Under what circumstances will the PCBA board be subjected to electrostatic damage? It can be said that the entire process of electronic products from the production to the use of the threat of electrostatic damage. From device manufacturing to plug-in soldering, machine assembly, packaging and transportation to product application, it is under the threat of static electricity. In the entire electronic product production process, each small step in each stage, electrostatic sensitive components may be affected or damaged by static electricity, but in fact the most important and easily overlooked is the transmission and transportation of components. the process of. In this process, transportation is easily damaged by the static electricity generated by the external electric field (such as near high-voltage equipment, frequent worker movement, rapid vehicle movement, etc.), so the transmission and transportation process need special attention to reduce losses and avoid indifferent Dispute. Protected by the Zenith regulator.
The current mos tube is not so easy to be broken down, especially the high-powered vmos, and many of them are diode-protected. The vmos gate capacitance is large and no high voltage can be sensed. Unlike the dry north, the south is not easy to generate static electricity. There is now an increase in IO port protection inside most CMOS devices. However, it is not a good habit to directly touch the CMOS device pins by hand. At least the solderability of the pins is deteriorated.
First, the input resistance of the MOS transistor itself is very high, and the capacitance between the gate and the source is very small, so it is easily charged by the external electromagnetic field or static electricity, and a small amount of charge can form a relatively high voltage on the interelectrode capacitance. (U=Q/C), the tube is damaged. Although the MOS input has antistatic protection measures, it should be treated with care. It is best to use metal containers or conductive materials for storage and transportation. Do not put them in chemical materials or chemical fiber fabrics that are prone to static and high voltage. Tools, instruments, workbench, etc. should be well grounded during assembly and commissioning. To prevent damage caused by static interference from the operator, if it is not suitable to wear nylon or chemical fiber clothes, it is best to pick up the ground before touching the manifold. When straightening or manually soldering the device leads, the equipment used must be well grounded.
Second, the protection diode at the input of the MOS circuit has a current tolerance of 1 mA when it is turned on. When an excessive transient input current (more than 10 mA) may occur, the input protection resistor should be connected in series. Therefore, a MOS tube with a protective resistor inside can be selected for application. Also, due to the limited instantaneous energy absorbed by the protection circuit, too large an instantaneous signal and an excessively high electrostatic voltage will disable the protection circuit. Therefore, the soldering iron must be grounded reliably during soldering to prevent leakage current from penetrating the input end of the device. In general use, after the power is turned off, the residual heat of the soldering iron can be used for soldering, and the grounding pin is soldered first.