Glass is used as a substrate in the touchscreen displays of virtually every manufacturers’ smartphones and tablet computers. The glass for these devices is invariably supplied in large sheets, which is processed and then eventually cut down to form individual displays.
Unfortunately, the traditional mechanical methods for cutting glass have drawbacks, particularly for the very thin substrates used in flat panel displays (FPDs). These include the creation of microcracks in the material, the introduction of mechanical stress into the glass, the production of small chips and debris, and the formation of an edge that is not necessarily perpendicular to the glass surface. Post-processing steps to grind or polish the cut surface may be required to correct for these deficiencies, as well as a cleaning step to remove debris.
Non-contact laser cutting
Non-contact laser cutting largely eliminates these problems. In particular, the use of an ultra-short pulse (USP) laser in a process called filamentation cutting delivers an unmatched combination of high speed, operational flexibility and superior cut quality. Filamentation cutting works because the high laser peak powers of a USP laser produce self-focusing of the beam due to the nonlinear Kerr optical effect. This self-focusing further increases power density, until, at a certain threshold, a low-density plasma is created in the glass. This plasma lowers the glass refractive index in the center of the beam path and causes the beam to defocus. This focusing/defocusing effect can be balanced to repeat periodically and form a stable filament that extends over several millimeters in depth within an optically transparent material.
To produce a cut, these laser-generated filaments are produced close to each other by a relative movement of the work piece with respect to the laser beam. Cutting speeds of 100 mm/s to 2000 mm/s can be achieved, depending on the material thickness and the desired cut geometry.
With chemically or thermally strengthened glass, internal stress within the part provides for automatic separation of outer contours (as opposed to cutouts), without an additional step. For non-strengthened transparent materials, such as soda lime, borosilicate and alumino-silicate glass, as well as sapphire, a separation step must follow filamentation.
The Coherent | Rofin embodiment of the filamentation technology is called SmartCleave. It pairs process technology acquired, and further developed by Rofin, together with advanced industrial ultrafast HyperRapid NX series lasers from Coherent. The resulting process enables high speed cutting of arbitrary shapes, including curves, freeform cuts and insets, without edge taper, in glass and other transparent and brittle materials from 0.05 mm to 10 mm thickness. SmartCleave delivers smooth surfaces, with a Ra of less than 1 μm, which are essentially free of chips and debris. This yields superior bend strength in the cut parts compared to parts generated with mechanical processes.
SmartCleave enables high speed cutting of curves and insets into glass, e.g., used for substrates of displays.
SmartCleave glass cutting is typically accomplished using HyperRapid NX lasers operating at 1064 nm. These products offer a unique combination of output power, reliability and operational flexibility, including burst mode and pulse on demand operation. The result is an unmatched ability to effectively implement filamentation cutting in a specific application.
Coherent | Rofin supplies products to enable SmartCleave processing in a variety of configurations. This can be simply the HyperRapid NX laser source and SmartCleave process recipe. But, the company also provide sub-systems, which integrate a laser with beam delivery optics and control electronics. These can also be configured as a so-called “black box” subsystem, in which the particular configuration to enable and optimize a specific process has already been developed and programmed. Finally, Coherent | Rofin can deliver complete, turnkey systems for SmartCleave processing, which are ready for use in a production setting.
Written by Joris van Nunen, Product Marketing Manager at Coherent, based in Kaiserslautern Rhineland-Palatinate, Germany