Solid tantalum capacitor mfr. - using two=stage anodic oxidn. of sintered anodes to lower residual current in capacitors (NL 11.7.78)

摘要

Sintered tantalum anodes are anodically oxidised for capacitors with a solid electrolyte. In a first stage (a) the anodic oxidn. is stopped when part of the thickness of the oxide layer is reached. The anodes are then washed in acid, followed by a neutralising rinse, before the anodic oxidn. is completed in a second stage (b). Stage (b) is pref. started at the same voltage as that existing at the end of stage (a). In stage (a) the max current is pref. applied to loosely connected anodes until the voltage has stabilised at the highest value plus-or-minus 10%; and the anodes are mounted on a belt for stage (b), which starts at max. current. The acid bath for washing is pref. an aq. soln. of HNO3, H2SO4 and HF but two acid solns. may be used with different concn., followed by neutralising rinse, then washing in de-ionised water. As compared with conventional Ta capacitors, the residual current is much less and is at a consistently low value.