Characteristics and development of damage in the interface of polyimide multilayer films under a repetitive-frequency-pulsed voltage

To study the initiation and development of interfacial electrical damage in multi-layer dielectrics, an aging test of 3-layer polyimide films was conducted under pulsed voltage with a repetitive frequency of 500 Hz and a maximal amplitude of 30 kV. The variation in the damage morphology with the number of applied pulses was analyzed by a statistical method. The circuit current and partial discharge at different aging stages was measured, and the Fourier transform infrared spectrum analysis results of the aged and unaged sample regions were compared. The results demonstrate that the partial discharge in the dielectric interface gap, which is unavoidable in manufacturing, is the main cause of damage. It initiates from the interface and grows into the interior of the dielectric with the application of pulses. When there are no macroscopic defects on dielectric films, damage presents a punctiform morphology. The damage process can be divided into the following three stages: surface roughening damage, steady growth stage of damage points, and pre-breakdown stage. Differing from dielectrics without macroscopic defects, dielectrics with original void defects present transverse dendritic damage channels that initiate from the edge of the defect.