Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-12-13
2004-03-30
Sellers, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S481000, C525S486000, C525S504000, C525S508000, C525S523000, C525S533000
Reexamination Certificate
active
06713571
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for producing an epoxy resin composition for use in the encapsulation of photosemiconductor elements.
DESCRIPTION OF THE RELATED ART
Epoxy resin compositions have conventionally been used extensively as resin compositions for use in the encapsulation of photosemiconductor elements such as LEDs (light-emitting diodes). Such an epoxy resin composition for photosemiconductor element encapsulation usually comprises an epoxy resin, a hardener, and a hardening accelerator. This composition is generally used in the following manner. These ingredients are melt-mixed beforehand to obtain semi-cured (B-stage) tablets. In molding, e.g., transfer molding, the tablets are thermally melted, charged into a mold in which a photosemiconductor element is disposed, and then cured to thereby encapsulate the photosemiconductor element.
However, when the melt of an epoxy resin composition for photosemiconductor element encapsulation has too low viscosity during molding, there are cases where the cured resin obtained therefrom has molding failures such as burrs and bubbles.
On the other hand, a technique for preventing such molding failures is known in which the viscosity of a resin composition to be used for molding is increased by, for example, incorporating a filler or the like thereinto.
However, epoxy resin compositions for photosemiconductor element encapsulation are required to give transparent cured resins because it is necessary to secure satisfactory luminescence of encapsulated photosemiconductor elements. It is therefore undesirable to incorporate a filler or the like so as to increase viscosity.
SUMMARY OF THE INVENTION
The invention has been achieved in view of these circumstances.
An object of the invention is to provide a process for producing an epoxy resin composition for photosemiconductor element encapsulation which, even when a filler or the like is not contained therein, can have a viscosity necessary for molding and hence be satisfactorily molded to give a cured resin less apt to have defects such as burrs or bubbles.
In order to accomplish the object, the invention provides a process for producing an epoxy resin composition for photosemiconductor element encapsulation comprising an epoxy resin, a hardener and a hardening accelerator, as constituent ingredients, the process comprising: a first step of melt-kneading the ingredients together; and a second step of regulating viscosity of the molten mixture obtained in the first step at a given temperature.
According to this process, since the molten mixture comprising an epoxy resin, a hardener and a hardening accelerator, obtained in the first step, is regulated in viscosity at a given temperature in the second step, the resulting epoxy resin composition can have a viscosity necessary for molding, e.g., transfer molding, when the mixture is thermally melted in the molding operation.
In the second step, the molten mixture is preferably spread into a sheet form and allowed to stand in this state at a given temperature.
By allowing the sheet-form spread mixture to stand at a given temperature, viscosity regulation can be conducted uniformly and efficiently.
DETAILED DESCRIPTION OF THE INVENTION
The term “given temperature” used herein generally means a temperature of about 35 to 80° C.
The epoxy resin composition for photosemiconductor element encapsulation to be produced by the invention comprises an epoxy resin, a hardener and a hardening accelerator.
Examples of the epoxy resin include bisphenol A epoxy resins; bisphenol F epoxy resins; novolac epoxy resins such as phenolic novolac epoxy resins and cresol novolac epoxy resins; alicyclic epoxy resins; nitrogen-containing epoxy resins such as triglycidyl isocyanurate and hydantoin epoxy resins; hydrogenated bisphenol A epoxy resins; aliphatic epoxy resins; glycidyl ether epoxy resins; bisphenol S epoxy resins; and biphenyl epoxy resins, dicyclo epoxy resins and naphthalene epoxy resins, which are mainly used as epoxy resins of the type giving low water absorption cured resins. These epoxy resins may be used alone or in combination of two or more thereof. Preferred of these epoxy resins are bisphenol A epoxy resins, bisphenol F epoxy resins, novolac epoxy resins, alicyclic epoxy resins and triglycidyl isocyanurate, which are excellent in transparency and resistance to discoloration.
Although such an epoxy resin may liquid at room temperature (e.g., about 15-35° C.), an epoxy resin which is solid at room temperature is preferably used. In general, epoxy resins having an average epoxy equivalent of from 90 to 1,000 are preferably used. Further, epoxy resins having a softening point of 160° C. or lower are preferably used. If an epoxy resin having an epoxy equivalent lower than 90 is used, there are cases where the epoxy resin composition for photosemiconductor element encapsulation, containing such an epoxy resin gives a brittle cured resin. On the other hand, if an epoxy resin having an epoxy equivalent exceeding 1,000 is used, there are cases where the composition containing such an epoxy resin gives a cured resin having a lowered glass transition temperature (T
g
).
Examples of the hardener used in the invention include acid anhydride hardeners and phenolic hardeners. Examples of the acid anhydride hardeners include phthalic anhydride, maleic anhydride, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methylnadic anhydride, nadic anhydride, glutaric anhydride, methylhexahydrophthalic anhydride and methyltetrahydrophthalic anhydride. These may be used alone or in combination of two or more thereof. Preferred of these acid anhydride hardeners are phthalic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, and methylhexahydrophthalic anhydride. Preferred acid anhydride hardeners are ones having a molecular weight of about from 140 to 200. Also preferred are acid anhydrides which are colorless or light-yellow.
Examples of the phenolic hardeners include phenolic novolac resin hardeners.
An epoxy resin and a hardener are mixed with each other in such a proportion that the amount of the active groups in the hardener (acid anhydride groups or hydroxyl groups) reactive with epoxy groups is preferably from 0.5 to 1.5 equivalents, more preferably from 0.7 to 1.2 equivalents, per equivalent of the epoxy groups of the epoxy resin. If the amount of the active groups of the hardener is smaller than 0.5 equivalents, there are cases where the epoxy resin composition for photosemiconductor element encapsulation has a decreased curing rate and gives a cured resin having a lowered glass transition temperature. On the other hand, if the amount thereof exceeds 1.5 equivalents, there are cases where moisture resistance of a cured resin is impaired.
Besides the acid anhydride hardeners and phenolic hardeners, conventional hardeners for epoxy resins may be used according to the intended use of the composition. Examples the conventional hardener include amine hardeners, hardeners obtained by partially esterifying acid anhydride hardeners with an alcohol, and carboxylic acid hardeners such as hexahydrophthalic acid, tetrahydrophthalic acid, and methylhexahydrophthalic acid. Such hardeners may be used alone or in combination with one or more of acid anhydride hardeners and phenolic hardeners. For example, use of a carboxylic acid hardener in combination with an acid anhydride or phenolic hardener is effective in increasing the rate of curing and hence in improving productivity. In the case of using those hardeners also, the proportion thereof (equivalent ratio) may be the same as in the case of using acid anhydride hardeners and phenolic hardeners.
The hardening accelerator is not particularly limited. Examples thereof include 1,8-diazabicyclo[5,4,0]undecene-7, triethylenediamine, tertiary amines such as tri-2,4,6-dimethylaminomethylphenol, imidazole derivatives such as 2-ethyl-4-methylimidazole and 2-methylimidazole, phosphorus compounds such as triphenylph
Nitto Denki Corporation
Sellers Robert
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