Finite Element Analysis and Design of Thermal-Mechanical Stresses in Multilayer Ceramic Capacitors

A three-dimensional finite element model describing the thermal-mechanical stress distribution in multilayer ceramic capacitors (MLCCs) during termination firing, soldering, and bending tests is presented. Numerical results indicate that the thermal residual stresses originating from the soldering process are approximately one-fifth to half of the magnitude of the flexural stresses at the crack occurrence during the board flex test. The peak tensile stress from numerical simulations correlates with the crack initiation site observed in situ in board flex tests. The effects of inner electrode number, solder wicking height, lateral margin length, and the thickness of nickel in the termination component on mechanical failure during the board flex test are also investigated. Numerical results demonstrate that the maximum tensile stress could be effectively relieved by increasing the length of the lateral margin. In addition, a judicious combination of the solder wicking height and nickel termination thickness can further diminish the peak tensile stress during the board flex test. Finally, better design criteria are also developed by modifying the geometric parameters of MLCCs using Taguchi orthogonal arrays to decrease the peak tensile stresses that occur during board flex tests.