In general, the failure rate of resistors is relatively large compared to other devices, so we generally estimate that the life of resistors is relatively small. However, the failure rate will increase at high pressure and high temperature, so in some scenarios, we still need to carefully evaluate the life of the resistor.
Factors affecting the resistance life:
(1) If the temperature is too high, it can be burned quickly.
(2) The acidity and alkalinity of the environment directly corrode the resistance and cause damage.
(3) When the external force exceeds a certain limit, the resistance will break.
Therefore, to extend the life of the resistor, heat dissipation should be good, to prevent burning, the environment should be dry, free of pollutants, and avoid external forces. A resistor with a large resistance value will have a relatively long life. The resistance of the MΩ level is very high. When used in low voltage, due to low power consumption, the working environment has little impact, and the general life is very long. No special attention is required (relative to other components such as electrolytic capacitors). Most of the problems are caused by high-voltage work. When working at high voltage, the manufacturing process and materials used for the resistors have considerable requirements. It is necessary to consider the maximum possible use of power (the safe power value of the resistor is more than twice the actual working power, and some products are not designed properly, and the power used and the rated power value of the resistor are often too close), so the temperature tolerance is The most basic requirements. The instantaneous pulse voltage and surge current will also cause a fatal blow to the resistance. For products with poor pin soldering and defective insulation processes, it will not take long to crash and burn. The correct use of resistors with a service life of more than 100,000 hours is not a problem.
Therefore, high-resistance resistors such as 1MΩ distinguish between high voltage and general purpose. High-voltage resistors are several times more expensive than general resistors, but resistors are low-cost components after all, and the number of resistors used in high-voltage is not much. For the scenario of high voltage and large current, leaving enough derating design can effectively improve the life of the resistor.
Therefore, the resistance must have different lifespans when used and not used. The resistance will have different lifespan in different usage scenarios. Therefore, the life of the resistor has two: load life and shelf life.
Load Life, the full name of resistive load life, should be Load Life Stability. The percentage of the relative change in resistance of a resistor under long-term load at the rated power indicates the parameter of the life of the resistor.
The so-called resistance load life is the estimated life of the resistor when it is used. In fact, the load life of the resistor is related to these three factors that affect the resistance: the power, temperature and time of use of the resistor. The active period of resistance change is several hundred hours before use, and it becomes more stable as the time of use increases. This is because the resistance element itself tends to stabilize over time, or the stress between the resistance element and the substrate is gradually released. The index of the resistance load life can only be tested by sampling, and the expected life of the product can be converted through the sample test. Because this test requires at least 1,000 hours, aerospace applications may require up to 10,000 hours of testing, and this test is a destructive experiment. The load life of the resistor is generally marked in the device data, as shown in the figure.
The shelf life of the resistor refers to the life of the resistor when it is not used, only when it is stored in the warehouse. The shelf life of the resistor also refers to the resistance stability under storage conditions. The shelf life of the resistor is the same as the load life. The longer the resistor is stored, the change in resistance will tend to be stable. Generally, precision resistors are not used immediately in some precision equipment manufacturing equipment, but stored for some time before use, because the resistance value stability is better after a period of storage. The storage of the resistance should pay special attention to humidity control, humidity will have a great impact on the resistance of any resistance.