Flexible printed circuit board (FPCB), consisting of copper sheets laminated onto non conductive film substrates with
multiple structures, are core elements in electronics with their flexibility and capability of high density 3 dimensional
wiring characteristics. In laser applied FPCB processing, a better understanding of the ablation mechanism leads to
precision control of the depth processing especially by monitoring of the material transition layer. For this purpose, here
we investigate the temporal and spectral behavior of the plasma plum generated on the single sided structure of FPCB
using the technique of laser induced breakdown spectroscopy (LIBS). Using KrF excimer laser, the characteristic
spectral emission lines of C2 swan band at the wavelength of 516.5 nm and neutral copper at the wavelength range from
510 nm to 522 nm are acquired under ambient pressure in the ablation process of polyimide film and copper coated
layer respectively. From a time delay from 50 ns to 4.05 μs from the beginning of the laser pulse, the temporal profiles
of the spectral intensity are obtained in steps of 200 ns, which have a tendency of exponential decrease on both C2 and
neutral copper. In particular, we concentrate our attention on the temporal intensity behavior of the Bremsstrahlung
continuum emission that decides the proper set of detection time window, by which the monitoring sensitivity of LIBS
is determined. Finally, using the information of the temporal analysis for each molecular, atomic, and continuum
emission, the transition layer between polyimide and copper film is distinguished by their characteristic peak
information.
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