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esd grounding cord

May 25, 2018

What does the esd grounding cord effect on electrostatic protection?


The grounding provides a good discharge path for electrostatic shock, which allows the static charge accumulated on the charged body to be released smoothly and quickly led into the earth to avoid discharge of sensitive components. The effect of the grounding effect directly affects the effect of the entire electrostatic protection. If the grounding effect is poor, the entire anti-static system will fail, and the product will be in a state of static electricity. Only from the test discharge point to the final ground connection point All links are kept open to ensure safe discharge of static electricity. IEC1340-5-1 regulates the grounding resistance. The domestic aerospace industry standard QJ1950-90 also has similar provisions. Considering that the grounding resistance in the production and use places of the electronic industry should be less than 10, the grounding line must be firmly connected and sufficient. The mechanical strength, otherwise it may generate sparks in the loose part, fixed equipment grounding wire should be more than 1.25mm2 flexible stranded wire, ground wire to provide anti-static wrist strap, floor and table surface.

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As the most active factor in the ESD process, operators entering the EPA environment must wear anti-static clothing, wear wristbands, and must have anti-static mats on their workstations. Anti-static wrist straps may be referred to as "putting on" electrostatic wrist straps that are more appropriate. The wrist straps and table mats provide a clear path for static electricity to reach the earth, allowing the wearer to approach zero volts. For people with frequent activities, static electricity should be released through anti-static shoes, socks, and straps on the heel and toes to communicate with static dissipative floors. If only from the perspective of "discharging" static electricity, the human body's resistance to ground is as small as possible, but considering the safety factor, the human body must have a certain resistance to earth, in case the metal device or device is shorted to the commercial frequency power supply, The resistance can limit the current flowing through the body of the operator, so usually a resistance of not less than 1M is to be connected in series at the connection between the wristband, the toe strap and the grounding conductor.


The static charges on insulators such as ordinary plastics cannot be electrostatically eliminated by grounding, but they can be neutralized with charges of opposite polarity. The ionizer, which is often used today, when its tip is close to a charged body, induces a charge on the tip opposite to the static polarity of the electrified body and forms a strong electric field near the tip, on the spot. Above 25-30 KV/cm, the air corona discharges, generating positive and negative ions, and the anisotropic ions move to the charged body under the action of the electric field, so that any charge accumulation that may occur on the surface of the insulator can be continuously neutralized.


Moderate control of environmental temperature and humidity can also effectively curb the lethality of static electricity. Humidity and temperature affect ESD. In the same atmospheric environment, the relative humidity is higher in the lower temperature region than in the higher temperature region, and the increase in humidity increases the surface conductivity of the non-conductor material. Enhanced, the static charge accumulated on the object can leak more quickly. The lower the ambient temperature is, the higher the humidity is, and the more favorable the protection against static electricity is. Therefore, when the process conditions permit, you can use air-conditioning humidifier, fan sprayer spray water mist, ground water and other methods to increase the relative humidity of the air and reduce the harm of static electricity. Of course, excessive humidity will lead to short-circuit and leakage faults in the product. Generally, the temperature should be controlled within the range of 18 to 28°C and the humidity should be controlled within the range of 40 to 65% RH.