ESD Generation and Hazards
Electrostatic Discharge (ESD) occurs when two objects collide or separate. ESD is the movement of static charge from one object to another between two objects with different potentials, similar to a small lightning strike. The magnitude and duration of the discharge depend on various factors, including the type of object and the surrounding environment. When ESD has sufficiently high energy, it can damage semiconductor devices. ESD can occur at any time, such as when plugging or unplugging cables, when a person touches the I/O port of a device, when a charged object touches a semiconductor device, when the semiconductor device touches ground, or when electrostatic fields and electromagnetic interference are generated, resulting in sufficiently high voltages that trigger ESD.
ESD can be broadly categorized into three types: ESD caused by various machines, ESD caused by moving furniture or equipment, and ESD caused by human contact or equipment movement. All three types of ESD are critical for the production of semiconductor devices and electronic products. Electronic products are most susceptible to damage from the third type of ESD during use, with portable electronic products particularly vulnerable to ESD caused by human contact. ESD typically damages connected interface devices. Alternatively, devices subjected to ESD may not immediately fail but experience performance degradation, leading to premature product failure. When an integrated circuit (IC) is subjected to ESD, the resistance of the discharge circuit is usually very low, unable to limit the discharge current. For example, when a static-charged cable is plugged into a circuit interface, the resistance of the discharge circuit is almost zero, resulting in a momentary discharge spike current of up to tens of amperes. This instantaneous large current flowing into the corresponding IC pins can severely damage the IC; the localized heat can even melt the silicon die.
ESD damage to ICs generally also includes the burning out of internal metal connections, damage to the passivation layer, and the burning out of transistor cells. ESD can also cause IC latch-up. This effect is similar to that inside CMOS devices, where the thyristor's structural units are activated. High voltage can activate these structures, forming a large current path, typically from VCC to ground. The latch-up current of serial interface devices can be as high as 1 ampere. The latch-up current will remain until the device is de-energized. However, by then, the IC has usually already burned out due to overheating. Two problems may arise after an ESD impact that are not easily detected. These problems are usually not detected by general users and IEC testing organizations using traditional loop feedback and insertion methods.