JPH05275256A - Powder press molding method and chip coil manufactured by it - Google Patents

Abstract

PURPOSE:To realize compactness of a core and a chip coil and to prevent disconnection of a lead wire by forming a core constituting a chip coil integrally by a press molding of powder raw material such as ceramics and ferrite and by forming a winding part thereof to a columnar body having a smooth surface. CONSTITUTION:An upper surface 12a of a first lower punch 12 is made flush with an upper surface of a die 11 and a second lower punch 13 is fixed below. In the state, an upper space of the second lower punch 13 is filled with raw powder 15 consisting of ferrite, alumina or ceramics by a feeder. Then, an upper punch 14 is lowered and pressed downward with a lower surface 14a in contact with the upper surface 12a of the first lower punch 12. It is pressed down to a position wherein an upper surface 13a of the second lower punch 13 smoothly continues to a recessed part 12b of the first lower punch 12. In the process, the raw powder 15 is pressed and molded in a space enclosed with the recessed part 12b of the first lower punch 12, the upper surface 13a of the second lower punch 13 and a recessed part 14b of the upper punch 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coil used as an inductor element in an electronic circuit, and a method for integrally press-molding an object having a flange such as a core forming the coil.

[0002]

2. Description of the Related Art Conventionally, JP-A-63-65606,
As disclosed in Japanese Patent Laid-Open No. 63-254710, a chip coil mounted directly on a printed circuit board is used. For example, as shown in FIG. 6, the structure of this chip coil is such that a conductor 24 is wound around a core 21 having flange portions 22 and 22 at both ends and a columnar winding portion 23 at the center, and both ends of the conductor 24 are It is connected to the extraction electrode 25.

Further, the core 2 which constitutes this chip coil
As the material of No. 1, ceramics such as alumina were used in addition to ferrite. Then, after preliminarily forming these powder raw materials into a columnar body, by a cutting process using a diamond cutter 30 as shown in FIG. 7, it is processed into a shape having a flange portion 22 at both ends and a winding portion 23 at the center,
After that, the core 21 was obtained by firing.

In addition to this, when a member having flanges at both ends and a columnar center portion is made of ceramics, such as a tape guide, it is formed by cutting.

[0005]

However, the conventional chip coil as described above has the following problems because the core 21 is formed by cutting the ferrite or ceramics.

First, when cutting with the diamond cutter 30, it is necessary to use diamond abrasive grains having a relatively large grain size in order to improve the processing efficiency. Therefore, the surface of the winding portion 23 of the core 21 after processing is rough. I could not avoid becoming. As a result, when the conductor wire 24 having a small wire diameter was used, disconnection was likely to occur. In order to prevent disconnection, the surface of the winding portion 23 may be polished, but in reality, the length B of the winding portion 23 is extremely small, about 0.3 mm. It was difficult to process itself.

Further, since the diamond cutter 30 is used for processing, even if an attempt is made to reduce the length B of the winding portion 23 of the core 21, the limit is about 0.3 mm, and a smaller chip coil cannot be manufactured. It was Particularly in recent years, there has been a demand for miniaturization of chip coils, and it is possible to set the winding width of the conductive wire 24 to about 0.1 to 0.15 mm from the viewpoint of coil characteristics. The length B of the winding portion 23 could not be set to 0.3 mm or less.

Further, when the diamond cutter 30 is used for processing, the edge portion 31 of the diamond cutter 30 is easily worn and rounded, so that the boundary 26 between the flange portion 22 and the winding portion 23 of the core 21 is a sharp edge. I couldn't. That is, the boundary 26
Becomes a curved surface with a radius of curvature of about 0.1 to 0.5 mm, and the conductor wire 24 wound around this portion is defective in characteristics near the center portion. Therefore, the conductor wire 24 is only in the center portion of the winding portion 23. Could not be wound, and the chip coil could not be miniaturized.

Further, the width A of the flange portion 22 and the winding portion 2
It is difficult to process the dimensions such as length B and diameter C of No. 3 with high accuracy, and as a result, the inductance of the chip coil varies widely.

[0010]

SUMMARY OF THE INVENTION In view of the above, the present invention is to integrally form a core constituting a chip coil by press molding of powder raw materials such as ceramics and ferrite, and smooth the winding portion thereof. It is a columnar body having a smooth surface.

Further, as a method for integrally powder-pressing a shape having such a flange, there is provided a first die having a through hole and a concave portion provided in the through hole and having a pressing surface. Using a press forming apparatus including a lower punch, a second lower punch that is combined with the first lower punch, and an upper punch that is disposed above these lower punches and that has a concave portion on a pressing surface, a first lower punch is used. The upper surface of the punch is flush with the upper surface of the die, and the second lower punch is arranged downward. The upper space of the second lower punch is filled with the raw material powder, and then the upper punch is lowered to move the upper punch. With the lower surface of the punch and the upper surface of the first lower punch being brought together, and further lowering the upper punch and the first lower punch, the raw material powder is formed in the concave portion of the upper punch and the concave portion of the first lower punch. Into the space It is obtained so as to press molding.

[0012]

EXAMPLES Examples of the present invention will be described below.

As shown in FIGS. 1A and 1B, the chip coil of the present invention comprises a core 1 and a conductive wire 4 wound around the core 1, and the core 1 has both ends. The flange portions 2 and 2 and the central columnar winding portion 3 are provided. Further, both ends of the conductor wire 4 are connected to the extraction electrodes 5 formed on the flange portion 2, so that this chip coil can be directly mounted on a printed board.

Further, in the figure, both the flange portion 2 and the winding portion 3 are shown to have a cylindrical shape, but the shape is not necessarily limited to this and may be a polygonal pillar shape or the like. However, the winding portion 3 is a columnar body having a smooth surface without sharp edges, and the surface has a center line average roughness Ra 0.5.
By having a smooth surface of μm or less, disconnection of the conductive wire 4 is prevented. Further, the boundary 6 between the flange portion 2 and the winding portion 3 has a sharp edge with a radius of curvature of 0.1 mm or less, and the conductor wire 4 can be wound up to the end of the winding portion 3. ing.

The core 1 constituting the above chip coil is made of ferrite or ceramics such as alumina or zirconia, and is integrally formed by press molding. The specific press molding method will be described below.

FIG. 2 shows a state of the press molding apparatus used in the press molding method of the core 1 when the raw material is filled. FIG. 2A is a cross-sectional view of a portion of the core 1 that serves as the winding portion 3.
FIG. 3B is a vertical cross-sectional view of the core 1. This press-forming apparatus comprises a die 11, a first lower punch 12, a second lower punch 13, and an upper punch 14, and FIG.
As shown in (A), smooth curved concave portions 12b and 14b are formed on the pressing surfaces of the first lower punch 12 and the upper punch 14, respectively. Further, as shown in FIG. 2B, a stepped portion 13 for forming the flange portion 2 of the core 1 is formed on each of the second lower punch 13 and the upper punch 14.
b and 14c.

First, as shown in FIG. 2 (A), with the upper surface 12a of the first lower punch 12 flush with the upper surface of the die 11, and the second lower punch 13 fixed downward, the feeder (not (As shown in the drawing)
Fill the headspace of 3. Next, the upper punch 14 is lowered, and the lower surface 14 a thereof is placed on the upper surface 1 of the first lower punch 12.
It is brought into contact with 2a and pressed downward as it is. At this time, the first lower punch 12 descends while giving an appropriate resistance by an air cylinder, a spring or the like, but the second lower punch 13 is fixed. Therefore, as the upper punch 14 and the first lower punch 12 are lowered, the raw material powder 15 filled in the upper space of the second lower punch 13 comes into the recess 14 b of the upper punch 14.

Finally, as shown in FIGS. 3A and 3B, the upper surface 13a of the second lower punch 13 may be pressed to a position where it is smoothly continuous with the recess 12b of the first lower punch 12. .. At this time, the recess 12b of the first lower punch 12,
The upper surface 13a of the second lower punch 13 and the recess 1 of the upper punch 14
The raw material powder 15 is pressure-molded in the space surrounded by 4b.

Thereafter, when the upper punch 14 is raised and the die 11 is lowered, the compact 1 is formed by the second lower punch 13 fixed as shown in FIGS. 4 (A) and 4 (B).
6 can be pushed out onto the upper surface of the die 11 and taken out.

Then, if necessary, after removing the raw material powder adhering to the obtained molded body 16 by air blow or the like, it is fired under a predetermined condition to obtain a core 1 made of ceramics or ferrite. ..

In the core 1 thus obtained, the winding portion 3 at the center has the concave portion 1 of the first lower punch 12 and the upper punch 14.
It is formed by 2b and 14b. Therefore, if the concave portions 12b and 14b are formed in advance to have a smooth curved surface shape without edges and the surface roughness thereof is made small, the winding portion 3 of the obtained core 1 also has a smooth curved surface shape and Surface roughness can be reduced. Further, since the first lower punch 12 and the upper punch 14 are lowered in a combined state and pressure-molded, no streaks or the like are formed on the surface of the molded body at the boundary between the two, and a smooth surface can be obtained. Therefore, it is possible to prevent disconnection of the conductor wire 4.

Further, since the core 1 is integrally formed by press molding, the width A of the flange 2 and the length B of the winding portion 3 are formed.
The dimensions such as diameter and diameter C can be made extremely precise,
It is possible to reduce variations in characteristics of the chip coil.
Further, since the molding is performed by the mold as described above, the boundary 6 between the flange portion 2 and the winding portion 3 of the core 1 can be made a sharp edge with a radius of curvature of 0.1 mm or less, and the winding portion 3 can be entirely wound. Since the wire 4 can be wound, the core 1 itself can be downsized.

Further, in the above embodiment, an example in which one core 1 is manufactured has been shown, but in order to improve the manufacturing efficiency, it is possible to manufacture a plurality of cores. For example, in FIG.
As shown in (A) and (B), a multi-piece shape body 7 in which a large number of cores 1 are connected at their flange 2 portions and slits 8 are formed at their boundary portions is integrally made of ceramic or ferrite. It is formed by press molding and firing. Then, the winding wire 4 may be wound around each winding wire portion 3, and finally divided by the slit 6. By doing so, a large number of minute chip coils can be efficiently manufactured.

Although only the tip coil has been described in the above embodiments, the powder press molding method of the present invention is not limited to the tip coil, and it has flanges at both ends.
Moreover, the present invention can be applied to the case where a member having a columnar center portion and a smooth curved surface is formed of ceramics or the like. For example, as a tape guide for guiding a magnetic tape or the like, when a columnar body having flanges at both ends is manufactured from ceramics, it can be easily manufactured by the powder press molding method of the present invention. ..

Experimental Example Here, the core 1 which actually constitutes the chip coil of the present invention
As a comparative example, a core 21 manufactured by conventional cutting was manufactured as a prototype.
We made a comparison with. As a material, Al ₂ O ₃ 92 to 99
After forming a core 1 having a shape as shown in FIG. 1 by a press molding method as shown in FIGS. 2 to 4 by using alumina ceramics whose weight% is balance with SiO ₂ , MgO, CaO, etc., an oxidizing atmosphere Medium, 1500-1700 ° C
Was fired to obtain a core 1 of the present invention. On the other hand, the core 21 of the comparative example was obtained by molding the same material as the above into a cylindrical body, followed by cutting using a diamond cutter 30 as shown in FIG. 7 and firing.

First, the surface roughness of the winding portions 3 and 23 of the cores 1 and 21 was measured. As shown in Table 1, the surface of the conventional core 21 was processed by the diamond cutter 30, and thus the surface roughness was measured. It was a big one. On the other hand, it can be seen that the surface roughness of the core 1 of the present invention is small and the surface is extremely smooth.

[0027]

[Table 1]

Next, when the radii of curvature of the boundaries 6 and 26 between the flange portions 2 and 22 and the winding portions 3 and 23 of both cores 1 and 21 were measured, as shown in Table 2, in the comparative example, diamond was used. Since the edge portion 31 of the cutter is worn and rounded during processing by the cutter 30, it is inevitable that the boundary 26 becomes a curved surface with a radius of curvature of about 0.3 mm. When the conductive wire 4 is wound around this curved surface portion, the conductive wire 4 cannot be wound around the curved surface portion because the characteristic becomes defective due to approaching to the central portion. On the other hand, in the core 1 of the present invention, the boundary 6 between the flange 2 and the winding portion 3 can be formed as a sharp edge with a radius of curvature of 0.06 mm because the core 1 is molded by a mold.

Therefore, for example, the winding width of the conductor wire 4 is 0.
When 3 mm is required, in the core 21 of the comparative example, in addition to this winding width, there are curved boundaries 26 with a radius of curvature of 0.3 mm at both ends. It should be 1.9 mm. On the other hand, in the core 1 of the present invention, since the radius of curvature of the boundary 6 is 0.06 mm, the length of the winding part 3 may be 0.42 mm in total, and it can be seen that the size can be reduced as compared with the comparative example.

[0030]

[Table 2]

Next, the width A of the flange portions 2 and 22 is set to 0.2.
5 mm, the length B of the winding portions 3 and 23 is 0.30 mm, and the diameter C is 0.8 mm, the core 1 of the present invention and the comparative example,
21 was produced. Then, the variation width (tolerance) of each of the above dimensions was examined. Further, the variation width of the inductance when the chip coils were formed by using the cores 1 and 21 was examined. The results are shown in Table 3.

As shown in Table 3, since the core 1 of the present invention is integrally formed by press molding, the variation width of each dimension is as small as 0.05%. Therefore, it can be seen that when the coil is used, the variation in inductance is 10% or less, which is superior to the comparative example.

[0033]

[Table 3]

Further, in the above experimental example, the width A of each of the two flange portions 2 and 2 is 0.25 mm, and the length B of the winding portion 3 is 0.3 mm. The length required was 0.9 mm. In order to shorten this length, a test was conducted to shorten the length B of the winding part 3. As a result, in the comparative example, the length B of the winding portion 3 could not be set to 0.3 mm or less due to the cutting work with the diamond cutter 30. On the other hand, in the core 1 of the present invention, the length B of the winding portion 3 can be shortened to about 0.1 mm by changing the size of the mold, and the total length of the core 1 is 0. It was possible to make it as small as 0.6 mm.

[0035]

As described above, according to the present invention, the core forming the chip coil is integrally formed by press molding of raw material powder such as ceramic or ferrite, and the winding portion thereof has a columnar shape having a smooth surface. With the body, the following effects can be achieved.

Since it is possible to obtain a core having a radius of curvature of 0.1 mm or less at the boundary between the flange portion and the winding portion, it is possible to wind the entire winding portion. Moreover, since the length of the winding portion can be reduced to about 0.1 mm, the core and the chip coil can be downsized.

Further, since the core has a smooth curved surface shape and its surface roughness is small, it is possible to prevent the conductor wire from breaking. Furthermore, since the dimensional accuracy of each part of the core can be increased, the variation in the characteristics of the coil can be reduced.
Further, the manufacturing process can be simplified and the manufacturing cost can be reduced.

Further, as a method of integrally forming the core of the above chip coil by press molding, a die having a through hole and a first lower punch having a concave portion on the pressing surface, which is disposed in the through hole. And a second lower punch combined with the first lower punch, and an upper punch that is arranged above these lower punches and has a concave portion on the pressing surface. The upper surface of the die is flush with the upper surface of the die, and the second lower punch is arranged below. The upper space of the second lower punch is filled with the raw material powder, and then the upper punch is lowered to move the upper punch. A space formed by the recesses of the upper punch and the recesses of the first lower punch with the raw material powder by bringing the lower surface and the upper surface of the first lower punch into a combined state and further lowering the upper punch and the first lower punch. It is sent inside and pressure is applied. By doing so, it is possible to easily integrally form a member having a shape with flanges at both ends of the columnar body by powder press molding, and yet to form the columnar body portion into a smooth curved surface shape. Therefore, it can be preferably used in a manufacturing process of a chip coil, a tape guide and the like.

[Brief description of drawings]

FIG. 1A is a perspective view showing a chip coil of the present invention,
(B) is a sectional view taken along line XX in (A).

2 (A) and 2 (B) are cross-sectional views for explaining a method of molding a core that constitutes the chip coil of the present invention.

3 (A) and 3 (B) are cross-sectional views for explaining a method of molding a core that constitutes the chip coil of the present invention.

4A and 4B are cross-sectional views for explaining a method for molding a core that constitutes the chip coil of the present invention.

5A is a side view showing a multi-cavity shaped body of the chip coil of the present invention, and FIG. 5B is a sectional view taken along line YY in FIG.

FIG. 6A is a perspective view showing a conventional chip coil,
(B) is a ZZ line sectional view in (A).

FIG. 7 is a diagram for explaining a cutting process of a core that constitutes a conventional chip coil.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Core 2 ... Flange part 3 ... Winding part 4 ... Winding 5 ... Extraction electrode 6 ... Boundary 7 ... Multi-piece shape object 8 ... Slit 11 ... Die 12 ... First lower punch 13 ... Second lower punch 14 ... Upper punch

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[Procedure amendment]

[Submission date] May 11, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

Further, although the flange portion 2 and the winding portion 3 are both in the shape of a quadrangular prism in the drawing, they are not necessarily limited to this shape and may be another polygonal prism. However,
As shown in the cross section in FIG. 1C, the winding portion 3 is a columnar body having a smooth surface without sharp edges, and the surface is a smooth surface having a center line average roughness Ra of 0.5 μm or less. This prevents the conductor wire 4 from breaking.
Furthermore, as shown in FIG. 1D, the cross section of the winding part 3 is
By forming the prismatic shape with protrusions on the sides, the length of the conductor wire 4 can be stabilized and the electrical characteristics of the chip coil can be stabilized. Further, in FIG. 1B, a boundary 6 between the flange portion 2 and the winding portion 3 is a sharp edge having a radius of curvature of 0.1 mm or less, and the conductor wire 4 is wound up to the end of the winding portion 3. You can do it.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

FIG. 1A is a perspective view showing a chip coil of the present invention,
(B) is a sectional view taken along line XX in (A), and (C) and (D) are sectional views taken along line WW in (B).

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (2)

[Claims] 1. A die having a through hole, a first lower punch disposed in the through hole and having a concave portion on a pressing surface, and the first lower punch.
A press forming apparatus comprising a second lower punch combined with a lower punch and an upper punch arranged on the upper side of the lower punch and having a concave portion on a pressing surface is used. First, the upper surface of the first lower punch is referred to as a die upper surface. On the same plane,
In addition, the second lower punch is arranged below, the raw material powder is filled in the upper space of the second lower punch, and then the upper punch is lowered to remove the lower surface of the upper punch and the first punch.
The upper punch and the first lower punch are lowered with the upper surfaces of the lower punches aligned with each other, whereby the raw material powder is fed into the space formed by the concave portions of the upper punch and the concave portions of the first lower punch, and pressed. A powder press molding method comprising a molding step. 2. A core having a flange portion at both ends and a winding portion at the central portion, which is obtained by integrally molding raw material powder such as ceramics and ferrite by press molding, and then firing. A chip coil in which the winding portion has a columnar shape with a smooth surface, and a conductive wire is wound around the winding portion.