U.S. patent application number 09/519436 was filed with the patent office on 2002-08-01 for semiconductor device, semiconductor device mounting structure, liquid crystal device, and electronic apparatus.
Invention is credited to Uchiyama, Kenji.
Application Number | 20020100974 09/519436 |
Document ID | / |
Family ID | 13142881 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020100974 |
Kind Code |
A1 |
Uchiyama, Kenji |
August 1, 2002 |
SEMICONDUCTOR DEVICE, SEMICONDUCTOR DEVICE MOUNTING STRUCTURE,
LIQUID CRYSTAL DEVICE, AND ELECTRONIC APPARATUS
Abstract
A semiconductor device, a mounting structure thereof, a liquid
crystal device, and an electronic apparatus having an improved bump
electrode structure, such that the bump electrodes and
corresponding electrode terminals can be electrically connected
through an anisotropic conductive film without compromising, or
causing deterioration of, the electrical characteristics or
reliability of the device, even when the bump electrodes are formed
with a narrow pitch. Since the bump electrodes of the semiconductor
device are tapered inward from top to bottom, the base portions of
adjacent bump electrodes are spaced apart from each other by wider
gaps than the corresponding upper portions. Thus, a large number of
conductive particles in the conductive film do not gather between
adjacent bump electrodes to cause short-circuiting therebetween.
Further, since the upper portions of the bump electrodes are wider
and the opposing surface areas of both the bump electrodes and the
electrode terminals are relatively large, a large number of
conductive particles are distributed between the bump electrodes
and the electrode terminals. This ensures that the bump electrodes
and the electrode terminals are electrically connected in a
satisfactory manner. Therefore, with this arrangement, a high level
of reliability can be achieved, even when the bump electrodes are
formed in high density.
Inventors: |
Uchiyama, Kenji;
(Hotaka-machi, JP) |
Correspondence
Address: |
EPSON RESEARCH AND DEVELOPMENT INC
INTELLECTUAL PROPERTY DEPT
150 RIVER OAKS PARKWAY, SUITE 225
SAN JOSE
CA
95134
US
|
Family ID: |
13142881 |
Appl. No.: |
09/519436 |
Filed: |
March 3, 2000 |
Current U.S.
Class: |
257/737 ;
257/778; 257/E21.508; 257/E21.514; 257/E23.021; 257/E23.068;
349/151; 349/152; 438/119; 438/666; 438/668 |
Current CPC
Class: |
G02F 1/13452 20130101;
H01L 2924/0105 20130101; H01L 2224/83101 20130101; H01L 2224/05571
20130101; H01L 24/11 20130101; H01L 2224/13017 20130101; H01L
2924/0001 20130101; H01L 2924/14 20130101; H01L 2224/1147 20130101;
H01L 2224/16 20130101; H01L 2924/3025 20130101; H01L 2924/01082
20130101; H01L 2224/8319 20130101; H01L 2224/05599 20130101; H01L
2224/13099 20130101; H01L 24/83 20130101; H01L 2924/01004 20130101;
H01L 2224/73204 20130101; H01L 23/49811 20130101; H01L 24/29
20130101; H01L 2924/01049 20130101; H01L 2924/00014 20130101; H01L
2924/01033 20130101; H01L 2224/13099 20130101; H01L 2224/05573
20130101; H01L 2924/01005 20130101; H01L 2224/838 20130101; H01L
2924/01006 20130101; H01L 2924/0001 20130101; H01L 2924/01078
20130101; H01L 2924/00014 20130101; H01L 2924/0781 20130101; H01L
24/13 20130101 |
Class at
Publication: |
257/737 ;
257/778; 438/666; 438/119; 438/668; 349/151; 349/152 |
International
Class: |
H01L 029/41 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 8, 1999 |
JP |
11-060459(P) |
Claims
What is claimed is:
1. A semiconductor device, comprising: a first substrate; and a
plurality of electrodes, each having a base portion formed on the
first substrate and an upper portion, and each adapted to be
electrically connected to a corresponding electrode terminal on a
second substrate through an anisotropic conductive film containing
conductive particles; wherein the base portion of each electrode
has a cross-sectional width that is substantially less than the
cross-sectional width of the upper portion facing the corresponding
electrode terminal to the base portion.
2. The semiconductor device of claim 1, wherein each electrode has
a reverse-taper structure, such that the cross-sectional width of
each electrode decreases linearly from the upper portion.
3. The semiconductor device of claim 1, wherein each electrode has
an upper surface facing a surface of the corresponding electrode
terminal, each upper surface having a width of between about 15
.mu.m and about 20 .mu.m.
4. The semiconductor device of claim 2, wherein the conductive
particles have a relatively high density of distribution between
facing surfaces of the electrodes and the electrode terminals and
at an outer periphery of the first substrate and have a relatively
low density of distribution between adjacent electrodes.
5. The semiconductor device of claim 1, wherein the upper portions
of adjacent electrodes are separated from each other by a gap of
between about 20 .mu.m and about 25 .mu.m.
6. A semiconductor device mounting structure, comprising: a
semiconductor device including a first substrate and a plurality of
electrodes, each having a base portion formed on the first
substrate and an upper portion; and a second substrate having a
plurality of electrode terminals formed thereon, each electrode
terminal being electrically connected to a corresponding one of the
electrodes through an anisotropic conductive film containing
conductive particles; wherein the base portion of each electrode
has a cross-sectional width that is substantially less than the
cross-sectional width of the upper portion facing the corresponding
electrode terminal.
7. The semiconductor device mounting structure of claim 6, wherein
each electrode has a reverse-taper structure, such that the
cross-sectional width of each electrode decreases linearly from the
upper portion to the base portion.
8. The semiconductor device mounting structure of claim 6, wherein
each electrode has an upper surface facing a surface of the
corresponding electrode terminal, each upper surface having a width
of between about 15 .mu.m and about 20 .mu.m.
9. The semiconductor device mounting structure of claim 6, wherein
the conductive particles have a relatively high density of
distribution between facing surfaces of the electrodes and the
electrode terminals and at an outer periphery of the first
substrate and have a relatively low density of distribution between
adjacent electrodes.
10. The semiconductor device mounting structure of claim 6, wherein
the upper portions of adjacent electrodes are separated from each
other by a gap of between about 20 .mu.m and about 25 .mu.m.
11. A liquid crystal device, comprising: a pair of transparent
substrates having liquid crystals sealed therebetween to form a
liquid crystal panel; and a semiconductor device, comprising: a
first substrate and a plurality of electrodes, each having a base
portion formed on the first substrate and an upper portion; and a
second substrate having a plurality of electrode terminals formed
thereon, each electrode terminal being electrically connected to a
corresponding one of the electrodes through an anisotropic
conductive film containing conductive particles; wherein the base
portion of each electrode has a cross-sectional width that is
substantially less than the cross-sectional width of the upper
portion facing the corresponding electrode terminal; and wherein
the semiconductor device is mounted on one of the pair of
transparent substrates or a wiring substrate electrically connected
to the liquid crystal panel.
12. The liquid crystal device of claim 11, wherein the
semiconductor device is mounted on a protruding portion of one of
the pair of transparent substrates.
13. An electronic apparatus comprising the liquid crystal device of
claim 12.
14. A method of manufacturing a semiconductor device, comprising:
forming a plurality of electrodes on a surface of a semiconductor
substrate; applying a photosensitive resist layer to the surface of
the semiconductor; exposing the photosensitive resist layer to
light through an exposure mask having a plurality of shielding
portions, each aligned with a respective one of the plurality of
electrodes; creating a plurality of openings in the photosensitive
resist layer, each opening being aligned with a corresponding one
of the plurality of electrodes and having a reversed-taper shape;
filling the plurality of openings with an electrode plating
material; and removing the photosensitive resist layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a semiconductor device
(hereinafter sometimes referred to as an "IC"), a mounting
structure thereof, a liquid crystal device using the mounting
structure, and an electronic apparatus using the liquid crystal
device.
[0003] 2. Description of the Related Art
[0004] With either the COG (chip on glass) or COF (chip on film)
mounting methods, mounting a face-down-bonding type IC using an ACF
(anisotropic conductive film) makes it possible to cope with fine
pitches and to collectively connect a plurality of contacts
electrically, thus making the method suitable for mounting a
driving IC on electrode terminals formed on a liquid crystal panel
or on a flexible wiring substrate.
[0005] As shown in FIG. 8A, when mounting an IC using such an
anisotropic conductive film 6, the film is deposited on an IC
mounting region 9 of a substrate, such as a glass or flexible
wiring substrate. A driving IC 13' is then arranged on the surface
of this anisotropic conductive film 6. Next, as shown in FIG. 8B,
the driving IC 13' is mounted to the substrate by thermal
compression bonding using a bonding head 5. As a result, the resin
component of the anisotropic conductive film 6 is melted and
fluidized. Thereafter, the anisotropic conductive film 6 is cured,
and then the resin component of the anisotropic conductive film 6
is solidified, to mount the driving IC 13' onto the IC mounting
region 9. During this step, the bump electrodes 130' of the driving
IC 13' are electrically connected to electrode terminals 16 on the
substrate side through conductive particles 60 contained in the
anisotropic conductive film 6. Here, the number of conductive
particles 60 positioned between the bump electrodes 130' and the
electrode terminals 16 greatly influences the electrical
resistance, reliability, etc.
[0006] In this mounting structure, each bump electrode 130' of the
driving IC 13' is conventionally formed at a pitch of approximately
100 .mu.m, and the shape of the bump electrodes 130' is straight
with a fixed width. The surface of the bump electrodes 130' facing,
i.e., opposing, the electrode terminals 16 may be curved.
[0007] However, in a liquid crystal device (e.g., a liquid crystal
display device), the bump electrodes 130' tend to be arranged in
higher density as the number of pixels increases, which causes a
problem that makes it difficult, if not impossible, to even use
conventional bump electrodes 130' in liquid crystal devices. That
is, when the bump electrode density is increased such that the
pitch of the bump electrodes 130' is approximately 40 .mu.m,
conductive particles 60 will gather in high density between
adjacent bump electrodes 130' when the anisotropic conductive film
6 is melted, causing short-circuiting between bump electrodes 130'.
On the other hand, when the bump electrodes 130' are made narrower
in width, the number of conductive particles 60 between the bump
electrodes 130' and the electrode terminals 16 will decrease,
impairing the electrical characteristics (e.g., resistivity, etc.)
and reliability of the device.
SUMMARY OF THE INVENTION
[0008] Objects of the Invention
[0009] Therefore, it is an object of the present invention to
overcome the aforementioned problems.
[0010] It is another object of the invention to provide an IC and a
mounting structure thereof with an improved bump electrode
structure, whereby the bump electrodes are electrically connected
to electrode terminals on a substrate through an anisotropic
conductive film without compromising, or causing deterioration of,
the electrical characteristics or reliability, even when the bump
electrodes are formed with a narrow (e.g., small) pitch.
[0011] It is further object of the invention to provide a liquid
crystal device employing such an IC or mounting structure
thereof.
[0012] It is yet another object of the invention to provide an
electronic apparatus employing such an IC or mounting structure
thereof.
[0013] To achieve the above objects, one aspect of the invention
provides a semiconductor device comprising a first substrate, and a
plurality of electrodes, each having a base portion formed on the
first substrate and an upper portion, and each adapted to be
electrically connected to a corresponding electrode terminal on a
second substrate through an anisotropic conductive film containing
conductive particles. In accordance with the invention, the base
portion of each electrode has a cross-sectional width that is
substantially less than the cross-sectional width of the upper
portion facing the corresponding electrode terminal to the base
portion.
[0014] When the semiconductor device of the present invention is
mounted to a substrate through an anisotropic conductive film to
electrically connect the electrode terminals on the second
substrate and the bump electrodes on the semiconductor device side,
the resin component of the anisotropic conductive film is melted
and the conductive particles will flow from the inner areas between
the semiconductor device and the substrate toward the outer
periphery. Because the base portions of the bump electrodes are
made narrower, there are wide gaps between the base portions of
adjacent bump electrodes even when such electrodes are formed in
high density. Thus, when the anisotropic conductive film is melted
and the conductive particles flow from the inner area between the
semiconductor device and the substrate toward the outer periphery
of semiconductor device, a large number of conductive particles do
not gather between adjacent bump electrodes, so that the conductive
particles do not cause short-circuiting between the bump
electrodes. Further, although the bump electrodes are made narrower
at the base portion, the upper portions thereof facing the
electrode terminals of the substrate are wider, such that the area
of the surface of each bump electrodes which faces a corresponding
electrode terminal is large. Thus, a large number of conductive
particles exist between the bump electrodes and the electrode
terminals, so that a satisfactory electrical connection is effected
between the bump electrodes and the electrode terminals. Thus, even
if the bump electrodes of the semiconductor device are formed in
high density, it is possible to achieve a high level of
reliability.
[0015] The semiconductor and semiconductor mounting structure of
the present invention is applicable to various types of
semiconductor devices. In a liquid crystal device, the
semiconductor device of the present invention is effectively
mounted on either one of the substrates forming a liquid crystal
panel or on a wiring substrate electrically connected to the liquid
crystal panel. When such a liquid crystal device is used as a
display device for an electronic apparatus, such as a mobile
telephone, a higher display quality can be achieved without
compromising reliablity. By utilizing a semiconductor device of the
present invention, which permits a higher density arrangement of
bump electrodes without short circuiting the device, the number of
display pixels in the liquid crystal device can be increased to
increase display quality. Although a large number of conductive
particles do not gather between bump electrodes to create short
circuiting problems, a large number of such particles are secured
between the bump electrodes and the electrode terminals, thereby
making it possible to effect satisfactory electrical connection
between the bump electrodes and the electrode terminals.
[0016] The invention also provides a method of manufacturing a
semiconductor device. The method comprises forming a plurality of
electrodes on a surface of a semiconductor substrate, applying a
photosensitive resist layer to the surface of the semiconductor,
exposing the photosensitive resist layer to light through an
exposure mask having a plurality of shielding portions, each
aligned with a respective one of the plurality of electrodes,
creating a plurality of openings in the photosensitive resist
layer, each opening being aligned with a corresponding one of the
plurality of electrodes and having a reversed-taper shape, filling
the plurality of openings with an electrode plating material; and
removing the photosensitive resist layer.
[0017] Other objects and attainments together with a fuller
understanding of the invention will become apparent and appreciated
by referring to the following description and claims taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In the drawings, wherein like reference symbols refer to
like parts:
[0019] FIG. 1 is a perspective view of a liquid crystal device,
constructed according to embodiments of the invention;
[0020] FIG. 2 is an exploded, perspective view of the liquid
crystal device shown in FIG. 1;
[0021] FIG. 3A is a plan view showing the surface of a driving IC,
including an arrangement of bump electrodes formed thereon,
according to embodiments of the invention;
[0022] FIG. 3B is a sectional view taken along the line X-X' of
FIG. 3A;
[0023] FIGS. 4A through 4C are sectional views showing the process
for mounting a driving IC of the type shown in FIGS. 3A and 3B onto
a second transparent substrate which may constitute a liquid
crystal panel;
[0024] FIGS. 5A through 5E are sectional views showing the method
of forming the bump electrodes of a driving IC of the type shown in
FIGS. 3A and 3B;
[0025] FIGS. 6A and 6B are sectional views showing the main parts
of a mobile telephone (electronic apparatus) having a liquid
crystal device constructed according to embodiments of the
invention;
[0026] FIG. 7 is a perspective view of a mobile telephone
(electronic apparatus) having a liquid crystal device constructed
according to embodiments of the invention; and
[0027] FIGS. 8A through 8C are sectional views showing the process
for mounting a conventional IC on a substrate.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Embodiments of the present invention will be described with
reference to the accompanying drawings.
[0029] General Construction
[0030] FIG. 1 is a perspective view showing a passive matrix type
liquid crystal device, and FIG. 2 is an exploded, perspective view
thereof In FIGS. 1 and 2, a liquid crystal device 10 includes a
first transparent substrate 1 and a second transparent substrate,
each of which can be formed, for example, by a transparent glass. A
seal material 3 is formed on one of these substrates by printing or
the like, and the first and second transparent substrates 1 and 2
are secured to each other, with the seal material 3 placed
therebetween. In the gap (e.g., cell gap) between the first and
second transparent substrates 1 and 2, a liquid crystal sealing
region 40 defined by the seal material 3 has liquid crystals 41
sealed therein. A polarizing plate 4a is attached to the outer
surface of the first transparent substrate 1 by adhesive or the
like, and another polarizing plate 4b is attached to the outer
surface of the second transparent substrate 2 by adhesive or the
like.
[0031] Because the second transparent substrate 2 is larger than
the first transparent substrate 1, a part of the second transparent
substrate 2 protrudes from the lower edge of the first transparent
substrate 1 when the first transparent substrate 1 is superimposed
on the second transparent substrate 2, as shown in FIG. 2. Formed
on this protruding portion is an IC mounting region 9, where a
driving IC 13, which is a semiconductor device, is COG-mounted by
face down bonding. Such mounting, which will be described in more
detail below, is effected by placing an anisotropic conductive film
between the second transparent substrate 2 and the driving IC 13
and thermal compression bonding them together. As a result, the
bump electrodes of the driving IC 13 are electrically connected to
the electrode terminals of the IC mounting region 9 of the second
transparent substrate 2 via the anisotropic conductive film.
[0032] Also, on the second transparent substrate 2, input terminals
12 are formed below the IC mounting region 9, and a flexible
printed circuit board (not shown) is connected to these input
terminals 12 by heat sealing or the like.
[0033] Further, although not shown in detail in FIGS. 1 and 2, on
the inner surface of the first transparent substrate 1, there is
formed an electrode pattern (thin film pattern) consisting of a
plurality of stripe-shaped electrodes extending horizontally inside
the liquid crystal sealing region 40, and a wiring pattern for
connecting the stripe-shaped electrodes to each terminal outside
the liquid crystal sealing region 40. This electrode pattern is
formed of a transparent ITO (indium tin oxide) film or the like. An
electrode pattern (thin film pattern) and wiring pattern are also
formed on the inner surface of the second transparent substrate 2.
In this case, the electrode pattern (thin film pattern) consists of
a plurality of stripe-shaped electrodes extending vertically inside
the liquid crystal sealing region 40, with the wiring pattern
connecting the stripe-shaped electrodes to the IC mounting region 9
or the like outside the liquid crystal sealing region 40. This
electrode pattern is also formed of a transparent ITO film or the
like.
[0034] When the first transparent substrate 1 and the second
transparent substrate 2, constructed as described above, are bonded
together as shown in FIG. 1 to form a panel (e.g., a liquid crystal
panel) while effecting electrical connection at specified
positions, the stripe-shaped electrodes of the first transparent
substrate 1 and the stripe-shaped electrodes of the second
transparent substrate 2 intersect with each other to thereby form
pixels. Further, in the gap between the first transparent substrate
1 and the second transparent substrate 2, liquid crystals 41 are
sealed in the liquid crystal sealing region 40. Thus, when driving
power and a driving signal are supplied to the driving IC 13, the
driving IC 13 applies voltage to a desired stripe-shaped electrode
in accordance with the driving signal to control the orientation of
the liquid crystals 41 for each pixel, so that a desired image is
displayed on the liquid crystal device 10.
[0035] Mounting Structure for Driving IC 13
[0036] FIG. 3A is a plan view showing the surface of the driving IC
13 which is mounted on the second transparent substrate 2, and FIG.
3B is a sectional view taken along the line X-X' in FIG. 3A. FIGS.
4A through 4C are diagrams showing the process by which the driving
IC 13 is mounted on the substrate.
[0037] In the liquid crystal device 10 shown in FIGS. 1 and 2, a
large number of wiring pattern ends are gathered in the IC mounting
region 9. These ends, e.g., the forward end portions of the wiring
pattern, constitute electrode terminals 16. One way to improve the
display quality of the liquid crystal device 10 is to increase the
number of pixels. This results in an increase in the number of
stripe-shaped electrodes formed in the liquid crystal panel, and
further results in a high density arrangement of the electrode
terminals 16 (see FIG. 4).
[0038] Thus, as shown in FIG. 3A, the plurality of bump electrodes
130 formed on a mounting surface 13a of the driving IC 13 will also
be disposed at a higher density, as the number of pixels of the
liquid crystal device 10 increases. That is, the bump electrodes
130 are formed with a narrower pitch along the chip sides 13b, for
example, with a pitch of approximately 40 .mu.m. The upper surface
of each bump electrode 130 is rectangular in shape and has a width
of approximately 15 to 20 .mu.m, so that upper portions 131 of
adjacent bump electrodes 130 are separated from each other by a
small gap of approximately 20 .mu.m to 25 .mu.m.
[0039] Here, as shown in FIG. 3B, the width of the base portions
132 of the bump electrodes 130 of the driving IC 13 are narrower
than that of the upper portions 131 that face the electrode
terminals 16 of the second transparent substrate 2. More
specifically, the width of the base portions 132 is about 10 to 15
.mu.m. Thus, while the upper portions 131 of adjacent bump
electrodes 130 are spaced apart from each other by narrow gaps of
20 .mu.m to 25 .mu.m, the base portions 132 thereof are spaced
apart from each other by wider gaps of about 25 to 30 .mu.m.
[0040] The IC mounting structure of this embodiment will be
described by describing the process of mounting the driving IC 13
constructed as described above.
[0041] When mounting the driving IC 13 of this embodiment on the
mounting region 9 of the second transparent substrate 2, the
anisotropic conductive film 6 is first deposited on the IC mounting
region 9 of the second transparent substrate 2, as shown in FIG.
4A. Then the driving IC 13 is arranged on the surface of this
anisotropic conductive film 6, with the bump electrodes 130 facing
downward for face down bonding. In this anisotropic conductive film
6, conductive particles 60 that are formed in a metallic film on
the surface of plastic balls are dispersed in a thermosetting
resin. Next, as shown in FIG. 4B, the driving IC 13 is heat-bonded
onto the second substrate 2 using a bonding head 5. As a result,
the resin component of the anisotropic conductive film 6 is
melted.
[0042] In the next step, shown in FIG. 4C, the melted anisotropic
conductive film 6 is fluidized and cured, and then the resin
component of the anisotropic conductive film 6 is solidified, to
securely mount the driving IC 13 onto the IC mounting region 9 and
to electrically connect the bump electrodes 130 of the driving IC
13 to the electrode terminals 16 on the substrate side through the
conductive particles 60 contained in the anisotropic conductive
film 6.
[0043] When the driving IC 13 is mounted in this way, the resin
component of the anisotropic conductive film 6 is melted, and, as
indicated by the arrows A in FIG. 3A, the resin component and the
conductive particles 60 between the driving IC 13 and the second
transparent substrate 2 will flow from an inner area of the driving
IC 13 toward an outer periphery thereof through the gaps between
the bump electrodes 130. In this embodiment, the base portions 132
of the bump electrodes 130 of the driving IC 13 are tapered and
relatively thin, as shown in FIG. 3B and FIGS. 4A through 4C, so
that even if the bump electrodes 130 are formed in high density,
the base portions 132 of the adjacent bump electrodes 130 are
spaced apart from each other by wider gaps than the corresponding
upper portions 131. These wider gaps at the base portions 132 act
as channels through which the resin component and the conductive
particles 60 of the anisotropic conductive film 6 pass to prevent
large numbers of conductive particles 60 from collecting between
adjacent bump electrodes 130 and short-circuiting the bump
electrodes 130. While the narrower base portions 132 of bump
electrodes prevent or at least minimize short-circuiting, the wider
upper portions 131 improve the electrical connection between the
bump electrodes and corresponding electrode terminals 16. The wider
upper portion 132 of each bump electrode provides more surface area
facing the electrode terminals 16 whose corresponding facing
surfaces have like-sized surface areas. As a result, a large number
of conductive particles 60 collect between the facing surfaces of
the bump electrodes 130 and the electrode terminals 16, so that the
bump electrodes 130 and the electrode terminals 16 are electrically
connected to each other in a satisfactory manner. Thus, with this
arrangement, it is possible to achieve a high level of reliability,
even if the bump electrodes 130 of the driving IC 13 are formed in
high density.
[0044] Method of Producing Bump Electrodes 130 of Driving IC 13
[0045] Regarding the method of producing the driving IC 13 used in
this mounting structure, the process for forming the bump
electrodes 130 will be described with reference to FIGS. 5A through
5E, which are sectional views showing the process for forming bump
electrodes 130.
[0046] First, as shown in FIG. 5A, electrodes 136 are formed on the
surface of a semiconductor substrate 135 forming the driving IC 13.
Then, as shown in FIG. 5B, a photosensitive resist 150 is applied.
This photosensitive resist 150 is a negative type. Thus, when the
photosensitive resist 150 is exposed to light through an exposure
mask 151, only the regions of the photosensitive resist 150 which
are covered with shielding portions 152 of the exposure mask 151
are removed in the etching (development) process, as shown in FIG.
5C.
[0047] When forming the resist 150 in such a specified or
predetermined pattern, the light applied is also diffused in the
horizontal direction in the exposure process shown in FIG. 5B, so
that the boundary between the non-exposed portion 155 and the
exposed portion 156 exhibits a reverse-tapered shape. Thus, as
shown in FIG. 5C, the side wall of the opening portions 157 of the
resist 150 exhibits a reverse-tapered shape.
[0048] After thus forming the resist 150 in a specified or
predetermined pattern, the surface of the electrodes 136 is plated.
As a result, as shown in FIG. 5D, plating 135 is effected on the
surface side of the electrodes 136 in such a way as to fill the
opening portions 157 of the resist 150.
[0049] Thus, when the resist 150 is removed after the plating, bump
electrodes 130 are formed with the base portions 132 narrower than
the upper portions 131 thereof, as shown in FIG. 5E.
[0050] Example of Mounting in Electronic Apparatus
[0051] FIG. 7 shows a mobile telephone 30 which is an example of
one type of electronic apparatus which may embody a liquid crystal
device constructed in accordance with the present invention. The
liquid crystal device of the present invention is also applicable
to other electronic apparatuses, such as mobile information
terminals, electronic organizers, or video camera finders.
[0052] The mobile telephone 30 comprises various components such as
an antenna 31, a speaker 32, a liquid crystal device 10, a key pad
33 and a microphone 34, accommodated in an outer case 36 that
serves as the housing. Also provided in the case 36 is a control
circuit board 37 on which a control circuit to control the
operation of the above components is mounted. The liquid crystal
device 10 is of the type shown in FIG. 1.
[0053] In this mobile telephone 30, signals input through the key
pad 33 and the microphone 34, reception data received by the
antenna 31, etc. are input to the control circuit on the control
circuit board 37. The control circuit displays images such as
numbers, characters, patterns, etc. in accordance with various
items of input data, and further receives reception data from the
antenna 31.
[0054] FIGS. 6A and 6B are sectional views showing the main parts
of a mobile telephone 100 (electronic apparatus) in which the
liquid crystal device 10 is mounted in accordance with this
embodiment of the invention.
[0055] In mobile telephone 100, shown in FIGS. 6A and 6B, a
transparent light guide plate 19 of acrylic resin or polycarbonate
is superimposed on the first transparent substrate 1 side of the
liquid crystal device 10, and a flexible wiring substrate 120 is
drawn out from between a light guide plate 19 and the second
transparent substrate 2 and is electrically and mechanically
connected to a printed circuit board 90 which forms the circuit
board of the mobile telephone 100 main body. Adjacent to a side (or
end portion) of the light guide plate 19, there is arranged a
backlight light emitting device 50 for emitting light toward the
end portion (light incident portion) of the light guide plate 19.
An LED or the like is used as this backlight light emitting device
50, and is mounted on the printed circuit board 90. While in this
embodiment the backlight device 50 is mounted on the printed
circuit board 90, device 50 can also be mounted on the flexible
wiring substrate 120 at any position which allows incident light to
fall on the light guide plate 19. Further, it is also possible to
mount device 50 on a sub-substrate which is separate from the
printed circuit board 90. Here, the liquid crystal device 10 is
fastened to the light guide plate 19 by a double-sided tape or the
like and restrained by frame 110. Further, the light guide plate 19
secures the liquid crystal device 10 and integrally holds the
printed circuit board 90 by, for example, engaging with it. The
light guide plate 19 is also fastened to the frame 110 of the
mobile telephone 100. A glass cover 111 is placed on the second
transparent substrate 2 side.
[0056] Other Embodiments
[0057] While in the above-described embodiments the driving IC 13
is COG-mounted on the second transparent substrate 2 which may
constitute the liquid crystal panel, the driving IC 13 may also be
COF-mounted on the flexible wiring substrate which is electrically
connected to the liquid crystal panel. Even in the latter case, the
driving IC 13 may be mounted on the flexible wiring substrate
through the anisotropic conductive film 6 instead of the second
transparent substrate 2, in the mounting process described with
reference to FIGS. 4A through 4C.
[0058] Advantages
[0059] As described above, in the present invention, the bump
electrodes of the IC are tapered toward the base portions, so that,
even when the bump electrodes are formed in high density, the base
portions of the adjacent bump electrodes are spaced apart from each
other by wide gaps. Thus, when the anisotropic conductive film is
melted and fluidized, during the mounting of the IC to the
substrate via the anisotropic conductive film, a large number of
conductive particles do not gather between adjacent bump
electrodes. Instead, most of the conductive particles that would
otherwise gather between adjacent bump electrodes flow out through
the wider gaps between the bump electrode bases and collect at the
periphery of the IC substrate. As a result, the conductive
particles do not cause short-circuiting between the bump
electrodes. Furthermore, since the upper portions of the bump
electrodes are wider and the opposing surface areas of both the
bump electrodes and the electrode terminals are relatively large, a
higher density and hence a relatively large number of conductive
particles become positioned between the bump electrodes and the
electrode terminals. This ensures that the bump electrodes and the
electrode terminals are electrically connected in a satisfactory
manner. Therefore, it is possible to achieve a high level of
reliability even when the bump electrodes of the IC are formed in
high density.
[0060] While the invention has been described in conjunction with
several specific embodiments, many further alternatives,
modifications, variations and applications will be apparent to
those skilled in the art in light of the foregoing description.
Thus, the invention described herein is intended to embrace all
such alternatives, modifications,, variations and applications as
may fall within the spirit and scope of the appended claims.
* * * * *