JPH03104199A - Electronic circuit device - Google Patents

Abstract

PURPOSE:To assure economical electromagnetic shielding with a simplified structure by electromagnetically shielding the necessary part of a circuit board with an electromagnetic shielding film. CONSTITUTION:The part requiring electromagnetic shielding on a circuit board 12, placed in a body casing 11, on which electronic parts 13, 14 and the like are mounted is electromagnetically shielded by an electromagnetic shielding film 17 provided in a corresponding region in the casing 11, on which film a metal thin film is formed on a surface connected and fixed to an conductive line 15a of the board 12 by a pin 18. With use of the electromagnetic shielding film easily cut down into a desired shape, economical electromagnetic shielding is assured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an electronic circuit device that requires electromagnetic shielding, such as a selective call receiver.

(Prior Art) In general, a selective call receiver receives a selective call signal sent out from a base station, compares the individual number code inserted in this signal with its own individual number code, and checks that both codes match. When this occurs, it is assumed that a call has occurred to the own device, and a ring tone is sounded from the speaker to notify the user.

Most of the radio circuits in this selective calling receiver are constituted by a single super circuit as shown in FIG. That is, this radio circuit uses the radio frequency f emitted from the base station.

An antenna 1 receives a signal carried on a radio wave, the received signal is amplified by an RF amplifier 2, and then an RF filter 3 limits the band of the signal. Then, in the local oscillation circuit 5, f
-C f A signal with a frequency of ±IF is oscillated, the mixer 4 converts the signal that has passed through the RF filter 3 into an IF signal, and the frequency-converted signal is sent to the IF filter 6.
Bandwidth is limited again.

Incidentally, in general, one of the important electrical characteristics of a radio device is a spurious response characteristic. This is a characteristic of responsiveness to unnecessary radio waves of frequencies other than desired waves. The RF filter 3 and the IF filter 6 are configured to remove unnecessary radio waves other than desired waves. A particular problem with spurious responses is the image spurious f'-fo±21F radio wave, and if this radio wave is not removed by the RF filter 3, it will pass through the IF filter 6, resulting in poor characteristics. Become. For this reason, it is necessary to remove unnecessary radio waves before the filter 6, and therefore the RF filter 3 removes the image spurious fo±
The amount of attenuation at 21F is strictly regulated.

However, the receiver receives radio waves not only from the antenna, but also from other parts of the receiver. Particularly in selective calling receivers, since the antenna and other circuits are integrated, radio waves are likely to penetrate through conductive lines formed on the circuit board or electronic components provided on the circuit board. Therefore, even if the radio waves received by the antenna 1 in the selective calling receiver are band-limited by the RF filter 3, unnecessary radio waves will enter the conductive line of the circuit board between the RF filter 3 and the mixer 4, as mentioned above. Unnecessary radio waves that have entered the filter cannot be removed by the IF filter 6, resulting in a deterioration of the characteristics. Therefore, in selective call receivers, RF
Conventionally, measures have been taken to electromagnetically shield a region in which a conductive line connecting the filter 3 and mixer 4 is formed to prevent unnecessary radio waves from entering the conductive line.

Conventional selective calling receivers employ the configurations shown in FIGS. 4 and 5 as means for electromagnetic shielding. 4 and 5 show the portion of the circuit board provided with the RF filter and mixer. In the figure, reference numeral 11 denotes a main body case of the selective call receiver, and this main body case 11 is made of synthetic resin. 12 is a circuit board, and this circuit board 12 is housed inside the main body case 11 and is attached to a support Fjj portion formed in the main body case 11 by screwing. An RF filter 13 and a mixer 14 are provided on one side of the circuit board 12, and a terminal 13a of the RF filter 13 and a terminal 14a of the mixer 14 penetrate the circuit board 12 and protrude to the other side. A conductive line 15 is formed on the other side of the circuit board 12 over the position where the RF filter 13 is disposed and the position where the mixer 14 is disposed. Terminal 14a is connected and fixed to conductive line 15 by soldering. Further, 16 is an electromagnetic shielding plate, and this electromagnetic shielding plate 16 is provided on the other side of the circuit board 12. That is, as shown in FIG. 6, the electromagnetic shielding plate 16 is formed of a metal plate material such as a copper alloy having electromagnetic shielding properties, and connects the RF filter 13 and mixer 14 on the circuit board 11 and the two. It has a rectangular shape with a length and width large enough to cover the conductive line 15, and bins 16a, 16a are formed at right angles at both ends. The electromagnetic shielding plate 16 is manufactured by punching a metal plate into a predetermined external shape using a press, and then bending both ends of the punched metal plate using a press.

The electromagnetic shield plate 16 is disposed on the other side of the circuit board 12 in a region corresponding to a conductive line 15 connecting the RF filter 13 and the mixer 14, and the pins 16a at both ends are connected to the circuit. It passes through a through hole formed in the substrate 12 and is fixed to a part of a conductive line 15a formed on one side of the circuit board 11 by soldering. As a result, the electromagnetic shield plate 16 covers the conductive line 15 connecting the RF filter 13 and the mixer 14 on the circuit board 12, and functions as an electromagnetic shield to prevent unnecessary radio waves from entering the conductive line 15 from the outside.

[Problems to be Solved by the Invention] However, the structure in which an electromagnetic shielding plate formed of a metal plate is used as the electrode shielding means has the following problems.

Pressing the electromagnetic shielding plate 16 requires a die for punching and bending, and manufacturing the die requires a large amount of manufacturing cost. When the specifications of the conductive lines formed on the circuit board are changed depending on the receiver model or design changes, it is necessary to change the dimensions and shape of the electromagnetic shielding plate 16 due to this change. In order to manufacture the electromagnetic shielding plate 16 with a different configuration, it is necessary to manufacture a dedicated mold for each. For these reasons, when the electromagnetic shielding plate 16 is used, the manufacturing cost increases.

If the electromagnetic shielding plate 16 is made smaller or has a more complicated shape, the mold must be made smaller and more complex. There is a limit to changing the dimensions and shape of the shield plate 16. Further, if the dimensions and shape of the electromagnetic shielding plate 16 are changed, a new dedicated mold must be manufactured accordingly, so it is difficult to easily change the dimensions and shape of the electromagnetic shielding plate 16. Therefore, it can be said that the electromagnetic shielding plate 16 lacks flexibility in setting specifications.

Furthermore, supporting the electromagnetic shield plate 16 on the circuit board 12 complicates the structure of the electromagnetic shield plate 16 and the circuit board 12, and the work of supporting the electromagnetic shield plate is troublesome.

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide an electronic circuit device equipped with electromagnetic shielding means that is low in manufacturing cost, can flexibly deal with changes in specifications, and has a simple installation configuration. .

In order to achieve the above object, the electronic circuit device of the present invention is a device equipped with a circuit board on which electronic components are mounted, in which a film having electromagnetic shielding properties is used to cover a portion of the circuit board that requires electromagnetic shielding. It is characterized by being shielded.

As the film having electromagnetic shielding, a resin film on which a metal thin film is formed, or a metal film is used.

The electromagnetic shielding film is supported by being attached to the inner wall of the case containing the circuit board.

A conductive protrusion is provided on the circuit board, and the protrusion is brought into contact with a film having electromagnetic shielding properties to conduct the two and establish grounding.

(Function) That is, since the film that is the electromagnetic shielding member can be easily cut into a predetermined size and shape, the manufacturing cost is low and the setting of specifications can be flexibly handled.

The film can be easily supported by attaching it to the inner wall of the main body case.

As such, the film is particularly suitable for electromagnetic shielding of a portion of a circuit board.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

The embodiment shown in FIGS. 1 and 2 is applied to a selective call receiver. FIGS. 1 and 2 show parts of a same circuit board provided with an RF filter and a mixer in a selective calling receiver, and the same parts as in FIGS. 4 and 5 are designated by the same reference numerals.

That is, in the figure, 11 is a main body case of the receiver, 12 is a circuit board, 13 is an RF filter, 14 is a mixer, and 15 is a conductive line.

In the figure, 17 is an electromagnetic shielding film. The electromagnetic shielding film 17 is made of a film having electromagnetic shielding properties, such as a resin film or a metal film on the surface of which a metal thin film is formed by vapor deposition. In the former, aluminum, for example, is used for the metal thin film.

In the latter case, for example, an aluminum film is used. As shown in FIG. 3, the electromagnetic shielding film 17 has a rectangular shape with a length and width large enough to cover the RF filter 13 and mixer 14 on the circuit board 11, and the conductive line 15 connecting them. The electromagnetic shielding film 17 is formed by cutting using a cutting tool or a cutting machine. Then, the electromagnetic shielding film 17 covers the RF filter 13 and the filter 14 on the other side of the circuit board 12.
It is attached to the inner surface of the main body case 11 corresponding to the area where the conductive line 15 connecting the two is formed.

Adhesives or double-sided adhesive tape can be used as a means of pasting. As a result, the electromagnetic shielding film 17
It covers a conductive line 15 connecting the RF filter 13 and mixer 14 on the circuit board 11, and functions as an electromagnetic shield to prevent unnecessary radio waves from entering the conductive line 15 from the outside.

Note that by connecting the electromagnetic shielding film 17 to the conductive line of the circuit board 12, it can be connected to the ground line of the receiver. This specific configuration includes, for example, a conductive line 15 formed on the temporary circuit board 12 by inserting a pin 18 made of conductive metal into a hole formed in the circuit board 12.
A is connected and fixed by soldering, and the pin 18 is brought into contact with the electromagnetic shielding film 17.

Therefore, the electromagnetic shielding film 17 used as an electromagnetic shielding means in the selective call receiver of this embodiment can be fabricated using cutting tools and cutting machines that are conventionally used for cutting film materials. It can be easily cut and formed into the required shape. Even if the dimensions and shape of the electromagnetic shielding film 17 are changed due to changes in the dimensions and shape of the conductive line 15 formed on the circuit board 12, there is no need to manufacture a new dedicated tool, and a general cutting tool or a The electromagnetic shielding film 17 is cut by cutting the film based on the changed dimensions and shape using a cutting machine.
can be manufactured. Therefore, the electromagnetic shielding film 17 can be formed at low cost.

In addition, electromagnetic shielding film 1 that has a small or complicated shape
7 can also be easily formed by cutting the material film. In particular, since an electromagnetic shielding film that electromagnetically shields a part of a circuit board, such as the electromagnetic shielding film 17 of the above-mentioned embodiment, is small in size,
Suitable for this type of electromagnetic shielding film.

Furthermore, the electromagnetic shielding film 17 can be attached and supported on the inner surface of the main body case 11, and the mounting structure is simpler and easier to support than in the conventional case where a metal shielding plate is supported on the circuit board 12. I can do it.

Note that the present invention is not limited to selective calling receivers, but can be widely applied to electronic circuit devices that require electromagnetic shielding of circuit boards.

[Effects of the Invention] As explained above, according to the electronic circuit device of the present invention, since a film having electromagnetic shielding properties is used as the electromagnetic shielding member, the manufacturing cost of the electromagnetic shielding member is low, and the electromagnetic shielding When the size and shape of a member needs to be changed, an electromagnetic shielding member whose shape and dimensions are changed can be easily and inexpensively manufactured, and furthermore, the electromagnetic shielding member can be supported with a simple structure.

[Brief explanation of drawings]

1 to 3 show an embodiment in which the present invention is applied to a selective calling receiver, FIG. 1 and a sectional view showing the second selective calling receiver, FIG. 6 is a diagram showing an electromagnetic shielding plate, FIG. 7 is a block diagram showing the radio section circuit of the selective calling receiver. 11... Main body case, 12... Circuit board, 17...
・Electromagnetic shielding film.

Claims (5)

[Claims] (1) An electronic circuit device comprising a circuit board on which electronic components are mounted, characterized in that a portion of the circuit board that requires an electromagnetic field is shielded with a film having electromagnetic shielding properties. (2) The electronic circuit device according to claim 1, wherein the film having electromagnetic shielding properties is a resin film with a metal thin film formed thereon. (3) The electronic circuit device according to claim 1, wherein the film having electromagnetic shielding properties is a metal sheet. (4) The electronic circuit device according to claim 1, wherein an electromagnetic shielding film is attached to the inner wall of the case housing the circuit board. (5) The electronic circuit device according to claim 1, wherein a conductive member is provided protruding from the circuit board, and this member is brought into contact with a film having an electromagnetic shield.