Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-03-24
2001-09-18
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S210000, C524S406000, C524S414000, C524S432000
Reexamination Certificate
active
06291556
ABSTRACT:
This invention relates to an epoxy resin composition for semiconductor encapsulation which cures into a product having flame retardance and moisture-proof reliability. It also relates to a semiconductor device encapsulated with a cured product of the composition.
BACKGROUND OF THE INVENTION
The current mainstream in the semiconductor industry resides in diodes, transistors, ICs, LSIs and VLSIs of the resin encapsulation type. Epoxy resins have superior moldability, adhesion, electrical properties, mechanical properties, and moisture resistance to other thermosetting resins. It is thus a common practice to encapsulate semiconductor devices with epoxy resin compositions. Semiconductor devices are now used in every area of the modern society, for example, in electric appliances and computers. As a guard against accidental fire, the semiconductor encapsulating materials are required to be flame retardant.
Halogenated epoxy resins combined with antimony trioxide are often blended in epoxy resin compositions in order to enhance flame retardance. This combination of a halogenated epoxy resin with antimony trioxide has great radical-trapping and air-shielding effects in the vapor phase, thus conferring a high fire-retarding effect. However, halogenated epoxy resins generate noxious gases during combustion, and antimony trioxide has powder toxicity. Given their negative impact on human health and the environment, it is desirable to entirely exclude these fire retardants from resin compositions.
In view of the above demand, studies have been conducted on the use of hydroxides such as Al(OH)
3
and Mg(OH)
2
or phosphorus-containing fire retardants in place of halogenated epoxy resins and antimony trioxide. Unfortunately, because of various problems associated with the use of these alternative compounds, such as inferior curability of the resin composition during molding and poor moisture resistance in the cured product, they are not yet ready for practical application.
Of the phosphorus-containing fire retardants, red phosphorus is effective for imparting a very high flame retardance to the composition since it forms a phosphoric acid compound during combustion, which bonds with a char layer to form a flame retardant film. However, red phosphorus needs careful handling because of inferior compound stability and an ignition danger upon impact. Additionally, red phosphorus has a serious drawback that if it is added to semiconductor encapsulating epoxy resin compositions, it gradually forms a phosphoric acid compound which can corrode aluminum wiring in semiconductor devices, resulting in a loss of reliability. Red phosphorus is thus inapplicable to semiconductor encapsulating epoxy resin compositions.
SUMMARY OF THE INVENTION
An object of the invention is to provide an epoxy resin composition for semiconductor encapsulation which is free of harmful halogenated epoxy resins and antimony oxide, is effectively moldable and cures into a product having a very high flame retardance and moisture-proof reliability. Another object is to provide a semiconductor device encapsulated with a cured product of the composition.
The invention provides a semiconductor encapsulating epoxy resin composition comprising (A) an epoxy resin, (B) a phenolic resin curing agent, (C) a first flame retardant in the form of microcapsules comprising a red phosphorus-base core covered with a thermoplastic resin and/or thermosetting resin, (D) a second flame retardant in the form of a molybdenum compound, and (E) an inorganic filler. This composition or its cured product has good moldability, moisture-proof reliability, and high flame retardance despite the absence of halogenated epoxy resins and antimony oxide.
DETAILED DESCRIPTION OF THE INVENTION
Component (A) is an epoxy resin which is not critical as long as it has at least two epoxy groups per molecule. Illustrative examples of suitable epoxy resins include novolac-type epoxy resins such as phenolic novolac epoxy resins and cresol novolac epoxy resins, triphenolalkane epoxy resins, aralkyl epoxy resins, biphenyl skeleton-containing aralkyl epoxy resins, biphenyl epoxy resins, heterocyclic epoxy resins, naphthalene ring-containing epoxy resins, bisphenol-type epoxy resins such as bisphenol A epoxy compounds and bisphenol F epoxy compounds, and stilbene epoxy resins. Any one or combination of two or more of these epoxy resins may be employed. Halogenated epoxy resins are excluded.
No particular limit is imposed on the phenolic resin serving as curing agent (B) so long as it has at least two phenolic hydroxy groups in a molecule in the invention. Illustrative examples of typical phenolic resin curing agents include novolac-type phenolic resins such as phenolic novolac resins and cresol novolac resins, naphthalene ring-containing phenolic resins, triphenolalkane phenolic resins, phenolaralkyl phenolic resins, aralkyl phenolic resins, biphenyl skeleton-containing aralkyl phenolic resins, biphenyl phenolic resins, alicyclic phenolic resins, heterocyclic phenolic resins, and bisphenol-type phenolic resins such as bisphenol A and bisphenol F. Any one or combination of two or more of these phenolic resins may be employed.
The relative proportions of the epoxy resin (A) and the phenolic resin curing agent (B) used in the epoxy resin compositions are not subject to any particular limits, although it is preferred that the amount of phenolic hydroxyl groups in the curing agent (B) be from 0.5 to 1.5 moles, and especially 0.8 to 1.2 moles, per mole of epoxy groups in the epoxy resin (A).
The semiconductor encapsulating epoxy resin compositions of the invention do not contain conventional flame retardants such as antimony trioxide and brominated or otherwise halogenated epoxy resins. Instead, the inventive compositions use as the flame retardant (C) microcapsules comprising a red phosphorus-base core coated with a thermoplastic resin and/or thermosetting resin and (D) a molybdenum compound, typically zinc molybdate, and especially zinc molybdate supported on an inorganic carrier.
The core of the microcapsules as component (C) is made of a material based on red phosphorus and having optional processing aids added thereto. It is not necessary to add other ingredients, that is, the core material consisting of red phosphorus is acceptable. The core is coated with a resin which may be either thermoplastic or thermosetting. Suitable examples include poly(meth)acrylic acid ester resins such as poly(methyl methacrylate) and poly(methyl acrylate), polystyrene, polybutadiene, methyl methacrylate-butadiene-styrene copolymers, silicone resin, epoxy resins, and phenolic resins.
In component (C), the cores based on red phosphorus are coated with a thermoplastic resin and/or thermosetting resin by a conventional method, obtaining microcapsules. Microencapsulation has several advantages. Although red phosphorus can be decomposed into a phosphoric acid compound, the microcapsules prevent the phosphoric acid compound from directly corroding aluminum wiring. Only when the resin covering the core material is thermally decomposed, the phosphoric acid compound can bond with a char layer to form a flame retardant film. Moreover, microencapsulation of the core material not only improves the dispersion thereof in the epoxy resin (A) and the phenolic resin curing agent (B) for enhancing flame retardance, but also reduces the ignition upon impact and thus ensures ease of handling.
In the microcapsules as component (C), the content of red phosphorus as the core is preferably 60 to 99.5%, and especially 80 to 99% by weight. The microcapsule particles preferably have a mean particle size of about 0.1 to 100 &mgr;m, more preferably about 0.2 to 40 &mgr;m, especially about 0.5 to 20&mgr;m from the viewpoint of flame retardancy, dispersibility and workability (low viscosity of the composition). Such microencapsulated red phosphorus is commercially available under the trade name of Nova-Excel series such as Nova-Excel 140 from Rin Kagaku Kogyo K.K.
Component (C) is preferably blended in amounts of 0.5 to 3 parts
Aoki Takayuki
Asano Eiichi
Ino Shigeki
Osada Shoichi
Shiobara Toshio
Birch & Stewart Kolasch & Birch, LLP
Cain Edward J.
Lee Katarzyna W.
Shin-Etsu Chemical Co. , Ltd.
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