ELECTROSTATIC DISCHARGE (ESD)
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How electrostatic charges occur
Electrostatic charging occurs when there is an excess of electrons (negative charge) or a lack of electrons (positive charge) at a material surface. This charge imbalance is produced by rubbing together and separating two insulators that are in contact with each other (static electricity) or when a body is exposed to an electric field (influence).
If the surfaces of two non-conductive materials touch each other, they exchange electrons, e.g. a glass rod (+) with a leather cloth (−) or plastic (−) with a woolen cloth (+). When these surfaces are suddenly separated, the charge that transfers remains on the object. A very strong electric field is produced between the oppositely charged surfaces. This is what makes your hair stand on end and attracts dust and fluff, and is also termed static electricity. The extent of the charge depends in particular on the materials’ tendency to become charged and the relative humidity of the environment.
When antistatic and electrically conductive surfaces rub against each other and are separated, the charges are dissipated and flow back to their original location. The surfaces do not become electrostatically charged.
Electrostatic discharge (ESD)
When charged and conductive objects are insulated from ground, this may lead to spark discharge. The sparks have a high voltage (up to 30,000 volts) and are perceived as an impulse (electric shock). This is why it is extremely important to dissipate electrostatic charges in a controlled manner, for example from machine and equipment glazing. This is done by correct grounding of the conductive glazing to a grounding point, which ensures that static charges are correctly dissipated by the glazing and provides genuine ESD protection.
Damage through electrostatic discharge
Objects made from insulators such as plastic or paper may become charged by friction during operational contact and separation procedures. Filling liquids into or out of containers, handling gaseous substances, and filtration, grinding and micronizing processes involving bulk materials are especially hazardous as regards electrostatic charging.
Areas where electrostatic discharge poses a particular risk for the long-term function of the end product (e.g. car electronics and medical technology) are the production of electronic parts and the manufacture of semiconductors and printed circuit boards.
Discharges with a voltage of less than 100 volts are enough to damage sensitive components like integrated circuits, light-emitting diodes and semiconductor lasers. The damage that is effectively caused cannot be detected by the naked eye. Humans only perceive ESD from a voltage of 3,000 volts. So the risk of ESD is not apparent. In areas with a risk of explosion, it is of the utmost importance to avoid ignition hazards resulting from uncontrolled electrostatic discharge. Where there are explosive dusts, vapors or gases, the spark energy caused by electrostatic discharges may be strong enough to trigger an explosion. A voltage of 50 V is enough to produce a spark.
DIN EN 61340-5-1: “Protection of electronic components from electrostatic phenomena” describes measures to prevent electrostatic discharge. The surface resistivity of materials is the crucial factor. This decides whether a surface becomes charged, whether the charge remains on the surface and causes static charging. High surface resistivity encourages charging, whereas low resistivity causes the charge to dissipate. Measures against electrostatic charging are only effective if the corresponding materials and items are electrostatically grounded (resistance to ground < 108 ohms), enabling controlled dissipation of the charge.