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

A high pulsed fiber laser was utilized to drill square microholes in SiN 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 SiN 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 SiN 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 SiN 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.