Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2000-08-22
2003-06-24
Talbott, David L. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S263000, C174S264000, C361S750000
Reexamination Certificate
active
06583364
ABSTRACT:
FIELD OF THE 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.
PRIOR 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 polyimlde 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 o
Fukuda Mitsuhiro
Kurita Hideyuki
Nakamura Masayuki
Usui Hiroyuki
Watanabe Masanao
Alcala José H.
Sony Chemicals Corp.
Talbott David L.
LandOfFree
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