ESD electrostatic maintenance components are very important maintenance equipment and their use is becoming more and more widespread. In the market, the variety of ESD maintenance equipment is also increasing. This article will introduce the three main categories of ESD maintenance equipment: polymer, varistor/suppressor, and diode, and how to choose the appropriate ESD maintenance equipment.

The three most commonly used categories of ESD maintenance equipment are polymers, varistors/suppressors, and diodes. The biggest challenge in choosing the appropriate ESD maintenance equipment is how to simply and clearly determine which equipment can provide the maximum maintenance. System suppliers generally compare the quality of ESD maintenance equipment based on the ESD rating (or nominal value) in the data sheet. However, from these rated values, it is not possible to determine how strong the equipment maintenance system is, and the key depends on other diode parameters.

In addition to the ESD nominal value of the maintenance equipment, the voltage value (clamping voltage) and how much current is left on the ASIC side (remaining current) are also key factors. The function of ESD maintenance equipment is achieved by short-circuiting most of the current to ground and clamping the voltage of the ASIC side to a value lower than the pulse voltage. Determining the clamping voltage and remaining current is not a simple task. The clamping voltage cited in most ESD maintenance data sheets (if this information is included in the data sheet) is easy to misunderstand. There is no remaining current in the data sheet because it is related to the system map and not to the equipment itself.

Polymer equipment is attractive for high-frequency use because their sub-pico farad capacitance is only 0.05~1.0pF. However, such low capacitance can also bring some minor side effects. Unlike diodes, polymer equipment requires the terminal voltage to reach the trigger voltage before breakdown, which is much higher than the clamping voltage. Typical polymer ESD equipment will not break down before 500V. Once it breaks down, it will quickly jump to the clamping voltage of up to 150V. After the charge is released, the polymer will return to a high-impedance state. However, this process may take several hours or even a day, so they are not attractive for consumer use. These devices are difficult to accurately characterize in production, and their data sheets generally only contain typical parameter values, not minimum and maximum guaranteed values. In addition, because they are physically flexible, their performance will decrease as the number of ESD pulse exposures increases.

Varistors and suppressors are non-linear variable resistors. Although they are relatively inexpensive, suppressors generally have high trigger voltage, high clamping voltage, and high impedance characteristics, so most of the energy is directed to the equipment being protected rather than being shunted to ground. The clamping voltage range of typical low-capacitance suppressors is 150-500V. The typical dynamic resistance of a low-capacitance suppressor is 20-40Ω. Due to their high impedance characteristics, almost all ESD surge currents will be transmitted to the "protected" equipment rather than shunted to ground.

Semiconductor diodes are another ESD maintenance method. ESD maintenance diodes are characterized by low clamping voltage, low impedance, fast conduction time, and very good reliability. Generally, semiconductor diodes can provide the best ESD maintenance, and today's diodes can achieve an equivalent capacitance of 1pF, so they have become the best choice for reliable ESD maintenance and excellent signal integrity.