MECHANICAL-BEHAVIOR OF CERAMIC CAPACITORS

Fracture toughness, modulus of rupture, and thermal shock resistance were evaluated on COG, X7R, and Z5U type commercial ceramic capacitors with and without internal electrodes. Fracture toughness was measured by precracking the samples followed by four point bend testing. Results show that the fracture toughness values for all the dielectrics are very similar, close to 1 MPa-m1/2. Relatively, COG dielectrics are slightly stronger followed by the X7R and Z5U dielectrics. The presence of electrodes slightly increases the strength of the dielectric materials. Modulus of rupture was measured by the three point bend testing, and the results were analyzed using the Weibull model. Dielectric type, sample size, presence of electrodes, and the fired chip surface condition all affect the modulus of rupture value of the ceramic capacitor. COG capacitors showed the highest strength values and X7R capacitors showed narrow distributions in strength. Thermal shock resistance measurements were made by heating the samples to different temperatures and then suddenly quenching them into water, followed by strength measurements. Critical temperature differences for fracture initiation for different dielectrics were determined from these results and compared with the thermal shock resistance parameters for fracture initiation (R and R') which were calculated using the measured physical and mechanical properties of these materials. Results show that the critical temperature difference for fracture initiation is close to 125-degrees-C for 1206 size Z5U and 150-degrees-C for X7R and COG dielectrics. These values compare very well with the predicted values.