Comparison Excimer Laser – Solid State Laser Rainer ... - Coherent

It consists of crossed cylindrical lenses. The incident laser beam is cut into segments by a lens
array and superimposed in the plane of integration. The more light segments are superimposed,
the better the homogeneity. With such an arrangement about 90% of the laser energy are
transferred into a homogeneous illumination field.
The ink jet nozzle drilling into polyimide or KAPTON is one prominent example for the hole
drilling by excimer laser. Utilizing 248 nm or 308 nm with energies of up to 1000 mJ allows cost
effective drilling of complete nozzle plates in one process step as used for the ink jet printer
industry.
Figure 5: Nozzle plate of Ink-Jet-Printer produced by excimer laser drilling
Other applications that also require a large and fixed pattern density are the production of
multi-chip-modules, pcb and flex-pcb. Depending on the process, 308 nm or 248 nm
wavelengths are utilized to ablate the insulator material such as Polyimide or Epoxy. Choosing a
suitable energy density of i.e. 250 mJ/cm 2 enables to “drilling” through the insulation layer
without affecting the underlying copper layer. The low energy density that is used for the
ablation using 248 nm or 308 nm leads to a large process area and as a result low operating cost
per work-piece.
The treatment of hard materials such as Al2O3, ZrO3, Sapphire and Si3N4 ceramics is also
achieved by 248 nm excimer laser with high precision. With energy densities of more than
25 J/cm 2 suitable flank angles and surface roughness are achieved for the production of so called
spinnerets. Spinnerets are used as tiny nozzles for chemical fiber production. The processing is
carried out by means of the “projection technique” typical for excimer laser micromachining.
With typical ablation rates of less than 0.1 µm per pulses structuring of a 200 µm ceramic plate is
achieved in less than 20 seconds with 100 Hz repetition rate of the excimer laser. Using a similar
set-up the excimer is also suitable for a variety of other applications such as electronics, sensors
and medical technologies where these ceramic substrates are structured with high precision down
to 10 µm.
As shown in Table 1 the photon energy of the excimer wavelength is very high. Using
193 nm or 157 nm wavelength gives an advantage for the machining of glass, quartz and PTFE,
which are transparent at longer wavelength. PTFE is a mechanically, electrically and chemically
stable material used in various applications from the life science to electronics industries. For the
micromachining of PTFE longer wavelengths require high fluence and thermally overload the