JP6186156B2 - Silver powder, method for producing the same, paste, electronic circuit component, electric product - Google Patents

Description

  The present invention relates to a silver powder comprising surface-treated silver particles and a method for producing the same. Moreover, it is related with the electrically conductive paste, electronic circuit component, and electric product using the silver powder.

  Conventionally, as a material for forming an electrode or a circuit of an electronic component or the like, a fired conductive paste in which silver powder is dispersed in an organic component is known. A general baked conductive paste contains, in addition to silver powder, for example, a vehicle in which ethyl cellulose or acrylic resin is dissolved in an organic solvent, glass frit, an inorganic oxide, a dispersant, and the like as constituent components. This type of conductive paste is formed into a predetermined pattern by dipping, printing, etc., and then fired to form a conductor. Low temperature fired multilayer substrate (LTCC), hybrid IC, multilayer ceramic capacitor, chip resistor It is used for such purposes.

  In the firing, the silver powder is sintered at a temperature lower than the melting point of silver (961 ° C.). At that time, the higher the firing temperature, the more advantageous is the reduction of the electrical resistance of the sintered body. However, in order to prevent the occurrence of various problems associated with firing, it is important to apply silver powder having characteristics suitable for the intended firing temperature. For example, in the case of a paste having a general composition of a type containing glass frit, the shrinkage characteristic accompanying sintering when the silver powder is heated to the firing temperature is as close as possible to the shrinkage characteristic of glass frit. It is extremely effective in forming a simple conductor.

Patent Document 1 describes a silver powder coated with an oxide. This document teaches that the noble metal powder obtained by coating the surface of the noble metal powder with a compound of a metal and an organic acid and then heat-treating in an inert atmosphere is suitable for high-temperature firing.
Patent Document 2 discloses a technique for achieving both solder wettability and high-temperature firing in a fired conductive paste using silver powder.

JP-A-8-7644 JP 2007-220332 A

However, in the technique disclosed in Patent Document 1, since the high temperature treatment of 350 to 700 ° C. is performed in the production process of silver powder, the dispersibility of the powder is lowered. In the technique disclosed in Patent Document 2, since the crystallinity of the silver powder itself is not good, the sintering may start at a temperature lower than the desired temperature, and when subjected to high-temperature firing, the silver powder and the glass frit are used. There is a problem that the difference in shrinkage characteristics tends to increase.
The present invention realizes a silver powder suitable for high-temperature firing that has good dispersibility as a powder and does not sinter to high temperatures, and a firing-type conductive paste suitable for high-temperature firing and an electronic circuit component using the same The purpose is to contribute to the provision of electrical products.

  As a result of diligent research to solve the above problems, the present inventors, as a silver powder coated with a metal compound containing chlorine, are more excellent as a silver powder for high-temperature firing when the crystallite diameter of silver is 400 nm or more. As a result, the present invention has been completed.

That is, in this invention, it is silver powder which consists of silver particles which the metal compound containing chlorine adhere | attached, Comprising: The said metal content in the said silver powder is 0.01-1.0 mass%, Silver crystallite Silver powder having a diameter of 400 nm or more is provided. The metal of the metal compound is, for example, tin.
This silver powder has a shrinkage rate δ ₇₅₀ determined from a change in diameter when a 5 mm diameter pellet obtained by applying a load of 490 N to 0.15 g of the silver powder placed in a cylindrical container for 1 minute is heated from 50 ° C. to 750 ° C. It has a characteristic of 0.5 to 5%. Further, the pellets having a diameter of 5 mm obtained by the same method have a characteristic that the shrinkage rate δ ₈₀₀ obtained from the change in diameter when the temperature is raised from 50 ° C. to 800 ° C. is 2 to 8%.

  As a method for producing the above silver powder, the metal chloride is hydrolyzed in a slurry in which silver particles having a crystallite diameter of 400 nm or more are dispersed in a liquid to cause precipitation of the metal compound containing chlorine. A manufacturing method is provided for depositing a precipitate on the silver particles. An example of the metal chloride is tin chloride.

  The said silver powder is used for a baking type conductive paste as a conductive filler. It is particularly suitable for a glass frit-containing type conductive paste. In addition, an electronic circuit component manufactured using the conductive paste and an electric product manufactured using the electric circuit component are provided.

  When the conductive paste according to the present invention is used, it is easy to stably form a good-quality conductor with few defects such as voids when fired at a high temperature close to the melting point of silver. The silver powder applied to the paste has good dispersibility in the paste. The solder wettability of the conductor obtained by firing is also good. Moreover, since the silver particle which comprises silver powder can be made into a spherical particle, the applicability to the photolitho method, the offset method, the dipping method, and the printing method which are the circuit formation methods before baking is favorable.

The SEM photograph of the silver powder obtained in Example 1. The SEM photograph of the silver powder obtained in Comparative Example 1.

The silver powder that is the subject of the present invention preferably has an average particle diameter of 0.4 to 10 μm represented by a cumulative 50% particle diameter D ₅₀ in a volume-based particle size distribution by laser diffraction, and is 0.5 to 5 μm. It is more preferable that If the particle size is too small, the thermal contraction of the silver powder increases and is not suitable for firing at a high temperature close to the melting point of silver. In addition, if the particle size is too large, it becomes difficult to cope with fine lines.

  The amount of metal element of the deposited metal compound contained in the silver powder (including the same metal element not derived from this compound) needs to be 0.01 to 1.0% by mass of the entire silver powder, and is in the range of 0.03 to 0.5. More preferably, it is mass%. If the metal content is too small, thermal shrinkage becomes excessive, and it becomes difficult to obtain a material suitable for firing at a high temperature close to the melting point of silver. On the other hand, if the metal content is too large, the resistance value of the sintered body increases.

  The amount of chlorine contained in the silver powder is preferably 0.001 to 0.6% by mass, more preferably 0.001 to 0.3% by mass, and 0.001 to 0.1% by mass. More desirable. If the amount of chlorine is too small, the contribution to improving the solder wettability will decrease, and if it is too large, wiring corrosion will occur or the migration resistance will deteriorate.

  By increasing the crystallite diameter of silver constituting the silver powder, the sintering start temperature rises, and it becomes possible to make the shrinkage rate of the silver powder close to glass frit when the temperature is raised to a high temperature. . As a result of various studies, it has been found that setting the crystallite diameter to 400 nm or more is extremely effective in constructing a paste applied to high-temperature firing. It does not need to be too large, for example, it may be in the range of 1000 nm or less. The crystallite diameter is determined by the 2θ / θ method by X-ray diffraction.

Whether the silver powder applied to the firing type conductive paste has a property suitable for high-temperature firing is determined by, for example, shrinkage when a green compact sample made of the silver powder is heated from 50 ° C. to 750 ° C. or 800 ° C. Can be evaluated by rate. Here, the shrinkage ratio δ _T when the temperature was raised to T ° C. was obtained by putting 0.15 g of silver powder to be evaluated into a cylindrical container and applying a load of 490 N for 1 minute to give a pellet having a diameter of 5 mm. From the change in diameter when the temperature is raised from 0 ° C. to T ° C., the following equation (1) can be used.
δ _T (%) = (L ₅₀ −L _T ) / L ₅₀ × 100 (1)
Here, L ₅₀ and L _T is the diameter of the pellets when the sample temperature, respectively is 50 ° C. and T ° C..

As a result of various investigations, when the firing temperature is subjected to a high temperature calcination exceeding 700 ° C. Preferably, the shrinkage rate [delta] ₇₅₀ is in the range of 0.5% to 5%. More preferably, the shrinkage rate δ ₈₀₀ is in the range of 2 to 8%. Silver powder having such properties is relatively suitable for high-temperature firing as a silver powder for firing type conductive paste having a general composition of glass frit-containing type with a shrinkage rate that is relatively close to the characteristics of glass frit up to a high temperature range. Can be evaluated.

  The above-mentioned surface-treated silver powder that is an object of the present invention can be produced by the following method using raw material silver powder having a crystallite diameter adjusted to 400 nm or more. That is, it can be produced by causing precipitation by hydrolysis of a metal chloride and depositing the precipitated substance on the surface of silver particles constituting the raw silver powder. “Deposition” means that precipitation due to hydrolysis of metal chlorides adheres to the surface of silver particles of silver powder. The process of performing this deposition is called “deposition process”. Since precipitation generated by hydrolysis of metal chloride involves chlorine, silver particles deposited with a metal compound containing chlorine can be easily produced. Further, it is desirable to perform the deposition operation by dispersing silver powder composed of silver particles of the raw material to be deposited in an aqueous solution not containing alcohol. This is because if the organic solvent such as alcohol is included, the manufacturing cost is significantly increased.

The raw material silver powder before the deposition treatment is preferably a high-purity silver powder having a purity of 99% by mass or more in which impurities such as tin, titanium, and chlorine are kept low. ₅₀ is preferably 0.1 to 10 μm. Further, it is desirable that the individual silver particles constituting the raw silver powder are coated with a dispersant. As the dispersant, select one or more of polymer dispersants such as polysaccharides, gelatin, collagen peptides, polyethyleneimine, fatty acids, fatty acid salts, surfactants, organometallics, chelating agents and protective colloids. Can be used.

  After depositing a metal compound on the surface of the silver particles of the raw material silver powder, solid-liquid separation is performed, and then washing with pure water is performed. Measure the electrical conductivity of the water used for washing (after washing) as a means to properly wash off the impurities adhering to the particle surface as long as they are not overwashed. It is effective to terminate the cleaning when it is within the range of the electric conductivity of the post-cleaning solution that can obtain an appropriate surface state. To give an example in a certain manufacturing facility, for example, a method of terminating the cleaning in the range where the electric conductivity of the solution after cleaning is 5 to 50 mS / m is effective. If the electrical conductivity of the solution after washing exceeds the set range, excess impurities are still attached. On the other hand, if the cleaning is continued until it falls below the set range, the deposited metal compound containing chlorine is excessively washed away, and it becomes difficult to maintain the amount of the metal compound containing chlorine contained in the product within the above-mentioned appropriate range. .

[Example 1]
100 g of industrial ammonia water was added to 3900 g of an aqueous silver nitrate solution containing 43.2 g of silver to form a silver ammine complex solution. After adding 0.022 g of polyethyleneimine to the silver ammine complex solution, 8 mL of a hydrous hydrazine aqueous solution was added as a reducing agent. Immediately thereafter, an aqueous solution of benzotriazole sodium was added at a ratio of 0.12% by mass with respect to the silver powder to obtain a slurry of silver particles coated with sodium benzotriazole. The silver particle slurry was filtered, washed with water, and dried to obtain silver powder. This silver powder was crushed with a high-speed stirrer to obtain a raw silver powder. The average particle diameter D ₅₀ of the raw silver powder as determined by laser diffraction was 3.6 μm, and the crystallite diameter was 460 nm.

  1 kg of the raw silver powder was added to 2000 g of pure water and stirred to obtain a dispersed slurry. A suspension obtained by adding 3 g of tin (II) chloride dihydrate to 50 g of pure water was prepared, and this was added to the slurry. After further stirring, the mixture was filtered and washed with water. The end of washing was judged by measuring the electrical conductivity of the solution after washing. In this example, the electric conductivity of the solution after washing at the end of washing was 15 mS / m. Then, it dried and obtained silver powder. This silver powder was pulverized with a food mixer (MK-61M, manufactured by Matsushita Electric Industrial Co., Ltd.) to obtain the intended silver powder.

The silver powder was examined for particle size distribution, specific surface area, tin content, shrinkage, and the like.
The specific surface area was measured by the BET method with a counter chrome monosorb.
The particle size distribution was measured with a laser diffraction particle size distribution measuring device (Honeywell-Nikkiso, Microtrac 9320-X100) after putting 0.3 g of silver powder in 30 mL of isopropyl alcohol and dispersing for 5 minutes with a 45 W ultrasonic cleaner. . From the particle size distribution, the cumulative 50% by mass particle diameter D ₅₀ was determined to be 4.0 μm.
The tin content was determined by ICP after dissolving silver powder using sulfuric acid and nitric acid.
The shrinkage rate δ _T is obtained by putting 0.15 g of silver powder in a cylindrical container and applying a load of 490 N for 1 minute to form a pellet having a diameter of 5 mm. The pellet is subjected to various temperatures T ranging from 50 ° C. to 600 to 800 ° C. The change in diameter when the temperature was raised to ° C. was measured and determined according to the above-described equation (1). The measuring apparatus used was DILATO METER 5010 manufactured by Mac Science / Bruker AXS, Inc., and the temperature rising rate was 10 ° C./min.

[Comparative Example 1]
180 mL of industrial ammonia water was added to 3600 mL of a 12 g / L silver nitrate solution as silver ions to form a silver ammine complex solution. After adjusting pH by adding sodium hydroxide 7.5g to this silver ammine complex solution, 192 mL of industrial formalin was added as a reducing agent. Immediately thereafter, a saturated fatty acid composed of stearic acid was dissolved in an ethanol solution and added at a ratio of 0.2% by mass with respect to the silver powder to obtain a slurry of silver particles coated with the saturated fatty acid. The silver particle slurry was filtered, washed with water, and dried to obtain silver powder. The silver powder was subjected to a surface smoothing treatment with a high-speed stirrer, and then classified to remove silver aggregates larger than 8 μm to obtain a raw silver powder. The average particle size D ₅₀ by laser diffraction method of the raw material silver powder is 1.8 .mu.m, the crystallite diameter was 345 nm.

  1 kg of this silver powder was dispersed in 600 g of ethanol using a stirrer. To this dispersion slurry, 1200 g of pure water was added and subsequently stirred. A suspension obtained by adding 3 g of tin (II) chloride dihydrate to 50 g of pure water was prepared, and this was added to the slurry. After further stirring, the mixture was filtered and washed with water. The electric conductivity of the liquid after washing at the end of washing with water was 18 mS / m. Then, it dried and obtained silver powder. This silver powder was pulverized with a food mixer (MK-61M, manufactured by Matsushita Electric Industrial Co., Ltd.) to obtain the intended silver powder.

The silver powder was examined in the same manner as in Example 1 for particle size distribution, specific surface area, tin content, shrinkage rate and the like. D ₅₀ was 2.2 μm. The results of each survey are shown in Table 1.

[Reference example]
Regarding the glass frit MLS-61A for LTCC manufactured by Nippon Electric Glass Co., Ltd., the shrinkage rate was measured in the same manner as in Example 1.

  As can be seen from Table 1, the sample of Example 1 is closer to the shrinkage rate of the reference example than that of Comparative Example 1, and is evaluated as a silver powder suitable for high-temperature firing.

  FIG. 1 shows an SEM photograph of the silver powder obtained in Example 1. It can be seen that spherical particles are obtained. FIG. 2 is an SEM photograph of the silver powder obtained in Comparative Example 1.

Claims (11)

A silver powder comprising silver particles coated with a metal compound containing chlorine, wherein the metal content in the silver powder is 0.01 to 1.0% by mass, and the crystallite diameter of silver is 400 to 1000 nm . A certain silver powder.   The silver powder according to claim 1, wherein the metal of the metal compound is tin. The shrinkage rate δ ₇₅₀ determined from the change in diameter when a 5 mm diameter pellet obtained by applying a load of 490 N to 0.15 g of the silver powder placed in a cylindrical container from 50 ° C. to 750 ° C. is 0.5 to The silver powder according to claim 1 or 2 which becomes 5%. The shrinkage rate δ ₈₀₀ obtained from the change in diameter when a 5 mm diameter pellet obtained by applying a load of 490 N to 0.15 g of the silver powder in a cylindrical container for 1 minute is increased from 50 ° C. to 800 ° C. is 2 to 8%. The silver powder according to claim 1 or 2.   The silver powder according to any one of claims 1 to 4, which is for a glass frit-containing type conductive paste. In a slurry in which silver particles having a crystallite diameter of 400 to 1000 nm are dispersed in a liquid, the metal chloride is hydrolyzed to cause precipitation of the metal compound containing chlorine, and the precipitate is converted into the silver particles. A method for producing silver powder to be deposited.   The method for producing silver powder according to claim 6, wherein the metal chloride is tin chloride.   The electrically conductive paste produced using the silver powder in any one of Claims 1-4.   A glass frit-containing type conductive paste produced using the silver powder according to claim 5.   An electronic circuit component produced using the conductive paste according to claim 8.   An electrical product produced using the electronic circuit component according to claim 10.