Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2002-01-18
2003-07-22
Lam, Cathy (Department: 1775)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S251000, C174S254000, C428S344000, C228S110100, C228S173200, C228S208000
Reexamination Certificate
active
06596947
ABSTRACT:
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 A 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, precut 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
255
. As shown in this example, a greater number of flexible wiring boards
255
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 c
Anzai Yukio
Fukuda Mitsuhiro
Kurita Hideyuki
Shinohara Toshihiro
Watanabe Masanao
Lam Cathy
Rosenthal & Osha L.L.P.
Sony Chemicals Corp.
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