Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2001-03-30
2003-10-07
Mayekar, Kishor (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C205S317000
Reexamination Certificate
active
06630064
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a composition for electrodeposition of polyimides and method for producing patterned polyimide membranes using the same. Since the electro-deposited polyimide membranes prepared by the method of the present invention are excellent in heat resistance, insulation performance, mechanical properties and chemical resistance, they are utilized in electric or electronic parts, airplanes, cars, semiconductors and their peripheral circuits.
BACKGROUND ART
Polyimides are excellent in heat resistance, electric insulation performance, mechanical properties, chemical resistance and the like, so that they are widely used in electric and electronic parts, airplane parts, car parts, peripheral circuits of semiconductors and the like.
Since conventional polyimides represented by Kapton are insoluble in solvents, the methods in which polyamic acids that are precursors of polyimides are made into films or molded products and then the resulting products are heated at 250° C. to 350° C. to imidize the polyamic acids to polyimides, are widely employed.
Polyimides having specific compositions are soluble in phenolic solvents, and polyimide block copolymers having various added functions have been synthesized by sequential reactions (U.S. Pat. No. 5,202,411). However, phenolic solvents have bad smell and are corrosive, so that countermeasures are necessary for environmental protection.
Polyimides free from the above-mentioned drawbacks, which are soluble in ordinary polar solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, tetramethylurea and sulfolane were discovered by the present applicant et al (U.S. Pat. No. 5,502,143). According to this, tetracarboxylic dianhydride and aromatic diamine are heated at 160° C. to 180° C. in the presence of a lactone-base composite catalyst to directly produce a polyimide. Since this polyimide solution is not decomposed by water, its stability is good. Further, since the imidizing treatment at 250° C. to 350° C. is not necessary, polyimide products having excellent processabilities are obtained by removing the solvent at a temperature not higher than 200° C.
Polyimides are also used as photoresists. Conventional photoresists are negative-type polyimide photoresists comprising acrylic esters of polyarnic acids with which the portions irradiated with light are solidified by radical polymerization and the non-irradiated portions are removed by development with an alkali. Negative-type polyimide photoresists have drawbacks in that the sensitivity is lower than that of positive-type polyimide photoresists, and that loss of membrane is large (Ao Yamaoka et al.; Polyfile 2, 14(1990)).
Soluble polyimide photoresists which exhibit positive photosensitivity in the presence of photoacid generators have been discovered by the present applicant (WO99/19771).
As the methods for coating polyimides, immersion method, spray method, roll coating method, spin coating method and the like are widely employed. As the method for coating thin membranes, spin coating method is used, but this method has a drawback in that loss of material is large. By employing electrodeposition method, uniform thin membranes are obtained irrespective of the shapes of the surfaces to be coated, and insulative thin membranes are easily obtained. From this point of view, a method for forming polyimide thin membranes by anion electrodeposition method using soluble polyimide having oxycarbonyl groups was discovered by co-inventors of the present invention (U.S. Pat. No. 5,741,599).
DISCLOSURE OF THE INVENTION
However, a technique by which the polyimide membrane after electrodeposition is patterned by photolithography is not known.
Accordingly, an object of the present invention is to provide a composition for electrodeposition of polyimides, by which the polyimide membrane formed by electrodeposition can be patterned by photolithography, and to provide a method for forming patterned polyimide membranes using the same.
The present inventors intensively studied to discover that by making the composition for electrodeposition contain a photoacid generator, a positive-type photosensitive polyimide having oxycarbonyl groups in side chains, a polar solvent which dissolves said polyimide, water, a dispersing agent, and an alkaline neutralizer, not only the polyimide can be electro-deposited, but also the deposited polyimide membrane can be patterned by photolithography, to complete the present invention.
That is, the present invention provides a composition for electrodeposition of polyimides comprising a photoacid generator, a positive-type photosensitive polyimide having oxycarbonyl groups in side chains, a polar solvent which dissolves said polyimide, water, a dispersing agent, and an alkaline neutralizer. The present invention also provides a method for electrodeposition of polyimides, comprising immersing an electric conductor in said composition according to the present invention, and flowing electric current therein to deposit polyimide membrane on said electric conductor which is an anode. The present invention also provides a method for producing a patterned electro-deposited polyimide membrane, comprising irradiating said polyimide membrane electro-deposited by the method according to the present invention with a light through a mask pattern, and forming a positive image by development with an alkali.
According to the present invention, coated polyimide thin membranes which are smooth and excellent in insulation performance can be obtained by electrodeposition of polyimides which are excellent in heat resistance, insulation performance and chemical resistance. Further, by irradiating the coated polyimide thin membrane with a light, positive-type fine images can be formed. Thus, since fine pattern images made of polyimide thin membranes can be formed on copperplated printed circuit boards, the method is useful for forming circuits in semiconductors and peripheries thereof.
BEST MODE FOR CARRYING OUT THE INVENTION
As mentioned above, the composition for electrodeposition according to the present invention comprises a positive-type photosensitive polyimide having oxycarbonyl groups in its side chains. Here, the term “oxycarbonyl group” means a group which gives free —COO
−
group in the composition for electrodeposition, and carboxyl group (—COOH) is preferred. By virtue of the oxycarbonyl group, electrodeposition can be attained.
The polyimide is synthesized by polycondensation between one or more tetracarboxylic dianhydrides and one or more diamines. The oxycarbonyl groups existing in the side chains of the polyimide may exist in either the tetracarboxylic dianhydride or the diamine, and the oxycarbonyl group preferably exists in the diamine.
The proportion (acid equivalent) of the oxycarbonyl groups existing in the polyimide is not restricted, and the acid equivalent (gram of the polyimide/COOH) may preferably be about 500 to 5000, more preferably about 700 to 3000.
As the tetracarboxylic dianhydride constituting the polyimide, aromatic tetracarboxylic dianhydrides are preferred in view of heat resistance. Preferred examples of the aromatic tetracarboxylic dianhydride (described in the form of monomer) include pyromellitic dianhydride (1,2,3,4-benzenetetracarboxylic dianhydride), 3,4,3′,4′-biphenyltetracarboxylic dianhydride, 3,4,3′,4′-benzophenonetetracarboxylic dianhydride, 2,3,2′,3′-benzophenonetetracarboxylic dianhydride, 2,3,3′,4′-biphenyltetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(2,3-dicarboxyphenyl)sulfone dianhydride, 4,4′-{2,2,2-trifluoro-1-(trifluoromethyl)ethylidene}bis(1,2-benzenedicarboxylic dianhydride), 9,9-bis{4-(3,4-dicarboxyphenoxy)phenyl}fluorene dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalen
Itatani Hiroshi
Matsumoto Shunichi
Mayekar Kishor
PI R&D Co., Ltd.
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