Fabrication of microchannel on polycarbonate below the laser ablation threshold by repeated scan via the second harmonic of Q-switched Nd:YAG laser

Laser micromachining (LMM) is widely used to manufacture precise microchannels required in micro-electro mechanical systems (MEMS) devices. This paper reports manufacturing of microchannels on transparent polycarbonate (PC) by using nanosecond Q-switched Nd:YAG laser at a visible wavelength of 532 nm. A number of experiments were carried out at various levels of laser fluence 3.97, 4.41, 7.35, 14.70 and 29.40 J/cm(2), and by repeating the number of laser scans from single to the maximum of fifteen scans. It was observed that the laser fluence below to ablation threshold results in bulging and formation of bubbles in the laser irradiated region. From the microscopic images, it was observed that with the repeated shots of laser, the ablation can be induced below the ablation threshold, mainly due to the incubation effect. The repeated-scanning at the ablation threshold fluence generates a channel. The channel depth was observed to increase with the increase in laser fluence. A U-shaped microchannel up to a width of 400 mu m having an aspect ratio of one was successfully manufactured at a laser fluence of 14.7 J/cm(2) and five number of laser scans. These channels were open channels and were closed afterwards which can be used in various micro-fluidic applications. These studies will also help in achieving the optimum process parameters for the required dimensions of the channel on the polycarbonates.