Ceramic-Chip-Capacitor Attachment

Soldering of ceramic-chip capacitors to various kinds of circuit bearing substrates has been accepted ever since capacitors were first introduced to electronic circuit and packaging designers. The palladium-silver end-cap terminals normally Supplied were, in fact, advertised as being solderable with minimum leaching of silver into the solder. Upon a detailed investigation of a capacitor failure it was discovered that a crack had occurred under the end termination of a capacitor and, furthermore, that this crack could not be detected from the outside. Indeed, very careful cross sectioning was required, followed by equally careful microscopic examination. Further investigation led to the conclusion that the crack thus discovered was not an isolated instance of this phenomenon. This paper, and the experimental data it reports, will show that capacitor attachment to alumina substrates using solder causes the capacitors to crack, but that these cracks rarely result in complete electrical failure of the capacitor. The paper will also show that preheating the substrate to a specific temperature during the soldering operation will minimize the cracking phenomenon. While some inferences may be drawn as to the mechanism causing the cracking, the elucidation of this mechanism was not the purpose of the study to be reported here. The elimination of cracking by using conductive epoxy for attaching ceramic-chip capacitors to alumina substrates will be shown.