Mechanism of electro-migration in ceramic package induced by chip-coating polyimide

The mechanism of electromigration between the inner leads in a ceramic package was investigated. The short-circuit failure between the neighboring pins of the ceramic package, in which a polyimide-coated LSI chip was assembled, was observed in tests after burn in. An analysis of the bypass which caused the failure found that the composition of the bypass was electromigrated nickel from the inner lead. Gas analysis showed that N-methyl-pyrrolidone (NMP) and water were included in the package. From these analyses, it was found that the progress of the migration was as follows: (1) NMP and water were evaporated from polyimide film during burn in if the polyimide was insufficiently baked; (2) NMP condensed on the inner leads and absorbed water during cooling to room temperature; and (3) the electromigration occurred between the inner leads with electric potential. This failure was eliminated by sufficiently baking the polyimide coating