Static electricity is a common physical phenomenon. When two different materials are rubbed, an electrostatic charge is generated because of the transfer of electrons. Objects that receive electrons are negatively charged, and objects that lose electrons are positively charged. This process is called triboelectric charging.
The harm of electrostatic discharge to the device can not be ignored. Some statistics show that the economic loss caused by static damage of electronic products every day in the world may reach more than one million US dollars, about 5 billion US dollars a year. A representative large-scale CMOS device manufacturer's products returned to the device due to quality problems in the first seven months after shipment, and 28% were directly related to electrostatic damage, accounting for the top failure rate. Therefore, all electronics factories have very high anti-static requirements.
In many electronics factories, they use a lot of anti-static products. Why are static damage often occurring? Let's talk about the common anti-static methods common in factories.
1. No anti-static product testing equipment
The most common mistake is that many companies have purchased a lot of anti-static products, but they have not purchased some common anti-static product testing instruments. We know that each product has a certain period of use, quality is good or bad, if there is no common testing equipment, we do not know whether the product is damaged, the quality is good. This will not achieve anti-static effects.
2. Ground connection is not good
a. The anti-static system must have an independent and reliable grounding device. The grounding resistance should be less than 10Ω. The embedding and testing methods should meet the requirements of GBJ97.
b. The anti-static ground wire shall not be connected to the power supply neutral line and shall not be shared with the lightning protection ground wire. Because lightning strikes and other phenomena will affect the performance and personal safety of the product through the circuit.
c. Use three-phase five-wire system to supply power, and its ground wire can be used as anti-static ground wire (but the neutral wire and ground wire must not be mixed).
d. The cross-sectional area of the grounding main line shall not be less than 100mm2; the cross-sectional area of the trunk line shall be not less than 6mm2; the grounding line of equipment and workbench shall be a multi-strand plastic coated wire with a cross-sectional area of not less than 1.25mm2, and the color of the grounding wire shall be yellow-green It is appropriate.
e. The connection method of the grounding main line should be brazed.
f. Anti-static equipment connection terminals should ensure reliable contact, easy to install and disassemble, and allow the use of various clip-on connectors, such as squid clips, plugs, etc.
g. The grounding system monitoring alarm should be installed in the workplace where the grounding resistance value is high.
3. Use anti-static products as ordinary products
Many companies use anti-static products as common products, thinking that the products are not deformed and can be used without breaking. In fact, this is a misunderstanding. For example, an anti-static wrist strap can only be used for a few months. When used for a period of time, the appearance may not be damaged, but the wrist strap is often found to be broken during testing.
4. Do not pay attention to socks and insoles
Usually people wear anti-static shoes, but also wear socks or pad insoles, people who are prone to sweat, these socks and insoles will also lead to static electricity, but some people who are not easy to sweat if wearing some non-static anti-static tweezers And the pad insole, this sock and insole can not lead to static electricity, so the static electricity of the human body can not be introduced into the earth through the shoes. Therefore, the "Human Body Integrated Resistance Tester" is placed at the entrance of the machine room or factory building. The human body comprehensive tester can quickly and accurately detect those who wear unqualified anti-static shoes, socks and pad insoles. Workers are advised to wear anti-static slippers in the summer while not wearing tweezers. In winter, they can wear cotton socks but not nylon socks.
5. Wear only anti-static shoes without anti-static clothing
In addition to wearing anti-static shoes, people must wear anti-static overalls to better control the static electricity of the human body. Because clothing can also carry a high degree of static electricity, especially most of the current clothing is chemical fiber, can produce thousands of volts of static electricity.
6. Wear only anti-static clothing without anti-static slippers
Some experiments have shown that people wear only anti-static overalls, such as not wearing anti-static shoes and not very good anti-static ground, anti-static effect is very poor.
7. Anti-static clothing and shoes are worn but no anti-static floor and no anti-static wrist strap
We know that the static electricity of the human body should be guided through the anti-static shoes or through the wrist strap. If the anti-static floor and the anti-static wrist strap are not available, the static electricity of the person will be difficult to guide away. It is best for qualified companies to have anti-static flooring and anti-static wrist straps. Unconditional companies must have at least an anti-static wrist strap.
8. Incorrect use of wrist straps
Because the wrist strap is relatively easy to damage, it should be tested every day. A good wrist strap will also be too loose and not conductive because the worker wears it. Therefore, the best method is to monitor the wrist monitor with an online monitor at any time. However, there are many companies that do not even have a wrist strap tester. A wrist strap has not been used for more than a year, so it is not effective.