JP7304727B2 - Composite magnetic material and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a composite magnetic body and a manufacturing method thereof.

Patent Literature 1 discloses an inductor comprising a composite magnetic body and a coil. The composite magnetic body is configured by binding soft magnetic metal powder having a flat shape with a binder component. The composite magnetic body is formed with a penetrating portion penetrating the composite magnetic body in the thickness direction. The penetrating portion includes a hole into which a pin forming the coil is inserted and a gap connected to the hole. In Patent Document 1, a milling machine is used to form the penetrating portion in the composite magnetic body.

JP 2016-39222 A

The composite magnetic material used in the inductor of Patent Document 1 has a high density of soft magnetic metal powder. These soft magnetic metal powders are each covered with an insulating film and electrically insulated from each other. However, the soft magnetic metal powder near the through portion is cut and deformed when the through portion is formed using a milling machine. As a result, the soft magnetic metal powders are electrically connected to each other, possibly reducing the electrical resistance of the inner wall surface of the through portion. Moreover, even if the soft magnetic metal powders are not electrically connected to each other, the withstand voltage in the in-plane direction of the inner wall surface of the penetrating portion may decrease, and the coil may short-circuit during use of the inductor.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a composite magnetic body in which the withstand voltage in the in-plane direction of the inner wall surface of the penetrating portion is improved, and a method for manufacturing the same.

The present invention provides, as a first composite magnetic body, a composite magnetic body in which flat soft magnetic metal powder is bound with a binder component,
A penetrating portion penetrating the composite magnetic body is formed,
The composite magnetic body is provided, wherein the surface roughness of the inner wall surface of the penetrating portion is 5 μm or more.

In addition, the present invention provides a first composite magnetic body as a second composite magnetic body,
The composite magnetic body is used as a magnetic core,
the penetrating portion is a hole for holding a penetrating conductor,
The inner wall surface provides a composite magnetic body that is the inner peripheral surface of the hole.

Further, the present invention provides a second composite magnetic body as a third composite magnetic body,
the through portion includes a hole for holding the through conductor and a gap connected to the hole;
The inner wall surface provides a composite magnetic body, which is the inner peripheral surface of the hole and the opposing side wall surfaces of the gap.

Further, according to the present invention, any one of the first to third composite magnetic bodies is provided as a fourth composite magnetic body,
The composite magnetic body contains 60% by volume or more of soft magnetic metal powder, 4% to 30% by volume of the binder component, and 10% to 30% by volume of pores. I will provide a.

Further, according to the present invention, any one of the first to fourth composite magnetic bodies as a fifth composite magnetic body,
The piercing part provides a composite magnetic body having a closed shape when viewed along the piercing direction.

The present invention also provides an inductor comprising any one of the first to fifth composite magnetic bodies and a coil,
The coil includes a first conductor provided on one of a pair of main surfaces of the composite magnetic body, a second conductor provided on the other of the main surfaces of the composite magnetic body, and disposed in the penetrating portion. A through conductor connecting a first conductor and the second conductor is provided.

Furthermore, the present invention provides a method for manufacturing a composite magnetic material in which flat soft magnetic metal powder is bound by a binder component,
Forming a compact from a mixture obtained by mixing the soft magnetic metal powder and a binder containing the binder component,
forming a thermoset by thermosetting the molding so that the Vickers hardness is 12HV1 or more and 55HV1 or less;
A method for manufacturing a composite magnetic body is provided, in which the thermosetting body is punched to form a penetrating part penetrating the thermosetting body.

By setting the surface roughness of the inner wall surface of the penetrating portion to 5 μm or more, it is possible to provide a composite magnetic body having a desired withstand voltage in the in-plane direction of the inner wall surface.

1 is a perspective view showing a magnetic core (composite magnetic body) according to one embodiment of the present invention; FIG. FIG. 5 is a perspective view showing a modification of the magnetic core according to one embodiment of the present invention; 2 is a flow chart showing a manufacturing method for manufacturing the magnetic core of FIG. 1; FIG. 4 is a diagram for explaining a measuring method for measuring the Vickers hardness of a sample (thermoset) produced by the manufacturing method of FIG. 3; FIG. 4 is a schematic diagram showing a test apparatus for performing a withstand voltage test on the inner wall surface of the through portion in the sample (magnetic core) produced by the manufacturing method of FIG. 3 ; FIG. 6 is a graph showing the results of a withstand voltage test (measurement results of resistance values with respect to applied voltage) performed on a plurality of samples using the test apparatus of FIG. 5; Test results for five samples (No. 11 to No. 15) in which the through portion was formed by milling, and test results for five samples (No. 21 to No. 25) in which the through portion was formed by punching. is shown. 7 is a graph showing surface resistivity versus applied voltage obtained based on the test results shown in FIG. Three samples with a high withstand voltage were selected from the samples (No. 11 to No. 15) in which the through portion was formed by milling, and the withstand voltage was selected from the samples (No. 21 to No. 25) in which the through portion was formed by punching. , the surface resistivity with respect to the applied voltage was determined for each of the three samples with the highest values. It is a figure for demonstrating the definition of surface roughness in this invention. A cut surface of the sample is partially shown. The cut surface is parallel to the thickness direction of the sample and perpendicular to the inner wall surface of the through portion. 4 is a graph showing the frequency distribution of surface roughness on the inner wall surface of the penetrating portion. A sample (No. 06) in which a through portion was formed by dicing, a sample (No. 16) in which a through portion was formed by milling, a sample (No. 31) in which a through portion was formed by drilling, and a through portion was formed by punching. Measurement results for the formed sample (No. 26) are shown. 4 is a graph showing the relationship between the surface roughness of the inner wall surface of the penetrating portion and the withstand voltage. Measurement results are shown for five samples (No. 11 to No. 15) in which through parts are formed by milling and five samples (No. 21 to No. 25) in which through parts are formed by punching. there is

Referring to FIG. 1, a magnetic core 10 according to one embodiment of the present invention has a rectangular plate-like shape. The magnetic core 10 is made of a composite magnetic body in which soft magnetic metal powder (not shown) is bound with a binder component (not shown). The magnetic core 10 is combined with a coil (not shown) to form an inductor (not shown). Since the magnetic core 10 has an integrally molded structure, there is no assembly variation, and it is easy to handle when configuring the inductor.

As shown in FIG. 1, the magnetic core 10 is formed with a penetrating portion 12 penetrating the composite magnetic body in the thickness direction. The through portion 12 has a plurality of holes (holes) 21 and gap portions 23 connected to the holes 21 . The penetrating portion 12 has a closed shape when viewed along the penetrating direction (thickness direction). In this embodiment, the thickness direction is the Z direction.

As shown in FIG. 1, the number of holes 21 is four in this embodiment. The hole 21 is for holding a penetrating conductor (not shown) forming a coil (not shown). The penetrating conductor is arranged in the hole portion 21 (penetrating portion 12). A second conductor (not shown) provided on the other main surface of 10 is connected. The first conductor and the second conductor form (a part of) a coil together with the penetrating conductor.

In the present embodiment, as shown in FIG. 1, the gap portion 23 includes two first gap portions (gaps) 31 connected between the holes 21 and a gap between the two first gap portions 31. It has a connected second gap portion (gap) 33 . The first gap portion 31 facilitates deformation of the hole portion 21 when the through conductor is inserted into the hole portion 21 and functions as a magnetic gap. The second gap portion 33 functions as a magnetic gap.

However, the present invention is not limited to the form shown in FIG. 1 described above. The number and arrangement of the holes 21 and the number, shape and arrangement of the gaps 23 are determined according to the required characteristics of the inductor. For example, although the inner wall surface of the first gap portion 31 is curved in the present embodiment, it may be flat. Also, the second gap portions 33 connect between the first gap portions 31, but as shown in FIG. Two second gap portions (outer leg gaps) 33A extending from the edge of the magnetic core 10A may be formed. In other words, the penetrating portion 12 may have an open shape when viewed along the penetrating direction. However, the middle leg gap is superior to the outer leg gap, which produces leakage flux, in that there is no leakage flux. In addition, the inductor using the magnetic core 10 with the middle leg gap also has the advantage that it is less affected by the peripheral conductor than the inductor using the magnetic core 10A with the outer leg gap. Note that the gap portion 23 is provided as necessary and is not essential.

Next, a method for manufacturing the magnetic core 10 will be described with reference to FIG. First, flattened soft magnetic metal powder is produced (step S301). Specifically, a Fe-based alloy is used as a raw material, and a soft magnetic metal powder is obtained by a method such as an atomizing method. Subsequently, the obtained soft magnetic metal powder is flattened using a flattening device such as a ball mill. Fe-based alloys are preferably Fe--Si-based alloys, more preferably Fe--Si--Al-based alloys (Sendust (registered trademark)) or Fe--Si--Cr-based alloys. Further, as the soft magnetic metal powder, a powder having an amorphous phase as a main phase or a powder obtained by nano-crystallizing a part thereof may be used.

Next, a binder and a solvent are weighed and mixed with the flattened soft magnetic metal powder, and if necessary, a thickener is weighed and mixed to prepare a mixture (magnetic paint) (step S302). . As the binder, it is preferable to use a binder containing an inorganic oxide as a main component. As the binder containing an inorganic oxide as a main component, for example, a methyl-based silicone resin, a methylphenyl-based silicone resin, or the like can be used. Subsequently, a magnetic paint is applied (printed) onto the substrate using a doctor blade method, a die slot method, or the like, and dried by heating to obtain a preform (green sheet) (step S303).

Next, the obtained preformed body is cut into an appropriate size, and one or a plurality of cut sheets are laminated to form a laminated body (step S304). Here, an appropriate size is, for example, a size equivalent to a two-dimensional arrangement of a plurality of magnetic cores 10 (see FIG. 1).

Next, the laminate is pressure-molded to obtain a compact (step S305). Subsequently, the obtained molded article is heated under a predetermined heating condition to be thermoset to obtain a thermoset (step S306).

In step S306, the molding is thermally cured so that the Vickers hardness is 12HV1 or more and 55HV1 or less. Heating conditions can be determined based on experiments. The Vickers hardness of the thermosetting body depends not only on the heating temperature when thermosetting the molded body, but also on the applied pressure when forming the molded body (step S305). Therefore, the heating conditions are determined in consideration of the applied pressure when forming the compact. Specifically, a plurality of samples (thermosets) were produced using various combinations of the applied pressure when forming the molded body and the heating temperature when thermosetting the molded body, and their Vickers hardnesses were measured. Determine the heating conditions based on the results.

Vickers hardness is measured as follows. First, as shown in FIG. 4, a square pyramidal diamond 41 is pressed against a sample (thermoset) 43 . Specifically, the regular quadrangular pyramid diamond 41 is pressed against the surface 45 of the sample 43 for 10 seconds with a pressing force F=1 kgf. Next, the diagonal lengths d1 and d2 of the indentation 47 formed on the surface 45 of the sample 43 are measured, and the average diagonal length d=(d1+d2)/2 is calculated. A plurality of measurements may be performed on the same sample 43, and the average value of the obtained plurality of average diagonal lengths d may be used. Vickers hardness HV≈1.8544×F (kgf)/d ² (mm ² ) is calculated using the obtained average diagonal length d. Based on this result, the thermosetting conditions under which the Vickers hardness is 12 HV1 or more and 55 HV1 or less are determined.

Referring to FIG. 3 again, the penetrating portion 12 (see FIG. 1) that penetrates the thermosetting body in the thickness direction is then formed by punching (step S307). If the Vickers hardness of the thermosetting material is lower than 12HV1, the formed through portion 12 cannot maintain its shape. For example, the lateral width of the second gap portion 33 (see FIG. 1) is reduced, and in the worst case, the second gap portion 33 is crushed. In this embodiment, the horizontal direction is the Y direction. Further, in the present embodiment, if the Vickers hardness of the thermosetting body is higher than 55HV1, damage such as cracks occurs in the thermosetting body when punching is performed. In the present embodiment, since the thermosetting body has a Vickers hardness of 12 HV1 or more and 55 HV1 or less, the thermosetting body can be punched, is not damaged by punching, and can maintain the shape of the penetrating portion 12 after working. It is possible. Moreover, the punching process requires less processing time than other processing methods such as milling, so that the penetrating portion 12 can be formed efficiently.

Next, the thermosetting body is cut into pieces corresponding to the plurality of magnetic cores 10 (see FIG. 1) (step S308). In addition, the cut thermosetting body is polished or cleaned as necessary. Note that step 308 may be performed in advance at the same time as step 307 . After that, the cut thermosetting body is baked (step S309). By this firing, the organic component of the binder is decomposed and lost, and pores are formed inside the sintered body. In addition, the inorganic component (binder component) of the binder remains and binds the soft magnetic metal powders together. More specifically, for example, the sintered body contains 60% by volume or more of soft magnetic metal powder, 4% to 30% by volume of a binder component, and 10% to 30% by volume of pores. In this way, the magnetic core 10 (composite magnetic body) in which the soft magnetic metal powder is bound by the binder component is completed. The completed magnetic core 10 has elasticity due to the existence of the pores, and its characteristics are less deteriorated by stress. In addition, since the magnetic core 10 undergoes very little shrinkage due to firing, it has high dimensional accuracy.

The reason why the through portion 12 (see FIG. 1) is formed by punching in the present embodiment will be described below.

Methods of forming penetrations 12 (see FIG. 1) include dicing, milling, drilling and stamping. Dicing, milling, and drilling all involve cutting the workpiece, while punching uses punches and dies to apply shear forces to the workpiece. In order to examine the difference in the surface state of the inner wall surface 121 of the penetrating portion 12 formed using these methods, a withstand voltage test was conducted in the in-plane direction of the inner wall surface 121 of the penetrating portion 12 . The samples were manufactured by the same manufacturing process except for the process of forming the through portion 12 . The through portion 12 was formed by dicing, milling and punching. In addition to the manufacturing process described above, a cutting process was performed to expose the inner wall surface 121 of the through portion 12 to the outside of the sample. The sample thickness was 1.15 mm.

As described above, the through portion 12 (see FIG. 1) has the hole portion 21 and the gap portion 23 . When the penetrating portion 12 is the hole portion 21, the inner wall surface 121 thereof is an inner peripheral surface, that is, a curved surface. On the other hand, the inner wall surface 121 of the gap portion 23 is a pair of side wall surfaces facing each other. The side wall surface is curved or flat. In the present embodiment, the side wall surface of the first gap portion 31 is curved, and the side wall surface of the second gap portion 33 is flat. In any case, the continuous inner wall surface 121 of the hole portion 21 and the inner wall surface 121 of the gap portion 23 are considered to have the same surface state regardless of their shape if the forming method is the same. Therefore, in the present embodiment, the withstand voltage test was performed on one of the inner wall surfaces 121 (plane) of the second gap portion 33 .

A test apparatus as shown in FIG. 5 was used for the withstand voltage test in the in-plane direction of the inner wall surface 121 of the penetrating portion 12 (see FIG. 1). The test apparatus shown in FIG. 5 has a measuring device 53 connected to two copper wires 51 arranged parallel to each other. A copper wire 51 having a diameter of 0.3 mm was used, and the distance between the copper wires 51 was 5 mm. As the measuring device 53, an insulation resistance tester TOS7200 manufactured by Kikusui Denshi Kogyo Co., Ltd. was used. The measurement was performed by pressing the sample 55 against the copper wire 51 under conditions of a temperature of 85° C. and a humidity of 85% for 1000 hours. The inner wall surface 121 of the penetrating portion 12 was brought into contact with the copper wire 51, and in this state, a voltage was applied between the copper wires 51 for 1 second to measure the resistance value. The applied voltage was increased stepwise and the measurements were repeated. The measurement results are shown in Table 1 and FIG.

As can be seen from Table 1, the resistance value of the inner wall surface 121 (samples No. 01 to 05) of the through portion 12 formed by dicing is the measurement limit value (0.3 MΩ ), and the withstand voltage could not be measured. In addition, as can be seen from Table 1 and FIG. 6, the resistance value of the inner wall surface 121 (Sample Nos. 11 to 15) of the through portion 12 formed by milling is 500 MΩ or less at an applied voltage of 10 V, and the withstand voltage is 100 V. was below On the other hand, the resistance value of the inner wall surface 121 (Sample Nos. 21 to 25) of the punched through portion 12 exceeded 700 MΩ at an applied voltage of 10V, and the withstand voltage exceeded 100V. Thus, the resistance value of the inner wall surface 121 of the through portion 12 formed by punching is generally higher than the resistance value of the inner wall surface 121 of the through portion 12 formed by other processing methods.

Based on the results in Table 1, the surface resistivity ρs of the inner wall surface 121 of the through portion 12 of each sample 55 was obtained. Based on the surface resistivity formula: surface resistivity ρs = resistance R * width W / length L, surface resistivity ρs = measured resistance value R × thickness (= 1.15 mm) / length (= 5 mm) asked. Table 2 shows the results.

From the results shown in Table 2, sample No. 1 in which the through portion 12 was formed by milling. 11 to No. Three of the fifteen samples with high withstand voltage were selected, and the average value of the surface resistivity ρs was obtained. Similarly, from the results shown in Table 2, Sample No. 1 in which the through portion 12 was formed by punching. 21 to No. Three of the 25 samples with high withstand voltage were selected, and the average value of the surface resistivity ρs was obtained. The results are shown in Table 3 and FIG.

As can be seen from Table 3 and FIG. 7, the surface resistivity ρs of the inner wall surface 121 of the through portion 12 formed by punching is one order of magnitude higher than the surface resistivity of the inner wall surface 121 of the through portion 12 formed by milling. In this way, the inner wall surface 121 of the through portion 12 formed by punching has a high surface resistivity ρs. No action required.

Next, differences in surface roughness of the inner wall surface 121 of the penetrating portion 12 due to differences in the forming method of the penetrating portion 12 were examined. Dicing, milling, drilling, and punching were used as methods for forming the through portion 12 . Samples were prepared in the same manner as in the withstand voltage test. The surface roughness in this embodiment is defined as follows.

As shown in FIG. 8 , a measurement section is set for a cut plane parallel to the thickness direction of the sample 80 and perpendicular to the inner wall surface 121 of the through portion 12 . Specifically, two portions of 90 μm (=30 μ×3) close to the surface layer are excluded from the measurement target, and the remaining portion is the measurement target. Then, a plurality of measurement sections each having a predetermined length in the thickness direction of the sample 80 are set for the portion to be measured. More specifically, in the thickness direction of the sample 80, a plurality of measurement sections are set such that the length of each measurement section is 30 μm. This setting may be performed so that mutually adjacent measurement sections partially overlap. In each set measurement section, measure the distance (Max-Min) between the most protruding portion (Max) and the most recessed portion (Min) in the horizontal direction, and use it as the section value. Then, the average value of all interval values measured for each sample 80 is obtained. The average value obtained in this manner was defined as the surface roughness of the inner wall surface 121 of the through portion 12 .

Table 4 shows the results of measuring the section values of the inner wall surface 121 of the through portion 12 of the sample 80 in which the through portion 12 was formed by dicing, milling, drilling, and punching. Table 4 shows the result of setting 38 measurement sections so that adjacent measurement sections partially overlap each other for a measurement target portion with a thickness of 970 μm (=1.15 mm−90 μ×2). Table 5 and FIG. 9 show the frequency distribution of the measured interval values. Furthermore, Table 6 shows the standard deviation σ and the average value (surface roughness) of the measured interval values. In addition, Table 7 shows the interval values, the standard deviation σ, and the average value measured for the 0.4 mm-thick sample in which the through portion 12 was formed by punching. Table 7 shows the results of setting 16 measurement sections so that adjacent measurement sections partially overlap each other for a measurement target portion with a thickness of 220 μm (=0.4 mm−90 μ×2).

As can be seen from Tables 4 and 5 and FIG. 9, the section values of the penetrating portions 12 formed by punching are generally larger than the section values of the penetrating portions 12 formed by other methods. In other words, it can be said that the surface of the inner wall surface 121 of the penetrating portion 12 formed by punching is rougher than the surface of the inner wall surface 121 of the penetrating portion 12 formed by other methods. This is also evident from the results shown in Table 6. That is, the standard deviation σ and the average value (surface roughness) of the interval values of the inner wall surface 121 of the through portion 12 obtained by punching are the standard deviation σ and the average value (surface roughness) of the interval values of the inner wall surface 121 of the through portion 12 obtained by other processing methods. Each is larger than the value (surface roughness). As can be seen from Table 7, even when the thickness of the sample 80 is small, the surface state of the inner wall surface 121 of the through portion 12 formed by punching can be said to be relatively rough.

From the results of the withstand voltage test and the measurement results of the surface roughness described above, it is estimated that the greater the roughness of the inner wall surface 121 of the penetrating portion 12, the higher the withstand voltage. Therefore, among the samples that were subjected to the withstand voltage test, the samples in which the through portion 12 was formed by milling and punching (Samples No. 11 to No. 15 and Samples No. 21 to No. 25) also had inner wall surfaces. 121 surface roughness was measured. Table 8 and FIG. 10 show the relationship between the measured surface roughness and withstand voltage.

As understood from Table 8 and FIG. 10, there is generally a proportional relationship between the surface roughness and the withstand voltage. It can also be seen that a surface roughness of 5 μm or more is sufficient to realize a withstand voltage of 100 (V) or more. Therefore, in the present embodiment, punching is used as a method for forming the through portion 12, and the surface roughness of the inner wall surface 121 of the through portion 12 is set to 5 μm or more. In other words, by adopting punching as a method of forming the penetrating portion 12, the surface roughness of the inner wall surface 121 of the formed penetrating portion 12 can be set to 5 μm. Thereby, the resistance value (surface resistivity) in the in-plane direction of the inner wall surface 121 of the penetrating portion 12 can be increased, and the withstand voltage can be increased. As a result, when the magnetic core 10 (see FIG. 1) is combined with a coil (not shown), the coil can be prevented from being short-circuited via the inner wall surface 121 of the through portion 12 .

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments, and various modifications and changes are possible without departing from the gist of the present invention. For example, although each first gap portion 31 is connected to two hole portions 21 in the above embodiment, each hole portion 21 may be connected to an independent gap portion. In this case, the second gap portion 33 is not formed.

10, 10A magnetic core (composite magnetic material)
12 through part 121 inner wall surface 21 hole 23 gap part 31 first gap part 33, 33A second gap part 41 square pyramidal diamond 43 sample 45 surface 47 indentation 51 copper wire 53 measuring instrument 55, 80 sample (magnetic core)

Claims (5)

A composite magnetic body in which flat soft magnetic metal powder is bound by a binder component,
A penetrating portion penetrating the composite magnetic body is formed,
The inner wall surface of the through portion has a surface roughness of 5 μm or more,
The composite magnetic body is used as a magnetic core,
the penetrating portion is a hole for holding a penetrating conductor and a gap connected to the hole;
the inner wall surface is an inner peripheral surface of the hole and a side wall surface of the gap facing each other;
The gap has a first gap portion connected to the hole and a second gap portion extending from the first gap portion.
Composite magnetic material. The composite magnetic body according to claim 1 ,
The composite magnetic body contains 60% by volume or more of soft magnetic metal powder, 4% to 30% by volume of the binder component, and 10% to 30% by volume of pores. . The composite magnetic material according to claim 1 or 2 ,
The composite magnetic body, wherein the penetrating portion has a closed shape when viewed along the penetrating direction. An inductor comprising the composite magnetic body according to any one of claims 1 to 3 and a coil,
The coil includes a first conductor provided on one of a pair of main surfaces of the composite magnetic body, a second conductor provided on the other of the main surfaces of the composite magnetic body, and disposed in the penetrating portion. An inductor comprising: a through conductor connecting a first conductor and the second conductor. A method for producing a composite magnetic material in which flat soft magnetic metal powder is bound by a binder component,
Forming a compact from a mixture obtained by mixing the soft magnetic metal powder and a binder containing the binder component,
forming a thermoset by thermosetting the molding so that the Vickers hardness is 12HV1 or more and 55HV1 or less;
The thermosetting body is punched to form a penetrating part that penetrates the thermosetting body,
the through portion comprises a hole for holding a through conductor and a gap connected to the hole,
The gap has a first gap portion connected to the hole and a second gap portion extending from the first gap portion.
A method for manufacturing a composite magnetic body.

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