JPH10241888A - Static discharge protecting structure and static discharge evaluating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and accurately reduce noise generated in an electronic circuit in electronic equipment when applying static electricity thereto and easily and accurately evaluate the magnitude of the noise. SOLUTION: When static electricity from a charged human body 2 is applied to an application point 15 on an operation part 12, the static electricity is discharged through a discharge route 16 containing the operation part 12, an earth terminal 13 and an earth line 14 to an ground earth GND. In this case, field coupling between inductance component from the discharge route 16 and inductance component from an electronic circuit in electronic equipment 10 generates noise in the electronic circuit, but mutual inductances are kept to a minimum to minimize noise generated in the electronic circuit because the discharge route 16 between the application point 15 and the ground earth GND has the shortest distance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic discharge protection structure and an electrostatic discharge evaluation method for an electrostatic discharge to electronic equipment such as a telephone exchange, a control panel, and a personal computer in which a printed circuit board is built in a housing, and in particular, to an electrostatic discharge evaluation method. The present invention relates to measures against noise of a housing or the like and a printed circuit board against electric discharge.

[0002]

2. Description of the Related Art Conventionally, techniques relating to an electrostatic discharge protection structure for electrostatic discharge and an electrostatic discharge evaluation method include:
For example, there is one described in the following literature. Reference 1: Printed Circuit Society of Japan, Proceedings of the Working Group, 2 [6]
(1990-2-15) Masanori Wakahara "Noise Countermeasures" 9-15 Literature 2: Japanese Patent Laid-Open Publication No. Sho 56-86368, "Method of Testing Noise Tolerance of Printed Circuit Board" The above-mentioned Literature 1 describes a technique of an electrostatic discharge protection structure for taking measures against noise by electrostatic discharge. In this technique, a countermeasure against noise is taken by setting a discharge route of electrostatic discharge and designing the discharge route to have a low impedance with respect to the ground. Reference 2 describes a technique of an evaluation (test) method for electrostatic discharge. In this technology, inconvenience occurs when the entire device on which a printed circuit board or the like is mounted is measured, so a general electrostatic discharge test is applied to directly apply noise to the printed circuit board on which the actual circuit elements are mounted. , The measurement is performed for each printed circuit board.

[0003]

However, the conventional electrostatic discharge protection structure and the conventional method for evaluating electrostatic discharge have the following problems (a) and (b), and it is difficult to solve them. . (A) In the electrostatic discharge protection structure described in the above document 1, only specific examples of the discharge route to the ground are mentioned, and there are few concrete means, and it is expected when the discharge route is considered by an equivalent circuit. There is a problem that the influence of mutual inductance is not considered. Further, there is a problem that a discharge shock to a charged human body is not considered. (B) The method for evaluating electrostatic discharge described in Document 2 has a problem that measurement results are easily affected by characteristic variations (variations including temperature characteristics) of actual circuit elements on a printed circuit board. Also, the structure of the housing and printed circuit board that make up the electronic device, the way of grounding, the mounting method of the printed circuit board, and the like differ depending on the individual electronic device. There is a problem that it is difficult to evaluate the countermeasure effect. Further, in the base technology described in Document 2,
An electrostatic discharge test is performed on the entire device on which a printed circuit board or the like is mounted, and such an electrostatic discharge evaluation method has a problem that the discharge route is different from a discharge route actually emitted from a human body.

[0004]

According to a first aspect of the present invention, there is provided an electrostatic discharge protection structure for an electronic device having an electronic circuit housed in a conductive housing. On the other hand, between the application point at which static electricity from a charged human body is assumed to be applied to the housing and the earth ground, the housing and a conductive member connected thereto (for example, a ground terminal, a ground wire, It is configured to be electrically connected directly or via a capacitive coupling (for example, stray capacity) by the shortest discharge route formed by a ground plane or the like. According to the second aspect of the present invention, in the electrostatic discharge protection structure, a static electricity from a charged human body is applied to an electronic device in which a printed board on which an electronic circuit is mounted is housed in a conductive subrack so as to be insertable and removable. Between the application point assumed to be applied to the subrack and the earth ground, the subrack and a conductive member connected thereto (for example, a contact, a ground terminal, a ground wire, a ground pattern, a package connector, It is configured to be electrically connected directly or through capacitive coupling (for example, stray capacity) by the shortest discharge route formed by a conductive wire or the like.

According to a third aspect of the present invention, in the electrostatic discharge protection structure of the first or second aspect, a film having a predetermined electric resistance is formed on the surface of the application point. According to a fourth aspect of the present invention, in the electrostatic discharge evaluation method, an actual printed circuit board mounted with an electronic circuit and mounted in an electronic device is imitated and located at an application point where static electricity from a charged human body is assumed to be applied. Conductive contacts (e.g., housing controls,
An operation section of a printed circuit board, etc.) and a pattern of a one-turn coil having predetermined outer dimensions and insulated from the contact section and corresponding to the electronic circuit are provided on the test board. And
The high voltage is applied by a discharge loop formed by a contact portion of the test board, a wiring member (eg, an earth pattern, a contact, an earth cable, etc.) and a high voltage output means (eg, a discharge gun, etc.) for outputting a high voltage. The noise applied to the contact portion and induced in the pattern of the one-turn coil electrostatically and magnetically coupled to the discharge loop is measured to evaluate the electrostatic discharge to the electronic device. According to a fifth aspect of the present invention, in the electrostatic discharge evaluation method of the fourth aspect, the discharge loop is a rectangular loop simulating a human body.

According to the first and second aspects of the present invention, since the electrostatic discharge protection structure is configured as described above, when the charged static electricity from the human body is applied to the application point, the applied static electricity is minimized. Discharged to earth ground through discharge route. At this time, noise is generated in the electronic circuit due to magnetic field coupling due to mutual inductance between the inductance component of the discharge route and the inductance component of the electronic circuit.
Since the static electricity is discharged by the shortest discharge route, the mutual inductance is minimized and the generated noise is also minimized. According to the third aspect of the present invention, when static electricity is applied to the application point, the electric resistance of the film makes the decrease in the electric charge of the human body slow, and the rise in the potential at the application point is suppressed, so that the current flowing through the discharge route is reduced. Changes also become small. According to the invention of claim 4, when a high voltage is applied to the contact portion of the test board by the discharge loop, noise is induced in the pattern of the one-turn coil by magnetic coupling, and the actual electronic device is modeled by measuring the noise. The evaluation can be performed for the generated electrostatic discharge. According to the invention of claim 5, since a high voltage is applied to the contact portion using a discharge loop that models an electrostatic discharge caused by an actual human body, the noise induced in the pattern of the one-turn coil is measured. It is possible to perform an evaluation close to an actual electronic device.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a configuration diagram showing a first embodiment of the present invention, which is an example of an electrostatic discharge protection structure. This electrostatic discharge protection structure is a cabinet type electronic device 1 installed on a floor 1.
0 protects against electrostatic discharge from the charged human body 2. The electronic device 10 has an electronic circuit housed in a conductive housing. The housing includes a cabinet-shaped housing main body 11 in which an electronic circuit is housed, and a conductive operation unit 12 provided on the front surface of the housing main body 11. Although the case body 11 is shown in FIG. 1 as a cabinet defined as a representative of the International Electrotechnical Commission (IEC) 917 standard, other shapes may be used. A switch, a lamp, a volume, and the like are usually mounted on the conductive operation unit 12 provided on the front surface of the housing body 11, but are omitted in FIG. Further, FIG. 1 shows a panel-shaped operation unit 12 formed by sheet metal processing of a metal plate (for example, a steel plate, an aluminum plate, or the like) so as to fit over the entire front surface of the housing body 11. The operation unit 12 may be a partial surface of the housing main body 11 or is used to include a part such as a frame part where the human body 2 may come into contact with the housing main body 11.

When the operation unit 12 is an insulating resin molded product, the conductivity to the ground GND is ensured by metal plating (for example, electroless copper plating or the like), metal evaporation, or sticking of metal foil. I have. Also, in the case where there is a door or a decorative cover having an insulating property (for example, an insulating property that withstands a voltage of several tens of KV applied instantaneously) on the front surface of the operation unit 12,
The same conductivity as that described above to the ground GND is secured inside the insulating material. A ground terminal 13 is provided below the operation unit 12 and is firmly connected to a conductive portion of the operation unit 12. The ground terminal 13 has a ground wire 1
4 is connected and electrically connected to the earth ground GND by a method according to the relevant laws and regulations of the electronic device (for example, ground with 100Ω or less). Since the ground wire 14 is usually wired from the floor 1 side, the mounting position of the ground terminal 13 is set so that the ground wire 14 is made as short as possible. It is arranged on one side. here,
Assuming the electrostatic discharge from the charged human body 2, the discharge route 16 in which the static electricity is dissipated through the electronic device 10 to the ground GND is usually the longest when the operation is performed with one hand 2a extended. For example, considering a Japanese male operator, when the height to the shoulder is L1 and the length of one hand 2a is L2, L1 × L2 = about 1400 mm × 740 mm
(Japanese physique survey report (1984 edition); edited by the Ministry of International Trade and Industry, Ministry of Industry and Technology). The application point 15 assumed here means a metal toggle such as a metal exposed portion or a switch on the operation unit 12 or a metal screw for attaching the operation unit 12 to the housing body 11.

Next, the operation of the electrostatic discharge protection structure shown in FIG. 1 will be described. The static electricity charged on the human body 2
2 is discharged to the expected application point 15 at the moment of touching or at the time of touching. At this time, since the assumed potential of the application point 15 instantaneously rises, the housing body 11
Causes a potential difference with the electronic circuit provided inside the
Due to the electrostatic coupling between the fingertip and the operation unit 12 due to the stray capacity, noise is generated in the internal electronic circuit. The potential difference can be considered as a transient phenomenon with respect to the impedance of the wiring to the ground GND. The static electricity applied to the application point 15 is transmitted from the operation unit 12 to the ground G through the ground terminal 13 and the ground wire 14.
The ND is dissipated, but noise is generated in the electronic circuit due to the magnetic field coupling due to the mutual inductance of the inductance component of the discharge route 16 and the inductance component of the electronic circuit in the housing body 11. As a measure against this,
In the present embodiment, the distance between the assumed application point 15 and the ground GND is minimized, so that the mutual inductance is minimized and the noise generated is also minimized.

As described above, in the first embodiment,
In the ground connection structure to the ground GND from the operation unit 12 which can be assumed to be charged with static electricity from the charged human body 2 or a contactable part (that is, the assumed application point 15), the conductive part such as the operation unit 12 can be used. A portion which can be wired by a ground terminal 13 or the like is provided for a portion having a characteristic, and a ground wire 14 connected to the ground GND is directly connected. In particular, in the connection between the operation unit 12 and the ground line 14, the ground line is connected to the operation unit 12 and the like on the side where the ground line 14 such as the floor 1 is laid in the building at a practically appropriate short distance. . Further, in the discharge route 16 between the human body 2 and the earth ground GND, the distance between the assumed application point 15 and the earth ground GND is the shortest except for an undefined portion (L2) from the human body 2 to the assumed application point 15. It has a structure to do. Therefore, there are the following advantages. The mutual inductance between the inductance component of the discharge route 16 and the inductance component of the electronic circuit provided in the housing body 11 is minimized. As a result, harmful noise generated in the electronic circuit can be minimized.

Second Embodiment FIG. 2 is a configuration diagram showing a second embodiment of the present invention, which is an example of an electrostatic discharge protection structure, and is common to the elements in FIG. 1 showing the first embodiment. Are given the same reference numerals. In this electrostatic discharge protection structure, the structure of an operation unit 12A provided on the front surface of a housing body 11 constituting the electronic device 10 is different from the operation unit 12 of FIG. Operation unit 12A
In this case, this surface is coated with a film having a predetermined electric resistance. The term “coating” used herein means to form a film having an appropriate surface electrical resistance, including painting. For example, a conductive coating (registered trademark “Elecoat One” manufactured by Musashi Paint Co., surface resistance about 300Ω) is applied to the surface of the operation unit 12A. Operation unit 1
The knob of the volume or the like on 2A is dipped with rubber having conductivity (conductive silicon rubber, manufactured by Shin-Etsu Chemical Co., Ltd.). Therefore, at the assumed application point 15, a coating material is interposed between the human body 2 and the metal part of the operation unit 12A. The ground terminal 13 is directly connected to the metal part by removing the coating material on the surface of the operation part 12A. Other configurations are the same as those in FIG.

Next, the operation of the electrostatic discharge protection structure shown in FIG. 2 will be described. Similarly to the first embodiment, when static electricity is applied to the application point 15 of the operation unit 12A that is assumed from the charged human body 2, the static electricity is applied to the ground through the operation unit 12A, the ground terminal 13, and the ground wire 14. Earth GND
Dissipated to Since the operation unit 12A is coated, the decrease in the charge (ie, the discharge) of the charged human body 2 becomes gentle due to the electric resistance of the coating material. Therefore, the assumed application point 15
Is suppressed, and the change in the current flowing through the discharge route 16 is also reduced. As described above, in the second embodiment, since a coating having a predetermined electric resistance is applied to the operation unit 12A and the like, it is possible to suppress the flow of the electrostatic charge applied from the charged human body 2. it can. That is, since the charge of the charged human body 2 decreases slowly, the discharge shock to which the human body 2 receives can be reduced.
In addition, due to the synergistic effect of suppressing the assumed increase in the potential of the application point 15 and reducing the change in the current flowing through the discharge route 16, noise generated in the electronic circuit in the housing body 11 is reduced. It can be further reduced.

Third Embodiment FIG. 3 is a block diagram showing an example of an electrostatic discharge evaluation method according to a third embodiment of the present invention. In this electrostatic discharge evaluation method, a test board 21 simulating (ie, modeling) an actual printed circuit board (actual printed circuit board) provided with an electronic circuit and provided in a housing of an electronic device is used. The test board 21 is simulated in terms of the structure of the actual printed circuit board and the method of grounding metal fittings.
Above, a conductive contact portion (for example, an operation portion) 22 matched with the actual one and a pattern of a one-turn coil 26 insulated from the operation portion 22 are provided. The operation unit 22
Similarly to the actual printed circuit board, it is connected to a ground plane 25 which is regarded as equivalent to the earth ground GND by an earth pattern 23, a contact 24 and the like.
On the other hand, the one-turn coil 26 provided on the test board 21 is a model of an integrated circuit (hereinafter, referred to as “IC”) represented by signal transmission on an actual printed board, and is an example of this modeling method. Is formed in a rectangular coil shape having the same dimensions as the external shape of the IC. One-turn coil 2
6, a connector (for example, an SMA type coaxial substrate mounted connector with good frequency characteristics) 27 is connected to a predetermined portion (for example, the center of one long side) by soldering or the like.

In order to apply static electricity to the test board 21, an electrostatic tolerance tester 31 is used. The static electricity tolerance tester 31 generates a high-voltage pulse, sends the high-voltage pulse to a high-voltage output means (for example, a discharge gun) 33 through a high-voltage cable 32, and the static electricity of the operation unit 22 is applied. The high voltage pulse S33 is applied to the application point that is assumed to be applied. Discharge gun 3
3, one end of an earth cable 34 is connected as a return circuit for the applied static electricity. Earth cable 3
4 is a minimum length, so that the other end of the ground cable 34 is close to the ground wiring such as the contact 24 from the operation unit 22 so that the discharge route is appropriate.
It is connected to the ground plane 25. On the other hand, an oscilloscope 36 is connected via a coaxial cable 35 connected to the connector 27 in order to measure induced noise generated in the one-turn coil 26.

FIGS. 4 (a) and 4 (b) are illustrations of the one-turn coil 26 in FIG. 3, wherein FIG. 4 (a) shows the component side and FIG. 4 (b) shows the connection side. is there. Test board 2
The pattern of the one-turn coil 26 provided on the component side is modeled on an IC and is formed in a rectangular coil shape having the same dimensions as the outer shape of the IC. For example, DIP (Dual I
In the case of an n-line Package) type 16-pin IC, when the vertical length is L11 and the horizontal length is L12, L11 × L1
2 = 7.62 × 21.59 mm. DIP type 6
In the case of a 4-pin IC, L11 × L12 = 25.4 × 81.
It becomes 28 mm. On the connection surface side of the test board 21, an SMA type coaxial board mounted connector 27 having good frequency characteristics is connected to a position corresponding to the center of one side of the long side of the one-turn coil 26. The reason why the connector 27 is arranged at the center of one side of the long side of the one-turn coil 26 is that the connection with the one-turn coil 26 is taken into consideration, and that the connection is easy even when the one-turn coil 26 is small. When the electrostatic discharge evaluation method is performed using the test board 21, there are a method of installing the test board 21 alone as shown in FIG. 3 and a method of mounting the test board 21 in a housing of the electronic device. Hereinafter, such a test board 2
1 will be described.

The high voltage pulse generated by the static electricity tolerance tester 31 is passed through the high voltage cable 32 to the discharge gun 3.
Send to 3. For example, in the case where a discharge gun 33 of a contact discharge method is used, the discharge gun 33 is brought into contact with the operation unit 22 and when the discharge gun 33 is turned on assuming an application point, a high voltage pulse S33 (for example, 10
KV) is applied to the application point of the operation unit 22. The high voltage generated by the static electricity tolerance tester 31 is applied to the discharge gun 3.
3 and accumulate electricity, and a switch of the discharge gun 33 generates a high voltage pulse S33. So far, it is a general test method. The static electricity applied to the application point of the operation unit 22 is formed by the operation unit 22, the wiring members (that is, the ground pattern 23, the contact 24, the ground plane 25, and the ground cable 34), and the discharge gun 33. And returns to the discharge gun 33 through the discharge loop. The inductance component of this discharge loop and the one-turn coil 26
Are coupled electrostatically and magnetically, and noise is induced in the one-turn coil 26. The induced noise is sent to the oscilloscope 36 through the connector 27 and the coaxial cable 35, and the oscilloscope 3
Numericalization is performed using 6. The evaluation results are shown in FIGS.
Shown in

FIG. 5 is a diagram showing the results of measuring the magnitude of induced noise with a one-turn coil 26 corresponding to DIP 16 pins. FIG. 6 is a diagram showing the result of measuring the magnitude of induced noise with the one-turn coil 26 corresponding to DIP 64 pins. 5 and 6 show a human body 2 described later.
The measurement result of the magnitude of the induced noise when the discharge loop is equivalent to the above is also included. As shown in FIGS. 5 and 6, the ground plane 25 passing through the ground pattern 23 and the contact 24 from the high voltage pulse application point of the discharge gun 33.
When the distance to is shortest, the magnitude of the induced noise induced in the one-turn coil 26 is 0.53 mV, the maximum value is 2 mV, the minimum value is 0.4 mV, and the minimum value is 0.4 mV when the DIP 16 pins are equivalent. In the case of, the average of the magnitude of the induced noise is 3.27 mV, and the maximum value is 5.6 m
V, the minimum value is 2.2 mV, indicating that the magnitude of the induced noise is a small value. Further, it can be seen that the larger the outer dimensions of the one-turn coil 26, the greater the induced noise.

As described above, in the third embodiment,
Hardware that imitates the shape of the actual printed circuit board used in the housing of the electronic device, and also imitates the actual operation unit and the like (ie, operation unit)
A test board 21 on which the IC 22 is mounted is provided, and a one-turn coil 26 that models an IC represented by signal transmission is provided on the test board 21 in a state insulated from the operation unit 22. Since the noise is measured by the oscilloscope 36, the following (a) to (c)
There are advantages such as: (A) An IC represented by an actual printed circuit board without using actual circuit elements on the actual printed circuit board
The magnitude of the noise induced in the one-turn coil 26 is evaluated by using the test board 21 provided with the one-turn coil 26 having the same external dimensions as that of the actual circuit element. Can be evaluated. (B) Since the test board 21 is installed alone as shown in FIG. 3 or the test board 21 is mounted in the housing of the electronic device and the magnitude of the induced noise is evaluated without using actual circuit elements. In addition, it is possible to accurately evaluate the structural countermeasure effect of a housing of an electronic device or a printed circuit board.
(C) Since the connector 27 is disposed at the center of one side of the long side of the one-turn coil 26, connection with the one-turn coil 26 becomes easy, and the induced noise can be accurately taken out.

Fourth Embodiment FIG. 7 is a block diagram showing an example of an electrostatic discharge evaluation method according to a fourth embodiment of the present invention. FIG. 1 shows the first embodiment and FIG. Elements common to those shown in FIG. 3 are denoted by common reference numerals. In this electrostatic discharge evaluation method, a discharge loop 17 that is close to the actual discharge loop 17 shown in the electrostatic discharge protection structure of FIG. 1 is provided in the electrostatic discharge evaluation method of the third embodiment shown in FIG. The noise induced in the provided electronic circuit is evaluated. That is, assuming the cabinet-type electronic device 10 of FIG. 1, the electronic device 10 is connected to the ground plane 25 from the ground terminal 13 on the lower side of the operation unit 12 provided on the front surface of the housing body 11 using the ground wire 14. In order to form a rectangular discharge loop 17 simulating the human body 2, the ground cable 34 of the return wiring member connected to the discharge gun 33 is moved from the connection position of the ground plane 25 of the ground wire 14 to one hand 2 a of the human body 2.
Are connected to the ground plane 25 at a distance of about 740 mm corresponding to the length L2. From there, the ground cable 34 is laid out vertically, and corresponds to about 140 corresponding to the shoulder height L1 of the human body 2.
It is lowered to 0 mm, from which it is connected to the discharge gun 33 almost horizontally. An electronic circuit provided in the housing body 11 is connected to an oscilloscope 36 via a coaxial cable 35, as in the third embodiment.

In the method for evaluating electrostatic discharge according to the fourth embodiment, similarly to the third embodiment shown in FIG. 3, a high-voltage pulse generated from an electrostatic tolerance tester 31 is discharged via a high-voltage cable 32. The discharge gun 33 applies a high voltage pulse S33 to the application point of the operation unit 12. The high-voltage pulse S33 returns to the discharge gun 33 through the ground terminal 13, the ground line 14, the ground plane 25, and the ground cable 34, which are wiring members. Noise is induced in the one-turn coil 26 by the electrostatic / magnetic coupling between the inductance component of the discharge loop 17 and the one-turn coil 26 of FIG. The induced noise is quantified using the oscilloscope 36 in the same manner as in the third embodiment shown in FIG. 3, and the induced noise is evaluated. The evaluation results are shown in FIGS.

As shown in FIG. 5, the magnitude of the induced noise is measured by modeling the electrostatic discharge caused by the actual human body 2 in the discharge loop 17. For this reason, the length of the discharge loop 17 of the fourth embodiment is longer than the discharge loop formed by the operation unit 22, the ground pattern 23, the contact 24, the ground cable 34, and the discharge gun 33 in FIG. Therefore, compared to the third embodiment, the average of the magnitude of the induced noise is 6.68 mV, the maximum value is 10 mV, and the minimum value is 4.4 mV. As described above, in the fourth embodiment, since the ground cable 34 of the return wiring member forming the discharge loop 17 is a rectangular loop simulating the actual human body 2, particularly, as shown in FIG. In the cabinet-type electronic device 10, it is possible to evaluate the induced noise that is actually brought closer.

Note that the present invention is not limited to the above embodiment, and various modifications are possible. Examples of the modifications include the following (i) to (v). (I) In the first embodiment, as shown in the electrostatic discharge protection structure in FIG. 1, an example in which the ground terminal 13 can be provided in the operation unit 12 has been described. However, the present invention is not limited to this. Such a configuration may be used. FIG. 8 is a configuration diagram showing a modification example of FIG. 1 and showing an example of an electrostatic discharge protection structure when a ground terminal cannot be provided. In the structure in which the ground terminal 13 and the like shown in FIG. 1 cannot be provided and only the ground wire 41a included in the power cord 41 can be provided, the bottom structure of the housing main body 11 is changed to a large bottom area. The ground plane 42 is made of a metal having a width of, and the ground plane 42 is connected to the operation unit 12 and the like and the ground line 41a. According to such a configuration, the apparent discharge route can be shortened by utilizing the stray capacity 43 between the ground plane 42 on the bottom surface of the housing body 11 and the ground GND.

(Ii) As another modified example of the above (i),
Some are as shown in FIG. FIG. 9 is a configuration diagram illustrating a modification example of the first embodiment of FIG. 1 and illustrating an example of an electrostatic discharge protection structure having a sub-operation unit. A main operation unit 12 is provided on a front surface of a housing main body 11 constituting the electronic device 10, and a sub operation unit 12 </ b> A is provided on a back side of the housing main body 11.
In this case, the bottom surface structure of the housing body 11 is a conductive ground plane 42, and the main operation unit 12 and the sub operation unit 12A are connected by the ground plane 42. As described above, the sub operation unit 1 is provided on the surface facing the main operation unit 12 and the like.
In the electronic device 10 having the 2A and the like, if the bottom structure of the housing body 11 is a ground plane 42 and the main operation unit 12 and the like and the sub operation unit 12A are connected by the ground plane 42, the first embodiment will be described. The discharge route can be shortened in almost the same manner, and noise generated in the electronic circuit in the housing body 11 can be minimized.

(Iii) In the electrostatic discharge protection structure of FIG.
Electronic device 10 containing an electronic circuit inside housing body 11
However, for example, the present invention can be applied to a book shell type subrack typified by the IEC917 standard and the like, and this example is shown in FIG. FIG. 10 is a configuration diagram showing an example in which the electrostatic discharge protection structure of the present invention is applied to a subrack. An electronic device 50 to be subjected to the electrostatic discharge protection structure has a book shell-type subrack 51, and a backplane substrate 52 is provided on the back side of the subrack 51. A plurality of package connectors 53 are mounted inside the backplane board 52. One ends of a plurality of insertable and removable printed circuit boards 54 are inserted into the plurality of package connectors 53. On the other end side of each printed circuit board 54, a conductive operation unit 55 on which switches, lamps, volumes, and the like are mounted is provided. The lower side of each operation unit 55 is electrically connected to the lower side of the conductive subrack 51 by a conductive member (for example, a contact) 56. A ground terminal 57 is attached near the contact 56 connected to the subrack 51, and the ground terminal 57 is connected to a ground GND by a ground wire 58. As described above, in the structure in which the operation unit 55 and the like provided on the printed board 54 are grounded, the contact 56 provided on the printed board 54 or the subrack 51 is used.
From the operation unit 55 to the contact 56, the ground terminal 5
7 and the ground line 58, a discharge route to the ground GND is secured. When the charged static electricity from the human body 2 is applied to the application point of the operation unit 55, the applied static electricity is used as the discharge route. Through Earth Earth G
Discharged to ND. At this time, since the discharge route between the application point at which the charged static electricity from the human body 2 is assumed to be applied to the operation unit 55 and the ground GND is minimized, the inductance component of the discharge route and the Mutual inductance with the inductance component on the substrate 54 side is minimized, and noise generated on the printed circuit board 54 side is also minimized.

(Iv) FIG. 11 shows another application example of the book shell type subrack of the above (iii). FIG.
FIG. 11 is a configuration diagram showing an example of a case where a contact cannot be provided on a bookshelf-type subrack in the electrostatic discharge protection structure of (1), and components common to the components in FIG. In the electronic device 50 having the subrack structure, the contact 56 as shown in FIG. 10 cannot be provided,
Ground pattern 54a wired on printed circuit board 54
When the installation is performed only by using the ground pattern 54a, the ground pattern 54a is arranged near the subrack 51. In such an electrostatic discharge protection structure, a ground pattern 54a, a package connector 53, a conductive wire 59, a ground terminal 57,
Then, the applied static electricity is discharged to the ground GND through the ground line 58. At this time, the ground pattern 54a
Are arranged near the sub-rack 51, the apparent discharge route is shortened by the stray capacity between the ground pattern 54a and the sub-rack 51. Mutual inductance with the inductance component of the substrate 54 is minimized, and noise generated on the printed circuit board 54 side can also be minimized. (V) In FIG. 4, the one-turn coil 26 is
Although the rectangular shape has the same size as the C outer shape, the shape is not limited to this, and a rectangular or other coil shape having a proportional relationship may be used.

[0026]

As described above in detail, according to the first and second aspects of the present invention, the point at which static electricity from a charged human body is assumed to be applied, the earth ground, Are connected by the shortest discharge route, the mutual inductance between the inductance component on the application point side and the inductance component on the electronic circuit side is minimized, and harmful noise generated in the electronic circuit is minimized. Can be suppressed. According to the third aspect of the present invention, since a film having a predetermined electric resistance is formed on the surface of the application point, when static electricity from a charged human body is applied to the application point, the film has a human body due to the electric resistance of the film. The charge decreases gradually, and the discharge shock to the human body can be reduced. Furthermore, the noise generated in the electronic circuit can be further reduced due to the synergistic effect of suppressing the potential increase at the assumed application point and reducing the change in the current flowing through the discharge route. According to the invention of claim 4, a one-turn coil pattern that models the actual printed board is provided on the test board, and noise induced in the one-turn coil pattern is measured. The magnitude of the induced noise can be evaluated without using the actual circuit element. As a result, an evaluation that is not affected by the variation in the characteristics of the actual circuit element can be performed. Further, since the actual circuit element is not used, the structural countermeasure effect in the housing of an electronic device or a printed circuit board can be accurately evaluated. According to the fifth aspect of the present invention, since the discharge loop is a rectangular loop that models a human body, it is possible to evaluate the magnitude of noise that is actually close to the electronic device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an example of an electrostatic discharge protection structure according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram illustrating an example of an electrostatic discharge protection structure according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram illustrating an example of an electrostatic discharge evaluation method according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of a one-turn coil in FIG.

FIG. 5 is a diagram showing a result of measuring the magnitude of noise with a one-turn coil corresponding to a DIP 16 pin in FIG. 4;

FIG. 6 is a diagram showing the result of measuring the magnitude of noise with a one-turn coil corresponding to a DIP 64 pin in FIG. 4;

FIG. 7 is a configuration diagram illustrating an example of an electrostatic discharge evaluation method according to a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram showing a modification example of FIG. 1 in which a ground terminal cannot be provided.

FIG. 9 is a configuration diagram showing a modification example of FIG. 1 and having a sub-operation unit.

FIG. 10 is a configuration diagram showing an example where the present invention is applied to a subrack.

11 is a configuration diagram showing an example in which a subrack cannot be provided with a contact in the configuration of FIG. 10;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Floor surface 2 Human body 10,50 Electronic device 11 Case main body 12,22,55 Operation part 12A Sub-operation part 13,57 Earth terminal 14,58 Ground wire 16 Discharge route 17 Discharge loop 21 Test board 23,54a Earth pattern 24 , 56 contacts 25, 42 ground plane 26 one-turn coil 27 connector 31 static electricity tolerance tester 33 discharge gun 34 ground cable 36 oscilloscope 41 power cord including ground wire 43 stray capacity 51 subrack 53 package connector

Claims (5)

[Claims] An electronic device in which an electronic circuit is housed in a conductive housing is provided between an application point where static electricity from a charged human body is assumed to be applied to the housing and a ground. An electrostatic discharge protection structure characterized by being electrically connected directly or through capacitive coupling by the shortest discharge route formed by the housing and a conductive member connected thereto. 2. A device according to claim 1, wherein a printed circuit board on which the electronic circuit is mounted is inserted into and removed from the conductive subrack so that static electricity from a charged human body is applied to the printed circuit board or the subrack. A structure in which the assumed application point and the earth ground are electrically connected directly or through capacitive coupling by the shortest discharge route formed by the subrack and the conductive member connected thereto. Characteristic electrostatic discharge protection structure. 3. The electrostatic discharge protection structure according to claim 1, wherein a film having a predetermined electric resistance is formed on the surface of the application point. 4. A conductive contact portion, which imitates a real printed circuit board provided with an electronic circuit and provided in an electronic device, is located at an application point where static electricity from a charged human body is assumed to be applied, A pattern of a one-turn coil insulated from the contact portion and having a predetermined external dimension corresponding to the electronic circuit is provided on a test board, and the contact portion of the test board, a wiring member, and high voltage output means for outputting a high voltage The high voltage is applied to the contact portion by a discharge loop formed by the method, and noise induced in a pattern of the one-turn coil electrostatically and magnetically coupled to the discharge loop is measured. An electrostatic discharge evaluation method characterized by evaluating an electrostatic discharge to a device. 5. The method according to claim 4, wherein the discharge loop is a rectangular loop imitating a human body.