Electrostatic hazard to electronic components

- May 03, 2016-

Electrostatic breakdown analysis

MOS tube is an ESD sensitive device. Its input resistance is very high, and the capacitance between gate and source is very small, so it is easily charged by external electromagnetic field or static electricity. A small amount of charge may form equivalent on the interelectrode capacitance. High voltage (think U=Q/C) damages the tube), and it is difficult to discharge the charge in the case of strong static electricity, which is likely to cause electrostatic breakdown. There are two ways of electrostatic breakdown: one is voltage type, that is, the thin oxide layer of the gate breaks down, short-circuit between the gate and the source, or short between the gate and the drain; the second is the power type, that is, the metal. The thin film aluminum strip is blown, causing the gate to be open or the source to be open. Like the MOS transistor, the JFET tube has a high input resistance, but the input resistance of the MOS tube is higher.

prototype pcb

The reverse biased pn junction is more prone to thermal failure than the positively biased pn junction, and the energy required to damage the junction under reverse bias conditions is only about one tenth of that under positive bias conditions. This is because most of the power is consumed in the center of the junction when reverse biasing, and more is consumed in the bulk resistor outside the junction. For bipolar devices, the area of the emitter junction is typically smaller than the area of the other junctions, and the junction is also closer to the surface than the other junctions, so degradation of the emitter junction is often observed. In addition, pn junctions with breakdown voltages above 100V or leakage currents less than 1nA (such as JFET gate junctions) are more sensitive to electrostatic discharge than conventional pn junctions of similar size.

All things are relative, not absolute. MOS tubes are only sensitive to other devices. ESD has a big feature that is random, and it can not be broken without touching the MOS tube. In addition, even if ESD is generated, the tube will not necessarily be broken down. The basic physical characteristics of static electricity are: (1) there is a force of attraction or repulsiveness; (2) there is an electric field, and there is a potential difference with the earth; (3) a discharge current is generated. These three situations, ESD, generally affect the electronic components in the following three situations: (1) the components adsorb dust, change the impedance between the lines, affect the function and life of the components; (2) destroy the insulation of the components due to electric fields or currents. And the conductor, so that the component can not work (complete destruction); (3) due to the instantaneous electric field soft breakdown or current overheating, the component is injured, although still working, but the life is impaired. Therefore, ESD damage to the MOS tube may be one or three. It is not always the second case. In the above three cases, if the component is completely destroyed, it must be detected and eliminated in the production and quality test, with less impact. If the component is slightly damaged, it is not easy to be found in normal tests. In this case, it is often found to be damaged after repeated processing or even when it is used. Not only is the inspection difficult, but the loss is also difficult to predict. Static electricity is as harmful to electronic components as serious fire and explosion accidents.

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