Principles of electrostatic discharge (ESD)

What is ESD?

Electrostatic discharge is most familiar from the electric shock that one feels when one walks on a dry nylon carpet and then touches a metal object. Such a spark-emitting discharge occurs, for example, every time that we greet someone with a handshake or touch metal. Those who feel such an electric shock when touching a conducting object have unleashed at least 3,500 Volts. Below this level one cannot feel it.

Many electronic components, however, can be damaged or destroyed by a discharge of less than 60 Volts!

What causes ESD?

First, a charge must build up. This is created by the separation of two surfaces – of which only one must be a relatively dry insulator – such as occurs when opening a plastic bag, picking up a box or walking over a carpet. One surface removes electrons from the other and becomes negatively charged, while the other surface becomes positive. In the case on non-conducting surfaces, such as those of practically all simple plastics and synthetic textiles, the charge remains intact.

This is called a STATIC CHARGE. If, however, even the slightest discharge to a nearby conductor (such as metal, metallic coal or perspiring skin) is now induced, it can very quickly become a spark-emitting discharge to other conducting surfaces.

Only three conductors are pivotal, namely:

  • metal,
  • coal, and
  • the layer of perspiration on human skin.

These are the “spark sprayers” in the world of ESD: all three can take up, store and give off discharges in the form of destructive ESD sparks.

It is often overlooked that one must separate a dry non-conductor from a surface to achieve a charging effect, and that two of these charge-releasing conductors are required to cause a spark-emitting ESD. This, in turn, generates heat, light, sound and high frequencies that cause the whole range of electromagnetic reactions – triggering fires, explosions, IT defects and the destruction or impairment of electronic components.

What effect does ESD have on microelectronics? 

The sudden spark-emitting discharge of what was initially a static charge can destroy or damage today’s highly sensitive microcircuits through the effects of its micro-sparks. Such damage could involve a penetration of the insulating layer of an oxide barrier or something similar. It is possible that metal can be made to vaporise, covering all parts in a layer of metal, causing a short-circuit; or, worse still, the device is so slightly damaged that it passes producer’s inspection systems but later breaks down during use. Static discharge of far less than 100 Volts can cause such short-circuits, and every discharge lasts less than one hundred billionth of a second!

The later that such a static discharge takes place in the production process of an assembly or device, the greater the repair and replacement costs. The problem of ESD is not the static charging itself, but the damage caused by static discharging. This sudden static discharge must be prevented!

The risks of ESD can only be prevented by avoiding large potential differences and using shielding layers. Safe potential equalisation can be achieved through the use of CORSTATTM and CORTRONIC® with a surface resistance of 107 to 108 Ohms.