Failure Analysis of Thin Film Resistors in High Temperature and High Humidity Environment

Ni-Cr thin film resistors are widely used for low-temperature coefficient, high precision, and stability. As we know, thin-film resistors are unstable in high temperature and high humidity environments. There is an urgent request for further research on the cause of the damage to Ni-Cr thin-film resistors under high temperature and high humidity. This paper welded thin-film resistors on the PCBs and used aging tests under 85°C and 85% RH to test their reliability and record the resistance value and change rate. In the aging tests, the resistance value of the thin film resistor shows an increasing trend. Over time the resistance value drifts or even opens in the aging test. In this paper, both non-destructive and destructive methods are used for failure analysis of the failed resistors, such as 3D confocal laser microscopy, 2D X-ray imaging, scanning electron microscopy (SEM), and energy dispersive analysis (EDS), and focused ion beam microscopy (FIB)The results show that the terminal electrode of the thin film resistor has a severe failure. The failure resistor will gradually crack due to the long-term water vapor erosion at the junction of the terminal electrode and the protective layer. These cracks will cause the resistance value to increase continuously. With the aging time, the trials continue to expand, resulting in the interlayer or intralayer fractures in the terminal electrodes, resulting in an open circuit of the resistor. In addition, the S-containing substances in the air will also enter the inside of the resistors and gradually vulcanize the surface electrode (Ag). At the same time, the resistance value of the resistor also increases, and the Ag layer becomes discontinuous when the surface electrode is vulcanized. It will also cause an open circuit in the resistor.