LASER MICROMACHINING
ratios are usually achieved using picosecond or even femtosecond lasers. Pulsed lasers can also be
used to create microvias – interconnects between different layers of microelectronic circuits. Some microvias cross over multiple layers of high-density interconnect (HDI) substrates and can be created by drilling sub-millimetre holes and filling them with electrically conductive metals. Here, lasers are a faster, cheaper and more reliable alternative to tungsten-carbide drills. USP laser sources can also
Oxford Lasers can drill 5μm holes in a tube with a 1.5mm outer diameter g
complex geometries of implantable devices such as stents, intraocular lenses, prosthetics and catheters, which now have smaller features to facilitate new treatments and improve patient outcomes. In the case of metal stents, including drug-eluting metal stents, reducing their dimensions allows for introduction into smaller coronary, peripheral and neurovascular blood vessels. There may be a correlation between positive clinical outcomes and the amount of metal deployed within the vessels, so makers of stents have had to find the means to create thinner-walled and smaller-diameter tubes with more complicated features. The addition of precise surface textures to stents and prosthetics can improve biocompatibility, for example, to reduce the risk of restenosis (the recurrence of arterial narrowing after treatment).
Micromachining processes Laser drilling
The main benefit of laser drilling is that it can be used to create very small holes quickly, precisely and repeatedly. One of the earliest industrial uses of laser micromachining was for creating small (30μm or less) holes in the nozzles of inkjet printers. Micrometre-scale
holes can be drilled in thin foils, for the production of sieves and filters, for instance, using lasers with pulse durations in the nanosecond, picosecond or even femtosecond ranges. Using pulse repetition rates in the kilohertz range, thousands of holes can potentially be drilled every second. For drilling thicker plates,
particularly in metals, small hole diameters imply large aspect ratios, and therefore the beam divergence angle of the laser being used becomes a significantly more important consideration than for drilling holes in foils. The best results for drilling holes with large aspect
be used to cost-effectively drill precise holes in the high- pressure fuel-injection nozzles employed in diesel engines.
Laser cutting and milling Laser cutting and milling (through which a material is ablated layer-by-layer) are being used to micromachine many metals, semiconductors, ceramics, glasses, polymers and composites. Consequently,
“The need to add more functionality to smartphones has forced
manufacturers to fabricate PCBs with smaller, more densely packed features”
a wide range of different pulsed lasers are used for these processes, including diode-
pumped solid-state lasers, CO2 lasers and excimer lasers. For the processing of
translucent materials, such as glasses, diamond or sapphire, ultrafast lasers in the UV and infrared wavelengths are proving to be particularly effective.
Surface microstructuring/ texturing Laser micromachining can also be used to create micrometre- scale structures on large parts. Laser honing, for instance, is often applied to pistons and cylinders for combustion engines to improve their durability and reduce friction. Here, intense pulses of UV light from an excimer laser are directed at the surfaces of the parts in a nitrogen atmosphere to yield surface textures of around 2μm in depth that, in use, are filled with lubricant. USP lasers are also being
increasingly deployed to produce nanostructures that imbue surfaces with a range of functional properties. Surfaces can be made to be hydrophobic/ hydrophilic, antibacterial, produce less friction, and reflect/ absorb more/less light.
Other processes Other applications of laser micromachining include the trimming of electrical resistors. Here, small amounts of a conducting material are ablated until the desired electrical resistance is achieved. Laser-based micromachining
can also be used to write waveguide structures into certain glasses, and fibre Bragg gratings can also be written point-by-point with a tightly focused laser beam. l
For more information about laser micromachining applications and systems, visit:
Laser micromachining firm Lightmotif micro-milling a stamp tool 52 LASER SYSTEMS EUROPE THE 2023 GUIDE TO LASER SYSTEMS
www.lasersystemseurope.com/ applications/micromachining
@LASERSYSTEMSMAG |
WWW.LASERSYSTEMSEUROPE.COM
Oxford Lasers
Lightmotif
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