Common Mode Noise Filters

Abstract

A common mode noise filter is provided that can improve the attenuation characteristics of common mode noise in a wide frequency range. The common mode noise filter disclosed in the present invention comprises: two magnetic parts (11) and a magnetic part (12) comprising a magnetic body; and a non-magnetic part (13) sandwiched by the magnetic parts (11) and the magnetic parts (12) in the stacking direction and comprising a non-magnetic body. It also comprises: two coils (14) and a coil (15) facing each other and built into the non-magnetic part (13); and a metal layer (16) formed inside at least one of the two magnetic parts (11) and the magnetic part (12) and connected to the ground. The metal layer (16) is located closer to the lower surface than the upper surface of the magnetic part (11), and is located closer to the upper surface than the lower surface of the magnetic part (12).

Description

Technical Field

[0001] The present disclosure relates to a common mode noise filter used in various electronic devices such as digital devices, AV devices, and information communication terminals. Background Art

[0002] Existing common mode noise filters are Figure 5 As shown, it includes: a non-magnetic body 1; a spiral first coil 2 and a second coil 3 provided inside the non-magnetic body 1; a magnetic body 4 formed with an insulating portion interposed therebetween; and a metal layer 5 formed on the magnetic body 4.

[0003] The metal layer 5 is opposed to the first coil 2 and the second coil 3. Furthermore, the metal layer 5 is connected to the ground, and the parasitic capacitance generated between the first coil 2, the second coil 3 and the metal layer 5 bypasses the high-frequency common mode noise to the ground, thereby attenuating the common mode noise in the high-frequency region.

[0004] In addition, as prior art document information related to this conventional invention, for example, Patent Document 1 is known.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2003-318687 Summary of the invention

[0008] The conventional common mode noise filter described above cannot increase the parasitic capacitance between the metal layer 5 and the first coil 2 and the second coil 3, and therefore cannot increase the attenuation characteristics of the common mode noise in the low frequency region. Therefore, there is a problem that the common mode noise cannot be attenuated in a wide frequency region.

[0009] The present disclosure has been made to solve the above-mentioned conventional problems, and an object of the present disclosure is to provide a common mode noise filter capable of improving the attenuation characteristics of common mode noise in a wide frequency range.

[0010] The common mode noise filter involved in the first scheme comprises: two magnetic body parts each having a layer containing a magnetic body; and a non-magnetic body part having a layer containing a non-magnetic body. It further comprises: two coils arranged inside the non-magnetic body part; and a metal layer arranged inside at least one of the two magnetic body parts and grounded. The non-magnetic body part is sandwiched by the two magnetic body parts in the stacking direction. The two coils respectively comprise: a center part; and a conductor wound on a plane around the center part. The planes of the two coils are arranged along the layer containing the non-magnetic body. The two coils are opposite to each other. The magnetic body part comprises: an interface with the non-magnetic body part; and a surface on the opposite side of the interface in the stacking direction. The metal layer is arranged so as to be closer to the surface on the opposite side than the interface.

[0011] The common mode noise filter according to the second aspect is based on the first aspect, and has a boundary surface between the non-magnetic body and the magnetic body having the metal layer. When the distance between the boundary surface and the coil located closest to the boundary surface is d1, and the distance between the boundary surface and the metal layer is d2, the relationship d2 / d1≥1 is satisfied.

[0012] The common mode noise filter according to the third aspect is based on the second aspect, and when the relative dielectric constant of the non-magnetic body is set to ε1 and the relative dielectric constant of the magnetic body is set to ε2, the relationship of ε2>2×ε1 and ε2 / ε1≥d2 / d1 is satisfied.

[0013] The common mode noise filter according to the fourth aspect is the common mode noise filter according to the first to third aspects, and further includes a core portion which includes a magnetic body and is located inside the coil in a plan view and does not overlap with the metal layer.

[0014] The common mode noise filter disclosed in the present invention can increase the size of the magnetic body portion with a high dielectric constant between the coil and the metal layer without increasing the thickness of the entire magnetic body, thereby increasing the parasitic capacitance between the coil and the metal layer. This can increase the attenuation characteristics of the common mode noise in the low frequency region. As a result, it has the excellent effect of improving the attenuation characteristics of the common mode noise in a wide frequency region. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a cross-sectional view of a common mode noise filter in one embodiment of the present disclosure.

[0016] Figure 2 This is a three-dimensional diagram of the common mode noise filter.

[0017] Figure 3 This is an exploded perspective view of the common mode noise filter.

[0018] Figure 4 This is a graph comparing the frequency characteristics of the common mode noise filters.

[0019] Figure 5 This is a cross-sectional view of a conventional common mode noise filter. DETAILED DESCRIPTION

[0020] A common mode noise filter according to an embodiment of the present disclosure will be described below with reference to the drawings.

[0021] Figure 1 is a cross-sectional view of a common mode noise filter in one embodiment of the present disclosure, Figure 2 This is a three-dimensional diagram of the common mode noise filter. Figure 3 This is an exploded perspective view of the common mode noise filter. Figure 1 yes Figure 2 II line cross-sectional view.

[0022] The common mode noise filter in one embodiment of the present disclosure is Figure 1 to Figure 3 . This common mode noise filter comprises: a first magnetic body 11 including a magnetic body; a second magnetic body 12 including a magnetic body; and a non-magnetic body 13 sandwiched by the first magnetic body 11 and the second magnetic body 12 and including a non-magnetic body. It further comprises: a first coil 14 and a second coil 15 which are built into the non-magnetic body 13 and face each other; and a metal layer 16 which is formed inside the first magnetic body 11 and the second magnetic body 12 and connected to the ground. In addition, when viewed from the non-magnetic body 13, the up and down directions are defined as the first magnetic body 11 side as the "lower side" and the second magnetic body 12 side as the "upper side". That is, the direction from the first magnetic body 11 to the second magnetic body 12 is the upper direction. According to this definition, the second magnetic body 12 is located "above" (or "above") the first magnetic body 11.

[0023] In the structure of the common mode noise filter, the first magnetic body 11 is formed by stacking the first magnetic body layer 11a, the second magnetic body layer 11b and the third magnetic body layer 11c, which are made of magnetic materials such as Ni-Zn ferrite, in order from the bottom. In this way, the first magnetic body 11 has a structure in which a large number of layers are stacked. The direction in which a large number of layers are stacked in order is hereinafter referred to as the "stacking direction". In addition, the direction perpendicular to the stacking direction and along the surface of the layer is referred to as the "in-plane direction".

[0024] The second magnetic body portion 12 is formed by laminating a fourth magnetic body layer 12 a , a fifth magnetic body layer 12 b , and a sixth magnetic body layer 12 c , which are made of a magnetic material such as Ni—Zn ferrite, in this order from the bottom. The second magnetic body portion 12 is located above the first magnetic body portion 11 .

[0025] In addition, the non-magnetic body 13 is formed by stacking the first non-magnetic body layer 17a to the fifth non-magnetic body layer 17e containing non-magnetic materials such as Cu-Zn ferrite and glass ceramic in order from the bottom. Moreover, the first magnetic body 11 and the second magnetic body 12 are stacked with the non-magnetic body 13 interposed therebetween. Here, the thickness h1 of the non-magnetic body 13 in the stacking direction is 1.0 times or more and 3.0 times or less of the thickness h2 of the first magnetic body 11 and the second magnetic body 12.

[0026] Furthermore, the first coil 14 includes a first coil conductor 14a and a second coil conductor 14b formed by spirally plating or printing a conductive material such as silver. The first coil conductor 14a and the second coil conductor 14b are connected via a via electrode 18. Moreover, the first coil conductor 14a is located below the second coil conductor 14b.

[0027] That is, the first coil 14 has a planar shape in which the first coil conductor 14 a and the second coil conductor 14 b are respectively formed in a spiral shape around a central portion.

[0028] In addition, the second coil 15 includes a third coil conductor 15a and a fourth coil conductor 15b formed by spirally plating or printing a conductive material such as silver. The third coil conductor 15a and the fourth coil conductor 15b are connected via a via electrode 19. The fourth coil conductor 15b is located above the third coil conductor 15a.

[0029] That is, the second coil 15 has a planar shape in which the third coil conductor 15a and the fourth coil conductor 15b are respectively formed in a spiral shape around a central portion.

[0030] The center of the first coil conductor 14a, the center of the second coil conductor 14b, the center of the third coil conductor 15a, and the center of the third coil conductor 15a are substantially aligned, forming the center 13e of the non-magnetic body portion ( Figure 1 The dotted line portion). Furthermore, the area where the center portion 13e is extended upward toward the second magnetic body portion 12 is the center portion 12e ( Figure 1 The area extending downward toward the first magnetic body 11 is the center portion 11e (the one-dot dashed line portion of the second magnetic body 12). Figure 1 In addition, the center portion 11e, the center portion 12e, and the center portion 13e extend in the stacking direction of the first magnetic body portion 11, the second magnetic body portion 12, and the non-magnetic body portion 13, respectively, and are therefore sometimes referred to as the center portion 11e in the stacking direction, the center portion 12e in the stacking direction, and the center portion 13e in the stacking direction.

[0031] The first coil 14 and the second coil 15 are independent of each other.

[0032] The first coil conductor 14a is formed on the first non-magnetic layer 17a. The second coil conductor 14b is formed on the third non-magnetic layer 17c. The third coil conductor 15a is formed on the second non-magnetic layer 17b. The fourth coil conductor 15b is formed on the fourth non-magnetic layer 17d. In addition, the fifth non-magnetic layer 17e is formed on the fourth coil conductor 15b.

[0033] Therefore, the first coil 14 and the second coil 15 are both buried in the non-magnetic body 13, and the first coil 14 and the second coil 15 are alternately stacked. In addition, the first coil 14 and the second coil 15 are substantially opposed to each other in a plan view.

[0034] In addition, the first coil 14 and the second coil 15 are not limited to Figure 1 , Figure 3 The structure shown can be set to sandwich the first coil 14 with the third coil conductor 15a and the fourth coil conductor 15b constituting the second coil 15. In addition, the coil conductor 14a located at the bottom of the first coil 14 and the coil conductor 15b located at the top of the second coil 15 can also be a shape other than a spiral shape, such as a straight line or an L shape.

[0035] Furthermore, the metal layer 16 contains Ag, is formed by printing, plating, or sticking of a plate-shaped metal, and is provided on the upper surface of the first magnetic layer 11 a and the upper surface of the fifth magnetic layer 12 b .

[0036] Therefore, the metal layer 16 is embedded in the first magnetic body portion 11 and the second magnetic body portion 12. The metal layer 16 embedded in the first magnetic body portion 11 is arranged at a position closer to the lower surface of the first magnetic body portion 11 than the upper surface of the first magnetic body portion 11. In addition, the metal layer 16 embedded in the second magnetic body portion 12 is arranged at a position closer to the upper surface of the second magnetic body portion 12 than the lower surface of the second magnetic body portion 12.

[0037] The metal layer 16 has a notch 16 a in the center and overlaps main portions (from the innermost circumference to the outermost circumference excluding the lead-out portions) of the first coil conductor 14 a , the second coil conductor 14 b , the third coil conductor 15 a , and the fourth coil conductor 15 b in a plan view.

[0038] Furthermore, with this structure, high-frequency common mode noise is bypassed to the ground by parasitic capacitance generated between the first coil 14 , the second coil 15 , and the metal layer 16 , thereby attenuating the common mode noise in the high-frequency region.

[0039] Furthermore, a nonmagnetic layer 20 made of a nonmagnetic material is formed on the lower surface of the first magnetic body portion 11 and the upper surface of the second magnetic body portion 12. In addition, a magnetic layer made of a magnetic material may be further formed outside the nonmagnetic layer 20 in the stacking direction.

[0040] Furthermore, a core portion 21 made of a magnetic body is formed inside (inside the innermost circumference) the coils of the first coil conductor 14a, the second coil conductor 14b, the third coil conductor 15a, and the fourth coil conductor 15b in a plan view. The core portion 21 is disposed in the center portion 13e.

[0041] The core 21 is formed integrally with the first to fifth nonmagnetic layers 17a to 17e and the first to third magnetic layers 11a to 11c. The core 21 mutually reinforces the magnetic fields generated by the first coil 14 and the second coil 15, thereby improving the common mode impedance.

[0042] The core portion 21 is not in contact with the first coil conductor 14a, the second coil conductor 14b, the third coil conductor 15a, and the fourth coil conductor 15b, and is formed flush with the metal layer 16 in the first magnetic body portion 11. That is, the core portion 21 is disposed in the notch portion 16a in a plan view.

[0043] Furthermore, the density of the core portion 21 is higher than the density of the first magnetic body portion 11 and the second magnetic body portion 12 .

[0044] By increasing the density of the magnetic core portion 21 , the mutually reinforcing magnetic fields become stronger, and thus the common mode impedance can be further improved.

[0045] In addition, after the first magnetic body 11 and the non-magnetic body 13 are stacked, a hole is opened by laser, and the hole is filled with a magnetic material to form the magnetic core 21. Then, the metal layer 16 and the magnetic core 21 do not overlap when viewed from above, but overlap with the notch 16a. This is to prevent the metal layer 16 from being damaged by the laser when forming the magnetic core 21.

[0046] Furthermore, due to the presence of the notch 16 a , the adhesion between the first to third magnetic layers 11 a to 11 c and the fourth to sixth magnetic layers 12 a to 12 c is improved, and the occurrence of delamination can be suppressed.

[0047] In the above description, the metal layer 16 is formed on both the first magnetic body portion 11 and the second magnetic body portion 12 , but may be formed on only one of them.

[0048] The number of the first non-magnetic layer 17a to the fifth non-magnetic layer 17e, the first magnetic layer 11a to the third magnetic layer 11c, and the fourth magnetic layer 12a to the sixth magnetic layer 12c may be different from the number in the above description. Figure 3 The number of pieces shown varies by the number of pieces.

[0049] Then, the laminate 22 is formed by the above-mentioned structure. The first external electrode 23a, the second external electrode 23b, the third external electrode 23c, and the fourth external electrode 23d connected to the lead-out portions of the first coil conductor 14a, the second coil conductor 14b, the third coil conductor 15a, and the fourth coil conductor 15b are formed on both side surfaces of the laminate 22. The fifth external electrode 24a and the sixth external electrode 24b connected to the metal layer 16 are formed on both end surfaces of the laminate 22. The fifth external electrode 24a and the sixth external electrode 24b are connected to the ground.

[0050] As described above, in one embodiment of the present disclosure, the size of the first magnetic body 11 and the second magnetic body 12 having a high dielectric constant between the first coil 14, the second coil 15 and the metal layer 16 can be increased. Therefore, the parasitic capacitance between the first coil 14, the second coil 15 and the metal layer 16 can be increased. This can lower the resonant frequency.

[0051] Furthermore, the common mode noise in the high frequency region can be attenuated by bypassing the high frequency common mode noise to the ground through the parasitic capacitance generated between the first coil 14, the second coil 15 and the metal layer 16. Therefore, the attenuation characteristics of the common mode noise can be improved in a wide frequency range from low frequency to high frequency.

[0052] In addition, the metal layer 16 is merely positioned away from the center portion 11e in the stacking direction of the first magnetic body portion 11 and away from the center portion 12e in the stacking direction of the second magnetic body portion 12. Therefore, the first magnetic body portion 11 and the second magnetic body portion 12 can be made low-profile without changing the thickness.

[0053] Here, Figure 4This is a graph comparing frequency characteristics (the horizontal axis is frequency (Frequency, unit MHz), and the vertical axis is common mode noise attenuation (Common mode attenuation, unit dB)) for the following cases: the case A (d2>d3) in which the metal layer 16 is arranged at a position closer to the lower surface of the first magnetic body 11 than the upper surface of the first magnetic body 11, and the metal layer 16 is arranged at a position closer to the upper surface of the second magnetic body 12 than the lower surface of the second magnetic body 12; and the case B (d2=d3) in which the metal layer 16 is formed at the center surface of the first magnetic body 11 and the center surface of the second magnetic body 12. In addition, the so-called "center surface of the first magnetic body 11" here refers to a surface that is parallel to the upper surface of the first magnetic body 11 and the lower surface of the first magnetic body 11 and the distance from the upper surface of the first magnetic body 11 and the distance from the lower surface of the first magnetic body 11 become equal. That is, it is also called a plane where d2 = d3. Similarly, the "central plane of the second magnetic body portion 12" is also called a plane where d2 = d3.

[0054] As from Figure 4 As is apparent, it can be understood that, for A, the attenuation amount of common mode noise in a wider frequency band is greater.

[0055] Furthermore, the distance between the boundary surface 25 (the fifth non-magnetic layer 17a and the fourth magnetic layer 12a) of the second magnetic body portion 12 and the non-magnetic body portion 13 and the second coil 15 (the fourth coil conductor 15b) located closest to the boundary surface 25 (hereinafter referred to as the distance on the metal layer side) is set to d1, and the distance between the boundary surface 25 and the metal layer 16 (hereinafter referred to as the distance on the coil side) is set to d2, and the relationship d2 / d1≥1 is achieved.

[0056] That is, the distance d2 on the metal layer side is made longer than the distance d1 on the coil side. This also applies to the boundary surface between the first magnetic body portion 11 and the non-magnetic body portion 13. This also applies to the following description.

[0057] In addition, when the distance between the boundary surface 26 between the second magnetic body portion 12 and the non-magnetic body layer 20 and the metal layer 16 is d3, d3 <d2。

[0058] This can increase the size of the first magnetic body 11 and the second magnetic body 12 portions with high dielectric constants between the first coil 14 and the second coil 15 and the metal layer 16. Therefore, the parasitic capacitance between the first coil 14 and the second coil 15 and the metal layer 16 can be increased.

[0059] Here, the total capacitance C between the metal layer 16 and the fourth coil conductor 15b is the capacitance obtained by adding the capacitance C1 between the boundary surface 25 and the fourth coil conductor 15b and the capacitance C2 between the boundary surface 25 and the metal layer 16. Therefore, C=(C1×C2) / (C1+C2)={(ε1 / d1)×(ε2 / d2)} / {(ε1 / d1)+(ε2 / d2)}. In addition, the relative dielectric constant of the non-magnetic body 13 is ε1, and the relative dielectric constants of the first and second magnetic body parts 11 and 12 are ε2.

[0060] When d1=d2=1 and ε1=ε2, C=ε1 / 2. However, if d2=2×d1, C=ε1×(2 / 3), and the total capacitance C increases. Therefore, it is preferable to set d2≥d1. However, considering the thickness h2 of the first and second magnetic parts 11 and 12 and the limit of the product thickness (low profile), it is preferable to set d2=2×d1 or less.

[0061] In addition, since ε1=ε2 is impossible, if ε2=2×ε1 is further set, C=ε1 / 2, and the total capacitance C does not change. Therefore, it is preferable to set ε2>2×ε1.

[0062] Furthermore, the thickness, number of layers, and material of each layer are appropriately set so as to achieve the above-mentioned relationship in thickness and relationship in dielectric constant.

[0063] In order to increase the parasitic capacitance between the first coil 14, the second coil 15 and the metal layer 16, as described above, the distance d2 on the metal layer side is made longer than the distance d1 on the coil side and d2 / d1≥1. In addition, regarding the dielectric constant, ε2 / ε1>1. In this case, the relationship of ε2 / ε1≥d2 / d1 (≥1) is satisfied.

[0064] This is because, with respect to increasing the parasitic capacitance between the first coil 14 , the second coil 15 , and the metal layer 16 , the effect of increasing the dielectric constant is more conducive to reducing the height of the product than the effect of the thickness dimension.

[0065] Industrial Applicability

[0066] The common mode noise filter of the present disclosure has the effect of improving the attenuation characteristics of common mode noise in a wide frequency range, and is particularly useful in common mode noise filters used as noise countermeasures for various electronic devices such as digital devices, AV devices, and information communication terminals.

[0067] Description of Reference Numerals

[0068] 11. First magnetic body

[0069] 12. Second magnetic body

[0070] 13 Non-magnetic body

[0071] 14 Coil 1

[0072] 15 2nd coil

[0073] 16 metal layers.

Claims

1. A common mode noise filter comprising: Two magnetic body parts each having a layer including a magnetic body; A non-magnetic body portion having a layer including a non-magnetic body; two coils disposed inside the non-magnetic body; and a metal layer provided inside at least one of the two magnetic parts and connected to the ground, The non-magnetic body portion is sandwiched by the two magnetic body portions in the stacking direction. The two coils each include a center portion and a conductive wire wound on a plane around the center portion. The planes of the two coils are arranged along the layer including the non-magnetic body. The two coils are opposed to each other. The magnetic body portion has: an interface with the non-magnetic body portion; and a surface on the opposite side of the interface in the stacking direction, The metal layer is opposite to the two coils. By arranging the metal layer closer to the opposite side than the interface, the parasitic capacitance between the two coils and the metal layer is increased. The common mode noise filter has a boundary surface between the non-magnetic body and the magnetic body having the metal layer, and when the distance between the boundary surface and the coil located closest to the boundary surface is set to d1, and the distance between the boundary surface and the metal layer is set to d2, a relationship of d2 / d1≥1 is satisfied, When the relative dielectric constant of the non-magnetic body is ε1 and the relative dielectric constant of the magnetic body is ε2, the relationship of ε2>2×ε1 and ε2 / ε1≥d2 / d1 is satisfied.

2. The common mode noise filter according to claim 1, wherein The common mode noise filter has a magnetic core portion including a magnetic body, which is located inside the coil in a plan view and does not overlap with the metal layer.

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