How to prevent ESD damage in electronics
Prevention
of ESD bases on Electrostatic Protective Area (EPA). EPA can be a small working
station 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. International
standards are used to define typical EPA and can be found for example from
International Electrotechnical Commission (IEC) or American National Standards
Institute (ANSI).
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. Humid conditions prevent electrostatic charge generation
because the thin layer of moisture that accumulates on most surfaces serves to
dissipate electric charges.
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. On aircraft, static dischargers are used on the
trailing edges of wings and other surfaces.
Manufacturers and users of integrated circuits must take precautions to avoid
ESD. 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 can not 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 1012 ohm-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.