Micromachining

Direct from the computer to submicron dimensions using excimer lasers in the UV.

Excimer lasers can be used to shape a wide range of materials including polymers, metals, glass, ceramics and even diamonds. The direct-write approach using CAD/CAM software for laser machining in the dimensions of microns allows almost any shape to be generated on a surface.

The combination of compact excimer lasers and precision motion systems, video imaging and CAD/CAM software allows precision machining on scale-sizes in the 1 to 100 micron range.

Raster scanning on the work surface is one means of producing such three-dimensional structures. This technique forms the part by removing the material layer by layer.

Summary
Since the single-pulse ablation depth varies from a few nanometers to some tenths of a nanometer, it is possible to produce smooth, sloping surfaces with continuous height variation by excimer laser ablation.

Coherent supplies laser sources and tools for wire feed welding and brazing.

Coherent’s HighLight 4000L is a line source laser product, excellent for wire feed welding and brazing. The line spot of the 4000L makes feeding wire into the laser beam very easy. There is no need for expensive vision systems and precision alignment devices. The long beam which can only conduction mode weld “wets out” the weld. This produces excellent weld bead profiles.

Characteristics of conduction mode weld:

• Very little evaporation of material
• Quiet process, little or no spatter in most cases
• Repeatable process
• Tolerant of part fit up
• Significantly smaller nugget than TIG or MIG weld
• Significantly smaller Heat Affected Zone (HAZ) than TIG or MIG weld
• 50% - 200% faster than TIG or MIG depending on thickness

As with wire feed welding, the HighLight product line is an excellent heat source for Silicon Bronze brazing. For Body-n-White brazing, the HighLight 4000L is an excellent source for creating braze joints that do not need rework after brazing. The long beam wets out the weld.

Benefits of Laser Brazing

• Low maintenance
• Non plasma process
• Splatter significantly reduced
• Zinc Fuming and sooting reduced
• Fouling of MIG/TIG not an issue
• Lower heat input
• Faster brazing process

A deep-UV excimer or ion laser, in conjunction with an interferometer or a phase mask, can create an intense fringe pattern in an irradiated Germanium-doped fiber, inducing a permanent periodic modulation structure known as a Fiber Bragg Grating (FBG).

The main use of FBGs is in telecommunications for wavelength division multiplexing, as well as sensing in applications such as petrochemical drilling and seismic monitoring.

Since desktop inkjet printers are being produced with higher resolutions, there is a need for more and smaller holes in the nozzle array of the printing head.

The position of the holes, as well as the shape, must fulfill very tight tolerances (<1µm). While former products used electroforming for nozzle drilling, the excimer laser offers significantly better production yields and better control over the nozzle shape.

Coherent’s industrial excimer lasers are designed for high duty-cycle production with low maintenance downtime and low running-costs. State-of-the-art line beam optics are used for beam forming and homogenization. The results are up to 100 holes drilled simultaneously in patterns of up to 18 mm in length on the printer head that can be machined simultaneously with sub-micron accuracy.

Excimer and fiber lasers enable industrial micromachining.

Ultraviolet (UV) laser light is an ideal tool for many micromachining applications. The short wavelength results in two major advantages: it allows the production of very small features and the effect on the surrounding material is minimal due to the non-thermal interaction.

There are two major technical breakthroughs that make UV lasers more and more useful in industrial applications. First is the dramatic maturation in excimer laser design. State-of-the-art excimer lasers using advanced technologies feature extended component lifetime, high reliability, low maintenance downtime and low running-costs. The second breakthrough is in the area of diode-pumped solid-state (DPSS) lasers. New generation lasers deliver high peak power, high repetition rates, and excellent beam quality (TEM₀₀). They are also available with frequency conversion down to the fourth harmonic (266 nm).

Both advances make UV lasers more attractive to industrial users. As a result, they have been implemented in a wide range of micromachining applications. The following text outlines some important applications and specific laser requirements.

The photo in the upper right shows excimer-micromachined script on a 120 micrometer diameter human hair. This is an example of high-resolution direct-ablation by mask imaging. This technique can produce resolved features down to a couple of microns.

MEMS combine mechanical and electrical functions on one chip, processed by traditional semiconductor techniques.

In the near future, gas sensors, chemical and biosensors, and actors like microvalves and microrelays will emerge. The field is now open for direct structuring of a wider range of materials and applications using UV lasers.

A very promising extension of 3D microstructuring has been explored by combining excimer laser ablation with the LIGA technique. Direct 3D microstructuring of the master by UV excimer light is much more flexible and economical than multi-step X-ray lithography.