ANALYSIS: ULTRAFAST LASERS
Dissimilar material microwelding gets ready for industry uptake
Matthew Dale learns that ultrafast lasers can now be used to bond transparent materials to metals, unlocking a plethora of applications
The ability to bond metals to transparent materials such as glass, quartz and sapphire using ultrafast lasers is now ready for industry uptake, and is generating interest in a number of different sectors. This was the message
for delegates of the recent Industrial Laser Application Symposium (ILAS). Bonding metals to transparent
materials is frequently needed in modern manufacturing, for example in the assembly of electro-optics, and for hermetic sealing. It is currently achieved using a number of conventional methods, each of which introduce their own undesirable issues while having limited material combinations that they can join. From January 2018 to
September 2020, the partners of the Innovate UK project ‘Ultraweld’ – Oxford Lasers, Heriot-Watt University, Coherent, Leonardo, CPI, Gooch & Housego and Glass Technology Services – were working to develop a process known as ultrafast laser microwelding for joining such dissimilar materials. They also aimed to design and build an ultrafast laser microwelding prototype machine and demonstrate it on real devices in key selected advanced applications.
12 LASER SYSTEMS EUROPE SUMMER 2021
‘All of these objectives have been achieved,’ stated Dimitris Karnakis, technical manager of R&D projects at laser systems integrator Oxford Lasers, who noted that there are only a few research groups around the world currently working on this process. ‘There’s a lot of work being done on glass-to-glass microwelding with ultrafast lasers, but very few groups have managed to do it on glass to metal.’
Why is it needed? Dissimilar materials such as glass and metal are typically difficult to weld together due to them having different thermal properties – the high temperatures and highly different thermal expansions involved can cause the glass to shatter. Several well established methods already exist for joining dissimilar materials in production, for example: adhesive, diffusion, glass frit, anodic and arc bonding; mechanical fastening; and soldering. However, each of these methods comes with its own drawbacks. While some are operator-skill dependent, leading them to being error- prone, others might not be truly hermetic, or require large heat input, the use of interlayers, or lengthy, multi-step processes (including post processing). Adhesives in particular cause
Spiral welds can be made at the interface between transparent material and metal to bond the two together
numerous issues that make them undesirable for use in electro-optics assembly. They are messy to apply and shrink around two to five per cent in volume when curing, which can cause stress and deformation. They are also sensitive to the environment: softening and losing strength at high temperatures; becoming stiff and brittle at low temperatures; losing strength in corrosive environments; and swelling in the presence of moisture. Outgassing – where organic chemicals from the adhesive are gradually released – is also a major issue, as this can contaminate any delicate electro-optics components they are used on, reducing their lifetime or even optically damage them.
The process Electro-optics assembly therefore still requires high- yield, repeatable and reliable bonding technologies that have long lifetimes and can resist harsh operating environments involving vibrations and large temperature changes. Ultrafast laser microwelding has the potential to offer such a process. The technique operates by focussing the beam of
an ultrafast (picosecond/ femtosecond) laser through a transparent material to its interface with metal. The ultrashort pulses create a very small and highly intense spot at the interface between the two materials – megawatt peak power is achieved over an area just a few microns across. This creates a microplasma – like a tiny ball of lightning – inside the material, surrounded by a highly- confined melt region which then cools to create a strong bond without cracking the transparent material. The pulsed beam is translated across the interface in the desired toolpath, such as a spiral, until the required weld is achieved. Ultrafast laser microwelding
offers the benefits of being a non-contact, high-precision and high-speed digital process that requires no intermediate layers or post processing. It can also bond a wide range of materials in a single machine, minimising the floor space required on a factory floor. What surprises Karnakis about ultrashort laser microwelding in particular, is that the laser intensity window for the process is relatively wide, meaning a wide range of laser intensities can be used without damaging the transparent
@LASERSYSTEMSMAG |
WWW.LASERSYSTEMSEUROPE.COM @researchinfo |
www.researchinformation.info
Heriot-Watt University
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30
