How to prevent serious static electricity?
First, the ubiquitous static electricity
A substance is made up of atoms, which have uncharged neutrons, positively charged protons, and negatively charged electrons. Under normal conditions, the protons and electrons in one atom are equal in number, and the positive and negative charges are balanced, so the external phenomenon is shown as being uncharged. When two objects rub against each other, the heat generated raises the electron energy level, making the inactive electrons become active electrons that are easy to escape. Such electrons can be transferred from one object to another, so that two An object that is originally neutral becomes a charged object, which is the phenomenon of "frictional electricity generation" that we are familiar with.
In the process of triboelectric generation, the amount of electron transfer and the transfer speed are not only related to the difference in material properties, but also related to the site temperature and humidity. In autumn and winter, due to low air humidity, the viscous force between molecules is small, the speed of movement is accelerated, and static electricity is easily generated. Not only does the flowing air generate static electricity, but we also generate static electricity when we walk around the floor, rotate the swivel chair, switch the drawer, take the paper pen, move the mouse, etc., so that these objects and the human body carry static charge.
In addition to frictional electricity generation, there are also electrostatic causes such as "induction electricity generation" and "capacitive electricity generation" in electrical equipment. Static electricity is generated by the above two methods even if no contact occurs between equipment, circuits, metal and non-metal structures. As the saying goes, there is no bird in the mountains, but the electrostatic induction between objects can occur even if they are separated by a distance: CRT monitor screen as a source of induction will also induce static electricity on the body, making our faces dusty; Because of the parasitic capacitance between the parallel wires, the charge is also transferred between each other.
A variety of static electricity generation methods cause static electricity everywhere in our environment. If we live in an electrostatic world, it is not an exaggeration.
Second, ESD is the invisible killer of computers
There are different levels of static electricity in our surroundings and even our bodies. When static electricity accumulates to a certain extent, static electricity discharge occurs. The ESD process is an electrostatic charge transfer process between objects at different potentials, the intensity of which is affected by the amount of electricity and the spacing of the objects. The lightning phenomenon in nature is a typical ESD phenomenon in a strong convective climate. The huge energy released in an instant can ionize the air passing through the lightning current, making the air become a conductive channel with a low resistance, forming a super-strong current and pole. High temperature and great destructive power.
The ESD phenomenon in daily life occurs frequently. Although it is not as strong as lightning, there will be spark-type discharge, not only accompanied by the sound of "sound", but also sparkling. Studies have shown that when the voltage is greater than 8000V, the light emitted by ESD can be seen. When the voltage is greater than 6000V, the discharge sound of ESD can be heard; when the voltage is greater than 3000V, ESD can be felt; when the electrostatic voltage is lower than 3000V, The ESD process will also happen, but we don't feel it. In other words, many ESD processes are quietly carried out.
ESD is the invisible killer of computers. I have experienced many computer failures during my maintenance career. I couldn't find out what the reason was. I felt inexplicable at the time, and now I think it should be related to ESD. When the electrostatic voltage is low, the electrical noise generated by ESD will interfere with the logic circuit, causing the logic circuit deadlock (LatchUp) in the IC chip, resulting in data transmission or operation error, or may cause slight physical damage to the chip and premature aging. Or potential failure; when the electrostatic voltage exceeds 250V, ESD can penetrate the computer chip.
When ESD is applied to a computer chip, since the resistance of the discharge circuit is usually small, the instantaneous discharge current of the charge release is large. For example, when a cable with static electricity is plugged into the interface of a computer, the resistance of the discharge circuit is almost zero, and a discharge current of up to several tens of amperes is formed. When such a large peak current flows from a certain pin of the chip, it is enough to Local melting, blowing the transistors and metal wires in the chip, causing permanent loss of function of the chip, or destroying the passivation layer in the chip, degrading the performance of the chip. After the chip is damaged, we can't see any change in appearance, but we can still see the circuit blown by using FESEM instrument.
Today's CPU chips, memory chips, and large-scale integrated circuit chips such as Southbridge and Northbridge on the motherboard are widely used in CMOS (composite metal oxide semiconductor) materials. CMOS devices have high integration, low cost, fast speed, and energy consumption. Low advantage, so it is used in a wide range. However, a fatal weakness of CMOS devices is that the input impedance is large and can easily be broken down by ESD. As the chip technology progressed, the work speed increased, but the chip became vulnerable. The increase in integration makes the device size smaller and smaller, the connection width between devices becomes narrower, and the passivation layer becomes thinner and thinner. These factors all make the chip more sensitive to electrostatic discharge. A not too high voltage can break down the transistor, and a tiny ESD current can blow the wire.
ESD has become the number one killer of today's computers. Intel's research shows that ESD is the biggest hidden danger in many factors that cause computer failure. Nearly half of computer failures are caused by EOS/ESD (Figure 3). EOS represents electrical stress (Electrical OverStress).
The destructive effect of ESD on computers is characterized by concealment, potential, randomness and complexity. When we are in contact with computer boards and chips, whether it is static electricity on the computer or static electricity on our body, ESD is possible. At the moment of contact, it can be said that it is impossible to prevent.
Written here, my brain suddenly flashed a large-scale damage to the computer that I experienced in an Internet cafe a year ago. There are 40 machines in this Internet cafe, and it has been damaged by almost half in less than half a year. After inspection, I found that there is no quality problem with the regulated power supply used in the Internet cafe. I checked the grounding wire and found that although there is a grounding wire in the room, the outside of the house is only driven into the ground with a steel bar less than one meter long. And the connection is rusty. After the Internet cafe owner redesigned the ground line according to my suggestion, the computer rarely went wrong.