Patent ID: 12255006

DETAILED DESCRIPTION

An inductor includes a body including a magnetic portion containing a magnetic powder and a first resin; a coil that is encapsulated in the body and includes a winding portion formed by winding a conductor and a pair of lead-out portions that extend from the winding portion; and a pair of outer electrodes to which at least end portions of the lead-out portions are connected at surfaces of the body. The outer electrodes each include an electrically conductive resin layer and a first cover layer arranged on the electrically conductive resin layer. The electrically conductive resin layers each contain an electrically conductive powder and a second resin and a plurality of electrically conductive metal portions composed of the same material as the first cover layers are contained inside the electrically conductive resin layers.

The connection resistance between the lead-out portions of the coil and the outer electrodes is further reduced due to the contact between the electrically conductive powder particles in the electrically conductive resin layers being increased by arranging the electrically conductive metal portions in the electrically conductive resin layers.

The end portions of the lead-out portions and the first cover layers may be directly connected to each other by the electrically conductive metal portions. The connection resistance between the lead-out portions of the coil and the outer electrodes is further reduced and the adhesion strength of the outer electrodes to the body is also improved by the end portions of the lead-out portions and the first cover layer being directly connected to each other by the electrically conductive metal portions provided in the electrically conductive resin layers.

The surfaces of the body on which the outer electrodes are arranged include magnetic powder exposed portions where the magnetic powder is exposed and at least some of the exposed magnetic powder and the first cover layers may be connected to each other by the electrically conductive metal portions. The adhesion strength between the body and the outer electrodes is improved by the body and the first cover layer being directly connected to each other by the electrically conductive metal portions provided in the electrically conductive resin layers.

The electrically conductive metal portions may be arranged in a branch-like manner. The electrically conductive metal portions that directly connect the lead-out portions of the coil and the outer electrodes to each other can be easily arranged inside the electrically conductive resin layers by forming the electrically conductive metal portions in a branch-like manner.

The outer electrodes may each further include a second cover layer arranged on the first cover layer. The reliability when mounting the inductor on a substrate is further improved by the outer electrodes each including a second cover layer.

The body may have a bottom surface and end surfaces that face each other and are adjacent to the bottom surface, and the outer electrodes may be arranged on at least the bottom surface and the end surfaces. The adhesion strength of the inductor to a substrate when the inductor is mounted on a substrate is further improved by arranging each outer electrode so as to extend along at least two surfaces of the body.

The end portions of the lead-out portions may be exposed at the end surfaces of the body. This allows the lead-out portions to be easily formed.

The first resin may be a different type of resin than the second resin. In addition, the first resin may contain a thermosetting resin and the second resin may contain a thermoplastic resin. This allows the electrically conductive metal portions to be easily formed by the electrically conductive resin layer.

The first cover layers may contain nickel and the second cover layers may contain tin. In addition, the thickness of the first cover layers may be around 100 μm or less. This enables the lead-out portions of the coil and the outer electrodes to be easily connected to each other by the first cover layers.

The term “step” used in this specification refers not only to an independent step but also a step that cannot be clearly distinguished from another step so long as the expected aim of that step is achieved. Hereafter, embodiments of the present disclosure will be described on the basis of the drawings. The following embodiments are exemplary examples of an inductor for making the technical concepts of the present disclosure clear, and the present disclosure is not limited to the inductors described below. Members described in the scope of the claims are in no way limited to the members described in the embodiments. In particular, unless specifically stated otherwise, it is not intended that scope of the present disclosure be limited to the dimensions, materials, shapes, relative arrangements, and so forth of constituent components described in the embodiments and these are merely explanatory examples. Identical parts are denoted by identical symbols in the drawings. Taking explanation of important points or ease of understanding into account, the embodiments are described in a separate manner for the sake of convenience, but parts of the configurations illustrated in the different embodiments may be substituted for one another or combined with each other. In embodiment 2 and embodiments thereafter, description of matters common to embodiment 1 is omitted and the description focuses on the points that are different. In particular, the same operational effects resulting from the same configurations will not be repeatedly described in the individual embodiments.

EMBODIMENTS

Hereafter, the present disclosure will be described in a specific manner using embodiments, but the present disclosure is not limited to these embodiments.

Embodiment 1

An inductor of embodiment 1 will be described while referring toFIGS.1to3.FIG.1is a partial see-through schematic perspective view in which an inductor100is viewed from above.FIG.2is a schematic sectional view of the inductor100along a plane perpendicular to the bottom surface and the top surface of the inductor100taken along line a-a inFIG.1.FIG.3is a partial enlarged schematic sectional view of part A inFIG.2.

As illustrated inFIG.1, the inductor100includes: a body10that includes a magnetic portion containing a magnetic powder and a first resin; a coil30that is encapsulated in the body10; and outer electrodes40are arranged on the surfaces of the body10and electrically connected to the coil30. The body10has a bottom surface12, which is on the mounting surface side, a top surface14that faces the bottom surface12in a height direction (T direction), two end surfaces16that are adjacent to and substantially perpendicular to the bottom surface12and face each other in a length direction (L direction), and two side surfaces18that are adjacent to and substantially perpendicular to the bottom surface12and the end surfaces16and face each other in a width direction (W direction). The coil30includes a winding portion32formed by winding a conductor around a winding axis N and a pair of lead-out portions34that extend from the winding portion32. The coil30is encapsulated in the body10such that the end portions of the lead-out portions34are exposed from the end surfaces16of the body10. The pair of outer electrodes40are arranged on five surfaces of the body10, namely, the bottom surface12, the end surfaces16, the top surface14, and the side surfaces18of the body10and are connected, at the end surfaces16, to the end portions of the lead-out portions34of the coil30, which are exposed from the end surfaces16. InFIG.1, dashed lines may be used as auxiliary lines to represent curved surfaces.

As illustrated inFIG.2, the outer electrodes40are each formed by sequentially stacking an electrically conductive resin layer42, a first cover layer44, and a second cover layer46. The electrically conductive resin layers42are formed by applying an electrically conductive resin composition containing an electrically conductive powder and a second resin to the surfaces of the body10and the electrically conductive resin layers42are electrically connected to the end portions of the lead-out portions34of the coil exposed from the end surfaces16. The electrically conductive powder may contain silver (Ag) particles, for example. The volume average particle diameter of the Ag particles may be around 10 nm to 100 μm, for example. The electrically conductive powder may contain nano-size Ag particles, may contain micro-size Ag particles, or may contain both nano-size and micro-size Ag particles. In addition, the second resin may contain a thermoplastic resin such as an acrylic resin, for example. The first cover layers44, for example, contain nickel and may be formed on the electrically conductive resin layers42by performing a plating process. The second cover layers46, for example, contain tin and may be formed on the first cover layers by a performing a plating process.

FIG.3schematically illustrates the connection state between the end portions of the lead-out portions34and the outer electrodes40. As illustrated inFIGS.2and3, a coating layer24is removed from the end portions of the lead-out portions34exposed at the end surfaces16and a conductor22is exposed at the end surfaces16. The electrically conductive resin layers42are arranged on the surfaces of the exposed conductor22. The electrically conductive resin layers42contain an electrically conductive powder62and a second resin64and further include electrically conductive metal portions66. A plurality of the electrically conductive metal portions66are formed inside the electrically conductive resin layers42in a branch-like manner. In the electrically conductive resin layers42, in addition to the conductor22and the first cover layers44being electrically connected to each other due to the proximity and contact between the particles of the electrically conductive powder62, the electrically conductive metal portions66directly connect the conductor22and the first cover layers44to each other. The branch-like electrically conductive metal portions66are formed in the following ways, for example. When the electrically conductive resin layers42are formed, voids are formed in the electrically conductive resin layers42due to curing shrinkage and thermal contraction of the second resin. In this case, the voids in the electrically conductive resin layers42may be formed by parts of the second resin being removed as a result of the electrically conductive resin layers42being subjected to laser irradiation. Subsequently, when the first cover layers44are formed by performing a plating process, the metal constituting the first cover layers44may be plated and grown in the voids in the conductive resin layers42to form the branch-like electrically conductive metal portions66. In other words, the electrically conductive metal portions66may be integrally formed with the first cover layers44. The electrically conductive metal portions66may alternatively be formed in network-like shape inside the electrically conductive resin layers42. The electrically conductive metal portions66arranged in a network-like shape may be arranged along boundaries between particles of the electrically conductive powder62. In one mode, the electrically conductive resin layers42may be formed to have a porous structure containing the electrically conductive powder and the second resin, and the electrically conductive metal portions66, which directly connect the conductor forming the coil and the first cover layers to each other, may be arranged in the voids of the porous structure. Contact between the particles of the electrically conductive powder62may be increased and the connection resistance may be reduced by forming the electrically conductive resin layers42to have a porous structure. At least some of the electrically conductive metal portions66may or may not directly connect the end portions of the lead-out portions34and the first cover layers44to each other. The electrically conductive metal portions66are preferably formed so as to be dispersed inside the electrically conductive resin layers42and the electrically conductive metal portions66are preferably formed as many branches.

The thickness of the electrically conductive resin layers42may be, for example, around 50 nm to 100 μm or around 1 μm to 20 μm. The thickness of the first cover layers may be, for example, around 30 μm or less or around 0.5 μm to 15 μm. The thickness of the second cover layers may be, for example, around 50 μm or less or around 1 μm to 30 μm.

As illustrated inFIG.2, the conductor22forming the coil30has the coating layer24on the surface thereof and the cross-sectional shape of the conductor in a direction perpendicular to the extension direction of the conductor (length direction) is a substantially rectangular shape defined by the thickness and width thereof. The thickness of the conductor may be around 0.01 to 1 mm, for example. The width of the conductor may be around 0.1 to 2 mm, for example. The aspect ratio (width/thickness) of the cross-section of the conductor may be, for example, around 1/1 or higher or around 1/1 to 30/1. In addition, the coating layer24covering the conductor22is formed of an insulating resin such as polyimide or polyamide-imide with a thickness of, for example, around 2 μm to 20 μm. In order to prevent the winding portion from unwinding, a fusion layer including a self-fusing component such as a thermoplastic resin or a thermosetting resin may be further provided on the surface of the coating layer24, and the thickness of the layer may be around 1 μm to 8 μm.

The winding portion32of the coil30is wound in a spiral shape so that both ends of the conductor are located at the outermost periphery and one of the surfaces defined by the width of the conductor is located at the outer periphery and the other surface defined by the width of the conductor is located at the inner periphery, and the winding portion32is wound vertically in two stages that are connected at the innermost periphery with the surfaces defined by the thickness of the conductor facing each other (a so-called alpha winding). The coil30is encapsulated by the body10with the winding axis N of the winding portion32being substantially perpendicular to the bottom surface12and the top surface14of the body10.

As illustrated inFIGS.1and2, one lead-out portion34extends from the outer periphery of the upper stage of the winding portion32, which is on the side near the top surface14, with the end portion thereof pointing toward one side surface18of the body10and a surface thereof defined by the width of the conductor22is exposed at one end surface16of the body10. The other lead-out portion34extends from the outer periphery of the lower stage of the winding portion32, which is on the side near the bottom surface12, with the end portion thereof pointing toward one side surface18of the body10and a surface thereof defined by the width of the conductor22is exposed at one end surface16of the body10. The coating layer24is removed from the surfaces of the conductor22exposed from the end surfaces16.

The body10may have a substantially rectangular parallelepiped shape. The body10has a length L of, for example, around 1 to 3.4 mm and preferably around 1 to 3 mm, a width W of, for example, around 0.5 to 2.7 mm and preferably around 0.5 to 2.5 mm, and a height T of, for example, around 0.5 to 2 mm and preferably around 0.5 to 1.5 mm. As specific examples of the size of the body, L×W×T may be 1 mm×0.5 mm×0.5 mm, 1.6 mm×0.8 mm×0.8 mm, 2 mm×1.2 mm×1 mm, or 2.5 mm×2 mm×1.2 mm, for example.

The magnetic portion of the body10is formed of a composite material containing a magnetic powder and the first resin. An iron-based metal magnetic powder such as Fe, Fe—Si, Fe—Ni, Fe—Si—Cr, Fe—Si—Al, Fe—Ni—Al, Fe—Ni—Mo, and Fe—Cr—Al, a metal magnetic powder having another composition basis, an amorphous metal magnetic powder or the like, a metal magnetic powder in which the surfaces of the powder particles are coated with an insulating layer such as glass, a surface-modified metal magnetic powder, or a nano-level fine metal magnetic powder is used as the magnetic powder. Furthermore, a thermosetting resin such as an epoxy resin, a polyimide resin, or a phenol resin, or a thermoplastic resin such as a polyethylene resin, a polyamide resin, or a liquid crystal polymer is used as the first resin. The filling ratio of the magnetic powder in the composite material is, for example, around 50 to 85% by mass and preferably around 60 to 85% by mass or around 70 to 85% by mass.

A protective layer may be arranged on the surfaces of the body10. The protective layer may be arranged on the surfaces of the body other than the regions where the outer electrodes are arranged or may be arranged on the surfaces of the body other than the regions where the end portions of the lead-out portions are exposed. The protective layer may contain a resin, for example. Furthermore, a thermosetting resin such as an epoxy resin, a polyimide resin, or a phenol resin, or a thermoplastic resin such as an acrylic resin, a polyethylene resin, or a polyamide resin is used as the resin forming the protective layer. The protective layer may contain a filler. An electrically non-conductive filler such as silicon oxide or titanium oxide is used as the filler. The protective layer is formed, for example, by applying a resin composition containing a resin and a filler to the surfaces of the body by performing coating, dipping, or the like, and curing the applied resin if necessary. The protective layer may be formed of a non-organic material. In addition, the protective layer may be formed on regions other than magnetic powder exposed regions, which are described later.

The body10may be provided with a marker (not illustrated). For example, the marker may be provided on the top surface14of the body, on the side where the lead-out portion34is led out from the lower stage of the winding portion32, to indicate the polarity of the inductor. The marker may be provided by performing printing, laser engraving, and so on.

For example, the inductor100can be manufactured using a manufacturing method including: a coil forming step of forming a coil by molding a conductor into a desired shape; a body forming step of molding the body by burying the formed coil in a composite material containing a magnetic powder and a resin with the end portions of the lead-out portions exposed and performing pressing using a die or the like; and an outer electrode forming step including forming electrically conductive resin layers on the end portions of the lead-out portions exposed from the surfaces of the body and forming the first cover layers on the electrically conductive resin layers. In order to form branch-like electrically conductive metal portions, voids may be formed by allowing the second resin to shrink when an electrically conductive resin paste is applied and cured and then plating may also be grown in the voids in the electrically conductive resin layers42when the first cover layers are formed using a plating process.

Embodiment 2

An inductor of embodiment 2 will be described while referring toFIGS.4and5.FIG.4is a schematic sectional view of an inductor110.FIG.5is a partial enlarged schematic sectional view of part B inFIG.4. The inductor110of embodiment 2 is configured similarly to the inductor100of embodiment 1 except that magnetic powder exposed regions are provided in parts of the surfaces of the body and the outer electrodes are formed on these magnetic powder exposed regions.

As illustrated inFIG.4, in the inductor110, magnetic powder exposed regions52are formed along portions of the bottom surface12, portions of the top surface14, portions of the side surfaces18, and the end surfaces16of the body, and the outer electrodes40are arranged on the magnetic powder exposed regions52. Magnetic powder non-exposed regions54are formed on the surfaces of the body in addition to the magnetic powder exposed regions52. A protective layer may be arranged on the magnetic powder non-exposed regions54.

The magnetic powder exposed regions52are formed by irradiating desired regions of the body with a laser, for example. In addition, the magnetic powder exposed regions52may be formed by sand blasting desired regions of the body, for example. The surfaces of metal particles constituting the magnetic powder may be exposed by removing at least part of an insulating layer covering the magnetic powder in the magnetic powder exposed regions52. Furthermore, the magnetic powder may be exposed at surfaces of the body by removing parts of the first resin included in the body in the magnetic powder exposed regions52.

FIG.5schematically illustrates the connection state between the magnetic powder exposed regions52and the outer electrodes40. As illustrated inFIG.5, the electrically conductive resin layers42are arranged on the magnetic powder exposed regions52. The electrically conductive resin layers42contain the electrically conductive powder62, the second resin64, and the electrically conductive metal portions66. The electrically conductive metal portions66connect the magnetic powder of the magnetic powder exposed regions52and the first cover layers44to each other. In one mode, the electrically conductive resin layers42may be formed to have a porous structure containing the electrically conductive powder and the second resin, and the electrically conductive metal portions66, which connect the magnetic powder forming the body and the first cover layers to each other, may be arranged in the voids of the porous structure. An anchor effect is improved in the magnetic powder exposed regions52due to the surface roughness being higher. In addition, the magnetic powder and the first cover layers are directly connected to each other. This allows the adhesion strength of the outer electrodes40to the body to be improved. In the magnetic powder exposed regions, the electrically conductive metal portions do not necessarily have to connect the magnetic powder and the first cover layers to each other, and even in this case, the DC resistance can be reduced.

Embodiment 3

An inductor of embodiment 3 will be described while referring toFIG.6.FIG.6is a schematic sectional view of an inductor120. The inductor120of embodiment 3 is configured similarly to the inductor100of embodiment 1 except that the outer electrodes are not arranged on the top surface14and the side surfaces18and are arranged on parts of the bottom surface12and parts of the end surfaces16.

In the inductor120, the outer electrodes40are arranged along parts of the bottom surface12and parts of the end surfaces16. This makes it possible to reduce the size of fillets formed when mounting the inductor120on a substrate and as a result higher mounting density is possible.

In the above-described inductor, a case has been described in which the outer electrodes are arranged along at least the bottom surface and the end surfaces of the body, but the outer electrodes may instead be arranged on only the bottom surface of the body. The end surfaces of the conductor in the extension direction of the body may be exposed at the side surfaces of the body. The end portions of the lead-out portions may be exposed at the bottom surface of the body rather than at the end surfaces of the body. A cross section of the conductor in a direction perpendicular to the extension direction of the conductor has been a substantially rectangular shape, but not limited to rectangular shape, the corners of the cross section may be chamfered and each side may form a curve such as a semicircle or a semi-ellipse. The shape of the winding portion of the coil when viewed in the direction of the winding axis may be a shape other than a substantially elliptical shape such as a substantially circular shape, a substantially oval shape, a chamfered substantially polygonal shape, or the like. A recess (standoff) may be formed in the region of the bottom surface of the body where the outer electrodes are not arranged. The recess on the bottom surface of the body may have a semicircular shape in the direction of the height T when viewed in the direction of the width W.

While preferred embodiments of the disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The scope of the disclosure, therefore, is to be determined solely by the following claims.