GLASS PROCESSING


SEE-THROUGH LASING C


Greg Blackman on the laser technology for cutting toughened display glass, as well as the various techniques for glass engraving


racked screens could be a thing of the past if smartphone manufacturers adopt sapphire to cover touchscreen displays. Apple, which already uses the material as a protective


cover for the camera lenses and home button on its latest iPhone model, announced in November a supply deal with GT Advanced Technologies for growing the gemstone. GTAT will receive $578 million from Apple to build its production capacity of sapphire at its factory in Mesa, Arizona. Sapphire is scratchproof and difficult to break,


which makes it appealing as a cover glass for electronic devices like mobile phones. However, because it’s so hard, sapphire is difficult to process mechanically, requiring a diamond-tipped saw to cut. Non-contact laser dicing is, therefore, an attractive alternative for processing the material. Te same challenges apply to dicing toughened


glass, called Gorilla Glass, which cover the displays of most of the smartphones made at the moment, and, again, laser processing is an excellent alternative to mechanical means. Frank Gäbler, director of marketing at laser manufacturer Coherent, commented: ‘Tere’s an interesting market for laser cutting the cover glass for flat panel displays. Te cover glass is now very thin, ranging from 400 to 700µm thick, so traditional cutting methods don’t work any longer. Mobile phone manufacturers are investigating alternative methods to cut strengthened glass.’ At the end of 2012, Coherent


Laser engraving in glass involves creating fractures in the glass to make the mark


the material to make the cuts. Te process is fast – Filaser claims a throughput of more than 500mm/s – it has a low cut face roughness, meaning there is very little post-processing required, and the glass is cut without generating any microcracks, which means the bending strength is high (Filaser claims more than 150MPa). ‘In the past, CO2


cutting cover glass,’ remarked Gäbler. ‘CO2


lasers have also been used for lasers


are relatively low cost, do the job, and are fast and reliable. Te downside is that they can only cut straight lines. In the past, the


fracturing, however, has to be controlled to avoid weakening the glass


The degree of


bought Lumera Laser, which produces picosecond pulsed lasers. Tese lasers are part of machines from German company InnoLas Systems made specifically for cutting brittle materials like chemically strengthened display glass and sapphire. Te machines use filament cutting developed by Filaser (Portland, Oregon). Tis is a type of ultrafast laser processing, whereby picosecond pulses are focused to a break line within


18 LASER SYSTEMS EUROPE ISSUE 21 • WINTER 2013


straight cuts were made with a CO2 laser, while the corners were cut by another method, which wasn’t ideal. Te new filament cutting technology is able to cut straight lines as well as curves.’ Gäbler says mobile phone


manufacturers and display manufacturers currently use


ultrafast laser technology for cutting display glass. Standard ultrafast laser processing ablates the material using multiple passes to produce a cut. Here, the laser is focused onto the surface to ablate the glass. However, an ablative process creates microcracks and is quite slow, Gäbler commented. Any microcracks need to be removed by a secondary polishing process. Scientists at the Fraunhofer Institute for Laser


Technology have been investigating the process to potentially fine tune the strategies for cutting glass with picosecond lasers. Te researchers used a Trumpf picosecond laser, which, in the experiments, delivered a peak pulse energy of 40µJ at 10ps pulse duration. Te work suggested potential mechanisms of why ultrafast lasers sometimes cause damage in the glass and it is hoped the results will be used to improve the process, both in terms of quality and speed.


Making a mark When it comes to marking glass with a laser the process is different, as here the idea is to create a certain amount of fracturing within the glass to make the mark. Te degree of fracturing, however, has to be controlled to avoid weakening the glass and to produce a legible mark. CO2


lasers at 10.6µm are ideal for marking glass,


because the material absorbs at this wavelength. David Earl, technical sales engineer at UK laser supplier Laser Lines explained that, by careful selection of laser parameters, glass fracturing can be controlled to achieve a high-quality mark: ‘It depends on what effect you are looking for and the type of glass you are marking. If you’re looking to mark a high-definition image, then you’ve got to try and create a fairly small spot and a localised crack , which is not going to create thermal stressing.’ Laser Lines is a distributor for Synrad, which


@lasersystemsmag | www.lasersystemseurope.com


Laser Lines


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