Patent Application
20240145141
This application is based on and claims the benefit of priority from Japanese Patent Application Serial No. 2022-174374 (filed on Oct. 31, 2022), the contents of which are hereby incorporated by reference in their entirety.
The present disclosure relates mainly to a magnetic base body, a coil component including the magnetic base body, a circuit board including the coil component, and an electronic device including the circuit board.
Some coil components include a soft magnetic base body containing a plurality of soft magnetic metal particles made of a soft magnetic material. In the soft magnetic base body, the surfaces of the soft magnetic metal particles are covered with insulating films, and adjacent soft magnetic metal particles are bonded to each other via the insulating films. Since the soft magnetic base body is less prone to magnetic saturation than a magnetic base body made of ferrite, the soft magnetic base body is suitable particularly for coil components used in large-current circuits.
The soft magnetic metal particles are made of a soft magnetic material mainly composed of Fe, for example. The raw powder used to fabricate the Fe-based soft magnetic metal particles mainly composed of Fe further contains additive elements such as Si, Cr, and Al in addition to Fe to improve magnetic and insulating properties.
The magnetic base body is fabricated by mixing raw powder made of a soft magnetic material with a resin to produce a mixed resin composition, and then heating the mixed resin composition. During the heat treatment, the additive elements (e.g., Si, Cr, Al) contained in the raw powder particles move to the surfaces of the raw powder particles and are oxidized. Thus, an insulating oxide film containing oxides of the elements of the raw powder is formed on the surfaces of the soft magnetic metal particles. This oxide film electrically insulates the adjacent soft magnetic metal particles.
The surfaces of the soft magnetic metal particles may be coated with an insulating coating film. The insulating coating film may be a glass film or an amorphous silicon oxide film.
Thus, there is formed on the surfaces of the soft magnetic metal particles an insulating oxide film originated from the elements contained in the raw powder or a coating film containing an insulating substance not originated from the elements contained in the raw powder.
The magnetic base body disclosed in Japanese Patent Application Publication No. 2021-158261 has an insulating film formed of four oxide layers stacked on the surfaces of the soft magnetic metal particles, so as to improve the voltage resistance between the soft magnetic metal particles.
With an insulating film formed of a plurality of insulating layers on the surfaces of the soft magnetic metal particles, the proportion of the insulating film in the magnetic base body is increased. When the proportion of the insulating film in the magnetic base body is increased, the insulating properties of the magnetic base body can be improved, but the proportion of the soft magnetic metal particles in the magnetic base body (i.e., the filling factor of the soft magnetic metal particles in the magnetic base body) decreases. The decreased filling factor of the soft magnetic metal particles in the magnetic base body causes degradation of the magnetic properties of the magnetic base body.
As described above, when the insulating film has a lamination structure formed of a plurality of insulating films stacked together, the insulating properties of the magnetic base body can be increased, but the magnetic properties thereof are unfavorably degraded. In view of the above problem, there is a demand for a magnetic base body capable of achieving high insulating properties without degrading magnetic properties.
It is an object of the present disclosure to solve or alleviate at least part of the drawbacks mentioned above. More specifically, one object of the invention disclosed herein is to provide a magnetic base body having excellent insulation properties and magnetic properties.
Other objects of the disclosure will be made apparent through the entire description in the specification. The inventions recited in the claims may also address any other drawbacks in addition to the above drawback.
A magnetic base body according to one embodiment comprises: a plurality of soft magnetic metal particles; and a plurality of insulating films covering surfaces of the plurality of soft magnetic metal particles. The plurality of soft magnetic metal particles include a first soft magnetic metal particle, and the plurality of insulating films include a first insulating film covering a surface of the first soft magnetic metal particle. The first insulating film includes a first oxide region and a second oxide region, the first oxide region containing an oxide of an element A as a main component and covering a first surface region constituting a part of the surface of the first soft magnetic metal particle, the second oxide region containing an oxide of an element B as a main component and covering a second surface region of the surface of the first soft magnetic metal particle different from the first surface region.
According to the embodiments of the invention disclosed herein, it is possible to obtain a magnetic base body having excellent insulating properties and magnetic properties.
Various embodiments of the present invention will be described hereinafter with reference to the appended drawings. Throughout the drawings, the same components are denoted by the same reference numerals. For convenience of explanation, the drawings are not necessarily drawn to scale. The following embodiments of the present invention do not limit the scope of the claims. The elements included in the following embodiments are not necessarily essential to solve the problem addressed by the invention.
One embodiment of the present disclosure relates to a magnetic base body of a coil component. The magnetic base body contains a plurality of soft magnetic metal particles. The following first describes a coil component 1 including a magnetic base body relating to one embodiment with reference to
By way of one example of the coil component 1,
As shown, the coil component 1 includes a base body 10, a coil conductor 25 provided in the base body 10, an external electrode 21 disposed on a surface of the base body 10, and an external electrode 22 disposed on the surface of the base body 10 at a position spaced apart from the external electrode 21. The base body 10 is a magnetic base body made of a magnetic material. The base body 10 is an example of the feature “magnetic base body” recited in the claims.
The base body 10 contains a lot of soft magnetic metal particles. An average particle size of the soft magnetic metal particles contained in the base body 10 is, for example, 1 μm to 20 μm. The average particle diameter of the soft magnetic metal particles contained in the base body 10 is determined as follows. The base body 10 is cut along the thickness direction (T-axis direction) to expose a section, and the section is scanned by a scanning electron microscope (SEM) to take an SEM image at an approximately 10000 to 50000-fold magnification. The SEM image is analyzed to determine the equivalent circle diameter (Heywood diameter) of each soft magnetic metal particle, and the average of the equivalent circle diameters of the soft magnetic metal particles is taken as the average particle diameter of the soft magnetic metal particles. The average particle diameter of the soft magnetic metal particles contained in the base body 10 may be 1 μm to 10 nm or may be 2 μm to 8 μm. Since the average particle diameter of the soft magnetic metal particles does not differ significantly from that of the raw powder, the particle size distribution of the raw powder may be measured by the laser diffraction scattering method according to JIS Z 8825, and the D50 value of the volume-based particle size distribution measured by the laser diffraction scattering method may be taken as the average particle diameter of the soft magnetic metal particles in the base body 10.
The external electrode 21 is electrically connected to one end of the coil conductor 25, and the external electrode 22 is electrically connected to the other end of the coil conductor 25.
The coil component 1 may be mounted on a mounting substrate 2a. In the embodiment shown, the mounting substrate 2a has lands 3a and 3b provided thereon. The coil component 1 is mounted on the mounting substrate 2a by bonding the external electrode 21 to the land 3a and bonding the external electrode 22 to the land 3b. A circuit board 2 according to one embodiment of the present invention includes the coil component 1 and the mounting substrate 2a having the coil component 1 mounted thereon. The circuit board 2 can be installed in various electronic devices. The electronic devices in which the circuit board 2 can be installed include smartphones, tablets, game consoles, electrical components of automobiles, servers, and various other electronic devices.
The coil component 1 may be an inductor, a transformer, a filter, a reactor, an inductor array and any one of various other coil components. The coil component 1 may alternatively be a coupled inductor, a choke coil, and any one of various other magnetically coupled coil components. Applications of the coil component 1 are not limited to those explicitly described herein.
In the case where the coil component 1 is an inductor array or a magnetically coupled coil component, the coil conductor 25 is constituted by two or more conductor sections. The two or more conductor sections constituting the coil conductor 25 are electrically insulated from each other in the base body 10.
In one embodiment of the present invention, the base body 10 is configured such that the dimension in the L-axis direction (length dimension) is greater than the dimension in the W-axis direction (width dimension) and the dimension in the T-axis direction (height dimension). For example, the length dimension is from 1.0 mm to 6.0 mm, the width dimension is from 0.5 mm to 4.5 mm, and the height dimension is from 0.5 mm to 4.5 mm. The dimensions of the base body 10 are not limited to those specified herein. The term “rectangular parallelepiped” or “rectangular parallelepiped shape” used herein is not intended to mean solely “rectangular parallelepiped” in a mathematically strict sense. The dimensions and the shape of the base body 10 are not limited to those specified herein.
The base body 10 has a first principal surface 10a, a second principal surface 10b, a first end surface 10c, a second end surface 10d, a first side surface 10e, and a second side surface 10f. The outer surface of the base body 10 is defined by these six surfaces. The first principal surface 10a and the second principal surface 10b are at the opposite ends in the height direction of the base body 10, the first end surface 10c and the second end surface 10d are at the opposite ends in the length direction of the base body 10, and the first side surface 10e and the second side surface 10f are at the opposite ends in the width direction of the base body 10. As shown in
As shown in
The body layer 20 includes magnetic films 11 to 17. In the body layer 20, the magnetic films 17, 16, 15, 14, 13, 12 and 11 are stacked in the stated order from the negative side toward the positive side in the T-axis direction.
The magnetic films 11 to 17 respectively have conductor patterns C11 to C17 formed on the top-side surface thereof. The conductor patterns C11 to C17 each extend around a coil axis Ax1 (see
The magnetic films 11 to 16 have vias V1 to V6, respectively, at a predetermined position therein. The vias V1 to V6 are formed by forming through holes at the predetermined positions in the magnetic films 11 to 16 so as to extend through the magnetic films 11 to 16 in the T-axis direction and filling the through holes with a conductive material. Each of the conductor patterns C11 to C17 is electrically connected to the respective adjacent conductor patterns through the vias V1 to V6.
The end of the conductor pattern C11 opposite to the end thereof connected to the via V1 is connected to the external electrode 22. The end of the conductor pattern C17 opposite to the end thereof connected to the via V6 is connected to the external electrode 21.
The top cover layer 18 includes magnetic films 18a to 18d made of a magnetic material, and the bottom cover layer 19 includes magnetic films 19a to 19d made of a magnetic material. In this specification of the present invention, the magnetic films 18a to 18d and the magnetic films 19a to 19d may be referred to collectively as “the cover layer magnetic films.” The components of the base body 10 do not necessarily have a lamination structure with a plurality of magnetic films stacked together. For example, the top cover layer 18 may be a molded body formed of a magnetic material, rather than a laminate including a plurality of magnetic films 18a to 18d stacked together.
As shown in
The following now describes the microstructure of the base body 10 with reference to
As shown in
The soft magnetic metal particles contained in the base body 10 should preferably contain Fe at a content percentage of 95 wt % or more so that the base body 10 has high magnetic saturation characteristics. The content percentage of Fe in the soft magnetic metal particles contained in the base body 10 is measured by cutting the base body 10 along the coil axis Ax to expose a section of the base body 10 and performing energy dispersive X-ray spectroscopy (EDS) analysis on this section. The content percentage of Fe can be measured by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS) detector. The EDS analysis by SEM equipped with the EDS detector is called SEM-EDS analysis. The content percentage of Fe is measured, for example, using a scanning electron microscope SU7000 from Hitachi High-Tech Corporation and an energy dispersive X-ray spectroscopy detector Octane Elite from Ametek Inc. at an acceleration voltage of 5 kV. The content percentages of elements other than Fe contained in the first soft magnetic metal particle 30a are also measured by SEM-EDS analysis, as is the content percentage of Fe.
The surface of each of the soft magnetic metal particles contained in the base body 10 is covered by an insulating film. Thus, the soft magnetic metal particles contained in the base body 10 are electrically insulated from each other. For example, the surface of the first soft magnetic metal particle 30a is covered by the first insulating film 40a, and the surface of the second soft magnetic metal particle 30b is covered by the second insulating film 40b. The first insulating film 40a should preferably cover the entire surface of the first soft magnetic metal particle 30a, and the second insulating film 40b should preferably cover the entire surface of the second soft magnetic metal particle 30b. In the base body 10, each soft magnetic metal particle is bonded to adjacent soft magnetic metal particles via insulating films provided on their respective surfaces. In other words, the insulating films provided on the surfaces of adjacent soft magnetic metal particles are bonded to each other, and this bonding of the insulating films forms bonding of the soft magnetic metal particles covered by the insulating films. For example, the first soft magnetic metal particle 30a is bonded to the second soft magnetic metal particle 30b adjacent to the first soft magnetic metal particle 30a via the first insulating film 40a provided on the surface of the first soft magnetic metal particle 30a and the second insulating film 40b provided on the surface of the second soft magnetic metal particle 30b.
The soft magnetic metal particles contained in the base body 10 are produced, for example, by heating a raw powder made of soft magnetic material. As will be described later, the base body 10 may be fabricated by mixing soft magnetic metal powder made of a soft magnetic material with a resin to produce a mixed resin composition, and then heating the mixed resin composition. The heat treatment in the manufacturing process of the base body 10 causes the elements contained in the raw powder to diffuse to the surface of the raw powder and oxidize on the surface of the raw powder, and as a result, insulating films that contain oxides of the elements contained in the raw powder are formed on the surfaces of the soft magnetic metal particles.
The raw powder for the soft magnetic metal particles contained in the base body 10 is mainly composed of Fe. The raw powder for the soft magnetic metal particles contained in the base body 10 can contain two or more types of additive elements in addition to Fe. For example, the raw powder for the soft magnetic metal particles contained in the base body 10 can contain an element A and an element B as additives in addition to Fe.
The element A and the element B are more apt to oxidation than Fe. The element A may be more apt to oxidation than the element B. The raw powder for the soft magnetic metal particles may contain an element C that is more apt to oxidation than Fe, in addition to the element A and the element B. In one embodiment, the element A is more apt to oxidation than the element B. In one embodiment, the element B is more apt to oxidation than the element C. For example, the elements A, B, and C are selected from the group consisting of Si, Ti, Al, Cr, Zr, and Mn. In one embodiment, the element A is Al. In one embodiment, the element B is Si. The element B may be Ti. In one embodiment, the element C is Cr. Since the elements A, B, and C are all more apt to oxidation than Fe, they are oxidized prior to Fe when the raw powder is heat-treated in an atmosphere containing oxygen. Thus, the presence of the elements A, B, and C in addition to Fe in the raw powder inhibits the oxidation of Fe. The raw powder for the soft magnetic metal particles can contain trace amounts of elements other than Fe and the elements A, B, and C. The elements that can be present in trace amounts in the raw powder for the soft magnetic metal particles can include vanadium (V), zinc (Zn), boron (B), carbon (C), and nickel (Ni).
The insulating films provided on the surfaces of the soft magnetic metal particles contained in the base body 10 contain oxides of the elements contained in the raw powder. The “insulating films provided on the surfaces of the soft magnetic metal particles contained in the base body 10” include the first insulating film 40a provided on the surface of the first soft magnetic metal particle 30a and the second insulating film 40b provided on the surface of the second soft magnetic metal particle 30b. For convenience of description, the insulating films provided on the surfaces of the soft magnetic metal particles contained in the base body 10 may be referred to simply as the “insulating films.” The elements A and B are more apt to oxidation than Fe. Thus, when the raw powder contains the elements A and B in addition to Fe, the insulating films contain the oxide of the element A and the oxide of the element B. The insulating films may contain an oxide of the element C. In addition to the above oxides, the insulating film may contain oxide of at least one of vanadium (V), zinc (Zn), boron (B), carbon (C), and nickel (Ni). In one embodiment, the thickness of the insulating film is equal to the distance between the soft magnetic metal particles adjacent to each other. The thickness of the insulating films provided on the surfaces of the soft magnetic metal particles may be an average of distances between adjacent ones of a plurality of soft magnetic metal particles included in an observation region within a section of the base body 10 observed with a predetermined magnification (e.g., 5000-fold magnification). The thickness of the insulating film is, for example, 5 to 20 nm. The thickness of the insulating film need not be uniform along the circumferential direction of the soft magnetic metal particles. In other words, the insulating film may have different thicknesses at different locations in the circumferential direction of the soft magnetic metal particle. If the insulating film has different thicknesses in accordance with the location in the circumferential direction of the soft magnetic metal particle, the average of the different thicknesses can be taken as the thickness of the insulating film. The thickness of the thinnest portion of the insulating film may be smaller than 5 nm. The thickness of the thickest portion of the insulating film may be larger than 20 nm. If the insulating film has different thicknesses in accordance with the location in the circumferential direction of the soft magnetic metal particle, its largest thickness is smaller than ten times its smallest thickness.
With reference to
When the element A is Al, the first oxide region 41a contains alumina (Al2O3) as the main component. In the case where the EDS analysis shows that the amount of Al element (atomic percentage (at %) of Al element) is the largest among those of the elements other than oxygen contained in the first oxide region 41a, it can be determined that the first oxide region 41a contains alumina as the main component. Since the first oxide region 41a is mainly composed of alumina, which is insulating, the first oxide region 41a has a high insulating quality. In the case where the first oxide region 41a may contain an oxide of aluminum other than alumina (e.g., aluminum oxide (II)), the Raman spectroscopic analysis may be performed to determine that the oxide contained as the main component in the first oxide region 41a is alumina (aluminum oxide (III)) rather than aluminum oxide (II).
When the element B is Si, the second oxide region 42a contains silica (SiO2) as the main component. In the case where the EDS analysis shows that the amount of Si element (atomic percentage (at %) of Si element) is the largest among those of the elements other than oxygen contained in the second oxide region 42a, it can be determined that the second oxide region 42a contains silica as the main component. Since the second oxide region 42a is mainly composed of silica, which is insulating, the second oxide region 42a has a high insulating quality. In the case where the second oxide region 42a may contain an oxide of silicon other than silica (e.g., silicon monoxide), the Raman spectroscopic analysis may be performed to determine that the oxide contained as the main component in the second oxide region 42a is silica (silicon dioxide) rather than silicon monoxide.
The insulating film may contain nitrides of the elements contained in the raw powder in addition to oxides of the elements. The percentage of oxides in the insulating film (on a mass basis) is greater than the percentage of nitrides in the insulating film. The nitrides contained in the insulating film may include aluminum nitride and silicon nitride. The presence of the nitrides of the elements contained in the raw powder in the insulating film inhibits excessive oxidation of the elements contained in the raw powder. In general, oxides have higher hardness than nitrides, so the presence of a larger amount of oxides than nitrides in the insulating film can increase the mechanical strength of the base body 10.
The surface of the first soft magnetic metal particle 30a is partitioned into the first surface region 31a and the second surface region 32a. Since the first surface region 31a of the surface of the first soft magnetic metal particle 30a is covered by the first oxide region 41a, and the second surface region 32a is covered by the second oxide region 42a, the entire surface of the first soft magnetic metal particle 30a is covered by the first and second oxide regions 41a and 42a each having a high insulating quality.
The first oxide region 41a may cover at least a part of the outer surface of the second oxide region 42a, in addition to the first surface region 31a of the first soft magnetic metal particle 30a. The first oxide region 41a covering the outer surface of the second oxide region 42a can cover any portion of the second oxide region 42a having a defect, thereby preventing dielectric breakdown from occurring from the defect in the second oxide region 42a. In the aspect shown in
It is also possible that the first oxide region 41a covers only a part of the outer surface of the second oxide region 42a. In this case, the amount of the first oxide region 41a on the surface of the first soft magnetic metal particle 30a can be reduced. Therefore, the first oxide region 41a covering only a part of the outer surface of the second oxide region 42a can improve the filling factor of the soft magnetic metal particles in the base body 10, compared to the aspect in which the first oxide region 41a covers the entire outer surface of the second oxide region 42a.
In the embodiment shown in
A second insulating film 40b is provided on the surface of the second soft magnetic metal particle 30b, which is positioned adjacent to the first soft magnetic metal particle 30a. The second insulating film 40b includes a first oxide region 41b and a second oxide region 42b. The first oxide region 41b covers a first surface region 31b constituting a part of the surface of the second soft magnetic metal particle 30b and contains an oxide of the element A as a main component. The second oxide region 42b covers a second surface region 32b constituting a part of the surface of the second soft magnetic metal particle 30b and contains an oxide of the element B as a main component. The first oxide region 41b contains an oxide of the element A as a main component, as does the first oxide region 41a. The above description related to the first oxide region 41a applies to the first oxide region 41b. The second oxide region 42b contains an oxide of the element B as a main component, as does the second oxide region 42a. The above description related to the second oxide region 42a applies to the second oxide region 42b.
In
In the base body 10, the soft magnetic metal particles are covered by the insulating films containing oxides of two types of elements (i.e., the element A and the element B), and thus the base body 10 has an excellent insulating quality. In one embodiment, the soft magnetic metal particles are covered by the insulating films containing oxides of two types of elements, and thus the insulating quality of the base body 10 can be increased. In order to achieve a high insulating quality with an insulating film composed of a single kind of oxide, the entire surfaces of the soft magnetic metal particles must be covered by a layer of this oxide. However, in the manufacturing process of the base body 10, when a molded body of the raw powder is fabricated so as not to reduce the filling factor of the raw powder, the element oxidized during heating of the molded body is not diffused sufficiently, resulting in thin portions of the oxide of this element formed on a part of the surfaces of the soft magnetic metal particles. Such thin portions of the oxide tend to occur between the soft magnetic metal particles. Depending on the filling factor and the heating condition of the molded body, a part of the surfaces of the soft magnetic metal particles may not be covered by the insulating films, such that adjacent ones of the soft magnetic metal particles directly contact with each other, resulting in degraded insulating quality of the magnetic base body. In the base body 10 of the present application, even when the molded body of the raw powder has a high filling factor, the insulating film contains oxides of two different elements, so the surfaces of the soft magnetic metal particles are coated by an insulating film containing oxides of two different elements. Therefore, even if there are regions on the surfaces of the soft magnetic metal particles that are not coated with the oxide of one element, those regions can be coated with the oxide of the other element. Specifically, in the base body 10, the second oxide region 42a is formed only on a part of the first soft magnetic metal particle 30a (i.e., only on the second surface region 32a), while the first oxide region 41a, which is mainly composed of the oxide of the element A, covers the other region of the surface of the first soft magnetic metal particle 30a (i.e., the first surface region 31a). Therefore, the decrease in insulating quality due to exposure of a part of the surface of the first soft magnetic metal particle 30a can be inhibited. The soft magnetic metal particles other than the first soft magnetic metal particle 30a contained in the base body 10 are also covered by the insulating film containing the oxides of two different elements (i.e., the element A and the element B), and thus the base body 10 can have a high insulating quality.
A description will now be given of the difference between the insulating film provided on the surfaces of the soft magnetic metal particles contained in the base body 10 of the present application (e.g., the first insulating film 40a) and the insulating film provided on the surfaces of the conventional soft magnetic metal particles. Conventionally, in the case where the insulating film covering the surfaces of soft magnetic metal particles contains oxides of two or more elements, the insulating film has a layered structure in which the oxide of each element is formed in a layer and these oxide layers are stacked. In other words, the insulating film of the conventional magnetic base body includes a first oxide layer mainly composed of the oxide of a first element and a second oxide layer mainly composed of the oxide of a second element. The first oxide layer covers the entire outer surface of the soft magnetic metal particle, and the second oxide layer covers the entire surface of the first oxide layer. One example of the conventional magnetic base body in which the insulating film has a layered structure is disclosed in Japanese Patent Application Publication No. 2021-158261.
In contrast, in the base body 10 of the present application, the first surface region 31a of the surface of the first soft magnetic metal particle 30a is covered by the first oxide region 41a, and the second surface region 32a of the first soft magnetic metal particle 30a is covered by the second oxide region 42a. Therefore, in the base body 10 to which the present invention is applied, the proportion of the insulating film in the base body 10 can be reduced compared to the conventional magnetic base bodies that have an insulating film with two or more oxide layers stacked together. As a result, the filling factor of the soft magnetic metal particles in the base body 10 can be increased, and thus the magnetic characteristics can be improved compared to conventional magnetic base bodies having an insulating film with two or more oxide layers stacked together.
As mentioned above, the oxide of the element A in the insulating films covering the surfaces of the soft magnetic metal particles contained in the base body 10 may be formed from the element A in the raw powder for the soft magnetic metal particles, but in another embodiment, it is possible that the oxide of the element A is not formed from the raw powder for the soft magnetic metal particles. In the case where the element A is Al, the raw powder for the soft magnetic metal particles and alumina particles may be mixed together in a friction mixer such that the alumina particles are fixed to the surfaces of the soft magnetic metal particles. This allows Al oxide that is not formed from the Al element contained in the raw powder to adhere to the surfaces of the soft magnetic metal particles. The first oxide regions 41a and 41b may be formed from the alumina particles adhered to the soft magnetic metal particles. In the case where the oxide of the element A in the insulating film covering the surfaces of the soft magnetic metal particles is not formed from an element contained in the raw powder, it is possible that the raw powder does not contain the element A.
As mentioned above, the oxide of the element B in the insulating films covering the surfaces of the soft magnetic metal particles contained in the base body 10 may be formed from the element B in the raw powder for the soft magnetic metal particles, but in another embodiment, it is possible that the oxide of the element B is not formed from the raw powder for the soft magnetic metal particles. In the case where the element B is Si, Si oxide (silica) can be formed on the surface of the raw powder (soft magnetic metal particles) by impregnating the raw powder with a mixed solution of TEOS (tetraethoxysilane), ethanol, and ammonia water, stirring this mixed solution, and then drying it. The Si oxide thus formed may be amorphous. This allows Si oxide that is not formed from the Si element contained in the raw powder to adhere to the surfaces of the soft magnetic metal particles. The second oxide regions 42a and 42b may be made from silica formed on the surfaces of the soft magnetic metal particles. In the case where the oxide of the element B in the insulating film covering the surfaces of the soft magnetic metal particles is not formed from an element contained in the raw powder, it is possible that the raw powder does not contain element B.
In the case where the oxide of the element A and the oxide of the element A in the insulating film covering the surfaces of the soft magnetic metal particles are not formed from the element A or the element B contained in the raw powder, it is possible to reduce the content percentages of the element A and the element B in the raw powder. In the case where the Al oxide in the insulating film is not formed from the element A contained in the raw powder, it is possible that the content percentage of the element A in the raw powder is 0.1 to 0.8 wt %. In the case where the Si oxide in the insulating film is not formed from the element B contained in the raw powder, it is possible that the content percentage of the element B in the raw powder is 0.7 to 2.5 wt %. By reducing the content percentages of Al and Si in the raw powder, the content percentage of Fe in the raw powder can be increased, and consequently the content percentage of Fe in the soft magnetic metal particles can also be increased.
The following describes another embodiment of a base body to which the present invention is applied, with reference to
The third oxide region 43a is spaced apart from the surface of the first soft magnetic metal particle 30a. In other words, at least one of the first oxide region 41a or the second oxide region 42a is interposed between the third oxide region 43a and the surface of the first soft magnetic metal particle 30a. In the embodiment shown, the third oxide region 43a is also spaced apart from the second oxide region 42a. In other words, the first oxide region 41a is interposed between the third oxide region 43a and the second oxide region 42a. It is also possible that the third oxide region 43a is in contact with the second oxide region 42a.
The third oxide region 43a is located on the outer side of the first oxide region 41a in the radial direction of the first soft magnetic metal particle 30a. In one embodiment, at least one of a plurality of third oxide regions 43a may be provided at a position corresponding to the first surface region 31a in the circumferential direction around the first soft magnetic metal particle 30a. In other words, at least one of the plurality of third oxide regions 43a may be provided on the radially outer side of the first surface region 31a. The region corresponding to the first surface region 31a in the circumferential direction of the first soft magnetic particle 30a contains the first oxide region 41a and does not contain the second oxide region 42a.
On the other hand, the region corresponding to the second surface region 32a in the circumferential direction of the first soft magnetic particle 30a contains the second oxide region 42a and the first oxide region 41a provided on the radially outer side thereof. Therefore, the first oxide region 41a is concave inwardly at a position corresponding to the first surface region 31a in the circumferential direction of the first soft magnetic metal particle 30a. In one embodiment, the third oxide region 43a is located in a cavity of the first oxide region 41a at a position corresponding to the first surface region 31a in the circumferential direction of the first soft magnetic metal particle 30a. Since the third oxide region 43a is provided in the cavity of the first oxide region 41a, the thickness of the first insulating film 40a can be uniform in the circumferential direction. In the case where a portion of the first insulating film 40a is thinner than other portions, dielectric breakdown may occur from the thinner portion. The uniform thickness of the first insulating film 40a in the circumferential direction prevents dielectric breakdown from occurring from a thin portion of the first insulating film 40a. In the case where the third oxide region 43a is provided on the radially outer side of the first surface region 31a, the straight line connecting the geometric center Ca of the first soft magnetic metal particle 30a and the third oxide region 43a provided on the radially outer side of the first surface region 31a passes through the first oxide region 41a but not through the second oxide region 42a.
As with the third oxide region 43a, the third oxide region 43b is spaced apart from the surface of the second soft magnetic metal particle 30b. The third oxide region 43b may also be spaced apart from the second oxide region 42b. It is also possible that the third oxide region 43b is in contact with the second oxide region 42b. Further, the third oxide region 43b may be located in a cavity of the first oxide region 41b at a position corresponding to the first surface region 31b in the circumferential direction of the second soft magnetic metal particle 30b.
The third oxide regions 43a and 43b contain an oxide of the element C as a main component. In the case where the element C is Cr, the third oxide regions 43a and 43b contain chromite (FeCr2O4) as a main component. When an oxide including Fe is formed in the insulating films covering the Fe-based soft magnetic metal particles, the Fe oxide may be present as hematite (Fe2O3) or magnetite (Fe3O4). The mixed presence of hematite, which is non-magnetic, and magnetite, which is ferromagnetic, between soft magnetic metal particles facilitates local magnetic saturation in the region where magnetite is present. With chromite, which is non-magnetic, as a main component of the third oxide region 43a containing Fe, the uniformity of magnetic flux between the soft magnetic metal particles can be improved, and as a result, the occurrence of local magnetic saturation between the soft magnetic metal particles can be inhibited. This improves the magnetic saturation characteristics of the base body 110 compared to magnetic base bodies containing more magnetite.
The third oxide regions 43a and 43b included in the insulating films may contain chromite (FeCr2O4), hematite (Fe2O3), and magnetite (Fe3O4). In one embodiment, in each of the third oxide regions 43a and 43b, the content percentage of chromite in the total of the aforementioned oxides (the total of chromite, hematite, and magnetite) may be 50% or more. With the content percentage of chromite, which is non-magnetic, being 50% or more, it is possible to reduce the specific permeability of the insulating films and improve the magnetic saturation characteristics of the base body 110, compared to the case with a high content percentage of ferromagnetic oxides (e.g., magnetite). In another embodiment, the sum of the content percentage of chromite and the content percentage of hematite in the total of the aforementioned oxides may be 80% or more. With the sum of the content percentages of chromite and hematite, which are non-magnetic, being 80% or more, it is possible to reduce the specific permeability of the insulating films and improve the magnetic saturation characteristics of the base body 110, compared to the case with a high content percentage of ferromagnetic oxides (e.g., magnetite).
The following describes a base body 210 to which the present invention is applied, with reference to
In the base body 210, there is a gap among the soft magnetic metal particles that is not filled with the insulating films. For example, as shown in
In the base body 210, a part of the gap among the soft magnetic metal particles is filled by the third oxide region 43d, and thus the mechanical strength of the base body 210 can be improved as compared to the case where the third oxide region 43d is not present. When the main component of the third oxide region 43d is chromite, a part of the gap is filled by the third oxide region 43d mainly composed of chromite having a high hardness, and thus the mechanical strength of the base body 210 can be further improved.
The first insulating film 40a may further contain a fourth oxide region, in addition to the first oxide region 41a, the second oxide region 42a, and the third oxide region 43a. The fourth oxide region may contain either oxides formed from elements contained in the raw powder for the soft magnetic metal particles or other oxides. The fourth oxide region may be insulating.
Next, one example of a manufacturing method of the coil component 1 will be described with reference to
In the first step S1, magnetic sheets are fabricated. The magnetic sheets are produced from a magnetic material paste obtained by mixing and kneading soft magnetic metal powder (raw powder), which is the raw material of the soft magnetic metal particles, with a binder resin and a solvent. The raw powder is formed of a soft magnetic metal material. The raw powder contains Fe, the element A, and the element B. The raw powder may contain the element C. In the following description of the manufacturing method, for clarity of description, it is assumed that the raw powder contains Al as the element A, Si as the element B, and Cr as the element C. The raw powder contains 95 wt % or more Fe. The total of the content percentages of the elements A to C and other additive elements is 5 wt % or less. The raw powder may contain 0.2 to 1 wt % Al. The raw powder may contain 1 to 3 wt % Si. The raw powder may contain 0.5 to 1.5 wt % Cr. The content percentage of Si in the raw powder may be higher than that of Al.
The binder resin for the magnetic material paste is, for example, an acrylic resin. The binder resin for the magnetic material paste may be PVB resins, phenolic resins, other resins known as binder resins, or mixtures thereof. One example of the solvent is toluene. The magnetic material paste is applied to the surface of a plastic base film by the doctor blade method or other common methods. The magnetic material paste applied to the surface of the base film is dried to obtain sheet-shaped molded bodies. A molding pressure of approximately 10 MPa to 100 MPa is applied for molding to the sheet-shaped molded bodies in the mold, so that a plurality of magnetic sheets are obtained.
Next, in step S2, a conductive paste is applied to some of the plurality of magnetic sheets prepared in step S1. The conductive paste is produced by mixing and kneading conductive powder made of conductive materials having excellent conductivity, such as Ag Pd, Cu, Al or alloys of these, with a binder resin and a solvent. The binder resin for the conductive paste may be the same as the binder resin for the magnetic material paste. Both the binder resins for the conductive paste and the magnetic material paste may be acrylic resins.
By applying the conductive paste to the magnetic sheets, unfired conductor patterns to be the conductor patterns C11 to C17 after firing are formed on the associated magnetic sheets. A through hole is formed in some of the magnetic sheets to penetrate the magnetic sheets in the stacking direction. When the conductive paste is applied to a magnetic sheet with a through hole, the conductive paste is also filled into the through hole. In this way, unfired via conductors are formed in the through-holes of the magnetic sheets, and these unfired via conductors will be via conductors V1 to V6 after firing. The conductive paste is applied to the magnetic sheets by, for example, screen printing.
Next, in step S3, the magnetic sheets prepared in step S1 are stacked together to form a top laminate to be the top cover layer 18, an intermediate laminate to be the body layer 20, and a bottom laminate to be the bottom cover layer 19. The top laminate and the bottom laminate are each formed by stacking four magnetic sheets prepared in step S1 and having no unfired conductor pattern formed thereon. The four magnetic sheets of the top laminate will be the magnetic films 18a to 18d respectively in the finished coil component 1, and the four magnetic sheets of the bottom laminate will be the magnetic films 19a to 19d respectively in the finished coil component 1. The intermediate laminate is formed by stacking in a predetermined order seven magnetic sheets each having an unfired conductor pattern formed thereon. The seven magnetic sheets of the intermediate laminate will be the magnetic films 11 to 17 respectively in the finished coil component 1. The intermediate laminate formed in the above-described manner is sandwiched between the top laminate on the top side and the bottom laminate on the bottom side, and the top laminate and the bottom laminate are bonded to the intermediate laminate by thermal compression to obtain a body laminate. Next, the body laminate is diced to a desired size by using a cutter such as a dicing machine or a laser processing machine to obtain a chip laminate. The chip laminate is an example of a molded body that includes a substrate body to be the base body 10 after the heat treatment and unfired conductor patterns to be the coil conductor 25 after the heat treatment. The molded body that includes the substrate body to be the base body 10 after the heat treatment and the unfired conductor patterns to be the coil conductor 25 after the heat treatment may be fabricated by a method other than the sheet lamination method.
In the molded body fabricated in step S3, the filling factor of the raw powder is 85% or higher. The filling factor of the raw powder in the molded body is achieved by adjusting the molding pressure for molding the magnetic sheets in accordance with the type of binder resin, the particle size of the raw powder, and other parameters. The filling factor of the raw powder in the molded body can be the proportion of the area occupied by the raw powder to the entire area of the observed field of view in a SEM image of a cross section of the molded body, expressed in percentage.
Next, in step S4, the molded body fabricated in step S3 is degreased. In the case where a thermally decomposable resin is used as the binder resin for the magnetic material paste and the conductive paste, the degreasing process for the molded body may be performed in a non-oxygen atmosphere such as a nitrogen atmosphere. By performing the degreasing process in a non-oxygen atmosphere, the oxidation of Fe contained in the raw powder can be prevented during the degreasing process. The degreasing process is performed at a temperature higher than the thermal decomposition starting temperature of the binder resin for the magnetic material paste. In the case where an acrylic resin is used as the binder resin for the magnetic material paste, the degreasing process is performed at a temperature higher than the thermal decomposition starting temperature of the acrylic resin, e.g., 300° C. to 500° C. Since the degreasing process decomposes the thermally decomposable resin contained in the molded body, no thermally decomposable resin remains in the molded body after the degreasing process is completed. When the binder resin for the conductive paste is the same thermally decomposable resin as the binder resin for the magnetic material paste, the thermally decomposable resin contained in the unfired conductor patterns is also thermally decomposed during the degreasing process in step S4. Thus, in step S4, both the magnetic sheets and the unfired conductor patters constituting the molded body are degreased.
Next, in step S5, the degreased molded body is subjected to first heat treatment. The first heat treatment is performed in a low oxygen concentration atmosphere containing oxygen in a range of 5 to 1000 ppm at a first heating temperature of 750° C. to 900° C. The first heat treatment may be performed in a low oxygen concentration atmosphere of 5 to 10 ppm. Since the raw powder is heated at 750° C. to 900° C., Al and Si in each raw powder diffuse to the vicinity of the surface by thermal diffusion and combine with oxygen in the atmosphere. In the case where the raw powder contains Cr, Cr also diffuses to the vicinity of the surface of the raw powder. In the first heat treatment, oxides of Al and Si, which are easily oxidized, are produced, among the additive elements transferred to the surface of the raw powder. As shown in
Next, in step S6, the molded body having been heated in the first heat treatment is subjected to second heat treatment at a higher oxygen concentration than in the first heat treatment. The second heat treatment may be performed in a low oxygen atmosphere with an oxygen concentration higher than 1000 ppm and equal to or lower than 10000 ppm. Since the second heat treatment is performed at a higher oxygen concentration than the first heat treatment, the oxidation of Si and Al is further progressed. In the case where the raw powder contains Cr, during the second heat treatment, magnetite produced in the first heat treatment combines with Cr to form chromite (FeCr2O4). As mentioned above, the filling factor of the raw powder in the molded body is as high as 85% or higher, and thus the excessive supply of oxygen to the surface of the raw powder can be inhibited. Therefore, in the second heat treatment, chromite (FeCr2O4) is more likely to be formed than hematite (Fe2O3) or chromium oxide (III) in the region where magnetite and Cr element are present near the surface of the raw powder.
Thus, in the case where the raw powder contains Cr, the second heat treatment produces an oxide region (e.g., the third oxide region 43a) containing chromite as a main component on the radially outer side of the first oxide region 41a or the second oxide region 42a. In the case where the raw powder does not contain Cr, chromite is not produced. Also, since the filling factor of the raw powder in the molded body is high (e.g., 85% or higher), the range of oxygen concentration in the atmosphere in which the second heat treatment is performed can be expanded (i.e., the upper limit can be raised).
During the second heat treatment, in addition to oxidation of the raw powder, sintering of the conductive powder in the unsintered conductor patterns also occurs. The coil conductor 25 is obtained by sintering the conductive powder in the unsintered conductor patterns. When copper powder is used as the conductive powder, the copper crystals sinter densely to form the coil conductor 25.
The second heat treatment is performed at a second heating temperature and for a second heating time. The second heating temperature and the second heating time are determined such that insulating films with a sufficient thickness enough to ensure insulation are formed on the surface of the raw powder. The second heating temperature may be, for example, between 500° C. and 700° C. The higher the second heating temperature, the faster the oxidation progresses, so the second heating time depends on the second heating temperature. When the second heating temperature is 500° C., the second heating time may be from one to six hours. When the second heating temperature is 700° C., the second heating time may be from 30 minutes to one hour.
Thus, the raw powder contained in the molded body is oxidized through the first heat treatment and the second heat treatment to produce, from the raw powder, soft magnetic metal particles with a surface covered by an insulating film. In the case where the raw powder does not contain Cr, produced are the first soft magnetic metal particle 30a covered by the first insulating film 40a and the second soft magnetic metal particle 30b covered by the second insulating film 40b, as shown in
Next, in step S7, the external electrode 21 and the external electrode 22 are formed on the surface of the base body 10 obtained in step S6. The external electrode 21 is connected to one end of the coil conductor 25, and the external electrode 22 is connected to the other end of the coil conductor 25. The molded body having gone through the second heat treatment may be impregnated with a resin before the external electrodes 21 and 22 are formed. The molded body is impregnated with, for example, a thermosetting resin such as an epoxy resin. This allows the resin to penetrate the gaps between the soft magnetic metal particles in the base body 10. The resin that has penetrated into the base body 10 may be set to increase the mechanical strength of the base body 10.
The coil component 1 is fabricated through the steps described above.
Next, another aspect of the manufacturing method of the coil component 1 will be described with reference to
As shown in
Next, in step S22, the degreased molded body is subjected to heat treatment. The heat treatment in step S22 can be performed under the same conditions as the second heat treatment performed in step S6 of
Next, in step S7, the external electrode 21 and the external electrode 22 are formed on the surface of the base body 10 obtained in step S22. The coil component 1 is fabricated through the steps described above.
The dimensions, materials, and arrangements of the constituent elements described for the above various embodiments are not limited to those explicitly described for the embodiments, and these constituent elements can be modified to have any dimensions, materials, and arrangements within the scope of the present invention.
Constituent elements not explicitly described herein can also be added to the above-described embodiments, and it is also possible to omit some of the constituent elements described for the embodiments.
The words “first,” “second,” “third” and so on used herein are added to distinguish constituent elements but do not necessarily limit the numbers, orders, or contents of the constituent elements. The numbers added to distinguish the constituent elements should be construed in each context. The same numbers do not necessarily denote the same constituent elements among the contexts. The use of numbers to identify constituent elements does not prevent the constituent elements from performing the functions of the constituent elements identified by other numbers.
This specification also discloses the following embodiments.
A magnetic base body comprising:
The magnetic base body of Additional Embodiment 1, wherein the first oxide region covers at least a part of an outer surface of the second oxide region.
The magnetic base body of Additional Embodiment 1 or 2, wherein the second oxide region includes a plurality of unitary second oxide regions spaced apart from each other.
The magnetic base body of any one of Additional Embodiments 1 to 3,
The magnetic base body of any one of Additional Embodiments 1 to 4, wherein the first insulating film further includes a third oxide region containing an oxide of an element C as a main component.
The magnetic base body of Additional Embodiment 5, wherein the third oxide region contains FeCr2O4 as a main component.
The magnetic base body of Additional Embodiment 5 or 6, wherein the third oxide region is located on a radially outer side of the first oxide region.
The magnetic base body of any one of Additional Embodiments 5 to 7, wherein the third oxide region is located on a radially outer side of the first surface region.
The magnetic base body of any one of Additional Embodiments 5 to 8, wherein the third oxide region includes a plurality of unitary third oxide regions spaced apart from each other.
The magnetic base body of any one of Additional Embodiments 5 to 9, wherein a line segment connecting between a geometric center of the first soft magnetic metal particle and one of the plurality of unitary third oxide regions passes through the first oxide region but does not pass through the second oxide region.
The magnetic base body of any one of Additional Embodiments 5 to 10,
The magnetic base body of any one of Additional Embodiments 1 to 11, wherein each of the plurality of soft magnetic metal particles contains Fe.
The magnetic base body of any one of Additional Embodiments 1 to 12, wherein a content percentage of Fe in each of the plurality of soft magnetic metal particles is 95 wt % or more.
The magnetic base body of any one of Additional Embodiments 1 to 13,
A coil component comprising:
A circuit board comprising the coil component of Additional Embodiment 15.
An electronic device comprising the circuit board of Additional Embodiment 16.
A magnetic base body comprising:
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-174374 | Oct 2022 | JP | national |
