Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2000-01-31
2004-04-06
Abrams, Neil (Department: 2839)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
Reexamination Certificate
active
06717064
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the technical field of flexible printed wiring boards. More particularly, it relates to a technique for producing flexible printed wiring boards enabling the formation of fine conductive bumps.
BACKGROUND OF THE INVENTION
There have been frequently employed flexible printed wiring boards carrying desired circuit patterns printed thereon. In recent years, flexible printed wiring boards in various shapes are required corresponding to the shapes of the parts where these flexible printed wiring boards are to be used.
FIG. 11
a
shows an arrangement plan for cutting out T flexible printed wiring boards
152
from a rectangular master sheet
150
. In this case, six flexible printed wiring boards
152
can be obtained.
In cutting out specially shaped flexible printed wiring boards as
152
in the above case, however, it is frequently observed that the master sheet
150
is much wasted.
In the conventional art, therefore, attempts have been made to take a flexible printed wiring board in a complicated shape apart into elemental pieces in simple shapes and then bond these pieces together to give a flexible printed wiring board. In
FIG. 11
c
, a flexible printed wiring board
155
having the same shape as the flexible printed wiring board
152
is formed by bonding two rectangular elemental pieces
153
and
154
to each other.
As
FIG. 11
b
shows, the master sheet
150
can be efficiently utilized by cutting out the elemental pieces
153
and
154
in simple shapes therefrom. In the case of
FIG. 11
b
, eight elemental pieces
153
and
154
can be respectively obtained. By bonding these pieces to each other, therefore, eight flexible printed wiring boards
155
can be formed. Namely, the flexible printed wiring boards can be thus obtained in a larger number than the case when the T flexible printed wiring boards
152
are directly cut out.
To bond plural elemental pieces to each other to thereby form a flexible printed wiring board, it is necessary to mechanically and electrically connect these elemental pieces to each other.
The elemental pieces
153
and
154
as described above are connected to each other via conductive bumps preliminarily formed on the master sheet
150
. Now, a method for producing the master sheet
150
by the conventional art will be described.
In
FIG. 10
a
,
113
stands for a supporting film made of polyimide and a metal wiring circuit
112
made of a patterned copper foil is adhered onto the surface of the supporting film
113
. Further, a cover lay
111
made of a polyimide film is adhered onto the copper foil
112
.
First, the cover lay film
111
is irradiated at the definite position with laser beams
114
(
FIG. 10
b
) to form plural openings
115
(
FIG. 10
c
) (
FIG. 10
c
shows only one opening
115
.). The supporting film
113
is provided with connecting openings
123
in which the bottom face of the metal wiring circuit
112
is exposed (only one connecting opening
123
is shown in each
FIG. 10
a~d
). In each opening
115
formed above, the surface of the metal wiring circuit
112
is exposed.
Subsequently, a protective film is formed on the back face of the supporting film
113
to protect the connecting openings
123
. After copper-plating, the protective film is stripped off. Thus, copper grows within each opening
115
by the copper-plating and thus conductive bumps
116
are formed (
FIG. 10
d
).
From the master sheet
150
in the above-described state, elemental pieces
153
and
154
are cut out. In
FIG. 10
e
,
153
and
154
stand for the elemental pieces thus cut out wherein members of these two elemental pieces
153
and
154
are each distinguished from the corresponding one by a or b.
The conductive bump
116
b
of the elemental piece
154
(i.e., one of the two elemental pieces
153
and
154
) is located toward the connecting opening
123
a
of the other elemental piece
153
. The tip of the conductive bump
116
b
is brought into contact with the metal wiring circuit
112
a
exposed in the connecting opening
123
a
via an anisotropic conductive film
160
. Thus, these two elemental pieces
153
and
154
are adhered to each other due to the anisotropic conductive film
160
thereby giving a specially shaped flexible printed wiring board
155
.
The metal wiring circuits
112
a
and
112
b
serving as two layers of this flexible printed wiring board
155
are electrically connected to each other via conductive particles dispersed in the anisotropic conductive film
160
, while the two elemental pieces
153
and
154
are adhered to each other owing to the adhesiveness of the anisotropic conductive film
160
.
When a semiconductor chip such as an integrated circuit device is to be packaged in the above-described flexible printed wiring board
155
, the anisotropic conductive film is located on the conductive bump
116
a
and then a bonding pad of the semiconductor device is brought into contact with the conductive bump
116
via the anisotropic conductive film followed by bonding. The inner circuit of the semiconductor device is connected to the metal wiring circuits
112
a
and
112
b
via the conductive particles in the anisotropic conductive film and the conductive bumps
116
a
and
116
b.
By adhering such elemental pieces as the above-described ones
153
and
154
, it is possible to obtain flexible printed wiring boards in a desired shape which are thin, light and freely bendable as the one
155
. Therefore, this technique has been frequently employed in recent years.
When the openings
115
are formed by using laser beams
114
as in the above case, however, the residue of the polyimide film
111
remains in the surface of the metal wiring circuit
112
exposed on the bottom of the openings
115
. In the conventional art, therefore, the elemental piece is soaked in a chemical solution, after the formation of the openings
115
, so as to eliminate the residue therefrom. As the openings
115
become finer, however, the chemical solution can hardly enter the openings
115
and thus the residue can be hardly eliminated.
When the residue cannot be eliminated, the copper deposition speed varies from opening to opening and, in its turn, uniform conductive bumps
116
cannot be formed.
Since the opening
115
is formed by irradiating a rigid polyimide film (i.e., the cover lay
111
) with laser beams
114
, the opening size varies, when the opening is fine (diameter about 40 to 50 &mgr;m). As a result, the diameter and height of the thus formed conductive bump varies, which causes a contact failure with the semiconductor. Although attempts have been made recently to form finer opening
115
, it is difficult to stop down the high output laser beams
114
. It is therefore impossible to form the opening
115
having diameter less than 40 &mgr;m.
Moreover, there arises another problem that the adhesion of the elemental pieces
153
and
154
to each other with the anisotropic conductive film
160
makes the flexible printed wiring board
155
expensive.
SUMMARY OF THE INVENTION
The present invention, which has been made to overcome the above-described troubles encountering in the prior art, aims at providing a flexible printed wiring board at a low cost by using finely patterned elemental pieces.
To achieve those objects, the present invention relates to an elemental piece of a flexible printed wiring board having a metal wiring circuit patterned into a definite shape, a supporting film located in the side of one face of said metal wiring circuit, and a resin film located in the side of the other face of said metal wiring circuit, wherein said supporting film is provided with at least one connecting opening in which the surface of said metal wiring circuit is exposed and at least one conductive bump connected to said metal wiring circuit projects on said resin coating.
The present invention relates to said elemental piece, wherein said resin film surface has an adhesiveness.
The present invention relates to said elemental piece, wherein said supporting film is made of polyimide.
T
Hishinuma Hiroyuki
Kurita Hideyuki
Nakamura Masayuki
Namiki Hidetsugu
Taniguchi Masato
Abrams Neil
Dinh Phuong K T
Oliff & Berridg,e PLC
Sony Chemicals Corp.
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