Analysis of soldering-induced cracking of BaTiO3ceramic capacitors

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Abstract
Cracks were found in ceramic capacitors after soldering on hydrid microcircuit boards during fabrication. Samples from an older batch of capacitors which had been successfully soldered were compared with capacitors from the problem group. X-ray elemental analysis showed differences in chemistries of the barium titanate (BaTiO3) dielectrics, the capacitor plate elements, and the termination and solder layers. Crack initiation sites were found along the outer surfaces originating at the metal/ceramic interface; in many cases crack growth from an initial flaw occurred in discrete steps. This fractographic evidence indicated that thermal stresses at the metal/ceramic interface were the driving force for crack propagation. These stresses could have originated at several times: during the original manufacture of the capacitors, the reflow board soldering process, or subsequent reworking operations. Fracture toughness and hardness measurements were made from cracks and impressions, respectively, of a Vickers pyramid diamond. The fracture toughness of the older capacitor material was only half the value of the newer capacitor. Thus, the material was not the source of cracking, but rather a difference in design application between the old and the new.

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