Abstract:

Multilayer ceramic capacitors (MLCCs) are known to experience flex cracking when subjected to bending stresses. An experimental study was conducted to determine the susceptibility to flex cracking of flexible- and standard-termination surface mount MLCCs assembled with lead-free or tin-lead solders and aged at two different temperatures for 200 h. Experimental results showed that MLCCs mounted on printed circuit boards with lead-free solder are less susceptible to flex cracking compared with MLCCs mounted on boards with eutectic tin-lead solder. Two factors which make capacitors assembled with lead-free solder less susceptible to flex cracking were discussed: the lower tensile stresses inside the capacitor body which are a result of the differing elastic-plastic mechanical properties of the solder, and the higher residual compressive stresses after solder reflow assembly which are a result of the higher solidification temperature for the Sn3.0Ag0.5Cu lead-free solder. Flexible-termination MLCCs showed much more resistance to flex cracking in comparison to standard-termination MLCCs assembled with both lead-free and tin-lead solders. Aging at elevated temperatures had little effect on flex cracking susceptibility of MLCCs assembled with tin-lead solder. For MLCCs assembled with lead-free solder, aging at 150 deg C increased the susceptibility to flex cracking in comparison with un-aged MLCCs.

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