Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-08-18
2002-12-31
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C257S787000, C257S789000, C257S793000, C257S795000, C428S417000, C428S418000, C523S211000, C523S434000, C523S440000
Reexamination Certificate
active
06500564
ABSTRACT:
This invention relates to a semiconductor encapsulating epoxy resin composition having satisfactory cure, catalyst latency, storage stability and adhesion 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.
On the other hand, a variety of shapes have been developed for the semiconductor package. When packages of advanced design are encapsulated with conventional epoxy resin compositions, the packages warp so that they cannot be mounted on boards. This is a serious problem with thin packages such as thin small outline packages (TSOP) and single-side molded packages such as ball grid arrays (BGA).
For reducing the warpage of packages, it is commonly employed to increase the glass transition temperature (Tg) of resins above 190° C. and to minimize the coefficient of linear expansion. The coefficient of linear expansion is reduced by increasing the amount of filler, which increases the viscosity of the composition, which in turn, hampers molding operation and causes bending of gold wires and deformation of die pads. The high glass transition temperature requires the use of resins having a high degree of polymerization, which also increases the viscosity of the composition, hampering molding operation.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel and improved semiconductor encapsulating epoxy resin composition which minimizes the warpage of packages and has satisfactory cure, catalyst latency, storage stability 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 phenolic resin, an inorganic filler, and a curing catalyst. We have found that by using a polyfunctional epoxy resin as the epoxy resin and microencapsulating the curing catalyst, there is obtained an epoxy resin composition which is suited for the encapsulation of packages, for example, thin packages such as TSOP and single-side molded packages such as BGA. Quite surprisingly, the warpage of the packages is minimized and the composition is endowed with fast-curing, catalyst latency, and storage stability and improved in cured strength and adhesion.
Accordingly, the invention provides an epoxy resin composition for semiconductor encapsulation comprising (A) a polyfunctional epoxy resin, (B) a phenolic resin, (C) an inorganic filler, and (D) curing catalyst-containing microcapsules having a mean particle size of 0.5 to 50 &mgr;m. A semiconductor device encapsulated with the epoxy resin composition in the cured state is also contemplated herein.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the epoxy resin composition of the invention, a polyfunctional epoxy resin is used as the epoxy resin (A). Preferably the polyfunctional epoxy resin is 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.
In addition to the polyfunctional epoxy resin, another epoxy resin may be used herein. Illustrative examples of suitable other epoxy resins include 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.
The polyfunctional epoxy resin should preferably account for 50 to 100% by weight, and more preferably 70 to 100% by weight of the entire epoxy resins.
The epoxy resins 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 Tg 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 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 such as triphenolmethane, triphenolethane and triphenolpropane resins and polymers thereof are preferable from the consideration of heat resistance, package warpage and moldability. These preferred phenolic resins may be combined with any of the above-described phenolic resins insofar as the desired effect is not impeded.
Amine curing agents and acid anhydride curing agents may also be used 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. Preferably the phenolic resin curing agent is 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.
Aoki Takayuki
Arai Kazuhiro
Ino Shigeki
Kimura Yasuo
Mizushima Hidenori
Aylward D.
Dawson Robert
Shin-Etsu Chemical Co. , Ltd.
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