High repetition rate effect on the chemical characteristics and composition of Upilex-S polyimide ablated by a UV Nd: YAG laser

X-ray photoelectron spectroscopy was applied to investigate the chemical and structural modification of Upilex-S polyimide films ablated by a 355 nm pulsed Nd:YAG laser at different high repetition rates. The changes in the chemical characteristics and composition of the ablated area were found to be markedly dependent on the repetition rate. With every increase in the repetition rate, the relative carbon content of the ablated area increased, while the nitrogen and oxygen contents were reduced. After being irradiated by the UV laser, a new component was detected at 287.4 eV, assigned to be the amide structure, as a result of a breakage of the imide ring occurring between the nitrogen and carbonyl carbon atoms. The peak area of the C-C group also increased, while the peak areas of C=O and the amide group decreased with each increase in the repetition rate. These results are attributed to both the cumulative heat and the increase of the input energy.