ESD Design Measures in Circuit Design

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ESD Design Measures in Circuit Design [Copy link]

Design measures for ESD in circuit design 1. Use avalanche diodes for ESD protection. This is also a method often used in design. The typical practice is to connect an avalanche diode in parallel to the ground on the key signal line. This method uses the avalanche diode to respond quickly and has the ability to clamp stably, which can consume the accumulated high voltage in a short time and protect the circuit board. 2. Use high-voltage capacitors for circuit protection. This practice usually places high-voltage ceramic capacitors or Y capacitors at the I/O connector or key signal position, and the connecting wires are as short as possible to reduce the inductive reactance of the connecting wires. If a capacitor with a low voltage resistance is used, it will cause damage to the capacitor and lose its protective function. 3. Use ferrite beads for circuit protection. Ferrite beads can effectively attenuate ESD current and suppress radiation. When faced with two problems, a ferrite bead would be a good choice. 4. Spark gap method. This method is seen in a material. The specific method is to use triangular copper foils with their tips aligned with each other in the microstrip line layer composed of copper foils. One end of the triangular copper foil is connected to the signal line, and the other triangular copper foil is connected to the ground. When there is static electricity, tip discharge will occur and consume electrical energy. 5. Use LC filter method to protect the circuit. The filter composed of LC can effectively reduce the high-frequency static electricity entering the circuit. The inductive reactance of the inductor can effectively suppress the high-frequency ESD from entering the circuit, while the capacitor has shunted the high-frequency energy of ESD to the ground. At the same time, this type of filter can also smooth the signal edge and reduce the RF effect, and the performance has been further improved in terms of signal integrity. 6. Multilayer board for ESD protection. When the cost allows, choosing a multilayer board is also an effective means to prevent ESD. In a multilayer board, since there is a complete ground plane close to the trace, ESD can be coupled to the low impedance plane more quickly, thereby protecting the key signal. 7. The method of leaving a protective belt around the circuit board. This method usually draws traces around the circuit board without a soldering layer. Connect the trace to the housing when conditions permit, and pay attention to the trace not forming a closed loop, so as not to form a loop antenna and introduce greater trouble. 8. Use CMOS devices or TTL devices with clamping diodes to protect the circuit. This method uses the principle of isolation to protect the circuit board. Since these devices are protected by clamping diodes, the complexity of the design is reduced in the actual circuit design. 9. Use decoupling capacitors. These decoupling capacitors should have low ESL and ESR values. For low-frequency ESD, decoupling capacitors reduce the area of the loop. Due to the effect of its ESL, the electrolyte effect is weakened, which can better filter out high-frequency energy. For electronic products/equipment - whole machine level & circuit board level blocking and conducting System blocking and conducting at the whole machine level 1. Shell and mounting parts: metal and conductive electroplating materials are materials that easily attract and accumulate static electricity; projects with high ESD requirements should avoid using these materials as much as possible. 2. When conductive materials must be used: effective and evenly arranged grounding points must be reserved in advance in the structure; generally speaking, the grounding effect of ejector pins or metal shrapnel is better than that of conductive foam and conductive cloth. 3. For parts that cannot be grounded, such as electroplated side buttons, special treatment must be done on the motherboard; including: (1) Adding components such as varistors, TVS or capacitors; (2) Reserving GND pins; (3) Exposed copper on the edge of the board attracts electrostatic discharge; 4. The metal parts on the casing must be more than 2 meters away from the components and traces.2mm or more distance. 5. Avoid exposing devices to holes and seams during stacking; if it cannot be avoided, find a way to block them during assembly; common practices include sticking high-temperature tape or anti-static tape to block them; all structural designs need to leave space for adding isolation sheets. Plugging and conducting at the circuit board level 1. Increase the area of PCB board to increase the GND area and enhance its ability to neutralize static electricity; cost or differentiated stacking allows us to make it smaller. 2. For really small boards, there must be at least one complete GND layer; and it must be able to maintain a good connection with the battery ground pin; we often cannot leave a complete ground layer due to cost. 3. For very small circuit boards, because the circuit board's ability to neutralize charge is limited, more consideration should be given to blocking the entire machine and less to conducting. 4. When selecting devices, high-voltage ESD devices should be selected; when selecting electrostatic protection devices, its capacitance should be considered to avoid inappropriate capacitance causing the failure of the signal itself of the protected signal line. 5. When placing devices, devices that are easily affected by ESD should be covered in shielding covers as much as possible. 6. The shielding cover must ensure effective and evenly distributed grounding! It should be directly connected to the main ground, and the blind hole should be directly combined with the buried hole; the grounding should be evenly distributed around. 7. For circuits that are easily exposed, such as IO ports and keyboards, electrostatic protection devices must be added. 8. When placing devices, the principle of release in the vicinity must be followed. ESD protection devices should be placed close to IO and side keys; secondly, they should be placed across the middle road; avoid placing them close to the chip; this can reduce the transient coupling of ESD pulse signals into nearby lines; although there is no direct connection, this secondary radiation effect will also cause other parts to work in disorder. 9. Layout routing must comply with the principle of effective protection; routing should go from the interface to the TVS first, and then to the CPU and other chips; electrostatic protection devices "hanging" on the signal line far away will cause protection failure due to excessive parasitic inductance of the lead, making the protection ineffective. 10. The connection between the ground pin of the TVS tube and the main ground must be as short as possible to reduce the parasitic inductance of the ground plane. 11. The TVS device should be as close to the connector as possible to reduce transient coupling into nearby lines. Although there is no direct path to the connector, this secondary radiation effect will also cause work disorder in other parts of the circuit board. 12. Avoid running important signal lines on the edge of the board; such as clock and reset signals. 13. Unused areas on the motherboard should be laid as much as possible; and connected to the main ground; laying more ground reduces the distance between the signal and the ground, which is equivalent to reducing the loop area of the signal. (The larger the area, the greater the field flow contained, and the greater the induced current) 14. It is important to note that direct discharge of ESD to the ground may damage sensitive circuits. When using TVS diodes, one or more high-frequency bypass capacitors should be used. These capacitors are placed between the power supply and ground of the vulnerable components. The bypass capacitor reduces charge injection and maintains the voltage difference between the power supply and ground ports. 15. It is better to have the power supply in the middle of the motherboard than at the edge of the board; it is better to have the ground layout in the middle of the board than at the edge of the board.