JP2007281179A - Shield case for electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shield case which can suppress noise radiated from the opening of the shield case for electronic apparatus and its periphery to the outside conveniently without altering the profile of the opening. <P>SOLUTION: The shield case for electronic apparatus comprises: a conductive case body 1 having an opening 2 and containing an electronic apparatus while shielding from radiation noise; and a conductive member 3 provided in the case body 1 and connected electrically with the case body 1. The conductive member 3 is connected to the vicinity of the opening 2 in order to reduce current density around the opening, by shunting a part of induction current E generated in the case body 1 by the radiation noise and flowing along the edge of the opening 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a shield case for an electronic device for shielding radiation noise generated from an electronic component such as an integrated circuit board, and particularly relates to a shield case for an electronic device that suppresses electromagnetic wave leakage from an opening of the shield case.

In recent years, in electronic devices such as communication devices and information devices equipped with electronic components such as integrated circuit boards, with the increase in circuit density and signal speed, electromagnetic waves (radiated noise) emitted from electronic components Problems such as equipment causing malfunctions are becoming more serious. For this reason, the level of radiation noise from electronic equipment is obliged to be less than or equal to a regulation value set by VCCI (Voluntary Interference of Information Processing Devices, etc.).
As one of countermeasures against radiation noise exceeding the above-mentioned regulation value, a method of taking an electromagnetic wave shield by storing an electronic component in a conductive shield case is taken.

  On the other hand, since the input / output or heat dissipation openings such as connectors are usually formed in the shield case, the input / output and heat dissipation openings become radiated noise as the signal frequency increases as described above. Therefore, it is important to take measures for suppressing radiation noise generated from the opening and the periphery of the opening. In other words, if the opening is blocked by a cable or connector, the directivity to the outside will change, but the amount of energy of the induced current flowing around the opening and the magnetic current generated thereby will not change. This causes energy transmission to the outside. There are various energy propagation paths, such as when a signal leaks from a gap between a cable, connector, or other component and the opening, and the signal is sent to the connector, cable, etc., and cannot be ignored as is the case with noise radiation from the opening. .

  The current path of the induced current differs depending on the resonance mode, but will be described below using the shield case shown in FIG. 7 as an example. FIG. 7 shows a general rectangular parallelepiped shield case 1 for electronic equipment having a rectangular opening 2 that is long in the lateral direction on the back surface, for example. In FIG. 7, the opening 2 is illustrated in a large size for explanation. In this case, the length of each side of the shield case 1 is y direction (horizontal direction)> x direction (front-rear direction)> z direction (vertical direction). In such a shield case 1, when radiation noise is generated from the internal electronic components, a radial induced current (not shown) is generated from one or more points on the xy plane (upper surface), which is shown in FIG. Thus, when there is no opening on the back surface, the induced current 4 flows straight from top to bottom. However, when the back surface has an opening, the induced current 4 flows around the opening 2 as shown in FIG. Flows. As described above, the induced current circulates around the opening 2 to increase the current density at both ends in the longitudinal direction of the opening 2 and to add acceleration motion to the charge. As a result, the opening (internal space) A transverse magnetic current M is generated, and an electromagnetic wave is generated as radiation noise from the periphery of the opening.

With respect to radiation noise generated from the opening and the periphery thereof, Patent Document 1 has a multilayer structure of a shield case that blocks radiation noise from the circuit board, and includes an opening on the inner layer wall and an opening on the outer layer wall. However, a technique for suppressing radiation noise by setting so as not to overlap in plan view is disclosed.
Patent Document 2 and Patent Document 3 disclose a technique for suppressing radiation noise generated from the opening and its periphery by arranging a magnetic material in the opening of the shield case or in the vicinity of the opening. .

JP 2003-69271 A JP 2000-174483 A Japanese Utility Model Publication No. 5-31297

However, in the technique described in Patent Document 1, since the shield case surrounding the circuit board has a multilayer structure, there is a problem that the number of parts, the number of manufacturing steps, and the cost increase in addition to the complexity of the structure.
With respect to Patent Documents 2 and 3, since a magnetic material different from the material of the shield case is provided in the vicinity of the opening, it is considered that the number of manufacturing steps and the cost increase as described above.
This invention is made | formed in view of such a situation, and provides the shield case which can suppress the radiation noise from an opening part effectively with a simple structure without cost.

  Thus, according to the present invention, there is provided an electrically conductive case body having an opening, for accommodating an electronic component and shielding radiation noise from the electronic component, and the case body. A conductive member electrically connected, and the conductive member shunts a part of the induced current generated along the edge of the opening due to the radiation noise and flowing along the edge of the opening. Provided is a shield case for an electronic device connected in the vicinity of the opening so as to reduce the density.

  According to the shield case for electronic equipment of the present invention, in the induced current generated in the conductive case main body due to the radiation noise from the electronic component, a part of the induced current (surface current) flowing so as to go around the opening of the case main body is The current is shunted through the conductive member in the direction of reducing the current density of the induced current flowing along the edge of the opening. The electromagnetic wave generated by the induced current that goes around the end of the opening is radiated to the outside of the shield case, but the electromagnetic wave generated by the induced current flowing through the conductive member is radiated to the inside of the shield case. That is, since the current density of the induced current that goes around the end of the opening is reduced by the conductive member, radiation noise to the outside due to the induced current around the opening can be suppressed.

  The shield case for an electronic device according to the present invention has an opening, a conductive case main body for storing an electronic component and shielding radiation noise from the electronic component, and a case provided inside the case main body. A conductive member electrically connected to the main body, and the conductive member shunts a part of the induced current generated in the case main body due to the radiation noise and flowing along the edge of the opening to surround the opening. It is characterized by being connected in the vicinity of the opening so as to reduce the current density.

  In the present invention, the material of the case main body and the conductive member is not particularly limited as long as it has conductivity, and examples thereof include copper, copper alloy, aluminum, aluminum alloy, and the like. The material may be the same or different. Moreover, the case main body does not need to be entirely formed of a conductive material, and for example, may have a multilayer structure in which an inner surface of a plastic casing is covered with a conductive material.

  In the present invention, the opening has a shape that is long in one direction, and the conductive material is connected to two locations in the vicinity of the opening on the inner surface of the case body, and the direction of the line connecting the two connection locations is The shield case may be configured to cross the opening so as to intersect the one direction. Examples of the shape that is long in the one direction include a rectangle, an ellipse, an oval, and a rhombus. For example, when the opening is rectangular, the two connecting portions of the conductive member are arranged near a pair of long sides of the opening. Is done. If it does in this way, it can arrange so that a conductive member may be crossed on an opening part seeing in a plane. Therefore, a part of the induced current flowing toward the opening can be passed through a path that crosses the opening as viewed in plan by the conductive member without causing the opening to wrap around the opening. Can be reduced.

  In the present invention, the conductive member may have a shape protruding inward from an inner surface having an opening of the case main body. Such a shape of the conductive member is not particularly limited as long as it protrudes into the case body, but for example, a linear square or a linear triangle, a linear U-shape, a line that opens to the opening side. C-shape, plate shape, cube shape and the like. Among these shapes, from the viewpoint that the radiation noise generated by the current flowing through the conductive member is maximized with respect to the inner direction of the shield case, the radiation noise to the outside can be effectively suppressed. Is a shape that protrudes in the vertical direction (right angle) with respect to the inner surface having the opening of the case body, and more preferably a linear shape (frame shape) that does not have a flat surface portion. However, the conductive member is not limited to these shapes, and may be linear.

  In the present invention, the conductive member is preferably disposed between the center of the opening and the end portion on the longitudinal direction side, and in this way, the induced current flowing along the edge of the opening is transmitted to the conductive member. It is effective to shunt. Furthermore, it is preferable that two or more conductive members are provided in the vicinity of both ends in the longitudinal direction of the opening in order to reduce the current density at both ends of the opening.

  The conductive member described above may be fixed and electrically connected to the inner surface of the case body by, for example, solder, conductive adhesive, welding, caulking, or the like, but the conductive member may be swingably attached to the case body. Good. That is, the shield case having the above-described configuration may further include a pair of cylindrical connection members that electrically connect the conductive member to the case body. In this case, the conductive member has both ends on the same axis. The linear member is bent so as to be formed, and both the bent ends are held swingably on the cylindrical connecting member. As the conductive member in this case, it is appropriate that the linear member is formed into the above-mentioned linear square, linear triangle, U-shape, C-shape, etc., and both ends are bent on the same axis. is there. In addition, the direction of both ends may be the same direction or the reverse direction. Further, the connecting member is made of a conductive material like the conductive member, and is fixed to the inner surface of the case body by the above-described solder, conductive adhesive, welding, caulking or the like.

  Furthermore, it is preferable that the conductive member held so as to be swingable by the cylindrical connecting member has a shape that does not overlap the opening in a state along the end of the opening. In this way, when a connector having a cross-sectional area larger than that of the cable is passed through the opening, the conductive member can be swung to the inner surface side of the case body to ensure the original opening area of the opening. That is, various components having a cross-sectional area within the opening area of the opening can be passed through the opening. On the other hand, when an opening area can be provided, for example, when a cable is passed through the opening, an EMC (Electromagnetic Compatibility) countermeasure is made effective by bringing the protruding direction of the conductive member close to a right angle with respect to the inner surface of the case body. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the dimensions, materials, shapes, and other relative arrangements of the components described in the present embodiment are not intended to limit the scope of the present invention to those unless otherwise specified. Absent.

(Embodiment 1)
FIG. 1 is a perspective view showing Embodiment 1 of a shield case of the present invention having an opening 2 on the back surface, and FIGS. 2 (a) and 2 (b) are side sectional views of the shield case of FIG. It is a cross-sectional view. 1 and 2, the coordinate system is an xyz rectangular coordinate system. In this case, the shape of the case body 1 of the shield case is a rectangular parallelepiped, and the relationship between the lengths of the respective sides is y direction> x direction> z direction. The opening 2 is formed on the back surface (yz plane) of the case body 1 in a rectangular shape in which the side in the y direction is a long side and the side in the z direction is a short side. At this time, the opening 2 is arranged so that the center coincides with the center of the back surface of the case body 1 having the opening 2. A pair of conductive members 3 that electrically connect one long side of the opening 2 and the other long side on the inner surface of the case body 1 are disposed near both ends of the opening 2. The conductive member 3 is formed in a linear quadrangle (U-shape) having an opening, and both ends are electrically connected to the inner surface of the case body 1 and protrude in a direction perpendicular to the inner surface of the case body 1. Yes. 1 and 2, an arrow E indicates an induced current flowing through the back surface of the case body 1.

  As shown in FIGS. 1 and 2, part of the induced current E that wraps around the opening 2 on the back surface of the case body 1 flows toward the end of the opening 2, and the rest flows through the conductive member 3. As a result, the current density of the induced current E that wraps around the end of the opening 2 decreases, so that the radiation noise due to the magnetic current generated between both ends of the opening 2 decreases. Radiation noise is also generated by the current flowing through the conductive member 3, but the induced current E loop formed by the conductive member 3 has an angle (in this case, substantially perpendicular) to the opening 2, so that generated radiation is generated. Only a part of the noise is radiated to the outside. As a result, external radiation noise can be suppressed. The direction in which the induced current flows changes in the reverse direction as time elapses, but the same effect as described above can be obtained even if the induced current flows in the reverse direction.

(Embodiment 2)
3 is a perspective view showing Embodiment 2 of the shield case of the present invention having an opening 2 on the back surface, and FIGS. 4 (a) and 4 (b) are side cross-sectional views showing conductive member mounting portions in the shield case of FIG. It is the figure and the cross-sectional view seen from the downward direction. In the second embodiment, the same elements as those in the first embodiment are denoted by the same reference numerals.
In the shield case of the second embodiment, the case body 1 is the same as that of the first embodiment, and the structure for attaching the conductive member 13 to the case body 1 is different from that of the first embodiment. Hereinafter, differences of the second embodiment from the first embodiment will be mainly described.

In Embodiment 2, the conductive member 13 is formed in a square having an opening formed by bending a conductive wire so that both ends are on the same axis. Further, in order to attach the conductive member 13 to the case body 1 so as to be swingable, a pair of cylindrical connecting members 14 and 14 are disposed on the same axis in the vicinity of the pair of long sides by, for example, soldering. It is electrically connected to the inner surface of the case body 1. The conductive member 13 is swingably held by inserting the bent ends into the respective cylindrical connecting members 14, 14.
In this shield case, when the countermeasure for suppressing the radiation noise to the outside is made effective, the surface area surrounded by the conductive member 13 and the opening 2 and the inner surface of the case body 1 are angled (as in the first embodiment). The conductive member 13 may be swung to a position having a right angle (preferably a right angle). On the other hand, when a cable or the like is taken in or out of the opening 2, the conductive member 13 is swung toward the end of the opening 2. Thus, the effective opening area of the opening 2 can be increased. In this case, the area surrounded by the straight line connecting the conductive member 13 and the connecting members 14 and 14 is conductive so as to be equal to or larger than the opening area of the opening 2 on the end side from the straight line connecting the connecting members 14 and 14. In other words, by forming the member 13, in other words, the conductive member 13 has a projecting dimension toward the inside of the case that is equal to or greater than the distance from the connection member 14 to the end of the opening 2. By configuring this, it becomes possible to put in and out components such as cables and connectors whose cross-sectional area is the same as or smaller than the area of the opening 2.

  In the case of the structure in which the conductive member 3 is fixed to the case body 1 as in the first embodiment, the mounting interval between the pair of conductive members 3 and 3 is set larger than the width of the connector. Needs to be set larger than the mounting interval between the conductive members 3 and 3. On the other hand, in Embodiment 2, since the conductive members 13 and 13 have a swingable structure, the length of the opening 2 can be shortened to a length that allows the connector to pass through. Radiation noise to the outside can be effectively suppressed while reducing an increase in necessary opening length. Therefore, the second embodiment is particularly effective when a connector having a larger cross-sectional area than a cable is passed.

(Other embodiments)
Note that two conductive members are not necessarily provided and may be one. In this case, the radiation noise suppression effect is slightly reduced as compared with the case where two conductive members are provided, but the effect is obtained as compared with the case where there is no conductive member.
In addition, if it is between both ends in the longitudinal direction of the opening, the radiation noise suppression effect is obtained wherever the mounting position of the conductive member is, and even if the conductive member is attached to the end, the effect is obtained, The effect of suppressing radiation noise is higher when it is attached between the end and the center of the opening.
With respect to the shape of the conductive member, it is necessary that the path of the induced current flowing through the conductive member is positioned inward of the inner surface of the case body. For example, when a linear or rectangular parallelepiped conductive member is attached to the inner surface of the case body, the conductive member is located inside the case body, but considering the shortest path of current, the inner surface of the case body and the conductive member Since the surface on the opening side of the same is on the same plane, there is little change in the current path, so that the effect of the present invention is not obtained so much. Taking such a case into consideration, it is desirable that at least a part of the conductive member that overlaps the opening as viewed in a plane is located inward of the inner surface of the case body.

Example 1
The shield case described in FIG. 1 was manufactured with the following dimensions and materials.
The case body 1 was manufactured using a copper plate having a thickness of 1 mm, with the side in the x direction being 200 mm, the side in the y direction being 75 mm, and the side in the z direction being 75 mm. The opening 2 has a long side of 160 mm and a short side of 5 mm. Each conductive member 3 is formed in a rectangular shape having an opening with a height of 5 mm and a depth of 10 mm using a copper wire having a diameter of 1.0 mm, and the connection point of each conductive member 3 is from the short side of the opening 2 toward the center. Each was connected to the inner surface of the case body 1 by solder at a position of 5 mm.

(Comparative Example 1)
As Comparative Example 1 with respect to Example 1 of the present invention, a shield case having no conductive member was prepared.

  The amount of radiation noise generated to the outside in Example 1 and Comparative Example 1 was obtained by electromagnetic field analysis, and the effect of the present invention was verified by comparison. In addition, the comparative example 1 is the structure similar to Example 1 except having no electroconductive member and having changed only the long side of the opening part 2 into 150 mm. The reason why the opening 2 in Comparative Example 1 is 150 mm is that the effective area of the opening is used when the use of the opening is for passing a cable or the like, and is compared with the distance between the conductive members 3 and 3 in Example 1. This is to make the opening lengths of Example 1 the same. A 10 mm micro dipole was used as the electromagnetic wave source, and a Gaussian pulse was used as the input signal. The frequency band to be evaluated was 0 to 2 GHz.

FIGS. 5A and 5B are graphs of the frequency characteristics of the electric field strength at a point 3 m away from the center of the opening 2 in Example 1 and Comparative Example 1 in the x direction. In FIG. 5, the vertical axis represents the electric field intensity (unit: dBV / m) in the z direction, and the horizontal axis represents the frequency (unit: GHz).
5 (a) and 5 (b), the electric field strength is maximum in the vicinity of 1 GHz. This is because resonance occurs at a frequency at which the length of 150 mm of the long side of the opening 2 is just a half wavelength. It is. When the maximum values of the electric field strengths of both were compared, it was found that Example 1 was -15.6 dBV / m, Comparative Example 1 was -13.4 dBV / m, and Example 1 had a lower electric field strength of about 2 dB. .

  6A and 6B are diagrams showing the results of analyzing the distribution of the induced current around the opening 2 in Example 1 and Comparative Example 1. FIG. In this case, the analysis was performed by the FI method (Finite Integration) using a commercially available analysis tool (Micro Wave-Studio: manufactured by AET Co., Ltd.). In the analysis model, the current generated when a Gaussian pulse was applied with one end of a small dipole antenna connected to the bottom of the metal case body was obtained. As for the frequency characteristic, the frequency characteristic of the applied Gaussian pulse is normalized so that the amplitude of the input signal is the same at all frequencies.

In FIG. 6, the distribution of the induced current is indicated by contour lines, and the asterisks in the figure indicate locations where the current value is maximum.
From the result of FIG. 6, it can be seen that the current value at the end of the opening 2 is lower in Example 1 than in Comparative Example 1, which goes around the end of the opening 2 in Example 1. It is considered that a part of the induced current is diverted to the conductive member 3. Also, from these results, it can be seen that radiation noise to the outside can be suppressed by the present invention.

  The present invention can be applied to a shield case for an electronic device, and is particularly suitable for a shield case for an electronic device such as a communication device or an information device provided with electronic components having a high integration density and a high frequency.

It is a perspective view which shows Embodiment 1 of the shield case of this invention. (A) And (b) is the cross-sectional view seen from the side sectional view and the downward direction of the shield case of FIG. It is a perspective view which shows Embodiment 2 of the shield case of this invention. (A) And (b) is the side sectional view which shows the electrically-conductive member attachment site | part in the shield case of FIG. 3, and the cross-sectional view seen from the downward direction. (A) And (b) is the graph which showed the electric field strength of the radiation noise in an Example and a comparative example. (A) And (b) is the figure which showed the electric current distribution on the case main body plane with the opening part in an Example and a comparative example. It is a perspective view which shows the conventional general rectangular parallelepiped-shaped shield case for electronic devices. (A) And (b) is a figure which shows the electric current path | route of the induced current which flows through the surface which does not have an opening part, and the surface which has an opening part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Case main body 2 Opening part 3, 13 Conductive member 14 Cylindrical connection member E Induced current

Claims (8)

A conductive case body having an opening, for storing electronic components and shielding radiation noise from the electronic components, and a conductive member provided inside the case body and electrically connected to the case body And
The conductive member is connected in the vicinity of the opening so as to divert part of the induced current generated along the edge of the opening due to the radiation noise and flowing along the edge of the opening to reduce the current density around the opening. Shield case for electronic equipment characterized by that. The opening has a shape that is long in one direction,
The conductive material is connected to two locations near the opening on the inner surface of the case body,
The shield case for an electronic device according to claim 1, wherein a direction of a line connecting the two connection portions is a direction crossing the opening so as to intersect the one direction.   The shield case for an electronic device according to claim 2, wherein the conductive member has a shape protruding inward from an inner surface having an opening of the case main body.   The shield case for an electronic device according to claim 3, wherein the conductive member projects in a direction perpendicular to an inner surface having an opening of the case body.   The shield case for electronic equipment according to any one of claims 2 to 4, wherein the conductive member is disposed between a center of the opening and an end portion on a longitudinal direction side.   The shield case for an electronic device according to claim 5, wherein two or more conductive members are provided in the vicinity of both ends in the longitudinal direction of the opening. A pair of cylindrical connecting members that electrically connect the conductive member to the case body;
7. The conductive member is formed by bending a linear member so that both ends are on the same axis, and the bent both ends are swingably held by the cylindrical connecting member. The shield case for electronic devices as described in any one of these.   The shield case for an electronic device according to any one of claims 2 to 7, wherein the conductive member has a shape that does not overlap the opening in a state along the end side of the opening.