The abrupt flow of electrical energy between two electrically charged objects is known as Electrostatic Discharge. This Electrostatic Discharge might happen as a result of short-circuit, conduction, or dielectric breakdown. Different objects can develop an electrostatic charge as a result of tribo-charging or electrostatic induction. Tribo-charging is the phenomena when an insulator gets charged as a result of sliding or rubbing against another insulator. Electrostatic induction is a phenomenon which occurs when an already charged object is brought near a neutral object which causes the induction of charge over the neutral object.
Electrostatic discharges are very harmful for electronic circuits, especially solid state integrated circuits. When subject to ESD, these solid state electronic chips can suffer from permanent damage. Due to this reason, it is important for the IC manufacturing facilities to maintain an ESD free environment. Different types of safety measures are in place in such facilities in order to avoid the ESD. Some of the common measures include electrical grounding of human workers, humidity level control, and use of antistatic devices.
In case of large build-up of electrostatic discharge and higher potential difference between the charged objects, the ESD might cause a visible spark with sound. However, it is quite possible for a human carrying electrostatic charge to damage a sensitive electronic component without being aware of it. For a human being to feel an ESD shock, the ESD magnitude must be greater than 3000V.
However, even small amounts of ESD (<100V) can damage the integrated circuits and other sensitive circuitry. Due to this reason, great precautions are taken during the manufacturing, assembly, shipping, and operation of such electronic devices.
Figure 1 ESD transfer from human to electronic chip
The severity of an electrostatic discharge depends on its magnitude and the charge build-up. The human body is very much capable of getting charged and experience the shock of various levels. The human body model (HBM) for ESD calculation is presented in the figure below.
Electrostatic discharges are very detrimental for the integrity of electronic chips, printed circuit boards, and oscillators.
Figure 3 Pin damage of IC pin due to ESD
Keeping the adverse effects of ESD on electronic components in mind, it is very important to pay attention to ESD protection methods. There are a number of ways in which electronic circuits can be protected from the harmful effects caused by ESD.
Following is a list of some of the ESD protection methods employed in electronic manufacturing and assembling units.
- Grounding of the mobile workers using heel grounder.
- Grounding of personnel at workstations using wrist straps.
- Proper demarcation and segregation of ESD protected areas.
- All the conductors and metallic objects are grounded in the facility.
- Use of ionization for the neutralization of static charge from insulators which cannot be easily discharged. Insulators like glass, plastics, rubbers and resins cannot be easily discharged and need ionization.
- Transportation of electronic components in static shielded containers or grounded movable racks.
- Use of foot grounders and conductive mats in the facility.
Figure 4 Electrostatic protected area
In addition the technical precautionary measures, the training and education of the staff and workers is of utmost importance as well. Human negligence is one of the key factors in the ESD contamination in chip fabrication and electronics assembling industries. This risk can only be minimized by proper training of staff and regular inspection of ESD protection countermeasures.
References
(2019, March). Retrieved from www.pcblayout.com: https://www.pcblayout.com/blog/3-ways-to-protect-your-pcb-part-2-electrostatic-discharge-and-workbench-safety
Systems, E. (2019, February). Retrieved from www.esdsystems.com
Systems, T. (2011, March). Retrieved from www.slideshare.net: https://www.slideshare.net/TransformingTech/electro-static-discharge-basics
Vermason. (2019, November). Retrieved from vermasonesd.wordpress.com: https://vermasonesd.wordpress.com/2015/11/13/what-you-need-to-set-up-an-esd-protected-area/
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