Patent Publication Number: US-2021183566-A1

Title: Coil component

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-223911, filed on 11 Dec. 2019, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a coil component. 
     BACKGROUND 
     As an example of coil components according to the related art, U.S. Unexamined Patent Publication No. 2016/0086714 (Patent Literature 1) discloses a coil component in which the surface of an element body made of a magnetic powder-containing resin is covered with an insulating layer. With such a coil component, the pressure resistance of the entire component can be improved by the insulating layer increasing the pressure resistance of the surface of the element body. 
     The inventors have repeated research on the pressure resistance of the surface of the element body and have newly found a technique with which the pressure resistance of the entire component can be further increased. 
     SUMMARY 
     An object of the present disclosure is to provide a coil component having an improved pressure resistance. 
     The coil component according to one aspect of the present disclosure includes an element body made of a metal magnetic powder-containing resin, and having a surface part having a resin ratio higher than an internal resin ratio, a coil is provided in the element body, and an insulating layer made of resin, and covering a surface of the element body including the surface part. 
     In the coil component, the pressure resistance is improved by the surface of the element body being covered with the insulating layer. The element body has the surface part, the resin ratio of the surface part is higher than the internal resin ratio, and insulation is enhanced at the surface part. As a result, the pressure resistance on the surface of the element body is further improved and the pressure resistance of the entire coil component is further improved. 
     In the coil component according to another aspect, a plurality of micro depressions are formed in the surface part of the element body. 
     In the coil component according to another aspect, the resin of the insulating layer fills in the plurality of micro depressions. 
     In the coil component according to another aspect, a depth of the micro depression is equal to or less than a maximum particle diameter of the metal magnetic powder constituting the metal magnetic powder-containing resin of the element body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of the coil component according to an embodiment. 
         FIG. 2  is an exploded view of the coil component illustrated in  FIG. 1 . 
         FIG. 3  is a cross-sectional view taken along line III-III of the coil component illustrated in  FIG. 1 . 
         FIG. 4  is a cross-sectional view taken along line IV-IV of the coil component illustrated in  FIG. 1 . 
         FIG. 5  is an enlarged cross-sectional view of a main part illustrating the interface between an element body and an insulating layer. 
         FIG. 6  is a side view illustrating the coil component of another aspect. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function and redundant description is omitted. 
     The structure of the coil component according to the embodiment will be described with reference to  FIGS. 1 to 4 . For convenience of description, XYZ coordinates are set as illustrated in the drawings. In other words, the thickness direction of the coil component is set as the Z direction, the facing direction of external terminal electrodes is set as the X direction, and the direction that is orthogonal to the Z direction and the X direction is set as the Y direction. 
     A coil component  10  is a flat coil element and includes a main body portion  12  (element body) having a rectangular parallelepiped shape and a pair of external terminal electrodes  14 A and  14 B provided on the surface of the main body portion  12 . The main body portion  12  has a pair of end surfaces  12   a  and  12   b  facing each other in the X direction, a pair of main surfaces  12   c  and  12   d  facing each other in the Z direction, and a pair of side surfaces  12   e  and  12   f  facing each other in the Y direction. The pair of external terminal electrodes  14 A and  14 B are provided so as to cover the entire surfaces of the pair of end surfaces  12   a  and  12   b . As an example, the coil component  10  is designed to have a long-side dimension of 2.5 mm, a short-side dimension of 2.0 mm, and a height dimension of 0.8 to 1.0 mm. 
     The main body portion  12  is configured to include an insulating substrate  20 , a coil C provided on the insulating substrate  20 , and a magnetic body  26 . 
     The insulating substrate  20  is a plate-shaped member made of a non-magnetic insulating material and has a substantially elliptical ring shape when viewed from the thickness direction of the insulating substrate  20 . An elliptical through hole  20   c  is provided at the middle part of the insulating substrate  20 . A substrate in which a glass cloth is impregnated with an epoxy-based resin and that has a plate thickness of 10 μm to 60 μm can be used as the insulating substrate  20 . It should be noted that BT resin, polyimide, aramid, and so on can also be used in addition to the epoxy-based resin. Ceramic or glass can also be used as the material of the insulating substrate  20 . A mass-produced printed board material may be the material of the insulating substrate  20 . in particular, a resin material used for a BT, FR4, or FR5 printed board may be the material of the insulating substrate  20 . 
     The coil C has a first coil portion  22 A where a first conductor pattern  23 A for a flat air-core coil provided on one surface  20   a  (upper surface in  FIG. 2 ) of the insulating substrate  20  is insulated and coated, a second coil portion  22 B where a second conductor pattern  23 B for a flat air-core coil provided on the other surface  20   b  (lower surface in  FIG. 2 ) of the insulating substrate  20  is insulated and coated, and a through hole conductor  25  connecting the first conductor pattern  23 A and the second conductor pattern  23 B. 
     The first conductor pattern  23 A (first planar coil pattern) is a planar spiral pattern serving as a flat air-core coil and is plating-formed of a conductor material such as Cu. The first conductor pattern  23 A is formed so as to be wound around the through hole  20   c  of the insulating substrate  20 . More specifically, as illustrated in  FIG. 2 , the first conductor pattern  23 A is wound clockwise, by three turns, and toward the outside when viewed from the upward direction (Z direction). The height of the first conductor pattern  23 A (length in the thickness direction of the insulating substrate  20 ) is the same over the entire length. 
     An outside end portion  23   a  of the first conductor pattern  23 A is exposed on the end surface  12   a  of the main body portion  12  and is connected to the external terminal electrode  14 A covering the end surface  12   a . An inside end portion  23   b  of the first conductor pattern  23 A is connected to the through hole conductor  25 . 
     As in the case of the first conductor pattern  23 A, the second conductor pattern  23 B (second planar coil pattern) is a planar spiral pattern serving as a flat air-core coil and is plating-formed of a conductor material such as Cu. The second conductor pattern  23 B is also formed so as to be wound around the through hole  20   c  of the insulating substrate  20 . More specifically, the second conductor pattern  23 B is wound counterclockwise, by three turns, and toward the outside when viewed from the upward direction (Z direction). In other words, the second conductor pattern  23 B is wound in the direction that is opposite to the winding direction of the first conductor pattern  23 A when viewed from the upward direction. The height of the second conductor pattern  23 B is the same over the entire length and can be designed to be the same as the height of the first conductor pattern  23 A. 
     An outside end portion  23   c  of the second conductor pattern  23 B is exposed on the end surface  12   b  of the main body portion  12  and is connected to the external terminal electrode  14 B covering the end surface  12   b . An inside end portion  23   d  of the second conductor pattern  23 B is aligned with the inside end portion  23   b  of the first conductor pattern  23 A in the thickness direction of the insulating substrate  20  and is connected to the through hole conductor  25 . 
     The through hole conductor  25  is provided through the edge region of the through hole  20   c  of the insulating substrate  20  and connects the end portion  23   b  of the first conductor pattern  23 A and the end portion  23   d  of the second conductor pattern  23 B. The through hole conductor  25  may include a hole provided in the insulating substrate  20  and a conductive material (for example, a metal material such as Cu) with which the hole is filled. The through hole conductor  25  has a substantially cylindrical or substantially prismatic outer shape extending in the thickness direction of the insulating substrate  20 . 
     In addition, as illustrated in  FIGS. 3 and 4 , the first coil portion  22 A and the second coil portion  22 B have resin walls  24 A and  24 B, respectively. The resin wall  24 A of the first coil portion  22 A is positioned between the lines and on the inner circumference and the outer circumference of the first conductor pattern  23 A. Likewise, the resin wall  24 B of the second coil portion  22 B is positioned between the lines and on the inner circumference and the outer circumference of the second conductor pattern  23 B. In the present embodiment, the resin walls  24 A and  24 B that are positioned on the inner and outer circumferences of the conductor patterns  23 A and  23 B are designed to be thicker than the resin walls  24 A and  24 B that are positioned between the lines of the conductor patterns  23 A and  23 B. 
     The resin walls  24 A and  24 B are made of an insulating resin material. The resin walls  24 A and  24 B can be provided on the insulating substrate  20  before the first conductor pattern  23 A and the second conductor pattern  23 B are formed. In this case, the first conductor pattern  23 A and the second conductor pattern  23 B are plated and grown between the walls that are defined in the resin walls  24 A and  24 B. The resin walls  24 A and  24 B can be provided on the insulating substrate  20  after the first conductor pattern  23 A and the second conductor pattern  23 B are formed. In this case, the resin walls  24 A and  24 B are provided on the first conductor pattern  23 A and the second conductor pattern  23 B by filling, coating, or the like. 
     Each of the first coil portion  22 A and the second coil portion  22 B has an insulating layer  27 , which integrally covers the first conductor pattern  23 A and the second conductor pattern  23 B and the resin walls  24 A and  24 B from the upper surface side. The insulating layer  27  may be made of an insulating resin or an insulating magnetic material. 
     The magnetic body  26  integrally covers the insulating substrate  20  and the coil C. More specifically, the magnetic body  26  covers the insulating substrate  20  and the coil C from the upward-downward directions and covers the outer circumference of the insulating substrate  20  and the coil C. In addition, the inner portion of the through hole  20   c  of the insulating substrate  20  and the inside region of the coil C are filled with the magnetic body  26 . The magnetic body  26  constitutes all the surfaces of the main body portion  12 , that is, the end surfaces  12   a  and  12   b , the main surfaces  12   c  and  12   d , and the side surfaces  12   e  and  12   f.    
     The magnetic body  26  is made of a resin containing metal magnetic powder. The metal magnetic powder-containing resin is binder powder in which metal magnetic powder  28  is bound by a binder resin  30 . The metal magnetic powder of the metal magnetic powder-containing resin constituting the magnetic body  26  is configured to include magnetic powder containing at least Fe (for example, iron-nickel alloy (permalloy alloy), carbonyl iron, amorphous, non-crystalline or crystalline FeSiCr-based alloy, and sendust). The binder resin  30  is, for example, a thermosetting epoxy resin. In the present embodiment, the content of the metal magnetic powder in the binder powder is 80 to 92 vol % by volume and 95 to 99 wt % by mass. From the viewpoint of magnetic properties, the content of the metal magnetic powder in the hinder powder may be 85 to 92 vol % by volume and 97 to 99 wt % by mass. The magnetic powder of the metal magnetic powder-containing resin constituting the magnetic body  26  may be powder having one type of average particle diameter or may be mixed powder having a plurality of types of average particle diameters. In a case where the metal magnetic powder of the metal magnetic powder-containing resin constituting the magnetic body  26  is mixed powder, the types and Fe composition ratios of the magnetic powders having different average particle diameters may be the same or different. As an example, in the case of mixed powder having three types of average particle diameters, the particle diameter of the magnetic powder having the maximum average particle diameter (large-diameter powder  28   a ) can be 15 to 30 μm, the particle diameter of the magnetic powder having the minimum average particle diameter (small-diameter powder  28   b ) can be 0.3 to 1.5 μm, and the magnetic powder having an average particle diameter between the large-diameter powder and the small-diameter powder (medium-diameter powder  28   c ) can be 3 to 10 μm. With respect to 100 parts by weight of the mixed powder, the large-diameter powder  28   a  may be contained in the range of 60 to 80 parts by weight, the medium-diameter powder  28   c  may be contained in the range of 10 to 20 parts by weight, and the small-diameter powder  28   b  may be contained in the range of 10 to 20 parts by weight. 
     The average particle diameter of the metal magnetic powder is defined by the particle diameter at an integrated value of 50% in the particle size distribution (d50, so-called median diameter) and is obtained as follows. A scanning electron microscope (SEM) photograph of a cross section of the magnetic body  26  is taken. Image processing is performed on the taken SEM photograph by software, the boundary of the metal magnetic powder is determined, and the area of the metal magnetic powder is calculated. The particle diameter is calculated by the calculated area of the metal magnetic powder being converted into a circle-equivalent diameter. For example, the particle diameter of 100 or more metal magnetic powders is calculated and the particle size distribution of these metal magnetic powders is obtained. The average particle diameter d50 is the particle diameter at an integrated value of 50% in the obtained particle size distribution. The particle shape of the metal magnetic powder is not particularly limited. 
     The magnetic body  26  is capable of containing metal magnetic powder having a particle diameter exceeding the upper limit value of the average particle diameter of the large-diameter powder  28   a  (for example, 30 μm). In the present embodiment, the magnetic body  26  contains metal magnetic powder having a maximum particle diameter of 100 μm. 
     In the coil component  10 , each of the pair of main surfaces  12   c  and  12   d  and the pair of side surfaces  12   e  and  12   f  of the main body portion  12  is entirely covered with an insulating layer  13 . The insulating layer  13  is made of a thermosetting resin. As an example, the insulating layer  13  is made of epoxy resin. The insulating layer  13  can be formed by, for example, the resin material applied on the main surfaces  12   c  and  12   d  and the side surfaces  12   e  and  12   f  being cured (for example, heat-cured). 
     Here, the state of the interface between the element body and the insulating layer will be described with reference to  FIG. 5 . 
     As illustrated in  FIG. 5 , a plurality of micro depressions  32  are formed in the main surface  12   c  of the main body portion  12 . These micro depressions  32  are formed by the metal magnetic powder  28  of the metal magnetic powder-containing resin constituting the magnetic body  26  being desorbed from the binder resin  30 . Accordingly, the maximum depth of the micro depression  32  is equal to or less than the maximum particle diameter of the metal magnetic powder  28  contained in the magnetic body  26  (for example, 100 μm). The desorption of the metal magnetic powder  28  can occur after the main surface  12   c  of the main body portion  12  is polished and etched. The main surface  12   c  of the main body portion  12  has a somewhat large surface roughness (for example, R max =50 μm) due to the plurality of micro depressions  32 . The resin material that constitutes the insulating layer  13  fills in each of the plurality of micro depressions  32 , and the micro depressions  32  are filled with the resin material. 
     It should be noted that the other main surface  12   d  of the main body portion  12  has the same surface state as the main surface  12   c  and the resin material of the insulating layer  13  covering the main surface  12   d  fills in the micro depression  32  formed in the main surface  12   d.    
     Due to the desorption of the metal magnetic powder  28  described above, the magnetic powder ratio of the main surface  12   c  of the main body portion  12  is lower than the magnetic powder ratio of the inner portion of the element body. In other words, the resin ratio of the main surface  12   c  of the main body portion  12  is higher than the resin ratio of the inner portion of the element body. 
     In the coil component  10 , the pressure resistance is improved by the main surfaces  12   c  and  12   d  of the main body portion  12  being covered with the insulating layer  13 . The main body portion  12  has a surface part, the resin ratio of the surface part is higher than the internal resin ratio, and insulation is enhanced at the surface part. As a result, the pressure resistance on the surface of the main body portion  12  is further improved and the pressure resistance of the entire coil component  10  is further improved. 
     In addition, in the coil component  10 , the surface part having the resin ratio higher than the internal resin ratio is formed only on the main surfaces  12   c  and  12   d  extending between the external terminal electrodes  14 A and  14 B and the surface part is covered with the insulating layer  13 . Alternatively, the surface part of the surface of the main body portion  12  where the resin ratio is higher than the internal resin ratio may be at least one of the main surfaces  12   c  and  12   d , may be at least one of the side surfaces  12   e  and  12   f , or may be both the main surfaces  12   c  and  12   d  and the side surfaces  12   e  and  12   f.    
     The insulating layer  13  may cover the main surfaces  12   c  and  12   d  and the side surfaces  12   e  and  12   f  in whole or in part. For example, the surface of the main body portion  12  may be exposed from between the insulating layer  13  and the external terminal electrodes  14 A and  14 B as in a coil component  10 A illustrated in  FIG. 6 . In the coil component  10 A, the insulating layer  13  is provided only in the middle regions of the main surfaces  12   c  and  12   d  and the side surfaces  12   e  and  12   f  without being provided on the end surface  12   a  and  12   b  sides of the main surfaces  12   c  and  12   d  and the side surfaces  12   e  and  12   f.    
     It should be noted that the present disclosure may take various aspects without being limited to the above-described embodiment. For example, the coil C may be provided with both the first coil portion and the second coil portionor may be provided only with the first coil portion.