JP2000340444A - Manufacture of chip type inductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a chip type inductor for improving the quality and productivity of a magnetic core, and for reducing working costs. SOLUTION: In this method for manufacturing a chip type inductor, a molding 22 for support is arranged in a metallic mold 20, and a coil-shaped conductor 12 constituted by spirally forming a metallic wire is supported on the molding 22 for support, and positioned at the central part of the metallic mold 20. Then, ceramic slurry 23 is injected into the metallic mold 20, and the ceramic slurry 23 is molded by a wet type press method so that a molding 27 in which the coil-shaped conductor 12 is embedded can be obtained. The molding 27 is temporarily burnt, and a temporarily burnt sintered body 28 is cut like a chip so that temporarily sintered bodies 29 can be obtained. Then, the temporarily sintered bodies are burnt so that a core 11 can be obtained, and outer electrodes to be connected with both the edge parts of the coil-shaped conductor 12 are formed on both the edge faces of the core 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a chip type inductor used for a noise filter, a transformer and the like.

[0002]

2. Description of the Related Art Chip inductors are widely used as high frequency filters for removing radiation noise emitted from digital devices such as computers. As such a chip inductor, for example, as described in Japanese Utility Model Application Laid-Open No. 6-50312, a chip body is constituted by laminated ceramic layers, and a ceramic interlayer is formed through a through-hole portion formed on the ceramic layer. There is known a laminated chip inductor in which a coil conductor is connected to form a coil orbiting in a chip body, and a starting end and an end of the coil are connected to different external electrodes.

[0003] Inductors for high-frequency filters are required to have high inductance and low resistance. In general, the inductance is proportional to the square of the number of turns of the coil and inversely proportional to the length. However, in the case of the above-described multilayer inductor, the manufacturing process is complicated, the manufacturing cost is high, and the number of turns of the coil cannot be increased, so that a large inductance cannot be obtained. Since it is composed of electrodes, there is a problem that the resistance value increases.

In order to solve this problem, Japanese Patent Application Laid-Open No.
As described in JP-A-1022, a core is formed by extruding magnetic ceramics, a conductor is wound around the core in a coil shape, and the magnetic ceramic is extruded thereon. There has been proposed a method of forming an inductor in which an envelope is formed. Thereafter, the ceramics are fired, and external electrodes are attached to both end surfaces of the fired magnetic core, thereby connecting both ends of the coiled conductive wire to the external electrodes. In this case,
The manufacturing method is simpler than that of the multilayer inductor, and since the metal wire is used as the coil-shaped conductor, there is an advantage that both a high inductance value and a low resistance value can be achieved.

[0005] In the above-mentioned manufacturing method, the part to be the core and the part to be the outer cover are both formed by extrusion, but the density of the formed body by extrusion is not so high. In addition, the jacket may not be filled around the coil without gaps, and a cavity may be formed between the core and the jacket. In addition, since a binder is required to bond the ceramic particles together, pores are generated during firing. Therefore, it was difficult to obtain a high quality inductor.

[0006]

There is a wet pressing method as a method for obtaining a ceramic molded body of higher quality than extrusion molding. In this method, after injecting a ceramic slurry into a cavity of a mold, the upper surface of the cavity is covered with a filter that allows only moisture to pass through, and packing is performed from above with a porous upper mold. Then, by pushing up the lower mold from below the mold, applying a high pressure to the ceramic slurry for a predetermined time and extracting moisture through the filter with the upper mold,
Press molding is performed.

[0007] Even when the above-mentioned inductor is formed, a high quality inductor can be obtained by applying a wet pressing method. However, in recent years, chip inductors have also been reduced in size, and are required to have a length of about several mm. Therefore, the length of the coil-shaped conductive wire contained in the magnetic core is also about several mm, and the size of the cavity of the mold is accordingly sized. Performing wet press molding by inserting small coiled conductors one by one into such a small cavity has a very poor productivity.

Therefore, the cavity of the mold is made long or large, and a long coil-shaped conductive wire is placed in this cavity.
By arranging books or a plurality of them, injecting ceramic slurry into them, performing wet press forming, and then cutting into individual chips, the productivity is improved.

However, when cutting is performed at the stage of the molded body, there is a difference in hardness between the molded body and the built-in coil, so that the molded body is easily cracked, resulting in quality deterioration. On the other hand, there is also a method of cutting after firing the molded body, but this method has the disadvantage that the hardness of the sintered body is extremely high, so that it takes a long time to cut, the wear of the cutting blade is large, and the cost is high. is there.

It is an object of the present invention to provide a method of manufacturing a chip type inductor capable of improving the quality of a magnetic core, improving the productivity, and reducing the processing cost.

[0011]

The above object is achieved by the present invention. That is, the invention according to claim 1 includes a step of inserting a coiled conductive wire formed by spirally forming a metal wire into a molding die, and a step of injecting a magnetic ceramic slurry into the molding die. Forming the ceramic slurry injected into the molding die by a wet press method to obtain a molded body in which the coil-shaped conductor is embedded, and calcining the molded body at a temperature not lower than the hardness of the coil-shaped conductor. A step of grinding the calcined sintered body to a predetermined size; a step of main-baking the sintered body grinded to a predetermined dimension at a temperature higher than that of the preliminary firing to obtain a magnetic core; Forming external electrodes connected to both ends of the coiled conductor on both end surfaces of the core.

First, a coiled conductive wire is inserted into a molding die, and a wet press is performed after injecting a magnetic ceramic slurry. A molded body in which coiled conductive wires are embedded can be obtained by wet pressing, but a molded body formed by wet pressing has a denser ceramic structure than a molded body formed by extrusion molding, and a molded body having a high density can be obtained. Since the rally is compressed, no or very little binder is required. Therefore, when this molded body is fired, the fired magnetic core has a high density and a small amount of binder, so that pores are hardly generated and a high quality inductor can be obtained.

As described above, since the coil is inserted into the molding die and wet pressing is performed, the inductor can be formed by one molding. Therefore, the number of manufacturing steps is reduced as compared with the multilayer inductor, and the process is simplified as compared with the extrusion molding method. In addition, since a metal wire is used as the coil-shaped conductive wire, it is needless to say that a high inductance value and a low resistance value can be obtained.

When firing the molded body, the molded body is first preliminarily fired at a temperature at which the hardness is equal to or higher than the hardness of the coil-shaped conductive wire, instead of firing at once. The calcination temperature may be, for example, about 700 to 900 ° C., as described in the second aspect. If the sintered body after pre-baking is ground, the sintered body has a hardness equal to or higher than that of the internal coil, so it can be cut without cracking. Can be shortened. After cutting the calcined sintered body to the specified dimensions,
This is calcined to obtain a magnetic core containing a coiled conductive wire. Then, an inductor can be obtained by forming external electrodes on both end surfaces of the magnetic core where both end portions of the coil-shaped conductive wire are exposed.

In the case of ordinary magnetic ceramics, firing shrinkage starts at around 700 ° C. and ends at around 900 ° C. The hardness of the sintered body increases from the start of sintering shrinkage, and becomes extremely high at a temperature equal to or higher than the end temperature of sintering shrinkage. Since the coil (metal) has an intermediate hardness between the start and end of shrinkage of the ceramic, the pre-sintering may be performed at a temperature higher than the hardness of the coil and lower than the end temperature of shrinkage.

When inserting the above-mentioned coiled conductive wire into a mold,
If the coiled wire is biased to one side, an inductor having stable characteristics cannot be obtained. Therefore, as described in claim 3, before the coil-shaped conductor is inserted, a non-fired molded body having the same composition as the magnetic core is formed in the molding die, and the coil-shaped conductor is supported at the center of the core. It is desirable to arrange the compact. If the supporting molded body is provided with a holding groove for positioning the coiled conductive wire, the stability is further improved and a high quality inductor is obtained.

When the molded body formed by wet press molding as described above is preliminarily fired and fully fired, the ceramic material shrinks during firing. In this case, since the ceramic shrinks but the coil does not shrink, a gap is formed inside the coil. There is a possibility that flux or the like may enter the gap from the outside and affect the characteristics. In addition, cracks may occur inside the coil due to firing shrinkage as well as gaps.

In order to solve such a problem, claim 5
Before inserting the coil-shaped conductor into the molding die as described above, it is desirable to insert a core made of preliminarily fired magnetic ceramic into the coil-shaped conductor. That is, since the core inside the coiled conductor does not shrink, no gap is generated inside the coiled conductor due to firing, and cracking due to firing shrinkage can be prevented. The core was made of pre-baked magnetic ceramic because when the core was cut into chips after pre-baking, if the hardness of the core was different from other pre-sintered bodies, cracks would occur during cutting, and the cutting time Because it can be long

The core may have the same composition as the magnetic core provided outside the coil, or may have a different composition. With the same composition, a homogeneous magnetic core can be obtained inside and outside the coil. In the case of different compositions, for example, the magnetic permeability can be made different between the inside and outside of the coil, and the characteristics of the inductor can be easily changed.

[0020]

1 and 2 show a first embodiment of a chip type inductor according to the present invention. This inductor 1
Numeral 0 has a prismatic magnetic core 11, which is obtained by firing magnetic ceramics such as Ni-Cu-Zn ferrite. The core 11
May be various shapes such as a columnar shape in addition to a prismatic shape. A coil-shaped conductive wire 12 in which a metal wire made of Ag, Cu or an alloy thereof is formed in a spiral shape is embedded in the core 11. Both ends of the coil-shaped conductive wire 12 are exposed at both end surfaces of the magnetic core 11, and external electrodes 13 and 14 made of a thick-film electrode or the like are formed on the exposed surfaces. Therefore, the external electrodes 13 and 14 and both ends of the coiled conductive wire 12 are electrically connected.

Here, a specific method of manufacturing the chip-type inductor 10 having the above configuration will be described with reference to FIG.
First, as shown in FIG. 3A, the supporting molded body 22 is housed in the cavity 21 formed by the molding die 20 and the lower die 26. The supporting molded body 22 is obtained by wet-pressing a ceramic material having the same composition as the core 11 under substantially the same conditions as a molded body 27 described later, and uses an unfired molded body. The shape of the supporting molded body 22 may be a flat plate shape as shown in FIG. 4A, but may be a plate having a holding groove 22a having a circular cross section on the upper surface as shown in FIG. As described above, a holding groove 22b having a V-shaped cross section may be provided. The holding grooves 22 a and 22 b have a function of holding the outer periphery of the coiled conductive wire 12, preventing the coiled conductive wire 12 from being biased when a ceramic slurry 23 described later is injected, and positioning the coiled conductive wire 12 at the center of the cavity 21. In addition, the support molding 2
The shape of 2 is not limited to FIG. 4 and can be arbitrarily changed as needed.

Next, as shown in FIG.
1, the coiled conductive wire 12 is inserted and placed on the support molding 22. The conducting wire 12 of this embodiment is, for example, φ200
A μm Ag wire is spirally wound so as to have an inner diameter of 1.25 mm and a pitch between coils of 0.4 mm, and corresponds to an integral multiple of the entire length of the inductor, especially in order to perform multi-cavity. It is formed long so as to be long. In order to prevent the ceramic from cracking during firing, a coat layer may be provided around the Ag wire with a substance that sublimates during firing (for example, epoxy resin).

Next, as shown in FIG.
The ceramic slurry 23 is poured into 1 and wet pressing is performed. As the ceramic slurry 23, for example, Ni-
The following additives and water were added to a raw material composed of Cu-Zn-based ferrite, and mixed with a ball mill for 20 hours to obtain a slurry. Dispersant: polyoxyalkylene glycol (1.0% by weight based on the weight of the raw material) Antifoaming agent: polyether-based antifoaming agent (0.1% by weight of the raw material)
5% by weight) Binder: Acrylic binder (0.5% by weight of raw material)
% By weight) Water: (50.0% by weight based on raw material weight)

After injecting the ceramic slurry 23, the upper surface of the cavity 21 is covered with a filter 24 that allows only moisture to escape, and the upper surface is packed with a porous upper mold 25 from above. Then, by pushing up the lower mold 26 from below the molding die 20, for example, 100 kg
Press molding is performed by extracting water through the filter 24 through the drain hole 25a of the upper die 25 under a pressure of f / cm ² for 5 minutes.

As shown in FIG. 3D, since the ceramic slurry 23 is pressurized at a high pressure, the green body 27 thus formed has a high density and a high density.
Is filled around the coiled conductive wire 12 without gaps. Then, the part formed of the ceramic slurry 23 and the part formed of the supporting molded body 22 are integrated.

Thereafter, the molded body 27 is taken out of the molding die 20, and the molded body 27 is dried at, for example, 40 ° C. for 50 hours, and then placed in an alumina box at a predetermined temperature (800 ° C. in this example). It was calcined to obtain a calcined body 28 as shown in FIG. When the ceramic having the composition of the present example was heat-treated with a temperature profile as shown in FIG.
Shrinkage starts around 00 ° C and ends at around 900 ° C. As the shrinkage proceeds, the hardness of the pre-sintered body 28 increases. Then, by performing the calcination at a temperature slightly higher than the shrinkage amount (Sc in FIG. 5) corresponding to the hardness of the coiled conductive wire 12, the tentative sintered body 28 has a strength necessary for cutting.

Next, as shown in FIG. 3 (f), the temporary sintered body 28 obtained by the preliminary firing was cut or polished to obtain a chip-shaped temporary sintered body 29. At this stage, both end portions of the coiled conductive wire 12 are exposed on both end surfaces of the temporary sintered body 29. When performing the cutting or polishing as described above, the temporary sintered body 29
Is softer than the sintered body after the main firing, so that the cutting time or the polishing time can be shortened and the wear of the cutting blade is reduced.

The pre-sintered body 29 cut into a chip shape is placed in an alumina box, and is heated to a temperature higher than the calcination temperature, for example, 93.
The main baking was performed at 0 ° C. or 960 ° C. for 2 hours. This allows
The ceramic component of the pre-sintered body 29 completes shrinkage, and becomes the magnetic core 11. Thereafter, external electrodes 13 and 14 were formed on both end surfaces of the core 11 where the coil-shaped conductive wires 12 were exposed, thereby obtaining a chip inductor 10 (see FIGS. 1 and 2). As a method for forming the external electrodes 13 and 14, for example, an Ag paste or an AgPd paste was applied, dried at 150 ° C. for 15 minutes, and baked at 800 ° C. for 10 minutes. If necessary, Ni-Sn plating or the like may be performed.

As described above, since the compact 27 is wet-pressed, it has a high density and a high filling degree. In addition, since the ceramic slurry 23 contains almost no binder, the generation of pores can be prevented. Therefore, by pre-firing and main firing the molded body 27, the high quality magnetic core 11 can be obtained. In addition, since the bias of the coil-shaped conductive wire 12 is prevented by the supporting molded body 22, the coil-shaped conductive wire 12 is located at the center of the core 11, and an inductor having stable characteristics can be obtained.

FIG. 6 shows a second embodiment of the present invention. In the above embodiment, the coiled conductive wire 12 was directly inserted into the molding die 20, but when the ceramic material contracted by firing,
There is a possibility that cracks or gaps may occur in the inner ceramic portion of the coiled conductive wire 12. Therefore, as shown in FIG. 6, the coiled conductive wire 12 is wound around the core 30 and inserted into the molding die 20. The coiled conductive wire 12 may be tightly wound around the outer periphery of the core 30 or may be simply inserted. As the winding core 30, a ceramic material having the same composition as that of the magnetic core 11 may be used, or a different ceramic material may be used. Since the core 30 hardly shrinks during the preliminary firing or the main firing of the molded body 27, it is possible to prevent the inner portion of the coil 12 from being cracked or a gap from being generated.

The core 30 may be fired under the same conditions as in the main firing, but is fired under substantially the same conditions as in the preliminary firing in FIG. The hardness is preferably equal to that of the temporary sintered body 28. This is because when the core 30 is cut into chips as shown in FIG. 3 (f) and the hardness of the core 30 is different from that of the other pre-sintered bodies 28, cracks may occur at the time of cutting or the cutting time may be prolonged. Because there is.

In the above embodiment, in order to hold the coiled conductive wire 12 at the center of the molding die 20, the supporting molding 22
However, a support portion for supporting the coiled conductive wire 12 or the core 30 may be formed on the inner surface of the mold 20 instead of the supporting molded body 22.

[0033]

As is apparent from the above description, claim 1
According to the invention described in the above, since a molded body in which the coil-shaped conductor is embedded by a wet press method is obtained, the molded body has a higher density than a molded body formed by an extrusion molding method,
In addition, a binder is unnecessary or a very small amount is required. for that reason,
When this molded body is fired, the fired magnetic core has a high density, and there is little binder so that no pores are generated.
A high quality inductor can be obtained. Also, after pre-baking the molded body at a temperature that is equal to or higher than the hardness of the coil-shaped conductor,
Since the grinding process is performed, the ceramic is relatively soft, chip processing is easy, and cracks do not occur. Then, since the large calcined body is cut into chips and then calcined to obtain an inductor, the mass productivity is excellent and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an external perspective view of an example of an inductor according to the present invention.

FIG. 2 is a sectional view of the inductor of FIG. 1;

FIG. 3 is a process drawing of an example of a method for manufacturing an inductor according to the present invention.

FIG. 4 is a perspective view of a supporting molding.

FIG. 5 is a change diagram of a temperature profile and a shrinkage amount during firing of a ceramic.

FIG. 6 is a perspective view of a state in which a coiled conductive wire is inserted through a core.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Chip-type inductor 11 Magnetic core 12 Coiled wire 13, 14 External electrode 20 Molding die 22 Supporting molded body 23 Ceramic slurry 27 Molded body 28 Temporary sintered body 29 Chip-shaped temporary sintered body

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor: Masashi Morimoto 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto F-term in Murata Manufacturing Co., Ltd. (reference) 5E062 FF01 FF02 FF10 FG07

Claims (5)

[Claims] A step of inserting a coiled conductive wire formed by spirally forming a metal wire into a molding die; a step of injecting a magnetic ceramic slurry into the molding die; The step of molding the injected ceramic slurry by a wet press method to obtain a molded body in which the coiled wire is embedded, the step of temporarily calcining the molded body at a temperature equal to or higher than the hardness of the coiled wire, A step of grinding the sintered body to a predetermined size, and a step of performing a main firing of the sintered body ground to a predetermined dimension at a higher temperature than during the preliminary firing to obtain a magnetic material core,
Forming external electrodes connected to both ends of the coil-shaped conductor on both end surfaces of the magnetic core. 2. The method for manufacturing a chip-type inductor according to claim 1, wherein the pre-baking temperature is 700 to 900 ° C. 3. An unsintered molded body having the same composition as that of the magnetic core before the coil-shaped conductor is inserted into the molding die, for supporting the coil-shaped conductor at the center of the core. The method for manufacturing a chip-type inductor according to claim 1, wherein a molded body is disposed. 4. The method for manufacturing a chip-type inductor according to claim 3, wherein said supporting molded body is provided with a holding groove for positioning a coiled conductive wire. 5. The method according to claim 1, wherein the coil-shaped conductive wire is inserted into a molding die in a state of being inserted around the outer periphery of a core made of pre-fired magnetic ceramic. 3. The method for manufacturing a chip-type inductor according to claim 1.