Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2002-12-02
2004-05-18
Vigushin, John B. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S255000, C174S257000, C174S258000, C174S259000, C174S261000
Reexamination Certificate
active
06737589
ABSTRACT:
This application claims the benefit of Japanese Application 2001-376,322, filed Dec. 10, 2001, the entirety of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flexible printed wiring board comprising an electrically insulating substrate, a conductive pattern having a plurality of parallel electrically conductive strips serving as signal conductors arranged on a surface of the substrate, and an electrically insulating cover adhered to the surface of the substrate such that the conductive pattern is covered with the electrically insulating cover.
2. Related Art Statements
Flexible printed wiring boards of the kind mentioned above have been used in various applications. For instance, flexible printed wiring boards are provided in camera, duplicating machine, printer and hard disk devices. Nowadays, various types of flexible printed wiring boards have been widely used in cellular phones.
FIG. 1
is a cross sectional view showing a typical structure of a known flexible printed wiring board. On a surface of a flexible insulating substrate
1
is arranged a conductive pattern
2
including a plurality of electrically conductive strips
2
-
1
,
2
-
2
—which are arranged in parallel with each other with a given line width and spacing, the electrically conductive strips serving as signal conductors. An electrically insulating cover
3
is cemented to the substrate by means of an adhesive layer
4
such that the conductive pattern
2
is covered with the electrically insulating cover
3
. Each of the conductive strips
2
-
1
,
2
-
2
—of the conductive pattern
2
has a width of, for instance 150-200 &mgr;m and the conductive strips are arranged in parallel with each other with a space of, for instance 150-200 &mgr;m. In a general manufacturing process of the conductive pattern
2
, a copper film is first formed on the substrate by electrolytic plating with a thickness of, for instance 30-40 &mgr;m and then the copper film is etched into a given pattern by a photolithography technique.
In the known flexible printed wiring board shown in
FIG. 1
, a symmetric structure is adopted in order to improve a flexibility, i.e. folding endurance. That is to say, the flexible printed wiring board is constructed such that a center of the conductive pattern
2
including a plurality of conductive strips
2
-
1
,
2
-
2
—is situated at a position which is substantially coincided with a geometrical center of the flexible printed wiring board viewed in a direction of a thickness of the flexible wiring board. It should be noted that the geometrical center may be considered as a neutral stress line of the flexible printed wiring board in a bent or folded condition. For example, when the electrically insulating substrate
1
is made of polyimide and has a thickness of 50 &mgr;m, a thickness of the electrically insulating cover
3
is set to 25 &mgr;m and a thickness of the adhesive layer
4
is also set to 25 &mgr;mm. In many applications, very severe conditions have been imposed upon the folding endurance. For instance, in a flexible printed wiring board for use in a folding type cellular phone, break down of the conductive strip should not occur even after 50,000 times of bending, preferably not even after 100,000 times of bending, and much more preferably not even after 200,000 times of bending. However, the known flexible printed wiring board illustrated in
FIG. 1
could not sufficiently satisfy such a severe condition.
When a flexible printed wiring board is used in a communicating machine such as cellular phone, it is required to transmit a higher frequency signal through the flexible printed wiring board in accordance with an increase in a communication speed. In such a high frequency application, in order to transmit a high frequency signal efficiently, accurate impedance matching is required. To this end, successive conductive strips of a conductive pattern are used alternately as signal lines and ground lines. However, in the known flexible printed wiring board shown in
FIG. 1
, impedance matching could not be attained accurately. In order to effect the impedance matching accurately, the spacing between successive conductive strips of the conductive pattern
2
has to be controlled precisely. However, this control is very difficult. Particularly, in recent cellular phones, it is required to set an impedance within a range of 50&OHgr;±10%, but the impedance of the flexible printed wiring board could not be fit within such a narrow range.
FIG. 2
is a cross sectional view depicting another known flexible printed wiring board, in which portions similar to those shown in
FIG. 1
are denoted by the same reference numerals used in FIG.
1
. Also in this known flexible printed wiring board, conductive strips
2
-
1
,
2
-
2
—having a given line width of a conductive pattern
2
are arranged in parallel with each other at a given spacing on a surface of a flexible electrically insulating substrate
1
, and an electrically insulating cover
3
is secured to the surface of the substrate
1
by means of an adhesive layer
4
such that the conductive pattern
2
is covered with the electrically insulating cover
3
. The conductive strips
2
-
1
,
2
-
2
—alternately serve assignal lines and ground lines. The conductive strips
2
-
1
,
2
-
3
,
2
-
5
—serving as signal lines are independent form each other, but the conductive strips
2
-
2
,
2
-
4
,
2
-
6
—serving as ground lines are commonly connected to a ground sheet or earth sheet
6
by means of vias
5
formed by embedding an electrically conductive material in via holes formed in the electrically insulating substrate
1
. The ground sheet
6
is covered with an electrically insulating cover
7
. This type flexible printed wiring board is disclosed in a Japanese Patent Specification No. 2,549,213.
In the conventional flexible printed wiring board illustrated in
FIG. 2
, since the ground sheet
6
is arranged below the signal lines, precise impedance matching can be performed. However, the structure is rather complicated and the manufacturing process is also cumbersome, and the cost is liable to be high. Moreover, a decrease in life time due to repeated bending is large, and the flexible printed wiring board could not be used for applications in which a folding endurance should be maintained after more than several tens of thousands times of bending.
In the known flexible printed wiring boards illustrated in
FIGS. 1 and 2
, the conductive strips
2
-
1
,
2
-
2
,
2
-
3
—arranged on the same plane are used alternately as signal lines and ground lines, and thus a utilization efficiency of a surface area of the flexible printed wiring board for the signal transmission is low. Due to the high performance of electronic devices, the amount of signal to be transmitted through the flexible printed wiring board becomes larger and larger. However, in the known flexible printed wiring boards shown in
FIGS. 1 and 2
, if the number of conductive strips is increased, the width of the wiring boards has to be larger and a high density package could not be attained. Alternatively, if the number of flexible printed wiring boards to be used is increased, the whole structure becomes large and complicated and the cost is increased. Moreover, the folding endurance becomes lower and the flexible printed wiring boards could not be used in applications in which the folding endurance should not be lost after several tens of thousands times of bending.
SUMMARY OF THE INVENTION
The present invention has for its object to provide a novel and useful flexible printed wiring board, in which the impedance matching can be attained easily and precisely without decreasing the amount of signal to be transmitted and without lowering the folding endurance, while the flexible printed wiring board can be manufactured in a simple and less expensive manner.
It is another object of the invention to provide a flexible printed wiring board in which impedance matching can be attained easily and prec
Adachi Takao
Inoue Kazuyoshi
Burr & Brown
NGK Insulators Ltd.
Vigushin John B.
LandOfFree
Flexible printed wiring board does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Flexible printed wiring board, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flexible printed wiring board will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3262719