Electrostatic Discharge - More Than Meets the Eye

In winters, we may experience electrostatic discharge (ESD) or shock by shaking hands with someone or touching a metal doorknob after walking on a carpet. People rarely notice the electrostatic discharge although it is always present and it is a serious problem for industries. In general, the electronic devices are becoming more sensitive to ESD as they are getting faster and smaller. It has a great impact on the performance, reliability and productivity of electronic devices and integrated circuits. Therefore, ESD is a major considerable factor in the design and manufacture of electronic devices and circuits.

What is Electrostatic Discharge?

Electrostatic charge occurs due to static charge buildup caused by friction. When two surfaces rub against each other, one surface loses electrons that accumulate on the other surface building up a potential difference known as static charge. The static charge is transferred to other surface with a different level of charge, giving you an unpleasant shock. ESD is usually harmless for humans, but they tend to damage electronic devices and components.

How ESD Affects Electronic Circuits and Devices?

The electrostatic charge could possibly drain in the device through sensitive circuity as a statistically charged object or person touches a device that is sensitive to electrostatic discharge. The sufficient energy possessed by the electrostatic discharge can cause damage to the device due to hot spots. Even low electrostatic discharges can cause permanent damage to smaller electronic devices, such as MEMS and NEMS due to their small size and tiny electronic components. ESD damage can occur in various modes, including discharge from the device, discharge to the device, or field induced charge.

Stress Methods for ESD Sensitivity

To avoid detrimental effects of ESD on electronics ICs and systems, standards and stress methods are developed to ensure the employed devices can withstand ESD thresholds. The defined models that are commonly used in the industry are Human Body Model (HBM), Machine Model (MM), and Charged Device Model (CDM).

ESD Protection Methods

Devices sensitive to electrostatic discharge should be handled at static safe workstations. A human operator working with such devices should wear antistatic wrist straps and any accumulated charge on the body should be discharged before opening the protective container of a sensitive device. Devices sensitive to ESD should be kept in static protective bag.

References

http://www.ti.com/lit/an/ssya010a/ssya010a.pdf

http://www.esda.org/fundamentalsp1.html

http://www.iec.ch/etech/2013/etech_0313/ca-4.htm

http://www.minicircuits.com/app/AN40-005.pdf