By: Xinghua Li and Sean Garner

Ultra-slim flexible glass substrates have many potential applications, spanning from photovoltaics to e-paper to touch sensors. Previously, these applications generally incorporated glass substrates in the thickness range of 0.3-1.0 mm and benefited from inherent glass properties including high optical transmission, low surface roughness, high thermal and dimensional stability, and low CTE. Recently, however, there is interest in reducing the thickness of the substrate to ≤200 mm. Glass substrates at this thickness still provide the inherent beneficial properties of glass, but they also enable substrate flexibility and end product devices that are thinner and lighter weight.

CO₂ laser cutting of flexible glass substrates possesses several advantages over mechanical and other laser-based cutting methods. It is non-contact, and it uses tensile stress to propagate a full-body crack along the direction of cutting.  The tensile stress is generated with CO₂ laser heating and a subsequent active or passive cooling process. A typical setup using CO₂ laser cutting technique is shown below.

We investigated CO₂ laser cutting of 100 mm and 200 mm flexible glass substrates suitable for display applications. The speed and quality of cutting 100 mm and 200 mm substrates were evaluated.  We observed that:

1. There is minimal dependence on the laser beam length for the laser cutting speed. A shorter laser beam is preferred since the cutting speed was observed to drop faster for longer laser beams as the jet-to-laser beam center distance increases.
2. The laser cutting speed dependence on width of the laser beam was minimal in all cases for 100 mm and 200 mm flexible glass. The cut edge straightness improves with a decreasing laser beam width. However, process stability generally decreases with decreasing beam width over large distances.
3. Cutting can be carried out without active cooling (water mist jet). In this case a rapid temperature drop due to air convection generates the tensile stress necessary for the propagation of the full-body crack. The cutting speed in this case was significantly lower than what can be achieved with mist jet cooling.
4. The cutting speed was affected by thermal contact between the glass sheet and the metal chuck. Adding a thermal insulation barrier such as polypropylene or polytetrafluoroethylene increased the cutting speed by as much as an additional 40 mm/s.

In summary, we investigated CO₂ laser cutting of flexible glass substrates using active cooling jets. We found that the laser cutting speed varies little with laser beam length and width. We attribute the weak dependence to a rapid thermal homogenizing process in flexible glass. We discussed the optimal laser cutting process and recommend that the laser cutting speed should be operated in a region which is defined by a lower boundary and an upper boundary. The lower boundary is defined by cutting action without active cooling. The upper boundary is defined by the maximum cutting speed. The distance of the water jet should be kept close to the laser beam to avoid reduction in speed due to thermal loss to the environment.