across all production scales. These constrains define our next criteria—time. From
the three enumerated methods milling is the only direct method; it provides a single
chip after a short processing time. In case the design stage is more advanced and
your device has performed well at the initial tests, then a mould can be made for
casting or hot embossing of multiple copies.
2.1 Photolithography and Mask Design
Photolithography is a keystone in the fabrication of microelectronics and
microelectromechanical systems (MEMS). A stencil mask is used to transfer the
designed patterns onto a wafer (Fig. 3.3). This technique requires dust-free
manufacturing conditions plus strict temperature and humidity control. Such con-
ditions are maintained in clean rooms with ISO standardised classes, depending on
the content of dust particles per cubic meter of air. Clean room processes are costly
because of the high maintenance expenditures; in addition, to gain access one must
follow multiple courses that can be also time intensive. Outsourcing the fabrication
Design (CAD)MillingLaser
ablation
Casting &
MouldingDevicePackaging &
BondingUVPhotolitographyFig. 3.2 Schematic representation of rapid prototyping techniques, which are commonly
implemented in microfluidics. Laser ablation and milling are direct fabrication methods because
of fast turnover times between design and ready-to-use device in minimum number of stages.
Indirect methods are photolithography, hot embossing, casting and moulding as they all consist of
intermediate stages. Tentatively, laser ablation can be used to create moulds for casting, shown
here with a dashed line
3 Manufacturing Methods Overview for Rapid Prototyping 87