Evaluation of polyimides as dielectric materials for multichip packages with multilevel interconnection structure

Using a temperature-humidity-bias (THB) screening test, nine commercial polyimides were evaluated for applications to multichip packages with a multilevel interconnection structure. Among these polyimides, DuPont PI2555 performed best under the test condition, i.e. 85 degrees C/85%RH (relative humidity)/180-V DC bias over 3-mil spacing. However, a slow increase of leakage current was observed in situ on TiPdAu triple-track test samples coated with PI2555. This THB performance was improved by modifying PI2555 with a proprietary additive. However, the thermal stability of PI2555 was degraded by the additive. The dielectric constant of the modified PI2555 was 3.4 at 1 kHz, which is similar to that of PI2555.>