Variable inductance element

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable inductance element, and more particularly, to a variable inductance element for use in a mobile communication device such as a mobile telephone or other suitable mobile communication device.

2. Description of the Related Art

In recent years, the size of mobile communication devices such as portable telephones has been substantially decreased, and demands for reducing the size of electronic components for use in the devices has substantially increased. Further, as higher frequencies are used in mobile communication devices, the circuits of the devices become more complex, and moreover, electronic components to be mounted in the devices must have uniform characteristics and high precision.

However, even where each electronic component included in a circuit has parameters with uniform characteristics and high precision, deviations in the parameters of the respective mounted electronic components have an overall or combined effect, so that in some cases, a desired function can be performed. Hence, some of the parameters of the electronic components included in an electronic circuit are variable, if necessary. By finely adjusting the parameters of some of the electronic components, a desired function of the circuit can be performed.

As a conventional trimming method for electronic components of the type described above, a method of trimming a variable inductance component, for example, as shown in

FIG. 4

has been generally known. A variable inductance element

55

includes a trimming area

53

provided on the surface of an insulating substrate

50

, connected to external electrodes

51

and

52

, which is arranged to function as an inductor. The trimming area

53

is irradiated with a laser beam emitted from a laser trimming machine (not shown) while the beam is linearly moved. The trimming area

53

is partially removed corresponding to the movement track of the laser beam, so that a linear trimming groove

54

is produced. Accordingly, the area of the trimming area

53

is altered such that the inductance of the trimming area

53

is finely adjusted.

In the conventional variable inductance element

55

, if the area of the trimming area

53

is relatively small, the variable range of the inductance is decreased, so that the circuit cannot be finely adjusted. Therefore, the trimming area

53

must have a large area. On the other hand, when a high precision laser trimming machine is used, the groove width (trimming width) of the trimming groove

54

produced by trimming once is relatively thin. For this reason, when a wide trimming width is required, irradiation with a laser beam must be repeated while the irradiation position is moved in parallel. Hence, the time required to achieve the fine adjustment is substantially increased.

Accordingly, a variable inductance element

65

is shown in FIG.

5

. The variable inductance element

65

includes an inductor pattern

61

provided on the surface of an insulating substrate

50

and connected to external electrodes

51

and

52

. The inductor pattern

61

is a ladder-shaped electrode including a U-shaped frame portion

61

a

and a plurality of lateral bars

61

b

arranged to cross two arms of the U-shaped frame portion

61

a

to be trimmed for adjustment of the inductance. The variable inductance element

65

is mounted on a printed circuit board or other suitable substrate, and is irradiated with a laser beam from above the variable inductance element

65

, so that a trimming groove

54

is produced in the inductance element

65

and simultaneously cuts the lateral bars

61

b

of the inductor pattern

61

individually and sequentially. Accordingly, the inductance between the external electrodes

51

and

52

can be altered in a stepwise manner.

The inductance element

65

has improved cutting workability, since the lateral bars

61

b

are arranged at relatively wide equal intervals. However, the amount of change of the inductance, caused every time one lateral bar

61

b

is cut, is relatively large, since all of the lateral bars

61

b

have an equal length. For this reason, in the inductance element

65

, the inductance cannot be altered equally in a stepwise manner. That is, fine adjustment of the inductance is difficult.

To solve this problem, a variable inductance element

75

is shown in FIG.

6

. The variable inductance element

75

has an inductor pattern

71

including a U-shaped frame portion

71

a

and a plurality of lateral bars

71

b

extending across two arms of the U-shaped frame portion

71

a

. The lateral bars

71

b

are arranged at intervals that become narrower in a stepwise manner. Hence, the amount of change of the inductance, caused every time one lateral bar

71

b

is cut, remains substantially constant. However, in the inductance element

75

, the intervals of the lateral bars

71

b

become narrower as the number of cut lateral bars

71

b

is increased. This increases the possibility that the lateral bars

71

b

may be erroneously cut, thus the adjustment of the inductance is difficult.

SUMMARY OF THE INVENTION

To overcome the above-described problems, preferred embodiments of the present invention provide a variable inductance element having a high Q factor, and in which the inductance is finely adjusted efficiently and accurately.

According to preferred embodiments of the present invention, a variable inductance element is provided including (a) an insulating substrate; and (b) an inductor pattern provided on the surface of the insulating substrate, (c) the inductor pattern being a ladder-shaped electrode having a substantially V-shaped frame portion and a plurality of lateral bars extending across two arms of the substantially V-shaped frame portion and arranged to be trimmed for adjustment of the inductance, the plurality of lateral bars being arranged at substantially equal intervals.

With the above-described configuration, the lengths of the respective lateral bars are sequentially decreased as the distance between the two arms of the substantially V-shaped frame portion is gradually reduced. Accordingly, when the lateral bars are sequentially cut in the order of decreasing length, the inductance of the variable inductance element does not change rapidly.

Preferably, the two arms of the substantially V-shaped frame portion have an angle of approximately 45° relative to the lateral bars. Accordingly, magnetic fields generated in the respective arms are substantially perpendicular to each other, thereby eliminating mutual interference.

Other features, elements, characteristics and advantages of preferred embodiments of the present invention will become apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a perspective view showing a variable inductance element according to a preferred embodiment of the present invention;

FIG. 2

is a plan view illustrating a method of adjusting the inductance of the variable inductance element of

FIG. 1

;

FIG. 3

is a graph showing the change of the inductance with the trimming distance of the variable inductance element of

FIG. 1

;

FIG. 4

is a perspective view of a conventional variable inductance element;

FIG. 5

is a perspective view of a further conventional variable inductance element; and

FIG. 6

is a perspective view of still a further conventional variable inductance element.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the variable inductance element of the present invention will be described with reference with the accompanying drawings.

As shown in

FIG. 1

, after the upper surface of an insulating substrate

1

is polished to have a smooth surface, an inductor pattern

4

is provided on the upper surface of the insulating substrate

1

by a thick-film printing method or a thin-film forming method such as photolithography or other suitable methods. According to the thick-film printing method, a mask having an opening in a desired pattern is placed on the upper surface of the insulating substrate

1

, and electrically conductive paste is applied from above the mask, whereby a conductor having a relatively large thickness is formed in the desired pattern (in this embodiment, the inductor pattern

4

) on the upper surface of the insulating substrate

1

exposed through the opening of the mask.

An example of photolithography will be described below. A relatively thin conductive film is provided on substantially the entire upper surface of the insulating substrate

1

. After this, a resist film (for example, a photosensitive resin or other suitable material) is provided on substantially the entire area of the conductive film by spin coating or printing. Next, a mask film having a desired image pattern is placed on the upper surface of the resist film, and the desired portion of the resist film is hardened by irradiation of UV rays or other suitable process or source. After this, the resist film is peeled off, with the hardened portion thereof remaining, and the exposed portion of the conductive film is removed, whereby a conductor is produced in the desired pattern, and thereafter, the hardened resist film is also removed.

Further, according to another photolithographic method, photosensitive conductive paste is applied on the upper surface of the insulating substrate

1

, and a mask film having a predetermined image pattern provided therein covers the photosensitive conductive paste, followed by exposure and development.

The inductor pattern

4

preferably is a ladder-shaped electrode including a substantially V-shaped frame portion

4

a

and a plurality of lateral bars

4

b

extending across two arms

41

and

42

of the substantially V-shaped frame portion

4

a

. The lateral bars

4

b

are arranged at intervals which are relatively wide and are substantially equal to each other, and the lengths of the lateral bars

4

b

become stepwise shorter as the bars

4

b

are positioned nearer to the joining-side of the two arms

41

and

42

of the substantially V-shaped frame portion

4

a

. One end

5

a

of the inductor pattern

4

extends out to the rear portion of the left-side, as viewed in

FIGS. 1 and 2

, of the insulating substrate

1

, while the other end

5

b

extends out to the rear portion of the right-side, as viewed in

FIGS. 1 and 2

, of the insulating substrate

1

. As materials for the insulating substrate

1

, glass, glass ceramic, alumina, ferrite, or other suitable materials may be used. As materials for the inductor pattern

4

, Ag, Ag—Pd, Cu, Au, Ni, Al, or other suitable materials may be used.

Moreover, a liquid insulating material (polyimide or the like) is coated onto the entire upper surface of the insulating substrate

1

by spin coating, printing or other suitable method, and is dried, whereby an insulating protection film covering the inductor pattern

4

is provided.

Next, external input-output electrodes

6

and

7

are provided on each end portion of the insulating substrate

1

on the right and left hand sides in the longitudinal direction, respectively. The external input-output electrode

6

is electrically connected to the end portion

5

a

of the inductor pattern

4

, and the external input-output electrode

7

is electrically connected to the end portion

5

b

of the inductor pattern

4

. The external input-output electrodes

6

and

7

are formed by coating and baking conductive paste of Ag, Ag—Pd, Cu, Ni, NiCr, NiCu, or other suitable materials, by dry or wet plating, or by a combination of the coating and the plating, or other suitable methods.

After a variable inductance element

9

obtained as described above is mounted onto a printed circuit board or other suitable substrate, the inductor pattern

4

is trimmed. In particular, as shown in

FIG. 2

, the upper surface of the variable inductance element

9

is irradiated with a laser beam while the beam is moved across the surface of the variable inductance element

9

, so that a trimming groove

10

is produced in the variable inductance element

9

and simultaneously cuts the lateral bars

4

b

of the inductor pattern

4

one by one in the order of decreasing length (

FIG. 2

shows the state in which three lateral bars

4

b

are cut). In this manner, the inductance between the external electrodes

6

and

7

can be stepwise altered in small amounts. As the number of cut lateral bars

4

b

is increased, the paths of current flowing through the arm

41

, the lateral bars

4

b

, and the arm

42

increases. Hence, the inductance between the external electrodes

6

and

7

is increased. In addition, the lengths of the lateral bars

4

b

become gradually shorter as the bars

4

b

are positioned nearer to the joining-side of the arms

41

and

42

. Therefore, when the lateral bars

4

b

are sequentially cut with a laser beam for achieving fine adjustment, the inductance of the inductance element

9

is not drastically altered, but rather is altered by a relatively small amount.

Regarding the inductance changing from the value at initial trimming with respect to the trimming distance, changes of the inductance of the conventional variable inductance element

65

having a size of approximately 3.2 mm×1.6 mm, shown in

FIG. 5

is increased more steeply as the trimming distance is larger, as indicated by solid line h

1

in FIG.

3

. On the other hand, for the variable inductance element

9

of this preferred embodiment of the present invention having the same size as the above conventional variable inductance element, the inductance changes linearly and constantly as indicated by solid line h

2

in FIG.

3

.

FIG. 3

clearly indicates that the inductance is not drastically altered.

Further, the lateral bars

4

b

are provided at intervals that are relatively wide and are substantially equal to each other. Hence, there is no risk that the lateral bars

4

b

will be erroneously cut when the bars

4

b

are trimmed. Thus, this trimming is easily performed.

Moreover, magnetic fields generated in the two arms

41

and

42

of the substantially V-shaped frame portion

4

a

do not interfere with each other. Thus, the variable inductance element

9

of this preferred embodiment of the present invention produces a high Q factor. In this preferred embodiment, the angle &thgr; between the two arms

41

,

42

and the lateral bars

4

b

of the substantially V-shaped frame portion

4

a

is approximately 45°. Accordingly, the two arms

41

and

42

are preferably substantially perpendicular to each other, so that the interference of the magnetic fields generated in the two arms

41

and

42

is minimized and prevented. Thus, a variable inductance element

9

having a further improved Q factor is produced. For example, for the variable inductance element

9

having a size of approximately 3.2 mm×1.6 mm, the Q factor is at least 100.

By setting the spreading angle between the two arms

41

and

42

of the substantially V-shaped frame portion

4

a

greater, the variable range of the inductance is widened. For example, in the case of a variable inductance element having a size of approximately 3.2 mm×1.6 mm, the adjustment is possible only over a range of about 0.2 nH for the conventional inductance element

55

shown in FIG.

4

. On the other hand, for the inductance element

9

shown in

FIG. 1

, the adjustment range is about 1.5 nH (about 7.5 times greater).

Trimming of the inductor pattern

4

is not restricted to a method using a laser beam, and may be carried out by any method such as sand blasting or any other suitable method. Further, it is not necessary to provide the trimming groove

10

. Provided that the inductor pattern

4

is electrically cut, the trimming groove

10

does not have to be formed in a physical sense.

The variable inductance element of preferred embodiments of the present invention is not restricted to the above-described preferred embodiments. Changes and modifications may be made without departing from the spirit and the scope of the present invention. Especially, the above preferred embodiments are described in the production of an individual variable inductance element. To efficiently mass-produce variable inductance elements, a mother substrate (wafer) provided with a plurality of variable inductance elements is produced, and in the final process, the wafer is cut to a product size by a technique such as dicing, scribe-break, laser cutting, or other suitable process.

As seen in the above-description, according to preferred embodiments of the present invention, as the distance between the two arms of the substantially V-shaped frame portion is gradually reduced, the lengths of the respective lateral bars are sequentially decreased, and also, the inductance of the respective lateral bars is sequentially reduced. Accordingly, when the lateral bars are sequentially cut in the order of decreasing length, the inductance of the variable inductance element is not drastically altered. Further, magnetic fields generated in the two arms of the substantially V-shaped frame portion do not readily interfere with each other. Thus, a variable inductance element having a substantially improved Q factor can be provided. Preferably, the two arms of the substantially V-shaped frame portion are set to have an angle of approximately 45° to the lateral bars. Accordingly, the interference of the magnetic fields generated in the respective arms is minimized. A variable inductance element having a further improved Q factor is produced. In addition, the lateral bars are arranged at intervals that are relatively wide and are equal to each other. Accordingly, when the lateral bars are trimmed by a laser trimming machine, adjacent lateral bars are cut accurately and precisely. Trimming work is performed simply and accurately.

It should be understood that the foregoing description is only illustrative of the present invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variations that fall within the scope of the appended claims.