JP2014031541A - Silver powder and method of producing the same, and silver paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make sinterability of a silver powder good and stable.SOLUTION: At least one selected from the group consisting of silver chloride, silver oxide and silver nitrate for which the total of contents of Sb, Bi, S, Se and Te is 2-1000 mass ppm relative to silver is dissolved to obtain a silver complex, and a solution including the silver complex and a reductant solution are mixed together and the silver complex is reduced, in order to obtain a silver powder for which the total of contents of Sb, Bi, S, Se and Te is 2-100 mass ppm relative to the silver powder.

Description

  The present invention relates to silver powder, a method for producing the same, and a conductive paste containing silver powder, and more particularly to a silver powder that is a main component of a silver paste used for forming a wiring layer, an electrode, and the like of an electronic device.

  Silver pastes such as resin-type silver paste and fired-type silver paste are widely used for forming wiring layers and electrodes of electronic devices. Conductive films such as wiring layers and electrodes are formed by applying or printing a silver paste, followed by heat curing or heat baking.

  For example, the resin-type silver paste is composed of silver powder, a resin, a curing agent, a solvent, and the like. After the resin-type silver paste is printed on a conductor circuit pattern or a terminal, the resin-type silver paste is heated and cured at 100 ° C. to 200 ° C. By doing so, a wiring layer, an electrode, etc. can be formed. The fired silver paste is made of silver powder, glass, solvent, etc., and after printing this sintered silver paste on a conductor circuit pattern or terminal, it is heated and fired at 600 ° C. to 800 ° C. to form a conductive film. Thereby, a wiring layer, an electrode, etc. can be formed. The conductivity of these wiring layers and electrodes formed by heating the silver paste is related to the sinterability of silver powder.

  Silver powder uses silver chloride, silver oxide or silver nitrate as a starting material, and mixes a silver complex solution containing a silver complex obtained by dissolving silver chloride, silver oxide or silver nitrate with a complexing agent, and a reducing agent solution, The silver particles obtained by reducing the silver complex can be produced by washing and drying.

  It is known that the sinterability of silver powder is greatly influenced by surface energy and grain boundaries. Therefore, in order to obtain good sinterability, there are techniques such as reducing the particle diameter to increase the specific surface area, or setting the crystallite diameter of silver powder to 10 nm or less as described in Patent Document 1, for example. There is also a technique for improving the sinterability by reducing the concentration of impurity components. The presence of an impurity component inhibits silver diffusion between the grains, and consequently inhibits the sintering reaction. In particular, silver easily generates a silver salt with a halogen element such as chlorine, and it is necessary to sufficiently remove the halogen element from the raw material in order to improve the sinterability of the silver powder. Since the silver salt with a halogen element has solubility in water, the halogen element is reduced by washing during the production of silver powder. However, it can be said that it is not practical to reduce the concentration of impurity components other than the halogen element because the manufacturing process becomes complicated and the cost is increased.

  In recent years, it has been required to exhibit sufficient sinterability with respect to silver powder even under severe conditions such as lowering the firing temperature. However, in the above situation, it cannot be said that the current silver powder is sufficiently stable in sinterability.

JP 2005-048236 A

  This invention is proposed in view of the said situation, and it aims at providing the silver paste which uses the silver powder which shows favorable sinterability stably, its manufacturing method, and the silver powder.

  In order to achieve the above object, the present inventors have made extensive studies, and as a result, in the process of producing silver powder by reducing the silver complex, the total concentration of Sb, Bi, S, Se and Te in the raw material is determined. By controlling the total concentration of Sb, Bi, S, Se and Te in the silver powder to a certain concentration or less by suppressing the concentration to a certain concentration or less, it is possible to obtain a silver powder that stably exhibits excellent low-temperature sinterability. The headline and the present invention were completed.

  The silver powder according to the present invention that achieves the above-described object is characterized in that the total content of Sb, Bi, S, Se, and Te is 2 to 100 ppm by mass with respect to the silver powder.

  In addition, the silver powder production method according to the present invention that achieves the above-described object includes silver chloride, silver oxide, and a total content of Sb, Bi, S, Se, and Te of 2 to 1000 ppm by mass with respect to silver. A solution containing a silver complex obtained by dissolving at least one selected from the group consisting of silver nitrate and a reducing agent solution are mixed, and the silver complex is reduced to obtain silver powder.

  Moreover, the silver paste which concerns on this invention which achieves the objective mentioned above contains the above-mentioned silver powder, It is characterized by the above-mentioned.

  In this invention, it is silver powder which shows favorable sinterability stably, The silver paste using this silver powder can also be made excellent in sinterability. Moreover, in this invention, by forming a wiring layer, an electrode, etc. with a silver paste, the wiring layer, an electrode, etc. can show the stable outstanding electroconductivity, and an industrial value is very large.

  Below, the silver powder to which this invention is applied, its manufacturing method, and a silver paste are demonstrated in detail. Note that the present invention is not limited to the following detailed description unless otherwise specified.

  The silver powder is contained in a resin-type silver paste composed of a curing agent, a resin, a solvent, or the like, or a fired silver paste composed of glass, a solvent, or the like. Resin-type silver paste and fired-type silver paste containing silver powder are used for forming wiring layers, electrodes, and the like. The sinterability of the silver powder is important for the conductivity of the wiring layer and the electrode.

  As impurities that hinder the sinterability of silver powder, sodium chloride, silver halide, and the like are known, but the inventors have found that trace amounts of Sb, Bi, S, Se, and Te affect the sinterability. . By reducing the content of Sb, Bi, S, Se and Te in the silver powder, the sinterability of the silver powder can be improved. In the silver powder according to the present embodiment, the total content of Sb, Bi, S, Se, and Te is 2 to 100 ppm by mass with respect to the silver powder, and does not inhibit the sintering and affects the sintering. There is no range.

  In order to obtain silver powder having excellent sinterability even at low temperatures, the total content of Sb, Bi, S, Se, and Te (hereinafter also referred to as specific impurities) is 100 with respect to the silver powder. It is necessary to set it to mass ppm or less, preferably 50 mass ppm or less.

  For example, Te easily forms a compound with silver to form silver telluride and exists in silver powder. On the other hand, the sintering reaction of silver particles is manifested by activation of the surface of the silver particles by heating and diffusion of silver toward the contact point between the particles. Since silver telluride is not originally sintered at a temperature that causes a silver sintering reaction, particularly when it exists on the surface of the particles, the above-described sintering reaction is greatly inhibited even if the silver particles are in contact with each other. Such reactions also occur with silver antimony compounds, silver bismuth compounds, silver sulfide, and silver selenide.

  However, when the content of the specific impurity is very small, that is, when the total content of the specific impurity is 100 ppm by mass or less, preferably 50 ppm by mass or less in the form of silver powder, The sintering reaction can be supplemented and reaction inhibition can be suppressed.

  Here, the content of the specific impurity is preferably as small as possible from the viewpoint of sinterability, but is disadvantageous in terms of cost. When the amount of specific impurities is less than 2 ppm by mass, the purity becomes 99.998% by mass or more. However, high-purity silver powder is not only suitable for supplying large quantities at a high cost. There is no significant difference in sinterability from silver powder having an impurity amount of about 2 mass ppm. Therefore, in order to achieve both sinterability and industrial cost advantages, it is realistic to set the lower limit of the amount of specific impurities contained in the silver powder to 2 mass ppm, preferably 5 mass ppm.

  The method for producing silver powder as described above comprises dissolving at least one selected from the group consisting of silver chloride, silver oxide and silver nitrate, wherein the total content of specific impurities is 2 to 1000 ppm by mass with respect to silver. A solution containing the obtained silver complex and a reducing agent solution are mixed, and the silver complex is reduced to obtain silver powder.

  Silver chloride, silver oxide and silver nitrate are obtained by, for example, using silver chloride obtained by dissolving copper ore and scrap raw materials in a solvent and purifying a residue obtained by removing copper by an electrolytic method, or using the obtained silver The produced silver nitrate or silver oxide can be used. As a mixing route of Sb, Bi, S, Se, and Te, not only mineral resources such as ore and concentrate, but also a scrap material of electronic parts that have been actively traded in recent years may be mixed. This is because an element such as Sb, Bi, S, Se, or Te is added from a very small amount to a high concentration in order to give the electronic component characteristics.

  Silver chloride or the like becomes a silver complex solution by dissolving in a solvent containing a complexing agent, but the specific impurity element also coexists in a dissolved state. When the silver complex solution is reduced, these specific impurity elements are also reduced, or a compound with silver is directly generated, and part of it is taken into the silver powder, and the impurity element and the silver compound inhibit the sintering reaction. Will do.

  Impurities such as sodium and halogen can be reduced by a cleaning process using an alkaline aqueous solution or water. However, Sb, Bi, S, Se, and Te tend to be in a form that is difficult to remove by cleaning when a compound is formed with silver, and thus cannot be sufficiently removed by cleaning.

  Therefore, as a method for reducing the content of the specific impurity element contained in the silver powder, a method for suppressing the concentration of the specific impurity element contained in the starting material, or a method for reducing the concentration of the specific impurity element contained in the silver powder during the reduction. There is. However, it is difficult to reduce the content during reduction. Therefore, it is effective to suppress specific impurities contained in the starting material, silver chloride, silver oxide or silver nitrate, and the total concentration of Sb, Bi, S, Se, Te is 2 to 1000 mass ppm as silver. Silver chloride, silver oxide or silver nitrate, preferably 2 to 500 ppm by mass, is used. Although the specific impurity amount taken into the silver powder varies depending on the form of the silver raw material and the reduction conditions, the specific impurity amount contained in the silver powder can be sufficiently suppressed by setting the specific impurity amount within the above range.

  The manufacturing method of silver powder is demonstrated concretely. In the method for producing silver powder, silver chloride, silver oxide or silver nitrate having a specific impurity content of 2 to 1000 ppm by mass is dissolved in a solvent containing a complexing agent to prepare a silver complex solution containing a silver complex. Although it does not specifically limit as a complex formation agent, It is preferable to use the ammonia water which is easy to form a complex with silver chloride, silver oxide, and silver nitrate, and does not contain the component which remains as an impurity.

  Next, a reducing agent solution to be mixed with the silver complex solution is prepared. As the reducing agent, general hydrazine, formalin, ascorbic acid and the like can be used. Ascorbic acid is particularly preferable because it has a moderate reducing action and thus the crystal grains in the silver particles are easy to grow. In order to control the uniformity and reaction rate of the reaction, the reducing agent may be used as an aqueous solution whose concentration is adjusted by dissolving or diluting with pure water or the like.

  It is preferable to add at least one water-soluble polymer selected from polyethylene glycol, polyvinyl alcohol, gelatin, polyethylene oxide and polyvinyl pyrrolidone to the reducing agent solution. By adding a water-soluble polymer, nuclei generated by reduction and aggregation of silver particles on which nuclei have grown can be suppressed and the dispersibility can be improved. In addition, when it adds excessively, the quantity of the water-soluble polymer which remains on the surface of silver particle will increase too much, and the electroconductivity of the wiring layer and electrode produced by making into a paste will fall. The addition amount of the water-soluble polymer may be appropriately determined depending on the type of the water-soluble polymer and the particle size of the silver powder to be obtained, but is 0.1 to 20% by mass with respect to the silver contained in the silver complex solution. It is preferable to set it as the range of 1-20 mass%.

  The water-soluble polymer can be mixed with the silver complex solution, but mixing with the reducing agent solution before mixing with the silver complex solution is preferable because a silver powder with good dispersibility can be obtained. This is a result confirmed experimentally. By mixing the reducing agent solution and the water-soluble polymer, the water-soluble polymer exists in the nucleation or nucleation field, and the generated nucleus or This is probably because the water-soluble polymer is rapidly adsorbed on the surface of the silver particles.

  When a water-soluble polymer is added, foaming may occur during the reduction reaction. Therefore, an antifoaming agent may be added to the silver complex solution or the reducing agent mixed solution. The antifoaming agent is not particularly limited, and may be one usually used during reduction. However, in order not to inhibit the reduction reaction, the addition amount of the antifoaming agent is preferably set to a minimum level at which an antifoaming effect can be obtained.

  In addition, about the water used when preparing a silver complex solution and a reducing agent solution, in order to prevent mixing of an impurity, it is preferable to use the water from which the impurity was removed, and it is especially preferable to use a pure water.

  Next, the silver complex solution prepared as described above and the reducing agent solution are mixed, and the silver complex is reduced to precipitate silver particles. This reduction reaction may be performed by a batch method or a continuous reduction method such as a tube reactor method or an overflow method. In order to obtain silver particles having a uniform particle diameter, it is preferable to use a tube reactor method in which the grain growth time is easily controlled. Silver powder can be stably deposited by quantitatively and continuously mixing the silver complex solution and the reducing agent solution. The particle size of the silver particles can be controlled by the mixing rate of the silver complex solution and the reducing agent solution and the reduction rate of the silver complex, and can be easily controlled to the intended particle size. The silver particles have a primary particle diameter of about 0.1 μm to 1.5 μm, and are appropriately adjusted depending on the thickness of the wiring to be formed and the thickness of the electrode.

  Next, it is preferable to perform a surface treatment on the obtained silver particles. This surface treatment is preferably performed before the silver particles adsorbed with the water-soluble polymer are washed with an alkaline solution or water. When washed with an alkaline solution or water, the water-soluble polymer adsorbed on the surface of the silver particles is easily removed, so that the silver particles are aggregated at the portion where the water-soluble polymer is removed. For this reason, if the surface treatment is performed after washing, the surface treatment is performed on the surface of the agglomerated silver particles, and a surface that has not been surface-treated appears due to crushing after drying, resulting in uneven surface treatment. Therefore, it is not preferable. Therefore, it is preferable to perform surface treatment before cleaning.

  The surface treatment is performed on the silver particles before washing with a surfactant or more preferably with a surfactant and a dispersant. It is preferable to use a cationic surfactant for the surface treatment. Since the cationic surfactant is ionized into positive ions without being affected by pH, an effect of improving the adsorptivity to silver powder can be obtained. When surface treatment is performed on silver particles, the surface of the silver particles obtained by reducing a silver complex obtained from silver chloride, silver oxide, or silver nitrate has, for example, a cationic interface that can be at least positive ions in an ionized state. The activator is adsorbed, or the dispersant is further adsorbed on the surfactant adsorbed on the surface of the silver particles.

  When surface treatment is performed with a surfactant and a dispersant, the surfactant can be strongly adsorbed on the surface of the silver particles, and the dispersant can be strongly adsorbed via the surfactant. it can. The surface-treated silver powder suppresses the aggregation of the silver powder due to the effects of the surfactant and the dispersant, and suppresses the aggregation of the surfactant and the dispersant even in the silver paste using the organic solvent. Good dispersibility is obtained in the paste.

  As the dispersant, for example, protective colloids such as fatty acids, organic metals, and gelatin can be used. However, in consideration of the possibility of contamination and adsorbability with a surfactant, it is preferable to use fatty acids or salts thereof. As the dispersant, it is preferable to use a fatty acid or a salt thereof emulsified with a surfactant, and the surface treatment with the dispersant can bind the fatty acid and the surfactant to the surface of the silver particles. Thus, dispersibility can be further improved.

  The addition amount of the dispersant is preferably in the range of 0.01 to 1.00% by mass with respect to the silver particle amount. Similar to the above-mentioned organic compound, the amount of adsorption of the dispersing agent on the silver particles varies depending on the type. A sufficient amount may not be adsorbed by the silver powder. On the other hand, if the added amount of the dispersant exceeds 1.00% by mass, the amount adsorbed on the silver particles becomes too large, and sufficient conductivity can be obtained for the wiring layers and electrodes formed using the silver paste. There may not be.

  The surfactant is not particularly limited, but a cationic surfactant is preferable. As addition amount of surfactant, the range of 0.002-1.000 mass% is preferable with respect to the amount of silver particles. The surfactant can adsorb a sufficient amount of the surfactant to the surface of the silver particles by the addition amount in the above range. When the addition amount of the surfactant is less than 0.002% by mass, the effect of suppressing aggregation of silver particles or improving the adsorptivity of the dispersant may not be obtained. On the other hand, when the addition amount exceeds 1.000% by mass, the adsorption amount is excessively increased, and there is a possibility that the conductivity of the wiring layer or electrode formed using the silver paste may be lowered. By adsorbing the surfactant to the silver particles, the dispersibility in the silver paste is improved, and good conductivity is achieved in the wiring layer and electrode formed using the silver paste.

  Next, the surface-treated silver particles are washed. Silver particles have impurities and excessive water-soluble polymers adsorbed on the surface. Therefore, in order to ensure sufficient conductivity of the wiring layer or electrode formed using the silver paste, the obtained silver particle slurry is washed to remove impurities adhering to the silver particles or excessively adhering water It is necessary to remove the functional polymer. Since the surface treatment layer remains even after impurities and water-soluble polymers are removed, it is possible to achieve both the suppression of the aggregation of silver particles and the high conductivity of the wiring layer, electrodes, and the like.

  As a cleaning method, a method is generally used in which silver particles solid-liquid separated from the silver particle slurry are put into a cleaning solution, stirred using a stirrer or an ultrasonic cleaner, and then solid-liquid separated again to recover silver particles. Used. Further, in order to sufficiently remove the surface adsorbate, it is preferable to repeat the operation of adding silver particles to the cleaning liquid, stirring and cleaning, and performing solid-liquid separation several times.

  The cleaning liquid uses an alkaline solution or water in order to efficiently remove the water-soluble polymer and impurities adsorbed on the surface of the silver particles. As the alkaline solution, it is preferable to use any one of an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous calcium hydroxide solution, and aqueous ammonia, or a mixture thereof. In addition, there is no problem even if an alkaline solution made of an inorganic compound or an organic compound is used. The water used for the cleaning liquid is preferably water that does not contain an impurity element harmful to silver particles, and pure water is particularly preferable.

  The concentration of the alkaline solution is preferably 0.01% by mass to 20% by mass. When the amount is less than 0.01% by mass, the cleaning effect is insufficient. When the amount exceeds 20% by mass, an alkali metal salt may remain unacceptably in the silver particles. Therefore, when a high-concentration alkaline solution is used, it is necessary to perform sufficient pure water cleaning after cleaning to suppress residual alkali metal salt.

  After washing, the silver particles are recovered by solid-liquid separation. The apparatus used for solid-liquid separation may be a commonly used apparatus such as a centrifuge, a suction filter, a filter press, or the like.

  Next, the separated silver particles are dried by evaporating water in the drying step. As a drying method, for example, silver powder collected after the completion of cleaning and surface treatment is placed on a stainless steel pad and heated at a temperature of 40 ° C. to 80 ° C. using a commercially available drying device such as an atmospheric oven or a vacuum dryer. That's fine.

  Next, weak crushing is performed on the dried silver particles to loosen the aggregates produced during drying. Note that the crushing may be performed if it is necessary to loosen the aggregates in the dried silver particles. When crushing, it can be crushed with weak force. This is because the aggregation of silver particles is suppressed by the surface treatment. The force at the time of crushing may be a small vibration, for example, a vibration level when silver particles are sieved with a gyro shifter.

  A silver powder having a desired particle size distribution can be obtained by performing a classification process after the above-described crushing process. The classifying apparatus used in the classification process is not particularly limited, and an airflow classifier, a sieve, or the like can be used.

  In the silver powder production method as described above, the total content of Sb, Bi, S, Se and Te in the raw material is 2 to 1000 mass ppm, preferably 2 to 500 mass ppm, based on silver powder, By using silver oxide or silver nitrate, the total content of Sb, Bi, S, Se and Te contained in the produced silver powder is 2 to 100 mass ppm, more preferably 2 to 50 mass ppm with respect to the silver powder. Silver powder with a low content of specific impurities can be produced. Since the obtained silver powder has a small content of specific impurities, it exhibits good and stable sinterability, and also exhibits good and stable sinterability even when the sintering temperature is low.

  Moreover, a silver paste can be produced by mixing such silver powder with a small content of specific impurities with glass, a solvent, and the like. The method for producing the silver paste is generally the same as the method for producing the silver paste. Since the silver paste uses silver powder with a low content of specific impurities, the silver powder is good and has stable sinterability, so that it is possible to form a wiring layer, an electrode, or the like with good conductivity.

  Specific examples of the present invention will be described below. However, the present invention is not limited to the following examples.

[Example 1]
In Example 1, 2900 g of silver chloride (manufactured by Sumitomo Metal Mining Co., Ltd., purity: 99.8% by mass Sb, Bi, S, Se was added to 40 L of 25% by mass ammonia water maintained at a liquid temperature of 36 ° C. in a 37 ° C. warm bath. The total concentration of Te was 15 mass ppm with respect to silver) while stirring to prepare a silver complex solution, and the obtained silver complex solution was kept at 36 ° C. in a warm bath.

  On the other hand, 1100 g of reducing agent ascorbic acid (manufactured by Kanto Chemical Co., Ltd., reagent) was dissolved in 14 L of pure water at 36 ° C. to prepare a reducing agent solution.

  Next, 100 g of polyvinyl alcohol which is a water-soluble polymer (manufactured by Kuraray Co., Ltd., PVA205) was dissolved in 550 ml of pure water at 36 ° C., and then mixed with the reducing agent solution.

  The prepared silver complex solution and the reducing agent solution are fed into the mixing tube at a silver complex solution of 2.7 L / min and a reducing agent solution of 0.9 L / min using a pump (Hyojin Equipment Co., Ltd.). Reduced the silver complex. A PVC pipe having an inner diameter of 25 mm and a length of 725 mm was used as the mixing tube. The slurry containing silver particles obtained by reduction of the silver complex was placed in a receiving tank while stirring.

  Thereafter, 19 g of stearic acid emulsion (Cerosol 920, manufactured by Chukyo Yushi Co., Ltd.) was added as a dispersant to the silver particle slurry obtained by the reduction, and the surface treatment was performed by stirring for 60 minutes. After the surface treatment, the silver particle slurry was filtered using a filter press, and the silver particles were solid-liquid separated.

  Subsequently, before the collected silver particles are dried, the silver particles are put into 23 L of a 0.2 mass% sodium hydroxide (NaOH) aqueous solution maintained at 40 ° C., washed with stirring for 15 minutes, and then filtered. And silver particles were collected.

  Next, the collected silver particles were put into 23 L of pure water maintained at 40 ° C., stirred and filtered, and then the silver particles were transferred to a stainless steel pad and dried at 60 ° C. for 10 hours in a vacuum dryer. Subsequently, the dried silver particles were crushed using a 5 L high-speed stirrer (manufactured by Nippon Coke Industries, Ltd., FM5C). After the crushing treatment, the silver particles were removed using a gas stream classifier (EJ-3, manufactured by Nippon Mining Co., Ltd.) to remove coarse particles with a classification point of 7 μm to obtain silver particles. About the obtained silver powder, when the density | concentration of Sb, Bi, S, Se, and Te was analyzed, the sum total of all these density | concentrations was 7 mass ppm with respect to silver powder.

  In addition, 9.2 g of silver powder obtained in a stainless steel small dish, 0.8 g of a 1: 7 weight ratio of epoxy resin (JER819 manufactured by Mitsubishi Chemical Corporation) and terpineol were weighed, and a metal spatula was measured. After mixing, the mixture was kneaded for 5 minutes at 2000 rpm (420 G as centrifugal force) using a self-revolving kneading machine (ARE-250 manufactured by Shinky Corporation) to produce a uniform silver paste. Furthermore, wiring was printed with the silver paste on the alumina base | substrate using the screen printing machine (MODEL-2300 by Minami Co., Ltd.), and the alumina base | substrate with which wiring was printed was heat-processed for 60 minutes at 200 degreeC in air | atmosphere.

  And the volume resistivity of the wiring printed with the silver paste which heat-processed was measured using the resistivity meter (Mitsubishi Chemical Arinatec Loresta GP). As a result, the volume resistivity of the silver paste was 7.2 μΩ · cm, and it was found that the paste had excellent conductivity. Thereby, it turns out that the sinterability of the silver powder contained in the silver paste is good.

[Example 2]
Example 2 was the same as Example 1 except that the purity of silver chloride was 99.7% by mass and the total concentration of Sb, Bi, S, Se, Te was 180 mass ppm with respect to silver. Silver powder was produced. About the obtained silver powder, the sum total of the density | concentration of Sb, Bi, S, Se, and Te was 12 mass ppm with respect to silver powder.

  As a result of producing and evaluating a silver paste in the same manner as in Example 1 using the silver powder of Example 2, the volume resistivity of the silver paste is 7.5 μΩ · cm, and the silver paste has excellent conductivity. I understood. Thereby, it turns out that the sinterability of the silver powder contained in the silver paste is good.

[Example 3]
Example 3 was the same as Example 1 except that the purity of silver chloride was 99.7% by mass and the total concentration of Sb, Bi, S, Se, Te was 590 mass ppm with respect to silver. Silver powder was produced. About the obtained silver powder, the sum total of the density | concentration of Sb, Bi, S, Se, and Te was 77 mass ppm with respect to silver powder.

  As a result of producing and evaluating a silver paste in the same manner as in Example 1 using the silver powder of Example 3, it was found that the volume resistivity of the silver paste was 12.1 μΩ · cm, and that the silver paste had conductivity. It was. Thereby, it turns out that the sinterability of the silver powder contained in the silver pace is favorable. However, in Example 3, the total concentration of Sb, Bi, S, Se, Te contained in the raw material silver chloride and the total concentration of Sb, Bi, S, Se, Te contained in the silver powder are the same as in Example 1 and Since it was more than Example 2, it was found that the conductivity was inferior compared to Examples 1 and 2.

[Comparative Example 1]
In Comparative Example 1, silver powder was produced in the same manner as in Example 1 except that the purity of silver chloride was 99.5% by mass and the total concentration of Sb, Bi, S, Se, and Te was 1600 ppm by mass. . About the obtained silver powder, the sum total of the density | concentration of Sb, Bi, S, Se, and Te was 230 ppm.

  As a result of evaluating in the same manner as in Example 1 using the silver powder of Comparative Example 1, the volume resistivity of the silver paste is 75.3 μΩ · cm, and the total concentration of Sb, Bi, S, Se, and Te is 100 mass ppm. It turned out that the electroconductivity of a silver paste is inferior compared with these samples 1-3.

  As mentioned above, the concentration of Sb, Bi, S, Se, Te is silver powder in the obtained silver powder by using the raw material whose concentration of Sb, Bi, S, Se, Te is 2-1000 mass ppm with respect to silver. Silver powder having good and stable sinterability can be obtained with 2-100 ppm by mass with respect to the whole, and wiring having excellent conductivity can be formed by using a silver paste containing this silver powder. Recognize.

Claims (7)

  A silver powder characterized in that the total content of Sb, Bi, S, Se and Te is 2 to 100 ppm by mass with respect to the silver powder.   The silver powder according to claim 1, wherein the total content of Sb, Bi, S, Se and Te is 2 to 50 ppm by mass with respect to the silver powder.   The silver powder according to claim 1 or 2, wherein the presence form of the Sb, Bi, S, Se and Te is a compound with silver.   Silver obtained by dissolving at least one selected from the group consisting of silver chloride, silver oxide and silver nitrate, wherein the total content of Sb, Bi, S, Se and Te is 2-1000 mass ppm with respect to silver A method for producing silver powder, comprising mixing a solution containing a complex and a reducing agent solution, and reducing the silver complex to obtain silver powder.   5. The method for producing silver powder according to claim 4, wherein the silver powder is obtained by quantitatively and continuously mixing the solution containing the silver complex and the reducing agent solution.   At least one water-soluble polymer selected from polyethylene glycol, polyvinyl alcohol, gelatin, polyethylene oxide and polyvinyl pyrrolidone is added to the reducing agent solution before mixing with the solution containing the silver complex. The method for producing a silver powder according to claim 4 or 5.   A silver paste comprising the silver powder according to any one of claims 1 to 3.