Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
2001-04-23
2003-07-01
Martin, David (Department: 2841)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S292000, C313S496000, C313S497000
Reexamination Certificate
active
06586873
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display panel module and a method of forming the same, and more particularly to a display panel module having an improved connection structure between a display panel and a circuit board and a method of forming the same.
2. Description of the Related Art
Flat display panels of various types such as liquid crystal display panels, plasma display panels and electroluminescent display panels have been well-known to persons skilled in the above-described field. Such a display panel comprises an insulating substrate which has electrode terminals. The display panel forms a display panel module in combination with a flexible printed circuit board for driving the display panel. The display panel and the circuit board are electrically connected to each other through the following connection structure.
The display panel has electrode terminals. The circuit board has lead terminals. The display panel and the circuit board sandwich an anisotropically conductive sheet, so that the electrode terminals and the lead terminals are spatially separated by the anisotropically conductive sheet but electrically connected to each other through the sheet. Japanese Patent No. 2964730 discloses a plasma display panel having such a connection structure.
FIG. 1
is a fragmentary cross sectional elevation view of a plasma display panel module with a conventional connection structure. The plasma display panel module comprises a plasma display panel and a flexible printed circuit board
5
. The plasma display panel has a supporting substrate
1
which has a surface, on which electrode terminals
2
and insulating barrier layers
12
are provided, wherein adjacent two of the electrode terminals
2
are separated by the insulating barrier layer
12
. The electrode terminals
2
has a lower height than the insulating barrier layer
12
. The flexible printed circuit board
5
has a surface having an alignment of lead terminals
6
which are positioned in correspondence with the electrode terminals
2
.
The plasma display panel and the circuit board
5
sandwich an anisotropically conductive film
4
which has conductive particles
15
, so that the electrode terminals
2
and the corresponding lead terminals
6
are spatially separated by the anisotropically conductive film
4
but electrically connected to each other through the conductive particles
15
in the anisotropically conductive film
4
. Since adjacent two of the conductive particles
15
are separated, the anisotropically conductive film
4
is conductive in a film thickness direction but insulative in an in-plane direction. For this reason, adjacent two of the electrode terminals
2
are electrically isolated and other adjacent two of the lead terminals
6
are also isolated.
The electrode terminals
2
are made of silver. The insulating baffler layers
12
are provided for preventing that the electrical isolation between the adjacent two of the electrode terminals
2
is deteriorated by silver migration upon a heat treatment which is carried out for a thermal compression bonding process for bonding the substrate
1
and the circuit board
5
through the film
4
. Assuming that the above insulating barrier layers
12
are not provided, then the silver migration may be caused via a migration path of a binder for the material of the film
4
, wherein the migration path is present at a gap between the adjacent two of the electrode terminals
2
.
Advanced displays have narrowed alignment-pitches of the electrode terminals and the lead terminals. Narrowing such alignment-pitches causes such an inter-electrode migration easily. The provision of the above insulating barrier layers
12
is effective to suppress the migration. The inter-electrode migration causes a short circuit between the electrode terminals. Such a migration is gradually caused during a long term operation of the display. The reason for the short circuit between the electrode terminals is not only the migration but also other factors on the manufacturing processes.
One of the other reasons is a difference in thermal expansion coefficient between the substrate
1
and the flexible printed circuit board
5
. As described above, the substrate
1
and the flexible printed circuit board
5
are bonded through the anisotropically conductive film
4
by the thermal compression bonding process. The flexible printed circuit board
5
is made of an organic material such as polyimide which has a thermal extension coefficient of about 26×10
−6
/° C. The supporting substrate
1
is made of a transparent glass material which has a thermal extension coefficient of about 5×10
−6
/° C. Namely, the flexible printed circuit board
5
has a higher thermal extension coefficient by approximate five times than the supporting substrate
1
.
Upon receipt of the heat in the thermal compression bonding process, the flexible printed circuit board
5
shows a larger expansion than the supporting substrate
1
.
FIG. 2
is a fragmentary perspective view of the display panel module after the thermal compression bonding process, wherein the electrode terminals of the substrate and the lead terminals of the circuit board have become misaligned due to those difference in thermal expansion coefficient. Before the thermal compression bonding process, the electrode terminals of the substrate and the lead terminals of the circuit board are just aligned. The thermal compression bonding process causes the substrate and the circuit board to show different thermal expansions, whereby the electrode terminals of the substrate and the lead terminals of the circuit board become different in pitch, resulting in a misalignment between them. The degree of the misalignment is larger at the opposite end portions than the center portion. A large relative displacement between the electrode terminals and the lead terminals causes a short circuit, wherein adjacent two of the electrode terminals are electrically connected to each other through the lead terminal having both edges in contact with edges of the adjacent two electrode terminals. Narrowing the terminal pitch reduces such a critical relative displacement, which causes the short circuit. Increasing the number of the terminals increases the relative displacement at the opposite end portions. The advanced display module has the serious problem with the short circuit formation.
Japanese laid-open patent publication No. 5-249479 discloses the following conventional technique for avoiding such a short circuit formation between the terminals.
FIG. 3
is a schematic perspective view of a flexible printed circuit board with a single slit at a center. The flexible printed circuit board
5
has a single slit
14
at a center position. The flexible printed circuit board
5
also has a surface on which plural lead terminals
6
are aligned. The single slit
14
extends in parallel to a longitudinal direction of the lead terminals
6
and in perpendicular to an alignment direction of the lead terminals
6
. The slit
14
reduces a thermal expansion of the circuit board
5
in the alignment direction. The slit
14
makes it necessary to do plural times alignment processes, thereby dropping the productivity of the display panel module. The formation of the slit
14
causes the increase of the manufacturing cost. The slit
14
weakens the mechanical strength of the circuit board
5
, thereby reducing the reliability of the display panel module.
In the above circumstances, it had been required to develop a novel display panel module and method of forming the same free from the above problem.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a novel display panel module free from the above problems.
It is a further object of the present invention to provide a novel bonding structure between a display panel and a circuit board free from the above problems.
It is a still further object of the present invention to provide a novel method of forming a disp
Kitazume Eiichi
Mizutani Kazuhiro
Levi Dameon E.
Young & Thompson
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