housing

Abstract

To provide a housing that effectively acts not only as a shield against low-frequency electromagnetic waves, but also as a shield against high-frequency electromagnetic waves.SOLUTION: In housings 2 and 3 for housing electronic / electrical equipment, at least one of a copper layer 12 as a diamagnetic layer and a nickel layer 14 as a ferromagnetic layer is laminated on each of front and back surfaces of a base material 11 made of iron, and a glossy tin layer 13 is further overlaid on the layer as the outermost layer.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] An embodiment of the present invention relates to a housing for containing electric / electronic equipment. [Background technology]

[0002] (Characteristics of the magnetic field source) We are surrounded by a wide variety of electrical and electronic devices. Electrical and electronic devices are magnetic field sources that generate low-frequency or high-frequency electromagnetic waves. For example, high-frequency devices such as communication equipment and mobile phones generate high-frequency electromagnetic waves. In addition, voltage conversion inverters for power circuits of household electrical appliances, electric vehicles, hybrid vehicles, and electrically assisted bicycles, motor drive inverters that drive motors, and other power circuits generate relatively low-frequency electromagnetic waves.

[0003] These magnetic fields leak due to the current flowing between the power supply circuit or motor itself, the battery or power source that supplies power to them, or between these components during regeneration, and there is a wide range of magnetic field sources from 50 Hz to 100 kHz, ranging from low power to high power.

[0004] The principle of controlling power is the same for all inverters, and they use pulse width modulation (PWM) to change the pulse width, and frequency modulation (PFM) to change the pulse frequency. The magnetic fields generated by these circuits are generated not only by the load motor and the inverter circuit of the pulse source, but also by wiring and batteries, and in electric vehicles, the magnetic field is larger due to the current flowing from the motor to the battery as regenerative braking rather than during acceleration. Furthermore, because it is pulse control, electromagnetic interference due to high frequency components caused by harmonics, not just the fundamental frequency, can exceed 1MHz. (Medical reports on medical hazards caused by magnetic fields) When these magnetic field sources, such as electric power equipment and electric vehicles, are located nearby, the magnetic field strength to which users are exposed increases, according to the law of electromagnetic wave propagation, which states that the strength of the magnetic field is inversely proportional to the square of the distance. In addition, these magnetic fields induce currents in the wiring of nearby devices, causing damage. The World Health Organization (WHO) has issued guidelines to regulate magnetic field strength on the body, and the Japan Electromagnetic Information Center (JEIC) has compiled medical papers on magnetic field damage (Non-Patent Document 1). However, these relate to short-term, strong exposure, and there are epidemiological research reports on the effects of long-term, weak exposure to low-frequency magnetic fields. Attention should also be paid to reports of childhood leukemia caused by 50 Hz magnetic fields, which are three orders of magnitude lower than the guideline value (Non-Patent Document 2), as well as reports on low-frequency bands (Non-Patent Document 3).

[0005] Passive methods have already been used to deal with this type of interference, such as reducing the magnetic field generated by lowering the current value of the magnetic field source or reviewing the wiring to reduce the magnetic field. If the passive methods are not effective enough, the magnetic field source can be magnetically shielded to reduce the magnetic field strength. (Measurement of the shielding properties of magnetic shielding materials) Physical constants such as the relative permeability of metal materials are functions of frequency, and the magnetic shielding factor of metals changes with frequency. The most common method for measuring the magnetic shielding factor of metals is the KEC method, which measures the shielding effect by placing a measurement target between opposing transmitting and receiving elements under near-field conditions (Non-Patent Document 4). In addition, there is the Advantest method, which places a transmitting element and a receiving element side by side and receives the electromagnetic wave of the transmitted wave by reflecting it off the measurement target (Non-Patent Document 5).

[0006] In both cases, measurements are based on frequencies above 1 MHz, and measurements below 1 MHz using the KEC method are cut off halfway. Reports of shielding rates are only for major metal materials, and measurements of surface treatment effects have not been a subject of industrial or academic research.

[0007] Here, in order to control the magnetic field and reduce its effect on electric and electronic equipment, and to reduce the amount of radiation exposure to the human body, there are two methods: using magnetic shielding materials to enclose the magnetic field source and prevent leakage to the surroundings, and placing shielding materials between the magnetic field source and the target equipment, circuit, or person. Magnetic shielding can be achieved by using magnetic field reflection or by absorbing the magnetic field. This invention uses a thin and lightweight reflection method.

[0008] Until now, iron-based materials with high relative magnetic permeability have been used to shield magnetic fields, but when using iron materials, a thickness of 1 mm is required to reduce the magnetic field shielding rate to one-tenth (-20 dBm) at 1 kHz. As an example of using a metal other than iron, Patent Document 1 uses an alloy material of copper and iron, which combines the electric field shielding properties of copper due to its good conductivity with the magnetic shielding effect of iron materials.

[0009] Patent Document 2 discloses a magnetic shielding material that uses an iron base material, plates a ferromagnetic material such as copper with nickel, and alloys it at high temperature. However, this does not have a magnetic shielding effect due to diamagnetic properties, and since the alloying process is carried out after plating, it cannot be said to be a laminated structure.

[0010] In Patent Document 3, a soft magnetic thin film of an iron-nickel alloy is manufactured by forming a multilayer thin film by alternately plating iron and nickel, and then heat-treating the thin film to diffuse the metal atoms of the material. This structure does not include a diamagnetic material, and the alloying process is used, so it cannot be called a layered structure. [Prior art documents] [Non-patent literature]

[0011] [Non-Patent Document 1] Electromagnetic Field Information Center, "Results of epidemiological studies relating to extremely low frequency electromagnetic fields and childhood leukemia", Internet,<URL:https: / / www.jeic-emf.jp / explanation / 1030.html> [Non-Patent Document 2] Kabuto et al. “Childhood leukemia and magnetic fields in Japan: A case-control study of childhood leukemia and residential power-frequency magnetic fields in Japan.” International Journal of Cancer, 119(3), pp.643-650(2006) [Non-Patent Document 3] Tomioka, Toshiya et al. (1998) Effects of low-frequency electromagnetic waves on mice. Clinical Environmental Medicine 7: 80-86 [Non-Patent Document 4] Mihoko Igarashi et al., "Evaluation Method of Electromagnetic Wave Absorbing Sheet and Shielding Materials," Tokyo Metropolitan Industrial Technology Research Center Research Report No. 3, 2008 [Non-Patent Document 5] R17303 EMI Probe Set Instruction Manual (Advantest Corporation 1993 Edition) [Patent documents]

[0012] [Patent Document 1] JP 2007-49104 A [Patent Document 2] Japanese Patent Application Publication No. 57-202706 [Patent Document 3] Japanese Patent Application Publication No. 6-346276 Summary of the Invention [Problem to be solved by the invention]

[0013] The object is to provide a housing that is effective in shielding not only low frequency electromagnetic waves but also high frequency electromagnetic waves. [Means for solving the problem]

[0014] The housing for accommodating electronic / electrical equipment according to this embodiment has at least one of a diamagnetic layer and a ferromagnetic layer laminated on each of the front and back surfaces of a base material, and a bright tin layer formed as the outermost layer. The substrate is composed of a resin substrate body and iron layers formed on both the front and back surfaces of the substrate body. [Brief description of the drawings]

[0015] [Figure 1] 1 is a diagram showing a housing for accommodating a high-frequency circuit board as an example of a housing according to the present invention; [Diagram 2] FIG. 1 is a diagram showing a housing for accommodating, in particular, a rear portion of a high-frequency device (a mobile phone) as an example of a housing according to the present invention. [Diagram 3]FIG. 2 is a cross-sectional view of a housing according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing the shielding effect of the housing shown in FIG. [Diagram 5] FIG. 11 is a cross-sectional view of a housing according to a second embodiment. [Figure 6] FIG. 6 is a diagram showing the shielding effect of the housing shown in FIG. 5. [Figure 7] FIG. 11 is a cross-sectional view of a housing according to a third embodiment. [Figure 8] 8 is a cross-sectional view showing a modified example of the housing of FIG. 7. [Figure 9] FIG. 11 is a cross-sectional view of a housing according to a fourth embodiment. [Figure 10] FIG. 13 is a cross-sectional view of a housing according to a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, a housing for accommodating electronic / electrical devices according to the present invention will be described with reference to the drawings. The housing according to the present invention is relatively thin, yet effectively shields not only low-frequency electromagnetic waves but also high-frequency electromagnetic waves. The electronic / electrical devices are, for example, high-frequency devices such as communication devices and mobile phones. The electronic / electrical devices are, for example, voltage conversion inverters for power circuits in household electrical appliances, electric vehicles, hybrid vehicles, and electrically assisted bicycles, motor drive inverters for driving motors, and other motors and power circuits. The electronic / electrical devices are, for example, magnetic field sources and radiation sources in medical devices such as magnetic resonance imaging devices (MRI) and radiotherapy devices.

[0017] As shown in FIG. 1, the housing is composed of a box part 2 and a lid part 3 for accommodating, for example, a high-frequency circuit board 1. As shown in FIG. 2, the housing is provided as a cover 5 that is placed on the back of, for example, a mobile phone 4 as a high-frequency device. By utilizing the magnetic field shielding effect of the housing, the amount of exposure of the hand to the magnetic field generated by the switching regulator of the mobile phone 4 can be reduced. For example, the metal thin plate used is a 0.3 mm thick iron plate plated on both sides with nickel to a thickness of about 2 μm, further plated with copper to a thickness of about 2 μm, and plated with tin to a thickness of about 2 μm for surface protection. A silicone rubber case with a thickness of 1 mm is attached to the main body of the so-called mobile phone 4 to be shielded, and the case is folded so that there is a 2 mm margin around it, so that the magnetic field of the mobile phone does not reach the hand that is operating it.

[0018] This housing shields the contained electronic and electrical equipment from relatively low frequency electromagnetic fields, and also shields it from relatively high frequency electromagnetic fields of 100 kHz or more.

[0019] The structure for shielding low-frequency electromagnetic waves is provided with at least one of a diamagnetic layer that expels magnetic flux to the outside by eddy currents and a ferromagnetic layer with a large relative permeability that confines the magnetic field that has penetrated into the material, preferably both layers. Furthermore, in order to reflect high-frequency electric fields, a glossy tin layer is typically formed as the outermost layer (surface layer) as a good conductor with a smooth surface.

[0020] The ferromagnetic layer is an iron layer, a nickel layer, or a cobalt layer, and the diamagnetic layer is a copper layer, a tin layer, or a carbon layer.

[0021] If the iron substrate is 0.1 mm or more thick, a diamagnetic metal layer such as copper or the like is laminated to a thickness of 1 μm to 10 μm on the surface of the ferromagnetic iron, and a non-magnetic material such as tin is laminated to a thickness of 1 μm or more to protect the surface, to form a magnetic shielding material. This structure clearly has a shielding effect, as shown in the actual measurement results of the first embodiment described later.

[0022] When weight reduction is important, a ferromagnetic nickel layer of 1 μm to 10 μm is formed between the above-mentioned base iron plate and diamagnetic copper, and tin is laminated for surface protection. Nickel has a relative permeability one order of magnitude smaller than that of iron, but has a higher electrical conductivity than iron, so it also has a diamagnetic effect due to eddy currents in the low frequency range of 1 MHz or less. It was confirmed by actual measurements that although it is a ferromagnetic material in bulk, it has a diamagnetic effect in thin film form. It is clear from the actual measurement results shown in the second embodiment described later that this structure has a shielding effect.

[0023] If even lighter weight is required, the base material iron can be made thinner to make it lighter, a nickel layer can be layered on the iron to increase the shielding effect as a ferromagnetic material, and then copper can be layered on top to combine the effects of the two diamagnetic materials. By repeating this nickel and copper layer multiple times, the shielding rate can be increased, and finally tin can be layered on to protect the surface.

[0024] As a material for shielding low-frequency magnetic fields, a diamagnetic layer, typically a copper layer, is laminated on the surface of an iron substrate as a ferromagnetic layer to obtain a shielding effect. In this structure, an external magnetic field induces eddy currents in the diamagnetic material, and these eddy currents reflect the external magnetic field to obtain a shielding effect. For this reason, a material with low resistivity is used for the surface diamagnetic material with a thickness of several μm to several tens of μm. If the iron substrate is 0.5 mm thick, the magnetic field strength combined with the two surface layers will be 17% or less, achieving a shielding effect exceeding (15.4 dBm) in the frequency band from 1 kHz to 100 kHz.

[0025] In frequency bands above 100 kHz, electric field reflection is effective in blocking electromagnetic waves, and the electric field reflecting material need only be a good conductor with a smooth surface. A shielding effect can be obtained by using a layered structure of diamagnetic copper, ferromagnetic nickel, and shiny tin for surface protection.

[0026] This sheet material acts on the magnetic field to reduce electromagnetic waves from 50Hz to 100kHz generated by currents flowing in power inverters for household use or in electric and hybrid vehicles, etc., and acts as a shielding material. Actual measurements showed that a 1.0mm thick iron material plated with 5μm of copper achieved an average shielding rate improvement of 10% or more in the frequency range frequently used by inverters of 400Hz to 60kHz, compared to iron of the same thickness.

[0027] After forming the structure of the object to be magnetically shielded, a laminated structure that provides a shielding effect using plating or the like is created, making it possible to use conventional manufacturing methods as is. (First embodiment) 3 shows a cross-sectional structure of the housing according to the first embodiment. The substrate 11 is a ferromagnetic layer having a thickness of 0.1 mm or more and 3.0 mm or less, and is typically made of iron. A copper layer 12 having a thickness of 1 μm or more and 10 μm or less is formed by plating on each of the front and back surfaces of the substrate 11 as a diamagnetic layer. A bright tin layer 13 having a thickness of 1 μm or more and 3 μm or less is formed by plating on the surface of the copper layer 12.

[0028] The copper layer 12 can be replaced with a carbon layer, which is a diamagnetic layer. The plating process can be replaced with a thermal spray process, a vapor deposition process, or a printing process.

[0029] The base material 11 and the copper layer 12 provide a shielding effect against low-frequency electromagnetic waves, and the bright tin layer 13 provides a shielding effect against high-frequency electromagnetic waves. The bright tin layer 13 also functions as a protective layer against external collisions.

[0030] Typically, a copper layer 12 is plated on both sides of a 0.5 mm thick iron substrate 11 to a thickness of about 2 μm, and a glossy tin layer 13 is plated on the copper layer 12 to a thickness of about 0.1 μm to provide a smooth surface in order to prevent oxidation of the copper layer 12, to provide protection from external physical collisions, and to exert a reflective shielding effect against high frequency electromagnetic waves.

[0031] Figure 4 shows the frequency characteristics of the shielding rate (FCS05) measured for this material. As a result, while the shielding effect was approximately 1 dBm from 100 Hz to 1 kHz, in the frequency range of 10 kHz to 100 kHz, which is the main operating range of inverters, it showed a shielding effect of 6 dBm (twice the actual value) compared to the frequency characteristics of iron material (Fe05) shown by the dashed line. This means that the thickness of the iron material can be halved, which is a great advantage in terms of cost and weight reduction. The iron plate is soft iron and contains no additives. The copper and tin are of high purity for electroplating. Second embodiment FIG. 5 shows a cross-sectional structure of a housing according to the second embodiment. The substrate 11 of this embodiment constitutes a relatively thin ferromagnetic layer having a thickness of 0.1 mm or more and 1.0 mm or less in order to reduce weight. On each of the front and back surfaces of the substrate 11, a nickel layer 14 as a ferromagnetic layer having a thickness of 1 μm or more and 10 μm or less is formed by plating in order to enhance the shielding effect. On the surface of the nickel layer 14, a bright tin layer 13 as a diamagnetic layer having a thickness of 1 μm or more and 3 μm or less is formed by plating. The nickel layer 14 can be replaced with a cobalt layer as the same ferromagnetic layer.

[0032] The substrate 11 and the nickel layer 14 provide a shielding effect against low frequency electromagnetic waves, and the bright tin layer 13 provides a shielding effect against high frequency electromagnetic waves. The bright tin layer 13 also functions as a protective layer against external collisions.

[0033] Typically, a nickel layer 14 is plated on both sides of a 0.3 mm thick iron substrate 11 to a thickness of about 2 μm, and a tin layer 13 is plated to a thickness of about 2 μm as in Example 1 to make the surface smooth. The frequency characteristics of the shielding factor (FNS03) measured for the frequency characteristics of this material are shown in FIG. 6. As a result, there is no difference between 100 Hz and 10 kHz, but in the frequency range of 30 kHz or higher, a shielding effect of up to 3 dBm (about 1.4 times in actual value) was shown compared to the frequency characteristics (Fe03) of iron material shown by the dashed line. This means that the thickness of the iron material can be reduced to 70%, and the effect of cost and weight reduction can be expected. Third embodiment When the substrate 11 is relatively thin, for example, having a thickness of 0.1 mm or more and 0.5 mm or less, a nickel layer 14 may be laminated on the copper layer 12 in order to effectively exhibit a shielding effect against low-frequency electromagnetic waves in particular.

[0034] As shown in FIG. 7, a copper layer 12 having a thickness of 1 μm or more and 10 μm or less is formed by plating on each of the front and back surfaces of an iron base material 11, a nickel layer 14 having a thickness of 1 μm or more and 10 μm or less is overlaid on the surface of the copper layer 12 by plating, a copper layer 12 having a thickness of 1 μm or more and 10 μm or less is further overlaid on the surface of the nickel layer 14 by plating, and a shiny tin layer 13 having a thickness of 1 μm or more and 3 μm or less is formed on the surface of the copper layer 14 by plating.

[0035] As shown in FIG. 8, a nickel layer 14 having a thickness of 1 μm or more and 10 μm or less is formed by plating on each of the front and back surfaces of an iron base material 11, a copper layer 12 having a thickness of 1 μm or more and 10 μm or less is overlaid on the surface of the nickel layer 14 by plating, a nickel layer 14 having a thickness of 1 μm or more and 10 μm or less is further overlaid on the surface of the copper layer 12 by plating, and a shiny tin layer 13 having a thickness of 1 μm or more and 3 μm or less is formed on the surface of the nickel layer 14 by plating. (Fourth embodiment) When the shape of the case or housing having the magnetic shielding function is complex, it may be difficult to form the base material from iron. Furthermore, in the case of small-scale production, a steel mold is required to press-form the iron base material, which may lead to a rise in manufacturing costs.

[0036] 9, the base material 111 of the housing according to this embodiment is made of resin such as polyamide (PA), polycarbonate (PC), polyacetal (POM), etc. By making the base material 111 from resin, injection molding becomes possible, complex shapes can be accommodated, and manufacturing costs can be reduced. The base material 111 may be wax or a non-ferrous metal.

[0037] In the housing according to this embodiment, the base material 111 is made of resin, and therefore the effect of "confining the magnetic field that has penetrated into the material" due to the ferromagnetic layer with a large relative magnetic permeability is not achieved. However, the effect of "expelling magnetic flux to the outside by eddy currents" of the diamagnetic layer, which blocks low-frequency electromagnetic waves, and the effect of blocking high-frequency electromagnetic fields by reflecting electromagnetic waves by the glossy tin layer, can be achieved.

[0038] 9 shows a cross-sectional structure corresponding to FIG. 3, but this embodiment includes a structure in which the base material in the cross-sectional structure of FIG. 5, FIG. 7 or FIG. 8 is replaced with a resin material. Fifth embodiment 10, the substrate 114 of the housing according to this embodiment is composed of a resin substrate main body 112 having a thickness of 1.0 mm or more and 10.0 mm or less, and iron ferromagnetic layers 113 having a thickness of 1 μm or more and 10 μm or less that are laminated by plating or thermal spraying on the front and back surfaces of the substrate main body 112. The substrate main body 112 may be made of wax or a non-ferrous metal.

[0039] The housing of this embodiment has a base material 114 constructed with a laminated structure of a resin layer 112 and a ferromagnetic layer 113, so that the ferromagnetic layer can exert an effect of "confining the magnetic field that has permeated the material", albeit to a small extent, and further exerts a low-frequency electromagnetic wave shielding effect of "expelling magnetic flux to the outside by eddy currents" due to the diamagnetic layer, and a high-frequency electromagnetic field shielding effect due to the reflection of electromagnetic waves by the glossy tin layer.

[0040] Note that, while FIG. 10 shows a cross-sectional structure corresponding to FIG. 3, this embodiment includes a structure in which the substrate in the cross-sectional structure of FIG. 5, FIG. 7 or FIG. 8 is replaced with a substrate 114 in which a substrate body (resin layer) 112 and an iron layer (ferromagnetic layer) 113 are laminated.

[0041] The housing according to the fourth embodiment includes a resin base material 111, and the housing according to the fifth embodiment includes a resin base material main body 112. After the laminated structure of the housing according to the fourth or fifth embodiment is completed, the resin constituting the base material 111 or base material main body 112 is removed by using a solvent, heating, or the like, and the remaining laminated structure consisting of a copper layer and a shiny tin layer, a nickel layer and a shiny tin layer, or a copper layer, a nickel layer and a shiny tin layer can be used as a lightweight and elastic functional structural material (thin film material) with a magnetic shielding function. In this case, the resin layer can be replaced with a brazing material layer.

[0042] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0043] 11...substrate, 12...copper layer, 13...bright tin layer, 14...nickel layer.

Claims

1. In a housing for accommodating electronic / electrical equipment, At least one of a diamagnetic layer and a ferromagnetic layer is laminated on each of the front and back surfaces of the substrate, and a bright tin layer is laminated as the outermost layer; The substrate is a housing comprising a resin substrate body and iron layers formed on both the front and back surfaces of the substrate body.

2. 2. The housing according to claim 1, wherein the antimagnetic layer and the ferromagnetic layer are laminated on the front and back surfaces of the base material.

3. 2. The housing according to claim 1, wherein the antimagnetic layer is laminated on each of the front and back surfaces of the base material, the ferromagnetic layer is laminated on the antimagnetic layer, and another antimagnetic layer is laminated on the ferromagnetic layer.

4. 2. The housing according to claim 1, wherein the ferromagnetic layer is laminated on each of the front and back surfaces of the base material, the diamagnetic layer is laminated on the ferromagnetic layer, and another ferromagnetic layer is laminated on the diamagnetic layer.

5. 2. The housing according to claim 1, wherein the diamagnetic layer is a copper layer, a tin layer or a carbon layer, and the ferromagnetic layer is an iron layer, a nickel layer or a cobalt layer.

Images