Effect of Mechanical Stresses on Characteristics of Chip Tantalum Capacitors

The effect of compressive mechanical stresses on chip solid tantalum capacitors is investigated by monitoring the characteristics of different part types under axial and hydrostatic stresses. An exponential increase of leakage currents was observed when stresses exceeded a critical value, which varied on average from 10 to 40 MPa depending on the part type. For the first time, reversible variations of leakage currents (up to two orders of magnitude) with stress have been demonstrated. Mechanical stresses did not cause significant changes of ac characteristics of the capacitors, whereas breakdown voltages measured during the surge-current testing decreased substantially, indicating an increased probability of failures of stressed capacitors in low-impedance applications. Variations of leakage currents are explained by a combination of two mechanisms: stress-induced scintillations and stress-induced generation of electron traps in the tantalum pentoxide dielectric.