JP7486917B2 - Inductance element and electronic device - Google Patents

Description

The present invention relates to an inductance element and an electronic device.

In recent years, inductance elements with internal conductors have become larger in current. To achieve larger currents, it is desirable to reduce the resistance value of the internal conductor. Thus, a structure in which multiple internal conductors are arranged in parallel inside the base is known (e.g., Patent Document 1). It is also known that the cross-sectional shape of multiple internal conductors is elliptical to suppress the decrease in inductance value due to magnetic saturation (e.g., Patent Document 2).

JP 2009-170446 A JP 2014-175349 A

Metal magnetic particles are increasingly being used in the base section that incorporates the internal conductor. The metal magnetic particles are bonded to each other via an oxide film that forms on the surface, thereby forming the base section. This oxide film also serves to maintain the insulation of the base section, and peeling off of the oxide film from the surface of the metal magnetic particles or damage to the oxide film can lead to a decrease in the insulation of the base section.

The present invention was developed in consideration of the above problems, and aims to prevent deterioration of the insulation properties of the base part.

The present invention is an inductance element comprising a base portion including a plurality of metal magnetic particles having an oxide film on a surface thereof, the plurality of metal magnetic particles being bonded to each other via the oxide film, and an internal conductor incorporated in the base portion, the internal conductor having a cross section having a longitudinal width and a lateral thickness in a plane perpendicular to the electrical current flow direction, the thickness of the cross section being greater on the outer side than at the central portion in the longitudinal direction compared to the thickness of the central portion, the plurality of metal magnetic particles being soft magnetic alloy particles containing iron as a main component at 70 wt % or more, and bonded to each other via the oxide film which is an oxide of the plurality of metal magnetic particles, and the internal conductor being formed containing silver or copper and being in contact with the plurality of metal magnetic particles via the oxide.

In the above configuration, the cross section of the internal conductor may be configured to have a thickness that gradually decreases from both ends toward the center in the longitudinal direction.

In the above configuration, the cross section of the internal conductor may be configured such that the thickness is smallest at the center in the region where a pair of sides extending in the longitudinal direction overlap.

In the above configuration, at least one of a pair of sides extending in the longitudinal direction in the cross section of the internal conductor may be curved.

In the above configuration, a portion of the base portion is in contact with the central portion of the internal conductor and a portion outside the central portion, and can be configured to have a linear expansion coefficient smaller than that of the internal conductor.

In the above configuration, in the cross section of the internal conductor, the central portion of each of a pair of sides extending in the longitudinal direction can be recessed relative to the outer sides.

In the above configuration, the device may be configured to include an external electrode provided on the surface of the base portion, and a lead conductor that connects the internal conductor that winds in a spiral shape with the external electrode.

In the above configuration, the base part may include a pair of external electrodes provided on a pair of opposing surfaces, and the internal conductor may extend linearly between the pair of opposing surfaces of the base part and be connected to the pair of external electrodes. In addition, in the above configuration, the cross section may have a first side extending in the longitudinal direction and a second side longer than the first side, and the thickness of the cross section may be greater on the outside than the central part in the longitudinal direction due to a recess formed on the second side. In addition, in the above configuration, the cross section may include particles or sintered bodies made of a material different from the plurality of metal magnetic particles and having a smaller linear expansion coefficient than the internal conductor and the plurality of metal magnetic particles , and the maximum depth of the recess may be greater than or equal to 1/15 and less than or equal to 1/4 of the maximum thickness of the cross section.

The present invention is an electronic device comprising the inductance element described above and a circuit board on which the inductance element is mounted.

According to the present invention, it is possible to suppress the deterioration of the insulation properties of the base part.

FIG. 1A is a perspective view of an inductance element according to a first embodiment, and FIG. 1B is a cross-sectional view taken along line AA in FIG. FIG. 2 is an exploded plan view of the base portion in the first embodiment. FIG. 3 is a diagram illustrating a state in which metal magnetic particles are bonded via an oxide film. FIG. 4 is an enlarged view of region B in FIG. 5A to 5E are cross-sectional views showing a manufacturing method of the inductance element according to the first embodiment. FIG. 6 is a cross-sectional view of an inductance element according to a first comparative example. FIG. 7 is a diagram illustrating a problem that occurs in the inductance element according to the first comparative example. FIG. 8 is a diagram illustrating the effect of the inductance element according to the first embodiment. 9A to 9G are cross-sectional views showing other examples of the internal conductor in the first embodiment. FIG. 10A is a cross-sectional view of an inductance element in accordance with Example 2, and FIG. 10B is an enlarged view of a region A in FIG. 11A to 11D are cross-sectional views showing a manufacturing method of the inductance element according to the second embodiment. 12(a) is a perspective view of an inductance element according to Example 3, FIG. 12(b) is a cross-sectional view taken along line A-A in FIG. 12(a), and FIG. 12(c) is a cross-sectional view taken along line B-B in FIG. 12(a). 13A is a perspective view of an inductance element according to Example 4, FIG. 13B is a cross-sectional view taken along line A-A in FIG. 13A, and FIG. 13C is a cross-sectional view taken along line B-B in FIG. 13A. FIG. 14 is a side view of an electronic device according to a fifth embodiment.

The following describes an embodiment of the present invention with reference to the drawings.

Figure 1(a) is a perspective view of the inductance element according to the first embodiment, and Figure 1(b) is a cross-sectional view taken along line A-A in Figure 1(a). Figure 1(b) is a cross-section of the central portion of the inductance element 100, and in this figure, the cross-section of the internal conductor 30 is shown perpendicular to the direction of electrical conduction. Figure 2 is an exploded plan view of the base portion in the first embodiment. As shown in Figures 1(a), 1(b), and 2, the inductance element 100 of the first embodiment comprises a base portion 10, an internal conductor 30, lead conductors 50a and 50b, and external electrodes 60a and 60b.

The base 10 has a rectangular parallelepiped shape having an upper surface 12, a lower surface 14, a pair of end surfaces 16a and 16b, and a pair of side surfaces 18a and 18b. The lower surface 14 is the mounting surface, and the upper surface 12 is the surface opposite the lower surface 14. The end surfaces 16a and 16b are surfaces connected to the short sides of the upper surface 12 and the lower surface 14. The side surfaces 18a and 18b are surfaces connected to the long sides of the upper surface 12 and the lower surface 14. The base 10 is not limited to a perfect rectangular parallelepiped shape, and may have, for example, rounded vertices, rounded edges (boundaries between each surface), or curved surfaces. In other words, the rectangular parallelepiped base 10 also includes bases 10 having such an approximately rectangular parallelepiped shape.

The base 10 is an assembly of multiple iron-based soft magnetic particles bonded together. An oxide film is formed on at least a portion of the periphery of the iron-based soft magnetic particles, preferably over the entire surface of the particles, by oxidation of the iron-based soft magnetic particles. The insulation of the base 10 is ensured by this oxide film. Adjacent metal magnetic particles are bonded mainly through the oxide film around each metal magnetic particle. This forms the base 10 with a certain shape. In addition, adjacent iron-based soft magnetic particles may be bonded partially through an insulating layer other than the oxide film formed by oxidation of the iron-based soft magnetic particles, or both bonding through the oxide film and bonding through the insulating layer may be performed. If the insulating layer is an oxide mainly composed of Si, it can improve mechanical strength and insulation.

Figure 3 is a diagram illustrating a state in which metal magnetic particles are bonded through an oxide film. As shown in Figure 3, an oxide film 22 is formed around the metal magnetic particle 20. Adjacent metal magnetic particles 20 are bonded to each other through the oxide film 22. The oxide film 22 is preferably made of an oxide of the metal magnetic particle 20 itself. For example, when the molded metal magnetic particle 20 is heat-treated in an oxygen-containing atmosphere to obtain the base part 10, it is preferable that the surface of the metal magnetic particle 20 is oxidized to form an oxide film 22, and a plurality of metal magnetic particles 20 are bonded through this oxide film 22. The presence of the oxide film 22 can be recognized as a difference in contrast (brightness) in an image taken by a scanning electron microscope (SEM). In addition, the above-mentioned insulating layer that bonds adjacent iron-based soft magnetic particles may be present outside the oxide film 22, or may cover the entire outside of the oxide film 22, or may cover only a part of it.

The metal magnetic particles 20 are soft magnetic particles mainly composed of iron (Fe), and may be alloy particles or iron (Fe) particles that do not contain any metal components other than iron (Fe) except for impurities, or may contain a combination of different types of particles. The main component may be, for example, iron (Fe) more than 50 wt%, 70 wt% or more, 80 wt% or more, or 90 wt% or more. The metal magnetic particles 20 are preferably made of an alloy containing iron (Fe) and at least one metal element (hereinafter sometimes referred to as metal element M) that is more easily oxidized than iron (Fe). Examples of the metal element M include chromium (Cr), aluminum (Al), and titanium (Ti), and preferably chromium (Cr) or aluminum (Al). The metal magnetic particles 20 may contain silicon (Si). The base portion 10 is preferably composed of iron (Fe), metal element M, silicon (Si), and oxygen (O). The base portion 10 may also contain manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), phosphorus (P), or carbon (C). The chemical composition of the base portion 10 can be determined, for example, by photographing a cross section of the base portion 10 with a SEM and using the ZAF method with energy dispersive X-ray spectrometry (EDS).

2 is an exploded plan view of the base 10 in the first embodiment, as described above. As shown in FIG. 2, the base 10 is formed by stacking a plurality of magnetic layers 24 on which the internal conductors 30 are formed, and a plurality of cover layers 26. The internal conductors 30 include a planar conductor 32 and a through conductor 34 that penetrates the magnetic layers 24. The magnetic layers 24 and the cover layers 26 are bonded to each other via an oxide film 22 around the plurality of metal magnetic particles 20. The planar conductors 32 formed in adjacent magnetic layers 24 are connected by the through conductors 34, so that the internal conductors 30 are connected in a spiral shape to form a coil-shaped conductor. The internal conductors 30 are formed of a conductive material such as silver (Ag), copper (Cu), or an alloy mainly composed of these.

Two of the magnetic layers 24 are formed with lead conductors 50a and 50b that connect to the internal conductor 30. The lead conductors 50a and 50b connect both ends of the spirally extending internal conductor 30 to external electrodes 60a and 60b (see FIG. 1(a)) provided on the surface of the base portion 10. The lead conductors 50a and 50b are formed of the same conductive material as the internal conductor 30, for example, but may be formed of a different conductive material.

The external electrodes 60a and 60b are external terminals for surface mounting. As shown in FIG. 1(a), the external electrodes 60a and 60b extend from the lower surface 14 of the base 10 via the end surface 16a or 16b to the upper surface 12 and cover part of the side surfaces 18a and 18b. That is, the external electrodes 60a and 60b are five-surface electrodes that cover the five surfaces of the base 10. The external electrodes 60a and 60b may be three-surface electrodes that extend from the lower surface 14 of the base 10 via the end surface 16a or 16b to the upper surface 12, or two-surface electrodes that extend from the lower surface 14 of the base 10 to the end surface 16a or 16b.

The external electrodes 60a and 60b are formed, for example, from multiple metal layers. The external electrodes 60a and 60b have a multi-layer structure with a lower layer formed of a metal material such as copper (Cu), aluminum (Al), nickel (Ni), silver (Ag), platinum (Pt), or palladium (Pd), or an alloy metal material containing these, a middle layer formed of silver (Ag) or a conductive resin containing silver (Ag), and an upper layer which is a plating layer of nickel (Ni) and/or tin (Sn). The layer configuration of the external electrodes 60a and 60b is not limited to only the layers exemplified, and may include cases where there is an intermediate layer between each layer or a top layer on the upper layer.

Figure 4 is an enlarged view of region B in Figure 1(b). In Figure 4, the internal conductor 30 is shown in a cross section perpendicular to the direction of electrical conduction. As shown in Figure 4, the internal conductor 30 has a longitudinal direction and a lateral direction in a cross section perpendicular to the direction of electrical conduction. The longitudinal direction is the width direction of the internal conductor 30, and the lateral direction is the thickness direction of the internal conductor 30. In the cross section of the internal conductor 30, the internal conductor 30 has a substantially trapezoidal shape having a pair of upper and lower sides 36 and 38 that extend in the width direction, which is the longitudinal direction, as the outer periphery of the internal conductor 30, and a pair of side sides 40 and 42 that connect the upper and lower sides 36 and 38. The corners of the internal conductor 30 may be rounded by a manufacturing method described later. The lower side 38 is longer than the upper side 36, and the side sides 40 and 42 are inclined so as to widen from the upper side 36 toward the lower side 38. The upper side 36 extends in a straight line. The bottom side 38 is curved so that the thickness of the internal conductor 30 gradually decreases from both ends toward the inside (e.g., the center). Therefore, in the cross section of the internal conductor 30, a recess 44 is formed on the bottom side 38 side.

The recess 44 is gradually deeper from both ends connected to the sides 40 and 42 of the lower side 38 toward the inside. The recess 44 is deepest, for example, at the center of the lower side 38. Therefore, in the width direction, which is the longitudinal direction of the internal conductor 30, the thickness of the internal conductor 30 in the region 48 where the upper side 36 and the lower side 38 overlap is thinner at the center of the region 48 than at the ends. In other words, the thickness of the internal conductor 30 in the short direction is gradually thinner from both outer sides toward the inside in the width direction, which is the longitudinal direction. In other words, the internal conductor 30 is thicker on the outside than the center compared to the thickness at the center in the width direction, which is the longitudinal direction, and it can also be said that it has a protrusion on the outside than the center.

Next, a method for manufacturing the inductance element according to the first embodiment will be described. Figures 5(a) to 5(e) are cross-sectional views showing the method for manufacturing the inductance element according to the first embodiment. As shown in Figure 5(a), a magnetic paste containing metal magnetic particles 20 is applied onto a film 70, such as a polyethylene terephthalate film (PET film), for example, by a doctor blade method or the like to form a magnetic film 72.

As shown in FIG. 5B, a magnetic paste containing metal magnetic particles 20 is applied onto the magnetic film 72 by a printing method such as screen printing to form a dome-shaped shape control film 74. The dome-shaped shape control film 74 can be formed by adjusting the viscosity of the magnetic paste used to form the shape control film 74. The viscosity can be adjusted by, for example, the amount of binder, the amount of solvent, and/or the particle size of the metal magnetic particles 20. Note that the shape control film 74 may be formed by applying a magnetic paste containing metal magnetic particles 20, or by applying a non-magnetic material to form an insulating film.

After the magnetic film 72 and the shape control film 74 are stacked and through holes are formed at predetermined positions using a laser, a conductive paste is applied to the shape control film 74 by a printing method such as screen printing to form a precursor of the internal conductor 30 that covers the shape control film 74, as shown in FIG. 5(c). The lower side 38 of the internal conductor 30 is curved by the shape control film 74 to form a recess 44. Note that when the internal conductor 30 is formed, the precursors of the lead conductors 50a and 50b are also formed, but are not shown here. The through holes formed at predetermined positions are filled with conductive paste to form the through conductors 34, but are not shown here.

As shown in FIG. 5(d), a magnetic paste containing metal magnetic particles 20 is applied onto the magnetic film 72 by a printing method such as screen printing to form a magnetic film 76 around the internal conductor 30.

As shown in FIG. 5(e), the film 70 is peeled off. This forms the magnetic layer 24 in FIG. 2.

The cover layer 26 in FIG. 2 is formed by applying a magnetic paste containing metal magnetic particles 20 onto a film such as a PET film, for example by a doctor blade method, to form a magnetic film, and then peeling off the film.

The magnetic layer 24 and cover layer 26 thus prepared are laminated in a predetermined order and compressed. The compressed magnetic layer 24 and cover layer 26 are cut into chip units, and then heat treated at a predetermined temperature (for example, about 600°C to 900°C) in an atmosphere in which the oxygen concentration is adjusted according to the composition of the metal magnetic particles 20. This heat treatment forms an oxide film 22 on the surfaces of the multiple metal magnetic particles 20 that constitute the magnetic layer 24 and cover layer 26, and the multiple metal magnetic particles 20 are bonded to each other via the oxide film 22. As a result, the magnetic layer 24 and cover layer 26 are laminated, and the base part 10 incorporating the internal conductor 30 is formed. Next, external electrodes 60a and 60b are formed on the surface of the base part 10. The external electrodes 60a and 60b are formed by a method used in thin film processes such as paste printing, plating, or sputtering.

Figure 6 is a cross-sectional view of an inductance element according to Comparative Example 1. As shown in Figure 6, in the inductance element 1000 of Comparative Example 1, the cross section of the internal conductor 130 is rectangular and has no recess on the outer periphery. The rest of the configuration is the same as in Example 1, so a description is omitted.

Figure 7 is a diagram illustrating the problems that arise in the inductance element according to Comparative Example 1. In FIG. 7, the rounded corners of the internal conductor 130 are omitted for clarity. As shown in FIG. 7, the internal conductor 130 and the metal magnetic particles 20 are in contact with each other via an oxide film 22. The internal conductor 130 and the metal magnetic particles 20 are made of different materials and have different linear expansion coefficients. When the internal conductor 130 is made of silver (Ag) and the metal magnetic particles 20 are made of iron (Fe) particles, the linear expansion coefficient of the internal conductor 130 is greater than that of the metal magnetic particles 20. Due to the difference in linear expansion coefficients between the internal conductor 130 and the metal magnetic particles 20, for example, in the heat treatment process in the above-mentioned manufacturing method, the internal conductor 130 and the metal magnetic particles 20 are sintered in a state in which stress due to the difference in linear expansion coefficients remains. Therefore, in the process of decreasing the temperature of the base part 10, the internal conductor 130 tries to move in the direction of shrinking as shown by the arrow in FIG. 7, which generates a force in the direction of peeling off the oxide film 22 from the surface of the metal magnetic particle 20. The movement of the internal conductor 130 in the direction of shrinking is larger in the width direction, which is the longitudinal direction in which the cross-sectional dimension of the internal conductor 130 is large. As a result, a gap is generated between the internal conductor 130 and the base part 10 due to the shrinkage of the internal conductor 130, and a force is generated in the direction of peeling off the oxide film 22 on the surface of the metal magnetic particle 20 that is in contact with the side edges 140 and 142 of the internal conductor 130 via the oxide film 22. This causes the surface of the metal magnetic particle 20 to be exposed and/or defects to occur in the oxide film 22, which causes a decrease in the insulation of the base part 10.

On the other hand, according to the first embodiment, as shown in FIG. 4, the internal conductor 30 has a shape having a recess 44 on the lower side 38 side extending in the width direction, which is the longitudinal direction of the internal conductor 30, and has a cross-sectional shape in which the outer side is thicker than the central part in the longitudinal direction. FIG. 8 is a diagram explaining the effect of the inductance element according to the first embodiment. In FIG. 8, the rounded corners of the internal conductor 30 are omitted for clarity. As shown in FIG. 8, the internal conductor 30 has a shape having a recess 44 on the lower side 38 side, that is, the internal conductor 30 has a cross-sectional shape in which the outer side is thicker than the central part in the width direction, which is the longitudinal direction. As a result, even if the internal conductor 30 tries to move in a direction in which it shrinks due to a temperature change, the recess 44 suppresses the shrinkage in the width direction, which is the longitudinal direction. Therefore, the oxide film 22 on the surface of the metal magnetic particle 20 that is in contact with the side edges 40 and 42 of the internal conductor 30 via the oxide film 22 is suppressed from peeling off. This can prevent the insulation of the base 10 from deteriorating and rusting. In addition, for example, if the lower side 38 is longer than the upper side 36 and a recess 44 is provided on the lower side 38, the position of the protrusions can be positioned from the center to the outside in the width direction of the internal conductor 30, and as a result, the spacing between the protrusions can be increased. By increasing the spacing between the protrusions, shrinkage of the internal conductor 30 can be effectively prevented.

The member in contact with the recess 44 of the internal conductor 30 may be the metal magnetic particle 20 or a member having a smaller linear expansion coefficient than the metal magnetic particle 20. The member in contact with the recess 44 of the internal conductor 30 is preferably a member having a smaller linear expansion coefficient than the internal conductor 30. The member different from the metal magnetic particle 20 is not limited to a magnetic material, and may be other materials such as a non-magnetic material. The smaller the linear expansion coefficient of the member in contact with the recess 44, the more the shrinkage of the internal conductor 30 is suppressed. Therefore, the linear expansion coefficient of the member in contact with the recess 44 is more preferably 1/2 or less than that of the metal magnetic particle 20, and even more preferably 1/3 or less. Furthermore, it is preferable that the member in contact with the recess 44 is a material having a higher resistivity than the metal magnetic particle 20. From these, examples of the member in contact with the recess 44 include inorganic materials or oxide materials such as zirconia, alumina, silicon, and ferrite. In addition, the member in contact with the recess 44 is a particle or a sintered body. It is preferable that the particles have an average particle size of 2 μm or less, and that the sintered body has a surface roughness Ra of 1 μm or less. By doing so, the smoothness of the internal conductor 30 can be increased, and the surface roughness Ra can be set to 1 μm or less, or 0.5 μm or less. This smoothness can achieve the same effect of preventing insulation deterioration even if the depth of the recess 44 is small. Furthermore, if the material in contact with the recess 44 is made of a highly insulating material such as zirconia, alumina, silicon, or ferrite, it can also reduce the distance between the internal conductors.

As shown in FIG. 4, preferably, the recess 44 is gradually deeper from both ends of the lower side 38 toward the inside. That is, the cross section of the internal conductor 30 is gradually thinner from both ends toward the center in the longitudinal direction, i.e., the thickness of the cross section of the internal conductor 30 is gradually thinner from both ends toward the center. This allows the shrinkage of the internal conductor 30 in the longitudinal direction, i.e., the width direction, to be dispersed and suppressed, and the stress applied from the internal conductor 30 to the base part 10 to be prevented from being concentrated partially, and the same effect such as prevention of insulation deterioration can be obtained even if the depth of the recess 44 is small. In other words, the thickness of the internal conductor 30 can be made thin, and the component can be made smaller. Note that the depth of the recess 44 becoming deeper from both ends of the lower side 38 toward the inside includes the case where the depth becomes deeper from both ends of the lower side 38 toward the inside, as well as the case where the depth becomes deeper from the vicinity of both ends of the lower side 38 toward the inside.

The recess 44 is preferably deepest at the center of the lower edge 38. In other words, the cross section of the internal conductor 30 is thinnest at the center in the region where the pair of upper edges 36 and lower edges 38 that extend in the longitudinal direction (width direction) overlap. This allows the shrinkage from both side surfaces of the internal conductor 30 to be distributed and suppressed on both sides, and the stress applied from the internal conductor 30 to the base portion 10 to be equalized on both sides.

The depth of the recess 44 is preferably deep in terms of suppressing shrinkage in the width direction, which is the longitudinal direction of the internal conductor 30. On the other hand, since it is preferable that the cross-sectional area of the internal conductor 30 is large, the maximum depth of the recess 44 is preferably 1/15 to 1/4 of the maximum thickness of the internal conductor 30, more preferably 1/10 to 1/5, and even more preferably 1/8 to 1/6. For example, the maximum depth of the recess 44 is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more. In addition, the recess 44 is preferably deep enough to contact five or more particles of the member in contact with the recess 44, more preferably deep enough to contact eight or more particles, and even more preferably deep enough to contact ten or more particles.

The recess 44 is preferably formed by making the lower side 38 longer than the upper side 36 and curving the entire lower side 38. That is, in the cross section of the internal conductor 30, at least one side in the width direction, which is the longitudinal direction, is curved. This prevents the internal conductor 30 from shrinking in the width direction, which is the longitudinal direction, over the entire width direction by the recess 44, and distributes the stress generated in the width direction by the internal conductor 30 over the entire width direction, preventing it from concentrating in a specific area. In particular, the stress applied to the member in contact with the recess 44 is distributed, and the same effect, such as preventing insulation deterioration, can be obtained even if the depth of the recess 44 is small. In other words, the thickness of the internal conductor 30 can be made thinner, making it possible to miniaturize the parts.

9(a) to 9(g) are cross-sectional views showing other examples of the internal conductor in the first embodiment. In FIG. 9(a) to 9(g), the corners of the internal conductor 30 are rounded, and are not shown for clarity. In FIG. 4, the recess 44 is shown as an example in which the depth increases from both ends of the lower side 38 toward the inside, but as in FIG. 9(a), the recess 44 may be deeper from the vicinity of both ends of the lower side 38 toward the inside. As in FIG. 9(b), the side edges 40 and 42 may extend linearly approximately parallel to the thickness direction of the internal conductor 30, or as in FIG. 9(c), they may be curved. As in FIG. 9(d), the recess 44 may be formed by the lower side 38 extending linearly from both ends toward the inside so that the thickness of the internal conductor 30 becomes thinner. As shown in FIG. 9(e), the recess 44 may be formed in a stepped shape on the lower side 38, or as shown in FIG. 9(f), the recess 44 may be formed only in the center of the lower side 38. As shown in FIG. 9(g), the side sides 40 and 42 may extend linearly from both ends toward the inside so that the width of the internal conductor 30 becomes wider. In any internal conductor 30, the thickness of the internal conductor 30 in the short direction has a cross section that is thicker on the outside than the center in the width direction, which is the longitudinal direction. This thicker part is preferably formed on both outsides of the center in the width direction, which is the longitudinal direction of the internal conductor 30, and over more than half the width of the internal conductor 30. This makes it possible to reduce the width length of the part of the internal conductor 30 outside the convex part, and to reduce the stress generated in the width direction of the internal conductor 30 in this part.

In the first embodiment, the internal conductor 30 has a shape with a recess 44 on the lower side 38, but the internal conductor 30 may have a shape with a recess as described above on the upper side 36.

10(a) is a cross-sectional view of the inductance element according to the second embodiment, and FIG. 10(b) is an enlarged view of region A in FIG. 10(a). FIG. 10(a) and FIG. 10(b) are cross-sectional views of the central portion of the inductance element 200, and in these views, the cross-section of the internal conductor 30a is shown in a direction perpendicular to the direction of electrical conduction. As shown in FIG. 10(a) and FIG. 10(b), in the inductance element 200 of the second embodiment, the lower side 38 of the internal conductor 30a is curved so that the thickness of the internal conductor 30a gradually decreases from both ends toward the inside (e.g., the center), and the upper side 36 is also curved so that the thickness of the internal conductor 30a gradually decreases from both ends toward the inside (e.g., the center). Therefore, in the cross-section of the internal conductor 30a, in addition to the recess 44 formed on the lower side 38 side, the internal conductor 30a has a recess 46 formed on the upper side 36 side.

The recess 46 gradually becomes deeper from both ends connected to the sides 40 and 42 of the top edge 36 toward the inside. The recess 46 is deepest, for example, at the center of the top edge 36. That is, the thickness of the internal conductor 30a in the short direction gradually becomes thinner from both outer sides toward the inside in the width direction, which is the longitudinal direction. In other words, the internal conductor 30a is thicker on the outside than the center compared to the thickness of the center in the width direction, which is the longitudinal direction, and it can also be said that it has a protrusion on the outside of the center. The other configuration is the same as in Example 1, so description will be omitted.

Figures 11(a) to 11(d) are cross-sectional views showing a manufacturing method of an inductance element according to Example 2. First, the manufacturing process described in Figures 5(a) to 5(d) of Example 1 is carried out to obtain the structure shown in Figure 11(a). Note that at the stage of Figure 11(a), the lower side 38 of the internal conductor 30a is curved, but the upper side 36 is not yet curved.

As shown in FIG. 11(b), a magnetic paste containing metal magnetic particles 20 is applied onto the internal conductor 30a by a printing method such as screen printing to form a dome-shaped shape control film 78. The magnetic paste used to form the shape control film 74 can be used to form the shape control film 78. Note that, in addition to applying a magnetic paste containing metal magnetic particles 20, the shape control film 78 may also be formed by applying a non-magnetic material to form an insulating film.

As shown in FIG. 11(c), the film 70 is peeled off. This forms the magnetic layer 24a.

As shown in FIG. 11(d), multiple magnetic layers 24a and multiple cover layers 26 are stacked in a predetermined order and compressed. As a result, the top surface of the internal conductor 30a is pressed by the shape control film 78, and the top edge 36 is curved. After that, a process is performed to cut the compressed magnetic layers 24a and cover layers 26 into chip units, but the subsequent processes are the same as those described in Example 1, so their description is omitted.

According to the second embodiment, the internal conductor 30a has a shape having recesses 44 and 46 on both sides of the upper side 36 and the lower side 38. That is, in the cross section of the internal conductor 30a, the central portions of both the upper side 36 and the lower side 38 extending in the width direction, which is the longitudinal direction, are recessed relative to the outer side from the central portion. Furthermore, it can be said that both the upper side 36 and the lower side 38 have convex portions on the outer side from the central portion. By providing convex portions on both the upper side 36 and the lower side 38, the shrinkage in the width direction, which is the longitudinal direction of the internal conductor 30a, can be suppressed on the upper side 36 side and the lower side 38 side. In addition, the recesses 44 and 46 are in contact with the metal magnetic particles 20, which are members constituting the base portion 10 and have a smaller linear expansion coefficient than the internal conductor 30. This effectively prevents shrinkage in the width direction, which is the longitudinal direction of the internal conductor 30a, on both the upper side 36 and the lower side 38 of the internal conductor 30a, and effectively prevents the oxide film 22 from peeling off from the surface of the metal magnetic particles 20, thereby preventing the insulation of the base portion 10 from deteriorating.

As in Example 1, the material in contact with the recesses 44 and 46 is preferably a material that constitutes the base portion 10 and has a smaller linear expansion coefficient than the internal conductor 30a, and is not limited to the metal magnetic particles 20 and may be other materials.

In FIG. 10(b), the recess 46 is shown as being deeper from both ends of the upper side 36 toward the inside, but it may be shaped similarly to the recess 44 shown in FIG. 9(a) to FIG. 9(g) of the first embodiment.

12(a) is a perspective view of the inductance element according to the third embodiment, FIG. 12(b) is a cross-sectional view taken along line A-A in FIG. 12(a), and FIG. 12(c) is a cross-sectional view taken along line B-B in FIG. 12(a). As shown in FIGS. 12(a) to 12(c), in the inductance element 300 according to the third embodiment, the internal conductor 30b extends linearly between the end faces 16a and 16b of the base part 10. The internal conductor 30b is connected to the external electrode 60a at the end face 16a of the base part 10, and is connected to the external electrode 60b at the end face 16b of the base part 10. The cross section of the internal conductor 30b has the same shape as the internal conductor 30 of the first embodiment. The other configurations are the same as those of the first embodiment, and therefore will not be described. In the third embodiment, the same effects as those of the first embodiment can be obtained for the parts common to the first embodiment.

In the first and second embodiments, the inductance element having an internal conductor is a coil component in which the internal conductor is wound in a spiral shape. However, this is not limited to this case, and an inductance element in which the internal conductor 30b extends linearly between the end faces 16a and 16b of the base portion 10 and connects to the external electrodes 60a and 60b, as in the third embodiment, may also be used. The inductance element may also be a transformer or a common mode filter for a power supply, or other type of inductance element.

In the third embodiment, a single internal conductor 30b is provided in the base 10, but multiple internal conductors 30b may be provided in parallel to each other. The internal conductor 30b does not necessarily have to be straight, and may be curved or meandering, as long as the internal conductor 30b is formed between the end face 16a and the end face 16b. As for the inductance element 300, if the internal conductor 30b is straight, the resistance between the external electrodes can be reduced, if there are multiple internal conductors 30b, the resistance between the external electrodes can be further reduced, and if there is a curve, the stress can be further distributed.

Figure 13(a) is a perspective view of the inductance element according to the fourth embodiment, Figure 13(b) is a cross-sectional view taken along line A-A in Figure 13(a), and Figure 13(c) is a cross-sectional view taken along line B-B in Figure 13(a). As shown in Figures 13(a) to 13(c), in the inductance element 400 according to the fourth embodiment, both ends of the internal conductor 30b are exposed from the base part 10 at the lower surface 14 of the base part 10. One end of the internal conductor 30b is connected to the external electrode 60a at the lower surface 14 of the base part 10, and the other end is connected to the external electrode 60b at the lower surface 14 of the base part 10. In this way, the external electrodes 60a and 60b are provided at least on the lower surface 14 of the base part 10.

In the third embodiment, the internal conductor 30b is connected to the external electrodes 60a and 60b at the end faces 16a and 16b of the base part 10, but as in the fourth embodiment, the internal conductor 30b may be connected to the external electrodes 60a and 60b at the lower face 14 of the base part 10. Although not shown in the figures, the internal conductor 30b may be connected to the external electrodes 60a and 60b on other faces of the base part 10.

FIG. 14 is a side view of an electronic device according to Example 5. As shown in FIG. 14, the electronic device 500 of Example 5 includes a circuit board 80 and the inductance element 100 of Example 1 mounted on the circuit board 80. The inductance element 100 is mounted on the circuit board 80 by joining the external electrodes 60a and 60b to the land electrode 82 of the circuit board 80 with solder 84.

According to the electronic device 500 of Example 5, the inductance element 100 is mounted on the circuit board 80. This makes it possible to obtain an electronic device 500 having an inductance element 100 that is less likely to cause a decrease in the insulation of the base part 10. Note that, although Example 5 shows an example in which the inductance element 100 of Example 1 is mounted on the circuit board 80, the inductance elements of Examples 2 to 4 may also be mounted.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

REFERENCE SIGNS LIST 10 Base portion 20 Metal magnetic particles 22 Oxide film 24, 24a Magnetic layer 26 Cover layer 30, 30a, 30b, 130 Internal conductor 32 Planar conductor 34 Through conductor 36 Upper edge 38 Lower edge 40, 42, 140, 142 Side edge 44, 46 Recess 50a, 50b Lead conductor 60a, 60b External electrode 80 Circuit board 82 Land electrode 84 Solder 100, 200, 300, 400, 1000 Inductance element 500 Electronic device

Claims (12)

a base portion including a plurality of metal magnetic particles having an oxide film on a surface thereof, the plurality of metal magnetic particles being bonded to each other via the oxide film;
an internal conductor embedded in the base portion;
the internal conductor has a cross section, in a plane perpendicular to a current-carrying direction, having a width in a longitudinal direction and a thickness in a lateral direction;
The thickness of the cross section is greater on the outer side than on the central portion in the longitudinal direction,
the plurality of metal magnetic particles are soft magnetic alloy particles containing iron as a main component at 70 wt % or more, and are bonded to each other via the oxide film which is an oxide of the plurality of metal magnetic particles;
An inductance element , wherein the internal conductor is formed to contain silver or copper and is in contact with the plurality of metal magnetic particles via the oxide . The inductance element according to claim 1, wherein the cross section of the internal conductor is a cross section whose thickness gradually decreases from both ends in the longitudinal direction toward the center. The inductance element according to claim 2, wherein the cross section of the internal conductor is a cross section in which the thickness is smallest at the center in the region where a pair of sides extending in the longitudinal direction overlap. An inductance element according to any one of claims 1 to 3, wherein at least one of a pair of sides extending in the longitudinal direction in the cross section of the internal conductor is curved. An inductance element according to any one of claims 1 to 4, in which a portion of the base is in contact with the central portion of the internal conductor and a portion outside the central portion, and has a linear expansion coefficient smaller than that of the internal conductor. An inductance element according to any one of claims 1 to 5, wherein in the cross section of the internal conductor, the central portion of both sides of a pair of sides extending in the longitudinal direction is recessed relative to the outer side of the central portion. an external electrode provided on a surface of the base portion;
The inductance element according to claim 1 , further comprising: a lead conductor that connects the internal conductor, which winds in a spiral shape, to the external electrode. a pair of external electrodes provided on a pair of opposing surfaces of the base portion;
The inductance element according to claim 1 , wherein the internal conductor extends linearly between the pair of opposing surfaces of the base portion and is connected to the pair of external electrodes. The cross section has a first side extending in the longitudinal direction and a second side longer than the first side,
9. An inductance element according to claim 1, wherein the thickness of the cross section is greater on the outer side than the central portion in the longitudinal direction due to a recess formed on the second side. The inductance element according to claim 9, comprising particles or sintered bodies provided in the recess and made of a material different from the plurality of metal magnetic particles, the particles or sintered bodies having a smaller linear expansion coefficient than the internal conductor and the plurality of metal magnetic particles . 11. The inductance element according to claim 9 , wherein the maximum depth of the recess is not less than 1/15 and not more than 1/4 of the maximum value of the thickness of the cross section. An inductance element according to any one of claims 1 to 11 ;
and a circuit board on which the inductance element is mounted.

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