Electrostatic discharge (ESD) is one of the main reasons for the destruction and subsequent
rejection of electronic circuits during their manufacture or installation in other devices. The
most susceptible elements to damage are oxide layer transistors, where the ESD current makes
a conductive path through the oxide.
The purpose of this work is to choose the appropriate protection and equipment for the
production line, on which the electronic circuits are installed in the motor housing. Adequacy
of protection and equipment must then be checked by measuring resistance and susceptibility
to electrification. However, the justification for protection must be proven with a sufficiently
quick recovery of the investment in protective equipment.
Electrostatic discharge occurs between two surfaces between which there is a sufficiently high
voltage or strength of the electrostatic field. The closer the two surfaces are, the less charge is
required for discharge. The distance and amount of charge at which discharge occurs also
depend on the material between the surfaces. In the production area this material is air.
Discharges in the production area are in an inhomogeneous field, because air is an
inhomogeneous substance. Discharge path is defined through streamers and leaders. An
approximation of the discharge for testing the durability of components can easily be achieved
with an RLC circuit, the parameters of which are determined according to the standard for
models of human body, machine and charged device.
The area, where protection is introduced and where we can handle electronic circuits, is called
ESD protected area (EPA). All equipment in this room, including the persons, must be
grounded. The equipment includes floors, work surfaces, machines, hand tools, packaging and
office material intended for the organization of work. Most equipment is grounded with a
conductor connected to the building's grounding point. Objects that cannot be grounded with a
conductor are made of conductive material and are grounded via a conductive work surface
which is grounded with a conductor. All equipment and EPA must be properly marked with
warning signs or markings on the equipment. The basic ESD symbol is a yellow hand in a black
triangle under a dome on a yellow background. In addition to grounding, we can also protect
electronic circuits with ionizers that blow positively and negatively charged air particles onto
the protected surface. Ionizers use the phenomenon of corona and can work on alternating
current, pulsating or constant direct current. Another type of ionizer utilizes the radioactive
decay of an element that emits alpha particles that ionize air particles.
Protective equipment must be regularly checked to see if it is still suitable for use.
Measurements are performed at monthly, on half-year or annual intervals. Every element of
ESD protection must be checked. We measure the resistance to the ground, work surface,
packaging, garments and grounding connections. Where possible, both surface and volume
resistivity must be measured. For flooring, we also measure charging of a person while walking.
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When measuring ionizers, we check the speed of discharging a charged surface and the
uniformity of the production of positive and negative ions.
The measurements showed that chosen protection is acceptable. Investments in protective
equipment are returned in short period of time. On this production line the investment is
returned in 31 working days.
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