Drilling with USP Laser Radiation

Drilling plastics with ultra-short UV laser pulses without thermal damage

Cross-section of a micro-hole <2 µm in PI film
© Fraunhofer ILT, Aachen Germany.
Cross-section of a micro-hole <2 µm in PI film

Fraunhofer ILT has developed a special UV microscanner that can be used to flexibly create micro- and nanostructures and drill holes in various materials. It uses aThe wavelength in the UV range that significantly improves absorption, especially in dielectrics such as plastics. This way, it can drill micro- and nanometer holes in polymer films such as PC, PE, PI and PP with high precision and reproducibility. Even with thermally sensitive plastic films with a thickness <15 µm and high hole density, there is no thermal deformation. Thanks to the adjustable Since the focus diameter can be adjusted, from 6.0 down to 0.5 µm, even hole diameters in the sub-µm range can be produced.


Multibeam drilling: 12,000 holes per second with 1 µm diameter

A new generation of ultrafast process technology is on the market. Higher average laser power and greater pulse energy promise higher throughput and efficiency. When processing microfilters, for example, this enables drilling of hole sizes down to below one micrometer with more than 10,000 holes/sec.

When ultrafast processes are scaled up, some non-trivial interaction mechanisms have to be  taken into account. One option to make use high pulse energies is the multibeam concept, which involves splitting a single laser beam into many beamlets. Fraunhofer ILT has been working on this technology since 2012. With diffractive optical elements (DOE), more than 200 partial beams can be used selectively in micro- and nanostructuring – for a precision down to the sub-micrometer range.

Laser-beam helical drilling of micro-holes with a high aspect ratio

Drill hole entry with 60 μm diameter.
© Fraunhofer ILT, Aachen, Germany.
Drill hole entry with 60 μm diameter.

Laser-beam helical drilling is a suitable technology for producing precision-shaped holes, but the achievable aspect ratio is limited to about 20:1 owing to beam propagation in the drilling hole. Several factors limit the aspect ratio of a precision drill hole with high roundness at the entrance and exit when drilled by ultrashort pulse laser (USP) radiation. In particular, the drilling technology or optics as well as the available maximum pulse energy of the applied USP laser radiation limit the maximum aspect ratios of the drilled hole. The removal rate decreases sharply with increasing drilling depth due to the beam divergence and multiple reflections. Therefore, making high aspect ratio micro-holes in thick material is a major challenge to manufacturing. Using a helical drilling optics developed at Fraunhofer ILT the degree of multiple reflections of the laser radiation and the temporal and spatial energy deposition in the drill hole can be adjusted selectively.