ELECTROSTATIC DISCHARGE (ESD) PROCESS AND PROTECTION

Thursday, July 14, 2011

Electrostatic Discharge (ESD) is a form of an impulsive transient exhibited by the rapid and momentary flow of electrostatic charge two things that are at different potentials. Generally, this sudden discharge of static electricity does not harm the human body, but it can create several problems such as damaged electronic components, equipment downtime, safety concerns and material handling issues in the manufacturing and production facilities. 

Also, it is possible for electronic devices to be damaged by an electrostatic discharge that is unnoticeable to the human body. As a result, ESD has become one of the major causes of device failures in the semiconductor industry and lead to financial losses and other quality problems. ESD’s potential hazards can’t be totally eliminated, thus, prevention and protection against it is necessary and very important.

Electrostatic Discharge (ESD)
Electrostatic Discharge (ESD)
ESD Process

Electrostatic charge build-up takes place as a result of an imbalance of electrons on the surface of a material. The charge build-up produces an electric field that has measurable effects on other things at a distance.  The process of electron transfer due to two objects coming into contact with each other and then separating is known as triboelectric charging. Subsequently, one object gains electrons on its surface, and therefore becoming negatively charged, and the other object becomes positively charged by losing electrons from its surface. A person can get triboelectrically charged in a number of ways, even by just walking across a room.

Countermeasures and Control

Electrostatic Discharge prevention and control are readily available. They range from the simple and basic passive discharge and grounding methods to the active continuous monitoring technology with Windows-based software feedback. However, the application of such countermeasures are dependent on the particular situation, such as if you have a clean room or not, the acceptable level of risk and investment or cost.

Passive Countermeasures

a. Wrist straps

It has a built-in resistor to prevent current flow, and may come with a ground cord to make sure that static electricity is provided with a proper exit from the production facility.

b. Air Ionizers

They are used to blow a stream of ionized air inhibiting the accumulation of static charges in a certain location. A variation of this method is the ionized air gun, which uses clean, dry air or nitrogen with antistatic technology to loosen the particles by neutralizing the static charge and then blows those particles away.

c. Sole Grounders (fitting over shoes)

Static charges are released into the ground, instead of building up. The best types are utilized with a conductive floor material so that the electrical charges can be dissipated.

ESD Protection - Sole Grounders
Sole Grounders

d. Floor mats and certain vinyl tile flooring

These things can act as continuous runners and dissipate static charges, respectively.

In addition, laminated sheeting products can be used as a static-dissipating work surface. Grounding hardware (i.e. adapters and snaps) as well as cords that connect the mats to ground or to one another can also be employed.

Active Protection

Several instruments are available to test and monitor workstation grounding and electrostatic conditions and give real-time measurements of ionization balance and decay, static voltage and ESD events. An effective electrostatic discharge monitor will diagnose and troubleshoot any static control issues at a critical location and can be chosen for specific machine types. Other monitors include grounding testers, verifying operator body voltage, whether wrist straps have been plugged in correctly, and if specific work surfaces and tools are appropriately grounded. Moreover, products especially designed for monitoring the grounding of multiple tools and wrist straps at workstations are also offered.

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I am an Electrical Engineer with a Masters Degree in Business Administration. My interest is in Power Quality, Diagnostic Testing and Protective Relaying. I have been working in an electric distribution utility for more than a decade. I handle PQ studies, power system analysis, diagnostic testing, protective relaying and capital budgeting for company projects.