Breakdown pattern identification in high temperature dielectric films using scanning electron microscopy (SEM)

In this research paper DC breakdown patterns identification were carried out after applying high voltages across samples of 25 μm Kapton® (polyimide) and Mylar® polyester (poly(ethylene terephthalate), PET) films. For pattern identifications, Scanning Electron Microscopy (SEM) technique was employed for acquiring 150× and 300× magnified images. In both images the shape of breakdown area was almost identical to the shape of electrodes. The SEM results clearly revealed that the melting process during high voltage DC breakdown process is higher in case of Mylar® polyester than that of Kapton® (polyimide). In case of Mylar® at room temperature, observed hole diameter was approximately 265.5 μm with the total effected area of 55.3×10^-9 m² at DC breakdown strength of 326.7 MV/m as compared to Kapton®, which was 155.7 μm with total effected area of 19×10^-9 m² at breakdown strength of 364.9 MV/m. In these films for the measurement of electrical breakdown strength a new type of environmental chamber was used. Two-parameter Weibull distribution has been used to analyze the results.