Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-04-03
2001-12-11
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C156S330000, C428S365000, C525S489000
Reexamination Certificate
active
06329474
ABSTRACT:
TECHNICAL FIELD
The present invention relates to epoxy resin compositions for printed wiring boards useful for the production of printed wiring boards, and to laminates for printed wiring boards produced with the use of the epoxy resin compositions.
BACKGROUND ART
As electronic instruments have been miniaturized and improved in performance, the density of printed wiring boards used therein has increased due to high multilayering, thinning and decreases in through-hole diameter and in the distance between the through-holes. Printed wiring boards are also used in recent semiconductor packages of plastic pin grid array or plastic ball grid array wherein semiconductor tips are mounted directly on printed wiring boards and sealed with resins. In the course of the production of such semiconductor packages, printed wiring boards experience high temperatures of 175° C. or higher during wire bonding or resin sealing. So printed wiring boards of low strength and low elastic modulus may cause disconnection of bonding wires or bow or twist after resin sealing. To improve the high temperature characteristics at 175° C. or higher, including strength and elastic modulus, printed wiring boards should have a higher Tg (glass transition temperature). Printed wiring boards for semiconductor packages have growing requirement for higher wiring density, and insulation reliability is an important property.
To meet these requirements, development work on new materials for printed wiring boards is proceeding. As disclosed in Japanese Patent Application Unexamined Publication No. 60-155453, as a means for increasing Tg, curing of polyfunctional epoxy resins with dicyandiamide is studied extensively. Unfortunately the epoxy resins cured with dicyandiamide have a high hygroscopicity and hardly satisfy the high insulation reliability necessary for the future printed wiring boards with higher density. Among various insulation troubles, metal migration (electrolytic corrosion) has been found to be a serious trouble. Metal migration is the phenomenon that the metal constructing wiring, circuit pattern or electrodes on or inside insulation materials migrates on or inside the insulation materials by the development of potential difference under the circumstances of high humidity.
To the contrary, printed wiring boards produced by using polyfunctional phenols as curing agents have a low hygroscopicity and a good resistance against electrolytic corrosion. Some polyfunctional phenols, however, discolor the printed wiring boards during heating processes. To prevent the color change due to heating, in Japanese Patent Application Examined Publication No. 62-28168 is proposed a curing agent which contains a high-ortho phenol-formaldehyde resin derived mainly from phenol or bisphenol A. Even this curing agent cannot provide printed wiring boards having a high Tg enough to tolerate high temperatures of 175° C. or higher.
In the circumstances, an object of the present invention is to provide epoxy resin compositions which are useful for the production of printed wiring boards having a low hygroscopicity, a high heat resistance, good high-temperature characteristics, a high resistance against electrolytic corrosion, a high resistance against color change due to heating and a high Tg.
Another object of the present invention is to provide laminates for printed wiring boards, which are produced by using the epoxy resin compositions and have a high heat resistance, good high-temperature characteristics, a high resistance against electrolytic corrosion, a high resistance against color change due to heating and a high Tg.
DISCLOSURE OF INVENTION
The present invention provides an epoxy resin composition for a printed wiring board, comprising (a) an epoxy resin obtained by epoxidizing a condensation product of a phenol with a hydroxybenzaldehyde, (b) a condensation product of bisphenol A with formaldehyde, (c) at least one flame retardant selected from the group consisting of a halogenated bisphenol A epoxy resin, a halogenated bisphenol F epoxy resin, a halogenated bisphenol S epoxy resin, a halogenated phenol novolac epoxy resin, a halogenated cresol novolac epoxy resin, a halogenated bisphenol A novolac epoxy resin, a halogenated bisphenol F novolac epoxy resin, a halogenated alicyclic epoxy resin, a halogenated aliphatic linear epoxy resin, a halogenation product of a glycidyl ester epoxy resin, a halogenation product of a glycidylamine epoxy resin, a halogenation product of a hydantoin epoxy resin, a halogenation product of an isocyanurate epoxy resin, a glycidyl ether of a halogenated dihydric phenol, a glycidyl ether of a halogenated dihydric alcohol, a halogenated bisphenol A, a halogenated bisphenol F, a halogenation product of a polyvinylphenol, a halogenated phenol novolac resin, a halogenated cresol novolac resin, a halogenated alkylphenol novolac resin, a halogenated catechol novolac resin and a halogenated bisphenol F novolac resin, and (d) a curing accelerator comprising at least one imidazole compound.
The present invention further provides a laminate for a printed wiring board produced by impregnating a base material with a resin varnish containing the above epoxy resin composition for printed wiring boards and drying to form prepreg, superposing at least two sheets of the prepreg on each other, with a metal foil superposed on one or both sides of the superposed composite, and heating and pressing the superposed composite.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter the present invention will be described in detail.
The epoxy resin (a) is obtained by epoxidizing a condensation product of a phenol with a hydroxybenzaldehyde. Typical phenols which are suitable for use in the present invention include phenol, cresol and other monohydric phenols having one or more alkyl groups, such as propyl or tert-butyl, with phenol particularly preferred. Typical hydroxybenzaldehydes which are suitable for use in the present invention include salicylaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, vanillin, syringaaldehyde, &bgr;-resorcylaldehyde and protocatechualdehyde, with salicylaldehyde particularly preferred.
The condensation of phenols with hydroxybenzaldehydes may be carried out by any non-limitative methods, desirably by allowing 1 mole of a phenol to react with 0.1 to 3.0 moles, preferably 0.3 to 1.5 moles of a hydroxybenzaldehyde, in the presence of an acid catalyst.
The condensation product is epoxidized with an epoxidizing agent, such as epichlorohydrin, to give the epoxy resin (a).
There is no particular limitation in the kinds of phenols, hydroxybenzaldehydes and epoxidizing agents which are to be used as the raw materials of the epoxy resin (a) nor in the methods of condensation and epoxidation. Preferred epoxy resins are produced by allowing 1 mole of phenol with 0.1 to 3.0 moles of salicylaldehyde in the presence of an acid catalyst, such as hydrochloric acid, at 80 to 250° C. for 1 to 6 hours, and allowing at least 3 equivalent of epichlorohydrin to react with 1 equivalent of the hydroxyl groups of the condensation product, and have a weight average molecular weight of 700 to 5,000, a softening temperature of 40 to 140° C. and an epoxy group equivalent weight of 130 to 280.
According to the present invention, the epoxy resins (a) may be used together with other epoxy resins; for example, bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol S epoxy resins, biphenol epoxy resins, phenol novolac epoxy resins, cresol novolac epoxy resins, bisphenol A novolac epoxy resins, bisphenol F novolac epoxy resins, alicyclic epoxy resins, aliphatic linear epoxy resins, glycidyl ester epoxy resins, glycidyl amine epoxy resins, hydantoin epoxy resins, isocyanurate epoxy resins, glycidyl ethers of dihydric phenols, glycidyl ethers of dihydric alcohols and hydrogenation products thereof. These epoxy resins may be used individually or as a mixture of two or more.
The amount of the epoxy resins other than the epoxy resins (a) is preferably 0 to 200 parts by weight, more preferably 10 to 100 parts by wei
Arata Michitoshi
Fukuda Tomio
Sase Shigeo
Takano Nozomu
Antonelli Terry Stout & Kraus LLP
Hitachi Chemical Company Ltd.
Sellers Robert E. L.
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