Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2001-02-01
2002-12-17
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C241S023000, C241S024100, C241S024120, C241S025000, C427S096400
Reexamination Certificate
active
06495260
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing an epoxy resin molding material low in voids generation during semiconductor encapsulation; a molding material produced by the process; and a semiconductor device obtained by encapsulation with the molding material.
BACKGROUND ART
For encapsulation of semiconductor elements such as IC, LSI and the like, epoxy resin molding materials, which are transfer-moldable, are widely used in view of the reliability and productivity of the encapsulation with these materials.
Epoxy resin molding materials are constituted by an epoxy resin, a phenolic resin, a curing accelerator, an inorganic filler, a releasing agent, a flame-retardant, a coupling agent, etc., and are generally produced by weighing individual raw materials by given amounts, premixing the raw materials using a stirrer and mixer such as Henschel mixer or the like, and then subjecting the resulting mixture to melt kneading using a hot kneader such as single-screw kneader, double-screw kneader, hot rolls, continuous kneader or the like to mix and disperse the raw materials uniformly.
Meanwhile, electronic appliances are becoming increasingly small, light and functional and, accordingly, the semiconductor packages used therein are becoming increasingly small, thin and narrow in pitch. In such a movement, epoxy resin molding materials used for semiconductor encapsulation are strongly required to have improved resistance to soldering heat and improved humidity resistance, since these resistances are relevant to the reliability of the semiconductor package obtained by encapsulation.
Hence, the amount of inorganic filler in epoxy resin molding material is being increased in order to reduce the stress and hygroscopicity of semiconductor package inside. However, this increase in amount of inorganic filler in epoxy resin molding material reduces the flowability of epoxy resin molding material during encapsulation and makes more serious the problems in molding such as deformation of lead frame, deformation of gold wire, generation of voids and the like.
As a countermeasure for the above, there is being continued an attempt of optimizing the shape and particle size distribution of inorganic filler, or an attempt of making very small the viscosity of resin components (e.g. epoxy resin and phenolic resin) at an encapsulation temperature to allow the resulting molding material to maintain a required flowability and have an improved chargeability. Nevertheless, the task of reducing voids is difficult to achieve and is becoming more and more important.
The voids of epoxy resin molding material are thought to be reduceable by increasing the degree of kneading of molding material during the step of melt kneading to increase the wettability between resin components and inorganic filler in molding material or the dispersibility of inorganic filler. However, increase in the degree of kneading during melt kneading step alone accelerates the curing of molding material by the heat applied in the step and, as a result, impairs the flowability of molding material.
Hence, there were disclosed a method which comprises selecting raw materials causing no curing in the step of premixing, melt-mixing them at a temperature higher than their melting or softening point, and then subjecting the resulting mixture to melt-kneading (e.g. JP-A-56-149454, JP-A-4-59863 and JP-A-3-195764); a method which comprises selecting an optimum hot kneader or optimum kneading conditions to minimize the proceeding of curing in the hot kneader and increase the wettability between resin components and inorganic filler in molding material or the dispersibility of inorganic filler (e.g. JP-A-9-52228); and so forth.
However, melt-mixing in the premixing step at a high temperature has restricted the raw materials usable; and selection of an optimum kneader or optimum kneading conditions alone has made it difficult to reduce voids generation stably.
DISCLOSURE OF THE INVENTION
Objects of the present invention are to provide a process for producing an epoxy resin molding material for semiconductor encapsulation, which is very low in voids generation; a molding material produced by the process; and a semiconductor device obtained by encapsulation with the molding material.
The present inventors made a research in view of the above situation. As a result, the present inventors newly found out that voids generation can be reduced remarkably by making raw materials into a finer and more homogeneous dispersion after their premixing but before their melt kneading. The present invention has been completed based on the finding.
The first aspect of the present invention lies in a process for producing an epoxy resin molding material for semiconductor encapsulation, which comprises premixing a composition containing at least an epoxy resin, a phenolic resin and an inorganic filler, then subjecting the resulting mixture to grinding by a grinder to obtain a powder having such a particle size distribution that the amount of particles having particle diameters of 250 &mgr;m or more is 10% by weight or less, the amount of particles having particle diameters of 150 &mgr;m to less than 250 &mgr;m is 15% by weight or less, and the amount of particles having particle diameters of less than 150 &mgr;m is 75% by weight or more, and thereafter subjecting the powder to melt kneading.
The second aspect of the present invention lies in a process for producing an epoxy resin molding material for semiconductor encapsulation, which comprises adding, to the composition set forth in the first aspect, at least one kind selected from a coupling agent, a curing accelerator, a flame retardant, a releasing agent, an ion-capturing agent, a coloring agent and a stress-reducing agent, premixing the resulting composition, then subjecting the resulting mixture to grinding by a grinder to obtain a powder having such a particle size distribution that the amount of particles having particle diameters of 250 &mgr;m or more is 10% by weight or less, the amount of particles having particle diameters of 150 &mgr;m to less than 250 &mgr;m is 15% by weight or less, and the amount of particles having particle diameters of less than 150 &mgr;m is 75% by weight or more, and thereafter subjecting the powder to melt kneading. In the first and second aspects, preferably the acetone-insoluble portion of the powder comprises particles having particle diameters of 212 &mgr;m or more in an amount of 0.5% by weight or less.
The third aspect of the present invention lies in a process for producing an epoxy resin molding material for semiconductor encapsulation, which comprises adding, to the composition set forth in the first aspect, a coupling agent, a curing accelerator, a flame retardant, a releasing agent, an ion-capturing agent, a coloring agent and a stress-reducing agent, premixing the resulting composition, then subjecting the resulting mixture to grinding by a grinder to obtain a powder having such a particle size distribution that the amount of particles having particle diameters of 250 &mgr;m or more is 10% by weight or less, the amount of particles having particle diameters of 150 &mgr;m to less than 250 &mgr;m is 15% by weight or less, and the amount of particles having particle diameters of less than 150 &mgr;m is 75% by weight or more, and thereafter subjecting the powder to melt kneading.
The fourth aspect of the present invention lies in an epoxy resin molding material for semiconductor encapsulation, produced by a process according to any of the first to third aspects.
The fifth aspect of the present invention lies in a semiconductor device obtained by encapsulating semiconductor elements with an epoxy resin molding material set forth in the fourth aspect.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The epoxy resin used in the present invention has no particular restriction as to the kind as long as it has two or more epoxy groups in the molecule and it is solid at ambient temperature. There can be mentioned, f
Anai Yoshiyuki
Takasaki Noriyuki
Takayama Kenji
Dawson Robert
Feely Michael J
Smith , Gambrell & Russell, LLP
Sumitomo Bakelite Company Limited
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