Winter is coming, the human body can release up to tens of thousands of volts of static electricity, the end of the project has also come to the end of the stage, we do not because of the hand carrying static electricity directly touch the motherboard and cause the motherboard to burn out!
It is common knowledge of electronic engineers that human hands cannot directly touch or touch circuit boards. Why?
First, the harm of static electricity
The electrostatic voltage carried by the human body varies from a few volts hundreds of volts to tens of thousands of volts in different environments. Human contact with electronic components (conductors) will produce electrostatic discharge, so that the device damage, reduce reliability; In serious cases, the device breakdown caused by electrostatic discharge will directly scrap the product.
In addition, the process of electrostatic discharge radiates radio waves in a certain frequency at the same time, which interferes with the surrounding microprocessor, causing the application program running disorder and seriously affecting the normal work of the equipment.
Therefore, it is necessary to standardize the operation in daily production and work (including correct wearing of electrostatic ring); Try to avoid direct contact with electronic components, especially in the electrified state.
The influence of static electricity on the feedback loop of the core board
The M3352 industrial core board (Cortex-A8 core) was taken as an example for testing (the core board passed the Level 4 test of EMC industry, including static electricity, surge, pulse group, conduction disturbance, etc.). In the energizing state, the engineer’s finger touched the yellow ring position as shown in Figure 3, which could induce the system restart. What is the reason for this?
Fig. 3M3352 industrial core board
Fig.3 The yellow ring injection area (R80, C116, R79, R78) is the negative feedback and compensation network (FB part) of the system’s main power supply of 3.3VDC-DC, as shown in Fig. 4.
Fig. 4 System power supply circuit
Touch by hand (interference introduced by equivalent resistance of human body) changes the characteristics of feedback loop (including pole deviation), causing feedback loop oscillation and resulting in unstable output voltage of DC-DC.
The output voltage of DC-DC is unstable, which may cause the system to restart (DC-DC automatically reduces the output voltage) or burn out the main chip of the circuit board (DC-DC automatically increases the output voltage) in serious cases. Therefore, it is forbidden to touch the mainboard when it is charged.
Three, how to prevent static electricity
1, anti-static cordless wrist band
According to the “corona discharge” effect and the principle of tip discharge, when the accumulated charge exceeds a certain value, it discharges into space due to potential difference, so as to achieve the purpose of eliminating static electricity. Features: convenient, reliable, mobile post only allowed to wear. Electrostatic dissipation time: less than 0.5s.
2, anti-static wrist band
The human skin is in direct contact with the conductive electrostatic material of the wrist band. When the wrist band is grounded, the static electricity generated by the human movement is quickly discharged through the grounding system. Electrostatic discharge time: less than 0.1s.
3. Anti-static PU coated gloves
Antistatic PU gloves can further prevent the transmission of human static electricity to the circuit board through hand contact. Conductive wire spacing on back of hand: 10mm.