JP2011238653A - Method for manufacturing magnetic core and inductor having the same manufactured thereby - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a magnetic core, in which low inductance, low resistance and an ultra low profile of 1 mm or less can be realized; and an inductor having the magnetic core manufactured thereby.SOLUTION: Green sheets 2 to 4 of upper, middle and lower layers including magnetic powder and organic binder are formed. On the green sheet 4 of the middle layer, a plurality of linear grooves spaced at an interval therebetween are then formed to be filled with a different material layer 5 made of a material different from a magnetic material. These three layers are then laminated and bonded by thermocompression to form a green sheet laminated body 7. Thereafter, the green sheet laminated body 7 is separated at positions between the different material layers 5 in the green sheet 4 of the middle layer. A resultant belt-shaped green sheet laminated body 7a is then baked and the different material layer 5 therein is removed. Consequently, a through-hole is formed instead at a position where the different material layer is formed, thus providing a magnetic core having the through-hole.

Description

  The present invention relates to a method of manufacturing a magnetic core having a through hole for inserting a flat conductor, and an inductor using the magnetic core obtained thereby.

Generally, an inductor for the purpose of voltage stabilization and noise removal is incorporated in a power supply board or the like of various electric devices.
For example, this inductor includes a pair of E-shaped cores made of a magnetic material facing each other on both sides of a coil made of a flat copper wire as shown in Patent Document 1, and the magnetic core of the E-shaped core is placed on the coil. It is configured by being inserted into the central part.

  By the way, in the mobile personal computer, in order to reduce power consumption mainly, a low voltage of the CPU and a large current of 30 to 40 A due to the low voltage are progressing. Along with this, a power inductor for a DC-DC converter incorporated in a power supply board is also required to have a small electrical resistance and a small inductance.

However, in the inductor using the coil described above, there is a problem that it is difficult to reduce the DC resistance because the total length of the copper wire is inevitably increased due to the necessity of inductance adjustment.
Thus, an inductor that uses silver as a material for the coil and is downsized as a multilayer inductor has been proposed. However, there is a problem that the price of parts rises and it is practically difficult to use.

On the other hand, in the following Patent Document 2, a plate-shaped rectangular copper wire is incorporated between a U-shaped magnetic core and a flat magnetic core so that both ends in the longitudinal direction are exposed. Inductors have been proposed.
According to such an inductor, since a plate-like rectangular copper wire is used as a conductor, there is an advantage that the electric resistance can be further reduced and the size can be reduced.

JP-A-9-232155 JP 2000-164431 A

However, in recent years, power inductors for DC-DC converters incorporated in the power board of this type of mobile personal computer are required to have an ultra-low profile such as a total thickness of 1 mm or less in addition to the low electrical resistance described above. is there.
On the other hand, even in the above-described conventional inductor that can be miniaturized, the overall thickness dimension is about 5.5 mm, and generally when a magnetic core is formed by cutting, Since it is difficult to make the thickness dimension 1 mm or less, further technical development to meet the demand is desired.

  The present invention has been made in view of the above circumstances, has a small inductance and electrical resistance, can realize an ultra-low profile of 1 mm or less, and can easily cope with SMT and array. It is an object of the present invention to provide a method of manufacturing a magnetic core that can be manufactured and an inductor having a magnetic core obtained by the method.

  In order to solve the above-described problem, the method for manufacturing a magnetic core according to claim 1 includes at least an upper layer and a lower layer green sheet including magnetic powder and an organic binder, and at least including magnetic powder and an organic binder. Forming a green sheet of an intermediate layer in which two belt-like magnetic layers and at least one belt-like different material layer made of a material different from the magnetic powder are alternately formed in the horizontal direction; After forming the green sheet laminate by laminating the green sheets of the upper layer, the intermediate layer and the lower layer and bonding them by thermocompression bonding, the green sheet laminate is bonded to the different material layer in the green sheet of the intermediate layer. The magnetic material layer is cut along the extending direction at a position sandwiched between them, and the obtained belt-shaped green sheet laminate is fired. By removing the dissimilar material layer before, during or after the firing of the green sheet laminate, it is finally possible to obtain a magnetic core having a through-hole formed at the position where the dissimilar material layer is formed. It is a feature.

  The invention according to claim 2 is the invention according to claim 1, wherein the green sheet laminate is cut at a position where one of the different material layers in the green sheet of the intermediate layer is sandwiched. It is characterized by doing.

  On the other hand, the invention according to claim 3 is the position of the invention according to claim 1, wherein the green sheet laminate is sandwiched between the two different material layers in the green sheet of the intermediate layer. It cut | disconnects in, It is characterized by the above-mentioned.

  The invention according to claim 4 is included in the green sheet of the upper layer and the lower layer in the different material layer in the green sheet of the intermediate layer in the invention of any one of claims 1 to 3. A magnetic powder having a magnetic permeability different from that of the magnetic powder is included.

  Furthermore, the invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein a water-soluble material is used as the foreign material layer, and the green sheet laminate is fired before the green sheet laminate is fired. The laminated body is ultrasonically cleaned to remove the foreign material layer.

  On the other hand, the invention according to claim 6 is the invention according to any one of claims 1 to 4, wherein the organic binder is used as the dissimilar material layer, and the dissimilar material layer is formed at the time of firing the green sheet laminate. It is characterized by removing.

  On the other hand, the invention according to claim 7 is the invention according to any one of claims 1 to 4, wherein the green sheet laminate is fired using a mixture of the organic binder and powder as the foreign material layer. Thereafter, the residual powder is removed.

  Next, the inductor according to claim 8 is configured such that a flat plate made of copper is inserted as a conductor into the through hole of the magnetic core obtained by the method for manufacturing a magnetic core according to any one of claims 1 to 7. It is characterized by.

  The invention according to claim 9 is the invention according to claim 8, wherein both end portions of the conductor extending from the through hole of the magnetic core are bent to a bottom surface level of the magnetic core. It is characterized by being.

  Furthermore, the invention described in claim 10 is a structure in which a flat plate made of copper is inserted as a conductor in each of the through holes of the magnetic core obtained by the method of manufacturing a magnetic core according to claim 3, and A groove is formed on the surface of the magnetic core located between the conductors along the extending direction of the conductor.

  According to the method for producing a magnetic core according to any one of claims 1 to 7, an upper layer and a lower layer green sheet are formed by drying a magnetic slurry obtained by kneading a magnetic powder and an organic binder, and the above The green sheet of the intermediate layer includes at least two strip-shaped magnetic layers including magnetic powder and an organic binder, and at least one strip-shaped dissimilar material layer made of a material different from the magnetic powder in the horizontal direction. The thickness at which the through-holes are finally formed at the formation position of the different material layer by alternately forming and sintering the green sheet laminate in which these layers are laminated and removing the different material layer of the intermediate layer An ultra-low magnetic core having a dimension of 1 mm or less can be easily manufactured.

  At this time, as in the invention described in claim 2, if the green sheet laminate is cut at a position sandwiching one of the different material layers in the green sheet of the intermediate layer, a conductor is inserted. Therefore, a magnetic core having a cross-sectional shape in which one through hole is formed can be obtained.

  On the other hand, according to the invention described in claim 3, the conductor is inserted by cutting the green sheet laminate at a position sandwiching two different material layers in the green sheet of the intermediate layer. Therefore, it is possible to obtain a letter-shaped magnetic core in which two through holes are formed with a wall portion formed by the magnetic layer interposed therebetween. As a result, it is possible to easily cope with arraying of inductors.

Furthermore, according to the invention described in claim 4, the magnetic permeability μ ₁ of the magnetic substance contained in the magnetic layer of the green sheet of the intermediate layer is set to the permeability of the magnetic substance contained in the green sheet of the upper layer and the lower layer. By changing the _{value with} respect to μ ₀ , the inductance of the inductor as the final product according to claims 8 to 10 can be adjusted to an appropriate value in advance.

  At this time, the intermediate layer is constituted by a plurality of layers of green sheets instead of one layer, and the magnetic permeability of the magnetic substance in the magnetic layer in one of the green sheets can be changed. By adopting, it becomes possible to adjust the inductance more finely.

In addition, the removal of the different material in the different material layer formed in the green sheet of the intermediate layer for finally forming the through hole at the position where the different material layer is formed should be performed before firing, during firing or after firing. Can do.
For example, when a water-soluble material is used as the dissimilar material layer as in the invention described in claim 5, the green sheet laminate is ultrasonically cleaned before firing the green sheet laminate, The foreign material can be removed.

  Further, as in the invention described in claim 6, when the different material layer is an organic binder having the same quality as the organic binder contained in the upper layer and lower layer green sheets, the green sheet laminate The foreign material layer can be removed at the same time as the body is fired. In this case, since a separate process for removing the different material is not necessary, the manufacturing becomes easy.

  Furthermore, when the green sheets of the upper layer and the lower layer are extremely thin, it is necessary to maintain the shape as a whole even during lamination and sintering. Thus, it is preferable to use a mixture of an organic binder and powder that is not integrated with the magnetic powder as the different material layer. In such a case, since the organic binder is removed when the green sheet laminate is fired, only the residual powder can be removed after firing.

  Therefore, according to the inductor according to any one of claims 8 to 10, a copper flat strip is used as a conductor in the through hole of the magnetic core obtained by the invention according to any one of claims 1 to 7. By inserting, the inductance and electric resistance are small, and an ultra-low height of 1 mm or less can be realized.

  Moreover, as in the ninth aspect of the invention, by bending both end portions of the conductor extending from the through hole of the magnetic core to the bottom surface level of the magnetic core, it can be used as a mounting terminal as it is. Therefore, it is possible to easily cope with SMT (Surface Mount Technology).

  Further, as in the invention described in claim 10, by inserting a copper flat strip as a conductor into each of two through holes formed in parallel in a magnetic core having a Ni-shaped cross section, It can also be used as an inductor array component. Moreover, if a groove is formed on the surface of the magnetic core located between the two conductors along the extending direction of the conductor, by adjusting the depth, width, etc. of the groove, by a simple method, By adjusting the coupling coefficient between the two conductors, an inductor having an appropriate value of inductance can be obtained.

It is a perspective view showing one embodiment of an inductor concerning the present invention. FIG. 8 is a perspective view showing a modification of the inductor in FIG. 1. It is process drawing which shows the manufacturing method of the magnetic body core of FIG. 1 in steps. FIG. 4 is three types of process diagrams showing removal of a different material layer in the manufacturing method of FIG. 3. 1A and 1B show a modified example in which the inductor of FIG. 1 is made into SMT, in which FIG. 1A is a perspective view of the whole, and FIG. 1B is a circuit diagram as its electrical component. FIG. 4 shows another embodiment of the inductor according to the present invention, in which (a) is a perspective view of the whole, and (b) is a circuit diagram as its electrical component. It is a perspective view which shows the modification of the magnetic body core in the inductor of FIG. FIG. 7 is a perspective view showing another modification of the inductor in FIG. 6. It is sectional drawing which shows typically the magnetic path in the inductor of FIG.

First, an embodiment of a method for manufacturing a magnetic core according to the present invention will be described with reference to FIGS.
In this manufacturing method, for example, ferrite powder (magnetic powder) such as Mn—Zn and an organic binder such as PVB (polyvinyl butyral) are kneaded to form a ferrite slurry 1, and this magnetic slurry is treated with a doctor blade method or An upper layer green sheet 2 and a lower layer green sheet 3 (see FIG. 3D) having a predetermined thickness are manufactured by forming into a sheet shape and drying using a sheet molding machine such as an extruder.

  In parallel with this, as shown in FIG. 5A, a slurry made of a different material different from ferrite is similarly formed into a sheet shape by a doctor blade method or the like and dried to obtain a predetermined thickness. The intermediate green sheet 4 is manufactured. Here, the foreign material slurry is a slurry containing a material that is not fixedly bonded to the ferrite slurry 1 or the sintered ferrite before and after sintering, and is a slurry of a water-soluble material such as PVA (polyvinyl alcohol). An organic binder such as PVB (polyvinyl butyral), or a slurry obtained by kneading powder such as alumina, silica, zirconia and the above organic binder, a dispersing material, a solvent, and a plasticizer can be applied.

  Then, as shown in FIG. 4B, a plurality of strip-shaped groove portions 4a having a predetermined width dimension are formed in the green sheet 4 at equal intervals in the horizontal direction by punching or the like. . Then, as shown in FIG. 3C, each of the grooves 4a is filled with the ferrite slurry 1 and dried. As a result, the belt-like different material layers 5 and the magnetic layers 6 are alternately formed in the horizontal direction on the green sheet 4 of the intermediate layer.

  Next, as shown in FIG. 4D, an intermediate layer green sheet 4 is placed between the upper layer green sheet 2 and the lower layer green sheet 3 and laminated, and these are integrated by thermocompression bonding. Thus, the green sheet laminate 7 is formed. The green sheet laminate 7 is cut along the extending direction at the central portion of the magnetic layer 6 with the different material layer 5 in the green sheet 4 of the intermediate layer interposed therebetween, so that a plurality of strips are formed. The green sheet laminate 7a is manufactured.

  Next, the band-like green sheet laminate 7a is fired, and the different material layer 5 is removed before, during or after firing the green sheet laminate 7a, thereby finally forming the different material layer 5. A magnetic core having a through-hole formed at a position is obtained.

  That is, when each of the green sheets 2, 3, 4 has a relatively high strength, use a water-soluble material such as PVA as the different material layer 5 as shown in FIG. In this case, the green sheet laminate 7a is ultrasonically cleaned before firing to remove the foreign material layer 5, and then fired in a sintering furnace to produce a magnetic core.

  Further, as shown in FIG. 4B, an organic binder such as PVB (polyvinyl butyral) similar to the ferrite slurry 1 that is a raw material of the green sheets 2 and 3 can be used as the different material layer 5. In this case, after degreasing the green sheet laminate 7a, the magnetic core from which the foreign material layer 5 is removed can be manufactured by supplying the green sheet laminate 7a to the sintering furnace as it is and sintering it.

  Further, when the strength of each of the green sheets 2, 3, 4 is relatively low, as shown in FIG. 4 (c), different materials are used to maintain the shape of the green sheet laminate 7 a until sintering. As the layer 5, it is preferable to use a slurry obtained by kneading a powder such as alumina, silica, zirconia and the like, a binder, a dispersant, a solvent, and a plasticizer. In this case, the binder etc. in the said different material layer 5 are removed by baking the green sheet laminated body 7a in a sintering furnace. After the sintering, the remaining powder 5a can be removed by ultrasonic cleaning.

  As shown in FIG. 4, the magnetic core manufactured by the above steps is formed by the top plate portion 8, the bottom plate portion 9 formed by the green sheets 2 and 3, and the magnetic layer 6 in the green sheet 4 of the intermediate layer. The side wall portion 10 is formed and has a cross-sectionally R shape in which a through hole is formed at a position where the different material layer 5 is formed. Then, according to the trial production by the present inventors, the thickness of the top plate 8 and the bottom plate 9 is set to 0.17 mm, and the thickness of the side wall 10 is set to 0.09 mm. It is possible to form an extremely low profile such as 0.43 mm.

Then, by inserting a copper flat strip as the conductor 11 into the through hole, a power inductor 12 as shown in FIG. 1 can be obtained.
As shown in FIG. 2, in the power inductor 13 of the final product, when a relatively large inductance is required, it can be dealt with by increasing the length dimension of the magnetic core 14. When the body core 14 is manufactured, a water-soluble material or a mixture of an organic binder and powder is used as the different material layer 5 as shown in FIGS. 4 (a) and 4 (c). In order to easily remove these, it is preferable to form an opening 6a in the center in the longitudinal direction of the magnetic layer in the green sheet of the intermediate layer.

  Further, in the above embodiment, as the magnetic substance contained in the magnetic layer 6 of the upper layer green sheet 2, the lower layer green sheet 3, and the intermediate layer green sheet 4, all are ferrites such as Mn—Zn type. Although it showed about the case where powder was used, not only this but as a magnetic substance contained in magnetic body 6 layer of green sheet 4 of an intermediate layer, Zn system, Mn system, Co system, Ni system, Zn-Ni system, In the final product such as Zn—Co, other ferrite powders having different magnetic permeability from the top plate portion 8 and the bottom plate portion 9 can be used.

  Then, as the magnetic powder of the green sheet 4 of the intermediate layer in this way, the magnetic powder of the green sheets 2 and 3 of the upper and lower layers and the one having different magnetic permeability from each other are used. The inductances at 12 and 13 can be adjusted to appropriate values in advance.

  Further, as shown in FIG. 5, if both ends 11a of the conductor 11 extending from the magnetic core of the power inductor 12 are bent to the same level as the bottom surface of the magnetic core, the end 11a is It can be used as a mounting terminal as it is, and therefore can be easily adapted to SMT.

Next, FIGS. 6A and 6B show a magnetic core 20 obtained by another embodiment of the method for manufacturing a magnetic core according to the present invention and a coupled inductor 21 using the same. is there.
First, the manufacturing method of the magnetic core 20 will be described. The upper layer green sheet 2, the lower layer green sheet 3, the strip-like dissimilar material layer 5 and the magnetic layer 6 having a predetermined thickness are alternately formed in the horizontal direction. The process of manufacturing the green sheet 4 of the intermediate layer, laminating these and integrating them by thermocompression bonding to form the green sheet laminate 7 is the same as that shown in FIG.

  In the present embodiment, the green sheet laminate 7 is sandwiched between the two different material layers 5 in the intermediate green sheet 4, and extends in the central direction of the outer magnetic layer 6. By cutting along, a plurality of strip-shaped green sheet laminates including two different material layers 5 in parallel are manufactured.

Next, in the same manner as shown in FIG. 4, the strip-shaped green sheet laminate is fired, and the two dissimilar material layers 5 are removed before, during or after firing the green sheet laminate. As a result, a magnetic core in which two through holes are formed in parallel at an interval at the formation position of the different material layer 5 is finally obtained.
The coupled inductor 21 can be obtained by inserting copper flat strips as the conductors 22a and 22b into the respective through holes.

Here, in the coupled-inductor 21, as shown in FIG. 6 (b), an inductance component due to one of the conductors 22a includes a self-inductance L _1, the sum of the leakage inductance L ₁ '. Further, the inductance component by the other conductor 22b has a self-inductance L _2, the sum of the leakage inductance L ₂ '.

And, this type of coupled inductor 21 has a low ripple because, in a steady state, self-inductances L ₁ and L ₂ are mainly used and inductance increases. On the other hand, in the transient state, the leakage inductances L ₁ ′ and L ₂ ′ are mainly used, and the inductance is reduced and the high-speed response is possible.
In addition, since copper flat strips are used as the conductors 22a and 22b, the electrical resistance is small.

  Such characteristics such as low voltage and large current compatibility, low ripple, and high-speed response are characteristics particularly required as a power source for digital devices such as the above-mentioned mobile personal computers. The inductor 21 can be suitably used as an inverter for a step-down DC-DC converter.

  At this time, as shown in FIG. 6A, if both end portions of the conductors 22a and 22b extending from the magnetic core 20 are bent to the same level as the bottom surface of the magnetic core 20, The end can be used as a mounting terminal as it is as shown in FIG.

  Similarly to the case shown in FIG. 2, when the inductance is adjusted by increasing the length of the magnetic core 20, it is easy to remove the different material layer filled in the through hole 20a. In order to achieve this, it is preferable to form an opening 23 communicating with the through hole 22a at the center in the longitudinal direction between the different material layers (through holes 20a).

  Furthermore, in this type of coupled inductor 21, it is important to accurately set the coupling coefficient of the coil portion constituted by the two conductors 22 a and 22 b in order to realize the characteristics of low ripple and high-speed response in a balanced manner. It is.

  FIGS. 8 and 9 show another embodiment of the inductor according to the present invention that can meet such a demand. The coupled inductor 25 is a magnetic body of the coupled inductor 21 shown in FIG. A top plate portion 20a and a bottom plate portion 20b of the core 20, and a groove portion 24 is formed between the conductors 22a and 22b in parallel with the conductors 22a and 22b.

  And the depth dimension of these groove parts 24 is adjusted appropriately, and the ratio of the magnetic path to be coupled (common magnetic path) shown by the solid line arrow in FIG. By changing it, the coupling coefficient can be set to a desired value within the range of 0 to 1 with high accuracy.

  In the above embodiment, a plurality of strip-shaped magnetic layers 6 including magnetic powder and an organic binder and a plurality of strip-shaped different material layers 5 made of a different material are alternately arranged in the horizontal direction. In order to obtain the formed intermediate layer green sheet 4, only the case where the intermediate layer green sheet 4 made of a different material and having a predetermined thickness is first manufactured, and the groove 4 a is formed in this to be filled with the ferrite slurry 1 will be described. However, the present invention is not limited to this, and conversely, a ferrite sheet 1 is used to produce a green sheet of an intermediate layer having a predetermined thickness, and a groove is formed on the green sheet to fill and dry the above-mentioned different material slurry. It is also possible to manufacture an intermediate layer green sheet in which strip-like different material layers 5 and magnetic layers 6 are alternately formed in the horizontal direction.

  It can be used as a method for manufacturing an ultra-low magnetic core having a small inductance and electrical resistance and having a thickness of 1 mm or less, and an inductor using the same.

2 Green sheet of the upper layer 3 Green sheet of the lower layer 4 Green sheet of the intermediate layer 5 Dissimilar material layer 6 Magnetic layer 7 Green sheet laminate 7a Band-shaped green sheet laminate 11, 22a, 22b Conductor 11a End portion 12, 13 Power inductor 14, 20 Magnetic core 20a Through hole 21, 25 Coupled inductor 24 Groove

Claims (10)

The upper and lower green sheets containing the magnetic powder and the organic binder, at least two belt-like magnetic layers containing the magnetic powder and the organic binder, and at least one made of a material different from the magnetic powder Form a green sheet of an intermediate layer in which strips of different material layers are alternately formed in the horizontal direction,
Next, after the green sheets of the upper layer, the intermediate layer, and the lower layer are laminated and bonded by thermocompression bonding, the green sheet laminate is formed. The magnetic layer is cut along the extending direction at a position between which the material layer is sandwiched,
The strip-shaped green sheet laminate thus obtained is fired, and the foreign material layer is finally removed by removing the foreign material layer before, during or after the firing of the green sheet laminate. A method for producing a magnetic core, comprising: obtaining a magnetic core having a through-hole formed at a position where the magnetic core is formed.   2. The method of manufacturing a magnetic core according to claim 1, wherein the green sheet laminate is cut at a position where one of the different material layers in the green sheet of the intermediate layer is sandwiched.   2. The method of manufacturing a magnetic core according to claim 1, wherein the green sheet laminate is cut at a position where the two different material layers in the green sheet of the intermediate layer are sandwiched therebetween.   2. The magnetic layer in the green sheet of the intermediate layer includes magnetic powder having a magnetic permeability different from that of the magnetic powder contained in the green sheets of the upper layer and the lower layer. The manufacturing method of the magnetic body core in any one of thru | or 3.   The water-soluble material is used as the foreign material layer, and the green sheet laminate is ultrasonically cleaned to remove the foreign material layer before firing the green sheet laminate. 5. A method for producing a magnetic core according to any one of 4 above.   5. The method of manufacturing a magnetic core according to claim 1, wherein the organic binder is used as the foreign material layer, and the foreign material layer is removed when the green sheet laminate is fired.   The mixture of the organic binder and powder is used as the foreign material layer, and the remaining powder is removed after the green sheet laminate is fired. The manufacturing method of the magnetic body core.   8. An inductor comprising a copper flat strip inserted as a conductor in a through hole of a magnetic core obtained by the method for manufacturing a magnetic core according to claim 1.   The inductor according to claim 8, wherein both end portions of the conductor extending from the through hole of the magnetic core are bent to a bottom surface level of the magnetic core.   A flat plate made of copper is inserted as a conductor in each of the through holes of the magnetic core obtained by the method for manufacturing a magnetic core according to claim 3, and the magnetic core located between these conductors An inductor having a groove formed on the surface along the extending direction of the conductor.

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