Modified cyanate ester group curable resin composition, and varnish, prepreg, metal clad laminated board, film, printed circuit board, and multilayered circuit board using the same

Abstract: A modified cyanate ester group curable resin composition, and varnishes, prepregs, laminated boards adhered with metal foil, films, printed circuit boards, and multilayered circuit boards using the same, comprising: (A) a cyanate ester group compound expressed by chemical formula (1), (where, R 1 is ―CH 2 ―, and respective of and R 2 and R 3 is any one of hydrogen or methyl group, and the both can be the same or different from each other, (B) a monovalent phenolic group compound expressed by chemical formula (2), or formula (3), where R 4 and R 5 is any one of hydrogen atom or low alkyl group having 1 to 4 carbon atoms, and the both can be the same or different from each other, n is a positive integer of 1 or 2. (where, R 6 is -CH 3 , -CH 2 CH 3 , or (C) a polyphenylene ether resin, (D) a flame retardant not reactive with the cyanate ester group compound, and (E) a metal group reaction catalyst.

Description: BACKGROUND OF THE INVENTION The present invention relates to a modified cyanate ester group curable resin composition, and varnish, prepreg, metal clad laminated board, film, printed circuit board, and multilayered circuit board using the same. A large volume of data are required to be processed with a high speed in a highly information-oriented society, and consequently, frequency of signals used in computers and information equipment terminals becomes higher and higher. However, since an electric signal has a property that its transmission loss becomes larger as the frequency becomes higher, developing a low-loss printed circuit board capable of coping with the high frequency is strongly required. The transmission loss of the printed circuit board comprises a conductor loss depending on the shape of circuit (conductor), skin-effect resistance, characteristic impedance, and the like, and a dielectric loss depending on dielectric properties of the insulating layer (dielectric) around the circuit. The dielectric loss is dominant in an-electric loss in a high frequency circuit. Therefore, in order to reduce the transmission loss of the high frequency circuit, it is thought that reducing the dielectric constant and the dissipation factor (tan δ) of the printed circuit board (particularly, the insulating resin) is necessary. For example, in the field of the mobile communication equipment dealing with high frequency signals, printed boards having a low dissapation factor are strongly required in order to reduce the transmission loss in a quasi-microwave band (1 to 3 GHz) as the frequency of signals is increased. On the other hand, in the field of the electronic information equipment such as computers, development of high speed microprocessors having an operating frequency exceeding 200 MHz and increase of signal frequency have been advancing in order to handle a large volume of information in a short time. In the equipment using such high speed pulse signals, signal delay time on the printed circuit board becomes a problem. Since the signal delay time on the printed circuit board becomes longer in proportion to square root of a specific dielectric constant ε r of the insulator around the circuit, resins having a low dielectric constant are required for circuit boards used in a computer and the like. Regarding resin compositions improving the high frequency property of the printed circuit board capable of coping with the trend moving toward increasingly higher frequency signals as described above, a method using a Cyanate ester/epoxy resin composition disclosed in JP-B-46-41112 (1971), and a method using a bismaleimide/Cyanate ester/epoxy resin composition disclosed in JP B-52-31279 (1977) as a composition using Cyanate ester resin having the lowest dielectric constant among thermosetting resins have been disclosed. As a method of improving the high frequency property using a thermoplastic resin, methods of using polyphenylene ether group resin compositions having a desirable dielectric property among heat-resistant thermoplastic resins such as a resin composition composed of polyphenylene ether resin (PPO or PPE) and a cross linking polymer/monomer disclosed in JP-B-5-77705 (1993), and a resin composition composed of a polyphenylene ether having a specific curable functional group and a cross linking monomer disclosed in JP-B-6-92533 (1994) have been disclosed. Further, as a method of improving the high frequency property using a resin composition composed of cyanate ester resin having a low dielectric constant and polyphenylene ether resin having a desirable dielectric property, a method of using a resin composition composed of cyanate ester/bismaleimide and a polyphenylene ether resin disclosed in JP-B-63-33506 (1988), and a method of using a resin composition composed of a phenol modified resin/ cyanate ester reactant and polyphenylene ether resin disclosed in JP-A-5-311071 (1993) have been disclosed. Furthermore, a resin composition prepared by kneading polyphenylene ether resin and cyanate ester resin has been disclosed in JP-B-61-18937 (1986) as a heat resistant molding material having a desirable frequency characteristics. The methods disclosed in JP-B-46-41112 (1971) and JP-B-52-31279 (1977), respectively, had such a problem that the high frequency property was insufficient though their dielectric constants were slightly lowered, because the resin compositions contained the thermosetting resins other than the cyanate ester resin. The methods disclosed in JP-B-5-77705 (1993) and JP-B-6-92533 (1994) had such a problem that the resin compositions were high in molten viscosity and lacked in resin flow though their dielectric constants were somewhat improved, because the main component of the resin compositions was polyphenylene ether resin which was essentially the thermoplastic resin. Therefore, the resin compositions required a high temperature and a high pressure at pressurized molding of the laminated board, and were unsuitable for forming a multilayer printed circuit board, which required to fill a very small space in a circuit pattern, because of insufficient moldability. The methods disclosed in JP-B-63-33506 (1988)and JP-A-5-311071 (1993) had such a problem that the high frequency property was still insufficient though their dielectric constants were somewhat improved, because the thermosetting resin used together with polyphenylene ether resin was the bismaleimide/ cyanate ester resin or the phenol modified resin/cyanate ester reactant. When the quantity of adding polyphenylene ether resin was increased, the resin composition became high in molten viscosity and lacked in fluidity to decrease moldability, as similar with the case of the polyphenylene group resin composition described above. The resin composition prepared by kneading polyphenylene ether resin and cyanate ester resin disclosed in JP-B-61-18937 (1986) had a desirable dielectric property and a relatively preferable moldability, because the molten viscosity was lowered by being modified by cyanate ester resin. However, a problem that, when cyanate ester was singly used as a curing composition, the dielectric property of the cured resin had a high dissapation factor while the dielectric constant was relatively low, was still remained. Further, when an adding quantity of cyanate ester was decreased (an adding quantity of polyphenylene ether resin was increased) in order to lower the dissapation factor, such a problem was still remained that the molten viscosity of the resin composition was increased to make the fluidity insufficient, and the moldability was decreased, as similar to the case of the polyphenylene group resin composition described above. SUMMARY OF THE INVENTION A first object of the present invention is to provide a modified cyanate ester group curable resin composition having a desirable heat resistance, similar moldability and workability as conventional thermosetting resin such as epoxy resin, a low dielectric property, and a low dissapation factor and a low loss property in the high frequency band. A second object of the present invention is to provide a flame retardant resin film using the modified cyanate ester group curable resin composition, and a method for manufacturing same. An object of the present invention is to provide a resin film using the modified cyanate ester group curable resin composition, and a method for manufacturing same. A third object of the present invention is to provide a modified cyanate ester group curable resin varnish for printed circuit board using the modified cyanate ester group curable resin composition, and a method for manufacturing same. A fourth object of the present invention is to provide methods of manufacturing prepreg for laminated board and metal clad laminated board, using the modified cyanate ester group curable resin varnish. A fifth object of the present invention is to provide a multilayered circuit board manufactured by laminating a printed circuit board and/or an inner layer circuit board, which are manufactured by patterning the circuit on the laminated board manufactured by the above method of manufacturing prepreg for laminated board and metal clad laminated board, and a prepreg, film, and/or a film adhered with metal foil, which are manufactured the above method, and forming circuits for making connections between the inner circuits each other and the metal foil. The present invention provides a modified cyanate ester group curable resin composition comprising essentially (A) a cyanate ester group compound expressed by the chemical formula (1), (B) a monovalent phenolic group compound expressed by any one of the chemical formula (2) and (3), (C) a polyphenylene ether resin, (D) a flame retardant not reactive with the cyanate ester group compound and (E) a metal group reaction catalyst. (where, R 1 is or and respective of R 2 and R 3 is hydrogen or methyl group, and the both can be the same or different from each other) (where, respective of R 4 and R 5 is any one of hydrogen atom and low alkyl group having carbon number of 1 to 4, and the both can be the same or different from each other. n is a positive integer of 1 or 2.) (where, R 6 is ―CH 3 , ―CH 2 CH 3 , or It is preferable to use a modified cyanate ester group curable resin composition, which is prepared by mixing (B) the monovalent phenolic group compound expressed by the chemical formula (2) or (3) of 4 to 30 parts by weight with 100 parts by weight of (A) the cyanate ester group compound expressed by the chemical formula (1). The present invention also provides the flame-retardant resin film manufactured by semi-curing or curing the modified cyanate ester group curable resin composition including the flame-retardant not reactive with the cyanate ester group compound. The method of manufacturing the flame-retardant resin film can be achieved by a method comprising the steps of applying the varnish comprising the modified cyanate ester group curable resin composition including the flame retardant and a solvent onto one side plane of a carrier by a flowing method, and removing the solvent by heating and drying to form the film. The present invention can also provide by the modified cyanate ester group curable resin film manufactured by semi-curing or curing the modified cyanate ester group curable resin composition, which does not include any flame-retardant not reactive with the cyanate ester group compound. The method of manufacturing the resin film can be achieved by a method comprising the steps of applying the varnish comprising the modified cyanate ester group curable resin composition, which does not include the flame retardant not reactive with the cyanate ester group compound, and a solvent onto one side plane of a carrier by a flowing method, and removing the solvent by heating and drying to form the film. The present invention further provides the modified cyanate ester group curable resin varnish comprising essentially (F) an aromatic hydrocarbon group solvent, and (G) a ketone group solvent, in addition to the modified cyanate ester group curable resin composition. The method of manufacturing the varnish with the modified cyanate ester group curable resin composition for the printed circuit board can be achieved by comprising the method with the steps of dissolving (C) polyphenylene ether resin into (F) the aromatic hydrocarbon group solvent by heating, reacting subsequently (A) the cyanate ester group compound with (B) the monovalent phenolic group compound in the presence of (E) the metal group reaction catalyst in the above solution to produce a mutually dissolving solution of the modified cyanate ester resin and the polyphenylene ether resin, and suspending the mutually dissolving resins by adding and agitating (G) the ketone group solvent. The present invention also provides the method for manufacturing prepreg for laminated board, which comprises impregnating the modified cyanate ester group resin varnish for printed circuit board into a substrate, and subsequently drying the impregnated substrate at a temperature in the range of 80 - 200 °C, and the method for manufacturing metal clad laminated board, which comprises piling up one or plural prepregs for the laminated board, piling up one or plural metal foils at the upper and lower end planes of the pile, or either one plane, and heating and pressurizing the pile to form the metal clad laminated board. The present invention also provides a method of manufacturing multilayered circuit board comprising the steps of; manufacturing a printed circuit board by patterning circuits onto the metal clad laminated board manufactured by the above method for obtaining metal clad laminated board, wherein the metal is plated onto both side planes and/or one side plane, with conventional process such as forming through-holes, metal plating, etching, and the others; laminating the prepreg, the film, or a combination of the prepreg and the film, onto the surface of the printed circuit board as an inner layer board, and a metal foil is further laminated thereon, by heating and pressurizing a pile of those materials; forming a window at a place on the metal foil, where a via-hole for connecting the inner layer circuit and the outer layer circuit must be formed, using a photosensitive resin or screen printing so that the metal foil at the place where the via-hole must be formed is exposed; forming via-holes through to the inner layer circuit by a laser beam drilling process using the metal foil as a mask after removing the metal foil exposed in the window by etching; connecting the inner layer circuit and the outer layer circuit by metal plating including the inner wall of the via-holes; and manufacturing circuits onto outer surface of the metal foil to obtain the multilayered circuit board. By repeating the above steps of the method of manufacturing multilayered circuit board using the multilayered circuit board manufactured by the once-through operation of the above steps as the inner layer board, the multilayered circuit board having a large number of layers can be manufactured. Another multilayered circuit board can be manufactured by using a film adhered with a metal foil instead of the prepreg and the film in the above steps, piling up the film adhered with the metal foil onto the inner layer board so that the film plane is contacted with the inner layer board, and heating and pressurizing to laminate them. The dielectric property of a polymer material is strongly affected by the polarization alignment of dipoles. Therefore, the dielectric constant can be decreased by decreasing the number of polar groups in the molecule, and the dissapation factor can be lowered by suppressing the mobility of the polar groups. Since cyanate ester resin produces a symmetric and rigid triazine structure when being cured though it has a strong polar cyanate group, cyanate ester resin can provide a cured material having the lowest dielectric constant and dissapation factor among the thermosetting resins. However, in the actual curing reaction, the cyanate groups in the cyanate ester resin cannot all react to produce the triazine structure. The reaction system gradually loses the fluidity as the curing reaction is progressed, and some cyanate groups are remained in the system as the non-reacted cyanate groups. As a result, only a cured resin having a dielectric constant and a dissapation factor values higher than what the cured resin should essentially have was manufactured. On the other hand, the resin composition in accordance with the present invention is aimed at decreasing the dielectric constant and the dissapation factor of the cured resin by adding an appropriate quantity of (B) monovalent phenolic group compound in order to convert the remaining non-reacted cyanate groups into imidocarbonate for decreasing the polarity of the cured resin. A suitable material used for this purpose is a chemical composition which is highly reactive with cyanate group, single functional, relatively low in molecular weight, and mutually soluble with cyanate ester resin (similar in molecular structure). The monovalent phenolic group compounds used in the resin composition of the present invention are specified by the above reason. Conventionally, a phenolic compound such as nonylphenol and the like was used as an auxiliary catalyst for trimerizing reaction of cyanate ester (forming triazine rings) by adding approximately 1 to 2 parts by weight to 100 parts by weight of cyanate ester. However, since the adding amount was actually a catalyst quantity, the effect of the phenolic compound to decrease the polarization by reacting with cyanate group as above was not observed. According to the inventors' study on the adding quantity of the phenolic compounds, it was found that the dielectric constant and the dissapation factor of the cured material could be decreased by adding the phenolic compound more than the conventional quantity, and decrease in heat resistance due to increase in the adding quantity of the phenolic compound could be suppressed by using a specific monovalent phenolic group compound. Therefore, according to the method of the present invention, it became possible to obtain the cured material having a dielectric constant and a dissapation factor lower than those of the conventional cured materials of single cyanate ester resin, and the conventional cured material of resin composed of epoxy resin, multivalent phenol group (hydroxyl in one side was apt to be remained as a non-reacted group, which deteriorated the dielectric property), bismaleimide, and the like. Therefore, preferably in the modified cyanate ester group curable resin composition of the present invention, the adding quantity of the monovalent phenolic group compound is selected. That is, the monovalent phenolic group compound cannot react with all the non-reacted remaining cyanate group to decrease the polarization when the adding quantity is small, and the monovalent phenolic group compound itself remains as non-reactants to deteriorate the dielectric property of the cured material by the polarity of the hydroxyl of the monovalent phenolic group compound itself when the adding quantity is more than necessary. Further, in accordance with the modified cyanate ester group curable resin composition of the present invention, improving the dielectric property is intended by adding (C) the polyphenylene ether resin, which is a thermoplastic resin having a desirable dielectric property, to the modified cyanate ester resin. The cyanate ester resin and the polyphenylene ether resin are essentially not soluble with each other, and it is difficult to obtain a uniform resin. However, according to a technique found by the inventors, it was found that when (A) the cyanate ester group compound and (B) the monovalent phenolic group compound were reacted in a solvent solution of polyphenylene ether resin, a uniform resin solution could be manufactured by forming the so-called "semi-IPN (interpenetrating polymer network) resin". The flame retardant used in the resin composition of the present invention must be not reactive with the cyanate ester group compound so as not to interfere with the reaction between (A) the cyanate ester group compound and (B) the monovalent phenolic group compound. Such a flame retardant is an alicyclic flame retardant (aliphatic ring type flame retardant) which is a hydrocarbon group low polar composition and accordingly hardly deteriorates the dielectric property of the cured material. Further, another kind of specified flame retardant is easily miscible with cyanate ester resin cured material because the specified flame retardant has a triazine structure similar to the cyanate ester cured material, and the specified flame retardant can give a flame retardant effect to the cyanate ester cured material without deteriorating the heat resistance and the dielectric property. (A) A modified cyanate ester group curable resin composition in accordance with the present invention comprises (A) a cyanate ester group compound expressed by the chemical formula (1), (B) a monovalent phenolic group compound expressed by the chemical formula (2) or an alkyl substituted phenolic compound expressed by the chemical formula (3), (C) a polyphenylene ether resin, (D) a flame retardant not reactive with the cyanate ester group compound and (E) a metal group reaction catalyst, as essential components. In accordance with the present invention, (A) the cyanate ester group compound is a cyanate ester group compound having two cyanate groups in one molecule as expressed by the chemical formula (1). The chemical compounds expressed by the chemical formula (1) are, for example, bis(4-cyanato-phenyl) ethane; 2, 2-bis(4-cyanato-phenyl) propane; bis(3, 5-dimethyl-4-cyanato-phenyl) methane; 2, 2-bis(4-cyanato-phenyl)-1, 1, 1, 3, 3, 3-hexafluoropropane; α, α'- bis(4-cyanato-phenyl)-m-diisopropylbenzen; a cyanate ester compound of phenol added dicyclopentadiene polymer; and the like. Among them, any one or a mixture of 2, 2-bis(4-cyanato-phenyl) propane and bis(3, 5-dimethyl-4-cyanato-phenyl) methane is preferable, because a balance between the dielectric property and the moldability of their cured material is particularly desirable. The (A) the cyanate ester group compounds can be used by a single kind or a mixture of two or more kinds. In accordance with the present invention, (B) the monovalent phenolic group compound is a monovalent phenolic group compound expressed by the chemical formula (2) or an alkyl substituted phenolic compound expressed by the chemical formula (3), and a compound having desirable heat resistance is preferable. The chemical compound expressed by the chemical formula (2) is, for example, p-(α-cumyl) phenol, and the chemical compounds expressed by the chemical formula (3) are, for instance, p-tert-butylphenol, p-tert-amylphenol, and p-tert-octylphenol. (B) the monovalent phenolic group compounds can be used by a single kind or a mixture of two or more kinds. The adding quantity of (B) the monovalent phenolic group compound in the present invention is desirably 4 to 30 parts by weight to 100 parts by weight of (A) the cyanate ester group compound, preferably 5 to 30 parts by weight, and more preferably 4 to 25 parts by weight. When the adding quantity of (B) the monovalent phenolic group compound is not more than 4 parts by weight, the sufficient dielectric property cannot be manufactured, and the dissapation factor particularly in a high frequency band is generally not decreased sufficiently. On the other hand, when the adding quantity of (B) the monovalent phenolic group compound exceeds 30 parts by weight, the dissapation factor becomes rather high. This is not preferable. Therefore, in order to obtain a cyanate ester group resin cured material having a low dissapation factor in a high frequency band provided by the present invention, an appropriate quantity of (B) the monovalent phenolic group compound must be added to (A) the cyanate ester group compound. In accordance with the present invention, (A) the cyanate ester group compound and (B) the monovalent phenolic group compound are used as the modified cyanate ester resin which is manufactured by reacting them. That is, they are used as a pre-polymer of (A) the cyanate ester group compound and imide-carbonated modified resin formed by adding (B) the monovalent phenolic group compound to (A) the cyanate ester group compound. When (A) the cyanate ester group compound is reacted with (B) the monovalent phenolic group compound, the modified cyanate ester resin can be manufactured by adding all the appropriate quantity of (B) the monovalent phenolic group compound to be reacted from the beginning of the reaction, or the modified cyanate ester resin can be manufactured by adding a part of the appropriate quantity of (B) the monovalent phenolic group compound at the initial stage of the reaction, and after cooling, adding the remaining amount of (B) the monovalent phenolic group compound at B-stage reacting time or curing time. In accordance with the present invention, (C) the polyphenylene ether resins are, for example, an alloyed polymer of poly(2, 6-dimethyl-1, 4-phenylene) ether, or poly(2, 6-dimethyl-1, 4-phenylene) ether, with polystyrene, an alloyed polymer of poly(2, 6-dimethyl-1, 4-phenylene) ether with styrene-butadiene copolymer., and the like. Particularly, the alloyed polymer of poly(2, 6-dimethyl-1, 4-phenylene) ether with polystyrene or styrene-butadiene copolymer and the alloyed polymer of poly(2, 6-dimethyl-1, 4-phenylene) ether with styrene-butadiene copolymer are desirable. A polymer containing the alloyed polymer of poly(2, 6-dimethyl-1, 4-phenylene) ether of more than 50 % by weight is desirable, because the dielectric property of the cured material is desirable, and more than 65 % by weight is particularly preferable. The adding quantity of (C) the polyphenylene ether resin in the present invention is desirably 5 to 300 parts by weight to 100 parts by weight of (A) the cyanate ester group compound, preferably 10 to 200 parts by weight, and more preferably 15 to 100 parts by weight. When the adding quantity of (C) the polyphenylene ether resin is not more than 5 parts by weight, the sufficient dielectric property cannot manufactured. On the other hand, when the adding quantity of (C) the polyphenylene ether resin exceeds 300 parts by weight, the moldability is deteriorated, because the molten viscosity becomes high and the fluidity becomes low, and the reactivity with (A) the cyanate ester group compound is also deteriorated. In accordance with the present invention, (D) the flame retardant not reactive with the cyanate ester group compounds are, for example, 1, 2-dibromo-4-(1, 2-dibromoethyl) cyclohexane, tetrabromocyclohexane, hexabromocyclododecane, polybromodiphenylether, polystyrene bromide, polycarbonate bromide, and triphenylcyanate bromide group flame retardants expressed by the chemical formula (4), and the like. Particularly, 1, 2-dibromo-4-(1, 2-dibromoethyl) cyclohexane; tetrabromocyclooctane; hexabromocyclododecane; 2, 4, 6-tris (tribromophenoxy)-1, 3, 5-triazine are desirable, because the manufactured cured materials have preferable dielectric properties. (where, respective of l, m, and n is an integer of 1 to 5, and the integers can be the same or different from each other.) The adding quantity of (D) the flame retardant not reactive with the cyanate ester group compounds of the present invention is desirably 5 to 30 parts by weight to 100 parts by weight of the total of (A) the cyanate ester group compound, (B) the monovalent phenolic group compound and (C) the polyphenylene ether resin, and preferably 5 to 20 weight part, and further preferably 10 to 20 parts by weight. When the adding quantity of (D) the flame retardant not reactive with the cyanate ester group compound is not more than 5 parts by weight, the flame retardant effect is insufficient. When the adding quantity of (D) the flame retardant exceeds 30 parts by weight, the heat resistance of the resin is decreased. In accordance with the present invention, (E) the metal group reaction catalyst accelerates the reaction between (A) the cyanate ester group compound and (B) the monovalent phenolic group compound, and used as the reaction catalyst in manufacturing the modified cyanate ester group curable resin composition and as the curing accelerator in manufacturing the laminated board. The metal group reaction catalysts used are metallic catalysts such as manganese, iron, cobalt, nickel, copper, and zinc. Practically, the catalysts are used as an organic acid metal salt compound such as 2-ethylhexanoic salts, naphthenic salts, and as an organic metal complex such as acetylacetone complex. The same kind of the metal group reaction catalyst can be solely used or two or more kinds of the metal group reaction catalysts can be respectively used as the reaction catalyst in manufacturing the modified cyanate ester group curable resin composition and as the curing accelerator in manufacturing the laminated board. The adding quantity of (E) the metal group reaction catalyst of the present invention is desirably 1 to 300 ppm to 1 (g) of (A) the cyanate ester group compound, preferably 1 to 200 ppm, and more preferably 2 to 150 ppm. When the adding quantity of (E) the metal group reaction catalyst is not more than 1 ppm, the reactivity and the curability become insufficient. On the other hand, when the adding quantity exceeds 300 ppm, the reaction becomes difficult to be controlled and the moldability is deteriorated, because the curing speed becomes too fast to be controlled. Adding timing of (E) the metal group reaction catalyst of the present invention can be at the time of manufacturing the modified cyanate ester group curable resin composition when the necessary quantity of the metal group reaction catalyst as the reaction accelerator and the curing accelerator is added together at a time, or at the time of manufacturing the modified cyanate ester group curable resin composition when the quantity of the metal group reaction catalyst necessary for accelerating the denaturalizing reaction is added and then at the time after completion of the reaction when the remaining catalyst or the other metallic catalyst is added and mixed as the curing accelerator. An inorganic filler and other additives other than the above-mentioned essential components can be added to the modified cyanate ester group curable resin composition of the present invention. The usable fillers are silica, alumina, aluminum hydride, calcium carbonate, clay, talk, silicon nitride, boron nitride, titanium oxide, barium titanate, lead titanate, strontium titanate and the like. In accordance with the present invention, the adding quantity is preferably less than 250 parts by weight to 100 parts by weight of the total resin composition, in order to obtain a uniform distribution in the adhered quantity of the resin and desirable appearance when the resin varnish of the present invention is impregnated into the supporting material such as glass cloth. The modified cyanate ester group curable resin composition of the present invention is used in manufacturing flame retardant films, films, varnishes, prepregs for laminated board, and metal clad laminated boards, for example, in a manner as described below. That is, initially, the prepreg is manufactured by dissolving or suspending the modified cyanate ester group curable resin composition of the present invention into a solvent to form a varnish, impregnating the varnish into a base material such as glass cloth, and then drying the impregnated base material. Next, the metal clad laminated board with metallic films on both side surfaces or with a metallic film on one side surface is manufactured by laminating one or an arbitrary number of sheets of the prepreg, laminating metallic films on both sides surfaces or an one side surface of the laminated prepreg; and then heating and pressurizing the laminated prepreg. The flame retardant films and films can be manufactured by semi-curing or curing the modified cyanate ester group curable resin composition of the present invention. Practical examples of the solvents used for making the varnish of the modified cyanate ester group curable resin composition in accordance with the present invention are aromatic hydrocarbon having a boiling point in the range of 70-170 °C such as benzene, toluene, xylene and the like, hydrocarbon halide such as trichloroethylene, chlorobenzene, and the like, amide group such as N, N-dimethyl formaldehyde, N, N-dimethylacetoamide, and the like, and nitrogen group solvents such as N-methylpyrolidone and the like. Particularly, aromatic hydrocarbon such as benzene, toluene, xylene, and the like are desirable. These solvents can be used by solely one kind or by mixing two or more kinds. The adding quantity of the aromatic hydrocarbon is desirably 150 to 500 parts by weight to 100 parts by weight of (C) the polyphenylene ether resin, preferably 150 to 400 parts by weight, and more preferably 150 to 300 parts by weight. Ketones having a boiling point in the range of 50-170 °C such as acetone, methylethylketone, methy-lisobutylketone, cyclohexanone, and the like have a low solubility to the modified cyanate ester group curable resin composition, but have such an advantage that when the ketones are used together with the above-mentioned solvents, a high density and low viscosity solution can be manufactured by forming a suspension of the resin composition in accordance with the present invention. From this viewpoint, the solvents used for making the varnish of the modified cyanate ester group curable resin composition in accordance with the present invention are desirably mixed solvents of the aromatic hydrocarbon such as benzene, toluene, xylene, and the like, with ketones such as acetone, methylethylketone, methy-lisobutylketone, cyclohexanone, and the like. The adding quantity of the ketone is desirably 50 to 500 parts by weight to 100 parts by weight of the organic hydrocarbon group solvent, preferably 50 to 400 parts by weight, and more preferably 50 to 300 parts by weight. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, details of the present invention are explained referring to preferred embodiments. The modified cyanate ester group curable resin composition varnishes were manufactured in accordance with the composition indicated in Table 1. (Embodiment 1) Toluene 450 g, and PKN 4752 (a trade name of a product of Japan GE Plastic Co.) 210 g as (C) polyphenylene ether resin were charged into a 5-liter 4-nozzle separable flask provided with a thermometer, a cooling pipe, and a stirrer, and heated to 80 °C with stirring to be dissolved. Next, 2, 2-bis(4-cyanatophenyl) propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) 700 g as (A) the cyanate ester group compound; p-(α-cumyl) phenol ( a product of Sun Technochemical Co.) 64 g as (B) the monovalent phenolic group compound; triphenylcyanulate bromide (Pyroguard SR-245, a trade name of a product of Dai-ichi Industrial Chemical Co.) 135 g as (D) the flame retardant not reactive with the cyanate ester group compounds were charged into the separable flask to be dissolved, and then 4 g of a toluene solution of 10 % by weight of cobalt naphthenate (content of Co = 8 by weight, a product of Japan Chemical Industry Co.) was added to the reaction liquid at a reflux temperature for 1 hour. Subsequently, the reaction liquid was cooled. When the inner temperature became 90 °C, methyl ethyl ketone (MEK) 600 g was charged into the separable flask with stirring to form a suspension. After further cooling the reaction liquid to room temperature, 1 g of a toluene solution of 10 % by weight zinc naphthenate (content of Zn = 8 % by weight, a product of Japan Chemical Industry Co.) was added and dissolved by stirring to obtain a varnish (solid content = 51 weight %). (Embodiment 2) Toluene 300 g and polyphenylene ether resin (PKN 4752, a trade name of a product of Japan GE Plastic Co.) 140 g were charged into a 5-liter 4-nozzle separable flask provided with a thermometer, a cooling pipe and a stirrer, and heated to 80 °C to be dissolved with stirring. Subsequently, 2, 2-bis(4-cyanatophenyl) propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) 700 g; p-(α-cumyl) phenol ( a product of Sun Technochemical Co.) 10g; triphenylcyanulate bromide (Pyroguard SR-245, a trade name of a product of Dai-ichi Industrial Chemical Co.) 125 g were charged into the separable flask to be dissolved, and then 3 g of a toluene solution of 10 % by weight manganese naphthenate (content of Mn = 8 % by weight, a product of Japan Chemical Industry Co.) was added to the reaction liquid at a reflux temperature for 1 hour. Subsequently, the reaction liquid was cooled. When the inner temperature became 90 °C, methyl ethyl ketone (MEK) 600 g was charged into the separable flask with stirring to form a suspension. After further cooling the reaction liquid to room temperature, 75 g of p-(α-cumyl) phenol and 1 g of a toluene solution of 10 % by weight zinc naphthenate (content of Zn = 8 % by weight, a product of Japan Chemical Industry Co.) was added and dissolved with stirring to obtain a varnish (solid content = 8 % by weight). (Embodiment 3) Toluene 300 g and polyphenylene ether resin (PKN 4752, a trade name of a product of Japan GE Plastic Co.) 80 g were charged into a 5-liter 4-nozzle separable flask provided with a thermometer, a cooling pipe, and a stirrer, and heated to 80 °C with stirring to be dissolved. Subsequently, α, α'- bis(4-cyanatophenyl)-m-diisopropylbenzen (RTX-366, a trade name of a product of Asahi Ciba Co.) 800 g; and p-(α-cumyl) phenol ( a product of Sun Technochemical Co.) 10 g were charged into the separable flask to be dissolved , and then 2 g of a toluene solution of 10 % by weight iron naphthenate (content of iron = 5 % by weight, a product of Japan Chemical Industry Co.) was added to the reaction liquid at a reflux temperature for 1 hour. Then, tetrabromocyclooctane (Saytex BC-48, a trade name of a product of Albemarl Co.) 110 g was added into the flask and dissolved. Subsequently, the reaction liquid was cooled. When the inner temperature became 90 °C, methyl ethyl ketone (MEK) 600 g was charged into the separable flask with stirring to form a suspension. After further cooling the reaction liquid to room temperature, 75 g of p-(α-cumyl) phenol and 2 g of a toluene solution of 10 % by weight copper naphthenate (content of copper = 8 % by weight, a product of Japan Chemical Industry Co.) were added into the flask and dissolved with stirring to obtain a varnish (solid content = 54 % by weight). (Embodiment 4) Toluene 600 g and polyphenylene ether resin (PKN 4752, a trade name of a product of Japan GE Plastic Co.) 300 g were charged into a 5-liter 4-nozzle separable flask provided with a thermometer, a cooling pipe, and a stirrer, and heated to 80 °C with stirring to be dissolved. Next, bis(3, 5-dimethyl-4-cyanato-phenyl) methane (Arocy M-10, a trade name of a product of Asahi Ciba Co.) 600 g; and p-(α-cumyl) phenol (a product of Sun Technochemical Co.) 30 g were charged into the separable flask to be dissolved , , and then 4 g of a toluene solution of 10 % by weight cobalt naphthenate (content of Co = 8 % by weight, a product of Japan Chemical Industry Co.) was added to the reaction liquid at a reflux temperature for 1 hour; and then hexabromocyclododecane (CD-75P, a trade name of a product of Grate Lakes Co.) 150 g was added into the flask and dissolved. Subsequently, the reaction liquid was cooled. When the inner temperature became 90 °C, methyl ethyl ketone (MEK) of 750 g was charged into the separable flask with stirring to form a suspension. After further cooling the reaction liquid to room temperature, 120 g of p-(α-cumyl) phenol was added and dissolved with stirring to obtain a varnish (solid content = 47 % by weight). (Embodiment 5) Toluene 750 g and polyphenylene ether resin (PKN 4752, a trade name of a product of Japan GE Plastic Co.) 400 g were charged into a 5-liter 4-nozzle separable flask provided with a thermometer, a cooling pipe and a stirrer, and heated to 80 °C with stirring to be dissolved. Next, 2, 2 bis (4-cyanatophenyl)-1, 1, 1, 3, 3, 3- hexafluoropropane (Arocy F-10, a trade name of a product of Asahi Ciba Co.) 500 g; and p-(α-cumyl) phenol (a product of Sun Technochemical Co.) 28 g were charged into the separable flask to be dissolved, and then 6 g of a toluene solution of 10 % by weight copper naphthenate (content of Cu = 5 % by weight, a product of Japan Chemical Industry Co.) was added to the reaction liquid at a reflux temperature for 1 hour; and then 1, 2-dibromo-4-(1, 2-dibromoethyl) cyclohexane (Saytex BCL-462, a trade name of a product of Albemarl Co.) 150 g was added into the flask and dissolved. Then, the reaction liquid was cooled. When the inner temperature became 90 °C, methyl ethyl ketone (MEK) 500 g was charged into the separable flask with stirring to form a suspension. After further cooling the reaction liquid to room temperature, 1 g of a toluene solution of 10 % by weight manganese naphthenate (content of Mn = 8 % by weight, a product of Japan Chemical Industry Co.) was added into the flask and dissolved with stirring to obtain a varnish (solid content = 46 % by weight). (Embodiments 6-10) The varnishes in the embodiment 6 - 10 were manufactured by the same method under the same condition as described in the above embodiments 1 - 5 except only replacing the component (B) the monovalent phenolic group compound with the compounds indicated in the embodiments 6 - 10 of Table 1, respectively. (Comparative Example 1) Toluene 1800 g , , polyphenylene ether resin (PKN 4752, a trade name of a product of Japan GE Plastic Co.) 210 g, 2, 2-bis(4-cyanato-phenyl) propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) 700 g, and 2, 2-bis(4-hydroxyphenyl) propane (BPA; bisphenol A, a product of Mitsui Toatsu Chemicals, Inc.) 69 g instead of p-(α-cumyl) phenol in the embodiment 1, were charged into the separable flask, and were stirred to be dissolved. Then, 3 g of a toluene solution of 10 % by weight cobalt naphthenate (content of Co = 8 % by weight, a product of Japan Chemical Industry Co.) was added to the reaction liquid at a reflux temperature for 1 hour. Next, bromated bisphenol A type epoxy resin (ESB 400, a trade name of a product of Sumitomo Chemicals Co., Ltd.) 200 g as a flame retardant reactive with cyanate group was charged into the separable flask to be dissolved, and the reaction liquid was cooled. However, because the reaction liquid was solidified (into a grease state) near room temperature, toluene of 1200 g was further added and was stirred to dissolve the reaction product to obtain a varnish (solid content = 28 % by weight). (Comparative Example 2) Toluene 1800 g , polyphenylene ether resin (PKN 4752, a trade name of a product of Japan GE Plastic Co.) 210 g, 2, 2-bis(4-cyanato-phenyl) propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) 700 g, and nonylphenol (a product of Mitsui Toatsu Chemicals, Inc.) 11 g instead of p-(α-cumyl) phenol in the embodiment 1 were charged into the separable flask, and were stirred to be dissolved. Then, 4 g of a toluene solution of 10 % by weight cobalt naphthenate (content of Co = 8 $ by weight, a product of Japan Chemical Industry Co.) was added to the reaction liquid at a reflux temperature for 1 hour. Next, bromated bisphenol A type epoxy resin (ESB 400, a trade name of a product of Sumitomo Chemicals Co., Ltd.) 190 g as a flame retardant reactive with cyanate group was charged into the separable flask to be dissolved, and the reaction liquid was cooled. However, because the reaction liquid was solidified (into a grease state) near room temperature, toluene 900 g was further added and was stirred to dissolve the reaction product to obtain a varnish (solid content = 29 % by weight). (Comparative Example 3) Toluene 1500 g, and polyphenylene ether resin (PKN 4752, a trade name of a product of Japan GE Plastic Co.) 210 g were charged into the separable flask, and were stirred to be dissolved. Next, an oligomer of 2, 2-bis(4-cyanatophenyl) propane (Arocy B-30, a trade name of a product of Asahi Ciba Co.) 700 g instead of 2, 2-bis(4-cyanato-phenyl) propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) in the embodiment 1; nonylphenol (a product of Mitsui Toatsu Chemicals, Inc.) 67 g instead of p-(α-cumyl) phenol; and bromated bisphenol A type epoxy resin (ESB 400, a trade name of a product of Sumitomo Chemicals Co., Ltd.) 200 g as a flame retardant reactive with cyanate group were let into the separable flask; were charged into the flask, heated and dissolved at 80 °C for 1 hour. Then, the reaction liquid was cooled to room temperature, and 2 g of a toluene solution of 10 % by weight zinc naphthenate (content of Zn = 8 % by weight, a product of Japan Chemical Industry Co.) was added into the flask to obtain a varnish (solid content = 44 % by weight). However, flocculated separation of polyphenylene ether resin was observed in the resin varnish after two days elapsed. (Comparative Example 4) In embodiment 4, toluene 1600 g, polyphenylene ether resin (PKN 4752, a trade name of a product of Japan GE Plastic Co.) 300 g, bis(3, 5-dimethyl-4-cyanatophenyl) methane (Arocy M-10, a trade name of a product of Asahi Ciba Co.) 600 g, and nonylphenol of 9 g instead of p-(α-cumyl) phenol (a product of Sun Techno Chemical Co.) were charged into the separable flask, and were stirred to be dissolved. Then, 3 g of a toluene solution of 10 % by weight manganese naphthenate (content of Mn = 8 % by weight, a product of Japan Chemical Industry Co.) was added to the reaction liquid at a reflux temperature for 1 hour. Next, tetrabromobisphenol A (Fire Guard FG-2000, a trade name of a product of Teijin Chemicals Co., Ltd.) 150 g as a flame retardant reactive with cyanate group was charged into the separable flask to be dissolved, and the reaction liquid was cooled. However, because the reaction liquid was solidified (into a grease state) near room temperature, toluene 1200 g was further added and was stirred to dissolve the reaction liquid to obtain a varnish (solid content = 27 % by weight). Emb (A) (B) (C) (D) (E) Cyanate ester Monovalent phenol Polyphenylene ether Flame retardant Metallic reaction catalyst Com Mix Com. Mix. Com. Mix. Com. Mix. Com. Mix. 1 B-10 700 PCP 64 PPO 210 SR- 135 Co 4 245 Zn 1 2 B-10 700 PCP 10 PPO 140 SR- 125 Mn 3 PCP 75 245 Zn 1 3 RTX- 800 PCP 10 PPO 80 BC-48 110 Fe 2 366 PCP 75 Cu 2 4 M-10 600 PCP 30 PPO 300 CD- 150 Co 4 PCP 120 75P 5 F-10 500 PCP 28 PPO 400 BCL- 150 Cu 6 462 Mn 1 6 B-10 700 POP 62 PPO 210 SR- 135 Co 4 245 Zn 1 7 B-10 700 POP 10 PPO 140 SR- 125 Mn 3 POP 73 245 Zn 1 8 RTX- 800 PBP 10 PPO 80 BC-48 110 Fe 2 366 PBP 51 Cu 2 9 M-10 600 POP 30 PPO 300 CD- 150 Co 4 POP 115 75p 10 F-10 500 PAP 21 PPO 400 BCL- 150 Cu 6 462 Mn 1 C-1 B-10 700 BPA 69 PPO 210 ESB-400 200 Co 3 C-2 B-10 700 NP 11 PPO 210 ESB-400 190 Co 4 C-3 B-10 700 NP 67 PPO 210 ESB-400 200 Zn 2 C-4 M-10 600 NP 9 PPO 300 TBA 150 Mn 3 A prepreg having adhered resin, of which quantity was 40 to 45 % by weight, was manufactured by impregnating an E glass cloth having a thickness of 0.2 mm (weight 209 g/m 2 ) with the manufactured resin varnish and heating it at 140 °C for 5 to 10 minutes (so that gelling time (170 °C) became 5 to 7 minutes). In the cases of the resin varnish of comparative examples 1, 2, and 4, the prepregs having adhered resin, of which quantities were in the range of 40 to 45 % by weight, were manufactured by repeating twice the impregnation applying work, because the solid content was low. In the prepreg of comparative example 3, separation between the cyanate ester resin and the polyphenylene ether resin was observed. Next, laminated boards with copper foil were manufactured by laminating four prepregs and copper foils having a thickness of 18 µm on the both sides, pressurizing to form the laminated board under a condition of 170 °C, 2.5 MPa for 60 minutes, and then performing a heat treatment at 230 °C for 120 minutes. Using the manufactured laminated boards with copper foil, dielectric property, resistance to heated solder, peeling strength of the copper foil and flame retardant property were measured in accordance with the following methods. The results are shown in Table 2. (Methods of evaluating properties) Specific dielectric constant and dissapation factor/ 1 GHz: the properties were measured through the tri-plate structure straight wiring resonance method. Resistance to heated solder: an outer appearance was inspected by holding a test piece, of which cooper foils were removed, in a PCT (121 °C, 0.22 MPa), and then immersing the test piece into a molten solder at 260 °C for 20 seconds. In the table, "OK" means no occurrence of measling nor swelling, and "NG" means occurrence of measling and swelling. Peeling strength of copper foil: Measurement was performed in accordance with JIS-C-6481. Flame retardant resistance: Measurement was performed in accordance with UL-94 Vertical Test Method. Emb Dielect. prop./1 GHz. Solder . heat res. P.S. of Cu foil Flame retard. Remarks: Sol.ct. D.c. D. f. 260°C, 20 s. (kN/m) UL-94 of v. (%) 1 3.5 0.0045 PCT 4h OK 1.5 V-0 51 2 3.5 0.0048 PCT 4h OK 1.7 V-0 54 3 3.3 0.0038 PCT 4h OK 1.7 V-0 54 4 3.4 0.0042 PCT 3h OK 1.4 V-0 47 5 3.3 0.0039 PCT 3h OK 1.3 V-0 46 6 3.5 0.0045 PCT 4h OK 1.5 V-0 51 7 3.5 0.0048 PCT 3h OK 1.7 V-0 54 8 3.3 0.0040 PCT 3h OK 1.6 V-0 54 9 3.4 0.0043 PCT 3h OK 1.4 V-0 47 10 3.3 0.0041 PCT 3h OK 1.3 V-0 46 C-1 3.9 0.0106 PCT 2h OK 1.4 V-0 28(apply twice) C-2 3.9 0.0092 PCT 2h OK 1.4 V-0 29(apply twice) C-3 3.8 0.0099 PCT 1h OK 1.1 V-0 44(PPO separatd) C-4 3.8 0.0088 PCT 1h OK 1.3 V-0 27(apply twice) It is clear from Table 2 that all the laminated boards using the modified cyanate ester group curable resin compositions of embodiments 1 to 10 have a low dielectric constant, a low dissapation factor at 1 GHz, desirable soldering heat resistance with absorbed moisture, and a desirable peeling strength of copper foil. On the contrary, the laminated boards of comparative examples have a high dielectric constant, a high dissapation factor at 1 GHz, and low heat resistance. (Embodiments 11-18, comparative examples 5-7) In accordance with the same method as the embodiment 1 a modified cyanate ester group curable resin composition varnish was manufactured with the composition indicated as embodiment 11 in Table 3. Toluene 360 g, and polyphenylene ether resin (nonylPKN 4752, a trade name of a product of Japan GE Plastic Co.) 160 g were charged into a 1-liter 4-nozzle separable flask provided with a thermometer, a cooling pipe, and a stirrer, and heated to 80 °C with stirring to be dissolved. Next, after charging 2, 2-bis(4-cyanatophenyl) propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) 80 g, and p-(α-cumyl) phenol ( a product of Sun Technochemical Co.) 2 g into the flask and dissolved, 0.3 g of a toluene solution of 10 % by weight of manganese naphthenate (content of Mn = 8 % by weight, a product of Japan Chemical Industry Co.) was added to the reaction liquid, and reacted at a reflux temperature for 3 hours. Then, tetrabromocyclooctane (Saytex BC-48, a trade name of a product of Albemarl Co.) 60 g was added into the flask and dissolved. Subsequently, the reaction liquid was cooled. When the inner temperature became 90 °C, methyl ethyl ketone (MEK) 600 g was charged into the separable flask with stirring to form a suspension. After further cooling the reaction liquid to room temperature, p-(α-cumyl) phenol 6 g, and a toluene solution of 10 % by weight zinc naphthenate (content of Zn = 8 % by weight, a product of Japan Chemical Industry Co.) 0.2 g were added and dissolved by stirring to obtain a modified cyanate ester group curable resin composition varnish (solid content = 32 weight %). Similarly, the modified cyanate ester group curable resin composition varnish of embodiment 12 was manufactured using the composition indicated as embodiment 12 in Table 3. Using the composition indicated as embodiment 13 in Table 3, the modified cyanate ester group curable resin composition varnish of embodiment 12 was manufactured Toluene 540 g, and polyphenylene ether resin (nonylPKN 4752, a trade name of a product of Japan GE Plastic Co.) 105 g were charged into a 1-liter 4-nozzle separable flask provided with a thermometer, a cooling pipe, and a stirrer, and heated to 80 °C with stirring to be dissolved. Next, after charging 2, 2-bis(4-cyanatophenyl) propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) 75 g, p-(α-cumyl) phenol 15 g, and triphenylcyanulate bromide (Pyroguard SR-245, a trade name of a product of Dai-ichi Industrial Chemical Co.) 45 g into the flask and dissolved, 0.7 g of a toluene solution of 10 % by weight of cobalt naphthenate (content of Co = 8 % by weight, a product of Japan Chemical Industry Co.) was added to the reaction liquid, and reacted at a reflux temperature for 2 hours. After cooling the reaction liquid room temperature, a toluene solution of 10 % by weight zinc naphthenate (content of Zn = 8 % by weight, a product of Japan Chemical Industry Co.) 0.1 g was added and dissolved by stirring to obtain a modified cyanate ester group curable resin composition varnish (solid content = 31 weight %). Similarly, the modified cyanate ester group curable resin composition varnish of embodiments 14-18, and the comparative examples 5, 7 were manufactured using the composition indicated in Table 3. Using the composition indicated as comparative example 6 in Table 3, the modified cyanate ester group curable resin composition varnish of embodiment 12 was manufactured Methyl ethyl ketone (MEK) 240 g, 2, 2-bis(4-cyanatophenyl) propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) 120 g, p-(α-cumyl) phenol 2g, and 40 g of bromated bisphenol A type epoxy resin ( ESB, a trade name of a product of Sumitomo Chemical Industries Co.), which was reactive with a cyanato group, as a flame retardant were charged into a 1-liter 4-nozzle separable flask provided with a thermometer, a cooling pipe, and a stirrer. After dissolved the charged chemicals with stirring, 1.2 g of a toluene solution of 10 % by weight of cobalt naphthenate (content of Co = 8 % by weight, a product of Japan Chemical Industry Co.) was added to the reaction liquid, and reacted at a reflux temperature for 2 hours. Then, the reaction liquid was cooled to room temperature to obtain a varnish (solid content = 40 weight %). A resin film adhered with film made of polyethylene terephthalate (PET) having a resin layer of 30 - 33 µm thick was manufactured by applying the manufactured varnish, respectively, onto a film made of PET (Burex A-63, a trade name of a product made by Teijin Co.) of 50 µm thick with a releasing agent using a comma type coater (made by Hirano techseed Co.), a kind of bar coater, and dried at 130 °C. The manufactured modified cyanate ester group curable resin films of the embodiments 11-18, and the comparative example 5 had no resin cracks nor powder spilling even if the film were cut by a cutter-knife, and were superior in handling properties. On the contrary, resin cracks and powder spilling were generated when the resin film of the comparative example 6 was cut by a cutter-knife, and the resin film could not be handled if the resin film was separated from the PET film. Separated coagulation of the polyphenylene ether resin was observed in the varnish of the comparative example 7 after a day elapsed, and any resin film could not be manufactured. (A) (B) (C) (D) (E) Cyanate ester Monovalent phenol Polyphenylene ether Flame retardant Metallic reaction catalyst Solid content Emb Com Mix Com. Mix. Com. Mix. Com. Mix. Com. Mix. wt% 11 B-10 80 PCP 2 PPO 160 BC- 60 Mn 0.3 32 PCP 6 48 Zn 0.2 12 B-10 80 POP 2 PPO 160 BC- 60 Mn 0.3 32 PBP 5 48 Zn 0.2 13 B-10 75 PCP 15 PPO 105 SR- 45 Co 0.7 31 245 Zn 0.1 14 B-10 75 POP 15 PPO 105 SR- 45 Co 0.7 31 245 Zn 0.1 15 B-10 90 PCP 11 PPO 90 CD- 35 Mn 0.7 30 75P 16 B-10 90 POP 11 PPO 90 CD- 35 Mn 0.7 30 75P 17 M-10 120 PCP 6 PPO 60 BCL- 30 Mn 0.4 29 462 Co 0.2 18 M-10 120 PAP 6 PPO 60 BCL- 30 Mn 0.4 29 462 Co 0.2 C-5 - - - - PPO 120 BC- 20 - - 28 48 C-6 B-10 120 PCP 2 - - ESB- 40 Co 1.2 40 400 C-7 B-30 90 NP 1 PPO 90 ESB- 60 Co 1.0 29 400 Next, the resin films adhered with PET film of the embodiments 11-18 were evaluated in handling properties of the resin film alone and solvent-resistance of the cured film. The PET film was peeled off from the adhered resin film adhered with PET film of the embodiments 11. Twelve sheets of the manufactured resin film were piled up, and a mirror plane of electrolyzed copper foil was piled onto respective of the upper plane and the lower plane of the piled resin sheets as a peeling plane. Then, The piled sheets were pressurized with 1.5 MPa at 200 °C for 1 hour to form a cured film of the modified cyanate ester group resin of approximately 0.4 mm in thickness. Similarly, the resin films of the embodiments 12-18 were pressurized to form respective cured resin films. Regarding the resin film adhered with PET film of the comparative example 5, the PET film was peeled off from the adhered resin film, twelve sheets of the manufactured resin film were piled up, and a mirror plane of electrolyzed copper foil was piled onto respective of the upper plane-and the lower plane of the piled resin sheets as a peeling plane. Then, The piled sheets were pressurized with 1.5 MPa at 200 °C for 1 hour to form a cured film of the modified cyanate ester group resin of approximately 0.4 mm in thickness. Similar operation was performed on the resin film adhered with PET film of the comparative example 6. However, the resin film adhered with PET film of the comparative example 6 was a film made of only cyanate ester resin, and the resin film was broken when the peeling operation of the PET film was tried, because the resin film itself was brittle. Therefore, the cured film of the resin could not be manufactured. The above cured resin film was cut out into pieces of 50 mm square, immersed into toluene, and kept at room temperature for 60 minutes. No swelling nor changes in appearance could be observed on the cured resin films of the embodiments 11-18. Surfaces of the separately prepared cured resin films of the embodiments 11-18 were wiped several times with a cloth wetted with toluene or methyl ethyl ketone (MEK), and changes in appearance of the film were observed. However, any changes could not be observed on the surface of the cured resin films of the embodiments 11-18. Similarly, the cured resin film of the comparative example 5 was cut out into pieces of 50 mm square, immersed into toluene, and kept at room temperature for 60 minutes. Swelling of the film was observed, because the cured resin film was made of only polyphenylene ether, and a part of the film was dissolved. When surface of the separately prepared cured resin film was wiped several times with a cloth wetted with toluene, the surface of the film was dissolved, and became sticky. When surface of the separately prepared cured resin film was wiped several times with a cloth wetted with methyl ethyl ketone (MEK), cracks were generated on the surface of the film, and finally the film was broken by generation of holes. In accordance with the above results, the modified cyanate ester group resin film of the present invention was confirmed to be capable of handling by the film alone, and to have preferable solvent-resistance. (Embodiments 19-26, and comparative example 8) Fused silica powder having an average particle size of 5 µm 25g was added as an inorganic filler to 170 g of the modified cyanate ester group resin varnishes manufactured by the compositions indicated in Table 3, further, 200 g of ceramic beads of 1.0 mm in diameter was added to the mixture, and the mixture was kneaded by 1500 rpm for one hour using a beads mill made by AIMEX Co. After the kneading, the beads were filtered off from the varnish, and a filler containing cured resin film adhered with PET having a resin layer(including the filler) of 55-60 µm in thickness was manufactured by the steps of applying the varnish onto a polyethylene terephthalate (PET) film (PUREX A=63, a trade name of a product made by Teijin Co.) of 50 µ m in thickness having a releasing agent thereon using a comma type coater, a kind of bar coater, and dried at 130 °C. Comparative example 8 A modified cyanate ester group curable resin composition varnish (solid content = 30 % by weight) was manufactured by the same method as the embodiment 15 except replacing the p-(α -cumyl)phenol in the embodiment 15 with 2 g of nonyl phenol (made by Mitsui Toatsu Chemical Co.), and adding and dissolving 45 g of tetrabromobisphenol A (Fire Guard FG-2000, a trade name of a product made by Teijin Chemicals Co.), which was reactive with the cyanato group, as a flame retardant. Using the above varnish, a filler containing cured resin film adhered with PET having a resin layer(including the filler) of 55-60 µm in thickness was manufactured by the steps of kneading fused silica powder with the varnish, applying and drying as same as the embodiment 15. The manufactured resin film had no resin cracks nor powder spilling even if the film were cut by a cutter-knife, and was superior in handling properties. The PET film was peeled off from the adhered resin film adhered with PET film of the embodiments 19. Twelve sheets of the manufactured filler containing resin film were piled up, and an electrolyzed copper foil of 18 µm in thickness was piled onto respective of the upper plane and the lower plane of the piled resin sheets. The piled sheets were pressurized with 1.5 MPa at 200 °C for 1 hour to form a cured resin composition of approximately 0.6 mm in thickness having copper foils at both ends. Similarly, the filler containing resin films adhered with PET film of the embodiments 20-26 and the comparative example 8 were pressurized with electrolyzed copper foils of 18 µm in thickness to form respective cured resin composition having copper foils at both ends. Next, triplates-line oscillators having a line length of approximately 200 mm were manufactured from these cured resin composition having copper foils at both ends by chemical etching, and the dielectric constants and the dissapation factors at 1 GHz were manufactured by measuring transmission loss at 1 GHz band using a network analyzer. The glass transition temperature (Tg) and the tensile elastic modulus/ 40 °C were measured in a tensile mode (frequency; 10 Hz, temperature rise; 5 °C/min.) on the filler containing cured resin composition by removing the copper foil by etching, and cutting out test pieces, with a wide band viscosity-elasticity measuring apparatus (DVE, made by Rheology Co.). The manufactured results are indicated in Table 4. Embodiment (comp.) Dielectric properties Glass trans. temp. (Tg) Tensile elasticity Diel. c. D. f. (°C) (MPa) 19 (Emb.11) 2.7 0.0048 174 4700 20 (Emb.12) 2.7 0.0048 170 4690 21 (Emb.13) 2.7 0.0054 176 4790 22 (Emb.14) 2.7 0.0056 172 4800 23 (Emb.15) 2.8 0.0044 178 5410 24 (Emb.16) 2.8 0.0044 180 5400 25 (Emb.17) 2.8 0.0045 188 5590 26 (Emb.18) 2.8 0.0047 184 5550 27 (Emb.19) 3.3 0.0122 172 4240 It was confirmed that the filler containing resin film using the modified cyanate ester group resin film of the present invention had low dielectric properties in Ghz band, particularly, a low dissapation factor because the cyanate ester group compounds were reacted with the specified monovalent phenol group, a preferable glass transition temperature, which can be deemed as an index of heat resistance, and a mechanical strength. (Embodiments 27-29, comparative examples 9, 10) In accordance with the embodiments 27-29, respective of copper foil clad resin films having a resin layer of 60-70 µ m in thickness of the embodiments 27-29 was manufactured by applying respective of the modified cyanate ester group curable resin composition varnishes in the embodiments 11, 13, and 15 onto a roughened surface of the electrolyzed copper foil of 18 µm in thickness using a comma type coater, a kind of coater, and drying. The manufactured resin film had no resin cracks nor powder spilling even if the film were cut by a cutter-knife, and was superior in handling properties. Then, respective of four layer printed circuit board was manufactured by the steps of piling up respective of the resin films having the copper foils of the embodiments 27-29 at the both end planes of an inner circuit board (copper foil thickness for circuit: 18 µm), which was a copper plated epoxy resin laminated board having a glass cloth base material whereon a conductive circuit was formed, so as to contact respective of the resin layers to the inner circuit, and pressurizing the pile to form the four layer circuit board under a condition of 200 °C, 2.5 MPa for 60 minutes. Similarly, using the varnish of the comparative example 8, a copper foil clad resin film having a resin layer of 60-70 µ m in thickness was manufactured by the same method as the embodiments 27-29, and a four layer circuit board was manufactured similarly as the comparative example 9. In accordance with comparative example 10, a four layer printed circuit board was manufactured by the steps of piling up respective of an epoxy resin prepreg (FR-4 grade) having the a glass cloth base material for multilayered circuit board of nominal thickness of 70 µm and a copper foil of 18 µm in thickness was laminated at each of end planes of the copper plated epoxy resin laminated board having a glass cloth base material, which was as same as the board used in the embodiments 27-29, and pressurizing the pile to form the four layer circuit board under a condition of 180 °C, 2.5 MPa for 60 minutes. Moldability (presence of voids and blur), soldering heat resistance, and a copper foil peeling strength of the four layer printed circuit boards manufactured by the embodiments 27-29, and the comparative examples 9 and 10, were evaluated by the following methods. The results are indicated in Table 5. (Evaluating methods of characteristics) Moldability : All the outer layer copper foil of the four layer circuit board were removed by chemical etching, and the filling condition of the resin into the inner circuit(presence of voids and blurs) was observed by eyes. Soldering heat resistance : A four layer board of 50 mm square with the outer layer copper foil was floated onto molten solder at 260 °C, and the time until generating a swell was measured. Copper foil peeling strength : The strength was measured substantially based on the method defined by JIS-C-6481. Flame retardance : All the copper foils on the FR-4 grade substrate of 0.2 mm in thickness were etched, and the resin films having copper foils at both end planes of the embodiments and the comparative examples were pressed for forming tests pieces. The test pieces were evaluated substantially based on a method defined by the UL-94 vertical evaluating method. Embodiment Moldability Soldering heat resistance (sec.) Peeling strengt h (KN/m) Flame retardance UL-94 27 No void, no blur > 180 1.5 Equ.to V-0 1) 28 No void, no blur > 180 1.5 Equ.to V-0 29 No void, no blur > 180 1.5 Equ.to V-0 C-9 No void, no blur 56 1.2 Equ.to V-0 C-10 No void, no blur > 180 1.5 Equ.to V-0 As the Table 5 indicated, it was confirmed that the copper foil clad resin film of the embodiments 27-29 had a desirable moldability as a material of the multilayered circuit board, and the four layer circuit boards using the copper foil clad resin film of the present invention had a desirable soldering heat resistance because the modified cyanate ester group resin was reacted with the specified monovalent phenolic compound, and had the same characteristics as the conventional prepreg for adhesion using a glass cloth as a basic material.

Claims: A modified cyanate ester group curable resin composition essentially comprising : (A) a cyanate ester group compound expressed by chemical formula (1), where, R 1 is and R 2 and R 3 is any one of hydrogen or methyl group, and both can be the same or different from each other, (B) a monovalent phenolic group compound expressed by chemical formula (2), or formula (3), where R 4 and R 5 is any one of hydrogen atom or low alkyl group having 1 to 4 carbon atoms, and both can be the same or different from each other, n is a positive integer of 1 or 2, where, R 6 is any one of ―CH 3 , ―CH 2 CH 3 , (C) a polyphenylene ether resin, (D) a flame retardant not reactive with the cyanate ester group compound, and (E) a metal group reaction catalyst. A modified cyanate ester group curable resin composition as claimed in claim 1, wherein said modified cyanate ester resin comprises; 100 parts by weight of (A) the cyanate ester group compound, and 4 to 30 parts by weight of (B) the monovalent phenolic group compound. A modified cyanate ester group curable resin composition as claimed in claim 1, which essentially comprises a modified cyanate ester resin manufactured by the reaction of A) the cyanate ester group compound with a part of or all of (B) the monovalent phenolic group compound, (C) the polyphenylene ether resin, (D) the flame retardant not reactive with the cyanate ester group compound, and (E) the metal group reaction catalyst. A modified cyanate ester group curable resin composition as claimed in claim 1, wherein said modified cyanate ester group curable resin composition essentially comprises; 4 to 30 parts by weight of (B) the monovalent phenolic group compound, and 5 to 300 parts by weight of (C) the polyphenylene ether resin, to 100 parts of (A) the cyanate ester group compound; 1 to 300 ppm of (E) the metal group reaction catalyst to the cyanate ester group compound of 1; and 5 to 30 parts by weight of (D) the flame retardant not reactive with the cyanate ester group compound to 100 parts by weight of the total of said (A), (B) and (C). A modified cyanate ester group curable resin composition as claimed in claim 1, wherein (A) the cyanate ester group compound is any one of or a mixture of 2, 2-bis(4-cyanato-phenyl) propane and bis(3, 5-dimethyl-4-cyanato-phenyl) methane. A modified cyanate ester group curable resin composition as claimed in claim 1, wherein (B) the monovalent phenolic group compound is any one of p-(α-cumyl)phenol, p-tert-butylphenol, p-tert-amylphenol, and p-tert-octylphenol. A modified cyanate ester group curable resin composition as claimed in claim 1, wherein (C) the polyphenylene ether resin is an alloyed polymer of poly(2, 6-dimethyl-1, 4-phenylene) ether and polystyrene or styrene-butadiene copolymer; and said poly(2, 6-dimethyl-1, 4-phenylene) ether is contained more than 50 % by weight. A modified cyanate ester group curable resin composition as claimed in claim 1, wherein (D) the flame retardant not reactive with the cyanate ester group compound is any one of single kind and mixture of alicyclic flame retardants selected from the group consisting of 1, 2-dibromo-4-(1, 2-dibromoethyl) cyclohexane, tetrabromocyclooctane and hexabromocyclododecane. A modified cyanate ester group curable resin composition as claimed in claim 1, wherein (D) the flame retardant not reactive with the cyanate ester group compound is any one of a triphenylcyanurate bromide group flame retardant expressed by the chemical formula (4), where, each of l, m, and n is an integer of 1 to 5, and the integers can be the same or different from one another. A modified cyanate ester group curable resin composition as claimed in claim 1, wherein (D) the flame retardant not reactive with the cyanate ester group compound is any one of mixtures of a triphenylcyanurate bromide group flame retardant expressed by the chemical formula (4) and two or more kinds of flame retardants not reactive with the cyanate ester group compound. A modified cyanate ester group curable resin composition as claimed in claim 1, wherein (E) the metal group reaction catalyst is any one of single kind and a mixture of two or more kinds selected from the group consisting of 2-ethylhexanoic salts, naphthenic salts, and acetylacetone complexes of manganese, iron, cobalt, nickel, copper and zinc. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 1, which comprises the steps of; dissolving (C) a polyphenylene ether resin into (F) an aromatic hydrocarbon solvent with heating, and reacting (A) a cyanate ester group compound with (B) a monovalent phenolic compound in said solution in the presence of (E) a metallic reaction catalyst to generate mutually dissolving solution of a modified cyanate ester resin and a polyphenylene resin. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 1, which comprises the steps of; dissolving (C) a polyphenylene ether resin into (F) an aromatic hydrocarbon solvent with heating, reacting (A) a cyanate ester group compound with (B) a monovalent phenolic compound in said solution in the presence of (E) a metallic reaction catalyst to generate a mutually dissolving solution of a modified cyanate ester resin and a polyphenylene resin, and suspending the mutually dissolving resins by adding (G) a ketone group solvent to said mutually dissolving solution. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 13, which comprises the step of; dissolving (D) a flame retardant not reactive with cyanate group compound into a reaction solution of (A) a cyanate ester group compound with (B) a monovalent phenolic compound in the presence of (E) a metallic reaction catalyst to generate a mutually dissolving solution of a modified cyanate ester resin and a polyphenylene resin. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 13, which comprises the steps of; dissolving (C) a polyphenylene ether resin into (F) an aromatic hydrocarbon solvent with heating, reacting (A) a cyanate ester group compound with (B) a monovalent phenolic compound in said solution in the presence of (E) a metallic reaction catalyst to generate a mutually dissolving solution of a modified cyanate ester resin and a polyphenylene resin, dissolving (D) a flame retardant not reactive with cyanate group compound into said mutually dissolving solution of a modified cyanate ester resin and a polyphenylene resin, and suspending the mutually dissolving resins by adding (G) a ketone group solvent to said mutually dissolving solution. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 13, which comprises the steps of; reacting (A) a cyanate ester group compound with a part of total mixing amount of (B) a monovalent phenolic compound in the presence of (E) a metallic reaction catalyst to generate a mutually dissolving solution of a modified cyanate ester resin and a polyphenylene resin, suspending the mutually dissolving resins by adding (G) a ketone group solvent to said mutually dissolving solution, and adding and dissolving the residual of the total mixing amount of (B) the monovalent phenolic compound into said suspended mutually dissolving solution. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 13, wherein, after suspending said mutually dissolving solution by adding and stirring (F) a ketone group solvent, (E) a metallic group reaction catalyst is further added into said suspending solution. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 12, wherein 100 parts by weight of (C) a polyphenylene ether resin is dissolved into 150-500 parts by weight of (F) an aromatic hydrocarbon group solvent by heating. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 13, wherein 50-500 parts by weight of (G) a ketone group solvent is used for 100 parts by weight of (F) an aromatic hydrocarbon group solvent, which is used for dissolving (C) said polyphenylene ether resin. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 12 or 13, wherein (F) said aromatic group solvent has a boiling point in the range of 70 - 170 °C. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 12 or 13, wherein (F) said aromatic group solvent is at least any one selected from the group consisting of toluene, xylene, ethylbenzene, iospropylbenezene, and mesitylene. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 13, wherein (G) said ketone group solvent has a boiling point in the range of 50 - 170 °C. A method of manufacturing varnish of the modified cyanate ester group curable resin composition as claimed in claim 13, wherein (G) said ketone group solvent is at least any one selected from the group consisting of acetone, methyl ethyl ketone, 2-pentanone, 3-pentanone, methyl isobutyl ketone, 2-hexanone, cyclopentanone, 2-heptanone, and cyclohexanone. A varnish of the modified cyanate ester group curable resin composition manufactured by said method as claimed in claim 12 or 13. A prepreg manufactured by the steps of; impregnating said varnish of the modified cyanate ester group curable resin composition as claimed in claim 24 into a base material, and drying at a temperature in the range of 80 - 200°C. A modified cyanate ester group curable resin film manufactured by the steps of; applying said varnish of the modified cyanate ester group curable resin composition as claimed in claim 24 onto one plane of supporting material by a flowing method, and heating and drying to remove the solvent to form said film. A metal foil clad modified cyanate ester group curable resin film manufactured by the steps of; applying said varnish of the modified cyanate ester group curable resin composition as claimed in claim 24 onto one plane of said metal foil by a flowing method, and heating and drying to remove the solvent to form said film. A metal foil clad laminated board manufactured by the steps of; piling up at least one of said prepreg as claimed in claim 25, and said film as claimed in claim 27 in a single form or a combined form, respectively, in a manner that one or plurality of said prepreg, said film, or said prepreg and said film, are piled alternately by every piece or every plural pieces to form a piled body, laminating said metal foil onto both end planes or one end plane of said piled body, and pressurizing said piled body laminated with said metal foil with heating to form said metal foil clad laminated board . A printed circuit board manufactured by forming a circuit onto said metal foil clad laminated board as claimed in claim 28. A multilayered circuit board manufactured by the steps of; laminating a metal foil, or said metal foil clad modified cyanate ester group curable resin film as claimed in claim 27, onto an inner layer circuit substrate via said prepreg as claimed in claim 25, or said film as claimed in claim 26, connecting said metal foil with circuits in said inner layer circuit board, and patterning a circuit onto said metal foil.

Inventors: MIZUNO YASUYUKI, NEGISHI HARUMI, SASE SHIGEO, SUGIMURA TAKESHI, MIZUNO, YASUYUKI, NEGISHI, HARUMI, SASE, SHIGEO, SUGIMURA, TAKESHI
Applicants: HITACHI CHEMICAL CO LTD, HITACHI CHEMICAL COMPANY, LTD.
Application year: 1998
Main classification: C08L79
IPC codes: H05K1, C08L71, C08K5, C08L79