JPH0745476A - Lc filter and fabrication thereof - Google Patents

Abstract

PURPOSE:To obtain a thin LC filter in which the cut-off frequency can be lowered. CONSTITUTION:A conductor film is formed by sputtering on the surface of a dielectric magnetic substrate 22 and then the the conductor film is etched to form a coil 23. The coil 23 is covered, except the terminal parts 24, 25 and the magnetic material connecting part 22a, with a dielectric film 26 and a conductor film 27 a part of which provides a terminal part 28. The conductor film 27 is covered with an interlayer insulating film 29 and a magnetic material film 30 bonded to the substrate 22 at the connecting part 22a. The terminal parts 24, 25 are connected, respectively, with the input side and the output side and the terminal part 28 is grounded in the digital circuit of the LC filter 21 in order to use the LC filter as a noise filter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LC filter used as a noise filter of a digital circuit, which is a distributed constant type filter having a thin structure, and can further reduce the cutoff frequency. , And a method of manufacturing an LC filter that can use thin film forming technology.

[0002]

9 is a perspective view showing a conventional pin type LC filter, FIG. 10 is an exploded perspective view of FIG. 9, FIG. 11 is a perspective view showing a conventional chip type LC filter, and FIG.
FIG. 12 is a partially exploded perspective view of FIG. 11. The LC filter shown in FIGS. 9 and 10 is a conductive foil 4 in which the first lead 1 and the third lead 3 are connected to both ends, and a conductive foil in which the second lead 2 is connected to one end. Foil 5 and insulating film 6,7
The conductive foil 4, the film 6, the conductive foil 5 and the edge film 7 are alternately laminated and wound into a cylindrical shape.

The LC filters shown in FIGS. 11 and 12 have a dielectric substrate 12 on which a U-shaped conductor 11 is formed and an insulator substrate 14 on which a substantially U-shaped conductor 13 is formed. The substrate 12 and the substrate 14 are superposed, and the conductor 11 and the conductor 13 are superposed in several stages so as to face each other with the dielectric substrate 12 interposed therebetween. LC of this kind
The filter is a so-called distributed constant type LC filter, and has excellent characteristics in terms of noise attenuation rate as compared with the lumped constant type filter.

[0004]

However, since the conventional pin type LC filter shown in FIGS. 9 and 10 has a structure in which four foils and films are wound, it is formed in a small shape. It is difficult and there is a limit to miniaturization. Further, the chip type shown in FIGS. 11 and 12 is relatively small in size because it has a structure in which two substrates 12 and 14 are stacked, but on the other hand, a manufacturing process is performed because the substrate 12 and the substrate 14 are laminated in multiple layers. However, it has a complicated structure. Also,
The cut-off frequency was also relatively large at 30 MHz, and frequencies below it could not be removed.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an LC filter which is thin and whose cutoff frequency can be set in a low frequency region, and a manufacturing method thereof. To do.

[0006]

An LC filter according to the present invention comprises a substrate, a coil member insulated from the substrate and wound in a flat shape, and a dielectric layer laminated on the coil member. It is characterized in that it has a plurality of terminals that are electrically conductive to the plurality of portions of the coil member and the dielectric layer, respectively.

Preferably, the substrate is made of a magnetic material, and the magnetic material layer is provided on the dielectric layer except for the terminals.

The method of manufacturing an LC filter according to the present invention includes the steps of forming a conductor layer insulated from the substrate on a substrate, removing unnecessary portions of the conductor layer, and winding the conductor layer into a planar shape. The method is characterized by including a step of forming a coil member and a step of laminating a dielectric layer on the coil member while leaving a terminal portion.

[0009]

In the above means, since the coil member wound in a planar shape is covered with the dielectric layer, a thin distributed constant type LC filter can be obtained.

Further, by using a magnetic substrate and further laminating a magnetic substance on the dielectric layer, the inductance can be increased and the cutoff frequency can be made lower than the conventional one.

Further, in the method for manufacturing the LC filter,
Since thin-film laminating technology can be used to form planar coil members and dielectric layers using conductors, LC filters of stable quality can be obtained, and thousands of units are identical on a large 4-inch square substrate, for example. An LC filter can be formed and mass production becomes possible.

[0012]

1 is an enlarged sectional view showing an embodiment of the LC filter of the present invention, FIG. 2 is an equivalent circuit diagram of the LC filter shown in FIG. 1, and FIGS. 3 to 7 are views of the LC filter shown in FIG. The manufacturing steps are shown in sequence, and FIG. 8 shows the LC of the above embodiment.
It is a diagram which compared the insertion loss of a filter and a prior art example.
The LC filter 21 shown in FIG. 1 includes a substrate 22 made of a magnetic material and having at least surface insulation, a coil 23 formed on the substrate 22 in a planar spiral shape, and the coil 2
On the dielectric film 26 formed on the portions other than the terminal portions 24, 25 and the magnetic body connecting portion 22a of the substrate 22, and on the dielectric film 26 excluding the magnetic body connecting portion 22a and the terminal portion 25. A formed conductor film 27, an interlayer insulating film 29 formed on the conductor film 27 excluding the magnetic body connecting portion 22a, the terminal portion 25, and the terminal portion 28 formed on the conductor film 27. , The terminal portion 25 and the terminal portion 2
8 and a magnetic film 30 provided on a portion other than 8. The magnetic film 30 is formed on the magnetic film connecting portion 22.
It is connected to the substrate 22 at a.

As shown in FIG. 2, the LC filter 21 having the above-mentioned configuration is used, for example, in the terminal section 2 in a digital circuit.
4 is connected to the input side, the terminal part 25 is connected to the output side, and the terminal part 28 is grounded and used. This filter is a distributed constant type covered with a magnetic material, and is used for removing noise of an input signal. Next, a method of manufacturing the LC filter having the above structure will be described with reference to FIGS.

(Substrate) The substrate 22 is shown in FIG. This substrate 22 is a part of a large substrate, and a large number of thousands of LC filters are simultaneously formed on the large substrate, and then separated into individual substrates 22. However, in Figure 3 and below, one LC
Described as a filter. The large substrate is, for example, a 4-inch square magnetic material and an insulating Ni-Zn ferrite substrate, has a volume resistivity ρ of 10 ⁴ Ω · cm, a saturation magnetic flux density Bs of 3000 gauss, and a coercive force Hc of 0.5. (Oe).
This ferrite substrate is mirror-polished until the average surface roughness Ra reaches 100 Å, and this substrate is washed with an organic solvent (acetone, isopropyl alcohol).

(Formation of Coil) The cleaned substrate is placed in a sputtering apparatus, and a coil material of Cr is continuously formed to a thickness of 500 angstroms and Cu to a thickness of 2000 angstroms. Next, using a spin coater, a photoresist film having a thickness of 11 μm is formed on the Cr / Cu metal film. As a photoresist, A manufactured by Hoechst
Z4620 (trade name) was used.

This is placed in a clean oven at 90 ° C. for 30 minutes.
After prebaking for a minute, contact exposure is performed using a photomask. The size of the photomask is 5 inches square, and 6000 coil patterns that can be arranged in the large substrate of 4 inches square are aligned with other photomasks to be used thereafter. Alignment marks are formed for this purpose, and light is transmitted through the coil pattern and alignment mark portions, and light is not transmitted through other portions. For contact exposure, PLA-501 (trade name) manufactured by Canon Sales Co., Ltd. was used. When the substrate after contact exposure is developed with a developing solution, the resist on the exposed coil-shaped portion and the alignment mark portion is removed, and the resist remains on the other portions. Place this substrate in a clean oven for 12
Post bake for 30 minutes at 0 ° C.

Next, this substrate is placed in a mixed plating solution of copper sulfide and sulfuric acid to remove Cr / Cu in the resist-removed portion.
Copper is electroplated on the surface of the metal film to a thickness of 10 μm.
Then, this substrate is immersed in acetone, and ultrasonic waves are simultaneously applied to remove the resist remaining on the metal film. After removing the resist, the Cr / Cu metal film in the portion where the resist has been removed, that is, the portion other than the copper plating, is removed by etching using an aqueous solution of ceric ammonium sulfate + perchloric acid. As a result, the Cr / Cu metal film remains on the coil pattern and the alignment mark portion, and the formation of the coil 23 shown in FIG. 3 is completed. As shown in FIG. 3, the spiral-shaped size of the coil 23 in this embodiment has an external dimension (A × B) of 700 μm × 1500 μm, a conductor width (W) of 50 μm, and a space between coils (δ). Is 50
μm, and the number of turns is 2.5.

(Formation of Dielectric Film) Next, a photoresist is spin-coated on the surface of the substrate 22 and the surface of the coil 23 by the same method as described above, prebaked, and then contact exposure is performed using a photomask. This contact exposure is for covering the dielectric film 26 except the sputter region with a resist as shown in FIG. That is, the pattern of the photomask is such that light does not pass through the rectangular area for forming the terminal portion 25 of the coil 23 and the magnetic material connecting portion 22a of the substrate 22 and the outer peripheral area including the terminal portion 24, and other than this. It is a shape that allows light to pass through in the region that covers the coil. Then, by developing the resist and removing the resist in the portion where the light is transmitted, there is no resist in the region where the dielectric film 26 is formed on the substrate, and the resist remains in the other regions. This substrate is placed in a sputtering apparatus and T, which is the material of the dielectric film,
a a ₂ O ₅ is formed at a thickness of 700 angstroms.
After that, the substrate is immersed in acetone and ultrasonic waves are applied to remove the resist remaining on the substrate together with the Ta ₂ O ₅ film formed thereon. As a result, as shown in FIG.
And the magnetic material connecting portion 22a is opened, and the terminal portion 24
A dielectric film (Ta ₂ O ₅ ) 26 that covers the coil 23 is formed in a portion excluding the outer peripheral region including. The relative permittivity εr of this dielectric film 26 was 25.

(Formation of Conductor Film) Next, this substrate is placed in a sputtering apparatus, and continuous film formation is performed so that Cr has a thickness of 500 Å and Cu has a thickness of 2000 Å. After that, a photoresist is spin-coated and prebaked, and then contact exposure is performed using a photomask. The photomask used at this time has a pattern in which light is transmitted in the region where the conductor film 27 shown in FIG. 5 is formed and light is not transmitted in other regions.
When this is developed, the resist in the region where the conductor film 27 is formed is removed, and the resist remains in the other regions. Post bake this. This substrate was placed in a mixed plating solution of copper sulfide and sulfuric acid in the same manner as in the coil forming step, and the surface of the Cr / Cu metal film where the resist was removed was plated with Cu to a thickness of 10 μm, and then with acetone. Immerse and apply ultrasonic waves to remove the remaining resist. This substrate is etched with an etching solution to remove the Cu / Cr metal film in the portion not plated with copper. As a result, as shown in FIG. 5, a conductor film 27 that covers the dielectric film 26 is formed.

(Formation of Interlayer Insulating Film) Next, a photosensitive polyimide pimmel (trade name of Asahi Kasei Co., Ltd.) was spin-coated on this substrate to a thickness of 5 μm, and contact exposure was carried out using a photomask. . The pattern of this photomask is
Light is transmitted through the formation region of the interlayer insulating film 29 shown in FIG.
Light is not transmitted in the other regions. The region where the interlayer insulating film 29 is formed is the magnetic body connecting portion 22a.
In addition to the terminal portion 25, a portion of the terminal portion 28 becomes a rectangular hollow region. After the contact exposure, pre-baking and development remove the photosensitive polyimide pimels outside the formation area. By post-baking this at 450 ° C., the interlayer insulating film 29 shown in FIG. 6 is formed.

(Formation of Magnetic Film) Next, this substrate was placed in a sputtering apparatus, and Fe ₇₈ Ta ₁₀ C was added while cooling the substrate with water.
A target having a composition of ₁₂ is used to form a film with a thickness of 5 μm. Thereafter, a photoresist is spin-coated and pre-baked in the same manner as described above, and a photo having a pattern in which light is not transmitted in a pattern in the formation region of the magnetic film 30 shown in FIG. 7 and light is transmitted in the other regions. Contact exposure is performed using a mask and development is performed. As a result, the resist other than the region where the magnetic film 30 is formed is removed. Then, post bake is performed.
This substrate was placed in an ion etching apparatus and Fe ₇₈
The region where the Ta ₁₀ C ₁₂ film is exposed, that is, the region other than the formation region is etched. Then, when the resist is removed, the magnetic film 30 having the shape shown in FIG. 7 is formed. The magnetic film 30 is connected to the substrate 22 in the magnetic connecting portion 22a (see FIG. 1). Then, the substrate is annealed at 450 ° C. for 60 minutes while rotating in a magnetic field of 300 (Oe) in vacuum. As a result, the magnetic substance film 30 having excellent magnetic characteristics with a magnetic flux density Bs of 16000 gauss and a coercive force Hc of 0.1 (Oe).
Is obtained. The LC filter formed by the above manufacturing method is of a distributed constant type and covered with a magnetic material, as in the equivalent circuit shown in FIG.

Next, the characteristics of the filter having the above structure will be described with reference to the diagram shown in FIG. In FIG. 8, the horizontal axis represents frequency (MH
z) and the insertion loss (dB) on the vertical axis, L of the above embodiment
12 is a comparison of the characteristics of the C filter and the conventional LC filter shown in FIG. 11. As shown in FIG. 8, in the LC filter according to the embodiment, the cutoff frequency (the frequency at which the insertion loss is 3 dB) is 1 MHz, and the cutoff frequency is 10 M.
The insertion loss at the frequency of Hz was 24 dB. On the other hand, in the conventional example, the cutoff frequency is 30 MHz or higher.
As described above, it is understood that the LC filter of the above-described embodiment has an excellent characteristic that noise can be removed in the low frequency range.

In the above embodiment, the substrate 22 is made of a magnetic material and is entirely insulative. However, a non-insulating magnetic material is used as the substrate and an insulating film is formed on the surface thereof. One can also be used. Alternatively, as the substrate 22, a magnetic film formed on the surface of a non-magnetic material and an insulating film formed on the surface of the magnetic film may be used. For example, Devitron L, which is a non-magnetic ceramic
Using P-861 (trade name of Ishizuka Glass Co., Ltd.), Fe ₇₈ Ta ₁₀ C ₁₂ is formed as a magnetic film on this substrate to a thickness of 5 μm, and further on this Fe ₇₈ Ta ₁₀ C ₁₂ film. It is possible to use a substrate on which SiO ₂ is deposited as an insulating film with a thickness of 1 μm. Using this substrate, the coil, the dielectric film, the conductor film, the interlayer insulating film, and the magnetic film can be formed to form an LC filter equivalent to that of the above embodiment. Further, as in the above-mentioned embodiment, this LC filter can simultaneously manufacture 6000 pieces from a large 4-inch square substrate and 12,000 pieces from a large 6-inch round substrate, which contributes to cost reduction by mass production. be able to.

[0024]

According to the first aspect of the invention, a thin distributed constant type LC filter can be obtained by covering the coil member wound in a planar shape with the dielectric layer.

According to the second aspect of the present invention, the magnetic substrate is used, and the magnetic substance is laminated on the dielectric layer, whereby the inductance can be increased and the cutoff frequency can be made lower than the conventional one.

According to the third aspect of the present invention, a planar coil member and a dielectric layer made of an electric conductor can be formed by using the thin film laminating technique, and an LC filter of stable quality can be mass-produced.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view showing an embodiment of an LC filter of the present invention.

FIG. 2 is an equivalent circuit diagram of the LC filter shown in FIG.

FIG. 3 is a perspective view showing a manufacturing process of the LC filter of the above embodiment, showing a state in which a coil is formed on the substrate.

FIG. 4 is a perspective view showing a state in which a dielectric film is formed on a coil.

FIG. 5 is a perspective view showing a state in which a conductor film is formed on a dielectric film.

FIG. 6 is a perspective view showing a state in which an interlayer insulating film is formed.

FIG. 7 is a perspective view showing a state in which a magnetic film is formed.

FIG. 8 is a diagram showing insertion loss characteristics of the LC filters of the above-described embodiment and the conventional example.

FIG. 9 is a perspective view showing a conventional pin type LC filter.

10 is an exploded perspective view of the conventional pin type LC filter shown in FIG.

FIG. 11 is a perspective view showing a conventional chip type LC filter.

12 is a partially exploded perspective view of the conventional chip type LC filter shown in FIG.

[Explanation of symbols]

 21 LC Filter 22 Substrate 22a Magnetic Material Connection Part 23 Coil 24 Terminal Part 25 Terminal Part 26 Dielectric Film 27 Conductor Film 28 Terminal Part 29 Interlayer Insulating Film 30 Magnetic Material Film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryokan Kakihara 1-7 Yukiya Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd. (72) Inventor Takehiro Takeshima 1-7 Yukiya Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd. (72) Inventor Isao Nakamura 1-7 Yukiya Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd.

Claims (3)

[Claims] 1. A substrate, a coil member which is insulated from the substrate and wound in a planar shape, a dielectric layer laminated on the coil member, a plurality of portions of the coil member and the dielectric layer. An LC filter, characterized in that it has a terminal portion which can be electrically conducted to and, respectively. 2. The LC filter according to claim 1, wherein the substrate is made of a magnetic material, and the magnetic material layer is provided on the dielectric layer except the terminal portion. 3. A step of forming a conductor layer insulated from the substrate on the substrate, a step of removing an unnecessary portion of the conductor layer to form a coil member wound in a planar shape,
And a step of laminating a dielectric layer on the coil member while leaving the terminal portion, the manufacturing method of the LC filter.