Machining of micro-channels on polycarbonate by using Laser-Induced Plasma Assisted Ablation (LIPAA)

Abstract

Micro-channels are essentially required to fabricate critical parts of optical, healthcare, energy and consumer electronics products and systems. These can be manufactured by employing various processes such as lithography, wire moulding, chemical etching, micro-milling, micro-electric discharge machining and laser micro-machining. Laser based machining of transparent materials with high optical properties is difficult due to the high transmittance of the transparent material in the visible and near infrared spectral range. This challenge can be addressed by using the Laser-Induced Plasma Assisted Ablation (LIPAA). This paper reports experimental investigations into the machining of micro-channels on transparent material polycarbonate by using LIPAA process. Nd: YAG laser was used to generate plasmas on the aluminium substrate which were utilised to ablate the transparent polycarbonate (PC) material. Interaction of the vapour from the aluminium sheet with the incoming laser produces hot plasma, which gets expanded by inverse bremsstrahlung absorption. The expanded plasma resulted into successful fabrication of micro-channels on the PC. One of the key findings of the present work is that the long wavelength and longer pulses can be utilised for micromachining of transparent polycarbonate material. Clean and uniform channels were obtained at quite a low pulse power density (3.055 MW/cm2) with moderate pulse duration of approximately 4 ms and pulse repetition rate of 40 Hz. EDX analysis of processed samples showed the traces of oxygen, aluminium and carbon deposits edge and channel bed. Further, the closed channels were formed by using thermal bonding technique to prevent leakage and uncontrollable flow of liquid through it. Finally, the sustainability of the Laser Induced Plasma Assisted Ablation technique was confirmed by carrying out flow tests of the fabricated closed micro-channels.