Epoxy resin composition

An epoxy resin composition comprising a trifunctional epoxy resin derived from a trisphenol having the structure represented by the following general formula ##STR1## wherein R represents a hydrogen atom, an alkyl group or a halogen atom, and a novolak-type phenolic resin. This epoxy resin composition gives a cured product having excellent pliability and a high glass transition temperature. It is especially useful as a semiconductor encapsulating material.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to an epoxy resin composition, and more 
specifically, to an epoxy resin composition capable of giving a cured 
product having excellent pliability and a high glass transition 
temperature. 
(2) Description of the Prior Art 
Epoxy resin molding materials of the type in which an epoxy resin is cured 
by using a novolak-type phenolic resin are much used as, for example, a 
semiconductor encapsulating material since they are excellent in 
adhesiveness and moisture resistance. In the molding materials of this 
type, however, internal stresses occur owing to shrinkage during molding 
and curing. This leads to the disadvantage that as the chip size 
increases, cracks are formed in the resin or chips, and bonding wires 
undergo breakage. 
It is known that as means for solving this problem, a flexibilizing agent 
such as silicone resins or polybutadiene is incorporated in the molding 
materials so as to lower the modulus of the encapsulating resin (to make 
it pliable). However, in this method, the glass transition temperature of 
the cured resin abruptly decreases, and its electrical characteristics in 
a high temperature region are degraded. It is difficult therefore to 
obtain molded products having high reliability. Another defect is that the 
mechanical strength of the cured product is reduced. 
SUMMARY OF THE INVENTION 
It is an object of this invention therefore to provide an epoxy resin 
composition capable of giving a cured product having pliability (low 
modulus) and a high glass transition temperature. 
The present invention provides an epoxy resin composition comprising as 
essential components 
(A) a trifunctional epoxy compound obtained by condensation reaction of a 
phenol derivative represented by the following general formula 
##STR2## 
wherein R.sub.1 to R.sub.3 represents a hydrogen atom or an alkyl group 
having not more than 6 carbon atoms, R.sub.4 to R.sub.11 represent a 
hydrogen atom, an alkyl group having not more than 6 carbon atoms or a 
halogen atom, and the groups R.sub.1 to R.sub.11 may be identical with 
each other, with epichlorohydrin, and 
(B) a novolak-type phenolic resin. 
The important feature of the present invention lies in the use of a 
specific trifunctional epoxy resin obtained from the phenol derivative of 
the above general formula. By combining this trifunctional epoxy resin 
with the novolak-type phenolic resin, it is possible to lower the modulus 
of the cured product (make it pliable) and increase the glass transition 
temperature. This also effectively inhibit the reduction of its strength. 
The novolak-type phenolic resin used as component (B) in the epoxy resin 
composition of this invention serves as a curing agent. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
(A) Epoxy resin 
The epoxy resin used in this invention can be produced by etherifying a 
trisphenol represented by general formula (I) 
##STR3## 
wherein R.sub.1 to R.sub.3 represents a hydrogen atom or an alkyl group 
having not more than 6 carbon atoms, R.sub.4 to R.sub.11 represent a 
hydrogen atom, an alkyl group having not more than 6 carbon atoms or a 
halogen atom, and the groups R.sub.1 to R.sub.11 may be identical with 
each other, with epichlorohydrin in the presence of a suitable 
etherification catalyst and then dehydrohalogenating the product. 
The trisphenol of general formula (I) is obtained by reacting an aromatic 
ketone or aldehyde having at the side chain an aliphatic group with an 
ethylenic double bond, with a monohydric phenol. 
When isopropenyl acetophenone, for example, is used as the aromatic ketone, 
a trisphenol is obtained in accordance with the following reaction scheme. 
##STR4## 
It is seen from this reaction scheme that the types of the groups R.sub.1 
to R.sub.3, R.sub.8 and R.sub.9 are determined depending upon the type of 
the aromatic ketone or aldehyde used, and the types of the groups R.sub.4 
to R.sub.7, R.sub.10 and R.sub.11 are determined depending upon the type 
of the monohydric phenol used. For example, when an aromatic aldehyde is 
used, R.sub.1 in general formula (I) is a hydrogen atom. 
A compound of general formula (I) in which all aromatic rings having a 
phenolic hydroxyl group are identical may be obtained by carrying out the 
above reaction using the corresponding phenol. A compound of general 
formula (I) in which all aromatic rings having a phenolic hydroxyl group 
are different may be obtained by carrying out the reaction using a mixture 
of the corresponding phenols. 
A trisphenol of general formula (I) having halogen atoms at the side chains 
of the aromatic rings may be produced by performing the above reaction 
using a halogen-substituted monohydric phenol. If desired, it may be 
obtained by first producing a trisphenol and then halogenating it. 
The reaction of the aromatic ketone or aldehyde with the monohydric phenol 
may be carried out, for example, by using a protonic acid such as 
hydrochloric acid as a catalyst and adding the aromatic ketone or aldehyde 
dropwise to a mixture of a stoicheometrically excessive amount of the 
monohydric phenol and the catalyst. As required, methylmercaptan or 
mercaptoacetic acid, for example, may be added to the reaction system as a 
promotor. This reaction is carried out usually at a temperature of 
40.degree. to 80.degree. C. under atmospheric or elevated pressure. 
The trifunctional epoxy resin used in this invention is obtained by 
etherifying the trisphenol with epichlorohydrin and then 
dehydrohalogenating the product. This reaction itself may be carried out 
by a known method. For example, the etherification may be carried out in 
the presence of about 0.005 to 5 mole %, per equivalent of the phenolic 
hydroxyl groups of the trisphenol, of an etherification catalyst, for 
example, a tertiary amine such as trimethylamine or triethylamine, a 
tertiary phosphine such as triphenylphosphine or tributylphosphine, a 
quaternary ammonium salt such as tetramethyl ammonium chloride, 
tetramethyl ammonium bromide, tetraethyl ammonium chloride, tetraethyl 
ammonium bromide or choline chloride, a quaternary phosphonium salt such 
as tetramethylphsphonium bromide, tetramethylphosphonium iodide or 
triphenylpropylphosphonium bromide or a tertiary sulfonium salt such as 
benzyldibutylsulfonium chloride or benzyldimethylsulfonium chloride, 
preferably in the presence of the quaternary ammonium salt. 
The etherification step is carried out until at least 50%, preferably at 
least 80%, of the hydroxyl groups of the trisphenol are etherified. The 
reaction is carried out generally at a temperature of about 60.degree. to 
110.degree. C. for about 1 to 12 hours. Preferably, water should not be 
present at this time. If water is present, its amount is adjusted to not 
more than 3.0% by weight. 
The etherification reaction product still containing the unreacted 
epihalohydrin is submitted to the next dehydrohalogenating step. This 
reaction is carried out by using at least 0.5 mole, especially at least 
0.8 mole, per equivalent of the phenolic hydroxyl groups of the 
trisphenol, of a catalyst, for example an alkali metal hydroxide such as 
sodium hydroxide, potassium hydroxide or lithium hydroxide, preferably 
sodium hydroxide. To avoid troubles such as gellation, the amount of the 
alkali metal compound as the catalyst is preferably limited to not more 
than 1 mole. 
After the reaction, the reaction mixture is distilled under reduced 
pressure to remove the unreacted epichlorohydrin and washed with water, 
for example, to remove the by-product salt, and as required neutralized 
with a weak acid such as phosphoric acid or sodium dihydrogen phosphate. 
Subsequent drying gives the desired epoxy resin. 
As can be seen from the structure of the trisphenol of general formula (I), 
the trifunctional epoxy resin used in this invention is characterized by 
the chemical structure in which the four benzene rings are linked in 
branches via one carbon atom. It has an epoxy equivalent of 198 to 400 and 
a softening point of 50.degree. to 120.degree. C. 
Specific examples of this epoxy resin include 
1-(.alpha.-methyl-.alpha.-(4'-glycidoxyphenyl)ethyl)-4-(.alpha.',.alpha.'-b 
is(4"-glycidoxyphenyl)ethyl)benzene, 
1-(.alpha.-methyl-.alpha.-(2'-methyl-4'-glycidoxy-5'-tert.butylphenyl)ethyl 
)-4-(.alpha.',.alpha.'-bis(2"-methyl-4"-glycidoxy-5"-tert.butylphenyl)ethyl 
)benzene, 
1-(.alpha.-methyl-.alpha.-(3',5'-dimethyl-4'-glycidoxyphenyl)ethyl)-4-(.alp 
ha.',.alpha.'-bis(3",5"-dimethyl-4"-glycidoxyphenyl)ethyl)benzene, 
1-(.alpha.-methyl-.alpha.-(3'-tert.butyl-4'-glycidoxyphenyl)ethyl)-4-(.alph 
a.',.alpha.'-bis(3"-tert.butyl-4"-glycidoxyphenyl)ethyl)benzene, 
1-(.alpha.-methyl-.alpha.-(3'-methyl-4'-glycidoxy-5'-tert.butylphenyl)ethyl 
)-4-(.alpha.',.alpha.'-bis(3"-methyl-4"-glycidoxy-5"-tert.butylphenyl)ethyl 
)benzene, and 
1-(.alpha.-methyl-.alpha.-(2',5'-dimethyl-4'-glycidoxyphenyl)ethyl)-4-(.alp 
ha.',.alpha.'-bis(2",5"-dimethyl-4"-glycidoxyphenyl)ethyl)benzene. 
In the trifunctional epoxy resin, each of the phenolic hydroxyl groups in 
formula (I) is preferably bonded to the para-position of the phenyl group. 
Preferably, each of R.sub.1 to R.sub.4 is an alkyl group having not more 
than 4 carbon atoms, especially a methyl group, and each of R.sub.4 to 
R.sub.9 is a hydrogen atom, a methyl group or a tertiary butyl group. 
Another epoxy resin such as an o-cresol novolak-type epoxy resin may be 
used jointly so long as it does not impair the purpose of this invention. 
It may be used, for example, in an amount of at least 5 parts by weight, 
especially at least 10 parts by weight, per 100 parts by weight of the 
trifunctional epoxy resin. 
(B) Novolak-type phenolic resin 
In the present invention, a novolak-type phenolic resin is used as a curing 
agent for the trifunctional epoxy resin (A). 
The phenolic resin is obtained by condensing phenol or an alkyl-substituted 
phenol such as o-cresol, p-cresol, t-butylphenol, cumylphenol or 
nonylphenol with formaldehyde in an acid catalyst. Those having a hydroxyl 
equivalent of 100 to 150 and a softening point of 60.degree. to 
110.degree. C. are preferably used. 
The phenolic resin is incorporated in an amount of 20 to 120 parts by 
weight, especially 40 to 100 parts by weight, per 100 parts by weight of 
the trifunctional epoxy resin (A). 
Additives 
The epoxy resin composition of this invention comprises the trifunctional 
epoxy resin and the novolak-type phenolic resin described above as 
essential components. It may contain known additives such as a curing 
promoter, a filler, a mold releasing agent, a coloring agent, a flame 
retardant, and a coupling agent. 
Examples of the curing promoter are imidazoles such as 
2-methyl-4-methylimidazole, 2-phenylimidazole and 
2-ethyl-4-methylimidazoleazine, hydrazide compounds such as dibasic acid 
hydrazide and a boron trifluoride-amine complex compound. The curing 
promoter may be used in an amount of 0.1 to 20 parts by weight per 100 
parts by weight of the trifunctional epoxy resin. 
Examples of the filler are silica, alumina, talc, mica, heavy calcium 
carbonate, kaolin, diatomaceous earth, asbestos, graphite, boron, silicon 
carbide, carbon fibers and glass fibers. The filler may be used in an 
amount of 50 to 900 parts by weight per 100 parts by weight of the 
components (A) and (B) combined. 
Examples of the mold releasing agent are carnauba wax, montan wax, ester 
wax, stearic acid, calcium stearate, zinc stearate, 12-hydroxystearic acid 
and calcium 12-hydroxystearate. The mold releasing agent may be used in an 
amount of 0.1 to 10 parts by weight per 100 parts by weight of the 
components (A) and (B) combined. 
Carbon black is an example of the coloring agent. It may be used in an 
amount of 0.01 to 5 parts by weight per 100 parts by weight of the 
components (A) and (B) combined. 
Halogenated polyphenols such as tetrabromobisphenol A and antimony oxide 
may, for example, be used as the flame retardant. The flame retardant may 
be used in an amount of 12 to 25 part by weight per 100 parts by weight of 
the components (A) and (B) combined. 
Silane compounds such as .gamma.-glycidoxypropyl-trimethoxysilane may, for 
example, be used as the coupling agent. It may be used in an amount of 0.1 
to 10 parts by weight per 100 parts by weight of the components (A) and 
(B) combined. 
Resin composition 
The resin composition of this invention may be prepared usually by kneading 
the above components at a temperature of about 80.degree. to 120.degree. 
C. by using a twin-screw extruder or a roll mill such as a two-roll mill. 
The resulting epoxy resin of the composition may be cooled and pulverized 
after kneading, and used as various molding materials. 
As shown in the following examples, cured molded articles having a low 
modulus, a high glass transition temperature and excellent mechanical 
properties such as high strength can be obtained. Thus, molded products 
having high reliability can be obtained from the epoxy resin composition 
of this invention. 
Since the occurrence of internal stresses owing to shrinkage during curing 
is suppressed, the epoxy resin composition of this invention is especially 
useful as a semiconductor encapsulating material.

The following examples illustrate the present invention more specifically. 
All parts in these examples are by weight. 
EXAMPLE 1 
The components in accordance with the following compounding recipe were 
kneaded by two rolls at 100.degree. C. for 5 minutes, cooled, and 
pulverized to obtain a molding material. 
______________________________________ 
Compounding recipe 
______________________________________ 
1-(.alpha.-methyl-.alpha.(4'-glycidoxy- 
100 parts 
phenyl)ethyl)-4-(.alpha.',.alpha.'-bis-(4"- 
glycidoxyphenylethyl)benzene 
(epoxy equivalent 269) 
Novolak-type phenolic resin 
38 parts 
(softening point 97.degree. C.) 
2-Ethyl-4-methylimidazoleazine 
2 parts 
(curing promoter) 
Amorphous silica 495 parts 
Carbon black 1 part 
Silane coupling agent (KBM-403, 
2.5 parts 
produced by Shin-etsu Chemical 
Co., Ltd.) 
Carnauba wax 2 parts 
______________________________________ 
The resulting molding material was molded at 160.degree. C. and 70 
kg/cm.sup.2 for 5 minutes by a transfer molding machine to form a sheet 
having a thickness of 4 mm. 
The sheet was then post-cured at 160.degree. C. for 8 hours to prepare test 
pieces in accordance with JIS K-6911, and its flexural strength, flexural 
moduluis and glass transition temperature were measured on these test 
pieces in accordance with JIS K-6911. The results are shown in Table 1. 
EXAMPLE 2 
A molding material was prepared in the same way as in Example 1 except that 
the following compounding recipe was used. The various properties were 
measured as in Example 1, and the results are shown in Table 1. 
______________________________________ 
Compounding recipe 
______________________________________ 
1-(.alpha.-methyl-.alpha.(4'-glycidoxy- 
50 parts 
phenyl)ethyl)-4-(.alpha.',.alpha.' -bis-(4"- 
glycidoxyphenyl)ethyl)benzene 
(epoxy equivalent 269) 
o-Cresol novolak-type epoxy 
50 parts 
resin (epoxy equivalent 215) 
Novolak-type phenol 43 parts 
(softening point 97.degree. C.) 
______________________________________ 
EXAMPLE 3 
A molding material was prepared in the same way as in Example 1 except that 
the following compounding recipe was used. The various propertiers were 
measured as in Example 1, and the results are shown in Table 1. 
______________________________________ 
Compounding recipe 
______________________________________ 
1-(.alpha.-methyl-.alpha.(4'-glycidoxy- 
30 parts 
phenyl)ethyl)-4-(.alpha.',.alpha.' -bis-(4"- 
glycidoxyphenyl)ethyl)benzene 
(epoxy equivalent 269) 
o-Cresol novolak-type epoxy 
70 parts 
resin (epoxy equivalent 215) 
Novolak-type phenol (softening 
47 parts 
point 97.degree. C.) 
______________________________________ 
COMATIVE EXAMPLE 1 
A molding material was prepared in the same way as in Example 1 except that 
the following compounding recipe was used. The various properties were 
measured as in Example 1, and the results are shown in Table 1. 
______________________________________ 
Compounding recipe 
______________________________________ 
o-Cresol novolak-type epoxy 
100 parts 
resin (epoxy equivalent 215) 
Novolak-type phenolic resin 
45 parts 
(softening point 97.degree. C.) 
2-Ethyl-4-methylimidazoleazine 
2 parts 
Amorphous silica 495 parts 
Carbon black 1 part 
Silane coupling agent (KBM-403, 
2.5 parts 
produced by Shin-etsu Chemical 
Co., Ltd.) 
Carnauba wax 2 parts 
______________________________________ 
COMATIVE EXAMPLE 2 
A molding material was prepared in the same way as in Comparative Example 1 
except that 8.6 parts of carboxyl-terminated polybutadiene rubber (HYCAR 
CTB 2000X162, a product of Ube Industries, Ltd.) was added further. The 
properties of the molding material were measured as in Example 1, and the 
results are shown in Table 1, 
COMATIVE EXAMPLE 3 
A molding material was prepared in the same way as in Comparative Example 1 
except that 8.6 parts of carboxyl-terminated polybutadiene acrylonitrile 
rubber (HYCAR CTBN 1300X8, a product of Ube Industries, Ltd.) was added 
further. The properties of the molding material were meaasured as in 
Example 1, and the results are shown in Table 1. 
It is understood from the results of the above Examples and Comparative 
Examples that when an attempt is made to lower the modulus of a cured 
molded article by adding a rubber component to the epoxy resin, both its 
strength and glass transition temperature are decreased, but that when the 
specific trifunctional epoxy resin is used in accordance with this 
invention, the decrease of the strength and the glass transition 
temperature is effectively suppressed. 
TABLE 1 
______________________________________ 
Ex. 1 Ex. 2 Ex. 3 CEx. 1 CEx. 2 CEx. 3 
______________________________________ 
Flexural 
14 14 13.5 12 11.5 11 
strength 
(kg/mm.sup.2) 
Flexural 
1350 1400 1450 1650 1350 1400 
modulus 
(kg/mm.sup.2) 
Glass 168 168 168 168 160 160 
transition 
tempera- 
ture (.degree.C.) 
______________________________________ 
Ex. = Example 
CEx. = Comparative Example