The present invention relates to a multilayer coil component.
Known multilayer coil components include an element body made of a ferrite sintered body and a coil (for example, see Japanese Unexamined Patent Publication No. 2010-040860). The coil is configured with a plurality of internal conductors that are juxtaposed in the element body and are electrically connected to one another.
For a multilayer coil component, an element body is usually obtained by the following processes. First, green sheets each containing a ferrite material are prepared. Conductor patterns for forming internal conductors are formed on the green sheets. The green sheets in which the conductor patterns are formed and the green sheets in which no conductor patterns are formed are laminated in an intended order. Through these processes, a laminated body of green sheets is obtained. After that, the obtained laminated body of green sheets is cut into a plurality of chips of a predetermined size. The obtained chips are fired to obtain element bodies.
Regarding a multilayer coil component, a residual stress may occur in the element body due to the residual strain in ferrite crystal grains, the stress from the internal conductors, or the like. If a residual stress occurs in the element body, magnetic characteristics of the element body (for example, a magnetic permeability) are deteriorated. In order to relax the residual stress in the element body, a sintered density of the element body may be made small by decreasing a sinterability of the ferrite crystal grains, for example. If the sinterability of the element body (ferrite crystal grains) has been made low, growth of the ferrite crystal grains is suppressed, and an average crystal grain size in the element body is smaller. If the average crystal grain size in the surface region of the element body is small, the ferrite crystal grains are likely to fall off from the element body.
An object of an aspect of the present invention is to provide a multilayer coil component in which ferrite crystal grains are prevented from falling off from an element body even if a sinterability of the element body is made low.
A multilayer coil component according to one aspect of the present invention includes an element body made of a ferrite sintered body and a coil. The coil is configured with a plurality of internal conductors juxtaposed in the element body and electrically connected to one another. An average crystal grain size in a surface region of the element body is smaller than an average crystal grain size in a region between the internal conductors in the element body. A surface of the element body is covered with a layer made of an insulating material. The insulating material is not present among the crystal grains in the surface region of the element body.
In the multilayer coil component according to the one aspect, the surface of the element body is covered with the layer made of an insulating material. Therefore, even if a sinterability of the element body is made low, the ferrite crystal grains are prevented from falling off from the element body.
In the case in which an insulating material is present among crystal grains in the surface region of an element body, a stress acts on the element body from the insulating material, whereby magnetic characteristics of the element body are likely to be deteriorated. In contrast, in the multilayer coil component according to the one aspect, because the insulating material is not present among the crystal grains in the surface region of the element body, a stress from the insulating material is hardly acts on the element body. As a result, in the multilayer coil component according to the one aspect, deterioration of the magnetic characteristics of the element body is suppressed.
In a manufacturing process of a multilayer coil component, in order to increase adhesiveness of the green sheets, a high pressure is generally applied to the laminated body of green sheets in the lamination direction of the green sheets. In the regions between the conductor patterns in the laminated body of green sheets, a higher pressure acts than in the other regions. Therefore, in the above regions between the conductor patterns, the ferrite material is high in density, and sinterability is thus increased. Thus, even if the sinterability of the element body is made low, the sinterability and the sintered density are higher in the regions between the internal conductors in the element body than in the surface region of the element body. That is, the average crystal grain size in the surface region of the element body is smaller than the average crystal grain size in the regions between the internal conductors in the element body.
The average crystal grain size in the surface region of the element body may be 0.5 to 1.5 μm. In which case, the residual stress occurring in the element body is suppressed low.
A porosity on the surface of the element body may be 10 to 30%. In which case, strength of the element body is secured.
The insulating material may be glass. In which case, a thin and uniform layer is obtained.
In the layer made of an insulating material, there may be formed through holes. In which case, the through holes in the layer made of an insulating material absorb stress acting on the layer made of an insulating material. As a result, in this embodiment, damage to the layer made of an insulating material is suppressed.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The embodiment of the present invention will be described below in detail with reference to the accompanying drawings. In the description, identical elements or elements with identical functionality will be denoted by the same reference signs, without redundant description.
A multilayer coil component 1 according to the embodiment will be described with reference to
With reference to
The element body 2 has a rectangular parallelepiped shape. The element body 2 includes a pair of end surfaces 2a and 2b opposing each other, a pair of principal surfaces 2c and 2d opposing each other, and a pair of side surfaces 2e and 2f opposing each other, as surfaces of the element body 2. The principal surfaces 2c and 2d extend to connect the pair of the end surfaces 2a and 2b. The side surfaces 2e and 2f extend to connect the pair of the principal surfaces 2c and 2d.
A direction in which the end surfaces 2a and 2b oppose each other, a direction in which the principal surfaces 2c and 2d oppose each other, and a direction in which the side surfaces 2e and 2f oppose each other are approximately orthogonal to each other. The rectangular parallelepiped shape includes a shape of a rectangular parallelepiped in which a corner portion and a ridge portion are chamfered and a shape of a rectangular parallelepiped in which a corner portion and a ridge portion are rounded. When the multilayer coil component 1 is mounted on an electronic device (not shown, e.g. a circuit board or an electronic component), for example, the principal surface 2c or the principal surface 2d is defined as a surface opposing the electronic device.
The element body 2 includes a plurality of insulator layers 6 (refer to
Each insulator layer 6 includes a sintered body of a green sheet including ferrite material (e.g. Ni—Cu—Zn based ferrite material, Ni—Cu—Zn—Mg based ferrite material, or Ni—Cu based ferrite material). The element body 2 includes a ferrite sintered body.
With reference to
The external electrode 4 is disposed at an end surface 2a side of the element body 2. The external electrode 5 is disposed at an end surface 2b side of the element body 2. The external electrodes 4 and 5 are separated each other in the direction in which the end surfaces 2a and 2b oppose each other. The external electrodes 4 and 5 each have a substantially rectangular shape in a plane view. The external electrodes 4 and 5 have rounded corners. In the embodiment, the insulating layer 3 and each of the external electrodes 4 and 5 are in contact with each other.
The external electrode 4 includes an underlying electrode layer 7, a first plating layer 8, and a second plating layer 9. The underlying electrode layer 7, the first plating layer 8, and the second plating layer 9 are disposed in this order from the element body 2. The underlying electrode layer 7 includes a conductive material. The underlying electrode layer 7 includes a sintered body of a conductive paste including conductive metal powder and glass frit, for example. That is, the underlying electrode layer 7 is a sintered electrode layer. The conductive metal powder is Ag power, for example. The first plating layer 8 is a Ni plating layer, for example. The second plating layer 9 is a Sn plating layer, for example.
The external electrode 4 includes an electrode portion 4a located over the end surface 2a, an electrode portion 4b located over the principal surface 2d, an electrode portion 4c located over the principal surface 2c, an electrode portion 4d located over the side surface 2e, and an electrode portion 4e located over the side surface 2f. The external electrode 4 includes the five electrode portions 4a, 4b, 4c, 4d, and 4e. The electrode portion 4a covers the entire end surface 2a. The electrode portion 4b covers a part of the principal surface 2d. The electrode portion 4c covers a part of the principal surface 2c. The electrode portion 4d covers a part of the side surface 2e. The electrode portion 4e covers a part of the side surface 2f. The five electrode portions 4a, 4b, 4c, 4d, and 4e are integrally formed.
The external electrode 5 includes an underlying electrode layer 10, a first plating layer 11, and a second plating layer 12. The underlying electrode layer 10, the first plating layer 11, and the second plating layer 12 are disposed in this order from the element body 2. The underlying electrode layer 10 includes a conductive material. The underlying electrode layer 10 includes a sintered body of a conductive paste including conductive metal powder and glass frit, for example. That is, the underlying electrode layer 10 is a sintered electrode layer. The conductive metal powder is Ag power, for example. The first plating layer 11 is a Ni plating layer, for example. The second plating layer 12 is a Sn plating layer, for example.
The external electrode 5 includes an electrode portion 5a located over the end surface 2b, an electrode portion 5b located over the principal surface 2d, an electrode portion 5c located over the principal surface 2c, an electrode portion 5d located over the side surface 2e, and an electrode portion 5e located over the side surface 2f. The external electrode 5 includes the five electrode portions 5a, 5b, 5c, 5d, and 5e. The electrode portion 5a covers the entire end surface 2b. The electrode portion 5b covers a part of the principal surface 2d. The electrode portion 5c covers a part of the principal surface 2c. The electrode portion 5d covers a part of the side surface 2e. The electrode portion 5e covers a part of the side surface 2f. The five electrode portions 5a, 5b, 5c, 5d, and 5e are integrally formed.
The multilayer coil component 1 includes a coil 15 disposed in the element body 2. With reference to
The coil conductors 16a to 16f include a conductive material with lower electric resistance than metal (Pd) included in below-described protrusions 20 and 21. In the embodiment, the coil conductors 16a to 16f include Ag as the conductive material. The coil conductors 16a to 16f include sintered bodies of a conductive paste including the conductive material that is made of Ag.
The coil conductor 16a includes a connection conductor 17. The connection conductor 17 is disposed on an end surface 2b side of the element body 2, and electrically connects the coil conductor 16a to the external electrode 5. The coil conductor 16f includes a connection conductor 18. The connection conductor 18 is disposed on an end surface 2a side of the element body 2, and electrically connects the coil conductor 16f to the external electrode 4. The connection conductors 17 and 18 each include Ag and Pd as a conductive material. In the embodiment, the coil conductor 16a and the connection conductor 17 are formed to be integrally connected. The coil conductor 16f and the connection conductor 18 are formed to be integrally connected. In the embodiment, the coil conductor 16a and the connection conductor 17 are formed to be integrally connected, and the coil conductor 16f and the connection conductor 18 are formed to be integrally connected.
The coil conductors 16a to 16f are juxtaposed to one another inside the element body 2 in the lamination direction of the insulator layers 6. The coil conductor 16a, the coil conductor 16b, the coil conductor 16c, the coil conductor 16d, the coil conductor 16e, and the coil conductor 16f are arranged in this order from a side closest to an outermost layer.
The coil conductors 16a to 16f include respective ends that are connected to one another via through-hole conductors 19a to 19e. The coil conductors 16a to 16f are electrically connected to one another by the through-hole conductors 19a to 19e. The coil 15 includes the coil conductors 16a to 16f electrically connected to each other. The through-hole conductors 19a to 19e include Ag as a conductive material. The through-hole conductors 19a to 19e include sintered bodies of a conductive paste including the conductive material.
With reference to
The connection conductor 18 includes the protrusion 21. The protrusion 21 is disposed on an end surface 2a side of the connection conductor 18. The protrusion 21 projects from the end surface 2a of the element body 2 toward the external electrode 4. The protrusion 21 passes through the insulating layer 3 and is connected to the underlying electrode layer 7 of the external electrode 4. The protrusion 21 includes metal (Pd) having a smaller diffusion coefficient than a main component of the material forming the external electrode 4 (the underlying electrode layer 7). In the embodiment, the protrusion 21 includes Ag and Pd. Matal (Pd) included in the protrusions 20 and 21 has higher electric resistance than the coil conductors 16a to 16f.
Next, with reference to
A structure 30 including the element body 2 and the coil 15 as shown in
A conductor pattern for forming the connection conductor 17 is formed of a conductive paste containing Ag and Pd as metal components. A conductor pattern for forming the connection conductor 18 is formed of a conductive paste containing Ag and Pd as metal components. The conductor patterns of the connection conductor 17 and the connection conductor 18 may be formed of a conductive paste containing Ag and Pd as metal components, on the green sheets. The conductor patterns of the connection conductor 17 and the connection conductor 18 may be formed by overlaying a conductive paste containing Ag and Pd as metal components on conductor patterns formed of a conductive paste formed of Ag as a metal component.
The laminated body of green sheets is obtained by laminating, in a predetermined order, the green sheets on which the conductor patterns are formed and the green sheets on which no conductor patterns are formed. The laminated body of green sheets is subjected to a debinding process in the atmosphere and is then fired under a predetermined condition. Through these processes, the structure 30 including the element body 2 and the coil 15 is obtained.
In order to increase adhesiveness of the green sheets, a high pressure is applied to the laminated body of green sheets in the lamination direction of the green sheets. Because a higher pressure acts in the regions between the conductor patterns than in the other regions, the density of ferrite material is high in the regions between the conductor patterns, and the sinterability is thus higher. Therefore, even if the sinterability of the element body 2 is made low, the sinterability and the sintered density are higher in the regions between the coil conductors 16a to 16f in the element body 2 than in the surface region of the element body 2.
As shown in
An average crystal grain size of ferrite can be obtained as described below, for example. A sample (the structure 30) is first broken, and the cross-sectional surface is ground and is further chemically etched. With respect to the etched sample, a SEM (scanning electron microscope) photograph of the surface region of the element body 2 and the regions between the coil conductors 16a to 16f in the element body 2 is taken. The SEM photograph is subjected to image processing by software, so that the boundaries between ferrite crystal grains are determined and the areas of the ferrite crystal grains are calculated. The calculated areas of the ferrite crystal grains are converted into circle-equivalent diameters, thereby obtaining the grain sizes. The average value of the obtained grain sizes of the ferrite crystal grains is the average crystal grain size.
A porosity in the surface of the element body 2 is 10 to 30%. The porosity can be obtained as described below, for example. A SEM photograph of the surface of a sample (the structure 30) is taken. The SEM photograph is subjected to image processing by software, so that the boundaries of voids are determined and a total value of the areas of the voids is calculated. The calculated total value is divided by the imaged area, and the thus obtained value is denoted by percentage and represents the porosity.
Subsequently, as shown in
As shown in
As shown in
Subsequently, as shown in
In detail, as shown in
Subsequently, as shown in
As described above, in the embodiment, the surface of the element body 2 is covered with the insulating layer 3. Therefore, even if the sinterability of the element body 2 is made low, the ferrite crystal grains are prevented from falling off from the element body 2.
In the case in which the glass constituting the insulating layer 3 is present among the crystal grains of ferrite in the surface region of the element body 2, a stress may act from the glass on the element body 2, so that the magnetic characteristics of the element body 2 are likely to be deteriorated. In contrast, in the multilayer coil component 1, because the glass is not present among the crystal grains of ferrite in the surface region of the element body 2, a stress from the glass hardly acts on the element body 2. As a result, in the multilayer coil component 1, deterioration of the magnetic characteristics of the element body 2 is suppressed.
The average crystal grain size in the surface region of the element body 2 is 0.5 to 1.5 μm. Consequently, the residual stress occurring in the element body 2 is suppressed low.
The porosity in the surface of the element body 2 is 10 to 30%. Consequently, the strength of the element body 2 is secured. If the porosity in the surface of the element body 2 is greater than 30%, the strength of the element body 2 is lower, and, for example, if the element body 2 is subjected to impact, an external force is likely to give damage to the element body 2. If the porosity in the surface of the element body 2 is less than 10%, the residual stress occurring in the element body 2 may not be reduced.
When the insulating layer 3 is a layer made of glass, the insulating layer 3 and the underlying electrode layers 7 and 10 can be formed by the same sintering process. In which case, the manufacturing process of the multilayer coil component 1 is simplified. Further, when the insulating material constituting the insulating layer 3 is glass, the insulating layer 3 is formed thin and uniform.
The plurality of through holes 3a are formed in the insulating layer 3. The through holes 3a in the insulating layer 3 absorb the stress acting on the insulating layer 3. As a result, in the multilayer coil component 1, damage to the insulating layer 3 is suppressed.
The various embodiments have been described. However, the present invention is not limited to the embodiments and various changes, modifications, and applications can be made without departing from the gist of the present invention.
In the above embodiment, the insulating layer 3 is not limited to a layer made of glass. The insulating layer 3 may be a layer made of an insulating material other than glass, for example, a resin material such as epoxy resin. Also when the insulating layer 3 is a layer made of an insulating material other than glass, the insulating material constituting the insulating layer 3 is not present among the crystal grains of ferrite in the surface region of the element body 2.
In the embodiment described above, the external electrodes 4 and 5 include the electrode portions 4a, 4b, 4c, 4d, and 4e, and the electrode portions 5a, 5b, 5c, 5d, and 5e, respectively. The configuration of the external electrodes is not limited to this disposition. The external electrode 4 may be formed only on the end surface 2a, and the external electrode 5 may be formed only on the end surface 2b, for example. The external electrode 4 may be formed on the end surface 2a and at least one of the principal surfaces 2c and 2d and the side surfaces 2e and 2f, and the external electrode 5 may be formed on the end surface 2b and at least one of the principal surfaces 2c and 2d and the side surfaces 2e and 2f, for example.
Number | Date | Country | Kind |
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2016-095421 | May 2016 | JP | national |