ESD Testing Machine and ESD Test: An Overview of the Technology Standards and Procedures

In order to assess the electrostatic discharge (ESD) immunity of electronic devices and systems, GB/T17626.2-2006 is a newly released standard in China. The ESD test is intended to examine the disturbance immunity of devices or systems to external ESD, and there are two discharge methods for ESD immunity testing, contact discharges and air-gap discharges. Contact discharges are preferred, but only air-gap discharges are used in cases such as on surfaces coated with insulation layers and computer keyboard gaps. At the same time, GB/T17626.2-2006 also takes into account indirect discharges, including horizontal coupling and vertical coupling.

When performing ESD testing machine, the laboratory requires air-discharge tests to be performed using a grounded reference plane setup. The grounded reference plane should be an ultra-thin metal sheet of copper or aluminum with a minimum thickness of 0.25mm, and its size should be at least 0.5m beyond the edges of the specimen device or coupling boards. The size of the grounded reference plane and the thickness of the metal material should be adjusted according to the environment temperature (15°C to 35°C), relative humidity (30% to 60%), and atmospheric pressure (86kPa to 106kPa). The coupling boards should also use the same metal and thickness, and a cable with a 470kΩ resistor is taped on top and connected to the grounded reference plane in order to resist the discharge voltages and to prevent the accumulation of electrostatic charges. During the laboratory’s air-discharge test process, climate conditions should also be taken into consideration to ensure that the temperature, humidity, and atmospheric pressure are all within acceptable ranges.

ESD61000-2_Electrostatic Discharge Simulator

For direct application of ESD to a specimen device, unless otherwise specified in a general standard, a product standard, or a class standard, the scope of application for ESD should be controlled, especially on circuit components that can be released by users during normal use, and specific simplification measures should be taken and clearly indicated in the documents. In addition, since some points and surfaces can only be exposed during maintenance or maintenance, different discharge-simplification measures should be taken to prevent damage to the equipment. In addition, during ESD test, discharge voltage should be gradually increased from minimum to the selected test voltage to identify the fault critical point, and the final test value should not exceed the maximum value specified by the device, thus avoiding damage to the specimen device.

In order to determine if a system is faulty, ESD test needs to be performed on the system. The operation procedure for the test typically includes single-pulse discharges, discharge-point selection, location of the discharge generator, discharge distance, and discharge mode. Firstly, the test should be performed in single-pulse mode, and at the preselected points, at least 10 single-pulse discharges should be applied (at the most sensitive polarity), and it is recommended that there should be a time interval of at least 1s between each single-pulse discharge; secondly, the ESD testing machine should be perpendicular to the physical medium currently in operation for discharge in order to ensure the repeatability of the results; in addition, to reduce the damage to the specimen device, the distance between the generator and the object being discharged should be at least 0.2m; finally, for objects surfaces with paint, the discharge mode should be selected according to the requirements of the equipment manufacturer; if the film is not stated to be an insulation layer, penetration of the film should be performed to make the electrode head of the generator and the conductive layer contact; on the other hand, only air-discharge is required without contact-discharge testing.

After each discharge, the discharge electrode should be moved away and then a new single-pulse should be triggered by the generator again after the time interval to complete the entire discharge-testing process.

For non-grounded devices, in order to ensure the charge on the device is not affected before the ESD pulse, thedevice cannot self-discharge. There are two ways to simulate single ESD discharge: eliminating the charge on the specimen device before each ESD pulse or let the time interval of continuous discharges be greater than the time required for the charge on the specimen device to naturally attenuate. Besides, the charge attenuation on the specimen device can be affected by using a grounding cable with a discharge resistor and carbon fibers brush. If there is any dispute on the application of such grounding cable for certain specimen devices, the cable should be disconnected before the ESD pulse is applied. To better simulate the single ESD discharge, the above points should be taken into consideration when testing non-grounded devices.

How can the results of ESD test be categorized?
The performance level of the specimen device can be determined according to the limit value of the manufacturer, the principal or the purchaser, or it can be determined by the manufacturers and the purchasers by consultation. According to the degree of damage of the specimen device under the ESD test, the results of the test can be divided into four categories: a) normal performance; b) temporary functional and performance reduction which can recover automatically after the discharge stops; c) temporary functional and performance reduction which needs different levels of manual intervention in order to recover; d) functional and performance reduction which cannot be recovered due to either hardware or software damage. In addition, the classification criteria should be in accordance with the consensus of the manufacturer, the principal or the purchaser.