An application note from Vishay on the causes of increased DC leakage current on solid chip tantalum capacitors. PDF link Here.
This paper is submitted as an educational medium for use by anyone who has interest in solid tantalum chip capacitor performance. It represents technical phenomena that are generic to all solid tantalum chip capacitors. This paper provides a general description of tantalum capacitor construction; a discussion of DC leakage failure mechanisms, and some process controls relating to these failure mechanisms.