5.

  Embodiments of the present invention will be described below.

[Nickel fine particles]
The nickel fine particles of the present embodiment are fine particles containing nickel as a main component. Here, “comprising nickel as a main component” means that nickel element is contained in an amount of 50% by weight or more, preferably 90% by weight or more, more preferably 100% by weight with respect to the total amount of metal elements. The nickel fine particles of the present embodiment are metals other than nickel, for example, base metals such as titanium, cobalt, copper, chromium, manganese, iron, zirconium, tin, tungsten, molybdenum, vanadium, gold, silver, platinum, palladium, Metal elements such as noble metals such as iridium, osmium, ruthenium, rhodium and rhenium may be contained alone or in combination of two or more.

The nickel fine particles of the present embodiment have a bulk density in the range of 0.5 to 3.5 g / cm ³ , and preferably in the range of 0.5 to 3.0 g / cm ³ . The bulk density contributes to low temperature sintering and handling properties. When the bulk density is less than 0.5 g / cm ³ , unnecessary necking and aggregation occur in the nickel fine particles, which hinders low-temperature sintering. On the other hand, even if the bulk density exceeds 3.5 g / cm ³ , there is no particular problem. However, for example, when pasting, depending on the type of material used for pasting, there is a risk of adversely affecting handling properties.

  In the nickel fine particles of the present embodiment, the carbon element content is in the range of 0.3 to 1.0% by mass, and preferably in the range of 0.3 to 0.6% by mass. The carbon element contributes to the dispersibility of the nickel fine particles if it is in an appropriate amount. Further, when the carbon element content is within the above range, the oxygen element present in the nickel fine particles can be efficiently reduced. When the carbon element content is less than 0.3% by mass, the effect of improving dispersibility cannot be obtained. If the carbon element content exceeds 1.0 mass%, the amount of residual carbon after sintering increases, and when used as a bonding material, the conductivity may be lowered.

  In the nickel fine particles of the present embodiment, the oxygen element content is in the range of 0.5 to 2.5% by mass, and preferably in the range of 0.5 to 2.3% by mass. The oxygen element is mainly derived from an oxide film present on the surface of the nickel fine particles. If the oxygen element content is less than 0.5% by mass, the carbon element is not sufficiently oxidized during the sintering of the nickel fine particles, and it tends to remain as residual carbon, which may reduce the strength of the bonding layer. is there. If the oxygen element content exceeds 2.5% by mass, when used as a bonding material, the electrical resistance increases, which may adversely affect the electrode characteristics, and the oxide is strong on the surface of the nickel fine particles. If present, the sintering at low temperature may be hindered.

  Further, the nickel fine particles of the present embodiment satisfy the following condition (1) and satisfy at least one of condition (2) or condition (3).

(1) When measured using time-of-flight secondary ion mass spectrometry (TOF-SIMS), fragments derived from organic substances consisting of C and H are not detected when the mass number (m / z) ≧ 80.
Here, “consisting of C and H” means “consisting only of C and H”. This condition (1) means that a fragment of an alkyl group having a large mass number is not detected. That is, the nickel fine particles of the present embodiment are, for example, R ₁ —O— (CH ₂ CH ₂ O) n—CH ₂ —COOH [where R ₁ represents a hydrocarbon group having 1 to 20 carbon atoms. ] Which do not contain a surfactant such as When such a long-chain alkyl group is included, the amount of residual carbon after sintering increases, and when used as a bonding material, it may adversely affect conductivity and shear strength.

In the condition (1), for example, the presence of CH ₂ CH ₂ O (including O) or siloxane-derived (including Si) fragments is allowed. This is because they are easily decomposed and volatilized at the time of sintering, and when used as a bonding material, it is considered that they hardly remain in the bonding layer. Therefore, the nickel fine particles of the present embodiment may contain a glycol compound or a siloxane compound.

(2) A CH ₂ CH ₂ O fragment is detected at a mass number (m / z) = 45 when measured using time-of-flight secondary ion mass spectrometry (TOF-SIMS).
The fragment of CH ₂ CH ₂ O means a fragment derived from polyethylene glycol. Polyethylene glycol is used in the process of synthesizing nickel fine particles, and has the effect of reducing the particle diameter of the produced nickel fine particles and lowering the CV value, but it is easily decomposed in the sintering process, as residual carbon. It is a component that is difficult to remain.

(3) Three or more types of spectra are confirmed in a chromatogram obtained by measuring a mass spectrum at the mass number (m / z) = 45 using gas chromatography mass spectrometry (GC-MS). about.
The three or more types of spectra detected at the mass number (m / z) = 45 mean a spectrum derived from polyethylene glycol.

  The above conditions (2) and (3) both confirm the presence of polyethylene glycol. Therefore, the nickel fine particles of the present embodiment contain polyethylene glycol.

  In the nickel fine particles of the present embodiment, the average particle diameter of primary particles is preferably in the range of 10 to 150 nm, and more preferably in the range of 10 to 60 nm. As the average particle diameter of the nickel fine particles decreases, the absolute value of the melting point greatly decreases due to the melting point drop due to the size effect. Accordingly, the sintering temperature of the nickel fine particles decreases as the average particle size decreases, but if the average particle size of the primary particles of the nickel fine particles is less than 10 nm, the dispersibility tends to decrease and the surface activity is high. Therefore, it becomes difficult to suppress the oxide. On the other hand, when the average particle diameter of the primary particles of the nickel fine particles exceeds 150 nm, sintering at a low temperature may be difficult. In this specification, the average particle diameter of the primary particles of the nickel fine particles, including the values used in the examples, is taken from a sample of a sample taken by a scanning electron microscope (SEM). This is a value calculated based on the number of particles as the number of particles when 200 are randomly extracted to obtain each area and converted to a true sphere.

  Further, the nickel fine particles of the present embodiment preferably have a narrow particle size distribution in order to obtain sufficient dispersibility. For example, the coefficient of variation (standard deviation / average particle size; CV value) of the particle size is 0. It is preferably .25 or less, more preferably 0.2 or less. When the CV value exceeds 0.25, the dispersibility tends to decrease.

  In addition, the nickel fine particles of the present embodiment preferably have a crystallite diameter calculated by the Scherrer method of 15 nm or less, and more preferably 13 nm or less. As the ratio of the crystallite diameter to the average particle diameter increases, the sintering temperature increases. For this reason, when the crystallite diameter of the nickel fine particles exceeds 15 nm, sintering at a low temperature may be difficult.

  When the nickel fine particles of the present embodiment are used as a bonding material, in addition to the nickel fine particles, for example, a dispersant, an organic solvent, a flux component, a viscosity modifier, a thixotropic agent, a reducing agent, a surfactant, and the like may be contained. it can. The bonding material can be in the form of, for example, a slurry, a paste, a grease, or a wax.

[Production method of nickel fine particles]
Next, the preferable manufacturing method of the nickel fine particle of this Embodiment is demonstrated. The production of the nickel fine particles according to the present embodiment includes, for example, a nickel salt, an excessive amount of hydrazine, an alkali metal hydroxide, and a water-soluble water having a molecular weight of 100 to 5000 having one or both of a plurality of hydroxyl groups and ether oxygen. A precursor aqueous solution containing a water-soluble organic compound (hereinafter sometimes simply referred to as “water-soluble organic compound”), and the precursor aqueous solution obtained in Step I is heated to 40 to 150 ° C. Heating and stirring at a temperature within the range to reduce nickel ions and produce nickel fine particles (step II) can be performed.

(Process I)
Step I includes mixing a nickel salt or an aqueous solution thereof with an excess amount of hydrazine hydrate or an aqueous solution thereof to produce a nickel hydrazine complex salt slurry, and the slurry obtained in Step IA Step IB of adding an alkali metal hydroxide or an aqueous solution thereof to dissolve the nickel hydrazine complex salt to prepare an aqueous nickel hydrazine complex solution. The water-soluble organic compound may be added to the aqueous solution before or after the formation of the hydrazine complex salt slurry in Step IA, and may be added to the nickel hydrazine complex solution after Step IB.

  Generally, it is known that nickel hydrazine complex salt having low solubility is precipitated when nickel chloride and hydrazine are mixed in an aqueous solution. In this production method, in Step IA, a nickel hydrazine complex salt is formed by mixing an excessive amount of hydrazine with respect to the nickel salt. Next, in Step IB, an alkali metal hydroxide or an aqueous solution thereof is added to the slurry mixture obtained in Step IA to make the aqueous solution strongly alkaline. By making the aqueous solution strongly alkaline, the nickel hydrazine complex salt dissolves and the slurry mixture becomes a uniform solution. Since the complexing agent is not added to the aqueous solution thus obtained, the precursor solution is an aqueous solution of a nickel hydrazine complex.

  As the nickel salt used for preparing the precursor aqueous solution, any nickel salt having water solubility can be used. Specific examples thereof include nickel fluoride, nickel chloride (II), nickel chloride (III), odor And nickel iodide, nickel iodide, nickel acetate, nickel nitrate, and nickel sulfate.

  In Step I, “excess hydrazine” means that the number of moles of hydrazine used in the preparation of the precursor aqueous solution is larger than the number of moles of nickel ions. Therefore, in the precursor aqueous solution, the content of hydrazine with respect to 1 mol of nickel ions is preferably in the range of 6 to 30 mol, for example. When the amount of hydrazine is less than the above range, the nickel hydrazine complex salt is not completely dissolved and a precursor solution cannot be obtained. On the other hand, when the amount of hydrazine exceeds the above range, the amount of hydrazine used is excessive, which is not economical.

  Examples of alkali metal hydroxides that can be used include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide. These alkali metal hydroxides can be used alone or in a mixture of two or more in any ratio. Of these alkali metal hydroxides, sodium hydroxide and potassium hydroxide are particularly preferable in view of availability and price.

  The pH of the aqueous precursor solution is preferably 13 or higher. If the pH is less than 13, the nickel hydrazine complex salt is not completely dissolved and a precursor solution cannot be obtained, which is not preferable from the viewpoint of uniform reaction. Therefore, the alkali metal hydroxide may be blended with reference to the pH of the precursor aqueous solution being 13 or more.

  The molecular weight of the water-soluble organic compound in the precursor aqueous solution is preferably in the range of 100 to 5000, for example. When the molecular weight of the water-soluble organic compound is less than 100, the dispersion effect is low and nickel fine particles are not efficiently generated. On the other hand, a molecular weight exceeding 5000 is not preferable because the water-soluble organic compound is difficult to dissolve in the precursor solution. Specific examples of preferable water-soluble organic compounds include polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polypropylene glycol. Among these, polyethylene glycol and polypropylene glycol are particularly preferable. In addition, when the heating temperature in the process II is low, carbohydrates, such as glucose, galactose, maltose, maltotriose, dextrin, amylose, can also be used. These water-soluble organic compounds may be used by mixing any two or more of them in an arbitrary ratio, and may be a mixture of the same kind of compounds having different molecular weights (polymerization degrees).

  The concentration of the water-soluble organic compound in the precursor aqueous solution is preferably in the range of 1 to 200 g / L. When the concentration of the water-soluble organic compound is less than 1 g / L, a sufficient effect as a dispersant cannot be obtained. Moreover, when the density | concentration of a water-soluble organic compound exceeds 200 g / L, the water-soluble compound contained in a precursor solution is excess, and it becomes difficult to produce | generate nickel fine particles efficiently.

(Process II)
In Step II, by heating the precursor aqueous solution to a temperature of 40 ° C. or higher, the water-soluble organic compound acts as a dispersant when the nickel fine particles are formed, and excessive particle growth and generation of secondary particles are suppressed. Nickel fine particles having a particle size of 150 nm or less are obtained.

  When the precursor aqueous solution is heated, a green uniform slurry is instantly formed, and then changes into a black precipitate. The green intermediate product is considered to be nickel hydroxide, and the nickel hydroxide is reduced to produce nickel fine particles. At this time, by using the above water-soluble organic compound having a weak adsorbing power to the intermediate product, as a dispersing agent that adsorbs weakly to the generated nickel fine particles without impeding the reduction of nickel hydroxide to nickel, Can prevent particle growth and aggregation.

In Step II, it is preferable to perform heating while stirring at a high speed for the purpose of adjusting the bulk density of the nickel fine particles within the range of 0.5 to 3.5 g / cm ³ . As a stirring speed in the heat treatment, for example, 300 r. p. m. Or more, preferably 400 r. p. m. The above is more preferable. The stirring speed is 300 r. p. m. If it is less than this, the nickel fine particles are necked, and the bulk density tends to be lower than 0.5 g / cm ³ . Necking stabilizes the surface activity of the nickel fine particles and hinders low-temperature sintering. Moreover, it is preferable that heating temperature shall be about 60 to 100 degreeC. When heating temperature is too higher than 100 degreeC, a solvent will volatilize easily and a liquid composition will become unstable. On the other hand, if the heating temperature is too lower than 60 ° C., the nickel fine particle formation reaction rate becomes slow, so that nickel fine particles are necked and the bulk density tends to be lower than 0.5 g / cm ³ .

  As described above, nickel fine particles can be prepared. In addition, when manufacturing a nickel alloy, it can carry out according to the said method.

  The nickel fine particles obtained in this way can be sintered and heat-sealed at a low temperature of about 150 ° C. in a uniform dispersion state. For example, when used as a bonding material, the shear strength of the bonding layer is reduced. Can be high enough.

<Application method as bonding material>
When the nickel fine particles of the present embodiment are used as a bonding material, the bonding material containing nickel fine particles is interposed between the members to be bonded, for example, 150 to 480 in a reducing gas atmosphere containing a reducing gas. What is necessary is just to heat to the temperature within the range of ° C. By this heating, the nickel fine particles can be sintered to join the members to be joined together.

  More specifically, for example, a step of applying a paste-like bonding material containing nickel fine particles to one or both of the surfaces to be bonded (application step), bonding the surfaces to be bonded together, for example, temperature Heating to a temperature in the range of 150 ° C. to 480 ° C., preferably 200 ° C. to 450 ° C., to solidify the step of sintering the bonding material (firing step) and cooling the sintered bonding material And a step of forming a bonding layer (solidification step).

  In the coating process for coating the bonding material, for example, methods such as spray coating, inkjet coating, and printing can be employed. The bonding material can be applied in an arbitrary shape such as a pattern shape, an island shape, a mesh shape, a lattice shape, or a stripe shape according to the purpose. In the application step, it is preferable to apply the bonding material so that the thickness of the solidified bonding portion (bonding layer) after bonding is 120 nm or more. By applying with such a thickness, defects in the joint portion can be reduced, so that an increase in electrical resistance and a decrease in joint strength can be prevented.

  In the firing step, the nickel fine particles are sintered, and a bonding layer having a uniform and strong adhesive force can be formed. Moreover, since the oxide film and organic compound contained in the nickel fine particles are reduced, oxygen is prevented from entering the bonding layer, and the conductivity of the bonding layer is ensured. The heating temperature for bonding is preferably 150 ° C. or higher, and more preferably 200 ° C. or higher in order to obtain sufficient bonding strength. In addition, when the heating temperature exceeds 480 ° C., there is a concern about damage to the peripheral circuit or the electrode.

The formation of the bonding layer with the nickel fine particles is preferably performed in an atmosphere in which a reducing gas such as H ₂ is present. Further, by reducing the pressure, an effect of suppressing the generation of voids can be obtained. For example, the effect is confirmed at a pressure of 95% or less of the atmospheric pressure. Moreover, when bonding a joint surface, it can be pressurized as needed.

  The thickness of the joining portion (joining layer) formed by sintering the nickel fine particles is preferably, for example, 120 nm or more. When the thickness of the joint portion is thinner than this, defects in the joint portion increase, which causes an increase in electrical resistance and a decrease in strength. Note that the joint portion (joint layer) may have a void when applied to an application that requires thermal stress relaxation.

  The nickel fine particles according to the present embodiment can be used for joining, for example, metal materials as well as Si and SiC semiconductor materials. In particular, when the base material deteriorates in the heat-affected zone in joining by wax material or welding, it is preferable to join at a low temperature. For example, the nickel fine particles of the present embodiment are hardened steel, stainless steel, metal material reinforced by work hardening, thermal oxidation, whose strength is reduced by recovery or recrystallization by heating at 450 ° C. or higher or 800 ° C. or higher. Suitable for bonding inorganic materials and metal materials that deteriorate due to heat distortion. Examples of the joined body include, but are not limited to, a pipe, a plate, a joint, a rod, a wire, and a bolt.

  The nickel fine particles of the present embodiment can be used as a bonding material in the manufacturing process of electronic components. Here, examples of the electronic component mainly include a semiconductor device and an energy conversion module component. When the electronic component is a semiconductor device, for example, between the back surface of the semiconductor element and the substrate, between the semiconductor electrode and the substrate electrode, between the semiconductor electrode and the semiconductor electrode, between the power device or the power module and the heat dissipation member. It can be applied to joining.

  When bonding electronic components, in order to increase the bonding strength, for example, a contact metal layer made of a material such as Au, Cu, Pd, Ni, Ag, Cr, Ti or an alloy thereof is previously formed on one or both of the surfaces to be bonded. Is preferably provided. When the material of the surface to be joined is SiC or Si or an oxide film on the surface thereof, a contact metal layer made of a material such as Ti, TiW, TiN, Cr, Ni, Pd, V or an alloy thereof is used. It is preferable to provide it. The thickness of each contact metal layer is preferably in the range of, for example, 50 nm or more and 2 μm or less. If the thickness of the contact metal layer is less than 50 nm, defects are likely to occur, and if it exceeds 2 μm, the vapor deposition process becomes long, and the production efficiency may be reduced.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited at all by these Examples. In the examples of the present invention, various measurements and evaluations are as follows unless otherwise specified.

[Average particle diameter of nickel fine particles]
For the average particle size, a sample photograph was taken with an SEM (scanning electron microscope), 200 samples were randomly extracted from the sample, and the average particle size (area average diameter) and standard deviation were obtained. Specifically, the area of each of the extracted fine particles was obtained, and the average particle size of the primary particles was determined based on the particle size when converted to a true sphere. The CV value (coefficient of variation) was calculated by (standard deviation) / (average particle diameter). In addition, it shows that a particle diameter is so uniform that a CV value is small.

[Crystal diameter of nickel fine particles]
From the powder X-ray diffraction (XRD) result, the calculation was performed according to Scherrer's equation.

[5% heat shrink temperature]
A sample is put into a 5Φ × 2 mm cylindrical molding machine, and a molded body obtained by press molding is produced, and measured by a thermomechanical analyzer (TMA) in an atmosphere of nitrogen gas (containing 3% hydrogen gas). The temperature of 5% heat shrinkage was taken as 5% heat shrinkage temperature.

(Example 1)
A solution containing 108 g / L nickel chloride hexahydrate, 272 g / L hydrazine monohydrate, 97.3 g / L sodium hydroxide and 50 g / L polyethylene glycol of molecular weight 1540 was prepared. Next, with vigorous stirring (stirring speed: 600 rpm), the solution was heated to 80 ° C. and kept at that temperature for 1 hour, whereby nickel fine particles 1 were obtained. The characteristics of the nickel fine particles 1 were as follows.
1) Elemental analysis of nickel fine particles 1; C: 0.4, O: 0.8 (unit: mass%).
2) Average particle diameter obtained from SEM measurement of nickel fine particles 1; 147 nm, CV value; 0.22.
3) No peaks other than Ni are detected by XRD. Ni crystallite diameter from XRD in nickel fine particles 1; 20.3 nm.
4) Temperature at 5% heat shrinkage during TMA measurement; 246 ° C
5) A peak was detected at a mass number of 45 indicating a functional group of (CH ₂ CH ₂ O) — derived from polyethylene glycol by TOF-SIMS analysis. In addition, when the mass number is 60 or more, no peaks other than nickel-derived peaks were detected.
6) Bulk density of nickel fine particles 1; 1.0 g / cm ³

  The measurement results of SEM, XRD, and TMA of the nickel fine particles 1 are shown in FIGS.

(Example 2)
A nickel fine particle 2 was obtained in the same manner as in Example 1 except that the concentration of polyethylene glycol having a molecular weight of 400 was 200 g / L. The characteristics of the nickel fine particles 2 were as follows.
1) Elemental analysis of nickel fine particles 2; C: 0.5, O: 1.1 (unit: mass%).
2) Average particle diameter obtained from SEM measurement of nickel fine particles 2; 87 nm, CV value; 0.26.
3) No peaks other than Ni are detected by XRD. Ni crystallite diameter from XRD in the nickel fine particles 2; 15.8 nm.
4) Temperature at 5% heat shrinkage during TMA measurement; 254 ° C
5) A peak was detected at a mass number of 45 indicating a functional group of (CH ₂ CH ₂ O) — derived from polyethylene glycol by TOF-SIMS analysis. In addition, when the mass number is 60 or more, no peaks other than nickel-derived peaks were detected.
6) Bulk density of the nickel fine particles 2; 0.7 g / cm ³

  The measurement results of SEM, XRD, and TMA of the nickel fine particles 2 are shown in FIGS.

(Example 3)
A nickel fine particle 3 was obtained in the same manner as in Example 1 except that the concentration of polyethylene glycol having a molecular weight of 200 was 100 g / L and the holding time was 30 minutes. The characteristics of the nickel fine particles 3 were as follows.
1) Elemental analysis of nickel fine particles 3; C: 0.4, O: 2.1 (unit: mass%).
2) Average particle diameter obtained from SEM measurement of nickel fine particles 3; 50 nm, CV value: 0.18.
3) No peaks other than Ni are detected by XRD. Ni crystallite diameter from XRD in nickel fine particles 4; 11.8 nm.
4) Temperature at 5% heat shrinkage during TMA measurement; 142 ° C
5) A peak was detected at a mass number of 45 indicating a functional group of (CH ₂ CH ₂ O) — derived from polyethylene glycol by TOF-SIMS analysis. In addition, when the mass number is 60 or more, no peaks other than nickel-derived peaks were detected.
6) Bulk density of the nickel fine particles 3; 0.6 g / cm ³

  The measurement results of SEM, XRD, TMA, and TOF-SIMS of the nickel fine particles 3 are shown in FIGS.

Example 4
A nickel fine particle 4 was obtained in the same manner as in Example 1 except that the concentration of polyethylene glycol having a molecular weight of 400 was 200 g / L and the holding time was 30 minutes. The characteristics of the nickel fine particles 4 were as follows.
1) Elemental analysis of nickel fine particles 4; C: 0.6, O: 1.9 (unit: mass%).
2) Average particle diameter obtained from SEM measurement of nickel fine particles 4; 51 nm, CV value: 0.18.
3) No peaks other than Ni are detected by XRD. Ni crystallite diameter from XRD in nickel fine particles 4; 13.7 nm.
4) Temperature at 5% heat shrinkage during TMA measurement; 220 ° C
5) A peak is detected at a mass number of 45 indicating a functional group of (CH ₂ CH ₂ O) — derived from polyethylene glycol by GC-MS analysis, and a mass indicating a functional group of (CH ₂ CH ₂ O) ₂ — A peak was also detected at 90.
6) Bulk density of nickel fine particles 4; 0.6 g / cm ³

  The measurement results of SEM, XRD, TMA, and GC-MS of the nickel fine particles 4 are shown in FIGS.

(Comparative Example 1)
<Dissolution process>
To 285 g (1.14 mol) of nickel acetate tetrahydrate, 690 g (2.58 mol) of oleylamine was added, and nickel acetate was dissolved in oleylamine by heating at 140 ° C. for 20 minutes under a nitrogen flow.

<Reduction process>
Next, the solution was irradiated with microwaves and heated to 250 ° C., and the temperature was maintained for 5 minutes to obtain nickel fine particles 5. The characteristics of the nickel fine particles 5 were as follows.
1) Elemental analysis of nickel fine particles 5: C: 0.3, O: 0.6 (unit: mass%).
2) Average particle diameter obtained from SEM measurement of nickel fine particles 5: 158 nm, CV value: 0.12.
3) No peaks other than Ni are detected by XRD. Ni crystallite diameter from XRD in nickel fine particles 5; 18.3 nm.
4) Temperature at 5% heat shrinkage during TMA measurement; 315 ° C
5) Bulk density of the nickel fine particles 5: 3.5 g / cm ³

  The measurement results of SEM, XRD, and TMA of the nickel fine particles 5 are shown in FIGS.

(Comparative Example 2)
<Dissolution process>
To 60.0 g (241.1 mmol) of nickel acetate tetrahydrate, 690 g (2.58 mol) of oleylamine was added, and nickel acetate was dissolved in oleylamine by heating at 140 ° C. for 20 minutes under a nitrogen flow.

<Reduction process>
Next, the solution was irradiated with microwaves and heated to 250 ° C., and the temperature was maintained for 5 minutes to obtain nickel fine particles 6. The characteristics of the nickel fine particles 6 were as follows.
1) Elemental analysis of nickel fine particles 6: C: 0.7, O: 1.3 (unit: mass%).
2) Average particle diameter obtained from SEM measurement of nickel fine particles 6; 90 nm, CV value: 0.19.
3) No peaks other than Ni are detected by XRD. Ni crystallite diameter from XRD in nickel fine particles 6; 16.0 nm.
4) Temperature at 5% heat shrinkage during TMA measurement; 295 ° C
5) Bulk density of the nickel fine particles 6: 3.3 g / cm ³

  The measurement results of SEM, XRD, and TMA of the nickel fine particles 6 are shown in FIGS.

(Comparative Example 3)
<Dissolution process>
To 479 g (1.93 mmol) of nickel acetate tetrahydrate, 690 g (2.58 mol) of oleylamine was added, and nickel acetate was dissolved in oleylamine by heating at 140 ° C. for 40 minutes under a nitrogen flow.

<Reduction process>
Next, 1.63 g of silver nitrate was added to the solution, microwave irradiation was performed, the mixture was heated to 250 ° C., and the temperature was maintained for 5 minutes, whereby nickel fine particles 7 were obtained. The characteristics of the nickel fine particles 7 were as follows.
1) Elemental analysis of nickel fine particles 7: C: 1.5, O: 2.9 (unit: mass%).
2) Average particle diameter obtained from SEM measurement of nickel fine particles 7; 51 nm, CV value: 0.15.
3) No peaks other than Ni are detected by XRD. Ni crystallite diameter from XRD in nickel fine particles 7; 14.1 nm.
4) Temperature at 5% heat shrinkage during TMA measurement; 300 ° C
5) Bulk density of the nickel fine particles 7; 3.0 g / cm ³

  The measurement results of SEM, XRD, and TMA of the nickel fine particles 7 are shown in FIGS.

(Comparative Example 4)
A solution containing nickel chloride hexahydrate at a concentration of 108 g / L, 272 g / L hydrazine monohydrate, and 97.3 g / L sodium hydroxide was prepared. Next, the solution was heated to 80 ° C. and held at that temperature for 1 hour, whereby nickel fine particles 8 were obtained. The characteristics of the nickel fine particles 8 were as follows.
1) Elemental analysis of nickel fine particles 8; C: 0.3, O: 0.2 (unit: mass%).
2) Average particle diameter obtained from SEM measurement of nickel fine particles 8: 539 nm, CV value: 0.14.
3) No peaks other than Ni are detected by XRD. Ni crystallite diameter from XRD in nickel fine particles 8; 24.6 nm.
4) Temperature at 5% heat shrinkage during TMA measurement; 500 ° C
5) Bulk density of nickel fine particles 8: 1.9 g / cm ³

  The measurement results of SEM, XRD, and TMA of the nickel fine particles 8 are shown in FIGS.

(Comparative Example 5)
A mixed solution of water and isopropanol having a concentration of nickel chloride hexahydrate of 194 g / L was added to an isopropanol solution having a concentration of hydrazine monohydrate of 254 g / L. A sodium hydroxide aqueous solution having a concentration of 404 g / L was added to the solution. Subsequently, after leaving still at 35 degreeC for 30 minutes, the nickel fine particle 9 was obtained by stirring for 1 hour. The characteristics of the nickel fine particles 9 were as follows.
1) Elemental analysis of nickel fine particles 9; C: 0.3, O: 0.7 (unit: mass%).
2) Average particle diameter obtained from SEM measurement of nickel fine particles 9; 80 nm, CV value: 0.17.
3) No peaks other than Ni are detected by XRD. Ni crystallite diameter from XRD in nickel fine particles 9; 15.0 nm.
4) Temperature at 5% heat shrinkage during TMA measurement; 320 ° C
5) Bulk density of nickel fine particles 9; 0.3 g / cm ³

  The SEM measurement result of the nickel fine particles 9 is shown in FIG.

(Reference Example 1)
Nickel fine particles 10 were obtained in the same manner as in Example 1 except that the stirring speed during heating in Example 1 was changed to 100 rpm. The characteristics of the nickel fine particles 10 were as follows.
1) Elemental analysis of nickel fine particles 10; C: 0.3, O: 0.7 (unit: mass%).
2) Average particle diameter obtained from SEM measurement of nickel fine particles 10; 80 nm, CV value: 0.17.
3) No peaks other than Ni are detected by XRD. Ni crystallite diameter from XRD in the nickel fine particles 10; 15.0 nm.
4) Temperature at 5% heat shrinkage during TMA measurement; 320 ° C
5) Bulk density of nickel fine particles 10; 0.3 g / cm ³

  The results of Examples 1 to 4, Comparative Examples 1 to 5 and Reference Example 1 are summarized in Table 1.

From the above results, the bulk density is in the range of 0.5 to 3.5 g / cm ³ , the carbon element content is in the range of 0.3 to 1.0 mass%, and the oxygen element content is 0.5. The nickel fine particles of Examples 1 to 4 satisfying at least one of the above condition (1) and the condition (2) or the condition (3) within the range of ~ 2.5% by mass. It was confirmed that the 5% heat shrinkage temperature was sufficiently lower than the nickel fine particles of No. 5 and Reference Example 1. In particular, the measurement result of TMA in Example 3 shows that there is a possibility of bonding even at a low temperature of about 150 ° C. Therefore, the nickel fine particles of Examples 1 to 4 can be sintered and heat-sealed at a low temperature, and are useful as bonding materials. Further, the nickel fine particles of Comparative Example 5 and Reference Example 1 had a lower bulk density than the nickel fine particles of Examples 1 to 4. As the cause, it can be considered that the nickel fine particles of Comparative Example 5 and Reference Example 1 are necked and not densely packed.

  As mentioned above, although embodiment of this invention was described in detail for the purpose of illustration, this invention is not restrict | limited to the said embodiment.

Claims (2)

The bulk density is in the range of 0.5 to 3.5 g / cm ³ , the carbon element content is in the range of 0.3 to 1.0 mass%, and the oxygen element content is in the range of 0.5 to 2. Within the range of 5% by mass, and the following conditions (1) and (2) or (3),
(1) When measured using time-of-flight secondary ion mass spectrometry (TOF-SIMS), a fragment derived from an organic substance consisting of C and H is not detected at a mass number (m / z) ≧ 80;
(2) a CH ₂ CH ₂ O fragment is detected at a mass number (m / z) = 45 as measured using time-of-flight secondary ion mass spectrometry (TOF-SIMS);
(3) Three or more types of spectra are confirmed in a chromatogram obtained by measuring a mass spectrum at the mass number (m / z) = 45 using gas chromatography mass spectrometry (GC-MS). about;
Nickel fine particles that satisfy the requirements.   The average primary particle size is in the range of 10 to 150 nm, the particle size variation coefficient (standard deviation / average particle size) is 0.25 or less, and the crystallite size calculated by the Scherrer method is 15 nm or less. Item 2. Nickel fine particles according to Item 1.