Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2003-02-05
2004-08-31
Buttner, David J. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C523S452000, C523S458000, C524S095000, C524S096000, C524S115000
Reexamination Certificate
active
06783859
ABSTRACT:
This invention relates to a flame retardant epoxy resin composition for semiconductor encapsulation which is effectively moldable and cures into a product having flame retardance and moisture-proof reliability despite the absence of bromides (e.g., brominated epoxy resins) and antimony compounds (e.g., antimony trioxide). It also relates to a semiconductor device encapsulated with a cured product of the composition.
BACKGROUND OF THE INVENTION
The current mainstream of semiconductor devices 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 devices are required to be flame retardant.
In semiconductor encapsulating epoxy resin compositions, halogenated epoxy resins combined with antimony trioxide (Sb
2
O
3
) are often included 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, the 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 based fire retardants such as red phosphorus and phosphates in place of halogenated epoxy resins and antimony trioxide. Unfortunately, various problems arise from the use of these alternative compounds. The hydroxides such as Al(OH)
3
and Mg(OH)
2
have less flame retardant effects and must be added in larger amounts in order that epoxy resin compositions be flame retardant. Then the viscosity of these compositions increases to a deleterious level to molding, causing molding defects such as voids and wire flow. On the other hand, the phosphorus-containing fire retardants such as red phosphorus and phosphates added to epoxy resin compositions can be hydrolyzed to generate phosphoric acid when the semiconductor devices are exposed to hot humid conditions. The phosphoric acid generated causes aluminum conductors to be corroded, detracting from reliability.
To solve these problems, Japanese Patent No. 2,843,244 proposes an epoxy resin composition using a flame retardant having red phosphorus coated with a surface layer of Si
x
O
y
although it still lacks moisture-proof reliability. JP-A 10-259292 discloses an epoxy resin composition in which a cyclic phosphazene compound is used in an amount to give 0.2-3.0% by weight of phosphorus atoms based on the total weight of other constituents excluding the filler. To provide flame retardance, a substantial amount of the cyclic phosphazene compound must be added to the epoxy resin composition, which can cause ineffective cure and a lowering of electrical resistance in a high-temperature environment.
SUMMARY OF THE INVENTION
An object of the invention is to provide a flame retardant epoxy resin composition for semiconductor encapsulation which is effectively moldable and cures into a product having improved flame retardance and moisture-proof reliability despite the absence of bromides (e.g., brominated epoxy resins) and antimony compounds (e.g., antimony trioxide). Another object is to provide a semiconductor device encapsulated with the composition in the cured state.
We have found that a semiconductor encapsulating, flame retardant epoxy resin composition comprising (A) an epoxy resin, (B) a curing agent, (C) an inorganic filler, (D) a molybdenum ingredient having zinc molybdate supported on an inorganic filler, (E) a first phosphazene compound of the average compositional formula (1), and (F) a second phosphazene compound of the average compositional formula (2), shown below, as essential components, and substantially free of bromides and antimony compounds is effectively moldable and cures into a product having improved flame retardance and moisture-proof reliability. A semiconductor device encapsulated with the epoxy resin composition in the cured state is improved in flame retardance and moisture-proof reliability.
Accordingly, the present invention provides a semiconductor encapsulating, flame retardant epoxy resin composition comprising as essential components, (A) an epoxy resin, (B) a curing agent, (C) an inorganic filler, (D) a molybdenum ingredient having zinc molybdate supported on an inorganic filler, (E) a first phosphazene compound having the average compositional formula (1), and (F) a second phosphazene compound having the average compositional formula (2), the epoxy resin composition being substantially free of bromides and antimony compounds.
Herein X is a single bond or a group selected from among CH
2
, C(CH
3
)
2
, SO
2
, S, O, and O(CO)O, subscripts d, e and n are numbers satisfying 0≦d≦0.25n, 0≦e<2n, 2d+e=2n, and 3≦n≦1000.
Herein Y is OH, SH or NH
2
, R
1
is selected from among alkyl and alkoxy groups having 1 to 4 carbon atoms, NH
2
, NR
2
R
3
and SR
2
, each of R
2
and R
3
is hydrogen or an alkyl group having 1 to 4 carbon atoms, and n is a number satisfying 3≦n≦1000.
Also contemplated herein is a semiconductor device encapsulated with a cured product of the epoxy resin composition.
As stated above, the epoxy resin composition of the invention is substantially free of bromides and antimony compounds. Although brominated epoxy resins and antimony trioxide are generally included in conventional epoxy resin compositions in order to impart flame retardance thereto, the epoxy resin composition of the invention clears the flame retardant specifications, UL-94, V-0 without resorting to brominated epoxy resins and antimony trioxide.
In the prior art, studies were conducted on the use of hydroxides such as Al(OH)
3
and Mg(OH)
2
or phosphorus-based fire retardants such as red phosphorus and phosphates in place of the brominated epoxy resins and antimony trioxide. Unfortunately, these known alternative flame retardants have the common drawback that they are less resistant to water, especially at elevated temperatures, so that they are dissolved and decomposed to increase impurity ions in the extracting water. As a consequence, if semiconductor devices encapsulated with conventional flame retarded epoxy resin compositions substantially free of bromides and antimony compounds are kept in a hot humid environment for a long period of time, the aluminum conductors in the devices can be corroded, detracting from moisture-proof reliability.
Addressing the above concerns, we have discovered that a semiconductor encapsulating epoxy resin composition using as a flame retardant a combination of three components, (D) a molybdenum ingredient having zinc molybdate supported on an inorganic filler, (E) a first phosphazene compound of the average compositional formula (1), and (F) a second phosphazene compound of the average compositional formula (2) does not increase impurity ions in the extracting water, is effectively moldable and cures into a product having improved flame retardance and moisture-proof reliability. These three components of flame retardant are fully resistant to water and do not increase impurity ions in the extracting water. When these three components are used alone, there arises the problem that the epoxy resin composition is given insufficient flame retardant effects, loses flow or becomes less curable. The use of the above three components (D), (E) and (F) in combination as a flame retardant allows the amounts of the individual components added to be minimized, and thus eliminates the
Ando Shingo
Osada Shoichi
Shiobara Toshio
Takenaka Hiroyuki
Tomiyoshi Kazutoshi
Birch Stewart Kolasch & Birch, LLP.
Buttner David J.
Keehan Christopher
Shin-Etsu Chemical Co. , Ltd.
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