Transformer component

Abstract

In the transformer component, the inner diameter area of the primary coil is designed to be larger than the inner diameter area of the secondary coil. Thus, in the inner diameter region of the primary coil, magnetic flux saturation is unlikely to occur, and a low-loss transformer component can be obtained. On the other hand, the inner diameter area of the secondary coil is designed so as to be small, thereby sufficiently ensuring the line width of the spiral conductor constituting the secondary coil, and achieving low resistance.

Description

Technical Field

[0001] The present invention relates to a transformer component. Background Art

[0002] In Japanese Patent Laid-Open No. 2012-89760, a transformer component having a primary coil and a secondary coil provided in a core body is disclosed. Summary of the Invention

[0003] Technical Problem to be Solved by the Invention

[0004] The inventors of the present invention have repeatedly studied the losses of transformer components and newly discovered a technique for reducing losses by alleviating magnetic flux saturation.

[0005] According to one aspect of the present invention, a transformer component capable of reducing losses can be provided.

[0006] Means for Solving the Technical Problem

[0007] A transformer component according to one aspect of the present invention includes: a core body; a primary coil provided in the core body and wound around a coil axis along a first direction; and a secondary coil formed on a substrate orthogonal to the first direction in the core body, overlapping the primary coil in the first direction, and wound around the coil axis to have a common magnetic path with the primary coil, wherein the number of turns of the primary coil is more than that of the secondary coil, and the inner diameter area of the primary coil is larger than the inner diameter area of the secondary coil.

[0008] In the above transformer component, the inner diameter area of the primary coil having more turns than the secondary coil is larger than the inner diameter area of the secondary coil, whereby magnetic flux saturation can be alleviated, and as a result, losses can be reduced. Brief Description of the Drawings

[0009] Figure 1 It is a schematic exploded perspective view of a transformer component showing one embodiment.

[0010] Figure 2 It is Figure 1 A schematic cross-sectional view of the transformer component shown in. Detailed Description of the Invention

[0011] Hereinafter, various embodiments and examples will be described with reference to the drawings. In addition, in each drawing, the same or corresponding parts are denoted by the same reference numerals, and repeated descriptions are omitted.

[0012] As shown in Figure 1 and Figure 2As shown, a transformer component 10 of one embodiment is constituted by having a primary coil L1 and a secondary coil L2 in a core body 11. More specifically, the transformer component 10 is constituted by having a ferrite substrate 12, a thin-film coil layer 14 including first and second spiral conductors 13A, 13B formed on the ferrite substrate 12, a printed circuit board 16 overlapped and disposed on the ferrite substrate 12, third and fourth spiral conductors 17A, 17B respectively formed on both surfaces of the printed circuit board 16, and four terminal electrodes 20a to 20d. In this embodiment, the primary coil L1 includes the ferrite substrate 12 and the thin-film coil layer 14, and the secondary coil L2 includes the printed circuit board 16 and the third and fourth spiral conductors 17A, 17B.

[0013] The core body 11 has a rectangular flat-plate shape and has a pair of main surfaces 11a, 11b opposite to each other in a first direction D1, and four side surfaces 11c to 11f connecting the main surfaces. The ferrite substrate 12, the thin-film coil layer 14, the printed circuit board 16, and the third and fourth spiral conductors 17A, 17B are embedded in the core body 11. Each of the terminal electrodes 20a to 20d is disposed on the side surfaces 11c to 11f of the core body 11. In this embodiment, a pair of terminal electrodes 20a, 20b are respectively provided on the side surface 11c of the side surfaces 11c and 11d opposite to each other, and a pair of terminal electrodes 20c, 20d are respectively provided on the side surface 11d.

[0014] The core body 11 is made of a magnetic material, and in this embodiment, it is made of a resin containing metal magnetic powder. When using a resin containing metal magnetic powder, there are a plurality of minute gaps between the metal magnetic powder and the resin, which improves the saturation magnetic flux density, and thus the gaps between the respective elements disposed in the core body 11 can be omitted. The resin containing metal magnetic powder refers to a magnetic material formed by mixing metal magnetic powder in a resin. As the metal magnetic powder, a permalloy-based material can be used. Specifically, a metal magnetic powder containing a Pb-Ni-Co alloy having an average particle diameter of 20 to 50 μm as a first metal magnetic powder and a carbonyl iron having an average particle diameter of 3 to 10 μm as a second metal magnetic powder at a weight ratio of, for example, 70:30 to 80:20, 75:25 can be used. The content rate of the metal magnetic powder can be 90 to 96% by weight.

[0015] If the amount of the metallic magnetic powder is reduced relative to the resin, the saturation magnetic flux density will become smaller. Conversely, if the amount of the metallic magnetic powder is increased, the saturation magnetic flux density will become larger. Therefore, the saturation magnetic flux density can only be adjusted by the amount of the metallic magnetic powder. Additionally, as the metallic magnetic powder, it is also possible to use a metallic magnetic powder obtained by mixing a first metallic magnetic powder with an average particle diameter of 5 μm and a second metallic magnetic powder with an average particle diameter of 50 μm at a prescribed ratio, for example, 75:25. In this way, when using two types of metallic magnetic powders with different particle diameters, a high-density magnetic core can be formed under low-pressure or non-pressure molding, and a magnetic core with high magnetic permeability and low loss can be achieved. The resin contained in the resin containing the metallic magnetic powder functions as an insulating binder material. As the resin material, a liquid epoxy resin or a powder epoxy resin can be used. In addition, the content rate of the resin can be 4 to 10% by weight.

[0016] The ferrite substrate 12 is a rectangular flat plate extending in a direction orthogonal to the first direction D1 and forms a part of a closed magnetic circuit. Although not particularly limited, the planar dimensions of the ferrite substrate 12 can be set to about 3.2 × 2.5 mm, for example. As the material of the ferrite substrate 12, sintered ferrite can be used, or a material with high magnetic permeability such as Ni-Cu-Zn ferrite or Mn-Zn ferrite can be used. By using such a magnetic material, the magnetic characteristics of the transformer can be improved.

[0017] The thin film coil layer 14 is formed on one main surface 12a (upper surface) of the ferrite substrate 12. The thin film coil layer 14 is formed by sequentially laminating a first insulating layer 15a, a first spiral conductor 13A, a second insulating layer 15b, a second spiral conductor 13B, and a third insulating layer 15c.

[0018] The first spiral conductor 13A is formed on the surface of the first insulating layer 15a formed on the ferrite substrate 12. This is to smooth the unevenness on the surface of the ferrite substrate 12 to ensure a flat surface and enable the formation of a fine pattern. However, if the flatness of the ferrite substrate 12 is sufficient, the first insulating layer 15a can be omitted, and in this case, the first spiral conductor 13A can be directly formed on the ferrite substrate 12.

[0019] The first to third insulating layers 15a to 15c can be formed by spin-coating a photosensitive insulating non-magnetic resin (for example, a photosensitive polyimide resin), and then exposing, developing, and thermally curing it.

[0020] The first and second spiral conductors 13A and 13B are circular spirals. Both the first and second spiral conductors 13A and 13B are wound around a coil axis Z parallel to the first direction D1. The first and second spiral conductors 13A and 13B are approximately overlapped but not completely coincident when viewed from above.

[0021] That is, when viewed from above, the first spiral conductor 13A forms a spiral that rotates counterclockwise from the outer peripheral end 13a toward the inner peripheral end 13b, and similarly, when viewed from above, the second spiral conductor 13B forms a spiral that rotates counterclockwise from the inner peripheral end 13b toward the outer peripheral end 13a. Thus, the directions of the magnetic fluxes generated by the currents flowing through the spiral conductors 13A and 13B are the same. For example, magnetic fluxes along the coil axis Z are generated in the inner diameter regions of the spiral conductors 13A and 13B. Since the magnetic fluxes generated by the spiral conductors 13A and 13B overlap and reinforce each other, a large inductance can be obtained.

[0022] The outer peripheral ends 13a of the first and second spiral conductors 13A and 13B are led out to the side surfaces of the ferrite substrate 12 or the first insulating layer 15a, and are respectively connected to a pair of terminal electrodes 20a and 20b. In addition, the inner peripheral end 13b of the first spiral conductor 13A and the inner peripheral end 13b of the second spiral conductor 13B are connected to each other via a contact hole conductor 13c that penetrates the second insulating layer 15b. Thus, the first and second spiral conductors 13A and 13B form a single coil (i.e., a primary coil) that is connected in series with each other.

[0023] The first and second spiral conductors 13A and 13B are formed by a microfabrication process. Specifically, after forming a Cu film by sputtering or evaporation and forming a multilayer film (Cr / Cu film) in which the Cu film and the Cr film are sequentially laminated as a base conductive film, a photoresist film is formed by a spin coating method. Next, a negative pattern of the spiral conductor is formed by exposing and developing the photoresist film, and the base conductive film can be selectively electroplated and grown using this mask pattern.

[0024] The printed circuit board 16 extends in a direction orthogonal to the first direction D1, similarly to the ferrite substrate 12. The printed circuit board 16 overlaps one side (upper side) of the ferrite substrate 12 with respect to the first direction D1. The printed circuit board 16 is a support substrate for providing a formation surface for the third and fourth spiral conductors 17A and 17B, and has a circular opening 16a at its center. The opening 16a of the printed circuit board 16 is formed in a region corresponding to the coil axis Z. The thickness of the printed circuit board 16 can be set to about 0.06 mm, for example. The material of the printed circuit board 16 can be a general printed circuit board material obtained by impregnating glass cloth with epoxy resin. For example, a BT substrate, an FR4 substrate, an FR5 substrate, etc. can be used. In addition, a ceramic substrate can also be used as the printed circuit board material. In the case of using these printed circuit board materials, the spiral conductor can be formed by electroplating instead of sputtering in the so-called thin film manufacturing method, so that the thickness of the conductor can be made sufficiently thick. In order to avoid an increase in parasitic capacitance, the dielectric constant of the printed circuit board 16 can also be 7 or less (μ ≤ 7).

[0025] The third and fourth helical conductors 17A and 17B are also circular helices. The third and fourth helical conductors 17A and 17B are each wound around a coil axis Z parallel to the first direction D1. The third and fourth helical conductors 17A and 17B are arranged so as to surround the opening 16a of the printed substrate 16.

[0026] When viewed from above, the third and fourth helical conductors 17A and 17B approximately overlap each other, but do not completely coincide.

[0027] That is, the third helical conductor 17A viewed from above forms a clockwise-turning helix from the outer peripheral end 17a toward the inner peripheral end 17b. Similarly, the fourth helical conductor 17B viewed from above forms a clockwise-turning helix from the inner peripheral end 17b toward the outer peripheral end 17a.

[0028] As a result, the directions of the magnetic fluxes generated by the currents flowing through the helical conductors 17A and 17B are the same. For example, in the inner diameter region of the helical conductors 17A and 17B, a magnetic flux along the coil axis Z parallel to the first direction D1 is generated. Since the magnetic fluxes generated in the helical conductors 17A and 17B overlap and reinforce each other, a larger inductance can be obtained.

[0029] The outer peripheral ends 17a of the third and fourth helical conductors 17A and 17B are led out to the side surface of the ferrite substrate 16 and are respectively connected to a pair of terminal electrodes 20c and 20d. In addition, the inner peripheral ends 17b of the third helical conductor 17A and the fourth helical conductor 17B are connected to each other via a through-hole conductor 17c passing through the printed substrate 16. Thus, the third and fourth helical conductors 17A and 17B constitute a single coil (i.e., a secondary coil) connected in series with each other.

[0030] In the present embodiment, the primary coil L1 and the secondary coil L2 overlap in the first direction D1 and have a common magnetic path. The formation regions of the first and second helical conductors 13A and 13B constituting the primary coil L1 and the formation regions of the third and fourth helical conductors 17A and 17B constituting the secondary coil L2 substantially overlap when viewed from above. The formation region of the coil here refers to the region occupied by the planar coil formed by the helical conductor. With such a structure in which the coil formation regions of the primary coil L1 and the secondary coil L2 overlap, the magnetic fluxes generated by the primary coil L1 and the magnetic fluxes generated by the secondary coil L2 overlap and reinforce each other. Therefore, a larger mutual inductance can be obtained. Therefore, the magnetic coupling between the primary coil L1 and the secondary coil L2 can be enhanced, and a transformer component with high conversion efficiency can be provided.

[0031] Both ends of the primary coil L1 including the first and second spiral conductors 13A and 13B are respectively connected to a pair of terminal electrodes 20a and 20b, and both ends of the secondary coil L2 including the third and fourth spiral conductors 17A and 17B are respectively connected to a pair of terminal electrodes 20c and 20d. The first and second spiral conductors 13A and 13B are fine patterns with a narrow pitch, and the conductor width can be 2 μm to 10 μm. According to this structure, the primary coil L1 composed of the first and second spiral conductors 13A and 13B can be used as the secondary side coil of a step-up transformer.

[0032] The thin film coil layer 14 including these spiral conductors 13A and 13B is formed by a so-called thin film manufacturing method, so that spiral conductors with a large number of turns can be formed with a very narrow pitch. On the other hand, the third and fourth spiral conductors 17A and 17B are thick film patterns wider than the first and second spiral conductors 13A and 13B. For example, the conductor width can be 20 to 100 μm, and the conductor thickness can be 25 to 150 μm. According to this structure, the secondary coil L2 including the third and fourth spiral conductors 17A and 17B can be used as the primary side coil of a step-up transformer. Although not particularly limited, the turn ratio of the primary side coil to the secondary side coil can be 1:2 to 1:20.

[0033] In order to form the third and fourth spiral conductors 17A and 17B on the surface of the printed circuit board 16, it can be formed by a so-called semi-additive method.

[0034] In the transformer component 10 of the present embodiment, it is designed such that the number of turns of the primary coil L1 is greater than the number of turns of the secondary coil L2. In this case, the magnetic flux density of the primary coil L1 is higher than the magnetic flux density of the secondary coil L2.

[0035] In the transformer component 10, the inner diameter area S1 of the primary coil L1 is designed to be larger and is greater than the inner diameter area S2 of the secondary coil L2. Thus, in the inner diameter region of the primary coil L1, it is difficult to generate magnetic flux saturation, and a transformer component with low loss can be obtained. On the other hand, the inner diameter area S2 of the secondary coil L2 is designed to be smaller, so as to fully ensure the line width of the spiral conductors 17A and 17B constituting the secondary coil L2 to achieve low resistance.

[0036] In addition, in the transformer component 10, in the first direction D1, it is designed such that the volume V1 of the magnetic material constituting the main surface 11b on the primary coil L1 side is greater than the volume V2 of the magnetic material constituting the main surface 11a on the secondary coil L2 side. In other words, the thickness of the magnetic material between the primary coil L1 and the main surface 11b is thicker than the thickness of the magnetic material between the secondary coil L2 and the main surface 11a. Thus, magnetic flux saturation and magnetic flux leakage on the main surface 11b on the primary coil L1 side are not likely to occur.

[0037] In addition, the relative distance between the primary coil L1 and the secondary coil L2 is very close. In the present embodiment, only the insulating layer 15c exists between the second spiral conductor 13B and the third spiral conductor 17A. Therefore, the magnetic coupling between the primary coil L1 and the secondary coil L2 can be further enhanced, and a transformer with high conversion efficiency can be realized.

[0038] The third and fourth spiral conductors 17A and 17B can be formed by the following method: after forming a base conductive film (such as a Cu film) by electroless plating, a photoresist is attached, and a negative pattern of the spiral conductor is formed by exposing and developing the photoresist film, and the base conductive film is selectively electroplated and grown by using this mask pattern.

[0039] The thickness of the third and fourth spiral conductors 17A and 17B formed in this way is much thicker than that of the first and second spiral conductors 13A and 13B, so the DC resistance can be sufficiently reduced.

[0040] The present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the coil is not limited to a circular shape, and may be, for example, an elliptical shape or a rectangular shape. In addition, the number of turns of the coil can be appropriately increased or decreased.

Claims

1. A transformer component, wherein: have: body; and a primary coil disposed in the body and wound around a coil axis along a first direction; and a secondary coil formed on a substrate orthogonal to the first direction in the element body, overlapping the primary coil in the first direction, and wound around the coil axis to have a common magnetic path with the primary coil; The number of turns of the primary coil is greater than that of the secondary coil, and the inner diameter area of ​​the primary coil is greater than that of the secondary coil.

2. The transformer component according to claim 1, wherein: The primary coil is formed on a magnetic substrate.

3. The transformer component according to claim 1 or 2, wherein: The element body is made of a magnetic material, and with respect to the first direction, a volume of the magnetic material constituting a surface of the element body on the primary coil side is larger than a volume of the magnetic material constituting a surface of the element body on the secondary coil side.

Images