JP2004186554A - Shield box and shielding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shielding box and a shielding method capable of simply and surely shielding electromagnetic waves by using the shielding box. <P>SOLUTION: The shielding box 1 comprises a molding formed like a box having a bottom wall 10, a sidewall 7 formed so as to be erected on the outer peripheral part of the bottom wall 10 and an aperture part formed so as to be surrounded by the end of the sidewall 7 which is the opposite side of the bottom wall 10, the sidewall 7 is connected to the bottom wall 10 through an elastic coupling part formed so as to be functioned as a plate spring for the bottom wall 10 and at least one of inner surface and outer surface of the molding has conductivity. The electromagnetic wave shielding method includes a process for storing the shield box in a casing in which a wiring board is stored, depressing the bottom wall 10 of the shielding box 1 to the inner surface of the casing which is faced to the wiring board, and while elastically deforming the elastic coupling part, pressing the end part of the sidewall 7 and/or diaphragm 7 in contact with the wiring board and covering an electric circuit formed on the wiring board with the shielding box. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a shield box and a shield method for protecting an electronic circuit in which an electronic component such as an IC is mounted on a wiring board from electromagnetic waves from the outside or preventing leakage of the electromagnetic waves from the electronic component.
[0002]
[Prior art]
In electronic devices such as mobile phones and small wireless devices, electronic circuits such as high-frequency circuits, logic circuits, transmission circuits, and reception circuits in which electronic components such as ICs and LSIs are mounted on a wiring board are affected by electromagnetic noise from the outside world. Electromagnetic wave shields are required to prevent malfunctions caused by the electromagnetic wave or to prevent electromagnetic waves leaking from the electronic circuit from affecting other devices or the human body.
[0003]
As a method of shielding electromagnetic waves, it is known to surround the electronic circuit with a ground of a wiring board and a shield box as a conductive casing. The shield box is required to be easily detachable for maintenance of the electronic components contained therein, and is required to be easy to assemble.Therefore, devising the connection between the shield box and the ground of the wiring board is required. It is elaborate.
In addition, as one of attempts to increase the mounting capacity of electronic components in a small electronic device and to further reduce the size, a resin housing integrated with a metal plate or a shield box having the same rigidity as a wiring board is engaged with a claw. Alternatively, there is a proposal in which the connection portion of the shield box is directly connected to the ground of the wiring board by fixing with a screw (for example, see Patent Document 1).
In addition, as a countermeasure against electromagnetic wave leakage due to the occurrence of a gap between the shield box and the ground of the wiring board due to the warpage of the board or the lack of dimensional accuracy when molding the shield box, etc., use a metal or resin shield box. There is also a proposal of using a plated material and connecting it to the ground of a wiring board via a small piece of metal having a spring property (for example, see Patent Document 2).
In addition, conductive small protrusions are provided on the walls of the resin-made protrusions plastically deformed on the walls of the resin shield box whose surface is made conductive by plating or the like, and the small protrusions are connected to the ground of the wiring board through the small protrusions. There is also a proposal for connection (for example, see Patent Document 3).
Also, there is a proposal of providing a conductive rubber on a joint surface of a shield box formed of a resin or a shield box formed in a housing with a ground of a wiring board and connecting them (for example, see Patent Documents 4 and 5). is there.
There is also a proposal (for example, see Patent Document 6) in which a tongue piece is provided at an end of a side wall of a resin-made shield box and is connected to a joint surface of a wiring board with a ground.
[0004]
[Patent Document 1]
JP 2000-151132 A [Patent Document 2]
Japanese Patent Application Laid-Open No. Hei 10-224074 [Patent Document 3]
Japanese Patent Application Laid-Open No. Hei 10-22671 [Patent Document 4]
Japanese Patent Application Laid-Open No. 2000-196278 [Patent Document 5]
Japanese Patent Application Laid-Open No. 2001-111283 [Patent Document 6]
Patent No. 3283161 Specification [0005]
[Problems to be solved by the invention]
However, in Patent Literature 1, distortion and warpage are likely to occur in the housing, shield box, or printed circuit board, and a gap is generated between the connection portion of the shield box and the ground of the wiring board to ensure sufficient shielding performance. There is a problem that there is a high possibility that the operation cannot be performed. Furthermore, in order to cause a rigid housing or the like to follow the connection partner with stress, that is, to connect, an excessive stress is required, and the periphery of the engaging claw or the screw portion must be in a rigid state. In addition, electronic devices such as mobile phones and small wireless devices have a problem that extra volume and weight are required.
Further, in Patent Document 2, a small piece having metallic spring properties must be provided in advance on a wiring board by soldering or the like, which is troublesome, and the small piece is deformed by handling during the process. Had to be fixed and was not productive. Furthermore, the number of parts increased, which was not rational. Also, at the time of recycling, it was not easy to separate and sort parts.
According to Patent Literature 3, the conductive small protrusion is likely to be plastically deformed when a force exceeding a certain level is applied, and once plastically deformed, even if the shield box is opened again for repair or the like and then reassembled, conduction is not achieved. There was a problem that it would be certain.
[0006]
In Patent Documents 4 and 5, the width of the connection portion between the shield box or the like and the ground of the wiring board, that is, the width of the outer wall or the rib portion of the shield box or the like is as narrow as 1 mm or less, and the conductive elastic member is fitted therein. Is very difficult, and the work is time-consuming because the elastic member is cut or stretched. In addition, when a liquid material is provided by a dispenser or the like, an expensive device having position control and discharge amount control must be used, and after the housing or shield box is manufactured, the material is transported to a place where dispensing can be performed. This has the disadvantage that the production time is prolonged, the casing and the like are damaged, and the pass rate is not increased.
Patent Document 6 shows a tongue piece connected to the ground of the wiring board of the shield box. However, the height of the tongue piece is not sufficient with respect to the amount of compressive displacement, and when assembled, the elastic limit is reduced. When the tongue piece is deformed, the side wall, which has lower strength, buckles before the tongue is deformed. Further, if the elasticity of the tongue piece is utilized, the diameter of the folded portion, that is, the thickness of the side wall portion increases, and the width of the ground of the wiring board to be connected must be increased, which is disadvantageous for miniaturization. Was.
As described above, in the conventional device, there is a limit in the shielding performance of a small electronic device such as a mobile phone, and it is not easy to assemble, and there is a problem in assemblability in a short time. Further, the number of parts is increased, and it is necessary to make the housing robust, and the advantage of the small, small, and small electronic devices is lost. In addition, special equipment and labor for transportation were required, and it was not economically reasonable.
In view of such circumstances, an object of the present invention is to provide a shield box and a shield method that can easily and reliably perform electromagnetic wave shielding by a shield box.
[0007]
[Means for Solving the Problems]
That is, the shield box according to the present invention includes a bottom wall, a side wall formed so as to rise on an outer peripheral portion of the bottom wall, and an opening formed by being surrounded by an end of the side wall opposite to the bottom wall. And a side wall is connected to the bottom wall through an elastic connecting portion formed to function like a leaf spring with respect to the bottom wall, At least one of the inner surface and the outer surface of the molded body has conductivity.
Further, in the method of shielding an electronic circuit according to the present invention, the shield box is housed inside a housing housing a wiring board therein, and a bottom wall of the shield box is pressed by an inner surface of the housing facing the wiring board. The end of the side wall and / or the partition is pressed against the wiring board while the elastic connecting portion is elastically deformed, whereby the electronic circuit on the wiring board is covered with a shield box to shield electromagnetic waves.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described in detail with reference to the drawings.
FIG. 1 is an exploded perspective view of an electronic device incorporating a shield box. As shown in FIG. 1, the shield box 1 and the wiring board 2 are arranged between the divided housings 3 and 3 'of the electronic device. Various electronic circuits 5 on the wiring board 2 are surrounded by the shield box 1 and a metal foil (not shown) on another layer of the wiring board 2. Used by being connected to the ground 4 on the substrate. The electronic circuit 5 is composed of functions of a high-frequency circuit, a logic circuit, a transmission circuit, a reception circuit, and the like. Since the degree of influence of external electromagnetic noise or the frequency and intensity of leaking electromagnetic waves is different, each electronic circuit 5 Are separated by the ground 4.
[0009]
FIG. 2 is a perspective view of the shield box with the bottom wall of the shield box facing upward, and FIG. 3 is a perspective view of the shield box with the opening facing upward. As shown in FIGS. 2 and 3, the shield box 1 of the present invention has a substantially box-like shape, and has a bottom wall 10, and a side wall 7 formed so as to stand up on an outer peripheral portion of the bottom wall 10. The side wall 7 has an opening 6 surrounded by a bottom wall 10 and an end opposite to the bottom wall 10. The shield box of the present invention may further include a partition 8 that partitions the inside of the shield box 1 into a plurality of small rooms 9.
The side wall 7 or the partition 8 is connected to the bottom wall 10 via an elastic connecting portion 12 formed so as to function like a leaf spring with respect to the bottom wall 10. The side wall 7 and the partition 8 are arranged at positions where the tips of the side wall 7 and the partition 8 on the opening 6 side can be connected to the ground 4 when the shield box 1 is pressed against the wiring board 2. The size of the shield box is determined by the volume of the electronic circuit included therein, and is not limited thereto, but is generally about 10 to 100 mm on one side and about 1 to 10 mm in height. The heights of the small rooms 9 may be the same as each other, or some of the small rooms may have different heights as shown in FIG.
The radius R of the corner formed by the two side walls is about 0.1 to 3 mm.
[0010]
Further, as shown in FIGS. 4 and 6, the side wall 7 or the partition 8 is connected to the bottom wall 10 via an elastic connecting portion 12 formed so as to function like a leaf spring with respect to the bottom wall 10. The stress applied to the shield box 1 is absorbed by the elastic connecting portion 12 being bent, and the tip of the side wall 7 or the partition 8 can be brought into contact with the ground 4 with a small pressing force (the ground is not shown). ).
[0011]
The elastic connecting portion 12 may have any structure as long as the elastic connecting portion can be elastically deformed by a pressing force applied to the bottom wall portion. As shown in the figure, a rising portion that once rises from the bottom wall in the direction of the opening, and a horizontal portion extending parallel to the bottom wall, connecting the end of the rising portion on the opposite side to the bottom wall and the opposite end of the side wall or partition wall. And preferably When the elastic connecting portion has such a structure, when a stress is applied to the bottom wall 10 of the shield box, a part of the stress is absorbed by bending the horizontal portion, and excessive force is applied to the side wall 7 and the partition 8. When the pressing force is released without applying any stress, the elastic member returns to the original shape.
As shown in FIG. 5A, in order for the elastic connecting portion 12 to function sufficiently, the distance H of the horizontal portion of the elastic connecting portion 12 is preferably larger than the height V of the rising portion. The longer the distance of the horizontal part (the distance from the rising part to the side wall or the end of the partition wall), the lower the load can be obtained. However, when the shield box is stressed, it may come into contact with the electronic components contained in the shield box. It is important not to. This H is preferably about 0.5 to 5 mm. The height V of the rising portion of the elastic connecting portion 12 is larger than the amount of compressive displacement of the shield box, and is preferably about 0.2 to 4 mm.
[0012]
Further, as shown in FIGS. 7 and 8, when the side wall 7 has a folded structure, the rigidity of the end of the opening increases, linearity can be secured, deformation due to compression can be suppressed, and the side wall 7 can be connected to the ground. There is no deviation and the connection can be made reliably. Even when only the inner surface is made conductive, the conductive surface can be pressed against the ground.
[0013]
The sharper tip of the partition wall 8 has higher contact stability, or a blade or a needle is contacted from above with the depression of the partition wall shown in FIG. Although a structure having a recess due to molding may be used, it is required that the gap formed between the ground 4 and the ground 4 has a relationship with the wavelength as shown below.
When the slit 11 is provided in the partition 8 and the partition 8 is divided into a plurality of pieces, the plurality of pieces sandwiched between the slits 11 can move independently, and the stability of the connection increases. preferable. Even when the slit 11 is provided, when the shield box 1 is compressed, the partition wall 8 only moves up and down, and the partition wall 8 does not collapse and spread or a gap is greatly opened. At the joint between the partition and the adjacent partition that partitions the small room of the partition or with the side wall 7, slits should be provided as much as possible in small rooms that contain electronic circuits that do not want to cause leakage of electromagnetic waves. Good to avoid.
When a slit is provided, the allowable size of the gap is 以下 or less, preferably １ ／ or less, of the wavelength that is not desired to pass.
Also, when the elastic connecting portion is distorted when the bottom wall is compressed and the side wall does not move up and down smoothly, as shown in FIG. By providing slits such as hooks at each corner, it is possible to cope with this by making the elastic connecting portions of each side independent and preventing them from competing.
Further, a ventilation opening having a size allowed in relation to the wavelength may be provided on the bottom wall for heat radiation. Further, in order to ensure insulation from the electronic components included therein, an insulating sheet may be provided on the inner surface of the bottom wall to make the inner surface of the bottom wall electrically insulating.
[0014]
The material of the shield box is such that the elastic connecting portion 12 is elastically deformed, and the ends of the side walls 7 and the partition walls 8 are connected to the ground 4 with a low pressing force. it is preferable that elastic deformation in the elastic modulus approximately ¹⁰ 5 ^~10 9 Pa.
The thickness of the elastic connecting portion depends on the shear modulus, but is preferably 1 mm or less, more preferably 0.05 to 0.5 mm. If the shear modulus is larger than this, the load for pressing the shield box against the ground becomes excessive, deforming the housing and the wiring board, resulting in poor contact. On the other hand, if it is small, the shape cannot be maintained, and there is a risk of short-circuit due to contact with the electronic components contained therein, resulting in insufficient contact pressure, which also results in poor contact.
On the other hand, the thickness of the side wall 7 and the partition 8 is preferably 1 mm or less, and more preferably substantially 0.2 to 0.8 mm. When the thickness exceeds 1 mm, a space is required around the electronic circuit, which hinders downsizing of the electronic device.
In the case where the side wall 7 and the partition 8 are folded back as shown in FIGS. 7 and 8, this thickness indicates the total thickness of two sheets and the gap size.
In the case where the elastic connecting portion has the rising portion and the horizontal portion as described above, even when the elastic connecting portion and the side wall or the partition have the same thickness, when the pressing force is applied to the bottom wall, the side wall or the partition may be formed. Without deforming, the elastic connecting portion can deform and absorb the stress.
As this material, a material made of metal or synthetic resin is selected, but synthetic resin is preferable in view of easiness of processing and weight. This synthetic resin includes thermoplastic resins such as polyethylene terephthalate, polystyrene, polycarbonate, polyacrylonitrile, polyamide, polyphenylene oxide, acrylonitrile-butadiene-styrene copolymer, ethylene-vinyl acetate copolymer, polyester-based elastomer, styrene-based Thermoplastic elastomers such as elastomers, polyamide elastomers, and polyurethane elastomers, and rubbers such as ethylene propylene rubber, styrene butadiene rubber, nitrile rubber, urethane rubber, and silicone rubber are exemplified. In addition, modified products, mixtures, and composites of the above materials may be used.
[0015]
Than the metal, since an insulating, at least one surface of the material is required to have conductivity, the surface resistance is preferably 10 ^{0 -} 10 is ^{-5 Ω} / □. If the resistance is higher than this, a sufficient shielding effect cannot be obtained. When the shield box is made of a synthetic resin, its surface can be plated with copper, nickel, silver, gold, or the like, or a known method such as sputtering or vapor deposition can be used, or a paint containing metal or carbon black can be used. Or by kneading a conductive filler such as carbon black into a synthetic resin in advance. There is no limitation on the shape of the conductive filler, but one having a high aspect ratio is efficient. When the surface resistance is low, the reflection of electromagnetic waves can be suppressed, but in order to attenuate efficiently, a soft magnetic material such as ferrite, chromium ferrite, permalloy, or a carbon microcoil may be used in combination.
[0016]
A box-shaped shield box can be formed by a known method using a sheet or a pellet of the above-described material, and can be formed by die molding, vacuum molding, blow molding, injection molding, or molding. The slit may be formed in advance so that the slit can be formed on a mold, but may be provided in a shaped box-shaped shield box with a blade.
Generally, vacuum molding or blow molding, which has a rapid molding cycle, is good. A thermoplastic film having a thickness of 50 to 500 μm is heated to 50 to 200 ° C., and is pressed or vacuumed so as to follow a mold. , Can be shaped.
When the sheet was shaped, as shown in FIGS. 4 to 8, the partition was formed by folding the sheet, and when injection molding was used, as shown in FIG. 9, the inside of the partition was filled with resin. It can be shaped into a shape. If a sheet is used, conductivity, cutout processing, inspection, trimming, etc. can be performed in a hoop shape, so transportation is easy, and if injection molding is used, the thickness of the elastic connecting portion can be changed. , Precision products can be manufactured.
[0017]
The shield box contacts and connects to the ground of the wiring board inside the divided housing, and is compressed and connected by combining the other divided housing. The free height of the shield box (height when no stress is applied to the shield box) must be larger than the gap between the housing and the ground of the wiring board after the combination, and is about 0 It is preferable that the diameter is as large as 0.1 to 2 mm. If it is smaller than this, it is not possible to obtain a sufficient amount of compressive displacement due to undulation, warpage, or variation in thickness of the housing or the wiring board. If it is larger than this, the deformation of the shield box becomes large, and an excessive load is applied. This may occur, which is not preferable for connection.
[0018]
In the shielding method of the present invention, the shield box is placed on a wiring board so as to surround various electronic circuits 5 of the wiring board housed in the housing, and the housing box is combined. Is housed inside the housing, and the bottom wall of the shield box is pressed by the inner surface of the housing facing the wiring board to press the shield box against the wiring board.
The shield box may be placed on the wiring board and the casing may be combined as it is, or may be temporarily fixed with an adhesive tape before combining the casings. When the partition wall of the shield box is formed by folding back the film, a rib for reinforcing the housing may be fitted into the recess of the partition wall and temporarily fixed.
When the shield box is pressed against the wiring board, the elastic connecting portion between the side wall and / or the partition and the bottom wall is elastically deformed, and the end of the side wall and / or the partition is connected to the ground of the wiring board. The electronic circuit is covered with a shield box, and is wrapped in a metal foil on another layer of the shield box 1 and the wiring board 2 to shield electromagnetic waves.
[0019]
【The invention's effect】
As described above, since the shield box of the present invention has the above-described configuration, it is possible to shield the electromagnetic wave simply by mounting it on the wiring board and assembling the housing as it is, so that the shield box can be easily attached and detached. In addition, it is possible to reliably perform electromagnetic wave shielding. In addition, since the above configuration is adopted, it has a feature that it can be easily shaped. Further, since a small amount of stress is applied to the shield box to perform the electromagnetic wave shielding, an excessive force is not applied to the wiring board or the like.
Further, according to the shielding method of the present invention, the shield box is mounted on the wiring board so as to surround various electronic circuits of the wiring board housed in the housing, and the housing is simply combined with the housing. Electromagnetic waves can be shielded in an electronic circuit reliably.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of an electronic device incorporating a shield box.
FIG. 2 is a perspective view of the shield box with a bottom wall facing upward.
FIG. 3 is a perspective view of the shield box with an opening facing upward.
FIG. 4 is a sectional view showing an embodiment of the shield box of the present invention.
FIG. 5 is a cross-sectional view of a main part showing a state before and after pressing a bottom wall of one embodiment of the shield box of the present invention.
FIG. 6 is a sectional view showing another embodiment of the shield box of the present invention.
FIG. 7 is a sectional view showing another embodiment of the shield box of the present invention.
FIG. 8 is a sectional view showing another embodiment of the shield box of the present invention.
FIG. 9 is a sectional view showing another embodiment of the shield box of the present invention.
FIG. 10 is a perspective view showing another embodiment of the shield box of the present invention.
FIG. 11 is a perspective view showing another embodiment of the shield box of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Shield box 9 Small room 2 Wiring board 10 Bottom wall 3 and 3 'Housing 11 Slit 4 Ground 12 Elastic connection part 5 Electronic circuit 6 Opening 7 Side wall 8 Partition wall

Claims (11)

It is formed in a box shape having a bottom wall, a side wall formed so as to stand up on an outer peripheral portion of the bottom wall, and an opening formed by being surrounded by an end of the side wall opposite to the bottom wall. And the side wall is connected to the bottom wall via an elastic connecting portion formed to function like a leaf spring with respect to the bottom wall, and the inner surface and the outer surface of the molded body are connected to each other. A shield box, at least one of which has conductivity. Furthermore, a partition partitioning the interior of the molded body into a plurality of small chambers, the partition being connected to the bottom wall via an elastic connecting portion formed to function as a leaf spring with respect to the bottom wall. The shield box according to claim 1, wherein 3. The shield box according to claim 1, wherein the material constituting the molded body has a shear modulus of 10 ⁵ to 10 ⁹ Pa. 4. The elastic connecting portion is a horizontal portion extending parallel to the bottom wall, the rising portion once rising from the bottom wall in the direction of the opening, and connecting the end of the rising portion on the opposite side to the bottom wall and the opposite end of the side wall or partition. The shield box according to any one of claims 1 to 3, wherein the shield box comprises: 5. The shield box according to claim 4, wherein when the distance of the horizontal portion of the elastic connecting portion is H and the height of the rising portion is V, H ≧ V. The shield box according to any one of claims 1 to 5, wherein the thickness of the side wall and / or the partition wall is 1 mm or less. Any one of claims shield box according to claim 1, wherein the at least one of the surface resistance of the inner and outer surfaces of said molded body is 10 ⁰ ~10 ^-5 Ω / □. The shield box according to claim 1, wherein the partition is divided into a plurality of pieces by a slit. The shield box according to any one of claims 1 to 8, wherein the molded body is formed by shaping from one sheet. The free height of the shield box is larger than the gap between the inner surface of the opposing housing and the wiring board in the space surrounded by the housing in which the shield box is housed and the wiring board. 10. The shield box according to any one of 9 above. The shield box according to any one of claims 1 to 9 is housed inside the housing housing the wiring board therein, and the bottom wall of the shield box is pressed by the inner surface of the housing facing the wiring board. An electronic circuit on the wiring board is covered with a shield box to shield an electromagnetic wave by pressing an end of the side wall and / or the partition wall against the wiring board while elastically deforming the elastic connecting portion. Shield method.

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