Absorption voltages and insulation resistance in ceramic capacitors with cracks

Time dependence of absorption voltages (V_abs) in different types of low-voltage X5R and X7R ceramic capacitors was monitored for a maximum duration of hundred hours after polarization. To evaluate the effect of mechanical defects on V_abs, cracks in the dielectric were introduced either mechanically or by thermal shock. The maximum absorption voltage, time to roll-off, and the rate of voltage decrease are shown to depend on the crack-related leakage currents and insulation resistance in the parts. A simple model that is based on the Dow equivalent circuit for capacitors with absorption has been developed to assess the insulation resistance of capacitors. Standard measurements of the insulation resistance, contrary to the measurements based on V_abs, are not sensitive to the presence of mechanical defects and fail to reveal capacitors with cracks.