Hybrid laser scribing and chemical etching technique using pulsed Nd<sup>3+</sup>:YAG laser to fabricate controlled micro channel profile

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Laser scribing is carried out using a Q-switched (Brilliant B, Quantel) Nd3+:YAG laser system to scribe micro channels on copper coated on polyimide film, where copper thickness is approximately 35 microns and polyimide film thickness is 50 microns. Chemical etching is performed using FeCl3 solution for the laser scribed micro channels and from the experimental results it is observed that depth of the channel after etching is increasing with a reduction in the recast height. It is observed that with the increase in concentration of FeCl3 and the etch time, the material removed from the copper target increased. The height of recast for the 50 μm wide micro channel scribed using 20 mJ of energy and a laser wavelength of 532 nm reduced from 10 μm to 5 μm in case of 10% FeCl3 etched for 1 min. However the overall thickness of the copper thin film is observed to reduce from 35 μm to 30 μm. Hence a hybrid technique using NaCl as the scribing medium is developed, so that CuCl2 formed in the process of scribing helped in achieving a localized etching inside the channel without affecting the total target thickness.
Copper thin films, Laser assisted chemical etching, Micro channels, Nano second laser scribing, Recast layer