Silver paste and silver sintered body

Abstract

The present invention addresses the problem of providing a silver sintered body obtained from a silver paste having high bonding reliability during firing. Several aspects of the present invention relate to a silver sintered body containing silver particles and a silver compound, in which the content of the silver compound is in the range of 0.31 wt% to 14 wt% with respect to the total weight of the silver sintered body.

Description

Technical Field

[0001] Several aspects of the present invention relate to a silver paste and a silver sintered body. Background Technology

[0002] Metal nanoparticles, which have properties different from bulk materials, are used or studied in various applications such as catalysts, ink materials, and electronic components.

[0003] Among them, silver nanoparticles have various excellent physicochemical properties on the functional surface, and various research and development have been carried out on their applications and manufacturing methods.

[0004] For example, Patent Document 1 discloses a silver powder coated with a silver compound, which includes silver particles having silver particles as core materials and silver compound coating portions covering the surface of the silver particles.

[0005] Patent Document 2 discloses a conductive paste comprising: silver particles having an average particle size in the range of 1 to 500 nm as a first average particle size; 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 having a mass of more than or equal to the mass of the metal.

[0006] Patent document 3 discloses a silver paste, characterized in that it contains silver particles (A), silver compound (B), amine (C) and solvent (D), wherein the proportion of silver particles (A) is 80% by mass or more and 92% by mass or less, and the proportion of amine (C) is less than 6% by mass.

[0007] Patent document 4 discloses a silver paste, characterized in that it comprises silver powder, solvent and citric acid.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2005-298933

[0011] Patent Document 2: International Publication No. 2019 / 065965

[0012] Patent Document 3: International Publication No. 2023 / 190591

[0013] Patent Document 4: Japanese Patent Application Publication No. 2023-92937 Summary of the Invention

[0014] In recent years, metal nanoparticles have been studied in the field of electronic packaging as lead-free bonding materials capable of bonding at low temperatures. Lead-free solders are difficult to bond at low temperatures, but pastes containing metal nanoparticles utilize the properties of metal nanoparticles: they have a low melting point compared to bulk materials, and when used for bonding and sintering, they have the melting point of bulk materials, thus enabling bonding at low temperatures.

[0015] However, in the manufacture of sintered bodies from conventional slurries, high firing temperatures above 250°C are often required to improve bond strength. Furthermore, slurries often require the addition of organic components, and by limiting the organic component itself or the solvent suitable for it, conductivity can sometimes deteriorate. Additionally, in the case of silver sintered bodies, there are instances where mixing particles of an element different from silver into the silver paste can improve bond strength through a pinning effect; however, adding this different element can lead to decreased sinterability, and sometimes the effect is not sufficient in bonding below 300°C. Moreover, the conductivity of elements different from silver is lower than that of silver, which may also cause a decrease in the conductivity of silver sintered bodies.

[0016] Therefore, one of the objectives of this invention is to provide a silver sintered body obtained from silver paste with high bonding reliability during firing.

[0017] The inventors conducted various studies to achieve the above-mentioned objectives and discovered that by adding a silver compound to a slurry composed of silver particles, the silver compound, which has low fluidity at high temperatures, acts as a needle-like particle between the silver particles. As a result, the propagation of cracks in the silver sintered body can be suppressed, thereby achieving high bonding reliability. This led to the completion of several aspects of the present invention.

[0018] That is, the main points of several aspects of the present invention are as follows.

[0019] (1) A silver sintered body comprising silver particles and a silver compound, wherein the content of the silver compound is in the range of more than 0.31% by weight and less than 14% by weight relative to the total weight of the silver sintered body.

[0020] (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.

[0021] (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 or more and 80 nm or less.

[0022] (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.

[0023] (5) A silver paste comprising silver particles, a silver compound and a solvent, wherein the silver compound exists in the form of solid particles, the content of the silver compound is in the range of more than 0.25% by weight and less than 12% by weight relative to the total weight of the silver paste, and the average particle size of the silver compound is in the range of more than 1 nm and less than 80 nm.

[0024] Through several aspects of the present invention, a silver sintered body obtained from silver paste with high bonding reliability during firing is provided. Attached Figure Description

[0025] Figure 1 This is a cross-sectional SEM image of the silver sintered body from Example 1.

[0026] Figure 2 This is a cross-sectional SEM image of the silver sintered body of Comparative Example 1. Detailed Implementation

[0027] Hereinafter, preferred embodiments of several aspects of the present invention will be described in detail.

[0028] In this specification, features of several embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, the silver paste and silver sintered bodies of the present invention are not limited to the embodiments described below, and can be implemented in various ways, such as modifications and alterations, that can be made by those skilled in the art, without departing from the spirit of the present invention.

[0029] Several aspects of the present invention relate to a silver paste for manufacturing silver sintered bodies, the silver paste comprising silver particles, a silver compound and a solvent, wherein 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.

[0030] Silver particles are particles composed of silver, and are not limited to any particular type of silver particle known in the art. In one embodiment, the silver particles are silver nanoparticles.

[0031] The average particle size of the silver particles is not limited. The average particle size is typically in the range of 1 nm to 1 μm, for example, in one embodiment it is in the range of 1 nm to 80 nm, in another embodiment it is in the range of 2 nm to 300 nm, and in yet another embodiment it is in the range of 2 nm to 60 nm. Furthermore, the average particle size is calculated by averaging the equivalent diameter of the projected area circles of at least 100 randomly selected silver particles in a TEM image of the silver particles.

[0032] By controlling the average particle size of the silver particles within the specified range, the dispersibility of the silver sintered body is improved, thereby enhancing its bonding properties. Furthermore, the average particle size of the silver particles can be maintained in the silver sintered body obtained after firing the silver paste.

[0033] The shape of silver particles is not limited. The shape of silver particles includes, for example, spherical (true sphere, approximately spherical, ellipsoidal, polygonal with approximately the same sides, etc.) and plate-like (polygonal plate-like) shapes.

[0034] The content of silver particles is not limited. The content of silver particles relative to the total weight of the silver paste is generally in the range of 20% by weight or more and 95% by weight or less, in one embodiment in the range of 70% by weight or more and 85% by weight or less, and in another embodiment in the range of 77% by weight or more and 80% by weight or less.

[0035] By adjusting the silver particle content within the specified range, the viscosity of the silver paste can be adjusted to an appropriate viscosity range, thereby suppressing the volume shrinkage caused by solvent evaporation during the sintering of the silver paste, and thus improving the density of the formed silver sintered body.

[0036] The silver compound is any compound containing silver and is not limited to any particular silver compound known in the art. Examples of silver compounds include silver salts, silver complexes, and silver complex salts; more specifically, examples include 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 can be a mixture of two or more compounds. In one embodiment, the silver compound is silver carbonate.

[0037] The silver compound exists in the slurry as solid particles. The average particle size of the silver compound is not limited. The average particle size is typically in the range of 1 nm to 80 nm, in one embodiment in the range of 5 nm to 60 nm, and in another embodiment in the range of 5 nm to 40 nm. Furthermore, the average particle size of the silver compound is calculated by averaging the equivalent diameter of the projected area circles of at least 100 randomly selected silver compound particles in a TEM image of the silver compound particles.

[0038] By ensuring that the average particle size of the silver compound particles is within the specified range, a small amount can be widely distributed within the silver sintered body, thereby improving adhesion. Furthermore, the average particle size of the silver compound particles can be maintained within the silver sintered body obtained after the silver paste is fired.

[0039] The shape of silver compound particles is not limited. The shape of silver compound particles includes, for example, spherical (true sphere, approximately spherical, ellipsoidal, polygonal with approximately the same sides, etc.) and plate-like (polygonal plate-like) shapes.

[0040] The content of silver compound relative to the total weight of silver paste is in the range of 0.25% by weight or more and 12% by weight or less, in one embodiment it is in the range of 0.50% by weight or more and 8% by weight or less, and in another embodiment it is in the range of 1% by weight or more and 5% by weight or less.

[0041] Silver compounds can also remain in the silver sintered body made from silver paste. By leaving silver compounds in the state of a silver sintered body, the silver compounds in the sintered body can act as needle-like particles to prevent the propagation of cracks.

[0042] The solvent is not limited and can be any solvent known in the art. Examples of solvents include those that are liquid at 20°C, such as alcohols, polyols, ketones, aldehydes, carboxylic acids, ethers, esters, amines, monosaccharides, polysaccharides, straight-chain hydrocarbons, fatty acids, aromatic compounds, and mixtures of two or more of these. The boiling point of the solvent is not particularly limited and is generally in the range of 100°C or higher and 300°C or lower. If the boiling point of the solvent is 100°C or higher, solvent evaporation at room temperature can be suppressed when using silver paste, resulting in ensuring the viscosity stability and coatability of the silver paste. Furthermore, if the boiling point of the solvent is 300°C or lower, during firing, especially in bonding processes based on pressureless firing, the solvent can be prevented from evaporating at the temperature at which the semiconductor element is connected to the support component and remaining in the silver sintered body, resulting in better preservation of the properties of the silver sintered body. Therefore, as solvents, specifically, examples include butyl cellosolve, carbitol, butyl acetate cellosolve, 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, isoborneol cyclohexanol, tributyltin, and mixtures of two or more of these.

[0043] The solvent content can be varied depending on the amount of silver particles and silver compounds contained in the silver paste.

[0044] In several embodiments of the present invention, the silver paste may contain a protective agent (dispersant) used in the manufacture of silver particles and / or silver compounds. The protective agent is a compound that bonds to a portion or the entire surface of the suspended silver particles in a solvent, and is a compound that inhibits the aggregation of the silver particles. The protective agent is not limited; examples 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.

[0045] The content of the protective agent is not limited. The content of the protective agent can be determined based on the content of the protective agent during manufacturing. The content of the protective agent relative to the total weight of the silver paste is generally in the range of 0.01% by weight or more and 10% by weight, in one embodiment it is in the range of 0.1% by weight or more and 3% by weight, and in another embodiment it is in the range of 0.1% by weight or more and 1% by weight.

[0046] In the silver paste of several embodiments of the present invention, high bonding reliability can be obtained by mixing silver particles and silver compounds, during firing at temperatures below 200°C. Furthermore, by adding silver compounds with good affinity to silver particles, a silver sintered body in which the silver compound is uniformly dispersed during firing (sintering) can be obtained. Moreover, the widespread presence of silver compounds in the silver sintered body at the sintering interface can also suppress crack propagation. In addition, when foreign elements or organic substances are added to improve bonding reliability, they become factors that hinder conductivity. However, silver compounds have physical properties very similar to those of silver particles, and therefore are uniformly and widely dispersed in the silver sintered body, resulting in a silver sintered body with high conductivity and bonding properties that can be achieved with only a small amount of addition.

[0047] The silver paste of several embodiments of the present invention may contain impurities, such as unavoidable impurities like Fe, K, etc. The silver paste of several embodiments of the present invention consists only of silver particles, silver compounds, solvents, protective agents, and unavoidable impurities.

[0048] The silver paste of several embodiments of the present invention can be manufactured by uniformly mixing, for example, compounding silver particles, silver compounds, and solvents at a temperature in the range of room temperature, for example, above 20°C and below 40°C. Additionally, a protective agent may be added to the silver paste, but the protective agent does not need to be added as an essential component; the amount of protective agent contained in the added silver particles and / or silver compounds is sufficient.

[0049] Commercially available silver particles can be used. Alternatively, silver particles can be manufactured using methods known in this technical field. For example, silver particles can be manufactured as follows.

[0050] First, it can be prepared by the following method: preparing a solution A containing silver particles and a solvent, and a solution B containing a protective agent, a reducing agent, and a solvent; then, mixing these solutions to prepare a reaction solution and allowing it to react.

[0051] As raw materials for silver particles, examples include silver salts, such as inorganic salts like silver hydrochloride, sulfate, nitrate, and phosphate, and organic salts like carboxylates and sulfonates, such as silver nitrate.

[0052] As a protective agent, as described above.

[0053] As solvents for solutions A and B, there are no limitations as long as they are solvents capable of dissolving silver salts or protective agents. Examples include low-boiling-point polar solvents, such as water, alcohols, such as methanol, ethanol, polyols, such as ethylene glycol, ketones, such as acetone, DMSO, DMF, other organic solvents, or mixtures of two or more of them.

[0054] As a reducing agent, there are no limitations; examples 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 using DMF as a reducing agent, DMF can also function as a solvent.

[0055] Solution B may contain a base. A base can be added to the reduction reaction of silver salts and reducing agents to increase the reaction rate. 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.

[0056] The concentration of silver ions in the reaction solution is not limited, but is generally in the range of 5 mmol / L (mM) or higher and 500 mM or lower relative to the total volume of the reaction solution (e.g., a mixture of solutions A and B). The concentration of the protective agent in the reaction solution is not limited, but is generally in the range of 1 mM or higher and 10,000 mM or lower relative to the total volume of the reaction solution. The concentration of the reducing agent in the reaction solution is not limited, but is generally in the range of 10 mM or higher and 10,000 mM or lower relative to the total volume of the reaction solution. If the reaction solution contains a base, the concentration of the base is not limited, but is generally in the range of 5 mM or higher and 500 mM or lower relative to the total volume of the reaction solution.

[0057] The order of addition, temperature, mixing method, and mixing time of the materials are not limited, and mixing is carried out in a manner that prepares a homogeneous reaction solution. In several embodiments of the present invention, the reaction begins after the homogeneous reaction solution is prepared.

[0058] The reaction can be carried out using heating-based methods known in the art. The reaction temperature is not limited, but is generally in the range of 50°C or higher and 300°C or lower (below the boiling point of the solvent). The reaction time is not limited, but is generally in the range of 0.1 hours or higher and 100 hours or lower, for example, in one embodiment in the range of 1 hour or higher and 3 hours or lower, and in another embodiment in the range of 24 hours or higher and 100 hours or lower.

[0059] In this reaction, the reaction liquid is stirred by a stirring mechanism, such as a propeller mixer or a vibratory mixer. Stirring the reaction liquid ensures that the silver particles generated in the reaction liquid are evenly dispersed and that the reaction liquid is kept uniform.

[0060] The reaction can be carried out batchwise or in a flow-through manner. Several embodiments of the present invention are carried out batchwise. By carrying it batchwise, the synthesis reaction itself can be completed, and the yield of the obtained silver particles can be increased. Furthermore, the concentration of the reaction solution can be made high, avoiding the problem of pipe blockage of silver particles that may occur in a flow-through manner.

[0061] The solution containing the silver particles produced by the reaction can be separated, purified (e.g., salting out or centrifugation) by methods known in the art to obtain the target silver particles and / or a dispersion containing the silver particles.

[0062] The silver particles produced by the reaction have a uniform particle size, i.e., a narrow particle size distribution.

[0063] Commercially available silver compounds can be used. Alternatively, silver compounds can be manufactured using methods known in the art. In the case of silver compounds such as silver carbonate, silver carbonate can be manufactured, for example, in the methods for manufacturing silver particles described above, by reacting silver ions with carbon dioxide in the air without the use of a reducing agent, or by adding a carbonic acid source such as sodium carbonate or sodium bicarbonate to cause the reaction.

[0064] The silver paste manufactured by several methods of the present invention can be used not only as a conventional catalyst, electronic component, ink material, etc., but also as a high heat-resistant lead-free bonding material in the field of electronic packaging.

[0065] Several aspects of the present invention relate to a silver sintered body based on silver paste obtained by firing several aspects of the present invention.

[0066] The firing temperature is not limited, but is generally in the range of 100°C to 300°C. In one embodiment, it is in the range of 120°C to 250°C; in another embodiment, it is in the range of 150°C to 200°C; and in yet another embodiment, it is in the range of 150°C to 180°C. The firing time is not limited, but is generally 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 yet another embodiment, it is in the range of 2 minutes to 1 hour. The firing temperature and firing time are adjusted to remove the solvent from the silver paste in the manufactured silver sintered body, maintain the particle size of the silver particles and silver compounds in the silver paste, and leave silver compounds remaining.

[0067] Several embodiments of the silver sintered body of the present invention comprise silver particles and silver compounds, wherein the content of the silver compounds relative to the total weight of the silver sintered body is in the range of 0.31% by weight or more and 14% by weight or less, in one embodiment in the range of 0.60% by weight or more and 9% by weight or less, and in another embodiment in the range of 1.5% by weight or more and 7% by weight or less. Several embodiments of the silver sintered body of the present invention may contain impurities, such as unavoidable impurities, such as Fe, K, etc. Several embodiments of the silver sintered body of the present invention consist only of silver particles, silver compounds, a protective agent, and unavoidable impurities. Several embodiments of the silver sintered body of the present invention consist only of silver particles, silver compounds, and unavoidable impurities.

[0068] In the silver sintered body of several embodiments of the present invention, the content of silver particles is not limited, but is generally in the range of 20% by weight or more and 99% by weight or less relative to the total weight of the silver sintered body, in one embodiment in the range of 70% by weight or more and 98% by weight or less, and in another embodiment in the range of 90% by weight or more and 95% by weight or less.

[0069] In several embodiments of the present invention, the silver sintered body is in which the silver compound remains undecomposed, thus maintaining the bond between the silver particles more firmly and thus inhibiting the propagation of cracks, resulting in a silver sintered body with high bonding reliability.

[0070] Example

[0071] Hereinafter, several embodiments related to certain aspects of the present invention will be described, but it is not intended that the present invention be limited to the aspects shown in these embodiments.

[0072] I. Preparation of silver paste

[0073] I-1. Preparation of Silver Particles

[0074] Silver particles were synthesized using solution A (500 mL) and solution B (1000 mL) as shown in Table 1 below.

[0075] [Table 1]

[0076]

[0077] I-2. Preparation of silver carbonate as a silver compound

[0078] Silver carbonate was synthesized using solution A (500 mL) and solution B (500 mL) from Table 2 below.

[0079] [Table 2]

[0080]

[0081] I-3. Preparation of Silver Paste

[0082] The silver particles and silver carbonate particles prepared above were mixed, impurities were removed by decantation with ethanol, and the mixture was dispersed in terpineol as an organic solvent to obtain silver paste. The composition of the prepared silver paste is shown in Table 4 of the evaluation results below.

[0083] II. Evaluation of silver paste and silver sintered bodies made from it

[0084] II-1. Evaluation of Particle Size

[0085] The particle sizes of silver particles and silver carbonate particles were confirmed by the following TEM images.

[0086] Silver particles or silver carbonate particles synthesized under the aforementioned conditions were dropped onto a TEM grid and allowed to dry to prepare a sample. Then, TEM observations were performed according to the TEM measurement conditions in Table 3.

[0087] [Table 3]

[0088]

[0089] The average particle size of silver particles or silver carbonate particles was calculated by determining the equivalent diameter of the projected area circle of more than 100 randomly selected silver particles and averaging them. The results showed that the average particle size of silver particles was 23 nm, and the average particle size of silver carbonate particles was 30 nm.

[0090] II-2. Evaluation of Volume Resistivity

[0091] Silver paste was applied to a glass substrate to a thickness of 100 μm and sintered at 120 °C for 2 hours to prepare a silver sintered body. The volume resistivity of the obtained silver sintered body was measured using a conductivity meter.

[0092] II-3. Evaluation of Bond Strength Test

[0093] Silver paste was applied to a Cu plate to a thickness of 100 μm, and a Cu block was placed on top. The gap was adjusted to achieve a film thickness of 45 μm. The plate was then preheated at 100 °C for 10 minutes. Next, it was sintered at 150 °C for 2 minutes to create a silver sintered body. A durability test was then conducted at 200 °C for 500 hours, and the bond strength was evaluated using a bond strength testing machine. A decrease in bond strength of more than 20% relative to the initial bond strength after durability testing was denoted as ×.

[0094] II-4. Observation of Silver Sintered Body

[0095] For Example 1 and Comparative Example 1 described in Table 4, the cross-section of the silver sintered body prepared by firing at 150°C for 30 minutes was observed by SEM.

[0096] III. Evaluation results of silver paste and silver sintered bodies made from it

[0097] Table 4 shows the composition of the prepared silver paste and the results of the volume resistivity and bonding reliability of the silver sintered body made from the silver paste.

[0098] [Table 4]

[0099]

[0100] As shown in Table 4, silver carbonate, which is the same metal compound as the silver particles added to the silver paste, exhibits good dispersibility and high needle penetration effect in the silver paste. The preferred content of silver carbonate as a silver compound is between 0.25% by weight and 12% by weight relative to the total weight of the silver paste. Increasing the amount of silver carbonate added results in a higher volume resistivity.

[0101] Figure 1 The image shows a cross-sectional SEM image of a silver sintered body prepared by sintering the silver paste of Example 1 at 150°C for 30 minutes. Figure 2 The image shows a cross-sectional SEM photograph of a silver sintered body prepared by sintering the silver paste of Comparative Example 1 at 150°C for 30 minutes. Figure 1 and Figure 2 It is known that in Example 1, particles containing light elements with thin contrast exist at the interface.

Claims

1. A silver sintered body comprising silver particles and a silver compound, characterized in that, 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.

2. The silver sintered body according to claim 1, characterized in that, The silver compound is selected from one or more compounds including silver carbonate, silver oxide, silver formate, silver acetate and silver citrate.

3. The silver sintered body according to claim 2, characterized in that, The average particle size of the silver compound is in the range of 1 nm or more and 80 nm or less.

4. The silver sintered body according to any one of claims 1 to 3, characterized in that, 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, characterized in that, The silver compound exists in the form of solid particles, and the content of the silver compound relative to the total weight of the silver paste is in the range of 0.25% by weight or more and 12% by weight or less. The average particle size of the silver compound is in the range of 1 nm or more and 80 nm or less.

Images