Flexible circuit board and method of fabricating the same

Details Flexible circuit board and method of fabricating the same Flexible circuit board and method of fabricating the same

2002-04-24

2004-05-18

Arbes, Carl J. (Department: 3729)

Metal working

Method of mechanical manufacture

Fluid pattern dispersing device making, e.g., ink jet

C029S831000, C029S846000, C029S884000, C347S050000, C427S096400

Reexamination Certificate

active

06735865

ABSTRACT:

This application incorporates by reference of Taiwan application Serial No. 90109954, filed Apr. 25, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to a flexible circuit board and the fabrication of the same, and more particularly to a method of fabricating a flexible circuit board by using photo-polymer.
2. Description of the Related Art
Flexible circuit boards used in the cartridge of an ink-jet printer serve as medium to lead the driving current to the chip for ink jetting. The driving current drives the cartridge and enables the cartridge to jet ink.
FIG. 1
shows a conventional flexible circuit board and its relative position to the dimple of the printer. Polyimide (PI) is a commonly used substrate
104
for the conventional flexible circuit board. Copper (Cu) and gold (Au) are two widely used materials for the conductive traces
106
in the flexible circuit board. The dimples
110
of the printer circuit contact the conductive traces
106
through holes
108
formed by tape automated bonding (TAB).
Etching and punching are two typical TAB manufacturing processes. Etching process is characterized by etching the tape while the punching process is characterized by punching the tape to form the holes.
FIGS.
2
A~
2
J illustrate the conventional etching process. On the substrate
202
, such as polyimide (PI), a copper film
204
with a thickness of about 100 Å is formed by sputtering. On the bottom side of the substrate
202
and over the copper film
204
, photo-resistors (PR)
206
are formed. After exposing and developing the PRs
206
, the patterns of the holes and the conductive traces are defined. Next, as shown in
FIG. 2F
, on the side of substrate
202
with the exposed copper film
204
, a copper layer
208
with several &mgr;m is plated. Then, as shown is
FIG. 2G
, the substrate
202
is etched to form holes
210
at the bottom side. The photo-resistors at both sides are then removed, as shown in FIG.
2
H. Then, as shown in
FIG. 2I
, by a photolithography process, including steps of forming a photo-resister layer, exposing, developing and etching, the copper film
204
not covered by the copper layer
208
is removed. Finally, as shown in
FIG. 2J
, an insulation layer
212
is formed over the copper layer
208
for the purpose of protection.
The conventional etching process has the following drawbacks: time consuming, producing thick and sticky precipitate and large amount of wastewater, high cost and low yield rate.
FIGS. 3A
to
3
I show the conventional punching method to form holes on an insulation layer.
As shown in
FIGS. 3A and 3B
, an adhesive layer
304
is coated on the substrate
302
. Then, the substrate
302
coated with the adhesive layer
304
is punched to form holes
306
. Next, a copper layer
308
is adhered over the substrate
302
coated with the adhesive layer
304
. Then, as shown in
FIGS. 3E
to
3
H, a photo-resistor layer
310
is formed on the copper layer
308
. After the photolithography process, including exposing, developing and etching, the pattern of the copper layer
308
is defined. Finally, as shown in
FIG. 3I
, an insulation adhesive layer
312
is formed on one side of the copper layer for the purpose of protection.
Compared with the etching process as mentioned before, this punching process is shorter in procedure, no problem of wastewater and lower cost. However, the intervals between each two holes are large and hard to reduce. So that, less holes can be formed in the same area, which therefore influences the precision contact between the printer and the TAB. Further more, the punching step could easily cause the breakage of the substrate and thus reduce the yield and increase the cost.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a flexible circuit board and a method of fabricating the same without having the problems of producing contaminating developer but with the advantages of shorter procedure, lower cost, high hole resolution, and high yield rate, which is suitable for mass production.
An improved and simplified process of forming a flexible circuit board for ink jetting comprises the steps of: providing an insulation tape; forming conductive traces on the insulation tape; and forming a photo-polymer layer filling between the conductive traces, wherein parts of the conductive traces are exposed to form a plurality of contacts. The material of the insulation tape can be polyimide, Teflon, polyamide, polymethylmethacrylate, polycarbonate, polyester, polyamide polyethylene-terephthalate copolymer, or any combination of the above materials. The material of the photo-polymer layer can be solder mask or polyimide.
It is another object of the invention to provide a flexible circuit board for ink jetting, comprising: an insulation tape as a substrate; a plurality of conductive traces on the insulation tape; and a photo-polymer layer filling between the conductive traces, wherein parts of the conductive traces are exposed to form a plurality of contacts.
Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.


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patent: 4740532 (1988-04-01), May et al.
patent: 4775573 (1988-10-01), Turek
patent: 5408738 (1995-04-01), Schantz et al.
patent: 5521425 (1996-05-01), Deeney
patent: 5531020 (1996-07-01), Durand et al.
patent: 6072236 (2000-06-01), Akram et al.
patent: 6309915 (2001-10-01), Distefano
patent: 296536 (1997-01-01), None
patent: 350785 (1999-01-01), None
Korsten, G.H., Photosensitive Soldering Masks. In: Circuit Board 86, vol. 1, Production of circuit boards today, VDI/VDE-Gesellschaft Feinwerktechnik, Dusseldorf, 1986, pp. 84-91.
Hummel, M., Introduction into the circuit board technology, Eugen Lenze Verlag, Saulgau/Wurtt., 1985, pp. 118-119.
Technical Information Du Pont, Pyralux PC 1000, 2000.

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