1. How is static electricity generated in SMT?
Matter is composed of molecules, and molecules are composed of atoms, which consist of negatively charged electrons and positively charged protons. Under normal conditions, the number of protons in an atom equals the number of electrons, resulting in a balanced electrical charge. However, when electrons are displaced from their orbits by external forces, they leave their original atoms and move to other atoms. This causes the original atom (A) to become positively charged, known as a cation, while the receiving atom (B) becomes negatively charged, known as an anion.
The imbalance in electron distribution occurs when external forces, which can include kinetic, potential, thermal, or chemical energy, disrupt the normal orbit of electrons. In everyday life, when two objects of different materials come into contact and then are separated, static electricity can be generated. Solids, liquids, and gases can all become charged with static electricity through such contact and separation, leading to varying levels of static charge in our environment and even on our bodies. When static electricity accumulates to a certain level, a discharge will occur.
2. How high is the static electricity on the human body?
In the dry season, if you wear synthetic clothing and walk on an insulated surface, the static electricity on the human body can reach thousands of volts or even tens of thousands of volts.
3. What are the forms of electrostatic damage to SMT electronic products?
The basic physical properties of static electricity include attraction or repulsion and a potential difference with the earth, which can generate a discharge current. These characteristics lead to three effects on electronic components:
1. Electrostatic adsorption of dust decreases the insulation resistance of components, shortening their lifespan.
2. Electrostatic discharge can destroy components, rendering them non-functional.
3. The electromagnetic field from electrostatic discharge can cause interference or damage electronic products, with amplitudes up to several hundred volts per meter.
If all components are damaged, they should be detected and removed during production and quality management to minimize impact. Slightly damaged components are harder to detect during normal inspection and often reveal issues only when in use, complicating detection and prediction of losses.
4. What does ESD mean?
ESD stands for “Electrostatic Discharge.” It originated in the mid-20th century to study static electricity generation, attenuation, discharge models, and effects such as current thermal effects (e.g., fire and explosion) and electromagnetic effects (e.g., interference). Recent advancements in microelectronics and complex electromagnetic environments have heightened focus on the magnetic field effects of electrostatic discharge, including electromagnetic interference (EMI) and electromagnetic compatibility (EMC).
5. What problems should be considered when using an anti-static wrist strap?
If the wrist strap is not fastened securely, the contact resistance between the body and the strap increases. The strap should be connected to the ground via a designated grounding wire and not attached to metal surfaces on or around the table, as these may have high resistance to ground. Additionally, the wrist strap’s resistance should be checked frequently.
6. What are the human safety issues with anti-static wrist straps?
In SMT processing, while minimizing the resistance of the human body to ground is ideal, safety limits this value. A certain level of resistance is necessary to prevent harm in case of contact with power sources. The minimum resistance should not be less than 100K ohms, with wrist strap current-limiting resistors typically set at 1M ohms.
Matter is composed of molecules, and molecules are composed of atoms, which consist of negatively charged electrons and positively charged protons. Under normal conditions, the number of protons in an atom equals the number of electrons, resulting in a balanced electrical charge. However, when electrons are displaced from their orbits by external forces, they leave their original atoms and move to other atoms. This causes the original atom (A) to become positively charged, known as a cation, while the receiving atom (B) becomes negatively charged, known as an anion.
The imbalance in electron distribution occurs when external forces, which can include kinetic, potential, thermal, or chemical energy, disrupt the normal orbit of electrons. In everyday life, when two objects of different materials come into contact and then are separated, static electricity can be generated. Solids, liquids, and gases can all become charged with static electricity through such contact and separation, leading to varying levels of static charge in our environment and even on our bodies. When static electricity accumulates to a certain level, a discharge will occur.
2. How high is the static electricity on the human body?
In the dry season, if you wear synthetic clothing and walk on an insulated surface, the static electricity on the human body can reach thousands of volts or even tens of thousands of volts.
3. What are the forms of electrostatic damage to SMT electronic products?
The basic physical properties of static electricity include attraction or repulsion and a potential difference with the earth, which can generate a discharge current. These characteristics lead to three effects on electronic components:
1. Electrostatic adsorption of dust decreases the insulation resistance of components, shortening their lifespan.
2. Electrostatic discharge can destroy components, rendering them non-functional.
3. The electromagnetic field from electrostatic discharge can cause interference or damage electronic products, with amplitudes up to several hundred volts per meter.
If all components are damaged, they should be detected and removed during production and quality management to minimize impact. Slightly damaged components are harder to detect during normal inspection and often reveal issues only when in use, complicating detection and prediction of losses.
4. What does ESD mean?
ESD stands for “Electrostatic Discharge.” It originated in the mid-20th century to study static electricity generation, attenuation, discharge models, and effects such as current thermal effects (e.g., fire and explosion) and electromagnetic effects (e.g., interference). Recent advancements in microelectronics and complex electromagnetic environments have heightened focus on the magnetic field effects of electrostatic discharge, including electromagnetic interference (EMI) and electromagnetic compatibility (EMC).
5. What problems should be considered when using an anti-static wrist strap?
If the wrist strap is not fastened securely, the contact resistance between the body and the strap increases. The strap should be connected to the ground via a designated grounding wire and not attached to metal surfaces on or around the table, as these may have high resistance to ground. Additionally, the wrist strap’s resistance should be checked frequently.
6. What are the human safety issues with anti-static wrist straps?
In SMT processing, while minimizing the resistance of the human body to ground is ideal, safety limits this value. A certain level of resistance is necessary to prevent harm in case of contact with power sources. The minimum resistance should not be less than 100K ohms, with wrist strap current-limiting resistors typically set at 1M ohms.
