Thermal stress analysis on laser scribing of glass

In the laser scribing of glass a thermal stress is introduced into a glass substrate by means of a CO2 laser irradiation. The glass substrate is then rapidly cooled down by water jet immediately after the irradiation. For the purpose of theoretical clarification of the factors ruling the scribable condition and the crack depth, scribable conditions were acquired in laser irradiation experiments using a soda-lime glass substrate having a thickness of 0.7 mm. Furthermore, the crack depth and the crack edge profile were observed for various values of the distance between the heating area and the cooling area. On the basis of the scribable conditions obtained from the experiments results, a thermal elasticity analysis was conducted by a finite element method. The following results were obtained. The scribable condition can be estimated from the maximum tensile stress in the cooling area and the maximum temperature in the heating area. The crack depth in laser scribing depends on the tensile stress in the cooling area and the compressive stress field immediately under the area.