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The benefits of USP fibre lasers

High-power, ultra-short pulse (USP) fibre lasers of the type being pioneered by Corelase offer a wide range of benefits in microfabrication and thin-film deposition compared to traditional methods. In particular, USP laser technology can meet the need for the higher average power required for the volume production of consumer products.

Relatively simple mechanical tools continue to be the equipment of choice for many core processes – such as drilling, cutting and sawing, etching, welding, soldering, and coating large metal products – in industries ranging from engineering to electronics and papermaking, although tool wear can often be excessive. In the case of paper, plastics, semiconductors, and thin films, however, chemical methods such as etching are more appropriate.

The use of lasers in material processing has grown significantly since the early 1980s, driven by the benefits of minimal tool wear and the fact that lasers place no mechanical burden on the material being processed. Lasers are also easy to integrate with robotic equipment.

With the growth of technologies that permit the production of smaller and smaller devices, there is a growing need for microfabrication in the 1-100 µm feature size range. Mobile phones, digital cameras, PDAs, and thin-film displays, for example, manufactured from insulators, semiconductors, and metals require increasingly precise and accurate processing methods that do not load, heat, or crack adjacent areas excessively.

Processing such small features is becoming increasingly challenging, even with chemical methods. And while lasers are sometimes used in microfabrication, their main technical limitation comes from the excessive heating resulting from the heat conduction encountered in areas immediately adjacent to the light/material interaction zone.

Corelase’s X-LASE, fitted with an X-HEAD.

New lasers for new jobs

New types of lasers are now being developed to reduce this excessive heating problem, based on ultra-short pulse length in the low picosecond and femtosecond range, rather than the more conventional nanosecond range.

Very high irradiance (W/cm2) is required during the laser pulse to ensure that the material being processed does not just melt but is ejected at high kinetic velocity, generating very little heat conduction. Residual heat is conducted away across the surface a number of nanoseconds after the laser pulse.

Building on this technology, Corelase has developed the X-LASE family of Ultra Short Pulse (USP) fibre lasers, optimised for industrial use.

The X-LASE family

Corelase’s X-LASE turnkey systems offer a winning combination of compact size, robust design, high efficiency, high processing speed, and fibre delivery for easy integration with automated material handling equipment.

The X-LASE family is ideal for micro-fabrication and applying functional coatings on large surfaces. X-LASE units can be used to groove, cut, and pattern materials directly, without creating large heat-affected zones, recasting problems, burr, or debris.

Unlike standard etching using lithographic masks, direct writing enables a digital image to be transferred directly from a computer to the target material. This mirrors the change that lasers have already been instrumental in implementing in the printing industry, where they are used to transfer data directly to the printing plate or even paper in a single, integrated process flow.

Steel processed with an X-LASE unit exhibits no recasting waste, burr, or other debris.

Ideal for thin-film displays

While laser-based microfabrication can handle features larger than 10 microns in electronics applications, it is unsuitable for replacing conventional lithography in the semiconductor industry when routinely processing materials at submicron dimensions down to 90 nm.

Ultra-short pulse lasers are ideal, however, for singulating semiconductor chips from thin wafers, and for new types of process, such as direct writing, used with packaged printed circuit boards, as well as flexible PCBs and PCBs integrated with the surfaces of end-products.

They are also perfect for thin-film displays and flexible organic LED technology, the production of which calls for a number of processes that only cold ablation/evaporation with ultra-short pulse lasers can address.

Metal and medical applications

Laser-based microfabrication, in the form of micropatterning, represents a major advance in the metal industry. Grooving the top dead centre of engine cylinders, for example, can cut oil consumption by as much as 15%, by reducing friction between piston rings and the cylinder wall.

Another promising application for microfabrication lies in the structuring of titanium-based medical implants or stents, used as an alternative to bypass surgery for treating plaque-blocked coronary blood vessels.

A lot to offer

Ultra-short pulse lasers of the X-LASE type also have a lot to offer in the area of thin-film coatings as well, in both the decorative and functional area.

Painting is the normal technique of choice for decorative coatings, while vacuum evaporation or sputtering is used for functional coatings. Painting is often problematic for environmental reasons, while the heat radiation associated with vacuum deposition tends to melt the polymer substrates often used in modern electronic equipment and displays.

Ultra-short pulse lasers, in contrast, can evaporate almost all materials, and are easily incorporated into vacuum systems.

Since ultra-short pulse laser deposition anneals only the area where ablation takes place, there is very little heat radiation. The high kinetic energy of the deposited atoms in this type of deposition also opens up the possibility of switching to room-temperature deposition, eliminating the need for substrate heating to enhance diffusion.

> Jari Sillanpää
(Published in High Technology Finland )