JPH03280511A - Heat treatment of ferromagnetic foil in a magnetic field - Google Patents

Abstract

PURPOSE:To manufacture a plane inductor having excellent heat dissipating characteristics and direct current superimposing characteristics by a method wherein the heat treatment is performed while feeding a current to plural coils so as to make the adjacent coils generate magnetic fluxes mutually in reverse directions and then magnetization facilitating axes of easy magnetization are given to ferromagnetic body foils. CONSTITUTION:Four square spiral coils are juxtaposed on the same plane so that outer peripheral parts may take a larger square shape in twice as much length of one side of respective spiral coils to be connected for feeding a current making magnetic flux on adjacent coils mutually in reverse directions. Next, intensive magnetic body foils are overlapped on one or both surfaces of the coils in the central parts of the plane coils for heat treatment in magnetic field and then direct current is fed to the coils. Next, the heat treatment is performed at the temperature lower than the Curie temperature of the ferromagnetic body to give a magnetization facilitating axes turning in the peripheral direction to the ferromagnetic body foils. Furthermore, the coils may be miniaturized without restricting to the four coils.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for heat-treating ferromagnetic foil in a magnetic field, which is used to obtain a planar interfter with improved DC superimposition characteristics.

(Prior Art) Conventionally, a planar inductor is known which has a structure in which a spiral or zigzag conductor coil is sandwiched between ferromagnetic layers on both sides via an insulating layer. FIG. 1(A) is a plan view showing an example of such a planar inductor, and FIG.
) is a sectional view taken along line AA' in FIG.

1 in FIG. 1 is a viral conductor coil.

The spiral conductor coil 1 has spiral coils 2a and 2b provided on both sides of an insulating layer 3b. The spiral coils 2a, 2b are electrically connected via a through hole 4 so that electricity flows in the same direction through each spiral coil 2a, 2b.

Here, the solid line and the broken line in FIG. 1(A) indicate the spiral coil 2 on the front side and the back side of the insulating layer 3b, respectively.
It represents the locus of the center of a and 2b. A planar inductor is constructed by sandwiching both surfaces of this spiral conductor coil l between ferromagnetic ribbons or ferromagnetic thin films 5a and 5b via insulating layers 3a and 3c. An inductance is formed between the terminals 6a and 6b of the planar inductor made of the above members.

(Problems to be Solved by the Invention) Such a planar inductor is applied, for example, to a choke coil on the output side of a DC-DC converter. In this case, since a high frequency current with a superimposed direct current flows through the planar inductor, good direct current superimposition characteristics are required.

However, conventional planar inductors have a problem of poor DC superimposition characteristics. This is because the magnetic properties of conventionally used ferromagnetic ribbons are inappropriate. In other words, in the case of the planar inductor shown in Figure 1, the magnetic flux is 5g of ferromagnetic ribbon on both sides.
, 5b in the in-plane direction. Therefore, in order to obtain high inductance, a high magnetic permeability ferromagnetic ribbon is required. However, when the saturation magnetization of the high permeability ferromagnetic ribbon is low, even if a small direct current magnetic field is superimposed, the magnetic flux density is saturated, the inductance is reduced, and the direct current superposition characteristics are deteriorated.

For example, a CO-based amorphous alloy is known as a high permeability ferromagnetic material. However, although its saturation magnetization is higher than that of ferrite, it is not sufficient, and its DC superimposition characteristics are poor.

Note that even when a CO-based amorphous alloy is used as the ferromagnetic ribbon, the direct current superimposition characteristics can be improved to some extent by stacking the CO-based amorphous alloy. However, if the amorphous alloy is laminated, the thickness of the planar inductor increases accordingly, so there is a problem that the planar inductor cannot be made thin.

If the DC superimposition characteristics of the planar inductor are poor as described above, the inductance will decrease and control will become difficult, resulting in DC-DC
Converter efficiency decreases. As a result, there was a problem that it could not be applied to DC-DC converters and the like.

Furthermore, the planar inductor has a so-called outer iron type structure, which has ferromagnetic layers on both sides of the planar coil. For this reason,
The Joule heat generated by the coil current has poor heat dissipation.
The temperature of a planar inductor tends to rise.

For example, when applied to a choke coil on the output side of a DC-DC converter, a large direct current (for example, about 0.5 A in a 2W class) flows through the planar inductor, so the temperature of the planar inductor increases considerably.

On the other hand, the effective magnetic permeability of the high magnetic permeability material used for the ferromagnetic layer generally changes significantly as the temperature rises, and the inductance of the planar inductor also changes significantly. Therefore, DC-
Problems such as a decrease in the control performance of the DC converter and a decrease in efficiency may occur.

Therefore, in order to solve such problems, it is necessary to improve the heat dissipation properties of the planar inductor and reduce the temperature rise.

The present invention has been made to solve these problems, and is a method of heat treatment in a magnetic field for a ferromagnetic layer that can obtain a planar inductor with excellent heat dissipation characteristics and good direct current superimposition characteristics. It provides law.

[Configuration of the Invention (Means and Effects for Solving the Three Problems) The present invention provides a method in which a plurality of spiral coils are arranged on the same plane, and current is applied so that magnetic fluxes in opposite directions are generated in the adjacent spiral coils. A planar coil for heat treatment in a magnetic field is configured by connecting the plurality of spiral coils in a flowing manner to form a region in which a magnetic flux loop is drawn in this plane, and then the planar coil for heat treatment in a magnetic field is formed. A ferromagnetic layer is stacked on the magnetic flux loop region, and while direct current is flowing through the coil, this is then heat-treated at a temperature lower than the Curie temperature of the ferromagnetic material to create an axis of easy magnetization in the ferromagnetic layer. This is a method of heat treatment in a magnetic field for a ferromagnetic layer.

The magnetic flux loop may be one that draws a loop when viewed as a direction even if the direction of the magnetic flux is different. More specifically, four square spiral coils are arranged on the same plane so that the outer periphery is 2 times the length of one side of each spiral coil.
A planar coil for heat treatment in a magnetic field is constructed by arranging the four spiral coils so as to form a double square shape and connecting the four spiral coils so that current flows in the adjacent spiral coils so that magnetic fluxes in opposite directions occur. Next, a ferromagnetic material layer is placed on one or both sides of the coil in the center of the planar coil for heat treatment in a magnetic field, and a direct current is passed through the coil, and then the Curie temperature of the ferromagnetic material is applied to the coil. This is a method for heat-treating a ferromagnetic layer in a magnetic field, characterized in that the ferromagnetic layer is heat-treated at a temperature lower than that of the ferromagnetic layer to provide the ferromagnetic layer with an axis of easy magnetization that rotates in the circumferential direction. Note that it goes without saying that the number of coils is not limited to four and may be further subdivided.

Here, the spiral conductor coil usually refers to a spiral two-layer conductor coil having a structure in which spiral coils are provided on the front and back surfaces of an insulating layer and each spiral coil is connected by a through hole, as shown in Fig. 1, for example. .

Note that the spiral conductor coil may have only one layer of spiral coils as long as there is no problem in taking out the terminal. Furthermore, when spiral conductor coils are stacked, the inductance increases, but in this case, it is preferable to interpose only an insulating layer between the spiral conductor coils and not to interpose a ferromagnetic ribbon. This is because interposing a ferromagnetic ribbon between spiral conductor coils hardly contributes to increasing inductance, but rather increases the overall thickness of the planar inductor and lowers the inductance per unit volume. .

Further, it is preferable that the planar conductor coil is a spiral coil provided on a ceramic plate with good heat dissipation, such as an AfiN plate.

In other words, as an insulator with high thermal conductivity, for example, AI
N etc. are known. When comparing the thermal conductivity of /IN at room temperature with other insulators, even Af1203, which has a relatively high thermal conductivity, has a value of about 35 W/m-, but Al)N has a value of 70 W/m-. - It has a fairly large value.

Further, the dielectric constant of these ceramics having good thermal conductivity is preferably small. That is, if a substrate made of A, 9N, etc. is used as the substrate of the spiral coil, the Joule heat generated by the coil current is radiated from the side surface of the planar inductor through the substrate made of AgN, etc. As a result, compared to the case where another insulator is used for the substrate of the spiral coil, the temperature rise of the planar inductor can be reduced, and a planar inductor with good heat dissipation properties can be obtained.

Note that the coil is not limited to a spiral shape, but may also be a zigzag shape.

Generally, when magnetic anisotropy is imparted to a magnetic material, if an attempt is made to magnetize it in a direction perpendicular to the axis of easy magnetization, a large magnetic field is required to saturate the magnetization. In other words, in the case of a planar inductor, if an axis of easy magnetization is provided in a direction perpendicular to the direction of magnetic flux flowing in the magnetic foil provided on both sides of the spiral coil or its laminate, DC current will flow through the coil. However, magnetization is difficult to saturate. Therefore, the inductance does not drop significantly, and excellent DC superimposition characteristics of inductance can be obtained.

On the other hand, the magnetic path in the planar inductor is oriented radially toward the periphery from the center, as shown in FIG. Therefore,
By using a magnetic foil having an axis of easy magnetization in the circumferential direction perpendicular to the magnetic path, a planar inductor with good DC superimposition characteristics of inductance can be obtained.

Examples of the present invention will be described in detail below.

Example 1 The spiral coil was made of a double-sided F made of a 25 μm thick polyimide film (insulating layer 3b) covered with 100 μta thick Cu foil on both sides and connected through the through hole 4 in the center.
A PC board (flexible printed circuit board) was used. The Cu foil on both sides of this FPC board is etched, and the external dimensions are 2.
0+amX20 connection.

Number of windings: 40. Coil line width 250μm, coil pitch 50
Spiral coils 2a and 2b with 0μ buttons were obtained.

The magnetic material had a width of 25 mm and an average thickness of 16 μm (COo, ssF e 6,66N b
O,02N j O,04) 75S j roB +
One side cut from an amorphous alloy ribbon with composition s is 25
−■ Square-shaped foil was used.

When giving the magnetic foil an axis of easy magnetization in the circumferential direction, a planar coil as shown in FIG. 3 was used.

That is, the four double-sided spiral coils were arranged in the same plane, and the four spiral coils were connected in such a way that current flowed in the adjacent spiral coils so that magnetic flux was generated in opposite directions.

FIG. 3 shows the locus of the center point of the spiral coil. The solid line and the dashed line indicate the locus of the center point of the spiral coil on the front and back sides of the base film, respectively.

A magnetic foil is placed on top of this coil, and a direct current (arrow) is applied.
When a magnetic flux is passed through the magnetic foil, the direction of the magnetic flux is as shown in FIG. 4 (CB). In the figure, the direction of magnetic flux in the magnetic foil is indicated by thick arrows. In other words, as shown in Figure 4(b), when a magnetic foil is placed in the center of this coil and a direct current is passed through the coil, it becomes magnetized in the direction of the large arrow.
In this state, when heat treatment is performed at a temperature below the Curie temperature without passing a direct current, magnetic anisotropy is imparted to the magnetic foil in the circumferential direction. If a magnetic foil is stacked on the underside of this coil, magnetic anisotropy is imparted in the same direction as that of the foil stacked above, although the direction is opposite.

In Example 1, as a coil for imparting magnetic anisotropy,
Four spiral coils were arranged and connected as shown in Figure 3. Amorphous alloy foils that had been heat-treated for strain relief in advance were stacked on both sides of the coil, and heat-treated in N2 gas at 200° C. for 30 minutes while passing a direct current of 0.2 A through the coil to impart magnetic anisotropy.

On both sides of the spiral coil obtained in this way, a thickness of 7
A planar inductor was fabricated by laminating amorphous alloy foils imparted with magnetic anisotropy via a μm polyimide film.

Comparative Example 1 A planar inductor was produced in the same manner as in Example 1, except that an amorphous alloy foil not imparted with magnetic anisotropy was used.

Regarding the planar inductors of Example 1 and Comparative Example 1, 10
FIG. 5 shows the results of measuring the DC superposition characteristics of the inductance L at kllz. As is clear from FIG. 5, it was confirmed that the DC superimposition characteristics of L were improved by using a ferromagnetic layer with an easy axis of magnetization in the circumferential direction using the method of the present invention.

Next, an embodiment of the present invention in which the heat dissipation characteristics are further improved will be described.

Example 2 A laminate prepared by adhering 100 μm thick copper foil to both sides of a 200 μm thick jIN group was etched on both sides.

As a result, the external dimensions are 10 degrees.

Number of windings: 40. Coil wire width 200μ, coil wire pressure 100
A square double-sided spiral coil with a μ plow and a coil wire pitch of 250 μm was obtained. A planar inductor was fabricated by laminating ferromagnetic layers on both sides of this double-sided spiral coil with a polyimide film having a thickness of 7 μm interposed therebetween.

The ferromagnetic layer had a width of 25 mm and a thickness of 15 μm (COo, ssFeo, o6Nbo) manufactured by a single roll method.

02N j O, 04) 7. 1, which was cut out from an amorphous alloy ribbon having the composition S i +oB +.
A 5 mm foil was used.

Comparative Example 2 200 μm thick polyimide film (thermal conductivity 0.9
By etching both sides of a laminate made by adhering copper foil with a thickness of 100 μg to both sides of the W/m-k), the external dimensions were 10 and the number of turns per fin was 40. A square double-sided spiral coil with a coil wire width of 200 μm, a coil wire pressure of 100 μm, and a coil wire pitch of 250 μm was produced. A planar inductor was manufactured by the same method as in Example 2 except that this double-sided spiral coil was used.

The temperature rise value of the coil was calculated from the rise value of the coil resistance after a direct current of 0.5 A was continuously passed through the planar inductors of Example 2 and Comparative Example 2 for 10 minutes.

As a result, the temperature increase value for the planar inductor of Example 2 was 13°C, and the temperature increase value for the planar inductor of Comparative Example 2 was 120°C.

[Effects of the Invention] As detailed above, according to the magnetic field heat treatment method according to the present invention, it is possible to easily obtain a planar inductor having excellent heat dissipation characteristics and good DC superimposition characteristics.

[Brief explanation of the drawing]

FIG. 1(A) is a plan view of a planar inductor according to the present invention, FIG. 1(B) is a sectional view taken along line AA' in FIG. 1(A), and FIG. Figure 3 is a plan view of a coil used to impart magnetic anisotropy in the circumferential direction to the magnetic material layer, and Figure 4 (a) is a diagram showing the coil used to impart magnetic anisotropy to the magnetic layer. Figure 4 (b) is a diagram showing the direction of magnetic flux generated in the magnetic foil when a magnetic material is stacked on top of the coil and a DC current is passed through the coil. A diagram showing how magnetic anisotropy is imparted to the amorphous alloy foil in the circumferential direction when alloy foils are stacked and a DC current is passed through the coil. Figure 5 is a diagram showing the DC superposition characteristics of the inductance of a planar inductor. It is. 1...Spiral conductor coil, 2a, 2b...Spiral coil, 3a, 3b, 3c...
- Insulating layer, 4... Through hole, 5a, 5b... Ferromagnetic material, 6... Magnetic flux. (A) b b CB) Fig. 4 (a) (b) Fig. 4 0.1 0.2 3 0.4 0.5 DC superimposed current (A) Fig.

Claims (1)

[Claims] A region in which a plurality of spiral coils are arranged on the same plane, and the plurality of spiral coils are connected so that a current flows so that magnetic fluxes in opposite directions are generated in the adjacent spiral coils, and a magnetic flux loop is drawn within this plane. A planar coil for heat treatment in a magnetic field is constructed so as to form a magnetic field heat treatment, and then a ferromagnetic foil is placed over the magnetic flux loop region formed by the planar coil for heat treatment in a magnetic field, and while a direct current is passed through the coil, the following A method for heat-treating a ferromagnetic foil in a magnetic field, characterized in that the ferromagnetic foil is heat-treated at a temperature lower than the Curie temperature of the ferromagnetic material to impart an axis of easy magnetization to the ferromagnetic foil.