JPH0818271A - Electronic device and noise suppressing method - Google Patents

Abstract

PURPOSE:To easily suppress the noise emitted out from an interconnection board, the mutual interference between parts in the board, and malfunction due to the electromagnetic induction between signal lines. CONSTITUTION:An LSI 2 is mounted on an interconnection board 1, interconnection conductor 3 is laid below the LSI 2 on the back side of the board, and an electromagnetic interference suppressor A of the same size as that of the LSI 2 is disposed between the LSI 2 and board 1. Before mounting the LSI 2, the suppressor A is fixed to it or the board 1. Since it attenuates unwanted radiation noise produced by the LSI 2, the inductive coupling between the LSI 2 and conductor 1 is made little to efficiently suppress the noise produced at the conductor 3. The suppressor A is composed of a conductive support and insulative soft magnetic layer formed on, at least, one side of the support.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device and a noise suppressing method therefor, and in particular, it is unnecessary in an electronic device in which an active element for radiating inductive noise such as a semiconductor element is mounted on a wiring board and the electronic device. The present invention relates to a method for suppressing electromagnetic interference caused by electromagnetic interference.

[0002]

2. Description of the Related Art In recent years, electronic devices such as digital electronic devices that utilize high frequencies have been remarkably miniaturized. Especially in digital electronic devices with a high density of parts mounted on wiring boards,
LSIs and ICs such as a central processing unit (CPU) and an image processor arithmetic logic unit (IPALU) are mounted on a wiring board. As is well known, LSIs and ICs are composed of many semiconductor elements. A semiconductor element is called an active element because it receives an energy supply from the outside and acts such as amplification and oscillation. Active devices such as these semiconductor devices generally radiate inductive noise. Due to this inductive noise, a high frequency magnetic field is induced on the same surface as the element mounting surface of the wiring board and the opposite surface. This induced high frequency magnetic field increases line coupling due to electromagnetic coupling and causes radiation noise. The generated radiation noise not only causes a malfunction inside the device, but also radiates to the outside through the external connection terminal and is conducted and adversely affects other devices. Such malfunctions and adverse effects on other devices are called electromagnetic interference.

Conventionally, with respect to such electromagnetic interference,
The following measures were taken. That is, a low pass filter is connected to the circuit. Move the circuit in question away from the circuit that affects it. Shield. Perform grounding. By taking such measures, conventionally, electromagnetic coupling, unnecessary radiation, and conduction noise that cause electromagnetic interference have been suppressed.

[0004]

However, in order to efficiently deal with the above-mentioned problems in a wiring board in which active elements are mounted at a high density, the conventional noise suppression method has the following drawbacks. That is, it requires specialized knowledge and experience in noise countermeasures. It takes time to take measures against noise. The filters used are expensive. There are often restrictions on the space for implementing filters. Filter mounting is not easy. The number of man-hours required for assembling the electronic device is large and the cost is large.

Particularly, in the case of suppressing electromagnetic induction between signal lines generated between components in the same circuit and mutual interference due to unnecessary electromagnetic waves, particularly sufficient measures are required. Furthermore, in order to reduce the size and weight of the electronic device, it is essential to eliminate the filter and its mounting space.

Therefore, an object of the present invention is to improve the electronic device itself instead of using a filter or the like to easily radiate noise from the wiring board to the outside, mutual interference between components inside the wiring board, and signal lines. It is to suppress malfunction due to electromagnetic induction between.

[0007]

In order to solve the above problems, according to a first aspect of the present invention, in an electronic device including a wiring board on which an active element that radiates inductive noise is mounted, a wiring board is provided. And an active element, the electromagnetic wave interference suppressor being sandwiched between the electromagnetic wave interference suppressor and the active element. The electromagnetic wave interference suppressor includes a conductive support and an insulating soft magnetic material layer provided on at least one surface of the conductive support. An electronic device is obtained which has:

In the electronic device according to the first aspect,
It is preferable that the insulating soft magnetic material layer comprises an organic binder and flat and / or acicular soft magnetic powder dispersed in the organic binder.

According to a second aspect of the present invention, there is provided a method for suppressing inductive noise in an electronic device including a wiring board on which an active element for radiating inductive noise is mounted, the method comprising: A method for suppressing noise in an electronic device is obtained, in which an electromagnetic wave interference suppressor having a conductive support and an insulating soft magnetic material layer is sandwiched between them.

[0010]

The electromagnetic interference suppressor basically has a conductive support having an insulating soft magnetic layer provided on one or both sides thereof. That is, the conductive support exhibits a shielding effect with respect to the other wiring conductor and the electronic circuit facing the one wiring conductor and the electronic circuit which are noise sources, and suppresses electromagnetic wave interference. On the other hand, increase in electromagnetic coupling due to reflection of unnecessary radiation is suppressed by the insulating soft magnetic material layer. The insulating soft magnetic layer is made of, for example, soft magnetic powder and an organic binder. This insulating soft magnetic material layer is essentially an insulating layer formed by finely powdering a soft magnetic metal that is a conductive material and kneading and dispersing it with an insulating organic binder. When the soft magnetic powder is flat or needle-shaped, magnetic anisotropy of shape appears and complex permeability increases due to magnetic resonance in a high frequency region, which effectively eliminates unnecessary radiation components. Can be absorbed and suppressed. The electromagnetic wave interference suppressor is described in Japanese Patent Application No. 6-4864 filed by the present applicant on January 20, 1994.

[0011]

The present invention will be described in detail with reference to the drawings.

FIG. 1 shows a cross section of an electronic device according to an embodiment of the present invention. The LSI 2 is mounted on the wiring board 1, and the wiring conductor 3 is wired on the back surface of the wiring board 1 below the LSI 2. Further, between the LSI 2 and the wiring board 1, the LS
About half the electromagnetic wave interference suppressor A having the same size as I2 is mounted.

The electromagnetic wave interference suppressor A is fixed to either the LSI 2 or the wiring board 1 before mounting the LSI 2. Since the electromagnetic wave interference suppressor A focuses the magnetic flux of the high-frequency electromagnetic field generated by the LSI 2, it weakens the inductive coupling between the LSI 2 and the wiring conductor 1 and efficiently suppresses the noise generated in the wiring conductor 3.

FIG. 2 shows a cross section of the electromagnetic wave interference suppressor A shown in FIG. The electromagnetic wave interference suppressor A is a conductive support 4
And an insulating soft magnetic material layer 5 provided on at least one surface (both surfaces in FIG. 2) of the conductive support 4. Instead of the conductive support 4, a conductive soft magnetic support exhibiting soft magnetism may be used. The insulating soft magnetic material layer 5 contains the soft magnetic material powder 6 and the organic binder 7. That is, the soft magnetic powder 6 is uniformly dispersed in the organic binder 7. The soft magnetic powder 6 has a flat shape and / or a needle shape.

As the conductive support 4, one of a conductive plate, a mesh-shaped conductive plate, and a woven fabric of conductive fibers can be selected. Further, as the conductive soft magnetic support, one of a soft magnetic metal plate, a mesh soft magnetic metal plate, or a soft magnetic metal fiber woven fabric can be selected.

Specific examples of the conductive support 4 include a metal plate such as a copper thin plate, a stainless thin plate and an aluminum thin plate,
And so-called,
A punching metal, or a so-called expanded metal in which a thin plate is finely cut and then stretched, or a wire mesh in which a thin wire is processed into a mesh shape is used. As a specific example of the conductive soft magnetic support, in the same form, only the material may be replaced with permalloy or iron-silicon steel exhibiting soft magnetism. In this case, a high electromagnetic wave interference suppressing effect at a relatively low frequency can be expected. In any case, it is desirable to select it according to the application.

Flat (or acicular) soft magnetic powder 6
As typical examples of such materials, iron-aluminum-silicon alloy (Sendust) and iron-nickel alloy (Permalloy) having high high-frequency permeability can be cited. Soft magnetic powder 6
Aspect ratio is large enough (approximately 5: 1 or more)
Is desirable.

Examples of the organic binder 7 include polyester resin, polyvinyl chloride resin, polyvinyl butyral resin, polyurethane resin, cellulose resin, nitrile-based resin.
Thermoplastic resins such as butadiene rubber and styrene-butadiene rubber or their copolymers, epoxy resins,
Examples thereof include thermosetting resins such as phenol resins, amide resins, and imide resins.

3 (a) and 3 (b) show a characteristic evaluation system of the electromagnetic wave interference suppressor A assuming the electromagnetic environment shown in FIG. 1 for verifying the effect of the present invention. FIG. 3 (a)
Is an evaluation system for measuring the transmission level [dB], and FIG. 3B is an evaluation system for measuring the binding level [dB]. In each case, the electromagnetic field wave source oscillator 8 and the electromagnetic field intensity measuring device (reception element) 9 include an electromagnetic field transmitting minute loop antenna 10 having a loop system of 2 mm or less,
A small loop antenna 11 for electromagnetic field reception is used. A spectrum analyzer (not shown) was used as a measuring instrument for measuring the transmission level or the coupling level. In the invention according to the above-mentioned prior application (Japanese Patent Application No. 6-4864), a network analyzer is used as a measuring instrument. Therefore, it should be noted that the measurement results of the present invention and the invention of the prior application are different.

[Verification Example 1] 120 as the conductive support 4
Using a stainless steel mesh, a soft magnetic paste comprising the following composition <composition 1> such that the total thickness after drying and curing of the conductive support 4 is 0.5 mm. > Flat soft magnetic fine powder ...... 90 parts by weight Composition: Fe-Al-Si alloy Average particle size: 10 μm Aspect ratio:> 5 Organic binder Polyurethane resin ...... 8 parts by weight Curing agent (isocyanate compound) ...... 2 parts by weight Solvent (compound of cyclohexanone and toluene) ... 40 parts by weight was applied by the doctor blade method and cured at 85 ° C. for 24 hours to obtain a sample for evaluation. When the obtained evaluation sample was analyzed using a vibration magnetometer and a scanning electron microscope, the easy axis of magnetization and the orientation direction of the magnetic particles were in the in-plane direction of the sample.

[Verification Example 2] 75 μ as the conductive support 4
A sample for evaluation was obtained in the same manner as in [Verification example 1] except that an aluminum film having a thickness of 3 μm was sputter-deposited on both sides of a polyimide film of m.

[Verification Example 3] 75 μ as the conductive support 4
Silver paste of <composition 2> below on both sides of the polyimide film of m <composition 2> Fine silver powder: 95 parts by weight Average particle size: 3 μm Organic binder polyvinyl butyral resin: 4 parts by weight Curing agent (isocyanate compound) …… 1 part by weight Solvent (ethyl cellosolve) …… 35 parts by weight, except that a film was formed by the doctor blade method so that the thickness after drying and curing would be 6 μm [Verification Example 1 ] The sample for evaluation was obtained like the above.

Comparative Example 1 A copper plate having a thickness of 100 μm was used as a comparative sample.

Comparative Example 2 80 parts by weight of iron powder having a substantially spherical shape and an average particle size of 30 μm was kneaded into 20 parts by weight of nitrile rubber to form a sheet having a thickness of 0.5 mm. Was used as a comparative sample.

The transmission level and the binding level of the evaluation sample and the comparative sample are shown in FIGS.
The results measured by the evaluation system shown in (b) are shown in FIGS. 4 (a) and 4 (b), 5 (a) and 5 (b).

4 (a) and 4 (b) show the frequency characteristics of the electromagnetic interference suppression effect of the comparative sample. FIG. 4A shows the frequency f [GHz] characteristic of the transmission level [dB]. Here, the reference of the transmission level is the electromagnetic field strength in the state where there is no electromagnetic wave interference suppressor. FIG. 4B shows the frequency f [GHz] characteristic of the coupling level [dB]. Here, the standard of the coupling level was the electromagnetic field strength without the electromagnetic wave interference suppressor.

5 (a) and 5 (b) show the frequency characteristics of the electromagnetic wave interference suppressing effect of the evaluation samples to. Figure 5
(A) is the frequency f [GHz] characteristic of the transmission level [dB]. Here, the reference of the transmission level is the electromagnetic field strength in the state where there is no electromagnetic wave interference suppressor. FIG. 5B shows the frequency f [GHz] characteristic of the coupling level [dB]. here,
The standard of the coupling level was the electromagnetic field strength without the electromagnetic wave interference suppressor.

As can be seen from FIGS. 4 (a) and 4 (b), when the conductor (copper foil) only [Comparative Example 1] was used, although the transmission level was significantly lowered (-50 dB or less), This is a problem because the level increases (about + 7db). On the other hand, in the case of the comparative example 2 in which spherical iron powder having soft magnetism and almost no shape anisotropy is dispersed in rubber, the binding level tends to decrease (about −0 dB), but the transmission attenuation is almost zero. None (transmission level is about -1 dB), there is almost no effect of suppressing interference.

With respect to the effects of these conventional electromagnetic wave interference suppressors, the electromagnetic wave interference suppressor according to the present invention ([verification example 3] to
[Verification Example 3]), FIG. 5 (a) and FIG. 5 (b)
As is clear from the above, the transmission level is sufficiently low (-39
(less than dB), the coupling level does not increase (less than +1 dB). Therefore, in the electronic device as shown in FIG. 1, it is possible to effectively suppress electromagnetic wave interference without being affected by reflection due to unnecessary radiation.

Although the present invention has been described with reference to some embodiments, it is needless to say that the present invention is not limited to the above embodiments and various modifications can be made without departing from the gist of the present invention. Nor.

[0031]

As described above, according to the present invention, a conductive support and an insulating soft magnetic material layer are provided between an active element such as a semiconductor element which becomes a noise source and a wiring conductor adjacent to the active element. By mounting the electromagnetic wave interference suppressor, it is possible to suppress mutual interference without increasing reflection of unnecessary electromagnetic waves. Further, since the electromagnetic wave interference suppressor is a thin plate, when considering the entire device including parts for suppressing noise, an electronic device that is smaller and lighter in weight and cheaper than conventional ones can be obtained. The electromagnetic wave interference suppressor according to the present invention can easily have flexibility, as can be seen from its constituent elements, and can respond to complicated shapes and to meet severe vibration resistance and shock requirements. It is possible.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an electronic device according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing an electromagnetic wave interference suppressor used in the electronic device shown in FIG.

FIG. 3 shows an evaluation system used for evaluating the characteristics of an electromagnetic wave interference suppressor, (a) is a schematic view of an evaluation system for measuring a transmission level, and (b) is a schematic view of an evaluation system for measuring a binding level. Is.

FIG. 4 shows a comparative sample and FIGS.
The frequency dependence of the electromagnetic wave interference suppression effect measured by the evaluation system of (b) is shown, (a) is a frequency characteristic graph of a transmission level, (b) is a frequency characteristic graph of a coupling level.

FIG. 5 shows evaluation samples 1 to 3 (a) and 3 (b).
Shows the frequency dependence of the electromagnetic interference suppression effect measured by the evaluation system of (a) is a frequency characteristic graph of the transmission level,
(B) is a frequency characteristic graph of the coupling level.

[Explanation of symbols]

 1 Wiring Board 2 LSI 3 Wiring Conductor 4 Conductive Support 5 Insulating Soft Magnetic Layer 6 Soft Magnetic Powder 7 Organic Binder 8 Electromagnetic Field Wave Source Oscillator 9 Electromagnetic Field Strength Measuring Device 10 Electromagnetic Field Transmitting Micro Loop Antenna 11 Micro loop antenna for electromagnetic field reception A Electromagnetic wave interference suppressor

Claims (3)

[Claims] 1. An electronic device including a wiring board on which an active element that radiates inductive noise is mounted, comprising an electromagnetic wave interference suppressor sandwiched between the wiring board and the active element. The electronic device, wherein the interference suppressor has a conductive support and an insulating soft magnetic material layer provided on at least one surface of the conductive support. 2. The electronic device according to claim 1, wherein the insulating soft magnetic material layer is composed of an organic binder and flat and / or acicular soft magnetic powder dispersed in the organic binder. . 3. A method for suppressing the inductive noise in an electronic device including a wiring board on which an active element for radiating inductive noise is mounted, comprising: A method for suppressing noise in an electronic device, comprising sandwiching an electromagnetic wave interference suppressor having a support and an insulating soft magnetic material layer.