GB2184606A

GB2184606A - Method of producing metallic thin film coil

Info

Publication number: GB2184606A
Application number: GB08629907A
Authority: GB
Inventors: Shigeru Watanabe; Osamu Sugiyama; Eigo Hashimoto
Original assignee: Citizen Watch Co Ltd
Current assignee: Citizen Watch Co Ltd
Priority date: 1985-12-20
Filing date: 1986-12-15
Publication date: 1987-06-24
Also published as: JPS62145703A; GB8629907D0

Abstract

On a surface of an insulated substrate 20, an insulating frame 50 in the shape of a spiral is formed and a metallic film having a thickness smaller than the height of the frame is vapor deposited simultaneously on a bottom 54 and a top 52 of the frame to form a first coil 41 on the bottom and a second coil 42 on the top. By connecting these coils in series, the number of turns are doubled, and by connecting them in parallel, electric resistance is reduced by half, so a limited space can be used effectively. The frame 50 is produced by etching a 4-micron layer 51 of photoresist. The undercut portions at 53 ensure the separation of the two coils which are formed by a 2-micron layer of copper, gold, silver or aluminium. The whole surface is then coated with an insulating protective layer. The coils may be circular or square. <IMAGE>

Description

SPECIFICATION Method of producing planar coil BACKGROUND OF THE INVENTION This invention relates to a method of producing a planar coil for use in thin film magnetic heads, inductance devices or the like.

The planar coil is a coil in which a metallic film is patterned into a spiral shape and used for thin film magnetic heads, inductance devices or the like. For such a coil, in a limited space, it is desired to increase the number of turns and reduce electric resistance, while it is essential to enhance reliability.

In order to increase the number of turns of a planar coil in a limited space, it is necessary to reduce the width of the coil and the spacing between the turns, but this will add the probability of defects such as disconnection, short circuit and increased electric resistance.

The single-layered coil is limited in the number of turns, and, therefore, it has been proposed to pile up coils in a plurality of layers so as to increase the number of turns, for example, in U.S. Patent No. 3,549,825. In this case, a planar coil and an insulation layer are alternately piled up in two or more layers. However, the patterning process becomes complicated, and the more the number of layers, the less the degree of flatness, resulting in lower reliability. Therefore, a multilayered coil including two or more layers is not practical.

SUMMARYOFTHE INVENTION Therefore, the object of the invention is to provide a planar coil having a large number of turns and low electric resistance produced by a relatively simple method.

In the above-mentioned method according to this invention, an insulating frame having a spiral shape is formed on a surface of an insulated substrate, a metallic film having a film thickness smaller than the height of the frame is vapor deposited on a bottom and a top of the frame to produce a first coil on the bottom and a second coil on the top, and the first coil and the second coil are connected in series or in parallel for practical use.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a planar coil of the prior art, showing a single spirally-shaped coil.

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1, showing details of the insulated substrate and the coil.

FIG. 3 is a plan view of a planar coil formed by the method according to this invention, showing a double spirally-shaped coil.

FIG. 4 is a sectional view taken along the line 4~4 of FIG. 3, showing details of the two coils separated from each other.

FIG. 5 (a), (b) and (c) are sectional views showing various steps in the method of producing the planar coil according to this invention.

DETAILED DESCRIPTION OF THE INVENTION Before describing one embodiment of this invention, a planar coil of the prior art will be described with reference to FIGS. 1 and 2.

FIG. is a plan view of a planar coil of the prior art in which a metallic thin film is patterned into a spiral shape on a surface of an insulated substrate 20 to form a planar coil 40. Both ends of the coil are connected to underlayer conductors 12 by way of through hole contacts 16, and the ends of the underlayer conductors 12 serve as terminals 30.

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1. The insulated substrate 20 comprises a base plate 10, underlayer conductors 12 and insulating overcoat 14 formed on a surface of the base plate 10. The ends of the planar coil 40 formed on the surface of the insulated substrate 20 are connected to the underlayer conductors 12 by way ofthrough hole contacts 16. Such a planar coil is disclosed, for example, in U.S. Patent No. 3,549,825 as a coil for thin film magnetic heads.

FIG. 3 is a plan view of a planar coil formed by the method according to the invention, in which two spirally-shaped planar coils 41 and 42 are connected to underlayer conductors 12 by way of through hole contacts 16, and the ends of the underlayer conductors 12 serve as terminals 31,32,33 and 34.

By connecting the terminals 32 to 33, two planar coils 41 and 42 are connected in series, thus making the number of turns double. On the other hand, by connecting the terminals 31 to 33 and the terminals 32 to 34, the two planar coils 41 and 42 are connected in parallel, thus reducing the electric resistance by half.

FIG. 4 is a sectional view taken along the line 4~4 of FIG. 3, showing details of the two coils separated from each other. An insulated substrate 20 comprises a base plate 10, underlayer conductors 12 and an insulating overcoat 14 formed on a surface of the base plate 10. A spirally-shaped insulating frame 50 is formed on the surface of the insulated substrate 20, a first planar coil 41 is formed in contact with the insulated substrate 20, and a second planar coil 42 is formed on the top of the insulating frame 50. Since the height of the insulating frame 50 is predetermined to become largerthanthethicknessofthe planar coil 41,the first planar coil 41 and the second planar coil 42 are three-dimensionally separated. The ends of the planar coils are connected to the underlayer conductors 12 by way of through hole contacts 16.

FIG. 5 is a sectional view showing various steps in the method of producing the planar coil according to this invention. In this figure, the underlayer conductors 12, the insulating overcoat 14 and the through hole contacts 16 are omitted for simplicity.

First of all, as shown in FIG. 5 (a), a positive type photoresist 51 is applied onto a surface of an insulated frame 20, and using an exposure mask having a spiral pattern, only a diagonal line portion 55 is exposed. In the positive type photoresist, only the exposed portion becomes soluble in a developer. Therefore, when the photoresist 51 shown in FIG. 5 (a) is developed, as shown in FIG. 5 (b), an insulating frame 50 is formed. In this case, it is preferable that before being developed, the exposed photoresist 51 should be immersed in a chlorobenzene liquid and dried.

This immersion treatment makes the surface layer of the photoresist 51 rather insoluble in the developer, and, therefore, the edge 53 of the top 52 of the insulating frame 50 is in an overhanging form.

In order to separate the two coils from each other, such overhanging form is preferred. In this embodiment, the height of the insulating frame 50 is adapted to be about 4 microns. Next, on a bottom 54 and a top 52 of the insulating frame 50, a copper film of about 2 microns in thickness is deposited as a coil material, and then as shown in FIG. 5 (c), a first coil 41 and a second coil 42 are simultaneously formed on the bottom 54 and the top 52 of the insulating frame 50, respectively.

In this manner, as shown in FIG. 4, the threedimensionally separated planar coils are completed.

For practical use, all the surfaces of the coils are coated with an insulating protective layer (not shown).

In the above embodiment, as the coil material, copper has been used, but a conductive metal or alloy such as gold, silver and aluminum can be used. Also, as a material for the insulating frame, the photoresist has been used, but if it is of an insulating material which permits to be patterned into the shape of a spiral, many materials can be used, and photosensitive glass, for example, is preferable.

Furthermore, in the embodiment, the planar coil is in the shape of a round spiral, but it is obvious that the invention is applicable to the square spiral shape, for example, as shown in U.S. Patent No. 3,549,825.

Claims

1. A method of producing a planar coil, comprising the steps of forming a spirally-shaped insulating frame on a surface of an insulated substrate; depositing a metallic film having a fiim thickness smaller than a height of said frame simultaneously on a bottom and a top of said frame to form a first coil on the bottom and a second coil on the top; and connecting said two coils in series or in parallel.

2. A planar coil formed by the method of claim 1.

3. A method of producing a planar coil substantially as herein described with reference to and as illustrated in Figures 3,4 and 5 of the accompanying drawings.

4. A planar coil formed by the method of claim 1 substantially as herein described with reference to and as illustrated in Figures 3,4 and 5 of the accompanying drawings.