Electrostatic Discharge

Dr. S. S. VERMA; Department of Physics, S.L.I.E.T., Longowal; Distt.-Sangrur (Punjab)-148 106

2017-12-01 07:41:28

Credit: RTP Company

Credit: RTP Company

In the era of industrialization, working with or use of different electronic and non-electronic equipments is inevitable for any one of us.  Industrial accidents will not only inflict injuries to human but also increase the costs due to damage to property.  Under these conditions, the safety of human plays an important role which can be ascertained by the prevention of industrial accidents.  By regulating the way that employers organize their work places and the way in which their employees carry out their work, the incidence of personal injury, damage to long-term health and damage to property can be much reduced. This is done by ensuring that the work places themselves are healthy and safe, and by training employees on how to carry out their jobs safely.

Electrostatic Discharge (ESD):

Static electricity derives its name from the fact that the charge involved is not flowing and in a sense is still or static. Electrostatic Discharge (ESD) is the term given to the discharge of static electricity which is sudden and momentary electric current that flows between two objects at different electrical potentials. The term is usually used in electronics and other industries to describe momentary unwanted currents that may cause damage to electronic equipment. We have all experienced some time or the other an unplanned discharge of static electricity, in our everyday lives. In its most dramatic form, the lightning in a thunderstorm is a huge electrostatic discharge.  It took a few centuries before the technique of grounding the spire, via a metal strip running down the outside of a building was understood and put into use as a more advanced form of ESD control.

Electrostatic Discharge (ESD) as a problem:

Static electricity has been an industrial problem for centuries. The age of electronics brought along new problems associated with static electricity and electrostatic discharge. As the electronic devices became faster and smaller, their sensitivity to ESD also increases. Electrostatic discharge is a significant cause of failures within the electronics industry. The cost of ESD damage is not simply the cost of the components. In addition to this, we must consider the cost of labour and all of the expenses associated with field repair. Another cost is that of lost business due to customer dissatisfaction.  High failure incidents are largely rooted in the extensive use of integrated circuits (ICs). As the world of microelectronics continues to advance in the areas of superconductivity, higher speeds and lower power consumption, the materials being used in electronic circuits have become increasingly static-sensitive. The small geometries of individual junction areas and/or thin insulative oxides that make up these circuits are so delicate that commonly encountered charged items can cause physical damage to the devices. Although the human body is probably the most common ESD source, static generation on other items such as shipping materials, clothing, furniture, tools (both metal and plastic) can be damaging as well.

There is no exaggeration in saying that "just about everything" is susceptible to ESD damage as most devices these days have some form of control circuit attached to them, containing some very fast integrated devices. Therefore, precautions must be taken to prevent damage to industrial equipments (small or big) due to ESD. Even packaging and transportation of electronic devices and components has to be accomplished in a manner to protect these from ESD damage. In spite of all the documented evidence of the detrimental effects of ESD within the electronics industry, there are still those who remain unconvinced of its severity. 

Electrostatic Discharge (ESD) Control:

Little attention is given to electrostatics in modern electronic age.  The basic principles like charge, static charge generation, conductors and insulators on which operation of electronic devices depends are poorly taken care off.  Various techniques and numerous products used in the service sector to control against ESD are:

i) Charge prevention

The prevention of charge generation is an important part of any ESD control programme and its prevention is accomplished through the elimination of unnecessary activities that create static charge like the removal of unnecessary materials that are known charge generators and the use of anti-static materials.

ii) Grounding

Grounding is a highly effective way of neutralizing the effects of static charge on devices. Grounding works only on conductors. It simply means to tie all conductors together at a common point so that electrostatic charges will flow from and through conductors to a common point and will therefore all ends up at the same level. Connecting a device to ground will effectively provide a conductive path for any excessive charge to flow.

iii) Shielding

Shielding is used to prevent a sensitive device from being charged by exposure to an external electrostatic field or being touched by a charged object during transport or storage. This is done using the Faraday Cage concept.

iv) Neutralization

As non-conductors do not conduct electricity, grounding will not work, so these must be neutralized in some other manner. The most common method of neutralizing insulators is through ionization in which the area is flooded with alternating positive and negative charged particles (ions). A charged material will then attract ions of the opposite polarity and quickly become neutralized.

v) Education

Education (often regarded simply as awareness) is necessary for a successful ESD protection programme. A common saying among ESD specialists is that awareness is 80 percent of the battle towards conquering the threat. As with all quality functions, ESD prevention depends upon the understanding and commitment of every person working with sensitive components. Person involved at any level with the handling of electronic devices must understand the danger of ESD and know the part each individual plays in preventing ESD failures.

vi) Wrist strap

The wrist strap is a typical means of controlling static charge on personnel. When worn correctly and connected to a reliable ground source, a wrist strap dissipates any build-up of static charge away from the human body to ground. Wrist straps have two chief components, the conductive cuff that goes around the person's wrist and the ground cord that connects the cuff to ground. Most wrist straps also have a current limiting resistor within the ground cord. This resistor is an important safety feature and ensures that any current passed through the human body to ground is done so at a safe level. Typically, the rating of such a resistor is one meg-ohm (1M ohm or 1MΩ). Wrist straps should be tested on a regular basis for both effective grounding and appropriate resistance.

vii) Clothing considerations

The friction created between one's clothes can be a major source of static charge generation. Certain types of material can generate more static than others can. Synthetic materials such as polyester and nylon are much more static-generative than natural materials such as cotton. However, some natural materials such as silk and wool generate and hold high static charges and should be controlled where possible.

viii) Work mat considerations

An anti-static servicing mat would typically be produced with a conductive coating (conductors allow for a free flow of electrons and as such a build-up of static charge is less likely to occur), which lends itself to working alongside electronic devices.