Ultra-short pulse lasers are used to separate transparent materials in the electronics industry. And with the newly developed TOP Cleave optics, those materials can now be cut at a speed of one metre per second. Using this option, the new, high-performance TruMicro 5080 ultra-short pulse laser can even cut glass one millimetre thick.
The use of light to machine glass is not an obvious concept as the material is transparent to light. The beams produced by a solid-state laser, usually in the infrared spectrum, simply pass through glass panes. However, this isn’t the case for ultra-short pulsed laser light in the picosecond or femtosecond range. The massive spatial and temporal density of the photons in the pulse modify the absorption mechanism in transparent materials. This makes it possible to use laser beams to process synthetic sapphire and glass.
TOP Cleave optics is the turbocharger for material modifications in glass
Instead of cutting glass by ablation, working pulse-by-pulse, an elegant technique was recently developed to cleave thin, hardened glass such as that used in smartphone displays. Material modification is the keyword.
Ultra-short pulsed laser beams are focused inside the glass and there they modify a narrow zone along the desired cleavage line. The modification generates intrinsic tensions; the glass fractures in a controlled manner. The resultant surface is as smooth as a mirror and accurate to a hundredth of a millimetre – no matter whether straight or curved.
TRUMPF displayed these new TOP Cleave optics at the recent Laser trade fair in Munich, which can accelerate this procedure a hundred-fold. TOP Cleave distributes the intensity of the laser light uniformly along the axis of the beam. In this way the focus is stretched in length; the beam spot becomes a focus line.
The laser pulses no longer scan the glass level by level, but instead modify – in a single pass – the complete interior separation surface. Depending on the pulse energy, this glass may be up to 700 microns thick.
When working this thickness, the high-performance TruMicro lasers equipped with TOP Cleave achieve cutting speeds of up to one metre per second – a hundred times faster than without the option.
TruMicro 5080 separates glass one millimetre thick
The new flagship among the TruMicro lasers is the TruMicro 5080. It delivers the highest repetition rate, at up to 1,000 kilohertz, with a maximum of 500 microjoules. This is the highest-energy pulse in the world for ultra-short pulse lasers in industrial use. The laser produces average power exceeding 150 Watts – making it extremely powerful in every application.
The TOP Cleave optics can distribute the high power of the TruMicro 5080 along such a long focus line that the laser light can use modification techniques to separate glass more than one millimetre thick.
The TruMicro 5080 is also available in the femto edition. It is the first industrial laser that can produce femtosecond pulses in the green spectrum. In this way it gives the best of two worlds. Despite high peak intensities, the femtosecond laser pulses inject even less thermal energy into the workpiece in comparison with a picosecond pulse.
This makes them especially suitable for extremely delicate processing of metals or thermally sensitive materials like special films. Green light can be focused down to a very small spot. Green radiation has a larger Rayleigh length than infrared light and, as a consequence, greater depth of focus. This makes the TruMicro 5080 especially well suited for drilling extremely fine and precise holes such as those found in injection nozzles.
A further advantage of the TruMicro 5080 is that it can easily be integrated into industrial machinery and can be maintained while still inside the equipment. This eliminates troublesome removal and the subsequent readjustment of the beam path. A new technical concept is responsible for this.
All the relevant components for maintenance and exchange – like power cables, cooling lines, the electronics and the optical area – are easily accessible from a single side. This lowers the downtime for machine tools and boosts their economy considerably. TRUMPF also presented the TruMicro 5080 to the public at the Laser fair in Munich.
Laser lift-off for flexible film displays
Another application of the TruMicro lasers demonstrated at the show; the laser lift-off process for flexible films. Curved but rigid displays and bendable panels are the latest trends, particularly for the so-called “wearables” – smart devices that one wears on the body – glasses or a wristband, for example.
To make up such displays the electronics industry coats backing glass panes with polyimide. The dried plastic then forms the substrate for the flexible display. Organic light-emitting diodes (OLEDs) are then applied to the polyimide and the flexible display released from the backing pane. To do this, a laser beam is aimed from the rear, through the backing glass, onto the surface of the polyimide film. It heats up the film which causes it to lose adhesion and detach from the backing pane. The sensitive OLEDs are completely untouched by the process.
At the Laser exhibition TRUMPF also introduced the TruMicro 7370 solid-state laser used for this process – a world premiere. When compared with the excimer laser normally employed for this purpose, the beam source requires little maintenance, increases the available operating time, and therefore lowers production costs.
The very short pulses make the process highly efficient as a single pulse can work a larger surface area. The TruMicro 7370 is extremely precise in its work and highly reliable in the process. This is due to the great stability of the pulse energy and the temporal sequence of the pulses. Both are ensured by TRUMPF with a special pulse synchronization technology. The regulation installed here lends additional stability to the overall process.
Image: Cleaving glass with material modification