Fluorescent luminous tube

FIELD OF THE INVENTION

The present invention relates to a fluorescent luminous tube; and, more particularly, to a fluorescent luminous tube having an improved connecting structure for cathode filaments.

BACKGROUND OF THE INVENTION

FIG. 5A

shows a plan view (a partial cross-sectional view) of a conventional fluorescent luminous tube (or fluorescent display device), and

FIGS. 5B and 5C

depict schematic views of a connecting structure for cathode filaments thereof.

Anode electrodes

63

on which a fluorescent material is deposited are formed on an anode substrate

61

made of an insulating material such as a glass. Grids

64

are arranged between the anode electrodes

63

and filaments

60

to control electrons emitted from the filaments

60

to the anode electrodes

63

. The filaments

60

are tightly suspended between an anchor

661

and a support

662

so that a display region

65

is covered. The anchor

661

and the support

662

are fabricated by shaping, e.g., a metal plate, and have three-dimensional shapes. The filament

60

is welded at one end on a resilient filament support member of the anchor

661

and at the other end on a filament support member of the support

662

. The anchor

661

and the support

662

are fixed on the anode substrate

61

and are respectively connected to cathode wirings

671

and

672

functioning as take-out leads. Cathode wirings

671

and

672

can be formed as one body with the anchor

661

and the support

662

, respectively. A reference numeral

62

represents a side plate made of an insulating material, e.g., a glass.

FIGS. 5B and 5C

depict possible arrangements of the display region

65

and the filaments

60

as well as electrical connection of the filaments

60

to the anchor

661

and the support

662

. The filaments

60

can be arranged either in a horizontal direction as shown in

FIG. 5B

or in a vertical direction as shown in

FIG. 5C

depending on a display pattern of the anode electrodes

63

as shown in FIG.

5

A.

If the aspect ratio of the display region

65

is 1:2, the length of a filament

60

in case of

FIG. 5B

is about twice that of a filament

60

shown in FIG.

5

C.

In general, the filaments

60

are fabricated by coating a core wire, made of tungsten or tungsten alloy, with carbonate for emitting thermal electrons. If an electrical current is supplied to the filaments

60

, heat is generated in the filaments

60

due to their own resistance and the carbonate heated by the generated heat emits electrons. The temperature of the filaments

60

is normally maintained at about 600 to 650° C. In case each of the filaments

60

has a thickness of about 0.64 MG (a diameter of about 15 μm), a current of about 27 mA is required to maintain the filament temperature at about 600 to 650° C. In case where a 0.64 MG filament has a length of 25 mm, its resistance value is about 48 Ω. Accordingly, a filament voltage should be set to be 1.3 V in order to apply the current of 27 mA through the 0.64 MG filament having the length of 25 mm.

Assuming that each filament

60

in

FIGS. 5B and 5C

has the thickness of 0.64 MG and that the length of each of the filaments

60

in case of

FIG. 5C

is 25 mm, each filament

60

in an arrangement shown in

FIG. 5B

will be of a length of 50 mm and, thus, a resistance thereof will be 96 Ω. Therefore, a filament voltage in case of

FIG. 5B

should be set to be 2.6 V, i.e., twice the filament voltage required in FIG.

5

C.

As can be seen from the above, since a power source module having a different voltage should be prepared for every filament having a different length, the cost for the power source modules is increased, which in turn raises the manufacturing cost for the fluorescent luminous tube as well.

FIGS. 6A

to

6

C show various schemes conventionally employed in connecting filaments in series.

FIG. 6A

illustrates an example where three filaments

60

are connected in series, in which two anchors

6611

and

6612

and two supports

6621

and

6622

are provided. The anchor

6611

and the support

6621

are connected to cathode wirings

671

and

672

, respectively, and the anchor

6612

and the support

6622

are employed for making series connection of filaments

60

.

FIG. 6B

offers an example where five filaments

60

are connected in series, in which an anchor

6613

and a support

6623

are added to the structure shown in FIG.

6

A.

FIG. 6C

describes an example where seven filaments

60

are connected in series, in which an anchor

6614

and a support

6624

are further added to the structure illustrated in FIG.

6

B.

As shown in

FIGS. 6A

to

6

C, as the number of the filaments

60

is increased to be 3, 5 and 7, both the number of the anchors and the number of the supports are respectively required to be increased to be 2, 3 and 4, accordingly. As a result, the cost for manufacturing and installing the anchors and the supports and for mounting filaments thereon is increased, resulting in the increase of the whole manufacturing cost for the fluorescent luminous tube. Further, it is difficult to scale-down the anchors and the supports because they are required to have predetermined strength. Accordingly, a footprint for mounting the anchors and supports is increased, so that a dead space other than the display region becomes also increased, hampering the fabrication of a scaled down, thin and light-weighted fluorescent luminous tube.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a fluorescent luminous tube using a single power source for various cathode filaments having different lengths and diameters and employing a connecting structure that allows cathode filaments to be easily connected in series in a reduced installation space.

In accordance with the present invention, there is provided a fluorescent luminous tube including a plurality of cathode filaments; a multiplicity of a cathode wirings, each cathode wiring including one or more terminal portions and a wiring portion and being formed of a metal layer; and one or more intermediate portions, each being made of a metal layer, wherein the cathode filament is grouped into at least one set of one or more filaments and filaments in each set are connected in series by fixing an end portion thereof on a terminal portion or an intermediate portion by ultrasonic wire bonding or ultrasonic bonding.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:

FIGS. 1A

to

1

C show various connecting structures of cathode filaments of a fluorescent luminous tube in accordance with a first preferred embodiment of the present invention;

FIGS. 2A

to

2

C describe various connecting structures of cathode filaments of a fluorescent luminous tube in accordance with a second preferred embodiment of the present invention;

FIGS. 3A and 3B

illustrate various connecting structures of cathode filaments of a fluorescent luminous tube in accordance with a third preferred embodiment of the present invention;

FIGS. 4A

to

4

D offer plan views (cross-sectional views for side plates) of a substrate on which filaments are installed in accordance with the preferred embodiment of the present invention;

FIGS. 5A

to

5

C provide plan views (partial cross-sectional views) of a conventional fluorescent luminous tube and schematic views of a connecting structure for cathode filaments thereof; and

FIGS. 6A

to

6

C depict various schemes conventionally employed in connecting filaments in series.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A

to

1

C describe various connecting structures of cathode filaments of a fluorescent luminous tube in accordance with a first preferred embodiment of the present invention. The configuration of a fluorescent luminous tube of the present invention is identical to that of the conventional one except for a connection mechanism and a fixation mechanism of the cathode filaments.

Referring to

FIG. 1A

, a reference numeral

10

denotes a substrate made of an insulation material such as glass, ceramic or the like;

11

, cathode filaments;

12

and

13

, a couple of cathode wirings (a set of two cathode wirings);

121

and

131

, terminal aluminum layers of the cathode wirings

12

and

13

, respectively;

122

and

132

, wiring aluminum layers of the cathode wirings

12

and

13

, respectively;

14

and

15

, intermediate aluminum layers for connecting two cathode filaments

11

; and

16

, a display region. In general, the cathode filaments

11

are fabricated by coating a core wire made of tungsten or tungsten alloy with carbonate for emitting thermal electrons. The wiring aluminum layers

122

and

132

, the terminal aluminum layers

121

and

131

, the intermediate aluminum layers

14

and

15

are arranged along two opposite sides of the display region.

The wiring aluminum layers

122

and

132

, the terminal aluminum layers

121

and

131

and the intermediate aluminum layers

14

and

15

are made of a thin or thick film formed on the substrate

10

by a deposition or a screen printing process.

Each end portion (and a fixation portion around the end portion of the filament

11

, to be described later) of the cathode filaments

11

is fixed on one of the terminal aluminum layers

121

and

131

and the intermediate aluminum layers

14

and

15

by an ultrasonic wire bonding technique or an ultrasonic bonding technique to be described later.

FIG. 1A

illustrates an example where four sets of three cathode filaments

11

are prepared, wherein the three filaments

11

in each set are connected in series. The cathode filaments

11

are arranged in a vertical direction (i.e., a direction of a shorter side) of the display region

16

. As shown for comparison, by dashed lines, filaments

17

can be alternatively arranged in a horizontal direction (a direction of a longer side) of the display region

16

. The four filaments

17

are connected in parallel between wiring aluminum layers

181

and

182

.

The three filaments

11

in each set are connected in series between a terminal aluminum layer

131

of the cathode wiring

13

and a terminal aluminum layer

121

of the cathode wiring

12

via an intermediate (in view of an electrical connection) aluminum layer

14

or

15

. Accordingly, the four sets of three filaments

11

are connected in parallel between the cathode wirings

12

and

13

.

If an aspect ratio of the display region

16

is 1:3, a total length of the three filaments

11

in each set is substantially identical to a length of the single filament

17

. If the filaments

11

and the filaments

17

have an identical diameter, each set of three filaments

11

has a same resistance as that of a single filament

17

. Therefore, the resistance between the cathode wirings

12

and

13

becomes substantially identical to that between the wiring aluminum layers

181

and

182

. Therefore, a single filament power source having a predetermined voltage can be used for both the filaments

11

and filaments

17

having different lengths.

If the filament

11

has a length of 25 mm, the filament

17

is of the length of 75 mm. Therefore, when both the filaments

11

and the filaments

17

have a same thickness of about 0.64 MG (a diameter of about 15 μm), the resistance of one filament

11

is 48 Ω and that of a filament

17

becomes 144 Ω, i.e. three times as large as that of the filament

11

. A current of about 27 mA is required to be supplied to each filament

11

having the length of 25 mm in order to maintain the filament at a temperature of about 600 to 650° C. In order to apply the current of about 27 mA to the filament

11

having the length of 25 mm, a filament voltage should be set as 1.3 V. The filament voltage can be AC or DC.

On the other hand, in order to supply the current of about 27 mA to the filament

17

having the length of 75 mm, a filament voltage is required to be 3.9 V. Also, if three filaments

11

, each having the length of about 25 mm as described above, are connected in series, a power source having the filament voltage of 3.9 V can be employed as in the case of the filament

17

.

If a precision of a voltage generated from the filament power source falls within a range from −10 to 10%, a permitted fluctuation value for an output voltage of the filament power source is set to be ±0.13 V when the filament voltage is 1.3 V and ±0.39 V when the filament voltage is 3.9 V. Thus, if the three filaments

11

connected in series are utilized as one group, the permitted fluctuation value of the output voltage of the filament power source becomes three times as large as that in the case where the filaments are individually utilized. Accordingly, it becomes easier to design the power source module, resulting in a reduction of a manufacturing cost for the fluorescent luminous tube.

In case twelve filaments

11

are individually used, the twelve filaments

11

are connected in parallel and the current of about 27 mA should be applied to each of the twelve filaments

11

. However, in case the twelve filaments

11

are grouped into four sets of the three filaments

11

in each set are connected in series, only the current of about 27 mA needs to be applied to each set, so that the total current flowing in the power source module can be reduced to ⅓. Therefore, if the three filaments

11

connected in series are used, an electric power wasted between the power source module and the filaments can be reduced. Further, the amount of heat generated in the power source module also decreases, so that it becomes much easier to cool down the power source module.

FIG. 1B

shows an example where three sets of five filaments

11

are prepared, wherein the five filaments

11

in each set are connected in series between the terminal aluminum layer

131

of the cathode wiring

13

and the terminal aluminum layer

121

of the cathode wiring

12

via two intermediate aluminum layers

14

and two intermediate aluminum layers

15

.

FIG. 1C

describes an example where two sets of seven filaments are prepared, wherein the seven filaments

11

in a set are connected in series between the terminal aluminum layer

131

of the cathode wiring

13

and the terminal aluminum layer

121

of the cathode wiring

12

via three intermediate aluminum layers

14

and three intermediate aluminum layers

15

.

As clearly seen from

FIGS. 1A

to

1

C, even though the number of filaments

11

in each set is increased to 3, 5 and 7, the numbers of rows of the wiring aluminum layers

122

and

132

, the terminal aluminum layers

121

and

131

, and the intermediate aluminum layers

14

and

15

remain unchanged. In other words, even though the number of the filaments

11

in each set is increased, a set of terminal aluminum layers

121

and intermediate aluminum layers

15

can be prepared in one row and that of terminal aluminum layers

131

and intermediate aluminum layers

14

also can be provided in one row, and such increased number of filaments can be accommodated by adjusting the number of layers in each row. Accordingly, even though the number of filaments

11

in each set is increased, no additional space is required for installing the wiring aluminum layers

122

and

132

, terminal aluminum layers

121

and

131

and the intermediate aluminum layers

14

and

15

.

The wiring aluminum layers

122

and

132

are electrically connected to the terminal aluminum layers

121

and

131

, respectively. The wiring aluminum layers

122

,

132

and the terminal aluminum layers

121

,

131

can be formed either separately or simultaneously. If they are formed in one processing step, portions of the wiring aluminum layers

122

,

132

on which the filaments

11

are fixed correspond to terminal aluminum layers

121

and

131

, respectively. Further, the term ‘row’ used herein refers to not only an arrangement where involved parts are positioned in a straight line but also an arrangement where they are disposed along a substantially straight line.

FIGS. 2A

to

2

C describe connecting structures of filaments included in a fluorescent luminous tube in accordance with a second preferred embodiment of the present invention.

FIGS. 2A and 2B

provide examples where each filament set has even number of filaments connected in series, while

FIG. 2C

describes an example where there exist filament sets of even and odd number of filaments connected in series. Referring to

FIG. 2A

, arranged at one side of a display region

16

are wiring aluminum layers

132

and

212

and terminal aluminum layers

131

and

211

of cathode wirings

13

and

21

, respectively. Arranged at the other side of the display region

16

are only intermediate aluminum layers

15

. No intermediate aluminum layers are disposed at the side of the cathode wirings

13

and

21

. Two filaments

11

are connected in series between the terminal aluminum layer

131

of the cathode wiring

13

and the terminal aluminum layer

211

of the cathode wiring

21

via the one intermediate aluminum layer

15

.

Referring to

FIG. 2B

, arranged at one side of the display region

16

are the wiring aluminum layers

132

and

212

and the terminal aluminum layers

131

and

211

of the cathode wirings

13

and

21

, respectively, as well as a plurality of intermediate aluminum layers

14

. Arranged at the opposite side of the display region is only the plurality of intermediate aluminum layers

15

. Four filaments

11

are connected in series between the terminal aluminum layer

131

of the cathode wiring

13

and the terminal aluminum layer

211

of the cathode wiring

21

via the intermediate aluminum layers

14

and

15

.

Referring to

FIG. 2C

, arranged at one side of the display region

16

are the wiring aluminum layers

132

and

212

and terminal aluminum layers

1311

to

1313

and

2111

of the cathode wiring

13

and

21

, respectively, as well as a plurality of intermediate aluminum layers

14

. Prepared at the opposite side of the display region

16

are the wiring aluminum layer

122

and terminal aluminum layers

1211

and

1212

of the cathode wiring

12

and a plurality of intermediate aluminum layers

15

.

Three filaments

11

are connected in series between the terminal aluminum layer

1311

of the cathode wiring

13

and the terminal aluminum layer

1211

of the cathode wiring

12

via intermediate aluminum layers

14

and

15

. Six filaments

11

are connected in series between the terminal aluminum layer

1312

of the cathode wiring

13

and the terminal aluminum layer

2111

of the cathode wiring

21

via intermediate aluminum layers

14

and

15

. Three filaments

11

are connected in series between the terminal aluminum layer

1313

of the cathode wiring

13

and the terminal aluminum layer

1212

of the cathode wiring

12

via intermediate aluminum layers

14

and

15

.

The cathode wirings

12

and

21

respectively disposed at the two opposite sides of the display region

16

are electrically connected at either inside or outside of the fluorescent luminous tube in such a manner that they have an identical electric potential. Therefore, the three cathode wirings

12

,

13

and

21

are involved in one wiring set in this case.

In

FIG. 2C

, there are illustrated three filament sets; two of them include three filaments

11

connected in series and the other set includes six filaments

11

connected in series. In this case, the filaments

11

in the set of six are thicker than those in the other two sets of three, and the resistance of one filament in the set of six is half of that of one filaments belonging to the other two sets of three.

FIGS. 3A and 3B

describe connecting structures of filaments included in a fluorescent luminous tube in accordance with a third preferred embodiment of the present invention.

FIG. 3A

shows an example where a plurality of display regions exists in a single fluorescent luminous tube, e.g., in case bar graphs having different shapes and sizes are displayed in a rounded display region and display patterns having different shapes coexist.

FIG. 3B

depicts an example where the display region has a complicated shape.

Referring to

FIG. 3A

, reference numerals

111

and

112

indicate cathode filaments;

1211

and

1212

, terminal aluminum layers of a cathode wiring

12

;

1311

and

1312

, terminal aluminum layers of a cathode wiring

13

;

311

and

312

, intermediate aluminum layers; and

161

and

162

, display regions.

Five filaments

111

are installed in such a manner as to cover the display region

161

. The five filaments

111

are connected in series between the terminal aluminum layer

1211

of the cathode wiring

12

and the terminal aluminum layer

1311

of the cathode wiring

13

via the four intermediate aluminum layers

311

. Five filaments

112

are arranged in such a manner as to cover the display region

162

. The five filaments

112

are connected in series between the terminal aluminum layer

1212

of the cathode wiring

12

and the terminal aluminum layer

1312

of the cathode wiring

13

via the four intermediate aluminum layers

312

. The five filaments

111

have identical or different lengths and the same goes for the five filaments

112

. Though the lengths of individual filaments

111

and

112

may differ from each other, the five filaments

111

between the terminal aluminum layer

1211

and the terminal aluminum layer

1311

are set to have a same series resistance value as that of the five filaments

112

between the terminal aluminum layer

1212

and the terminal aluminum layer

1312

.

Referring to

FIG. 3B

, twelve filaments

11

are installed in such a manner as to cover a display region

16

having a complicated shape. The twelve filaments

11

, each having one of three different lengths, are grouped into four sets of three. The filaments

11

in each set have three different lengths and are arranged differently in terms of their order of lengths. The cathode wiring

12

is provided with four terminal aluminum layers

121

and the cathode wiring

13

has four terminal aluminum layers

131

. The three filaments

11

in each set are connected in series between two terminal aluminum layers

121

and

131

via two intermediate aluminum layers

14

and

15

. The series resistance of each set of filaments

11

is identical.

FIG. 4A

shows a plan view (a cross-sectional view for side plates) of a substrate

10

on which filaments

11

are installed in accordance with the preferred embodiment of the present invention.

FIG. 4B

depicts an enlarged view of a portion Z in FIG.

4

A and

FIGS. 4C and 4D

represent a cross-sectional view taken along the line X

1

—X

1

shown in FIG.

4

B.

In

FIGS. 4A

to

4

D, reference numerals

101

to

104

denote side plates made of the insulating material such as glass or ceramic;

43

, an aluminum wire bonded by the ultrasonic wire bonding technique;

44

, a spacer aluminum wire fabricated by the ultrasonic wire bonding technique; and

45

, an aluminum layer processed by an ultrasonic bonding technique.

Referring to

FIG. 4A

, a wiring aluminum layer

122

of the cathode wiring

12

is placed between the substrate

10

and the side plate

103

, and a wiring aluminum layer

132

of the cathode wiring

13

is disposed between a substrate

10

and the side plate

101

. Though it is possible that the wiring aluminum layers

122

and

132

are prepared inside the fluorescent luminous tube, such an arrangement is not preferable since in that case the wiring aluminum layers

122

and

132

occupy a certain space inside the fluorescent luminous tube, lowering the utilization efficiency of the limited inner volume of the fluorescent luminous tube. Terminal aluminum layers

121

and

131

and intermediate aluminum layers

15

and

14

also can be arranged between the substrate

10

and the side plates

103

and

101

, respectively. Respective end portions

12

a

and

13

a

of the wiring aluminum layers

122

and

132

are taken out of the fluorescent luminous tube. The end portions

12

a

and

13

a

can be replaced with those

12

b

and

13

b

shown by the dotted lines, respectively.

Referring to

FIGS. 4B and 4C

, each end portion of the filaments

11

is fixed by the aluminum wires

43

on a terminal aluminum layer

121

or

131

or an intermediate aluminum layer

14

or

15

through the use of an ultrasonic wire boding process. Further, in order to maintain the filaments

11

at a predetermined height, the spacer aluminum wires

44

are placed between a filament

11

and the base aluminum layer

121

,

131

,

14

or

15

by using the ultrasonic wire bonding technique.

As shown in

FIG. 4D

, the filament

11

can be fixed on the base aluminum layer, e.g., the terminal aluminum layer

121

, by using an aluminum layer

45

in lieu of the aluminum wire

43

in FIG.

4

C. The aluminum layer

45

is fabricated by coating a core wire of the filament

11

. The aluminum layer

45

is fixed on the base layer by using the ultrasonic bonding technique instead of the ultrasonic wire boning technique as employed in FIG.

4

C.

An insulation material such as a glass fiber or a ceramic bar can be used in lieu of the spacer aluminum wires

44

shown in

FIGS. 4A

to

4

D on the terminal aluminum layers

121

and

131

, the intermediate aluminum layers

14

and

15

, or the substrate

10

through the use of a frit glass.

In

FIGS. 4B

to

4

D, each filament

11

needs to be partially or entirely of a coil shape in order for each filament

11

to be stretched tightly by the tensile force generated by the resilience of the coil-shaped portion thereof. If a filament is partially coil-shaped, it is preferable that one end or both end portions thereof are made to be of the coil shape.

The thickness of each of the side plates

101

to

104

is preferably 3 to 5 mm; the width of each of the wiring aluminum layers

122

and

132

, 1 to 2 mm; the diameter of the aluminum wire

43

, 100 to 500 μm; the diameter of each of the spacer aluminum layers

44

, 300 to 350 μm; the thickness of each of the wiring aluminum layers

122

and

132

, the terminal aluminum layers

121

and

131

and the intermediate aluminum layers

14

and

15

, 1.2 to 2.0 μm; the thickness of each of the aluminum layers

45

, 1.2 to 2.0 μm; and the diameter of each end portion of the filaments

11

, 20 μm.

Since the filaments

11

are fixed on the terminal aluminum layers

121

and

131

and the intermediate aluminum layers

14

and

15

by employing the ultrasonic wire bonding or the ultrasonic bonding technique in the preferred embodiments in accordance with the present invention, the damage on the aluminum layers and/or crack generation in the substrate

10

or the like due to the heat generation during the bonding process can be avoided. Even in case where the terminal aluminum layers

121

and

131

and the intermediate aluminum layers

14

and

15

are thin films having a thickness of about 1.2 to 2.0 μm, no damage is incurred to those aluminum layers.

Further, since the filaments

11

are directly fixed on the terminal aluminum layers

121

and

131

and the intermediate aluminum layers

14

and

15

prepared on the substrate

10

by employing the ultrasonic wire bonding or the ultrasonic bonding technique, it becomes much easier and faster to install the filaments

11

in the preferred embodiments of the present inventions than in the conventional cases where the filaments

11

are mounted on metal parts such as a filament anchor and a filament support. Accordingly, the manufacturing cost for the fluorescent device can be decreased.

In the preferred embodiments of the present invention described above, an anode substrate or a front substrate can be employed as a substrate on which filaments are installed, as in the conventional fluorescent luminous tubes.

If the filaments are installed on the anode substrate, intermediate aluminum layers and cathode wirings including wiring aluminum layers and terminal aluminum layers can be concurrently fabricated together with anode electrodes and/or take-out wirings (anode wirings) thereof, so that a manufacturing cost can be reduced. On the other hand, if the filaments are installed on the front substrate, only the arrangement of tin oxide films (formed if necessary) needs to be considered in arranging the aluminum layers for filament installation, allowing more freedom in the arrangement thereof. This advantage is particularly useful in case the display region has a complicated shape. Further, if the filaments are installed on the front substrate, the aluminum layers are fabricated independently of the processes for the anode substrate, so that the anode substrate is still usable even for a case of a failure in the installation of the filaments. Therefore, both the throughput and the quality of the fluorescent luminous tube can be improved.

The wiring aluminum layers, the terminal aluminum layers, the intermediate aluminum layers, the aluminum wires and the aluminum layers in the preferred embodiments of the present invention can be formed of a metal, e.g., copper, gold, silver, platinum or vanadium, other than aluminum.

Even though the present invention has been described with regard to the fluorescent luminous tube, the present invention can also be applied to any other type devices, e.g., a fluorescent luminous tube for print head or a flat cathode-ray tube (CRT), which employ the principle of the fluorescent luminous tube described above.

The filaments have been described to run parallel in the above-described preferred embodiments of the present invention. However, it will be apparent to those skilled in the art that the filaments can also be arranged in a non-parallel manner.

The present invention allows a desired number of filament sets including even or odd number of filaments connected in series to be coupled in parallel by a simple method of forming wiring metal layers and intermediate metal layers of a set of cathode wirings which respectively have a terminal portion. Further, filament sets including even and odd number of filaments can also be connected in parallel by forming wiring metal layers and intermediate metal layers of three cathode wirings which respectively have a terminal portion.

As described above, the present invention provides a simple method for connecting a plurality of filaments in series. Accordingly, if the employed filaments differ from each other in length and thickness, and, thus, their resistances are also different, those filaments can be grouped into several sets of filaments connected in series in such a manner that the series resistance of each set becomes substantially identical. As a result, a single filament power source having a predetermined voltage can be used in various types of fluorescent luminous tubes employing filaments of different lengths and diameters in accordance with the present invention, which is different from conventional cases where an individual power source module is required for every filament having a different resistance. Therefore, the cost for the power source modules can be reduced.

Further, if the employed filaments have a small resistance for some reasons, e.g., due to a short length thereof, a filament power source is required to have a small voltage as well in accordance with the prior art. Moreover, since a permitted fluctuation value for an output voltage of the filament power source is reduced as the filament voltage is decreased, a high degree of precision is required to control the output voltage generated from the filament power source having the small voltage, resulting in an increase of the cost for the power source modules. In accordance with the present invention, however, the filaments having a small resistance are connected in series and are utilized as one group, so that the involved resistance is increased and a filament power source having a large voltage is utilized. If the filament voltage is increased, the permitted fluctuation value is also increased, thereby allowing for a simple control of the power source module.

Still further, arrangements of filaments can be easily modified according to various display patterns of a fluorescent luminous tube by a simple method of changing positions of terminal metal layers of cathode wirings and intermediate metal layers.

Still further, since the filaments are directly fixed on the terminal metal layers and the intermediate metal layers by employing an ultrasonic wire bonding or an ultrasonic bonding technique, and filament spacers are installed thereon by using metal wires through the use of the ultrasonic wire bonding technique, a footprint for mounting the filaments and the spacers and their installation heights can be reduced in comparison with conventional cases where anchors and supports are utilized. Therefore, it becomes easier to obtain a scaled-down, thin and light-weighted fluorescent luminous tube.

While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Fluorescent luminous tube

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