In order to evaluate the anti-static discharge capability of electronic equipment and systems, IOS 17626.2-2006 is a new standard issued by my country. Among them, the purpose of the test is to test the immunity of the equipment or system to external electrostatic discharge, and ESD immunity test> has two discharge methods to choose from, namely contact discharge and air gap discharge . Contact discharge is the preferred form, but air-gap discharge is only used when there are insulating coatings on surfaces, gaps in computer keyboards, etc. At the same time, IOS17626.2-2006 also considers indirect discharge, including horizontal coupling and vertical coupling.
During Electrostatic Discharge Immunity Test>, The laboratory requires that the ground reference plane be set up for air discharge tests. The ground reference plane should be a thin copper or aluminum metal plate with a minimum thickness of 0.25mm. The outer edge of the coupling plate is at least 0.5m. The size of the ground reference plane and the thickness of the metal material should also be regulated by the ambient temperature (15°c~35°c), relative humidity (30%~60%) and atmospheric pressure (86kPa~106kPa). The coupling plate should also be of the same metal and thickness, and a cable with a 470kΩ resistor attached to it should be connected to the ground reference plane to resist the discharge voltage and prevent the accumulation of electrostatic charges. During the laboratory air discharge test, attention should also be paid to the climatic conditions to ensure that the temperature, humidity and atmospheric pressure are within acceptable ranges.
For the direct application of electrostatic discharge to the equipment under test, unless there are requirements in the general standards, product standards, and class standards, the scope of the applied discharge should be controlled, especially when it can be released by the user during normal use. On the circuit components, targeted simplification measures can be adopted and clearly indicated in the document. In addition, since some points and surfaces are only touched during repair or maintenance, they should be handled with different discharge simplifications to prevent damage to the equipment. In addition, in the electrostatic discharge immunity test, it is necessary to gradually increase from the minimum voltage value to the selected test voltage value to determine the critical point of failure, and the final test value should not exceed the maximum value specified by the equipment, so as to avoidavoid damage to the equipment under test.
In order to determine whether the system is malfunctioning, it is necessary to perform an electrostatic discharge immunity test> on the system. The operating procedures of the test generally include: single discharge, discharge point selection, discharge generator location, discharge distance and discharge method, etc. First of all, the test should be carried out in the form of a single discharge. At the pre-selected point, at least 10 single discharges (the most sensitive polarity) should be applied, and it is recommended that the time interval between single discharges be at least 1s; The discharge generator should be perpendicular to the physical medium of the current operating discharge to ensure the repeatability of the test results; in addition, in order to reduce the damage to the equipment under test, the distance between the generator and the object implementing the discharge should be kept at least 0.2m; Finally, for objects painted on the surface, the discharge method should be selected according to the requirements of the equipment manufacturer: if it is not specified that the coating film is an insulating layer, it is necessary to penetrate the paint film so that the electrode tip of the generator contacts the conductive layer; otherwise, then Only air discharge is required, no contact discharge test is required. After each discharge, the discharge electrode should be removed, and then the generator should be retriggered for a new single discharge after waiting for the time interval to complete the entire discharge test process.
When using ungrounded equipment, in order to ensure that the charge is not affected before the electrostatic discharge pulse, the equipment under test must not be allowed to discharge itself. A single ESD can be simulated in two ways: by removing the charge on the EUT before each ESD pulse is applied, or by allowing successive discharges to be separated by a time interval greater than the time required for the EUT's charge to naturally decay. Furthermore, charge decay on the EUT can be influenced by using a ground cable with bleeder resistors and carbon fiber brushes. If the use of such a grounding cable by some EUT becomes controversial, it is best to disconnect this cable before applying the ESD pulse. To better simulate a single ESD, the above points should be kept in mind when testing ungrounded devices.
How the results of the electrostatic discharge immunity test> are classified
The performance level of the tested equipment can be determined according to the limit value of the manufacturer, commissioner or purchaser, or It is determined by negotiation between the manufacturer and the purchaser. According to the damage degree of the equipment under test in the electrostatic discharge test, the test results are divided into four categories: a) normal performance; b) temporary function and performance reduction, which will automatically recover after the discharge stops; c) temporary function and performance reduction, Requires varying degrees of manual intervention to restore; d) Unrecoverable degradation of functionality and performance due to hardware or software damage. In addition, the classification standard shall be subject to the agreement of the manufacturer, consignor or purchaser.