Mechanical Failure Characteristics of Ceramic Multilayer Capacitors

The results of both uniaxial and biaxial flexure as well as toughness testing on actual commercial ceramic capacitor samples are reported. Necessary procedural adjustments are outlined for miniaturizing the applied-moment double-cantilever-beam test to accommodate these small samples. Strength and toughness testing showed that the metal electrodes lowered the fracture toughness and that the metal-ceramic interface was a preferred fracture path for crack propagation parallel to the electrodes. However, toughness did not clearly depend on crack propagation parallel or perpendicular to the electrodes, nor with flexural strengths. Flexural strengths were 0 to 40% lower, with the electrodes perpendicular to the tensile surface vs. parallel to the tensile surface. Fractures initiated from machining (or impact) flaws, or voids of various sizes, shapes, and locations, thus explaining the poor correlation between strength and toughness. Biaxial flexure tests of dielectric specimens of various sizes indicate that such a test could be scaled down and "calibrated" for actual testing of capacitors; e.g., a decrease in strength with increasing specimen thickness to support diameter ratio is indicated.