Title: Process for manufacturing multilayer flexible wiring boards
Abstract: The multilayer flexible wiring board includes first and second patterned wiring layers, a resin film interposed between a surface of the first wiring layer and a surface of the second wiring layer, and a bump connected to the surface of the second wiring layer. The resin film is adapted to form an opening when the bump is forced into the resin film and an ultrasonic wave is applied to the bump. The bump is left in the opening to electrically connect the top of the bump to the first wiring layer.
Patent Number: 6,991,148 Issued on 01/31/2006 to Kurita, et al.
| Inventors:
|
Kurita; Hideyuki (Yokohama, JP);
Watanabe; Masanao (Kanuma, JP);
Nakamura; Masayuki (Kanuma, JP);
Fukuda; Mitsuhiro (Kanuma, JP);
Usui; Hiroyuki (Kanuma, JP)
|
| Assignee:
|
Sony Corporation (Tokyo, JP);
Sony Chemicals Corp. (Tokyo, JP)
|
| Appl. No.:
|
423978 |
| Filed:
|
April 28, 2003 |
Foreign Application Priority Data
| Aug 26, 1999[JP] | 11-239358 |
| Sep 01, 1999[JP] | 11-246954 |
| Sep 01, 1999[JP] | 11-246963 |
| Current U.S. Class: |
228/110.1 |
| Current Intern'l Class: |
B23K 1/06 (20060101); B23K 20/12 (20060101) |
| Field of Search: |
228/1101,11
29/830,837
174/250,251,262,264
|
References Cited [Referenced By]
U.S. Patent Documents
| 4099038 | Jul., 1978 | Purdy.
| |
| 4604160 | Aug., 1986 | Murakami et al.
| |
| 4857482 | Aug., 1989 | Saito et al.
| |
| 5014162 | May., 1991 | Clark et al.
| |
| 5118386 | Jun., 1992 | Kataoka et al.
| |
| 5401913 | Mar., 1995 | Gerber et al.
| |
| 5478972 | Dec., 1995 | Mizutani et al.
| |
| 5600103 | Feb., 1997 | Odaira et al.
| |
| 5672400 | Sep., 1997 | Hansen et al.
| |
| 5688584 | Nov., 1997 | Casson et al.
| |
| 5736681 | Apr., 1998 | Yamamoto et al.
| |
| 5737833 | Apr., 1998 | Motomura et al.
| |
| 5886409 | Mar., 1999 | Ishino et al.
| |
| 5915753 | Jun., 1999 | Motomura et al.
| |
| 6252176 | Jun., 2001 | Kuramochi et al.
| |
| 6368896 | Apr., 2002 | Farnworth et al.
| |
| 6586686 | Jul., 2003 | Enomoto et al.
| |
| 6840430 | Jan., 2005 | Kurita et al.
| |
| Foreign Patent Documents |
| B 37-2441 | May., 1962 | JP.
| |
| A 59-1874/99 | Oct., 1984 | JP.
| |
| A 62-1209/64 | Jun., 1987 | JP.
| |
| A 64-70036 | Mar., 1989 | JP.
| |
| A 04-40566 | Apr., 1992 | JP.
| |
| A 5-21961 | Jan., 1993 | JP.
| |
| A 6-140739 | May., 1994 | JP.
| |
| A 06-1691/49 | Jun., 1994 | JP.
| |
| A 6-188560 | Jul., 1994 | JP.
| |
| A 6-216258 | Aug., 1994 | JP.
| |
| A 6-283866 | Oct., 1994 | JP.
| |
| A 6-326438 | Nov., 1994 | JP.
| |
| A 7-79075 | Mar., 1995 | JP.
| |
| A 8-125344 | May., 1996 | JP.
| |
| A 08-2159/09 | Aug., 1996 | JP.
| |
| A 8-264939 | Aug., 1996 | JP.
| |
| A 10-0162/44 | Jan., 1998 | JP.
| |
| A 10-3033/55 | Nov., 1998 | JP.
| |
| A 11-1121/47 | Apr., 1999 | JP.
| |
Primary Examiner: Edmondson; Lynne R.
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
What is claimed is:
1. A process for manufacturing a multilayer flexible wiring board by using a
first single-wiring layer board piece having a first patterned wiring layer and
a first resin film in close contact with said first wiring layer and a second single-wiring
layer board piece having a second patterned wiring layer and a plurality of bumps
connected to said second wiring layer at the bottoms to laminate said first and
second single-wiring layer board pieces into a multilayer flexible wiring board,
said process comprising:
bringing the top of each of said bumps into contact with said first resin film,
applying ultrasonic wave to at least one of said first and second single-wiring
layer board pieces under pressure,
forcing into said first resin film in contact with said each bump by vibration
force of said ultrasonic wave to form an opening,
bringing said each bump into contact with said first wiring layer,
continuing said application of ultrasonic wave to said each bump and said first
wiring layer in contact condition,
electrically and mechanically bonding said each bump and said bump contacting
said first wiring layer by the vibration force of said ultrasonic wave, and wherein
said each bump is ultrasonically vibrated in the direction along said first resin film.
2. The process for manufacturing a multilayer flexible wiring board according
to claim 1 wherein said application of ultrasonic wave is continued after the top
of said each bump comes into contact with said first wiring layer to ultrasonically
bond said each bump to said first wiring layer.
3. The process for manufacturing a multilayer flexible wiring board according
to claim 2 wherein said first and second wiring layers and said bumps include a
metal material based on copper, and either one or both of the surface of at least
the top of said each bump or the surface of said first wiring layer in contact
with at least the top of said each bump is coated with a metal material based on
one or more metals selected from gold, silver, platinum, palladium, tin, zinc,
lead, nickel or iridium.
4. The process for manufacturing a multilayer flexible wiring board according
to claim 2 wherein said application of ultrasonic wave is carried out under pressure.
5. The process for manufacturing a multilayer flexible wiring board according
to claim 1 wherein said first resin film includes a thermosetting resin and is
precured before an opening is formed by said each bump.
6. The process for manufacturing a multilayer flexible wiring board according
to claim 5 wherein said first resin film includes a thermosetting polyimide film.
7. The process for manufacturing a multilayer flexible wiring board according
to claim 1 wherein said each bump is brought into contact with said first resin
film to apply ultrasonic wave after a second resin film is provided on the side
of said second wiring layer having said bumps in such a manner that said second
resin film is in close contact with said second wiring layer and the top of said
each bump projects above said second resin film.
8. The process for manufacturing a multilayer flexible wiring board according
to claim 7 wherein at least the surface of said second resin film includes a resin
developing adhesiveness upon heating.
9. The process for manufacturing a multilayer flexible wiring board according
to claim 8 wherein said second resin film is heated during said application of
ultrasonic wave.
10. The process for manufacturing a multilayer flexible wiring board according
to claim 8 wherein at least the surface of said second resin film includes a thermoplastic
polyimide film.
11. The process for manufacturing a multilayer flexible wiring board according
to claim 1 wherein said each bump has a size expressed as the cross sectional area
parallel to said second wiring layer of 19.6×10
-8 m
2 or
less at maximum.
12. A process for manufacturing a multilayer flexible wiring board by using a
first single-wiring layer board piece having a first patterned wiring layer and
a first resin film in close contact with said first wiring layer, and a second
single-wiring layer board piece having a second patterned wiring layer and a plurality
of bumps connected to said second wiring layer at the bottoms, to laminate said
first and second single-wiring layer board pieces into a multilayer flexible wiring
board, said process comprising bringing a projection on an ultrasonic manufacturing
apparatus into contact with said first resin film, applying ultrasonic wave to
said projection to force into said first resin film to form an opening, and then
bringing the top of each of said bumps of said second single-wiring layer board
piece into contact with said first wiring layer at the bottom of said opening,
wherein the ultrasonic vibrating in a direction parallel to said flat surface
of said first resin film is applied to said each projection.
13. The process for manufacturing a multilayer flexible wiring board according
to claim 12 wherein said first wiring layer is exposed at the bottom of said opening.
14. The process for manufacturing a multilayer flexible wiring board according
to claim 12 wherein said ultrasonic manufacturing apparatus has a plurality of
said projections to form a plurality of said openings in said first resin film
by a single application of ultrasonic wave.
15. The process for manufacturing a multilayer flexible wiring board according
to claim 14 wherein said each projection is ultrasonically vibrated in the direction
along the surface of said first resin film.
16. The process for manufacturing a multilayer flexible wiring board according
to claim 12 wherein said first resin film is formed by applying a liquid raw material
on said wiring layer and curing it by heating, and said opening is formed in said
first resin film in a cured state.
17. The process for manufacturing a multilayer flexible wiring board according
to claim 12 wherein an adhesive film developing adhesiveness upon heating is applied
after said opening is formed, and said first and second single-wiring layer board
pieces are bonded together via said adhesive film.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to the field of flexible printed wiring boards,
particularly to the field of flexible printed wiring boards of multilayer structure.
2. Description of Related Art
Recently, flexible wiring boards of multilayer structure are used in many
electronic circuits.
As an example, a process for manufacturing a multilayer flexible printed wiring
board is explained. Referring to FIG. 20(
a), the reference number
311
represents a copper foil having a thickness of dozens of micrometers.
A polyimide varnish is first applied on this copper foil
311 to form a
base
film
312 consisting of a polyimide film (FIG. 20(
b)). Then, a resist
layer
313 is formed on base film
312 (FIG. 20(
c)), and resist
layer
313 is patterned via photographic processes. The reference number
331 in FIG. 20(
d) represents an opening in resist layer
313,
and base film
312 is exposed at the bottom of this opening
331.
Then, the part of base film
312 exposed at the bottom of opening
331
is etched off (FIG. 20(
e)). Then, resist layer
313 is removed to
give a patterned base film
312 (FIG. 20(
f)).
In FIG. 21(
g), base film
312 is inverted with copper foil
311
upward. A masking film
317 is applied on base film
312 (FIG. 21(
h)),
and a resist layer
315 is formed on copper foil
311 (FIG. 21(
i)).
Then, resist layer
315 is patterned via exposure and development processes.
The reference number
332 in FIG. 21(
j) represents an opening formed
by patterning in resist layer
315. Copper foil
311 is exposed at
the bottom of this opening
332.
Then, copper foil
311 at the bottom of opening
332 is etched
to pattern copper foil
311 into a first wiring layer
316 (FIG. 21(
k)).
The reference number
333 represents the part from which copper foil
311
has been removed and an opening segmenting first wiring layer
316. The top
of base film
312 is exposed at the bottom of opening
333. Resist
layer
315 is removed (FIG. 21(
l)) and a polyimide varnish is applied
on the top of first wiring layer
316 so that the polyimide varnish flows
into opening
333 in first wiring layer
316 to form a cover film
318
consisting of a polyimide film having a flat surface. A resist layer
319
is formed on the top of cover film
318 (FIG. 22(
n)) and resist layer
319 is patterned via exposure and development processes.
The reference number
334 in FIG. 22(
o) represents an opening formed
by patterning in resist layer
319. Cover film
318 is exposed at the
bottom of this opening
334.
Then, the part of cover film
318 located at the bottom of opening
334
is etched off with a metallic etching solution to pattern cover film
318
so that first wiring layer
316 is exposed at the bottom of the opening
334.
The etching solution used here is selected not to etch first wiring layer
316.
Finally, resist layer
319 is removed and followed by heat treatment
to imidate base film
312 and cover film
318, whereby a first single-wiring
layer board piece
310 is obtained (FIG. 22(
q)).
Thus obtained first single-wiring layer board piece
310 comprises first
wiring layer
316, patterned base film
312 provided on one side of
first wiring layer
316 and patterned cover film
318 provided on the
opposite side of first wiring layer
316. Opening
333 in first wiring
layer
316 is filled with cover film
318.
The reference number
380 in FIG. 23(
a) represents a second single-wiring
layer board piece to be laminated to first single-wiring layer board piece
310.
This second single-wiring layer board piece
380 comprises a base film
381
consisting of a polyimide film, a second wiring layer
386 provided on said
base film
381 and a cover film
382 provided on said second wiring
layer
386.
Said second wiring layer
386 consists of a patterned copper foil and
said cover film
382 consists of a polyimide film.
Second single-wiring layer board piece
380 has a plurality of bumps
384 connected to second wiring layer
386 at the bottoms and projecting
from cover film
382 at the tops.
First single-wiring layer board piece
310 is opposed to the plane of
second single-wiring layer board piece
380 from which the tops of bumps
384 project in parallel thereto, and bumps
384 are aligned with openings
331 in base film
312 to bring bumps
384 into contact with
the surface of first wiring layer
316, whereby first and second wiring layers
316 and
386 are connected via bumps
384.
If either one of two cover films
312,
382 includes of a thermoplastic
resin having the property of developing adhesiveness upon heating, first and second
single-wiring layer board pieces
310,
380 can be bonded together
by heating them while bumps
384 are in contact with the surface of first
wiring layer
316. The reference number
351 in FIG. 23(
b) represents
a multilayer wiring board comprising first and second single-wiring layer board
pieces
310,
380 bonded together.
The process for forming an opening by patterning a polyimide film by etching
as described above provides finer openings than laser etching or drilling so that
it is widely used in the manufacture of high-density multilayer flexible wiring
boards in which openings should be provided with narrow gaps.
However, the etching process using an alkali solution as described above
involves complex control of the temperature or state of the solution. Particularly
when etching conditions are insufficiently controlled, variation may occur in the
size of openings formed in polyimide.
Moreover, the use of a resist layer consisting of a photosensitive film
for forming an opening adds production costs.
An object of the present invention is to simplify the complex conventional process
for manufacturing a multilayer wiring board as described above and to provide a
single-layer flexible wiring board suitable for preparing a multilayer flexible
wiring board, the resulting multilayer flexible wiring board, a process for manufacturing
a multilayer flexible wiring board and an ultrasonic manufacturing apparatus suitable
for use in the manufacturing process.
SUMMARY OF THE INVENTION
In order to attain the above object, the present invention provides a process
for manufacturing a multilayer flexible wiring board by using a first single-wiring
layer board piece having a first patterned wiring layer and a first resin film
in close contact with said first wiring layer, and a second single-wiring layer
board piece having a second patterned wiring layer and a plurality of bumps connected
to said second wiring layer at the bottoms to laminate said first and second single-wiring
layer board pieces into a multilayer flexible wiring board, said process comprising
bringing the top of each of said bumps into contact with said first resin film,
applying ultrasonic wave to at least one of said first and second single-wiring
layer board pieces to force into said first resin film in contact with said each
bump to form an opening, and bringing said each bump into contact with said first
wiring layer to electrically connect said first and second wiring layers via said
each bump.
According to this aspect of the present invention, said each bump may be
ultrasonically vibrated in the direction along the surface of said first resin film.
According to the present invention, said application of ultrasonic wave
may be continued after the top of said each bump comes into contact with said first
wiring layer to ultrasonically bond said each bump to said first wiring layer.
According to the present invention, said first and second wiring layers
and said bumps may consist of a metal material based on copper, and either one
or both of the surface of at least the top of said each bump or the surface of
said first wiring layer in contact with at least the top of said each bump may
be coated with a metal material based on one or more metals selected from gold,
silver, platinum, palladium, tin, zinc, lead, nickel or iridium.
According to the present invention, said application of ultrasonic wave
may be carried out under pressure.
According to the present invention, said first resin film may include a
thermosetting resin and may be precured before an opening is formed by said each bump.
According to the present invention, said first resin film may include a
thermosetting polyimide film.
According to the present invention, said each bump may be brought into
contact with said first resin film to apply ultrasonic wave after a second resin
film is provided on the side of said second wiring layer having said bumps in such
a manner that said second resin film is in close contact with said second wiring
layer and the top of said each bump projects above said second resin film.
According to the present invention, at least the surface of said second
resin film may include a resin developing adhesiveness upon heating.
According to the present invention, said second resin film may be heated
during said application of ultrasonic wave.
According to the present invention, at least the surface of said second
resin film may consist of a thermoplastic polyimide film.
According to the present invention, said each bump may have a size expressed
as the sectional area parallel to said second wiring layer of 19.6×10
-8
m
2 or less at maximum.
The present invention also provides a process for manufacturing a multilayer
flexible wiring board by using a first single-wiring layer board piece having a
first patterned wiring layer and a first resin film in close contact with said
first wiring layer, and a second single-wiring layer board piece having a second
patterned wiring layer and a plurality of bumps connected to said second wiring
layer at the bottoms to laminate said first and second single-wiring layer board
pieces into a multilayer flexible wiring board, said process comprising bringing
a projection on an ultrasonic manufacturing apparatus into contact with said first
resin film, applying ultrasonic wave to said projection to force into said first
resin film by said projection to form an opening, and then bringing the top of
each of said bumps of said second single-wiring layer board piece into contact
with said first wiring layer at the bottom of said opening.
According to this aspect of the present invention, said first wiring layer
may be exposed at the bottom of said opening.
According to the present invention, said ultrasonic manufacturing apparatus
may have a plurality of said projections to form a plurality of said openings in
said first resin film by a single application of ultrasonic wave.
According to the present invention, said each projection may be ultrasonically
vibrated in the direction along the surface of said first resin film.
According to the present invention, said first resin film may be formed
by applying a liquid raw material on said first wiring layer and curing it by heating,
and said opening may be formed in said first resin film in a cured state.
According to the present invention, an adhesive film developing adhesiveness
upon heating may be applied after said opening is formed, and said first and second
single-wiring layer board pieces may be bonded together via said adhesive film.
The present invention also provides a multilayer flexible wiring board comprising
first and second patterned wiring layers, a first resin film interposed between
said first and second wiring layers, and a bump connected to said second wiring
layer at the bottom, wherein said first resin film has an opening formed by applying
ultrasonic wave to said bump to force into it and said bump is left in said opening
to electrically connect the top of said bump to said first wiring layer.
According to this aspect of the present invention, a plurality of said
openings may be provided and said bump may be left in said each opening.
According to the present invention, said first resin film may include a
resin developing adhesiveness upon heating.
According to the present invention, the top of said each bump and said
first wiring layer may be ultrasonically bonded to each other.
According to the present invention, the surface of the top of said each
bump or the surface of said first wiring layer to be connected to the top of said
each bump may be coated with a metal material based on one or more metals selected
from gold, silver, platinum, palladium, tin, zinc, lead, nickel or iridium.
The present invention also provides a multilayer flexible wiring board comprising
first and second patterned wiring layers, a first resin film interposed between
said first and second wiring layers, and a plurality of bumps connected to said
second wiring layer at the bottoms, wherein said first rein film has a plurality
of openings formed by applying ultrasonic wave to a projection of an ultrasonic
manufacturing apparatus to force into it and each of said bumps is located in each
of said openings to electrically connect the top of said each bump to said first
wiring layer.
According to this aspect of the present invention, said each opening may
have an area of 19.6×10
-8 m
2 or less.
The present invention also provides an ultrasonic manufacturing apparatus comprising
an ultrasonic wave generator generating ultrasonic vibration and a resonator transmitting
said ultrasonic vibration, wherein said resonator has a plurality of projections
capable of simultaneously coming into contact with a flat surface of a work.
According to this aspect of the present invention, an ultrasonic wave vibrating
in the direction parallel to said flat surface of said work may be applied to said
each projection.
According to the present invention, said each projection may have a size
expressed as the cross sectional area parallel to said second wiring layer of 19.6×10
-8
m
2 or less at maximum. When a shape of the bump having a size
as cross sectional area parallel to said second wiring board of 19.6×10
-8
m
2, or a shape of the opening having same size as said bump is
circle, for example, the diameter of circle is 5×10
-4 m or less.
When the diameter of the projection formed semisphere is 5×10
-4 m
or less, the projection height is 2.5×10
-4 m or less. Therefore,
the H
1 of bump height and projection height are 2.5×10
-4 m
or less.
According to the present invention, said ultrasonic wave generator may
be oblique to said flat surface of said work.
When said ultrasonic manufacturing apparatus is used to form a plurality of
openings in a first single-wiring layer board piece having a first patterned wiring
layer and a first resin film in close contact with said first wiring layer, said
each projection may be provided at the location corresponding to the location of
each bump on a second single-wiring layer board piece to be bonded to said first
single-wiring layer board piece.
According to this embodiment of the present invention, said resonator may
be replaceable.
The present invention also provides an ultrasonic manufacturing apparatus comprising
an ultrasonic wave generator generating ultrasonic vibration and a resonator transmitting
said ultrasonic vibration, wherein said resonator has a pressing face to be pressed
against a flat surface of a work and said resonator is oblique to said flat surface
of said work when said pressing face is pressed against said flat surface of said work.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(
a)-(
g) shows a process for manufacturing a first single-wiring
layer board piece for use in a multilayer flexible wiring board according to the
present invention.
FIG. 2(
a)-(
e) shows early steps of a process for manufacturing
a second single-wiring layer board piece for use in a multilayer flexible wiring
board according to the present invention.
FIG. 3(
f)-(
j) shows the subsequent steps.
FIG. 4(
k)-(
n) shows the subsequent steps.
FIG. 5 shows an ultrasonic manufacturing apparatus according to the present invention.
FIG. 6 shows an alternative ultrasonic manufacturing apparatus according to
the present invention.
FIG. 7(
a)-(
c) shows a process for manufacturing a multilayer flexible
wiring board according to the present invention.
FIG. 8(
a),(b) shows the step of further multiplying said multilayer flexible
wiring board.
FIG. 9(
a)-(
d) shows a process for manufacturing an alternative
single-wiring layer board piece according to the present invention and a process
for manufacturing a multilayer flexible wiring board using said single-wiring layer
board piece.
FIG. 10(
a)-(
f) shows a process for manufacturing a multilayer
flexible wiring board according to the present invention before an opening is formed.
FIG. 11(
g)-(
i) shows the step of forming an opening according
to the present invention.
FIG. 12(
j)-(
m) shows steps after an opening is formed according
to the present invention.
FIG. 13(
a),(b) shows a process for manufacturing a multilayer flexible
wiring board according to the present invention.
FIG. 14(
a),(b) shows a process for manufacturing an alternative multilayer
flexible wiring board according to the present invention.
FIG. 15 shows an alternative ultrasonic manufacturing apparatus according to
the present invention.
FIG. 16 is an enlarged view of its head portion.
FIG. 17 shows a still alternative ultrasonic manufacturing apparatus according
to the present invention.
FIG. 18 is an enlarged view of its head portion.
FIG. 19(
a)-(
d) shows embodiments of the opening according to the
present invention.
FIG. 20(
a)-(
f) shows early steps of a process for manufacturing
a single-wiring layer board piece for use in a multilayer flexible wiring board.
FIG. 21(
g)-(
l) shows the subsequent steps.
FIG. 22(
m)-(
q) shows the subsequent steps.
FIG. 23(
a),(b) shows a process for manufacturing a multilayer flexible
wiring board.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
First, a single-wiring layer board piece of the present invention and a process
for manufacturing it are explained.
The reference number
11 in FIG. 1(
a) represents a metal film consisting
of a copper foil. A polyimide varnish including a polyimide precursor is applied
on said metal film
11 to form a base film
12 including a polyimide
film (FIG. 1(
b)).
Then, a resist layer
13 is formed on the opposite side of metal film
11 (FIG. 1(
c)) and patterned. The reference number
31 in FIG.
1(
d) represents an opening in the patterned resist layer
13. Then,
resist layer
13 is used as a mask and the assembly is immersed into an etching
solution to etch metal film
11, whereby metal film
11 exposed at
the bottom of opening
31 is removed. As a result of this etching, metal
film
11 is patterned to form a first wiring layer
16 as shown in
FIG. 1(
e). During etching of metal film
11, base film
12 is
not etched.
Resist layer
13 is removed (FIG. 1(
f)), and a polyimide varnish
having the same composition as above is applied on first wiring layer
16
so that the polyimide varnish flows into opening
32 in first wiring layer
16 to form a cover film
17 including a polyimide film having a flat
surface all over the surface of first wiring layer
16.
Finally, base film
12 and cover film
17 are imidated by heat
treatment into a first single-wiring layer board piece
10 shown in FIG.
1(
g). As a result of imidation, base film
12 and cover film
17
have been cured.
Then, a second single-wiring layer board piece to be laminated to first single-wiring
layer board piece
10 is explained.
Referring to FIG. 2(
a), a metal film
81 consisting of a copper
foil is prepared and a protective film
82 is applied to the bottom of metal
film
81 while a UV-exposable mask film
83 is applied to the top.
Then, mask film
83 is patterned by photographic processes and development
processes. Metal film
81 is exposed at the bottoms of a plurality of openings
91 formed by patterning in mask film
83 (FIG. 2(
c)).
When current is applied across the assembly immersed in a copper plating solution
in this state, copper grows at the top of metal film
81 exposed at the bottom
of each opening
91 to form a bump
84 of copper in each opening
91
(FIG. 2(
d)).
Each bump
84 is connected to metal film
81 at the bottom and projects
above mask film
83 at the top. Each bump
84 grows over opening
91
above mask film
83 and becomes greater than opening
91. Each bump
84 normally has a maximum size at the part in contact with mask film
83.
Opening
91 is normally in the form of a circle having a diameter between
100 μm and 250 μm, and the maximum diameter of bump
84 taken
along the direction parallel to metal film
81 is about 200 μm for
opening
91 having a diameter of 100 μm or about 500 μm for opening
91 having a diameter of 250 μm.
Therefore, the cross area of bump
84 taken along the direction
parallel to metal film
81 is between 3.14×10
-8 m
2 and
19.6×10
-8 m
2.
Although only one bump
84 is shown in FIG. 2(
d), a plurality
of bumps
84 are formed on metal film
81 to correspond to a plurality
of openings
91.
Then, mask film
83 and protective film
82 are removed so that
a plurality of bumps
84 are upright on one side of metal film
81
as shown in FIG. 2(
e).
In this state, a carrier film
85 is applied on the opposite side to the
side on which bumps
84 are formed (FIG. 3(
f)). Then, a polyimide
varnish including a polyimide precursor is applied and dried on the side on which
bumps
84 are formed, whereby an insulating layer
87a including
a polyimide layer is formed (FIG. 3(
g))
Then, an adhesive polyimide varnish is overcoated on insulating layer
87a
to form an adhesive layer
87b, whereby a cover film
87
including a double-layer polyimide film is obtained (FIG. 3(
h)). The surface
of this cover film
87 has the property of developing adhesiveness upon heating
and insulation.
This cover film
87 is thicker on the surface of metal film
81
and thinner on the top of bump
84. Thus, the part of each bump
84
projecting above cover film
87 is exposed when an alkali solution is sprayed
on the surface of cover film
87 to etch the surface of cover film
87
(FIG. 3(
i)).
Then, carrier film
85 on the bottom of metal film
81 is separated
(FIG. 3(
j)), and instead a resist layer is formed and patterned by exposure
and development.
The reference number
88 in FIG. 4(
k) represents the resist layer
patterned to have a plurality of openings
91. The surface of metal film
81 is exposed at the bottom of each opening
91.
Metal film
81 exposed at the bottom of each opening
91 is etched
in this state from the bottom side to pattern metal film
81 in conformity
to the pattern of resist layer
88.
The reference number
86 in FIG. 4(
l) represents a second wiring
layer formed by patterning in metal film
81. The reference number
92
represents an opening segmenting second wiring layer
86.
Then, resist layer
88 is removed (FIG. 4(
m)) and a polyimide
varnish including a polyimide precursor is applied on the surface of wiring layer
86 so that the polyimide varnish flows into opening
92 in wiring
layer
86 to form a base film
89 including a polyimide film having
a flat surface. The reference number
80 in FIG. 4(
n) represents a
second single-wiring layer board piece having base film
89.
Next, a process for manufacturing a multilayer wiring board using said first
and second single-wiring layer board pieces
10,
80 is explained.
The reference number
50 in FIG. 5(
a) represents an ultrasonic manufacturing
apparatus according to the present invention.
This ultrasonic manufacturing apparatus
50 comprises a platform
56,
two guide posts
571,
572 upright on platform
56, a cylindrical ultrasonic wave generator
51 fitted to be vertically
movable to guide posts
571,
572, and a resonator
52 attached to an end of ultrasonic wave generator
51.
A flat support
58 is mounted on platform
56 and a first single-wiring
layer board piece
10 is placed on the top of support
58 with base
film
12 downward and cover film
17 upward.
The reference number
801 in FIG. 7(
a) represents a second
single-wiring layer board piece. This second single-wiring layer board piece
801
has a plurality of bumps
841 of almost the same height
in contact with cover film
17 of first single-wiring layer board piece
10
at the tops. First and second single-wiring layer board pieces
10,
801
are superposed in this state.
Resonator
52 has a head portion
54 having a flat pressing
face
59 to be contacted with a work. FIG. 5(
b) shows an enlarged
view of head portion
54. Pressing face
59 to be contacted with a
work is in parallel with the surface of support
58. When a cylinder
53
on ultrasonic manufacturing apparatus
50 is activated so that ultrasonic
wave generator
51 and resonator
52 vertically descend along guide
posts
571,
572, head portion
54 comes
into close contact with second single-wiring layer board piece
801
(FIG. 7(
b)).
When ultrasonic wave generator
51 is activated to generate ultrasonic
wave while second single-wiring layer board piece
801 is pressed
against first single-wiring layer board piece
10 by head portion
54,
the ultrasonic wave is transmitted to resonator
52 to apply ultrasonic vibration
from head portion
54 of resonator
52 to second single-wiring layer
board piece
801.
First single-wiring layer board piece
10 on support
58 is fixed
in this state so that a plurality of bumps
841 simultaneously
ultrasonically vibrate in the direction parallel to the surface of first single-wiring
layer board piece
10, whereby each bump
841 forces into
the resin constituting cover film
17 of first single-wiring layer board
piece
10 to penetrate into the cover film.
The reference number H
1 in FIG. 4(
n) represents the height
of each bump
841 above the surface of cover film
87, and
T
1 in FIG. 1(
g) represents the thickness of cover film
17
into which bump
841 penetrates. The height H
1 of each
bump
841 is greater than the thickness T
1 of cover
film
87 (H
1>T
1).
First wiring layer
16 underlies cover film
17 in contact with
bump
841. As ultrasonic wave is applied to the bump
841,
the part of cover film
17 between bump
841 and first wiring
layer
16 is softened and an opening is formed. Bump
841 is
pressed into the opening. The cover film
17 forced by the bump
841
is risen around the opening. The reference number
95 in FIG. 7(
b)
represents the part of cover film
17 to be forced by bump
841.
When the top of bump
841 comes into contact with first wiring
layer
16 and ultrasonic application continues in this state, the top of
bump
841 is ultrasonically bonded to first wiring layer
16.
When bump
841 is in contact with or connected to first wiring
layer
16, first single-wiring layer board piece
10 placed on support
58 begins to ultrasonically vibrate in synchronism with second single-wiring
layer board piece
801 so that bump
841 cannot
pierce first wiring layer
16.
When bump
841 comes into contact with first wiring layer
16,
cover film
87 of second single-wiring layer board piece
801
comes into close contact with cover film
17 of first single-wiring
layer board piece
10. Therefore, if ultrasonic wave is applied to press
second single-wiring layer board piece
801 against first single-wiring
layer board piece
10 while directly heating second single-wiring layer board
piece
801 by a heater in resonator
52 or platform
58
or heating second single-wiring layer board piece
801 via first
single-wiring layer board piece
10, heated cover film
87 develops
adhesiveness to bond cover films
87,
17 together.
As a result, first and second single-wiring layer board pieces
10,
801
are bonded together into a single multilayer flexible wiring board
41. Electric
connection between first and second wiring layers
16,
861 of
first and second single-wiring layer board piece
10,
801 is
ensured via bumps
841.
As described above, the present invention allows wiring layers to be connected
to each other by using bumps to form openings without preliminarily exposing the
wiring layers.
The height H
1 of bump
841 should be greater than
the thickness T
1 of cover film
87 to be ultrasonically forced
above first wiring layer
16 to ensure connection between each bump
841
and first wiring layer
16.
First single-wiring layer board pieces were prepared by varying the thickness
T
1 of cover film
17 above first wiring layer
16 and a
second single-wiring layer board piece having bumps
841 of 20
μm in height H
1 was laminated by the process described above to
prepare multilayer flexible wiring boards. Then the various thickness of cover
film
17 was tested for the resistance at the connection zone. The relationship
between the thickness T
1 of cover film
17 and the resistance
value at the zone connected by bumps
841 is shown in the following
Table 1.
In the following Table 1, the cover film thickness of "0" corresponds to the
case
in which cover film
17 of first single-wiring layer board piece
10
was opened to bring bumps into direct contact with the wiring layer.
| TABLE 1 |
|
| Bump height and connection resistance |
| (bump height 20 μm) |
|
| |
| Thickness of |
5 |
10 |
15 |
20 |
25 |
0 |
| cover film T1 (μm) |
| Connection |
0.5 |
0.5 |
0.5 |
∞ |
∞ |
0.5 |
| resistance (Ω) |
|
|
|
(open) |
(open) |
|
During preparation of multilayer flexible wiring boards, a load of 3-7 kg
was applied per bump
841 under ultrasonic wave application.
The thickness of cover film
87 above second wiring layer
86 having
bumps
841 is 20 μm, and therefore, the height of bump
841
from second wiring layer
86 is 40 μm. Bump
841 is
in the form of a circle having a maximum diameter of 150 μm. First wiring
layer
16 was patterned in the form of a circle of 250 μm in diameter
at the part to be connected to bump
841.
Table 1 shows that the connection resistance obtained by opening a cover film
is reproduced when the bump height H
1 is greater than the thickness
of the resin film to be forced into, or the thickness of the resin film above the
wiring layer is smaller than the height of bumps projecting from the resin film.
Next, the step of further laminating a single-wiring board piece to multilayer
flexible wiring board
41 is explained.
As shown in FIG. 8(
a), a secondary piece of second single-wiring layer
board piece
802 is superposed on base film
891 of
second single-wiring layer board piece
801 constituting multilayer
flexible wiring board
41 shown in FIG. 7(
c) with bumps
842
being in contact with said base film
891, and head portion
54 of resonator
52 is brought into contact with base film
892
of secondary piece of second single-wiring layer board piece
802.
When ultrasonic wave is applied to secondary piece of second single-wiring layer
board piece
802 under pressure in this state, bumps
842
force and penetrate into base film
891 on the top of multilayer
flexible wiring board
41.
The reference T
2 in FIG. 4(
n) represents the thickness of base
film
89 of second single-wiring layer board piece above second wiring layer
86.
This thickness T
2 is smaller than the bump height H
1 and
corresponds to the thickness of base film
891 in contact with
bump
842, so that bump
842 penetrates into
base film
891 at the site
96 located between bump
842
and wiring layer
861 to connect bump
842 to
second wiring layer
861 underlying base film
891.
The reference number
42 in FIG. 8(
b) represents thus formed multilayer
flexible wiring board having a trilayer structure. First wiring layer
16
and two other wiring layers
861,
862 are connected
via bumps
841,
842 to electrically connect
desired wiring of a plurality of wiring layers
16,
861,
862.
Although first and other wiring layers
16,
861,
862 and bumps
841,
842 consist
of copper to provide direct ultrasonic connection via copper in the foregoing embodiments,
either one or both of wiring layers and bumps may be coated with a metal having
better ultrasonic connectivity than copper such as a gold coat or solder coat.
Referring to FIG. 9(
a), the assembly of base film
12 and
first wiring layer
16 in the state of FIG. 1(
f) is first immersed
into a gold plating solution to form a gold-based metal coat
14 on the surface
of at least first wiring layer
16 by electroplating. The reference number
18 represents a first wiring layer having metal coat
14 on the surface.
Then, a polyimide varnish is applied on first wiring layer
18 to imidate
it into a cover film
17, whereby a first single-wiring layer board piece
20 having metal coat
14 as shown in FIG. 9(
b) is obtained.
FIG. 9(
c) shows that a plurality of bumps
841 of second
single-wiring layer board piece
801 are in contact with cover
film
17 of first single-wiring layer board piece
20 and that head
portion
54 of resonator
52 is pressed against base film
891
of second single-wiring layer board piece
801.
When ultrasonic vibration is given to resonator
52 in this state to ultrasonically
vibrate bumps
841 in the direction parallel to the surface of
cover film
17, bumps
841 penetrate into cover film
17
until the tops of bumps
841 come into contact with metal coat
14.
When ultrasonic wave is applied while the tops of bumps
841
are pressed against metal coat
14, the tops of bumps
841 are
ultrasonically bonded to metal coat
14. During ultrasonic connection, cover
film
871 of second single-wiring layer board piece
801
is pressed against the surface of cover film
17 of first single-wiring
layer board piece
20. Therefore, if cover film
871 of
second single-wiring layer board piece
801 is heated by a heater
in resonator
52 or platform
58 to develop adhesiveness of adhesive
layer
871b on the surface of cover film
871,
first and second single-wiring layer board pieces
20,
801 are
bonded together into a single multilayer flexible wiring board
42 as shown
in FIG. 9(
d).
Although metal coat
14 was provided on the side of first wiring layer
18 in this example, it may also be provided on the top of bump
841.
Although an adhesive layer was used to adhere single-wiring layer board
pieces into a multilayer flexible wiring board in the foregoing embodiments, a
multilayer flexible wiring board may also be formed only by connection force between
bumps and wiring layers.
Although polyimide films were used as resin films in the foregoing embodiments,
the present invention is not limited to these embodiments but also applicable to
other rein films such as polyethylene films, polyester films, epoxy films, etc.
Wiring layers may also include other metals such as aluminum instead of copper.
Although a general-purpose ultrasonic manufacturing apparatus
50
was used in the foregoing embodiments, the present invention also includes an ultrasonic
manufacturing apparatus
60 in which central axis
63 of ultrasonic
wave generator
61 and resonator
62 is inclined from the horizontal
direction as shown in FIG. 6.
In this ultrasonic manufacturing apparatus
60, head portion
64
of
resonator
62 is oblique to ultrasonic wave generator
61 and resonator
62. Head portion
64 has a flat pressing face
69, which is
designed to be horizontal when the assembly is obliquely fitted to guide posts
671,
672.
Although ultrasonic manufacturing apparatus
50 described before had
to place single-wiring layer board pieces
10,
80 on support
58,
resonator
62 cannot strike platform
68 or support
68 when
the inclination of central axis
63 from the horizontal direction is adjusted
between 5° and 60° in ultrasonic manufacturing apparatus
60. Thus,
a large-area support
68 can be used, whereby single-wiring layer board pieces
10,
80 can be easily placed.
As has been described above, the present invention can simplify the process for
manufacturing a multilayer flexible wiring board by connecting bumps to wiring
layers without providing openings in a resin film.
Although gold-based metal coat
14 was provided in the foregoing embodiments,
either one or both of the surfaces of at least the tops of bumps or the surface
of the first wiring layer in contact with at least the tops of bumps may be coated
with a metal material based on one or more metals selected from gold, silver, platinum,
palladium, tin, zinc, lead, nickel or iridium.
Next, an alternative multilayer flexible wiring board according to the present
invention and a process for manufacturing it are explained.
Referring to FIG. 10(
a), the reference number
101 represents
a metal film consisting of a copper foil of 18 μm-30 μm in thickness
having a carrier film
102 including a resin film applied to the bottom.
A photosensitive film
103 is applied to the top of this metal film
101
(FIG. 10(
b)), and photosensitive film
103 is patterned by exposure
and development (FIG. 10(
c)).
Then, patterned photosensitive film
103 is used as a mask for alkali
etching to pattern metal film
101 to form a first wiring layer
109
(FIG. 10(
d)). The reference
105 in FIG. 10(
d) represents a
groove formed by patterning in first wiring layer
109 or a part segmenting
the wiring. The top of carrier film
102 is exposed at the bottom of this
groove
105.
Then, photosensitive film
103 is separated to expose first wiring layer
109 (FIG. 10(
e)), and a polyimide precursor solution is applied on
its top to fill groove
105 with the polyimide precursor solution. Imidation
by heating in this state gives a base film
106 including a thermosetting
polyimide resin film (FIG. 10(
f)). This base film
106 has a flat
surface. The reference number
104 in FIG. 10(
f) represents a single-wiring
layer board piece having base film
106.
This single-wiring layer board piece
104 is placed as a work in an ultrasonic
manufacturing apparatus to form an opening in base film
106.
The reference
160 in FIG. 15 represents an ultrasonic manufacturing apparatus
of the present invention used for forming an opening. This ultrasonic manufacturing
apparatus
160 comprises a cylindrical ultrasonic wave generator
161,
a resonator
162 applying ultrasonic vibration to a work, a platform
166
and two guide posts
1671,
1672.
Guide posts
1671,
1672 are upright on platform
166 and ultrasonic wave generator
161 is fitted to guide post
1671,
1672 in such a manner that it can vertically move in a horizontal position.
One end of resonator
162 is fitted to
