U.S. patent application number 09/766269 was filed with the patent office on 2001-07-26 for flexible wiring board, method of manufacturing flexible wiring board and display device equipped with flexible wiring board.
Invention is credited to Saito, Hirokazu.
Application Number | 20010009299 09/766269 |
Document ID | / |
Family ID | 27342136 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009299 |
Kind Code |
A1 |
Saito, Hirokazu |
July 26, 2001 |
Flexible wiring board, method of manufacturing flexible wiring
board and display device equipped with flexible wiring board
Abstract
A flexible wiring board comprises a relatively thin polyimide
film and, thus, can be bent easily. Therefore, the flexible wiring
board can be bent easily in the vicinity of a semiconductor chip
mounting region without forming slits for facilitating the bending
in the film substrate. As a result, it is possible to decrease the
length of that portion of the flexible wiring board which is
positioned ahead of the semiconductor chip mounting region.
Inventors: |
Saito, Hirokazu; (Tokyo,
JP) |
Correspondence
Address: |
Frishauf, Holtz, Goodman
Langer & Chick, P.C.
25th Floor
767 Third Avenue
New York
NY
10017-2023
US
|
Family ID: |
27342136 |
Appl. No.: |
09/766269 |
Filed: |
January 19, 2001 |
Current U.S.
Class: |
257/684 ;
257/688; 257/696; 257/E23.065 |
Current CPC
Class: |
H05K 1/189 20130101;
H05K 2201/10681 20130101; H01L 23/4985 20130101; H01L 2924/07811
20130101; H05K 2201/09227 20130101; H01L 2924/01079 20130101; H05K
1/028 20130101; H01L 2924/01078 20130101; H01L 2924/01322 20130101;
H01L 2224/16 20130101; H01L 2224/16225 20130101; H01L 2924/07811
20130101; H01L 2924/00 20130101 |
Class at
Publication: |
257/684 ;
257/688; 257/696 |
International
Class: |
H01L 023/48 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2000 |
JP |
2000-016491 |
Jan 26, 2000 |
JP |
2000-016492 |
Dec 7, 2000 |
JP |
2000-372946 |
Claims
What is claimed is:
1. A flexible wiring board for connection to an electronic part,
comprising: a film having a semiconductor chip mounting region in
which a semiconductor chip is to be mounted, a connection terminal
region, and an inclined wiring region, which is to be bent freely,
and positioned between the connection terminal region and the
semiconductor chip mounting region; a plurality of connection
terminals arranged in the connection terminal region of said film;
and a plurality of drawing wirings which electrically connect said
connection terminals and said semiconductor chip, said drawing
wiring having an inclined wiring section, which is to be bent
freely, and arranged in the inclined wiring region of the film.
2. The flexible wiring board according to claim 1, wherein the
entire region of said inclined wiring sections is supported by said
film.
3. The flexible wiring board according to claim 1, wherein said
drawing wirings include parallel wiring sections arranged in
parallel, and said film includes a parallel wiring region in which
said parallel wiring sections are arranged.
4. The flexible wiring board according to claim 3, wherein the
shortest distance between the inclined wiring sections of the
adjacent drawing wirings is shorter than the shortest distance
between the parallel wiring sections of the adjacent drawing
wirings.
5. The flexible wiring board according to claim 3, wherein the
width of said inclined wiring section of said drawing wiring is
smaller than the width of said parallel wiring section.
6. The flexible wiring board according to claim 1, wherein said
film is formed of polyimide and has a thickness not smaller than 10
.mu.m and smaller than 40 .mu.m.
7. The flexible wiring board according to claim 1, which further
includes a plurality of semiconductor chip connection terminals
supported by said film and arranged in said semiconductor chip
mounting region, said semiconductor chip being bonded to said
semiconductor chip connection terminals a COF system.
8. A display device comprising; (a) a flexible wiring board
including: a film having a semiconductor chip mounting region in
which a semiconductor chip is mounted, a connection terminal
region, and an inclined wiring region, which is bent, and
positioned between the connection terminal region and the
semiconductor chip mounting region; a plurality of connection
terminals arranged in the connection terminal region of said film;
and a plurality of drawing wirings which electrically connect said
connection terminals and said semiconductor chip, said drawing
wiring having an inclined wiring section, which is bent, and
arranged in the inclined wiring region of the film; and (b) a
display panel electrically connected to said connection terminals
of said flexible wiring board.
9. The display device according to claim 8, wherein the entire
region of said inclined wiring sections is supported by said
film.
10. The display device according to claim 8, wherein said drawing
wirings include parallel wiring sections arranged in parallel, and
said film includes parallel wiring regions in which said parallel
wiring sections are arranged.
11. The display device according to claim 10, wherein the shortest
distance between the inclined wiring sections of the adjacent
drawing wirings is shorter than the shortest distance between the
parallel wiring sections of the adjacent drawing wirings.
12. The display device according to claim 10, wherein the width of
said inclined wiring section of said drawing wiring is smaller than
the width of said parallel wiring section.
13. The display device according to claim 8, wherein said film is
formed of polyimide and has a thickness not smaller than 10 .mu.m
and smaller than 40 .mu.m.
14. The display device according to claim 8, which further includes
a plurality of semiconductor chip connection terminals supported by
said film and arranged in said semiconductor chip mounting region,
said semiconductor chip being bonded to said semiconductor chip
connection terminals a COF system.
15. The display device according to claim 8, wherein said display
panel includes a liquid crystal display panel.
16. A method of manufacturing a flexible wiring board connected to
a semiconductor chip, comprising the steps of: heating one surface
of said semiconductor chip; aligning a plurality of bump electrodes
made of a metal and arranged on the opposite surface of said
semiconductor chip with a plurality of connection terminals formed
on one surface of said flexible wiring board; and applying a
pressure while heating an opposite surface of said flexible wiring
board to bond said plural bump electrodes to said plural connection
terminals.
17. The method of manufacturing a flexible wiring board according
to claim 16, wherein said flexible wiring board comprises a film
made of polyimide and having a thickness not smaller than 10 .mu.m
and smaller than 40 .mu.m, said film having said one surface and
said other surface.
18. The method of manufacturing a flexible wiring board according
to claim 16, wherein, in said bonding step, said opposite surface
of said flexible wiring board is pressurized by a bonding tool
heated to 250.degree. C. to 350.degree. C.
19. The method of manufacturing a flexible wiring board according
to claim 16, wherein, in said semiconductor chip heating step, said
semiconductor chip is disposed on a stage heated to 350.degree. C.
to 450.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Applications No.
2000-016491, filed Jan. 26, 2000; No. 2000-016492, filed Jan. 26,
2000; and No. 2000-372946, filed Dec. 7, 2000, the entire contents
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a flexible wiring board, a
method of manufacturing a flexible wiring board, and a display
device such as a liquid crystal panel for a liquid crystal display
module connected to a flexible wiring board.
[0003] FIGS. 12 to 14 collectively show an example of a
conventional liquid crystal display module. As shown in the
figures, the conventional liquid crystal display module comprises a
liquid crystal display panel 1 and a flexible wiring board 11. The
liquid crystal panel 1 is prepared by bonding a segment substrate 2
and a common substrate 3 to each other with a substantially
frame-like seal member 5 interposed therebetween and by sealing a
liquid crystal 7 between these substrates 2 and 3 positioned inside
the seal member 5. Segment electrodes 2a and a common electrode 3a
are mounted to those surfaces of the substrates 2 and 3,
respectively, which are positioned to face each other so as to
permit a predetermined voltage to be applied to the liquid crystal
7. The lower side portion in FIG. 12 of the segment substrate 2
protrudes from the lower side of the common substrate 3 to form a
protruding portion 2b. A plurality of connection terminals 4
including segment terminals connected to the segment electrodes 2a
and common terminals connected to the common electrode 3a via the
seal member 5 are arranged in parallel on one surface of the
protruding portion 2b.
[0004] The flexible wiring board 11 comprises an oblong film
substrate 12 on which electronic parts are mounted by a TAB (tape
automated bonding) system. The film substrate 12, which is about 75
.mu.m to 150 .mu.m thick, is formed of, for example, a polyimide
film. A semiconductor chip 13 for driving the liquid crystal
display panel 1 such as an LSI and chip parts 14 required for
driving the liquid crystal display panel 1 and each comprising a
capacitor, a resistor, etc. are mounted on predetermined positions
in substantially the central portion of the film substrate 12. In
this case, the semiconductor chip 13 is mounted on a region the
film substrate 12, in which a device hole 15 is formed.
[0005] A large number of output wirings 16 are connected to the
semiconductor chip 13 on the upper surface of the film substrate 12
in an upper region in FIG. 12 of the mounting region of the
semiconductor chip 13, and a large number of input wirings 17
extending in parallel are connected to the semiconductor chip 13
and the chip parts 14 in the lower portion in FIG. 12 of the
mounting region of the semiconductor chip 13. The lower end portion
in FIG. 12 of each input wiring 17 constitutes a first connection
terminal 17a, with that portion of each input wiring 17 which
protrudes into the device hole 15 constituting a second connection
terminal 17b.
[0006] The output wiring 16 will now be described. It should be
noted that two slits 18 and 19 extending in parallel in a lateral
direction are formed in the film substrate 12 in predetermined two
positions in an upper portion in FIG. 12 of the mounting region of
the semiconductor chip 13. The roles played by these two slits 18,
19 will be described herein later. The output wirings 16 comprise a
plurality of first connection terminals 16a formed in parallel in
an upper end portion of the film substrate 12, a plurality of
second connection terminals 16b protruding into the device hole 15
in a portion of the device hole 15, first drawing wire sections 16c
formed in parallel in the portions of these slits 18, 19 and
between these slits 18 and 19, and second drawing wire sections 16d
arranged between the first drawing wire sections 16c and the second
connection terminals 16b such that the pitch of these second
drawing wire sections 16d is gradually increased from the second
connection terminals 16b toward the first drawing wire sections
16c. A protective film 10 made of a solder resist is formed on the
upper surface of the film substrate 12 including the wirings 16 and
17 except the mounting region of the semiconductor chip 13, the
mounting region of the chip parts 14, the upper end portion in FIG.
12 including the first connection terminals 16a and the lower end
portion including the second connection terminals 17a. The
protective film 10 is provided with slits 10a and 10b in positions
corresponding to the slits 18 and 19, respectively, of the film
substrate 12.
[0007] The bonding portions comprising the portions of the first
connection terminals 16a of the flexible substrate 11 are bonded to
the bonding portions comprising the connection terminals 4 of the
liquid crystal display panel 1 with an anisotropic conductive
adhesive (not shown) interposed therebetween.
[0008] The reason for forming the device hole 15 in the film
substrate 12 will now be described. First the mounting state of the
semiconductor 13 will be described. A plating layer (not shown)
made of a metal having a low melting point such as tin or a solder
is formed on the surfaces of the output wirings 16 and the input
wirings 17. As shown in FIG. 13, the upper surfaces of a plurality
of bump electrodes 6 made of gold and formed in a peripheral
portion on one surface of the semiconductor chip 13 are bonded to
the upper surfaces of the second connection terminals 16b, 17b by a
eutectic alloy of gold-tin or gold-solder so as to bond the
semiconductor chip 13 to the portion surrounding the device hole 15
of the film substrate 12.
[0009] When the bump electrodes 6 of the semiconductor chip 13 are
bonded to the connection terminals 16b, 17b by a eutectic alloy,
the semiconductor chip 13 is disposed on a stage (not shown), and
then the film substrate 12 is moved to a region above the
semiconductor chip 13 so as to align the positions of the
connection terminals 16b, 17b of the film substrate 12 with the
positions of the bump electrodes 6 of the semiconductor chip 13.
Further, a bonding tool is brought into direct contact with the
connection terminals 16b, 17b for the pressurizing under heat. For
the operation described above, the device hole 15 is formed in the
film substrate 12. The reason for forming the device hole 15 is as
follows. Since the film substrate 12 is relatively thick, i.e., the
thickness is about 75 .mu.m to 150 .mu.m, the film substrate 12 is
unfavorably melted before the bump electrodes 6 and the connecting
terminals 16b, 17b are heated to reach the bonding temperature,
when the film substrate 12 is pressurized directly from above by
the bonding tool at 530 to 550.degree. C. without forming the
device hole 15. As a result, a defective bonding is generated by
the deviation in the position of the wiring.
[0010] An example of mounting the liquid crystal display module
shown in FIG. 12 to a circuit board will now be described with
reference to FIG. 14. The liquid crystal display panel 1 is
disposed in a predetermined position on the upper surface of a
circuit board 21 with the segment substrate 2 being positioned on
the lower side. The flexible wiring board 11 is bent at
substantially 90.degree. in each of the portions of the slit 18
(10a) and 19 (10b). The portion between the slits 18 and 19 of the
flexible wiring board 11 is inserted into a slit 22 formed in a
predetermined position of the circuit board 21, and the portion
below the circuit board 21 is allowed to extend along the lower
surface of the circuit board 21. Under this state, the bonding
portions comprising the second connection terminals 17a of the
flexible wiring board 11 are bonded to bonding portions comprising
the connection terminals formed at predetermined positions on the
lower surface of the circuit board 21 with an anisotropic
conductive adhesive (not shown) interposed therebetween so as to
communicate with an electronic part 9 via a wiring 8.
[0011] The roles played by the slits 18 (10a) and 19 (10b) will now
be described. It should be noted that the film substrate 12 of the
conventional flexible wiring board 11 is relatively thick, i.e.,
about 75 .mu.m thick. Also, the flexible wiring board 11 is bent
when the display module is housed in a package. If the slits 18 and
19 are not formed, it is difficult to bend the flexible wiring
board 11 as desired. Therefore, the slits 18 and 19 are formed so
as to facilitate the bending of the flexible wiring board 11. Also,
if the slit is formed in the arranging region of the second drawing
wiring sections 16d, the second drawing wiring sections 16d are put
in an inclined state toward the longitudinal direction, i.e., in
the vertical direction in FIG. 12, of the film substrate 12. As a
result, the length of each second drawing wiring section 16d
corresponding to the slit is made larger than the length in lateral
direction of the slit. In addition, the presence of the slit causes
the second drawing wiring section 16d not to be supported by the
film substrate 12 and, thus, to be irregularly twisted, giving rise
to the occurrence of a short circuit. Such being the situation, a
slit is not formed in the arranging region of the inclined second
drawing wiring sections 16d, and the first drawing wiring sections
16c are arranged in parallel in the portions of the slits 18, 19
and between the slits 18 and 19.
[0012] As described above, in the conventional flexible wiring
board 11, the first drawing wiring sections 16c are arranged in
parallel in the portions of the slits 18, 19 and between the slits
18 and 19, with the result that the length in the vertical
direction of the upper portion in FIG. 12 of the mounting region of
the semiconductor chip 13 is rendered larger, leading to an
increase in the entire length in the vertical direction. It follows
that a first problem is generated that the flexible wiring board 11
is rendered bulky so as to increase the manufacturing cost.
[0013] What should also be noted is that, in the conventional
semiconductor device, the inner leads 16b, 17b protrude into the
device hole 15 of the film substrate 12. The protruding inner leads
16b and 17b tend to be deformed so as to bring about a short
circuit between these inner leads 16b and 17b. Particularly, the
pitch of the bump electrodes 6 is being made smaller and smaller in
recent years in accordance with increase in the degree of
integration of the semiconductor chip 13. As a result, the width of
and the distance between the inner leads 16b and 17b are being
diminished so as to cause the inner leads 16b, 17b to be highly
likely to be deformed. A second important problem to be solved is
how to cope with the defective bonding and occurrence of short
circuit caused by the deformation.
BRIEF SUMMARY OF THE INVENTION
[0014] A first object of the present invention is to solve the
first problem given above so as to miniaturize the flexible wiring
board that can be connected satisfactorily to an external
circuit.
[0015] A second object of the present invention is to solve the
second problem given above so as to prevent the connection terminal
mounted to the film substrate from being deformed, thereby
improving the reliability of the bonding with the bump electrode of
the semiconductor chip.
[0016] For achieving the first object described above, there is
provided a flexible wiring board in which the inclined wiring
sections of a plurality of drawing wirings are rendered capable of
being bent freely, and the inclined wiring region of the film
having the inclined wiring sections mounted thereon are also
rendered capable of being bent freely. As a result, it is
unnecessary to arrange the wirings and the film covering the length
of a plurality of slits for the bending and also covering the
length of the parallel wiring section between these slits, which
were formed in the past in the region other than the inclined
wiring section, so as to achieve miniaturization of the flexible
wiring board.
[0017] In order to achieve the bending degree that does not cause
the wiring to be peeled off with a small stress, it is desirable
for the film to have a thickness not smaller than 10 .mu.m and
smaller than 40 .mu.m.
[0018] In order to achieve the second object described above, a
semiconductor chip is bonded to a film substrate by heating the
surface of the semiconductor chip other than the surface on which a
plurality of bump electrodes are mounted and by also heating the
surface of the flexible wiring board other than the surface on
which a plurality of connection terminals are mounted.
[0019] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0020] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention, and together with the
general description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
[0021] FIG. 1 is a plan view showing a liquid crystal display
module according to a first embodiment of the present
invention;
[0022] FIG. 2 is a plan view showing a wiring structure of a
flexible wiring board of the liquid crystal display module shown in
FIG. 1;
[0023] FIG. 3 is a cross sectional view showing a portion a
flexible wiring board having a semiconductor chip mounted
thereto;
[0024] FIG. 4 is a view for exemplifying the state that the liquid
crystal display module shown in FIG. 1 is mounted to a circuit
board;
[0025] FIG. 5 is a cross sectional view for explaining the step of
moving a flexible wiring board to a region above the semiconductor
chip;
[0026] FIG. 6 is a cross sectional view for explaining the step of
bonding the flexible wiring board to the semiconductor chip;
[0027] FIG. 7 is a plan view showing the wiring structure of a
flexible wiring board of a liquid crystal display module according
to a second embodiment of the present invention;
[0028] FIG. 8 is a plan view showing the wiring structure of a
flexible wiring board of a liquid crystal display module according
to a third embodiment of the present invention;
[0029] FIG. 9 is a cross sectional view showing a portion of a
flexible wiring board according to a fourth embodiment of the
present invention;
[0030] FIG. 10 is a cross sectional view for explaining the step of
moving the flexible wiring board according to the fourth embodiment
of the present invention to a region above the semiconductor
chip;
[0031] FIG. 11 is a cross sectional view for explaining the step of
bonding the flexible wiring board according to the fourth
embodiment of the present invention to a semiconductor chip;
[0032] FIG. 12 is a plan view exemplifying a conventional liquid
crystal display module;
[0033] FIG. 13 is a cross sectional view showing a connection
structure between a conventional flexible wiring board and a
semiconductor chip; and
[0034] FIG. 14 is a side view for explaining as an example the
state that the conventional liquid crystal display module is
mounted to a circuit board.
DETAILED DESCRIPTION OF THE INVENTION
[0035] FIGS. 1 and 4 collectively show a liquid crystal display
module according to a first embodiment of the present invention. As
shown in the drawing, the liquid crystal display module in this
embodiment comprises a liquid crystal display panel 31 and a
flexible wiring board 41. The liquid crystal display panel 31
includes a segment substrate 32, a common substrate 33, a
substantially frame-like seal member 35 arranged between these
substrates 32 and 33 and serving to bond these two substrates 32
and 33 with a predetermined clearance provided therebetween, and a
liquid crystal material 37 sealed in the clearance between the
segment substrate 32 and the common substrate 33 and inside the
seal member 35. A plurality of segment electrodes 32a and a common
electrode 33a are mounted to those surfaces of the substrates 32
and 33 which are positioned to face each other so as to permit a
predetermined voltage to be applied to the liquid crystal material
37. A lower side portion 32b in FIG. 1 of the segment substrate 32
protrudes from the lower side of the common substrate 33 to form a
protruding portion 32b. A plurality of connection terminals 34
comprising the segment terminals connected to the segment
electrodes 32a and common terminals connected to the common
electrode 33a via the seal member 5 are arranged in parallel on one
surface of the protruding portion 32b.
[0036] The flexible wiring board 41 has a construction that it is
possible to mount electronic parts such as a semiconductor chip 43
and chip parts 44 to a film substrate 42 of a predetermined shape
by a COF (Chip On Film) system, or any or all of the electronic
parts noted above are mounted to the film substrate 42. The film
substrate 42 is constructed by a polyimide film having a thickness
not smaller than 10 .mu.m and smaller than 40 .mu.m, preferably
between 25 .mu.m and 38 .mu.m, and a wiring formed on one surface
of the polyimide film, i.e., a wiring supported by the polyimide
film. As described herein later, the wiring comprises a plurality
of output wirings 45 and a plurality of input wirings 46 shown in
FIG. 3 and is formed directly on the polyimide film without using
an interposing insulating material such as an adhesive. To be more
specific, a copper layer is formed on the polyimide film in a
thickness of several thousand angstroms by means of an electroless
plating or a sputtering, followed by applying an electrolytic
plating of copper for forming the wiring without using an
interposing layer as described above. A metal having a low melting
point such as tin or solder is plated on the surface of the wiring.
The semiconductor chip 43 for driving the liquid crystal display
panel 31, such as an LSI, and the chip parts 44 required for
driving the liquid crystal display panel 31 and including a
capacitor, a resistor, etc. are mounted in predetermined portions
in the substantially central portion of the film substrate 42.
Since a COF system may be employed for mounting the electronic
parts onto the film substrate 42, any device hole is not formed in
the mounting region of the semiconductor chip 43. How to mount the
semiconductor chip 43 will be described herein later.
[0037] On the upper surface of the film substrate 42, the output
wiring 45 is connected to the semiconductor chip 43 in an upper
region in FIG. 1 of the mounting region of the semiconductor chip.
On the other hand, the input wiring 46 is connected to the
semiconductor chip 43 and the chip parts 44 in a lower region in
FIG. 1. A thin protective film 47 made of a solder resist covers
the upper surface of the film substrate 42 including the output
wiring 45 and the input wiring 46 except the mounting region of the
semiconductor chip, the mounting region of the chip part, and the
upper end and lower end portions in FIG. 1.
[0038] The output wiring 45 comprises a plurality of first
connection terminals 45a that are not covered with the protective
film 47 so as to be exposed to the upper end portion in FIG. 1, a
plurality of second connection terminals 45b arranged in parallel
in predetermined positions in the mounting region of the
semiconductor chip and in the vicinity of said predetermined
positions, and a plurality of drawing wires 45c formed between the
first and the second connection terminals 45a, 45b. As shown in
FIG. 2, the drawing wire 45c comprises inclined wiring sections 45d
positioned on the side of the first connection terminals 45a and
arranged in an inclined fashion in a plurality of directions and
parallel wiring sections 45e positioned on the side of the second
connection terminals 45b and arranged parallel to each other.
[0039] In the flexible wiring board 41, the second connection
terminals 46b of the input wiring 46 are arranged at positions
facing bump electrodes on one side in a longitudinal direction of
the rectangular semiconductor chip 43, and the second connection
terminals 45b of the output wiring 45 are arranged at positions
facing the bump electrodes on the other three sides of the
rectangular semiconductor chip 43. It follows that, since the
number of the first connection terminals 45a arranged in a
concentrated fashion on one side of the film substrate 42
corresponds to the number of bump electrodes on the other three
sides of the semiconductor chip 43, the distance between the
adjacent first connection terminals 45a is required to be shorter
than the distance between the adjacent second connection terminals
45b.
[0040] Such being the situation, the inclined wiring sections 45d
are inclined so as to be concentrated in a central portion of one
side on the side of the first connection terminals 45a in the
flexible wiring board 41, thereby permitting the distance between
adjacent first connection terminals 45a to be made smaller. In
addition, the inclined wiring sections 45d are constructed such
that (1) the pitches between the inclined wiring sections 45d of
the adjacent drawing wiring sections 45c, i.e., the length of the
width of one drawing wiring section 45c and the sum of the shortest
distances between adjacent drawing wiring sections 45c, are equal
to each other and the pitches are constant in the direction of the
length of the inclined wiring sections 45d, or (2) the distances of
the lines positioned on a straight line in a predetermined
direction and joining the adjacent drawing wiring sections 45c are
equal to each other, and even if the straight line in a
predetermined direction is slid in the longitudinal direction of
the inclined wiring sections 45d, the length of the line is
rendered constant. It follows that the inclined wiring section 45d
is made shorter if positioned closer to the center of one side of
the film substrate 42 and is made longer if positioned closer to
both ends of one side of the film substrate 42.
[0041] A plurality of parallel wiring section 45e are positioned
closer to the second connection terminals 45b than the inclined
wiring sections 45d and the length of each parallel wiring section
45e is determined in accordance with, for example, the length of
the inclined wiring section 45d and the position of the second
connection terminal 45b.
[0042] In the liquid crystal module of the wiring structure
described above, the inclined wiring sections 45d and the parallel
wiring sections 45e may be readily bent so as to permit the
flexible wiring board 41 to be moderately bent in a U-shape
together with the film substrate 42 as shown in FIG. 4. As a
result, the physical stress applied to the wiring is not
concentrated on a single point but is dispersed so as to produce
the effect that the breakage of the wiring is unlikely to take
place.
[0043] It should be noted that the shortest distance between the
adjacent first connection terminals 45a is shorter than the
shortest distance between the adjacent second connection terminals
45b, with the result that the shortest distance between the
adjacent inclined wiring sections 45d on the side of the first
connection terminals 45a is unavoidably made shorter than the
shortest distance between the adjacent parallel wiring sections
45e. It follows that it is desirable for the width of each inclined
wiring section 45d to be shorter than the width of each parallel
wiring section 45e. The inclined wiring section 45d of such a fine
structure tends to be bent more easily. In the conventional
structure, the thickness of the film substrate 42 is increased, and
a slit is formed below the inclined wiring section 45d so as to
locally bend the structure. In the conventional structure, however,
the wire breakage tends to take place easily. The technical idea of
the present invention may produce a prominent effect in
particularly the case of such a wiring structure.
[0044] If the inclined wiring section 45d is independently capable
of connecting the first connection terminal 45a and the second
connection terminal 45b under the conditions (1) and (2) described
above, it is not absolutely necessary to use the parallel wiring
section 45e.
[0045] A reinforcing plate 48 is bonded with an adhesive (not
shown) to the lower surface of the film substrate 42 to cover the
region corresponding to the arranging region of the connection
terminals 46a and region in the vicinity of the region noted above.
The reinforcing plate 48, which is formed of, for example,
polyethylene terephthalate, has a thickness of about 50 to 70
.mu.m.
[0046] As shown in FIG. 3, bump electrodes 114 each made of gold
are mounted on the peripheral portions of the upper surface of the
semiconductor chip 43. These bump electrodes 114 are bonded to the
lower surfaces of the connection terminals 45b and 46b of the film
substrate 42 by using a eutectic alloy, with the result that the
semiconductor chip 43 is mounted on a predetermined portion of the
lower surface of the film substrate 42.
[0047] The bonding portion constructed by the first connection
terminal 45a of the flexible wiring board 41 is bonded to the
bonding portion constructed by the connection terminal 34 of the
liquid crystal display panel 31 via an anisotropic conductive
adhesive (not shown).
[0048] How to mount the liquid crystal display module shown in FIG.
1 onto a circuit board will now be described with reference to FIG.
4. As shown in the figure, the liquid crystal display panel 31 is
mounted on a predetermined position of a circuit board 51 with the
segment substrate 32 of the liquid crystal display panel 31
positioned on the lower side. As described herein later, the
flexible wiring board 41 is bent substantially in a U-shape in the
arranging region of the drawing wirings 45c shown in FIG. 1. The
term "bending" noted above differs from the local bending achieved
by the conventional molding and implies that the flexible wiring
board is moderately bent by its own flexibility without relying on
the molding. It should be noted that a portion of the flexible
wiring board 41 under the liquid crystal display panel 31 is
allowed to extend along the upper surface of the circuit board 51.
Under this state, the connector portions formed by the portions of
the first connection terminals 46a of the flexible wiring board 41
is inserted into a female connector 52 formed in a predetermined
position on the upper surface of the circuit board 51.
[0049] As described above, the flexible wiring board 41 is bent in
substantially a U-shape in the arranging region of the drawing
wirings 45c. It should be noted in this connection that the film
substrate 42 was made thin, i.e., the thickness of the film
substrate 42 was not smaller than 10 .mu.m and smaller than 40
.mu.m, and the semiconductor chip was heated. Further, pressure was
applied under heat with a bonding tool brought into direct contact
with the other surface of the film substrate 42 so as to obtain the
flexible wiring board 41 in which the bump electrode was bonded to
the connection terminal with a high reliability. Since the flexible
wiring board 41 is constructed by the film substrate 42 formed of a
polyimide film having a thickness not smaller than 10 .mu.m and
smaller than 40 .mu.m, the flexible wiring board 41 is excellent in
flexibility so as to be bent optionally unlike the case where the
film substrate 42 is formed of a polyimide film having a thickness
of about 75 .mu.m to 150 .mu.m. What should be noted is that the
film substrate 42 itself can be bent moderately and uniformly in
substantially a U-shape by applying a slight stress, though the
film substrate 42 is not provided with any slit. In other words,
the flexible wiring board 41 can be bent easily in even the
arranging region of the drawing wirings 45c including the inclined
wiring sections 45d without forming a slit in the film substrate
42. As a result, the drawing wirings in the portion corresponding
to the drawing wiring section 16c between the conventional slits 18
and 19 (FIG. 12) and in the portion corresponding to the slits 18
and 19 is rendered unnecessary, making it possible to set the
output wiring 45 short. It follows that it is possible to shorten
the length in the extending direction of the output wiring 45,
i.e., in the vertical direction in the upper portion in FIG. 1 of
the mounting region of the semiconductor chip. As a result, the
flexible wiring board 41 can be miniaturized while maintaining a
good connection and can be made excellent in the mounting
capability with a high mounting density. Further, the manufacturing
cost can be lowered.
[0050] How to bond the semiconductor chip 43 onto the flexible
wiring board 41 will now be described. In the first step, prepared
is a bonding apparatus as shown in FIG. 5. The bonding apparatus
comprises a stage 121 having a heater (not shown) housed therein
and a bonding tool 122 arranged vertically movable above the stage
121. The semiconductor chip 43 is mounted on the stage 121 with the
bump electrodes 114 facing upward. Also, the film substrate 42,
which has lower and upper surfaces, facing the semiconductor chip
43 over the entire region of the mounting region of the
semiconductor chip is arranged above the semiconductor chip 43 such
that the lower surface of the film substrate 42 on which the
wirings 45 and 46 are formed faces the semiconductor chip 43. Then,
the bump electrodes 114 of the semiconductor chip 43 are aligned
with the connection terminals 45b, 46b on the film substrate
42.
[0051] In the next step, for example, the stage 121 is moved upward
so as to bring the bump electrodes 114 into contact with the
connection terminals 45b, 46b, as shown in FIG. 6. Also, the
bonding tool 122 is moved downward. Under this state, the stage 121
is heated to 350.degree. C. to 450.degree. C., preferably about
400.degree. C., so as to heat the semiconductor chip 43. Also, the
bonding tool 122 is heated to 250.degree. C. to 350.degree. C.,
preferably about 300.degree. C., and the bonding tool 122 is
brought into direct contact with the upper surface of the film
substrate 42 so as to press the upper surface of the film substrate
42. The bump electrodes 114 are kept pressurized under heat for 1
to 3 seconds against the connection terminals 45b, 46b mounted to
the film substrate 42.
[0052] As described above, since the film substrate 42 is very
thin, i.e., the thickness is not smaller than 10 .mu.m and smaller
than 40 .mu.m, the heat applied to the film substrate 42 is
promptly transmitted to the connection terminals 45b, 46b so as to
heat the film substrate 42 with a relatively low temperature and
for a short time. It follows that the thermal deformation does not
take place in the film substrate 42. Further, since the stage 121
heats the semiconductor chip 43, the bump electrodes and the
connection terminals 45b, 46b are heated from both above and below.
As a result, the temperature required for the bonding is reached
promptly even under a relatively low temperature, making it
possible to obtain bonding of a high reliability. In the flexible
wiring board 41 thus bonded, a device hole is not formed in the
mounting region of the semiconductor chip of the film substrate 42,
unlike the prior art. Therefore, the connection terminals 45b, 46b
formed on the film substrate 42 are unlikely to be deformed before
and after the bonding. It follows that an inconvenience such as a
defective bonding between the connection terminals 45a, 45b and the
bump electrodes 114 does not take place, leading to the effect of
improving the production efficiency. Further, since the wirings 45
and 46 are bonded to the film substrate 42 without interposing an
adhesive, it is impossible for the adhesive to be melted in the
bonding step so as to deviate the positions of the connection
terminals 45b and 46b, making it possible to achieve the bonding
with a high accuracy.
[0053] FIG. 7 is a plan view showing a liquid crystal display
module according to a second embodiment of the present invention.
The liquid crystal display module in the second embodiment is
substantially equal to the liquid crystal display module according
to the first embodiment of the present invention described above
except the arrangements of the output wiring 45 and the input
wiring 46 of the flexible wiring board 41.
[0054] In the flexible wiring board 41 according to the first
embodiment described above, the second connection terminals 46b of
the input wiring 46 are arranged on one side in the longitudinal
direction of the rectangular semiconductor chip 43 in the positions
facing the bump electrodes, and the second connection terminals 45b
of the output wiring 45 are arranged on the other three sides,
i.e., the other side on the longitudinal direction and on the two
short sides on the both edges of the semiconductor chip in the
positions facing the bump electrodes. In the flexible wiring board
41 according to the second embodiment of the present invention,
however, the second connection terminals 46b of the input wiring 46
are arranged on one side in the longitudinal direction of the
rectangular semiconductor chip 43 and on the two short sides at
both edges of the semiconductor chip 43 in the positions facing the
bump electrodes, and the second connection terminals 45b of the
output wiring 45 are arranged on the other side in the longitudinal
direction of the semiconductor chip 43 in the positions facing the
bump electrodes.
[0055] Therefore, in the second embodiment of the present
invention, the distance between the adjacent first connection
terminals 45a can be designed longer than the distance between the
adjacent second connection terminals 45b.
[0056] The output wiring 45 comprises the first connection
terminals 45a that are not covered with the protective film 47 so
as to be exposed to the upper edge portion in FIG. 7, the second
connection terminals 45b arranged in parallel in a predetermined
position in the mounting region of the semiconductor chip and in a
region in the vicinity of said predetermined position, and the
drawing wirings 45c extending between the second connection
terminals 45b and the first connection terminals 45a.
[0057] As shown in FIG. 7, the drawing wirings 45c in the second
embodiment of the present invention comprise the inclined wiring
sections 45d arranged such that the arranging pitch is gradually
increased from the second connection terminals 45b toward the first
connection terminals 45a, and the parallel wiring sections 45e
arranged in parallel. In other words, the inclined wiring sections
45d in the adjacent drawing wirings 45c are set such that the pitch
P.sub.2 on the side of the first connection terminals 45a is made
longer than the pitch P.sub.1 on the side of the second connection
terminals 45b. On the other hand, that portions of the input wiring
46 which is not covered with the protective film 47 so as to be
exposed to the lower end portion in FIG. 1 constitute the first
connection terminals 46a, and the portions in the mounting region
of the semiconductor chip constitute the second connection
terminals 46b.
[0058] As described above, in the liquid crystal module of the
wiring structure described above, the inclined wiring sections 45d
and the parallel wiring sections 45e are readily bent so as to
permit the flexible wiring board 41 to allow the film substrate 42
to be bent in a U-shape as shown in FIG. 4, thereby making it
possible to permit the film substrate 42 to have a short
structure.
[0059] In the second embodiment described above, each drawing
wiring section 45c comprises both the inclined wiring section 45d
and the parallel wiring section 45e. However, it is also possible
for the drawing wiring section 45c to constitute the inclined
wiring section 45d alone. It is also possible for the drawing
wiring section 45c, which comprises the inclined wiring section 45d
and the parallel wiring section 45e, to include further a second
parallel wiring section consisting of a plurality of wirings
arranged in parallel like the parallel wiring section 45e, said
second parallel wiring section being arranged between the inclined
wiring section 45d and the second connection terminals 45d.
Alternatively, even if the drawing wiring 45c is formed by only the
second parallel wiring section and the inclined wiring section 45d,
it is possible to obtain the similar effect as far as the bent
portion includes the inclined wiring section 45d.
[0060] FIG. 8 is a plan view showing a liquid crystal module
according to a third embodiment of the present invention. The
liquid crystal display module according to the third embodiment is
substantially equal to the liquid crystal display module according
to the first embodiment described previously except the
arrangements of the output wiring 45 and the input wiring 46 of the
flexible wiring board 41.
[0061] In the flexible wiring board 41 according to the third
embodiment of the present invention, the second connection
terminals 46b of the input wiring 46 are arranged on one side in
the longitudinal direction of a rectangular semiconductor chip 43
in positions facing the bump electrodes, and the second connection
terminals 45b of the output wiring 45 are positioned on the other
three sides of the semiconductor chip 43 in the positions facing
the bump electrodes, as in the first embodiment. Therefore, since
the number of first connection terminals concentrated on one side
of the film substrate 42 corresponds to the number of bump
electrodes on the three sides of the semiconductor chip 43, the
distance between the adjacent first connection terminals 45a is
required to be shorter than the distance between the adjacent
connection terminals 45b.
[0062] The drawing wiring section 45c are formed by the inclined
wiring sections 45d arranged such that the arranging pitch of the
inclined wiring sections 45d is gradually diminished from the side
of the second connection terminal 45b toward the first connection
terminal 45a, and the parallel wiring sections 45e arranged in
parallel. In other words, the pitch P.sub.3 of the adjacent
inclined wiring sections 45d on the side of the second connection
terminal 45b is set longer than the pitch P.sub.4 on the side of
the first connection terminal 45a. Since the inclined wiring
sections 45d are inclined and thus concentrated in a central
portion on one side on the side of the first connection terminals
45a in a manner to make shorter the distance between the adjacent
first connection terminals 45a, the inclined wiring section 45d is
shorter in a region closer to the center of one side of the film
substrate 42 and is longer in regions closer to both ends of one
side of the film substrate 42.
[0063] The wiring sections 45e, which are parallel to each other,
of the output wiring 45 are positioned closer to the first
connection terminals 45a than to the inclined wiring sections 45d,
and the length of each of the parallel wiring sections 45e is set
at a predetermined value, though it is not absolutely necessary for
the lengths of the parallel wiring sections 45e to be set at
predetermined values.
[0064] In the liquid crystal module of the wiring structure
described above, the inclined wiring section 45d and the parallel
wiring section 45e can be bent easily so as to permit the flexible
wiring board 41 to be bent together with the film substrate 42 in a
substantial U-shape as shown in FIG. 4, thereby allowing the film
substrate 42 to be of a short structure.
[0065] In the third embodiment described above, the drawing wiring
section 45c is formed by the inclined wiring section 45d and the
parallel wiring section 45e. Alternatively, it is possible for the
drawing wiring section 45c to consist of the inclined wiring
section 45d alone. In this case, the inclined wiring section 45d is
bent so as to produce the effect described above. It is also
possible for the drawing wiring section 45c, which is formed by the
inclined wiring section 45d and the parallel wiring section 45e, to
include further a second parallel wiring section consisting of a
plurality of wirings arranged in parallel like the parallel wiring
section 45e. The second parallel wiring sections are arranged
between the inclined wiring sections 45d and the second connection
terminals 45d. Alternatively, even if the drawing wiring 45c is
formed by only the second parallel wiring section and the inclined
wiring section 45d, it is possible to obtain the similar effect as
far as the bent portion includes the inclined wiring section
45d.
[0066] In each of the first to third embodiments of the present
invention described above, the thickness of the film substrate 42
may be defined to be not smaller than 10 .mu.m and to be smaller
than 40 .mu.m. However, it is more desirable for the thickness of
the film substrate 42 to be not smaller than 20 .mu.m and to be
smaller than 40 .mu.m in view of the case where the film substrate
is transferred as a carrier tape having sprocket holes formed on
both sides of the film substrate.
[0067] In each of the first to third embodiments of the present
invention described above, a liquid crystal display panel is used
as the display panel. However, the technical idea of the present
invention can also be applied to the cases where an
electroluminescence element, which is a spontaneous light emitting
element, a plasma display or a field emission display is used as
the display panel.
[0068] When it comes to the semiconductor device shown in FIG. 3,
the semiconductor chip 43 is bonded with the film substrate 42 kept
flat. In this case, the distance between output and input the
wirings 45, 46 and the edge on the upper surface of the
semiconductor chip 43 is small. Therefore, where there is a small
burr in the edge or if the film substrate 42 is deformed in the
bonding step, short-circuiting tends to be brought about between
the edge on the upper surface of the semiconductor chip 43 and the
wirings 45, 46 on the film substrate 42.
[0069] Such being the situation, it is important to prevent the
short circuit between the edge on the upper surface of the
semiconductor chip 43 and the wirings 45, 46 of the film substrate
42. A flexible wiring board according to a fourth embodiment of the
present invention will now be described with reference to FIG. 9.
In the wiring board according to the fourth embodiment of the
present invention, the film substrate 42 in the vicinity of the
connection terminals 45b, 46b bonded to the bump electrodes 114 and
in the portion corresponding to said vicinity is deformed so as to
permit the film substrate 42 to be positioned apart from the upper
surface of the semiconductor chip 43. It follows that it is
possible to prevent the short circuit between the edge on the upper
surface of the semiconductor chip 43 and the wirings 45, 46 of the
film substrate 42.
[0070] A method of manufacturing the flexible wiring board of the
present embodiment will now be described with reference to FIGS. 10
and 11. In the first step, the bonding apparatus as shown in FIG.
10 is prepared. The bonding apparatus comprises the stage 121
having a heater (not shown) arranged therein, and the bonding tool
122 arranged movable in a vertical direction above the stage 121.
Further, a clamp 123 is arranged to surround the bonding tool 122
above the stage 121. The semiconductor chip 43 is disposed on the
stage 121, and that portion of the film substrate 42 surrounding a
region in which the semiconductor chip 43 is disposed is held by
the clamp 123. Under this state, the distance between the
connection terminals 45b, 46b and the bump electrodes 114 is set
at, for example, about 200 .mu.m.
[0071] Then, the bonding tool 122 is moved downward as shown in
FIG. 11 so as to permit the lower surface of the bonding tool 122
to push a region of the upper surface of the film substrate 42
corresponding to the connection terminals 45b and 46b and a portion
inside the terminals. As a result, the film substrate 42 is
partially deformed downward appropriately in the vicinity of the
portions where the connection terminals 45b and 46b are bonded to
the bump electrodes 114 and in the portion corresponding to said
vicinity. Under this state, the bump electrodes 114 are bonded to
the connection terminals 45b and 46b, respectively. In this case,
the heating temperature of the bonding tool 122 is set at 250 to
350.degree. C., preferably about 300.degree. C., and the heating
temperature of the stage 121 is set higher than the heating
temperature of the bonding tool 122. To be more specific, the
heating temperature of the stage 121 is set at 350 to 450.degree.
C., preferably about 400.degree. C., and the bonding time is set at
about 1 to 3 seconds. As a result, the wiring board as shown in
FIG. 9 can be obtained.
[0072] In the manufacturing method described above, the film
substrate 42 in the vicinity of the regions where the connection
terminals 45b, 46b are bonded to the bump electrodes 114 and in the
portion corresponding to said vicinity is deformed to be positioned
apart from the upper surface of the semiconductor chip 43
simultaneously with the mounting of the semiconductor chip 43 to
the lower surface of the film substrate 42. In other words, since
the connection terminals 45b, 46b are formed to include inclined
regions positioned to be gradually apart from the semiconductor
chip 43 together with the film substrate 42 from the portions
bonded to the bump electrodes 114 toward the outside of the
mounting region of the semiconductor chip, it is possible to
prevent the number of manufacturing steps from being increased.
[0073] Another example of a method of manufacturing the flexible
wiring board shown in FIG. 9 will now be described. In this
example, the semiconductor chip 43 is mounted first on the lower
surface of the film substrate 42 as shown in FIG. 6. Then, that
region of the film substrate 42 in which the semiconductor chip 43
is held by the clamp 123 as shown in FIGS. 10 and 11, followed by
moving downward the bonding tool 122 so as to deform the film
substrate 42 in the regions in which the connection terminals 45b,
46b are bonded to the bump electrodes 114 and in the portion
corresponding to said vicinity so as to permit the particular
portions of the film substrate 42 to be positioned apart from the
semiconductor chip 43.
[0074] As described above, in the present invention, a bonding tool
is brought into direct contact with the other surface of the film
substrate under certain conditions with the semiconductor chip kept
heated so as to pressurize the semiconductor chip under heat and,
thus, to obtain the bonding of a high reliability, even where the
film substrate has one surface corresponding to one surface of the
semiconductor chip over the entire mounting region of the
semiconductor chip and other surfaces. What should also be noted is
that, since a device hole is not formed in the semiconductor chip
mounting region of the film substrate, it is possible to prevent
the connection terminals mounted to the film substrate from being
deformed.
[0075] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *