Modelling and analysis of UV laser micromachining of copper

UV laser micromachining of metallic materials has been used in microelectronic and other industries. Knowledge and data about the process vary with feature size, material, laser wavelength and pulse duration. This paper reports on experimental and numerical investigation of micromachining of copper using a frequency tripled Nd: YAG laser with 50 ns pulse duration. An axisymmetric model is developed which allows consideration of laser beam distribution and its coupling with the target material. This is important for the process where the removal extent is in the same order of the removal depth. The model uses an enthalpy method to track the solid/liquid interface. Stefan and kinetic boundary conditions are applied at the liquid-vapour interface, and property discontinuity across the Knudsen layer is considered. Relevant experimental results are also presented and compared with the model predicted results. The range of thermal vaporisation dominated machining of copper using nanosecond time scale lasers was studied, and optimum laser intensity for micromachining of copper was suggested.