Electrostatic Discharge Sensitive(ESD) integrated circuit needs to be protected against high voltage before it is mounted on PCB. In most cases, static electricity is generated due to improper handling of the IC causing harmful surge voltages, it called discharge phenomena. Unfortunately, engineers sometimes were not able to detect that the IC was damaged and still tested or assembled causing damage.

Where does electrostatic discharge come from?

Usually electrostatic discharge (ESD) occurs in the following two situations:

1. Contact discharge - After direct contact between two different potential surfaces, discharge through a high voltage switch

2. Air discharge - When two high electrostatic field objects approach, through the air discharge

 

Static charges generally accumulate in insulator materials such as vinyl plastic, insulated plastic shoes, plastic packages, or ungrounded soldering irons. When the charge accumulates on the object to a certain intensity, a discharge phenomenon occurs close to the material. The accumulated charge will vary depending on the material and the surrounding environment. For example:

Walk on the carpet: 15,000V

Walking on vinyl floor: 5,000V

Remove the Bubble Pack from the package: 20,000V

(Note: Assuming 40% relative humidity)

Because materials that are prone to static electricity are commonly used in the workplace, workstations for processing ICs need to have good ESD control to prevent ESD damage to the IC being processed.

In the process of handling ICs, due to differences in the operating environment, procedures, and contact materials, the methods for preventing electrostatic hazards will be different.

Four points of the ESD workbench:

ESD Static Control Grounding Pad - Protect Desktop

In addition to the ESD protection desktop material, which provides a static-free work surface area, which limits the generation of static electricity, it also allows the conductive objects placed on the work surface to remove charges, so the grounding resistance value of the protection material will not be too high, so as not to hinder charge flow. According to the ANSI/ESD S4.1 standard, the material surface resistance should be between 106-109 ohms

ESD Static Control Grounding Pad - Protecting the Ground

Protective floor products can generally be divided into three categories: Conductive, Static Dissipative, and Insulation. According to the ANSI/ESD S20.20 standard, the surface resistance of a conductive floor or mat is less than 109 ohms.

Static electricity dissipation type product surface resistance is less than 1011 ohms.

ESD protective trays and shunts

Pay attention to the protective materials used in the trays and shunts. According to the ANSI/ESD S541 standard, the surface resistance of packaging materials needs to be between 104 and 1011 ohms, so some manufacturers will also make a mark in the specification.

Grounding strap

According to the IEC 61340 international standard, a 106 ohm resistor is usually used for the wrist strap grounding resistance. If an operator touches a live conductor, the resistor limits the current flowing through the body to 500 mA for a normal mains supply.