Metal powder, method for producing same, and metal paste

Abstract

The present invention relates to a metal powder which has an average particle diameter of 0.1-0.4 [mu] m and contains a metal selected from among Au, Ag and Cu having a purity of 99.9 mass% or more, or an alloy thereof. In the metal powder, the abundance ratio of the non-spherical metal powder having a ratio of the minor axis a to the major axis b of 3 or more is 1% or less based on the number of particles. In addition, preferably, the abundance ratio of coarse particles having a particle diameter of 0.5 [mu] m or more on the basis of the number of particles is 10% or less. The method for producing the metal powder is a wet reduction method comprising a metal colloid synthesis step and a metal powder granulation step in which metal colloid particles are granulated to form a metal powder, it is preferable that the first dispersant / second dispersant used in the metal colloid synthesis step and the metal powder granulation step be a surfactant having an alkyl group having a carbon number in a predetermined range.

Description

Technical Field

[0001] The present invention relates to metal powders for use in electrode / wiring formation, bonding, sealing, etc. in the electronic fields such as semiconductor devices and semiconductor elements, and a method for manufacturing the same. In particular, it relates to a metal powder with a reduced ratio of non-spherical particles and a method for manufacturing the same. Background Art

[0002] In recent years, the use of metal pastes has been expanding in various processes such as element bonding, electrode / wiring formation, and hermetic sealing in electrical / electronic components, semiconductor devices, semiconductor elements, power devices, MEMS, etc. Regarding the metal pastes for such uses, the inventors of the present application have previously proposed that a metal paste formed by mixing metal powders composed of high-purity (99.9 mass% or more) metals (such as gold, silver, palladium, copper, etc.) and having a submicron size (1 μm or less) in an organic solvent is useful in the above uses. (For example, Patent Documents 1 to 3).

[0003] For example, in the manufacturing process of semiconductor devices, in bonding processes such as die bonding and flip-chip bonding when bonding a semiconductor chip to a substrate (substrate, IC driver, etc.), the metal paste is coated in such a way as to form a desired shape / pattern on the substrate using photolithography or the like. Then, the above metal paste is dried and appropriately pre-sintered to form bumps, and a semiconductor chip is placed on the bumps. Then, the metal powder constituting the bumps is sintered by heating / pressurization to become a metal powder sintered body as a bonding medium. In such a bonding process, the metal paste obtained by the inventors of the present application ensures low-temperature sinterability by specifying the purity and average particle size of the metal powder as described above, and contributes to the low-temperatureization of the bonding process. The sintering temperature of the metal powder applied to the metal paste has a correlation with the particle size of the metal powder, and there is a tendency for the sintering temperature to increase as the particle size becomes coarser. In addition, the purity of the metal powder affects the plastic deformation ability of the metal powder during sintering, and thus affects the denseness of the metal powder sintered body after sintering. Therefore, by applying metal powders with a specified average particle size and high purity, low-temperature sinterability is ensured, and an increase in the resistance of the bonding medium as a conductor is suppressed.

[0004] Moreover, as a method for manufacturing metal powders while controlling the average particle size, a method based on the wet reduction method is also known. For example, in the method for manufacturing metal powders (gold powders) based on the wet reduction method in Patent Document 4, a reducing agent and a metal salt are supplied to a solution in which ultrafine particles (colloidal particles) of gold are dispersed as core particles, and gold is deposited on the surface of the core particles to form gold powders. In this method, by adjusting the particle size and number of the core particles and the concentration and amount of the supplied gold compound solution, submicron-sized gold powders can be manufactured.

[0005] Prior Art Documents

[0006] Patent Document

[0007] Patent Document 1: Specification of Japanese Patent No. 5613253

[0008] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2013-206765

[0009] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2021-025091

[0010] Patent Document 4: Japanese Unexamined Patent Application Publication No. 9-20903 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] As described above, the known metal pastes and metal powders so far have the basic required characteristics such as low-temperature sinterability and conductivity (low resistivity). However, in the situation where the use of metal pastes in the electronic field is expanding, higher-quality and more diverse metal pastes and metal powders are also required. For example, it can be said that the behavior of metal powders during the coating of metal pastes does not directly affect the characteristics such as the resistance of the formed bumps / joints, and there are many aspects to be studied. Therefore, in the present invention, for metal powders and metal pastes used in various processes such as bonding / electrode formation / sealing in the electronic field, higher-quality metal powders and metal pastes and their manufacturing methods have been clarified.

[0013] Means for Solving the Problems

[0014] Regarding the above problems, as the composition of metal powders manufactured by the wet reduction method, the present inventors have studied the improvement of the particle size distribution of metal powders for the following reasons. That is, even in the bonding process in the electronic field where low-temperature bonding is required, the average particle size of metal powders should not be the only factor evaluated. In the study of the present inventors, it was found that metal powders manufactured by the wet reduction method are mostly spherical and regular-shaped metal particles, but sometimes contain a part of non-spherical (rod-shaped, plate-shaped, rectangular, etc.) particles. It is considered that such non-spherical particles do not affect the average particle size and have little influence on the sintering temperature, etc. However, if the ratio of non-spherical particles with a different shape from the surrounding spherical particles increases, it is judged as an abnormal appearance in the electron microscope image of the whole metal powder. Moreover, in addition to the appearance problem, it is also possible to affect the behavior of metal powders during the coating / sintering process of metal pastes. For example, when coating a metal paste on a substrate having holes / grooves, sometimes the non-spherical particles hinder the filling of metal powders into the holes / grooves. In addition, there is also the possibility of affecting the shape of electrodes, bumps, etc. formed by metal powders, and the possibility of unsuitability caused by rod-shaped particles bridging the bumps, etc.

[0015] Based on the above research, the present inventors can list the constituent elements of a higher-quality metal paste / metal powder composed of spherical particles while suppressing the generation of non-spherical particles. Therefore, based on this policy, the present inventors optimized the raw materials, manufacturing conditions, etc. for the method of manufacturing metal powder based on the conventional wet reduction method. As a result, metal powder with an appropriately suppressed ratio of non-spherical particles was discovered, leading to the present invention.

[0016] The present invention for solving the above problems is a metal powder having an average particle diameter of 0.1 μm or more and 0.4 μm or less, containing a metal of Au, Ag, Cu with a purity of 99.9 mass% or more or an alloy thereof, characterized in that the ratio (b / a) of the short diameter a to the long diameter b is 3 or more, and the presence ratio based on the number of non-spherical metal powder particles is 1% or less. Hereinafter, the metal powder of the present invention, its manufacturing method, and a metal paste using the metal powder will be described in more detail.

[0017] A. Composition of the metal powder of the present invention

[0018] As described above, the metal powder of the present invention contains a metal of Au, Ag, Cu with a high purity (99.9 mass% or more) or an alloy thereof. The constituent metal of the metal powder is set to Au, Ag, Cu because they are metals that can be sintered at a relatively low temperature by making fine powder and are all metals with good electrical conductivity. The metal powder may also contain an alloy of the above metals, and a metal powder of an alloy in which Au, Ag, and Cu are alloyed with each other or an alloy having Au, Ag, and Cu as main components (80 mass% or more) can be applied. Particularly preferred is Au. Au is relatively soft and can form a dense sintered body through plastic deformation during sintering, and has excellent electrical conductivity, so that a low-resistance joint / bump, etc. can be formed.

[0019] The purity of the metal powder is set to 99.9 mass% or more because the hardness of a low-purity metal containing impurities becomes high, and plastic deformation during the formation of a sintered body as a bonding material, etc. is difficult to perform. It should be noted that the purity here refers to the concentration of the metal element for a metal powder containing any one of Au, Ag, Cu, and refers to the concentration of the metal and alloy elements for a metal powder containing an alloy of Au, Ag, Cu.

[0020] The average particle diameter of the metal powder is set to be 0.1 μm or more and 0.4 μm or less in order to optimize the sintering temperature of the metal powder. The sintering temperature of the metal powder tends to increase as its average particle diameter increases. In the present invention, particularly as a range with good low-temperature sinterability, the upper limit of the average particle diameter is set to 0.4 μm. On the other hand, 0.1 μm is set as the lower limit because metal powder with an average particle diameter smaller than this value tends to aggregate when made into a paste. Moreover, in the present invention, metal powder with a particle diameter of 0.5 μm or more, which exceeds the upper limit value (0.4 μm) of the average particle diameter, is determined as coarse particles.

[0021] It should be noted that the average particle diameter of the metal powder in the present invention is the number average particle diameter (M N ). Regarding the measurement of the average particle diameter of the metal powder, the metal powder is observed and photographed through a microscope (optical microscope, electron microscope (SEM, TEM), etc.), and a plurality of metal powders in these photos / images are arbitrarily selected to measure the particle diameter. In this observation / particle diameter measurement, it is preferable to set a plurality of observation regions (preferably 5 or more), and observe and measure a plurality of (preferably N = 100 or more) metal powders in each region. The observation magnification is preferably 10,000 times or more, and more preferably set to 20,000 times or more and 30,000 times or less. The particle diameter of the metal powder can be measured by measuring the particle diameter of each metal powder in the photo / image, or by using computer software such as image analysis software. The particle diameter can be the particle diameter based on the biaxial method calculated from the major axis and minor axis of the particle in the image, the Feret diameter (caliper diameter) based on the length of the side of the rectangle circumscribing the particle in the image, etc. Regarding the Feret diameter, it is preferable to obtain at least any one of the minimum Feret diameter, the maximum Feret diameter, and the average Feret diameter.

[0022] Moreover, in the present invention, the presence ratio of non-spherical particles is below a specified value. In the present invention, metal powder with a ratio (b / a) of the minor axis a to the major axis b of 3 or more is defined as non-spherical particles. In the metal powder of the present invention, the presence ratio of non-spherical particles based on the number of particles is 1% or less. Even with such a tiny presence ratio of 1%, non-spherical particles cause defects in the overall appearance of the metal powder and problems during the coating / sintering process of the metal paste. The determination of non-spherical particles using the ratio of the minor axis a to the major axis b can be carried out in conjunction with the measurement of the particle diameter and the average particle diameter of the above-mentioned metal powder. At this time, when the biaxial method is used as the calculation method for the particle diameter of the metal powder, the measured minor axis and major axis are set as the minor axis a and major axis b, respectively. In addition, when the Feret diameter is used as the particle diameter, the minimum Feret diameter and the maximum Feret diameter are set as the minor axis a and major axis b, respectively.

[0023] In addition, the metal powder of the present invention preferably limits the proportion of coarse metal powder in addition to non-spherical particles. In the metal powder of the present invention where the average particle size is specified, metal powder having a particle size above the average value is of course included, and thus it is difficult to completely eliminate the presence of coarse particles. However, when the proportion of coarse metal powder significantly deviating from the average particle size increases, it will affect the sinterability. Therefore, as a factor affecting the quality of the metal powder, it is preferable to consider the presence of coarse particles in addition to irregularly shaped particles. In the present invention, coarse particles refer to particles of 0.5 μm or more, and the proportion of these coarse particles based on the number of particles is preferably 10% or less. It should be noted that the calculation of the particle size of the coarse particles can be applied using the same method as described above.

[0024] In addition, when the metal powder of the present invention has undergone the manufacturing process of the present invention based on the wet reduction method described below, a compound / derivative derived from a surfactant as a dispersant may sometimes be bound to the surface. This surface material activity exists on the powder surface from the stage before the metal powder is made into a metal paste. Specifically, an alkylamine salt or quaternary ammonium salt having an alkyl group with 14 or more and 18 or less carbon atoms may sometimes be bound to at least a part of the metal powder surface. In addition, an alkylamine salt or quaternary ammonium salt having an alkyl group with 12 or more and less than 14 carbon atoms may sometimes also be bound to at least a part of the metal powder surface. Although these compounds do not affect the sintering characteristics of the metal powder, it indicates that a specified surfactant has been applied in its manufacturing process (the metal colloid synthesis process described below). When these surfactants are bound to the metal powder, the amount thereof is preferably 0.01% or more and 5% or less, more preferably 0.03% or more and 3% or less by mass ratio. This is because the attachment of an excessive amount of the compound may affect the sintering of the metal powder later.

[0025] B. Manufacturing method of the metal powder of the present invention

[0026] As described above, the present inventors aimed to improve the wet reduction method as a manufacturing method for the problem of finding a metal powder of higher quality than before. In the manufacturing method of metal powder based on the wet reduction method, a reducing agent and a metal salt are supplied to a solution in which metal colloid particles are dispersed as core particles, and crystal grains grow to form metal powder (granulation). In addition, the synthesis of metal colloid particles is also basically based on the wet reduction method, in which a metal salt as a raw material is mixed with a reducing agent in a solvent to reduce and precipitate the metal to form metal colloid particles. And in the metal colloid particle synthesis process, a dispersant is mixed together with the metal salt and the reducing agent. The dispersant is an additive that binds to the surface of the reduced and precipitated metal colloid particles to inhibit coarsening caused by excessive aggregation of the particles. In the present invention, considering the binding property to various metals, etc., a surfactant having an alkyl group (cationic surfactant) is used as the dispersant.

[0027] In a method for manufacturing metal powder based on a wet reduction method, a dispersant is an essential additive in the metal colloid synthesis step. It binds to the metal colloid particles formed by reduction precipitation and is supplied to the subsequent metal powder granulation step in this state. In addition, in the metal powder granulation step, a dispersant that is the same as or different from the dispersant used in the metal colloid synthesis step is often added on the basis of suppressing the aggregation of metal powder during the growth process. Furthermore, as described later, it is assumed that all or part of the reaction solution obtained in the synthesis step of metal colloid particles is used. In this case, the dispersant that has not bound to the metal colloid particles in the metal colloid synthesis step remains in the reaction solution of the metal powder granulation step.

[0028] Therefore, it can be said that the reaction solutions in both the synthesis step of metal colloid particles and the granulation step of metal powder contain a dispersant. The present inventors studied the influence of the number of carbon atoms in the alkyl group of the surfactant as a dispersant in each of the metal colloid synthesis step and the metal powder granulation step on the metal colloid particles and the metal powder, and obtained the following insights (i) and (ii).

[0029] (i) In the metal colloid synthesis step, when a surfactant with a small number of carbon atoms in the alkyl group is used, it is easy to generate coarse metal colloid particles, and there is a tendency for the particle size distribution to become wider.

[0030] Moreover, there is a tendency for the particle diameter of the metal colloid particles to become smaller as the number of carbon atoms in the alkyl group of the surfactant used increases. In addition, as the number of carbon atoms increases, the particle diameter distribution becomes narrower, and metal colloid particles with small non-uniformities in the generated particle diameter are formed. A small particle diameter of the generated metal colloid particles means an increase in the number of its particles. It is considered that due to the generation of a large number of small particle diameter metal colloid particles, the metal colloid particles effectively play a catalytic role in the subsequent metal powder granulation step, promoting uniform grain growth and forming metal powder with a good shape.

[0031] (ii) On the other hand, if a surfactant with a large number of carbon atoms in the alkyl group is used in the metal powder granulation step, it will affect the shape of the metal powder and promote the growth of non-spherical particles.

[0032] In contrast, using a surfactant with a small number of carbon atoms in the alkyl group in the metal powder granulation step has little effect on the particle shape of the metal powder.

[0033] In the metal powder of the present invention, the proportion of non-spherical particles is reduced, and preferably the proportion of coarse particles is also reduced. In order to produce such a metal powder, it is necessary to reduce the non-uniformity of the particle size distribution while suppressing the growth of non-spherical particles. Referring to the above two viewpoints, it is considered preferable to use a surfactant having an alkyl group with a large number of carbon atoms as a dispersant in the metal colloid synthesis step and a surfactant having an alkyl group with a small number of carbon atoms as a dispersant in the metal powder granulation step.

[0034] Based on the above findings, the present inventors have found that: as a threshold value of the number of carbon atoms of the alkyl group of the surfactant for distinguishing the action of improving the particle size distribution and suppressing the generation of coarse particles from the action of suppressing the generation of non-spherical particles, 14 carbon atoms is appropriate. Moreover, by using a surfactant having an alkyl group with 14 or more carbon atoms as an essential dispersant in the metal colloid synthesis step, and on the other hand, containing a surfactant having an alkyl group with less than 14 carbon atoms in the metal powder granulation step, the metal powder of the present invention can be produced.

[0035] That is, the method for producing a metal powder of the present invention includes: a metal colloid synthesis step in which a metal salt and a reducing agent are reacted in a first solvent containing a first dispersant to synthesize metal colloid particles; and a metal powder granulation step in which a metal salt, a reducing agent, and an optional second dispersant are added to a second solvent containing the metal colloid particles synthesized in the above metal colloid synthesis step to form the metal colloid particles into metal powder. In the production method, the first solvent in the metal colloid synthesis step contains at least a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms as the first dispersant, and the second solvent in the metal powder granulation step contains a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms as the second dispersant. Hereinafter, each step of the method for producing a metal powder of the present invention will be described.

[0036] (a-1) Metal colloid synthesis step

[0037] As described above, the metal colloid synthesis step is a step of synthesizing metal colloid particles that become nuclei of metal powder based on a wet reduction method. In the metal colloid synthesis step, a metal salt and a reducing agent are reacted in a first solvent in the coexistence of a dispersant to reduce and precipitate the metal. As the metal salt as a raw material, for Au, chloroaurate, gold sulfite, gold cyanide, etc. can be cited. In addition, for Ag, silver chloride, silver nitrate, silver acetate can be cited, and for Cu, copper chloride, copper nitrate, copper sulfate can be cited. In addition, as the reducing agent, hydroxylamine hydrochloride, sodium borohydride, dimethylamine borane, trisodium citrate dihydrate, etc. can be applied. They can be mixed in the form of a solution. The first solvent is not limited as long as it can dissolve the metal salt, the reducing agent, and the dispersant. It is preferable to use a polar solvent. Specifically, an organic solvent such as water or alcohol, or a mixed solvent of water and an organic solvent is a preferable solvent.

[0038] Moreover, in the metal colloid synthesis step, in the solvent (reaction solution), as the first dispersant, a dispersant must be contained, and this dispersant contains a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms. A surfactant having an alkyl group with less than 14 carbon atoms increases the non-uniformity of the particle diameter of the metal colloid particles in the metal colloid synthesis step and also causes coarsening of the particle diameter. If such metal colloid particles are grown in the metal powder granulation step, the ratio of non-spherical metal powder may increase. On the other hand, if a surfactant having an alkyl group with more than 18 carbon atoms is used as the dispersant in the metal colloid synthesis step, when this dispersant is present in the reaction solution of the metal powder granulation step, the growth of non-spherical particles such as rod-shaped particles is promoted, and the ratio of non-spherical particles increases. For these reasons, in the present invention, first, as the first dispersant in the metal colloid synthesis step, a dispersant containing a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms is applied. The specific constitution of this first dispersant will be described in detail together with the constitution of the second dispersant later.

[0039] It should be noted that in the reaction solution of the metal colloid particle synthesis step, as long as the first dispersant (a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms) is contained, not only that, but also a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms may be present.

[0040] Metal colloid particles are synthesized by mixing a metal salt, a reducing agent, and a first dispersant in the first solvent. The mixing order thereof is not particularly limited. For example, a metal salt (solution) can be added to a mixed solution of the dispersant and the reducing agent.

[0041] As the composition of the preferred reaction solution in the metal colloid synthesis process, it is preferred to set the metal concentration contained in the reaction solution to 0.01 g / L or more and 1 g / L or less, and more preferably to 0.01 g / L or more and 0.1 g / L or less. By reducing the gold concentration of the reaction solution, uniform metal colloid particles can be formed. However, when the metal concentration is too low, the colloid formation reaction is difficult to proceed. Therefore, the above range is preferred. In addition, regarding the amount of the reducing agent, it is preferably set to 2.5 times or more and 10 times or less the molar concentration of the metal in the reaction solution. Regarding the reducing agent concentration, although there is a tendency to synthesize uniform metal colloid particles by setting it to a high concentration, if the concentration is too high, unreacted reducing agent may be generated, causing aggregation of the particles. Moreover, the concentration of the dispersant is preferably set to 0.1 g / L or more and 10 g / L or less. When it is less than 0.1 g / L, it does not function as a dispersant, and even if it exceeds 10 g / L, it does not affect its function as a dispersant. The concentration of the dispersant is more preferably set to 1 g / L or more and 10 g / L or less.

[0042] In addition, regarding the reaction conditions for metal colloid particle synthesis, the reaction temperature is preferably set to 80 °C or more and 90 °C or less. When it is lower than 80 °C, the formation reaction of metal colloid particles is difficult to proceed. Even if it exceeds 90 °C, the reactivity does not change, and manufacturing problems such as significant evaporation of the reaction solution may occur.

[0043] (a-2) Metal powder granulation process

[0044] The metal powder granulation process is a process of growing the metal colloid particles synthesized in the above metal colloid synthesis process to produce metal powder. In the metal powder granulation process, a metal salt and a reducing agent are added to the second solvent containing the metal colloid particles to grow the metal colloid particles and granulate the metal powder. The metal salt and the reducing agent added in this process can be the same substances as those used as the metal salt and the reducing agent in the above metal colloid synthesis process. However, they may also be metal salts and reducing agents of different types (compositions).

[0045] When dispersing the metal colloid particles in the second solvent in the metal powder granulation process, the entire reaction solution synthesized in the metal colloid synthesis process can be directly used in the metal powder granulation process. In addition, a part of the reaction solution synthesized in the metal colloid synthesis process can be taken out and the taken-out reaction solution can be supplied to the metal powder granulation process. In this case, the second solvent is the same as the first solvent.

[0046] Alternatively, a new solvent can be additionally added to a part or all of the reaction solution synthesized in the metal colloid synthesis step while using it. The additional addition of such a solvent can be carried out for the purpose of adjusting the concentration of metal salts, reducing agents, etc., and adjusting the liquid volume to ensure the operability of the reaction solution. As the solvent added in this case, the same type of solvent as the above-mentioned first solvent can be used, or the same solvent as the first solvent can be used. Here, the mixed solvent of the added solvent and the first solvent becomes the second solvent. Here, of course, the same solvent as the first solvent can also be added. Furthermore, it is also possible to only separate and recover the metal colloid particles from the reaction solution synthesized in the metal colloid synthesis step and disperse the metal colloid particles in a new solvent. The second solvent in this case is also the same as the first solvent, and polar solvents such as water and alcohol are preferred.

[0047] Moreover, in the metal powder granulation step, a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms needs to be contained in the second solvent as the second dispersant. As described above, a surfactant having an alkyl group with a large number of carbon atoms has the effect of promoting the growth of non-spherical particles, so a surfactant with more than 14 carbon atoms is not actively used. However, it is preferred to have the dispersant coexist during the process of growing the metal colloid particles into metal powder. If it is a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms, it will not promote the growth of non-spherical particles and acts as a dispersant for metal powder, so it is used as the necessary dispersant (second dispersant) in this step.

[0048] However, in the metal powder granulation step, the addition of the second dispersant (surfactant having an alkyl group with 12 or more and less than 14 carbon atoms) is not essential. When a part or all of the reaction solution of the metal colloid synthesis step is used in the metal powder granulation step, when the reaction solution contains a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms, the surfactant acts as the second dispersant. In this case, the addition operation of the second dispersant is not required. Especially when using the mixed dispersant described later, the addition operation of the second dispersant is sometimes not required. In the present invention, the state of containing a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms in the reaction solution in the metal powder granulation step is taken as a necessary condition. The details of this second dispersant will be described in detail later together with the first dispersant.

[0049] In addition, in the reaction solution of the metal powder granulation step, it is sufficient to contain the second dispersant (surfactant having an alkyl group with 12 or more and less than 14 carbon atoms). Moreover, a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms can also be present.

[0050] Metal powder is produced by mixing a metal salt, a reducing agent, and an optional second dispersant in the second solvent described above. The mixing order thereof is not particularly limited. Regarding the preferred composition of the reaction solution in the metal powder granulation step, the metal concentration is preferably set to 10 g / L or more and 150 g / L or less. The metal salt added in the metal powder granulation step is a precursor of the metal powder for growing fine metal colloid particles into metal powder having a specified average particle diameter. Therefore, the metal concentration in the metal powder granulation step can be set according to the average particle diameter of the metal powder to be manufactured. However, an excessive metal concentration may cause non-uniform nucleation, and thus the above range is preferred. It should be noted that the metal concentration in the reaction solution of the metal powder granulation step refers to the total of the mass of the metal in the metal salt added in the metal powder granulation step and the mass of the metal colloid particles that become nuclei. In addition, regarding the amount of the reducing agent, it is preferably mixed at 2.5 times or more and 5 times or less with respect to the molar concentration of the metal in the reaction solution. When the reducing agent is too little, unreacted metal salt may remain. In addition, when the reducing agent is too much, a rapid reaction easily occurs, making it difficult to control the particle diameter and sometimes also interfering with safe and stable manufacturing.

[0051] Moreover, regarding the concentration of the dispersant in the reaction solution of the metal powder granulation step, it is preferably set to 1 / 80 times or more and 1 / 6 times or less with respect to the metal concentration in the reaction solution. In addition, when based on the concentration value of the dispersant in the reaction solution of the metal colloid synthesis step, it is preferably set to 1 / 50 times or more and 2 times or less with respect to it. Compared with the effect of suppressing particle aggregation, the dispersant in the metal powder granulation step can better maintain the particle size distribution, and the concentration of the dispersant does not need to exceed the metal concentration. In this regard, it is different from the dispersant concentration in the metal colloid synthesis step. However, to maintain the particle size distribution, a certain degree of dispersant concentration is required. Especially in the metal powder granulation step, in order to grow fine metal colloid particles into submicron-sized metal powder, a considerable amount of metal salt is added to increase the metal concentration, and thus it is preferable to add a dispersant. Moreover, the surfactant having 14 or more and 16 or less carbon atoms in particular in the present invention can suppress non-spherical particles / coarse particles, and thus allows active addition in the metal powder granulation step. For these reasons, it is preferable to set the dispersant concentration in the reaction solution within the above range.

[0052] It should be noted that the concentration of the dispersant in the reaction solution of the metal powder granulation step is calculated based on the total amount of the dispersant contained in the reaction solution, regardless of the presence or absence of binding to metal colloid particles.

[0053] The reaction temperature in the metal powder granulation process is preferably set to be 80 °C or higher and 90 °C or lower. The reason is that when the temperature is lower than 80 °C, even if the conditions such as the amounts of metal salts and reducing agents are appropriate, unreacted metal salts may sometimes remain. At temperatures above 90 °C, a rapid reaction is likely to occur, which may sometimes interfere with the production of stable metal powders.

[0054] (b) Specific compositions of the first dispersant and the second dispersant

[0055] As described above, in the method for producing metal powders of the present invention, for the metal colloid synthesis process and the metal powder granulation process, the number of carbon atoms in the alkyl group of the first dispersant and the second dispersant (surfactant) that must be contained in the reaction solution is specified respectively.

[0056] In the present invention, regarding surfactants having an alkyl group, specifically preferred substances include alkylamine salts and quaternary ammonium salts as cationic surfactants.

[0057] Regarding the surfactant preferably used as the first dispersant, based on the number of carbon atoms in its alkyl group (14 or more and 18 or less), as alkylamine salts, examples include tetradecylamine acetate (alkyl carbon atoms: 14), pentadecylamine acetate (alkyl carbon atoms: 15), hexadecylamine acetate (alkyl carbon atoms: 16), heptadecylamine acetate (alkyl carbon atoms: 17), octadecylamine acetate (alkyl carbon atoms: 18), tetradecylamine hydrochloride (alkyl carbon atoms: 14), pentadecylamine hydrochloride (alkyl carbon atoms: 15), hexadecylamine hydrochloride (alkyl carbon atoms: 16), heptadecylamine hydrochloride (alkyl carbon atoms: 17), octadecylamine hydrochloride (alkyl carbon atoms: 18), etc. In addition, as quaternary ammonium salts, examples include tetradecyltrimethylammonium salt (alkyl carbon atoms: 14), pentadecyltrimethylammonium salt (alkyl carbon atoms: 15), hexadecyltrimethylammonium salt (alkyl carbon atoms: 16), heptadecyltrimethylammonium salt (carbon atoms: 17), octadecyltrimethylammonium salt (carbon atoms: 18), etc.

[0058] In addition, regarding the surfactant preferably used as the second dispersant, based on the number of carbon atoms in its alkyl group (12 or more and less than 14), as alkylamine salts, examples include dodecylamine acetate (carbon atoms: 12), tridecylamine acetate (carbon atoms: 13), dodecylamine hydrochloride (carbon atoms: 12), tridecylamine hydrochloride (carbon atoms: 13), etc. In addition, as quaternary ammonium salts, examples include dodecyltrimethylammonium salt (alkyl carbon atoms: 12), tridecyltrimethylammonium salt (alkyl carbon atoms: 13).

[0059] In the present invention, the first solvent in the metal colloid synthesis step containing a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms means that it is sufficient to contain at least any one of the surfactants having an alkyl group with 14 or more and 18 or less carbon atoms, and it is not necessary to contain all of them. Two or more surfactants can be contained within the above carbon atom number range. For example, it can contain two kinds of surfactants, namely a surfactant having an alkyl group with 14 carbon atoms (such as tetradecylamine acetate) and a surfactant having an alkyl group with 16 carbon atoms (such as hexadecylamine acetate). With the same gist, the second solvent in the metal powder granulation step contains at least any one of the surfactants having an alkyl group with 12 or more and less than 14 carbon atoms. It should be noted that regarding the range of the carbon atom number of the above alkyl group related to the first dispersant and the second dispersant, it is preferably 14 or more and 16 or less for the carbon atom number in the first dispersant, and 12 for the carbon atom number in the second dispersant.

[0060] As the usage methods of these first dispersant and second dispersant (surfactant), the following can be listed: In the metal colloid synthesis step, the surfactant having an alkyl group with 14 or more and 18 or less carbon atoms is mixed as the first dispersant in the first solvent. Then, in the metal powder granulation step, the surfactant having an alkyl group with 12 or more and less than 14 carbon atoms is added as the second dispersant to the second solvent.

[0061] In addition, as the form of the dispersant useful in the present invention, a mixed dispersant formed by mixing a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms and a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms can be listed. Moreover, this mixed dispersant can be used only in the metal colloid synthesis step, or in both the metal colloid synthesis step and the metal powder granulation step. As described above, when a part or all of the reaction solution in the metal colloid synthesis step is supplied to the metal powder granulation step, the dispersant in the metal colloid synthesis step is also contained in the metal powder granulation step. In the metal colloid synthesis step, although it is necessary to add a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms, if the dispersant at this stage contains a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms, this surfactant is contained in the reaction solution in the metal powder granulation step and effectively plays a role. Thus, it is not necessary to add a dispersant in the metal powder granulation step. In addition, when a dispersant is added in the metal powder granulation step, it is not necessary to separately use the dispersant in each step, and convenient reagent management can be achieved.

[0062] However, in the metal powder granulation process, surfactants with alkyl groups having a large number of carbon atoms may promote the growth of non-spherical particles. Therefore, it is preferable to appropriately adjust the composition of the mixed dispersant. Specifically, the mixed dispersant preferably contains a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms in an amount of 50% or more and 80% or less by mass, and a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms in an amount of 20% or more and 50% or less by mass. When considering the influence of each carbon atom number range on the surfactant, it is preferable to increase the proportion of the surfactant having an alkyl group with 12 or more and less than 14 carbon atoms in the mixed dispersant.

[0063] It should be noted that, in addition to the surfactant having an alkyl group with 12 or more and less than 14 carbon atoms and the surfactant having an alkyl group with 14 or more and 18 or less carbon atoms, the mixed dispersant may further contain a surfactant having an alkyl group with 10 or more and less than 12 carbon atoms. The surfactant having an alkyl group with 10 or more and less than 12 carbon atoms is a dispersant not preferred in the metal colloid synthesis process, but can function as a dispersant in the metal particle granulation process. In addition, the surfactant having an alkyl group with 10 or more and less than 12 carbon atoms has a high solubility in various solvents and is likely to disappear at a lower temperature during the firing of the metal paste. For these reasons, the surfactant having an alkyl group with 10 or more and less than 12 carbon atoms is useful for adjusting the solubility and volatility of the mixed dispersant in the solvent and can be used as a dispersant only when using the mixed dispersant. When the mixed dispersant contains a surfactant having an alkyl group with 10 or more and less than 12 carbon atoms, its content is preferably set to 10% or less by mass.

[0064] Furthermore, in the above-mentioned mixed dispersant, it is more preferable to contain a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms in an amount of 50% or more and 80% or less by mass, and a surfactant having an alkyl group with 14 or more and 16 or less carbon atoms in an amount of 20% or more and 50% or less by mass. This is because, among the surfactants having an alkyl group with 14 or more and 18 or less carbon atoms, the surfactant having an alkyl group with 18 or more carbon atoms has a tendency to cause the growth of non-spherical particles in the metal powder granulation process, so its content is restricted.

[0065] It should be noted that when manufacturing metal powder using a mixed dispersant, a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms is bonded to the manufactured metal powder. However, the existence ratio of surfactants with each carbon atom number in the surfactant bonded to the metal powder is mostly different from the mixing ratio of surfactants with each carbon atom number in the mixed dispersant. This is because, in the metal powder granulation process, surfactants with a smaller number of carbon atoms tend to bond to the metal powder more preferentially than surfactants with a larger number of carbon atoms.

[0066] Through the above metal powder granulation process, metal powder with the target average particle size / particle size distribution is manufactured. Then, the metal powder is recovered and appropriately washed with alcohol or the like, whereby metal powder can be obtained. In addition, for this metal powder, post-treatment such as treatment using a cyanide solution for removing chlorine described in Patent Document 2 can also be performed.

[0067] C. Metal paste obtained from the metal powder of the present invention

[0068] The metal paste of the present invention is formed by mixing the above metal powder with an organic solvent as a dispersion medium. In the manufacture of the metal paste, the mixing of the metal powder and the organic solvent can be carried out at room temperature. In addition, when adding the above additives, they can be added simultaneously with the metal powder and the organic solvent, or added after mixing the metal powder and the organic solvent.

[0069] The content of the metal powder in the metal paste is preferably 80% by mass or more and 99% by mass or less based on the mass basis (based on the mass of the entire paste). When it is less than 80% by mass, there may be seepage such as the solvent seeping out of the paste during processes such as paste coating. In addition, due to the generation of voids during heating, it is difficult to obtain a joint with a suitable bonding state. On the other hand, when it exceeds 99% by mass, aggregation of metal powder sometimes occurs. The content of the metal powder is more preferably 87 - 96% by mass.

[0070] As the organic solvent serving as the dispersion medium, an organic solvent having a boiling point of 200 - 400°C (under atmospheric pressure) is preferred. When the boiling point of the organic solvent is lower than 200°C, the evaporation rate may be too fast and metal particles may aggregate. In addition, it may start to volatilize from the stage of paste coating, making the treatment difficult. On the other hand, an organic solvent with a boiling point exceeding 400°C may remain in the joint even after heating.

[0071] Specific examples of the organic solvent that can be used in the present invention preferably include branched saturated aliphatic diols and monoterpenols. More specifically, as the branched saturated aliphatic diol, propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,4-diethyl-1,5-pentanediol, and their derivatives, etc. can be used. In addition, as the monoterpenol, citronellol, geraniol, nerol, menthol, terpineol (α, β), carveol, thujyl alcohol, pinocarveol, β-phenylethyl alcohol, dimethyloctanol, hydroxycitronellol, 2,4-diethyl-1,5-pentanediol, trimethylpentanediol monoisobutyrate, and their derivatives, etc. can be used. In addition, compounds obtained by the condensation reaction of a monocarboxylic acid and a polyol are also effective, for example, triethylene glycol / di-2-ethylhexanoate, triethylene glycol / di-2-ethylbutyrate. It should be noted that the boiling point of the organic solvent has a tendency to depend on the number of its carbon atoms. Therefore, the solvents to be applied are preferably solvents having 5 to 20 carbon atoms respectively. From this viewpoint, aromatic hydrocarbons such as alkylbenzenes are also okay in terms of function.

[0072] As the organic solvent, one organic solvent can be applied, or a solvent obtained by mixing two or more organic solvents having different boiling points can be applied. This is because, by using solvents with low boiling points and high boiling points to form the organic solvent, in the treatment of adjusting the metal particle content rate, the organic solvent on the low boiling point side can be volatilized and removed, making the adjustment easier.

[0073] It should be noted that the metal paste of the present invention is basically composed of two constituent elements, namely metal powder and organic solvent, but additives can also be appropriately contained. As the additives, one or more selected from acrylic resins, cellulose resins, and alkyd resins are sometimes contained. When these resins, etc. are further added, the aggregation of the metal powder in the paste can be prevented, and a more homogeneous joint part can be formed. It should be noted that, respectively, as the acrylic resin, methyl methacrylate polymer can be cited, as the cellulose resin, ethyl cellulose can be cited, and as the alkyd resin, phthalic anhydride resin can be cited. And ethyl cellulose is particularly preferred among them.

[0074] The metal paste of the present invention is effective in various applications such as bonding, sealing, and forming electrodes / bumps / wiring in the electronic field, etc. When used for these applications, the metal paste of the present invention is coated on an object such as a substrate or a material to be bonded and dried. The dried body composed of the metal powder becomes the precursor of the bonding material, sealing material, and bump.

[0075] Then, after the dry body of the metal powder is made into a state suitable for this use, heating / pressurization is performed, whereby the metal powder is sintered. For example, a convex dot-shaped bonding material is formed by coating / drying a metal paste, a semiconductor element / chip is placed thereon, and heating / pressurization is performed, whereby a bonding portion made of a sintered body of gold is formed. The heating temperature for this sintering is preferably set to 150 °C or higher and 300 °C or lower.

[0076] Advantages of the Invention

[0077] As described above, the metal powder of the present invention is a metal powder in which the ratio of non-spherical particles such as rod-shaped / plate-shaped particles is reduced. According to the present invention, it is possible to make the characteristics after forming a metal paste and the sinterability required for uses such as bonding / sealing good. The metal powder of the present invention can be manufactured by optimizing the dispersant in the wet reduction method. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 is an SEM image showing the appearance of gold colloidal particles synthesized from surfactants having different numbers of carbon atoms in the alkyl group in the first embodiment.

[0079] Figure 2 is an SEM image showing the appearance of the gold powder of Example 1 and Comparative Example manufactured in the first embodiment.

[0080] Figure 3 is an SEM image showing the appearance of the gold powder manufactured using a mixed dispersant in Examples 2 and 3 of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0081] First Embodiment : Hereinafter, preferred embodiments of the present invention will be described. In the present embodiment, gold (Au) powder is manufactured as the metal powder by a wet reduction method (metal colloid synthesis step and metal powder granulation step). Here, after finding an appropriate range of the number of carbon atoms in the alkyl group of the surfactant as the dispersant in the metal colloid synthesis step, the content of non-spherical particles when surfactants having different numbers of carbon atoms are applied in the metal powder granulation step is evaluated.

[0082] [Study on Appropriate Conditions in the Gold Colloid Synthesis Step]

[0083] Alkylamine acetate as a dispersant is mixed in 20 mL of pure water. In this dispersant solution, 2 mg of hydroxylamine hydrochloride as a reducing agent is added, and heating / stirring is performed at 80 °C for dissolution. Then, 0.45 mL of an aqueous chloroauric acid solution (Au amount 0.32 mg (3.6 mM)) is mixed in the solution containing the dispersant and the reducing agent, and stirring is maintained at 80 °C for 2 hours to synthesize gold colloidal particles.

[0084] In the above-described colloid synthesis process, in the present embodiment, regarding alkylamine acetate as a dispersant, five types of alkylamine acetates, namely decylamine acetate (alkyl having 10 carbon atoms), dodecylamine acetate (alkyl having 12 carbon atoms), tetradecylamine acetate (alkyl having 14 carbon atoms), hexadecylamine acetate (alkyl having 16 carbon atoms), and octadecylamine acetate (alkyl having 18 carbon atoms), are used. When preparing the dispersant solution as described above, 0.13 mmol of each alkylamine acetate is mixed.

[0085] Then, for the gold colloidal particles synthesized using each alkylamine acetate, SEM observation, particle size distribution, and average particle diameter (M N ) were measured. 5 μL of the prepared solution of gold colloidal particles was taken and placed on a grid and dried, and then observed with a TEM (transmission electron microscope, JEM-1400 manufactured by JEOL Ltd.) (acceleration voltage: 120 V, magnification: 150,000 times). Then, based on multiple photos taken during TEM observation, 200 vertical Feret diameters were measured for each sample, and the particle size distribution was prepared. The median diameter was used as the average particle diameter of the gold colloidal particles. It should be noted that for decylamine acetate (alkyl having 10 carbon atoms), precipitation occurred and the precipitated particles adhered to the wall of the reaction vessel, making it difficult to recover, so SEM observation and measurement of the particle size distribution could not be performed. Figure 1 SEM images of the gold colloidal particles synthesized using each alkylamine acetate (alkyl having 12, 14, 16, and 18 carbon atoms) are shown. In addition, regarding the particle size distribution of the gold colloidal particles synthesized using each alkylamine acetate, the proportion of gold colloidal particles with a particle diameter of 10 nm or less and the measurement results of the average particle diameter are shown in Table 1.

[0086]

[0087] Referring to Figure 2 and Table 1, there is a tendency for the average particle diameter of the gold colloidal particles to decrease as the number of carbon atoms of the alkylamine used as the dispersant increases. Moreover, it was confirmed that as the number of carbon atoms increases, the proportion of gold colloidal particles on the small particle diameter side (10 nm or less) increases, and the particle size distribution becomes narrower. These tendencies are in good agreement with the views of the above (i) and (ii). Moreover, regarding the number of carbon atoms of the alkylamine, when comparing 12 carbon atoms with 14 carbon atoms, a sharp increase in the proportion of gold colloidal particles on the small particle diameter side was found in the case of 14 carbon atoms, so it is considered appropriate to set the threshold value of the number of carbon atoms to 14. As described above, in order for the metal powder to grow in the metal powder granulation process after the metal colloid synthesis process, it is considered preferable to reduce the non-uniformity of the particle size distribution. Based on the above research results, it was confirmed that in the metal colloid synthesis process, a surfactant having a long-chain alkyl group is preferable.

[0088] [Study on Appropriate Conditions in Gold Powder Granulation Process]

[0089] Therefore, based on the gold colloid particles synthesized using a dispersant (octadecylamine acetate) having 18 carbon atoms in the above gold colloid synthesis process, gold powder granulation was carried out (Example 1).

[0090] 3 mL (15%) of the reaction solution after the above gold colloid synthesis process was taken, a dispersant solution prepared by dissolving the dispersant in 70 mL of pure water was added, and further a solution prepared by dissolving 5 g of hydroxylamine hydrochloride as a reducing agent in 8 mL of pure water was added. Then, while the liquid temperature was stabilized at 80 °C, 20 mL of an aqueous chloroauric acid solution (Au amount 2.25 g (571 mM)) as a gold salt for granulation was added, and the mixture was stirred for 30 minutes to produce gold powder. Then, the gold powder was recovered.

[0091] In the above gold powder granulation process, in the present embodiment, as the dispersant, two kinds of alkylamine acetates, dodecylamine acetate (alkyl carbon atom number 12) and octadecylamine acetate (alkyl carbon atom number 18), were used. When preparing the dispersant solution as described above, 1 mmol of each alkylamine acetic acid was mixed.

[0092] After producing gold powder through the gold powder granulation process, the gold powder was recovered by centrifugation, and SEM observation was carried out, and the particle size distribution and average particle diameter were measured. At this time, the particle diameter (maximum Feret diameter) of the gold powder particles (more than 400) in the image was measured for the SEM image by using image analysis software (software used: MIPAR manufactured by LightStone Co., Ltd.). Then, the number average particle diameter (M N ) was calculated. In addition, at the same time, the minimum Feret diameter was set as the short diameter a and the maximum Feret diameter was set as the long diameter b to determine non-spherical particles, and the existence ratio of non-spherical particles was calculated.

[0093] The SEM images of the gold powder (Example 1) manufactured using dodecylamine acetate (alkyl carbon atom number 12) as the dispersant in the gold powder granulation process and the gold powder (Comparative Example) manufactured using octadecylamine acetate (alkyl carbon atom number 18) as the dispersant in the gold powder granulation process are shown in Figure 2 in. Figure 2From the SEM images, it can be seen that most of the gold powder produced from dodecylamine acetate (with 12 carbon atoms in the alkyl group) has a good spherical shape. In contrast, non-spherical (rod-shaped) particles can be seen in the gold powder produced using octadecylamine acetate (with 18 carbon atoms in the alkyl group). As a result of measuring the ratio of non-spherical particles in these gold powders, it is 0% for the gold powder using dodecylamine acetate (with 12 carbon atoms in the alkyl group) in the gold powder granulation process, and 8.15% for the gold powder produced from octadecylamine acetate (with 18 carbon atoms in the alkyl group).

[0094] Based on the results of the present embodiment described above, it was confirmed that: in the method for manufacturing metal powder composed of a metal colloid synthesis process and a metal powder granulation process, it is preferable to use a surfactant with a large number of carbon atoms in the alkyl group in the previous process and a surfactant with a small number of carbon atoms in the alkyl group in the subsequent process.

[0095] Second Embodiment : In the present embodiment, two kinds of mixed dispersants are used as dispersants in the two processes of the metal colloid synthesis process and the metal powder granulation process to manufacture gold powder (Examples 2 and 3). The dispersants used in the present embodiment are a mixed dispersant of decylamine hydrochloride (with 10 carbon atoms in the alkyl group), dodecylamine acetate (with 12 carbon atoms in the alkyl group) and tetradecylamine acetate (with 14 carbon atoms in the alkyl group), hexadecylamine hydrochloride (with 16 carbon atoms in the alkyl group), and the composition is as follows.

[0096] · Mixed dispersant of Example 2

[0097] Tetradecylamine acetate (14 carbon atoms): 27% by mass

[0098] Dodecylamine acetate (12 carbon atoms): the balance

[0099] · Mixed dispersant of Example 3

[0100] Decylamine hydrochloride (10 carbon atoms in the alkyl group): 5% by mass

[0101] Dodecylamine acetate (12 carbon atoms in the alkyl group): 60% by mass

[0102] Tetradecylamine acetate (14 carbon atoms in the alkyl group): 25% by mass

[0103] Hexadecylamine hydrochloride (16 carbon atoms in the alkyl group): 10% by mass

[0104] [Gold colloid synthesis process]

[0105] Add the substance obtained by dissolving 0.32 g of the above mixed dispersant in 12.8 mL of pure water to 147.2 mL of pure water. Then, add the substance obtained by dissolving 0.016 g of hydroxylamine hydrochloride as a reducing agent in 5.0 mL of pure water to the dispersant solution, and heat / stir at 80 °C for dissolution. Mix 4.5 mL of an aqueous solution of chloroauric acid (Au amount: 0.0064 g (7.2 mM)) into this solution, and stir at 80 °C for 1 hour. Thus, a red transparent solution of gold colloidal particles is obtained.

[0106] [Gold powder granulation process]

[0107] Add the solution obtained by dissolving 2.56 g of the same surfactant mixture as the above as a dispersant in 102.4 mL of pure water to the total amount of the above solution of gold colloidal particles (reaction solution), and add hydroxylamine hydrochloride, 20 g as a reducing agent, after dissolving it in about 200 mL of pure water. Then, while maintaining the liquid temperature at 80 °C, add 100 mL of an aqueous solution of chloroauric acid (Au amount: 22 g (1120 mM)) as a gold salt for granulation, stir for 30 minutes, and produce gold powder. Then, recover the gold powder.

[0108] For the recovered gold powder, SEM observation is carried out in the same manner as in the first embodiment, the average particle size is measured, and the ratio of the presence of non-spherical particles is calculated. In this embodiment, the ratio of the presence of coarse particles is further measured / calculated. Figure 3 These are SEM images of the gold powder of Examples 2 and 3 produced in this embodiment. Moreover, the measurement results such as the average particle size are shown in Table 1. The results of the first embodiment (Example 1) are also shown in Table 1.

[0109]

[0110] As can be seen from Table 2, it is also possible to produce appropriate gold powder without non-spherical particles by using a mixed dispersant obtained by mixing surfactants with different ranges of the number of alkyl carbon atoms. In Examples 2 and 3, the same mixed dispersant was used in both the metal colloid synthesis process and the metal powder granulation process. It is considered that the dispersants with different carbon atom numbers in the mixed dispersant effectively played a role in each process. It was also confirmed that when using a mixed dispersant, an alkylamine salt with 10 alkyl carbon atoms can be mixed.

[0111] It should be noted that from the viewpoint of the ratio of the presence of coarse particles, by appropriately setting the number of carbon atoms of the alkyl group of the surfactant as a dispersant as in Examples 1 to 3, the generation of coarse particles can be suppressed.

[0112] [Characteristics evaluation of metal paste]

[0113] Next, a gold paste is manufactured using the gold powder produced in Examples 2 and 3 of the second embodiment. The gold paste is manufactured by mixing menthol (dihydromyrcenol), which is an organic solvent, into the gold powder. The mixing ratio of the organic solvent is set at 10% by weight. Then, the produced gold paste is coated on a substrate and sintered to form bumps, and their morphology and resistance values are measured. In the coating of the gold paste, a 2-inch-diameter disc-shaped Al 2 O 3 plate is used as the substrate. After a metal mask (made of stainless steel) with a thickness of 350 μm and having a rectangular hole of 5 mm × 20 mm is coated on this substrate, it is coated on the entire surface of the substrate. In this coating process, the gold paste is dropped onto the metal mask and spread with a squeegee to fill the inside of the holes of the metal mask with the gold paste. After coating the gold paste, the excess paste is wiped off. After removing the metal mask, it is heated at 100°C for 1 hour to dry it, and then heated at 230°C for 30 minutes for sintering.

[0114] Regarding the sintered gold bumps, the cross-section was observed with a metallurgical microscope, and the result was a rectangle following the hole shape of the metal mask, and the surface of the bumps was also in a good shape without roughness. Regarding these gold bumps, the volume resistance value was measured using a resistivity meter (Loresta GP MCP-T610 manufactured by Nitto Seiko Analysis Technology Co., Ltd.). As a result, it was confirmed that in any of the examples, it was about 7.0 μΩ / cm, which is a good conductive material. And it was confirmed that by applying the gold powder excluding non-spherical particles and coarse particles, the coating characteristics became good, and a homogeneous sintered body was also obtained during sintering.

[0115] Industrial Applicability

[0116] The gold powder of the present invention is composed of gold powder of spherical particles in which the ratio of the presence of non-spherical particles is suppressed. Due to the particle shape and the exclusion of coarse particles, the gold powder of the present invention has excellent appearance during microscopic observation and also excellent stability / fillability during the coating of the metal paste. Moreover, the manufacturing method of the gold powder of the present invention is achieved by optimizing the dispersant when synthesizing the gold colloid particles that form the core of the gold powder. The gold paste of the present invention has the above characteristics while maintaining low-temperature sinterability. Moreover, the gold paste of the present invention is useful in various processes such as bonding / sealing / electrode / wiring formation in electrical / electronic components, semiconductor devices, semiconductor elements, power devices, MEMS, etc.

Claims

1. A metal powder, which is a metal powder with an average particle size of 0.1 μm or more and 0.4 μm or less, containing a metal of Au, Ag, Cu with a purity of 99.9 mass% or more or an alloy thereof, characterized in that, the particle number-based existence ratio of non-spherical metal powder particles with a ratio of minor axis a to major axis b (b / a) of 3 or more is 1% or less.

2. The metal powder according to claim 1, wherein a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms is bonded to at least a part of the surface.

3. The metal powder according to claim 2, wherein, the surfactant is an alkylamine salt or a quaternary ammonium salt.

4. A metal paste, which contains the metal powder according to any one of claims 1 to 3 and an organic solvent.

5. A method for manufacturing a metal powder, which comprises: a metal colloid synthesis step, in which metal colloid particles are synthesized by reacting a metal salt with a reducing agent in a first solvent containing a first dispersant; and a metal powder granulation step, in which a metal salt, a reducing agent, and optionally a second dispersant are added to a second solvent containing the metal colloid particles synthesized in the metal colloid synthesis step to form the metal colloid particles into metal powder, in the method for manufacturing the metal powder, the first solvent in the metal colloid synthesis step contains at least a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms as the first dispersant, the second solvent in the metal powder granulation step contains a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms as the second dispersant.

6. The method for manufacturing a metal powder according to claim 5, wherein, the second solvent in the metal powder granulation step contains a part or all of the reaction liquid generated in the metal colloid synthesis step.

7. The method for manufacturing a metal powder according to claim 5 or claim 6, wherein, in the metal colloid synthesis step, a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms is mixed in the first solvent as the first dispersant, in the metal powder granulation step, a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms is added to the second solvent as the second dispersant.

8. The method for manufacturing a metal powder according to claim 5 or claim 6, wherein, in the metal colloid synthesis step, a mixed dispersant containing a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms and a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms is mixed in the first solvent as the first dispersant.

9. The method for manufacturing a metal powder according to claim 8, wherein, in the metal powder granulation step, a mixed dispersant containing a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms and a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms is mixed in the second solvent as the second dispersant.

10. The method for manufacturing a metal powder according to claim 8, wherein, The mixed dispersant contains a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms in an amount of 50% or more and 80% or less by mass, a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms in an amount of 20% or more and 50% or less by mass, and the balance is a surfactant having an alkyl group with 10 or more and less than 12 carbon atoms.

11. The method for producing a metal powder according to claim 9, wherein, The mixed dispersant contains a surfactant having an alkyl group with 12 or more and less than 14 carbon atoms in an amount of 50% or more and 80% or less by mass, a surfactant having an alkyl group with 14 or more and 18 or less carbon atoms in an amount of 20% or more and 50% or less by mass, and the balance is a surfactant having an alkyl group with 10 or more and less than 12 carbon atoms.

12. The method for producing a metal powder according to claim 5 or claim 6, wherein, The surfactant is an alkylamine salt or a quaternary ammonium salt.

13. The method for producing a metal powder according to claim 7, wherein, The surfactant is an alkylamine salt or a quaternary ammonium salt.

14. The method for producing a metal powder according to claim 8, wherein, The surfactant is an alkylamine salt or a quaternary ammonium salt.

15. The method for producing a metal powder according to claim 9, wherein, The surfactant is an alkylamine salt or a quaternary ammonium salt.

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