Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-05-13
2001-10-02
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C523S200000, C523S424000, C523S427000
Reexamination Certificate
active
06297306
ABSTRACT:
This invention relates to an epoxy resin composition for semiconductor encapsulation which is effectively moldable and cures into a product having high-temperature storage stability, reflow crack resistance and flame retardance. 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 are generally used as the encapsulating resin because they 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.
Recently, halogenated epoxy resins combined with antimony trioxide are often blended in epoxy resin compositions in order to clear the V-0 rating of Underwriters Laboratory flame retardant standard UL-94. 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, these fire retardants are not suitable for resin compositions and 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.
SUMMARY OF THE INVENTION
An object of the invention is to provide an epoxy resin composition for semiconductor encapsulation which is effectively moldable and cures into a product having high-temperature storage stability, reflow crack resistance, flame retardance, and safety. Another object is to provide a semiconductor device encapsulated with a cured product of the composition.
The inventors have found that by blending a molybdenum compound as a flame retardant in an epoxy resin composition for semiconductor encapsulation comprising an epoxy resin of the following general formula (1), a phenolic resin curing agent of the following general formula (2), and an inorganic filler as essential components, there is obtained an epoxy resin composition which is effectively moldable and cures into a product having improved reflow crack resistance, moisture resistance, high flame retardance, and safety. Then a semiconductor device encapsulated with the cured epoxy resin composition remains highly reliable.
Herein R
1
which may be the same or different is a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, or a phenyl group, and n is an integer of 0 to 10.
Herein R
2
which may be the same or different is a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, or a phenyl group, and m is an integer of 0 to 10.
Molybdenum compound such as zinc molybdate by itself is known to have a smoke-reducing and charring effect in burning plastic. Like antimony trioxide, molybdenum compound is conventionally used in combination with halogenated resins. The inventors have found that by combining molybdenum compound with a heat resistant epoxy resin of formula (1) and a phenolic resin of formula (2), sufficient flame retardance is exerted without a need for halogenated resins. Since molybdenum compound is free of powder toxicity as found with antimony trioxide, and not detrimental to such properties as curing and moisture resistance, it is a very effective flame retardant to be blended in epoxy resin compositions.
Accordingly, the present invention provides an epoxy resin composition for semiconductor encapsulation comprising, in admixture, (A) an epoxy resin of formula (1), (B) a phenolic resin curing agent of formula (2), (C) molybdenum compound, and (D) an inorganic filler.
Also contemplated herein is a semiconductor device encapsulated with a cured product of the composition.
DETAILED DESCRIPTION OF THE INVENTION
In the semiconductor-encapsulating epoxy resin composition of the invention, both the epoxy resin of formula (1) as component (A) and the phenolic resin curing agent of formula (2) as component (B) are resins having biphenyl and phenol skeletons, respectively. A combination of these resins affords a cured product having a low water absorption, high toughness and improved reflow crack resistance. The combination is a highly heat resistant material because of a high thermal decomposition initiating temperature and a low rate of thermal decomposition.
Component (A) is an epoxy resin of the following general formula (1), which is a phenolaralkyl type epoxy resin having a biphenyl skeleton or an epoxy resin having a biphenylaralkyl skeleton.
Herein, R
1
represents identical or different atoms or groups selected from the class consisting of a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, and a phenyl group. Exemplary alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and t-butyl. Letter n is an integer of 0 to 10, preferably 0 to 4, and more preferably 0 to 2.
Illustrative examples of the epoxy resin of formula (1) are given below.
In the formulae, n is an integer of 0 to 10, preferably 0 to 4, and more preferably 0 to 2.
Desirably, the epoxy resin of formula (1) has a melt viscosity of 0.1 to 2.5 poises, especially 0.1 to 0.8 poise as measured at 150° C. by a cone plate type ICI viscometer. An epoxy resin with a melt viscosity of more than 2.5 poises would become extremely low in melt flow when the loading of inorganic filler is made as high as 80 to 90% by weight in order to improve reflow crack resistance. An epoxy resin with a melt viscosity of less than 0.1 poise tend to generate internal voids during molding, losing reliability.
As the epoxy resin, another epoxy resin may be used in combination with the epoxy resin of formula (1), if desired. Examples of the other epoxy resin which can be combined include novolac type epoxy resins such as phenol novolac type epoxy resins and cresol novolac type epoxy resins; triphenolalkane type epoxy resins such as triphenolmethane type epoxy resins and triphenolpropane type epoxy resins; biphenyl type epoxy resins; phenolaralkyl type epoxy resins free of a biphenyl skeleton; heterocyclic epoxy resins; naphthalene ring-containing epoxy resins; bisphenol type epoxy resins such as bisphenol A type epoxy resins and bisphenol F type epoxy resins, and stilbene type epoxy resins. These epoxy resins may be used alone or in admixture of two or more. Of these, biphenyl type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, and stilbene type epoxy resins are preferable because they exhibit a low viscosity when melted.
The amount of the epoxy resin of formula (1) blended is desirably 50 to 100% by weight, more desirably 70 to 100% by weight based on the total weight of epoxy resins (that is, epoxy resin of formula (1) plus other epoxy resins). Less than 50% by weight of the epoxy resin of formula (1) would fail to achieve satisfactory reflow crack resistance and flame retardance.
Component (B) is a phenolic resin curing agent of the following general formula (2), which is an aralkyl type phenolic resin having a biphenyl skeleton or a phenolic resin having a biphenylaralkyl skeleton.
Herein, R
2
represents identical or different atoms or groups selected from the class consisting of a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, and a phenyl group. Exemplary alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and t-butyl. Letter m is an integer of 0 to 10, preferably 0 to 4, and more preferably 0 to 2.
Aoki Takayuki
Asano Eiichi
Osada Shoichi
Shiobara Toshio
Tomiyoshi Kazutoshi
Birch & Stewart Kolasch & Birch, LLP
Cain Edward J.
Shin-Etsu Chemical Co. , Ltd.
Wyrozebski-Lee Katarzyna
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