COMPACT INDUCTOR AND A METHOD FOR MANUFACTURING THE SAME

• US 20100194511A1
• Filed: 01/22/2010
• Published: 08/05/2010
• Est. Priority Date: 01/22/2009
• Status: Active Grant

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Mizuno, Kazuyuki, Kobayashi, Nobuyuki, Ozawa, Shuichi, Shimogawa, Natsumi
• Granted Patent: US 8,054,151 B2
• Time in Patent Office: Days
• US Class Current: 336/83
• CPC Class Codes: H01F 17/04 with magnetic core
• CPC Class Codes: H01F 2017/048 with encapsulating core, e.g. made of resin and magnetic powder
• CPC Class Codes: H01F 27/255 made from particles H01F27/26 takes precedence
• CPC Class Codes: H01F 27/34 Special means for preventing or reducing unwanted electric or magnetic effects, e.g. no-load losses, reactive currents, harmonics, oscillations, leakage fields
• CPC Class Codes: H01F 41/0246 Manufacturing of magnetic circuits by moulding or by pressing powder magnetic cores made by moulding or by pressing powder H01F27/255; soft magnetic particles H01F1/20, H01F1/36
• CPC Class Codes: Y10T 29/49073 by assembling coil and core

Abstract

A compact inductor comprises a coil, a coil-burying body, and a body for a closed magnetic circuit. The coil-burying body is a fired porous ceramic body having a first magnetic permeability, in which the coil is buried. In the coil-burying body, “a through-hole 12a passing through inside of the coil along an axis of the coil” is formed. The body for a closed magnetic circuit is a fired dense ceramic body having a second magnetic permeability greater than the first magnetic permeability. The body for a closed magnetic circuit is arranged closely/densely at an outer circumference portion of the coil-burying body and in the through-hole. A magnetic path is therefore formed mainly within the body for a closed magnetic circuit, and the magnetic flux density is reduced in an area close to the coil. Accordingly, an inductor having the excellent superimposed DC current characteristic is provided.

Claims

1. A compact inductor comprising:

a helically wound coil made of a conductor;

a coil-burying body made of a fired ceramic having a first magnetic permeability, in which said coil is buried and a through-hole passing through inside of said coil along an axis of said coil is formed; and

a body for a closed magnetic circuit made of a fired ceramic having a second magnetic permeability greater than said first magnetic permeability, which are densely arranged at an outer circumference portion of said coil-burying body and in said through-hole so as to provide a closed magnetic circuit having no cut section for said coil by burying said coil-burying body.

2. A compact inductor according to claim 1, wherein said coil-burying body is made of a porous ceramic.

3. A compact inductor according to claim 1, wherein a ratio (μ

1/μ

2) of said first magnetic permeability (μ

1) to said second magnetic permeability (μ

2) is equal to or greater than 0.19 and is smaller than or equal to 0.75.

4. A compact inductor according to claim 1, wherein

both of said coil-burying body and said body for a closed magnetic circuit are made of porous ceramic bodies, in which the same kind powders having the same diameter are dispersed, and

a ratio (ρ

1/ρ

2) of a relative density (ρ

1) of said coil-burying body to a relative density (ρ

2) of said body for a closed magnetic circuit is equal to or greater than 0.73 and is smaller than or equal to 0.92, when said relative density is defined as a ratio of an actual density to a theoretical density.

5. A compact inductor according to claim 1, wherein

a distance between an outer circumference of said coil and an outer circumference of said coil-burying body is the same as a distance between an inner circumference of said coil and an inner circumference of said coil-burying body;

and

a thickness (t) of said coil-burying body which is equal to said distance is equal to or greater than 30 μ

m and is smaller than or equal to 100 μ

m.

10. A compact inductor according to claim 2, wherein

a distance between an outer circumference of said coil and an outer circumference of said coil-burying body is the same as a distance between an inner circumference of said coil and an inner circumference of said coil-burying body;

and

a thickness (t) of said coil-burying body which is equal to said distance is equal to or greater than 30 μ

m and is smaller than or equal to 100 μ

m.

11. A compact inductor according to claim 3, wherein

a distance between an outer circumference of said coil and an outer circumference of said coil-burying body is the same as a distance between an inner circumference of said coil and an inner circumference of said coil-burying body;

and

a thickness (t) of said coil-burying body which is equal to said distance is equal to or greater than 30 μ

m and is smaller than or equal to 100 μ

M.

12. A compact inductor according to claim 4, wherein

a distance between an outer circumference of said coil and an outer circumference of said coil-burying body is the same as a distance between an inner circumference of said coil and an inner circumference of said coil-burying body;

and

a thickness (t) of said coil-burying body which is equal to said distance is equal to or greater than 30 μ

m and is smaller than or equal to 100 μ

m.

6. A method for manufacturing a compact inductor comprising the steps of:

a coil forming step for forming a coil made of a helically wound conductor;

a coil-burying-body-before-fired forming step for forming a coil-burying-body-before-fired, in which said coil is buried and which has a through-hole at an inner side of said coil, including,

preparing a first mold having a concave portion for holding said coil and a columnar portion, said columnar portion being vertically arranged in said concave portion and having a shape which allows said columnar portion to pass through the inner side of said coil to form said through-hole;

placing said coil within said first mold in such a manner that said columnar portion passes through said inner side of the coil;

filling said first mold with a first ceramic slurry containing first magnetic powders and having a heat-gelling characteristic or a thermoset characteristic, the first ceramic slurry being adjusted in such a manner that a magnetic permeability of a body obtained by firing said first ceramic slurry becomes equal to a first magnetic permeability; and

changing said first ceramic slurry in said first mold in such a manner that said first ceramic slurry keeps its shape by itself;

an inductor-before-fired forming step for forming an inductor-before-fired, including,

preparing a second mold having a space for holding said coil-burying-body-before-fired;

placing said coil-burying-body-before-fired within said second mold;

filling said second mold with a second ceramic slurry containing second magnetic powders and having a heat-gelling characteristic or a thermoset characteristic, said second ceramic slurry being adjusted in such a manner that a magnetic permeability of a body obtained by firing said second ceramic slurry becomes a second magnetic permeability greater than said first magnetic permeability, so that said second ceramic slurry exists densely at an outer circumference portion of said coil-burying-body-before-fired and in said through-hole; and

changing said second ceramic slurry in said second mold in such a manner that said second ceramic slurry keeps its shape by itself; and

a firing step for firing said inductor-before-fired.

7. A method for manufacturing a compact inductor according to claim 6, wherein said first ceramic slurry contains a pore-forming agent which functions so as to change a portion obtained by firing said first ceramic slurry in said firing step into a porous body.

8. A method for manufacturing a compact inductor according to claim 6, wherein

said first ceramic slurry contains, as said first magnetic powders, magnetic powders whose median diameter is adjusted to be equal to a first grain diameter in such a manner that a portion obtained by firing said first ceramic slurry in said firing step changes into a porous body, and

said second ceramic slurry contains, as said second magnetic powders, magnetic powders whose median diameter is adjusted to be equal to a second grain diameter smaller than said first grain diameter in such a manner that a portion obtained by firing said second ceramic slurry in said firing step changes into a dense body.

13. A method for manufacturing a compact inductor according to claim 7, wherein

said first ceramic slurry contains, as said first magnetic powders, magnetic powders whose median diameter is adjusted to be equal to a first grain diameter in such a manner that a portion obtained by firing said first ceramic slurry in said firing step changes into a porous body, and

said second ceramic slurry contains, as said second magnetic powders, magnetic powders whose median diameter is adjusted to be equal to a second grain diameter smaller than said first grain diameter in such a manner that a portion obtained by firing said second ceramic slurry in said firing step changes into a dense body.

9. A method for manufacturing a compact inductor comprising the steps of:

a coil-burying-body-before-fired forming step for forming a coil-burying-body-before-fired, including,

preparing a plurality of ceramic green sheets adjusted in such a manner that a magnetic permeability of a body obtained by firing said ceramic green sheets becomes equal to a first magnetic permeability;

forming thin conductive films in such a manner that each of said thin conductive films has a predetermined pattern which surrounds a predetermined area on each of said ceramic green sheets;

forming a layered body by layering said plurality of ceramic green sheets, electrically connecting said thin conductive films formed on said ceramic green sheets adjacent to each other in a direction of layering with each other through via holes so as to form a coil made of a helically wound conductor, and forming a through-hole at said predetermined area;

an inductor-before-fired forming step for forming an inductor-before-fired, including,

preparing a mold having a space for holding said coil-burying-body-before-fired;

placing said coil-burying-body-before-fired within said mold;

filling said mold with a ceramic slurry containing magnetic powders and having a heat-gelling characteristic or a thermoset characteristic, said ceramic slurry being adjusted in such a manner that a magnetic permeability of a body obtained by firing said ceramic slurry becomes a second magnetic permeability greater than said first magnetic permeability, so that said ceramic slurry exists densely at an outer circumference portion of said coil-burying-body-before-fired and in said through-hole; and

changing said ceramic slurry in said mold in such a manner that said ceramic slurry keeps its shape by itself; and

a firing step for firing said inductor-before-fired.