In this work, the effects of design parameters on the mechanical reliability of multilayer ceramic capacitors (MLCC) are evaluated by a board flex test. Using the finite element method (FEM), thermo-mechanical stresses that accumulated in the ceramic of MLCC during termination firing, soldering, and board flex test are determined by varying design parameters. The calculation results revealed that the sizes of Cu terminations are the parameters that affect the stress the most. The degree of sensitivity of the stress to the dominant parameters depends significantly on the thickness ratio of the MLCC to the board. Based on our investigation, better design rules are proposed and verified experimentally.