Compositions – Electrically conductive or emissive compositions – Free metal containing
Reexamination Certificate
1999-05-20
2001-05-22
Kopec, Mark (Department: 1751)
Compositions
Electrically conductive or emissive compositions
Free metal containing
C252S062570, C428S209000, C428S210000, C428S673000
Reexamination Certificate
active
06235221
ABSTRACT:
ART FIELD
The present invention relates to a multilayer ceramic part.
BACKGROUND ART
With recent breakthroughs in radio communications technologies, there is an increasing demand for electronic parts that can be used at high frequencies ranging from a few hundred MHz to a few GHz or greater. With size reductions of radio communications equipment such as portable telephones, there is also a strong demand for size, and cost reductions of high frequency-conscious electronic parts used with such equipment. To meet these requirements, multilayer ceramic parts are now manufactured by the application of a diversity of integration technologies.
A multilayer electronic part is obtained by co-firing a ceramic material that is an oxide magnetic material and a conductive material, and has one or two or more functions by itself. Such a multilayer electronic part is manufactured by laminating the ceramic and conductive materials one upon another by printing or sheet-making processes to form a laminate, and cutting the laminate according to the desired shape and size followed by firing, or firing the laminate followed by cutting according to the desired shape and size. If required, an external conductor is provided on the electronic part. Thus, this multilayer ceramic part has a structure comprising an internal conductor between ceramic layers. In general, a material such as Ag or Cu is used for an internal conductor suitable for high-frequencies, especially microwaves. With the above production method, however, it has been considered until now that the melting of the internal conductor should be prevented so as to achieve satisfactory properties, and so firing should be carried out at a temperature equal to or lower than the melting point of the internal conductor. Accordingly, it has been believed that a ceramic material fired at elevated temperatures cannot possibly be used in combination with an internal conductor-forming electrical conducting material having a low resistivity yet a low melting point, e.g., Ag, and Cu.
In this regard, the applicant has filed a Japanese patent application (JP-A 6-252618) to come up with a method wherein an internal conductor having a low melting point as mentioned above is formed in a ceramic material unsuitable for low-temperature firing. This is called a conductor melting method wherein an electrical conducting material to form an internal conductor is fired at a temperature that is equal to or higher than the melting point of the electrical conducting material and lower than the boiling point of the electrical conducting material, and solidifying the fired electrical conducting material in the process of cooling. According to this method, the grain boundary between metal grains formed upon the solidification of the molten electrical conducting material becomes as thin as can be regarded as vanishing substantially, and the asperity of the interface between the ceramic material and the internal conductor tends to become small, resulting in a decrease in the high-frequency resistance of the internal conductor and an increase in the Q value at a high-frequency region. Further, a low-cost electrical conducting material having a relatively low melting point, e.g., Ag, and Cu may be used for the internal conductor. Furthermore, it is possible to co-fire the ceramic material and the internal conductor. These are very favorable in view of productivity and cost.
DISCLOSURE OF THE INVENTION
With the above conductor melting method, however, voids are often formed in the internal conductor upon the solidification of the internal conductor material in the cooling process subsequent to the melting of the internal conductor material. This in turn causes the resistance value of the internal conductor to increase with a decrease in the Q value of the multilayer ceramic part. On very rare occasion, the internal conductor itself breaks due to the presence of such voids. When there are voids in the internal conductor, gases present in the voids expand under the influence of latent heat of solidification in the cooling process, resulting in cracking of the internal conductor material. This in turn gives rise to an yield drop. When a multilayer ceramic part is manufactured by the conductor melting method, therefore, it is required to inhibit the formation of voids in the internal conductor.
For the purpose of providing a high-quality conductive paste which can prevent formation of voids, and generation of cracking due to such voids, even when an internal conductor composed mainly of silver is co-fired with a ceramic material by the conductor melting method, and so improve productivity with cost reductions, and which has excellent electrical characteristics as well as a multilayer ceramic part obtained using such a conductive paste, the applicant has proposed in WO98/05045 such a conductive paste as mentioned below as well as a multilayer ceramic part comprising an internal conductor formed using this conductive paste.
That is, the above conductive paste is a conductive paste obtained by dispersing an electrical conducting material composed mainly of silver and a metal oxide in a vehicle. For the metal oxide, at least one oxide selected from Ga, La, Pr, Sm, Eu, Gd, Dy, Er, Tm and Yb oxides is used.
When a multilayer ceramic part is fabricated by using this conductive paste, i.e., by co-firing the conductive paste and a ceramic material by the conductor melting method, no voids are generated; the ceramic material is quite unlikely to crack. The resistivity of the conductor, too, is low. By use of this conductive paste, it is thus possible to fabricate a multilayer ceramic part of very excellent quality in high yields.
However, multilayer ceramic parts having such applications as mentioned above, too, are now increasingly required to be further reduced in size in conjunction with the demand for size reductions of mobile communications equipment in particular.
It is an object of the invention to provide a multilayer ceramic part which, albeit being reduced in size, 10 can be manufactured in high yields.
Such an object is achieved by the inventions defined below as (1) to (7).
(1) A multilayer ceramic part comprising an internal conductor layer and a ceramic layer which are formed by co-firing, wherein said internal conductor layer is formed of an electrical conducting material containing silver as a main component and said ceramic layer is formed of an yttrium-iron-garnet based oxide magnetic material with silver added thereto.
(2) The multilayer ceramic part according to (1), wherein said silver is added to said oxide magnetic material in an amount of up to 10% by weight.
(3) The multilayer ceramic part according to (2), wherein said silver is added to said oxide magnetic material in an amount of up to 5% by weight.
(4) The multilayer ceramic part according to any one of (1) to (3), wherein said internal conductor layer is formed by firing a conductive paste obtained by dispersing in a vehicle an electrical conducting material containing silver as a main component and further containing at least one metal oxide selected from a Ga oxide, an La oxide, a Pr oxide, an Sm oxide, an Eu oxide, a Gd oxide, a Dy oxide, an Er oxide, a Tm oxide, and a Yb oxide.
(5) The multilayer ceramic part according to (4), wherein said metal oxide is contained in an amount of 0.1 to 20 parts by weight per 100 parts by weight of said electrical conducting material.
(6) The multilayer ceramic part according to any one of (1) to (5), wherein a firing temperature is equal to or igher than a melting point of said electrical conducting material and lower than a boiling point of said electrical conducting material.
(7) The multilayer ceramic part according to any one of (1) to (6), which is a non-reversible circuit element.
ACTION AND EFFECT OF THE INVENTION
In the multilayer ceramic part of the invention comprising an internal conductor layer and a ceramic layer which are formed by co-firing, the internal conductor layer is formed of an electrical conducting material containing silver as a main component a
Kurahashi Takahide
Ohata Hidenori
Suzuki Kazuaki
Kopec Mark
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
LandOfFree
Multilayer ceramic part does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multilayer ceramic part, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multilayer ceramic part will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2569616