The degradation mechanism of ruthenium-based thick film resistors is investigated in accelerated tests under various
conditions of humidity, temperature and overload stress. This study shows that the variation of resistance is mainly
caused by hydration and dehydration in the conductive component RuO2: RuO2+xH2O↔RuO2 • xH2O. In
addition to measuring resistance, the Third Harmonic Index (THI) is studied as the characteristic which may indicate
the degree of various defects in resistors. A strong correlation exists between “the initial THI” and “the variation
rate of resistance during an accelerated test”. A resistor which indicates a quite large initial THI shows remarkable
variation of resistance, and has scratches and/or foreign substances on the surface of the thick film resistor. As a
result, it becomes evident that the initial THI can be used to predict the stability of a resistor in a nondestructive test.
