Materials and plant-including people-acquire and accumulate electrostatic charge during normal activity. The electric field produced at the surface of such a charged body or layer can exceed the normal electric strength of the ambient medium and so produce an electrical discharge. Injection of the suddenly released electrical energy into an electronic device can lead to catastrophic failure.
Here are some methods of protection during manufacture of an electronic device and during its use from electrostatic discharge. The effects electronic systems will suffer from an electrostatic discharge largely depend on its size and altitude. Essentially, anything that can operate on a charge or on batteries when not plugged into an AC outlet is likely to be spared.
If the device is kept away from other large metal objects and large swaths of wiring, it should remain relatively unharmed. Some electronics are inherently electrostatic discharge-proof, including large electric motors, vacuum tube equipment, electrical generators, transformers and relays, and other large systems often housed in surge-resistant housing. Ultimately, it’s all about how you insulate and shield our electronic devices.
Protection during manufacture: In manufacturing, prevention of ESD is based on an Electrostatic Discharge Protected Area (EPA). The EPA can be a small workstation or a large manufacturing area. The main principle of an EPA is that there are no highly-charging materials in the vicinity of ESD sensitive electronics, all conductive materials are grounded, workers are grounded, and charge build-up on ESD sensitive electronics is prevented.
ESD prevention within an EPA may include using appropriate ESD-safe packing material, the use of conductive filaments on garments worn by assembly workers, conducting wrist straps and foot-straps to prevent high voltages from accumulating on workers’ bodies, anti-static mats or conductive flooring materials to conduct harmful electric charges away from the work area, and humidity control.
Ion generators are sometimes used to inject ions into the ambient airstream. Ionization systems help to neutralize charged surface regions on insulative or dielectric materials. Insulating materials prone to triboelectric charging should be kept away from sensitive devices to prevent accidental charging of devices through induction. ESD prevention can be part of the device itself and include special design techniques for device input and output pins. External protection components can also be used with circuit layout.
Due to dielectric nature of electronics component and assemblies, electrostatic charging cannot be completely prevented during handling of devices. Most of ESD sensitive electronic assemblies and components are also so small that manufacturing and handling is done with automated equipment. ESD prevention activities are therefore important with those processes where components come into direct contact with equipment surfaces.
In addition, it is important to prevent ESD when an electrostatic discharge sensitive component is connected with other conductive parts of the product itself. An efficient way to prevent ESD is to use materials that are not too conductive but will slowly conduct static charges away. These materials are called static dissipative and have resistivity values in the range of 105 to 1012ohm-meters. Materials in automated manufacturing which will touch on conductive areas of ESD sensitive electronic should be made of dissipative material, and the dissipative material must be grounded.
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