Generally speaking, compared with other devices, the failure rate of resistors is relatively large and low, so we generally evaluate that the lifetime of resistors is relatively short. However, due to the increase of efficiency under high pressure and high temperature, some scenarios need to carefully evaluate the life of resistors. What are the factors that affect the working life of SMD resistors? The following small series is introduced in detail.
Factor affecting that work life of patch resistors
(1) the temperature is too high, which can make it burn quickly;
(2) The pH value of the environment, which directly corrodes the resistance and causes its damage;
(3) If the external force exceeds a certain force limit, the resistance will break;
Therefore, it is necessary to prolong the life of resistors, dissipate heat well, prevent burning, keep the environment dry, avoid pollutants and avoid external forces. Resistors with large resistance values have relatively long life. Mω class has high resistance value, low power consumption when used at low voltage, little influence on working environment, long service life in general, and no special attention (compared with other electrolytic capacitors and other components). Problems often occur in high-pressure work. When working at high voltage, the manufacturing process and materials of resistors have considerable requirements. It is necessary to consider that the maximum possible power will be used (the safe power value of the resistor is more than twice the actual working power, and some products are improperly designed, so the power used is too close to the rated power value of the resistor), so the temperature tolerance is the most basic requirement. In addition, instantaneous pulse voltage and surge current also bring fatal blow to resistance. Products with poor pin welding and defective insulation technology will soon collapse and burn out. If the resistor is used correctly, there is no problem if its service life is over 100,000 hours.
Therefore, high resistance resistors like 1mω can distinguish high voltage from general use. The price of special resistors for high voltage is several times higher than that of general resistors, but resistors are cheap components after all, and the number of resistors used in high voltage is not much. For the scene of high voltage and high current, enough derating design can effectively prolong the life of the resistor.
However, the life of resistors is quite different when they are used or not. The life of resistors will be different in different usage scenarios. Therefore, there are two life of resistors: load life and shelf life. The full name of resistance Load Life loadlife should be Load Life Stability. The relative change percentage of resistance value of resistor under rated power and long-term load is a parameter indicating the life of resistor.
The so-called resistance load life is the estimated life when the resistance is used. In fact, the load life of the resistance is related to the three factors that affect the resistance: the power, temperature and service time of the resistance. The active period of resistance change is in the first few hundred hours of use, and it tends to be stable with the longer the use time. This is because with the passage of time, the resistance element itself tends to be stable, or the stress between the resistance element and the matrix is gradually released. The index of resistance load life can only pass sampling test, and the expected life of products can be calculated by sample test. Because this test takes at least 1,000 hours, aerospace applications may take up to 10,000 hours, and this test is a destructive experiment. The load life of resistors is generally marked in the device data, as shown in the following table.
| Load Life |
70℃on-off cycle 1,000hrs |
+5% |
End: The shelf life of resistors refers to the life when resistors are only stored in the warehouse when they are not used. The shelf life of resistors refers to the stability of resistance under storage conditions. The shelf life of a resistor is the same as that of a load. The longer a resistor is stored, the more stable its resistance will be. Usually, some precision resistors used in precision instrument manufacturing equipment are not used immediately, but stored for some time before being used, because the resistance value is more stable after being stored for a period of time. We should pay special attention to humidity control in the storage of all resistors. Humidity will have a great influence on the resistance of any resistor.
