JP7560245B2 - Coil component and method for manufacturing the coil component - Google Patents

Description

The present invention mainly relates to coil components and methods for manufacturing coil components.

A variety of magnetic materials have traditionally been used as materials for the magnetic substrate of electronic components. For example, ferrite is often used as a magnetic material for coil components such as inductors. Ferrite has high magnetic permeability, making it suitable as a magnetic material for the substrate of coil components.

Metal magnetic materials containing metal magnetic particles are known as magnetic materials for electronic components other than ferrite. Metal magnetic materials have a higher saturation magnetic flux density than ferrite, making them suitable as materials for the magnetic base of coil components through which large currents flow.

An insulating film is provided on the surface of each metal magnetic particle contained in the magnetic base to prevent short circuits between adjacent metal magnetic particles. However, magnetic bases made from metal magnetic materials have a lower volume resistivity than magnetic bases made from ferrite, and are prone to insulation breakdown. JP 2017-092431 A discloses a coil component that improves insulation in the area between the internal conductors of the magnetic base by arranging three or more metal magnetic particles between the internal conductors.

JP 2017-092431 A

Coil components are required to be compact as well as have high insulation reliability. Increasing the distance between opposing parts of the internal conductor improves insulation reliability, but this increases the dimension in the thickness direction.

One of the objects of the present invention is to provide a coil component that can be miniaturized while ensuring insulation reliability between internal conductors, and a method for manufacturing such a coil component. Other objects of the present invention will become apparent throughout the entire specification.

A coil component according to one embodiment of the present invention includes a base body including metal magnetic particles having a first average particle size and ceramic particles having a second average particle size smaller than the first average particle size, and a coil conductor provided within the base body, the coil conductor including a first conductor portion and a second conductor portion provided within the base body so as to face the first conductor portion. In one embodiment, in an inter-conductor region of the base body between the first conductor portion and the second conductor portion, the volume ratio of the ceramic particles to the total volume of the metal magnetic particles and the ceramic particles is 3 vol% or more.

In one embodiment of the present invention, the content ratio of the ceramic particles to the metal magnetic particles in the inter-conductor region is 15 vol% or less.

In one embodiment of the present invention, the first conductor portion and the second conductor portion are made of a conductive material containing a metal, and the substrate does not substantially contain atoms of the metal in the inter-conductor region.

In one embodiment of the present invention, the ceramic particles are made of silica, alumina, zirconia, or titania.

In one embodiment of the present invention, the second average particle size is 1/50 or less of the first average particle size. In one embodiment of the present invention, the second average particle size is 1/200 or more of the first average particle size.

One embodiment of the present invention relates to a circuit board equipped with the above-mentioned coil component.

One embodiment of the present invention relates to an electronic component having the above-mentioned circuit board.

A method for manufacturing a coil component according to one embodiment of the present invention includes the steps of preparing a molded body containing metal magnetic particles having a first average particle size and ceramic particles having a second average particle size smaller than the first average particle size, with a coil conductor disposed therein, and heating the molded body at a temperature lower than the melting temperature of the ceramic particles. In one embodiment, the volume ratio of the ceramic particles to the total volume of the metal magnetic particles and the ceramic particles is 3 vol% or more.

The present invention provides a coil component that can improve the reliability of insulation.

FIG. 1 is a perspective view of a coil component according to an embodiment of the present invention. FIG. 2 is an exploded perspective view of the coil component of FIG. 1 . 2 is a cross-sectional view showing a schematic cross section taken along line XX in FIG. 1. FIG. 4 is an enlarged cross-sectional view showing a schematic enlargement of an area A in FIG. 3 .

Various embodiments of the present invention will be described below with reference to the drawings as appropriate. Note that components common to multiple drawings are given the same reference numerals throughout the multiple drawings. Please note that the drawings are not necessarily drawn to scale for ease of explanation.

A coil component 1 according to one embodiment of the present invention will be described with reference to Figures 1 to 4. Coil component 1 is an example of a coil component to which the present invention is applied. In the illustrated embodiment, coil component 1 is a laminated inductor. This laminated inductor can be used as a power inductor incorporated in a power line and various other inductors. The present invention can be applied to various coil components other than the laminated inductor shown in the figures.

As shown in the figure, the coil component 1 includes a base 10, a coil conductor 25 provided within the base 10, an external electrode 21 provided on the surface of the base 10, and an external electrode 22 provided on the surface of the base 10 at a position spaced apart from the external electrode 21.

The coil component 1 is mounted on a circuit board 2. The circuit board 2 is provided with two land portions 3a, 3b. The coil component 1 may be mounted on the circuit board 2 by soldering each of the external electrodes 21, 22 to the corresponding land portion 3 of the circuit board 2. The circuit board 2 may include the coil component 1 and various electronic components other than the coil component 1. The circuit board 2 may be mounted on various electronic devices. Electronic devices in which the circuit board 2 may be mounted include smartphones, tablets, game consoles, electronic devices used in automotive electrical equipment, and various other electronic devices. The uses of the coil component 1 are not limited to those explicitly stated in this specification.

The base body 10 is formed in a roughly rectangular parallelepiped shape. The base body 10 has a first main surface 10a, a second main 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 main body 10 is defined by these six surfaces. The first main surface 10a and the second main surface 10b face each other, the first end surface 10c and the second end surface 10d face each other, and the first side surface 10e and the second side surface 10f face each other. In FIG. 1, the first main surface 10a is on the upper side of the main body 10, so the first main surface 10a may be referred to as the "upper surface". Similarly, the second main surface 10b may be referred to as the "lower surface". The magnetically coupled coil component 1 is disposed so that the second main surface 10b faces the circuit board 2, and therefore the second main surface 10b is sometimes referred to as the "mounting surface." When referring to the up-down direction of the magnetically coupled coil component 1, the up-down direction in FIG. 1 is used as a reference. In this specification, unless otherwise understood in the context, the "length" direction, "width" direction, and "thickness" direction of the coil component 1 are the "L-axis" direction, "W-axis" direction, and "T-axis" direction in FIG. 1, respectively. The L-axis, W-axis, and T-axis are mutually orthogonal. The coil axis Y extends along the T-direction. For example, the coil axis Y passes through the intersection of the diagonals of the first main surface 10a, which has a rectangular shape in a plan view, and extends in a direction perpendicular to the first main surface 10a.

In one embodiment of the present invention, the coil component 1 is formed so that the length dimension (dimension in the L axis direction) is 0.2 to 6.0 mm, the width dimension (dimension in the W axis direction) is 0.1 to 4.5 mm, and the thickness dimension (dimension in the T axis direction) is 0.1 to 4.0 mm. These dimensions are merely examples, and the coil component 1 to which the present invention can be applied can have any dimensions as long as they are not contrary to the spirit of the present invention. In one embodiment, the coil component 1 is formed to have a low height. For example, the coil component 1 is formed so that its width dimension is greater than its thickness dimension.

2 and 3, the base 10 has a plurality of stacked magnetic layers. As shown, the base 10 includes a main body portion 20, an upper cover layer 18 provided on the upper surface of the main body portion 20, and a lower cover layer 19 provided on the lower surface of the main body portion 20. The main body portion 20 includes stacked magnetic layers 11 to 16. In the base 10, the upper cover layer 18, magnetic layer 11, magnetic layer 12, magnetic layer 13, magnetic layer 14, magnetic layer 15, magnetic layer 16, magnetic layer 17, and lower cover layer 19 are stacked in this order from top to bottom in FIG. 2.

The upper cover layer 18 includes four magnetic layers 18a to 18d. In the upper cover layer 18, the magnetic layers 18a, 18b, 18c, and 18d are stacked in this order from bottom to top in FIG. 2.

The lower cover layer 19 includes four magnetic layers 19a to 19d. In the lower cover layer 19, the magnetic layers 19a, 19b, 19c, and 19d are stacked in this order from top to bottom in FIG. 2.

The magnetic layers 11 to 16 are provided with corresponding conductor patterns C11 to C16. These conductor patterns C11 to C16 form the coil conductor 25. This coil conductor 25 has a coil axis Y. Each of the conductor patterns C11 to C16 is formed to extend around the coil axis Y. In the illustrated embodiment, the coil axis Y extends in the T-axis direction, which coincides with the stacking direction of the magnetic layers 11 to 16.

In another embodiment of the present invention, the magnetic layers 11 to 16 may be stacked in the L-axis direction. In this case, by forming the conductor patterns C11 to C16 on the surfaces of the magnetic layers 11 to 16, the coil axis Y faces the L-axis direction, which is the same as the stacking direction of the magnetic layers 11 to 16. In another embodiment of the present invention, the magnetic layers 11 to 16 may be stacked in the W-axis direction. In this case, by forming the conductor patterns C11 to C16 on the surfaces of the magnetic layers 11 to 16, the coil axis Y faces the W-axis direction, which is the same as the stacking direction of the magnetic layers 11 to 16.

The coil component 1 may include any number of insulating layers as necessary, in addition to insulating layers 11 to 16, insulating layers 18a to 18d, and insulating layers 19a to 19d. Some of insulating layers 11 to 16, insulating layers 18a to 18d, and insulating layers 19a to 19d may be omitted as appropriate. In FIG. 3, the boundaries between the magnetic layers are shown, but in the base of an actual coil component to which the present invention is applied, the boundaries between the magnetic layers may not be visible.

The conductor patterns C11 to C16 are formed on the corresponding insulating layers 11 to 16, respectively. The conductor patterns C11 to C16 are formed by printing such as screen printing, plating, etching, or any other known method. The vias V1 to V5 are formed at predetermined positions of the insulating layers 11 to 15, respectively. The vias V1 to V5 are formed by forming through holes penetrating the insulating layers 11 to 15 in the T-axis direction at predetermined positions of the insulating layers 11 to 15, and filling the through holes with a conductive material. The conductor patterns C11 to C16 and the vias V1 to V5 contain a metal with excellent conductivity, such as Ag, Pd, Cu, Al, or an alloy of these.

In this specification, the region of the substrate 10 between adjacent conductor patterns C11 to C16 is referred to as an inter-conductor region. In other words, the inter-conductor region is a part of the substrate 10, and is a region sandwiched between adjacent conductor patterns. Five inter-conductor regions 10X are shown in FIG. 3. One of the inter-conductor regions 10X is between the conductor pattern C11 and the conductor pattern C12 adjacent to the adjacent pattern C11. The other inter-conductor regions 10X are also disposed between adjacent conductor patterns as shown.

The inter-conductor region 10X will be further described with reference to FIG. 4. FIG. 4 shows an enlarged view of region A in FIG. 3. Region A includes a portion of conductor pattern C12, a portion of conductor pattern C13, and a portion of inter-conductor region 10X between conductor pattern C12 and conductor pattern C13. As shown, the base 10 includes a plurality of metal magnetic particles 31 and a plurality of ceramic particles 32 in the inter-conductor region 10X.

The metal magnetic particles 31 are particles or powder made of a soft magnetic metal material. The soft magnetic metal material for the metal magnetic particles 31 is, for example, particles of (1) metallic Fe or Ni, (2) alloys Fe-Si-Cr, Fe-Si-Al, or Fe-Ni, (3) amorphous Fe-Si-Cr-B-C or Fe-Si-B-Cr, (4) or a mixture of these materials.

The average particle size of the metal magnetic particles 31 is, for example, 2 μm to 10 μm. The average particle size of the metal magnetic particles 31 is not limited to the range of 2 μm to 10 μm and can be changed as appropriate. In this specification, the "average particle size" of the magnetic particles means the volume-based average particle size unless otherwise interpreted. The volume-based average particle size of the magnetic particles is measured by a laser diffraction scattering method in accordance with JIS Z 8825. As a laser diffraction/scattering device, for example, a laser diffraction/scattering type particle size distribution measuring device (model number: LA-960) manufactured by Horiba, Ltd., Kyoto City, Kyoto Prefecture, Japan, can be used.

The metal magnetic particles 31 may contain two types of metal magnetic particles with different average particle sizes. When the metal magnetic particles 31 contain two types of metal magnetic particles with different average particle sizes, the larger of the metal magnetic particles 31 has an average particle size of, for example, 2 μm to 10 μm, and the smaller of the metal magnetic particles 31 has an average particle size of, for example, 1/20 to 1/2 of the larger. The smaller of the metal magnetic particles 31 with different average particle sizes has an average particle size of, for example, 0.2 μm to 1 μm. The metal magnetic particles 31 may contain three or more types of metal magnetic particles with different average particle sizes.

An insulating film is provided on the surface of the metal magnetic particle 31. The insulating film on the surface of the metal magnetic particle 31 may be, for example, an oxide film formed by oxidizing the surface of the metal magnetic particle 31. An insulating coating film may be provided on the surface of the metal magnetic particle 31. This coating film may be, for example, a thin film made of silica or containing silica.

The ceramic particles 32 are particles or powder made of a ceramic material having an average particle size smaller than that of the metal magnetic particles 31. The ceramic particles 32 are made of a ceramic material having a higher electrical resistivity than the metal magnetic particles 31. The ceramic particles 32 are, for example, particles made of silica, alumina, zirconia, or titania, or mixed particles made of a mixture of these. The ceramic particles 32 have higher insulating properties than the metal magnetic particles 31 on which an insulating film is provided.

The average particle size of the ceramic particles 32 is, for example, 10 to 50 nm. The average particle size of the ceramic particles 32 may be 1/50 or less of the average particle size of the metal magnetic particles 31. The average particle size of the ceramic particles 32 may be 1/100 or less of the average particle size of the metal magnetic particles 31. In one embodiment, the average particle size of the ceramic particles 32 may be 1/200 or more of the average particle size of the metal magnetic particles 31. The average particle size of the ceramic particles 32 may be 1/50 or less and 1/200 or more of the average particle size of the metal magnetic particles 31. When the metal magnetic particles 31 include two or more types of metal magnetic particles having different average particle sizes, the average particle size of the ceramic particles 32 is compared with the average particle size of the largest of the multiple types of metal magnetic particles 31. In other words, the average particle size of the ceramic particles 32 may be 1/50 or less of the average particle size of the largest of the multiple types of metal magnetic particles 31.

In one embodiment of the present invention, the content of ceramic particles 32 in the inter-conductor region 10X of the base 10 with respect to the total volume of the metal magnetic particles 31 and the ceramic particles 32 is 3 vol% or more in volume ratio. In one embodiment of the present invention, the content of ceramic particles 32 in the inter-conductor region 10X of the base 10 with respect to the total volume of the metal magnetic particles 31 and the ceramic particles 32 is 15 vol% or less in volume ratio.

The volume of the metal magnetic particles 31 contained in the base 10 is obtained by measuring the particle size of each metal magnetic particle appearing on a cross section obtained by cutting the base 10 using the laser diffraction scattering method according to JIS Z 8825 described above, and converting the particle size obtained as a result of this measurement into a volume. When converting from particle size to volume, each magnetic particle is assumed to be spherical, in consideration of the measurement principle of the laser diffraction scattering method according to JIS Z 8825. The volume of the ceramic particles 32 is also measured and calculated in the same manner as the volume of the metal magnetic particles 31.

In one embodiment of the present invention, the inter-conductor region 10X is substantially free of atoms of the metal contained in the coil conductor 25. For example, when the conductor patterns C11 to C16 contain a certain metal (e.g., Ag), if the elemental amount of the metal contained in the inter-conductor region 10X is 1% or less of the elemental amount of the metal contained in a predetermined region in the conductor patterns C11 to C16, it can be determined that the inter-conductor region 10X is substantially free of atoms of the metal contained in the coil conductor 25. More specifically, the coil component 1 is cut along its thickness direction (T direction) to expose a cross section including at least one of the conductor patterns C11 to C16 and the inter-conductor region 10X, and energy dispersive X-ray analysis (EDS) is performed on the region included in the conductor patterns C11 to C16 and the region included in the inter-conductor region 10X of the cross section, thereby making it possible to compare the elemental amount of the metal contained in the conductor patterns C11 to C16 with the elemental amount of the metal contained in the inter-conductor region 10X. For example, when the conductor patterns C11 to C16 contain Ag, the element amount of Ag in the 1 μm square region A1 in the conductor pattern C12 shown in FIG. 4 and the 1 μm square region A2 in the inter-conductor region 10X are analyzed by EDS, and when the count value of the detection peak of Ag element obtained in the region A2 is 1/100 or less of the count value of the detection peak of Ag element obtained in the region A1, it can be determined that the atoms of the metal contained in the conductor patterns C11 to C16 (i.e., the metal contained in the coil conductor 25) are substantially not present in the inter-conductor region 10X. Since the base in the conventional coil component does not contain ceramic particles corresponding to the ceramic particles 32 in the above embodiment, the metal atoms contained in the conductor pattern diffuse into the inter-conductor region. Therefore, the atoms of the metal contained in the coil conductor (conductor pattern) are present in the inter-conductor region of the base in the conventional coil component. In contrast, in the embodiment of the present invention, the inter-conductor region 10X contains 3 vol % or more of ceramic particles 32, so that metal atoms do not diffuse from the conductor patterns C11 to C16 into the inter-conductor region 10X. As a result, the metal atoms contained in the conductor patterns C11 to C16 are substantially absent in the inter-conductor region 10X. Therefore, the physical property values in the inter-conductor region 10X of the base 10 are not affected by the metal atoms contained in the conductor patterns C11 to C16 (for example, by the diffusion of the metal atoms into the inter-conductor region 10X). For example, the insulation resistance in the inter-conductor region 10X is not affected by the metal atoms contained in the conductor patterns C11 to C16. In other words, the metal atoms contained in the conductor patterns C11 to C16 do not substantially reduce the insulation resistance value of the inter-conductor region 10X.

The substrate 10 may contain a binder for strengthening the bond between the metal magnetic particles 31. The binder contained in the substrate 10 may be a thermosetting resin with excellent insulating properties, such as an epoxy resin, a phenolic resin, a polyimide resin, a silicone resin, a polystyrene (PS) resin, a high density polyethylene (HDPE) resin, a polyoxymethylene (POM) resin, a polycarbonate (PC) resin, a polyvinyldiene fluoride (PVDF) resin, a phenolic resin, a polytetrafluoroethylene (PTFE) resin, a polybenzoxazole (PBO) resin, a polyvinyl alcohol (PVA) resin, a polyvinyl butyral (PVB) resin, or an acrylic resin.

The base 10 may also contain metal magnetic particles 31 and ceramic particles 32 in regions other than the inter-conductor regions 10X. The content of ceramic particles 32 in regions of the base 10 other than the inter-conductor regions 10X may be less than the content of ceramic particles 32 in the inter-conductor regions 10X. For example, in the core region of the base 10, which is located inside the coil conductor 25 in the radial direction centered on the Y axis, the content of ceramic particles 32 can be less than the content in the inter-conductor regions 10X. This allows the content of metal magnetic particles 31 in the core region to be increased, thereby improving the effective permeability of the coil component 1.

Next, an example of a method for manufacturing the coil component 1 will be described. In one embodiment of the present invention, the coil component 1 is manufactured by a sheet manufacturing method using a magnetic sheet. When manufacturing the coil component 1 by the sheet manufacturing method, first, an upper laminate that becomes the upper cover layer 18, an intermediate laminate, and a lower laminate that becomes the lower cover layer 19 are formed. The upper laminate is formed by stacking a plurality of magnetic sheets that become the magnetic layers 18a to 18d, the lower laminate is formed by stacking a plurality of magnetic sheets that become the magnetic layers 19a to 19d, and the intermediate laminate is formed by stacking a plurality of magnetic sheets that become the magnetic layers 11 to 16. The magnetic sheet is manufactured by, for example, putting a slurry obtained by kneading a particle group including the metal magnetic particles 31 and the ceramic particles 32 with a resin into a molding die and applying a predetermined molding pressure. As the resin to be kneaded with the metal magnetic particles 31 and the ceramic particles 32, for example, a resin material with excellent insulating properties such as polyvinyl butyral (PVB) resin or epoxy resin can be used.

The intermediate laminate is formed by stacking multiple magnetic sheets on which conductor patterns corresponding to conductor patterns C11 to C16 are formed. Each of the magnetic sheets for the intermediate laminate has a through hole penetrating in the stacking direction, and the conductor patterns corresponding to conductor patterns C11 to C16 are formed on the magnetic sheets with the through holes by screen printing or the like. At this time, the metal material constituting each conductor pattern is embedded in the through hole of the magnetic sheets to form vias. After each sheet containing conductor patterns C11 to C16 is formed, the base film is removed, and the sheets are stacked in order from the sheet containing conductor pattern C16 to the sheet containing conductor pattern C11, to obtain the intermediate laminate.

Next, the intermediate laminate produced as described above is sandwiched between an upper laminate and a lower laminate from above and below, and the upper laminate and the lower laminate are thermocompression bonded to the intermediate laminate to obtain a main laminate. Next, the main laminate is divided into pieces of the desired size using a cutting machine such as a dicing machine or laser processing machine to obtain a chip laminate.

Next, the chip stack is degreased, and the degreased chip stack is heat-treated. The chip stack is heat-treated at a temperature lower than the melting temperature of the ceramic particles 32 contained in the chip stack. The ceramic particles 32 melt at 1000°C or higher. If the ceramic particles 32 are silica, they melt at approximately 1500°C. The chip stack is heat-treated, for example, at 400°C to 900°C for 20 minutes to 120 minutes. The ceramic particles 32 are not oxidized or reduced during the heat treatment of the stack. A material that does not undergo oxidation or reduction reactions at temperatures below 900°C is selected for the ceramic particles 32.

Next, a conductive paste is applied to both ends of the heat-treated chip stack to form the external electrodes 21 and 22. Through these steps, the coil component 1 is obtained.

The coil component 1 may be manufactured by a method known to those skilled in the art other than the sheet manufacturing method, such as a slurry build method or a thin film process manufacturing method. By manufacturing the coil component 1 by a slurry build method or a thin film process manufacturing method, it is easy to make the content of ceramic particles 32 in the inter-conductor region 10X of the base 10 different from the content of ceramic particles 32 in the core region of the base 10, which is located inside the coil conductor 25 in the radial direction centered on the Y axis. For example, by making the content of ceramic particles 32 in the core region of the base 10 less than the content of ceramic particles 32 in the inter-conductor region 10X, the content of metal magnetic particles 31 in the core region can be increased, thereby improving the effective magnetic permeability of the coil component 1.

The illustrated laminated inductor is an example of a coil component to which the present invention can be applied, and the present invention can be applied to various types of coil components other than laminated inductors. For example, the present invention can also be applied to planar coils.

The coil component according to the present invention may be manufactured by a compression molding process instead of a lamination process. When manufacturing the coil component 1 by a compression molding process, a particle group including the metal magnetic particles 31 and the ceramic particles 32 is first kneaded with a binder resin to create a slurry. Next, the slurry is placed in a molding die in which the coil conductor is placed, and molding pressure is applied to obtain a molded body including the coil conductor inside. Next, the molded body is subjected to a heat treatment at a temperature lower than the melting temperature of the ceramic particles 32 to obtain the base body 10. Next, the base body 10 is coated with a conductor paste to form the external electrodes 21 and 22 on the surface of the base body 10. In this manner, the coil component 1 is manufactured by the compression molding process.

An embodiment of the present invention will be described. First, metal magnetic particles having a composition of Fe-Si-Cr (Fe: 92 wt%, Si: 3.5%, Cr: 4.5 wt%) were prepared. Next, the metal magnetic particles were mixed with silica particles as ceramic particles in the ratio shown in Table 1 to obtain a mixed powder. Table 1 shows the content of the metal magnetic particles and the ceramic particles relative to the total volume of the metal magnetic particles and the ceramic particles in this mixed powder, converted into a volume ratio. Next, this mixed powder was kneaded with polyvinyl butyral to create a slurry. Next, this slurry was formed into a long sheet using a coating machine such as a die coater, and cut to create multiple rectangular parallelepiped magnetic sheets with a thickness of 8 μm. In this way, nine types of magnetic sheets (nine types of magnetic sheets: first magnetic sheet to ninth magnetic sheet) with different ceramic particle contents were produced.

Next, through holes were provided at predetermined positions of the first magnetic sheet using a laser or the like, and then the through holes were filled with conductive paste containing Ag, and the conductive paste containing Ag was printed on the magnetic sheet in a predetermined pattern. The first magnetic sheets on which the conductive patterns were formed in this way were stacked so that the conductive patterns formed on different first magnetic sheets were electrically connected to each other via the conductors embedded in the through holes, and temporary pressure bonding was performed at 60°C to obtain a laminate. Similarly, laminates were produced using each of the second magnetic sheet to the ninth magnetic sheet. Next, each of these nine types of laminates was divided into individual pieces by a dicing machine. Next, the individualized chip laminates were degreased, and the degreased chip laminates were subjected to a heat treatment at 800°C. External electrodes were formed on the evaluation chips after the heat treatment to obtain nine types of evaluation coil conductors (samples A1 to A9). The dimensions of this evaluation coil conductor in the L, W, and T directions were 1.6 mm, 0.8 mm, and 0.8 mm, respectively, and it had 4.5 turns of coil conductor inside.

Twenty pieces each of samples A1 to A9 were prepared, and a deflection test was performed on each of the evaluation coil conductors of samples A1 to A9. The deflection test was performed as follows. First, the evaluation coil conductor was mounted on a glass epoxy board with a thickness of 0.8 mm. The board was attached between a pair of support pillars with a radius of 2.5 mm arranged at 90 mm intervals, and the board was deflected by pressing the center of the bottom surface of the board attached between the support pillars to a depth of 10 mm at a speed of 2.5 mm/sec with an indenter with a tip having a curvature radius of R340. This deflection test was performed while monitoring the resistance of the evaluation coil. Among the evaluation coil conductors, those that did not break down electrically and did not show visible cracks when the indenter was pressed to a depth of 10 mm were determined to be good products.

The results of the deflection test are shown in Table 1. As shown in Table 1, for samples A1 to A6, which had a ceramic particle content of 15 vol% or less, no electrical breakdown or cracks occurred in any of the 20 evaluation coil components. Thus, it was found that even when the base of the coil conductor contains ceramic particles, the coil component has sufficient deflection strength as long as the content is 15 vol% or less.

As described above, increasing the content of ceramic particles 32 in the inter-conductor region 10X leads to a deterioration in flexural strength. If the content of ceramic particles 32 in the inter-conductor region 10X is further increased, for example to 100 vol%, delamination becomes more likely to occur during the manufacturing process. This delamination during the manufacturing process is undesirable as it reduces yield. Furthermore, when the content of ceramic particles 32 in the inter-conductor region 10X reaches 100 vol%, inductance degradation occurs in the coil component.

Next, nine types of magnetic sheets (first magnetic sheet to ninth magnetic sheet) were prepared in the same manner as in the preparation process of samples A1 to A9. Next, a conductive paste containing Ag was printed in a predetermined pattern on each of the two first magnetic sheets. The two first magnetic sheets on which the conductive patterns were printed were stacked so that the conductive patterns faced each other. A predetermined number of first magnetic sheets on which the conductive patterns were not printed on the upper and lower surfaces of the two first magnetic sheets were stacked and temporarily pressed at 60°C to obtain a laminate. Similarly, laminates were prepared using each of the second magnetic sheet to the ninth magnetic sheet. Next, each of these nine types of laminates was divided into individual pieces by a dicing machine. Next, the individual chip laminates were degreased, and the degreased chip laminates were subjected to a heat treatment at 800°C. External electrodes were formed on the evaluation chips after the heat treatment to obtain nine types of evaluation capacitor chips (samples B1 to B9). The dimensions of this evaluation capacitor chip in the L, W, and T directions are 1.6 mm x 0.8 mm x 0.8 mm, respectively.

In addition, for each of the evaluation capacitor chips of samples B1 to B9, the voltage applied between the external electrodes was increased stepwise, and the voltage at which a short circuit occurred was measured. The voltage at which a short circuit occurred was divided by the distance between the electrodes, and the value was shown in Table 2 as the withstand voltage of each sample.

As shown in Table 2, samples B3 to B9, which contain 3 vol% or more of ceramic particles, had a withstand voltage of 2.0 V/μm or more. For inductors in power supply systems, where a coil component with a high current capacity is desired, a withstand voltage of 2 V/μm or more is desirable. As shown in Table 2, it was found that if the ceramic particle content is 3 vol% or more, a substrate with a withstand voltage of 2 V/μm or more can be obtained. By using this substrate as the substrate for the coil component, a coil component with a withstand voltage of 2 V/μm or more can be obtained.

Next, the effects of the above embodiment will be described. In the above embodiment, the base 10 contains ceramic particles 32 in the inter-conductor regions 10X that have higher insulating properties than the metal magnetic particles 31, so that the volume resistivity in the inter-conductor regions 10X of the base 10 can be improved. This results in a coil component 1 with improved insulation resistance, i.e., voltage resistance, between the conductor patterns C11 to C16. In particular, when the content of the ceramic particles 32 is 3 vol% or more, a coil component 1 with a high voltage resistance of 2 V/μm or more can be obtained.

According to the above embodiment, since the average particle size of the ceramic particles 32 is smaller than the average particle size of the metal magnetic particles 31, the ceramic particles 32 penetrate into the gaps between the metal magnetic particles 31. Therefore, even if the ceramic particles 32 are added, the volume of the inter-conductor region 10X hardly increases. Therefore, according to the above embodiment, the volume resistivity of the inter-conductor region 10X can be improved while suppressing an increase in the size of the inter-conductor region 10X. By setting the average particle size of the ceramic particles 32 to 1/50 or less or 1/100 or less of the average particle size of the metal magnetic particles 31, the ceramic particles 32 can easily penetrate between the particles of the metal magnetic particles 31. In this case, even if the ceramic particles 32 are added, the size of the inter-conductor region 10X does not substantially increase, so the volume resistivity can be improved without increasing the size of the inter-conductor region 10X. If the average particle size of the ceramic particles 32 is smaller than 1/200 of the average particle size of the metal magnetic particles 31, the ceramic particles 32 will not easily penetrate into the gaps between the metal magnetic particles 31 due to aggregation of the slurry, etc. For this reason, it is preferable that the average particle size of the ceramic particles 32 be at least 1/200 of the average particle size of the metal magnetic particles 31.

The conductor patterns C11 to C16 contain a metal. A part of this metal is present in the conductor patterns C11 to C16 as a cation. In the heat treatment during the manufacture of the coil component 1, the metal element (e.g., Fe) contained in the metal magnetic particles 31 is oxidized. When the electrons emitted when the metal magnetic particles 31 are oxidized react with the cations (Ag+) of the metal (e.g., Ag) in the conductor patterns C11 to C16 in the inter-conductor region 10X, the metal (Ag) precipitates in the inter-conductor region 10X. In other words, the metal contained in the conductor patterns C11 to C16 can diffuse into the inter-conductor region 10X. According to the above embodiment, the presence of the ceramic particles 32 in the inter-conductor region 10X reduces the contact area between the conductor patterns C11 to C16 and the metal magnetic particles 31 contained in the inter-conductor region 10X, so that the atoms of the metal contained in the conductor patterns C11 to C16 are less likely to diffuse into the inter-conductor region 10X. In one embodiment, metal atoms contained in the conductor patterns C11 to C16 are substantially absent in the inter-conductor region 10X. If the metal atoms contained in the conductor patterns C11 to C16 diffuse into the inter-conductor region 10X, this will cause the insulation of the inter-conductor region 10X to deteriorate. However, according to the above embodiment, the metal atoms contained in the conductor patterns C11 to C16 do not diffuse into the inter-conductor region 10X, so the insulation resistance, i.e., the voltage resistance, of the inter-conductor region 10X can be further improved.

According to the above embodiment, in the inter-conductor region 10X of the base 10, the content of the ceramic particles 32 relative to the total volume of the metal magnetic particles 31 and the ceramic particles 32 is 15 vol% or less in terms of volume ratio, so that the volume resistivity of the inter-conductor region 10X can be improved while suppressing deterioration of the flexural strength of the base 10 caused by adding the ceramic particles 32. The flexural strength of the base 10 including the metal magnetic particles 31 is ensured by the bonding between the metal magnetic particles 31 in the base 10. By setting the content of the ceramic particles 32 to 15 vol% or less, the bonding between the metal magnetic particles 31 is not inhibited, and as a result, the decrease in the flexural strength of the base 10 can be prevented or suppressed.

According to the above embodiment, the heating in the manufacturing process of the coil component 1 is performed at a temperature lower than the melting temperature of the ceramic particles 32, so that it is possible to prevent the shape of the base body 10 from being distorted due to the flow of the ceramic particles 32. This makes it possible to prevent a decrease in the insulation resistance, i.e., the withstand voltage, caused by a decrease in the gap between the opposing parts of the coil conductor 25.

According to the above embodiment, the withstand voltage of the coil component 1 can be made higher than in the past. As a result, even if the distance between the opposing portions of the coil conductor 25 is designed to be smaller than the distance between the coil conductors in a conventional coil component that does not contain ceramic particles, the same insulation resistance as the conventional coil component can be obtained. This allows the size of the component to be reduced in height.

Compared to information and communication devices such as smartphones, coil components used in automotive electrical equipment may not only pass large currents but also be subjected to high voltages. For this reason, coil components used in automotive electrical equipment may be required to have insulation properties that are more than twice as high as conventional coil components that are primarily used in information and communication devices. The coil components according to the above embodiments may also be used in applications that require such high insulation properties.

The dimensions, materials, and arrangement of each component described in this specification are not limited to those explicitly described in the embodiments, and each component can be modified to have any dimensions, materials, and arrangement that can be included in the scope of the present invention. In addition, components not explicitly described in this specification can be added to the described embodiments, and some of the components described in each embodiment can be omitted.

Reference Signs List 1 Coil component 10 Base body 10X Inter-conductor area 21, 22 External electrode 25 Coil conductor 31 Metal magnetic particles 32 Ceramic particles C11 to C16 Conductor patterns

Claims (6)

preparing a laminate including a plurality of magnetic sheets containing metal magnetic particles , ceramic particles , and resin , the plurality of magnetic sheets including a magnetic sheet having a conductor pattern formed thereon, the conductor patterns formed on adjacent magnetic sheets being opposed to each other, and an inter-conductor region being formed between the opposed conductor patterns ;
a heat treatment step of heating the laminate at a temperature of 400° C. to 900° C., which is lower than the melting temperature of the ceramic particles;
Equipped with
In the inter-conductor region of the laminate after the heat treatment step,
a volume ratio of the ceramic particles to a total volume of the metal magnetic particles and the ceramic particles is 3 vol% or more;
the metal magnetic particles have a first average particle size and have an insulating film containing silica on a surface thereof;
the ceramic particles have a second average particle size smaller than the first average particle size.
A method for manufacturing a multilayer inductor. The laminate after the heat treatment step includes a plurality of insulating layers including the inter-conductor regions, and the conductor patterns respectively disposed between the plurality of insulating layers,
The laminate is formed such that boundaries between the plurality of insulating layers are not visible in areas other than the inter-conductor areas.
The method for producing the laminated inductor according to claim 1 . The ceramic particles include silica, alumina, zirconia, or titania;
The method for producing the laminated inductor according to claim 1 or 2. The method for producing a laminated inductor according to claim 1 , wherein the metal magnetic particles are bound by a binder in the inter-conductor regions of the laminate after the heat treatment step. The method for producing a laminated inductor according to claim 4 , wherein the binder includes the resin contained in the laminate, or the resin that has been subjected to the heat treatment step. The method for manufacturing a laminated inductor according to claim 4 , wherein the binder includes a thermosetting resin.

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