KR101616787B1 - Magnetic shielding sheet and method for manufacturing the same - Google Patents

Abstract

An embodiment of the present invention relates to a magnetic shield sheet and a method of manufacturing the same, and a technical problem to be solved is to make the electromagnetic wave absorption rate excellent in an electromagnetic noise frequency band of 100 kHz to 300 kHz.
To this end, an embodiment of the present invention is an electromagnetic wave absorbing sheet comprising a plurality of braked amorphous piece pieces; A protective film adhered on one surface of the electromagnetic wave absorbing sheet; And an adhesive film adhered on the other surface of the electromagnetic wave absorbing sheet which is the opposite surface of the one surface, and has a quality factor value Q of 80 or more with a frequency of 100 kHz to 300 kHz.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a magnetic shield sheet and a magnetic shield sheet,

An embodiment of the present invention relates to a magnetic shield sheet having a large electromagnetic wave absorbing effect and a method of manufacturing the same.

It is intended to equip mobile phones with local communication and local card payment functions. As a result of incorporating the three films having these functions into the cellular phone case, the desired characteristics were not obtained.

However, when the amorphous sheet is inserted, the desired characteristics are obtained.

In order to increase the permeability, the amorphous sheet is pressed by a roller to be crushed. The amorphous sheets were respectively attached to both sides of the double-sided tape before being pressed by the rollers, and a protective film was attached to the outer surface of the amorphous body, followed by pressurizing with a roller to braking and consequently obtaining an imaginary part permeability of 50 or more at 300 kHz.

In recent years, there has been a growing demand for higher speed, higher performance, miniaturization and thinning of product form of circuit signal processing speed of electronic devices in relation to digital electronic devices. The data processing speed of various semiconductor devices mounted on a printed circuit board (PCB) is increased, and the mounting density of the active device and the passive device mounted on the printed circuit board (PCB) is also increasing.

Such devices are accompanied by rapid changes in voltage and current due to high-speed signals, and thus induce inductive noise, which is a source of high frequency noise. Components such as active and passive components are located very close to the print wiring circuitry, causing cross talk problems between internal components of small digital electronic devices or between components and wiring, EMI (Electro Magnetic Interference) that affects other devices may be caused.

In addition, when electromagnetic waves generated from electronic devices are exposed to the human body for a long period of time, they affect the human body such as glaucoma and deterioration of reproductive ability.

Electro Magnetic Shielding (EMI), which is proposed as a countermeasure against the above-mentioned EMI, refers to absorbing or interrupting the electromagnetic noise generated from the outside without radiating the electromagnetic noise generated inside the electronic device out of the case.

In the case of a digital electronic device having a space inside the device, a filter may be connected to a circuit for generating inductive noise to remove noise or to reduce the distance between the circuits, shielding with an electromagnetic shielding material, And EMI measures are taken.

However, in the case of small-sized digital electronic devices, electronic components are mounted on a printed circuit board (PCB) at a high density. As a countermeasure against noise caused by the above-mentioned filter and the like, not only a mounting space is required but also consideration from the design stage It is not suitable as an urgent noise countermeasure for a product having a short product life.

For this reason, in recent years, in order to suppress inductive electromagnetic noise generated by active components, which are major noise sources in a circuit board of a small digital electronic device, a relatively thick soft magnetic compound sheet ) Are used.

The magnetic permeability of the composite magnetic sheet material is composed of the real magnetic permeability and the imaginary magnetic permeability. The suppression efficiency of the noise is suppressed as the imaginary magnetic permeability is increased in the electromagnetic noise frequency band to be suppressed, .

On the other hand, since the size of a digital electronic device is becoming smaller, a product having such a thin composite magnetic body and excellent electromagnetic wave suppression effect is desired. In addition, with the trend toward miniaturization of electronic devices, it is required to reduce the thickness of composite magnetic sheet for noise countermeasures used in the above-mentioned sub-microwave band.

In the composite magnetic sheet, the imaginary part permeability must be larger in order to reduce the noise by the magnetic loss. The present magnetic material has a problem that it can not simultaneously satisfy the thin thickness and the conduction noise suppressing effect in a frequency band lower than about 10 to 100 MHz or higher.

Published Japanese Patent Application No. 2003-0022890 " Near infrared ray shielding film " Japanese Patent Application Laid-Open No. 10-2012-0102082 'Anti-reflection film'

An embodiment of the present invention provides a magnetic shield sheet having an excellent electromagnetic wave absorption rate in an electromagnetic noise frequency band of 100 kHz to 300 kHz and a method of manufacturing the same.

The electromagnetic shielding sheet according to an embodiment of the present invention includes: an electromagnetic wave absorbing sheet having a plurality of braked amorphous pieces; A protective film adhered on one surface of the electromagnetic wave absorbing sheet; And an adhesive film adhered on the other surface of the electromagnetic wave absorbing sheet which is the opposite surface of the one surface, and the quality factor value may be 80 or more at a frequency of 100 kHz to 300 kHz.

The Q value can be calculated by Equation (1).

[Equation 1]

Here, k is a constant, u 'is a first permeability, and u " is a second permeability.

The first magnetic permeability is a real permeability of the electromagnetic wave absorbing sheet.

And the second magnetic permeability is an imaginary magnetic permeability of the electromagnetic wave absorbing sheet.

The Q value in the unbraked state may be 10 to 50. [

The amorphous piece may include a plurality of amorphous ribbons, and the amorphous ribbon may be composed of an Fe-based amorphous alloy, a Co-based amorphous alloy, or a nanocrystalline alloy.

An adhesive layer may be provided between the electromagnetic wave absorbing sheets provided at least one.

According to another aspect of the present invention, there is provided a method of manufacturing an electromagnetic wave absorbing sheet, including: a first step of supplying at least one electromagnetic wave absorbing sheet; A second step of heat-treating the electromagnetic wave-absorbing sheet at 300 ° C to 600 ° C for 30 minutes to 4 hours; A third step of attaching an adhesive film between the electromagnetic wave absorbing sheets; A fourth step of attaching a protective film to one surface of the electromagnetic wave absorbing sheet opposite to the surface to which the adhesive film is attached to form a magnetic shielding sheet; A fifth step of braking the magnetic shielding sheet; And laminating the braked magnetic shielding sheet. The laminating magnetic shielding sheet may have a quality factor (Q) of 80 or more at a frequency of 100 kHz to 300 kHz.

And a seventh step of cutting the laminated magnetic shielding sheet to a predetermined size.

The magnetic shield sheet according to an embodiment of the present invention and the method of manufacturing the same provide a magnetic shield sheet having an excellent electromagnetic wave absorption rate because the amorphous ribbon is subjected to a braking treatment to increase the quality factor in the electromagnetic noise frequency band of 100 kHz to 300 kHz can do.

In addition, since the embodiment of the present invention is a thin film and the manufacturing process is simple, it is possible to realize an improvement in productivity and a reduction in manufacturing cost.

1 is a cross-sectional view illustrating a magnetic shield sheet according to an embodiment of the present invention.
FIG. 2 is a graph showing changes in the first magnetic permeability and the second magnetic permeability according to frequency in the magnetic shield sheet according to an embodiment of the present invention. FIG.
3A and 3B are graphs showing changes in the first magnetic permeability and the second magnetic permeability according to the frequency in the presence or absence of the braking process in the magnetic shield sheet according to the embodiment of the present invention.
4 is a flowchart showing a method of manufacturing a magnetic shield sheet according to another embodiment of the present invention.

The terms used in this specification will be briefly described and the present invention will be described in detail.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Also, in certain cases, there may be a term selected arbitrarily by the applicant, in which case the meaning thereof will be described in detail in the description of the corresponding invention. Therefore, the term used in the present invention should be defined based on the meaning of the term, not on the name of a simple term, but on the entire contents of the present invention.

When an element is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements as well, without departing from the spirit or scope of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

FIG. 1 is a cross-sectional view illustrating a magnetic shield sheet according to an embodiment of the present invention. FIG. 2 is a graph illustrating changes in a first magnetic permeability and a second magnetic permeability according to frequency in a magnetic shield sheet according to an embodiment of the present invention 3A and 3B are graphs showing changes in the first magnetic permeability and the second magnetic permeability according to the frequency in the presence or absence of the braking process in the magnetic shield sheet according to the embodiment of the present invention.

Referring to FIG. 1, a magnetic shield sheet 100 according to an embodiment of the present invention includes an electromagnetic wave absorbing sheet 120, a protective film 110, an adhesive film 130, and a release film 140.

In general, the magnetic shielding sheet can be widely applied to electronic appliances including wireless charging of a smart phone, NFC (short-range wireless communication), MST (magnetic security transmission), and the like. Here, wireless charging can be classified into three methods: electromagnetic induction method, magnetic resonance method, and electromagnetic wave method. Most of the commercially available wireless charging technologies use electromagnetic induction. In this electromagnetic induction method, when a magnetic field is generated in a primary coil, which is a power transmitter, electromagnetic induction in which the magnetic field is induced in a secondary coil Technology. The electromagnetic induction method as the wireless charging technology has been standardized around the WPC (Wireless Power Consortium) and the PMA (Power Matters Alliance) called QI standard. WPC uses the power frequency band of 100 ~ 205kHz, and PMA uses 277 ~ 357kHz or 118 ~ 153kHz band. In addition, Near Field Communication (NFC) is one of radio frequency identification (RFID) technologies, and is a non-contact type short range wireless communication technology using a frequency band of 13.56 MHz. Tickets, and payments. In addition, Magnetic Secure Transmission (MST) is a technology designed to generate a magnetic field when a magnetic credit card is scratched, and card information is transmitted to a terminal. In this way, although the resonance frequencies are different for each function of wireless charging, NFC (short range wireless communication), MST (magnetic security transmission), etc. in which the magnetic shield sheet can be utilized, the magnetic shield sheet is not limited at a certain frequency, It can also have electromagnetic wave shielding function in frequency. However, according to the present invention, it is possible to provide a magnetic shield sheet having a high Q-value performance for a frequency of 100 to 300 kHz, which is a main frequency for application to a magnetic shielding sheet applicable to PMA in popularized WPC.

The electromagnetic wave-absorbing sheet 120 is a thin plate ribbon made of an amorphous alloy or a nano-crystal alloy, and comprises a plurality of pieces of amorphous pieces separated by heat treatment of a ribbon of an amorphous alloy or a nano-crystal alloy and then braking.

The electromagnetic wave-absorbing sheet 120 is divided into a plurality of amorphous pieces by heat treatment of the ribbon of the amorphous alloy or the nano-crystal alloy and then braking. The thickness of the electromagnetic wave absorbing sheet 120 is set to 10 to 25 mu m, and the use frequency band is 100 kHz to 300 kHz. At this time, when the thickness of the electromagnetic wave absorbing sheet 120 is more than 25 mu m, it can not be applied to a portable terminal that tends to be thinned. The thickness of the electromagnetic wave absorbing sheet 120 can be changed as the applied amorphous layer increases.

The amorphous alloy may be an Fe-based or a Co-based amorphous alloy.

The Fe-Si-B alloy or the Fe-Si-B-Co alloy may be used as the Fe-based amorphous alloy, and the Co-Fe-Ni-Si- Cr-Si-B alloy can be used.

The Fe-Si-B alloy may have 70-90 atomic% of Fe and 10-30 atomic% of the sum of Si and B in the Fe-Si-B alloy. The higher the content of Fe and other metals, the higher the saturation magnetic flux density. However, when the content of Fe element is excessive, it is difficult to form amorphous. Therefore, in the present invention, the content of Fe is preferably 70-90 atomic%. When the sum of Si and B is in the range of 10-30 atomic%, the amorphous formability of the alloy is the most excellent. In order to prevent corrosion in such a basic composition, corrosion resistance elements such as Cr and Co may be added in an amount of 20 atomic% or less, and a small amount of other metal elements may be added as needed to impart different properties.

The nanocrystalline alloy may be Fe-Si-B-Cu-Nb alloy. In this case, the total amount of Fe is 73-80 at%, the sum of Si and B is 15-26 at%, the sum of Cu and Nb is 1-5 at%. An amorphous alloy having such a composition range in the form of a ribbon can be easily precipitated into nano-phase grains by a heat treatment to be described later.

The protective film 110 is a film adhered to the upper portion of the electromagnetic wave absorbing sheet 120. The protective film 110 may be a polyethylene terephthalate (PET) film, a polyimide film, a polyester film, a polyethylene naphthalate, (PPS) film, a polypropylene (PP) film, and a fluororesin-based film such as polyterephthalate (PTFE). Although not shown, the protective film 110 may be adhered to the upper portion of the electromagnetic wave absorbing sheet 120 through a predetermined adhesive layer.

The adhesive film 130 is a bonded film adhered to the lower part of the electromagnetic wave absorbing sheet 120, and a PET (polyethylene terephthalate) film may be used. The adhesive film 130 is formed on both sides of the substrate with an adhesive layer. The adhesive film 130 may be of a type having a base material or an inorganic material type having no base material and formed of only an adhesive layer. The adhesive layer may be an acrylic adhesive, or other types of adhesives may be used.

The release film 140 is attached to the lower portion of the adhesive film 130 and is integrally formed at the time of manufacturing the adhesive film 130. When the electromagnetic wave absorbing sheet 120 is attached to an electronic device, do.

The electromagnetic-wave-absorbing sheet 120 of the magnetic-shielding sheet having the above-described structure may be formed of a plurality of layers, and may have a thickness of 10 to 25 μm per layer. The thickness of the electromagnetic wave absorbing sheet 120 may be set to 20 to 25 占 퐉, considering the handling process of the electromagnetic wave absorbing sheet 120 after the heat treatment. The thinner the ribbon, the more likely it is to break the ribbon even after a slight impact during handling after heat treatment.

In addition, a plurality of amorphous pieces of the amorphous ribbon may have a size of several tens of micrometers to 3 mm or less.

Also, the protective film 110 may be in the range of 1-75 μm, and the adhesive film 130 may have a thickness of 10, 20, and 30 μm.

However, the present invention does not limit the size of the plurality of amorphous pieces and the thickness of the protective film 110 and the adhesive film 130.

The magnetic shield sheet 100 manufactured through the above-described processes has improved Q factor as a quality coefficient value in a frequency range of 100 kHz to 300 kHz, and thus has a characteristic of excellent electromagnetic wave absorption rate. Here, the higher the Q value as the quality factor, the greater the electromagnetic wave absorbing effect.

On the other hand, the quality factor is calculated by the following equation (1).

Here, k is a constant, u 'is a first permeability, u' is a second permeability, and μ is a permeability.

The permeability is a coefficient that quantifies whether a magnetic flux for a certain material is passed. The permeability has a complex permeability, and the complex permeability is composed of a real permeability and an imaginary permeability.

At this time, the first permeability corresponds to the real permeability of the laminated electromagnetic wave absorbing sheet 120, and the second permeability corresponds to the imaginary permeability of the laminated electromagnetic wave absorbing sheet 120.

The real permeability is a component representing a magnetic property, and the imaginary permeability is a component representing a loss.

Therefore, according to Equation (1), the higher the value of u ', the higher the value of Q, and the higher the value of u', the lower the value of Q.

2, the magnetic shield sheet 100 according to the present invention has a Q (quality factor) value of 80 or more at a frequency of 100 kHz to 300 kHz, .

As shown in Table 1, the magnetic shield sheet 100 according to the present invention shows a remarkable difference in the Q value depending on the presence or absence of the braking process.

Process Property (@ 100kHz) L (uH) Q Non-Breaking 6.2 to 6.5 (single layer) 20-25 Breaking 5.9 to 6.2 (1-layer) > 75 6.55 to 6.8 (2-layer) > 80 7.2 to 7.3 (7-layer) > 115

In particular, the magnetic shielding sheet 100 according to the present invention refers to a case where at least one electromagnetic wave absorbing sheet 120 is stacked. As described above, the magnetic shielding sheet 100 according to the present invention is stacked on one or more sheets, and when one or more sheets are stacked, the Q value is remarkably high.

That is, as shown in FIG. 3A, the electromagnetic wave-absorptive sheet 120 not subjected to the braking process shows a Q value of 10 to 50 in a state of a frequency of 100 kHz to 300 kHz, but as shown in FIG. 3B, It can be seen that the absorbing sheet 120 has a Q value of 80 or more.

On the other hand, in the case of one electromagnetic wave absorbing sheet, the electromagnetic shielding sheet 100 has an adhesive film adhered to the lower part of the electromagnetic wave absorbing sheet to have a total thickness of 15 to 30 um and, when there are two electromagnetic wave absorbing sheets, When the film is attached and has a total thickness of 25 to 55 μm, an adhesive film is attached between the upper electromagnetic wave absorbing sheet and the intermediate electromagnetic wave absorbing sheet and between the intermediate electromagnetic wave absorbing sheet and the lower electromagnetic wave absorbing sheet when the electromagnetic wave absorbing sheet is three sheets, / RTI > to 85 < RTI ID = 0.0 > um. On the same principle, when the number of electromagnetic wave absorbing sheets is seven, the magnetic shielding sheet has a total thickness of 100 to 205 μm.

Accordingly, the thickness of the magnetic shield sheet 100 according to an embodiment of the present invention can be changed according to the number of the electromagnetic wave absorbing sheets, but it is preferable that the magnetic shield sheet 100 has a thickness of 15 to 400 um Do.

As a result, since the magnetic shield sheet 100 according to the embodiment of the present invention brakes the amorphous ribbon to increase the quality factor in the electromagnetic noise frequency band of 100 kHz to 300 kHz, (100).

4 is a flowchart showing a method of manufacturing a magnetic shield sheet according to another embodiment of the present invention.

Referring to FIG. 4, a method of manufacturing a magnetic shield sheet according to another embodiment of the present invention includes a first step (S10) of supplying at least one electromagnetic wave absorbing sheet 120, A second step S20 of heat treatment at 600 캜 for 30 minutes to 4 hours, a third step S30 of attaching the adhesive film 130 between the electromagnetic wave absorbing sheets 120, A fourth step S40 of attaching the protective film 110 to one surface of the electromagnetic wave absorbing sheet 120 which is opposite to the surface of the electromagnetic wave absorbing sheet 120 to which the adhesive film 130 and the protective film 110 are attached, A sixth step S60 of laminating the braked electromagnetic wave absorbing sheet 120 and a seventh step S70 of cutting the laminated electromagnetic wave absorbing sheet 120 to a predetermined size .

More specifically, in the first step (S10), an amorphous ribbon made of an amorphous alloy or a nano-crystal alloy is supplied to the electromagnetic wave absorbing sheet 120 manufactured by rapid quenching (RSP) by melt spinning.

In the second step S20, the electromagnetic wave-absorbing sheet 120 is heat-treated at 300 ° C to 600 ° C for 30 minutes to 4 hours so as to obtain a desired permeability. At this time, the annealing atmosphere may be annealed in an atmosphere, an atmosphere, or an oxidizing atmosphere or a nitrogen atmosphere depending on the Fe content of the amorphous ribbon or the nano-crystal alloy. If the heat treatment temperature is less than 300 ° C, the stress relief of the internal stress generated in the production of the magnetic sheet is not completely achieved, and unevenness of magnetic properties such as magnetic permeability is not solved, If the temperature exceeds 600 ° C, crystallization in the magnetic sheet rapidly occurs due to the superheat treatment, which results in a remarkably low permeability and does not exhibit a desired permeability. In general, a low heat treatment temperature requires a long treatment time, while a high heat treatment temperature means a short treatment time. As described above, when the electromagnetic wave absorbing sheet 120 is subjected to the heat treatment, the brittleness becomes strong, so that the braking can be easily performed when the braking process is performed in the subsequent process.

In the third step S30 and the fourth step S40, the heat-treated electromagnetic wave absorbing sheet is used as one or two to four layers of multilayer, and an adhesive film 130 And a protective film 110 is attached to one surface of the electromagnetic wave absorbing sheet 120 opposite to the surface on which the adhesive film 130 is adhered to form the magnetic shielding sheet 100. At this time, the release film 140 may be attached onto the adhesive film 130.

Then, in the fifth step S50, the magnetic shielding sheet 100 is braked.

The braking process is performed by, for example, disposing a magnetic shielding sheet 100 in which a protective film 110, an electromagnetic wave absorbing sheet, an adhesive film 130 and a release film 140 are sequentially stacked, (Not shown) to separate the amorphous ribbon into a plurality of pieces. At this time, the plurality of separated pieces are separated by the adhesive layer adhered to both sides. In addition, since the plurality of pieces separated by the braking process are formed to have a size in the range of about several tens of m to 3 mm, the hysteresis loss can be removed by increasing the half-magnetic field, thereby increasing the uniformity of the magnetic permeability to the sheet.

In the sixth step S60, the magnetic shielding sheet 100 subjected to the braking process is filled with an adhesive in a gap between the pieces, and performs a lamination process for planarization, slimming and stabilization. At this time, the laminate apparatus (not shown) for the lamination process may be a roll press type or a hydraulic press type comprising two pressing rollers or pressing members. At this time, an adhesive capable of being deformed when pressurized at normal temperature is used, or a thermoplastic adhesive which is deformed when heat is applied can be used.

The braking device and the laminating device according to the present invention can be applied to any device that can perform the braking process or the laminating process.

Finally, in the seventh step S70, the laminated magnetic shielding sheet 100 is cut to a desired length by the manufacturer. Accordingly, since the laminated magnetic shield sheet 100 is cut in the latter half of the process, the magnetic shield sheet of large area and large capacity can be manufactured, and the process efficiency can be further improved.

Since the magnetic shield sheet and the method of manufacturing the same according to the embodiment of the present invention have a high quality factor in an electromagnetic noise frequency band of 100 kHz to 300 kHz by braking the amorphous ribbon, A shielding sheet can be provided. In addition, since the embodiment of the present invention is a thin film and the manufacturing process is simple, it is possible to realize an improvement in productivity and a reduction in manufacturing cost.

As described above, the present invention is not limited to the above-described embodiments, and it is to be understood that the present invention is not limited to the above- It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention.

100: magnetic field shielding sheet 110: protective film
120: electromagnetic wave absorbing sheet 130: adhesive film
140: release film

Claims (13)

Two electromagnetic wave absorbing sheets provided with a plurality of braked amorphous ribbons; And
A protective film adhered on one surface of the electromagnetic wave absorbing sheet; And
Shielding sheet comprising an adhesive film adhered on the other surface of the electromagnetic wave absorbing sheet which is the opposite surface of the one surface,
Wherein the amorphous ribbon is an Fe-Si-B alloy having 70 to 90 at% of Fe, 10 to 30 at% of Si and B,
The thickness of the magnetic shielding sheet is 25 to 55 탆,
Wherein the magnetic shield sheet has a quality factor (Q) calculated by the following formula (1) at a frequency of 100 kHz of 80 or more,
Wherein the Q value before the braking treatment is in the range of 10 to 50.
[Equation 1]

Here, k is a constant, μ 'is a first permeability, which is the real permeability of the electromagnetic wave absorbing sheet, and μ "is a second permeability, which is an imaginary permeability of the electromagnetic wave absorbing sheet.
delete delete delete delete delete delete A first step of supplying two electromagnetic wave absorbing sheets having a plurality of braking processed amorphous ribbons;
A second step of heat-treating the electromagnetic wave-absorbing sheet at 300 ° C to 600 ° C for 30 minutes to 4 hours;
A third step of attaching an adhesive film between the electromagnetic wave absorbing sheets;
A fourth step of attaching a protective film to one surface of the electromagnetic wave absorbing sheet opposite to the surface to which the adhesive film is attached to form a magnetic shielding sheet;
A fifth step of braking the magnetic shielding sheet; And
And a sixth step of laminating the braked magnetic shielding sheet,
Wherein the amorphous ribbon is an Fe-Si-B alloy having 70 to 90 at% of Fe, 10 to 30 at% of Si and B,
The thickness of the magnetic shielding sheet is 25 to 55 탆,
The laminated magnetic shield sheet has a quality factor value of 80 or more at a frequency of 100 kHz to 300 kHz,
Wherein the Q value before the braking treatment is in the range of 10 to 50.
[Equation 1]

Here, k is a constant, μ 'is a first permeability, which is the real permeability of the electromagnetic wave absorbing sheet, and μ "is a second permeability, which is an imaginary permeability of the electromagnetic wave absorbing sheet.
The method of claim 8,
Further comprising a seventh step of cutting the laminated magnetic shielding sheet to a predetermined size.
delete delete delete delete

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