ANALYSIS & OPINION

New wave of applications for fibre lasers

Research has revealed that fibre lasers could replace other technologies to cut silicon, weld and cut plastics and mark metals. The discoveries, performed at the SPI Lasers’ applications laboratory in Santa Clara, California, could signal a wave of new applications for a laser source that has already been causing a stir in the laser industry.

‘So far, fibre lasers have been a most disruptive technology,’ Jack Gabzdyl, business development manager of SPI Lasers, told electrooptics.com. ‘Since coming to market they have been displacing the dominant position of YAG lasers, but they have also carved out applications of their own.’

Other laser sources have been used to cut silicon for some time, by shooting pulses of green or UV light to chip away at the wafer. However, this can be a slow process using expensive laser sources.

Cutting silicon with infrared lasers, typically with pulsed beams, has been achieved but cut quality is poor due to the poor absorption characteristics of the silicon. This results in rough surfaces, high heat affected zones and small cracks in the cut surface.

In place of short-wavelength lasers and pulsed beams, the team used a continuous wave IR laser beam to melt a line in the silicon wafer. A jet of gas then blows away the excess silicon to provide a smooth cut. This proprietary process is subject to a patent application, but Gabzdyl did reveal that one of the biggest hurdles was finding a way to overcome silicon’s low absorbance of IR light.

Fibre lasers produce a better quality beam than other laser sources, which means the amount of energy that is delivered can be better controlled, producing smooth surfaces with minimal debris or spatter. Fibre lasers also provide a very narrow cut width, which could minimise the amount of wasted material.

Gabzdyl believes these advantages could one day benefit the production of solar cells and semiconductor wafers. ‘It’s currently being evaluated for production; we’re working on transferring the technology now,’ he said.

This fine control of the shape and intensity of the laser beam could also assist the welding of other substances, like plastic. Many plastics do not absorb a 1μm light beam, so the beam would ordinarily travel through the material without causing the two layers to melt and weld together.

To take advantage of the excellent beam quality and control of the fibre laser, the team used painted an existing substance, Clearweld from Gentex, on this interface. Clearweld absorbs well in the IR range, causing the surrounding plastic to heat to melting point to create a successful join.

In addition to these applications, the laboratory has also been working on the use of high-frequency fibre laser pulses to create marks in plastics and metals. The fibre lasers can produce a greater range of pulse repetition rates (from 1-500kHz compared to a maximum of 100kHz from conventional YAG lasers), which also allows a greater control of energy to produce finer patterns.

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