JP2000261183A - Electronic unit and radiation preventing member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the ground potential of a circuit board, to reduce electromagnetic wave radiation and to provide ventilation between the circuit board and an outer metal face. SOLUTION: A waveform-like spacer 14 is arranged along the periphery of a circuit board 10. Trough parts 22 are electrically brought into contact with an outer metallic face 12 and crest parts 20 to a surface pad connected to a ground layer. Thus, ground potential is stabilized and the occurrence of resonance owing to the interval of a conventional spacer can be suppressed. Then, effect equal to that when radiation is shielded from a wiring on the circuit board can be given. Since air passes through the waveform-like parts, ventilation can be kept.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device in which a ground surface of a circuit board is electrically contacted and fixed to an external metal surface such as a housing or a frame, and a radiation preventing member.

[0002]

2. Description of the Related Art In various electronic devices, as shown in FIG. 26, four corners of a circuit board 100 are
02, and fixed by screws 108 with a predetermined gap on the structure itself such as a housing or a frame or on an external metal surface 104 provided on these structures. In order to stabilize the ground potential in the circuit board 100, the spacer 102 is made of metal, and the ground surface of the circuit board 100 is electrically connected to the external metal surface 104.

However, as in today, the circuit board 10
When the switching speed of a signal used above 0 is increased, high-frequency noise generated in the circuit board 100 propagates to the external metal surface 104 via the spacer 102, and a resonance current corresponding to the distance L between the spacer 102 and the spacer 102. Flow, and large electromagnetic wave radiation noise is generated.

In order to solve such a problem, Japanese Patent Laid-Open No.
According to Japanese Patent No. 225634, when the ground layer of the circuit board and the conductive main body frame are electrically connected at a plurality of connection points, the ground layer is connected to the connection pad via a resistance member on the circuit board. Noise current flowing from the circuit board to the body frame is suppressed.

In Japanese Patent Application Laid-Open No. 9-23083, when a signal ground of a circuit board and a housing forming a frame ground are electrically connected by a columnar metal spacer, a magnetic core is provided on the peripheral surface of the metal spacer. By mounting, or by interposing a resistance sheet between the metal spacer and the signal ground or the housing, noise current flowing from the circuit board into the housing is suppressed.

Further, in Japanese Patent Application No. 10-121963, a signal ground of a circuit board and an external metal surface forming a frame ground are connected to each other via a conductive spacer in the form of a wall to surround the circuit ground, thereby preventing generation of resonance radiation. Along with
Electromagnetic radiation is shielded and suppressed from wiring.

[0007]

However, the method disclosed in Japanese Patent Application Laid-Open No. Hei 7-225634 or Japanese Patent Application Laid-Open No. 9-23083 involves connecting a circuit board and an external metal surface with several columnar spacers. Because there is no change, the generation of resonance radiation due to the distance between the spacers cannot be essentially prevented.

Further, in order to stabilize the ground potential in the circuit board, the current is suppressed by a resistance member or a magnetic core, so that the ground potential in the circuit board becomes unstable and causes new noise. Was. Further, there is a disadvantage that additional components such as a resistance member and a magnetic material are required.

[0009] On the other hand, the method disclosed in Japanese Patent Application No. 10-121963 has a structure in which most of the gap between the circuit board and the external metal surface is closed. As a result, it becomes difficult to dissipate heat from the elements on the circuit board. Further, when a cable is pulled out from the wiring on the circuit board, it is necessary to newly provide an opening in the wall-shaped conductive spacer, and it is not easy to change the position where the cable is drawn out.

Accordingly, an object of the present invention is to stabilize the ground potential of a circuit board, reduce electromagnetic radiation, and provide air permeability between the circuit board and an external metal surface.

[0011]

According to the first aspect of the present invention, a circuit board, an external metal surface to which the circuit board is attached, and a ground plane arranged along the periphery of the circuit board are provided. A wave-shaped conductive member in which peaks and valleys are in electrical contact with the external metal surface, respectively.

In the above configuration, the corrugated conductive member is disposed along the periphery of the circuit board, and the valleys are in electrical contact with the external metal surface and the ridges are in electrical contact with the ground surface of the circuit board. For this reason, the path of the resonance current generated between the conventional columnar spacers is complicatedly formed in a portion other than the portion for fixing the circuit board, so that the occurrence of a high-strength resonance state can be suppressed, Generation of electromagnetic radiation noise can be suppressed. Further, the impedance of the connection portion can be reduced as compared with the conventional case, the circuit ground potential can be stabilized, and the occurrence of noise due to the instability of the circuit ground potential can be prevented.

Further, since the conductive member does not block the space between the ground surface of the circuit board and the external metal surface,
The heat generated from the elements on the circuit board can be released by the flow of air passing between the corrugated portions.

According to the second aspect of the present invention, since the conductive member is in contact with the ground surface and the external metal surface of the circuit board in an elastically deformed state, the electrical contact is ensured.

According to the third aspect of the present invention, a line connecting the ground surface and the contact portion (peak portion) of the circuit board and the contact portion (valley portion) with the external metal surface obliquely intersects the external metal surface. Thus, a wave shape is configured.

As a result, current components are generated in the conductive member in directions parallel to the circuit board and the external metal surface and in opposite directions. For this reason, the electromagnetic fields generated from this current component cancel each other, and the current flowing through the conductive member occupies a high proportion of the current distributed on the ground surface and the external metal surface of the circuit board. The fields cancel each other, producing an effect of reducing electromagnetic radiation.

[0017]

1 to 6 show an electronic apparatus according to the present invention.

In this embodiment, as shown in FIGS. 1 and 2,
A conductive spacer 14 on a corrugated plate is interposed between the circuit board 10 and the external metal surface 12 so as to be in contact with the circuit board 10 and the external metal surface 12 so as to surround the entire periphery of the circuit board 10. I have. Four points at the corners of the circuit board 10 are fixed to the external metal surface 12 by screws 18 inserted into the screw holes 16.

The spacer 14 is a long metal plate having a constant width, and is bent so that a peak 20 and a valley 22 having a constant angle are continuously arranged in a corrugated shape.

At both ends of the spacer 14, the circuit board 10
And a flat plate portion 24 which is in contact with. This flat plate part 2
4, a column plate portion 26 that bends downward is formed. In a state where the spacer 14 is not fixed to the circuit board 10 on the external metal surface 12, the height of the column plate portion 26 becomes larger than the height D of the column plate portion 26.
The vertical height between the valley portion 22 and the valley portion 22 is longer by ΔD.

As a result, only by inserting the four screws 18 into the screw holes 28 and fixing the spacers 14, the spacers 14 are elastically deformed, and the ridges 20 are formed on the surface pads 30 and the external metal surface 12, which will be described later. The valleys 22 are securely contacted, so that the circuit board 10 and the external metal surface 12 can be completely electrically connected, and can be electrically connected to the external metal surface 12 with low impedance.

A surface pad 30 is provided at a predetermined width around the circuit board 10 (a surface facing the external metal surface 12).
The ground layer 3 in the circuit board 10 is provided through the via 32 penetrating the power supply layer 36 and the screw 18 inserted into the screw hole 16.
4 is connected with low impedance over a frequency range from DC to high frequency. The pitch of the vias 32 is preferably as small as possible, preferably 5 cm or less, more preferably 2 cm or less. In addition, overlapping portions of the spacer 14 (portions fixed by the screws 18) need to be processed as appropriate so that the columnar plate portions 26 do not interfere with each other.

The effect of the electronic device according to the first embodiment will be described in comparison with a conventional electronic device. FIG. 7 shows the result confirmed by simulation. This is 170mm x 110
5 is a result of a moment spectrum method of an emission spectrum when a microstrip line of 80 mm is formed on a circuit board of 1 mm.

A broken line indicates a conventional electronic device in which the ground surface of the circuit board 100 and the external metal surface 104 are connected at four corner points of the circuit board via a columnar metal spacer 102 (see FIG. 26). The emission spectrum and thin solid line of
The radiation spectrum and the bold solid line in the case where the wall-shaped conductive spacer disclosed in Japanese Patent Application Laid-Open No. 0-121963 is applied to the same circuit board and shielded all around are grounded on the circuit board 10 via the spacer 14 of the first embodiment. 9 is an emission spectrum of an electronic device in which the layer 34 and the external metal surface 12 are connected. At this time,
The plate width of the spacer viewed from the upper surface direction is 10 mm.

As is clear from FIG. 7, in the first embodiment,
The radiation intensity E is greatly reduced in all frequency regions, and the radiation peak around 700 MHz generated in the conventional electronic device disappears. The emission peak near 700 MHz is a resonance mode newly generated by a loop circuit between columnar spacers in a conventional electronic device. According to the present invention, it can be confirmed that the generation of this new resonance radiation can be prevented. , Japanese Patent Application No. 10-1219
An electromagnetic radiation reduction effect almost equivalent to that of the all-around shield of No. 63 was confirmed.

The corrugated shape of the corrugated plate-like spacer 14 is not limited to the shape in which only the valley portion 22 is located down as in the spacer 14 of FIG. Like the spacer 38, the peak portion 38A is
A structure in which only the upper part is located may be used. FIG. 8B
Like the spacer 40, the peak 40A and the valley 40B may both be located above or below the column plate 26. That is, when there are a plurality of peaks and valleys of the spacer, it is not necessary that all the peaks and valleys be at the same height.

The peaks and valleys of the corrugated spacer do not have a single apex as viewed from the side as shown in FIGS. 8A and 8B, but have the shape shown in FIG. 8C. As in the case of 42, a structure having a straight portion 48B partly or entirely parallel to the circuit board or the external metal surface may be used. FIG.
Like the spacer 44 of (D), the corrugated plate shape may be constituted by a curved structure such as a sine wave. FIG. 8 (E)
Like the spacer 46, when the valley portion 46B is viewed from the side, the shape may have a plurality of vertices 46B.

In the above-described example, a structure having a valley between the peaks is adopted. However, it is not always necessary to adopt the structure, and the peak and the valley are formed like the spacer 48 in FIG. An upright surface 48C that is on a straight line perpendicular to the circuit board surface may be formed.

Further, the shape of the column plate portion of the spacer is shown in FIG.
In addition to the structure shown in FIG. 9, the circuit board 10 may be directly supported without forming a bent portion below the columnar plate portion 50D like the spacer 50 in FIG. 9A. Also,
Like the spacer 52 in FIG. 9B, the circuit board 10 and the external metal surface 12 may be connected to each other by using a conventional columnar spacer 102 or the like instead of the columnar plate portion.
When the distance between the circuit board 10 and the external metal surface 12 does not need to be determined strictly, there is no need to use a columnar spacer or the like, and as shown in FIG. It is possible.

In this case, since the spacer 52 has elasticity, it extends parallel to the external metal surface when the circuit board 10 is fixed with the screw 18, so that the screw hole of the spacer 52 and the screw come into stable contact. A state of contact between the circuit board 10 and the external metal surface and the spacer 52 is maintained in a good contact state.

9D, the columnar plate portion 54D is bent outward and fixed to the external metal surface 12 with screws 56, and the flat plate portion 54E is fixed to the circuit board 10 with screws 58. It may be shaped to connect with further,
Like the spacer 58 in FIG. 9E, a claw piece 60 having elasticity is formed on the upper portion of the columnar plate portion 58D, and the circuit board 10 is sandwiched between the claw piece 60 and the flat plate portion 58E. The structure which fixes the board | substrate 10 may be sufficient. Also,
The spacer of the present invention may be used upside down, and the combination of both end portions and the corrugated portion is also arbitrary.

The spacer 62 shown in FIGS.
Has a structure in which the peaks 62A and the valleys 62B are not linearly aligned in the length direction of the spacer 62 when viewed from above, but alternately meander in the width direction. FIG. 11 comparing the effect of reducing the electromagnetic wave radiation by the spacer 62 with a conventional electronic device is 170 mm ×
5 is a calculation result by a moment method of a radiation spectrum when an 80 mm microstrip line is formed on a 110 mm circuit board.

The dashed lines indicate the emission spectrum of a conventional electronic device in which four points at the corners of the circuit board 10 are connected to the ground plane of the circuit board 100 and the external metal surface 104 via the conventional columnar spacer 102, and a solid line. Is an emission spectrum when the spacer 62 is used. In this case, the plate width W of the spacer 62 is 2 mm, and the distance a is 2 mm when the staggered ridges 62A and the valleys 62B are viewed from above.

The spacer 14 having the shape shown in FIG.
It has the same electromagnetic wave radiation reduction effect as the spacer 14 having the shape shown in FIG. Further, in the configuration of FIG.
Each of the valleys 62B is arranged on a straight line. However, it is not always necessary to adopt a configuration in which all the peaks or valleys are arranged on a straight line.

The spacer 64 shown in FIG. 12 and FIG.
This is the case where the width of the corrugated plate-shaped portion is not constant when viewed from above. FIG. 14 is a graph comparing the effect of reducing the electromagnetic wave radiation by the spacer 64 with a conventional electronic device.

This is a calculation result by the moment method of a radiation spectrum when a microstrip line of 80 mm is formed on a circuit board of 170 mm × 110 mm. The broken lines indicate the four points at the corners of the circuit board 100 via the conventional metal spacer 102 having a columnar shape.
13 is a radiation spectrum of a conventional electronic device in which the ground plane 00 and the external metal surface 12 are connected, and the solid line is a radiation spectrum when the spacer 64 of FIG. 13 is used.

In this case, the plate width W1 of the peak 64A of the spacer 64 is 1 mm, the plate width W2 of the valley 64B is 10 mm, and the spacer 14 shown by the thin line, that is, the plate width is 10 mm
It has the same electromagnetic wave radiation reduction effect as that of. When the width of the spacer is small, the space for providing the surface pads 30 on the circuit board is reduced, and the effect that the space that can be used for other purposes on the circuit board such as component mounting is increased.

In the structure of the spacer 64 shown in FIG. 12, the widths of all the ridges 64A and the valleys 64B have a constant value, however, the widths of the respective parts do not necessarily have to be constant. May have a different width.

The spacer 66 shown in FIGS. 15 and 16 has two rows of corrugated plates 68 and 70 in parallel in the longitudinal direction, and when viewed from the side, the peaks 68A and 70A and the valleys 68B and 7
OB are alternately formed.

FIG. 17 is a graph comparing the effect of reducing the electromagnetic wave radiation by the spacer 66 with a conventional electronic device.
This is 80 m on a 170 mm x 110 mm circuit board.
9 is a calculation result of a radiation spectrum when m microstrip lines are formed by the moment method.

The broken lines indicate the four points at the corners of the circuit board 100 via the conventional metal spacer 102 having a columnar shape.
0, the emission spectrum of a conventional electronic device in which the ground plane and the external metal surface 104 are connected, the dotted line shows the emission spectrum using the corrugated plate-shaped portion shown in FIG. The solid line is an emission spectrum when the spacer 66 shown in FIG. 16 having a width of each corrugated plate portion of 2 mm is used. The spacer 66 has a width of 2 mm and a width of 2 mm.
Although it is 4 mm in a row, it has the same electromagnetic wave radiation reduction effect as the spacer 14 having a width of 10 mm. When the width of the spacer is small, the space for providing the surface pads 30 on the circuit board is reduced, and the effect that the space that can be used for other purposes on the circuit board such as component mounting is increased.

In FIG. 15, the peaks 68A, 70A and the valleys 68B, 70B are staggered, but need not be completely staggered.

Next, another type of spacer will be described.

As shown in FIG. 18, not a spacer formed by bending a plate but a rectangular block is cut out.
A spacer 78 in which a corrugated plate portion 76 is formed between the top wall 72 and the bottom wall 74 may be used. Also, like the spacer 82 shown in FIG. 19, the side wall of the U-shaped block may be cut out in a triangular shape to form the wavy portion 80. It may be plate-shaped or rod-shaped.

Even in the above case, a high-intensity current does not flow intensively in the spacer 102 as in the conventional columnar spacer 102 shown in FIG. That is, as shown in FIG. 24, a current E that is not parallel to the external metal surface 12 flows from the peak to the valley in the wavy portion S, so that the electromagnetic field components generated by the current components Ex and Ey in opposite directions to each other. Cancel each other, and the current flowing through the wavy portion S accounts for a high proportion of the current distributed on the ground surface and the external metal surface 12 of the circuit board 10, thereby producing an electromagnetic wave radiation reducing effect.

Next, a modified example of the circuit board will be described.

As shown in FIG. 20, when the position where the spacer and the surface pad are in contact can be predicted in advance, the surface pad 84 may be provided only in the portion where the spacer 14 is in contact. According to the present invention, the ground surface (surface pad 8) of the circuit board 86 is normally provided in the same manner as the circuit board 10 shown in FIG.
4) is directly connected to the spacer 14, but depending on the purpose, the ground plane of the circuit board and the corrugated spacer 14 may be connected via an appropriate circuit element.

In the circuit board 88 shown in FIG. 21, a surface ground pad 92 connected to an internal ground layer by a pier 90 and a spacer pad 94 directly connected to the corrugated spacer 14 are formed on the surface thereof. The surface ground pad 92 and the spacer pad 94 are connected via a circuit element 98 attached to a circuit board 88 so as to straddle both.

As the circuit element 98, a resistance element, an inductance, a capacitor and the like can be used. When the impedance of this connection part increases, the ground potential stabilizing effect is suppressed, but other effects are exhibited. The screw holes 16 are for inserting the screws 18 shown in FIG. 3 and the like.

The corrugated spacer is usually formed of a low-impedance metal, but may have a DC resistance loss of about several ohms or less. Also in this case, the effect of stabilizing the ground potential is suppressed by the increase in the loss, but other effects are exhibited.

In the embodiments described so far, the circuit board 10 and the external metal surface 12 have the same size. However, even when the external metal surface is larger than the circuit board, The present invention can be applied even when the circuit board is large. If the circuit board is larger than the external metal surface, a corrugated spacer may be provided on the peripheral portion inside the outer periphery of the circuit board.

The external metal surface includes a metal surface (metal layer) provided on a structure of a metal plate or a metal body (metal layer) provided on a structure other than metal, and a metal surface (metal layer) provided on another circuit board. ). In the latter case, a plurality of circuit boards are joined together, and these circuit boards are connected via a corrugated spacer, and the above effects are realized for the plurality of connected circuit boards. You.

Further, the corrugated spacer usually has elasticity in order to maintain good connection with the circuit board and the external metal surface. However, when it is considered that the circuit board and the external metal surface are not deformed, Need not necessarily have elasticity. Therefore, the corrugated plate portion may be formed of a metal plate having a thickness with a corrugated spacer or a metal body having a thickness formed by a mold or the like.

It is desirable that the corrugated plate-shaped spacers 14 extend over the entire circumference of the circuit board 10, but it is not necessarily required that the circuit board 10
It does not need to be all around. FIG. 22 shows a case where the corrugated spacer does not extend all around the circuit board.

In FIG. 22A, the corrugated spacers 14 are arranged only on one side of the circuit board 10, and the columnar spacers 102 are arranged at both corners of the opposing sides. FIG.
In FIG. 2 (B), one side of the circuit board 10 is an opening without the spacer 14, and the corrugated spacer 1 extends over the other three sides.
4 is arranged. FIG. 22C shows a case where the corrugated spacers 14 are arranged in an L-shape at the peripheral portion including the respective corners of the circuit board 10 so that each side of the circuit board 10 is an opening. FIG. 22D shows the circuit board 10.
In this case, a corrugated spacer 14 is arranged so as to surround the substrate portion of FIG. However, these combinations or modified forms are also possible.

When a circuit board and an external metal surface are connected by using a corrugated spacer, not only one kind of spacer shape but also a combination of other spacer shapes may be used. In that case, as another thing, Japanese Patent Application No. 10-12196
No. 3 may be used.

In the arrangement structure of the spacers shown in FIG. 22, since an opening exists in a part of the periphery of the circuit board 10, the effect of reducing electromagnetic wave radiation is reduced, but the effect of stabilizing the ground potential is exhibited. .

FIG. 23 shows the result of examining the effect of the opening by simulation using the moment method. This plots the ratio of the length of the non-opening part, that is, the portion where the spacers are present on the corrugated sheet, to the entire circumference of a 170 mm x 110 mm circuit board, and plots the radiant intensity change with respect to the coverage. It is.

As is clear from this table, the coverage was 40%.
%, The radiation reduction effect cannot be expected. However, when the coverage is increased to 40% or more and the coverage is increased, the radiation is reduced. When the coverage is 40% or more, the same radiation reduction effect as in the case of covering the entire circumference can be obtained. However, this result mainly shows the radiation reduction effect, and the coverage is 40%.
The ground potential stabilizing effect is exhibited even below.

In this embodiment, the member for electrically contacting the circuit board and the external metal surface has been described as a spacer for determining the distance between the circuit board and the external metal surface. However, the present invention is not limited to the spacer. If there is another device such as a member and a mechanism that determines the distance between the circuit board and the external metal surface, a conductive member having a corrugated shape is attached to the circuit board via the device or independently of the device. And may be simply arranged between the outer metal surface.

[0061]

Since the present invention has the above-described structure, it is not necessary to add other components, the generation of resonance radiation can be suppressed, and the same effect as when radiation from wiring on a circuit board is shielded can be obtained. The effect can be provided, and at the same time, high air permeability can be secured.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an electronic apparatus according to an embodiment.

FIG. 2 is a perspective view illustrating an electronic apparatus according to the embodiment.

FIG. 3 is a cross-sectional view illustrating an internal structure and a connection portion of the electronic device according to the embodiment.

FIG. 4 is a plan view of a circuit board of the electronic device according to the embodiment.

FIG. 5 is a side view showing the electronic apparatus according to the embodiment.

FIG. 6 is a side view showing the electronic apparatus according to the embodiment.

FIG. 7 is a graph comparing the operation of an electronic device using a spacer as a radiation prevention member of the present embodiment with that of a conventional electronic device.

FIG. 8 is a side view showing another embodiment of the spacer.

FIG. 9 is a side view showing another example of a portion for connecting a circuit board and an external metal surface.

FIG. 10A is a plan view showing another embodiment of the spacer, and FIG. 10B is a side view showing another embodiment of the spacer.

FIG. 11 is a graph comparing the operation of an electronic device using a spacer according to a modification with that of a conventional electronic device.

FIG. 12 is a perspective view showing another embodiment of the spacer.

FIG. 13A is a plan view showing another embodiment of the spacer, and FIG. 13B is a side view showing another embodiment of the spacer.

FIG. 14 is a graph comparing the operation of an electronic device using a spacer according to a modification with that of a conventional electronic device.

FIG. 15 is a perspective view showing another embodiment of the spacer.

FIG. 16A is a side view showing another embodiment of the spacer, and FIG. 16B is a plan view showing another embodiment of the spacer.

FIG. 17 is a graph comparing the operation of an electronic device using a spacer according to a modification with that of a conventional electronic device.

FIG. 18 is a perspective view showing another embodiment of the spacer.

FIG. 19 is a perspective view showing another embodiment of the spacer.

FIG. 20 is a plan view showing another embodiment of the circuit board.

FIG. 21 is a plan view showing another embodiment of the circuit board.

FIG. 22 is a plan view showing an example of the arrangement of spacers.

FIG. 23 is a graph showing a simulation result of a spacer coverage and an electromagnetic wave radiation intensity in an electronic device.

FIG. 24 is a schematic diagram showing the direction of a current flowing through a spacer.

FIG. 25 is a schematic diagram showing a direction of a current flowing through a conventional spacer.

FIG. 26 is a perspective view showing an electronic device using a conventional spacer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Circuit board 12 External metal surface 14 Spacer (anti-radiation member) 20 Mountain part 22 Valley part 24 Flat plate part 26 Column board part 28 Screw hole 30 Surface pad 32 Via 34 Ground layer

Claims (8)

[Claims] 1. A circuit board, an external metal surface to which the circuit board is attached, and a crest and a valley are disposed along a periphery of the circuit board. An electronic device, comprising: a corrugated conductive member that makes electrical contact. 2. The electronic device according to claim 1, wherein the conductive member is elastically deformed so that a valley contacts an external metal surface and a ridge contacts a ground surface of the circuit board. 3. The electronic apparatus according to claim 1, wherein a line connecting a valley and a peak of the conductive member obliquely intersects an external metal surface. 4. The electronic device according to claim 1, wherein the conductive member is a corrugated plate having a predetermined plate width. 5. The electronic device according to claim 4, wherein a width of the corrugated plate changes in a longitudinal direction. 6. The electronic device according to claim 4, wherein the corrugated sheets are provided in parallel along a periphery of the circuit board. 7. The electronic device according to claim 1, wherein the external metal surface is a metal surface provided on another circuit board. 8. A circuit according to claim 1, further comprising a corrugated portion electrically contacting a ground surface of the circuit board and an external metal surface to which the circuit board is attached, and disposed between the external metal surface and the circuit board. Radiation prevention member.