How to eliminate static electricity hazards
Static electricity is harmful to any electronic product, but it is a top priority for the electronics industry to effectively prevent static electricity.
First, the damage of ESD to the chip computer is composed of boards, and today's boards are mostly made of MOS technology, and the circuit is quite sensitive to electrostatic high voltage. Electrostatic discharge (ESD) occurs when a person or substance with static electricity touches these devices. When the electrostatic high voltage impacts the MOS circuit, the internal oxide film will be broken down and destroyed, causing the electrical device to be damaged or malfunctioning on the spot. Of course, devices that are generally electrostatically discharged do not immediately fail, which is why most people do not pay attention to ESD. In fact, in the daily life of static electricity, the practice proves that people can feel the static electricity at least 3.5kV or more, and the static electricity that can hear the sound is above 4.5kV, and the flash static electricity on the sweater is more than 5kV.
In addition to the above-mentioned ESD directly damaging the device, ESD also induces a latch-up effect (or parasitic thyristor effect) inside the MOS circuit. As a result, the internal current of the MOS increases greatly, and the internal logic function fails, resulting in a so-called locking effect. Once the MOS circuit is in the locked state, as long as the power supply is not cut off, the circuit will continue to be deadlocked for a long time, which may burn out the circuit or degrade the performance of the circuit. For example, when the printer is plugged or unplugged and the computer is abnormal (the mouse cannot move, the printer alarms), the first remedy is to shut down immediately.
To this end, international organizations have developed corresponding standards to classify electrical faults caused by ESD into the following categories:
1. Operation of ESD failure The person operating the computer is equipped with static electricity. When he touches the appearance of the computer such as keyboard, mouse, reset button, it may cause the following computer failure due to ESD: abnormal situation such as computer restart, pause, crash, etc. You need to reset or reinstall a piece of software, but you need to replace the hardware.
2. Maintenance of ESD failure The person operating the computer is electrostatically charged, and he touches the metal conductive portion inside the chassis. For example, touching the inner board and card by hand may cause the above malfunction.
3. Overhaul ESD Failure The person operating the computer is electrostatically charged, and the ESD that occurs when he touches the computer's CPU, board, etc., will cause damage to the components.
Second, the elimination of ESD measures 1. Correct grounding Today's computers generally have a ground wire, the ground wire and the AC live and ground wire are connected to two small capacitors at the same time, the grounding state is not good for more sensitive people, As long as you touch the chassis metal, you will feel the electric shock (only 110V, the current is very small). The ability of the chip to withstand voltage is much less than 110V, so if the computer equipment (such as the host computer, printer, monitor, etc.) is not fully grounded, the print port and display card will be damaged. Nowadays, many inferior terminal blocks appear to be three-wire, and the internal ground wire is not connected at all. Users should pay special attention when purchasing.
2. Chip and board carrier packaging manufacturers generally attach great importance to ESD. Computer accessories will use anti-static bags before leaving the factory. Packaging materials with good insulation properties are prone to ESD, such as bubble plastic bags, foam plastics, etc. These materials are not suitable for packaging computer accessories.
3. Operation or maintenance personnel's own static treatment As a computer operator, always remember the HSD hazard, try to avoid touching the internal board of the computer. If you must touch the internal circuit, you should also add a grounding ring to your finger.
4. Workplace static treatment Conditionable workplace should use anti-static floor (Note: high voltage static electricity is easy to walk on all kinds of carpets, if the indoor humidity is too low, it is easy to generate static electricity), and the ideal humidity should be 40%-60 %.
5. Mount the chip on the board to improve the anti-ESD capability. The single chip has low ESD resistance. If the chip is mounted on the board, it has high ESD resistance. This is the reason, such as shorting the pins of a easily damaged CMOS chip and then transporting it away.
6. Measuring instrumentation and soldering iron work also need to be grounded. 7. Improvement of the quality of the device itself In order to protect the computer port from ESD damage, the most effective method is to improve the inherent quality of the device product.