JP2006049723A - Core manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a core manufacturing method which can effectively utilize a core material and can increase a core yield. <P>SOLUTION: A green sheet is fabricated (S102), the green sheet is positioned on a mold, and then the sheet and mold are vacuum-packaged while holding the positional relation (S104). Thereafter, the package is compressed by isostatic pressing (S106) to transfer the shape of a core to the green sheet. As a result, the loss of a core material can be reduced more than when the core shape is formed, for example, by mechanically cutting. And the green sheet having the core shape transferred thereto is subjected to binder removing and baking operations (S108) to obtain a sintered body having the core shape transferred thereto. Consequently, cracking or chipping can be suppressed more than when the core shape is formed, for example, by mechanically cutting. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a manufacturing method of a core used for a surface mount type coil element or the like.

As a conventional method for manufacturing this type of core, there are the following techniques. In other words, this is a technique in which a surface of a sintered substrate made of a core material is machined to produce an assembly of cores, and the assembly is cut to extract a plurality of cores (see, for example, Patent Document 1).
JP 2002-353056 A

  However, in the above-described technology, there is room for improvement in terms of effective use of the core material because the core assembly is produced by machining. In addition, since mechanical cutting is performed on the sintered substrate, cracks and chips are more likely to occur as the core becomes smaller, so there is room for improvement in terms of improving the core yield.

  Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a core manufacturing method capable of realizing effective use of the core material and improvement of the core yield.

  In order to achieve the above object, a core manufacturing method according to the present invention includes a step of producing a green sheet with a core material, a binder and a solvent, and the green sheet and the mold in a state where the green sheet is disposed on the mold. A step of vacuum packaging in a packaging bag, a step of pressurizing the vacuum-packed green sheet and mold by an isotropic hydrostatic press, and removing the pressurized green sheet and mold from the packaging bag to make green A step of removing the binder from the green sheet and firing after removing the sheet from the mold.

  In this core manufacturing method, the green sheets are vacuum packaged in a state where they are placed on a mold, and then pressed by an isotropic hydrostatic press to transfer the shape of the core to the green sheets. Thereby, for example, the loss of the core material can be reduced as compared with the case where the shape of the core is formed by mechanical cutting. Then, by performing binder removal and firing of the green sheet to which the core shape is transferred, a sintered body to which the core shape is transferred is obtained. Thereby, generation | occurrence | production of a crack and a chip | tip can be suppressed compared with the case where the cutting shape is given to a sintered compact and the shape of a core is formed. Therefore, according to this core manufacturing method, effective use of the core material and improvement of the core yield can be realized.

  According to the core manufacturing method of the present invention, it is possible to effectively use the core material and improve the core yield.

  DESCRIPTION OF EMBODIMENTS Hereinafter, a preferred embodiment of a core manufacturing method according to the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same or an equivalent part, and the overlapping description is abbreviate | omitted.

  First, a surface mount type coil element using a core manufactured by the core manufacturing method of the present embodiment will be described.

  As shown in FIG. 1, the surface-mounted coil element 1 includes a core unit 4 constituted by a T-type ferrite core (core) 2 and a U-type ferrite core (core) 3. As shown in FIG. 2 and FIG. 3, the T-type ferrite core 2 is integrally formed by a rectangular flat plate portion 2a and a prismatic leg portion 2b erected at the center of the flat plate portion 2a. ing. On the other hand, the U-type ferrite core 3 is integrally formed by a rectangular flat plate portion 3a and wall-shaped leg portions 3b provided upright at both ends of the flat plate portion 3a. These T-type ferrite core 2 and U-type ferrite core 3 are combined such that the leg portion 2b is positioned between the pair of leg portions 3b and the flat plate portion 2a and the flat plate portion 3a face each other. The core unit 4 having

  A coil substrate 5 is arranged in the core unit 4. The coil substrate 5 has a rectangular insulating plate 6, and a spiral coil conductor is provided on the front and back surfaces of the insulating plate 6 so as to surround a through-hole 5 a formed in the central portion of the coil substrate 5. 7 is formed. Inner ends 7 a of the coil conductors 7 are electrically connected to each other through the through electrodes 8, and outer ends 7 b of the coil conductors 7 are lead-out ends formed at both edges of the insulating plate 6. Each of the electrodes 9 is electrically connected. Each coil conductor 7 is covered with a protective resin layer 11 on the insulating plate 6.

  The coil substrate 5 configured in this way is such that the leg portion 2b of the T-type ferrite core 2 is located in the through hole 5a and each lead-out end electrode 9 faces each of the openings 4a and 4b of the core unit 4. Arranged in the core unit 4. The gap formed by the T-type ferrite core 2, the U-type ferrite core 3 and the coil substrate 5 is filled with an adhesive 12 such as an epoxy resin, and the T-type ferrite core 2, the U-type ferrite core 3 and the coil. The substrate 5 is integrated.

  In addition, as FIG. 2 shows, the core unit 4 comprises the closed magnetic circuit by flat plate part 2a, 3a and a pair of leg part 3b. A gap G is provided between the tip of the leg 2b and the flat plate 3a. This is to prevent the ferrite cores 2 and 3 from being magnetically saturated by the current flowing through the coil conductor 7 of the coil substrate 5. As an example, when one side of the core unit 4 is several mm or less, the gap G is preferably set to 0.1 μm to 100 μm, and more preferably set to 0.1 μm to 50 μm. Setting the gap G to be less than 0.1 μm is difficult in terms of processing accuracy of the ferrite cores 2 and 3, and setting the gap G to exceed 100 μm is problematic in that the inductance may decrease. There is.

  Further, as shown in FIGS. 1 and 3, the core unit 4 is formed with a terminal electrode 13 having a U-shaped cross section so as to cover each of the openings 4a and 4b. Each terminal electrode 13 is electrically connected to the lead-out end electrode 9 facing each of the openings 4a and 4b.

  Next, as a method for manufacturing the core of the present embodiment, a method for manufacturing the T-type ferrite core 2 and the U-type ferrite core 3 of the surface-mounted coil element 1 described above will be described with reference to the flowchart of FIG.

  First, a core material (for example, Ni—Cu—Zn-based ferrite material), a binder (for example, butyral resin) and a solvent (for example, diethyl phthalate) are mixed to form a slurry, and then, for example, a doctor blade method is used. Thus, a green sheet having a thickness of 180 μm is produced (step S102).

  Subsequently, as shown in FIG. 5, a plurality of green sheets 18 produced in step S102 (for example, for example, via a film 17 made of polyvinylidene chloride on a mold 16 having a plurality of molding portions 15 (for example, 6) Laminate. Then, the mold 16 is arranged on the shape holding plate 19 made of stainless steel with a thickness 21 μm made of PET (polyethylene terephthalate), and the film 21 is put on the green sheet 18. In a state where a plurality of sheets (for example, two sheets) are laminated, the green sheet 18 and the molding die 16 are put in a packaging bag 22 made of nylon and vacuum-packed to produce a vacuum packaging unit 23 (step S104). At this time, in order to remove the gas of the volatile residual solvent in the green sheet 18, it is preferable to seal the packaging bag 22 containing the green sheet 18 and the mold 16 in a vacuum under vacuum.

  The forming die 16 is formed by forming a plurality of forming portions 15 on a sheet made of the same material as the green sheet 18 and then performing binder removal and firing. The shape retaining plate 19 is used to prevent warping. It is preferable that the surface to be pressed is polished. The material of the packaging bag 22 is not limited to nylon, and may be rubber, plastic, or the like as long as it is flexible and can be sealed under vacuum.

Subsequent to step S104, as shown in FIG. 6, a plurality of vacuum packaging units 23 are arranged in a rack 24 and placed in the water in the isotropic hydrostatic press apparatus 25. Then, for example, the isotropic hydrostatic pressure press is performed by the isostatic hydrostatic press device 25 under the conditions of a water temperature of 35 ° C., a pressure of 2000 kg / cm ² , and a time of 60 seconds, and the green sheet 18 and the mold 16 that are vacuum-packed. Is pressurized (step S106). As a result, the shapes of the plurality of molded portions 15 are transferred to the green sheet 18.

  Subsequently, the vacuum packaging unit 23 is taken out from the isotropic isostatic pressing device 25, and the pressurized green sheet 18 and the mold 16 are taken out from the packaging bag 22. At this time, since a plurality of films 21 are laminated on the green sheet 18, the green sheet 18 and the mold 16 can be easily taken out from the packaging bag 22 without the packaging bag 22 adhering to the green sheet 18. Can do. Then, the green sheet 18 is removed from the mold 16. At this time, since the film 17 is interposed between the mold 16 and the green sheet 18, the green sheet 18 can be easily detached from the mold 16 without the green sheet 18 adhering to the mold 16. it can.

  The film 21 interposed between the shape holding plate 19 and the mold 16 is for preventing the shape holding plate 19 from being scratched. Further, since the shape retaining plate 19 is for preventing the molding die 16 from being deformed during the isotropic isostatic pressing, the shaping die 16 is made of a material such as a metal that can withstand the pressure during the isostatic pressing. If the shape is produced, the shape retaining plate 19 becomes unnecessary.

  After removing the green sheet 18 from the mold 16, the binder and firing of the green sheet 18 are performed (step S108). As an example, the binder removal condition is a top temperature of 400 ° C. (from 170 ° C. to 400 ° C. for 24 hours), and the firing condition is a top temperature of 980 ° C. (from 100 ° C. to 980 ° C. for 21 hours and 40 minutes).

  In this manner, since the binder and firing of the green sheet 18 are performed after the shapes of the plurality of molding portions 15 are transferred, the shape of the green sheet 18 contracts. Therefore, the shape of the molding part 15 of the molding die 16 is designed in consideration of the shrinkage rate after the green sheet 18 is fired. In firing, a weight such as an alumina substrate may be placed on the green sheet 18 in order to prevent warping.

  As described above, according to the shape of the molding part 15 of the molding die 16, as shown in FIGS. 7 to 10, the aggregate 26 of the T-type ferrite core 2 and the aggregate 27 of the U-type ferrite core 3 can be obtained. it can. A plurality of T-type ferrite cores 2 and U-type ferrite cores 3 can be taken out by cutting the aggregates 26 and 27 along the cutting lines Lx and Ly. The assembly 26 of the T-type ferrite core 2 and the assembly 27 of the U-type ferrite core 3 are integrated by the adhesive 12 with the assembly of the coil substrate 5 sandwiched therebetween, and then cut along the cutting lines Lx and Ly. May be.

  As described above, in the core manufacturing method of the present embodiment, the green sheets 18 are vacuum-packed in a state where they are arranged on the mold 16 and then pressed by an isotropic hydrostatic press, whereby the green sheets are obtained. The shape of the T-type ferrite core 2 or the U-type ferrite core 3 is transferred to 18. Thereby, compared with the case where the shape of the cores 2 and 3 is formed by, for example, machining, the loss of the core material can be reduced. Then, the green sheet 18 on which the shape of the T-type ferrite core 2 or the U-type ferrite core 3 is transferred is debindered and fired, whereby the shape of the T-type ferrite core 2 or the U-type ferrite core 3 is transferred. The bodies 26 and 27 are obtained. Thereby, generation | occurrence | production of a crack and a chip | tip can be suppressed compared with the case where the cutting of a sintered compact is performed, for example and the shape of the cores 2 and 3 is formed. Therefore, according to the core manufacturing method of the present embodiment, effective use of the core material and improvement in the yield of the cores 2 and 3 can be realized.

  Further, in order to improve the dimensional accuracy of the T-type ferrite core 2 and the U-type ferrite core 3, the aggregate 26 of the T-type ferrite core 2 and the aggregate 27 of the U-type ferrite core 3 may be subjected to mechanical cutting as finishing. Good. In this case as well, the machining allowance can be smaller than when machining the sintered body to form the shapes of the cores 2 and 3, so that the loss of the core material is reduced and cracks and chips are eliminated. Generation | occurrence | production suppression can be implement | achieved.

It is a perspective view of the surface mount type coil element in which the core manufactured by the manufacturing method of the core of this embodiment is used. It is sectional drawing along the II-II line of FIG. It is sectional drawing along the III-III line of FIG. It is a flowchart which shows the manufacturing method of the core of this embodiment. It is sectional drawing of a vacuum packaging unit. It is sectional drawing of an isotropic isostatic press apparatus. It is a top view of the aggregate | assembly of a T-type ferrite core. It is sectional drawing along the VIII-VIII line of FIG. It is a top view of the aggregate | assembly of a U-type ferrite core. It is sectional drawing along the XX line of FIG.

Explanation of symbols

  2 ... T-type ferrite core (core), 3 ... U-type ferrite core (core), 16 ... molding die, 18 ... green sheet, 22 ... packaging bag.

Claims (1)

Producing a green sheet with a core material, a binder and a solvent;
Placing the green sheet and the mold in a packaging bag in a state where the green sheet is placed on the mold, and vacuum packaging;
Pressurizing the vacuum-packed green sheet and the mold with an isotropic isostatic press;
And removing the green sheet from the molding die after removing the pressurized green sheet and the molding die from the inside of the packaging bag, and then debinding and firing the green sheet. Core manufacturing method.

Images