Semiconductor device-encapsulating epoxy resin composition

Disclosed is a semiconductor device-encapsulating epoxy resin composition comprising (i) an epoxy resin (A) containing at least one of a bifunctional epoxy resin (a1) having a biphenyl skeleton and a bifunctional epoxy resin (a2) having a naphthalene skeleton, (ii) a curing agent (B), and (iii) a filler containing fused silica (C) having a specified kind and specified mean particle diameter. This composition has an excellent heat resistance of solder, and further reliability after thermal cycles and reliability after solder-bath dipping.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an epoxy resin composition having good heat 
resistance of solder and further having excellent reliability. 
2. Description of the Prior Art 
Epoxy resins have excellent heat resistance, moisture resistance, 
electrical characteristics and adhesion properties, and they can acquire 
various characteristics on modifying the recipes thereof. Accordingly, 
therefore, epoxy resins are used in paints, adhesives, and industrial 
materials such as electrically insulating materials. 
As methods of encapsulating electronic circuit parts such as semiconductor 
devices, there have been proposed a hermetic encapsulating method using 
metals or ceramics, and a resin encapsulating method using phenolic resin, 
silicone resin, epoxy resin or the like. From the view point of balancing 
economy, productivity and physical properties, however, the resin 
encapsulating method using an epoxy resin is mainly adopted. 
On the other hand, integration and automated processing have recently been 
promoted in the step of mounting parts to a circuit board, and a "surface 
mounting method" in which a semiconductor device is soldered to the 
surface of a board has been frequently employed in place of the 
conventional "insertion mounting method" in which lead pins are inserted 
into holes of a board. Packages are correspondingly in a transient stage 
of from conventional dual inline package (DIP) to thin-type flat plastic 
package (FPP) suitable for integrated mounting and surface mounting. 
As with the transition to the surface mounting method, the soldering 
process which conventionally has not attracted attention has now come to 
be a serious problem. According to the conventional pin insertion-mounting 
method, only a lead part is partially heated during soldering, whereas 
according to the surface mounting method a package in its entirety is 
dipped and heated in a heated solvent. As the soldering method for the 
surface mounting method, there are used solder-bath dipping method, solder 
reflow method in which heating is carried out with inert-liquid saturated 
vapor and infrared ray, and the like. By any of the methods, a package in 
its entirety is to be heated at a high temperature of 210.degree. to 
270.degree. C. Accordingly, in a package encapsulated with a conventional 
encapsulating resin, a problematic cracking of the resin portion occurs at 
the soldering step, whereby the reliability is lost, and hence, the 
obtained product cannot be practically used. 
The occurrence of cracking during the soldering process is regarded due to 
the explosive vaporization and expansion, at heating for soldering, of the 
moisture absorbed in the time period from procuring to the mounting 
process. For the countermeasure, there is employed a method to completely 
dry up a post-cured package and enclose it in a hermetically sealed 
container for shipping. 
The improvement of encapsulating resins has been investigated in a wide 
variety of ways. For example, heat resistance of solder can be improved by 
a method of adding an epoxy resin having a biphenyl skeleton and a rubber 
component (Japanese Unexamined Patent Publication No. 251419/1988), but it 
is not sufficient. The method of adding an epoxy resin having a biphenyl 
skeleton and microparticles in powder of a particle diameter less than 14 
.mu.m (Japanese Unexamined Patent Publication No. 87616/1989) does not 
yield a satisfactory level of heat resistance of solder. 
Alternatively, there has been proposed the addition of spherical fused 
silica microparticles (Japanese Unexamined Patent Publication No. 
263131/1989), whereby only the fluidity of encapsulating resins is 
improved and the heat resistance of solder is not sufficient. 
SUMMARY OF THE INVENTION 
One of the objects of the present invention is to solve the problem 
concerning the occurrence of cracking during the soldering process, namely 
to provide an epoxy resin composition having excellent heat resistance of 
solder. 
Another object of the present invention is to provide an epoxy resin 
composition having both of excellent heat resistance of solder and 
reliability after thermal cycles. 
Other object of the present invention is to provide an epoxy resin 
composition having both excellent heat resistance of solder and 
reliability after solder-bath dipping. 
Such objects in accordance with the present invention can be achieved by a 
semiconductor device-encapsulating epoxy resin composition comprising 
(i) an epoxy resin (A) containing as the essential component thereof at 
least one of a bifunctional epoxy resin (a1) having a biphenyl skeleton 
and a bifunctional epoxy resin (a2) having a naphthalene skeleton, 
(ii) a curing agent, and 
(iii) a filler containing a fused silica (C) consisting of 97 to 50 wt % of 
crushed fused silica (C1) of a mean particle diameter not more than 10 
.mu.m and 3 to 50 wt % of spherical fused silica (C2) of a mean particle 
diameter not more than 4 .mu.m, wherein the mean particle diameter of the 
spherical fused silica is smaller than the mean particle diameter of the 
crushed fused silica, and the amount of the filler being 75 to 90 wt % of 
the total of the composition. The objects can be achieved by further 
allowing the composition to contain a styrene type block copolymer (D), or 
a copolymer (E) of (1) at least one compound selected from the group 
consisting of ethylene and .alpha.-olefin and (2) at least one compound 
selected from the group consisting of unsaturated carboxylic acid and 
derivatives thereof. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
In accordance with the present invention, it is important that an epoxy 
resin (A) contains as the essential component thereof at least one of a 
bifunctional epoxy resin (a1) having a biphenyl skeleton and a 
bifunctional epoxy resin (a2) having a naphthalene skeleton, and that a 
filler containing a fused silica (C) is contained at 75 to 90 wt % to the 
total of the composition. The fused silica (C) consists of 97 to 50 wt % 
of crushed fused silica (C1) of a mean particle diameter not more than 10 
.mu.m and 3 to 50 wt % of spherical fused silica (C2) of a mean particle 
diameter not more than 4 .mu.m wherein the mean particle diameter of the 
spherical fused silica is smaller than the mean particle diameter of the 
crushed fused silica. Due to the bifunctionality of the epoxy resins (a1) 
and (a2), crosslinking density can be lowered. Biphenyl and naphthyl 
skeletons with high resistance to heat are contained, whereby there are 
obtained the effect of reducing the water absorption potency of the cured 
epoxy resin, as well as the effect of making the cured epoxy resin tough 
at a higher temperature (a solder-treating temperature). The through-out 
use of the fused silica of a smaller particle diameter can prevent the 
localization of internal stress imposed on the cured epoxy resin. By 
making the spherical fused silica of a smaller mean particle diameter 
present among the crushed silica of a small mean particle diameter, the 
internal stress being imposed on the cured epoxy resin can be reduced more 
greatly. Consequently, there is obtained an effect of improving the 
strength of the cured epoxy resin, in particular the strength at a high 
temperature (at the solder-treating temperature). According to the present 
invention, the independent effects of the epoxy resin and the silica are 
simultaneously brought about to produce a synergistic, remarkable effect 
on heat resistance of solder, far beyond expectation. 
The epoxy resin (A) to be used in accordance with the present invention 
contains as the essential component thereof at least one of a bifunctional 
epoxy resin (a1) having a biphenyl skeleton and a bifunctional epoxy resin 
(a2) having a naphthalene skeleton. 
The effect of preventing the occurrence of cracking during the soldering 
process cannot be exhibited in cases where the epoxy resins (a1) and (a2) 
are not contained. 
The epoxy resin (a1) of the present invention includes a compound 
represented by the following formula (I) : 
##STR1## 
wherein R.sub.1 through R.sub.8 independently represent hydrogen atom, 
halogen atom or a lower alkyl group having 1 to 4 carbon atoms. 
As preferred specific examples of R.sup.1 through R.sup.8 in the 
above-mentioned formula (I), there can be mentioned hydrogen atom, methyl 
group, ethyl group, propyl group, i-propyl group, n-butyl group, sec-butyl 
group, tert-butyl group, chlorine atom and bromine atom. 
As preferred examples of the epoxy resin (a1), there can be mentioned 
4,4'-bis(2,3-epoxypropoxy)biphenyl, 4,4'-bis(2,3 
-epoxypropoxy)-3,3',5,5'-tetramethylbiphenyl, 
4,4'-bis(2,3-epoxypropoxy)-3,3',5,5'-tetramethyl-2-chlorobiphenyl, 
4,4'-bis(2,3-epoxypropoxy)-3,3',5,5'-tetramethyl-2-bromobiphenyl, 
4,4'-bis(2,3-epoxypropoxy)-3,3',5,5'-tetraethylbiphenyl, and 
4,4'-bis(2,3-epoxypropoxy)-3,3',5,5'-tetrabutylbiphenyl. 
As particularly preferable examples, there can be mentioned 
4,4'bis(2,3-epoxypropoxy)biphenyl, and 
4,4'-bis(2,3-epoxypropoxy)-3,3',5,5'-tetramethylbiphenyl. 
In accordance with the present invention, the epoxy resin (a2) includes a 
compound represented by the following formula (II) : 
##STR2## 
wherein two of R.sup.9 to R.sup.16, independently represent a group 
represented by 
##STR3## 
and those remaining independently represent hydrogen atom, halogen atom or 
a lower alkyl group having 1 to 4 carbon atoms. 
Those among R.sup.9 to R.sup.16, excluding the two representing the group 
##STR4## 
independently represent hydrogen atom, halogen atom or a lower alkyl group 
having 1 to 4 carbon atoms. As specifically preferable examples, there can 
be mentioned hydrogen atom, methyl group, ethyl group, propyl group, 
t-propyl group, n-butyl group, sec-butyl group, tert-butyl group, chlorine 
atom and bromine atom. 
As preferred specific examples of the epoxy resin (a2), there can be 
mentioned 1,5-di(2,3-epoxypropoxy)naphthalene, 
1,5-di(2,3-epoxypropoxy)-7-methylnaphthalene, 1,6-di(2,3 
-epoxypropoxy)naphthalene, 1,6-di(2,3-epoxypropoxy)-2-methylnaphthalene, 
1,6-di(2,3-epoxypropoxy)-8-methylnaphthalene, 
1,6-di(2,3-epoxypropoxy)-4,8-dimethylnaphthalene, 
2-bromo-1,6-di(2,3-epoxypropoxy)naphthalene, 
8-bromo-1,6-di(2,3-epoxypropoxy)naphthalene, 
2,7-di(2,3-epoxypropoxy)naphthalene, etc. As particularly preferred 
examples, there can be mentioned 1,5-di(2,3-epoxypropoxy)naphthalene, 
1,6-di(2,3-epoxypropoxy)naphthalene and 
2,7-di(2,3-epoxypropoxy)naphthalene. 
The epoxy resin (A) of the present invention can contain epoxy resins other 
than the epoxy resins (a1) and (a2), in combination with the epoxy resins 
(a1) and (a2). As the other epoxy resins concurrently usable, there can be 
mentioned cresol-novolac type epoxy resin, phenol-novolac type epoxy 
resin, various novolac type epoxy resins synthesized from bisphenol A, 
resorcine, etc., bisphenol A type epoxy resin, linear aliphatic epoxy 
resin, alicyclic epoxy resin, heterocyclic epoxy resin, halogenated epoxy 
resin, etc. 
There is no specific limitation to the ratio of the epoxy resins (a1) and 
(a2) to be contained in the epoxy resin (A), and the effects of the 
present invention can be exerted only if the epoxy resin. (a1) or (a2) is 
contained as the essential component. In order to exert the effects more 
sufficiently, either one or both of the epoxy resins (a1) and (a2) should 
be contained in total at 50 wt % or more in the epoxy resin (A), 
preferably 70 wt % or more in the epoxy resin (A). 
In accordance with the present invention, the compounding amount of the 
epoxy resin (A) is generally 4 to 20 wt %, preferably 6 to 18 wt % to 
total of the composition. 
No specific limitation is imposed on the curing agent (B) in accordance 
with the present invention, so long as the agent reacts with the epoxy 
resin (A) and cures the resin. As specific examples of them, there can be 
mentioned phenol type curing agents including phenol-novolac resin, 
cresol-novolac resin, various novolac resins synthesized from bisphenol A, 
resorcine, etc., phenol alkylallylic resin represented by the following 
formula: 
##STR5## 
wherein n is an integer not less than 0; R is hydrogen atom or a lower 
alkyl group having 1 to 4 carbon atoms, all Rs being not necessarily 
identical, trihydroxyphenyl methane, etc.; acid anhydrides including 
maleic anhydride, phthalic anhydride, pyromellitic anhydride, etc.; 
aromatic amines including methaphenylene diamine, diaminodiphenyl methane, 
diaminodiphenyl sulfone, etc. For encapsulating a semiconductor device, 
there is preferably used a phenolic curing agent from the viewpoint of 
heat resistance, moisture resistance and storage stability; there are 
particularly preferably used phenol-novolac resin, phenol alkylallylic 
resin, trihydroxyphenyl methane, etc. Depending on the use, two or more 
curing agents may be used in combination. 
According to the present invention, the mixing amount of the curing agent 
(B) is generally 3 to 15 wt %, preferably 4 to 10 wt % to the total of the 
composition. In view of mechanical properties and moisture resistance. The 
compounding amount of the epoxy resin (A) and the curing agent (B) is such 
that the chemical equivalent ratio of the curing agent (B) to the epoxy 
resin (A) is in the range of 0.7 to 1.3, preferably in the range of 0.8 to 
1.2. 
In the present invention, a curing catalyst may be used for promoting the 
curing reaction between the epoxy resin (A) and the curing agent (B). Any 
compound capable of promoting the curing reaction can be used in the 
present invention without specific limitation. For example, there can be 
included imidazole compounds such as 2-methylimidazole, 
2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 
2-phenyl-4-methylimidazole, 2-heptadecylimidazole; tertiary amine 
compounds such as triethylamine, benzyldimethylamine, 
.alpha.-methylbenzyldimethylamine, 2-(dimethylaminomethel)phenol, 
2,4,6-tris(dimethylaminomethyl)phenol, and 
1,8-diazabicyclo(5,4,0)undecene-7; organic metal compounds such as 
zirconium tetramethoxide, zirconium tetrapropoxide, 
tetrakis(acetylacetonate)zirconium and tri(acetylacetonate)aluminum; and 
organic phosphine compounds such as triphenylphosphine, 
trimethylphosphine, triethylphosphine, tributylphosphine, 
tri(p-methylphenyl)phosphine, and tri(nonylphenyl)phosphine. From the 
viewpoint of moisture resistance, an organic phosphine compound is 
preferable, and triphenylphosphine in particular is preferably used. A 
combination of two or more of these curing catalysts may be used, 
depending on the use. Preferably, the curing catalyst is incorporated in 
an amount of 0.5 to 5 parts by weight per 100 parts by weight of the epoxy 
resin (A). 
In the present invention, the filler contains the fused silica (C). 
The fused silica (C) in accordance with the present invention consists of 
90 to 50 wt % of crushed fused silica of a mean particle diameter not more 
than 10 .mu.m and 3 to 50 wt % of spherical fused silica of a mean 
particle diameter not more than 4 .mu.m, wherein the mean particle 
diameter of the spherical fused silica is smaller than the mean particle 
diameter of the crushed fused silica. Preferably, the fused silica (C) in 
accordance with the present invention consists of 97 to 60 wt % of crushed 
fused silica of a mean particle diameter not more than 10 .mu.m and 3 to 
40 wt % of spherical fused silica of a mean particle diameter not more 
than 4 .mu.m, wherein the mean particle diameter of the spherical fused 
silica is smaller than the mean particle diameter of the crushed fused 
silica. The crushed fused silica of a mean particle diameter exceeding 10 
.mu.m cannot yield satisfactory heat resistance of solder. There is no 
specific limitation to the crushed fused silica herein, as long as its 
mean particle diameter is not more than 10 .mu.m. Crushed fused silica of 
a mean particle diameter 3 .mu.m or more and 10 .mu.m or less is 
preferably used, from the viewpoint of heat resistance of solder. A 
crushed fused silica of a mean particle diameter of not less than 3 .mu.m 
and less than 7 .mu.m is specifically preferably used. When the mean 
particle diameter of crushed fused silica comes to be 10 .mu.m or less, 
two or more types of crushed fused silica, with different mean particle 
diameters, may be used in combination. The spherical fused silica of a 
mean particle diameter exceeding 4 .mu.m cannot yield satisfactory heat 
resistance of solder. There is no specific limitation to the spherical 
fused silica, as long as its mean particle diameter is not more than 4 
.mu.m, but a spherical fused silica of a mean particle diameter of 0.1 
.mu.m or more and 4 .mu.m or less is preferably used, in view of heat 
resistance of solder. When the mean particle diameter of spherical fused 
silica comes to be 4 .mu.m or less, two or more types of spherical fused 
silica, with different mean particle diameters, may be used in 
combination. The mean particle diameter referred to herein means the 
particle diameter (median size) at which the cumulative weight reaches 50 
wt %. As the measuring method of particle diameter, a particle diameter 
distribution measuring method of laser diffraction type is employed. As 
laser diffraction type measurement, there is used, for example, a Laser 
Granulometer Model 715 manufactured by CILAS Co., Ltd. In the fused silica 
(C), it is also important that the mean particle diameter of spherical 
fused silica is smaller than the mean particle diameter of crushed fused 
silica. In the case that the mean particle diameter of spherical fused 
silica is greater than the mean particle diameter of crushed fused silica, 
a composition with excellent heat resistance of solder cannot be obtained. 
The mean particle diameter of spherical fused silica smaller than the mean 
particle diameter of crushed fused silica is permissible, and preferably, 
the mean particle diameter of spherical fused silica is two-thirds or less 
of the mean particle diameter of crushed fused silica, more preferably 
half or less. Furthermore, in the case that the ratio of crushed fused 
silica to spherical fused silica is not in the above-mentioned range, a 
composition with excellent heat resistance of solder cannot be obtained. 
In the present invention, the ratio of the fused silica (C) is at least 80, 
preferably at least 90 wt % to the total amount of the filler. The ratio 
of the filler is 75 to 90 wt %, more preferably 77 to 88 wt % to the total 
amount of the composition. When the ratio of the filler is less than 75 wt 
% or exceeds 90 wt % to the total amount of the composition or when the 
ratio of the fused silica (C) is less than 80 wt % to the total amount of 
the filler, heat resistance of solder is not sufficient. 
To the epoxy resin composition of the present invention may be added, as 
filler, crystalline silica, calcium carbonate, magnesium carbonate, 
alumina. magnesia, clay, talc, calcium silicate, titanium oxide, antimony 
oxide, asbestos, geass fiber, etc., besides fused silica (C). 
In accordance with the present invention, a polystyrene type block 
copolymer (D) is preferably used. The polystyrene type block copolymer (D) 
includes linear, parabolic or branched block copolymers comprising blocks 
of an aromatic vinyl hydrocarbon polymer having a glass transition 
temperature of at least 25.degree. C., preferably at least 50.degree. C., 
and blocks of a conjugated diene polymer having a glass transition 
temperature not higher than 0.degree. C., preferably not higher than 
-25.degree. C. 
As the aromatic vinyl hydrocarbon, there can be mentioned styrone, 
.alpha.-methylstyrone, o-methylstyrene, p-methylstyrene, 
1,3-dimethylstyrene, vinylnaphthalene, etc., and among them, styrone is 
preferably used. 
As the conjugated diene, there can be mentioned butadiene (1,3-butadiene), 
isoprene (2-methyl-1,3-butadiene), methylisoprene 
(2,3-dimethyl-1,3-butadiene), 1,3-pentadiene, etc., and of these 
conjugated dienes, butadiene and isoprene are preferably used. 
The proportion of the blocks of the aromatic vinyl hydrocarbon, which are 
blocks of the glass phase, in the block copolymer, is preferably 10 to 50 
wt %, and the blocks of the conjugated diene polymer, which are blocks of 
the rubber phase, is preferably 90 to 50 wt %. 
A great number of combinations of the blocks of the glass phase and the 
blocks of the rubber phase are usable and any of these combinations can be 
adopted. A diblock copolymer comprising a single block of rubber phase 
bonded to a single block of glass phase, and a triblock copolymer 
comprising blocks of the glass phase bonded to both ends of the 
intermediate block of the rubber phase are preferably used. In this case, 
the number averaged molecular weight of the block of the glass phase is 
preferably 1,000 to 100,000, more preferably 2,000 to 50,000, and the 
number averaged molecular weight of the block of the rubber phase is 
preferably 5,000 to 200,000, more preferably 10,000 to 100,000. 
The polystyrene type block copolymer (D) can be prepared by the known 
living anion polymerization process, but the preparation thereof is not 
limited to this polymerization process. Namely, the polystyrene type block 
copolymer (D) can be produced also by a cationic polymerization process 
and a radical polymerization process. 
The polystyrene type block copolymer (D) includes also a hydrogenated block 
copolymer formed by reducing parts of unsaturated bonds of the 
above-mentioned block copolymer by hydrogenation. 
In this case, preferably not more than 25% of the aromatic double bonds of 
the blocks of the aromatic vinyl hydrocarbon polymer is hydrogenated, and 
not less than 80% of aliphatic double bonds of the blocks of the 
conjugated diene polymer is hydrogenated. 
As preferable examples of the polystyrene type block copolymer (D), there 
can be mentioned polystyrene/polybutadiene/polystyrene triblock 
copolymer(SBS), polystyrene/polyisoprene/polystyrene triblock 
copolymer(SIS), hydrogenated copolymer of SBS(SEBS), hydrogenated 
copolymer of SIS, polystyrene/isoprene diblock copolymer and hydrogenated 
copolymer of the polystyrene/isoprene diblock copolymer (SEP). 
The amount of polystyrene type block copolymer (D) incorporated is 
generally 0.2 to 10 wt %, preferably 0.5 to 5 wt % to total of the 
composition. The effect of improving the heat resistance of solder and 
reliability on moisture resistance are not sufficient in case of less than 
0.2 wt %, whereas the amount exceeding 10 wt % is not practical because 
molding gets hard due to the lowered fluidity. 
In the case that polystyrene type block copolymer (D) is additionally used 
in the present invention, heat resistance of solder is thereby improved, 
and the reliability after thermal cycling is more improved. The reason is 
assumed to be in the synergistic action of the following two effects; 
(1) Polystyrene type block copolymer (D) makes the cured epoxy resin 
hydrophobic. 
(2) Over a wide temperature range, the block of the conjugated diene 
copolymer in the polystyrene type block copolymer reduces the internal 
stress generating between semiconductor chips and the cured epoxy resin. 
In the present invention, it is preferred to use the copolymer (E) of (1) 
at least one compound selected from the group consisting of ethylene and 
.alpha.-olefin and (2) at least one compound selected from the group 
consisting of unsaturated carboxylic acid and derivatives thereof. 
As a compound selected from the group consisting of the ethylene and 
.alpha.-olefin in the copolymer (E), there can be mentioned ethylene, 
propylene, butene-1, pentene-1, 4-methylpentene-1, octene-1, etc, and of 
these, ethylene is preferably used. Two or more species of ethylene or 
.alpha.-olefin may be concurrently used, depending on the use. As the 
unsaturated carboxylic acid, there can be mentioned acrylic acid, 
methacrylic acid, ethyl acrylic acid, crotonic acid, maleic acid, fumaric 
acid, itaconic acid, citraconic acid, butene dicarboxylic acid, etc. As 
the derivative thereof, there can be mentioned alkyl ester, glycidyl 
ester, acid anhydride or imide thereof. As specific examples, methyl 
acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl 
methacrylate, ethyl methacrylate, glycidyl acrylate, glycidyl 
methacrylate, glycidyl ethyl acrlylate, diglycidyl itaconate ester, 
diglycidyl citraconate ester, diglycidyl butene dicarboxylate ester, 
monoglycidyl butene dicarboxylate ester, maleic anhydride, itaconic 
anhydride, citraconic anhydride, maleic imide, N-phenylmaleic imide, 
itaconic imide, citraconic imide, etc., and of these, acrylic acid, 
methacrylic acid, glycidyl acrylate, glycidyl methacrylate, maleic 
anhydride are preferably used. These unsaturated carboxylic acids and the 
derivatives thereof may be used in combination with two or more. 
In view of heat resistance of solder and moisture resistance, the 
copolymerizing amount of a compound selected from the group consisting of 
unsaturated carboxylic acid and derivatives thereof is preferably 0.01 to 
50 wt %. 
Preferably, the melt index of the copolymer (E), measured according to 
ASTM-D1238, is 0.1 to 5,000, more preferably 1 to 3,000, from the 
viewpoint of moldability and heat resistance of solder. 
In view of heat resistance of solder and moisture resistance, the added 
amount of the copolymer of (E) is generally 0.1 to 10 wt %, preferably 0.5 
to 5 wt %, more preferably 1 to 4 wt % to the total of the composition. 
The copolymer (E) may be preliminarily made into powder, by means of 
grinding, crosslinking, and other means, in accordance with the present 
invention. 
The copolymer (E) can be compounded by appropriate procedures. For example, 
there can be mentioned a method in which the copolymer is preliminarily 
melt mixed with the epoxy resin (A) or the curing agent (B) followed by 
addition of other components, a method in which the copolymer is 
compounded simultaneously with the epoxy resin (A), the curing agent (B) 
and other components. 
In the case that the copolymer of (E) is used in the present invention, 
heat resistance of solder is thereby further improved and the reliability 
after dipping in a solder bath is much more improved. The reason is 
assumed to be due to the synergistic action of the following two effects; 
(1) The copolymer makes the cured epoxy resin hydrophobic. 
(2) Parts of the unsaturated carboxylic acid or a derivative thereof in the 
copolymer reacts with the epoxy resin or the curing agent to render the 
cured epoxy resin tough. 
In view of the reliability, preferably the filler such as fused silica (C) 
is preliminarily surface treated with coupling agents including silane 
coupling agent and titanate coupling agent. Preferably, silane coupling 
agents such as epoxysilane, aminosilane, mercaptosilane, etc., are 
preferably used as the coupling agent. 
A flame retardant such as a halogenated epoxy resin or phosphorus 
compounds, a flame retardant assistant such as antimony trioxide, a 
colorant such as carbon black or iron oxide, an elastomer such as silicone 
rubber, modified nitrile rubber, modified polybutadiene rubber, erc., a 
thermoplastic resin such as polyethylene, a release agent such as 
long-chain fatty acid, metal salt of long-chain fatty acid, ester of 
long-chain fatty acid, amide of long-chain fatty acid, paraffin wax, 
modified silicone oil, etc., and a crosslinking agent such as organic 
peroxide can be added to the epoxy resin composition of the present 
invention. 
The epoxy resin composition of the present invention is preferably 
melt-kneaded. For example, the epoxy resin composition can be prepared by 
carrying out the melt-kneading according to a known kneading method using 
a Banbury mixer, a kneader, a roll, a single-screw or twin-screw extruder 
or a cokneader.