JPH11186782A - Shield structure of electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shielding structure for an electronic apparatus which ensures a shield effect of a conductor layer and suppresses more effectively the electromagnetic waves from leaking out of bonded parts. SOLUTION: An electromagnetic wave absorber 107 having a magnetic layer made by forming soft magnetic particulates or flat particulates mixed with an org. binder is settled on a base conductor 101 and with a shield case 104 is fixed mounted on the absorber 107. The base conductor 101 has protrusions 102 which make contact with the shield case 104 to pierce through openings 108 of the radio wave absorber 107 when assembled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shield structure for preventing leakage of electromagnetic waves radiated from electronic equipment.

[0002]

2. Description of the Related Art In recent years, there has been a problem that electromagnetic waves radiated from an electronic device such as a computer cause electromagnetic interference or radio interference in peripheral devices. As a countermeasure against such a problem, a countermeasure for reducing an electromagnetic wave in which noise is confined inside using a casing plating or a shield case is taken.

FIG. 8 is a schematic cross-sectional view of a conventional shield structure using a metal shield case. In the figure, reference numeral 801 denotes an electronic component, 802 denotes a housing, 803a, 803.
b is a shield case, 804 is a printed circuit board, and 809 is a gasket.

FIG. 8 shows an example in which a part of a printed circuit board 804 on which an electronic component 801 is mounted is covered with a shield case 803b, and an example in which the entire printed circuit board 804 is mounted so as to be covered with a shield case 803a. It is shown. In these shielding methods, it has been pointed out that the leakage of the electromagnetic wave from the joint surface occurs due to the warpage of the substrate or the housing, and the leakage has further increased due to the recent increase in the operating frequency of electronic circuits. It is the current situation that a sufficient response is required.

FIG. 9 is a cross-sectional view of a tube type gasket for preventing leakage of electromagnetic waves from a gap.
Reference numeral 0 is a cross-sectional view of an elastic prismatic gasket having an adhesive layer. In the figure, reference numeral 911 denotes a metal net, 912 denotes an elastic body, 913 denotes a hollow portion, 1011 denotes an elastic body, 1012 denotes a conductive tubular cloth, and 1014 denotes a conductive adhesive layer.

A so-called gasket as shown in FIG. 9 and FIG. 10 is frequently used for a connection portion between parts constituting a housing. FIG. 9 shows a tube-like elastic body 912 covered with a metal net 911, and FIG. 10 shows a sponge-like elastic body 1 in a conductive tubular cloth 1012.
011 and formed into a prismatic shape, and a conductive adhesive layer 1
014 is provided. However, in the method using these gaskets, a contact pressure according to the material of the elastic bodies 912 and 1011 can be obtained. However, with the recent increase in the operating frequency, leakage of electromagnetic waves due to contact resistance has increased, and sufficient shielding has been achieved. At present, no effect has been obtained.

FIG. 11 is a partial cross-sectional perspective view of a shield material using a magnetic material disclosed in Japanese Patent Application Laid-Open No. 05-013979. In the figure, reference numeral 1106 denotes a plate-like magnetic material;
Reference numeral 5 denotes a plate-shaped magnet having conductivity, and 1116 denotes a box-shaped conductor.

As in the case of the above-described shield material, the electromagnetic wave absorbing layer is used to suppress the leakage of electromagnetic waves by using the electromagnetic wave absorbing layer around the joints and doors of the metal housing. The magnetic material 1106 and the magnet 1115 are embedded to obtain a higher shielding effect in a low frequency region. However, at present, a gasket is used in combination in a higher frequency range.

FIG. 12 is a cross-sectional view of a composite electromagnetic shielding material using a magnetic material together.
1206 is a composite ferrite.

The electromagnetic shielding material shown in FIG.
-40 (Annual report of the Environmental Electromagnetics Department of the Institute of Electrical Communication) This is an electromagnetic wave absorbing material of "composite electromagnetic shielding material of conductive fiber cloth and ferrite". The structure is such that both surfaces of the composite ferrite 1206 are lined with conductive fibers 1204, which are conductors, and a shield effect is exerted on the entire surface of the material, but an electromagnetic wave absorbing material is stuck on the entire inner surface of the case. Therefore, there is a concern that a large amount of material is required, that the weight increases, and that the heat radiation effect with respect to the heat generated by the internal components deteriorates.

[0011]

As described above, various shield structures using a conductor or a magnetic material are used. However, in an electronic device in a high frequency range, a sufficient shielding effect by a plating casing or a shield case is provided. In order to obtain the above, it is necessary to ensure the shielding effect of the conductor layers such as the plating housing and the shield case, and to prevent the leakage of the electromagnetic wave due to the discontinuity of the impedance at the joint. However, the conventional shield structure does not always have a sufficient effect.

The problem will be described with reference to the results of the theory and experiments of the prior art. Metal layer shielding effect (SE)
Is a function of the electric field strength ratio attenuated by the shield, and is expressed as follows in Schelknov theory considered on an infinite plane.

SE (dB) = 20 log El / E2 where El: incident electric field intensity (V / m) E2: transmitted electric field intensity (V / m) SE (dB) = R + A where reflection loss R = 50 + 10 log (ρ × f) − 1
(DB) Absorption loss A = 1.7t (f / ρ) 1/2 (dB)

Accordingly, the shielding effect is determined by the plating thickness t.
If the frequency f is the same, it can be said that it is inversely proportional to the square root of the volume resistivity ρ.

However, a realistic shield layer is a finite plane, and may be affected by the ground impedance. Therefore,
For the shielding effect of the actual shield case, it is important to reduce the junction resistance of the electrical connection part.

FIGS. 13A and 13B are explanatory diagrams of a state of a change in contact resistance due to a tightening torque of a screw at a boss portion of a printed board and a plated casing, wherein FIG. 13A is a graph of a measurement result, and FIG. FIG. 2 is a schematic perspective view of a measuring device. In the figure, reference numeral 1301 denotes a printed circuit board, 1302 denotes a housing, 1303
Is a screw, 1304 and 1305 are probes.

As shown in FIG. 13 (b), the measurement was performed on a plating casing 1302 coated with a copper plating having a thickness of 1 micron.
And a printed circuit board 1301 made of a copper plate
The contact resistance when the tightening torque of the screw 1303 is changed is determined by the probe 130.
4 and 1305 using the four-terminal method.

From FIG. 13A, it is estimated that the resistance value does not converge to a constant value due to the pressurization, and the resistance value at the joint becomes discontinuous.

FIGS. 14A and 14B are explanatory views of a shield effect evaluation apparatus, in which FIG. 14A is a schematic sectional view of a shield effect evaluation chamber, and FIG. 14B is a block diagram of a shield effect evaluation system. In the figure, reference numeral 1401 denotes a shield evaluation chamber, 1402 denotes a sample, 1403 denotes a gasket, 1
405 and 1406 are magnetic field antennas, 1407 is a standard signal generator, 1408 is a spectrum analyzer, 140
Reference numerals 9 and 1410 denote amplifiers, and 1411 denotes a shield effect evaluator.

In the shield effect evaluation apparatus shown in FIG. 14, a shield evaluator (TR17301) of the Advantest method is used in a shield effect evaluation chamber, and a standard signal generator 140 is used.
7 is Anritsu MG3601A, amplifier 1401 is Advantest TR45002, amplifier 1409
HP4747D, spectrum analyzer 14
10 was HP 8568B. This is a system for evaluating the shielding effect of the sample 1402 and the gasket 1403 attached to the shielding effect evaluation chamber 1401, using a standard signal generator 1407 connected to the magnetic field antenna 1405 on the input side, and using the magnetic field antenna 1406 on the output side. Is used to display the power of the attenuated electromagnetic wave in dBm.

FIG. 15 is a graph showing the measurement results of the shielding effect of a flat plate having a 1 μm copper plating layer formed by a double-sided plating method using the apparatus shown in FIG. The connection between the flat plate and the ground was connected using a phosphor bronze gasket. The horizontal axis shows the frequency, and the vertical axis shows the shielding effect. From this result, it can be seen that the shielding effect is greatly attenuated in the frequency range of 500 MHz or more at the bonding pressure of a general phosphor bronze or beryllium gasket used in the Advantest method. Therefore, in order to sufficiently exhibit the shielding effect of the shield case, it is important to lower the junction resistance of this junction and absorb and attenuate the leaked noise. Here, the Advantes method using a gasket for connection is used, but the same sample is obtained without attenuation in a high frequency region by the KEC method in which a sample is connected with a thick metal plate and a large screw. Therefore, the contact pressure is insufficient, and the shielding effect is attenuated in a high frequency region.

The present invention has been made to solve such a problem, and in addition to providing a strong conductive structure between the shield case and the base conductor, the present invention has been made to solve the above problem. The object of the present invention is to provide a shield structure for electronic devices in which an electromagnetic wave absorbing layer having good high-frequency characteristics is interposed, thereby ensuring a shielding effect of the conductor layer and more effectively suppressing leakage of electromagnetic waves from the joint. And

[0023]

According to the present invention, there is provided a shield structure for an electronic device, wherein an opening is provided between a case formed of a conductor and a base conductor for fixing the case in a housing structure of the electronic device. In the joint structure sandwiching the provided electromagnetic wave absorber, a projection is formed on at least one of the base conductor side and the case side to penetrate the opening and connect the case and the base conductor. .

Preferably, the electromagnetic wave absorber has a magnetic support layer formed of an organic binder mixed with at least one of soft magnetic fine particles and flattened fine particles. The fine particles and the flattened fine particles constituting the support layer of the body are preferably any of ferrite, an amorphous alloy, and permalloy.

The electromagnetic wave absorber may have one or more openings.

Further, it is preferable that the joint surface of the base conductor is subjected to shield plating by electroplating.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1A and 1B are explanatory views of a shield structure of an electronic device according to the present invention. FIG. 1A is a partial cross-sectional view taken along line XX of FIG. (b) is a top view of a plating casing that is a base conductor layer, (c) is a top view of an electromagnetic wave absorber composed of four sheets, (d) is a side view of a steel shield case, and (e) is steel. It is a top view of a shield case made of. In the figure, reference numeral 101 denotes a base conductor, 102 denotes a projection of the base conductor, 103 denotes shield plating of the base conductor, 1
04 is a shield case, 105 is a flange portion of the shield case, 107 is an electromagnetic wave absorber, and 108 is an opening provided in the electromagnetic wave absorber.

In the shield structure according to the embodiment of the present invention, an electromagnetic wave absorber 107 having a magnetic layer formed by mixing soft magnetic particles or flattened particles with an organic binder is inserted on the base conductor 101. And shield case 104
Are fixed on the base conductor 101, and the projections 102 that come into contact with the shield case 104 during assembly are provided on the base conductor 101.
The electromagnetic wave absorber 107 is provided with an opening 108 through which the projection 102 penetrates during assembly. Thus, the base conductor 101 and the shield case 10
4, the electromagnetic wave absorber 107 has a magnetic layer formed by mixing soft magnetic particles or flattened particles with an organic binder, and the joining surface of the base conductor 101 It is a feature of the present invention that the shield plating is applied to the substrate. In FIG. 1, a base conductor 10 is formed via a rectangular projection 102 formed on the base conductor 101.
1 and the shield case 104 are electrically connected, but there is no limitation on the shape of the projections or the method of conducting.

Next, an example of this embodiment will be described in detail with reference to FIG. The base conductor 101 is formed by electroplating copper as a shield plating 103 to a thickness of 1.0 μm.
m, and the protrusion 102 of the base conductor 101
3mm width, 10mm length, 5mm height, 30mm
It is formed on the base conductor 101 in advance in a rectangular shape with a pitch. The base conductor 101 is formed by applying a shield plating 103 thereon. The electromagnetic wave absorber 107 is formed into a strip having a thickness of 5 mm and a width of 7 mm, and the openings 106 having a width of 3 mm and a length of 10 mm are punched and formed at intervals of 30 mm along the center line. Since a commercially available electromagnetic wave absorber often has a thickness of about 1 mm, five sheets may be stacked at this time. Next, the opening 108 of the molded electromagnetic wave absorber 107 is formed with the protrusion 10 of the base conductor 101.
2 and the flange 105 of the shield case 104.
The base conductor 101 is cut at a length corresponding to the flange 105 of the shield case 104. The electromagnetic wave absorber 107 is formed by fixing a ferrite powder with a rubber binder, and can be easily deformed and fixed. On this, the flange portion 105 of the nickel-plated steel shield case 104 was placed, and the four corners were fixed with screws to complete the shield structure of the present embodiment.

Next, another embodiment will be described. 2A and 2B are explanatory views of an embodiment of a shield structure of an electronic device according to the present invention. FIG. 2A is a partial cross-sectional view taken along line XX of FIG. (B) is a top view of a plating casing as a base conductor layer, (c) is a top view of an electromagnetic wave absorber composed of four sheets, (d) is a side view of a steel shield case, and (e) is It is a top view of a steel shield case. In the figure, reference numeral 201 denotes a base conductor,
203 is a shield plating of the base conductor, 204 is a shield case, 205 is a flange portion of the shield case, 20
6 is a projection of the shield case, 207 is an electromagnetic wave absorber, 2
08 is an opening provided in the electromagnetic wave absorber.

In this embodiment, on the contrary to FIG. 1, a projection 206 is formed on the shield case 204 side so that an electromagnetic wave absorber 207 is formed.
Are connected to the planar base conductor 201 through the opening 208 of the first embodiment. Also, the shield case 204 and the base
Projections are formed on both of the conductors 201 and the electromagnetic wave absorber 20
7 may be connected inside the opening 208.

Further, the shape of the opening is not limited to the shape of the above embodiment. In the above embodiments, the shape is rectangular. However, the shape may be circular or elliptical. FIG. 3 is a top view showing an example of the opening of the electromagnetic wave absorber.
(A) is an example having a continuous elongated opening,
(B) is an example in which elongated openings are provided at predetermined intervals. 307, 357 are electromagnetic wave absorbers, 308,
358 is an opening. In this case, the projection becomes an elongated projection corresponding to the opening, and the extension of the side wall of the shield case can be used for contact, which facilitates processing.

The number of openings may be one or more. In a low frequency region, if there are four or five ground connection points, there is no problem in the shielding effect of the shield case itself. .

The choice of the electromagnetic wave absorber is usually 1 G
Many have an absorption peak near Hz.
But there is an effect as shown. Further, in order to obtain a good result, it is ideal to have an absorption peak in the range of 500 MHz to 1 GHz.

Next, the effect of the shield structure of the electronic device of the present invention will be described with reference to experimental examples. As described above, there is a large difference in the shielding effect due to the characteristics of the electromagnetic wave absorbing layer used in combination with the conductor and the gasket. FIG. 4 is a schematic configuration diagram of a simple electromagnetic wave absorbing layer shield evaluation system. In the figure, reference numeral 406 denotes a core electromagnetic absorber, 407 denotes a signal source, 408 denotes an output unit, 409 denotes a signal line, and 410
Is an antenna, 411 is a spectrum analyzer, 412
Is a printer. Signal source 40 as a noise source
7, a signal line 409 is attached, and an electromagnetic wave absorber 406 such as a core type sintered ferrite is inserted in the middle, and an output unit 408 is provided.
The electromagnetic waves radiated from the
The intensity according to the frequency band is detected by the spectro analyzer 411 using 0.

FIG. 5 is a schematic perspective view of a sintered fairite core which is one of the objects to be measured by the electromagnetic wave absorbing layer shielding effect evaluation system of FIG. 4 and has a conductor connected to the ground inside. 503 in the figure is a conductor, 50
4, 505 are ground connection ends, 506 is a sintered ferrite core, and 509 is a signal line. Sintered ferrite core 50
6, a conductor 503 whose both ends are connected to the ground at ground connection ends 504 and 505 penetrates.

FIG. 6 is a graph showing the measurement results obtained by the system for evaluating the shielding effect of the electromagnetic wave absorbing layer shown in FIG.
Shows a case where only a signal line is used, (b) shows a case where only a sintered ferrite core is used, and (c) shows a case where a conductor connected to the ground enters a sintered fairite core.

The evaluation of the shielding effect of the electromagnetic wave absorbing layer was performed using sintered ferrite which is often used as a noise countermeasure for the cable. FIG. When only the sintered ferrite of b) is used, a large damping effect is obtained at around 100 MHz, but the effect is extremely small at 500 MHz or more. FIG. 5C shows a case where cables connected to the ground are inserted in parallel as shown in FIG. 5, that is, a case where the shield case corresponding to the ground layer is in the electromagnetic wave absorbing layer. , Around 100 MHz,
The shielding effect disappears, and no effect is seen even in the 500 MHz class.

On the other hand, FIG. 7 shows a measurement by a shielding effect evaluation system when a ferrite fine particle is mixed with an organic binder having a pressure deformation characteristic such as resin or rubber for the electromagnetic wave absorbing layer. It is a graph of a result, (a) is a case where only the resin core containing ferrite is used, and (b) is a case where the conductor connected to the ground is contained in the resin core containing ferrite.

As compared with FIG. 6A, which is the target area, 100 M
In the vicinity of Hz, there is not much effect, but 500 MHz
In the z class, even if there is a conductor connected to the ground in the electromagnetic wave absorbing layer, all show a good shielding effect,
The properties differ greatly from those of sintered ferrite. A commercially available example of this ferrite-containing resin core is “TDK
IR materials and IV in the electromagnetic wave absorption type electromagnetic shielding material catalog
For example, materials such as "material" and Tokin's "electromagnetic interference suppressor busterade" are preferable, and as shown in the above-mentioned EMCJ83-40, a material having a large magnetic loss in a range corresponding to a used frequency region is preferable.

[0041]

As described above, in the shield structure of the electronic device according to the present invention, the base conductor and the shield case are in conduction, and the intermediate electromagnetic wave absorber is made of soft magnetic fine particles or flat fine particles. It has a magnetic layer formed by mixing with an organic binder, and shield plating is applied to the joint surface of the base conductor, so the connection resistance of the fitting part and the electrical connection part of the housing is sufficiently reduced, Since the shielding effect of the conductor on the body is sufficiently exhibited to its original ability, there is an effect that the shielding effect of the conductor layer is secured and the leakage of the electromagnetic wave from the joint is more effectively suppressed.

Further, by using electroplating on the joint surface of the base conductor, it is possible to effectively suppress radiated interference while reducing the thickness of plating other than the joint.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a shield structure of an electronic device of the present invention. FIG. 3A is a partial cross-sectional view of the shield structure of the electronic device according to the embodiment of the present invention, taken along section line XX of FIG.
(B) is a top view of the plating housing which is a base conductor layer. (C) is a top view of the electromagnetic wave absorber constituted by four sheets. (D) is a side view of the shield case made of steel. (E) is a top view of the steel shield case.

FIG. 2 is an explanatory diagram of an embodiment of a shield structure of an electronic device of the present invention. FIG. 3A is a partial cross-sectional view of the shield structure of the electronic device according to the embodiment of the present invention, taken along section line XX of FIG.
(B) is a top view of the plating housing which is a base conductor layer. (C) is a top view of the electromagnetic wave absorber constituted by four sheets. (D) is a side view of the shield case made of steel. (E) is a top view of the steel shield case.

FIG. 3 is a top view showing an example of an opening of the electromagnetic wave absorber. (A) is an example having a continuous elongated opening.
(B) is an example in which elongated openings are provided at predetermined intervals.

FIG. 4 is a schematic configuration diagram of a simple electromagnetic wave absorbing layer shield evaluation system.

FIG. 5 is a schematic perspective view of a sintered fairite core, which is one of the objects to be measured by the electromagnetic wave absorbing layer shielding effect evaluation system of FIG. 4, and has a conductor connected to the ground inside.

6 is a graph showing measurement results obtained by the system for evaluating a shielding effect of an electromagnetic wave absorbing layer shown in FIG. 4; (A) is a case of only a signal line. (B) is a case where only a sintered ferrite core is used. (C) is a case where a conductor connected to the ground enters the sintered fairite core.

FIG. 7 is a graph of a measurement result obtained by a shielding effect evaluation system when a material obtained by mixing fine particles of ferrite in an organic binder having pressure deformation characteristics such as resin or rubber is used for an electromagnetic wave absorbing layer. (A) is a case where only a resin core containing ferrite is used. (B) shows a case where a conductor connected to the ground enters the resin core containing ferrite.

FIG. 8 is a schematic cross-sectional view of a conventional example of a shield structure using a metal shield case.

FIG. 9 is a sectional view of a tube-type gasket for preventing leakage of electromagnetic waves from a gap.

FIG. 10 is a sectional view of an elastic prismatic gasket having an adhesive layer.

FIG. 11 is a partial cross-sectional perspective view of a shield material using a magnetic material disclosed in Japanese Patent Application Laid-Open No. 05-013979. body

FIG. 12 is a cross-sectional view of a composite electromagnetic shielding material using a magnetic material in combination.

FIG. 13 is an explanatory diagram of a state of a change in contact resistance due to a screw tightening torque at a boss portion of a printed circuit board and a plated housing. (A) is a graph of a measurement result.
(B) is a schematic perspective view of the measuring device.

FIG. 14 is an explanatory diagram of a shield effect evaluation device.
(A) is a schematic sectional view of a shield effect evaluation chamber. (B) is a block diagram of a shield effect evaluation system.

15 is 1 μm by a double-sided plating method using the apparatus of FIG.
5 is a graph showing measurement results of a shielding effect of a flat plate having a copper plating layer of FIG.

[Explanation of symbols]

 101, 201 Base conductor 102 Base conductor projection 103, 203 Base conductor shield plating 104, 204 Shield case 105, 205 Shield case flange 107, 207 Electromagnetic wave absorber 108, 208 Opening provided in electromagnetic wave absorber 206 Projection of shield case 307,357 Electromagnetic wave absorber 308,358 Opening 406 Core type electromagnetic absorber 407 Signal source 408 Output unit 409 Signal line 410 Antenna 411 Spectrum analyzer 412 Printer 503 Conductor 504,505 Ground connection end 506 Sintered ferrite Core 509 Signal line 801 Electronic component 802 Housing 803a, 803b Shield case 804 Printed circuit board 809 Gasket 911 Metal net 912 Elastic body 913 Hollow portion 1011 Elastic body 1012 Conductive cylindrical cloth 1014 Conductive adhesive layer 1106 Plate magnetic body 1115 Plate magnet having conductivity 1116 Box conductor 1204 Conductive fiber 1206 Composite ferrite 1301 Printed circuit board 1302 Housing 1303 Screw 1304, 1305 Probe 1401 Shield evaluation chamber 1402 Sample 1403 Gasket 1405, 1406 Magnetic field antenna 1407 Standard signal generator 1408 Spectrum analyzer 1409, 1410 Amplifier 1411 Shield effect evaluator

Claims (6)

[Claims] 1. A housing structure of an electronic device, wherein said electromagnetic wave absorber having an opening is sandwiched between a case formed of a conductor and a base conductor for fixing said case. A shielding structure for an electronic device, wherein a projection is formed on at least one of the base conductor side and the case side to penetrate the opening and connect the case and the base conductor. 2. The magnetic wave absorber according to claim 1, further comprising a magnetic support layer formed of an organic binder mixed with at least one of soft magnetic fine particles and flattened fine particles. Item 2. A shield structure for an electronic device according to item 1. 3. The fine particles and flattened fine particles constituting a support layer of a magnetic material of the electromagnetic wave absorber are made of ferrite,
3. The shield structure for an electronic device according to claim 2, wherein the shield structure is one of an amorphous alloy and a permalloy. 4. An opening perforated in said electromagnetic wave absorber is one.
The shield structure for an electronic device according to claim 1, wherein the shield structure is a unit. 5. The shield structure for an electronic device according to claim 1, wherein the electromagnetic wave absorber has a plurality of openings. 6. The shield structure for an electronic device according to claim 1, wherein a shield plating by electroplating is applied to a joint surface of the base conductor.