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          Electronic products anti-static (ESD) design [the most reliable knowledge]
          Publish:Shenzhen Tergy Technology Co., Ltd.  Time:2017-01-12
          ESD (Electro-Staticdischarge) means "electrostatic release"
          Static electricity is a kind of natural phenomenon which exists objectively, and it has many kinds of ways, such as contact, friction and induction. Electrostatic has high potential, low power consumption (without Coulomb mc:10-9 C), small current (uA:10-6 A) and the short action time (us:10-6 S), the electrostatic measurement reproducibility is poor, transient phenomenon. In our daily life, we have a very high electrostatic voltage on and around the body.
          The ESD problem is a system engineering, which can be started from several aspects in design. One is to ensure that the product itself will not produce strong electrostatic induction and self destruction, such as increasing the shielding and isolation measures, by increasing the PCB grounding area improved charge leakage path; the two is to choose the ESD characteristics of the chip, with a chip performance of different manufacturers will be different in the chip that in general there are three is mentioned; additional protection against external electrostatic circuit.
          The best technology should be able to meet the requirements, but also to achieve the lowest cost. The product is damaged during the warranty period, the manufacturer usually needs to be repaired or replaced for free. If the failure rate of the product is high, it will not only increase the maintenance cost, reduce the profit, but also recall the failure product, which will affect the manufacturer‘s reputation. In the face of more and more fragile chips, the research and implementation of anti-static technology to improve the yield and reduce the failure rate is the problem that all chip manufacturers and manufacturers must solve. In this paper, the computer as an example, the introduction of ESD related knowledge, we hope to learn from.
          Electronic products anti-static (ESD) design [the most reliable knowledge]
          Anti static design of the chip
          With the chip to improve the speed, in order to shorten the length of pin and reduce crosstalk, CPU and SoC (System on Chip), more and more ultra large scale IC chip package using flip chip (flip chip), flip chip is usually larger, and the thickness is very thin. = epsilon S / D according to the calculation formula of C capacitor, chip electrostatic charge may carry a large amount of Q (=CxV), in other words, the chip itself has become a giant capacitor.
          If the chip designer does not know enough about the problem, the current release is not set up in the chip, so that the accumulation of net charge. As a result, when the chip is in contact with the working table or the packing box, the utility model can generate a strong electrostatic release, so that the chip is damaged in the manufacturing process, the finished product rate is reduced, and the production cost is increased.
          In addition, CPU, GPU chip on the metal cover and heat sink, a curse is mischievous. Connaught large metal body is tantamount to an electrostatic receiving antenna, easy to absorb the electric field around the chip, as well as the charge on the wire near the chip, this factor also poses a threat to the security of the chip. If the design of the chip and the designer does not take this into account, the user‘s hands and then find a common problem and had to recall the product, the greater the loss.

          Two, shielding and grounding design of the whole machine
          In the production workshop, the floor is anti-static, anti-static equipment manufacturing is the testing instrument is anti-static, chip box and warehouse is anti-static, even the operator must wear anti-static clothing, anti-static gloves, a heavily armed. However, the computer in the application process, or will give ESD an opportunity. In order to avoid the harm of static electricity, it is necessary to shield and ground the whole machine.
          Products such as the metal chassis of the computer is an important measure of electrostatic shielding, good grounding can greatly reduce the risk of electrostatic hazards. The motherboard, chassis interface card, hard disk, floppy drive, CD-ROM and other equipment, and wrapped in a signal line outside the metal shielding net, are connected into a whole through the case, and then through the power wire access to the earth, which can not only eliminate the electrostatic induction outside, also can eliminate the static friction generated rotating equipment the. In order to ensure good contact between the components, the chassis is provided with a plurality of elastic contact or elastic contact pieces.

          Three, the interface circuit implanted ESD protector
          The chip is the most easily damaged by the ESD device, it has become the focus of protection products. The interface circuit is located in the periphery of the board circuit is an important defense against ESD. Since the logic circuit on the board can not withstand the voltage of kV, it must be excluded from the circuit. An electrostatic protection device is connected at each interface, so that the electrostatic high voltage is released in the utility model, and the invasion of the deep area of the circuit board is avoided.
          The interface circuit is the most simple anti-static measures: a series of low resistance in the circuit, the current limit of ESD, or between the signal line and the ground as a small capacitor to release ESD current. However, these measures will produce signal attenuation and delay, is not conducive to signal transmission.
          In recent years, the main board in the keyboard, mouse PS/2 interface and RS - 232C serial port and IEEE1284A parallel port and other low-speed ports, the use of embedded anti-static function of the data transceiver chip. The ESD protection circuit embedded in the interface chip is realized by the parasitic circuit. When ESD, the parasitic circuit is triggered, the discharge current of ESD or ESD voltage clamp, to protect the purpose.
          For high-speed USB and IEEE1394 hot swap interface, because the pin is less, usually access to TVS and MLV and other new electrostatic protection devices. TVS (Transient Voltage Suppresser, transient voltage suppressor) can rapidly release ESD fault current to the ground terminal, and the leakage current and junction capacitance are very low, the response time is very short (about 1ns), is a high-speed data path in the ideal, is widely used in computer motherboards and various USB devices.
          TVS devices usually contain a number of TVS diodes, with multiple protection role of micro SMD components, the common form of packaging SOT23 and SC-70 two.
          ESD protector is often not noticed, but it is the protection of god. They played a role in the computer, played a few times, we can not know. However, without their protection, computers will often cause us trouble.

          Four, the product ESD test
          As we all know, electronic products must pass EMC (electromagnetic compatibility) performance testing, affixed to the EMC logo, in order to enter the international market. At present the most authoritative formulation of EMC standard is the International Electrotechnical Commission IEC61000-4 standards, including IEC61000-4-2 (ESD), IEC61000-4-3 (electromagnetic interference) and IEC61000-4-4 (Electrical fast transient), IEC61000-4-5 (surge sensitivity). The ESD test for computer products is also based on IEC61000-4-2.
          IEC61000-4-2 provides two items of ESD testing: contact voltage test and air discharge test. When the contact voltage is measured, the ESD signal generator generates an adjustable DC voltage of up to 4kV, when the probe tip of the signal generator is connected to the device under test. When the air discharge is tested, the ESD tester provides the highest 8kV adjustable pulse voltage, from the tester‘s hair to the device to be tested.
          Qianlizhidi, ulcer in the colony.
          In product design, component selection and manufacturing process of each link, can lead to catastrophic accidents, while the ESD test is a useful way to find design problems, test components quality and finding manufacturing defects.
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