Hot embossing

Hot embossing is a fast, clean, and economical fully additive structuring process that has the added benefits of a limited number of process steps and low investment costs. A distinction can be drawn between stroke and roll versions of the process (Fig. 3.15). The stroke version is the more common in MID technology, simply because the parts are three-dimensional. 

FIGURE 3.15 Schematic of the stroke and roll process variants 

The tool used for roll embossing is a wheel or roller with built-in heating. The plastic molding follows a linear track as it passes underneath the tool on a conveyor belt, for example. By contrast with stroke embossing, the force is applied only locally, mapping the line of contact between roller with film and the blank. The ability to produce large, uninterrupted surfaces without air inclusions is one of the big advantages of this process [48]. 

Embossing pressure is built up Heat is applied to the substrate The surface melts Conductor pattern is cut out 

The plastic molding requires no postembossing chemical treatment whatsoever, and this is one of the major advantages of the process. The plastic is exposed to less process load and is suitable for decorative finishes. The savings in process time and costs are also considerable. Hot embossing is a process that can be used for many different thermoplastic compounds. 

Having initially demonstrated its power in fabrication of complex microfluidic devices [18-20], hot embossing technologies are now also used to manufacture cell culturing substrates [21,22], 

Medium to mass production processes require metal tools, which could be made of tool steel or any other kinds of metal in the case of common machining. For excellent surface properties of the tools and molds, brass tools are preferable. Due to precision 

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Becker H., Heim U., Hot embossing as a method for the fabrication of polymer high aspect ratio structures, Sensor. Actuat. A-Phys. 2000 83 130-135. 

Datta, P., and Goettert, J. (2007). Method for polymer hot embossing process development. Microsystem Technol. 13, 265—270. 

The thermal-reflow process (or hot embossing) has also been used to reduce significantly sidewall surface roughness in polymer (polystyrene)... 

Qi, S., X. Liu, S. Ford, J. Barrows, G. Thomas, K. Kelly, A. McCandless, K. Lian, J. Goettert, and S. A. Soper. Microfluidic devices fabricated in poly(methyl methacrylate) using hot-embossing with integrated sampling capillary and fiber optics for fluorescence detection. Lab on a Chip, 2, 88-95 (2002). 

Zhu et al. [76] designed and fabricated microfluidic devices on polymethylmethacrylate (PMMA) substrates for electrochemical analysis applications using an improved UY-LIGA process. The microchannel structures were transferred from a nickel mold onto the plastic plates by the hot embossing... 

Figure 2.17 Schematic representation of a simplified fabrication process used for proposed GNEE NCE microchip, (a) Contact electrode exposure, (b) electrode developing, (c) platinum etching, (d) GNEE direct bonding, (e) master fabrication, (f) hot embossing, (g) alignment, and (h) low temperature solvent bonding [146],...

Microfabrication was achieved by UV-lithography with a negative photoresist SU-8 2035 based on a nickel plate [163], By means of electroforming of the exposed and developed resist structure, a nickel mold was prepared (see Figure 1.182). By hot embossing, the final polymer mixer structures were prepared. Holes for fluid connectors were drilled. The microstructured substrate was joined with a blank polymer plate by thermal fusion bonding. 

Moreover, a Zeonor plastic plate, normally used to manufacture CDs and DVDs, was hot-embossed (130°C, 250 psi) using a Si master. The embossed chip (with microchannels 60 im wide and 20 pm deep) was thermally bonded to another Zeonor plate (85°C, 200 psi, 10-15 min) [808], In another report, a 2-mm-thick cyclo-olefin (Zeonor 1020 R) substrate was embossed using a Si master to create 20-pm-wide and 10-pm-deep channels [788],... 

Besides using a Si master, hot embossing was also carried out using a Ni master (300 pm). This was electroformed from a Si master using a Ti/Ni seed metal layer on Si. After electroplating Ni on the Si, the Si was etched away, exposing the opposite relief of the Ni master. The Ni master was used to emboss on PC and PMMA substrates [213],... 

When an elevated temperature (110°C) is used to bond PMMA chips, hot embossing must be used to create channels on the PMMA substrate, 5.1 x 106 Pa or 740 psi for 1 h. If room-temperature embossing was used, the PMMA channel will be distorted during the thermal bonding process [216,259]. 

FIGURE 2.23 Scheme for fabrication of plastic microdevices from silicon master using an intermediate soft mold, (a) Silicon structures are fabricated using conventional photolithography and reactive ion etching, (b) PDMS is cured in situ over the silicon master, (c) Polystyrene is hot embossed onto the PDMS mold or polymerized in situ from partially polymerized styrene, (d) Polystyrene replica is separated from the mold [85]. Reprinted with permission from Springer Science and Business Media. 

Compare and contrast hot wire-imprinting and hot embossing for fabrication of polymeric chips [1011]. (4 marks)... 

Becker, H., Dietz, W., Dannberg, P., Microfluidic manifolds by polymer hot embossing for p- I AS applications. Micro Total Analysis Systems 98, Proceedings jlTAS 98 Workshop, Banff, Canada, 13-16 Oct. 1998. Kluwer Academic Publishers, Dordrecht, the Netherlands, 1998, 253-256. 

Since plasticized PVC is thermoplastic both compact and expanded wallcoverings can be given a surface texture by hot embossing. This usually is the last stage of production before trimming and reeling. 

Smith PJ, Hendriks C, Perelaer J, Schubert US. Conductive silver tracks produced by hot-embossing and inkjet printing, http //www. parthen-impact.com/parthen-uploads/add26321.pdf. 

Martiradonna, L., Carbone, L., De Giorgi, M., Manna, L., Gigli, G., Cingolani, R., and De Vittorio, M. (2006). High Q-factor colloidal nanocrystal-based vertical microcavity by hot embossing technology. Appl. Phys. Lett. 88 181108. 

Figure 25.1 Schematics of typical nano and micro fabrication techniques Photolithography, soft lithography, hot embossing, and direct writing. See color plates.

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