U.S. patent application number 11/728406 was filed with the patent office on 2007-07-19 for method for manufacturing a multilayer flexible wiring board.
This patent application is currently assigned to Sony Chemical & Information Device Corporation. Invention is credited to Yutaka Kaneda.
Application Number | 20070163111 11/728406 |
Document ID | / |
Family ID | 18855488 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070163111 |
Kind Code |
A1 |
Kaneda; Yutaka |
July 19, 2007 |
Method for manufacturing a multilayer flexible wiring board
Abstract
In one embodiment, the present invention provides a process for
manufacturing a multilayer flexible wiring board, which allows
individual layers of wiring boards to be precisely positioned and
to be readily stacked. A mask for exposure is prepared in which a
plurality of pattern holes corresponding to individual layers of
wiring boards of a multilayer flexible wiring board are arranged in
the direction perpendicular to the transporting direction P of
substrate. This mask for exposure is used to form a plurality of
wiring patterns corresponding to individual layers of wiring boards
of a multilayer flexible wiring board on the same sheet-like
substrate.
Inventors: |
Kaneda; Yutaka; (Tochigi,
JP) |
Correspondence
Address: |
OSHA LIANG L.L.P.
1221 MCKINNEY STREET
SUITE 2800
HOUSTON
TX
77010
US
|
Assignee: |
Sony Chemical & Information
Device Corporation
Tokyo
JP
|
Family ID: |
18855488 |
Appl. No.: |
11/728406 |
Filed: |
March 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10028624 |
Dec 20, 2001 |
7211735 |
|
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11728406 |
Mar 26, 2007 |
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Current U.S.
Class: |
29/831 ; 174/254;
29/852 |
Current CPC
Class: |
H05K 3/0082 20130101;
H05K 2201/0166 20130101; H05K 1/0393 20130101; Y10T 428/24917
20150115; H05K 3/4007 20130101; H05K 3/0002 20130101; H05K 3/064
20130101; H05K 2203/1545 20130101; H05K 3/4614 20130101; Y10T
29/49155 20150115; Y10S 428/901 20130101; H05K 3/4635 20130101;
H05K 3/002 20130101; H05K 2201/0367 20130101; H05K 2203/056
20130101; Y10T 29/49128 20150115; H05K 2203/0733 20130101; Y10T
29/49165 20150115; H05K 3/423 20130101 |
Class at
Publication: |
029/831 ;
174/254; 029/852 |
International
Class: |
H05K 3/20 20060101
H05K003/20 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 2000 |
JP |
JP2000-388816 |
Claims
1.-10. (canceled)
11. A method for manufacturing a multilayer flexible wiring board,
comprising: preparing a sheet-like flexible substrate comprising a
metal foil and a resin layer formed on the metal foil and
configured to be transported in a predetermined direction, and a
mask for exposure comprising a sheet-like mask body and a plurality
of pattern holes formed in the mask body and a group of the pattern
holes corresponding to wiring patterns of individual layers of a
multilayer flexible wiring board are directly arranged in width
direction of the mask body and a plurality of the groups of the
pattern holes corresponding to wiring patterns of the individual
layers of multilayer flexible wiring boards are directly arranged
corresponding to the mask in a transporting direction of a flexible
board on which a predetermined wiring patterns are to be formed,
placing the mask for exposure and the flexible substrate to be
opposed each other with the metal foil of the flexible substrate
facing toward the mask, and forming a stock sheet part for a
multilayer flexible wiring board by arranging a plurality of wiring
patterns in predetermined region of the flexible substrate on a
same surface of the flexible substrate through a photolithography
process including performing an exposure using the mask.
12. The method of claim 11, further comprising: transporting the
flexible substrate to the predetermined direction after forming the
stock sheet part for a multilayer flexible wiring board in the
predetermined region of the flexible substrate; and forming another
stock sheet part for a multilayer flexible wiring board in a region
different from the predetermined region on the same surface of the
flexible substrate through the photolithography process.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to processes for manufacturing
flexible wiring boards made of a polyimide for example. More
particularly, the invention relates to a technique of stacking a
plurality of layers of flexible wiring boards.
BACKGROUND OF THE INVENTION
[0002] Flexible printed wiring boards comprising a circuit formed
of a layer of a conductor such as a copper foil stacked on a
flexible insulating film are known in the art.
[0003] With recent trends toward smaller electronic components,
such flexible wiring boards involve connecting electrodes with
finer pitches and an advanced multilayer structure.
[0004] This type of multilayer flexible wiring boards have
typically been prepared by positioning each layer of wiring board
to form a wiring pattern and bonding these layers into a multilayer
structure.
[0005] With the prior art as described above, dimensional changes
may vary between layers of wiring boards due to heat shrinkage
during manufacturing processes or other factors, which means
difficulty in stacking the wiring boards to electrically connect
them.
[0006] Further, it is difficult to control dimensional changes in
each layer of wiring board by this technique.
[0007] A film-like mask for exposure is sometimes used to form a
circuit pattern in each layer of wiring board, which may add the
influence of the shrinkage of the mask for exposure itself.
[0008] What is needed, therefore, is a process for manufacturing a
multilayer flexible wiring board, which allows individual layers of
wiring boards to be precisely positioned and to be readily
stacked.
SUMMARY OF INVENTION
[0009] In one aspect, the present invention relates to a stock
sheet for a flexible wiring board comprising a flexible sheet-like
substrate, and a plurality of wiring patterns arranged in a
predetermined direction on the substrate and corresponding to
patterns on individual layers of wiring boards of a multilayer
flexible wiring board.
[0010] In another aspect, the present invention relates to a stock
sheet wherein each wiring pattern is arranged in a direction
perpendicular to a transporting direction of the substrate.
[0011] In another aspect, the present invention relates to a mask
for exposure used in a photoetching process, comprising a
sheet-like mask body, and a plurality of pattern holes arranged in
a predetermined direction in the mask body and corresponding to
individual layers of wiring boards of a multilayer flexible wiring
board.
[0012] In another aspect, the present invention relates to a stock
sheet wherein each pattern hole is arranged in a direction
perpendicular to a transporting direction of the mask body.
[0013] In another aspect, the present invention relates to a stock
sheet wherein each of the pattern holes corresponds to a wiring
pattern.
[0014] In another aspect, the present invention relates to a
process for manufacturing a multilayer flexible wiring board
comprising the step of using a mask for exposure in which a
plurality of pattern holes corresponding to individual layers of
wiring boards of a multilayer flexible wiring board are arranged in
a predetermined direction in a sheet-like mask body and exposing
the mask body to light while it is transported in a predetermined
direction.
[0015] In another aspect, the present invention relates to a stock
sheet wherein each pattern hole is arranged in a direction
perpendicular to a transporting direction of the mask body.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 (a) shows a schematic structure of a stock sheet for
a flexible wiring board according to an embodiment of the present
invention and FIG. 1 (b) shows a sectional view along A-A line in
FIG. 1 (a).
[0017] FIG. 2 (a)-(g) is a flow chart showing an example of a
process for manufacturing a flexible wiring board according to one
embodiment of the present invention (part 1).
[0018] FIG. 3 (a)-(g) is a flow chart showing an example of a
process for manufacturing a flexible wiring board according to one
embodiment of the present invention (part 2).
[0019] FIG. 4 (a) shows an example of a mask for exposure used in
one embodiment of in the present invention, and FIG. 4 (b) shows a
sectional view along B-B line in FIG. 4(a).
DETAILED DESCRIPTION
[0020] One embodiment of a flexible wiring board in accordance with
the present invention will now be described in detail with
reference to the drawings.
[0021] FIG. 1 (a) shows a schematic structure of a stock sheet for
a flexible wiring board according to the present embodiment and
FIG. 1 (b) shows a sectional view along A-A line in FIG. 1 (a).
[0022] As shown in FIG. 1 (a), a stock sheet for a flexible wiring
board 1 according to the present embodiment is transported in the
direction shown by an arrow and taken up by a roll (not shown), and
comprises a long film-like substrate 2 on which a plurality of
identical wiring patterns 3 corresponding to a plurality of layers
(6 layers in this embodiment) of a multilayer flexible wiring board
(not shown) are arranged in the direction (width direction)
perpendicular to the transporting direction P of substrate 2.
[0023] In the present embodiment, wiring patterns 3 are formed on
one side of substrate 2 and overlaid with a cover film 7 except for
lands 3a of wiring patterns 3 as shown in FIG. 1 (b).
[0024] In the present embodiment, a predetermined plural number of
wiring patterns 3 corresponding to individual layers of wiring
boards are arranged at predetermined intervals in the transporting
(longitudinal) direction of substrate 2.
[0025] On the other side of substrate 2 , bumps 11 are disposed and
connected to lands 3a of wiring patterns 3.
[0026] FIG. 2 (a)-(g) and FIG. 3 (a)-(g) are flow charts showing an
example of a process for manufacturing a flexible wiring board
according to the present invention.
[0027] As shown in FIG. 2 (a), a polyamic acid 2a is initially
applied, in this particular embodiment as a polyamic/solvent
solution, in a predetermined thickness, which may be from about 100
.mu.m to about 500 .mu.m in thickness, on a cupper (Cu) foil 4, for
example, and heated at a predetermined temperature to give a
substrate 2 made of a polyimide as shown in FIG. 2 (b). If imidized
at a high temperature, a polyimid layer of approximately 8.mu. to
40 .mu.m will be formed. In a dry condition, in this embodiment,
the layer ranges from about 10.mu. to 50.mu. in thickness.
[0028] Then, a photosensitive resist film (for example, dry film
resist SPG152 made by Asahi Chemical Industry Co., Ltd.) 5a is
applied on the surface of copper foil 4 as shown in FIG. 2 (c) and
the assembly is exposed to light as shown in FIG. 2 (d) through a
mask for exposure 6 shown in FIGS. 4 (a) and (b).
[0029] Here, FIG. 4 (a) shows an example of a mask for exposure
used in the present invention, and FIG. 4 (b) shows a sectional
view along B-B line in FIG. 4 (a).
[0030] As shown in FIGS. 4 (a) and (b), the mask for exposure 6
according to the present embodiment comprises a film-like negative
mask in which pattern holes 6a corresponding to wiring patterns 3
on individual layers of a multilayer flexible wiring board are
arranged in the direction perpendicular to the transporting
direction P of substrate 2.
[0031] In the present embodiment, a predetermined number of such
pattern holes 6a are arranged at predetermined intervals in the
transporting direction P of substrate 2.
[0032] A latent image is formed on resist film 5a by exposure
through such a mask 6 for exposure and developed with a suitable
developing solution (for example, sodium carbonate) to form resist
patterns 5 as shown in FIG. 2 (e).
[0033] Then, a suitable etching solution (for example, cupric
chloride) is used for etching to remove exposed parts 40 of copper
foil 4 as shown in FIGS. 2 (e) and (f).
[0034] Then, a suitable solution (for example, sodium hydroxide) is
used for stripping to remove resist patterns 5 as shown in FIG. 2
(g). Thus, desired wiring patterns 3 are formed on substrate 2.
[0035] Then, a cover film 7 made of the same material as that of
resist film 5a is applied on substrate 2 and wiring patterns 3 as
shown in FIG. 3 (a).
[0036] Then, cover film 7 is exposed and developed as desired with
a mask for exposure 8 having light screens 8a corresponding to
lands 3a of wiring patterns 3 as shown in FIG. 3 (b) to expose
lands 3a of wiring patterns 3 as shown in FIG. 3 (c).
[0037] Then, a photosensitive resist film 10 is applied on the
reverse side of substrate 2 as shown in FIG. 3 (d) and exposed to
light through a film-like mask or exposure 9 having negative
pattern holes 9a corresponding to lands 3a.
[0038] Then, a suitable developing solution (for example, sodium
carbonate) is used for development to form holes 10a in resist film
10 as shown in FIG. 3 (e).
[0039] A suitable alkaline etching solution (for example, TMAH
(tetramethylammonium hydroxide)) is used for etching to form via
holes 2a in substrate 2 as shown in FIG. 3 (f).
[0040] Then, electroplating is performed to fill a solder into each
via hole 2a in substrate 2 and form bumps for connection 11 as
shown in FIG. 3 (g).
[0041] Other suitable developing/etching/stripping solutions are
known in the art and no limitation on the present invention is
intended by reference to specific solutions.
[0042] According to the present embodiment, the thickness of
substrate 2 or the like scarcely varies between individual layers
of wiring boards and dimensional changes in individual layers
during manufacturing processes can be homogenized because a
plurality of wiring patterns 3 corresponding to individual layers
of wiring boards of a multilayer flexible wiring board are arranged
on the same substrate 2 as described above.
[0043] As a result, the present embodiment allows connecting
electrodes on individual layers of wiring boards to be precisely
positioned and therefore individual layers of wiring boards to be
readily stacked.
[0044] According to the present embodiment, the variation in the
thickness of substrate 2 or the like with different product lots
can be limited because wiring patterns 3 are arranged in the
direction perpendicular to the transporting direction P of
substrate 2.
[0045] Also according to the present embodiment, the structure of
the apparatus for manufacturing a multilayer flexible wiring board
can be simplified because patterns of wirings on individual layers
of wiring boards can be formed with a single mask for exposure
6.
[0046] Thus, the present embodiment allows each layer of readily
stackable wiring board for a multilayer flexible wiring board to be
efficiently prepared.
[0047] The present invention is not limited to the foregoing
embodiment, but may be modified in various aspects.
[0048] For example, the present invention is not limited to the
foregoing embodiment in which identical wiring patterns are
arranged and formed on a substrate, but different wiring patterns
may be arranged layer by layer.
[0049] Although the foregoing embodiment relates to a multilayer
flexible wiring board consisting of 6 layers of wiring boards, the
present invention is not limited to such an embodiment but may also
be applied to various multilayer flexible wiring boards comprising
2 or more layers.
[0050] The present invention can be applied not only to fully stack
wiring boards but also partially stack them.
[0051] As described above, the present invention allows individual
layers of wiring boards to be precisely positioned and to be
readily stacked.
[0052] Also according to the present invention, the structure of
the apparatus for manufacturing a multilayer flexible wiring board
can be simplified because patterns of wirings on individual layers
of wiring boards can be formed with a single mask for exposure.
[0053] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
* * * * *