Epoxy resin sealing material for molding semiconductor chip and method for manufacturing the same

An epoxy resin encapsulating material for molding in a semiconductor chip by the use of a transfer molding device. The material has constituents of an epoxy resin, a curing agent, an inorganic filler, and a release agent. The material consists of 99 wt % or more of granules having a diameter of 0.1 to 5.0 mm and 1 wt % or less of minute particles having a diameter of less than 0.1 mm. The mass of the material exhibit an angle of slide of 20 to 40.degree., which demonstrates good flowability free from clogging a passage leading to a mold cavity in the transfer molding device, thereby assuring enhanced encapsulation quality. The material is prepared firstly by kneading the encapsulating composition having the above constituents and by solidifying the composition into a semi-cured solid body of B-stage condition. The sem-cured solid body is then pulverized into pieces having a diameter of 5.0 mm or less. The pieces are composed of granules having a diameter of 0.1 mm to 5.0 mm and minute particles having a diameter of less than 0.1 mm. Subsequently, heat is applied to melt a resin component of the encapsulating composition in the surfaces of the granules while continuously moving the granules so as to entrap the minute particles in a molten phase of the resin component. Thereafter, the molten phase is cooled to obtain epoxy resin encapsulating grains coated with a resin layer incorporating the minute particles having the diameter of less than 0.1 mm.

BACKGROUND ART 
1. Field of the Invention 
The present invention is directed to an epoxy resin encapsulating material 
for molding in a semi-conductor chip and method of preparing the same. 
2. Description of the Prior Art 
Encapsulation of semiconductor chips has been made by a transfer molding 
using so-called tablets of an encapsulating composition composed of an 
epoxy resin, a curing agent, and an inorganic filler. The tablets are 
prepared by the steps of kneading the encapsulating composition and 
processing the same into a semi-cured body in the form of a sheet or wire, 
pulverizing the solid body into granules followed by being compacted into 
a cylindrical form. Thus prepared tablets are fed in a pot of a 
transfer-molding device and are forced into a mold cavity where they are 
molded to surround the semiconductor chip. Nowadays, there is proposed for 
enhancing encapsulation quality to use a multi-pot transfer molding device 
in which a plurality of pots are provided to encapsulate a plurality of 
the semiconductor chips at once with reduced length of runner leading from 
the pot to the associated mold cavity. As the number of the pots 
increases, the size of the tablets are required to be reduced to give the 
sufficient number of the tablets into each pot. In this respect, it is 
envisaged to utilize the pulverized granules of the encapsulating 
composition prior to being compacted into the tablet. 
However, the granules after being pulverized from the semi-cured epoxy 
composition inherently includes a number of minute particles which are 
very likely to clog passages for supplying the encapsulating material to a 
metering section of the transfer molding device and for supplying it to 
the pots, thereby failing to supply a sufficient amount of the material to 
the mold cavity with attendant poor encapsulation. Such minute particles 
have a tendency to adhere to the large granules, they are difficult to be 
filtered out by the use of a sieve and are easily separated from the large 
granules when subjected to vibrations applied in the course of feeding the 
granules to the pot and/or the molding cavity. Further, the granules may 
be chipped at their corners when subjected to the vibrations to add 
resulting minute particles. 
Even by the use of the tablets, the minute particles are easily separated 
from the tablets when subjected to the vibration while being fed to the 
pots and/or the cavities, thereby causing undesired clogging of the 
passages to the cavities. 
In view of the problems, it is demanded to provide the epoxy encapsulating 
material in the form of the granules which can successfully avoid to clog 
the passages of the material in the transfer molding device. 
SUMMARY OF THE INVENTION 
The above problem has been solved in the present invention which provides 
an improved epoxy resin encapsulating material for molding in the 
semiconductor chip and method of preparing the same. The epoxy resin 
encapsulating material in accordance with the present invention has 
constituents of an epoxy resin, a curing agent, an inorganic filler, and a 
release agent and consists of 99 wt % or more of granules having a 
diameter of 0.1 to 5.0 mm and 1 wt % or less of minute particles having a 
diameter of less than 0.1 mm. The mass of the epoxy resin encapsulating 
material is characterized to exhibit an angle of slide of 20 to 
40.degree., which demonstrates good flowability free from clogging the 
passage leading to the mold cavity, thereby assuring enhanced 
encapsulation quality. When the minute particles having a diameter of less 
than 0.1 mm are included in an amount of more than 1 wt % or the granules 
having a diameter of 0.1 mm to 5.0 mm are inclued in an amount of less 
than 99 wt %, the material is likely to clog the passage. Also, such 
clogging of the material is likely to occur with the use of the material 
having the angle of slide of more than 40.degree.. Although it may be 
possible to prepare the encapsulating material having the angle of slide 
of less than 20.degree., the preparation takes a long period of time and 
is not practical for an economic reason. 
The epoxy resin encapsulating material is prepared firstly by kneading the 
encapsulating composition having the above constituents to prepare a 
semi-cured body of B-stage condition. The semi-cured solid body is then 
pulverized into pieces having a diameter of 5.0 mm or less. The pieces are 
composed of granules having a diameter of 0.1 mm to 5.0 mm and minute 
particles having a diameter of less than 0.1 mm. Subsequently, heat is 
applied to melt a resin component of the encapsulating composition in the 
surfaces of the granules while continuously moving the granules so as to 
entrap the minute particles in a molten phase of the resin component. 
Thereafter, the molten phase is solidified to obtain an epoxy resin 
encapsulating grains coated with a resin layer incorporating the minute 
particles. In this manner, the grains having a diameter of 0.1 mm to 5.0 
mm are formed respectively with resin coats which entrap the minute 
particles having a diameter of less than 0.1 mm. With this process, the 
epoxy resin encapsulating materials free from separate minute particles 
can be successfully prepared to satisfy the above size distribution as 
well as the angle of the slide. 
In a preferred embodiment, the granules are heated while being stirred for 
effectively melting the resin component of the encapsulating composition 
in the surfaces of the whole granules as well as for avoiding the granules 
from combining too much with each other into unduly large bulks, thus 
facilitating to prepare the epoxy resin encapsulating material of uniform 
size. 
Further, prior to forming the resin coat on the surface of the granules by 
application of heat, it is preferred to make a pre-treatment of adding 
water to a volume of the pulverized pieces in order to wet the surfaces of 
the granules. With this pre-treatment, the minute particles can be readily 
adhered to the wetted surfaces of the granules before the resin component 
is melted to form the molten phase, thereby increasing efficiency of 
entrapping the minute particles in the molten phase of the resin component 
in the immediately subsequent step. 
A solvent or wetting agent may be added to a volume of the granules while 
stirring the granules for agglomeration thereof. The solvent is selected 
to be one capable of dissolving a resin component of the encapsulating 
composition in the surfaces of the granules to wet the surface for 
absorbing the minute particles therein. The wetting agent is selected for 
the same purpose of wetting the surfaces of the granules to absorb the 
minute particles therein and includes at least one selected from a group 
consisting of an epoxy resin, a curing agent, a release agent, and a 
surfactant each of which may be the same as or different from that of the 
epoxy encapsulating composition. The use of the release agent as the 
wetting agent is preferred to facilitate the encapsulation process. 
These and still other objects and advantageous features of the present 
invention will become more apparent from the following detailed 
description of the invention and examples when taking in conjunction with 
the attached drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
An epoxy resin encapsulating material of the present invention is prepared 
in the form of grains for use to mold in a semiconductor chip within a 
transfer molding device. The encapsulating material is prepared from an 
encapsulating composition composed of an epoxy resin, a curing agent, a 
release agent and an inorganic filler. Additionally, the composition may 
include a curing accelerator, a surfactant, a silane coupling agent, a 
coloring agent, a stress reducing agent, a flame retardant as necessary. 
The epoxy includes orthocresol-novolak-type epoxy resin, bisphenol-A-type 
epoxy resin, biphenyl-type epoxy resin, dicyclopentadiene-type epoxy 
resin, linear aliphatic epoxy resin, alicyclic epoxy resin, and a 
heterocyclic epoxy resin. The particular epoxy resin may be utilized alone 
or in combination. 
The curing agent includes a phenol-novolac resin and its derivative, 
cresol-novolac resin and its derivative, a monohydroxy- or 
dihydroxy-naphthalene-novolac resin and its derivative, a condensation of 
p-xylene and a phenol or a naphthol, a phenol curing agent such as a 
copolymer of dicyclopentadiene and phenol, an amine curing agent, and an 
acid anhydride. The particular curing agent may be utilized alone or in 
combination. The phenol-novolac resin is preferred for reason of reducing 
hydroscopicity of the cured resin. The curing agent is blended in 
equivalent amount of 0.1 to 10 times in relation to the epoxy resin. 
The release agent includes a fatty acid such as stearic acid, montanic 
acid, palmitic acid, oleic acid, and linoleic acid, a salt of the fatty 
acid such as a calcium salt, magnesium salt, aluminum salt and a zinc 
salt, of the fatty acid, an amido of the fatty acid, phosphoric ester, 
polyetylene, bisamide, polyolefin containing carboxyl group, and natural 
carnauba. The inclusion of the release agent enables the use of the epoxy 
resin having inherently high adhesive characteristic to the semiconductor 
chip and/or the lead-frame thereof, yet assuring release of cured resin 
from the mold and/or a plunger of transfer molding device. 
The inorganic filler includes crystalline silica, fused silica, alumina, 
magnesia, titan oxide, calcium carbonate, magnesium carbonate, silicone 
nitride, talc, and calcium nitrate. The inorganic filler may be utilized 
either alone or in combination. The use of crystalline or fused silica is 
preferred to reduce coefficient of linear expansion of the cured epoxy 
resin as near as that of the semiconductor chip. The inorganic filler is 
preferred to be included in an amount of 60 to 95 parts by weight in 
relation to 100 parts of the sum of the resin component and the inorganic 
filler for lowering hygroscopicity as well as for assuring superior 
thermal resistance to the heat applied at the time of soldering the 
encapsulated semiconductor chip. The inorganic filler is selected to have 
an average diameter of 0.5 to 50 .mu.m. 
The curing accelerator includes 1,8-Diaza-bicyclo (5,4,0) undecene-7, a 
third-grade amine compound such as triethylenediamine and 
benzyldimethylamine, an imidazole compound such as 2-methylimidazole, 
2-ethyl-4-methylimidazole, 2-phenylimidazole, and 
2-phenyl-4-methylimidazole, and an organic phosphine compound such as 
triphenylphosphine and tributylphosphine. 
The silane coupling agent includes an epoxy silane such as 
.gamma.-glycidoxy-propyltrimethoxy silane, and an amino silane such as 
N-phenyl-.gamma.-amino-propyltrimethoxy silane. 
The surfactanct includes polyethylene glycol fatty acid ester, sorbitan 
fatty acid ester, and fatty acid monoglyceride. 
The silane coupling agent includes an epoxy silane such as 
.gamma.-glycidoxy-propyltrimethoxy silane, and an amino silane such as 
N-phenyl-.gamma.-amino-propyltrimethoxy silane. 
The coloring agent includes carbonblack and titanium oxide. 
The stress-reducing agent includes a silicone gel, silicone rubber, and 
silicone oil. 
The flame retardant includes antimony trioxide, a halide, and a phosphide. 
One or more specific agent or compound may be utilized as each of the 
curing accelerator, silane coupling agent, release agent, coloring agent, 
stress reducing agent, surfactant, and flame retardant. 
For preparation of the epoxy resin encapsulating material, the above resin 
component and the inorganic fillers are intermingled by a mixer, for 
example, HENSCHEL mixer and then kneaded while being heated to soften the 
resin component followed by being extruded into a sheet or rod, or like 
semi-cured solid body. The kneading and extrusion is made by the use of, 
for example, a pressure rollers, double-screw kneader, or extruder. The 
kneading is continued over such a period as to make the resin component 
sufficient compatible with the inorganic filler but not to proceed the 
curing of the resin component to a greater extent. Thereafter, the solid 
body is pulverized into pieces having a diameter of 5.0 mm or less. 
Filtering is made to remove greater granules having a diameter of more 
than 5.0 mm by the use of a sieve, when such greater granules remains 
after pulverization. The pulverization is made, for example, by the use of 
a rotary cutter, roller mill, or hammer mill. Thus pulverized pieces 
include granules having a diameter of not less than 0.1 mm and minute 
particles having a diameter less than 0.1 .mu.m. 
The pulverized granules are then agglomerated into the final epoxy resin 
encapsulating grains with respective resin coats entrapping therein the 
minute particles. A combination of heat or the like with stirring is 
applied to the volume of the pulverized granules to make the agglomeration 
with the entrapment of the minute particles. That is, as the heat or the 
like is applied to the granules being stirred, the resin component in the 
surface of the pulverized granules are melted to form molten phase which 
act to entrap the minute particles. 
Agglomeration Process A 
One process of making the above agglomeration of the granules utilizes a 
mixer which, as shown in FIG. 1, comprises a top-open container 10, a 
mixing blade 11 driven by a motor 12 to rotate within the container. By 
rotating the blade 11 at a relatively high speed, the pulverized granules 
G filled in the container 10 are stirred violently and are consequently 
caused to collide with each other to develop frictional heat which melts 
the resin component of the encapsulating composition present in the 
surface of the granules and having a lowest melting point. The temperature 
or the amount of the frictional heat can be adjusted by selecting the 
motor speed in order to melt the resin component having the lowest melting 
point. The granules with the resulting molten phase are caused to collide 
with each other to agglomerate through the interfaces of the molten phase. 
When the agglomerated granules becomes to have a certain enlarged size, 
they are sheared by the rotating mixing blade 11 back into grains of a 
smaller size. The above agglomeration and shearing are repeated to give 
the grains of the suitable size during which the minute particles have 
increased chances of being entrapped into the molten phase of the 
granules. Thereafter, the rotating speed of the mixing blade 11 is lowered 
to cease melting the resin component but to keep stirring the granules, 
allowing the molten phase to cool and solidify in order to obtain the 
grains with the minute particles confined in the resulting resin coat in 
the surface thereof. Through this stirring process, the resulting grains 
are made to have the angle of slide in the range of 20 to 40.degree.. In 
this process, it is preferred to add an extra amount of the release agent 
at the time of lowering the rotating speed of the blade so as to provide a 
coat of the release agent on the pellets or provide a combination coat in 
which the release agent is dissolved in or mixed with the resin. The 
incorporation of the additional release agent in the surfaces of the 
grains facilitates the encapsulation process. The mixer available in this 
process includes HENSCHEL mixer, universal mixer, ribbon blender, and 
super mixer. 
Agglomeration Process B 
Another agglomeration process is to use a heater in combination with the 
above mixer. The heater is installed within the wall of the container 10 
of FIG. 1 to heat the pulverized pieces or granules to a temperature for 
melting the resin component of the encapsulating composition present in 
the surfaces of the granules and having a lowest melting point. The 
stirring by the blade 11 continues during the heating so that the granules 
are agglomerated through the interfaces of the molten phase of the resin 
component while being prevented from becoming too large by the shear of 
the rotating blade. During this agglomeration, the minute particles are 
entrapped within the molten phase. Thereafter, the heating is stopped 
while keep stirring the granules by rotating the blade at a rotation speed 
not to cause melting of the resin component, thereby solidifying the 
molten phase to provide the grains with the resulting resin coat 
restricting the minute particles therewith. During this stirring, the 
agglomerated granules are caused by the shearing action of the blade to be 
broken into the resulting grains of uniform size. Through this stirring 
process, the resulting grains are made to have the angle of slide in the 
range of 20 to 40.degree.. Also in this process, the release agent is 
preferred to be added to form on the granules the coat of the release 
agent or combination coat of the resin component and the release agent. 
Agglomeration Process C 
A further agglomeration process utilizes a fluidizing vessel which, as 
shown in FIG. 2, comprises a vessel 20, a blower 21, and a heater 22. The 
pulverized granules G are placed on a screen 23 within the vessel 20 and 
are suspended in a rising flow of air fed from the blower 21 to form a 
fluidized bed. A filter 24 is provided adjacent to an exhaust port for 
collection of the granules. Firstly, the heater is activated to heat the 
granules being suspended and stirred by the air flow so as to melt the 
resin component of the encapsulating composition appearing in the surface 
of the granules and having a lowest melting point. The granules with the 
resulting molten phase are caused to collide with each other in the 
fluidized bed to be agglomerated into a suitable size through the 
interfaces of the molten phase, during which the minute particles are 
entrapped by the molten phase. Since the granules are forced to move 
continuously in the fluidized bed, there occurs constant break-down of the 
agglomerated granules such that the granules are prevented from 
agglomerated into unduly large bulk but are agglomerated into a suitable 
size. Thereafter, the heater temperature is lowered to make solidification 
of the agglomerated granules in the fluidized bed to give the resulting 
grains of the uniform size in which the minute particles are entrapped by 
the resulting resin coat. The minute particles failing to be entrapped in 
the molten phase are flown upward of the fluidized bed and recovered in 
the filter 24. Through this stirring process, the resulting grains are 
made to have the angle of slide in the range of 20 to 40.degree.. 
Also in this process, the release agent is preferably added at the lowered 
heater temperature in order to form on the pellets the coat of the release 
agent or combination coat of the resin component and the release agent. 
The fluidizing vessel available for this process includes the device 
utilizing a centrifugal air flow and spiral air flow. 
Agglomeration Process D 
A further agglomeration process utilizes the mixer of FIG. 1 and is made to 
add a solvent to a volume of the pulverized granules being stirred in the 
mixer. With the addition of the solvent, the resin component of the 
encapsulating composition in the surface of the granules is dissolved to 
wet the surface for absorbing the minute particles therein as well as for 
aggregating the granules while the granule are being stirred. When the 
agglomerated granules becomes to have a certain enlarged size, they are 
sheared by the rotating mixing blade 11 back into a smaller size. The 
above agglomeration and shearing are repeated to give the grains of the 
suitable size during which the minute particles have increased chances of 
being absorbed in the wetted surfaces of the granules. Thereafter, a cool 
or hot air blow is fed to the volume of the agglomerated granules while 
continuing the stirring so as to dry the surfaces of the granules, thereby 
obtaining grains with the minute particles entrapped in the surfaces 
thereof. Through this stirring process, the resulting grains are made to 
have the angle of slide in the range of 20 to 40.degree.. The solvent may 
be added at once or several times while stirring the granules. The solvent 
includes acetone, methanol, xylene, toluene, hexane, methyl-ethyl keton, 
ethyl acetate, cyclohexane, isopropanol, benzen, methyl acetone, and 
ethanol anhydride. The specific solvent may be used alone or in 
combination. 
Agglomeration Process E 
A further agglomeration process utilizes the mixer of FIG. 1 and is made to 
add to a wetting agent to a volume of the pulverized granules being 
stirred in the mixer. The wetting agent is at least one selected from a 
group consisting of an epoxy resin, a curing agent, a release agent, and a 
surfactant each of which may be the same as or different from that of the 
epoxy encapsulating composition. The wetting agent in the form of a liquid 
will spread over the surfaces of the granules to wet the same while the 
granules are being stirred, so as to absorb the minute particles in the 
wetted surfaces as well as to aggregate the granules. Thereafter, a cool 
or hot air blow is fed to the volume of the agglomerated granules while 
continuing the stirring so as to solidify the wetting agent covering the 
surfaces of the granules, thereby obtaining the granules with the minute 
particles entrapped in the surfaces thereof. Through this stirring 
process, the resulting grains are made to have the angle of slide in the 
range of 20 to 40.degree.. The wetting agent may be added at once or 
several times while stirring the granules. The wetting agent which is 
solid at room temperatures is heated to be liquefied prior to being added 
to the granules. With the use of such wetting agent which is solid at the 
room temperatures, the desired granules can be obtained without forcibly 
cooling the granules. The release agent is preferable as the wetting agent 
to facilitate the encapsulation process. It is preferred to add 0.1 to 5.0 
weight parts of the wetting agent in relation to 100 weight parts of the 
pulverized granules for balancing the agglomeration performance and the 
drying performance. 
Agglomeration Process F 
A still further agglomeration process utilizes a kneader-extruder to knead 
the epoxy encapsulating composition and extrude the resulting composition 
through a die opening to give a softened rod. The rod is then cut into 
pieces followed by being rounded while being cooled to provide grains 
having the diameter of 0.5 to 5.0 mm. 
Prior to make the agglomeration of the pulverized granules in accordance 
with the above agglomeration processes of A to E, it is preferred to give 
a preliminary treatment for enhancing efficiency of entrapping and 
confining the minute particles in the surface of the granules. Following 
treatment is found advantageous for this purpose. 
Pre-agglomeration Treatment 
Water is added to a volume of the pulverized granules being stirred to wet 
the surface of the granules for aggregating the granules as well as 
absorbing the minute particles. Thus formed grains are then dried while 
being continuously stirred to remove the water content from the grains. 
With this treatment, the minute particles are adhered to wetted surfaces 
of the granules. This aggregation can be made by the use of the above 
mixer or fluidizing vessel. Thus treated granules are then agglomerated by 
one of the above processes A to E. Another liquid may be utilized instead 
of water provided that the liquid will not melt the resin component of the 
epoxy encapsulating composition. The liquid includes epoxy resin, curing 
agent, release agent and surfactant which may be of the same or different 
type as incorporated in the epoxy encapsulating composition. 
The following examples are intended to illustrate the invention and should 
not be construed to impose limitations on the claims. 
EXAMPLE 1 
The example was intended to prepare the epoxy resin encapsulating material 
in accordance with the above Agglomeration process A. 
An epoxy resin encapsulating composition was prepared by blending the 
following ingredients in the listed proportion. 
Epoxy resin: 
3 weight parts of orthocresol-novolak-type epoxy resin [available from 
SUMITOMO CHEMICAL Co. Ltd. Japan as a tradename of ESCN195XL]; 
3 weight parts of biphenyl-type epoxy resin [available from YUKA SHELL 
EPOXY Inc. Japan as a tradename of YX4000H]; 
Curing agent: 
5 weigth parts of phenol resin [available from ARAKAWA CHEMICAL INDUSTRY 
Ltd., Japan as a tradename of Tamanol 752]; 
Inorganic filler: 
80 weight parts of fused silica [available from TATSUMORI Ltd., Japan, as a 
tradename of R08]; 
Release agent: 
0.3 weight parts of stearic acid [available from DAINICHI CHEMICAL INDUSTRY 
Co., Ltd., Japan as a tradename of W02]; 
0.3 weigth parts of natural carnauba [available from DAINICHI CHEMICAL 
INDUSTRY Co., Ltd., Japan as a tradename of .quadrature.F-1-100]; 
Coupling agent: 
1 weight part of .gamma.-glycidoxy-propyltrimethoxy silane [available from 
TORAY-DOW CORNING SILICONE Inc., Japan as a tradename of SH6040]; 
Curing accelerator: 
1 weight part of 2-phenylimidazole; 
Coloring agent: 
0.2 weight part of carbon black; 
Flame retardant: 
5 weight part of antimony trioxide. 
Thus blended epoxy resin encapsulating composition was then fed to a double 
screw kneader where it was kneaded at 85.degree. C. for 5 minutes. Then, 
the composition was cooled to be solidified followed by being pulverized 
by a cutter mill into the pulverized granules having a diameter of not 
greater than 0.5 mm and having a melting point of 63.degree.. Thus 
pulverized granules consist of 90 wt % of granules having a diameter of 
0.1 mm to 5.0 mm and 10 wt % of minute particles having a diameter of less 
than 0.1 mm. 
50 Kg of the pulverized granules were placed into HENSCHEL mixer in order 
to agglomerate the granules based upon above agglomeration process A. The 
mixing blade 11 was rotated at 1500 rpm for 10 minutes to stir the 
granules and melt the resin component in the surface of the granules due 
to friction heat developed between the granules being stirred, thereby 
entrapping the minute particles to the resulting molten phase. Then, the 
rotation speed of the mixing blade was lowered 400 rpm to develop no 
substantial frictional heat, thereby cooling the molten phase into a solid 
phase while continuously stirring the granules for 20 minutes to provide 
the epoxy resin encapsulating grains formed on its surface with the 
resulting resin coat entrapping the minute particles. 
EXAMPLE 2 
This example was intended to prepare the epoxy resin encapsulating material 
in accordance with the above Agglomeration process A with the 
pre-treatment 
50 Kg of thus pulverized granules prepared in Example 1 were placed into 
HENSCHEL mixer [manufactured by MITSUI MINING Co., Ltd.]. 2 Kg of pure 
water was sprayed to the granules while rotating a mixing blade 11 of the 
mixer at 400 rpm. Then, the mixing blades were kept rotated for 20 minutes 
so as to effect wetting of the granules for absorbing the minute particles 
on the wetted surfaces. Subsequently, the mixing blade 11 was rotated at 
1500 rpm for 10 minutes to develop a friction heat due to the stirring and 
therefore melt the resin component in the surface of the granules for 
entrapping the minute particles to the resulting molten phase. Thereafter, 
the rotation speed of the mixing blade is lowered to 400 rpm and kept 
rotated for 20 minutes during which air was blown into the mixer for 
drying the granules, thereby obtaining the epoxy resin encapsulating 
grains formed on its surface with the resulting resin coat entrapping the 
minute particles. 
EXAMPLE 3 
This example was intended to prepare the epoxy resin encapsulating material 
in accordance with the above Agglomeration process C. 
50 Kg of the pulverized granules prepared in Example 1 was placed into a 
fluidizing vessel [manufactured by OKAWARA MFG. Co., Ltd. Japan] as 
typically shown in FIG. 2, where a rising air flow at a room temperature 
was fed continuously upward from the bottom of the vessel to form a 
fluidized bed of the granules. Then, 0.5 Kg of toluene was added to the 
fluidized bed and the granules were kept stirred in the fluidized bed for 
10 minutes, thereby melting a resin component of the epoxy resin 
composition in the surfaces of the granules to form a molten phase. 
Thereafter, the air flowing upward was heated to 40.degree. C. and kept 
flowing upward to stir the granules for 60 minutes in order to dry the 
molten phase, thereby obtaining the epoxy resin encapsulating grains 
formed on its surface with the resulting resin coat entrapping the minute 
particles. 
EXAMPLE 4 
This example was intended to prepare the epoxy resin encapsulating material 
in accordance with the above Agglomeration process E 
50 Kg of the pulverized granules prepared in Example 1 was placed into a 
ribbon blender. 0.5 Kg of stearic acid which is the same as incorporated 
in the epoxy encapsulating composition was added at a raised temperature 
of 70.degree. C. while stirring the granules at 200 rpm for 15 minutes. 
During this stirring, the stearic acid effects to wet the surfaces of the 
granules to agglomerate the granules with the minute particles entrapped 
to the wetted surfaces after which the stearic acid was allowed to cool, 
thereby providing the epoxy resin encapsulating grains with the minute 
particles entrapped in the surface of the grains. 
EXAMPLE 5 
This example was intended to prepare the epoxy resin encapsulating material 
in accordance with the above Agglomeration process F. 
The epoxy resin encapsulating composition was placed into a 
kneader-extruder to be kneaded therein and extruded through a 1.5 mm 
diameter heated die opening to give a soft rod. Immediately thereafter, 
the rod was cut into pieces which were then caused to roll down on a slant 
surface so as to be shaped into a rounded configuration while being 
cooled, thereby providing the epoxy resin encapsulating grains. 
COMATIVE EXAMPLE 1 
The pulverized granules of the epoxy resin encapsulating composition 
obtained in accordance with Example 1 
COMATIVE EXAMPLE 2 
The pulverized granules of the epoxy resin encapsulating composition 
obtained in accordance with Example 1 were classified through a sieve 
which passes the granules having the size of 0.3 mm or less. The resulting 
granules not passing the sieve were collected as specimens for comparative 
example 2. 
COMATIVE EXAMPLE 3 
The pulverized granules of the epoxy resin encapsulating composition 
obtained in accordance with Example 1 were compacted at a compression 
ratio of 92% into a 1.2 g weight cylindrical tablet having a diameter of 
7.4 mm. 
COMATIVE EXAMPLE 4 
The grains obtained in Example 1 were again pulverized in the universal 
mixer rotating at 400 rpm for 10 minutes. 
EVALUATION OF EXAMPLES AND COMATIVE EXAMPLES 
The grains of Examples 1 to 5 and granule or tablet of comparative Examples 
1 to 4 were evaluated in terms of the following characteristics as listed 
in Tables 1 and 2 below. 
TABLE 1 
______________________________________ 
Ratio of 
Size distribution Secondary Dust 
(%) Angle (%) 
Less 0.1 to of Amount 
After After 
than 5.0 slide of dust 
30 60 
0.1 mm 
mm (.degree.) 
(mg/m.sup.3) 
min. min. 
______________________________________ 
Example 1 
0.05 99.95 26 0.03 0.1 0.2 
Example 2 
0 100 20 0.01 0.1 0.2 
Example 3 
0.01 99.99 21 0.02 0.1 0.2 
Example 4 
0.09 99.91 31 0.04 0.1 0.2 
Example 5 
0.09 99.91 39 0.04 0.1 0.2 
Comparative 
10 90 51 0.31 1.0 2.0 
Example 1 
Comparative 
0.1 99.9 41 0.12 2.0 4.0 
Example 2 
Comparative 
-- -- -- 0.12 2.0 4.0 
Example 3 
Comparative 
5 95 35 0.12 2.0 2.0 
Example 4 
______________________________________ 
TABLE 2 
______________________________________ 
Metering Error (g) 
Metering Error (g) 
with 5 cc container 
with 10 cc container 
______________________________________ 
Example 1 0.15 0.15 
Example 2 0.05 0.05 
Example 3 0.10 0.10 
Example 4 0.2 0.2 
Example 5 0.2 0.3 
Comparative 2.0 3.0 
Example 1 
Comparative 0.5 1.0 
Example 2 
Comparative -- -- 
Example 3 
Comparative 0.5 1.0 
Example 4 
______________________________________ 
Size distribution was determined by the use of a series of sieves attached 
to a low-tap vibrator. 200 g of specimen were classified through the 
sieves while vibrating the sieves for 30 minutes to measure the weights of 
the grains or granules held on the respective sieves. Thus measured 
weights were calculated in relation to the weight of the specimens before 
classified to give the weight percentages of the granules having a 
diameter of 0.1 mm to 5.0 mm as well as the minute particles having a 
diameter of less than 0.1 mm. 
Angle of slide was determined by the use of a 50 mm long glass-made conical 
funnel having a 50 mm diameter upper opening from the bottom end of which 
a 7 mm long and 7 mm diameter outlet tube 
##EQU1## 
extends. The funnel was set vertical above a 30 mm thick and 100 mm 
diameter glass-made plate at a height of 100 mm from the glass plate to 
the lower end of the outlet tube in concentric relation therewith. In 
accordance with a sampling method prescribed in JIS K6911, 300 g of grains 
or granules were placed gently on the plate through the funnel to form 
thereon a sloped mass of grains or granules. When the funnel was clogged 
by the grains or granules, a 2 mm diameter copper rod was utilized to 
discharge the grains or granules out of the funnel. The height (h) of the 
sloped mass to give the slide of angle as defined in the following 
formula. The measurements of the angle of slide (.theta.) were made seven 
times for each specimen and an average of five intermediate values except 
for the maximum and minimum was selected for evaluation. 
Amount of dust was determined by the use of a piezo-balance dust monitor to 
concentration of dust appearing in a clean room of which dust 
concentration is maintained below 0.1 mg/m.sup.3 when 200 g of specimen 
were caused to fall freely from a height of 0.5 m. 
Ratio of secondary dust was determined by the use of a 2 litter plastic 
bottle attached to the low-tap vibrator. 500 g of specimen were placed 
into the bottles and vibrated respectively for 30 minutes and 60 minutes 
to measure a weight ratio (%) of dust having a diameter of 0.1 mm or less 
in relation to the weight of the specimen before subjected to the 
vibration, respectively for the specimens after 30 minutes and 60 minutes 
vibrations. 
Metering error was measured as an index of metering stability or reluctance 
of the grains or granules causing the clogging in the passages of 
supplying the grains or granules to the mold cavity in the transfer 
molding device. Two measuring containers of 5 cc and 10 cc were employed 
to measure the grains or granules. The metering error was obtained by 
repeating to take the grains or granules in and out of the containers 
through the passage in the molding device in the over 1000 cycles and 
defined to be an error between the maximum and minimum weight of the 
granules taken out from each of the containers. Following table 2 shows 
the results. 
As is clear from the above tables, Examples of the present invention are 
found to have extremely less content of the minute particles of a diameter 
less than 0.1 mm and to show small angle of slide (.theta.), and low 
metering error (high metering stability), which demonstrates good 
flowability responsible for preventing undesired clogging of the passage 
to the mold cavity in the molding device. In other words, the grains of 
Examples 1 to 5 exhibits low metering error (high metering stability) as 
less as 0.05 to 0.2 for each of the measuring containers, in contrast to 
granules of comparative Examples 1, 2 and 4 of which metering error is 0.5 
to 2.0. Thus, the grains of Examples are found to demonstrate very low 
extent to which the grains remain adhered to the container, i.e., the 
passage of the transfer molding device. 
Also, the amount of dust as well as ratio of secondary dust are reduced to 
minimum so that the minute particles are not caused to scatter around even 
subjected to the vibrations during the course of being fed to the mold 
cavity, thereby preventing the clogging of the passage as well as 
realizing a clean work environment.