Investigation of interactions between fiber lasers and Si3N4 sheets for drilling square microholes with multi-ring strategy

A high pulsed fiber laser was utilized to drill square microholes in Si₃N₄ sheets in an atmospheric environment. Various processing parameters including scan spacing, number of scan passes, and number of multi-ring paths with a multi-ring strategy were adjusted to laser-drill Si₃N₄ sheets. The geometric characteristics of laser-drilled square microholes with shoulder height, taper angle, and corner radius were measured using a laser scanning microscope. X-ray diffraction was applied to examine the residual stress of the Si₃N₄ sheets before and after laser drilling. Moreover, the heat-affected zone and element content were examined using a scanning electron microscope. The experimental results exhibited that the optimal shoulder height of the square microhole drilled with the multi-ring strategy was 6.67 ± 0.21 μm, which was approximately 77% lower than that of 29.05 ± 10.95 μm for the square microhole drilled with the single-ring strategy. Moreover, the residual stresses of the original Si₃N₄ sheet and the square microholes laser-drilled by single-ring and multi-ring strategies were − 181.2 ± 41, 164.5 ± 31.9, and 104.6 ± 7.8 MPa, respectively. The proposed laser drilling technology with the multi-ring strategy can be widely used in the semiconductor industry for probe cards.