JP2005109173A - Planar magnetic element for non-contact charger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a safe magnetic element for a non-contact charger in which temperature rise is suppressed by remarkably improving heat dissipating property with respect to the magnetic element mounted on the non-contact charger. <P>SOLUTION: The planar magnetic element for non-contact charger having a structure in which a plane coil is buried in one side of a magnetic layer while exposing the upper surface thereof, comprises a dummy electrode arranged on the other side of the magnetic layer, in addition to a coil terminal electrode for the plane coil. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a planar magnetic element mounted on a non-contact charger, and in particular, achieves a significant reduction in thickness.

  With the spread of information technology in recent years, mobile phones and electronic information terminals are rapidly becoming smaller, thinner and lighter. In connection with this, the form driven with a secondary battery like a Li ion battery or a nickel metal hydride battery is often used.

  However, since a portable device is often provided near the human body and there is a possibility of causing a problem in reliability when the contact is exposed, a contactless charging system is desired.

  Until now, the non-contact charging system has been mainly used for water-related devices such as electric toothbrushes and shavers, but recently, for example, as shown in Patent Document 1, it is also used for portable information devices such as mobile phones and PHS. Accordingly, there is a demand for weight reduction, size reduction, and thickness reduction.

  In particular, as a thin type, there is an example of card-type non-contact charging (see Non-Patent Document 1, Non-Patent Document 2, etc.).

  A magnetic element in such a contactless charging system employs a structure in which a copper wire is wound around a ferrite plate or an amorphous ribbon, or an air-core coil structure.

However, these conventional magnetic elements have the following problems due to their structure.
(1) Since the coil thickness is about 1 mm and the dimensions are as large as several centimeters, the occupied area and volume are large, which hinders the downsizing and thinning of the equipment.
(2) Since the magnetic flux from the power transmission side crosses the coil, the loss due to the eddy current generated in the power receiving coil is large.

  On the other hand, a planar magnetic element for a non-contact charger using a ferrite magnetic film formed by a printing method is known (see Patent Document 2). This flat magnetic element is formed by forming a flat coil by a plating method, etc., and then forming a high-resistance ferrite magnetic film by printing and thermosetting a magnetic paste in which an epoxy resin is mixed with ferrite powder on the flat coil. Of course, it has succeeded in improving the charging efficiency.

  However, the magnetic element having such a structure is provided with only the coil terminal electrode, and the heat radiation of the element is only heat transfer to the printed circuit board or the like through the two electrodes and air dissipation.

In the non-contact charger, the power transmission / reception coil is arranged on the surface of the casing of the charger and the portable device or in the vicinity thereof, so the temperature rise of the coil element when the output is increased corresponding to the load increase on the power receiving side It is often directly related to the temperature rise of the housing. Since there should be no accident in which the vicinity of the power transmission coil of the charger and the power reception coil of the portable device is overheated and a human touches the hand, ΔT < 25 ° C (temperature T <50 ° C), and stricter requirements are imposed compared to ordinary power supply coils.
JP 2000-78763 A JP 2002-299138 A Kanai et al: IEEE APEC Record, pp.1157-1162 (2000) Kanai et al .: MAG-00-150

  The present invention has been developed in view of the above-described situation, and for a magnetic element mounted on a non-contact charger, a safe magnetic element for a non-contact charger that significantly improves heat dissipation and suppresses temperature rise. The purpose is to provide.

  As a result of intensive studies to achieve the above object, the present inventors have embedded a planar coil on one side of the magnetic layer with its upper surface exposed, and more preferably one in addition to the coil terminal electrode. It has been found that the intended purpose is advantageously achieved by arranging the above dummy electrodes on the other surface of the magnetic layer.

  The present invention has been made based on the above findings.

That is, this invention is a planar magnetic element for non-contact chargers described in the following items.
1 A planar magnetic element for a non-contact charger having a structure in which a planar coil is embedded with an upper surface exposed on one side of a magnetic layer, and in addition to the coil terminal electrode of the planar coil on the other surface of the magnetic layer A planar magnetic element for a non-contact charger, comprising a dummy electrode.
2. The planar magnetic element for a non-contact charger according to 1 above, wherein the magnetic layer is composed of a ferrite magnetic body, and the volume fraction of the ferrite magnetic body in the magnetic layer is 25 vol% or more.
3. The planar magnetic element for a non-contact charger according to 1 or 2 above, wherein the magnetic layer is made of a magnetic material having a relative permeability of 5 or more.
4 The width and thickness of the coil wire of the planar coil is in the range of 0.25 to 4 times the skin thickness δ represented by the following formula, respectively, for the non-contact charger according to any one of the above 1 to 3 Planar magnetic element.

Δ = {2 / (μ × σ × ω)} ^1/2
Where μ: permeability (H / m),
σ: electrical conductivity (S / m),
ω: angular frequency (rad / s).
5. The flat magnetic element for a non-contact charger according to any one of the above 1 to 4, wherein the total thickness of the magnetic layer, the flat coil, and the electrode is less than 1 mm.

  According to the present invention, it is possible to obtain a thin magnetic element for a non-contact charger, in which the temperature rise during charging is extremely small.

  A typical planar magnetic element according to the present invention is schematically shown in FIG.

  The coil shape may be either a spiral type or a meander type, and the spiral type may be one or a combination of two or more. In FIG. 1, a spiral type is shown as an example.

  By arranging the upper surface of the planar coil 2 exposed from the magnetic layer 1 so as to face the power transmission coil (not shown here), the magnetic flux generated in the power transmission coil is separated between the lines of the planar coil 2 that is the power reception coil. And can be taken into the magnetic layer on the lower surface, so that power can be effectively transmitted to the receiving coil.

  In the present invention, an electrode for external connection is formed on the surface of the magnetic layer opposite to the planar coil 2. Of the formed electrodes, the one joined to the coil terminal is called the coil terminal electrode 9, and the one not joined is called the dummy electrode 10. These electrodes are used after being bonded to a printed circuit board or the like.

Conventionally, only the coil terminal electrode is used, but by arranging the dummy electrode in the present invention, the heat generated by the planar magnetic element can be radiated from the magnetic layer to the printed circuit board via the dummy electrode. As the amount of heat radiation increases, the temperature rise of the planar magnetic element is suppressed, and as shown in FIG. 4, the temperature can be lowered if the same power receiving side output (output current I ₀ ) is used (in FIG. 4). A), if the temperature rises the same, a higher output (b in FIG. 4) can be used.

  By joining directly to the formed heat dissipation structure (thermal via, heat spreader, heat sink, etc.), an extremely large heat dissipation effect can be obtained.

  Here, the number arrangement of the dummy electrodes 10 is not limited to that shown in FIG. Individual electrodes may have different shapes and sizes. For example, as shown in FIGS. 3 (a) and 3 (b), the coil terminal electrode 9 and the dummy electrode 10 can be enlarged to increase the heat dissipation. An effect can also be obtained.

  As shown in FIG. 3C, it is possible to obtain a heat dissipation effect even if the coil terminal electrode 9 is enlarged without using a dummy electrode, but it causes noise dissipation. For this reason, the coil terminal electrode cannot be bonded to the heat dissipation structure of the substrate described above, and the heat dissipation effect is limited.

  The electrode is pre-fired on the ferrite substrate with the vias of the coil terminals by simultaneous firing, such as Ag, Cu, Ni, Au, etc., or Cu formed by a plating method such as electroless plating or barrel plating after coil formation, An electrode having a laminated structure such as Ni, Sn, or Au, or an electrode obtained by combining these techniques is preferable for improving the heat dissipation effect. In addition, it is important to finish the electrode with a surface suitable for bonding during mounting. Here, the bonding includes solder bonding, wire bonding bonding, flip chip bonding, and the like.

  Moreover, although the example which connected the coil terminal 4 and the coil terminal electrode 9 via the via hole of a magnetic layer is shown in FIG. 1, the structure to connect is not restricted to this.

  Next, in the second aspect of the invention, the volume fraction of the ferrite magnetic material in the magnetic layer is set to 25 vol% or more. Below this, the magnetic coupling between the power transmitting coil on the charger side and the power receiving coil on the device body side ( (This is expressed by the coupling coefficient k shown in the following equation.) Is reduced, and sufficient charging characteristics cannot be obtained.

k = M / (L ₁ × L ₂ ) ^1/2
Where M: Mutual inductance (H)
L ₁ : Self-inductance of transmission coil (H)
L ₂ : Self-inductance of receiving coil (H)
The volume ratio is not necessarily the same for the entire magnetic element, and a magnetic material having one or more volume ratios can be used depending on the location.

  In the invention of 3 above, the relative permeability of the magnetic layer is set to 5 or more by concentrating the magnetic flux from the power transmission coil on the magnetic layer and reducing the magnetic flux crossing the planar coil, thereby reducing the eddy current loss in the coil. This is because it can be reduced. Moreover, if the relative permeability is less than 5, the magnetic coupling between the power transmission coil on the charger side and the power reception coil on the device body side becomes small, and sufficient charging characteristics cannot be obtained.

  The relative magnetic permeability does not necessarily have to be the same for the entire magnetic element, and a magnetic material having one or more relative magnetic permeability can be used depending on the location.

  Here, the magnetic layer may be composed of a ferrite sintered body or a mixture in which ferrite magnetic powder is dispersed in an insulating material such as a resin. Moreover, what combined these partially may be used. In this way, the relative permeability of the magnetic layer can be changed.

  As the ferrite magnetic body in the present invention, NiZn ferrite which is an insulator is suitable. The composition is not particularly limited, but the representative composition is as follows. In addition, this composition does not necessarily need to be the same composition in the whole magnetic element, and can change a composition suitably according to a place.

Fe ₂ 0 ₃ : 40 to 50 mol%
When Fe ₂ 0 ₃ exceeds 50 mol%, the electric resistance value decreases abruptly due to the presence of Fe ²⁺ ions. The decrease in electrical resistance not only causes a sudden increase in loss in the ferrite core due to the generation of eddy currents when used in a high frequency region, but also causes an electrical short circuit at the portion in contact with the coil or terminal. Further, since a large deterioration of the inductance associated with the less than 40 mol% to the permeability reduction in the ferrite, Fe ₂ 0 ₃ is preferably about 40~50mol%.

ZnO: 15-35mol%
ZnO has a large effect on inductance and Curie temperature. The Curie temperature is an important parameter that determines the heat resistance of the magnetic element. Below 15 mol%, the Curie temperature is high, but the inductance decreases. On the other hand, when it exceeds 35 mol%, although the inductance is high, the Curie temperature decreases. Therefore, ZnO is preferably about 15 to 35 mol%.

CuO: 20mol% or less
CuO is added to lower the firing temperature. However, if it exceeds 20 mol%, the firing temperature is lowered but the inductance is deteriorated. Therefore, CuO is preferably about 20 mol% or less.

Bi ₂ 0 ₃ : 10 mol% or less
Bi ₂ 0 ₃ has the effect of lowering the firing temperature, like CuO. However, although more than 10 mol% and calcination temperature is lowered, since the inductance is deteriorated, Bi ₂ 0 ₃ is preferably on the order or less 10 mol%. The balance is NiO.

  As described above, the NiZn-based ferrite has been mainly described as a suitable ferrite, but it goes without saying that any other ferrite can be used as long as it has the same characteristics as the NiZn-based ferrite.

  In the present invention, the thickness of the ferrite magnetic layer is preferably about 5 to 500 μm. By adjusting the volume density of the magnetic material, it is possible to adjust the thickness of the appropriate magnetic layer. However, if this thickness is less than 5 μm, the effect of capturing magnetic flux from the power transmission side is poor, while if it exceeds 500 μm, the magnetic element This is because it becomes thick and obstructs the thinning of the device.

  In the fourth aspect of the invention, the thickness and width of the coil wire are each defined within a preferable range. When a high-frequency current is passed through a coil having a coil wire thickness or width equal to or greater than the skin thickness δ, the current concentrates on the coil surface, does not flow through the center of the coil, and the AC resistance increases with frequency. However, if these values are made equal to the skin thickness, the coil cross-sectional area becomes small and the direct current resistance becomes large. As a result, when it is mounted on a circuit in which direct current is superimposed, the loss becomes large. In order to avoid this, a coil in which the thickness and width of the coil wire is divided to the skin thickness has been used, but not only does the downsizing of the element be impaired because the space that insulates between the coils increases. It has become clear that there is a limit in reducing the coil loss due to the proximity effect.

  Therefore, as a result of various studies on combinations that minimize the sum of the loss due to AC resistance and the loss due to DC resistance under the environment where the contactless charger is used as a power transmission / reception coil, the thickness and width of the coil wire are as follows. It has been found that it is effective to set the skin thickness δ represented by the formula to 0.25 times or more and 4 times or less.

δ = {2 / (μ × σ × ω)} ^1/2
If the thickness and width of the coil wire is less than 0.25 times the skin thickness δ, the coil direct current resistance increases and the coil heat generation increases. On the other hand, if it exceeds four times, the direct current resistance is reduced, but the alternating current resistance due to the skin effect is increased, leading to an increase in the loss as a whole, and the size of the magnetic element is increased. In addition, it is 0.4 times or more and 2 times or less more suitably.

  In the present invention, the thickness of the coil is preferably about 5 to 200 μm. If this thickness is less than 5 μm, the resistance of the coil increases and the loss increases. To compensate for this, it is necessary to make the width of the coil wire extremely wide. However, since the coil wire length increases as the line width increases, there is a limit to the reduction in coil resistance, and the magnetic element Increases the occupied area of the device and hinders downsizing of the device. On the other hand, when the thickness of the coil exceeds 200 μm, it becomes difficult to form the coil by both the additive method and the subtract method, and further, the space between the coil wires needs to be increased to fill the space between the coil wires with a ferrite magnetic material. Occupied area increases, preventing miniaturization of equipment.

  Here, the planar magnetic element of the present invention may be used as it is, but in order to protect the surface, as shown in FIG. 2, the exposed surface of the coil is made of an epoxy resin, a polyimide resin or the like. It is preferable to cover the protective film 5 made of a nonmagnetic and electrically insulating material such as an insulating resin or glass. Further, in addition to such a coating, covering the coating or the side opposite to the planar coil 2 with a reinforcing base material 6 such as a non-magnetic and high thermal conductivity thin plate material such as ceramics such as alumina or aluminum nitride, silicon, etc. This is effective not only for ensuring the heat dissipation but also for improving the heat dissipation. However, since the protective coating on the surface of the planar coil and the reinforcing substrate act as a magnetic gap, the total thickness of the protective coating and the reinforcing substrate is preferably less than 0.5 mm.

  From the above, it is preferable that the thickness of the planar magnetic element of the present invention is less than 1 mm in total of the magnetic layer, the planar coil, and the electrode.

  When the thickness is 1 mm or more, the heat conduction is deteriorated, and sufficient heat radiation cannot be performed, and the planar magnetic element may be overheated.

  A 25 μm thick polyimide resin film with a 1 μm thick Cu film formed in advance on one side is bonded to a glass substrate with the Cu film as the front, and a photoresist is applied onto this Cu film, and then desired by photolithography. A coil-shaped resist frame was formed. Then, after Cu was deposited in the resist frame by electroplating, the resist was peeled off, and then chemical etching was performed to remove the underlying plating between the coil wires, thereby obtaining a planar coil. At this time, a coil terminal was also formed.

  Thus, a spiral planar coil having a coil wire thickness of 100 μm, a width of 85 μm, an interval of 20 μm and a turn number of 30.5 was produced.

After that, an epoxy prepared by mixing ferrite magnetic powder having a composition of Fe ₂ 0 ₃ : 49.5 mol%, ZnO: 28 mol%, CuO: 8 mol% and NiO: 14.5 mol% so that the volume fraction of ferrite after curing is 50 vol% A resin paste was applied onto the above planar coil by a screen printing method and thermally cured at 150 ° C. to form a ferrite magnetic layer having a thickness of 50 μm from the top surface of the coil. The relative magnetic permeability of this ferrite magnetic layer is 20. Further, a 300 μm thick sintered ferrite plate having a composition of Fe ₂ 0 ₃ : 49 mol%, ZnO: 30 mol%, and NiO: 21 mol% with via holes at the coil terminal position was bonded onto the ferrite magnetic layer. . The relative permeability of this sintered ferrite plate is 900.

  Further, a Cu film having a thickness of 0.5 μm was formed by electroless copper plating at the position of the coil terminal electrode and the dummy electrode on the surface of the sintered ferrite plate. With this as a base, a 10 μm thick Cu film, a 5 μm thick Ni film, and a 5 μm thick Sn film were sequentially laminated by barrel plating to form the coil terminal electrode and the dummy electrode shown in FIG. In the process of forming these electrodes, simultaneously, a coil terminal and a coil terminal electrode were connected by forming a Cu / Ni / Sn film on the inner wall surface of the via hole.

  Finally, the glass substrate was removed together with the adhesive to complete a planar magnetic element having a width of 10 mm × depth of 10 mm × thickness of 0.52 mm.

  The power transmission coil is made by combining an E-type MnZn ferrite core with a winding coil and driven at a frequency of 100 kHz. The above planar magnetic element faces the top surface of the planar coil with a gap of 1.5 mm. The temperature rise ΔT of the planar magnetic element was measured when the output current Io was increased while changing the power receiving side load at an output voltage of 4.5V. The obtained results are shown in FIG. In FIG. 4, as a comparative example, the temperature rise of the planar magnetic element only with the coil terminal electrode (that is, without the dummy electrode) is also shown.

  As is apparent from FIG. 4, in the embodiment of the present invention, the heat dissipation is greatly improved by the arrangement of the dummy electrodes, and the temperature rise is successfully suppressed.

Composition _{Fe 2 0 3: 49.5mol%,} ZnO: 28mol%, CuO: 8mol% and NiO: a 14.5mol%, the external electrodes of Ag on the coil terminal position to the position of the via and the coil terminal electrodes and the dummy electrodes of Ag A Cu film with a thickness of 0.5μm was deposited on the sintered ferrite substrate with a thickness of 500μm (relative magnetic permeability is 700) formed in advance by co-firing by electroless plating. After applying the photoresist, a resist frame having a desired coil shape was formed by photolithography. Thereafter, Cu was deposited in the resist frame by electroplating, and then the resist was peeled off. Then, chemical etching was performed to remove the plating base between the coil wires to obtain a planar coil and a coil terminal.

  Thus, a spiral planar coil having a coil wire thickness of 100 μm, a width of 70 μm, an interval of 20 μm and a turn number of 20.5 was produced.

_{Thereafter, Fe 2 0 3: 49.5mol%} , ZnO: 28mol%, CuO: 8mol% and NiO: a ferrite magnetic powder to be 14.5Mol% of the composition, epoxy resin ferrite volume after curing might be prepared to have 30% A paste was applied to the space between the planar coil wires by a screen printing method, and was thermally cured at 150 ° C. The relative magnetic permeability of this ferrite magnetic layer is 7.

  Next, an epoxy resin insulating protective film having a thickness of about 20 μm was formed on the upper surface of the coil.

  Further, using a Ag electrode formed on a ferrite sintered substrate as a base, a Ni film having a thickness of 5 μm and a Sn film having a thickness of 5 μm were sequentially laminated by barrel plating to form a coil terminal electrode and a dummy electrode.

  Thus, a planar magnetic element having a width of 8 mm, a depth of 8 mm and a thickness of 0.65 mm was completed.

  The power transmission coil is made of a cylindrical MnZn ferrite and driven at a frequency of 300 kHz. The power reception coil is placed close to the 1.Omm gap, and the output is the same as in Example 1. The temperature rise ΔT of the planar magnetic element when the voltage was 4 V × current 0.3 A was measured when only the coil terminal electrode was added and when a dummy electrode was added.

  The obtained results are shown in Table 1.

  As can be seen from the table, the temperature rise is reduced by the addition of the dummy electrode, and the charging operation is possible in a safe temperature range. Further, both the coupling coefficient k and the induced voltage are both large, and it goes without saying that it contributes to the reduction in thickness, and is suitable for non-contact charging.

It is the plane coil side perspective view (a), electrode side perspective view (b), and AA view sectional drawing (c) of the planar magnetic element for typical contactless chargers according to this invention. It is a schematic diagram which shows the example of arrangement | positioning of a protective film and a reinforcement base material. It is a perspective view which illustrates other suitable electrode arrangement of the present invention. It is a graph which shows the dependence with respect to the output current Io of the temperature rise (DELTA) T of the planar magnetic element for non-contact chargers.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic layer 2 Planar coil 4 Coil terminal 5 Protective film 6 Reinforcement base material 9 Coil terminal electrode
10 Dummy electrode
11 Via

Claims (5)

A planar magnetic element for a non-contact charger having a structure in which a planar coil is embedded with an upper surface exposed on one side of a magnetic layer,
A planar magnetic element for a non-contact charger, wherein a dummy electrode is arranged on the other surface of the magnetic layer in addition to the coil terminal electrode of the planar coil.   2. The planar magnetic element for a non-contact charger according to claim 1, wherein the magnetic layer is made of a ferrite magnetic body, and a volume fraction of the ferrite magnetic body in the magnetic layer is 25 vol% or more.   The planar magnetic element for a non-contact charger according to claim 1, wherein the magnetic layer is made of a magnetic material having a relative permeability of 5 or more. The width and thickness of the coil wire of the planar coil are in the range of 0.25 to 4 times the skin thickness δ represented by the following formula, respectively, for a non-contact charger according to any one of claims 1 to 3 Planar magnetic element.
Δ = {2 / (μ × σ × ω)} ^1/2
Where μ: permeability (H / m),
σ: electrical conductivity (S / m),
ω: angular frequency (rad / s).   The flat magnetic element for a non-contact charger according to any one of claims 1 to 4, wherein the total thickness of the magnetic layer, the flat coil, and the electrode is less than 1 mm.

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