Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-09-30
2001-06-19
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C523S211000
Reexamination Certificate
active
06248454
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an epoxy resin composition for semiconductor encapsulation, which is excellent in curability and storage stability, and to a semiconductor device encapsulated with the epoxy resin composition.
BACKGROUND OF THE INVENTION
In the field of semiconductor elements, such as transistors, IC chips, and LSI chips, plastic packages have now prevailed from the standpoint of cost and suitability to mass production. Epoxy resin composition have been of wide use as an encapsulating resin, achieving satisfactory results. In particular, an epoxy resin composition comprising an epoxy resin, a novolak phenolic resin as a hardener, a cure accelerator, and an inorganic filler such as silica powder has been made frequent use of for its excellent encapsulating properties.
In recent years, the competition for the cost of plastic packages has been heated up. As an approach to cost reduction, efforts have been made to reduce a molding cycle thereby to improve production efficiency. With this tendency, the demand for an encapsulating material with improved curing properties has been increasing, which has been met by increasing the amount of a cure accelerator to be added.
An epoxy resin composition previously added with a cure accelerator undergoes curing reaction while stored. In particular where added with a large quantity of a cure accelerator, the composition undergoes rapid reaction before use, having an extremely short pot life and reducing the working efficiency. Therefore, it has recently been proposed to use an epoxy resin composition containing microcapsules of a cure accelerator.
While excellent in storage stability, the epoxy resin composition containing encapsulated cure accelerator as a sole cure accelerating component has the following drawback. Because of the microcapsule shell to be melted and destroyed, a delay is produced in allowing the cure accelerator to act in molding the resin composition for semiconductor encapsulation. As a result, the composition is inferior in rapid curability. The disadvantage is particularly conspicuous when the molding temperature is low (usually 140 to 180° C.).
SUMMARY OF THE INVENTION
In the light of the above-mentioned circumstances, one object of the invention is to provide an epoxy resin composition for semiconductor encapsulation, which is excellent in both storage stability and rapid curability.
Another object of the present invention is to provide a semiconductor device using the epoxy resin composition.
To accomplish the above objects, the invention provides in its first embodiment an epoxy resin composition for semiconductor encapsulation, which comprises:
(A) an epoxy resin,
(B) a phenol resin,
(C) a cure accelerator, and
(D) cure accelerator-containing microcapsules having a core/shell structure in which a cure accelerator as a core is encapsulated in a shell comprising a thermoplastic resin.
The invention also provides, in its second embodiment, a semiconductor device comprising a semiconductor element encapsulated with the above-described epoxy resin composition.
The inventor of the present invention has conducted a series of studies for the purpose of solving the problems associated with conventional epoxy resin compositions for semiconductor encapsulation. In order to satisfy the requirements for storage stability and rapid curability, which are conflicting with each other, the inventor has focused his study on compounding additives. As a result, he has found that a combined use of a cure accelerator and an encapsulated cure accelerator, i.e., cure accelerator-containing microcapsules, affords an encapsulating material satisfying both the requirements and thus completed the present invention.
In a preferred embodiment, the mixing ratio of the cure accelerator and the cure accelerator-containing microcapsules is specified to secure the improvements in rapid curability and storage stability.
In another preferred embodiment, the shell of the cure accelerator-containing microcapsules comprises polyurea prepared by using specific triisocyanate compounds at a specific mixing ratio. According to this embodiment, because the destruction temperature of the shell can be controlled suitably, it is possible to melt-knead the microcapsules with other components at high temperatures around 130° C. This means that the kneading system will have a reduced viscosity, which is advantageous for achieving thorough kneading, to give an epoxy resin composition having the components dispersed uniformly.
In still another preferred embodiment, a biphenyl type epoxy resin is used as the epoxy resin so that the epoxy resin composition exhibits improved flowability, i.e., improved moldability.
In yet another preferred embodiment, a phenol aralkyl resin is used as the phenolic resin. In this case, the epoxy resin composition exhibits improved flowability and provides a cured product with reduced hygroscopicity and reduced elastic modulus in favor of soldering resistance and the like.
DETAILED DESCRIPTION OF THE INVENTION
REFERENCES:
patent: 5294835 (1994-03-01), Igarashi et al.
patent: 08301978 (1995-05-01), None
patent: 8-301978 (1996-11-01), None
Aylward D.
Dawson Robert
Nitto Denko Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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