Classification of Hazards of Static Electricity
The main hazard of static electricity lies in electrostatic discharge (ESD). ESD lasts only milliseconds, with a high instantaneous pulse and an average power exceeding kilowatts, sufficient to break down components and cause electronic equipment or systems to malfunction.
The prominent characteristics of ESD damage are its randomness, unpredictability, and difficulty in detection. In modern industry, especially in large-scale electronics production, ESD damage occurs without people noticing and is difficult to detect. The consequences of ESD damage to components are hard breakdown and soft breakdown. Hard breakdown causes internal heating of the chip in one step, followed by secondary breakdown of metal bonding, molten media, and surface defects, ultimately leading to complete and permanent failure of the integrated circuit. Soft breakdown can cause performance degradation or a decrease in parameters of components, but without complete damage, thus creating hidden dangers that are difficult to detect during final quality inspection. During use, the potential damage caused by static electricity to the circuit will cause changes in parameters, quality degradation, and reduced lifespan, leading to various malfunctions after a period of operation due to changes in temperature, time, and voltage, ultimately preventing normal operation. If the damaged chip belongs to a critical control system, such as a network center control system, automatic broadcast control system, production scheduling control center, electronic warfare command system, automatic navigation system, or various launch control system, the resulting damage can be unpredictable. Potential damage can actually be more dangerous, causing more severe direct or indirect losses. Data shows that 90% of ESD-induced device damage is potential soft breakdown damage, and 10% is immediate failure.
Furthermore, electromagnetic pulses generated during electrostatic induction and electrostatic discharge also pose a certain hazard: electrostatic discharge typically generates electromagnetic pulse interference with frequencies ranging from hundreds of kilohertz (kHz) to tens of megahertz (MHz), and levels as high as tens of millivolts, which can damage electrostatic discharge sensitive devices (SSDs).
Some people believe that integrated circuit boards with ESD protection circuits are immune to electrostatic damage. However, while protective circuits do provide some protection, even with internal protection circuits, sensitive devices cannot withstand thousands of volts of static electricity from the human body or the work environment. All integrated circuits are sensitive to electrostatic discharge; the only difference lies in the threshold voltage they can withstand.
Static Electricity and Hazards on Semiconductor and IC Production Lines:
1. Walking slowly on a clean floor while wearing nylon clothing and plastic-based shoes can generate a static voltage of 7-8KV on the body.
2. When a crystal carrier made of fiberglass slides across a polyethylene tabletop, it can easily generate 10KV of static electricity.
3. On wafer assembly lines: wafer static electricity can reach 5KV, wafer loading boxes 35KV, work clothes 10KV, plexiglass covers 8KV, quartz crystals 1.5KV, and wafer trays 6KV.
4. In photolithography rooms, plastic floors reach 500-1000V; in metal mesh partitions, 500-1000V; in diffusion rooms, plastic floors reach 500-1500V; plastic walls reach approximately 700V; and metal movable leather chair surfaces reach 500-3000V.