Silver paste and silver sintered body

Abstract

The present invention provides a silver sintered body obtained from a silver paste that offers high bonding reliability during firing. [Solution] Some aspects of the present invention relate to a silver sintered body comprising silver particles and a silver compound, wherein the content of the silver compound is in the range of 0.31% by weight or more and 14% by weight or less of the total weight of the silver sintered body.

Description

Technical Field

[0001] Some aspects of the present invention relate to silver paste and silver sintered body.

Background Art

[0002] Metal nanoparticles, which may have properties different from those of bulk materials, are being used and studied in various applications such as catalysts, ink materials, and electronic component members.

[0003] Among them, silver nanoparticles have various excellent physical and chemical properties in terms of function, and various research and developments have been conducted on their uses and manufacturing methods.

[0004] For example, Patent Document 1 discloses silver compound-coated silver powder containing silver particles as a core material and a coating portion of a silver compound coated on the surface of the silver particles.

[0005] Patent Document 2 discloses a conductive paste containing silver particles having an average particle diameter within the range of 1 to 500 nm as a first average particle diameter, one or more metals selected from the group consisting of aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, indium, tin, gallium, germanium, and bismuth, and an amine compound, wherein the amount of substance of the amine compound is not less than the amount of substance of the metal.

[0006] Patent Document 3 discloses a silver paste containing silver particles (A), a silver compound (B), an amine (C), and a solvent (D), wherein the proportion of the silver particles (A) is 80% by mass or more and less than or equal to 92% by mass, and the proportion of the amine (C) is less than 6% by mass.

[0007] Patent Document 4 discloses a silver paste characterized by containing silver powder, a solvent, and citric acid.

Prior Art Documents

[0008] [Patent Document 1] Japanese Patent Publication No. 2005-298933 [Patent Document 2] International Publication No. 2019 / 065965 [Patent Document 3] International Publication No. 2023 / 190591 [Patent Document 4] Japanese Patent Publication No. 2023-92937 [Overview of the project] [Problems that the invention aims to solve]

[0009] In recent years, metal nanoparticles have been investigated in the field of electronics packaging as lead-free bonding materials that can be bonded at low temperatures. While lead-free solder is difficult to bond at low temperatures, pastes containing metal nanoparticles can enable bonding at low temperatures by utilizing the properties of metal nanoparticles, namely, that they have a lower melting point compared to bulk materials, but when used for bonding and sintered, they acquire the melting point of bulk materials.

[0010] However, conventional paste-based sintering methods often require high firing temperatures of 250°C or higher to increase bonding strength. Furthermore, many require the addition of organic components, and these organic components themselves, or the solvents that can be used due to them, can lead to a deterioration in conductivity. Additionally, in the case of silver sintered bodies, mixing particles of elements other than silver into the silver paste can improve bonding strength through a pinning effect. However, adding these different elements can reduce sinterability, making it difficult to achieve sufficient effectiveness when bonding at temperatures below 300°C. Moreover, since elements other than silver have lower electrical conductivity than silver, this can also lead to a decrease in the conductivity of the silver sintered body.

[0011] Therefore, some aspects of the present invention aim to provide a silver sintered body obtained from a silver paste that has high bonding reliability during firing. [Means for solving the problem]

[0012] As a result of various investigations into means to solve the above-mentioned problems, the inventors of the present invention have found that by adding a silver compound to a paste made of silver particles, the silver compound, which has low fluidity at high temperatures, acts as a pinning particle between the silver particles, and as a result, the propagation of cracks in the silver sintered body can be suppressed, and high bonding reliability can be obtained, and have completed several embodiments of the present invention.

[0013] In other words, the gist of some aspects of the present invention is as follows: (1) A silver sintered body comprising silver particles and a silver compound, wherein the content of the silver compound is in the range of 0.31% by weight or more and 14% by weight or less of the total weight of the silver sintered body. (2) The silver sintered body according to (1), wherein the silver compound is one or more compounds selected from the group consisting of silver carbonate, silver oxide, silver formate, silver acetate, and silver citrate. (3) The silver sintered body according to (1) or (2), wherein the average particle size of the silver compound is in the range of 1 nm to 80 nm. (4) The silver sintered body according to any one of (1) to (3), wherein the average particle size of the silver particles is in the range of 1 nm or more and 1 μm or less. (5) A silver paste comprising silver particles, a silver compound, and a solvent, wherein the silver compound exists as solid particles, the content of the silver compound is in the range of 0.25% by weight or more and 12% by weight or less relative to the total weight of the silver paste, and the average particle size of the silver compound is in the range of 1 nm or more and 80 nm or less. [Effects of the Invention]

[0014] According to several aspects of the present invention, a silver sintered body obtained from a silver paste with high bonding reliability during firing is provided. [Brief explanation of the drawing]

[0015] [Figure 1] It is a cross-sectional SEM photograph of the silver sintered body of Example 1. [Figure 2] It is a cross-sectional SEM photograph of the silver sintered body of Comparative Example 1.

Mode for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments of some aspects of the present invention will be described in detail. In this specification, the features of some aspects of the present invention will be described with reference to the drawings as appropriate. Note that the silver paste and the silver sintered body of some aspects of the present invention are not limited to the embodiments described below, and various modifications and improvements that can be made by those skilled in the art can be implemented in various forms without departing from the gist of some aspects of the present invention.

[0017] Some aspects of the present invention relate to a silver paste for manufacturing a silver sintered body, which contains silver particles, a silver compound, and a solvent, and the content of the silver compound is in the range of 0.25% by weight or more and 12% by weight or less based on the total weight of the silver paste.

[0018] The silver particles are particles made of silver and are not limited, and may be silver particles known in the art. In one embodiment, the silver particles are silver nanoparticles.

[0019] The average particle size of the silver particles is not limited. The average particle size of the silver particles is usually in the range of 1 nm or more and 1 μm or less, for example, in one embodiment, in the range of 1 nm or more and 80 nm or less, in one embodiment, in the range of 2 nm or more and 300 nm or less, and in one embodiment, in the range of 2 nm or more and 60 nm or less. The average particle size of the silver particles is a value calculated as an average value from the equivalent diameters of the projected areas of 100 or more randomly selected silver particles in the TEM image of the silver particles.

[0020] When the average particle size of the silver particles is within the above range, the dispersibility in the silver sintered body is improved, and the bonding property can be improved. Note that the average particle size of the silver particles is also maintained in the silver sintered body obtained after firing the silver paste.

[0021] The shape of the silver particles is not limited. The shape of the silver particles may include, for example, spherical (including perfectly spherical, nearly spherical, ellipsoidal, polygonal shapes with nearly identical sides, etc.), plate-like (polygonal plate-like), etc.

[0022] The silver particle content is not limited. The silver particle content is typically in the range of 20% to 95% by weight relative to the total weight of the silver paste, in one embodiment in the range of 70% to 85% by weight, and in another embodiment in the range of 77% to 80% by weight.

[0023] By having the silver particle content within the aforementioned range, the viscosity of the silver paste can be adjusted to an appropriate viscosity range, and furthermore, volume shrinkage due to the evaporation of the solvent when the silver paste is sintered can be suppressed, thereby improving the density of the formed silver sintered body.

[0024] The silver compound is a compound containing silver, and is not limited to silver compounds known in the art. Examples of silver compounds include silver salts, silver complexes, silver complex salts, and specifically, silver carbonate, silver oxide, and silver organic acids. Examples of silver organic acids include silver carboxylate, such as silver formate, silver acetate, and silver citrate. The silver compound may be a mixture of two or more types. In one embodiment, the silver compound is silver carbonate.

[0025] The silver compound exists as solid particles in the paste. The average particle size of the silver compound is not limited. Typically, the average particle size of the silver compound is in the range of 1 nm to 80 nm, in one embodiment it is in the range of 5 nm to 60 nm, and in another embodiment it is in the range of 5 nm to 40 nm. The average particle size of the silver compound is calculated as the average value from the equivalent circle diameter of the projected area of ​​100 or more randomly selected silver compound particles in the TEM image of the silver compound particles.

[0026] Because the average particle size of the silver compound particles is within the aforementioned range, a small amount can be widely distributed within the silver sintered body, thereby improving bonding properties. Furthermore, the average particle size of the silver compound particles is maintained even in the silver sintered body obtained after firing the silver paste.

[0027] The shape of the silver compound particles is not limited. The shape of the silver compound particles includes, for example, spherical (including perfectly spherical, nearly spherical, ellipsoidal, polygonal shapes with nearly identical sides, etc.), plate-like (polygonal plate-like), etc.

[0028] The silver compound content is in the range of 0.25% to 12% by weight relative to the total weight of the silver paste, in one embodiment it is in the range of 0.50% to 8% by weight, and in another embodiment it is in the range of 1% to 5% by weight.

[0029] Silver compounds remain in the silver sintered body produced from silver paste. The presence of silver compounds in the sintered body allows them to act as pinning particles, preventing crack propagation.

[0030] The solvent is not limited and may be any solvent known in the art. Examples of solvents include solvents that are liquid at 20°C, such as alcohols, polyhydric alcohols, ketones, aldehydes, carboxylic acids, ethers, esters, amines, monosaccharides, polysaccharides, linear hydrocarbons, fatty acids, aromatics, and mixtures of two or more of these. The boiling point of the solvent is not particularly limited, but is usually in the range of 100°C to 300°C. If the boiling point of the solvent is 100°C or higher, the evaporation of the solvent at room temperature during use of the silver paste can be suppressed, and as a result, viscosity stability and coatability of the silver paste can be ensured. Furthermore, if the boiling point of the solvent is 300°C or lower, during firing, especially during the bonding process by non-pressure firing, the solvent can be suppressed from remaining in the silver sintered body without evaporating at the temperature at which the semiconductor element is connected to the support member, and as a result, the properties of the silver sintered body can be maintained more favorably. Therefore, specific examples of solvents include butyl cellosolve, carbitol, butyl cellosolve acetate, carbitol acetate, ethylene glycol diethyl ether, dipropylene glycol methyl ether acetate, dipropylene glycol mono-n-butyl ether, dipropylene glycol mono-n-methyl ether, terpineol, ethylene glycol, isobornylcyclohexanol, triptyline, and mixtures of two or more of these.

[0031] The solvent content may vary depending on the amount of silver particles and silver compounds contained in the silver paste.

[0032] In some embodiments of the present invention, the silver paste may contain a protective agent (dispersant) used in the production of silver particles and / or silver compounds. The protective agent is a compound that binds to part or all of the surface of silver particles suspended in a solvent, thereby suppressing aggregation of the silver particles. Examples of protective agents, though not limited to them, include polyvinylpyrrolidone (PVP), thiols, polyvinyl alcohol (PVA), etc. In one embodiment, the protective agent is PVP. The protective agent may be a mixture of two or more types.

[0033] The amount of protective agent is not limited. The amount of protective agent may depend on the amount of protective agent used during manufacturing. The amount of protective agent is typically in the range of 0.01% to 10% by weight, 0.1% to 3% by weight, and 0.1% to 1% by weight, relative to the total weight of the silver paste.

[0034] In some embodiments of the present invention, silver pastes, when silver particles and silver compounds are mixed, high bonding reliability can be obtained by firing at temperatures below 200°C. Furthermore, by adding a silver compound that is compatible with silver particles, a silver sintered body in which the silver compound is uniformly dispersed during firing (sintering) can be obtained. In addition, the widespread presence of the silver compound at the sintering interface in the silver sintered body can suppress crack propagation. Moreover, while the addition of foreign elements or organic substances for bonding reliability can inhibit conductivity, the silver compound has physical properties very similar to those of silver particles, so it is uniformly and widely dispersed within the silver sintered body, resulting in a silver sintered body with high conductivity and bonding properties with only a small amount of addition.

[0035] Silver pastes of some embodiments of the present invention may contain impurities, such as unavoidable impurities, such as Fe, K, etc. Silver pastes of some embodiments of the present invention consist only of silver particles, silver compounds, solvents, protective agents, and unavoidable impurities. Silver pastes of some embodiments of the present invention consist only of silver particles, silver compounds, solvents, and unavoidable impurities.

[0036] Silver paste according to some aspects of the present invention can be manufactured by mixing, for example, kneading, silver particles, a silver compound, and a solvent until uniform at room temperature, for example, in the range of 20°C to 40°C. A protective agent may be added to the silver paste, but it is not necessary to add the protective agent as an essential component; the amount of protective agent contained in the added silver particles and / or silver compound is sufficient.

[0037] Commercially available silver particles can be used. Alternatively, silver particles can be manufactured by methods known in the relevant art. Silver particles can be manufactured, for example, as follows:

[0038] First, solution A containing the raw materials for silver particles and a solvent is prepared, and solution B containing a protective agent, a reducing agent, and a solvent is prepared. Subsequently, these solutions are mixed to prepare a reaction solution, which is then reacted to prepare the product.

[0039] Examples of raw materials for silver particles include silver salts, such as inorganic salts like silver hydrochloride, sulfate, nitrate, and phosphate, and organic salts like silver carboxylate and sulfonate, such as silver nitrate.

[0040] The protective agents are those listed above.

[0041] The solvents for solutions A and B are not limited to any solvent capable of dissolving silver salts or protective agents, and include low-boiling polar solvents such as water, alcohols such as methanol and ethanol, polyhydric alcohols such as ethylene glycol, ketones such as acetone, DMSO, DMF, other organic solvents, or mixtures of two or more of these.

[0042] Examples of reducing agents, though not limited to them, include DMF, citric acid or its salts, such as trisodium citrate, disodium citrate, monosodium citrate, oxalic acid or its salts, such as sodium oxalate, ascorbic acid or its salts, such as sodium ascorbate, and mixtures of two or more of these. When DMF is used as a reducing agent, DMF can also act as a solvent.

[0043] Solution B may contain a base. The base can be added to improve the reaction rate of the reduction reaction of the silver salt and the reducing agent. Examples of bases include alkali metal hydroxides or alkaline earth metal hydroxides, or mixtures thereof, such as potassium hydroxide, sodium hydroxide, lithium hydroxide, calcium hydroxide, magnesium hydroxide, or beryllium hydroxide, or mixtures thereof.

[0044] The concentration of silver ions in the reaction solution is not limited, but is usually in the range of 5 mmol / L (mM) to 500 mM relative to the total volume of the reaction solution (e.g., a mixed solution of solutions A and B). The concentration of the protective agent in the reaction solution is not limited, but is usually in the range of 1 mM to 10,000 mM relative to the total volume of the reaction solution. The concentration of the reducing agent in the reaction solution is not limited, but is usually in the range of 10 mM to 10,000 mM relative to the total volume of the reaction solution. If a base is present in the reaction solution, the concentration of the base in the reaction solution is not limited, but is usually in the range of 5 mM to 500 mM relative to the total volume of the reaction solution.

[0045] The order of addition, addition temperature, mixing method, and mixing time of each material are not limited, and the mixture is prepared in such a way that a homogeneous reaction solution is obtained. In some aspects of the present invention, the reaction is started after a homogeneous reaction solution has been prepared.

[0046] The reaction can be carried out by heating methods known in the art. The reaction temperature is not limited, but is usually in the range of 50°C to 300°C (below the boiling point of the solvent). The reaction time is not limited, but is usually in the range of 0.1 hours to 100 hours, for example, in one embodiment it is in the range of 1 hour to 3 hours, and in one embodiment it is in the range of 24 hours to 100 hours.

[0047] In this reaction, the reaction mixture is stirred using a stirring mechanism, such as a propeller-type stirrer or a vibrating stirrer. By stirring the reaction mixture, the silver particles generated in the reaction mixture can be uniformly dispersed, and the reaction mixture can be kept uniform.

[0048] The reaction may be carried out in a batch or flow manner. Some aspects of the present invention are carried out in a batch manner. By carrying out the reaction in a batch manner, the synthesis reaction itself can be completed, and the yield of silver particles obtained can be improved. In addition, the concentration of the reaction solution can be increased, and the problem of clogging of the piping by silver particles that can occur in a flow manner does not occur.

[0049] The solution containing the silver particles produced by the above reaction can be separated and purified (e.g., by salting out or centrifugation) by methods known in the art to obtain the desired silver particles and / or a dispersion containing silver particles.

[0050] The silver particles produced by the above reaction have a uniform particle size, that is, a narrow particle size distribution.

[0051] As the silver compound, commercially available products can be used. Alternatively, the silver compound can be manufactured by methods known in the art. If the silver compound is, for example, silver carbonate, then silver carbonate can be manufactured, for example, in the method for manufacturing silver particles described above, without using a reducing agent, by reacting silver ions with carbon dioxide in the air, or by adding a carbon dioxide source, such as sodium carbonate or sodium bicarbonate, and allowing the reaction to proceed.

[0052] Silver pastes manufactured according to several aspects of the present invention can be used not only as conventional catalysts, electronic component materials, and ink materials, but also as high-temperature-resistant, lead-free bonding materials in the field of electronics packaging.

[0053] Some aspects of the present invention relate to a silver sintered body produced by firing a silver paste according to some aspects of the present invention.

[0054] The firing temperature is not limited, but is usually in the range of 100°C to 300°C, in one embodiment it is in the range of 120°C to 250°C, in one embodiment it is in the range of 150°C to 200°C, and in one embodiment it is in the range of 150°C to 180°C. The firing time is not limited, but is usually in the range of 1 minute to 10 hours, for example, in one embodiment it is in the range of 1 minute to 2 hours, and in one embodiment it is in the range of 2 minutes to 1 hour. The firing temperature and firing time are adjusted so that the solvent in the silver paste is removed from the silver sintered body produced, and the silver compounds remain while maintaining the particle size of the silver particles and silver compounds in the silver paste.

[0055] A silver sintered body according to some embodiments of the present invention comprises silver particles and a silver compound, wherein the content of the silver compound is in the range of 0.31% to 14% by weight, 0.60% to 9% by weight in one embodiment, and 1.5% to 7% by weight in another embodiment, based on the total weight of the silver sintered body. A silver sintered body according to some embodiments of the present invention may contain impurities, such as unavoidable impurities, such as Fe and K. A silver sintered body according to some embodiments of the present invention consists only of silver particles, a silver compound, a protective agent, and unavoidable impurities. A silver sintered body according to some embodiments of the present invention consists only of silver particles, a silver compound, and unavoidable impurities.

[0056] In some embodiments of the present invention, the silver particle content is not limited, but is typically in the range of 20% to 99% by weight of the total weight of the silver sintered body, 70% to 98% by weight in one embodiment, and 90% to 95% by weight in another embodiment.

[0057] In some aspects of the present invention, the silver sintered body retains the silver compound without decomposition, and the bonding between the silver particles is strengthened, resulting in a silver sintered body with high bonding reliability in which crack propagation is suppressed. [Examples]

[0058] The following describes some embodiments of the present invention, but it is not intended to limit the embodiments of the present invention to those shown in these embodiments.

[0059] I. Preparation of Silver Paste I-1. Preparation of Silver Particles Silver particles were synthesized using Solution A (500 mL) and Solution B (1000 mL) shown in Table 1 below.

[0060] [Table 1]

[0061] I-2. Preparation of silver carbonate as a silver compound Silver carbonate was synthesized using Solution A (500 mL) and Solution B (500 mL) shown in Table 2 below.

[0062] [Table 2]

[0063] I-3. Preparation of Silver Paste The silver particles prepared as described above were mixed with silver carbonate particles, impurities were removed by decantation using ethanol, and the mixture was dispersed in terpineol, an organic solvent, to obtain a silver paste. The composition of the prepared silver paste is shown in Table 4 of the evaluation results below.

[0064] II. Evaluation of silver paste and silver sintered bodies made from said silver paste II-1. Evaluation of Particle Size The particle sizes of silver particles and silver carbonate particles were confirmed using TEM images taken as follows.

[0065] Silver particles or silver carbonate particles synthesized under the aforementioned conditions were dropped onto a TEM grid, dried, and a sample was prepared. Subsequently, TEM observation was performed according to the TEM measurement conditions shown in Table 3.

[0066] [Table 3]

[0067] The average particle size of silver particles or silver carbonate particles was calculated by determining the equivalent diameter of the projected area circle of 100 or more randomly selected silver particles and averaging them. As a result, the average particle size of silver particles was 23 nm, and the average particle size of silver carbonate particles was 30 nm.

[0068] II-2. Evaluation of Volume Resistivity A silver paste was applied to a glass substrate to a thickness of 100 μm, and the mixture was fired at 120°C for 2 hours to produce a silver sintered body. The volume resistivity of the obtained silver sintered body was measured using an electrical conductivity meter.

[0069] II-3. Bonding Strength Test Evaluation A silver paste was applied to a copper plate to a thickness of 100 μm. A copper block was placed on top, and the clearance was adjusted so that the film thickness was 45 μm. The plate was then preheated at 100°C for 10 minutes. Subsequently, it was fired at 150°C for 2 minutes to produce a silver sintered body. Furthermore, a durability test was conducted at 200°C for 500 hours, and the bonding strength was evaluated using a bond tester. Bonds that decreased by 20% or more compared to the initial bonding strength were marked as "fail".

[0070] II-4. Observation of Silver Sintered Bodies For Example 1 and Comparative Example 1, described in Table 4, the cross-sections of the silver sintered bodies prepared by firing at 150°C for 30 minutes were observed using SEM.

[0071] III. Evaluation results of silver paste and silver sintered bodies made from said silver paste Table 4 shows the composition of the prepared silver paste and the results for the volume resistivity and bonding reliability of the silver sintered body made from the said silver paste.

[0072] [Table 4]

[0073] Table 4 shows that silver carbonate, which is the same metal compound as the silver particles added to the silver paste, exhibits good dispersibility in the silver paste and has a high pinning effect. The preferred content of silver carbonate as a silver compound is in the range of 0.25% to 12% by weight relative to the total weight of the silver paste, and it was found that the volume resistivity increases as the amount of silver carbonate added increases.

[0074] Figure 1 shows a cross-sectional SEM image of a silver sintered body prepared by firing the silver paste of Example 1 at 150°C for 30 minutes, and Figure 2 shows a cross-sectional SEM image of a silver sintered body prepared by firing the silver paste of Comparative Example 1 at 150°C for 30 minutes. From Figures 1 and 2, it was found that in Example 1, particles containing light elements with low contrast were present at the interface.

Claims

1. A silver sintered body containing silver particles and a silver compound, The content of the silver compound is in the range of 0.31% by weight or more and 14% by weight or less relative to the total weight of the silver sintered body. Silver sintered body.

2. The silver sintered body according to claim 1, wherein the silver compound is one or more compounds selected from the group consisting of silver carbonate, silver oxide, silver formate, silver acetate, and silver citrate.

3. The silver sintered body according to claim 2, wherein the average particle size of the silver compound is in the range of 1 nm to 80 nm.

4. The silver sintered body according to any one of claims 1 to 3, wherein the average particle size of the silver particles is in the range of 1 nm or more and 1 μm or less.

5. A silver paste comprising silver particles, a silver compound, and a solvent, The silver compound exists as solid particles, The content of the silver compound is in the range of 0.25% by weight or more and 12% by weight or less relative to the total weight of the silver paste. The average particle size of the silver compound is in the range of 1 nm to 80 nm. Silver paste.

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