Introduction to SMT Processing Technology Electrostatic

Introduction to SMT Processing Technology Electrostatic
1. Surface mounting of how static electricity is generated
Matter is composed of molecules, molecules are composed of atoms, and atoms are composed of negatively charged electrons and positively charged protons. Under normal circumstances, an atom has the same number of protons and electrons, and the positive and negative balance is balanced. It seems to be electrically neutral. However, electrons surround the nucleus and deviate from their orbits under the action of external forces, leaving the original atoms and invading other atoms B. A atom is positively charged because it lacks electrons and is called a cation. Because of the increase in the number of electrons, B atom is charged. The phenomenon of negative charge is called negative ion.
The reason for the imbalance of electron distribution is that the electron deviates from the orbit under the action of external force. This external force includes various energies (such as kinetic energy, potential energy, thermal energy, chemical energy, etc.). In daily life, if you separate any two objects with different data after contact, static electricity will be generated. Solids, liquids and gases are charged due to contact and separation, and the environment around us and even our bodies will generate static electricity to varying degrees. When static electricity accumulates to a certain extent, discharge will occur.
Circuit board

2. How high is the static electricity on the human body
In the dry season, if you wear fiber clothes and walk on the insulated ground, the static electricity on your body can reach thousands or even tens of thousands of volts.
3 What is the form of electrostatic damage
The basic physical property of static electricity is: attraction or repulsion, and there is a potential difference with the earth, which will produce a discharge current. These three characteristics have three effects on electronic components:
1. Electrostatic adsorption of dust will reduce the insulation resistance of components (shorten the life).
2. The electrostatic discharge is damaged, which causes the parts to be damaged and unable to work (completely damaged).
3. The amplitude of electromagnetic field generated by electrostatic discharge is large (up to hundreds of volts/meter), causing interference or even damage to electronic products (electromagnetic interference).
If all parts are damaged, they must be detected and eliminated in production and quality control, with less impact. If the components are slightly damaged, it is not easy to find them under normal inspection. In this case, it is usually caused by multi-layer processing. The damage was found in use. This is not only difficult to check, but also difficult to predict losses.
4 What does ESD mean
ESD stands for "electrostatic discharge" in English. Electrostatic discharge (ESD) was formed in the middle of this century, mainly studying the generation and attenuation of static electricity, electrostatic discharge model, electrostatic discharge effects such as current heat (spark) effects (such as fire and explosion caused by static electricity) and electromagnetic effects (such as electromagnetic interference). In recent years, with the rapid development of science and technology, the extensive application of microelectronics technology and increasingly complex electromagnetic environment, the magnetic field effect of electrostatic discharge (ESD) has attracted more and more attention, such as electromagnetic interference (EMI) and electromagnetic compatibility (EMC).
5 What should be paid attention to when using anti-static wrist strap
If the wrist strap is not fastened, the contact resistance between the human body and the wrist strap will increase. The wrist strap shall be grounded through a dedicated grounding wire with a socket. It should not be clamped on the table or the metal body on the side of the table, because the resistance of these metal bodies to the ground may be very large. At the same time, always check the resistance of the wrist strap.
6 Personal safety problems in the use of anti-static wrist strap
When considering the anti-static point, the surface mounting patch processing, the total resistance of the human body to the ground should be as small as possible, but the minimum value is limited by safety If it is metal equipment or equipment, the human body must have a certain grounding resistance value In case of short circuit with power frequency power supply, the resistor can limit the current flowing through the human body during operation The minimum value should not be less than 100K ohms, and the current limiting resistance of the wrist strap is usually 1M ohms

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