Long term in vitro monitoring of polyimide microprobe electrical properties

In vitro soak tests lasting over 400 days were performed on polyimide sieve electrodes (PI2611D) using a method that allows in situ measurement of the impedance and relative dielectric constant of polyimide or alternate polymers. It was found that following an initial period of change, both values stabilized after a period of about 100 days. The dielectric constant was measured at 1 kHz and found to increase by 18% over 406 days. A short-term comparison (23 days) between polyimide cured on a hotplate in air versus using an oven with N₂ was also performed. No difference could be seen between the 2 methods.