Note: Descriptions are shown in the official language in which they were submitted.
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SPECIFICA110~3
TITLE OF THE lNY~. ~ lON
SEMI~ON~u~lOn UNIT P~r-~GF, SEMI~O~U~,~ UNIT PACKAGING
.0~, AND ENCAPSULANT FOR USE IN SEMI~N~u~ UNIT
PACRAGING
lr:~nNlCAL FIELD
This invention is directed generally to a semiconductor
unit package and to a semiconductor unit packaging method.
More specifically, the present invention pertains to a
t~hn;que wherein a semiconductor device is mounted by means
of flip-chip bonding onto a substrate, with a conductive
adhesive sandwiched therebetween, and the substrate and the
semiconductor device are -~h~n; cally conn~cted together,
with a resin encapsulating layer sandwiched therebetween.
R~ ~GROUND ART
Generally, solder inter~onnection has been used for
establishing interco~n~tions between connection term;n~lc of
electronic components such as semiconductor devices and
te . 1 n~ 1 electrodes of circuit patterns on a substrate. As
the size of semiconductor packages has been decreased
dramatically, and as the spacing between ~-o~nection te~ ;n~l~
has been reduced owing to, for example, increase in the
number of ~-on~ction tel ; n~l c, conventional soldering finds
it difficult to catch up with such recent advances, since it
requires large adhesive area.
Various flip-chip bo~;ng approaches, in which the chip
is flipped or inverted such that its active element surface
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faces the substrate and is directly connected to the
substrate with tel ;nAl electrodes, have been proposed for
effective use of packaging areas. Typical examples of the
flip-chip bon~;ng are described below.
(l) Junction By Low Melting-Point Metal
As shown in FIGURE 8, a solder bump electrode 8 is
formed on an electrode pad 2 of a semiconductor device l.
The solder bump electrode 8 is aligned with a terminal
electrode 5 on a substrate 6, Thereafter, solder is melted
to establish electrical connection between the semiconductor
device l and the substrate 6. FIGURE 9 shows a t~chnigué
similar to the one of FIGURE 8. In this t~hn;que, a bump
electrode 3 of gold is formed. A deposit of a low melting-
point metal, e.g., a deposit 9 of indium, is formed between
lS the gold bump electrode 3 and the terminal electrode 5. The
indium deposit 9 is melted and the bump electrode 3 and the
terminal electrode 5 are electrically connected together.
Subsequently, the semiconductor device l and the substrate 6
are m~h~n;cally connected together, with an encapsulating
layer lO sandwiched therebetween.
(2) Junction By Curing Contraction Stress
As shown in FIG. lO, a bump electrode 3 of gold is
formed on an electrode pad 2 of a semiconductor device l.
Alignment of the bump electrode 3 on the semiconductor device
l with a tel ;nAl electrode 5 on a substrate 6 is carried
out. Then, an encapsulating material is filled between the
semiconductor device l and the substrate 6. This
encapsulating material cures or hardens to form an
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encapsulating layer 12. Contraction stress produced by such
har~n;n~ results in application of ~- Lessive stress
between the bump electrode 3 and the tel inAl electrode 5,
whereupon the bump electrode 3 and the terminal electrode.5
S are electrically ro~n~cted together and, at the same time,
the semiconductor device 1 and the substrate 6 are
mechanically connected together. Additionally, in order to
improve connection reliability, a deposit 11 of gold may be
formed on the terminal electrode 5 (see FIGURE lO).
(3) Junction By Anisotropic Conductive Adhesive
Referring now to FIGURE 11, a bump electrode 3 of gold
is formed on an electrode pad 2 of a semiconductor device 1.
An anisotropic conductive adhesive, which includes a binder
in which conductive particles are dispersed, is filled
between the semiconductor device 1 and a substrate 6. This
conductive adhesive is heated while at the same time having
application of pressure, whereupon it cures or hardens to
form an anisotropic conductive adhesive layer 13. As a
result, the bump electrode 3 and a terminal electrode 5 are
electrically ~o~n~cted together and, at the same time, the
semiconductor device 1 and the substrate 6 are ?.ch~nically
co~n~cted together.
. . (4) Junction By Conductive Adhesive
As shown in FIGURE 12, a bump electrode 3 of gold is formed
on an electrode pad 2 of a semiconductor device 1.
Thereafter, a conductive adhesive is transferred to the bump
electrode 3. Alignment of the bump electrode 3 with a
terminal electrode 5 formed on a substrate 6 is carried out
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and thereafter the transferred ~-on~ll~tive adhesive cures to
form a conductive adhesive layer 4. As a result, the bump
electrode 3 and the terminal electrode 5 are electrically
~nnected together, with the conductive adhesive layer 4
5 sandwiched therebetween. An encapsulating material is filled
between the semiconductor device 1 and the substrate 6, as a
result of which the semiconductor device 1 and the substrate
6 are ech~nlcally ~on~cted together. This encapsulating
material cures to form an encapsulating layer 7, whereupon
the semiconductor device 1 and the substrate 6 are
?ch~n~cally co~nected together. A typical encapsulating
material has a composition essentially formed of (a) a resin
binder including a cresol NOVOLAC type epoxy resin and a
NOVOLAC type phenol resin (curing agent) and (b) a filler
15 formed of dielectric particles.
The above-described packaging techniques (1)-(4),
however, have their respective drawbacks.
The packaging t~hniques (1) and (2) have the problem
that, since their structures have difficulties in reducing
20 thermal stress produced by the difference in expansion
coefficient between semiconductor device and substrate, they
are unsuitable for applications where connection stability is
required over a wide range of temperature.
Next, the packaging t~chnique (3) is discussed. The
25 packaging t~rhn~que (3) employs an anisotropic conductive
adhesive that contains a resin binder formed of a resin
material with high flexibility, thereby making it possible to
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reduce thermal stress. In spite of such an advantage, the
hygroscopic of the resin binder increases and the packaging
t~chn~que (3) suffers the problem of ~onn~ction stability
under conditions of high humidity. Additionally, in the
S packaging t~chn~que (3), it is possible to reduce thermal
stress by mat~h~ the thermal expansion coefficient of the
binder with that of the semiconductor device 1 and with that
of the substrate 6. However, a filler having a low thermal
expansion coefficient is cont~ine~ in large amounts, so that
~o~n~ction reliability at the early stage is likely to be
degraded.
Finally, the packaging technique (4) is discussed. This
packaging t~-hnique (4) is able to reduce thermal stress by
a conductive adhesive with flexibility and by matching the
thermal expansion coefficient of the encapsulating material
with that of the semiconductor device 1 and with that of the
substrate 6. Because of such an advantage, the packaging
technique (4) appears to be most attractive as compared to
the other packaging t~chn;ques.
The packaging technique (4), however, has the following
drawbacks. The previously-described encapsulant, which is
formed of a mixture composition of (A) a cresol NOVOLAC type
epoxy resin and (B) a NOVOLAC type phenol resin, has a high
viscosity coefficient. Additionally, mat~h;ng of thermal
expansion coefficients requires a high proportion in content
of a filler in the encapsulant, resulting in increasing the
viscosity of the encapsulant. Therefore, at the time of
filling such an encapsulant between the semiconductor device
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and the substrate, it b~ _ -~ necessary to heat the
encapsulant up to 70-80 degrees centigrade or more to reduce
the viscosity. This results in poor productivity. Further,
at the time of the encapsulant filling, conductive
S interro~nections may be damaged by thermal stress produced by
the thermal expansion difference when temperature is
increased, thereby reducing co~n~ction reliability.
On the other hand, a resin binder as an encapsulant may
be used which is formed essentially of (A) a polyepoxide the
viscosity of which is very low at normal room temperature and
(B) an acid anhydride. Note that "polyepoxide" is a general
term for epoxy resins and/or epoxy compounds. However, if a
large ~uantity of a filler is added to such a resin binder
for the purpose of reducing the thermal expansion
coefficient, this will hold the viscosity of the encapsulant
low but increase the thixotropy index. This produces the
problem that the encapsulant is unable to enter between the
semiconductor device and the substrate, or the problem that,
even if the encapsulant manages to enter, such entrance is
accompanied with a great number of air bubbles. The presence
of such air bubbles in the encapsulant contributes to non-
uniformity in, for example, thermal expansion of the cured
encapsulant. Connection reliability is reduced. For this
reaSon, it has been considered impractical to use a resin of
polyepoxide and acid anhydride as a binder.
DT~TOSURE OF THE lNv~..LlON
Bearing in mind the above-described problems with the
prior art t~chn; ~ues, this invention was made. Accordingly
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a general object of the present invention is to provide an
improved semiconductor unit package and associated packaging
method capable of achieving high connection reliability and
high productivity. The inventors of the present invention
investigated the limitation of the characteristics of
viscosity and thixo~Lo~y index necessary for obt~;n;ng
desirable encapsulating characteristics of fillers. It is to
be noted that "polyepoxide" is a general term for epoxy
resins and/or epoxy compounds.
The inventors of this invention found out the fact that
the reason that conventional materials are unsuitable for an
encapsulant lies not only in viscosity but also in thixotropy
index (high thixotropy index). For example, for the case of
resin binders cont~;n;ng polyepoxides and acid anhydrides,
the inventors of the present invention found out that the
flowability is impeded by interaction between free acids in
the acid anhydride and polar groups at the surface of a
filler. From this knowledge found out by the present
inventors, the following means are provided to achieve the
object of the present invention.
More specifically, in accordance with the present
invention, a composition, the viscosity and the thixoLl~y of
which are below 100 Pa s and below 1.1, respectively, is
used as an encapsulating material in the flip-chip bon~;ng.
This composition cures to form an encapsulating layer by
which a semiconductor device and a substrate are ~h~n~cally
co~nected together.
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WO96/42106 PCT/~96/01600
The present invention provides a semiconductor unit
package that comprises:
(a) a semiconductor device having an electrode pad;
(b) a substrate having a terminal electrode;
(c) a bump electrode formed on the electrode pad of the
semiconductor device;
(d) a conductive adhesive layer which is formed of a
conductive adhesive with flexibility and which establishes an
electrical co~nection between the bump electrode and the
terminal electrode; and
(e) an encapsulating layer which is formed by curing a
composition having a viscosity of below 100 Pa s and a
thixotropy index of below 1.1 and which fills a gap defined
between the semiconductor device and the substrate in such a
way that the semiconductor device and the substrate are
m~ch~nically joined together.
The encapsulating layer, which ?ch~nically joins a
semiconductor device and a substrate, is formed of an
encapsulant, which is in the state of liquid in a packaging
step and which has not only a low viscosity coefficient of
below 100 Pa s but also a low thixotropy index of below 1.1.
As a result of such arrangement, in a packaging step, such an
encapsulant readily flows and spreads, even into tiny gaps
with no air bubbles. The temperature of filling may be
decreased. These arrangements make it possible to improve
not only electrical ~onn~ction reliability (e.g-,
semiconductor device-to-substrate adhesion, and resistance to
thermal shock) but also productivity.
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It is preferred that the composition consists
essentially of (A) a resin binder that contains at least a
polyepoxide, a carboxylic acid's anhydride, a rheology
modifier, and a latent curing accelerator, and (B) a filler
that is formed of a dielectric material, and that the
rheology modifier functions to impede interaction between a
free acid in the anhydride of the carboxylic acid and a polar
group at the surface of the filler.
It is preferred that the rheology modifier contains a
substance capable of selective adsorption of the free acid in
the anhydride of the carboxylic acid.
It is preferred that the rheology modifier is a Lewis-
base compound.
It is preferred that the rheology modifier is either a
tertiary amine compound, a tertiary phosphine compound, a
quaternary ~mon ium salt, a quaternary phosphonium salt, or
a heterocyclic compound that contains in a cyclic chain
thereof an atom of nitrogen.
As described above, the encapsulant is formed
essentially of (A) an acid anhydride-curing type epoxy resin
and (B) a material having a low thermal expansion coefficient
(e.g , a dielectric material). This arrangement reduces
thermal stresses applied to the encapsulating layer.
Additionally, the rheology modifier used is a rheology
modifier operable to impede interaction between a free acid
in the acid anhydride and a polar group at the surface of the
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filler and hence a low viscosity coefficient and a low
thixotropy index can be achieved.
It is preferred that the anhydride of the carboxylic
acid in the resin binder contains at least an anhydride of an
alicyclic acid.
It is preferred that the foregoing alicyclic acid
anhydride contains at least an anhydride of a
trialkyltetrahydrophthalic acid.
The characteristics of alicyclic acid's anhydrides with
low water absorption are utilized to give the desirable
resistance of resin binder to moisture. Additionally, the
viscosity of the resin binder which is in the state of liquid
in a packaging step is low, so that encapsulant filling can
be f;n;Ch~ in a short time. The costs of production can be
lS cut down.
It is preferred that the bump electrode of the
semiconductor device is a stud bump electrode with a two
stepped protuberance.
Such arrangement makes it possible to increase the
density of bump electrode. When mounting a semiconductor
device onto a substrate, densely-placed bump electrodes of
the semiconductor device and tel ; n~l electrodes on the
substrate are electrically ~o~nected together. Subsequently,
an encapsulant having a low viscosity coefficient and a low
thixotropy index is employed so that it can readily flow and
fill a gap defined between the semiconductor device and the
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substrate. As a result, even in high-density semiconductor
units, electrical and r~~h~n; cal connections between
semiconductor device and substrate are improved in
reliability.
S The present invention provides a semiconductor unit
packaging method wherein a semiconductor device having an
electrode pad is mounted on a substrate having a terminal
electrode. More specifically, this method comprises:
(a) a first step of forming a bump electrode on the
electrode pad of the semiconductor device;
(b) a second step of applying a conductive adhesive
around the tip of the bump electrode;
(c) a third step comprising:
performing alignment of the bump electrode and the
terminal electrode;
placing the semiconductor device onto the substrate; and
establishing, through the conductive adhesive, an
electrical connection between the bump electrode and the
tel ;n~l electrode;
(d) a fourth step of preparing an encapsulant formed of
a composition the viscosity and thixotropy index of which are
below 100 Pa-s and below 1.1, respectively;
(e) a fifth step of f~lling a gap defined between the
~ semiconductor device and the substrate with the encapsulant;
and
(f) a sixth step of curing the. encapsulant to
mech~n;cally joint' the semiconductor device and the
substrate.
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Since the encapsulant has not only a low viscosity
coefficient of below lO0 Pa-s but also a low thixotropy
index of below l.l, this makes it possible for such an
encapsulant in a packaging step to readily flow and spread,
S even into tiny gaps with no air bubbles. The temperature of
f~lli ng may be decreased. These arrangements make it
possible to improve not only electrical ~onne~tion
reliability (e.g., semiconductor device-to-substrate
adhesion, and resistance to thermal shock) but also
productivity, and to shorten the packaging time.
It is preferred that the composition of the fourth step
consists essentially of (A) a resin binder that contains at
least a polyepoxide, an anhydride of a carboxylic acid, a
rheology modifier, and a latent curing accelerator, and (B)
a filler that is formed of a dielectric material, and that
the rheology modifier functions to impede interaction between
a free acid in the carboxylic acid's anhydride and a polar
group at the surface of the filler.
Such arrangement makes it possible to reduce both the
viscosity and thixotropy index of the encapsulant in the
fifth step. Additionally, the encapsulant is formed
essentially of (A) an acid anhydride-curing type epoxy resin
and (B) a material having a low thermal expansion coefficient
(e.g., a dielectric material). This arrangement reduces
thermal stresses applied after the packaging to the
encapsulating layer.
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It is preferred that the rheology modifier contains a
substance, which acts also as a curing accelerator for a
double-liquid epoxy resin type encapsulant, by such a trace
amount as to prevent the substance from exhibiting its curing
function.
,.
Such arrangement controls an encapsulant in such a way
that the encapsulant does not start curing between the fourth
step and the fifth step and is cured in the sixth step. When
cured in the six~h step, a rheology modifier is incorporated
into an encapsulating resin layer's network structure. This
eliminates the possibility that addition of a rheology
modifier reduces resistance to heat and resistance to
moisture.
It is preferred that the anhydride of the carboxylic
lS acid in the resin binder of the fourth step contains at least
an anhydride of an alicyclic acid.
It is preferred that the alicyclic acid anhydride of the
fourth step contains at least an anhydride of a
trialkyltetrahydrophthalic acid.
Since an anhydride of an alicyclic acid is low in
viscosity as well as in water absorption, time required for
f~ ng of an encapsulant in the sixth step is reduced, and
resistance to moisture is e~h~n~
It is preferred that the bump electrode of the first
step is a stud bump electrode with a two stepped
protuberance.
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Such arrangement enables the high-density pl~ce~?nt of
bump electrodes, and the encapsulant, which is low in
viscosity as well as in thixotropy index, readily spreads,
even into tiny gaps defined between the densely-placed bump
electrodes and teL i n~ 1 electrodes of the substrates. As a
result, electrical and m~h~nical connections between
semiconductor~ device and substrate are improved in
reliability.
It is preferred that in the fifth step the encapsulant
is injected between the semiconductor device and the
substrate at room temperature.
Such arrangement achieves a reduction of the thermal
stress thereby improving resistance to thermal shock. As a
result, a semiconductor unit package with improved electrical
lS ~onn~ction reliability is achieved.
It is preferred that in the fifth step the encapsulant
is injected between the semiconductor device and the
substrate under a depressurized condition.
Such arrangement not only achieves an i , L~V. ~nt in
productivity but also provides a semiconductor unit package
with improved electrical connection reliability.
It is preferred that in the fourth step the composition
o~ the encapsulant is prepared by providing a mixture of an
anhydride of a carboxylic acid and a part of a filler,
subjecting the mixture to an aging process, and
A~i ng a polyepoxide and the remaining filler to the mixture.
14
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~NO 96J42106 PCI~/JP96~01600
As a result of such arrangement, interaction between a
free acid and a polar group is ~i i ni ~he~. This achieves an
en~psulant having a low viscosity and a low thixotropy
index.
S It is preferred that the rheology modifier contains a
substance capable of selective adsorption of the free acid in
the anhydride of the carboxylic acid.
As a result of such arrangement, a free acid in an acid
anhydrlde is selectively adsorbed by a rheology modifier,
whereupon interaction between free acid and polar group is
impeded. This achieves an encapsulant having a low viscosity
and a low thixotropy index.
It is preferred that the rheology modifier is a Lewis-
base compound.
It is preferred that the rheology modifier is either a
tertiary amine compound, a tertiary phosphine compound, a
guaternary ~oni um salt, a quaternary phosphonium salt, or
a heterocyclic compound that contains in a cyclic chain
thereof an atom of nitrogen.
As a result of such arrangements, interaction between
free acid and polar group is impeded. This achieves an
encapsulant having a low viscosity and a low thixotropy
index.
The present invention provides an encapsulant for
filling a gap between a semiconductor device and a substrate
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WO96/42106 PCT1~96/01600
for use in the packaging of a semiconductor unit. This
encapsulant essentially consists of:
(A) a resin binder that contains at least a polyepoxide,
an anhydride of a carboxylic acid, a rheology modifier, and
a latent curing accelerator wherein the weight percentage of
the resin binder is within the range of from 80% to 25~; and
(B) a filler that is formed of a dielectric material
wherein the weight percentage of the filler is within the
range of from 20% to 75%;
wherein the rheology modifier functions to impede
interaction between a free acid in the anhydride of the
carboxylic acid and a polar group at the surface of the
filler.
Since the encapsulant has not only a low viscosity
lS coefficient of below lO0 Pa s but also a low thixotropy
index 4f below l.l! this makes it possible for such an
encapsulant to readily flow and spread, even into tiny gaps
with no air bubbles. The temperature of filling may be
lowered. Additionally, the latent curing accelerator ensures
the storage stability of the encapsulant and practical curing
accelerant function. These arrangements make it possible to
improve not only electrical connection reliability (e.g.,
semiconductor device-to-substrate adhesion, and resistance to
thermal shock) but also productivity.
It is preferred that the rheology modifier contains a
substance capable of selective adsorption of the free acid in
the anhydride of the carboxylic acid.
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W096/42106 PCT/~96/01600
It is preferred that the rheology modifier is a Lewis-
base compound.
It is preferred that the rheology modifier is either a
tertiary amine compound, a tertiary phosphine compound, a
quaternary ~ -~;um salt, a quaternary phosphonium salt, or
a heterocyclic compound that contains in a cyclic chain
thereof an atom of nitrogen.
The encapsulant is formed essentially of (A) an acid
anhydride-curing type epoxy resin and (B) a material having
a low thermal expansion coefficient (e.g., a dielectric
material). This arrangement reduces thermal stresses applied
to the encapsulating layer in a semiconductor unit package to
be formed. Additionally, the rheology modifier used is a
rheology modifier operable to impede interaction between a
lS free acid in the acid anhydride and a polar group at the
surface of the filler and hence a low viscosity coefficient
and a low thixotropy index can be achieved.
It is preferred that the anhydride of the carboxylic
acid in the resin binder contains at least an anhydride of an
alicyclic acid.
It is preferred that the aforesaid alicyclic acid
anhydride contains at least an anhydride of a
trialkyltetrahydrophthalic acid.
The characteristics of alicyclic acid's anhydrides with
low water absorption are utilized to give the desirable
resistance of resin binder to moisture. Additionally, the
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viscosity of the resin binder which is in the state of liquid
in a packaging step is low, so that encapsulant filling can
be finished in a short time. The costs of packaging can be
cut down.
It is preferred that the resin binder and the filler are
arranged to stay as a single liquid.
Such arrangement facilitates uniform dispersion of the
filler thereby providing a desirable encapsulant for the
manufacture of LSIs.
It is preferred that the resin binder in the encapsulant
has a composition wherein:
(a) the chemical equivalent ratio of the anhydride of
the carboxylic acid to the polyepoxide is within the range of
from 0.8 to 1.1;
(b) the weight percentage of the curing accelerator to
the entirety o~f the resin binder is within the range of from
0.3% to 3%; and
(c) the weight percentage of the rheology modifier to
the entirety of the resin binder is within the range of from
0.02% to 0.3%.
The present invention provides an encapsulant for
f~ ng a gap between a semiconductor device and a substrate
for use in the packaging of a semiconductor unit. This
encapsulant essentially consists of:
(A) a resin binder that contains at least a polyepoxide,
an anhydride of a carboxylic acid, a rheology modifier, and
CA 02221286 1997-11-17
WO 96142106 PCT~JP96/016aO
a latent curing accelerator wherein the weight percentage of
the resin binder is within the range of from 80% to 25%; and
(B) a filler that is formed of a dielectric material
wherein the weight percentage of the filler is within the
range of from 20% to 75%;
wherein the encapsulant is prepared by:
providing a mixture of an anhydride of a carboxylic acid
and a part of a filler;
subjecting the mixture to an aging process; and
0 A~; ng a polyepoxide and the ~ n;ng filler to the
mixture.
As a result of such arrangement, interaction between the
free acid in the anhydride of the carboxylic acid and the
polar group at the surface of the filler, is suppressed and
the thixotropy index of the encapsulant is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a cross-section of a semiconductor unit of
an embodiment in accordance with the present invention.
FIGURE 2 is a cross-section of a joint of the FIG. 1
semiconductor unit.
FIGURE 3 is a cross-section of a semiconductor unit
formèd by a stud bump t~chn;que of an embodiment in
accordance with the present invention.
FIGURES 4(a)-4(e~ are cross-sections of a semiconductor
unit at different process stages of a flip-chip bon~;ng
~ 19
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WO96/42106 PCT/~96/01600
t~hni~ue of an embodiment in accordance with the present
invention.
FIGURE 5 is a flow diagram showing steps of a flip-chip
hon~i ng te~hn~ que of an embodiment in accordance with the
present invention.
t
FIGURE 6~shows the generic chemical composition of a
bisphenol type epoxy resin in a resin binder used in an
embodiment in acaordance with the present invention.
FIGURE 7 shows the generic chemical composition of a
trialkyltetrahydrophthalic acid in a resin binder used in an
embodiment in accordance with the present invention.
FIGURE 8 is a cross section of a conventional
semiconductor unit in which ~onnection is established by a
solder bump electrode.
lS FIGURE 9 is a cross section of a conventional
semiconductor unit in which co~n~ction is established by a
low melting-point metal layer.
FIGURE lO is a cross section of a conventional
semiconductor unit in which co~nection is established by
makiny use of contraction stresses exerted when an
encapsulating resin cures.
FIGURE ll is 'a cross section of a conventional
semiconductor unit in which ~onn~ction is established by an
anisotropic conductive adhesive.
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WC~ 96S42~06 PCT/JP9610~600
FIGURE 12 is a cross section of a conventional
semiconductor unit in which ~-on~tion is estab~ by a
conductive adhesive.
BEST MODE FOR CAnnYl~ OUT THE lNV~ lON
5Preferred embodiments of the present invention are
described by making reference to the accompanying drawing
figures.
FIGURE 1 is,a cross section depicting a semiconductor
unit package in accordance with the present invention.
FIGURE 2 is a cross section of a joint of the FIG. 1
semiconductor unit package. This semiconductor unit package
is formed by a flip-chip bon~;ng method. Reference numeral
1 denotes a semiconductor device such as an LSI chip.
Reference numeral 2 denotes an electrode pad formed in the
semiconductor device 1. Reference numeral 3 denotes a bump
electrode of gold. Reference numeral 4 denotes a conductive
adhesive layer of a composition (i.e., a conductive adhesive)
essentially formed of a special epoxy resin and conductive
powders of, for example, an alloy of AgPd. Reference numeral
6 is a substrate, e.g., a ceramic substrate, onto which the
semiconductor device 1 is mounted. Reference numeral 5
denotes a terminal electrode formed on the substrate 6.
Reference numeral 7 denotes an encapsulating layer formed of
an encapsulant. Such an encapsulant is essentially formed of
an acid anhydride-curing type epoxy resin. This encapsulant
7, when it re~ fluid, has a thixotropy index of below 1.1
and a viscosity coefficient of lOO Pa-s. The encapsulant 7
is injected between the semiconductor device 1 and the
21
CA 02221286 1997-11-17
WO 96/42106 PCI~/JP96/01600
substrate 6 by capillary action and is cured. It is to be
noted that the thixotropy index is the index expressed by
~ where ~ is the shear rate and ~ is the viscosity
coefficient. Here, the thixoLlo~y index when the shear rate
~ falls in the range of 2 (l/sec) to 20 (1/sec), is shown.
FIGURE 3 is a cross-section of a semiconductor unit
package by means of a flip-chip bo~ing method using a stud
bump electrode. The semiconductor unit package of FIGURE 3
and the semiconductor unit package of FIG. 1 are basically
the same, except that the former semiconductor unit package
employs a stud bump electrode 14 with a two stepped
protuberance instead of the bump electrode 13. Employment of
a flip-chip bonding method using a stud bump electrode with
a two stepped protuberance makes it possible to deal with a
semlconductor device with a greater number of electrode pads,
which is detailed later.
A flip-chip bonding method, which uses the stud bump
electrode 14 of FIGURE 3, is illustrated by making reference
to FIGURES 4(a)-4(e) and to FIGURE 5. FIGURES 4(a)-4(e) are
cross-sections of a semiconductor unit package at different
stages of a flip-chip bond; ng method. FIGURE 5 is a flow
diagram showing steps of the flip-chip bon~; ng method. The
packaging process is described step by step with reference to
FIGURE 5.
2SAt step STl, an wire of gold (Au) is used to form stud
bump electrodes 14 at electrode pads 2 in the semiconductor
device (LSI chip) 1. At step ST2, a leveling process is
22
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carried out and each stud bump electrode 14 is pressed
against a level surface so that the l~i ng ends of the stud
bump electrodes 14 are flush with one another.
Next, at step ST3, as shown in FIGURES 4(a)-4(c), the
semiconductor device 1, with the side of the stud bump
electrode 14 facing down, is placed above a substrate 20 with
application of a conductive adhesive 4a. Thereafter, the
semiconductor device 1 is lowered towards the substrate 20
such that the stud bump electrode 14 is soaked in the
conductive adhesive 4a on the substrate 20. Subse~uently,
the semiconductor device 1 is lifted up, as a result of which
transfer of the conductive adhesive 4a onto the stud bump
electrode 14 is completed.
Next, at steps ST4 and ST5, as shown in FIGURE 4(d), the
semiconductor device 1 is placed onto the ceramic substrate
6 having thereon the terminal electrode 5. At this time,
alignment of the stud bump electrode 14 of the semiconductor
device 1 with the terminal electrode 5 of the substrate 6 is
carried out, and the conductive adhesive 4a is heated to cure
to form the conductive adhesive layer 4. As a result, the
stud bump electrode 14 of the semiconductor device 1 and the
terminal electrode 5 of the substrate 6 are electrically
connected together.
At step ST6, testing for the presence or absence of an
electrical connection failure is carried out. If an
electrical co~nection failure is found, chip repl~cs ?nt is
~ carried out at step ST7 and the flip-chip bonding process
23
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returns back to step ST4. If no electrical connection
failure is found, the process advances to step ST8.
At step ST8, an encapsulant, which is formed of a
composition having a low viscosity of below lO0 Pa s and a
low thixotropy index of below l.l, is injected between the
semiconductor?device l and the substrate 6 at normal room
temperature to resin-encapsulate ~o~nection parts.
Subsequently, at step ST9, a heating treatment is carried out
to cure a resin~binder contained in the injected encapsulant.
As a result, the encapsulating layer 7 is formed (see FIGURE
4(e)), whereupon the semiconductor device l and the substrate
6 are ~ch~n;cally connected together by the encapsulating
layer 7.
At step STlO, final testing is made and the flip-chip
bon~; ng process is completed.
The present embo~i~?nt employs a low-viscosity, low
thixotropy-index encapsulant. This produces the advantages
that an encapsulant injection process can be done smoothly
even at room temperature and the encapsulant injected readily
flows and well spreads to fill a tiny gap between the
semiconductor device l and the substrate 6. This is time
saving, and the Go~ction reliability of a joint made by the
conductive adhesive 4 can be maint~;n~. Additionally, the
encapsulant is a composition essentially formed of (a) an
acid anhydride-curing type epoxy resin with improved
flowability and (b) a filler such a fused silica, in other
words it has a low post-curing thermal expansion coefficient.
24
-
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Since the coefficient of thermal expansion of the
encapsulating layer 7 is low, this controls thermal stresses
produced by the differences in the coefficient of thermal
expansion between the semiconductor device 1 of silicon and
the substrate 6 of, for example, alumina. Additionally, an
encapsulant, ~ormed of a resin of the epoxy group, exhibits
high resistance to heat and has strong adhesion, therefore
achieving connection reliability that r~-~; ns stable even
under high temperature and high humidity conditions.
Since the conductive adhesive 4 has great flexibility,
this contributes to reducing thermal stresses and connection
reliability is further improved.
In the present embodiment, the bump electrode 3 is
formed of gold. Other functionally equivalent metals, e.g.,
copper, may be used to form the bump electrode 3.
Additionally, in the present embodiment, the stud bump
electrode 14 is used. Other types of bump electrodes used in
usual flip-chip bon~; ng techniques may be used. It is,
however, to be noted that use of stud bump electrodes
controls lateral spreading of the conductive adhesive layer
4 thereby achieving a much higher packaging density.
In the present embodiment, the conductive adhesive 4 is
formed of a material of the epoxy group. Other materials
with flexibility may be used, e.g., a material of the rubber
2~ group (e.g., SBR, NBR, IR, BR, CR), a material of the acrylic
group, a material of the polyester group, a material of the
polyamide group, a material of the polyether group, a
CA 02221286 1997-11-17
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material of the polyurethane group, a material of the
polyimide group, and a material of the silicon group. As a
conductive powder material that is cont~ine~ in the
conductive adhesive, powders of noble metals (silver, gold,
p~ um), powders of base metals (nickel, copper), powders
of alloys (solder, AgPd), mixture powders of silver-plated
copper, and powders of nonmetals with conductivity (carbon).
These powders may be used separately or in combination. The
diameter of powders is not limited to a particular one. The
shape of powders is not limited to a particular one.
The encapsulant is formed essentially of (A) a resin
binder and (B) a filler. The resin binder's essential
components are a polyepoxide, an acid anhydride, and a
rheology modifier. Such a polyepoxide is the so-called epoxy
compounds (epoxy resins) and there are no limitations on its
elements. Examples of the polyepoxide are a bisphenol type
epoxy resin (see the FIG. 6), a NOVOLAC type epoxy resin, a
glycidylether type epoxy resin, a glycidylester type epoxy
resin, a glycidylamine type epoxy resin, an alicyclic type
epoxy resin, a biphenyl type epoxy resin, a naphthalene type
epoxy resin, a styrene oxide, an alkylglycidylether, and an
alkylglycidylester. They are used separately or in
combination.
,
As the acid anhydride used here in the present
invention, curing agents for epoxy compounds and epoxy resins
may be used. One of the most preferable acid anhydrides is
a trialkyltetrahydrophthalic acid's anhydride (see FIGURE 7).
Other preferable ones are a methyltetrahydrophthalic acid's
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anhydride, and a methylh~x~hydrophthalic acid's anhydride and
a methylhymic acid's anhydride of the cyclic aliphatic group
that are in the state of li~uid at 25 degrees centigrade.
Other acid anhydrides may be used. These acid anhydrides may
be u~ed separately or in combination. If these acid
anhydrides mentioned above are used as pr~_ ;n~nt elements
of the resin binder, this provides an improved encapsulant
that has very low viscosity, high heat resistance, high
humidity resistance, and high adhesion.
In addition to the foregoing essential elements of the
resin binder, a third binder element may be added as
required, for imp.ove,..ant in heat resistance, humidity
resistance, adhesion strength and for adjustment of thermal
expansion coefficient, rheology, and reactivity.
lS Any powdery filler may be used as one of the pr~o~;n~nt
elements of the encapsulant as long as its average particle
diameter falls in the range of from 1 ,um to 50 ,um. For
example, silica oxides, alumina oxides, aluminum nitrides,
silicon carbides, and silicification compounds all of which
are thermally stable and have low thermal expansion
coefficients. These filler elements are used in any
combination. There are no particular limits on the filler
dose, preferably 20-80 percent, on a we$ght basis, of the
entirety of the encapsulant. Use of these filler elements
achieves an improved encapsulant which is superior in
insulation and which produces less thermal stress.
.
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Any rheology modifier for modification of the
~n~psulant flowability may be used as long as it functions
to prevent a free acid in the acid anhydride from interacting
with a polar group at the surface of the filler and to reduce
the thixotropy index of the encapsulant. The following are
preferred examples of the rheology modification.
(l) Rheology Modification Method I
In Method l, an acid anhydride is pre-mixed with a part
of a filler. The mixture is subjected to an aging process.
For example, the mixture may be heated up to lO0 degrees
centigrade or less. This is followed by addition of a
polyepoxide compound, the r~;n;ng filler, and other
addition agents, to obtain a desirable encapsulant.
(2) Rheology Modification Method II
lS In Method II, a substance capable of selective
adsorption of free acids in an acid anhydride is added to an
encapsulant.
(3) Rheology Modification Method III
In Method III, a substance (e.g., a Lewis-base compound
having neither N-H groups nor O-H groups) that interacts more
strongly with a free acid than a polar group at the surface
of a filler, is added to an encapsulant.
Suitable Lewis-base compounds include tertiary amine
compounds, tertiary phosphine compounds, quaternary ammonium
salts such as the tetrabutylammonium bromide, quaternary
p h o s p h o n i u m s a l t s s u c h a s t h e
tetrabutylphosphoniumbenzotriazolate, mel~;n~, and
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heterocyclic compounds that contain in cyclic ch~ ns thereof
atoms of nitrogen such as imidazole compounds. There are
many Lewis-base compounds other than the above. These Lewis-
base compounds may be used separately or in combination.
The encapsulant may contain, as required, a solvent, a
dispersing agent, a rheology regulatory agent such as a
leveling agent, an adhesion improving agent such as a
coupling agent, or a reaction regulatory agent such as a
curing accelerator.
The rheology modifier of the present invention, which
consists of a Lewis-base compound such as the amine compound,
is usually used as a reaction (curing) accelerator between a
polyepoxide and an anhydride of an carboxylic acid.
When the rheology modifier is used as a curing
accelerator for an encapsulant, curing reaction progresses
even when stored at low temperature to enter the stage of
gel. This limits the type of encapsulant to double-liguid
type ones, in other words mixing must be made just before
use. On the other hand, LSI encapsulant require that large
amounts of fillers must be dispersed uniformly, in other
words a single-liquid type encapsulant is required for LSI.
To sum up, the rheology modifier of the present
invention may be used as a curing accelerator for a double-
liquid type encapsulant but not for a single-liquid type
encapsulant.
29
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If the dose is reduced to such an extent as to prevent
g~lling during the storage, the present rheology modifier may
find applications in the single-liquid type encapsulant. In
such a case, a curing accelerant function that the rheology
5 modifier performs is too poor to meet practical requirements,
in other words no high-level encapsulant curing
characteristics are obt~in~.
The present invention is characterized in that it
employs a latent curing accelerator with both storage
stability and practical curing accelerant functions, and that
subst~n~, e.g., amines, which are usually used as a curing
accelerator for the double-liquid type encapsulant, are
employed as a rheology modifier. Such a rheology modifier is
added in such an amount that it performs no curing functions
15 but functions to improve interface characteristics.
A latent curing accelerator is the catalyst whose
catalyst activities are greatly promoted upon application of,
for example, thermal energy. Generally, latent curing
accelerators are melted (liquefied) or reaction-dissociated
upon application of energy, to be ~nh~n~ in activity.
It is preferred that the encapsulant has the following
composition.
Wt. percent
Resin binder ................. ..80-25
Filler element ............... ..20-77
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It is preferred that the resin binder essentially
consists of a polyepoxide, an anhydride of a carboxylic acid,
a curing accelerator, and a rheology modifier according to
the following element ratios.
S
E~uivalent ratio
Carboxylic acid's anhydride/Polyepoxide ......... Ø8-1.1
Wt. percent
10 Curing accelerator/Resin binder ................. 0.3-3
Rheology modifier/Resin binder .................. 0.02-0.3
In the present invention, the substrate 6 is formed of
ceramic (e.g., alumina). Metal glaze substrates, glass
substrates, resin substrates (e.g., glass epoxy substrates),
polymer film substrates are applicable.
There are no specific limitations on the material of the
terminal electrode 5.
The following are embodiments for investigation of the
characteristics of semiconductor units obt~in~ by the above-
20- desc~ibed flip-chip bo~i~g method.
EMBODIMENT 1
A semiconductor unit with the FIG. 1 structure is formed
in accordance with steps of FIGS. 4(a)-4(e). Bump electrode
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3 is formed by means of gold plating. Conductive adhesive 4a
has a composition formed essentially of powders of AgPd and
an epoxy resin with flexibility. Conductive adhesive 4a is
heated at 120 degrees centigrade and, as a result, cures.
Further, an encapsulant of COMPOSITION a in TABLE l is cured
at 150 degrees centigrade.
EMBODIMENT 2
Stud bump electrode 14 of FIG. 3 is formed on electrode
pad 2 of semiconductor device l by means of a gold-wire
bonder. The following steps are the same as the first
embodiment and are carried out under the same conditions as
the first embodiment.
EMBODIMENT 3
Semiconductor device l is mounted onto substrate 6 under
the same conditions as the first embodiment, except that in
the third embodiment an encapsulant injection process is
carried out under depressurized condition.
EMBODIMENT 4
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Semiconductor device 1 is mo~nted onto substrate 6 under
the same conditions as the second embo~;~?nt, except that in
the fourth embodiment COMPOSITION b of TABLE 1 is used.
. EMBODIMENT 5
Semiconductor device 1 is mounted onto substrate 6 under
the same conditions as the second embodiment, except that in
the fifth embo~im~nt substrate 6 is a glass epoxy substrate
and COMPOSITION c of TABLE 1 is used.
EMBODIMENT 6
Semiconductor device 1 is mounted onto substrate 6 under
the same conditions as the second embodiment, except that in
the sixth embodiment substrate 6 is a glass epoxy substrate,
con~l~ctive adhesive 4 contains powders of silver as
conduçtive powders, and COMPOSITION d of TABLE 1 is used.
EMBODIMENT 7
Semiconductor device 1 is mounted onto substrate 6 under
the same conditions as the second embodiment, except that in
the seventh 2 hoA 1 nt substrate 6 iS a glass substrate,
conductive adhesive 4 is formed essentially of powders of
silver and an urethane resin, COMPOSITION e of TABLE 1 is
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used, and encapsulant injection is carried out under
depressurized condition.
EMBODIMENT 8
Bump electrode 3 of FIG. 1 is formed on electrode pad 2
of semiconductor device 1 by means of gold plating.
Semiconductor device 1 is mounted onto substrate 6 in the
same way as the seventh emboAi~o~t and under the same
conditions as the seventh embodiment.
COMPARE EXAMPLE 1
10 Semiconductor device 1 is mounted onto substrate 6 under
the same conditions as the second embodiment, except that in
the first compare example COMPOSITION f of TABLE 1 is used.
COMPARE EXAMPLE 2
Semiconductor device 1 is mounted onto substrate 6 under
the same conditions as the second embodiment, except that in
the second _ -~e example COMPOSITION g of TABLE 1 is used.
COMPOSITIONS a-g are shown below.
,
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TABLE 1
___,__________ ___ __ __ _________________________
COMPOSITION a:
b$sphenol F type epoxy resin (epoxy equivalent: 162) 85phr
bisphenol A type epoxy resin (epoxy equivalent: 182) 15phr
trialkyltetrahydro phthalic acid's anhydride
(anhydride equiv.: 234) 126phr
2-(2-methylimidazolylethyl)-4, 6-diamino
triazine-isocyanuric acid addition product 1.6phr
10 diazabicyclo~ ~cPn~ O.lphr
fused silica 340phr
___________________________________________________________
COMPOSITION b:
trialkyltetrahydro phthalic acid's anhydride
(anhydride equiv.: 234) 126phr
fused silica 340phr
These two material were kn~ and subjected to an aging
process for 10 hours at 60 degrees centigrade. Thereafter
the following materials were added to them.
bisphenol F type epoxy resin (epoxy equivalent: 162) 85phr
bisphenol A type epoxy resin (epoxy equivalent: 182) 15phr
2-(2-methylimidazolylethyl)-4, 6-diamino
triazine-isocyanuric acid addition product 1.6phr
1-cyanoethyl-2-ethyl-4-methylimidazole 0.2phr
__________________________________________________________
COMPOSITION c:
bisphenol F type epoxy resin (epoxy equivalent: 162) 80phr
alicyclic epoxy resin (ERL4221)* 20phr
trialkyltetrahydro phthalic acid's anhydride
(anhydride equiv.: 234) 135phr
AMI~URE PN** 5phr
tetrabutylammonium bromide 0.2phr
fused silica 400phr
__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
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WO96/42106 PCT/~96/01600
COMPOSITION d:
bisphenol F type epoxy resin (epoxy equivalent: 162) 90phr
bisphenol A type epoxy resin (epoxy equivalent: 182) 10phr
trialkyltetrahydro phthalic acid's anhydride
(anhydride equiv.: 234) 128phr
FUJIHARD FXE1000*** 5phr
tetrabutylphosphoniumbenzotriazolate 0.2phr
fused silica 350phr
________________________________
COMPOSITION e:
bisphenol F type epoxy resin (epoxy equivalent: 162) 70phr
naphthalene type epoxy resin (epoxy equivalent: 148) 30phr
trialkyltetrahydro phthalic acid's anhydride
(anhydride equiv.: 234) 82phr
methyltetrahydro phthalic acid's anhydride
(anhydride equiv.: 166) 40phr
triphenylphosphinetriphenylborate 3.6phr
tetrabutylphosphoniumbenzotriazolate 0.2phr
fused silica 225phr
_______________________
COMPOSITION f:
bisphenol F type epoxy resin (epoxy equivalent: 162) 85phr
bisphenol A type epoxy resin (epoxy equivalent: 182) 15phr
trialkyltetrahydro phthalic acid's anhydride
(anhydride equiv.: 234) 126phr
2-(2-methylimidazolylethyl)-4, 6-diamino
triazine-isocyanuric acid addition product 1.6phr
fused silica 340phr
_____________________ _____________________________________
COMPOSITION g:
bisphenol F type epoxy resin (epoxy equivalent: 162) 100phr
alkyl modified phenol resin (hydroxyl group equiv: 113)
70phr
triphenylphosphine 0.6phr
fused silica 255phr
___________________________________________________________
Note: * = product by UCC;
** ~ product by AJINOMOTO; and
*** = product by FUJI KASEI
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COMPARE EXAMPLE 3
Semiconductor device 1 is mounted onto substrate 6 in a
~"~.,tional way shown in FIG. 9. Substrate 6 is an alumina
~ substrate. Bump electrode 3 is formed of gold. Terminal
el~Llode 5 is~indium-plated. Alignment of bump electrode 3
with terminal~electrode 5 is carried out and, thereafter
semiconductor device 1 is pressed by a Jig and, at the same
time, is heated up to 170 degrees centigrade, whereupon bump
electrode 3 and terminal electrode 5 is ~-o~-ted together.
Further, a silicon encapsulant of zero stress type is
injected between semiconductor device 1 and substrate 6.
This encapsulant is cured to form encapsulating layer 10.
COMPARE EXAMPLE 4
Semiconductor device 1 is mounted onto substrate 6 in a
conventional way shown in FIG. 10. 8ump electrode 3 is
formed of gold. Gold deposit 11 is formed on terminal
electrode 5. Gold deposit 11 is coated with an acrylic
encapsulant. Alignment of bump electrode 3 with terminal
electrode S is carried out. Subsequently, semiconductor
device 1 is pressed by a jig while at the same time the
~n~rsulant is cured by W irradiation or by application of
heat, to form encapsulating layer 12.
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COMPARE EXAMPLE 5
Semiconductor device 1 is mounted onto substrate 6 in a
conventional way shown in FIG. 11. Bump electrode 3 is
formed of gold. Substrate 6 is formed of alumina. Alumina
substrate 6 is coated with an anisotropic conductive adhesive
in which particles of gold are dispersed in an epoxy binder.
Alignment of bump electrode 3 and terminal electrode 5 iS
carried out. Thereafter, semiconductor device 1 is pressed
by a jig while at the same time the adhesive is cured by W
irradiation or by application of heat, to form anisotropic
conductive adhesive layer 13. As a result, bump electrode 3
and tel ;nAl electrode 5 are electrically and ?chAn;cally
connected together.
The viscosity, thixotropy index, injection time of each
of the encapsulant used in the first to eight embo~i ents and
the first to fifth compare exàmples, are shown below (TABLE
2).
38
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TABLE 2
COMP. VISCOSITY T~IXOTROPY TIME(min)
INDEX
EX.1 & EX.2 a7Pa-s 1.0 3.5
~X.3 t a7Pa s 1.0 0.4
EX.4 b8Pa s 0.9 3.0
SEX.5 c4Pa-s 1.0 2.3
EX.6 d5Pa s 1.0 2.5
EX.7 & EX.8 ellPa~s 1.0 0.6
COMPARE EX.1 f7Pa s 4.8100 or
COMPARE EX.2 g120Pa-s 1.3 45
~0 NOTE:VISCOSITY: measured by E-type viscometer
(25 ~C; lOrpm);
THIXOTROPY INDEX: measured by E-type ~iscometer
(25 C; lrpm/lOrpm);
INJECTION TIME: time required for encapsulation of
15 5-mm square semiconductor chip at 25
~C
As can be seen from TABLE 2, in the embodiments of the
present invention, the in~ection time is short falling in the
range of 0.4 to 3.5 minutes. The present invention is
suitable ~or practical applications, accordingly.
Conversely, in the compare examples, the injection time is
much longer than that of the present invention. The compare
exa~ples are unsuitable for practical applications. TABLE 2
shows that the injection time correlates with the
39
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viscosity/thixotropy index. In other words, in the present
invention, the viscosity is low (i.e., below lOO Pa-s) and
the thixo LL~Y index is also low (i.e., below l.l), which
results in reducing the encapsulant injection time. On the
S other hand, in the second compare example, the viscosity
Qxc~e~s lOO Pa s and, in the first compare example, the
thixotropy index exceeds l.l, which results in greatly
increasing the encapsulant injection time. To sum up, when
the encapsulant viscosity is below l00 Pa-s and when the
thixotropy index is below l.l, the flowability of encapsulant
be~_ -~ improved to be suitable for practical applications.
.For the purpose of evaluating the stability. of
~.o~nection in each of the first to eighth embodiments of the
present invention and the first to fifth compare examples,
lS various envilo ental tests were made as shown in TABLES 3
and 4.
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WO96/42106
TABLE 3
TEST 1 TEST 2 TEST 3 TEST 4 TEST.5
EX. 1 0 O O O O
EX. 2 0 O O O O
EX. 3 0 0 0 0 0
EX. 4 0 0 0 0 0
EX. 5 0 0 0 0 0
EX. 6 0 O O O O
EX. 7 0 0 0 0 0
EX. 8 0 0 0 0 0
COMP. 1 0 O X O X
COMP. 2 0 O X O o
COMP. 3 0 O X O O
COMP. 4 0 O X X O
COMP. 5 X O O X X
Note: TEST 1: semiconductor devices are subj ected to a
high-temperature condition for a specified period;
TEST 2: semiconductor devices are subj ected to a low-
temperature condition for a specified period; TEST 3:
semiconductor devices are subj ected to a thermal
shock; TEST 4: semiconductor devices are subj ected to
a high humidity condition for a specified period;
TEST 5: solder-heat resistance testing.
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TABLE 4
POST-TESTING CONNECTION RESISTIVITY:
CRITERION BELOW 200 Q = O
ABOVE 200 Q = X
TESTING CONDITIONS
TEST 1 150 C; 1000hr
S TEST 2 - 55 C; 1000 hr
TEST 3 150 to - 55 C; 500 cycles
TEST 4 121 C; 100%; 100 hr
TEST 5 270 C; 10 sec; 5 cycles
The evaluation results are demonstrated. As can be seen
from the tables, none of the first to eighth examples of this
invention suffer problems in ~o~nection stability. Each
embodiment uses an encapsulant the viscosity and thixotropy
index of which are below 100 Pa s and below 1.1,
respectively. Use of such a low-viscosity, low-thixotropy
encapsulant achieves semiconductor unit packages of high
productivity and, high resistivity against various
' environmental conditions, regardless of the structure of bump
electrodes, the type of substrate, the type of addition
agent, and the type of conductive adhesive.
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In each of the first to eighth embodiments, a Lewis-base
compound, which interacts more strongly with a free acid than
a polar group at the surface of a filler, is used as a
rheology modifier. This rheology modifier not only modifies
S rheology but ialso acts as a catalyst for reaction of
polyepoxide with acid anhydride. This improves the
encapsulant's resistance to various environmental conditions.
The first compare example is now discussed. This
compare example uses an encapsulant that is low in viscosity
but high in thixo~o~y index and, as a result of being high
in thixotropy index, the encapsulant injection time b~ç e~
long. This causes some interconnections to cut off upon
application of heat and thermal shock. Such failure may be
caused by the fact that when the encapsulant injection time
is long the encapsulant loyer holds unwanted air bubbles, as
a result of which non-uniform application of thermal stress
to the encapsulating layer occurs thereby damaging conductive
interconn~ctions.
The second compare example is discussed. In this
cnmr~re example, the conductive adhesive used has high
flexibility and the encapsulant used is, for example, a high-
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WO 96/42106 PCT/JP96/01600
viscosity resin of the phenol curing type epoxy resin group.
The encapsulant must be heated for the purpose of
facilitating injection. This causes some interco~nections to
have high ~onne~tion resistivity when the encapsulant is
injected, and cutoff is likely to occur where unstable
inter~o~n~tions exist in a thermal shock resistance testing,
since the encapsulant viscosity is high and the conductive
~h~lVe~S junction is damaged by stress produced when the
encapsùlant is injected.
The third and fourth compare examples are discussed. In
these compare examples, interconne~tions will cut off in a
relatiyely short time. The fourth compare example suffers
great connection resistivity variation when subjected to
TESTS 4 and 5. In the third compare example,
interconnections fail to reduce thermal stresses and cutoff
results. In the fourth compare example, the encapsulant
exerts strong thermal stresses and has high water absorption,
and ,cutoff results.
The fifth ~omp~e example is discussed. This compare
example undergoes great increase in connection resistivity
when sub;ected to TESTS 1, 4, or 5. The reason may be that
44
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WO 96/42106 PCI'~JP96/01600
the anisotropic conductive adhesive's binder has low humidity
resistance, and low adhesion at high temperature. Use of an
anisotropic conductive adhesive formed of a binder having
high humidity resistance will cause interconnections to cut
off when sub;eoted to a thermal shock test.
A semiconductor unit package in accordance with the
present invention is highly reliable against various
environmental conditions. Conventionally, encapsulant, which
contain polyepoxide and acid anhydride (curing agent) as a
resin binder, have not been used in the flip-chip bonding
method by a conductive adhesive. If a resin binder made up
of polyepoxide and acid anhydride (curing agent) is used as
an encapsulant for semiconductor unit packaging, this
increases the thixotropy index of the encapsulant, therefore
lS produaing the problem that the encapsulant is injected to
only a part of a gap between the semiconductor device and the
substrate.
The inventors of the present invention discovered that
a high thix~py index results from interaction between a
free acid cont~; n~ in an acid anhydride and a polar group at
the surface of a filler. Based on this knowledge, the
CA 02221286 1997-11-17
WO96/42106 PCT/~96/01600
present invention provides a means capable of impeding
interaction between free acid and polar group.
There is another reason why an encapsulant, which
contains a polyepoxide and an acid anhydride (curing agent)
as a resin binder, has not been used. That is, such a resin
binder undergoes hydrolysis in a high humid atmosphere, so
that it has been considered that use of the resin binder
causes problems in humidity resistance of co~ctions
establ1~e~ by a conductive adhesive, and in reliability.
It was confirmed by the present invention that even if
a resin blnder, which uses an acid anhydride (particularly a
trialkyltetrahydro phthalic acid's anhydride) as a curing
agent, is used as an encapsulant in a flip-chip bo~i ng step,
a resulting encapsulating layer has sufficient resistance to
lS humidity to meet requirements of practical applications.
Additionally, such an encapsulant is low in viscosity and
also low in thixotropy index, so that even if the encapsulant
is injected at room temperature (low température), it well
penetrates even into tiny gaps. Such characteristics of the
present encapsulant produce various advantageous
characteristics such as high resistance to thermal shock.
46
CA 02221286 1997-11-17
WO 96142106 PCT/JP96/01600
In the case of conventional semiconductor unit packages
wherein in a flip-chip bon~; ng step COMPOSITION f of TABLE 1
is used as a resin binder, the encapsulant thixotropy index
is so high that air bubbles are held in the encapsulating
layer. Conductive lnter~s~n~tions are damaged in TESTS 3
and 5. On the other hand, in the case of conventional
semiconductor unit packages wherein in a flip-chip bonding
step COMPOSITION g of TABLE 1 is used as a resin binder, the
resin binder must be heated for injection. As a result,
conductive interconnections are damaged, and resistance to
thermal shock becomes low.
. lN~ nIAL APPLICABILITY
The present invention is generally applicable to a
semiconductor unit package in which a semiconductor chip is
mounted on a substrate through a conductive adhesive by means
of flip-chip bo~i ng, For instance, the present invention is
applicable to a multi-chip module tMcM) in which a device
such as LSI chip, chip condenser is mounted on a circuit
board, and to a metbod of manufacturing the same.
