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Spherical silver powder and method for producing same

a technology of spherical silver and powder, which is applied in the direction of non-conductive materials with dispersed conductive materials, conductors, transportation and packaging, etc., can solve the problems of resin deterioration, cracks and delamination, and the resistance value of the sintered body of silver is reduced, and achieves good dispersibility and good degree of sintering

Inactive Publication Date: 2005-11-24
DOWA ELECTRONICS MATERIALS CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0013] It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a spherical silver powder which is capable of obtaining a good degree of sintering even if it is used for forming a paste to be fired at a low temperature of 600° C. or less to form a conductor, and a method for producing the same. It is another object to provide a spherical silver powder having a good dispersibility, and a method for producing the same.
[0017] According to the present invention, it is possible to produce a spherical silver powder which has a good dispersibility and which is capable of obtaining a good degree of sintering even if it is used for forming a paste to be fired at a low temperature of 600° C. or less to form a conductor.

Problems solved by technology

The value of resistance of the sintered body of silver lowers if the paste is fired at a temperature as high as possible below the melting point of silver which is 960° C. However, various problems are caused unless a silver powder suitable for the firing temperature is used.
For example, if the paste is fired at a high temperature on a ceramic substrate, there are some cases where cracks and delamination are caused by a difference in shrinkage between the sintered body of silver and the ceramic substrate.
Furthermore, the resin is deteriorated to deteriorate the resistance and bond strength of the conductor at a temperature above 300° C.
However, for example, in the case of a plasma display panel (PDP) substrate, a glass being the material of the substrate has a low heat resistance, so that the paste can not be fired at a high temperature of about 750 to 900° C. unlike the case of the ceramic substrate.
Thus, it is difficult to lower the value of resistance of the conductor.
However, in the case of a PDP substrate formed by repeatedly carrying out firing, it is undesirable to use a glass frit having an excessively low softening point since the variation in value of resistance of the conductor is caused.
In addition, when a silver powder is used for forming a photosensitive paste, if the silver powder has an undecided shape or a flake shape, the scattering and / or reflection of ultraviolet rays is caused, so that defective patterning is caused.
Moreover, when a conductive pattern is formed by another method, e.g., a printing or transferring method, if the silver powder has an undecided shape or a flake shape, it is not possible to form a good conductive pattern in view of the releasability from a screen plate and transferability.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0028] To 3600 ml of an aqueous solution containing 12 g / l silver nitrate as silver ions, 300 ml of industrial aqueous ammonia was added to form an aqueous silver ammine complex solution. To the aqueous silver ammine complex solution thus formed, 60 g of sodium hydroxide was added to control the pH of the solution. Then, 90 ml of industrial formalin serving as a reducing agent was added to the solution in 10 seconds. Immediately thereafter, 0.5 g of stearic acid emulsion was added to the solution to obtain a silver slurry. Then, the silver slurry thus obtained was filtered, washed with water, dried to obtain a silver powder. Then, the surface of the silver powder thus obtained was smoothed by a surface smoothing process using a high-speed mixer, and the silver powder thus smoothed was classified to remove silver agglomerates having a greater diameter than 8 μm.

[0029] The crystallite diameter of the silver powder thus obtained was calculated. In addition, the BET specific surface ar...

example 2

[0033] To 3600 ml of an aqueous solution containing 12 g / l silver nitrate as silver ions, 180 ml of industrial aqueous ammonia was added to form an aqueous silver ammine complex solution. To the aqueous silver ammine complex solution thus formed, 7 g of sodium hydroxide was added to control the pH of the solution. Then, 192 ml of industrial formalin serving as a reducing agent was added to the solution in 10 seconds. Immediately thereafter, 0.1 g of oleic acid was added to the solution to obtain a silver slurry. Then, the silver slurry thus obtained was filtered, washed with water, dried to obtain a silver powder. Then, the silver powder thus obtained was pulverized by a food mixer.

[0034] With respect to the silver powder thus obtained, the calculation of a crystallite diameter, the measurement of a BET specific surface area, tap density and mean particle diameter D50, and the evaluation of conductivity were carried out by the same methods as those in Example 1. As a result, the cr...

example 3

[0035] To 3600 ml of an aqueous solution containing 12 g / l silver nitrate as silver ions, 180 ml of industrial aqueous ammonia was added to form an aqueous silver ammine complex solution. To the aqueous silver ammine complex solution thus formed, 1 g of sodium hydroxide was added to control the pH of the solution. Then, 192 ml of industrial formalin serving as a reducing agent was added to the solution in 15 seconds. Immediately thereafter, 0.1 g of stearic acid was added to the solution to obtain a silver slurry. Then, the silver slurry thus obtained was filtered, washed with water, dried to obtain a silver powder. Then, the surface of the silver powder thus obtained was smoothed by a surface smoothing process using a high-speed mixer, and the silver powder thus smoothed was classified to remove silver agglomerates having a greater diameter than 11 μm.

[0036] With respect to the silver powder thus obtained, the calculation of a crystallite diameter, the measurement of a BET specifi...

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Abstract

A spherical silver powder has a good dispersibility and is capable of obtaining a good degree of sintering even if used for forming a paste to be fired at a low temperature of 600° C. or less to form a conductor. An aqueous solution containing a reducing agent is added to a water reaction system containing silver ions, to deposit silver particles by reduction, to produce a spherical silver powder wherein a ratio (Dx / BET) of a crystallite diameter Dx (nm) to a BET specific surface area (m2 / g) is in the range of from 5 to 200 and which has a crystallite diameter of not greater than 40 nm, a mean particle size of not greater than 5 μm, a tap density of not less than 2 g / cm3, and a BET specific surface area of not greater than 5 m2 / g.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention generally relates to a spherical silver powder and a method for producing the same. More specifically, the invention relates to a spherical silver powder used for forming terminal electrodes of electronic parts, patterns of circuit boards and so forth, and a method for producing the same. [0003] 2. Description of the Prior Art [0004] In order to form electrodes and circuits of electronic parts and so forth, there has been used a conductive paste wherein a silver powder is dispersed in an organic component. Conductive pastes are generally classified into cermet type pastes (or pastes of a type to be fired) and polymer type pastes (or resin type pastes). The cermet type pastes have different uses and components from those of polymer type pastes. [0005] A typical cermet type paste includes a silver powder, a vehicle containing ethyl cellulose or acrylic resin dissolved in an organic solvent, a gla...

Claims

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Application Information

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IPC IPC(8): B22F1/05B22F1/065B22F9/24H01B1/00H01B1/22H01B5/00H01B13/00H05K1/09
CPCB22F1/0011B22F1/0044B22F1/0048B22F9/24B22F2998/00H05K1/092H01B1/22B22F1/0085B22F1/05B22F1/07B22F1/065B22F1/142
Inventor OGI, KOZOFUJINO, TAKATOSHI
Owner DOWA ELECTRONICS MATERIALS CO LTD
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