Evaluation of degradation in polyimide by recovery voltage measurement

Polyimide (PI) has been widely used for insulation in motors, integrated circuits, electric wire, cable, and so on, due to its high mechanical strength, thermal stability, chemical stability, and radiation resistance. We have examined the degradation of API (all-aromatic polyimide) and TPI (thermoplastic polyimide) soaked in H/sub 2/O or KOH by measuring recovery voltage. The peak value of the recovery voltage was found to depend on the soaking time. We have developed a theoretical equation of recovery voltage, and have found that the peak value of recovery voltage is a function of the dielectric constant. By measuring the recovery voltage, it is possible to diagnose the degradation of API and TPI.