Some chip capacitors are specifically designed to absorb static electricity (ESD). However, the typical anti-static capacitor is just a common chip capacitor. It is usually placed directly on the PCB connector. Its main purpose is to absorb static electricity generated on the connector, prevent static electricity from entering the PCB, and cause electronic components on the PCB board. Potential damage. They are usually low resistance (most commonly 0.1uF), 0603 package (large enough physical size to avoid electrostatic breakdown), medium voltage (50V and 100V is the most common) MLCC capacitor. For example, as shown in the circuit diagram below, C3, C4, and C5 are all anti-static capacitors.

Antistatic capacitors are commonly found in automotive and industrial electronics. These products are typically high reliability products and typically require repeated testing of each connector pin on the PCB to ensure that static electricity does not damage it. This type of static is common, especially during vehicle/machine manufacturing and maintenance, if the electrical connector is plugged and unplugged. Because the pins of any connector are actually exposed, the static electricity generated by humans and machines is easy to occur, so the cost of all additional capacitors and other static protection devices is worthwhile, they can avoid disasters ( Especially potential loss of life) or even

It is an expensive failure (for example, because an IC on the PCB is burned by static electricity, the entire engine control unit has to be replaced).

Special-purpose "antistatic capacitors" are usually constructed from slightly different multilayer geometries, making them more resistant to breakdown. At the price, they are more expensive, but smaller size (such as 0402) chip capacitors can be placed on the board to save board space.

So why not all connector pins have anti-static capacitors? Some of the lines on the PCB cannot withstand additional capacitance because they typically carry some high-speed digital communication signals. In the picture above, the RS485 line uses a TVS (low capacitance value) protection scheme, so the signal is not distorted (slower). The actual board layout might look like this (image courtesy of Texas Instruments SLLA292A)

For example, RS485 is not as expensive as devices such as USB, and there are ultra-low capacitance ESD solutions for devices such as USB.