Dielectric filter, and method of manufacturing the same

BACKGROUND OF THE INVENTION

The present invention relates to a dielectric filter which comprises a plurality of resonators disposed side by side and is suitable for forming input/output terminal electrodes on a side surface.

There have hitherto been proposed various types of dielectric filters, in which terminal electrodes are formed on a side surface perpendicular to an open end face of a dielectric porcelain block

42

(i.e., an exposed-dielectric surface having conductors exposed thereon).

Terminal electrodes formed on the side surface perpendicular to an open end face of the dielectric porcelain block

42

are soldered to another circuit board and act as I/O terminals of the dielectric filter. Another electrode placed on the same plane where the terminal electrodes are provided acts as a ground electrode.

Commonly-used terminal electrodes include a terminal electrode formed by means of printing and sintering conductive material, and a terminal electrode formed by means of plating (see, for example, Japanese Patent Publication 8-307119/(1996) and 9-260903/(1997)). The terminal electrode assumes a structure such as that shown in FIG.

13

.

In a dielectric porcelain block

2

of the dielectric filter

1

shown in

FIG. 13

, a plurality of resonators

10

are provided side by side, wherein each resonator

10

is formed by coating the interior surface of a through hole

11

with an interior conductor

12

. I/O terminal electrodes

20

are provided on a side surface

4

perpendicular to an open end face

3

of the dielectric porcelain block

2

having the through holes

11

formed therein. The remaining side surfaces and bottom (i.e., a surface opposite the open end face

3

) of the dielectric porcelain block

2

are covered with an exterior conductor

22

such that the I/O terminal electrodes

20

are isolated from the exterior conductor

22

by means of an exposed-dielectric section

21

.

There have also hitherto been proposed a method of forming independent I/O terminal electrodes, by means of metallizing the entire side surfaces of a dielectric porcelain block; forming recesses in one of the side surfaces by means of sandblasting, laser, or etching; and masking electrodes with resist before the dielectric porcelain block is metallized.

As is evident from an enlarged portion shown in

FIG. 13

, the terminal electrode

20

and the ground electrode (i.e., the exterior conductor

22

) are higher than the exposed dielectric porcelain block

2

located therebetween by an amount corresponding to the thickness of the electrodes.

The terminal electrodes

20

are located at the highest position above amount surface of the dielectric porcelain block

2

. When a dielectric filter is soldered to another circuit board by use of cream solder, the dielectric filter is mounted on a circuit board by means of squeezing cream solder, since no gap exists between a circuit board and a terminal electrode. Accordingly, if the amount of solder is greater than appropriate, a solder bridge arises between adjacent terminals, thus causing a short circuit. Occurrence of a short circuit will be described specifically by reference to

FIGS. 14A through 14C

.

FIGS. 14A through 14C

show an example solder bridge arising in a dielectric filter having a related-art terminal electrode. As shown in

FIG. 14A

, a cream solder layer

33

a

is applied over an electrode

32

a

, and a cream solder layer

33

b

is applied over an electrode

32

b

. When the dielectric porcelain block

2

is mounted on the electrodes

32

a

and

32

b

laid on a circuit board

31

and is pressed against the electrodes

32

a

and

32

b

, the cream solder layers

33

a

and

33

b

squeeze out in a manner as shown in

FIG. 14B

, because no gap exists between a terminal electrode

20

, a ground electrode (i.e., an exterior conductor

22

), and a circuit board

31

of the dielectric porcelain block

2

.

So long as a sufficient space exists between the electrodes

32

a

and

32

b

, occurrence of solder bridges between the electrodes

32

a

and

32

d

can be prevented. However, in a high-frequency dielectric filter which is to be used for higher frequencies and miniaturization, an interval between electrodes becomes narrower, and a short circuit due to solder bridges becomes apt to arise between the electrodes

20

and

22

, as shown in FIG.

14

C.

In connection with a dielectric filter, a dielectric porcelain block per se is greater in area than electrodes. Hence, the strength of a connection must be enhanced by means of increasing the area of a place to be soldered, and the amount of solder to be used must be increased. An increase in the amount of solder eventually results in ease of occurrence of a short circuit.

When terminal electrodes and a ground electrode of a dielectric filter are formed, by means of electric plating, areas where terminal electrodes are to be formed assume island-shaped geometries, and as a result plating of the terminal electrodes becomes thinner. A pattern is formed by means of resist, and hence variations may arise in positions where terminals are to be formed, depending on the precision of printing of resist, thereby adversely affecting a filtering characteristic of the dielectric filter.

In a case where electrodes are formed by means of plating, a plating bridge (elongation of plating) may arise between a terminal electrode

20

and a ground electrode (i.e., an exterior conductor

22

) formed on the dielectric porcelain block

2

of the dielectric filter

1

, thereby resulting in a short circuit such as that shown in FIG.

15

. After removal of resist, the bridge still remains, thereby inducing a short circuit.

When molded bodies which are to become dielectric porcelain blocks are sintered, a maximum number of molded bodies are put into a furnace as close to each other as possible. If contact of large area arises between molded bodies, the molded bodies will stick to each other after sintering, thus resulting in occurrence of defectives.

SUMMARY OF THE INVENTION

The present invention is aimed at obviating drawbacks of a dielectric filter having a related-art structure and at providing a dielectric filter which is easy to mount and provides a high manufacturing yield and stable quality, as well as a method of manufacturing the dielectric filter.

Other objects and novel features of the present invention will be manifest by reference to embodiments to be described later.

To this end, the present invention provides a dielectric filter formed from a dielectric block and a plurality of resonators formed in the dielectric block side by side, each resonator being formed by coating an interior surface of a through section with an interior conductor, wherein, on a side surface of the dielectric block perpendicular to an open end face having the through sections formed therein, there are formed protrusions having a height lower than that of the through sections.

By means of such a construction, when terminal electrodes are provided on a side surface of a dielectric block, dielectric protrusions are located between the electrodes. Hence, when the dielectric porcelain block is mounted on a circuit board by means of cream solder, the amount of solder which enters the exposed dielectric of the protrusions from electrodes becomes less, thereby eliminating squeezing out of solder to adjacent electrodes. Consequently, there can be prevented occurrence of a short circuit, which would otherwise be caused by solder bridges.

One or more protrusions are provided on at least one of the side surfaces of the dielectric porcelain block during molding. As a result, there can be prevented occurrence of contact between molded bodies over a wide area. Consequently, there can be prevented failures, which would otherwise be caused when molded bodies come into contact with each other over a wide area during sintering.

Preferably, each of the protrusions is formed so as to spread across two or more side surfaces.

By means of such a construction, a terminal electrode can be provided at a corner of the dielectric block.

Preferably, a plurality of protrusions can be formed on the same plane.

By means of such a construction, a plurality of terminal electrodes can be provided on a single plate of the dielectric block.

Preferably, terminal electrodes are formed such that the protrusions are located as a boundary between the electrodes.

By means of such a construction, since protrusions have been formed on a side surface beforehand, the positional accuracy of the terminal electrodes can be improved, thereby diminishing variations in the filtering characteristic of a dielectric filter.

Preferably, the protrusions are located at least between adjacent terminal electrodes.

By means of such a construction, when terminal electrodes are provided on a side surface of a dielectric block, dielectric protrusions are located between the electrodes. Hence, when the dielectric porcelain block is mounted on a circuit board by means of cream solder, the amount of solder which enters the exposed dielectric of the protrusions from electrodes becomes less, thereby eliminating squeezing out of solder to adjacent electrodes. Consequently, there can be prevented occurrence of a short circuit, which would otherwise be caused by solder bridges.

Preferably, the protrusions are provided in a position other than the boundary between the terminal electrodes.

By means of such a construction, there can be prevented failures, which would otherwise be caused when molded bodies come into contact with each other over a wide area during sintering. Thus, the construction is effective for improving molding yield and useful for stabilizing the position of the dielectric filter when the filter is mounted to a circuit board.

Preferably, the extent to which the protrusions are to protrude from a side surface of the dielectric block is greater than the thickness of an exterior conductor formed on the side surface.

By means of such a construction, when the dielectric porcelain block is mounted on a circuit board by means of cream solder, the protrusions projecting from the exterior conductor prevents squeezing out of solder to adjacent electrodes. Consequently, there can be prevented occurrence of a short circuit, which would otherwise be caused by solder bridges.

Preferably, the interior and exterior conductor layers are formed by plating.

By means of such a construction, the terminal electrodes, the interior conductor, and the exterior conductor can be formed simultaneously by means of plating.

The present invention also provides a method of manufacturing a dielectric filter formed from a dielectric block and a plurality of resonators formed in the dielectric block side by side, each resonator being formed by coating an interior surface of a through section with an interior conductor, the method comprising the steps of: molding the dielectric block such that protrusions having a height lower than that of the through sections are formed on a side surface of the dielectric block perpendicular to an open end face having the through sections formed therein; coating the dielectric block including the surfaces of the protrusions with a conductor layer; and abrading tops of the protrusions, thereby causing the surface of the dielectric block to become exposed and forming electrodes defined by the protrusions.

By means of such a construction, when terminal electrodes are formed by means of plating, top surfaces of protrusions—which have been formed on a side surface beforehand after the entire surface of a dielectric porcelain block exclusive of an open end face has been plated—are abraded, thus eliminating the conductor layer from the top of each of the protrusions and forming terminal electrodes defined by the protrusions. The number of steps of forming a resist mask on a surface on which terminals are to be formed can be reduced. Further, protrusions are formed between terminal electrodes so as to constitute a boundary between the terminal electrodes, thereby preventing occurrence of a short circuit, which would otherwise be caused by elongation of plating. Moreover, the positional precision of electrodes can also be improved.

When the entire surface of a dielectric porcelain block is plated after resist mask has been formed over an open end face according to the related-art method, terminal electrodes become island-shaped floating electrodes. When the dielectric porcelain block is electrically plated, a reduction arises in the thickness or strength of plating. Since the present method prevents occurrence of floating electrodes, the foregoing problems do not arise. Thus, there can be formed terminal electrodes having stable strength and thickness.

The present invention also provides a method of manufacturing a dielectric filter formed from a dielectric block and a plurality of resonators formed in the dielectric block side by side, each resonator being formed by coating an interior surface of a through section with an interior conductor, the method comprising the steps of: forming the dielectric block by means of injection molding, such that protrusions having a height lower than that of the through sections are formed on a side surface of the dielectric block perpendicular to an open end face having the through sections formed therein.

By means of such a construction, protrusions of complicated shapes can be formed by means of injection molding, thereby enabling formation of terminal electrodes of various patterns.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a perspective view showing a dielectric filter according to a first embodiment of the present invention;

FIGS. 2A

to

2

C are descriptive views showing one example of a method of forming electrodes in the first embodiment;

FIGS. 3A and 3B

are descriptive view showing mounting of a dielectric filter to a circuit board in the first embodiment;

FIG. 4

is a perspective view showing a dielectric filter according to a second embodiment of the present invention;

FIG. 5

is a perspective view showing a dielectric filter according to a third embodiment of the present invention;

FIG. 6A

is a perspective view showing a dielectric filter according to a fourth embodiment of the present invention;

FIG. 6B

is a perspective view showing a dielectric filter according to a fifth embodiment of the present invention;

FIG. 6C

is a perspective view showing a dielectric filter according to a sixth embodiment of the present invention;

FIG. 6D

is a perspective view showing a dielectric filter according to a seventh embodiment of the present invention;

FIG. 7

is a perspective view showing a dielectric filter according to an eighth embodiment of the present invention;

FIG. 8

is a perspective view showing a dielectric filter according to a ninth embodiment of the present invention;

FIG. 9

is a perspective view showing a dielectric filter according to a tenth embodiment of the present invention;

FIGS. 10A and 10B

are perspective views showing a dielectric filter according to an eleventh embodiment of the present invention;

FIGS. 11A and 11B

are perspective views showing a dielectric filter according to a twelfth embodiment of the present invention;

FIGS. 12A and 12B

are perspective views showing a dielectric filter according to a thirteenth embodiment of the present invention;

FIGS. 13A and 13B

are perspective views showing a related-art dielectric filter;

FIGS. 14A

to

14

C are descriptive views showing drawbacks arising when a related-art dielectric filter is mounted on a circuit board; and

FIG. 15

is a front view showing drawbacks arising when terminal electrodes are formed on a related-art dielectric filter by means of plating.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A dielectric filter and a method of manufacturing the dielectric filter according to the present invention will be described hereinbelow by reference to the accompanying drawings.

FIG. 1

shows a dielectric filter according to a first embodiment of the present invention, and

FIG. 2

shows a method of manufacturing the dielectric filter.

In the dielectric filter shown in

FIG. 1

, a plurality of resonators

50

are formed side by side in a dielectric porcelain block

42

serving as a dielectric block. Each of the resonators

50

is constituted by means of covering an interior circumferential surface of a through section with an interior conductor

54

, and the through section is constituted of a through hole

51

and a cup-shaped recess

52

formed at one end of the through hole

51

. (In the illustrated example, the length of the through section is defined as the sum of the length of the through hole

51

and the length of a cup-shaped recess

52

, and three resonators are provided, thus constituting a three-stage dielectric filter). Through sections, each consisting of the through hole

51

and the cup-shaped recess

52

continuous therewith, are formed in an open end face

43

of the dielectric porcelain block

42

having a dielectric exposed thereon. Upwardly-oriented C-shaped protrusions

45

having a height L smaller than that of the through section (i.e., the height of the through hole

51

and the height of the cup-shaped recess

52

) are formed beforehand integrally with the dielectric porcelain block

42

on a side surface

44

perpendicular to the open end face

43

. Such a dielectric porcelain block

42

can be formed by means of injection molding so as to have the through hole

51

, the cup-shaped recesses

52

, and the upwardly-oriented C-shaped protrusions

45

.

Here, the C-shaped protrusions

45

are set so as to protrude from the side surface

44

such that the thickness of the C-shaped protuberance

45

exceeds the thickness of I/O terminal electrodes

60

a

and

60

b

to be provided on the side surface

44

of the dielectric porcelain block

42

and the thickness of an exterior conductor (ground electrode)

62

covering the exterior surface (i.e., the side and bottom surfaces) of the dielectric porcelain block

42

. The tip ends of the C-shaped protrusions

45

are arranged so as to come into contact with the open end face

43

. Consequently, each of the I/O terminal electrodes

60

a

and

60

b

is defined by the respective C-shaped protuberance

45

having a dielectric exposed thereon and is electrically isolated from the exterior conductor

62

(i.e., ground electrode) covering the remaining exterior surface of the dielectric porcelain block

42

. The exterior conductor

62

is connected to the interior conductor

54

covering the interior surfaces of the through holes

51

on the bottom surface (i.e., the surface opposite the open end face

43

). As will be described later, the I/O terminal electrodes

60

a

and

60

b

are used for mounting the dielectric filter

41

onto a circuit board by use of cream solder.

FIGS. 2A through 2C

show one example of method of producing the dielectric filter

41

shown in FIG.

1

. As shown in

FIG. 2A

, the protrusions

45

are formed on the dielectric porcelain block

42

by means of injection molding, and then the dielectric porcelain block

42

is sintered at a predetermined temperature. Next, as shown in

FIG. 2B

, the dielectric porcelain block

42

, including the surfaces of through holes

51

, the surfaces of the cup-shaped recesses

52

, and the surfaces of the protrusions

45

, are subjected to electroless plating, such as Cu plating. In order to facilitate plating, the surface of the dielectric porcelain block

42

is roughened beforehand, and the dielectric porcelain block

42

is plated with a catalyst.

At this time, in order to protect the open end face

43

from plating, the.dielectric porcelain block

42

is plated while the open end face

43

is coated with resist. Subsequently, either of two methods may be employed: one method is to coat the surface of the dielectric porcelain block

42

exclusive of the open end face

43

with a conductor layer by means of plating and to remove the resist from the open end face

43

, as shown in

FIG. 2B

; and the other method is to removing the plating layer from the open end face

43

by means of abrasion after the entire surface of the dielectric porcelain block

42

has been plated. According to the method shown in

FIG. 2B

, an upper end face

45

a

of the protuberance

45

is also plated. However, as shown in

FIG. 2C

, a conductor layer provided on the upper end face

45

a

of the protuberance

45

is abraded, thereby causing dielectric of the upper end face

45

a

of the protuberance

45

to become exposed. As a result, there are produced the I/O terminal electrodes

60

a

and

60

b

, which are isolated from each other by means of the protrusions

45

, and the exterior conductor (ground electrode)

62

. Simultaneously, the interior conductor

54

is formed on the interior surfaces of the through holes

51

and on the interior surfaces of the cup-shaped recesses

52

, by means of plating.

As shown in

FIG. 3A

, in the present embodiment, the dielectric protrusions

45

—which protrude higher than the exterior conductor provided on the terminal electrodes

60

a

and

60

b

—are formed between the terminal electrodes

60

a

and

60

b

and between the terminal electrodes

60

a

and

60

b

and the ground electrode

62

on the side surface

44

of the dielectric porcelain block

42

. Hence, even when the dielectric porcelain block

42

is mounted on a circuit board

31

having electrodes

32

a

and

32

b

coated with the cream solder layers

33

a

and

33

b

similar to those shown in

FIG. 14

, the dielectric porcelain block

42

can be joined to the circuit board

31

without involvement of occurrence of solder bridges, which would otherwise arise between the terminal electrodes

60

a

and

60

b

in the same manner as in FIG.

3

B.

In order to prevent occurrence of soldering failures, the extent T to which the protuberance

45

is to protrude from the surface of the exterior conductor

62

shown in

FIG. 3

is preferably set to 300 microns or less. If a gap arising between electrodes on the circuit board

31

and the terminal electrodes

60

a

and

60

b

exceeds a value of 100 microns or thereabouts, solder may stick to only the electrodes of either the circuit board

31

or to those of the dielectric porcelain block

42

, for reasons of a self-alignment characteristic of solder. Even in consideration of such a self-alignment characteristic of solder, the extent T is preferably set to 150 microns or less. By means of such a construction, a gap arising between the surface of electrodes of a circuit board and the surfaces of the terminal electrodes

60

a

and

60

b

of the dielectric filter is maintained at a level appropriate for soldering (e.g., 100 microns or less), thus ensuring soldering.

The protrusions

45

are formed on the dielectric porcelain block

42

beforehand, thereby yielding advantages in terms of positional precision and the number of man-hours involved. The protrusions may be formed by means of injection molding, ordinary powder compression molding, or subjecting a rectangular-parallelepiped dielectric porcelain block to post-treatment. When an attempt is made to form a structure having protruding elements provided thereon, metal molds for powder compression molding become complex and difficult to materialize. Designing metal molds for injection molding is easy and very advantageous. Further, injection molding is superior to powder compression molding in terms of homogeneity of molding density.

According to the manufacturing method shown in

FIGS. 2A through 2C

, a conductor layer may be provided on the dielectric porcelain block by means of immersing the dielectric porcelain block into a conductor paste such as silver.

The first embodiment yields the following advantages.

(1) The plurality of resonators

50

are formed by means of coating the interior surfaces of through sections with the interior conductor

54

, wherein each of the through sections is formed from the through hole

51

and the cup-shaped recess

52

. In a case where the plurality of resonators

50

are provided side by side in the dielectric porcelain block

42

, the protrusions

45

are formed on the side surface

44

perpendicular to the open end face

43

having the through holes

51

formed therein. The protrusions

45

are shorter than the through sections (each consisting of the through hole

51

and the cup-shaped recess

52

) in the axial direction of the trough sections. The dielectric protrusions

45

are located between the I/O terminal electrodes

60

a

and

60

b

and between the I/O terminal electrodes

60

a

and

60

b

and the exterior conductor

62

(i.e., the ground electrode). Hence, when the dielectric porcelain block

42

is mounted on the circuit board

31

by means of cream solder, the amount of solder which enters the exposed dielectric of the protrusions

45

from electrodes becomes less, thereby eliminating squeezing out of solder to adjacent electrodes. Consequently, there can be prevented occurrence of a short circuit, which would otherwise be caused by solder bridges.

(2) Two upwardly-oriented C-shaped protrusions

45

are provided on the same plane, and the tip ends of the C-shaped protrusions

45

are arranged so as to come into contact with the open end face

43

. Consequently, the protrusions

45

can define the I/O terminal electrodes

60

a

and

60

b

such that the I/O terminal electrodes

60

a

and

60

b

are electrically isolate and separate from the exterior conductor

62

without fail.

(3) The terminal electrodes

60

a

and

60

b

are formed with the protrusions

45

being taken as a boundary therebetween. As a result of the protrusions

45

having been formed on a side surface beforehand, the positional accuracy of the terminal electrodes

60

a

and

60

b

can be improved, thereby diminishing variations in the filtering characteristic of the dielectric filter.

(4) The extent to which the protuberance

45

is to protrude from the surface of the exterior conductor

62

is larger than the thickness of the exterior conductor formed on the same side surface. Hence, when the dielectric porcelain block

42

is mounted on the circuit board

31

, the protrusions

45

protruding from the exterior conductor

62

prevent cream solder from squeezing out to adjacent electrodes, thereby reliably eliminating occurrence of a short circuit, which would otherwise be caused by solder bridges. If the extent T to which the protuberance

45

is to protrude from the surface of the exterior conductor

62

is set to 300 microns or less, a gap arising between the surface of electrodes of the circuit board

31

and the surfaces of the terminal electrodes

60

a

and

60

b

of the dielectric filter becomes appropriate, thereby enabling proper soldering of the dielectric filter to the circuit board

31

. If the extent T is set to 150 microns or less, the gap arising between the surface of electrodes of the circuit board

31

and the surfaces of the terminal electrodes

60

a

and

60

b

assumes a value of 100 microns or less. Thus, an appropriate gap can be maintained in consideration of solder sticking to only the electrodes of either the circuit board

31

or to those of the dielectric porcelain block

42

, which would be induced by a self-alignment characteristic of solder. Thus, the dielectric filter can be soldered to the circuit board

31

more appropriately.

(5) The dielectric porcelain block

42

is molded so as to have the protrusions

45

, and the dielectric porcelain block

42

including the surfaces of the protrusions

45

are coated with a conductor layer. Subsequently, the upper end faces of the protrusions

45

are abraded, as a result of which the surface of the dielectric porcelain block

42

is exposed. The terminal electrodes

60

a

and

60

b

are defined by the respective protrusions

45

. The terminal electrodes

60

a

and

60

b

, the interior conductor

54

, and the exterior conductor

62

can be produced with good productivity by utilization of the plating technique. The protrusions

45

of dielectric substance are present between the terminal electrodes

60

a

and

60

b

so as to determine a boundary between the terminal electrodes

60

a

and

60

b

, thus preventing a short circuit, which would otherwise be caused by elongating of plating. When the entire surface of the dielectric porcelain block

42

is plated while resist is applied to the open-end face

43

, the terminal electrodes

60

a

and

60

b

become island-shaped floating electrodes. Further, when the dielectric porcelain block

42

is electrically plated, a reduction arises in the thickness or strength of plating. Since the present method prevents occurrence of floating electrodes, the foregoing problems do not arise. Thus, there can be formed terminal electrodes having stable strength and thickness.

(6) The dielectric porcelain block

42

is formed by means of injection molding such that the protrusions

45

having a height smaller than that of the through section

51

are formed on the side surface

44

perpendicular to the open end face

43

of the dielectric porcelain block

42

having the through holes

51

formed therein. The protrusions

45

having complicated geometries can be formed by means of injection molding, thus enabling formation of terminal electrodes of various patterns.

FIG. 4

shows a dielectric filter according to a second embodiment of the present invention. An upwardly-oriented E-shaped protuberance

46

is formed on the side surface

44

of the dielectric porcelain block

42

. Terminal electrodes

60

c

and

60

d

are formed with the protuberance

46

being taken as a boundary. In other respects, the dielectric filter is identical in construction with that described in connection with the first embodiment.

In the case of the dielectric filter according to the second embodiment, the terminal electrodes

60

c

and

60

d

are formed with the protuberance

46

taken as a boundary, thus improving the positional accuracy of the terminal electrodes

60

c

and

60

d

. Further, variations in the filtering characteristic of the dielectric filter can be diminished. A portion of the protuberance

46

(i.e., a center projection

46

a

) is located between the adjacent terminal electrodes

60

c

and

60

d

. Since the exterior conductor

62

serving as a ground electrodes does not enter between the terminal electrodes

60

c

and

60

d

. Hence, capacitive coupling between the resonators

50

is made relatively stronger, thus broadening a pass band. In this case, the effect can be made greater, by means of dielectric protrusions being interposed between the terminal electrodes

60

c

and

60

d

as well as by means of preventing extension of the exterior conductor

62

between the terminal electrodes

60

c

and

60

d

. In other respects, the dielectric filter is identical in working-effect with that described in connection with the first embodiment.

FIG. 5

shows a dielectric filter according to a third embodiment of the present invention. An upwardly-oriented substantially-E-shaped protuberance

47

is formed on the side surface

44

of the dielectric porcelain block

42

. Terminal electrodes

60

e

and

60

f

are formed with the protuberance

47

being taken as a boundary therebetween. The terminal electrodes

60

e

and

60

f

are formed from square portions. A strip-shaped extension E extends from each of the square portions such that the extensions E become close to each other. In other respects, the dielectric filter is identical in construction with that described in connection with the second embodiment.

In addition to the protuberance to be used for defining a terminal electrode, a protuberance to be used for stabilization during mounting of a dielectric filter can be formed on the side surface of the dielectric porcelain block.

FIGS. 6A through 6D

show a dielectric filter having such a protuberance. In a fourth embodiment of the present invention shown in

FIG. 6A

, a fifth embodiment of the present invention shown in

FIG. 6B

, a sixth embodiment of the present invention shown in

FIG. 6C

, and a seventh embodiment of the present invention shown in

FIG. 6D

, one or a plurality of protrusions

48

a

,

48

b

,

48

c

, and

48

d

are provided on the side surface

44

of the dielectric porcelain block

42

in positions other than the boundary between the terminal electrodes

60

a

and

60

b

, in addition to the upwardly-oriented C-shaped protrusions

45

described in connection with the first embodiment. As can be seen from these drawings, a protuberance(s) is provided in arbitrary positions on the side surface (in terms of stabilization of the dielectric filter during mounting operation, an additional protuberance(s) is preferably provided in a lower position on the side surface spaced a certain distance away from the protrusions

45

provided in an upper position on the side surface). The additional protuberance(s) assumes an arbitrary geometry, such as a circular shape or a rectangular shape. In terms of electrical characteristic, the protrusions

48

a

,

48

b

,

48

c

, and

48

d

are preferably coated with the exterior conductor

62

. In other respects, the dielectric filters described in connection with the fifth through seventh embodiments are identical with that described in connection with the first embodiment.

When a dielectric filter is mounted with a terminal surface thereof facing down or when a plurality of dielectric filters are mounted side by side, the filters may be inclined out of balance. Since the protrusions

48

a

,

48

b

,

48

c

, and

48

d

are provided at positions other than the boundary between the terminal electrodes

60

a

and

60

b

, stability required for mounting the dielectric filter on a circuit board can be ensured reliably. In other respects, the dielectric filters yields the same working-effect as that yielded by the dielectric field described in connection with the first embodiment.

FIG. 7

shows a dielectric filter according to an eighth embodiment of the present invention. In this case, protrusions

49

act as boundaries between the terminal electrodes

60

g

and

60

h

and the exterior conductor

62

. The protrusions

49

assume the shape of a square frame. The terminal electrodes

60

g

and

60

h

can be placed at arbitrary positions on the side surface

44

of the dielectric porcelain block

42

in the axial direction of the through holes

51

serving as through sections. In short, the terminal electrodes

60

g

and

60

h

are arranged so as to be spaced away from the open-end face. As a result, such a construction can cope with a case where the interior conductor

54

is provided so as to extend to any position on the through hole

51

. In terms of construction and working-effect, the dielectric filter according to the eighth embodiment is identical with that described in connection with the first embodiment. In this case, the open end

43

has no cup-shaped recess, and hence the length of a through section is defined as being equal to the length of the through hole

51

.

There is no necessity of forming terminal electrodes on only one surface of the dielectric filter. Terminal electrodes may be formed so as to spread across two or more surfaces of the dielectric porcelain block. Such a dielectric filter is described as a ninth embodiment of the present invention, by reference to FIG.

8

. In this embodiment, each of the upwardly-oriented C-shaped protrusions

55

is formed so as to spread two side surfaces

44

and

44

′ of the dielectric porcelain block

42

. Consequently, terminal electrodes

60

i

and

60

j

are formed so as to be isolated and separated from the exterior conductor

62

by means of the upwardly-oriented protrusions

55

such that each of the terminal electrodes spreads across two surfaces. In other respects, the dielectric filter is identical in construction with that described in the first embodiment.

In the ninth embodiment, since the terminal electrodes

60

i

and

60

j

are provided such that each of the terminal electrodes spreads across two surfaces of the dielectric porcelain block

42

, there is achieved a higher degree of freedom in laying out a dielectric filter on a circuit board. In other respects, the dielectric filter is identical in working-effect with that described in connection with the first embodiment.

Terminal electrodes are not necessarily formed on an open-end face and may be formed so as to spread across two or more surfaces. A dielectric filter having such a layout will be described as a tenth embodiment of the present invention by reference to FIG.

9

. In this example, the square-frame-shaped protrusions

56

are formed such that each of the protrusions

56

spreads across two or more surfaces

44

and

44

′. Consequently, terminal electrodes

60

m

and

60

n

are formed so as to be isolated and separated from the exterior conductor

62

by means of the square-frame-shaped protrusions

56

such that each of the terminal electrodes

60

m

and

60

n

spreads across two surfaces. In other respect, the dielectric filter is identical with that described in connection with the first embodiment (the filter having no cup-shaped recesses).

In the tenth embodiment, since each of the terminal electrodes

60

m

and

60

n

is entirely surrounded by the square-frame-shaped protuberance

56

, the terminal electrodes

60

m

and

60

n

can be provided at arbitrary positions on the side surfaces

44

and

44

′ of the dielectric porcelain block

42

in the axial direction of the through holes

51

. More specifically, the terminal electrodes can be arranged so as not to come into contact with the open-end surface. For instance, the dielectric filter can cope with a case where the interior conductor

54

is provided so as to extend to any position on the through hole

51

. Since the terminal electrodes

60

m

and

60

n

is provided such that each of the terminal electrodes spreads across two surfaces of the dielectric porcelain block

42

, there is achieved a higher degree of freedom in laying out a dielectric filter on a circuit board. In other respects, the dielectric filter is identical in working-effect with that described in connection with the first embodiment.

FIGS. 10A and 10B

show the structure of a dielectric filter effective for preventing molded bodies of dielectric porcelain blocks from sticking each other, which would arise over a wide area at the time of sintering. As shown in

FIG. 10A

, protrusions

57

are formed at a plurality of positions (e.g. at positions in the vicinity of four corners) on the adjacent side surface

44

′ perpendicular to the side surface

44

having the terminal electrodes

60

a

and

60

b

of the dielectric porcelain block

42

mounted thereon, as well as on the side surface

44

. When molded bodies of dielectric porcelain blocks are sintered while being arranged side by side, as shown in

FIG. 11B

, there can be reliably prevented occurrence of contact between the molded bodies over a wide area, which would otherwise be caused as a result of the molded bodies coming into contact with each other. The protrusions

57

to be provided on the adjacent side surface

44

′ can be formed into, for example, semi-spherical protrusions. As a result, the area of contact between molded bodies can be reduced to a much greater extent. In other respect, the dielectric filter yields the same working-effect as that yielded by the dielectric filter according to the first embodiment.

The protrusions

57

may be provided on all four side surfaces of the dielectric porcelain block

42

for the same purpose.

FIGS. 11A and 11B

show a dielectric filter according to a twelfth embodiment of the present invention. As has been shown in connection with the eleventh embodiment of the present intention, the protrusions

57

are utilized for positioning a shield plate

70

which shields the open end face

43

of the dielectric porcelain block

42

in the manner as described in connection with the eleventh embodiment. As shown in

FIG. 11A

, the protrusions

57

are provided on the surface of the dielectric porcelain block

42

opposite to that having terminal electrodes provided thereon. The dielectric filter

41

is mounted to the circuit board

31

by utilization of the terminal electrodes

60

a

and

60

b

through soldering. When the shield plate

70

is fixed on the circuit board

31

in the same manner as in the embodiment shown in

FIG. 3

, the protrusions

57

can position the shield

70

(those elements which are identical with or correspond to the element shown in

FIG. 3

are assigned the same reference numerals). In other respects, the dielectric filter is identical in working-effect with that described in connection with the first embodiment.

FIGS. 12A and 12B

show a dielectric filter according to a thirteenth embodiment of the present invention. As shown in

FIG. 12A

, a protuberance

58

to be formed at a position other than the boundary between the terminal electrodes

60

a

and

60

b

is formed on the same side surface on which the terminal electrodes

60

a

and

60

b

are provided and at a position in the vicinity of the end section opposite to the end section close to the protuberance

45

. More specifically, the protuberance

58

is formed at a position close to the bottom surface of the dielectric porcelain block

42

. Further, the protuberance

58

is coated with the exterior conductor

62

, thus constituting a ground terminal

59

. As shown in

FIG. 12B

, the areas to be used for mounting can be defined by the surfaces of the terminal electrodes

60

a

and

60

b

and the surface of the ground terminal electrode

59

. When the dielectric filter

41

is soldered to the circuit board

31

by means of the terminal electrodes

60

a

and

60

b

and the ground terminal electrode

59

, another circuit conductor pattern

80

may be placed on the circuit board

31

by utilization of a gap between the protrusions

45

defining the terminal electrodes

60

a

and

60

b

and the protuberance

58

. Here, the protrusions

45

are not required to be identical in height with the protuberance

58

. In other respects, the dielectric filter is identical with that described in connection with the first embodiment.

If the front and back of each of the side surfaces of the dielectric porcelain block is given orientation, the protrusions described in the preceding embodiments maybe used as protrusions for identifying an orientation.

The cup-shaped recesses are formed in the open end face of the dielectric porcelain block so as to become continuous from the respective through holes. However, cup-shaped recesses are formed for making the filter characteristic of the dielectric filter for a required application. Hence, the cup-shaped recesses can be obviated. Further, the number of resonators (i.e., the number of stages of dielectric filters), each resonator being formed from an interior conductor applied over a through hole formed in the dielectric porcelain block, can be increased or decreased, as required.

As has described in connection with the embodiments, the present invention is not limited to the embodiments. It is obvious to those who are skilled in the art that the present invention is susceptible to various modifications or alterations within the scope of the invention described in the appending claims.

As described above, according to the present invention, when terminal electrodes are provided on a side surface of a dielectric block, dielectric protrusions are located between the electrodes. Hence, when the dielectric porcelain block is mounted on a circuit board by means of cream solder, the amount of solder which enters the exposed dielectric of the protrusions from electrodes becomes less, thereby eliminating squeezing out of solder to adjacent electrodes. Consequently, there can be prevented occurrence of a short circuit, which would otherwise be caused by solder bridges.

One or more protrusions are provided on at least one of the side surfaces of the dielectric porcelain block during molding. As a result, there can be prevented occurrence of contact between molded bodies over a wide area. Consequently, there can be prevented failures, which would otherwise be caused when molded bodies come into contact with each other over a wide area during sintering.

Protrusions are formed so as to protrude from the exterior conductor provided on the side surfaces and bottom surface of the dielectric porcelain block. As a result, squeezing out of cream solder to adjacent electrodes can be prevented more reliably, thus eliminating occurrence of a short circuit, which would otherwise be caused by solder bridges.

When terminal electrodes are formed by means of plating, there may be employed a method in which protrusions—which have been formed on a side surface beforehand after the entire surface of a dielectric porcelain block exclusive of an open end face has been plated—are abraded, thus eliminating the conductor layer from the top of each of the protrusions and forming terminal electrodes. The positional precision of the electrodes can be improved, and the number of steps for forming a resist mask can be diminished. Further, protrusions are formed between terminal electrodes so as to constitute a boundary between the terminal electrodes, thereby preventing occurrence of a short circuit, which would otherwise be caused by elongation of plating.

When the entire surface of a dielectric porcelain block is plated after resist has been applied over an open end face according to the related-art method, terminal electrodes become island-shaped floating electrodes. When the dielectric porcelain block is electrically plated, a reduction arises in the thickness or strength of plating. Since the present method prevents occurrence of floating electrodes, the foregoing problems do not arise. Thus, there can be formed terminal electrodes having stable strength and thickness.

Accordingly, there can be provided a dielectric filter which is superior in ease of mounting, provides high yield when electrodes are formed by plating, and has a stable film thickness.

Number	Name	Date	Kind
4220810	Arai et al.	Sep 1980	A
5329687	Scott et al.	Jul 1994	A
5537082	Tada et al.	Jul 1996	A

Number	Date	Country
0 797 266	Sep 1997	EP
3-240302	Oct 1991	JP
5-63102	Aug 1993	JP
6-53709	Feb 1994	JP
7-147502	Jun 1995	JP
7-176915	Jul 1995	JP
8-307119	Nov 1996	JP
9-260903	Oct 1997	JP
10-41703	Feb 1998	JP
10-242705	Sep 1998	JP
WO 9530250	Nov 1995	WO

Dielectric filter, and method of manufacturing the same

Information

Patent Number

Date Filed

Date Issued

Inventors

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CPC

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Abstract

Description

Claims

US Referenced Citations (3)

Foreign Referenced Citations (11)