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Micro-processing
Lasers are sources of light whose outputs can be extremely well controlled in terms of direction, wavelength, power and focusability. The most commonly used lasers for precision micromachining are pulsed in nature, with pulse durations typically less than one microsecond (1µsec), a millionth of a second. There are countless combinations of laser wavelengths, powers, pulse durations and pulse repetition rates that are used in laser micromachining, depending primarily on the application.
Microchannels in polycarbonate – the widths/depths of the channels range from = 0µm to 200µm.
Laser beams, due to their inherent properties, can be focused to very small spots of high intensity. In laser micromachining such focused beams are used to remove material from the surface of a workpiece, leaving behind some permanent structure. Proper control of the processes can lead to the machining of features of extremely high quality, precision and resolution. Typical feature sizes for laser machining range from a few microns to many hundreds of microns.
An unlimited range of materials can be laser micromachined. The challenge is to use the correct laser for the material and the structure to be made. Common materials to be machined include polymers, metals, glasses, semiconductors and ceramics. Choosing the correct laser type will determine factors such as the speed of machining, smallest features that can be created and the quality of the machined surface.
Precision machining of 50µm thick polyimide showing excellent definition and lack of damage to plastic.
Laser micromachining is a very flexible technique. It is generally carried out by one of two fundamental methods. The simplest method involves focusing a laser beam to a small spot at the surface of a material, machining structures by moving the spot over the surface of the material in a similar manner to a pen plotter. The second method makes use of a mask projection technique to project an image from a photo mask onto the surface of the material, thereby removing material from the exposed regions. Extensions of these methods, where the mask and/or the workpiece also move, allow an enormous range of structures to be produced.
There is, in principle, no limit to the structures that can be fabricated using lasers. Almost any feature can be machined but the most common are holes, slots, grooves and channels of different shapes and cross-sections.
Shape cut with a laser from a 0.5mm thick silicon wafer.
The major advantages offered by laser micro machining are simplicity, flexibility, cost-effectiveness and precision. Many applications can benefit by using these attributes, especially in the prototyping or development stages, where laser micromachining can shorten evaluation cycles and costs. Many applications use laser options to define and refine project goals even if lasers are not used ultimately in high volume production, although in many areas such as displays and microelectronics, high volume laser production methods themselves have become standard practice.