JP4257987B2 - Portable wireless device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic shielding technique for a mobile mobile radio such as a mobile phone.
[0002]
[Prior art]
A mobile radio device such as a cellular phone generally includes an RF (high frequency) circuit for transmission and a digital circuit for reception. In a radio device in which transmission and reception are performed at the same time, an electromagnetic shield is required to suppress mutual interference between the reception unit and the transmission unit and EMI (Electromagnetic Interference) from the reception unit digital control circuit. In addition, even in a radio device that does not transmit and receive simultaneously, as in the PDC (Personal Digital Communications) system, which is currently the mainstream of Japanese mobile phones, the transmitted wave is transmitted to the PLL (Phase Locked) of the modulation circuit in the RF circuit. In order to prevent deterioration of the modulation factor due to wrapping around the loop), an electromagnetic shield is required. In addition, since the modulation circuit cannot use a long transmission line due to its nature, the specifications required for the shield are stricter because the modulation circuit is arranged as close as possible to the antenna.
[0003]
FIG. 6 is a schematic diagram showing the inside of a mobile phone as a conventional portable radio apparatus, wherein 1 is a shield case, 2 is a substrate in which a transmission circuit and a reception circuit are incorporated, and 3 is a ground pattern provided on the circuit substrate. , 4 is an antenna pulled out from the shield case 1, and 5 is an electrical contact.
[0004]
The shield case 1 is formed in a “box” shape, in which a metal film such as Cu or Ni is stacked by electroless plating or vapor deposition on a plastic such as sheet metal or ABS (acrylonitrile butadiene styrene). 1 is used so as to cover a portion of the substrate 2 where a high-frequency RF circuit such as a transmission circuit is located. In this case, the shield case 1 is in a floating and floating shape only by being covered, and does not operate as a shield. As an electromagnetic shield, it is necessary to make electrical contact with the ground pattern 3 on the edge of the substrate on which the RF part is placed so as to cover the circuit. In general, it is impossible to uniformly contact a thin metal plate or metal film used for a shield case with a conductive portion of a substrate, and an electrical contact 5 such as a protrusion or a spring is used to reliably establish electrical connection at a fixed point. The method is used. Among them, the method of making contact using a spring is used in many portable devices as the most reliable method. In addition, as shown in FIG. 6, the electrical contacts 5 are conventionally arranged more densely near the antenna and sparsely located at a portion far from the antenna. 1
[0005]
[Problems to be solved by the invention]
In order to shield the electromagnetic wave, it is necessary to make several electrical connections between the shield case and the lower substrate so that the electromagnetic wave does not leak from the gap. Conventionally, without considering the direction of the induced current flowing through the shield metal, electrical contacts are arranged in the dark clouds at almost equal intervals or at a portion close to the antenna in a concentrated manner to make electrical contact. In particular, the electrical contacts were reduced at the lower end far from the antenna. For this reason, the shielding effect may be weakened.
[0006]
In addition, when using a shield case made of plastic coated with a metal thin film, there is an example in which Sendust (FeAlSi) magnetic powder is applied as a metal film, but these magnetic materials are used by current mobile phones. At high frequencies near 1 GHz or higher, the relative permeability is almost 1, which is not effective.
[0007]
The present invention has been made to solve the above-described problems relating to the shield, and an object thereof is to obtain a reliable shield with a simple configuration.
[0008]
[Means for Solving the Problems]
In the portable radio apparatus according to the present invention, the electric current is generated at a portion where the current density of the current component flowing from the shield case to the ground pattern of the substrate is high among the high-frequency induced current induced in the shield case when radio waves are emitted from the antenna. The arrangement density of the contacts is increased .
[0009]
Further, the arrangement density of the electric contacts is increased in the vicinity of the position where the antenna is pulled out from the shield case and in the portion far from the position where the antenna is pulled out from the shield case.
[ 0010 ]
Furthermore, the shield case is composed of a member having a conductive film formed on the resin surface, and an anisotropic magnetic film is further laminated on the conductive film, and the current flowing through the antenna in the direction of the easy axis of magnetization of the anisotropic magnetic film. In the same direction.
[ 0011 ]
The anisotropic magnetic film is an anisotropic granular film.
[ 0012 ]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing Embodiment 1 of the present invention. The configuration is almost the same as the conventional one of FIG. 5, 1 is a shield case, 2 is a transmission circuit, a substrate on which a reception circuit and a logic circuit are incorporated, 3 is a ground pattern provided on the substrate 2, 4 Is an antenna drawn out from the shield case 1, and 5 is an electrical contact. Here, the electrical contacts 5 are arranged with a high arrangement density in the upper part close to the antenna and in the lower part far from the antenna. The reason for this arrangement is that, as a result of the electromagnetic wave analysis by the inventors, the current flowing from the shield case 1 to the ground pattern 3 through the electric contact 5 is blocked, focusing on the upper and lower ends in the direction in which the mirror image current flows. This is because it has been found that the wraparound of the transmission wave to the internal circuit can be reduced by making electrical contact so as not to occur. In addition to the upper end close to the antenna, the electromagnetic wraparound from the side is reduced by taking a means for improving the electric contact at the lower end opposite to the antenna, which has not been improved in electrical contact.
[ 0013 ]
By arranging the electric contacts 5 in this way, even if the number of the electric contacts 5 is the same as that of the conventional one, a high shielding effect can be obtained. Moreover, even if the number of electrical contacts 5 is reduced, the same shielding effect as that of the prior art can be obtained. In this example, the electric contact 5 is not provided on the side, but a small amount of electric contact may be provided on the side, and it is particularly effective to provide the electric contact 5 on the side near the antenna. It goes without saying that there is.
[ 0014 ]
FIG. 2 shows an example of the electric contact 5. As an electrical contact, a spring metal 5 is securely fixed to the ground pattern 3 of the substrate 2 with solder 51 or the like, and the shield case 1 is attached to the substrate 2 with screws (not shown) or the like on the substrate side. The spring metal 5 as an electrical contact is reliably brought into contact with the metal film 1a of the shield case 1 by pressing. In this way, electrical contact is reliably ensured. Here, the smaller the number of electrical contacts 5, the lighter the weight, the simpler the assembly process, and the lower the cost. In portable wireless devices such as mobile phones, there is a strong demand for light weight and low cost, and these effects are very large. According to the present invention, it is possible to obtain a larger shielding effect with a smaller number of electrical contacts by placing the electrical contacts 5 in a concentrated manner at a portion having a high shielding effect. In addition, although the thing of a spring metal was shown here as the electric contactor 5, it is not restricted to this, The thing which provided the metal protrusion on the grounding pattern may be sufficient, and the grounding pattern 3 and the shield case Any means may be used as long as a means for making good electrical contact with the metal portion is provided.
[ 0015 ]
The above effect is demonstrated using an analysis result. FIG. 3 shows three-dimensional finite element method electromagnetic field analysis of the electric field intensity distribution on the substrate 2 inside the shield case by changing three kinds of electrical contact states between the shield case and the substrate. FIG. 3A shows a case where the shield case is simply placed on the substrate and no electrical contact is made with the substrate. FIG. 3B shows a case where electrical contact is made only on the left and right sides of the shield box. ) Shows a case where the upper and lower portions are also in electrical contact, and the shaded portion shows a region where the electric field strength value is higher than a certain value. FIG. 3B shows that the area of the hatched portion is almost unchanged compared to FIG. 3A, that is, the electrical contact on the side is hardly effective. On the other hand, in FIG. 3C, the area of the shaded portion is greatly reduced, and it can be seen that the electrical connection in the vertical direction works extremely well.
[ 0016 ]
The above is because the surface current (high-frequency induced current) of the shield case induced by the transmission wave from the antenna is induced to flow mainly in the direction in which the antenna current flows, that is, in the vertical direction of the shield case. A high-frequency induced current flows so as to flow from the shield case to the ground pattern even at the lower end of the shield case, that is, far from the antenna, that is, across the contact portion. It is thought from. Further, since the high-frequency induced current crossing the contact portion is small on the side of the shield case, the electrical contact hardly affects the shield, and it is not necessary to provide many means for improving the electrical contact. Thus, in order to increase the shielding effect, when there is a contact surface in a direction orthogonal to the high frequency induced current, it is necessary to provide means for improving the electrical contact so that this portion is not thin and becomes a long slit, in order to improve the shielding effect. It is essential.
[ 0017 ]
Embodiment 2. FIG.
FIG. 4 is an internal schematic diagram of the portable radio apparatus for explaining the second embodiment of the present invention. In FIG. 4, a shield case 1a is formed by laminating a magnetic film such as Ni on a conductive metal shield film such as Cu or Al, and the direction of easy magnetization of the magnetic film is set as indicated by an arrow 6 in the figure. The vertical direction is the same as the high-frequency induced current. By doing so, the high-frequency magnetic permeability in the lateral direction can be kept high, and the reflection coefficient of radio waves is increased, that is, a high shielding effect is obtained.
[ 0018 ]
Here, a magnetic film generally used like Ni has a low magnetic permeability at a high frequency such as several hundred MHz to several GHz used in a mobile phone, and the above effect is reduced. Even in such a film, if anisotropy is added, the decrease in the magnetic permeability in the high-frequency region is reduced in the direction of the hard axis, and the above effect can be obtained. Further, if the anisotropic magnetic film such as an anisotropic FeAlO granular soft magnetic film (anisotropic granular film), the permeability of the hard axis (direction perpendicular to the easy axis) is 1 GHz or more, High permeability can be obtained. That is, if it is an anisotropic granular film, it is used as a good magnetic film even at a high frequency of several hundred MHz to several GHz, which is used in a cellular phone, by making the easy axis direction the same as the high frequency induced current. Therefore, the effect of the present embodiment is remarkable.
[ 0019 ]
FIG. 5 shows a case where a magnetic film having a relative permeability of 100 is laminated on a conductive metal shield film such as Cu or Al with a thickness of 100 angstroms using a three-dimensional finite element method electromagnetic field analysis by magnetism. This is a calculation of how much a region where isolation of −80 dB can be taken with respect to a microstrip line having a length of 10 mm on a substrate at an antenna current value of 0 dB at a high frequency of 940 MHz. Here, the portion where the substrate is shielded is calculated in a shape closer to an actual portable wireless device. FIG. 4A shows a calculation result when there is no magnetic film, and FIG. 4B shows a calculation result when there is a magnetic film. The hatched portion in the figure indicates a region where the isolation is lower than −80 dB. When the magnetic film is present, there is almost no hatched portion, and it has been clarified that the shield characteristics are remarkably improved by the present invention. Thus, the present inventors have revealed that a magnetic film having a thickness of only 100 angstroms has a very great shielding effect.
[ 0020 ]
Here, in the case of the anisotropic magnetic film, the film thickness is 1/50 or more of the high-frequency skin depth inherent in the magnetic film considering the permeability in the hard axis direction, more preferably 20 If it is more than 1 / min, it is considered that the shielding effect is exhibited.
[ 0021 ]
【The invention's effect】
In the portable wireless device according to the present invention, of the high-frequency induced current induced in the shield case when radiating radio waves from the antenna, the electrical contact in the portion where the current density of the current component flowing from the shield case to the ground pattern of the substrate is high However, since the means for improving the electrical contact of other parts is provided, the electromagnetic shielding effect can be surely enhanced.
[ 0022 ]
In addition, since a means for improving electrical contact is provided in the vicinity of the position where the antenna is pulled out from the shield case and in the part far from the position where the antenna is pulled out from the shield case, a simple structure with high electromagnetic shielding effect can be obtained. It is done.
[ 0023 ]
In addition, since the electrical contact is formed by a plurality of electrical contacts, the arrangement density of the electrical contacts is increased in the portion where the current density of the current component flowing from the shield case to the ground pattern of the substrate is high, and the electrical contact is increased. Even if the number of contacts is small, a high electromagnetic shielding effect can be obtained.
[ 0024 ]
Furthermore, the shield case is composed of a member having a conductive film formed on the resin surface, and an anisotropic magnetic film is further laminated on the conductive film, and the current flowing through the antenna in the direction of the easy axis of magnetization of the anisotropic magnetic film. Therefore, a thin magnetic film having a high electromagnetic shielding effect can be obtained.
[ 0025 ]
Further, since the anisotropic magnetic film is an anisotropic granular film, a higher electromagnetic shielding effect can be obtained.
[Brief description of the drawings]
[ 0026 ]
FIG. 1 is a schematic diagram showing the inside of a portable radio apparatus according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing an example of an electrical contact.
FIG. 3 is a diagram for explaining the effect of the first embodiment of the present invention.
FIG. 4 is a schematic diagram showing the inside of a portable radio apparatus according to a second embodiment of the present invention.
FIG. 5 is a diagram for explaining the effect of the second embodiment of the present invention.
FIG. 6 is a schematic diagram showing the inside of a conventional portable wireless device.
[Explanation of symbols]
[ 0027 ]
DESCRIPTION OF SYMBOLS 1 Shield case 2 Board | substrate 3 Grounding pattern 4 Antenna 5 Electric contact 6 The magnetization easy axis direction of a magnetic film

Claims (4)

A shield case covering at least a portion where the transmission circuit is configured on the substrate is provided so as to be in electrical contact with the ground pattern of the substrate, and an antenna for radiating radio waves from the transmission circuit is provided outside the shield case. In the portable radio device, the electric contact in a portion where a current density of a current component flowing from the shield case to the ground pattern of the substrate is high in a high frequency induced current induced in the shield case when radio waves are radiated from the antenna. A portable radio apparatus characterized by having a higher arrangement density . 2. The portable radio according to claim 1, wherein the arrangement density of the electric contacts is increased in a vicinity of a position where the antenna is pulled out from the shield case and a portion far from a position where the antenna is pulled out from the shield case. apparatus. In a portable wireless device provided with a shield case covering at least a portion where a transmission circuit is configured on a substrate, and having an antenna for radiating radio waves from the transmission circuit outside the shield case, the shield case has a resin surface An anisotropic magnetic film is further laminated on the conductive film, and the magnetization easy axis direction of the anisotropic magnetic film is set to the same direction as the current flowing through the antenna. The portable radio apparatus according to claim 1 or 2, wherein 4. The portable radio apparatus according to claim 3, wherein the anisotropic magnetic film is an anisotropic granular film.

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