JP2010206182A - Electromagnetic shielding sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic shielding sheet having excellent magnetic field shielding characteristics even if the sheet is reduced in thickness, which solves such a problem that, since the use of a thin conductive sheet lowers a magnetic field shielding effect, the thickness of the conductive sheet should be increased to some extent, and as a result, it is difficult to completely seal electronic parts because of the poor flexibility of the sheet, thus failing to obtain the high shielding effect. <P>SOLUTION: The electromagnetic shielding sheet includes a laminate film formed by laminating ferromagnetic layers 2 between conductive layers 1 formed of a non-magnetic material. The ferromagnetic layer 2 has electric field/magnetic field shielding effects in both cases that μF is a positive value and where the μF is a negative value when the μF is the specific magnetic permeability of a ferromagnetic material. The electric field/magnetic field shielding effects become greater as the absolute value of the μF becomes greater. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electromagnetic shield sheet for shielding electromagnetic noise.

  In mobile devices such as mobile phones and notebook personal computers, a sheet metal shield made of a metal plate shaped to cover electronic components is used to shield electromagnetic noise generated from electronic components operating at high frequencies. It has been.

  However, the sheet metal shield is an obstacle to making the mobile device thinner because the height of the shield case is increased.

  As a technique related to the electromagnetic shield, for example, Patent Document 1 discloses a method for manufacturing a magnetic sheet in which the shielding effect does not decrease even if the thickness is thin. In this magnetic sheet manufacturing method, a metal is vapor-deposited on a releasable PET having a release layer, a metal vapor-deposited layer is formed, and a magnetic paint in which flat metal powder is dispersed in a resin and a solvent is applied thereon. After drying and forming the magnetic layer, the magnetic layer and the metal vapor-deposited layer are peeled from the releasable PET at the same time.

JP 2000-348916 A

  In order to reduce the thickness of mobile devices, it is conceivable to shield electromagnetic noise by covering electronic components with a thin conductive sheet made of copper (Cu) or silver (Ag) instead of a sheet metal shield. .

  However, when a thin conductive sheet is used, the magnetic field shielding effect is reduced, so the thickness of the conductive sheet needs to be increased to some extent. As a result, the flexibility is inferior and it becomes difficult to completely seal the electronic component, and thus there is a problem that a large shielding effect cannot be obtained.

  The subject of this invention is providing the electromagnetic shielding sheet excellent in the magnetic field shielding characteristic, even if it reduced in thickness.

  In order to solve the above problems, the electromagnetic shield sheet according to the present invention is characterized by comprising a laminated film in which conductive layers made of a non-magnetic material are laminated so as to sandwich a conductive ferromagnetic layer.

  According to the present invention, an electromagnetic shield sheet having excellent electromagnetic shielding characteristics can be provided by forming a laminated film in which conductor layers and conductive ferromagnetic layers are alternately laminated. Can do.

It is sectional drawing which shows the structure of the electromagnetic shielding sheet which concerns on Example 1 of this invention. It is a perspective view which shows the structure of the simulation model of the electromagnetic shielding sheet which concerns on Example 1 of this invention. It is sectional drawing which shows the structure of the simulation model of the electromagnetic shielding sheet which concerns on Example 1 of this invention. It is a figure which shows the average value of the magnetic field intensity computed with the simulation model of the electromagnetic shielding sheet which concerns on Example 1 of this invention. It is a figure which shows the average value of the electric field strength computed with the simulation model of the electromagnetic shielding sheet which concerns on Example 1 of this invention. It is a figure which shows the relationship between the relative magnetic permeability of the ferromagnetic material in 5 GHz, and the average value of the magnetic field intensity in a measurement surface. It is a figure which shows the relationship between the relative magnetic permeability of the ferromagnetic material in 5 GHz, and the average value of the electric field strength in a measurement surface. It is a perspective view which shows the structure of the simulation model of the electromagnetic shielding sheet which concerns on Example 2 of this invention. It is sectional drawing which shows the structure of the simulation model of the electromagnetic shielding sheet which concerns on Example 2 of this invention. It is sectional drawing which shows the structure of the simulation model of the electromagnetic shielding sheet which concerns on Example 2 of this invention. It is sectional drawing which shows the structure of the simulation model of the electromagnetic shielding sheet which concerns on Example 2 of this invention. It is sectional drawing which shows the structure of the simulation model of the electromagnetic shielding sheet which concerns on Example 2 of this invention. It is a figure which shows the relationship between the number of layers of the ferromagnetic material which concerns on Example 2 of this invention, the thickness of a shield, and the amount of magnetic field shields. It is a figure which shows the relationship between the number of layers of the ferromagnetic material which concerns on Example 2 of this invention, and the thickness of a shield, and the amount of magnetic field shields. It is a figure which shows the relationship between the number of layers of the ferromagnetic material which concerns on Example 2 of this invention, and the thickness of a shield, and the amount of magnetic field shields. It is a figure which shows the relationship between the number of layers of the ferromagnetic material which concerns on Example 2 of this invention, and the thickness of a shield, and the amount of magnetic field shields. It is a figure showing the frequency characteristic of the relative magnetic permeability of the ferromagnetic material used for the analysis which concerns on Example 2 of this invention. It is a figure which shows the relationship between the frequency which concerns on Example 2 of this invention, and the magnetic field shield amount of a Y direction. It is a perspective view which shows the structure of the simulation model of the electromagnetic shielding sheet which concerns on Example 3 of this invention. It is a figure which shows the relationship between the frequency which concerns on Example 3 of this invention, and the magnetic field shield amount of a Y direction.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating a configuration of an electromagnetic shield sheet according to Example 1 of the present invention. This electromagnetic shield sheet is composed of a laminated film composed of five layers in which a conductor layer 1, a ferromagnetic layer 2, a conductor layer 1, a ferromagnetic layer 2, and a conductor layer 1 are sequentially laminated. The ferromagnetic layer 2 is preferably composed of a conductive ferromagnetic material.

  In the example shown in FIG. 1, it is composed of two ferromagnetic layers 2 and three conductor layers 1 formed so as to sandwich them, but a structure in which a ferromagnetic layer is sandwiched between conductor layers. If so, the number of layers of the conductor layer 1 and the ferromagnetic layer 2 is not limited to the above. Increasing the number of ferromagnetic layers 2 can enhance the magnetic field shielding effect.

  The conductor layer 1 is made of a nonmagnetic material (conductor) such as silver (Ag), copper (Cu), or aluminum (Al).

The ferromagnetic layer 2 is composed of a ferromagnetic material made of iron (Fe), nickel (Ni) or cobalt (Co) alone or a compound containing iron (Fe), nickel (Ni) or cobalt (Co). Has been. An example of the compound is Co ₈₅ Nb ₁₂ Zr ₃ .

  Many ferromagnetic materials have a negative relative permeability at a frequency of 1 GHz or more.

  Moreover, since this magnetic field shield sheet contains the conductor layer 1, it can shield an electric field and becomes an electromagnetic shield sheet that shields not only a magnetic field but also an electric field.

  Next, since the shielding effect of electromagnetic noise of the electromagnetic shielding sheet configured as described above was confirmed by simulation, the result will be described.

  FIG. 2 is a perspective view showing the configuration of the simulation model, and FIG. 3 is a cross-sectional view thereof. This simulation model is configured by laminating an inductor L as a noise source embedded in an insulator on an electromagnetic shield sheet. Note that the noise source is not limited to the inductor L, and any circuit component may be used.

  In this simulation model, the size of the inductor L that generates a magnetic field is 0.1 × 0.1 mm. The inductor L has an insulator therein, and the distance between the inductor L and the surface (conductor layer) of the electromagnetic shield sheet is 6.6 um.

  The electromagnetic shield sheet is composed of a laminated film of five layers in which the conductor layer 1, the ferromagnetic layer 2, the conductor layer 1, the ferromagnetic layer 2 and the conductor layer 1 are sequentially laminated, and the thickness of the conductor layer 1 is 1 μm. The thickness of the ferromagnetic layer 2 is 0.2 μm, and the total film thickness of the electromagnetic shield sheet is 3.4 μm.

  For comparison, in addition to the electromagnetic shield sheet simulation model (model 1) according to the first embodiment, only copper (Cu) is a one-layer model 2 and stainless steel (Sus: Stainless Used Steel) as the material of the sheet metal shield. Only one-layer model 3 was simulated. The total film thickness of Model 1 to Model 3 electromagnetic shield sheets was all 3.4 μm.

  For these three models, the average values of the magnetic field strength and the electric field strength of the measurement surface (surface 1 shown in FIG. 3) 10 μm away from the surface of the electromagnetic shield sheet were calculated. The results are shown in FIG. 4 and FIG. FIG. 4 shows the average value of the magnetic field strength on the measurement surface, and FIG. 5 shows the average value of the electric field strength on the measurement surface.

As shown in FIGS. 4 and 5, when model 1 using a laminated film has μ _F (relative permeability of ferromagnetic material) of −30, model 2 only with copper (Cu), stainless steel (Sus) only Both the magnetic field and the electric field were lower than those of the model 3 in FIG.

  Therefore, the laminated film of the conductor and the ferromagnetic body has a higher shielding effect against magnetic field noise and electric field noise than conventional copper (Cu) or stainless steel (Sus).

  FIG. 6 shows the relationship between the relative permeability of the ferromagnetic material at 5 GHz and the average value of the magnetic field strength on the measurement surface. According to this, it can be seen that the magnetic field strength on the measurement surface is lower as the absolute value of the relative permeability is larger, regardless of whether the relative permeability of the ferromagnetic material is positive or negative. Moreover, when the absolute value of relative magnetic permeability is 10 or more, the magnetic field strength is lower than 1.78 A / m in the case of an electromagnetic shield sheet made of Cu alone.

  FIG. 7 shows the relationship between the relative permeability of the ferromagnetic material at 5 GHz and the average value of the electric field strength on the measurement surface. According to this, it can be seen that the electric field strength on the measurement surface is lower as the absolute value of the relative permeability is larger, regardless of whether the relative permeability of the ferromagnetic material is positive or negative. Moreover, when the absolute value of relative magnetic permeability is 10 or more, the electric field strength is lower than 1.92 V / m in the case of an electromagnetic shield sheet made of Cu alone.

  Therefore, in the laminated film of the conductor and the ferromagnetic material, the electric field shielding effect and the magnetic field shielding effect are higher as the absolute value of the relative magnetic permeability is higher regardless of the relative magnetic permeability of the ferromagnetic material. When the absolute value was 10 or more, a shielding effect higher than that of the copper (Cu) electromagnetic shielding sheet was obtained.

  FIG. 8 is a perspective view showing a configuration of a simulation model of the electromagnetic shield sheet according to Example 2 of the present invention. The distance between the signal line serving as the electromagnetic wave source and the electromagnetic shield sheet is set to 0.1 mm, and the amount of magnetic field shielding is such that a 0.2 mm square surface 1 is disposed at a position separated by 0.2 mm from the signal line. It calculated from the difference of the average value of magnetic field intensity.

  The electromagnetic shield sheets used for the analysis are four types shown in FIGS. 9 is a cross-sectional view of an electromagnetic shield sheet having only a conductor (Cu), FIG. 10 is a cross-sectional view of an electromagnetic shield sheet including two conductor layers and one ferromagnetic layer, and FIG. 11 is a three-layer structure. FIG. 12 is a cross-sectional view of an electromagnetic shield sheet comprising five conductor layers and four ferromagnetic layers, and FIG. 12 is a cross-sectional view of an electromagnetic shield sheet comprising two conductor layers and two ferromagnetic layers.

The thickness of the ferromagnetic layer was fixed at 0.2 μm, and the thickness of the electromagnetic shield sheet was changed by changing the thickness of the conductor layer. The frequency was analyzed at 100 MHz. As the ferromagnetic material, four types of magnetic material having a relative permeability of 1000, a magnetic material having a relative permeability of −1000, Co ₈₅ Nb ₁₂ Zr ₃ , and Ni ₈₀ Fe ₂₀ were used. A magnetic body having a relative permeability of 1000 has a real part of the relative permeability of 1000 and an imaginary part of 0. A magnetic body having a relative permeability of −1000 has a real part of the relative permeability of −1000 and an imaginary part of 0. In Co ₈₅ Nb ₁₂ Zr _3, the real part of relative permeability was 1011 and the imaginary part was 55. Ni ₈₀ Fe ₂₀ has a real part of relative permeability of 3290 and an imaginary part of 392. The thickness was varied from 0.5 to 64 um. FIG. 13 shows the relationship between the thickness of the electromagnetic shielding sheet of magnetic material having a relative permeability of 1000 and the amount of magnetic shielding. FIG. 14 shows the relationship between the thickness of a magnetic shield sheet of magnetic material having a relative permeability of −1000 and the amount of magnetic field shield. FIG. 15 shows the relationship between the thickness of the electromagnetic shield sheet of magnetic material of Co ₈₅ Nb ₁₂ Zr _{3 and} the amount of magnetic field shield. FIG. 16 shows the relationship between the thickness of the magnetic shield sheet of magnetic material of Ni ₈₀ Fe _{20 and} the amount of magnetic field shield. FIGS. 13 to 16 are semi-logarithmic graphs in which the thickness (um) of the electromagnetic shield sheet on the horizontal axis is expressed logarithmically and the magnetic field shield amount dB (decibel) on the vertical axis is linearly expressed.

As shown in FIGS. 13 to 16, it can be seen that the amount of magnetic field shield is higher when the electromagnetic shield sheet according to the present invention is used than when the electromagnetic shield sheet is made of only a conductor. Specifically, the thickness of the electromagnetic shield sheet is 0.50 μm or more for a magnetic material having a relative permeability of 1000, and the thickness of the electromagnetic shield sheet is 0.71 μm or more for a magnetic material having a relative permeability of −1000, In Co ₈₅ Nb ₁₂ Zr ₃ , the thickness of the electromagnetic shield sheet is 0.50 μm or more, and in Ni ₈₀ Fe ₂₀ , the thickness of the electromagnetic shield sheet is 0.50 μm or more. It can be seen that the larger the number, the higher the magnetic shielding amount.

  Since the skin thickness of the conductor (Cu) at 100 MHz is 6.6 um, the electromagnetic shield sheet according to the present invention has a thickness of about 1/10 or more (for example, 0.5 um to 1 um) of the skin thickness of the conductor. Thus, the electromagnetic shielding amount becomes higher than the electromagnetic shielding sheet having only a conductor, and the electromagnetic shielding amount increases as the thickness increases. The skin thickness δ is a thickness at which the electromagnetic field attenuates to 1 / 2.7 in the conductor, and is represented by the following equation (1).

ここで、μは透磁率［Ｈ／ｍ］、σは導電率［Ｓ／ｍ］、ｆは周波数［Ｈｚ］である。

Here, μ is permeability [H / m], σ is conductivity [S / m], and f is frequency [Hz].

  Next, in the simulation model shown in FIG. 8, using the electromagnetic shield sheet consisting of only the conductor shown in FIG. 9 and the electromagnetic shield sheet consisting of two conductor layers and one ferromagnetic layer shown in FIG. And the result of analyzing the relationship between the magnetic field shielding amount and the magnetic field shielding amount.

  Each electromagnetic shield sheet was 1 um thick. The frequency characteristics of the real part μ ′ and the imaginary part μ ″ of the relative permeability of the ferromagnetic material are given as shown in FIG. 17. The real part μ ′ of the relative permeability is 0 and the imaginary part is maximum. Is the ferromagnetic resonance frequency, which is 890 MHz in the example shown in FIG.

  FIG. 18 shows the analysis result of the frequency characteristics of the magnetic field shield amount in the Y direction. As shown in FIG. 18, the highest magnetic field shielding amount was obtained at the ferromagnetic resonance frequency of 890 MHz, and the higher magnetic field shielding amount was obtained from 10 MHz to 890 MHz.

  According to the electromagnetic shielding sheet according to Example 2, an electromagnetic shielding sheet having a high shielding amount at a desired frequency can be realized by selecting a ferromagnetic material whose ferromagnetic resonance frequency is close to the frequency at which the shielding amount is desired to be the highest. .

  FIG. 19 is a perspective view showing a configuration of a simulation model of the electromagnetic shield sheet according to Example 3 of the present invention. This simulation model is used to analyze the relationship between the anisotropy of the magnetic body of the electromagnetic shield sheet and the shielding effect. The electromagnetic shield sheet used for the analysis is the electromagnetic shield sheet composed of only the conductor shown in FIG. 9 and the electromagnetic shield sheet composed of the three conductor layers and the two ferromagnetic layers shown in FIG.

  As shown in FIG. 19, the electromagnetic shield sheet composed of three conductor layers and two ferromagnetic layers is composed of a magnetic layer far from the signal line, the magnetic layer A, and a magnetic substance closer to the signal line. The magnetic layer B is the easy axis direction of uniaxial magnetic anisotropy, “the magnetic layer A is the Y direction, the magnetic layer B is the Y direction”, “the magnetic layer A is the Y direction, and the magnetic layer B The analysis was performed on four types: “X direction”, “Magnetic layer A is X direction, Magnetic layer B is Y direction”, and “Magnetic layer A is X direction, and Magnetic layer B is X direction”. The relative permeability of the magnetic material is 1 in the easy axis direction, and the frequency characteristic shown in FIG. 20 is given to the hard axis perpendicular to the easy axis. The distance between the signal line and the electromagnetic shield sheet is 0.1 mm, and the amount of magnetic field shielding is the difference of the average value of the magnetic field strength of the surface 1 by arranging the 0.2 mm square surface 2 at a position 0.2 mm away from the signal line. Calculated from

  FIG. 20 shows the frequency characteristics of the magnetic field shield amount in the Y direction. When the easy axis of the magnetic body is “the magnetic body A is in the Y direction and the magnetic body B is in the Y direction”, the magnetic shield amount is lower than that of the electromagnetic shield sheet having only the conductor. “B is in the X direction” and “Magnetic body A is in the X direction and magnetic body B is in the Y direction” were higher than the conductor-only electromagnetic shield sheet at 10 to 8900 MHz. Therefore, the electromagnetic shield sheet according to the present invention has two or more ferromagnetic layers, and the uniaxial magnetic anisotropy is formed in a direction orthogonal to each other by different layers, thereby providing a high shield in two directions perpendicular to the plane. Has an effect. When three or more ferromagnetic layers are formed, a high shielding effect is obtained in three or more intersecting directions in the plane by forming the uniaxial magnetic anisotropy in a direction intersecting with different layers.

  INDUSTRIAL APPLICABILITY The present invention can be used as an electromagnetic shield sheet for mobile devices such as mobile phones and notebook personal computers that operate at high frequencies.

1. Conductor layer, 2. Magnetic layer, L. Inductor.

Claims (7)

  An electromagnetic shield sheet comprising a laminated film in which conductor layers made of a non-magnetic material are laminated so as to sandwich a ferromagnetic layer. The ferromagnetic layer, when the mu _F and relative permeability of the ferromagnetic body, if mu _F is positive, there is the electrical or magnetic field shielding effect in both cases in case of negative, the electrical or magnetic field shielding effect electromagnetic shielding sheet according to claim 1, wherein the higher the absolute value of mu _F is large.   The electromagnetic shield sheet according to claim 1, wherein the ferromagnetic layer is made of a conductive ferromagnetic material.   4. The electromagnetic shield according to claim 1, wherein the ferromagnetic layer is formed of a plurality of layers, and the magnetic field shield amount is increased as the number of layers increases. 5. Sheet.   5. The thickness according to claim 1, wherein the thickness is equal to or more than a predetermined value of the skin thickness of the conductor, and the electromagnetic shielding amount increases as the thickness increases. The electromagnetic shielding sheet as described.   The magnetic field shield amount is increased as the frequency is higher than the ferromagnetic resonance frequency of the ferromagnetic material, and the magnetic field shield amount is highest at the ferromagnetic resonance frequency. Item 6. The electromagnetic shield sheet according to any one of items 5 to 6.   It has two or more ferromagnetic layers, and is formed so that uniaxial magnetic anisotropy is formed in a direction intersecting with different layers, and has a high magnetic field shielding amount in a plurality of intersecting directions. The electromagnetic shielding sheet according to any one of claims 1 to 6.

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