This application note is intended to provide an introduction to Electrostatic Discharge (ESD) and the damage it can cause to LEDs. Techniques to prevent damage due to ESD are also discussed.
While this application note provides information on ESD and recommendations for users to prevent such damage, Violumas recommends that standard industry practices must be utilized in conjunction with these recommendations. The documentation is not geared towards providing detailed information on regulations and safety certifications.
This resource is intended for engineers using Violumas LED products. Product designers are solely responsible for selecting the appropriate Violumas products and ensuring that the applicable standards and safety requirements are met. Violumas cannot be held responsible for any damage caused by following these guidelines.
According to the ESD association, electrostatic discharge is defined as:
“The rapid, spontaneous transfer of electrostatic charge induced by a high electrostatic field. Note: Usually, the charge flows through a spark between two conductive bodies at different electrostatic potentials as they approach one another.”
Definition from ESD ADV1.0-2017: ESD Association Advisory for Electrostatic Discharge Terminology – Glossary
ESD can be felt in daily life when one touches a metal doorknob after walking on a dry carpet. Lightning is also a form of electrostatic discharge. This shock can be experienced by electronic components as well which can lead to performance degradation and early failures.
Typical sources of ESD are human contact, operating equipment and insulating material. A charged device when in contact with ground or another object at a different potential can create an ESD event. ESD damage events are random and unpredictable and are mostly non-repetitive. These events are characterized by a short duration, high voltage pulse with a medium current flow. In most cases, it is difficult to identify an ESD event and so utmost care should be taken to minimize the chances of an ESD event.
ESD events are characterized by high-power pulses of short duration delivering high energy in a short time period. This results in damage to the semiconductor structure, often creating holes and cracks in the LED die which may be invisible to the naked eye. While not visible on the surface, such failures can be detected by looking at the opto-electrical characteristics of the LED.
LEDs may fail completely or appear to be working after an ESD event initially but will eventually fail. A much lower optical output than what is expected might indicate an imminent failure.
At the LED circuit level, ESD protection can be provided by adding Transient Voltage Suppressing (TVS) diodes in parallel with the LED. TVS diodes provide a separate path for the high-energy pulse to pass through, thereby, protecting the LED circuit. These devices can suppress several hundred volts of surges for a few microseconds. Figure 1 shows a Violumas device with a TVS on board.
At the component assembly and handling level, ESD can be prevented by properly grounding personnel, equipment and tools, and by using static dissipation materials. Care must be taken when shipping electronic components to avoid any ESD damage during transportation. A wrist strap and conductive footwear can be used for ground personnel working with the LEDs. Anti-static mats should be placed in work areas and should be grounded appropriately.
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