TWI Industrial Member Report Summary 663/1998
C P J Foster, J Cole and C C Otter
The machining of very small structures (ie having features in the range 1µm-1mm) which may be integrated with semiconductor control electronics to form complete 'microsystems' is of growing importance because of the need to sense and respond to changes in environments. The technology has its roots in the diffusion, deposition and etching processes developed by the semiconductor industry and, whilst, initially, microsystems products were based on silicon, there is developing trend into a variety of materials.
As the market for these products grows, so does the need for appropriate machining technologies that cover traditional silicon and other materials including metals, polymers and ceramics. The technologies available fall into one of the following three categories:
- Subtractive processes such as anisotropic (bulk) etching of silicon substrates or isotropic (surface) etching of metal and/or oxide layers on the surface of the substrate. These are used to produce, high volume,silicon microstructures. Alternatively laser machining, electrodischarge machining, abrasion/grinding, miniature 'conventional' machining and focused ion beam machining, may be used on a variety of other materials.
- Additive processes such as plating and printing technologies. Photolithographic processes with deep X-ray sensitive resists allow aspect ratios up to 2O:l in microstructures produced by electroplating.Alternatively, it is possible to build up microstructures by printing and firing many layers of metal loaded inks.
- Shaping processes such as moulding of plastics and ceramics with tools derived from the additive (plating) process, photoforming (rapid prototyping) or alternatively the embossing of polymers.