Flexible Electronics Manufacturing and Selective Polymer Ablation
Polymers are widely used in diverse fields of everyday life starting from household goods to delicate bio-medical devices and MEMS. Molding and extrusion are common processes for manufacturing parts from polymers. Micro-parts are produced by different etching techniques. Lithography requires use of masks and is acceptable for mass-production. Excimer lasers are usually used for processing polymers. Their usage is also related to the mask technique. Because of specific features of the excimer lasers there is an overall tendency to replace them by solid-state lasers with the laser-direct-write possibility. The technique offers flexibility, which is especially important at the development stage of micro-devices.
The wavelength of the laser is an important parameter for micromachining of polymers. Special care should be taken to minimize the thermal damage of the device when fabricating devices for biomedical applications. UV radiation is able to break chemical bonds directly without significant heat transfer to the surrounding material. Short laser pulses inspire rapid evaporation of the material by a high energy input rate, preventing dissipation of excitation in the form of heat. New challenges in real-world applications of the laser micro-fabrication induce the picosecond lasers with UV radiation. The pulse duration of the lasers is comparable to the time of electron-phonon relaxation and is short enough for “cold” ablation. Easy and effective conversion to UV radiation offers a costeffective source for photochemical ablation of polymers.
Ablation of organic materials, such as polymers, is quite different from that of metals and other inorganic materials. Vaporisation and melting are the main methods of material removal for inorganic materials. Most of polymers tend to decompose before evaporation. Long chains of molecules are cut into fragments before they are able to leave bulk of the material. Some fragments are volatile. The ablation rate is closely related to a number of broken bonds in a polymeric chain. Volume of the fragments and monomers is bigger than that of the polymer. Volume explosion is the force for expelling of the material.