Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-11-15
2003-03-04
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C427S127000, C427S128000, C427S130000, C427S216000, C427S217000, C252S062560, C252S062580, C252S062530, C252S062620
Reexamination Certificate
active
06528166
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel nickel composite particle suitable for use in a thick-film conductor paste and to a production process therefor, and further to a conductor paste containing the nickel composite particles and to a multilayer electronic part having a conducive layer formed using the paste.
2. Description of the Prior Art
In the electronic field, a thick-film paste such as a conductor paste or resistor paste is used to produce electronic circuits and parts such as resistors, capacitors and IC packages. This thick-film paste is prepared by uniformly mixing conductive particles such as metal, alloy or metal oxide particles with an organic vehicle together with a vitreous binder and other additives as required and dispersing them into the organic vehicle to obtain a paste state. The thick-film paste is applied to a substrate and then fired at a high temperature to form a conductor film or resistor film.
Ceramic multilayer electronic parts such as multilayer capacitors and multilayer inductors, and ceramic multilayer substrates are generally produced by laminating a plurality of unfired ceramic green sheets of a dielectric or magnetic material, etc., and a plurality of internal conductor paste layers alternately and cofiring the resulting multilayer stack at a high temperature. A precious metal such as palladium, silver-palladium or platinum has been mainly used as an internal conductor in the prior art but a base metal material such as nickel has been attracting much attention to meet a demand for saving resources and eliminating the problems of delamination or cracking, etc., caused due to the expansion of palladium or silver-palladium by oxidation during the firing step.
There is a tendency that the number of layers to be laminated together is increased more in these multilayer parts and multilayer substrates. For example, a multilayer capacitor consisting of several hundreds of layers has recently been produced. Therefore, a reduction in the thickness of each ceramic layer and a further reduction in the thickness of an internal conductor layer are required. For example, when the thickness of a ceramic layer is 3 &mgr;m or so, the thickness of an internal conductor film must be 1 &mgr;m or less, preferably 0.5 &mgr;m or so. If not, a center portion of the obtained multilayer stack will become thick and a structural defect and a reduction in reliability will be caused.
However, when normal nickel particles are used in the internal conductor paste, the obtained internal conductor becomes a discontinuous film due to the oversintering of the nickel particles at the time of firing, which causes such problems as a rise in resistance value, internal disruption and an increase in the thickness of the conductor. Thus, there has been limitation in reducing the thickness of the internal conductor. That is, when the nickel particles are fired in a non-oxidative atmosphere such as an inert atmosphere or reducing atmosphere to prevent oxidation, sintering begins early, even monocrystal particles having relatively low activity begin to sinter and shrink at a low temperature of 400° C. or less. The temperature at which a ceramic layer begins to sinter is generally much higher than that temperature, for example, about 1,200° C. in the case of barium titanate. Since barium titanate does not shrink together with a nickel film even when it is co-fired with the nickel film, the nickel film is pulled in a planar direction. Therefore, it is considered that small voids generated in the nickel film by sintering at a relatively low temperature easily grow to large holes along with the proceeding of sintering at a high temperature range and also the film easily grows in a thickness direction. Therefore, to reduce the thickness of the nickel internal conductor layer, it is considered to be necessary to make nickel particles finer and highly dispersible to prevent the generation of voids at the time of firing as much as possible and further to make coincide the sintering and shrinkage behaviors of the conductor layer with those of a ceramic layer.
When a thick film is formed, uncoincidence of sintering and shrinking behaviors between the conductor layer and the ceramic layer as described above creates structural defects, such as delamination and cracking, etc., thereby lowering the yield and reliability, which is a problem.
Heretofore, various studies have been made to delay the sintering of a conductor until the sintering initiation temperature of the ceramic layer. For example, the addition of various metal oxides or ceramic particles having the same composition as those used in the ceramic layer makes it possible to delay the apparent initiation temperature of shrinkage of the conductor film to around 800° C. However, since the sintering properties of metal particles themselves are not suppressed, when sintering is carried out at a high temperature of 1,300° C., or so, the continuity and conductivity of a conductor film are impaired. Further, since these additives must be added in large quantities to achieve an effect, such a problem as an increase in resistance value arises.
U.S. Pat. No. 5,126,915 discloses a method for suppressing sintering by coating each metal particle with a metal oxide such as titanium oxide, aluminum oxide or chromium oxide by a wet process. However, this method has an effect of increasing the sintering initiation temperature but is liable to cause sintering and shrinkage abruptly after the initiation of sintering. Therefore, this method does not overcome disagreement between the sintering and shrinkage behaviors of the conductor layer and those of the ceramic layer at a high temperature range. This is assumed to be because these oxide layers decompose rapidly or separate from the nickel particles quickly in a non-oxidative atmosphere at a high temperature, for example, 1,200° C. or more.
The inventors of the present invention have developed a method for controlling sintering by forming a vitreous thin film on the surface of a metal particle and further a method for preventing the oversintering of a nickel particle by forming a specific composite oxide layer on the surface of a nickel particle. They have conducted further studies based on the above studies and have arrived at the present invention.
SUMMARY OF THE INVENTION
It is an object of the present invention to obtain a conductor film having high conductivity by suppressing the sintering of a nickel particle effectively even when the film is thin.
It is another object of the present invention to provide a method for preventing the disruption and structural defects of a conductor film by delaying the initiation of sintering of a nickel particle so as to bring the sintering and shrinkage behaviors of the nickel particle as close as possible to those of a ceramic layer and reduce the thickness of the conductor film where the nickel particle is used for a conductor paste to be cofired with unfired ceramic layers to provide multilayer electronic parts and the like.
It is still another object of the present invention to provide a simple and excellent process for producing such a nickel particle.
The inventors of the present invention have continued further studies based on the above studies, have found that the above objects can be attained by forming a layer of a nickel-containing spinel on the surface of nickel particles and have accomplished the present invention.
More specifically, the present invention is directed to nickel composite particles having a layer of a nickel-containing spinel on at least a part of the surface of nickel particles, or nickel composite particles having an oxide layer of metals other than nickel on at least a part of the surface of nickel particles and a layer of a nickel-containing spinel at an interface between the nickel particle and the metal oxide layer.
The present invention is also directed to a process for producing the above composite nickel particles, comprising:
forming fine liquid droplets from a solution contain
Akimoto Yuji
Ma Yiyi
Nagashima Kazuro
Yoshida Hiroshi
Flynn ,Thiel, Boutell & Tanis, P.C.
Shoei Chemical Inc.
LandOfFree
Nickel composite particle and production process therefor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nickel composite particle and production process therefor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nickel composite particle and production process therefor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3020036