Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1997-12-19
2001-01-30
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of metal
C523S457000
Reexamination Certificate
active
06180250
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an epoxy resin composition for printed circuit boards, and prepreg and a metal laminated board using the same.
BACKGROUND OF THE INVENTION
With the progress in compact design and performance improvement in the field of electronic equipment production, an increasingly high density design has come to be required in the design of printed circuit boards used in the electronic equipment as exemplified in the increase in the number of layers of the printed circuit board, the reduction in the thickness of the board, and the reduction in the diameters and the spacing of the through holes. According to a more recent proposal, semiconductor chips are directly mounted on a printed circuit board, and the entire assembly is sealed in a resin package. Semiconductor packages such as plastic pin grid arrays and plastic ball grid arrays often consist of printed circuit boards. A printed circuit, when applied to a semiconductor package, may be subjected to temperatures exceeding 175° C. for wire bonding and resin sealing during the manufacturing process. In such a case, if the mechanical strength or the resiliency of the printed circuit board is insufficient, it could lead to various problems such as poor connection of the bonding wire, and warping and twisting of the circuit board following the sealing process. To achieve favorable material properties such as hardness and resiliency at high temperatures in excess 175° C., Tg (the glass transition temperature) must be raised to a level which has not been hitherto possible. Also, because the printed circuit board for a semiconductor package requires an extremely high density wiring pattern, the reliability in ensuring electric insulation is important for the material of the printed circuit board.
To meet such requirements, there have been proposals to raise Tg (the glass transition temperature) of epoxy resin for printed circuit boards. For instance, it was proposed to cure multi-functional epoxy resin by using dicyandiamide in Japanese patent laid open publication (kokai) No. 60-155453). However, the epoxy resin which is cured by using dicyandiamide tends to absorb moisture, and is therefore known to be inadequate for ensuring the level of electric insulation capability which can meet the demand for insulating printed circuit boards of high density design. In particular, migration of the material of the metal, which forms wiring, circuit patterns and terminals in or on the printed circuit board, on or inside the insulating material under the influence of high temperatures and voltage differences poses a serious problem.
On the other hand, the printed circuit board obtained by curing epoxy resin by using multi-functional phenol resin has a significantly loss tendency to absorb moisture, and therefore demonstrates a better ability to avoid metal migration. However, a printed circuit board made by using multi-functional phenol may fade in color during the heating process depending on the kind of the phenol used. In Japanese patent publication (kokoku) No. 62-28168, it was proposed to use material mainly consisting of phenol or bisphenol A mixed with high orthophenol-formaldehyde resin to avoid the fading of the printed circuit board, but Tg which allows the printed circuit board to withstand temperatures in excess of 175° C. cannot be attained.
Also, when multi-functional epoxy resin is cured by multi-functional phenol, Tg may be raised to a sufficient level, but the cured resin becomes so rigid and inflexible that the adhesion to the metallic foil may become poor, and small cracks may be produced when through holes are drilled in the printed circuit board. Such small cracks are known to cause metal migration, and are highly detrimental to the reliable insulation of the printed circuit board.
BRIEF SUMMARY OF THE INVENTION
In view of such problems of the prior art, a primary object of the present invention is to provide an epoxy resin composition for printed circuit boards which demonstrates little tendency to absorb moisture, high heat-resistance, favorable high temperature properties, resistance to metal migration, favorable anti-fade property at high temperatures, high Tg, high electric insulating performance and resistance against peeling of the copper foil when formed into a printed circuit board.
A second object of the present invention is to provide prepreg having favorable properties by being formed from such a composition.
A third object of the present invention is to provide a metal laminated board suitable for use as a printed circuit board which has favorable properties by being formed from such a composition.
According to the present invention, such an object can be accomplished by providing an epoxy resin composition for printed circuit boards, comprising: (a) epoxy resin obtained by glycidyl etherifying a condensation product of a phenol and hydroxybenzaldehyde; (b) a condensation product of bisphenol A and formaldehyde; (c) a flame retardant; (d) a curing agent; (e) one or both of a phenol antioxidant and an organic sulfur compound antioxidant; and (f) a urea derivative.
The present invention further provides epoxy resin prepreg for printed circuit boards obtained by impregnating a base member with a varnish of the above mentioned epoxy resin composition for printed circuit boards, and a metal laminated board obtained by laminating metal foil with the above mentioned epoxy resin prepreg.
The epoxy resin of (a) may be prepared by using a condensation product of monohydric phenol having such alkyl groups as propyl group and tert-butyl group, such as phenol and creosol, and hydroxybenzaldehyde such as salicylaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, vanillin, syringaldehyde, &bgr;-resorcylaldehyde, and protocatechualdehyde in the presence of catalytic acid, as a base material, and glycidyl etherifying it by using epichlorohydrin or the like. However, the kinds of phenol and hydroxybenzaldehyde are not limited to those listed above, and the methods of condensation and glycidyl etherification in no way limit the present invention. According to the present invention, epoxy resins other than those listed in (a) may be used in combination. Such epoxy resins may include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenol type epoxy resin, phenol novolac type epoxy resin, creosol novolac type epoxy resin, bisphenol A novolac type epoxy resin, bisphenol F novolac type epoxy resin, alicyclic epoxy resin, aliphatic chain epoxy resin, glycidyl ester type epoxy resin, glycidyl amine type epoxy resin, hydantoin type epoxy resin, and isocyanurate type epoxy resin. Also, glycidyl compounds of bifunctional phenols, glycidyl esters of bifunctional alcohols, hydrogen added products of these compounds, and halides of these compounds may be used. These compounds can be freely used without any reservation, and any number of them can be used in combination.
The molecular weight of the condensation product of bisphenol A type epoxy resin and formaldehyde of (b) may be freely selected, and the product may contain bisphenol A monomer. It is also possible to use curing agents other than the condensation product of bisphenol A type epoxy resin and formaldehyde in combination. Such curing agents may include phenols such as bisphenol F, polyvinylphenol or phenol, creosol, alkylphenol, catecohl, and novolac resins such as bisphenol F. The molecular weights of these compounds can also be freely selected, and any number of them may be used in combination. The equivalent ratio of the phenol hydroxyl group to the epoxy group should be preferably in the range of 0.5 to 1.5. If the equivalent ratio is less than 0.5, the epoxy group would be in excess. If the equivalent ratio is more than 1.5, the phenol hydroxyl group would be in excess. Curing of the resin would be inadequate in either case. More preferably, the equivalent ratio should be in the range of 0.8 to 1.2.
The flame retardant of (c) can be selected from any compounds that are known as flame retardant
Arata Michitoshi
Fukuda Tomio
Sase Shigeo
Takano Nozomu
Aylward D.
Dawson Robert
Dickstein , Shapiro, Morin & Oshinsky, LLP
Hitachi Chemical Co. Ltd.
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