Tham khảo tài liệu 'microengineering mems and interfacing - danny banks part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 80 Microengineering MEMS and Interfacing A Practical Guide widespread form is photolithographic processing in the form of photoresists polyimides and photoformable epoxies SU-8 the latter also being a class of photoresist . At the time of writing these were closely followed by PDMS casting but hot embossing appears to be making its mark as a mass production technique. This section also addresses stereolithography and microcontact printing. The latter is a lithographic technique that is not restricted to polymers but can also pattern biomolecules for instance. However it usually requires a polymer PDMS original. Polyimides Polyimides are UV photoformable polymers that are common in the electronics industry. These have several different trade names and different properties. Fabrication of polyimide structures is normally performed on a polished silicon wafer to provide a convenient flat rigid substrate to which the material can be applied and which holds it flat during subsequent machining steps. Polyimides are usually spun on and patterned using conventional UV lithography techniques usually to several microns thickness. Metal films can also be deposited patterned and sandwiched between layers to provide a variety of different electrode or interconnection structures. Polyimide structures are often used as part of the packaging of silicon microsystems they are flexible and more robust than individually bonded wires. The silicon die must be bonded to the ribbon cable either by conventional wire-bonding processes or flip-chip techniques see Chapter 9 . Unfortunately many polyimides are not very resistant to ingress of water. Photoformable Epoxies SU-8 SU-8 from Microchem Corp. . is a photoformable epoxy negative photoresist that has gained a considerable following among the MEMS community. It is easy to see why it is available in several different formulations and can be applied in films of 1 pm to 200 pm thickness in a single spin process can be exposed
