Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2002-05-02
2004-05-11
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C257S787000, C257S793000, C257S795000, C428S413000, C523S443000, C523S466000
Reexamination Certificate
active
06733901
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing an epoxy resin composition for semiconductor encapsulation which, when used in encapsulation of a semiconductor chip, can minimize voids appearing in the semiconductor device obtained; an epoxy resin composition produced by using the above process; and a semiconductor device produced by using the above epoxy resin composition.
BACKGROUND ART
Epoxy resin compositions, which can be subjected to transfer molding, are in wide use for encapsulation of semiconductor chips such as IC, LSI and the like, from the viewpoints of their reliability and productivity.
Epoxy resin compositions are composed of an epoxy resin, a phenolic resin, a curing accelerator, an inorganic filler, a releasing agent, a flame retardant, a coupling agent, etc. The compositions are ordinarily produced by weighing required amounts of raw materials, premixing them by using a mixer such as Henschel mixer or the like, then melt-kneading the resulting premix by using a heated kneader such as monoaxial kneader, biaxial kneader, heated roll, continuous kneader or the like, to mix and disperse the individual raw materials uniformly.
As electronic appliances have become smaller, lighter and more functional, the semiconductor packages used therein have become increasingly smaller, thinner and narrower in pitch. In such a situation, epoxy resin compositions used for semiconductor encapsulation are strongly required to have higher soldering heat resistance and higher moisture resistance, because the heat resistance and moisture resistance have an influence on the reliability of the semiconductor packages obtained by encapsulation using the epoxy resin compositions.
Therefore, epoxy resin compositions have come to contain an increased amount of an inorganic filler so that the semiconductor packages obtained therewith can have lower internal stress and lower hygroscopicity. This increase in the amount of the inorganic filler used, however, has reduced fluidity during encapsulation and has increased defects in molding, such as lead frame deformation, gold wire deformation, voids generation and the like.
Against the above problems, it is being tried to keep fluidity of an epoxy resin composition and improve the filling characteristic thereof by optimizing the particle shape and particle diameter distribution of the inorganic filler used or by minimizing the viscosities of the used epoxy resin, phenolic resin, etc. at encapsulation temperature. However, the task of decreasing voids is difficult to achieve and is drawing increasing attention.
The voids of an epoxy resin composition is considered to be reducible by increasing the degree of kneading of the composition in the melt-kneading step to improve the wettability between the resin components and the inorganic filler and the dispersibility of the inorganic filler. However, in some cases the increase in the kneading degree in the melt-kneading step alone causes a curing reaction of the composition by the thermal history added in the step and consequently impairs the fluidity of the composition.
Hence, there have been used, for example, processes which comprise combining only those raw materials which cause no curing reaction at the premixing step, among all materials, and melt-mixing the combined raw materials at a temperature higher than the temperature at which they melt or soften, and then conducting melt-kneading for all the raw materials (e.g. JP-A-56-149454, JP-A-4-59863 and JP-A-3-195764).
There have also been proposed, for example, processes which comprise selecting an optimum heated kneader and employing optimum kneading conditions to minimize the curing reaction occurring in the heated kneader and improve the wettability between the resin components and the inorganic filler and the dispersibility of the inorganic filer (e.g. JP-A-9-
52228).
However, in conducting melt-mixing at a high temperature in the premixing step, the raw materials usable therein have been restricted. Further, only with the selection of an optimum kneader and the use of optimum kneading conditions, it has been difficult to reduce the generation of voids stably.
For solution thereof, it is considered to make finer and more homogeneous the premix of raw materials prior to their melt-mixing, to reduce the generation of voids.
However, it has been found that only with making finer and more homogeneous the premix of raw materials prior to their melt-mixing, remarkable reduction in voids generation is difficult and further improvement is necessary, in a resin composition wherein a low-viscosity resin, particularly a crystalline epoxy resin and a low-viscosity phenolic curing agent are used and thereby the content of an inorganic filler is increased in order to further increase the soldering heat resistance of the composition.
DISCLOSURE OF THE INVENTION
The present invention relates to a process for producing an epoxy resin composition for semiconductor encapsulation which, when used in encapsulation of a semiconductor chip, can minimize voids appearing in the semiconductor device obtained. The present invention also provides an epoxy resin composition for semiconductor encapsulation, very low in voids generation, and a semiconductor device produced by encapsulation with the composition.
The present inventors made a study in view of the above-mentioned situation. As a result, the present inventors found out newly that the voids generation in an encapsulated material produced with an epoxy resin composition can be remarkably reduced by making finer and more homogeneous a premix of raw materials prior to their melt-kneading, then melt-kneading the resulting material under a reduced pressure using a kneader, or melt-kneading the material using a kneader, followed by, for example, passing the resulting molten material through an apparatus of reduced pressure. The present invention has been completed based on the above finding.
The present invention lies in a process for producing an epoxy resin composition for semiconductor encapsulation, which comprises premixing raw materials containing at least an epoxy resin, a phenolic resin, a curing accelerator and an inorganic filler, then grinding the resulting premix using a grinder to obtain a ground material having such a particle size distribution that particles having particle diameters of 250 &mgr;m or more are 10% by weight or less, particles having particle diameters of 150 &mgr;m to less than 250 &mgr;m are 15% by weight or less and particles having particle diameters of less than 150 &mgr;m are 75% by weight or more, and melt-kneading the ground material under a reduced pressure.
The present invention lies also in a process for producing an epoxy resin composition for semiconductor encapsulation, which comprises premixing raw materials containing at least an epoxy resin, a phenolic resin, a curing accelerator and an inorganic filler, then grinding the resulting premix using a grinder to obtain a ground material having such a particle size distribution that particles having particle diameters of 250 &mgr;m or more are 10% by weight or less, particles having particle diameters of 150 &mgr;m to less than 250 &mgr;m are 15% by weight or less and particles having particle diameters of less than 150 &mgr;m are 75% by weight or more, melt-kneading the ground material, and exposing the resulting molten material to a reduced pressure.
In a preferred embodiment of the above processes, the reduced pressure is 460 mmHg or less when normal pressure is 760 mmHg and the melt-kneading is conducted using a biaxial kneader or a monoaxial kneader.
The present invention lies further in an epoxy resin composition for semiconductor encapsulation, produced by using the above process for producing an epoxy resin composition for semiconductor encapsulation, as well as in a semiconductor device produced by using the epoxy resin composition for semiconductor encapsulation.
DETAILED DESCRIPTION OF THE INVENTION
As to the epoxy resin used in the present invention, there is no particular restriction as lon
Noda Kazuo
Takasaki Noriyuki
Takayama Kenji
Aylward D.
Dawson Robert
Sumitomo Bakelite Company Limited
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