There are various causes of electrostatic discharge, but GB/T17626.2-2006 mainly describes that in the case of low humidity, through friction and other factors, the human body accumulates an electric charge. When a person with an electric charge comes into contact with equipment, an electrostatic discharge may occur.
Causes of electrostatic discharge:
1, the purpose of the test:
2, test the ability of a single piece of equipment or system to resist electrostatic interference. It simulates:
(1) the discharge of an operator or object in contact with the equipment.
(2) the discharge of a person or object to neighboring objects.
The following are possible consequences of electrostatic discharges:
(1) Damage to semiconductor devices caused directly by energy exchange.
(2) Changes in electric and magnetic fields caused by the discharge, resulting in equipment malfunction.
3, discharge mode:
(1) direct discharge (discharge directly to the equipment): contact discharge is the preferred form; only in places where contact discharge can not be used (such as the surface coated with an insulating layer, the computer keyboard gap, etc.) before switching to air gap discharge.
(2) indirect discharge: horizontal coupling, vertical coupling
Test Methods:
1, there are two types of tests (in the laboratory) and installation site test, the standard specifies that the former is the main. The test is generally 1 / s rate of discharge, so that the equipment on the test has not had time to respond to the other formal test before the discharge rate of 20 / s rate of discharge, on the surface of the test equipment quickly scanned once, in order to find out the equipment on the electrostatic discharge sensitive parts. Test voltage should be from low to high gradually increased to the specified value.
3, electrostatic discharge in the usual can be used to touch the point. Test used:
(1) a single discharge. (2) Discharge between the selected point and the ground. (3) At least 10 discharges (positive or negative polarity) on each point. (4) At least 1 second between two adjacent discharges When selecting a discharge point, the discharge is performed at a rate of 20 discharges per second, focusing on finding points that may be sensitive to electrostatic discharge. For discharges between neighboring objects, they can be simulated by discharging a metal plate (1250px x 1250px) near the butt floor and the specimen (250px apart).
Laboratory test configuration and climatic environment:
(1) The floor of the laboratory shall be provided with a grounding reference plane, which shall be a sheet metal of copper or aluminum with a minimum thickness of 0.25mm, although other metallic materials may be used they shall have a thickness of at least 0.65mm. The minimum size of the grounding reference plane 1m?, the actual size depends on the size of the test equipment, and each side should be at least 0.5m outside the test equipment or coupling plate, and connect it with the protective earthing system. The distance between the test equipment and laboratory walls and other metallic structures shall be a minimum of 1 m.
(2) Provide that where coupling plates are provided, for example, where indirect discharges are permitted, these plates are of the same metal and thickness as the earth reference plane, and that each break of cable with a 470 kΩ resistor is connected to the earth reference plane, and that when the cable is placed on the earth reference plane, these The resistors shall withstand the discharge voltage and be well insulated to avoid short-circuiting to the ground reference plane and also to prevent the accumulation of electrostatic charges.
(3) Climatic conditions: In the case of an air discharge test, the climatic conditions shall be within the following ranges:
(4) Ambient temperature: 15°C to 35°C Relative humidity: 30% to 60% Atmospheric pressure: 86kPa to 106kPa
Discharge applied directly to the equipment under test:
(1) Unless otherwise provided for in the General Standard, Unless otherwise specified in the general standards, product standards, product category standards, electrostatic discharge is applied only to points and surfaces on the test equipment that can be discharged by personnel during normal use. The following are exceptions (i.e., the discharge is not applied to the following points):
(a) Points and surfaces accessible only during maintenance. In this case, the specific simplified method of electrostatic discharge shall be indicated in the documentation.
(b) Points and surfaces that are accessed during end-user maintenance, these rarely accessed points, such as batteries accessed during battery changes, tapes in recorded telephones, etc.
(c) Points and surfaces that are no longer accessible after the equipment has been installed and secured or used in accordance with the instructions for use, e.g., the underside and the wall side of the equipment or the area behind the mounting terminals.
(d) Points accessible to coaxial connectors and multiconductor connectors with metal shells. In this case, a contact discharge is applied to the connector's shell only. Accessible points within non-conductive (e.g. plastic) connectors shall be subjected to an air discharge test only.
(2) In order to determine the critical point of failure, the test voltage shall be gradually increased from the minimum to the selected test voltage value, and the final test value shall not exceed the product specification value in order to avoid damage to the equipment.
(3) The test shall be conducted as a single discharge, with a minimum of ten single discharges (of the most sensitive polarity) applied at preselected points.
(4) The time interval between consecutive single discharges is recommended to be at least 1s, but longer intervals may be necessary to determine if the system has failed. NOTE: The discharge point is selected by trial testing at a discharge repetition rate of 20 discharges/s or more.
(5) The electrostatic discharge generator shall be kept perpendicular to the surface on which the discharge is applied to improve the repeatability of the test results.
(6) The distance between the discharge circuit cable of the generator and the subject equipment shall be maintained at least 0.2 m when the discharge is applied.
(7) In the case of a contact discharge, the tip of the discharge electrode shall be in contact with the subject equipment prior to operation of the discharge switch.
(8) In the case of painted surfaces, the following operating procedure shall be used:
(9) If the equipment manufacturer does not specify that the painted film is an insulating layer, the electrode tip of the generator shall be penetrated into the painted film in order to contact the conductive layer, and if the manufacturer specifies that it is an insulating layer, only air discharge shall be performed, and such surfaces shall not be subjected to contact discharge tests.
(10) In the case of air discharges, the circular discharge head of the discharge electrode shall approach and touch the equipment under test as quickly as possible (without causing mechanical damage). After each discharge, the discharge electrode shall be removed from the test equipment and the generator shall be retriggered for a new single discharge, and this procedure shall be repeated until the discharge is complete.
Test methods for ungrounded equipment:
(1) Ungrounded equipment or ungrounded parts of equipment shall not discharge themselves as in the case of Class I powered equipment. If the charge is not removed before the next electrostatic discharge pulse is applied, the accumulation of charge on the equipment under test or on the components of the equipment under test may make the voltage twice the expected test voltage. As a result, the insulator capacitance of the double insulated equipment may be charged to an abnormally high level after several electrostatic discharge accumulations, and then discharged at the insulation breakdown voltage with high energy.
(2) To simulate a single electrostatic discharge (air gap discharge or contact discharge), the charge on the equipment under test shall be removed prior to the application of each electrostatic discharge pulse.
(3) The capacitance between the test equipment and the horizontal coupling plate (bench-top) and between the test equipment and the grounded reference plane (floor-mounted) depends on the size of the test equipment. Electrostatic discharge test, if the function allows, should be installed with the discharge resistance of the cable. One resistance of the discharge cable should be as close as possible to the test point of the equipment under test, preferably less than 20mm, and the second resistance should be close to the end of the cable, the cable for benchtop equipment is connected to the horizontal coupling plate, for vertical equipment the cable is connected to the reference plane.
(4) Note: The presence of a cable with a discharge resistor can affect the test results for some devices, and when in dispute, if the charge can be effectively attenuated between successive discharges, the test with the cable disconnected when an electrostatic discharge pulse is applied is preferred to the test with the cable connected
The following choices can be used as alternatives:
(1) The time interval between successive discharges should be longer than the time required for the natural decay of charge on the device under test. The time required for the charge to decay naturally
(2) Use of a grounding cable with a discharge resistor and carbon fiber brushes (e.g., 2 x 470 KΩ)
Results of electrostatic discharge immunity tests
(1) The results of the tests shall be classified on the basis of loss of functionality or degradation of the performance of the equipment subjected to the tests. The relevant performance level shall be determined by the manufacturer of the equipment or the demand side of the test, or agreed upon by the manufacturer and the purchaser of the product. It is recommended that the classification be based on the following requirements:
a) Normal performance within the limits specified by the manufacturer, commissioner, or purchaser
b) Temporary loss or degradation of function or performance that recovers on its own after the harassment has ceased, without operator intervention;
c) Temporary loss or degradation of function or performance that recovers with operator intervention;
d) Loss of function or degradation of performance as a result of loss of function or degradation of performance that cannot be recovered due to damage to the hardware or software of the device, or loss of data.