Patent Grant
12094642
One aspect of the present disclosure relates to a multilayer inductor component.
Japanese Unexamined Patent Publication No. H04-280616 discloses a multilayer ceramic capacitor including a bare chip, terminal electrodes baked on both ends of the bare chip, and plating layers formed on surfaces of the terminal electrodes. In this multilayer ceramic capacitor, excess inorganic binder that has appeared on the surface of the terminal electrode after firing is removed by polishing to improve the adhesion of the plating layer to the terminal electrode.
Since an inductor generates heat more easily than other electronic components such as a capacitor, solder used for mounting the inductor is required to have heat resistance. A high-strength solder having excellent heat resistance is harder than a normal solder and is inferior in shock absorption. Therefore, the plating layer is easily peeled off after mounting when the high-strength solder is used for mounting the inductor.
An object of one aspect of the present disclosure is to provide a multilayer inductor component in which the adhesion of a plating layer is further improved.
A multilayer inductor component according to an aspect of the present disclosure includes an element body, an internal conductor, and an external electrode. The internal conductor is disposed in the element body. The external electrode is disposed on a surface of the element body and electrically connected to the internal conductor. The external electrode includes a sintered metal layer and a plating layer. The sintered metal layer is disposed on the surface of the element body. The plating layer covers the sintered metal layer. The sintered metal layer includes a thick portion and thin portions. The thick portion covers the surface of the element body. A plurality of glass particles is dispersed in the thick portion. The thin portions cover glass particles exposed on a surface of the thick portion among the plurality of glass particles and being in contact with the plating layer.
In the multilayer inductor component, the sintered metal layer further includes the thin portions in addition to the thick portion. The thin portions cover the glass particles exposed on the surface of the thick portion. The thin portions are in contact with the plating layer. Due to the thin portions, the plating layer is also formed in close contact with the glass particles exposed on the surface of the thick portion. Therefore, the adhesion of the plating layer to the sintered metal layer is further improved.
The thickness of each of the thin portions may be less than the thickness of the plating layer. In this case, unevenness of the surface of the sintered metal layer can be reduced. As a result, the current distribution in the electroplating step becomes uniform. Therefore, the plating layer can be uniformly formed.
The thickness of the thin portions may be 1.0 μm or less. In this case, the unevenness of the surface of the sintered metal layer can be further reduced. As a result, the current distribution in the electroplating step becomes more uniform. Therefore, the plating layer can be formed more uniformly.
The element body may include an end surface, a side surface, and a ridge portion. The side surface may be disposed adjacent to the end surface. The ridge portion may be disposed between the end surface and the side surface. The external electrode may be disposed over the end surface, the side surface, and the ridge portion. A coverage of the thin portions covering the glass particles exposed on the surface of the thick portion is greater at the ridge portion than at the end surface. In this case, the adhesion of the plating layer at the ridge portion is further improved.
The thin portions and the thick portion may include the same metal. In this case, the deposition property of the plating layer becomes more uniform.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same elements or elements having the same functions are denoted with the same reference numerals and overlapped explanation is omitted.
A configuration of a multilayer inductor component 1 according to a present embodiment will be described with reference to
As shown in
The element body 2 has a rectangular parallelepiped shape. The element body 2 has, as its surfaces, a pair of end surfaces 2a and 2b and four side surfaces 2c, 2d, 2e, and 2f. The end surfaces 2a and 2b are opposed to each other. The side surfaces 2c and 2d are opposed to each other. The side surfaces 2e and 2f are opposed to each other. The end surfaces 2a and 2b are adjacent to the four side surfaces 2c, 2d, 2e, and 2f, respectively. The side surface 2c or the side surface 2d constitutes a mounting surface. The mounting surface is defined as a surface opposed to another electronic device (not shown) when the multilayer inductor component 1 is mounted on the other electronic device (for example, the circuit substrate or an electronic component).
In the present embodiment, the direction in which the pair of end surfaces 2a and 2b opposed to each other (the first direction D1) is the length direction of the element body 2. The direction in which the pair of side surfaces 2c and 2d opposed to each other (second direction D2) is the height direction of the element body 2. The direction in which the pair of side surfaces 2e and 2f opposed to each other (third direction D3) is the width direction of the element body 2. The first direction D1, the second direction D2, and the third direction D3 are orthogonal to each other.
The length of the element body 2 in the first direction D1 is longer than the length of the element body 2 in the second direction D2 and the length of the element body 2 in the third direction D3. The length of the element body 2 in the second direction D2 is equal to the length of the element body 2 in the third direction D3. That is, in the present embodiment, the end surfaces 2a and 2b have square shapes, and the four side surfaces 2c, 2d, 2e, and 2f have rectangular shapes. The length of the element body 2 in the first direction D1 may be equal to the length of the element body 2 in the second direction D2 and the length of the element body 2 in the third direction D3. The length of the element body 2 in the second direction D2 and the length of the element body 2 in the third direction D3 may be different from each other.
In addition to equality, values including a slight difference within a preset range, a manufacturing error, or the like may be “equal”. For example, when a plurality of values is included in a range of ±5% of an average value of the plurality of values, the plurality of values is defined to be equal.
The end surfaces 2a and 2b extend in the second direction D2 in such a way to connect the pair of side surfaces 2c and 2d. That is, the end surfaces 2a and 2b extend in a direction intersecting the side surfaces 2c and 2d. The end surfaces 2a and 2b also extend in the third direction D3. The pair of side surfaces 2c and 2d extend in the first direction D1 in such a way to connect the pair of end surfaces 2a and 2b. The pair of side surfaces 2c and 2d also extend in the third direction D3. The pair of side surfaces 2e and 2f extend in the second direction D2 in such a way to connect the pair of side surfaces 2c and 2d. The pair of side surfaces 2e and 2f also extend in the first direction D1.
The element body 2 includes 12 ridge portions 2g disposed between two adjacent surfaces among the pair of end surfaces 2a and 2b and the four side surfaces 2c, 2d, 2e, and 2f. The 12 ridge portions 2g include a ridge portion 2g disposed between the side surface 2c and the side surface 2e, a ridge portion 2g disposed between the side surface 2e and the side surface 2d, a ridge portion 2g disposed between the side surface 2d and the side surface 2f, a ridge portion 2g disposed between the side surface 2f and the side surface 2c, a ridge portion 2g disposed between the end surface 2a and the side surface 2c, a ridge portion 2g disposed between the end surface 2a and the side surface 2d, a ridge portion 2g disposed between the end surface 2a and the side surface 2e, a ridge portion 2g disposed between the end surface 2a and the side surface 2f, a ridge portion 2g disposed between the end surface 2b and the side surface 2c, a ridge portion 2g disposed between the end surface 2b and the side surface 2d, a ridge portion 2g disposed between the end surface 2b and the side surface 2e, and a ridge portion 2g disposed between the end surface 2b and the side surface 2f.
The element body 2 is formed by stacking a plurality of insulator layers 6 (see
Each insulator layer 6 is formed of a sintered body of a ceramic green sheet containing a ferrite material (for example, a Ni—Cu—Zn-based ferrite material, a Ni—Cu—Zn—Mg-based ferrite material, or a Ni—Cu-based ferrite material). That is, the element body 2 is made of a ferrite sintered body.
The multilayer inductor component 1 further includes, as internal conductors disposed inside the element body 2, a plurality of coil conductors 16a, 16b, 16c, 16d, 16e, and 16f, a pair of connection conductors 17,18 and, and a plurality of through-hole conductors 19a, 19b, 19c, 19d, and 19e. The coil conductors 16a to 16f constitute the coil 15 inside the element body 2. The coil conductors 16a to 16f include a conductive material (for example, Ag or Pd). The coil conductors 16a to 16f are formed as sintered bodies of a conductive paste containing a conductive material (for example, Ag powder or Pd powder).
The connection conductor 17 is connected to the coil conductor 16a. The connection conductor 17 is disposed on the end surface 2b side of the element body 2. The connection conductor 17 has an end portion 17a exposed on the end surface 2b. The end portion 17a is exposed at a position closer to the side surface 2c than the center portion of the end surface 2b when viewed from the direction orthogonal to the end surface 2b. The end portion 17a is connected to the external electrode 5. That is, the coil conductor 16a is electrically connected to the external electrode 5 through the connection conductor 17. In the present embodiment, the conductor pattern of the coil conductor 16a and the conductor pattern of the connection conductor 17 are formed integrally and continuously.
The connection conductor 18 is connected to the coil conductor 16f. The connection conductor 18 is disposed on the end surface 2a side of the element body 2. The connection conductor 18 has an end portion 18a exposed on the end surface 2a. The end portion 18a is exposed at a position closer to the side surface 2d than the center portion of the end surface 2a when viewed from the direction orthogonal to the end surface 2a. The end portion 18a is connected to the external electrode 4. That is, the coil conductor 16f is electrically connected to the external electrode 4 through the connection conductor 18. In the present embodiment, the conductor pattern of the coil conductor 16f and the conductor pattern of the connection conductor 18 are formed integrally and continuously.
The coil conductors 16a to 16f are arranged side by side in the lamination direction of the insulator layers 6 in the element body 2. The coil conductors 16a to 16f are arranged in the order of 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 from the side closer to the side surface 2c.
The through-hole conductors 19a to 19e connect ends of the coil conductors 16a to 16f to each other. The coil conductors 16a to 16f are electrically connected to each other by through-hole conductors 19a to 19e. The coil 15 is configured by electrically connecting a plurality of coil conductors 16a to 16f. Each of the through-hole conductors 19a to 19e contains a conductive material (for example, Ag or Pd). Like the coil conductors 16a to 16f, each of the through-hole conductors 19a to 19e is configured as a sintered body of a conductive paste containing a conductive material (for example, Ag powder or Pd powder).
The through-hole conductors 19a to 19e are arranged side by side in the stacking direction of the insulator layers 6 in the element body 2. The plurality of through-hole conductors 19a to 19e are arranged in the order of the through-hole conductor 19a, the through-hole conductor 19b, the through-hole conductor 19c, the through-hole conductor 19d, and the through-hole conductor 19e from the side closer to the side surface 2c.
The external electrode 4 is located at an end portion on the end surface 2a side of the element body 2 when viewed from the first direction D1. The external electrode 4 includes an electrode portion 4a located on the end surface 2a, electrode portions 4b located on the side surfaces 2c and 2d, and electrode portions 4c located on the side surfaces 2e and 2f. That is, the external electrode 4 is formed on the five surfaces 2a, 2c, 2d, 2e, and 2f. The external electrode 4 is disposed over the end surface 2a and the side surfaces 2c, 2d, 2e, and 2f adjacent to each other.
The electrode portions 4a, 4b, and 4c adjacent to each other are connected and electrically connected to each other at the ridge portions 2g of the element body 2. The electrode portion 4a and each of the electrode portions 4b are connected at the ridge portion 2g between the end surface 2a and each of the side surfaces 2c and 2d. The electrode portion 4a and each of the electrode portions 4c are connected at the ridge portion 2g between the end surface 2a and each of the side surfaces 2e and 2f. Each of the electrode portion 4b and each of the electrode portion 4c are connected at the ridge portion 2g between each of the side surfaces 2c and 2d and each of the side surfaces 2e and 2f.
The electrode portion 4a is disposed in such a way to entirely cover the end portion 18a of the connection conductor 18 exposed at the end surface 2a, and the connection conductor 18 is directly connected to the external electrode 4. That is, the connection conductor 18 connects the coil conductor 16a (one end of the coil 15) and the electrode portion 4a. Thus, the coil 15 is electrically connected to the external electrode 4.
The external electrode 5 is located at an end portion on the end surface 2b side of the element body 2 when viewed from the first direction D1. The external electrode 5 includes an electrode portion 5a located on the end surface 2b, an electrode portions 5b located on the side surfaces 2c and 2d, and an electrode portions 5c located on the side surfaces 2e and 2f. That is, the external electrodes 5 are formed on the five surfaces 2b, 2c, 2d, 2e, and 2f. The external electrode 5 is disposed over the end surface 2b and the side surfaces 2c, 2d, 2e, and 2f adjacent to each other.
The electrode portions 5a, 5b, and 5c adjacent to each other are connected and electrically connected to each other at the ridge portions 2g of the element body 2. The electrode portion 5a and each of the electrode portions 5b are connected at a ridge portion 2g between the end surface 2b and each of the side surfaces 2c and 2d. The electrode portion 5a and each of the electrode portions 5c are connected at a ridge portion 2g between the end surface 2b and each of the side surfaces 2e and 2f. Each of the electrode portion 5b and each of the electrode portion 5c are connected at a ridge portion 2g between each of the side surfaces 2c and 2d and each of the side surfaces 2e and 2f.
The electrode portion 5a is disposed in such a way to entirely cover the end portion 17a of the connection conductor 17 exposed at the end surface 2b, and the connection conductor 17 is directly connected to the external electrode 5. That is, the connection conductor 17 connects the coil conductor 16f (the other end of the coil 15) and the electrode portion 5a. Thus, the coil 15 is electrically connected to the external electrode 5.
Each of the external electrodes 4,5 includes a sintered metal layer 21, a first plating layer 23, and a second plating layer 25. That is, the electrode portions 4a, 4b, and 4c and the electrode portions 5a, 5b, and 5c include the sintered metal layer 21, the first plating layer 23, and the second plating layer 25, respectively. The second plating layer 25 constitutes the outermost layer of the external electrode 4,5.
The sintered metal layer 21 is disposed on the surface of the element body 2. The sintered metal layer 21 is formed by applying a conductive paste to the surface of the element body 2, baking the conductive paste, and then forming the thin portions 35 described later. As the conductive paste, for example, a mixture of a conductor component, a glass component, an organic binder, and an organic solvent is used. The conductor component is, for example, a metal powder such as Ag or Cu. In the present embodiment, the conductor component is Ag powder.
In the sintered metal layer 21, the thickness of the portion disposed on the end surfaces 2a and 2b (the sintered metal layer 21 included in the electrode portions 4a and 5a) decreases toward the ridge portion 2g and increases toward the central portion of the end surfaces 2a and 2b. In the sintered metal layer 21, the thickness of the portion disposed on the end portion 17a of the connection conductor 17 is not less than the thickness of the portion disposed in the central portion of the end surface 2b or not less than ½ of the maximum thickness of the portion disposed on the end surface 2b. In the sintered metal layer 21, the thickness of the portion disposed on the end portion 18a of the connection conductor 18 is not less than the thickness of the portion disposed in the central portion of the end surface 2a or not less than ½ of the maximum thickness of the portion disposed on the end surface 2a.
The thick portion 31 covers the surface of the element body 2. The thick portion 31 is a portion having the same thickness as the sintered metal layer 21. The thickness of the thick portion 31 is greater than at least the thickness of the first plating layer 23. The thickness of the thick portion 31 is, for example, 2.5 μm or more and 50 μm or less. The thick portion 31 has a surface 31a facing the first plating layer 23 side. The thick portion 31 is formed by sintering a conductor component contained in the conductive paste. The thick portion 31 is made of a metal such as Ag or Cu. In the present embodiment, the thick portion 31 is made of Ag.
The thick portion 31 constitutes a majority of the sintered metal layer 21. The proportion (occupancy) of the thick portion 31 in the sintered metal layer 21 is, for example, 50% or more and 95% or less. The occupancy of the thick portion 31 is obtained, for example, as follows. First, a cross-sectional view of the sintered metal layer 21 is obtained. The cross-sectional view is, for example, a cross-sectional view of sintered metal layer 21 taken along a plane parallel to a pair of surfaces (for example, a pair of side surfaces 2e and 2f) opposed each other and located at an equal distance from the pair of surfaces. Subsequently, the sum of the area of the thick portion 31 and the area of the sintered metal layer 21 in the obtained cross-sectional view are calculated. Finally, the sum of the obtained area of the thick portion 31 is divided by the area of the sintered metal layer 21, and the obtained quotient is defined as the occupancy of the thick portion 31 in the sintered metal layer 21. A plurality of cross-sectional views may be obtained, and the respective quotients may be obtained for each cross-sectional view. In this case, an average value of a plurality of obtained quotients may be used as the occupancy.
The plurality of glass particles 33 is dispersed in the thick portion 31. The glass particles 33 are substantially uniformly dispersed throughout the thick portion 31. A part of the glass particles 33 is exposed on the surface 31a of the thick portion 31. That is, the part of the glass particles 33 has exposed portions 33a exposed on the surface 31a. Another part of the glass particles 33 is disposed inside the thick portion 31 in such a way that the entire surface thereof is covered by the thick portion 31.
The proportion (occupancy) of the glass particles 33 in the sintered metal layer 21 is, for example, 5% or more and 50% or less. The occupancy of the glass particles 33 is obtained by the same method as the occupancy of the thick portion 31. First, a cross-sectional view of the sintered metal layer 21 is obtained. Subsequently, the sum of the cross-sectional areas of the glass particles 33 and the cross-sectional area of the sintered metal layer 21 are obtained. Finally, the sum of the areas of the glass particles 33 is divided by the area of the sintered metal layer 21, and the obtained quotient is defined as the occupancy of the glass particles 33 in the sintered metal layer 21. A plurality of cross-sectional views may be obtained, and an average value of a plurality of obtained quotients may be used as the occupancy.
The thin portions 35 cover the glass particles 33 exposed on the surface 31a of the thick-film-like portion 31 among the plurality of glass particles 33. The thin portions 35 are in contact with the first plating layer 23. The thin portions 35 is a thin layer of conductor. The thin portion 35 is made of a metal such as Ag or Cu, for example. In the present embodiment, the thin portion 35 is made of the same metal (that is, Ag) as the metal constituting the thick-film-like portion 31. The thickness of the thin portion 35 is, for example, greater than 0 and equal to or less than 1.0 μm. The thickness of the thin portion 35 may be 0.5 μm or less. The thickness of the thin portion 35 is ½ or less of the thickness of the first plating layer 23. The thickness of the thin portion 35 may be ⅓ or less of the thickness of the first plating layer 23, or may be ¼ or less.
The thin portions 35 cover at least a portion of the exposed portion 33a. Among the plurality of exposed portions 33a, there may be an exposed portion 33a not covered with the thin portions 35. The coverage of the thin portions 35 covering the glass particles 33, that is, the coverage of the thin portions 35 covering the exposed portion 33a is obtained, for example, as follows. First, a cross-sectional view of the sintered metal layer 21 is obtained in the same manner as in the case of obtaining the occupancy described above. Subsequently, in the acquired cross-sectional view, the sum of the lengths of the exposed portions 33a and the sum of the lengths of the thin portions 35 are calculated. Finally, the calculated sum of the lengths of the thin portions 35 is divided by the sum of the lengths of the exposed portions 33a, and the obtained quotient is defined as the coverage of the thin portions 35 covering the glass particles 33. A plurality of cross-sectional views may be obtained, and an average value of a plurality of obtained quotients may be used as the coverage.
The thin portions 35 are formed after applying a conductive paste to the surface of the element body 2 and firing. The thin portions 35 are formed by, for example, surface treatment using ultrasonic waves. Specifically, the element body 2 on which the conductive paste is baked is put into an ultrasonic bath together with water and media balls, and ultrasonic waves are generated. As the media balls, for example, zirconia balls are used. The ultrasonic vibration causes the media balls to hit the surface of the sintered metal layer 21. As a result, the unevenness of the surface of the sintered metal layer 21 can be reduced, and the flatness of the surface of the sintered metal layer 21 can be improved.
Since metal is ductile, the thick portion 31 is stretched by being hit by the media ball. As a result, the thin portions 35 covering the exposed portion 33a of the glass particle 33 are formed. In the sintered metal layer 21, the portion formed on the ridge portion 2g is more easily brought into contact with the media ball than the portions formed on the end surfaces 2a and 2b and the side surfaces 2c, 2d, 2e, and 2f. Therefore, on the ridge portion 2g, the thin portions 35 are more easily formed than on the end surfaces 2a and 2b and the side surfaces 2c, 2d, 2e, and 2f. Therefore, the coverage of the thin portions 35 covering the glass particles 33, that is, the coverage of the thin portions 35 covering the exposed portion 33 is greater at each ridge portion 2g between each end surface 2a, 2b and each side surface 2c, 2d, 2e, 2f than at each end surface 2a, 2b. The coverage at the end surfaces 2a and 2b is, for example, 60% or more and 80% or less. The coverage at the ridge portion 2g is, for example, 85% or more and 99% or less.
The first plating layer 23 covers the sintered metal layer 21. The first plating layer 23 covers the sintered metal layer 21 with a substantially uniform thickness. The thickness of the first plating layer 23 is, for example, 0.5 μm or more and 5.0 μm or less. The first plating layer 23 is formed on the sintered metal layer 21 by plating. The first plating layer 23 is, for example, a Ni plating layer and contains Ni.
The second plating layer 25 covers the first plating layer 23. The second plating layer 25 covers the first plating layer 23 with a substantially uniform thickness. The thickness of the second plating layer 25 is, for example, 1.5 μm or more and 10.0 μm or less. The second plating layer 25 is formed on the first plating layer 23 by plating. The second plating layer 25 is, for example, a Sn plating layer and contains Sn.
The multilayer inductor component 1 may further include a third plating layer (not shown) covering the second plating layer 25. In this case, for example, the first plating layer 23 may be a Cu plating layer, the second plating layer 25 may be a Ni plating layer, and the third plating layer may be a Sn plating layer.
As described above, in the multilayer inductor component 1, the sintered metal layer 21 further includes the thin portions 35 in addition to the thick portion 31. The thin portions 35 cover the glass particles 33 exposed on the surface 31a of the thick portion 31. The thin portions 35 are in contact with the first plating layer 23. The thin portions 35 cover at least a part of the exposed portion 33a of the glass particles 33. Due to the thin portions 35, the first plating layer 23 are also formed in close contact with the glass particles 33 exposed on the surface 31a of the thick portion 31. Therefore, the adhesion of the first plating layer 23 to the sintered metal layer 21 is further improved. Therefore, even when the laminated inductor component 1 is mounted with a hard high-strength solder, interfacial peeling between the sintered metal layer 21 and the first plating layer 23 can be suppressed. In addition, even when the laminated inductor component 1 is used as an on-vehicle chip bead in a high-temperature environment and stress is applied due to a difference in thermal expansion coefficient, peeling of the first plating layer 23 can be suppressed.
Since the first plating layer 23 is also formed on the exposed portion 33a via the thin portion 35s, the continuity of the first plating layer 23 is improved. As a result, not only the adhesiveness of the first plating layer 23 but also the flatness of the surface of the first plating layer 23 can be improved.
The thickness of the thin portion 35 is smaller than the thickness of the first plating layer 23, and is, for example, 1.0 μm or less. By suppressing the thickness of the thin portion 35, the unevenness of the surface of the sintered metal layer 21 can be reduced, and the flatness of the surface of the sintered metal layer 21 can be improved. As a result, since the current distribution in the electroplating step becomes uniform, the first plating layer 23 can be formed uniformly. In addition, the influence of the thin portions 35 on the characteristics of the sintered metal layer 21 can be reduced. In the present embodiment, the thin portions 35 are made of the same metal as the metal constituting the thick-film-like portion 31. The deposition properties vary from material to material. By using the same material, the deposition property of the first plating layer 23 becomes more uniform. Also, in this respect, the influence of the thin portions 35 on the characteristics of the sintered metal layer 21 can be reduced.
The coverage at which the thin portions 35 cover the glass particles 33 exposed on the surface 31a of the thick portion 31 is greater at the ridge portion 2g than at the end surfaces 2a and 2b. Therefore, the adhesion of the first plating layer 23 to the ridge portion 2g is further improved. In the solder-mounted multilayer inductor component 1, stress tends to concentrate on the ridge portion 2g. Since the adhesion of the first plating layer 23 is further improved on the ridge portion 2g, the peeling of the first plating layer 23 can be suppressed.
Although the embodiments and modifications of the present invention have been described above, the present invention is not necessarily limited to the embodiments and modifications, and the embodiment can be variously changed without departing from the scope of the invention.
The multilayer inductor component 1 may not include the second plating layer 25. The multilayer inductor component 1 may have a linear conductor as an internal conductor instead of the coil conductors 16a to 16f.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-096115 | Jun 2020 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20170018362 | Nishisaka et al. | Jan 2017 | A1 |
| 20180090271 | Ito et al. | Mar 2018 | A1 |
| 20190156988 | Nakamura | May 2019 | A1 |
| 20210043363 | Ooi | Feb 2021 | A1 |
| Number | Date | Country |
|---|---|---|
| H04-280616 | Oct 1992 | JP |
| H06-096986 | Apr 1994 | JP |
| H07-192967 | Jul 1995 | JP |
| 2017-028253 | Feb 2017 | JP |
| 2018-060999 | Apr 2018 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20210375527 A1 | Dec 2021 | US |
