Fabrication of CaSiO3 LTCC high aspect ratio microstructure by laser chemical assisted micro-milling

Abstract

As a new generation of chip-packaging materials, CaSiO3 LTCC substrates have the characteristics of high frequency, low thermal expansion coefficient, and low dielectric loss. These materials are widely used in radar communication and other industries. However, in the condition of high heat density, it is difficult to adapt calcium silicate with a low thermal conductivity to the heat dissipation requirements. To improve the heat dissipation performance, high-aspect-ratio heat-dissipation microchannels must be prepared on the surface of the CaSiO3 LTCC substrate. In this study, a new nanosecond laser and chemical milling-assisted micro-milling (NLCAM) method is proposed. The processing mechanism of the nanosecond laser ablation of CaSiO3 is explored and the influence of the laser parameters on the depth of the etching groove, top width, and hardness of the residual modified layer are studied by establishing a laser energy superposition model and test method. The improvement of milling force and milling surface quality by laser is studied. The results demonstrate that the laser power has the most significant effect on the ablation depth and width of the top of the CaSiO3; the excess heat diffuses outside the laser irradiation area, increasing the width of the top of the CaSiO3 beyond the designed width. With an increase in the scanning speed and scanning distance, the ablation depth exhibited a decreasing trend, corresponding to the laser energy model. Nanosecond laser chemical milling (NLCM) can reduce the hardness of the material by 72.0–77.2%. The maximum reduction in the average axial milling force was 56.8%, and the fluctuation of milling force is reduced. Compared to pure micro milling, the tool wear area of NLCAM was reduced by 89.3% and the average roughness Sa of the bottom surface of the microgroove was reduced to 0.392 μm, which confirms the high-quality and efficient machining of the CaSiO3 LTCC substrate.