Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2001-06-11
2002-12-03
Paladini, Albert W. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S261000, C174S262000
Reexamination Certificate
active
06489573
ABSTRACT:
This application incorporates by reference Taiwanese application Serial No. 089111796, filed Jun. 16, 2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electrode bonding structure for reducing the thermal expansion of the flexible printed circuit board during the bonding process, and more particularly to the electrode bonding structure used in the flat display substrate.
2. Description of the Related Art
A flat display substrate, such as a liquid crystal display (LCD) or a plasma display panel (PDP) substrate, uses several flexible printed circuit (FPC) boards to connect the outer driving circuit and the substrate. The control signals of the driving circuit are transmitted through the FPC board to the substrate. The substrate and the flexible printed circuit boards include a plurality of electrodes to transmit the control signals.
Referring to FIG
1
A,
1
B and
1
C, FIG
1
A shows the layout of electrodes in a conventional substrate; FIG
1
B is a cross-sectional view along the Y direction of FIG
1
A, and FIG
1
C is a cross-sectional view along the X direction of FIG
1
A. The conventional panel
100
has a glass substrate
102
and the electrodes, such as electrode
104
and
106
. These electrodes are bar-shaped and spaced apart from each other on the glass substrate
102
. The pitch between the electrodes is P, for example, P can be 300 &mgr;m. Besides, the electrodes are made of silver.
The silver electrodes of the conventional panel
100
in FIG
1
A have a problem of silver ion migration. This problem becomes more severe as time goes by and eventually resulting in a short circuit. If the resolution of the flat display is increased, the pitch between the electrodes is reduced, then the influence of the ion migration becomes more remarkable.
Referring to
FIG. 2
, it illustrates the cross-sectional diagram of the substrate and the flexible printed circuit (FPC) board before bonded. The FPC board
200
includes a polyimide layer
202
and a number of electrodes
216
. The arrangement of the electrodes
216
on the FPC board
200
is similar to that of the electrodes
218
on the glass substrate
102
. Before the bonding process, the sum of all pitches between the electrodes
216
on the FPC board
200
is A &mgr;m, and the sum of all pitches between the electrodes
218
on the glass substrate
102
is B &mgr;m. Besides, an anisotropic conductive film (ACF, not illustrated) is formed between the FPC board
200
and the panel
100
. The ACF further includes a lot of conductive particles for electrically connecting the electrodes
216
and
218
in the vertical direction.
The thermal expansion coefficients of the substrate
102
and the FPC
200
are different because the materials of the substrate
102
and the FPC
200
are different. After the bonding process, the sum of all pitches between the electrodes
216
on the FPC
200
will be changed to A′ &mgr;m and all pitches between the electrodes
218
on the substrate
102
will be changed to B′ &mgr;m. In order to bond the FPC and the substrate tightly, A′ must be equal to B′. The relations between A, A′, B, B′ are listed below.
A′=A&agr; &agr; is the thermal expansion coefficient of the FPC board
B′=B&ggr; &ggr; is the thermal expansion coefficient of the glass substrate
Since A′ equals to B′
B=A &agr;/&ggr; &agr;/&ggr; is the coefficient of thermal expansion compensation
The coefficient of thermal expansion compensation varies according to the materials of the glass substrate
102
, the anisotropic conductive film (ACF), the polyimide layer
202
, and the materials used for transmitting heat in the process. Since the materials used in the substrate
102
and the FPC board
200
will affect the coefficient of thermal expansion compensation, the design of the FPC board becomes more complicated. Further, in the manufacturing process, the coefficient of thermal compensation will be affected by environmental conditions (e.g. temperature, pressure), resulting in an inaccuracy in connecting all the electrodes
218
on the substrate
102
and all the electrodes
216
on the FPC board
200
. Therefore, the quality of the products will be affected.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an electrode bonding structure that can reduce the thermal expansion of the FPC board during the bonding process of the FPC board and the display panel. Besides, the silver ion migration problem can be solved by:
1) enlarging the ends of the electrodes and changing the position of the electrodes; and
2) covering the electrodes with a dielectric layer.
The shape of the electrodes on the substrate of the display panel and the FPC board is changed to reduce errors occurring in the bonding process.
The invention provides an electrode bonding structure comprising a substrate, a circuit board, and an anisotropic conduct film ACF. A substrate dielectric layer and an indenting pad are formed on the surface of the substrate, and the indenting pad is lower than the surface of the substrate dielectric layer by a depth H
3
. The circuit board is placed parallel to the substrate, a circuit dielectric layer and a bump pad are formed on the surface of the circuit board. The bump pad is higher than the surface of the circuit dielectric layer by a height H
1
. The ACF is placed between the substrate and the circuit board, and has a thickness H
2
. The position of the indenting pad is corresponded to that of the bump pad. Further, the height H
1
is greater than or equal to the sum of the thickness H
2
and the depth H
3
(H
1
>=H
2
+H
3
) so that the ACF above the bump pad is squeezed after the substrate and the circuit board are bonded for electrically connecting the substrate and the circuit board, and the bump pad is positioned into the indenting pad for reducing a thermal expansion of the circuit board caused during the process for bonding the substrate and the circuit board.
Another electrode bonding structure is also disclosed in the present invention. The electrode bonding structure comprises: a substrate, a circuit board, and an anisotropic conduct film (ACF). A substrate dielectric layer is formed on the substrate and a bump pad is further formed on the surface of the substrate dielectric layer. The top of the bump pad is higher than the surface of the substrate dielectric layer by a height H
1
. The circuit board is placed parallel to the substrate, a circuit dielectric layer and an indenting pad are formed on the circuit board. The inner surface of the indenting pad is lower than the circuit dielectric layer by a depth H
3
. The ACF, is placed between the substrate and the circuit board, and has a thickness H
2
. The height H
1
is greater than or equal to the sum of the thickness H
2
and the depth H
3
(H
1
>=H
2
+H
3
) such that the ACF above the bump pad is squeezed after the substrate and the circuit board are bonded for electrically connecting the substrate and the circuit board, and the bump pad is positioned into the indenting pad for reducing a thermal expansion of the circuit board caused during the process for bonding the substrate and the circuit board.
REFERENCES:
patent: 5404265 (1995-04-01), Moresco et al.
patent: 5943598 (1999-08-01), Lin
patent: 6146995 (2000-11-01), Ho
patent: 76212079 (1989-05-01), None
patent: 85114766 (1996-11-01), None
Chen Po-Cheng
Tsai Tzeng-Shii
Wu Jiun-Han
Acer Display Technology
Paladini Albert W.
Rabin & Berdo P.C.
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