C. Hillman, N. Blattau, and D. Barker
CALCE Electronic Products and Systems Center
University of Maryland
College Park, MD 20742
Flex cracking of multilayer ceramic capacitors is often initiated during manufacturing. The resulting defect is often latent in nature and can result in unacceptable failure rates in the field. Flex cracking is an overstress failure mechanism and can be avoided by understanding when the stress being applied exceeds the strength of the ceramic. The stress being applied was determined by using normalized radius of curvature and finite element analysis. The fracture strength of X7R dielectric was determined by using beam theory and finite element analysis to evaluate experimental results from three point bending. A comparison of stress vs. strength provides design guidelines for placement of ceramic capacitors based on capacitor size, amount of flexing, the potential of rework, and an acceptable level of risk.
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