Mechanism of electromigration in ceramic packages induced by chip-coating polyimide

The mechanism of electromigration between the inner leads of large-scale integrated (LSI) chips in ceramic packages that are coated by thick polyimides to prevent alpha-particle-induced soft errors is discussed. Short-circuit failures between neighboring inner leads in the packages were monitored in the final test after burn-in of LSI devices. The shorting paths between the leads were observed by an optical microscope and scanning electron microscope (SEM). It was found that the path was produced by a deposit between the inner leads. The deposit was found to be composed of electromigration nickel from the inner lead. Also, n-methyl-pyrrolidone (NMP) and water were found in the package by gas analysis. A possible short-circuiting mechanism is discussed. >