JP7731138B2 - Method for manufacturing bonding paste - Google Patents

Description

The present invention relates to a method for producing a metal paste and a method for producing a joining paste.

The use of a paste containing metal particles as a bonding agent between a semiconductor element and a substrate is being considered. For example, the metal paste can be applied to a substrate to form a coating, and the semiconductor element can be placed on the coating and then sintered to bond the substrate and semiconductor element. The sintered metal paste has advantages such as excellent heat resistance, thermal conductivity (heat dissipation), and electrical conductivity.

Patent Document 1 discloses a bonding composition containing metal powder, specific coated metal particles, and a specific solvent.
In Patent Document 2, the composition is prepared by sequentially mixing metal powder and coated metal particles into a solvent and stirring the mixture.

Patent Document 2 describes a method in which copper powder used in a conductive paste is plastically deformed using a high-energy ball mill to produce flake-shaped copper powder.

Japanese Patent Application Laid-Open No. 2020-87766 Japanese Patent Application Laid-Open No. 2004-169155

There is a demand for further improvement in bonding strength of bonding pastes.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a metal paste and a method for producing a bonding paste that further improves bonding strength.

The present disclosure provides a method for producing a metal paste and a method for producing a bonding paste having the following configurations [1] to [8].
[1] A method for producing a metal paste containing a metal powder having a particle size of 120 nm to 10,000 nm and a solvent,
preparing a mixture containing the metal powder, beads having a particle size of 0.1 mm to 10 mm, and a first solvent;
agitating the mixture with a stirrer;
and removing the beads.
A method for manufacturing metal paste.
[2] The method for producing a metal paste according to [1], wherein the agitator is a planetary agitator or a vibration agitator.
[3] The method for producing a metal paste according to [1] or [2], wherein the material of the beads is the same metal as the metal powder or zirconia.
[4] The method for producing a metal paste according to any one of [1] to [3], wherein the first solvent contains liquid paraffin.
[5] The method for producing a metal paste according to any one of [1] to [4], wherein the first solvent contains an aldehyde and/or a lactone.
[6] A method for producing a bonding paste, comprising:
Adding metal nanoparticles having a particle size of 5 to 100 nm to the metal paste produced by the metal paste production method according to any one of [1] to [5];
and stirring the paste after adding the metal nanoparticles with a stirrer.
Method for manufacturing bonding paste.
[7] The method for producing a bonding paste according to [6], wherein the metal nanoparticles are added by adding a metal nanoparticle dispersion liquid containing the metal nanoparticles and a second solvent.
[8] The method for producing a bonding paste according to [6] or [7], wherein the metal nanoparticles are coated with a coating layer containing an aliphatic carboxylic acid and/or an aliphatic aldehyde.

The present invention provides a method for manufacturing a metal paste and a method for manufacturing a joining paste that further improves joining strength.

Hereinafter, an embodiment of the present invention will be described.
In this disclosure, the term "metal paste" refers to a dispersion of metal powder containing at least metal powder with a particle size of 120 nm to 10,000 nm (10 μm) and a solvent, and is a preparatory product (intermediate product) suitable for use in producing a "joining paste." The "metal paste" may contain metal nanoparticles, but the proportion of metal nanoparticles is preferably 1% by mass or less, more preferably 0.1% by mass or less, based on the total mass of the metal powder and metal nanoparticles, and even more preferably is substantially free of them.
In the present disclosure, a "bonding paste" refers to a dispersion of metal powder and metal nanoparticles containing at least metal powder having a particle size of 120 nm to 10,000 nm, metal nanoparticles having a particle size of 5 to 100 nm, and a solvent. The "bonding paste" is preferably used for bonding two members to be bonded, but may also be used as a conductive composition used, for example, to form a conductive pattern on a substrate by printing.
In this disclosure, unless otherwise specified, the use of "to" indicating a range of values means that the values before and after it are included as the lower and upper limits.

[Metal Paste Manufacturing Method]
The method for producing a metal paste according to the present disclosure is a method for producing a metal paste containing a metal powder having a particle size of 120 nm to 10,000 nm (10 μm) and a solvent,
preparing a mixture containing the metal powder, beads having a particle size of 0.1 mm to 10 mm, and a first solvent;
agitating the mixture with a stirrer;
and removing the beads.

The bonding paste described below contains metal powder and metal nanoparticles, and when a coating film is formed, the metal nanoparticles are arranged in the gaps between the metal powder particles, and the metal nanoparticles that melt during sintering contribute to bonding the metal powder particles together, thereby achieving high bonding strength.
However, when metal powder with a particle size of 120 nm to 10,000 nm is dispersed in a solvent using a stirrer, the resulting metal paste may have a rough surface. It is believed that this roughness is due to the presence of aggregates of the metal powder.
The inventors discovered that adding beads with a particle size of 0.1 mm to 10 mm and dispersing them with a stirrer reduces the roughness of the liquid surface and produces a glossy finish. This change is presumed to be due to a reduction in the number of agglomerates of the metal powder, and it has been confirmed that metal pastes dispersed with the addition of beads show a decrease in particle size, as measured by the particle gauge method described in JIS K5600-2-5, for example.
The bonding paste using the metal paste produced in this way has improved uniformity and allows metal nanoparticles to be more easily arranged between the metal powder particles, resulting in an improved bonding strength of the resulting sintered body (bonding layer) and reduced cracking within the sintered body.

<Metal powder>
In this embodiment, the metal powder may have a particle size of 120 nm to 10,000 nm. The metal powder is a component contained in the bonding paste and forms a bonding layer together with metal nanoparticles (described later) after heating. The material of the metal powder may be appropriately selected depending on the application of the resulting bonded body. Specific examples of the material include gold, silver, copper, platinum, aluminum, iron, chromium, tin, nickel, zinc, lead, indium, bismuth, germanium, antimony, cobalt, palladium, rhodium, molybdenum, tungsten, titanium, zirconium, gallium, arsenic, boron, silicon, and alloys thereof. For example, when electrical conductivity is required for the bonding layer, gold, silver, or copper is preferred, with silver or copper being more preferred, from the standpoint of bonding strength and electrical conductivity. The metal powder may be used alone or in combination of two or more types.

The particle size of the metal powder is the primary particle size, and may be 120 nm to 10,000 nm. By using metal powder with a particle size of 10 μm or less, the metal powder is densely packed within the coating film, suppressing voids in the resulting bonding layer. The particle size of the metal powder is preferably 0.3 μm to 10 μm, more preferably 0.4 μm to 5 μm, and even more preferably 0.5 μm to 1.0 μm. Two or more types of metal powder with different particle sizes may also be combined.
Incidentally, metal powders that are nearly monodisperse are available, and the median diameter D ₅₀ of the metal powder is preferably 120 nm to 10,000 nm, more preferably 0.3 μm to 10 μm, more preferably 0.4 μm to 5 μm, and even more preferably 0.5 μm to 1.0 μm.

The shape of the metal powder may be spherical, plate-like, rod-like, or the like, with spherical being preferred. By using spherical metal powder, gaps are less likely to form during coating film formation, and bonding strength is further improved. In the present disclosure, spherical refers to metal powder with an aspect ratio (a/b) of 1 to 2, expressed as the ratio of the major axis a to the minor axis b of the metal powder, and the aspect ratio is preferably 1 to 1.5.
The particle size and shape of the metal powder can be measured from an image obtained by an electron microscope.
The median diameter can be measured using a dynamic light scattering particle size distribution measuring device, a laser diffraction particle size distribution measuring device, or the like.
The metal powder may be a commercially available product having the desired material and particle size.

<Beads>
In this embodiment, the beads may be 0.1 mm to 10 mm in diameter. The beads are a component that does not remain in the metal paste or bonding paste. The material of the beads is not particularly limited, and examples include ceramic beads such as zirconia, titania, silicon nitride, silicon carbide, alumina, and zirconium silicate; glass beads such as quartz; and metal beads such as stainless steel, copper, and silver. Zirconia beads are preferred in terms of bead strength and abrasion resistance. On the other hand, considering slight contamination due to bead wear, metal beads are preferred, and metal beads of the same type (same material) as the metal powder are more preferred. Note that when the metal powder is an alloy or a combination of metal powders of two or more materials, the metal beads need only be made of the same material as at least one of the metals constituting the metal powder. For example, when the metal powder contains copper and silver, copper and/or silver beads are preferred.

The particle size of the beads is the primary particle size. Because the particle size of the beads is 0.1 mm or more, they are easy to remove from the metal paste. In order to reduce the number of agglomerates of the metal powder, the particle size of the beads should be 10 mm or less, preferably 0.15 mm to 8 mm, and more preferably 0.2 mm to 5 mm. The shape of the beads is also preferably spherical.

In this production method, the mixing ratio of the beads is preferably 10 to 200 parts by mass, more preferably 20 to 150 parts by mass, per 100 parts by mass of the metal powder, in order to reduce agglomerates of the metal powder.
In this manufacturing method, the mixing ratio of beads is preferably 2:8 to 8:2, more preferably 3:7 to 7:3, in terms of the volume ratio of metal powder to beads, in order to reduce agglomerates of metal powder.

<First Solvent>
The first solvent is used as a dispersion medium when stirring the metal powder and beads, and may have the same composition as the solvent of the metal paste obtained by this manufacturing method, or may be part of the solvent of the metal paste, taking into account that the solvent will be added after stirring.

The first solvent can be appropriately selected depending on the dispersibility of the metal powder, the method for forming the coating film of the bonding paste (printing method), etc. The first solvent may be a single solvent or a mixed solvent combining two or more solvents. In this disclosure, the solvent refers to a solvent that is liquid at least at room temperature (25°C).
Examples of the first solvent include amine-based solvents, alcohol-based solvents, aminoalcohol-based solvents, carboxylic acid-based solvents, aldehyde-based solvents, terpine acetate-based solvents, alkane-based solvents, carbitol-based solvents, and ester-based solvents.

The first solvent preferably contains the following solvents from the viewpoints of dispersibility of metal powder, dispersibility of metal nanoparticles, and compatibility with a coating layer that the metal nanoparticles may have.
Examples of the amine solvent include aliphatic amine solvents such as octylamine, decylamine, dodecylamine, and oleylamine.
Examples of alcohol solvents include aliphatic alcohols such as hexanol, octanol, decanol, dodecanol, and oleyl alcohol, and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate.
Examples of the amino alcohol solvent include aliphatic amino alcohol solvents such as ethanolamine, propanolamine, octanolamine, decanolamine, dodecanolamine, and oleyl alcoholamine.
Examples of the carboxylic acid solvent include aliphatic carboxylic acid solvents such as hexanoic acid, heptanoic acid, octanoic acid, and nonanoic acid.
Examples of the aldehyde solvent include aliphatic aldehyde solvents such as octanal, decanal, dodecanal, and tridecanal.
Examples of terpine acetate solvents include 1,8-terpine-1-acetate, 1,8-terpine-8-acetate, and 1,8-terpine-1,8-diacetate.
Examples of the alkane solvent include octane, decane, dodecane, liquid paraffin, and the like.
Examples of the carbitol solvent include butyl carbitol, hexyl carbitol, and decyl carbitol.
Examples of the ester solvent include aliphatic ester solvents such as ethyl acetate, butyl acetate, and isobutyl acetate, and cyclic ester solvents such as β-propiolactone, β-butyrolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, γ-octalactone, γ-nonalactone, γ-decanolactone, δ-decanolactone, γ-undecalactone, δ-undecalactone, ω-undecalactone, and ω-pentadecalactone.

From the viewpoint of improving the dispersibility of the metal powder and the adhesive strength of the resulting bonding paste, the first solvent preferably contains liquid paraffin. Liquid paraffin is a mixture of aliphatic hydrocarbons with different carbon numbers and has a wide range of vaporization temperatures. Therefore, liquid paraffin gradually volatilizes during firing and is less likely to remain in the coating film. This suppresses the formation of large voids that can form during solvent evaporation, resulting in a bonded body with excellent bonding strength.
Commercially available liquid paraffin products include, for example, Hicol K series liquid paraffin manufactured by Kaneda Co., Ltd., and liquid paraffin (S type) manufactured by Sanko Chemical Industry Co., Ltd.

The first solvent preferably contains an aldehyde-based solvent and/or an ester-based solvent, which inhibits surface oxidation of the metal powder during stirring and further improves bonding strength.
Of the aldehyde solvents, the aliphatic aldehyde solvents are preferred, and of the ester solvents, the cyclic ester solvents are preferred.

When liquid paraffin is used as the first solvent, the proportion thereof is preferably 10 to 100 mass %, more preferably 20 to 90 mass %, and even more preferably 25 to 85 mass %, based on the total mass of the first solvent.
When an aldehyde-based solvent or an ester-based solvent is used as the first solvent, the total content thereof is preferably 0.1 to 30 mass%, more preferably 0.5 to 20 mass%, and even more preferably 1 to 10 mass%, relative to the total mass of the first solvent.

In a mixture containing metal powder, beads, and a first solvent, the proportion of the first solvent can be 1 to 40 mass% of the total mass of the metal powder and first solvent (excluding the beads), and 5 to 20 mass% is preferred.

The above mixture may further contain other components as long as the effects of the present invention are achieved. Such other components include antioxidants, dispersants, thickeners, gelling agents, etc.

<Mixing>
The mixture containing the above components is stirred with a stirrer. By stirring the mixture containing the beads with a stirrer, it is possible to reduce the agglomeration of the metal powder while suppressing deformation of the metal powder. The stirrer is preferably a planetary stirrer or a vibration stirrer, since it can reduce the agglomeration of the metal powder while suppressing deformation of the metal powder.
In the case of a planetary centrifugal mixer, the device conditions are, for example, a revolution speed of 500 rpm or more, and a ratio of the revolution speed V1 to the rotation speed V2 (V1/V2) of 10/8 to 10/3, which makes it possible to reduce agglomerates of the metal powder while suppressing deformation of the metal powder.
In the case of a vibration mixer, for example, by vibrating the container containing the mixture at 500 to 2000 reciprocations/min, it is possible to reduce the agglomerates of the metal powder while suppressing deformation of the metal powder.

Next, the beads are removed from the mixture after stirring. There are no particular restrictions on the method for removing the beads, but for example, they can be filtered out using a mesh filter, taking advantage of the difference in particle size between the metal powder and the beads.

Depending on the intended use of the metal paste, various components may be added to the mixture after the beads have been removed. These components include known components that can be used in joining pastes, such as antioxidants, dispersants, thickeners, gelling agents, resin components (such as binder resins), and solvents. Adding thickeners and resin components at this stage can improve the efficiency of the dispersion process. The solvent can be used alone or, when other additive components are added, mixed with the additive components. The solvent may be the same as the first solvent, or a different solvent.

As a result, a metal paste with reduced metal powder agglomerates can be obtained. The metal paste obtained by this manufacturing method has little roughness on the liquid surface and a visible gloss. Furthermore, the metal paste obtained by this manufacturing method can have a particle size of 80 μm or less, preferably 60 μm or less, and more preferably 50 μm or less, as measured by the particle gauge method described in JIS K5600-2-5.
The metal paste obtained by this production method can be suitably used as a preliminary preparation of a bonding paste to be used in combination with metal nanoparticles.

[Method of manufacturing bonding paste]
The method for producing a bonding paste according to the present disclosure includes:
adding metal nanoparticles having a particle size of 5 to 100 nm to the metal paste produced by the method for producing a metal paste;
and a step of stirring the paste after adding the metal nanoparticles with a stirrer.

<Metal nanoparticles>
In this embodiment, the metal nanoparticles may have a particle size of 5 nm to 100 nm. The use of such metal nanoparticles can impart low-temperature sintering properties to the bonding paste. The material of the metal nanoparticles may be appropriately selected depending on the intended use of the resulting bonded body. Specific examples of such materials include gold, silver, copper, platinum, aluminum, iron, chromium, tin, nickel, zinc, lead, indium, bismuth, germanium, antimony, cobalt, palladium, rhodium, molybdenum, tungsten, titanium, zirconium, gallium, arsenic, boron, silicon, and alloys thereof. For example, when electrical conductivity is required for the bonding layer, gold, silver, or copper is preferred, with silver or copper being more preferred, from the standpoint of bonding strength and electrical conductivity. Furthermore, the metal nanoparticles are preferably metal nanoparticles of the same type (same material) as the metal powder. When the metal powder is an alloy or a combination of metal powders of two or more materials, the metal nanoparticles may be made of the same material as at least one of the metals constituting the metal powder. For example, when the metal powder contains copper and silver, the metal nanoparticles are preferably copper nanoparticles and/or silver nanoparticles. The metal nanoparticles may be used alone or in combination of two or more types.

The particle size of the metal nanoparticles is the primary particle size, and may be 5 nm to 100 nm. From the viewpoints of low-temperature sintering property and bonding strength, the particle size of the metal nanoparticles is preferably 8 nm to 95 nm, and more preferably 10 nm to 90 nm. Two or more types of metal nanoparticles with different particle sizes may be combined.
According to the method described below, metal nanoparticles that are close to monodisperse can be produced, and the average particle size of the metal nanoparticles is preferably 5 nm to 100 nm, more preferably 8 nm to 95 nm, and even more preferably 10 nm to 90 nm.
The particle size and average particle size of the metal nanoparticles can be measured from an image obtained by a scanning electron microscope (SEM).
The shape of the metal nanoparticles may be any shape such as spherical, plate-like, or rod-like, but spherical is preferred.

The surface of the metal nanoparticles may be coated with a coating layer. The presence of a coating layer inhibits oxidation of the surface of the metal nanoparticles, resulting in a bonding layer with excellent bonding strength and conductivity. Note that the particle size of the metal nanoparticles does not include the coating layer.

It is preferable to select and use a coating compound that easily decomposes or volatilizes when heated at 100 to 300°C as the coating layer. The coating compound is preferably physically adsorbed or ionically adsorbed in terms of desorption properties upon heating, and an organic compound having a polar group is preferred. Examples of polar groups include amino groups, hydroxyl groups, carboxy groups, aldehyde groups, and amide groups. A straight-chain hydrocarbon group is preferred in terms of dispersibility of metal nanoparticles. Furthermore, aliphatic amines, aliphatic alcohols, amino alcohols, fatty acids (aliphatic carboxylic acids), aliphatic aldehydes, fatty acid alkanolamides, and fatty acid amino alkyl esters are preferred in terms of suppressing surface oxidation of aromatic nanoparticles and suppressing aggregation of metal nanoparticles, with aliphatic carboxylic acids and aliphatic aldehydes being more preferred. The coating compound can be used alone or in combination of two or more types.

Specific examples of the coating compound include aliphatic amines such as octylamine, decylamine, dodecylamine, and oleylamine;
aliphatic alcohols such as hexanol, octanol, decanol, dodecanol, and oleyl alcohol;
Amino alcohols such as ethanolamine, propanolamine, octanolamine, decanolamine, dodecanolamine, and oleyl alcoholamine;
Fatty acids such as butyric acid, caproic acid, caprylic acid, pelargonic acid, undecanoic acid, stearic acid, palmitoleic acid, oleic acid, vaccenic acid, linoleic acid, and linolenic acid;
Aliphatic aldehydes such as butanal, hexanal, octynal, nonanal, decanal, undecyl aldehyde, octadecyl aldehyde, and hexadecenyl aldehyde;
fatty acid alkanolamides such as caproic acid ethanolamide, caprylic acid propanolamide, lauric acid ethanolamide, tridecylic acid propanolamide, and palmitic acid propanolamide;
Examples thereof include fatty acid aminoalkyl esters such as aminoethyl caproate, aminopropyl caprylate, aminoethyl laurate, aminopropyl laurate, and aminopropyl palmitate.

The carbon number of the linear hydrocarbon group constituting the coating compound is preferably 3 or more, more preferably 5 or more, and even more preferably 7 or more, from the viewpoints of oxidation inhibition and dispersibility in solvents. Furthermore, from the viewpoint of elimination upon heating, the carbon number of the aliphatic group is preferably 24 or less, more preferably 16 or less, and even more preferably 12 or less.

The coating compound preferably forms a monomolecular film in which polar groups are arranged on the metal particle side, from the viewpoints of suppressing surface oxidation of the metal nanoparticles and of detachment during heating. Furthermore, when the coating compound forms a monomolecular film, the coating density on the metal nanoparticle surface is preferably 2.5 to ^5.2 molecules/nm².

Furthermore, aliphatic carboxylic acids or aliphatic aldehydes are preferred as coating compounds because they can reduce the particle size distribution of metal nanoparticles using the method described below, making it easier to obtain metal nanoparticles with a relatively uniform particle size. Furthermore, if the metal powder has an oxide film, aliphatic carboxylic acids or aliphatic aldehydes also have the effect of removing the oxide film during sintering, contributing to improved bonding strength and conductivity.

Metal nanoparticles are particles that are essentially composed of metal, but may contain other elements, such as metal oxides and metal hydroxides, that are inevitably included, as long as the effects of the present invention are not impaired. From the standpoint of bonding strength, the content of other elements is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, of the total amount of metal nanoparticles.

Coated metal nanoparticles coated with aliphatic carboxylic acids or aliphatic aldehydes can be produced with reference to, for example, JP 2015-227476 A and JP 2017-179403 A. According to the method described in these publications, a fatty acid or aliphatic aldehyde is disposed on the surface of spherical metal nanoparticles having an average particle size of 10 to 80 nm and a particle size distribution of approximately ±10 nm of the average particle size, forming a monomolecular coating layer. The coating density of this coating layer is 2.5 to 5.2 molecules/ ^nm² , resulting in metal nanoparticles with excellent surface oxidation inhibition and dispersibility. The coating density can be calculated using the method described in JP 2017-179403 A.
Alternatively, commercially available metal nanoparticles coated with a desired coating compound may be used.

The ratio of metal nanoparticles (A) to metal powder (B) is preferably 0.1 to 1.5 by mass (A/B), and more preferably 0.2 to 1.2. By keeping A/B within this range, the occurrence of coarse pores in the sintered body can be suppressed, resulting in a bonded body with excellent bonding strength.

There are no particular limitations on the method for adding metal nanoparticles to the bonding paste, but from the perspective of dispersibility, it is preferable to add them in the form of a metal nanoparticle dispersion. The metal nanoparticle dispersion contains at least the above-mentioned metal nanoparticles and a second solvent.

<Second Solvent>
The second solvent can be appropriately selected depending on the dispersibility of the metal nanoparticles, the method for forming the coating film of the bonding paste (printing method), etc. Specific examples of the second solvent include those similar to the first solvent, and from the viewpoint of the dispersibility and dispersion stability of the metal nanoparticles, it is preferable that the second solvent contains an alcohol-based solvent.
The proportion of the second solvent in the metal nanoparticle dispersion is preferably 1 to 30 mass %, more preferably 5 to 20 mass %, based on the total mass of the metal nanoparticle dispersion.

The metal nanoparticle dispersion may also contain other components as long as the effects of the present invention are achieved. Examples of such other components include antioxidants, dispersants, thickeners, and gelling agents.

After adding the metal nanoparticles to the metal paste, the resulting paste is stirred using a stirrer. The stirrer can be appropriately selected from known stirrers, such as a planetary stirrer or a vibration stirrer.

The proportion of the solvent in the resulting bonding paste may be adjusted as appropriate depending on the application method to the members to be bonded, etc. For example, the solvent may be 1 to 40 mass % of the total mass of the bonding paste including the solvent, and preferably 5 to 20 mass %.
The total content of the metal nanoparticles and metal powder in the bonding paste can be 60 to 99 mass %, preferably 80 to 95 mass %, of the total mass of the bonding paste.

The joining paste obtained by this manufacturing method can be suitably used, for example, to join two members to be joined. Specifically, for example, two members to be joined can be joined by forming a coating of this joining paste on the joining surface of a first member to be joined, placing the second member to be joined on the coating, and sintering the coating. The joining paste obtained by this manufacturing method produces a joined body with a sintered body having excellent joining strength.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

(Production Example 1: Production of coated copper nanoparticle dispersion)
With reference to JP 2015-227476 A, coated copper nanoparticles in which the surface of copper nanoparticles was coated with lauric acid were produced.
The coated copper nanoparticles were dispersed in 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (solvent, Kyowanol M manufactured by KH Neochem Co., Ltd.) to prepare a dispersion (coated copper nanoparticles 90% by mass, solvent 10% by mass).

[Comparative Example 1]
As a first solvent, 1 part by mass of liquid paraffin 40-S (manufactured by Sanko Chemical Co., Ltd.), 5 parts by mass of liquid paraffin 100-S (manufactured by Sanko Chemical Co., Ltd.), 0.98 parts by mass of Kyowanol M, 0.6 parts by mass of 1-decanal, and 0.05 parts by mass of γ-decanolactone were blended, and the mixture was stirred for 30 seconds at a revolution speed of 2000 rpm using a planetary centrifugal mixer to prepare a mixed solvent.
As the metal powder, a mixture of 40 parts by mass of copper powder (1050Y, manufactured by Mitsui Kinzoku Co., Ltd.) having _{a D50} of 0.8 μm and 20 parts by mass of copper powder (1020Y, manufactured by Mitsui Kinzoku Co., Ltd.) having a D50 of 0.3 μm was prepared.
The metal powder was added to the first solvent, and the mixture was stirred for 60 seconds at a revolution speed of 2000 rpm using a planetary centrifugal mixer, and then stopped. This process was repeated six times to obtain a metal paste.
To the metal paste, 40 parts by mass of the coated copper nanoparticle dispersion was added, and the mixture was stirred at a revolution speed of 2000 rpm for 30 seconds using a rotation and revolution stirrer, and then stopped. This was repeated three times, and then filtered through a 25 μm mesh. A bonding paste was obtained.

[Example 1]
The same first solvent and metal powder were prepared as in Comparative Example 1. As beads, 3 mm copper beads were prepared.
The metal powder and copper beads of the same volume as the metal powder were added to the first solvent to prepare a mixture. The mixture was stirred for 10 minutes using a vibration stirrer, and then stopped. This process was repeated three times, and the mixture was then filtered through a 25 μm mesh to remove the copper beads, thereby obtaining a metal paste.
To the metal paste, 40 parts by mass of the coated copper nanoparticle dispersion was added, and the mixture was stirred at a revolution speed of 2000 rpm for 30 seconds using a rotation and revolution stirrer, and then stopped. This was repeated three times, and then filtered through a 25 μm mesh. A bonding paste was obtained.

[Example 2]
The same first solvent and metal powder as those in Comparative Example 1 were prepared. The same copper beads as those in Example 1 were prepared.
The metal powder and copper beads of the same volume as the metal powder were added to the first solvent to prepare a mixture, which was then stirred using a planetary centrifugal mixer at a revolution speed of 1000 rpm for 60 seconds and then stopped. This process was repeated four times to obtain a metal paste.
To the metal paste, 40 parts by mass of the coated copper nanoparticle dispersion was added, and the mixture was stirred at a revolution speed of 2000 rpm for 30 seconds using a rotation and revolution stirrer, and then stopped. This was repeated three times, and then filtered through a 25 μm mesh. A bonding paste was obtained.

[Example 3]
The same first solvent and metal powder were prepared as in Comparative Example 1. As beads, 3 mm zirconia beads were prepared.
A metal paste and a bonding paste were obtained in the same manner as in Example 2, except that the copper beads in Example 2 were changed to zirconia beads.

[Comparative Example 2]
As a first solvent, 1.2 parts by mass of liquid paraffin 40-S (manufactured by Sanko Chemical Co., Ltd.), 5 parts by mass of liquid paraffin 100-S (manufactured by Sanko Chemical Co., Ltd.), 0.26 parts by mass of Kyowanol M, 0.6 parts by mass of 1-decanal, and 0.05 parts by mass of γ-decanolactone were blended, and the mixture was stirred for 30 seconds at a revolution speed of 2000 rpm using a planetary centrifugal mixer to prepare a mixed solvent.
As the metal powder, 45 parts by mass of copper powder (1050Y, manufactured by Mitsui Kinzoku Co., Ltd.) having a _D50 of 0.8 μm was prepared.
The metal powder was added to the first solvent, and the mixture was stirred at a revolution speed of 2000 rpm for 30 seconds using a planetary centrifugal mixer, and then stopped. This process was repeated three times to obtain a metal paste.
To the metal paste, 61.1 parts by mass of the coated copper nanoparticle dispersion was added, and the mixture was stirred at a revolution speed of 2000 rpm for 30 seconds using a rotation and revolution stirrer. This was repeated four times, and then filtered through a 15 μm mesh to obtain a bonding paste.

[Example 4]
The same first solvent and metal powder were prepared as in Comparative Example 2. As beads, 3 mm copper beads were prepared.
The metal powder was added to the first solvent, and copper beads of the same mass as the metal powder were added to prepare a mixture. The mixture was stirred at a revolution speed of 1000 rpm for 180 seconds using a planetary centrifugal mixer, and then stopped. This process was repeated twice, and the mixture was then filtered through a 15 μm mesh to remove the copper beads, thereby obtaining a metal paste.
To the metal paste, 61.1 parts by mass of the coated copper nanoparticle dispersion was added, and the mixture was stirred at a revolution speed of 2000 rpm for 30 seconds using a rotation and revolution stirrer. This was repeated four times, and then filtered through a 15 μm mesh to obtain a bonding paste.

[Example 5]
The same first solvent and metal powder were prepared as in Comparative Example 2. As beads, 3 mm copper beads were prepared.
The metal powder was added to the first solvent, and copper beads were added in an amount equal to half the mass of the metal powder to prepare a mixture. The mixture was stirred at a revolution speed of 1000 rpm for 180 seconds using a planetary centrifugal mixer, and then stopped. This process was repeated twice, and the mixture was then filtered through a 15 μm mesh to remove the copper beads, thereby obtaining a metal paste.
To the metal paste, 61.1 parts by mass of the coated copper nanoparticle dispersion was added, and the mixture was stirred at a revolution speed of 2000 rpm for 30 seconds using a rotation and revolution stirrer. This was repeated four times, and then filtered through a 15 μm mesh to obtain a bonding paste.

[evaluation]
<Metal paste>
The liquid surface of each of the metal pastes obtained in the above Examples and Comparative Examples was visually observed. The results are shown in Table 1.
(Liquid level evaluation criteria)
◯: No roughness was observed on the liquid surface, and gloss was observed.
×: Roughness on the liquid surface was observed.

<Particle size>
The particle size of the metal pastes obtained in the above examples and comparative examples was measured by the particle gauge method described in JIS K5600-2-5. The results are shown in Table 1.

<Joining strength>
Using the bonding pastes obtained in the above Examples and Comparative Examples, bonded bodies were produced by the following method.
The bonding paste was applied to a 5 mm square silicon substrate to form a coating film, and then a 3 mm square silicon chip was placed on the coating film and pressed to form a laminate with a thickness of approximately 50 μm before firing.
The laminate was heated to 350° C. at a rate of 3° C./min under a nitrogen-substituted atmosphere while continuing a nitrogen flow of 5 L/min, and fired for 60 minutes to obtain a bonded body.

The resulting bonded structures were each subjected to a die shear test using a bond tester (Condor Sigma, manufactured by XYZTEC, Netherlands) to determine the shear strength [kgf]. The results are shown in Table 1.

[Summary of results]
As shown by comparing Comparative Example 1 with Examples 1 to 3, in which the ratios of each component were adjusted in the same way, and Comparative Example 2 with Examples 4 and 5, it was shown that by adding beads and stirring the metal powder, the particle size can be reduced and the bonding strength can be improved.
As described above, it was demonstrated that the method for producing a metal paste according to the present embodiment can produce a metal paste with reduced particle size due to reduced agglomerates of metal powder. It was also demonstrated that the bonding strength formed from the bonding paste obtained using the metal paste is excellent.

Claims (7)

A method for producing a bonding paste, comprising:
preparing a mixture including metal powder having a particle size of 120 nm to 10,000 nm, beads having a particle size of 0.1 mm to 10 mm, and a first solvent;
agitating the mixture with a stirrer;
removing the beads to obtain a metal paste ;
adding metal nanoparticles having a particle size of 5 to 100 nm to the metal paste;
and stirring the paste after adding the metal nanoparticles with a stirrer.
Method for manufacturing bonding paste . The method for producing a joining paste according to claim 1 , wherein the agitator is a planetary agitator or a vibration agitator. The method for producing a bonding paste according to claim 1 , wherein the material of the beads is the same type of metal as the metal powder, or is zirconia. The method for producing a joining paste according to claim 1 , wherein the first solvent includes liquid paraffin. The method for producing a joining paste according to claim 1 , wherein the first solvent includes an aldehyde-based solvent and/or an ester-based solvent. The method for producing a bonding paste according to claim 1 , wherein the metal nanoparticles are added by adding a metal nanoparticle dispersion liquid containing the metal nanoparticles and a second solvent. The method for producing a joining paste according to claim 1 , wherein the metal nanoparticles are coated with a coating layer containing an aliphatic carboxylic acid and/or an aliphatic aldehyde.