Why are MOS transistors broken down and how to solve this problem:

Why are MOS transistors broken down and how to solve this problem:

The input resistance of MOS transistor itself is very high, and the capacitance between gate and source is very small, so it is easily charged by external electromagnetic fields or static electricity induction. A small amount of charge can form a relatively high voltage (U=Q/C) on the inter electrode capacitance, which can damage the transistor. Although MOS input terminals have anti-static protection measures, they still need to be handled with care. During storage and transportation, they should be packaged in metal containers or conductive materials, and not placed in chemical materials or synthetic fabrics that are prone to static high voltage. During assembly and debugging, tools, instruments, workbenches, etc. should be well grounded. To prevent damage caused by static interference from operators, it is not advisable to wear nylon or synthetic clothing, and to ground hands or tools before touching the integrated block. When straightening, bending, or manually welding device leads, the equipment used must be well grounded.

Secondly, the protection diode at the input of the MOS circuit has a current tolerance of generally 1mA when conducting. In the event of excessive transient input current (exceeding 10mA), an input protection resistor should be connected in series. However, in the initial design of 129 #, no protective resistor was added, which is also the reason why the MOS transistor may break down. By replacing the MOS transistor with an internal protective resistor, this failure can be prevented from occurring. Also, due to the limited instantaneous energy absorbed by the protective circuit, excessive instantaneous signals and high electrostatic voltages will render the protective circuit ineffective. Therefore, during welding, the soldering iron must be reliably grounded to prevent electrical leakage through the input end of the device. Generally, when in use, the power can be turned off and the residual heat of the soldering iron can be used for welding, and the grounding pin should be soldered first.

The basic physical characteristics of static electricity are: the ability to attract or repel; There is an electric field present, with a potential difference from the earth; It will generate discharge current. These three situations will have the following impacts on electronic components:

1. Components absorb dust, change the impedance between circuits, and affect the functionality and lifespan of the components.

2. The insulation layer and conductor of the component are damaged by an electric field or current, rendering the component inoperable (completely destroyed).

3. Due to instantaneous electric field soft breakdown or current overheating, the component may be damaged, and although it can still work, its lifespan is compromised.

In the above three situations, if the component is completely damaged, it will be detected and eliminated in production and quality testing, with less impact. If the component is slightly damaged, it is not easy to detect during normal testing. In this case, it is often discovered to be damaged after multiple processing and even during use. Not only is it difficult to inspect, but the loss is also difficult to predict. The harm of static electricity to electronic components is no less than the losses caused by serious fire and explosion accidents