JP2001332826A - Electronic circuit board having decoupling function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate whose decoupling performance is improved in an electronic circuit substrate that has an electromagnetic wave absorption performance and hence prevents the decoupling between signal and ground lines. SOLUTION: Fe powder whose average particle diameter is equal to or less than 5 μm, preferably 3 μm or less, and more preferably 1 μm or less which is fine soft magnetic powder having the covering layer of Fe nitride on the surface is dispersed into an organic matrix material that is selected from rubber or plastic, or is dispersed into an inorganic matrix material that is combined using water glass with the inorganic powder as a binder so that the fine soft magnetic powder occupies 30%, preferably 50% or higher in terms of vol.% before forming in a flat shape as a substrate 1. A feature where a signal line 2 is formed on the front and a conductor layer 4A with ground potential is provided on the rear, and a feature where the signal line 2 and a ground line 3 are formed on the front, and a conductive layer 4B with the ground potential is provided on the rear are available.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic circuit board having a decoupling function.

[0002]

2. Description of the Related Art A board that has been used for a long time as a board of an electronic circuit is a board made of a bakelite resin or a glass / epoxy resin with copper foil attached to both sides thereof. Used for forming, Gnd on the copper foil on the back
A common use is to apply a potential. However,
In the high-frequency region, the copper foil layer on the back surface functions as an antenna for picking up and transmitting a signal from the line, and noise electromagnetic waves are radiated therefrom.

In order to prevent such coupling between the signal line and the Gnd potential layer and suppress the emission of noise electromagnetic waves, a material having a shielding effect is used for the substrate of the electronic circuit itself, and the signal line is connected to the Gnd. The effect on the potential layer has been attenuated. For example, it has been proposed to use a composite material obtained by mixing a ferromagnetic metal powder and an insulating resin as an insulating layer in a circuit board provided with a conductive layer on both sides of the insulating layer (see JP-A-8-7879).
8). Specifically, a powder having a particle size of about 2 μm of iron is mixed in a phenol resin at 60% by volume to obtain a composite material.

One of the inventors has developed various materials exhibiting high electromagnetic wave absorption by dispersing a soft magnetic metal powder, particularly a flake-like powder, in a matrix material made of rubber or plastic. During the course of the research, they attempted to use those electromagnetic wave absorbers for electronic circuit boards and succeeded, and this was also disclosed (JP-A-2000-13086). The electronic circuit board is made of Fe
-Flat powder of soft magnetic metal such as Cr-Al alloy,
A powder dispersed in a matrix so as to occupy 30% by volume or more is formed into a plate shape, and the flat surface of the powder is arranged so as to be parallel to the surface of the plate. The feature is that it is secured to 10 ¹⁰ Ω · cm or more.

The soft magnetic metal powder used in this type of electromagnetic wave absorber is usually obtained by atomizing a powder obtained by spraying a molten metal with water or gas and flattening the powder by an attritor treatment. Manufacturing. The metal powder obtained by the atomization method has an average particle size of 30.
About 50 μm. From the viewpoint of enhancing the electromagnetic wave absorption performance, the soft magnetic powder preferably has a smaller particle size. However, fine metal powder on the order of microns has difficulty in handling, such as being easily ignited in air, and has never been used as a soft magnetic metal powder constituting an electromagnetic wave absorber.

Recently, the present inventors have established a technique for producing extremely fine iron powder whose surface is coated with inert iron nitride and has no risk of ignition. Good results were obtained when used as a material for electromagnetic wave absorbers.
Because this powder is much finer than conventional powders,
The electromagnetic wave absorbing sheet using this has higher electromagnetic wave absorbing performance than conventional products. In addition, since the powder surface is covered with a non-conductor, there is an advantage that even if a large amount of the powder is mixed with the matrix, the specific resistance is not reduced.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique for an electromagnetic wave absorber using the above-mentioned fine and inert soft magnetic powder, that is, an iron powder whose surface is coated with iron nitride, to an electronic circuit board. It is an object of the present invention to provide a substrate having improved decoupling performance.

[0008]

According to the first aspect of the electronic circuit board having a decoupling function of the present invention, as shown in FIG. 1, the average particle size is 5 μm or less, preferably 3 μm or less.
More preferably, Fe powder of 1 μm or less, fine soft magnetic powder having a coating layer of Fe nitride on its surface, an organic matrix material selected from rubber or plastic, or water glass using inorganic powder as a binder. % By volume in the inorganic matrix material bonded using
A substrate (1) formed by dispersing a fine soft magnetic powder so as to occupy at least 30% into a plate shape, wherein a signal line (2) is formed on a front surface and Gnd is formed on a rear surface.
It has a potential conductor layer (4A).

A second embodiment of the electronic circuit board having a decoupling function according to the present invention is, as shown in FIG. 2, a Fe powder having an average particle diameter of 5 μm or less, and a coating layer of Fe nitride on the surface thereof. The fine soft magnetic powder having at least 30% by volume of the fine soft magnetic powder in an organic matrix material selected from rubber or plastic, or in an inorganic matrix material obtained by combining inorganic powder with water glass as a binder. A substrate (1) formed into a plate shape by dispersing so that the signal line (2) and the Gnd line (3) are formed on the front surface, and Gn is formed on the rear surface.
It has a conductor layer (4B) of d potential.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The Fe powder has an average particle size of 1 μm.
It is preferable to use the following, particularly fine ones.
When a material having a large particle size exceeding 5 μm is used, conduction may occur when a through hole is opened from the signal layer to the Gnd layer. Various rubbers and plastics can be used as the matrix material. When high heat resistance is required, a material obtained by solidifying an inorganic matrix material with a water glass binder is useful. In this case, alumina powder, epoxy resin, Teflon (registered trademark) and the like can be used.

The thickness of the electronic circuit board is arbitrary, and is 0.1%.
It will be used in the range of
~ 2 mm is appropriate. As is well known, the characteristic impedance of an electronic circuit board is determined by factors such as the width and height of a signal line and the distance between the signal line and the Gnd potential layer, and the absolute value of the dielectric constant of the board. The operating frequency of a common electronic circuit is in the range of 40 to 200 MHz. For example, from the viewpoint of removing harmonic noise, the substrate operates as a low-pass filter that cuts a high frequency of 1 GHz or more, for example. Then, the above design factors may be selected and combined.

In order to produce the fine soft magnetic powder used in the present invention, an Fe oxide powder having an average particle size of 5 μm or less, preferably 1 μm or less is prepared by mixing H ₂ : NH ₃ = 5 by volume ratio.
A reduction step of heating to a temperature of 500 ° C. or more in an atmosphere of hydrogen or a mixed gas of hydrogen and ammonia of 10 to 5 to 0;
Then, a nitriding step of heating to a temperature of 600 ° C. or more in an atmosphere of ammonia or a hydrogen / ammonia mixed gas of H ₂ : NH ₃ = 0 to 9: 10-1 is sequentially performed.

Extremely fine Fe oxides as raw materials can be used as raw materials in wastes of the steel industry, such as converter dust and mill-scale pulverized materials. These are Fe
It is represented by the formula of ₂ O ₃ or Fe ₃ O ₄ , and the particle size is on the order of microns. In addition, acicular ferrite Fe ₂ O ₃ OH
Is also a material that exhibits a submicron particle size and is suitable for producing fine iron powder.

The reduction step is performed in an atmosphere of hydrogen gas, and the nitriding step is performed in an atmosphere of ammonia gas. At this time,
Ammonia gas or hydrogen gas may be mixed in the atmosphere. When the temperature reaches 500 ° C. or higher, the reduction proceeds at a practical rate. If the temperature is up to 600 ° C., the reduction of iron oxide occurs first, and the iron oxide particles change into iron particles. Then, when heated to a temperature of 600 ° C. or higher, nitriding occurs and iron particles are generated. Changes to iron nitride. Therefore, reduction and nitridation are performed in a H ₂ + NH ₃ mixed gas atmosphere at a constant high temperature or by changing the temperature from a low temperature to a high temperature, or the gas composition is changed from H ₂ → NH ₃ or H _2. It can be performed by changing the temperature to be constant or changing from low temperature to high temperature by changing ₂ + NH ₃ . The reaction is advantageously carried out using a rotary kiln while circulating gas.

[0015]

EXAMPLE A powder of acicular ferrite was placed in a tubular furnace, and a mixed gas of H ₂ : NH ₃ = 9: 1 by volume was passed through the furnace at 500 ° C. × 1 hour, then at 650 ° C. × 10 minutes. By heating, an iron powder having an iron nitride coating layer on the surface was obtained. This powder was a fine powder having an average particle size of 1 μm or less.
When analyzed by X-ray diffraction, it was α-Fe containing about 3% Fe ₄ N. However, the content of iron nitride obtained by elemental analysis was about 2%. The different analysis results indicate that the powder surface was rich in iron nitride, which greatly affected the X-ray diffraction.

Nylon is selected as a matrix material, and iron powder produced as described above is mixed with a powder having a volume ratio of 50%.
%. The mixture was injection molded into a 1.0 mm thick plate.

Using the above-mentioned plate, an electronic circuit board having the cross-sectional structure shown in FIG. 1 is manufactured, and an oscillator (Osc), a transmitter (Drv) and a receiver are formed thereon as shown in FIG. The equipment (Rcv) was arranged. The transmitter clock is 25
MHz, termination is 1kΩ resistor, driver is 74HCO
4A. Harmonic noise radiated from a line connecting the transmitter and the receiver was measured in a anechoic chamber (3 m method) as a vertically polarized wave in the range of 556 to 778 MHz.

For comparison, an electronic circuit board using a conventional glass epoxy resin was also tested under the same conditions. The results are shown in the bar graph of FIG. In the figure,
Solid bars are comparative examples, and white bars are examples.
At 651 MHz, which is the highest effect, an attenuation effect of about 10 dB was observed.

[0019]

According to the electronic circuit board having decoupling performance of the present invention, the soft magnetic powder is dispersed in an organic matrix material or an inorganic matrix material, and is used as a soft magnetic powder. Since the iron powder having a very fine diameter is used, the electromagnetic wave absorbing performance is remarkably high, and thus the decoupling performance is excellent.

This effect is obtained through a mechanism in which harmonics in a desired frequency range are effectively cut by appropriately selecting the characteristic impedance of the substrate according to the frequency range in which the electronic circuit operates. The characteristic impedance of the substrate depends on the type of matrix material to be combined,
It is determined by the compounding ratio of the iron powder, the thickness of the substrate, the width and height of the signal line (and the Gnd line if formed into a line), and other factors.

Since the iron nitride coating the surface of the fine soft magnetic powder does not have electric conductivity, when the powder is dispersed in a matrix, even if the powder particles come into contact with each other, an electric current is not generated between them. No conduction occurs. As a result, the specific resistance of the electronic circuit board of the present invention, which is an electromagnetic wave absorber, is higher than that of the conventional electronic circuit board in which conductive metal powder is dispersed. Therefore, this electronic circuit board can ensure high insulation even in a range where the mixing ratio of the powder is high, and the insulation between the through holes is also ensured. This benefit reduces the constraints on board design.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing one embodiment of an electronic circuit board according to the present invention.

FIG. 2 is a partial cross-sectional view showing another embodiment of the electronic circuit board according to the present invention.

FIG. 3 is a perspective view showing a circuit for testing the decoupling performance of an electronic circuit board according to the present invention.

FIG. 4 is a bar graph showing the decoupling performance of the electronic circuit board of Example 1 in comparison with a conventional product. Fill-in is the comparative example, and white is the example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Signal line 3 Gnd line 4A, 4B Conductive layer of Gnd potential

Claims (5)

[Claims] 1. A fine soft magnetic powder having an average particle size of 5 μm or less and having a coating layer of Fe nitride on its surface, in an organic matrix material selected from rubber or plastic, or in an inorganic material. A substrate (1) obtained by forming a dispersion in which a fine soft magnetic powder occupies at least 30% by volume in an inorganic matrix material in which the powder is bound by using water glass as a binder to form a plate (1). Then, a signal line (2) is formed on the surface,
An electronic circuit board having a decoupling function, having a conductor layer (4A) of Gnd potential on the back surface. 2. A fine soft magnetic powder having an average particle size of 5 μm or less and having a coating layer of Fe nitride on its surface, in an organic matrix material selected from rubber or plastic, or in an inorganic powder. (1) is a plate (1) formed by dispersing so that a fine soft magnetic powder occupies at least 30% by volume in an inorganic matrix material bonded by using water glass as a binder. A signal line (2) and a Gnd line (3) are formed on the front surface, and a conductor layer (4
B) An electronic circuit board having a decoupling function. 3. The electronic circuit board according to claim 1, wherein the Fe powder has an average particle size of 1 μm or less. 4. The electronic circuit board according to claim 1, wherein the matrix material is selected from chlorinated polyethylene, nylon, and an alumina plate. 5. The electronic circuit board according to claim 1, wherein the electronic circuit board has a sheet shape having a thickness of 0.1 to 10 mm.