The Generation, Impact, and Protection of Static Electricity
I. The Generation of Static Electricity:
1. Friction: In daily life, static electricity is generated when any two objects of different materials come into contact and then separate. The most common method of generating static electricity is through friction. The better the insulation of a material, the easier it is to generate static electricity through friction. Additionally, static electricity can also be generated when any two objects of different substances come into contact and then separate.
2. Induction: For conductive materials, electrons can flow freely on their surface. If placed in an electric field, positive and negative electrons will transfer due to the repulsion of like charges and the attraction of unlike charges.
3. Conduction: For conductive materials, electrons can flow freely on their surface. If they come into contact with a charged object, charge transfer will occur.
II. The Impact of Static Electricity on the Electronics Industry
The miniaturization of circuitry, lower voltage withstand capability, and smaller circuit area in integrated circuit components weakens their resistance to electrostatic discharge (ESD). Electrostatic fields and currents become deadly threats to these high-density components. Simultaneously, the widespread use of highly insulating materials such as plastics greatly increases the chances of static electricity generation. Static electricity is generated in daily life through activities such as walking, air movement, and handling. While it's commonly believed that only CMOS chips are sensitive to static electricity, in reality, highly integrated electronic components are quite sensitive.
A. Effects of Static Electricity on Electronic Components
1. Static electricity attracts dust, altering the impedance between circuits and affecting product functionality and lifespan.
2. Electric fields or currents can damage the insulation or conductors of components, rendering them inoperable (completely destroyed).
3. Heat generated by instantaneous electric fields or currents can damage components, allowing them to continue functioning but shortening their lifespan.
B. Characteristics of Static Electricity Damage:
1. Insidious: The human body cannot directly perceive static electricity unless an electrostatic discharge occurs. Even then, the sensation of an electric shock is not always felt. This is because the human body can only perceive an electrostatic discharge voltage of 2-3KV.
2. Latent: Some electronic components do not show an obvious performance decline after static electricity damage, but repeated discharges can cause internal damage, creating hidden dangers and increasing the component's sensitivity to static electricity. There is no cure for existing problems. 3. Randomness: Under what circumstances will electronic components suffer electrostatic discharge (ESD) damage? It can be said that from the moment a component is manufactured until it fails, it is threatened by ESD, and the generation of this ESD is random. Because the generation and discharge of ESD occur instantaneously, they are difficult to predict and protect against.
4. Complexity of ESD Damage: The complex and delicate structure of electronic products makes ESD work time-consuming, labor-intensive, and expensive. It often requires sophisticated technology, often necessitating the use of precision instruments such as scanning electron microscopes. Even so, some ESD damage phenomena are difficult to distinguish from damage caused by other reasons, leading to the misinterpretation of ESD failures as other types of failures. Before a full understanding of ESD damage is achieved, it is often attributed to early failures or failures of unknown origin, thus unconsciously obscuring the true cause of the failure.
5. Severity: While ESD problems may seem to only affect the users of finished products, they actually impact manufacturers at all levels, such as warranty costs, repair costs, and company reputation.
III. Three Types of ESD
1. Human Body Type: This refers to the frictional charge generated between the body and clothing during human activity. 1. When people hold ESD-sensitive devices without first grounding them, triboelectric charges will transfer to the ESD-sensitive devices and cause damage.
2. Charging type of microelectronic devices: This refers to ESD-sensitive devices, especially plastic parts. During automated production, triboelectric charges are generated. These charges can be rapidly discharged through low-resistance lines to a highly conductive, firmly grounded surface, causing damage; or they can cause the metal parts of the ESD-sensitive device to become charged through induction, resulting in damage.
3. Field-induced type: This occurs when a strong electric field surrounds the device, which may originate from plastic materials or clothing. Electron conversion occurs across the oxide layer. If the potential difference exceeds the dielectric constant of the oxide layer, an electric arc will be generated to destroy the oxide layer, resulting in a short circuit.
IV. Electrostatic Protection
1. Grounding
Grounding directly discharges static electricity to the earth through a wire connection. This is the most direct and effective anti-static measure. For conductors, grounding is commonly used, such as by wearing anti-static wrist straps and grounding work surfaces.
Grounding is implemented through the following methods:
1) Grounding of the human body via wrist straps.
2) Grounding of the human body via anti-static shoes (or shoelaces) and anti-static flooring.
3) Grounding of the workbench surface.
4) Grounding of testing instruments, tool holders, and soldering irons.
5) Grounding of anti-static flooring and mats.
6) Grounding of anti-static transport carts, boxes, and racks whenever possible.
7) Grounding of anti-static esd chairs.
2. Electrostatic Shielding
Electrostatic sensitive components may be exposed to static electricity during storage or transportation. Electrostatic shielding can reduce the impact of external static electricity on electronic components. The most common methods are using electrostatic shielding bags and anti-static turnover boxes for protection. Additionally, anti-static clothing provides some shielding against static electricity.