Comparative analysis between CTR and low-frequency noiseto characterize the optocoupler reliability

The CTR(Current Transfer Ratio) is usually used as characterization parameters in the optocoupler ALT(Accelerated Life Test). With the adventage of high reliability components, the time of ALT becomes too long to meet the needs of engineering. The CTR degradation appears after more than a year in the accelerated test of optocoupler storage life. The low-frequency noise of optocoupler is a characterization of reliability carrying rich information of the interface defect. The failure modes and failure mechanism of the optocouplers in storage environment was summarized and analyzed, the characterization of the relationship was researched between low-frequency noise and inter defect. The main failure mode is performance degradation in storage environment, and the corresponding failure mechanism is the CTR reduction caused by interface defect. The defect is concentrated in the light-emitting diode and phototransistor impacting the low-frequency noise directly. A accelerated test at 125 °C, 150 °C and 175 °C was conducted monitoring CTR and four other parameters related with low-frequency noise. The five parameters had different degrees of degradation. The noise amplitude at 1 Hz had the largest degradation, and the degradation of noise parameters appeared earlier than CTR.