Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-08-18
2002-01-29
Moore, Margaret G. (Department: 1712)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S413000, C523S211000
Reexamination Certificate
active
06342309
ABSTRACT:
This invention relates to an epoxy resin composition having satisfactory catalyst latency, storage stability, adhesion to metals and hot strength, and a semiconductor device encapsulated with the cured product thereof.
BACKGROUND OF THE INVENTION
The semiconductor devices in use today are predominantly resin encapsulated diodes, transistors, integrated circuit (IC) chips, large scale integration (LSI) chips, and very large scale integration (VLSI) chips. Resin encapsulation is usually carried out with epoxy resin compositions because epoxy resins offer superior properties (e.g., moldability, adhesion, electrical characteristics, mechanical characteristics, and moisture resistance), compared with other thermosetting resins.
For cost reduction purposes, attempts to improve the package manufacturing cycle have been made in the semiconductor art. The epoxy resin compositions are required to be fast-curing. However, increasing the amount of catalyst to impart fast-curing tends to cause gold wire flow and short-filling during molding because of thickening and rapid curing. The increased amount of catalyst has another problem that the epoxy resin composition loses storage stability.
Microencapsulation is known in the art. JP-A 3-182520 discloses the microencapsulation of a curing agent in an epoxy resin composition. Conventional microcapsules, however, are difficult to provide a significantly increased reaction rate because the capsule shell is thick and the catalyst concentration is low. If the reaction rate is increased to improve the productivity, the composition is not so improved in storage stability. The microencapsulation technique has not reached the practical level.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel and improved epoxy resin composition comprising catalyzed microcapsules which are dispersible in resins and highly reactive so that the composition has satisfactory catalyst latency and storage stability as well as cured strength and adhesion, and a semiconductor device encapsulated with the cured product thereof.
The invention pertains to an epoxy resin composition comprising an epoxy resin, a curing agent, an inorganic filler, and a curing catalyst. We have found that by microencapsulating the curing catalyst, specifically forming microcapsules containing an imidazole compound or organic phosphorus compound as the curing catalyst and having a mean particle size of 0.5 to 50 &mgr;m such that the quantity of the catalyst leached out from the microcapsules in o-cresol at 30° C. for 15 minutes may be at least 70% by weight of the entire catalyst quantity, there is obtained an epoxy resin composition which finds a good compromise between curability and storage stability. The composition has satisfactory catalyst latency and storage stability while it is effectively curable upon molding and improved in cured strength and adhesion. The composition is suited for the encapsulation of semiconductor packages.
Accordingly, the invention provides an epoxy resin composition comprising (A) an epoxy resin, (B) a curing agent, (C) an inorganic filler, and (D) catalyzed microcapsules containing at least one of imidazole compounds and organic phosphorus compounds and having a mean particle size of 0.5 to 50 &mgr;m, the quantity of the catalyst leached out from the microcapsules in o-cresol at 30° C. for 15 minutes being at least 70% by weight of the entire catalyst quantity in the microcapsules. A semiconductor device encapsulated with the epoxy resin composition in the cured state is also contemplated herein.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The epoxy resin (A) used in the epoxy resin composition of the invention is selected from a variety of epoxy resins including novolac-type epoxy resins such as phenolic novolac epoxy resins and cresol novolac epoxy resins, aralkyl type epoxy resins, biphenyl skeleton-containing aralkyl type epoxy resins, biphenyl type epoxy resins, heterocyclic epoxy resins, naphthalene ring-containing epoxy resins, bisphenol type epoxy resins such as bisphenol A epoxy resins and bisphenol F epoxy resins, and stilbene type epoxy resins, alone or in admixture of two or more.
Especially for the purpose of reducing the warpage of packages, polyfunctional epoxy resins are recommended. The preferred polyfunctional epoxy resins are of the following structure.
In the formula, R is hydrogen or a monovalent hydrocarbon group of 1 to 6 carbon atoms, as typified by alkyl groups including methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl and hexyl. R′ is hydrogen, methyl or ethyl, and preferably hydrogen. The letter n is an integer of 0 to 6. Of the polyfunctional epoxy resins, triphenolalkane type epoxy resins such as triphenolmethane type epoxy resins and triphenolpropane type epoxy resins are preferred.
It is also acceptable to use the polyfunctional epoxy resins in combination with the aforementioned epoxy resins.
The epoxy resins may be either liquid or solid and should preferably have a softening point of 50 to 120° C. and an epoxy equivalent of 100 to 400. Epoxy resins with a softening point of lower than 50° C. tend to form burrs and voids when molded and would result in cured products having a lower glass transition temperature whereas epoxy resins with a softening point of high than 120° C. would be too viscous to mold.
When the epoxy resins are used for the encapsulation of semiconductor devices, it is preferred that the content of hydrolyzable chlorine be up to 1,000 ppm, more preferably up to 500 ppm, and the contents of sodium and potassium be each up to 10 ppm. If semiconductor devices are encapsulated with compositions containing an epoxy resin with more than 1,000 ppm of hydrolyzable chlorine or more than 10 ppm of sodium or potassium, the encapsulated devices would experience deterioration of moisture resistance during long-term storage under hot humid conditions.
The curing agent (B) for the epoxy resins is preferably a phenolic resin having at least two phenolic hydroxyl groups per molecule. Exemplary curing agents include phenolic resins, for example, novolac-type phenolic resins such as phenolic novolac resins and cresol novolac resins; p-xylylene-modified novolac resins, m-xylylene-modified novolac resins, o-xylylene-modified novolac resins, bisphenol type resins such as bisphenol A type resins and bisphenol F type resins, biphenyl type phenolic resins, resole type phenolic resins, phenolaralkyl resins, and triphenolalkane resins and polymerized products thereof; and naphthalene ring-bearing phenolic resins and dicyclopentadiene-modified phenolic resins.
Of these phenolic resins, phenolic novolac resins and triphenolalkane resins and polymers thereof are preferable from the consideration of heat resistance, package warpage and moldability.
Also amine curing agents and acid anhydride curing agents may be used alone or in combination with the phenolic resins.
The phenolic resin curing agents should preferably have a softening point of 60 to 150° C., especially 70 to 130° C. and a hydroxyl equivalent of 90 to 250. When the phenolic resins are used for the encapsulation of semiconductor devices, it is preferred that the contents of sodium and potassium be each up to 10 ppm. If semiconductor devices are encapsulated with compositions containing a phenolic resin with more than 10 ppm of sodium or potassium, the encapsulated devices would experience accelerated deterioration of moisture resistance during long-term storage under hot humid conditions.
The curing agent may be blended in any desired amount insofar as the epoxy resin can be effectively cured. When a phenolic resin is used as the curing agent, it is preferably blended in such amounts that the molar ratio of phenolic hydroxyl groups in the phenolic resin to epoxy groups in the epoxy resin may range from 0.5 to 1.5, especially from 0.8 to 1.2.
The inorganic filler (C) is selected from fillers commonly used in epoxy resin compositions. The inorganic filler is blended in order to reduce the coefficient of expansion of encapsulants for red
Aoki Takayuki
Arai Kazuhiro
Ino Shigeki
Kimura Yasuo
Mizushima Hidenori
Feely Michael J
Moore Margaret G.
Shin-Etsu Chemical Co. , Ltd.
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