Any time two dissimilar materials come into contact with one another, there is friction. This friction causes electric charges to accumulate on the surfaces of those dissimilar materials. That accumulation can cause an electrostatic discharge (ESD), commonly known as a shock. Such is life in the world of subatomic particles, with protons, electrons, and neutrons battling to keep everything balanced. That interaction at the subatomic level goes unseen, but it is constantly impacting the daily lives of consumers. With the continuing rapid growth of handheld and wearable electronics, the human body is the largest ESD threat of all. A person will definitely notice pain from a sudden 6kV static discharge, but these discharges can be as high as 15kV. Although lower voltage discharges sometimes go unnoticed, they can cause catastrophic damage to unprotected components and circuits.
ESD is characterized by fast rise times and high peak voltages and currents up to 30A (per IEC 61000- 4-2, level 4), which can melt silicon and conductor traces. See Figure 1. However, the damage caused by ESD effects is not always so apparent. ESD can actually cause three types of damage:
- Soft failures: Electrical currents due to ESD can change the state of internal logic, causing a system to latch up or behave unpredictably, or cause corruption of a data stream. Although this effect is temporary, it may slow down communications or require a system reboot in the case of lockup.
- Latent defects: ESD can damage a component or circuit and degrade its function even if the system continues to operate. However, this type of defect often progresses to a premature failure.
- Catastrophic failures:ESD can damage a component to the point where it does not function as intended, or doesn’t work at all.
As IC dimensions continue to shrink, the opportunities for electronic circuit damage increase.
Most ICs operate at low voltages and have structures and conductive paths that are unable to withstand the high currents and voltages associated with ESD transients. As higher frequency communication devices are developed to transmit more information in less time, it becomes increasingly challenging to identify solutions that won’t compromise stringent signal integrity requirements at the higher data rates. The ESD suppressors used must have low internal capacitance so that data communication signals are not distorted.
IC designers add a limited amount of ESD suppression to their chips to help prevent damage during manufacturing and assembly processes. However, the level of protection that is added may not be sufficient to protect ICs and other semiconductor devices from ESD during actual use. Many electronic products, especially portable ones, are used in uncontrolled environments and can experience a charge buildup as users carry them. This energy can then be discharged to another device as the two are connected, usually when a user touches I/O pins on a cable connector. Therefore, end product designers need to consider adding ESD suppressors to their circuits. They also need to consider potential coupling paths that would allow ESD to enter their equipment and circuits. These weak points identify areas that should be considered for ESD suppressor installation. Ultimately, designers need to select ESD suppressors with characteristics appropriate for their type of product, the component sensitivity, and the environment where it will be used.
The selection of proper ESD suppression is dependent upon striking a sensible balance between the operating requirements of a particular circuit and the level of protection necessary to adequately shield that circuit from ESD, Additionally, the form factor of any potential suppression device needs to be considered, so that a cohesive design for the device as a whole can be maintained.
