Method for producing metallic particle and metallic particle

Abstract

To realize a method for producing metallic particles having excellent handling properties in the printing process, in which viscosity of a paste does not increase excessively even when a paste with a high metal content is prepared, and to realize the metallic particles.SOLUTION: Provided is a method that includes mixing the following components: a solid metal compound; a reducing agent having at least two hydroxy groups per molecule; a protecting agent having at least one carboxy group per molecule; and a solvent.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing metal particles, and to metal particles. [Background technology]

[0002] In the manufacture of semiconductors and electronic circuits, a method is widely used in which various electronic components are placed on a substrate and the electrical continuity between the electronic components and the substrate is ensured by soldering. In recent years, lead-free solder has been required as the solder used for this type of soldering, and paste containing silver nanoparticles (silver nanoparticle paste) is used as one of the materials that meets the demand for a replacement for high-temperature lead-free solder. Silver particles used in conventional silver nanoparticle paste are disclosed in International Publication No. 2009 / 090846 (Patent Document 1) and International Publication No. 2006 / 082996 (Patent Document 2), and are applied to a substrate using a printing technique to form contacts on the substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2009 / 090846 [Patent Document 2] International Publication No. 2006 / 082996 Summary of the Invention [Problem to be solved by the invention]

[0004] When the silver particles described in Patent Document 1 and Patent Document 2 are made into a paste and used to bond electronic components to a substrate, the viscosity of the paste tends to be high due to the fineness of the particles. If the viscosity of the paste is excessively high, printing defects such as poor mask removal and poor printing surface accuracy may occur in the printing process in which the paste is applied to the substrate. In order to avoid this, it is necessary to reduce the silver content of the paste, but in this case, voids or cracks may occur at the bonding portion, resulting in poor bonding. Thus, the silver particles described in Patent Document 1 and Patent Document 2 have room for improvement in terms of handleability in the printing process.

[0005] Therefore, there is a need to realize a manufacturing method for metal particles and metal particles that are easy to handle in the printing process and do not increase the viscosity of the paste excessively even when a paste with a high metal content is prepared. [Means for solving the problem]

[0006] The method for producing metal particles according to the present invention is characterized in that it includes mixing a solid metal compound, a reducing agent having at least two hydroxyl groups per molecule, a protecting agent having at least one carboxyl group per molecule, and a solvent.

[0007] The metal particles according to the present invention comprise a particle core containing metal atoms and an organic compound layer disposed around the particle core, the organic compound layer having a reducing agent residue derived from a reducing agent having at least two hydroxyl groups per molecule and a protecting agent residue derived from a protecting agent having at least one carboxy group per molecule, and are characterized in that the average particle diameter d50 is 10 nm or more and 200 nm or less.

[0008] These features provide metal particles that do not excessively increase the viscosity of a paste even when a paste with a high metal content is prepared. The metal particles have excellent handleability in the printing process.

[0009] Preferred embodiments of the present invention will be described below. However, the scope of the present invention is not limited to the preferred embodiments described below.

[0010] In one aspect, the method for producing metal particles according to the present invention preferably includes mixing the metal compound with the protective agent to produce an intermediate, and mixing the intermediate with the reducing agent to produce the metal particles.

[0011] According to this configuration, it is easy to control the speed of the reaction when the metal particles are produced, and it is also easy to control the particle size of the metal particles.

[0012] In one embodiment, the method for producing metal particles according to the present invention preferably includes preparing a slurry containing the metal compound.

[0013] According to this configuration, it is easy to keep the reaction rate constant, and therefore it is easy to control the particle size of the metal particles.

[0014] In one aspect of the method for producing metal particles according to the present invention, the solvent preferably has reducing properties.

[0015] According to this configuration, unreacted metal compounds are less likely to be produced.

[0016] In one aspect of the method for producing metal particles according to the present invention, the metal particles preferably have an average particle size d50 of 10 nm or more and 200 nm or less.

[0017] This configuration makes it easier to obtain a metal particle paste with a viscosity suitable for the printing process.

[0018] In one aspect of the method for producing metal particles according to the present invention, the metal particles preferably have a weight loss rate of 2 mass % or less at 200° C. in thermogravimetry.

[0019] According to this configuration, shrinkage during firing of the metal particle paste can be suppressed, so that defects such as cracks and voids are less likely to occur at the joint.

[0020] In one embodiment of the method for producing metal particles according to the present invention, a peak is preferably detected at 200° C. or less in differential thermal analysis of the metal particles.

[0021] According to this configuration, a circuit bonding material that sinters at 200° C. or less can be obtained.

[0022] In one aspect of the method for producing metal particles according to the present invention, the oxygen concentration of the atmosphere in which the metal compound, the reducing agent, the protective agent, and the solvent are mixed is preferably 1000 ppm or more.

[0023] This configuration is preferable in that aggregation of metal particles is suppressed.

[0024] In one embodiment of the method for producing metal particles according to the present invention, the metal compound is preferably a silver compound.

[0025] According to this configuration, silver particles suitable as a circuit bonding material can be obtained.

[0026] Further features and advantages of the present invention will become more apparent from the following description of illustrative and non-limiting embodiments. [Brief description of the drawings]

[0027] [Figure 1] 1 is a scanning electron microscope image of silver particles according to Example 1. [Diagram 2] FIG. 2 is a graph showing the particle size distribution of silver particles according to Example 1. [Diagram 3] 1 is a scanning electron microscope image of silver particles according to Example 2. [Figure 4] FIG. 4 is a graph showing the particle size distribution of silver particles according to Example 2. [Diagram 5] 1 is a scanning electron microscope image of silver particles according to Example 3. [Figure 6] FIG. 11 is a graph showing the particle size distribution of silver particles according to Example 3. [Figure 7]1 is a scanning electron microscope image of silver particles according to Example 4. [Figure 8] FIG. 11 is a graph showing the particle size distribution of silver particles according to Example 4. [Figure 9] 1 is a scanning electron microscope image of silver particles according to Example 5. [Figure 10] FIG. 11 is a graph showing the particle size distribution of silver particles according to Example 5. [Figure 11] 1 is a scanning electron microscope image of silver particles according to Example 6. [Figure 12] FIG. 13 is a graph showing the particle size distribution of silver particles according to Example 6. [Figure 13] 1 is a scanning electron microscope image of silver particles according to Example 7. [Figure 14] FIG. 11 is a graph showing the particle size distribution of silver particles according to Example 7. [Figure 15] 1 is a scanning electron microscope image of silver particles according to Example 8. [Figure 16] 1 is a scanning electron microscope image of silver particles according to Example 9. [Figure 17] 1 is a scanning electron microscope image of silver particles according to Example 10. [Figure 18] 1 is a scanning electron microscope image of silver particles according to Comparative Example 1. [Figure 19] FIG. 2 is a graph showing the particle size distribution of silver particles according to Comparative Example 1. [Figure 20] 1 is a TG-DTA chart of silver particles according to Example 1. [Figure 21] 1 is a TG-DTA chart of silver particles relating to Comparative Example 1. [Figure 22] 1 is a scanning electron microscope image of silver particles according to Example 1 after heating at 130° C. [Figure 23] 1 is a scanning electron microscope image of silver particles according to Example 1 after heating at 180° C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] An embodiment of the metal particles and the method for producing the same according to the present invention will be described.

[0029] [Constitution of Metal Particles] The metal particle according to the present embodiment includes a particle core containing a metal atom and an organic compound layer disposed around the particle core. The metal atom contained in the particle core is not particularly limited, but may be, for example, silver. The organic compound layer has a reducing agent residue derived from a reducing agent having at least two hydroxyl groups per molecule, and a protecting agent residue derived from a protecting agent having at least one carboxyl group per molecule.

[0030] The reducing agent residue is a residue derived from the reducing agent used in producing the metal particles. Such reducing agents may be, for example, but are not limited to, ethylene glycol, diethylene glycol, polyethylene glycol, glycerin, etc. For example, metal particles produced using ethylene glycol HOCH2CH2OH as a reducing agent have a reducing agent residue OCH2CH2O, and this reducing agent residue exists in a state where oxygen atoms at both ends are coordinately bonded to metal atoms of the particle core.

[0031] The protective agent residue is a residue derived from a protective agent used in producing the metal particles. Such protective agents can be, but are not limited to, hexanoic acid, citric acid, acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, ascorbic acid, etc. For example, hexanoic acid C5H 11 Metal particles produced using COOH have a protective agent residue of CH 11 The protecting agent has a COO group, and the carboxyl group from which a proton has been released exists in a coordinate bond with the metal atom of the particle core.

[0032] The metal particles according to this embodiment have an average particle size d50 of 10 nm or more and 200 nm or less. The average particle size d50 was measured by analyzing an image taken with a scanning electron microscope (SEM) using image analysis software Image, and calculating the arithmetic mean of the maximum diameter of the particles in the image. When the average particle size d50 of the metal particles is 10 nm or more, it is easy to avoid the viscosity of the paste containing the metal particles from becoming excessively high, so that the paste can be easily used for paste printing. In addition, when the average particle size d50 is 200 nm or less, the sintering property of the metal particles is good. The average particle size d50 of the metal particles is preferably 50 nm or more, more preferably 70 nm or more. The average particle size d50 of the metal particles is preferably 150 nm or less.

[0033] The metal particles according to this embodiment preferably have a weight loss rate of 2% by mass or less at 200°C in thermogravimetry. The metal particles according to this embodiment preferably have a peak detected at 200°C or less in differential thermal analysis. This peak is a peak caused by sintering of the metal particles. The thermogravimetry and differential thermal analysis can be carried out, for example, under the following conditions. Note that it is not prohibited to carry out the thermogravimetry and differential thermal analysis separately. Equipment: Bruker TG-DTA2000SA Temperature range: Room temperature to 200℃ Heating rate: 5℃ / min Atmosphere: Air

[0034] [Method for producing metal particles] The method for producing metal particles according to the present invention includes mixing a solid metal compound, a reducing agent having at least two hydroxyl groups per molecule, a protecting agent having at least one carboxyl group per molecule, and a solvent.

[0035] (Substances and equipment used) The metal compound used in this embodiment is a compound containing a metal atom and is in a solid state. The metal atom is not particularly limited, but may be, for example, silver. The compound containing a metal atom may be, but is not limited to, a metal carbonate or a metal oxide. The form of the metal compound is not limited as long as it is in a solid state, and may be in any form such as a powder or a pellet.

[0036] The reducing agent used in this embodiment may be, for example, ethylene glycol, diethylene glycol, polyethylene glycol, glycerin, etc., but is not limited thereto.

[0037] The protecting agent used in this embodiment may be, for example, hexanoic acid, citric acid, acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, ascorbic acid, and the like, but is not limited thereto.

[0038] The solvent used in this embodiment may be, for example, 1-hexanol, n-dodecane, dimethylformamide, dimethylsulfoxide, etc., but is not limited thereto. When a solvent having reducing properties is used, unreacted metal oxide is unlikely to be generated even in the case where the reducing agent is insufficient. In addition, it is also preferable in that oxidation of the substrate during paste bonding can be suppressed.

[0039] In this embodiment, the apparatus used for producing the metal particles is not limited as long as it is an apparatus capable of promoting a solid-liquid reaction between the protective agent and the reducing agent in the solvent and the solid metal compound. Therefore, known apparatuses such as glass containers such as flasks and metal containers such as autoclaves can be used. Such apparatuses may have auxiliary devices such as a stirring device and a temperature control device.

[0040] (Reaction conditions) When a metal compound, a reducing agent, a protective agent, and a solvent are mixed, a first reaction occurs in which the metal compound and the protective agent react in the solvent to produce an intermediate, and a second reaction occurs in which the intermediate reacts with the reducing agent to produce metal particles.

[0041] As an operation for producing metal particles, the order of mixing the four components of the metal compound, the reducing agent, the protective agent, and the solvent is not limited. Therefore, a method of mixing the metal compound, the protective agent, and the solvent to cause a first reaction and then adding the reducing agent to cause a second reaction, a method of mixing the four components of the metal compound, the reducing agent, the protective agent, and the solvent at once, a method of mixing the reducing agent, the protective agent, and the solvent and then adding the metal compound, and the like can be selected. The metal compound may be mixed as a solid such as a powder, or a slurry prepared in advance by mixing the metal compound and a dispersion medium may be mixed. The dispersion medium used to prepare the slurry at this time may be the same as or different from the above-mentioned solvent. It is not prevented from isolating the intermediate.

[0042] For example, when the metal compound is silver carbonate, the protective agent is hexanoic acid, and the reducing agent is ethylene glycol, a first reaction produces silver hexanoate (an example of an intermediate). The silver hexanoate is then at least partially reduced by a reaction between the silver hexanoate and ethylene glycol (a second reaction) to produce silver particles (an example of metal particles). The silver particles are an example of metal particles according to this embodiment, and include a particle core containing silver atoms (an example of metal atoms) and an organic compound layer having hexanoic acid residues (an example of protective agent residues) and ethylene glycol residues (an example of reducing agent residues).

[0043] The temperature at which the metal compound, the reducing agent, the protecting agent, and the solvent are mixed (hereinafter referred to as the reaction temperature) is not particularly limited, but may be, for example, 60° C. or higher. The reaction temperature is preferably 120° C. or higher. The upper limit of the reaction temperature is not particularly limited, but may be a temperature lower than the boiling point of the solvent. For example, when the solvent is hexanol, the reaction temperature may be a temperature lower than 157° C., which is the boiling point of hexanol.

[0044] The atmosphere in which the metal compound, the reducing agent, the protective agent, and the solvent are mixed may be an air atmosphere or an inert gas atmosphere such as nitrogen or argon. If the oxygen concentration in the atmosphere is 1000 ppm or more, it is preferable in that aggregation of metal particles is suppressed.

[0045] The end of the reaction can be determined by the appearance of the mixture of the metal compound, reducing agent, protective agent, and solvent. For example, if the metal compound is silver carbonate, carbon dioxide gas is generated and bubbles are observed in the mixture. When the entire amount of silver carbonate added as a raw material has reacted, the generation of bubbles stops. Therefore, the end of the reaction can be determined based on the presence or absence of bubbles. Note that when metal particles are produced multiple times under similar conditions, the end of the reaction may be determined based on the time required for the reaction to end in past productions.

[0046] The reacted metal particles can be collected by any method, for example, by filtering the reacted mixture after cooling it to room temperature.

[0047] Other embodiments Regarding other configurations, it should be understood that the embodiments disclosed in this specification are illustrative in all respects and that the scope of the present invention is not limited thereto. A person skilled in the art would easily understand that appropriate modifications are possible without departing from the spirit of the present invention. Therefore, other embodiments modified without departing from the spirit of the present invention are naturally included in the scope of the present invention. EXAMPLES

[0048] The present invention will be further described below with reference to examples, but the following examples are not intended to limit the invention.

[0049] 〔reagent〕 (metal compound) Silver carbonate was used as the metal compound.

[0050] (reducing agent) Ethylene glycol (molecular weight 62.07) or diethylene glycol (molecular weight 106.12) was used as the reducing agent.

[0051] (Protective agent) Hexanoic acid or citric acid was used as the protecting agent.

[0052] (solvent) Hexanol or dodecane was used as the solvent.

[0053] [Production of Silver Particles] Example 1 In a 1 L three-neck flask equipped with a reflux condenser, add 76.5 g of hexanol, 5.0 g of hexanoic acid, and 5.0 g of ethylene glycol (8.0 × 10 ―2 mol) was added to the flask, and the mixture was heated and stirred in an oil bath at 120°C while air was circulating in the flask. After the temperature of the mixture in the flask reached 120°C, 15g of silver carbonate powder was added to the flask. The inside of the flask was observed, and 10 minutes after the generation of bubbles in the mixture had stopped, the stirring was stopped and the flask was removed from the oil bath. After the temperature of the mixture in the flask had dropped to room temperature, the silver particles were filtered out from the mixture. The filtered silver particles were washed with isopropyl alcohol to obtain a silver particle sample of Example 1.

[0054] The obtained silver particle sample was observed using a scanning electron microscope (SEM) and the particle size was measured (Figure 1). The average particle size d50 of the obtained silver particle sample was 86.1 nm, and the standard deviation σ was 36.8 (Figure 2).

[0055] Example 2 The amount of ethylene glycol used was 1.0 g (1.6 x 10 ―2 Except for changing the concentration of silver in the silver particles to 1.5 moles, the test was conducted in the same manner as in Example 1. The average particle size d50 of the obtained silver particle sample was 51.5 nm, and the standard deviation σ was 21.4 (FIGS. 3 and 4).

[0056] Example 3 The amount of ethylene glycol used was 2.5 g (4.0 x 10―2 Except for changing the concentration of silver in the silver particles to 1.0 moles, the test was conducted in the same manner as in Example 1. The average particle size d50 of the obtained silver particle sample was 58.3 nm, and the standard deviation σ was 32.4 (FIGS. 5 and 6).

[0057] Example 4 The amount of ethylene glycol used is 10 g (1.6 x 10 ―1 Except for changing the concentration of silver in the silver particles to 100% by mass (mol), the test was conducted in the same manner as in Example 1. The average particle size d50 of the obtained silver particle sample was 107.6 nm, and the standard deviation σ was 44.6 (FIGS. 7 and 8).

[0058] Example 5 Except for changing the amount of hexanoic acid used to 1.0 g, the test was performed in the same manner as in Example 1. The average particle size d50 of the obtained silver particle sample was 161.8 nm, and the standard deviation σ was 85.0 (FIGS. 9 and 10).

[0059] Example 6 Except for changing the amount of hexanoic acid used to 10 g, the test was performed in the same manner as in Example 1. The average particle size d50 of the obtained silver particle sample was 74.7 nm, and the standard deviation σ was 37.7 (FIGS. 11 and 12).

[0060] Example 7 The test was carried out in the same manner as in Example 1, except that the reaction temperature was set to 140° C. The average particle size d50 of the obtained silver particle sample was 70.5 nm, and the standard deviation σ was 32.0 (FIGS. 13 and 14).

[0061] Example 8 Ethylene glycol was replaced with 8.5g of diethylene glycol (8.0 x 10 ―2 The test was carried out in the same manner as in Example 7, except that 1000 μg / mol of silver was used. The average particle size d50 of the obtained silver particle sample was 110.2 nm, and the standard deviation σ was 107.7 (FIG. 15).

[0062] Example 9 Hexanol was replaced with 127.8 g of dodecane (8.0 x 10 ―2The test was carried out in the same manner as in Example 1, except that 100% (mol) of hexanoic acid and ethylene glycol were used. In Example 1, hexanoic acid and ethylene glycol were dissolved in hexanol, resulting in a single liquid phase, whereas in Example 9, hexanoic acid and ethylene glycol were not dissolved in dodecane, resulting in a double liquid phase. The average particle size d50 of the obtained silver particle sample was 52.9 nm, and the standard deviation σ was 26.3 (Figure 16).

[0063] Example 10 Instead of hexanoic acid, use 8.6 g of citric acid (8.0 x 10 ―2 The test was conducted in the same manner as in Example 7, except that a 100% aqueous solution (mol) of silver carbonate was used. The time from the addition of silver carbonate powder until the generation of bubbles stopped was 10 minutes in Example 7, but 140 minutes in Example 10. The average particle size d50 of the obtained silver particle sample was 24.9 nm, and the standard deviation σ was 11.8 (Figure 17).

[0064] Comparative Example 1 A test was performed in the same manner as in Example 7, except that hexanoic acid and ethylene glycol were not used, to obtain a silver particle sample according to Comparative Example 1. The obtained silver particle sample was observed and the particle size was measured in the same manner as in Example 1 (FIG. 18). The average particle size d50 of the obtained silver particle sample was 17.1 nm, and the standard deviation σ was 3.8 (FIG. 19).

[0065] [Thermogravimetry and differential thermal analysis] For each of the silver particle samples of Example 1 and Comparative Example 1, thermogravimetry and differential thermal analysis were carried out under the following conditions. Equipment: Bruker TG-DTA2000SA Temperature range: Room temperature to 200℃ Heating rate: 5℃ / min Atmosphere: Air

[0066] For the silver particle sample obtained in Example 1, the weight loss rate at 200°C was 0.5% by mass (FIG. 20). On the other hand, for the silver particle sample obtained in Comparative Example 1, the weight loss rate at 200°C was 2.5% by mass (FIG. 21). In the differential thermal analysis of the silver particle sample obtained in Example 1, a peak was detected at 169.8°C (FIG. 20). On the other hand, in the differential thermal analysis of the silver particle sample obtained in Comparative Example 1, a peak was detected at 235.1°C (FIG. 21).

[0067] [Sintering test] The silver particle sample obtained in Example 1 was placed on a sample stage and heated to 130°C, and the state of the particles was observed in the same manner as in Example 1 (Fig. 22). In addition, the silver particle sample obtained in Example 1 was placed on a sample stage and heated to 180°C, and the state of the particles was observed in the same manner as in Example 1 (Fig. 23). In both tests, necking between the silver nanoparticles was observed, and it was found that the silver nanoparticles could be sintered at each temperature. [Industrial Applicability]

[0068] The present invention can be used, for example, in the production of silver particles.

Claims

1. A solid metal compound; a reducing agent having at least two hydroxy groups per molecule; a protecting agent having at least one carboxy group per molecule; A method for producing metal particles comprising mixing a metal powder and a solvent.

2. mixing the metal compound and the protective agent to form an intermediate; and mixing the intermediate with the reducing agent to produce the metal particles.

3. The method of claim 1 , comprising preparing a slurry containing the metal compound.

4. The method according to claim 1 , wherein the solvent has reducing properties.

5. The method according to claim 1, wherein the metal particles have an average particle size d50 of 10 nm or more and 200 nm or less.

6. The method according to claim 1 , wherein the weight loss rate of the metal particles at 200° C. in thermogravimetry is 2% by mass or less.

7. The method according to claim 1 , wherein a peak is detected at 200° C. or less in differential thermal analysis of the metal particles.

8. 2. The method according to claim 1, wherein the oxygen concentration in an atmosphere in which the metal compound, the reducing agent, the protective agent, and the solvent are mixed is 1000 ppm or more.

9. The method according to any one of claims 1 to 8, wherein the metal compound is a silver compound.

10. A particle core including a metal atom; an organic compound layer disposed around the particle core; The organic compound layer is a reducing agent residue derived from a reducing agent having at least two hydroxy groups per molecule; a protecting agent residue derived from a protecting agent having at least one carboxy group per molecule, Metal particles having an average particle size d50 of 10 nm or more and 200 nm or less.

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