Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,...
Reexamination Certificate
2000-11-21
2003-10-14
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
C428S403000, C428S402000, C252S512000, C252S513000
Reexamination Certificate
active
06632524
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to nickel powder having a specific particle size distribution or specific powder characteristic properties, such nickel powder in which a fatty acid is supported on the surface of the nickel particles, a method for preparing these powdery nickel products and a paste containing such a powdery nickel product and used in making an electrode for electronic parts. More specifically, the present invention pertains to nickel powder having a specific particle size distribution or is suitably used in a paste for making an internal electrode powder characteristic properties, which or an external electrode for electronic parts, in particular, suitably used for preparing a paste for forming an external electrode, such nickel powder, in which a fatty acid is supported on the surface of the nickel particles, a method for preparing these powdery nickel products and a paste containing such a nickel powder product and suitably used for preparing a paste for forming an internal electrode or an external electrode of electronic parts, in particular, suitably used for preparing a paste for forming an external electrode.
(b) Description of the Prior Art
Conventionally, an external electrode (thick film-like electrode) has in general been formed on a ceramic electronic part or element such as a multilayer ceramic capacitor element by applying, onto the part or element, a conductive paste containing powder of a noble metal such as platinum, palladium, silver, a silver-palladium alloy and then baking the applied paste. However, there have recently been developed techniques which make use of base metals such as copper and nickel in place of the foregoing noble metals and an alloy of a noble metal and a base metal such as those disclosed in Japanese Un-Examined Patent Publication No. Hei 6-236707, in order to save the production cost and a great progress has been made in such techniques.
A copper powder-containing paste has widely been used for forming an external electrode for ceramic electronic parts or elements. However, nickel powder has a melting point higher than that of copper powder and the temperature-depending characteristics during sintering of the nickel powder are quite different from those of the copper powder. Accordingly, good moldability upon the formation of an external electrode cannot necessarily be obtained even if using, in a nickel powder-containing paste, nickel powder having a particle size distribution and powder characteristics identical to those of the copper powder used in a copper paste.
An electrode for electronic parts or elements is in general formed by applying a nickel powder-containing paste onto positions on which an internal or external electrode for ceramic electronic parts or elements is formed and then baking the applied paste. However, various problems arise in the practical operations for forming such an electrode. For instance, pores are formed within the resulting electrode and the joining strength of the resulting electrode is insufficient.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide nickel powder suitably used in a paste, which permits the formation of an internal or external electrode for electronic parts or elements. As has been described above, such an electrode is in general formed by applying a nickel powder-containing paste onto positions, on which the electrode for ceramic electronic parts or elements is formed, and then baking the applied paste. However, the nickel powder of the present invention permits the formation of a paste, which is not accompanied by the formation of any pores within the resulting electrode, the powder can ensure sufficient joining strength and permits the formation of a dense electrode having good moldability. When the resulting electrode is used as an external electrode and other parts are soldered onto the external electrode, excess solder is not incorporated into the electrode and therefore, cracks are hardly formed.
It is another object of the present invention to provide nickel powder in which a fatty acid is supported on the surface of nickel particles. The presence of the fatty acid on the particle surface permits the improvement of the film density of an electrode produced using the nickel powder and the nickel powder is suitably used for forming not only an external electrode, but also an internal electrode.
It is a still another object of the present invention to provide a paste containing such nickel powder and used for forming an electrode for electronic parts.
It is a further object of the present invention to provide a method for preparing such nickel powder.
The inventors of this invention have conducted various studies to accomplish the foregoing objects and have found that the foregoing problems associated with the conventional techniques can be solved by the use of nickel powder having a specific particle size distribution or powder characteristic properties. More specifically, the inventors have found that pores are not formed within an electrode and the resulting electrode has sufficient joining strength even if such an electrode is formed by applying a paste containing such nickel powder to a substrate and then baking the applied paste and that the resulting electrode is dense and has good moldability. The inventors have further found out the following facts. When the resulting electrode is used as an external electrode and other parts are soldered onto the external electrode, excess solder is not incorporated into the electrode and therefore, cracks are hardly formed. A paste containing nickel powder in which a fatty acid is supported on the surface of the nickel particles can be suitably used for forming not only an external electrode, but also an internal electrode. Such nickel powder having a specific particle size distribution or powder characteristic properties can be prepared by separating nickel particles from an aqueous solution containing a nickel-containing salt and a hydrazine reducing agent without forming any hydroxide as an intermediate. Alternatively, the nickel powder can be prepared by adding an aqueous solution containing a hydrazine reducing agent and an alkali to an aqueous nickel salt solution to thus precipitate nickel without forming any hydroxide as an intermediate. Further, nickel powder on which a fatty acid is supported can be prepared by bringing such nickel powder having a specific particle size distribution or powder characteristic properties into contact with a fatty acid solution. Thus, the inventors of this invention have completed the present invention on the basis of the foregoing findings.
According to a first aspect of the present invention, there is provided nickel powder, wherein the rate of particles having a particle size of not less than 1.2 time the average particle size as determined by the SEM observation is not less than 10% on the basis of the total number of nickel particles and the rate of particles having a particle size of not more than 0.8 time the average particle size as determined by the SEM observation is not less than 10% on the basis of the total number of nickel particles.
In a preferred embodiment, the nickel powder according to the present invention is characterized in that a coefficient of variation (CV) is not less than 30%, in which the CV is determined using an average particle size and a standard deviation obtained on the basis of the Feret diameter as determined by the SEM observation, according to the following equation:
CV
(%)=[(Standard Deviation)/(Average Particle Size)]×100
In another preferred embodiment, the nickel powder of the present invention is characterized in that it has the foregoing specific particle size distribution or powder characteristic properties and that a fatty acid is supported on the surface of the nickel particles.
According to a second aspect of the present invention, there is provided a paste for forming an electrode used in electronic parts. The paste is cha
Hayashi Takao
Shimamura Hiroyuki
Toshima Yoshiharu
Yamaguchi Yasuhide
Mitsui Mining and Smelting Co. Ltd.
Thibodeau Paul
Uhlir Nikolas J
Young & Thompson
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