Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-06-22
2001-08-14
Buttner, David J. (Department: 1712)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C523S466000, C525S481000, C525S485000, C525S489000
Reexamination Certificate
active
06274251
ABSTRACT:
This invention relates to an epoxy resin composition for semiconductor encapsulation having improved moldability, curability, and shelf stability, and 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.
In the epoxy resin compositions, curing catalysts are often blended in order to enhance the reactivity of epoxy resins with curing agents. Phosphorus compounds, imidazole compounds, and amine compounds are well known as the curing catalysts. Of these, phosphorus compounds are commonly used because they afford cured products which are highly reliable in terms of moisture resistance or the like, as compared with the imidazole and amine compounds.
To comply with the recent demand for electronic equipment of reduced size and weight, the trend is to reduce the outer dimensions, especially thickness of packages. In order that resin compositions be molded around such thin packages, the resin compositions must have a sufficiently low viscosity and be effectively curable and mold releasable.
Of the phosphorus curing catalysts, triphenyl-phosphine and tetraphenylphosphonium tetraphenylborate are well known and commonly used. Because of low catalytic activity, triphenylphosphine must be blended in epoxy resin compositions in so large amounts that when molded, the resulting high viscosity compositions tend to give rise to troubles such as wire flow, pad shift, void formation, and short molding. Tetraphenylphosphonium tetraphenylborate has lower catalytic activity than triphenylphosphine and is thus difficult to endow resin compositions with sufficient curability even when blended in considerably large amounts. The curing catalysts blended in large amounts give rise to a problem that reaction can take place even at temperatures near room temperature. The resin compositions accordingly increase their viscosity and become less stable during shelf storage.
JP-B 56-45491 discloses an epoxy resin composition comprising an epoxy resin and a curing agent, having good shelf stability and affording highly moisture resistant cured products. The curing agent is obtained by heat treating a mixture of a novolac type phenolic resin and tetraphenylphosphonium tetraphenylborate at a temperature above the softening point of the phenolic resin until the resin is colored slightly yellowish brown or dark brown. However, since this curing catalyst yet has low activity and lacks fast curing ability, it must be used in a large amount at the sacrifice of the shelf stability of the epoxy resin composition.
In JP-A 7-242683 corresponding to U.S. Pat. No. 5,473,091, the same assignee as the present invention proposed an epoxy resin composition having blended therein a curing catalyst which is obtained by mixing for reaction a quaternary phosphorus compound with a compound having phenolic hydroxyl groups at a temperature of 120 to 250° C. This epoxy resin composition is still insufficient with respect to low viscosity, good cure, smooth mold release, and shelf stability.
SUMMARY OF THE INVENTION
An object of the invention is to provide a semiconductor-encapsulating epoxy resin composition having improved moldability, cure, and shelf stability, and a semiconductor device encapsulated with a cured product of the composition.
We have found that an epoxy resin composition comprising an epoxy resin, a phenolic resin curing agent, and an inorganic filler is improved in moldability, curability, and shelf stability by blending a quaternary phosphorus compound of the following general formula (1) as a curing catalyst.
Herein R
1
and R
2
are independently selected from the group consisting of alkyl groups having 1 to 4 carbon atoms and alkoxy groups having 1 to 4 carbon atoms, each of m and n is an integer of 1 to 3, a is an integer of 1 to 3, and b is an integer of 1 to 4. Similar effects are exerted when a mixed reaction product obtained by mixing for reaction at a temperature of 100 to 250° C. a phenolic resin having at least two phenolic hydroxyl groups in the molecule with the quaternary phosphorus compound of formula (1) is blended as a curing catalyst. This epoxy resin composition is effective for semiconductor encapsulation. A semiconductor device encapsulated with the composition in a cured state is highly reliable.
Therefore, the present invention provides a semiconductor-encapsulating epoxy resin composition comprising (A) an epoxy resin, (B) a phenolic resin curing agent, (C) a curing catalyst, and (D) an inorganic filler. The curing catalyst (C) is the quaternary phosphorus compound of formula (1) or its mixed reaction product with a phenolic resin having at least two phenolic hydroxyl groups.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Component (A) of the epoxy resin composition according to the invention is an epoxy resin which has at least two epoxy groups in one molecule and can be cured with various curing agents to be described later. The epoxy resin is not particularly limited in molecular structure, molecular weight and the like, and any appropriate one may be selected from a variety of known epoxy resins. Examples of the epoxy resin which can be used herein include novolac type epoxy resins such as phenol novolac type epoxy resins and cresol novolac type epoxy resins; triphenolalkane type epoxy resins and polymers thereof such as triphenolmethane type epoxy resins and triphenolpropane type epoxy resins; biphenyl skeleton-bearing epoxy resins; naphthalene skeleton-bearing epoxy resins; dicyclopentadiene-phenol novolac resins; phenolaralkyl type epoxy resins; glycidyl ester type epoxy resins; alicyclic epoxy resins; heterocyclic epoxy resins; bisphenol type epoxy resins such as bisphenol A type epoxy resins and bisphenol F type epoxy resins. These epoxy resins may be used alone or in admixture of two or more.
The curing agent (B) is a phenolic resin having at least two phenolic hydroxyl groups in one molecule. Examples of the phenolic resin curing agent include novolac type phenolic resins such as phenol novolac resins and cresol novolac resins; resol type phenolic resins; phenolaralkyl type phenolic resins; triphenolalkane type phenolic resins and polymers thereof such as triphenol-methane type phenolic resins and triphenolpropane type phenolic resins; bisphenol type phenolic resins such as bisphenol A type phenolic resins and bisphenol F type phenolic resins; naphthalene ring-bearing phenolic resins; biphenyl skeleton-bearing phenolic resins; and dicyclopentadiene-modified phenolic resins. These curing agents may be used alone or in admixture of two or more.
The epoxy resin (A) and the curing agent (B) are blended in any desired ratio insofar as the amount of the curing agent is effective for curing. They are preferably blended in such a ratio that 0.5 to 1.5 mol, especially 0.8 to 1.2 mol of phenolic hydroxyl groups in the phenolic resin (B) is available per mol of epoxy groups in the epoxy resin (A).
In the embodiment wherein a preliminary reaction product of a quaternary phosphorus compound with a phenolic resin is used as the curing catalyst (C′) as will be described later, the components are blended such that the molar ratio of entire phenolic hydroxyl groups in both the phenolic resin used in the preliminary reaction and the phenolic resin added as the curing agent to epoxy groups in the epoxy resin may fall within the above-defined range of from 0.5 to 1.5, especially from 0.8 to 1.2.
In the practice of the invention, another curing agent such as an amine compound or acid anhydride may be blended if desired.
In the epoxy resin composition of the invention serving as an encapsulant for semiconductor devi
Asano Eiichi
Ishizaki Tatsuya
Ohashi Kenji
Osada Shoichi
Shiobara Toshio
Buttner David J.
Hokko Chemical Industry Co. Ltd.
Millen White Zelano & Branigan P.C.
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