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BACKGROUND OF THE INVENTION
The present invention relates to an epoxy resin-based curable composition
capable of giving cured products having excellent mechanical and electric
properties and resistance against water as well as remarkably improved
resistance against formation of cracks with a glass transition temperature
not lower than in conventional epoxy resin-based cured products. In
particular, the invention relates to and provides a basic formulation of
an epoxy resin-based curable composition capable of giving a cured product
having remarkably improved resistance against formation of cracks with low
internal stress as are the essential requirements in the resin
compositions suitable for packaging or encapsulation of electric or
electronic parts and devices.
As is well known, a variety of resin compositions are currently used for
the plastic packaging or encapsulation of electric or electronic parts and
devices including the compositions formulated with the base resins of, for
example, thermosetting resins such as epoxy resins, silicone resins,
polybutadienes, polyurethanes, phenolic resins and the like as well as
various thermoplastic resins utilizing their respective advantageous
properties according to the desired applications.
Among the above named resin compositions, those based on an epoxy resin are
used most widely and in the largest quantities by virtue of their
excellent mechanical and electric properties, heat resistance and adhesion
as well as their good workability or moldability. In particular, epoxy
resin-based curable compositions predominantly occupy an outstanding
position by virtue of the excellent performance thereof as a resin
composition for encapsulation of semiconductor devices such as diodes,
transistors, ICs, LSIs and the like under rapid technical growth in recent
years.
Even though the epoxy resin-based curable compositions have been hitherto
quite satisfactory in almost all respects as an encapsulating resin
composition, there is a growing demand for an epoxy resin-based curable
composition having more and more improved performance to comply with the
development of the technology of electronics or, in particular, the trend
of thinner and thinner or smaller and smaller design of the electronic
devices and the increase in the density of integration as in LSIs.
Accordingly, the conventional epoxy resin-based curable compositions are
already not always quite satisfactory materials to meet such high-grade
requirements in the modern electronics technology.
That is, improvements are desired for epoxy resin-based curable
compositions in several aspects including, for example, higher and higher
purity to prevent contamination of the semiconductor devices, higher
electric performance as a matter of course, improved moldability to ensure
shortened molding cycles contributing to the increased productivity,
higher heat conduction or heat dissipation to ensure applicability to
high-power devices, lower stress in the cured product to protect the
encapsulated electronic device from an excessive physical stress and
increased resistance against formation of cracks to withstand any severe
thermal and mechanical shocks. Needless to say, many attempts have been
undertaken to obtain epoxy resin-based curable compositions improved in
these respects but particular difficulties are encountered in obtaining
compatibility between the higher heat conductivity and the improved
resistance against crack formation or decreased stress without adversely
affecting the other characteristics so that no epoxy resin-based curable
compositions have not yet been developed as imparted with the above
described improved properties in combination to be a promising
encapsulating resin composition in modern electronics industry.
Most of the epoxy resin-based curable compositions currently on use for the
encapsulation of semiconductor devices are formulated with a
bisphenol-type epoxy resin or a novolactype epoxy resin as the base
component filled with a large volume of a crystalline or amorphous silica
filler together with a crosslinking or curing agent to effect crosslinking
of the polymer molecules with heating.
Although it is a relatively easy matter to satisfy either one of the above
described requirements alone, it is sometimes rather a formidable problem
to obtain improvement of the performance of the resin compositions in one
particular point without sacrifice of one or more of the other properties
and the requirements for different properties are sometimes incompatible
with each other so that mere extension of hitherto undertaken way of
investigations is of power no more.
For example, it is a conventional measure hitherto undertaken when
improvements in the decreased stress and increased resistance against
crack formation are desired to formulate the epoxy resin-based composition
with a flexibility-improver such as 1,4-butanediol, polyoxyalkylene ether
glycol, glycerin, polysulfide polymer, polyoxyalkylene glycidyl ether and
the like but formulation of these additives is always accompanied by
lowering of the glass transition temperature and decrease in the heat
resistance as well as resistance against moisture or water. On the other
hand, improvement in the heat conductivity is readily achieved by
formulating the resin composition with a large volume of powdery
crystalline silica alone as the filler though with unavoidable problems of
decreased resistance against crack formation and larger stress or a
coefficient of thermal expansion. In short, extreme difficulties are
encountered in solving the above mentioned problem of obtaining
compatibility in the improvements in respects of the high heat
conductivity and resistance against crack formation as the largest
requirements for the epoxy resin-based curable compositions insofar as the
way of investigations is limited on the conventional route.
SUMMARY OF THE INVENTION
It is therefore the primary object of the present invention to provide a
novel and improved epoxy resin-based curable composition suitable for use
as an encapsulating resin composition of electronics or semiconductor
devices to meet the very high performance requirements in the modern
electronics technology.
A further object of the invention is to provide an epoxy resin-based
curable composition capable of giving a cured product exhibiting
remarkably low stress and high resistance against crack formation but yet
having a very high glass transition temperature as being improved over
conventional compositions in both of these two properties with
compatibility.
Thus, the epoxy resin-based curable composition of the present invention
developed as a result of the extensive investigations undertaken by the
inventors to solve the above described difficult problems essentially
comprises:
(a) 100 parts by weight of a curable epoxy resin blend composed of an epoxy
resin and a crosslinking or curing agent therefor in such a proportion as
to effect full curing of the epoxy resin, and
(b) from 5 to 100 parts by weight of a block copolymer having at least one
hydroxyl group or epoxy group reactive with the component (a) and composed
of
(b-1) at least one segment of an aromatic polymeric moiety containing at
least two mono- to tetravalent aromatic groups bonded together mutually or
through one or more of divalent linking units expressed by the formula
--(--CR.sub.2 --).sub.t --, in which R is a hydrogen atom or a monovalent
hydrocarbon group and t is a positive integer of 1 to 6, each of the mono-
to tetra-valent aromatic groups being derived from a monocyclic aromatic
compound with a single benzene ring devoid of 1 to 4 hydrogen atoms or
substituent atoms or groups therefor directly bonded to the benzene ring,
and
(b-2) at least one segment of an organopolysiloxane moiety having from 30
to 200 silicon atoms in the polysiloxane linkage and expressed by the
average unit formula
R.sup.a.sub.1 SiO.sub.(4-a)/2, (I)
in which R.sup.1 is a monovalent organic group, at least 70 % in number of
the groups R.sup.1 being alkyl groups and a part of the groups R.sup.1
optionally being hydrogen atoms, and a
is a positive number in the range from 1.8 to 2.7, said segments (b-1) and
(b-2) being bonded together through a silicon-to-carbon linkage, and
(c) an inorganic filler in an amount in the range from 100 to 500 % by
weight based on the total amount of the components (a) and (b).
The above defined aromatic polymeric moiety containing at least two mono-
to tetravalent aromatic groups is preferably a phenol novolac or an epoxy
phenol novolac.
It is further preferable that the above defined epoxy resin-based
composition is filled with an inorganic filler in an amount of, for
example, up to 500 parts by weight per 100 parts by weight of the curable
epoxy resin blend as the component (a).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As is proposed by some of the inventors in Japanese Patent Kokai 56-129246,
organopolysiloxanes or, in particular, those having a linear molecular
structure are promising modifiers for epoxy resin-based curable
compositions to improve the flexibility or pliability of the cured
products thereof in a wide range of temperature. This advantageous effect
of organopolysiloxane is presumably due to the excellent heat resistance
thereof with the extraordinarily high bond energy amounting to 106
kilocalories/mole of the siloxane linkages forming the skeletal structure
of the molecule as well as the special interfacial property as a
consequence of the flexibility of the siloxane chain with high
rotatability of the siloxane linkages relative to each other.
Different from other kinds of flexibility-imparting agents for epoxy
resins, furthermore, organopolysiloxanes are hardly miscible with the
epoxy resin even at a considerably high temperature so that the glass
transition temperature of the cured products of epoxy resin compositions
is little decreased by compounding with an organopolysiloxane different
from other kinds of flexibility-imparting agents which unavoidably cause a
decrease in the glass transition temperature.
The above mentioned relatively low compatibility of an organopolysiloxane
and an epoxy resin, on the contrary, sometimes causes another problem that
high uniformity and stability of dispersion cannot always be expected
between these components resulting in rather low mechanical strengths and
high moisture permeation of the cured products of the resin composition
although these defective points are not detrimental against the practical
application of organopolysiloxanes as a modifier of epoxy resin-based
curable compositions. This is presumably due to the good affinity of the
organopolysiloxane molecules to the surface of the particles of silica
fillers most widely used in the epoxy resin-based compositions in
comparison with the other kinds of organic polymers sometimes used as a
modifier of epoxy resin compositions.
Taking the above described situations into consideration, the inventors
have conducted extensive investigations to obtain a modifier for epoxy
resin-based curable compositions and arrived at a conclusion that a block
copolymer composed, as is mentioned above, of polymeric aromatic segments
and organopolysiloxane segments having a specified degree of
polymerization is the most suitable with very high dispersibility in the
epoxy resin and without adversely affecting the mechanical strengths and
the moisture permeability of the cured products of the composition.
The base component, i.e. the component (a), is a curable epoxy resin blend
composed of an epoxy resin and a curing agent therefor. The epoxy resin
here implied includes those epoxy resins having at least two epoxy groups
in a molecule and various kinds of commercially available epoxy resins are
suitable without particular limitations on the molecular structure and
molecular weight insofar as they are curable when blended with a
crosslinking or curing agent. Suitable epoxy resins include, for example,
those epoxy resins synthesized from epichlorohydrin and a bisphenol as
well as from various kinds of novolac resins, alicyclic epoxy resins,
halo- gen-, e.g. chlorine- and bromine-, containing epoxy resins and the
like. The epoxy resins may be used either singly or as a combination of
two kinds or more of different types according to need.
Further, certain monoepoxy compounds may be included, according to need, in
combination with the component (a) above defined including, for example,
styrene oxide, cyclohexene oxide, propylene oxide, methyl glycidyl ether,
ethyl glycidyl ether, phenyl glycidyl ether, allyl glycidyl ether,
octylene oxide, dodecene oxide and the like.
The crosslinking or curing agent as the other essential constituent of the
curable epoxy resin blend as the component (a) may be one of the well
known ones in the art of epoxy resins exemplified by the amine compounds
such as diamino diphenyl methane, diamino diphenyl sulfone, 1,3-phenylene
diamine and the like, acid anhydride compounds such as phthalic anhydride,
pyromellitic anhydride, benzophenone tetracarboxylic acid anhydride and
the like and novolac resins containing at least two phenolic hydroxy
groups in a molecule such as phenol novolac, cresol novolac and the like.
In addition to the above described crosslinking or curing agents, it is
generally preferable that, when a novolac resin or an acid anhydride is
used as the crosslinking or curing agent, in particular, the inventive
composition contains a curing accelerator with an object to accelerate the
reaction of the epoxy resin and the crosslinking or curing agent. Suitable
curing accelerators include, for example, imidazole compounds, tertiary
amine compounds, phosphine compounds, cycloamidine compounds and the like.
The amount of the crosslinking or curing agent relative to the amount of
the epoxy resin in the curable epoxy resin blend is not particularly
limitative provided that complete curing of the epoxy resin can be
obtained according to the established formulation for the epoxy resin.
Exemplarily, the amount of the crosslinking or curing agent is in the
range from 1 to 200 % by weight based on the amount of the epoxy resin.
As is known, it is esential in order to obtain long durability and high
reliability of resin-encapsulated semiconductor devices that the intrusion
of moisture is completely prevented through the cracks in the
encapsulating resin and interstices between the encapsulating resin and
metallic leads unavoidably formed when the encapsulating resin and the
chips or frames have thermal expansion coefficients greatly differing from
each other. The component (b), which is the most characteristic and
essential component in the inventive composition in this regard, is the
above defined block copolymer composed of at least one polymeric aromatic
segment and at least one organopolysiloxane segment. When the component
(b) is not the above mentioned block copolymer but is composed only of
organopolysiloxane segments, various drawbacks are unavoidable including
poor dispersion of the component in the composition, poor adhesion between
the encapsulating resin and the chips or leads resulting in moisture
intrusion, migration of the component toward the surface to cause poor
reception of marking inks and segregation and inhomogenization of the
components in the lapse of time. The block copolymer of this type is
characteristically effective in increasing the resistance of the cured
products of the resin composition against formation of cracks as the
primary object of the present invention. Such an improving effect on the
resistance against crack formation may be expected to a considerable
extent even when the epoxy resin blend is admixed with a block copolymer
composed of polymeric non-aromatic segments and organopolysiloxane
segments but the block coolymer of such a type has a relatively low
miscibility as an additive with the epoxy resin blend so that the additive
may migrate in the article shaped of the resin composition toward the
surface in the lapse of time. In contrast thereto, the aromaticity of the
here proposed block copolymer serves to adequately control the miscibility
of the additive with the epoxy resin blend and suppress the migration
thereof in the cured products.
The aromatic polymeric segment as a part of the block copolymer essentially
and basically contains at least two mono-to tetravalent aromatic groups
bonded together mutually. The mono- to tetravalent aromatic group is
derived from a monocyclic aromatic compound with a single benzene ring by
removing one to four hydrogen atoms or substituent atoms or groups
therefore directly bonded to the benzene ring. Such an aromatic group may
be expressed by the formula C.sub.6 A.sub.m, in which A is a hydrogen atom
or a monovalent atom or group bonded to the benzene ring such as halogen
atoms, hydroxy group, mercapto group, amino group, carboxyl group,
isocyanato group, glycidyloxy group, substituted or unsubstituted
monovalent hydrocarbon groups or hydrocarbyloxy groups having from 1 to 6
carbon atoms and m is an integer of 2 to 5 inclusive.
The hydrocarbon groups as the substituent groups on the benzene nucleus are
exemplified by methyl, ethyl, propyl, tert-butyl, vinyl, allyl, phenyl and
cyclohexyl groups. These hydrocarbon groups may be further substituted
with other substituent atoms or groups which may contain one or more of
hetero atoms such as oxygen, sulfur, silicon, nitrogen and the like.
Several of the examples of the substituent groups include alkoxy groups
such as methoxy and ethoxy groups and those groups represented by the
following formulas, in which R is a hydrogen atom or a monovalent
hydrocarbon group having 1 to 6 carbon atoms, W is a hydroxy, alkoxy or
acyloxy group and u is an integer from 0 to 6 inclusive:
--(--CR.sub.2 --).sub.u --OH; --(--CR.sub.2 --).sub.u --SiR.sub.2 H;
--O--(--CR.sub.2 --).sub.u+1 --SiR.sub.2 ; --(--CR.sub.2 --).sub.u --COOH;
--(--CR.sub.2 --).sub.u --SiR.sub.2 W; --O--(--CR.sub.2 --).sub.u+1
--SiR.sub.2 W; --(--CR.sub.2 --)
##STR1##
and --O--(--CR.sub.2 --)
##STR2##
The preferable substituent groups among those expressed by the above given
formulas are those terminated with a hydroxy group or an epoxy group.
Namely, the aromatic segment should preferably have at least one hydroxy
or epoxy group reactive with the epoxy groups in the component (a).
These mono- to tetravalent aromatic groups may be bonded mutually but
preferably they are bonded together through a divalent linking group
--(--CR.sub.2 --).sub.t --as mentioned before as in a phenol novolac resin
in which hydroxy-substituted aromatic groups are bonded together through a
methylene group therebetween. The manner in which the aromatic groups are
bonded together, optionally, through the linking groups, is not
particularly limitative according to the types of the aromatic groups.
Several of the examples for the aromatic polymers to be introduced into the
block copolymer as the aromatic segments are expressed by the following
formulas in which A is a hydrogen atom or one of the substituent atoms or
groups as above mentioned, B is a monovalent group such as vinyl, hydroxy
and methoxy groups, u is an integer of 0 to 6, x and y are each an integer
showing the number of repetition of the group in the square brackets and m
and n are each a number of the substituent atoms or groups sufficient to
satisfy the hexavalency of the benzene ring.
##STR3##
The aromatic polymeric moiety should preferably be an epoxyphenol novolac
or a phenol novolac expressed by the first of the above given formulas.
The other class of the segments constituting the block copolymer together
with the above described aromatic polymeric moiety is derived from the
organopolysiloxane expressed by the average unit formula (I) above given,
in which R.sup.1 is a monovalent organic group, a part of the groups
R.sup.1 in a molecule being optionally hydrogen atoms, and a is a positive
number in the range from 1.8 to 2.7, and having from 30 to 200 silicon
atoms in a molecule.
It is preferable that most of the monovalent organic groups in a molecule
denoted by R.sup.1 are substituted or unsubstituted monovalent hydrocarbon
groups exemplified by methyl, ethyl, propyl, butyl, vinyl, allyl and
phenyl groups as well as those groups obtained by partly replacing the
hydrogen atoms in these hydrocarbon groups with halogen atoms, mercapto
groups, amino groups, hydroxy groups and the like such as hydroxymethyl,
N-(2-aminoethyl)aminomethyl, 3-aminopropyl, 2-mercaptoethyl,
3-mercaptopropyl, 3-cyanopropyl, hydroxyphenoxymethyl, 3-glycidyloxy
propyl, 2-(3,4-epoxycyclohexyl)ethyl and the like groups. A part of the
groups R.sup.1 may be alkoxy groups, e.g. methoxy and ethoxy groups.
Furthermore, the organopolysiloxane may contain a small number of
silanolic hydroxy groups bonded to the silicon atoms.
As is mentioned above, each of the organopolysiloxane segments should have
from 30 to 200 silicon atoms or, in other words, the degree of
polymerization of each organopolysiloxane segment should be 30 to 200. A
block copolymer prepared using an organopolysiloxane having a degree of
polymerization smaller than 30 is excessively compatible with the epoxy
resin so that the resultant resin composition would have a decreased glass
transition temperature although the resistance against crack formation can
be improved. When the degree of polymerization of the organopolysiloxane
is larger than 200, on the other hand, the block copolymer is poorly
miscible with the epoxy resin due to the increased molecular weight so
that the block copolymer can hardly be dispersed in the epoxy resin in a
fineness of, for example, 1 .mu.m or finer and the resultant resin
composition may have somewhat decresed resistance against crack formation.
Thus, the above mentioned limitation of 30 to 200 is essential of the
degree of polymerization of the organopolysiloxane in order to improve the
resistance against crack formation without decreasing the glass transition
temperature.
It is preferable that the organopolysiloxane segments may have a linear
structure composed of diorganosil-oxane units excepting the monofunctional
terminal groups in order that the cured products of the resultant
inventive composition may have a sufficiently high resistance against
crack formation. Of course, small amounts of branched structures have no
particular adverse effects.
The block copolymer as the component (b) in the inventive composition is
obtained by reacting an aromatic polymer and an organopolysiloxane in a
manner which is readily understood by those skilled in the art of
organosilicon chemistry. In this case, it is preferable that the aromatic
polymeric moieties and the organosiloxane moieties are bonded together
each through a carbon-to-silicon linkage and not through a Si--O--C
linkage. The reasons for this preference are as follows.
1. The Si--O--C linkage is less resistant than the Si--C linkage against
hydrolysis to cause segregation of the organopolysiloxane moiety leading
to the above mentioned drawbacks.
2. The same problem of hydrolysis is also involved in the long-term storage
of an uncured composition.
3. In view of the instability of the linkage of Si--O--C, each of the
ingredients is required to have a high degree of purity, in particular, in
respect of water-soluble ionic impurities so that it is sometimes
necessary to wash the materials with water before compounding in order to
remove impurities. Such a washing treatment is naturally not free from the
problem of hydrolysis.
4. The hydrolysis reaction of the Si--O--C linkages proceeds even in a
cured resin composition, in particular, under a high-humidity condition to
cause migration of the organopolysiloxane toward surfaces resulting in the
decrease of the adhesive bonding strength which is detrimental for the
long-term reliability of the encapsulated devices due to moisture
intrusion.
5. As is typical in phenol silicone products, phenolic compounds are
liberated by the hydrolysis reaction to cause corrosion of aluminum-made
paterns on semiconductor chips due to the acidity thereof.
Several of the reactions leading to the formation of the desired block
copolymer are as follows.
(1) The dehydrohalogenation reaction between a phenolic hydroxy group in
the aromatic polymer and an .omega.-halogenoalkyl group bonded to the
silicon atom in the organopolysiloxane.
(2) The platinum-catalyzed addition reaction between a vinyl or allyl group
bonded to the benzene ring of the aromatic polymer and a hydrogen atom
directly bonded to the silicon atom in the organopolysiloxane.
(3) The addition reaction between a glycidyloxy group bonded to the benzene
ring in the aromatic polymer and a functional group reactive with the
glycidylic epoxy group such as hydroxy, mercapto, carboxyl, amino and
methylamino groups bonded to the silicon atom in the organopolysiloxane,
preferably, through an alkylene group.
(4) The condensation reaction between a phthalic anhydride group in the
aromatic polymer and an .omega.-aminoalkyl group bonded to the silicon
atom in the organopolysiloxane to form a phthalimido structure.
It should be noted that the above given methods for the preparation of the
block copolymer from an aromatic polymer and an organopolysiloxane are
merely for exemplification and the block copolymers can be obtained by any
other methods known in the art.
The mode in which these two classes of segments are bonded block-wise
together to form the block copolymer is not limitative according to the
types of the segments including a simple alternation of the two classes of
segments and complicated branching of one from the other. The weight
proportion of these two classes of segments in the block copolymer may be
widely diversified but, usually, the block copolymer should contain from
15 to 80 % by weight of the segments derived from the organopolysiloxane.
The physical or rheological property of such a block copolymer is
determined depending on the degree of polymerization of the
organopolysiloxane and the content of the same in the block copolymer and
may be liquid, resinous or gummy.
It is further preferable that the block copolymer has one or more of
functional groups reactive with the epoxy resin or the curing agent
therefor in the curable epoxy resin blend as the component (a) in order to
reduce the migration of the block copolymer as the additive toward the
surface of the cured product of the inventive composition. The functional
group in the block copolymer as the component (b) is preferably a hydroxy
group or an epoxy group from the standpoint of reactivity with the epoxy
resin blend as the component (a) although residual hydroxy groups directly
bonded to the silicon atoms are less preferable.
The amount of the block copolymer as the component (b) in the inventive
composition should be in the range from 5 to 100 parts by weight per 100
parts by weight of the curable epoxy resin blend as the component (a).
When the amount of the block copolymer is smaller than above, no
satisfactory improvements can be obtained in the resistance against crack
formation and decreased stress in the cured products of the inventive
composition while an excessive amount of the block copolymer over the
above range may result in the decrease of the mechanical strengths of the
cured products even though the requirements for the anti-cracking
resistance and the decreased stress are fully satisfied.
Although the inventive compositions composed of the curable epoxy resin
blend and the block copolymer are sufficiently of practical value for some
applications, it is preferable for most of the applications that the
composition is further admixed with a substantial amount of an inorganic
filler. Suitable inorganic fillers include various kinds of particulate or
fibrous inorganic materials known in the art of synthetic resins and
rubbers, among which silica or silicate fillers are preferred.
The silica fillers above mentioned may be crystalline or non-crystalline
and various commercial products are available and can be used as such.
Several of the examples are finely pulverized crystalline quartz powders
and amorphous silica powders having an average particle diameter of 1 to
30 .mu.m. In particular, powders of quartz are suitable as the filler in
the inventive composition and can be used in an amount of up to 1000 parts
by weight per 100 parts by weight of the curable epoxy resin blend as the
component (a). When the inventive composition is to be used for
encapsulation of semiconductor devices, the amount of filler loading
should be as high as possible due to the decreased thermal expansion from
the standpoint of preventing crack formation and formation of gaps
permitting intrusion of atmospheric moisture as well as distortion or
stress caused on the aluminum-made patterns on the silicon substrate
responsible for disorder in the performance of the device as a result of a
large difference in the thermal expansion coefficients between the silicon
substrate or device frame and the cured encapsulating resin composition.
Other kinds of inorganic fillers than the silica or silicate fillers may be
used either as themselves or as a combination with a silica or silicate
filler. Suitable inorganic fillers include, for example, talc, mica
flakes, clay, kaolin, calcium carbonate, alumina, zinc oxide, aluminum
hydroxide, titanium dioxide, iron oxides, glass fibers and the like. These
non-silica fillers may be used in combination of two kinds or more
according to need.
The siloxane linkage in the block copolymer as the component (b) is highly
affinitive to the surface of these inorganic fillers or, in particular,
silica fillers rendering the surface thereof hydrophobic and contributing
to the improvement of the dispersibility of the filler particles in the
polymeric matrix composed of the components (a) and (b). Therefore,
favorable influences are effected on the properties of the cured products
of the inventive composition even when the composition is loaded with a
large volume of the silica filler.
The amount of the inorganic filler in the inventive composition should not
exceed, preferably, 500 parts by weight per 100 parts by weight of the
total amount of the components (a) and (b) since an exces-sively large
amount of the inorganic filler not only can hardly be dispersed uniformly
in the composition but also can give no curable composition with good
workability or moldability of which cured products with satisfactory
anti-cracking resistance and low internal stress are obtained. When a
substantial advantageous effect is desired by the addition of the
inorganic filler, in particular, the amount thereof in the inventive
composition should be at least 150 parts by weight per 100 parts by weight
of the components (a) and (b). That is, the amount of the inorganic filler
is preferably in the range from 150 to 500 parts by weight per 100 parts
by weight of the components (a) and (b).
It is of course optional that the inventive composition may contain various
kinds of additives conventionally used in curable resin compositions such
as, for example, fillers of the types not mentioned above including carbon
black, graphite powder, wallastonite and the like, mold releasing agents
including higher fatty acids, waxes and the like, coloring agents
including pigments, e.g. pigment-grade carbon black, and the like,
coupling agents including epoxysilanes, vinylsilanes, alkyl titanates and
the like and flame retardant agents including antimony compounds and the
like.
The inventive epoxy resin-based curable composition is prepared by
uniformly blending the components (a), which in turn is a combination of
an epoxy resin and a curing agent therefor, and the component (b) together
with or without the addition of an inorganic filler and other additives in
a suitable blending machine such as roller mills, kneaders, screw blenders
and the like, if necessary, with application of heat to melt one or more
of the components. The blending can be performed as dry but an organic
solvent may be added according to need to obtain a solution-type or
dispersion-type composition. The thus prepared composition can be put to
practical use in diversified methods of application, for example, as a
molding compound to be shaped by a known molding method such as
compression molding, transfer molding, injection molding and the like.
When the molding compound in a powdery or pelletized form is stored for a
length of time before molding, care should be taken to avoid the influence
of the moisture either from the ambient atmosphere or adsorbed on the
filler particles. In this regard, the component (b) in which the aromatic
segments and the organopolysiloxane segments are bonded together through a
silicon-to-carbon linkage is more advantageous than those through a
Si--O--C linkage which is more susceptible to hydrolysis by the moisture
in the presence of the curing catalyst to isolate the organopolysiloxane
in a free from detrimental to the adhesion of the cured molding
composition and the devices encapsulated therewith or marking receptivity
on the surface.
The cured products obtained from the inventive composition have remarkably
improved resistance against crack formation and excellent electric
properties as well as resistance against heat and moisture maintaining the
original high glass transition temperature so that the inventive
composition is very useful as an encapsulating material of semiconductor
devices and as a base of coating compositions, casting material, molding
compound for shaped articles, material for electric insulation as in the
preparation of laminated materials and the like.
Following are the examples to illustrate the present invention in further
detail preceded by the description of the preparation procedures of the
block copolymers as the component (b). In the following description, the
expression of "parts" always refers to "parts by weight" and the symbol Me
denotes a methyl group.
Preparation 1 (Preparation of block copolymer I).
Into a four-necked flask equipped with a reflux condenser, a thermometer, a
stirrer rod and a dropping funnel were introduced 200 g of a phenol
novolac resin modified with allyl glycidyl ether and having a softening
point of 100.degree. C., phenol equivalent of 125 and allyl equivalent of
1100, 800 g of chloromethyloxirane and 0.6 g of cetyl trimethyl ammonium
chloride and the mixture was heated at 110.degree. C. for 3 hours under
agitation. Thereafter, the mixture was cooled to 70.degree. C. and 128 g
of a 50 % aqueous solution of sodium hydroxide were added thereto dropwise
over a period of 3 hours under a reduced pressure of 160 mmHg for
azeotropic dehydration. The thus obtained reaction mixture was then freed
from the solvent by distillation under reduced pressure and dissolved in a
solvent mixture of 300 g of methyl isobutyl ketone and 300 g of acetone.
The solution was washed with water and freed from the solvents by
distillation under reduced pressure to give an allyl-containing epoxy
resin having an allyl equivalent of 1590 and an epoxy equivalent of 190.
Then, 120 g of this allyl-modified epoxy resin were reacted with 80 g of
an organopolysiloxane of the formula H--SiMe.sub.2 --O).sub.100 SiMe.sub.2
--H, Me denoting a methyl group, to give a block copolymer, referred to as
the block copolymer I hereinbelow, which was a pale yellow opaque solid at
room temperature, exhibiting a melt viscosity of 660 centipoise at
150.degree. C. and weight loss of 0.40 % by heating at 150.degree. C. for
1 hour.
Preparation 2 (Preparation of block copolymer II).
Into the same flask as used in the preceding Preparation 1 were introduced
32 g of a dimethylpolysiloxane having an average degree of polymerization
of 52 and terminated at both molecular chain ends each with a
silicon-bonded 3-aminopropyl group, 53 g of an epoxycresol novolac resin
commercially available with a tradename of EOCN-102 from Nippon Kayaku
Co., Japan, 5 g of methyl alcohol and 80 g of N,N-dimethyl formamide to
form a reaction mixture which was heated for 5 hours | | |
