JP2016017873A - Discharge current measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect and display a discharge current from a charged object.SOLUTION: A discharge current measuring device 1 consists of a current probe part 2, a detection display part 3 and a connector 4. The current probe part 2 is connected to a contact needle 5 by a connector 6, and connected to a terminator 7 by a connector 8. A discharge current, generated by bringing the contact needle 5 into contact with a charged object, is discharged to GND through the terminator 7. A discharge current waveform is sent to the detection display part 3 through the connector 4 and a discharge current value is displayed by a display part 10. A shape of the contact needle 5 can be changed by replacing the contact needle 5 using the connector 6, and resistance of the terminator 7 can be changed by replacing the terminator 7 using the connector 8. Thereby, the discharge current can be detected in an immediate and general-purpose manner.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an apparatus for bringing a contact needle into contact with an electrostatically charged object and measuring a discharge current flowing at that time.

  In recent years, devices such as semiconductors and magnetic heads have become more sensitive to electrostatic discharge (ESD) and more easily destroyed as the degree of integration increases and the detection section thereof becomes more sensitive. When there is a potential difference when the terminal part of such a device comes into contact with a charged metal object, a discharge accompanying the contact occurs. Since the discharge due to the contact between the metals has a low contact resistance, it is likely to be a large current discharge even if the potential difference is small, and is a main factor causing the electrostatic breakdown of the device. Such electrostatic breakdown due to contact with a device has attracted attention in the industry, and there is a report on electrostatic breakdown of a GMR head due to contact discharge (for example, see Non-Patent Document 1). Further, there are detailed reports on contact discharge between minute capacities and their current waveforms (see, for example, Non-Patent Document 2).

  FIG. 8 shows an example of an experimental apparatus for performing an electrostatic breakdown test of a device. The experimental apparatus is assembled on a measurement table 51 connected to GND. A device 53 to be measured is placed on a charged insulator or a metal plate 52 to which a voltage is applied. At this time, the device is inductively charged by an electrostatic field. When the discharge needle 54 is lowered from above and contacts the terminal of the device, a discharge current 55 flows from the contact needle to the GND through the lead wire due to electrostatic discharge. The measurement of the current waveform of the discharge current is performed by passing the conductor portion through the current probe 56 and connecting it to the oscilloscope 57 using the coaxial cable 57a and observing the current waveform.

  An example in which a typical magnetic head (GMR head) is used as a device and an electrostatic breakdown test is measured is shown in FIG. A GMR head is a device that detects a magnetic field by resistance change. In the example of FIG. 9A, the applied voltage of the charging voltage is increased, and the head resistance after discharge is plotted. What was an initial resistance of about 50Ω increases the applied voltage and exceeds 60 V, the resistance increases and a part of the element is destroyed. The current waveform at this time was as shown in FIG. This discharge current has a pulse waveform of 1 nanosecond or less, and its peak current value reaches 200 mA. As described above, since the electrostatic discharge current is a short-time pulse and has a high peak value, a current measuring device having a band of gigahertz or more is required to measure the current waveform.

  In the prior art, there is a method of measuring the charged voltage of an object using a surface electrometer in order to evaluate the electrostatic environment of the device. In this method, the potential can be measured, but the discharge current that flows when contacting the object cannot be measured. There is a coulomb meter as a device for measuring the amount of electric charge charged on a metal object. Although this coulomb meter can measure the amount of electric charge accumulated in a metal object, it has the disadvantage that it cannot measure the discharge current when it is actually discharged.

  In a conventional device for measuring the amount of charge, there is a technique for measuring a discharge current waveform (see, for example, Patent Document 1). In this patent, a probe is brought into contact with a charged object to be measured, and the charge on the object to be measured is detected by an integrator composed of a resistor and a capacitor. In this method, it is possible to measure the charge, but since an integrator is used, the discharge current flows at a speed corresponding to the time constant of the integrator, so the discharge current that actually occurs at the metal contact is measured. There is an inconvenience that it cannot be done.

  In a conventional method for evaluating discharge characteristics, there is a technique for measuring a discharge current waveform (see, for example, Patent Document 2). In this patent, a metal member attached to a charged capacitor is brought into contact with the mat using an annular current probe arranged on the mat, and the discharge current at that time is measured with the current probe. This method is assembled to evaluate the conductivity of the mat, and the contact member and the current probe are arranged separately, and thus are not suitable for evaluating electrostatic discharge of a device or the like. Also, the current probe is not intended for gigahertz frequency characteristics.

  Therefore, in the past, in order to measure the discharge current from the device, an apparatus as shown in FIG. 8 was made, and evaluation was performed using a measurement method using the oscilloscope 57 and the current probe 56. The current probe used here is, for example, a Ct6 current probe manufactured by Tektronix. In such a conventional current probe, as shown in FIG. 10A, a through-hole 56a for passing a current is opened. When such a current probe is used, as shown in FIG. 10B, the current probe is used through the through hole 56a. This current line passes through the pattern on the board 56c and is connected to the outside by a connector 56d mounted on the board. In such a usage pattern, the additional inductance L and capacitance C increase depending on the length and diameter of the current line, which has the disadvantage of affecting the current waveform.

  It is already known that the inductance L of the wire is generally expressed by the following formula 1.

  In the above formula, D is the wire diameter and W is the length. The permeability and circumference are known values. When the inductance L is estimated from this equation, a wire having a diameter of 0.4 mm and a length of 10 mm has an inductance of 2.5 nH. When the length is halved to 5 mm with the same diameter, the inductance becomes 0.95 nH. It can be generally understood that the nH-order inductance due to the wire affects the current waveform in the gigahertz band. As described above, the conventional measurement method has an inconvenience that the inductance of the wire is generated depending on the length of the current line, and as a result, the high-frequency characteristic of the current waveform observed through the current probe is affected.

  In addition, in devices such as magnetic heads that cause electrostatic breakdown due to current values, it is necessary to read the peak value from the oscilloscope current waveform and use it as an index for electrostatic breakdown. . For this reason, it is necessary to assemble an evaluation apparatus using a current probe and an oscilloscope in order to test electrostatic breakdown in a production line, which is difficult to put into practical use.

  In general, in a dry winter season where static electricity is likely to occur, when a person comes into contact with a metal such as a door knob, an electric shock may be felt due to electrostatic discharge. Such discharge from the charged human body to the device may cause electrostatic breakdown of the device in the production line. Regarding the danger of charging of the human body, there is no device for appropriately measuring current, and the voltage is used as a guideline for evaluation using a human electrometer. However, this method has the disadvantage that the actual discharge current cannot be evaluated.

JP 2002-365322 A JP 2005-207927 A

RCJ Reliability Symposium, 2009 Proceedings 19E-14, p. 125, “Electrostatic breakdown of devices due to contact discharge -capacitance change and discharge-” “Characterization of Contact Discharge Between Small-Capacitance Devices”, Industry Applications, IEEE Transactions on Volume: 48, Issue: 4, 2012, Page (s): 1189-1194.

  A conventional method for measuring a discharge current using a current probe and an oscilloscope can evaluate the influence on electrostatic breakdown. However, this method is difficult to measure because it is not versatile in a factory line that is actually required. For example, when the line is in operation, placing an oscilloscope and a current probe at the appropriate measurement location, and creating a discharge path to GND, space is limited and measurement takes time. Therefore, it was not a practical method.

  In addition, the electrostatic waveform having a gigahertz band undergoes a change in current waveform due to additional L and C due to the discharge path. In particular, when the wire connected to GND becomes longer, the rise of the waveform becomes slower and the peak value becomes lower, so it is difficult to measure under conditions close to actual discharge.

  Furthermore, since the current waveform changes and the peak value changes due to the discharge resistance and the contact needle that affect the discharge, it is difficult to perform reliable measurement with constant conditions. The present invention has been made in view of such a problem, and in order to grasp the danger of electrostatic discharge due to charging of an object, a discharge current capable of quickly and accurately performing a current evaluation by discharge. The object is to provide a measuring device.

  For this reason, the object of the present invention is to make it possible to measure current by contacting a charged object without adding special parts. This provides a reproducible evaluation method with stable conditions.

  In the prior art, it has been difficult to perform a destructive inspection on a device that is weak against static electricity mounted on a circuit board. Therefore, when a mounting board failure occurs, it takes time to elucidate the cause, and it may be difficult to take countermeasures. By using the current probe portion of the present invention and mounting it on a substrate in advance, there is provided a method that enables an analysis of a discharge experiment when it is defective.

  For discharge from the human body, a measuring device is provided that can measure the discharge current in a state close to the actual condition when a charged person contacts the measurement terminal with a fingertip or the like.

In order to solve the above-described problems, the present invention provides a measurement method for detecting a discharge current from a charged object, a current probe unit for measuring the discharge current in contact with the charged object, and a detection display for measuring and displaying the output. A discharge current measuring device comprising a portion is provided.
The current probe section includes a current line, a current probe main body composed of a transformer, a winding, and a circuit element, a contact needle connected thereto by a connector, and a terminator connected by the connector. A current discharged when the contact needle is brought into contact with a charged object passes through the transformer through the current line, and then is discharged to GND through a resistor built in the terminator section. On the other hand, the output from the secondary winding of the transformer passes through the circuit element and is then sent to the detection display unit connected by a connector. After measurement, the display unit displays the peak value of discharge current and the amount of charge. , Energy values, etc. are displayed.

  The path through which the discharge current flows is a portion from the contact needle through the current line to the resistance of the terminator section, and is built in the probe body. This provides reproducible and stable measurements since it does not require the addition of new parts by the experimenter. In addition, for the high frequency characteristics required for measurement, the current line only passes through a transformer between the contact needle connector and the terminator connector terminal, and can be designed with a minimum length. . Therefore, the structure can minimize the generation of additional inductance L and capacitance C due to the length of the wire forming the current line, and provides a gigahertz band characteristic.

The discharge current is affected by the shape and deterioration of the contact needle. In the present invention, the contact needle is attached to a connector, and it is proposed that the contact needle be replaced and used as necessary. The shape of the contact needle can be changed from a needle shape to a rod shape to a circular shape according to the object. Further, it is possible to use a contact needle that has a built-in spring and absorbs an impact. As for the material, a conductive metal (copper, tungsten, brass, SUS, etc.) that is reliable and workable is used. Also, conductive ceramics having resistance may be used. These provide reproducible and reliable measurements. Further, the discharge current is affected by the current waveform and peak value due to the discharge resistance. In the present invention, the resistance of the terminator section can be exchanged with a connector, and the discharge resistance can be changed according to the necessity of the experiment, thereby providing an environment in which the influence of the discharge resistance can be measured.
As described above, according to the present invention, it is possible to select the condition of the contact needle and the resistance when detecting the discharge current, and propose a measurement under more realistic conditions.

  Further, in the present invention, the current probe portion is separated from the detection display portion from the connector portion and connected to an oscilloscope using a cable so that the current waveform can be observed. By this method, when it is necessary to measure an accurate current waveform, the measurement environment is provided so that it can be immediately handled by separating from the connector portion.

  The current probe unit of the present invention can be mounted on a circuit board using a connector. In the actual use of the circuit board, when a static electricity problem occurs, the current due to the discharge can be observed by connecting an oscilloscope to the previously mounted current probe unit. By using this method, it is possible to proceed with the analysis of the static electricity failure that has become a problem without changing the circuit board.

  Further, when detecting the discharge current from the human body, the shape of the contact needle of the current probe portion can be changed to a circular shape that can be easily touched by a human fingertip or the like. Accordingly, a human body discharge measuring apparatus that enables stable contact and has reproducibility is provided.

  As described above, when the discharge current measuring device of the present invention is used, the discharge current can be measured by contacting a charged conductive object. Thereby, the discharge from the charged device can be evaluated by the current value, and detailed information about the electrostatic breakdown of the device can be obtained. On the other hand, by evaluating the discharge from the tool such as a charged screwdriver by the current value, the danger when the tool contacts the device can be predicted. Furthermore, since the product of the present invention is small and easy to handle, it does not require specialized knowledge and can be used for general purposes by ordinary people.

  In addition, since the current waveform can be observed with an oscilloscope using an independent current probe, detailed information on the current waveform associated with the charged object and electrostatic discharge can be obtained, and the breakdown phenomenon of devices and other devices can be evaluated in more detail. It becomes possible to do. Furthermore, since the discharge resistance can be changed by replacing the terminator, it is possible to quantitatively evaluate the effects of resistance and contact resistance in the device.

  In addition, the discharge needle of the product of the present invention can be replaced, and when measuring the discharge current from the human body or the like, it is possible to appropriately evaluate human body discharge by adopting a shape suitable for human body contact. .

It is an external view which shows the whole structure of a discharge current measuring apparatus. It is a figure which shows the example which uses the apparatus of this invention. It is a block diagram which shows the inside of the current probe part of this invention. (A) is the internal cross section seen from the side, (b) is the internal cross section seen from the upper part. It is a figure which shows the circuit structure of this invention. It is a block diagram when measuring a discharge current waveform using the current probe part of this invention. It is a block diagram when mounting the current probe part of this invention on a board | substrate and measuring a current waveform. It is an external view of the integrated discharge current measuring apparatus of this invention. It is a figure which shows the example of a measurement when observing a discharge current waveform from the conventional charged object. It is a figure which shows the graph of the resistance change of the GMR head by discharge, and the example of a discharge current waveform. It is a figure which shows the usage example of the conventional current probe and current measurement. (A) is an external view of a conventional current probe. (B) is an example of use when a conventional current probe is used.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an external view showing an overall configuration of a discharge current measuring apparatus according to an embodiment of the present invention.
A discharge current measuring apparatus 1 shown in FIG. 1 is an apparatus for making contact with a charged object to generate electrostatic discharge and measuring a current peak value, a charge amount, and an energy value at that time. In this embodiment, a discharge current is measured. The measuring device 1 includes a current probe unit 2 and a detection display unit 3 and is connected by a connector 4. The current probe unit 2 includes a contact needle 5 and a connector 6, and a terminator 7 and a connector 8. The detection display unit 3 includes a power supply SW 9, a display unit 10 and a GND terminal 11.

  The current probe unit 2 is a device that contacts a charged object to generate electrostatic discharge, converts the discharge current by a transformer, adjusts frequency characteristics and sensitivity, and then sends them to a detection display unit. The contact needle 5 is a contact needle for contacting and discharging a measurement object, and is attached to the current probe unit 2 by a connector 6. Therefore, the connector 6 is used when changing the shape of the contact needle or when replacing due to deterioration. The terminator 7 has a built-in resistor 7a for passing the discharge current that has entered from the contact needle 5 to GND, and is attached to the current probe unit 2 by a connector 8. Therefore, when changing the discharge resistance during discharge, the connector 8 is replaced. Here, for example, when the resistance value is 0Ω, it indicates that there is no contact resistance. When the resistance value is set to the resistance value of the device, the discharge current when the device is contact-discharged can be tested.

The detection display unit 3 is a device that detects and displays a peak value from a signal sent from the current probe unit 2 via the connector 4. SW9 turns the power of the main unit on and off. The display unit 10 displays the peak value, and simultaneously displays the discharge polarity +, −, the current unit mA, and the like. The GND terminal 11 is configured to connect the terminal of the cable to an external GND in order to take the GND of the entire apparatus.
Here, the display unit may display a charge amount of the discharge current. At that time, a unit of charge C (coulomb), nC (nanocoulomb), or the like is displayed. Further, the energy value of the discharge current may be displayed. At that time, an energy unit J (joule), nJ (nanojoule) or the like is displayed.
The power supply SW 9 can also be used to switch the charge amount and energy value, which are the contents of display.

  The connectors 4, 6 and 8 each consist of a pair of male and female and are used to connect two parts. For example, in the contact needle, the female side of the SMA connector is used for the main body, and the contact needle is attached to the male side. The type of connector used here can be selected from the viewpoint of the transmission frequency band, size, and ease of use.

  A basic measurement example using this measuring apparatus is shown in FIG. The measurement table 51 is connected to GND and serves as a measurement reference. There is a charged body 52 arranged on the measurement table 51. A device 53 to be a measurement object is placed on the charged object. In such an arrangement, the measurement object is inductively charged by the electrostatic field from the charged object. When the contact needle 5 of the discharge current measuring device 1 according to the present invention is brought close to and in contact with the measurement object in this state, the discharge current flows at the moment of contact, and the GND terminal 11 passes through the resistor 7a built in the terminator 7. It flows to. The peak value of the discharged discharge current is displayed on the display unit 10.

  Here, for example, the measurement object 53 may be a conductive object that stores charges. Furthermore, the measurement object may be a human body. Further, the shape of the contact needle 5 is not a needle shape, and may be a rod shape or a circle shape that is easy to contact an object, or may be an arbitrary shape that is safe for human contact. The contact needle 5 is made of a conductive metal (such as copper, tungsten, brass, or SUS) or conductive ceramics. Moreover, the structure of the contact needle 5 may include a spring or the like that has elasticity. Further, the environment in which the measurement object is placed is not limited to a charged object. For example, the measurement object may be placed at any place on the production line or suspended.

FIG. 3 shows the configuration of the current probe unit 2. 3A is an internal cross-sectional view seen from the side, and FIG. 3B is an internal cross-sectional view seen from the top. The discharge current entered from the contact needle 5 passes through the current line 22 and flows to the GND via the resistor 7a built in the terminator 7. The current line 22 passes through the central hole of the cylindrical magnetic core 21, and the discharge current generates magnetic flux in the magnetic core by magnetic coupling. A secondary winding 23 is wound around the magnetic core 21, and a current corresponding to the number of turns is generated by magnetic coupling. The frequency characteristic and sensitivity of the secondary current are adjusted by the correction circuit 24 and then sent to the detection display unit 3 by the connector 4.
The case 2a of the current probe portion 2 is made of metal, has a shielding effect to the inside of the current probe, and serves as the GND of the connector.
Here, the current line 22 may wind an arbitrary number of turns around the magnetic core 21. Further, the magnetic core may have a polygonal shape instead of a cylinder.
Further, the correction circuit 24 may be provided inside the detection display unit 3.

  FIG. 4 shows a circuit configuration. The discharge current I1 (25) entering from the contact needle 5 flows through the current line 22 and through the resistor 7a of the terminator 7 to GND. Here, the current line 22, the magnetic core 21, and the winding 23 form a transformer 20 by magnetic coupling. The discharge current flowing in the current line 22 generates a secondary current corresponding to the current value in the winding 23 by magnetic coupling. Assuming that the number of turns of the current line 22 is n1 and the number of turns of the winding 23 is n2, a current I2 (26) is generated in the secondary winding 23 by the relationship of n1 × I1 = n2 × I2. This current I2 becomes a voltage output by the load resistor R24a in the correction circuit and is sent to the detection display unit 3. Here, the correction circuit is a circuit network including an inductance, a resistor, and a capacitor (not shown), and is a circuit for correcting the frequency characteristics of the current probe flatly and determining a use band. The load resistor R24a due to provides a voltage output proportional to the input current.

  The detection display unit performs peak detection 31 from the waveform of the voltage output sent from the current probe unit, and the output is sent to the AD conversion / CPU 32. After being digitized and measured by the AD conversion / CPU 32 and converted to an input current value, the peak value of the input current is displayed on the display unit 10 together with the polarity +, − and the unit mA. Here, the total charge amount discharged can be calculated and displayed by bypassing the peak detection circuit and time-integrating the current value from the current waveform by the AD conversion / CPU 32. Further, the AD conversion / CPU 32 can perform I2R time integration from the resistance 7a of the terminator 7 and the current waveform, and the generated discharge energy amount can be calculated and displayed.

  FIG. 5 shows an example in which the current probe unit 2 according to the present invention is used as an independent discharge current probe. A signal output from the current probe unit 2 is connected to the oscilloscope 57 by a coaxial cable 57 a connected to the connector 4. By making such a connection, the discharge needle 5 is brought into contact with the charged object, and the waveform of the discharge current generated at that time can be observed with an oscilloscope.

  FIG. 6 shows a configuration when the current probe unit 2 is mounted on a substrate and used as a current probe. In the circuit board 58, a current probe portion is mounted in advance by a connector at a portion where current is to be measured. In this case, the connectors 6 and 8 are used as current measurement terminals and mounted on the circuit board. The current that enters the current probe from the circuit board by the connector 6 goes out from the connector 8 to the circuit board. The output is observed by an oscilloscope 57 via a coaxial cable 57a connected to the connector 4. When the oscilloscope is not connected for this purpose, connect a 50Ω terminator to the connector 4 in advance, for example, corresponding to the characteristic impedance of the coaxial cable and the termination resistance of the oscilloscope. There is no change in impedance due to observation, and accurate measurement is possible.

  FIG. 7 shows the appearance of the integrated discharge current measuring apparatus of the present invention. Here, the current probe unit and the detection display unit are integrated, and the current entered from the charged object by the contact needle 5 flows to the GND through the built-in resistor through the current path. After being converted by the transformer of the current probe unit, it is calculated by the detection circuit, and the peak current value is displayed by the display unit. With such a configuration, the current line, the transformer, and the resistor are built in, and the connection with the connector is unnecessary, and the current line can be designed to be short. As a result, it is possible to reduce the generation of inductance and obtain good high frequency characteristics. In addition, the present invention enables simple handling and cost reduction by being integrated.

    DESCRIPTION OF SYMBOLS 1 ... Discharge current measuring device, 2 ... Current probe part, 2a ... Current probe part case, 3 ... Detection display part, 4 ... Connector, 5 ... Contact needle, 6 ... Connector, 7 ... Terminator 7a ... resistor, 8 ... connector, 9 ... SW, 10 ... display, 11 ... GND terminal, 12 ... power supply, 20 ... transformer, 21 ... magnetic core, 22 ... current line, 23 .. Winding, 24... Correction circuit, 24 a ....... Load resistance R, 25... Discharge current I 1, 26... Secondary side current I 2, 31. ... Display circuit, 51 ... Measurement table, 52 ... Charge, 53 ... Device, 54 ... Discharge needle, 55 ... Discharge current, 56 ... Current probe, 56a ... Through hole, 56b ... Current line, 56c ... Board, 56d ... Connector, 57 ... Oscilloscope, 57a ... Same Cable, 58 ...... circuit board

Claims (4)

  A discharge current measuring device having a contact needle for making contact with a charged object, a current line connected to the contact needle, and a resistor connected to the current line and discharging to GND, on the primary side of the magnetic core Means for measuring the discharge current waveform and displaying the peak value, charge amount, and energy value by providing a transformer configured to obtain the secondary current by the current line through which the discharge current flows and the secondary winding of the magnetic core A discharge current measuring apparatus comprising:   The discharge current measuring device includes the current probe from the contact needle, the resistance, a current probe unit provided with the transformer, and a detection display unit that measures and displays a discharge current waveform, and the current probe unit The detection display unit is connected by a connector, and when separated from the connector, the current probe unit can be used as an independent current probe. apparatus.   The current probe section is characterized in that the shape of the contact needle, a connection connector that can exchange a conductive material, and a connection connector that can exchange a terminator incorporating the resistor are provided. Discharge current measuring device.   As the form of the discharge current measuring device in the previous period, the current probe part and the detection display part are integrated, the current line and the resistor are built in, and it is possible to respond to high frequency by reducing the generation of inductance, and simple Discharge current measuring device characterized by a structure that enables easy handling and cost reduction.