JP2006012495A - Electrostatic discharge structure of electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic discharge structure such as an electronic device using a metal casing and capable of discharging static electricity without requiring a ground wire.
An electrostatic discharge ground pattern formed on a circuit board housed in a metal casing, and a part of the electrostatic discharge ground pattern formed across an insulating portion, and It is composed of an FG pattern 7a electrically connected to the housing 1, and an RC component 8 connected between the electrostatic discharge ground pattern 7 and the FG pattern 7a, and is discharged from the human body to the housing 1. Since the static electricity is attenuated by the RC component 8 and discharged to the electrostatic discharge ground pattern 7, the static electricity is not directly discharged to the electronic components mounted on the circuit board 2. It becomes possible to prevent destruction or malfunction of the circuit.
[Selection] Figure 2

Description

  The present invention relates to an electrostatic discharge structure of an electric device or an electronic device (hereinafter referred to as an electronic device or the like) using a metal casing.

  Many electronic devices and the like house a circuit board such as a printed circuit board on which electrical components and electronic components (hereinafter referred to as electronic components) are mounted.

  The electronic components mounted on these circuit boards may cause electrical breakdown due to the discharge phenomenon due to static electricity or cause the circuit to malfunction. Therefore, conventional electronic devices have countermeasures against electrostatic discharge. It has been.

  Causes of electrical breakdown of electronic components, etc. due to static electricity or malfunction of the circuit are such that when the housing of electronic equipment is made of metal, static electricity charged on the human body is mounted on the circuit board or circuit board via the metal housing It often occurs when discharged to a discharged electronic component or the like.

  For this reason, conventionally, as described in Patent Document 1, by connecting a ground wire to the housing and discharging the static electricity to the ground by the ground wire, electronic parts in the housing are destroyed by the static electricity. This prevents the circuit from malfunctioning.

Further, in Patent Document 2, the casing is formed of a resin that is not easily affected by static electricity from the outside, and a relatively thin carbon resin plate mixed with carbon powder is provided on the inner surface of the casing so as to obtain a shielding effect. A method of manufacturing a control box for countermeasures against electricity has been proposed.
JP-A-6-342612 Japanese Patent Laid-Open No. 6-104094

  However, in the case where the casing described in Patent Document 1 is grounded with a ground wire, grounding work of the ground wire is required, and there is a problem that the cost for installation increases.

  In particular, in the case of electronic devices such as information communication devices manufactured in recent years, a system is constructed by connecting devices with LAN cables, USB cables, and the like. In addition, the wiring work is simplified and the system can be constructed in a short period of time. For this reason, the housing of the electronic device or the like is grounded by the ground wire as described in Patent Document 1 above. Such a requirement impairs the ease of use of the equipment for the user, which not only lowers the product value, but also if the user neglects to ground the housing with the ground wire, damage to electronic components, etc. due to static electricity or circuitry There is a problem that it becomes impossible to prevent the malfunction of.

  On the other hand, in the case where the casing is formed of resin as in Patent Document 2, an expensive mold is required to form the casing, so that the component cost is higher than that of a casing manufactured by processing a metal plate. There's a problem.

  In particular, electronic devices used in the field of information and communication in recent years have a short life cycle, and high-mix low-volume production has become mainstream. However, there is also a problem that the competitiveness of the product decreases due to the high price of electronic equipment.

  The present invention has been made in order to improve such a conventional problem, and provides an electrostatic discharge structure such as an electronic device using an inexpensive metal casing and capable of discharging static electricity without requiring a ground wire. It is for the purpose.

  The electrostatic discharge structure of an electronic device or the like of the present invention is an electrostatic discharge structure of an electronic device or the like having a metal casing that houses a circuit board on which electronic components or the like are mounted, and the electrostatic discharge structure formed on the circuit board. A ground pattern for electrostatic discharge, an FG pattern formed on a portion of the ground pattern for electrostatic discharge with an insulating portion therebetween and electrically connected to the housing, and connected between the ground pattern for electrostatic discharge and the FG pattern. RC component.

  With the above configuration, when a person touches the casing of an electronic device or the like, static electricity discharged from the human body to the casing is attenuated by an RC component provided between the FG pattern and the electrostatic discharge ground pattern. Since it is discharged to the ground pattern for electrostatic discharge, the static electricity is not directly discharged to the electronic components mounted on the circuit board. This prevents damage to the electronic components due to static electricity or malfunction of the circuit. It will be possible to prevent it.

  In addition, since grounding work for grounding the chassis with a ground wire is not required, the convenience of using the equipment for the user is not impaired, so the product value is improved and the installation cost can be reduced. Since the user neglects to ground the housing with the ground wire, problems such as the destruction of electronic components due to static electricity and the malfunction of the circuit cannot be prevented.

  In addition to reducing the cost of parts by using an inexpensive metal housing, we plan new products even for electronic devices that have a short life cycle and are mainly used in high-mix, low-volume production. Since it is not necessary to raise a mold every time and to manufacture a new housing, it is possible to reduce the price of electronic equipment and increase the competitiveness of the product.

  The electrostatic discharge structure of an electronic device or the like according to the present invention is obtained by connecting the FG pattern to the housing via a fixing tool that fixes the circuit board to the housing.

  With this configuration, it is not necessary to provide a separate means for electrically connecting the FG pattern to the housing, and therefore the number of assembly steps and part costs can be reduced.

  The electrostatic discharge structure of an electronic device or the like of the present invention is obtained by connecting an electrostatic discharge ground pattern to the ground of an external device via a cable connecting the electronic device or the like and the external device.

  With the above configuration, the static electricity that has reached the ground pattern for electrostatic discharge can be discharged to the ground of the external device via the cable, so that the destruction of electronic components and the malfunction of the circuit due to static electricity can be more reliably prevented. Become.

  The electrostatic discharge structure of an electronic device or the like according to the present invention is obtained by connecting an RC component different from the RC component between a circuit ground pattern formed on a circuit board and an electrostatic discharge ground pattern.

  With the above configuration, the static electricity reaching the ground pattern for electrostatic discharge can be attenuated by another RC component and discharged to the ground pattern of the circuit pattern, so that even when static electricity cannot be discharged to an external device, This makes it possible to prevent destruction of electronic components and the like due to static electricity and malfunction of circuits.

  According to the electrostatic discharge structure of the electronic device or the like of the present invention, the static electricity discharged from the human body to the housing is attenuated by the RC component provided between the FG pattern and the electrostatic discharge ground pattern, and the electrostatic discharge ground. Since the pattern is discharged, static electricity is not directly discharged to the electronic components mounted on the circuit board. This prevents damage to the electronic components due to static electricity or malfunction of the circuit. Will be able to prevent.

  Embodiments of the present invention will be described in detail with reference to the drawings.

  1 is a perspective view of an electronic device such as a modem, which is a telephone terminal connected to various communication networks, FIG. 2 is an exploded perspective view of a circuit board removed from a housing, and FIG. 3 is a circuit board. FIG. 4 is an enlarged view of the circle A in FIG. 3, FIG. 5 is an enlarged view of the electrostatic discharge structure, FIG. 6 is a circuit diagram of the electrostatic discharge structure, and FIG.

  A casing 1 such as a communication device such as a modem that is a telephone terminal has a rectangular box shape with a front surface opened by processing a metal plate, and a front panel (not shown) is formed in the front opening 1a. Is detachably attached.

  On the upper surface of the housing 1, a cable such as a LAN cable 3 a or a USB cable 3 b for connecting the circuit board 2 accommodated in the housing 1 and an external electronic device (external device 9) via a communication network. A cable outlet 1b for pulling out 3 is opened.

  In the housing 1, a plurality of brackets 4 for fixing the circuit board 2 are installed at diagonal positions of the circuit board 2, and are drilled at one corner of the circuit board 2 and in the vicinity of the other corner. The circuit board 2 is mounted in the housing 1 by screwing the fixing tool 5 such as a screw inserted through the mounting holes 2 a and 2 b into the screw hole 4 a formed in the bracket 4.

  The circuit board 2 is formed of, for example, a printed circuit board, and a plurality of electronic components (not shown) as functional parts are mounted on the circuit board 2. A connector 6 including a plurality of connectors 6a and 6b for connecting the cable 3 drawn from the cable drawing port 1b is provided.

  On at least one surface of the circuit board 2, an electrostatic discharge ground pattern 7 is formed in a frame shape along each side as shown in FIG.

  The electrostatic discharge ground pattern 7 is formed separately from a ground pattern (not shown) forming a circuit pattern, and the ground patterns are electrically insulated.

  In the electrostatic discharge pattern 7 of the mounting hole 2a formed in the corner of the circuit board 2, an annular FG pattern 7a is formed so as to surround the mounting hole 2a as shown in FIG. The FG pattern 7a and the electrostatic discharge ground pattern 7 are electrically insulated by an annular insulating portion 7b.

  As shown in FIG. 5, the FG pattern 7a is formed when the fixing member 5 inserted into the attachment hole 2a is screwed into the bracket 4 in the housing 1 and the circuit board 2 is attached in the housing 1 as shown in FIG. RC is formed by connecting a resistor R and a capacitor C in parallel between the FG pattern 7a and the electrostatic discharge ground pattern 7 between the FG pattern 7a and the ground pattern 7 for electrostatic discharge. Component 8 is soldered.

  As for the RC component 8 for electrostatic discharge, even if there are a plurality of (two in the embodiment) fixing points for fixing the circuit board 2 to the housing 1, at least one is sufficient as a countermeasure against discharge. As shown in FIG. 3, a part of the electrostatic discharge brand pattern 7 is extended to the attachment hole 2b in a tongue-like shape in the attachment hole 2b provided in the vicinity of the part, and the tongue-like part 7c is attached to the attachment hole 2b. It fixes to the housing 1 through the fixing tool 5 inserted in the.

  Of course, the GF pattern 7a may be formed also on the mounting hole 2b side, and the RC component 8 may be provided between the GF pattern 7a and the ground pattern 7 for electrostatic discharge.

  Next, the operation of the electrostatic discharge structure such as the electronic apparatus configured as described above will be described.

  An electronic device or the like is installed at a predetermined location, and a LAN cable 3a drawn from the cable lead-in port 1b is connected to one connector 6a provided on the circuit board 2 in the housing 1, and the electronic device or the like is connected by this cable 3. Is connected to an external device 9 such as a private branch exchange (PBX) via a communication network.

  A personal computer (not shown) is connected to the other connector 6b of the circuit board 2 by a USB cable 3b.

  The circuit configuration of the circuit board 2 connected to the external device as described above is as schematically shown in FIG.

  A worker who installs an electronic device or the like and performs wiring work or a user who uses the electronic device or the like is usually in a state where static electricity is charged on the human body, and such a human body is a housing 1 such as an electronic device. Is touched, the static electricity charged in the human body in step S1 of the flowchart shown in FIG. 7 is discharged to the housing 1 side due to the potential difference between the human body and the housing 1.

  The static electricity discharged to the housing 1 reaches the FG pattern 7a provided around the mounting hole 2a of the circuit board 2 from the bracket 4 fixing the circuit board 2 in the housing 1 through the fixing tool 5, and the housing 1 and the FG pattern 7a have the same potential.

  The static electricity that has reached the FG pattern 7a is discharged to the electrostatic discharge pattern 7 via the RC component 8 provided between the FG pattern 7a and the electrostatic discharge ground pattern 7 in step S2.

  In order to prevent the impedance of the RC component 8 from becoming larger than the resistance value of the insulating portion 7b formed between the GF pattern 7a and the electrostatic discharge ground pattern 7, for example, a resistance R of about 1 MΩ and a level of about 0.1 μF, for example. The capacitor C is connected in parallel, and the discharge from the FG pattern 7a to the electrostatic discharge ground pattern 7 passes through the capacitor C side having a lower impedance than the resistor R when passing through the RC component 8. First, the capacitor C is charged with electric charge.

  When the capacitor C approaches a saturated state, the impedance of the capacitor C exceeds the impedance of the resistor R at a certain point, so that the electric charge is discharged to the electrostatic discharge ground pattern 7 through the resistor R. Discharge is continued in step 3 until the FG pattern 7a and the electrostatic discharge ground pattern 7 are at the same potential while the electric charge moving in time units, that is, the current is limited (attenuated) by the resistance value of R.

  The static electricity that has reached the electrostatic discharge ground pattern 7 is discharged from the ground of the external interface (not shown) to which the connector 6a is connected in step S4 to the ground side of the external device 9 via the LAN cable 3a. Static electricity is not directly discharged to the electronic components and the like mounted on the circuit board 2, thereby preventing the electronic components and the like from being damaged by the static electricity and malfunctioning of the circuit.

  The above is a case where the static electricity discharged from the human body to the housing 1 is discharged from the electrostatic discharge ground pattern 7 to the external device 9 through the cable 3 connecting the electronic device and the external device 9 as shown in FIG. As in the modification, the discharge may be made to an external device through the ground pattern 10 of the circuit of the circuit board 2 provided in the housing 1.

  In this case, another RC component 8a similar to the RC component 8 is connected between the electrostatic discharge pattern 7 and the circuit ground pattern 10. The circuit configuration at this time is as shown in FIG. Become.

  In this modification, the flow until the human body touches the housing 1 such as an electronic device and the static electricity charged on the human body is discharged to the housing 1 until the static electricity reaches the FG pattern 7a is shown in step S3 of the flowchart shown in FIG. As in the above, the electric charge that has reached the electrostatic discharge ground pattern 7 is further attenuated and reaches the circuit ground pattern 10 when passing through another RC component 8a in step S4 of the flowchart shown in FIG. .

  At this time, the static electricity is generated in two locations, an RC component 8 provided between the FG pattern 7a and the electrostatic discharge ground pattern 7, and an RC component 8a provided between the electrostatic discharge ground pattern 7 and the ground pattern 9 of the circuit pattern. Therefore, even if it reaches the ground pattern 10 of the circuit, the electronic component is not destroyed or the charge does not cause the circuit to malfunction, so the electronic component is destroyed or the circuit malfunctions. Can be reliably prevented.

  In the above-described embodiment, a case has been described in which the electronic device or the like is a modem that connects a telephone and an information communication network, and the external device 9 is a private branch exchange. However, there is a possibility that the device may be damaged by static electricity or the circuit may malfunction. The present invention can be applied to all electronic devices such as certain electric devices and communication devices.

  In the electrostatic discharge structure of the electronic device or the like of the present invention, the static electricity discharged from the human body to the housing is attenuated by the RC component provided between the FG pattern and the electrostatic discharge ground pattern to the electrostatic discharge ground pattern. Therefore, it is optimal for an electrostatic discharge structure such as an electronic device using a metal casing.

The perspective view of the electronic device etc. which employ | adopted the electrostatic discharge structure which becomes embodiment of this invention. The disassembled perspective view of the state which removed the circuit boards, such as an electronic device which employ | adopted the electrostatic discharge structure which becomes embodiment of this invention. The top view of the circuit board used for the electrostatic discharge structure of the electronic device etc. which become embodiment of this invention. The enlarged view in A circle of FIG. 1 is a perspective view of an electrostatic discharge structure such as an electronic device according to an embodiment of the present invention. 1 is a circuit diagram of an electrostatic discharge structure of an electronic device or the like according to an embodiment of the present invention. The flowchart which shows the effect | action of electrostatic discharge structures, such as an electronic device which becomes embodiment of this invention. The circuit diagram which shows the modification of electrostatic discharge structures, such as an electronic device which becomes embodiment of this invention. The flowchart which shows the effect | action of the modification of electrostatic discharge structures, such as an electronic device which becomes embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Case 2 Circuit board 3 Cable 5 Fastening tool 7 Ground pattern for electrostatic discharge 7a FG pattern 7b Insulation part 8 RC component 8a RC component 9 External device

Claims (4)

An electrostatic discharge structure of an electronic device or the like having a metal housing that houses a circuit board on which electronic components or the like are mounted, the electrostatic discharge ground pattern formed on the circuit board, and the electrostatic discharge ground pattern An FG pattern that is formed on a part of the insulating film and is electrically connected to the casing, and an RC component that is connected between the electrostatic discharge ground pattern and the FG pattern. Electrostatic discharge structure for electronic devices, etc. The electrostatic discharge structure for an electronic device or the like according to claim 1, wherein the FG pattern is connected to the housing via a fixing tool that fixes the circuit board to the housing. The electrostatic discharge structure for an electronic device or the like according to claim 1 or 2, wherein the electrostatic discharge ground pattern is connected to a ground of the external device via a cable connecting the electronic device or the like to the external device. The electrostatic discharge of an electronic device or the like according to claim 1 or 2, wherein an RC component different from the RC component is connected between a ground pattern of a circuit formed on the circuit board and the ground pattern for electrostatic discharge. Construction.

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