JP2003109830A - Planar magnetic element and switching power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provided a small-sized and lightweight planar magnetic element for remarkably reducing coil direct current resistance. SOLUTION: In the planar magnetic element having a planar coil on a face of a lower ferrite magnetic layer, including a gap between coil wires of the planar coil, providing an upper ferrite magnetic layer thereon and making a whole to be a rectangle, a width of the coil wire of the planar coil in parallel to a short side of the planar magnetic element is wider than that of the coil wire in parallel to a long side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectangular planar magnetic element and a switching power supply using the same.

[0002]

2. Description of the Related Art In recent years, the use of small electronic devices driven by batteries, such as portable devices and notebook computers, has been increasing. For such electronic devices, further miniaturization and weight reduction have been desired, and recently, in addition to these, correspondence to multimedia, that is, enhancement of communication function and display function, or There is a demand for high functionality such as high-speed processing of large amounts of information including image data.

Along with this, the single voltage from the battery is
There has been an increasing demand for small power supplies that can be accurately converted to the voltage levels required by various on-board devices such as U, LCD modules, and communication power amplifiers. Therefore, in order to achieve both small size and light weight and high functionality of electronic devices,
It is an important issue to reduce the size and weight of the power supply combined with magnetic elements such as transformers and inductors mounted on the power supply.

Under these circumstances, in order to reduce the size and weight of the magnetic element, a metal magnetic film layer /
Planar inductor composed of insulating layer / plane coil layer / insulating layer / metal magnetic film layer (for example, Journal of Japan Society for Applied Magnetics 20
(1996) 922, JP-A-4-363006). However, the planar inductor described above still has problems in terms of manufacturing cost and characteristics. That is, first, regarding the cost aspect, in the above planar inductor, it is necessary to form a metal magnetic film having a thickness of about 6 to 7 μm by a sputtering method or the like, and an insulating layer is provided between the metal magnetic film and the plane coil. Since it needs to be formed, an increase in cost is inevitable as compared with the conventional magnetic element.

Further, the problems of characteristics are as follows. That is, since the planar inductor is driven at a high frequency in the MHz band, the iron loss increases due to the generation of an eddy current inside the metal magnetic film that is an electrical conductor. Further, since the upper and lower metal magnetic layers face each other through a slight non-magnetic space, the vertical alternating magnetic flux interlinks with the planar coil, and an eddy current is generated in the coil, which causes an increase in loss. For the former problem, a high resistance region is formed on the same plane as the metal magnetic film to subdivide the eddy current (Japanese Patent Laid-Open No. 6-77055), while for the latter problem, a planar coil is used. Attempts have been made to improve the loss by using a conductor line divided into a plurality of conductors (Japanese Patent Laid-Open No. 9-134820), but these methods have not been able to obtain a sufficient improvement effect.

In order to solve the above problem, a flat magnetic element using a ferrite magnetic film formed by a printing method or a sheet method instead of the metal magnetic film has been proposed (Japanese Patent Laid-Open No. 11-26).
No. 239). In this technology, a magnetic paste prepared by mixing ferrite powder with a binder is printed on a silicon substrate and baked to form a high-resistance ferrite magnetic film, and then a coil pattern is formed on this film by a plating method or the like. Further, a ferrite magnetic film is formed thereon in the same manner to form a magnetic element. With such a structure, the magnetic element has been successfully thinned and the loss in the high frequency region has been reduced.

[0007]

However, even the technique disclosed in Japanese Patent Laid-Open No. 11-26239 mentioned above has the following problems. That is, when the planar magnetic element is used as a surface mount component, it is conceivable to use the planar magnetic element in a rectangular shape with external electrodes attached to its short sides. In such a usage mode of the planar magnetic element, when a normal rectangular coil is arranged as the planar coil, the coil width is determined by the length of the short side. Therefore, the coil is arranged in the longitudinal direction of the planar magnetic element. Not dead space occurs.

The present invention advantageously solves the above-mentioned problems. By effectively utilizing the dead space described above, a planar magnetic element that achieves an advantageous reduction of the coil DC resistance is switched using the planar magnetic element. It is intended to be proposed together with the power supply.

[0009]

The fact that there is a dead space on both sides in the longitudinal direction of a rectangular planar magnetic element means that the coil wire width of the planar coil parallel to the short side of the planar magnetic element is correspondingly increased. It means that you can afford it. Therefore, the inventors have increased the width of the coil wire parallel to the short side of the planar magnetic element by utilizing the above-mentioned dead space, and as a result, it is possible to significantly reduce the coil DC resistance as compared with the conventional case. I got the knowledge. The present invention is based on the above findings.

That is, the gist of the present invention is as follows. 1. A planar magnetic element having a planar coil on the surface of the lower ferrite magnetic layer and an upper ferrite magnetic layer including the gap between the coil wires of the planar coil and having a rectangular shape, A planar magnetic element characterized in that a width of a coil wire of a plane coil parallel to a short side of the element is made wider than a width of a coil wire parallel to a long side.

2. In the above 1, the long side length of the planar magnetic element is a, the long side length of the middle window is f, the width of the coil wire parallel to the long side is d, the coil wire interval is s, and the number of turns of the coil is n. The planar magnetic element is characterized in that the width e of the coil wire parallel to the short side satisfies the following expression d <e ≦ (a−f + s) / 2 n.

The second aspect of the present invention defines a preferable range of the coil wire width of the plane coil parallel to the short side of the plane magnetic element. That is, if the width of the coil wire parallel to the short side is wide as much as the space allows, the resistance of the entire coil can be reduced accordingly. However, if the width of the coil wire becomes too wide, in other words, the distance between the coil wires becomes too narrow, the magnetic flux across the upper and lower ferrite magnetic layers will cross the coil, resulting in an increase in eddy current loss. Therefore, the present inventors examined an appropriate range of the coil wire width parallel to the short side, and as shown in FIG. 1, the long side length of the planar magnetic element is a and the short side length is c (c <A), the long side length of the middle window is f, and the short side length is b (f
≧ b), where d is the width of the coil wire parallel to the long side, s is the spacing between the coil wires, and n is the number of turns of the coil, the width e of the coil wire parallel to the short side is It has been clarified that particularly good results are obtained when the relationship of d <e ≦ (a−f + s) / 2 n is satisfied.

3. A switching power supply comprising the planar magnetic element according to 1 or 2 above. 3 above
Of the invention is a switching power supply equipped with the planar magnetic element according to 1 or 2 above, and by using such a planar magnetic element, not to mention reduction in size and weight of the switching power supply, its energy efficiency is also improved. Can be significantly improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, as the ferrite magnetic layer in the present invention,
Those having a spinel structure are preferable, and NiZn-based ferrite having the following composition is particularly preferable. Note that the following composition is a value when the entire magnetic element is averaged, and the composition may be appropriately changed depending on the location, such as the ferrite filled between the lower ferrite magnetic layer, the upper ferrite magnetic layer and the coil wire. it can.

The _{Fe 2 0 3: 40~50 mol%} Fe 2 0 3 is larger deterioration in inductance due to no magnetic permeability reduction in the ferrite less than 40 mol%. On the other hand, if it exceeds 50 mol%, the electrical resistance will drop sharply due to the presence of Fe ²⁺ ions, and when used in the high frequency range, the loss of the ferrite core will increase sharply due to the generation of eddy currents. Thus Fe ₂ 0 ₃ is 40
It is preferably about 50 mol%.

NiO: 15 to 50 mol% If the NiO content is less than 15 mol%, the Curie temperature required for practical use cannot be obtained. On the contrary, if it exceeds 50 mol%, a different phase precipitates and the magnetic properties deteriorate. Therefore, the NiO content is preferably about 15 to 50 mol%.

ZnO: 15-35 mol% ZnO has a great influence on the inductance and the Curie temperature. The Curie temperature is an important parameter that determines the heat resistance of the magnetic element. If the content of ZnO is less than 15 mol%, the Curie temperature is high, but the inductance decreases, whereas if it exceeds 35 mol%, the inductance is high but the Curie temperature decreases. Therefore, it is preferable to set ZnO to about 15 to 35 mol%.

CuO: 0 to 20 mol% CuO is a useful component for reducing the firing temperature. However, if it exceeds 20 mol%, the firing temperature is lowered but the inductance is deteriorated. Therefore, when it is contained, it is preferable that the content of CuO is 20 mol% or less.

Bi ₂ 0 ₃ : 0 to 10 mol% Bi ₂ 0 ₃ has the same effect of lowering the firing temperature as CuO. However, if the content exceeds 10 mol%, the firing temperature decreases, but the inductance deteriorates. Therefore, when it is contained, it is preferable to contain it at 10 mol% or less.

MnO: 0 to 20 mol%, MgO: 0 to 20 mol% MnO and MgO are both components effective in increasing the inductance, but if they exceed 20 mol%, the saturation magnetization is lowered. When it is contained, it is preferably contained at 20 mol% or less.

Although NiZn-based ferrite has been mainly described as the preferred ferrite, any ferrite other than this can be used as long as it has characteristics equivalent to those of NiZn-based ferrite. Nor.

In the planar magnetic element of the present invention, the shape of the planar coil is preferably a rectangular spiral as shown in FIG. In such a rectangular spiral coil, the shape of the outermost coil terminal is shown in FIG.
As shown in (3), it is more advantageous to make the connection area with the external electrode on the back side larger by making the triangle larger. Further, the coil shape does not necessarily have to be rectangular, and as shown in FIG. 2 (b), the coil wire has an elliptical spiral shape, and the width of the coil wire of the portion corresponding to the short side coil corresponds to the long side. It may be made wider than the width of the coil wire of a part.

As the material of the plane coil, it is preferable to use a conductor material having a low specific resistance, and examples of such a material include Ag (1.47 × 10 ⁻⁸ Ω · m) and Cu (1.55 × 10 ^−8). Ω
・ M). Since Ag is more expensive than Cu, a plane coil made of a Cu conductor is more suitable for the coil of the plane magnetic element.

Next, a preferred method for manufacturing the planar magnetic element of the present invention will be described. First, the lower ferrite magnetic layer is formed by applying a paste containing ferrite magnetic powder on a substrate such as silicon or alumina by using a thick film forming method such as screen printing, and then applying 800
The ferrite magnetic layer may be formed by firing at about 1000 ° C., or a thin ferrite sintered plate manufactured separately may be used as it is. The preferable thickness of such a sintered plate is about 0.2 to 0.6 mm.

Then, if necessary, a resin coat (polyimide or the like) having a thickness of several μm is applied to smooth the surface, and then a Cu film having a thickness of 0.5 μm is formed thereon by electroless plating as an underlayer for coil formation. The film is formed to a degree. Then, a photoresist is applied on the base plating layer, and then a resist frame having a desired coil shape is formed by photoetching. Subsequently, by electroplating, after depositing Cu in the resist frame, the resist is peeled off,
Then, the underlying plating layer between the coil wires is removed by chemical etching to form a plane coil on the lower ferrite magnetic layer. At this time, it is preferable to also form the coil terminal.

After that, a resin paste in which a resin such as an epoxy resin or a polyimide resin and ferrite powder are mixed is applied by a printing method on the flat coil including the space between the coil wires, and then a heat curing treatment is applied to the upper portion. A ferrite magnetic layer is formed. In forming the upper ferrite magnetic layer, the curing temperature of the resin paste is preferably about 150 to 400 ° C.

When the lower ferrite magnetic layer is formed on the substrate, silicon is suitable as the substrate material at low cost, but alumina or ferrite magnetic substrate may be used. When the ferrite magnetic substrate is used, the lower ferrite step is unnecessary. When a lower ferrite is formed on a silicon or alumina substrate, the element portion may be peeled off from the substrate or the substrate may be scraped off to form a substrate-free planar magnetic element.
In this case, further thinning can be achieved.

Further, according to the present invention, a switching power supply can be manufactured by mounting the above planar magnetic element. The planar magnetic element described above is not only small and lightweight, but also can greatly reduce the coil DC resistance. Therefore, by using such a planar magnetic element, it is possible to reduce the size and weight of the switching power supply. , A significant improvement in energy efficiency can be achieved.

In addition, such a rectangular planar magnetic element is
When connecting to the switching power supply body, it is connected via an external electrode. For example, as shown in Fig. 3 (a), the outermost coil terminal part on the back side of the planar magnetic element and the middle window of the center part When the external electrode is provided only on the coil terminal portion of the portion, when the planar magnetic element is actually attached, it is not possible to know which of the left and right ends the external electrode is provided. However, regarding this point, as shown in FIG. 3 (b), by increasing the electrode area of the coil terminal portion of the middle window portion to the end region opposite to the outermost coil terminal portion, Such inconvenience can be eliminated.

[0030]

EXAMPLES on a silicon _{substrate, Fe 2 0 3 / ZnO /} CuO / Ni
A paste containing ferrite magnetic powder having a composition of O = 49/23/12/16 (mol%) was formed as a lower ferrite layer having a long side of 4 mm and a short side of 3 mm by a screen printing method. Subsequently, it was fired at 950 ° C in the atmosphere. The film thickness after firing was 40 μm. Next, a polyimide resin was applied onto the ferrite magnetic layer by spin coating and then heat-cured to form a smooth layer having a thickness of 3 μm. Subsequently, a Cu film having a thickness of 0.5 μm was formed as an underlying plating layer on this by electroless plating. Next, a photoresist was applied on the underlying plating layer, and then a photoresist frame of a rectangular spiral coil was formed by photoetching from a position of 50 μm from the outer peripheral portion of the lower ferrite layer to a range of 550 μm in the middle window. After that, Cu is deposited to 70 μm in the resist frame by electroplating, and then
The resist frame is peeled off, and then the base plating between the coil wires is removed by chemical etching, as shown in FIG.
A plane coil was produced. At this time, the width d of the coil wire parallel to the long side is 60 μm, and the interval s between the coil wires is 25 μm.
The number of turns n of the coil was fixed at 14, and the width e of the coil wire parallel to the short side was variously changed as shown in Table 1.

[0031] _{Then, Fe 2 0 3 / ZnO /} CuO / NiO = 49/23
An epoxy resin paste containing ferrite magnetic powder having a composition of / 12/16 (mol%) was formed as an upper ferrite layer by a screen printing method, and heat-cured at 150 ° C. The film thickness from the coil top after thermosetting was 100 μm.
Each planar magnetic element thus obtained was used as a coil of a switching power supply having a circuit as shown in FIG.
Driven by. Input and output are 3.8 V / 1.5 V, 0.1 A. Table 1 also shows the results of examining the shape of the inductor, the coil DC resistance Rdc, and the energy efficiency of the switching power supply at this time.

[0032]

[Table 1]

As is apparent from Table 1, when the planar magnetic element according to the present invention is used as a coil of a switching power supply, it is possible to achieve a low DC resistance and high efficiency as compared with the conventional one.

[0034]

As described above, according to the present invention, it is possible to obtain a planar magnetic element which is small in size and lightweight and has a greatly reduced coil DC resistance. Further, according to the present invention, by mounting the above planar magnetic element, it is possible to obtain a switching power supply which is also lightweight and small in size and excellent in energy efficiency.

[Brief description of drawings]

FIG. 1 is a diagram showing a shape of a rectangular spiral coil suitable as a planar coil of a planar magnetic element according to the present invention.

FIG. 2 is a diagram showing the shapes of another example (a) of a rectangular spiral coil and an elliptical spiral coil (b) suitable as a planar coil of a planar magnetic element according to the present invention.

FIG. 3 is a diagram showing the shape of an external electrode provided on the back surface of the planar magnetic element.

FIG. 4 is a diagram showing the shape and dimensions of a rectangular spiral coil formed in an example.

FIG. 5 is a diagram showing a circuit of a switching power supply.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideaki Kohioki             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. F-term (reference) 5E049 AB03                 5E070 AA01 AA11 BA12 CB03 CB12

Claims (3)

[Claims] 1. A planar magnetic element having a planar coil on the surface of a lower ferrite magnetic layer, and an upper ferrite magnetic layer including a gap between coil wires of the planar coil, and having a rectangular shape as a whole. In the flat magnetic element, the width of the coil wire of the flat coil parallel to the short side of the flat magnetic element is made wider than the width of the coil wire parallel to the long side. 2. The flat magnetic element according to claim 1, wherein a long side length of the planar magnetic element is a, a long side length of the middle window is f, a width of a coil wire parallel to the long side is d, a coil wire interval is s, The width e of the coil wire parallel to the short side satisfies the following expression d <e ≦ (a−f + s) / 2 n, where n is the number of turns in the plane magnetic element. 3. A switching power supply comprising the planar magnetic element according to claim 1 or 2.