Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Utility Patent
1998-12-24
2001-01-02
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C523S451000, C525S500000, C525S523000, C528S089000
Utility Patent
active
06168872
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an epoxy resin composition or semiconductor encapsulation which is effectively moldable and stable during storage. It also relates to a semiconductor device encapsulated with a cured product of the composition.
2. Prior Art
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 proofness to other thermosetting resins. It is thus a common practice to encapsulate semiconductor devices with epoxy resin compositions.
Nowadays, semiconductor devices have an increasing degree of integration and the chip size is accordingly increasing. On the other hand, packages of smaller outer size are needed in order to comply with the desired size and weight reduction of electronic equipment. To accommodate such changes of chip size and package configuration, resin compositions must have a sufficiently low viscosity. Encapsulation with resin compositions having a high viscosity tends to invite molding troubles including wire flow, pad shift, void occurrence, and short fill.
To minimize damage to chips, resin compositions must be effectively curable and mold releasable. The curing and parting properties are generally improved by blending a more proportion of curing accelerator. Increased amounts of the curing accelerator blended help the resin compositions cure quickly to a higher strength and thus contribute to an improvement in mold release.
The above approach is successful in improving mold release, but causes to increase the viscosity of resin compositions, tending to invite molding troubles including wire flow, pad shift, void occurrence, and short fill as mentioned above. Also, the increased amounts of the curing accelerator blended help reaction proceed even at temperature approximate to room temperature, resulting in an increased viscosity. That is, the resin compositions lack storage stability.
An object of the invention is to provide an epoxy resin composition for semiconductor encapsulation which is effectively moldable and stable during storage while it is effectively curable and mold releasable. Another object of the invention is to provide a semiconductor device encapsulated with a cured product of the composition.
SUMMARY OF THE INVENTION
The invention pertains to a semiconductor encapsulating epoxy resin composition comprising an epoxy resin, a curing agent, an inorganic filler, and a curing accelerator as essential components. We have found that blending an organic phosphorus compound of formula (1), shown below, as the curing accelerator provides a composition which is storage stable, effectively moldable, curable and mold releasable. Therefore, semiconductor devices encapsulated with cured products of the composition are highly reliable.
In formula (1), R
1
is independently hydrogen, C
1-4
alkyl or C
1-4
alkoxy, n is an integer of 0 to 5, and X is —(CH
2
)
p
— wherein p is an integer of 3 to 12, or a group represented y the following general formula (2).
In formula (2), R
2
is independently hydrogen, C
1-4
alkyl or C
1-4
alkoxy, q and r each are an integer of 0 to 12, and m is an integer of 0 to 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The epoxy resin composition of the present invention contains an epoxy resin, a curing agent, an inorganic filler, and a curing accelerator as essential components.
The epoxy resin used herein is not limited in molecular structure and molecular weight insofar as it has at least two epoxy groups in a molecule and is curable with various curing agents as will be described later. It may be selected from prior art well-known epoxy resins. Illustrative epoxy resins include bisphenol type epoxy resins such as bisphenol A type epoxy resins and bisphenol F type epoxy resins, novolak type epoxy resins such as phenol novolak type epoxy resins and cresol novolak type epoxy resins, triphenol alkane type epoxy resins such as triphenol methane type epoxy resins and triphenol propane type epoxy resins, and polymers thereof, biphenyl skeleton-bearing epoxy resins, naphthalene skeleton-bearing epoxy resins, dicyclopentadiene-phenol novolak resins, phenol aralkyl type epoxy resins, biphenyl aralkyl type epoxy resins, glycidyl ester type epoxy resins, cycloaliphatic epoxy resins, heterocyclic epoxy resins, and halogenated epoxy resins.
The curing agent may be selected from conventional well-known compounds used as a curing agent for epoxy resins, for example, phenolic compounds, amine compounds and acid anhydrides. In particular, phenol resins having at least two phenolic hydroxyl groups in a molecule are useful. Exemplary phenolic resins are novolak type phenolic resins such as phenol novolak resins and cresol novolak resins, resol type phenolic resins, phenol aralkyl resins, triphenol alkane type phenol resins such as triphenol methane resins and triphenol propane resins, and polymers thereof, biphenyl type phenol resins, biphenyl aralkyl type phenol resins, naphthalene ring-containing phenolic resins, and dicyclopentadiene-modified phenolic resins. These curing agents may be used alone or in admixture of two or more.
The curing agent is used in a sufficient amount to cure the epoxy resin. Where a phenolic resin is used as the curing agent, the epoxy resin and the phenolic resin are preferably mixed such that 0.5 to 1.5 mol, especially 0.8 to 1.2 mol of phenolic hydroxyl groups in the phenolic resin is available per mol of epoxy groups in the epoxy resin.
Also blended in the epoxy resin composition is an inorganic filler. The filler is effective for reducing the coefficient of expansion of an encapsulant for thereby reducing the stress applied to semiconductor devices. The inorganic filler may be selected from those commonly used in conventional epoxy resin compositions. Often used are fused silica and crystalline silica in ground and spherical forms. Alumina, silicon nitride, aluminum nitride, boron nitride, titanium oxide, and glass fibers are also useful.
A blend of spherical and ground form fillers or only a spherical form filler is preferably used to meet both the requirements of moldability and minimized expansion of a cured product. The preferred inorganic filler has a mean particle size of about 5 to 30 &mgr;m. The mean particle size can be measured as a mean weight value (or a median diameter) by means of the conventional analytical methods such as a laser beam diffractometry.
For augmenting the bond between the resin and the surface of inorganic filler, it is preferred to blend an inorganic filler previously surface treated with a silane coupling agent including alkoxy silanes having a functional group such as epoxy group, (meth)acryl group, amino group, mercapto group or vinyl group. The amount of the coupling agent and the surface treatment method are not critical.
Although the amount of the inorganic filler blended is not critical, the inorganic filler is preferably blended in an amount of about 200 to 1,200 parts, especially about 400 to 1,000 parts by weight per 100 parts by weight of the epoxy resin and curing agent combined. On this basis, less than 200 parts of the filler would allow the composition to have an increased coefficient of expansion which can increase the stress applied to semiconductor devices and thus deteriorate the properties thereof. More than 1,200 parts of the filler would cause the composition to increase its viscosity to restrain molding.
According to the invention, an organic phosphorus compound of the following general formula (1) is blended as the curing accelerator for accelerating the curing reaction of the epoxy resin with the curing agent.
In formula (1), R
1
is independently hydrogen, C
1-4
alkyl or C
1-4
alkoxy, n is an integer of 0 to 5, and X is
13
(CH
2
)
p
— wherein p is an integer of 3 to 12, or a group represented by the following general formula (2).
In formula (2),
Asano Eiichi
Ishizaki Tatsuya
Ohashi Kenji
Osada Shoichi
Shiobara Toshio
Aylward D.
Dawson Robert
Hokko Chemical Industry Co. Ltd.
Millen White Zelano & Branigan
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