Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
1999-01-28
2001-04-10
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C525S489000, C156S330000
Reexamination Certificate
active
06214468
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a flame retardant epoxy resin composition for printed boards for use in a metal foil clad lamination board or a multilayer interconnection board.
DESCRIPTION OF RELATED ART
With an increasing need for further compactness and improved performance of electronics devices, developments of laminates for use in printed circuit boards are progressing aiming at a greater number of lamination and a thinner sheet of laminates, minimization of hole gaps by reducing throughhole diameters, and inter-insulation distances by reducing line widths. On the other hand, packaging techniques for packaging very thin low thermal expansion parts which include a flip-chip packaging to mount bare chips directly on the laminates and Thin Small Outline Package (TSOP) are increasing rapidly, thereby demanding a substantially improved and excellent package level reliability than ever before. Therefore, further improvements in adhesiveness with metal foils and glass, insulation reliability to be ensured with substantially reduced inter-insulation distances, as well as in the heat resistance are becoming important characteristics to be addressed.
Epoxy resins have been widely used as insulation materials for printed circuit boards. As a curing agent therefor, dicyandiamide is normally used which has an excellent adhesion with the metal foil and a good pot life stability.
However, dicyandiamide has such disadvantages that because it is not compatible with epoxy resin, dicyandiamide is likely to precipitate when used in a prepreg, and in addition that a printed circuit board prepared using this curing agent has a low softening temperature, thereby easily causing smear or resin contamination of interconnection circuit copper during drilling, and also that its long-term heat resistance is inferior. Still further, because its cured substance has a high moisture absorption rate, it is difficult for this material to be used as a substrate for packaging which must avoid moisture absorption. In addition, this high moisture absorption rate easily causes the occurrence of metal migration, thereby introducing a major cause to deteriorate the insulation reliability in fine patterned wiring.
This metal migration is a phenomenon in which metals that constitute insulation materials, interconnections or circuit patterns within insulation materials are caused to migrate and precipitate on the insulation materials or inside thereof due to a potential difference under a high moisture environment.
As good migration resistant resins, there are known bismaleimide-triazine resin and polyimide resin. These resins, however, have such disadvantages that their curing contraction is large, adhesiveness is low, and they are too hard and brittle and so on. JP No.63-54300 discloses a method of adding a triazine compound as a migration inhibitor to the epoxy resin. However, it is difficult for the triazine compound to be dispersed uniformly, thereby causing a large variation in resultant properties.
On the other hand, as a means to solve these problems associated with the prior art, JP No. 63-36621 discloses a composition of a phenol curing group. A cured compound using the phenol curing group, in particular, using a high orthophenol-formaldehyde resin selected therefrom has an excellent discoloring property, and exhibits a high glass transition temperature (hereinafter referred to as Tg). However, any cured resin that has a high Tg tends to become hard and brittle, thereby easily lowering adhesion with metal foils, and causing a crack (peel-off) in the boundary between glass fiber and the resin during drilling and molding. This crack or peel allows permeation of plating substances and of water contents absorbed, thereby introducing a large factor for a substantial decrease in the insulation property.
The present invention is contemplated to solve the aforementioned problems associated with the prior art, and provide a flame retardant epoxy resin composition that has an improved heat resistance, adhesion and insulation reliability suitable for use in a printed circuit board and a multilayered interconnection board, as well as to provide a prepreg and a metal clad laminate using the same.
Namely, the present invention discloses a flame retardant epoxy resin composition suitable for printed circuit boards, comprising:
(a) an epoxy resin containing a glicidylether compound which is a condensation polymer (addition condensate) between bisphenol A or bisphenol F and formaldehyde;
(b) a condensation polymer (addition condensate) between bisphenol A and formaldehyde;
(c) a halogenated bisphenol A; and
(d) a hardening accelerator, wherein
a quantity of the halogenated bisphenol A contained is less than 45 weight percent inclusive relative to that of a whole solid resin weight.
Another aspect of the invention discloses a flame retardant epoxy resin composition suitable for printed circuit boards, wherein the halogenated bisphenol A is preferably a tetrabromo-2, 2-bis (4-hydroxyphenyl)propane.
Still another aspect of the invention discloses a flame retardant epoxy resin composition for printed circuit boards, wherein an equivalence weight ratio A:B between epoxy group's equivalence weight (A) of the epoxy resin and hydroxyl group's equivalence weight (B) of the halogenate bisphenol A is preferably that A:B=1:0.20 to 0.75.
Still further aspect of the invention discloses a flame retardant epoxy resin composition for printed circuit boards, wherein the hardening accelerator is preferably a compound obtained by masking an imino group of imidazole.
Then, the flame retardant epoxy resin composition according to the invention is used as a vanish which is impregnated into a base material and dried to provide for a prepreg. Further, according to the invention, a metal foil clad laminate is provided using more than one sheet of the aforementioned prepreg, and by cladding a metal foil on one surface or both surfaces thereof, laminating the same, then heating under pressure. This metal foil clad laminate can be fabricated into a printed circuit board by processing the metal foil into a circuit pattern. Further, the aforementioned prepreg can be used as inter-layer insulation between respective internal laminations, or between the internal lamination and the metal foil as well.
DETAILED DESCRIPTION OF THE INVENTION
The epoxy resin of (a) described above contains as its essential element the glicidylether compound obtained as a condensation product of bisphenol A or bisphenol F with formaldehyde in an amount of 1 to 100 weight part, wherein there is no limit for the molecular weight of the epoxy resin. As for the other epoxy resin components to be used other than the preceding epoxy resin, any type of epoxy resins can be used without limitation. The epoxy resin according to the invention using the glicidylether compound that is the condensate product of bisphenol A or bisphenol F with formaldehyde features a faster curing speed, an improved crosslinking density and a higher Tg compared with those of a phenol novolac type epoxy resin or cresol novolac type epoxy resin which is used alone.
Another type of epoxy resin that can be used together with the epoxy resin according to the invention includes a bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, salicylaldehyde novolac type epoxy resin, alicyclic epoxy resin, glicydyl esther type epoxy resin, glicydylamine type epoxy resin, hydantoin type epoxy resin, isocyanate type epoxy resin, aliphatic chain type epoxy resin, and their haloganates and hydrites, and wherein a plurality types thereof can be used in combination as well. As for a method of mixing these epoxy resins and a temperature therefor, there is no limitation.
As for the molecular weight of the polymer condensate of bisphenol A and formaldehyde of (b), there is no particular limitation, and a bisphenol A monomer a be contained as well. When a conventional phenol resin is used as
Arata Michitoshi
Murai Hikari
Takano Nozomu
Takeda Yoshiyuki
Aylward D.
Dawson Robert
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Hitachi Chemical Company Ltd.
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