Title: Board pieces, flexible wiring boards and processes for manufacturing flexible wiring boards
Abstract: A board piece 2 of the present invention comprises a non-thermoplastic resin film 11, a thermoplastic resin film 10 formed on the non-thermoplastic resin film 11 and a metal wiring 8 formed on the surface of the thermoplastic resin film 10. Metal wiring 8 is partially exposed on board piece 2 to form a contact 12. A low-melting metal coating 13 is formed on contact 12 and two board pieces 2a, 2b are pressed against each other under heating with contacts 12a, 12b thereof being in contact with each other so that thermoplastic resin films 10a, 10b soften to adhere board pieces 2a, 2b to each other and low-melting metal coatings 13a, 13b melt and then solidify to connect contacts 12a, 12b to each other. The region of metal wiring 8 not used for connection is wiring 17 connecting contacts 12 to each other and a cover film 19 can be provided on the surface thereof. Contacts 12a, 12b can also be connected by applying ultrasonic wave.
Patent Number: 6,840,430 Issued on 01/11/2005 to Kurita, et al.
| Inventors:
|
Kurita; Hideyuki (Yokohama, JP);
Watanabe; Masanao (Kanuma, JP);
Shinohara; Toshihiro (Kanuma, JP);
Fukuda; Mitsuhiro (Kanuma, JP);
Anzai; Yukio (Kanuma, JP)
|
| Assignee:
|
Sony Chemicals, Corp. (Tokyo, JP)
|
| Appl. No.:
|
458175 |
| Filed:
|
June 10, 2003 |
| Current U.S. Class: |
228/173.2; 228/208; 428/347 |
| Intern'l Class: |
B21D 039/00 |
| Field of Search: |
428/347
228/173.2,208,110.1
|
References Cited [Referenced By]
U.S. Patent Documents
| 5296649 | Mar., 1994 | Kosuga et al. | 174/250.
|
| 5714252 | Feb., 1998 | Hogerton et al. | 428/344.
|
| 6280828 | Aug., 2001 | Nakatsuka et al. | 428/209.
|
| 6395993 | May., 2002 | Nakamura et al. | 174/254.
|
| 6437251 | Aug., 2002 | Kurita et al. | 174/254.
|
| 6596947 | Jul., 2003 | Kurita et al. | 174/255.
|
Primary Examiner: Lam; Cathy F.
Attorney, Agent or Firm: Osha & May L.L.P.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a divisional of U.S. patent application Ser. No.
09/937,590, filed Sep. 27, 2001, now U.S. Pat. No. 6,596,547. Ser. No.
09/937,590 is a 371 of PCT/JP00/00443 filed on Jan. 28, 2000.
Claims
What is claimed is:
1. A process for manufacturing a flexible wiring board by assembling a
plurality of board pieces having a resin film and a metal wiring provided
on the resin film, comprising:
providing a thermoplastic resin film between the metal wirings of the board
pieces to be assembled to each other, and
connecting the metal wirings of the board pieces to each other by pressing
the board pieces against each other under heat to force the metal wirings
into the thermoplastic resin film.
2. The process for manufacturing a flexible wiring board according to claim
1, further comprising:
providing a protective film on a part of a surface of a board piece to be
assembled to cover a part of the metal wiring before assembling the board
pieces,
wherein the thermoplastic resin film is provided on a region not covered by
the protective film, and the board pieces are as assembled to each other.
3. The process for manufacturing a flexible wiring board according to claim
2, further comprising:
forming a low-melting metal coating on a surface of the metal wiring of at
least one of the board pieces to be assembled,
melting the low-melting metal coating forced into the thermoplastic resin
film while the board pieces are heated under pressure, and
solidifying the low-melting metal coating to connect the metal wirings to
each other.
4. The process for manufacturing a flexible wiring board according to claim
1, further comprising:
exposing a region of the metal wiring of at least one board piece when the
board pieces are assembled to each other, and
providing a protective film on the exposed region after the board pieces
are assembled each other.
5. The process for manufacturing a flexible wiring board according to claim
4, wherein at least a part of the metal wiring on the exposed region is
not covered by the protective film.
6. The process for manufacturing a flexible wiring board according to claim
4, further comprising:
protruding a first board piece from second board piece to be assembled to
each other before assembling, and
providing a protective film on the board pieces, wherein the protective
film is arranged to extend across the first board piece to the second
board piece.
7. The process for manufacturing a flexible wiring board according to claim
4, further comprising:
forming a low-melting metal coating on a surface of the metal wiring of at
least one of the board pieces to be assembled,
melting the low-melting metal coating forced into the thermoplastic resin
film while the board pieces are heated under pressure, and
solidifying the low-melting metal coating to connect the metal wirings each
other.
8. The process for manufacturing a flexible wiring board according to claim
1, further comprising:
adhering a surface of a first board piece and a surface of a second board
piece to a same surface side of a third board piece.
9. The process for manufacturing a flexible wiring board according to claim
8, further comprising:
providing a protective film partially on the adhering surfaces of the
first, second, and third board pieces to partially cover the metal wirings
of the first, second, and third board pieces before assembling,
providing a thermoplastic resin film on an exposed region of each metal
wiring, and
adhering the first and second board pieces to the third board piece.
10. The process for manufacturing a flexible wiring board according to
claim 8, further comprising:
providing a protective film on the metal wirings of the first, second, and
third board pieces after adhering the first, second, and third board
pieces.
11. The process for manufacturing a flexible wiring board according to
claim 10, further comprising:
protruding the third board piece from the first and second board pieces
before assembling, and
providing a protective film on the board pieces, wherein the protective
film is arranged to extend across the first and third board pieces.
12. The process for manufacturing a flexible wiring board according to
claim 11, further comprising:
providing a second protective film on the first, second, and third board
pieces, wherein the second protective film is arranged to extend across
the second board piece to the third board piece.
13. A process for manufacturing a flexible wiring board by assembling at
least a first board piece, a second board piece, and a third board piece,
each having a resin film and a metal wiring provided on the resin film,
comprising:
connecting and fixing a region of the metal wiring of the first board piece
and a region of the metal wiring of the second board piece to the third
board piece,
filling thermoplastic resin in at least one space between the connecting
and fixing regions of the metal wirings, and
providing an exposed region and a covered region on the metal wirings
except for the regions where the metal wirings of the first and the second
board pieces are connected and fixed, wherein the exposed regions are
covered with a protective film.
14. The process for manufacturing a flexible wiring board according to
claim 13, further comprising:
providing a protective film on the third board piece on a surface having
the connecting and fixing regions, wherein the protective film is not
provided on the connecting and fixing regions.
15. The process for manufacturing a flexible wiring board according to
claim 13, wherein the resin film of at least one of the first, second, and
third board pieces has a structure laminating non-thermoplastic resin film
and thermoplastic resin film, and the metal wiring is formed on the
thermoplastic resin film.
16. The process for manufacturing a flexible wiring board according to
claim 11, further comprising:
providing protective film on the board pieces, wherein the protective film
is arranged to extend across the second and third board pieces.
Description
FIELD OF THE INVENTION
The present invention relates to the field of flexible wiring boards,
particularly to the field of board pieces constituting flexible wiring
boards and flexible wiring boards formed by assembling the board pieces.
PRIOR ART
Flexible wiring boards having a desired circuit pattern printed thereon
have been widely used, and in recent years, there are demands for flexible
wiring boards having various shapes suitable for the contours of the place
where they are used.
FIG. 10(a) shows a layout for cutting T-shaped flexible wiring boards 252
from a rectangular pre-cutted substrate 250, in which six flexible wiring
boards 252 are obtained.
However, a significant part of pre-cutted substrate 250 is uselessly
discarded when such shaped flexible wiring boards 252 are cut.
Thus, a technique for preparing a flexible wiring board in a complex shape
was proposed by dissolving the complex shape into simple shapes and
assembling board pieces in the simple shapes. Reference 255 in FIG. 10(c)
represents a flexible wiring board having the same shape as that of
flexible wiring board 252 described above and formed by assembling two
rectangular board pieces 253, 254.
When rectangular board pieces 253, 254 are used in this manner, a close
layout can be achieved as shown in FIG. 10(b) and therefore, pre-cutted
substrate 250 can be effectively used by cutting board pieces 253, 254 in
simple shapes. In FIG. 10(b), eight board pieces each 253, 254 are
obtained and assembled into eight flexible wiring boards 256. As shown in
this example, a greater number of flexible wiring boards 256 can be
obtained by using board pieces in simple shapes than directly cutting
T-shaped flexible wiring boards 252.
When a plurality of board pieces are assembled into a flexible wiring board
as described above, board pieces 253, 254 must be mechanically and
electrically assembled.
An example of the assembling technique is explained with reference to FIGS.
11(a), 11(b), in which references 220, 230 represent board pieces having
metal wirings 222, 232 consisting of a patterned copper thin film formed
on polyimide films 221, 231, respectively. In order to assemble these
board pieces 220, 230, boards elements 220, 230 are first opposed to each
other with metal wirings 222, 232 facing each other.
Metal wirings 222, 232 have solder coatings 223, 233 formed by plating on
their surfaces, respectively, and solder coatings 223, 233 of the
respective board pieces 220, 230 are brought into close contact with each
other and heat and pressure are applied to melt solder coatings 223, 233,
which are then cooled to form a solder layer 204. This solder layer 204
forms a metallic bond with metal wirings 222, 232, whereby metal wirings
222, 232 are firmly connected to each other via solder layer 204 to give a
flexible wiring board 203 (FIG. 11(b)).
However, the recent need for forming a large number of metal wirings on a
small-area flexible wiring board leads to an increasingly narrower pitch
between metal wirings 222 (or metal wirings 232) on the same board piece
220, 230.
When solder coatings 223, 233 are heated under pressure as described above,
molten solder scatters and remains here and there as scatter 215 in
flexible wiring board 203, and in extreme cases, molten solder flows out
to form a bridge 216 at connection 212 between metal wirings 222, 232,
which causes a short circuit between metal wirings 222 (or metal wirings
232) to be insulated.
As the pitch between metal wirings 222 (or metal wirings 232) becomes
narrower, bridge 216 becomes more likely to occur. Especially when a
plurality of board pieces are to be assembled into a flexible wiring
board, even one short circuit at the connection between board pieces means
a faulty flexible wiring board as a whole, which extremely lowers the
manufacturing yield of flexible wiring boards.
DISCLOSURE OF THE INVENTION
A board piece of the present invention comprises a non-thermoplastic resin
film, a thermoplastic resin film formed on the non-thermoplastic resin
film and a metal wiring formed on the surface of the thermoplastic resin
film.
In this board piece, the metal wiring can be partially covered with a resin
film.
The metal wiring can also be partially exposed.
A low-melting metal coating can be formed on at least a part of the exposed
metal wiring.
A solder can be used as a material for the low-melting metal coating.
A gold coating can also be formed on at least a part of the exposed metal
wiring.
The non-thermoplastic resin film can consist of a polyimide film.
The thermoplastic resin film can consist of a thermoplastic polyimide film.
A flexible wiring board of the present invention comprises at least two
board pieces each having a non-thermoplastic resin film, a thermoplastic
resin film formed on the non-thermoplastic film and a metal wiring formed
on the surface of the thermoplastic resin film, wherein the board pieces
are adhered to each other via the thermoplastic resin films by heating the
metal wirings of the board pieces in contact with each other to soften the
thermoplastic resin films and insert them between connections of the metal
wirings in contact with each other.
In the flexible wiring board, a low-melting metal coating can be formed on
the surface of at least one of the metal wirings in contact with each
other so that the board pieces are heated to melt the low-melting metal
coating, which then solidifies to connect the metal wirings to each other.
The metal wirings in contact with each other can also be connected by
ultrasonic wave vibration.
In this case, a gold coating is preferably formed on at least one of the
metal wirings to be connected by ultrasonic wave vibration.
Another flexible wiring board of the present invention is formed by
assembling at least three board pieces each having a resin film and a
metal wiring, wherein the metal wirings of a first and second board pieces
among the board pieces are partially connected and fixed to the metal
wiring of a third board piece and a thermoplastic resin is filled between
the connecting and fixing regions of the metal wirings while the other
regions of the metal wirings are partially covered with a protective film
on their surfaces and partially exposed.
In the flexible wiring board, the resin film of at least one of the board
pieces to be assembled has a multilayer structure consisting of a
non-thermoplastic resin film and a thermoplastic resin film and the metal
wiring can be formed on the thermoplastic resin film.
The board pieces can be connected to each other by applying a thermoplastic
resin film on each of the metal wirings and then assembling the board
pieces with a thermoplastic resin constituting the thermoplastic resin
film being filled between the connecting regions of the metal wirings.
The metal wirings can be fixed to each other with a solder.
An opening can be formed in the protective film provided on at least one of
the first to third board pieces.
In a process for manufacturing a flexible wiring board of the present
invention by assembling a plurality of board pieces having a resin film
and a metal wiring provided on the resin film, the resin film of at least
one of the board pieces to be assembled has a multilayer structure
consisting of a non-thermoplastic resin film and a thermoplastic resin
film and the metal wiring is provided on the thermoplastic resin film and
the board pieces to be assembled are pressed against each other under
heating.
In this case, the metal wirings of the board pieces can be connected to
each other by forming a low-melting metal coating on the surface of the
metal wiring of at least one of the board pieces to be assembled and
pressing the board pieces against each other under heating to melt the
low-melting metal coating.
The board pieces can be assembled by pressing the board pieces against each
other under heating after applying ultrasonic wave to the board pieces in
a superposed state to connect the metal wirings of the board pieces to
each other by vibration energy of the ultrasonic wave.
The board pieces can also be assembled by pressing the board pieces in a
superposed state against each other under heating while applying
ultrasonic wave to connect the metal wirings to each other by vibration
energy of the ultrasonic wave.
In this case, a gold coating is preferably formed in advance on the surface
of at least one of the metal wirings to be connected.
In another process for manufacturing a flexible wiring board of the present
invention by assembling a plurality of board pieces having a resin film
and a metal wiring provided on the resin film, the metal wirings of the
board pieces are connected to each other by providing a thermoplastic
resin film between the metal wirings of the board pieces to be assembled
and pressing the board pieces against each other under heating to force
the metal wirings into the thermoplastic resin film.
In this case, the metal wirings of the board pieces can be connected to
each other by forming a low-melting metal coating on the surface of the
metal wiring of at least one of the board pieces to be assembled and
pressing the board pieces against each other under heating to melt the
low-melting metal coating.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a)-(h) is a diagram for illustrating a first example of flexible
wiring board of the present invention and a manufacturing process thereof.
FIGS. 2(a), (b) is a diagram for illustrating a variation of the first
example of flexible wiring board of the present invention and a
manufacturing process thereof.
FIG. 3 shows an example of an ultrasonic wave apparatus used in a process
of the present invention.
FIGS. 4(a)-(d) is a diagram for illustrating a second example of flexible
wiring board of the present invention and a manufacturing process thereof.
FIGS. 5(a)-(d) is a diagram for illustrating a third example of flexible
wiring board of the present invention and a manufacturing process thereof.
FIGS. 6(a)-(e) is a diagram for illustrating a fourth example of flexible
wiring board of the present invention and a manufacturing process thereof.
FIGS. 7(a)-(d) is a diagram for illustrating a fifth example of flexible
wiring board of the present invention and a manufacturing process thereof.
FIGS. 8(a)-(e) is a diagram for illustrating a sixth example of flexible
wiring board of the present invention and a manufacturing process thereof.
FIGS. 9(a)-(c) is a diagram for illustrating an example of a layout of
board pieces.
FIGS. 10(a)-(c) is a diagram for illustrating a layout of board pieces and
flexible wiring boards.
FIGS. 11(a), (b) is a diagram for illustrating disadvantages of an
assembling technique of the prior art.
THE MOST PREFERRED EMBODIMENTS OF THE INVENTION
The present invention was made to overcome the above disadvantages of the
prior art with the purpose of providing a technique for assembling a
plurality of board pieces to give a shaped flexible wiring board with high
reliability and high durability.
Board pieces and flexible wiring boards of the present invention will now
be explained as well as manufacturing processes of flexible wiring boards
with reference to the attached drawings.
FIGS. 1(a)-(h) shows a process for manufacturing a first example of
flexible wiring board of the present invention.
Referring FIGS. 1(a) and 1(b), a thermoplastic resin film 10 consisting of
a thermoplastic polyimide synthesized from an aliphatic amine and an acid
anhydride and a non-thermoplastic resin film 11 consisting of a
non-thermoplastic polyimide synthesized from an aromatic amine and an acid
anhydride are first prepared.
An adhesive layer (not shown with a release paper applied thereon) is
formed on each side of thermoplastic resin film 10 (preferably having a
thickness of 15 .mu.m-50 .mu.m and here consisting of a polyimide film
having a thickness of 25 .mu.m) and the adhesive layer on one side is
exposed, and thermoplastic resin film 10 is applied on non-thermoplastic
resin film 11 (preferably having a thickness of 10 .mu.m-50 .mu.m and here
consisting of a polyimide film having a thickness of 25 .mu.m available
from DuPont under trade name Kapton) (FIG. 1(b)), and then the other
adhesive layer is exposed and a metal foil 9 (preferably having a
thickness of 5 .mu.m-75 .mu.m and here consisting of a copper foil having
a thickness of 18 .mu.m) is applied on the surface of thermoplastic resin
film 10 (FIG. 1(c)).
Then, metal foil 9 is patterned by a photolythographic process using a
photosensitive dry film or a resist film to form a metal wiring 8
consisting of copper (FIG. 1(d)). Metal wiring 8 typically has a pattern
width of about 100 .mu.m with a pitch of about 10 .mu.m-200 .mu.m, here
200 .mu.m (0.2 mm).
This metal wiring 8 has a wide contact for connecting board pieces to each
other to form a flexible wiring board or, after a flexible wiring board
has been prepared, for connecting the flexible wiring board to an electric
component such as a semiconductor device or an electronic circuit. It also
has an elongate wiring for electrically connecting contacts via metal
wiring 8.
In FIG. 1(e), reference 12 represents the contact and reference 17
represents the wiring. After metal wiring 8 is formed and surface-cleaned,
a cover film 19 is applied on wiring 17 while contact 12 is exposed as
shown in FIG. 1(e).
The assembly is immersed in a plating solution of a low-melting metal
(here, a solder of Sn:Pb=6:4) to form a low-melting metal coating 13 on
the top of contact 12, whereby a board piece 2 is obtained (FIG. 1(f)).
Preferably, low-melting metal coating 13 has a thickness of 1 .mu.m-10
.mu.m. The thickness here is 3 .mu.m.
Then, two board pieces 2a, 2b having the structure described above are
prepared and their contacts 12a, 12b are opposed (FIG. 1(g)) and heat and
pressure are applied while low-melting metal coatings 13a, 13b on the tops
of contacts 12a, 12b are in close contact with each other (thermal
compression bonding). As an example, thermal compression bonding
conditions involve a heating temperature of 150-300.degree. C. at a
pressure of 20-50 kg/cm.sup.2 for 10-20 seconds, and here 200.degree. C.
at 30 kg/cm.sup.2 for 10 seconds.
During thermal compression bonding of board pieces 2a, 2b, thermoplastic
resin films 10a, 10b and contacts 12a, 12b are first heated via
non-thermoplastic films 11a, 11b and thermoplastic resin films 10a, 10b
heat up and soften.
Thermoplastic resin films 10a, 10b located between contacts 12a (and
between contacts 12b) are not in contact with each other before heating,
but they are flown out and inserted between contacts 12a (and between
contacts 12b) as they soften.
After thermoplastic resin films 10a, 10b soften, the temperature of
contacts 12a, 12b rises, and when it reaches the melting point of the
low-melting metal or more, low-melting metal coatings 13a, 13b melt. At
that time, melts of low-melting metal coatings 13a, 13b cannot scatter or
flow out to form a bridge by molten solder because softened thermoplastic
resin films 10a, 10b are filled between contacts 12a (and between contacts
12b) in board pieces 2a, 2b of the present invention.
When cooling after thermal compression bonding, two molten low-melting
metal coatings 13a, 13b combine to form a low-melting metal coating 14.
Contacts 12a, 12b and low-melting metal coating 14 combine to form
connection 16 (FIG. 1(h)).
Copper on the surfaces of contacts 12a, 12b forms a metallic bond with
low-melting metal coating 14 so that two board pieces 2a, 2b are
electrically and mechanically connected via connection 16. Around this
connection 16 is formed a flange 14' protruding from low-melting metal
coating 14.
When cooling after the end of compression bonding, two softened
thermoplastic resin films 10a, 10b also combine to form a thermoplastic
resin film 15. As thermoplastic resin films 10a, 10b develop adhesiveness
when then soften, two non-thermoplastic resin films 11a, 11b are adhered
to each other via single layer thermoplastic resin film 15 to give a first
example of flexible wiring board 5 of the present invention. In this
flexible wiring board 5, wirings 17a, 17b of two board pieces 2a, 2b
adhered are covered with cover films 19a, 19b, respectively.
Although boards elements 2a, 2b described above both have contacts 12a, 12b
formed on thermoplastic resin films 10a, 10b, either one board piece may
have a contact formed on the thermoplastic resin film.
For example, a flexible wiring board can be prepared by assembling a board
piece represented by reference 3 in FIG. 2(a) and a board piece
represented by reference 2 in FIG. 1. Board piece 3 in FIG. 2(a) has a
contact 32 and a wiring 37 consisting of a metal wiring formed on a
non-thermoplastic resin film 31.
Also in this case, low-melting metal coatings 13, 33 on the tops of
contacts 12, 32 of two board pieces 2, 3 are first brought into contact
with each other and heat and pressure are applied in this state to form a
low-melting metal coating 34, whereby the low-melting metal coating 34 and
contacts 12, 32 form a connection 36. Board pieces 2, 3 are mechanically
and electrically connected via connection 36 to give a flexible wiring
board represented by reference 7 in FIG. 2(b).
The low-melting metal neither scatters nor forms a bridge because
low-melting metal coatings 13, 33 melt after thermoplastic resin film 10
of one board piece 2 softens to fill the gap between contacts 32 directly
formed on non-thermoplastic resin film 31 of the other board piece 3.
Although each of board pieces 2 (2a, 2b) and 3 used for assembly described
above and board pieces described below has metal wiring 8 formed on one
side, a metal wiring may be formed on each side.
Although non-thermoplastic resin films 11 (11a, 11b), 31 and thermoplastic
resin film 10 (10a, 10b) described above are polyimide resin films, the
present invention is not limited thereto. In the case of board pieces 2
(2a, 2b) and 3 described above and board pieces described below,
thermoplastic resin films that cannot dissolve during thermal compression
bonding but develop adhesiveness as they soften can be used. Resins for
thermoplastic resin films are desirably polyimide resins from the
viewpoint of chemical resistance and flame retardance.
When metal wirings are to be connected via a low-melting coating, the
softening point of each of thermoplastic resin films 11 (11a, 11b) and 31
described above and thermoplastic resin films described below must be
lower than the melting temperature of low-melting metal coatings 13, 33,
but common thermoplastic resin films satisfy this condition.
Suitable low-melting metals for use in the present invention other than
solders include tin series metals, bismuth series metals, etc. A corrosion
resistant metal coating such as an oxidation resistant and corrosion
resistant gold coating may be formed on the surfaces of low-melting metal
coatings of the embodiments described above and below.
According to the present invention, the non-thermoplastic resin film of one
of board pieces to be assembled and the non-thermoplastic resin film of
the other board piece are adhered to each other via a thermoplastic resin
film.
Therefore, a flexible wiring board of the present invention can also be
formed by providing a contact on the surface of each metal wiring without
forming a low-melting metal coating and applying heat and pressure while
the contacts of board pieces are in contact, whereby the contacts are
bonded to electrically connect metal wirings.
Metal wirings can also be ultrasonically connected.
Reference 60 in FIG. 3 represents an ultrasonic wave apparatus used for
ultrasonic wave connection. This ultrasonic wave apparatus 60 comprises a
cylindrical ultrasonic wave generator 61, a resonator 62 transmitting
ultrasonic wave vibration to an object, a platform 66 and two guides
67.sub.1, 67.sub.2.
In this ultrasonic wave apparatus 60, guides 67.sub.1, 67.sub.2 are upright
almost perpendicularly on platform 66 and ultrasonic wave generator 61 is
fitted to guide 67.sub.1, 67.sub.2 in a horizontal position to be
vertically movable. Ultrasonic wave generator 61 is designed to rest at a
desired position on guide 67.sub.1, 67.sub.2.
The base of resonator 62 is fitted to the tip end of ultrasonic wave
generator 61. The tip end of resonator 62 is bent so that its surface is
horizontal. Reference 69 represents such a horizontal surface of the tip
end of resonator 62. Reference 81 represents the central axis of
ultrasonic wave generator 61 and resonator 62, and the central axis 81 is
designed to be horizontal together with the surface 69 of the tip end.
References 4a, 4b in FIGS. 4(a)-(d) represent board pieces to be worked by
the ultrasonic wave apparatus 60. These board pieces 4a, 4b have the same
structure as that of board piece 2 shown in FIG. 1(e) except that
low-melting metal coatings 13a, 13b are replaced with gold coatings 23a,
23b, and similar members are designated by similar references and not
explained. A process for manufacturing a second example of flexible wiring
board of the present invention using these board pieces 4a, 4b is
explained below.
A workbench 68 having a flat upper surface is provided on platform 66 and
two board pieces 4a, 4b are mounted on workbench 68 with gold coatings
23a, 23b formed on their contacts 12a, 12b being in contact with each
other.
Then, an air cylinder 63 located above resonator 62 is activated so that
ultrasonic wave generator 61 and resonator 62 vertically descend along
guides 67.sub.1, 67.sub.2 until the surface 69 of the tip end of resonator
62 comes into contact with non-thermoplastic resin film 11b of board piece
4b.
This state is shown in FIG. 4(a), and when ultrasonic wave generator 61 is
activated, ultrasonic wave vibration generated from the ultrasonic wave
generator 61 is transmitted to board pieces 4a, 4b via resonator 62.
The direction of ultrasonic wave vibration generated in ultrasonic wave
generator 61 has almost no components vertical to the surface 69 of the
tip end of ultrasonic wave generator 61 but consists of only components
parallel to central axis 81 of ultrasonic wave generator 61.
As ultrasonic wave generator 61 is horizontally oriented, ultrasonic wave
vibration is applied in the direction horizontal to the surfaces of board
pieces 4a, 4b.
During then, board piece 4a directly mounted on workbench 68 remains fixed
by frictional force against the surface of workbench 68. Thus, gold
coatings 23a, 23b are slid on each other under ultrasonic wave vibration
so that they are joined. This state is shown in FIG. 4(b), in which two
gold coatings 23a, 23b are joined to form a single layer gold coating 24.
Reference 26 represents a connection for electrically connecting board
pieces 4a, 4b. This connection 26 consists of gold coating 24 formed by
ultrasonic wave connection and contacts 12a, 12b.
Then, ultrasonic wave generator 61 is stopped and then air cylinder 63 is
activated so that resonator 62 and ultrasonic wave generator 61 ascend
along guides 67.sub.1, 67.sub.2 to remove connected board pieces 4a, 4b
from the top of workbench 68.
Then, board pieces 4a, 4b are mounted on another workbench 28 and a
heat-generating member 29 is pressed against the part including gold
coating 24 to heat thermoplastic resin films 10a, 10b, whereby
thermoplastic resin films 10a, 10b heat up and soften and after cooling, a
thermoplastic resin film 15 is formed. Thermoplastic resin films 10a, 10b
enter into connection 26 when they are heated. Board pieces 4a, 4b are
connected to each other via the resulting thermoplastic resin film 15 to
give a second example of flexible wiring board 6 of the present invention
(FIG. 4(c)).
If resonator 62 can be made to generate heat, resonator 64 is heated to a
specific temperature and brought into contact with board pieces 4a, 4b
superposed as shown in FIG. 4(a) and ultrasonic wave is applied under
pressure so that ultrasonic wave is first applied between two metal
coatings 23a, 23b to connect contacts 12a, 12b of board pieces 4a, 4b via
metal coating 24 obtained by ultrasonic wave connection.
When ultrasonic wave application is terminated while resonator 62 remains
in a pressed state, thermoplastic resin films 10a, 10b soften to give a
second example of flexible wiring board 6 of the present invention in the
same way as described above as shown in FIG. 4(d). In this case, board
pieces 4a, 4b can be assembled via thermoplastic resin films 10a, 10b
without moving them from the top of workbench 68 of ultrasonic wave
apparatus 60.
Although this second example of flexible wiring board 6 uses board pieces
4a, 4b having gold coatings 23a, 23b, gold coatings may be replaced with
non low-melting coatings based on gold and further containing other
metals. Platinum, silver and palladium coatings as well as non low-melting
coatings based on these metals and further containing other metals may
also be used.
Instead of using gold coatings or platinum coatings, board pieces 2a, 2b, 3
having low-melting metal coatings 13a, 13b, 33 such as board pieces 2a, 2b
shown in FIG. 1 or board piece 3 shown in FIG. 2 can be used to
ultrasonically connect low-melting metal coatings 13a, 13b, 33. In this
case, a flexible wiring board can be prepared by applying heat and
pressure after ultrasonic wave connection or by using a heated resonator
for applying ultrasonic wave under heat and pressure. When ultrasonic wave
is applied to board pieces 2, 3 shown in FIG. 2 under heat and pressure,
the resonator of the ultrasonic wave apparatus should preferably be
brought into contact with board piece 3 having a metal wiring (contact 32
and wiring 37) formed on non-thermoplastic resin film 31. When heat is
applied after or during ultrasonic wave application, board pieces shown in
FIGS. 5-8 can also be used.
Next, other examples of flexible wiring board of the present invention are
explained together with manufacturing processes thereof with reference to
the attached drawings.
FIG. 9(a) shows a layout for cutting H-shaped flexible wiring boards 192
from a rectangular pre-cutted substrate 190, in which four flexible wiring
boards 192 are obtained.
In contrast, three kinds of board pieces 193, 194, 195 can be closely
arranged on pre-cutted substrate 190 according to the present invention as
shown in FIG. 9(b). A flexible wiring board 196 shown in FIG. 9(c) can be
prepared by cutting and assembling these three kinds of board pieces 193,
194, 195. With the layout of board pieces 193, 194, 195 in FIG. 9(b), six
flexible wiring boards 196 can be obtained.
A process for assembling at least three board pieces 193, 194, 195 to form
a flexible wiring board 192 as described above is explained below.
References 101a, 101b, 101c in FIGS. 5(a)-5(d) represent board pieces
corresponding to the board pieces 193, 194, 195, and these board pieces
101a, 101b, 101c are assembled to form a third example of flexible wiring
board 105 of the present invention (flexible wiring board represented by
reference 105 in FIGS. 5(c), 5(d)) as follows.
Referring to FIG. 5(a), each of board pieces 101a, 101b, 101c has a
multilayer resin film consisting of a non-thermoplastic resin film 111 and
a thermoplastic resin film 115 formed on the non-thermoplastic resin film
111. On the surface of thermoplastic resin film 115 is formed a patterned
metal wiring 161.
Non-thermoplastic resin film 111 consists of a polyimide film synthesized
from an aromatic diamine and an acid anhydride, while thermoplastic resin
film 115 consists of a polyimide film synthesized from an aliphatic amine
and an acid anhydride.
Metal wiring 161 consists of a copper thin film 121 and a low-melting metal
coating (solder coating) 125 formed on the copper thin film 121. On the
top of metal wiring 125 of each board piece 101a, 101b, 101c, a polyamidic
acid film before imidation is first formed and a photoresist is applied
all over the surface, and then the photoresist is patterned by exposure
and development and the polyamidic acid film is etched according to the
pattern of the photoresist and imidated by heat treatment after removal of
the photoresist to form a non-thermoplastic protective film 151.
At openings in this protective film 151 is exposed metal wiring 161 as
shown by reference 135 as exposed regions. In regions where protective
film 151 exists, metal wiring 161 is covered with protective film 151 to
form protected regions shown by reference 131.
Referring to FIG. 5(b), two exposed regions 135 of one board piece 101a
among these board pieces 101a, 101b, 101c are opposed to exposed regions
135 of the other two board pieces 101b, 10c. Metal wiring 161 of the one
board piece 101a is brought into contact with metal wirings 161 of the
other board pieces 101b, 101c (low-melting coatings 125 on the surfaces of
metal wirings 161 are brought into contact with each other) and heat and
pressure are applied so that thermoplastic resin film 115 first softens
and thermoplastic resin film 115 below the bottom of pressed metal wiring
161 softens and enters into the gap between metal wirings 161. As a
result, the gap between metal wirings 161 is filled with the thermoplastic
resin.
As the temperature of metal wirings 161 further rises in this state,
low-melting metal coatings 125 on the surfaces of copper thin films 121
melt. However, melts of low-melting metal coatings 125 cannot scatter so
that no short circuit occurs between metal wirings 161 because the
thermoplastic resin of thermoplastic resin films 115 is filled between
metal wirings 161.
Referring to FIG. 5(c), low-melting metal coatings 125 melt and then
solidify into one piece when cooled. Reference 119 represents a
low-melting metal coating as one piece. Metal wirings 161 are electrically
and mechanically connected via the resulting one piece low-melting metal
coating 119 to form a connection 141. Non-thermoplastic resin films 111 of
board pieces 101a, 101b, 101c opposed to each other are also connected to
each other via thermoplastic resin films 115.
Thus, board pieces 101a, 101b, 101c are firmly connected via connections
141 of metal wirings 161 and thermoplastic resin films 115 to give a
flexible wiring board 105 (FIG. 5(c)).
FIG. 5(d) shows an end region of board pieces 101b, 101c where connection
141 is not formed among exposed regions 135 of board pieces 101b, 101c. In
this region, metal wiring 161 is exposed and used as an external terminal
145 for connecting flexible wiring board 105 to an outer circuit.
In this flexible wiring board 105, protective film 151 is provided on metal
wiring 161 except for connection 141 or external terminal 145 to form
protected region 131.
Next, a fourth example of flexible wiring board of the present invention is
explained.
Referring to FIG. 6(a), reference 102a, 102b, 102c represent board pieces
used for preparing a fourth example of flexible wiring board 106 of the
present invention (flexible wiring board represented by reference 106 in
FIGS. 6(d), (e)).
This board piece 102a, 102b, 102c has a multilayer resin film consisting of
a non-thermoplastic resin film 112 and a thermoplastic resin film 116
formed on the surface thereof. On the top of the thermoplastic resin film
116 is formed a patterned metal wiring 162. Metal wiring 162 consists of a
copper thin film 122 and a low-melting metal coating 126 formed on the
surface thereof.
Unlike board pieces 101a, 101b, 101c of the above third example, each board
piece 102a, 102b, 102c has no protective film on metal wiring 62.
Referring to FIG. 6(b), some of exposed regions 136 of metal wiring 162 of
one board piece 102a among board pieces 102a, 102b, 102c is opposed to
exposed regions 136 of the other two board pieces 102b, 102c.
Metal wirings 162 in the exposed regions 136 are brought into contact with
each other and heat and pressure are applied so that thermoplastic resin
films 116 first soften and flow out from the bottoms of pressed metal
wirings 162 and the gap between metal wirings 162 is filled with the
thermoplastic resin. Then, low-melting metal coatings 122 melt without
scattering, and board pieces 102a, 102b, 102c are cooled to form a
connection 142 at which metal wirings 162 are connected and fixed to each
other. This state is shown in FIG. 6(c). In this figure, reference 129
represents a low-melting metal coating formed by melting and solidifying
two low-melting metal coatings 122.
After connection 142 is formed, a resin material is applied on metal
wirings 162 exposed at the surface and opened at desired parts by exposure
and development and then baked to form a patterned protective film 152.
The region where this protective film 152 is formed constitutes protected
region 132 of exposed metal wiring 62 to give a flexible wiring board 106
with no metal wiring 162 exposed at undesired parts (FIG. 6(d)).
During patterning protective film 152, metal wiring 162 used for connection
to outer circuits remains exposed to form an external terminal 146 as
shown in FIG. 6(e).
This flexible wiring board 106 is also formed by assembling a plurality of
board pieces 102a, 102b, 102c via low-melting metal coatings 126 and
thermoplastic resin films 116, and protected by protective film 152 or
non-thermoplastic resin film 112 except for external terminal 146 of metal
wiring 162.
Next, a fifth example of flexible wiring board of the present invention is
explained.
Referring to FIG. 7(a), references 103a, 103b, 103c represent board pieces
used for preparing a fifth example of flexible wiring board (flexible
wiring board represented by reference 107 in FIG. 7(c), 7(d)) and having a
non-thermoplastic resin film 113. On the top of the non-thermoplastic
resin film 113 is formed a patterned metal wiring 163.
Metal wiring 163 consists of a copper thin film 123 and a low-melting metal
coating 127 formed on the surface thereof, and has a patterned protective
film 153 formed on the surface thereof.
Openings in protective film 153 form exposed regions 137, while metal
wiring 163 is not exposed at the surface in protected regions 133 where
protective film 153 exists. Exposed regions 137 are used for connecting
board pieces 103a, 103b, 103c to each other or to outer circuits as
described later.
A thermoplastic resin film 117 is applied on some of exposed regions 137 of
one board piece 103a among these board pieces 103a, 103b, 103c, and then
exposed regions 137 of the other two board pieces 103b, 103c are opposed
to the thermoplastic resin film 117 (FIG. 7(b)).
Then, metal wirings 161 of board pieces 103a, 103b, 103c are brought into
contact with each other via thermoplastic resin film 117 and heat and
pressure are applied so that thermoplastic resin film 117 first softens to
fill the gap between metal wirings 163.
During then, thermoplastic resin film 117 flows out from the gap between
two metal wirings 163 pressed against each other and metal wirings 163
come into direct contact with each other. As the temperature of metal
wirings 163 rises in this state, low-melting metal coatings 127 melt
without scattering, and low-melting metal coatings 127 combine when
cooled. Reference 139 represents the resulting single layer low-melting
metal coating. Metal wirings 163 are electrically and mechanically
connected via the low-melting metal coating 139. Reference 143 represents
a connection formed by low-melting metal coating 139 and metal wirings
163.
Board pieces 103a, 103b, 103c are firmly connected via connection 143 and
thermoplastic resin film 117 to give a flexible wiring board 107 (FIG.
7(c)).
In exposed regions 137 of board pieces 103b, 103c other than connection
143, metal wiring 163 remains exposed to form an external terminal 147 for
connecting this flexible wiring board to an outer circuit (FIG. 7(d)).
Next, a sixth example of flexible wiring board of the present invention is
explained.
Referring to FIG. 8(a), references 104a, 104b, 104c represent board pieces
used for preparing a sixth example of flexible wiring board (flexible
wiring board represented by reference 108 in FIGS. 8(d), (e)). Each board
piece 104a, 104b, 104c has a non-thermoplastic resin film 114 and a
patterned metal wiring 164 formed on the non-thermoplastic resin film 114.
This metal wiring 164 consists of a copper thin film 124 and a low-melting
metal coating 128 formed on the surface thereof.
Each board piece 104a, 104b, 104c has no protective film and metal wiring
164 is exposed at the surface. A thermoplastic resin film 118 is applied
on some of exposed regions 138 of one board piece 104a, and opposed to
exposed regions 138 of the other two board pieces 104b, 104c (FIG. 8(b)).
Then, metal wirings 164 in the exposed regions 138 are brought into contact
with each other and heat and pressure are applied so that thermoplastic
resin film 118 softens and then low-melting metal coatings 128 melt
without scattering to form a connection 144 at which metal wirings 164 are
connected (FIG. 8(c)). Reference 149 in this figure represents a
low-melting metal coating formed by combining two low-melting metal
coatings 128.
Then, a patterned protective film 154 is formed on the top of exposed
copper thin film 164 to give a flexible wiring board 108 with no copper
thin film 164 exposed at undesired parts (FIG. 8(d)). The surface of metal
wiring 164 is exposed at openings in protective film 154 to form an
external terminal 148 used for connection with outer circuits (FIG. 8(e)).
As described above, flexible wiring boards 105-108 of the present invention
have high strength because copper thin films 161-164 are protected by
non-thermoplastic resin films 111-114 or protective films 151-154 except
for regions of external terminals 145-148 and board pieces 101-104 are
firmly connected via connections 141-144 and thermoplastic resin films
115-118, and they can be produced with high yields because low-melting
metals 125-128 cannot scatter so that no short circuit occurs between
metal wirings 161-164.
Although the foregoing description relates to assembling board pieces of
the same type 103-106, a board piece 101a having a metal wiring 161 formed
on a thermoplastic resin film 115 as shown in FIG. 5(a) and board pieces
103b, 103c having a metal wiring 163 formed on a non-thermoplastic resin
film 113 as shown in FIG. 7 (a) may also be assembled, for example. In
this case, thermoplastic resin film 117 need not be applied on metal
wiring 163 if thermoplastic resin film 115 has a large thickness.
Although the foregoing description relates to assembling three board
pieces, the present invention is not limited thereto but widely includes
flexible wiring boards formed by assembling a plurality of board pieces
such as assembling two or four or more elements or layering three or more
elements.
Flexible wiring boards 105-108 of the present invention are highly reliable
and especially suitable for flexible wiring boards having a relative large
area and a complex shape formed by assembling three or more board pieces
because they have protective films 151-154 and metal wirings 161-164 are
exposed only at regions required to be exposed (such as external terminals
145-148).
Although solders are suitable for the above low-melting metal coating 125,
the present invention is not limited thereto but metals and metal alloys
having a melting temperature which is higher than the softening
temperatures of thermoplastic resin films but not extremely high can be
widely used. Low-melting metal coatings 125-128 need not be exposed at the
surface, but a gold thin film or the like may be formed for preventing
oxidation without any influence on melting and solidifying low-melting
metal coatings 125-128 to give a flexible wiring board by assembling board
pieces.
Low-melting metal coatings 125-128 need not be formed over the whole region
of metal wirings 161-164, but may be formed on at least regions forming
connections 141-144.
Low-melting metal coatings 125-128 need not be formed on both of copper
thin films 121-124 to be connected to each other, but one of metal wirings
161-164 to be connected to each other may have a low-melting metal coating
125-128.
Flexible wiring boards can also be obtained without necessarily having a
low-melting metal coating. When thermoplastic resin films 117, 118 applied
on metal wirings 163, 164 have anisotropic conductivity, flexible wiring
boards 107, 108 can be obtained only by bonding board pieces 103, 104
under thermal compression without melting and solidifying low-melting
metal coatings 127, 128.
As described above, when board pieces of the present invention using a
low-melting metal coating are assembled to prepare a flexible wiring
board, no melt scatters and no short circuit occurs because thermoplastic
resin films soften and fill the gap between metal wirings before the
low-melting metal melts.
Thermoplastic resin films used in board pieces and flexible wiring boards
of the present invention develop adhesiveness when they soften and return
to the original state when they are cooled, whereby non-thermoplastic
resin films of board pieces are adhered to each other via the
thermoplastic resin films. As a result, the board pieces are assembled via
the thermoplastic resin films.
Metal wirings of flexible wiring boards of the present invention should be
connected to semiconductor chips or electronic circuits.
Therefore, metal wirings can be partially exposed on flexible wiring boards
to serve as external terminals used for connecting flexible wiring boards
to outer circuits.
Regions of metal wirings neither located in assembled board pieces nor
forming external terminals can be covered with a protective film. Thus,
flexible wiring boards have high reliability and durability because metal
wirings are protected by non-thermoplastic resin films or protective
films.
In this case, two flexible boards can be electrically connected by bonding
the flexible boards under thermal compression while metal wirings of the
flexible boards are in contact with each other and partially exposed.
When a low-melting metal coating is formed on the metal wiring of at least
one of two flexible boards to be assembled and the flexible boards are
bonded under thermal compression, the low-melting metal coating melts and
then solidify by cooling to form a metallic bond between the metal wiring
and the low-melting metal coating, whereby the metal wirings are
electrically and mechanically firmly connected via the low-melting metal
coating.
However, there is no danger of solder metals or the like scattering when
metal wirings are ultrasonically connected and then board pieces are
assembled.
When two flexible boards are to be assembled, both flexible boards may have
a metal wiring formed on a thermoplastic resin film, but either one
flexible board may have a metal wiring formed on a thermoplastic resin
film depending on the thickness of the thermoplastic resin film and the
area and pitch of the part of the metal wiring used for assembling.
INDUSTRIAL APPLICABILITY
Flexible wiring boards having a complex shape can be obtained by assembling
board pieces having a simple shape.
Flexible wiring boards of the present invention are suitable for electronic
circuits because of the high reliability and durability.
*
