U.S. patent application number 12/421876 was filed with the patent office on 2009-10-15 for silicone adhesive for semiconductor element.
This patent application is currently assigned to Shin-Etsu Chemical Co., Ltd.. Invention is credited to Kei Miyoshi, Yoshinori Ogawa, Toshiyuki Ozai, Naoki YAMAKAWA.
Application Number | 20090258216 12/421876 |
Document ID | / |
Family ID | 41164246 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090258216 |
Kind Code |
A1 |
YAMAKAWA; Naoki ; et
al. |
October 15, 2009 |
SILICONE ADHESIVE FOR SEMICONDUCTOR ELEMENT
Abstract
A silicone adhesive for a semiconductor element that is suitable
as a die bonding material for fixing a light emitting diode chip to
a substrate. The adhesive includes (a) an addition reaction-curable
silicone resin composition having a viscosity at 25.degree. C. of
not more than 100 Pas, and yielding a cured product upon heating at
150.degree. C. for 3 hours that has a type D hardness prescribed in
JIS K6253 of at least 30, (b) a white pigment powder having an
average particle size of less than 1 .mu.m, and (c) a white or
colorless and transparent powder having an average particle size of
at least 1 .mu.m but less than 10 .mu.m. The adhesive exhibits high
levels of concealment, effectively reflects light emitted from the
LED chip, and also exhibits favorable chip positioning properties,
superior adhesive strength, and excellent durability.
Inventors: |
YAMAKAWA; Naoki;
(Takasaki-shi, JP) ; Miyoshi; Kei; (Annaka-shi,
JP) ; Ozai; Toshiyuki; (Takasaki-shi, JP) ;
Ogawa; Yoshinori; (Kamakura-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Shin-Etsu Chemical Co.,
Ltd.
Tokyo
JP
|
Family ID: |
41164246 |
Appl. No.: |
12/421876 |
Filed: |
April 10, 2009 |
Current U.S.
Class: |
428/323 ;
524/430; 524/497; 524/588 |
Current CPC
Class: |
C09J 183/14 20130101;
H01L 33/56 20130101; Y10T 428/25 20150115 |
Class at
Publication: |
428/323 ;
524/588; 524/497; 524/430 |
International
Class: |
B32B 7/12 20060101
B32B007/12; C09J 183/00 20060101 C09J183/00; C09J 183/06 20060101
C09J183/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2008 |
JP |
2008-103740 |
Claims
1. A silicone adhesive for a semiconductor element, comprising
components (a), (b) and (c) shown below: (a) an addition
reaction-curable silicone resin composition, having a viscosity at
25.degree. C. of not more than 100 Pas, and yielding a cured
product upon heating at 150.degree. C. for 3 hours that has a type
D hardness prescribed in JIS K6253 of at least 30, (b) a white
pigment powder having an average particle size of less than 1
.mu.m, and (c) a white or colorless and transparent powder having
an average particle size of at least 1 .mu.m but less than 10
.mu.m, wherein a combination of components (b) and (c) is used in
an amount of 12 to 600 parts by mass per 100 parts by mass of
component (a).
2. The silicone adhesive according to claim 1, wherein the white
pigment of component (b) comprises at least one material selected
from the group consisting of titanium oxide, zinc oxide, white
lead, zinc sulfide, calcium carbonate and kaolin.
3. The silicone adhesive according to claim 1, wherein component
(b) is composed of titanium oxide.
4. The silicone adhesive according to claim 1, wherein component
(c) is composed of alumina.
5. The silicone adhesive according to claim 3, wherein component
(c) is an alumina powder composed of alumina particles with a shape
of flake.
6. The silicone adhesive according to claim 1, wherein component
(a) comprises components (A), (B), (C) and (D) described below: (A)
an organopolysiloxane having at least two alkenyl groups bonded to
silicon atoms within each molecule, and having a viscosity at
25.degree. C. of not more than 1,000 mPas, (B) a polyorganosiloxane
represented by an average composition formula (1) shown below:
(R.sup.1R.sup.2.sub.2SiO.sub.1/2).sub.m(R.sup.1R.sup.2SiO.sub.2/2).sub.n(-
R.sup.2.sub.2SiO.sub.2/2).sub.p(R.sup.1SiO.sub.3/2).sub.q(SiR.sup.2(OR.sup-
.3)SiO.sub.2/2).sub.r(SiO.sub.4/2).sub.s (1) wherein R.sup.1
represents an alkenyl group or a monovalent hydrocarbon group other
than an alkenyl group; R.sup.2 represents a monovalent hydrocarbon
group that does not contain an alkenyl group, provided that at
least 80% of R.sup.2 groups are methyl groups; R.sup.3 represents a
hydrogen atom or an alkyl group; m, n, p, q, r and s are numbers
that satisfy m.gtoreq.0, n.gtoreq.0, p.gtoreq.0, q.gtoreq.0,
r.gtoreq.0 and s>0 respectively, provided that m+n>0,
q+r+s>0, and m+n+p+q+r=1, which at 25.degree. C. is either a
liquid having a viscosity of at least 1,000 Pas or a solid, in an
amount that provides 60 to 90 parts by mass of component (B) per
100 parts by mass of a combination of component (A) and component
(B), (C) an organohydrogenpolysiloxane represented by an average
composition formula (2) shown below:
R.sup.4.sub.aH.sub.bSiO.sub.(4-a-b)/2 (2) wherein R.sup.4
represents a monovalent hydrocarbon group other than an alkenyl
group, and at least 50% of R.sup.4 groups are methyl groups; and a
and b are positive numbers that satisfy 0.7.ltoreq.a.ltoreq.2.1,
0.001.ltoreq.b.ltoreq.1.0 and 0.8.ltoreq.a+b.ltoreq.3.0, having at
least two SiH bonds within each molecule, and having a viscosity at
25.degree. C. of not more than 1,000 mPas, in an amount that yields
a total number of SiH bonds that is 0.5 to 5.0 times a total number
of alkenyl groups within a combination of component (A) and
component (B), and (D) an effective amount of a platinum group
metal-based catalyst.
7. A silicone adhesive according to claim 6, wherein the
organopolysiloxane of component (A) is a linear organopolysiloxane
having at least two alkenyl groups bonded to silicon atoms within
each molecule, in which a main chain is composed of repeating
diorganosiloxane units, and both molecular chain terminals are
blocked with triorganosiloxy groups.
8. The silicone adhesive according to claim 6, wherein an amount of
alkenyl groups is within a range from 0.01 to 1 mol/100 g relative
to a solid fraction of component (B).
9. The silicone adhesive according to claim 6, wherein an amount of
component (B) is within a range from 70 to 80 parts by mass
relative to 100 parts by mass of a combination of component (A) and
component (B).
10. The silicone adhesive according to claim 1, wherein component
(a) comprises components (P), (Q) and (R) described below: (P) an
organopolysiloxane represented by an average composition formula
(3) shown below: R.sub.x(C.sub.6H.sub.5).sub.ySiO.sub.(4-x-y)/2 (3)
wherein R represents identical or different, unsubstituted or
substituted monovalent hydrocarbon groups or alkoxy groups, or a
hydroxyl group, provided that 0.1 to 80 mol % of all R groups are
alkenyl groups; and x and y are positive numbers that satisfy
1.ltoreq.x+y<2 and 0.20.ltoreq.y/(x+y).ltoreq.0.95, which at
25.degree. C. is either a liquid having a viscosity of at least 100
mPas, or a solid, (Q) an organohydrogenpolysiloxane represented by
an average composition formula (4) shown below:
R''.sub.cH.sub.dSiO.sub.(4-c-d)/2 (4) wherein R' represents
identical or different, substituted or unsubstituted monovalent
hydrocarbon groups other than aliphatic unsaturated hydrocarbon
groups; and c and d are positive numbers that satisfy
0.7.ltoreq.c.ltoreq.2.1, 0.002.ltoreq.d.ltoreq.1.0 and
0.8.ltoreq.c+d.ltoreq.2.6, having at least two Si--H bonds within
each molecule, and having a viscosity at 25.degree. C. of not more
than 1,000 mPas, wherein at least 5 mol % of a total number of R'
groups and silicon atom-bonded H atoms within the composition
formula (4) are phenyl groups, and (R) an effective amount of a
platinum group metal-based catalyst.
11. The silicone adhesive according to claim 10, wherein in the
formula (3) that represents component (P), 0.5 to 50 mol % of all R
groups are alkenyl groups.
12. The silicone adhesive according to claim 10, wherein component
(Q) has at least three Si--H bonds within each molecule.
13. The silicone adhesive according to claim 10, wherein in the
formula (4) that represents component (Q), 10 to 50 mol % of all
silicon atom-bonded R' groups and hydrogen atoms are phenyl
groups.
14. The silicone adhesive according to claim 10, wherein component
(Q) is composed of an organohydrogenpolysiloxane mixture containing
an organohydrogenpolysiloxane in which at least 15 mol % of all
silicon atom-bonded R'' groups and hydrogen atoms are phenyl
groups, and an organohydrogenpolysiloxane in which less than 15 mol
% of all silicon atom-bonded R'' groups and hydrogen atoms are
phenyl groups, in a weight ratio of 1:9 to 9:1.
15. The silicone adhesive according to claim 10, wherein component
(Q) is composed of an organohydrogenpolysiloxane mixture containing
an organohydrogenpolysiloxane in which 15 to 70 mol % of all
silicon atom-bonded R'' groups and hydrogen atoms are phenyl
groups, and an organohydrogenpolysiloxane in which 0 to 14 mol % of
all silicon atom-bonded R'' groups and hydrogen atoms are phenyl
groups, in a weight ratio of 1:9 to 9:1.
16. A light emitting device comprising a substrate, a light
emitting element and a cured resin layer interposed between the
substrate and the light emitting element, wherein said cured resin
layer comprises a cured product of a silicone adhesive comprising
components (a), (b) and (c) shown below: (a) an addition
reaction-curable silicone resin composition, having a viscosity at
25.degree. C. of not more than 100 Pas, and yielding a cured
product upon heating at 150.degree. C. for 3 hours that has a type
D hardness prescribed in JIS K6253 of at least 30, (b) a white
pigment powder having an average particle size of less than 1
.mu.m, and (c) a white or colorless and transparent powder having
an average particle size of at least 1 .mu.m but less than 10
.mu.m, wherein a combination of components (b) and (c) is used in
an amount of 12 to 600 parts by mass per 100 parts by mass of
component (a).
17. The light emitting device according to claim 16, wherein the
substrate is a gold-plated substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a white die bonding
material that is suitable for fixing a light emitting diode (LED)
chip to a gold-plated substrate. More specifically, the invention
relates to a heat-curable silicone adhesive for a semiconductor
element that produces favorable chip positioning properties when a
chip is pressed onto a substrate, exhibits high levels of
concealment and adhesive strength, displays excellent durability,
and effectively reflects light emitted from the chip.
[0003] 2. Description of the Prior Art
[0004] Epoxy resins have conventionally been used as the die
bonding material for fixing LED light emitting elements (chips).
However, die bonding materials used for fixing blue or white LED
light emitting elements (chips) tend to yellow over time upon
extended use, and in a similar manner to that observed for epoxy
encapsulating materials, the die bonding material tends to absorb
light, causing a reduction in the brightness.
[0005] Nowadays, the demands relating to the durability of light
emitting devices that use an LED as a module are even more
stringent, and the LED encapsulating materials are gradually being
replaced with silicone-based materials. In a similar manner to
encapsulating materials, die bonding materials also require
favorable durability, and it is expected that improved heat
resistance will be demanded together with improved brightness. Die
bonding materials formed from silicone resin compositions have
already been proposed (Patent Document 1).
[0006] Silver electrodes and gold electrodes are typically used for
LED electrodes, but in those cases where a silver electrode is
used, oxygen permeation or the like through the encapsulating
material can cause oxidation and blackening of the surface of the
silver electrode, resulting in a deterioration in the light
reflection efficiency. In contrast, in those cases where a gold
electrode is used, because the electrode itself is inert, it offers
the advantage of being unaffected by the surrounding environment.
However, if a transparent silicone die bonding material such as
that disclosed in Patent Document 1 is used with a gold electrode,
then a problem arises in that the light emitted from the LED chip
is absorbed at the gold surface, causing a deterioration in the
light extraction efficiency. Accordingly, in order to improve the
light extraction efficiency, for those cases where an LED chip is
fixed to a gold-plated substrate, the development of a silicone die
bonding material which blocks and effectively reflects light
emitted from the LED chip, namely a silicone die bonding material
with excellent concealment properties, has been keenly sought.
[0007] [Patent Document 1] US2006/0275617A1
DISCLOSURE OF THE INVENTION
[0008] The present invention has been developed in light of the
above circumstances, and has an object of providing a silicone
adhesive for a semiconductor element that exhibits a high degree of
concealment, effectively reflects light emitted from LED chips, and
can be used as a die bonding material.
[0009] As a result of intensive investigation aimed at achieving
the above object, the inventors of the present invention discovered
that the above object could be achieved by using a silicone
adhesive for a semiconductor element comprising the components (a),
(b) and (c) shown below:
[0010] (a) an addition reaction-curable silicone resin composition,
having a viscosity at 25.degree. C. of not more than 100 Pas, and
yielding a cured product upon heating at 150.degree. C. for 3 hours
that has a type D hardness prescribed in JIS K6253 of at least
30,
[0011] (b) a white pigment powder having an average particle size
of less than 1 .mu.m, and
[0012] (c) a white or colorless and transparent powder having an
average particle size of at least 1 .mu.m but less than 10 .mu.m,
wherein
[0013] the combination of the components (b) and (c) is used in an
amount of 12 to 600 parts by mass per 100 parts by mass of the
component (a).
[0014] Furthermore, the present invention provides a light emitting
device comprising a substrate (e.g., in particular, a gold-plated
substrate), a light emitting element and a cured resin layer
interposed between the substrate and the light emitting element,
wherein said cured resin layer comprises a cured product of a
silicone adhesive comprising components (a), (b) and (c) shown
below:
[0015] (a) an addition reaction-curable silicone resin composition,
having a viscosity at 25.degree. C. of not more than 100 Pas, and
yielding a cured product upon heating at 150.degree. C. for 3 hours
that has a type D hardness prescribed in JIS K6253 of at least
30,
[0016] (b) a white pigment powder having an average particle size
of less than 1 .mu.m, and
[0017] (c) a white or colorless and transparent powder having an
average particle size of at least 1 .mu.m but less than 10 .mu.m,
wherein
[0018] a combination of components (b) and (c) is used in an amount
of 12 to 600 parts by mass per 100 parts by mass of component
(a).
[0019] The present invention is able to provide a silicone adhesive
for a semiconductor element that exhibits a high degree of
concealment and effectively reflects light emitted from LED chips,
thereby improving the light extraction efficiency. This adhesive
also produces favorable chip positioning properties, and exhibits a
high level of adhesive strength and excellent durability.
Incidentally, herein, what is meant by the adhesive having
favorable chip positioning properties, is that when a tip is placed
and pressed on the adhesive applied on a substrate, the chip can be
placed well at a desired position without deviation, lift or the
like.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] A more detailed description of each of the components is
presented below. In the following description and the description
of the claims, "type D hardness" refers to the hardness measured
using a D-type durometer prescribed in JIS K6253. Furthermore, in
the following description, unless stated otherwise, viscosity
values refer to values measured at 25.degree. C. using a rotational
viscometer such as a BM-type rotational viscometer. Furthermore, Vi
represents a vinyl group and Me represents a methyl group.
[Component (a)]
[0021] The component (a) is an addition reaction-curable silicone
resin composition, having a viscosity at 25.degree. C. of not more
than 100 Pas, typically within a range from 1 to 100 Pas, and
preferably from 1 to 10 Pas, and yielding a cured product upon
heating at 150.degree. C. for 3 hours that has a type D hardness
prescribed in JIS K6253 of at least 30, typically within a range
from 30 to 90, and preferably from 40 to 90. The resin composition
usually comprises a main component formed from an
organopolysiloxane containing two or more alkenyl groups, a
cross-linking agent formed from an organohydrogenpolysiloxane
containing at least two SiH bonds, and a reaction catalyst formed
from a platinum group metal-based catalyst.
[0022] In a preferred aspect of the present invention, the
component (a) is composed of a composition comprising the
components (A), (B), (C) and (D) described below:
[0023] (A) an organopolysiloxane having at least two alkenyl groups
bonded to silicon atoms within each molecule, and having a
viscosity at 25.degree. C. of not more than 1,000 mPas,
[0024] (B) a polyorganosiloxane represented by an average
composition formula (1) shown below:
(R.sup.1R.sup.2.sub.2SiO.sub.1/2).sub.m(R.sup.1R.sup.2SiO.sub.2/2).sub.n-
(R.sup.2.sub.2SiO.sub.2/2).sub.p(R.sup.1SiO.sub.3/2).sub.q(SiR.sup.2(OR.su-
p.3)SiO.sub.2/2).sub.r(SiO.sub.4/2).sub.s (1)
[wherein R.sup.1 represents an alkenyl group (for example, an
alkenyl group of 2 to 6 carbon atoms, and preferably 2 to 4 carbon
atoms, such as a vinyl group, allyl group, propenyl group or
butenyl group) or a monovalent hydrocarbon group other than an
alkenyl group (for example, a monovalent hydrocarbon group of 1 to
10 carbon atoms, and preferably 1 to 8 carbon atoms, including an
alkyl group such as a methyl group, ethyl group or propyl group, an
aryl group such as a phenyl group, or an aralkyl group such as a
benzyl group); R.sup.2 represents a monovalent hydrocarbon group
that does not contain an alkenyl group, provided that at least 80%
of R.sup.2 groups are methyl groups; R.sup.3 represents a hydrogen
atom or an alkyl group; m, n, p, q, r and s are numbers that
satisfy m.gtoreq.0, n.gtoreq.0, p.gtoreq.0, q.gtoreq.0, r.gtoreq.0
and s.gtoreq.0 respectively, provided that m+n>0, q+r+s>0,
and m+n+p+q+r=1, and in a preferred configuration, m is a number
from 0 to 0.65, n is a number from 0 to 0.5, p is a number from 0
to 0.5, q is a number from 0 to 0.8, r is a number from 0 to 0.8,
and s is a number from 0 to 0.6], which at 25.degree. C. is either
a liquid having a viscosity of at least 1,000 Pas or a solid, in an
amount that provides 60 to 90 parts by mass of component (B) per
100 parts by mass of the combination of component (A) and component
(B),
[0025] (C) an organohydrogenpolysiloxane represented by an average
composition formula (2) shown below:
R.sup.4.sub.aH.sub.bSiO.sub.(4-a-b)/2 (2)
(wherein R.sup.4 represents a monovalent hydrocarbon group other
than an alkenyl group, and at least 50% of R.sup.4 groups are
methyl groups; and a and b are positive numbers that satisfy
0.7.ltoreq.a.ltoreq.2.1, 0.001.ltoreq.b.ltoreq.1.0 and
0.8.ltoreq.a+b.ltoreq.3.0, and preferably satisfy
1.0.ltoreq.a.ltoreq.2.0, 0.01.ltoreq.b.ltoreq.1.0 and
1.1.ltoreq.a+b.ltoreq.2.6), having at least two, and preferably
three or more, SiH bonds within each molecule, and having a
viscosity at 25.degree. C. of not more than 1,000 mPas, in an
amount that yields a total number of SiH bonds that is 0.5 to 5.0
times the total number of alkenyl groups within the combination of
component (A) and component (B), and
[0026] (D) an effective amount of a platinum group metal-based
catalyst.
[0027] A description of each of these components is presented
below.
-Component (A)-
[0028] The component (A) is a component that is required for
imparting post-curing stress relaxation within the silicone resin
composition that functions as the component (a) of the silicone
adhesive of the present invention. The component (A) is a linear
organopolysiloxane having at least two alkenyl groups bonded to
silicon atoms within each molecule, in which the main chain is
composed essentially of repeating diorganosiloxane units and both
the molecular chain terminals are blocked with triorganosiloxy
groups. Examples of the component (A) include organopolysiloxanes
represented by the formulas shown below:
ViR.sub.2SiO(SiR.sub.2O).sub.nSiR.sub.2Vi,
ViR.sub.2SiO(SiRVi).sub.m(SiR.sub.2O).sub.nSiR.sub.2Vi
(Vi).sub.2(R)SiO[Si(R).sub.2O].sub.nSi(R)(Vi).sub.2
(Vi).sub.3SiO[Si(R).sub.2O].sub.nSi(Vi).sub.3
(Vi).sub.2(R)SiO[Si(R)(Vi)O].sub.m[Si(R).sub.2O].sub.nSi(R)(Vi).sub.2
(Vi).sub.3SiO[Si(R)(Vi)O].sub.m[Si(R).sub.2O].sub.nSi(Vi).sub.3
(R).sub.3SiO[Si(R)(Vi)O].sub.m[Si(R).sub.2O].sub.nSi(R).sub.3
(wherein, R represents a monovalent hydrocarbon group that contains
neither an aliphatic unsaturated group nor an aryl group, and
preferably contains not more than 10 carbon atoms, m is an integer
of 0 to 5, and n is an integer of 0 to 200). From the viewpoints of
light resistance and heat resistance, R is most preferably a methyl
group.
[0029] Specific examples of the component (A) include the compounds
shown below.
##STR00001##
[0030] The viscosity of the component (A) must be not more than
1,000 mPas at 25.degree. C. If a compound with a viscosity
exceeding this limit is used, then the degree of cross-linking
within the cured product obtained upon curing the adhesive of the
present invention is inadequate, and achieving the desired high
degree of hardness becomes difficult. The viscosity is preferably
not more than 700 mPas (typically from 10 to 700 mPas), and is more
preferably within a range from 20 to 200 mPas.
-Component (B)-
[0031] The component (B) is required for providing reinforcement
while retaining the colorless transparency of the silicone resin
composition of the component (a). Specifically, the component (B)
is a polyorganosiloxane represented by an average composition
formula (1) shown below:
(R.sup.1R.sup.2.sub.2SiO.sub.1/2).sub.m(R.sup.1R.sup.2SiO.sub.2/2).sub.n-
(R.sup.2.sub.2SiO.sub.2/2).sub.p(R.sup.1SiO.sub.3/2).sub.q(R.sup.2(OR.sup.-
3)SiO.sub.2/2).sub.r(SiO.sub.4/2).sub.s (1)
(wherein R.sup.1, R.sup.2, R.sup.3, m, n, p, q, r and s are as
defined above for formula (1)), which at 25.degree. C. is either a
liquid having a viscosity of at least 1,000 Pas, or a solid. In
terms of availability and cost, the alkenyl groups within this
component are most preferably vinyl groups. The amount of alkenyl
groups is preferably within a range from 0.01 to 1 mol/100 g
relative to the solid fraction of the component (B). If the amount
of alkenyl groups is less than 0.01 mol/100 g, then this component
is not adequately incorporated within the cross-linking process,
and as a result, a silicone adhesive capable of producing a cured
product with the desired high degree of hardness is unobtainable.
In contrast, if the amount of alkenyl groups exceeds 1 mol/100 g,
then because the total number of alkenyl groups within the system
increases significantly, the cross-linking process does not proceed
satisfactorily with the small amount of the cross-linking agent
(component (C)) described below, meaning the desired degree of
hardness cannot be achieved. If the amount of the cross-linking
agent is increased, then this results in a reduction in the
concentration of the component (B), which tends to make the
resulting cured product more brittle. For these reasons, the amount
of alkenyl groups within the component (B) is more preferably
within a range from 0.05 to 0.5 mol/100 g.
[0032] The ratio of the component (B) relative to the component (A)
is an important factor within this composition. The blend amount of
the component (B) must be within a range from 60 to 90 parts by
mass, and is preferably from 70 to 80 parts by mass, per 100 parts
by mass of the combination of the component (A) and the component
(B). If the blend amount of the component (B) is less than 60 parts
by mass, then the desired degree of hardness may be unattainable,
whereas if the quantity exceeds 90 parts by mass, then the cured
product of the resulting silicone resin composition becomes
extremely brittle, meaning the silicone adhesive comprising the
composition is no longer suitable as a die bonding material for LED
elements.
-Component (C)-
[0033] The component (C) is an organohydrogenpolysiloxane
represented by the average composition formula (2) shown below:
R.sup.4.sub.aH.sub.bSiO.sub.(4-a-b)/2 (2)
(wherein R.sup.4, a and b are as defined above for formula (2)),
having at least two SiH bonds (namely, hydrogen atoms bonded to
silicon atoms, or hydrosilyl groups) within each molecule, and
having a viscosity at 25.degree. C. of not more than 1,000
mPas.
[0034] This component functions as a cross-linking agent that
undergoes cross-linking with the alkenyl groups within the
component (A) and the component (B) via a hydrosilylation reaction,
and also functions as a reactive diluent that dilutes the component
(B) to a viscosity best suited to the intended application.
[0035] For these reasons, the viscosity of this component at
25.degree. C. is not more than 1,000 mPas, is typically within a
range from 0.5 to 1,000 mPas, and is preferably from 2 to 200 mPas.
Further, in order to achieve balanced cross-linking, the amount of
the component (C) is controlled so as to provide a total number of
SiH bonds that is 0.5 to 5.0 times, and preferably 0.7 to 3.0
times, the total number of alkenyl groups within the combination of
the component (A) and the component (B).
[0036] The two or more (typically from 2 to 200), preferably three
or more (for example, 3 to 100), and still more preferably 4 to
approximately 50 SiH groups within each molecule may be positioned
either at the molecular chain terminals or at non-terminal
positions within the molecular chain, or may also be positioned at
both these locations. Furthermore, the molecular structure of this
organohydrogenpolysiloxane may be any one of a linear, cyclic,
branched, or three dimensional network structure, although the
number of silicon atoms within a single molecule (or the
polymerization degree) is typically within a range from 2 to 200,
preferably from 3 to 100, and even more preferably from 4 to
approximately 50.
[0037] In the formula (2), R.sup.4 represents a monovalent
hydrocarbon group other than an alkenyl group, and this R.sup.4
group typically contains from 1 to 10 carbon atoms, and preferably
from 1 to 8 carbon atoms. Specific examples of R.sup.4 include
alkyl groups such as a methyl group, ethyl group, propyl group,
isopropyl group, butyl group, isobutyl group, tert-butyl group,
pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl
group, nonyl group or decyl group; aryl groups such as a phenyl
group, tolyl group, xylyl group or naphthyl group, and aralkyl
groups such as a benzyl group, phenylethyl group or phenylpropyl
group. Of these, a methyl group or phenyl group is particularly
desirable.
[0038] Specific examples of the organohydrogenpolysiloxane of the
above formula (2) include 1,1,3,3-tetramethyldisiloxane,
1,3,5,7-tetramethylcyclotetrasiloxane,
tris(hydrogendimethylsiloxy)methylsilane,
tris(hydrogendimethylsiloxy)phenylsilane,
methylhydrogencyclopolysiloxane, cyclic copolymers of
methylhydrogensiloxane and dimethylsiloxane,
methylhydrogenpolysiloxane with both molecular chain terminals
blocked with trimethylsiloxy groups, copolymers of dimethylsiloxane
and methylhydrogensiloxane with both terminals blocked with
trimethylsiloxy groups, dimethylpolysiloxane with both terminals
blocked with dimethylhydrogensiloxy groups,
methylhydrogenpolysiloxane with both terminals blocked with
dimethylhydrogensiloxy groups, copolymers of dimethylsiloxane and
methylhydrogensiloxane with both terminals blocked with
dimethylhydrogensiloxy groups, copolymers of methylhydrogensiloxane
and diphenylsiloxane with both terminals blocked with
trimethylsiloxy groups, copolymers of methylhydrogensiloxane,
diphenylsiloxane and dimethylsiloxane with both terminals blocked
with trimethylsiloxy groups, copolymers of methylhydrogensiloxane,
methylphenylsiloxane and dimethylsiloxane with both terminals
blocked with trimethylsiloxy groups, copolymers of
methylhydrogensiloxane, dimethylsiloxane and diphenylsiloxane with
both terminals blocked with dimethylhydrogensiloxy groups,
copolymers of methylhydrogensiloxane, dimethylsiloxane and
methylphenylsiloxane with both terminals blocked with
dimethylhydrogensiloxy groups, copolymers composed of
(CH.sub.3).sub.2HSiO.sub.1/2 units, (CH.sub.3).sub.3SiO.sub.1/2
units and SiO.sub.4/2 units, copolymers composed of
(CH.sub.3).sub.2HSiO.sub.1/2 units and SiO.sub.4/2 units, and
copolymers composed of (CH.sub.3).sub.2HSiO.sub.1/2 units,
SiO.sub.4/2 units and (C.sub.6H.sub.5).sub.3SiO.sub.1/2 units, as
well as compounds in which some or all of the methyl groups within
each of the above compounds have been substituted with phenyl
groups.
[0039] Specific examples of the component (C) include compounds
represented by the formula shown below:
Me.sub.3SiO(MeHSiO).sub.nSiMe.sub.3
(wherein, n is an integer of 2 to 100, and preferably 2 to 20), and
cyclic siloxanes represented by the formula shown below.
##STR00002##
-Component (D)-
[0040] The component (D) is a reaction catalyst for accelerating
the reaction between the components (A) and (B), and the component
(C), and is an effective amount of a platinum group metal-based
catalyst.
[0041] Any of the conventional hydrosilylation reaction catalysts
can be used as this platinum group metal-based catalyst. Specific
examples include platinum group metals such as platinum black,
rhodium and palladium; platinum chlorides such as
H.sub.2PtCl.sub.4.nH.sub.2O, H.sub.2PtCl.sub.6.nH.sub.2O,
NaHPtCl.sub.6nH.sub.2O, KHPtCl.sub.6nH.sub.2O,
Na.sub.2PtCl.sub.6.nH.sub.2O, K.sub.2PtCl.sub.4.nH.sub.2O,
PtCl.sub.4.nH.sub.2O, PtCl.sub.2 and Na.sub.2HPtCl.sub.4.nH.sub.2O
(wherein, n represents an integer of 0 to 6, and is preferably
either 0 or 6); chloroplatinic acid and chloroplatinates;
alcohol-modified chloroplatinic acid (see U.S. Pat. No. 3,220,972);
complexes of chloroplatinic acid and olefins (see U.S. Pat. No.
3,159,601, U.S. Pat. No. 3,159,662 and U.S. Pat. No. 3,775,452); a
platinum group metal such as platinum black or palladium supported
on a carrier such as alumina, silica or carbon; rhodium-olefin
complexes; chlorotris(triphenylphosphine)rhodium (Wilkinson's
catalyst); and complexes of platinum chloride, chloroplatinic acid
or a chloroplatinate with a vinyl group-containing siloxane and
particularly a vinyl group-containing cyclic siloxane. Of these,
from the viewpoints of compatibility and reducing chlorine
impurities, silicone-modified chloroplatinic acid materials are
preferred, and a specific example is a platinum catalyst prepared
by modifying chloroplatinic acid with tetramethylvinyldisiloxane.
The amount added of the component (D), reported as an equivalent
mass of platinum metal within the component (a), is typically
within a range from 1 to 500 ppm, preferably from 3 to 100 ppm, and
still more preferably from 5 to 40 ppm.
[0042] In another preferred aspect of the present invention, the
component (a) is composed of a composition comprising the
components (P), (Q) and (R) described below:
[0043] (P) an organopolysiloxane represented by an average
composition formula (3) shown below:
R.sub.x(C.sub.6H.sub.5).sub.ySiO.sub.(4-x-y)/2 (3)
(wherein R represents identical or different, unsubstituted or
substituted monovalent hydrocarbon groups or alkoxy groups, or a
hydroxyl group, provided that 0.1 to 80 mol % of all R groups are
alkenyl groups; and x and y are positive numbers that satisfy
1.ltoreq.x+y<2 and 0.20.ltoreq.y/(x+y).ltoreq.0.95), which at
25.degree. C. is either a liquid having a viscosity of at least 100
mPas, or a solid,
[0044] (Q) an organohydrogenpolysiloxane represented by an average
composition formula (4) shown below:
R'.sub.cH.sub.dSiO.sub.(4-c-d)/2 (4)
(wherein R' represents identical or different, substituted or
unsubstituted monovalent hydrocarbon groups other than aliphatic
unsaturated hydrocarbon groups; and c and d are positive numbers
that satisfy 0.7.ltoreq.c.ltoreq.2.1, 0.002.ltoreq.d.ltoreq.1.0 and
0.8.ltoreq.c+d.ltoreq.2.6), having at least two Si--H bonds within
each molecule, and having a viscosity at 25.degree. C. of not more
than 1,000 mPas, wherein at least 5 mol % of the total number of R'
groups and silicon atom-bonded H atoms within the composition
formula (4) are phenyl groups, and
[0045] (R) an effective amount of a platinum group metal-based
catalyst.
-Component (P)-
[0046] The component (P) is a component for improving the
mechanical strength of the cured product obtained upon curing the
silicone adhesive of the present invention. This component (P) is
an organopolysiloxane represented by the average composition
formula (3):
R.sub.x(C.sub.6H.sub.5).sub.ySiO.sub.[(4-x-y)/2] (3)
(wherein R, x and y are as defined above for formula (3)), which at
25.degree. C. is either a liquid having a viscosity of at least 100
mPas, and preferably 100 Pas or more, or a solid.
[0047] As is evident from the fact that 1.ltoreq.x+y<2 in the
formula (3), this organopolysiloxane is a branched or three
dimensional network structure comprising one or more RSiO.sub.3/2
units, (C.sub.6H.sub.5)SiO.sub.3/2 units or SiO.sub.2 units within
the molecule.
[0048] In the formula (3), R preferably represents identical or
different, substituted or unsubstituted monovalent hydrocarbon
groups or alkoxy groups of 1 to 20 carbon atoms, and more
preferably 1 to 10 carbon atoms, or a hydroxyl group. Specific
examples of these types of hydrocarbon groups include saturated
hydrocarbon groups, including alkyl groups such as a methyl group,
ethyl group, propyl group, isopropyl group, butyl group, tert-butyl
group or hexyl group, and cycloalkyl groups such as a cyclohexyl
group; aryl groups other than a phenyl group, such as a tolyl
group, xylyl group or naphthyl group; aralkyl groups such as a
benzyl group or phenylethyl group; unsaturated hydrocarbon groups
including alkenyl groups such as a vinyl group, allyl group,
propenyl group, isopropenyl group or butenyl group; halogenated
hydrocarbon groups such as a 3,3,3-trifluoropropyl group; and
cyano-substituted hydrocarbon groups. Examples of the alkoxy group
include unsubstituted alkoxy groups such as a methoxy group, ethoxy
group, propoxy group or phenoxy group, and alkoxy-substituted
alkoxy groups such as a methoxyethoxy group or ethoxyethoxy group.
Of all the R groups, 0.1 to 80 mol %, and preferably 0.5 to 50 mol
%, are alkenyl groups. If the alkenyl group content is less than
0.1 mol %, then the hardness following curing is inadequate for a
silicone adhesive, whereas if the alkenyl group content exceeds 80
mol %, then the number of cross-linking points becomes excessively
high, and the cured product tends to become brittle. Furthermore, x
and y are positive numbers that satisfy 1.ltoreq.x+y<2 and
preferably 1.2.ltoreq.x+y.ltoreq.1.9, and also satisfy
0.20.ltoreq.y/(x+y).ltoreq.0.95 and preferably
0.25.ltoreq.y/(x+y).ltoreq.0.90. If the value of x+y is less than
1, or 2 or greater, then the hardness and strength of the cured
product tend to be unsatisfactory. Furthermore, if the phenyl group
content, represented by y/(x+y) is less than 0.25, then the
hardness and strength of the cured product tend to be
unsatisfactory. If the value of y/(x+y) exceeds 0.90, then the
strength of the cured product deteriorates.
-Component (Q)-
[0049] The component (Q) is an organohydrogenpolysiloxane that
forms cross-linking via a hydrosilylation reaction with the alkenyl
groups contained within the component (P). The component (Q)
functions as a cross-linking agent, and also functions as a
reactive diluent. The organohydrogenpolysiloxane is a compound
represented by the average composition formula (4) shown below:
R'.sub.cH.sub.dSiO.sub.(4-c-d)/2 (4)
(wherein R'', c and d are as defined above for the formula (4)),
having at least two (typically from 2 to 200), preferably three or
more (for example, 3 to 100), and still more preferably 4 to
approximately 50 Si--H bonds (namely, hydrogen atoms bonded to
silicon atoms) within each molecule, and having a viscosity at
25.degree. C. of not more than 1,000 mPas, wherein at least 5 mol %
of the total number of silicon atom-bonded R'' groups and H atoms
are phenyl groups. The component (Q) is preferably essentially a
linear organohydrogenpolysiloxane, although cyclic, branched or
three dimensional network structures may also be used. The number
of silicon atoms within a single molecule (or the polymerization
degree) is typically within a range from 4 to 200, preferably from
4 to 100, and even more preferably from 4 to approximately 50.
[0050] R' represents identical or different, substituted or
unsubstituted monovalent hydrocarbon groups other than aliphatic
unsaturated hydrocarbon groups, which preferably contain 1 to 20
carbon atoms, and still more preferably 1 to 10 carbon atoms.
Specific examples of these types of hydrocarbon groups include
saturated hydrocarbon groups, including alkyl groups such as a
methyl group, ethyl group, propyl group, isopropyl group, butyl
group, tert-butyl group or hexyl group, and cycloalkyl groups such
as a cyclohexyl group; aryl groups such as a phenyl group or tolyl
group; aralkyl groups such as a benzyl group or phenylethyl group;
halogenated hydrocarbon groups such as a 3,3,3-trifluoropropyl
group; and cyano-substituted hydrocarbon groups. A phenyl group or
methyl group is particularly preferred as R'.
[0051] Furthermore, c is a positive number that satisfies
0.7.ltoreq.c.ltoreq.2.1, and preferably satisfies
1.0.ltoreq.c.ltoreq.1.8. d is a positive number that satisfies
0.002.ltoreq.d.ltoreq.1.0, preferably satisfies
0.02.ltoreq.d.ltoreq.1.0, and still more preferably satisfies
0.10.ltoreq.d.ltoreq.1.0. Moreover, c and d also satisfy
0.8.ltoreq.c+d.ltoreq.2.6, preferably satisfy
1.01.ltoreq.c+d.ltoreq.2.4, and still more preferably satisfy
1.6.ltoreq.c+d.ltoreq.2.2. If d is less than 0.002, then sufficient
hardness tends to be unobtainable when the adhesive of the present
invention is cured. In contrast, if d exceeds 1.0, then the
compatibility of the component (Q) with the component (P)
deteriorates, and there is a possibility of phase separation. At
values of c+d less than 0.8, the viscosity increases dramatically,
and the action of the component (Q) as a reactive diluent tends to
be lost. In contrast, if c+d exceeds 2.6, then the cured product
becomes brittle.
[0052] In the case of this aspect, in order to achieve favorable
compatibility with the component (P) and favorable physical
properties for the cured product, this organohydrogenpolysiloxane
is preferably a compound in which at least 5 mol %, and preferably
10 to 50 mol %, of all the silicon atom-bonded R' groups and H
atoms (hydrogen atoms) are phenyl groups. Alternatively, an
organohydrogenpolysiloxane mixture containing an
organohydrogenpolysiloxane in which at least 15 mol %, and
typically 15 to 70 mol %, and preferably 20 to 50 mol %, of all the
silicon atom-bonded R' groups and H atoms (hydrogen atoms) are
phenyl groups, and an organohydrogenpolysiloxane in which less than
15 mol %, and typically 0 to 14 mol %, and preferably 1 to 10 mol
%, of all the silicon atom-bonded R'' groups and H atoms (hydrogen
atoms) are phenyl groups, in a weight ratio of 1:9 to 9:1, and
preferably 2:8 to 8:2, can also be used favorably. The R' groups
other than the phenyl groups are most preferably methyl groups.
[0053] Furthermore, the viscosity of the organohydrogenpolysiloxane
of the component (Q) is as defined above. The lower limit for the
viscosity is typically 0.5 mPas at 25.degree. C., meaning that at
25.degree. C., the viscosity is typically within a range from 0.5
to 1,000 mPas, and is preferably from 1 to 500 mPas.
[0054] The blend amount of the organohydrogenpolysiloxane of the
component (Q) is typically within a range from 10 to 100 parts by
mass, and is preferably from 15 to 80 parts by mass, per 100 parts
by mass of the component (P). If this blend amount is less than 10
parts by mass, then the low viscosity suitable for molding cannot
be achieved, whereas if the blend amount exceeds 100 parts by mass,
then the cured product obtained upon curing the adhesive of the
present invention does not exhibit satisfactory hardness or
strength.
[0055] Furthermore, the organohydrogenpolysiloxane of this
component (Q) may also be added in an amount that provides a molar
ratio of the silicon atom-bonded hydrogen atoms (namely, SiH
groups) within the component (Q) relative to the alkenyl groups
within the component (P) of 0.5 to 5 mol/mol, and preferably 1 to 3
mol/mol. Specific examples of the organohydrogenpolysiloxane of the
component (Q) include the same compounds as those described above
in relation to the component (C) (provided that the compound
includes 4 or more silicon atoms).
-Component (R)-
[0056] The component (R) is used for accelerating the reaction
between the components (P) and (Q), and is an effective amount of a
platinum group metal-based catalyst. The same catalysts as those
listed above for the component (D) can be used as the platinum
group metal-based catalyst, although from the viewpoints of
compatibility and reducing chlorine impurities, silicone-modified
chloroplatinic acid materials are preferred, and a specific example
is a platinum catalyst prepared by modifying chloroplatinic acid
with tetramethylvinyldisiloxane. The amount added of the component
(R), reported as an equivalent mass of platinum metal within the
component (a), is typically within a range from 1 to 500 ppm,
preferably from 3 to 100 ppm, and still more preferably from 5 to
40 ppm.
[Component (b)]
[0057] The component (b) is a pigment powder used for coloring the
silicone adhesive a white color, and powders that yield a
transparent mixture when added to the composition of the present
invention are not suitable.
[0058] Examples of the pigment powder used for coloring the
silicone adhesive a white color include titanium oxide, zinc oxide,
white lead, zinc sulfide, calcium carbonate and kaolin, although
from the viewpoint of achieving a balance between opacifying
strength, coloring strength and light reflectance, titanium oxide
or zinc oxide is preferred, and titanium oxide is particularly
desirable.
[0059] From the viewpoint of the concealment properties achieved,
the average particle size of the white pigment powder must be less
than 1 .mu.m, and is preferably within a range from 0.01 to 0.9
.mu.m, and more preferably from 0.1 to 0.3 .mu.m. Here, the
"average particle size" refers to the accumulated weight average
size D.sub.50 (or the median size) measured using a particle size
distribution analyzer that employs a laser diffraction method.
[0060] The blend amount of the component (b) is preferably within a
range from 10 to 200 parts by mass, and is preferably from 20 to
150 parts by mass, per 100 parts by mass of the component (a). If
the amount of the component (b) is too large, then the viscosity of
the resulting silicone adhesive becomes too high, and the
composition tends to develop trailing threads, meaning application
of the adhesive by stamping becomes problematic. In contrast, if
the amount of the white pigment powder is too small, then the
coloring strength is weak, and the desired level of concealment may
be unobtainable.
[Component (c)]
[0061] The component (c) is a powder that is used as a spacer for
ensuring that the thickness of the white silicone adhesive layer
remains constant between substrates, and has the purpose of
maintaining the white coloring of the composition even when the
adhesive layer is thin. In addition, the component (c) is also
added to the composition for the purpose of improving the
positioning properties when an LED light emitting element is
pressed down onto the adhesive. Because the component (c) is used
to regulate the thickness of the adhesive layer, the average
particle size of the component (c) must be larger than that of the
component (b), and the average particle size is therefore at least
1 .mu.m. On the other hand, the maximum value for the average
particle size of the component (c) is typically less than 10 .mu.m
and is preferably not more than 9 .mu.m, and an average particle
size within a range from 1 to 5 .mu.m is particularly
desirable.
[0062] In the same manner as that described for the component (b),
the "average particle size" for the component (c) refers to the
accumulated weight average size D.sub.50 (or the median size)
measured using a particle size distribution analyzer that employs a
laser diffraction method. If the average particle size of the
component (c) is too large, then although the thickness of the
adhesive layer increases, providing superior concealment
properties, a major drawback arises in that the heat radiating
properties for the heat generated from the bonded LED element tend
to deteriorate. When a light emitting element is bonded by pressing
the element onto the adhesive layer, the thickness of the adhesive
layer is preferably not more than 30 .mu.m, and is more preferably
within a range from 5 to 10 .mu.m. Examples of the powder of the
component (c) include ceramic powders such as metal oxide powders
like crystalline silica, fused silica or alumina, and because it is
undesirable that the silicone adhesive layer loses its white
coloring upon addition of the component (c), a white or colorless
powder is preferred. Furthermore, if consideration is also given to
the concealment and heat radiating properties, then the use of an
alumina powder is particularly desirable. The alumina may be
composed of sub-angular particles, flake-like particles or
spherical particles, although for reasons including the fill
properties relative to the silicone, and the positioning properties
of the light emitting element, flake-like particles are
particularly effective.
[0063] The blend amount of the component (c) is preferably within a
range from 2 to 400 parts by mass, and is more preferably from 5 to
200 parts by mass, per 100 parts by mass of the component (a).
[0064] The blend ratio between the components (b) and (c) is
preferably such that the mass ratio of the component (b) relative
to the component (c) is within a range from 0.1 to 20, more
preferably from 0.2 to 10, and still more preferably from 0.5 to 5.
As the proportion of the component (b) having the smaller particle
size is increased, trailing threads become more significant,
whereas if the proportion of the component (c) having the larger
particle size is increased, then because the alumina or the like of
the component (c) has a lower degree of whiteness than the white
powder such as the titanium oxide of the component (b), the
concealment properties tend to deteriorate. The combined amount of
the component (b) and the component (c) per 100 parts by mass of
the component (a) is typically within a range from 12 to 600 parts
by mass, preferably from 25 to 350 parts by mass, and more
preferably from 40 to 350 parts by mass.
[0065] When either the component (b) or the component (c) is used
alone, absolutely no concealment is obtained upon curing, meaning
the component (b) and the component (c) must be used in
combination. If only the component (b) is added to the component
(a), then although an extremely white adhesive is obtained, because
the adhesive layer lacks thickness when a light emitting element is
pressed onto the adhesive, almost no concealment effect is
achieved. Further, if only the component (c) is added to the
component (a), then the adhesive tends to have a gray-white color,
and once again, when a light emitting element is bonded to the
adhesive, no concealment effect is obtained.
[Other Components]
[0066] Other components such as those described below may also be
added to the silicone adhesive of the present invention, provided
they do not impair the effects of the present invention. These
other components include viscosity control agents such as
petroleum-based solvents and silicone-based non-functional oils;
adhesion improvers such as carbon functional silanes and silicone
compounds that have been modified with an epoxy group, Si--H group,
Si-Vi group or alkoxy group or the like (and may be modified with a
single type of group or a plurality of different types of group);
and components for controlling the curing rate such as
tetramethyltetravinylcyclosiloxane, acetylene alcohol compounds
typified by ethynylcyclohexanol, and triallyl isocyanurate or
modified products thereof. Furthermore, in order to improve the
heat resistance durability, compounds such as hindered amines,
antioxidants and polymerization inhibitors may also be added.
[0067] Although there are no particular restrictions on the curing
conditions used for the silicone adhesive of the present invention,
curing is preferably conducted at 120 to 180.degree. C. for a
period of 60 to 180 minutes.
[0068] Examples of semiconductor elements to which the silicone
adhesive of the present invention may be applied include light
emitting diode (LED) chips.
[0069] The present invention is described in more detail below
using a series of examples and comparative examples, but the
present invention is in no way limited by the examples presented
below.
EXAMPLES
Example 1
[0070] (1) A linear dimethylpolysiloxane (A1) with both terminals
blocked with vinyl groups and having a viscosity at 25.degree. C.
of 70 mPas,
[0071] a toluene solution of a silicone resin (B1) composed of
Me.sub.3SiO.sub.1/2, ViMe.sub.2SiO.sub.1/2 (wherein Vi represents a
vinyl group, this definition also applies below) and SiO.sub.4/2
units, with a molar ratio of the combination of the
Me.sub.3SiO.sub.1/2 and ViMe.sub.2SiO.sub.1/2 units relative to the
SiO.sub.4/2 units of 0.8, and having an amount of vinyl groups
relative to the solid fraction of 0.085 mols/100 g, and
[0072] a methylhydrogensiloxane (C1) of the above average
composition formula (2): R.sup.4.sub.aH.sub.bSiO.sub.(4-a-b)/2
wherein R.sup.4 represents a methyl group, a=1.44 and b=0.78, with
both terminals blocked with trimethylsiloxy groups, and having a
viscosity at 25.degree. C. of 7.5 mPas
[0073] were mixed together in a solid fraction equivalent mass
ratio of 25:75:10. The toluene was removed from the resulting
mixture by treatment at 120.degree. C. under a reduced pressure of
not more than 10 mmHg, thereby yielding a viscous liquid at room
temperature.
(2) 100 parts by mass of this liquid was mixed with 3 parts by mass
of tetramethyltetravinyltetracyclosiloxane and 5 parts by mass of
the epoxy group-containing siloxane compound represented by a
structural formula (5) shown below,
##STR00003##
yielding a transparent liquid with a viscosity of 5 Pas (silicone
base 1, molar ratio of total SiH groups relative to total alkenyl
groups within the composition: 1.65).
[0074] (3) To 100 parts by mass of this silicone base 1 were added
50 parts by mass of a spherical titanium oxide powder (b1) having
an average particle size of 0.26 .mu.m (product name: R-820,
manufactured by Ishihara Sangyo Kaisha, Ltd.), 10 parts by mass of
a crystalline silica (c1) having an average particle size of 2.0
.mu.m (product name: NIN-SIL-5, manufactured by U.S. Silica
Company), and a platinum catalyst (D1) derived from chloroplatinic
acid and having tetramethylvinyldisiloxane as a ligand, in
sufficient amount to provide the equivalent of 10 ppm of platinum
atoms relative to the silicone component, and the mixture was then
stirred thoroughly, yielding a white paste with a viscosity of 20
Pas.
Example 2
[0075] The silicone base 1 was prepared in the same manner as
example 1, and to 100 parts by mass of this silicone base 1 were
added 50 parts by mass of the same titanium oxide powder (b1) used
in example 1, 90 parts by mass of an alumina powder (c2) having an
average particle size of 4.0 .mu.m (product name: AL-43PC,
manufactured by Showa Denko K.K.), and the same platinum catalyst
(D1) used in example 1, in sufficient amount to provide the
equivalent of 10 ppm of platinum atoms relative to the silicone
component. The mixture was then stirred thoroughly, and 3 parts by
mass of a hydrocarbon solvent with a boiling point of at least
200.degree. C. was added, yielding a white paste with a viscosity
of 20 Pas.
Example 3
[0076] A mixture containing 45.8 g of vinylmethyldichlorosilane,
111.0 g of phenyltrichlorosilane (molar ratio 38:62) (average
composition of mixture:
(CH.sub.3).sub.0.38(C.sub.6H.sub.5).sub.0.62(CH.sub.2.dbd.CH).su-
b.0.38SiO.sub.1.31) and 20 g of toluene was added gradually, in a
dropwise manner, to a mixture of 120 g of toluene and 320 g of
water being stirred inside a flask, with the addition controlled so
that the temperature inside the flask did not exceed 50.degree. C.,
thereby effecting a cohydrolysis. A polycondensation was then
conducted by continuing the reaction at not more than 70.degree. C.
for two hours, thus forming a toluene solution of a three
dimensional network structure organopolysiloxane (silicone resin)
(P1) that exhibited a non-volatile component of 70% when heated for
30 minutes at 150.degree. C. The solid fraction (P1) within this
solution existed in a non-fluid gum-like state at 25.degree. C.
This organopolysiloxane solution was stripped for one hour under
conditions of 80.degree. C. and 15 mmHg, and to 100 parts by mass
of the resulting organopolysiloxane component were added 43 parts
by mass of a methylhydrogenpolysiloxane (Q1) represented by the
formula (4): R''.sub.cH.sub.dSiO.sub.(4-c-d)/2 wherein R''
represents a methyl group, c=1.67 and d=0.67, having a viscosity at
25.degree. C. of 30 mPas, and 10 parts by mass of a
hydrogensiloxane having an epoxy group and methoxy groups,
represented by a formula (6) shown below, thus obtaining a
transparent liquid with a viscosity at room temperature of 5.0 Pas
(silicone base 2, molar ratio of total SiH groups relative to total
alkenyl groups within the composition: 0.91).
##STR00004##
[0077] To 100 parts by mass of this silicone base 2 were added 60
parts by mass of the same titanium oxide powder (b1) used in
example 1, 12 parts by mass of the same crystalline silica (c1)
used in example 1, and a platinum catalyst (D1) derived from
chloroplatinic acid and having tetramethylvinyldisiloxane as a
ligand, in sufficient amount to provide the equivalent of 10 ppm of
platinum atoms relative to the silicone component, and the mixture
was then stirred thoroughly, yielding a white paste with a
viscosity of 10 Pas.
Comparative Example 1
[0078] With the exception of not adding the titanium oxide powder
of the component (b), a white paste having a viscosity of 15 Pas
was prepared in the same manner as example 1.
Comparative Example 2
[0079] With the exception of not adding the alumina powder of the
component (c), a white paste having a viscosity of 10 Pas was
prepared in the same manner as example 2.
[0080] Each of the white pastes prepared in the manner described
above was subjected to the tests described below. The results of
these tests are shown in Table 1.
i. Hardness of Cured Product of Component (a):
[0081] With the exception of not adding the components (b) and (c),
pastes were prepared in the same manner as each of the examples and
comparative examples, and each paste was heated for three hours at
150.degree. C. The type D hardness of the resulting cured product
was measured in accordance with JIS K6253.
ii. Concealment:
[0082] Each of the white pastes was applied to a glass plate, a 1
mm square silicon wafer fragment of thickness 300 .mu.m was pressed
onto the paste, the wafer fragment was observed from beneath the
glass plate, and the degree of concealment was evaluated visually.
The evaluation was made against the following criteria.
[0083] OO: the wafer is completely obscured (the degree of
concealment is large)
[0084] O: the wafer is faintly visible (the degree of concealment
is fair)
[0085] x: the wafer is clearly visible (the paste offers no
concealment)
iii. Adhesive Strength
[0086] Each white paste was applied to a test piece prepared by
silver plating a flat sheet of nickel, a 1 mm square silicon wafer
fragment of thickness 300 .mu.m was pressed onto the paste, and
following curing of the paste by heating at 150.degree. C. for
three hours, the die shear strength was measured using a die bond
tester.
TABLE-US-00001 TABLE 1 Ex- Ex- Comparative Comparative Example 1
ample 2 ample 3 example 1 example 2 Hardness 55 55 75 55 55 (type
D) Concealment .largecircle. .largecircle..largecircle.
.largecircle. X X Adhesive 2000 2100 3500 1800 1700 strength
(g)
* * * * *