Patent Publication Number: US-2019198225-A1

Title: Inductor component

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority to Japanese Patent Application No. 2017-245301, filed Dec. 21, 2017, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to an inductor component. 
     Background Art 
     Hitherto, electronic components are mounted in various electronic devices. One of the electronic components is a multilayer inductor component as described, for example, in Japanese Patent No. 5821535. A multilayer inductor component includes an element body including laminated multiple insulating layers and coil conductor layers winding on the main surfaces of the insulating layers. 
     SUMMARY 
     In the production of the above-described inductor component, internal defects such as delamination, cracking and so on between the insulating layer and the coil conductor layer may occur. This may result in a low yield rate. 
     Accordingly, the present disclosure provides and inductor component to reduce internal defects. 
     An inductor component according to a one aspect of the present disclosure includes an element body including a plurality of insulating layers laminated on one another, and a coil conductor layer winding on a main surface of one of the plurality of insulating layers. The coil conductor layer contains sulfur. This configuration reduces internal defects. 
     In the inductor component, preferably, the coil conductor layer contains sulfur in an amount of not greater than about 1 atm %. This configuration is less likely to adversely affect the properties, strength, and reliability of the inductor component. 
     Preferably, the inductor component further includes an outer electrode electrically connected to the coil conductor layer and exposed from the element body. Preferably, the outer electrode is not exposed from at least one of surfaces of the element body located at opposite ends in a lamination direction of the plurality of insulating layers. This configuration improves the Q value of the inductor component. 
     The inductor component, preferably, further includes another coil conductor layer winding on a main surface of another of the plurality of insulating layers. Preferably, the coil conductor layers are electrically connected in series and form a helical coil extending in the lamination direction of the plurality of insulating layers. With this configuration, a multilayer inductor component having a smaller size is obtained. 
     In the inductor component, preferably, the number of turns of the coil conductor layer on the main surface is less than one. This configuration allows the inner diameter of the coil conductor layer to be large, contributing to improvement in the inductance acquisition efficiency relative to the length of the coil conductor layer. 
     In the inductor component, preferably, the outer electrode includes an external conductor layer embedded in the element body. Preferably, the external conductor layer is exposed only from surfaces of the element body located at ends in a direction perpendicular to the lamination direction. 
     In this configuration, the magnetic flux passing through the radially inner side of the coil conductor layer is unlikely to be blocked by the external conductor layer. Furthermore, when the inductor component is mounted on the circuit board, the magnetic flux is substantially parallel to the main surface of the circuit board and is unlikely to be blocked by the circuit wiring on the circuit board. Thus, the Q value of the inductor component is improved. 
     In the inductor component, preferably, the element body has a substantially cuboidal shape, and the external conductor layer is exposed only from two of the surfaces of the element body located at ends in the direction perpendicular to the lamination direction. This configuration reduces the possibility that the magnetic flux passing through the outer side of the coil conductor layer is blocked by the external conductor layer. Thus, the Q value of the inductor component is improved. 
     According to one aspect of the present disclosure, internal defects are reduced. 
     Other features, elements, characteristics and advantages of the present disclosure will become more apparent from the following detailed description with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view illustrating an external appearance of an inductor component; 
         FIG. 2  is a schematic plan view illustrating a configuration of the inductor component; 
         FIG. 3  is a schematic front view illustrating a configuration of the inductor component; 
         FIG. 4  is a schematic view illustrating a photograph of a cross-section of the coil conductor layer; 
         FIG. 5  is a diagram indicating heat-treatment temperatures and volume changes; and 
         FIGS. 6A and 6B  are photographs of a cross-section of a coil conductor layer. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, one aspect of this disclosure is described as an embodiment. 
     In the attached drawings, some of the components are illustrated in magnified scale for ease of understanding. The dimension ratio of the components may be different from the actual dimensions or may differ from one figure to another. 
     As illustrated in  FIG. 1 , an inductor component  1  includes an element body  10 . The element body  10  has a substantially cuboidal shape. Herein, the “cuboidal shape” includes a cuboidal shape having chamfered corners or chamfered edges and a cuboidal shape having rounded corners or rounded edge. In addition, the “cuboidal shape” may have a corrugated section, for example, over an entire or a portion of a main surface or a side surface. Opposing surfaces of the “cuboidal shape” may be imperfectly parallel to each other and may be slightly tilted with respect to each other. 
     The element body  10  has a mounting surface  11 . The mounting surface  11  faces a circuit board when the inductor component  1  is mounted on the circuit board. The element body  10  has an upper surface  12  extending parallel to the mounting surface  11 . The element body  10  further has two pairs of surfaces perpendicular to the mounting surface  11 . One of the pairs includes a first side surface  13  and a second side surface  14 . The other of the pairs includes a first end surface  15  and a second end surface  16 . 
     Herein, a direction perpendicular to the upper surface  12  and the mounting surface  11  is referred to as a “height direction”, a direction perpendicular to the first side surface  13  and the second side surface  14  is referred to as a “width direction”, and a direction perpendicular to the first end surface  15  and the second end surface  16  is referred to as a “length direction”. In  FIG. 1 , a “length direction L”, a “height direction T”, and a “width direction W” are indicated as specific examples. The dimension in the “width direction” is a “width”, a dimension in the “height direction” is a “height”, and a dimension in the “length direction” is a “length”. 
     The element body  10  preferably has a size in the length direction L (length L 1 ) of larger than 0 mm and not greater than about 1.0 mm (i.e., from larger than 0 mm to about 1.0 mm). For example, the length L 1  is about 0.6 mm. The element body  10  preferably has a size in the width direction W (width W 1 ) of larger than 0 mm and not greater than about 0.6 mm (i.e., from larger than 0 mm to about 0.6 mm). The width W 1  is more preferably not greater than about 0.36 mm, and still more preferably not greater than about 0.33 mm. For example, the width W 1  of the element body  10  is about 0.3 mm. The element body  10  preferably has a size in the height direction T (height T 1 ) of larger than 0 mm and not greater than about 0.8 mm (i.e., from larger than 0 mm to about 0.8 mm). For example, the height T 1  of the element body  10  is about 0.4 mm. In this embodiment, the height T 1  of the element body  10  is larger than the width W 1  (T 1 &gt;W 1 ). 
     As illustrated in  FIG. 2  and  FIG. 3 , the inductor component  1  includes a first outer electrode  20 , a second outer electrode  30 , and a coil  40 . In  FIG. 2  and  FIG. 3 , the coil  40  and external conductor layers  21  and  31  of the first and second outer electrodes  20  and  30 , which are described later, are indicated by solid lines and the other components such as the element body  10  are indicated by two-dot chain lines for easy recognition of the coil  40  and the external conductor layers  21  and  31 . 
     The first outer electrode  20  is exposed from the mounting surface  11  of the element body  10 . The first outer electrode  20  is also exposed from the first end surface  15  of the element body  10 . 
     In the same way, the second outer electrode  30  is exposed from the mounting surface  11  of the element body  10 . The second outer electrode  30  is also exposed from the second end surface  16  of the element body  10 . 
     In short, the first and second outer electrodes  20  and  30  are exposed from the mounting surface  11  of the element body  10 . In other words, the surface of the element body  10  through which the first and second outer electrodes  20  and  30  are exposed is the mounting surface  11 . 
     In this embodiment, the first outer electrode  20  includes an external conductor layer  21  and a cover layer  22 . The external conductor layer  21  is embedded in the element body  10 . The external conductor layer  21  has an L-like shape when viewed in the width direction W. The external conductor layer  21  includes an end surface electrode  23   a  exposed from the first end surface  15  of the element body  10  and a lower surface electrode  23   b  exposed from the mounting surface  11  of the element body  10 . The end surface electrode  23   a  and the lower surface electrode  23   b  are integral along a ridge line of the first end surface  15  and the mounting surface  11 . The cover layer  22  covers the external conductor layer  21  exposed from the first end surface  15  and the mounting surface  11  of the element body  10 . Thus, the first outer electrode  20  is exposed only from the surfaces of the element body  10  located at ends in a direction perpendicular to the width direction W. Specifically described, the first outer electrode  20  is exposed only from the mounting surface  11  and the first end surface  15 , i.e. two surfaces. 
     In this embodiment, the second outer electrode  30  includes an external conductor layer  31  and a cover layer  32 . The external conductor layer  31  is embedded in the element body  10 . The external conductor layer  31  has an L-like shape when viewed in the width direction W. The external conductor layer  31  includes an end surface electrode  33   a  exposed from the second end surface  16  of the element body  10  and a lower surface electrode  33   b  exposed from the mounting surface  11  of the element body  10 . The end surface electrode  33   a  and the lower surface electrode  33   b  are integral along a ridge line of the second end surface  16  and the mounting surface  11 . The cover layer  32  covers the external conductor layers  31  exposed from the second end surface  16  and the mounting surface  11  of the element body  10 . Thus, the second outer electrode  30  is exposed only from the surfaces of the element body  10  located at the ends in the direction perpendicular to the width direction W. Specifically described, the second outer electrode  30  is exposed only from the mounting surface  11  and the second end surface  16 , i.e., two surfaces. 
     In the above-described configuration, since the external conductor layers  21  and  31  are exposed only from the surfaces of the element body  10  located at the ends in the direction perpendicular to the width direction W, the magnetic flux passing through the inner hole of the coil conductor layer  41  is unlikely to be blocked by the external conductor layers  21  and  31 . Furthermore, in the inductor component  1  mounted on a circuit board, the magnetic flux is parallel to the main surface of the circuit board and is unlikely to be blocked by the circuit wiring on the circuit board. Thus, the Q value of the inductor component  1  is improved. 
     In particular, the external conductor layers  21  and  31  are exposed only from the two surfaces of the element body  10  (the first end surface  15  and the mounting surface  11 , the second end surface  16  and the mounting surface  11 ) located at the ends in the direction perpendicular to the width direction W. This reduces the possibility that the magnetic flux passing through the outer side of the coil conductor layer  41  is blocked by the external conductor layers  21  and  31 . Thus, the Q value of the inductor component  1  is improved. 
     The cover layers  22  and  32  may be formed of a material having high solder resistance and high solder wettability. Examples of the material include metals such as nickel (Ni), copper (Cu), tin (Sn), and gold (Au) and alloys containing such metals. The cover layer may be composed of multiple layers. For example, the cover layer may include a nickel plate and a tin plate covering a surface of the nickel plate. The cover layers  22  and  32  may be eliminated. In such a case, the external conductor layer  21  is the first outer electrode  20 , and the external conductor layer  31  is the second outer electrode  30 . 
     The first outer electrode  20  on the first end surface  15  extends from the mounting surface  11  of the element body  10  to a substantially half of the height T 1  of the element body  10 . The first outer electrode  20  is positioned at substantially the center of the element body  10  in the width direction W. In this embodiment, the size (width) of the first outer electrode  20  in the width direction W is smaller than the width W 1  of the element body  10 . In other words, the first outer electrode  20  is not exposed from the first and second side surfaces  13  and  14  of the element body  10 , which are located at opposite ends in the width direction W. The width of the first outer electrode  20  may be changed as necessary. For example, the first outer electrode  20  may extend over the entire width of the element body  10  in the width direction W. Alternatively, the first outer electrode  20  may be exposed from the mounting surface  11  but not through the first end surface  15  or vice versa. 
     The second outer electrode  30  on the second end surface  16  extends from the mounting surface  11  of the element body  10  to a substantially half of the height T 1  of the element body  10 . The second outer electrode  30  is positioned at substantially the center of the element body  10  in the width direction W. In this embodiment, the size (width) of the second outer electrode  30  in the width direction W is smaller than the width W 1  of the element body  10 . In other words, the second outer electrode  30  is not exposed from the first and second side surfaces  13  and  14  of the element body  10 , which are located at opposite ends in the width direction W. The width of the second outer electrode  30  may be changed as necessary. For example, the second outer electrode  30  may extend over the entire width of the element body  10  in the width direction W. Alternatively, the second outer electrode  30  may be exposed from the mounting surface  11  but not through the second end surface  16  or vice versa. 
     As illustrated in  FIG. 2 , the element body  10  includes laminated multiple insulating layers  51 . A boundary between the insulating layers  51  is not clear in some cases. 
     The insulating layers  51  each have an oblong planar shape. The element body  10  has a substantially cuboidal shape defined by the insulating layers  51  laminated on one another. The insulating layer  51  is a sintered body formed of a magnetic material such as ferrite or a non-magnetic material, such as glass and alumina, for example. The insulating layer  51  is not limited to the sintered body and may be formed of an insulating material that is not melt at a low temperature. Insulating layers  51   a  and  51   b  of the insulating layers  51 , which constitute the first and second side surfaces  13  and  14 , have a color different from that of the other insulating layers  51  located between the insulating layers  51   a  and  51   b.    
     As illustrated in  FIG. 2  and  FIG. 3 , the coil  40  is embedded in the element body  10 . The coil  40  is connected to the first outer electrode  20  at the first end and connected to the second outer electrode  30  at the second end. The coil  40  includes coil conductor layers  41  winding on the main surfaces of the insulating layers  51  and via conductor layers  42  connecting the coil conductor layers  41  to each other. 
     The number of turns of each of the coil conductor layers  41  on the main surface of the insulating layer  51  is less than one. The coil conductor layers  41  each extend in substantially circle while partly overlapping each other when viewed in the width direction W (a direction perpendicular to the first side surface  13  and the second side surface  14  in  FIG. 1  and a lamination direction of the insulating layers  51  in which the insulating layers  51  are laminated). Furthermore, since the coil conductor layers  41  adjacent to each other in the width direction W are connected to each other at the end portions via the via conductor layers  42 , the coil conductor layers  41  are electrically connected in series. This forms the helical coil  40  extending in the width direction W. The coil  40  has a substantially circular shape when viewed in the width direction W. The phrase “overlap each other” includes slightly away from each other due to production variation, for example. The shape of the coil  40  is not limited to the above-described shape. The coil  40  may extend in other shapes, such as an ellipse, a rectangle, other polygonal shapes, and combinations of the above-described shapes, when viewed in the width direction W. 
     The outermost coil conductor layers  41  in the width direction each have an extension extending from the circle and connected to the outer electrode  20  or  30  (the external conductor layers  21  or  31 ). Thus, the outer electrodes  20  and  30  are electrically connected to the coil conductor layers  41 . As described later, the outermost coil conductor layers  41  in the width direction W and the external conductor layers  21  and  31  connected to the outermost coil conductor layers  41  are integrally formed as an integral component. 
     The coil  40  (the coil conductor layers  41  and the via conductor layers  42 ) may be formed of a conducting material containing silver (Ag) as a main component and sulfur (S), for example. For example, the material of the coil  40  may contain silver (Ag), sulfur (S), silicon (Si), and zirconium (Zr). The content of sulfur is preferably not greater than about 1 atm %, for example. The contents of Ag, S, Si, and Zr are, respectively, about 97.5, about 0.5, about 1.3, and about 0.7 (atm %), for example. The coil  40  may be formed of metal having relatively small electrical resistance, such as copper and gold, or a conducting material containing an alloy of such metals as a main component, for example. Any metal material that undergoes necking at a lower temperature than the material of the insulating layers  51  may be employed. 
     (Production Method) 
     Next, a method of producing the inductor component  1  is briefly described. 
     First, a mother insulator layer is formed. The mother insulator layer includes portions to be the element bodies  10  in continuous rows and columns. Specifically described, an insulating paste containing borosilicate glass as a main component is applied onto a polyethylene terephthalate (PET) film by screen printing to form an insulating sheet (a green sheet). A plurality of such sheets is prepared. 
     Then, through holes are formed in the insulating sheet by laser, for example, at portions where the external conductor layers  21  and  31  and the via conductor layers  42  are to be formed. A conductive paste including a conductive material used in the coil  40  is applied by screen printing into the through holes and onto portions of the main surfaces of the insulating sheets where the external conductor layers  21  and  31 , the coil conductor layers  41 , and the via conductor layers  42  are to be formed. A predetermined number of the insulating sheets having the conductive paste thereon and a predetermined number of insulating sheets not having the conductive paste thereon are laminated on one another and fixed by application of pressure to form the mother insulator layer. 
     Then, the mother insulator layer is cut with a dicing machine or a guillotine cutter, for example, into pieces of insulator layers to be the element bodies  10 . The pieces of the insulator layers are fired in a furnace, for example, to form the element bodies  10  having the external conductor layers  21  and  31 , the coil conductor layers  41 , and the via conductor layers  42  therein. The pieces of the insulator layers have a larger size than the element bodies  10 , since the insulator layers may be shrink when fired. 
     Then, the corners of the element body  10  are chamfered by barrel finishing. In this process, nickel, copper, and tin are applied in this order by barrel plating onto the surfaces of the external conductor layers  21  and  31  to form the cover layers  22  and  32 . Thus, the outer electrodes  20  and  30  are formed, and the inductor component  1  is obtained. 
     (Operations) 
     The inductor component  1  includes the element body  10  including the insulating layers  51  laminated on one another and the coil conductor layers  41  winding on the main surfaces of the insulating layers  51 . The coil conductor layer  41  contains sulfur. Hereinafter, the operations of this configuration are described. 
       FIG. 6A  illustrates the cross-section of the coil conductor layer  41  including sulfur.  FIG. 6B  is a result of mapping of sulfur obtained through analysis of the components of the conductor layer  41  (WDX analysis). 
     In the firing of the inductor component  1 , the insulating pastes to be the insulating layers  51  and the conductive pastes to be the coil conductor layers  41  are different in the volume change. Thus, the insulator layers to be the element body  10  is internally stressed a lot during firing. The internal stress may cause an internal defect such as delamination and cracking in the element body  10  that has been fired. To solve the problem, the inventor of this application has conceived an idea of using the coil conductor layer  41  containing sulfur. 
       FIG. 5  indicates volume changes of a conductive paste containing sulfur and a conductive paste not containing sulfur with the progress of firing. In  FIG. 5 , a broken line PL 1  indicates a volume change of an insulating paste. A solid line PL 2  indicates a volume change of a conductive paste containing sulfur. A solid line PL 3  indicates a volume change of a conductive paste not containing sulfur. 
     As indicated in  FIG. 5 , around a temperature Tm 1  where the firing has progressed to some degrees, the volume change PL 3  of the conductive paste not containing sulfur is distant from the volume change PL 1  of the insulating paste. In contrast, the volume change PL 2  of the conductive paste containing sulfur is not distant from the volume change PL 1  of the insulating paste. In particular, around the temperature Tm 2  where the firing has progressed more, the volume change PL 3  of the conductive paste not containing sulfur is still distant from the volume change PL 1  of the insulating paste, but the volume change PL 2  of the conductive paste containing sulfur is substantially equal to the volume change of the insulating paste. 
     Next, it was determined as below if the gap between the volume change PL 1  of the insulating paste and the volume change PL 2  or PL 3  of the conductive paste during firing causes the internal defect, such as delamination and cracking. 
     First, thirty samples of the inductor components  1  including the coil conductor layers  41  containing sulfur and thirty samples of the inductor components including the coil conductor layers not containing sulfur were prepared. The number of internal defects in the samples was checked. In the defect checking, the cross-section of the sample was polished and observed by using an SEM to determine whether the cross-section has a void (internal defect). If the cross-section has a void, the size of the void was determined. In this defect checking, a scratch (polishing flaw) made in the polishing may be an obstacle in the checking of the internal defects. Thus, voids having a size of about 10 μm or more are determined as the internal defects to eliminate the polishing flaw. 
     In the samples including the coil conductor layers not containing sulfur, the occurrence of the internal defect was 100%. In other words, every sample had the internal defect. The maximum size of the observed void (internal defect) was about 29.0 μm. In contrast, in the samples including the coil conductor layers  41  containing sulfur, the occurrence of the internal defect was 0%. In other words, every sample did not have the internal defect. The sizes of the observed voids were not greater than about 5 μm. The results show that the internal defects are reduced in the inductor component  1  including the coil conductor layers  41  containing sulfur. 
     As described above, the inventors of the present application found that the employment of the coil conductor layer  41  containing sulfur does not allow the volume change of the conductive paste during firing to be distant from the volume change of the insulating paste, leading to less internal defects in the inductor component. 
     The content of sulfur in the coil conductor layer  41  is preferably not greater than about 1 atm %.  FIG. 4  is a schematic view illustrating a photograph of the cross-section of the coil conductor layer  41  having the sulfur content of larger than about 1 atm %. As indicated in  FIG. 4 , when the content of sulfur (S) is too high, the coil conductor layer  41  has many voids  34  and is not dense. In this case, although the internal defects possibly caused between the insulating layers  51  and the coil conductor layers  41  are reduced, the voids  34  may adversely affect the properties, strength, and reliability of the inductor component  1 . 
     As described above, the employment of the coil conductor layer  41  containing sulfur reduces the internal stress in the element body  10 . This allows the coil conductor layer  41  to have a larger size. For example, in this embodiment, the thickness of the coil conductor layer  41  is able to be made larger in the width direction W (the lamination direction of the insulating layers  51 ). In such a case, the cross-sectional area of the coil conductor layer  41  is made large while the inner diameter of the coil conductor layer  41  being fixed. Thus, the Q value of the inductor component  1  is increased. 
     Furthermore, in this embodiment, the outer electrodes  20  and  30  are not disposed on the first and second side surfaces  13  and  14  of the element body  10 , which are located at opposite ends in the width direction W. In this case, the land size of the inductor component  1  on the circuit board does not exceed the width W 1  of the inductor component  1 . Specifically described, this allows the width W 1  to increase to the edge of the space of the circuit board for the inductor component  1 , or this allows the thickness of the coil conductor layer  41  to increase in the width direction W. Thus, the cross-sectional area of the coil conductor layer  41  is made large while the inner diameter of the coil conductor layer  41  being fixed. Thus, the Q value of the inductor component  1  is increased. 
     As described above, according to the embodiment, the advantages below can be achieved. 
     (1) The inductor component  1  includes the element body  10  including the insulating layers  51  laminated on one another and the coil conductor layers  41  winding on the main surfaces of the insulating layers  51 . The coil conductor layers  41  contain sulfur. This configuration reduces internal defects. 
     (2) The coil conductor layers  41  containing sulfur improve the Q value of the inductor component  1 . 
     (3) The inductor component  1  further includes the outer electrodes  20  and  30  electrically connected to the coil conductor layers  41  and exposed from the element body  10 . The outer electrodes  20  and  30  are not exposed from at least one of the surfaces (the first and second side surfaces  13  and  14 ) of the element body  10  located at opposite ends in the lamination direction (the width direction W) of the insulating layers  51 . This configuration improves the Q value of the inductor component  1 . 
     (4) the coil conductor layers  41  contain sulfur in an amount of not greater than about 1 atm %. This configuration suppresses the decrease in sinterability and is less likely to adversely affect the properties, strength, and reliability of the inductor component  1 . 
     The embodiment may be modified as below. The attached drawings merely illustrate one example of the inductor component  1  according to the embodiment. The shape, the number of layers, and other configurations may be modified as necessary. 
     In the inductor component  1 , the outer electrodes  20  and  30  include the external conductor layers  21  and  31  embedded in the element body  10 . However, the outer electrodes  20  and  30  may have a different configuration. For example, the extension of the coil conductor layer  41  may be exposed from the first and second end surfaces  15  and  16 . A conductive paste may be applied to the entire of the first and second end surface  15  and  16  including the exposed portions by a dipping method. Then, the element body  10  may be baked to form baked electrodes. The baked electrodes may be formed not only on the first and second end surface  15  and  16  but also on the mounting surface  11 , the upper surface  12 , the first side surface  13 , and the second side surface  14  to provide a “five-surface electrode structure”. 
     As an example of a method of producing the inductor component  1 , a sheet lamination method is described. However, the inductor component  1  may be produced by a different method. For example, a print lamination method and other known method may be employed. The contents of the disclosure are essentially applicable to any inductor components including fired coil conductor layers and are not restricted by the production method. 
     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.