Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-10-04
2003-07-01
Metzmaier, Daniel S. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S400000, C524S403000, C524S497000, C516S077000, C204S489000
Reexamination Certificate
active
06586513
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aqueous dispersion for electrodeposition, a high dielectric constant film formed from the aqueous dispersion and electronic parts provided with the high dielectric constant film.
2. Description of the Prior Art
A technique is known whereby a high dielectric constant layer is formed on a multilayer printed wiring board or the like and the layer is utilized as a condenser. The high dielectric constant layer is fabricated, for example, by a method in which a solution of a thermosetting resin in an organic solvent also containing an added high dielectric constant inorganic powder is impregnated into afiber-reinforcement such as glass fibers to compensate for the fragility of the thermosetting resin, and the solvent is then scattered and allowed to harden.
Because this prior art method uses a fiber-reinforcement it is not possible to achieve significant reduction in the thickness of the high dielectric constant layer (for example, to under 50 &mgr;m), and since the dielectric constant of a fiber-reinforcement is lower than that of an inorganic powder such as TiO
2
, it has not been possible to obtain condensers with high capacitance.
In order to solve this problem, Japanese Laid-open Patent Publication No. 12742 of 1997 discloses a high dielectric constant film that eliminates the need for the fiber-reinforcement in the aforementioned construction by using a thermosetting resin with film forming properties. According to this publication, a resin varnish is prepared containing the thermosetting resin and high dielectric constant inorganic powder, and this is coated and dried to produce a film.
However, since high dielectric constant inorganic powders usually have a high specific gravity and thus settle in resin varnishes with time, causing a lack of shelf life for such resin varnishes, it has been necessary to prepare a fresh resin varnish just before production of the film. Because the film is formed by coating and drying the solution, it is difficult to achieve a high film thickness precision for the obtained film, and the manageability has not been very good for formation of films on only specific locations of boards.
In addition, when forming a high dielectric constant layer selectively on a desired wiring, it has been necessary to prescribe the location of formation by a combination of photolithography and printing methods for conventional resin varnishes. However, formation methods using photolithography are associated with problems of high cost and complicated steps, while printing methods are associated with the problem of poor working precision.
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
It is an object of the present invention to provide an aqueous dispersion for electrodeposition which has excellent shelf life and can form thin, high dielectric constant films by electrodeposition, as well as a high dielectric constant film formed from the aqueous dispersion and electronic parts provided with the high dielectric constant film.
Features of the Invention
The present inventors have completed the present invention upon finding that the aforementioned problems can be overcome by using an aqueous dispersion for electrodeposition that comprises electrodepositable organic particles and small-sized inorganic particles dispersed in an aqueous medium.
That is, the aqueous dispersion for electrodeposition according to the first aspect of the invention is characterized by comprising inorganic particles with a mean particle size of no greater than 1 &mgr;m and a dielectric constant of at least 30, and organic particles composed of either or both a polymerizable compound and a polymer, dispersed in an aqueous medium. The aqueous dispersion is preferably used for electrodeposition to give a film with a dielectric constant of 6 or greater. The inorganic particles are preferably composed of a titanium-based metal oxide, and the organic particles are preferably charged on the particle surfaces and are composed of a polyimide-based resin. The volume ratio of the inorganic particles and organic particles is preferably in the range of 5/95-80/20.
The high dielectric constant film according to the second aspect of the invention is characterized by being formed by electrodeposition using the aqueous dispersion for electrodeposition according to the first aspect.
The electronic part according to the third aspect of the invention is characterized by being provided with a high dielectric constant film according to the second aspect.
Effect of the Invention
The aqueous dispersion for electrodeposition of the invention has excellent shelf life as explained above, and hence it is not necessary to prepare the solution for each high dielectric constant film fabrication. The aqueous dispersion of the invention can therefore enhance productivity for high dielectric constant films. Furthermore, since an aqueous medium is used unlike the varnish, an advantage is also provided in terms of the working environment. Since the high dielectric constant film of the invention is formed by electrodeposition using the aforementioned aqueous dispersion, the film thickness control is facilitated through adjustment of the electrodeposition conditions, while the film formability and follow-up properties to the substrate are superior to cases where the film is formed by application. It is also possible to form the high dielectric constant film selectively on a conductive substrate (wiring and the like), and to produce highly precise high dielectric constant films more inexpensively than by photolithography or printing methods. The high dielectric constant film of the invention has both low thickness and high dielectric constant, and can therefore be suitably used for such electronic parts as printed circuit boards, semiconductor packages, condensers and high-frequency antennas. Electronic parts of the invention provided with the aforementioned high dielectric constant film can be produced in miniature and thin-film form.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be explained in further detail.
(1) Inorganic Particles
The dielectric constant of the inorganic particles used for the invention is 30 or greater, preferably 50 or greater and most preferably 70 or greater. The inorganic particles used are preferably composed of a metal oxide, and titanium-based metal oxides are particularly preferred. Here, “titanium-based metal oxides” means compounds including titanium element and oxygen element as essential elements. Specifically there may be mentioned metal oxides based on titanium dioxide, barium titanate, lead titanate, strontium titanate, bismuth titanate, magnesium titanate, neodymium titanate, calcium titanate and the like. Metal oxides based on “titanium dioxide” include titanium dioxide alone, as well as systems of titanium dioxide also containing small amounts of other added compounds, and they maintain the crystal structure of the major component of titanium dioxide; these conditions also apply to metal oxides of other systems. According to the invention, it is particularly preferred to use inorganic particles composed of titanium dioxide-based (rutile structure) or barium titanate-based metal oxides. For improved dispersability in aqueous media, particles composed of these materials having the particle surfaces modified with silica, alumina or the like are suitable for use.
The mean particle size of the inorganic particles must be no greater than 1 &mgr;m, preferably no greater than 0.5 &mgr;m and more preferably no greater than 0.2 &mgr;m. If the mean particle size exceeds 1 &mgr;m, the dispersability of the inorganic particles in aqueous media will be insufficient, making it impossible to achieve sufficient shelf life. There is no particular restriction for the minimum mean particle size, but it is normally 0.02 &mgr;m or greater.
(2) Organic Particles
(2-1) Composition of Organic Particles
The organic particles used for the invention are composed of “either or both a polymeriz
Goto Hirofumi
Ito Nobuyuki
JSR Corporation
Metzmaier Daniel S.
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