Water-assisted laser drilling for miniature internal thread in glass and evaluation of its strength

We report fabrication of miniature internal threads in glass substrates using water-assisted laser drilling, and evaluation of its fracture strength. Miniature internal threads of S0.4 and S0.5 were fabricated using a subnanosecond laser as a light source. The fracture strength of the fabricated in-ternal S0.5 threads was evaluated by applying a load to the commercial male screw that was fitted to the fabricated thread. A model, in which tensile stress causes the fracture, was developed to analyze the fracture phenomenon. The validity of the model was confirmed by the agreement of fracture size between the model and experimental values. Fracture strength of about 1.1±0.1 MPa was obtained, and this value could be further improved.