Dowa Mining Co., Ltd.

Dowa Electronics Materials Co., Ltd.

Yoshihiro Okada

Hiromasa Miyoshi

Kazushi Sano

Yoshiomi Takada

Atsushi Ebara

A highly oxidation-resistant copper powder for conductive paste, which is a copper powder containing not more than 5 wt % of Si, is characterized in that substantially all of the Si is adhered to the surfaces of the copper particles as SiO-system gel coating film.

Highly oxidation-resistant copper powder for conductive paste and process for producing the powder

Copper particle clusters constituting a powder suitable for making a conductive paste are provided that are individually composed of not fewer than two and not more than 20 unit particles joined through neck portions. A conductive paste made from the powder is excellent in conductivity. A conductive filler for conductive paste is provided that consists essentially of a mixture of copper particle clusters A individually composed of two or more unit particles joined through neck portions and spherical metallic particles B of smaller diameter than the particles A. A conductive paste made from the filler is low in viscosity and excellent in conductivity.

Copper particle clusters and powder containing the same suitable as conductive filler of conductive paste

When copper powder manufactured by a wet reduction method is kneaded with resin in a high filling rate, it is difficult to maintain a low viscosity. The invention is to solve the problem of high viscosity without changing the characteristics such as particle size and specific surface area of the copper powder obtained by a wet reduction method. This invention relates to copper powder for an electrically conductive paste wherein copper powder manufactured by a wet reduction method is subjected to a surface-flattening treatment in which the particles are mechanically collided each other.

Copper powder for electrically conductive paste

A copper powder is provided that has an average particle diameter in the range of from not less than 0.1 &#x3bc;m to less than 1.5 &#x3bc;m, that has a narrow particle size distribution width whose value A defined by Equation (1) below in terms of X25, X50 and X75 defined below is not greater than 1.2, and that forms a pseudo-fused sintered product when held at a temperature of 800&#xb0; C. under an atmosphere of inert gas at one atmosphere pressure:=(75&#x2212;25)/50&#x2003;&#x2003;(1),where X25, X50 and X75 are values of particle diameter X corresponding to Q %=25%, 50% and 75% on a cumulative particle-size curve plotted in an orthogonal coordinate system whose abcissa represents particle diameter X (&#x3bc;m) and ordinate represents Q % (ratio of particles present of a diameter not greater than the corresponding value of X; expressed in units of vol % of particles). The copper powder is produced by conducting wet reduction of cuprous oxide into metallic copper powder in the presence of ammonia or an ammonium salt. When used to form the terminal electrodes of multi-layer capacitor, it enables the electrodes to form into solid sintered bodies with few pores by sintering at a low temperature.

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Okayama, Japan

Yoshihiro Okada