Static electricity is all too familiar a natural phenomenon. Many of the features of static electricity has been applied to military or civilian products, such as electrostatic precipitation, electrostatic spraying, electrostatic separation, electrostatic photocopying. However, the electrostatic discharge ESD (Electro-Static Discharge) but as a kind of electronic products and equipment damage, resulting in electronic products and equipment dysfunction or even damage components. The size of modern semiconductor devices increases, more and more low voltage, resulting in semiconductor devices sensitive to external electromagnetic interference is also greatly improved. ESD circuit caused by the interference of the components, CMOS circuit and interface circuit damage caused by such issues as more and more people's attention. ESD electronic equipment, electromagnetic compatibility testing began as an important part of writing the national and international standards.
1.
static causes and hazards are two static dielectric constant friction between different materials, the positive and negative polarity of the charge accumulated in the two special bodies were formed on. When two objects touch, one trend to another attraction from the electron, which will form the two different charging potential. On the human body, clothes and skin friction between the occurrence of static electricity is mainly due to one of the body charged. Static power
contact with other objects,
coach outelt store online, according to the mechanism of charge and there in the flow of electric charge, send enough power to offset voltage. In the high-speed power transmission process, will produce a potential breakdown voltage, current, and electromagnetic fields, of which the object will be destroyed seriously, this is the electrostatic discharge. Definition of national standards: electrostatic discharge is a special body with different electrostatic potentials near or direct contact with each other due to charge transfer (GB/T4365-1995), the general said with ESD. ESD will cause serious damage to electronic equipment or operator malfunction.
electrostatic damage to the device are explicit and implicit two. Hidden damage can not tell at the time, but the devices become more fragile, over-voltage, high temperature and other conditions are easily damaged.
ESD damage to two main mechanisms: the heat generated by the ESD current cause the device to the thermal failure; induced by the ESD voltage causes a high insulation breakdown. Two failure may occur simultaneously in one device, for example, insulation breakdown may stimulate the large current, which further lead to thermal failure. In addition to likely to cause circuit damage, the electrostatic discharge can easily cause interference in electronic circuits. ESD interference of electronic circuits in two ways. One is conducted interference, the other is radiated interference.
2. the construction of digital products and ESD issues
various types of digital products are now more powerful, and circuit boards are getting smaller and smaller, more integrated . And are more or less with some interface for human-computer interaction, so that there is problem of human body electrostatic discharge ESD. Digital products in general need to have parts of ESD protection: USB Interface, HDMI Interface, IEEE1394 interface, antenna connector, VGA interface,, DVI, key circuit, SIM cards, headsets and other types of data transmission interface.
ESD may cause the product working properly, crashes, and even damage and lead to other security issues. So before the product market, domestic or foreign inspection departments require ESD surge impact and other tests. Which need to contact discharge ± 8kV, air discharge need to ± 15kV, ESD design which made of high demand.
3. digital products in the ESD problem solving and protection
3.1
structural design of the product will be released if the static as a flood, then the main solution and water control Similarly, is the If we design the products are an ideal case is airtight, there can be no static electricity into the room, of course, there will be no static problems. But the actual case is often in the closing lid at the cracks, and many decorative pieces of metal there, so be sure to take note.
First, use the To maximize the thickness of the shell from that case to the circuit board to increase the distance between, or through some equivalent ways of increasing the distance shell gap, so to avoid or significantly reduce the energy intensity of ESD.
through structural improvements to increase the shell to the internal circuit so that the distance between the air-gap ESD energy greatly reduced. Based on experience, 8kV of ESD in the distance through the 4mm power after the general decay to zero.
Second, use the EMI conductive paint, and can be viewed as a metal shield, which can be static pathway in the shell; then shell and PCB (Printed Circuit Board) of the connected, the static electricity away from the ground lead. In addition to this treatment method can prevent static electricity, but also effectively suppress EMI interference. If there is enough space, you can also use a metal shield to one of the circuit protected, metal shield to be connected to PCB's GND.
short, ESD design in many parts of the shell should be noted, first, try not to ESD into the shell interior, the maximum decrease of its energy into the shell. ESD into the shell for the internal guidance as far as possible away from the GND, do not let it harm the rest of the circuit. Metal decoration on the shell when used must be careful because it may bring unexpected results, require special attention.
3.2 products are now products
PCB design PCB (Printed Circuit Board) are high density, usually 4 laminates. As the density increases, the trend is to use the 6-layer, the design has been to consider the balance of performance and area. On the one hand, the bigger the space can have more space to display components, the same time, take the line width and line spacing is wider, for EMI, audio, ESD and other aspects of performance are good. On the other hand, digital product design is compact and trends and needs. Therefore, the design need to find balance. For ESD issues, the design should be noted that in many places, especially on the GND wiring design and line spacing, very particular about. Some of the products there is a big issue in the ESD, the reasons have been found,
cheap coach bags, through repeated studies and experiments,
coach online outlet, found to be PCB design problems. To this end, I came up with the PCB design of the main points should be noted:
(1) PCB edge (including through-hole Via border) and other wiring should be greater than the distance between the 0.3mm;
( 2) PCB's edge all the best to go with the GND contour;
(3) GND and the distance between the other wiring in the 0.2mm ~ 0.3mm;
(4) Vbat and other wiring between keep the distance 0.2mm ~ 0.3mm;
(5) important lines, such as Reset, Clock, etc. and other wiring should be greater than the distance between the 0.3mm;
(6) high-power lines and other wiring of the keep the distance between 0.2mm ~ 0.3mm;
(7) between the different layers of GND vias should be as much as possible (VIa) is connected;
(8) at the end of the floor should be kept avoid sharp corners, sharp edges should be so smooth.
3.3
products in the circuit design and PCB design of the shell, the problem of attention after ESD, ESD will inevitably enter the product's internal circuitry, especially following ports: USB Interface, HDMI Interface, IEEE1394 interface, antenna connector, VGA interface,, DVI, key circuit, SIM cards, headsets and other types of data transfer interface, these ports will likely be the body's static electricity brought in-house circuit. Therefore, the need to use these ports ESD protection devices.
past the main use of ESD protection devices are varistors and TVS devices, but the disadvantage of these devices is generally slow to respond, the discharge voltage is not precise enough, capacitances of large, life is short, electrical performance deterioration due to repeated use. Therefore, the widespread use of current industry professional It is made by the Polymer polymer materials, internal diamond-like arrangement of discrete elements of rules, when the electrostatic voltage exceeds the trigger voltage of the device, the internal edge of the cutting-edge molecular rapidly produce the discharge, electrostatic discharge into the ground in an instant. Its biggest feature is the reaction speed (0.5ns ~ 1ns), very low capacitances of (0.05pf ~ 3pf), a small leakage current (1μA), is ideal for a variety of joints.
is small because of static electricity suppressor (0603,0402), polarity, fast response, and many other advantages, the design is now used as a protective device ESD Suppressor increasing the proportion of in use should note the following:
1, the devices need to be protected as the ports placed in the vicinity;
2, to the GND connection as short as possible;
3, GND of the connected area as large as possible.
ESD issue is one of many important issues. Electronic equipment in different ways in different circuits to avoid hazards. Now that digital products small size, density, the ESD protection has unique characteristics. Through a large number of static test results show, using this design approach, a discharge will crash the original ± 2kV to protect and improve the product, ± 8kV of electrostatic discharge in the case of the work can still be stable, played a very good static protective effect. With the increasingly widespread use of electronic devices, ESD design is a design engineer and every electronic design engineers need to focus on issues of concern, by continuously reviewing and learning, ESD issues will no longer be a problem
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